advances in membrane technologies for water treatment – materials, processes and...

643

Upload: others

Post on 11-Sep-2021

2 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier

Woodhead Publishing Series in EnergyNumber 75

Advances in MembraneTechnologies for WaterTreatmentMaterials Processes and Applications

Edited by

Angelo Basile Alfredo Cassanoand Navin K Rastogi

AMSTERDAM bull BOSTON bull CAMBRIDGE bull HEIDELBERGLONDON bull NEW YORK bull OXFORD bull PARIS bull SAN DIEGOSAN FRANCISCO bull SINGAPORE bull SYDNEY bull TOKYO

Woodhead Publishing is an imprint of Elsevier

Woodhead Publishing is an imprint of Elsevier80 High Street Sawston Cambridge CB22 3HJ UK225 Wyman Street Waltham MA 02451 USALangford Lane Kidlington OX5 1GB UK

Copyright copy 2015 Elsevier Ltd All rights reserved

No part of this publication may be reproduced stored in a retrieval system or transmittedin any form or by any means electronic mechanical photocopying recording or otherwisewithout the prior written permission of the publisher

Permissions may be sought directly from Elsevierrsquos Science amp Technology RightsDepartment in Oxford UK phone (+44) (0) 1865 843830 fax (+44) (0) 1865 853333email permissionselseviercom Alternatively you can submit your request online byvisiting the Elsevier website at httpelseviercomlocatepermissions and selectingObtaining permission to use Elsevier material

NoticeNo responsibility is assumed by the publisher for any injury andor damage to personsor property as a matter of products liability negligence or otherwise or from any use oroperation of any methods products instructions or ideas contained in the material hereinBecause of rapid advances in the medical sciences in particular independent verificationof diagnoses and drug dosages should be made

British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library

Library of Congress Control Number 2014954883

ISBN 978-1-78242-121-4 (print)ISBN 978-1-78242-126-9 (online)

For information on all Woodhead Publishing publicationsvisit our website at httpstoreelseviercom

Typeset by TNQ Books and JournalswwwtnqcoinPrinted and bound in the United Kingdom

CONTENTS

List of contributors

WL Ang Research Centre for Sustainable Process Technology UniversitiKebangsaan Malaysia UKM Bangi Selangor Malaysia

A Antony The University of New South Wales Sydney NSW Australia

P Argurio Universita della Calabria Rende (CS) Italy

P Arribas Campus of International Excellence Moncloa Campus (UCM-UPM)Madrid Spain Department of Applied Physics I University Complutense of MadridAvda Complutense Madrid Spain

N Bajraktari Technical University of Denmark Lyngby Denmark

A Basile Institute on Membrane Technology ITM-CNR University of CalabriaRende (CS) Italy Ast-Engineering srl Rome Italy

M Bodzek Institute of Environmental Engineering of the Polish Academy ofSciences Zabrze Poland Silesian University of Technology Institute of Water andWastewater Engineering Gliwice Poland

SI Bouhadjar Institute of Applied Research (IAF) Karlsruhe University ofApplied Sciences Karlsruhe Germany

A Cassano Institute on Membrane Technology ITM-CNR University of CalabriaRende (CS) Italy

E Curcio University of Calabria (DIATIC-UNICAL) Cosenza Italy Institute onMembrane TechnologyndashNational Research Council of Italy (ITM-CNR) CosenzaItaly

L Daal DNV GL Energy Arnhem The Netherlands

SA Deowan Institute of Applied Research (IAF) Karlsruhe University of AppliedSciences Karlsruhe Germany

F de Vos DNV GL Energy Arnhem The Netherlands

T de Vries GDF SUEZ Energie Nederland Zwolle The Netherlands

G Di Profio Institute on Membrane TechnologyndashNational Research Council of Italy(ITM-CNR) Cosenza Italy

E Drioli University of Calabria (DIATIC-UNICAL) Cosenza Italy Institute onMembrane TechnologyndashNational Research Council of Italy (ITM-CNR) CosenzaItaly

E Fontananova Institute on Membrane TechnologyndashNational Research Council ofItaly (ITM-CNR) Cosenza Italy

VS Frenkel San Francisco CA USA

MC Garciacutea-Payo Department of Applied Physics I University Complutense ofMadrid Avda Complutense Madrid Spain

N Ghaemi Department of Chemical Engineering Kermanshah University ofTechnology Kermanshah Iran

L Gil School of Forest Engineering University Polytechnic of Madrid AvdaComplutense Madrid Spain

S Guclu Istanbul Technical University Civil Engineering Faculty EnvironmentalEngineering Department Istanbul Turkey National Research Center on MembraneTechnologies (MEM-TEK) Istanbul Turkey

C Heacutelix-Nielsen University of Maribor Maribor Slovenia Technical University ofDenmark Lyngby Denmark

J Hoinkis Institute of Applied Research (IAF) Karlsruhe University of AppliedSciences Karlsruhe Germany

Y Ji School of Resources and Environmental Engineering East China University ofScience and Technology Shanghai PR China

M Kallioinen Lappeenranta University of Technology Laboratory of SeparationTechnology Skinnarilankatu Lappeenranta Finland

M Khayet Department of Applied Physics I University Complutense of MadridAvda Complutense Madrid Spain Madrid Institute for Advanced Studies of Water(IMDEA Water Institute) Alcala de Henares Madrid Spain

I Koyuncu Istanbul Technical University Civil Engineering FacultyEnvironmental Engineering Department Istanbul Turkey National Research Centeron Membrane Technologies (MEM-TEK) Istanbul Turkey

M Lee Imperial College London London UK

GL Leslie The University of New South Wales Sydney NSW Australia

K Li Imperial College London London UK

SS Madaeni Membrane Research Centre Department of Chemical EngineeringRazi University Kermanshah Iran

M Meuroantteuroari Lappeenranta University of Technology Laboratory of SeparationTechnology Skinnarilankatu Lappeenranta Finland

AW Mohammad Research Centre for Sustainable Process Technology UniversitiKebangsaan Malaysia UKM Bangi Selangor Malaysia

R Molinari Universita della Calabria Rende (CS) Italy

xiv List of contributors

M Nystreuroom Lappeenranta University of Technology Laboratory of SeparationTechnology Skinnarilankatu Lappeenranta Finland

L Palmisano Universita di Palermo Palermo Italy

ME Pasaoglu Istanbul Technical University Civil Engineering FacultyEnvironmental Engineering Department Istanbul Turkey National Research Centeron Membrane Technologies (MEM-TEK) Istanbul Turkey

I Petrinic University of Maribor Maribor Slovenia

H Rajabi Membrane Research Centre Department of Chemical Engineering RaziUniversity Kermanshah Iran Department of Civil Engineering Razi UniversityKermanshah Iran

NK Rastogi Department of Food Engineering Central Food TechnologicalResearch Institute Council of Scientific and Industrial Research Mysore India

Seyed MK Sadr Centre for Environmental and Health Engineering (CEHE)Department of Civil and Environmental Engineering University of Surrey GuildfordSurrey United Kingdom

Devendra P Saroj Centre for Environmental and Health Engineering (CEHE)Department of Civil and Environmental Engineering University of Surrey GuildfordSurrey United Kingdom

R Sengur National Research Center on Membrane Technologies (MEM-TEK)Istanbul Turkey Istanbul Technical University Nanoscience and NanoengineeringDepartment Istanbul Turkey

J Soons PWN Waterleidingbedrijf Noord Holland Velserbroek The Netherlands

KH Tng The University of New South Wales Sydney NSW Australia

T Turken Istanbul Technical University Civil Engineering Faculty EnvironmentalEngineering Department Istanbul Turkey National Research Center on MembraneTechnologies (MEM-TEK) Istanbul Turkey

B Van der Bruggen KU Leuven Leuven Belgium

Y Wang The University of New South Wales Sydney NSW Australia

Z Wu Imperial College London London UK

List of contributors xv

Preface

Water is the most abundant and renewable resource in the world Unfortunately only asmall quantity is fit for use to sustain human life In addition population growthcoupled with industrialization and urbanization has led to the increased pollution ofexisting freshwater resources resulting in an increased demand for fresh water Atthe same time challenges related to water systems are expected to increase in thenear future requiring further investment and technological innovation to meet globalneeds

Currently water recycling is widely accepted as a sustainable option in response tothe general increase in the demand for fresh water and to water shortages and environ-mental protection According to this view industrial companies are increasingly inter-ested in recycling wastewater to reach an ideal zero-discharge condition

Membrane technology has become a significant separation technology in the fieldof water filtration over the past two decades providing effective alternatives to relatedtechnologies such as adsorption extraction distillation ion exchangers and sand fil-ters It enables desalination or obtaining drinking water from saltwater as well as puri-fication of groundwater or wastewater

Low-energy consumption continuous separation easy scale-up modularityremote control and no phase separation are well-recognized key advantages of mem-brane processes over conventional separation technologies

The growth of the global membranes market is mainly the result of the impressivedevelopment of materials used for membrane fabrication and modification improve-ments in membrane modules and the evolution of different related systems plantsand equipment

This book covers the most recent and applicable achievements regarding materialsprocesses and applications of membranes for water treatment

The book is split into three parts The first is related to both novel membrane mate-rials and advances in membrane operations The second part considers how to improvemembrane performance and the last part illustrates selected applications in water treat-ment In the following section each chapter is briefly introduced

Chapter 1 (Madeani Ghaemi and Rajabi) illustrates the recent development of newmaterials and methods for the fabrication and modification of polymeric membranesfor water treatment Chapter 2 (Lee Wu and Li) provides an extensive analysis con-cerning recent progress in ceramic membranes for drinking water production and in thetreatment of municipal and industrial wastewater produced water (waste stream gen-erated from oil and gas operations) and wastewater generated in the food and beverage

industry In Chapter 3 (Koyuncu Sengur Turken Guclu and Pasaoglu) after a gen-eral overview of the global membrane market and various membrane fabrication tech-niques advances in water treatment by membrane processes such as ultrafiltrationmicrofiltration and nanofiltration are extensively illustrated Water treatment byboth reverse and forward osmosis for the desalination of water is described in Chapter 4(Rastogi Cassano and Basile) Differences among various membrane processesand the fundamentals of water treatment by reverse osmosis and forward osmosisare also considered Chapter 5 (Deowan Bouhadjar and Hoinkis) introduces mem-brane bioreactor technology with particular attention to water treatment Both aero-bic and anaerobic reactors are described The various factors affecting membraneperformance in both reactors (membrane fouling hydraulic residence time waterflux decline and so on in aerobic reactors and temperature organic loadingrate membrane properties and so on in anaerobic reactors) are seen as importantissues in this application of technology For each reactor a case study is also pro-posed The state of the art in the use of electrodialysis and electrodialysis with bipo-lar membranes for water treatment is reported in Chapter 6 (Van der Bruggen) Inparticular after a general description of the operational mechanisms of electrodial-ysis progress in anion and cation exchange membranes and new developments inmodule configurations and process integration are described Finally a brief over-view of applications of electrodialysis for water treatment is given Chapter 7 (Moli-nari Argurio Palmisano and Grillone) discusses both the basic principles ofphotocatalysis and advantages related to its coupling with membrane separationin so-called photocatalytic membrane reactors (PMRs) Important aspects for appro-priate large-scale implementation are the types of membranes used their criteria ofselection PMR configuration and membrane operation Some case studies in watertreatment are also discussed evidencing possibilities drawbacks and future trendsChapter 8 (Arribas Khayet Garciacutea-Payo and Gil) describes pressure-driven mem-brane processes and significant progress achieved over the past few years regardingthe fabrication of novel membranes and their modification In particular the chapterfocuses on novel flat-sheet and hollow-fiber membranes made with innovative mate-rials and with improved properties suitable for specific applications In Chapter 9(Arribas Khayet Garciacutea-Payo and Gil) the authors of the previous chapter extendconsideration to the electric potential and concentration gradient membrane pro-cesses In particular in this chapter the authors focus on water treatment by electro-dialysis with forward osmosis Also special attention is dedicated to alternativetechnologies of emerging interests used to produce power such as reverse electro-dialysis and pressure-retarded osmosis able to generate electricity from salinity gra-dients Some critical challenges (eg concentration polarization membrane foulingreverse solute diffusion and draw solute design) are also discussed

Chapter 10 (Frenkel) introduces the importance of membrane technologies whenthe water supply is considered for the community industry or agricultural user Infact membrane technologies have entered every aspect of water and wastewater treat-ment such as municipal and industrial water advanced wastewater treatment andreuse and seawater and brackish water desalination This chapter pays attention tothe design of both low- and high-pressure membrane systems for water treatment

xxii Preface

Finally integrated membrane systems and a combination of membrane treatment andother technological processes are briefly considered After distinguishing betweenmembrane ageing and failure Chapter 11 (Tng Antony Wang and Leslie) describesmembrane ageing during water treatment with particular attention to the modes andmechanisms of failure The authors review possible monitoring and control techniquesnecessary for the early detection of membrane ageing They also suggest some meas-ures for mitigating membrane failure caused by ageing Chapter 12 shows the impor-tance of mathematical modeling in membrane operations for water treatment (Ang andMohammad) In particular this chapter provides useful data on designing the plant andhelpful prediction of the performance of the membrane water treatment plant Differenttransport mechanisms are involved in pressure-driven membrane operations Thus themathematical models necessary to predict their performance are also different Theauthors show that the selection of a particular model of membrane water treatmentplant is crucial because it leads to a better understanding of its long-term performanceChapter 13 (Curcio Di Profio Fontananova and Drioli) provides a general overviewof membrane operations currently in use in seawater and brackish water desalinationfor potable water production In this chapter reverse osmosis novel salinity gradientpower technologies (with emphasis on pressure-retarded osmosis and reverse electro-dialysis) and membrane distillation are treated as viable options in the logic of zeroliquid discharge After introducing a section on drivers and barriers to membrane tech-nologies for municipal wastewater treatment Chapter 14 (Sadr and Saroj) describesvarious membrane-assisted processes and technologies in wastewater treatmentAnother important part of the chapter is related to both applications of nanofiltra-tionreverse osmosis after biological treatment and the design operation and controlof membrane processes in municipal wastewater treatment The optimization of mem-brane processes in municipal wastewater treatment is also well described taking intoconsideration cost assessment energy efficiencies and operational costs In Chapter15 (Bodzek) an analysis of the main organic and inorganic micropollutants of watersources is presented Membrane processes such as reverse osmosis and nanofiltrationultrafiltration and microfiltration in integrated systems Donnan dialysis and electro-dialysis as well as membrane bioreactors and liquid membranes are presented as alter-native technologies for producing high-quality drinking water as well as purifiedwastewater that can be drained off into natural water sources Chapter 16 (Yang) high-lights key advantages of pressure-driven membrane operations and their integrationinto existing systems for water treatment and reuse in the gas and petrochemical indus-tries Methods to reduce concentration polarization and membrane fouling phenom-ena which mainly affect membrane system performance and directly determine thecapital and operational costs of membrane systems in this field are also presentedand discussed Membrane technologies for water treatment and reuse in the textileindustry are described in Chapter 17 (Petrinic Bajraktari and Heacutelix-Nielsen) Theauthors present various examples of reverse osmosisnanofiltrationultrafiltration-based systems and membrane bioreactor technology that have been investigated fortextile wastewater remediation Forward osmosis used to concentrate textile dyes isalso presented Chapter 18 (Cassano Rastogi and Basile) presents an overview ofmembrane-based processes for water reuse and the environmental control in the

Preface xxiii

treatment of wastewaters from food-processing industries Various applicationsinvolving the use of pressure-driven membrane operations electrodialysis membranebioreactors and integrated membrane systems are shown and discussed In particularthe authors illustrate typical applications for the treatment of process waters from thefruit and vegetables dairy fish meat soya and wine industries highlighting theiradvantages and drawbacks with respect to conventional technologies Chapter 19(Meuroantteuroari Kallioinen and Nystreuroom) focuses on the use of membrane technologiesto purify raw water and wastewaters circulate process waters and recover valuablematerials in the pulp and paper industry The driving forces to use membranes and bar-riers as well as their challenges are discussed in the introduction Chapter 20 (Daal)focuses on water treatment required for the production of demineralized wateremployed for the watersteam cycle in industrial plants Water purification technolo-gies including membrane technologies and operational experiences with membranesare presented and discussed

The editors wish to take this opportunity to thank all of the authors of the chaptersfor preparing developing and improving their text Special thanks to all of the staff ofWoodhead for their excellent help to both the authors and the editors

Angelo BasileAlfredo CassanoNavin K Rastogi

xxiv Preface

Related titles

Advanced membrane science and technology for sustainable energy and environmentalapplications

(ISBN 978-1-84569-969-7)

Handbook of water and energy management in food processing

(ISBN 978-1-84569-195-0)

Metropolitan sustainability Understanding and improving the urban environment

(ISBN 978-0-85709-046-1)

Woodhead Publishing Series in Energy

1 Generating power at high efficiency Combined cycle technology for sustainableenergy productionEric Jeffs

2 Advanced separation techniques for nuclear fuel reprocessing and radioactive wastetreatmentEdited by Kenneth L Nash and Gregg J Lumetta

3 Bioalcohol production Biochemical conversion of lignocellulosic biomassEdited by Keith W Waldron

4 Understanding and mitigating ageing in nuclear power plants Materials andoperational aspects of plant life management (PLiM)Edited by Philip G Tipping

5 Advanced power plant materials design and technologyEdited by Dermot Roddy

6 Stand-alone and hybrid wind energy systems Technology energy storage andapplicationsEdited by John K Kaldellis

7 Biodiesel science and technology From soil to oilJan C J Bart Natale Palmeri and Stefano Cavallaro

8 Developments and innovation in carbon dioxide (CO2) capture and storagetechnology Volume 1 Carbon dioxide (CO2) capture transport and industrialapplicationsEdited by M Mercedes Maroto-Valer

9 Geological repository systems for safe disposal of spent nuclear fuels and radioactivewasteEdited by Joonhong Ahn and Michael J Apted

10 Wind energy systems Optimising design and construction for safe and reliableoperationEdited by John D Soslashrensen and Jens N Soslashrensen

11 Solid oxide fuel cell technology Principles performance and operationsKevin Huang and John Bannister Goodenough

12 Handbook of advanced radioactive waste conditioning technologiesEdited by Michael I Ojovan

13 Membranes for clean and renewable power applicationsEdited by Annarosa Gugliuzza and Angelo Basile

14 Materials for energy efficiency and thermal comfort in buildingsEdited by Matthew R Hall

15 Handbook of biofuels production Processes and technologiesEdited by Rafael Luque Juan Campelo and James Clark

16 Developments and innovation in carbon dioxide (CO2) capture and storagetechnology Volume 2 Carbon dioxide (CO2) storage and utilisationEdited by M Mercedes Maroto-Valer

17 Oxy-fuel combustion for power generation and carbon dioxide (CO2) captureEdited by Ligang Zheng

18 Small and micro combined heat and power (CHP) systems Advanced design perfor-mance materials and applicationsEdited by Robert Beith

19 Advances in clean hydrocarbon fuel processing Science and technologyEdited by M Rashid Khan

20 Modern gas turbine systems High efficiency low emission fuel flexible powergenerationEdited by Peter Jansohn

21 Concentrating solar power technology Principles developments and applicationsEdited by Keith Lovegrove and Wes Stein

22 Nuclear corrosion science and engineeringEdited by Damien Feacuteron

23 Power plant life management and performance improvementEdited by John E Oakey

24 Electrical drives for direct drive renewable energy systemsEdited by Markus Mueller and Henk Polinder

25 Advanced membrane science and technology for sustainable energy and environ-mental applicationsEdited by Angelo Basile and Suzana Pereira Nunes

26 Irradiation embrittlement of reactor pressure vessels (RPVs) in nuclear power plantsEdited by Naoki Soneda

27 High temperature superconductors (HTS) for energy applicationsEdited by Ziad Melhem

28 Infrastructure and methodologies for the justification of nuclear power programmesEdited by Agustiacuten Alonso

29 Waste to energy conversion technologyEdited by Naomi B Klinghoffer and Marco J Castaldi

30 Polymer electrolyte membrane and direct methanol fuel cell technology Volume 1Fundamentals and performance of low temperature fuel cellsEdited by Christoph Hartnig and Christina Roth

31 Polymer electrolyte membrane and direct methanol fuel cell technology Volume 2In situ characterization techniques for low temperature fuel cellsEdited by Christoph Hartnig and Christina Roth

32 Combined cycle systems for near-zero emission power generationEdited by Ashok D Rao

33 Modern earth buildings Materials engineering construction and applicationsEdited by Matthew R Hall Rick Lindsay and Meror Krayenhoff

34 Metropolitan sustainability Understanding and improving the urban environmentEdited by Frank Zeman

35 Functional materials for sustainable energy applicationsEdited by John A Kilner Stephen J Skinner Stuart J C Irvine and Peter P Edwards

36 Nuclear decommissioning Planning execution and international experienceEdited by Michele Laraia

37 Nuclear fuel cycle science and engineeringEdited by Ian Crossland

xviii Woodhead Publishing Series in Energy

38 Electricity transmission distribution and storage systemsEdited by Ziad Melhem

39 Advances in biodiesel production Processes and technologiesEdited by Rafael Luque and Juan A Melero

40 Biomass combustion science technology and engineeringEdited by Lasse Rosendahl

41 Ultra-supercritical coal power plants Materials technologies and optimisationEdited by Dongke Zhang

42 Radionuclide behaviour in the natural environment Science implications andlessons for the nuclear industryEdited by Christophe Poinssot and Horst Geckeis

43 Calcium and chemical looping technology for power generation and carbon dioxide(CO2) capture Solid oxygen- and CO2-carriersPaul Fennell and E J Anthony

44 Materialsrsquo ageing and degradation in light water reactors Mechanisms andmanagementEdited by K L Murty

45 Structural alloys for power plants Operational challenges and high-temperaturematerialsEdited by Amir Shirzadi and Susan Jackson

46 Biolubricants Science and technologyJan C J Bart Emanuele Gucciardi and Stefano Cavallaro

47 Advances in wind turbine blade design and materialsEdited by Povl Broslashndsted and Rogier P L Nijssen

48 Radioactive waste management and contaminated site clean-up Processestechnologies and international experienceEdited by William E Lee Michael I Ojovan and Carol M Jantzen

49 Probabilistic safety assessment for optimum nuclear power plant life management(PLiM) Theory and application of reliability analysis methods for major powerplant componentsGennadij V Arkadov Alexander F Getman and Andrei N Rodionov

50 The coal handbook Towards cleaner production Volume 1 Coal productionEdited by Dave Osborne

51 The coal handbook Towards cleaner production Volume 2 Coal utilisationEdited by Dave Osborne

52 The biogas handbook Science production and applicationsEdited by Arthur Wellinger Jerry Murphy and David Baxter

53 Advances in biorefineries Biomass and waste supply chain exploitationEdited by Keith Waldron

54 Geological storage of carbon dioxide (CO2) Geoscience technologies environmentalaspects and legal frameworksEdited by Jon Gluyas and Simon Mathias

55 Handbook of membrane reactors Volume 1 Fundamental materials science designand optimisationEdited by Angelo Basile

56 Handbook of membrane reactors Volume 2 Reactor types and industrialapplicationsEdited by Angelo Basile

57 Alternative fuels and advanced vehicle technologies for improved environmental per-formance Towards zero carbon transportationEdited by Richard Folkson

Woodhead Publishing Series in Energy xix

58 Handbook of microalgal bioprocess engineeringChristopher Lan and Bei Wang

59 Fluidized bed technologies for near-zero emission combustion and gasificationEdited by Fabrizio Scala

60 Managing nuclear projects A comprehensive management resourceEdited by Jas Devgun

61 Handbook of Process Integration (PI) Minimisation of energy and water use wasteand emissionsEdited by Jiriacute J Klemes

62 Coal power plant materials and life assessmentEdited by Ahmed Shibli

63 Advances in hydrogen production storage and distributionEdited by Ahmed Basile and Adolfo Iulianelli

64 Handbook of small modular nuclear reactorsEdited by Mario D Carelli and Dan T Ingersoll

65 Superconductors in the power grid Materials and applicationsEdited by Christopher Rey

66 Advances in thermal energy storage systems Methods and applicationsEdited by Luisa F Cabeza

67 Advances in batteries for medium and large-scale energy storageEdited by Chris Menictas Maria Skyllas-Kazacos and Lim Tuti Mariana

68 Palladiummembrane technology for hydrogen production carbon capture and otherapplicationsEdited by Aggelos Doukelis Kyriakos Panopoulos Antonios Koumanakos andEmmanouil Kakaras

69 Gasification for synthetic fuel production Fundamentals processes and applicationsEdited by Rafael Luque and James G Speight

70 Renewable heating and cooling Technologies and applicationsEdited by Gerhard Stryi-Hipp

71 Environmental remediation and restoration of contaminated nuclear and NORMsitesEdited by Leo van Velzen

72 Eco-friendly innovation in electricity networksEdited by Jean-Luc Bessede

73 The 2011 Fukushima nuclear power plant accident How and why it happenedYotaro Hatamura Seiji Abe Masao Fuchigami and Naoto Kasahara Translated byKenji Iino

74 Lignocellulose biorefinery engineering Principles and applicationsHongzhang Chen

75 Advances in membrane technologies for water treatment Materials processes andapplicationsEdited by Angelo Basile Alfredo Cassano and Navin K Rastogi

76 Membrane reactors for energy applications and basic chemical productionEdited by Angelo Basile Luisa Di Paola Faisal Hai and Vincenzo Piemonte

xx Woodhead Publishing Series in Energy

Advances in polymericmembranes for water treatment 1SS Madaeni1 N Ghaemi2 H Rajabi131Membrane Research Centre Department of Chemical Engineering Razi UniversityKermanshah Iran 2Department of Chemical Engineering Kermanshah University ofTechnology Kermanshah Iran 3Department of Civil Engineering Razi UniversityKermanshah Iran

11 Introduction

As themost precious and renewable resource in the world water is an important aspect oflife Theworldrsquos population tripled in the twentieth century and it will increase by another40 to 50 within the next 50 years Population growth coupled with industrializationand urbanization has resulted in the rapidly increasing demand for fresh water Further-more some existing fresh water resources have gradually become polluted because ofhuman or industrial activities Problems with water are expected to grow in the comingdecades with water scarcity occurring globally even in regions currently consideredwater-rich Therefore many researchers have focused on suitablemethods to obtain freshwater by purifying and reusing water to support future generations Water purification isthe process of removing unpleasant agents such as chemicals organic and biologicalcontaminants and suspended solids from water to obtain satisfactory water

Owing to its low cost and high efficiency membrane technology has dominatedwater purification technologies Compared with the other types of membranes poly-meric membranes lead the membrane separation industries and markets because theyare economically and practically beneficial However limited chemical mechanicaland thermal resistance restricts their application Extensive efforts have been imple-mented to improve both flux and selectivity and reduce membrane fouling as the mostimportant problem in application of membranes To eliminate obstacles and decreasethe problems in membrane use much research and numerous studies have been conduct-ed to develop newmaterials and methods for fabricating and modifying polymeric mem-branes This chapter covers the most recent and applicable achievements regarding thepreparationmodification and performance of polymericmembranes for water treatment

12 Advances in polymeric membranes

121 Composite (mixed matrix) membranes

Sometimes when fabricating membranes structural modification is necessary toenhance overall performance as well as the mechanical chemical and thermal stability

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400001-0Copyright copy 2015 Elsevier Ltd All rights reserved

of the membrane Methods to overcome the challenges of membrane modification havebeen well established for polymeric membranes Much research on membrane scienceand technology has focused on the development of new membrane preparation tech-niques and material An alternate way to improve membrane performance includingpermeability and selectivity involves introducing second phases into the membranematrix Polymers and some nanofillers were mostly introduced as a second phaseinto polymeric membranes to prepare different kinds of composite membranes

1211 Composite membranes prepared via blendingof polymers

Blending of additives into the casting solution is one of the most applicable methods tochange the phase separation process and consequently membrane characteristicsPolymeric materials are applied considerably as additives into the dope solution(Musale Kumar amp Pleizier 1999 Ochoa et al 2001) Although certain polymerssuch as polyethersulfone (PES) and poly(vinylidenefluoride) (PVDF) possess excel-lent thermal and mechanical stability as well as acceptable film-forming propertiesthat make them ideal materials for membrane preparation their application is oftenrestricted because of their hydrophobic nature which results in low water permeationand high fouling On the other hand the membranes made of hydrophilic polymerssuch as poly(vinyl alcohol) (PVA) cellulose acetate (CAc) and polyacrylonitrile(PAN) are also applied for the fabrication of liquid separation membranes howeverthe thermal and mechanical resistance and chemical stability of these membrane arelow Blending of polymers in membrane fabrication has been widely investigatedbecause of the simplicity of procedure and high efficiency in developing newmembranes with elevated properties and performance

The main focus in blending polymers is to increase hydrophilicity and decreasemembrane fouling Rahimpour and Madaeni (2007) prepared PES membrane byblending different concentrations of CAP (20 30 and 40 wt) and PVP (2 4 and8 wt) as a pore former Contact angle measurements showed that the hydrophilicityof membranes was enhanced for all compositions because of numerous acidic andcarbonyl functional groups in the CAP structure Pure water flux milk water perme-ation and protein rejection also increased with an increase in PESCAP compositionsup to 8020 Moreover the antifouling property of PES membranes was improved byadding even small amounts of CAP into the casting solution In another study(Masuelli Marchese amp Ochoa 2009) a PVDF ultrafiltration membrane was modifiedby blending PVDF with PVP and sulfonated polycarbonate to enhance permeation fluxand reduce fouling Surprisingly the hydraulic permeability of the membrane wasreduced and fouling increased for composite membranes (Masuelli et al 2009)Composite polysulfone (PSf) membranes were synthesized by Adams NxumaloKrause Hoek and Mamba (2012) by blending PSf with different concentrations ofb-CPU (0e10) using a phase inversion technique Addition of 5 b-CPU to PSfmembrane greatly improved the hydrophilicity of composite membranes comparedwith higher amounts because fewer pores were created on the membrane surfaceand owing to the chemical interaction between OHNH and the sulfonyl backbone

4 Advances in Membrane Technologies for Water Treatment

of PSf Moreover it was revealed that a low concentration of b-CPU was effective inimproving flux without compromising membrane rejection (Adams et al 2012)Table 11 summarizes some studies on composite membranes and the main propertiesof blending polymers

Table 11 Studies on composite polymeric membranes

Materials Feed solution

Properties ofcomposite versusnascentmembrane References

CASPSf mdash Larger pore size MalaisamyMahendran andMohan (2002)

PVDFPMMA Effluent fromengine factory

Largermacrovoideshigherhydrophilicitylower fouling

Ochoa Masuelliand Marchese(2003)

PSPA Solution of CNeZn2thorn ZnethCN2

4 THORNGood chemicalstability lessmechanicalresistance goodselectivity

Amado GondranFerreiraRodrigues andFerreira (2004)

PESCAPPVP Milk Higherhydrophilicitymore pure waterflux milk waterpermeation andprotein rejection

Rahimpour andMadaeni (2007)

PESPIPVP Salt solution Higherhydrophilicitymore pure waterflux more saltrejection

MansourpanahMadaeni Adeliand Rahimpour(2009)

SPCPVDF Oilewateremulsion

Lower fouling Masuelli et al(2009)

PSfPAN Aqueous solution ofheavy metals

Decrease in meansurface-pore sizeoverall porosityand permeabilityhigh leadcadmium andchromiumrejection

Mbareck NguyenAlaoui andBarillier (2009)

Continued

Advances in polymeric membranes for water treatment 5

1212 Thin-film composite membranes

Dense membranes generally have low flux but high selectivity whereas porousmembranes have low selectivity but high permeability To increase flux through adense membrane with high selectivity the thickness of the membrane should bereduced as much as practically possible However the membrane should be

Table 11 Continued

Materials Feed solution

Properties ofcomposite versusnascentmembrane References

CAPU Aqueous solutionscontaining textiledye

Lower thermalstability

Zavastin et al(2010)

HPAAPSf BSA solutionaqueous solutioncontaining heavymetal

Higher water fluxhigher rejectionof BSA and Cd(II)

Han Yu et al(2012)

CNCPSf Papermakingeffluent

Decreasingmechanicalstrength byincreasing CNCcontent higherpermeation goodability inpapermakingeffluent filtration

Zhou Zhao BaiZhang and Tang(2012)

PVDFSPPO Ionic solution Higher watercontent and ion-exchangecapacitysuperiorperformance by60 SPPO and40 PVDF

Khodabakhshi et al(2012)

PSfb-CPU Solution of heavymetal

Higherhydrophilicitymore water fluxand rejectionlower porosityless mechanicalstrength

Adams et al (2012)

6 Advances in Membrane Technologies for Water Treatment

defect-free and possess adequate mechanical strength This may be achieved with theuse of thin-film composite (TFC) membranes

Such composite membranes often consist of two layers a thin dense selective toplayer supported by a porous substrate The main role of the porous support is to providemechanical strength whereas the thin skin layer is responsible for permselectivityA TFC membrane is usually formed by a two-step process formation of a thickporous and nonselective substrate followed by coating with an ultrathin skin layerAmong different methods for forming the top layer dip-coating (Lang SourirajanMatsuura amp Chowdhury 1996 Peng Huang Jawor amp Hoek 2010 Susanto ampUlbricht 2008) and interfacial polymerization (Kim Kim Yu amp Deng 2009 PrakashRao Desai amp Rangarajan 1997 Rahimpour Jahanshahi Mortazavian Madaeni ampMansourpanah 2010 Reddy et al 2005 Shao et al 2013 Verissimo Peinemann ampBordado 2005 Wu et al 2006) were widely used Of these interfacial polymerizationis particularly interesting taking into account the considerable amount of research inthis field

TFC membranes have had remarkable development since the concept of interfa-cial polymerization was introduced by Mogan in 1965 (Lau Ismail Misdan ampKassim 2012) In this technique polymerization reaction takes place between tworeactive monomers at the interface of two immiscible solvents First the pores ofa membrane used as the support are filled with liquid A then the support isimmersed in a bath containing a reactant for liquid A As the result of interfacialpolymerization reaction a dense highly cross-linked polymer layer is formed onthe surface of the membrane at the interface of two solutions Heat ultraviolet(UV) and plasma treatment are often applied to control and complete interfacialpolymerization The top skin layer is extremely thin (01 mm or less) so TFCmembrane permeability is high Also membrane selectivity is high as a result ofthe high cross-linking of polymers

Commonly used reactive monomers are aliphaticaromatic diamines such as piper-azine (PIP) m-phenylenediamine (MPDA) and p-phenylenediamine (PPD) and acidchloride monomers such as trimesoyl chloride (TMC) isophthaloyl chloride (IPC)and 5-isocyanatoisophthaloyl chloride (ICIC) Among these materials and preparedTFC membranes polyaniline (PA) membranes prepared by interfacial polymerizationof multifunctional amine and acyl chloride monomers (Han Chung et al 2012 KimHwang Gamal El-Din amp Liu 2012 Kim et al 2009 Maurya Parashuram SinghRay amp Reddy 2012 Rahimpour et al 2010 Shao et al 2013 Verissimo et al2005 Yu Liu Liu and Gao 2009 Wu et al 2006) are the most typical and successfulTFC membranes Rahimpour et al (2010) prepared a TFC PA nanofiltration mem-brane using interfacial polymerization of PDA with TMC The TFC polyamide mem-branes displayed a higher ability to soften water The composite membrane exhibitedwater permeability of 7 and 21 kgm2 h for salt solution containing NaCl (1 gl) andMgSO4 (1 gl) at 5 and 10 bar respectively Also rejection of the divalent saltMgSO4 (85 and 90) was high compared with the monovalent salt NaCl (64and 67) at 5 and 10 bar respectively In other research Han chang et al (2012)demonstrated that blending a certain amount of sulphonated poly(ether ketone)(SPEK) material into the PSf substrate of TFC forward osmosis (TFC-FO) membranes

Advances in polymeric membranes for water treatment 7

not only has a key role in forming a fully spongelike structure but also enhances mem-brane hydrophilicity and reduces structure parameters In this study MPDA and135-TMC were employed as monomers for the interfacial polymerization reactionto form a thin aromatic polyamide selective layer The TFC-FO membranes withthe most hydrophilic SPEK (50 wt) in the substrates exhibited the lowest membranethickness a fully spongelike structure and the highest water flux of 50 and 35 lm2 hwhen deionized water and 2 M NaCl were used as the feed and draw solutionrespectively

New synthesized monomers were also employed to prepare TFC membranes withnotable properties Li and Kim (2008) synthesized a series of isomeric tetra-functionalbiphenyl acid chloride (mm-BTEC om-BTEC and op-BTEC) to prepare TFC reverseosmosis membranes through an interfacial polymerization technique with MPDA asthe amine monomer in aqueous solution According to this study the organic phasereactants had a considerable impact on membrane performance compared with theaqueous phase reactant Experimental results showed that the membrane preparedfrom op-BTEC revealed the highest permeability (542 lm2 h) followed by mem-branes prepared from om-BTEC (500 lm2 h) and mm-BTEC (317 lm2 h) whentested using a 2000 ppm NaCl solution at 2 MPa The rougher and larger surfacearea of the op-BTEC membrane which led to greater contact with water moleculeswas reported as the reason for the flux enhancement of this membrane (Li ZhangZhang amp Zheng 2008) In another study Chen Li Zhang and Zhang (2008) synthe-sized a new class of polymeric amine named SPES-NH2 which was applied for thepreparation of TFC reverse osmosis membranes Polysulfone was used as substrateand TFC membrane was prepared through interfacial polymerization of TMC solu-tions and amine solutions containing SPES-NH2 and m-Phenylenediamine (MPDA)The salt rejection and water flux of the composite membrane prepared under the opti-mum condition (acyl chloride monomer frac14 10 ratio of MPDA to SPES-NH2 frac14 214 min contact time with organic solution) reached 973 and 512 lm2 h respectivelyThe improvement in water flux was due to the incorporation of hydrophilic SPES-NH2

to polyamides On the other hand the high salt rejection was related to the chain stiff-ness of the copolymer and the high degree of cross-linking A novel amine monomerb-cyclodextrin polyurethane (DABA) with three amino groups was synthesized andapplied along with MPDA in TFC membrane preparation by Wang Li Zhang andZhang (2010) to increase the hydrophilicity of a PAN nanofibrous substrate Withan increase in the DABA content in the aqueous phase from 0 to 025 (wv)the TFC membranes showed an increment in water flux from 375 to 554 lm2 h whilemaintaining high salt rejection (w98) in the filtration of a salt solution containing2000 ppm NaCl at 2 MPa

With respect to the fouling resistance Abu Seman Khayet and Hilal (2010 2011)reported on the preparation of TFC membranes with improved antifouling tendency bymeans of interfacial polymerization between BPA andor TMBPA with TMCIrreversible fouling of modified polyester TFC PES membranes decreased duringfiltration of solutions containing humic acid at different pH values The highly uniformtop polyester layer coupled with the negative charge of the composite membranewas introduced as the main reason for the lower fouling of the TFC membrane

8 Advances in Membrane Technologies for Water Treatment

Furthermore An Li Ji and Chen (2011) incorporated PVA into composite nanofiltra-tion membranes by adding different amounts of PVA into PIP during interfacialpolymerization with TMC to improve the antifouling performance of compositemembranes The incorporation of a hydrophilic PVA chain into the PA active layerhad beneficial effects on developing a smoother surface and increasing membranehydrophilicity that were effective in diminishing the fouling of protein over thelong run

The application of additives such as synthesized hydrophilic surface modifyingmacromolecules (Abu Tarboush Rana Matsuura Arafat amp Narbaitz 2008 RanaKim Matsuura amp Arafat 2011) was shown to be effective in altering TFC mem-brane performance Abu Tarboush et al (2008) prepared a TFC membrane with amore hydrophilic surface by incorporating the synthesized additive hydrophilicsurface modifying macromolecules (LSMM) into the active PA thin top layer Itwas observed that during in situ polymerization LSSMs could migrate toward thetop airepolymer interface rendering the membrane hydrophilic and producing acomposite membrane with improved flux stability over an extended operationalperiod compared with an LSMM-free composite membrane Another importantdevelopment in TFC membrane technology was the incorporation of nanoparticlesinto the TFC membrane structure (Kim Kwak Sohn amp Park 2003 Lee ImKim Kim amp Min 2008) Kim et al (2003) prepared a hybrid TFC reverse osmosismembrane by the self-assembly of anatase TiO2 nanoparticles through coordinationand H-bonding interaction with the COOH functional groups of an aromatic poly-amide thin-film layer to reduce membrane biofouling The photocatalytic bactericidalability of the hybrid TFC membrane was examined by determining the survival ratiosof Escherichia coli cells with and without UV light illumination Photocatalyticbactericidal efficiency was remarkably higher for the hybrid TFC membrane underUV light illumination than that without illumination and the neat TFC membranesLee et al (2008) also reported on a preparation of PA nanocomposite membranecontaining TiO2 nanoparticles synthesized via in situ interfacial polymerization un-der various curing temperatures and curing times The interfacial reaction occurredbetween the aqueous phase of MPDA and the organic phase of TMC in whichTiO2 nanoparticles were homogeneously dispersed The incorporation of TiO2 nano-particles into PA resulted in an increase in water flux owing to the enhancement ofhydrophilicity in the membranes When the concentration of TiO2 nanoparticleswas 50 wt the optimum membrane performance was obtained together withstrong mechanical properties In more concentration of TiO2 the permeation fluxincreased and salt rejection decreased significantly Moreover the decrease inmechanical strength of the membranes resulted in easier peeling-off of thePA-TiO2 layer from PES substrate after the filtration experiment These resultswere attributed to the fact that a lower degree of polymerization of PA occurs athigh TiO2 concentrations because of an increase in the interference of interfacialpolymerization by TiO2 nanoparticles The incorporation of zeolite-A nanoparticles(Jeong et al 2007) and multi-walled nanotubes (MWNTs) (Wu Tang amp Wu 2010)throughout the thin-film layer were also explored as a facile approach to producesuperior hydrophilic membranes with improved performance

Advances in polymeric membranes for water treatment 9

The addition of co-solvent into the organic phase is another alternative to improveTFC membrane performance (Kim Kwak amp Suzuki 2005 Kong KanezashiYamomoto Shintani amp Tsuru 2010) Kong et al (2010) applied this method andadded acetone as the co-solvent into the organic phase to synthesize TFC nanofiltra-tion membranes with controllable active layer thickness and effective nanopores Thepresence of acetone could eliminate the large immiscibility gap between waterand hexane therefore it caused the interfacial polymerization reaction zone tobe controllable Consequently the permeation flux increased noticeably from21 1012 m3m2 Pa s for membranes prepared by conventional interfacial polymer-ization to 80 1012 m3m2 Pa s for TFC membranes prepared by adding co-solvent

122 Nanocomposite membranes (nano-enhanced membranes)

In another approach to membrane development processes researchers focused onincorporating inorganic nanoparticles into polymeric materials which resulted in theformation of nanocomposite (nano-enhanced) membranes with improved mechanicaland physicochemical properties Various nanomaterials have been employed as fillersuch as carbon nanotubes (CNTs) nanoclay nanosilver and nanosized TiO2 ZnOAl2O3 Fe3O4 SiO2 and ZrO2 More details about developments in nanocompositemembranes and their performance in water treatment are presented in the followingsections

1221 Carbon nanotubes

Among the various nanomaterials studied CNTs have received a great deal of atten-tion With high hydrophilicity good chemical stability and high surface area CNTsinduce highly antibacterial properties and increase the porosity of nanocompositemembranes They are ideal for reinforcing membranes because of their high aspectratio and high axis strength (Daraei Madaeni Ghaemi et al 2013) The wide rangeof possible applications for CNTs has been a driving force for the production of high-quality single-walled (SW) double-walled (DW) and MW CNTs for incorporationinto CNTepolymer composites (Vatanpour Madaeni Moradian et al 2012)

Several methods have been applied to produce inorganic-polymer membranessuch as filtration of the solvent containing dispersed CNTs through the membraneand then in situ polymerization onto the membrane surface (Madaeni Zinadini ampVatanpour 2011a) dispersion of CNTs in the monomer solution and then interfacialpolymerization onto a membrane as substrate (Roy Addo Ntim Mitra amp Sirkar2011) and blending nanoparticles into the casting solution followed by immersioninto the coagulation bath (Celik Park Choi amp Choi 2011 Choi Jegal amp Kimb2006 Mansourpanah et al 2011) or evaporation (Tang Zhang Wang Fu andZhang 2009)

Blending has some advantages over other methods The method is simple and hasmild conditions reproducibility and capability for industrialization Also preparationthrough polymer solution casting permits the use of polymers which were previouslyfound not to be suitable for in situ polymerization (Vatanpour Madaeni Moradian

10 Advances in Membrane Technologies for Water Treatment

et al 2012) Previous studies by Choi et al (2006) showed that MWCNT-blended PSfmicrofiltration membranes had slightly higher flux and rejection rates than nascent PSfmembrane Also those authors found that MWCNT-blended membranes were morehydrophilic than PSf ones In a related work Qui et al (2009) showed thatMWCNT-blended PSf ultrafiltration membranes had higher flux and lower rejectionas well as lower protein adsorption compared with nascent PSf membrane

Although CNTs have excellent separation characteristics and electrical and me-chanical properties there are problems in preparing mixed matrix membranes usingthis material such as no suitable dispersion of synthesized CNTs in organic solventsand different polymers (Celik et al 2011 Shirazi Ahmadzadeh Tofighy andMohammadi 2011 Vatanpour Madaeni Moradian et al 2012) Thus surfacemodification of this material is necessary to fabricate a homogeneous nanocompositemembrane Recent studies showed that surface modification can increase thedispersing properties of CNTs Chemical modification and functionalization ofCNTs surfactant treatment and polymer wrapping are several methods that havebeen widely used for uniform dispersion of nanotubes in a polymer matrix and forenhancing CNT adhesion to the polymer (Choi et al 2006 Eitan Jiang DukesAndrews amp Schadler 2003 Islam Rojas Bergey Johnson amp Yodh 2003 OrsquoConnellet al 2001 Qu et al 2004 Yang Chen et al 2007) In this regard ShawkyChae Lin and Wiesner (2011) added different concentrations of MWCNTs tothe PA membrane casting solution to form a nanocomposite structure improvethe mechanical properties of these membranes and increase their ability to rejectsalts The MWCNTs were dispersed into a mixture of dimethylacetamide(DMAc) (solvent) and lithium chloride salts Benzoyl peroxide (BPO) initiatorwas added into the casting solution with the goal of forming free-radicals onboth CNTs and PA This process resulted in polymer-grafted nanotubes thatdispersed better throughout the casting solution and a more homogeneousMWCNTsePA composite membrane was formed Investigation of the hydrophilic-ity and mechanical strength of nanocomposite membranes revealed a decrease inhydrophilicity owing to the hydrophobic nature of nanomaterials and an increasein the mechanical strength of the membranes because of the strong interactionsbetween the PA matrix and MWCNTs and homogeneous dispersion of CNTs

The decrease in permeability from 32 to 28 lm2 h and increase in salt rejection from24 to 76 respectively for the PA and MWCNTsPA (15 mgg) composite mem-brane were attributed to this network structure In addition humic acid removal byMWCNT composite membranes increased from 54 to 90 as the MWCNT loadingincreased from 0 to 10 mgg (Shawky Chae Lin and Wiesner 2011)

The introduction of hydrophilic functional groups onto the surface of the CNTsusing chemical modification especially acid is one of the simplest most widelyused and least expensive methods for uniform dispersion of nanotubes in the polymermatrix (Balasubramanian amp Burghard 2005 Celik et al 2011 Eitan et al 2003Shirazi et al 2011 Vatanpour Madaeni Moradian Zinadini amp Astinchap 2011)Vatanpour et al (2011) fabricated nanocomposite membranes composed of PES andacid-treated functionalized MWCNTs using a solution of 3 M HNO3H2SO4 (13vv) Functionalized MWCNTs were embedded in PES matrix using the phase

Advances in polymeric membranes for water treatment 11

inversion method The treated MWCNTs exhibited good dispersion and compatibilitywith the polymer matrix The blending of MWCNTs into PES matrix resulted in anincrease in hydrophilicity and water flux along with a decrease in fouling of the nano-composite membrane caused by Bovine Serum Albomin (BSA) filtration

In another work the same author (Vatanpour Madaeni Moradian et al 2012)fabricated an anti-bifouling nanofiltration membrane by mixing PES with TiO2-coated functionalized MWCNTs They coated MWCNTs with TiO2 nanoparticlesto enhance the dispersion of CNTs in organic solvent and polymer and improvethe interaction between the CNTs and the polymer matrix To purify and functional-ize CNTs the MWCNTs were dispersed into a mixture of H2SO4 and HNO3 with aratio of 31 The functionalized MWCNTs could participate in a reaction with otherreagents as a result of the formation of carboxylic acid groups on the surface ofMWCNTs (Vatanpour Madaeni Moradian et al 2012) To better deposit TiO2

nanoparticles onto the surface of oxidized MWCNTs dendrimer polycitric acidwas grafted onto functionalized CNTs At the final step MWCNTs were coatedwith TiO2 nanoparticles A schematic of the preparation of TiO2-coated MWCNTsis presented in Figure 11

The TiO2-coated MWCNTs showed suitable compatibility with polymeric matrixresulting in a low agglomeration of MWCNTs Addition of the modified MWCNTsinfluenced the surface mean pore size and porosity of the nanocomposite membranes

31H2SO4HNO3

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

COOH

COOHCOOH

COOH

COOHCOOHCOOH

COOH

COOHCOOHCOOH

COOH

HOOCCOOH

COOH

OH

COOHHOOC

HO

TiOC2H5

OC2H5

OC2H5

OC2H5

OC2H5

OC2H5C2H5OC2H5OC2H5O

C2H5OC2H5OC2H5O

Oxidized MWCNT

Monohydrate citric acid

Heated in vaccumfor 3h150 0C

Heated at 500 0C in N2 mediumfor 100 min

Polycitric acid-grafted MWCNTs

1) TiCI41 M HCI2) 5 M NH3stiring

for 3 h

Ti

O-Ti(OC2H5)(C2H5O)Ti-O

Ti

Anatase TiO2

TiO2-coated MWCNTS

Ti COOH

MWCNT

12 h reflux

Figure 11 Schematic showing coating of multi-walled carbon nanotubes (MWCNTs) withTiO2 nanoparticlesReprinted from Vatanpour Madaeni Moradian et al (2012) with permission from Elsevier

12 Advances in Membrane Technologies for Water Treatment

The prepared mixed matrix membranes showed higher hydrophilicity compared withnascent PES membrane which resulted in an increase in pure water flux Also theanti-biofouling characteristics of the nanoparticle-embedded membranes improvedas a result of increased hydrophilicity and decreased membrane surface roughness(Vatanpour Madaeni Moradian et al 2012) Daraei Madaeni Ghaemi Ahmadiet al (2013) and Daraei Madaeni Ghaemi Khadivi et al (2013) studied the effectsof blending polymer-modified MWCNTs and PES membranes and compared the re-sults with acid-functionalized MWCNTs They modified acid functionalizedMWCNTs using three hydrophilic polymers through an in situ polymerization reac-tion Citric acid acrylic acid and acryl amide were polymerized on acid-functionalized MWCNTs to achieve a higher number of functional groups onMWCNTs (Daraei Madaeni Ghaemi Khadivi et al 2013) The CNT-mixed mem-branes were fabricated using the phase inversion precipitation method Although thistreatment process caused a higher pure water flux with unchanged protein retention byadding a constant amount of PAA and PAAm-modified MWCNT into the membranematrix the best antifouling performance was shown by the membrane containingPCA-modified MWCNT The hyperbranched PCA caused an efficient dispersion ofMWCNTs because of good compatibility with PES This membrane also showedacceptable reusability and durability during three cycles of foulingewashing steps

1222 Clay nanoparticles

Clay nanoparticles are another inorganic additive for enhancing membrane perfor-mance Unmodified montmorillonites (NathornMMT) and Cloisite grades (modifiedMMT) are widely used nanofillers in the preparation of polymer nanocompositesMontmorillonite contains phyllosilicate groups and possesses an octahedral sheetsandwiched between two tetrahedral sheets forming a plate-shaped structure (withthe average diameter around 1 mm) (Abdollahi Rahmatpour Aalaie amp Khanbabae2008 Xie Tan Liao and Liu 2010) The layered structure of silicate has attractivehydrophilic properties and good thermal stability at high temperature (BebinCaravanier amp Galiano 2006) The most common methods used to prepare polymerclay nanocomposite technology are in situ polymerization melt intercalation andsolution dispersion In the latter method the clay mineral is exfoliated in single layersin the solvent medium and polymer chains are intercalated into these clay minerallayers The clay mineral platelets are joined by weak van der Waals forces and caneasily be dispersed in the solvent because of the increase in entropy caused by theirdisorganization Then polymer is adsorbed onto the delaminated clay mineral layersand the layers are reassembled after evaporation of the solvent and filled with polymerchains forming an intercalated nanocomposite (Anad~ao Sato Wiebeck Rolando ampDiaz 2010 Ghaemi Madaeni Alizadeh Rajabi amp Daraei 2011)

The clays most applied in polymer clay nanocomposite materials are generallythose containing clay minerals of the smectic group especially those containingMMT which are often employed for several innovative uses for example asabsorbers in the retention of pollutant gases in acid catalysis in sensors and as nano-fillers in nanocomposite preparation

Advances in polymeric membranes for water treatment 13

Many researchers have investigated the effects of adding clay particles on themorphology and thermal mechanical and hydrophilic properties as well as on theperformance of composite polymericmembranes Bebin et al (2006) prepared a compos-ite membrane containing clay particles Membranes were prepared by a recasting proce-dure using a Nafion solution mixed with Laponite particles comprising sulfonic acidgroups bonded to its surface The surface of clay particles was modified using plasmaactivation to bond styrenesulfonic moieties at their surface The dispersion of modifiedclay particles had a significant effect on the behavior of the Nafion membrane andenhanced both thewater retention and proton conductivity of nanocompositemembranesMonticelli Bottino ScandaleCapannelli andRusso (2007) reported on improvingwaterpermeability for PSf membranes blended with cationically modified clays The cationicclayePSf membranes showed the most flux and the least water contact angle (mosthydrophilicity) resulting in the enhancement of membrane performance Anad~ao et al(2010) also used modified clay as a PSf dopant and reported significant changes to themembrane morphology and thermal mechanical and hydrophilic properties

Another typical polymer used to prepare polymer clay composites is PVDFLi and Kim (2008) investigated the effect of adding modified clay (Closite Nathorn) onthe thermal properties of microporous PVDF membranes The authors reportedthat the thermal properties of PVDF nanocomposite membrane diminished afteradding modified clay nanoparticles In another work various kinds of clay particles(Closite Nathorn Closite 15A Closite 20A and Closite 30B) were incorporated intoPVDF membrane by a solution mixing method and PVDFeclay nanocomposite mem-branes were prepared by the phase inversion method (Hwang Kim Kim Hong ampNam 2011) Improved mechanical properties and thermal stability against shrinkagewere obtained by incorporating clay particles into the PVDF matrix In contrastKoh et al (2010) did not find considerable improvement in the mechanical propertiesof PVDFehexafluoropropylene (PVDFeHFP)eclay nanocomposite membranesbecause of the increased porosity of the nanocomposite membranes

Ghaemi et al (2011) synthesized PESorganically modified montmorillonite(OMMT) nanocomposites using Closite 15A and reported significant changes to themembrane skin layer and sublayer with increasing clay concentration in the casting so-lution They declared that the addition of OMMT can be effective in considerablyimproving membrane hydrophilicity and thermal and mechanical resistance as wellas pesticide retention capability at different solution conditions (acidic and neutral)In similar work Mierzwa Arieta Verlage Carvalho and Vecitis (2013) investigatedthe effect of incorporating unmodified clay nanoparticles (single platelet MMT) withand without sodium hexametaphosphate as a clay nanoparticle dispersant into the cast-ing solution on the morphology and performance of PES ultrafiltration membranesThey showed that clay additives have the ability to increase membrane permeabilityas a result of changes induced on the structure of the internal and surface pores ofthe membrane The addition of clay nanoparticles resulted in a reduction in hydrophi-licity and the negative charge of the membrane surface Surprisingly it was revealedthat although the clay membranes were more prone to fouling membrane permeabilityin the filtration of alginate solution was still greater than the nascent membrane(Mierzwa et al 2013)

14 Advances in Membrane Technologies for Water Treatment

Wan Ngah Teong and Hanafiah (2011) used chitosan-based composites containingMMT clay bentonite etc for dye removal from effluents Improvement of chitosanproperties and performance was considered the main achievement of fabricating suchnanocomposites An increase in mechanical and thermal strength as well as higher plas-ticity of chitosaneOMMT nanocomposite was also reported by researchers (Abdollahiet al 2008 Casariego et al 2009 Han Lee Choi amp Park 2010) Moreover manystudies were conducted on the adsorption of pollutants onto the chitosaneclay compos-ites in which the increment of the adsorption capacity of chitosan membranes wasproved as a result of adding clay nanoparticles (An ampDultz 2007 Bleiman ampMishael2010 Celis Adelino Hermosin amp Cornejo 2012 Chang amp Juang 2004 NesicVelickovic amp Antonovic 2012 Pandey amp Mishra 2011) For example Nesic et al(2012) tested the adsorption capability of chitosanMMT (Closite Nathorn) with BezactivOrange V-3RBO (BO) solution The effect of different amounts ofMMT on the adsorp-tion of BO was evaluated under different pHs and temperatures It was revealed thatchitosan in combination with clays produced a reliable adsorbent The main advantageof these membranes compared with similar systems is that these membranes possessedsignificantly higher adsorption capacity at low acidic conditions (pH above 6) There-fore the pretreatment of wastewater is not needed in real applications Despite relativelylong adsorption tests thesemembraneswere applicable as the result of a high adsorptioncapacity Thin-film composite membranes using chitosanenanoclay (Closite 15A and30B) coated onto the PVDF microfiltration membrane was fabricated by Daraei et al(2013) Insertion of organoclays with various percentages into the chitosan made itmore efficient for fabricating TFC membranes with the valuable ability to removedye (methylene blue and acid orange 7) from effluents

1223 Silver nanoparticles

Compared with other nanoparticles silver (Ag) is one of the first nanomaterials thatgained attention for fabricating composite membranes The bactericidal nature of silvernanoparticles brought them into the field of mixed matrix membranes Silver nanopar-ticles have a large surface-to-volume ratio thus they are used as a sustained local supplyfor Agthorn ions and provide a prolonged prevention of bacterial adhesion (Cao Tang LiuNie amp Zhao 2010 Martinez-Gutierrez et al 2012 Mollahosseini RahimpourJahamshahi Peyravi amp Khavarpour 2012) Silver is believed by some researchers(Danilczuk Lund Saldo Yamada amp Michalik 2006) to be nonallergic nontoxicand environmentally friendly Other researchers believe that silver is less harmful tohuman cells compared with bacteria (Taurozzi et al 2008) Research has shown thatincorporation of Ag nanoparticles onto the surface or in the matrix of membranes iseffective against the bacteria E coli Pseudomonas mendocina KR1 P aeruginosaand Staphylococcus aureus (Li Shao Zhou Li amp Zhang 2013 Liu Zhang HeZhao amp Bai 2010 Liu Rosenfield Hu ampMi 2013 Mollahosseini et al 2012 ZhangZhang Gusseme amp Verstraete 2012 Zodrow et al 2009) Also it was proved that theaddition of Ag nanoparticles into the membrane matrix not only makes the membranesbactericidal but also results in a significant improvement in virus removal (Zhang et al2012 Zodrow et al 2009) Chamakura Perez-Ballestero Luo Bashir and Liu (2011)

Advances in polymeric membranes for water treatment 15

described in detail the steps of the antibacterial mechanism including (1) generation ofreactive oxygen species indirectly (2) direct interaction of Ag with proteins and lipids inthe cellwall and alsoproteins in the cytoplasmicmembrane and (3) interactionwith deox-yribonucleic acid Some investigators (Koseoglu-Imer Kose Altinbas amp Koyuncu2013) suggested that Ag nanoparticles might pass through cell barriers and then releaseAgthorn ions Then Agthorn ions interact with the thiol groups of enzymes and cell proteinsdamage bacterial respiration and transport systems across the cell membrane

Silver ions were employed in membrane fabrication because of their low toxicity to-ward humans and their antibacterial ability In this regard researchers prepared mem-branes with silver ions to obtain a superior antifouling performance (Basri et al2010 Chou Yu amp Yang 2005) In contrast with silver ions silver nanoparticlesinduced long-lasting antibacterial and anti-adhesive effects and consequently consider-able resistance to biofouling in the membranes (Li et al 2013 Zodrow et al 2009) Totake advantage of Ag nanoparticles Ag does not necessarily need to be embedded intothe membrane structure during preparation It can be added to a commercial membraneand regenerated if needed However loss of antimicrobial and antiviral activity ofAg-coated membranes might occur as a result of depleting silver particles from themembrane surface and ineffectiveness against silver-resistant bacterial strains (Zodrowet al 2009) For this reason silver nanoparticles have received more attention in less-ening biofouling through embedding into the membrane backbone so far most studieson antifouling nanocomposite membranes have focused on incorporating silver nano-particles inside the membranes (Gusseme et al 2011 Li et al 2008 Sawada et al2012 Thomas et al 2009 Travan et al 2009 Zhang et al 2012 Zodrow et al2009) This way silver nanoparticles were added into the PAN (Yu et al 2003) poly(2-ethyl-2-oxazoline) (Kang Kim Char Won amp Kang 2006) PA (Lee et al 2007)polyimide (PI) (Deng Dang Zhou Rao amp Chen 2008) PES (Basri Ismail amp Aziz2011 Basri et al 2010 Cao et al 2010 Huang Arthanareeswaran et al 2012) CA(Barud et al 2011 Chou et al 2005) chitosan (Liu et al 2010 Zhu Bai Wee Liuamp Tang 2010) PVDF (Li et al 2013) and PSf (Zodrow et al 2009) compositemembranes Antibacterial experiments confirmed that bacterial growth was effectivelyinhibited and anti-biofouling performance rose in these kind of nanocompositemembranes

An increase in the hydrophilicity and selectivity of membranes blended with Agnanoparticles was also reported apart from the antibactericidal and antifouling proper-ties of silver (Basri et al 2011 Koseoglu-Imer et al 2013 Yong et al 2010 Zodrowet al 2009) Silver nanoparticles can be used as a suitable candidate for the simulta-neously improvement of membrane surface hydrophilicity and antifouling perfor-mance under proper conditions This phenomenon occurs because Ag particlesdiminish the surface tension of a pristine membrane and so water can easily spreadonto membrane surfaces (Li et al 2013)

1224 Titanium dioxide nanoparticles

Titanium dioxide (TiO2) is a special semiconductor that has been the focus ofnumerous investigations because of its excellent photocatalytic and hydrophilicity

16 Advances in Membrane Technologies for Water Treatment

properties in absorbing UV rays and its stability cheapness and commercial availabil-ity Therefore many researchers have prepared TiO2-mixed matrix membranes toimprove membrane performance by increasing hydrophilicity and reducing fouling(Madaeni amp Ghaemi 2007 Vatanpour Madaeni Khataee et al 2012 Yang ampWang 2006 Yang Zhang et al 2007)

Ebert Fritsch Koll and Tjahjawiguna (2004) investigated the influence of incorpo-rating TiO2 particles on the performance of PVDF and PAI membranes at elevatedpressures and temperatures Membranes fabricated by the phase inversion methodrevealed considerable thermal and mechanical stability In another work Yang andWang (2006) prepared a PSTiO2 organiceinorganic hybrid ultrafiltration membranewith high hydrophilicity and permeability and mechanical and thermal stability using asol-gel and phase inversion process The hybrid membranes exhibited extraordinaryhydrophilicity increased porosity and superior permeability without changingretention

The main benefit of using TiO2 nanoparticles in a mixture with polymeric mem-branes is the reduction of membrane fouling Much work has been conducted inblending TiO2 nanoparticles with different polymeric membranes to prepare compos-ite membranes with antifouling properties Table 12 lists some prepared polymericTiO2 composite membranes with antifouling properties

Regarding the photocatalytic bactericidal ability of TiO2 nanoparticles in recentyears heterogeneous photocatalysis UVeTiO2 systems have been also applied tosolve a variety of important environmental problems such as detoxifying water andproducing self-cleaning materials Damodar et al (2009) prepared PVDFeTiO2 com-posite membranes via the phase inversion method by mixing different amounts of TiO2nanoparticles (04 wt) into the PVDF casting solution The photocatalytic bacteri-cidal ability of composite PVDFeTiO2 membranes was tested using E coli (initialconcentration frac14 66 10thorn07 colony-forming unitsml) with and without the presenceof UV light (Figure 12)

These results were compared with a reference E coli solution that was kept indarkness Result showed that almost all E coli cells survived in the dark whereasabout 58 of cells survived on pristine PVDF membrane exposed to UV light for1 min The number of surviving E coli cells decreased by adding TiO2 particles andincreasing their content in the PVDFeTiO2 composite membrane and almost completeremoval of E coli occurred with a 4 TiO2ePVDF membrane during 1 min (Damodaret al 2009) In similar work with similar results Rahimpour Jahanshahi Rajaeian andRahimnejad (2012) induced bactericidal ability into a PVDFeSPES-blend membraneby incorporating TiO2 nanoparticles into the membrane to remove E coli

To increase homogeneous dispersion reduce agglomeration enhance nanofillerepolymer interaction and improve the stability of TiO2 nanoparticles chemicalapproaches have been applied to modify TiO2 nanoparticles (Li Zhu amp Zheng2007 Madaeni Zinadini amp Vatanpour 2011b Razmjou et al 2011) Li et al(2007) organically modified TiO2 nanoparticles with silane couple to overcomeaggregation and improve the dispersion of TiO2 nanoparticles in organic solventThe morphology and structure of PPESK ultrafiltration membrane indicated thatthe addition of TiO2 nanoparticles increased the thickness and porosity of the skin

Advances in polymeric membranes for water treatment 17

layer as well as the surface wettability and hydrophilicity of the membrane Thetensile mechanical strength of the membrane was also enhanced after the additionof TiO2 Moreover permeability and rejection tests showed that the pure waterflux and solute rejection of composite membranes were remarkably elevated whena small amount of TiO2 nanoparticles was added into the membrane structure

In other research Razmjou et al (2011) employed mechanical and chemical mod-ifications of TiO2 nanoparticles to improve their dispersion into the PES membranematrix For mechanical modification TiO2 nanoparticles with a volume of 50 cm3

Table 12 Some prepared polymericeTiO2 composite membraneswith antifouling properties

Polymer TiO2 (type) TiO2 (size nm) Reference

PSf-PVDF-PAN Degussa P25 20 Bae and Tak (2005)

PVDF Rutile 26e30 Cao et al (2010)

PVB Anatase 180 Fu Matsuyama and Nagai(2008)

PES Degussa P25 20 Rahimpour MadaeniTaheri and Mansourpanah(2008)

PES Rutile 30 Wu Gan Cui and Xu (2008)

PVDF Degussa P25 20 Damodar You and Chou(2009)

PVDF Degussa P25 20 Oh Kimb and Lee (2009)

PES Degussa P25 20 Li et al (2009)

PVDF Degussa P25 20 Yu Shen et al (2009)

PES Degussa P25 20 Hamid et al (2011)

CA Anatase 62 Abedini Mousavi andAminzadeh (2011)

PVDFSPES Degussa P25 20 Rahimpour et al (2011)

PVDF Degussa P25 25 Wei et al (2011)

PVDF Degussa(80 anataseand 20 rutile)

20 Madaeni Zinadini andVatanpour (2011b)

PES Degussa P25anatase

20 8 15e25 Vatanpour MadaeniKhataee et al (2012)

PVDF Anatase 20 Shi Ma Ma Wang and Sun(2012)

Reprinted from Vatanpour Madaeni Khataee et al (2012) with permission from Elsevier

18 Advances in Membrane Technologies for Water Treatment

were ground into fine powder until the volume decreased to 125 cm3 Afterward thepowder was dispersed in DMAc by sonication in a bath for 15 min followed by 10 minsonication by probe at an amplitude of 20 kHz The chemical modification of TiO2 wasalso carried out by surface modification of TiO2 nanoparticles with aminopropyltrie-thoxysilane (APTES) as silane coupling agent First 25 g of mechanically modifiedTiO2 nanoparticles was added into pure ethanol under nitrogen purging this was fol-lowed by 30 and 10 min sonication in bath and by probe respectively Differentamounts of APTES (2 20 50 and 80 wt) were added drop-wise to the mixture underan N2 atmosphere After stirring for 2 h at 65 C the particles were separated from thesolution by centrifuging at 10000 RPM for 10 min Finally the TiO2 particles weredried in an oven for 24 h at 50 C and then were ground into fine powder The com-bination of chemical and mechanical modifications was significantly effective for thefree energy and roughness of the surface pore size and protein absorption resistanceof the membrane surface as well as improved hydrophilicity of the membraneAlthough most researchers reported that an increase in hydrophilicity is the most likelyreason for decreased fouling Razmjou et al (2011) believed that the other parameterssuch as changes in the membrane morphology and local surface modifications mighthave a similar effect on the higher fouling resistance of TiO2-embedded membranes

1225 Zinc oxide nanoparticles

Another applicable nanoparticle used in modifying membranes is nano-zinc oxide(ZnO) As a multifunctional inorganic nanoparticle ZnO nanoparticles have recentlydrawn increasing attention owing to their prominent physical and chemical propertiessuch as high catalytic activity and effective antibacterial and bactericide capabilities(Balta et al 2012 Hong amp He 2012) Moreover ZnO nanoparticles are moreeconomical than some other nanoparticles such as TiO2 and Al2O3 nanoparticles

CFU0 = 66E+07 CFUml

Figure 12 Removal efficiency of Escherichia coli in water on the surface of differentpoly(vinylidenefluoride) (PVDF)TiO2 membranes with and without the radiation of UV lightReprinted from Damodar You and Chou (2009) with permission from Elsevier

Advances in polymeric membranes for water treatment 19

On the other hand ZnO nanoparticles are easily able to absorb hydrophilic hydroxylgroups (OH) (Shen et al 2012) Thus the supplementation of ZnO nanoparticlescan improve the hydrophilicity and mechanical and chemical properties of the polymermatrix (Hong amp He 2012 Lin et al 2009 Shen et al 2012)

Balta et al (2012) significantly reduced fouling of PES nanofiltration membranesafter blending with different concentrations of ZnO nanoparticles (0035 0070085 0125 0250 0375 0500 0750 1 2 and 4 wt) The ZnO-blended mem-branes showed a lower decline in flux and better permeability compared with pristinemembrane owing to the significantly higher hydrophilicity of nanocomposite mem-branes even at ultra-low concentrations of ZnO nanoparticles Also raising the nano-particle concentration to 0125 wt increased the relative flux of nanocompositemembranes but at higher concentrations no further increment was observed Further-more the addition of ZnO nanoparticles considerably improved the fouling resistanceof composite membranes during filtration of solutions containing humic acid This wasattributed to the reduction of adsorption of organic pollutants within the membranestructure as a result of increments of membrane hydrophilicity after the addition ofZnO nanoparticles Shen et al (2012) obtained similar results in fabricating aPESeZnO composite membrane Hydrophilicity thermal resistance porosity waterflux and antifouling capability of the nanocomposite membrane improved after addingZnO nanoparticles (Shen et al 2012)

In other work (Leo Cathie Lee Ahmad amp Mohammad 2012) ZnO nanoparticleswere added into a PSf ultrafiltration membrane to create antifouling properties not onlyon the membrane surface but also inside the pores Based on the results the addition ofZnO nanoparticles significantly increased the membrane hydrophilicity As a result ofincreasing the mean pore size and membrane hydrophilicity an increase as much as100 was observed in permeability The PSf membranes blended with ZnO nanopar-ticles also exhibited less fouling compared with nascent PSf membranes during filtra-tion of an aqueous solution containing oleic acid Moreover the composite membranesshowed improved thermal stability

In a study conducted by Liang Xiao Mo and Huang (2012) ZnO nanoparticleswith different concentrations were blended with PVDF polymer and applied for thefabrication of a composite PVDFeZnO membrane using the wet phase separationmethod Multi-cycle filtration tests demonstrated significant anti-irreversible foulingof the modified PVDF membrane Specifically all modified membranes reachedalmost 100 water flux recovery and maintained the initial fluxes constant in multi-cycle tests Similar to much other research this change was attributed to an increasein the surface hydrophilicity of the membrane

1226 Aluminum oxide nanoparticles

The stability availability hydrophilicity and suitable mechanical strength ofaluminum oxide (Al2O3) nanoparticles make this inorganic material another optionfor preparing of nanocomposite membranes By the aid of Al2O3 blending the mem-brane can combine the basic properties of these materials and display specific bene-fits with respect to thermal and chemical resistance separation performance and

20 Advances in Membrane Technologies for Water Treatment

adaptability to the severe water and wastewater conditions Much research has beendone in applying Al2O3 nanoparticles blending with a PVDF membrane to determinethe effect of Al2O3 particles on the hydrophilicity permeation flux morphologymechanical properties and antifouling performance of membranes

Various mixed matrix membranes of alumina (Al2O3) with CAc (Wara Francisand Velamakkani 1995) CAP (Mukherjee amp De 2013) PA (Saleh amp Gupt 2012)and PVDF (Yan Li amp Xiang 2005 Yan Li Xiang amp Xianda 2006 YanHong Li amp Li 2009) were prepared to change membrane properties such as hydro-philicity permeability and fouling resistance Yan et al (2005 2006) prepared aPVDFeAl2O3 nanocomposite membrane with different concentrations of Al2O3

(1 nm) using the phase inversion method The addition of nanosized Al2O3 particlesincreased membrane permeability with no change in the membrane pore size andnumber just by improving the surface hydrophilicity of the membrane The improve-ment in the hydrophilicity of the nanocomposite membrane also increased its anti-fouling performance in filtering oilewastewater solution from the oil field (Yanet al 2005) In another work the same authors prepared the phase inversion methodusing a nanocomposite tubular ultrafiltration PVDFeAl2O3 membrane (Yan et al2009) The flux of the modified membranes was always higher (about twice) thanthat of the unmodified membranes owing to the improvement of membrane hydro-philicity caused by adding nanosized alumina particles into the PVDF Interestinglythe permeation performance of the modified membrane increased significantlywithout sacrificing its retention properties All of these studies indicate that thepermeability and antifouling performance of the modified PVDF membranes wereconsiderably changed by incorporating Al2O3 nanoparticles into the membranematrix (Yan et al 2009 Yi et al 2011)

On the other hand Liu Moghareh Abed and Li (2011) used g-Al2O3 nanoparticlesThe authors tried to modify PVDF chains and impede segregation of nanoparticles by agrafting reaction between g-Al2O3 nanoparticles (containing a substantial amount ofhydroxyl groups [OH]) and the PVDF polymer catalyzed by some acid (H2SO4)The authors presented a mechanism for the reaction between g-Al2O3 and PVDFshown in Figure 13 The PVDFeg-Al2O3 nanocomposite membranes revealedhigh hydrophilicity and fouling resistance owing to their surface activity high adsorp-tive ability and surface enrichment of reactive functional hydroxyl groups

CF2 CF2

CF2

CH2 CH2

CH2

n

n

nn

OH-

CF CH

H+ FCH

FCH

CHCHγ -Al2O3-OH

γ -Al2O3-O

Basic γ -alumina

y

ndash

+

x

Figure 13 Schematic of the reaction between g-Al2O3 and poly(vinylidenefluoride) polymerReprinted from Liu Moghareh Abed and Li (2011) with permission from Elsevier

Advances in polymeric membranes for water treatment 21

In studies conducted by Maximous Nakhla Wan and Wong (2009) andMaximous Nakhla Wan et al (2010) PES membranes were modified by insertingdifferent concentrations of nanosized alumina (48 nm) particles inside the polymermatrix The increase in porosity and decrease in the hydrophobic interaction betweenmembrane surface and foulants changed the performance of the PES membrane afteradding Al2O3 nanoparticles into the casting solution As a result of the inducedchanges on the membrane after adding Al2O3 nanoparticles the nanocomposite mem-brane showed less flux decline compared with a pristine PES polymeric membrane(Maximous Nakhla Wan et al 2010 Maximous et al 2009)

1227 Iron oxide nanoparticles

Magnetic nanoparticles have gained much attention by researchers in recent yearsBecause of their inherent super paramagnetic properties magnetic nanoparticleshave been studied for various applications including drug and gene targeting cell sep-aration and hyperthermia (Ye Liu Wang Huang amp Xu 2009) Iron oxide (Fe3O4)has excellent thermal and chemical stability and good magnetic performance butalso good biocompatibility and biodegradation ability (Dudek et al 2012 Huanget al 2008) In this regard a PSfeFe3O4 composite ultrafiltration membrane wasfabricated by Fe3O4 nanoparticles (8e12 nm in size) wrapped in the oleic acid usingthe phase inversion method and the membrane performance in retaining lysozyme wasinspected under the magnetic field (Jian Yahui Yang amp Linlin 2006) Although thethermal stability and porosity of the PSf membrane increased after adding Fe3O4membrane hydrophilicity declined as the result of the hydrophobicity of Fe3O4 nano-particles which were wrapped in the oleic acid The rejection of lysozyme using PSfmembrane remained constant within and without the presence of the magnetic fieldHowever the rejection of the nanocomposite membrane was clearly reduced underthe magnetic field the retention recovered quickly when the magnetic field wasremoved On the other hand with the increase in magnetic intensity the decline inrejection was more noticeable The authors concluded that it is possible to separatesome substances using a PSfeFe3O4 nanocomposite membrane by altering themagnetic intensity

In various studies Huang Guo Guo and Zhang (2006) Huang Chen ChenZhang and Xu (2010) and Huang Zheng et al (2012) investigated the effects ofincorporating Fe3O4 nanoparticles on the performance of polymeric membranesThe authors showed that magnetization of a PAN membrane using Fe3O4 nanopar-ticles led to an increment of membrane permeation and antifouling performance inthe ultrafiltration of pig blood (Huang et al 2006) Moreover Fe3O4 nanoparticleswith different concentrations were applied in fabricating PSfeFe3O4 (Huang et al2010) and PVDFe Fe3O4 (Huang Zheng et al 2012) nanocomposite membranesThe composite membranes showed the best performance in terms of pure waterflux rejection and fouling resistance

Apart from improvements in membrane characteristics obvious benefits of ironoxide nanoparticles in the removal of arsenic (Sabbatini et al 2010 Sabbatini RossiThern amp Marajofsky 2009 Park amp Choi 2011) and adsorption of heavy metals

22 Advances in Membrane Technologies for Water Treatment

(Daraei et al 2012 Gholami Moghadassi Hosseini Shabani amp Gholami 2013Mansour Ossman amp Farag 2011) were proved in some research Daraei et al(2012) prepared Fe3O4ePA nanoparticles as adsorbent and used them in the PESmatrix to obtain a nanocomposite membrane with enhanced affinity for the removalof copper ions According to the experiments nanocomposite membranes indicatedhigher Cu(II) ion removal but lower pure water flux compared with pristine PESmembrane This was due to the surface pore blockage as a result of the presence ofnanoparticles in the superficial pores of the membrane during preparation (Figure 14)In other research conducted by Gholami et al (2013) iron oxide nanoparticles wereblended with polyvinyl chloride-blend cellulose membrane to apply the adsorbentproperties of Fe3O4 nanoparticles in the removal of lead from aqueous solution As ex-pected the permeability and rejection of lead rose in nanocomposite membranescompared with pristine membrane

1228 Silicon dioxide nanoparticles

Silicon dioxide (SiO2) is another convenient nanoparticle widely used in fabricatingnanocomposite membranes because of the mild reactivity and distinguished abilityin increasing hydrophilicity and improving the thermal and mechanical stability andfouling resistance of membranes (Jin Shi et al 2012 Jin Yu et al 2012 Ogoshi ampChujo 2005 Wu Xu amp Yang 2003) Silica was widely used with polymericmembranes such as PMMA (Zulfikar Mohammad amp Hilal 2006) PES (ShenRuan Wu amp Gao 2011 Wu et al 2003) PSf (Zhang Liu Lu Zhao amp Song2013) PA (Jin Shi et al 2012 Kim amp Lee 2001) PVA (Nagarale Shahi ampRangarajan 2005 Thanganathan Nishina Kimura Hayakawa amp Bobba 2012Yang James Li amp Liou 2011) and PVDF (Cho amp Sul 2001 Cui Liu Xiao amp

Figure 14 Field emission scanning electron microscopic image of cross-section of membraneprepared with 1 wt polyacrylonitrile (PAN)Fe3O4 nanoparticlesReprinted from Daraei et al (2012) with permission from Elsevier

Advances in polymeric membranes for water treatment 23

Zhang 2010 Liao Zhao Yu Tong amp Luo 2012 Yu Xu et al 2009 Zhang MaCao Li amp Zhu 2014) using sol-gel (Thanganathan et al 2012 Wu et al 2003)phase inversion (Cui Liu Xiao amp Zhang 2010 Liao Zhao Yu Tong amp Luo2012 Shen et al 2011 Zhang et al 2013) and interfacial polymerization (JinShi et al 2012 Namvar-Mahboub amp Pakizeh 2013) The sol-gel technique allowsthe formation of an inorganic framework under mild conditions and incorporation ofminerals into the polymers results in increased chemical mechanical and thermalstability without obviously decreasing the properties of the polymers (Kim andLee 2001 Wu et al 2003 Yu Xu et al 2009) Furthermore the hydrogen bondclusters remaining at the surface of the materials after the sol-gel reaction improvedmembrane hydrophilicity and enhanced the stability of composite materials (Cho ampSul 2001 Nagarale et al 2005 Yu Xu et al 2009) A simple method to obtain anorganiceSiO2 hybrid is to mix an organic polymer with a metal alkoxide such astetraethoxysilane (TEOS) followed by a sol-gel process involving hydrolysis andpolycondensation of TEOS (Wu et al 2003 Yu Xu et al 2009) Yu Xu et al(2009) synthesized organiceinorganic PVDFeSiO2 composite hollow fiber ultrafil-tration membranes using a sol-gel and wet-spinning process The microstructuremechanical property thermal stability hydrophilicity permeability and foulingresistance of composite membranes improved significantly by an appropriate choiceof TEOS concentration (3 wt)

The phase inversion process was also used by researchers as a simple and applicabletechnique to prepare polymeresilica-mixed matrix membranes The addition of hydro-philic SiO2 nanoparticles into the casting solution enhanced membrane hydrophilicity(Cui et al 2010 Shen et al 2011) On the other hand the permeability and anti-fouling ability of nanocomposite membranes also improved as the result of increasedhydrophilicity and the decreased adsorption of foulants on the membrane surface

Interfacial polymerization is another valuable method because the characteristics ofthe skin layer as a key factor in determining membrane performance can be optimizedseparately (Jin Shi et al 2012) Jin Yu et al (2012) and Jin Shi et al (2012)prepared a nanofiltration membrane with poly(amidoamine) (PAMAM) dendrimerand TMC containing SiO2 nanoparticles through an interfacial polymerization reactionon PSf ultrafiltration membrane The addition of nano-SiO2 in the skin layer improvedthermal stability and membrane hydrophilicity The results of raw water filtration bypristine PA membrane and PA-SiO2 membrane (1 wt SiO2 nanoparticles) are shownin Figure 15

As shown in the figure the flux of both PA and PA-SiO2 membranes was reducedduring the filtration time however the pristine PA membrane showed a greateramount of flux decline compared with the hydrophilic PA-SiO2 membrane Surfacewater typically contains three potential groups of foulants including microbial (bacte-ria viruses etc) organic and inorganic (humic acid and minerals) compounds Theaddition of SiO2 nanoparticles to the membrane significantly increased the antifoulingability of the PA membrane as the result of the presence of a huge number of hydroxylgroups on the surface of SiO2 nanoparticles This increased the negative charge on themembrane surface weakening the force between the negatively charged micelles andthe surface of the membrane (Jin Shi et al 2012)

24 Advances in Membrane Technologies for Water Treatment

1229 Zirconium oxide nanoparticles

Polymerezirconium dioxide (ZrO2) composite membranes are known to be chemi-cally more stable than titanium dioxide and aluminum oxide membranes and aremore suitable for liquid phase applications under rough conditions (MaximousNakhla Wan et al 2010) although a few studies have investigated the incorporationof ZrO2 into the membrane matrix Bottino Capannelli and Comite (2002) preparedZrO2ePVDF membranes using the phase inversion method Membrane performancedepended on the PVDF solvent (NMP or TEP) or ZrO2 concentration Other work con-ducted by Zheng Zou Nadeeshani Nanayakkara Matsuura and Paul Chen (2011)found that the addition of zirconia nanoparticles in PVDF membrane increased the hy-drophilicity and surface porosity of the membrane and resulted in an increment of fluxin the composite membrane It was proved that the ZrO2PVDF-blend membrane couldbe applied effectively to remove arsenate from an aqueous solution in a wide range ofpHs the optimal pH was 30e80

Furthermore Maximous Nakhla Wan et al (2010) found that ZrO2ePES mem-brane was stronger than pristine membrane and membranes blended with ZrO2 showedless flux decline and fouling resistance compared with unmodified PES membrane Onthe other hand Pang et al (2014) prepared ZrO2ePES hybrid ultrafiltration membranesby combining the ion-exchange process with the immersion precipitation technique toincrease membrane hydrophilicity and decrease membrane fouling The authors reportedthat the adsorption of foulants on the membrane surface decreased considerablycompared with pristine membranes because of an increase in membrane hydrophilicity

123 Nanostructured membranes

Based on the ISO definition membranes with pores in the range of 1e100 nm wouldevidently be considered nanostructured materials Hence ultrafiltration and most

PAPA-SiO2

Timeh

Flux

( L

sdot(m2

sdoth)-1

)

Figure 15 Flux of polyaniline (PA) and PA-SiO2 membranes versus filtration timeReprinted from Jin Shi et al (2012) with permission from Elsevier

Advances in polymeric membranes for water treatment 25

nanofiltration membranes that reject particles about 02e200 kDa corresponding to ananoscale diameter of around 1e100 nm should be classified as nanostructured mem-branes (Bhadra amp Mitra 2013 Muellera et al 2012) Generally membranes aredefined on the basis of the size of the particles that are rejected therefore the termldquonanordquo in ldquonanofiltrationrdquo does not refer to structural elements of the membranesuch as pore size (Bhadra amp Mitra 2013)

Rahimpour Madaeni Shockravi and Ghorbani (2009) added different concentra-tions of PSAm (2 5 10 and 15 wt) into the PES casting solution to prepare nano-structured ultrafiltration membranes Addition of PSAm not only resulted in theformation of an ultrafiltration membrane with nanopores it improved the hydrophilic-ity mechanical strength permeability and protein rejection of PES membranes More-over Mansourpanah and Momeni Habili (2013) employed the interfacialpolymerization technique to prepare a PA skin layer on the PES support using TMCand PIP as reagents Acrylic acid as a hydrophilic monomer and UV irradiation as aphysical procedure were used to modify the obtained thin layers The effect of UV irra-diation times (30 60 and 120 s) and acrylic acid concentration (1 5 and 10 wt)on the performance and morphology of modified TFC membranes was investigated bythe authors This modification technique resulted in the fabrication of a nanoporousmembrane by reducing the membrane pore size from 110 to 30 nm Meanwhile thehydrophilicity permeation flux rejection and antifouling ability of the modified mem-branes improved considerably

124 Bio-inspired membranes

Bio-inspired studies have drawn much attention as a potentially feasible approach toimprove current technologies In this method nature is considered a large database towhich its scientific rules might be applied in engineering applications as efficientsolutions for difficult problems In this way biological materials or natural biopoly-mers are considered for the fabrication of bio-inspired membranes because of theirwell-controlled structures and superior properties and the improvement of anyaspect of biological materials has the possibility of improving the structure and func-tion of bio-inspired membranes Moreover the conditions under which the mem-brane is fabricated are mild an aqueous solution controlled temperature moderatepressure and neutral or near neutral pH As a result of numerous advantages wideareas of application and high efficiency bio-inspired membranes have the chanceto be the next generation of membranes (Morones-Ramırez 2013 RawlingsBramble amp Staniland 2012)

Several bio-inspired platform methods such as bio-adhesion and bio-mimetic adhe-sion have been created (Li Liu et al 2009 Pan et al 2009) In addition a platformcalled bio-mineralization or bio-mimetic mineralization was developed from theformation process of bio-silica (Pan Jia Cheng amp Jiang 2010) Bio-inspired mem-branes have great benefits such as high permeability catalytic reactivity and foulingresistance and hence have the potential to be employed in water treatment processesPan et al (2010) proposed an innovative procedure to fabricate a polymereinorganicskin layer of a composite membrane by combining bio-mimetic mineralization and

26 Advances in Membrane Technologies for Water Treatment

polymer network structure manipulation In this work the silica nanoparticles showeduniform size and homogeneous distribution within the PVA structure The compositemembrane consisting of a PVAesilica skin layer and PSf hollow fiber support layershowed appropriate free volume properties

Inspired by the hierarchical structures in biology Xu et al (2011) proposed theconcept of vertically aligned nanotubes to emulate the biological channels within amembrane matrix As a result of the presence of nanopores inside the membranematrix the permeability selectivity and durability of bio-inspired membraneincreased Furthermore Balme et al (2011) conducted a research project focusingon bio-inspired membranes with biological ion channels These channels wereconfined inside the nanopores of solid-state materials The solvent had an effectiverole on membrane performance in terms of ion permeability and selectivity

Aside from the transport properties and membrane structure the development ofintelligent properties such as self-cleaning self-healing and stimuluseresponse inbio-inspired membranes are other concerns that have drawn the attention of someresearchers (Capadona Shanmuganathan Tyler Rowan amp Weder 2008 Madaeni ampGhaemi 2007 Wang Janout amp Regen 2011)

13 Applications for water treatment

Polymeric membranes are employed extensively for water treatment applications suchas desalination water softening purification of industrial and municipal wastewatersproduction of ultra-pure water and the food chemical and pharmaceutical industriesMembrane processes offer significant advantages such as operational simplicity andflexibility cost-effectiveness reliability low energy consumption good stabilityenvironment compatibility and easy control handling and scale-up under a widespectrum of operating conditions such as temperature pressure and pH Howeverthere are still unresolved problems regarding the employment of polymeric membranesunder more stringent applications Membrane fouling insufficient separation andrejection treatment of concentrates membrane lifetime and resistance to some chem-icals are the most important and well-known problems related to polymericmembranes

Fouling is the most important and well-known problem in membrane separationprocesses The urgent need for pretreatment cleaning limited recovery and short life-time are some negative results of fouling problems Membrane lifetime and chemicalresistance are also related to fouling and consequent cleaning as well as the conditionsunder which the membranes are employed Many researchers have concentrated onproposing efficient solutions and strategies to prolong the lifetime and chemical resis-tance of membranes improve membrane morphology increase hydrophilicitydecrease surface roughness and increase the degree of cross-linking of the polymerictop layer to decrease membrane fouling and increase the chemical resistance andlifetime of the membrane

Another inherent problem for pressure-driven membranes is the concentrate streamConcentrate is usually an unwanted by-product of water treatment using membrane

Advances in polymeric membranes for water treatment 27

technologies and needs to be further treated This treatment may include reuse furthertreatment by removal of contaminants and direct or indirect discharge into the surfacewater or groundwater and landfills

14 Concluding remarks and future trends

One of the most crucial problems facing the world in this century is the provision ofclean water with adequate quality from water resources Given the numerous privilegesof membranes such as relatively high selectivity and permeability low energyconsumption operational simplicity control scale-up and adaptability as well assatisfactory stability under various conditions over the years membranes have beenthe dominant technology in the water treatment industry Hence many studies havebeen conducted and much progress has been achieved in optimizing membrane char-acteristics and performance However some challenges still need to be addressed suchas decreasing membrane fouling increasing the membrane lifetime selectivity andpermeability improving thermal mechanical and chemical resistance and reducingenergy consumption

Some important incentives for the further development of polymeric membranes inwater treatment are fabrication of antifouling and self-cleaning membranes enhance-ment of membrane permselectivity an increase in membrane stability at extreme oper-ational conditions the production of new polymers with special properties for use incomposite membranes synthesis of novel nanomaterials for application in nanocom-posite membranes and the expansion of applications of bio-inspired and environmen-tally responsive membranes

Abbreviations

AA Acrylic acidAAm Acryl amideAPTES AminopropyltriethoxysilaneBPA Bisphenol ABO Bezactiv Orange V-3RCA Citric acidCAc Cellulose acetateCAP Cellulose acetate phthalateCNC Cellulose nanocrystallineCNTs Carbon nanotubesDABA b-Cyclodextrin polyurethaneDMAc DimethylacetamideDW Double-walledHPAA Hyperbranched poly(amidoamine)ICIC 5-Isocyanatoisophthaloyl chlorideIPC Isophthaloyl chloride

28 Advances in Membrane Technologies for Water Treatment

LSMM Hydrophilic surface modifying macromoleculesmm-BTEC 330550-biphenyl tetra acyl chlorideMMT MontmorilloniteMPDA m-PhenylenediamineMWCNT Multi-walled carbon nanotubeMWNTs Multi-walled nanotubesNMP N-methyl-2-pyrrolidoneom-BTEC 220440-biphenyl tetra acyl chlorideOMMT Organically modified montmorillonitesop-BTEC 220550-biphenyl tetra acyl chloridePA PolyanilinePAA Poly acrylic acidPAAm Poly acryl amidePAm PolyamidePAMAM Poly(amidoamine)PAI Poly(amide-imide)PAN PolyacrylonitrilePCA Polycitric acidPDA 13-PhenylenediaminePES PolyethersulfonePI PolyimidePIP PiperazinePMMA Poly(methyl methacrylate)PPD p-PhenylenediaminePPESK Poly(phthalazine ether sulfone ketone)PS PolystyrenePSAm Poly(sulfoxide-amide)PSf PolysulfonePU PolyurethanePVA Poly(vinyl alcohol)PVB Poly(vinyl butyral)PVDF Poly(vinylidenefluoride)PVP PolyvinylpyrrolidoneSEM Scanning electron microscopeSPC Sulfonated polycarbonateSPEK Sulphonated poly(ether ketone)SPES Sulfonated poly(ether sulfone)SPES-NH2 Sulfonated cardo poly(arylene ether sulfone)SPPO Sulfonated poly(26-dimethyl-14-phenylene oxide)SPSf Sulfonated polysulfoneSW Single-walledTEOS TetraethoxysilaneTEP TriethylphosphateTFC Thin-film compositeTFC-FO TFC forward osmosisTMBPA Tetramethyl bisphenol ATMC Trimesoyl chlorideTiO2 Titanium dioxide

Advances in polymeric membranes for water treatment 29

Greek symbol

b-CPU b-Cyclodextrin polyurethane

References

Abdollahi M Rahmatpour A Aalaie J amp Khanbabae G (2008) Preparation and evaluationof the microstructuer and properties of natural rubbersodiumemontmorillonite nano-composites Iran Polymer Journal 17 519e529

Abedini R Mousavi S M amp Aminzadeh R (2011) A novel cellulose acetate (CA) mem-brane using TiO2 nanoparticles Preparation characterization and permeation studyDesalination 277 40e45

Abu Seman M N Khayet M amp Hilal N (2010) Nanofiltration thin-film composite polyesterpolyethersulfone-based membranes prepared by interfacial polymerization Journal ofMembrane Science 348 109e116

Abu Seman M N Khayet M amp Hilal N (2011) Development of antifouling properties andperformance of nanofiltration membranes modified by interfacial polymerization Desali-nation 273 36e47

Abu Tarboush B J Rana D Matsuura T Arafat H A amp Narbaitz R M (2008)Preparation of thin film composite polyamide membranes for desalination using novelhydrophilic surface modifying marcromolecules Journal of Membrane Science 325166e175

Adams F V Nxumalo E N Krause R W M Hoek E M W amp Mamba B B (2012)Preparation and characterization of polysulfonecyclodextrin polyurethane compositenanofiltration membranes Journal of Membrance Science 405e406 291e299

Amado F D R Gondran E Ferreira J Z Rodrigues M A S amp Ferreira C A (2004)Synthesis and characterisation of high impact polystyrenepolyaniline composite mem-branes for electrodialysis Journal of Membrance Science 234 139e145

Anad~ao P Sato L F Wiebeck H Rolando F amp Diaz V (2010) Montmorillonite as acomponent of polysulfone nanocomposite membranes Applied Clay Science 48 127e132

An J amp Dultz S (2007) Adsorption of tannic acid on chitosanemontmorillonite as a functionof pH and surface charge properties Applied Clay Science 36 256e264

An Q Li F Ji Y amp Chen H (2011) Influence of polyvinyl alcohol on the surfacemorphology separation and anti-fouling performance of the composite polyamide nano-filtration membranes Journal of Membrane Science 367 158e165

Bae T H amp Tak T M (2005) Effect of TiO2 nanoparticles on fouling mitigation of ultra-filtration membranes for activated sludge filtration Journal of Membrane Science 2491e8

Balasubramanian K amp Burghard M (2005) Chemically functionalized carbon nanotubesSmall 1 180e192

Balme S Janot J M Dejardin P Beacuterardo L Henn F Bonhenry D et al (2011) Ionicdiffusion through a bio-inspired membrane Basic Principle of Diffusion Theory Experi-ment and Application 16(31) 1e2

Balta S Sotto A Luis P Benea L Van der Bruggen B amp Kim J (2012) A new outlookon membrane enhancement with nanoparticles The alternative of ZnO Journal ofMembrane Science 389 155e161

30 Advances in Membrane Technologies for Water Treatment

Barud H S Regiani T Marques R F C Lustri W R Messaddeq Y amp Ribeiro S J L(2011) Antimicrobial bacterial cellulose-silver nanoparticles composite membranesJournal of Nanomaterials 2011 1e8

Basri H Ismail A F amp Aziz M (2011) Polyethersulfone (PES)esilver composite UFmembrane Effect of silver loading and PVP molecular weight on membrane morphologyand antibacterial performance Desalination 273 72e80

Basri H Ismail A F Aziz M Nagai K Matsuura T Abdullah M S et al (2010) Silver-filled polyethersulfone membranes for antibacterial applications-effect of PVP and TAPaddition on silver dispersion Desalination 261 264e271

Bebin P Caravanier M amp Galiano H (2006) Nafionclay-SO3H membrane for protonexchange membrane fuel cell application Journal of Membrane Science 278 35e42

Bhadra M amp Mitra S (2013) Nanostructured membranes in analytical chemistry Trends inAnalytical Chemistry 45 248e263

Bleiman N amp Mishael Y G (2010) Selenium removal from drinking water by adsorption tochitosaneclay composites and oxides Batch and columns tests Journal of HazardousMaterials 183 590e595

Bottino A Capannelli G amp Comite A (2002) Preparation and characterization of novelporous PVDFeZrO2 composite membranes Desalination 146 35e40

Cao X Tang M Liu F Nie Y amp Zhao C (2010) Immobilization of silver nanoparticlesonto sulfonated polyethersulfone membranes as antibacterial materials Colloids andSurfaces B 81 555e562

Capadona J R Shanmuganathan K Tyler D J Rowan S J amp Weder C (2008) Stimuli-responsive polymer nanocomposites inspired by the sea cucumber dermis Science 3191370e1374

Casariego A Souza B W S Cerqueira M A Teixeira J A Cruz L Diaz R et al (2009)Chitosanclay films properties as affected by biopolymer and clay micronanoparticlesconcentrations Food Hydrocolloids 23 1895e1902

Celik E Park H Choi H amp Choi H (2011) Carbon nanotube blended polyethersulfonemembranes for fouling control in water treatment Water Resources 45 274e282

Celis R Adelino M A Hermosin M C amp Cornejo J (2012) Montmorilloniteechitosanbionanocomposites as adsorbents of the herbicide clopyralid in aqueous solution and soilwater suspensions Journal of Hazardous Materials 209e210 67e76

Chamakura K Perez-Ballestero R Luo Z Bashir S amp Liu J (2011) Comparison ofbactericidal activities of silver nanoparticles with common chemical disinfectants Colloidsand Surfaces B 84 88e96

Chang M amp Juang R (2004) Adsorption of tannic acid humic acid and dyes from waterusing the composite of chitosan and activated clay Journal of Colloid and InterfaceScience 278 18e25

Chen G Li S Zhang X amp Zhang S (2008) Novel thin-film composite membranes withimproved water flux from sulfonated cardo poly(arylene ether sulfone) bearing pendantamino groups Journal of Membrane Science 310 102e109

Choi J H Jegal J amp Kimb W N (2006) Fabrication and characterization of multi-walledcarbon nanotubespolymer blend membranes Journal of Membrane Science 284 406e415

Cho J W amp Sul K I (2001) Characterization and properties of hybrid composites preparedfrom poly(vinylidene fluoride-tetrafluoroethylene) and SiO2 Polymer 42 727e736

Chou W L Yu D G amp Yang M C (2005) The preparation and characterization of silverloading cellulose acetate hollow fiber membrane for water treatment Polymers forAdvanced Technologies 16(8) 600e607

Advances in polymeric membranes for water treatment 31

Cui A Liu Z Xiao C amp Zhang Y (2010) Effect of micro-sized SiO2-particle on the per-formance of PVDF blend membranes via TIPS Journal of Membrane Science 360259e264

Damodar R A You S J amp Cho H H (2009) Study the self cleaning antibacterial andphotocatalytic properties of TiO2 entrapped PVDF membranes Journal of HazardousMaterials 172 1321e1328

Danilczuk M Lund A Saldo J Yamada H ampMichalik J (2006) Conduction electron spinresonance of small silver particles Spectrochimica Acta Part A 63 189e191

Daraei P Madaeni S S Ghaemi N Ahmadi Monfared H amp Khadivi M A (2013)Fabrication of PES nanofiltration membrane by simultaneous use of multi-walled carbonnanotube and surface graft polymerization method Comparison of MWCNT and PAAmodified MWCNT Separation and Purification Technology 104 32e44

Daraei P Madaeni S S Ghaemi N Khadivi M A Astinchap B amp Moradian R (2013)Enhancing antifouling capability of PES membrane via mixing with various types of polymermodified multi-walled carbon nanotube Journal of Membrane Science 444 184e191

Daraei P Madaeni S S Ghaemi N Salehi E Khadivi M A Moradian R et al (2012)Novel polyethersulfone nanocomposite membrane prepared by PANIFe3O4 nanoparticleswith enhanced performance for Cu(II) removal from water Journal of Membrane Science415e416 250e259

Daraei P Madaeni S S Salehi E Ghaemi N Sadeghi Ghari H Khadivi M A et al(2013) Novel thin film composite membrane fabricated by mixed matrix nanoclaychitosanon PVDF microfiltration support Preparation characterization and performance in dyeremoval Journal of Membrane Science 436 97e108

Deng Y Q Dang G D Zhou H W Rao X H amp Chen C H (2008) Preparation andcharacterization of polyimide membranes containing silver nanoparticles in pores distrib-uting on one side Materials Letters 62 1143e1146

Dudek G Turczyn R Strzelewicz A Rybak A Krasowska M amp Grzywn Z J (2012)Preparation and characterization of iron oxidesepolymer composite membranes Separa-tion Science and Technology 47 1390e1394

Ebert K Fritsch D Koll J amp Tjahjawiguna C (2004) Influence of inorganic fillers on thecompaction behavior of porous polymer based membranes Journal of Membrane Science233 71e78

Eitan A Jiang K Dukes D Andrews R amp Schadler L S (2003) Surface modification ofmultiwalled carbon nanotubes Toward the tailoring of the interface in polymer compositesChemistry of Materials 15 3198e3201

Fu X Matsuyama H amp Nagai H (2008) Structure control of asymmetric poly(vinyl butyral)-TiO2 composite membrane prepared by nonsolvent induced phase separation Journal ofApplied Polymer Science 108 713e723

Ghaemi N Madaeni S S Alizadeh A Rajabi H amp Daraei P (2011) Preparation char-acterization and performance of polyethersulfoneorganically modified montmorillonitenanocomposite membranes in removal of pesticides Journal of Membrane Science 382135e147

Gholami A Moghadassi A R Hosseini S M Shabani S amp Gholami F (2013) Prepa-ration and characterization of polyvinyl chloride based nanocomposite nanofiltrationmembrane modified by iron oxide nanoparticles for lead removal from water Journal ofIndustrial and Engineering Chemistry 20(4) 1517e1522

Gusseme B D Hennebel T Christiaens E Saveyn H Verbeken K Fitts J P et al(2011) Virus disinfection in water by biogenic silver immobilized in polyvinylidenefluoride membranes Water Resources 45 1856e1864

32 Advances in Membrane Technologies for Water Treatment

Hamid N A A Ismail A F Matsuura T Zularisam A W Lau W J Yuliwati E et al(2011) Morphological and separation performance study of polysulfonetitaniumdioxide (PSFTiO2) ultrafiltration membranes for humic acid removal Desalination 27385e92

Han G Chung T S Toriida M amp Tamai S (2012) Thin-film composite forward osmosismembranes with novel hydrophilic supports for desalination Journal of MembraneScience 423e424 543e555

Han Y S Lee S H Choi K H amp Park I (2010) Preparation and characterization ofchitosaneclay nanocomposites with antimicrobial activity Journal of Physics andChemistry of Solids 71 464e467

Han K N Yu B Y amp Kwak S Y (2012) Hyperbranched poly(amidoamine)polysulfonecomposite membranes for Cd(II) removal from water Journal of Membrane Science 39683e91

Hong J amp He Y (2012) Effects of nano sized zinc oxide on the performance of PVDFmicrofiltration membranes Desalination 302 71e79

Huang J Arthanareeswaran G amp Zhang K (2012) Effect of silver loaded sodium zirconiumphosphate (nanoAgZ) nanoparticles incorporation on PES membrane performanceDesalination 285 100e107

Huang Z Q Chen L Chen K Zhang Z amp Xu H T (2010) A novel method for controllingthe sublayer microstructure of an ultrafiltration membrane The preparation of thePSF-Fe3O4 ultrafiltration membrane in a parallel magnetic field Journal of AppliedPolymer Science 117 1960e1968

Huang Z Q Chen K C Li S N Yin X T Zhang Z amp Xu H T (2008) Effect offerrosoferric oxide content on the performances of polysulfoneeferrosoferric oxide ultra-filtration membranes Journal of Membrane Science 315 164e171

Huang Z Q Guo X P Guo C L amp Zhang Z (2006) Magnetization influence on theperformance of ferrosoferric oxide Polyacrylonitrile membranes in ultrafiltration of pigblood solution Bioprocess and Biosystems Engineering 28 415e421

Huang Z Q Zheng F Zhang Z Xu H T amp Zhou K M (2012) The performance of thePVDF-Fe3O4 ultrafiltration membrane and the effect of a parallel magnetic field usedduring the membrane formation Desalination 292 64e72

Hwang H Y Kim D J Kim H J Hong Y T amp Nam S Y (2011) Effect of nanoclay onproperties of porous PVDF membranes Transactions of Nonferrous Metals Society ofChina 21 141e147

Islam M F Rojas E Bergey D M Johnson A T amp Yodh A G (2003) High weightfraction surfactant solubilization of single-wall carbon nanotubes in water Nano Letters3 269e273

Jeong B H Hoek E M V Yan Y Subramani A Huang X Hurwitz G et al (2007)Interfacial polymerization of thin film nanocomposites A new concept for reverse osmosismembranes Journal of Membrane Science 294 1e7

Jian P Yahui H Yang W amp Linlin L (2006) Preparation of polysulfoneeFe3O4 com-posite ultrafiltration membrane and its behavior in magnetic field Journal of MembraneScience 284 9e16

Jin L Shi W Yu S Yi X Sun N Ma C et al (2012) Preparation and characterization ofa novel PA-SiO2 nanofiltration membrane for raw water treatment Desalination 29834e41

Jin L Yu S L Shi W X Yi X S Sun N Ge Y L et al (2012) Synthesis of a novelcomposite nanofiltration membrane incorporated SiO2 nanoparticles for oily wastewaterdesalination Polymer 53 5295e5303

Advances in polymeric membranes for water treatment 33

Kang S W Kim J H Char K Won J amp Kang Y S (2006) Nanocomposite silverpolymer electrolytes as facilitated olefin transport membranes Journal of MembraneScience 285 102e107

Khodabakhshi A R Madaeni S S Xu TW Wu L Wu C Li C et al (2012) Preparationoptimization and characterization of novel ion exchange membranes by blending of chem-ically modified PVDF and SPPO Separation and Purification Technology 90 10e21

Kim E S Hwang G Gamal El-Din M amp Liu Y (2012) Development of nanosilver andmulti-walled carbon nanotubes thin-film nanocomposite membrane for enhanced watertreatment Journal of Membrane Science 394e395 37e48

Kim E S Kim Y J Yu Q amp Deng B (2009) Preparation and characterization of poly-amide thin-film composite (TFC) membranes on plasma-modified polyvinylidene fluoride(PVDF) Journal of Membrane Science 344 71e81

Kim S H Kwak S Y Sohn B H amp Park T H (2003) Design of TiO2 nanoparticles self-assembled aromatic poylamide thin-film composite (TFC) membrane as an approach tosolve biofouling problem Journal of Membrane Science 211 157e165

Kim S H Kwak E Y amp Suzuki T (2005) Positron annihilation spectroscopic evidence todemonstrate the flux-enhancement mechanism in morphology-controlled thin film com-posite (TFC) membrane Environmental Science and Technology 39 1764e1770

Kim J H amp Lee Y M (2001) Gas permeation properties of poly(amide-6-b-ethylene oxide)-silica hybrid membranes Journal of Membrane Science 193 209e225

Koh M J Hwang H Y Kim D J Kim H J Hong Y T amp Nam S Y (2010) Preparationand characterization of porous pvdf-HFPclay nanocomposite membranes Journal ofMaterials Science and Technology 26(7) 633e638

Kong C Kanezashi M Yamomoto T Shintani T amp Tsuru T (2010) Controlled synthesisof high performance polyamide membrane with thin dense layer for water desalinationJournal of Membrane Science 362 76e80

Koseoglu-Imer D Y Kose B Altinbas M amp Koyuncu I (2013) The production of pol-ysulfone (PS) membrane with silver nanoparticles (AgNP) Physical properties filtrationperformances and biofouling resistances of membranes Journal of Membrane Science428 620e628

Lang K Sourirajan S Matsuura T amp Chowdhury G (1996) A study on the preparation ofpolyvinyl alcohol thin-film composite membranes and reverse osmosis testing Desalina-tion 104 185e196

Lau W J Ismail A F Misdan N amp Kassim M A (2012) A recent progress in thin filmcomposite membrane A review Desalination 287 190e199

Lee H S Im S J Kim J H Kim J P amp Min B R (2008) Polyamide thin film nano-filtration membranes containing TiO2 nanoparticles Desalination 219 48e56

Lee S Y Kim H J Patel R Im S J Kim J H amp Min B R (2007) Silver nanoparticlesimmobilized on thin film composite polyamide membrane Characterization nanofiltrationantifouling properties Polymers for Advanced Technologies 18 562e568

Leo C P Cathie Lee W P Ahmad A L amp Mohammad A W (2012) Polysulfonemembranes blended with ZnO nanoparticles for reducing fouling by oleic acid Separationand Purification Technology 89 51e56

Liang S Xiao K Mo Y amp Huang X (2012) A novel ZnO nanoparticle blended poly-vinylidene fluoride membrane for anti-irreversible fouling Journal of Membrane Science394e395 184e192

Liao C Zhao J Yu P Tong H amp Luo Y (2012) Synthesis and characterization of lowcontent of different SiO2 materials composite poly (vinylidene fluoride) ultrafiltrationmembranes Desalination 285 117e122

34 Advances in Membrane Technologies for Water Treatment

Li B Liu W P Jiang Z Y Dong X Wang B Y amp Zhong Y R (2009) Ultrathin andstable active layer of dense composite membrane enabled by poly (dopamine) Langmuir25 7368e7374

Li H amp Kim H (2008) Thermal degradation and kinetic analysis of PVDFmodified MMTnanocomposite membranes Desalination 234 9e15

Li J B Zhu J W amp Zheng M S (2007) Morphologies and properties of poly(phthalazinoneethersulfoneketone) matrix ultrafiltration membranes with entrapped TiO2 nanoparticlesJournal of Applied Polymer Science 103 3623e3629

Li J F Xu Z L Yang H Yu L Y amp Liu M (2009) Effect of TiO2 nanoparticles on thesurface morphology and performance of microporous PES membrane Applied SurfaceScience 255 4725e4732

Li J H Shao X S Zhou Q Li M Z amp Zhang Q Q (2013) The double effects of silvernanoparticles on the PVDF membrane Surface hydrophilicity and antifouling perfor-mance Applied Surface Science 265 663e670

Li Q L Mahendra S Lyon D Y Brunet L Liga M V Li D et al (2008) Antimicrobialnanomaterials for water disinfection and microbial control Potential applications andimplication Water Resources 42(18) 4591e4602

Lin W Xu Y Huang C C Ma Y Shannon K B Chen D R et al (2009) Toxicity ofnano- and micro-sized ZnO particles in human lung epithelial cells Journal of Nano-particle Research 11 25e39

Liu C X Zhang D R He Y Zhao X S amp Bai R (2010) Modification of membranesurface for anti-biofouling performance Effect of anti-adhesion and anti-bacteriaapproaches Journal of Membrane Science 346 121e130

Liu F Moghareh Abed M R amp Li K (2011) Preparation and characterization ofpoly(vinylidene fluoride) (PVDF) based ultrafiltration membranes using nano g-Al2O3Journal of Membrane Science 366 97e103

Liu Y Rosenfield E Hu M amp Mi B (2013) Direct observation of bacterial deposition onand detachment from nanocomposite membranes embedded with silver nanoparticlesWater Resources 47 2949e2958

Madaeni S S amp Ghaemi N (2007) Characterization of self-cleaning RO membranes coatedwith TiO2 particles under UV irradiation Journal of Membrane Science 303 221e233

Madaeni S S Zinadini S amp Vatanpour V (2011a) Convective flow adsorption of nickelions in PVDF membrane embedded with multi-walled carbon nanotubes and PAA coatingSeparation and Purification Technology 80 155e162

Madaeni S S Zinadini S amp Vatanpour V (2011b) A new approach to improve antifoulingproperty of PVDF membrane using in situ polymerization of PAA functionalized TiO2nanoparticles Journal of Membrane Science 380 155e162

Malaisamy R Mahendran R amp Mohan D (2002) Cellulose acetate and sulfonated poly-sulfone blend ultrafiltration membranes II Pore statistics molecular weight cutoff andmorphological studies Journal of Applied Polymer Science 84(2) 430e444

Mansour M S Ossman M E amp Farag H A (2011) Removal of Cd (II) ion from waste waterby adsorption onto polyaniline coated on sawdust Desalination 272 301e305

Mansourpanah Y Madaeni S S Adeli M Rahimpour A amp Farhadian A (2009) Surfacemodification and preparation of nanofiltration membrane from polyethersulfonepolyimideblend e use of a new material (polyethyleneglycol-triazine) Journal of Applied PolymerScience 112(5) 2888e2895

Mansourpanah Y Madaeni S S Rahimpour A Adeli M Hashemi Y amp Moradian M R(2011) Fabrication new PES-based mixed matrix nanocomposite membranes usingpolycaprolactone modified carbon nanotubes as the additive Property changes andmorphological studies Desalination 277 171e177

Advances in polymeric membranes for water treatment 35

Mansourpanah Y amp Momeni Habili E (2013) Preparation and modification of thin film PAmembranes with improved antifouling property using acrylic acid and UV irradiationJournal of Membrane Science 430 158e166

Martinez-Gutierrez F Thi E P Silverman J M Camargo de Oliveira C Svensson S LVanden Hoek A et al (2012) Antibacterial activity inflammatory response coagulationand cytotoxicity effects of silver nanoparticles Nanomedicine Nanotechnology 8 328e336

Masuelli M Marchese J amp Ochoa N A (2009) SPCPVDF membranes for emulsified oilywastewater treatment Journal of Membrane Science 326(2) 688e693

Maurya S K Parashuram K Singh P S Ray P amp Reddy A V R (2012) Preparation ofpolysulfoneepolyamide thin film composite hollow fiber nanofiltration membranes andtheir performance in the treatment of aqueous dye solutions Desalination 304 11e19

Maximous N Nakhla G Wan W amp Wong K (2009) Preparation characterization andperformance of Al2O3PES membrane for wastewater filtration Journal of MembraneScience 341 67e75

Maximous N Nakhla G Wan W amp Wong K (2010b) Performance of a novel ZrO2PESmembrane for wastewater filtration Journal of Membrane Science 352 222e230

Maximous N Nakhla G Wong K amp Wan W (2010) Optimization of Al2O3PESmembranes for wastewater filtration Separation and Purification Technology 73294e301

Mbareck C Nguyen Q T Alaoui O T amp Barillier D (2009) Elaboration characterizationand application of polysulfone and polyacrylic acid blends as ultrafiltration membranes forremoval of some heavy metals from water Journal of Hazardous Materials 171(1e3)93e101

Mierzwa J C Arieta V Verlage M Carvalho H amp Vecitis C D (2013) Effect of claynanoparticles on the structure and performance of polyethersulfone ultrafiltration mem-branes Desalination 314 147e158

Mollahosseini A Rahimpour A Jahamshahi M Peyravi M amp Khavarpour M (2012) Theeffect of silver nanoparticle size on performance and antibacteriality of polysulfoneultrafiltration membrane Desalination 306 41e50

Monticelli O Bottino A Scandale I Capannelli G amp Russo S (2007) Preparation andproperties of polysulfoneeclay composite membranes Journal of Applied PolymerScience 103 3637e3644

Morones-Ramırez J R (2013) Bioinspired synthesis of optically and thermally responsivenanoporous membranes NPG Asia Materials 5 1e9

Muellera N C Bruggen B Keuterc V Luis P Melin T Pronk W et al (2012)Nanofiltration and nanostructured membranes should they be considered nanotech-nology or not Journal of Hazardous Materials 211e212 275e280

Mukherjee R amp De S (2013) Adsorptive removal of phenolic compounds using celluloseacetate phthalate alumina nanoparticle mixed matrix membrane Journal of HazardousMaterials 265 8e19

Musale D A Kumar A amp Pleizier G (1999) Formation and characterization of polyacrylonitrile)Chitosan composite ultrafiltration membranes Journal of Membrane Science154 163e173

Nagarale R K Shahi V K amp Rangarajan R (2005) Preparation of polyvinyl alcoholesilicahybrid heterogeneous anion-exchangemembranes by solegelmethod and their character-ization Journal of Membrane Science 248 37e44

Namvar-Mahboub M amp Pakizeh M (2013) Development of a novel thin filmcomposite membrane by interfacial polymerization on polyetherimidemodified SiO2 supportfor organic solvent nanofiltration Separation and Purification Technology 119 35e45

36 Advances in Membrane Technologies for Water Treatment

Nesic A R Velickovic S J amp Antonovic D G (2012) Characterization of chitosanmontmorillonite membranes as adsorbents for Bezactiv Orange V-3R dye Journal ofHazardous Materials 209e210 256e263

Ochoa A Masuelli M amp Marchese J (2003) Effect of hydrophilicity on fouling of anemulsified oil wastewater with PVDFPMMA membranes Journal of Membrane Science226 203e211

Ochoa N A Pradanos P Palacio L Pagliero C Marchese J amp Hernandez A (2001)Pore size distributions based on AFM imaging and retention of multidisperse polymersolutes characterisation of polyethersulfone UF membranes with dopes containing differentPVP Journal of Membrane Science 187 227e237

OrsquoConnell M J Boul P Ericson L M Huffman C Wang Y H Haroz E et al (2001)Reversible water-solubilization of single-walled carbon nanotubes by polymer wrappingChemical Physics Letters 342 265e271

Ogoshi T amp Chujo Y (2005) Synthesis of poly(vinylidene fluoride)(PVDF)silica hybridshaving interpenetrating polymer network structure by using crystallization between PVDFchains Journal of Polymer Science A Polymer Chemistry 43 3543e3550

Oh S J Kimb N amp Lee Y T (2009) Preparation and characterization of PVDFTiO2organiceinorganic composite membranes for fouling resistance improvement Journal ofMembrane Science 345 13e20

Pan F Jia H Cheng Q amp Jiang Z (2010) Bio-inspired fabrication of composite membraneswith ultrathin polymeresilica nanohybrid skin layer Journal of Membrane Science 362119e126

Pan F Jia H Qiao S Jiang Z Wang J Wang B et al (2009) Bioinspired fabrication ofhigh performance composite membranes with ultrathin defect-free skin layer Journal ofMembrane Science 341 279e285

Pandey S amp Mishra S B (2011) Organiceinorganic hybrid of chitosanorganoclaybionanocomposites for hexavalent chromium uptake Journal of Colloid and InterfaceScience 361 509e520

Pang R Li X Li J Lu Z Sun X amp Wang L (2014) Preparation and characterization ofZrO2PES hybrid ultrafiltration membrane with uniform ZrO2 nanoparticles Desalination332 60e66

Park H amp Choi H (2011) As (III) removal by hybrid reactive membrane process combinedwith ozonation Water Resources 45 1933e1940

Peng F Huang X Jawor A amp Hoek E M V (2010) Transport structural and interfacialproperties of poly (vinyl alcohol)epolysulfone composite nanofiltration membranesJournal of Membrane Science 353 169e176

Prakash Rao A Desai N V amp Rangarajan R (1997) Interfacially synthesized thin filmcomposite RO membranes for seawater desalination Journal of Membrane Science 124263e272

Qui S Wu L Pan X Zhang L Chen H amp Gao C (2009) Preparation and properties offunctionalized carbon nanotubePSF blend ultrafiltration membranes Journal of Mem-brane Science 342 165e172

Qu L Lin Y Hill D E Zhou B Wang W Sun X et al (2004) Polyimide-functionalizedcarbon nanotubes Synthesis and dispersion in nanocomposite films Macromolecules37 6055e6060

Rahimpour A Jahanshahi M Mortazavian N Madaeni S S amp Mansourpanah Y (2010)Preparation and characterization of asymmetric polyethersulfone and thin-film compositepolyamide nanofiltration membranes for water softening Applied Surface Science 2561657e1663

Advances in polymeric membranes for water treatment 37

Rahimpour A Jahanshahi M Rajaeian B amp Rahimnejad M (2011) TiO2 entrapped nano-composite PVDFSPES membranes Preparation characterization antifouling andantibacterial properties Desalination 278 343e353

Rahimpour A amp Madaeni S S (2007) Polyethersulfone (PES)cellulose acetate phthalate(CAP) blend ultrafiltration membranes Preparation morphology performance and anti-fouling properties Journal of Membrane Science 305 299e312

Rahimpour A Madaeni S S Shockravi A amp Ghorbani S (2009) Preparation and char-acterization of hydrophile nano-porous polyethersulfone membranes using synthesizedpoly(sulfoxide-amide) as additive in the casting solution Journal of Membrane Science334 64e73

Rahimpour A Madaeni S S Taheri A H amp Mansourpanah Y (2008) Coupling TiO2nanoparticles with UV irradiation for modification of polyethersulfone ultrafiltrationmembranes Journal of Membrane Science 313 158e169

Rana D Kim Y Matsuura T amp Arafat A H (2011) Development of antifouling thin-filmcomposite membranes for seawater desalination Journal of Membrane Science 367110e118

Rawlings A E Bramble J P amp Staniland S S (2012) Innovation through imitationBiomimetic bioinspired and biokleptic research Soft Matter 8 2675e2679

Razmjou A Mansouri J amp Chen V (2011) The effects of mechanical and chemicalmodification of TiO2 nanoparticles on the surface chemistry structure and fouling per-formance of PES ultrafiltration membranes Journal of Membrane Science 378 73e84

Reddy A V R Trivedi J J Devmurari C V Mohan D J Singh P Rao A P et al (2005)Fouling resistantmembranes in desalination andwater recoveryDesalination 183 301e306

Roy S Addo Ntim S Mitra S amp Sirkar K K (2011) Facile fabrication of superiornanofiltration membranes from interfacially polymerized CNT-polymer compositesJournal of Membrane Science 375 81e87

Sabbatini P Rossi F Thern G amp Marajofsky A (2009) Iron oxide adsorbers for arsenicremoval A low cost treatment for rural areas and mobile applications Desalination 248184e192

Sabbatini P Yrazu F Rossi F Thern G Marajofsky A amp Fidalgo de Cortalezzi M M(2010) Fabrication and characterization of iron oxide ceramic membranes for arsenicremoval Water Resources 44 5702e5712

Saleh T A amp Gupt V K (2012) Synthesis and characterization of alumina nano-particlespolyamide membrane with enhanced flux rejection performance Separation and Purifi-cation Technology 89 245e251

Sawada I Fachrul R Ito T Ohmukai Y Maruyama T amp Matsuyama H (2012) Develop-ment of a hydrophilic polymer membrane containing silver nanoparticles with both organicantifouling and antibacterial properties Journal of Membrane Science 387e388 1e6

Shao L Cheng X Q Liu Y Quan S Ma J Zhao S Z et al (2013) Newly developednanofiltration (NF) composite membranes by interfacial polymerization for Safranin O andAniline blue removal Journal of Membrane Science 430 96e105

Shawky H A Chae R Y Lin S amp Wiesner M R (2011) Synthesis and characterization ofa carbon nanotubepolymer nanocomposite membrane for water treatment Desalination272 46e50

Shen L Bian X Lu X Shi L Liu Z Chen L et al (2012) Preparation and character-ization of ZnOpolyethersulfone (PES) hybrid membranes Desalination 293 21e29

Shen J Ruan Wu L amp Gao C (2011) Preparation and characterization of PESeSiO2organiceinorganic composite ultrafiltration membrane for raw water pretreatmentChemical Engineering Journal 168 1272e1278

38 Advances in Membrane Technologies for Water Treatment

Shi F Ma Y Ma J Wang P amp Sun W (2012) Preparation and characterization of PVDFTiO2 hybrid membranes with different dosage of nano-TiO2 Journal of MembraneScience 389 522e531

Shirazi Y Ahmadzadeh Tofighy M ampMohammadi T (2011) Synthesis and characterizationof carbon nanotubespoly vinyl alcohol nanocomposite membranes for dehydration ofisopropanol Journal of Membrane Science 378 551e561

Susanto H amp Ulbricht M (2008) High-performance thin-layer hydrogel composite mem-branes for ultrafiltration of natural organic matter Water Resources 42 2827e2835

Tang C Zhang Q Wang K Fu Q amp Zhang C (2009) Water transport behavior of chi-tosan porous membranes containing multi-walled carbon nanotubes (MWNTs) Journal ofMembrane Science 337 240e247

Taurozzi J S Arul H Bosak V Z Burban A F Voice T C Bruening M L et al(2008) Effect of filler incorporation route on the properties of polysulfoneesilvernanocomposite membranes of different porosities Journal of Membrane Science 32558e68

Thanganathan U Nishina Y Kimura K Hayakawa S amp Bobba R (2012) Character-ization of hybrid composite membrane based polymerprecursorSiO2 Materials Letters81 88e91

Thomas V Yallapu M M Sreedhar B amp Bajpai S K (2009) Fabrication characterizationof chitosannanosilver film and its potential antibacterial application Journal of Bio-materials Science-Polymer E 20(14) 2129e2144

Travan A Pelillo C Donati I Marsich E Benincasa M Scarpa T et al (2009) Non-cytotoxic silver nanoparticle-polysaccharide nanocomposites with antimicrobial activityBiomacromolecules 10(6) 1429e1435

Vatanpour V Madaeni S S Khataee A R Salehi E Zinadini S amp Ahmadi Monfared H(2012) TiO2 embedded mixed matrix PES nanocomposite membranes Influence ofdifferent sizes and types of nanoparticles on antifouling and performance Desalination292 19e29

Vatanpour V Madaeni S S Moradian R Zinadini S amp Astinchap B (2011) Fabricationand characterization of novel antifouling nanofiltration membrane prepared from oxidizedmultiwalled carbon nanotubepolyethersulfone nanocomposite Journal of MembraneScience 375 284e294

Vatanpour V Madaeni S S Moradian R Zinadini S amp Astinchap B (2012) Novelantibifouling nanofiltration polyethersulfone membrane fabricated from embeddingTiO2 coated multiwalled carbon nanotubes Separation and Purification Technology90 69e82

Verissimo S Peinemann K V amp Bordado J (2005) Thin-film composite hollow fibermembranes An optimized manufacturing method Journal of Membrane Science 26448e55

Wan Ngah W S Teong L C amp Hanafiah M A K M (2011) Adsorption of dyes and heavymetal ions by chitosan composites A review Carbohydrate Polymers 83 1446e1456

Wang M Janout V amp Regen S L (2011) Hyper-thin organic membranes with exceptionalH2CO2 permeation selectivity Importance of ionic crosslinking and self-healingChemical Communications 47 2387e2389

Wang H Li L Zhang X amp Zhang S (2010) Polyamide thin-film composite membranesprepared from a novel triamine 35-diamino-N-(4-aminophenyl)-benzamide monomer andm-phenylenediamine Journal of Membrane Science 353 78e84

Wara N M Francis L F amp Velamakkani B V (1995) Addition of alumina to celluloseacetate membranes Journal of Membrane Science 104 43e49

Advances in polymeric membranes for water treatment 39

Wei Y ChuHQ Dong B Z Li X Xia S J ampQiang ZM (2011) Effect of TiO2 nanowireaddition on PVDF ultrafiltration membrane performance Desalination 272 90e97

Wu G Gan S Cui L amp Xu Y (2008) Preparation and characterization of PESTiO2composite membranes Applied Surface Science 254 7080e7086

Wu H Tang B amp Wu P (2010) MWNTsPolyester thin film nanocomposite membrane Anapproach to overcome the trade-off effect between permeability and selectivity Journal ofPhysical Chemistry C 114 16395e16400

Wu C Xu T amp Yang W (2003) A new inorganiceorganic negatively charged membraneMembrane preparation and characterizations Journal of Membrane Science 224 117e125

Wu C Zhang S Yang D Wei J Yan C amp Jian X (2006) Preparation characterizationand application in wastewater treatment of a novel thermal stable composite membraneJournal of Membrane Science 279 238e245

Xie Y Tan S Liao M amp Liu R (2010) Structure and antibacterial activity of modifiedmontmorillonite Chemical Research in Chinese Universities 26 509e513

Xu T Zhao N Ren F Hourani R Lee M T Shu J Y et al (2011) Subnanometer porousthin films by the co-assembly of nanotube subunits and block copolymers ACS Nano 51376e1384

Yan L Hong S Li M L amp Li Y S (2009) Application of the Al2O3ePVDF nano-composite tubular ultrafiltration (UF) membrane for oily wastewater treatment and itsantifouling research Separation and Purification Technology 66 347e352

Yan L Li Y S amp Xiang C B (2005) Preparation of poly(vinylidene fluoride)(pvdf)ultrafiltration membrane modified by nano-sized alumina (Al2O3) and its antifoulingresearch Polymer 46 7701e7706

Yan L Li Y S Xiang C B amp Xianda S (2006) Effect of nano-sized Al2O3-particleaddition on PVDF ultrafiltration membrane performance Journal of Membrane Science276 162e167

Yang C C James Li Y J amp Liou T H (2011) Preparation of novel poly(vinyl alcohol)SiO2 nanocomposite membranes by a solegel process and their application on alkalineDMFC Desalination 276 366e372

Yang Y amp Wang P (2006) Preparation and characterizations of a new PSTiO2 hybridmembranes by solegel process Polymer 47 2683e2688

Yang Y Zhang H Wang P Zheng Q amp Li J (2007) The influence of nano-sized TiO2fillers on the morphologies and properties of PSF UF membrane Journal of MembraneScience 288 231e238

Yang Z Chen X H Chen C S Li W H Zhang H Xu L S et al (2007) Noncovalent-wrapped sidewall functionalization of multiwalled carbon nanotubes with polyimidePolymer Composites 28 36e41

Ye X Y Liu Z M Wang Z G Huang X J amp Xu Z K (2009) Preparation and char-acterization of magnetic nanofibrous composite membranes with catalytic activity Mate-rials Letters 63 1810e1813

Yi X S Yu S L Shi W X Sun N Jin L M Wang S et al (2011) The influence ofimportant factors on ultrafiltration of oilwater emulsion using PVDF membrane modifiedby nano-sized TiO2Al2O3 Desalination 281 179e184

Yong Ng L Wahab Mohammad A Peng Leo C amp Hilal N (2010) Polymeric membranesincorporated with metalmetal oxide nanoparticles A comprehensive review Desalination308 15e33

Yu D G Teng M Y Chou W L amp Yang M C (2003) Characterization and inhibitoryeffect of antibacterial PANbased hollow fiber loaded with silver nitrate Journal of Mem-brane Science 225 115e123

40 Advances in Membrane Technologies for Water Treatment

Yu L Y Shen H M amp Xu Z L (2009b) PVDF-TiO2 composite hollow fiber ultrafiltrationmembranes prepared by TiO2 solegel method and blending method Journal of AppliedPolymer Science 113 1763e1772

Yu L Y Xu Z L Shen H M amp Yang H (2009a) Preparation and characterization ofPVDFeSiO2 composite hollow fiber UF membrane by solegel method Journal ofMembrane Science 337 257e265

Yu S Liu M Liu X amp Gao C (2009) Performance enhancement in interfacially synthe-sized thin-film composite polyamide-urethane reverse osmosis membrane for seawaterdesalination Journal of Membrane Science 342 313e320

Zavastin D Cretescu I Bezdadea M Bourceanu M Driagan M Lis G et al (2010)Preparation characterization and applicability of cellulose acetateepolyurethane blendmembrane in separation techniques Colloids and Surfaces A Physicochemical andEngineering Aspects 370(1e3) 120e128

Zhang Y Liu Lu Y Zhao L amp Song L (2013) Investigation of phosphorylatedTiO2eSiO2 particlespolysulfone composite membrane for wastewater treatment Desa-lination 324 118e126

Zhang F Ma X Cao C Li J amp Zhu Y (2014) Poly(vinylidene fluoride)SiO2composite membranes prepared by electrospinning and their excellent properties fornonwoven separators for lithium-ion batteries Journal of Power Sources 251423e431

Zhang M Zhang K S Gusseme B D amp Verstraete W (2012) Biogenic silver nano-particles (bio-Ag0) decrease biofouling of bio-Ag0PES nanocomposite membranesWaterResources 46 2077e2087

Zheng Y M Zou S W Nadeeshani Nanayakkara K G Matsuura T amp Paul Chen J(2011) Adsorptive removal of arsenic from aqueous solution by a PVDFzirconia blend flatsheet membrane Journal of Membrane Science 374 1e11

Zhou Y Zhao H Bai H Zhang L amp Tang H (2012) Papermaking effluent treatment Anew cellulose nanocrystallinepolysulfone composite membrane Procedia EnvironmentalSciences 16 145e151

Zhu X Y Bai R Wee K H Liu C amp Tang S L (2010) Membrane surfaces immobilizedwith ionic or reduced silver and their anti-biofouling performances Journal of MembraneScience 363 278e286

Zodrow K Brunet L Mahendra S Li D Zhang A Li Q et al (2009) Polysulfoneultrafiltration membranes impregnated with silver nanoparticles show improved biofoulingresistance and virus removal Water Resources 43 715e723

Zulfikar M A Mohammad A W amp Hilal N (2006) Preparation and characterization ofnovel porous PMMA-SiO2 hybrid membranes Desalination 192 262e270

Advances in polymeric membranes for water treatment 41

Advances in ceramic membranesfor water treatment 2M Lee Z Wu K LiImperial College London London UK

21 Introduction

211 Water treatment

Water is the most abundant natural resource on our planet but only a small percentageis accessible and fit for use in sustaining human life Many areas of the world have noaccess to safe and clean drinking water and are in urgent need of economical reliableand effective methods of treating local raw water sources In addition the global waterconsumption rate continues to increase because of the rapid rise in population andincreased industrialization and agricultural needs The strain placed on the limitedclean water supply will lead to rises in water price which can significantly increasethe operating costs in many industries where water is used extensively and in largevolumes Furthermore regulations on the quality of drinking ground surface andwastewater qualities are becoming increasingly stringent and thus effective watermanagement is of paramount importance more than ever Many industriesrsquo ideal statewould be to recycle all of their wastewater and reach a lsquozero-dischargersquo conditionSignificant developments have been made over the past half-century in the water treat-ment field in particular in the development of cost-effective low-pressure membraneprocesses such as microfiltration (MF) and ultrafiltration (UF) (Judd 2010 Staff2011 Van Der Bruggen et al 2003)

212 Micro- and ultrafiltration processes in water treatment

The commercialization of cost-effective MFUF membranes may be of the most sig-nificant changes in water and wastewater treatment since the 1960s MF and UF arelow pressure-driven separation processes that are less energy-intensive than traditionaltreatment methods The two processes can separate components by a sieving mecha-nism without the need for chemical or physical pre- or post-treatment Hence they arewidely used in many applications for a range of different purposes such as removingsuspended solids bacteria and viruses and heavy metals achieving oil and water sep-aration and pretreating desalination (Lens et al 2001 Mallada amp Meneacutendez 2008)MFUF membranes are porous with pore sizes ranging from microns to nanometresthey can be easily incorporated into existing processes as a standalone unit or com-bined with other technologies

A hybrid system that has broadened the use of MFUF in wastewater treatment isthe membrane bioreactor (MBR) It combines the biological treatment of wastewater

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400002-2Copyright copy 2015 Elsevier Ltd All rights reserved

with a membrane filtration process and is commonly used to treat industrial and munic-ipal wastewater (Judd 2008 2010 Meng et al 2009) However fouling and replace-ment costs of polymeric membranes still challenge the widening and large-scale useof MBRs Although the capital costs of ceramic membranes are higher their robust-ness higher resistance to microorganisms and ease of cleaning lead to lower main-tenance and replacement requirements cutting down long-term operating costs andoffering a competitive alternative to polymeric systems (Gander Jefferson amp Judd2000 Judd 2008)

213 Ceramic membranes in water treatment

Ceramic membranes may be an alternative material for use in MFUF applications inthe place of polymeric membranes Because of their superior chemical thermal and me-chanical properties they can be backwashed cleaned with harsh cleaning agents andsterilized at high temperatures offering reliable performance over longer periods oftime Ceramic membranes have found commercial success in applications in whichthe operating conditions are harsh such as at high temperatures and in aggressive chem-icals (solvents and highly acidic or caustic solutions) Examples of successfulcommercial-scale plants that use MFUF ceramic membranes include purifying andconcentrating valuable components such as enzymes and (Krstic et al 2007) clarifyingfermentation broths in biotechnology industries (Finley 2005 Sondhi Bhave amp Jung2003) clarification of fruit or sugar cane juices (Daufin et al 2001 Girard FukumotoampSefa Koseoglu 2000 Sondhi et al 2003) and treatment of highly oily wastewaterand degreasing baths (Cheryan amp Rajagopalan 1998 Majewska-Nowak 2010)

In contrast ceramic membranes are much less commonly used in water and waste-water treatment such as for the production of drinking water and treatment of munic-ipal wastewater This has historically been because of their high fabrication costscompared with commercially available polymeric membranes Common configura-tions of ceramic membranes include flat-sheet tubular and monolith elements asshown in Table 21 They are normally thicker than polymeric hollow-fibremembranes leading to lower packing densities They are also intrinsically brittleand therefore more expensive to pack and seal

However as the result of sustainable developments in ceramic membranescheaper more effective higher-performing and more compact ceramic systems canbe formed potentially allowing the widening of their applications Table 21 listssome current major international ceramic MFUF membrane suppliers Tubularmonolithic and flat-sheet ceramic membranes currently dominate over hollow-fibremembranes with great water permeation fluxes

22 Development in ceramic membranes and theirfabrication processes

Amembrane can be defined as a semi-permeable active or passive barrier which whenplaced under a certain driving force separates one or more selected species or

44 Advances in Membrane Technologies for Water Treatment

Table 21 List of commercially available ceramic membranes for MFUF

Company Product Material

Technical specifications

Pore size (mm)

Channeldiameterouterdiameter(mm)

Packingdensity(m2m3)

Purewater flux(L(m2hbar))

Flat sheet ItN NanovationAG

CFM Systems

(Itn-nanovation waterfiltration Itn-nanovation Filtrationrack Itn-nanovationT-series)

Substratea-Al2O3

Selectivelayera-Al2O3ZrO2

02 30e 918 e

MeidenshaCorporation

Ceramic membrane unit(Ceramic membraneunit 2013)

a-Al2O3 01 e 361 1670

LiqTechInternationalInc

Silicon carbide flat sheetmembrane (Liqtech)

SiC 02 e 377 e

Flat disc LiqTechInternationalInc

Silicon carbideFlat disc membrane(Liqtech Dynamic)

SiC 004 01 10 e e 3000 400010000

Tubularmonolith

Tami Industries CeacuteRAM (Inside ceacuteram)ISOFLUX (Isoflux)

e MF 014e14UF MWCO1 kDae150 kDa

e e e

AtechInnovationsGmbH

Ceramic membranes(Atech-innovations)

MF a-Al2O3

UF TiO2

MF 01e12UF up to 005and MWCO5 kDa

25e80100e520

e e

Continued

Table 21 Continued

Company Product Material

Technical specifications

Pore size (mm)

Channeldiameterouterdiameter(mm)

Packingdensity(m2m3)

Purewater flux(L(m2hbar))

LiqTechInternationalInc

SteriMem (LiqTech SiCSteriMem) CoMem(COMEM) CoMemConduit (COMEM

CONDUIT) andAquasolution(AQUASOLUTION)

SiC 004 01 10 30e170250e1460

e e

Pall Corporation Membralox (Pall

MembraloxMembralox)

Substrate Al2O3

Selective layerMF Al2O3 orZrO2

UF TiO2

MF 01e50UF 002e01and MWCO1e5 kDa

30e60e 285 e

Veolia WaterLtd

Ceramem

(TundrasolutionsCeraMem Full-sizemembrane modules2013 Veoliawaterst ampCERAMEM)

MF a-Al2O3SiC TiO2

UF SiC SiO2TiO2

MF 01e05UF 0005e005

20e501420 782 MF 400e1200UF 200e800

Hollowfibre

Hyflux Ltd InoCep (Inocepmembrane InoCep)

a-Al2O3 002e14 3040 157 250e4500

Media andProcessTechnologyInc

MPT hollow-fibremembranes (Mediaand process)

a-Al2O3 0004e02 10e35e 502 e

components of a liquid mixture whilst the rest is rejected (Mulder 1996) Micro- andultrafiltration are low pressure-driven processes in which physical separation ofthe different-sized feed components is achieved via a sieving mechanism across themembrane with a specific pore size

In 1989 the Membrane Technology and Research Inc (MTR) performed a studyaddressing the research priorities in the membrane separation industry (Ruutenhuch1992) For MF and UF the highest priority research topics include fouling-resistantlong-life membranes that are high temperature solvent wide pH and oxidant resistantlow-cost membrane modules and low energy module designs Although the study wasperformed more than 20 years ago many of the issues still remain as importantresearch areas today The development of cheap asymmetric inorganic membraneswith high packing densities can be seen as a possible solution to most of the challengeslisted above Significant progresses have been made in recent years regarding theceramic membranes and their fabrication processes

221 Desirable membrane characteristics and their design

To understand the type of membrane properties desired for pressure-driven membraneprocesses it is important to understand the membrane transport mechanisms Transportmodels can help identify the structural parameters that affect the membrane perfor-mance Different pore geometries exist depending on the fabrication processes andhence different models can be used to describe the transport through these different ge-ometries For example the pores can be depicted as parallel cylinders or a network oftightly packed spheres For pores formed from voids between tightly packed spheresthe CarmaneKozeny relationship can be used to describe membrane flux assumingno interaction exists between the fluids and surface of the membrane (Mulder 1996)

J frac14 ε3

khS2eth1 εTHORN2Dp

Dx(21)

where J is the membrane flux (m3(m2 s)) k is the CarmaneKozeny constant(depending on pore shape and tortuosity) ε is the porosity S is the specific surface area(m2m3) h is the permeate viscosity (N sm2) Dp is the pressure difference (Nm2) andDx is the membrane thickness (m) Membrane selectivity and permeation flux aremajor indicators of membrane performance Eqn (21) shows that structural parameterssuch as high porosity narrow pore size distribution and thin membrane thickness arealways desirable for improved membrane performance The different characteristics ofthe membrane can be designed and tailored using different fabrication techniques andcontrolling the related fabricating parameters during the course of production

222 Material and microstructure

Various membrane materials are available for MFUF processes The choice of themembrane material affects the practicality and sustainability of the filtration operationand hence can be chosen based on the specific application requirements

Advances in ceramic membranes for water treatment 47

Examples of ceramic materials include alumina (g-Al2O3 and a-Al2O3) zirconia(ZrO2) titania (TiO2) glass (SiO2) and silicon carbide (SiC) Ceramic membranesoffer superior temperature and chemical tolerances leading to an extensive range ofapplications across many industries They can be an important and environmentallyfriendly component in helping companies achieve a lsquozero-dischargersquo state Howeverthe main drawback of using ceramic membranes for water treatment is their highcapital cost hence large-scale membrane applications or less challenging water puri-fication processes are still dominated by polymeric membranes As shown in Table21 commercial ceramic membranes for MFUF processes consist mainly ofa-Al2O3 as the substrate and a-Al2O3 TiO2 or ZrO2 as the selective separation layerAccording to experiments in the literature there is a general consensus that chemicalstability (in highly acidic or basic environments) decreases with the following trendTiO2gt ZrO2gt a-Al2O3gt g-Al2O3gt SiO2 (Hofman-Zeurouter 1995 Mallada ampMeneacuten-dez 2008 Van Gestel et al 2003) Generally inorganic membranes can withstandorganic solvents chlorine and other oxidants are less susceptible to microbial attackthan polymeric membranes and can be used at pH values close to 0 and up to 14 (TiO2and a-Al2O3) (Hsieh 1996 Mallada amp Meneacutendez 2008)

Ceramic membranes are generally accepted to have high mechanical strengthBecause of this they can be backwashed at elevated pressures and operated over alonger period of time compared with polymer membranes (Guerra Pellegrino ampDrewes 2012 Sondhi amp Bhave 2001) However a disadvantage of ceramic mem-branes is their brittleness hence they must be handled with care and the choice ofhousing and sealing should be carefully considered The pressure required to driveMF is 01e2 bar and much higher for UF (Van Der Bruggen et al 2003) Themaximum operating pressure specified by a hollow-fibre ceramic membrane manufac-turer is 6 bar (Hyfluxmembranes InoCep) much higher than the 25-bar maximumallowable for polyethersulphone (PESf) membranes (Hyfluxmembranes Kristal)

As mentioned in Section 21 the microstructure across the membrane cross-sectionand surfaces is a key property that dictates the performance and usability of amembrane for a certain applications A membrane can be categorized into symmetricand asymmetric structures A symmetric membrane has a uniform cross-sectionthroughout whereas an asymmetric membrane does not as shown in Figure 21(a)and (b) (or Figure 21(c)) respectively

For MF and UF processes asymmetric membranes consisting of a thin skin layer ontop of a porous sub-layer are desired The top layers of UF membranes are much denserthan MF membranes hence they require higher trans-membrane pressures and gener-ally have lower permeability The asymmetric structures are associated with higherpermeation flux because the effective membrane thickness can be much thinnerthan in symmetric membranes The porous sub-layer acts to provide adequate mechan-ical strength This type of structure combines high selectivity of the skin layer withgood permeation fluxes

An asymmetric membrane can be integral or made of several layers known as acomposite The top and porous layers of an integral asymmetric membrane are normallymade of the same material (Figure 21(c)) and for composite membranes the top skinlayer and the porous sub-layer can be made of different materials (Figure 21(b))

48 Advances in Membrane Technologies for Water Treatment

A composite membranersquos properties and performance can be tailored usingdifferent materials in different layers Some disadvantages of composite membranesinclude the high complexity of the membrane fabrication process which requiresmany steps and the possibility of membrane failure owing to delamination of theseparation layer which occurs during sintering or variations in filtration pressures(wang Jerome Morris amp Kesting 1999) Integral membranes are homogeneous incomposition but can also be highly structurally varied in layers or distinct regionsdepending on their fabrication methods

As shown in Figure 21(c) and (b) the cross-sectional microstructure of the integralmembrane and the composite membrane vary significantly even though both are asym-metric membranes The integral membrane in Figure 21(c) is normally achieved viathe combined phase inversionsintering method (Li 2007) whereas the composite inFigure 21(b) is made by skin deposition on top of a multi-layer substrate supportThe integral membrane consists of two different types of sub-structures sponge-likeand finger-like The sponge-like structure can provide the membrane with the desiredselectivity and the finger-like structures can reduce the overall membrane resistance to

Figure 21 Scanning electron micrograph of the cross-section of (a) a symmetric aluminasubstrate (Reprinted from Kingsbury and Li (2009) with permission from Elsevier) (b) a three-layered alumina membranesupport composite (Reprinted from Hsieh Bhave and Fleming(1988) with permission from Elsevier) and (c) an asymmetric integral alumina membrane(Reprinted from Kingsbury et al (2010) with permission from Elsevier)

Advances in ceramic membranes for water treatment 49

permeate flow On the other hand the composite membrane consists of pores formedby voids between the particle packing only and the membrane selectivity is providedby the finer particles at the top layer and at a lower magnification the entire cross-section will appear to have a sponge-like structure

Integral and composite ceramic membranes can be made via different fabricationmethods the choice of method will largely depend on the membrane configurationand microstructures that are desired

223 Membrane configurations

There is a wide variety of membrane geometries available depending on the shapeformation technique chosen in the fabrication process Ceramic membranes exist intwo main types of element configurations ie flat and cylindrical The choice of mem-brane configuration depends largely on the application such as the required operatingand feed conditions

2231 Flat membranes

Flat ceramic membranes can come in a disc or sheet form The packing density of discmembranes is generally low and hence they are limited to use in small-scale industrialmedical and laboratory applications Commercial ceramic flat-sheet membranes mayhave thicknesses of around 6 mm and can be multi-channelled across their cross-section as shown in Table 21 and Figure 22 Flat-sheet membranes are easy toreplace when packed in modules and can handle high-turbidity feeds Mechanicalcleaning of ceramic flat-sheet membranes is also versatile it can withstand air scrub-bing backwashing and high-pressure water jet cleaning

Figure 22 Product photographof a commercial multi-channelledalumina flat-sheet membrane(CFM Systems)From ItN Nanovation AG(CFM-Flyer) (Reproduced bypermission of ItN NanovationAG)

50 Advances in Membrane Technologies for Water Treatment

2232 Cylindrical membranes

Single-channel tubular membranes generally have diameters of between 10 and25 mm shown in Table 21 and Figure 23 They are more suitable for separating feedsthat have high turbidity and large amounts of suspended solids Because of their largerdiameters and robustness they can be more easily cleaned mechanically and highcross-flow velocities can also be used to control fouling To further improve the pack-ing density of the tubular membranes they can be fabricated as multi-channel tubescalled monoliths with a surface area to volume ratio up to 782 m2m3 as shown inTable 21 In an effort to improve the packing density hexagonal monoliths werealso developed by Pall Corporation (Pall Membralox) (Figure 23(a)) Monolithmembranes offer the same advantages as singular tubular membranes Howeverwhen running in the inside-out configuration the pressure drop of the permeateflow across the monolith could be high as a result of the long and tortuous path ithas to travel to reach the outer surface of the monolith which limits the size of theouter diameter that can be used The patented CeraMem from Veolia Water Ltd (Tun-drasolutions) solves this problem by adding multiple conduits across the monoliththrough which permeate will flow through and then be collected at the end of the mod-ule (Figure 23(c))

Ceramic hollow-fibre membranes have diameters of 20e40 mm (Han et al 2011Kingsbury amp Li 2009 Liu Li amp Hughes 2003 Tan Liu amp Li 2001) (Figure 24)which means that compact modules with highly effective membrane surface areas can

(a) (b)

(c)

Figure 23 Product photograph of (a) Pall Corporation Membralox multi-channelled aluminamembranes (Pall Membralox) (Image courtesy of Pall Corporation) (b) LiqTech Interna-tional Incrsquos SiC SteriMem products (LiqTech SiC SteriMem) (Reproduced by permission ofLiqTech International AS) and (c) Veolia Water Ltd CeraMem element (Tundrasolutions)(Reproduced by permission of Veolia Water Technologies)

Advances in ceramic membranes for water treatment 51

be achieved Furthermore Fraunhofer IGB Ltd stated that ceramic hollow fibres withan outer diameter as low as 05 mm have been fabricated via combined phase inversionand sintering (Ceramic capillary membranes) potentially increasing the packingdensity that can be further achieved In addition they require lower trans-membranepressures to drive permeate flow because of the thinner membrane and can be cleanedeasily using methods such as backwashing and forward flushing

224 Fabrication techniques

Fabrication of composite ceramic membranes is generally a multi-step process It cangenerally be broken down into three different stages preparation of the ceramicpowder paste or suspension shaping of the ceramic powder into the desired geometryand heat treatment which includes calcination and sintering (Li 2007) After thesemain steps additional layer deposition followed by further heat treatment steps cantailor membrane selectivity as well as other membrane properties The choice ofmethod for each step depends on the desired membrane configuration qualitymorphology mechanical and chemical stability and selectivity of the final membranesHowever the fabrication method should also be economical and easy to replicatewithout compromising the quality of the final membrane

2241 Ceramic powder paste and suspension preparation

The ceramic powder preparation stage processes the raw inorganic material intothe shape and size distribution desired for membrane fabrication This can be in the

Figure 24 Product photograph of hollow-fibre alumina membranes from Hyflux Ltd(InoCep) (Reproduced by permission from Hyflux Ltd)

52 Advances in Membrane Technologies for Water Treatment

form of milling or chemical particle preparation Often the ceramic powder is madeinto a paste or suspension so that shape formation is possible During this step addi-tives can also be introduced to the ceramic material The choice of suspension mediumadditives and powder is important and affects the membranersquos microstructure andquality Deflocculants or dispersants often in the form of various fatty acids and esterscan be added to stabilize the ceramic particles in suspension to achieve high particleloadings and continuously high-quality ceramic membranes (Calvert et al 1986 Li2007 Sushumna Gupta amp Ruckenstein 1992 Zeurourcher amp Graule 2005) Magnesiumoxide has been used as a sintering additive to lower the sintering temperature requiredto form alumina hollow-fibre membranes via a combined phase-inversion and sinter-ing method (Choi et al 2006) Other additives such as the polymer binder are used tomaintain the shape of the ceramic membrane precursor and plasticizers can be usedto increase flexibility and ease of handling of the suspensions for tape casting or extru-sion methods (Burggraaf amp Cot 1996)

2242 Shaping

The shaping step is the physical process whereby the ceramic material is transformedfrom a suspension or powder paste form into the membrane geometry Methods thatcan create ceramic membranes and substrates include pressing tape casting slip cast-ing extrusion phase inversion foam techniques and leaching techniques

Pressing is a simple and quick method for producing flat ceramic membranes (Silvaet al 2012 Wang et al 2008a Xin et al 2007) A force is applied over an area ofceramic powder (varying from 10 to 100 MPa (Drioli amp Giorno 2010)) until the parti-cles are consolidated This method produces membranes of a symmetric structure owingto the uniform force applied across the area of ceramic material and are commonly usedto make disc membranes Meanwhile this method is not flexible in fine-tuning micro-structures and there is a limitation on the thickness to diameter ratio of the membranethat can be achieved In addition it is a batch fabrication process and has been usedprimarily to make membranes for use in laboratories rather than commercially

The tape casting method is used to form flat-sheet ceramic membranes (Das ampMaiti 2009 Das et al 1996 Lindqvist amp Lideacuten 1997) A tape cast suspension is firstprepared with the ceramic material a liquid-dispersing medium and organic additivesto provide the suspension with pseudo-plastic behaviour Then the suspension is trans-ferred into a reservoir controlled by a blade that can be height adjusted over a mobilecarrier film Subsequently the suspension film is dried in a controlled environmentTape casting is a more flexible method that can make flat-sheet membranes as wellas coat layers onto membrane supports

Slip casting uses a porous mould to form the shape of the ceramic membrane(Falamaki amp Beyhaghi 2009 Lin amp Tsai 1997) When the ceramic suspension ispoured into the mould the solvent is extracted into the pores of the mould as a resultof the capillary force leaving ceramic particles on the surface of the mould Slip cast-ing is commonly used to form tubular membranes with high surface quality densityand uniformity Important factors that affect the final quality of the membranes createdvia this method include slip density and viscosity

Advances in ceramic membranes for water treatment 53

Extrusion is a method popular for fabricating tubular monolith and hollow-fibrecapillary membranes (Castillon amp Laveniere 1995 Feenstra Terpstra amp Van Eijk1998 Smid et al 1996 Terpstra Bonekamp amp Veringa 1988 Wang et al 1998)It is a process in which an inorganic stiff paste is forced through an orifice of adesigned shape and compacted by applying high pressure The paste must have plasticproperties to form and maintain the shape of the membrane precursors hence addi-tives are added to the ceramic powder The paste is then forced through a die athigh pressure (around 20 MPa) to produce hollow tubes

Combined phase-inversionsintering (Kingsbury amp Li 2009 Liu et al 2003 Tanet al 2001) is a relatively new method for fabricating microstructured ceramic hollow-fibre membranes Solventenon-solvent exchange-induced precipitation of the poly-meric binder and viscous fingering phenomenon occur during membrane fabricationwhich distinguishes this method from conventional ram extrusion and will be furtherintroduced in Section 25

2243 Heat treatment

After the forming step the ceramic membrane precursors are produced They are thendried and treated with heat This heat treatment step consists of three main steps (Li2007) pre-sintering thermolysis and final sintering with the purpose of removingcomponents other than the ceramic material to strengthen the membrane and consol-idate the microstructure and dimensions of the final membrane

Presintering occurs at around 200 C Presintering is used to remove water from themembrane precursors which may be in the form of water chemically bonded to theceramic particle surfaces or as crystallized water within the inorganic phases Thermol-ysis or the calcination step is the process by which all organic components in the mem-brane precursor are removed The sintering stage is where the major changes to theporosity and pore size occur the final shape of the ceramic membrane is consolidatedand mechanical strength is improved In general the higher the sintering temperaturethe higher the mechanical strength but the porosity of the final membrane is lowered

Important parameters that affect thermal stability of ceramic membranes are sinteringactivity and phase transformation of the membrane material and the support (Mallada ampMeneacutendez 2008) During sintering the ceramic material is kept at a certain temperaturelong enough for the material to approach its equilibrium structure The membrane struc-ture can be maintained for temperatures up to 100e150 C below the sintering temper-ature which is normally extremely high (over 1000 C) (Burggraaf amp Cot 1996)

2244 Layer deposition for composite membranes

Additional layer deposition can be used to alter or enhance the ceramic membraneproperties for example by changing the membrane selectivity porosity hydrophilic-ity conductivity permeability biocompatibility etc

To form composite membranes layer deposition methods are required to add layersonto a symmetric substrate Each layer normally consists of ceramic particles ofdifferent sizes to achieve a gradient pore structure across the membrane cross-section Multiple layers are normally required to reach the desired selectivity at the end

54 Advances in Membrane Technologies for Water Treatment

Dip or spin coating is the most commonly used method for layer deposition onto asupport (Babaluo et al 2004 Gu amp Meng 1999 Lindqvist amp Lideacuten 1997) Dipcoating is when a support is dipped into and then withdrawn from a ceramic powdersuspension Upon withdrawal from the suspension the liquid will be sucked into thesupport pores because of capillary forces along with the ceramic particles if they aresmall enough in size Spin coating rotates the substrate while the suspension is depos-ited over the substrate surface

Sol-gel method can be used to fabricate membranes with high selectivity with poresfrom 100 nm down to a few nanometres and is commonly used to form ceramic UFmembranes (Agoudjil Kermadi amp Larbot 2008 Das amp Maiti 2009 Hao et al2004 Kim amp Lin 1998 Larbot et al 1988 Wu amp Cheng 2000) A colloidal (consistsof alkoxide) or polymeric solution is first deposited over a membrane substrate bymeans of dip coating whilst it is converted into a gel form by hydrolysis and conden-sation or polymerization Afterward it is heat treated to form a thin and uniform skinover the membrane

There are many other coating techniques such as chemical vapour depositionneutron sputtering and plasma details about these can be found elsewhere(Burggraaf amp Cot 1996 Hsieh 1996 Li 2007)

225 Combined phase-inversion and sintering fabricationtechnique

As described in the previous section the traditional and common method for pro-ducing hollow-fibre membranes is to use extrusion followed by sintering Howeverthis would give rise to symmetric membranes and additional layer deposition andheat treatment steps are required to produce the required selectivity with a gradientpore size along the membrane cross-section as shown in Figure 21(b) An alter-native and innovative method for producing ceramic hollow-fibre membranes isthe combined phase-inversion and sintering technique (Choi et al 2006 Kings-bury amp Li 2009 Kingsbury Wu amp Li 2010 Koonaphapdeelert amp Li 2007Liu et al 2003 Tan et al 2001 Wang et al 2008b Wang et al 2009 Weiet al 2008) It is a flexible technique that can produce both symmetric ceramicmembranes and a wide range of asymmetric ones in a single step for both flat-sheet and hollow-fibre geometries as shown in Figure 21(a) and (c) Because ofthe presence of large finger-like structures they can reduce mass transfer resistancefor permeation fluxes competitive to the membranes formed via conventionalmethods

A suspension consisting of ceramic particles and polymer binder in a solvent is firstprepared and then through solventenon-solvent exchange induced phase inversion ofthe polymer binder the ceramic particles are immobilized in their desired geometry bycasting (flat membrane) or spinning (hollow-fibre membrane) This method can easilytailor and form membrane precursors with various specific morphologies Thensimilar to all other ceramic fabrication methods the membrane precursors undergo aheat treatment session (Section 243) to remove all organics as well as consolidatethe final membrane structure and mechanical strength

Advances in ceramic membranes for water treatment 55

Preparation of the ceramicesolventepolymer suspension solution is a step that hasa major impact on the properties of the final membrane The particle size and particlesize distribution of the ceramic components can affect the pore size and selectivity ofthe membrane as well as the suspension rheology Porous alumina hollow-fibremembranes developed using this method have selectivity in the MF range when1-mm particles are used (Kingsbury amp Li 2009) and in the UF range when mixturesof 001- and 1-mm particles are used (Tan et al 2001) Yttria-stabilized zirconia(YSZ) porous membranes have pore sizes in the UF range when polydispersed YSZparticles (01 and 002 mm) are used (Wei et al 2008) Other factors such as theceramic to polymer binder ratio can affect the mechanical strength and quality ofthe sintered membrane and a ratio of up to 10 has been suggested (Kingsbury ampLi 2009 Tan et al 2001)

Although the process of spinning ceramic hollow-fibre membranes is similar tospinning polymeric ones the rules and optimization of the polymeric spinning systemcannot be applied directly to the ceramic spinning process because of the significantlydifferent composition of the spinning suspension The presence of a large amount ofceramic particles also changes the mechanisms behind the formation of the differentmembrane sub-structures Two basic sub-structures have been achieved within themembrane cross-section sponge-like denser structures and finger-liker structuresthat can be isolated or micro-channels as shown from Figure 25 The positioningand dimensions of these different sub-structures can be tailored mainly by changingthe parameters during spinning

Improved understanding of spinning parameters such as the air gap bore fluidchoice and bore fluid flow rate on the alumina membrane morphology was achievedby Kingsbury and Li (Kingsbury amp Li 2009 Kingsbury et al 2010) The designingand engineering of the two types of sub-structures led to distinctively differentmembrane morphologies (Figure 25) and generated a string of potential applicationsThese applications include hollow-fibre membrane micro-reactors membrane contac-tors solid-oxide fuel cells gas separation etc (Kanawka et al 2011 Kingsburyet al 2010 Koonaphapdeelert Wu amp Li 2009 Othman et al 2012 Rahman et al2011) In particular the morphology consisting of one sponge-like skin layer on topof a layer of finger-like micro-channels (Figure 25(d)) is expected to dramaticallyreduce the trans-membrane resistance to permeate flow The single thin separation layerprovides the membrane with its selectivity and the finger-like micro-channels canreduce the mass transfer resistance significantly This morphology is expected to excelin aqueous MFUF applications compared with conventional composite asymmetricceramic membranes

Current research has made significant progress in understanding the effects ofdifferent process parameters on membrane morphology and properties but the scientificmechanisms behind the formation of different sub-structures need further researcheffort In recent years the common viscous fingering phenomenon has been appliedto explain formation of the finger-like structures in the ceramicepolymeresolventand non-solvent systems (Kingsbury amp Li 2009 Kingsbury et al 2010 Wang ampLai 2012) Viscous fingering is a hydrodynamic phenomenon in which a less viscousfluid displaces a more viscous fluid forming finger-like patterns Important factors that

56 Advances in Membrane Technologies for Water Treatment

affect the initiation propagation and termination of these finger-like structures includeviscosity difference density difference moving interface velocity and polymer precip-itation rate Finger-shielding coalescing and spitting of the finger-like structures havealso been observed (Wang amp Lai 2012) A clearer understanding of the mechanismsbehind the formation of the unique sub-structures would allow easier and moreadvanced designing of the different morphologies and engineering of the productionprocess

The combined phase-inversion and sintering technique has been successfullyapplied to a wide range of ceramics as well as metals with a range of different pore sizes(Liu et al 2003 Luiten-Olieman et al 2011 2012 Yang Tan amp Ma 2008 Zhanget al 2009b 2012) However a compromise always has to be made between theporosity and mechanical strength when a high sintering temperature is involved Astudy suggested the use of a controlled sintering process by using PESf as not just apolymer binder but also a pore structure lsquostabilizerrsquo (Wu et al 2013) By thermallytreating the membrane precursors the PESf is not completely removed during the firststage of heat treatment Instead some of the PESf is converted to carbon at 1450 C inan environment devoid of oxygen which allows mechanical strengthening of thealumina membranes without losing significant porosity

Figure 25 Scanning electron micrograph of (a) cross-section morphology of a symmetricalumina hollow fibre and (bed) different asymmetric alumina hollow fibres formed by combinedphase-inversion and sintering (Reprinted from Kingsbury amp Li (2009) with permission fromElsevier Reprinted from Kingsbury et al (2010) with permission from Elsevier Reprinted fromTan et al (2011) with permission from Elsevier)

Advances in ceramic membranes for water treatment 57

As a result the combined phase-inversion and sintering method can potentiallycreate the opportunity to use ceramic membranes in large-scale water and wastewatertreatments by offering a hugely reduced fabrication process cost and great flexibilitiesin microstructure design However further improvements are required before thismethod can be fully commercialized for example to improve surface porosity andpure water permeation without sacrificing its mechanical strength and to have a betterfundamental understanding of the microstructure formation mechanisms to enablereliable and reproducible fabrication process on a large scale

23 Development in membrane modules and units

The design of the membrane module is important for achieving the highest packingdensity possible for the particular membrane element whilst offering effective filtra-tion The different membrane elements are packed in a unit called a module and thesemodules are often arranged and connected in a specific way to form a unit offeringgreat efficiency The unit(s) is then integrated with other components such as pumpspipes control systems etc to form a membrane system and part of the water or waste-water treatment plant The following section describes the ceramic MFUF modulesand units available commercially

231 Module and unit designs

Many different module designs are available for the different ceramic membranes andtheir choice depends largely on the application the demand of the process and anyspatial limitations and economical factors The arrangement and packing of themembrane elements can be divided into two main types ie flat membranes andcylindrical membranes

The membrane elements may be contained in pressure vessels or immersed in afluid medium at atmospheric pressure For the contained modules the ceramicmembranes are packed and fitted inside a pressure vessel and trans-membrane pressureis applied at one end of the vessel with the feed The immersed unit allows easierreplacement of the membrane elements or modules and is also more flexible to tailorto specific needs and demands Furthermore it enables air sparging in the unit toimprove permeation and reduce fouling by promoting turbulence Both flat-sheetand cylindrical membranes can be packed in this way and this type of system requiresless energy to operate than contained units

2311 Flat membranes

Ceramic flat membranes can come in the form of flat sheets or flat discs as described inSection 231 and can both be packed into plate-and-frame modules The containedplate-and-frame configuration consists of stacking the flat membranes on top of oneanother with porous spacers in between The size of the spacing depends on the amountand size of suspended solids in the feed The feed enters the module from one end and is

58 Advances in Membrane Technologies for Water Treatment

collected at the membrane support plates Such a module is easy to operate and mem-brane defects can be detected and replaced simply However their packing density islow and so most of the time they are limited to use for small-scale applications

Flat-sheet membranes with multiple channels can be stacked next to each other andform an immersed module as shown in Figure 26 These flat-sheet membranes are con-nected at the two ends to permeate collector(s) and then packed together and supportedby a metal framework that is then immersed into the feed medium Permeate enters fromthe membranersquos outer surface into the channels inside the flat sheets and is thencollected at the end(s) of the membrane These modules can then be further stackedtogether to easily increase productivity The energy consumption of the immersed mod-ule is lower than that of the contained module because of the lower pressureedrivingforce requirements The membranes can also be replaced easily because they are pro-duced and sealed sheet by sheet In addition their ability to handle feeds with a highcontent of suspended solids means that they are commonly used inMBRs to treat waste-water Packing densities of about 918 m2m3 are reached using the CFM Systems

from ItN Nanovation AG by stacking units on top of each other (Table 21) Howeverthis is still significantly lower than the packing densities offered by polymeric flat-sheetmembranes that are spiral wound (700e1000 m2m3) (Crittenden et al 2012)

2312 Cylindrical membranes

Tubular membranes are often packed as a bundle inside a casing which could be a con-tained vessel (Figure 27) or an open vessel The feed solution may be fed though the

(a) (b)

Figure 26 Product photograph of (a) a ceramic flat-sheet module from ItN Nanovation AG(Itn-nanovation) (Reproduced by permission of ItN Nanovation AG) and (b) a ceramic flat sheetsystem from Meidensha Corporation (Ceramic membrane unit 2013) (Reproduced bypermission of Meidensha Corporation)

Advances in ceramic membranes for water treatment 59

centre of the tubular or monolith membranes and permeate is collected outside the tubein the module casing This operating mode requires high operating flow rates and thepressure drop can be large hence energy consumption is highest compared with othermodule designs However because of the relatively large channel diameters of tubularand monolith membranes they are suitable for feed streams with larger particles andcleaning these membranes is also more facile The tubular or monolith membranescan also be packed and supported by a partly open housing support and operated byimmersion into the feed solution similar to the immersed flat-sheet modules offeringsimilar advantages and disadvantages The immersed tubular modules are commonlyused in MBRs for larger-scale applications and also to treat harsh feed streams

Hollow-fibre membranes can also be packed in a similar way in their modules asshown in Figure 24 Ceramic hollow-fibre membranes are generally packed togetherand immobilized at both ends and then placed in a cylindrical housing The fullycontained module is more suited to small-scale applications such as domestic-scaledrinking water treatment Hollow-fibre modules can potentially offer a much higherpacking density and form more compact systems saving space and improving produc-tivity As shown in Table 21 the packing density offered by commercial ceramichollow-fibre modules is not as competitive (502 m2m3 offered by Media and ProcessTechnology Inc) as some of the multi-channel tubular module designs (up to 782 m2m3 offered by Ceramem module from Veolia Water Ltd) This is mainly because ofthe relatively large ceramic hollow-fibre outer diameters from most of the suppliers(3e4 mm from Table 21) Furthermore their intrinsic brittleness makes it more diffi-cult to pack them into bundles and it limits their length Hence cassette-style modulesfor ceramic hollow-fibre membranes are not available in which the hollow fibres aresupported at the top and bottom only and are immersed fully into the feed solutionwith no housing In addition the lack of open vessel designs for hollow-fibre mem-brane elements means that their application in immersed MBR is limited

Figure 27 Product photograph of a containedmodule from Pall Corporation (Pall

Membralox IC) (Image courtesy of PallCorporation)

60 Advances in Membrane Technologies for Water Treatment

232 Housing sealing and operation

Membrane modules consist of the housing sealing materials and membrane The typeof housing used for the membrane varies depending on the membrane and module typeand operating configuration For contained cylindrical membranes the membrane ispacked and enclosed in a vessel shown in Figure 28 For outside-in feed configurationor immersed cylindrical membranes the housing may have openings that exposecertain areas of the membrane element Flat-sheet ceramic membranes are normallysealed at the top and bottom to a permeate collector They are then stacked togetherand supported by a stainless-steel frame into modules such as the Meidensha Corpo-rationrsquos ceramic membrane unit (Ceramic membrane unit 2013) and ItN NanovationAGrsquos CFM System (Itn-nanovation) (Figure 26)

Typical module housing materials include stainless steel titanium and plasticStainless steel is most commonly used because of its good chemical and thermalstability as well as great robustness Although plastic housing is a cheaper option itoften limits the conditions within which the membranes can operate

The type of seal used on the membranes varies depending on the membrane andmodule type They are important because they prevent contaminant leakage into thepermeate stream Mostly O-rings and gaskets are used to cover the perimeter of themembrane ends where both the feed and permeates are exposed The material usedto seal the membranes depends on the required operating conditions of the MFUFwhich will change depending on the application Typical sealing material includesrubber silicon polytetrafluoroethylene and poly(vinyl chloride)

There are many different module designs for flat-sheet and tubular (single andmulti-channel) ceramic membranes However because of the much larger dimensionsof the flat-sheet and tubular elements their packing density is lower than the polymericmembrane modules offered which makes them less competitive for large-scale appli-cations or when space is limited in a treatment plant Hollow-fibre membrane moduleshave the potential to improve the packing density significantly but most of the onesoffered on the market have relatively large outer diameters leading to lower packing

Figure 28 Product photograph of the CeraMem contained module and housing from VeoliaWater LtdReproduced by permission of Veolia Water Technologies (Tundrasolutions)

Advances in ceramic membranes for water treatment 61

densities Commercially available hollow-fibre modules are limited for example thereare limited open-vessel modules and no cassette-style ceramic hollow-fibre modulesfor large-scale immersion applications which is a problem for their application tosmall-scale MFUF applications

24 Ceramic membranes for water treatment

Because of the high chemical and thermal stability and robustness of ceramicmembranes they have been commonly applied in applications for which polymericmembranes cannot be used because of their lower stability For example ceramicscan be used in harsh environments such as at high temperatures and in aggressivechemicals (solvents highly acidic or caustic solutions) and oily water Unlike poly-meric membranes ceramic membranes do not swell in solvent and can be treatedwith strong cleaning agents and sterilized at high temperatures and can withstandhigh pressures for backwashing All of these advantages have made long-termflux stability possible for ceramic membranes to be used on a commercial scale(Mallada ampMeneacutendez 2008) Recently ceramic membranes have garnered increasingattention for applications in milder operating conditions in which polymericmembranes dominate because of the increase in the packing density of the membranemodules and reductions in capital costs

241 Drinking water production

MF and UF membranes are used extensively in producing drinking water and canhandle both small- and large-scale capacities (Staff 2011) Small-scale MFUF appli-cations include portable membrane systems and in large-scale applications MFUFmembranes can be used as stand-alone or hybrid systems in a water treatment processtrain This market has been and is still currently dominated by polymeric membranesbut recently the incorporation of ceramic membranes to produce drinking water hasbeen increasing (Bottino et al 2001 Li et al 2011 Mahesh Kumar Madhu ampRoy 2007 Muhammad et al 2009) Water sources used to produce drinking watercan vary considerably from groundwater lakes and rivers to municipal wastewaterand seawater The final water that is safe to drink must fulfil standards set by the WorldHealth Organisation or by the European Union and be free of suspended solidsmicroorganisms and harmful chemicals

Small-scale ceramic membrane MFUF systems can serve several purposes such asto improve the quality of tap water reduce the volume or recycle household waste-water provide safe drinking water in remote areas with limited resources such as dur-ing camping or hiking and provide safe drinking water in developing nations or duringhumanitarian crises

To produce drinking water from surface water for a large community e in otherwords for municipal use e large systems are required The water purification processwill consist of a process train of different steps Because the design of the process

62 Advances in Membrane Technologies for Water Treatment

depends on the feed quality and the final water quality preparing drinking water fromsurface water is much more expensive because it requires more purification steps Atypical process train for purifying surface water consists of a pre-filtration unit addi-tion of chemicals natural filtration disinfection fine filtration and preservation andstorage Ceramic MFUF membrane units may be used to replace conventional particleremoval units such as coagulation and sedimentation as well as disinfection unit(s)Furthermore the ability to reject microorganisms bacteria and viruses can reducethe amount of chemicals required to be added to drinking water saving considerablespace overall For the production of drinking water from seawater ceramic MFUFunits may be used to provide pre-treatment to reverse osmosis

Studies in literature have shown that ceramic MFUF membranes alone can providepermeate turbidity low enough for drinking standards and are effective in removingmicroorganisms organic matter and disinfection byproduct (DBP) precursors (Bottinoet al 2001 Harman et al 2010 Muhammad et al 2009) Because of the hydrophilicand inorganic characters of the ceramic membranes they are less affected by organicfouling compared with polymeric membranes (Hofs et al 2011) However high-turbidity water (up to 80 NTU) can lead to membrane fouling and significant permeateflux declination which can be recovered via chemical cleaning The membrane poresize also appears to affect the rate of flux decline because Harman et al suggestedthat the smaller 4-nm pore-size membrane fouls mainly by forming a cake layerwhereas pore clogging may dominate in the larger 10-nm pore-size membrane(Harman et al 2010)

To minimize the effect of fouling much research has been carried out to analyse theperformance of hybrid ceramic membrane systems such as the combination of ceramicmembrane MFUF with activated carbon for natural organic matter (NOM) removal(Karnik et al 2005b Konieczny amp Klomfas 2002 Lee Park amp Yoon 2009 Stoquartet al 2012) coagulation for reducing organics and viruses (Fiksdal amp Leiknes 2006Konieczny Bodzek amp Rajca 2006 Lerch et al 2005 Matsushita et al 2005) photo-catalytic reactions (Alem Sarpoolaky amp Keshmiri 2009 Chin et al 2007 Mozia2010) and ozonation to remove NOM (Karnik et al 2005a Kim et al 2008) andsubsequent formation of DBPs (Karnik et al 2005b) The use of the coagulationand MFUF hybrid system is preferred from an economic point of view

242 Municipal wastewatersewage treatment

Treatment and recycling of municipal wastewater is common and a highly importantpart of todayrsquos water management Municipal wastewater consists of household com-mercial and institutional wastewater A typical sewage treatment plant consists of thefollowing steps pre-treatment to remove large and heavy debris followed by primarytreatment used to remove the suspended inorganic and some organic particles and thensecondary treatment for the biological conversion of dissolved and colloidal organicsinto biomass and finally tertiary treatment for the further removal of suspended solidsor nutrients and disinfection

MFUF can be incorporated in the treatment train as stand-alone processes or com-bined with the activated sludge process to form hybrid systems such as the MBR

Advances in ceramic membranes for water treatment 63

This can reduce the steps in secondary and tertiary treatment for example eliminatingthe need for sedimentation and secondary disinfection saving space as well as reducingwaste such as DBPs that need to be treated and disposed of Ceramic membranes can beused to replace the traditional polymeric membranes for sewage treatment because thequick fouling of polymeric membranes limits them to short operating lifetimes Theycan be cleaned under harsher cleaning conditions and therefore offer longer andmore reliable operation as well as less servicing and maintenance reducing long-term operating costs Flat-sheet and cylindrical membrane elements are suitable forbeing combined with MBRs and the modules can be operated in the immersed modeor as a separate external unit The immersed mode consists of the membrane moduleimmersed in the aeration basin and permeate is extracted via suctioning The externalconfiguration consists of pumping the mixed liquor at high pressure through themembrane from one surface Because of the higher trans-membrane pressure requiredfor the external configuration their permeate flux is also generally higher (Marrot et al2004) However the energy and space consumption of the immersed configurationtends to be lower which makes them more suited to large-scale wastewater treatment

Many studies have been carried out to analyse the effectiveness of ceramic MBRsystems to treat municipal wastewater (Waeger Delhaye amp Fuchs 2010 Xinget al 2000 Xu et al 2003 Zhang et al 2009a) Xing et al (2000) looked at usingexternal cross-flow ceramic UF MBRs for urban wastewater reclamation The systemprovided high removal efficiency removing carbon oxygen demand (COD) of anaverage of 97 and the reclaimed water could be reused directly for municipal orindustrial purposes after additional treatment (Xing et al 2000) The lab-scaleimmersed ceramic MBR offered COD removal of more than 92 during the courseof a prolonged sludge retention time (142 days) to treat simulated high-strength waste-water (consisting of glucose and protein) (Sun Zeng amp Tay 2003) Using longersludge retention times can reduce the amount of sludge produced and cut down onthe cost of sludge treatment

Fouling was mainly affected by the membranersquos microstructure surface roughnessand pore sizes in immersed ceramic bioreactor systems (Jin Ong amp Ng 2010) Theceramic membrane with the roughest surface and largest pore size (03 mm) has thehighest fouling potential whereas the membrane with the smoothest surface and small-est pore size (008 mm) fouls the least Air sparging has been found to be an effectivesimple and economical method to improve permeate flux and reduce concentrationpolarization and fouling in external-loop air-lift ceramic MBRs and the immersedceramic MBR (Fan et al 2006 Sun et al 2003 Zhang et al 2009a) AnaerobicMBRs may have lower energy consumption (Liao Kraemer amp Bagley 2006) How-ever inorganic fouling in anaerobic MBRs by struvite has been observed in ceramicmembranes (Kang Yoon amp Lee 2002) and requires periodic alkaline backflushingto recover permeate flux

243 Industrial wastewater treatment

The composition of industrial wastewater varies dramatically across the industries andthe choice of membrane technology will vary according to the contaminants Because

64 Advances in Membrane Technologies for Water Treatment

of increasingly stringent regulations on waste discharge and the increasing cost ofclean water industries are more motivated to treat and recycle wastewater whichcan potentially save significant operating costs

Typical contaminants in industrial wastewater are suspended solids particulatescolloids bacteria and viruses dissolved inorganics such as heavy metals salts nuclearwastes acids or alkalis volatile organics such as aromatics aliphatics alcohols andhalogenated hydrocarbons and non-volatile organics such as phenolics polyaromaticcompounds pesticides insecticides surfactants and dyes Similar to sewage treatmentMBRs are a popular treatment unit in the treatment train Upstream and downstreamtreatment units will vary depending on the desired quality of the final effluent(ultra-pure water process water etc) Ceramic MBRs are commonly used for small-scale treatment of high-strength industrial wastewater because they are robust stableand reliable

244 Produced water

Produced water is the largest waste stream generated from oil and gas operations MFUF is a promising technology for use to treat produced water because it is a low-energyconsumption process and can cut down on the amount of harsh and expensive chem-icals required to treat the wastewater Polymeric membranes have been commonlyused to remove organic contaminants as well as suspended particles before desalina-tion so that the water can be reused However because the feed has a high compositionof organic contaminants oil and grease the polymeric membranes can be degradedand fouled easily requiring regular replacement Ceramic membranes offer higherstability in such conditions and may prolong the lifetime of the membrane and canalso be cleaned more easily

Many studies have been carried out to investigate the performance of ceramicmembranes in oilewater treatment in the laboratory or on a pilot scale (AshaghiEbrahimi amp Czermak 2007 Chen et al 1991 Ebrahimi et al 2010 Li amp Lee2009) Studies showed that using MFUF ceramic membranes gives permeate streamsof very high quality with less than 6 ppm total hydrocarbons and perform better thanpolymeric membranes However an important limitation is permeate flux decline as aresult of fouling by waxes and asphaltenes Backwashing is a useful cleaning methodto prevent permeate flux decline (Abadi et al 2011)

245 Food and beverage industries

MF and UF are important processes in the food and beverage industries They can beused to achieve clarification sterilization concentration and purification of the finalproduct in place of multiple traditional process units For the dairy industry MF canbe used to clarify cheese whey (Skrzypek amp Burger 2010) and to concentrate anddefat milk and sterilize it by rejecting microorganisms (Fernandez Garciacutea AlvarezBlanco amp Riera Rodriacuteguez 2013) In the sugar-refining and beverages industryMF and UF membranes are used to clarify products such as maple syrup wine

Advances in ceramic membranes for water treatment 65

beer juice and vinegar (Ceramic membranes 2000 Fukumoto Delaquis amp Girard1998 Gan et al 1999 Hinkova et al 2002 van der Horst amp Hanemaaijer 1990Li et al 2010) Wastewater generated in these industries can also be recycled withthe help of MFUF membranes to save operating costs Ceramic porous MFUFmembranes have demonstrated success in the food and beverage industries offeringsuperior long-term performance in these applications over polymeric membranes

246 Commercial ceramic applications

Ceramic membranes have been implemented commercially in the industriesmentioned in Sections 41e45 to treat aqueous feeds In terms of producing drinkingwater there are far fewer portable ceramic membrane drinking production systemsthan polymeric ones mainly owing to their high capital costs However Veolia WaterLtd developed a mobile ceramic UF system for providing emergency drinking water(Veoliawaterst Berkefeld) The system consists of a treatment train in the order ofcoagulation adsorption pre-filtration and UF using ceramic monolith elements andultraviolet and chlorination disinfection providing up to 360 m3day permeate flowfit for drinking purposes

For large-scale drinking water production the cost of ceramic membranes can berecuperated by their reliable performance and long operating lifetimes for examplea ceramic MF system by Metawater Co Ltd has been operating for 15 years(Metawater) Metawater Co Ltdrsquos systems typically consist of coagulation dead-end MF using ceramic monolith elements followed by disinfection with chlorineand have the treatment capacity of 1000e100000 m3day for the treatment of clearraw water

Because of the superior stability and operating lifetimes of ceramic MFUFmembranes they can also be used as a pre-treatment step before reverse osmosis fordesalination A drinking water plant in Qassim replaced polymeric UF pre-treatmentmembranes with ceramic flat-sheet ones which reduced the membrane replacementfrequency dramatically and has a treatment capacity of 42000 m3day (Itn-nanovationGround water)

For the treatment of municipal wastewater or sewage the performance of ceramicMBRs is highly competitive compared with polymeric systems Similar to drinkingwater production plants implementation of ceramic membranes is limited mainly bytheir high cost There are examples of commercial ceramic MBR systems being imple-mented in small-scale wastewater treatments such as in a school and an airport byLikuid Nanotek (Likuid-CBR) They use an external cross-flow configuration to treatdomestic wastewater with capacities ranging from 38 to 50 m3day and permeate flux isrecovered solely by periodic chemical cleaning For larger-scale wastewater treatmentthe ceramic immersed MBR is more commonly used for example ItN NanovationAG installed immersed ceramic flat-sheet membrane modules with a capacity to treat150 and 1300 m3day of sewage feed in two different sewage treatment plants(Itn nanovationMBR Itn nanovationMBCR) No membrane servicing or maintenancehas been required since operation began in 2011 for one of the plants and chemicalcleaning is used once a year (oxidant and chelating agent) to maintain permeation flux

66 Advances in Membrane Technologies for Water Treatment

Ceramic membranes have found more frequent use in the treatment of industrialwastewater because they are normally more challenging to treat An example of aceramic MBR includes an external MBR using ceramic tubular membranes fromLikuid Nanotech to treat industrial waste of 3e300 m3day which has been commer-cially used in olive oil wine and narcotics production plants For all of their ceramicMBRs the quality of the final effluent is clean enough to be directly discharged(Likuid-CBR) Another application includes the ceramic MBR installed for treatmentand recycling of up to 1400 m3day of highly pigmented wastewater by Pall Corpora-tion (Membralox pall) Complete retention of insoluble pigments is achieved usingmonolith ceramic membranes running in external configuration and up to 50 ofwastewater can be recycled A larger-scale ceramic MBR has been scheduled forinstallation in a demonstration plant by Meidensha Corporation to treat and recycleup to 4550 m3day of industrial wastewater by combining up-flow anaerobic sludgeblanket technology with the 01-mm alumina flat-sheet MBR system (Singaporecollaborate on ceramic membrane MBR demonstration plant 2012)

The commercial operation of ceramic membranes in produced water treatment ismuch more limited compared with other application areas such as in the food andbeverage industry and industrial wastewater treatment To treat produced water theceramic membranes typically run in cross-flow configuration (Elshorbagy 2013)An example is the full-scale facility in Colorado which uses ceramic membranes asone of the units to treat oily wastewater (Aqwatec) The process train consists ofdissolved air floatation pre-filtration ceramic MF and activated carbon adsorptionand then the water is supplied to a reverse osmosis plant providing municipal drinkingwater In addition Veolia Water Ltd has developed a system consisting of ceramicmonolith membranes to treat produced water which so far has been installed at 60locations (Veoliawaterst CeraMem) Their typical performance includes removalof 987 turbidity and effluent has less than 1 ppm oil and grease (Veoliawaterstna)Furthermore a ceramic (SiC) membrane module will be installed for commercial usein Columbia and Venezuela after the trial period offered consistent reductions of oilconcentration from 20e100 ppm to less than 5 ppm (Success for LiqTech ceramicmembranes in oil amp gas trial 2012)

Ceramic membranes are most commonly used in the food and beverage industry(Fernandez Garciacutea et al 2013) One commercial system for the removal of bacteriaand spores from milk using MF is the Tetra Alcross Bactocatch The raw milk is firstseparated into skim milk and cream and then the former undergoes MF leaving theconcentration of bacteria in permeate to be less than 05 of the original value(Peinemann Nunes amp Giorno 2011) Ceramic membranes were also chosen andinstalled by Atech Innovations GmbH over polymeric membranes in a commercialcitrus fruit juice production plant because of their high performance as well as resis-tance to essential oils from the fruit skins Another example of commercializationincludes the use of tubular ceramic monolith membranes in a high-velocity cross-flowconfiguration in a glucose production plant to minimize gel layer formation which isable to produce 180 m3day of glucose (Bolduan amp Latz 2005)

Ceramic MFUF membranes have been used across a wide range of different ap-plications involving water and wastewater treatment They are most commonly

Advances in ceramic membranes for water treatment 67

used in the food and beverage industry and in the small-scale treatment of industrialwastewater Laboratory pilot and some commercial case studies have shown poten-tial and advantages of using ceramic membranes for large-scale municipal waste-water treatment and the provision of safe drinking water As a result of the manybenefits offered by ceramic membranes their global incorporation into more drink-ing water treatment plants is anticipated Promising developments include theinstallation of ceramic flat-sheet membranes from ItN Nanovation AG in Saudi Ara-bia to pre-treat seawater in 2013 (Itn nanovation receives significant orders fromSaudi Arabia 2013) In addition three pilot plants using ceramic membrane hybridsystems with suspended ion exchange and ozone for drinking water treatment plantswill be installed in the United Kingdom Australia and Singapore by PWN Technol-ogies (Pwntechnologies) The incorporation of ceramic membranes in MBRs alsoclearly offers many advantages including ease of maintenance and long-term reli-ability High capital membrane costs along with energy consumption from contin-uous aeration contribute to a large proportion of the MBRrsquos operating costs andboth deter the growth of ceramic MBRs for large-scale sewage treatment There-fore further research and optimization of the immersed MBR is anticipated towiden the use of ceramic membranes The main overriding limitation to the com-mercial implementation of ceramic membranes for most large-scale water treat-ments is their high capital cost despite their overall longer lifetime and ease ofmaintenance

25 Ceramic membrane cleaning

Over time permeate flux of the ceramic membrane will inevitably decrease which issame as for their polymeric counterparts To recover as much as the initial flux aspossible many different cleaning methods are available The choice of the cleaningmethod(s) depends on the reversibility of the fouling the foulant(s) characteristicsthe membrane material and the membrane element and module design

251 Physical cleaning methods

Physical cleaning methods remove reversible foulants from the membrane surface viamechanical forces Examples of physical cleaning include forward and reverse flush-ing back-pulsingbackwashing use of turbulence promoters air flushing rinsing andsponge ball cleaning

Forward flushing is achieved by using high cross-flow velocities at the feedside to loosen and then remove foulants from the membrane surface The directionof the flush is often reversed for a few seconds to improve the effectiveness of thecleaning which is called reverse flushing Rinsing the membrane can also beused to dislodge and remove fouling layers One study found that rinsing withwater alone for 15 min could recover 90 of the original membrane flux ofmulti-channel tubular membranes fouled by whey proteins (Cabero Riera ampAlvarez 1999)

68 Advances in Membrane Technologies for Water Treatment

Backwashing is when a larger pressure is applied on the permeate side causing thereverse flow of permeate into the feed side and can help flush membrane pores as well(Laitinen et al 2001 Mugnier Howell amp Ruf 2000) For MF tubular ceramicmembranes fouled during treatment of oily wastewater over 95 recovery of the orig-inal flux or prevention of flux decline was achieved by periodic backwashing (Abadiet al 2011) However once permeate flux has dropped to 40e50 of the originalvalue chemical cleaning is required

Air flushingsparging can be used during MFUF to reduce the rate and extent offouling or it can be used periodically to clean the membrane surfaces (Cui Bellaraamp Homewood 1997 Matis et al 2004 Mercier-Bonin Lagane amp Fonade 2000)It can also increase permeate flux when used during filtration because the air bub-bles on the feed side can increase turbulence in the stream but increase energy con-sumption for the entire process Sponge ball cleaning scrubs foulants from themembrane surfaces and is suitable for use in cleaning large-diameter tubular mem-branes fouled by high-turbidity feed streams such as industrial wastewater (Psoch ampSchiewer 2006)

Forward flushing backwashing and air sparging can be combined because back-washing can loosen the fouling cake layer and forward flushing and air spargingcan sweep the foulants away

252 Chemical cleaning methods

Chemical cleaning methods are required to remove physically irreversible fouling bydissolving foulants without damaging the membrane A wide range of chemicals canbe used to clean the membranes their choice depends mainly on the type of foulant aswell as the membrane material For example acids may be used to treat inorganicfouling (Yoon Kang amp Lee 1999) and alkalis are commonly used to remove organicfouling (for membranes fouled by organic contaminants in surface water (Zondervanamp Roffel 2007) and whey protein (Bartlett Bird amp Howell 1995)) Ozone andoxidants have also been used to improve the removal of organic fouling (Changet al 1994) The chemical cleaning cycle normally consists of several steps andfactors such as cleaning temperature chemical concentration pH pressure and flowrates and time all of which can affect the cleaning efficiency (Bartlett et al 1995Bird amp Bartlett 2002) The cleaning agent can be introduced into the membrane chan-nels or the membranes can be immersed into cleaning agents

Often physical cleaning and chemical cleaning methods are combined for betterfouling control and shorter membrane cleaning time Using mechanical rinsing orbackflushing with caustic soda (NaOH) and oxidation (H2O2) leads to fast and effec-tive cleaning in which 87 of permeate flux is recovered within 8 min for ceramicmembrane fouled during beer filtration (Gan et al 1999)

253 Unconventional physical cleaning methods

The use of chemical cleaning methods generates undesired additional waste streams andconventional physical cleaning removes only reversible fouling Unconventional or

Advances in ceramic membranes for water treatment 69

developing techniques targeted for efficient and more environmentally friendly means toremove fouling material include the use of ultrasonic electric or magnetic fields

Ultrasonic fields can be used to aid in cleaning membranes Cavitation caused byultrasound can prevent the membranes from clogging when applied during operationand has the potential to improve permeation flux (Kylleuroonen et al 2006) They work byfirst loosening particles of the cake layer and then transporting them away by acousticstreaming (Lamminen Walker amp Weavers 2004) The same research found that fre-quencies between 70 and 620 kHz could be used without damaging the alumina mem-branes However damage to the membrane has been observed when it is placed withinthe cavitation region of the system (Chen Weavers amp Walker 2006) Furthermorethis may be an expensive method because the cost of energy to implement this maybe high and can potentially be used to remove foulants periodically instead

Electric fields can be used to clean membranes or enhance MFUF processesbecause they can provide an additional driving force to the filtration system Chargedsolids or species on the membrane can be moved as a result of the electric field appliedto the membrane surface thus reducing the effects of concentration polarization aswell (Jagannadh amp Muralidhara 1996) When electric fields are applied to the mem-brane fouling that is irreversible and resistant to physical cleaning methods canbecome physically reversible especially for membranes that are fouled by proteinsMagnetic fields can also potentially be applied to remove or reduce the extent of inor-ganic membrane fouling (Baker Judd amp Parsons 1997) This is because magneticfields change the calcium carbonate scale from its calcite form to the less solubleform aragonite and hence enhance the crystallization of CaCO3 preventing its forma-tion on membrane surfaces (Zaidi et al 2013)

There is a lot of freedom in choosing the cleaning method for ceramic membranesowing to their high thermal chemical and mechanical stabilities Fouling can beremoved effectively via a combination of physical and chemical cleaning methodsbut the use of chemicals to clean introduces new potentially hazardous wastes thatmay then need further treatment Unconventional methods such as using ultrasonicelectric and magnetic fields can potentially be useful in aiding membrane cleaningand reducing the need for chemical cleaning agents However the available literatureregarding the performance and mechanisms of these methods in realistic situations islimited and does not provide adequate evidences to prove their feasibility in improvingmembrane lifetime

26 Prospects and challenges

From a technical viewpoint the outstanding robustness and integrity of ceramic mem-branes have secured their positions in dealing with wastewater systems where at leastan aggressive environment is involved and contribute to sustainable and strong growthtoward wider applications Technical innovations in promoting separation performanceand engineering designs keep driving the development of ceramic membrane products

70 Advances in Membrane Technologies for Water Treatment

toward an application-oriented pattern In particular new membrane fabrication tech-niques such as the combined phase-inversion and sintering methods are expected tosee wider applications in membrane production facilities They offer a much simplerfabrication cycle and can make highly microstructurally varied membrane morphol-ogies that can be tailored according to the application In terms of membrane designthe presence of hollow-fibre membranes is expected to grow in the ceramic membranemarket to offer much greater treatment capacities for larger-scale applications Thepotential of a wider range of ceramic materials other than the commonly used aluminamembranes and membrane substrates is also expected In terms of applications there isa trend toward the increasing use of ceramic membranes for larger-scale wastewatertreatments especially in MBRs because the cost of ceramic membranes is reducedAnticipated cheaper ceramic membrane prices combined with higher packing densitiesof hollow-fibre configuration will increase applications in municipalities and morespace-efficient module designs especially for hollow-fibre membranes are expectedto penetrate the market to meet the higher demands

The widespread use of ceramic MFUF membranes in water treatment is limited bymany problems A key challenge is to reduce the capital cost of ceramic membraneswhich can be met by reducing the steps in the fabrication process and lowering the sin-tering temperature The emergence of cheaper fabrication processes such as the com-bined phase-inversion and sintering method can potentially reduce the fabricationcosts of ceramic membranes However further research and development are requiredto reduce the sintering temperature and maintain a continuously high-quality mem-brane The performance of the porous membranes formed by this method needs tobe improved so that both good mechanical strength and high porosity can be achievedImproved fundamental understanding of the formation mechanisms of ceramic mem-brane microstructures can help improve the reliability and reproducibility of the fabri-cation process which is particularly useful when producing membranes from differentceramic materials and when production is scaled up Furthermore challengesregarding the up-scaling of the combined phase-inversion and sintering processinclude developing a continuous fabrication and sintering process To meet the de-mands for large-scale treatment capacities more space-effective module and unit de-signs would also be required to cut down the costs of housing material as well asimprove productivity Hollow-fibre membrane elements may offer much higher pack-ing densities but improvements in element and module designs will be required suchas creating smaller-diameter hollow fibres and improving their mechanical strengthIn terms of fouling the mechanism varies from case to case depending on the appli-cation Although a combination of physical and chemical cleaning of ceramic mem-branes can be easily achieved this leads to additional waste products that requiretreatment and disposal hence more environmentally friendly approaches to mem-brane cleaning are desired This means that challenges arising in this area include bet-ter understanding of fouling mechanisms in ceramic membranes particularly theinteractions between ceramic membranes and the different foulants to ensure thatthe right choice of cleaning methods is made for reliable long-term operation

Advances in ceramic membranes for water treatment 71

Abbreviations

COD Carbon oxygen demandDBP Disinfectant byproductMBR Membrane bioreactorMF MicrofiltrationNOM Natural organic matterUF Ultrafiltration

Acknowledgements

The authors gratefully acknowledge the research funding provided by EPSRC in the UnitedKingdom (Grant no EPJ0149741)

References

Abadi S R H Sebzari M R Hemati M Rekabdar F amp Mohammadi T (2011) Ceramicmembrane performance in microfiltration of oily wastewater Desalination 265(1e3)222e228 Retrieved from httpdxdoiorg101016jdesal201007055

Agoudjil N Kermadi S amp Larbot A (2008) Synthesis of inorganic membrane by solegelprocess Desalination 223(1e3) 417e424 Retrieved from httpdxdoiorg101016jdesal200701187

Alem A Sarpoolaky H amp Keshmiri M (2009) Sol-gel preparation of titania multilayermembrane for photocatalytic applications Ceramics International 35(5) 1837e1843

AQUASOLUTION MEMBRANE [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileAQS-80mmpdf

Ashaghi K S Ebrahimi M amp Czermak P (2007) Ceramic ultra- and nanofiltration mem-branes for oilfield produced water treatment A mini review The Open EnvironmentalJournal 1 1e8

Babaluo A A Kokabi M Manteghian M amp Sarraf-Mamoory R (2004) A modified modelfor alumina membranes formed by gel-casting followed by dip-coating Journal of theEuropean Ceramic Society 24(15e16) 3779e3787 Retrieved from httpdxdoiorg101016jjeurceramsoc200401007

Baker J S Judd S J amp Parsons S A (1997) Antiscale magnetic pretreatment of reverseosmosis feedwater Desalination 110(1e2) 151e165 Retrieved from httpdxdoiorg101016S0011-9164(97) 00094e5

Bartlett M Bird M R amp Howell J A (1995) An experimental study for the developmentof a qualitative membrane cleaning model Journal of Membrane Science 105(1e2)147e157 Retrieved from httpdxdoiorg1010160376-7388(95)00052-E

Bird M R amp Bartlett M (2002) Measuring and modelling flux recovery during the chemicalcleaning of MF membranes for the processing of whey protein concentrate Journal ofFood Engineering 53(2) 143e152 Retrieved from httpdxdoiorg101016S0260-8774(01) 00151e0

Bolduan P amp Latz M (2005) Filtration by means of ceramic membranes - practical examplesfrom the chemical and food industries Germany Atech innovations gmbh

72 Advances in Membrane Technologies for Water Treatment

Bottino A Capannelli C Del Borghi A Colombino M amp Conio O (2001) Water treatmentfor drinking purpose Ceramic microfiltration application Desalination 141(1) 75e79Retrieved from httpdxdoiorg101016S0011-9164(01) 00390e3

Burggraaf A J amp Cot L (1996) Fundamentals of inorganic membrane science and tech-nology Amsterdam The Netherlands Elsevier Science

Cabero M L Riera F A amp Alvarez R (1999) Rinsing of ultrafiltration ceramic membranesfouled with whey proteins Effects on cleaning procedures Journal of Membrane Science154(2) 239e250 Retrieved from httpdxdoiorg101016S0376-7388(98) 00294e4

Calvert P D Lalanandham R R Parish M V Fox J Lee H Pober R L et al (1986)Dispersion of ceramic particles in organic liquids (Vol 73) MRS Online ProceedingsLibrary Retrieved from httpdxdoiorg101557PROC-73-579 p 579

Castillon R amp Laveniere J P (1995) Monolithic ceramic supports for filtration membranesUS Patent No 5415775 Washington DC US Patent and Trademark Office

CeraMem Full-size membrane modules 2013 [cited 2013 2108] Retrieved from httpwwwveoliawaterstcomceramemenfullsizemodulesceramemhtm

CeraMem Ceramic Membrane Technology Technology brief [cited 2014 1001] Retrievedfrom httpwwwtundrasolutionscafilesTechnologyBriefVWSCeramicMembranespdf

Ceramic capillary membranes [cited 2014 1001] Retrieved from httpwwwigbfraunhoferdeencompetencesinterfacial-materialsmembranescapillary-membraneshtml

Ceramic flat membrane ItN water filtration [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomfileadminuser_uploadpdf-downloadsTechnologyDataSheet_CFMpdf

Ceramic membrane filtration system Drinking water treatment [cited 2014 1001] Retrievedfrom httpwwwmetawatercojpengproductdrinkingmembrane_clarifylocationhtml

Ceramic membrane unit 2013 [cited 2014 0402] Retrieved from httpwater-solutionmeidenshacojpdownloadimgbb60-3163pdf

Ceramic membranes and their application in food and beverage processing Filtration amp Separation37(3) (2000) 36e38 Retrieved from httpdxdoiorg101016S0015-1882(00)88497e9

Ceramic membrane modules - existing and planned sizes CeraMem Ceramic Membranes[cited 2014 1101] Retrieved from httpwwwveoliawaterstcomceramemenceramemelementsizeshtm

Chang I-S Choo K H Lee C H Pek U H Koh U C Kim S W et al (1994)Application of ceramic membrane as a pretreatment in anaerobic digestion of alcohol-distillery wastes Journal of Membrane Science 90(1e2) 131e139 Retrieved fromhttpdxdoiorg1010160376-7388(94) 80040e5

Chen A Flynn J T Cook R G amp Casaday A L (1991) Removal of oil grease andsuspended solids from produced water with ceramic crossflow microfiltration SPE Pro-duction Engineering 6(2) 131e136

Chen D Weavers L K amp Walker H W (2006) Ultrasonic control of ceramic membranefouling by particles Effect of ultrasonic factors Ultrasonics Sonochemistry 13(5)379e387 Retrieved from httpdxdoiorg101016jultsonch200507004

Cheryan M amp Rajagopalan N (1998) Membrane processing of oily streams Waste-water treatment and waste reduction Journal of Membrane Science 151(1) 13e28Retrieved from httpdxdoiorg101016S0376-7388(98) 00190e2

Chin S S Lim T M Chiang K amp Fane A G (2007) Factors affecting the performanceof a low-pressure submerged membrane photocatalytic reactor Chemical EngineeringJournal 130(1) 53e63 Retrieved from httpdxdoiorg101016jcej200611008

Choi I-H Kim I C Min B R amp Lee K H (2006) Preparation and characterization ofultrathin alumina hollow fiber microfiltration membrane Desalination 193(1e3)256e259 Retrieved from httpdxdoiorg101016jdesal200507051

Advances in ceramic membranes for water treatment 73

COMEM [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileCoMem-OD25mm-monotubepdf

COMEM CONDUIT [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileCoMem-Conduit-OD146mm C3983pdf

Crittenden J C Trussell R R Hand D W Howe K J amp Tchobanoglous G (2012)MWHrsquos water treatment Principles and design New Jersey Wiley

Cui Z F Bellara S R amp Homewood P (1997) Airlift crossflow membrane filtration mdash Afeasibility study with dextran ultrafiltration Journal of Membrane Science 128(1) 83e91Retrieved from httpdxdoiorg101016S0376-7388(96) 00280e3

Das N Bandyopadhyay S Chattopadhyay D amp Maiti H S (1996) Tape-cast ceramicmembranes for microfiltration application Journal of Materials Science 31(19)5221e5225 Retrieved from httpdxdoiorg101007BF00355928

Das N amp Maiti H S (2009) Ceramic membrane by tape casting and solegel coating formicrofiltration and ultrafiltration application Journal of Physics and Chemistry of Solids70(11) 1395e1400 Retrieved from httpdxdoiorg101016jjpcs200908016

Daufin G Escudier J P Carrere H Beacuterot S Fillaudeau L amp Decloux M (2001) Recentand emerging applications of membrane processes in the food and dairy industry Food andBioproducts Processing 79(2) 89e102 Retrieved from httpdxdoiorg101205096030801750286131

Drioli E amp Giorno L (2010) Comprehensive membrane science and engineering OxfordUnited Kingdom Elsevier Science

Dynamic cross flow filtration silicon carbide membrane discs Future filtration [cited 2014 1001] Retrieved from httpliqtechcomimguserfileSiC-Disc-Sheet_V1pdf

Ebrahimi M Willershausen D Ashaghi K S Engel L Placido L Mund P et al (2010)Investigations on the use of different ceramic membranes for efficient oil-field producedwater treatment Desalination 250(3) 991e996 Retrieved from httpdxdoiorg101016jdesal200909088

Elshorbagy W (2013) Water treatment Rijeka Croatia IntechEmergency mobile drinking water News amp media [cited 2014 1001] Retrieved from http

wwwveoliawaterstcomnews-mediacase-studiesemergency-mobile-water-germanyhtmFalamaki C amp Beyhaghi M (2009) Slip casting process for the manufacture of tubular

alumina microfiltration membranes Materials Science-Poland 27(2) 427e441Fan Y B Li G Wu L L Yang W B Dong C S Xu H F et al (2006) Treatment and

reuse of toilet wastewater by an airlift external circulation membrane bioreactor ProcessBiochemistry 41(6) 1364e1370 Retrieved from httpdxdoiorg101016jprocbio200601023

Feenstra F K Terpstra R A amp Van Eijk J P G M (1998) Method for the production ofceramic hollow fibres US Patent No 5707584 Washington DC US Patent andTrademark Office

Fernandez Garciacutea L Alvarez Blanco S amp Riera Rodriacuteguez F A (2013) Microfiltrationapplied to dairy streams Removal of bacteria Journal of the Science of Food and Agri-culture 93(2) 187e196 Retrieved from httpdxdoiorg101002jsfa5935

Fiksdal L amp Leiknes T (2006) The effect of coagulation with MFUF membrane filtration forthe removal of virus in drinking water Journal of Membrane Science 279(1e2) 364e371Retrieved from httpdxdoiorg101016jmemsci200512023

Filtration module T-series ItN water filtration [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomfileadminuser_uploadpdf-downloadsProductDataSheet_FiltrationModulepdf

74 Advances in Membrane Technologies for Water Treatment

Filtration module T-series Components [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomdeproductscomponentsfiltration-module-t-serieshtml

Filtration rack Product program [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomindexphpidfrac1421

Finley J (2005) Ceramic membranes A robust filtration alternative Filtration amp Sepa-ration 42(9) 34e37 Retrieved from httpdxdoiorg101016S0015-1882(05)70695e9

Fukumoto L R Delaquis P amp Girard B (1998) Microfiltration and ultrafiltrationceramic membranes for apple juice clarification Journal of Food Science 63(5) 845e850Retrieved from httpdxdoiorg101111j1365-26211998tb17912x

Gan Q Howell J A Field R W England R Bird M R amp Mckechinie M T (1999)Synergetic cleaning procedure for a ceramic membrane fouled by beer microfiltrationJournal of Membrane Science 155(2) 277e289 Retrieved from httpdxdoiorg101016S0376-7388(98)00320e2

Gander M Jefferson B amp Judd S (2000) Aerobic MBRs for domestic wastewater treatmentA review with cost considerations Separation and Purification Technology 18(2)119e130 Retrieved from httpdxdoiorg101016S1383-5866(99)00056e8

Girard B Fukumoto L amp Sefa Koseoglu S (2000) Membrane processing of fruit juices andbeverages A review Critical Reviews in Biotechnology 20(2) 109e175

Ground water replacement of polymer ultra filtration system Case studies [cited 2014 1001]Retrieved from httpwwwitn-nanovationcomdeapplicationscase-studiespre-filtration-of-deep-ground-waterhtml

Gu Y amp Meng G (1999) A model for ceramic membrane formation by dip-coating Journalof the European Ceramic Society 19(11) 1961e1966 Retrieved from httpdxdoiorg101016S0955-2219(99)00013e8

Guerra K Pellegrino J amp Drewes J E (2012) Impact of operating conditions on permeateflux and process economics for cross flow ceramic membrane ultrafiltration of surfacewater Separation and Purification Technology 87(0) 47e53 Retrieved from httpdxdoiorg101016jseppur201111019

Han L-F Xu Z L Cao Y Wei Y M amp Xu H T (2011) Preparation characterization andpermeation property of Al2O3 Al2O3eSiO2 and Al2O3ekaolin hollow fiber membranesJournal of Membrane Science 372(1e2) 154e164 Retrieved from httpdxdoiorg101016jmemsci201101065

Hao Y X Li J S Yang X J Wang X amp Lu L D (2004) Preparation of ZrO2eAl2O3

composite membranes by solegel process and their characterization Materials Scienceand Engineering A 367(1e2) 243e247 Retrieved from httpdxdoiorg101016jmsea200310321

Harman B I Koseoglu H Yigit N O Sayilgan E Beyhan M amp Kitis M (2010) Theremoval of disinfection by-product precursors from water with ceramic membranes WaterSci Technol 62(3) 547e555 Retrieved from httpdxdoiorg102166wst2010260

Hinkova A Bubnık Z Kadlec P amp Pridal J (2002) Potentials of separation membranes inthe sugar industry Separation and Purification Technology 26(1) 101e110 Retrievedfrom httpdxdoiorg101016S1383-5866(01)00121e6

Hofman-Zeurouter J M (1995) Chemical and thermal stability of (modified) mesoporous ceramicmembranes

Hofs B Ogier J Vries D Beerendonk E F amp Cornelissen E R (2011) Comparison ofceramic and polymeric membrane permeability and fouling using surface water Separationand Purification Technology 79(3) 365e374 Retrieved from httpdxdoiorg101016jseppur201103025

Advances in ceramic membranes for water treatment 75

van der Horst H C amp Hanemaaijer J H (1990) Cross-flow microfiltration in the food in-dustry State of the art Desalination 77(0) 235e258 Retrieved from httpdxdoiorg1010160011-9164(90) 85028e9

Hsieh H P Bhave R R amp Fleming H L (1988) Microporous alumina membranes Journalof Membrane Science 39(3) 221e241 Retrieved from httpdxdoiorg101016S0376-7388(00)80931-X

Hsieh H P (1996) Inorganic membranes for separation and reaction Oxford UnitedKingdom Elsevier Science

InoCep ceramic hollow fibre membrane [cited 2014 0402] Retrieved from httpwwwhyfluxmembranescompdfbrochuresinoceppdf

InoCep ceramic hollow fibre membrane [cited 2014 1101] Retrieved from httpwwwhydrasystcomwp-contentuploadsHydrasyst Inoceppdf

Module Specifications InoCep [cited 2014 1001] Retrieved from httpwwwhyfluxmembranescominocep_modulehtml

Inside ceacuteram Industrial products [cited 2013 1001] Retrieved from httpwwwtami-industriescomINSIDE-CeRAM-TM1090html

Isoflux Industrial products [cited 2013 1001] Retrieved from httpwwwtami-industriescomIsoflux-TM1110html

ItN nanovation receives significant orders from Saudi ArabiaMembrane Technology 2013(10)(2013) 2e3 Retrieved from httpdxdoiorg101016S0958-2118(13) 70196e4

Jagannadh S N amp Muralidhara H (1996) Electrokinetics methods to control membranefouling Industrial amp Engineering Chemistry Research 35(4) 1133e1140

Jin L Ong S L amp Ng H Y (2010) Comparison of fouling characteristics in different pore-sized submerged ceramic membrane bioreactors Water Research 44(20) 5907e5918Retrieved from httpdxdoiorg101016jwatres201007014

Judd S (2008) The status of membrane bioreactor technology Trends in Biotechnology 26(2)109e116 Retrieved from httpdxdoiorg101016jtibtech200711005

Judd S (2010) The MBR book Principles and applications of membrane bioreactors for waterand wastewater treatment Oxford United Kingdom Elsevier Science

Kanawka K Othman M H D Wu Z T Droushiotis N Kelsall G amp Li K (2011) A duallayer NiNi-YSZ hollow fibre for micro-tubular SOFC anode support with a current col-lector Electrochemistry Communications 13(1) 93e95 Retrieved from httpdxdoiorg101016jelecom201011022

Kang I-J Yoon S-H ampLeeC-H (2002) Comparison of thefiltration characteristics of organicand inorganic membranes in a membrane-coupled anaerobic bioreactor Water Research36(7) 1803e1813 Retrieved from httpdxdoiorg101016S0043-1354(01) 00388e8

Karnik B S Davies S H R Chen K C Jaglowski D R Baumann M J amp Masten S J(2005a) Effects of ozonation on the permeate flux of nanocrystalline ceramic membranesWater research 39(4) 728e734

Karnik B S Davies S H Baumann M J amp Masten S J (2005b) The effects of combinedozonation and filtration on disinfection by-product formation Water Research 39(13)2839e2850 Retrieved from httpdxdoiorg101016jwatres200504073

Kim J H Davies S H R Baumann M J Tarabara V V amp Masten S J (2008) Effect ofozone dosage and hydrodynamic conditions on the permeate flux in a hybrid ozona-tioneceramic ultrafiltration system treating natural waters Journal of Membrane Science311(1) 165e172

Kim J amp Lin Y S (1998) Sol-gel synthesis and characterization of yttria stabilized zirconiamembranes Journal of Membrane Science 139(1) 75e83 Retrieved from httpdxdoiorg101016S0376-7388(97) 00250e0

76 Advances in Membrane Technologies for Water Treatment

Kingsbury B F K amp Li K (2009) A morphological study of ceramic hollow fibre mem-branes Journal of Membrane Science 328(1e2) 134e140 Retrieved from httpdxdoiorg101016jmemsci200811050

Kingsbury B F K Wu Z amp Li K (2010) A morphological study of ceramic hollow fibremembranes A perspective on multifunctional catalytic membrane reactors Catalysis Today156(3e4) 306e315 Retrieved from httpdxdoiorg101016jcattod201002039

Konieczny K amp Klomfas G (2002) Using activated carbon to improve natural water treat-ment by porous membranes Desalination 147(1e3) 109e116 Retrieved from httpdxdoiorg101016S0011-9164(02) 00584e2

Konieczny K Bodzek M amp Rajca M (2006) A coagulationeMF system for water treatmentusing ceramic membranes Desalination 198(1e3) 92e101 Retrieved from httpdxdoiorg101016jdesal200609014

Koonaphapdeelert S amp Li K (2007) Preparation and characterization of hydrophobicceramic hollow fibre membrane Journal of Membrane Science 291(1e2) 70e76Retrieved from httpdxdoiorg101016jmemsci200612039

Koonaphapdeelert S Wu Z amp Li K (2009) Carbon dioxide stripping in ceramic hollow fibremembrane contactors Chemical Engineering Science 64(1) 1e8 Retrieved from httpdxdoiorg101016jces200809010

Krstic D M Antov M G Pericin D M Heurooflinger W amp Tekic M N (2007) The pos-sibility for improvement of ceramic membrane ultrafiltration of an enzyme solutionBiochemical Engineering Journal 33(1) 10e15 Retrieved from httpdxdoiorg101016jbej200608016

Kylleuroonen H Pirkonen P Nystreuroom M Nuortila-Jokinen J amp Greuroonroos A (2006)Experimental aspects of ultrasonically enhanced cross-flow membrane filtration of indus-trial wastewaterUltrasonics Sonochemistry 13(4) 295e302 Retrieved from httpdxdoiorg101016jultsonch200504006

Laitinen N Luonsi A Leveuroanen E amp Nystreuroom M (2001) Effect of backflushing conditionson ultrafiltration of board industry wastewaters with ceramic membranes Separation andPurification Technology 25(1e3) 323e331 Retrieved from httpdxdoiorg101016S1383-5866(01) 00059e4

Lamminen M O Walker H W amp Weavers L K (2004) Mechanisms and factors influencingthe ultrasonic cleaning of particle-fouled ceramic membranes Journal of Membrane Science237(1e2) 213e223 Retrieved from httpdxdoiorg101016jmemsci200402031

Larbot A Fabre J P Guizard C amp Cot L (1988) Inorganic membranes obtained by sol-geltechniques Journal of Membrane Science 39(3) 203e212 Retrieved from httpdxdoiorg101016S0376-7388(00) 80929e1

Lee H C Park J Y amp Yoon D-Y (2009) Advanced water treatment of high turbidsource by hybrid module of ceramic microfiltration and activated carbon adsorptionEffect of organicinorganic materials Korean Journal of Chemical Engineering 26(3)697e701

Lens P Zeeman G amp Lettinga G (2001) Decentralised sanitation reuse Concepts systemand implementation Oxford United Kingdom Taylor amp Francis Group

Lerch A Panglisch S Buchta P Tomita Y Yonekawa H Hattori K et al (2005) Directriver water treatment using coagulationceramic membrane microfiltration Desalination179(1e3) 41e50 Retrieved from httpdxdoiorg101016jdesal200411054

Li M S Zhao Y J Zhou S Y amp Xing W H (2010) Clarification of raw rice wine byceramic microfiltration membranes and membrane fouling analysis Desalination256(1e3) 166e173 Retrieved from httpdxdoiorg101016jdesal201001018

Advances in ceramic membranes for water treatment 77

Li M Y Wu G X Guan Y T amp Zhang X H (2011) Treatment of river water by a hybridcoagulation and ceramic membrane process Desalination 280(1e3) 114e119 Retrievedfrom httpdxdoiorg101016jdesal201106059

Li L amp Lee R (2009) Purification of produced water by ceramic membranes Material screeningprocess design and economics Separation Science and Technology 44(15) 3455e3484

Li K (2007) Ceramic membranes for separation and reaction Chichester United KingdomWiley

Liao B-Q Kraemer J T amp Bagley D M (2006) Anaerobic membrane bioreactors ap-plications and research directions Critical Reviews in Environmental Science and Tech-nology 36(6) 489e530 Retrieved from httpdxdoiorg10108010643380600678146

Likuid-CBRfiltration systems for MBRS [cited 2014 1001] Retrieved from httpdioxide

com20130916_Likuid_CBR_ENpdfLin P-K amp Tsai D-S (1997) Preparation and analysis of a silicon carbide composite

membrane Journal of the American Ceramic Society 80(2) 365e372 Retrieved fromhttpdxdoiorg101111j1151-29161997tb02839x

Lindqvist K amp Lideacuten E (1997) Preparation of alumina membranes by tape casting and dipcoating Journal of the European Ceramic Society 17(2e3) 359e366 Retrieved fromhttpdxdoiorg101016S0955-2219(96) 00107e0

LiqTech SiC SteriMem [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileLiqTech SiC SteriMem Ceramic Membranespdf

Liu S Li K amp Hughes R (2003) Preparation of porous aluminium oxide (Al2O3) hollow fibremembranes by a combined phase-inversion and sintering method Ceramics International29(8) 875e881 Retrieved from httpdxdoiorg101016S0272-8842(03) 00030e0

Luiten-Olieman M W J Raaijmakers M J T Winnubst L Wessling M Nijmeijer A ampBenes N E (2011) Porous stainless steel hollow fibers with shrinkage-controlled smallradial dimensions Scripta Materialia 65(1) 25e28 Retrieved from httpdxdoiorg101016jscriptamat201103023

Luiten-Olieman M W J Raaijmakers M J T Winnubst L Bor T C Wessling MNijmeijer A et al (2012) Towards a generic method for inorganic porous hollow fiberspreparation with shrinkage-controlled small radial dimensions applied to Al2O3 Ni SiCstainless steel and YSZ Journal of Membrane Science 407e408(0) 155e163 Retrievedfrom httpdxdoiorg101016jmemsci201203030

Mahesh Kumar S Madhu G M amp Roy S (2007) Fouling behaviour regeneration optionsand on-line control of biomass-based power plant effluents using microporous ceramicmembranes Separation and Purification Technology 57(1) 25e36 Retrieved from httpdxdoiorg101016jseppur200703002

Majewska-Nowak K M (2010) Application of ceramic membranes for the separation of dyeparticles Desalination 254(1e3) 185e191 Retrieved from httpdxdoiorg101016jdesal200911026

Mallada R amp Meneacutendez M (2008) Inorganic membranes Synthesis characterization andapplications Oxford United Kingdom Elsevier Science

Marrot B Barrios-Martinez A Moulin P amp Roche N (2004) Industrial wastewater treatmentin a membrane bioreactor A review Environmental Progress 23(1) 59e68 Retrieved fromhttpdxdoiorg101002ep10001

Matis K A Peleka E N Zamboulis D Erwe T amp Mavrov V (2004) Air spargingduring the solidliquid separation by microfiltration application of flotation Separa-tion and Purification Technology 40(1) 1e7 Retrieved from httpdxdoiorg101016jseppur200312017

78 Advances in Membrane Technologies for Water Treatment

Matsushita T Matsui Y Shirasaki N amp Kato Y (2005) Effect of membrane pore sizecoagulation time and coagulant dose on virus removal by a coagulation-ceramic micro-filtration hybrid system Desalination 178(1e3) 21e26 Retrieved from httpdxdoiorg101016jdesal200411026

Membralox ceramic membrane bio-reactor for industrial wastewater treatment Water pro-cessing [cited 2014 1001] Retrieved from httpjapanesepallcompdfCSMEMBRALOXENpdf

Membralox Ceramic membrane products Products [cited 2014 1101] Retrieved fromhttpwwwpallcommainfood-and-beverageproductpageidfrac1441052

Membrane specifications [cited 2013 2108] Retrieved from httpwwwhyfluxmembranescominocep_membranehtml

Meng F Chae S R Drews A Kraume M Shin H S amp Yang F L (2009) Recentadvances in membrane bioreactors (MBRs) Membrane fouling and membrane materialWater Research 43(6) 1489e1512 Retrieved from httpdxdoiorg101016jwatres200812044

Mercier-Bonin M Lagane C amp Fonade C (2000) Influence of a gasliquid two-phase flowon the ultrafiltration and microfiltration performances Case of a ceramic flat sheet mem-brane Journal of Membrane Science 180(1) 93e102 Retrieved from httpdxdoiorg101016S0376-7388(00) 00520e2

Mobile drinking water treatment TWA 15 UF Berkefeld Retrieved from httpwwwberkefeldcomberkefeldressourcesdocuments313300Mappe_ENpdf

Module Specifications Kristal [cited 2014 1001] Retrieved from httpwwwhyfluxmembranescomkristal_modulehtml

Mozia S (2010) Photocatalytic membrane reactors (PMRs) in water and wastewater treatmentA review Separation and Purification Technology 73(2) 71e91 Retrieved from httpdxdoiorg101016jseppur201003021

MPT hollow fiber ceramic membranes [cited 2013 1604] Retrieved from httpwwwmediaandprocesscomproductsproducts01html

Mugnier N Howell J A amp Ruf M (2000) Optimisation of a back-flush sequence for zeolitemicrofiltration Journal of Membrane Science 175(2) 149e161 Retrieved from httpdxdoiorg101016S0376-7388(00) 00412e9

Muhammad N Sinha R Krishnan E R amp Patterson C L (2009) Ceramic filter for smallsystem drinking water treatment Evaluation of membrane pore size and importance ofintegrity monitoring Journal of Environmental Engineering 135(11) 1181e1191

Mulder M (1996) Basic principles of membrane technology The Netherlands SpringerOthman M H D Droushiotis N Wu Z T Kelsall G amp Li K (2012) Dual-layer hollow

fibres with different anode structures for micro-tubular solid oxide fuel cells Journal of PowerSources 205(0) 272e280 Retrieved from httpdxdoiorg101016jjpowsour201201002

Pall Membralox Ceramic Membranes and modules [cited 2014 1001] Retrieved fromhttpwwwpallcompdfsFuels-and-ChemicalsPIMEMBRAENpdf

Membralox IC Pall Membralox IC ceramic membranes and modules [cited 2014 1101]Retrieved from httpwwwpallcompdfsFood-and-BeveragePIMEMBRAICENpdf

Peinemann K V Nunes S P amp Giorno L (2011)Membrane technology Vol 3 Membranesfor food applications Weinheim Germany Wiley

Produced water beneficial use case studies Case studies [cited 2014 1001] Retrieved fromhttpaqwatecmineseduproduced_waterassessbucase

Projects Innovative designs for sustainable advanced water treatment [cited 2014 1001]Retrieved from httpwwwpwntechnologiesnlprojectsindexhtml - six-ceramac-pilot-south-west-water-united-kingdom

Advances in ceramic membranes for water treatment 79

Psoch C amp Schiewer S (2006) Direct filtration of natural and simulated river water with airsparging and sponge ball application for fouling control Desalination 197(1e3)190e204 Retrieved from httpdxdoiorg101016jdesal200511027

Rahman M A Garciacutea-Garciacutea F R Irfan Hatim M D Kingsbury B F K amp Li K(2011) Development of a catalytic hollow fibre membrane micro-reactor for high purityH2 production Journal of Membrane Science 368(1e2) 116e123 Retrieved fromhttpdxdoiorg101016jmemsci201011025

Ruutenhuch R (1992) Membrane separation systems - recent developments and future di-rections Von R W Baker ua Noyes Data Corp Park Ridge 1991 XV 451 S zahlrAbb u Tab geb US-$64 Chemie Ingenieur Technik 64(6) 584 Retrieved from httpdxdoiorg101002cite330640633

Sewage treatment plant ceramicMBR Case studies [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomapplicationscase-studiessewage-treatment-plant-ceramic-mbrhtml

Sewage treatment plant MBCR Case studies [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomapplicationscase-studiessewage-treatment-plant-mbcrhtml

Silva L L O Vasconcelos D C L Nunes E H M Caldeira L Costa V C Musse A Pet al (2012) Processing structural characterization and performance of alumina supportsused in ceramic membranes Ceramics International 38(3) 1943e1949 Retrieved fromhttpdxdoiorg101016jceramint201110025

PUB and Meiden Singapore collaborate on ceramic membrane MBR demonstration plantMembrane Technology 2012(9) (2012) 1e16 Retrieved from httpdxdoiorg101016S0958-2118(12) 70171e4

Skrzypek M amp Burger M (2010) Isoflux ceramic membranes mdash practical experiencesin dairy industry Desalination 250(3) 1095e1100 Retrieved from httpdxdoiorg101016jdesal200909116

Smid J Avci C G Geurounay V Terpstra R A amp Van Eijk J P G M (1996) Preparationand characterization of microporous ceramic hollow fibre membranes Journal ofMembrane Science 112(1) 85e90 Retrieved from httpdxdoiorg1010160376-7388(95)00274-X

Sondhi R amp Bhave R (2001) Role of backpulsing in fouling minimization incrossflow filtration with ceramic membranes Journal of Membrane Science 186(1)41e52 Retrieved from httpdxdoiorg101016S0376-7388(00) 00663e3

Sondhi R Bhave R amp Jung G (2003) Applications and benefits of ceramic membranesMembrane Technology 2003(11) 5e8 Retrieved from httpdxdoiorg101016S0958-2118(03) 11016e6

Staff A (2011) Microfiltration and ultrafiltration membranes for drinking water (M53)Denver Colorado American Water Works Association

Stoquart C Servais P Beacuterubeacute P R amp Barbeau B (2012) Hybrid membrane processes usingactivated carbon treatment for drinking water A review Journal of Membrane Science411e412(0) 1e12 Retrieved from httpdxdoiorg101016jmemsci201204012

Submersible silicon carbide flat sheet membranes Future filtration [cited 2014 1001] Retrievedfrom httpliqtechcomimguserfileSiC Ceramic Flat Sheet Membranepdf

Success for LiqTech ceramic membranes in oil amp gas trial Filtration Industry Analyst2012(11) (2012) 4 Retrieved from httpdxdoiorg101016S1365-6937(12) 70350e7

Sun D Zeng J amp Tay J (2003) A submerged tubular ceramic membrane bioreactor for highstrength wastewater treatment Water Science amp Technology 47(1) 105e111

SURVEY Technical data of atech Al2O3 membranes [cited 2014 1001] Retrieved fromhttpwwwatech-innovationscomfileadmindownloadatech_product_data_en_080206_01pdf

80 Advances in Membrane Technologies for Water Treatment

Sushumna I Gupta R amp Ruckenstein E (1992) Effective dispersants for concentratednonaqueous suspensions Journal of Materials Research-Pittsburgh- 7 2884e2893Retrieved from httpdxdoiorg101557JMR19922884

Tan X Liu N Meng B amp Liu S M (2011) Morphology control of the perovskitehollow fibre membranes for oxygen separation using different bore fluids Journal ofMembrane Science 378(1e2) 308e318 Retrieved from httpdxdoiorg101016jmemsci201105012

Tan X Liu S amp Li K (2001) Preparation and characterization of inorganic hollow fibermembranes Journal of Membrane Science 188(1) 87e95 Retrieved from httpdxdoiorg101016S0376-7388(01) 00369e6

Terpstra R A Bonekamp B C amp Veringa H J (1988) Preparation characterization andsome properties of tubular alpha alumina ceramic membranes for microfiltration and as asupport for ultrafiltration and gas separation membranesDesalination 70(1e3) 395e404Retrieved from httpdxdoiorg1010160011-9164(88) 85069e0

The ROSS System Produced water treatment [cited 2014 1001] Retrieved from httpwwwveoliawaterstnacomnews-resourcesinformation-filesROSSproducedwaterhtm

The Ross System Produced water treatment CeraMem Ceramic Membranes[cited 2014 1001] Retrieved from httpwwwveoliawaterstcomceramemen

Van Der Bruggen B Vandecasteele C Van Gestel T Doyen W amp Leysen R (2003) Areview of pressure-driven membrane processes in wastewater treatment and drinking waterproduction Environmental Progress 22(1) 46e56 Retrieved from httpdxdoiorg101002ep670220116

Van Gestel T Vandecasteele C Buekenhoudt A Dotremont C Luyten J Van derBruggen B et al (2003) Corrosion properties of alumina and titaniaNFmembranes Journalof Membrane Science 214(1) 21e29 Retrieved from httpdxdoiorg101016S0376-7388(02) 00517e3

Wang B amp Lai Z (2012) Finger-like voids induced by viscous fingering during phaseinversion of aluminaPESNMP suspensions Journal of Membrane Science 405e406(0)275e283 Retrieved from httpdxdoiorg101016jmemsci201203020

Waeger F Delhaye T amp Fuchs W (2010) The use of ceramic microfiltration and ultrafil-tration membranes for particle removal from anaerobic digester effluents Separation andPurification Technology 73(2) 271e278 Retrieved from httpdxdoiorg101016jseppur201004013

Wang H T Liu X Q Chen F L Meng G Y amp Soslashrensen O T (1998) Kinetics andmechanism of a sintering process for macroporous alumina ceramics by extrusion Journalof the American Ceramic Society 81(3) 781e784 Retrieved from httpdxdoiorg101111j1151-29161998tb02412x

Wang I-F D Jerome F Morris Richard A amp Kesting Robert (1999) Highly asymmetricultrafiltration membranes US Patent No 5958989 Washington DC US Patent andTrademark Office

Wang T Zhang Y Z Li G F amp Li H (2009) Preparation and characterization of aluminahollow fiber membranes Frontiers of Chemical Engineering in China 3(3) 265e271Retrieved from httpdxdoiorg101007s11705-009-0010-2

Wang Y H Cheng J G Liu X Q Meng G Y amp Ding Y W (2008a) Preparation andsintering of macroporous ceramic membrane support from titania sol-coated aluminapowder Journal of the American Ceramic Society 91(3) 825e830 Retrieved from httpdxdoiorg101111j1551-2916200702207x

Wang Z Yang N T Meng B Tan X Y amp Li K (2008b) Preparation andoxygen permeation properties of highly asymmetric La06Sr04Co02Fe08O3a Perovskite

Advances in ceramic membranes for water treatment 81

hollow-fiber membranes Industrial amp Engineering Chemistry Research 48(1) 510e516Retrieved from httpdxdoiorg101021ie8010462

Water filtration by ceramic flat membranes e CFM ItN water filtration [cited 2014 1101]Retrieved from httpwwwitn-nanovationcomfileadminuser_uploadpdf-downloadsCFM-Flyerpdf

Wei C C Chen O Y Liu Y amp Li K (2008) Ceramic asymmetric hollow fibre mem-branesmdashone step fabrication process Journal of Membrane Science 320(1e2) 191e197Retrieved from httpdxdoiorg101016jmemsci200804003

Wu J C-S amp Cheng L-C (2000) An improved synthesis of ultrafiltration zirconia mem-branes via the solegel route using alkoxide precursor Journal of Membrane Science167(2) 253e261 Retrieved from httpdxdoiorg101016S0376-7388(99)00294-X

Wu Z Faiz R Li T Kingsbury B F K amp Li K (2013) A controlled sintering process formore permeable ceramic hollow fibre membranes Journal of Membrane Science 446(0)286e293 Retrieved from httpdxdoiorg101016jmemsci201305040

Xin X S Lu Z Zhu Q S Huang X Q amp Su W H (2007) Fabrication of dense YSZ electro-lyte membranes by a modified dry-pressing using nanocrystalline powders Journal of Mat-erials Chemistry 17(16) 1627e1630 Retrieved from httpdxdoiorg101039B615548K

Xing C H Tardieu E Qian Y ampWen X H (2000) Ultrafiltration membrane bioreactor forurban wastewater reclamation Journal of Membrane Science 177(1e2) 73e82 Retrievedfrom httpdxdoiorg101016S0376-7388(00)00452-X

Xu N Xing W H Xu N P amp Shi J (2003) Study on ceramic membrane bioreactor withturbulence promoter Separation and Purification Technology 32(1e3) 403e410Retrieved from httpdxdoiorg101016S1383-5866(03)00073-X

Yang N Tan X amp Ma Z (2008) A phase inversionsintering process to fabricate nickelyttria-stabilized zirconia hollow fibers as the anode support for micro-tubular solid oxidefuel cells Journal of Power Sources 183(1) 14e19 Retrieved from httpdxdoiorg101016jjpowsour200805006

Yoon S H Kang I J amp Lee C H (1999) Fouling of inorganic membrane and fluxenhancement in membrane-coupled anaerobic bioreactor Separation Science and Tech-nology 34(5) 709e724 Retrieved from httpdxdoiorg10108001496399908951140

Zaidi N S Sohaili J Muda K amp Sillanpeuroaeuroa M (2013) Magnetic field application and itspotential in water and wastewater treatment systems Separation amp Purification Reviews43(3) 206e240 Retrieved from httpdxdoiorg101080154221192013794148

Zhang F Jing W H Xing W H amp Xu N P (2009a) Experiment and calculation offiltration processes in an external-loop airlift ceramic membrane bioreactor ChemicalEngineering Science 64(12) 2859e2865 Retrieved from httpdxdoiorg101016jces200902046

Zhang J W Fang H Hao L Y Xu X amp Chen C S (2012) Preparation of silicon nitridehollow fibre membrane for desalination Materials Letters 68(0) 457e459 Retrievedfrom httpdxdoiorg101016jmatlet201111041

Zhang X Fang D Lin B Dong Y C Meng G Y amp Liu X Q (2009b) Asymmetric porouscordierite hollow fiber membrane for microfiltration Journal of Alloys and Compounds487(1e2) 631e638 Retrieved from httpdxdoiorg101016jjallcom200908028

Zondervan E amp Roffel B (2007) Evaluation of different cleaning agents used for cleaningultra filtration membranes fouled by surface water Journal of Membrane Science304(1e2) 40e49 Retrieved from httpdxdoiorg101016jmemsci200706041

Zeurourcher S amp Graule T (2005) Influence of dispersant structure on the rheological propertiesof highly-concentrated zirconia dispersions Journal of the European Ceramic Society25(6) 863e873 Retrieved from httpdxdoiorg101016jjeurceramsoc200405002

82 Advances in Membrane Technologies for Water Treatment

Advances in water treatmentby microfiltration ultrafiltrationand nanofiltration

3I Koyuncu12 R Sengur23 T Turken12 S Guclu12 ME Pasaoglu121Istanbul Technical University Civil Engineering Faculty Environmental EngineeringDepartment Istanbul Turkey 2National Research Center on Membrane Technologies(MEM-TEK) Istanbul Turkey 3Istanbul Technical University Nanoscience andNanoengineering Department Istanbul Turkey

31 Introduction

In 2012 access to safe drinking water became the first millennium developmentgoal to be met by the international community (Url-1) The original aim set in2000 was to halve by 2015 the proportion of the population without sustainable ac-cess to safe drinking water and basic sanitation (UN 2010 pp 58e60) This encour-aging achievement should underscore the progress that can be made through thedevelopment of often simple and cheap technologies in low-income economies Atthe same time it can be expected that challenges related to water systems willcontinue to increase requiring further investment and technological innovation tomeet global needs Access to clean water is a simple human need and an importantdriver of social and economic development (UN Water 2006) Predictable andconsistent access to clean drinking water is globally seen as a core function of statesbecause it is crucial to a societyrsquos public health economic vitality and national secu-rity (Elimelech amp Phillip 2011)

311 Global membrane market

The global membrane market for microfiltration (MF) products used in liquidseparations was estimated to be $16 billion in 2013 It was projected to rise at a com-pound annual growth rate (CAGR) of 100 during the next 5 years to reach$26 billion in 2018 (Url-2)

The US market for ultrafiltration (UF) technologies was worth $882 million in2009 and reached $932 million at the end of 2010 By 2015 the market is estimatedto be valued at $12 billion a CAGR of 57 (Url-3)

The global market for nanofiltration (NF) membranes increased from$1728 million in 2012 to 1902 million in 2013 at the end of 2014 and 2019 it is esti-mated to reach $2156 million and 4451 million respectively CAGR will be 156during 2014e2019 (Url-4)

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400003-4Copyright copy 2015 Elsevier Ltd All rights reserved

312 Membrane filtration technology for water treatment

Membrane technology has become a significant separation technology over the past2 decades Continuing advances in regulatory constraints and aesthetic criteria forconsumer water quality have driven the water community to seek new technologiesMembrane technology is one of those new technologies In this technology mem-branes are used as filters in separation processes in various applications They pro-vide effective alternatives to related technologies such as adsorption ionexchangers and sand filters Major uses of this technology are water filtration(including desalination) and purification (including groundwater and wastewater)as well as industries such as food and beverages and biotechnology (Kurt KoseogluDizge Chellam amp Koyuncu 2012 Ozgun et al 2012) It also has medical uses suchas in dialysis

313 Membrane processes

A membrane is defined as a selective barrier between two homogenous phases Inprinciple membranes can carry out most of the separation processes and can com-plement or form an alternative for chemical processes such as distillation extractionfractionation and adsorption Some advantages of membrane filtration are lowenergy consumption the possibility of continuous separation and simpleup-scaling (Baker 2004)

The membrane process is not suitable for every fluid stream because of the contentof feed and product requirements as well as the nature of the membrane process and themembrane designed for that process There are four developed industrial membraneprocesses for water treatment The main difference in these processes is the poresize of the membranes Membrane processes are

1 Microfiltration2 Ultrafiltration3 Nanofiltration4 Reverse osmosis (RO)

RO is beyond the scope of this chapter but the other processes will be covered hereThe schematic separation spectrum given for membrane processes is shown inFigure 31 (Baker 2004)

1Aring 10 Aring 100 AringPore diameter

Reverseosmosis

UltrafiltrationMicrofiltration

Conventionalfiltration

1000 Aring 1 microm 10 microm 100 microm

Figure 31 Schematic spectrum for membrane processes and conventional filtrationReprinted from Baker (2004) Overview of membrane science and technology p 7

84 Advances in Membrane Technologies for Water Treatment

Membrane processes can be used for various applications There are variousguidelines for selecting the proper membrane process For example if particlesgt02 mm are removed the process becomes MF if dissolved contaminants can beprecipitated or coagulated the proper process may be MF or UF In the NF processit is possible to remove both organic and inorganic ions however if monovalentions exist or total dissolved solids removal of 3000 mgL is achieved the RO processis required (AWWA 2007)

General comparisons between MF UF and NF membranes can be found in Table 31

32 Water treatment by MF UF and NF

321 Microfiltration process

The MF and UF processes are commonly used for water treatment systems Af-ter a sand filter or cartridge filter MF can be applied to groundwater and surfacewaters In RO systems generally MF is in the pretreatment section of the treat-ment plant

The pore size of MF typically varies from 01 to 10 mm However the separationmechanism is not simple because particles of sizes are smaller than the pore sizeflow freely through the pore while the larger particles are rejected

Volume flow through MF membranes can be described by Darcyrsquos law where fluxJ through the membrane is directly proportional to the applied pressure (DP)

J frac14 A$DP

where permeability constant A contains structural factors such as the porosity and poresize distribution (Mulder 1996)

MF is used in a wide variety of industrial applications where particles of a sizegt01 mm have to be retained from a suspension The most important applicationsare still based on dead-end filtration using cartridges However for larger-scale appli-cations dead-end filtration will slowly be replaced by cross-flow filtration One of themain industrial applications is the sterilization and clarification of all kinds ofbeverages and pharmaceuticals industries Other applications are summarized below(Eykamp 1995 Mir Micheals Goel amp Kaiser 1992 Mulder 1996)

bull Ultrapure water in the semiconductorbull Drinking water treatmentbull Clarification of fruit juice wine and beerbull Wastewater treatmentbull Pretreatment

322 Ultrafiltration process

For UF pore sizes generally range from 001 to 005 mm (nominally 001 mm) orless UF membranes have the ability to retain larger organic macromolecules

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 85

Table 31 Characteristic features of MF and UF membranes

Microfiltration (MF) Ultrafiltration (UF) Nanofiltration (NF)

Operation mode Cross-flow and dead-endoperation

Cross-flow and dead-endoperation

Cross-flow operation

Operating pressure 01e3 bar (Transmembrane) 05e10 bar (Transmembrane) 2e40 bar (Transmembrane)

Separating mechanism Separation based on particle size Separation based on basedparticle size

Separation based on differencesin solubility and diffusivity

Molecular separation size Solids gt01 mmSeparation of particles

Colloids 20000e200000 DaSolids gt05 mmSeparation of macromolecules

Dissolved matter200e20000 Dasolids gt0001 mmSeparation of low-MW solutes(salt glucose lactose micro-pollutants)

Membrane types Predominantly symmetricpolymer or ceramic membranes

Asymmetric polymer compositeor ceramic membrane

Asymmetric polymer orcomposite membrane

Module types Spiral-wound hollow-fiber andtube modules plate or cushionmodules

Spiral-wound hollow-fiber andtube modules plate or cushionmodules

Spiral-wound tube and cushionmodules

Osmotic pressure negligible Osmotic pressure negligible Osmotic pressure negligible Osmotic pressure high(1e25 bar)

Thickness of separating layer Symmetric frac14 10e150 mmAsymmetric frac14 1 mm

01e10 mm 01e10 mm

Source Adapted from Pinnekamp and Friedrich (2006) volume 2 2nd edition

86Advances

inMem

braneTechnologies

forWater

Treatm

ent

they have been historically characterized by a molecular weight cutoff (MWCO)rather than by a particular pore size (Membrane Filtration Guidance Manual2005) Both UF and MF membranes can be considered porous membranes in whichrejection is determined mainly by the size and shape of the solutes relative to thepore size in the membrane In fact MF and UF involve similar membrane processeswith the same separation principle However an important difference is that UFmembranes have an asymmetric structure with a much denser top layer (smallerpore size and lower surface porosity) and consequently much higher hydrodynamicresistance (Mulder 1996)

There are two different operation modes for MF and UF systems Figure 32 showsthe cross-flow configuration in which the feed water is pumped tangential to the mem-brane Clean water passes through the membrane while the water that is rejected isrecirculated as concentrate and combined with additional feed water In dead-end ordirect filtration all of the feed water passes through the membrane Therefore recoveryis almost 100 and a small fraction is periodically used for backwash in the system(2e15) (Jacangelo et al 1997)

Permeate

Backwash waste

Recycle

Permeate

Air or liquidbackwash

Air or liquidbackwash

Recirculation pumpPre-screen

Pre-screen

Feed pump

Feed pump

Rawwater

Rawwater

(a)

(b)

Figure 32 (a) Cross-flow configuration MF and (b) dead-end filtration for microfiltration (MF)Reprinted from Jacangelo Trussell and Watson (1997) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 87

NowadaysmostMFUFplants operate in dead-endfiltrationmode because the energyrequired is lower compared with cross-flow systems as the high cross-flow velocityrequired to prevent fouling results in increased head loss and energy consumption

323 Nanofiltration process

NF membranes have applications in several areas (Koyuncu amp Cakmakci 2010) Themain applications of NF are in water treatment for drinking water production as well aswastewater treatment and also reuse (Debik Kaykioglu Coban amp Koyuncu 2010)NF can be used to treat all kinds of water including groundwater surface water andwastewater or as a pretreatment for desalination (Cakmakci Baspinar BalabanKoyuncu amp Kinaci 2009 Koyuncu Arikan Weisner Mark amp Rice 2008 UyakKoyuncu Oktem Cakmakci amp Toreurooz 2008) The introduction of NF as a pretreat-ment is considered a breakthrough in the desalination process NF membranes haveability to remove turbidity microorganisms and hardness as well as a fraction ofthe dissolved salts This results in a significantly lower operating pressure and providesa much more energy-efficient process compared with RO (Hilal Al-Zoubi DarwishMohammad amp Abu Arabi 2004)

These membranes which fall into a transition region between pure RO membranesand pure UF membranes are called loose RO low-pressure RO or more commonlyNF membranes Typically NF membranes have sodium chloride rejections between20 and 80 andMWCOs for dissolved organic solutes of 200e1000 Da These prop-erties are intermediate between RO membranes with a salt rejection of more than 90andMWCOof less than 50 andUFmembranes with a salt rejection of less than 5 Theneutral NF membrane rejects various salts in proportion to their molecular size so theorder of rejection is simply Na2SO4 gt CaCl2 gt NaCl (Baker 2004)

Many researchers have studies the softening of groundwater using NF Scheap et al(1998) used different NF membranes and their experimental results showed that60e70 ofmultivalent ions can be removed byNFmembranes Sombekke Voorhoeveand Hiemstrap (1997) compared NF membranes with activated carbon adsorptionAccording to the results both processes had goodperformanceHoweverNFmembraneshad some advantages in terms of investment costs (Hilal et al 2004 Schaep et al 1998Sombekke et al 1997)

NF membranes are used for their ion selectivity The retention of a dissolved salt isdetermined by the valence of the anions Therefore most salts with monovalent anions(eg Cl) can pass through the membrane whereas multivalent anions (eg SO2)are retained The separation spectrum for NF membranes is given in Figure 33

Some parameters are crucial for the operation of an NF unit solvent permeabilityflux through the membrane rejection of solutes and yieldrecovery Similar to otherpressure-driven membrane processes the flux J or the permeability (flux per unitof applied pressure) of a membrane is a crucial parameter Most NF membranes arehydrophilic except some used for solvent applications

Rejection in NF is mainly determined by molecular size hydrophobicity andcharge but the effects of the molecular shape and dipole moment for example mighthave an important role as well The porevoid dimensions are statistically distributed

88 Advances in Membrane Technologies for Water Treatment

and can be described by a log-normal distribution (Bowen amp Welfoot 2005) Thisexplains the smooth transition from no rejection to complete rejection in a typicalS-shaped curve when molecular size is varied The MWCO value is often used to indi-cate the lower limit of molecules that are (almost completely) retained similar to UFmembranes For NF membranes with MWCO values between 150 and 1000 (but oftenin the range 150e300) this concept should be used with care Hydrophobic moleculeslarger than the MWCO for example often have a low rejection The pH of the solutionmight change the membranersquos surface charge as well as the charge of the solute so therejection of this solute can be higher or lower than expected

Another parameter is the recovery or yield which is generally used for the design ofan industrial application rather than a membrane characteristic The recovery is theratio of the permeate stream to the feed stream values range from 40 to 90

3231 Applications of NF membranes

NF membranes can reduce the ionic strength of the solution Moreover hardnessorganics and particulate contaminants can be removed by NF membranes Manyresearchers have used NF to achieve those objectives

Some researchers have investigated the softening of groundwater using NFsystems All of the results gave good data Retentions higher than 90 were foundfor multivalent ions whereas monovalent ions were about 60e70 (Hilal et al2004 Scheap et al 1998) NF membranes with pellet softening and granular activatedcarbon for softening water were compared Although all methods had good results NFmembranes had several advantages from the point of health and lower investmentcosts The advantage of NF softening is that a smaller stream of water can be softenedbecause NF membranes remove essentially all hardness cations In municipal watertreatment works it is not necessary to reduce hardness to very low values and there-fore the use of NF membranes allows for side-stream treatment This involves sending

Reverse

osmosis

region

Nano-

filtration

region

100 105

104

103

102

10

80

60

40

20

0001 10 10 10001

Ultrafiltration

region

Water pressure-normalized flux

(m3 m2 middot bar middot day)

Mole

cula

r w

eig

ht cuto

ff

(90

rete

ntion

)

NaC

l re

jection (

)

Figure 33 Separation permeability spectrum of nanofiltration and other processesReprinted from Baker (2004) Membrane transport theory p 83

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 89

only a portion of the flow to be softened to the membranes and permeate is thenblended with the bulk flow stream to obtain a target blended value In contrast precip-itated lime softening cannot reduce hardness to below approximately 50 mgL CaCO3and therefore side-stream treatment is generally not practical

A typical NF membrane system consists of three separate subsystems pretreatmentmembrane processes and posttreatment

The primary application of NF membranes is desalting of saline surface orgroundwater Surface waters often have unsettled chemistry or composition owingto seasonal changes or after dilution with rain NF is a reliable option for surface watertreatment although the focus is on removing organics rather than on softening (Hilalet al 2004 Van der Bruggen amp Vandecasteele 2003)

Disinfection by-products (DBPs) are a significant regulatory concern NFmembranes are increasingly applied to remove DBP precursors such as natural organicmatter (NOM) which can react with various disinfectants used in the water treatmentprocess to form potential carcinogens NOM removal is an important water treatmenttarget for many utilities NF as a standalone process has been shown in many cases toreduce total organic carbon (TOC) to less than 05 mgL (AWWA 2007)

NF is also more effective than RO for lime softening removing naturally occurringcolor and DBP precursors both consist primarily of organic carbon

Semipermeable NF membranes are not porous they have the ability to screenmicroorganisms and particulate matter in the feed water This ability has been verifiedin a number of studies such as one that demonstrated that NF membranes providebetween 4 and 5 log removal of viruses

324 Integrated membrane systems

For acquiring regulation standards for drinking water NF and low pressure ROprocesses are considered however they are too sensitive to fouling and advanced pre-treatment processes like UF and MF are used to increase the productivity of systemsThese integrated systems are called as integrated membrane system (IMS) and theirpurpose is to reduce and control fouling

33 Pretreatment requirements

Pretreatment is typically applied to the feed water before entering the membranesystem to minimize membrane fouling However in some cases it may be used toaddress other water quality concerns or treatment objectives Pretreatment is mostoften used to remove foulants optimize recovery and system productivity and extendmembrane life Pretreatment may also be used to prevent physical damage to themembranes

Different types of pretreatment can be used in conjunction with any givenmembrane type Pilot testing can be used to compare various pretreatment optionsoptimize pretreatment andor demonstrate pretreatment performance (Membrane

90 Advances in Membrane Technologies for Water Treatment

Filtration Guidance Manual 2005) The feed water may contain various concentra-tions of dissolved matter and suspended solids depending on the source Suspendedsolids may include inorganic particles colloids and biological debris such as micro-organisms and algae Dissolved matter may consist of highly soluble matterssuch as chlorides soluble salts and sparingly soluble salts such as carbonate andsulfates

Depending on the raw water quality the pretreatment process may follow stepssuch as

bull Removal of large particles using a coarse strainerbull Water disinfection with chlorinebull Clarification with or without flocculationbull Clarification and hardness reduction using lime treatmentbull Media filtrationbull Reduction of alkalinity by pH adjustmentbull Addition of scale inhibitorbull Reduction of free chlorine using sodium bisulfite or activated carbon filtersbull Water sterilization using ultraviolet (UV) radiationbull Final removal of suspended particles using cartridge filters (Membrane Fouling

Considerations 2001)

331 General pretreatment methods

Membranes can be fouled by organic or inorganic substances Therefore pretreatmentof the feed stream is required to control colloidal organic and biological fouling aswell as scaling For low-pressure membranes a number of pretreatment methods arecurrently used (Abdelrasoul Doan amp Lohi 2013)

UF can sufficiently produce disinfected water directly from surface water fordifferent applications MF can also be used for disinfection although not all virusesare removed Because direct membrane filtration is limited by fouling it leads to acontinuous increase in transmembrane pressure during constant flux filtration(Kennedy et al 2008)

3311 Prefiltration

Prefiltration involving screening or coarse filtration is a common means ofpretreatment for membrane filtration systems that is designed to remove large particlesand debris Prefiltration can be applied to the membrane filtration system as a wholeand to each membrane unit separately The particular pore size associated with theprefiltration process varies depending on the type of membrane filtration system andthe feed water quality Generally hollow-fiber MF and UF systems are designedspecifically to remove suspended solids large particulate matter that can damage orclog the membranes fibers Use of these types of filtration system depend on theinfluent water quality and manufacturer specifications the pore sizemicron rating ofa chosen prefiltration process may range from as small as 100 mm to 3000 mm orhigher Because of this hollow-fiber MFUF membrane systems that operated in an

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 91

inside-out mode are more suitable to fiber clogging and thus may require prefiltration(Membrane Filtration Guidance Manual 2005)

NF and RO are nonporous membranes that cannot be backwashed and are mostcommonly designed in a spiral-wound configuration for municipal water treatment ap-plications NF and RO systems must use finer prefiltration to minimize membraneexposure of particulates of any size At this point spiral-wound membrane modulesare highly sensitive to particulate fouling that can reduce system productivity andreduce membrane life (Membrane Filtration Guidance Manual 2005) Table 32 listsrequired prefiltration systems for NFRO according to the silt density index (SDI) value

In cartridge filtration technology applications prefiltration is not required inhigh-quality source water treatment

Typical prefiltration requirements associated with various types of membranefiltration are presented in Table 33

In some cases one type of membrane filtration may be used as prefiltration foranother This type of treatment scheme is known as an IMS Generally this involvesMFUF use as pretreatment for NFRO applications that require the removal ofparticulates and microorganisms as well as some dissolved contaminants such as hard-ness iron and manganese or DBP precursors The most significant advantages of an

Table 32 Required prefiltration systems for NFRO according to SDIvalue

Feed water SDI value Proposed prefiltration Rating ranges

5 Cartridge filters 5e20 mm

gt5 MFUF 01e001 mm

Source Membrane Filtration Guidance Manual (2005)

Table 33 Typical membrane system prefiltration requirements

Membrane system Prefiltration requirements

Classification Configuration Size (mm) Type(s)

Membrane cartridgefiltrationa

Cartridge 300e3000 Strainersbag filters

MFUF Hollow-fiberinside-out

100e300 Strainersbag filters

Hollow-fiberoutside-in

300e3000 Strainersbag filters

NFRO Spiral-wound 5e20 Cartridge filters

aPrefiltration is not necessarily required for membrane cartridge filtration systemsSource Membrane Filtration Guidance Manual (2005)

92 Advances in Membrane Technologies for Water Treatment

IMS treatment scheme is that MFUF filtrate is of consistently high quality with respectto particulate matter and maintains stable operation by reducing the rate of membranefouling (Membrane Filtration Guidance Manual 2005)

3312 Coagulation and filtration

Coagulation as a pretreatment process can substantially reduce the concentration ofbiodegradable organic matter found in raw water thus it can decrease the potentialfor fouling and enhance membrane rejection However this method can be a problembecause coagulant residuals and increased solids loading can reduce membrane fluxesand increase cleaning requirements Generally coagulation is required for MF pro-cesses in water treatment Some research suggested that flocs need to reach a certaincritical floc size before MF on the contrary pores of MF membranes are irreversiblyfouled by small particles (Judd amp Hillis 2001)

3313 In-line coagulation

In-line coagulation (IC) involves the use of coagulants without the removal ofcoagulated solids After that coagulated water is given to MF or UF Conventionalcoagulation and IC are different from each other in terms of initial membrane fluxdecline IC has better results than conventional coagulation for initial membraneflux (Escobar project report)

The IC (without settling)UF process improves membrane performance and waterquality for surface water treatment Employing coagulation before UF increasedpermeate quality to the extent that dissolved organic matter removal is controlled bythe coagulation step (Guigui Rouch Durand-Bourlier Bonnelye amp Aptel 2002)

Antelmi Cabane Meireles and Aimar (2001) reported that aggregates producedunder sweep floc conditions are more compressible than for charge neutralization con-ditions resulting in compaction when the membrane filtration system is pressurizedThey thought that cake resistance is lower than the resistance resulting from theunsettled flocs and the noncoagulated organics

3314 Coagulationesedimentation process

In coagulation and sedimentation processes a coagulant is applied to form flocs thatare settled out by sedimentation After sedimentation the supernatant is fed to themembranes If coagulation and sedimentation are applied before UF UF membranesare less fouled Experimental studies showed that membrane life can be increased as aresult of coagulationesedimentation processes (Kruithof Nederlof Hoffmanamp Taylor 2004 Minegishi Jang Watanabe Hirata amp Ozawa 2001)

3315 Coagulationeadsorption process

Some research showed that membrane fouling can be minimized by pretreatmentNOM in feed water can be caused trihalomethane (THM) formation in the disinfectionstep Although coagulation and MF are a good flowchart for water treatment THM

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 93

precursors cannot be removed by the MF process When pre-adsorption is used forNOM the removal of THM precursors or NOM is improved (Beacuterube MavinicHall Kenway amp Roett 2002 Carroll King Gray Bolto amp Booker 2000 MaartensSwarta amp Jacobs 1999)

3316 Flocculation and filtration

Colloids can be removed by co-precipitation with Al(III) Fe(III) or Si(IV)hydroxides The negatively charged colloids are surrounded by the metal cationsand thus form a nucleus for their precipitation The same thing happens when limeis used for softening When polymer is added for coagulation the long chains canact as bridges linking colloidal particles and aiding in floc formation

Flocculation and filtration processes are used to achieve three objectiveseliminating the penetration of colloidal particles into the membrane pores increasingthe critical flux and modifying the characteristics of the deposits (Abdelrasoul et al2013 Kennedy et al 2008)

3317 Ion exchange

Some dissolved salts or divalent cations in feed water can cause scaling on themembrane surface To overcome this problem softening of feed water is requiredIon exchange process can be used for this purpose

The softening approach uses cationic resins to replace the calcium ions (or other diva-lent cations) with sodium ions which do not form insoluble salts with carbonate ion Ionexchange is well-suited for incorporation into an RO system Depending on the salinityand pH the RO concentrate may be used as a regenerate solution Cation exchange resinscan be adequately regenerated at lower concentrations than 10 with lower flow ratesand longer regeneration cycles (Wilbert Leitz Abert Boegli amp Linton 1998)

3318 Chemical conditioning

Chemical conditioning is used for various pretreatment purposes such as pHadjustment disinfection biofouling control scale inhibition and coagulation Sometype of chemical conditioning is almost always used with NFRO systems most oftenthe addition of an acid or proprietary scale inhibitor recommended by the membranemanufacturer to prevent the precipitation of sparingly soluble salts such as calciumcarbonate (CaCO3) barium sulfate (BaSO4) strontium sulfate (SrSO4) or silica spe-cies (eg SiO2) (Membrane Filtration Guidance Manual 2005)

A number of different chemicals can be added to MF or UF systems as apretreatment related to treatment objectives However as with NF and ROmembranesapplied pretreatment chemicals must be compatible with the particular membrane ma-terial used An MFUF system may be able to operate efficiently with the in-line addi-tion of lime or coagulants On the other hand presettling in association with thesepretreatment processes can enhance membrane flux and increase system efficiency(Membrane Filtration Guidance Manual 2005)

94 Advances in Membrane Technologies for Water Treatment

332 Pretreatment requirements for membrane bioreactors

The first generation of membrane bioreactors (MBR) in the 1970 and 1980s were builtwith large-diameter tubular membranes and were primarily used for small-scale indus-trial effluents containing little waste Pretreatment to MBR first became an issue whenhollow fibers and plate-immersed membranes were introduced in the 1990s forapplication to municipal wastewater

Today municipal MBR systems capacities are up to 50000 m3d and much largersystems are under construction or in the planning stages Current research goals are toreduce the cost of technology and increase the packing density These improvementsmake it significantly important to install adequate pretreatment to protect the mem-branes at the core of an MBR Possible negative effects of poor pretreatment on themembranes themselves include

bull Buildup of trash hair lint and other fibrous materialsbull Increased risk of sludge accumulationbull Eventually damage to the membrane (Co

ˇ

teacute Brink amp Adnan 2006)

34 Advances in membrane materials for watertreatment by MF UF and NF

Membrane technology is used to improve water quality treat wastewater and reuseprocesses for years The surge of interest in membrane separations increased owingto two developments high-flux defect-free membranes and high-surface-areaeconomical modules Membranes range from porous structures to nonporous onesand can be asymmetric or symmetric They are used for removal from macropollutantsup to ions Because pressure-driven membranes consist of selective barriers pore char-acteristics are important Macrofiltration UF and NF processes are classified by theirpore structure (pore size pore size distribution and porosity) Hydrophilicity surfacecharge roughness etc should also be considered The membrane material has greatsignificance An appropriate membrane material should resist chemical and thermalattack and should be robust thin defect-free and cheap (Baker 2004 Fane Tangamp Wang 2011)

For membrane materials polymers are generally preferred because they areinexpensive and easily formpore structures In additionmetallic ceramic andcompositematerials are used These materials are now thought of as conventional Recently mem-brane materials have improved Some novel membrane materials exist such as nano-structured reactive bioinspired membranes (Ng Mohammad Leo amp Hilal 2010Pendergast amp Hoek 2011)

341 Conventional membrane materials

Conventional membranes include polymeric ceramic and thin-film composite (TFC)membranes in general

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 95

Polymers are by far the most popular membrane material used for membranefabrication A good polymer material should resist thermal and chemical attack andhave good mechanical strength and the ability to form flat-sheet or hollow-fiberconfigurations easily Mostly polymeric membranes are fabricated with the phaseinversion technique Commonly used polymeric membrane materials are cellulose ac-etate (Chou amp Yang 2005 Saljoughi Amirilargani amp Mohammadi 2010) polyviny-lidene fluoride (PVDF) (Han Xu Yu Wei amp Cao 2010 Li Liu Xiao Ma amp Zhao2012) polyacrylonitrile (PAN) polypropylene (PP) polyethersulfone (PES) (ChenLi Han Xu amp Yu 2010 Loh Wang Shi amp Fane 2011 Xu Leurou Zhen Ku amp Yi2008) and polysulfone (PS) (Ohya Shiki amp Kawakami 2009 Rugbani 2009) Poly-meric membranes have varying process uses they can be applied from MF to ROCommercial UFMF membranes can be fabricated from both hydrophilic and hydro-phobic polymers Both polymers have some pros and cons because hydrophilic mem-branes lower the attachment of bacteria owing to adsorption but they are less robustthan hydrophobic polymers Table 34 shows commonly used polymeric materialsand their properties

Cellulose acetate membranes have good permeability and rejection characteristicsare susceptible to hydrolysis have limited pH resistance and low chlorine toleranceand are resistant to fouling On the other hand PES PVDF PS and PAN can be modi-fied as a blend to improve their limited abilities They show good permeability flex-ibility and high strength PP polymer has limited blending capacity and is prone tooxidation (Fane et al 2011)

Ceramic membranes are better than polymeric membranes because of their narrowpore size distribution higher porosity separation characteristics mechanical and chem-ical stability and lower fouling Typical ceramic membranes are fabricated using thesol-gel process and are asymmetric in structure Generally materials used for ceramicmembranes are zirconia silica alumina mullite oxide mixtures and sintered metals(Harman Koseoglu Yigit Beyhan amp Kitis 2010 Hofs Ogier Vries Beerendonkamp Cornelissen 2011 Mohammadi amp Maghsoodloorad 2013 Pendergast amp Hoek2011) They are well-suited for water treatment because they have higher stabilitiesFlux decrease can be easily recovered after fouling because they can resist destructivecleaning conditions so their lifetime is extended However they are expensive inindustry and owing to their inexpensiveness polymeric membranes are preferred

TFC membranes are asymmetric in structure therefore support and selectivelayers can be independently selected for optimization they are generally fabricatedthrough interfacial polymerization or coating and then cross-linking By changingthe properties of cross-linking thin-film structure stability selectivity and perme-ability can be changed Generally used TFC membranes are polyurea polyamideand polyurea-amide (Lau Ismail Misdan amp Kassim 2012 Pendergast amp Hoek2011) The support part of the membrane can be fabricated from PES PS PANetc The film structure is important for TFC membranes By changing monomers sur-factants and additives within the film composition different types of structure can beobtained (Lau et al 2012) TFC membranes are used to obtain high flux and highselectivity in desalination Also these kinds of membranes are used to desalt brackishwater and for water reclamation water softening and removing dissolved organics

96 Advances in Membrane Technologies for Water Treatment

Table 34 Commonly used polymeric materials and their properties

Polymer material Specifications

Cellulose acetate Cellulose acetate and its blends are widelyused for MF and UF membranes Celluloseacetate is susceptible to hydrolysis andmicrobial attacks and has a stable pHbetween 4 and 65

Polysulfone Polysulfone is an amorphous polymer It hasexcellent chemical and thermal stability It ismainly used for UF and MF membranes andas a support layer for NF and ROmembranes Polysulfone membranes have awide range of pore sizes and their modulescan be capillary flat-sheet and hollow-fiber

Polyethersulfone Polyethersulfone membranes have highchemical and thermal stability They aremainly used for UF and MF Flat-sheet orhollow-fiber module configurations exist

Polyacrylonitrile Polyacrylonitrile possesses superior resistanceto hydrolysis and oxidation It is mainlyused to prepare UF membranes and poroussupports of composite membranes

Polyamide Polyamide has good thermal and mechanicalstability It is resistant to organic solventattacks However it is susceptible tochlorine attacks It is used as a thin layer forRO and NF

Polyimide Polyamides exhibit excellent thermal andchemical stability because of their high glasstransition temperature They are used tomake NF membranes

Polycarbonate Polycarbonate is a transparent thermoplasticwith high-performance properties It hasgood mechanical strength and can be used tomake UF and MF membranes by the phaseinversion process

Polyvinylidene fluoride Polyvinylidene fluoride is semicrystalline witha low glass transition temperature It isresistant to chemical and thermal attacks aswell as to most inorganic and organicsolvents It can tolerate a wide range of pH

Source Adapted from Fane et al (2011) and Gupta (2013)

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 97

342 Novel membrane materials

Novel membrane materials can be defined as nanotechnology based membranesThese materials can be zeolite-coated ceramic membranes reactivecatalytic mem-branes nanocomposite membranes which can be either mixed matrix or TFC andbiologically inspired membranes that are aquaporin vertically aligned carbon nano-tube or block copolymer membranes (Pendergast amp Hoek 2011)

Zeolites are naturally occurring alumina silicate minerals that have high uniformityand nanometer-scale crystallinity People prefer zeolite-coated ceramic membranesbecause by using them one can obtain permeability in the range of UF membranesand also selectivity in the range of NF or higher Typical zeolite membranes are fabri-cated by hydrothermal layer-by-layer crystallization etc synthesis methods withamorphous silicate aluminosilicate which is inert and has good thermal and chemicalstability Zeolite crystals are tetrahedral frameworks that consist of cross-linked (SiAl)O4 (Figure 34) (Georgiev Bogdanov Angelova Markovska amp Hristov 2009) Waterpermeability and ion selectivity are primarily affected by the ore and framework den-sity of zeolite particles On the other hand the SiAl ratio is the most important factorfor obtaining chemical stability and hydrophilic properties They can be applied toboth polymers and ceramic membranes (Pendergast amp Hoek 2011) Dahe Teotiaand Bellare (2012) fabricated nanozeolitepolysulfone composite membranes for UFpurposes They found that the addition of nanozeolite increased water permeabilityup to 22 Lm2 h bar and also increased the MWCO value from 9500 to 54000 Da

Other novel membranes are reactive catalytic ones Reactive catalytic membranesactivate semiconductor-based membranes by sunlight or UV to degrade organiccontaminants Semiconductors are characterized by a filled valence band and anempty conduction band When photon energy (hn) exceeds band gap energy an elec-tron leaps from the valence band to the conduction band (Figure 35) This excitedstate of bands can recombine or dissipate input energy as heat and can get trappedin metastable surface states or react with electro-donors and acceptors that areadsorbed on the surface of semiconductors or within the electrical double layer ofcharged particles If there is a surface defect this defect can trap an electron orhole so that the band cannot recombine subsequently a redox reaction mayoccur Valence bands are good oxidants whereas conduction bands are goodreductants For interactions in bulk semiconductors an electron or hole is available

HOxygen

Silicon or Aluminum

Si Al

Ondash

Figure 34 (Left) Chemical structure of zeolite (Right) Building unit of a zeolite structureReprinted from Georgiev Bogdanov Angelova Markovska and Hristov (2009)

98 Advances in Membrane Technologies for Water Treatment

nanomaterials allow highly efficient interactions owing to their surfaces Organicphoto-degradation requires oxidizing and reducing species This degradation couldbe by indirect or direct oxidation With semiconductors contaminants such asalkanes phenols polychlorinated biphenyls alkenes alkanes surfactants and pes-ticides as well as heavy metals such as chromium(VI) can be removed (HoffmannMartin Choi amp Bahnemannt 1995)

Titanium zinc oxide and ferric oxide are the most commonly used semi-conductor-based membranes (Chong Jin Chow amp Saint 2010) The performance of this kind ofmembrane for degrading contaminants and inactivating complex dense cell wall struc-tures is limited Also these types of membranes have a high cost and low packing den-sity (Pendergast amp Hoek 2011) Crock Rogensues Shan and Tarabara (2013)fabricated exfoliated graphite nano-platelets decorated with Au nanoparticles(Figure 36) The resulting membrane was catalytic with UF properties When nano-platelets and the amount of Au were changed different catalytic activities wereobtained Ma Zhang Quan Fan and Zhao (2010) fabricated photocatalytic MF mem-branes with Ag-TiO2hydroxyapatiteAl2O3 to treat surface water According to theirresults humic acid removal synergistically affected filtration and photocatalysis Theantifouling ability of the membrane comes mainly from photocatalytic activityZhu et al (2011) fabricated MF ceramic membranes combined with titaniumoxide and alumina with ozonation for water treatment They obtained a fluxes of79 Lm2 h and 90 Lm2 h with alumina and titanium oxide respectively

Nanocomposite membranes are advantageous because of their low cost easyfabrication and high mechanical stability and because they show both polymericand inorganic material properties Typically used nanoparticles are silver- magne-sium- iron- aluminum- silica- zirconium- and titanium-based as well as carbonnanotubes and graphenes Nanoparticles can be formed by sol-gel processes ion sput-tering spray pyrolysis pulsed laser ablation laser pyrolysis mechanical alloyingmill-ing electrodeposition and so forth (Buonomenna 2013 Goh Ismail amp Ng 2013Mishra amp Ramaprabhu 2011 Ng et al 2010 Pendergast amp Hoek 2011)

Reduction

hv

∆EEnergy

Oxidation

Conductionband

Valenceband

Figure 35 Schematic of photocatalysisReprinted from Pendergast and Hoek (2011) with permission from Royal Society of Chemistry

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 99

Many applications exist for these kinds of membranes in water treatmentapplications Nanoparticles used within these types of membranes enhanced mem-brane selectivity and pore connectivity inhibit macro void formation and increase sur-face to volume ratios Attention is given to nanoparticles because of their ability todisinfect adsorb and degrade organics (Akar Asar Dizge amp Koyuncu 2013 Koseo-glu Kose Altinbas amp Koyuncu 2013) In this manner for example silver nanopar-ticles can be used to decrease fouling and increase antibacterial properties RazmjouResosudarmo Holmes and Li (2012) studied the effects of TiO2 nanoparticles on PEShollow fiber (HF) membranes They used both mechanically modified and chemicallyand mechanically modified TiO2 Higher thermal resistance permeability hydrophi-licity porosity and pore size and lower elasticity and tensile strength were foundfor chemically and mechanically modified TiO2 Han et al (2010) spun hollow-fibermembranes by adding aluminum silica and titanium oxide nanoparticles at thesame dope solution with different concentrations They observed high flux valuesand high tensile strength values Bovine serum albumin (BSA) rejection changeddiscordantly Morphology changed from a macroporous to an asymmetric structureDenser top layers were obtained and the most obvious effect on membranemorphology was on the inner surface Liang Xiao Mo and Huang (2012) fabricateda novel ZnO nanoparticle-blended PVDF membrane for anti-irreversible fouling Theaddition of ZnO nanoparticle increased the hydrophilicity of the membranes and 100water flux recovery was observed Permeability values were doubled compared withpristine membranes In addition they found that adding ZnO increased the mechanicalstability of the membranes Sengur (2013) fabricated PES hollow-fiber membranes

2nd functional nanoparticles

1st ˝carrier mats˝exfoliated graphite nanoplatelets

Hierarchy level

Nanocomposite membraneMembrane casting mixture

PolymerPhase inversion

Hierarchicalnanofiller

Solvent

Porogen

ReactantsProducts

-15 microm -12 nm

-30 nm

Catalyticreaction

Figure 36 Catalytic nanocomposite membrane fabricated with exfoliated graphitenanoplatelets and Au nanoparticlesReprinted from Crock et al (2013) with permission from Elsevier

100 Advances in Membrane Technologies for Water Treatment

with UF properties with both hydroxylated and carboxylated multi-walled carbonnanotube (MWCNT) The effects of different MWCNTs were different Fabricatedcarboxylated MWCNT membranes had antifouling ratios and better water recoveryratios whereas hydroxylated MWCNT membranes had higher permeabilities Turken(2013) fabricated PESAg-nanocomposite UF hollow-fiber membranes According totheir results the membranes showed improved antibacterial properties antifoulingand mechanical stability

Thin-film nanocomposite (TFN) membranes are fabricated through interfacialpolymerization by incorporating nanomaterials into the active layer of TFC mem-branes via doping into casting solutions or by surface modification their advantagesare enhanced separation reduced fouling antimicrobial activity and some other novelproperties For TFN membranes the particles most used are zeolites carbon nano-tubes TiO2 silica and silver (Buonomenna 2013 Kim Hwang El-Din amp Liu2012 Pendergast amp Hoek 2011 Qu Alvarez amp Li 2013) Tiraferri Vecitis andElimelech (2011) used covalently bonded single-walled carbon nanotubes (SWCNT)to a TFC membrane With that method they used a tiny amount of nanomaterials Theresulting membrane had improved antibacterial properties and potentially decreasedfouling In the literature TFN membranes are generally used for RO so there is littleliterature containing NF UF or MF applications

On the other hand biologically inspired membranes offer huge potential andimproved membrane properties However they are far from commercialization becausethere are some difficulties in scaling Aquaporin-based membranes one of the biolog-ically inspired membranes are highly productive and selective but not cost-effectiveAquaporins are protein channels that have the ability to control water flux within mem-branes Their ability to transport to water is higher than any kind of commercial ROmembrane Their water permeability is in the order of glucose glycerol salt andurea (Pendergast amp Hoek 2011 Qu et al 2013 Tang Zhao Wang Heacutelix-Nielsenamp Fane 2013 Zhong Chung Jeyaseelan amp Armugam 2012) Generally they areapplied in desalination and water reuse Table 35 shows studies from the literature

Another kind of biologically inspired membrane is vertically aligned carbonnanotubes (CNTs) (Figure 37) Water transport within CNTs is as high as aquaporinsSelectivity of the vertically aligned CNT membranes is described in Corry (2008)CNTebased membranes also have excellent mechanical properties Aligned CNTsare generally fabricated by chemical vapor deposition (CVD) such as microwaveplasma-enhanced CVD catalytic CVD spray pyrolysis and self-assembly (Pender-gast amp Hoek 2011) Vertically aligned CNT membranes can be used to remove micro-bial contaminants from drinking water They are superior to conventional membranesbecause they can be cleaned by ultrasonication or autoclaving whereas conventionalmembranes should be disposed of at the end of their limited life which is affected byfouling (Pendergast amp Hoek 2011)

The last type is block copolymer membranes These are macromolecules thathave the ability to self-assemble into highly ordered structures when added intothe proper solvent Their densely packed cylindrical pores are ideal for waterseparation In the literature there are many studies using block copolymers tofabricate UF membranes Wandera Himstedt Marroquin Wickramasingh and

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 101

Table 35 Examples of biomimetic membranes designed for water reuse and desalination Performance dataare presented as water permeability (WP) (lm2 h bar) NaCl rejection (RNaCl) () membrane area (A)(cm2) and maximal external pressure applied (Pmax) (bar) when operated in RO CA cellulose acetatePC polycarbonate

Approach WP (lm2 h bar) RNaCl () Area (cm2)Pmax

(bar) Upscaling issues Remarks

Charged lipid mixturevesicles depositionsonto NF membranes

083 nda 35 10 Difficult to producelarge defect-freemembranes

No aquaporinincluded

Vesicle fusionfacilitated byhydraulic pressure onhydrophilic NFmembranes coatedwith positivelycharged lipids

36 02 35 8 126 1 Difficult to producelarge defect-freemembranes

Low RNaCl Onlysuitable for NF

Membranes acrossmultiple micron-scaleapertures asfreestanding lipid orpolymer membranes

nda nda 4 nda Nanofabricationrequired Lowrobustness

WPRNaCl not testedNot suitable forRO

Membranes acrossmultiple micron-scaleapertures andstabilized byhydrogelencapsulation

12e40 nda 35 2 Nanofabricationrequired Highrobustness

Characterization withgramicidinchannels Noaquaporinincluded

102Advances

inMem

braneTechnologies

forWater

Treatm

ent

Aquaporin containingpolymersomes onmethacrylatefunctionalized CAmembranes

342 69 329 91 007 5 Medium robustness Small area High WPbut low RNaClOnly suitable forNF

Detergent-stabilizedHis-tagged aquaporinadded to monolayerswith nickel-chelatinglipids

nda nda nda nda Complex fabricationLow robustness

WPRNaCl not testedMay be notsuitable fordesalination

Proteopolymersomedeposition onto gold-functionalized PCtrack-etchedsubstrates

nda nda 0096 nda Complex fabricationLow robustness

Small areaRelatively highWP in FO No ROdata

Interfacialpolymerizationmethod withembeddedproteoliposomes

4 04 963 13 gt200 14 Simple fabricationHigh robustness

Combined high WPand RNaClSuitable for RO

and not definedSource Adapted from Tang et al (2013) Copyright (2013) with permission from Elsevier

Advances

inwater

treatment

bymicro

filtrationultrafiltrationand

nanofiltration

103

Husson (2012) modified low-MWCO cellulose UF membranes with block copol-ymer nanolayers They used poly(N-isopropylacrylamide)-block-poly([polyethyleneglycol] methacrylate) (PNIPAAm-b-PPEGMA) nanolayers and investigated therole of polymer on the performance of the membrane According to their resultsthe nanolayer structure affected fouling Optimization resulted in high stable fluxThe coating chemistry and structural properties of coating affected antifouling prop-erties Fabricated Ps-b-PMMA films showed unique porous morphology (Figure 38)(Kim Yang Lee amp Kim 2010) Nanopores were observed only at the bottom andtop membrane surfaces The structure had high resistance to all organic solvents andshowed great dimensional stability after filtration tests In another study (Zhao SuChen Peng amp Jiang 2011) the block-like copolymer poly(butyl methacrylate)-b-poly(methacrylic acid)-b-poly(hexafluorobutyl methacrylate) (PBMA-b-PMAA-b-PHFBM) material which has hydrophobic hydrophilic and fluorine-containingsegments was used Copolymer was added into the PES membrane matrix Accord-ing to the results the membrane showed excellent pH-responsive permeability anddesirable fouling release properties To increase the hydrophilicity of PS membranesRoux Jacobs van Reenen Morkel and Meincken (2006) used branchedPEO-block-PS copolymers and incorporated them into the membrane matrix Fluxand rejection data showed that the membrane morphology was changed after itwas modified with copolymer Figure 39 compares conventional and novel-basedmembranes

Figure 37 Carbon nanotube membrane simulationReprinted from Corry (2008) with permission from American Chemical Society

104 Advances in Membrane Technologies for Water Treatment

Figure 38 Scanning electron microscopy image for block copolymer film with mixedorientationReprinted from Kim Yang Lee and Kim (2010) with permission from Elsevier

ZeoliteTFNs

NanoparticleTFNs

NanostructuredceramicmembranesInorganic-organicmembranesBiologicallyinspiredmembranes

Blockcopolymers

Reactivecatalyticsurfaces

Mixedmatrices

Zeoliticfilms

Conventionalmembranes

Potential commercial viability

Pote

ntia

l per

form

ance

enh

ance

men

t

Aquaporins

Alignedcarbon nanotubes

Far

None

Evolutionary

Revolutionary

Near Immediate

Figure 39 Conventional and novel membrane current statusReprinted from Pendergast and Hoek (2011) with permission from Royal Society of Chemistry

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 105

35 Advances in membrane modules and systemconfigurations for water treatmentby MF UF and NF

Industrial membrane plants require a large amount of membrane area to performseparation on a useful scale If membranes are to be used on an industrial scale effi-cient packaging methods are required These packages are called membrane modulesBetween 1960 and the 1970s commercial membrane processes had a significant break-through with the development of low-cost membrane modules The earliest designswhich were tubular plate and frame hollow-fiber and spiral wound were mainly builton basic filtration technology including flat sheet membranes in a type of filter pressBecause of this these systems are called plate-and-frame modules At the same time1- to 3-cm-diameter tubes were developed These designs are still used but becauseof their relatively high cost in most applications two other designs have been largelydisplaced the spiral wound and hollow fiber modules Conventional membranemodules can be seen in Table 36

351 Recent advances in membrane modules

Liu Xu Zhao and Yang (2010) carried out research using a helical membrane moduleunit A terylene filter cloth without modification and with a pore size around 22 nm hadbeen used in the filtration test as a filter membrane Two pieces of membrane sheets(6 18 2 cm total area 0022 m2) were supported on a plastic spacer The fishboneor broom-like structured spacer is shown in the middle in Figure 310(a-1) and (a-3)resembling a deoxyribonucleic acid helix (Figures 310(a-4)) The cover membraneforms an empty sleeve outside the spacer once it is sealed around the edge(Figure 311) It has a tubing outlet at one end of the membrane to conduct thepermeate water The plastic spacer is flexible for helical rotation and its final total rota-tion angle together with the membrane sleeve can be kept at a certain value by fixingthe top and bottom edges The top end of the membrane can be fixed at a final angleto the bottom end while maintaining a certain helical rotation Several short pieces ofhelical membrane or extensions of membrane length can form modules with morehelixes (Figure 310(a-1))

Table 36 Membrane and module forms

Tubular Flat

Conventional membranemodules

Tube module Spiral-wound module

Capillary module Cushion module

Hollow-fiber module Plate module

Disc-tube module

106 Advances in Membrane Technologies for Water Treatment

Figure 310 Helical membrane module support spacer and final helical anglesReprinted from Liu et al (2010) with permission from Elsevier

Cross view of

the module

Mounting

of the

module in

filtration

chamberb

Water

permeation

Spacer

Permeate

Cross flow

Shearing

force

from

bubbles

Membrane

peeled openHold the two pieces

together with

thread

Seal with glue

Figure 311 Cross-view of helical membrane and its mount in a filtration chamberReprinted from Liu et al (2010) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 107

The long and rectangular new membrane modules are narrower thinner and lighterthan conventional wide flat-sheet membrane modules The helical membrane mayenhance vortex mixing just like a static stirrer in liquid phase Liu et al (2010) showedthat the higher the cross-flow the better the mixing

3511 Rotating disk module systems

Rotating disk module systems including a larger area and capacity module led to theintroduction of multi-disk systems mounted on a single shaft and rotating betweenfixed circular membranes This module is used for biotechnological applications andhas an area of 2 m2 Dyno manufactured by Bokela GmbH (Karlsruhe Germany)has a similar system design This system has a diameter of 137e85 cm and a totalmembrane area from 013 to 12 m2 This system is available with both polymericand ceramic membranes (Figure 312)

Another multi-disk system is produced by Spintek (Huntington CA) with rotatingmembranes of 23 m2 Initially it was available with organic membranes currently it isproduced with mineral membranes (Figure 313)

In Germany multi-shaft systems with overlapping rotating membranes per modulearea are common For example the multi-shaft disk (MSD) system has a diameter of312 cm in several ceramic membrane units All rotating disks turn at the same timethe Hitachi model (Japan) is available at up to a 150- and 100-m2 membrane area atparallel axes at the same time (Figure 314)

3512 Vibrating module systems

Vibrating module systems use an original concept called Vibratory Shear EnhancedProcessing System (VSEP) including a set of circular organic membranes separatedby gaskets and permeate collectors (Figure 315) The most important parameter isthe maximum azimuthal displacement of the membrane rim (Jaffrin 2008)

Figure 312 Dyno rotating disk module (Bokela Germany)Reprinted from Jaffrin (2008) with permission from Elsevier

108 Advances in Membrane Technologies for Water Treatment

Figure 314 Industrial multi-disk shaft module with eight parallel shafts and 31-cm ceramicdisksCourtesy of Westfalia Separator Reprinted from Jaffrin (2008) with permission from Elsevier

Figure 313 Spintek moduleReprinted from Jaffrin (2008) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 109

36 Applications of water treatment by MF UF and NF

Typically there are four main water sources for drinking and potable water supply sur-face water groundwater seawater and rainwater Different membrane technologiesare applicable to these sources because of their chemical and physical characteristicsFigure 316 shows a schematic describing water sources and possible membrane stepsto safe water For instance surface water can be converted into safe water using an MFUF MF plus UF plus an auxiliary or NF membrane Groundwater has generally highhardness and metal concentrations so MF and UF will not be efficient alone They needan auxiliary system

361 Applications for surface water treatment

Macrofiltration UF and NF membranes can be used in surface water treatmentalone or with an auxiliary system They are becoming popular in surface watertreatment because of their high efficiency Macrofiltration and UF process are effec-tive in removing turbidity particles bacteria and cysts If a high organic content ofwater exists MF and UF may not be used to obtain high water quality On the otherhand the NF process is able to treat many water contaminants such as DBPs andsynthetic organic compounds (Glucina Alvarez amp Laicircneacute 2000) Table 37 listsstudies concerning the use of the MF UF and NF membrane process to treatsurface water

362 Membranes for groundwater treatment

Owing to limited rainfall in some places surface water is scarce In these types of pla-ces groundwater sources become important Although they are variable in nature

Figure 315 Industrial VSEP vibrating modulesReprinted from Jaffrin (2008) with permission from Elsevier

110 Advances in Membrane Technologies for Water Treatment

groundwater sources generally contain calcium magnesium carbonatealkalinity andsilica If these ion concentrations reach high concentrations that exceed mineral solu-bility limits precipitation starts This precipitation forms deposits at the end andscales Scale formation can be problematic To solve this problem membrane technol-ogies are effective (Kinsela Jones Collins amp Waite 2012) Table 38 summarizesstudies applying MF UF and NF to groundwater treatment

363 Nanofiltration for seawater desalination

MWCO values of NF membranes are between 200 and 2000 Da They reject 98 ofdivalent ions and 30e85 of monovalent ions NF membranes have higher perme-ability than RO membranes which gives them an advantage in energy consumptionA flow diagram of dual-step NF is given in Figure 317 There is disagreement

Nanofiltration

Drinking water

MF+UF+auxillary

Surfacewater

MF+UF

Rainharvesting

Seawater

Groundwater

Figure 316 Water sources and applicable membrane steps to achieve potable water

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 111

Table 37 Studies related to microfiltration (MF) ultrafiltration (UF) and nanofiltration (NF) for thetreatment of surface waters

Process used and module type Approach Remarks References

Integrated membrane system wasused (UF thorn RO) spiral-woundand hollow-fiber configuration

Low-salinity water was used toevaluate efficiency of IMS

UF process found to be effective in controllingRO fouling UF reduced SDI

Glucina et al (2000)

MF and UF tubular and ceramicmembranes

Membrane permeability andfouling properties of ceramicand polymeric membraneswere compared

Increase TMP rate owing to fouling inverselyfollows the measured pore size Higherdegree of fouling on the polymericmembranes results from the lower volumearea ratio Aggressive methods are neededto clean non-purgeable organic carbon

Hofs et al (2011)

NF capillary and flat-sheetmembranes

New capillary NF membranewas compared with flat-sheetmembranes to find foulingproperties and pretreatmentrequirements

In capillary membranes flux decline can beincreased by forward flushing and airflushing Water permeability of capillarymembranes was 3e15 times higher thanflat-sheet membranes

Van der BruggenHawrijkCornelissen andVandecasteele(2003)

UF-MF Capillary membranes Application of UF polymericmembranes in the disinfectionand treatment of surfacewaters was investigated

Membranes were able to remove ironturbidity bacteria Escherichia coli organiccompounds and mesophilic bacteria

Konieczny (1998)

UF Carbosep M8 tubularinorganic membrane

Different kinds of surface waterswere tested for disinfection byUF membranes Differenthardnesses and organic loadswere tested

UF was a reliable method for disinfectingsurface waters

Di Zio Prisciandaroand Barba (2005)

112Advances

inMem

braneTechnologies

forWater

Treatm

ent

PVDF MF PVDF and PES UF Effects of different magnetic ionexchanges (MIEXs)pretreatment on low-pressuremembrane filtration wereinvestigated by using differentfeed water qualitiesmembrane properties andMIEX doses

Decrease in total and irreversible fouling wasobserved for PVDF MF and PES UF afterMIEX treatment Fouling of PVDF UFmembrane was not decreased after MIEXtreatment which showed the importance ofmembrane properties MIEX treatment waseffective

Huang Cho Schwaband Jacangelo(2012)

UF rotating membrane diskmodule

Irreversible fouling caused byconstituents in surface waterinvestigated

Evolution of irreversible fouling was due topolysaccharide-like organic matterpresumably iron and manganese contributedto some extent

Kimura HaneWatanabe Amyand Ohkuma(2004)

MFUF Irreversible membrane fouling inan MF membrane wasinvestigated Feed watercontaining humic acid ororganic matter was coagulatedwith polyaluminum chloride

Coagulation conditions (dosage) wereeffective for irreversible fouling Acidicconditions enhanced the treated waterquality and increased irreversible fouling

Kimura MaedaYamamura andWatanabe (2008)

NF UF MF spiral wound Efficiency of NF modules for therejection of DBPs from low-turbidity surface waters wasinvestigated

Dissolved organic carbon (DOC)trihalomethane formation potential(THMFP) haloacetic acid formationpotential (HAAFP) and chloral hydrateformation potential (CHFP) rejections werehigher than 86 in NF MF was moderatelyeffective in particle removals UF did notshow significant changes in operationalconditions

Siddiqui Amy Ryanand Odem (2000)

Continued

Advances

inwater

treatment

bymicro

filtrationultrafiltrationand

nanofiltration

113

Table 37 Continued

Process used and module type Approach Remarks References

NF flat-sheet Study aimed to treat surfacewater contaminated withpesticides

NF membranes were able to reduce hardnessCOD and TOC and remove microbialcontent completely

Sarkar et al (2007)

UF hollow-fiber Performance of UF membraneswas investigated by using rawwater from the Bin XianReservoir

Before UF use of coagulation increasedpermeate flux and retarded membrane fluxdecline UF was able to remove turbiditycoliform bacteria iron manganese andaluminum

Xia Nan Liu and Li(2004)

UF hollow-fiber PVDF UF membranes weretested for the treatment ofsurface waters

Permeate quality was stable regardless ofdifferent surface waters TMP should bebelow 1 bar to decrease irreversible fouling

Guo Zhang Fangand Su (2009)

114Advances

inMem

braneTechnologies

forWater

Treatm

ent

concerning whether it is possible to desalinate seawater by using dual-step NF at alower cost than RO In the dual-step NF process seawater is fed to the first NF mem-brane and then the collected permeate is fed to the second NF membrane Finallypotable water is obtained Concentrates are pumped into the NF feed tank optionallyThe energy requirement for seawater desalination using dual-stage NF is proportionalto the salinity of the permeate More energy is needed for lower permeate salinity(AlTaee amp Sharif 2011)

Table 38 Microfiltration (MF) ultrafiltration (UF) andnanofiltration (NF) groundwater applications

Process used andmodule type Approach Remarks References

Electro-ultrafiltration(EUF)

Effectiveness ofEUF system wasdetermined forarsenic removal

Arsenic removalincreased from1 to 14 toover 79

Hsieh WengHuang and Li(2008)

NF piperazinemembrane

Different hardnessand salinityvalues were used

High hardnessretentioncoefficients(70e76)satisfactorypermeate fluxesand high mineralfouling resistancebut low salinityremoval wereobtained

GalanakisFountoulis andGekas (2012)

NF polyamidemembrane

Ozonation slowsand filtrationand NF processeswere combined toremove dissolvedorganic matter(DOM) fromgroundwater

NF was able toremove aromatichumic acid andfulvic acid-likesubstances andDOM

Linlin Xuan andMeng (2011)

NF flat-sheetmembrane module

For fluorideremoval fromcontaminatedgroundwater NFmoduleperformance wasmodeled andsimulated

NF membrane wasable to removefluoride and dropthe level of pH ofgroundwater tothe desired level

Chakrabortty Royand Pal (2013)

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 115

364 Membranes for harvesting rainwater

Harvested rainwater is preferred for irrigation purposes On the other hand there isgrowing interest in harvesting rainwater for drinking and other indoor uses Rainwatercan be filtered by MF UF and NF according to the desired quality MF treatment issuitable for gray water production UF and NF treatment can be used for the drinkingwater supply Home size water treatment units can be used in drinking water produc-tion UF provides a good option for disinfection to remove viruses and bacteriaA number of companies supply UV granulated activated carbon and membranefiltration systems for rainwater purification

365 Applications of membranes for specific contaminantremoval

Arsenic (As) exists in natural water sources in both organic and inorganic forms Long-term exposure to arsenic causes cancer The World Health Organization limits thepresence of As in water to less than 001 mgL Removal of As with membranes is suc-cessful and is popular nowadays There is both pilot and lab-scale research in the liter-ature Nguyen Vigneswaran Ngo Shon and Kandasamy (2009) used both MF andNF NF membranes are more efficient for the removal of As than MF membraneswhich have bigger pores Sato Kang Kamei and Magara (2002) also evaluated Asremoval efficiency using NF and a rapid sand filtration inter-chlorination systemNF membranes with 996 NaCl rejection capacity removed 95 of As(V) and75 of As(III) with no chemical addition under low pressure Floch and Hideg(2004) conducted a study with 200e300 mgL As containing deep well water UsingZenon ZW 1000 hollow-fiber membranes they achieved As concentration less than10 mgL

Pesticides are used to control pests such as weeds and insects They are beneficial inpreventing disease and are used for food production Unfortunately they have anadverse effect on water quality and may have negative effects on human and aquatic

Figure 317 Dual-stage desalination processReprinted from AlTaee and Sharif (2011) with permission from Elsevier

116 Advances in Membrane Technologies for Water Treatment

life Chen Taylor Mulford and Norris (2004) proved that NF membranes can rejectpesticides from 46 up to 100 They found that the rejection rate is directly propor-tional to the molecular weight (MW) of the pesticide When the MW increased therejection rate also increased They also revealed rejection could be increased by adjust-ing the operational flux and recovery Van der Bruggen Schaep Maes Wilms andVandecasteele (1998) researched the removal of pesticides with membrane filtrationsystems that showed good efficiency of membranes in pesticide removal They triedNF membranes and obtained approximately 95 rejection of arsenic with an NF-70membrane

Disinfection is used in the final step of drinking water treatment to deactivate bio-logical agents However NOM in water reacts with disinfectants and causes DBPs toform such as THMs halogenated acetic acids (HAAs) haloacetonitriles (HANs) andhaloketones (HKs) which are detrimental to human health Lee and Lee (2007) usedNF membranes to remove NOMs from surface water and researched the effect ofmembrane pretreatment and membrane material They found that membraneswith an MWCO less than 200 Da were better for controlling NOM in surface waterHydrophobic and positively charged membranes fouled more than hydrophilic andnegatively charged membranes They also revealed that ozone pretreatment wasinefficient for preventing NF fouling but powdered activated carbon (PAC) or UFpretreatment was efficient

Pharmaceuticals have gained attention recently owing to their effects on biologicalactivities Pharmaceutical emissions to the environment should be controlled Radje-novic Petrovic Ventura and Barcelo (2008) studied the removal of pharmaceuticalsin a full-scale NF and RO drinking water treatment plant using groundwater An 85rejection rate was obtained using NF and RO Boleda Galceran and Ventura (2011)studied pharmaceuticals in a full-scale drinking water treatment plant treatment con-sisted of dioxychlorination coagulationflocculation and sand filtration units Aftersand filtration the system was split into two parallel lines conventional (ozonationand carbon) and advanced (UF and RO) treatment A flow diagram of the plant isshown in Figure 318 To remove pharmaceuticals an advanced system was moreeffective than a conventional system

RemineralizationReverseosmosisUVUltrafiltration

CoagulationFloculationSettling

Sandfiltration

Groundwater

Blending Finishedwater

CI2Ozonization GAC

filtration

Riverwater

CIO2

Figure 318 Treatment scheme of drinking water treatment plantReprinted from Boleda et al (2011) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 117

37 Future trends

Water has been a main problem of mankind for years and will continue to be problem-atic Membrane technology has a significant role in the water industry In the futurenovel membrane materials processes and modules will be used so that we cancome closer to obtaining an optimum membrane structure Membrane technologyhas some shortcomings such as higher energy requirements and fouling Todayrsquos tech-nology related to research on this subject consists of fabricating new membrane mate-rials designing modules calculating hydrodynamics and finding new operationmodes to decrease energy requirements or application setups to treat water or waste-water more effectively Future trends will be the reuse of process waters recoveryof valuable compounds creation of new technologies such as pervaporation and for-ward osmosis monitoring of fouling in real time improvement of new fouling analysismethods and fabrication of tailored novel membranes and developments ofmembranes can be used under extreme conditions

As these aims are realized cost capacity and selectivity should optimized and theirenvironmental impact such as concentrate handling and minimized chemical con-sumption should also be considered

As novel membrane materials are investigated the future lies in block copolymersand biomimetic and patterned membranes such as vertically aligned CNs Thesematerials show great potential because they have greater permeability rates and higherselectivity however commercialization is still a problem If they are commercializedin near future we will obtain lower energy consumption and thus the treatment cost ofpollutants will also decrease The ultimate challenge is extreme conditions such as hightemperatures On this point developments in ceramic membranes are promising(Abetz et al 2006 Url-5 Url-6)

Another problem is housing the membranes Hollow-fiber and spiral wound mod-ule geometry are the main membrane housings as already mentioned in this chapterMembrane module design focuses on mechanical considerations such as pressure butalso on how to limit concentration polarization According to studies on membranesurface there is a valley that causes roughness on membranes surface because ofthat a concentration of rejected species occurs To resolve these problems futureresearch will need to resolve them with fluid mechanical and mass transfer ap-proaches Also designing new membrane modules can decrease the cost and energyrequirements of the membranes For example when the transmembrane pressure islow high fluxes can be obtained Using novel membrane module technologies suchas vibrational modules can decrease the effect of fouling on the membrane surface(Fane et al 2011 Url-7)

Membrane processes are also significant With an improvement in membrane pro-cesses and materials it will become easier to use some new applications for instancepervaporation forward osmosis and new MBR systems Anaerobic MBRs use anaer-obic bacteria to degrade organic substances In this system it is possible to use biogasinstead of air in the submerged reactor Anaerobic MBR systems are better thanconventional systems because of their lower energy consumption Anaerobic MBR

118 Advances in Membrane Technologies for Water Treatment

systems are promising because they can sustain high organic loadings high biomassconcentration can be maintained energy and organic acid are recovered and sludgeproduction is low Another new technology is microbial fuel cells which are a noveltype of MBR Decentralized treatment systems can be used to lower cost and increasesanitation and reuse in wastewater systems (Abetz et al 2006 Fane et al 2011)

In this century great challenges will need to be overcome such as energy waterand a clean environment Membrane technology and its development have an impor-tant role in solving these problems efficiently with new research and development andinnovations in process designs

38 Sources of further information and advice

In the future we will see membranes much more in the water treatment sector Highperformance and low fouling membranes are the main targets in all membrane researchdevelopments and applications Membrane materials module configurations and pro-cesses are becoming more important for improving membrane system performance anddecreasing membrane fouling They will have a critical role in the future performance ofmembranes Interdisciplinary studies should be increased to improve performance basedon materials configurations and processes

39 Conclusion

This chapter summarizes MF UF and NF membranes for water treatment New mem-brane materials have improved membrane technology by enhancing permeability andselectivity As a result of these improvements in membrane performance concentra-tion polarization and fouling phenomena have become important factors in deter-mining membrane performance Membrane modules improve fluid flow so thatfouling and concentration polarization problems decrease In this chapter novel mem-brane materials and module design to increase membrane performance were summa-rized Applications of MF UF and NF membranes were also provided They may beapplied to treat surface water groundwater and seawater desalination and to harvestrainwater Many specific contaminants can be removed efficiently with thesemembrane processes

List of acronyms

AMBR Anaerobic membrane bioreactorCA Cellulose acetateCAGR Compound annual growth rateCHFP Chloral hydrate formation potentialCNT Carbon nanotube

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 119

COD Chemical oxygen demandCVD Chemical vapor depositionDBP Disinfection by-productsED ElectrodialysisEDR Electrodialysis reversalFO Forward osmosisGAC Granulated Activated CarbonHAA Halogenated acetic acidsHAAFP Haloacetic acid formation potentialHAN HaloacetonitrileHK HaloketoneIC In-line coagulationIMS Integrated membrane systemMBR Membrane bioreactorMCF Membrane cartridge filtrationMSD Multi-shaft diskMF MicrofiltrationMIEX Magnetic ion exchangeMWCNT Multi-walled carbon nanotubesMWCO Molecular weight cutoffNF NanofiltrationNOM Natural organic matternZVI Nano zero valent ironPAC Powdered activated carbonPAN PolyacrylonitrilePBMA-B-PMAA-B-PHFBM Poly(butyl methacrylate)-b-poly(methacrylic

acid)-b-poly(hexafluorobutyl methacrylate)PC PolycarbonatePES PolyethersulfonePI PolyimidePNIPAAm-B-PPEGMA poly(N-isopropylacrylamide)-block-poly([polyethylene

glycol] methacrylate)PP PolypropylenePS PolysulfonePS-B-PMMA Polysulfone-b-polymethylmethacrylatePVDF Polyvinylidene fluorideRO Reverse osmosisSDI Silt density indexSWCNT Single-walled carbon nanotubeTDS Total dissolved solidsTFC Thin-film compositeTFN Thin-film nanocompositeTHM TrihalomethanesTHMFP Trihalomethane formation potentialTMP Transmembrane pressureTOC Total organic carbonUF UltrafiltrationUV UltravioletWP Water permeability

120 Advances in Membrane Technologies for Water Treatment

List of symbols

A Membrane areaDa DaltonE Band gap energyhn Photon energyJ Membrane fluxDP Applied pressure

References

Abdelrasoul A Doan H amp Lohi A (2013) Fouling in membrane filtration and remediationmethods Retrieved from httpdxdoiorg10577252370

Abetz V Brinkmann T Dijkstra M Ebert K Fritsch D Ohlrogge K et al (2006)Developments in membrane research From material via process design to industrial appli-cation Advanced Engineering Materials 8(5) httpdxdoiorg101002adem200600032

Akar N Asar B Dizge N amp Koyuncu I (2013) Investigation of characterization andbiofouling properties of PES membrane containing selenium and copper nanoparticlesJournal of Membrane Science 437 216e226 httpdxdoiorg101016jmemsci201302012

AlTaee A amp Sharif A O (2011) Alternative design to dual stage NF seawater desalinationusing high rejection brackish water membranes Desalination 273 391e397 httpdxdoiorg101016jdesal201101056

Antelmi D Cabane B Meireles M amp Aimar P (2001) Cake collapse in pressure filtrationLangmuir 17 7137e7144 httpdxdoiorg101021la0104471

AWWA (2007) Reverse osmosis and nanofiltration (2nd ed) Denver American Water WorksAssociation ISBN 9781583214916

Baker W R (2004) Membrane technology and applications (2nd ed) John Wiley and SonsLtd httpdxdoiorg1010020470020393

Beacuterube P R Mavinic D S Hall E R Kenway S E amp Roett K (2002) Evaluation ofadsorption and coagulation as membrane pretreatment steps for the removal of organicmaterial and disinfection-by-product precursors Journal of Environmental Engineeringand Science 1(6) 465e476

Boleda M R Galceran M T amp Ventura F (2011) Behavior of pharmaceuticals and drugs ofabuse in a drinking water treatment plant (DWTP) using combined conventional andultrafiltration and reverse osmosis (UFRO) treatments Environmental Pollution 1591584e1591 httpdxdoiorg101016jenvpol201102051

Bowen W R amp Welfoot J S (2005) Modelling the performance of nanofiltration mem-branes In A I Schafer A G Fane amp T D Waite (Eds) Nanofiltration Principles andapplications (pp 119e146) Oxford Elsevier

Buonomenna M G (2013) Nano-enhanced reverse osmosis membranes Desalination 31473e88 httpdxdoiorg101016jdesal201301006

Cakmakci M Baspinar A B Balaban U Koyuncu I amp Kinaci C (2009) Comparison ofnanofiltration and adsorption techniques to remove arsenic from drinking water Desali-nation and Water Treatment 9 149e154 httpdxdoiorg105004dwt2009765

Carroll T King S Gray S R Bolto B A amp Booker N A (2000) The fouling ofmicrofiltration membranes by NOM after coagulation treatment Water Research 342861e2868 httpdxdoiorg101016S0043-1354(00)00051-8

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 121

Chakrabortty S Roy M amp Pal P (2013) Removal of fluoride from contaminated ground-water by cross flow nanofiltration Transport modeling and economic evaluation Desali-nation 313 115e124 httpdxdoiorg101016jdesal201212021

Chen G E Li F J Han L F Xu Z L amp Yu L Y (2010) Preparation of microporouspolyethersulfone hollow fiber membranes using non-solvent vapour induced phase sepa-ration Iranian Polymer Journal 19(11) 863e873

Chen S Taylor J Mulford L A amp Norris C D (2004) Influences of molecular weightmolecular size flux and recovery for aromatic pesticide removal by nanofiltration mem-branes Desalination 160 103e111 httpdxdoiorg101016S0011-9164(04)90000-8

Chong M N Jin B Chow C W K amp Saint C (2010) Recent developments in photo-catalytic water treatment technology A reviewWater Research 44 2997e3027 httpdxdoiorg101016jwatres201002039

Chou W L amp Yang M C (2005) Effect of take-up speed on physical properties andpermeation performance of cellulose acetate hollow fibers Journal of Membrane Science250 259e267 httpdxdoiorg101016jmemsci200410030

Corry B (2008) Designing carbon nanotube membranes for efficient water desalinationJournal of Physical Chemistry B 112 1427e1434 httpdxdoiorg101021jp709845u

Crock C A Rogensues A R Shan W amp Tarabara V V (2013) Polymer nanocompositeswith graphene-based hierarchical fillers as materials for multifunctional water treatmentmembranes Water Research 47(12) 3984e3996 httpdxdoiorg101016jwatres201210057

Co

ˇ

teacute P Brink D amp Adnan A (2006) Pretreatment requirements for membrane bioreactorsZENON membrane solutions Water Environment Foundation httpdxdoiorg102175193864706783750169

Dahe G Teotia R S amp Bellare J (2012) The role of zeolite nanoparticles additive onmorphology mechanical properties and performance of polysulfone hollow fiber mem-branes Chemical Engineering Journal 197 398e406 httpdxdoiorg101016jcej201205037

Debik E Kaykioglu G Coban A amp Koyuncu I (2010) Reuse of anaerobically andaerobically pre-treated textile wastewater by Uf and Nf membranes Desalination256(1e3) 174e180 httpdxdoiorg101016jdesal201001013

Di Zio A Prisciandaro M amp Barba D (2005) Disinfection of surface waters with UFmembranes Desalination 179 297e305 httpdxdoiorg101016jdesal200411075

Elimelech M amp Phillip W A (2011) The future of seawater desalination Energy technol-ogy and the environment Science 33 712e717 httpdxdoiorg101126science1200488

Eykamp W (1995) Microfiltration and ultrafiltration In R D Noble amp S A Stern (Eds)Membrane separation technology Principles and applications Amsterdam ElsevierISBN 0 444 81633 X

Fane A G Tang C Y amp Wang R (2011) Membrane technology for water Microfiltrationultrafiltration nanofiltration and reverse osmosis Reference Module in Earth Systems andEnvironmental Sciences Treatise on Water Science 4 301e335 Water-Quality Engi-neering httpdxdoiorg101016B978-0-444-53199-500091-9

Floch J ampHidegM (2004) Application of ZW-1000membranes for arsenic removal fromwatersources Desalination 162 75e83 httpdxdoiorg101016S0011-9164(04)00029e3

Galanakis C M Fountoulis G amp Gekas V (2012) Nanofiltration of brackish groundwaterby using a polypiperazine membrane Desalination 286 277e284 httpdxdoiorg101016jdesal201111035

122 Advances in Membrane Technologies for Water Treatment

Georgiev D Bogdanov B Angelova K Markovska I Hristov Y (2009) Synthetic zeolites -structure clasification current trends in zeolite synthesis review International ScienceConference 4e5 June Stara Zagora Bulgaria

Glucina K Alvarez A amp Laicircneacute J M (2000) Assessment of an integrated membrane systemfor surface water treatment Desalination 132 73e82 httpdxdoiorg101016S0011-9164(00)00137e5

Goh P S Ismail A F amp Ng B C (2013) Carbon nanotubes for desalination performanceevaluation and current hurdles Desalination 308 2e14 httpdxdoiorg101016jdesal201207040

Guigui C Rouch J C Durand-Bourlier L Bonnelye V amp Aptel P (2002) Impact ofcoagulation conditions on the in-line coagulationUF process for drinking water produc-tion Desalination 147 95e100 httpdxdoiorg101016S0011-9164(02)00582e9

Guo X Zhang Z Fang L amp Su L (2009) Study on ultrafiltration for surface water by apolyvinylchloride hollow fiber membrane Desalination 238 183e191 httpdxdoiorg101016jdesal200711064

Gupta V K (2013) Water treatment by membrane filtration techniques Environmental Waterhttpdxdoiorg101016B978-0-444-59399-300005-2

Han L F Xu Z L Yu L Y Wei Y M amp Cao Y (2010) Performance of PVDFmul-tinanoparticles composite hollow fibre ultrafiltration membranes Iranian Polymer Journal19(7) 553e565

Harman B I Koseoglu H Yigit N O Beyhan M amp Kitis M (2010) The use of ironoxide-coated ceramic membranes in removing natural organic matter and phenol fromwaters Desalination 261 27e33 httpdxdoiorg101016jdesal201005052

Hilal N Al-Zoubi H Darwish N A Mohammad A W amp Abu Arabi M (2004)A comprehensive review of nanofiltration membranes Treatment pretreatment modellingand atomic force microscopy Desalination 170 281e308 httpdxdoiorg101016jdesal200401007

Hoffmann M R Martin S T Choi W amp Bahnemannt D W (1995) Environmentalapplications of semiconductor photocatalysis Chemical Reviews 95 69e96 httpdxdoiorg101021cr00033a004

Hofs B Ogier J Vries D Beerendonk E F amp Cornelissen E R (2011) Comparison ofceramic and polymeric membrane permeability and fouling using surface water Sepa-ration and Purification Technology 79 365e374 httpdxdoiorg101016jseppur201103025

Hsieh L C Weng Y Huang C amp Li K (2008) Removal of arsenic from groundwater byelectro-ultrafiltration Desalination 234 402e408 httpdxdoiorg101016jdesal200709110

Huang H Cho H Schwab K J amp Jacangelo J G (2012) Effects of magnetic ion exchangepretreatment on low pressure membrane filtration of natural surface waterWater Research46 5483e5490 httpdxdoiorg101016jwatres201207003

Jacangelo J G Trussell R R amp Watson M (1997) Role of membrane technology indrinking water treatment in the United States Desalination 113(2e3) 119e127 httpdxdoiorg101016S0011-9164(97)00120e3

Jaffrin M Y (2008) Dynamic shear-enhanced membrane filtration A review of rotating disksrotating membranes and vibrating systems Journal of Membrane Science 324 7e25httpdxdoiorg101016jmemsci200806050

Judd S J amp Hillis P (2001) Optimisation of combined coagulation and microfiltration forwater treatment Water Research 35(12) 2895e2904 httpdxdoiorg101016S0043-1354(00)00586-8

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 123

Kennedy M D Kamanyi J Salinas Rodriguez S G Lee N H Schippers J C ampAmy G (2008) Water treatment by microfiltration and ultrafiltration In N N LiA G Fane W S Winston Ho amp T Matsuura (Eds) Advanced membranetechnology and applications (pp 131e165) John Wiley and Sons Inc ISBN 978-0-471-73167-2

Kim E-S Hwang G El-Din M G amp Liu Y (2012) Development of nanosilver and multi-walled carbon nanotubes thin film nanocomposite membrane for enhanced water treatmentJournal of Membrane Science 394e395 37e48

Kim J K Yang S Y Lee Y amp Kim Y (2010) Functional nanomaterials based on blockcopolymer self-assembly Progress in Polymer Science 35(11) 1325e1349 httpdxdoiorg101016jprogpolymsci201006002

Kimura K Hane Y Watanabe Y Amy G amp Ohkuma N (2004) Irreversible membranefouling during ultrafiltration of surface water Water Research 38 3431e3441 httpdxdoiorg101016jwatres200405007

Kimura K Maeda T Yamamura H amp Watanabe Y (2008) Irreversible membrane foulingin microfiltration membranes filtering coagulated surface water Journal of MembraneScience 320 356e362 httpdxdoiorg101016jmemsci200804018

Kinsela A S Jones A M Collins R N amp Waite T D (2012) The impacts of low-costtreatment options upon scale formation potentialin remote communities reliant on hardgroundwaters A case study Northern Territory Australia Science of the Total Environ-ment 416 22e31 httpdxdoiorg101016jscitotenv201112005

Konieczny K (1998) Treatment of natural waters using capillary membranes Polish Journal ofEnvironmental Studies 7(4) 213e220

Koseoglu D Y Kose B Altinbas M amp Koyuncu _I (2013) The production of polysulfone(PS) membrane with silver nanoparticles (AgNP) Physical properties filtration perfor-mances and biofouling resistances of membranes Journal of Membrane Science 428620e628 httpdxdoiorg101016jmemsci201210046

Koyuncu I Arikan O Wiesner M R amp Rice C (2008) Removal of hormones and anti-biotics by nanofiltration membranes Journal of Membrane Science 309 94e101 httpdxdoiorg101016jmemsci200710010

Koyuncu _I amp Cakmakci M (2010) Nanofiltration for water and wastewater treatmentNanotechnology in water treatment applications Horizon Press ISBN 978-1-904455-66-0

Kruithof J C Nederlof M M Hoffman J A M H amp Taylor J S (2004) Integratedmembrane systems Elbert CO AWWA Research Foundation and American Water WorksAssociation

Kurt E Koseoglu D Y Dizge N Chellam S amp Koyuncu _I (2012) Pilot-scaleevaluation of nanofiltration and reverse osmosis for process reuse of segregatedtextile dyewash wastewater Desalination 302 24e32 httpdxdoiorg101016jdesal201205019

Lau W J Ismail A F Misdan N amp Kassim M A (2012) A recent progress in thin filmcomposite membrane A review Desalination 287 190e199 httpdxdoiorg101016jdesal201104004

Lee S amp Lee C (2007) Effect of membrane properties and pretreatment on flux and NOMrejection in surface water nanofiltration Separation and Purification Technology 56 1e8httpdxdoiorg101016jseppur200701007

Li X Liu H Xiao C Ma S amp Zhao X (2012) Effect of take-up speed on polyvinylidenefluoride hollow fiber membrane in a thermally induced phase separation process Journal ofApplied Polymer Science httpdxdoiorg101002app37919

124 Advances in Membrane Technologies for Water Treatment

Liang S Xiao K Mo Y amp Huang X (2012) A novel ZnO nanoparticle blended poly-vinylidene fluoride membrane for anti-irreversible fouling Journal of Membrane Science394e395 184e192 httpdxdoiorg101016jmemsci201112040

Linlin W Xuan Z amp Meng Z (2011) Removal of dissolved organic matter in municipaleffluent with ozonation slow sand filtration and nanofiltration as high quality pre-treatmentoption for artificial groundwater recharge Chemosphere 83 693e699 httpdxdoiorg101016jchemosphere201102022

Liu L Xu X Zhao C amp Yang F (2010) A new helical membrane module for increasingpermeate flux Journal of Membrane Science 360 142e148 httpdxdoiorg101016jmemsci201005014

Loh C H Wang R Shi L amp Fane A G (2011) Fabrication of high performance poly-ethersulfone UF hollow fiber membranes using Pluronic block copolymers as pore formingadditives Journal of Membrane Science 380 111e123 httpdxdoiorg101016jmemsci201106041

Ma N Zhang Y Quan X Fan X amp Zhao H (2010) Performing a microfiltration integratedwith photocatalysis using an Ag-TiO2HAPAl2O3 composite membrane for water treat-ment evaluating effectiveness for humic acid removal and anti-fouling properties WaterResearch 44(20) 6104e6114 httpdxdoiorg101016jwatres201006068

Maartens A Swarta P amp Jacobs E P (1999) Feed-water pretreatment Methods to reducemembrane fouling by natural organic matter Journal of Membrane Science 163 51e62httpdxdoiorg101016S0376-7388(99)00155e6

Membrane Filtration Guidance Manual (November 2005) United States EnvironmentalProtection Agency(EPA) Office of Water(4601) EPA 815-R-06e009

Membrane Fouling Considerations (January 2001) Hydranautics high performance membraneproducts technical paper

Minegishi S Jang N-Y Watanabe Y Hirata S amp Ozawa G (2001) Fouling mechanismof hollow fibre ultrafiltration membrane with pre-treatment by coagulationsedimentationprocess Water Science and Technology Water Supply 1(4) 49e56

Mir L Micheals S L Goel V amp Kaiser R (1992) Crossflow microfiltration Applicationsdesign and cost membrane handbook New York Van Nostrand Reinhold httpdxdoiorg101007978-1-4615-3548-5_35

Mishra A K amp Ramaprabhu S (2011) Functionalized graphene sheets for arsenic removaland desalination of sea water Desalination 282 39e45 httpdxdoiorg101016jdesal201101038

Mohammadi T amp Maghsoodloorad H (2013) Synthesis and characterization of ceramicmembranes (W-type zeolite membranes) International Journal of Applied CeramicTechnology 10(2) 365e375 httpdxdoiorg101111j1744-7402201102749x

Mulder M (1996) Basic principles of membrane technology (2nd ed) Kluwer AcademicPublishers ISBN 978-94-009-1766-8

Ng L Y Mohammad A W Leo C P amp Hilal N (2010) Polymeric membranes incor-porated with metalmetal oxide nanoparticles A comprehensive review Desalinationhttpdxdoiorg101016jdesal201011033

Nguyen V T Vigneswaran S Ngo H H Shon H K amp Kandasamy J (2009) Arsenicremoval by a membrane hybrid filtration system Desalination 236 363e369 httpdxdoiorg101016jdesal200710088

Ohya H Shiki S amp Kawakami H (2009) Fabrication study of polysulfone hollow fibermicrofiltration membranes Optimal dope viscosity for nucleation and growth Journal ofMembrane Science 326 293e302 httpdxdoiorg101016jmemsci200810001

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 125

Ozgun H Ersahin M E Erdem S Atay B Kose B Kaya R et al (2012) Effects of thepre-treatment alternatives on the treatment of oil-gas field produced water by nanofiltrationand reverse osmosis membranes Journal of Chemical Technology and Biotechnologyhttpdxdoiorg101002jctb4007

Pendergast M T M amp Hoek E M V (2011) A review of water treatment membranenanotechnologies Energy and Environmental Science 4 1946e1971 httpdxdoiorg101039C0EE00541J

Pinnekamp J amp Friedrich H (2006) Municipal water and waste management Membranetechnology for wastewater treatment Aachen FIW Verlag ISBN 3-939377-01-5

Qu X Alvarez P J J amp Li Q (2013) Applications of nanotechnology in water andwastewater treatment Water Research 47(12) 3931e3946 httpdxdoiorg101016jwatres201209058

Radjenovic J Petrovic M Ventura F amp Barcelo D (2008) Rejection of pharmaceuticals innanofiltration and reverse osmosis membrane drinking water treatment Water Research42 3601e3610 httpdxdoiorg101016jwatres200805020

Razmjou A Resosudarmo A Holmes R L amp Li H (2012) The effect of modified TiO2

nanoparticles on the polyethersulfone ultrafiltration hollow fiber membranes Desalination287 271e280 httpdxdoiorg101016jdesal201111025

Roux S P Jacobs E P van Reenen A J Morkel C amp Meincken M (2006) Hydro-philisation of polysulphone ultrafiltration membranes by incorporation of branchedPEO-block-PSU copolymers Journal of Membrane Science 276(1e2) 8e15 httpdxdoiorg101016jmemsci200509025

Rugbani A (2009) Investigating the influence of fabrication parameters on the diameter andmechanical properties of polysulfone ultrafiltration hollow-fibre membranes (MScthesis) University of Stellenbosch

Saljoughi E Amirilargani M amp Mohammadi T (2010) Effect of PEG additive andcoagulation bath temperature on the morphology permeability and thermalchemical sta-bility of asymmetric CA membranes Desalination 262 72e78 httpdxdoiorg101016jdesal201005046

Sarkar B Venkateshwarlu N Nageswara Rao R Bhattacharjee C amp Kale V(2007) Potable water production from pesticide contaminated surface watermdashAmembrane based approach Desalination 204 368e373 httpdxdoiorg101016jdesal200602041

Sato Y Kang M Kamei T amp Magara Y (2002) Performance of nanofiltration for arsenicremoval Water Research 36 3371e3377 httpdxdoiorg101016S0043-1354(02)00037e4

Schaep J Van der Bruggen B Uytterhoeven S Croux R Vandecasteele C Wilms Det al (1998) Removal of hardness from groundwater by nanofiltration Desalination 119295e302 httpdxdoiorg101016S0011-9164(98)00172e6

Sengur R (2013) Fabrication and characterization of polyethersulfone (pes)multiwalledcarbon nanotube hollow fiber ultrafiltration membranes (MSc thesis) Istanbul TechnicalUniversity

Siddiqui M Amy G Ryan J amp Odem W (2000) Membranes for the control of naturalorganic matter from surface watersWater Research 34(13) 3355e3370 httpdxdoiorg101016S0043-1354(00)00024-5

Sombekke H D M Voorhoeve D K amp Hiemstrap P (1997) Environmental impactassessment of groundwater treatment with nanofiltration Desalination 113 293e296httpdxdoiorg101016S0011-9164(97)00144-6

126 Advances in Membrane Technologies for Water Treatment

Tang C Y Zhao Y Wang R Heacutelix-Nielsen C amp Fane A G (2013) Desalination bybiomimetic aquaporin membranes Review of status and prospects Desalination 30834e40 httpdxdoiorg101016jdesal201207007

Tiraferri A Vecitis C amp Elimelech M (2011) Covalent binding of single-walled carbonnanotubes to polyamide membranes for antimicrobial surface properties ACS AppliedMaterials amp Interfaces 3 2869e2877 httpdxdoiorg101021am200536p

Turken T (2013) Nanocomposite hollow fiber membrane fabrication with silver nanoparticlescharacterization and application (MSc thesis) Istanbul Technical University

UN (2010) The millennium development goals report (pp 58e60)UN-Water United Nations Educational Scientific and Cultural Organisation (2006) Water a

shared responsibility The united nations world water development report 2 World WaterAssessment Programme

Url-1 httpwwwwhointmediacentrenewsreleases2012drinking_water_20120306en Accessed231114

Url-2 httpwwwbccresearchcommarket-researchmembrane-and-separation-technologymembrane-microfiltration-mst028ehtml Accessed 241114

Url-3 httpwwwbccresearchcommarket-researchmembrane-and-separation-technologyultrafiltration-membrane-markets-mst044chtml Accessed 231114

Url-4 httpwwwbccresearchcommarket-researchnanotechnologynanofiltration-nan045bhtml Accessed 231114

Url-5 httpwwwceicunsweduaucentersmembraneimstec03contentpapersplenaryfellpdf Dateretrieved 231114

Url-6 httpwwwvttfifilesnews2011future_water_technologiesmari_kallioinen_future_rd_needs_in_membrane_technologiespdf Date retrieved 231114

Url-7 httplinkspringercomchapter1010072F978-1-59745-278-6_1page-39 Date retrieved231114

Uyak V Koyuncu I Oktem I Cakmakci M amp Toreurooz I (2008) Removal of tri-halomethanes from drinking water by nanofiltration membranes Journal of HazardousMaterials 152 789e794 httpdxdoiorg101016jjhazmat200707082

Van der Bruggen B Hawrijk I Cornelissen E amp Vandecasteele C (2003) Direct nano-filtration of surface water using capillary membranes Comparison with flat sheet mem-branes Separation and Purification Technology 31 193e201 httpdxdoiorg101016S1383-5866(02)00184e3

Van der Bruggen B Schaep J Maes W Wilms D amp Vandecasteele C (1998) Nano-filtration as a treatment method for the removal of pesticides from ground waters Desa-lination 117 139e147 httpdxdoiorg101016S0011-9164(98)00081e2

Van der Bruggen B amp Vandecasteele C (2003) Removal of pollutants from surface water andgroundwater by nanofiltration Overview of possible applications in the drinking waterindustry Environmental Pollution 122 435e445 httpdxdoiorg101016S0269-7491(02)00308e1

Wandera D Himstedt H Marroquin M Wickramasingh S R amp Husson S M (2012)Modification of ultrafiltration membranes with block copolymer nanolayers for producedwater treatment the roles of polymer chain density and polymerization time on perfor-mance Journal of Membrane Science 403e404 250e260 httpdxdoiorg101016jmemsci201202061

Wilbert C M Leitz F Abert E Boegli B amp Linton K (July 1998) The desalting andwater treatment membrane manual (2nd ed) Denver CO Water Treatment Engineeringand Research R-98e5

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 127

Xia S Nan J Liu R amp Li G (2004) Study of drinking water treatment by ultrafiltration ofsurface water and its application to China Desalination 170 41e47 httpdxdoiorg101016jdesal200403014

Xu P D Leurou S L Zhen W X Ku B K amp Yi X Y (2008) Effect of coagulation bathtemperature on the structure and performance of polyerthersulfone hollow fiber membranesby drywet process Journal of Clinical Rehabilitative Tissue Engineering Research 125381e5384

Zhao X Su Y Chen W Peng J amp Jiang Z (2011) pH-responsive and fouling-releaseproperties of PES ultrafiltration membranes modified by multi-functional block-likecopolymers Journal of Membrane Science 382(1e2) 222e230 httpdxdoiorg101016jmemsci201108014

Zhong P S Chung T-S Jeyaseelan K amp Armugam A (2012) Aquaporin-embeddedbiomimetic membranes for nanofiltration Journal of Membrane Science 407e40827e33 httpdxdoiorg101016jmemsci201203033

Zhu B Hu Y Kennedy S Milne N Morris G Jin W et al (2011) Dual functionfiltration and catalytic breakdown of organic pollutants in wastewater using ozonationwith titania and alumina membranes Journal of Membrane Science 378(1e2) 61e72httpdxdoiorg101016jmemsci201011045

128 Advances in Membrane Technologies for Water Treatment

Water treatment by reverse andforward osmosis 4NK Rastogi1 A Cassano2 A Basile231Department of Food Engineering Central Food Technological Research InstituteCouncil of Scientific and Industrial Research Mysore India 2Institute on MembraneTechnology ITM-CNR University of Calabria Rende (CS) Italy 3Ast-Engineering srlRome Italy

41 Introduction

Water shortages have plagued many communities and humans have long searched fora solution to Earthrsquos limited freshwater supplies Less than 1 of the total water avail-able on the earth is considered freshwater Almost 965 of Earthrsquos water is located inthe seas and oceans 17 is present in icebergs and the remaining percentage is madeup of brackish water (Gleick 1996 Greenlee Lawler Freeman Marrot amp Moulin2009) The population explosion and the expansion of cities have made the productionof potable water undependable and have led to an increase in demand compared withavailability Today the production of potable water has become a worldwide concernfor many communities the projected population growth and demand exceed availableconventional water resources

Over the years purified water standards have become more stringent Watercontaining less than 1000 mgL of salts or total dissolved solids (TDS) is referred asfreshwater above this concentration properties such as taste color corrosion propen-sity and odor are adversely affected (Sandia 2003) Many countries have adoptednational drinking water standards for specific contaminants as well as for TDS butthe standard limits vary from country to country or from region to region within thesame country The World Health Organization and Gulf Drinking Water standardsAustralia recommend a drinking water standard of 1000 mgL TDS (FritzmannLowenberg Wintgens amp Melin 2007) Most desalination facilities are designed toachieve a TDS of 500 mgL or less (Gaid amp Treal 2007 Xu et al 2007) Desalinatedwater used for other purposes such as crop irrigation may have a higher TDS concen-tration Depending on the salinity of the feed water it can be divided into two typessuch as brackish water (often groundwater sources 1000e10000 mgL TDS) andseawater (30000e45000 mgL TDS) (Mickley 2001) The type of feed water decidesthe use of pretreatment method the design of the treatment plant the waste disposalmethod and the recovery of water

The expanding global population increasing water pollution and increasing stan-dard of living have put relentless pressure on water and energy resources Low-costmethods of purifying freshwater and desalting seawater are required to contend withthis destabilizing trend Hence the need for water is increasing rapidly and current

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400004-6Copyright copy 2015 Elsevier Ltd All rights reserved

freshwater resources may not be able to meet all requirements Desalination of sea (orsaline) water has been practiced regularly for over 50 years and is a well-establishedmeans to obtain a water supply in many countries In the 1970s exploration beganinto using membranes for water desalination Proving successful at producing purifiedwater from saltwater membranes became a viable alternative to evaporation-basedtechnologies in the water treatment market Over the years purified water standardshave become more stringent However membranes have risen to the challenge andcontinue to perform efficiently and effectively (Rastogi amp Nayak 2011)

42 Thermal or membrane desalination

Membrane and distillation processes equally share current desalination productioncapacity worldwide However reverse osmosis (RO) will emerge as the leader infuture desalination installations and will be the key to increasing water supplies fordrinking water production RO technology can now produce freshwater (fromseawater) at one-half to one-third the cost of distillation (Miller 2003) Brackish waterRO membranes typically have higher permeate flux and lower salt rejection andrequire lower operating pressures whereas seawater RO membranes have highersalt rejection and lower permeate fluxes and membrane permeability and requirehigher operating pressures to compensate for the higher osmotic pressure of seawaterBrackish water desalination is even less expensive than seawater desalination

The demand for additional freshwater production can be met by adopting waterreuse or desalination (Sauvet-Goichon 2007) Water reuse can be used for irrigationpower plant cooling and groundwater recharge (Focazio et al 2008) Desalination hasbeen identified as a potential source for producing drinking water Desalination is ageneral term for the process of separating salt from saline water for the productionof freshwater Thermal and membrane desalination both the processes are beingused for the recovery of water (Gleick 2006)

Middle East countries initiated the use of seawater thermal desalination and todaytheir share is more than 50 of the worldrsquos desalination capacity (Henthorne 2003Van der Bruggen amp Vandecasteele 2002) Membrane processes have rapidly devel-oped since the 1960s (Drsquosouza amp Mawson 2005 Loeb amp Sourirajan 1963) andnow surpass thermal processes in new plant installations (75 of new production ca-pacity) The advent of such membranes with high retention of low-molecular-weightorganic compounds and good physical and chemical stability has enabled RO to beused more widely on a commercial scale RO membrane technology has been devel-oped for both brackish and seawater applications RO membranes however are able toreject monovalent ions (sodium and chloride) Currently RO membranes are made sothat these can reject more than 99 salts (Brehant Bonnelye amp Perez 2003Reverberi amp Gorenflo 2007)

Membrane and distillation processes equally share current desalination productioncapacity worldwide RO has emerged as the leader in future desalination installationsRO will be the key to increasing water supplies for drinking water productionthroughout the world Although wealthy Middle Eastern countries have been able to

130 Advances in Membrane Technologies for Water Treatment

afford distillation processes RO technology can now produce freshwater (fromseawater) at one-half to one-third the cost of distillation (Miller 2003) Brackish waterdesalination is even less expensive than seawater desalination

Membranes have risen to the challenge of supplying desalinated water and continueto perform efficiently and effectively Another membrane process forward osmosis(FO) can be used to desalinate saline water sources at a notably reduced cost Itinvolves the use of a draw solution of aluminum sulfate or ammonium sulfate whichis used to transport water from saline water These draw solutions on chemical treat-ment or heating result in freshwater (Chanukya Patil amp Rastogi 2013 Frank 1972)This new athermal membrane process has been developed as a possible alternative todesalination It employs a semipermeable dense hydrophilic membrane that separatestwo aqueous solutions (feed and osmotic agent solution) with different osmoticpressures The difference in osmotic pressure acts as a driving force An osmoticpressure-driven process operates on the principle of osmotic transport of water acrossa semipermeable hydrophilic membrane from a dilute feed solution into a concentratedosmotic agent or draw solution (Nayak amp Rastogi 2010) Recently FO concentrationis gaining importance for concentrating liquid foods and natural colors (BabuRastogi amp Raghavarao 2006 Bolin amp Salunke 1971 Garcia-Castello Mccutcheonamp Elimelech 2009 Gusti amp Wrolstad 1996 Loeb amp Bloch 1973 MartinettiChildress amp Cath 2009 Popper et al 1966 Rodriguez-Saona Giusti Durst ampWrolstad 2001) generating electricity (Kravath amp Davis 1975) treating wastewater(Holloway Childress Dennett amp Cath 2007) and desalinating seawater(Mccutcheon Mcginnis amp Elimelech 2006)

43 Difference between osmosis RO and FO

Osmosis is the movement of solvent molecules through a selectively permeable mem-brane into a region of higher solute concentration with the aim of equalizing the soluteconcentrations on both sides The net movement of the solvent from a less concen-trated (hypotonic) to a more concentrated (hypertonic) solution tends to reduce the dif-ference in concentrations When a semipermeable membrane separates two solutionswater always diffuses from the solution with the lower osmotic potential to the onewith the higher osmotic potential This diffusion-driven motion of water through amembrane is termed osmosis It is the tendency of fluids to pass through a membraneso that equal concentrations are achieved on both sides (Figure 41(a)) RO is apressure-driven membrane process that entails forcing fluids through a membrane Itis a separation technique that can be used to concentrate or purify liquids without aphase change The RO process uses hydraulic pressure as the driving force for sepa-ration which serves to counteract the osmotic pressure gradient that would otherwisefavor water flux from the permeate to the feed (Figure 41(b)) FO is an osmotic pro-cess that like RO uses a semipermeable membrane to effect separation of water fromdissolved solutes The driving force for this separation is an osmotic pressure gradientsuch that a draw solution of high concentration (relative to that of the feed solution) isused to induce a net flow of water through the membrane into the draw solution thus

Water treatment by reverse and forward osmosis 131

effectively separating the feed water from its solutes FO uses the osmotic pressure dif-ferential (Dp) across the membrane as the driving force for transport of water throughthe membrane rather than the hydraulic pressure differential (similar to RO) The FOprocess results in the concentration of feed solution and the dilution of draw solution(Figure 41(c)) (Cath Childress amp Elimelech 2006 Rastogi amp Nayak 2011)

44 Fundamentals of water treatment by RO

Osmosis is the basis for RO When a semipermeable membrane separates a dilutesolution from a concentrated solution the solvent (water) crosses from the dilute solu-tion side to the concentrated solution side of the membrane to equalize concentrations onboth sides this process is known as osmosis The flow of solvent can be prevented byapplying an opposing hydrostatic pressure to the concentrated solution The magnitudeof the pressure required to completely impede the flow of water is defined as the osmoticpressure In the case of RO a hydrostatic pressure greater than the osmotic pressure isapplied for water to move from a high-solute to a low-solute concentration(Figure 41(b)) It necessitates high-pressure requirements The positive difference inpressure creates a chemical potential difference (concentration gradient) across the mem-brane that drives the liquid through the membrane against the natural direction ofosmosis (the movement of water molecules from an area of high concentration to anarea of low concentration) while the salts are retained and concentrated on the influentsurface of the membrane Some salt passage through the membrane occurs salt passagefor the same membrane increases with the salt concentration and temperature

The RO process requires high operating pressures ranging from 2300 to 3500 kPafor seawater and 100 to 300 kPa for brackish water to overcome the osmotic pressureof feed water (Perry amp Green 1997 Sagle amp Freeman 2004)

The dominant mechanism governing transport through RO membranes can beexplained as solution-diffusion which involves preferential dissolution of solvent

Feed

Feed

Feed

Feed

Wat

er

Wat

er

Wat

er

Dra

w s

olut

ion

(a) (b) (c)

Force( P)

nabla

Figure 41 Migration of water during (a) osmosis (b) reverse osmosis and (c) forward osmosisThe arrows indicate the direction of mass transfer DP is the hydraulic pressureReprinted from Rastogi (in press) with permission of Taylor amp Francis LLC (httpwwwtandfonlinecom)

132 Advances in Membrane Technologies for Water Treatment

(water) in the membrane and its transport through diffusion Water transport across anRO membrane occurs in three separate steps absorption onto the membrane surfacediffusion through the thickness of the membrane and desorption from the permeatesurface of the membrane Once a water molecule has absorbed onto the membranesurface the water concentration gradient (of the water-membrane system) across themembrane causes the water molecules to diffuse down the concentration gradient tothe permeate side of the membrane The water molecule then desorbs from the mem-brane and becomes part of the bulk permeate (Lonsdale Merten amp Riley 1965 Paul2004)

The equation that gives the water flux through a membrane as a function of pressuredifference during RO can be written in a simple form (Mulder 1996 p 298)

Jw frac14 AwethDp DpTHORN (41)

where Aw is the water permeability coefficient Dp is the transmembrane pressure andDp is the difference in the osmotic pressures of feed and permeate

The permeate flux during the course of RO decreases rapidly owing to reversibleand irreversible fouling of the membrane that significantly affects the process effi-ciency (Kwang-Sup Joo-Heon Dong-Ho Seok-Joong amp Soon-Dong 2004) Thepermeate fluxes are primarily affected by the phenomena of concentration polariza-tion (ie solute buildup) and fouling (eg microbial adhesion gel layer formationand solute adhesion) at the membrane surface Fouling is generally caused by thedeposition of colloidal particles inorganic and organic compounds and microbeson the surface of the membrane (Chien-Hwa Lung-Chen Shaik Khaja Chung-Hsin amp Cheng-Fang 2010) It is considered a group of physical chemical and bio-logical effects leading to irreversible loss of membrane permeability (Chien-Hwaet al 2010 Sablani Goosen AL-Belushi amp Wilf 2001) Concentration polariza-tion is mainly limited to the buildup of retained solute ie accumulation of matteron the surface of the membrane It is considered to be reversible and can becontrolled in a membrane module by means of velocity adjustment pulsation(back flush) ultrasound or an electric field (Vladisavljevic Vukosavljevic ampBukvic 2003)

Considering a situation in which a solution consisting of solvent and solute is sub-jected to a pressure-driven membrane process such as RO the solute is preferentiallyretained on the membrane surface whereas solvent permeates through the membraneAs solvent is removed from the feed the difference in the osmotic pressure (Dp)increases which in turn results in a decrease in flux At the same time a concentrationgradient is developed owing to the rejection of solute with the passage of solventthrough the membrane (Figure 42) The solvent flux through the membrane increaseswith an increase in the applied pressure until the concentration of solute on the mem-brane surface reaches a critical concentration which is referred to as the gel concen-tration (CG) Further increases in pressure do not change the solute concentration atthe membrane surface however they result in a thicker and compacted gel layerAt equilibrium the rate of solvent transport through the membrane (flux) can be calcu-lated on the basis of the convective transport of solutes to the membrane surface

Water treatment by reverse and forward osmosis 133

ethJw$CTHORN by the solvent which is equal to the sum of the diffusive back transport of

soluteD$

dCdx

and permeate flow ethJw$CpTHORN ie

Jw$C frac14D

dCdx

thorn Jw$Cp (42)

where D is the diffusion coefficient for solute transport through solvent C is the soluteconcentration retained on the membrane Cp is the solute concentration in permeate (inthe case of RO the solute is completely retained by the membrane ie Cp frac14 0) anddCdx

is the solute concentration gradient

The integration of Eqn (42) with appropriate boundary conditions (x frac14 0 C frac14 CGx frac14 x C frac14 CB) results in the following equation

Jw frac14 D

d$ln

CG

CB

frac14 k$ln

CG

CB

(43)

where d is the thickness of the boundary layer k is mass transfer coefficient CB and CG

are the bulk and gel layer solute concentrations and CGCB

is the concentration polari-zation modulus Equation (43) shows that at this juncture the flux through themembrane is independent of the transmembrane pressure drop or permeability anddepends only on the solute characteristics (D and CG) and boundary layer thickness(d) Concentration polarization is a reversible fluid dynamic phenomenon If CB

reaches CG solutes will start to precipitate or deposit on the membrane forming a gel

Figure 42 Formation of concentration gradient near the surface of the membrane

134 Advances in Membrane Technologies for Water Treatment

layer which leads to the permanent loss of flux known as fouling (Echavarria TorrasPagan amp Ibarz 2011)

45 Conventional and membrane pretreatmentfor RO feed water

The primary goal of any RO pretreatment system is to lower the fouling propensity ofthe water in the RO membrane system Conventional pretreatment typically consists ofchemical additions including acid coagulant and flocculent that prepare the feedwater for granular media filtration (Isaias 2001 Sauvet-Goichon 2007) Acid treat-ment reduces the pH of the feed water (typical pH range 5e7) which increases thesolubility of calcium carbonate the key potential precipitate in many feed waters(Bonnelye et al 2004) Coagulants are typically small positively charged moleculesthat effectively neutralize like charges (on aqueous particulate and colloidal matter)and allow the suspended solids to group together in flocs (large groups of looselybound suspended particles) Inorganic coagulants are commonly iron or aluminumsalts such as ferric chloride or aluminum sulfate whereas organic coagulants are typi-cally cationic low-molecular-weight (lt500000 Da) polymers (ie dimethyldially-lammonium chloride or polyamines) Granular media filtration includes materialssuch as sand anthracite pumice gravel and garnet (Bonnelye et al 2004) often acombination of materials is used in layers in the filtration bed to reduce the feed watersilt density index (Morenski 1992) Cartridge filtration (filter cartridges are usually1e10 mm) acts as a final polishing step to remove larger particles that passed throughmedia filtration in conventional RO pretreatment (Morenski 1992 Petry et al 2007)

Antiscalants are primarily used as pretreatment typically performed after granularmedia filtration either before or after cartridge filtration (Sauvet-Goichon 2007)Disinfection is achieved by adding a strong oxidant such as ozone chlorine (gaschlorine dioxide or sodium hypochlorite) chloramine or potassium permanganate(Morenski 1992)

A new trend in pretreatment has been the movement toward using larger pore-sizemembranes (microfiltration (MF) ultrafiltration (UF) and nanofiltration (NF)) to useRO as a pretreatment to feed water that avoids the passage of colloids and suspendedparticles contributing to RO membrane fouling (Brehant et al 2003) The mem-branes act as a defined barrier between the RO system and any suspended particlesThey can reduce silt density index as well as turbidity of the feed water (Pearce 2007Vedavyasan 2007) MF membranes are an appropriate choice for the removal oflarger particulate matter whereas NF membranes are used to remove dissolved con-taminants as well as particulate and colloidal material UF membranes represent thebest balance between the removal of contaminants and permeate production of theother three membrane types Typical final permeate fluxes for a UF-RO systemwere reported to be in the range of 15e24 Lm2 h (Kamp Kruithof amp Folmer2000) whereas the permeate flux exiting the UF pretreatment stage was within60e150 Lm2 h (Brehant et al 2003)

Water treatment by reverse and forward osmosis 135

Membrane pretreatment reduces the general aging and destruction of RO mem-branes by feed water components membrane replacement and the frequency of chem-ical (acid or base) cleaning However the RO system can be operated at a higherpermeate flux Membrane pretreatment systems are decreasing in capital cost andare becoming more cost-competitive with conventional systems The risk of membranefouling prevents general operation at high permeate flux especially for feed waters withimpurities such as hydrocarbons (oil) and cellular or extracellular material (frombacteria) (Jian Kitanaka Nishijima Baes amp Okada 1998 Williams amp Edyvean1998) Fouling results in membrane damage and flux decline requires membranereplacement every 5e10 years (Pearce 2007)

46 Fundamentals of water treatment by FO

FO can be considered a technique for the recovery of the water from saline water Itemploys an asymmetric semipermeable dense hydrophilic membrane that separatestwo aqueous solutions (feed and draw solution) with different osmotic pressuresThe osmotic pressure gradient is the sole driving force for the transport of water Con-centration polarization is a significant problem in pressure-driven membrane processessuch as RO It reduces permeate flow as a result of buildup of the retained moleculesleading to enhanced osmotic pressure at the membrane surface The FO phenomenonwith a dense symmetric membrane can result in the occurrence of concentration polar-ization on both sides of the membrane The solute is concentrated and diluted on thefeed and permeate sides leading to concentrative and dilutive external concentrationpolarization respectively (Figure 43(a)) The standard flux equation for forward equa-tion is given by the following equation

Jw frac14 Aethpd pf THORN (44)

where pd and pf are the bulk osmotic pressures of draw and feed solutions respec-tively Jw is the water flux and A is the pure water permeability coefficient

The asymmetric membrane employed in the case of FO consists of a dense activemembrane layer (active layer) and a loosely bound support layer (porous support layer)(Figure 43 Nayak amp Rastogi 2010) The membrane can be placed between the feedand the osmotic agent solutions in two different ways such that they feed toward thesupport layer (normal mode) and toward the active layer (reverse mode) which arereferred as modes I (Figure 43(b)) and II (Figure 43(c)) respectively (GrayMccutcheon amp Elimelech 2006 Nayak amp Rastogi 2010)

461 Modeling of flux when feed toward support layer(internal concentration polarization concentrative)

When the feed (05 M NaCl solution) is placed against a porous support layer and adraw solution is kept on the active layer side (mode I) water is diffused into the poroussupport layer and traversed to the draw solution side through the active layer of mem-brane as a result of the osmotic pressure gradient across the membrane The use of

136 Advances in Membrane Technologies for Water Treatment

sodium chloride solution results in buildup of salt within the porous support layer dueto the diffusion of water to the draw solution side Subsequently it results in a signif-icant internal concentration polarization (concentrative) and negligible external con-centration polarization At the same time permeation of water to the draw solutionside results in external concentration polarization (dilutive) But internal concentrationpolarization may not be highly significant Both the internal (concentrative) andexternal (dilutive) concentration polarization phenomena are responsible for the reduc-tion in the effective osmotic driving force The internal concentration polarization oc-curs within the porous support layer and it cannot be lessened by hydrodynamics suchas turbulence (since it is occurring within the pores of the support layer) leading todrastic reduction of effective osmotic driving force (McCutcheon amp Elimelech2007 Tang amp Ng 2008) The extent of external polarization is much less than the in-ternal concentration polarization during forward osmosis when permeate water fluxesare relatively low (Cath et al 2006 McCutcheon et al 2006)

The concentration profile across asymmetric FO membrane for concentrative inter-nal concentration polarization is illustrated in Figure 43(b) Assuming negligibleexternal concentration polarization at the outer surfaces of the membrane the waterand salt flux (Jw Js) across the membrane is given by

Jw frac14 AethDpeffTHORN frac14 Aethpd pf THORN (45)

Figure 43 Mechanism of forward osmosis indicating water transport (a) with a densesymmetric membrane and with asymmetric membrane (b) feed toward the support layer (mode I)and (c) feed toward active layer (mode II) pd and pf are the bulk osmotic pressures of draw andfeed solutions respectively p

d and pf the osmotic pressures on the membrane surface of draw

and feed solutions respectively p0f and p0

d are the osmotic pressures of the feed and drawsolutions on the inside of the active layer within the porous support for concentrative internalconcentration polarization on the feed side and dilutive internal concentration polarization on thedraw side for modes I and II respectively Dp1 Dp2 and Dp3 are the corresponding effectivedriving forces in (a) (b) and (c) situations respectively ECP and ICP refer to external andinternal concentration polarizations respectivelyReprinted from Rastogi (in press) with permission of Taylor amp Francis LLC (httpwwwtandfonlinecom)

Water treatment by reverse and forward osmosis 137

JS frac14 BethC2 C3THORN (46)

where A and B are the water and solute permeation coefficients respectively pd and pf

are the bulk osmotic pressure of draw and feed solutions respectively at the mem-brane surface and the corresponding solute concentrations are C2 and C3 Because pf

is not known this quantity can be obtained by the following analysis provided byMehta and Loeb (1978) The diffusion of solute is considered to be in the oppositedirection of water flux and hence it was taken as negative The salt flow consists oftwo components acting in opposite directions a diffusive part caused by diffusiondown the salt concentration gradient and a convective part caused by bulk flow ofwater through the membrane The salt flux across the porous support layer can thus bewritten as per the following equation

Js frac14 DεdCdx

JwC (47)

where ε and D are the porosity of the substrate and diffusion coefficient of the salt inthe membrane porous substrate respectively The distance x is measured fromthe membraneesolution interface on the porous support layer Substituting the valueof Js from Eqn (42) to Eqn (43) results in the following equation

BethC2 C3THORN frac14 DεdCdx

JwC

Boundary conditions x frac14 0 C frac14 C4 x frac14 st C frac14 C3

(48)

On rearranging

Z frac14 dCdx

frac14 JwC

Dεthorn BethC2 C3THORN

Dε Boundary conditions

x frac14 0 Z1 frac14 JwC4

Dεthorn BethC2 C3THORN

Dε x frac14 st Z2 frac14 JwC3

Dεthorn BethC2 C3THORN

Dε(49)

where t and s are the thickness and tortuosity of the support layer respectivelySolving Eqn (47) with the boundary conditions above yields Eqn (49)Differentiating Eqn (49) with respect to x results in the following equation

dZdx

frac14 JwDε

dCdx

(410)

Integrating Eqn (49) results in the following equation

Jw

ZZ2

Z1

1ZdZ frac14

Zst

0

dx orDε

Jwfrac12ln ZZ1

Z2frac14 st (411)

138 Advances in Membrane Technologies for Water Treatment

or lnJwC3 thorn BethC2 C3THORNJwC4 thorn BethC2 C3THORN frac14 st

DεJw frac14 KDJw (412)

where stDε is defined as a membrane (support and active layer) resistivity (KD) (sm or

dm)

orJwC3 thorn BethC2 C3THORNJwC4 thorn BethC2 C3THORN frac14 expethKDJwTHORN (413)

On rearranging Eqn (413)

C3

C2frac14 B

eKDJw 1

thorn JwC4C2eKDJw

BetheKDJw 1THORN thorn Jwor

1 C3

C2frac14 ethC2 C3THORN

C2frac14

1thorn C4

C2eKDJw

1thorn B

JwetheKDJw 1THORN

(414)

pd pf

pdfrac14

1 p

f

pdeKDJw

1thorn B

JwetheKDJw 1THORN

(415)

Substituting the values of (p2 p3) from Eqn (415) to Eqn (41)

Jw frac14 Apd pf

frac14Ap2

1 p

f

pdeKDJw

1thorn B

JwetheKDJw 1THORN

(416)

The rearrangement of Eqn (416) results in the following equation

Jw frac14

1KD

lnethApd thorn B JwTHORN

Bthorn Apf

(417)

where pd and pf are the bulk osmotic pressures at the draw side and osmotic pressures

on membrane surface at the feed side respectivelyFor low water flux pd and p

f can be replaced with bulk osmotic pressures of drawand feed sides (pd and pf) respectively Hence Eqn (417) becomes

Jw frac14

1KD

ln

Apd thorn B Jw

Bthorn Apf

(418)

The value of KD can be inferred from the plot of Jw versus lnApdthornBJwBthornApf

Water treatment by reverse and forward osmosis 139

462 Modeling of flux when feed is toward active layer(internal concentration polarization dilutive)

When the feed (05-M NaCl solution) is placed against the active layer and the drawsolution on the support layer side the water from the feed is diffused into the activelayer which in turn is diffused to the porous support layer and then to the bulk throughthe boundary layer resulting in dilutive internal concentration polarization on the drawsolution side (Figure 43(c)) The external and internal concentration polarizationstoward the feed side are considered negligible The osmotic solute from the drawsolution may penetrate the porous support layer before flux can occur As water fluxcrosses the active layer and enters into the porous support layer it results in dilutionof the draw solution owing to convection The solute diffuses back to the interiorsurface A steady state is quickly reached but the concentration at the interior surfaceof the active layer is far lower than in the bulk draw solution (Gray et al 2006) Thecombined effect of both the diffusion of water through the active layer and thediffusion of the draw solute into the support layer results in dilutive internal concen-tration polarization The extent of external concentration polarization is negligiblecompared with the internal concentration polarization which has a dominant role ina situation when the draw solution in placed against the support layer (Gray et al2006 Tan amp Ng 2008)

Similar to the analysis provided in the above section for concentrative internal con-centration polarization the equation for the dilutive internal concentration polarizationcan be written as

Jw frac14

1KC

ln

Bthorn Apd

Bthorn ApF thorn Jw

(419)

The value of KC can be inferred from the plot Jw versus ln BthornApdBthornApFthornJw

Constants A (0019 matmday) and B (0023 matmday) refer to the water andsolute permeability coefficients of the active layer of the membrane respectively(Gray et al 2006 Loeb Titelman Korngold amp Freiman 1997) and the valueswere determined as per Eqns (45) and (46) respectively based on the data presentedfor the ammonium bicarbonate draw solution by Achilli et al (2012)

463 Quantitative analysis of internal concentrationpolarization

Studies on the effect of draw solution concentration and temperature on transmem-brane flux in the case of modes I and II indicate that transmembrane flux for mode Iwas higher compared with mode II for all values of the draw solution concentrationAt the same time the transmembrane flux in modes I and II increased with an increasein feed temperature from 30 C to 45 C (Figure 44(a) and (b)) The increase in trans-membrane flux with temperature can be explained using the WilkeeChang equation(Treybal 1982) according to which the diffusion coefficient is proportional to theabsolute temperature divided by the viscosity of the solvent The increase in

140 Advances in Membrane Technologies for Water Treatment

temperature reduces the viscosity of solution and increases the diffusion coefficientswhich results in an increase in transmembrane flux (Holloway et al 2007Mccutcheon amp Elimelech 2006)

The severity of concentration polarizations in modes I and II can be inferred fromthe resistance to diffusion within the membrane porous layer (KD and KC values)

(Figure 44(c) and (d)) The values of Jw were plotted against lnApdthornBJw

BthornApf

and

ln BthornApdBthornApFthornJw

as per Eqns (418) and (419) respectively to determine the values of

KD and KC The relevant values are reported in Figure 44(c) and (d) which indicatesthat the predicted values are in good agreement with the experimental values(R2 gt 090) Higher values indicate a higher internal concentration polarization result-ing in lower flux

The low concentration of solute in the feed solution and draw solution results in ahigher effective driving force in mode I compared with mode II (Dpeff1 gt Dpeff2)hence in this situation mode I is most desirable for desalination to have a higher waterflux than mode II In the case of mode I external concentration polarization on both the

25

25

20

2020

15

15

10

10

05

0500

00

252015100500

25

20

15

10

05

00

25

20

15

10

05

00

25

20

15

10

05

00

00 10 30 40 50

2000 10 30 40 50

(a)

(b) (d)

(c)

Mode IIMode II

Mode I Mode I

Draw solution concentration (M)

Draw solution concentration (M)

Temp (degC) KC (dm)

Temp (degC)

Tran

smem

bran

e flu

xx

10ndash6

(m3 m

2 s)Tr

ansm

embr

ane

flux

x 10

ndash6 (m

3 m2 s)

Tran

smem

bran

e flu

xx

10ndash6

(m3 m

2 s)Tr

ansm

embr

ane

flux

x 10

ndash6 (m

3 m2 s)

KD (dm)30354045

30354045

1692 plusmn 032 1445 plusmn 027

1354 plusmn 0321168 plusmn 0261043 plusmn 012

1478 plusmn 022

1251 plusmn 033 1108 plusmn 018

In((B + Aπd ndashJw)(B + Aπf))

d fIn((B + Aπ )(B + Aπ + Jw))

Figure 44 (a b) Effect of the draw solution concentration at different temperatures on

transmembrane flux (c d) Plot of Jw versus lnBthornApdJw

BthornApF

and Jw versus ln

BthornApdBthornApFthornJw

as per

Eqns (418) and (419) respectively Modes I and II refer to the membrane orientation in whichthe feed was toward the support layer and active layer respectively (A 30 C 35 C- 40 C bull 45 C)Reprinted from Chanukya et al (2013) with permission from Elsevier

Water treatment by reverse and forward osmosis 141

feed and draw solution sides as well as internal concentration polarization on the drawside can be considered insignificant whereas internal concentration polarization(concentrative) toward the feed side will be the only dominant concentration polariza-tion Conversely in the case of mode II internal concentration polarization (dilutive)toward the draw side will be the most dominant concentration polarization which willbe higher because of the higher concentration of draw solution

The orientation of the asymmetric membrane had a significant effect on the perfor-mance of the membrane The feed toward the support layer (mode I) was the bestoption to maximize the flux owing to less concentrative internal concentration polar-ization compared with higher dilutive internal concentration polarization in the othercase when the feed was toward the active layer (mode II) The high agreement betweenthe experimental and predicted values indicated that the proposed model was a good fitand can be used to predict flux at variable conditions

Nayak and Rastogi (2010) and Nayak Valluri and Rastogi (2011) described themechanism of water transport in FO in a situation in which feed solution was a mixtureof low-and high-molecular-weight compounds When the solution of low-molecular-weight compounds was taken as a feed mode I was most desirable However whenthe solution of high-molecular-weight compounds was taken as a feed mode IIgave a higher driving force that in turn led to a higher transmembrane flux Mi andElimelech (2008 2010) also indicated that these high-molecular-weight compoundsmay be deposited within the porous structure of the membrane leading to cake layerformation owing to the lack of shear force as well as hindered back diffusion in theporous structure Fouling of the FO membrane as a result of alginate was reportedto be almost fully reversible after a simple water rinse with no chemical cleaningreagents It was attributed to the less compact formation of the fouling layer owingto the lack of hydraulic pressure Zhao and Zou (2011a b) and Zhao Zou Chuyanget al (2012) demonstrated that internal concentration polarization in the support layerstrongly depended on the physicochemical properties of the solution facing the supportlayer In a situation in which the feed was facing active layer it resulted in a more sta-ble and higher water flux than that of the situation in which support layer was towardthe feed

47 Membranes for FO

Membranes for FO should have high water flux high solute rejection minimumporosity high hydrophilicity reduced fouling and high mechanical strength Thesemembranes are different from standard RO membranes that typically consist of athin active layer (less than 10 mm) and a thick porous support layer Any dense nonpo-rous selectively permeable material commonly used for RO can also be used as amembrane for FO However the presence of a thick support layer results in the occur-rence of concentration polarization within the membrane support structure which mayrequire large osmotic driving forces to sustain adequate water flux (Dova Petrotos ampLazarides 2007ab Gray et al 2006 Mccutcheon Mcginnis amp Elimelech 2005Mcginnis Mccutcheon amp Elimelech 2007)

142 Advances in Membrane Technologies for Water Treatment

A special membrane for FO made of cellulose triacetate was developed by MsHydration Technologies Inc USA (thickness less than 50 mm) (Figure 45(a) and(b)) in which the support layer was embedded in a polyester mesh to provide mechan-ical support (Mccutcheon et al 2005) A scanning electron microscope image of thecross-section of the cellulose acetate polyamide composite and cellulose triacetatemembrane is presented in Figure 46 (Ng Tang amp Wong 2006)

FO membranes can also be made as hydration bags that can be used to recover water(Figure 47) They are double-lined bags The internal bag is made of a FO membraneand is filled with draw solution (eg flavored sucrose) and the external bag is a sealedplastic bag Upon immersing the bag in an aqueous solution water diffuses into the bagbecause of the osmotic pressure difference and slowly dilutes the draw solution Theconcept of a hydration bag was developed for military recreational and emergencyrelief situations in which reliable drinking water was scarce or not available Thehydration bag is one of the few commercial applications of FO (Cath et al 2006)

(a)

(b)

Figure 45 Scanning electron microscope images of cross-sections of cellulosic forwardosmosis membrane (CA) A polyester mesh is embedded within the polymer material formechanical support The membrane thickness is less than 50 mmReprinted from Garcia-Castello et al (2009) and Mccutcheon et al (2005) with permissionfrom Elsevier

Water treatment by reverse and forward osmosis 143

Figure 46 Scanning electron microscope images of the cross-section of (a) cellulose acetate(CA) membrane (b) polyamide composite (AD) membrane (c) forward osmosis (FO)membrane and (d) FO membrane at higher resolution where 1 is the dense selective layer and2 is the support layerReprinted with permission from Ng et al (2006) Copyright 2006 American Chemical Society

Figure 47 Water purification hydration bagReprinted from Cath et al (2006) with permission from Elsevier

144 Advances in Membrane Technologies for Water Treatment

With a view to reducing internal concentration polarization Wang Ong et al(2010) designed a cellulose acetate FO membrane composed of a highly poroussublayer sandwiched between two selective skin layers by using the phase inversiontechnique It prevented salt and other solutes in the draw solution from penetratinginto the membrane porous support It also resulted in higher water flux and lowersalt transport Zhang et al (2010) developed a double dense membrane structure usingphase inversion of cellulose acetate that produced low salt leakage and resulted in lessinternal concentration polarization in the FO process

A novel dual-layer hollow-fiber NF membrane suitable for FO using co-extrusiontechnology was developed consisting of an ultra-thin selective skin (around 10 mm)with a fully open-cell water channels underneath and a micro-porous sponge-like sup-port structure which could achieve high throughput and high salt rejection (YangWang amp Chung 2009ab) Later Wang et al (2010) fabricated a polyethersulfonethin-film composite hollow-fiber membrane for FO using a dry-jet wet spinning pro-cess with an ultra-thin RO-like skin layer (300e600 nm) on either surface of a poroushollow-fiber substrate by interfacial polymerization The active layers presented excel-lent intrinsic separation properties with a hydrophilic rejection layer and good mechan-ical strength A high-flux and high-rejection FO membrane for water reuse andseawater desalination was developed by fabricating polybenzimidazole NF hollow-fiber membranes with a thin wall and desired pore size by nonsolvent induced phaseinversion which was chemically modified by cross-linking with p-xylylene dichloride(Wang Yang Chung amp Rajagopalan 2009) Cross-linking finely tuned the mean poresize and enhanced the salt selectivity Furthermore Su Yang Teo and Chung (2010)developed cellulose acetate NF hollow-fiber membranes suitable for FO processes bysubjecting them to a two-step heat treatment (60 C 60 min and 95 C 20 min) whicheffectively shrank the membrane pores on the membrane surface with a denser outerskin layer (mean pore radius reduced from 063 to 030 nm) The resultant fiber hasa high rejection to NaCl and MgCl2 and low pure water permeability Chou et al(2010) developed a FO hollow-fiber membrane fabricated by the dry-jet wet spinningprocess The outer UF skin was made by increasing the air gap in the spinning processand the inner RO skin layer was made by interfacial polymerization using anm-phenylenediamine aqueous solution and trimesoyl chloride hexane solution Thedeveloped membrane showed excellent intrinsic separation properties with a waterflux of 426 Lm2h Yip Tiraferri Phillip Schiffman and Elimelech (2010) made ahigh-performance thin-film composite membrane consisting of a selective polyamideactive layer formed by interfacial polymerization on top of a polysulfone support layerfabricated by phase separation onto a thin (40 mm) polyester nonwoven fabric

Jia Li Wang Wu and Hu (2010) demonstrated the suitability of carbon nanotubemembranes for seawater desalination using FO The membrane could achieve theoptimal salt rejection property but also the largest water flux which broke the limitof the tradeoff effect between selectivity and permeability existing in traditional liquidseparation membranes The antifouling ability and good mechanical strength renderedit more suitable for FO According to a rough estimation carbon nanotube mem-branes can achieve a higher water flux far in excess of existing commercial FOmembranes

Water treatment by reverse and forward osmosis 145

Qiu Qi and Tang (2011) successfully fabricated FO membranes using layer-by-layer assembly of polyallylamine hydrochloride and polysodium 4-styrene-sulfonate on a porous polyacrylonitrile substrate The chemical cross-linking oflayer-by-layer polyelectrolyte layers was performed with glutaraldehyde The cross-linked and non-cross-linked membranes both had relatively high water permeabilityHowever the cross-linked membranes showed better MgCl2 rejection which clearlydemonstrated the potential of layer-by-layer membranes for high-flux FO applicationsLater Qiu Setiawan Wang Tang and Fane (2012) fabricated high-performance flat-sheet FO membranes using polyamide-imide materials via phase inversion followedby polyelectrolyte polyethyleneimine after treatment to form an NF-like rejection layerwith positive charges Polyamide-imide micro-porous substrate was embedded with awoven fabric the enhanced mechanical strength of the membrane made it possible toreduce the thickness of the substrate to 55 mm and the resultant membranes was able toreach a water flux of 2965 and 192 Lm2h when the active layer was facing draw orfeed solutions respectively

48 Desalination by FO

Research has been reported on the desalination of seawater by FO FO can be used effi-ciently and effectively to desalinate water FO using semipermeable polymeric mem-branes may be a viable alternative to RO as a lower-cost and more environmentallyfriendly desalination technology

Frank (1972) described a method of FO using a solution of aluminum sulfate as anosmotic agent which upon treatment with calcium hydroxide resulted in a precipitateof aluminum hydroxide and calcium sulfate which was removed by standard methodsleaving freshwater Mccutcheon et al (2006) reported FO desalination as a lower-costand more environmentally friendly technology The driving force was provided by adraw solution composed of highly soluble gases ammonia and carbon dioxide Waterfluxes ranging from 36 to 360 Lm2h for a wide range of draw and feed solution con-centrations were reported Ammonium bicarbonate was used as a draw solution toextract water from saline feed water by Mccutcheon Mcginnis and Elimelech(2009) and Chanukya et al (2013) in a FO desalination process High osmotic pres-sures generated by the highly soluble ammonium bicarbonate draw solute yieldedhigh water fluxes leading to high feed water recoveries The ammonium bicarbonatesolution was used as an osmotic solution (Jung et al 2011 Mccutcheon et al2005) that can be decomposed into ammonia and carbon dioxide gases at about60 C The water transferred from the feed side (seawater) to the osmotic solutioncan be obtained by distillation methods (Cath et al 2006 Ng Tang amp Wong2006) and the separated gases can then be recycled to use as a draw solution again(Jung et al 2011) Mcginnis and Elimelech (2007) presented a schematic diagramof the ammonia carbon dioxide FO desalination process to recover freshwater(Figure 48) Similarly Low (2009) studied the performance of FO with respect todifferent ammoniaecarbon dioxide draw solutions and membranes The internalconcentration polarization resulted in lowering of the flux The draw solution used

146 Advances in Membrane Technologies for Water Treatment

for desalination using FO should be highly soluble highly recoverable nontoxicnonreactive with membranes easily separable from water and economically feasible

Kravath and Davis (1975) described a process of seawater desalination by FOacross a cellulose acetate membrane using glucose as the draw solute Upon dilutionsalinity was reduced to a level where ingestion would be possible for short-term con-sumption The performance of flat-sheet cellulose acetate membranes was reported tobe poor in terms of salt rejection Stache (1989) used a semipermeable membrane bagfilled with concentrated fructose solution to desalinate small volumes of seawaterwhile simultaneously creating a nutritious drink Yaeli (1992) used a concentratedglucose solution as a draw solution and water was extracted from seawater by osmosisThe diluted glucose solution was fed to an RO unit in which a low-pressure RO mem-brane separated potable water from the glucose draw solution

An integrated FO process consisting of an RO process to generate potable waterwas proposed FO was used to generate significant hydraulic pressure used to drivingthe RO process in which it could separate salt from seawater to generate potable waterfrom water with a high salt content (Lampi Beaudry amp Herron 2007) BamagaYokochi and Beaudry (2009) designed an integrated desalination unit consisting ofa closed FO and RO process in which RO brine was used as the osmotic draw solutionand thus the chemical energy stored in the RO brine was recovered and used by the FOmembrane process Also Choi et al (2009 2010) investigated systems combining FOand RO for seawater desalination Pilot-scale combined systems with FO resulted inhigher recovery with higher quality and fluxes than conventional RO-based desalina-tion systems Similarly Valladares Yangali Li and Amy (2011) focused on rejecting13 selected micropollutants employing a clean or fouled FO membrane using Red Seawater as a draw solution The resulting effluent was then desalinated at low pressurewith an RO membrane to produce a high-quality permeate Tan and Ng (2010) pro-posed a hybrid FOeNF process for seawater desalination The process achievedgood-quality product water that met the recommended drinking water total dissolvedsolids guideline (500 mgL) Zhao Zou and Mulcahy (2012) designed a hybrid

Salinewater

Membrane

Product water

Brine

DrawsolutionNH3CO2

Soluterecovery system

Figure 48 Schematic diagram of the ammoniaecarbon dioxide forward osmosis desalinationprocessReprinted from Mcginnes and Elimelech (2007) with permission from Elsevier

Water treatment by reverse and forward osmosis 147

FOeNF system designed for brackish water desalination and compared it with a stand-alone RO process Lay et al (2010) examined possible factors for the slower decline offlux in the FO process The transmission of draw solutes from the draw solution intothe feed had significant effect on performance Yangali Li Valladares Li and Amy(2011) indicated that FO coupled with low-pressure RO used for indirect desalinationconsumed only half of the energy used for high-pressure seawater RO desalination andproduced good-quality water extracted from the impaired feed water A cost analysisrevealed that FO is a viable and promising technology

A comparison of vacuum-enhanced direct contact membrane distillation(VEDCMD) and FO for the desalination of brackish water indicated that water recov-ery in FO was higher (90) than with VEDCMD (81) (Martinetti et al 2009) Lingand Chung (2011) developed a potentially sustainable integrated FOeUF system forwater reuse During FO water was transferred from the salt solution to the draw solu-tion (containing super hydrophilic nanoparticles) which was regenerated from thedraw solution using UF

49 Conclusion

Membrane processes for water desalination are becoming increasingly interesting Theyallow improvements in quality enhanced process efficiency and profitability Theexpanding capabilities of membrane processes will certainly continue to benefit the in-dustry in future to obtain the required product quality purity yield and throughputalong with economic viability The use of RO and FO on an industrial scale will beeven more lucrative in the future if membranes with high selectivity improved fluxrobustness and greater chemical and mechanical stability are developed

List of symbols

A or Aw Water permeability coefficientB Solute permeation coefficientsCB Bulk layer solute concentrationCG Gel layer solute concentrationC Solute concentration retained on membraneCp Solute concentration in permeateD Diffusion coefficient for solute transport through solventdCdx

Solute concentration gradient

K Mass transfer coefficientpd and pf Bulk osmotic pressures of draw and feed solutionsJw and Js Water and salt fluxeskd and kf Mass transfer coefficients on draw and feed solution sidesDp Difference in the osmotic pressures of feed and permeateDp Transmembrane pressureD Thickness of the boundary layerε Porosity of the substrate

148 Advances in Membrane Technologies for Water Treatment

x Distance measured from membraneesolution interface on porous support layert Thickness of the support layers Tortuosity of the support layer

Abbreviations

TDS Total dissolved solidsRO Reverse osmosisFO Forward osmosisUF UltrafiltrationMF MicrofiltrationNF Nanofiltration

References

Achilli A Cath T Y amp Childress A E (2010) Selection of inorganic-based draw solutionsfor forward osmosis applications Journal of Membrane Science 364 233e241

Babu B R Rastogi N K amp Raghavarao K S M S (2006) Effect of process parameter ontransmembrane flux during direct osmosis Journal of Membrane Science 280 185e194

Bamaga O A Yokochi A amp Beaudry E G (2009) Application of forward osmosisin pretreatment of seawater for small reverse osmosis desalination units Desalination andWater Treatment 5 183e191

Bolin H R amp Salunke D K (1971) Physicochemical and volatile flavor changes occurringin fruit juices during concentration and foam-mat drying Journal of Food Science 36665e668

Bonnelye V Sanz M A Durand J P Plasse L Gueguen F amp Mazounie P (2004)Reverse osmosis on open intake seawater Pre-treatment strategy Desalination 167191e200

Brehant A Bonnelye V amp Perez M (2003) Assessment of ultrafiltration as a pretreatmentof reverse osmosis membranes for surface seawater desalination Water Science andTechnology Water Supply 3(5e6) 437e445

Cath T Y Childress A E amp Elimelech M (2006) Forward osmosis Principles applica-tions and recent developments Journal of Membrane Science 281 70e87

Chanukya B S Patil S amp Rastogi N K (2013) Influence of concentration polarization onflux behavior in forward osmosis during desalination using ammonium bicarbonateDesalination 312 39e44

Chien-Hwa Y Lung-Chen F Shaik Khaja L Chung-Hsin W amp Cheng-Fang L (2010)Enzymatic treatment for controlling irreversible membrane fouling in cross-flow humicacid-fed ultrafiltration Journal of Hazardous Materials 177 1153e1158

Choi Y J Choi J S Oh H J Lee S Yang D R amp Kim J H (2009) Toward a combinedsystem of forward osmosis and reverse osmosis for seawater desalination Desalination247 239e246

Choi J S Kim H Lee S Hwang T M Oh H Yang D R et al (2010) Theoreticalinvestigation of hybrid desalination system combining reverse osmosis and forwardosmosis Desalination and Water Treatment 15 114e120

Water treatment by reverse and forward osmosis 149

Chou S Shi L Wang R Tang C Y Qiu C amp Fane A G (2010) Characteristics andpotential applications of a novel forward osmosis hollow fiber membrane Desalination261 365e372

Dova M I Petrotos K B amp Lazarides H N (2007a) On the direct osmotic concentration ofliquid foods Part I Impact of process parameters on process performance Journal of FoodEngineering 78 422e430

Dova M I Petrotos K B amp Lazarides H N (2007b) On the direct osmotic concentration ofliquid foods Part II Development of a generalized model Journal of Food Engineering78 431e437

Drsquosouza N amp Mawson A J (2005) Membrane cleaning in the dairy industry A reviewCritical Reviews in Food Science and Nutrition 45(2) 125e134

Echavarria A Torras P C Pagan J amp Ibarz A (2011) Fruit juice processing and membranetechnology application Food Engineering Reviews 3 136e158

Focazio M J Kolpin D W Barnes K K Furlong E T Meyer M T Zaugg S D et al(2008) A national reconnaissance for pharmaceuticals and other organic wastewatercontaminants in the United States e (II) untreated drinking water sources Science of theTotal Environment 402(2e3) 201e216

Frank B S (1972) Desalination of sea water US Patent No 3670897 WI USAFritzmann C Lowenberg J Wintgens T amp Melin T (2007) State of-the-art of reverse

osmosis desalination Desalination 216 1e76Gaid K amp Treal Y (2007) Reverse osmosis desalination The experience of Veacute olia water

Desalination 203 1e14 (original language French)Garcia-Castello E M Mccutcheon J R amp Elimelech M (2009) Performance evaluation of

sucrose concentration using forward osmosis Journal of Membrane Science 338 61e66Gleick P H (1996) In S H Schneider (Ed) Water resources in encyclopedia of climate and

weather (Vol 2 pp 817e823) New York University PressGleick P H (2006) The worldrsquos water 2006e2007 the biennial report on freshwater

resources Chicago IL Island PressGray G T Mccutcheon J R amp Elimelech M (2006) Internal concentration polarization in

forward osmosis Role of membrane orientation Desalination 197 1e8Greenlee L F Lawler D F Freeman B D Marrot B amp Moulin P (2009) Reverse

osmosis desalination Water sources technology and todayrsquos challenges Water Research43 2317e2348

Gusti M M amp Wrolstad R E (1996) Radish anthocyanin extract as a natural red colorantfrom maraschino cherries Journal of Food Science 61 688e694

Henthorne L (2003) Desalination today Southwest Hydrology 12e13Holloway R W Childress A E Dennett K E amp Cath T Y (2007) Forward osmosis for

concentration of anaerobic digester centrate Water Research 41 4005e4014Isaias N P (2001) Experience in reverse osmosis pretreatment Desalination 139 57e64Jia Y X Li H L Wang M Wu L Y amp Hu Y D (2010) Carbon nanotube Possible

candidate for forward osmosis Separation and Purification Technology 75 55e60Jian W Kitanaka A Nishijima W Baes A U amp Okada M (1998) Removal of oil

pollutants in seawater as pretreatment of reverse osmosis desalination process WaterResearch 33(8) 1857e1863

Jung D H Lee J Kim D Y Lee Y G Park M Lee S et al (2011) Simulation offorward osmosis membrane process Effect of membrane orientation and flow direction offeed and draw solutions Desalination 277 83e91

Kamp P C Kruithof J C amp Folmer H C (2000) UFRO treatment plant Heemskerk Fromchallenge to full scale application Desalination 131 27e35

150 Advances in Membrane Technologies for Water Treatment

Kravath R E amp Davis J A (1975) Desalination of seawater by direct osmosis Desalination16 151e155

Kwang-Sup Y Joo-Heon H Dong-Ho B Seok-Joong K amp Soon-Dong K (2004)Effective clarifying process of reconstituted apple juice using membrane filtration withfilter-aid pretreatment Journal of Membrane Science 228 179e186

Lampi K Beaudry E amp Herron J (2007) Forward osmosis pressurized device and processfor generating potable water US Patent No 7303674 B2 Arizona USA

Lay W C L Chong T H Tang C Y Fane A G Zhang J amp Liu Y (2010) Foulingpropensity of forward osmosis Investigation of the slower flux decline phenomenonWaterScience and Technology 61 927e936

Ling M M amp Chung T S (2011) Desalination process using super hydrophilic nanoparticlesvia forward osmosis integrated with ultrafiltration regeneration Desalination 278194e202

Loeb S amp Bloch M R (1973) Counter current flow osmotic processes for the productionof solutions having a high osmotic pressure Desalination 13 207e215

Loeb S amp Sourirajan S (1963) Seawater dimineralization by means of an osmotic membraneAdvances in Chemistry Series 38 117e132

Loeb S Titelman L Korngold E amp Freiman J (1997) Effect of porous support fabric onosmosis through a Loeb-Sourirajan asymmetric membrane Journal of Membrane Science129 243e249

Lonsdale H K Merten U amp Riley R L (1965) Transport properties of cellulose acetateosmotic membranes Journal of Applied Polymer Science 9 1341e1362

Low S C (2009) Preliminary studies of seawater desalination using forward osmosisDesalination and Water Treatment 7 41e46

Martinetti C R Childress A E amp Cath T Y (2009) High recovery of concentrated RObrines using forward osmosis and membrane distillation Journal of Membrane Science331 31e39

Mccutcheon J R amp Elimelech M (2006) Influence of concentrative and dilutive concen-tration polarization on flux behavior in forward osmosis Journal of Membrane Science284 237e247

Mccutcheon J R amp Elimelech M (2007) Modeling water flux in forward osmosis Impli-cations for improved membrane design AIChE Journal 53 1736e1744

Mccutcheon J R Mcginnis R L amp Elimelech M (2005) A novel ammoniaecarbon dioxideforward (direct) osmosis desalination process Desalination 174 1e11

Mccutcheon J R Mcginnis R L amp Elimelech M (2006) Desalination by ammonia-carbondioxide forward osmosis Influence of draw and feed solution concentrations on processperformance Journal of Membrane Science 278 114e123

Mccutcheon J R Mcginnis R L amp Elimelech M (2009) A novel ammonia-carbon dioxideforward (direct) osmosis desalination process Desalination 174 1e11

McGinnis R L amp Elimelech M (2007) Energy requirements of ammoniaecarbon dioxideforward osmosis desalination Desalination 207 370e382

Mcginnis R L Mccutcheon J R amp Elimelech M (2007) A novel ammonia-carbon dioxideosmotic heat engine for power generation Journal of Membrane Science 305 13e19

Mehta G D amp Loeb S (1978) Internal polarization in the porous substructure of asemi-permeable membrane under pressure-retarded osmosis Journal of MembraneScience 4 261

Mickley M C (2001) Membrane concentrate disposal Practices and regulation Report No69 US Department of the Interior Bureau of Reclamation Boulder CO Mickley ampAssociates

Water treatment by reverse and forward osmosis 151

Mi B amp Elimelech M (2008) Chemical and physical aspects of organic fouling of forwardosmosis membranes Journal of Membrane Science 320 292e302

Mi B amp Elimelech M (2010) Organic fouling of forward osmosis membranes Foulingreversibility and cleaning without chemical reagents Journal of Membrane Science 348144e151

Miller J E (2003) Review of water resources and desalination technologies Sandia NationalLaboratories Available from httpwwwprodsandiagovcgi-bintechlibaccess-controlpl2003030800pdf Retrieved on 05012015

Morenski F (1992) Current pretreatment requirements for reverse osmosis membrane appli-cations In Official proceedings of the 53rd international water conference (pp 325e330)

Mulder M (1996) Basic principles of membrane technology The Netherlands KluwerAcademic Publisher

Nayak C A amp Rastogi N K (2010) Forward osmosis for concentration of anthocyanin fromKokum (Garcinia indica Choisy) Separation and Purification Technology 71 144e151

Nayak C A Valluri S S amp Rastogi N K (2011) Effect of high or low molecular weight ofcomponents of feed on transmembrane flux during forward osmosis Journal of FoodEngineering 106 48e52

Ng H Y Tang W amp Wong W S (2006) Performance of forward (direct) osmosis processMembrane structure and transport phenomenon Environmental Science and Technology40 2408e2413

Paul D R (2004) Reformulation of the solution-diffusion theory of reverse osmosis Journalof Membrane Science 241 371e386

Pearce G K (2007) The case for UFMF pretreatment to RO in seawater applicationsDesalination 203 285e295

Perry R H amp Green D W (Eds) (1997) Perryrsquos chemical engineersrsquo handbook New YorkMcGraw Hill

Petry M Sanz M A Langlais C Bonnelye V Durand J P Guevara D et al (2007)The El Coloso (Chile) reverse osmosis plant Desalination 203 141e152

Popper K Camirand W M Nury F amp Stanley W L (1966) Dialyzer concentratesbeverages Food Engineering 38 102e104

Qiu C Qi S amp Tang C Y (2011) Synthesis of high flux forward osmosis membranesby chemically crosslinked layer-by-layer polyelectrolytes Journal of Membrane Science381 74e80

Qiu C Setiawan L Wang R Tang C Y amp Fane A G (2012) High performance flat sheetforward osmosis membrane with an NF-like selective layer on a woven fabric embeddedsubstrate Desalination 287 266e270

Rastogi N K Opportunities and challenges in application of forward osmosis in foodprocessing Critical Reviews in Food Science and Nutrition (in press)

Rastogi N K amp Nayak C A (2011) Membranes for direct osmosis In A Basile ampS P Nunes (Eds) Advanced membrane science and technology for sustainable energyand environmental applications (pp 680e717) Cambridge UK Woodhead Publisher

Reverberi F amp Gorenflo A (2007) Three year operational experience of a spiral-woundSWRO system with a high fouling potential feed water Desalination 203 100e106

Rodriguez-Saona L E Giusti M M Durst R W amp Wrolstad R E (2001) Developmentand process optimization of red radish concentrate extract as potential natural red colourantJournal of Food Processing Preservation 25 165e182

Sablani S Goosen M AL-Belushi R amp Wilf M (2001) Concentration polarization inultrafiltration and reverse osmosis A critical review Desalination 141(3) 269e289

152 Advances in Membrane Technologies for Water Treatment

Sagle A amp Freeman B (2004) Fundamentals of membranes for water treatment InJ A Arroyo (Ed) The future of desalination in Texas (vol II pp 137e153) AustinTX Texas Water Development Board

Sandia (2003) Desalination and water purification Roadmap e a report of the executivecommittee DWPR Program Report 95 US Department of the Interior Bureau ofReclamation and Sandia National Laboratories Available from httpwrrinmsuedutbndrcroadmapreportpdf (accessed 260814)

Sauvet-Goichon B (2007) Ashkelon desalination plante a successful challenge Desalination203 75e81

Stache K (1989) Apparatus for transforming sea water brackish water polluted water or thelike into a nutritious drink by means of osmosis US Patent No 4879030

Su J Yang Q Teo J F amp Chung T S (2010) Cellulose acetate nanofiltration hollow fibermembranes for forward osmosis processes Journal of Membrane Science 355 36e44

Tan C H amp Ng H Y (2008) Modified models to predict flux behavior in forward osmosis inconsideration of external and internal concentration polarizations Journal of MembraneScience 324 209e219

Tan C H amp Ng H Y (2010) A novel hybrid forward osmosisenanofiltration (FO-NF)process for seawater desalination Draw solution selection and system configurationDesalination and Water Treatment 13 356e361

Tang W amp Ng H Y (2008) Concentration of brine by forward osmosis Performance andinfluence of membrane structure Desalination 224 143e153

Treybal R E (1982) Mass transfer operations (3rd ed) New Delhi McGraw-Hill ChemicalEngineering Series

Valladares L R Yangali Q V Li Z amp Amy G (2011) Rejection of micropollutants byclean and fouled forward osmosis membrane Water Research 45 6737e6744

Van der Bruggen B amp Vandecasteele C (2002) Distillation vs membrane filtration Over-view of process evolutions in seawater desalination Desalination 143 207e218

Vedavyasan C V (2007) Pretreatment trends e and overview Desalination 203 296e299Vladisavljevic G T Vukosavljevic P amp Bukvic B (2003) Permeate flux and fouling

resistance in ultrafiltration of depectinized apple juice using ceramic membranes Journal ofFood Engineering 60 241e247

Wang K Y Ong R C amp Chung T S (2010) Double-skinned forward osmosis membranesfor reducing internal concentration polarization within the porous sublayer IndustrialEngineering and Chemistry Research 49 4824e4831

Wang R Shi L Tang C Y Chou S Qiu C amp Fane A G (2010) Characterization ofnovel forward osmosis hollow fiber membranes Journal of Membrane Science 355158e167

Wang K Y Yang Q Chung T S amp Rajagopalan R (2009) Enhanced forward osmosisfrom chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membraneswith a thin wall Chemical Engineering Science 64 1577e1584

Williams C J amp Edyvean R G (1998) An investigation of the biological fouling in thefiltration of seawater Water Science and Technology 38(8e9) 309e316

Xu J Ruan G Chu X Yao Y Su B amp Gao C (2007) A pilot study of UF pretreatmentwithout any chemicals for SWRO desalination in China Desalination 207 216e226

Yaeli J (1992) Method and apparatus for processing liquid solutions of suspensions partic-ularly useful in the desalination of saline water US Patent No 5098575

Yang Q Wang K Y amp Chung T S (2009a) A novel dual-layer forward osmosis membranefor protein enrichment and concentration Separation and Purification Technology 69269e274

Water treatment by reverse and forward osmosis 153

Yang Q Wang K Y amp Chung T S (2009b) Dual-Layer hollow fibers with enhanced fluxas novel forward osmosis membranes for water production Environmental Science andTechnology 43 2800e2805

Yangali Q V Li Z Valladares R Li Q amp Amy G (2011) Indirect desalination of RedSea water with forward osmosis and low pressure reverse osmosis for water reuseDesalination 280 160e166

Yip N Y Tiraferri A Phillip Schiffman J amp Elimelech M (2010) High performancethin-film composite forward osmosis membrane Environmental Science and Technology44 3812e3818

Zhang S Wang K Y Chung T S Chen H Jean Y C amp Amy G (2010) Well-constructed cellulose acetate membranes for forward osmosis Minimized internalconcentration polarization with an ultra-thin selective layer Journal of Membrane Science360 522e535

Zhao S amp Zou L (2011a) Relating solution physicochemical properties to internalconcentration polarization in forward osmosis Journal of Membrane Science 379459e467

Zhao S amp Zou L (2011b) Effects of working temperature on separation performancemembrane scaling and cleaning in forward osmosis desalination Desalination 278157e164

Zhao S Zou L Chuyang T Y amp Mulcahy D (2012) Recent developments in forwardosmosis Opportunities and challenges Journal of Membrane Science 396 1e21

Zhao S Zou L amp Mulcahy D (2012) Brackish water desalination by a hybrid forwardosmosis-nanofiltration system using divalent draw solute Desalination 284 175e181

154 Advances in Membrane Technologies for Water Treatment

Membrane bioreactors for watertreatment 5SA Deowan SI Bouhadjar J HoinkisInstitute of Applied Research (IAF) Karlsruhe University of Applied SciencesKarlsruhe Germany

51 Introduction

Water is another synonym of life According to the World Health Organization themost dangerous threat to the health of mankind emerging within the next few years ispolluted water In underdeveloped countries the shortage of clean freshwater will bethe most important cause of death for children under 5 years The low quantities offreshwater for industrial agricultural and municipal use have to be well preserved byefficient sustainable and cost-effective technologies Water contaminated fromindustry and agriculture with heavy metal ions pesticides organic compoundsendocrine disruptive compounds nutrients (phosphates nitrates and nitrites) hasto be efficiently treated to protect humans from being intoxicated with these com-pounds or with bacteria Furthermore incidental sludge from industrial wastewatertreatment facilities is commonly highly contaminated with toxic compounds(BioNexGen 2013)

Clean water as a basis for health and good living conditions is too far out of reachfor most of the world population Thus neither sustainable consumption nor reinforce-ment of governmental regulations is an effective driver to force the industry to adoptsustainability policies Although polluted water and water shortages demand sustain-able water use and recycling of wastewater the barriers are high for adopt them(BioNexGen 2013)

Water recycling is widely accepted as a sustainable option to respond to the generalincrease in water shortages and the demand for freshwater and for environmentalprotection Water recycling is commonly seen as one of the main options to providea remedy for water shortage caused by the increase in the demand for water anddraughts as well as a response to some economical and environmental drivers Themain options for wastewater recycling are industrial irrigation aquifer rechargeand urban reuse (Pidou 2006)

Membrane bioreactor (MBR) technology is recognized as a promising technologyto provide water with reliable quality for reuse Today MBRs are robust simple tooperate and even more affordable They take up little space need modest technicalsupport and can remove contaminants in one step This makes it practical to providesafely reusable water for nonpotable use

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400005-8Copyright copy 2015 Elsevier Ltd All rights reserved

52 Fundamentals

MBR technology is a combination of the conventional biological sludge process awastewater treatment process characterized by a suspended growth of biomass anda microfiltration (MF) or ultrafiltration (UF) membrane system (Judd 2011) Thebiological unit is responsible for the biodegradation of waste compounds and themembrane module for the physical separation of treated water from the mixed liquorThe pore diametre of the membranes is in the range between 001 and 01 mm so thatparticulates and bacteria can be kept out of permeate and the membrane systemreplaces the traditional gravity sedimentation unit (clarifier) in the biological sludgeprocess Hence MBR offers the advantage of higher product water quality andlow footprint Because of its advantages MBR technology has great potential inwide-ranging applications including municipal and industrial wastewater treatmentand process water recycling By 2006 around 100 municipal full-scale plants(gt500 population equivalent) and around 300 industrial large-scale plants (gt20 m3day) were in operation in Europe (Lesjean amp Huisjeslow 2008) MBR installation ca-pacity grew in 2007 but declined in 2008 and 2009 The market was affected by lowerindustrial spending because of the economic downturn However there was an in-crease in demand for large plants during the past 2e3 years Installations of MBRincreased significantly in the years of 2010 and early 2011 (GIA 2013)

The main industrial applications are in the food and beverage chemical pharma-ceutical and cosmetics and textile industries as well as in laundries The technicalfeasibility of this technology has been demonstrated through a large number of small-and large-scale applications

521 MBR configurations

According to MBR configurations both aerobic and anaerobic MBRs can be dividedinto two classes as side-stream MBR (sMBR) and submerged or immersed MBR(iMBR) (Figure 51)

In side-stream MBRs the membrane module is placed outside the MBR Thesludge from the MBR is pumped into the membrane module which creates cross-flow at the membrane surface and thus permeate is generated The concentratedsludge rejected by the membrane is recycled to the MBR This is a pressure-drivenmembrane filtration process In the early development of stream MBRs both thetransmembrane pressure (TMP) and cross-flow velocity were generated by the recir-culation pump However a few modifications were made to reduce the high-energyconsumption associated with the side-stream configuration Therefore a suctionpump was added to the recirculation pump on the permeate side which increasedoperation flexibility and decreased the cross-flow rate and energy consumption(Shimizu Okuno Uryu Ohtsubo amp Watanabe 1996) The latest side-stream MBRseven introduced air flow into the membrane module which intensified turbulenceon the feed side of the membrane and reduced the fouling and operational costs(Jiang 2007)

156 Advances in Membrane Technologies for Water Treatment

In submerged MBRs the membrane module is directly submerged in the reactor Asuction or vacuum pump is needed to create a TMP difference for permeate produc-tion In this case no circulation pump is needed because cross-flow is created by aera-tion This concept was first developed by Yamamoto Hiasa Mahmood and Matsuo(1989) to reduce energy consumption compared with side-stream MBR configurationIn some cases (eg MF membrane and very low filtration fluxes) the permeate side isplaced in a lower position and gravity itself is the only driving force for the filtration(Ueda amp Hata 1999)

Table 51 compares the side-stream and submerged MBRs The submerged MBRhas a simpler configuration because it needs less equipment The coarse bubbleaeration in the membrane tank is multifunctional In addition to membrane fouling con-trol it supplies oxygen to the biological process (although the efficiency of oxygen useis low) The biggest advantage of submerged over side-stream configuration is energysavings using coarse bubble aeration instead of the high-rate recirculation pump in side-stream MBRs The capillary and hollow-fibre membranes used in many submergedMBRs have high packing density and low cost which make it feasible to use moremembranes However typical tubular membranes used in side-stream MBRs havelow packing density and are more expensive Gander Jefferson and Judd (2000)reviewed four side-stream and four submerged MBR systems and concluded thatside-stream MBRs have higher total energy cost by up to two orders of magnitudemainly owing to the high recycle flow velocity (1e3 ms) and head loss within themembrane module In addition the submerged MBRs experienced fouling and couldbe cleaned more easily than the side-stream MBRs (Gander et al 2000)

However side-stream MBRs have the advantages of more robust physicalstrength and more flexible cross-flow velocity control and hydraulic loading They

Return sludge

InfluentInfluent

EffluentEffluent

AerationAeration

Bioreactor BioreactorExtra sludge

Extra sludge

Side-stream MBR Submerged MBR

Figure 51 Configuration of side-stream and submerged MBRsModified from Jiang (2007)

Membrane bioreactors for water treatment 157

are mostly used in industrial wastewater treatment and small-scale wastewater treat-ment plants where influent flow rate and composition have larger variation andoperational conditions are tough (eg high-temperature conditions) (Jiang 2007)Furthermore both MBR systems can be applied as aerobic (in the presence of anaeration system for the module) and anaerobic (in the absence of an aeration systemfor the module)

522 Membrane material types and morphology

Membrane materials and pore size are important criteria for MBR application Thereare two different types of membrane materials polymeric and ceramic Metallicmembrane filters exist but these have specific applications that do not relate toMBR technology To be made useful the membrane material must then be formed(or configured) to allow water to pass through it In MBRs a dense MF or a looseUF membrane is often applied (average pore size around 05e005 mm)

A number of different polymeric and ceramic materials are used to formmembranes but they are nearly always composed of a thin surface layer that providesthe required permselectivity on top of a more open thicker porous support thatprovides mechanical stability A classical membrane is thus anisotropic in structurewith symmetry only in the plane orthogonal to the membrane surface Polymericmembranes are also usually fabricated to have high surface porosity or percent totalsurface pore cross-sectional area and narrow pore size distribution so as to provideas high throughput and as selective a degree of rejection as possible The membranemust also be mechanically strong (ie have structural integrity) Finally the materialwill normally have some resistance to thermal and chemical attacks (ie extremes of

Table 51 Comparison of side-stream MBRs and submerged MBRs

Parameters Side-stream Submerged

Complexity Complicated Simple

Flexibility Flexible Less flexible

Robustness Robust Less robust

Flux High (40e100 Lm2 h) Low (10e30 Lm2 h)

Fouling reducing methods bull Cross-flowbull Airliftbull Backwashingbull Chemical cleaning

bull Air bubble agitationbull Backwashing (notalways possible)

bull Chemical cleaning

Membrane packing density Low High

Energy consumption withfiltration

High (2e10 kW hm3) Low (02e04 kW hm3)

Source Jiang (2007 p 11)

158 Advances in Membrane Technologies for Water Treatment

temperature pH andor oxidant concentrations that normally arise when the membraneis chemically cleaned) and should ideally offer some resistance fouling (Judd 2006)

In principle any polymer can be used to form a membrane only a limited numberof materials are suitable for the duty of membrane separation the most common ofwhich are

bull Polyvinylidene difluoride (PVDF)bull Polyethylsulphone (PES)bull Polyethylene (PE)bull Polypropylene (PP)bull Polysulphone (PS)

The membrane materials most often used in MBRs are organic polymers eg PEPP and PVDF (Judd 2006) Some are blended with other materials to change their sur-face charge or hydrophobicity (Mulder 1996) Ceramic materials have been shown tobe suitable for MBR technology because of their thermal chemical and mechanicalstability

Through specific manufacturing techniques all of these polymers can be formedinto membrane materials with desirable physical properties and each has reasonablechemical resistance (Judd 2011) Based on the common membrane materials the prin-ciple types of membrane are shown in Figure 52 which describes the typicalmorphology of membranes in MBR technology isotropic and anisotropic micropo-rous membranes are usually applied The two other types of membrane representthe morphology of dense membranes applied in reverse osmosis (RO) and nanofiltra-tion (NF)

Figure 52 Principle types of membranesModified from Baker (2004 p 4)

Membrane bioreactors for water treatment 159

523 Membrane module types

The configuration of the membrane ie its geometry and the way it is mounted andoriented in relation to the flow of water is crucial in determining overall processperformance (Judd 2011) Large membrane areas are normally required whenmembranes have to be applied on an industrial scale The smallest unit into whichthe membranes are packed is called a module (Mulder 1996) Three types ofmembrane modules such as flat sheet (FS) hollow fibre (HF) and multi-tubular(MT) are available that are suited to MBR technologies (Judd 2011) Two populartypes of modules are shown in Figure 53

Flat-sheet capillary and HF membranes are applied in iMBR and typical tubularmembranes are used in sMBR (Gander et al 2000) The geometric structure of amembrane is valuable if it is capable of minimizing fouling during the filtration processand if its module has good specific surface where for lsquospecific surfacersquo meansthe filtering surface per unity of occupied volume Structural simplicity managementflexibility and modularity are also important when deciding whether a membranemodule is valuable An important parameter often taken into account while consid-ering the membrane filtration process is the molecular weight of the compound thatcan be retained by the membrane This is called the molecular weight cutoff it refersto the molecular weight cutoff the solute at which 90 rejection takes place and isexpressed in daltons (Manigas 2008)

53 Aerobic MBR

Aerobic MBR is an MBR configuration associated with aeration systems In thisregard aeration has two functions (1) it supplies oxygen to microorganisms in thebioreactor and (2) it scours the membrane surface to create cross-flow which keeps

(a) (b)

Figure 53 Membrane bioreactor (MBR) module types (a) flat sheet (from Kubota Japan)(b) hollow fibre (from Motian China)

160 Advances in Membrane Technologies for Water Treatment

the membrane surface comparatively clean Normally air is supplied through an airdiffusion system The diffusion rate of oxygen from air to water depends on the airbubble size generated by the diffuser Coarse air bubbles are preferred for betterscouring whereas fine air bubbles are preferred for higher oxygen mass transferinto the water phase

531 Areas of application

Generally aerobic MBR is applied for low- to intermediate-level strength organicload-oriented wastewater such as municipal wastewater (low organic load) industrialwastewater and textile wastewater (organic load of intermediate level) Some aerobicMBR applications for treating wastewater are

bull Municipal wastewaterbull Textile wastewaterbull Agriculture wastewaterbull Wastewater from slaughterhousesbull Fisheriesbull Food processing industry

According to Lesjean et al (2009) and Zheng Zhou Chen Zheng and Zhou(2010) the growth of MBR applications in the European and Chinese marketsis increasing almost exponentially (Figures 54 and 55) Figures 54 and 55 indicatethat the application of MBRs in European countries is more in the industrial sectorswhereas in China it is more in the municipal field Globally there is also a pro-nounced upward trend in plant size as well as in the diversity of technology

0

100

200

300

400

500

600

1990ndash1998

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Num

ber o

f pla

nts

(cum

val

ues)

30 new refsyear

45 new refsyear

65 new refsyearIndustrial (capacity gt20m3d)

Municipal (capacity gt20m3d)

Total municipal in EuropeAbout 2 millions ep (05 population)

Figure 54 Development of industrial andmunicipalMBRmarket inEurope (Lesjean et al 2009)

Membrane bioreactors for water treatment 161

providers - although the largest MBRs are predominantly fitted with GE Zenon Tech-nology (Judd 2011) In 2010 GE Zenon provided more than 40 of the total globalinstalled capacity from MBR treatment (Judd 2011) In 2014 the United States wasthe country with the largest number of large-scale MBR plants (over 50 MLD) world-wide (The MBR Site 2014)

532 Factors affecting membrane performance

MBRs use a membrane filtration process based on pressure gradient The process isaffected by the following factors

bull Intrinsic resistance of the membranebull TMPbull Hydrodynamic regime at the interface between the membrane and the solution to be filteredbull Fouling

Among these factors hydraulic geometry including microbiological aspects ofMBR and fouling of the membranes are the most important

Microbiological species of MBR are influenced by several common parameterssuch as

bull Hydraulic residence time (HRT)bull Mixed liquor suspended solids (MLSS)bull Sludge retention time (SRT)bull Sludge loading (SL) or organic loading rate (OLR)

An overview of these most common influencing parameters is been provided in thefollowing sections

Figure 55 Capacity development of industrial and municipal MBR markets in China (Zhenget al 2010)

162 Advances in Membrane Technologies for Water Treatment

5321 Hydraulic residence time

The HRT indicates the duration in hours that the feed solution remains in the MBRbefore it is processed as permeate by the membrane The formula for HRT is

HRT ethhTHORN frac14 Hydraulic volume ethLTHORNPermeate flow ethL=hTHORN (51)

From Eqn (51) it is evident that HRT depends on the hydraulic volume of thereactor and the permeate flow If HRT is high it is easier for bacterial biocenosis toacclimate to reactor conditions but low HRT affects conditions inversely

HRT is an important operating parameter in aerobic MBR operation (Le ClechChen amp Faine 2006 Meng et al 2009) Lower HRT values result in higher OLRwhich result in a reduction of reactor volumes required to achieve a specified removalperformance On the other hand higher HRTs usually result in better removal perfor-mance Qin Oo Tao and Kekre (2007) reported that for the operation of a submergedMBR for treatment of petrochemical wastewater the use of HRTs in the range13e19 h results in effluents that have acceptable qualities Chang et al (2006) founda negligible effect of HRT in the range of 12e30 h on the removal performanceof MBR used to treat the wastewater of an acrylonitrileebutadieneestyrene unitVisvanathan Thu Jegatheesan and Anotai (2005) reported similar chemical oxygendemand (COD) and pentachlorophenol removal performance at HRTs in the range of12e24 h in an MBR used to treat synthetic wastewater Decreased HRT has also beenreported to result in an increase in the rate of membrane fouling in MBRs although itseffect seems to be mostly indirect rather than direct (Chang et al 2006 Meng ShiYang amp Zhang 2007 Meng et al 2009 Qin et al 2007)

5322 Mixed liquor suspended solids

MLSS are the concentration of suspended solids in mixed liquor usually expressedin grams per litre (Wateronline 2011) Mixed liquor is a mixture of raw or settledwastewater and activated sludge contained in an aeration basin in the activated sludgeprocess MLSS are used to control the wastewater treatment plant in the suspendedgrowth process

According to Lousada-Ferreira et al (2010) MLSS are a critical operational param-eter for aerobic MBR The possibility of using high solid contents results in a reducedfootprint that is considered one of the biggest advantages of MBR technologyHowever the influence of MLSS on fouling is not consistent and sometimes is contra-dictory MLSS concentrations have a direct impact on viscosity (Hasar Kinaci euroUnleurouTogrul amp Ipek 2004 Rosenberger Kruger Witzig Manz Szewyk amp Kraume2002) According to Hasar et al (2004) suspensions with higher viscosity requirehigher cross-flow velocities to create turbulent regimes If the cross-flow is not enoughto scour the solids away from the membrane it is reasonable that the fouling layer willbuild up faster on the membrane surface

Membrane bioreactors for water treatment 163

Therefore the theoretical explanation suggests that increasing concentrations ofsolids result in increasing fouling However some authors report no effect of solidson TMP (Harada Momonoi Yamazaki amp Takizawa 1994) or permeate quality(Rosenberger Kubin amp Kraume 2002) and demonstrate a decrease in TMP for sam-ples with higher MLSS concentrations (Defrance amp Jaffrin 1999 Le Clech Jeffersonamp Judd 2003) One explanation for these apparently contradictory results is that theeffect of MLSS concentration on filtration resistance varies according to the appliedMLSS range in the MBR operation (Lousada-Ferreira et al 2010)

5323 Sludge retention time

SRT indicates how frequently sludge is taken away from the MBR It also means theage of the sludge Laeraa Polliceb Saturnob Giordanob and Sandullia (2009)observed a significant correlation between the SRT and the OLR That study suggestedthat the biomass activity is weakly affected by the age of the sludge Membrane clean-ing requirements also appear to depend slightly on the SRT

According to Ahmed Cho Lim Song and Ahn (2007) the SRT affects the mixedliquor characteristics and induces changes in the physiological state of microorganismsthus variations in membrane fouling substances such as extracellular polymeric sub-stances (EPS) and soluble microbial products (SMP) can occur (Chang amp Lee 1998Masse Sperandio amp Cabassud 2006) However contradictory reports exist in the liter-ature regarding the effects of SRT on membrane biofouling Several studies demon-strated that EPS increases as SRT increases (Chang amp Lee 1998 Cho 2004 Masseet al 2006) others have shown the opposite trend (Lee Kang amp Shin 2003Ng amp Hermanowicz 2005)

5324 Sludge loading or organic loading rate

The SL or ratio of feed to microorganism (FM) is an important design parameter in theMBR process Generally the MBR process can operate at higher FM ratios comparedwith an activated sludge plant (Robinsion 2003) It is defined as kilograms of CODdivided by kilograms of MLSS times days It can also be expressed as kilograms ofCOD divided by cubic metres times days

The OLR has an important role in the treatment of wastewater by MBRs Anincreased OLR decreases the filterability of the MBR Kornboonraksa and Lee (2009)reported that an increase in influent COD biological oxygen demand (BOD) andNH4eN from 1150 to 2050 mgL 683 to 1198 mgL and 154 to 248 mgL respec-tively resulted in a decrease in the removal efficiency of COD BOD and NH4eNTrussell Merlo Hermanowicz and Jenkins (2006) reported increased membranefouling with higher OLR They reported that steady-state membrane fouling ratesincreased 20-fold over a fourfold increase in FM Khoshfetrat Nikakhtari Sadeghifarand Khatibi (2011) found a reduction of COD removal efficiency from 90 to 74when OLR increased from 1 to 25 kg CODm3 day Shen Zhou Mahendran Bagleyand Liss (2010) reported a higher degradation of organics (glucose) of 98 at OLRs

164 Advances in Membrane Technologies for Water Treatment

of 13 g CODL day or less compared with an OLR of 30 g CODL day which had adegradation of about 70

In the biochemical stage of wastewater treatment organic carbon and nutrients areremoved from wastewater by microbes These microbes live and grow enmeshed inEPS that bind them into discrete micro-colonies forming three-dimensional aggre-gated microbial structures called flocs The ability of microorganisms to form flocsis vital for the activated sludge treatment of wastewater The floc structure enablesthe adsorption of soluble substrates but also the adsorption of colloidal matter andmacromolecules found in wastewaters (Liwarska-Bizukojc amp Bizukojc 2005Michael amp Fikret 2002) The diversity of microbial community in activated sludgeis large containing prokaryotes (bacteria) eukaryotes (protozoa nematodes androtifers) and viruses In this complex microsystem bacteria dominate the microbialpopulation and have a critical role in the degradation process (Michael amp Fikret2002)

5325 Fouling

When treating organic solutions (such as macromolecule solutions) the solute concen-tration at the membrane surface can attain a high value and a maximum concentration(the gel concentration) may be reached The formation of a gel layer on the membranesurface is often seen as fouling which causes a decrease in the permeate flux orincrease in TMP during a membrane process The gel concentration depends on thesize shape chemical structure and degree of solvation but is independent of thebulk concentration

Generally membrane fouling can be caused by a variety of constituents amongwhich are bacteria suspended solids and colloids as well as dissolved inorganicand organic compounds (Hilal Kochkodan Al-Khatib amp Levadna 2004)In MBRs fouling can be attributed to pore blocking (deposition within the pores)or to cake layer formation on the membrane surface (Jiang Kennedy van der MeerVanrolleghem amp Schippers 2003) (Figure 56) Colloidal and soluble foulants(SMP) can cause pore blocking and irreversible fouling because of their small size

Soluble microbial products(SMP)Colloids

Extracellular polymericsubstances (EPS)Polysaccarides proteinsnatural organic matter

Floc characteristics Size Structure

Biomass characteristics

Pore blocking Cake formationFigure 56 Biomass characteristics and biofouling

Membrane bioreactors for water treatment 165

533 Case study wastewater reuse by aerobic MBR in acommercial laundry

In addition to municipal wastewater treatment aerobic MBR is widely used in indus-trial wastewater treatment There are a multitude of industrial sectors such as laundrytannery textile wheat starch dairy beverage palm oil and pharmaceutical (Hoinkiset al 2012 Mutamim Noor Hassan Yuniarto amp Olsson 2013)

Several operational factors need to be considered such as HRT MLSS SRT andOLR to achieve high water quality and high water flux (ie to reduce the foulingeffect) The hydraulic performance indicates the productivity of the process in termsof water permeability or flux water quality is usually expressed in terms of COD inpermeate Section 5331 presents a typical case study on the treatment and reuse oflaundry textile wastewater

5331 Background

The process applied in the case study was developed through cooperation betweenthe Karlsruhe University of Applied Sciences and Textile Service KlingelmeyerDarmstadt Germany The wastewater was treated in a two-step process and wasrecycled in the laundryrsquos washing and rinsing process (Figure 57) After coarsescreening using a vibrating sieve to retain suspended particles the wastewater wascollected in a storage tank (WW) Subsequently the wastewater was treated in anMBR as the principal cleaning unit Air was injected into the reactor to scour themembranes and drive the biological treatment The MF permeate was stored in ancollecting tank (TWW) It was free of turbidity and considerably reduced in microbesSome of the MF permeate was treated in a second step by a low-pressure RO unit withspiral-wound modules to retain salts as well as organic residues The MF and RO

TWWTWWWWWW

Rain-Rain-waterwater SurplusSurplus

sludgesludge

SewageSewagetreatmenttreatmentplantplant

Mixed water

MBR ROTWWWWScreen

Sewagetreatmentplant

Surplussludge

Rain-water

MWMWMWMW

Figure 57 Schematic of the water reuse process (WW wastewater TWW treated wastewaterMW mixed wastewater)

166 Advances in Membrane Technologies for Water Treatment

permeates were mixed in a tank (MW) and were used for washing and rinsing Theratio of mixing (RO permeate to MBR permeate) lies between 21 and 11 dependingon the salt level of the MBR permeate Before storage the MBR and RO permeateswere treated with a small amount of chlorine dioxide to prevent the growth of germsBecause rainwater did not meet the water quality criteria for the process it wascollected in the wastewater collecting tank The integrated process generated twokinds of waste that needs to be disposed The surplus sludge was stored in a separatetank and was collected by commercial waste management enterprises The concentratefrom the RO treatment was drained into the municipal treatment plant (Hoinkis et al2012)

5332 Plant components

A commercial-scale MBR plant consists of

bull Vibrating sieve (Sweco) with a mesh size of 200 mmbull An MBRbull An RO unitbull Three storage tanks (wastewater WW MBR permeate TWW mixed MBR plus RO

permeate MW)

The MBR contained a submerged Kubota Type 510 MF plate and frame mem-branes (single plate 08 m2) with 04-mm pore size made of chlorinated polyethyleneThe MBR tank had a total volume of 126 m3 It was separated by a barrier into twocompartments connected by a spill One compartment was designed only for biodeg-radation the other was for biodegradation and membrane filtration This gavemaximum flexibility for adjusting aeration to the needs of the filtration and biodegra-dation process The biomass was circulated between compartments every other dayThe filtration compartment contained two double-deck Kubota stacks (SystemEK300) with 600 plate and frame modules (total membrane area of 480 m2) TheRO unit was fitted with six 8040 spiral-wound modules (Dow LE) The plant wascomposed of three collecting tanks (wastewater MBR drain and MBR plus RO drain)the first with an enamel steel collecting tank of 400 m3 for wastewater and two 200 m3

tanks for the MBR and MBR plus RO drains

5333 Results

The results of the case study are shown in Figures 58 through 510 Average flux wasaround 15 L(m2 h) at a permeability between 300 and 1000 L(m2 h bar) (Figure 58)After 1 year of operation without chemical cleaning the flux was lowered to 12 L(m2 h) at an average permeability of 150e300 L(m2 h bar) as can be seen inFigure 59 Figure 510 shows the COD values in feed and permeate as well as theelimination rate over more than 2 years of operation The feed COD started at600e800 mgL and increased to more than 1000 mgL whereas the COD in permeateremained at values below 100 mgL and the elimination rate was higher than 90The aeration rate in the filtration compartment of the MBR tank was 52 m3minThe biodegradation compartment was intermittently aerated by a fine diffuser at

Membrane bioreactors for water treatment 167

72 m3min The flux rate does not represent full flow capacity the plant was designedfor an eventual flux rate of 12e15 Lm2 h The concentration of MLSS in the reactorincreased from 3 to 10e15 kgm3 The COD sludge loading decreased from 014to 004 kg CODkg MLSS day The average yield factor for biomass growth wascalculated to 013 kg MLSSkg COD degraded The surplus sludge was collected ina storage tank and delivered to a commercial sludge processing unit

Typical water quality parameters of the MBR unit are shown in Table 52 whichdemonstrates that the COD removal efficiency was high (94) and the total N conver-sion rate was also relatively high (72)mdashindications of good permeate quality

54 Anaerobic MBRs

541 Areas of application

Because anaerobic digestion in wastewater treatment combines pollution reductionand energy production it is the most interesting process for industrial effluent

30FL

ux

L(m

2 h)

Per

mea

bilit

y L

(m2

h ba

r)

25

20

15

10

5

0

3000

2500

2000

1500

1000

500

0

0 7 14 21 28Time days

0 7 14TIme days

21 28

Figure 58 Permeate flux and permeability of the MBR treatment plant during a typicaloperation period of 28 days after start-up

168 Advances in Membrane Technologies for Water Treatment

30

25

20

15

10

5

0

400

350

300

250

200

150

100

50

0

0 7 14 21 28

Time days

0 7 14 21 28

Time days

Per

mea

bilit

y L

(m2

h ba

r)FL

ux

L(m

2 h)

Figure 59 Permeate flux and permeability of the MBR treatment plant during a typicaloperation period of 28 days after 1 year of operation

0 0

20

40

60

80

100

200400600800

10001200140016001800

Removal

Feed

Permeate

Timedate

230

620

0623

08

2006

231

020

06

231

220

06

230

220

07

230

420

0723

06

2007

230

820

07

231

020

07

231

220

0723

02

2008

230

420

08

230

620

08

231

020

0823

08

2008

CO

D

mg

L

CO

D re

mov

al

Figure 510 COD values in MBR feed permeate and COD removal efficiency

Membrane bioreactors for water treatment 169

treatment Historically anaerobic processes have been mainly employed for industrialhigh strength wastewater and less for municipal wastewater because (1) it is difficult toretain slow-growth anaerobic microorganisms with short HRT for the treatment oflow-strength wastewater and (2) anaerobic digestion rarely meets discharge standards(Lin et al 2013)

Similar to aerobic MBRs (see Section 53) AnMBRs combine biodegradation withthe MF and UF membrane process which provides solideliquid separation The mostsalient features of AnMBRs compared with aerobic MBRs are no need of oxygensupply biogas (methane) production and lower sludge yield which significantlylowers the operating costs

Compared with conventional anaerobic digestion AnMBRrsquos most important aspectis its ability to offer complete biomass retention owing to membrane filtration Thisprovides sufficient SRT for the methanogens Conventional anaerobic biodegradationshows relatively poor settling properties of the biomass and hence results in the loss ofbiomass into the effluent (Lin et al 2013) In conventional systems only the strategyof biofilm or granule formation in modern high-rate anaerobic reactors offers highbiomass retention but at the cost of a long start-up period and complex process con-ditions (Lin et al 2013) Many industrial wastewater characterized by hightemperature high fat oil and grease content toxicity high salinity or drastic changesin OLR eg have a negative impact on the sludge granulation process and eventuallycould lead to degranulation (Dereli Ersahin et al 2012) Table 53 compares the mainfeatures of conventional anaerobic treatment (CAT) and AnMBR treatment in whichAnMBR treatment shows better effluent quality than conventional anaerobic treat-ment but also total pretreatment and complete biomass retention Because of its ben-efits such as complete biomass retention enhanced effluent water quality andpotential net energy production AnMBR is becoming increasingly interesting formunicipal wastewater treatment (Lew Tarre Beliavski Dosoretz amp Green 2009)

Similar to aerobic MBRs two configurations are used side-stream and submerged(see Section 521) In a side-stream configuration the membrane filtration module isplaced outside the reactor and after filtration the biomass is recirculated into the

Table 52 Typical water quality parameters of the MBR unit

Parameter UnitFeeda

(wastewater)Permeatea

(microfiltrate) Removal rate ()

BOD5 mgL 390 lt9 gt97

COD mgL 1120 67 94

NeNO3 mgL 77 21 73

NeNH4thorn mgL 15 01 93

Total N mgL 160 45 72

PePO43 mgL 14 13 7

aTypically average values based on several measurements

170 Advances in Membrane Technologies for Water Treatment

reactor This offers high fluxes but at the cost of frequent cleaning and high energyconsumption around 10 kW hm3 (Le Clech et al 2006)

In addition high cross-flow velocity has a negative impact on biomass activities(Choo amp Lee 1996 Ghyoot amp Verstraete 1997) In submerged MBR the membranesare placed inside the reactor Because air cannot be used to provide cross-flow on themembranes as in aerobic MBR maintaining high permeability is more difficult inAnMBRs In many cases gas sparging with generated biogas is used to scour themembranes (Smith Stadler Love Skerlos amp Raskin 2012) Most laboratory researchor small-scale pilot trials have been conducted with side-stream AnMBRs Howeveron a large or full scale submerged systems are preferred for their lower energyconsumption

Most research work was done at laboratory and on a small pilot scale only a fewstudies have been conducted with large-scale AnMBR (Dereli Ersahin et al 2012)Although laboratory-scale studies provide invaluable information on treatabilityand membrane fouling mechanisms with scientific insight hydraulics and shear forcesacting on a small membrane module will significantly differ from a full-scale mem-brane module (Dereli Ersahin et al 2012) Table 54 shows treatment performanceon a large pilot and full scale for various industrial wastewaters All of these studiesused submerged membrane configurations

Table 53 Comparison of conventional anaerobic treatment (CAT)and anaerobic membrane bioreactor (AnMBR)

Feature CAT AnMBR

Organic removal efficiency thorn thornEffluent quality o thornOrganic loading rate thorn thornSludge production Footprint thorno Biomass retention Complete

Nutrient requirement Alkalinity requirement thorn For certain industrial

streamsthorno

Energy requirement Temperature sensitivity o o

Start-up time 2e4 months lt2 weeks

Bioenergy recovery Yes Yes

Mode of treatment Primarily pretreatment Total or pretreatment

thornthorn Excellent thorn high o moderate lowpoorModified from Lin et al (2013)

Membrane bioreactors for water treatment 171

Table 54 Treatment performance of various industrial wastewaters

Reactorvolumem3

temperatureCOLRkgCODm3 day HRTdays TSSgL

CODremoval

MembranetypePore sizeFluxLm2 hTMPbar Reference

Food processing 870033

12 29 23 994 Flat sheet04 mm25e42003

Christian et al(2011)

Potato processing 3335

2e12 35e14 40 99 Flat sheet04 mm083e5003e004

Singh Burkeand Grant(2010)

Stillage from tequilaproduction

1337

48 124 e 95 Flat sheetee

Grant ChristianVite andJuarez (2010)

Snack factory 07635

51 e 79e104 97 Hollow fibre04 mm65e8e

Diez Ramosand Cabezas(2012)

Ethanol thin stillage 1237

45e7 16 24 98 Flat sheet008 mm43 1101e02

Dereli Urbanet al (2012)

Modified from Dereli Urban et al (2012)

172Advances

inMem

braneTechnologies

forWater

Treatm

ent

542 Factors affecting performance

Regarding aerobic MBRs membrane fouling presents one of the main bottlenecks forAnMBR application (Dereli Ersahin et al 2012) Because of the fouling of organicand inorganic compounds permeate flux through the membrane can be significantlyreduced Compared with aerobic MBRs AnMBRs show lower permeate fluxes as aresult of less flocculation of the sludge and hence increased concentrations of fineparticles and colloidal solids at the membrane surface Cake layer formation was identi-fied as themost important foulingmechanism inAnMBRs (Dereli Ersahin et al 2012)

5421 Temperature

Regarding process temperature anaerobic digestion basically falls into one ofthe following categories (Rajeshwari Balakrishnan Kansal Lata amp Kishore 2000)psychrophilic (0e20 C) mesophilic (20e42 C) or thermophilic (ca 42e75 C) InAnMBRs a higher temperature can increase membrane flux owing to reducedviscosity and higher membrane permeability This is advantageous for loweringenergy requirements With lower sludge viscosity lower shear rates will be requiredto obtain the same shear stress (Jeison amp van Lier 2006) Because of higher membranepermeability the same water flux can be achieved at a lower TMP (Smith et al 2012)Higher temperatures in thermophilic operations proved to be advantageous only in short-term experiments in the long-term theywere disadvantageous (JeisonampvanLier 2007)

Jeison and van Lier (2007) showed that permeate water flux in a thermophilic oper-ation was two to three times lower compared with water flux in a mesophilic operationHence it was concluded that in the long-term adverse temperature effects on the prop-erties and composition of the sludge were more important than the beneficial influenceof membrane filtration These findings are in line with the results of Lin et al (2009)who investigated the influence of sludge properties on membrane fouling in sub-merged AnMBRs treating kraft evaporation condensate The AnMBRs were operatedunder similar hydrodynamic conditions and MLSS concentrations under both meso-philic and thermophilic conditions In the long-term the permeate water flux of themesophilic system was significantly higher than that for the thermophilic system(74 L(m2 h) versus 18 L(m2 h) respectively) (Lin et al 2009) This was attributedto the increased formation of small particles under thermophilic conditions whichresulted in a more compact and less porous cake layer on the membrane in the caseof thermophilic operation In addition Lin et al (2009) found that the concentrationof bound EPS and protein in the cake layer was higher under thermophilic conditionswhich might be because of the increased decay rate of bacteria at elevated tempera-tures Furthermore the permeate water quality of the mesophilic system was consid-erably better than that of the thermophilic reactor

5422 Organic loading rate

In theory a high OLR and short HRT can be employed in AnMBRs However OLRshould always be evaluated together with SRT and sludge activity (Dereli Ersahinet al 2012) A variety of experimental studies carried out up to very high OLR still

Membrane bioreactors for water treatment 173

showed high COD removal efficiency Treatment of simulated wastewater from thepetrochemical industry demonstrated high COD removal efficiency at OLR up to25 kg CODm3day (van Zyl Wenzel Ekama amp Riedel 2008) Similar high treat-ment efficiency has been shown for slaughterhouse and palm oil wastewater aswell at ORL up to 133 and 11 kg CODm3day respectively (Abdurraham Rosli ampAzhari 2011 Saddoud amp Sayadi 2007)

5423 Hydraulic residence time and SRT

The performance of AnMBR and membrane fouling is affected by HRT and SRTGenerally speaking a low HRT is preferred because it reduces tank volume and hencethe overall footprint of the system A high SRT is required to achieve better treatmentperformance especially at lower temperatures (OFlaherty Collins amp Mahony 2006)However increasing the SRT causes higher SMP and EPS production and results in ahigher propensity for membrane fouling Moreover increasing the SRT under constantHRT increases the biomass concentration resulting in lower permeate flux (Smith et al2012) A variety of publications are concerned with the study of treatment performanceon HRT An insignificant decrease in COD removal efficiency (ca 5) was observedby Hu and Stuckey when they studied the treatment of simulated domestic wastewaterat mesophilic temperatures (35 C) lowering HRT from 48 h down to 3 h (Hu ampStuckey 2006) Even at an HRT of 3 h COD removal efficiency was higher than90 Several other studies similarly concluded that HRT had little effect on AnMBRpermeate quality (Smith et al 2012) Those studies suggested that adequate AnMBRperformance may be obtained at relatively short HRTs even at lower temperaturesbut that a lower limit on HRT may exist primarily owing to concerns regarding mem-brane fouling (Smith et al 2012) For AnMBR SRT is an easily controllable opera-tional parameter because membrane separation allows complete retention of biomassHuang et al studied low-strength domestic wastewater and observed better treatmentperformance at a longer SRT but at the cost of increased membrane fouling as a resultof higher biomass concentrations and SMP production (Huang Ong amp Ng 2011)Despite this many publications observed that EPS is a major contributor to directfouling However the role of EPS quantity and characteristics in membrane foulingas a function of SRT is not well understood in AnMBRs (Smith et al 2012)

5424 Membrane properties

Fouling in AnMBRs is very much affected by membrane properties such as materialspore size and surface characteristics Although hydrophobic membrane materials aremore durable under harsh chemical and thermal conditions hydrophilic membranesare typically favoured because they are less prone to fouling (Dereli Urban et al2012) Membrane materials used for AnMBRs can be classified into three major cat-egories ceramic metallic and polymeric In early experimental studies ceramic wasthe most widely used material for AnMBRs (Lin et al 2013) In AnMBRs metallicmembranes have also been applied because of their better hydraulic performance bet-ter fouling recovery and better tolerance to oxidation and high temperature (Kim ampJung 2007 Zhang et al 2005) However because of economic constraints in

174 Advances in Membrane Technologies for Water Treatment

commercial applications cheaper polymeric materials have gained more interestTypically materials such as PVDF PES PE and PP are applied with pore sizes inthe MF or UF range (003e1 mm) and in hollow fibre flat sheet or tubular configu-rations In general preferred polymeric membrane materials for MBRs are PVDFand PES which account for around 75 of total products on the market including9 of the 11 commercially most important products (Santos amp Judd 2010) Becauseof the high fouling propensity modification of the hydrophobic membrane surfaceby hydrophilic coating is a main goal in reducing fouling propensity Choo et al(2000) modified the surface of an organic membrane by grafting with2-hydroxyethyl methacrylate (HEMA) which resulted in 35 flux increase A135 flux increase was reported by Sainbayar Kim Jung Lee and Lee (2001)who modified the surface of a PP membrane material by 70 grafting withHEMA Kochan Wintgens Melin and Wong (2009) studied surface coating viathe adsorption of surfactants in which different UF flat-sheet membranes were coatedwith branched poly(ethyleneimine) poly(diallyldimethyl ammonium chloride) andpoly(allylamine chloride) and filtered with sludge supernatant The experimentsshowed lower fouling but also low physical tolerance and chemical stability underMBR conditions To overcome this drawback Asatekin et al (2006) developed aself-assembling technique by coating commercial PVDF UF membranes with theamphophilic graft copolymer PVDFegraft-polyoxyethylene methacrylate

543 Case study treatment of high-strength industrialwastewater using a full-scale AnMBR

Most AnMBR research has been carried out at the laboratory or small pilot scale onlya few studies have been concerned with large- or full-scale applications Most full-scale AnMBR installations were established in Japan Kanai reported about 14large-scale AnMBR implementations in the food and beverage industries in Japan(Kanai Ferre Wakahara Yamamoto amp Moro 2010)

A typical case study on the treatment of high-strength industrial wastewater using afull-scale AnMBR is presented here

The study is the first AnMBR installation in North America and the largest AnMBRinstallation in the world It was built at Kenrsquos Foods in Massachusetts (ChristianGrant McCarthy Wilson amp Mills 2011)

Due to lack of space positive economics and the ability to provide additional ca-pacity for flow and organic load the system was converted from Kenrsquos Foodsrsquo existinganaerobic process to AnMBR in July 2008 It provides waste treatment but also a largegain in energy production from salad dressing and barbeque sauce wastewater

The process uses Kubota flat-plate membrane cartridges (with nominal pore size of04 mm) that are submerged directly into the anaerobic biomass and completely blockall suspended solids from escaping to the effluent Figure 511 shows a general processflow diagram of the AnMBR process

The design of this AnMBR system has an effluent flow rate of 475 m3day with39000 mgL COD 18000 mgL BOD and 12000 mgL total suspended solids(TSS) under mesophilic conditions ensured by an average operating temperature of

Membrane bioreactors for water treatment 175

33 C for all four anaerobic membrane tanks a pH of 69 01 for anaerobic sludgeacclimatization an operating volumetric flux rate in the range of 006e010 m3m2

day and a TMP fluctuating between 0005 and 01 bar Once the TMP reaches01 bar membrane cleaning is required (three of four membrane compartments werecleaned once during the first 20 months of operation) Table 55 presents the rawwastewater characteristics and average effluent quality after 20 months of runningthe pilot test

In Table 55 this AnMBR process consistently provides an effluent with undetect-able TSS concentrations and COD and BOD concentrations of 209 39 and16 5 mgL corresponding to COD and BOD removals of 994 and 999 respec-tively By dint of biogas scouring across the membrane surface a very low rate ofmembrane fouling is an important result in this study because membrane foulingunder anaerobic conditions is a considerable issue for the AnMBR process

Anaerobic MBR

Biogas

Feed

Methanefermentation

tank

Separation tankwith submerged

membrane

Wastewatertreatmentequipment

Powergenerating

facility

Sludgedehydrationequipment

Pretreatmentequipment

Optional

Figure 511 General process flow diagram of the AnMBR processModified from Christian et al (2011)

Table 55 Raw wastewater and AnMBR effluent characteristics(July 2008 to April 2010)

Parameter Raw wastewater AnMBR effluent Removals

Flow rate m3day 300 300 e

BOD mgL 18000 20 999

COD mgL 33500 210 994

TSS mgL 10900 lt1 100

pH e 705 e

176 Advances in Membrane Technologies for Water Treatment

Upgrading the existing anaerobic treatment system to an AnMBR demonstratedthe simplicity and suitability of the process for a wastewater treatment system that pre-viously experienced difficulty with solids management and sludge settling ability(Christian et al 2011)

This installation at Kenrsquos Foods can be considered an ideal technology forthe development of renewable energy from waste especially when containing ahigh suspended solids concentration

55 Forward osmosis MBRs

The combination of FO and activate sludge treatment is a relatively new process FO isa natural process driven by the osmotic pressure difference that retains solutes but al-lows water to permeate through a semipermeable membrane (Cath Childress ampElimlech 2006) FO is attractive because of the high rejection efficiency of its mem-branes hence the drawback of conventional MF and UF MBRs can be overcomewhich are limited in the retention of low-molecular-weight compounds (LMWC)To increase efficiency in LMWC removal conventional MBRs need to be combinedwith downstream RONF units which results in high capital cost and energy consump-tion (Alturki et al 2010)

In FO-MBRs treated water is drained without a pump by osmotic pressure into adraw solution with higher solute concentration than the feed solution this results indilution of the draw solution Therefore the draw solution needs to be concentratedby either mechanical (RO) or thermal processes (distillation) In doing so the treatedclean water can be drained off the system Figure 512 shows a schematic of theprocess FO-MBR offers the possibility of high cleaning efficiency in wastewatertreatment and reuse Achilli Cath Marchand and Childress (2009) reported morethan 99 of organic carbon and more than 98 of NH4eN removal combining thebiological and FO processes using flat-sheet cellulose triacetate FO membranes(Achilli et al 2009) With this process the draw solution is reconcentrated by RO

Draw solution

Reconcentration

Treated water

MBR

Feed

Figure 512 Schematic of FO-MBR system

Membrane bioreactors for water treatment 177

Most research work on FO-MBRs was conducted on the laboratory scale There areonly a few examples of larger pilot-scale studies Quin et al (2009) studied optimi-zation of an FO-MBR on the pilot scale using NaCl and MgSO4 salts in draw solu-tions The NaCl performed at much higher efficiency than MgSO4 as an osmoticagent owing to a greater solute diffusion coefficient

Chen et al (2014) combined a submerged AnMBR with an FO membrane to treatsynthetic low-strength wastewater The FO-AnMBR showed greater than 96 carbonremoval and 100 of total phosphorous and 62 of NH4eN removal This was betterremoval efficiency than for the conventional AnMBR The most salient feature ofFO-AnMBR is its ability to provide biogas that can be used as an energy source todrive the combined process

56 Conclusion and perspectives

Over the past 2 decades the development of MBRs has made great progress In partic-ular the application of aerobic MBRs showed rapid growth in many municipal andindustrial large-scale implementations This is mainly because of their potential forrecycling and reusing grey water and industrial effluents Major improvements havebeen achieved for aerobic MBRs (Brepols 2011)

bull Improved module hydraulics and optimized process control helped reduce energy consump-tion for air scouring

bull Advances in membrane production led to improvement in materials stability and resiliencewhereas market prices have come down

bull In terms of investment cost todayrsquos MBR plants are not necessarily more expensive thancomparable conventional activated sludge plants

MBR technology is expected to grow in the near future because of the increasingscarcity of water worldwide which makes wastewater reclamation necessary Thiswill be further aggravated by climate change Based on the estimated global MBRmarket of US$8382 million in 2011 the MBR market is projected to grow at anaverage rate of 224 reaching a total market size of US$344 billion in 2018(WaterWorld 2012) The Chinese market is expected to grow at an even higher rateof 289 with the key drivers of high economic growth rate increased confidencein technology and public awareness as well as a strong need for wastewater reclama-tion (Sartorius Walz amp Orzanna 2013)

Besides China the MBR market in Middle Eastern and North African countries isexpected to witness a high growth trajectory in the next 5e10 years because of a largenumber of projects commissioned in medium and large range plants with capacitiesranging between 5000 and 50000 m3day (Frost amp Sullivan 2012)

Future research and development should focus on further lowering energy demands(operating costs) and membrane costs (capital costs) as well as FO-MBRs because oftheir advantages regarding the high rejection of low-molecular-weight contaminantsand their lower fouling propensity

178 Advances in Membrane Technologies for Water Treatment

List of abbreviations

AnMBR Anaerobic MBRBOD Biological oxygen demandCAT Conventional anaerobic treatmentCOD Chemical oxygen demandEPS Extracellular polymeric substancesFS Flat sheetFM Feed to microorganismsHF Hollow fibreHRARs High-rate anaerobic reactorsHRT Hydraulic residence timeiMBR Immersed MBRLMWC Low molecular-weight compoundsMBR Membrane BioreactorMF MicrofiltrationMT Multi-tubularMLD Million liter per dayMLSS Mixed liquor suspended solidsMW Mixed wastewaterOLR Organic loading ratePCP PentachlorophenolPE Polyethylenepe Population equivalentPP PolypropylenePES PolyethylsulphonePS PolysulphonePVDF Poly vinylidene diflurideRO Reverse osmosisSL Sludge loadingSMP Soluble microbial productssMBR Side-stream MBRSRT Sludge retention timeTMP Transmembrane pressureTSS Total suspended solidsTWW Treated wastewaterUF UltrafiltrationWW Wastewater

References

Abdurraham N H Rosli Y M amp Azhari N H (2011) Development of a membraneanaerobic system (MAS) for palm oil mill effluent treatment (POME) Desalination 266208e212

Achilli A Cath T Y Marchand E A amp Childress A E (2009) The forward osmosis mem-brane bioreactor A low fouling alternative to MBR processes Desalination 239 10e21

Membrane bioreactors for water treatment 179

Ahmed Z Cho J Lim B-R Song K-G amp Ahn K-H (2007) Effects of sludge retentiontime on membrane fouling and microbial community structure in a membrane bioreactorJournal of Membrane Science 287 211e218

Alturki A A Tadkaew N McDonald J A Khan S J Price W E et al (2010) CombiningMBR and NFRO membranes filtration fort the removal of trace organics in indirect potablewater reuse applications Journal of Membrane Science 365 206e215

Asatekin A Menniti A Kang S Elimelech M Morgenroth E amp Mayes A M (2006)Antifouling nanofiltration membranes for membrane bioreactors from self-assembling graftcopolymers Journal of Membrane Science 285 81e89

Baker R W (2004) Membrane technology and applications (2nd ed) New York WileyBioNexGen (2013) Development of the next generation membrane bioreactor system www

bionexgeneu Accessed 60913Brepols C (2011) Operating large scale membrane bioreactors for municipal wastewater

treatment London UK IWA PublishingCath T Y Childress A E amp Elimlech M (2006) Forward osmosis Principles applications

and recent developments Journal of Membrane Sciences 281 70e87Chang I-S amp Lee C-H (1998) Membrane filtration characteristics in membrane coupled

activated sludge systemmdashthe effect of physiological states of activated sludge on mem-brane fouling Desalination 120 221e233

Chang J S Chang CY Chen A C Erdei L ampVigneswaran S (2006) Long term operationof submerged membrane bioreactor for the treatment of high strength acrylonitrile-butadiene-styrene (ABS) wastewater Effect of hydraulic retention time Desalination 19145e51

Chen L Gu Y Cao C Zhang J Ng J W amp Tang C (2014) Performance of a submergedanaerobic membrane bioreactor with forward osmosis membrane for low-strength waste-water treatement Water Research 50 114e123

Cho J (2004) Model development for a submerged membrane bioreactor with the effect ofextracellular polymeric substances Seoul Seoul National University

Choo K H Kang I J Joon S H Park H Kim J H Adia S et al (2000) Approaches tomembrane fouling control in anaerobic membrane bioreactors Water Science Technology41 363e371

Choo K H amp Lee C H (1996) Membrane fouling mechanisms in the membrane coupledanaerobic bioreactor Water Research 30 1771e1789

Christian S Grant S McCarthy P Wilson D ampMills D (2011) The first two years of full-scale anaerobic membrane bioreactor (AnMBR) operation treating high-strength industrialwastewater Proceedings of IWA 12th world congress on anaerobic digestion GuadalajaraMexico

Defrance L amp Jaffrin M Y (1999) Reversibility of fouling formed in activated sludgefiltration Journal of Membrane Science 157 73e84

Dereli R K Ersahin M E Ozgun H Ozturk I Jeison D van der Zee F et al (2012)Potentials of anaerobic membrane bioreactors to overcome treatment limitations induced byindustrial wastewaters Bioresource Technology 122 160e170

Dereli R K Urban D R Heffernan B Jordan J A Ewing J Rosenberger G T et al(2012) Performance evaluation of a pilot scale anaerobic membrane bioreactor (AnMBR)treating ethanol thin stillage Environmental Technology 33 1511e1516

Diez V Ramos C amp Cabezas J L (2012) Treating wastewater with high oil and greasecontent using an anaerobic membrane bioreactor (AnMBR) filtration and cleaning assaysWater Science and Technology 65(10) 1847e1853

180 Advances in Membrane Technologies for Water Treatment

Frost amp Sullivan (2012) The Middle East and North Africa membrane bioreactor market to growat a CAGR of 1777 per cent by 2015 httpwwwfrostcomprodservletpress-releasepagdocidfrac14251074704 Accessed 07012015 at 1132h

Gander M Jefferson B amp Judd S (2000) Aerobic MBRs for domestic wastewater treatment Areview with cost considerations Separation and Purification Technology 18(2) 119e130

Ghyoot W R amp Verstraete W H (1997) Coupling membrane filtration to anaerobic primarysludge digestion Environmental Technology 18 569e580

GIA Global Industrial Analysts Inc (2013) Global membrane bioreactors market to reachUS$888 million by 2017 httpwwwprwebcomreleasesmembrane_bioreactorsMBRprweb8973361htm Accessed 221113

Grant S Christian S Vite E amp Juarez V (2010) Anaerobic membrane bioreactor(AnMBR) pilot-scale treatment of stillage from tequila production Proceedings of IWA12th world congress on anaerobic digestion Guadalajara Mexico

Harada H Momonoi K Yamazaki S amp Takizawa S (1994) Application of anaerobic UFmembrane reactor for treatment of a wastewater containing high strength particulate or-ganics Water Science and Technology 30(12) 307e319

Hasar H Kinaci C euroUnleurou A Togrul H amp Ipek U (2004) Rheological properties ofactivated sludge in a sMBR Biochemical Engineering Journal 20 1e6

Hilal N Kochkodan V Al-Khatib L amp Levadna T (2004) Surface modified polymericmembranes to reduce (bio) fouling A microbiological study using E coli Desalination167 293e300

Hoinkis J Deowan S A Panten V Figoli A Huang R R amp Drioli E (2012) Membranebioreactor (MBR) technology e a promising approach for industrial water reuse ProcediaEngineering 33 234e241

Hu A Y amp Stuckey D C (2006) Treatment of dilute wastewaters using a novel sub-merged anaerobic membrane bioreactor Journal of Environmental Engineering 132190e198

Huang Z Ong S L amp Ng H Y (2011) Submerged anaerobic membrane bioreactor for low-strength wastewater treatment Effect of HRT and SRT on treatment performance andmembrane fouling Water Research 45 705e713

Jeison D amp van Lier J B (2006) Cake layer formation in anaerobic submerged membranebioreactors (AnSMBR) for wastewater treatment Journal of Membrane Science 284227e236

Jeison D amp van Lier J B (2007) Thermophilic treatment of acidified and partially acidifiedwastewater using anaerobic submerged MBR Factors governing long-term operationalflux Water Research 41 3868e3879

Jiang T (2007) Characterization and modelling of soluble microbial products in membranebioreactors (PhD thesis) (pp 241e248) Ghent University Belgium

Jiang T Kennedy M D van der Meer W G J Vanrolleghem P A amp Schippers J C(2003) The role of blocking and cake filtration in MBR fouling Desalination 157(1e3)335e343

Judd S (2006) The MBR book Principles and applications of membrane bioreactors for waterand wastewater treatment Cranfield University UK Elsevier ISBN 978-1-85617-481-7

Judd S (2011) The MBR book Principles and applications of membrane bioreactors for waterand wastewater treatment Cranfield University UK Elsevier

Kanai M Ferre V Wakahara S Yamamoto T amp Moro M (2010) A novel combinationof methane fermentation and MBR-Kubota submerged anaerobic membrane bioreactorprocess Desalination 250 960e967

Membrane bioreactors for water treatment 181

Khoshfetrat A B Nikakhtari H Sadeghifar M amp Khatibi M S (2011) Influence of organicloading and aeration rates on performance of a lab-scale upflow aerated submerged fixed-film bioreactor Process Safety and Environmental Protection 89 193e197

Kim J O amp Jung J T (2007) Performance of membrane-coupled organic acid fermenter fortthe resource recovery from municipal sewage sludge Water Science and Technology 55245e252

Kochan J Wintgens T Melin T amp Wong J (2009) Characterisation and filtrationperformance of coating-modified polymeric membranes used in membrane bioreactorsChemical Papers 63 152e157

Kornboonraksa T amp Lee S H (2009) Factors affecting the performance of membranebioreactor for piggery wastewater treatment Bioresource Technology 100 2926e2932

Laeraa G Polliceb A Saturnob D Giordanob C amp Sandullia R (2009) Influence ofsludge retention time on biomass characteristics and cleaning requirements in a membranebioreactor for municipal wastewater treatment Desalination 236 104e110

Le Clech P Chen V amp Faine T A G (2006) Fouling in membrane bioreactors usedin wastewater treatment Journal of Membrane Science 284 17e53

Le Clech P Jefferson B amp Judd S J (2003) Impact of aeration solids concentration andmembrane characteristics on the hydraulic performance of a membrane bioreactor Journalof Membrane Science 218 117e129

Lee W Kang S amp Shin H (2003) Sludge characteristics and their contribution to micro-filtration in submerged membrane bioreactors Journal of Membrane Science 216217e227

Lesjean B Ferre V Vonghia E amp Moeslang H (2009) Market and design considerationsof the 37 larger MBR plants in Europe Desalination and Water Treatment 6 227

Lesjean B amp Huisjeslow E H (2008) Survey of the European MBR market Trends andperspectives Desalination 231 71e81

Lew B Tarre S Beliavski M Dosoretz C amp Green M (2009) Anaerobic membranebioreactor (AnMBR) for domestic wastewater treatment Desalination 243 251e257

Lin H Peng W Zhang M Chen J Hong H amp Zhang Y (2013) A review on anaerobicmembrane bioreactors Applications membrane fouling and future perspectives Desali-nation 314 169e188

Lin H J Xie K Mahedran B Bagley D M Leung K T Liss S N et al (2009) Sludgeproperties and their effects in submerged anaerobic membrane bioreactors (SAnMBR)Water Research 43 3827e3837

Liwarska-Bizukojc E ampBizukojcM (2005) Digital image analysis to estimate the influence ofsodium dodecyl sulphate on activated sludge flocs Process Biochemistry 40 2067e2072

Lousada-Ferreira M Geilvoet S Moreau A Atasoy E Krzeminski P vanNieuwenhuijzen A et al (2010) MLSS concentration Still a poorly understoodparameter in MBR filterability Desalination 250 618e622

Manigas L (2008) Use of membrane bioreactor for the bioremediation of groundwaterpolluted by chlorinated compounds (PhD thesis) University of Cagliari Italy

Masse A Sperandio M amp Cabassud C (2006) Comparison of sludge characteristics andperformance of a submerged membrane bioreactor and an activated sludge process at highsolids retention time Water Research 40 2405e2415

The MBR Site (2014) Immersed anaerobic MBRs are they viable wwwthembrsitecomAccessed 150314

Meng F Chae S R Drews A Kraume M Shin H S amp Yang F (2009) Recent advancesin membrane bioreactors (MBRs) Membrane fouling and membrane material WaterResearch 43 1489e1512

182 Advances in Membrane Technologies for Water Treatment

Meng F Shi B Yang F amp Zhang H (2007) Effect of hydraulic retention time on membranefouling and biomass characteristics in submerged membrane bioreactors Bioprocess andBiosystems Engineering 30 359e367

Meng F amp Yang F (2007) Fouling mechanisms of deflocculated sludge normal sludge andbulking sludge in membrane bioreactor Journal of Membrane Science 305 48e56

Michael L S amp Fikret K (2002) Bioprocess engineering Basic concepts (2nd ed) UpperSaddle River NJ Prentice Hall

Mulder M (1996) Basic principles of membrane technology (2nd ed) Boston KluwerAcademic ISBN 0-7923-4248

Mutamim N S A Noor Z Z Hassan M A A Yuniarto A amp Olsson G (2013)Membrane bioreactor Applications and limitations in treating high strength industrialwastewater Chemical Engineering Journal 225 109e119

Ng H Y amp Hermanowicz S W (2005) Membrane bioreactor operation at short solidsretention times Performance and biomass characteristics Water Research 39 981e992

OFlaherty V Collins G amp Mahony T (2006) The microbiology and biochemistry ofanaerobic bioreactors with relevance to domestic sewage treatment Reviews in Environ-mental Science and Biotechnology 5 39e55

Pidou M (2006)Hybrid membrane processes for water reuse (PhD thesis) School of AppliedScience Department of Sustainable Systems Centre for Water Science CranfieldUniversity UK

Qin J J Oo H M Tao G Cornelissen E R Ruiken C J de Korte K F et al (2009)Optimization of operating conditions in forward osmosis for osmotic membrane bioreactorOpen Chemical Engineering Journal 3 27e32

Qin J J Oo M H Tao G amp Kekre K A (2007) Feasibility study on petrochemicalwastewater treatment and reuse using submerged MBR Journal of Membrane Science293 161e166

Rajeshwari K V Balakrishnan M Kansal A Lata K amp Kishore V V N (2000) State-of-the-art of anaerobic digestion technology for industrial wastewater treatment Renewableand Sustainable Energy Reviews 4 135e156

Robinsion T (2003) The MBR for industrial effluent Wakefield UK CIWEM amp Aqua EnviroConference

Rosenberger S Kruger U Witzig R Manz W Szewyk U amp Kraume M (2002) Per-formance of a bioreactor with submerged membranes for aerobic treatment of municipalwaste water Water Research 36 413e420

Rosenberger S Kubin K amp Kraume M (2002) Rheology of activated sludge in membranebioreactors Engineering in Life Sciences 2 269e275

Saddoud A amp Sayadi S (2007) Application of acidogenic fixed bed reactor prior to anaerobicmembrane bioreactor for sustainable slaughterhouse wastewater treatment Journal ofHazardous Materials 149 700e706

Sainbayar A Kim J S Jung W J Lee Y S amp Lee C H (2001) Application of surfacemodified polypropylene membranes to an anaerobic membrane bioreactor EnvironmentalTechnology 22(9) 1035e1042

Santos A amp Judd S (2010) The commercial status of membrane bioreactors for municipalwastewater Separation Science and Technology 45 850e857

Sartorius C Walz R amp Orzanna R (2013) Lead market for membrane bioreactor (MBR)technologyeChinarsquos second-mover strategy for the development and exploitation of its leadmarket potential Karlsruhe Fraunhofer Institute for Systems and Innovation Research ISIhttpkooperationenzewdefileadminuser_uploadRedaktionLead_MarketsWerkstattberichteWB_11_MBR_Sartorius_et_alpdf Accessed 010314

Membrane bioreactors for water treatment 183

Shen L Zhou Y Mahendran B Bagley D M amp Liss S N (2010) Membrane fouling in afermentative hydrogen producing membrane bioreactor at different organic loading ratesJournal of Membrane Science 360(1) 226e233

Shimizu Y Okuno Y Uryu K Ohtsubo S ampWatanabe A (1996) Filtration characteristicsof hollow fiber microfiltration membranes used in MBR for domestic wastewater treatmentWater Research 30(10) 2385e2392

Singh K Burke D amp Grant S (2010) Anaerobic flat sheet membrane bioreactor treating foodprocessing wastewater Pilot-scale performance Proceedings of IWA 12th world congresson anaerobic digestion Guadalajara Mexico

Smith A L Stadler L B Love N G Skerlos S J amp Raskin L (2012) Perspectiveson anaerobic membrane bioreactor treatment of domestic wastewater A critical reviewBioresource Technology 122 149e159

Trussell R S Merlo R P Hermanowicz S W amp Jenkins D (2006) The effect of organicloading on process performance and membrane fouling in a submerged membrane biore-actor treating municipal wastewater Water Research 40 2675e2683

Ueda T amp Hata K (1999) Domestic wastewater treatment by a submerged membranebioreactor with gravitational filtration Water Research 33(12) 2888e2892

Visvanathan C Thu L N Jegatheesan V amp Anotai J (2005) Biodegradation of penta-chlorophenol in a membrane bioreactor Desalination 183 455e464

Wateronline (2011) Mixed liquor suspended solids in wastewater httpwwwwateronlinecomarticlemvcMixed-Liquor-Suspended-Solids-In-Wastewater-0002 Accessed 230211

WaterWorld (2012) Membrane multiplier MBR set for global growth e water world wwwwaterworldcomarticleswwiprintvolume-27issue2regularscreative-financemembrane-multiplier-mbr-html Accessed 010314

Yamamoto K Hiasa M Mahmood T amp Matsuo T (1989) Direct solid-liquid separationusing hollow fiber membrane in an activated-sludge aeration tank Water Science andTechnology 21 43e54

Zhang S QuY Liu Y Yang F ZhangX FurukawaK et al (2005) Experimental study ofdomestic sewage treatment with a metal membrane bioreactor Desalination 177 83e93

Zheng X Zhou Y Chen S Zheng H amp Zhou C (2010) Survey of MBR market Trendsand perspectives in China Desalination 250 609e612

van Zyl P J Wenzel M C Ekama G A amp Riedel K J (2008) Design and start-up of ahigh rate anaerobic membrane bioreactor for the treatment of a low pH high strengthdissolved organic wastewater Water Science and Technology 57(2) 291e295

184 Advances in Membrane Technologies for Water Treatment

Advances in electrodialysis forwater treatment 6B Van der BruggenKU Leuven Leuven Belgium

61 Introduction

Electrodialysis is a membrane process driven by a difference in electrical potentialover a membrane stack in which charged compounds are removed from a feed solu-tion It is a process with a relatively long history with several papers published in the1950s on applications such as the demineralization of sugar solutions (Anderson ampWylam 1956) desalination (Dewhalley 1958) and protein separation (Laurence1956) which are still among applications of interest more than half a century laterWhat is remarkable is that although the direction has not substantially changed the in-terest in electrodialysis has boomed during the past decade The number of publica-tions on electrodialysis has doubled in 10 years and has increased by a factor of 10in 30 years Moorersquos law seems to be valid for electrodialysis as well This is partlythe result of the global tendency to publish more and more papers not necessarilyof higher or even the same quality Nevertheless it is interesting to observe thechanges in research interest over the years The most conservative conclusion fromthe numbers is that electrodialysis has remained a process of particular interest in termsof its potential for separation as well as in terms of applications over 6 decades It wasalready considered a mature process in 1972 (Solt 1972) and it is not surprising thatthe research topics have only partially shifted since the early days Scaling problemsfor example were reported in one of the earliest publications on electrodialysis(Cooke 1958) and are still on the research agenda today Examples include the devel-opment of pretreatment methods such as pre-softening with a pellet reactor (TranJullok Meesschaert Pinoy amp Van der Bruggen 2013) and the use of electrochemicalprocesses to remove scaling from membranes (Zaslavschi Shemer Hasson amp Semiat2013) The separation of proteins was already understood in earlier days to have po-tential (Laurence 1956) although the breakthrough in this area came much latermany applications today are in the dairy industry for whey protein concentrationmilk protein standardization etc (Daufin et al 2001) Applications and methodshowever are much more advanced today Electrodialysis with ultrafiltration mem-branes for example allows for advanced separation of peptides by exploiting the com-bined effect of charge and size separation by fine-tuning the pH and cutoff of themembrane (Firdaous et al 2009 Roblet Doyen Amiot amp Bazinet 2013) Electrodi-alysis in that context would touch the performance of a nanofiltration membranealthough the potential for specific separations is different (Langevin Roblet MoresoliRamassamy amp Bazinet 2012) Coupling nanofiltration and electrodialysis (with

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400006-XCopyright copy 2015 Elsevier Ltd All rights reserved

ultrafiltration membranes) in a single process line would optimize the overall separa-tion performance and allow the production of more specific peptide fractions The prin-ciple of electrodialysis can be further extended in view of the improved separation ofpeptides In the electrophoretic membrane contactor a porous membrane is used toestablish contact across two flowing liquids between which an electrically drivenmass transfer takes place (Galier amp Roux-de Balmann 2011)

In terms of applications comparison with the early days yields more surprisesUrine separation is currently a topic of considerable interest Historically the use ofelectrodialysis for salt separation was described in 1960 in a publication that appearedin Nature (Wood 1960) At that moment it did not attract much interest (it was citedan impressive three times) but today urine separation has been revived Scientific in-terest has shifted and the separation needed today is more challenging than only theremoval of salts the focus is rather on recycling of nutrients while micropollutantsshould be kept out of the eventual product (Pronk Biebow amp Boller 2006) Electro-dialysis is probably a critical process to achieve this although none of the processessuggested for urine separation including electrodialysis have so far advanced beyondthe laboratory stage a combination of solutions may be needed to meet the require-ments (Maurer Pronk amp Larsen 2006) A combination of electrodialysisprecipitation and evaporation has perspectives of application in developing countriesthis can be linked to local business development which is an important prerequisitefor the implementation of new technologies in developing countries (Pronk ampKone 2009)

Despite the continuous presence of electrodialysis on the separations scene it is byno means a static process Apart from the logical shift in attention for various applica-tions the main advances in electrodialysis are related to the breakthrough of electro-dialysis with bipolar membranes (which allows for integrated reactions in situcombination of fermentation and electrodialysis and in general the conversion ofsalts to their corresponding acids and base in a wide range of applications) and theuse of non-classical membrane materials and configurations for advanced separationsThese are described in more detail in this chapter Other advances are the integration ofelectrodialysis with traditional unit operations and other membrane separations in thechemical biochemical food and pharmaceutical industries (Xu amp Huang 2008) thedevelopment of reverse electrodialysis to capture renewable energy from mixing saltand freshwater (Vermaas et al 2013) and ionic liquideassisted electrodialysis forconcentrating acidifying and removing organic salts from aqueous solution(Lopez amp Hestekin 2013) or for the selective recovery of lithium from seawater(Hoshino 2013)

In addition even after over half a century the fundamental understanding ofall phenomena related to electrodialysis is still a point of attention For examplemechanisms for overlimiting current and concentration polarization are not yet well un-derstood and only recently was a first-principles model involving the NernstePlanckePoisson equations fully coupled with the NaviereStokes equations proposed(Urtenov et al 2013) At the same time the leaky membrane model was proposed as asimplified model based on the NernstePlanck equation (Dydek amp Bazant 2013) Otherefforts aim to translate the process fundamentals to a simulation model (Tanaka 2013)

186 Advances in Membrane Technologies for Water Treatment

which surprisingly has not yet converged for electrodialysis To understand the flow inan electrodialysis stack computational fluid dynamics can be used (Tamburini La Bar-bera Cipollina Ciofalo amp Micale 2012)

This chapter describes the fundamentals of electrodialysis in brief with the aim ofunderstanding the process principles (for a more in-depth analysis of the fundamentalsthe reader is referred to the publications mentioned above) followed by a review of theadvances of electrodialysis in water treatment as stated previously

62 Fundamentals of electrodialysis for water treatment

Two kinds of membranes are used in electrodialysis anion exchange and cationexchange These two membrane types are alternated in a membrane stack so that arepeating unit is obtained consisting of a compartment with an anion exchangemembraneon the left side and a cation exchange membrane on the right followed by anothercompartment with an anion exchange membrane on the right side and a cation exchangemembrane on the left

Over this membrane stack a difference in electrical potential is applied using elec-trodes at both ends of the stack The feed solution is pumped through the stack Cationsmigrate in the direction of the negatively charged cathode and are allowed to migratethrough the first cation exchange membrane The next membrane is an anion exchangemembrane so that the cation cannot migrate further Anions migrate in the direction ofthe positively charged anode and can migrate through the first anion exchange mem-brane The next membrane is a cation exchange membrane so that the anion cannotmigrate further (Figure 61) The membranes are in principle not permeable for wateralthough osmosis and electro-osmosis are known to occur in an electrodialysis stack

Cathode(ndash)

Anode(+)

+

ndash ndash ndash ndash ndash

+ + + + +

Electrode rinse

ConcentrateDiluate

Figure 61 Ion migration in a salt solution through the membrane stack

Advances in electrodialysis for water treatment 187

In this way positive as well as negative ions are removed from the feed solutionwhereas the neighboring compartments are concentrated

The flow through the feed compartments is usually denoted as the diluate streamthe flow with increasing concentration is denoted as the concentrate stream

The combination of a series of cells (consisting of an anion exchange and a cationexchange membrane and a diluate compartment and a concentrate compartment) isnecessary to decrease the time needed to purify a given stream (in a batch configurationwith recycling) or decrease the size of the membranes in the system (in a flow-throughsystem)

Because of the flow of ions through the stack the electrical current is transferredThe extent to which the electrical current is effectively used for migration of ionsthat should be removed determines the efficiency of electrodialysis

Apart from the diluate and concentrate flow an electrode rinse solution is generallyapplied The electrodes are positioned in separate compartments to protect the elec-trode material At the cathode hydrogen gas and hydroxyl ions may be formed owingto the dissociation of water (after application of a voltage) The hydroxyl ions maypossibly damage the electrode when the electrode material is not carefully selectedAn acid is usually added to the rinse liquid of the cathode to prevent damage

At the anode the electrode material is at risk because of the formation of metal ox-ides at the electrode surface (corrosion) which can then dissolve in an acid environ-ment Possible materials with sufficient resistance are graphite stainless steel nickelalloys or a Platinum coating Reactions with a metal M are

Mthorn xOH5MethOHTHORNx thorn xe

2Mthorn 2xOH5M2Ox thorn xH2Othorn 2xe

Because of the consumption of OH hydrogen ions are left which make the solu-tion more acidic This dissolves metal ions

MethOHTHORNx thorn xHthorn5Mxthorn thorn xH2O

M2Ox thorn xHthorn52Mxthorn thorn xH2O

H2 Cl2 and O2 may be formed as a result of oxidation reactions at the anode Thesecause negative effects Therefore it is important to make sure that negative ions (suchas Cl) do not have access to the electrode compartments For the cathode this is notproblematic because it repels anions but the anode needs sufficient protection Thiscan be achieved by using two cation exchange membranes The electrode rinse solu-tion usually contains SO2

4 which would not cause problems at the anodeMembranes are often exposed to aggressive compounds Furthermore because of

the electrical resistance the temperature may increase Many feed flows (eg surfacewater) contain suspended solids These may damage the membrane as the result of fric-tion and scouring The chemical thermal and mechanical resistance of the membranesis therefore an important parameter to consider

188 Advances in Membrane Technologies for Water Treatment

Between the membranes a spacer is positioned that is usually made of a polymer(polyethylene polyvinylchloride (PVC) or specialty polymers) The spacers providemechanical support to the membranes They are made in a maze configuration thatensures the membranes are not pressed onto each other They also provide goodflow dynamics by promoting turbulence

When the membranes are brought into the solution a chemical potential differencearises between the solution and the inner structure of the membrane This brings ionsof the same sign as the fixed ions into the membrane These are called co-ions For thesame reason counter-ions migrate from the membrane to the bulk of the solutionThen a dominant charge emerges in the membrane (co-ions and fixed ions have ahigher concentration and the same charge) giving rise to an electrical potential thatopposes the chemical potential This electrical potential (the Donnan potential) limitsthe co-ion concentration in the membrane and the removal of counter-ions from themembrane

When the electrical potential difference is applied over the electrodes a current willarise in which the counter-ions and co-ions take part Mainly counter-ions are trans-ported because their concentration is higher

This also demonstrates that there cannot be an ideally selective membrane becausetransport of ions always starts with the transport of co-ions The co-ion concentrationin the membrane is never zero at the startup This selectivity is described by the perm-selectivity and therefore also by the transport number

The selectivity of ion exchange membranes for anions or cations is related to thecharge which is in turn due to the presence of specific functional groups Anion ex-change membranes contain positively charged groups (typically quaternary ammo-nium salts) that attract anions Cations on the other hand are repelled Cationexchange membranes contain negatively charged groups (sulfonic acid or carboxylicacid groups) that attract cations Anions on the other hand are repelled

The selectivity of the membranes is determined by the transport number andpermselectivity A transport number of 1 for a cation exchange membrane meansthat it permeates all cations and retains all anions and vice versa for an anionexchange membrane In practice membranes with a transport number of 09 areconsidered good

The transport number ti of a component c is defined as

tc frac14 jci

(61)

where jc is the ion flow density and i is the current density

The permselectivity Pthorn is Pthorn frac14 tthorn tthorn1 tthorn

(62)

where tthorn is the value in the middle of the membrane The permselectivity is con-centration dependent when the concentration in the electrolyte solution is high moreco-ions end up in the membrane

Advances in electrodialysis for water treatment 189

The electrical resistance of a membrane largely determines the current losses occur-ring in the stack The lower this resistance is the less the temperature in the stack willincrease and therefore the fewer losses will occur Thus the electrical resistance of themembranes should be kept as low as possible to limit losses because the resistance ofthe flows through the stacks cannot be changed The order of magnitude of the elec-trical resistance of a membrane is 2e10 ohmcm2

When the electrical potential of the process is increased the current density in-creases as well More ions are transported This may lead to a total depletion ofions in the boundary layer at the diluate side of the membrane Then the current densitycannot increase further because no ions are left to transport the electrical current Thisis called the limiting current density At this point the efficiency of the process hasbecome low The electrical energy is consumed to split water into its ions whichcan transport the electrical charge and maintain the potential difference and currentdensity The electrical resistance has enormously increased It is important not toexceed this limiting current density The limiting current density can be determinedexperimentally using the method of Cowan and Brown which involves measuringelectrical resistance R as a function of the reciprocal current I 1 (Figure 62) Theintersection of the two lines tangential to the legs of the curves determines the limitingcurrent (from which the limiting current density can be calculated)

Another phenomenon that may occur is back-diffusion This occurs when thedriving force of the concentration difference between the diluate and the concentratecompartment has increased so much that ions diffuse from the concentrate compart-ment back to the diluate compartment against the electrical flow This should be taken

1I (Andash1)

R (VA)

Limiting current

Figure 62 Determination of the limiting current and the limiting current density inelectrodialysis

190 Advances in Membrane Technologies for Water Treatment

into account when applying concentrated solutions to an electrodialysis unit Electro-dialysis allows one to obtain a concentration factor up to ca 200e250

At the diluate side the ion concentration in the boundary layer (close to the mem-brane) is lower than in the bulk of the flow At the concentrate side the ion concentra-tion in the boundary layer (close to the membrane) is higher than in the bulk of theflow This is the result of diffusion Both concentrations can be calculated as

cm frac14 cb tm tbl

$i$d

z$F$Dethfor the diluate sideTHORN (63)

cm frac14 cb thorntm tbl

$i$d

z$F$Dethfor the concentrate sideTHORN (64)

The limiting current density in the boundary layer can be calculated from (eg atthe diluate side)

ilim frac14 z$D$F$ethcb cmTHORNd$tm tbl

(65)

where cb is the bulk concentration of the solute at a distance d from the membrane cmis the concentration of the solute near the membrane F is the Faradayrsquos constant(96487 Cmol) D is the diffusion coefficient (ms) z is the valence of the ion d isthe thickness of the boundary layer (m) tm is the transport number of the ion in themembrane and tbl is the transport number of the ion in the boundary layer

The limiting current density is reached when cm goes to zero The above equationfor the current density for cm frac14 0 (limiting current density) is

ilim frac14 z$D$F$cbd$tm tbl

It has been experimentally demonstrated that the limiting current density of a solu-tion increases linearly with temperature

ilim frac14 Athorn 4$T

where A is the limiting current density (ilim) at 0 C T is the temperature and 4 is thetemperature coefficient for the limiting current density

A and 4 are constants for a given concentration and a given species The concen-tration dependency for a given compound is linear as well

The temperature in the stack increases during electrodialysis so that during the pro-cess the limiting current density increases The flow velocity also increases themaximal current

Membrane fouling however will decrease the limiting current density All of thisshould be taken into account to ensure that the limiting current density is not exceeded

Advances in electrodialysis for water treatment 191

The limiting current density of the cation exchange and anion exchange membranesfor a solution with a single salt is not necessarily the same It is only the same when thecation and the anion have the same transport number If not the transport number ofthe cation is usually smaller than that of the anion and in that case the limiting currentdensity will first be attained at the cation-selective membrane In the ReI1 curve twoseparate minima are then visible for the two types of membranes

For solutions containing several solutes or a mixture of ions each compound willhave its own limiting current density

63 Advances in membrane materials for electrodialysisfor water treatment

Electrodialysis membranes are dense membranes that can be either heterogeneous orhomogeneous Heterogeneous membranes are made of an ion exchange resin whichis milled to a small grain size and then mixed with a solution of binding polymers(PVC rubber styrenedivinylbenzene copolymer etc) The ratio of resin grains andbinding polymer determines the electrical and mechanical properties of the membraneMore binding polymer improves the mechanical strength but also increases the elec-trical resistance Heterogeneous membranes have a limited mechanical strength and ahigh electrical resistance in general

Homogeneous membranes are synthesized by adding ionizable functional groups toa polymeric film The polymers that are used have to

bull induce a uniform charge distributionbull have good mechanical stability and low electrical resistancebull be cross-linked to reduce swelling when applied in water

The more charges are introduced the better is the conductivity but this leads toswelling because the material becomes more hydrophilic Cross-linking anchors thepolymeric chains in the polymer by chemically linking the chains to one anotherthis reduces swelling

Homogeneous membranes are thinner than heterogeneous membranes which re-duces their resistance They are mechanically stronger because they are directlymade as a film (unlike heterogeneous membranes)

The charge density of typical membranes is 1e2 mEqg (dry polymer)The membrane material contains functional groups that enable ion transport The

charged groups remaining on the membrane surface are the fixed ions the ions thatare dissociated from their functional group are the counter-ions Both are hydratedwhen an aqueous feed is applied Anion exchange membranes often contain quater-nary ammonium groups as fixed ions cation exchange membranes contain sulfonylor carboxyl groups Anion exchange membranes can be recognized by their trans-parent white color Cation exchange membranes vary in color from amber-brown towhite depending on the type

Regular ion exchange membranes are not selective However some anion exchangemembranes have been developed with selectivity for monovalent ions (such as the

192 Advances in Membrane Technologies for Water Treatment

ACS series of anion exchange membranes of Eurodia Industrie SA (WissousFrance)) This allows for the selective removal of eg nitrates compared with (diva-lent) sulfates This is important to manage the total dissolved solids (TDS) of the prod-uct stream which should not be too low for most applications including potable waterwhereas nitrates should be removed to a larger extent A typical outcome is a reductionof the nitrate concentration by 84 with a reduction in TDS by 49 The advantage ofthis is that remineralization after nitrate removal is no longer necessary

Whereas the number of ion-exchange membranes was limited until a decade agoresearch efforts have resulted in a much wider range of polymeric membranes (eventhough these are generally not commercially available) Synthesis of anion exchangemembranes includes poly(vinyltrimethoxysilane-co-2-(dimethylamine)ethylmethacry-late) copolymer (Chakrabarty Prakash amp Shahi 2013) membranes composed of4-vinylbenzyl chloride styrene and ethylmethacrylate (Koo Kwak amp Hwang2012) cross-linked polystyrene (Sachdeva Ram Singh amp Kumar 2008) acryloni-trilebutadienestyrene with activated carbon and silver fillers (Zendehnam RobarmiliHosseini Arabzadegan amp Madaeni 2013) and aliphatic-hydrocarbonebased anionexchange membranes prepared from glycidyl methacrylate and divinylbenzene(Tanaka Nagase amp Higa 2011) to name just a few Such membranes may be appli-cable in other electromembrane applications such as fuel cells (Merle Wessling ampNijmeijer 2011)

Cation exchange membranes include polystyrene and polyaniline blends (AmadoGondran Ferreira Rodrigues amp Ferreira 2004) heterogeneous polyvinylchloridestyreneebutadieneerubber blends (Hosseini Madaeni Heidari amp Moghadassi2011) and monovalent selective membranes made of blends of sulfonated poly(ethersulfone) with sulfonated poly(ether ether ketone) (Gohil Nagarale Binsu amp Shahi2006) Furthermore ceramic cation exchange membranes synthesized by impregna-tion of microporous ceramic supports with zirconium phosphate have been developedfor aggressive wastewater applications (Marti-Calatayud Garcia-Gabaldon Perez-Herranz Sales amp Mestre 2013) and phosphotungstic acidebased membranes ongraphite support intended for use as electrolyte-filled separators for batteries andsuper-capacitors (Seepana Pandey amp Shukla 2012)

This shows the large potential of various materials as anion exchange or cationexchange membranes although commercialization today is still limited

A bipolar membrane consists of a combination of a cation exchange and an anionexchange membrane (Figure 63) Between the two membranes a water film is presentfrom which water is dissociated the bipolar membrane is a source of anions (OH) aswell as cations (Hthorn) although they end up in different compartments on both sides ofthe bipolar membrane

Development and application of bipolar membranes have emerged especially in thepast decade Research on synthesis has resulted in eg sulfonated polystyrene ethylenebutylene polystyrene-poly(vinyl alcohol)equaternized polystyrene ethylene butylenepolystyrene bipolar membranes (Venugopal amp Dharmalingam 2013) poly(vinyl alco-hol)esodium alginate chitosan with TiO2 and ZnO (Chen Hu Chen Chen amp Zheng2011) and poly(vinyl alcohol)epoly(anetholesulfonic acid sodium salt) (cation selec-tive) and poly(vinyl alcohol)epoly(diallyldiethylammonium bromide) (anion selective)

Advances in electrodialysis for water treatment 193

bipolar membranes (Espinoza-Gomez Flores-Lopez Rogel-Hernandez amp Martinez2009) Several more examples can be found in the literature

64 Advances in membrane modules and systemconfigurations for electrodialysis for watertreatment

The classical stacked module is still the standard configuration Advances in moduledesign are primarily related to the use of spacers in the stack Spacers increase the elec-trical resistance which translates into higher power consumption Optimization of thefluid dynamics within the channels is still a problem as demonstrated by computa-tional fluid dynamics simulations to predict the fluid flow field inside a single channelinside an electrodialysis stack (Tamburini et al 2012) An appropriate choice of netspacer material can influence the slipno-slip condition of the flow on the spacer wiresthus significantly affecting the channel fluid dynamics in terms of pressure drops(Gurreri Tamburini Cipollina amp Micale 2012) A conducting spacer instead of thetraditional non-conducting spacer may help overcome electrical resistance (ZhangWang amp Goa 2012) whereas fluid dynamics and electrical resistance may beimproved simultaneously when using ion exchange membranes in which the spaceris formed directly on the membrane surface (Balster Stamatialis amp Wessling2010) so that it is no longer a separate entity

Further innovations are related to the stack configuration The use of bipolar mem-branes as described above yields a four-compartment membrane stack which is anextension of the classical three-compartment approach Such configuration is alsoapplied in selectrodialysis a process using a four-compartment stack without bipolar

Cathode

OHndash

H+

H2O

Bipolar membrane

Anode

Figure 63 Representation of a bipolar membrane for electrodialysis

194 Advances in Membrane Technologies for Water Treatment

membranes but with a combination of selective and nonselective membranes toachieve fractionation of ions so that for example phosphates can be selectivelyremoved from a feed stream (Zhang Paepen Pinoy Meesschaert amp Van der Bruggen2012) This is shown in Figure 64

A feed solution containing cations monovalent anions and divalent anions ispumped through the first compartment which is sealed by a cation exchangemembrane (CM) and an anion exchange-selectivemembrane (AM) The cationsmigrateunder the influence of the applied electrical potential difference toward the cathodepassing the CM The anions monovalent as well as bivalent migrate toward the anodeand thus pass theAMThus the solution of themiddle compartment the product will beenriched with anions At the same time monovalent ions available in this productcompartment migrate toward the anode passing the AMV This compartment iswhere the selection of the monovalent versus bivalent ions occurs and is denoted asthe selector This compartment is enriched in bivalent anions monovalent ions areremoved The third compartment (brine compartment) is enriched by the migratingmonovalent anions This process was shown to be feasible for concentrating phosphateions selectively from wastewater (Zhang et al 2013)

Other innovations relate to the flow through electrodialysis stacks A co-current hy-draulic flow mode of the salt solutions through the compartments of the stack is oftenapplied which requires a series of separation modules This can be improved bychanging the classical co-current hydraulic flow mode into a mixed flow mode inwhich the internal hydraulic flow of diluate and concentrate is co-current in the stackcompartments but is externally counter-current over the total series of stacks (Braunset al 2012)

Integrated processes may further extend the range of applications for water treat-ment As an example the separation of Co2thorn and Ni2thorn is discussed two cations

AM AMV CM

ProductFeed Brine

Clndash

ERS

SO42ndash

Na+

Na+

CM

Clndash

SO42ndash

Na+Na+Clndash

Clndash

Figure 64 Selectrodialysis stack for ion fractionation ERS electrode rinse solutionCM cation exchange membrane AM anion exchange membrane (nonselective) AMV anionexchange membrane (selective for monovalent ions)

Advances in electrodialysis for water treatment 195

with the same charge and approximately the same size (Xu 2001) Separation can beachieved by two electrodialysis stacks in series the first one of which is a conventionalelectrodialysis unit followed by an electrodialysis unit with bipolar membranes(Figure 65)

A wastewater stream containing a mixture of Co2thorn and Ni2thorn is supplied to compart-ment 1 The positive ions in this case Co2thorn and Ni2thorn migrate through the cationexchange membrane to compartment 2 In this compartment a complexing agent ispresent denoted as HR This agent selectively forms a complex with one of the twocations according to the reactions

Co2thorn thorn 2R Kc

CoR2

Ni2thorn thorn 2R Kc

NiR2

For the separation considered here Kc is much larger for Ni2thorn than for Co2thorn so thatonly the nickel complex is formed The cobalt ions are not complexed and can there-fore migrate through the two consecutive cation exchange membranes to compartment4 There they combine with an anion to the corresponding metal salt This concentratestream contains only the cobalt salt and no nickel

Nickel occurs now as a neutral complex in the solution and therefore cannot migrateto another compartment

++++++ +

++++++ +

++++++ +

++++++ +

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

++++++ +

Ni2+

Co2+

Clndash

Co2+

Ni2+

Co2+Co2+

Clndash

CoCl2

ClndashH+

Ni2+ Ni2+

NiCl2

OHndash

1 2 3 4

5 6 7

Ni2+

Co2+

Clndash

8

HR

Figure 65 Separation of ions with the same charge and similar size using electrodialysis andelectrodialysis with bipolar membranes (EDBM)

196 Advances in Membrane Technologies for Water Treatment

The solution in compartment 2 is fed to compartment 7 of the EDBM system In thiscompartment there is an excess of Hthorn ions so that the pH is sufficiently low for thefollowing reaction to occur

NiR2 thorn 2Hthorn Kc

Ni2thorn thorn 2HR

At low pH the Ni2thorn ions are exchanged for protons and are again released The pro-tons come from the bipolar membrane The free nickel ions can further migratethrough the cation exchange membrane to compartment 8 where they can be separatedas a metal salt

The complexing agents from compartment 5 are recycled to compartment 2together with the hydroxyl ions that are released in compartment 6 to increase thepH again to a neutral value These hydroxyl ions are also generated by the bipolarmembrane

The net result is that the Co2thorn ions accumulate in compartment 4 and the Ni2thorn ionsare collected in compartment 8

The concentration difference between Ni2thorn and Co2thorn ions in the correspondingcompartments can reach up to 120

65 Applications of electrodialysis for water treatment

The dominant application of electrodialysis is still in desalination This is a well-established application that can be readily applied Emerging applications are thereforein (1) the use of electrodialysis for alternative feed waters (2) ion fractionation and (3)the use of bipolar membranes in a wide range of production or conversion processes

A typical example of alternative feed water is concentrated brine from an reverseosmosis (RO) plant in which electrodialysis is used as a technology to prevent damageto marine ecosystems (Jiang Wang Zhang amp Xu 2014) Similarly the concentrateresulting from RO of treated wastewater is applied to reduce the volume of salty waterdischarge (Zhang Ghyselbrecht Meesschaert Pinoy amp Van der Bruggen 2011)Electrodialysis was found to be a viable technology but scaling may be a problembecause of the enhanced concentration of carbonates after wastewater treatmentIndustrial wastewater applications have been considered as well (Silva Poiesz ampvan der Heijden 2013) electrodialysis is feasible in terms of the separation of mono-valent and divalent ions with energy requirements ranging from 6 to 11 kW hm3 offeed stream depending on the water reclamation rate

Fractionation using electrodialysis has main applications for amino acids Aminoacids can be transported selectively across a double membrane system composed of acation exchange and an anion exchange membrane via pH adjustment of the sourcephase solution (Tsukahara Nanzai amp Igawa 2013) Electrodialysis with commerciallyavailable ion exchange membranes was applied to isolate the basic amino acids L-lysine(Lys) and L-arginine (Arg) (Readi Girones Wiratha amp Nijmeijer 2013) This has evenmore potential when electrodialysis is applied with ultrafiltration membranes This wasdemonstrated in several applications such as the separation of a pepsinepancreatin soy

Advances in electrodialysis for water treatment 197

protein isolate hydrolysate (Roblet et al 2013) and to recover and concentrate the activeantibacterial fraction of a snow crab by-products hydrolysate which is the result of apeptide with a molecular weight of about 800 Da (Doyen Saucier Beaulieu Pouliotamp Bazinet 2012) The attraction of using ultrafiltration membranes for electrodialysisapplications is in the possibility of fine-tuning the separation on the basis of either chargeseparation or size exclusion which allows for specific separation of charged organiccompounds typically related to peptides

However selective removal of other ions is also interesting One example is the useof monovalent permselective membranes for selective removal of arsenic and mono-valent ions from brackish water RO concentrate (Xu Capito amp Cath 2013) Mono-valent permselective anion exchange membranes have high selectivity in removingmonovalent anions over di- and multivalent anions In general transport of monova-lent and divalent ions is different because of steric effects and different charge inter-actions for example a removal rate of more than 70 for monovalent ions mightcorrespond to a removal rate below 50 for divalent ions (Silva et al 2013) Thiscan be exploited and optimized for eg the removal of nutrients from wastewater

The use of bipolar membranes has been considered in many studies The moststraightforward one is when concentrates from seawater desalination are used asfeed This yields a mixture of sulfuric acid and hydrochloric acid on the one sideand sodium hydroxide on the other A concentration of 1 molL can be obtained inrealistic conditions with a good prospect for long-term operation (Shen Huanget al 2013) Similar observations were made for industrial saline water mainlycomposed of NaCl and KCl which yielded an acid and a base stream with a concen-tration of around 2 molL (Ghyselbrecht et al 2013) Bipolar membranes were used inanother application on a pilot scale to recover glyphosate and the production of baseacid with high concentration in view of the zero discharge of wastewater (Yang GaoFan Fu amp Gao 2014) Electrodialysis with bipolar membranes may be coupled withdiffusion dialysis for two-step recovery with electrodialysis as the second step torecover the remaining concentrations of acid (Zhuang et al 2013) More applicationsinclude the production of morpholine (Jiang Wang amp Xu 2013) the separation oflithium and cobalt in view of the recycling of waste lithiumeion batteries in a similarapproach as described above for nickel and cobalt (Iizuka Yamashita NagasawaYamasaki amp Yanagisawa 2013) the production of tetrapropyl ammonium hydroxideon a pilot scale with a perspective for full-scale industrial application (Shen YuHuang amp Van der Bruggen 2013) and the production of L-ascorbyl-2-monophosphate a stable substitute of vitamin C (Song et al 2012) Many moreapplications have been reported which indicates the potential of electrodialysis withbipolar membranes as a versatile process A complete overview however is beyondthe scope of this chapter

66 Future trends

Electrodialysis has been of interest for the past 5 decades although for a limited rangeof applications such as the desalination of brackish water This will not substantially

198 Advances in Membrane Technologies for Water Treatment

change in years to come although an increase in these applications is not expectedbecause of competition with more cost-effective processes (at higher salt concentra-tions) such as RO and membrane distillation Other applications related to selectiveremoval of one or more ions however may become attractive when membrane mate-rials are developed with better selectivity (eg for nitrate specific peptides or phos-phate) or when alternative stack configurations are applied in which a fractionationeffect can be obtained

Since the turn of the century bipolar membranes have been increasingly studiedand applied This opens up a new range of applications related to combined reactionand purification owing to the acidebase splitting effect Numerous applications canbe based on this feature and many more are on the agenda to be further developedin coming years This will in turn stimulate the availability of bipolar membraneswith a further positive effect on the application market

One question remains for electrodialysis which is related to the sustainability of thesystem Although the process is claimed to be a green technology this may be arguedfrom an energetic point of view particularly when taking the exergetic value of therequired electrical energy into account Therefore more attention to this aspect is crit-ical Combined systems based on renewable energy may overcome this issue whichthen will allow for example remote applications of electrodialysis

Sources of further information and advice

Tanaka Y (2013) Ion exchange membrane electrodialysis Fundamentals desalination sep-aration (Water resource planning development and management series) New YorkNova

Bernardes A Siqueira Rodrigues M A amp Zoppas Ferreira J (Eds) (2014) Electrodialysisand water Reuse Berlin Heidelberg Springer

Strathmann H (2011) Introduction to membrane science and technology WeinheimGermany Wiley

Sata T (2004) Ion exchange membranes Preparation characterization modification andapplication London Royal Society of Chemistry

Strathmann H (2004) Ion-exchange membrane separation processes New York Elsevier

References

Amado F D R Gondran E Ferreira J Z Rodrigues M A S amp Ferreira C A (2004)Synthesis and characterisation of high impact polystyrenepoly aniline composite mem-branes for electrodialysis Journal of Membrane Science 234(1e2) 139e145

Anderson A M amp Wylam C B (1956) Ion exchange electrodialysis for demineralisation ofsugar solutions Chemistry and Industry 12 191e192

Balster J Stamatialis D F ampWessling M (2010) Membrane with integrated spacer Journalof Membrane Science 360(1e2) 185e189

Brauns E Bossaer J Toye S Mijnendonckx K Pinoy L amp Van der Bruggen B (2012) Astudy of electrodialysis operating with mixed flow mode Separation and PurificationTechnology 98 356e365

Advances in electrodialysis for water treatment 199

Chakrabarty T Prakash S amp Shahi V K (2013) End group cross-linked 2-(dimethylamino)ethylmethacrylate based anion exchange membrane for electrodialysis Journal of Mem-brane Science 428 86e94

Chen R Y Hu Y Y Chen Z Chen X amp Zheng X (2011) Preparation and char-acterization of bipolar membranes modified using photocatalyst nano-TiO2 and nano-ZnO Journal of Applied Polymer Science 122(2) 1245e1250

Cooke B A (1958) Scaling problems in electrodialysis using permselective membranesChemistry and Industry 19 555e556

Daufin G Escudier J P Carrere H Berot S Fillaudeau L amp Decloux M (2001) Recentand emerging applications of membrane processes in the food and dairy industry Food andBioproducts Processing 79(C2) 89e102

Dewhalley C H (1958) Desalting of water by electrodialysis Chemistry and Industry 18e13

Doyen A Saucier L Beaulieu L Pouliot Y amp Bazinet L (2012) Electroseparation of anantibacterial peptide fraction from snow crab by-products hydrolysate by electrodialysiswith ultrafiltration membranes Food Chemistry 132(3) 1177e1184

Dydek E V amp Bazant M Z (2013) Nonlinear dynamics of ion concentration polarization inporous media The leaky membrane model AIChE Journal 59(9) 3539e3555

Espinoza-Gomez H Flores-Lopez L Z Rogel-Hernandez E amp Martinez M (2009)Preparation and characterization of PVAPASA-PVAPDDAB bipolar membrane Journalof the Brazilian Chemical Society 20(7) 1294e1301

Firdaous L Dhulster P Amiot J Gaudreau A Lecouturier D Kapel R et al (2009)Concentration and selective separation of bioactive peptides from an alfalfa white proteinhydrolysate by electrodialysis with ultrafiltration membranes Journal of Membrane Science329(1e2) 60e67

Galier S amp Roux-de Balmann H (2011) The electrophoretic membrane contactor A mass-transfer-based methodology applied to the separation of whey proteins Separation andPurification Technology 77(2) 237e244

Ghyselbrecht K Huygebaert M Van der Bruggen B Ballet R Meesschaert B amp Pinoy L(2013) Desalination of an industrial saline water with conventional and bipolar membraneelectrodialysis Desalination 318 9e18

Gohil G S Nagarale R K Binsu V V amp Shahi V K (2006) Preparation and charac-terization of monovalent cation selective sulfonated poly(ether ether ketone) and poly(ethersulfone) composite membranes Journal of Colloid and Interface Science 298(2)845e853

Gurreri L Tamburini A Cipollina A amp Micale G (2012) CFD analysis of the fluid flowbehavior in a reverse electrodialysis stack Desalination and Water Treatment 48(1e3)390e403

Hoshino T (2013) Preliminary studies of lithium recovery technology from seawater byelectrodialysis using ionic liquid membrane Desalination 317 11e16

Hosseini S M Madaeni S S Heidari A R amp Moghadassi A R (2011) Preparation andcharacterization of polyvinyl chloridestyrene butadiene rubber blend heterogeneous cationexchange membrane modified by potassium perchlorate Desalination 279(1e3)306e314

Iizuka A Yamashita Y Nagasawa H Yamasaki A amp Yanagisawa Y (2013) Separationof lithium and cobalt from waste lithium-ion batteries via bipolar membrane electrodialysiscoupled with chelation Separation and Purification Technology 113 33e41

Jiang C X Wang Y M amp Xu T W (2013) An excellent method to produce morpholineby bipolar membrane electrodialysis Separation and Purification Technology 115 100e106

200 Advances in Membrane Technologies for Water Treatment

Jiang C X Wang Y M Zhang Z H amp Xu T W (2014) Electrodialysis of concentratedbrine from RO plant to produce coarse salt and freshwater Journal of Membrane Science450 323e330

Koo J S Kwak N S amp Hwang T S (2012) Synthesis and properties of an anion-exchangemembrane based on vinylbenzyl chloride-styrene-ethyl methacrylate copolymers Journalof Membrane Science 423 293e301

Langevin M E Roblet C Moresoli C Ramassamy C amp Bazinet L (2012) Comparativeapplication of pressure- and electrically-driven membrane processes for isolation ofbioactive peptides from soy protein hydrolysate Journal of Membrane Science 40315e24

Laurence D J R (1956) Separation of proteins by electrodialysis through filter-paper mem-branes Biochemical Journal 62(3) 36

Lopez A M amp Hestekin J A (2013) Separation of organic acids from water using ionicliquid assisted electrodialysis Separation and Purification Technology 116 162e169

Marti-Calatayud M C Garcia-Gabaldon M Perez-Herranz V Sales S amp Mestre S(2013) Synthesis and electrochemical behavior of ceramic cation-exchange membranesbased on zirconium phosphate Ceramics International 39(4) 4045e4054

Maurer M Pronk W amp Larsen T A (2006) Treatment processes for source-separated urineWater Research 40(17) 3151e3166

Merle G Wessling M amp Nijmeijer K (2011) Anion exchange membranes for alkaline fuelcells A review Journal of Membrane Science 277(1e2) 1e35

Pronk W Biebow M amp Boller M (2006) Electrodialysis for recovering salts from a urine so-lution containing micropollutants Environmental Science amp Technology 40(7) 2414e2420

Pronk W amp Kone D (2009) Options for urine treatment in developing countries Desali-nation 248(1e3) 360e368

Readi O M K Girones M Wiratha W amp Nijmeijer K (2013) On the isolation of singlebasic amino acids with electrodialysis for the production of biobased chemicals Industrialand Engineering Chemistry Research 52(3) 1069e1078

Roblet C Doyen A Amiot J amp Bazinet L (2013) Impact of pH on ultrafiltration membraneselectivity during electrodialysis with ultrafiltration membrane (EDUF) purification of soypeptides from a complex matrix Journal of Membrane Science 435 207e217

Sachdeva S Ram R P Singh J K amp Kumar A (2008) Synthesis of anion exchangepolystyrene membranes for the electrolysis of sodium chloride AIChE Journal 54(4)940e949

Seepana M M Pandey J amp Shukla A (2012) Synthesis and characterization of PWA basedinorganic ion-exchange membrane Separation and Purification Technology 98 193e198

Shen J N Huang J Liu L F Ye W Y Lin J Y amp Van der Bruggen B (2013) The useof BMED for glyphosate recovery from glyphosate neutralization liquor in view of zerodischarge Journal of Hazardous Materials 260 660e667

Shen J Yu C Huang J amp Van der Bruggen B (2013) Preparation of highly purified tet-rapropyl ammonium hydroxide using continuous bipolar membrane electrodialysisChemical Engineering Journal 220 311e319

Silva V Poiesz E amp van der Heijden P (2013) Industrial wastewater desalination using elec-trodialysis Evaluation and plant design Journal of Applied Electrochemistry 43(11)1057e1067

Solt G (1972) Electrodialysis comes of age Effluent and Water Treatment Journal 12(6) 293Song S Tao Y F Shen H Q Chen B Q Qin P Y amp Tan T W (2012) Use of bipolar

membrane electrodialysis (BME) in purification of L-ascorbyl-2-monophosphate Separationand Purification Technology 98 158e164

Advances in electrodialysis for water treatment 201

Tamburini A La Barbera G Cipollina A Ciofalo M amp Micale G (2012) CFD simulationof channels for direct and reverse electrodialysis Desalination and Water Treatment48(1e3) 370e389

Tanaka Y (2013) Development of a computer simulation program of batch ion-exchangemembrane electrodialysis for saline water desalination Desalination 320 118e133

Tanaka N Nagase M amp Higa M (2011) Preparation of aliphatic-hydrocarbon-based anion-exchange membranes and their anti-organic-fouling properties Journal of MembraneScience 384(1e2) 27e36

Tran A T K Jullok N Meesschaert B Pinoy L amp Van der Bruggen B (2013) Pelletreactor pre-treatment A feasible method to reduce scaling in bipolar membrane electro-dialysis Journal of Colloid and Interface Science 401 107e115

Tsukahara S Nanzai B amp Igawa M (2013) Selective transport of amino acids across adouble membrane system composed of a cation- and an anion-exchange membraneJournal of Membrane Science 448 300e307

Urtenov M K Uzdenova A M Kovalenko A V Nikonenko V V Pismenskaya N DVasilrsquoeva V I et al (2013) Basic mathematical model of overlimiting transfer enhancedby electroconvection in flow-through electrodialysis membrane cells Journal of MembraneScience 447 190e202

Venugopal K amp Dharmalingam S (2013) Fundamental studies on a new series ofSPSEBS-PVA-QPSEBS bipolar membrane Membrane preparation and characterizationJournal of Applied Polymer Science 127(6) 4983e4990

Vermaas D A Veerman J Yip N Y Elimelech M Saakes M amp Nijmeijer K (2013)High efficiency in energy generation from salinity gradients with reverse electrodialysisACS Sustainable Chemistry and Engineering 1(10) 1295e1302

Wood T (1960) Desalting of urine by electrodialysis Nature 186(4725) 634e635Xu T W (2001) Development of bipolar membrane based processes Desalination 140(3)

247e258Xu P Capito M amp Cath T Y (2013) Selective removal of arsenic and monovalent ions from

brackish water reverse osmosis concentrate Journal of Hazardous Materials 260885e891

Xu T W amp Huang C (2008) Electrodialysis-based separation technologies A critical reviewAIChE Journal 54(12) 3147e3159

Yang Y Gao X L Fan A Y Fu L L amp Gao C J (2014) An innovative beneficial reuseof seawater concentrate using bipolar membrane electrodialysis Journal of MembraneScience 449 119e126

Zaslavschi I Shemer H Hasson D amp Semiat R (2013) Electrochemical CaCO3 scaleremoval with a bipolar membrane system Journal of Membrane Science 445 88e95

Zendehnam A Robarmili N Hosseini S M Arabzadegan M amp Madaeni S S (2013)Fabrication of novel (acrylonitrile butadiene styreneactivated carbonsilver nanoparticles)heterogeneous anion exchange membrane Physico-chemical and antibacterial character-istics Journal of the Taiwan Institute of Chemical Engineers 44(4) 670e677

Zhang Y Desmidt E Van Looveren A Pinoy L Meesschaert B amp Van der Bruggen B(2013) Phosphate separation and recovery from wastewater by novel electrodialysisEnvironmental Science amp Technology 47(11) 5888e5895

Zhang Y Ghyselbrecht K Meesschaert B Pinoy L amp Van der Bruggen B (2011)Electrodialysis on RO concentrate to improve water recovery in wastewater reclamationJournal of Membrane Science 378(1e2) 101e110

202 Advances in Membrane Technologies for Water Treatment

Zhang Y Paepen S Pinoy L Meesschaert B amp Van der Bruggen B (2012) Selec-trodialysis Fractionation of divalent ions from monovalent ions in a novel electrodialysisstack Separation and Purification Technology 88 191e201

Zhang K Wang M amp Gao C J (2012) Ion conductive spacers for the energy-saving pro-duction of the tartaric acid in bipolar membrane electrodialysis Journal of MembraneScience 387 48e53

Zhuang J X Chen Q Wang S Zhang W M Song W G Wan L J et al (2013) Zerodischarge process for foil industry waste acid reclamation Coupling of diffusion dialysisand electrodialysis with bipolar membranes Journal of Membrane Science 432 90e96

Advances in electrodialysis for water treatment 203

Photocatalytic membranereactors for water treatment 7R Molinari1 P Argurio1 L Palmisano21Universita della Calabria Rende (CS) Italy 2Universita di Palermo Palermo Italy

71 Introduction

Heterogeneous photocatalysis is an advanced oxidation process (AOP) based on theuse of a semiconductor (the photocatalyst) It has been extensively studied for aboutfour decades when Fujishima and Honda (1972) discovered the photocatalytic split-ting of water on TiO2 electrodes It has been object of a large amount of studies relatedto environment recovery by the total degradation to innocuous substances of organicand inorganic pollutants (Hoffmann Martin Choi amp Bahnemann 1995) and for syn-thesis (Molinari Caruso amp Poerio 2009 Palmisano et al 2010) It is a discipline thatincludes a large variety of reactions (Molinari Argurio amp Lavorato 2013) partial ortotal oxidations dehydrogenation hydrogenation (eg hydrogen transfer) metal depo-sition water detoxification gaseous pollutant removal bactericidal action etc

The main advantages of photocatalysis making it a very promising lsquogreenrsquo processconsist in the mild operating conditions and the possibility to abate refractoryvery toxic and nonbiodegradable molecules (Molinari Caruso amp Palmisano 2010Palmisano Augugliaro Pagliaro amp Palmisano 2007) Besides photocatalysis (1)avoids the use of environmentally and unhealthy dangerous heavy metal catalystsby using safer photocatalysts (mainly TiO2) (2) uses mild oxidants (O2 in some casesfrom the air) (3) needs few auxiliary additives (4) does not produce harmful chemi-cals (5) offers a good alternative to the energy-intensive conventional treatmentmethods and (6) can be combined with other physical and chemical technologies(eg membrane separations)

Because the photocatalyst is generally used as a powder suspended in a liquidmedium the catalyst-recovering step from the reaction environment is a pivotal stagein view of large-scale applications Photocatalytic membrane reactors (PMRs) repre-sent a promising approach to overcome this limitation A PMR can be defined as a de-vice existing in various configurations that combines a photocatalyst and a membraneto produce chemical transformations A PMR improves the potentialities of classicalphotoreactors (PRs) and those of membrane processes with a synergy of both technol-ogies thus minimizing environmental and economic impacts (Molinari CarusoArgurio amp Poerio 2008 Molinari et al 2009) The membrane permits continuousoperation in systems in which the recovery of the photocatalyst (immobilized or in sus-pension) the reaction and the product separation simultaneously occurs resulting in adevice that is competitive with other separation technologies in terms of material

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400007-1Copyright copy 2015 Elsevier Ltd All rights reserved

recovery energy costs reduction of the environmental impact and selective removalof the components Higher energy efficiency modularity and easy scale-up are someother advantages of PMRs compared to conventional PRs

Water treatment by removing both organic and inorganic pollutants represents themain use of the photocatalytic techniques Water pollution caused by hazardousorganic chemicals used in industry and agriculture is a serious problem Environ-mental laws are severe and they will become more and more restrictive in the nextyears Furthermore various directives suggest the use of green chemistry conceptsand clean technologies inside the manufacturing processes to protect the environmentTraditional chemical and biological treatments (eg adsorption on active carbonchemical oxidation and aerobic biological treatments) to clean-up water often failto remove most organic pollutants because of the high resistance of these compoundsresulting in high concentrations discharged in treated effluents On the basis of this inthe last years the attention of the international scientific community has been focusedon the development of alternative methods In this context photocatalytic processesrepresent a promising alternative green process (Huo et al 2013 Mozia amp Morawski2006 2012 Mozia Tomaszewska amp Morawski 2005 2007) because as a conse-quence of the highly unselective reactions involved in the photocatalytic processesa wide range of organic pollutants can be totally degraded (ie mineralized) into smalland harmless species (carbon to carbon dioxide hydrogen to water nitrogen to nitrateetc) without using chemicals avoiding sludge production and its disposal

In the pertinent literature different studies in which photocatalysis is coupled withpressure-driven membrane techniques such as nanofiltration (NF) and ultrafiltration(UF) for the degradation of organic pollutants are reported (Molinari Borgese DrioliPalmisano amp Schiavello 2002 Molinari Palmisano Drioli amp Schiavello 2002Patsios Sarasidis amp Karabelas 2013 Zhang et al 2013) Membrane fouling is oneof the main drawbacks of these systems On the basis of this some authors proposedto couple photocatalysis with (1) membrane distillation (Huo et al 2013 Mozia ampMorawski 2006 Mozia amp Morawski 2012 Mozia Tomaszewska amp Morawski2007) obtaining an almost complete total organic carbon (TOC) removal butrequiring energy to activate the evaporation phenomenon (2) dialysis (AzragueAimar Benoit-Marquieacute amp Maurette 2007) to mineralize organic compounds con-tained in artificial turbid water operating at ambient temperature and (3) pervaporation(Camera-Roda amp Santarelli 2007 Camera-Roda et al 2011) improving the detoxi-fication efficiency of wastewater containing organic pollutants at low concentrationlevels

In this chapter the basic principles of photocatalysis and PMRs are reportedwith the advantages related to their coupling thanks to the synergistic effectsThe importance in making a correct choice of membrane (type and material) is evi-denced discussing the choices made in literature and the criteria used for selectionMoreover a classification of the PMRs based both on their configuration (pressurizedand depressurizedsubmerged) and on the particular membrane separation with photo-catalysis (pressure-driven membrane separation membrane distillation dialysis andpervaporation) is also presented providing evidence that the opportune choice ofPMR configuration and membrane separation is a key step to limit membrane fouling

206 Advances in Membrane Technologies for Water Treatment

Finally some applications of PMRs for water treatment in particular for pharmaceu-ticals removal are reported with evidence of the potentialities the drawbacks and thefuture trends

72 Fundamentals of PMRs for water treatment

721 Basic principles of photocatalysis and typesof photocatalysts and membranes

The main difference of photocatalysis compared to conventional catalysis is the pho-tonic activation mode of the catalyst which replaces the thermal activation (Herrmann2005) The electronic structure of a semiconductor is characterized by a valence band(VB) and a conduction band (CB) which are separated by an energy band gap (Eg)When a semiconductor particle is excited by irradiation with photons of energy (hn)equal or higher than its energy band gap (Eg) valence electrons (e) are promotedfrom VB to CB thus leaving a positive hole (hthorn) in the VB For semiconductorTiO2 this step is expressed as

TiO2 thorn hvTiO2e thorn hthorn

(71)

In the absence of suitable electron andor hole scavengers the photo-generated elec-trons and holes can recombine in bulk or on the surface of the semiconductor within ashort time releasing energy in the form of heat or photons Electrons and holes thatmigrate to the surface of the semiconductor without recombination can reduce andoxidize respectively the substrates adsorbed on the semiconductor A schematizationof both the photonic activation of the photocatalyst and the photocatalytic oxidationand reduction reactions that take place onto a photo-activated semiconductor particleis reported in Figure 71

The process in Figure 71 can be divided in four steps

1 Absorption of light followed by the separation of the electronehole couple2 Adsorption of the reagents3 Redox (reduction and oxidation) reaction4 Desorption of the products

The redox reactions involving the species adsorbed onto the semiconductor surfaceoccur only if the potentials of the redox couple to which the substrates belong (E0

1 E02)

are compatible with both the VB and CB potentials (EVB ECB) In particular the redoxpotential of the species to be oxidized E0

2 should be less positive than EVB so that thephoto-produced holes hthorn can oxidize the reduced form of this species (red2 ox2 seeFigure 71) At the same time the redox potential of the species to be reduced E0

1should be more positive than ECB so that the photo-produced electrons ee can reducethe oxidized form of this species (ox1 red1 see Figure 71) Only if both E0

2 lt EVB

and E01 lt ECB conditions are met both reduction and oxidation are thermodynami-

cally favoured and the overall photocatalytic process takes place

Photocatalytic membrane reactors for water treatment 207

The redox reactions that take place onto the semiconductor surface represent thebasic mechanisms of photocatalytic waterair purification and photocatalytic hydrogenproductionsubstrate hydrogenation respectively In the VB photo-generated holescan oxidize surface hydroxyl groups into hydroxyl radical in the aqueous reactingenvironment

OH thorn hthornOH (72)

As widely accepted hydroxyl radicals are the primary oxidants that attack thesubstrates to be degraded by reducing them to their elemental form

In the CB photo-promoted electrons can reduce the molecular oxygen dissolved inthe aqueous phase to superoxide radical metal ions to their lower oxidation states orHthorn ions to H

O2 thorn eO2 (73)

Menthorn thorn eMeethn1THORNthorn (74)

Hthorn thorn eH (75)

The so-generated hydrogen radicals can follow two main fates combination forH2 production or hydrogenation of adsorbed substrate

Thanks to (1) the favourable energetics of its band structure (2) its relatively highquantum yield (3) its stability under irradiation and (4) its low cost and availabilityTiO2 represents the archetypical photocatalyst a virtual synonym for photocatalysis

Eg

endash

h+

ox1Red1

ox2Red2

CB

VB

Light

Figure 71 Schematization of the photocatalytic process that occurs on a photo-activatedsemiconductor particle ox1 red1 ox2 and red2 represent respectively the oxidized and thereduced species of two different redox couples indicated as 1 and 2

208 Advances in Membrane Technologies for Water Treatment

Nevertheless this material does not present photo-response under visible light illumi-nation because of its wide band gap taking advantage of only less than 6 of the solarenergy Thus its potential as a green technology cannot be entirely fulfilled Conse-quently in the last years a great number of new photocatalysts have been synthesizedand tested as possible alternatives to TiO2 (Di Paola Garciacutea-Lopez Marcigrave ampPalmisano 2012 Hernandez-Alonso Fresno Suarez amp Coronado 2009) particularlyin view of the solar application The most important requirements that such a materialshould possess are a suitable band gap chemical and physical stability nontoxic na-ture good availability and low cost The most common materials used are oxidesor sulfides which redox potentials for the VBs and the CBs range are betweenthorn40 and 15 V versus a normal hydrogen electrode (NHE) Their photocatalyticproperties depend mainly on the position of the energetic level and on the band gapTable 71 summarizes the most common semiconductors used as photocatalystsreporting their band gap and wavelength of the radiation needed for the activation

The photoactivity of a semiconductor depends also on the mobility and lifetimeof the photo-produced electronhole couples on the light absorbance coefficientand on the method used to prepare the photocatalytic powder which affects manyphysicochemical properties of the semiconductor such as surface area distributionof particle size and crystallinity

Despite the photocatalytic process offering interesting advantages with respect toother catalytic process (eg milder operating conditions use of safer catalyst etc)its use in the industry is still limited for three different reasons (Ni Leung Leungamp Sumathy 2007) (1) recombination of photo-generated electronhole pairs that dissi-pate their energy as heat (2) fast backward reaction and (3) difficulty to use visiblelight which limits the effectiveness of the use of solar energy

Table 71 Band gaps and wavelengths of the most commonsemiconductors used as photocatalysts

Photocatalyst Band gap (eV) Wavelength (nm)

SnO2 38 318

TiO2 anatase 32 387

TiO2 rutile 30 380

WO3 28 443

Fe2O3 22 560

ZnO 32 387e390

ZnS 37 335e336

CdS 25 496e497

CdSe 17 729e730

GaAs 14 886e887

Photocatalytic membrane reactors for water treatment 209

To solve these problems continuous efforts have been made to enhance the photo-catalytic activity and promote the visible light response

A simple approach consists in the addition of electron donors or electron scaven-gers able to react irreversibly with the photo-generated VB holes or CB electronsrespectively Practically electron scavengers or electron donors can be reduced byCB electrons or oxidized by VB holes respectively the remaining strong oxidizingVB holes or strong reducing CB electrons can oxidizereduce the substrate Operatingin this way the electronhole recombination can be suppressed or reduced and higherquantum efficiency can be achieved

Another way to suppress or to reduce the recombination of photo-generatedelectronhole pairs consists in doping the semiconductor with a noble metal like PtAu Pd Rh Ni Cu and Ag By using this method photo-promoted electrons canbe transferred from CB of the semiconductor to metal particles deposited on its surfacewhile photo-generated VB holes remain on the photocatalyst Thus the possibility ofelectronehole recombination is greatly reduced resulting in an enhancement of photo-catalytic efficiency (Ara~na et al 2008 Chen et al 2008 Colmenares AramendiacuteaMarinas Marinas amp Urbano 2006 Rosu Suciu Lazar amp Bratu 2013 Wu et al2008 Yang et al 2013) A combined effect of metal ion doping consists in the reduc-tion of the band gap energy of the photocatalyst thus shifting the radiation absorptiontowards higher wavelengths permitting the use of visible light (Ge 2008 Ling Sunamp Zhou 2008) The same effect also can be obtained by doping the catalyst with an-ions such as N F C S and B (Collazzo Foletto Jahn amp Villetti 2012 Di Valentin ampPacchioni 2013)

Other ways to overcome previous limitations consist in dye sensitization compositesemiconductors metal-ion implantation etc

PMRs are hybrid systems in which photocatalysis is coupled with a membrane sep-aration In general a membrane can be defined as a barrier that separates two phasescontrolling the mass transport between them

The most important classification of membranes is based on their morphologicalproperties In particular a membrane can be porous allowing the permeation throughits pores and then the transport mechanisms (sieving mechanism andor Knudsendiffusion) depend on the pore size or dense in which the mass transport takes placeby the so-called solutiondiffusion mechanism ie dissolution of the permeationspecies in the membrane phase and diffusion across the membrane thickness

Another morphological classification of membrane distinguishes symmetric andasymmetric membranes In a symmetric membrane structural and transport proper-ties are the same throughout its section and the thickness of the entire membrane de-termines the flow In asymmetric membranes consisting of a dense thin layersupported by a porous layer that acts as mechanical support of the fragile skin layerstructural and transport properties change along the membrane thickness In this waythe high selectivity of a dense membrane is combined with the high permeation rateof a thin layer membrane Asymmetric membranes are mainly used in membrane sep-aration processes that use hydrostatic pressure as the driving force (the so-calledpressure-driven processes) reverse osmosis (RO) NF UF and microfiltration(MF) (Mulder 1996)

210 Advances in Membrane Technologies for Water Treatment

In a PMR system the appropriate choice of the membrane (material and type) andmembrane module configuration is mainly determined by the type of photocatalyticreaction Indeed the membrane can assume many roles The main purpose in couplinga membrane process with a photocatalytic reaction is the necessity to recover and reusethe catalyst So it is important to choose a membrane (type and material) with com-plete catalyst rejection thus maintaining it in the reaction environment Besideswhen the process is used for the degradation of organic pollutants the membranemust be able to reject the substrates and their intermediate products which otherwisepass in the permeate For example when the photocatalytic process is used as asynthetic pathway the main objective can be the selective separation of the producteg minimizing its successive oxidation which leads to undesirable byproducts

In this context the rejection (R) is a useful parameter that expresses the ability ofthe membrane to maintain the substrate and its intermediates in the reactiveenvironment

R frac14 Cf Cp

Cf frac14 1

CpCf

(76)

in which Cf and Cp are the solute concentrations in the feed and permeate respectivelyThe retention of the substrates and degradation byproducts is important also to con-

trol the residence time of substrates in the photocatalytic system This parameterstrongly influences the efficiency of photodegradation Longer retention times usuallyobtained by reducing the permeate flux results in higher pollutant degradation dueto the greater contact time between the molecules to be degraded and the catalystHowever since the PMR must be able to offer a high water permeate flux it is impor-tant to find a good compromise among the permeate flux and the residence time toachieve a system for application purpose

722 Membrane materials development and designfor photocatalysis

Because the main problem encountered when the photocatalytic process is coupled to apressure-driven process such as MF and UF (which requires porous membranes) is thedecrease of permeate flux caused by concentration polarization and fouling the choiceof membrane material is strongly determined by the need to limit these phenomena andby the chemical and thermal stability of the materials

Polymeric membranes are generally used in photocatalysis although inorganicones which generally present higher chemical and thermal stability are attractivefor PMR applications But they have the disadvantage of a significantly higher costcompared to polymeric ones (Chin Chiang amp Fane 2006 Moritz Benfer Arki ampTomandl 2001) In view of this economic factor suitable polymeric membranesshould be sought for this application

Molinari et al (2000) reported an investigation of the stability under ultraviolet(UV) irradiation of some eligible commercial membranes composed by variousmaterials Tests of photo-resistance under UV light were carried out by irradiating

Photocatalytic membrane reactors for water treatment 211

the membranes immersed in distilled water Samples were periodically withdrawn andanalysed by TOC optical microscopy (OM) and scanning electron microscopy (SEM)to verify any damage to the membrane surface Membrane stability was also deter-mined by measuring the changes in pure water permeation flux (WPF) before and afterUV irradiation Table 72 shows the main characteristic of the 11 commercialmembranes used in the UV irradiation tests

Membranes made of polyacrylonitrile (PAN) fluoride thorn polypropylene (PP) andpolysulphone thorn PP seemed to be stable to UV light over a 24-h period of irradiationPAN membrane was chosen to carry out some photo-reactivity experiments because itshowed the highest permeate flux which was constant in the time TiO2 was immobi-lized on the flat sheet membrane by ultrafiltrating TiO2 suspensions in water (600 mL)at 005 01 02 and 03 gL the amounts of immobilized TiO2 were respectively076 204 408 and 612 mgcm2 of membrane The best uniform coverage was givenby loading 408 mgcm2 although the best results for the photocatalytic reaction wereobtained in a suspended TiO2 system 4-nitrophenol (4-NP) was used as model mole-cule and 80 degradation was obtained in around 5 h by using 05 gL of suspendedTiO2 whereas degradation around 51 was obtained with the same irradiation time inthe system with deposited TiO2 regardless of the amount of catalyst

Some years later Chin et al (2006) reported a study focused on the selection ofpolymeric membranes for PMR applications providing a protocol similar to that

Table 72 Types of commercial membranes used in the UV irradiationtest

Type of membrane Pore size Polymer Supplier

MPPS 0000 u002 15 kDa Polysulphone Separem

MPPS 0000 u006 40 kDa Polysulphone Separem

MPPS 0000 u20 25 kDa Polyamide Separem

MPPS 0000 u25 20 kDa Polyamide Separem

P-12-10 e PEEK Homemade

FS 50 PP 50 kDa Fluoride thorn PP Dow

PES 40 kDa Polyethersulphone TechSep

PVDF 01 mm Polyvinyldenefluoride

TechSep

GR 51 PP 50 kDa Polysulphone thorn PP TechSep

PAN 40 kDa Polyacrylonitrile TechSep

CA 600 PP 20 kDa Cellulose acetate-PP

Dow

Note PP polypropyleneSource Molinari et al (2000)

212 Advances in Membrane Technologies for Water Treatment

one proposed byMolinari et al (2000) for testing the stability of polymeric membranesbefore using them with photocatalytic reactions Membrane stability was characterizedby (1) changes in WPF before and after UV irradiation (2) release of TOC in the50 mL of Milli-Q water in which the membrane were immersed before and afterthe predefined time of UV exposure and (3) SEM to observe the surface morphologyof the membranes before and after the exposure to UV light The overall change in sur-face hydrophobicity or hydrophilicity of the membranes was determined by contactangle measurements (CAM) Ten types of polymeric membranes (Table 73) were sub-jected to the initial UV screening test Polytetrafluoroethylene (PTFE) hydrophobicpolyvinylidene fluoride (PVDFphobic) and PAN membranes were stable after30 days of UV illumination However in a study of the oxidative stability of mem-branes (under UV hydrogen peroxide [H2O2] and combined UVH2O2 conditions)it was found that the stability of PAN membrane declined considerably when it wasexposed to 10 days of 200 mM H2O2UV conditions Then the author concludedthat on the basis of their UV and oxidative screening tests PTFE and hydrophobicPVDF are the better choice for photocatalytic applications

Different papers reported in the literature suggest the use of PVDF for PMRs Fu JiWang Jin and An (2006) successfully used a submerged membrane photocatalyticreactor (SMPR) in which the MF module was made of PVDF hollow fibre membranes(pore size frac14 02 mm filtration area frac14 02 m2) for the degradation of fulvic acid bynanostructured TiO2 Chin Lim Chiang and Fane (2007) studied a low-pressurePVDF submerged hollow fibre membrane module to retain the TiO2 particles in thephotodegradation of bisphenol A (BPA) used as a model pollutant

Table 73 Types of commercial membranes used in the UV irradiationtest

Type of membrane Pore size Suppliers

Polyvinyldene fluoride(PVDF)

022 mm Millipore

PVDF-MP 022 mm Millipore

PVDF-Pall 01 mm Pall filtration

Polycarbonate (PC) 01 mm Millipore

Polysulphone (PS) 600 kDa Osmonics

Polytetrafluoroethylene(PTFE)

02 mm Cole Parmer

Polypropylene (PP) 01 mm Osmonics

Polyacrylonitrile (PAN) 40 kDa Cleanseas

Polyethersulphone (PES) 50 kDa Millipore

Cellulose acetate (CA) 02 mm MFS

Source Chin et al (2006)

Photocatalytic membrane reactors for water treatment 213

Despite all the properties that make PVDF one of the most extensively applied UFmembrane materials (eg antioxidation good thermal and hydrolytic stabilities aswell as good mechanical and membrane-forming properties) the hydrophobic natureof PVDF often results in severe membrane fouling and permeability decline sinceorganic contaminants (hydrophobic) deposition on this materials results favoureddue to chemical affinity This has become a conspicuous drawback for their applicationin water treatment (Lang Xu Yang amp Tong 2007) Many methods have been testedto improve the membrane performances Among these ones blending with inorganicmaterials especially nanoparticles has attracted great attention owing to the relativelyeasy preparation by the method of phase inversion which is carried out under mildconditions (Shon et al 2010 Wei et al 2011) On the basis of this DamodarYou and Chou (2009) reported a study on the self-cleaning antibacterial and photo-catalytic properties of TiO2-entrapped PVDF membranes The modified PVDF mem-branes were prepared by using the phase inversion method adding different amountsof TiO2 particles (0e4 wt) into the casting solution The TiO2ePVDF membraneswere tested for their antibacterial property by using Escherichia coliform photoactiveproperty using reactive black 5 (RB5) dye and self-cleaning (antifouling) propertiesusing 1 Bovine Serum Albumin (BSA) solution Obtained results evidenced thatthe hydrophilicity and pore size of composite PVDFTiO2 membranes were variedby addition of different amounts of TiO2 This also improves the permeability of modi-fied PVDFTiO2 membrane The PVDFTiO2 membrane showed better bactericidalability as compared to neat PVDF membrane under UV light The rate of RB5 removalwas higher as compared to neat PVDF membrane Among the tested membranes theones with 2e4 PVDFTiO2 showed better antifoulingself-cleaning ability ascompared to neat PVDF membrane

On the same topic Wei et al (2011) proposed a new PVDFeTiO2 nanowire hybridUF membrane prepared via phase inversion by dispersing TiO2 nanowires in PVDFcasting solutions Obtained results showed that the microstructure mechanical prop-erty thermal stability hydrophilicity permeation and antifouling performance ofhybrid membranes were improved significantly by addition of hydrophilic inorganicTiO2 nanowires

In a recent work You Semblante Lu Damodar andWei (2012) evaluated the anti-fouling and photocatalytic properties of a membrane in which polyacrylic acid (PAA)was plasma-grafted on commercial PVDF membrane to introduce functional groupson the membrane surface that can support the TiO2 nanoparticles Obtained resultsshowed that the membrane hydrophilicity was tremendously enhanced by the self-assembly of TiO2 following a direct proportionality to TiO2 loading However greaterhydrophilicity did not necessarily implicate better antifouling properties since exces-sive nanoparticles plugged membrane pores The membrane with 05 TiO2 loadingmaintained the highest pure water flux and the best antifouling property Beyond thisconcentration a significant permeate flux decline was observed The TiO2-modifiedmembranes were able to remove 30e42 of 50 mgL aqueous RB5 dye and thedegradation reaction was highly dependent on TiO2 amount The overall resultsevidenced that the fabricated membranes are good candidates for use in membranereactors with high hydrophilicity fouling mitigation and photocatalytic capability

214 Advances in Membrane Technologies for Water Treatment

Chin et al (2006) demonstrated that PTFE (a highly crystalline polymer thatexhibits excellent thermal stability and high chemical resistance) membranes arealso good candidates for PMR applications On the basis of this Damodar and You(2010) proposed a PMR assembled by integrating a novel flat plate PTFE membranemodule that was placed at the centre of the tank and surrounded by two UV lamps (seeFigure 72)

The performance of the assembled PMR was evaluated in the mineralization ofRB5 and the efficiency of catalyst recycling and reuse was studied using batchand long-term continuous experiments The obtained data showed that during contin-uous long-term operations the membrane module was able to maintain the catalysteffectively within the reactor and the catalyst was also reused without much loss indye degradation efficiency Indeed the catalyst that gradually deposited on mem-brane surface during continuous operation was effectively recycled by using simpleand quick cleaning method after which the original behaviour of the membrane andRB5 degradation performance were restored The performance of the reactor wasstable with nearly 75e82 TOC removal and 85e90 chemical oxygen demand(COD) removal and showed similar trend for about five to six days after eachmembrane-cleaning step

Raja et al (2007) studied the discolouration of orange II on synthesized PTFECo3O4 films under visible light irradiation An innovative way to prepare PTFECo3O4 supported catalyst by a suitable thermal treatment of the PTFE film in contactwith the Co3O4 colloid was presented The so prepared catalyst allowed the accelerateddiscolouration of orange II

Another hydrophobic polymer largely used in PMR is PP PP hollow fibre mem-branes were used by Erdim Soyer Tasiyici and Koyuncu (2009) to study the effectof natural organic matter (NOM) fouling Synthetic and natural raw waters wereused in their photocatalytic experiments The experimental data showed that the in-crease in NOM concentration increased the pressure while raw water experimentsshowed a higher pressure increase and lower removal efficiencies compared to thatof synthetic water

Magnetic stirrer

Feed

Permeate

Air inlet

UV lampsMembrane module

Air diffuser

Figure 72 Schematization of the assembled photocatalytic membrane reactor (PMR)Adapted from Damodar and You (2010)

Photocatalytic membrane reactors for water treatment 215

Because of their hydrophobic nature PP membranes can be used in MD (Mozia ampMorawski 2006 Mozia Morawski Toyoda amp Tsumura 2010)

Many works are reported in literature on the coupling of the photocatalytic processwith NF membranes which have the advantage of retaining low molecular weightmolecules better in comparison to low-pressure MF and UF modules

Different NF membranes were tested in the photodegradation of different pharma-ceuticals by Molinari Pirillo Loddo and Palmisano (2006) Table 74 reports the maincharacteristic of these NF membranes

Obtained results evidenced that membrane retention depended on both the pH of theaqueous solution to be treated and on the chemical characteristics of the particularpharmaceutical compound to be degraded NF PES 10 at alkaline pHs NTR 7410at neutral and alkaline pHs and N 30 F at acidic pHs were the membranes that showed

Table 74 Main characteristics of commercial membranes tested

Type of membrane Material Characteristics Manufacturer

NTR 7410 Sulfonatedpolysulfone

Rejection 10 with02 NaCl at49 bar 25 Cand pH 65

Nitto DenkoTokyo

PAN GKSS HV3T Polyacrylonitrile Cut-off frac14 30 kDawater flux4231 Lhm2 at2 bar and8462 Lhm2 at4 bar

GKSS Germany

N 30 F Modifiedpolysulfone

Rejection 25e35with 02 NaCland 85e95with 05 ofNa2SO4 waterflux 40e70 Lhm2 at 40 bar and20 C

Hoechst CelgardGermany

NF PES 10 Polyethersulfone Rejection 10e20with 05 NaCland 40e70with 05 ofNa2SO4 waterflux 200e400 Lhm2 at 40 barand 20 C

Hoechst CelgardGermany

Source Molinari et al (2006)

216 Advances in Membrane Technologies for Water Treatment

the best rejection percentages for furosemide at pressures of 4e8 bar NTR 7410 wasthe best membrane for ranitidine rejection over the whole pH range although its rejec-tion at 8 bar was lower than that found for NF PES 10

In another work (Molinari et al 2002) NF PES 10 and NTR 7410 membraneswere tested for the photocatalytic removal of 4-NP and benzoic acid from aqueoussolutions TiO2 P25 Degussa was used as the catalyst both suspended and depositedon the polymeric membranes Obtained results showed that the treatment of 4-NPsolution in acidic medium allowed the total removal of the substrate by using a contin-uous system NTR 7410 was also an efficient NF membrane for separating two dyesCongo red and direct blue from aqueous solutions (Molinari Pirillo Falco Loddoamp Palmisano 2004)

73 Advances in membrane modules and systemconfigurations for PMRs for water treatment

Despite the important advantages of the photocatalytic processes with respect to thetraditional ones their application at industrial level is limited by different drawbacksrelated to the involved reactions and reactor configuration

With regard to the configuration of the reactor and in particular by considering thephotocatalyst two operative configurations can be identified the first one in whichthe photocatalyst is suspended in the aqueous reacting phase and another one withthe photocatalyst immobilized on a support

Slurry photocatalytic reactors in which the catalyst is suspended in the aqueousreacting phase have been widely used In these reactors the nondegraded moleculesor their byproducts are freely transported in the final stream Photocatalyst recoveryand recycle is another problem The coupling with pressure-driven membrane separa-tions in PMRs can solve these problems

731 Pressurized membrane PRs

Different types of PMRs were built with the purpose of obtaining an easy separation ofthe catalyst from the reaction environment and an efficient removal of pollutants fromaqueous media The most studied configurations were pressurized systems in whichpressure-driven membrane processes such as MF UF and NF were combined tothe photocatalytic process In these systems the catalyst used both in the suspendedconfiguration and immobilized on the membrane is confined in the pressurized sideof the permeation cell

In 2002 Molinari et al (2002) reported some experimental results obtained byusing two different pressurized PMR configurations for the degradation of 4-NPIn particular the configurations studied were (1) a first one in which the irradiationof the catalyst was performed in the permeation cell containing the membrane withthree sub-cases (a) catalyst in suspension (b) catalyst deposited on the membrane(c) catalyst entrapped in the membrane and (2) a second one in which the irradiation

Photocatalytic membrane reactors for water treatment 217

of the suspended catalyst was performed in the recirculation tank The results showedthat the second configuration appeared to be the most interesting for industrial appli-cations in terms of irradiation efficiency and membrane permeability For example inreactor optimization high irradiation efficiency high membrane permeate flow rateand selectivity can be obtained by sizing separately the lsquophotocatalytic systemrsquo andthe lsquomembrane systemrsquo and taking advantage of all the best research results for eachsystem

In a successive work the same group Molinari et al (2004) studied the photodegra-dation process of two commercial azo dyes ie Congo red (C32H22N6Na2O6S2) andpatent blue (C27H31N2NaO6S2) in a membrane PR by using TiO2 Degussa P25 asthe photocatalyst and an NF membrane Two different PR configurations a cylindricalone with an external lamp and an annular one with an immersed lamp in the axial po-sition (Figure 73) were studied and the influence of some operational parameterssuch as the pressure in the membrane cell and the initial concentration of the substrateswas determined A comparison between suspended and entrapped TiO2 was also done

The rate of pollutant photodegradation was strongly affected by the UV irradiationmode In particular the rate of photodegradation with the immersed lamp resulted 50times higher than that of suspended one (0274 versus 000548 mgmin) although thepower of the last was four times greater Congo red was photodegraded with higherrate under the same experimental conditions probably due to its higher adsorptiononto the catalyst surface The reactor containing the suspended photocatalyst wassignificantly more efficient than the reactor containing the catalyst entrapped intothe membrane as also found by other authors (Mascolo et al 2007) The observed

(5)

(2)

(6)

(3)

(1)(1)

(2)

(3)

(6)

(5)

(4)(4)

Figure 73 Scheme of the batch system with external lamp and with immersed lamp used in theexperimental runs without membrane with the suspended catalyst (1) oxygen cylinder (2)cylindrical reactor with cooling jacket (3) thermostatic baths with cooling water (4) powersupplies (5) medium pressure Hg lamp (6) magnetic stirrer (Reprinted from Molinari et al(2004) with permission from Elsevier)

218 Advances in Membrane Technologies for Water Treatment

reduction of photoactivity was probably due to the lower available active surface area ofthe catalyst compared to the suspended immobilized system The results evidenced thatit was possible to treat successfully highly concentrated solutions (500 mgL) of bothdyes by means of a continuous process obtaining good values of permeate fluxes(30e70 Lm2h) this could be interesting for industrial applications

732 Depressurized (submerged) membrane PRs

The main problem observed by coupling photocatalysis with a pressure-driven mem-brane process is the decrease of permeate flux caused by membrane fouling due tocatalyst deposition on the membrane Submerged membrane systems represent oneof the different approaches proposed to overcome this limitation In this configurationthe catalyst is suspended in an open-air reaction environment the membrane isimmersed in the batch and the permeate is sucked by means a vacuum pump

Fu et al (2006) reported the degradation of FA by using synthesized nanostructuredTiO2silica gel catalyst particles in a submerged membrane photocatalytic reactor(SMPR) schematized in Figure 74 It was found that the photocatalyst at 05 gLand airflow at 006 m3h were the optimal conditions for the removal of FA The resultsshowed a reduction of fouling phenomena when nanostructured TiO2 was used as thephotocatalyst

An additional way to prevent photocatalyst deposition and then reduce membranefouling consists in controlling the hydrodynamic conditions near the membrane sur-face In this context gas sparging at the bottom of the membrane represents a prom-ising strategy On this basis Chin et al (2007) studied the removal of BPA in waterby using low-pressure submerged module and they observed that the aeration allow-ing a mechanical agitation reduced the fouling of the membrane and maintained theTiO2 well suspended in the solution In addition in this study another strategy toreduce membrane fouling was proposed an intermittent membrane filtration whichpermitted to maintain high flux at low aeration rate Practically when suction across

(1)

(2)

Feed

(3)

(4)

Submerged membrane module

Permeate

Aeration

Cooling water

(5)

Figure 74 Schematic diagram of the submerged membrane photocatalytic reactor (SMPR)system (1) feed tank (2) feed pump (3) thermostated jacket protoreactor (4) UV lamp(5) suction pumpReprinted from Fu et al (2006) with permission form Elsevier

Photocatalytic membrane reactors for water treatment 219

the membrane was stopped the aeration could shear the membrane surface facilitatingthe detachment of catalyst particles The results summarized in Figure 75 showedthat TOC photomineralization by operating with intermittent operation was similarto that ones obtained with continuous operation ie 94 BPA reduction at250 min Moreover it was found that with the intermittent mode the transmembranepressure (TMP) of the system decreased by five times compared to the continuousoperation Because TMP is proportional to the filtration energy cost intermittentoperation would reduce the operating cost of the continuous SMPR

The advantages of this approachwere also studied byHuangMeng Liang andQian(2007) They demonstrated that sedimentation of the suspended semiconductor can becontrolled by applying fine-bubble aeration and intermittent membrane filtration

Choi (2006) used the same intermittent approach studying the performance of apilot-scale SMPR in the degradation of 4-Chlorophenol (4-CP) The results evidenceda complete degradation of the pollutant in 2 h Besides in continuous runs no mem-brane fouling was observed when the intermittent operation was used

Therefore the SMPR with fine-bubble aeration and intermittent membrane filtra-tion can be potentially applied in the photocatalytic oxidation process during drinkingwater treatment

733 Coupling of photocatalysis and membrane distillation

Coupling of photocatalysis and MD could avoid fouling problems related to the use ofpressure-driven membrane separations MD is a separation process based on the prin-ciple of vapoureliquid equilibrium The nonvolatile components (eg ions macromol-ecules etc) are retained on the feed side whereas the volatile components passthrough a porous hydrophobic membrane and then they condense in a cold distillate(usually distilled water)

0

20

40

60

80

100

120

140

Continuous membranefiltration

Intermittent membranefiltration

Perc

enta

ge (

)

Change in TMPEfficiency of TOC degradationEfficiency of production of water

Figure 75 Comparison of the transmembrane pressure (TMP) change total organic carbon(TOC) degradation and production of water between continuous and intermittent permeationoperationReprinted from Chin et al (2007) with permission from Elsevier

220 Advances in Membrane Technologies for Water Treatment

The possibility on the way to use a PMR obtained by coupling photocatalysis anddirect contact MD (DCMD) for degradation of azo dyes (acid red 18 acid yellow 36and direct green 99) in aqueous solution was investigated by Mozia et al (2007) Theinitial concentration of a dye was equal to 30 mgL and the catalyst (TiO2 Aeroxide

P25 Degussa Germany) loadings amounted to 01 03 and 05 gL The resultsshowed that the MD process was very effective in separation of photocatalyst particlesIndeed after 5 h of the experiment the turbidity of distillate was similar to thatmeasured for ultrapure water regardless of the TiO2 amount in the reacting phaseThe highest effectiveness of photodecomposition was obtained in the case of acidred 18 and the most difficult compound to be degraded was acid yellow 36 havingthe lowest molecular weight among all the dyes used (Figure 76)

A complete rejection of the dye and other nonvolatile compounds (organic mol-ecules and inorganic ions) was achieved Some volatile compounds crossed themembrane as indicated by the measurements of TOC concentration into the distil-late However the amount of these substances remained in the range 04e10 mgL so that it can be concluded that the product (distillate) was practically pure waterA permeate flux of 034 m3m2d was obtained similarly to those obtained during theprocess in which ultrapure water was used regardless of the TiO2 amount This resultevidenced that MD permitted to avoid the significant fouling observed whenpressure-driven membrane processes were coupled with photocatalysis althoughthe higher energetic consumption of MD represents an important disadvantage

Thus the hybrid process coupling the photocatalysis and DCMD is a promisingmethod for the removal of organic compounds such as azo dyes from water becausethe MD membrane is a very effective barrier for the catalysts particles and the nonvol-atile compounds present in the feed solution

0

25

50

75

100

Acid red 18 Acid yellow 36 Direct green 99

Deg

rada

tion

()

01 gL03 gL05 gL

Figure 76 Photodegradation of Acid red 18 Acid yellow 36 and Direct green 99 in the PMRobtained by coupling photocatalysis and direct contact membrane distillation (DCMD) usingdifferent TiO2 concentration in the reacting phase (evaluated on the basis of dyes concentrationin the feed phase after 5 h of illumination)Data from Mozia et al (2007)

Photocatalytic membrane reactors for water treatment 221

734 Coupling of photocatalysis and dialysis

The results summarized in the previous section show that only the combination ofphotocatalysis and MD avoids fouling but it needs energy to reach evaporationphenomena

On this basis Azrague et al (2007) proposed the combination of dialysis and photo-catalysis to mineralize organic compounds (24-dihydroxybenzoic acid [24-DHBA]was used as a model pollutant) contained in artificial turbid waters obtained by usinga natural clay named bentonite In this PMR configuration the dialysis membraneused as a membrane contactor permits to separate the polluted turbid water fromthe PR compartment (Figure 77)

Operating in this way the membrane acts as a barrier for the photocatalyst particlesand it allows to extract the organic compounds from the turbid water thanks to theconcentration difference between the turbid polluted compartment and the one inwhich the photocatalytic reaction takes place The absence of TMP avoids the forma-tion of fouling even in case of highly turbid water Besides the membrane permits (1)to maintain the TiO2 in the PR compartment avoiding a final filtration stage and (2) tokeep the bentonite away from the PR thus avoiding the loss of efficient irradiationsdue to the scattering by bentonite particles

All these advantages combined with the complete removal of a high 24-DHBAconcentration demonstrate the effectiveness of the proposed PMR combiningphotocatalysis and dialysis These results should lead to the design of a PMR workingin a continuous mode

735 Coupling of photocatalysis and pervaporation

Recently it has been demonstrated that the integration of photocatalysis with PV is apromising method to improve the efficiency of the detoxification of water streams con-taining recalcitrant organic pollutants at a low concentration (Camera-Roda amp Santar-elli 2007) as the integration of the two processes generates a synergistic effect In PVseparation is not based only on the relative volatility of the components in the mixture

(1)

(2)

(3)

(4)

(5) (6)

(7)

(8)

Figure 77 Schematization of the experimental set-up of the integrated photocatalysiseMDprocess (1) magnetic stirrer (2) feed (artificial turbid water) tank (3) and (4) circulation pumps(5) hollow fibre module or flat sheet membrane (6) thermostated photoreactor (7) pressureregulation valve (8) oxygen cylinderAdapted from Azrague et al (2007)

222 Advances in Membrane Technologies for Water Treatment

but also depends on the relative affinity of the components with the membrane Thusthe choice of membrane material is important to obtain a selective separation of themolecules

The experimental apparatus used for the integrated photocatalysis-PV process isschematically represented in Figure 78 The liquid is continuously recycled by a mem-brane pump to an annular photocatalytic reactor (APR) and kept at a constant temper-ature after passing through a small tank immersed in a thermostatic bath Oxygen iscontinuously supplied inside the tank to maintain a constant concentration of8 mg L1 in the system At the exit of the APR the water passes through one ortwo plane PV modules (membrane surface area frac14 160 cm2) through which the compo-nents permeate selectively thanks to the vacuum (6 mbar) that is kept downstream

The results (Figure 79) showed that the rate of disappearance of a model pollutant(4-chlorophenol [4-CP]) is highly improved by using the integrated system as the

(1)

(2)

(3)

(4)Permeate

Retentate

Figure 78 Schematization of the experimental set-up utilized for the integrated photocatalysis-PV process (1) termostated feed tank (2) membrane pump (3) annular photocatalytic reactor(APR) (4) plane pervaporation moduleAdapted from Camera-Roda and Santarelli (2007)

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35Time (h)

4-C

P re

mov

ed (

)

IntegrationPC+PV no integrationOnly photocatalysisOnly pervaporation

Figure 79 Percentage of 4-chlorophenol (4-CP) removed versus time in the integratedphotocatalysis-PV processAdapted from Camera-Roda and Santarelli (2007)

Photocatalytic membrane reactors for water treatment 223

membrane was efficient in continuously eliminating some intermediate productsthat could slow down the rate of the photocatalytic reaction and concurrently thephotocatalysis transforms the weakly permeable 4-CP into organic compounds thatPV can remove at a high rate

Process intensification by synergistic effect depends on the optimization of the ratiobetween the characteristic rates of the photocatalytic and PV processes

Recently the use of a highly selective membrane allowed to recover somechemical products with high added value as vanillin starting from trans-ferulic acid(Camera-Roda et al 2013)

74 Applications of PMRs for water treatment

In the last years the interest in the presence of pharmaceutical active compounds(PhACs) and their metabolites in waterways has increased significantly (JonesVoulvoulis amp Lester 2002 Kasprzyk-Hordern Dinsdale amp Guwy 2008) Largeamount of PhACs in terms of thousands of tons are annually used for therapeuticpurposes or in animal farming in each European country and may be excreted bothas unmetabolized and as active metabolites thus reaching the aquatic environmentBesides improper disposal of industrial waste may also contribute to their occurrencein aquatic environment The wastewater is generally treated in sewage treatment plants(STP) that often fail to remove the majority of PhACs resulting in high concentrationsdischarged in treated effluents (Braga Smythe Schafer amp Feitz 2005 Carballa et al2004 Castiglione et al 2006 Colpin et al 2002 Comeau Surette Brun amp Losier2008) so PhACs are detectable in the aquatic environment with concentration levelsup to the mgL These amounts are much lower than maximum concentrations reportedfor typical industrial contaminants but their toxicological chronic effects on aquaticenvironment due to the continuous exposure to mixtures of pharmaceuticals areunknown

On this basis the demand for developing efficient systems alternative to the tradi-tional purification methods to remove PhACs from water has assumed a great researchinterest PMRs could represent a useful solution to this problem

The photodegradation of different pharmaceuticals (furosemide ranitidine (hydro-chloride) ofloxacine phenazone naproxen carbamazepine and clofibric acid)contained in aqueous medium at various pHs by using a batch PR and a PMR workingin recirculation regime was studied by Molinari et al (2006) The experimental testswere performed by using polycrystalline TiO2 as the photocatalyst determining theperformances of different commercial membranes mainly of the NF type (Table 74)in the PMR To analyse the results of the photodegradation experiments in the PMRthe main factors involved in the overall performance of the PR were separately studiedby carrying out the following tests (1) adsorption tests on the TiO2 particles (2) degra-dation tests in the absence of the membrane (3) membrane rejection by changing theoperating pressures and (4) degradation tests in the PMR The results evidenced thatthe adsorption of the substrates onto the catalyst is affected by the pH owing to theinfluence of this operating parameter on the hydrophilichydrophobic character of

224 Advances in Membrane Technologies for Water Treatment

the photocatalyst All the seven considered molecules were successfully photode-graded in the batch reactor (without the membrane) with pseudo-first order kinetics

Furosemide and ranitidine were selected to carry out the study of rejection and pho-todegradation in the PMR During the photocatalytic tests in the PMR the permeateflux through the NTR 7410 membrane had an average value of 45 Lhm2 at bothacidic and alkaline pHs Rejection values were in the range 10e60 for furosemideand 5e30 for ranitidine in the dark (without photoreaction) but a net decreasedown to zero was observed in the contemporary presence of light photocatalystand oxygen Then the degradation results in the PMR (Figure 710) showed that rejec-tion measured in the presence of photocatalyst and oxygen both in the dark and underirradiation conditions was almost zero so that the membrane in this case was benefi-cial only because it allowed the confinement of the photocatalyst

In a successive work the same group Molinari et al (2008) reported the degradationof two pharmaceuticals (Gemfibrozil [GEM] and Tamoxifen [TAM]) selected astarget molecule using suspended TiO2 as catalyst in two configurations of PMRs(pressurized and depressurized) operated in both batch and continuous mode Thelatter mode consisted in the continuous withdrawn of the permeate from the reactorand its replacing by an equal volume of polluted water until reaching a steady state(approximately 190 min) in terms of flux and rejection values of intermediates Theobjective of these tests was to simulate the continuous photodegradation processthat could be applied at industrial level The experimental plant consisted of an annularPR with an immersed UV lamp connected to the permeation cell in which a pressurizedflat sheet membrane or a submerged membrane module was located The effects of pa-rameters such as pH of the aqueous TiO2 suspensions pump flow rate and membraneclean-up on the efficiency of the PMR were studied Closed and continuous

0

4

8

12

16

20

0 50 100 150 200Time (min)

Con

cent

ratio

n (m

gL)

Figure 710 Substrate concentrations versus time for runs carried out by using the hybridsystem with the NTR 7410 membrane at initial pH 3 (TiO2 frac14 1 gL O2 frac14 22 ppm immersedlamp 125 W) Furosemide (A) retentate (gt) permeate Ranitidine (-) retentate ()permeateReprinted from Molinari et al (2006) with permission from Elsevier

Photocatalytic membrane reactors for water treatment 225

procedures were used to investigate the behaviour of the pressurized PMRs The dataobtained for the closed membrane system showed complete photodegradation of GEMand TAM with an abatement of 99 after 20 min and mineralization higher than 90after approximately 120 min

Regard to the pressurized system the membrane used (commercial flat sheet NFmembrane NTR 7410 Nitto Denko Tokyo) allowed to maintain the drug and the cata-lyst in the reaction environment but it was not able to reject significantly the degrada-tion intermediates which were also found in the permeate A good operating stabilitywas observed by operating in continuous mode reaching a steady state for approxi-mately 120 min (Figure 711) with a complete abatement of the drug and values ofmineralization (60) and permeate flux (386 Lhm2) that remained constant untilthe end of a run A TOC rejection of about 62 at steady state confirmed the needto identify a membrane with higher rejection to the intermediate products Catalystdeposition on the membrane surface and fouling caused a flux decline during the pho-tocatalytic process

The depressurized system in which the submerged membrane module was locatedseparately from the PR and the oxygen was bubbled on the membrane surface couldbe of interest both to separate the photocatalytic zone from the separation zone and toreduce membrane fouling thanks to oxygen sparging The UF membrane (PES com-mercial capillary membrane 005e01 mm average pore size) used in the submergedsystem showed retention of only the catalyst in the reaction environment whileGEM and its oxidation products moved in the permeate However the submergedPMR permitted to obtain a steady-state flux of 651 Lhm2 higher than those obtainedoperating with the pressurized module resulting it interesting for application purposes

Retentate

Permeate

0 50 100 150 200 250 3000

Time (min)

TOC

(mg

L)

2

4

6

8

10

Figure 711 Total organic carbon (TOC) values versus the time in the degradation ofGemfibrozil (GEM) in the continuous submerged membrane photoreactor (continuous feed ofGEM at concentration of 10 mgL Reprinted from Molinari et al (2008) with permission fromElsevier)

226 Advances in Membrane Technologies for Water Treatment

The overall results reported by Molinari et al (2006) and Molinari et al (2008)confirmed that PMRs can be of interest in the removal of organic pollutants from waterbecause they allowed the recovery and reuse of the catalyst permitted to achieve acontinuous process and if a suitable membrane is found it is possible to retain thepollutant and its degradation products in the reaction environment

With regard to the possibility of using solar radiation to activate the photocatalystin 2005 Augugliaro et al studied lincomycin (a common antibiotic) degradation inaqueous suspensions of polycrystalline TiO2 Degussa P25 irradiated by sunlight Ahybrid system consisting of a solar PR coupled with a membrane module was testedwith the aim to improve system sustainability and performance The results of prelim-inary tests without the membrane separation step showed that lincomycin was success-fully oxidized in the pilot plant solar PR The presence of the membrane whichconfined both photocatalyst and pollutants in the reaction environment allowed oper-ation in continuous mode The data collected by using the hybrid system both in totalrecycle (batch) and in continuous mode (Figure 712) indicated that the presence of themembrane allows the reduction of both the substrate and intermediates down to lowconcentration levels

Benotti Stanford Wert and Snyder (2009) reported a study on the use of a PMRpilot system using UVTiO2 photocatalysis in the removal of 32 PhACs from waterThe results showed that concentrations of all compounds decreased during the treat-ment In particular removal efficiency higher than 70 was obtained for 29 of thetargeted compounds while a removal efficiency lower than 50 was achieved foronly three compounds During the treatment of all the considered PhACs no oestro-genically active transformation products were formed Thus the PMR developed inthis work is a useful technology for water treatment as determined by pharmaceuticaland endocrine-disrupting compound destruction as well as the removal of oestrogenicactivity

In 2012 Mozia and Morawski on the basis of their previous encouraging resultsobtained in dye removal from water compared the efficiency of photodegradationof ibuprofen (IBU) sodium salt present in tap water in a PMR using DCMD under a

90(a) (b)8070605040302010

00 1 2 3 0

E [einstein]E [einstein]

C [μ

M]

C [μ

M]

0

5

10

15

20

25

1 2 3 4

Figure 712 Lincomycin concentrations versus the cumulative photon energy E for runscarried out in (a) total recirculation regimens and (b) in continuous regimen by using the hybridsystem at different initial lincomycin concentrations Full symbol retentate open symbolpermeateReprinted from Augugliaro et al (2005) with permission from Elsevier

Photocatalytic membrane reactors for water treatment 227

batch and continuous operation The results revealed that the influence of the operationmode on the effectiveness of IBU decomposition and mineralization and on the prod-uct (distillate) quality was not significant The permeate did not contain IBU regard-less of the process conditions Despite that the authors recommended the operation ofthe PMR in the continuous mode due to its higher potential for a large-scaleapplication

Membrane scaling during a long-term process was also studied The results sum-marized in Figure 713 showed a decline of permeate flux during the long-term exper-iments In particular after 54 h of the PMR continuous operation the flux was lowerby approximately 7 compared to pure water flux (272 Lm2d versus 294 Lm2d)whereas after 188 h an 86 flux decline was detected The deposit layer formed ona membrane surface had a composite structure on a thin porous TiO2 layer the calciteand aragonite crystals were present The application of cleaning with HCl solutionallowed to dissolve the CaCO3 scale deposit and to recover the flux However about70 h after washing with HCl solution the flux started decreasing with a similar rate asbefore cleaning

In a successive work the same authors (Mozia Darowna Przepiorski amp Moraw-ski 2013) reported the removal of a nonsteroidal anti-inflammatory drug (diclofenacsodium salt [DCF]) from water in two hybrid systems coupling photolysis or photoca-talysis with DCMD The results are summarized in Figure 714 in terms of TOCamounts in distillate (permeate) at the end of various experiments in comparisonwith the initial and final amounts of organic carbon in feed solutions A completeDCF decomposition in the feed was obtained in both processes In the case of the pho-tolysiseDCMD hybrid system the effectiveness of TOC mineralization after 5 h ofirradiation ranged from 273 to 487 depending on the DCF initial concentrationThe addition of TiO2 allowed the improvement of the efficiency of TOC removal Af-ter 5 h of the hybrid photocatalysiseDCMD process the mineralization efficiency was

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300Time (h)

Perm

eate

fulx

(Lm

2 d)

HCl cleaning

Figure 713 Changes of permeate flux during long-term operation of photocatalytic membranereactor (PMR) using direct contact membrane distillation (DCMD) in continuous modeAdapted from Mozia and Morawski (2012)

228 Advances in Membrane Technologies for Water Treatment

in the range of 825e100 the highest for the lowest DCF concentration Applicationof DCMD in the hybrid systems ensured high efficiency of separation of DCF as wellas the products of its degradation Indeed regardless of the process applied distillatewas high purity water DCF was not detected TOC concentration did not exceed08 mgdm3 and conductivity was lower than 16 mScm

The results obtained by Mozia and Morawski (2012) and Mozia et al (2013)showed that because the MD efficiently separated not only TiO2 particles but alsoorganic contaminants present in feed solution the PMR using DCMD represents apromising method for treatment of waters containing pharmaceuticals Low permeate(distillate) flux assured relatively long residence time of contaminants which resultedin high effectiveness of their photodegradation

The overall results reported in this section confirm that PMRs can be of interest inthe removal of organic pollutants (eg pharmaceuticals) from water because the mem-brane (1) separates TiO2 particles efficiently thus permitting the recovery and reuse ofthe catalyst (2) permits the realization of a continuous process and (3) allows theretention of organic pollutants and their degradation products thus avoiding theirrelease in the permeate and controlling the residence time of contaminants in the reac-tion environment Then PMRs can be considered a useful technology for water treat-ment as determined by PhACs destruction and the removal of oestrogenic activity Animportant issue to take into consideration in developing photocatalysisemembranehybrid processes is membrane fouling mainly due to photocatalyst deposition onthe membrane feed side In this context the approach proposed by Mozia et al inwhich MD is coupled with photocatalysis seems to be promising because MD allowsto obtain the points (1) (2) and (3) previously reported and also permits the avoidanceof the significant fouling observed when a pressure-driven membrane process is usedalthough the higher energetic consumption of MD could represent a limitation of thishybrid process

642 640

00

627

377

05

640

110

0700

100

200

300

400

500

600

700

Feed 0 Feed 5 h Permeate 5 h

TOC

(mg)

DCMD

Photolysis - DCMDPhotocatalysis - DCMD

Figure 714 Comparison of TOC amounts in distillate (permeate) after 5 h of direct contactmembrane distillation (DCMD) photolysiseDCMD and photocatalysiseDCMD processeswith the initial and final total organic carbon (TOC) amounts in feed solutionsData from Mozia et al (2013)

Photocatalytic membrane reactors for water treatment 229

75 Advantages and limitations of PMRs in watertreatment

Based on the results summarized in the previous sections the use of PMRs can be pro-posed as an attractive green process because it is effective in abating harmful andrecalcitrant substances present in aqueous effluents

The main advantages related to the use of the PMRs to degrade pollutants are

1 Possibility to be applied to a wide range of compounds in aqueous gaseous and solid phase2 Short reaction times and mild experimental conditions usually ambient temperature and pressure3 Generally only oxygen from air without any additional additive is necessary4 Effectiveness with low concentration of pollutant(s)5 Possibility to destroy a variety of hazardous molecules with the formation of innocuous prod-

ucts solving the disposal pollutant problem associated to the conventional wastewatertreatment methods

6 Possibility to convert toxic metal ions in their nontoxic forms which can be recovered andreused

7 Synergistic effects by coupling the potentialities of classical PRs and those of membraneprocesses ie catalyst recovery and reuse (immobilized or in suspension) rejection of thesubstrate andor separation of degradation products thus allowing to perform the reactionof interest and the separation of the desired product(s) simultaneously in continuous mode

8 Possibility to control the residence time of substrates in the photocatalytic system thus verifyingthe contact time between the molecules to be degraded and the catalyst and then the photocata-lytic degradatione this feature is very important when the process is used for synthetic purposes

9 Possibility to use sunlight

Despite these important advantages the application of the photocatalytic process at in-dustrial level is limited by different drawbacks mainly related to the membrane fouling

As reported in previous sections the choice of the membrane is a key step forachieving a successful application of PMRs For example Molinari et al (2006) andMollinari et al (2008) demonstrated the potentialities of PMR applications in both pres-surized and submerged configurations in water detoxification because they allowed therecovery and reuse of the catalyst and permitted the achievement of a continuous pro-cess while the membrane rejection towards the pollutants was not very satisfactoryThese results show the necessity to identify a membrane selective to intermediate prod-ucts to retain the pollutant and its degradation products in the reaction environment

76 Conclusion

All the results reported in this chapter on coupling the photocatalytic process withmembrane separations show numerous advantages derived from a synergistic effectof these two techniques In particular it has been shown that PMRs can be considereda useful technology for the removal of organic pollutants (eg pharmaceuticals) fromwater thanks to PhAC destruction and the removal of oestrogenic activity

An important limitation related to photocatalysisemembrane coupling is related tothe decrease of permeate flux caused by concentration polarization and membrane

230 Advances in Membrane Technologies for Water Treatment

fouling mainly due to photocatalyst deposition on membrane surface This drawbackcan be limited by appropriately choosing membrane material which must also ensureadequate chemical and thermal stability and type and PMRs configuration

The ideal membrane process to be coupled with photocatalysis should possess thesefeatures (1) complete retention of the catalyst and controlled fouling and (2) goodrejection of the substrates and of degradation byproducts to avoid the release ofdangerous substances in the treated water and to assure a residence time in the photo-catalytic system sufficient for obtaining complete pollutant degradation and minerali-zation Longer residence times are usually obtained by reducing the permeate flux so itis important to find a good compromise among the permeate flux and the residencetime to achieve a system for application purpose In other words the process intensi-fication by synergistic effect depends on the optimization of the ratio between the char-acteristic rates of the photocatalytic and membrane separation processes

Many methods have been tested to improve the membrane performances Amongthese blending with inorganic materials (eg immobilization of TiO2) to increasethe hydrophilic character of the membrane surface exposed to the reacting environ-ment of TiO2 is a promising approach that produces photocatalytic membranes withantifoulingself-cleaning ability The so-prepared membranes are good candidatesfor use in membrane reactors for wastewater treatment and reuse processes

Considering PMR configuration the use of SMPRs with fine-bubble aeration andintermittent membrane filtration can be potentially applied in the photocatalytic oxida-tion process during drinking water treatment because this approach significantly re-duces membrane fouling

The hybrid process obtained by coupling photocatalysis with MD seems very prom-ising for the removal of organic pollutants from waters because it possesses the idealfeaturespreviously reported In particular this couplingavoids fouling but it needs energyto obtain evaporation On the basis of this the combination of dialysis and pervaporationwith photocatalysis has been also reported showing that this coupling also possesses thefeatures of the ideal membrane process to be coupled with photocatalysis

77 Future trends

The use of submerged membrane systems operated with fine-bubble aeration in theintermittent membrane filtration mode and the coupling of photocatalysis with MDdialysis and pervaporation represent some promising approaches for overcomingthe limitation related to membrane fouling In particular the coupling with DCMDseems to be more promising asMD (1) separates TiO2 particles efficiently (2) permitsthe retention of organic pollutants and their degradation byproducts (the MDdistillate is practically high purity water) (3) permits the realization of a continuousprocess and (4) allows the avoidance of membrane fouling although the higherenergetic consumption of MD could represent a limitation of this hybrid process

On this basis it is foreseen that hybrid system photocatalysisemembranes will havea significant impact in designing processes for the abatement of organic pollutantscontained in waters

Photocatalytic membrane reactors for water treatment 231

78 Sources of further information

An exhaustive reference book on the fundamentals and applications of heterogeneousphotocatalysis that was recently published is Clean by light irradiation Practicalapplications of supported TiO2 by Augugliaro V Loddo V Pagliaro M PalmisanoG amp Palmisano L (2010) Cambridge (UK) RCS Publishing

Fundamentals of photocatalysis and some interesting information about membranePR regarding membrane materials and some operational issues can be found inChapter 6 - Photocatalytic membrane reactors Fundamentals membrane materialsand operational issues by Mozia S Morawski AW Molinari R Palmisano Lamp Loddo V (2013) In A Basile (Ed) Handbook of membrane reactors - volume2 Reactor types and industrial applications (pp 236e295) Cambridge (UK) Wood-head Publishing Limited ISBN 978-0-85709-415-5

Other interesting information about configuration and performance of PMRs and anexample of this integrated technology in water treatment and chemical production canbe found in Chapter 21 - Photocatalytic membrane reactors Configurations perfor-mance and applications in water treatment and chemical production by MolinariR Palmisano L Loddo V Mozia S amp Morawski AW (2013) In A Basile(Ed) Handbook of membrane reactors - volume 2 Reactor types and industrialapplications (pp 808e845) Cambridge (UK) Woodhead Publishing LimitedISBN 978-0-85709-415-5

List of symbols

Cf Solute concentration in the feedCp Solute concentration in the permeateeL Photogenerated electronEg Energy band gaph Plankrsquos constanthD Photogenerated holen Frequency of light radiation

List of acronyms

E01 Redox potential of the species to be reduced

E02 Redox potential of the species to be oxidized

24-DHBA 24-dihydroxybenzoic acid4-CP 4-Chlorophenol4-NP 4-NitrophenolAOP Advanced oxidation processAPR Annular photocatalytic reactorBPA Bisphenol ACAM Contact angle measurementCB Conduction band

232 Advances in Membrane Technologies for Water Treatment

COD Chemical oxygen demandDCF DiclofenacDCMD Direct contact membrane distillationECB Redox potential of the conduction bandEVB Redox potential of the valence bandFA Fulvic acidGEM GemfibrozilIBU IbuprofenMD Membrane distillationMF MicrofiltrationNF NanofiltrationNHE Normal hydrogen electrodeNOM Natural organic matterOM Optical microscopyPAA Polyacrylic acidPAN PolyacrylonitrilePES PolyethersulfonePhAC Pharmaceutical active compoundPMR Photocatalytic membrane reactorPP PolypropylenePR PhotoreactorPTFE PolytetrafluoroethylenePV PervaporationPVDF Polyvinylidene fluorideR Membrane rejectionRB5 Reactive black 5 dyeRO Reverse osmosisSEM Scanning electron microscopySMPR Submerged membrane photocatalytic reactorSTP Sewage treatment plantsTAM TamoxifenTOC Total organic carbonUF UltrafiltrationUV Ultraviolet irradiationVB Valence bandWPF Water permeation flux

References

Ara~na J Pe~na Alonso A Do~na Rodriacuteguez J M Herrera Melian J A G Diacuteaz O amp PeacuterezPe~na J (2008) Comparative study of MTBE photocatalytic degradation with TiO2 andCu-TiO2 Applied Catalysis B-Evironmental 78 355e363 Retrieved from httpdxdoiorg101016japcatb200709023

Augugliaro V Garciacutea-Lopez E Loddo V Malato-Rodriacuteguez S Maldonado I Marcigrave Get al (2005) Degradation of lincomycin in aqueous medium Coupling of solar photo-catalysis and membrane separation Solar Energy 79 402e408 Retrieved from httpdxdoiorg101016jsolener200502020

Photocatalytic membrane reactors for water treatment 233

Azrague K Aimar P Benoit-Marquieacute F amp Maurette M T (2007) A new combination of amembrane and a photocatalytic reactor for the depollution of turbid water AppliedCatalysis B-Environmental 72 197e204 Retrieved from httpdxdoiorg101016japcatb200610007

Benotti M J Stanford B D Wert E C amp Snyder S A (2009) Evaluation of a photo-catalytic reactor membrane pilot system for the removal of pharmaceuticals and endocrinedisrupting compounds from waterWater Research 43 1513e1522 Retrieved from httpdxdoiorg101016jwatres200812049

Braga O Smythe G A Schafer A amp Feitz A J (2005) Fate of steroid estrogens inAustralian inland and coastal wastewater treatment plants Environmental Science ampTechnology 39 3351e3358 Retrieved from httpdxdoiorg101021es0501767

Camera-Roda G Augugliaro V Cardillo A Loddo V Palmisano G amp Palmisano L (2013)A pervaporation photocatalytic reactor for the green synthesis of vanillin Chemical Engi-neering Journal 224 136e143 Retrieved from httpdxdoiorg101016jcej201210037

Camera-Roda G amp Santarelli F (2007) Intensification of water detoxification by integratingphotocatalysis and pervaporation Journal of Solar Energy Engineering 129 68e73Retrieved from httpdxdoiorg10111512391204

Camera-Roda G Santarelli F Augugliaro V Loddo V Palmisano G Palmisano L et al(2011) Photocatalytic process intensification by coupling with pervaporation CatalyisToday 161 209e213 Retrieved from httpdxdoiorg101016jcattod201010052

Carballa M Omil F Lema J Llompart M Garcia-Jares C Rodriguez I et al (2004)Behaviour of pharmaceuticals cosmetics and hormones in a sewage treatment plant WaterResearch 38 2918e2926 Retrieved from httpdxdoiorg101016jwatres200403029

Castiglione S Magnati R Fanelli R Pomati F Calamari D amp Zuccato E (2006)Removal of pharmaceuticals in sewage treatment plants in Italy Environmental Scienceand Technology 40 357e363 Retrieved from httpdxdoiorg101021es050991m

Chen C Wang Z Ruan S Zou B Zhao M amp Wu F (2008) Photocatalyticdegradation of CI Acid Orange 52 in the presence of Zn-doped TiO2 prepared by a stearicacid gel method Dyes and Pigments 77 204e209 Retrieved from httpdxdoiorg101016jdyepig200705003

Chin S S Chiang K amp Fane A G (2006) The stability of polymeric membranes in a TiO2

photocatalysis process Journal of Membrane Science 275 202e211 Retrieved fromhttpdxdoiorg101016jmemsci200509033

Chin S S Lim T M Chiang K amp Fane A G (2007) Hybrid low-pressure submergedmembrane photoreactor for the removal of bisphenol A Desalination 202 253e261Retrieved from httpdxdoiorg101016jdesal200512062

Choi W (2006) Pure and modified TiO2 photocatalysts and their environmental applicationsCatalysis Surveys from Asia 10 16e28 Retrieved from httpdxdoiorg101007s10563-006-9000-2

Collazzo G C Foletto E L Jahn S L amp Villetti M A (2012) Degradation of Direct Black38 dye under visible light and sunlight irradiation by N-doped anatase TiO2 as photo-catalyst Journal of Environmental Management 98 107e111 Retrieved from httpdxdoiorg101016jjenvman201112029

Colmenares J C Aramendiacutea M A Marinas A Marinas J M amp Urbano F J (2006)Synthesis characterization and photocatalytic activity of different metal-doped titaniasystems Applied Catalysis A-General 306 120e127 Retrieved from httpdxdoiorg101016japcata200603046

Colpin D W Furlon E T Meyer M T Thurman E M Zaugg S D Barber L B et al(2002) Pharmaceuticals hormones and other organic wastewater contaminants in US

234 Advances in Membrane Technologies for Water Treatment

streams 1999e2000 A national reconnaissance Environmental Science amp Technology36 1202e1211 Retrieved from httpdxdoiorg101021es011055j

Comeau F Surette C Brun G L amp Losier R (2008) The occurrence of acidic drugs andcaffeine in sewage effluents and receiving waters from three coastal watersheds in AtlanticCanada Science of the Total Environment 396 132e146 Retrieved from httpdxdoiorg101016jscitotenv200802031

Damodar R A amp You S J (2010) Performance of an integrated membrane photocatalyticreactor for the removal of the reactive Black 5 Separation and Purification Technology 7144e49 Retrieved from httpdxdoiorg101016jseppur200910025

Damodar R A You S J amp Chou H H (2009) Study the self cleaning antibacterial andphotocatalytic properties of TiO2 entrapped PVDF membranes Journal of HazardousMaterials 172 1321e1328 Retrieved from httpdxdoiorg101016jjhazmat200907139

Di Paola A Garciacutea-Lopez E Marcigrave G amp Palmisano L (2012) A survey of photocatalyticmaterials for environmental remediation Journal of Hazardous Materials 3e69211e212 Retrieved from httpdxdoiorg101016jjhazmat201111050

Di Valentin C amp Pacchioni G (2013) Trends in non-metal doping of anatase TiO2 B C Nand F Catalysis Today 206 12e18 Retrieved from httpdxdoiorg101016jcattod201111030

Erdim E Soyer E Tasiyici S amp Koyuncu I (2009) Hybrid photocatalysissubmergedmicrofiltration system for drinking water treatment Desalination and Water Treatment 9165e174 Retrieved from httpdxdoiorg105004dwt2009767

Fu J Ji M Wang Z Jin L amp An D (2006) A new submerged membrane photocatalysisreactor (SMPR) for fulvic acid removal using a nano-structured photocatalyst Journal ofHazardous Materials 131 238e242 Retrieved from httpdxdoiorg101016jjhazmat200509039

Fujishima A amp Honda K (1972) Electrochemical photolysis of water at a semiconductorelectrode Nature 238 37e38 Retrieved from httpdxdoiorg101038238037a0

Ge L (2008) Novel visible-light-driven PtBiVO4 photocatalyst for efficient degradation ofmethyl orange Journal of Molecular Catalysis A-Chemical 282 62e66 Retrieved fromhttpdxdoiorg101016jmolcata200711017

Hernandez-Alonso M D Fresno F Suarez S amp Coronado J M (2009) Development ofalternative photocatalysts to TiO2 Challenges and opportunities Energy amp EnvironmentalScience 2 1231e1257 Retrieved from httpdxdoiorg101039b907933e

Herrmann J M (2005) Heterogeneous photocatalysis State of the art and present applicationsTopics in Catalysis 34 49e65 Retrieved from httpdxdoiorg101007s11244-005-3788-2

Hoffmann M R Martin S T Choi W amp Bahnemann D W (1995) Environmentalapplication of semicondutor photocatalysis Chemical Reviews 95 69e96 Retrieved fromhttpdxdoiorg101021cr00033a004

Huang X Meng Y Liang P amp Qian Y (2007) Operational conditions of a membranefiltration reactor coupled with photocatalytic oxidation Separation and PurificationTechnology 55 165e172 Retrieved from httpdxdoiorg101016jseppur200611018

Huo Y Xie Z Wang X Li H Hoang M amp Caruso R A (2013) Methyl orange removalby combined visible-light photocatalysis and membrane distillation Dyes and Pigments98 106e112 Retrieved from httpdxdoiorg101016jdyepig201302009

Jones Q A H Voulvoulis N amp Lester J N (2002) Aquatic environmental assessment of thetop 25 English prescription pharmaceuticals Water Research 36 5013e5022

Kasprzyk-Hordern B Dinsdale RM ampGuwy A J (2008) The occurrence of pharmaceuticalspersonal care products endocrine disruptors and illicit drugs in surface water in SouthWales

Photocatalytic membrane reactors for water treatment 235

UK Water Research 42 3498e3518 Retrieved from httpdxdoiorg101016jwatres200804026

Lang W Z Xu Z L Yang H amp Tong W (2007) Preparation and characterization ofPVDFePFSA blend hollow fiber UF membrane Journal of Membrane Science 288123e131 Retrieved from httpdxdoiorg101016jmemsci200611009

Ling Q Sun J amp Zhou Q (2008) Preparation and characterization of visible-light-driventitania photocatalyst co-doped with boron and nitrogen Applied Surface Science 2543236e3241 Retrieved from httpdxdoiorg101016japsusc200711001

Mascolo G Comparelli R Curri M L Lovecchio G Lopez A amp Agostiano A (2007)Photocatalytic degradation of methyl red by TiO2 Comparison of the efficiency of immo-bilized nanoparticles versus conventional suspended catalyst Journal of Hazardous Mate-rials 142 130e137 Retrieved from httpdxdoiorg101016jjhazmat200607068

Molinari R Argurio P amp Lavorato C (2013) Review on reduction and partial oxidation oforganics in photocatalytic (membrane) reactors Current Organic Chemistry 172516e2537 Retrieved from httpdxdoiorg10217413852728113179990063

Molinari R Borgese M Drioli E Palmisano L amp Schiavello M (2002) Hybrid processescoupling photocatalysis and membranes for degradation of organic pollutants in waterCatalysis Today 75 77e85

Molinari R Caruso A Argurio P amp Poerio T (2008) Degradation of the drugs Gemfibroziland Tamoxifen in pressurized and de-pressurized membrane photoreactors using sus-pended polycrystalline TiO2 as catalyst Journal of Membrane Science 319 54e63Retrieved from httpdxdoiorg101016jmemsci200803033

Molinari R Caruso A amp Palmisano L (2010) Photocatalytic processes in membrane re-actors In E Drioli amp L Giorno (Eds) Comprehensive membrane science and engineering(Vol 3 pp 165e193) Oxford Elsevier Science BV

Molinari R Caruso A amp Poerio T (2009) Direct benzene conversion to phenol in a hybridphotocatalytic membrane reactor Catalysis Today 144 81e86 Retrieved from httpdxdoiorg101016jcattod200902034

Molinari R Mungari M Drioli E Di Paola A Loddo V Palmisano L et al (2000) Studyon a photocatalytic membrane reactor for water purification Catalysis Today 55 71e78

Molinari R Palmisano L Drioli E amp Schiavello M (2002) Studies on various reactorconfigurations for coupling photocatalysis and membrane processes in water purificationJournal of Membrane Science 206 399e415

Molinari R Pirillo F Falco M Loddo V amp Palmisano L (2004) Photocatalytic degra-dation of dyes by using a membrane reactor Chemical Engineering and Processing 431103e1114 Retrieved from httpdxdoiorg101016jcep200401008

Molinari R Pirillo F Loddo V amp Palmisano L (2006) Heterogeneous photocatalyticdegradation of pharmaceuticals in water by using polycrystalline TiO2 and ananofiltration membrane reactor Catalysis Today 118 205e213 Retrieved from httpdxdoiorg101016jcattod200511091

Moritz T Benfer S Arki P amp Tomandl G (2001) Investigation of ceramic membranematerials by streaming potential measurements Colloids and Surfaces A 195 25e33

Mozia S Darowna D Przepiorski J amp Morawski A W (2013) Evaluation of performanceof hybrid photolysis-DCMD and photocatalysiseDCMD systems utilizing UV-C radiationfor removal of diclofenac sodium salt from water Polish Journal of Chemical Technology15(1) 51e60

Mozia S amp Morawski A W (2006) Hybridization of photocatalysis and membrane distil-lation for purification of wastewater Catalysis Today 118 181e188 Retrieved fromhttpdxdoiorg101016jcattod200512003

236 Advances in Membrane Technologies for Water Treatment

Mozia S amp Morawski A W (2012) The performance of a hybrid photocatalysis-MD systemfor the treatment of tap water contaminated with ibuprofen Catalysis Today 193213e220 Retrieved from httpdxdoiorg101016jcattod201203016

Mozia S Morawski A W Toyoda M amp Tsumura T (2010) Integration of photo-catalysis and membrane distillation for removal of mono- and poly-azo dyes from waterDesalination 250 666e672 Retrieved from httpdxdoiorg101016jdesal200906075

Mozia S Tomaszewska M amp Morawski A W (2005) A new photocatalytic membranereactor (PMR) for removal of azo-dye Acid Red 18 from water Applied CatalysisB-Environmental 59 131e137 Retrieved from httpdxdoiorg101016japcatb200501011

Mozia S Tomaszewska M amp Morawski A W (2007) Photocatalytic membrane reactor(PMR) coupling photocatalysis and membrane distillationmdasheffectiveness of removal ofthree azo dyes from water Catalysis Today 129 3e8 Retrieved from httpdxdoiorg101016jcattod200706043

Mulder M (1996) Basic principles of membrane technology AH Dordrecht The NetherlandsKluwer Academic Publishers

Ni M Leung M K H Leung D Y C amp Sumathy K (2007) A review and recent de-velopments in photocatalytic water-splitting using TiO2 for hydrogen productionRenewable and Sustainable Energy Reviews 11 401e425 Retrieved from httpdxdoiorg101016jrser200501009

Palmisano G Augugliaro V Pagliaro M amp Palmisano L (2007) Photocatalysis Apromising route for 21st century organic chemistry Chemical Communications3425e3437 Retrieved from httpdxdoiorg101039b700395c

Palmisano G Garcıa-Lopez E Marcigrave G Loddo V Yurdakal S Augugliaro V et al(2010) Advances in selective conversions by heterogeneous photocatalysis ChemicalCommunications 46 7074e7089 Retrieved from httpdxdoiorg101039c0CC02087g

Patsios S I Sarasidis V C amp Karabelas A J (2013) A hybrid photocatalysis-ultrafiltrationcontinuous process for humic acids degradation Separation and Purification Technology104 333e341 Retrieved from httpdxdoiorg101016jseppur201211033

Raja P Bensimon M Klehm U Albers P Laub D Kiwi-minsker L et al (2007) Highlydispersed PTFECo3O4 flexible films as photocatalyst showing fast kinetic performance fordiscoloration of azo-dyes under solar irradiation Journal of Photochemistry and Photo-biology 187 332e338 Retrieved from httpdxdoiorg101016jjphotochem200610033

Rosu M C Suciu R C Lazar M D amp Bratu I (2013) The influence of alizarin andfluorescein on the photoactivity of Ni Pt and Ru-doped TiO2 layersMaterials Science andEngineering B 178 383e390 Retrieved from httpdxdoiorg101016jmseb201301001

Shon H K Puntsho S Vigneswaran S Kandasamy J Kim J B Park H J et al (2010)PVDF-TiO2 coated microfiltration membranes Preparation and characterization Mem-brane Water Treatment 1(3) 193e206

Wei Y Chu H Q Dong B Z Li X Xia S J amp Qiang Z M (2011) Effect of TiO2

nanowire addition on PVDF ultrafiltration membrane performance Desalination 27290e97 Retrieved from httpdxdoiorg101016jdesal201101013

WuG Chen T SuW ZhouG ZongX Lei Z et al (2008)H2 productionwith ultra-lowCOselectivity viaphotocatalytic reformingofmethanol onAuTiO2 catalyst International Journalof Hydrogen Energy 33 1243e1251 Retrieved from httpdxdoiorg101016jijhydene200712020

Photocatalytic membrane reactors for water treatment 237

Yang D Zhao J Liu H Zheng Z Adebajo M O Wang H et al (2013) Enhancingphotoactivity of TiO2(B)anatase core-shell nanofibers by selectively doping cerium ionsinto the TiO2(B) core Chemistry-A European Journal 19 5113e5119 Retrieved fromhttpdxdoiorg101002chem201202719

You S J Semblante G U Lu S C Damodar R A amp Wei T C (2012) Evaluation of theantifouling and photocatalytic properties of poly(vinylidene fluoride) plasma-grafted pol-y(acrylic acid) membrane with self-assembled TiO2 Journal of Hazardous Materials237e238 10e19 Retrieved from httpdxdoiorg101016jjhazmat201207071

Zhang J W Wang L Zhang G L Wang Z Y Xu L S amp Fan Z (2013) Influence of azodye-TiO2 interactions on the filtration performance in a hybrid photocatalysisultrafiltrationprocess Journal of Colloid and Interface Science 389 273e283 Retrieved from httpdxdoiorg101016jjcis201208062

238 Advances in Membrane Technologies for Water Treatment

Novel and emerging membranesfor water treatment byhydrostatic pressure and vaporpressure gradient membraneprocesses

8

P Arribas12 M Khayet23 MC Garciacutea-Payo2 L Gil41Campus of International Excellence Moncloa Campus (UCM-UPM) Madrid Spain2Department of Applied Physics I University Complutense of Madrid Avda ComplutenseMadrid Spain 3Madrid Institute for Advanced Studies of Water (IMDEA Water Institute)Alcala de Henares Madrid Spain 4School of Forest Engineering University Polytechnic ofMadrid Avda Complutense Madrid Spain

81 Introduction

Membrane-based separation technologies are environmentally friendly separation pro-cesses that are designed to provide effective and economic solutions to a wide varietyof environmental issues related to water and energy use including climate change andglobal warming The growth of membrane science and technology is mainly due to theimpressive developments in materials used for membrane fabrication and modifica-tion improvements in membrane modules and the evolution of related systemsplants and equipment

In general membranes are semipermeable barriers used for selective permeation ofthe desired species in liquid or gaseous phases by means of an appropriate drivingforce(s) One of the provided classifications of membrane separation processes isaccording to the nature of the membrane and the applied transmembrane driving forceEach membrane process exhibits its advantages and drawbacks and as consequence ithas its fields of applications Providing that this chapter is focused on water treatmentTable 81 summarizes the common considered membrane separation processes in thisfield with the corresponding driving forces and their applications

It is worth mentioning that membranes of different forms and characteristics aregenerally made from a wide variety of chemically and thermally stable polymersBoth single polymers and polymer blends are considered Other materials such asceramics metals and glasses are also used and mixed matrix membranes (MMMs)are fabricated Various membrane fabrication techniques are being proposed andimproved (ie phase inversion sintering stretching track-etching electrospinningetc) In addition various methods have been developed for membrane modification(ie chemical modification surface coating grafting etc) to improve its performance

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400008-3Copyright copy 2015 Elsevier Ltd All rights reserved

Table 81 Membrane separation processes used for water treatmentwith their driving force and main fields of applications

Membraneprocess

Transmembranedriving force Main fields of applications

Microfiltration(MF)

Hydrostaticpressure gradient

Pre-treatment for other processesClarification and biological stabilization in thebeverage industry

AnalysisSterilization in food and pharmaceuticalindustries

Removal of bacteria clarification

Ultrafiltration(UF)

Hydrostaticpressure gradient

Pre-treatment for other processesSeparation of oilwater emulsionDewaxingDeasphaltingElectrophoretic paintRemoval of macromolecules and virus

Nanofiltration(NF)

Hydrostaticpressure gradient

Drinking water productionRemoval of ions and small organicsChemical and pharmaceutical industryConcentrationdewateringWater softeningFractionation of monovalent and divalentcations

Reverse osmosis(RO)

Hydrostaticpressure gradient

Sea and brackish water desalinationDrinking water productionWastewater treatment (industrial andmunicipal pulp and paper textile)

Petroleum industry

Membranedistillation(MD)

Vapor pressuregradient(temperaturegradientdownstreampressure)

Desalination and concentration of brinesUltrapure water productionNear 100 separation of nonvolatile solutespresent in water

Extraction of volatile organic compoundsRecovery of valuable compoundsFood medical radioactive wastewaters

Pervaporation(PV)

Vapor pressuregradient(downstreampressure)

Dehydration of organic solventsRemoval of organics from waterOrganicorganic separation

Electrodialysis(ED)

Electric potentialgradient

Sea and brackish water desalinationUltrapure water productionDemineralization of food productsTable salt productionConcentration of brines

240 Advances in Membrane Technologies for Water Treatment

Novel membranes with innovative materials and improved properties suitable forspecific applications and compact module designs with better hydrodynamic flowchannels and new areas of applications are continuously reported Besides the highprocess performance of a given membrane that includes both the high liquid or vaporproduction rate and selectivity or separation efficiency there are other basic propertiesthat must be taken into account such as operational simplicity high energy efficiencylow cost good stability under wide operating conditions long-term durability lessfouling and scaling susceptibility environment compatibility customizable and adap-tive between different membrane operations in integrated systems easy control of itsstructure and scale-up

82 Pressure-driven membrane processes

In general pressure-driven membrane processes (PDMPs) include microfiltration(MF) ultrafiltration (UF) nanofiltration (NF) and reverse osmosis (RO) These filtra-tion processes can be distinguished by the size of the particles or molecules that thecorresponding membrane is capable of retaining or passing through (Porter 1988)This is roughly related to the membrane pore size which is the main responsibleparameter dictating the field of the process applications

The membranes fabricated for each of the PDMPs exhibit specific characteristicsaccording to the operating conditions and the subjected application A commoncharacteristic of the PDMP membranes is the high mechanical property to bear theapplied hydrostatic pressure especially for NF and RO In the following sections

Table 81 Continued

Membraneprocess

Transmembranedriving force Main fields of applications

Reverseelectrodialysis(RED)

Electric potentialgradient

Power generationSea and brackish water desalination

Osmoticdistillation(OD)

Vapor pressuregradient(concentrationgradient)

Near 100 separation of non-volatile solutespresent in water

Recovery of valuable compoundsFood wastewaters

Forward osmosis(FO)

Concentrationgradient

Sea and brackish water desalinationDrinking water production

Pressure retardedosmosis(PRO)

Concentrationgradient

Power generationSea and brackish water desalination

Novel and emerging membranes for water treatment 241

the recent progress made in each individual PDMP is thoroughly described with itsnovel and emerging membranes proposed for water treatment

821 Microfiltration

As shown in Table 82 the pore size of anMFmembrane ranges between 01 and 10 mmThe MF membranes must have a high porosity and a pore size distribution as narrow aspossibleA large number ofmaterialswere considered for fabrication ofMFmembranesboth organic (hydrophilic or hydrophobic polymers) and inorganic materials (ceramicsmetals glasses) Some of the fabrication techniques such as sintering stretching track-etching and phase inversion were used for fabrication of polymeric MF membranes

Table 82 Characteristics of the different pressure-driven membraneprocesses

Microfiltration(MF)

Ultrafiltration(UF)

Nanofiltration(NF)

Reverseosmosis (RO)

Pore size(nm)

100e10000 1e100 05e2 lt05

MWCOa

(Da)gt5$105 2e5$105 5$102e2$103 lt5$102

Pressure(MPa)

01e2 1e10 10e30 15e30(brackish)

40e80(seawater)

Permeability(kgm2 s)

lt278 25e278 05e85 lt05

Membranematerialsb

CeramicPS PESPVDF CA

Ceramic PSPES PVDFCA TF

CA TF CA TF

Rejection ParticlesBacteria

MacromoleculesProteinsVirusColloids

High Mwcompounds

Multivalentions

Glucose

High and lowMwcompounds

Monovalentions

Inorganic ionsAmino acids

Separationmechanism

Sieving Sieving Sievingchargeeffectsdiffusion

Solutiondiffusion

aMWCO frac14Molecular weight cut-off of the membrane (corresponding solute rejection 90)bPS polysulfone PES Polyethersulfone PVDF polyvinylidene fluoride CA cellulose acetate TF thin-film

242 Advances in Membrane Technologies for Water Treatment

The main problems of MF are the concentration polarization and fouling phe-nomena Both reduce the water production rate and the efficiency of the whole pro-cess Therefore MF membranes are designed or modified taking into considerationboth phenomena and MF modules are cleaned periodically It must be pointed outthat the selection of a suitable material for MF is an important factor because sol-ute(s) adsorption phenomenon also plays an important role in irreversible foulingeffects

Dong et al (2012) used hydrophilic Mg(OH)2 nanoparticles (NPs) as inorganicfillers to prepare polyvinylidene fluoride PVDFMg(OH)2 MF hybrid membraneswith enhanced antifouling property Due to the addition of Mg(OH)2 NPs a largeamount of hydroxyl (eOH) groups were formed This results in an increase of thehydrophilicity of the prepared hybrid membrane reducing the permeate flux lossescaused by membrane biofouling of Escherichia coli and bovine serum albumin(BSA)

Wu Tang and Wu (2014) developed a novel silica (SiO2)egraphene oxide(GO) nano-hybridpolysulfone (PS) membrane which exhibited excellent anti-fouling ability and improved water permeability maintaining a high rejectionfactor to egg albumin These results were attributed to the specific properties ofSiO2eGO nanohybrid such as the high hydrophilicity and the good dispersionderived from SiO2 NPs

Wang Guan et al (2013) developed novel nanofibrous MF composite mem-branes consisting of a two-layered electrospun polyacrylonitrile (PAN)polyeth-ylene terephthalate (PET) fibrous scaffold infused with oxidized or modifiedcellulose nanofibers which were subsequently grafted by amine such as polyvinyl-amine (PVAm) polyethyleneimine (PEI) or ethylenediamine (see Figure 81) Thesemembranes have a web-like structure with high charge density high porosity andlarge surface area per unit volume These characteristics enabled the membranes tosimultaneously remove bacteria viruses andor toxic heavy metal ions maintaininga good permeation flux

PAN layer CNF in PAN layer Cellulose nanofibers

Figure 81 SEM images of electrospun polyacrylonitrilepolyethylene terephthalate(PANPET) membrane (a) electrospun polyacrylonitrilepolyethylene terephthalate (PANPET) membrane (cross-section) and (b) PANPET membrane infused with polyvinylamine(PVAm) grafted CNF (top view) (c) TEM image taken at a small section of the cellulosenetwork containing pores and individual polymer chains with spaghetti-like configurationReprinted from Wang Guan et al (2013) with permission from Elsevier

Novel and emerging membranes for water treatment 243

822 Ultrafiltration

UF is a PDMP placed between MF and NF However MF and UF both ivolve similarmembrane processes based on the same separation principle being the differencebetween both the structure of the membrane which is asymmetric for UF membranewith a much denser top layer and consequently a much higher hydrodynamic resis-tance than MF UF is commonly used to retain macromolecules and colloids fromaqueous solutions and to remove un-dissolved suspended or emulsified solids fromwater Cellulose acetate (CA) and polyelectrolytes are among the first syntheticpolymers used for UF membranes Today UF membranes are made from awide variety of chemically and thermally stable synthetic polymers including PSPAN polyethersulfone (PES) polyvinyl chloride (PVC) polycarbonate (PC)aliphatic and aromatic polyamides (PA) polyimides (PI) polyarylsulfone (PAS)and PVDF

Kong et al (2014) studied the effect of adding hydrophilic TEMPO-oxidizedcellulose nanofibrils (TOCNs) as a modifying agent on the structure and performanceof cellulose triacetate (CTA) UF membranes The obtained results showed that theincorporation of TOCNs to CTA membranes enhanced its mechanical properties(tensile strength and breakeelongate ratio) and its hydrophilicity resulting in higherpermeate fluxes and better antifouling performance

Another innovative and interesting study was performed by Wang Luo and Chung(2014) who developed tri-bore UF hollow fiber membranes made from Matrimid

and PES polymers with round-shape bore channels and a regular triangle-shape outergeometry Figure 82 shows the mechanism of formation of these UF membranestogether with their scanning electron microscopy (SEM) cross-section images Thisparticular geometry is claimed to be advantageous in terms of uniform mechanicalstrength and enhanced permeation properties due to the evenly distributed membranewall thickness

Recently a variety of inorganic particles or fillers such as SiO2 (Wu Mansouri ampChen 2013 Yu Zhang Zhang Liu amp Zhang 2013 ZhangWang et al 2014) silver(Ag) (Li et al 2013) ferrous ferric oxide (Fe3O4) alumina (Al2O3) (Arsuaga et al2013) zirconia (ZrO2) (Arsuaga et al 2013 Arthanareeswaran amp Thanikaivelan2010 Pang et al 2014) titania (TiO2) (Arsuaga et al 2013 Hamid et al 2011Razmjou Mansouri amp Chen 2011 Razmjou Resosudarmo et al 2012 Zhang Luet al 2013 Zhao Wang Wang Sun amp Zhang 2012) zinc oxide (ZnO) (Hong ampHe 2014) and zeolites (Leo Ahmad Kamil Junaidi Kamal amp Ahmad 2013) havebeen used to develop novel UF MMMs or organiceinorganic hybrid membraneswith improved permeabilities mechanical strengths and fouling resistant ability

Among the different inorganic NPs blended with polymeric membranes TiO2 hasalso been used in numerous studies due to its superhydrophilic photocatalytic andantibacterial properties under ultraviolet (UV) irradiation Rahimpour JahanshahiMollahosseini and Rajaeian (2012) performed an approach to improve the propertiesstructure and performance of PVDFsulfonated polyethersulfone (SPES) blend UFmembranes by using self-assembly of TiO2 NPs on the membrane surface followedby UV irradiation to activate their photocatalytic property The water contact angle

244 Advances in Membrane Technologies for Water Treatment

measurements showed that the hydrophilicity of PVDFSPES membranes wasstrongly improved by TiO2 deposition and UV irradiation The initial permeate fluxesof both pure water and BSA aqueous solutions were lower for the TiO2 depositedmembranes compared to the PVDFSPES membranes However the fouling propen-sity (bacterial activity) was significantly reduced and the long-term permeate fluxstability was enhanced

As was mentioned previously SiO2 is another common NP used for membranemodification SiO2 has the advantage to improve the membrane mechanical proper-ties and membrane porosity Yu et al (2013) used modified SiO2 NPs graftedwith N-Halamine to develop novel hydrophilic PES UF membranes By SEM imageanalysis and contact angle measurements it was confirmed that the additionof this modified SiO2 exerted a slight influence on the microstructure of the PESmembrane but significantly improved its surface hydrophilicity and permeability

Spinneret exit

Color change at air gap region

Externalcoagulant

Uponextrusion

Die swelleffect

Nascent fiber with ablossom geometry

Immediate phaseinversion at the

inner surface

Counterforce

Stretching to from atriangle shape

DF 3 mlmin DF 4 mlmin DF 5 mlmin

DF Dope flowrate

(a)

(b)

1mm

1mm

05mm

05mm

Figure 82 (a) Mechanisms of formation of triangle-shape tri-bore hollow fiber membranes(b) SEM images ofMatrimid tri-bore hollow fiber membranes using different dope compositionsAdapted from Wang et al (2014) with permission from Elsevier

Novel and emerging membranes for water treatment 245

Song and Kim (2013) prepared PS composites UF membranes with poly(1-vinylpyrrolidone) (PVP)-grafted SiO2 NPs (PVP-g-SiO2) by phase inversion method(see Figure 83) The resulted UF membranes exhibited higher water permeate fluxthan PS membranes without scarifying the solute rejection factors when the amountof PVP-g-SiO2 was less than or equal to 5 wt in the casting solution The hydro-philicity of the PVP-g-SiO2 membranes was increased with increasing PVP-g-SiO2

content and the PVP-g-SiO2 membranes exhibited enhanced fouling resistance to-ward non-ionic surfactants

Multifunctional inorganic ZnO NP has also attracted a significant attention due toits outstanding physical and chemical properties including promising catalytic activ-ity and efficient antibacterial and bactericidal capabilities ZnO as an additive NP ismore economical than TiO2 and Al2O3 (Liang Xiao Mo amp Huang 2012) Hong andHe (2014) successfully prepared PVDF UF membrane blended with ZnO NP viaphase inversion method The photocatalysis tests clearly showed that the modifiedPVDF membranes had significant photocatalysis self-cleaning capability whichwas due to the addition of nano-ZnO on the inner surface of the membrane (iethe pore wall) The water permeate flux of nano-ZnOPVDF blend membranes washigher than that of single PVDF membrane decreasing the membrane foulingresistance

Mehrparvar Rahimpour and Jahanshahi (2014) prepared novel modified PES UFmembrane for humic acid removal by blending different concentrations of twohydrophilic organic monomers 35-diaminobenzoic acid (DBA) and gallic acid(GA) with PES Experimental results showed that the different component ratios ofeach monomer affected the structural property of the blended membranes and thetop surface roughness As can be seen in Figure 84 with the addition of DBA andGA the size of the macrovoids became smaller and a denser surface was formed atthe top membrane surface The addition of DBA and GA monomers in the castingsolution increased the water content and the hydrophilicity of the membranes More-over the modified membranes exhibited better antifouling properties and the bestmembrane was prepared with 8 wt DBA and 6 wt GA

During the last 5 years GO nanosheets a two-dimensional carbon material havereceived tremendous attentions thanks to its fantastic properties such as good hydro-philicity easy to be modified and its ability to be dispersed in water yielding to aprolonged and stable suspension Wang et al (2012) used GO nanosheets to developnovel organiceinorganic nanocomposite GOPVDF-blended UF membranes TheGO addition played an important role in the membrane microstructure due to the af-finity of GO with many types of hydrophilic groups which increase the rapid masstransfer between the solvent and non-solvent during phase inversion When the GOcontent increased up to 030 wt lateral pore structures appeared within theGO-blended PVDF membranes (Figure 85) These features enhanced the hydro-philicity mechanical properties and water permeate flux recovery ratio comparedto the PVDF membrane Yu Zhang Zhang Liu Zhang amp Song (2013) also devel-oped a novel hyperbranched polyethylenimine (HPEI)-GOPES blend UF membranewith enhanced antifouling and antibacterial performance via the phase inversionmethod

246 Advances in Membrane Technologies for Water Treatment

NaOH 05molL

Water70ordmC 24h

Silica

SiO2

1-vinyl 2-pyrrolidone

Ethanol + AIBN70ordmC 3h

γ-MPSO

OO

Si O

O

HOHO

HOHO

OHOHOH

OHOH

OH

Silica-OH

(3-methacryloxypropyltrimethoxysilane)

OHOH

OHHO

HO

HOHO

OO

OSi O

O

ON

nPVP-g-silica

SiO2

Methanol + Water70ordmC 24h

NO

SiO2

SiO2

OHOH

OH

HOHO

HOHO

OO

OSi

Silica-MPS

O

O

Figure 83 Reaction procedure for preparation of PVP grafted silica nanoparticles (PVP-g-SiO2)Reprinted from Song and Kim (2013) with permission from Elsevier

Novel

andem

ergingmem

branesfor

water

treatment

247

823 Nanofiltration

NF is a PDMP using semipermeable membranes with a molecular weight cut-off(MWCO) in the range of 05e2 kDa and pore sizes in the range of 05e20 nm (seeTable 82) The origin of NF dates back to 1970s when efforts started to be madedeveloping RO membranes with reasonable water permeate fluxes at relatively lowpressures (Li Fane Ho Matsuura et al 2008) The NF process exhibits separationcharacteristics between RO and UF The specific features of NF membranes are mainlythe combination of very high rejection factors for multivalent ions (99) with low tomoderate rejection factors for monovalent ions (0e70) and high rejection factors(90) for organic compounds with molecular weights above that of the membraneMWCO The major separation mechanisms of NF involve a steric (ie size exclusion)effect and an electrostatic partitioning interaction (ie Donnan exclusion) between agiven NF membrane and a feed aqueous solution (Sun Hatton Chan amp Chung2012) In general the traditional materials used for fabrication of NF membranesare polymers using the phase inversion or the interfacial polymerization (IP)techniques The phase inversion membranes are homogeneous and asymmetric andthey are often made of CA or PES while the NF membranes made by IP are

(a) (b) (c)

Figure 84 SEM cross-section images of (a) neat polyethersulfone (PES) membrane and PESmembrane with (b) 15 wt diaminobenzoic acid (DBA) and (c) 15 wt gallic acid (GA)Reprinted from Mehrparvar et al (2013) with permission from Elsevier

(b)(a)

Figure 85 SEM cross-section images of the GO-blended polyvinylidene fluoride (PVDF)membranes with (a) 0 and (b) 03 wt graphene oxide (GO)Reprinted from Wang et al (2012) with permission from Elsevier

248 Advances in Membrane Technologies for Water Treatment

heterogeneous consisting of a thin-film composite (TFC) layer on the top of an UFsubstrate Typically used polymers are (aromatic) PA PI PS PES sulfonated PSand poly(piperazine amide) among others

Recently there has been a growing interest in developing novel NF hollow fibermembranes because of their flexibility and they are self-supporting and easy to packin modules with high membrane area per unit module volume (Nunes amp Peinemann2001 Yu Cheng et al 2013) Most NF membranes have a TFC structure because ofvarious key advantages compared to asymmetric membranes Sun et al (2012) devel-oped a TFC NF dual-layer hollow fiber membrane via IP of HPEI and isophthaloylchloride on a Torlon polyamide-imide (PAI) dual-layer hollow fiber substrateThis NF membrane exhibited a double repulsion effect a negatively charged substrateand a positively charged selective layer resulting in superior rejection factors (gt99)for both positively and negatively charged dye molecules This type of membrane wassuggested to recycle valuable products and reuse water for textile pharmaceutical andother industries Fang Shi and Wang (2013) prepared TFC NF hollow fiber mem-branes for water softening under low operating pressure (lt2 bar) using IP of PEIand trymesoyl chloride (TMC) on the inner surface of a PES UF membrane substrateThe prepared membrane showed a pure water permeability (PWP) of about17 Lm2 h bar an MWCO of around 500 Da (ie effective pore radius of about065 nm) an MgCl2 rejection factor of 967 and an MgSO4 rejection factor of806 Wei Kong Sun and Chen (2013) prepared also TFC NF hollow fiber mem-branes by IP of piperazine (PIP) and TMC on PSPES UF supporting membranes Thefabricated composite NF hollow fiber membranes had a relatively hydrophilic surfacewith an MWCO of approximately 520 Da a PWP of 119 Lm2 h bar and rejectionfactors of 398 and 962 to NaCl and Na2SO4 respectively Zheng et al (2013)followed the dip-coating method to prepare positively charged TFC NF hollow fibermembranes for cationic dyes removal using polypropylene (PP) hollow fiber MFmembrane as support PVA and polyquaternium-10 as coating materials and glutaral-dehyde (GLA) as a crosslinking agent The prepared membrane had an MWCO of 650Da a PWP of 86 Lm2 h bar and rejection factors of 928 and 350 to CaCl2 andNaCl respectively

Not only hollow fiber membranes have been proposed for NF but also flat sheetmembranes Guan Zhang Han Zhang and Jian (2013) developed TFC NF flat sheetmembranes with improved thermal stability and high performance by coating sulfo-nated copoly (phthalazinone biphenyl ether sulfone SPPBES) on poly(phthalazinoneether sulfone ketone) UF membranes used as support The prepared SPPBES compos-ite membranes exhibited a PWP of 73 Lm2 h bar and 84 Na2SO4 rejection factorTFC NF flat sheet membranes were also prepared by Han (2013) followingthe IP of melamine and TMC on a PEI UF membrane reinforced on PP non-wovenfabric as a backing material The membranes prepared under the optimum preparationconditions achieved a PWP of 34 Lm2 h bar and a rejection factor to Na2SO4 of778

As occurred with membranes designed for UF different polymers and inorganicNPs have been used to improve the NF performance of TFC membranes For instanceto solve the biofouling problem Ag NPs were used Kim Hwang Gamal El-Din and

Novel and emerging membranes for water treatment 249

Liu (2012) used Ag NPs to enhance the antifouling and antibacterial property ofthe surface of NF membranes Recently a stable Ag-doped fly ashpolyurethane(Ag-FAPU) nanocomposite multifunctional spider-web-like membrane was preparedby Pant et al (2014) via one-step electrospinning process using fly ash particles It wassuggested that the direct reduction of the Ag metal precursor (AgNO3) into Ag NPscaused by the solvent of PU (NN-dimethylformamide) in the blend solution couldbe the responsible of the simultaneous formation of spider-web-like nanonets anddeposition of Ag NPs on the surface of the fibers during electrospinning (Figure 86)These features enhanced absorption capacity to remove carcinogenic arsenic and toxicorganic dyes with the antibacterial properties reducing biofouling of the membrane

Mollahosseini and Rahimpour (2014) tried to improve the antibacterial and anti-fouling property of TFC NF membranes by first coating TiO2 NPs on an UF PS mem-brane support followed by the IP of m-phenylenediamine (MPD) and TMC monomerson the coated TiO2 layer With increasing TiO2 content in TFC membranes smootherand thicker surfaces appeared on the selective PA layer reducing the probability ofmembrane fouling by macromolecules

A novel b-cyclodextrin (b-CD)polyester TFC NF membrane was prepared by WuTang and Wu (2013b) via in situ IP of TMC and triethanolamine (TEOA) in presenceof b-CD By adding an appropriate amount of b-CD the membrane NF performancewas improved in terms of water permeability hydrophilicity water permeate fluxrejection factor and antifouling property To enhance acid stability of TFC NFmembranes Yu Zhou et al (2013) followed the IP of TMC and naphthalene-136-trisulfonylchloride (NTSC) and PIP to modify a PS UF membrane used as sup-port It was observed that the increase of the NTSC content in TMC-organic solutionresulted in a more hydrophilic and negatively charged membrane surface with an in-crease of both MWCO and PWP up to 660 Da and 106 Lm2 h bar respectively WuTang and Wu (2013a) performed an improved process to develop high-performancethin-film nanocomposite (TFN) membranes using IP of TEOA and TMC on PS UFsupporting membrane in presence of multiwalled carbon nanotubes (MWCNTs) By

Figure 86 Field-emission scanning electron microscopy (FESEM) images of AgFAPU (M1)mat (obtained from 1 h stirring solution) at different magnifications (a) lower magnification(b) higher magnification (inset is FESEM EDX of AgFAPU (M1) mat)Reprinted from Pant et al (2014) with permission from Elsevier

250 Advances in Membrane Technologies for Water Treatment

using an adequate amount of MWCNTs an appropriate surfactant and a proper reac-tion time MWCNTspolyester nanocomposite membranes can be fabricated with bothhigh permeation flux and excellent selectivity

A novel antifouling mixed matrix PES NF membrane was prepared by ZinadiniZinatizadeh Rahimi Vatanpour and Zangeneh (2014) by embedding GO nano-plates in PES matrix The modified GOPES membranes showed a wider finger-likestructure in comparison to those of the unmodified PES membrane with a significantlyhigher water permeate flux higher hydrophilicity higher dye removal capacity andhigher retention factor In addition it was found that the membrane prepared with05 wt GO exhibited the best antibiofouling property with the highest mean poresize porosity and therefore the greater water permeate flux

Recently positively charged composite NF membranes were prepared via cross-linking modification with an active PEI layer and a PAN substrate (Feng Xu LiTang amp Gao 2014) The PANPEI membrane with a PEI layer crosslinked with120 wt epichlorohydrin at 65 C for 15 h exhibited an optimum NF performancewith relatively high salt rejection factor and a high permeate flux (ie salt rejectionfactors of 9282 6976 and 6131 for feed aqueous solutions containing2000 mgL of MgCl2 MgSO4 and NaCl respectively with the correspondingPWP 163 160 and 179 Lm2 h bar)

Another type of NF membranes aquaporin (AQP)-based biomimetic membranehas attracted increasing attention during the last two years because of its potentialapplication for water purification and seawater desalination attributed to the excep-tionally high permeability and selectivity of AQPs In late 2013 Li et al (2014) intro-duced a novel and simple method to prepare an aquaporin Z (AQP-Z)-basedbiomimetic NF membrane consisting first on the deposition of polydopamine(PDA)-coated proteoliposomes on the surface of a substrate and then crosslinkingPEI with the PAI substrate to encapsulate these deposited proteoliposomes(Figure 87) The resultant AQP-Z-based membrane prepared under the optimal con-ditions achieved 95 MgCl2 rejection factor and a PWP of 37 Lm2 h bar (50higher than the control membrane with inactive AQPs) This type of membrane couldpreserve its activity even under harsh environmental conditions such as a high thermaltreatment at 343 K for 2 h (Li et al 2014)

824 Reverse osmosis

RO is a PDMP used to separate dissolved solids such as ions high and low molecularweight compounds and amino acids from water-based solutions More details on ROmembrane and process applications are summarized in Tables 81 and 82 CurrentlyRO is the most important desalination technology Different types of membranes wereproposed for the RO process but the most common ones are CA membranes andaromatic PA composite membranes The first was an asymmetric CA-based ROmembrane invented by Loeb and Sourirajan in 1960 (Hasson 2010) Today TFCmembranes are the most used in RO applications However the main drawbacksof RO membranes are the ldquotrade-offrdquo between permeability and salt rejectionfactors the membrane fouling and the chlorination problem resulting in a significant

Novel and emerging membranes for water treatment 251

membrane degradation by the presence of chlorine in feed water solutions (Xu Wangamp Li 2013) As a consequence research studies considered these three obstacles indeveloping novel suitable membranes for different RO applications (Misdan Lauamp Ismail 2012)

Innovative RO membrane engineering is still required because of the continuousincreasing demands of desalination and membrane wastewater treatments withenhanced water production rates greater salt rejection factors and overall higher resis-tance to fouling (Li amp Wang 2010) Various strategies have been explored to tacklethese needs among which surface modifications (eg surface coating) and incorpora-tion of specific additives nanoparticles andor co-solvents in the aqueousorganicphase during the IP have been identified to be the most effective (Xu et al 2013)

Wang Dai Zhang Li and Zhang (2013) prepared TFC RO membranes through IPof TMC 24406-biphenyl tetraacyl chloride 2304506-biphenyl pentaacyl chlorideand 220440660-biphenyl hexaacyl chloride with MPD The RO membrane skin layerbecame more negatively charged thinner and smoother as the functionality of the acid

AQPs (LPR 400) Mutants (LPR 400)

(A) (B)

(a) (b)

Figure 87 FESEM images (A and B scale bar 100 nm) and confocal fluorescence microscopyimages (a and b scale bar 50 mm) of different membranes with AQP-Z incorporated membrane(called LPR 400)Reprinted from Li et al (2014) with permission from Elsevier

252 Advances in Membrane Technologies for Water Treatment

chloride monomer increased The lower permeate flux of the highly functional acidchloride-based membrane owing to the greater extent of carboxylic acid groups onthe membrane surface lower surface roughness and lower mobility of the crosslinkedPA chains was observed A novel high permeability PA TFC RO membrane wassynthesized by Zhao Chang and Ho (2013) by introducing four different hydrophilicadditives (o-aminobenzoic acid-triethylamine salt m-aminobenzoic acid-triethylaminesalt 2-(2-hydroxyethl) pyridine and 4-(2-hydroxyethyl) morpholine) in the MPDaqueous solution for IP The obtained optimum membrane exhibited a stable desalina-tion performance over a one-month test with a salt rejection factor of 988 and apermeate flux of 1072 Lm2 h

Functionalized polyethylene glycol (PEG)-based polymers also have been synthe-sized and used to modify the PA TFC RO membrane surface to enhance its antifoulingproperties A comb-like amphiphilic copolymer methylmethacrylate-hydroxypoly(oxyethylene) methacrylate was synthesized by Choi Park Tak and Kwon (2012)via free-radical polymerization and used to modify the surface of the PA TFC ROmembrane by the dip-coating method In addition to introduce antifouling qualityin RO membranes without compromising their separation properties a new type ofpolymer coating made from hydrophilic dendritic polymers was used to modify thesurface of PA TFC RO membrane rendering it more hydrophilic (Sarkar et al2010) As it can be seen in Figure 88 the hydrophilic dendritic polymers were cross-linked to form a network and this was modified with hydrophilic linear chains (egPEG polyvinyl alcohol (PVA) and polyacrylamide) to form polymer brushes whichcan help to prevent formation of biofilm Moreover antimicrobial metal ions such asAg Zn or potassium could be chelated into the polymer network to further preventbiofouling Examples of dendritic polymers are hyperbranched polymers or den-drimers The chosen dendrimers were NH2-terminated PAMAM (PAMAM G2) andPAMAM G2-PEG Both dendrimers polymers can be crosslinked with glycidylether-functionalized au-telechelic PEG to from the PAMAM G2-PEG networkswhich were then used as hydrophilic coating layers

Zwitterionic materials can bind water molecules more strongly than other hydro-philic materials via electrostatically induced hydration Therefore zwitterionic-basedmaterials have been developed as promising candidates for preparation of antifoulingsurfaces (Xu et al 2013) In this sense Azari and Zou (2012) incorporated red-oxfunctional amino acid 3-(34-dihydroxyphenyl)-L-alanine onto commercial PA TFCRO membranes to create a zwitterionic surface resistant to membrane foulingIt was found that the coated membranes exhibited remarkably improved hydrophilic-ity which resulted in an increase of the membrane water permeability preserving thesalt rejection factor

For the purpose of improving the antifouling properties of ROmembranes Ishigamiet al (2012) used the layer-by-layer (LbL) assembly to modify their surfaces by poly(sodium 4-styrenesulfate) (PSS) and poly(allylamine hydrochloride) forming a thinpolyelectrolyte coating layer This antifouling capability increased with increasingthe number of layers due to the enhanced hydrophilicity and smoothness of the mem-brane surface The obtained optimal layer number based on the highest obtained waterpermeability when BSA was used as a foulant solute in water was found to be four

Novel and emerging membranes for water treatment 253

+

Ultra-purewater layer

Organiccontaminant

Bacteria NN NH

N

N

N

N

N

N

N

NH

N

NHN

N

NN

OH

HO OH

OH

OH

HO

OHOH

HO

HO

NH 8

8

8

8

8

8

5

5

6

6

7

N

N

NH

OH

HO

8(NH2)

16(NH2)

HN

O

O))

) )

Hydrophilicbrushes

Dendriticpolymercoating

PAMAMG2

PAMAMG2

PAMAM G2 (dendrimer)

PAMAM G2-PEG (dendrimer)

PAMAM G2-PEG network

AgRO membraneactive layer

Membranesupport

DGE-PEG

O

OO

O

O

O

O

OO OOn

O

O

OO

OO

O

))

)

)

)

)

))

)

)PAMAM

G2

PAMAMG2

PAMAMG2

PAMAMG2

PAMAMG2

PEG network chain segments

Figure 88 Schematic illustration of hydrophilic coating with dendritic polymers on the polyamide (PA) active layer of thin-film composite reverseosmosis (TFC RO) membraneReprinted from Xu et al (2013) and Sarkar et al (2010) with permission from Elsevier

254Advances

inMem

braneTechnologies

forWater

Treatm

ent

It was concluded that LbL assembly on a membrane surface could reduce fouling notonly by electrostatic repulsion between foulant and membrane surface but also byelectrostatic attraction due to the fact that the surface charge could be controlled byalternatively choosing the outer polyelectrolyte

As was pointed out previously chlorination is another trade-off for PA TFC ROmembranes Several researchers focused their studies to enhance chlorine toleranceof PA TFC RO membranes For instance Zhang Wang Wang and Wang (2013)modified a commercial TFC aromatic PA RO membrane (RE2521-TL WoongjinChemical Co Ltd Korea) via free-radical graft polymerization of 3-allyl-55-dimethylhydantoin (ADMH) followed by crosslinking by NN0-methylenebis(a-crylamide) (MBA) After graft polymerization it was observed that the ADMHMBA modified membrane was more hydrophilic with higher salt rejection factorsbut lower permeate flux than the unmodified membrane Recently Ni Meng Liand Zhang (2014) synthesized a novel hydrophilic random terpolymer poly(methyla-cryloxyethyldimethyl benzyl ammonium chloride-r-acryl-amide-r-2-hydroxyethylmethacrylate) via simple free-radical copolymerization using as a coating material acommercial PA TFC RO membranes (LCLE and BW30 DOW Chemical Co LtdMinneapolis USA) to improve their membrane antifouling performance and chlorineresistance (Figure 89) This innovative membrane modification method was demon-strated to be an effective way to render the PA TFC RO membrane more hydrophilicwith antimicrobial properties and more resistance to chlorine and fouling

The introduction of NPs with multifunctionalities in RO TFC membranes couldlead to another breakthrough in membrane desalination by further enhancing waterpermeability without scarifying the salt rejection factors (Misdan et al 2012)Recently a number of organiceinorganic TFC nanocomposite membranes con-taining NPs such as zeolite (Kim Hyeon Chun Chun amp Kim 2013 Liu ampChen 2013) SiO2 (Bao Zhu Wang Wang amp Gao 2013 Park Kim ChunChun amp Kim 2012) Ag (Nisola Park Beltran amp Chung 2012) TiO2 (KimKwak Sohn amp Park 2003) ZnO (Schwartz et al 2012) organo-selenium com-pounds (Vercellino et al 2013) and carbon nanotubes (CNTs) (Baro~na LimChoi amp Jung 2013 Zhao et al 2014) have been investigated for their potentialuse in RO applications Hydrophilic polyether-block-polyamide copolymer solu-tions with different contents of Ag NPs were used to prepare dense films andcoating layers to improve the biofouling resistance of commercial PS UF mem-branes (Nisola et al 2012) ZnO NPs in biocompatible poly(N-isopropylacryla-mide) (PNIPAAm) hydrogel layers were used by Schwartz et al (2012) toprepare novel antimicrobial composite membranes via mixing the PNIPAAm pre-polymer with ZnO NPs followed by spin-coating and photocrosslinking It wasalso found that these ZnOhydrogel nanocomposite coated films exhibited differen-tial toxicity between bacterial and cellular species which qualified them as prom-ising candidates for novel biomedical device coatings

It must be pointed out that different types of zeolite NPs such as NaA zeolite(Huang Qu Dong Zhang amp Chen 2013) NaX zeolite (Fathizadeh Aroujalian ampRaisi 2011) and A zeolite (Pendergast Ghosh amp Hoek 2013) have been added inPA active layer of TFC RO membranes to improve their RO performance

Novel and emerging membranes for water treatment 255

Carboxy-functionalized MWCNTs were incorporated by Zhao et al (2014) in PATFC RO membranes via IP of MPD and TMC to improve their RO performance Thedeveloped nanocomposite membranes were more negatively charged than theMWCNTs-free PA membrane and the increase of MWCNT concentration inthe membrane resulted in a higher permeate flux (50 higher) with almost the samesolute rejection factor

Surface topography modification of TFC RO membranes has been shown tobe another potential approach for fouling mitigation Functional TFC RO mem-brane with well-controlled surface patterns was reported by Maruf GrenbergPellegrino and Ding (2014) As it shown in Figure 810 this membrane fabricationprocedure consisted on the formation of a dense PA layer via IP with TMC and

Figure 89 Schematic diagram for synthesis of the terpolymer P(MDBAC-r-Am-r-HEMA)(a) and surface modification of reverse osmosis (RO) membranes (b)Reprinted from Ni et al (2014) with permission from Elsevier

256 Advances in Membrane Technologies for Water Treatment

NH2

NH2

Trimesoyl chloride O

O

O OO

O

CI

CI

CI

N

NH NH

NH

H

Crosslinked polyamide

m-phenylenediamine

(a)

(b) (c)

Figure 810 (a) Schematic diagram of the interfacial polymerization process used to fabricatethe patterned thin-film composite (TFC) membranes The monomers m-phenylenediamine andtrymesoyl chloride (TMC) react to form a highly crosslinked polyamide (PA) layer at top of thepatterned polyethersulfone (PES) ultrafiltration (UF) membrane used as a support SEM imagesof the non-patterned (b) and patterned (c) TFC membrane surface after 24 h of CaSO4 filtrationexperimentReprinted from Maruf et al (2014) with permission from Elsevier

Novel and emerging membranes for water treatment 257

MPD solutions on a nano-imprinted commercial PES UF support membrane (PWGE Water and Infrastructure) The results showed that the patterned TFC membranehad a separation performance comparable to the current commercial TFC RONFmembranes (ie commercial TFC RO membranes XLE-440 (DOW Filmtec)CPA 3 (Hydranautics) ACM 2 (Trisep) TM-700 (Toray) and commercial TFCNF membranes NF 270 (Hydranautics) and ES-10 (Nitto Denko)) It is importantto note that the surface patterns induced hydrodynamic secondary flow at themembrane-feed interface which is an effective way to decrease concentrationpolarization and reduce scaling effects

83 Vapor pressure gradient driven membraneprocesses

831 Membrane distillation

In contrast to the previous reported PDMPs (MF UF NF and RO) technology whichis isothermal membrane distillation (MD) is a non-isothermal separation process inwhich only molecules in the vapor phase are transported from the feed to the permeatethrough a porous hydrophobic membrane being the driving force the transmembranevapor pressure (Alkhudhiri Darwish amp Hilal 2012 Khayet amp Matsuura 2011)Simultaneous heat and mass transfer occur in MD and different MD configurationscan be used to establish the driving force The difference between the MD configura-tions is localized only in the permeate side of the membrane module In direct contactMD (DCMD) sweeping gas MD (SGMD) and air gap MD (AGMD) the temperaturedifference induces the necessary vapor pressure difference There is also anotherconfiguration termed vacuum MD (VMD) in which the permeate side of the mem-brane is kept at lower pressure by a vacuum pump to establish the transmembranevapor pressure

MD is applied in different fields (desalination treatment of wastewaters containingnon-volatile contaminants including radioactive wastes recovery of valuable com-pounds production of distilled and ultrapure water food medical etc) Comparedto RO separation process MD does not require the application of a high hydrostaticpressure (atmospheric pressure is enough) can process very high salinity brinesincluding those generated by RO and produce water with very high quality whichmeans almost total rejection factors of non-volatile contaminants Moreover MDcan be combined with other processes in integrated systems such as MF UF NFRO and forward osmosis among others making MD promising for various industrialapplications (Khayet amp Matsuura 2011) However MD technology also suffers somedrawbacks such as the low membrane permeability low thermal efficiency high waterproduction cost temperature and concentration polarization effects risk of membranepore wetting fouling and scaling phenomena (Alkhudhiri et al 2012 Khayet ampMatsuura 2011)

MD membranes are porous with a high porosity (void volume fractions) low poretortuosity low thermal conductivity and hydrophobic More details of the membrane

258 Advances in Membrane Technologies for Water Treatment

requirements for an effective MD application were outlined by Khayet (2011) Themost common used techniques for preparation of MD membranes are phase inversionstretching track-etching sintering drywet spinning or wet spinning electrospinningor membrane surface modification by physical or chemical techniques such as coatinggrafting and plasma polymerization Most of the MD membranes are made via phaseinversion methods because of its simplicity

Some authors focused their MD membrane engineering toward the preparation ofdual-layered membranes Wang Teoh and Chung (2011) investigated the morpholog-ical architecture of dual-layer PVDF hollow fiber membranes consisting of a fullyfinger-like macrovoid inner-layer and a totally sponge-like outer-layer Edwie andChung (2012) also designed novel hollow fiber membranes with improved wettingresistances for desalination and salt recovery from highly concentrated NaCl aqueoussolution by DCMD and crystallization Three types of hollow fiber membraneswere fabricated single-layer PVDF dual-layer hydrophobicehydrophobic PVDFand dual-layer hydrophobicehydrophilic PVDFPAN membranes The single-layerPVDF membrane had a superior wetting resistance compared to other types of dual-layer membranes in addition to the smallest reduction of membrane permeability(177) and the highest purity of product water (11e13 mScm)

Su Teoh Wang Su and Chung (2010) performed experimental and theoreticalstudies to investigate the effect of the inner-layer thermal conductivity on theDCMD permeate flux of hydrophobicehydrophilic dual-layer hollow fiber mem-branes prepared by drywet spinning technique Graphite particles and MWCNTswere embedded in the inner hydrophilic layer (Figure 811) It was found that incor-porating graphite alone led to only a minor improvement of the thermal conductivitybut using both graphite and MWCNT the thermal conductivity was increased from059 to 130 Wm K This enhancement of the thermal conductivity was attributedto the network formed by the MWCNT which bridges the polymer nodules As aconsequence of the improved thermal conductivity of the inner-layer a higher vaporpressure difference was established between both sides of the hydrophobic porouslayer (see Figure 811(b) and (c)) and therefore a significant increase of the DCMDpermeate flux was observed from 412 to 669 kgm2 h when using an inlet feed tem-perature of 804 C

Polytetrafluoroethylene (PTFE) is an attractive membrane material for MD due toits superior hydrophobicity chemical resistance thermal stability and mechanicalstrength compared to PP and PVDF It has also excellent stability in many organicand inorganic solvents Teoh Chung and Yeo (2011) prepared PVDFPTFE dual-layer composite hollow fiber membranes for seawater desalination by DCMD Theincorporation of PTFE particles in the PVDF spinning solution could efficiently sup-press the formation of macrovoids and enhance the outer surface hydrophobicity ofthe membranes Recently Zhu et al (2013) also used PTFE for the preparation ofnovel PTFE hydrophobic hollow fiber membranes for VMD by a cold pressingmethod including extrusion stretching and sintering It was observed that thePTFE hollow fiber membranes with four stretching ratios (120 160 180and 220) showed microstructures of nodes interconnected by fibrils (Figure 812)and achieved salt rejection factors of 999 The increase of the stretching ratio

Novel and emerging membranes for water treatment 259

(1)

(2)

(3)

R1

R3

R2

Tf

Tf

T1

T1rsquo

T2rsquoT3rsquo

T2

T3Td

Feed

FeedFeed

FeedDistillate

Distillate

Hydrophobic layerHydrophilic layer

Fillers with highthermal conductivity

(a)

(b)

Nodule

Graphite

Cloisite NA+

MWCNT

Td

Figure 811 (a) Schematic dual-layer hydrophobichydrophilic hollow fiber membranes(1) Cross-section of dual-layer hollow fiber membranes (2) temperature distribution acrossdual-layer hydrophobichydrophilic membranes and (3) temperature distribution across dual-layer hydrophobichydrophilic membranes filled with high thermal conductivity fillers blendedinto the inner-layer (b) SEM images of the inner-layer filled with graphite Cloisite NAthorn andMWCNTReprinted from Su et al (2010) with permission from Elsevier

260 Advances in Membrane Technologies for Water Treatment

significantly increased the pore size and porosity and therefore improved thepermeate flux but decreased the water entry pressure in the pores and reduced themechanical property of the membrane

It is well known that ceramic membranes exhibit excellent chemical structural andthermal stabilities Therefore it would be interesting to explore this type of membranesin MD applications Fang Gao Wang and Cheng (2012) developed a novel hydro-phobic porous alumina ceramic hollow fiber membrane by phase inversion and sinter-ing method for desalination by VMD process When using a feed salt aqueous solution(4 wt NaCl) at 80 C and a vacuum pressure of 4 kPa applied in the lumen side of thehollow fibers a water permeate flux as high as 429 Lm2 h was achieved with a saltrejection factor over 995 which was comparable to polymeric membranes

Yang Wang Shi Fane and Debowski (2011) proposed plasma or chemical modi-fication of the surface of PVDF hollow fiber-based membranes The plasma coatinginvolved a surface activation by exposing the membrane to a continuous plasmaand a polymerization with the vapor of activated monomer On the other hand thechemical modification involved the hydroxylation of the PVDF membrane by anaqueous lithium hydroxide solution and successive reduction with an organic sodiumborohydride (NaBH4) solution followed by crosslinking with a perfluoro-compound ofperfluoropolyether containing ethoxysilane terminal groups Compared to the unmod-ified PVDF hollow fiber membrane both modified membranes showed a greaterhydrophobicity higher liquid entry pressure (LEP) values better mechanicalstrengths smaller maximum pore sizes and narrower pore size distributions withreasonably high DCMD permeate fluxes over a long-term operation (one month) aswell as a high water quality Wei et al (2012) also used plasma surface modificationapproach to develop suitable membranes for MD The surface of asymmetric hydro-philic PES flat sheet and hollow fiber membranes were modified by CF4 plasma poly-merization to form a hydrophobic layer with a water contact angle up to 120 DCMDresults proved that these plasma-modified PES membranes were good membranes forMD with high water permeate fluxes up to 667 kgm2 h using 4 wt NaCl as feedaqueous solution and the salt rejection factors were as high as 9997 A comparativecompilation of DCMD performance for different novel hollow fiber membranes issummarized in Table 83

Figure 812 SEM images of the polytetrafluoroethylene (PTFE) hollow fiber membraneprepared by a stretching ratio of 220 (a) X27 cross-section (b) X1000 inner-surface and(c) X1000 outer-surfaceReprinted from Zhu et al (2013) with permission from Elsevier

Novel and emerging membranes for water treatment 261

Table 83 Direct contact membrane distillation (DCMD) performance of different single and dual-layer hollow fibermembranes fabricated in the literature

Membrane(reference)

Thickness(mm)

Hollow fiberporosity()

Mean poresize (mm)

Feed parameters Distillate parameters

DCMD flux(kgm2 h)Solution

Inlettemperature(C)

Flow rate(ms)

Inlettemperature(C)

Flow rate(ms)

Accurel PP S62a

(Gryta 2007)400 730 022 Concentrated

tap water90 096 20 029 340

PVDF single-layer HFb

(Teoh andChung 2009)

140 860 016 35 wt NaCl 795 19 175 09 461

PVDF single-layer HF(Wang et al2009)

180 867 e 35 wt NaCl 813 18 175 12 792

PVDF single-layer HF (Yanget al 2011)

275 830 0145 35 wt NaCl 70 e 25 e 540

PVDF single-layer HF(Edwie andChung 2012)

1275 696 023c 35 wt NaCl 80 07 17 07 351

PVDF single-layer HF (Houet al 2009)

130 797 028 35 wt NaCl 818 05 20 015 405

PVDF single-layer HF(Song et al2012)

180 719 028 35 wt NaCl 800 e 20 004 275

PVDF single-layer HF(Bonyadiet al 2009)

120 800 044 35 wt NaCl 799 16 194 08 543

PVDF single-layer HF(Drioli et al2013)

230 834 032 Distillatewater

70 e 25 e 220

Si3N4 single-layer HF(Zhang Fanget al 2014)

e 50 074 4 wt NaCl 80 e 20 e 108

PES single-layerHF (Wei et al2012)

210 790 lt007 4 wt NaCl 738 2 20 068 667

PVDFPANdual-layer HF(Bonyadi andChung 2007)

340 800 041 35 wt NaCl 782 16 166 08 374

Continued

Table 83 Continued

Membrane(reference)

Thickness(mm)

Hollow fiberporosity()

Mean poresize (mm)

Feed parameters Distillate parameters

DCMD flux(kgm2 h)Solution

Inlettemperature(C)

Flow rate(ms)

Inlettemperature(C)

Flow rate(ms)

PVDFPAN dual-layer HF (Suet al 2010)

271 700 041 35 wt NaCl 804 18 153 07 669

PVDFPANdual-layer HF(Edwie Teohand Chung2012)

153 754 047c 35 wt NaCl 80 14 17 07 834

PVDFPTFEdual-layer HF(Wang et al2011)

141 840 e 35 wt NaCl 798 14 17 07 986

PVDFPTFEdual-layer HF(Teoh et al2011)

145 825 026c 35 wt NaCl 80 19 175 09 509

aAccurel PP S62 Commercial membrane from GmbH GermanybHF frac14 hollow fibercMaximal pore size others are mean pore size

Novel and emerging flat sheet membranes were also developed for MD KhayetMengual and Matsuura (2005) proposed for the first time the use of double-layeredporous hydrophobichydrophilic composite membranes for DCMD using fluorinatedsurface modifying macromolecules (SMMs) and the phase inversion method Thispromising type of membrane exhibited a thin hydrophobic layer of about 10 mmhigher permeate flux than the commonly used commercial membranes and veryhigh salt rejection factors Then a series of studies were performed using differenttypes of SMMs and hydrophilic host polymers such as PES and PS (Essalhi amp Khayet2012 Khayet 2013 Khayet amp Matsuura 2011 Peng et al 2013 Qtaishat RanaKhayet amp Matsuura 2009 Suk Matsuura Park amp Lee 2010) Recently Khayet(2013) used this type of membrane in nuclear technology for the treatment of low-and intermediate-level radioactive liquid wastes

Dumeacutee Sears Finn Duke and Gray (2010) explored the possibility of developingnovel self-supporting CNT Bucky-Paper (BP) membranes via vacuum filtration forDCMD desalination CNTs have exceptional mechanical electrical and thermal prop-erties It was reported that the CNT-BP membranes exhibited a high water contactangle (113) a high porosity (90) and relatively low thermal conductivity (ie27 kWm2 h) However a decline of the DCMD permeate flux and delamination ofBP membranes due to the formation of micro-cracks were observed To optimizethis type of BP membrane Dumeacutee Sears Scheuroutz et al (2010) developed novelCNT-BP-based composite and supported membranes with significantly improvedMD performance Furthermore the same researchers also coated the CNT-BP mem-branes with a thin layer of PTFE to enhance their hydrophobicity and improve theirmechanical stability without drastically changing their average pore size and porosity(Dumeacutee et al 2011)

Various studies have been focused on the preparation of more hydrophobic mem-branes for MD to reduce the risk of pore wetting A variety of techniques such asplasma treatment lithography sol-gel technology NP deposition on both smoothand rough substrates fluoroalkylsilane coatings and phase separation of a multicom-ponent mixture were considered for fabrication of superhydrophobic surfaces (iewater contact angles higher than 150) Razmjou Arifin Dong Mansouri andChen (2012) prepared a superhydrophobic PVDF membrane for MD applicationswith a 163 water contact angle by generating a hieralchical structure with multilevelroughness and reducing the surface free energy of the membranes via TiO2 coatingthrough a low-temperature hydrothermal process followed by fluorosilanizationof the surface with 1H 1H 2H 2H-perfluorododecyltrichlorosilane (FTCS)(Figure 813) The multilevel hierarchical structure was attributed to the templatingagent which was found to be decisive in the final wettability of the membrane surfaceMoreover TiO2 coating layer on the membrane provided sites for covalent bondingwith hydrolyzed silane coupling agents The modified FTCSeTiO2ePVDF mem-branes showed good thermal and mechanical resistance while both the LEP and watercontact angle of the membrane were increased

During last five years novel flat sheet nanofibrous membranes prepared by electro-spinning were proposed for MD because of their attractive characteristics for MDsuch as the high void volume fraction high hydrophobicity high roughness high

Novel and emerging membranes for water treatment 265

surface-to-mass (volume) ratio interconnected open space between nanofibers lowthermal conductivity etc (Khayet amp Garciacutea-Payo 2011) Self-sustained electro-spun nanofibrous membranes (ENMs) were prepared varying the PVDF concentra-tions in the solvent mixture acetone (Ac)NN-dimethylacetamide from 15 to30 wt and the electrospinning time (Essalhi amp Khayet 2013a Essalhi amp Khayet2014) The optimum PVDF concentration and electrospinning time for ENM forma-tion was found to be 25 wt and 2 h respectively This ENM exhibited a DCMDpermeate flux of 1215 103 kgm2 s and the NaCl rejection factor was higherthan 9999 The permeate flux of the ENMs was lower for longer electrospinningtime Essalhi and Khayet (2013b) developed a novel theoretical model that considered

Figure 813 Mechanism for the fluorosilanization on the surface of polyvinylidene fluoride(PVDF) membranes with and without TiO2 (a) Hydrolyzation of 1H 1H 2H2Heperfluorododecyltrichlorosilane (FTCS) (b) interaction of the hydroxyl groups with thesurface of TiO2 can form covalent bonds of SieOeTi (c) the intermolecular crosslinkingbetween the tri-silanols can lead to a 2D network of polysiloxane (d) condensation of tri-silanolsin the solution in absence of TiO2 coating and (e) surface SEM image of FTCSePVDFmembraneReprinted from Razmjou Arifin et al (2012) with permission from Elsevier

266 Advances in Membrane Technologies for Water Treatment

the gas transport mechanisms through the inter-fiber space of ENMs to predict theDCMD permeate flux of ENMs

Maab et al (2012) used both the phase inversion technique and the electrospinnigmethod to prepare a novel flat sheet porous membrane for MD based on hydrophobicsynthesized aromatic fluorinated polyoxadiazoles and polytriazoles By combining thehigh polymer hydrophobicity (ie 162 water contact angle) the high void volumefraction and the LEP of about 09 bar the salt rejection factors of these membraneswere as high as 9995 and the water permeate fluxes were as high as 85 Lm2 hfor a feed temperature of 80 C and a permeate temperature of 22 C Similarly Princeet al (2012) developed novel ENMs consisting of PVDF blended with clay nano-composite for DCMD An increase of the surface hydrophobicity with the additionof clay nanocomposite was also observed and the prepared PVDF-clay ENMs showedgood DCMD performance

Lalia Guillen-Burrieza Arafat and Hashaikeh (2013) also prepared ENMsfor MD using the copolymer polyvinylidene fluoride-co-hexafluoropropylene(PVDF-HFP) To fuse the fibers together and enhance the ENMs structural integritywith the mechanical properties the ENMs were hot pressed Among all preparedENMs the one fabricated with 10 wt PVDF-HFP in the electrospinning solutionhad the optimum properties for MD application with 026 mm mean pore size 58porosity 125 water contact angle and a LEP value of 1317 kPa

To further improve the hydrophobicity of the PVDF ENMs used in MD the electro-spinning technique was followed by surface modification (Liao Wang amp Fane 2013)As shown in Figure 814 this procedure included PDA surface activation to improvethe adhesive force between the fibers and Ag NPs Ag NP deposition to optimize themorphology and roughness of the membrane and hydrophobic treatment with1-dodecanethiol Compared to the unmodified ENM the integrally-modified mem-brane could achieve a stable MD permeate flux of 316 Lm2 h using a 35 wtNaCl feed aqueous solution at 60 C and permeate temperature of 20 C

To enhance the MD performance of the ENMs Prince AnbharasiShanmugasundaram and Singh (2013) prepared PVDF ENM on a porous PVDFsupported membrane fabricated by the immersion precipitation method and used itfor desalination by AGMD configuration The addition of the nanofiber layer on thePVDF supported membrane was found to increase the permeate flux the salt rejectionfactor and the AGMD long-term performance

832 Pervaporation

PV is a membrane process in which an organic solventwater mixture or an organicsolvent mixture can be selectively separated by a dense membrane placed betweenthe liquid feed mixture and a downstream permeate maintained by a vacuum pumpPV technology is similar to VMD the difference being the characteristics of the mem-brane used which is porous and hydrophobic for VMD There is also a similaritybetween PV and SGMDwhen PV is carried out by gas stripping Both a solution diffu-sion model and a pore flowmodel were considered in PV in which the phase change ofthe diffused species takes place inside the membrane and the desorption step occurs at

Novel and emerging membranes for water treatment 267

Integral modification

(1)

(1)

(2)

(2)

(3)

(3)

I-PVDF

S-PVDFSurface modification

PVDFnanofibers

(a1) (a2)

(b2)

(c2)

(b1)

(c1)

(b)

(a)

Figure 814 (a) Schematic method used for preparation of superhydrophobic polyvinylidenefluoride electrospun nanofibrous membranes (PVDF ENMs) ((1) PDA-modification (2) silvernanoparticle coating (3) 1-dodecanethiol hydrophobic modification) (b) SEM images of un-modified PVDF ENMs ((a1) (a2)) integral modified PVDF ENMs (I-PVDF (b1) (b2)) andsurface modified PVDF ENMs (S-PVDF (c1) (c2))Reprinted from Liao et al (2013) with permission from Elsevier

268 Advances in Membrane Technologies for Water Treatment

the permeate side of the membrane There are mainly two PV applications thoseinvolving hydrophilic membranes used for the dehydration of organicwater mixturessuch as PVA and NaA zeolite membranes (Liu Wei Jin amp Xu 2012) and thoseinvolving hydrophobic membranes used to extract organic solvents or volatile organiccompounds from water such as polydimethylsiloxane (PDMS) and silicalite-1 mem-branes (Liu et al 2012)

Zuo Wang Sun and Chung (2012) developed high-performance hollow fibermembranes for PV dehydration of isopropanol (IPA) consisting of a TFC PA selectivelayer and a porous Torlon 4000T-MV PAI (Solvay Advanced Polymers) substrateprepared via IP of MPD or HPEI with TMC The TFC membrane prepared fromHPEI showed a higher hydrophilicity and fractional free volume than that madefrom MPD which exhibited a better permeability The TFC membrane fabricated un-der the optimum IP conditions from HPEI having a molecular weight of 2 kgmolshowed the best selectivity (ie 624) with a total permeate flux of 13 kgm2 h anda permeate water concentration of 991 wt using a feed composition of 8515 wtIPAwater at 50 C

Wang Gruender and Chung (2010) developed high-performance dual-layer poly-benzimidazole (PBI)PEI hollow fiber membranes for ethylene glycol dehydration byPV process Three types of membranes were prepared PBI flat sheet dense mem-branes which had the lowest PV separation performance due to its severe swellingPBI single-layer hollow fiber membranes which showed better PV separation perfor-mance but had very low tensile strains and PBIPEI dual-layer hollow fiber mem-branes which exhibited the best PV separation performance An enhancement ofthe separation performance of PBIPEI dual-layer hollow fiber membrane afterexposing it to 75 C thermal treatment was also detected A novel approach to preparemultilayered membranes with excellent PV dehydration of different solventwatermixtures has been performed by Zhang Dai and Ji (2011) This approach is basedon a dynamic pressure-driven LbL technique to obtain a covalent assembly ofGLA-crosslinked PEI multilayers on the inner surfaces of PAN hollow fiber poroussubstrate membranes The dynamic pressure-driven LbL assembly was demonstratedto be an effective way to fabricate a defect-free selective layer only on a single side ofthe hollow fiber which has the advantage of reducing the membrane transport resis-tance compared to the membranes made with traditional LbL process Zhang SongJi Wang and Liu (2008) prepared novel polyacrylic acid (PAA)PEI multilayer poly-electrolyte complex (PEC) films on the inner side of hydrolyzed PAN hollow fibermembranes by the dynamic negative pressure LbL technique Others papers also pro-posed an electric field enhanced method to fabricate multilayered PEC membranes byusing modified PA RO membranes as supports and poly(diallyl dimethylammonium-chloride) (PDDA) PEI PSS PAA as assembly components (Yin et al 2010 ZhangQian et al 2008 2009 Zhao An Ji Qian amp Gao 2011) Zhao Qian An and Sun(2010) used charged PEC colloidal aggregates as novel LbL building blocks to prepareLbL multilayered membranes for PV dehydration

As mentioned previously the hydrophilicity of the PV membrane is necessary forthe dehydration of organic solvents The more hydrophilic the membrane is the higherare the water sorption selectivity and water permselectivity To improve the membrane

Novel and emerging membranes for water treatment 269

hydrophilicity many polymer materials were modified using different methods such assulfonation quaternization grafting etc However an increase of the mem-brane hydrophilicity might increase the membrane swelling excessively leading toa membrane with an open structure which reduces the membrane strengthCrosslinking with an organic chemical reagent such as GA PAA maleic acidformaldehyde or fumaric acid is an effective way to reduce membrane swelling ZhangLiu Zhu Xiong and Ren (2009) synthesized quaternized PVA by grafting with(23-epoxypropyl) trimethylammonium chloride to enhance the hydrophilicity andthen crosslinked by GLA to restrict its swelling in an aqueous ethanol solutionRachipudi Kariduraganavar Kittur and Sajjan (2011) also developed PV membranesfor IPA dehydration by crosslinking sulfonated-PVA membranes with sulfophthalicacid (SPTA) The membrane prepared with 15 wt of SPTA showed the highest waterseparation selectivity of 3452 with a total permeate flux of 351102 kgm2 h

Novel chitosan (CS)TiO2 nanocomposite membranes were prepared by Yang LiJiang Lu and Chen (2009) using an in situ solegel process using tetrabutyl titanate asprecursor and acetyl acetone as chelating agent controlling the forming rate of TiO2NPs Compared to CS and CSTiO2 blended membranes CSTiO2 nanocompositemembranes exhibited better PV performance for ethanol dehydration CS-wrappedMWCNTs incorporated in sodium alginate membranes were prepared by SajjanJeevan Kumar Kittur and Kariduraganavar (2013) for the separation of waterIPAmixtures CS was chosen to wrap MWCNTs to improve their hydrophilicity ThePV membranes containing the highest amount of CS-wrapped MWCNTs (2 wt)showed a water selectivity of 6419 and a permeate flux of 2176102 kgm2 h at30 C and 10 wt of water in the feed solution

UVO3 surface modification technology was used by Lai et al (2012) to developPDMS PV membranes for the treatment of 90 wt aqueous ethanol mixture Watercontact angle measurements demonstrated that the hydrophilicity of PDMS mem-branes surface was significantly improved due to the change in its chemical structurefrom siloxane to silica PV results indicated that both the treatment time and the work-ing distance during the UVO3 treatment were important variables affecting the PVperformance of the PDMS membrane

To improve the PV permeate flux of polymeric membranes Xiangli Chen Jin andXu (2007) prepared PDMSceramic composite membrane by depositing uniformly acrosslinked PDMS layer on the top of tubular non-symmetric ZrO2Al2O3 porousceramic supports The resulted PDMSceramic composite membranes exhibited a totalpermeate flux of 195 kgm2 h and an ethanol selectivity of 57 when using a 43 wtethanol feed aqueous mixture Liu Hou Wei Xiangli and Jin (2011) used thesePDMSceramic composite membrane for butanol removal from its dilute aqueoussolution and obtained a total permeate flux of 0457 kgm2 h with an acceptablebutanol selectivity of 261 using a 1 wt butanol in the feed solution at 40 C Becauseof the good long-term stability of these PDMSceramic composite membranes LiuWei et al (2011) decided to use them for recovering biobutanol from biomassacetone-butanol-ethanol (ABE) fermentation broth exhibiting a high average totalflux of 0670 kgm2 h and an applicable ABE selectivity of 167 The performanceof PDMSceramic composite PV membranes was improved by a homogeneous

270 Advances in Membrane Technologies for Water Treatment

dispersion of ZSM-5 zeolite in PDMS via a surface graftcoating approach (LiuXiangli Wei Liu amp Jin 2011) Lue Chien and Mahesh (2011) also prepared aheterogeneous PDMS MMMs containing 10 mm sized zeolite (TZP-9023 TricateZeolites Bitterfeld Germany) for PV of ethanolwater solutions

Zhu Xia Liu and Jin (2010) synthesized hydrophilic crosslinked PVACSlayers on tubular asymmetric ZrO2Al2O3 ceramic supports and demonstrated thatthese ceramic-supported PVACS composite membranes were suitable candidatesfor PV dehydration of alcoholwater and esterwater mixtures The compositemembrane exhibited excellent PV performance achieving a permeate flux of125 kgm2 h and a water selectivity larger than 10000 for 35 wt ethyl acetatewater mixture

To achieve higher membrane stability and improve the PV performance variousattempts have been made to develop blend membranes of PVA with other poly-mers Mixed matrix blend membranes of PVAPVP loaded with phosphomolybdicacid (PMA) were prepared for ethanol dehydration by Magalad Gokavi Raju andAminabhavi (2010) It was demonstrated that the extent of PMA loaded in themembrane affected the PV performance 4 wt of PMA particles in PVAPVPblended matrix resulted in an enhancement of the PV performance but higherPMA amounts (8 and 12 wt) did not result in any improvement of PVperformance

It is worth mentioning that there are few research studies on homogeneous poly-electrolyte complex membranes (HPECMs) although these membranes exhibitgood PV performance for dehydration of different organic aqueous solutions contain-ing IPA ethanol Ac etc The required PECs to prepare HPECMs were synthesized byPAA sodium carboxymethyl cellulose (CMCNa) as anionic polyelectrolyte andPDDA CS poly(2-methacryloyloxy ethyl tri-methylammonium chloride) (PDMC)and poly(N-ethyl-4-vinylpyridiniumbromide) (PEVP) as cationic polyelectrolyteFor example the PECs were first synthesized in aqueous hydrochloric acid Thenthe obtained solid PECs were dissolved in aqueous NaOH and subsequently theHPECMs were made by casting the solution on a clean and smooth porous PS UFmembrane All the fabricated HPECMs from CMCNaePDDA PECs (Zhao QianAn Yang amp Zhang 2008 Zhao Qian An Gui et al 2009) PAAePDDA PECs(Zhao Qian An Yang amp Gui 2009) CMCNaeCS PECs (Zhao Qian An Gaoet al 2009) CMCNaePDMC (Zhao An et al 2010) and CMCNaePEVP (JinAn Zhao Qian amp Zhu 2010) were used in PV dehydration of aqueous IPA or ethanolsolutions and showed very high water selectivity and high permeability (see Table 84)Attempts were also made to improve the mechanical properties of the HPECMsby modification using inorganic SiO2 (Zhao Qian Zhu An Xu et al 2009) andMWCNTs (Zhao Qian Zhu amp An 2009) but even under the optimal membranefabrication conditions the elongations at break were maintained low whereas the ten-sile strengths increased In addition CMCNaePDDA PEC (Zhao Qian An Zhuet al 2009) PDDAePAANa PEC (Zhu Qian Zhao An amp Li 2010) andCMCNaePDMC PEC (Zhu et al 2011) were blended with the commercial PVA toincrease both the mechanical properties and the PV performance of the HPECMs Itwas found that the PECPVA blended membrane with PVA content of 30 wt

Novel and emerging membranes for water treatment 271

Table 84 Pervaporation performance of various polyelectrolytemembranes (PECMs) for dehydration of isopropanol (IPA) andethanol (EtOH) at 70 C

Membrane Feed solutionWaterselectivity

Permeationflux (kgm2 h) Reference

CMCNa-PDDAHPECM55

10 wt waterIPA

960 247 Zhao et al (2008)

CMCNa-PDDAHPECM26

10 wt waterIPA

1791 192 Zhao et al (2008)

CMCNa-PDDAHPECM019

10 wt waterIPA

1049 247 Zhao Qian AnGui et al(2009)

CMCNa-PDDATPECM

10 wt waterIPA

1484 149 Zhao Qian AnGui et al(2009)

PDMC-CMCNaPECM046

10 wt waterIPA

1641 425 Zhao An et al(2010)

PDMC-CMCNaPECM036

10 wt waterIPA

1641 385 Zhao An et al(2010)

CMCNa-PDDA5 wt SiO2

10 wt waterIPA

2186 21 Zhao Qian ZhuAn Xu et al(2009)

CMCNa-PDDA5 wtMWCNTs

10 wt waterIPA

2565 235 Zhao Qian Zhuamp An (2009)

PDDA-PAANa30 wt PVA

10 wt waterIPA

978 236 Zhu Qian et al(2010)

CMCNa-PDMC30 wt PVA

10 wt waterIPA

2084 212 Zhu et al (2011)

CS-CMCNaHPECM039

10 wt waterIPA

1657 217 Zhao Qian AnYang et al(2009)

PERVAP 2510a 10 wt waterIPA

810 075 Chapman et al(2008)

CMCNa-PDDATPECM

10 wt waterEtOH

188 049 Zhao Qian AnGao et al(2009)

CS-CMCNaHPECM0025

10 wt waterEtOH

1062 114 Zhao Qian AnGao et al(2009)

272 Advances in Membrane Technologies for Water Treatment

(PECPVA70-30) achieved the best mechanical properties with a tensile strengthYoungrsquos modulus and elongation at break of about 15 36 and 14 times those ofthe original HPECM respectively

84 Conclusions

The growth of membrane science and technology for water treatment is mainly due tothe developments of materials used for membrane fabrication and for their modifica-tion A wide variety of innovative materials such as chemically and thermally stablepolymers ceramics metallics etc are used for preparing novel membranes ofdifferent configurations and characteristics Moreover various membrane fabricationtechniques are being proposed and improved (ie phase inversion sintering stretch-ing track-etching drywet spinning or wet spinning electrospinning LbL assemblylithography sol-gel etc) and various methods have been developed for membranemodification (ie IP chemical modification surface coating grafting crosslinkingplasma polimerization polymer sulfonation or quaternization nanoparticles (NPs)deposition etc) to improve both the properties of the membranes and theperformance of the specific processes and their applications

It has been observed that the incorporation of different additives polymers andinorganic NPs or fillers (ie zeolite organo-selenium compounds SiO2 Fe3O4Al2O3 ZrO2 TiO2 ZnO CNTs MWCNTs GO TOCNs b-CD zwitterionic mate-rials etc) on the MF UF NF and RO membranes has improved their antifoulingand antibacterial ability has increased their hydrophilicity and water permeability pre-serving or improving the solute rejection factors and in some cases has enhancedmembrane mechanical properties porosity and thermal stability

In contrast to PDMP technology MD is a non-isothermal separation process whichuses porous hydrophobic membranes for water treatment In general there is agrowing interest on MD membrane engineering In particular various researchersare developing composite hollow fiber membranes for MD with a dual-layered config-uration (hydrophobicehydrophobic or hydrophobicehydrophilic) to reduce mem-brane pore wetting temperature and concentration polarization effects fouling and

Table 84 Continued

Membrane Feed solutionWaterselectivity

Permeationflux (kgm2 h) Reference

PECM0284 10 wt waterEtOH

1419 093 Jin et al (2010)

PECM0440 10 wt waterEtOH

782 132 Jin et al (2010)

aPERVAP 2510 commercial membrane from Sulzer Chemtech GmbH Linden Germany

Novel and emerging membranes for water treatment 273

scaling phenomena The addition of different materials and NPs (ie graphite parti-cles PTFE Al2O3 ZrO2 TiO2 ZnO CNTs MWCNTs SMMs etc) resulted ingreater membrane hydrophobicity and thermal conductivity higher LEP values waterquality and long-term operation and also better mechanical strengths permeatefluxes and salt rejections

High permeate fluxes and water selectivities were achieved when ceramic-supported composite membranes and HPECMs have been used for PV dehydrationof organic alcoholwater and esterwater mixtures containing solvents such as IPAethanol Ac etc Some attempts were made to improve the mechanical properties ofHPECMs using inorganic SiO2 and MWCNTs or blending their PEC with PVA

85 Future trends

Although the current use of membrane technology for water treatment is constantlygrowing thanks to the discovery and development of novel and advanced materialsfor membrane fabrication and modification there are still some involved phenomenawith effects that need to be reduced further (eg temperature and concentration polar-ization phenomena membrane fouling long-term operation etc)

Innovative membrane engineering is required because of the still continuousincreasing demands of desalination and treatments of different and emerging typesof wastewaters with improved water production rates greater salt rejection factorsand higher resistance to fouling

PMDPs and MD technologies can be adequately integrated for water productionoffering a wide range of industrial water treatment applications

List of acronyms

b-CD b-cyclodextrinABE Acetone-butanol-ethanolAc AcetoneADMH 3-allyl-55-dimethylhydantoinAg SilverAGMD Air gap membrane distillationAl2O3 AluminaAQP AquaporinAQP-Z Aquaporin ZBP Bucky-PaperBSA Bovine serum albuminCA Cellulose acetateCMCNA Sodium carboxymethyl celluloseCNTs Carbon nanotubesCS ChitosanCTA Cellulose triacetate

274 Advances in Membrane Technologies for Water Treatment

DBA 35-diaminobenzoic acidDCMD Direct contact MDEDX Energy-dispersive X-ray spectroscopyENMs Electrospun nanofibrous membranesFA Fly ashFe3O4 Ferrous ferric oxideFESEM Field-emission scanning electron microscopyFTCS 1H 1H 2H 2H-perfluorododecyltrichlorosilaneGA Gallic acidGLA GlutaraldehydeGO Graphene oxideHPECMs Homogeneous polyelectrolyte complex membranesHPEI Hyperbranched polyethylenimineIP Interfacial polymerizationIPA IsopropanolLbL Layer-by-layerLEP Liquid entry pressureMBA NN0-methylenebis(acrylamide)MD Membrane distillationMF MicrofiltrationMMMs Mixed matrix membranesMPD m-phenylenediamineMWCNTs Multiwalled carbon nanotubesNaBH4 Sodium borohydrideNF NanofiltrationNPs NanoparticlesNTSC Naphthalene-136-trisulfonylchloridePA PolyamidesPAA Polyacrylic acidPAH Poly (allylamine hydrochloride)PAI Polyamide-imidePAMAM G2 NH2-terminated PAMAMPAMAM Amine-functional polyamidoaminePAN PolyacrylonitrilePAS PolyarylsulfonePBI PolybenzimidazolePC PolycarbonatePDA PolydopaminePDDA Poly(diallyl dimethylammoniumchloride)PDMC Poly(2-methacryloyloxy ethyl tri-methylammonium chloride)PDMS PolydimethylsiloxanePEC Polyelectrolyte complexPEG Polyethylene glycolPEI PolyethyleneiminePES PolyethersulfonePET Polyethylene terephthalatePEVP Poly(N-ethyl-4-vinylpyridiniumbromide)PI PolyimidesPIP Piperazine

Novel and emerging membranes for water treatment 275

PMA Phosphomolybdic acidPNIPAAm Poly(N-isopropylacrylamide)PP PolypropylenePS PolysulfonePSS Poly(sodium 4-styrenesulfate)PTFE PolytetrafluoroethylenePU PolyurethanePVA Polyvinyl alcoholPVAm PolyvinylaminePVC Polyvinyl chloridePVDF Polyvinylidene fluoridePVDF-HFP Polyvinylidene fluoride-co-hexafluoropropylenePVP Poly(1-vinylpyrrolidone)PWP Pure water permeabilityRO Reverse osmosisSEM Scanning electron microscopySGMD Sweeping gas MDSiO2 SilicaSMMs Fluorinated surface modifying macromoleculesSPES Sulfonated polyethersulfoneSPPBES Sulfonated copoly (phthalazinone biphenyl ether sulfone)SPTA Sulfophthalic acidTEOA TriethanolamineTFC Thin-film compositeTFN Thin film nano-compositetio2 TitaniaTMC Trymesoyl chloridetocns TEMPO-oxidized cellulose nano-fibrilsUF UltrafiltrationVMD Vacuum MDZnO Zinc oxideZrO2 Zirconia

References

Alkhudhiri A Darwish N amp Hilal N (2012) Membrane distillation A comprehensivereview Desalination 287 2e18

Arsuaga J M Sotto A Del Rosario G Martiacutenez A Molina S Teli S B et al (2013)Influence of the type size and distribution of metal oxide particles on the properties ofnanocomposite ultrafiltration membranes Journal of Membrane Science 428 131e141

Arthanareeswaran G amp Thanikaivelan P (2010) Fabrication of cellulose acetateezirconiahybrid membranes for ultrafiltration applications Performance structure and foulinganalysis Separation and Purification Technology 74 230e235

Azari S amp Zou L (2012) Using zwitterionic amino acid l-DOPA to modify the surface of thinfilm composite polyamide reverse osmosis membranes to increase their fouling resistanceJournal of Membrane Science 401e402 68e75

276 Advances in Membrane Technologies for Water Treatment

Bao M Zhu G Wang L Wang M amp Gao C (2013) Preparation of monodispersedspherical mesoporous nanosilicaepolyamide thin film composite reverse osmosismembranes via interfacial polymerization Desalination 309 261e266

Baro~na G N B Lim J Choi M amp Jung B (2013) Interfacial polymerization of polyamide-aluminosilicate SWNT nanocomposite membranes for reverse osmosis Desalination 325138e147

Bonyadi S amp Chung T S (2007) Flux enhancement in membrane distillation by fabricationof dual layer hydrophilicehydrophobic hollow fiber membranes Journal of MembraneScience 306 134e146

Bonyadi S Chung T S amp Rajagopalan R (2009) A novel approach to fabricate macrovoid-free and highly permeable PVDF hollow fiber membranes for membrane distillationAIChE Journal 55 828e833

Chapman P D Oliveira T Livingston A G amp Li K (2008) Membranes for the dehy-dration of solvents by pervaporation Journal of Membrane Science 318 5e37

Choi H Park J Tak T amp Kwon Y N (2012) Surface modification of seawater reverseosmosis (SWRO) membrane using methyl methacrylate-hydroxy poly(oxyethylene) meth-acrylate (MMA-HPOEM) comb-polymer and its performance Desalination 291 1e7

Dong C He G Li H Zhao R Han Y amp Deng Y (2012) Antifouling enhancement ofpoly(vinylidene fluoride) microfiltration membrane by adding Mg(OH)2 nanoparticlesJournal of Membrane Science 387e388 40e47

Drioli E Ali A Simone S Macedonio F Al-Jlil S A Al Shabonah F S et al (2013)Novel PVDF hollow fiber membranes for vacuum and direct contact membrane distillationapplications Separation and Purification Technology 115 27e38

Dumeacutee L Campbell J L Sears K Scheuroutz J Finn N Duke M et al (2011) The impact ofhydrophobic coating on the performance of carbon nanotube bucky-paper membranesin membrane distillation Desalination 283 64e67

Dumeacutee L Sears K Finn N Duke M amp Gray S (2010) Carbon nanotube based compositemembranes for water desalination by membrane distillation Desalination Water Treat-ment 17 72e79

Dumeacutee L F Sears K Scheuroutz J Finn N Huynh C Hawkins S et al (2010) Charac-terization and evaluation of carbon nanotube Bucky-Paper membranes for direct contactmembrane distillation Journal of Membrane Science 351 36e43

Edwie F amp Chung T S (2012) Development of hollow fiber membranes for water and saltrecovery from highly concentrated brine via direct contact membrane distillation andcrystallization Journal of Membrane Science 421e422 111e123

Edwie F Teoh M M amp Chung T S (2012) Effects of additives on dual-layer hydro-phobicehydrophilic PVDF hollow fiber membranes for membrane distillation andcontinuous performance Chemical Engineering Science 68 567e578

Essalhi M amp Khayet M (2012) Surface segregation of fluorinated modifying macro-molecule for hydrophobichydrophilic membrane preparation and application in air gapand direct contact membrane distillation Journal of Membrane Science 417e418163e173

Essalhi M amp Khayet M (2013a) Self-sustained webs of polyvinylidene fluoride electrospunnanofibers at different electrospinning times 1 desalination by direct contact membranedistillation Journal of Membrane Science 433 167e179

Essalhi M amp Khayet M (2013b) Self-sustained webs of polyvinylidene fluoride electrospunnanofibers at different electrospinning times 2 theoretical analysis polarization effects andthermal efficiency Journal of Membrane Science 433 180e191

Novel and emerging membranes for water treatment 277

Essalhi M amp Khayet M (2014) Self-sustained webs of polyvinylidene fluoride electrospunnano-fibers Effects of polymer concentration and desalination by direct contact membranedistillation Journal of Membrane Science 455 133e143

Fang H Gao J F Wang H T amp Chen C S (2012) Hydrophobic porous alumina hollowfiber for water desalination via membrane distillation process Journal of MembraneScience 403e404 41e46

Fang W Shi L ampWang R (2013) Interfacially polymerized composite nanofiltration hollowfiber membranes for low-pressure water softening Journal of Membrane Science 430129e139

Fathizadeh M Aroujalian A amp Raisi A (2011) Effect of added NaX nano-zeolite intopolyamide as a top thin layer of membrane on water flux and salt rejection in a reverseosmosis process Journal of Membrane Science 375 88e95

Feng C Xu J Li M Tang Y amp Gao C (2014) Studies on a novel nanofiltration membraneprepared by cross-linking of polyethyleneimine on polyacrylonitrile substrate Journal ofMembrane Science 451 103e110

Gryta M (2007) Influence of polypropylene membrane surface porosity on the performance ofmembrane distillation process Journal of Membrane Science 287 67e78

Guan S Zhang S Han R Zhang B amp Jian X (2013) Preparation and properties of novelsulfonated copoly (phthalazinone biphenyl ether sulfone) composite nanofiltrationmembrane Desalination 318 56e63

Hamid N A A Ismail A F Matsuura T Zularisam A W Lau W J Yuliwati E et al(2011) Morphological and separation performance study of polysulfonetitanium dioxide(PSFTiO2) ultrafiltration membranes for humic acid removal Desalination 273 85e92

Han R (2013) Formation and characterization of (melamineeTMC) based thin film compositeNF membranes for improved thermal and chlorine resistances Journal of MembraneScience 425e426 176e181

Hasson D (2010) In memory of Sidney Loeb Desalination 261 203e204Hong J amp He Y (2014) Polyvinylidene fluoride ultrafiltration membrane blended with nano-

ZnO particle for photo-catalysis self-cleaning Desalination 332 67e75Hou D Wang J Qu D Luan Z amp Ren X (2009) Fabrication and characterization of

hydrophobic PVDF hollow fiber membranes for desalination through direct contactmembrane distillation Separation and Purification Technology 69 78e86

Huang H Qu X Dong H Zhang L amp Chen H (2013) Role of NaA zeolites in theinterfacial polymerization process towards a polyamide nanocomposite reverse osmosismembrane RSC Advances 3 8203e8207

Ishigami T Amano K Fujii A Ohmukai Y Kamio E Maruyama T et al (2012)Fouling reduction of reverse osmosis membrane by surface modification via layer-by-layerassembly Separation and Purification Technology 99 1e7

Jin H An Q Zhao Q Qian J amp Zhu M (2010) Pervaporation dehydration of ethanol byusing polyelectrolyte complex membranes based on poly (N-ethyl-4-vinylpyridiniumbromide) and sodium carboxymethyl cellulose Journal of Membrane Science 347183e192

Khayet M (2011) Membranes and theoretical modeling of membrane distillation A reviewAdvances in Colloid and Interface Science 164 56e88

Khayet M (2013) Treatment of radioactive wastewater solutions by direct contact membranedistillation using surface modified membranes Desalination 321 60e66

Khayet M amp Garciacutea-Payo M C (2011) Nanostructured flat membranes for direct contactmembrane distillation PCTES2011000091

278 Advances in Membrane Technologies for Water Treatment

Khayet M amp Matsuura T (2011) Membrane distillation Principles and applicationsThe Netherlands Elsevier

Khayet M Mengual J I amp Matsuura T (2005) Porous hydrophobichydrophilic compositemembranes Journal of Membrane Science 252 101e113

Kim E S Hwang G Gamal El-Din M amp Liu Y (2012) Development of nanosilver andmulti-walled carbon nanotubes thin-film nanocomposite membrane for enhanced watertreatment Journal of Membrane Science 394e395 37e48

Kim S G Hyeon D H Chun J H Chun B H amp Kim S H (2013) Nanocompositepoly(arylene ether sulfone) reverse osmosis membrane containing functionalzeolite nanoparticles for seawater desalination Journal of Membrane Science 44310e18

Kim S H Kwak S Y Sohn B H amp Park T H (2003) Design of TiO2 nanoparticle self-assembled aromatic polyamide TFC membrane as an approach to solve bio-foulingproblem Journal of Membrane Science 211 157e165

Kong L Zhang D Shao Z Han B Lv Y Gao K et al (2014) Superior effect ofTEMPO-oxidized cellulose nanofibrils (TOCNs) on the performance of cellulose triacetate(CTA) ultrafiltration membrane Desalination 332 117e125

Lai C L Fu Y J Chen J T An Q F Liao K S Fang S C et al (2012) Pervaporationseparation of ethanolwater mixture by UVO3-modified PDMS membranes Separationand Purification Technology 100 15e21

Lalia B S Guillen-Burrieza E Arafat H A amp Hashaikeh R (2013) Fabrication andcharacterization of polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) electro-spun membranes for direct contact membrane distillation Journal of Membrane Science428 104e115

Leo C P Ahmad Kamil N H Junaidi M U M Kamal S N M amp Ahmad A L (2013)The potential of SAPO-44 zeolite filler in fouling mitigation of polysulfone ultrafiltrationmembrane Separation and Purification Technology 103 84e91

Li D amp Wang H (2010) Recent developments in reverse osmosis desalination membranesJournal of Materials Chemistry 20 4551e4566

Li N N Fane A G Ho W S W amp Matsuura T (2008) Advanced membrane technologyand applications New Jersey John Wiley amp Sons Inc

Li X Pang R Li J Sun X Shen J Han W et al (2013) In situ formation of Agnanoparticles in PVDF ultrafiltration membrane to mitigate organic and bacterial foulingDesalination 324 48e56

Li X Wang R Wicaksana F Tang C Torres amp Fane A G (2014) Preparation of highperformance nanofiltration (NF) membranes incorporated with aquaporin Z Journal ofMembrane Science 450 181e188

Liang S Xiao K Mo Y amp Huang X (2012) A novel ZnO nanoparticle blended poly-vinylidene fluoride membrane for anti-irreversible fouling Journal of Membrane Science394e395 184e192

Liao Y Wang R amp Fane A G (2013) Engineering superhydrophobic surface onpoly(vinylidene fluoride) nanofiber membranes for direct contact membrane distillationJournal of Membrane Science 440 77e87

Liu Y amp Chen X (2013) High permeability and salt rejection reverse osmosis by a zeolitenano-membrane Physical Chemistry Chemical Physics 15 6817e6824

Liu G Hou D Wei W Xiangli F amp Jin W (2011) Pervaporation separation of butanol-water mixtures using polydimethylsiloxaneceramic composite membrane ChineseJournal of Chemical Engineering 19 40e44

Novel and emerging membranes for water treatment 279

Liu G Wei W Jin W amp Xu N (2012) Polymerceramic composite membranes and theirapplication in pervaporation processChinese Journal of Chemical Engineering 20 62e70

Liu G Wei W Wu H Dong X Jiang M amp Jin W (2011) Pervaporation performance ofPDMSceramic composite membrane in acetone butanol ethanol (ABE) fermentationePVcoupled process Journal of Membrane Science 373 121e129

Liu G Xiangli F Wei W Liu S amp Jin W (2011) Improved performance of PDMSceramic composite pervaporation membranes by ZSM-5 homogeneously dispersed inPDMS via a surface graftcoating approach Chemical Engineering Journal 174495e503

Lue S J Chien C F amp Mahesh K P O (2011) Pervaporative concentration of etha-nolewater mixtures using heterogeneous polydimethylsiloxane (PDMS) mixed matrixmembranes Journal of Membrane Science 384 17e26

Maab H Francis L Al-Saadi A Aubry C Ghaffour N Amy G et al (2012) Synthesisand fabrication of nanostructured hydrophobic polyazole membranes for low-energy waterrecovery Journal of Membrane Science 423e424 11e19

Magalad V T Gokavi G S Raju K V S N amp Aminabhavi T M (2010) Mixed matrixblend membranes of poly(vinyl alcohol)epoly(vinyl pyrrolidone) loaded with phospho-molybdic acid used in pervaporation dehydration of ethanol Journal of Membrane Science354 150e161

Maruf S H Greenberg A R Pellegrino J amp Ding Y (2014) Fabrication and character-ization of a surface-patterned thin film composite membrane Journal of MembraneScience 452 11e19

Mehrparvar A Rahimpour A amp Jahanshahi M (2014) Modified ultrafiltration membranesfor humic acid removal Journal of the Taiwan Institute of Chemical Engineers 45275e282

Misdan N Lau W J amp Ismail A F (2012) Seawater reverse osmosis (SWRO) desalinationby thin-film composite membranemdashcurrent development challenges and future prospectsDesalination 287 228e237

Mollahosseini A amp Rahimpour A (2014) Interfacially polymerized thin film nanofiltrationmembranes on TiO2 coated polysulfone substrate Journal of Industrial and EngineeringChemistry 20 1261e1268

Ni L Meng J Li X amp Zhang Y (2014) Surface coating on the polyamide TFC ROmembrane for chlorine resistance and antifouling performance improvement Journal ofMembrane Science 451 205e215

Nisola G M Park J S Beltran A B amp Chung W J (2012) Silver nanoparticles in apolyether-block-polyamide copolymer towards antimicrobial and antifouling membranesRCS Advances 2 2439e2448

Nunes S P amp Peinemann K V (2001) Membrane technology in the chemical IndustryWeinheim Wiley-VCH Verlag GmbH

Pang R Li X Li J Lu Z Sun X amp Wang L (2014) Preparation and characterization ofZrO2PES hybrid ultrafiltration membrane with uniform ZrO2 nanoparticles Desalination332 60e66

Pant H R Kim H J Joshi M K Pant B Park C H Kim J I et al (2014) One-stepfabrication of multifunctional composite polyurethane spider-web-like nanofibrous mem-brane for water purification Journal of Hazardous Materials 264C 25e33

Park S Y Kim S G Chun J H Chun B H amp Kim S H (2012) Fabrication andcharacterization of the chlorine-tolerant disulfonated poly(arylene ether sulfone)hyperbranched aromatic polyamide-grafted silica composite reverse osmosis membraneDesalination and Water Treatment 43 221e229

280 Advances in Membrane Technologies for Water Treatment

Pendergast M M Ghosh A K amp Hoek E M V (2013) Separation performance andinterfacial properties of nanocomposite reverse osmosis membranes Desalination 308180e185

Peng Y Dong Y Fan H Chen P Li Z amp Jiang Q (2013) Preparation of polysulfonemembranes via vapor-induced phase separation and simulation of direct-contact membranedistillation by measuring hydrophobic layer thickness Desalination 316 53e66

Porter M C (Ed) (1988) Handbook of industrial membrane technology Westwood NJNoyer Publications

Prince J A Anbharasi V Shanmugasundaram T S amp Singh G (2013) Preparation andcharacterization of novel triple layer hydrophilicehydrophobic composite membrane fordesalination using air gap membrane distillation Separation and Purification Technology118 598e603

Prince J A Singh G Rana D Matsuura T Anbharasi V amp Shanmugasundaram T S(2012) Preparation and characterization of highly hydrophobic poly(vinylidene fluoride)eclay nanocomposite nanofiber membranes (PVDFeclay NNMs) for desalination usingdirect contact membrane distillation Journal of Membrane Science 397e398 80e86

Qtaishat M Rana D Khayet M amp Matsuura T (2009) Preparation and characterization ofnovel hydrophobichydrophilic polyetherimide composite membranes for desalination bydirect contact membrane distillation Journal of Membrane Science 327 264e273

Rachipudi P S Kariduraganavar M Y Kittur A A amp Sajjan A M (2011) Synthesis andcharacterization of sulfonated-poly(vinyl alcohol) membranes for the pervaporationdehydration of isopropanol Journal of Membrane Science 383 224e234

Rahimpour A Jahanshahi M Mollahosseini A amp Rajaeian B (2012) Structural andperformance properties of UV-assisted TiO2 deposited nano-composite PVDFSPESmembranes Desalination 285 31e38

Razmjou A Arifin E Dong G Mansouri J amp Chen V (2012) Superhydrophobicmodification of TiO2 nanocomposite PVDF membranes for applications in membranedistillation Journal of Membrane Science 415e416 850e863

Razmjou A Mansouri J amp Chen V (2011) The effects of mechanical and chemicalmodification of TiO2 nanoparticles on the surface chemistry structure and fouling per-formance of PES ultrafiltration membranes Journal of Membrane Science 378 73e84

Razmjou A Resosudarmo A Holmes R L Li H Mansouri J amp Chen V (2012) Theeffect of modified TiO2 nanoparticles on the polyethersulfone ultrafiltration hollow fibermembranes Desalination 287 271e280

Sajjan A M Jeevan Kumar B K Kittur A A amp Kariduraganavar M Y (2013) Novelapproach for the development of pervaporation membranes using sodium alginate andchitosan-wrapped multiwalled carbon nanotubes for the dehydration of isopropanolJournal of Membrane Science 425e426 77e88

Sarkar A Carver P I Zhang T Merrington A Bruza K J Rousseau J L et al (2010)Dendrimer-based coatings for surface modification of polyamide reverse osmosis mem-branes Journal of Membrane Science 349 421e428

Schwartz V B Theacutetiot F Ritz S Peuroutz S Choritz L Lappas A et al (2012) Antibacterialsurface coatings from zinc oxide nanoparticles embedded in poly(N-isopropylacrylamide)hydrogel surface layers Advanced Functional Materials 22 2376e2386

Song H J amp Kim C K (2013) Fabrication and properties of ultrafiltration membranescomposed of polysulfone and poly(1-vinylpyrrolidone) grafted silica nanoparticlesJournal of Membrane Science 444 318e326

Song Z Xing M Zhang J Li B amp Wang S (2012) Determination of phase diagram of aternary PVDFg-BLDOP system in TIPS process and its application in preparing hollow

Novel and emerging membranes for water treatment 281

fiber membranes for membrane distillation Separation and Purification Technology 90221e230

Su M Teoh M M Wang K Y Su J amp Chung T S (2010) Effect of inner-layer thermalconductivity on flux enhancement of dual-layer hollow fiber membranes in direct contactmembrane distillation Journal of Membrane Science 364 278e289

Suk D E Matsuura T Park H B amp Lee Y M (2010) Development of novel surfacemodified phase inversion membranes having hydrophobic surface-modifying macromol-ecule (nSMM) for vacuum membrane distillation Desalination 261 300e312

Sun S P Hatton T A Chan S Y amp Chung T-S (2012) Novel thin-film compositenanofiltration hollow fiber membranes with double repulsion for effective removal ofemerging organic matters from water Journal of Membrane Science 401e402152e162

Teoh M M amp Chung T S (2009) Membrane distillation with hydrophobic macrovoid-freePVDFePTFE hollow fiber membranes Separation and Purification Technology 66229e236

Teoh M M Chung T S amp Yeo Y S (2011) Dual-layer PVDFPTFE composite hollowfibers with a thin macrovoid-free selective layer for water production via membranedistillation Chemical Engineering Journal 171 684e691

Vercellino T Morse A Tran P Song L Hamood A Reid T et al (2013) Attachment oforgano-selenium to polyamide composite reverse osmosis membranes to inhibit biofilmformation of S aureus and E coli Desalination 309 291e295

Wang K Y Foo S W amp Chung T S (2009) Mixed matrix PVDF hollow fiber membraneswith nanoscale pores for desalination through direct contact membrane distillationIndustrial amp Engineering Chemistry Research 48 4474e4483

Wang P Luo L amp Chung T S (2014) Tri-bore ultra-filtration hollow fiber membranes witha novel triangle-shape outer geometry Journal of Membrane Science 452 212e218

Wang P Teoh M M amp Chung T S (2011) Morphological architecture of dual-layer hollowfiber for membrane distillation with higher desalination performance Water Research 455489e5500

Wang R Guan S Sato A Wang X Wang Z Yang R et al (2013) Nanofibrousmicrofiltration membranes capable of removing bacteria viruses and heavy metal ionsJournal of Membrane Science 446 376e382

Wang T Dai L Zhang Q Li A amp Zhang S (2013) Effects of acyl chloride monomerfunctionality on the properties of polyamide reverse osmosis (RO) membrane Journal ofMembrane Science 440 48e57

Wang Y Gruender M amp Chung T S (2010) Pervaporation dehydration of ethylene glycolthrough polybenzimidazole (PBI)-based membranes 1 Membrane fabrication Journal ofMembrane Science 363 149e159

Wang Z Yu H Xia J Zhang F Li F Xia Y et al (2012) Novel GO-blended PVDFultrafiltration membranes Desalination 299 50e54

Wei X Kong X Sun C amp Chen J (2013) Characterization and application of a thin-filmcomposite nanofiltration hollow fiber membrane for dye desalination and concentrationChemical Engineering Journal 223 172e182

Wei X Zhao B Li X M Wang Z He B Q He T et al (2012) CF4 plasma surfacemodification of asymmetric hydrophilic polyethersulfone membranes for direct contactmembrane distillation Journal of Membrane Science 407e408 164e175

Wu H Mansouri J amp Chen V (2013) Silica nanoparticles as carriers of antifouling ligandsfor PVDF ultrafiltration membranes Journal of Membrane Science 433 135e151

282 Advances in Membrane Technologies for Water Treatment

Wu H Tang B ampWu P (2013a) Optimization characterization and nanofiltration propertiestest of MWNTspolyester thin film nanocomposite membrane Journal of MembraneScience 428 425e433

Wu H Tang B amp Wu P (2013b) Preparation and characterization of anti-foulingb-cyclodextrinpolyester thin film nanofiltration composite membrane Journal ofMembrane Science 428 301e308

Wu H Tang B amp Wu P (2014) Development of novel SiO2eGO nanohybridpoly-sulfone membrane with enhanced performance Journal of Membrane Science 45194e102

Xiangli F Chen Y Jin W amp Xu W (2007) Polydimethylsiloxane (PDMS)eceramic com-posite membrane with high flux for pervaporation of ethanol-water mixtures Industrail ampEngineering Chemistry Research 46 2224e2230

Xu G R Wang J N amp Li C J (2013) Strategies for improving the performance of thepolyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes Surfacemodifications and nanoparticles incorporations Desalination 328 83e100

Yang D Li J Jiang Z Lu L amp Chen X (2009) ChitosanTiO2 nanocompositepervaporation membranes for ethanol dehydration Chemical Engineering Science 643130e3137

Yang X Wang R Shi L Fane A G amp Debowski M (2011) Performance improvement ofPVDF hollow fiber-based membrane distillation process Journal of Membrane Science369 437e447

Yin M Qian J An Q Zhao Q Gui Z amp Li Y (2010) Polyelectrolyte layer-by-layer self-assembly at vibration condition and the pervaporation performance of as-sembly multilayer films in dehydration of isopropanol Journal of Membrane Science358 43e50

Yu H Zhang X Zhang Y Liu J amp Zhang H (2013) Development of a hydrophilic PESultrafiltration membrane containing SiO2N-Halamine nanoparticles with both organicantifouling and antibacterial properties Desalination 326 69e76

Yu L Zhang Y Zhang B Liu J Zhang H amp Song C (2013) Preparation and charac-terization of HPEI-GOPES ultrafiltration membrane with antifouling and antibacterialproperties Journal of Membrane Science 447 452e462

Yu S Cheng Q Huang C Liu J Peng X Liu M et al (2013) Cellulose acetate hollowfiber nanofiltration membrane with improved permselectivity prepared through hydrolysisfollowed by carboxymethylation Journal of Membrane Science 434 44e54

Yu S Zhou Q Shuai S Yao G Ma M amp Gao C (2013) Thin-film compositenanofiltration membranes with improved acid stability prepared from naphthalene-136-trisulfonylchloride (NTSC) and trimesoyl chloride (TMC) Desalination 315 164e172

Zhang G Dai L amp Ji S (2011) Dynamic pressure-driven covalent assembly of inner skinhollow fiber multilayer membrane AIChE Journal 57 2746e2754

Zhang G Lu S Zhang L Meng Q Shen C amp Zhang J (2013) Novel polysulfone hybridultrafiltration membrane prepared with TiO2-g-HEMA and its antifouling characteristicsJournal of Membrane Science 436 163e173

Zhang J W Fang H Wang J W Hao L Y Xu X amp Chen C S (2014) Preparation andcharacterization of silicon nitride hollow fiber membranes for seawater desalinationJournal of Membrane Science 450 197e206

Zhang Q G Liu Q L Zhu A M Xiong Y amp Ren L (2009) Pervaporation performanceof quaternized poly(vinyl alcohol) and its crosslinked membranes for the dehydration ofethanol Journal of Membrane Science 335 68e75

Novel and emerging membranes for water treatment 283

Zhang P Qian J An Q Liu X Zhao Q amp Jin H (2009) Surface morphology andpervaporation performance of electric field enhanced multilayer membranes Journal ofMembrane Science 328 141e147

Zhang P Qian J Yang Y An Q Liu X amp Gui Z (2008) Polyelectrolyte layer-by-layerself-assembly enhanced by electric field and their multilayer membranes for separatingisopropanolewater mixtures Journal of Membrane Science 320 73e77

Zhang G Song X Ji S Wang N amp Liu Z (2008) Self-assembly of inner skin hollow fiberpolyelectrolyte multilayer membranes by a dynamic negative pressure layer-by-layertechnique Journal of Membrane Science 325 109e116

Zhang S Wang R Zhang S Li G amp Zhang Y (2014) Treatment of wastewater containingoil using phosphorylated silica nanotubes (PSNTs)polyvinylidene fluoride (PVDF) com-posite membrane Desalination 332 109e116

Zhang Z Wang Z Wang J amp Wang S (2013) Enhancing chlorine resistances and anti-biofouling properties of commercial aromatic polyamide reverse osmosis membranes bygrafting 3-allyl-55-dimethylhydantoin and NN0-Methylenebis(acrylamide) Desalination309 187e196

Zhao L Chang P C Y amp Ho W S W (2013) High-flux reverse osmosis membranesincorporated with hydrophilic additives for brackish water desalination Desalination 308225e232

Zhao Q An Q F Ji Y Qian J amp Gao C (2011) Polyelectrolyte complex membranes forpervaporation nanofiltration and fuel cell applications Journal of Membrane Science 37919e45

Zhao Q An Q Sun Z Qian J Lee K R Gao C et al (2010) Studies on structures andultrahigh permeability of novel polyelectrolyte complex membranes The Journal ofPhysical Chemistry B 114 8100e8106

Zhao Q Qian J An Q Gao C Gui Z amp Jin H (2009) Synthesis and characterization ofsoluble chitosansodium carboxymethyl cellulose polyelectrolyte complexes and thepervaporation dehydration of their homogeneous membranes Journal of MembraneScience 333 68e78

Zhao Q Qian J An Q Gui Z Jin H amp Yin M (2009) Pervaporation dehydrationof isopropanol using homogeneous polyelectrolyte complex membranes ofpoly(diallyldimethylammonium chloride)sodium carboxymethyl cellulose Journal ofMembrane Science 329 175e182

Zhao Q Qian J An Q amp Sun Z (2010) Layer-by-layer self-assembly of polyelectrolytecomplexes and their multilayer films for pervaporation dehydration of isopropanol Journalof Membrane Science 346 335e343

Zhao Q Qian J An Q Yang Q amp Gui Z (2009) Synthesis and characterization ofsolution-processable polyelectrolyte complexes and their homogeneous membranes ACSApplied Materials amp Interfaces 1 90e96

Zhao Q Qian J W An Q F Yang Q amp Zhang P (2008) A facile route for fabricatingnovel polyelectrolyte complex membrane with high pervaporation performance in iso-propanol dehydration Journal of Membrane Science 320 8e12

Zhao Q Qian J An Q Zhu M Yin M amp Sun Z (2009) Poly(vinyl alcohol)poly-electrolyte complex blend membrane for pervaporation dehydration of isopropanolJournal of Membrane Science 343 53e61

Zhao Q Qian J Zhu C An Q Xu T Zheng Q et al (2009) A novel method forfabricating polyelectrolyte complexinorganic nanohybrid membranes with high iso-propanol dehydration performance Journal of Membrane Science 345 233e241

284 Advances in Membrane Technologies for Water Treatment

Zhao Q Qian J Zhu M amp An Q (2009) Facile fabrication of polyelectrolyte com-plexcarbon nanotube nanocomposites with improved mechanical properties and ultra-high separation performance Journal of Materials Chemistry 19 8732e8740

Zhao H Qiu S Wu L Zhang L Chen H amp Gao C (2014) Improving the performance ofpolyamide reverse osmosis membrane by incorporation of modified multi-walled carbonnanotubes Journal of Membrane Science 450 249e256

Zhao S Wang P Wang C Sun X amp Zhang L (2012) Thermostable PPESKTiO2

nanocomposite ultrafiltration membrane for high temperature condensed water treatmentDesalination 299 35e43

Zheng Y Yao G Cheng Q Yu S Liu M amp Gao C (2013) Positively charged thin-filmcomposite hollow fiber nanofiltration membrane for the removal of cationic dyes throughsubmerged filtration Desalination 328 42e50

Zhu H Wang H Wang F Guo Y Zhang H amp Chen J (2013) Preparation and propertiesof PTFE hollow fiber membranes for desalination through vacuum membrane distillationJournal of Membrane Science 446 145e153

Zhu M Qian J Zhao Q An Q amp Li J (2010) Preparation method and pervaparationperformance of polyelectrolyte complexPVA blend membranes for dehydration of iso-propanol Journal of Membrane Science 361 182e190

Zhu M Qian J Zhao Q An Q Song Y amp Zheng Q (2011) Polyelectrolyte complex(PEC) modified by poly(vinyl alcohol) and their blend membranes for pervaporationdehydration Journal of Membrane Science 378 233e242

Zhu Y Xia S Liu G amp Jin W (2010) Preparation of ceramic-supported poly(vinylalcohol)echitosan composite membranes and their applications in pervaporation dehy-dration of organicwater mixtures Journal of Membrane Science 349 341e348

Zinadini S Zinatizadeh A A Rahimi M Vatanpour V amp Zangeneh H (2014) Prepa-ration of a novel antifouling mixed matrix PES membrane by embedding graphene oxidenanoplates Journal of Membrane Science 453 292e301

Zuo J Wang Y Sun S P amp Chung T S (2012) Molecular design of thin film composite(TFC) hollow fiber membranes for isopropanol dehydration via pervaporation Journal ofMembrane Science 405e406 123e133

Novel and emerging membranes for water treatment 285

Novel and emerging membranesfor water treatment by electricpotential and concentrationgradient membrane processes

9

P Arribas12 M Khayet 23 MC Garciacutea-Payo2 L Gil41Campus of International Excellence Moncloa Campus (UCM-UPM) Madrid Spain2Department of Applied Physics I University Complutense of Madrid Avda ComplutenseMadrid Spain 3Madrid Institute for Advanced Studies of Water (IMDEA Water Institute)Alcala de Henares Madrid Spain 4School of Forest Engineering University Polytechnic ofMadrid Avda Complutense Madrid Spain

91 Introduction

Recently salinity gradient power (SGP) has been recognized as a renewable andsustainable alternative technology for energy generation This approach is able toconvert osmotic pressure difference of salt solutions (ie high-concentrated andless-concentrated salt solutions) into mechanical or electrical energy by using selectivemembranes (Brauns 2009) The worldwide availability of SGP is considered to be ahuge energy resource with an estimated potential power of 24e26 TWwhen the totaldischarge of all rivers in the world is taken into account (Hong Zhang Luo amp Chen2013) Each cubic meter of water in the river can generate 15 MJ of energy whenmixed with equal amounts of seawater (comparable to 05 molL NaCl) and morethan 169 MJ when mixed with brine solution (5 molL NaCl) (Post Hamelers ampBuisman 2008) Pressure retarded osmosis (PRO) and reverse electrodialysis (RED)are the most frequently studied membrane-based processes for energy conversion ofsalinity gradient energy (Hong et al 2013) While PRO is a mechanical processthat uses water selective membranes and turbines to produce electrical energy REDis an electrochemical process that uses ionic selective membranes and electrodes forelectricity production (Burheim Seland Pharoah amp Kjelstrup 2012) FurthermoreRED is often considered to be more favorable for power generation because of itsgreater energy efficiency and reduced sensitivity to membrane fouling comparedwith PRO (Post et al 2007)

Electrodialysis (ED) is an electrochemical process in which ions migrate throughion-selective exchange membranes (IEMs) as a result of their attraction to two electri-cally charged electrodes ED is able to remove most charged dissolved ions and is usedto produce potable water from saline aqueous solutions

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400009-5Copyright copy 2015 Elsevier Ltd All rights reserved

The interest in osmotically driven membrane processes such as forward osmosis(FO) and PRO has increased during last decade (Alsvik amp Heuroagg 2013a) Both pro-cesses belong to the emerging platform technology known as engineered osmosis(EO) that has the potential to sustainably produce clean drinking water and electricpower (Huang Bui Meyering Hamlin amp Mccutcheon 2013) Unlike the pressure-driven membrane processes (PDMPs) EO offers the possibility to use osmoticpressure gradients in a wide range of applications These include FO for water desali-nation PRO for electric power generation and direct osmotic concentration fordewatering (Arena Mc Closkey Freeman amp Mc Cutcheon 2011)

92 Electric potential gradient driven membraneprocesses EDRED

A typical ED system includes a membrane stack with a number of cell pairs each con-sisting of cation and anion exchange membranes (CEM and AEM respectively)stacked in an alternating pattern between a cathode and an anode (see Figure 91(a))The compartments between the membranes are alternately filled with a concentratedsalt aqueous solution and a diluted salt aqueous solution The electrodes are continuallyflushed to reduce fouling or scaling Some of the advantages of ED compared with othermembrane processes such as reverse osmosis (RO) and nanofiltration (NF) include thehigh water recovery the long useful life of the membranes due to their high chemicalmechanical stability the possibility to operate at temperatures up to 50 C and theachievement of higher brine concentrations ED technology is also used for the treat-ment of industrial effluents and the removal of fluoride nitrate and heavy metalsfrom water sources (Mulyati Takagi Fujii Ohmukai amp Matsuyama 2013) Whenthe polarity of the electrodes is regularly reversed the process is called electrodialysisreversal (EDR) This variation on the ED process uses electrode polarity reversal toclean automatically the membrane surfaces increasing membrane life This processminimizes the effect of inorganic scaling and fouling by converting product streamsinto waste streams and allows running at higher recovery rates (Valero amp Arbos2010) However EDR requires additional plumbing and electrical controls

A typical RED membrane unit consists of an alternating series of CEM and AEMsituated between two electrodes (see Figure 91(b)) The salinity gradient between bothsolutions induces an electrochemical potential difference through each membraneThis electrochemical potential difference causes the transport of ions through the mem-branes from the concentrated solution to the diluted solution At the electrodes theionic species accumulate and induce electron current via red-ox reactions whichcan be used to power on an external device (Hong et al 2013) To optimize bothED and RED processes various research studies were focused on the improvementof the IEMsrsquo performance including their physicochemical (eg thickness andswelling degree) and electrochemical (eg area resistance ie electrical membraneresistance (U cm2) permselectivity and charge density) characteristics (Geurouler ElizenVermaas Saakes amp Nijmeijer 2013)

288 Advances in Membrane Technologies for Water Treatment

When the ED process is used to produce NaCl (table salt) from high-salinity brinethe salt rejection factor (or membrane selectivity) to monovalent and multivalent ionsis important to avoid the possible salt precipitation taking placing in the concentrating

Figure 91 Schematic diagrams (a) Electrodialysis unit with five cell pairs and (b) Reverseelectrodialysis unit

Novel and emerging membranes for water treatment 289

compartments (Wang Jia Yao amp Wang 2013) It is worth noting that high processcost and low selectivity efficiency and durability of IEMs are still important issuesin ED technology (Kumar Khan Alothman amp Siddiqui 2013) Many researchersare investigating to develop specific selective membranesmaterials to overcome theseproblems

Chakrabarty et al (2011) developed thermally and chemically cross linked stableIEMs in an aqueous medium for water desalination by ED CEM was prepared by sul-fonation of poly (ether sulfone) (SPES) while AEM was fabricated by using polyvinylalcohol (PVA) and 4-vinylpyridine (4-VP) in three steps (1) solegel process (2)chemical cross linking and (3) quaternization The membrane electrochemical proper-ties and stabilities could be controlled by either the degree of sulfonation of SPES (inthe case of CEM) or chemical cross linking (in the case of AEM) Both CEM and AEMshowed excellent electro-transport properties and a good ED performance and energyconsumption (429 kWhkg of NaCl removed) for water desalination

Zendehnam Robatmili Hosseini Arabzadegan and Madaenic (2013) preparedacrylonitrilebutadienestyrene heterogeneous AEMs using anion exchange resin pow-der as functional group agents and tetrahydrofuran as a solvent In addition a silver(Ag) nanolayer was deposited on the prepared membrane surface using the magnetronsputtering method Activated carbon (AC) was also used as an inorganic filler additiveto create adsorptive active sites in the membrane matrix The results showed amaximum of the membrane permselectivity for 2 wt AC concentration in the castingsolution Both the ionic permeability and permeate flux were enhanced by increasingthe AC amount up to 05 wt and then they declined with further increase of AC con-centration from 05 to 4 wt The modified membranes showed good ability inEscherichia coli removal due to the increase of the coating thickness of Agnanolayer which reduced the growth rate of E coli

To improve the ED membrane monovalent selectivity Wang et al (2013) per-formed a promising modification method consisting on a photo-induced covalentimmobilization and self-crosslinking of a chitosan (CS) layer on a conventionalCEM surface This modification resulted in both chemical and morphological mem-brane surface changes such as the formation of chemical bonds between the basemembrane and the covalently immobilized and self-crosslinked CS layer The EDexperimental results with respect to NathornMg2thorn and HthornZn2thorn systems showed thatthe modified CEMs achieved a superior monovalent selectivity after the immobiliza-tion of CS layer The Zn2thorn and Mg2thorn leakage of the modified membrane were reducedby 274 and 624 respectively whereas the diffusion coefficient of Nathorn electricalresistance and limiting current density were not declined remarkably after the modi-fication by CS immobilization

Other research studies have demonstrated that the modification of CEMs with poly-aniline (PANI) is an efficient approach for improving the stability and selectivity ofIEMs toward monovalent ions For example Kumar et al (2013) developed PANIchemically modified organiceinorganic hybrid CEMs by in situ polymerization of an-iline in an HCl aqueous solution using ferric chloride (FeCl3) as an oxidizing agentThe PANI modified membranes were thermally stable in ED separation of Nathorn

from binary mixtures of (NathornZn2thorn and NathornAl3thorn) in aqueous solutions The water

290 Advances in Membrane Technologies for Water Treatment

uptake ion exchange capacity cation transport number in the membrane phase andequivalent membrane conductivity of the modified membranes were improved for a001 M NaCl aqueous solution The cation transport number value for Zn2thorn andAl3thorn (040 and 034 respectively) of the PANI modified membranes were lowerthan the cation transport number value for Nathorn (092) which indicated that the modi-fied membranes were more selective for Nathorn in comparison to Zn2thorn and Al3thorn ions

Mulyati et al (2012) improved the ED anti fouling properties of the commercialAEM (NEOSEPTA AMX Astom Corp Tokyo Japan) by surface modificationwith poly(sodium 4-styrene sulfonate) (PSS) Antifouling potential of the AEM wasevaluated based on the elapsed time before fouling took place using sodium dodecyl-benzene sulfonate (SDBS) as a model organic foulant It was observed an enhancedantifouling property of the modified membrane attributed to the increase of the nega-tive charge density and hydrophilicity of the membrane surface However the mono-valent anion selectivity was not improved by the deposition of a single layer of PSS Ayear later the same research group developed a new approach to simultaneouslyimprove the monovalent anion selectivity and antifouling properties of commercialAEMs (Mulyati et al 2013) The method was based on the generation of a high nega-tive charge on the membrane surface using layer-by-layer (LbL) deposition of differentpolyelectrolyte solutions in which PSS was used as a polyanion while poly(allylaminehydrochloride) (PAH) was used as a polycation A commercial AEM (NEOSEPTAAMX membrane Astom Corp Tokyo Japan) was modified via alternating contactwith the PSS and PAH solutions for 30 min The results showed that the increase ofthe number of layers resulted in better monovalent anion selectivity and anti foulingcharacter

Cross-linked zirconium tri-ethylene tetra-amine (ZrT) chelating membranes wereprepared by solegel method for Cu2thorn removal in the presence of other bivalent metalions (Chakrabarty Shah Srivastava Shahi amp Chudasamab 2013) The incorporationof ZrT in the PVA polymer matrix ensures the formation of homogeneous andinterconnected polymer network The developed ZrT membrane exhibited good ther-mal mechanical and chemical stabilities with a controlled pore size ED studiesrevealed high Cu2thorn permeate flux (55$107 molm2 s at 10 mAcm2 applied currentdensity) of ZrT membranes in comparison with other bivalent metal cations(15e2$107 molm2 s for Ni2thorn Zn2thorn and Mn2thorn) The selective recovery of Cu2thorn

was attributed to the hydrophilic structural membrane morphology having many aminogroups and highly cross linked The separation factor was estimated from the ratio ofCu2thorn permeate flux (JCu2thorn ) and other bivalent cation permeate flux (JCu2thorn=JM2thorn ) inequimolar solution metal ion mixtures The obtained high separation factor(30e40) for separating Cu2thornNi2thorn Cu2thornZn2thorn and Cu2thornMn2thorn suggested the appli-cation of ZrT chelating membranes for Cu2thorn recovery from industrial wastewaters

Hosseini Askari Koranian Madaeni and Moghadassia (2014) and Hosseini et al(2013) investigated the effects of the concentration of different additives iron oxide(Fe3O4) nanoparticles (NPs) and multiwalled carbon nanotubes (MWCNTs) on thephysicochemical and electrochemical properties of polyvinylchloride (PVC)-basedED CEM An increase of the water content (from 22 to 259) and the ion exchangecapacity (from 143 to 172 meqg) of the CEM with the increase of Fe3O4 NPs from

Novel and emerging membranes for water treatment 291

0 to 2 wt followed by a decline of both parameters for high NPs concentrations wasobserved The same behavior was observed for the ionic permeability for sodium andbarium ions achieving high values of 355$107 and 337$107 ms respectively at2 wt Fe3O4 content The membrane permselectivity was enhanced with the increaseof the additive content from 0 to 4 wt in sodium (790e860) and barium chloride(364e425) ionic solutions These results suggested that the prepared membraneswere less selective to bivalent ions (Ba2thorn) compared to monovalent ions (Nathorn) ForMWCNTs the prepared membrane water content also showed a maximum of283 for 4 wt MWCNT concentration in the casting solution The increase ofMWCNTsrsquo loading ratio also resulted in an increase of the permeability for monova-lent ions (Nathorn) from 2398$107 to 2420$107 ms while the permeability for bivalentions (Ba2thorn) did not show a straightforward relationship with MWCNTsrsquo loading ratio

ED was also carried out using bipolar membranes (BPMs) which are compositeIEMs consisting of a layered ion exchange structure composed of a cation exchangelayer (CEL) and an anion exchange layer (AEL) with a hydrophilic intermediate layerin between (Venugopal amp Dharmalingam 2012 Xu 2005) This composition ofanionic and cationic exchange layers exhibits various advantages in ED such as theseparation of monovalent and divalent ions antideposition antifouling water dissoci-ation into OH and Hthorn ions increase of reusability and recyclability of waste throughchemical production (acidic and alkaline solutions) low initial cost and no electro-chemical reactions (oxidation andor reduction species) that may produce undesirableproducts etc (Kariduraganavar Nagarale Kittur amp Kulkarni 2006) Today syntheticBPMs are receiving much attention because of their potential for application indifferent industries such as chemical production and separation industry biochemicalengineering (ie producing inorganic acidbase from the corresponding salts recov-eryproduce organic from fermentation broth etc) environmental conservation puri-fication or separation in food industries (ie inhabitation of polyphenol oxidase inapple juice) etc When applied to treat salt-containing wastewater BPM ED can pro-duce acids and bases due to its ability to split water into OH and Hthorn ions and over-come salt pollution and be discharged without treatment (see Figure 92) Venugopaland Dharmalingam (2012) developed a novel functionalized polysulfone (PS)-basedBPM with an intermediate layer of PVA and investigated its ED performance forseawater desalination and recovery of acid and alkali The prepared BPM possessedexcellent mechanical and chemical stabilities due to its unique ply structures in bothAEL and CEL forms The PS-based BPM showed higher current efficiency (ie18) lower power consumption (ie 8) greater salt rejection factor and higherprocess efficiency for the production of acid and alkali than those of the commercialBPM made of gel polystyrene crosslinked with divinylbenzene (PSDVB) (Arun Elec-tro chemicals Chennai)

Wang Peng et al (2010) developed a hybrid BPM for high temperature applica-tions The CEL was prepared by hybridizing sulfonated poly(26-dimethyl-14-phenylene oxide) with (3-aminopropyl) triethoxysilane (A1100) while the AELwas prepared from a hybrid anion exchange material poly(VBC-co-g-MPS) (vinyl-benzyl chloride (VBC) and g-methacryloxypropyl trimethoxy silane (g-MPS)) andPVA Palygorskite (a silicate mineral) and FeCl3 were added in the intermediate layer

292 Advances in Membrane Technologies for Water Treatment

as catalysts to further enhance water dissociation improving the generation of Hthorn andOH although the voltage drop across the BPM was detected By incorporatinginorganic silane (A1100 and g-MPS) in both the AELCEL the BPM showed higherthermal stability dimensional stability and catalytic effect on water dissociation in therange 25e80 C

Not only the improvement of the membrane properties is necessary to achieve highED and RED performances but it is also important to consider the scale-up and designof the EDRED unit and the optimization of the electrode systems Geurouler et al (2013)successfully constructed a RED unit completely built with tailor-made IEMs in whichCEMs were fabricated by sulfonated polyetheretherketone (SPEEK) and AEMs withpolyepichlorohydrin (PECH) The bulk membrane properties (ie area resistancepermselectivity and charge density) of both series of commercially available mem-branes and tailor-made ones were investigated and correlated to the obtained RED per-formance Experimental and theoretical statistical results showed that increasing thearea resistance resulted in an increase of the power density in RED whereas permse-lectivity did not show any straightforward relationship with the power densityFurthermore the performance of the tailor-made RED unit exhibited a higher powerdensity (128 Wm2) than other RED units based on the commercially consideredmembranes Fumatech FKSFAS (111 Wm2) Tukuyama CMXAMX (107 Wm2)Qianqui CEMAEM (083 Wm2) or Ralex CMHAMH (060 Wm2)

For the design of a typical system of both RED and ED processes metal oxide cat-alysts are commonly used to convert the electronic current to ionic current This conver-sion results from the red-ox reaction that occurs in the electrodes of the system Burheimet al (2012) studied the performance of electrode systems for RED and ED separation

Figure 92 Schematic diagram of electrodialysis with bipolar membranes cell to treat salt-containing wastewater

Novel and emerging membranes for water treatment 293

processes by testing two different electrode materials and red-ox salts demonstratingthat these electrochemical reactions were controlled by mass transfer in the electrolyterather than by the electro-catalytic properties of the electrode material It was concludedthat relatively cheap carbon materials (graphite and glassy carbon) with FeCl2FeCl3could act as good electrodes in a red-ox system with lower electrode concentration over-potential The power losses (ie dissipated energy) in the electrode compartments werereduced by increasing the concentration of the electroactive species Vermaas Saakesand Nijmeijer (2011) developed a RED unit using membranes with a specific labora-tory-made profile (profiled membranes) and evaluated its performance comparing itto that of RED unit of commercial IEMs (Ralex CMH and AMH Mega as CzechRepublic) separated by non-conductive spacers This new morphology resulted in aslight reduction in permselectivity (from 89 to 87) a significant decrease in arearesistance (from 73 to 27 U cm2) a large increase in conductivity (from 91 to177 mScm) and a slightly higher maximum power density (from 069 to 080 Wm2)

93 Concentration gradient driven membrane processesFO and PRO

In the case of FO a high-concentration solution (ie draw solution) is separated froma low-concentration solution by a water-selective semipermeable membrane As it isshown in Figure 93 the concentration gradient between both the feed and drawsolutions results in a transmembrane osmotic pressure Consequently water flowsspontaneously through the membrane from the low-concentration side to the draw-solution side PRO and FO are similar separation processes except for the additionalback pressure applied on the draw solution for PRO In both processes water flowsfrom the low-concentration side of the membrane to the high-concentration side aslong as the applied pressure is lower than the transmembrane osmotic pressureWhen the applied pressure is greater than the osmotic pressure difference the direc-tion of the water flux is reversed leading to the well-known RO separation process(Figure 94) Unlike RO in which mechanical energy is used for pumping the feedsaline aqueous solution through a water-selective membrane to overcome the trans-membrane osmotic pressure PRO converts the chemical potential (osmotic energy)of a salt-concentrated aqueous solution into mechanical energy (Xu Peng TangFu amp Nie 2010)

It must be pointed out that the membranes used in FO and PRO are not ideal andreverse solute(s) permeate fluxes also occur through the membrane opposite to the di-rection of water permeate flux This causes solute(s) concentration polarization insidethe membrane known as internal concentration polarization (ICP) phenomenon (Xuet al 2010) ICP is one of the most severe drawbacks in the osmotic membrane pro-cesses because it significantly reduces the membrane water permeability (Achilli ampChildress 2010 Chou et al 2012) Therefore preparation of specific membranes isessential for the development of FO and PRO technologies In this case three main

294 Advances in Membrane Technologies for Water Treatment

challenges must be addressed ICP weak mechanical strength of the membranes andmembrane fouling propensity (Chou et al 2012)

An ideal FOPROmembrane should be a semipermeable membrane with a high wa-ter permeability and a high solute rejection factor a small resistance toward solutediffusion high chemical stability low ICP using thin and highly porous supportswith low mass transfer resistance high mechanical strength to support high hydraulicpressure when used in PRO applications low susceptibility to fouling (ie hydrophilicmembrane to get high permeate fluxes and reduce membrane fouling) and low struc-tural parameter (S) defined as the ratio of the pore tortuosity and porosity multiplied bythe thickness of the membrane (S frac14 thickness tortuosityporosity) (Cath Childressamp Elimelech 2006 Chou et al 2010 Han Zhang et al 2013 Sivertsen HoltThelin amp Brekke 2013 Zhang et al 2010) In addition the surface structure ofthe FO membrane facing the feed aqueous solution is critical because it is directlyassociated with fouling tendency while a relatively dense substrate surface is desirablefor a membrane with an active layer facing draw solution (AL-DS)

For the preparation of FO and PRO membranes different polymers are usedincluding cellulose acetate (CA) (Herron 2008) cellulose triacetate (CTA) (HTI2013) PS (Yip Tiraferri Phillip Schiffman amp Elimelech 2010) polyethersulfone(PES) (Yu Seo Kim amp Lee 2011) polybenzimidazole (PBI) (Wang Chung ampQin 2007) polyamide (PA) (Alsvik amp Heuroagg 2013b) and poly(amide-imide) (PAI)(Setiawan Wang Li amp Fane 2011) These FO and PRO membranes were designedas thin-film composite (TFC) flat sheet membranes using different types of supportsand hollow fiber membranes

Until now three methods have been adopted to prepare polymeric FO membranesthe non-solvent phase inversion method developed by Loeb and Sourirajan (Loeb ampSourirajan 1963) the interfacial polymerization (IP) on porous substrates inventedby Cadotte (Cadotte 1981) to prepare TFC membranes and the LbL deposition ofnanometer thick polycations and polyanions on porous charged substrates (Qi Qiu

Initial nonequilibriumosmotic state

FO ( P = 0)∆∆ PRO ( P lt π)∆ ∆∆ RO ( P gt π)∆ ∆∆

Figure 93 Illustration of forward osmosis (FO) reverse osmosis (RO) and pressure retardedosmosis (PRO) processes (a) Initial non-equilibrium osmotic state (b) FO process in whichno pressure is applied on the draw solution (c) PRO process in which a hydrostatic pressurelower than the transmembrane osmotic pressure is applied on the draw solution (d) RO processused for desalination of a saline feed solution by applying a hydrostatic pressure greater than thetransmembrane osmotic pressure

Novel and emerging membranes for water treatment 295

amp Tang 2011) Fully integrated asymmetric FO membranes made of CTA (Herron2008) PBI (Wang et al 2007 Wang Goh et al 2009 Yang Wang amp Chung2009) CA (Su amp Chung 2011 Su Yang Teo amp Chung 2010) and PES (Yuet al 2011) are typical examples of the first method while FO membranes made of

Figure 94 (a) Water flux direction and (b) energy consumptionproduction in forward osmosis(FO) pressure retarded osmosis (PRO) and reverse osmosis (RO) using a selectivesemipermeable membrane

296 Advances in Membrane Technologies for Water Treatment

PA via IP on PS-based substrates (Wang Shi et al 2010 Yip et al 2010) sulfonatedsubstrates (Wang Chung amp Amy 2012 Widjojo Chung Weber Maletzko ampWarzelhan 2011) cellulose acetate propionate substrates (Li Wang Helmer ampChung 2012) and nanofibrous supports (Bui Lind Hoek amp Mc Cutcheon 2011)belong to the second method A comparison of the performance of membranes appliedin FOPRO process is listed in Table 91

It is worth noting that CA has been widely used to prepare FO membranes via phaseinversion because of its relatively high hydrophilicity that favors high water perme-ability and low fouling propensity good mechanical strength wide availability andgood resistance to degradation by various compounds including chlorine (ZhaoZou Tang amp Mulcahy 2012) The company Hydration Technology Innovations(HTI Albany OR USA) has provided asymmetric cellulose-based membranes forFO for nearly 25 years This company developed flat sheet membranes using celluloseesters exclusively for FO applications In 2008 HTI patented commercial asymmetricCACTA FO membranes composed of a thin skin layer for salt separation (10e20 mm)and a thicker porous scaffold layer (about 100 mm thick) with a woven or non-wovenmesh embedded within it (Herron 2008) These membranes exhibit high permeate fluxand salt rejection factors low resistance to water diffusion lack of defects and goodstructural integrity It was claimed that these membranes have far superior permeatefluxes than other commercially available composite membranes such as cellulose esterblend RO membrane (Osmonics now GE Water Systems) used in FO

Recently Nguyen Yun Kim and Kwon (2013) prepared CTACA flat sheet mem-branes with enhanced FO performance by immersion precipitation using different cast-ing compositions and support layers (Figure 95) The optimized membrane (WF1Figure 95(a)) was prepared by casting 63 wt CTA 126 wt CA 499 wt14-dioxane 172 wt acetone 37 wt maleic acid and 103 wt methanol to athickness of 250 mm on a porous woven support layer with a subsequent evaporationfor 30 s at 25 C and 70 relative humidity and then annealing at 85 C The opti-mized membrane showed a more hydrophilic and smoother surface than the commer-cial CTA FO membrane (090128-NW-1 HTI) with lower fouling the highest waterpermeate flux (9270 Lm2 h for a draw solution of 1 M NaCl) 99533 NaCl rejec-tion factor and a reverse salt permeate flux of 0248 mol Brm2 h

To develop FO membranes with a high salt rejection factor Su et al (2010) fabri-cated a CA-based NF hollow fiber membrane modified by heat treatment The heat-treated hollow fiber membrane at 95 C resulted in a significant shrinkage of poresat the membrane surface with a denser outer skin layer but a low FO performancewith increasing saline concentration in the feed solution due to the more severe ICPeffect One year later Su and Chung (2011) carried out both experimental and theoret-ical studies using different CA hollow fiber membranes prepared with different borefluid compositions via a dryjet wet spinning technique It was observed that the inter-nal membrane structure did not exert any apparent influence on the membraneperformance used in PRO mode whereas it affected significantly the concentrationpolymerization and the FO performance It was also claimed that the preferred internalsublayer of a hollow fiber for FO should have a high porosity low tortuosity and smallthickness to enhance the water permeate flux

Novel and emerging membranes for water treatment 297

Table 9 1 Overview of recent researches on forward osmosispressure retarted osmosis (FOPRO) process withdifferent membranes

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

CA NF HF 047 967 7350 052e PROFO DI water 2 M MgCl2 22e25 Su et al (2010)

CA HF 097 7416 36383 1010 PROFO DI water 2 M MgCl2 e Su and Chung(2011)

CA double denselayer FS

017 990 173103 1208 PROFO DI water 2 M MgCl2 22 Zhang et al (2010)

920 11378 4438 PROFO DI water 2 M NaCl 22

CA double-skinned FS

078 790 255168 4625 PROFO DI water 2 M MgCl2 22 Wang Ong et al(2010)

CA HTIc FS e e 45 27 FO DI water 15 MMgSO4

20 Cornelissen et al(2008)

CA HTIc FS e e 432181 e PROFO DI water 15 M NaCl 20 Mc Cutcheon andElimelech (2008)

CTA HTIc FS 068 e 196124 8862 PROFO DI water 15 M NaCl 25 Bui and McCutcheon (2013)

CTA HTIc FS e 910 119 55 FO DI water 2 M NaCl 20e25 You et al (2013)

CTA HTIc FS(CTA-W)

033 819 65550 4829 PROFO 10 mMNaCl

05 M NaCl 23 Wei Qiu TangWang and Fane(2011)229121 e PROFO 10 mM

NaCl2 M NaCl 23

Asymmetric PBINF HF

05 481 38 e PRO DI water 2 M NaCl 225 Wang et al (2007)

865 9053 e PROFO DI water 2 M MgCl2 225

PBI NF HF(original)

243 762 250126 e PROFO DI water 2 M MgCl2 230 Wang Yang et al(2009)

PBI NF HF(2h modified)

153 856 221112 e PROFO DI water 2 M MgCl2 230 Wang Yang et al(2009)

PBI-PESPVPdual-layer NFHF

174 872 195148 e PROFO DI water 2 M MgCl2 230 Yang et al (2009)

Positively chargedPAI single-layer HF

225 927 13284 9926 PROFO DI water 05 MMgCl2

230 Setiawan et al(2011)

179132 17549 PROFO DI water 2 M MgCl2 230

PAIPES dual-layer HF

159 890 155275 83755 PROFO DI water 05 MMgCl2

230 Setiawan WangShi Li and Fane(2012)

Positively chargedPAI with PETsubstrate FS

756 875 239192 36692 PROFO DI water 05 MMgCl2

22e25 Qiu SetiawanWang Tang andFane (2012)325275 107

333PROFO DI water 2 M MgCl2 22e25

PES with PETsubstrate FS

e e 314 82 FO DI water 3 M NaCl 200 Yu et al (2011)

Continued

Table 9 1 Continued

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

Cellulosic ROc

withoutPET FS GEOsmonics

e e 360186 e PROFO DI water 15 M NaCl 200 Mc Cutcheon andElimelech (2008)

TFC-PA-PES HF(A-FO)

095 780 12950 5021 PROFO DI water 05 M NaCl 230 Wang et al (2010)

25986 e PROFO DI water 2 M NaCl 230

TFC-PA-PES HF(B-FO)

222 910 32214 3518 PROFO DI water 05 M NaCl 230 Wang et al (2010)

450225 4425 PROFO DI water 2M NaCl 230

TFC-PA-PES HF(C-FO)

35 900 426187 4016 PROFO DI water 05 M NaCl 230 Chou et al (2010)

680295 5826 PROFO DI water 2 M NaCl 230

TFC-PA- PESwaterHF

118 8795 256225 3228 PROFO DI water 05 M NaCl 20-25 Sukitpaneenit andChung (2012)571321 6961 PROFO DI water 2 M NaCl 20-25

TFC-PA-PESwaterNMPPEG

HF

183 8152 651345 12399 PROFO DI water 2 M NaCl 20-25 Sukitpaneenitand Chung(2012)

TFC-PA-PES HF 19 878 383 106 PRO DI water 1 M NaCl e Han Wang et al(2013)

TFC-PA-sPPSUHF

199 909 494225 11055 PROFO DI water 05 M NaCl 23 Zhong Fu ChungWeber andMaletzko (2013)

TFC-PA-PS FS 178 934 205120 5949 PROFO 10 mMNaCl

05 M NaCl 23 Wei et al (2011)

543222 e PROFO 10 mMNaCl

2 M NaCl 23

TFC-PA-PS FS 31 700 376249 7532 PROFO 10 mMNaCl

2 M NaCl 23 Amini Jahanshahiand Rahimpour(2013)

TFC-PA-PS FS e e 325141 14453 PROFO DI water 2 M NaCl e Emadzadeh LauMatsuura Ismailand Rahbari-Sisakht (2014)

TFC-PA-PS withPET substrate FS

19 986 250 e FO DI water 1 M NaCl 23 Tiraferri YipPhillipSchiffman andElimelech (2011)

TFC-PA-PS withPET substrate FS

144 984 167 e FO DI water 1 M NaCl 25 Hoover Schiffmanand Elimelech(2013)

TFC-PA-PSSPEK FS

075 895 201161 4533 PROFO DI water 05 M NaCl 23 Han ChungToriida andTamai (2012)

500350 9070 PROFO DI water 2 M NaCl 23

Continued

Table 9 1 Continued

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

TFC-PA-SPPSUFS

323 841 322300 4752 PROFO DI water 05 M NaCl e Widjojo ChungWeberMaletzko andWarzelhan(2013)

540480 8876 PROFO DI water 2 M NaCl e

TFC-PA-CPSFFS

e e 275179 7348 PROFO DI water 1 M MgCl2 25 Cho Han HanGuiver and Park(2013)

TFC-PA-PESsulfonatedpolymersubstrate FS

073 910 162153 2730 PROFO DI water 05 M NaCl 20e25 Widjojo et al(2011)

330210 2822 PROFO DI water 2 M NaCl 20e25

TFC-PA-PESSPSf FS

077 935 241130 4536 PROFO DI water 05 M NaCl 20e25 Wang et al (2012)

475260 12483 PROFO DI water 2 M NaCl 20e25

TFC-PA-PVDF FS 082 e 217150 10278 PROFO DI water 05 M NaCl 20-25 Wang et al (2012)

360233 183112

PROFO DI water 2 M NaCl 20e25

TFC-PA-CAP FS 182 892 15578 0809 PROFO DI water 05 M NaCl 20e25 Li et al (2012)

35175 19518 PROFO DI water 2 M NaCl 20e25

TFC-PA-nylon66 MF FS

092 958 21962 0807 PROFO DI water 15 M NaCl 20 Huang et al (2013)

TFC-PA-Matrimid FS

100 e 891 154 PRO DI water 1 M NaCl 25 Han Zhang et al(2013)

TFC-PA PSnanofiber withPET substrate FS

174 e 260 23 FO DI water 15 M NaCl 23 Bui et al (2011)

TFC-PA-PESnanofiber FS

17 970 637576 e PROFO DI water 15 M NaCl 23 Song Liu and Sun(2011)

TFC-PA-PVDFnanofiber FS

315 844 621365 281169

PROFO DI water 15 M NaCl 23 Tian Qiu LiaoChou and Wang(2013)

TFC-PA-PANnanofiber FS

204 e 619350 5284 PROFO DI water 15 M NaCl 25 Bui and McCutcheon (2013)

TFC-PA-PANCAnanofiber FS

18 e 548301 42106 PROFO DI water 15 M NaCl 25 Bui and McCutcheon (2013)

TFC NF FS(TS80)Trisep

e e 11 004 FO DI water 15 MMgSO4

200 Cornelissen et al(2008)

TFC RO FS(SWC1)Hydranautics

e e 04 001 FO DI water 15 MMgSO4

200 Cornelissen et al(2008)

TFC-PA RO PSwith PET FS(SW30 XLE)Dow FilmTec

e e 8136 e PROFO DI water 15 M NaCl 200 Mc Cutcheon andElimelech (2008)

Continued

Table 9 1 Continued

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

TFC-PA HTIc FS e e 490200 e PROFO DI water 1 M NaCl 23 HTI (2013)

TFN-PAF-MWCNT-PSFS

447 730 951390 5229 PROFO 10 mMNaCl

2 M NaCl 23 Amini et al (2013)

TFN-PATiO2

ePS FS299 774 391225 208

102PROFO DI water 05 M NaCl e Emadzadeh et al

(2014)

751374 438233

PROFO DI water 2 M NaCl e

LbLnanocompositePVAMMt-TALiCl FS

e e 189100 01003 PROFO DI water 05M NaCl 230 Pardeshi andMungray (2014)

377255 028005

PROFO DI water 2 M NaCl 230

LbLnanocompositeNF-PANPSSAg FS

e 950 422178 3028 PROFO 10 mMNaCl

05 MMgCl2

260 Liu et al (2013)

LbLTFI-SSMsilica xerogelsTEOS FS

e 920 603598 106105

PROFO DI water 2 M NaCl 20e25 You et al (2013)

LbL double-skinned PANPAH-PSS FS

16 955 354766 119214

PROFO DI water 05 MMgCl2

22e23 Qi Qiu Zhao andTang (2012)

5011061

203516

PROFO DI water 2 M MgCl2 22e23

Note HF Hollow fiber FS flat sheet The superscript ldquocrdquo refers to commercial and PROFO refers to such membrane that the bottom layer faces the draw solution in the PRO mode and the top layer faces drawsolution in the FO mode

Recently Alsvik and Heuroagg (2013b) coated hydrolyzed commercial CACTA (CAfrom Alfa Laval and CTA from HTI) support membranes with a PA layer by amodified IP method forming a covalent bond between the active layer and the supportThe prepared membranes displayed salt rejection factors up to 97 and waterpermeate fluxes varying from 076 to 47 Lm2 s at transmembrane pressure of13$106 Pa (RO mode)

During the last eight years several studies have been published on the formation ofhollow fiber membranes specially designed for osmotically driven processes (Alsvik ampHeuroagg 2013a) Wang Yang et al (2009) fabricated hollow fiber membranes for FOapplications by the dryjet phase inversion method using PBI and modified via cross-linking using p-xylylene dichloride To improve the FO performance Yang et al

Figure 95 Images of supports (first row) and SEM cross-sectional images of forward osmosismembranes (second row) fabricated on the corresponding support layers Three woven fabricslabeled WF1 (a) WF2 (b) andWF3 (c) and three non-woven fabrics labeled NWF1 (d) NWF2(e) and NWF3 (f) were used as support layers for the cellulose triacetatecellulose acetate(CTACA)-based membranes Two commercial membranes were used to compare a cartridgeCTA-based membrane (090128-NW-1 HTI1 (g)) and a pouch CTA-based membrane(081118-SS-2 HTI2 (h))Reprinted from Nguyen et al (2013) with permission from Elsevier

306 Advances in Membrane Technologies for Water Treatment

(2009) developed a dual-layer PBIePES hollow fiber membrane via a co-extrusiontechnique This membrane consisted on an ultrathin selective skin layer fully porouswater channels underneath and a microporous sponge-like support structure The pre-pared PBIePESpolyvinylpyrrolidone (PVP) dual-layer membrane achieved a purewater permeability (PWP) of 174 Lm2 h bar and an MgCl2 rejection factor of872 The obtained water permeate fluxes in FO and PRO mode using 2 M MgCl2as a draw solution at 23 C (148 and 195 kgm2 h respectively) were higher thanthose of the commercial RO membranes (AG GE Osmonics 25 kgm2 h and ADGE Osmonics 11 kgm2 h) (Miller amp Evans 2006) but comparable to most commer-cial HTI FO flat sheet membranes (ie 129 kgm2 h for FO experiment and 85 kgm2 h for PRO experiment (Cornelissen et al 2008))

Setiawan et al (2011) fabricated hollow fiber membranes with a positively chargedlayer (ie NF-like skin layer) using asymmetric microporous hollow fibers made ofTorlon PAI material as substrates followed by chemical crosslinking using polyethy-leneimine (PEI) The PAI hollow fiber membranes exhibited a PWP of 219e225Lm2 h bar and a high MgCl2 rejection factor more than 911 under a pressure of1 bar By using 1 M MgCl2 draw solution better FO water permeate fluxes(104e110 kgm2 h) than those of previously reported PBI NF modified hollow fibers(Wang Yang et al 2009) prepared with 4 and 9 h of crosslinking time (50 and17 kgm2 h respectively) and CA-based NF hollow fiber (31 kgm2 h) (Su et al2010) However it was noted that the chemical crosslinking of the PAI hollow fibermembranes resulted in a denser substrate which adversely affected the water permeateflux To overcome this problem Setiawan et al (2012) developed asymmetric micro-porous PAIPES dual-layer hollow fiber membranes that consisted of an external layermade from PAI polymer and an internal layer made of PES Subsequently PEI poly-electrolyte modification was carried out on the outer PAI layer to produce an NF-likethin layer while the PES porous inner layer remained intact because PES is inert toPEI The developed PAIPES dual-layer hollow fiber membranes achieved a PWPof 159 Lm2 h bar and high MgCl2 rejection factors up to 89 In FO process thedual-layer hollow fiber exhibited a water permeate flux of 275 Lm2 h by using05 M MgCl2 as draw solution and deionized water as feed at room temperature

Fang Wang Chou Setiawan and Fane (2012) also fabricated novel compositedouble-skinned PAI hollow fiber membranes for FO In this case two selective skinlayers were integrated in each side of an ultrafiltration (UF) hollow fiber substratevia IP and chemical modification to yield a PA RO-like inner skin layer and a posi-tively charged NF-like outer skin layer The hydrophilic nature of the two skin layersreduced the contact angle of the membrane from 80 for PAI hollow fiber substrate to46 for the composite FO membrane The prepared double-skinned composite hollowfiber membrane exhibited a high PWP of 205 Lm2 h bar and 85 NaCl rejection at1 bar pressure Furthermore compared to commercial HTI FO flat sheet membranes(water flux of 186 kgm2 h (Mc Cutcheon Mc Ginnis amp Elimelech 2006)) and otherdouble-selective layer membranes reported in the literature (195 kgm2 h for dual-layer PBIePES hollow fiber membrane (Yang et al 2009)) the prepared double-skinned composite hollow fiber membrane presented higher water permeate flux of413 kgm2 h and a low salt fluxwater flux (JsJw) ratio of 0126 when using distilled

Novel and emerging membranes for water treatment 307

water and 2 M NaCl as feed and draw solution respectively the active layer faced theAL-DS orientation (PRO mode)

Compared to the conventional asymmetric membranes (ie CA-based membranes)made by the non-solvent induced phase inversion TFC membranes made by IP onporous support layers have several advantages such as a higher PWP greater soluterejection factors higher chemical stability and mechanical strength (Han et al2012) In addition TFC membranes have more design flexibility by separately tuningselective skins and sub-layers with the aid of using specific designed substrates TFCmembranes are widely used in RO process separation with high performance espe-cially in desalination and high energy efficiency However these RO TFC membraneshave poor permeate water fluxes when used in FO mainly due to the thick and densersupport layer that results in high ICP effect (Yip et al 2010) In fact the porous sup-port layer acts as a diffusive boundary layer which severely reduces the osmotic pres-sure difference across the active layer (Mc Cutcheon amp Elimelech 2006) Thereforean enhancement of this support layer is essential to minimize the ICP effect It wasdemonstrated that the additional resistance to mass transfer of this boundary layer isproportional to the thickness of the support layer and it is inversely proportional toits porosity (Mc Cutcheon amp Elimelech 2007 Yip et al 2010) Consequently thesupport layer for FO membranes must be as thin as possible with a high porosityand a minimal resistance for osmotically driven water transport across the membrane(Widjojo et al 2011)

It is also believed that the membrane performance limiting effects can be reduced bymodifying the support layer of the FO membranes (Alsvik amp Heuroagg 2013a) Wei et al(2011) synthesized flat sheet TFC-FO membranes based on a PS substrate witha straight finger-like structure under a thin sponge-like skin layer The PA selectivelayers were prepared by IP of trimesoyl chloride (TMC) and N-methyl-2-pyrrolidone (NMP) The obtained FO membranes had relatively small structural pa-rameters (S 670e710 mm) as a result of the thin cross-section (728e761 mm) lowtortuosity and high porosity (77e82) of the membrane substrates In addition thesemembranes had high PWP (115e178 Lm2 h bar) and NaCl rejection factors(934e945) in the RO testing mode Compared to the commercial CTA-basedasymmetric FO membranes (HTI Albany) and the brackish water RO membrane(BW30 Dow FilmTec Minneapolis MN) both prepared TFC membranes exhibitedsuperior FO performance achieving FO water permeate flux from 181 to 205 Lm2 hin the AL-DS orientation and water permeate flux from 953 to 120 Lm2 h in theactive layer facing feed solution (AL-FS) orientation when using 05 M NaCl drawsolution Moreover the TFC-FO membranes achieved high water permeate flux main-taining relatively low JsJw (29$10

4e35$104) as a result of their excellent rejectionlayer selectivity (ie their low salt permeabilitywater permeability ratio)

Tiraferri et al (2011) prepared PA TFC flat sheet membrane with PS support layerby casting different polymer solution concentrations and confirmed that the optimalFO membrane consisted of a mixed structure support layer in which a thin sponge-like layer was formed on top of a highly porous macrovoids structure The authorsconcluded that both the active layer transport properties and the support layer structuralcharacteristics needed to be optimized to fabricate a high-performance FO membrane

308 Advances in Membrane Technologies for Water Treatment

Water permeate fluxes of 25 Lm2 h with a consistently high salt rejection factor(gt955) were produced using 1 M NaCl aqeous solution as a draw solution anddeionized water as feed

To improve the FO membrane performance by reducing and delaying the foulingeffect Tiraferri Kang Giannelis and Elimelech (2012) fabricated a highly hydrophil-ic PA TFC-FO flat sheet membrane by surface functionalization with tailored silica(SiO2) NPs The surface of SiO2 NPs was functionalized by coating with two differentsuper-hydrophilic cationic ligands ((3-aminopropyl)trimethoxysilane and N-trime-thoxysilylpropyl-NNN-trimethylammonium chloride) to produce either quaternaryammonium or amine functional groups which were used to irreversibly bind theNPs to the native carboxylic groups of PA FO membranes Lower adhesion forceswere obtained when using 2000 mgL model organic foulant solution bovine serumalbumin and the hydrophilic surfaces compared to the unmodified PA membranesindicating an increase of membrane fouling resistance

With the purpose to prepare high hydrophilic flat sheet TFC membranes fordesalination by FO with a reduced thickness and a sponge-like structure instead of afinger-like structure Han et al (2012) prepared a super-hydrophilic support using sul-fonated poly(ether ketone) (SPEK) polymer It was observed that the TFC-FO mem-branes with the most hydrophilic support exhibited the lowest membrane thickness afully sponge-like structure morphology and the highest water permeate fluxes 50 Lm2 h and 35 Lm2 h tested under PRO and FO modes respectively when usingdistilled water as feed and 2 M NaCl as draw solution The highest water permeateflux of this type of membranes was 22 Lm2 h when tested under PRO mode with amodel seawater solution (35 wt NaCl) used as feed and 2 M NaCl as draw solutionMoreover a reduced S value of the membrane and ICP effects were observed whenblending a hydrophilic material in the membrane support

The FO performance of TFC-FO membranes was found to be further enhanced ifthe hydrophilicity of the substrates was increased as reported by Wang et al(2012) By blending 3 wt of hydrophilic sulfonated PS and PES into the membranesubstrates the resultant TFC-FO flat sheet membranes showed a water permeate fluxas high as 475 Lm2 h in the PRO mode with a salt permeate flux up to 124 gm2 husing 2 M NaCl as draw solution An enhancement of FO performance can be realizedby either increasing the hydrophilicity of the membrane substrate or fabricating mem-brane substrates with finger-like structures to enhance water transport through themembranes

Widjojo et al (2013) also used a sulfonated polyphenylenesulfone (SPPS) mem-brane as a support to prepare FO membranes Compared to TFC-FO membranesmade of hydrophobic non-sulfonated PPS supports those prepared with the hydrophilicSPPS supports comprising 25 mol of sulfonated monomer 330-di-sodiumdisulfate-440-dichlorodiphenyl sulfone achieved 44-fold increment of water permeate flux upto 54 Lm2 h with 88 gm2 h salt reverse permeate flux in PRO mode using 2 MNaCl as draw solution Surprisingly the newly developed TFC-FOmembranes showeda much smaller difference in water permeate flux between PRO and FO modescompared to previous studies indicating much lower ICP effects particularly at lowdraw solution concentrations (ie 05e2 M NaCl) When tested for seawater

Novel and emerging membranes for water treatment 309

desalination using 35 wt NaCl as feed and 2 M NaCl as a draw solution these mem-branes showed the highest water permeate flux ever reported for PRO process (ie22 Lm2 h)

Zhong et al (2013) also developed TFC-FO hollow fiber membranes using SPPSsupports The obtained water permeate fluxes were 306 and 820 Lm2 h for FOand PRO modes respectively using distilled water as feed and 2 M NaCl as a drawsolution while the salt reverse fluxes were maintained below 127 gm2 h The S ofthese membranes was reduced 45 times when the membrane support was changedfrom a non-sulfonated to a sulfonated one

Sukitpaneenit and Chung (2012) assumed that the existing macrovoids in the mem-brane support were undesirable because of their mechanically weak points whichcould cause membrane failure under continuous vibration and backwashing opera-tions In addition a macrovoid-free hollow fiber with a highly sponge-like structurecould reduce the ICP effects and enhance the water permeate flux In this sense novelhigh performance TFC-FO hollow fiber membranes with a high porous structure andmacrovoid-free were prepared As expected this structure enhanced the mechanicalproperties of the membranes which had an S value in the range 219e261 mm and ahigher permeate flux than the membrane prepared using a support containingmacrovoids (Chou et al 2010)

Wang et al (2010) prepared two types of TFC-FO hollow fibers with an ultrathinlayer PA-based RO-like skin layer on either the outer surface (A-FO with a skin layerthickness of 300 nm) or inner surface (B-FO 600 nm) of a porous PES hollow fibersubstrate It was observed that the B-FO hollow fiber membrane had an S parametercomparable to that of pouch-type HTI or cartridge-type HTI FO flat sheet membranes(Figure 96) The A-FO membrane had less water permeate flux and salt rejection fac-tor than the B-FO membrane which showed a water permeate flux of 322 Lm2 h fora draw solution of 05 M NaCl at 23 C Wang et al (2010) finally suggested that theoptimal FO membrane structure should exhibit a small portion of sponge-like layer in athin and a highly porous substrate

Last year the company HTI announced the production of a new highly durable anddimensionally stable TFC flat sheet membrane (the OsMem FO membrane line)designed by HTI (2013) The new TFC membrane has a high permeability and ahigh rejection factor and it is pH tolerant in the range 20e120 with a permeateflux of 20 Lm2 h in FO mode and 49 Lm2 h in PRO mode when tested using 1 MNaCl draw solution and distilled water as feed solution at 23 C The salt rejection fac-tor was 993 Comparatively HTIrsquos CTA FO membrane (HTI-CTA) has a permeateflux of 9 Lm2 h The tested new membrane has a power rate of 35 Wm2 for PRO at10 C and 10 bar

Various research studies were performed to improve the characteristics of the sup-port of PRO membranes PA-based TFC membranes over a polyacrylonitrile (PAN)support were studied by Zhang Fu and Chung (2013) It was revealed that the me-chanical strength pore structure and hydrophilicity of the support could be tailoredby increasing PAN concentration pre-compressing the substrate and coating withpolydopamine (PDA) By increasing the PAN polymer concentration in the supportbetter mechanical strength smaller and more uniform pore sizes and increased

310 Advances in Membrane Technologies for Water Treatment

hydrophilicity were obtained The resultant TFC membranes in PRO tests showed anincreased burst pressure from05 to 8 bar and a power density from almost 0 to 13 Wm2Much higherwater permeateflux andmechanical stabilitywere achieved after immersingthe TFCmembranes in methanol and ethanol It was proved that the ethanol-treated TFCmembrane could support a hydraulic pressure of 10 bar and exhibited a power density of26 Wm2

High-performance TFC PRO membranes with excellent mechanical strength andpower density were designed for osmotic power generation by Han Zhang et al(2013) These PRO membranes consisted of an aromatic PA selective layer formedby IP on the top of a porous polyimide (Matrimid 5218) microporous membrane sup-port The support layer showed a fully sponge-like structure with a small S and excel-lent mechanical properties while the PA selective layer was chemically modified usingpost-fabrication procedures The membranes not only exhibited an excellent PWP ofabout 10 Lm2 h bar and an outstanding power density of 7e12 Wm2 depending onthe feed and water salinity but they also could withstand a hydraulic pressure of15 bar The obtained superior PRO performance is a combinative result of the robustsupport layer with small S and highly permeable PA active layer with a moderate saltpermeability

(a)

(c) (d)

(b)

Figure 96 Cross-section SEM images of forward osmosis (FO) membranes (a) A-FO hollowfiber at X5000 (b) B-FO hollow fiber at X5000 (c) Cartridge-type HTI flat sheet at X300(d) Pouch-type HTI flat sheet at X300Reprinted from Wang Shi et al (2010) with permission from Elsevier

Novel and emerging membranes for water treatment 311

Thin-film nanocomposite (TFN) membranes were also prepared by incorporatingdifferent amounts of titanium dioxide (TiO2) NPs (ranging from 0 to 090 wt) ina PS substrate to reduce the ICP effect (Emadzadeh et al 2014) The results revealedthat both the hydrophilicity and porosity of the substrate were increased and a largenumber of finger-like macrovoids were formed leading to an enhancement of themembrane PWP The TFN membrane prepared with 060 wt TiO2 NPs (designatedas TFN 060) exhibited the best FO performance tested at AL-FS orientation withdistilled water as feed and 05 M NaCl as a draw solution with no significant changein reverse solute flux (ie a water permeate flux of 1881 Lm2 h which is 97 higherthan that of the TFC membrane prepared without TiO2) The enhancement of the waterpermeate flux was attributed to the decrease of the S (039 mm) mainly due to the for-mation of the finger-like macrovoids throughout the substrate and the reduced tortuos-ity It was also observed that a further increase of TiO2 NPs content to 090 wtincreased the membrane PWP but the FO performance of these membranes wascompromised by the significant increase in the reverse solute permeate flux

Amini et al (2013) used functionalized MWCNTs (F-MWCNTs) to synthesizenovel TFN FO flat sheet membranes Amine F-MWCNTs were used as additive inan aqueous solution of 13-phenylendiamine (MPD) to enhance the FO membrane per-formance Different concentrations of F-MWCNTs (001 005 and 01 wt) wereadded and dispersed in the MPD aqueous solution via sonication for 4 h at 30 C(Figure 97) The PA active layer was formed by IP on the top of a cast PS substrateThe obtained water permeate flux of these membranes (in both AL-FS and AL-DSmodes) and their salt rejection factors were simultaneously improved The highest wa-ter permeate flux was 957 Lm2 h which is nearly 160 greater than that of TFCmembranes These improvements were in accordance with the increase of the rough-ness and hydrophilicity of the TFN membranes when F-MWCNTs were incorporatedin the PA selective layer

Electrospun nanofibrous supports were also used to prepare FO and PRO mem-branes because of their superior void volume fraction (ie porosity) and pore intercon-nectivity which results in reduced ICP effects A novel flat sheet PA compositemembrane supported by a non-woven web of electrospun nanofibers was preparedby Bui et al (2011) This TFC membrane comprises an electrospun polymeric nano-fiber support layer and a PA skin layer formed by in situ polymerization It wasobserved that these membranes exhibited greater water permeate fluxes two to fivetimes higher than those of the commercial HTI-CTA membrane Recently Bui andMc Cutcheon (2013) used different materials to develop hydrophilic nanofibrous sup-ports by electrospinning different blends of CA at different ratios and PAN(Figure 98) In this study PA selective layer was formed on the PANCA nanofibroussupports by IP between MPD and TMC The prepared membranes exhibited excellentpermselectivity a reduced resistance to mass transfer low S and high water perme-abilities two to three times greater than HTI-CA membranes (2036 Lm2 h bar forPAN nanofibrous supports and 0683 Lm2 h bar for HTI-CA membranes)

Hoover et al (2013) prepared TFC membranes composed of an electrospun tere-phthalate (PET) nanofibrous support a PS phase inversion microporous layer and aPA selective layer formed by IP The obtained PWP was 113 Lm2 h bar the salt

312 Advances in Membrane Technologies for Water Treatment

(a)

(c) (d)

(b)

Figure 97 Conceptual model of amine functionalized MWCNTs in 13-phenylendiamine(MPD) solution used to prepare novel thin-film nanocomposite (TFN) membranes for forwardosmosis process SEM micrographs displaying the top surface and cross-section of conventionalthin-film composite (TFC) membranes (a and c) and TFNmembranes with 001 wtvol (b andd) respectivelyReprinted from Amini et al (2013) with permission from Elsevier

Novel and emerging membranes for water treatment 313

permeability was 023 Lm2 h and the S value was 0651 mm It was detected that theuse of electrospun fibers in the support layer enhanced the membrane resistance todelamination at high cross-flow velocities

It is worth noting that most supports used for the fabrication of FO membranes arehydrophilic mainly because of the concerns of higher fouling tendency of the morehydrophobic supports However hydrophobic materials such as polyvinylidene fluo-ride (PVDF) normally possess strong chemical resistance which could extend the useof FO process to some harsh environments with chemical wastes such as aromatic hy-drocarbons ketones ethers and esters Tian et al (2013) used electrospun PVDF

(a) (b)

(d)

(e)

(c)

Figure 98 SEM images of thin-film composite membranes supported on a polyacrylonitrile(PAN) nanofibrous support Cross-sectional (a) X1500 and (b) X2500 Top surface (c) X10 000and (e) X40 000 Bottom surface (d) X20 000 and zoom-in image showing the pores that wereformed on the bottom side of the polyamide (PA) selective layer when a fiber was removed fromthis layerReprinted with permission from Bui and Mc Cutcheon (2013) Copyright 2012 AmericanChemical Society

314 Advances in Membrane Technologies for Water Treatment

nanofibrous supports followed by IP to prepare high-performance TFC-FO mem-branes The S value of the TFC membrane was found to be as low as 0315 mm whichis better than most of the FO membranes reported in the literature As a result a waterpermeate flux of 304 Lm2 h was obtained when using 1 M NaCl as a draw solutionand distilled water as feed in ALeDS orientation

LbL assembly method was used for the fabrication of high-FO-performance mem-branes because of the formed ultrathin layers For instance LbL method was used toproduce ultrathin barrier layers assembled by oppositely charged polyelectrolytes(Pardeshi amp Mungray 2014) NaOH treated PAN membrane substrate (PAN-OH)is immersed in a polycation solution (1 gL PAH05 M NaCl solution) and a poly-anion solution (1 gL PSS05 M NaCl solution) following an alternative sequenceThis type of membranes exhibits high PWP and good retention against divalentions which makes them suitable candidates for FO membranes In addition LbLpolyelectrolyte layers generally have high solvent resistance (except in some ternarysolvent mixtures) and high thermal stability (eg no deterioration under 200 Cannealing temperature) (Qi et al 2011)

By using the LbL assembly method Qi et al (2011) synthesized a novel NF-likeFO membrane with good magnesium chloride retention factors The membrane sub-strate was tailored (high porosity finger-like pores thin cross-section and high hydro-philicity) to achieve a small S of 05 mm It was observed that the increased number ofpolyelectrolyte layers from one to six improved the selectivity but reduced the PWPSevere solute reverse transport was also detected for the ALeDS orientation Incontrast the ALeFS orientation showed remarkable FO performance (water permeatefluxes of 15 20 and 28 Lm2 h at 01 05 and 10 M MgCl2 respectively for themembrane 3LbL using distilled water as feed solution) superior to other NF-likeFO membranes reported in the literature (Setiawan et al 2011 Su et al 2010Wang et al 2007 Wang Yang et al 2009 Yang et al 2009) (see Table 91)

With the aim to investigate and compare the FO performance and fouling behaviorof double-skinned and single-skinned FO membranes Qi et al (2012) synthesizednovel membranes following the LbL assembly method as shown in Figure 99 TheLbL rejection skin on the top surface was formed by soaking only the top substratein PAH solution and then in PSS solution Three polyelectrolyte layers were depositedfor the top rejection skin The bottom LbL rejection skin was similarly prepared byexposing only the bottom surface of the substrate during the soaking steps and theeffects of the number of polyelectrolyte layers (from 0 to 3) on the FO membrane per-formance were studied The results revealed that both the top and bottom skins contrib-uted to the overall water resistance of the double-skinned LbL membranes Howeverthe overall salt rejection factor was mainly determined by the top skin layer Thedouble-skinned LbL FO membranes achieved excellent FO water permeate fluxesup to 501 and 1061 Lm2 h when the bottom skin layer was faced the draw solution(DS-PROmode) or the feed solution (FSeFOmode) respectively and low JsJw ratios(0405 and 0487 gL for PRO and FO mode respectively) when using 2 M MgCl2 asdraw solution at 23 C and distilled water as feed Furthermore the double-skinnedLbL membranes demonstrated much better antifouling performance compared to thesingle-skinned counterpart

Novel and emerging membranes for water treatment 315

(1) Formation of top selective layer

PAH polycation PSS polyanion

Top surface of PAN

Bottom surface of PAN

Negative charged PAN substrate

Step 1b coating substrate top surface with PSS

Step 1a coating substrate top surface with PAH

Step 2b coating substrate bottom surface with PSS

Steps 2a and 2b can be repeated to form multiple PAHPSS layers on the bottom surface ifneeded

Step 2a coating substrate bottom surface with PAH

Steps 1a and 1b can be repeated to form multiple PAHPSS layers on the surface if needed

(2) Formation of bottom selective layer

Figure 99 Conceptual illustrations of double-skinned LbL membrane fabrication and SEMcross-section of the PAN-OH supports of a single-skinned forward osmosis (FO) membrane(1 a) and a double-skinned FO membrane (2 b)Figure 99a reprinted with permission from Qi et al (2011) Copyright 2011 American ChemicalSociety and Figure 99b reprinted from Qi et al (2012) with permission from Elsevier

316 Advances in Membrane Technologies for Water Treatment

To reduce biological fouling and enhance the performance of the membranes inFO applications Liu et al (2013) added Ag NPs to the top surface of the membranesupports The LbL assembly method was used to fabricate novel Ag nanocomposite(LbL-Ag) NF and FO membranes It was observed that the surface roughnessincreased with the amount of Ag NPs The incorporation of Ag NPs also increasedthe hydrophilicity of the membrane surface (ie the contact angle decreased from691 to 513) The experimental results indicated that the small amount of AgNPs incorporated in the LbL-Ag FO membranes had little effect on the membranestructure and thus maintaining their original separation properties Around001 wt was chosen as the optimal Ag NPs concentration to obtain LbL-Ag mem-branes with good FO performance (MgCl2 rejection factor of 95 and waterpermeate fluxes of 422 and 178 Lm2 h in PRO and FO mode respectively using10 mM NaCl as feed and 05 M MgCl2 as draw solution at 23 C) MoreoverLbL-Ag membranes exhibited excellent antibacterial properties against Gram-positive (Bacillus subtilis) and Gram-negative bacteria (E coli)

Pardeshi and Mungray (2014) used polymer nanocomposites to tailor membranesupport and develop FO LbL self-assembled membranes with appropriate transportcharacteristics Nanocomposite of PVA lithium chloride (LiCl) and montmoril-lonite clay (surface modified with 25e30 wt methyl dihydroxyethyl hydrogenat-ed tallow ammonium MMt-TA) were used to synthesize the substrate of the FOmembrane (PVAMMt-TALiCl nanocomposite substrate) This type of substratesshowed a spongy structure a high porosity (81) an average thickness of about2643 mm and a high hydrophilicity The active layer of the membrane was pre-pared by LbL assembly of polyelectrolytes (CS as a polycation and polyacrylicacid as a polyanion) Three layers of polyelectrolyte were applied on PVAMMt-TALiCl substrate The resultant membranes (PVAMMt-TALiCl 3LbL) had athin sponge-like skin layer (about 3 mm) which was responsible for the observedlow reverse salt diffusion (0281 and 0051 gm2 h for PRO and FO mode respec-tively) The high hydrophilic nature of the PVAMMt-TALiCl support enhancedthe water permeate flux up to 3765 Lm2 h (PRO mode) and 255 Lm2 h (FOmode) when distilled water was used as feed and 2 M NaCl solution as drawsolution at 26 C

You et al (2013) developed a thin-film inorganic (TFI) membrane by LbL depo-sition of microporous SiO2 xerogels immobilized onto a stainless steel mesh supportIt was observed that the quasi-symmetry TFI microporous structure of the SiO2 mem-brane was responsible for the low ICP effect enhancing the water permeate flux dur-ing the FO process The TFI membrane showed a good NaCl rejection factor of 92and high water permeate fluxes of 603 Lm2 h and 598 Lm2 h for PRO and FOmode respectively when using distilled water as feed and 2 M NaCl solution asdraw solution at ambient temperature Particularly by increasing the temperatureto 70 C the water permeate flux was increased to 8502 Lm2 h at pH 6 It wasclaimed that the ability of the TFI membrane to sustain FO process without any curl-ing wrinkling cracking deformation or dissolution under harsh conditions also sug-gested a superior mechanical strength and thermal and chemical stability of thesemembranes over polymeric FO membranes

Novel and emerging membranes for water treatment 317

94 Conclusions

This chapter focuses on water treatment by ED and FO with special attention to thealternative technologies of emerging interests RED and PRO used for energy generationthrough a salinity-gradient difference Although membranes typically used for ED andRED processes are IEMs (AEMs and CEMs) BPMs are also reviewed due to their ad-vantages (eg separation of monovalent and divalent ions antideposition antifoulingwater dissociation into OHe and Hthorneions increase of reusability and recyclability ofwaste through chemical production low initial cost etc) Most of the research studieshave been focused on the improvement of the performance of these membranesincluding their physicochemical and electrochemical properties to optimize both EDand RED processes Various membrane-based polymers (SPES PS PVC PVASPEEK PECH etc) have been used and different membrane modification techniqueshave been applied such as thermal and chemical crosslinking quaternization sulfona-tion photo-induced covalent immobilization in situ polymerization addition of NPs orinorganic fillers as functional groups or additives etc Not only is the improvement ofthe membrane properties necessary to achieve high ED and RED performances butit is also important to consider the scale-up and design of the EDRED unit and theoptimization of the electrode systems

For the preparation of FO and PRO membranes different polymers were usedincluding CA CTA PS PES PBI PA PAI PVP PAN and PET Three differentmethods have been adopted to prepare polymeric FOPRO membranes (non-solventphase inversion IP on porous substrates and the LbL deposition) IP is the most-used technique TFC membrane structure either in flat sheet or hollow fiberconfiguration exhibits high water permeability solute rejection factor chemical stabilityand mechanical strength and good design flexibility by separately tuning the selectiveskins and sub-layers

Improved membrane characteristics and performance were achieved using differentmodification techniques such as chemical or thermal post-treatment chemical cross-linking surface functionalization via coating pre-compressing and coating the substrateincorporating different amounts of additives or fillers etc

95 Future trends

Membrane technologies experienced significant development during the last decadesdriven by available advanced materials novel technologies changes of environmentalregulations increasing demand of water supply and sanitation etc The availability ofnovel tailored membranes with specific properties and new membrane processes offersimportant tools for the design of alternative production systems appropriate for a sus-tainable growth

Researchers have made sufficient progress in the development of new membranematerials modifying the membrane surface to improve their performance detectingnew application fields and emerging membrane technologies etc Furthermore theintegration of different membrane processes was also explored because it potentially

318 Advances in Membrane Technologies for Water Treatment

allows the possibility to redesign important industrial processes with enhanced benefitsin terms of product quality quantity energy efficiency and cost

Some technologies especially the emerging ones are still far from fulfilling all thedeposited expectations on them However they are still in continuous improvementtrying to overcome the many challenges and barriers to extend their field of industrialapplications

List of acronyms

g-MPS g-methacryloxypropyl trimethoxy silane4-VP 4-vinylpyridineA1100 (3-aminopropyl) triethoxysilaneAC Activated carbonAEL Anion exchange layerAEM Anion exchange membraneAg SilverAL-DS Active layer facing draw solutionAL-FS Active layer facing feed solutionBPM Bipolar membraneCA Cellulose acetateCEL Cation exchange layerCEM Cation exchange membraneCS ChitosanCTA Cellulose triacetateED ElectrodialysisEDR Electrodialysis reversalEO Engineered OsmosisFe3O4 Iron oxideFeCl3 Ferric chlorideF-MWCNTs Functionalized MWCNTsFO Forward osmosisHTI Hydration Technology InnovationsICP Internal concentration polarizationIEMs Ion-exchange membranesIP Interfacial polymerizationLbL Layer-by-layerLiCl Lithium chlorideMMt-TA Methyl dihydroxyethyl hydrogenated tallow ammoniumMPD 13-phenylendiamineMWCNTs Multiwalled carbon nanotubesNF NanofiltrationNMP N-methyl-2-pyrrolidoneNPs NanoparticlesPA PolyamidePAH Poly(allylamine hydrochloride)PAI Poly(amide-imide)PAN PolyacrylonitrilePANI Polyaniline

Novel and emerging membranes for water treatment 319

PBI PolybenzimidazolePDA PolydopaminePECH PolyepichlorohydrinPEI PolyethyleneiminePES PolyethersulfonePET TerephthalatePRO Pressure retarded osmosisPS PolysulfonePSS Poly(sodium 4-styrene sulfonate)PVA Polyvinyl alcoholPVC PolyvinylchloridePVDF Polyvinylidene fluoridePVP PolyvinylpyrrolidoneRED Reverse electrodialysisRO Reverse osmosisSDBS Sodium dodecylbenzene sulfonateSGP Salinity gradient powerSiO2 SilicaSPEEK Sulfonated polyetheretherketoneSPEK Sulfonated poly(ether ketone)SPES Sulfonated poly(ether sulfone)SPPS Sulfonated polyphenylenesulfoneTFC Thin-film compositeTFI Thin-film inorganicTFN Thin-film nanocompositeTiO2 Titanium dioxideTMC Trimesoyl chlorideUF UltrafiltrationVBC Vinylbenzyl chlorideZrT Zirconium tri-ethylene tetra-amine

List of symbols

JM2D Bivalent cation permeate fluxJCu2D Cu2thorn permeate fluxJS Saltsolute permeate fluxJW Water permeate fluxPWP Pure water permeabilityS Structural parameter

References

Achilli A amp Childress A E (2010) Pressure retarded osmosis From the vision of SidneyLoeb to the first prototype installationmdashreview Desalination 261 205e211

Alsvik I amp Heuroagg M B (2013a) Pressure retarded osmosis and forward osmosis membranesMaterials and methods Polymers 5 303e327

320 Advances in Membrane Technologies for Water Treatment

Alsvik I L amp Heuroagg M B (2013b) Preparation of thin film composite membranes withpolyamide film on hydrophilic supports Journal of Membrane Science 428 225e231

Amini M Jahanshahi M amp Rahimpour A (2013) Synthesis of novel thin film nano-composite (TFN) forward osmosis membranes using functionalized multi-walled carbonnanotubes Journal of Membrane Science 435 233e241

Arena J T Mc Closkey B Freeman B D amp Mc Cutcheon J R (2011) Surface modi-fication of thin film composite membrane support layers with polydopamine Enablinguse of reverse osmosis membranes in pressure retarded osmosis Journal of MembraneScience 375 55e62

Brauns E (2009) Salinity gradient power by reverse electrodialysis Effect of modelparameters on electrical power output Desalination 237 378e391

Bui N N Lind M L Hoek E M V amp Mc Cutcheon J R (2011) Electrospun nanofibersupported thin film composite membranes for engineered osmosis Journal of MembraneScience 385e386 10e19

Bui N N amp Mc Cutcheon J R (2013) Hydrophilic nanofibers as new supports for thin filmcomposite membranes for engineered osmosis Environmental Science and Technology47 1761e1769

Burheim O S Seland F Pharoah J G amp Kjelstrup S (2012) Improved electrode systemsfor reverse electro-dialysis and electro-dialysis Desalination 285 147e152

Cadotte J E (1981) Interfacially synthesized reverse osmosis membrane US Patent 4277344Cath T Childress A amp Elimelech M (2006) Forward osmosis Principles applications and

recent developments Journal of Membrane Science 281 70e87Cornelissen E R Harmsen D de Korte K F Ruiken C J Qin J J Oo H et al (2008)

Membrane fouling and process performance of forward osmosis membranes on activatedsludge Journal of Membrane Science 319 158e168

Chakrabarty T Rajesh A M Jasti A Thakur A K Singh A K Prakash S et al(2011) Stable ion-exchange membranes for water desalination by electrodialysisDesalination 282 2e8

Chakrabarty T Shah B Srivastava N Shahi V K amp Chudasamab U (2013) Zirconiumtri-ethylene tetra-amine ligand-chelator complex based cross-linked membrane forselective recovery of Cu2thorn by electrodialysis Journal of Membrane Science 428462e469

Cho Y H Han J Han S Guiver M D amp Park H B (2013) Polyamide thin-filmcomposite membranes based on carboxylated polysulfone microporous support mem-branes for forward osmosis Journal of Membrane Science 445 220e227

Chou S Shi L Wang R Tang C Y Qiu C amp Fane A G (2010) Characteristics andpotential applications of a novel forward osmosis hollow fiber membrane Desalination261 365e372

Chou S Wang R Shi L She Q Tang C amp Fane A G (2012) Thin-film compositehollow fiber membranes for pressure retarded osmosis (PRO) process with high powerdensity Journal of Membrane Science 389 25e33

Emadzadeh D Lau W J Matsuura T Ismail A F amp Rahbari-Sisakht M (2014)Synthesis and characterization of thin film nanocomposite forward osmosis membranewith hydrophilic nanocomposite support to reduce internal concentration polarizationJournal of Membrane Science 449 74e85

Fang W Wang R Chou S Setiawan L amp Fane A G (2012) Composite forwardosmosis hollow fiber membranes Integration of RO- and NF-like selective layers toenhance membrane properties of anti-scaling and anti-internal concentration polarizationJournal of Membrane Science 394e395 140e150

Novel and emerging membranes for water treatment 321

Geurouler E Elizen R Vermaas D A Saakes M amp Nijmeijer K (2013) Performance-determining membrane properties in reverse electrodialysis Journal of Membrane Science446 266e276

HTI (2013) HTIrsquos new thin film forward osmosis membrane in production Retrieved fromwwwhtiwatercom

Han G Chung T S Toriida M amp Tamai S (2012) Thin-film composite forward osmosismembranes with novel hydrophilic supports for desalination Journal of MembraneScience 423-424 543e555

Han G Wang P amp Chung T S (2013) Highly robust thin-film composite pressureretarded osmosis (PRO) hollow fiber membranes with high power densities for renewablesalinity-gradient energy generation Environmental Science and Technology 478070e8077

Han G Zhang S Li X amp Chung T S (2013) High performance thin film compositepressure retarded osmosis (PRO) membranes for renewable salinity-gradient energy gen-eration Journal of Membrane Science 440 108e121

Herron J (2008) Asymmetric forward osmosis membranes US Patent 7445712 B2Hong J G Zhang W Luo J amp Chen Y (2013) Modeling of power generation from the

mixing of simulated saline and freshwater with a reverse electrodialysis system The effectof monovalent and multivalent ions Applied Energy 110 244e251

Hoover L A Schiffman J D amp Elimelech M (2013) Nanofibers in thin-film compositemembrane support layers Enabling expanded application of forward and pressure retardedosmosis Desalination 308 73e81

Hosseini S M Askari M Koranian P Madaeni S S amp Moghadassia A R (2014)Fabrication and electrochemical characterization of PVC based electrodialysis heteroge-neous ion exchange membranes filled with FE3O4 nanoparticules Journal of Industrialand Engineering Chemistry 20 2510e2520

Hosseini S M Koranian P Gholami A Madaeni S S Moghadassi A R Sakinejad Pet al (2013) Fabrication of mixed matrix heterogeneous ion exchange membrane bymultiwalled carbon nanotubes Electrochemical characterization and transport properties ofmono and bivalent cations Desalination 329 62e67

Huang L Bui N N Meyering M T Hamlin T J amp McCutcheon J R (2013) Novelhydrophilic nylon 66 microfiltration membrane supported thin film composite membranesfor engineered osmosis Journal of Membrane Science 437 141e149

Kariduraganavar M Y Nagarale R K Kittur A A amp Kulkarni S S (2006) Ion-exchangemembranes Preparative methods for electrodialysis and fuel cell applications Desalina-tion 197 225e246

Kumar M Khan M A Alothman Z A amp Siddiqui M R (2013) Polyaniline modifiedorganiceinorganic hybrid cation-exchange membranes for the separation of monovalentand multivalent ions Desalination 325 95e103

Li X Wang K Y Helmer B amp Chung T S (2012) Thin-film composite membranes andformation mechanism of thin-film layers on hydrophilic cellulose acetate propionate sub-strates for forward osmosis processes Industrial and Engineering Chemistry Research 5110039e10050

Liu X Qi S Li Y Yang L Cao B amp Tang C Y (2013) Synthesis and characterization ofnovel antibacterial silver nanocomposite nanofiltration and forward osmosis membranesbased on layer-by-layer assembly Water Research 47 3081e3092

Loeb S amp Sourirajan S (1963) Sea water demineralization by means of an osmoticmembrane In A I Chemistry (Ed) Saline water conversion-II American ChemicalSociety

322 Advances in Membrane Technologies for Water Treatment

Mc Cutcheon J R amp Elimelech M (2006) Influence of concentrative and dilutive internalconcentration polarization on flux behavior in forward osmosis Journal of MembraneScience 284 237e247

Mc Cutcheon J R amp Elimelech M (2007) Modeling water flux in forward osmosis Impli-cations for improved membrane design AIChE Journal 53 1736e1744

Mc Cutcheon J R amp Elimelech M (2008) Influence of membrane support layer hydro-phobicity on water flux in osmotically driven membrane processes Journal of MembraneScience 318 458e466

Mc Cutcheon J R Mc Ginnis R L amp Elimelech M (2006) Desalination by ammo-niaecarbon dioxide forward osmosis Influence of draw and feed solution concentrationson process performance Journal of Membrane Science 278 114e123

Miller J E amp Evans L R (2006) Forward osmosis A new approach to water purificationand desalination United States of America Sandia National Laboratories

Mulyati S Takagi R Fujii A Ohmukai Y Maruyama T amp Matsuyama H (2012)Improvement of the antifouling potential of an anion exchange membrane by surfacemodification with a polyelectrolyte for an electrodialysis process Journal of MembraneScience 417-418 137e143

Mulyati S Takagi R Fujii A Ohmukai Y amp Matsuyama H (2013) Simultaneousimprovement of the monovalent anion selectivity and antifouling properties of an anionexchange membrane in an electrodialysis process using polyelectrolyte multilayer depo-sition Journal of Membrane Science 431 113e120

Nguyen T P N Yun E T Kim I C amp Kwon Y N (2013) Preparation of cellulosetriacetatecellulose acetate (CTACA)-based membranes for forward osmosis Journal ofMembrane Science 433 49e59

Pardeshi P ampMungray A A (2014) Synthesis characterization and application of novel highflux FO membrane by layer-by layer self-assembled polyelectrolyte Journal of MembraneScience 453 202e211

Post J W Hamelers H V M amp Buisman C J N (2008) Energy recovery from controlledmixing salt and fresh water with a reverse electrodialysis system Environmental Scienceand Technology 42 5785e5790

Post J W Veerman J Hamelers H V M Euverink G J W Metz S J Nymeijer K et al(2007) Salinity-gradient power Evaluation of pressure-retarded osmosis and reverseelectrodialysis Journal of Membrane Science 288 218e230

Qi S Qiu C Q amp Tang C Y (2011) Synthesis and characterization of novel forwardosmosis membranes based on layer-by-layer assembly Environmental Science andTechnology 45 5201e5208

Qi S Qiu C Q Zhao Y amp Tang C Y (2012) Double-skinned forward osmosis membranesbased on layer-by-layer assemblymdashFO performance and fouling behavior Journal ofMembrane Science 405-406 20e29

Qiu C Setiawan L Wang R Tang C Y amp Fane A G (2012) High performance flat sheetforward osmosis membrane with an NF-like selective layer on a woven fabric embeddedsubstrate Desalination 287 266e270

Setiawan L Wang R Li K amp Fane A G (2011) Fabrication of novel poly(amideeimide)forward osmosis hollow fiber membranes with a positively charged nanofiltration-likeselective layer Journal of Membrane Science 369 196e205

Setiawan L Wang R Shi L Li K amp Fane A G (2012) Novel dual-layer hollow fibermembranes applied for forward osmosis process Journal of Membrane Science 421-422238e246

Novel and emerging membranes for water treatment 323

Sivertsen E Holt T Thelin W amp Brekke G (2013) Pressure retarded osmosis efficiency fordifferent hollow fibre membrane module flow configurations Desalination 312 107e123

Song X Liu Z amp Sun D D (2011) Nano gives the answer breaking the bottleneck ofinternal concentration polarization with a nanofiber composite forward osmosis membranefor a high water production rate Advanced Materials 23 3256e3260

Su J amp Chung T S (2011) Sublayer structure and reflection coefficient and their effects onconcentration polarization and membrane performance in FO processes Journal ofMembrane Science 376 214e224

Su J Yang Q Teo J F amp Chung T S (2010) Cellulose acetate nanofiltration hollow fibermembranes for forward osmosis processes Journal of Membrane Science 355 36e44

Sukitpaneenit P amp Chung T S (2012) High performance thin-film composite forwardosmosis hollow fiber membranes with macrovoid-free and highly porous structure forsustainable water production Environmental Science and Technology 46 7358e7365

Tian M Qiu C Liao Y Chou S amp Wang R (2013) Preparation of polyamide thin filmcomposite forward osmosis membranes using electrospun polyvinylidene fluoride (PVDF)nanofibers as substrates Separation and Purification Technology 118 727e736

Tiraferri A Kang Y Giannelis E P amp Elimelech M (2012) Highly hydrophilic thin-filmcomposite forward osmosis membranes functionalized with surface-tailored nanoparticlesACS Applied Materials and Interfaces 4 5044e5053

Tiraferri A Yip N Y Phillip W A Schiffman J D amp Elimelech M (2011) Relatingperformance of thin-film composite forward osmosis membranes to support layer formationand structure Journal of Membrane Science 367 340e352

Valero F amp Arbos R (2010) Desalination of brackish river water using electrodialysisreversal (EDR) Desalination 253 170e174

Venugopal K amp Dharmalingam S (2012) Desalination efficiency of a novel bipolar mem-brane based on functionalized polysulfone Desalination 296 37e45

Vermaas D A Saakes M amp Nijmeijer K (2011) Power generation using profiled mem-branes in reverse electrodialysis Journal of Membrane Science 385-386 234e242

Wang A Peng S Wu Y Huang C amp Xu T (2010) A hybrid bipolar membrane Journalof Membrane Science 365 269e275

Wang K Y Chung T S amp Amy G (2012) Developing thin-film-composite forwardosmosis membranes on the PESSPSf substrate through interfacial polymerization AIChEJournal 58 770e781

Wang K Y Chung T S amp Qin J J (2007) Polybenzimidazole (PBI) nanofiltration hollowfiber membranes applied in forward osmosis process Journal of Membrane Science 3006e12

Wang K Y Ong R C amp Chung T S (2010) Double-skinned forward osmosis membranesfor reducing internal concentration polarization within the porous sublayer Industrial andEngineering Chemistry Research 49 4824e4831

Wang K Y Yang Q Chung T S amp Rajagopalan R (2009) Enhanced forward osmosisfrom chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membraneswith a thin wall Chemical Engineering Science 64 1577e1584

Wang M Jia Y X Yao T T amp Wang K K (2013) The endowment of monovalentselectivity to cation exchange membrane by photo-induced covalent immobilization andself-crosslinking of chitosan Journal of Membrane Science 442 39e47

Wang R Shi L Tang C Y Chou S Qiu C amp Fane A G (2010) Characterization ofnovel forward osmosis hollow fiber membranes Journal of Membrane Science 355158e167

324 Advances in Membrane Technologies for Water Treatment

Wang Y Goh S H Chung T S amp Na P (2009) Polyamide-imidepolyetherimidedual-layer hollow fiber membranes for pervaporation dehydration of C1eC4 alcoholsJournal of Membrane Science 326 222e233

Wei J Qiu C Tang C Y Wang R amp Fane A G (2011) Synthesis and characterization offlat-sheet thin film composite forward osmosis membranes Journal of Membrane Science372 292e302

Widjojo N Chung T S Weber M Maletzko C amp Warzelhan V (2011) The role ofsulphonated polymer and macrovoid-free structure in the support layer for thin-filmcomposite (TFC) forward osmosis (FO) membranes Journal of Membrane Science 383214e223

Widjojo N Chung T S Weber M Maletzko C amp Warzelhan V (2013) A sulfonatedpolyphenylenesulfone (sPPSU) as the supporting substrate in thin film composite (TFC)membranes with enhanced performance for forward osmosis (FO) Chemical EngineeringJournal 220 15e23

Xu T (2005) Ion exchange membranes state of their development and perspective Journal ofMembrane Science 263 1e29

Xu Y Peng X Tang C Y Fu Q S amp Nie S (2010) Effect of draw solution concentrationand operating conditions on forward osmosis and pressure retarded osmosis performance ina spiral wound module Journal of Membrane Science 348 298e309

Yang Q Wang K Y amp Chung T S (2009) Dual-layer hollow fibers with enhanced flux asnovel forward osmosis membranes for water production Environmental Science andTechnology 43 2800e2805

Yip N Y Tiraferri A Phillip W A Schiffman J D amp Elimelech M (2010) High per-formance thin-film composite forward osmosis membrane Environmental Science andTechnology 44 3812e3818

You S Tang C Yu C Wang X Zhang J Han J et al (2013) Forward osmosis with anovel thin-film inorganic membrane Environmental Science and Technology 478733e8742

Yu Y Seo S Kim I C amp Lee S (2011) Nanoporous polyethersulfone (PES) membranewith enhanced flux applied in forward osmosis process Journal of Membrane Science 37563e68

Zendehnam A Robatmili N Hosseini S M Arabzadegan M amp Madaenic S S (2013)Fabrication of novel (acrylonitrile butadiene styrene-activated carbon-silver nano-particules) heterogeneous anion exchange membrane Physico-chemical and antibacterialcharacteristics Journal of the Taiwan Institute of Chemical Engineering 44 670e677

Zhang S Fu F amp Chung T S (2013) Substrate modifications and alcohol treatment onthin film composite membranes for osmotic power Chemical Engineering Science 8740e50

Zhang S Wang K Y Chung T S Chen H Jean Y C amp Amy G (2010)Well-constructed cellulose acetate membranes for forward osmosis Minimized internalconcentration polarization with an ultra-thin selective layer Journal of MembraneScience 360 522e535

Zhao S Zou L Tang C Y amp Mulcahy D (2012) Recent developments in forwardosmosis Opportunities and challenges Journal of Membrane Science 396 1e21

Zhong P Fu X Chung T S Weber M amp Maletzko C (2013) Development of thin-filmcomposite forward osmosis hollow fiber membranes using direct sulfonatedpolyphenylenesulfone (sPPSU) as membrane substrates Environmental Science and Tech-nology 47 7430e7436

Novel and emerging membranes for water treatment 325

Planning and designof membrane systems forwater treatment

10VS FrenkelSan Francisco CA USA

101 Introduction

Population and industry growth and limits to the current water supply are driving theneed to find new sources of water develop the more sustainable use of current watersources and improve water reuse Membrane technologies are playing a vital role inall these areas in increasing the available water supply portfolio for communitiesindustry or agricultural users As a confirmation membrane projects are demon-strating significant growth of membrane technology applications by increasing capac-ities of new membrane projects and upgrading existing facilities with membranesMembrane technologies have entered every corner of water and wastewater treatmentsuch as municipal and industrial water advanced wastewater treatment and reuseand sea and brackish water desalination The major reasons are the unique featuresthat membrane technologies can provide for solving water shortages which is in closeassociation with global climate change This trend accelerated the growth of themembrane market in past years and fuels the expected growth for the future

Because membrane technologies are separation technologies the simplified sche-matic of the membrane separation process is shown using the example of the reverseosmosis (RO) membrane process in Figure 101

The membrane process comprises three major streams

bull Feedbull Permeate (product water)bull Concentrate (reject or brine)

The mass balance for the entire system can be represented as follows

Qf Cf frac14 Qc Cc thorn Qp Cp

in which

bull Qf - feed flow (gpm or m3hr)bull Cf - salt concentration in feed water (mgL or ppm)bull Qc - concentrate flow (gpm or m3hr)bull Cc - salt concentration in concetrate (mgL or ppm)bull Qp - product flow (gpm or m3hr)bull Cp - salt concentration in product water (mgL or ppm)

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400010-1Copyright copy 2015 Elsevier Ltd All rights reserved

The membrane technology mass and hydraulic balance is a cross-check that allowsone to perform validation of the process integrity

102 Membrane types and configurations forwater treatment

Membranes are represented by four major membrane types categorized by the rate oftreatment and are in commercial use at present (Design of Municipal Waste 2009Frenkel 2011)

bull Microfiltration (MF) - screens particles from 01 to 05 mmbull Ultrafiltration (UF) - screens particles from 0005 to 005 mmbull Nanofiltration (NF) - screens particles from 00005 to 0001 mmbull RO - ranging molecular size down to 10 MWCO

Figure 102 demonstrates the relative size of different membrane types compared tothe conventional treatment processes and constituents of concern when treating water

MF and UF membranes were commercialized for drinking water treatment justabout 15 years ago Because they provide significant technical benefits and havebecome cost-competitive membrane technologies are rapidly replacing traditionalprocesses verified by the centuries

The differences in membrane shape and the type of membrane process drivingforces can be categorized as shown in Figure 103

Membrane shape type Spiral wound hollow fiber flat sheetMembrane type depending on driven pressure

bull Pressure-driven (low-pressure MF UF and high-pressure NF and RO)bull Immersed vacuum driven (low-pressure MF UF only)

The electrical current can drive membrane treatment as well and it is used inelectrodialysis (ED) electrodialysis reversal (EDR) and electrodeionization (EDI)membrane treatment processes

Membrane

Concentrate

Reject

Brine

Feed

Raw water

Qf cf

QC Cc

Qp Cp

Recovery = QpQf

Rejection = CcCf

Permeate

Treated water

Figure 101 Simplified diagram of reverse osmosis (RO) process major RO streams

330 Advances in Membrane Technologies for Water Treatment

Figure 102 Membranes and water treatment processesCourtesy of Val S Frenkel

Planning

anddesign

ofmem

branesystem

sfor

water

treatment

331

103 Low- and high-pressure membranes

As shown in Figure 102 membranes are broken down to two major categories

bull Low-pressure membranes represented by MF and UF membranes andbull High-pressure membranes represented by NF and RO membranes

One of the key difference between high- and low-pressure membranes is that thehigh-pressure membranes were developed to remove dissolved matter from the waterwhile they are not tolerant of suspended and colloidal matter The low-pressure mem-branes are opposite having high tolerance and high efficiency in the removal of sus-pended and organic matter while dissolved matter passes through the membranes Anumber of techniques were developed for numerous applications to convert certain dis-solved ions to the solid phase followed by removal using low-pressure membranesDue to the different treatment properties between low- and high-pressure membranesthe integrated membrane systems (IMS) found a niche in numerous applications whenhigh-pressure membranes are following low-pressure membranes in the treatmenttrain using low-pressure membranes as a pretreatment for high-pressure membranes

104 Low-pressure membrane applications

Low-pressure membranes are represented by MF and UF membranes

1041 Microfiltration and ultrafiltration

Membrane technologies include MF and UF membranes These membranes canremove particles and colloidal matter and are often selected over conventionalgranular-media filters based on their high removal efficiencies for Giardia cysts Cryp-tosporidium oocysts bacteria and viruses and the consistently high-quality water

Flat

Membrane type depending on driven power1 Pressure driven (MF UF NF and RO)2 Vacuum driven (MF and UF only)3 High voltage current (EDR and EDI)4 Osmotic power (FO and PRO)

Hollow fiber Spiral wound

Figure 103 Membranes shape type configuration and driven forces

332 Advances in Membrane Technologies for Water Treatment

produced by membranes independent from the source water quality variation andoperator skill (Frenkel amp Mourato 1998)

Membrane separation is a well-developed technology that is becoming a standardpractice in water treatment Membrane separation provides a physical barrier to path-ogens and can produce high-quality safe drinking water at a reasonable cost

1042 Microfiltration

MF is the ldquoloosestrdquo membrane and it screens particles in the range 01e05 mmremoving bacteria protozoan pathogens (Cryptosporidium oocysts Giardia cystsand some viruses) silt colloids and precipitates

MF is a pressure-driven or vacuum-driven (immersed type) membrane separationprocess that separates particulate matter from a fluid (water wastewater or industrialprocess fluid) by physical straining MF membranes have demonstrated more than6-log removal of particles and are credited by regulatory agencies up to 4-log removalfor Giardia and Cryptosporidium MF membranes remove some viruses and arecredited by regulatory agencies up to 05e25-log removal for viruses dependingon the brand and model

The MF membrane filtration surface is a thin synthetic polymer manufactured into ahollow fiber It can be supported or not supported The membrane surface can be on theoutside of the fiber (ldquooutside-inrdquo flow path) or on the inside of the fiber (ldquoinside-outrdquoflow path) Most MF membranes have an outside-in flow configuration in which thefeed water is on the outside surface of the fiber and treated water is collected in theinside of the fiber This outside-in configuration typically permits treating waterwith greater solids loading MF membranes can be also operated either in a cross-flow or in a dead-end flow mode In the dead-end mode all the source water passesthrough the membrane and periodically by batches is discharged on solid concentra-tion around membranes In the cross-flow mode a portion of the source water is dis-charged or recycled back to the inlet of the system continuously The cross-flow modecan accommodate higher solids loading but it may require more energy

Most MF membranes are manufactured from the polymers that are hydrophilic innature such as polyvinylidene fluoride (PVDF) polysulfone (PSF) polytetrafluoro-ethylene (PTFE) polypropylene (PP) and nylon The newer version of Teflon mem-branes were introduced to the market within last few years Most of the membranes areresistant to oxidants such as chlorine with the exception of PP Special agents are oftenadded to the membranes during the fabrication process to reduce fouling of the mem-branes by dissolved organics

The MF filtration system typically consists of membrane modules cassettes unitsand trains as shown in Figure 104

Membrane fibers are grouped together and secured into a single common moduleThe membrane module is repairable and replaceable Multiple membrane modules aresupported and manifolded together with common piping valves and instrumentationto form a complete integrated unit pressure MF skids or immersed MF units in basinsThe membrane unit has independent flow control and is backwashed cleaned andintegrity-tested as a complete unit Multiple membrane units are manifolded together

Planning and design of membrane systems for water treatment 333

into trains or banks to meet the overall capacity requirements for a system as shown inFigure 105

MF systems consistently provide high-quality low-turbidity filtered water (typi-cally below 01 NTU) independently of the source water turbidity fluctuations andoperator skills Depending on the source water characteristics most MF membraneapplications do not require pretreatment In some applications coagulant can be addedto the water to form flocs increasing the membrane treatment efficiency reduce mem-brane fouling andor to adsorb and to allow increasing removal efficiency of dissolvedtotal organic carbon (TOC) from the water In applications with high source watersolids a clarification process or dissolved air flotation (DAF) ahead of the MF system

(a) (b)

Figure 104 Hollow fiber microfiltrationultrafiltration membrane fibers (a) and cassette withmodules (b)

Figure 105 Flat plate microfiltrationultrafiltration immersed membrane trainbankbasin

334 Advances in Membrane Technologies for Water Treatment

may help reduce the membrane system capital and operating costs Depending on thewater chemistry and operational parameters the average MF recovery range is90e95 When coagulant is used the higher recovery of 95e98 can be achievedMF systems typically operate with feed pressures of 25e40 psi

1043 Ultrafiltration

UF screens particles from 0005 to 005 mm and removes most viruses and pathogensin addition to the particles removed by an MF system

Similarly to MF the UF is a pressure-driven or vacuum-driven (immersed type)membrane separation process that separates particulate matter from a fluid (waterwastewater or industrial process fluid) by physical straining UF membranes have ahigh removal efficiency for particles greater than approximately 005 mm includingbacteria pathogens (Cryptosporidium oocysts Giardia cysts) and viruses UF mem-branes have demonstrated removal of more than 6-log for particles and are credited byregulatory agencies with 4-log removal for Giardia and Cryptosporidium UF mem-brane systems also remove most viruses and are credited by regulatory agencieswith 2- to 4-log removal of viruses

Similarly to MF the UF membrane filtration surface is a thin synthetic polymermanufactured into a hollow fiber Many pressure UF membranes have an inside-outflow configuration in which the source water is on the inside surface of the fiberand filtered water is collected on the outside of the fiber This inside-out configurationpermits improved hydrodynamics at the membrane surface to minimize membranefouling and also permits higher pressure across the membrane for greater flux ratesHowever the inside-out configuration requires more energy and cannot handle ashigh a solid loading as the outside-in configuration The inside-out configurationcan be operated in the pressurized mode only not allowing the use of theimmersedvacuum concept The pressurized UF membranes can be also operatedeither in a cross-flow or in a dead-end flow mode In the dead-end mode all the sourcewater passes through the membrane In the dead-end mode all the source water passesthrough the membrane and periodically by batches is discharged on solid concentra-tion around the membranes In the cross-flow mode a portion of the source water isdischarged or recycled back to the inlet of the system continuously The cross-flowmode can accommodate higher solids loading but may require more energy UF mem-branes typically operate in a cross-flow mode on the high solid water

Similarly to MF most UF membranes are manufactured from the polymers that arehydrophilic in nature such as PVDF PSF polyethersulfone (PES) and PTFE MostUF membranes are resistant to oxidants such as chlorine Specific agents are oftenadded to the membranes during the fabrication process to reduce fouling of the mem-branes by dissolved organics

Like MF the UF filtration system typically consists of membrane modules unitsand trains Hollow fiber membranes are grouped together and secured into a singlecommon module This membrane module is repairable and replaceable Multiplemembrane modules are supported and manifolded together with common pipingvalves and instrumentation to form a complete integrated unit pressure UF skids

Planning and design of membrane systems for water treatment 335

or immersed UF units in basins The membrane unit has independent flow controland is backwashed cleaned and integrity-tested as a complete unit Multiple mem-brane units are manifolded together into trains or banks to meet the overall capacityrequirements for a system

UF systems provide consistent high-quality low-turbidity filtered water (typicallybelow 01 NTU) independent of the source water turbidity variations and operatorskills Depending on the source water characteristics UF membrane applicationsmay not require pretreatment In some applications coagulant can be added to the wa-ter to form floc particles to increase the membranersquos filtration efficiency andor toadsorb and reduce dissolved TOC in the water In applications with high source watersolids a clarification process ahead of the UF system may help reduce the capital andoperating costs of the membrane system Depending on the water chemistry and oper-ational parameters the average UF recovery range is 85e95 When coagulant isused the higher recovery of 95e98 can be achieved UF systems typically operatewith feed pressures of 35e50 psi

105 Applications of low-pressure membranes for watertreatment surface water and groundwater

When introduced to the market the low-pressure membranes MF and UF were analternative technology to the media filtration as illustrated schematically inFigure 106 (Frenkel amp Mourato 1998)

Conventional water treatment process

Sedimentation

Sedimentation

Surfacewater

Surfacewater

Coagulation

Coagulation

Media filtration

Membrane filtration

Membrane filtration treatment process

Figure 106 Example of one of the technological process using low-pressure membranes

336 Advances in Membrane Technologies for Water Treatment

In applications in which the solideliquid separation is required the low-pressuremembranes performed providing treated water with the quality superior compared tothe media filtration in most cases

Most applications were related to the surface water treatment replacing mediafiltration Due to the low-pressure membranesrsquo relatively high tolerance to the sus-pended solids applications of MFUF membranes allowed the removal of the clari-fication step in the treatment process for many projects providing significantreduction in the project cost and overall footprint of the plant This concept hasbeen called direct membrane filtration MFUF membranes were successfully appliedfor iron and manganese removal from the groundwater similarly to greensand filtersBecause low-pressure membranes are tolerant to suspended solids they are used as apretreatment for the high-pressure membranes NFRO as highlighted in clause twoabove compiling the IMS process Low-pressure membranes attracted significant in-terest by the wastewater industry and were successfully applied as a tertiary treatmenttechnology and as a basic technology for MBRs (Cui Muralidhara amp Frenkel 2010Frenkel Reardon Shlater Gharagozian amp Kondo 2011 Using Reclaimed Water2008)

106 Planning and designing low-pressure membranetreatment

Similarly to any water-treatment technology planning the low-pressure membraneproject needs careful planning and administration The major differences in the low-pressure membrane project compared to the basic conventional technology such asmedia filtration are

bull Membranes can tolerate higher solids loadbull Membranes can produce higher quality water compared to the conventional processesbull Most of the membrane plants are designed for continuous reject flow rather than batch filtra-

tion compared to the batch operation of the medial filters In this case the overall recovery ofthe membrane plant may be lower To improve membrane plant recovery the secondarystage of the membrane treatment train concentrating reject from the major treatment traincan be applied

bull When water is coagulated membranes may need smaller size flocs and less flocculation timeto achieve similar or better performance compared to the conventional processes

bull Because membranes provide higher-quality product water fewer UV doses andor a lowerchlorine injection rate are required

Because low-pressure membranes are still not standardized across the industry theyare manufacturer specific and not replaceable widely by the other suppliers This sit-uation complicates the membrane planning process and most of the membrane plantsthat were using the design-bid-build conventional procurement process are using thetwo-step procurement process During the first step the membrane suppliers are pre-qualified and preselected or membranes are prepurchased during the second step thegeneral contractor is selected This concept extends the overall project schedule

Planning and design of membrane systems for water treatment 337

requiring more time for the project procurement Because low-pressure membranes areshowing signs of standardization this situation may change in the future

The design of low-pressure membranes depends on the source water quality localconditions project size project preferences and requirements for the treated waterquality Depending on the solid load in the source water the low-pressure membranescan be designed to be operated in the dead-end filtration mode or cross-flow filtrationmode The dead-end filtration mode is limited by the solid content in the source waterwhile it provides higher overall system recovery and lower reject flow rate as a resultThe cross-flowmode is the opposite The system design needs to account the followingmajor plant components and parameters

bull Pretreatment requirements including fine screens chemical injection and clarification ifrequired

bull System recovery rate the ratio of the product flow to the feed flow expressed in percentbull Membrane active filtration area which is a function of the flow load on the membranes per

membrane area which is called membrane flux and expressed in gallonssquare feetday(GFD) or literhourmeter square (LHM)

bull Energy requirementsbull Posttreatment requirementsbull Solids treatment

Good design practice accommodates the maximum system recovery at the lowestenergy consumption and the best possible project economics both capital andoperational

107 High-pressure membrane applications

High-pressure membranes are represented by NF and RO membranes

1071 Nanofiltration and reverse osmosis

Membrane technology for groundwater treatment to remove color andor total dis-solved solids (TDS) includes NF and RO membranes These membrane-separationprocesses have a tighter membrane than MF and UF membranes which allowsthem to remove dissolved matter from the water organic and inorganic in nature

NF and RO also have been used as finishing processes in recycled water projectsremoving salt and constituents of concern being an integrated part of any indirectpotable reuse (IPR) or direct potable reuse (DPR) project

1072 Nanofiltration

NF separates particles in the range of 00005e0001 mm and is effective in removinghardness some TDS and TOC

NF is a pressure-driven membrane separation process that separates sparinglysoluble salts and large organic molecules from a fluid (water wastewater or industrial

338 Advances in Membrane Technologies for Water Treatment

process fluid) NF membranes have a high removal efficiency for multivalent ions suchas calcium and magnesium (hardness) but will also remove partially monovalent saltssuch as sodium and chloride depending on the size cutoff of the NF membrane

The NF membrane separation surface is a thin synthetic polymer manufactured intoa flat sheet and then spiral wound to form a membrane element The source water ispressurized and passed through the membrane module As the pressurized sourcewater passes along the membrane surface water molecules pass through the NF mem-brane and the larger salt ions and organic molecules are rejected and concentrated inthe water passing along the membrane

The NF system produces a high-quality (low TDS) permeate and a concentratedhigh salinity reject

The first generation of the NF membranes were manufactured from cellulose acetate(CA) the newer generation of NF membranes are manufactured from polyamide thinfilm composites (TFC) The CA material is resistant to strong oxidants while havinglower permeability and needing higher operational pressure as a result compared tothe TFC membranes The TFC material operates at lower pressures while it has rela-tively low tolerance to the oxidizing agents in the water and it can be damaged byoxidants Hydrophilic agents are often added to the membranes during the fabricationprocess to reduce fouling of the membranes by dissolved organics

An NF separation system typically consists of membrane elements pressure vessels(PVs) units and trains The membrane element is repairable and replaceable NFmembrane elements are loaded into PVs that are fabricated mainly from fiberglassreinforced plastic (FRP) or stainless steel The PVs can be different sizes and lengthsto accommodate from one to eight membrane elements While MF and UF membraneelements are not standardized across the industry NF membrane elements have stan-dard diameters of 25 4 and 8 inches and standard element lengths of 40 and 60inches This standardization permits flexibility in designing and operation of the NFsystem Currently the large-diameter RO elements in the range of 16e185 incheswere used for numerous RO facilities while they are not standardized across the indus-try at this time Groups of parallel PVs are supported and manifolded together withcommon piping valves and instrumentation to form a complete integrated NF unitor skids

The NF unit has independent flow control and is chemically cleaned and operated asa complete unit Multiple NF units are manifolded together into trains or banks to meetthe overall capacity requirements for a system as shown in Figure 107

Because NF membranes do not tolerate suspended and colloidal matter in the waterthey require pretreatment ahead of the membranes to protect them from solids and toprevent fouling of the membrane surface Because the spiral-wound NF membranescannot be backwashed the suspended solids must be removed from the NF feed waterDepending on the source water quality MF andor other filtration technologies aretypically used to protect membranes from the large particles Acids andor antiscalentsalso can be added to the feed water to reduce scale formation on the membrane surfaceDepending on the water chemistry and system operational parameters the average NFrecovery range is 75e85 Depending on the source water TDS NF systems typicallyoperate with feed pressures in the range 70e150 psi (5e10 Bar-g)

Planning and design of membrane systems for water treatment 339

1073 Reverse osmosis

RO separates ions and molecules down to less than 10 molecular weight units andis effective in removing TDS hardness TOC constituents of concern such as endo-crine disruptors pharmaceutically active compounds and personal care products(Frenkel 2009)

Similarly to NF RO is a pressure-driven membrane separation process that separatessoluble salts and organic molecules from a fluid (water wastewater or industrial pro-cess fluid) Osmosis is a natural process in which water passes through a semipermeablemembrane from low TDS concentration to high TDS concentration (Bartels FranksRybar Schierach amp Wilf 2005) The RO process is a reverse of the natural osmosisprocess which is the pressure-driven process in which the high TDS source water ispressurized and water then passes through the semipermeable membrane RO mem-branes have high removal efficiency for monovalent ions such as sodium and chlorideand will also remove organic molecules depending on the size and charge of the mole-cule Typical RO salt rejection is up to 998 by one single element at standard con-ditions However the overall RO system rejection rate is lower because RO elementsare operated in series within the PVs which results in the increased salt concentration inthe feed to each element as water moves along the PV Some rejections rates by one ROsingle membrane element at the standard conditions are shown in Figure 108

Similarly to NF the RO membrane separation surface is a thin synthetic polymermanufactured into a flat sheet and then spiral wound to form a membrane elementThe source water is pressurized and passed through the membrane module As thepressurized source water passes along the membrane surface water molecules passthrough the RO membrane and the salt ions and organic molecules are rejected andconcentrated in the water passing along the membrane The RO system produces ahigh-quality (low TDS) permeate and a concentrated (high TDS) reject

(a) (b)

Figure 107 High-pressure membrane nanofiltrationreverse osmosis element (a) and system (b)

340 Advances in Membrane Technologies for Water Treatment

The first generation of the RO membranes were manufactured from CA the newergeneration of NF membranes are manufactured from polyamide TFCs The CA mate-rial is resistant to strong oxidants while having lower permeability and needing higheroperational pressure as a result compared to the TFC membranes The TFC materialoperates at lower pressures while it has relatively low tolerance to the oxidizing agentsin the water and it can be damaged by oxidants Hydrophilic agents are often added tothe membranes during the fabrication process to reduce fouling of the membranes bydissolved organics

An RO separation system typically consists of membrane elements PVs units andtrains The membrane element is repairable and replaceable RO membrane elementsare loaded into the PVs fabricated mainly from the FRP or stainless steel The PVs canbe different sizes and lengths to accommodate from one to eight membrane elements(Frenkel 2011 Liberman amp Wilf 2005) While MF and UF membrane elements arenot standardized across the industry RO membrane elements have standard diametersof 25 4 and 8 inches and standard element lengths of 40 and 60 inches This standard-ization permits flexibility in designing and operation of the RO system Currently thelarge-diameter RO elements in the range of 16e185 inches were used for numerousRO facilities while they are not standardized across the industry at this time Groups ofparallel PVs are supported and manifolded together with common piping valves and

Contaminant Contaminant Nominal rejection Nominal rejection

Aluminum Ammonium

Bacteria

Boron

Cadmium

Copper

Chloride

Fluoride

Iron

Manganese

Mercury

Nitrate

Phosphate

Potassium

Silica

Silver

Sulfate

Zinc

96-98

99+

50-70

93-97

96-98

96-98

93-96

93-97

96-98

96-98

96-98

93-97

92-95

92-98

96-98

95-98

80-90

80-90

96-98

96-98

96-98

94-97

90-95

90-95

95-98

92-95

Borate

Bromide

Calcium

Chromate

Cyanide

Hardness Ca amp Mg

Lead

Magnesium

Nickel

Orthophosphate

Polyphosphate

Radioactivity

Silicate

Sodium

Thoisulfate

93-97

92-95

30-50

85-95

93-98

93-98

85-95

Figure 108 Typical contaminants removal rates from the water by reverse osmosis system

Planning and design of membrane systems for water treatment 341

instrumentation to form a complete integrated RO unit or skids The RO unit has in-dependent flow control and is chemically cleaned and operated as a complete unitMultiple RO units are manifolded together into trains or banks to meet the overall ca-pacity requirements for a system

RO membranes require pretreatment ahead of the membranes to protect them fromsolids and to prevent fouling of the membrane surface Because the spiral-wound ROmembranes cannot be backwashed suspended solids must be removed from the ROfeed water Depending on the source water quality MF andor other filtration technol-ogies are typically used to protect membranes from the large particles Acids andorantiscalants are also added to the feed water to reduce scale formation on the mem-brane surface Depending on the water chemistry and system operational parametersthe average brackish water RO recovery range is 75e85 Seawater RO (SWRO) usu-ally operates with a recovery of 40e60 Depending on the source water TDS ROsystems typically operate with feed pressures in the 150e1200 psi (10e83 Bar-g)range

1074 Seawater reverse osmosis

Membrane technology to remove salt from seawater to provide an alternative drinkingwater source can be designed with MF or UF pretreatment ahead of SWRO mem-branes This process currently represents a small segment of the US market but isexpected to see future growth in Florida Texas California and numerous other costalplaces where there is no other drinking water source (Desalination of Seawater 2011Stevens Kowal Herd Wilf amp Bates 2003 Wilf et al 2006)

108 Applications of high-pressure membranes forwater treatment brackish water seawateroceanwater

High-pressure membranes are widely applied to treat groundwater to reduce saltcontent nitrates and specific contaminants of concerns RO membranes became thedominant technology for seawater desalination providing beneficial process eco-nomics compared to thermal desalination processes RO membranes are becomingthe integrated part of the process in the water reuse and in IPR and DPR which areattracting attention lately and in light of the global warming and climate changesparticularly Another niche for the high-pressure membranes is preparation of thedeionized (DI) water and ultrapure water (UPW) of which many industries are in need

109 Planning and designing high-pressure membranetreatment

Similarly to low-pressure membrane planning the high-pressure membrane projectsneed careful planning and administration The major differences in the high-pressure

342 Advances in Membrane Technologies for Water Treatment

membrane projects compared to the low-pressure membrane projects and conventionaltechnologies are

bull Membranes cannot tolerate high suspended and colloidal solids load while being efficient inremoving dissolved matter from the water to be treated

bull Reliable pretreatment is required to reduce particular matter and colloids load prior to treat-ing water by high-pressure membranes

bull As membranes provide higher-quality product water the fewer ultraviolet doses andor lowerchlorine injection rate are required compared to the conventional processes

Because high-pressure membranes are well standardized across the industrythey are not manufacturer-specific and are replaceable by other suppliers(Frenkel amp Wilf 2009) The current status in the industry simplifies the high-pressure membrane planning process and most of the conventionally procuredmembrane plants are using a one-step procurement process the opposite ofthe low-pressure membrane procurement process The one-step procurementprocess reduces the project schedule compared to the low-pressure membraneprocurement process

Similarly to low-pressure membranes the design of high-pressure membranesdepends on the source water quality local conditions project preferences and require-ments of the treated water quality Because high-pressure membranes do not toleratesuspended and colloidal matter in the water design and performance of the high-pressure membranes depend on design and performance of pretreatment either con-ventional or low-pressure membranes Since development most of the engineeringand design efforts were directed to design high-pressure membranes in the continuousoperation The continuous operation has certain benefits and negatives as highlightedbelow

Benefits of RO operation in continuous mode

bull All membranes are operated continuously allowing a relatively simple system fittings andpiping arrangements

bull Equipment fittings and components are not cycling periodically increasing the lifetime ofequipment

bull Energy recovery devices can be easily added reducing overall energy demand by thesystem

bull There are number of techniques developed allowing system operation to be flexible such asconcentrate recycling and hybrid design

Within the last few years RO operation in a semibatch mode was proposed whichbrings the following benefits compared to the continuous RO operation

bull Flux can be better balanced between RO membrane elements within the PVbull Higher overall system recovery can be achieved at the same conditions compared to the

continuous RO operationbull Less potential membrane fouling may be achieved due to the change in the salt load within

each cycle

Planning and design of membrane systems for water treatment 343

The high-pressure membrane system design needs to account for the followingmajor plant components and parameters

bull Pretreatment requirements including chemical injection clarification when required filtra-tion using conventional processes or low-pressure membranes

bull System recovery rate the ratio of the product flow to the feed flow expressed in percentbull Membrane active filtration area which is a function of the flow load on the membranes per

membrane area which is called membrane flux and is expressed in GFD or LHMbull Energy requirementsbull Posttreatment requirements due to the low alkalinity of the product water and water aggres-

siveness as a resultbull Concentrate dischargemanagementbull Treatmentmanagement solids from pretreatment

Good design practice accommodates the maximum system recovery at the lowestenergy consumption and the best possible project economics both capital and opera-tional (Desalination of Seawater 2011)

1010 Integrated membrane systems

As described above low-pressure mmbranes were designed to remove suspendedmatter from the water similarly to media filtration or other solids-water separationtechnology High-pressure membranes are not tolerant of suspended and colloidal mat-ter while being designed to remove dissolved matter from the water similarly to theion exchange resins or water evaporators IMS found their application in a numberof industries and in municipal applications

A number of seawater desalination plants were designed by applying the IMSconcept when low-pressure membranes are followed by high-pressure membranesSurface water treatment adopted the IMS concept in which dissolved matter inorganicor organic in nature needs to be removed from the water Many industries adoptedIMS design when preparing to make up DI or UPW or when treating industrial effluentfor reuse As IPR is gaining popularity and DPR is knocking on the door the IMSconcept is becoming the gold standard for these applications

1011 Combination of membrane treatment with othertechnological processes

Membrane technologies have number of beneficial features allowing for rapidlyexpanding market shares such as

bull Absolute barrier for treatmentremovalbull Smaller footprintlayoutbull Product water is not affected by the feed water hydraulic and contaminant overloads spikes

and fluctuationsbull Less or no chemicals requiredbull Minimal or no pretreatment requiredbull Single-step processbull Modular expandability (for future expansion)

344 Advances in Membrane Technologies for Water Treatment

bull Less volume of discharged wastes (including sludge and chemicals)bull Simplicity of operation with remote monitoringbull Lower postdisinfection demand in chlorine UV intensity

Also membrane technologies have certain limitations such as

bull Prompt to foulbull Needs pretreatmentbull Have low rejection rate of non-ionized ionsbull Have low rejection rate of dissolved gases

Depending on the application feed water quality and criteria of the treated watermembrane technologies can be successfully combined with conventional processesGood examples could be

bull Using clarification upstream of low-pressure membranes to reduce suspended matter load tothe membranes

bull Using DAF to minimize low-pressure membrane fouling caused by the colloidal matter fineorganics and algae

bull Applying chemicals similarly to the conventional processes to form flocs coagulate waterand change water pH

bull Polish permeate from high-pressure membranes by activated carbonbull Add decarbonators to remove CO2 and balance pH in the product from high-pressure

membranesbull Use advanced oxidation concept to destruct constituents of concert and low molecular weight

organics that may pass through the high-pressure membranes

1012 Conclusions future trends in membranetreatment development for water treatment

Membranes are gaining popularity and market growth While traditionally membranetechnologies started to develop in the United States Europe and Japan the latesttrends are that more membranes companies are being established in different partsof the world including Korea and China Besides traditional membrane technologysuppliers there is a good number of players showing up on the market Competitiondrives improvements in membrane technology developments finding newer applica-tions improving technical features of membranes and reducing cost

Several trends in membrane technology developments can be identified

bull Improvements of membrane properties such as increase of permeability eg higher flux atlower pressure

bull Fouling minimizationbull Overall system energy reductionbull Minimization of the treatment plant footprint by applying larger-size treatment trains com-

mon headers and large-diameter membrane elements (RO)bull Newer membrane technology developments such as forward osmosis pressure retarded

osmosis membrane distillation and combinations of the newer processes with the estab-lished technologies

As the membrane market grows sooner or later membrane technology will be oneof the preferred choices for projects

Planning and design of membrane systems for water treatment 345

List of acronyms

BWRO Brackish water reverse osmosisC Concentration ppm or mgLCA Cellulose acetateDPR Direct potable reuseFRP Fiberglass reinforced plasticgpm Gallons per minute (US units of flow)IMS Integrated membrane systemIPR Indirect potable reusem3hr Cubic meter per hour (metric units of flow)mgL Milligram per liter (metric units of concentration)MBR Membrane bioreactorMF MicrofiltrationMWCO Molecular weight cut offNF NanofiltrationNTU Nephelometric turbidity unitsppm Part per million (fractional units of concentration equal to mgL)PV Pressure vesselQ Flow gpm or m3hrRO Reverse osmosisSWRO Seawater reverse osmosisTDS Total dissolved solidsTFC Thin film compositeTOC Total organic carbonUCLA University of California at Los AngelesUF UltrafiltrationUPW Ultrapure water

References

Bartels C Franks R Rybar S Schierach M amp Wilf M (2005) The effect of feed ionicstrength on salt passage through reverse osmosis membranes Desalination 184 185e195

Cui Z F Muralidhara H S amp Frenkel V (June 2010) Chapter 8 Membranetechnologies for food processing waste treatment A practical guide to membranetechnology and applications in food and bioprocessing Oxford United KingdomButterworth-Heinemann Elsevier Publisher

Desalination of Seawater (May 2011) Chapter 3 M61 In Treatment approaches (1st ed)Denver CO American Water Works Association (AWWA)

Design of municipal wastewater treatment plants (October 2009) Chapter 16 WEF MOP8 In Water environmental federation (5th ed) New York WEF Press and McGraw-Hill

Frenkel V amp Wilf M (2009) Using the flexibility of RO system configuration In Worldcongress on desalination and water reuse international desalination associationNovember 07e12 2009 Dubai UAE

Frenkel V (March 2011) Chapter 6 Seawater desalination trends and technologies InDesalination trends and technologies Vienna Austria INTECH

346 Advances in Membrane Technologies for Water Treatment

Frenkel V Reardon R Shlater N Gharagozian A amp Kondo (2011) Chapters 5 and 6WEF MOP 36 In Membrane bioreactors (1st ed) Alexandria VA Water environmentalfederation

Frenkel V (2009) Reverse osmosis How it began and where it is now Chennai India WaterToday Magazine MayeJune 2009

Frenkel V amp Mourato D (1998) Application of immersed microfiltration membranes fordrinking water treatment In NSF international conference Washington DC

Liberman B amp Wilf M (2005) Evolution of configuration of RO seawater desalinationsystems In Proceedings of IDA water desalination conference Singapore

Stevens L Kowal J Herd K Wilf M amp Bates W (2003) Tampa Bay seawater desali-nation facility start to finish In Proceedings of IDA water desalination conferenceBahamas

Using reclaimed water to augment potable water resources (2008) Alexandria and DenverA special publication by WEF and AWWA

Wilf M Bartels C Awerbuch L Mickley M Pearce G amp Voutchkov N (2006) Theguidebook to membrane desalination technology Reverse osmosis nanofiltration andhybrid systems Process design and applications Italy Balaban Desalination Publications

Planning and design of membrane systems for water treatment 347

Membrane ageing during watertreatment mechanismsmonitoring and control

11KH Tng A Antony Y Wang GL LeslieThe University of New South Wales Sydney NSW Australia

111 Introduction

Microporous and semipermeable membrane filtration processes are used to efficientlyand reliably achieve consistent product water quality and quantity on a range of watersources (see Figure 111) In general membrane processes are less complex comparedto conventional water treatment processes that use chemical flocculation clarificationand chlorination Product water quality can be easily monitored using a range of tech-niques that check for membrane integrity Similarly the capacity to maintain productquantity can be assessed by online monitoring of membrane permeability One chal-lenge unique to drinking water plants using membrane technology is anticipatingand scheduling activities to renew the inventory of membranes in service

The prorated warranty provided by membrane manufacturers can range from 3 to10 years However experience teaches that some plantsrsquo effective membrane lifecan either exceed or fall short of the manufacturerrsquos expectations Moreover it isnot uncommon to have significant variability in the integrity and productivity of

Application

Membrane type

Function

Surface water

Water treatment

Wastewater Seawater Groundwater

MFUF MFUF + RO MFUF + RO NFRO

Removes solids and pathogens

Removes solids and pathogens

+ removal of salts and

divalent ions

Removes colloids

+ removes

salts divalent ions and organics

Removes salts divalent

ions and organics

Figure 111 Typical membrane filtration applications in the water treatment industry

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400011-3Copyright copy 2015 Elsevier Ltd All rights reserved

membrane modules on site at any given time The capacity of an individual membraneelement or module can range from 42000 L per day for a microporous MFUF mem-brane to 21600 L per day for a semipermeable reverse osmosis (RO) membraneConsequently operators of plants with a treatment capacity of 50 MLD would needto manage a membrane inventory of several thousand membranes

The paramount operating objective is to avoid any failure that could compromisequality and restrict capacity Developing a strategy that relies exclusively on manufac-turerrsquos warranty to estimate membrane lifespan and replacement schedules is fraughtwith uncertainty

Membrane ageing and failure occurs throughout the membranersquos operational life-time The literature has been silent with regard to the understanding and predictionof membrane failure and has largely been focused on ageing due to exposure to strongoxidants such as sodium hypochlorite This chapter reviews the mechanisms andmodes of membrane failure approaches and methods used to monitor and the controlmembrane ageing and integrity in the water treatment industry

1111 Membrane ageing and failure

Membrane ageing is usually the main cause behind overall membrane failure as amembrane reaches the end of its lifespan (Prulho Therias Rivaton amp Gardette2013) This section would make a clear distinction between ageing and failure andfurther discuss how membrane ageing can lead to a membrane that is more susceptibleto failure

11111 Membrane ageing

Membrane ageing is defined as the deterioration of the surface layer and sublayers ofcomposite membranes due to irreversible deposition of foulants or by frequent expo-sure to chemical cleaning agents (Antony Fudianto Cox amp Leslie 2010 Benaventeamp Vazquez 2004 Thominette Farnault Gaudichet-Maurin Machinal amp Schrotter2006) Membrane productivity and removal efficiency are undermined by the retentionof dissolved salts organics microorganisms and suspended solids after extendedoperation also known as fouling (see Figure 112(a) (b) and (d)) Membrane foulingis the central bottleneck for all membrane filtration processes therefore the industryuses routine chemical cleaning protocols In some cases strong oxidants such assodium hypochlorite are used to control fouling Regrettably repeated chemicalcleaning exacerbates membrane aging

During the cleaning in place (CIP) process chemicals are intermittently applied tothe fouled membranes at specific concentrations temperatures and extended timesThe combination of these factors can lead to ageing of the membrane with mem-branes becoming discoloured over time (see Figure 112(c)) Prolonged filtrationand cleaning cycles not only have an adverse effect on membrane integrity butcan also lead to internal fouling of membranes which is irreversible and detrimentalto membrane performance (see Figure 112(b)) This also reduces the lifespan of themembrane leading to a higher likelihood of failure

350 Advances in Membrane Technologies for Water Treatment

11112 Membrane failure

Membrane failure can be defined as the loss of membrane mechanical integrity leadingto the inability to achieve rated log removal values (LRV) (Childress Le-ClechDaugherty Chen amp Leslie 2005 Gijsbertsen-Abrahamse Cornelissen amp Hofman2006 Mallevialle et al 1996) Membrane failure can occur during two phases ofthe membranersquos operational lifespan Membrane fibres can be damaged before andduring installation and also during membrane filtration Failure before and duringinstallation is often caused by inconsistent manufacturing and fabrication techniquesand installation This issue is kept in check via implementation of more rigorous qual-ity control methods and integrity testing of membrane modules before commissioning

Age

ing

Failure

(a)

(b)

(c)

(e)

(f)

(g)

(h)

(d)

Figure 112 Effects of membrane ageing and failure (a) Foulant accumulation (b) Membraneinternal fouling (c) Membrane fibre discolouration (d) Membrane surface fouling (e) Surfacepunctures (f) Fibre embrittlement (g) Surface delamination (h) Surface scratches and scores

Membrane ageing during water treatment mechanisms monitoring and control 351

Membrane failure during the filtration process can largely be attributed tooperating parameters and maintenance protocols (Johnson amp Maccormick 2003)During operation the likelihood of damage to the membrane is high given theastringent nature of operating protocols such as vigorous mechanical cleaning chem-ical cleaning using strong oxidants and high-pressure backwashes Although thisensures that the membranersquos performance is maintained it indirectly puts a strain onthe membranersquos integrity leading to accelerated membrane aging and subsequentfailure According to Childress et al (2005) failure results from physical damage tothe membrane module structure The damage maybe caused as a result of a suite offactors actions by chemicals excessive external forces scores scratches and punc-tures due to the presence of foreign bodies (see Figure 112(h)) all of which are exac-erbated by faulty membrane module structures and designs Membrane fibre breakagedue to chemical attack leads to embrittlement of membrane fibres leading to bothdiscolouration and breakage of membrane fibres (see Figure 112(f)) Membrane dam-age and integrity compromise can also be caused by unexpected water quality fluctu-ations or failure of pretreatment processes leading to inadequate removal of material(Gijsbertsen-Abrahamse et al 2006) These foreign bodies coupled with the effectsof strong aeration can puncture the membrane resulting in a rapid pressure loss anddetection of bubbles in a pressure decay test (PDT) (Cui Chang amp Fane 2003)(see Figure 112(e))

Although membrane ageing and failure are closely related a distinction should bemade between these two aspects Ageing results in membrane degradation and theonset of these adverse effects in turn leads to membrane failure Subsequently mem-brane failure results in loss of process removal efficiency reduction in product waterthroughput and product water noncompliancy

112 Reliability maintainability and resilience

Many communities rely on hollow-fibre membranes to remove pathogens from drink-ing water The resilience of water treatment plants using hollow-fibre membranes isdefined as the ability to meet a specified log reduction in pathogen concentration inroutine as well as in unexpected circumstances The reliability of a membrane filtra-tion system is therefore critical to ensuring that treated water meets regulatory require-ments Maintainability of the system is also important because that would determinethe systemrsquos downtime before being put back into service once the failure has beenrectified Therefore the reliability and maintainability of an asset are two factorsthat are crucial in evaluation of the assetrsquos resilience

1121 Reliability

The reliability of a membrane filtration process unit is an essential factor in maintain-ing the continuous compliance with specific performance criteria such as environ-mental discharge consent requirements and water quality parameters The evaluationof the reliability of such process units is an important part of its design and operation

352 Advances in Membrane Technologies for Water Treatment

However this has always been difficult to assess and quantify and often has been basedon the number of redundancies andor backup facilities (Eisenberg Soller Sakaji ampOlivieri 2001)

11211 Mean time to failure and mean time between failure

Process equipment is said to be completely reliable if there is no failure in the processperformance and it meets the required effluent discharge standards and targets Equip-ment reliability can be measured in terms of mean time to failure (MTTF) and meantime between failure (MTBF) (Stanley 2011) Although MTTF and MTBF can beused to quantify equipment reliability there is a distinct difference between thesetwo terms MTTF can only be applied to nonrepairable components and equipmentwhile MTBF is applied to repairable equipment (Kagan 2004) MTTF is the averagetime equipment remains functional until its failure and can be calculated by dividingthe total operation time of equipment by the number of units of equipment Formean time to repair (MTTR) to be accurate this statistical value should be measuredfor a long period and over a large number of units (Stanley 2011)

MTTF frac14 Cumulative operational time of equipment ethhoursTHORNNumber of equipment

(111)

In the case of repairable components MTBF is used instead of MTTF MTBF isthe average time equipment remains in service until it fails and can be calculated bythe following equation (Smith amp Mobley 2008)

MTBF frac14 Cumulative time in service ethhoursTHORNNumber of failures

(112)

For example MTTF could be applied to irreparable failure events of RO mem-branes in which delamination or damage to the membrane housing had occurreddue to excessive backwash pressure whereas MTBF would apply to repairable faultssuch as sealing of detected leaks in compromised hollow-fibre membranes beforebeing returned to service

11212 Failure rates

Equipment failure rates (eventstime) also can be used to quantify reliability A higherfailure rate or a greater number of failure incidences will directly translate to less-reliable equipment The failure rate of any given piece of equipment can be describedby a ldquobathtubrdquo curve (see Figure 113) The bathtub curve is divided into three sec-tions The first section is known as the ldquowearing in periodrdquo During this period thefailure rates are high due to infant mortality failures caused by defective componentsand improper quality control measures prior to operation An example in a membranesystem would be a failure that occurs during the commissioning stages when poorinstallation manufacturing defects and incorrect membrane preconditioning proto-cols can result in an early failure of the membrane units (Johnson amp Maccormick

Membrane ageing during water treatment mechanisms monitoring and control 353

2003) The failure rate then decreases rapidly as the equipment and its componentsare worn in until it reaches the second section the ldquointrinsic failure periodrdquoThis period is when most of the equipmentrsquos lifespan remains and throughout thislong period the equipment has a constant failure rate due to random failures Failureevents that occur during this period could be a result of a pretreatment processrsquoineffective removal of gross particles or unintentional operator error leading todamage and failure of the membranes (Yang Cicek amp Ilg 2006) The last sectionis the ldquowearing out periodrdquo In this period the failure rate increases again becauseof cumulative damage caused by wear and mechanical fatigue over time (KlutkeKiessler amp Wortman 2003) This period occurs toward the end of the membranersquoslifespan and would be replaced when it eventually fails to maintain removalefficiency and process integrity The typical lifespan of a membrane usually rangesfrom 5 to 10 years and varies with material type and manufacturers (LesjeanRosenberger Schrotter amp Recherche 2004)

11213 Availability

The availability of an equipment or component is defined as the proportion of time thatit is functioning properly and is available for operation Availability is the ratio of thetotal operational time to the sum of operational time and repair times Repair times arequantified via the equipmentrsquos MTTR This is the average time required for repairsto be made to restore the equipment back to its operational state The equipmentrsquosavailability can be calculated via the equation below

Availability frac14 MTBFMTBFthornMTTR

(113)

To maximise availability a balance between component reliability and mainte-nance has to be achieved Downtime is inevitable because both scheduled preventa-tive maintenance and repairs require time and cause disruptions to the systemrsquosoperation (Marshall amp Chapman 2002) Implementation of different design

Failu

re ra

te (λλ

)

Time (t)

Constant (random) failurerate

Wearoutfailures

Infant mortality failures

Figure 113 Bathtub curve describing equipmentrsquos failure rates with time

354 Advances in Membrane Technologies for Water Treatment

approaches for example having multiple smaller systems integrated to form a largercomplete system working with an optimised maintenance protocol can result in ahigher system reliability and availability

1122 Maintainability

Maintainability of a membrane filtration system is defined as the probability of thefailed system returning back to an operable condition using the recommended proce-dures in a specific period (Sutton 2010a)

Conventional maintenance can be divided into three categories repair condition-based maintenance and scheduled maintenance Repair and condition-based mainte-nance are performed when the process equipment has either failed or starts showingsigns of imminent failure with the only difference being repairs are usually donewithout equipment shutdown and condition-based are done with a shutdown In amembrane system an example of repair and condition-based maintenance would beisolating and replacing membrane modules on detection of a compromise in membraneintegrity Scheduled maintenance is regular maintenance performed regardless of con-dition or performance during operation Routine chemical backwashing is an exampleof scheduled maintenance that is used to restore membrane flux and control foulingduring membrane filtration To reduce process equipment downtime and labour costsreliability centred maintenance (RCM) was developed RCM uses a risk-basedapproach to prioritise process equipment so that equipment that is critical to processintegrity is inspected and maintained more frequently (Sutton 2010b)

1123 Resilience

A systemrsquos resilience is defined as the ability for the system to tolerate the distur-bance and return back to its steady-state following the perturbation (Gunderson ampPritchard 2002) In the case of membrane filtration systems the resilience isdescribed as how robust the system is in recovering from a failure event and canbe defined by the duration of the failure occurrence (Zhang Achari Sadiq Langfordamp Dore 2012) For example having only one operator responsible for an entire treat-ment system would result in the operator requiring a longer time to isolate and reme-diate the failing process leading to a longer downtime and deeming the process to beless resilient Therefore the resilience of the membrane system plays a critical role inensuring that continuous process throughput is maintained while the treated waterstill remains compliant with strict water discharge guidelines upholding public healthand safety

113 Membrane failure modes

There are two categories of membrane failure failure during installation and failureduring operation (see Table 111) Of the two aspects failure during operation ismore critical because it could lead to product water noncompliancy which is a threat

Membrane ageing during water treatment mechanisms monitoring and control 355

Table 111 Common failure modes of membranes and modules

Failure modeFailurelocation Cause Incidence of failure Consequences

Membranetypes

Manufacturingdefects

Module ormembrane

Accidental Installation oroperation

Poor removal efficiencyabnormal differential pressures

All

Cracks andruptures

Module Hydraulic shock accidentalhigh pressure or shearstress abrasion orbackwash pressure

Operation start-upsshutdowns

Abnormal differential pressures All

O-ring andseal failures

Module Accidental Operation Poor removal efficiencyabnormal differential pressures

All

Mechanicaldamage

Module Accidental Installation oroperation

Abnormal differential pressures All

Damage ofactive layer

Membrane Pretreatment failure presenceof crystalline or abrasiveparticles

Operation Poor removal efficiencyabnormally high permeate flux

All

Oxidativedamage ofmembrane

Membrane Use of strong oxidants Prolonged operation Poor removal efficiencyabnormally high permeate flux

All

356Advances

inMem

braneTechnologies

forWater

Treatm

ent

Colloidal orinorganicfouling

Membrane Pretreatment failure Prolonged operation Permeate flux decline high TMP All

Organicfouling

Membrane High organic loading of feedwater

Prolonged operation Permeate flux decline high TMP All

Internalfouling(lumen-side)

Membrane Prolonged operation Prolonged operation Permeate flux decline high TMP Hollow fibre

Fractures andcleavages

Membrane Hydraulic shock accidentalhigh pressure or shearstress

Operation start-upsshutdowns

Poor removal efficiencyabnormally high permeate flux

Hollow fibre

Delaminationof activelayer

Membrane High backwash pressure Operation shutdowns Poor removal efficiency Flat sheet

Compaction Membrane High operation pressure andsudden pressure surges

Operation Low permeate flux Flat sheet

Mem

braneageing

duringwater

treatment

mechanism

smonitoring

andcontrol

357

to public health Failure during installation is less critical given that it can be easilyovercome by having more rigorous inspections prior to commissioning Thereforethis section will focus on failure modes of membrane systems during operation

Hollow-fibre membranes are widely used in municipal and industrial wastewatertreatment (Chang 2011 Cheryan 1998 Oschmann Nghiem amp Scheuroafer 2005)Large bundles of hollow-fibre membranes are often either encapsulated in a pressurevessel forming a module or potted into large curtains for submerged filtration inwastewater (Gijsbertsen-Abrahamse et al 2006) Fibre failure can occur via fourdifferent mechanisms however only three are related to membrane ageing that leadsto its subsequent failure chemical attack excessive fibre movement and impropermembrane module design The fourth aspect presence of foreign bodies can beattributed to poor removal efficiency of pretreatment processes and thus does notdirectly contribute to membrane ageing

1131 Failure due to chemical attack

The removal efficiency of both microporous and semiporous membranes is optimalonly when membrane fouling is kept to the minimum while maintaining overallintegrity Therefore to control the fouling on the membrane surface frequentin-situ backwash regimens using strong oxidants are implemented Oxidativedamages are largely caused by the chemical incompatibility of the chemicals usedand the membrane material itself (Childress et al 2005) Due to this exposure toharsh chemicals the membrane properties would be altered resulting in membranedegradation (Antony amp Leslie 2011) Oxidants are the main causes behindmembrane integrity deterioration with sodium hypochlorite being the most commoncleaning agent used and studied However it should be noted that sodium hypochlo-rite is not universally used given the health and environmental impacts of thechlorinated organic by-products and the low chlorine tolerance of certain membranetypes (Kang et al 2007 Kwon amp Leckie 2006) From the equilibria equationsbelow sodium hypochlorite dissociates into hypochlorous acid HClO when itcomes in contact with water and further dissociates into hypochlorite ions ClOThe pH largely affects the stoichiometric ratio of hypochlorous acid dissociatedwith a low pH favouring a higher dissociation of the stronger oxidant HClO (RouaixCausserand amp Aimar 2006)

NaClOthorn H2O4HClOthorn NaOH (114)

HClO4Hthorn thorn ClO (115)

An example of the chemical incompatibility between cleaning reagents and mem-branes is the unexpected internal fouling of membranes in the presence of iron speciesIn Australia iron salts are dosed in wastewater treatment plants with the aim to aidphosphorous removal and odour control The presence of iron salts coupled with theoxidative nature of hypochlorite can lead to formation of amorphous ferric oxides(AFO) that could accumulate in the lumen side of the hollow-fibre membranes

358 Advances in Membrane Technologies for Water Treatment

causing internal fouling and sudden unexpected fibre failure (Tng Wang Waite ampLeslie 2013)

1132 Failure due to faulty membrane module structure

Membrane module design is usually correlated to the efficiency of membrane foulingprevention Current membrane modules consist of up to 20000 hollow fibres heldtogether with either an epoxy or urethane resin Depending on the manufacturing pro-cess the resin can be cured under static or dynamic conditions In static conditions theresin is allowed to cure without heat or external forces acting on it This method isslower than the dynamic curing method that uses centrifugal forces under elevatedtemperatures Each method would produce varying results and thus would havedifferent mechanical tensile strengths

Membranes that are potted statically would have the resin wick up the fibrersquos edgedue to the effects of capillary forces This leads to a development of a sharp edge thatcan cause fibre breakage (Figure 114(a)) Application of an elastomer overlay is addedto minimise the sharp edges (Figure 114(b)) However only the dynamic cured resinscan almost negate the development of these sharp edges (Figure 114(c)) (Childresset al 2005) With the addition of air scouring the probability of fibre breakage dueto the type of potting method increases

Membrane filtration and routine backwashes carried out at pressures higher thanthe manufacturerrsquos recommendations can lead to membrane failure via delaminationof membrane sheets (see Table 112(f)) damage to membrane module housing (seeTable 112(a)) and degradation of membrane module seals (see Table 112(c))Consequently the tolerable stress load on a membrane module will depend on thetype of membranes the way the membrane is packed into the module and themethod used to cure the resin that holds the membrane in place

The optimal membrane module design would have to find a balance between stressimposed on the membrane fibre and the amount of force required to hold the mem-brane fibres firmly in place Presently there is a lack of fundamental data on stressesexperienced by fibres during the filtration and cleaning cycles in the presence of airscouring (Regula et al 2014) This coupled with the difficulty in accuratelymeasuringcalculating stresses in multiple fibre systems has significantly limited thedevelopment of better-designed membrane modules This underlines the need forboth a better understanding in membrane potting methods and stressestrain forcesacting on the membrane fibres for better membrane module design

1133 Failure due to excessive movement

The advantage of submerged membranes is that the hydrostatic pressure generateddoes away with the need for the membrane modules to be pressurised For such con-figurations air scouring or bubbling is used to provide a shear force along the mem-brane surface to help alleviate the fouling phenomena (Cui Chang amp Fane 2003) Thehigher the shear force on the membrane surface the more efficient the removal of fou-lants however the excessive membrane movement due to the higher shear force can

Membrane ageing during water treatment mechanisms monitoring and control 359

also lead to fibre breakage (Wicaksana 2006) This phenomenon coupled with degra-dation of membrane fibres due to ageing could lead to a higher occurrence of fibrefailure

Flat sheet thin film composite (TFC) membranes are widely used in desalinationand water recycling applications via an RO process (Cadotte John 1985 CadotteJohn amp Petersen Robert 1981 Prakash Rao Desai amp Rangarajan 1997) TFC mem-branes consist of a polyamide active top layer on top of a polysulfone microporoussubstrate support layer on a woven or nonwoven polyester reinforcing backing to pro-vide additional mechanical strength (Antony amp Leslie 2011) These membranes areusually used in submerged or tubular module configurations TFC membranes witha polyamide active layer are able to operate at high recovery rates and wide pH rangeshowever similar to hollow-fibre membranes they are highly susceptible to chemicalattack by chlorine (Antony et al 2010 Glater Hong amp Elimelech 1994) To mitigatebiofouling chlorine disinfection is often introduced through upstream dosing before

Hollow fibre

Mold

Mold

Mold

Potting resin

Potting resin

Potting resin

(a)

(b)

(c)

Hollow fibre

Hollow fibre

Figure 114 (a) Static conditions (b) static with elastomer overlay and (c) dynamic conditionsAdapted from Childress et al (2005)

360 Advances in Membrane Technologies for Water Treatment

Table 112 Failure of membrane modules

2(a) Cracks in module housing

2(b) Cracks in module end caps

2(c) Module seal failure 2(d) Improper seal installation

Membrane ageing during water treatment mechanisms monitoring and control 361

the RO membrane system and excess residual chlorine is removed via the dosing ofsodium bisulfate However due to unexpected changes in the quality of the feed watera higher than tolerable amount of free chlorine is present in the RO system thus lead-ing to the degradation of membrane integrity by chemical attack

Flat sheet membranes are also more prone to delamination during routine back-washing When cake layer fouling occurs on the membrane surface the hydraulicresistance increases resulting in a decrease in membrane flux As a way to restorethe flux a backwash is used The backwash entails pumping either permeate wateror compressed air in the reverse direction from the permeate side to the feed sideThis would dislodge caked particles from the membrane surface back into the bulkfeed water (Ratnayaka Brandt amp Johnson 2009) Conventional backwash fre-quencies range from once every 30e90 min with a backwash duration of 30e90 s(Howe Hand Crittenden Trussell amp Tchobanoglous 2012) Backwash pressuresshould be performed according to the membrane manufacturerrsquos specifications andshould also take into account site-specific considerations to prevent delamination ofmembrane sheets formation of hairline cracks in the membrane module and mem-brane module seal failure all of which can result in membrane failure and subsequentcontamination of product water

114 Membrane ageing monitoring methods

Membrane ageing affects the performance of membranes via three different aspectsAs the membrane ages the permeate quality flux restoration after cleaning and themechanical strength are all adversely affected Membrane ageing also presents itselfas degradation in the membranersquos functional properties and characteristics Becausemembranes are extensively used in the production of drinking water integrity breachescan result in an increase in microbial contamination of the permeate (AntonyBlackbeard amp Leslie 2012) and can also lead to a public health compromise shouldthe pathogens and viruses not be removed prior to distribution (Gitis Haught ClarkGun amp Lev 2006) Therefore to monitor the effects of membrane ageing monitoringmethods are used to detect and assess the impacts of membrane ageing

1141 Membrane ageing assessment tools

Multiple analytical techniques are used to assess membrane ageing and are categorisedbased on five different membrane aspects They range from filtration characteristics tomorphological characteristics (see Figure 115) These techniques are well establishedand have been used by many researchers in the field of membrane characterisation Theprinciples behind these techniques will be briefly covered in the sections below

11411 Filtration characteristics

Permeability membrane resistance and solute rejection are filtration characteristicsthat can provide useful real-time information regarding the membranersquos filtration

362 Advances in Membrane Technologies for Water Treatment

properties These methods are also nondestructive and are fundamental in principlethus are usually the first tools used to monitor membrane ageing

Membrane permeability and resistance provides a direct measurement of the mem-brane flux restoration after a cleaning cycle The membrane is said to have undergonedegradation if the flux restored is greater than the initial membrane flux (Yadav ampMorison 2010) Although membrane permeability is a clear and distinctive way todetect membrane degradation it is often too late because it only occurs when a grossintegrity loss has happened and thus is not a reliable tool for real-time monitoring ofmembrane ageing

Solute rejection is determined by the molecular weight cut-off (MWCO) of themembrane Changes in the membranersquos pore size and subsequent rejection can bedetected via solute rejection tests Molecular weight markers or molecules with spe-cific known molecular weights are used to test the membranersquos rejection capabilities(Arkhangelsky Kuzmenko amp Gitis 2007) This method is superseded by other moreaccurate analytical techniques such as pore size distribution measurements based onbubble point and gas permeation methods Despite the limitations of these filtrationcharacteristic assessment tools they still provide the most distinct and fundamental in-formation about membrane aging and degradation in real time

11412 Surface characteristics

Two critical parameters that affect fouling on the membrane surface are membranehydrophilicity and surface charge After multiple cleaning cycles the membranesurface properties are altered due to the exposure to harsh cleaning chemicalsTherefore two analytical techniques are used to measure changes of these twoparameters

For surface hydrophilicity contact angle measurements are conducted via thesessile drop technique and the angle obtained determines the nature of the membranesurface Streaming potential is an electrokinetic measurement used to characterise themembrane surfacersquos zeta potential (see Figure 116) Membranes that were exposed tochlorine became more hydrophilic due to leaching of polymeric additives resulting information of larger pores With chain scission the membranersquos surface charge was also

Membrane ageing assessment tools amp techniques

Filtration characteristics

Surface characteristics

Chemical amp structural characteristics

Morphological characteristics

Mechanical characteristics

Membrane flux measurements

Solute rejection amp

MWCO

Contact angle measurements

Streaming potential

ATR-FTIR measurements

Elemental amp chemical

composition

Membrane mechanical properties

Thermogravimetric analysis

Morphological microscopy

(AFM SEM amp FESEM)

Figure 115 Membrane ageing assessment tools and techniques

Membrane ageing during water treatment mechanisms monitoring and control 363

altered resulting in a more hydrophilic membrane surface (Arkhangelsky et al 2007Wang Wang Wu Zhou amp Yang 2010)

11413 Chemical and structural characteristics

To assess the membranersquos chemical and structural properties two techniques arewidely used Attenuated total reflectanceeFourier transform infrared(ATReFTIR) is used to identify the membranersquos functional groups and shifts intransmission peaks would mean that the membrane chemical structure was altered(see Figure 117) X-ray photoelectron spectroscopy (XPS) measures the elementalcomposition and chemical binding of the membrane surface For both techniquescomparison of the results obtained from the virgin and aged membranes wouldprovide a definitive conclusion as to whether the membrane was missing certainfunctional groups or there were chemical depositions on the membrane surface(Antony et al 2010 Arkhangelsky et al 2007 Puspitasari Granville Le-Clechamp Chen 2010 Rouaix et al 2006) ATReFTIR is a qualitative measure of changewhile XPS is quantitative and thus these two techniques are complementary to oneanother

Exposure to harsh chemical cleaning regimes can cause membrane polymer chainscission and breaking reactions resulting in an ageing membrane that has lost its func-tional groups thus making it more susceptible to failure

11414 Mechanical and thermomechanical characteristics

Mechanical properties of the membrane such as the ultimate tensile strength breakingforce yield stress and Youngrsquos modulus are measured to determine whether ageinghas occurred Physical ageing of the membrane would result in an increase in yieldstress and Youngrsquos modulus and a decrease in tensile strength and breaking force indi-cating that the membrane has become stiffer more brittle and mechanically weaker(Arkhangelsky et al 2007 Rouaix et al 2006) It should be noted that results from

-40

-30

-20

-10

0

10

20

30

40

2 3 4 5 6 7 8 9 10

Zeta

-pot

entia

l (m

V)

pH

001mM

005mM

010mM

Figure 116 Streaming potential graph of membranes with varying additive concentrations

364 Advances in Membrane Technologies for Water Treatment

each mechanical property have to be cross-referenced before a sound conclusion canbe drawn with regard to the membranersquos mechanical integrity

Thermogravimetric analysis (TGA) is also used to detect loss of membrane materialdue to ageing (see Figure 118) TGA detects changes in the mass of the membranesample as a function of both temperature and time It is based on the principle thateach polymeric material has a unique degradation temperature and disappearancesof polymeric peaks at specific temperatures would indicate an alteration to the mem-branersquos mechanical properties (Yadav Morison amp Staiger 2009)

11415 Morphological characteristics

To have a better understanding of the membranersquos surface morphology microscopicvisualisation techniques are used Atomic force microscopy (AFM) scanning electronmicroscopy (SEM) and field emission scanning electron microscopy (FESEM) arevisualisation techniques that can provide accurate high-resolution images of variousmembrane characteristics

AFM is widely used to determine surface morphology and roughness via a preci-sion tip that is dragged along the membrane surface The repulsive interaction betweenthe surface and the tip is measured and a micrograph based on the force is measuredThe micrograph provides information on characteristics such as pore size distributionsurface roughness and membrane surface charge interactions (Arkhangelsky et al2007 Hilal Johnson Bowen amp Williams 2009) By comparing micrographs of thevirgin and aged membrane samples changes in the membranersquos morphological char-acteristics can be detected and could help with assessing and predicting membraneageing and failure

20

30

40

50

60

70

80

90

100

700 900 1100 1300 1500 1700

Abs

orba

nce

Wavelength (cm-1)

Figure 117 Typical Fourier transform infrared spectra for chemical functional groupcomparison

Membrane ageing during water treatment mechanisms monitoring and control 365

SEM and FESEM are able to capture high-resolution images of the membrane sur-face and can provide detailed information that can aid in the understanding of degra-dation on the membrane surface Through the captured high-resolution imagescharacterisation of the membranersquos pore size thickness membrane symmetry andphysical damage that has occurred on the membrane surface can be performedChanges in these parameters would indicate membrane ageing or failure SEM is com-bined with energy dispersive X-ray spectroscopy (EDS) to characterise the chemicalcomposition of the foulant on the membrane surface or the membrane itself (seeFigure 119)

1142 Membrane integrity tests

Membrane failure leads to the compromise of membrane integrity resulting in patho-gens being able to breach the membrane system and increase the microbial contami-nation risk of the treated water and subsequently pose a serious threat to publichealth and safety (Phattaranawik Fane amp Wong 2008) Therefore continuous

0

20

40

60

80

100

0 100 200 300 400 500 600

Wei

ght (

)

Temperature (degC)

Figure 118 Typical thermogravimetric analysis thermogram profile of weight loss as a functionof temperature

(a) (b)

Figure 119 (a) Cross-sectional scanning electron microscopy image and (b) energy dispersiveX-ray spectroscopy elemental map of a hollow-fibre membrane

366 Advances in Membrane Technologies for Water Treatment

integrity monitoring and testing are required to ensure that pathogens are completelyremoved and the product water meets the regulatory guidelines Membrane integritytesting can be divided into two groups direct and indirect testing methods (GuoWyart Perot Nauleau amp Moulin 2010)

11421 Direct testing methods

Direct integrity testing methods refer to tests conducted on the membrane or membranemodule directly and are the most obvious ways to determine membrane integrityTable 113 below summarises the advantages and limitations of the conventional directtesting methods (Guo et al 2010)

Pressure decay testA PDT is a pressure-driven test that is widely used and accepted in the water industryas a way to evaluate the integrity of a membrane During a PDT one side of the

Table 113 Advantages and disadvantages of direct integrity tests

Direct integrity test Advantages Disadvantages

Pressure decay test (PDT) bull Independent of feed waterquality

bull Ease of applicationbull High sensitivitybull High reliabilitybull Low maintenance of testequipment

bull Well-establishedtechnique

bull Performed offlinebull Limited by membranersquosbubble point

bull Requires a large range ofpressures

bull No information of filtratequality

Diffusive air flow (DAF) test bull Independent of feed waterquality

bull Higher sensitivity thanPDT

bull Ease of application

bull Performed offlinebull No information of filtratequality

Vacuum decay test (VDT) bull Independent of feed waterquality

bull Higher sensitivity thanPDT

bull Performed offlinebull No information of filtratequality

bull Difficult for large-scalesystems

Acoustic sound test (AST) bull High failure detectionaccuracy

bull Online operationbull Simple andnondestructive

bull No information of filtratequality

bull Dependent on back-ground noise andinterferences

bull Requires competentoperator training

Membrane ageing during water treatment mechanisms monitoring and control 367

membrane is drained and pressurised up to the test pressure which is set below themembranersquos bubble point The pressure is held for a specific duration and the pressuredecay is monitored It is normal for minor pressure decay (05e15 kPa) due to airdiffusion across the membrane however a faster decrease in pressure would indicatethat the membranersquos integrity has been compromised (ASTM 2013)

PDT is a reliable membrane integrity monitoring technique because it is sensitiveto leak detection and integrity breaches but can only be performed offline resulting inmembrane system downtime Because the membrane is subjected to pressure duringthe PDT and with the effects of membrane ageing or the membrane being not wettedproperly membrane breakage can occur during PDTs and thus may yield a false-positive result (USEPA 2005)

Diffusive air flow testThe diffusive air flow (DAF) test is based on the same principle as the PDT Instead ofmeasuring the pressure decay rate in the PDT DAF tests measure the rate of liquiddisplaced by the diffusive air flow DAF is also limited by the same disadvantagesas the PDT but is more sensitive when detecting integrity changes at levels of greaterthan six LRV Leaks in the additional pipework required for DAF tests could affect thesensitivity of the integrity tests and thus might not be feasible for routine use in largescale plants

Vacuum decay testThe vacuum decay test (VDT) is very similar to the PDT but instead of pressurising thedrained side a vacuum is applied and the vacuum pressure decay is measured Thismethod is more sensitive than a PDT because it negates the effect of air diffusionthrough the membrane and can also detect points of leakage and is nondestructive How-ever this method is rarely used in large-scale membrane systems (Guo et al 2010)

Acoustic sound testA more novel approach to direct integrity monitoring is the acoustic sound test (AST)This technique entails the use of an accelerometer to detect the vibrations generated byair leaks in the membrane module This process is time-consuming and in practice isused in conjunction with a PDT PDT is first used to detect any breaches in the moduleand AST is then used to accurately pinpoint the location of the defect so the membranecan be isolated for replacement or repairs (Johnson 1998) The advantage that ASThas over other direct integrity tests is that it can be performed online while membraneoperation is on thus cutting down on the plantrsquos downtime However ASTrsquos acousticdetection is hampered significantly by background noises and high-process flow ratestherefore it has yet to be implemented in a large-scale system (Laicircne GlucinaChamant amp Simonie 1998)

11422 Indirect testing methods

Indirect integrity testing methods often involve measuring a specific parameter ofthe product water and is used to represent the integrity of the membrane The

368 Advances in Membrane Technologies for Water Treatment

sensitivity of the chosen test should be relatively high so as to detect minor fluctuationsin a measured parameter This would ensure that the treated water achieves the targetedLRV and meets regulatory requirements Table 114 summarises the pros and cons ofindirect testing methods used by industry (Guo et al 2010)

Particle counting and monitoringParticle counting and monitoring is a laser-based light scattering technique usedto count the number of particles of a specific size in the feed and filtrate It is an

Table 114 Advantages and disadvantages of indirect integrity tests

Indirect integrity test Advantages Disadvantages

Particle counting bull Ease of applicationbull Independent of membraneconfigurations

bull Online operation

bull Low detection sensitivitybull Dependent on feed waterquality and operatingconditions

bull Relatively high cost toinstall and maintain

Particle monitoring bull As per particle countersbull Cheaper than particlecounting

bull More sensitive thanturbidity monitors

bull As per particle countersbull Not widely used in waterindustry

Turbidity monitoring bull As per particle monitoringbull Well-established tech-nique in water industry

bull As per particle counters

PhageSpore challengetesting

bull Online operationbull High sensitivitybull High accuracybull Provides actual logremoval value rates

bull Long preparation timefor microbial cultivationand analysis

bull Does not provide real-time integrity results

Powdered activated carbon(PAC) challenge testing

bull Online operationbull High sensitivity

bull High PAC feed concen-tration required

bull Difficult to ensure uni-form PAC particle size

bull May cause membranefouling

FluorescentMagneticparticles challenge testing

bull Independent of feed waterquality

bull Online operationbull High sensitivitybull Can detect virus-sizedbreaches

bull May cause membranefouling

bull Not a well-establishedtechnique

bull Not tested on industrialscale

Membrane ageing during water treatment mechanisms monitoring and control 369

in situ monitoring technique and can be applied to membrane systems of varying con-figurations The measurement sensitivity of the particle counter is directly related to thesize or size distribution of the particles measured and increases as the particle measure-ment threshold is reduced (Guo et al 2010) Therefore the particle counter shouldhave a low threshold that suits its application because the more sensitive the counteris the more expensive it becomes as well

Particle counters do suffer from a number of distinct disadvantages They can onlymeasure particles of a specific size and thus have no selectivity in particle size mea-surements and would produce false readings when micro air bubbles are present inthe permeate stream In a full-scale plant study carried out by Landsness in which fi-bres were progressively cut and the particle count measured the particle count mea-surements were inconsistent thus suggesting that particle counting might not besuitable for full-scale membrane plants (Landsness 2001)

Particle monitoring uses the same principle as particle counters except that itprovides a qualitative assessment of the particle size distribution of the feed orfiltrate It is therefore cheaper than particle counting but is less sensitive (BanerjeeLambertson amp Carlson 1999)

Turbidity monitoringTurbidity is described as the opaqueness of a fluid due to the presence of suspendedsolids and is measured in terms of nephelometric turbidity units (NTU) The turbidityof the feed and filtrate is monitored and a noncompromised membrane should be ableto reduce the turbidity by at least 90 This is cheaper than particle counting andmonitoring however even treated water with a turbidity less than 01 NTU could stillhave bacterial contamination (Banerjee Lambertson Lozier amp Colvin 2001)In the same study carried out by Landsness an insignificant change in turbidity(0024e0037 NTU) was observed when 200 fibres were intentionally cut (Landsness2001) Consequently turbidity monitoring has limited sensitivity for detection mem-brane breaches

Phage and spore challenge testingPhage and spore challenge tests are microbial integrity tests that are spiked into thefeed water and subsequently measured in the permeate Microbial tests are easy toimplement can be done online in situ with membrane system operation and arenondestructive Depending on the application and site-specific considerations thecorrect surrogate should be chosen for the challenge tests

Bacteriophages are virus-infected bacteria surrogates that are used in regulatoryrequired challenge tests to determine membrane integrity and LRV of treatment plantsMS2 bacteriophage is the most common surrogate given its similarly to enteric viruses(Antony et al 2012) Despite the advantages of bacteriophage and spore challengetesting there are also disadvantages Microbial challenge testing requires the longlead time for preparation and cultivation of the surrogate phage It also entails a lengthyanalysis after sampling due to the complexity of plaque forming unit (PFU) countingthus bacteriophage challenge testing cannot provide real-time membrane integrityinformation (Gitis et al 2006)

370 Advances in Membrane Technologies for Water Treatment

With microbial testing it is difficult to distinguish whether microbial reduction wasdue to biological inactivation or retention on the membrane surface Not only are thesephages prone to contamination from other viruses they can also accumulate in thepermeate piping system and lead to false-positive membrane breach detection (Guoet al 2010)

Powdered activated carbon challenge testingAn alternative that mitigates the disadvantages of microbial challenge testing ispowdered activated carbon (PAC) challenge testing It is based on the same principleas its microbial counterpart with the only difference being small controlled doses ofPAC are spiked into the system instead of bacteriophage or spore surrogates The PACparticle size has to be in the similar size range as Giardia and Cryptosporidium so as tomimic microbes (Van Hoof Broens Nahrstedt Panglisch amp Gimbel 2003) Thismethod relies on particle counters and thus suffers from the drawbacks of particlecounting In addition the sensitivity of the test is largely affected by the particlesize distribution of PAC and could lead to membrane fouling if not monitoredproperly

Fluorescent and magnetic particles challenge testingAnother novel surrogate challenge testing option is to either tag particles with fluores-cent or magnetic materials Fluorescent tagged particles can be easily detected bymeasuring the intensity of fluorescence A high fluorescent intensity indicates a largeamount of particles It should be noted that the mass of the particle should be below1 mg so as to maintain the linear relationship between mass and fluorescence Likewiseparticles tagged with magnetic materials such as iron can be easily detected andcollected after the testing (Choi Yang Suh amp Cho 2011) Notwithstanding these ad-vantages fluorescent and magnetic surrogates do experience similar disadvantages asthe other challenge testing methods and thus are not widely used in the water industry

115 Membrane ageing control methods

Membrane ageing and failure are the main challenges faced by water treatment plantsthat use membrane systems for water treatment and recycling Membrane degradationand failure increases the rate at which the membranes would need to be replaced andthus makes membrane filtration more costly Given that membrane ageing eventuallyleads to membrane failure more emphasis should be placed on controlling membraneageing so as to limit the occurrence of membrane failure

1151 Membrane train redundancies

The traditional ldquobelt and bracesrdquo approach in engineering relies on implementation ofmultiple process redundancies Redundancies can be either active or standby In thewater treatment industry active redundant membrane systems reduce the load on

Membrane ageing during water treatment mechanisms monitoring and control 371

one particular membrane train by sharing the overall processing load over multipleredundant trains when a surge in influent flow is detected Standby trains on the otherhand do not come into operation until a failure has occurred and the redundancy iscalled into service to maintain the water treatment systemrsquos functionality and treatedwater quality Therefore having standby redundancies would maintain the membranefiltration unitrsquos efficiency and performance but it will also lead to a higher capital andoperational expenditure thus highlighting the need for membrane process reliabilitymodelling

1152 Membrane modification

Polymeric membranes are often used in various chemical-based environments and arehighly susceptible to membrane degradation due to chemical exposure Therefore oneeffective way to mitigate this issue is to develop new polymeric membranes with sur-face modifications The chemistry of the surface properties of microporous and semi-porous membranes are changed via a surface coating These coatings would render themembranes fouling resistant antimicrobial and chlorine resistant (Geise et al 2010Mansouri Harrisson amp Chen 2010)

From studies conducted it has been proven that membranes become fouling resis-tant after different modifications An increase in the membrane surfacersquos hydrophilic-ity does decrease fouling because this prevents hydrophobic organic foulants frombeing attracted onto the membrane surface Changing the surface charge of the mem-brane can also aid the membrane in becoming more antifouling Similar to increasinghydrophilicity changing the surface charge would generate a repulsive force betweenthe membrane surface and the charged ions of the foulant thus preventing foulantdeposition (Rana amp Matsuura 2010)

Formation of biofilms or membrane biofouling has adverse effects on both mem-brane filtration flux and the membranersquos lifespan Biofouling is unlike other formsof fouling that can be reduced by effective pretreatment of the feedwater due to theself-replicating nature of microbial organisms Biofouling starts with the initial depo-sition of a film of organic molecules and is followed by bacterial colonisation As thebiofilm matures a fouling layer builds up and thus leads to a decline in membrane fluxIt has also been reported that biofouling in the feed channel can lead to a severe in-crease in internal pressure drop and in some cases result in deformation and damageto the membrane module (Mansouri et al 2010)

To control biofouling chlorine is often used as a disinfectant but it suffers from thenegative side effects of chlorine on membrane surfaces Thus chlorine resistance andsurface modification are highly favoured modifications given the high cost involved inthe dechlorinationerechlorination process and replacement of membranes in watertreatment plants

More recently nanoclay nanocomposites have been added to flat sheet membranesto increase the membranersquos abrasion resistance The study concluded that the mem-brane with 1 wt nanoclay showed superior abrasive resistance with the membranelasting two times longer than a normal membrane without the nanoclay addition How-ever the nanoclay concentration would require further optimisation work because an

372 Advances in Membrane Technologies for Water Treatment

increase in the concentration resulted in a decrease in the membranersquos permeability andadverse changes in the membranersquos essential mechanical properties (Lai Groth Grayamp Duke 2014)

116 Conclusion

Currently there are no standard protocols for assessing the membranersquos mechanicalintegrity after prolonged membrane operation and although there are multiple modesand mechanisms that can result in membrane failure membrane ageing and degrada-tion due to chemical attack via strong oxidants is the most common With better char-acterisation of the effects and quantification of membrane ageing at different stages ofa membranersquos lifespan membrane ageing can be mitigated thus prolonging the life-span of the membrane while still maintaining its resilience and reliability With theever-improving membrane modifications being developed the effects of membraneageing can be further controlled thus making membranes more robust cost-effective and efficient for water treatment processes

117 Future trends

The current state-of-the-art of membrane integrity monitoring tools is limited to detect-ing compromises via a variety of in situ and ex situ techniques and tools Despiteextensive research performed on membrane failure mechanisms and their resultant ef-fects these studies are often based on ex situ analytical techniques and can only pro-vide information when a serious breach in membrane integrity is detected Thereforethis highlights the need for the development of nondestructive computer-aided model-ling techniques to predict and quantify membrane ageing at various stages of mem-brane operation through to the end of the membranersquos lifespan

1171 Membrane failure prediction

Apart from monitoring membrane ageing and detecting integrity breaches and failureanother method to limit and control membrane degradation is membrane failure pre-diction Prediction of failure in membrane systems is achieved via a finite elementmethod known as finite element analysis (FEA) FEA is a computer-aided modellingtechnique that can perform mechanical analyses on structures to compute displace-ments from applied loads and is a tool that is widely used by structural and mechanicalengineers (Nicholson 2003) It has also been used by biomedical engineers to predictstress distribution within teeth for tooth fracture prediction (Xie Swain amp Hoffman2009)

FEA can determine stress strain and displacements in complicated shapes by firstdividing the complicated structure into smaller elements and this process is known asdiscretisation Simple equations are then used to solve each element Once all the

Membrane ageing during water treatment mechanisms monitoring and control 373

smaller elements are solved the equation for the whole structure can then be solvedand thus generating the stresses strains and displacements on the entire structureThrough FEA stresses at the locations where they are most likely to cause failurecan be determined Such analyses would aid in design of membrane modules and opti-misation of operation protocols FEA can also be diagnostic by providing supportiveinterpretations via simulation at similar operation conditions when performingautopsies on failed membranes and modules FEA with ageing monitoring tools willyield a more comprehensive understanding of membrane aging and failure and theirmechanisms as well as allow for better process efficiency through improved moduledesign

1172 Membrane reliability modelling

The evaluation of a membrane process unitrsquos reliability should be an important part ofits design and operation However this has traditionally been difficult to assess andquantify and as a consequence its management has largely been ignored Reliabilitymodelling can be used throughout the membrane modulersquos life cycle to predict the fail-ure and the subsequent process shortfalls This would also yield significant savings oncapital and operating costs via the implementation of better strategies derived from thesimulationrsquos results while enabling utilities and plant designers to effectively manageand quantify the risk of noncompliance due to membrane failure With the use ofreliability modelling membrane process performance is no longer just limited tomembrane fouling but can now encompass membrane ageing and failure

List of acronyms

AST Acoustic sound testAFO Amorphous ferric oxideAFM Atomic force microscopyATReFTIR Attenuated total reflectanceeFourier transform infraredCIP Cleaning in placeDAF Diffusive air flowEDS Energy dispersive X-ray spectroscopyFESEM Field emission scanning electron microscopyFEA Finite element analysisLRV Log removal valuesMF MicrofiltrationMLD Megaliter per dayMTBF Mean time between failureMTTF Mean time to failureMTTR Mean time to repairMWCO Molecular weight cut-offNTU Nephelometric turbidity unitsPFU Plaque forming unitPAC Powdered activated carbon

374 Advances in Membrane Technologies for Water Treatment

PDT Pressure decay testRCM Reliability centred maintenanceRO Reverse osmosisSEM Scanning electron microscopyTGA Thermogravimetric analysisTFC Thin film compositeUF UltrafiltrationVDT Vacuum decay testXPS X-ray photoelectron spectroscopy

References

Antony A Blackbeard J amp Leslie G (2012) Removal efficiency and integrity monitoringtechniques for virus removal by membrane processes Critical Reviews in EnvironmentalScience and Technology 42 891e933

Antony A Fudianto R Cox S amp Leslie G (2010) Assessing the oxidative degradation ofpolyamide reverse osmosis membranemdashaccelerated ageing with hypochlorite exposureJournal of Membrane Science 347 159e164

Antony A amp Leslie G (2011)Degradation of polymeric membranes in water and wastewatertreatment Advance membrane Woodhead Publishing Limited

Arkhangelsky E KuzmenkoDampGitisV (2007) Impact of chemical cleaning onproperties andfunctioning of polyethersulfone membranes Journal of Membrane Science 305 176e184

ASTM (2013) Standard practice for pressure decay leak test method ASTM E2930 WestConshohocken PA ASTM International

Banerjee A Lambertson M amp Carlson K (1999) Sub-micron particles in drinking water andtheir role in monitoring the performance of filtration processes In AWWA water qualitytechnology conference proceedings October 31eNovember 4 Tampa FL

Banerjee A Lambertson M Lozier J amp Colvin C (2001) Monitoring membrane integrityusing high sensitivity laser turbidimetry Water Supply 1 273e276

Benavente J amp Vazquez M (2004) Effect of age and chemical treatments on characteristicparameters for active and porous sublayers of polymeric composite membranes Journal ofColloid and Interface Science 273 547e555

Cadotte John E (1985) Evolution of composite reverse osmosis membranes In ACS symposiumseries (Vol 269 pp 273e294) Oxford University Press

Cadotte John E amp Petersen Robert J (1981) Thin-film composite reverse-osmosismembranes Origin development and recent advances [Water purification] In ACSsymposium series (USA)

Chang S (2011) Application of submerged hollow fiber membrane in membrane bioreactorsfiltration principles operation and membrane fouling Desalination 283 31e39

Cheryan M (1998) Ultrafiltration and microfiltration handbook Lancaster PA TechnomicPublishing Company

Childress A E Le-Clech P Daugherty J Chen C amp Leslie G L (2005)Mechanical analysisof hollow fiber membrane integrity in water reuse applications Desalination 180 5e14

Choi S H Yang J Suh C amp Cho J (2011) Use of fluorescent silica particles for checkingthe integrity of microfiltration membranes Journal of Membrane Science 367 306e313

Cui Z F Chang S amp Fane A G (2003) The use of gas bubbling to enhance membraneprocesses Journal of Membrane Science 221 1e35

Membrane ageing during water treatment mechanisms monitoring and control 375

Eisenberg D Soller J Sakaji R amp Olivieri A (2001) A methodology to evaluate water andwastewater treatment plant reliability Water Science and Technology A Journal of theInternational Association on Water Pollution Research 43 91e99

Geise G M Lee H S Miller D J Freeman B D Mcgrath J E amp Paul D R (2010)Water purification by membranes The role of polymer science Journal of Polymer SciencePart B Polymer Physics 48 1685e1718

Gijsbertsen-Abrahamse A J Cornelissen E R amp Hofman J A M H (2006)Fiber failure frequency and causes of hollow fiber integrity loss Desalination 194251e258

Gitis V Haught R C Clark R M Gun J amp Lev O (2006) Application of nanoscaleprobes for the evaluation of the integrity of ultrafiltration membranes Journal ofMembrane Science 276 185e192

Glater J Hong S-K amp Elimelech M (1994) The search for a chlorine-resistant reverseosmosis membrane Desalination 95 325e345

Gunderson L H amp Pritchard L (2002) Resilience and the behavior of large-scale systemsWashington DC Island Press

Guo H Wyart Y Perot J Nauleau F amp Moulin P (2010) Low-pressure membraneintegrity tests for drinking water treatment A review Water Research 44 41e57

Hilal N Johnson D Bowen W R amp Williams P M (2009) Chapter 2eMeasurement ofparticle and surface interactions using force microscopy In W R Bowen amp N Hilal(Eds) Atomic force microscopy in process engineering Oxford Butterworth-Heinemann

Howe K J Hand D W Crittenden J C Trussell R R amp Tchobanoglous G (2012)Principles of water treatment Hoboken NJ Wiley

Johnson W T (1998) Predicting log removal performance of membrane systems using in-situintegrity testing Filtration amp Separation 35 26e29

Johnson W amp Maccormick T (2003) Issues of operational integrity in membrane drinkingwater plants Water Supply 3 73e80

Kagan A (2004) Example 3-Mean time between failures (MTBF) In A Kagan (Ed) Excel byexample Burlington Newnes

Kang G-D Gao C-J Chen W-D Jie X-M Cao Y-M amp Yuan Q (2007) Study onhypochlorite degradation of aromatic polyamide reverse osmosis membrane Journal ofMembrane Science 300 165e171

Klutke G-A Kiessler P C amp Wortman M (2003) A critical look at the bathtub curve IEEETransactions on Reliability 52 125e129

Kwon Y-N amp Leckie J O (2006) Hypochlorite degradation of crosslinked polyamidemembranes I Changes in chemicalmorphological properties Journal of MembraneScience 283 21e26

Lai C Y Groth A Gray S amp Duke M (2014) Preparation and characterization of poly(vinylidene fluoride)nanoclay nanocomposite flat sheet membranes for abrasion resistanceWater Research 57 56e66

Laicircne J M Glucina K Chamant M amp Simonie P (1998) Acoustic sensor A noveltechnique for low pressure membrane integrity monitoring Desalination 11973e77

Landsness L B (2001) Accepting MFUF technology-making the final cut In AWWAMembrane technology conference proceedings March 4e7 2001 Texas San Antonio

Lesjean B Rosenberger S Schrotter J-C amp Recherche A (2004) Membrane-aided bio-logical wastewater treatmentean overview of applied systems Membrane Technology2004(8) 5e10

376 Advances in Membrane Technologies for Water Treatment

Mallevialle J Odendaal P E Foundation A R Wiesner M R Eaux-Dumez L D ampCommission S A W R (1996) Water treatment membrane processes New York NYMcGraw-Hill

Mansouri J Harrisson S amp Chen V (2010) Strategies for controlling biofouling inmembrane filtration systems Challenges and opportunities Journal of Materials Chemistry20 4567e4586

Marshall G amp Chapman D (2002) Resilience reliability and redundancy Retrieved fromhttpadmincopperallianceeudocslibrariesprovider5power-quality-and-utilisation-guide41-resilience-reliability-and-redundancypdfsfvrsn=4ampsfvrsn=4

Nicholson D W (2003) Finite element analysis Thermomechanics of solids Boca Raton FLCRC Press

Oschmann N Nghiem L D amp Schafer A (2005) Fouling mechanisms of submerged ul-trafiltration membranes in greywater recycling Desalination 179(1) 225e233

Phattaranawik J Fane A G amp Wong F (2008) Novel membrane-based sensor for onlinemembrane integrity monitoring Journal of Membrane Science 323 113e124

Prakash Rao A Desai N V amp Rangarajan R (1997) Interfacially synthesized thin filmcomposite RO membranes for seawater desalination Journal of Membrane Science 124263e272

Prulho R Therias S Rivaton A amp Gardette J-L (2013) Ageing of polyethersulfonepolyvinylpyrrolidone blends in contact with bleach water Polymer Degradation andStability 98 1164e1172

Puspitasari V Granville A Le-Clech P amp Chen V (2010) Cleaning and ageing effect ofsodium hypochlorite on polyvinylidene fluoride (PVDF) membrane Separation andPurification Technology 72 301e308

Rana D amp Matsuura T (2010) Surface modifications for antifouling membranes ChemicalReviews 110 2448e2471

Ratnayaka D D Brandt M J amp Johnson M (2009)Water Supply Burlington WA ElsevierScience

Regula C Carretier E Wyart Y Geacutesan-Guiziou G Vincent A Boudot D et al (2014)Chemical cleaningdisinfection and ageing of organic UF membranes A review WaterResearch 56 325e365

Rouaix S Causserand C amp Aimar P (2006) Experimental study of the effects of hypo-chlorite on polysulfone membrane properties Journal of Membrane Science 277137e147

Smith R amp Mobley R K (2008) Chapter 17eMTBF user guide Measuring mean timebetween failures In R Smith amp R K Mobley (Eds) Rules of thumb for maintenance andreliability engineers Burlington WA Butterworth-Heinemann

Stanley S (2011)MTBF MTTR MTTFamp FIT Explanation of terms Tech Rep IMC NetworksAvailable httpwww imcnetworks comAssetsDocSupportWP-MTBF-0311 pdf

Sutton I (2010a) Chapter 7-Reliability availability and maintainability In I Sutton (Ed)Process risk and reliability management Oxford William Andrew Publishing

Sutton I (2010b) Chapter 8eOperations maintenance and safety In I Sutton (Ed) Processrisk and reliability management Oxford William Andrew Publishing

Thominette F Farnault O Gaudichet-Maurin E Machinal C amp Schrotter J-C (2006)Ageing of polyethersulfone ultrafiltration membranes in hypochlorite treatment Desali-nation 200 7e8

Tng K H Wang Y Waite D amp Leslie G (2013) Unexpected iron fouling during mem-brane cleaning in wastewater treatment process 8th International Membrane Science andTechnology Conference (IMSTEC) conference proceedings November 25e29

Membrane ageing during water treatment mechanisms monitoring and control 377

USEPA (2005) Membrane filtration guidance manual EPA 815-R-06-009 Washington DCUnited States Environmental Protection Agency

Van Hoof S Broens L Nahrstedt A Panglisch S amp Gimbel R (2003) Development ofa new integrity testing system Water Supply 3 101e108

Wang P Wang Z Wu Z Zhou Q amp Yang D (2010) Effect of hypochlorite cleaningon the physiochemical characteristics of polyvinylidene fluoride membranes ChemicalEngineering Journal 162 1050e1056

Wicaksana F (2006) Submerged hollow fibre membranes in bubbling systems (PhD thesis)The University of New South Wales Sydney NSW

Xie Z Swain M V amp Hoffman M J (2009) Structural integrity of enamel Experimentaland modeling Journal of Dental Research 88 529e533

Yadav K amp Morison K R (2010) Effects of hypochlorite exposure on flux through poly-ethersulphone ultrafiltration membranes Food and Bioproducts Processing 88 419e424

Yadav K Morison K amp Staiger M P (2009) Effects of hypochlorite treatment on thesurface morphology and mechanical properties of polyethersulfone ultrafiltration mem-branes Polymer Degradation and Stability 94 1955e1961

Yang W Cicek N amp Ilg J (2006) State-of-the-art of membrane bioreactors Worldwideresearch and commercial applications in North America Journal of Membrane Science270 201e211

Zhang K Achari G Sadiq R Langford C H amp Dore M H I (2012) An integratedperformance assessment framework for water treatment plants Water Research 461673e1683

378 Advances in Membrane Technologies for Water Treatment

Mathematical modeling ofmembrane operations for watertreatment

12WL Ang AW MohammadResearch Centre for Sustainable Process Technology Universiti Kebangsaan MalaysiaUKM Bangi Selangor Malaysia

121 Introduction

This chapter will review the mathematical modeling used in water treatment plants thatincorporate membranes in the operation processes Recently more and more watertreatment plants have chosen membranes as the alternative process in producing cleanand potable water due to the processrsquo advantages over conventional treatment pro-cesses Hence a short review about the different mathematical equations used in watertreatment processes with different types of membranes should be carried out The firstsection will briefly introduce the current development trend in the water treatmentsector and the reasons behind the change The second section will focus on the math-ematical models used in membrane water treatment processes It reveals the mainmechanisms of transport in membranes introduces the fundamentals of membranefouling elaborates the phenomenon of concentration polarization (CP) and the deri-vation of the equation The design equation used in membranes processes accordingto the type of membranes will be briefly covered too The following sections willcover the design equations used in nanofiltration (NF) and reverse osmosis (RO) mem-branes and discuss the derivation and use of mathematical equations for microfiltration(MF)ultrafiltration (UF) membranes under different conditions The last part of thischapter provides information about the importance of mathematical modeling in mem-brane operations for water treatment plants and will look into the future trends andchallenges

1211 Water treatment process and its trend

Water scarcity has becomes a worldwide problem that threatens our daily activitiesand sustainable developments One of the main factors that contributed to this prob-lem is the reduction in clean water resources due to pollution Pollution especiallyfrom industry and agriculture has introduced toxins pesticides herbicides heavymetals and deleterious chemicalsresidues into our watercourse Conventional watertreatment plants that use chemical and physical processes are not able to removethose contaminants and are unable to produce consumable water with required

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400012-5Copyright copy 2015 Elsevier Ltd All rights reserved

qualities (Gibs et al 2007 Harisha Hosamani Keri Nataraj amp Aminabhavi 2010Radjenovic Petrovic Ventura amp Barcelo 2008 Saitua Giannini amp Padilla 2012Sarkar Venkateshwarlu Rao Bhattacharjee amp Kale 2007)

Besides the limited clean water resources several other challenges are alsocreating tension in potable water supply such as high blooming population and rapidurbanization stringent regulations for potable water uncertainty in climate changesoveruse and improper management of water resources All these factors coupledwith the underperformance of conventional water treatment processes have led tothe search for new technologies for a better safer and stable potable water supplyOne of the most popular alternatives is the membrane process in drinking water pro-duction plants In recent years membrane technology has emerged as one of the mainprocesses to resolve the problem of water scarcity The membrane process is veryversatile and it has been used for desalting softening and the removal of dissolvedorganics color particles and microbes Its performance has been proven to be betterthan conventional water treatment methods Hence the shortcomings of conven-tional water treatment processes and the strengths of membrane technology havebeen the reasons that contribute to the trend of membrane processes for watertreatment

Basically four types of membranes MF UF NF and RO have been widely usedin the drinking water industry A number of water treatment plants have alreadyimplemented membrane-based processes and the outcomes were encouragingwith the performances of membrane filtration better than those of conventionalprocesses Hence the focus now is on the track to optimize the membrane filtrationprocess and reduce the fouling problems that might affect a membranersquos rejectioncapabilities

122 Mathematical modeling

Modeling of membranes is very important because it will allow users to obtain usefulinformation especially on a membranersquos ability in retaining certain solutes and allow-ing the permeation of particular substances The mechanism of permeation and rejec-tion of membrane is a complicated process Thus a good predictive model will enablethe performance of the membrane to be predicted accurately without involving tediousand complicated procedures to obtain raw data for prediction and enhance theefficiency of the process by optimizing it A reliable modeling will result in a smallernumber of experiments and consequently a reduction in cost and time (HilalAl-Zoubi Darwish Mohammad amp Arabi 2004) Normally in the membrane processtwo aspects of performance will be predicted by using modeling flux prediction andrejection prediction (Van der Bruggen Meuroantteuroari amp Nystreuroom 2008) Several theoriesand models have been proposed for membrane transport mechanisms to derive anacceptable model The models used for each membrane might be different due tothe difference in membranes properties Several types of fouling also affect the compli-cation of the models Further details will be elaborated in the following section

380 Advances in Membrane Technologies for Water Treatment

1221 Transport and fouling mechanisms for membranes

Transport mechanisms of solutesolvent molecules through membranes are shown inFigure 121 Generally there are four types of transport mechanisms (Seader ampHenley 1998)

1 Bulk flow through pores2 Diffusion through pores3 Restricted diffusion through pores4 Solution-diffusion through dense membranes

Different types of membranes will have different transport mechanisms applied onthem For example an RO membrane is a dense membrane so the transport of compo-nents through the membrane will be a solution-diffusion type while for microporousmembranes such as MF and UF the transport mechanisms will involve the pore sizeof membranes NF membranes show a behavior between dense and microporous mem-branes In addition size exclusion and electrostatic interaction are the two fundamentalphenomena that govern the solute rejection by RONF The transport mechanism willdetermine how the performance (flux and rejection) of membranes are being modeledin the water treatment process Figure 122 shows a simple classification of transportmodels for the four membranes discussed in this chapter and the factors that affect thetype of transfermodels to be used inwater treatment (Mulder 1996 ShonVigneswaranKandasamy amp Shim 2008 Wiesner amp Buckley 1996 Williams 2003)

From Figure 122 it can be seen that the transport models used to predict anddescribe the water treatment process depend on the membranes used and the foulantsin the raw water Membrane class is further separated into porous and nonporous typeseach one having its own suitable equationstheories for mathematical modelingFor foulants its characteristic will determine which model is the most suitable and ac-curate in describing the retention mechanism Indeed transport mechanisms rely on acombination of several principles including size exclusion and charge or dielectricexclusion (DE) (Yaroshchuk amp Staude 1992) For uncharged solutes sieving effector steric hindrance will be the main rejection mechanism Solutes with larger molecularweight cutoff than the membrane will be retained Besides that the transport ofuncharged solutes is also contributed by convection due to pressure difference and

Figure 121 Transport mechanisms in membranes (Flow is downward) (a) Bulk flow throughpores (b) Diffusion through pores (c) Restricted diffusion through pores (d) Solution-diffusionthrough dense membranesSource Adapted from Seader and Henley (1998)

Mathematical modeling of membrane operations for water treatment 381

Transport models

Solutes(foulants)

Nonchargedcolloids

Chargedcolloids

Generalorganicmatter

Ions

Membranes

Porousmembranes

Nonporous (dense)membranes

CP relationshipconvection and diffusionNernstndashPlanck equationresistance in series and

cake filtration theory

CP relationshipthermodynamic modeldiffusivity resistance in

series and adsorption layers

NF

RO

MF

UF

Basic models-HagenndashPoiseulle equation

-KozenyndashCarman relationship

Homogeneous membrane models-Solution-diffusion

-Extended solution-diffusion-Solution-diffusion-imperfection

Convection and diffusion Donnanexclusion extended NernstndashPlanckequation resistance in series and

cake filtration theory

Donnan exclusion andextended NernstndashPlanck

equation

Pore based models-Preferential sorption-capillary flow

-Finely porous and surface force-pore flow

Knudsen flow

Friction model

Concentration polarization (CP)model

Resistance in series modelosmotic pressure model and

mechanistic interpretation

Irreversible thermodynamics models-KedemndashKatchalsky

-SpeiglerndashKedem

Figure 122 Classification of transport models according to the type of membranes and foulantsSource Adapted from Williams (2003) Mulder (1996) Shon et al (2008) and Wiesner and Buckley (1996)

382Advances

inMem

braneTechnologies

forWater

Treatm

ent

diffusion through a concentration gradient across the membrane The main transportmechanism of charged solutes (ions) is charged exclusion or the Donnan effect whichinvolves the interaction between the rejection of co-ions and the fixed electric chargesattached to the membrane matrix (Hassan Ali Abdull amp Ismail 2007) Some of thecommonly used transport models will be discussed in the following sections It shouldbe noted that so far there is not any mathematical modeling that is valid for wide-range applications Most of the established models are only applicable for certain andspecific conditions

Fouling is a major obstacle for membranes to be used widely Fouling may exist indifferent forms (Field 2010)

1 Adsorptionmdashoccurs when there are specific interactions between the membrane and foulantsolute in the solution

2 Pore blockagemdashfoulantsparticles block and clog the pores of membrane3 Depositionmdashdeposit of particles that grows layer by layer at the membrane surface (known

as cake resistance fouling as well)4 Gel formationmdashCP leads to the formation of a gel layer in the immediate vicinity of the

membrane surface

Fouling will affect membrane flux and rejection of unwanted components in waterHence modeling of membrane performance in water treatment should take into ac-count membrane fouling because fouling phenomena is unavoidable for current stage

1222 Concentration polarization

CP is a process of accumulation of retained solutes in the membrane boundary at thefeed side It is a natural consequence of membrane selectivity (Field 2010) CP com-plicates the modeling of the membrane filtration unit because the wall concentration ofsolute is not the same as the bulk feed concentration It is difficult to determine the so-lute wall concentration The boundary layer film model has been used to describe thisphenomenon Under steady-state conditions the convective flow of solute to themembrane surface is equal to the solute that permeates through the membrane deductwith diffusion of solute back to the bulk feed solution (as shown in Eqn (121))

J$C frac14 J$Cp DjidCdz

(121)

Integration of Eqn (121) with the following boundary conditions

z frac14 0 C frac14 Cm

z frac14 lbl C frac14 Cb

will yield Eqn (122)

J frac14Dij

lbl

ln

Cm Cp

Cb Cp

(122)

Mathematical modeling of membrane operations for water treatment 383

At the end this equation derived from film theory model will be used to determinethe solute concentration at the membrane surface Rearranging Eqn (122) yields

Cm frac14 ethCb CpTHORNexp J$lblDij

(123)

Solute concentration at the membrane surface is very important because it will beused in many membrane transport models

Usually the term Dij=lb in Eqns (122) and (123) will be described as a mass trans-fer coefficient kib and it can be determined from conventional chemical engineeringcorrelations such as the Sherwood number (Sh) Reynolds number (Re) Schmidtnumber (Sc) and Peclet number (Pe) (Baker 2000 Field 2010) The bulk andpermeate concentrations can be determined by using analytical instruments

CP might have some negative effects on the performance of a membrane filtrationunit It will decrease the water flux and rejection of undesired solute cause precipitationdue to high surface concentration that exceeds the solubility limit change the membraneseparation properties and enhance other fouling such as colloidal or particulate materialsthat will block the membrane surface Hence the design of the membrane module andoperating conditions are important to prevent and reduce the impact of CP

1223 Mathematical modeling for RO membranes

RO is a process especially applied in desalination that uses membranes only perme-able to water but impermeable to salt and other impurities Many mathematicalmodels have been proposed for the solute and solvent transport mechanism andthe most acceptable and widely applied is solution-diffusion transport mechanismThe water transport across the membrane can be expressed by Fickrsquos law (Baker2000) With some assumptions and further derivation the equation is reduced to aformula in which the water flux is linked to pressure and concentration gradientsacross the membrane For solute flux it depends on salt concentration at the feedside and permeate side

Design equations for RO membranes will be based on the solution-diffusiontransport mechanism Water flux and solute flux are expressed as (Baker 2000)

Jw frac14 PwethDp DpTHORN (124)

Js frac14 PsethC1 C2THORN (125)

One of the considerations when deciding on the operating pressure for RO is theosmotic pressure of the liquid feed Osmotic pressure is being defined as the pressurerequired to be applied to a solution to prevent the inward flow of water across the mem-brane For small to minimum concentration of solute osmotic pressure p is directlyproportional to the concentration of the solute and temperature according to the

384 Advances in Membrane Technologies for Water Treatment

experimental data done by other researchers (Senthilmurugan Ahluwalia amp Gupta2005) Osmotic pressure can be calculated by using the formula proposed by VanrsquotHoff (Geankoplis 2003) or using the Pitzer equation (Hu Wu amp Gao 1999) How-ever the calculation steps of the Pitzer equation are complicated as shown in the refer-ence cited So here is the easier form of Vanrsquot Hoff equation

p frac14 n

VmRGT (126)

However this equation is suitable for dilute water solutions For solutions with highconcentration of solutes modifications have to be made For concentration of dis-solved solids in the range of 20000e50000 ppm the osmotic pressure can be calcu-lated from the equation modified by (Kaghazchi Mehri Ravanchi amp Kargari 2010)

p frac14 09524C2 thorn 81633C 236143 (127)

Hence the osmotic pressure gradient is

Dp frac14 pm pp frac14 09524C2m C2

p

thorn 81633

Cm Cp

23614 (128)

in which the concentration of a solute at the membrane surface could be obtained fromthe CP correlation

An industrial seawater RO desalination plant with a spiral-wound module wassimulated using the solution-diffusion model and the model was found to be ableto predict the steady-state behavior of the plant with good accuracy Tables 121and 122 show the comparison between the actual results from the industrial unitand calculated data from the solution-diffusion model It can be concluded that themathematical model has a good accuracy of prediction for that particular seawaterRO desalination plant (Kaghazchi et al 2010)

Besides the well-known solution-diffusion model (under the category of nonporousor homogeneous membrane models as depicted in Figure 122) RO transport modelscan be derived from one of two main groups irreversible thermodynamics models andporous models (Gambier Krasnik amp Badreddin 2007) Table 123 presents a sum-mary of available transport models and basic equations for determining the soluteand solvent fluxes for RO membranes (Malaeb amp Ayoub 2011) Details of derivationcan be found in the reference cited

Models based on irreversible thermodynamics treat the membrane as a blackbox One of the irreversible thermodynamics models is the SpieglereKedem modelThis black box approach allows the performance of the membranes to be character-ized in terms of salt permeability Ps and the reflection coefficient s (LevensteinHasson amp Semiat 1996 Schirg amp Widmer 1992 Xu amp Spencer 1997)No particular mechanism of solute transport and structure of membrane arerequired

Mathematical modeling of membrane operations for water treatment 385

There are several assumptions being made for the classical hydrodynamic or poremodel It is assumed that (Nakao 1994 Zhao Zhou amp Yue 2000)

1 The membrane is crossed by cylindrical pores with uniform radius and length2 Solute molecules are simulated as rigid spheres moving slowly inside the pores3 Poiseuille flow applies in the pores of the solvent4 Steady-state flow occurs and5 Solute concentration is so small that there is no interaction among solute molecules inside

the pores

Membrane is being considered as a charged porous layer by steric hindrance pore(SHP) model and TeorelleMeyereSievers (TMS) model The partitioning effects aredescribed by steric hindrance and electrostatics and mass transfer through the mem-brane is based on the extended NernstePlanck equation Space charge models ofSpiegler-Kedem provide a relatively stable numerical solution but are computation-ally expensive (Malaeb amp Ayoub 2011)

Agriculture and industry the two largest water consumption sectors have producedand released a lot of new contaminants into our various drinking water sources Pes-ticides herbicides insecticides pharmaceutical products and heavy metals are a fewof the emerging trace contaminants that currently receive more attention in water treat-ment plants With the health threats from the emerging and newly discovered trace

Table 121 Simulation results of the first industrial unit

Parameter Industrial unit Calculated Error ()

Permeate flow rate(m3s)

830 105 753 105 93

Permeateconcentration(kgm3)

061 060 11

Concentrate flowrate (m3s)

225 103 223 103 09

Concentrateconcentration(kgm3)

6411 6472 09

Source Kaghazchi et al (2010)

Table 122 Performance comparison between actual and simulatedfirst unit

Parameter Industrial unit Calculated Error ()

Recovery 00259 00233 003

Rejection percent 09902 09905 003

Source Kaghazchi et al (2010)

386 Advances in Membrane Technologies for Water Treatment

Table 123 Available transport models for reverse osmosis membrane

Models Model reference Basic featuresequations

Models based on irreversiblethermodynamics

Kedem and Katchalsky (KK) model bull Describes the flow of solution and solute in which perfor-mance is measured through the dissipation function and doesnot address the mechanism of rejectionJv frac14 LpethDP sDpTHORNJs frac14 Psethcm cpTHORN thorn eth1 sTHORNJv

KedemeKatchalskyeZelman model bull Proposed for the multiple solute system in membranefiltration

bull Considers the differential equations for the transport ofmultiple solutes and involves the usage of finite-differenceequations

SpieglereKedem model bull Accounts for the variability of the concentration profile atlarge fluxes and high concentration gradients

bull Transport through membrane is characterized by solvent andsolute permeability and reflection coefficient

bull Calculated based on the average concentration inside themembrane

bull Mostly used in single-solute systems

Js frac14 P0dcdx

thorn eth1 sTHORNJv

Extended SpieglereKedem model bull A one-dimensional model for multiple solutes incorporatingsoluteesolute interactions

bull Characterized by parameters estimated using theLevenbergeMarquardt method coupled with theGausseNewton algorithm and based on experimental datafrom the literature

Continued

Mathem

aticalmodeling

ofmem

braneoperations

forwater

treatment

387

Table 123 Continued

Models Model reference Basic featuresequations

Stefan-Maxwell model Peppas amp Meadows (1983)Roberson amp Zydney (1988)

bull Have shown to be equivalent to models based on irreversiblethermodynamics

Js frac14 D2CxsdlnethysxsTHORN

dz thorn D2D1

JvCxs

xs is the solute mole fraction ys is the solute activitycoefficient C is the total molar concentration and D1 and D2

are overall transfer coefficients given in terms of the binaryStefan-Maxwell diffusivities

Teorell-Meyer-Sievers (TMS) model(Hassan et al 2007)

bull Describes the membrane electrical properties in terms ofeffective charge density and electrostatic effects

bull Assumes a uniform radial distribution of fixed charges andmobile species

ssalt frac14 1 2

eth2a 1THORNzthorn ethz2 thorn 4THORN1=2

Psalt frac14 Dseth1 ssaltTHORNAk

Dx

Space charge model

bull Suggests a radial distribution of the potential and concen-tration gradient across the pores

bull Ions are treated as point charges so steric effects of the size ofions are neglected

388Advances

inMem

braneTechnologies

forWater

Treatm

ent

bull The NernstePlanck equation is used for ion transport thenonlinear PoissoneBoltzmann equation for ionconcentration and radial distribution of electric potential andthe NaviereStokes equation for the force balance in narrowpores relative to pore length

Hydrodynamic or pore models Pappenheimer (1953) Solute flux due to diffusion onlyJds frac14 Dof ethqTHORNSDAkdC=dx DeffAkdC=dxSD steric factor restricting the entrance of the molecule intothe poref(q) viscous drag at the wall once the molecule has enteredthe poreDo and Deff diffusion coefficients in a free solution and in apore respectivelyAk corresponds to the membrane surface porositySD frac14 eth1 qTHORN2f ethqTHORN frac14 1=eth1thorn 24qTHORN

Renkin (1954) Solute flux is given in terms of both diffusion flow andconvection flowJs frac14 DoethqTHORNSDAkethCm Cf THORN thorn f ethqTHORNScJvCm

The restriction factor Sc for the convection flow isintroducedSc frac14 2eth1 qTHORN2 eth1 qTHORN4f ethqTHORN frac14 1 2104qthorn 209q3 095q5

Verniory DuBois Decoodt Gasseeamp Lambert (1973)

bull Modified the above classical pore models by adopting awall correction factor and relating it to the treatment withthermodynamic and frictional forcesJs frac14 Dof ethqTHORNSDAkDCs=Dxthorn gethqTHORNScJvCs

bull Introduced the convective friction forces function g(q) inaddition to f(g) f ethqTHORN frac14 eth1 2105q2 thorn 2865q3

17068q5 thorn 072603THORN=eth1 075857q5THORNgethqTHORN frac14 eth1 2=3q2 020217q5THORN=eth1 075857q5THORN

Continued

Mathem

aticalmodeling

ofmem

braneoperations

forwater

treatment

389

Table 123 Continued

Models Model reference Basic featuresequations

Steric hindrance pore (SHP) model bull Modified pore model by eliminating the wall correctionfactors used to predict pore radius and the ratio of membraneporosity to thickness

bull Particularly used for the permeation of a single neutral soluteand not suitable for salt retention application

Ji frac14 viki

HFiuxc HDiDi

dcdx thorn c ziFdf

RTdx

bull The HF and HD parameters are for steric hindrance andfrictional forces that impede convective and diffusivetransport respectively

Source Malaeb and Ayoub (2011)

390Advances

inMem

braneTechnologies

forWater

Treatm

ent

contaminants in natural water resources membrane technology (RONF) has been sug-gested and accepted as the most appropriate method to remove them Thus mathemat-ical modeling of the rejection of those trace contaminants is very useful in predictingthe removal of deleterious substances in water

The issue of boron in drinking water has received more attention judging from theincreasing number of scientific investigations on the removal of boron by RONFmembranes (Tu Nghiem amp Chivas 2010) Because boron exists in a solution inthe form of boric acid and borate salts the currently widely accepted solution-diffusion model can be used to explain the transport mechanism of boron throughRONF membranes Another model used to describe the transport of boron is the irre-versible thermodynamics model developed by Kedem and Katchalsky (Kedem ampKatchalsky 1958) The transport equations of solution-diffusion and irreversible ther-modynamics models have been presented above and in Table 123

The detection of pesticides and endocrine compounds in natural water is of greatconcern to the public and especially potable water production plants (CornelissenVerdouw Gijsbertsen-Abrahamse amp Hofman 2005) Pesticide removal by RONF isa complicated process However in general there is ample evidence that the mainmechanism that determines the retention of pesticides is size exclusion (sieving mecha-nism) (Plakas amp Karabelas 2012) For charged pesticides both size exclusion and elec-trostatic interaction are the twomechanisms that are responsible in controlling the degreeof separation Few models have been applied to predict the trace organic rejection andTable 124 shows the pros and cons of different models applied for modeling andpredicting trace organic rejection by NFRO membranes (Plakas amp Karabelas 2012)

In membrane water treatment processes water temperature is an important factorthat must be considered when operating the plants Higher temperature will requirelower operating pressure to produce the desired production capacity and the reverseis true for low-temperature raw water By assuming all the factors affecting perfor-mance of a membrane remain constant the permeate flow at any temperature relativeto flow at 25 C can be estimated by (AWWA amp ASCE 2012)

QT frac14 Q25C 103ethT25THORN (129)

This equation is applicable for both RO and NF membranesThe selectivity of RO membranes normally will be measured as solute rejection

coefficient as (AWWA amp ASCE 2012)

R frac14 Cb Cp

Cb 100 frac14

1 Cp

Cb

100 (1210)

Due to the high rejection of solute for RO membranes the concentration of solutebeing retained at the membrane surface (feed side) will be very high This leads to theproblem of CP The solute concentration at the membrane surface (feed side) will bedifferent from bulk concentration Hence the film theory model is used to determinethe solute wall concentration (as shown in the previous section) The solute wallconcentration is required to obtain the real rejection percentage of the RO membrane

Mathematical modeling of membrane operations for water treatment 391

Table 124 Main advantages and disadvantages of the models applied for modeling andor predicting traceorganic rejection by nanofiltrationreverse osmosis membranes

Models Advantages Disadvantages

Models based on irreversiblethermodynamics (SpieglereKedemmodel combined film theory-SpieglereKedem model models withand without convection)

bull No particular mechanism of solutetransport and structure of membraneis specified (membrane treated as aldquoblack boxrdquo)

bull Suitable for predicting theperformance of multiple solutes innanofiltrationreverse osmosissystems

bull Highly dependant on the driving forces (pressure andconcentration gradients) which restricts their practicalapplication

bull A number of assumptions made which in many cases areunrealistic

bull The system should not be too far from equilibrium inorder for the model to be applicable

bull Valid for high rejection membranes

Mass transport models (solution-diffusion models porous modelsnonporous or homogeneousmembrane models etc)

bull Simple models providing estimateseven for technically demandingseparations

bull The linearization of these modelsfacilitates rapid calculations

bull Variation of the solute mass transfer coefficients withdifferent water qualities and operating conditions intrin-sically membrane physicochemical properties constrainsthe model application from one system to another

bull Mainly applicable to single-solute systemsbull Solute mass transfer coefficients depend on the test unitscale (as different operating conditions may exist in theseunits) limiting the model accuracy in membrane scale-up

Artificial neural network models inconjunction (or not) with quantitativestructure activity relationship models

bull Easy to usebull Do not apply any physical laws andtransport phenomena thus over-coming the problems of complexity

bull More accurate estimates than exist-ing models

bull Valid models regardless of rejectionperformance of the membranes tested

bull Specific applicable in the range of experimental condi-tions employed for their development

bull Changes of membrane properties as a result of fouling orswelling influence the accuracy of models

Source Plakas amp Karabelas (2012)

392Advances

inMem

braneTechnologies

forWater

Treatm

ent

The model equations for water and solute flux also will be changed after taking the CPeffect into consideration Concentration of solute at membrane surface could beobtained from the final derivation shown in previous subsection

For rejection

RCP frac14 Cm Cp

Cm 100 frac14

1 Cp

Cm

100 (1211)

The CP effect will be included in modeling for more precise prediction An exampleis the incorporation of the CP ratio for tubular membranes in the turbulent region thathas been derived out as shown below (Wiesner amp Buckley 1996)

Cm

Cbfrac14 1

Drthorn1 1

Dr

expethkTHORN (1212)

Dr frac14 Cb

Cp

jd frac14 0023Re017

By incorporating the CP ratio into the solution-diffusion transport equations forwater and solute flux the following equation could be obtained

Jw frac14 kw

Dp Dp

Cm

Cb

thorn Dp

Dr

(1213)

Js frac14 kiCb

Cm

Cb 1Dr

(1214)

These equations allow the performance of RO membranes to be estimated andpredict what the effect of CP would be on the given operating conditions

1224 Mathematical modeling for NF membranes

NF has been defined by many as a process between UF and RO Indeed NF is a verycomplex process Generally NF is a charged membrane and the modeling mustconsider the interaction between the charged membrane and ionic solute Manycharged membrane transport theories have been proposed that account for electrostaticeffects as well as diffusive and convective flow to describe the solute separationIndeed NF and RO membranes both share most of the same models but under thissubsection a few models that are widely accepted for NF membrane will be discussedOne of them is the solution diffusion model which has been depicted in the previoussubsection However the most popular mathematical model for NF is the extendedNernstePlanck equation It has been widely adopted for NF membrane modeling

Mathematical modeling of membrane operations for water treatment 393

This equation consists of a few different terms that accounted for the different transportphenomena Donnan effect and dieletric exclusion are included in this model

The most commonly adopted form of the extended NernstePlanck equation (TsuruNakao amp Kimura 1991) is

Ji frac14 KicciJv Dipdcidx

ziciDip

RGTFdjdx

(1215)

The first term in Eqn (1215) represents the solute flux contribution due to convectionthe second term accounts for solute transport due to diffusion and the last term describesthe solute flux due to the Donnan potential (Williams 2003) This extendedNernstePlanck equation will be the base model for other models When a chargedmembrane is brought into contact with an electrolyte solution the concentrationpartition of co-ions and counter-ions occurs at the membraneesolution interfaces onboth the feed and permeate sides The potential differences associated at these boundariesare calledDonnan potentials andDonnan potentials exist tomaintain the electrochemicalequilibrium (Nguyen Bang ChoampKim 2009) TheDonnan potential helps in repellingions where co-ions are rejected because of the potential at the membrane-feed interfacewhereas counter-ions are attracted (Greenlee Lawler FreemanMarrotampMoulin 2009)

For uncharged solute transport through the membrane the Donnan effect will notbe considered so the third term in Eqn (1215) will be zero (Luo amp Wan 2011)The application of the modified extended NernstePlanck equation for unchargedsolutes can be obtained elsewhere (Bowen amp Welfoot 2005 2002) and Figures123 and 124 show the good agreement between the predicted and experimentaldata for organic solute (iminodiacetic acid IDA and glutamic acid Glu) rejectionby NF 270 membrane (Luo amp Wan 2011)

10

08

06

04

02

0000 50x10-6 10x10-5 15x10-5 20x10-5 25x10-5

Flux (ms)

0 M NaCl05 M NaCl10 M NaCl20 M NaClBest fitting 05 M NaClPrediction 10 M NaCl

Prediction 20 M NaCl

Rin

t

Figure 123 Measured and predicted iminodiacetic acid retentions for NF 270Reprinted from Luo and Wan (2011) with permission from Elsevier

394 Advances in Membrane Technologies for Water Treatment

Various studies have used a model termed the Donnan-Steric-Pore model (DSPM)to predict the behavior of ionic rejections in NF membranes (Bowen amp Mohammad1998 Bowen Mohammad amp Hilal 1997) DSPM is a model developed based onthe extended NernstePlanck equation in conjunction with the Donnan equilibriumIt has been widely accepted as one of the most effective models for NF membranesin predicting the rejection of ionic compounds (Mohammad 2008) The potentialgradient is

djdx

frac14Pn

ifrac14 1 ziJvDip

Kicci Cip

ethF=RGTTHORN

Pnifrac14 1 z

2i ci

(1216)

With the inclusion of the steric effect (4) and Donnan exclusion effect (Dj)

gicigoi Ci

frac14 4 exp

ziF

RGTDjD

(1217)

The DSPM model has been further modified to include the DE effect for chargedions (Mohammad Hilal Al-Zoubib Darwish amp Ali 2007) and this model hasbeen termed the DSPM-DE model The DSPM-DE model differs from the DSPMmodel due to the inclusion of the DE effect in the partitioning coefficients of eachion as follows

ciCi

frac14 4 exp

ziF

RGTDjD

exp

DWi

kBT

(1218)

10

08

06

04

02

00000 750x10-6 150x10-5 225x10-5 300x10-5

Flux (ms)

0 M NaCl05 M NaCl10 M NaCl20 M NaClPrediction 05 M NaClPrediction 10 M NaClBest fitting 20 M NaCl

Rin

t

Figure 124 Measured and predicted glutamic acid retentions for NF 270Reprinted from Luo and Wan (2011) with permission from Elsevier

Mathematical modeling of membrane operations for water treatment 395

The DE effect is represented by the Born solvation energy barrier The electro-static interactions between the ions of the solutions with the polarization chargesinduced by ions at the interfaces between the media of different dielectricconstants (in this case a membrane matrix and a solvent) will create DE (Bandiniamp Vezzani 2003 Yaroshchuk 2000) The derivations and the applications of theabove equations are not within the scope of this chapter and they could be obtainedfrom the references cited

1225 Mathematical modeling for MFUF membranes

Both MF and UF membranes are porous membranes which indicate that the basicmechanism of rejection will be the sieving mechanism Molecules with a greatersize than the pores of membranes will be rejected Hence the pore flow model canbe used to describe the flux through the membranes According to Darcyrsquos law fluxis proportional to applied pressure difference across the membrane as shown in Eqn(1219) (Baker 2000)

J frac14 P$ethpf ppTHORN frac14 P$Dp (1219)

This equation is the basic design equation used to model the performance of MFUF(clean membranes) in water treatment processes Unlike RONF membranes the os-motic pressure of macromolecules (solutes being rejected from passing through MFUF) is very low and can be neglected So the osmotic pressure effect is not beingconsidered for MFUF (Geankoplis 2003) The permeability constant P dependson the membrane structure (pore size distribution and porosity) and permeate quality(viscosity) There are two approaches normally used to define the permeability con-stant The first approach is using the Hagen-Poiseuille law in which the membranestructure can be assumed to be uniform capillaries (Seader amp Henley 1998)

v frac14 D2

32mLethpf ppTHORN (1220)

By combining the HagenePoiseuille equation the porosity of membrane 3 and thetortuosity of the pores s the flux can be described by

J frac14 εD2

32msDp

L(1221)

In real porous membranes the pores might not be cylindrical and straight so anotherapproach is assuming the membrane is an arrangement of near-spherical particles inwhich CarmaneKozeny equation can be applied to obtain the flux as (Field 2010)

J frac14 ε3

KmS2eth1 εTHORN2Dp

L(1222)

396 Advances in Membrane Technologies for Water Treatment

However both of the above two equations are idealized equations because the realstructure of the membrane deviates from the assumptions Thus usually a morecommonly accepted equation will be used to describe the pure water flux of MFUF known as the osmotic pressure model (Ahmad Chong amp Bhatia 2006 Karode2001)

J frac14 Dp Dp

mRmfrac14 Dp

mRm(1223)

Because the osmotic effect for MFUF membranes usually is very small this termwill be neglected To have a better prediction on the membrane performance thefouling effect has to be taken into consideration when treating the real water samplewhich might contain foulants Equation (1223) will be modified to include thepossible fouling resistance when the membranes are being used to treat nonpure wa-ter This leads to the development of a widely used mathematical model known asthe hydraulic model of filtration resistance (resistance in series model) (Konieczny2002 Rajca Bodzek amp Konieczny 2009 Shengji Juanjuan amp Naiyun 2008) Thismodel is based on the equation that describes the correlation between permeate fluxand pressure taking into account the hydraulic resistance fluid meets flowingthrough a membrane By looking at the equation below it can be seen that the liquidflowing through the membrane will not only encounter the resistance from mem-brane itself but also reversible and irreversible resistances ariseing due to foulingphenomena

J frac14 Dp

methRm thorn RtTHORN frac14 Dp

methRm thorn Rrev thorn RirrTHORN (1224)

Reversible fouling is a fouling process where the membrane capability can berecovered by either backwash or chemical cleaning methods while irreversible foulingis the permanent loss of a membranersquos productivity that could not be recovered by acleaning method The ways to obtain the values of resistance are shown elsewhere(Rajca et al 2009) Figure 125 depicts the comparison between volume water fluxobtained experimentally and calculated using Eqn (1224) under different operatingconditions It was shown that this resistance model is capable of characterizing thewater treatment process by UF membrane

Another simple mathematical model that has been tried out to calculate the fluxfrom the UF membrane water treatment process is the filtration model in a nonsta-tionary process (relaxation model) (Konieczny 2002) It uses the mass transportbalance equation during membrane filtration in which the decrease in the permeateflux is proportional to its value

ddtethJ JNTHORN thorn 1

t0ethJ JNTHORN frac14 0 (1225)

Mathematical modeling of membrane operations for water treatment 397

for t frac14 0 J frac14 J0

for t frac14 N J frac14 JN

After integration with the above boundary conditions

Jt frac14 ethJ0 JNTHORNe tt0 thorn JN (1226)

Figure 126 shows that the model curve (relaxation model) did not fit with the filtra-tion results (feed water from raw water reservoir) initially which might indicate thatthe system has not reached equilibrium yet The model adequately fits into themembrane water treatment process

In reality natural water for the potable water treatment process might containvarious contaminantsfoulants So to understand and describe the fouling mechanism(pore blocking) more precisely a mathematical model that can give a clue on whichpore blocking mechanisms should be developed and used Such a model has beendeveloped and it is known as Hermiarsquos model

Most of the fouling mechanisms for porous membranes like MF and UF are relatedto their pores As shown in Figure 127 porous membrane fouling mechanisms can bedivided into four categories (Field 2010)

J momentary experimental4

3

2

1

4

3

2

1

4

3

2

1

4

3

2

10 50 100 150 200 250 300 0 50 100 150 200 250 300

0 50 100 150 200 250 3000 50 100 150 200 250 300

Time (min) Time (min)

Time (min) Time (min)

J momentary theoreticalJ momentary experimentalJ momentary theoretical

J momentary experimentalJ momentary theoretical

J momentary experimentalJ momentary theoretical

J x

105 (m

3 m2 s)

J x

105 (m

3 m2 s)

J x

105 (m

3 m2 s)

J x

105 (m

3 m2 s)

(a)

(c) (d)

(b)

Figure 125 Comparison of experimental and theoretical volume flux for ceramic ultrafiltration(UF) membrane (a) Direct UF (b) Coagulation FeCl3-UF (c) Coagulation Al2(SO4)3-UF(d) Coagulation PAX-25-UFReprinted from Rajca et al (2009) with permission from Elsevier

398 Advances in Membrane Technologies for Water Treatment

The transport equations for each case have been derived from Hermiarsquos equationand the results can be seen in Table 125 (Field 2010 Field amp Wu 2011 FieldWu Howell amp Gupta 1995) Those equations could be used to diagnose thetype of fouling and predict the causes of it Originally these equations are

2

10 50 100 150 200 250

T (min) T (min)

T (min) T (min)

2

3

4

5

6

0 50 100 150 200 250 300 0 50 100 150 200 250 300

3

2

1

1

2

3

4

0 100 200 300 400 500 600

J experimental fluxJ theoretical flux

J experimental fluxJ theoretical flux

J experimental fluxJ theoretical flux

J experimental fluxJ theoretical flux

J v x

105 (

m3 m

2 s)

J v x

105 (

m3 m

2 s)

J v x

105 (

m3 m

2 s)

J v x

105 (

m3 m

2 s)

(a) (b)

(d)(c)

Figure 126 Comparison of experimental and theoretical volumetric flux (relaxation model)for MF membranes (a) Membrane 01 mm (01 MPa) (b) Membrane 02 mm (01 MPa)(c) Membrane 02 mm (02 MPa) (d) Membrane 045 mm (01 MPa)Source Reprinted from Konieczny (2002) with permission from Elsevier

Figure 127 Fouling mechanisms of porous membranes (a) Complete pore blocking(b) Internal pore blocking (c) Partial pore blocking (d) Cake filtrationSource Adapted from Field (2010) and Konieczny (2002)

Mathematical modeling of membrane operations for water treatment 399

Table 125 Fouling mechanisms phenomenological background and transport equations

Foulingmechanism n Phenomenological background Flux equation for dead-end Flux equation for crossflow

Complete poreblocking

2 Particles larger than the pore sizecompletely block pores

J frac14 J0 expethKbtTHORN J frac14 ethJ0 JTHORNexpethk2tTHORN thorn J

Internal poreblocking

15 Particles smaller than pore sizeenter the pores and get eitheradsorbed or deposited onto thepore walls this restricts theflow of permeate

J frac14 J0$

1thorn 1

2$Ks$ethA$J0THORN05$t2

J frac14 J0$

1thorn 1

2$Ks$ethA$J0THORN05$t2

Particle poreblocking

1 Particles reaching surface mayseal a pore or bridge a pore orpartially block it or adhere oninactive regions

J frac14 J0$eth1thorn Ki$ethA$J0THORN$tTHORN1 J frac14 J1

J0JJ0

exp

Jk1t

Cake filtration 0 Formation of a cake on themembrane surface by particlesthat neither enter the pores norseal the pores

J frac14 J0$eth1thorn 2$Kc$ethA$J0THORN2$tTHORN12 k0t frac14 1

J2

ln

JJ0$ethJ0JTHORNethJJTHORN

J

1J 1

J0

Note J - critical flux ki - constant in a crossflow fouling equation (i frac14 012)Source Field and Wu (2011) Field (2010) Field et al (1995)

400Advances

inMem

braneTechnologies

forWater

Treatm

ent

applicable to dead-end filtration but with some allowance for crossflow made itcan be applied to both modes of filtration

Besides than the fouling effect temperature will affect the flux performance ofmembranes as well For MF and UF systems the flow of permeate at any temperaturerelative to the flow at 20 C can be estimated by using (AWWA amp ASCE 2012)

QT frac14 Q20C

e00239ethT20THORN (1227)

This approximation is very useful and important because the effect from the fluctu-ation of raw water temperature can be minimized and the production of potable watercan be controlled

Another term used to define the performance of membranes is the removal percent-age of unwanted solute (foulants) from the raw water The solute rejection equationwill be the same as the one being used in NFRO membranes

R frac14 Cb Cp

Cb 100 frac14

1 Cp

Cf

100 (1228)

If the CP effect is to be taken into consideration then the concentration of solute atthe membrane surface should be used instead of the concentration of solute in bulksolution

123 Future work

Understanding the transport models and fouling mechanisms is very important andessential especially for reliable plant performance With better and accurate mathe-matical modeling membrane water treatment plants can be controlled monitoredand operated easily when the performance of the plants can be predicted preciselyThis will be very beneficial to automated plants in which the systems are controlledby sophisticated automation systems Without reliable mathematical modeling theautomated plants are vulnerable to membrane fouling because this problem couldnot be predicted properly in the initial stage and it will be too late to prevent thefouling problem when it is discovered Hence study about mathematical modelingfor the membrane water treatment process should be carried out more thoroughly Itis hoped that a predictive model that takes into account the effect of fouling andlong-term process operation could be developed because the main problem encoun-tered by the membrane process is membrane fouling

The challenge now is the ability to develop the mathematical models that canconvey the fundamental understanding and simple quantification of the governing phe-nomena in a way that has the potential for industrial application An accurate and pre-cise mathematical modeling not only will ease the design stage of the membrane watertreatment plant but also will smooth the operation of the plant because the fouling pro-pensity could be diagnosed earlier and preventive measures could be taken to curb it

Mathematical modeling of membrane operations for water treatment 401

Thus the models developed should be validated with real industrial data so that theapplicability and validation of the models could be tested With such a comparisonthe weakness of the mathematical modeling can be identified and improved

As shown in this chapter currently more and more new substances that might proveto be detrimental to our health and environment have been discovered Studies aboutthe removal of pesticides have been carried out and several models have been used topredict their retention by membranes However with the emerging deleterious compo-nents being discovered from time to time it is unsure whether the currently availablepredictive models could be used for membrane rejection performance Furthermore itseems like the mathematical model used by the membrane water treatment plant doesnot only depend solely on the membrane used but also the quality and foulant in theraw water will affect the suitability of the model used Until now there has not beenany mathematical modeling that could be applied to all the membranes and sourcewater Hence to have a better prediction on the membrane performance severalmodels might be required and the computational steps might be tedious Thus worksdeveloping a simpler and compact model should be focused to benefit all membraneapplications in the water treatment process

124 Conclusion

Process modeling plays a very important role in membrane operations for water treat-ment applications It allows users to obtain reliable prediction results that can be veryhelpful in membrane water treatment plants from the design stage toward the commis-sioning implementation and maintenance phases Mathematical modeling ensuresthat the fundamentals of the separation phenomena during the water treatment processof membranes can be understood With that specific preventative methods could beapplied to avoid the fouling problems In the earlier stage of designing a good predic-tive model will result in a smaller number of experiments and subsequently save timeand money With the appropriate design equation for the membrane the size of thewater treatment system as well as the area of membrane required to meet certainproduction rate could be determined Besides that mathematical modeling can beincorporated into the control system to predict the fouling potential of the membranesystem and thus suitable measures can be taken to reduce and mitigate the problem ofmembrane fouling Hence it can be concluded that with a good predictive modelingfor the membrane process the problem of water scarcity could be mitigated withthe wide acceptance of membranes in the water industry because the water treatmentplant can be controlled and operated stably

Nomenclature

ci Concentration of ion i within pore (kg molm3)C Solute concentration (kgm3 kg molm3)Cb Feed solute concentration (kgm3 kg molm3)Ci Ionic solute bulk solution concentration (kg molm3)

402 Advances in Membrane Technologies for Water Treatment

Cip Ionic solute bulk permeate concentration (kg molm3)Cm Membrane surface solute concentration (kgm3 kg molm3)Cp Permeate solute concentration (kgm3 kg molm3)CP Concentration polarizationD Pore diameter (m)Dij Diffusion coefficient of solute (m2s)Dip Pore diffusion coefficient of ion i (m2s)Dr Desalination ratio (CbCp)DE Dielectric exclusionDSPM Donnan-Steric-Pore-modelF Faraday constant (96487) (Cmol)jd Chilton-Coburn factorJ Volumetric flux (m3s m2)Ji Molar flux of solute (kg mols m2)J0 Initial flux (m3s m2)Js Solute flux (kgs m2)Jt Permeate flux at time t (m3s m2)Jv Solvent velocity (ms)Jw Pure water permeate flux (m3s m2)JN Equilibrium flux (m3s m2)k Mass transfer coefficient (ms)kib Mass transfer coefficient for concentration polarization (ms)kB Boltzmann constant (138066 1023) (JK)ki Membrane permeability coefficient for solute (ms)kw Mass transfer coefficient for water (ms atm)K Constant for CarmaneKozeny equationKic Hindrance factor for convection of ion ilbl Thickness of the mass transfer boundary layerL Length of pore (m)MF Microfiltrationn Number of kg mol of soluteNF Nanofiltrationpf Feed pressure (atm)pp Permeate pressure (atm)P Permeability coefficient (m3s m2 atm)Ps Solute permeability coefficient (ms)Pw Water permeability coefficient (m3s m2 atm)Q20 C Permeate flow at 20 C (m3s)Q25 C Permeate flow at 25 C (m3s)QT Permeate flow at temperature T (m3s)R Solute rejectionRe Reynolds numberRCP Solute rejection (after taking into CP effect)RG Gas law constant (82057 103) (m3 atmkg mol K)Rirr Resistance due to irreversible fouling (1m)Rm Membrane resistance (1m)Rrev Resistance due to reversible fouling (1m)Rt Resistance from foulants (total) (1m)RO Reverse osmosis

Mathematical modeling of membrane operations for water treatment 403

S Specific area (m2m3)Sc Schmidt numberSHP Steric hindrance poreT Temperature (K oC)TMS TeorelleMeyereSieversUF Ultrafiltrationv Flow velocity (ms)Vm Volume of pure solvent water in m3 associated with n kg mol of solute (m3)x Axial position within the pore (m)z Thickness of boundary layer (m)zi Valence of ion i

Greek letters

s Tortuosity of membrane3 Porosity of membranem Viscosity of liquid (kgs m)gi Activity coefficient of ion i within poregio Bulk activity coefficient of ion i

j Potential within the pore (V)DjD Donnan potential (V)DWi Born solvation energy barrier (J)Dp Transmembrane pressure (atm)Dp Transmembrane osmotic pressure (atm)p Osmotic pressure (atm)pm Osmotic pressure at membrane surface (atm)pp Osmotic pressure at permeate side (atm)

References

Ahmad A L Chong M F amp Bhatia S (2006) Ultrafiltration modeling of multiple solutes systemfor continuous cross-flow process Chemical Engineering Science 61(15) 5057e5069Retrieved from httplinkinghubelseviercomretrievepiiS0009250906001795

AWWA amp ASCE (2012) Water treatment plant design (5th ed) United States of AmericaMcGraw-Hill

Baker R W (2000) Membrane technology and applications United States of AmericaMcGraw-Hill

Bandini S amp Vezzani D (2003) Nanofiltration modeling The role of dielectric exclusion inmembrane characterization Chemical Engineering Science 58(15) 3303e3326 Retrievedfrom httplinkinghubelseviercomretrievepiiS0009250903002124

Bowen W R amp Mohammad A W (1998) Characterisation and prediction of nanofiltrationmembrane performancemdasha general assessment Transaction IChemE 76A 885e893

Bowen W R Mohammad A W amp Hilal N (1997) Characterisation of nanofiltrationmembranes for predictive purposesmdashuse of salts uncharged solutes and atomic forcemicroscopy Journal of Membrane Science 126 91e105

404 Advances in Membrane Technologies for Water Treatment

Bowen W R amp Welfoot J S (2002) Predictive modelling of nanofiltration Membranespecification and process optimisation Desalination 147(1e3) 197e203 Retrieved fromhttplinkinghubelseviercomretrievepiiS0011916402005349

Bowen W R amp Welfoot J S (2005) Modelling the performance of nanofiltrationmembranes In Nanofiltration principles and applications Great Britain Elsevier Ltd

Cornelissen E R Verdouw J Gijsbertsen-Abrahamse A J amp Hofman J A M H (2005) Ananofiltration retention model for trace contaminants in drinking water sources Desali-nation 178(2005) 179e192

Field R (2010) Fundamentals of fouling In Membranes for water treatment Great BritainWiley-VCH Verlag GmbH amp Co KGaA

Field R W Wu D Howell J A amp Gupta B B (1995) Critical flux concept for micro-filtration fouling Journal of Membrane Science 100(3) 259e272 Retrieved from httplinkinghubelseviercomretrievepii037673889400265Z

Field R W amp Wu J J (2011) Modelling of permeability loss in membrane filtrationRe-examination of fundamental fouling equations and their link to critical fluxDesalination 283 68e74 Retrieved from httplinkinghubelseviercomretrievepiiS0011916411003596

Gambier A Krasnik A amp Badreddin E (11e13 July 2007) Dynamic modeling of a simplereverse osmosis desalination plant for advanced control purposes In American controlconference New York Institute of Electrical and Electronics Engineers Inc

Geankoplis C J (2003) Transport processes and separation process principles (4th ed)United States of America Pearson Education Inc

Gibs J Stackelberg P E Furlong E T Meyer M Zaugg S D amp Lippincott R L (2007)Persistence of pharmaceuticals and other organic compounds in chlorinated drinking water asa function of time Science of the Total Environment 373(1) 240e249 Retrieved from httpwwwncbinlmnihgovpubmed17188338

Greenlee L F Lawler D F Freeman B D Marrot B amp Moulin P (2009) Reverseosmosis desalination Water sources technology and todayrsquos challenges Water Research43(9) 2317e2348 Retrieved from httpwwwncbinlmnihgovpubmed19371922

Harisha R S Hosamani K M Keri R S Nataraj S K amp Aminabhavi T M (2010)Arsenic removal from drinking water using thin film composite nanofiltration membraneDesalination 252(1e3) 75e80 Retrieved from httplinkinghubelseviercomretrievepiiS0011916409012600

Hassan A R Ali N Abdull N amp Ismail A F (2007) A theoretical approach on membranecharacterization The deduction of fine structural details of asymmetric nanofiltrationmembranes Desalination 206(1e3) 107e126 Retrieved from httplinkinghubelseviercomretrievepiiS0011916406014056

Hilal N Al-Zoubi H Darwish N A Mohammad A W amp Arabi M A (2004) Acomprehensive review of nanofiltration membranes Treatment pretreatment modellingand atomic force microscopy Desalination 170(3) 281e308 Retrieved from httplinkinghubelseviercomretrievepiiS0011916404800328

Hu Z-A Wu H-Y amp Gao J-Z (1999) Calculation of osmotic pressure differenceacross membranes in hyperfiltration Desalination 121(2) 131e137 Retrieved fromhttplinkinghubelseviercomretrievepiiS0011916499000144

Kaghazchi T Mehri M Ravanchi M T amp Kargari A (2010) A mathematical modeling oftwo industrial seawater desalination plants in the PersianGulf regionDesalination 252(1e3)135e142 Retrieved from httplinkinghubelseviercomretrievepiiS0011916409012211

Karode S K (2001) Unsteady state flux response A method to determine the nature of thesolute and gel layer in membrane filtration Journal of Membrane Science 188(1) 9e20Retrieved from httplinkinghubelseviercomretrievepiiS037673880000644X

Mathematical modeling of membrane operations for water treatment 405

Kedem O amp Katchalsky A (1958) Thermodynamics analysis of the permeability ofbiological membranes to non-electrolytes Biochimica et Biophysica Acta 27 229e246

Konieczny K (2002) Modelling of membrane filtration of natural water for potable purposesDesalination 143(2) 123e139 Retrieved from httplinkinghubelseviercomretrievepiiS0011916402002345

Levenstein R Hasson D amp Semiat R (1996) Utilisation of the Donnan effect for improvingelectrolyte separation with nanofiltration membranes Journal of Membrane Science 11677e92

Luo J amp Wan Y (2011) Effect of highly concentrated salt on retention of organic solutes bynanofiltration polymeric membranes Journal of Membrane Science 372(1e2) 145e153Retrieved from httplinkinghubelseviercomretrievepiiS0376738811000871

Malaeb L amp Ayoub G M (2011) Reverse osmosis technology for water treatment State ofthe art review Desalination 267(1) 1e8 Retrieved from httplinkinghubelseviercomretrievepiiS0011916410006351

Mohammad A W (16e19 November 2008) Nanofiltration membranes in desalinationmdashfromfundamental to applications In The 3rd international conference on water resources andarid environments and the 1st Arab water forum Riyadh Saudi Arabia Prince SultanInstitute for Environmental Water amp Desert Research King Saud University

Mohammad A W Hilal N Al-Zoubib H Darwish N A amp Ali N (2007) Modelling theeffects of nanofiltration membrane properties on system cost assessment for desalinationapplications Desalination 206(1e3) 215e225 Retrieved from httplinkinghubelseviercomretrievepiiS0011916406014184

Mulder M (1996) Basic principles of membrane technology (2nd ed) Boston Kluwer Aca-demic Publishers

Nakao S (1994) Determination of pore size and pore size distribution 3 Filtration membranesJournal of Membrane Science 96 131e165

Nguyen C M Bang S Cho J amp Kim K W (2009) Performance and mechanism of arsenicremoval from water by a nanofiltration membrane Desalination 245(1e3) 82e94Retrieved from httplinkinghubelseviercomretrievepiiS0011916409003282

Pappenheimer J (1953) Passage of molecules through capillary walls Physiological Reviews33 387e423

Peppas N amp Meadows D (1983) Macromolecular structure and solute diffusion in mem-branes An overview of recent theories Journal of Membrane Science 16 361e377

Plakas K V amp Karabelas A J (2012) Removal of pesticides from water by NF and ROmembranesmdasha review Desalination 287 255e265 Retrieved from httplinkinghubelseviercomretrievepiiS0011916411006874

Radjenovic J Petrovic M Ventura F amp Barcelo D (2008) Rejection of pharmaceuticals innanofiltration and reverse osmosis membrane drinking water treatment Water Research42(14) 3601e3610 httpwwwncbinlmnihgovpubmed18656225

Rajca M Bodzek M amp Konieczny K (2009) Application of mathematical models to thecalculation of ultrafiltration flux in water treatment Desalination 239(1e3) 100e110Retrieved from httplinkinghubelseviercomretrievepiiS0011916409000253

Renkin E (1954) Filtration diffusion and molecular sieving through porous cellulosemembranes The Journal of General Physiology 38 225e243

Roberson B amp Zydney A (1988) A Stefan-Maxwell analysis of protein transport in porousMembranes Separation Science and Technology 23 1799e1811

Saitua H Giannini F amp Padilla A P (2012) Drinking water obtaining by nanofiltration fromwaters contaminated with glyphosate formulations Process evaluation by means of toxicitytests and studies on operating parameters Journal of Hazardous Materials 227e228204e210 Retrieved from httpwwwncbinlmnihgovpubmed22664256

406 Advances in Membrane Technologies for Water Treatment

Sarkar B Venkateshwarlu N Rao R N Bhattacharjee C amp Kale V (2007) Potable waterproduction from pesticide contaminated surface watermdasha membrane based approachDesalination 204(1e3) 368e373 Retrieved from httplinkinghubelseviercomretrievepiiS0011916406013415

Schirg P ampWidmer F (1992) Characterisation of nanofiltration membranes for the separationof aqueous dye-salt solutions Desalination 89 89

Seader J D amp Henley E J (1998) Separation process principles United States of AmericaJohn Wiley amp Sons Inc

Senthilmurugan S Ahluwalia A ampGupta SK (2005)Modeling of a spiral-woundmodule andestimation of model parameters using numerical techniquesDesalination 173(3) 269e286Retrieved from httplinkinghubelseviercomretrievepiiS0011916404007234

Shengji X Juanjuan Y amp Naiyun G (2008) An empirical model for membrane fluxprediction in ultrafiltration of surface water Desalination 221(1e3) 370e375 Retrievedfrom httplinkinghubelseviercomretrievepiiS0011916407007163

Shon H K Vigneswaran S Kandasamy J amp Shim W G (2008) Ultraflitration of waste-water with pretreatment Evaluation of flux decline models Desalination 231(1e3)332e339 Retrieved from httplinkinghubelseviercomretrievepiiS0011916408003779

Tsuru T Nakao S amp Kimura S (1991) Calculation of ion rejection by extended Nernst-Planck equation with charged reverse osmosis membranes for single and mixedelectrolyte solutions Journal of Chemical Engineering of Japan 24 511e517

Tu K L Nghiem L D amp Chivas A R (2010) Boron removal by reverse osmosis mem-branes in seawater desalination applications Separation and Purification Technology 75(2)87e101 Retrieved from httplinkinghubelseviercomretrievepiiS1383586610003114

Van der Bruggen B Meuroantteuroari M amp NystreuroomM (2008) Drawbacks of applying nanofiltrationand how to avoid them a review Separation and Purification Technology 63(2) 251e263Retrieved from httplinkinghubelseviercomretrievepiiS1383586608002104

Verniory A DuBois R Decoodt P Gassee J amp Lambert P (1973) Measurement of thepermeability of biological membranes application to the glomerular wall The Journal ofGeneral Physiology 62 489e507

Wiesner M R amp Buckley C A (1996) Principles of rejection in pressure-driven membraneprocesses In Water treatment membrane processes United States of AmericaMcGraw-Hill

Williams M E (2003) A review of reverse osmosis theory Retrieved from httpwwweetcorpcomheepmRO_TheoryEpdf

Xu X amp Spencer H G (1997) Dye-salt separations by nanofiltration using weak acidpolyelectrolyte membranes Desalination 114 129e137

Yaroshchuk A E (2000) Dielectric exclusion of ions from membranes Advances in Colloidand Interface Science 85(2e3) 193e230 Retrieved from httpwwwncbinlmnihgovpubmed10768481

Yaroshchuk A amp Staude E (1992) Charged membranes for low-pressure reverse osmosisproperties and applications Desalination 86 115e134

Zhao C Zhou X amp Yue Y (2000) Determination of pore size and pore size distribution onthe surface of hollow-fiber filtration membranes A review of methods Desalination129(2) 107e123 Retrieved from httplinkinghubelseviercomretrievepiiS0011916400000540

Mathematical modeling of membrane operations for water treatment 407

Membrane technologiesfor seawater desalinationand brackish water treatment

13E Curcio12 G Di Profio2 E Fontananova2 E Drioli121University of Calabria (DIATIC-UNICAL) Cosenza Italy 2Institute on MembraneTechnologyeNational Research Council of Italy (ITM-CNR) Cosenza Italy

131 Introduction

In past decades the number of countries experiencing water scarcity has increasedsignificantly owing to steady demographic expansion and the amplified demand forwater in industrial activities in agriculture and for municipal (including domestic)purposes In particular agriculture accounts for about 70 of global freshwaterwithdrawal (FAO Water Report 2012) Average consumption per capita of water perday spans from 150 L in Western countries to about 20 L on the African continentthe latter value dramatically approaches the lower limit fixed by the World HealthOrganization which is sufficient to guarantee basic needs such as drinking personal hy-giene and food preparation The demand for water is expected to increase by 50 in thenext 40 years driving about 39 billion people under water stress (Mountford 2011)

Paradoxically water is one of the most abundant resources on earth (the estimatedamount in the ocean is 14 109 km3 (Bengtsson 2010)) Seawater (SW) representsabout 967 of total available water the remaining part is underground and surfacewaters mostly frozen in glaciers Only 07 of the total amount (12 107 km3) isavailable in lakes rivers and aquifers (Figure 131)

Water is classified primarily according to its salinity content Freshwater hassalinity up to 1500 ppm brackish water (BW) has a saline content in the range of1500e10000 ppm and SW salinity is between 10000 and 45000 ppm Forreference the average salinity of SW is conventionally normalized at 35000 ppm(lsquostandard SWrsquo is arbitrarily defined on the basis of certain samples taken from NorthAtlantic surface water as first proposed by Martin Knudsen at the InternationalConference for the Exploration of the Sea held in Stockholm in 1899 (Knudsen1903)) The main ionic constituents of SW are sodium (30) and chloride (55)Table 131 lists the composition of standard SW

To date SW and BW desalination represents the most reliable and economicallysustainable way to produce drinking water for human consumption The total globaldesalination capacity is currently around 664 million m3day and is expected to reachabout 100 million m3day by 2015 the annual market growth is about 55 SWrepresents the main source for the desalination industry (about 589) whereas BWaccounts for 212 (Global Water Intelligence)

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400013-7Copyright copy 2015 Elsevier Ltd All rights reserved

Thermal desalination processes dominate in the Gulf region (more than 90 of totalproduction) where water is generated together with electricity in large cogenerationplants There steam drives turbines and acts as a source for SW evaporation Multi-stage flash (MSF) distillation is the prevalent desalination technology in the MiddleEast with more than 80 of installed capacity followed by multiple effect distillation(MED) (IDA Media Analytics Ltd 2007)

MSF consumes a larger amount of total energy than other desalination processes(around 17e18 kWhm3) with a gain output ratio (GOR) of 8e10 kg of distillate per ki-logram of steam however its highly reliable performance (early plants began operationin 1978 with an expected life of over 30 years) makes MSF competitive in the MiddleEasteNorth Africa region MSF plants are generally built to be large The Jebel Ali MSFplant in Dubai contracted by Fisia and officially opened in 2013 has a productivity of626400 m3day and 2060 MWday of generated power (Borsani amp Ghiazza 2012)

MED plants are generally designed for operative temperature below 70 C to limitscale formation on the outside surface of evaporator tubes total energy consumption is6e7 kWhm3 for a GOR of 8e16 kg of distillate per kilogram of steam In recentyears the productivity of MED integrated with thermal vapour compression (TVC)units has increased exponentially For example the MEDeTVCMarafiq Jubail (SaudiArabia) desalination plant (27 units) completed in 2010 by Veoliarsquos subsidiarySidem produces a total of 800000 m3day of desalted water with a GOR of 984kg of distillate per kilogram of steam Huge MED plants are in operation at FujairahUnited Arab Emirates (463000 m3day) Ras Laffan Qatar (286000 m3day) and AlHidd Bahrain (272000 m3day) (sidem-desalinationcom 2014)

Developed in the 1980s mechanical vapour compression units have a small capac-ity with respect to MSF and MED (usually lower than 5000 m3day) and an averageenergy consumption of around 8 kWhm3 of electrical power (Lokiec amp Ophir 2007)

Desalination processes are classified according to the type of separation Conven-tionally two groups are identified membrane systems and thermal technologies

Atmosphere 0001

00132

00158

169

174 9654

200 40Amount ()

Water source

60 80 100

Lakes amp rivers

Groundwater

Oceans seas amp bays

Ground ice amp permafrost

Ice caps glaciers amp permanent snow

Figure 131 Rough estimate of global water distributionData elaborated from Shiklomanov (1993)

412 Advances in Membrane Technologies for Water Treatment

(Figure 132) The first group includes reverse osmosis (RO) which currentlydominates desalination technology the second is electrodialysis Both membraneoperations require electrical energy

Currently the largest SWRO plant with a productivity of 624000 m3day isinstalled in Sorek Israel and is operated by IDE Technologies The SWRO plant inAshkelon Israel operated by Veolia Water since 2005 reaches a daily productivityof 320000 m3day Feed water passes through 32 modules that decrease salt

Table 131 Standard seawater composition

Ion Concentration (ppm) Total salt content ()

Chloride Cl 19345 5503

Sodium Nathorn 10752 3059

Sulphate SO24 2701 768

Magnesium Mg2thorn 1295 368

Calcium Ca2thorn 416 118

Potassium Kthorn 390 111

Bicarbonate HCO3 145 041

Bromide Br 66 019

Borate BO33 27 008

Strontium Sr2thorn 13 004

Fluoride F 1 0003

Source Millero Feistel Wright and McDougall (2008)

Desalination technology

Membrane processes

Reverse osmosis (RO)

Electrodialysis (ED)

Thermal processes

Multiple effect distillation (MED)

Multistage flash (MSF)

Thermal vapour compression (TVC)

Mechanical vapour compression (MVC)

Figure 132 Classification of major technologies currently in use for seawater and brackishwater desalination

Membrane technologies for seawater desalination and brackish water treatment 413

concentration down to 30 mgL with a cost of 050 Eurom3 The SWRO plantinstalled in Perth Australia designed and built in only 18 months by MultiplexDegreacutemont Joint Venture in 2006 produces 144000 m3day of desalinated water(Clemente amp Mercer 2011)

Electrodialysis and electrodialysis reversal (EDR) are electrochemical separationprocesses in which ions are transferred through ion exchange membranes under directcurrent both are typically operated for BW desalination purposes One of the majorfacilities installed in Europe is the 57000-m3day EDR plant operated in Sant Boide Llobregat Spain (Segarra Iglesias Peacuterez amp Salas 2009)

132 Principle of RO

RO allows dissolved ions to be separated from feed water using semipermeablemembranes operated under the driving force of a difference in chemical potential(function of pressure concentration and temperature) From a phenomenologicalpoint of view RO separation is based on countering the natural osmotic processby applying hydrostatic pressure to the side contacted by SW thus driving thesolvent flux in the opposite direction with respect to that established by naturalosmosis

The value of osmotic pressure P (defined as the equilibrium pressure at which thenet flux of solvent stops) depends on the salt concentration ci according to thefollowing equation (Fell 1995)

P frac14 RTXi

nici (131)

The osmotic pressure of SW is typically around 23 MPa As long as the appliedhydrostatic pressure DP is higher than the osmotic pressure difference DPbetween the feed and permeate solutions the solvent (water) will flow from themore concentrated solution (feed) to the dilute solution (permeate) and the trans-membrane flux will reverse from the direction of natural osmosis as illustrated inFigure 133

The solution-diffusion model is frequently adopted with the aim of describing thetransport phenomenon in RO (Merten 1966) It is assumed that the volumetric flux ofwater (Jv) and the flux of solutes (Js) both of which occur by diffusing through themembrane are related to their mobility driving force (effective pressure differenceof DP DP) and salt concentration gradient

Jv frac14 kwDwVw

RT

DP DP

d

(132)

Js frac14 ksDs

d

c fs cps

(133)

414 Advances in Membrane Technologies for Water Treatment

133 RO membranes and modules

The RO membrane market is essentially based on thin-film composite (TFC) poly-amide membranes generally consisting of a polyester web used as a support(120e150 mm thick) a microporous interlayer usually made of polysulphonic polymer(40e50 mm) and a top ultrathin barrier layer with selectivity properties and low resis-tance to mass transfer of permeate (w02 mm) The selective layer which is generallyable to provide salt rejection higher than 995 to NaCl is commonly made of13-phenylenediamine (also known as 13-benzenediamine) and tri-acid chloride ofbenzene (Figure 134) (Lee Arnot amp Mattia 2011) Historically RO technologystarted with cellulose acetate (CA) membranes Although they are characterized byhigher resistance to chlorine (extensively used as a disinfectant to prevent bacterialgrowth on membranes) asymmetric CA or triacetate hollow-fibre modules are muchless frequently installed in RO plants because of their lower rejection ability Amongthe unresolved challenges the boron rejection of any commercially available mem-brane is still insufficient (w93) to meet WHO water drinking standards by one-pass RO process (Kumano amp Fujiwara 2008)

With few exceptions RO membranes are prepared in the flat-sheet form and areassembled in spiral-wound module (SWM) configuration with a high specific mem-brane surface area (the packing density is about 500e800 m2m3) and low replacementcost (Pearce 2007) In SWM two rectangular flat-sheet membranes are placed back toback and sealed on three sides to form an envelope One or multiple envelopes arewound around a collector tube connected to the fourth side which remains open

P

Nat

ural

osm

osis

Rev

erse

osm

osis

Applied pressure

ΔP gt Δ Fl

ux o

f sol

vent

0

Π

ΔP lt Δ Π

ΔP = Δ Π

Figure 133 Trans-membrane flux of solvent through an ideally semipermeable membrane as afunction of applied hydrostatic pressure

Membrane technologies for seawater desalination and brackish water treatment 415

Feed water enters tangentially in the module and the permeate goes through the mem-brane and flows perpendicularly in the collector tube while the retentate leaves themodule at the opposite end

Advances in membrane desalination (innovation in membrane materials optimiza-tion of module fluid dynamics and improvement in process design pretreatment andenergy recovery systems) resulted in progressive enhancement of membrane rejectionand a decrease in overall energy consumption as illustrated in Figure 135

Currently some major suppliers of RO membrane modules are Dow (Filmtech)Toray Hydranautics (Nitto Group) and Koch Membrane Systems Standard modulesfor current SWRO desalination plants are 8 inches in diameter However recent devel-opments in module design and hydrodynamics optimization are moving towards largermodules (Yun Gabelich Cox Mofidi amp Lesan 2006) Tables 132 and 133 summa-rize the main characteristics of eight modules commercialized by these companies

SWMs are contained in pressure vessels consisting of a cylindrical housing eachhosting typically six to eight modules From a technical point of view each groupof parallel connected vessels forms a lsquostagersquo Connection in parallel leads to an in-crease in productivity A configuration ratio of 21 representing the ratio betweenthe number of pressure vessels from one stage to the next is generally adopted inRO plants SWRO plants are typically composed of two stages to increase the total wa-ter recovery factor to 50e60 at an operating pressure of 50e70 bar The number oflsquopassesrsquo identifies the number of times that permeate is treated in the system Addi-tional passes are necessary whenever high permeate quality is requested A single-pass RO plant typically guarantees a total dissolved solids (TDS) content around

H2N NH2 H2N NH2

COClOClC

COCl

COClOClC

COCl

HN NHOC

CO

CO HN NHOC CO

COOH

nm

Trimesoyl chloride in hexane

m-Phenylenediaminein water

PolymerizationInterfacial

Figure 134 Sample scheme of interfacial polymerization for the preparation of the top layer ofa thin-film composite fully aromatic polyamide membrane

416 Advances in Membrane Technologies for Water Treatment

500 mgL whereas a two-pass configuration decreases TDS below 300 mgL Stagesinterconnected in series form a lsquotrainrsquo SWRO plants are generally composed ofseveral trains Typical examples of RO flow sheets are given in Figure 136(a) and (b)

134 Fouling and pretreatment strategies

Composition and characteristics of BW and SW used as a feed in desalination plantsdirectly affect the efficiency of membrane processes (El-Manharawy amp Hafez 2001)The presence of sparingly soluble salts colloids and suspended matters organic com-pounds or microorganisms if not appropriately controlled might result in a severeimpact of fouling phenomena on the performance of RO plants leading to irreversibledamage to membranes and a significant decrease in their lifetime (see Figure 137 foran overview)

Membrane damage primarily results from oxidation and hydrolysis of the polymericmaterial In general membranes cannot tolerate residual chlorine concentrations whichare used extensively in desalination processes to prevent biological growth Adjust-ment of the pH to recommended operational values is therefore required to fit optimaloperation protocols and mitigate scaling (acidification is usually made by adding sul-phuric acid) Moreover oxidizing agents and dissolved oxygen must be removed byadding appropriate reducing compounds such as sodium thiosulphate or sodium bisul-phite More details on pretreatment procedures are provided in paragraph 1541

Scaling refers to the precipitation of sparingly soluble salts onto the membrane sur-face often exacerbated by concentration polarization In fact owing to the progressive

Figure 135 Improvement in salt rejection () and energy consumption (kWhm3) of SWROtechnologyData from Lee Arnot and Mattia (2011)

Membrane technologies for seawater desalination and brackish water treatment 417

Table 132 Product specifications of selected brackish water desalination modules

Element modelDowtrade FilmtectradeBW30-365a

Toray StandardBWRO TM720-370b

NittoHydranauticsESPA1c

Koch MembraneSystemsFluidSystemsreg TFCreg-FR400-34d

Active area (m2) 34 34 371 372

Permeate flow rate (m3day) 36 36 454 416

Stabilized salt rejection () 995 997 993 9955

Diameter (inch) 8 8 8 8

Membrane type Polyamide thin-filmcomposite

Cross-linked fullyaromatic polyamidecomposite

Composite polyamide TFC polyamide

NoteaTest conditions 2000 ppm NaCl 153 bar 25 C 15 recovery pH 8bTest conditions 2000 ppm NaCl 155 MPa 25 C 15 recovery pH 7cTest conditions 1500 ppm NaCl 105 MPa 25 C 15 recovery pH 65e7dTest conditions 2000 ppm NaCl 155 MPa 25 C 15 recovery pH 75

418Advances

inMem

braneTechnologies

forWater

Treatm

ent

Table 133 Product specifications of selected seawater desalination modules

Element model Filmtectrade SW30HR-380aToray StandardSWRO TM820C-400b

NittoHydranauticsSWC4-LDc

Koch MembraneSystemsFluidSystemsreg

TFCreg-SW 400-34d

Active area (m2) 35 37 371 372

Permeate flow rate (m3day) 23 246 246 272

Stabilized salt rejection () 997 9975 998 9975

Diameter (inch) 8 8 8 8

Applied pressure (bar) 55 55 55 55

Membrane type Polyamide thin-filmcomposite

Cross-linked fully aromaticpolyamide composite

Composite polyamide TFC polyamide

NoteaTest conditions 32000 ppm NaCl 55 bar 25 C 8 recovery pH 8bTest conditions 32000 ppm NaCl 552 MPa 25 C 15 recovery pH 7cTest conditions 32000 ppm NaCl 55 MPa 25 C 10 recovery pH 65e7dTest conditions 32800 ppm NaCl 552 MPa 25 C 7 recovery pH 75

Mem

branetechnologies

forseaw

aterdesalination

andbrackish

water

treatment

419

removal of solvent through the membrane the solubility limit of some componentsdissolved in the feed (typically calcium carbonate magnesium carbonate calcium sul-phate silica barium sulphate strontium sulphate and calcium fluoride) may beexceeded (van de Lisdonk Rietman Heijman Sterk amp Schippers 2001)

The scaling propensity of a given feed water is usually evaluated by the Langeliersaturation index for BW (Patzay Stahl Karman amp Kalman 1998) and by the Stiffand Davis stability index for SW (Al-Shammiri amp Al-Dawas 1997) Scaling doesnot occur for negative values of these indexes

Typical countermeasures to limit scaling problems are to

bull reduce the water recovery factor to operate below solubility limitsbull decrease pH by adding acids to regulate the calcium carbonate speciation (moving solubility

equilibrium towards the formation of carbonates and bicarbonates into carbon dioxide)bull add inhibitors or antiscalants that delay the induction time of precipitationbull eliminate calcium and magnesium to limit the risk of calciummagnesium carbonate precip-

itation (softening)bull use ion exchange resins to eliminate undesirable ions

Particulate fouling is caused by particles and suspended colloidal matter present insolution Clogging can be mitigated by limiting the amount of particles by conven-tional coagulationeflocculation (a critical issue is the appropriate dosage of

FeedDischarged

brine

Permeate

1st Stage 2nd Stage

Retentate(a)

Figure 136 Reverse osmosis train configuration (a) single-passtwo stages Example TampaBay SWRO plant United States (b) two-passtwo stages per pass Example Point Lisas SWROplant Trinidad

420 Advances in Membrane Technologies for Water Treatment

coagulanteflocculants that might damage membranes) or by pressure-drivenmembrane operations (microfiltration (MF) or ultrafiltration (UF)) (Ning amp Troyer2007) To quantify the potential of particulate fouling a gravimetric procedure isnormally used to express the concentration of particles in terms of total suspendedsolids In addition turbidity measurements expressed in nephelometric turbidity units(NTU) provide quick and easy measurements for low solid concentrations

Colloidal fouling is caused by the accumulation of colloids on the membrane sur-face leading to the formation of a cake layer As a result the permeate flux decreases

FeedReject to

waste

Permeate1st pass(fed to

2nd pass)

1st Stage 2nd Stage

Retentate

Permeate2nd pass

Recycle

1st Stage 2nd Stage

1st Pass

2nd Pass

(b)

Figure 136 Continued

Membrane technologies for seawater desalination and brackish water treatment 421

because of the additional cake layer resistance moreover the hindered back-diffusionof salt ions within the deposit layer increases the ion concentration at the membranesurface thus enhancing the osmotic pressure and decreasing the net driving force

Biological fouling originates from the growth of colonies of bacteria or algae on thesurface of the membrane (Nguyen Roddick amp Fan 2012) Washing with biocidesmay be necessary to prevent the development of biomass for membranes resistantto chlorine shock chlorination is the preferred option

Natural organic matter (NOM) is considered a major foulant among all species pre-sent in natural water (Pressman et al 2012) NOM is a complex mixture of both inor-ganic and organic components characterized by a wide range of molecular weight andfunctional groups (phenolic hydroxyl carbonyl groups and carboxylic acid) origi-nated by allochthonous (terrestrial and vegetative debris) and autochthonous input(algae) Particularly aggressive fouling is caused by dissolved organic mattercomposed of humic substances polysaccharides amino acids proteins fatty acidsphenols carboxylic acids quinines lignins carbohydrates alcohols etc (ZularisamIsmail amp Salim 2006) Fouling mechanisms of NOM typically include preliminaryadsorption on the surface followed by the formation of a continuous gel The structureof the gel layer depends on both chemical conditions (pH ionic strength and the pres-ence of multivalent cations) and physical conditions (permeate flux and cross-flowvelocity) The presence of inorganic ions in solution exacerbates the fouling problem(for example through NOMecalcium complexation) resulting in the formation of adense and highly resistant fouling layer (Lee Cho amp Elimelech 2005)

Cleaning procedures partially restore the efficiency of a membrane process As arule membrane elements should be cleaned whenever a critical performance parameter(usually permeate flux salt rejection or trans-membrane pressure) changes by at least10e15 Cleaning methods are usually classified into four groups mechanicalhydrodynamic airewater cleaning and chemical

Fouling

Scaling

Precipitation ofsparingly soluble

compounds(calcium

magnesiumcarbonate

calciumbariumStrontium

sulphate calciumfluoride

magnesiumhydroxide silica etc)

Particulate fouling

Deposition of suspended

solidscolloidal mater

algae nongrowing

microorganismsMonitored by

silt densityindex (SDI) test

modifiedfouling index(MFI-UF) etc

Inorganicfouling

Deposition ofinorganic particles(aluminum silicate

clays andcolloids of

ironndashiron oxidealuminum oxide

silica)

Organicfouling

Biologicalfouling

Formation ofbiofilm due to

bacteria algaefungi viruses

protozoabacterial cell wall

fragments

Due to naturalorganic matter

(NOM)proteins

carbohydratesfats oil

tannins aromaticacids such as humic

acid

Figure 137 Qualitative classification of fouling phenomena

422 Advances in Membrane Technologies for Water Treatment

Mechanical cleaning is accomplished by promoting high shear forces at the mem-brane surface by mechanical action (for example using sponge balls for cleaningtubular membranes or using ultrasound waves causing the cavitation of fluids andthe consequent increase in turbulence and promotion of shear forces at the mem-brane surface) mechanical cleaning is not frequently applied on an industrial scale(Al-Amoudi amp Lovitt 2007)

Hydrodynamic cleaning methods consist in a temporary increase of cross-flow ve-locity in a pulsed feed flow or in a temporary reversal of the flow through the mem-brane elements In particular periodic back-washing of membranes is an effective andcommonly used method to remove accumulated cake although it is energeticallyexpensive (Sagiv amp Semiat 2010) Air bubbling (periodic injection of compressedair) also increases turbulence and results in high shear forces at the membrane surface(Cornelissen et al 2007)

Chemical cleaning methods aim to dissolve complexate oxidize inactivatesolubilize hydrolyze and denature membrane fouling (Madaenl Mohamamdi ampMoghadam 2001 Zondervan amp Roffel 2007) Common cleaning agents are

1 acid cleaning agents used to dissolve inorganic precipitates caused by scaling (CaCO3FeSO4 FeO FeOH Al2(SO4)3 BaSO4 SrSO4 CaSO4 etc) or the inorganic matrixin a biofilm Most frequently used chemicals are citric acid sulphuric acid and phosphoricacid

2 alkaline cleaning agents used to dissolve organic deposits Typically used chemicals areNaOH andor Na2CO3

3 complexing or anti-precipitating agents used to remove metals (mostly bivalent ions) andother precipitating ions from the solution For example ethylenediaminetetraacetic acidremoves Ca2thorn and Mg2thorn ions

4 biocides used to inactivate microorganisms (for example chlorine chloramines organic per-oxides glutaraldehyde sodium bisulphite)

5 detergents or surfactants that reduce the surface tension of the water resulting in betterhydration and solubility of the fouling layer

6 enzymatic cleaning agents aiming at hydrolyzing the extra polymeric substances formed bymicroorganisms

7 chaotrophic cleaning agents that induce denaturation of proteins resulting in the bettersolvability of organic compounds

1341 Conventional pretreatment

Conventional pretreatment operations for an SWRO plant usually include (1) screensfor preliminary coarse prefiltration (2) chlorination and acidification steps (3) addi-tion of flocculation agents and coagulationflocculation units (4) single or doublemedia filtration (5) dechlorination and addition of antiscalants and (6) cartridgefiltration before RO trains Main disadvantages of conventional pretreatment systemsinclude high sensitivity to fluctuations of feed characteristics difficulties in supplyingfeed a constant silt density index (SDI) less than 30 and large footprint owing to slowfiltration velocities A schematic representation of a conventional pretreatment systemis illustrated in Figure 138

Membrane technologies for seawater desalination and brackish water treatment 423

Screens are used to protect water pumps from particle clogging and remove coarsefloating solids from the feed (used for both BW and SW) To limit the environmentalimpact screens are designed to reduce the risk of impingement on marine organismsTraditional travelling water screens are equipped with revolving wire mesh panels with6- to 95-mm openings

Chlorination is a standard disinfection method aiming at destroying or inactivatingpathogenic microorganisms (bacteria amoebic cysts algae spores and viruses)In general sodium hypochlorite is dispersed in SW where the following reactionoccurs

NaOClthorn H2OHOClthorn NaOH

In principle chlorine gas can be injected directly into the feed stream it readily dis-solves in water to a maximum concentration of 3500 mgL and reacts as

Cl2 thorn H2OHOClthorn HCl

However direct injection is not a common practice in large desalination plantsIn solution hypochlorous acid dissociates to hydrogen and hypochlorite ionsThe sum of Cl2 NaOCl HOCl and OCl is indicated as free residual chlorinethis value should be maintained within 05e10 mgL along the pretreatmentline to prevent biofouling Contact or detention times of 10e120 min may berequired which depend on the level of residual chlorine (Shams El Din Arain ampHammoud 2000)

Coagulationflocculation is applied to remove fine suspended solids (size range of1 nm to 10 mm) soluble organic and toxic substances and trace metals Coagulantssuch as aluminum sulphate (or alum) ferric sulphate or ferric chloride quicklimeand synthetic cationicanionicnonionic polymers are efficiently dispersed in floccula-tion chambers by diffuser grids chemical jets or in-line blender systems Flocculationis achieved through slow mixing using paddles or propellers Usually several floccu-lation chambers are built in series with successively decreasing mixing velocitiesAlum is the most commonly used primary coagulant theoretically 1 mgL of alumwill consume approximately 050 mgL of alkalinity (as CaCO3) and produce

Intake pump

SeawaterScreen

ChlorinationFlocculants

pH adj

Flocculation chambers

Clarifier

Dual media filtration

Antiscalingdechlorination

Cartridgefiltration

To RO trains

Figure 138 Typical conventional SWRO pretreatment system

424 Advances in Membrane Technologies for Water Treatment

044 mgL of carbon dioxide If the natural alkalinity of the water is not sufficient toreact with the alum and buffer the pH alkalinity is increased by adding lime orsoda ash (coagulant aids)

After the coagulationflocculation stage simple and inexpensive slow sand filtra-tion (SSF) can be successfully applied to treat feed with a turbidity of less than 50NTU SSF consists of the filtration of BW or SW through a bed of fine sand at lowvelocity which causes the retention of organic and inorganic suspended matter inthe upper 05e2 cm of the filter bed Slow sand filters are also appropriate forremoving pathogenic organisms that are eventually present in surface waters Scrapingoff the top layer cleans the filter and restores its original efficiency Although sludgehandling is negligible and close control by an operator is not strictly necessaryslow sand filters require a large footprint huge quantities of filter medium and exten-sive labour for manual cleaning

Dual media filtration (DMF) more efficiently removes suspended solids and path-ogens and reduces the turbidity of the RO feed water to about 04 NTU with an SDItypically around 25 or slightly less DMF consists of coarse anthracite coal over a bedof fine sand (Zouboulis Traskas amp Samaras 2007) Cleaning is usually required whenwater head loss through the filter exceeds 15e25 m

Before entering the cartridge filters the pH value of feed water has to be reduced atmoderate values to prevent calcium carbonate scaling and damage to RO membranesSulphuric acid is typically injected to adjust the pH to around 75 The addition of anti-scaling agents is also requested for SWRO systems operated with a recovery greaterthan 35 (Hasson Drak amp Semiat 2003) In past decades sodium hexametaphos-phate (SHMP) was extensively used as an antiscalant today it has been replacedby polymeric compounds such as polyphosphates and polyacrylates because of theeutrophicating properties of SHMP and associated disposal problems Dechlorinationhas to be performed before the RO stage to avoid oxidation damage by residual chlo-rine in the feed water (Saeed 2002) Commonly sodium metabisulphite (SMBS) isused for dechlorination owing to its high cost effectiveness 30 mg of SMBS isused to remove 10 mg of free chlorine

Cartridge filters with a pore size of 5e10 mm represent the last pretreatment stagebefore RO trains they are used to capture contaminants and particles throughout thewhole thickness of the filtering medium

1342 Membrane pretreatment

Interest in pretreatment operations based on membrane technology has recentlyincreased MF is a low energy-consuming membrane unit commonly used to removesuspended solids reduce the chemical oxygen demand below 25 mgL and achieve anSDI less than 5 UF is a versatile separation process able to retain suspended solidsbacteria macromolecules and colloids turbidity is also significantly decreased (lessthan 04 NTU) and SDI is below 2 in the permeate stream The main benefits of inte-grated MFUF pretreatment technologies are (Buscha Chub Kolbe Meng amp Li2009 Vial amp Doussau 2002) (1) the potential for higher RO flux and water recoveryfactor (2) a low footprint with respect to the conventional coagulationflocculation

Membrane technologies for seawater desalination and brackish water treatment 425

DMF method (3) improved membrane lifetime and (4) a significant reduction inchemical dosing

Although the capital cost of membrane pretreatment still exceeds that of conven-tional processes by about 10 (for instance membranes are about twice as expensiveas dual media filters) this is compensated for by the reduction of operation and main-tenance (OampM) costs in subsequent RO trains Whereas a typical annual replacementrate for RO membranes operated with a conventional pretreatment system is 15e20it is reduced to 10e15 when MFUF pretreatment technology is used The frequencyof RO cleaning is also shortened As the desalination industry gains long-term expe-rience with membrane pretreatment systems MF and UF are expected to become thestandard for the next generation of BWRO and SWRO plants (operational scheme inFigure 139) (Voutchkov 2010)

135 Energy requirements for RO plant

The energy consumption of modern large SWRO desalination plants is currentlyaround 4 kWhm3 which makes membrane desalination the most energy-efficienttechnology for drinking water production (Darwish Hassabou amp Shomar 2013)Because of the lower salinity of the treated feed BWRO requires less energy input(015e08 kWhm3) than a corresponding SWRO plant About 80 of the total energyinput is absorbed by high-pressure pumps that pressurize the feed entering RO trainstherefore increasing of energy efficiency of both BWRO and SWRO trains is a criticalissue According to this perspective various energy recovery devices (ERDs) such asthe Francis turbine and Pelton wheel and the turbochargers DWEER and PressureExchanger have been used over the past 15 years

The goal of Pelton wheels and Francis turbines is to recover the energy of ROretentate (pressurized at 60e70 MPa) in the form of mechanical energy (Figure 1310)

Intake pump

Seawater

Screen

ChlorinationFlocculants

pH adj

Antiscalingdechlorination

To RO trains

Air bubbling

MFUF

Figure 139 Seawater pretreatment based on submerged MFUF unit (Di Profio Ji Curcio ampDrioli 2011) Integration of standard MFUF modules is also frequently applied

426 Advances in Membrane Technologies for Water Treatment

Pelton wheels and Francis turbines (usually denoted as Class III ERD) convert thehydraulic energy of the reject stream into rotational energy which is delivered in theform of mechanical shaft power Although these systems can reach 80e88 efficiencyin converting hydraulic energy into rotational mechanical power a second conversionis needed to obtain useful hydraulic energy Overall the real net transfer efficienciesfall to 63e76 (MacHarg 2001)

Hydraulically driven pumps such as hydraulic turbochargers Pelton-drive pumpsand hydraulic pressure boosters are centrifugal in nature and belong to the secondclass of ERDs their hydraulic energy transfer efficiency is less than Class III devices

Class I energy recovery technologies use the principle of positive displacementEnergy is transferred directly from the reject stream to an incoming SW stream thatcombines with the total feed stream to the RO membranes (operational principles ofDesalcorsquos Work Exchanger Energy Recovery (DWEER) system and EnergyRecovery Incrsquos Pressure Exchanger (PX) are illustrated in Figure 1311(a) and (b))Positive displacement devices achieve net energy transfer efficiencies between91 and 96 (Clemente amp Mercer 2011) Theoretically Class I devices areable to decrease the energy consumption of SWRO plants to about 2 kWhm3

(MacHarg 2001)

136 Energy from SW

The sea is more than just a potentially unlimited source of drinking water Thermody-namic considerations based on evaluation of the energy of mixing suggest that a hugeamount of energy can be potentially generated when waters of different salinities aremixed together (salinity gradient power generation) Vermaas et al (2013) showed thatthe theoretical obtainable Gibbs free energy of mixing typical SW (30 gL NaCl) andriver water (1 gL NaCl) both at a flow rate of 1 m3s is 139 MW (Vermaas et al2013)

The global potential for salinity gradient power is reported to be 1650 TWhyear Inthe United States with a total flow of rivers into the ocean of about 1700 km3year this

M

Turbine

Feed

Brine

Permeate

Retentate

60 bar 1 bar

58 bar

Figure 1310 Scheme of an SWRO desalination unit with a Pelton wheel energy recoverydevice (ERD)

Membrane technologies for seawater desalination and brackish water treatment 427

technology could generate about 55 GW assuming an energy conversion efficiency of40 (Thorsen amp Holt 2009)

Theoretical calculations using the vanrsquot Hoff equation (Eqn (131)) show that themaximum extractable energy from mixing freshwater with SW is 075 kWhm3

(assuming 055 M NaCl concentration) this value increases to 15 kWhm3 whenconsidering SWRO brine from a desalination plant operating at a 50 recovery factor(Helfer Lemckert amp Anissimov 2014)

To date pressure retarded osmosis (PRO) and reverse electrodialysis (RE) are themost investigated technologies to recover energy from saline gradients

In PRO a semipermeable membrane separates a low-concentration and a high-concentrated salt solution (also called a draw solution) Under the difference ofosmotic pressure water flows from the low-concentration compartment to the oppositeside thus increasing the volume of the concentrate flow A turbine is coupled to thepipe containing the increased pressure flow to generate power In the scheme ofFigure 1312 PRO is used to recover the osmotic energy of SWRO brine by operatingwith SW

The performance of PRO strictly depends on the properties of the membrane Sofar membranes specifically developed for forward osmosis and PRO are almostexclusively commercialized by Hydration Technology Innovations (HTI) althoughthe market is now accelerating driven by renewed interest in osmotic processesPRO laboratory tests using commercial flat-sheet cellulose triacetate forward osmosis(FO) membranes from HTI resulted in the generation of a power density of 22 and27 Wm2 membrane area when operating with SWBW and SWpure water

Brine

PistonBarrier

Feed

Permeate

High pressureretentatePistonBarrier

Feed Permeate

Low pressurereject

PX

High pressurepump

High pressureretentate

(a)

(b)

Figure 1311 Operational schemes of (a) DWEER system (Ashkelon SWRO plant Israel)and (b) PXs (Qingdao SWRO plant China)

428 Advances in Membrane Technologies for Water Treatment

respectively (Achilli Cath amp Childress 2009) When using SWRO brine (6 NaCl)lab-made TFC hollow fibres specifically developed for PRO resulted in a power den-sity higher than 10 Wm2 (Wang Tang amp Fane 2012)

The first osmotic power plant prototype with a designed capacity to generate10 kW of electricity was constructed by the Norwegian state-owned power companyStatkraft in 2009 It is currently operated by Sintef Energy Research a research divi-sion of the Sintef Group (Melanson 2014)

RE is an emerging technology with the potential to generate energy from salinitygradients power (SGP) In a typical SGP-RE module cation exchange membranesand anion exchange membranes are stacked alternately in a module (Figure 1313)

Turbine

Generator

Water

Pretreatedseawater

PX

Pressureexchanger

To RO train

SWRO brine

Diluted brinedischarge

Figure 1312 A possible scheme of pressure retarded osmosis (PRO) system to recover osmoticpower from SWRO brine

Load

CEM AEM

SWR

O

SWR

O

brin

e

brin

e

SWR

Obr

ine

Seaw

ater

Seaw

ater

Seaw

ater

AEM AEMCEM CEM CEM

ndash ndash ndash+++ +

Electron flow

Recirculating electrolyte solution

Ele

ctro

deE

lectrode

Figure 1313 Scheme of an reverse electrodialysis (RE) unit operated with SWRO brine andseawater

Membrane technologies for seawater desalination and brackish water treatment 429

Driven by a concentration gradient the diffusive flux of ions generates an electrochem-ical membrane potential recorded as a voltage across electrodes (Tedesco CipollinaTamburini van Baak amp Micale 2012)

RE-SGP investigations carried out with aqueous NaCl solutions mimicking SW andriver water salinity reached a power density of about 2 Wm2 (Dlugolecki GambierNijmeijer amp Wessling 2009 Post et al 2010 Vermaas Saakes amp Nijmeijer2011) and energy efficiency around 50 Daniilidis Vermaas Herber and Nijmeijer(2014) achieved a power density of 67 Wm2 of total membrane area using 001 MNaCl solution against 5 M at 60 C in general the power density increased monoton-ically for high-concentrated feed solutions (Daniilidis et al 2014)

Theoretical predictions on a 12-cell stack equipped with Fujifilm ion exchangemembranes and operated with 05 M54 M NaCl diluteconcentrate solutions resultedin a maximum gross power density of 24 Wm2 (Veerman Saakes Metz amp Harmsen2009)

1361 Environmental impact of membrane desalination plants

Coastal and near-shore constructions (including intake and outfall structures) use oflarge quantity of SW causing impingement and entrainment of marine organismsand disposal of large amount of brines and chemicals severely impact the environment

Open intakes (the most common option in large desalination plants) and single openoutfall or diffuser systems when placed above the seafloor may cause wave refrac-tions and a change in current patterns thus interfering with marine sediment The localincrease of turbidity results in an increased level of pollutants or a reduced level ofdissolved oxygen burying benthic flora and fauna Moreover structures above the sea-floor might provide a substrate to which algae anemones or mussels might attachthese species attract echinoderms and crustaceans and ultimately result in a significantalteration in the marine community (Latterman amp Hopner 2008) Intake screensrepresent a high-mortality source for larger marine organisms and fish owing toimpingement (causing suffocation starvation or exhaustion) for these reasons theintake velocity of SW should be reduced as much as possible

However the highest impact on the marine environment is caused by the rejectedSWRO concentrate stream A typical plant operating at 50 recovery factor producesa brine with a salinity of about 70 that has a density of 1053 kgL (higher than the SWdensity of 1025 kgL) at room temperature The brine spread through multi-portdiffuser systems over the seafloor affects benthic communities Studies on Posidoniaoceanica showed that salinity around 45 causes about 50 mortality in 15 days(Latorre 2005)

1362 Membrane distillation

Membrane distillation (MD) is a membrane contactor technology with the potential tosignificantly reduce the amount of RO concentrate to be discharged In MD a micro-porous hydrophobic membrane contacts a heated solution on one side (lsquofeedrsquo or lsquoreten-tatersquo) The hydro-repellent nature of the membrane avoids the permeation of any liquid

430 Advances in Membrane Technologies for Water Treatment

while sustaining a vapoureliquid interface at the entrance of each pore There waterevaporates (whereas nonvolatile solutes are retained) diffuses across the membraneand condenses on the opposite side (lsquodistillatersquo) of the module (Figure 1314)

The specific method used to activate the vapour pressure gradient across the mem-brane (driving force) has four major MD configurations In the most common andsimplest arrangement direct contact MD the permeate side of the membrane consistsof condensing pure water Alternatively the water vapour can be extracted by vacuumrecovered on a condensing metallic surface separated from the membrane by an air gap(AGMD) or removed by a sweep gas

Ideally MD guarantees the complete rejection of nonvolatile solutes such as mac-romolecules colloidal species and ions Low-temperature gradients are generally suf-ficient to establish an acceptable trans-membrane flux (1e20 kgm2h) typical feedtemperatures vary in the range of 50e80 C permitting the efficient recycle of low-grade or waste heat streams as well as the use of alternative energy sources (solarwind or geothermal) An interesting advantage with respect to RO is that MD doesnot have the limitations of concentration polarization therefore it can be applied toRO brines to increase the water recovery factor and decrease the amount of disposedbrine

Currently no MD systems have reached a large industrial scale or are available onthe market most installations are at the pilot stage The Swedish company ScarabDevelopment provides flat-plate MD modules Production rates of 10e20 kgh arereported for high-temperature gradients across the membrane These modules werealso tested within European Union (EU)-funded project MEDESOL (SW desalinationby innovative solar-powered MD system) (psa 2014)

The Memstill process was developed by TNO (The Netherlands) for SW desali-nation using air gap MD carried out in a countercurrent flow configuration Cold SWflows through a condenser with nonpermeable walls through a heat exchanger andfrom there into the membrane evaporator The wall of the evaporator is a microporoushydrophobic membrane through which water vapour diffuses and liquid salted water isretained (Hanemaaijer et al 2006)

Seawater

Pure water (DCMD)Vacuum (VMD)

Sweep gas (SGMD)Air gap (AGMD)

Tfeed Vapour

Vapour

Vapour

Microporous hydrophobicmembrane

Figure 1314 Principle of membrane distillation

Membrane technologies for seawater desalination and brackish water treatment 431

Within the EU-funded project MEDIRAS (Membrane Distillation in RemoteAreas) a two-loop MD system with a nominal production of 5 m3day was installedin an 8-MW diesel power plant on Pantelleria island Italy The system which usesthermal energy (20) from 40 m2 of solar collectors and waste heat (80) at 90 Cfrom the refrigeration of engines is an example of a prototypal solar MD unit(Figure 1315)

Air gap MD modules integrated with an appropriate heat recovery system weredeveloped by SolarSpring GmbH a Fraunhofer spin-off company The module setupconsists of three channels condenser evaporator and distillate (Figure 1316)Condenser and distillate channels are separated by a metallic foil whereas a micropo-rous hydrophobic membrane is interposed between the evaporator and the distillatechannels The hot SW (typically at 80 C) is directed in the evaporator channel therewater vapour diffuses across the membrane and condenses at the metallic foil surfacewhere the heat of evaporation is partially recovered Cold feed water (around 20 C)enters in the distillate channel (in countercurrent with respect to the flow directionof the evaporator stream) to increase the temperature when in contact with the conden-sate foil (Koschikowski Wieghaus amp Rommel 2009)

The concept of integrated membrane desalination systems with MD operated on theRO retentate to increase the water recovery factor and reduce the volume of discharged

(a) (b)

Figure 1315 MEDIRAS project Membrane Distillation (MD) pilot plant installed inPantelleria Italy (a) Solar thermal collectors (b) multi-module MD systemFrom MEDIRAS Project website (2014) with kind permission

Metallic foil

Membrane

Condenser channel

Evaporator channelDistillate channelHeat

exchanger

Condenser inlet(feed at 20 degC)

Condenser outlet(ca 70 degC)

Evaporator inlet(80 degC)

Evaporator outlet(ca 30 degC)

Distillate outlet(ca 25 degC)

Figure 1316 Principle of AGMD module with integrated heat recovery developed bySolarSpring GmbH

432 Advances in Membrane Technologies for Water Treatment

brine (thus approaching the concept of zero liquid discharge) was developed within theEU-funded project MEDINA (membrane-based desalination an integrated approach)(Al Obaidani et al 2008 Macedonio Curcio amp Drioli 2007) The possibility ofdriving MD towards concentrations overcoming the saturation levels of salts dissolvedin solution (MDecrystallization) led to the recovery of pure crystallized salts (sodiumchloride epsomite etc) from SW brine (Drioli Criscuoli amp Curcio 2005 Ji et al2010)

137 Economics of membrane desalination

Over the past 3 decades the unit cost of water produced by SWRO desalinationprocesses has progressively decreased (Figure 1317) In particular the economicsof membrane desalination was found to be sensitive to the plant capacity Despitea higher initial capital investment plants with large capacities reduce the unitcost of water to 05e07 $m3 Table 134 reports the estimated unit water cost pro-duced in some large industrial SWRO desalination plants On the other hand thecost of desalinated water unit produced from BW by RO plants with a capacityless in 1000 m3day might range between 06 and 1 $m3 (Karagiannis amp Soldatos2008)

The unit cost of water ($m3) is obtained by dividing the total annual cost ($year)and the annual yield (m3year)

The annual yield is determined by multiplying the maximum daily water production(m3day) and the annual plant utility (number of days on-line per year percentage ofdaily plant capacity)

0 05 1 15 2

1982

1992

2002

2010

Unit water cost ($m3)

Yea

r

Electric power

Maintenance

Capex charges

Figure 1317 Historical trend of unit cost of drinking water produced by SWRO desalinationData from Water Reuse Association (2012)

Membrane technologies for seawater desalination and brackish water treatment 433

The total annual cost is determined by (1) the annual cost of debt service on capitalitems ($year) and (2) the annual operating and maintenance cost ($year)

The annual cost of debt service on capital items ($year) is composed of (11) theannual debt service on water conveyance ($year) and (12) the annual debt service ofwater production ($year) (11) is calculated by multiplying the total capital cost ofconveyance ($) by the capital recovery factor (CRF) (12) is calculated by multiplyingthe total capital cost of concerns and treatment ($) by the CRF

The total capital cost of conveyance refers to the cost of constructing pipelines andany accessories and turnout on the pipeline route including water storage tanks Thetotal capital cost of concerns and treatment includes both the cost of the contract asso-ciated with the delivery of the desalination plant and the cost of the engineering legaland administrative tasks associated with developing the contract documentation andexecuting the contract

The CRF is calculated on the basis of a net present value of the asset defined for agiven discount rate (usually 6) and a series of future payments over a defined periodof time (usually serviced over 25 years)

The annual OampM costs which emerge after plant commissioning and during plantoperation include (21) the cost of energy (in RO plants primarily electrical powertypically in the range of 35e5 KWhm3) (22) chemical costs (typically chlorinefor disinfection acid against calcium carbonate precipitation antiscaling agents coag-ulants and flocculants caustic soda etc) (23) membranes and filtration mediareplacement (24) maintenance costs covering all activities and consumables associ-ated with scheduled and emergency servicing of mechanical equipment calibratingand servicing instrumentation data acquisition and electrical systems and monitoring(collecting analysing and reporting on water quality data) and (25) labor costs

A rough breakdown of total capital costs and OampM costs is provided inFigure 1318(a) and (b)

Table 134 Unit water cost of some large SWRO plants

SWRO plant Start-up Productivity (m3day) Unit water cost ($m3)

Ashkelon (Israel) 2001 320000 052

Palmachim(Israel)

2005 83000 078

Perth (Australia) 2006 144000 075

Carlsbad(California)

2006 189000 076

Skikda (Algeria) 2008 100000 073

Hamma (Algeria) 2008 200000 082

Hadera (Israel) 2010 348000 063

Source Ghaffour Missimer and Amy (2013) Pankratz (2009)

434 Advances in Membrane Technologies for Water Treatment

138 Conclusions

Driven by RO membrane science has exponentially grown over the past 40 years tobecome the leader in technology for BW and SW desalination Despite this enormoussuccess many technological challenges still need to be addressed

The recent development of ERDs has resulted in a drastic improvement in theenergetic efficiency of desalination plants however the large energetic potential ofconcentrated streams remains unexploited In this regard emerging technologies

3 210

20

2Testing and

commissioning35

Mechanical andprocess works

5 2 1

Civilworks20

Electrical works

Control andinstrumentation

Structural works

Architectural and landscape

General and preliminariesExternal

works

Maintenance and spares

under warranty

(a)

(b)

10

10

12

8

Energy60

Maintenance and monitoring

Membrane replacement

Labour

Chemicals

Figure 1318 Percent breakdown of (a) capital costs elements and (b) OampM cost elementsAfter UNESCO Centre for Membrane Science and Technology (2008)

Membrane technologies for seawater desalination and brackish water treatment 435

such as PRO and RE promise a considerable reduction in the energy input andultimately the unit water costs

Further advances are expected to come from new RO membrane materialsand module designs and in particular from larger-diameter SWMs and high-fluxmembranes with enhanced selectivity

Driven by rapid technological development MFUF operations are expected to in-crease in acceptance as standard pretreatment methods in the near future with majorbenefits in terms of improvedwater quality and a lower ROmembrane replacement rate

Today extensive expansion in the number and capacity of coastal desalination plantsexacerbates the negative impact of rejected concentrate on the fauna and flora of the sur-rounding seas Although far from being fully implemented on an industrial scale MDand related operations (such as membrane crystallization) have emerged as an inter-esting answer to the brine disposal problem in the logic of zero liquid discharge

In general considering the strategic relevance of the desalination industry formany countries continuous multidisciplinary research efforts are mandatory tomake BWRO and SWRO affordable worldwide

List of symbols

Italic font

c Molar concentrationD Diffusion coefficientJs Solute molar fluxJv Volumetric fluxk Partition coefficientR Ideal gas constantT Absolute temperatureV Partial molar volume

Greek font

d Membrane thicknessn Vanrsquot Hoff coefficientP Osmotic pressure

Superscripts

f Feedp Permeate

Subscripts

i ith ions Solutew Water

436 Advances in Membrane Technologies for Water Treatment

List of acronyms

AEM Anion exchange membraneAGMD Air gap membrane distillationBW Brackish waterCA Cellulose acetateCEM Cation exchange membraneCOD Chemical oxygen demandCRF Capital recovery factorDCMD Direct contact membrane distillationDMF Dual media filtrationDOM Dissolved organic matterED ElectrodialysisEDR Electrodialysis reversalEDTA Ethylenediaminetetraacetic acidERD Energy recovery devicesGOR Gain output ratioLSI Langelier saturation indexMD Membrane distillationMED Multiple effect distillationMENA Middle East and North AfricaMF MicrofiltrationMSF Multistage flashMVC Mechanical vapour compressionNOM Natural organic matterNTU Nephelometric turbidity unitsOampM Operating and maintenance (costs)PRO Pressure retarded osmosisPX Pressure exchangerRE Reverse electrodialysisRO Reverse osmosisSDI Silt density indexSampDSI Stiff and Davis stability indexSHMP Sodium hexametaphosphateSMBS Sodium metabisulphiteSGMD Sweep gas membrane distillationSGP Salinity gradient powerSSF Slow sand filtrationSW SeawaterSWM Spiral-wound moduleTCA Cellulose triacetateTDS Total dissolved solidsTFC Thin-film compositeTSS Total suspended solidsTVC Thermal vapour compressionUF UltrafiltrationVMD Vacuum membrane distillationWHO World Health Organization

Membrane technologies for seawater desalination and brackish water treatment 437

References

Achilli A Cath T Y amp Childress A E (2009) Power generation with pressure retardedosmosis An experimental and theoretical investigation Journal of Membrane Science343 42e52

Al Obaidani S Curcio E Macedonio F Di Profio G Al Hinai H amp Drioli E (2008)Potential of membrane distillation in seawater desalination Thermal efficiency sensitivitystudy and cost estimation Journal of Membrane Science 323 85e98

Al-Amoudi A amp Lovitt W L (2007) Fouling strategies and the cleaning system of NF mem-branes and factors affecting cleaning efficiency Journal of Membrane Science 303 4e28

Al-Shammiri M amp Al-Dawas M (1997) Maximum recovery from seawater reverse osmosisplants in Kuwait Desalination 110 37e48

Bengtsson L (2010) The global atmospheric water cycle Environmental Research Letters5(2) 025202

Borsani R amp Ghiazza E (8e11 April 2012) New development in MSF technology for highperformances plant In Proceedings of water desalination conference in Arab countriesARWADEX Riyad Saudi Arabia

Buscha M Chub R Kolbe U Meng Q Q amp Li S J (2009) Ultrafiltration pretreatment toreverse osmosis for seawater desalination mdash three years field experience in the WangtanDatang power plant Desalination and Water Treatment 10 1e20

Clemente R amp Mercer G (4-9 September 2011) A five year lifecycle analysis of the Perthseawater desalination plant In Proceedings of IDA World Congress Perth Australia

Cornelissen E R Vrouwenvelder J S Heijman S G J Viallefont X D Van Der Kooij D ampWessels L P (2007) Periodic airwater cleaning for control of biofouling in spiral woundmembrane elements Journal of Membrane Science 287 94e101

Daniilidis A Vermaas D A Herber R amp Nijmeijer K (2014) Experimentally obtainableenergy from mixing river water seawater or brines with reverse electrodialysis RenewableEnergy 64 123e131

Darwish M Hassabou A H amp Shomar B (2013) Using seawater reverse osmosis(SWRO) desalting system for less environmental impacts in Qatar Desalination 309113e124

Di Profio G Ji X Curcio E amp Drioli E (2011) Submergedhollow fiber ultrafiltration asseawater pretreatment in the logic of integrated membrane desalination systems Desali-nation 128e135

Dlugolecki P Gambier A Nijmeijer K amp Wessling M (2009) The practical potential ofreverse electrodialysis as process for sustainable energy generation Environmental Scienceand Technology 43 6888e6894

Drioli E Criscuoli A amp Curcio E (2005) Membrane contactors Fundamentals applica-tions and potentialities Amsterdam Elsevier Science Ltd

El-Manharawy S amp Hafez A (2001) Water type and guidelines for RO system designDesalination 139 97e113

FAO Water Report (2012) Coping with water scarcity Rome FAO Sales and MarketingGroup ISSN 1020e1203

Fell C J D (1995) Membrane separations technology mdash principles and applicationsMembrane Science and Technology 2 113e142

Ghaffour N Missimer T M amp Amy G L (2013) Technical review and evaluation of theeconomics of water desalination Current and future challenges for better water supplysustainability Desalination 309 197e207

438 Advances in Membrane Technologies for Water Treatment

GlobalWater Intelligence (GWIIDADesalData) (2013)Market profile and desalination markets2009e2012 yearbooks and GWI website Retrieved from httpwwwdesaldatacom

Hanemaaijer J H van Medevoort J Jansen A E Dotremont C Van Sonsbeek EYuan T et al (2006) Memstill membrane distillationmdasha future desalination technologyDesalination 199 175e176

Hasson D Drak A amp Semiat R (2003) Induction times induced in an RO system byantiscalants delaying CaSO4 precipitation Desalination 157 193e207

Helfer F Lemckert C amp Anissimov Y (2014) Osmotic power with pressure retarded osmosistheory performance and trends e a review Journal of Membrane Science 453 337e358

IDA Media Analytics Ltd (2007) The 20th IDA worldwide desalting plant inventory OxfordUK

Ji X Curcio E Al Obaidani S Di Profio G Drioli E amp Fontananova E (2010)Membrane distillation-crystallization of seawater reverse osmosis brines Separation andPurification Technology 71 76e82

Karagiannis I C amp Soldatos P G (2008) Water desalination cost literature Review andassessment Desalination 223 448e456

Knudsen M (1903) On the standard-water used in the hydrographical research until July1903 Conseil permanent international pour lrsquoexploration de la mer Publications decirconstance no 2 Copenhagen

Koschikowski J Wieghaus M amp Rommel M (2009) Membrane distillation for solardesalination In A Cipollina G Micale amp L Rizzuti (Eds) Seawater desalination BerlinHeidelberg Springer-Verlg

Kumano A amp Fujiwara N (2008) Cellulose triacetate membranes for reverse osmosis InA G Fane N Li W S W Ho amp T Matsuura (Eds) Advanced membrane technologyand application Hoboken NJ John Wiley amp Sons

Latorre M (2005) Environmental impact of brine disposal on Posidonia seagrasses Desali-nation 182 517e524

Latterman S amp Hopner T (2008) Impacts of seawater desalination plants on the marineenvironment of the Gulf In A H Abuzinada H J Barth F Krupp et al (Eds) Protectingthe Gulfrsquos marine ecosystems for pollution Basel Birkhauser

Lee S Cho J amp Elimelech M (2005) Combined influence of natural organic matter (NOM)and colloidal particles on nanofiltration membrane fouling Journal of Membrane Science262 27e41

Lee K P Arnot T C amp Mattia D (2011) A review of reverse osmosis membrane materialsfor desalinationmdash development to date and future potential Journal of Membrane Science370 1e22

van de Lisdonk C A C Rietman B M Heijman S G J Sterk G R amp Schippers J C(2001) Prediction of supersaturation and monitoring of scaling in reverse osmosis andnanofiltration membrane systems Desalination 138 259e270

Lokiec F amp Ophir A (21e26 October 2007) The mechanical vapor compression 38 yearsof experience In Proceedings of IDA world congress Maspalomas Gran Canaria Spain

Macedonio F Curcio E amp Drioli E (2007) Integrated membrane systems for seawaterdesalination Energetic and exergetic analysis economic evaluation experimental studyDesalination 203 260e276

MacHarg J P (2001) The evolution of SWRO energy-recovery systemsDesalination ampWaterReuse 11(3) 49e53

Madaenl S S Mohamamdi T amp Moghadam M K (2001) Chemical cleaning of reverseosmosis membranes Desalination 134 77e82 Retrieved from httpwwwmediraseuindexphpidfrac14121html

Membrane technologies for seawater desalination and brackish water treatment 439

Melanson D Norwayrsquos statkraft kick-starts worldrsquos first osmotic power plant EngadgetRetrieved from httpwwwengadgetcom20091125norways-statkraft-kick-starts-worlds-first-osmotic-power-plant

Merten U (1966) Transport properties of osmotic membranes In U Merten (Ed) Desali-nation by reverse osmosis Cambridge MA The MIT Press

Millero F J Feistel R Wright D G amp McDougall T J (2008) The composition ofstandard seawater and the definition of the reference-composition salinity scale deep searesearch part I Oceanographic Research Papers 55(1) 50e72

Mountford H (25e26 October 2011) Water The environmental outlook to 2050 In Pro-ceedings of OECD global forum on environment Paris Making Water Reform Happen

Nguyen T Roddick F A amp Fan L (2012) Biofouling of water treatment membranes Areview of the underlying causes monitoring techniques and control measuresMembranes2 804e840

Ning R Y amp Troyer T L (2007) Colloidal fouling of RO membranes following MFUF inthe reclamation of municipal wastewater Desalination 208 232e237

Pankratz T (13e16 September 2009) The total water cost of seawater desalination In Pro-ceedings of the 24th water reuse symposium Seattle Washington

Patzay G Stahl G Karman F H amp Kalman E (1998) Modeling of scale formation andcorrosion from geothermal water Electrochimica Acta 43 137e147

Pearce G (2007) Water and wastewater filtration Membrane module format Filtration ampSeparation 44 31e33

Post J W Goeting C H Valk J Goinga S Veerman J Hamelers H V M et al (2010)Towards implementation of reverse electrodialysis for power generation from salinitygradients Desalination and Water Treatment 16 182e193

Pressman J G McCurry D L Parvez S Rice G E Teuschler L K Miltner R J et al(2012) Disinfection byproduct formation in reverse-osmosis concentrated andlyophilized natural organic matter from a drinking water source Water Research 46(16)5343e5354 Retrieved from httpwwwpsaeswebengprojectsmedesolresultsphp

Saeed M O (2002) Effect of dechlorination point location and residual chlorine on thebiofouling in a seawater reverse osmosis plant Desalination 143 229e235

Sagiv A amp Semiat R (2010) Parameters affecting backwash variables of RO membranesDesalination 261(3) 347e353

Segarra J Iglesias A Peacuterez J amp Salas J (2009) Construccion de la planta con mayorcapacidad de produccion mundial con tecnologiacutea EDR para agues regeneradas Tecnologiacuteadel Agua 309 56e62

Shams El Din A M Arain R A amp Hammoud A A (2000) On the chlorination of seawaterDesalination 129 53e62

Shiklomanov I (1993) World fresh water resources In P H Gleick (Ed) Water in crisis Aguide to the worldrsquos fresh water resources New York Oxford University Press Retrievedfrom httpwwwsidem-desalinationcomsidemressourcesfiles116543Sidem-Company-Profile-Dec-2011pdf

Tedesco M Cipollina A Tamburini A van Baak W amp Micale G (2012) Modelling thereverse electrodialysis process with seawater and concentrated brine Desalination andWater Treatment 49 404e424

Thorsen T amp Holt T (2009) The potential for power production from salinity gradients bypressure retarded osmosis Journal of Membrane Science 335 103e110

UNESCO Centre for Membrane Science and Technology (October 2008) Emerging trends indesalination A review In Waterlines report series 9 University of New South WalesNational Water Commission Canberra (Australia)

440 Advances in Membrane Technologies for Water Treatment

Veerman J Saakes M Metz S J amp Harmsen G J (2009) Reverse electrodialysisPerformance of a stack with 50 cells on the mixing of sea and river water Journal ofMembrane Science 327 136e144

Vermaas D A Saakes M amp Nijmeijer K (2011) Doubled power density from salinitygradients at reduced intermembrane distance Environmental Science amp Technology 457089e7095

Vermaas D A Veerman J Yip N Y Elimelech M Saakes M amp Nijmeijer K (2013)ACS Sustainable Chemistry amp Engineering 1 1295e1302

Vial D amp Doussau G (2002) The use of microfiltration membranes for seawaterpre-treatment prior to reverse osmosis membranes Desalination 153 141e147

Voutchkov N (2010) Considerations for selection of seawater filtration pretreatment systemDesalination 261 354e364

Wang R Tang C amp Fane A G (2012) Development of pressure retarded osmosis (PRO)membranes with high power density for osmotic power harvesting In Proceedings of the3rd osmosis membrane summit statkraft Barcelona Spain

Water Reuse Association (2012) Seawater desalination costs Retrieved from httpswwwwatereuseorgsitesdefaultfilesu8WateReuse_Desal_Cost_White_Paperpdf

Yun T I Gabelich C J Cox M R Mofidi A A amp Lesan R (2006) Reducing costs forlargescale desalting plants using large-diameter reverse osmosis membranesDesalination189 141e154

Zondervan E amp Roffel B (2007) Evaluation of different cleaning agents used for cleaningultra filtration membranes fouled by surface water Journal of Membrane Science 30440e49

Zouboulis A Traskas G amp Samaras P (2007) Comparison of single and dual mediafiltration in a full-scale drinking water treatment plant Desalination 213 334e342

Zularisam A W Ismail A F amp Salim R (2006) Behaviours of natural organic matter inmembrane filtration for surface water treatment mdash a review Desalination 194 211e231

Membrane technologies for seawater desalination and brackish water treatment 441

Membrane technologiesfor municipal wastewatertreatment

14Seyed MK Sadr Devendra P SarojCentre for Environmental and Health Engineering (CEHE) Department of Civiland Environmental Engineering University of Surrey Guildford Surrey United Kingdom

141 Introduction

1411 Membrane technologies for advanced wastewatertreatment

Membrane technology is increasingly becoming popular for the advanced treatmentof municipal wastewater This is mainly because of growing concerns about waterquality and pollution trends in relation to more complex global challenges such asrapid urbanisation and increasing water demands in the domestic and industrialsectors In the past few decades wastewater treatment and reuse has gained interestand so has advanced wastewater treatment technologies Among these new technol-ogies membrane-assisted ones offer consistently high-quality treatment of effluentMembrane technologies have also been shown to be promising in the removal ofemerging compounds such as endocrine disturbing compounds (EDCs) and phar-maceutically active compounds (PhACs) It is projected that membrane-assistedtechnologies will be among the most reliable systems for water reclamation in com-ing decades (Shannon et al 2008) Membrane technologies encompass a widerange of membrane processes depending on the desired quality of the effluentFor instance by itself microfiltration (MF) can remove particulate and colloidalforms of contaminants whereas as a part of a membrane bioreactor (MBR) MFforms an integral part of a biological treatment system Various membrane-assisted configurations for wastewater treatment exist all of which have theirown advantages and disadvantages depending on various factors such as effluentquality energy consumption and system complexity Often membrane technolo-gies are employed in a combination of physical chemical and biological processesresulting in an efficient process configuration for a particular scenario of wastewatertreatment For example MBR technology combines activated sludge processes(ASPs) or an anaerobic biodegradation process with MF or ultrafiltration (UF)and MF or UF is also integrated as a posttreatment for tertiary treatment of munic-ipal wastewater to achieve high effluent quality

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400014-9Copyright copy 2015 Elsevier Ltd All rights reserved

1412 Drivers and barriers to membrane technologiesfor municipal wastewater treatment

14121 Advantages

Membrane technologies for municipal wastewater treatment particularly MBRs havebeen considered a reliable option for applications requiring a smaller footprint andorhigher effluent quality In most cases of domestic wastewater treatment in developedurban areas carbon (usually indicated by biochemical oxygen demand [BOD]) andnitrogen (NH4-N and total nitrogen (TN)) removal are achieved using biologicalaerobic (BOD oxidation and nitrification) and anoxic treatment (denitrification) aspart of the ASP The conventional activated sludge process (CASP) is normallydesigned and operated at a mixed liquor suspended solids (MLSS) concentration ofless than 4 gL and a lower range of solids retention times (SRTs) to maintain theMLSS In MBRs however the typical MLSS range between 8 and 15 gL allowsthe intensification of microbial suspended growth and raises the possibility of reusingexisting units to increase the plantrsquos capacity with little or no increase in the footprint(Kraemer et al 2012) In general an advantage of membrane technology is the capitalcosts of constructioninstallation which are similar to or lower than those of conven-tional technologies although membrane cost can have an important role depending onthe market trend in coming years Current membrane technologies generally demand ahigh level of automation because of their need for continuous management of foulingConsequently membrane-assisted technologies can be controlled by computerisedmonitoring and control systems This means that they can also be widely applied indecentralised and household systems in the coming decade

14122 Disadvantages

Clear disadvantages of MBRs can be seen in regions where conventional secondarywastewater treatment plants have already established In this regard although it wouldbe possible to use existing bioreactors or clarifiers for the membrane basins majorretrofit modifications and reconstruction are required to meet the requirements of pro-cess geometry the number of basins and provisions for high mixed liquor recycle flowrates Regarding retrofitting it might be possible to use the clarifiers for other pur-poses eg sludge storage In the case of posttreatment membrane technologies (MFor UF units) the cost of membrane modules and operation are compared against theresulting high effluent quality after tertiary treatment

In addition there are limitations to the widespread application of membrane tech-nologies in municipal wastewater treatment eg energy consumption membrane costand process complexity Moreover the scarcity of operational and equipment stan-dards is evident Although standardisation was contemplated in the European regionthrough the European Commissionrsquos Amadeus project (de Wilde Richard Lesjeanamp Tazi-Pain 2007) this has not been widely considered successful so far Membranemanufacturers have their own membrane module configurations and features and theyalso differ in recommended process unit geometry and sizes (Kraemer et al 2012)Other operational disadvantages have been observed eg the limited peak flow

444 Advances in Membrane Technologies for Water Treatment

capacity and performance abilities compared with conventional clarifier-based sys-tems As a result of high energy consumption and in some cases chemical consump-tion the operational costs of membrane technologies are still higher than those ofconventional technologies although the trend of energy consumption has recentlydecreased based on some new process modifications and the use of new materials

142 Process fundamentals and indicators

1421 Membrane-assisted processes and technologies

A membrane can be defined as a barrier that allows some components either physicalor chemical to pass more freely through it than others As normally applied to waterand wastewater treatment membranes are perm-selective Main components in theprocess of membrane filtration are

1 The permeate that passes through the membrane2 The retentate that is rejected by the membrane

Membranes can be classified depending on their pore size applied pressure molec-ular weight cutoff and permeability Commonly accepted classifications in the field ofwater and wastewater treatment include MF UF nanofiltration (NF) and reverseosmosis (RO) Coarser membranes are associated with MF and the most selectivemembranes are associated with RO processes As shown in Figure 141 the first twomembranes operated at low pressures (01e5 bar) are normally used in MBR systemsThey are capable of retaining bacteria pathogens and large fraction of viruses the NFand RO membranes operated at higher pressures (3e100 bars) are able to reject soluble

Figure 141 Various pressure-driven membrane processes

Membrane technologies for municipal wastewater treatment 445

organic compounds EDCs and PhACs Reverse osmosis can also remove monovalentions eg sodium (Nathorn) These well-established capabilities of various types of mem-brane processes are used in the design and operation of wastewater treatment systems

There are several commonly observed operational issues with membrane processesin wastewater treatment The rejected constituents in the retentate tend to accumulate atthe membrane surface This leads to various phenomena and a reduction in the waterflow rate at a given transmembrane pressure (TMP) or conversely an increase in theTMP for a given flux (Judd 2011) These phenomena are collectively referred to asfouling A number of physicochemical and biological mechanisms are related to anincreased deposition of fouling materials onto the membrane structure Importantfactors in the type and the extent of fouling are the membrane material feed watercomposition and flux through the membrane

1422 Membrane-assisted systems in wastewater treatment

Because water quality in wastewater treatment and reuse applications is crucialadvanced treatment technologies are used to achieve the desired level of effluentquality Principal unit operations and processes as well as constituent classes arelisted in Figure 141 As suggested by Asano Burton Leverenz Tsuchihashi andTchobanoglous (2007) an almost endless number of treatment processes can beapplied in water reuse applications to improve the quality of treatment effluent forvarious purposes such as different water reuse scenarios Table 141 shows differentprocesses and their capability of removing various classes of contaminants Mostestablished wastewater treatment processes employ biological treatment to removeBOD total suspended solids (TSS) and even for total nitrogen and phosphorus Inmembrane-assisted processes membranes have an important role in removing resid-ual suspended solids and improving the effectiveness of disinfection

14221 Conventional treatments versus MBRs

The main aerobic biological processes of municipal wastewater treatment applicationscan be categorised into three groups

bull Suspended growth biological treatment processes In these processes microorganisms aremaintained in liquid suspension by mixing and aerating The ASP is one of the most success-fully applied processes for biological wastewater treatment Various reactor types are used inthe design of suspended growth processes for municipal wastewater treatment such ascompletely mixed reactor and sequencing batch reactor

bull Attached growth processes A medium eg a rotating disc or fixed packing is used to whichmicroorganisms attach and form a biofilm Then the biofilm microorganisms come in contactwith wastewater and oxidise the organic matters

bull Hybrid processes These use a combination of attached growth and suspended growth reac-tors to meet different conditions An example of such processes is moving biofilm bioreactortechnology

These processes form the fundamental components of widely applicable biologicalwastewater treatment In conventional treatment systems these processes are applied

446 Advances in Membrane Technologies for Water Treatment

Table 141 Unit operation and processes used to remove various constituents in wastewater

Unitprocess

Suspendedsolids

Colloidalsolids

Particulateorganicmatter

Dissolvedorganicmatter Nitrogen

Phosp-horous

Traceconstituents

Totaldissolvedsolids Bacteria

Protozoancysts andoocysts Viruses

Secondarytreatment

Secondary thornnutrientremoval

Depthfiltration

Surfacefiltration

Micro-filtration

Ultrafiltration

Dissolved airflotation

Nanofiltration

Reverseosmosis

Electro-dialysis

Carbonadsorption

Ion exchange

Advancedoxidation

Disinfection

Source Asano et al (2007)

Mem

branetechnologies

formunicipal

wastew

atertreatm

ent447

combined with well-established solideliquid separation unit operations such as sedi-mentation tanks or clarifiers The major advantage of applying these conventionaltreatment processes is that they are well understood therefore coping with the oper-ation and maintenance is relatively simple The other benefit is that automation of theseprocesses is possible to a certain extent However conventional systems may not bemost suitable especially in an area with a lack of sufficient land The effluent qualityis also relatively lower than that of advanced membrane technologies Table 142compares conventional processes and MBRs

Combined with conventional biological treatment processes membrane processescan form robust membrane technologies offering a higher level of treatment Forexample MBR technology which combines membrane technology and the high-rate biological process forms a unique technology for municipal wastewater treatment(Stephenson Judd Jeferson amp Brindle 2000) Membrane bioreactors use two mainconfigurations for solideliquid separation

bull Side-stream MBR (sMBR) In this configuration the membrane module is separated fromthe main reactor (Figure 142(a)) The mixed liquor in the bioreactor is pumped into a mem-brane module and a concentrated stream is retained by the membrane and returned to thebioreactor Two major developments have been made in this configuration A suctionpump was added on the permeate side to increase flexibility and simultaneously decreasethe cross-flow rate and energy consumption

bull Submerged or immersed MBR (iMBR) This configuration was introduced by YamamotoHissa Mahmood and Matsuo (1989) with the aim of reducing energy consumption associ-ated with the recirculation pump in the side-stream configuration In this configuration amembrane is directly immersed in the reactor (Figure 142(b)) As a result only a suctionpump is applied on the permeate side to create the TMP Table 143 compares sMBR andiMBR

Membrane bioreactors produce high effluent quality with a greater reuse potentialTable 144 compares the effluent quality of conventional treatments with a typicalMBR system In addition the footprint of an MBR is much smaller than a conventionaltreatment process mainly because of the higher SRT and higher MLSS in the biore-actor and the small footprint of the membrane separation units The Nordkanal plantin Germany eg has five main parts the sludge mechanical dewatering processlidded sludge the sludge liquor holding tanks a grit chamber the fine screen thecoarse screen the MBR with nitrification and denitrification tanks and processcontrol The plant has consistently achieved acceptable purification results eg thechemical oxygen demand (COD) removal is about 97 The biochemical oxygen de-mand (BOD) detected in effluent is below 3 mgL when the average BOD in raw wateris 300 mgL The elimination rate of TSS is 100 In addition to this plant and othercommissioned plants various pilot studies have shown that MBR technologies are reli-able for water reuse andor can be applied to decentralised and household-scale waste-water treatment systems It is evident that wastewater treatment plants that employMBRs can produce effluent (Table 144) that can meet various requirements for reusestandards eg landscape and agricultural irrigation and surface water discharge Forexample the Urban Wastewater Treatment Directive in Europe provides mandatoryminimum design rules for sewerage systems as well as treatment plants (minimum

448 Advances in Membrane Technologies for Water Treatment

Table 142 Advantages and disadvantages of conventional treatmentprocesses versus MBRs

Advantages Disadvantages

Conventional wastewater treatment processes

Technologies are well understood Greater sludge production

Process potentials are universally accepted More bio-solids handling and costs required

Different configurations allow the processto be designed to maximise contact timebetween macromolecules andmicroorganisms

Clarifier performance is reduced owing todevelopment of filamentous organisms orpoor settling sludge in aeration process

Energy requirement is less Limited suspended solid removal thatrequires a high level of disinfection

Slow rate of kinetic reaction Large footprint

Skilled operation and maintenancepersonnel are available

Subsequent filtration is needed for effectivedisinfection

MBRs

Very high and stable effluent quality High capital and operation costs

High potential for water reuse scenarios More energy consumption

Smaller footprint and compact design More extensive pretreatment required

Low sludge production More chemical cleaning

Possibility of growth of specificmicroorganisms

Inevitable membrane fouling formation

Low suspended solid concentration andremoval of large particles leads to moreeffective disinfection

Fouling mechanism and control still underinvestigation

Lower effluent production capacity

Possible to add nutrient removal processes Low oxygen transfer efficiency

Effluent quality independence from influentquality based on buffering effect of highMLSS values

Pilot scale often needed for full-scale design

Membrane replacement is relativelyexpensive

Adaptable to decentralised and satellitetechnologies

Complicated control systems

Automation is fairly achievable No standard configuration is available

High rate of nitrification owing to longerretention of nitrifying bacteria

Source Adapted from Asano et al (2007)

Membrane technologies for municipal wastewater treatment 449

design requirement is the highest maximum weekly average load throughout the year)European regulations state that regardless of water reusewastewater treatmentpurposes effluent from wastewater treatment plants in Europe must not exceed25 mgL BOD and 125 mgL COD (Bloch 2005)

14222 Emerging membrane-assisted technologies applicationof NFRO after biological treatment

After the conventional secondary or MBR-based treatment the level of treatment canbe further improved by using membranes with tighter pore sizes When an advancedlevel of removal of dissolved organics and inorganics is desired membrane

Figure 142 Configurations of (a) side-stream and (b) submerged MBRs

Table 143 Comparison of sMBRs and iMBRs

Side-stream MBR Immersed MBR

Complexity High Fair

Flexibility High Low

Robustness High Fair

Flux High (40e100 Lm2$h) Low (10e30 Lm2$h)

Fouling Cross-flow Air bubble agitation

Air lift Back-washing (not alwayspossible eg flat-sheet[FS] membranes)

Chemical cleaning Chemical cleaning

Membrane packing density Low High

Energy consumption High (2e10 kWhm3) Low (02e04 kWhm3)

450 Advances in Membrane Technologies for Water Treatment

technologies such as NF and RO can be applied The process of removing dissolvedconstituents can be accomplished by a pressure-driven separation process Nanofiltra-tion and RO require hydrostatic pressure to overcome the osmotic pressure of the feedstream whereas MF and UF separations are based on the pore size and porosity of themembranes and the size of the contaminant constituents Osmotic pressure can be seenwhere two solutions with different solute concentrations are separated by a thin semi-permeable tissue eg a membrane If a difference in chemical potential exists acrossthe membrane water will diffuse through the membrane from the lower concentratedside (higher chemical potential) to the higher concentrated side (lower chemical poten-tial) until a potential equilibrium occurs (the concentrations on both sides are similar)

Nanofiltration and RO are very similar in terms of rejection mechanisms and oper-ation However some fundamental differences make these two technologies distin-guishable from each other for wastewater treatment applications Nanofiltration andRO remove particles with a molecular weight (MW) of 300e1000 gmol and lowerthan 300 gmol respectively Reverse osmosis is capable of removing monovalentions eg sodium and chloride from 98 to 100 whereas NF can reject theseions in the 50e90 range They are also different in terms of water reuse applicationNF is usually used for water softening and reducing the concentration of TDS inreclaimed water whereas RO is used to desalinate seawater and brackish water Thecharacteristics and main applications of each technology are presented in Table 145

1423 Membrane modules

All commercial membrane modules have a particular membrane geometry and orien-tation in relation to the water flow All membrane designs permit modularisation andprovide limited economy scale with respect to membrane costs these are directly pro-portional to the membrane area that correlates directly with the flow (Judd 2011) Theother factor is promoting turbulence which results in a significant increase in energycosts and is adversely affected by high packing densities A lower packing densitywould be preferred for promoting turbulence and hence reducing fouling On the otherhand low packing densities can lead to high membrane unit costs For an efficientmodule narrowing the retentate flow channels is preferred to produce a high mem-brane packing density Six types of membrane modules are commonly applied onan industrial scale

bull Flat sheet (FS)bull Hollow fibre (HF)bull Multi-tubular (MT)bull Capillary tube (CT)bull Pleated filter cartridge (FC)bull Spiral wound (SW)

Flat sheet HF and MT are suitable for MBR technologies owing to the reasonsmentioned above as well as for effective cleaning Modules SW and HF are normallyused in NF and RO technologies mainly because of their high packing densities andsmall pores

Membrane technologies for municipal wastewater treatment 451

Table 144 Typical range of influent and effluent quality after CASPs and MBRs

Constituent Unit Untreated waterConventionalactivated sludge

Activated sludge withbiological nutrientremoval (BNR) MBR

TSS mgL 120e400 50e250 50e200 pound10

BOD mgL 110e350 50e250 50e150 lt10e50

COD mgL 250e800 40e80 200e400 lt100e300

Total organic carbon mgL 80e260 100e400 80e200 05e50

Ammonia nitrogen mg NL 12e45 10e100 10e30 lt10e50

Nitrate nitrogen mg NL 0 to trace 100e300 20e80 lt100a

Nitrite nitrogen mg NL 0 to trace 0 to trace 0 to trace 0 to trace

Total nitrogen mg NL 20e70 150e350 30e80 lt100a

Total phosphorous mg PL 4e12 40e100 10e20 05e20a

Turbidity NTU lt15 20e150 20e80 pound10

Volatile organiccompounds

mgL 100e400 100e400 100e200 100e200

Metals mgL 15e25 10e15 10e15 Trace

Surfactants mgL 40e100 05e20 01e10 01e05

TDS mgL 270e860 500e700 500e700 500e700

Trace constituents mgL 100e500 50e400 50e300 05e200

Total coliforms No100 mL 106e109 104e105 104e105 lt100

Protozoan cystsand oocysts

No100 mL 101e104 101e102 00e100 00e10

Viruses Plaqueeformingunits100 mL

101e104 101e103 101e103 100 to lt103

NoteaWith BNR processSource Adapted from Asano et al (2007)

452Advances

inMem

braneTechnologies

forWater

Treatm

ent

1424 Operational factors of membrane technologiesin wastewater treatment

As one of the most important operational factors flux (J) or permeate is the quantityof fluid passing through a unit area of membrane per unit area (m3m2$s or Lm2$h)The regular flux unit used in wastewater applications is metres per day (md) or litresper metre square per hour (Lm2$h or LMH) Membrane bioreactors are normallyoperated at 0025e0400 md of permeate Transmembrane pressure is another

Table 145 Characteristics of NF and RO applications

Factor Nanofiltration Reverse osmosis

Membrane driving force Hydrostatic pressuredifference

Hydrostatic pressuredifference

Separation mechanisms Sieve electrostatic repulsionsolutiondiffusionexclusion

Electrostatic repulsionsolutiondiffusionexclusion

Pore size (nm) Microspores (lt20) Dense (lt20)

Operating range (mm) 0001e001 00001e0001

Molecular weightcutoff (Da)

300e1000 lt300

Typical removedconstituents

Small molecules colourhardness bacteria virusesproteins multivalent ions

Very small moleculescolour hardness bacteriaviruses proteins nitratesodium multivalent andmonovalent ions

Operating pressure (bar)a 35e55 120e180

Energy consumption(kWhm3)a

06e12 15e25

Membrane configuration Spiral wound (SW) hollowfibre (HF)

SW HF

Typical application Water softening (to reduce theconcentration ofmultivalent ions leading towater hardness) and waterreuse (used for both non-potable and potable waterreuse applications)

Desalination (removingdissolved organics andinorganics for bothseawater and brackishwater) water reuse (usedfor both nonpotable andpotable water reuseapplications)

NoteaBased on treating reused water with a TDS concentration in the range of 1000e2500 mgL It is widely believed that higheroperating pressures are needed for seawaterSource Adapted from Asano et al (2007)

Membrane technologies for municipal wastewater treatment 453

important operational parameter it defines the driving force for solideliquid separa-tion in MBRs or MFUF applications as posttreatment

Other parameters are used to describe the operational characteristics of membraneprocesses in municipal wastewater treatment For example resistance (R) is the ratio ofthe pressure difference (DP) to the flux and viscosity (h) It is inversely correlated tothe permeability (K) The units normally used for resistance and permeability are me1

and LMHbar respectively The resistance in membrane processes for municipalwastewater treatment consists of different components

1 Membrane resistance This component mainly depends on membrane characteristics such asmaterial pore size and surface porosity

2 Resistance of the fouling layer This is normally correlated with filtration mechanismsdepending on feed constituents andor microbial products

3 Solution interfacial region This component is associatedwith concentration polarisation (CP)

143 Membrane fouling in wastewater treatment

Membrane fouling refers to the adsorption and deposition of constituents on a mem-brane surface or in the membrane pores Consequently fouling leads to a reductionin membrane permeability Fouling in general is divided into two subgroups

bull Reversible fouling usually formed on the membrane surface It can be removed by physicalcleaning

bull Irreversible fouling which designates internal fouling in the membrane pores and can beremoved only by chemical cleaning

1431 Characteristics of membrane fouling

Common compounds and materials (foulants) causing membrane fouling can becategorised into four groups (Table 146)

bull Particulate components Small particles can accumulate on the membrane surface conse-quently forming a filter cake This type of fouling is common in MBRs using MF and UF

bull Organic compounds Adsorption of dissolved organics on membrane surface results inmembrane fouling Natural organic matters (NOMs) eg humic substances in drinkingwater filtration processes have a significant role In membrane processes for wastewater treat-ment organics remaining after biodegradation also can contribute to fouling

bull Biofouling This refers to the adhesion and growth of microorganisms on the membranesurface It results in a loss of membrane performance Membrane processes other than MFand UF commonly used in MBRs and posttreatment after conventional ASP NF and ROmay have more biofouling (Jiang 2007)

bull Scaling This occurs when dissolved salts exceed their solubility product This phenomenonis of main concern in the operation of NF and RO with regard to the deposition of salts suchas CaCO4 CaSO4 BaSO4 SrSO4 MgCO3 and SiO2 (Baker 2012)

The interaction between foulants and membrane mainly concerns the phenomenoninvolving colloidal and macromolecular organic matter rather than the particulatesA number of factors can affect this complex interaction (Table 146)

454 Advances in Membrane Technologies for Water Treatment

14311 Electrostatic repulsion

If a colloid or microorganism contains a similar charge to a membrane surface it willbe repelled by the membrane surface as a result of electrostatic forces As a conse-quence the adsorption will be much less Therefore manufacturers develop membranemodules with appropriate membrane surface properties

14312 pH

Various organics compounds present in a wastewater matrix will be more negativelycharged at higher pH conditions because of the proton deficiency This increases thedissociation of protons into the solution In other words pH is likely to influenceelectrostatic repulsion

14313 Hydrophobicity

Opposite hydrophobicity in the microorganisms and the membrane surface also leadsto hydrophobic repulsion this also causes adsorption Many membranes are made ofhydrophilic materials (or coated) which is advantageous in terms of high permeabilityand low affinity with various NOMs

14314 Ionic strength

Adsorption of microorganisms and colloids to the membrane is reduced by the lowionic strength of the feed water For example in the filtration of proteins andNOMs screening of the charges is decreased at a low ionic strength As a result thesemolecules repel each other at the membrane surface

1432 Concentration polarisation

Concentration polarisation relates to the continuous transport of polluted influent to themembrane surface and the selective retention of some constituents that leads to theaccumulation of some solutes on or near the membrane surface Over the operationtime their concentration increases consequently a boundary layer of higher concen-tration is created This layer contains near-stagnant fluid and the velocity at the mem-brane surface is zero It means that the only transport mode within this layer isdiffusion The concentration build-up causes a particle back-transport flux into thebulk Cross-flow filtration can improve particle back-transport and reduce foulingbecause higher flux leads to higher diffusion

1433 Fouling mechanisms in MBRs

Fouling mechanisms observed in MBRs can be divided into four different groups

14331 Complete blocking

Complete blocking refers to the situation in which each particle upon arriving at themembrane surface participates in blocking some pore with no superposition of parti-cles These particles have sizes comparable to the membrane pore sizes

Membrane technologies for municipal wastewater treatment 455

Table 146 Characteristics of different types of foulants

Particulate fouling Organic fouling Biofouling Scaling

Foulants Colloid suspended solids Organic matters Microorganisms Salts metal cations

Major factors affectingfouling

Concentration particle sizedistributioncompressibility ofparticles

Concentration chargehydrophobicity pH ionicstrength calcium

Temperature nutrients Temperatureconcentration pH

Fouling predictionindicator

Silt density indexModified fouling indexspecific resistance tofouling

Dissolved organic carbon (DOC)ultraviolet254 (UV254) specificultraviolet adsorption (SUVA)

Assimilable organiccarbon biofilmformation rate

Solubility

Feed water pretreatment Coagulation MF and UF Adjustment of pH coagulation Sand filtration biofiltercoagulationflocculation MF UF

Acid antiscalant

Source Jiang (2007)

456Advances

inMem

braneTechnologies

forWater

Treatm

ent

14332 Standard blocking

This mechanism refers to conditions under which particles are deposited onto the in-ternal pore walls This leads to a decrease in pore volume

14333 Cake filtration

Cake filtration is defined as a phenomenon in which each particle locates on the otherdeposited particles It implies that there is no room for particles to directly obstruct themembrane area

14334 Intermediate blocking

Intermediate blocking is pronounced when each particle can either settle on other par-ticles that have already arrived or directly block some membrane area It may beconsidered an intermediate step between complete blocking and cake filtration(Bowen Calvo amp Hernandez 1995)

1434 Fouling control chemical and physical cleaning

Membrane cleaning is achieved by physical and chemical cleaning Physical cleaningis usually accomplished by backwashing and relaxation in wastewater treatment bymembrane-assisted technologies Backwashing is simply referred to reversing theflow toward membranes whereas relaxation is defined as ceasing permeation to scourthe membrane with aeration (air bubbles) On the other hands chemical cleaning isachieved with some mineral and organic acids caustic soda and sodium hypochloriteSometimes the cleaning process can be carried out with backwashing with the additionof a lower concentration of a chemical agent (chemically enhanced backwash) Table147 compares various cleaning methods

In most membrane-assisted technologies fouling control is determined by consid-ering the balance between flux physical and chemical cleaning and CP control Con-trolling and reducing CP-related fouling can be divided into two methods (Judd 2011)

bull Promoting turbulence This reduces the thickness of the boundary layer Promoting turbu-lence in iMBRs and sMBRs can be achieved by increasing membrane aeration andincreasing cross-flow velocity respectively

bull Reducing flux This decreases fouling formation on the membrane surface

A successful MBR project the cleaning method at the Nordkanal wastewatertreatment plant in Germany is summarised (Blastakova Engelheardt Drensla ampBondik 2009)

bull Physical cleaning by employing air scouring backwashing and relaxation of filters duringthe time of low inflow when the installed capacity is reduced by 125

bull Chemical cleaning by using backwashing with chemical cleaning agents for maintenancecleaning in place in biomass andor on air and occasional intensive cleaning out of place

bull Additional mechanical cleaning to remove debris from the membrane modules after COPwhen necessary

Membrane technologies for municipal wastewater treatment 457

144 Design operation and control of membraneprocesses in municipal wastewater treatment

Various process components of the entire technology need to be considered whendesigning membrane-assisted technology Wastewater characteristics and the pur-pose of wastewater treatment are important factors in the design of membranetechnologies

The required membrane surface area is a function of the membrane flux and hy-draulic load The net flux is an important parameter that characterises the averageflow rate including the relaxation and backwash phases (Li Fane Ho amp Matsuura2008) With the help of net flux the treatment capacity of the whole plant is esti-mated The normal range for the maximum fluxes of iMBRs in municipal waste-water treatment is 25e30 L(m2$h) with a net flux about 20 lower In termsof the optimal operation of a pilot-scale plant it is usually recommended to recordthe initial flux and test different cleaning strategies to reconcile fouling controlmeasures cleaning procedures and required flux Estimation of recycle ratio andan appropriate flow regime and filtration tank are important steps in the designand operation of membrane technologies Some important parameters and theirvalue ranges for NF and RO are summarised in Table 145 Regarding operationalissues the membrane lifetime is important It is directly correlated to operation andmaintenance costs eg repair replacement and operation efficiencies Operatingefficiencies can be considered a consequence of the membrane lifetime and perfor-mance stability (Asano et al 2007) The following factors have a high impact on

Table 147 Comparison between physical and chemical cleaning

Physical cleaning Chemical cleaning

Methods Backwashing without air Base (eg caustic sodacitric oxalic)

Backwashing with air Acid (eg hydrochloricsulphuric citricoxalic)

Relaxation Oxidant (eg hydrogenperoxide hypochlorite)

Advantages Simpler and less complex Much higher cleaningefficiencies (generally)

No chemical neededconsequently no chemicalwaste

Capable of returning flux tooriginal or betterconditions

No membrane degradation Capable of removingtenacious materials frommembrane surface

Capable of removing gross solids

458 Advances in Membrane Technologies for Water Treatment

the operational efficiency of all membrane technologies in municipal wastewatertreatment (Celenza 2000)

bull Consistent membrane fouling involving frequent and long regeneration timesbull Membrane failure and then replacementbull Failure of high-pressure pumpsbull Failure of membranes and pumps as a result of abrasive waste materials and components

145 Optimisation of membrane processes in municipalwastewater treatment

1451 Cost assessment

Cost assessment in most membrane technology projects is divided into capital costs(CAPEX) and operation and maintenance (OPEX) costs Generally it is challengingto obtain an appropriate cost assessment It is evident that membrane prices have grad-ually decreased and are still slowly dropping Judd (2011) reported that the prices ofMBRs in the United Kingdom decreased from 320 to 80 Vm2 membrane surface areafrom 1992 to 2000 However the other parts of these systems (eg aeration devicescontrol systems cleaning devices and pipes) are almost at the same prices Moreoverit is reported that at different wastewater treatment plants with MBRs eg the plant atNordkanal Germany the space requirement could be significantly reduced comparedwith conventional design capacity planning (Blastakova et al 2009 Henze vanLoosdrecht Ekama amp Brdjanovic 2008) Consequently capital costs would be sub-stantially decreased Investment costs for the Nordkanal MBR wastewater treatmentplant amounted to V215 million (including VAT) In addition approxV32 million was spent for engineering special consults acquisition of land andcharges for environmental compensation (Blastakova et al 2009) Life cycle costanalysis which can be defined as a sensitivity analysis on uncontrollable expendituresshows that although the capital cost often needs enormous investment a more capitalintensive technology might be selected when the OampM costs are more reasonable andcontrollable (Li et al 2008)

1452 Energy efficiencies and operational costs

There are a number of equations and evaluation methods for energy efficiency in waterreuse technologies but according to Li et al (2008) most of these formulas whichwere developed a few decades ago have not been updated and reconsidered properlyTherefore it is necessary to revisit these evaluation methods especially because of thedevelopment of new technologies with different materials and methods of construc-tion Various factors are associated with energy consumption and operational costsHydraulic factors have an important role in improving energy efficiency Aging infra-structures and redundant equipment should also be taken into consideration Otherimportant factors for this evaluation are the appropriate adaptation and replacement

Membrane technologies for municipal wastewater treatment 459

of membranes and other parts of membrane-assisted technologies to ensure acceptableenergy efficiency

The aeration process may be considered a major part of total energy demand andoperational costs The energy consumption of aeration in MBRs in a normal waste-water treatment plant is about 04 kWhm3 effluent whereas in CASPs it is in the rangeof 025e040 kWhm3 (Krause 2005) Fouling control is another main part of energyconsumption The cost of chemical cleaning regardless of the energy demand is about02e10 Vm2 membrane surface area per year (Li et al 2008) Based on a biologicalactivated sludge model study of the Schilde MBR the energy consumption of theentire MBR is 063 kWhm3 with a yearly average permeate production of 220 m3h Therefore the energy cost can be determined as 220 m3h 24 hd 365 dyr 063 kWhm3 008VkWfrac14 97130Vyr In this evaluation the energy consump-tion for coarse bubble aeration compressors warming of the permeate for cleaningmixing energy and pretreatment are 352 31 66 70 and 26 respec-tively for a total of 540 of the total energy when the system is operated at220 m3h (Greenlee Lawler Freeman Marrot amp Moulin 2009) Blastakova et al(2009) reported that with the Nordkanal wastewater treatment plant at full capacityspecific energy consumption ranges between 04 and 08 kWhm3 wastewater Onaverage the energy demands of membrane air scouring process aeration bioreactormixing permeate suction and biomass circulation are 49 121 115 27and 13 respectively The remaining 232 is consumed by pumping stations pre-treatment dewatering units and miscellaneous process units (Blastakova et al 2009Judd 2011)

Membrane lifetime is also an important factor in cost assessment Studies haveshown that membrane lifetime relates to the composition and pretreatment of thewastewater membrane material module construction and cleaning strategies (Liet al 2008) Moreover toward the end of an effective membrane lifetime energy con-sumption can increase to 170 owing to the reduced flow rate (Fenu et al 2012)

146 Future trends and conclusion

Emerging global issues such as rapid urbanisation increasing water pollution andclimate change have resulted in water scarcity in many regions of the world As aresult improvement in water quality treatment technologies and a move toward waterreuse are increasingly being adapted to satisfy growing water demand From a sus-tainability point of view wastewater treatment and reuse will be essential placingresultant responsibility on wastewater treatment companies to provide clean waterto suite end users Membrane-assisted technologies are an undisputed part of high-quality wastewater treatment and reuse systems However there are still variouschallenges and issues eg high CAPEX and OPEX costs low flow rate andoperational complexities In looking to develop new approaches it is importantto be able to meet both existing and new water reuse regulations and guidelinesconsistently Regarding future regulations and guidelines the additional issue is toconsider removing micropollutants and emerging contaminants such as PhACs

460 Advances in Membrane Technologies for Water Treatment

endocrine-disruptive compounds and personal care products legislation shouldclearly require their removal

Furthermore development of new membrane technologies is needed that can beless expensive in terms of investment and OPEX andor more effective in terms of wa-ter quality New membranes have been successfully developed using different mate-rials but they still need improvement For example according to Howell (2004) it ispossible to make HF membranes with different materials the membranes can beconcentric leaving an annular gap that can be filled by microorganisms so as to createan MBR in which feed streams and product streams can be totally separated or wheredifferent nutrients can be supplied from two different streams Various ongoing devel-opments may lead to the emergence of cost-effective and energy-efficient membranetechnologies that can transform municipal wastewater treatment practices for higheffluent-quality production with a high potential of water reuse

List of acronyms and abbreviations

AnMBR Anaerobic biodegradation processASM Activated sludge modelASP Activated sludge processBOD Biochemical oxygen demandCAPEX Capital costsCASP Conventional activated sludge processCIP Cleaning in placeCOD Chemical oxygen demandCOP Cleaning out of placeCP Concentration polarisationCT Capillary tubeDOC Dissolved organic carbonEDCs Endocrine disturbing compoundsFC Pleated filter cartridgeFS Flat sheetHF Hollow fibreiMBR Immersed membrane bioreactorK PermeabilityMBBR Moving biofilm bioreactorMBR Membrane bioreactorMF MicrofiltrationMLSS Mixed liquor suspended solidsMT Multi-tubularMW Molecular weightMWCO Molecular weight cutoffNF NanofiltrationNOMs Natural organic mattersOPEX Operation and maintenance costsPCPs Personal care productsPhACs Pharmaceutically active compounds

Membrane technologies for municipal wastewater treatment 461

R ResistanceRO Reverse osmosisRSS Residual suspended solidssMBR Side-stream MBRSOCs Soluble organic compoundsSRT Solids retention timeSUVA Specific ultraviolet adsorptionSW Spiral woundTMP Transmembrane pressureTN Total NitrogenTSS Total suspended solidsUF UltrafiltrationUV254 Ultraviolet254h ViscosityDP Pressure difference

References

Asano T Burton F L Leverenz H L Tsuchihashi R amp Tchobanoglous G (2007) Waterreuse Issues technologies and applications New York Metcalf amp Eddy Inc

Baker R W (2012) Membrane technology and applications (3rd ed) Chichester New YorkJ Wiley

Blastakova A Engelheardt N Drensla K amp Bondik I (2009) Operation of the biggestmembrane waste water treatment plant in Europe In The 36th international conference ofSlovak society of chemical engineering Slovak University of Technology in BratislavaISBN 978-80-227-3072-3

Bloch H (2005) European Union legislation on wastewater treatment and nutrients removal(pp 1e8) Marlow UK European Commission Directorate General Environment Foun-dation for Water Research

Bowen W R Calvo J I amp Hernandez A (1995) Steps of membrane blocking in flux declineduring protein microfiltration Journal of Membrane Science 101(1e2) 153e165 httpdxdoiorg1010160376-7388(94)00295-A

Celenza G J (2000) Industrial waste treatment process engineering Specialized treat-ment system (vol III) Lancaster Basel PA Technomic Publication Co Inc

de Wilde W Richard M Lesjean B amp Tazi-Pain A (2008) Towards standardisation of theMBR technology Desalination 231(1) 156e165

Fenu A DeWildeWGaertnerMWeemaesM deGueldre G ampVanDe Steene B (2012)Elaborating the membrane life concept in a full scale hollow-fibers MBR Journal ofMembrane Science 421e422 349e354 httpdxdoiorg101016jmemsci201208001

Greenlee L F Lawler D F Freeman B D Marrot B amp Moulin P (2009) Reverseosmosis desalination Water sources technology and todayrsquos challenges Water research43(9) 2317e2348 httpdxdoiorg101016jwatres200903010

Henze M van Loosdrecht M C M Ekama G A amp Brdjanovic D (2008) Biologicalwastewater treatment Principles modelling and design (pp 1e528) London UK IWAPublishing

Howell J A (2004) Future of membranes and membrane reactors in green technologies and forwater reuseDesalination 162(0) 1e11 httpdxdoiorg101016S0011-9164(04)00021-9

462 Advances in Membrane Technologies for Water Treatment

Jiang T (2007) Characterization and modelling of soluble microbial products in membranebioreactors (p 241) Belgium Ghent University

Judd S (2011) The MBR book principles and applications of membrane bioreactors in waterand wastewater treatment (2nd ed) Oxford UK Elsevier Ltd

Kraemer J T Menniti A L Erdal Z K Constantine T A Johnson B R amp Daigger G T(2012) A practitionerrsquos perspective on the application and research needs of membranebioreactors for municipal wastewater treatment Bioresource Technology 122 2e10httpdxdoiorg101016jbiortech201205014

Krause S (2005) Undersuchungen zum Energiebedarf von MembranelebungsanlagenUnpublished PhD Technische Universitaet Darmstadt

Li N N Fane A G Ho W S W amp Matsuura T (2008) Advanced membrane technologyand applications Hoboken New Jersery USA John Wiley amp Sons Inc ISBN9780471731672

Shannon M A Bohn P W Elimelech M Georgiadis J G Mari~nas B J amp Mayes A M(2008) Science and technology for water purification in the coming decades Nature452(7185) 301e310

Stephenson T Judd J Jeferson B amp Brindle K (2000) Membrane bioreactors forwastewater treatment (1st ed) London IWA Publishing ISBN 1 900222 07 8

Yamamoto K Hissa M Mahmood T amp Matsuo T (1989) Direct solid liquid separationusing hollow fibre membrane in an activated sludge aeration tank Water Science ampTechnology 21 43e54

Membrane technologies for municipal wastewater treatment 463

Membrane technologies for theremoval of micropollutants inwater treatment

15M BodzekInstitute of Environmental Engineering of the Polish Academy of Sciences Zabrze PolandSilesian University of Technology Institute of Water and Wastewater EngineeringGliwice Poland

151 Introduction

In the treatment of natural water for drinking and household needs and industrialwastewaters pressure-driven membrane techniques are principally applied Otherprocesses are taken into consideration as well such as electrodialysis (ED) and electro-deionization (EDI) Donnan dialysis (DD) and diffusion dialysis membrane contac-tors and bioreactors The choice of an appropriate membrane process depends onthe scope of removed effluents and admixtures present in water They can be usedto remove effluents as independent processes or be combined with unit complementaryprocesses forming a treatment process line Potential membrane techniques in thetreatment of natural waters and wastewaters are

bull Reverse osmosis (RO) which retains monovalent ions and most low-molecular organic com-pounds - principally desalination of waters and removal of inorganic and organicmicropollutants

bull Nanofiltration (NF) which retains colloids low-molecular organic compounds and bivalentions - softening and removal of micropollutants from water

bull Ultrafiltration (UF) and microfiltration (MF) clarification methods for the removal ofturbidity retention of suspended substances and microorganisms and disinfection

bull Hybrid processes covering membrane techniques especially UF and MF with coagulationadsorption onto activated carbon and in bioreactors and treatment of drinking water andwastewaters

bull Processes with ion-exchange membranes (ED and EDI and DD and diffusion dialysis) toremove inorganic pollutants

bull Membrane bioreactors (MBRs) for the removal of organics and to some extent inorganics

Increasingly numerous micropollutants occur in the degenerated water environmentmainly in surface waters but also in underground waters Micropollutants in surfacewaters come from rainfall sewage industrial wastewaters and landfill leachate aswell as earth flow from the drainage area The concentration of micropollutants in sur-face waters depends on their source and the pollution grade of the drainage area andsewage Pollutants and organic additives present in natural waters are mainly dispersedsubstances and microorganisms organic compounds including natural organic matter

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400015-0Copyright copy 2015 Elsevier Ltd All rights reserved

(NOM) endocrine active compounds (EAC) and pharmaceutical residues and personalcare products as well as inorganic substances such as heavy metals and toxic anions

152 Inorganic micropollutant removal

A number of inorganic compounds including anions (nitrate (V) chlorate (VII) (V)and (III) bromate (V) arsenate (III) and (V) borate and fluoride) and heavy metalshave been found at potentially harmful concentrations in natural water sourcesand wastewaters (Bodzek amp Konieczny 2011a 2011b Bodzek Konieczny ampKwiecinska 2011 Crespo Velizarov amp Reis 2004 Velizarov Crespo amp Reis2004 Velizarov et al 2008) Some of these compounds are highly soluble in waterand dissociate completely resulting in the formation of ions that are chemically stableat normal water conditions The maximum permissible levels of these compounds indrinking water and wastewaters discharged to environment set by the World HealthOrganization (WHO) and a number of countries are very low (in the range of micro-grams per liter to a few milligrams per liter) Thus most of them can be referred to ascharged micropollutants

Pollution of the aquatic environment with metals and anions may be of either nat-ural or anthropogenic origin Several common treatment technologies includingcoagulationesedimentationefiltration chemical precipitation adsorption ion-exchange classical solvent extraction evaporation and biological methods whichare currently used to remove inorganic contaminants from natural waters or wastewa-ters represent serious exploitation problems (Bodzek amp Konieczny 2011a 2011bCrespo et al 2004 Velizarov et al 2004 2008) Increasingly membrane processesare applied to remove inorganic micropollutants from the aquatic environment Pri-marily RO NF UF and MF in hybrid systems DD and ED as well as these com-bined with extraction (liquid membranes) and bioreactors are used (Bodzek ampKonieczny 2011a 2011b Bodzek et al 2011 Crespo et al 2004 Velizarov et al2004 2008)

1521 Anion removal

15211 Pressure-driven membrane processes

The RO process is highly efficient in directly removing inorganic anions during drink-ing water production In addition it guarantees safe detoxification However completedesalination is undesirable because of possible corrosion problems and remineraliza-tion requirements (Kołtuniewicz amp Drioli 2008) Water with a hardness below50 mgL is corrosive to copper iron zinc and other metals (Bodzek amp Konieczny2011a 2011b Bodzek et al 2011) As a result other processes suitable for selectiveremoval of toxic anions and moderate desalination are desired Nanofiltration fulfillssuch requirements because it enables selective desalination ie the separation of poly-valent ions from monovalent ions with the higher capacity obtained for lower trans-membrane pressures compared with RO process Asymmetric membranes used in

466 Advances in Membrane Technologies for Water Treatment

NF have a negative electrical charge in neutral and alkaline solutions Thus the sepa-ration of anions consists of the difference in the rate of transport through a membranebut also the electrostatic repulsion between anions and the membrane surface chargewhich is greater for polyvalent ions than for monovalent anions (Velizarov et al 2004)Charge of the surface of NF membranes results in the presence of functional groupspossessing an electrical charge but also in the adsorption of anions from water Hencethe charge of a membrane surface depends on the concentration of anions in the solu-tion (Velizarov et al 2004) and varies from negative values to zero in the isoelectricpoint of a membrane up to positive values in an acidic environment (usually pH lt 4)when the adsorption of cations takes place The NF process is much more sensitive tothe ionic strength and pH of raw water than RO hence the selection of proper processconditions is crucial to its application Many studies considering the removal of toxicanions from natural waters and purified wastewaters by means of RO and NF have beenperformed Promising results were obtained in a significant part of them (Bodzek ampKonieczny 2011a 2011b Velizarov et al 2004)

The pollution of natural waters with nitrates (V) is a result of the application of ni-trogen fertilizers and the disposal of municipal and industrial solid and liquid wastesinto the environment (Bodzek amp Konieczny 2011a 2011b) Ion exchange RO EDand biological denitrification are the methods most often used to remove excessiveamounts of nitrates (Bodzek amp Konieczny 2011a 2011b Kołtuniewicz amp Drioli2008) Nitrates can have several adverse effects on human health the most notableare methemoglobinemia gastric cancer and non-Hodgkinrsquos lymphoma (Raczuk2010) The RO process allows the amount of NO

3 in drinking water to be decreasedto the level established in regulations (10 mg NL) Reverse osmosis membranes arecharacterized by high values for the retention coefficient of inorganic salts Thusthe required decrease in NO

3 concentrations in drinking water can be achieved bymixing permeate and raw water (Bodzek amp Konieczny 2011a Kołtuniewicz amp Drioli2008) Nitrates as monovalent ions are not totally retained by NF for example theretention coefficient of NO

3 for an NF-70 membrane (DowFilmTec) is equal to76 which is lower than for an RO membrane (Van der Bruggen amp Vandecasteele2003) Nanofiltration can be also used as a first step in the NO

3 removal process incombination with RO or ion exchange (Bodzek amp Konieczny 2011a Kołtuniewiczamp Drioli 2008) However the presence of sulfates decreases the retention coefficientof NO

3 ions during NF Under such conditions NF membranes practically do noteliminate NO

3 nevertheless they retain multivalent ions (Ca and Mg) which has apositive effect on RO and ion-exchange performance Relative purification costs ofboth processes are comparable with the costs of ion exchange and ED including thecosts of disposing the concentrate

Reverse osmosis and NF membranes used to remove nitrates from water are twiceas expensive as membranes applied in low-pressure membrane processes Moreovertheir application is much more energy-consuming because they require a much higherpressure Hence alternative methods consisting of UF membranes and surfactants orpolymers complexing nitrate ions are applied (Kołtuniewicz amp Drioli 2008) Com-plexes or micelles containing nitrate ions can be retained by UF membranes Forthe application of UF membranes at a surfactant concentration below the critical

Membrane technologies for the removal of micropollutants in water treatment 467

concentration of micelle formation the rate of removal of nitrate ions exceeds 79depending on the type and dose of surfactant used (Kołtuniewicz amp Drioli 2008)

Contamination of drinking water with bromates (V) ethBrO3 THORN is usually associated

with the formation of disinfection by-products (DBP) during ozonation of waters con-taining bromides (Bre) The concentration of BrO

3 in natural waters varies between 15and 200 mgL whereas the larger content appears in the groundwater Removal ofBrO3

in the NF process reaches up to 75100 with an initial content of 285 mgLwhereas for the RO process an average retention coefficient of 97 is obtained (ButlerGodley Lytton amp Cartmell 2005) Prados-Ramirez Ciba and Bourbigot (1995)observed 77 removal of BrO

3 and 63 of Bre using NF membranes to treat riverwater at the initial concentration of BrO

3 amounting to 300 mgL They found thatthe NF was more economical in terms of cost mainly as a result of the lower pressureapplied Disadvantages of these techniques include the deep deionization of permeatewhich requires remineralization and the formation of a waste stream ie retentate(concentrate) which needs to be treated before discharge into the environment

Because of widespread use high mobility in natural waters and a low tendency todegrade chlorates (VII) constitute a serious environmental problem mainly because oftheir toxicity and negative impact on the development and function of the human or-ganism Studies have shown that RO and NF can be applied to remove ClO

4 fromaqueous solutions (Bodzek amp Konieczny 2011b Lee et al 2008) For NF ClO

4retention amounts are up to 75e90 whereas for RO it is 96 at an initial concen-tration of 100 mg ClO4L (Bodzek amp Konieczny 2011a 2011b) High-pressure ROmembranes allow even 999 of ClO

4 ions to be removed for low-pressure ROmem-branes the retention coefficient of ClO

4 is lower (95) (Anonymous 2008) Hencein some cases additional treatment of permeate before its introduction into the waternetwork may be required eg by means of ion exchange or adsorption on activatedcarbon or in bioreactors (Anonymous 2008) In principle RO can be used as a stand-alone technology to remove chlorates (VII) during the production of drinking wateronly at low ClO

4 concentrations Because RO and NF are not destructive processesretentate contains chlorate (VII) and other pollutants that must be removed beforedischarge into the environment In general biological treatment and evaporation aretaken into consideration (Anonymous 2008)

The appearance of fluorides (F) in natural waters is a result of their presence in thelithosphere and anthropogenic industrial activity According to the WHO themaximum fluoride concentration in drinking water is established at 15 mgL(Kołtuniewicz amp Drioli 2008 Velizarov et al 2004) Adsorption coagulation withsedimentation ion exchange and membrane processes ie RO NF and ED arethe main methods proposed to remove fluorides from water (Bodzek amp Konieczny2011a 2011b) The application of RO to fluoride removal is connected with the partialdemineralization of water which is the main disadvantage of the process(Kołtuniewicz amp Drioli 2008) Reverse osmosis membranes for water desalinationallow the removal of 9899 of salts which results in the almost total retention offluorides eg below 003 mgL compared with the initial content range of13e18 mgL (Sehn 2008) During the treatment of water characterized by a highfluoride content the application of NF is beneficial because the remineralization of

468 Advances in Membrane Technologies for Water Treatment

permeate is not always required The final concentration of F ions in permeate ob-tained for commercially available NF membranes ie NF-90 and NF-270 (FilmTec)and TR-60 (Toray) was in the range of 005e40 mgL depending on the initial con-centration and membrane type (Tahaikt et al 2008) Results obtained during similarstudies confirmed the possibility of producing drinking water from brackish water witha high fluorides content using other commercial NF membranes ie NTR-7250NTR-7450 F-70 (FilmTec) Desal-5-DL and Desal 51-HL (Osmonics) MT-08(PCI) and SR-1 (Koch) (Hu amp Dickson 2006) Analysis of the retention of monova-lent ions for NF membranes indicates that smaller ions (fluorides) are retained moreefficiently than other halogen ions (eg chlorides) The difference in selectivity resultsfrom differences in the hydration energy of particular ions because higher energycauses better retention (a hydration energy of F equals 515 kJmol whereas for Cl

it is 381 kJmol) (Hu amp Dickson 2006) This explains the possibility of selective desa-lination of brackish water containing F using NF and allows drinking water to be pro-duced less expensively than when RO is applied

Besides RO and NF a membrane coagulation reactor (MCR) ie a combination ofcoagulation and MF can be used to remove fluorides during drinking water production(Zhang Gao Zhang amp Gu 2005) In the MCR aluminum salt is used as the coagulantand its hydroxide is the adsorbent Sodium hydroxide can be added to provide hydrox-ide ions and adjust the pH during coagulation and adsorption Hydrolysis (Eqn (151))coprecipitation (Eqn (152)) and adsorption (Eqn (153)) may occur when A12(SO4)3and NaOH are simultaneously added into raw water The primary fluoride removalmechanism results in the low solubility constant of Al(OH)3 (solubility product19 1033) and hard dissolution of the aluminumefluoride complex Thus theyare precipitated out of the solution or can be separated by the MF membrane

Al3thorn thorn 3OHAlethOHTHORN3Y (151)

Al3thorn thorn 3 x

OH thorn xFAlethOHTHORN3xFxY (152)

AlethOHTHORN3 thorn xFAlethOHTHORN3xFxYthorn xOH (153)

Boron appears in the environment mainly in the form of boric acid (H3BO3) and itssalts (Bick amp Oron 2005 Kołtuniewicz amp Drioli 2008) At a lower pH the hydrationof boric acid does not occur which causes its low retention during membrane separa-tion The dissociated form of the contaminant is totally hydrated and is characterizedby a greater diameter and negative ion charge resulting in higher retention (Bick ampOron 2005) In the European Union the permissible concentration of boron in drink-ing water is 10 mgL whereas for industrial wastewater disposed to sewage it is10 mgL (Bick amp Oron 2005) Boron is removed from the environment mainly bymeans of coagulation and electrocoagulation adsorption and ion exchange as wellas membrane processes ie RO NF ED and polymer-enhanced UF (PEUF) (Bickamp Oron 2005 Bodzek amp Konieczny 2011a 2011b Bodzek et al 2011) Howeveronly two of those methods are used in the industry ie RO at high pH conditions andion exchange (Bick amp Oron 2005)

Membrane technologies for the removal of micropollutants in water treatment 469

The removal of boron compounds from natural waters by means of RO is especiallyimportant because any of the conventional desalination methods (distillation or ED)are capable of reducing boron content to a permissible level The retention of boronat low or neutral pH varies from 40 to 60 which is insufficient to obtain a permis-sible level for drinking water but also for seawater desalination or water disposed intothe environment On the other hand high pH process conditions lead to fouling andscaling which are mainly caused by the precipitation of calcium and magnesium com-pounds Thus RO permeate is alkalized to pH c 95 and once more treated by RO orion exchange (Figure 151) (Bick amp Oron 2005 Bodzek amp Konieczny 2011a 2011bKołtuniewicz amp Drioli 2008) The cost of boron removal via the two-step process ishigh usually multistep (34 steps) RO processes are applied (Kołtuniewicz amp Drioli2008) Hence second- and third-stage RO membranes are operated at lower concen-trations and pressure Currently studies are focusing on developing and testing novelRO membranes that can be applied in a one-step process

UF and MF can also be used to remove boron from water An interesting solution isthe hybrid process of sorption-membrane separation used in boron removal fromseawater or the permeate after seawater desalination with RO Boron is removed byion-exchange resins (eg Dowex XUS 43594 Dow Chemicals Diaion CRB01Mitsubishi) of very small grain size (20 mm) and after the sorption the resin is sepa-rated by means of MF The small size of grains of resin causes the boron content todecrease after 2 min from 2 mgL to 02430124 mgL depending on the dose ofion exchanger (025e10 gL) (Dilek Ozbelge Bicak amp Yilmaz 2002) Other studieshave focused on removing boron from water solutions using PEUF usually withpoly(vinyl alcohol) (PVA) or other specially synthesized polymers (Dilek et al2002) The process consists of two stages the complexation of boron with a polymerand the separation of complexes by a capillary UF membrane (Dilek et al 2002)However a decrease in the boron retention coefficient is observed during the process(starting from values close to 1) as the number of active centers of the chelating poly-mer decreases The retention also depends on pH and boron and polymer concentra-tions in the feed

Inorganic arsenic occurs in water in anionic forms as As(III) and As(V) and alower-oxidation stage dominates in groundwater and a higher one in surface watersAt a pH close to neutral As(III) occurs in the form of inert molecules H3AsO3 andAs(V) as H2AsO

4 HAsO24 and AsO3

4 The form of As(V) ions has a direct impact

Raw water1st stage RO 2nd stage RO

2nd stagepermeate

Brine

Ionexchange

Cleanwater

NaOH

Figure 151 Two-stage RO system for boron removal (Bodzek amp Konieczny 2011a 2011b)RO reverse osmosis

470 Advances in Membrane Technologies for Water Treatment

on the choice and effectiveness of the treatment method To decrease arsenic content indrinking water RO and NF membranes as well as a hybrid process of coagula-tioneMFUF are applied (Bodzek amp Konieczny 2011a 2011b Shih 2005) Reverseosmosis membranes eg TFC-ULP (Koch) allow 99 of arsenic to be removed fromgroundwater (a decrease from 60 to 09 mgL) whereas DK2540F membranes (Desal)retain 8896 of the pollutant (Shih 2005) The amount of As(III) removed is alwayslower than for As(V) and oxidizing conditions during the process are recommended(Pawlak Zak amp Zabłocki 2006) The pH and the content of dissolved organic matterhave a great influence on arsenic removal The rate of As(V) removal at pH 3 reaches80 whereas it can be up to 95 at pH 5e10 (NTR-729HF membrane) A higherremoval of arsenic(V) (90) is observed for waters with a lower organic matter con-tent whereas compared with a higher concentration of organics it is equal to 80(Pawlak et al 2006) Other laboratory and pilot research on arsenic removal usingRO membranes has been performed (Bodzek amp Konieczny 2011a 2011b) NF mem-branes can be also applied for As removal For NF-70 FilmTec membrane 97removal of As(V) is obtained and for NF-45 membrane it varies from 45 to 90depending on the initial concentration of the pollutant in water (Nguyen BangCho amp Kim 2009) In the case of As(III) as for RO retention coefficients aremuch lower and decrease from 20 to 10 with an increase in the pollutant concen-tration in water The rate of removal of As(V) with the use of NF-45 membrane signif-icantly increases with an increase in pH (Shih 2005) according to the difference in Asion hydration An influence of pH in the range of 4e8 on the retention coefficient ofAs(III) was not observed which indicates that the mechanism of arsenic removal usingNF membranes is based on both sieving separation and electrostatic repulsion betweenions and the charged membrane surface Microfiltration and UF can be also used toremove arsenic from water but mainly by means of integrated systems with coagula-tion (Han Runnells Zimbron amp Wickramasinghe 2002 Shih 2005) For examplefrom water with an As content equal to 40 mgL water containing less than 2 mgLAs can be obtained using ferric coagulants and membranes with a pore size of 022and 122 mm (Shih 2005) In the integrated process As removal is caused by theadsorption of As on coagulation flocks and the separation of those flocks by the MFmembrane In such a case the removal of As(III) is also less effective than that ofAs(V) and preliminary oxidation of As(III) to As(V) is often required

15212 Ion-exchange membrane processes

Donnan dialysis is a process that uses an ion-exchange membrane without applying anexternal electric potential difference across the membrane (Velizarov et al 2004Wisniewski 2001) For anion removal anion-exchange membranes are used whereasfor cation removal cation-exchange membranes are employed (Figure 152) Mem-branes separate two solutions ie raw solution and stripping solution (concentrate)that differ in both composition and concentration The type of operation such as DDrequires the addition of a so-called driving counter-ion to the stripping solution (usu-ally an NaCl solution of 01e1 M concentration is used) which is transported in theopposite direction of the target anion or cation to maintain electroneutrality

Membrane technologies for the removal of micropollutants in water treatment 471

(Figure 152) (Bodzek amp Konieczny 2011b Wisniewski 2001) The ions which arepermeable to the membrane equilibrate between the two solutions until the Donnanequilibrium is obtained Because the concentration differences and their ratios deter-mine the Donnan equilibrium DD allows the charged micropollutants to be transportedagainst their concentration gradients which is important for drinking water suppliesbecause they usually contain only trace amounts of polluting ions As a result of itsproperties DD has received attention in the removal of inorganic ions from drinkingwater especially nitrates (V) and fluorides and some cations (Velizarov et al 2004)

Because the mechanism of ion transport in DD is governed solely by the Donnanequilibrium principle the ion fluxes achieved may be low for certain applicationsIn ED the transport of ions is accelerated owing to an externally applied electric po-tential difference which allows one to obtain higher anion fluxes than those in DD Inthis process anion-exchange and cation-exchange membranes are applied alternatelywhich allows solutions of varying concentration (diluate and concentrate) to be ob-tained (Bodzek amp Konieczny 2011b Velizarov et al 2004) The ED systems are usu-ally operated in the so-called ED reversal (EDR) mode to prevent membrane foulingand scaling Because most known toxic anions are monovalent the use of monovalentanion permselective exchange membranes is especially attractive (Velizarov et al2004) The suitability of ED depends strongly on the ionic composition of contami-nated water Thus the process appears to be less applicable to waters of very lowsalinity (conductivity less than 05 mS) for which DD can be a better solution In casesin which low-molecular-weight non-charged compounds besides ion removal is neces-sary pressure-driven membrane processes may be preferable Successful applicationsof ED and EDR include the removal of various anions eg nitrates (V) bromates (V)chlorates (VII) arsenic (V) boron and fluorides as well as various heavy metals(Velizarov et al 2004 Wisniewski 2001) The brine discharge or treatment remainsimportant for all of these separation processes

The use of a monovalent anion permselective membrane in the ED process provedsuccessful in a full-scale ED plant located in Austria which was designed to removenitrates (V) from groundwater (Velizarov et al 2004 Wisniewski 2001) The NO

3concentration in the raw water was 120 mg NO3L and the removal efficiency

Anion exchangemembrane

Cation exchangemembrane

Raw water(water+NaA)

Raw water(water+CaSO4)

Stripping solutioneg NaCl solution

Stripping solutioneg NaCl solution

AndashClndash

Andash

Na+ Na+

Na+

SO42ndash SO4

2ndash

Kn+

Kn+

Figure 152 Scheme of Donnan dialysis process (A target anion Knthorn target cation) (Bodzek ampKonieczny 2011b)

472 Advances in Membrane Technologies for Water Treatment

(66) was adjusted to obtain a product concentration of 40 mg NO3L at a desalinationrate of c 25

ED and EDR are also proposed to remove bromates from water (Bodzek ampKonieczny 2011a 2011b Wisniewski amp Kliber 2010) Studies on ED with anion-exchange membranes (Neosepta AMX) resulted in BrO

3 removal efficiencies of8687 and with the use of mono-anion-selective membranes (Neosepta ACS) upto 99 at a current density of 20 Am2 The removal rates of other anions werefrom 80 (HCO

3 ) to 93 (NO3 ) (Wisniewski amp Kliber 2010) This means that

the ED of water with an initial concentration of BrO3 of 100 mgL causes a decrease

in the final concentration to approximately 1 mgl which is significantly below thelimit value of drinking water (for BrO

3 10 mgL) The increase in power densityfor ED with standard anion-exchange membranes results in an increase in the aniontransport rate of 36

Investigations were also carried out on chlorate (VII) ion removal by ED and EDRand at high concentrations of silica (approximately 80 mgL) Regardless of the pres-ence of SiO2 and its concentration water recovery in the EDR installations was notaffected Pilot studies have shown that the removal of ClO

4 varied in the range of70e97 depending on the initial concentration of the anion and the number of stepsin the configuration of the EDR system (Anonymous 2008) During removal ofchlorate (VII) ions using the EDR method the retention coefficients of other anionswith similar valence (eg nitrate) are also important

ED can be applied to fluoride removal from water that contains a significant amountof this contaminant The removal rate of F is often higher than that obtained for ROand it increases with an increase in the electrical potential difference temperature andflow rate (Velizarov et al 2004 Wisniewski 2001) To minimize the precipitation ofsalts of bivalent ions (sulfates and carbonates) in the concentrate chambers prelimi-nary removal of bivalent ions is proposed using two-step ED with the application ofvarious ED membranes in each step or by chemical methods followed by conventionalED (Bodzek amp Konieczny 2011b) The content of fluorides generally decreases from30 to 063 mgL for the first configuration and to 081 mgL for the second one whichallows water of municipal quality to be obtained The first method is preferred becauseof its simplicity and the elimination of the need to add other chemicals

Similar to RO electrodialytic removal of boron from water and wastewater requiresa high pH because boric ions are transported through an anion-exchange membrane(Bick amp Oron 2005 Kabay et al 2008) The main advantage of ED comparedwith RO is the lesser sensitivity of ion-exchange membranes to pH and foulingHigh pH values also prevent the precipitation of Mg(OH)2 and CaCO3 Howevereven for such a high pH (910) chlorides are preferably transported and sulfatesare removed in an extent similar to boron (Bick amp Oron 2005 Kabay et al 2008)The low mobility of boric ions compared with others is the main disadvantage ofED because boron can be transported only after a significant decrease in other salt con-tents in diluate (Kabay et al 2008) To omit high demineralization of the diluate amonopolar membrane at alkali process conditions (pH 910) should be applied(Bick amp Oron 2005)

Membrane technologies for the removal of micropollutants in water treatment 473

Studies on arsenic removal fromwater by EDhave shown that it is possible to removeAswith an efficiency exceeding 80 for As(V) and 50 for As(III) (KartinenampMartin1995) with a water recovery of 85 In other studies with EDR a concentration ofarsenic in eluate was decreased to 0003 mgL (its initial level was 0021 mgl) whichcorresponded to a retention coefficient of 86 (Bodzek amp Konieczny 2011b)

15213 Membrane bioreactors

The main disadvantage of pressure-driven membrane processes and ED is the produc-tion of a concentrate highly loaded with anions Thus the use of MBRs to removemicropollutants from RO NF and ED concentrates as well as natural water and waste-waters is proposed The concentration of pollutants can be decreased to a value corre-sponding to drinking water quality (Bodzek amp Konieczny 2011a 2011b Crespo et al2004 Velizarov et al 2004 2008)

The biological degradation of oxyanions (NO3 ClO

4 and BrO

3 ) is based on their

reduction to harmless substances (N2 Cl and Br) at anaerobic conditions the pres-

ence of microorganisms (heterotrophic or autotrophic bacteria) and proper electrondonors (ethanol methanol and acetates for heterotrophic conditions and sulfur com-pounds and hydrogen for autotrophic ones) (Bodzek amp Konieczny 2011ab Crespoet al 2004 Velizarov et al2004) The kinetic of the reaction depends on the kind ofmicroorganism and the biodegradation process conditions (pH and anion concentra-tion) (Crespo et al 2004) The advantage of autotrophic degradation is the lower pro-duction of excess sludge however the process runs slowly (Kołtuniewicz amp Drioli2008) When heterotrophic process is applied the removal of dissolved organiccarbon (DOC) and biomass from treated water is required (Velizarov et al2004) Dis-advantages of conventional biological anion biodegradation can be eliminated byapplying an MBR which ensures the total retention of biomass The configurationof MBR processes can be arranged as a system with pressure-driven membrane mod-ules (MF and UF) (Figure 153) (Bodzek amp Konieczny 2011a 2011b) or as extractiveMBRs (membrane contactors) (Figure 154) (Bodzek amp Konieczny 2011a 2011bCrespo et al 2004)

In the case of an MBR with a pressure-driven membrane process an MF or UFmembrane may be placed inside or outside the bioreactor because the retention ofions and low-molecular-mass compounds (electron donors and some metabolicby-products) by porous membranes is generally insufficient therefore either processmodifications or water posttreatments are necessary The solution is an extractiveMBR (Figure 154) in which water with anions is supplied to the inside (lumenside) of hollow-fiber membranes and anions diffuse to the outside (shell side) Thereexisting microorganisms use anionic micropollutants as an electron donor for thereduction process (Bodzek amp Konieczny 2011a 2011b) Under these conditionsboth electron donor and biomass are separated from the water by a membrane

Biological degradation of oxyanions may also be used to remove nitrates (V) bro-mates (V) and chlorates (VII) Studies have shown their full reduction to nitrogenbromides and chlorides by the same bacterial cultures that are used for nitrate (V)reduction (Wang Lippincott amp Meng 2008)

474 Advances in Membrane Technologies for Water Treatment

A new membrane bioprocess for the removal and bioconversion of ionic micropol-lutants from water streams is the ion-exchange MBR (IEMB) (Crespo et al 2004Velizarov et al 2004) In this process the ionic micropollutant is transported fromthe water stream through a nonporous ion-exchange membrane into a biologicalcompartment There it is simultaneously converted into a harmless product by a suit-able microbial culture in the presence of an adequate carbon source and other requirednutrients The mechanism of anion pollutant transport through the membrane is thesame as in DD (Figure 155) (Bodzek amp Konieczny 2011a) The co-ions (cations)are excluded from the positively charged membrane and the target anion(s) transportis combined with its bioconversion In addition the bioconversion of the pollutant inthe IEMB keeps its concentration at low levels which guarantees an adequate drivingforce for transport

This concept was first demonstrated in the example of synthetic waters preparedfor the removal and bioconversion of nitrate to harmless nitrogen gas using a Neo-septa ACS mono-anion permselective membrane and ethanol as the carbon source(Velizarov et al 2004) Because of its very low diffusion coefficient (three ordersof magnitude lower than that in water) carbon source penetration into the treatedwater was avoided by employing this nonporous type of membrane and thedevelopment of an ethanol-consuming biofilm on the membrane surface contacting

Recirculation Water withoutnitrates

Water withoutnitrates

GasSludge to

waste

Sludge towaste

Electron donornutrient

Electron donornutrient

Bioreactor

Bioreactor

Water containingnitrates

Water containingnitrates

Reactionmixture Capillary

Water withoutnitrates

Biofilm

Figure 153 Membrane bioreactors with pressure-driven membrane module (Bodzek ampKonieczny 2011a 2011b)

Bioreactor Recirculation

Sludge towaste

Electron donornutrient

Water withoutnitrates

Water withnitrates

Biofilm

Capillary

Figure 154 Extractive membrane bioreactor (Bodzek amp Konieczny 2011a 2011b)

Membrane technologies for the removal of micropollutants in water treatment 475

the biocompartment Chloride ions were used as major counterions in IEMB for oxy-anion removal Within the concentration relevant to nitrate polluted water(50e350 mg NO

3 L) complete denitrification was achieved without the accumula-tion of NO

3 and NO2 ions in the biocompartment (Velizarov et al 2004)

1522 Heavy metals

Heavy metals are one of the most dangerous impurities present in natural waters andwastewaters Because natural waters are the main source of drinking water it ispossible that heavy metals will appear in them When the daily monthly or annualconsumption of water is considered the danger resulting from the presence of heavymetals in water is significant Metals such as lead mercury selenium iron nickelmanganese copper cobalt cadmium zinc and chromium are present in drinking wa-ter The permissible concentration for only part of them is established in each countryrsquosregulations regarding tapwater Except for iron manganese and aluminum in Polishregulations permissible concentrations of the following metals are specifiedantimony 0005 mgL arsenic 0010 mgL chromium 0050 mgL cadmium005 mgL nickel 0020 mgL copper 20 mgL lead 0025 mgL mercury0001 mgL selenium 0010 mgL and silver 0010 mgL (Bodzek amp Konieczny2011b) Conventional methods such as precipitation extraction and ion exchangehave many shortcomings especially with respect to the processing of large volumesof water containing a low concentration of metal ions Nowadays these contaminantsare most frequently precipitated as hydrated metal oxides hydroxides or sulfides withthe use of flocculation or coagulation A major problem pertaining to the precipitationprocess involves the formation of substantial quantities of sludge containing metals(Bodzek 1999) Often the concentration of metal ions in the filtrate after the finalfiltration process is still above the level of several milligrams per liter Membranetechniques such as RO NF UF and ED are more often applied to remove heavymetals from water solutions on an industrial scale (Bodzek 2012)

15221 Application of high-pressure membrane processes

Metal ions can be successfully removed from water solutions by means of RO or NFbecause the membranes applied in those processes are able to retain dissolved salts of

BiofilmAnion exchange

membrane

BioreactorCations

Electron donornutrients

Nontoxicproducts

Rawwater

Anionicmicropollutants

Clndash

Xndash

Xndash

Clndash

Purified water

Figure 155 Schematic diagram of ion transport mechanism in the ion-exchange membranebioreactor (Bodzek amp Konieczny 2011a)

476 Advances in Membrane Technologies for Water Treatment

molecular sizes as small as a few nanometers as shown in a number of studies(Bakalar Bugel amp Gajdosova 2009 Mehiguene Garba Taha Gondrexon ampDorange 1999 Qdais amp Moussa 2004)

The application of RO in the removal of heavy metals from solutions can be shownin the example of wastewater treatment in the electroplating industry The wastewaterconsists mainly of effluent from product-washing processes after electroplatingcoating in electroplating baths The concentration of metal ions in such wastewaterranges from 0025 to 1 mgL (Bodzek 1999) Frequently electroplating effluentscontain Cr Cu Cd Zn Ni Pb and Ag ions and because the metal-coating technol-ogies are based to a great extent on cyanide solutions the presence of toxic cyanideanion is also important The RO process allows the recovery of water at a very highpurity level which in many cases can be directly returned to the technological processwithout additional treatment The concentrated solution (retentate) may be reused tofill up the electroplating bath (Bodzek 1999) Figure 156 presents a typical diagramof the installation operating in a closed cycle applied to such a process (Bodzek 1999Bodzek amp Konieczny 2011b)

A series of investigations were conducted on the removal of heavy metals fromaqueous solutions using RO technology For example Bakalar et al (2009) presentedthe results of removing copper nickel and zinc using composite polyamide membraneTW30-1812-50 (Dow Filmtec) They determined the effect of the accompanying an-ions (co-ions) the concentration of cations and the transmembrane pressure on theseparation efficiency In turn Qdais and Moussa (2004) tested removing Cu2thorn andCd2thorn ions by means of RO and NF Results showed that the removal efficiency of in-dividual heavy metals by RO was high and amounted to 98 for copper and 99 forcadmium whereas for NF it was above 90 In the case of a solution containing bothmetals RO membranes reduced the concentration of ions from 500 to about 3 mgL(removal rate of 994) whereas the rejection efficiency of NF amounted to anaverage of 97 These studies showed that NF was also an appropriate technique toremove heavy metals from wastewater to a level acceptable according to

Chemicals

Metalproducts

Galvanic bathsConcentrate

Preliminary filtration

Reverse osmosis

Washing system

Water

Metalproducts

Deionized water

Figure 156 Diagram of electroplating process line integrated with reverse osmosis (Bodzek ampKonieczny 2011b)

Membrane technologies for the removal of micropollutants in water treatment 477

environmental regulations In addition as with RO it was possible to reuse permeatefor rinsing purposes and to recycle the retentate containing heavy metals Retention ofthe cations in the process strongly depends on the energy of hydration the type andvalence of co-ions passing through the NF membrane and the applied pressure andpH For example the retention of Cu2thorn and Cd2thorn ions is greater for the higher co-ion valence and higher cation hydration energy (Mehiguene et al 1999) The obtainedretention coefficients of copper and cadmium sulfates are close to 100 independentof pressure In the case of chlorides and nitrates the retention rates increase with pres-sure to specific values that depend on the nature of the co-ions Heavy metal retentionduring NF also strongly depends on the pH In a highly acidic environment a high con-centration of hydrogen ions in solution causes gradual neutralization of the negativeactive centers on the membrane surface so the impact of the membrane charge oncation and anion retention is significantly reduced Under such conditions nitrateand chloride ions easily pass through a membrane and to maintain the electrostaticbalance of the solution through the membrane protons also penetrate it Thereforecopper and cadmium ions are retained in retentate

15222 Ion-exchange membrane processes

Electrodialysis is particularly useful and often applied to treat rinsing effluents andother wastewaters from electroplating plants (Bodzek 1999) The diagram of installa-tion is similar to Figure 156 but instead of RO ED is applied The retentate which isa concentrated solution of metal ions is used to fill up the electroplating bath whereasthe dialysate is returned to the washing installation Hence practically the entire quan-tity of water and salts present in washing effluents can be used (Bodzek 1999)Recently the application of ED to recover metals for electroplating with such metalsas Au Pt Ni Ag Pd Cd Zn and SnPb from diluted electroplating wastewaters hasgained attention (Bodzek 1999) The solution of metal salt can be concentrated to alevel corresponding to the componentsrsquo content in the electroplating bath eg forNi from 1 to 60 gL (Bodzek 1999) which is much greater than with the applicationof RO The principal disadvantage of ED is the inability to simultaneously remove thenon-ionic substances (eg organic compounds) from the dilute stream which can bedone using RO

15223 Integrated low-pressure membrane processes

An interesting solution to removing heavy metals from aqueous solutions is the PEUF(Bodzek Korus amp Loska 1999 Korus 2012) It combines UF with metal complex-ation using water-soluble polymers The formed complexes are sufficiently large to beretained by a UF membrane Permeate is deprived of metal ions and retentate can un-dergo regeneration to recover both the metal and polymer

The process was applied to deactivate radioactive liquid waste containing metalions ie cesium cobalt strontium antimony and technetium isotopes themajor components of radioactive wastewater and to separate the lanthanides(140La 152Eu and 169Y) (Zakrzewska-Trznadel 2003) A significant reduction inpermeate radioactivity was observed

478 Advances in Membrane Technologies for Water Treatment

Mavrov Nikolov Islam and Nikolova (1992) carried out investigations into theremoval of Cu(II) Ni(II) and Co(II) ions from synthetic aqueous solutions with aninitial metal concentration of 104 molL using the hybrid PEUF method with polyac-rylonitrile membranes (UF-25-PAN) (cutoff of 25 kDa) Polyvinyl alcohol(50000 Da) and polyethyleneimine (PEI) (30000e40000 Da) were used as complex-ing agents The optimal concentration of PEI was two to six times higher comparedwith the stoichiometric concentration and retention rates of formed complexes whichranged within 85e99 The highest retention rate was obtained for PVA complexes(97e99) at a ratio of metal concentration to polymer concentration ranging from 14to 18 (Mavrov et al 1992)

Korus (2010 2012) conducted studies on the removal of heavy metals (Ni Cu andZn) from synthetic and galvanic wastewater by applying the hybrid complexationeUFprocess Poly(vinyl alcohol) (50000 Da) PEI (30000e40000 Da) polyacrylic acidand sodium polyacrylate as complexing agents were used in connection with polysul-fone and polyamide membranes The efficiency reached 85e97 for polyamide mem-brane depending on the polymer to the metal ratio pH and kind of metal A highremoval efficiency of zinc and nickel ions (97e99) was obtained for polysulfonemembrane The decomplexing process enabled metal to be recovered from the concen-trated solution to an extent suitable for its reuse

Sodium poly(styrene sulfonate) a water-soluble anionic polymer with strongcation-exchange groups was used as a complexing agent for lead ion complexing(Korus 2010) The high rate of metal removal (85e99) depended on the ratio ofmetals to polymer the pH of the solution and the operating UF conditions obtainedfor the polysulfone membrane It was possible to obtain the retentate with a concentra-tion of Pb 20 times higher than the concentration of the feed solution which contained50 mg PbL The main process parameters were a fivefold excess of polymer in rela-tion to metal as well as a pH of 6 and a pressure of 01 MPa The decomplexationeUFprocess involved breaking the polymeremetal bond and allowed it to recover 85of metal whereas diafiltration conducted with a sufficient volume of water enabledfive- to 15-fold reduction of the concentration of metal remaining in retentate sothe recovery and reuse of the polymer were possible

The use of membrane separation combined with the biological removal of metalsfrom a solution (MBRs) is of a great interest Wastewaters with a high load of metalsusually contain compounds that may be toxic for microorganisms or inhibit theirgrowth they often have a high salinity or pH Therefore it is often impossible to carryout conventional biological removal of metals from wastewater owing to the inactiva-tion of microorganisms The solution may be extractive MBRs with sulfate-reducingbacteria (EMBR-SRB) which eliminate these restrictions because of the physical sep-aration of biomass from effluents (Figure 157) (Bodzek amp Konieczny 2011b MackBurgess amp Duncan 2004) Membranes which are usually made of silicone polymersperform two functions they separate two water phases and enable H2S transport fromthe phase containing biomass to wastewater where the precipitation of metal sulfide(s)takes place Study of zinc removal from synthetic wastewater using EMBR-SRBMBRs showed that the reaction rate between H2S and Zn ions was high owing tothe large concentration gradient of H2S on both sides of the membrane When the

Membrane technologies for the removal of micropollutants in water treatment 479

pH of the biological mixture decreased the quantity of nondissociated H2S grewincreasing its concentration gradient More than 90 removal of Zn ions from solu-tions containing 250 mgL of this metal was obtained The transport rate of H2Salso depends on the membrane thickness On the side of wastewater a thin layer ofzinc sulfide formed on the membrane surface constituting significant resistance toH2S transport This problem can be solved by changing the hydrodynamic conditionsof the water stream or using pulse flow

1523 Removal of chromium

A separate discussion on chromium is associated with the fact that in the natural envi-ronment chromium most commonly occurs in the third oxidation state as cation (Crthorn3)and sixth Cr(VI) in the form of anions Chromium (VI) is a strong oxidant easilyreduced to Cr(III) (Jacukowicz-Sobala 2009) Chromium (III) which is naturally pre-sent in the environment is an essential nutrient whereas chromium (VI) is formed inindustrial processes and enters the environment as anthropogenic pollution Chromium(VI) and chromium (III) compounds are widely used in many industries because of thedurability of the metal and its aesthetic effects One can mention the galvanic industrythe production of dyes and pigments and textile and leather articles tanneries andwood maintenance That is why chromium compounds are increasingly found inwastewaters groundwater or soil Chromium (VI) compounds are soluble in waterand at pH 1e6 they appear as HCrO

4 and Cr2O27 ions whereas at pH gt 6 CrO2

4ions are formed The influence of chromium compounds on living organisms dependson the oxidation state of chromium the solubility and the method of entry into thebody Chromium (III) is trace element essential to the proper functioning of plants an-imals and humans (Bodzek amp Konieczny 2011b) whereas Cr(VI) is highly toxic toliving organisms so their permissible concentration in drinking water amounts to005 mgL including 3 mgL for Cr(VI) The traditional way to remove and recoverchromium salts from contaminated water and wastewater is to reduce Cr(VI) to Cr(III)and then precipitate Cr(III) hydroxide and in the final stages filter the suspension

Biofilm Wastewater

Membrane

Heavy metalsacids bases andsalts

Metal sulfidesdrain as asuspension

H2S

H2S

Figure 157 Scheme of bioreactor with sulfate-reducing bacteria EMBR SRB (Bodzek ampKonieczny 2011b)

480 Advances in Membrane Technologies for Water Treatment

(Owlad Aroua Daud amp Baroutian 2009) For Cr(III) the reduction stage is omittedFor chromium removal several other methods are also proposed such as adsorptionand biosorption ion exchange (used on an industrial scale) solvent extraction andelectrochemical methods (Owlad et al 2009) Membrane processes both high-pres-sure and low-pressure membrane processes enhanced with surfactants and polymersare very important to the recovery and disposal of chromium (Bodzek amp Konieczny2011b Kołtuniewicz amp Drioli 2008 Owlad et al 2009) Application has also beenfound for liquid membranes and processes based on ion-exchange membranesincluding ED EDI and membrane electrolysis (Bodzek 2012)

Reverse osmosis and NF permit the direct separation of chromium compoundsfrom the solutions and find practical application in this respect (Bodzek 2012Kołtuniewicz amp Drioli 2008 Owlad et al 2009) To remove Cr(III) and Cr(VI)both inorganic membranes and polymer membranes can be used Studies carried outon Cr(VI) removal from water involved RO using Osmonics membranes Sepa-Stype and membranes made of cellulose acetate (CA) (Bodzek et al 2011Kołtuniewicz amp Drioli 2008 Owlad et al 2009) It was found that the CAmembranesretained 96 of Cr(VI) ions whereas Osmonics membranes retained 8096depending on the membrane compactness (Bodzek amp Konieczny 2011a) Applicationof RO for the treatment of chromium tanning wastewater is limited by chloride andsulfate ion concentration High concentrations require the use of high transmembranepressure This causes removal of chromium to become economically justifiable only ifthe salt concentration does not exceed 5 gL and the chromium concentration 1 gLHowever to treat galvanic wastewater with a concentration of chromium amountingto 2 gL the RO process can be successfully applied (Bodzek 2012) In this casepermeate with a concentration of 00017 mg CrL suitable for reuse can beobtained as well as concentrated chromic acid anhydride (concentration of Cr 5 gL)(Jacukowicz-Sobala 2009)

It seems that NF is a better solution for the removal of chromium from water(tannery and galvanic wastewaters) The obtained filtrate is then without chromiumbut it contains a significant amount of salt that can be used to prepare etching bathsAs for the retentate a concentrated solution of chromium after further concentrationhydroxide is precipitated and then dehydrated sludge is dissolved in sulfuric acid Theresulting solution can be used directly in the process of tanning (Religa amp Gawronski2006) For NF the retention coefficient of Cr increases with an increase in pH but theeffect is more pronounced for membranes with lower separation capacity (eg from47 to 945 for Osmonics membranes) compared with more compact membranes(eg from 84 to 997 for Osmonics membranes) (Hafiane Lemordant amp Dhahbi2000) The dependence of the retention coefficient on the concentration of Cr in feedwas also observed for NF membranes (Hafiane et al 2000) but the range of the effectalso depended on the pH In an acidic solution at higher concentrations of Cr in feed ahigher retention was found whereas at pH 65e11 the nature of this relationship wasthe opposite ie lower retention was obtained for higher concentrations of Cr Thisphenomenon is important because Cr(VI) changes its ionic form with a change inpH In the highly acidic environment Cr(VI) occurs in the form of no dissociated chro-mic acid (H2CrO4) and when the pH is changed to 65 HCrO4

e ions are formed the

Membrane technologies for the removal of micropollutants in water treatment 481

concentration of which increases with an increase in the parameter A furtherincreasing in pH above 7 causes the formation of CrO2

4 ions the concentration ofwhich also depends on pH Cr2O2

7 ions are also present in the solution and their con-centration depends on the initial concentration of the contaminant in the feed and pHThis ion is usually dominant at high concentrations of Cr and in a strongly acidic envi-ronment (pH 17) but its concentration decreases with an increase in pH (Bodzek ampKonieczny 2011a 2011b Hafiane et al 2000)

Characteristics of membranes used in UF and MF processes do not allow chromiumions to be retained directly in the retentate That is why low-pressure membrane pro-cesses are used to remove Cr in an integrated process In this respect the followingpossibilities can be identified (Bodzek 2012 Kołtuniewicz amp Drioli 2008 Owladet al 2009)

bull Preliminary MFUF before further treatment with conventional or membrane processesbull Modification of UF membranes to reduce pore size or ion-exchange propertiesbull Polymer-enhanced UF or surfactantmicellar-enhanced UF (MEUF)

The first method was used in the initial stages of tanning and galvanic wastewatertreatment MicrofiltrationUF removes suspended solids fats and emulsions from theaqueous phase (without added chemicals) which makes it easier and improves the per-formance of subsequent purificationprocess separation (Religa amp Gawronski 2006)The main methods of introducing the charge on the surface and inside the pores of UFmembranes are sulfonation of polysulfone membranes and the introduction of aminoand carboxylic groups Modification of UF membranes extends their separation prop-erty by giving them ion-exchange properties (Bryjak 2001) Polymer-enhanced UF orMEUF allows separation of metal ions including chromium Polymer-enhanced UFhas been successfully applied to remove chromate (VI) from groundwater usingcomplexing agents such as 1-hexa-decylopiridine chloride sodium polyacrylatepoly(dimethyldiallylammonium) chloride chitosan and pectin (Bodzek amp Konieczny2011b) Polyethylenimine (PEI) is used for the concentration and recovery of chro-mium (III)

Electrochemical separation techniques are an alternative method of removing chro-mium from the water environment This toxic metal is present in various streams pro-duced by a number of industrial processes which also contain other substances(mainly metals) that should be separated from chromium Therefore electrochemicaltechnology is more flexible than other membrane techniques and is applied to recoverchromic acid (VI) from the bath coating metal parts (a large concentration of chro-mium) or as a method of disposal and recovery of chromium from wastewater derivedfrom washing these elements In most cases among others in the plating industry so-called three-compartment electro-electrodialysis (EED) is applied It is based on elec-trolysis reactions running on electrodes and the ED process (Bodzek amp Konieczny2011b Frenzel Holdik Stamatialis Pourcelly amp Wessling 2005) (Figure 158) Itcan simultaneously manage three different tasks removal of impurities chromicacid recovery and purification of rinse water The treated solution feeds the centerchamber of the device which is separated from the anolite chamber by the anion-exchange membrane and from the catolite chamber by the cation-exchange membrane

482 Advances in Membrane Technologies for Water Treatment

(Frenzel et al 2005) The anolite chamber is supplied with water whereas the catolitechamber is supplied with sulfuric acid Chromium (VI) ions migrate to the anolitewhere they form chromic acid (VI) with protons formed on the anode In turn metalcations permeate to catolite chamber where sulfuric acid neutralizes the hydroxideions formed on the cathode so in this part of the device soluble metal sulfates (VI)are formed

Both the ED and EDI processes can be applied to remove and separate metal ionsand their mixtures including chromium In ED the electrical resistance in dialysatechambers increases in time as the ions are removed from the diluted solution to theconcentrate chamber which causes higher energy consumption and decreases theefficiency of the process One solution to this problem is the EDI process in whichthe dilute solution chamber is filled with an ion-exchange resin (Bodzek amp Konieczny2011b) The applied voltage improves the migration of ions to the respectiveelectrodes and thus to concentrated stream and causes water dissociation into Hthorn

and OH ions which regenerate the ion-exchange resin Alvarado Ramirez andRodriacuteguez-Torres (2009) assessed the feasibility of EDI and ED continuous processesfor the removal of chromium (VI) from synthetic solutions at pH 5 The EDEDIinstallation consisted of electrodes and two acrylic separation plates between whichan anion-exchange membrane manufactured by Neosepta was placed (Figure 159)(Alvarado et al 2009 Bodzek amp Konieczny 2011b)

Two cation-exchange membranes by the same producer separated the electrodesfrom the separation plates In this way two chambers with diluate and concentratedsolution were formed Synthetic wastewater containing 100 mgL Cr(VI) was treatedDuring the EDI process a chamber with diluted solution was filled with a mixed

Collectingsolution

AEM

Chromicacid

Regeneratedsolution

(eg rinse water)

Metalsulfates

O2

Cr2O72ndash

Cr3+

Ni2+

Cu2+

Fe2+3+

CrO42ndash

SO42ndash

H2O

H2

H+

H+

+ ndash

CEM

H2SO4 dil

Figure 158 Principles of three-compartment electro-electrodialysis for chromic (Bodzek ampKonieczny 2011b) acid recovery AEM anion-exchange membrane CEM cation-exchangemembrane

Membrane technologies for the removal of micropollutants in water treatment 483

ion-exchange resin In the ED process the removal of Cr amounted to 98 during625 h at an energy consumption of approximately 12 kWhm3 and at a maximumlimited current (Ilim) of 85 In the EDI process with the use of a mixed bed at thesame Ilim 998 removal of Cr(VI) was reached within 13 h (energy consump-tion frac14 0167 kWhm3)

153 Removal of microorganisms and NOM

1531 Removal of dispersed substances and microorganismsby low-pressure membrane processes

The turbidity of water is caused by the presence of suspended mineral and organic mol-ecules of different sizes (colloids and coarse and fine suspensions) Usually MF or UFis applied to decrease water turbidity to the level below 1 nephelometric turbidity unit(NTU) ie the value that corresponds to regulations for drinking water Only severalstudies discussed in the literature focused on turbidity removal by means of membraneprocesses although it is proven that the use of those techniques enables the productionof water with a turbidity below 1 NTU from water with an initial turbidity of 100 NTUand greater (Taylor amp Wiesner 2000) It is accepted that UF and MF can also be usedfor water clarification (Bodzek amp Konieczny 2005) The study of application of a UFAquasource membrane (France) revealed that from waters of different turbidityranging from 01 to 115e248 NTU drinking water of a turbidity of 003e004NTU could be obtained (Taylor amp Wiesner 2000) The publication (Anonymous2005) summarizes the results of a series of studies carried out on membrane filtrationin 1989e2001 which showed that the use of MF and UF allowed for maximumremoval of turbidity regardless of raw water turbidity the kind of membrane and

A

V

V

Concentrate

CEM

H+

H+ OHndash

HCrO4O2

O2

K+

CEM

Diluate

ndash+

AEM

Figure 159 Diagram of apparatus for electrodialysiselectrodeionization processes AEManion-exchange membrane CEM cation-exchange membrane (Bodzek amp Konieczny 2011b)

484 Advances in Membrane Technologies for Water Treatment

its producer as well as the application of precoagulation The average value of thefiltrate turbidity was 0097 NTU at a standard deviation of 006 for 72 measurementsSimilar results were obtained for various membrane modules during studies in theUnited States France and other countries (Taylor amp Wiesner 2000) Sometimeswhen turbidity is caused by colloidal fraction membrane filtration is preceded bycoagulation to obtain flocks of a greater size (Bodzek amp Konieczny 2005) Reverseosmosis and NF also can eliminate these types of impurities and organic admixturesbut those processes are not applied because of the fouling phenomenon Table 151summarizes the percent removal of turbidity and NOM by various membrane tech-niques (Bodzek 2013)

Water and wastewater that contain microorganisms ie viruses bacteria and pro-tozoa (fungi algae snails worms and Crustacea) may have many negative health ef-fects (Anonymous 2005 Taylor amp Wiesner 2000) Polish regulations regarding thequality of drinking water establish the maximum permissible content of Escherichiacoli and Enterococcus and as additional requirements the amount of Coli bacteriagroup the total number of microorganisms and the amount of Clostridium perfringens(Bodzek amp Konieczny 2005) Water contamination can occur at its source at the siteof its intake or treatment and directly in the water supply system Various methods canbe applied to water disinfection each of which has some advantages and disadvan-tages Sand filters remove 99e999 of bacteriophages whereas commercial watertreatment devices based on ultraviolet (UV) and ozonation do not guarantee theremoval of all pathogenic microorganisms Chlorination causes the formation of tri-halomethanes (THMs) and is ineffective in the case of microorganisms associatedwith suspension Some microorganisms (eg Cryptosporidium) are resistant to its ac-tion (Taylor amp Wiesner 2000)

Membrane filtration (MF and UF) may significantly improve the disinfection pro-cess because it almost completely eliminates viruses bacteria and protozoa The sizeof viruses varies from 20 to 80 nm whereas the pore size of UF membranes is less than10 nm Thus at least theoretically the elimination of microorganisms is possible On theother hand bacteria (05e10 mm) cysts and oocytes (3e15 mm) are larger and thusthey can be totally eliminated during MF (Bodzek amp Konieczny 2005 Taylor ampWiesner 2000) A comparison of the pore sizes of UF and MF membranes with thesize of microorganisms indicates that the UF process can be successfully used for water

Table 151 Turbidity and NOM removal using membrane techniques

Process Pressure kPaTurbidityremoval

NOMremoval

Waterwastage

Microfiltration lt100 gt97 lt2 5e10

Ultrafiltration lt100 gt99 lt10 10e15

Nanofiltration lt500 gt99 gt90 15e30

Note NOM natural organic matter

Membrane technologies for the removal of micropollutants in water treatment 485

disinfection (Bodzek amp Konieczny 2005) Figure 1510 shows the rates of removal ofviruses bacteria and protozoa for different UF membranes (Bodzek amp Konieczny2010 Taylor amp Wiesner 2000) The obtained retention for all types ofmicroorganisms was greater than 4 log ie 9999

However it has been shown in practice that UF membranes are not always able toeliminate bacteria and viruses completely from water This is mainly connected to im-perfections in membranes and membrane modules and the secondary growth of bac-teria in water after its passage through a membrane In commercial membranes adiscontinuous skin layer through which microorganism can pass takes place In addi-tion the design of the modules often requires the raw stream to be sealed off from thepermeate stream which is not always appropriate The most efficient disinfection isobtained using capillary modules in which isolation of raw water from permeate iseasier than in the spiral-wound and hollow-fiber modules (Bodzek amp Konieczny2005) Furthermore cells of microorganisms could penetrate membrane pores with di-ameters much smaller than the dimensions of the cells themselves owing to pressuredeformation with the filtration of intracellular fluid but tonus of the cellular membraneremains unchanged (Figure 1511) (Bodzek 2013 Bodzek amp Konieczny 2010

8

6

4

2

0Viruses

Red

uctio

n (lo

g)

Bacteria GiardiaWater I

63

7271

74

47

51

Water II

Level of disinfection expressedas reduction in logarithmic scale1 log = 90 of inactivation2 log = 99 of inactivation3 log = 999 of inactivation4 log = 9999 of inactivation

Figure 1510 Removal of microorganisms using UF (Bodzek amp Konieczny 2010) UFultrafiltration

Figure 1511 Deformation of Cryptosporidium parvum in the microfiltration process (Bodzek2013 Bodzek amp Konieczny 2010)

486 Advances in Membrane Technologies for Water Treatment

Sosnowski Suchecka amp Piątkiewicz 2004) In addition it was demonstrated that theshape of microorganisms could be a key factor determining the efficiency of bacteriaremoval via a membrane For example bacteria or viruses of a slim elongated shapewere removed to a greater extent than ones of more compact shape (Bodzek 2013)

1532 Natural organic matter

NOM present in aqueous ecosystems is the mixture of many compounds characterizedby various chemical structure and properties Fulvic acids soluble in water(MW 2000 Da) more hydrophobic humic acids (MW 2000e5000 Da) andinsoluble humic fraction (humins) of bituminous character are part of NOM (Bodzek2013 Domany Galambos Vatai amp Bekassy-Molnar 2002) Humic substances usu-ally appear in water as dissolved compounds colloids and non-dissolved admixturesusually the appearance of a given form strongly depends on the water pH The dis-solved NOM fraction in natural water is equal to c 80e90 of the total NOM contentHumic substances cause intensive coloration of water from brown to black In addi-tion complexation reactions of humic substances with heavy metals or adsorptionof toxic organic substances creates many health hazards Humic substances are alsodisinfection by-product (DBP) precursors (Domany et al 2002) These are the mainreasons for the need to remove NOM from water

The elimination of NOM is one of the most important processes in water treatmenttechnology The main advantage of applying membrane techniques in water treatmentis to remove DBP precursors including part of NOM (Taylor amp Wiesner 2000 Wilf2010) As one of the most popular disinfection methods chlorination results in the for-mation of adsorbable organic halides (AOX) including THMs halogenated aceticacids halogenated aldehydes and ketones halogenated acetonitriles amines and otherDBPs (Bodzek 2013 Bodzek amp Konieczny 2005) The introduction of pressure-driven membrane processes to water treatment allows the formation of DBP to becontrolled as semipermeable membranes retain NOM including DBP precursors(Van der Bruggen amp Vandecasteele 2003) The removal of NOM also decreasesthe amount of chlorine required for disinfection which results in a reduction of the bio-logical activity of water in the distribution system (Bodzek 2013 Bodzek ampKonieczny 2005) According to a very wide molecular size distribution of NOM(from c 1 nm to c 045 mm) the effectiveness of its removal depends on propertiesof the applied membranes (Bodzek 2013) Table 152 compares the effectiveness ofNF UF and MF processes in NOM content control in natural waters (Bodzek2013 Bodzek amp Konieczny 2010)

15321 Application of RO and NF

By introducing NF or RO systems to water treatment one can directly control forma-tion of the DBP because semipermeable membranes retain NOM including the precur-sors of DBP Nanofiltration membranes are particularly important for removing NOMand DBP precursors because they are an effective barrier against organic compounds iftheir molecular weight (particle diameter) is greater than the cutoff of the membrane

Membrane technologies for the removal of micropollutants in water treatment 487

Nanofiltration membranes are able to retain 90 of DBP precursors from naturalwaters because they have a cutoff of 200e500 Da (eg Filmtec NF-50 and NF-70)(Bodzek 2013 Taylor amp Wiesner 2000 Thorsen 1999 Van der Bruggen ampVandecasteele 2003) The obtained permeate is high-quality drinking water with alow amount of DBP and a small risk of secondary bacteria growth after chlorinationwhich precedes water distribution to the network The results of removing DBP pre-cursors are given in Table 153 (Bodzek 2013 Bodzek amp Konieczny 2010 TaylorampWiesner 2000) High removal rates of DBP precursors are obtained for both surfaceand groundwater However because of greater fouling mainly caused by the high con-tent of colloids and suspensions surface waters are more difficult to clean using mem-brane methods As a consequence to keep appropriate membrane flux more advancedpretreatment or a combination of NF and low-pressure membrane techniques isrequired

Long-term research on DBP precursor content in Flagler Beach Florida (ground-water) and Punta Gorda Florida (surface water) treatment stations compared theeffectiveness of groundwater and surface water purification using RO and NF (Tayloramp Wiesner 2000) Although satisfactory levels of THM precursor removal wereachieved permeate flux was low for surface water and the system required adequateregeneration A pilot study of water treatment from Florida River using NF showeda 95 reduction in THM precursor content (Siddiqui Amy Ryan amp Odem 2000)In addition RO membranes (cutoff of 100 Da) were significantly more effective inremoving THM precursors (98) than NF ones with a cutoff of 400 Da (96)(Siddiqui et al 2000)

Table 152 Comparative assessment of MF UF and NF processes forNOM removal

Parameters MF UF NF

NOM removal lt10 0 30 gt80

Removal ofsuspensions andcolloids

20 40 70 90 gt95

DBP removal No 50 THM 32HAA

gt80

Requirements forcleaning

Required back-washing

Cyclical cleaningrequired

Cyclical cleaningrequired

Performanceproblems

Moderate fouling Fouling Fouling clogging

Pretreatment In-line coagulationor other process

In-line coagulationor other process

No

Note MF microfiltration UF Ultrafiltration NF nanofiltration NOM natural organic matter HAA haloacetic acidsTHM trihalomethane DBP disinfection by-product

488 Advances in Membrane Technologies for Water Treatment

Amy Alleman and Cluff (1990) conducted laboratory- pilot- and full-scalestudies of the NF treatment of water from the Colorado River A relatively low reduc-tion in the content of THM precursors (65e70) was associated with their small mo-lecular weight (a significant amount of compounds of a molecular weight lt 500 Da)Tan and Amy (1991) compared ozonation and NF used in color and DBP precursorremoval and found that membranes were much more effective Laine Clark andMallevialle (1990) and Jacangelo Aieta Carns Cummings amp Mallevialle (1989) pro-posed the use of UFMF as water pretreatment before NF and observed that MF mem-branes with a high cutoff (eg 100000 Da) were effective only in removing fineparticles of suspended solids in the range of 005e2 mm whereas UF membraneswith a lower cutoff (eg 10000e50000 Da) caused the retention of a certain groupof DBP precursors

15322 Microfiltration and UF

Aside from for NF and RO processes low pressure-driven membrane filtration is alsowidely used in water treatment (Thorsen 1999) Ultrafiltration and MF membraneseffectively remove colloids and ionic and non-ionic organic compounds of sizesthat correspond to the nominal molecular weight cutoff of UF or MF membranesThus single-step UFMF can be directly used to remove greater fractions of NOMfrom water including part of high-molecular-weight DBP precursors whereasmedium- and low-molecular-weight compounds can be eliminated in integratedsystems (Bodzek 2013 Thorsen 1999) To eliminate humic substances from waterdirect UF with modules equipped with dense membranes (eg c 1000 Da) or hybrid

Table 153 Natural organic matter (NOM) removal by nanofiltration(NF) (NF-50 and NF-70 membranes from Filmtec)

Water type Pretreatment

Raw water Purified water

Removal NOM content mgL

Ground Antiscalant 961 28e32 97

Preliminaryfiltration

961 31e39 96e97

Surface Preliminaryfiltration

157e182 55e84 49e70

Ground Preliminaryfiltration

259 39 85

Ground Preliminaryfiltration

120 6 95

Surface Preliminaryfiltration

40e460 NA 30e90

Note NA data not available

Membrane technologies for the removal of micropollutants in water treatment 489

systems of UF or MF with coagulation activated carbon adsorption or oxidation(ozonation or photocatalysis) can be applied (Bodzek 2013)

For the application of powdered activated carbon (PAC) the removal rate dependson the concentration of DOC the concentration of an adsorbate on the surface of anadsorbent and adsorbent dose pH temperature and contact time For direct UFMFremoval of DOC precursors of AOX including precursors of THM and haloaceticacids (HAA) do not exceed 20 On the other hand retention obtained for combina-tion with activated carbon increases to values between 7 and 82 for DOC20e85 for AOX precursors including 0e97 for THM precursors and 26e81for HAA precursors (Bodzek 2013 Bodzek amp Konieczny 2010) (Table 154) Hybridsystems are effective in view of the extended contact time and a greater concentrationof adsorbent in a membrane system

Results on the efficiency of hybrid systems using coagulation and MFUF(aluminum and iron (III) coagulants) indicate the removal rates between 12 and83 for DOC 30 and 88 for THM precursors 39 and 92 for HAA precursorsand 20 and 85 for precursors of AOX (Anonymous 2005) Retention rates are afunction of the dose and type of coagulant pH temperature and time and speed formixing the reaction mixture Organic pollutants are adsorbed onto coagulation flocksand these in turn are retained by the MFUF membrane In the coagula-tionesedimentationeUFMF (ceramic membrane and capillary) integrated processremoval of organic compounds was approximately 90 (DOC and UV254) in the firststage of the purification process whereas in the second it increased almost to 100(Bodzek amp Konieczny 2005) In coagulationemembrane filtration the removal oforganic compounds increases among other things because of the increased retentiontime of flocks in the reaction system (Anonymous 2005) Membrane flux observed inan integrated system also increased with reference to single-step UF This was accord-ing to the removal of organic compounds and thus the intensity of NOM foulingreduction but it depended on the coagulation mode used in the integrated system(Bodzek amp Konieczny 2005 Konieczny Bodzek amp Rajca 2006) Processes conduct-ed with coagulation and sedimentation exhibit relative permeability values close tounity but in the case of in-line hybrid processes relative permeability amounts to

Table 154 Characterization of NOM removal processes using UFMF

Process Direct UFMF UFMF-PAC process

Diameter of membrane pores nm 1e5 10e100

Transmembrane pressure MPa 02e08 01e04

Permeate flux Lm2 h 15e25 50e200

Removal of NOM Partial (10e20) 60e80

Removal of particles bacteria andviruses

Yes Yes

Note UF Ultrafiltration MF microfiltration NOM natural organic matter PAC powdered activated carbon

490 Advances in Membrane Technologies for Water Treatment

083e089 for ceramic membranes and 074e078 for capillary ones (Bodzek ampKonieczny 2005 Konieczny et al 2006) This is caused by a reduction in the foulingsubstance penetration of the membrane pores and the creation of a filter cake charac-terized by much greater porosity and smaller hydraulic resistance compared with oneformed during direct UFMF Such a process increases the lifetime of membranes andreduces the frequency of back-washing and chemical cleaning

Recently an ion-exchangeeUFMF integrated process was proposed for NOMremoval especially with the use of magnetic ion-exchange (MIEX) resin(Kabsch-Korbutowicz Biłyk and Mołczan 2006 Rajca 2012) The effectiveness ofNOM removal from water with the ion-exchange process is 30e90 (Kabsch-Korbutowicz et al 2006) and depends on the properties of water and the mode ofprocess conduction Application of MIEX resins before UFMF allows the filtrationcycle to be extended and water with better parameters than in the case of directmembrane filtration to be obtained However fine resin particles present in the watercould cause the membrane surface to be blocked Therefore an integrated processie the use of ion exchange as water pretreatment before MFUF is a more usefulsolution (Kabsch-Korbutowicz et al 2006) Interesting comparative studies conductedby Kabsch-Korbutowicz et al (2006) showed the superiority of an ion-exchangeeUFover a coagulationeUF system

The problem with the membrane filtration of surface water and groundwater is adrop in permeate flux caused by membrane fouling especially in the case of MFUF membranes (Laine Campos Baudin amp Janex 2002) It is known that NOMand in particular its hydrophobic fraction is the primary substance that causes fouling(Bodzek 2013) A symptom of this phenomenon is the formation of a brown gel on themembrane surface which can cause a decrease in flux by up to 75 over 2000 h ofoperation (Bodzek 2013) To determine the role of natural organic substances andtheir properties in membrane fouling many studies have been carried out (BodzekPłatkowska Rajca amp Komosinski 2008) However their results are often contradic-tory possibly because of the number of factors affecting this phenomenon Foulingdepends on the characteristics of both filtered water and the membrane used Adsorp-tive properties connected with membrane hydrophobicity pore sizes cutoff surfacecharge performance or surface roughness have a significant impact on fouling Inthe case of water properties the ionic strength of the solution is important in partic-ular the content of calcium cations which affects the solubility of organic substancesand influences the distribution of NOM molecular weight type of organic matter andpH of the water

154 Organic micropollutant removal

The following organic micropollutants can be found in water and wastewater (Bodzek2013)

1 DBPs2 EACs and endocrine-disrupting compounds (EDCs)3 PhACs

Membrane technologies for the removal of micropollutants in water treatment 491

Both secondary DBPs and residues of pharmaceuticals in the aquatic environmentmay exhibit properties of compounds with estrogenic biological activity Organicmicropollutants have strong carcinogenic and mutagenic properties The presence ofNOM in water especially humic substances may change the chemical properties ofmicropollutants and contribute to their migration to a significant distance It hasbeen shown that humic substances can hydrophobically bind water additives throughcovalent bonds hydrogen bonds and van der Waals forces (Nawrocki 2005) Theycan also increase the water solubility of nonpolar compounds cause hydrolysis ofsome pesticides photodegrade organic substances and restrict the bioaccessibilityof aquatic organisms (Nawrocki 2005) These properties significantly depend onthe form of the organic micropollutants ie whether they are a free state or areadsorbed onto other substances The removal of micropollutants during water treat-ment is usually performed using activated carbon sorption or advanced oxidation pro-cesses (AOPs) The first method is economically unattractive when the amount ofNOM in water is high whereas for AOPs the possibility exists of forming by-productsof undefined biological activity (Bodzek 2013) This results in the need to developnew separation processes among which pressure-driven membrane processes seemto be a good solution In addition they can be performed as independent processesas well as be a part of integratedhybrid systems with coagulation or sorption on activecarbon or in MBRs (Bodzek 2013 Bodzek amp Konieczny 2005)

1541 Oxidation and DBPs

Disinfection and oxidation by-products constitute a group of undesirable substancesformed as a result of the reaction of disinfectants and other strong oxidants with waterpollutants and admixtures Table 155 shows the number of DBPs among which themost important are THMs and HHAs (Bodzek 2013)

Reverse osmosis and NF are most often applied to remove THMs halogenated ace-tic acids and other halogenated hydrocarbons from water In Poland permissible con-centrations of THMs in water are established as follows total THM lt100 mgLchloroform 30 mgL and bromodichloromethane 15 mgL (Bodzek et al 2011)

Table 155 Organic water disinfection and oxidation by-products ofcontaminants and impurities present in natural waters

Disinfectant Organic by-products

Chlorine Trihalomethanes haloacetic acids halocetonitriles haloaldehydeshaloketones halopicrates nitroso-dimethylamine 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX)

Chlorine dioxide Aldehydes carboxylic acids

Ozone Aldehydes carboxylic acids aldo- and ketoacids

492 Advances in Membrane Technologies for Water Treatment

A study in which RO and NF Osmonics membranes (SS10 and MQ16) wereapplied for the removal of THMs revealed that the retention depended on the mem-brane capacity ie the higher permeate flux the lower retention coefficient (Bodzek2013 Waniek Bodzek amp Konieczny 2002) (Table 156) The increase in molecularweight of the halogenated compound resulted in an increase of the retention coefficientaccording to the following series CHCl3 lt CHBrCl2 lt CHBr3 lt CHBr2Cl Theremoval rate of chloroform varied from 67 to 87 bromodichloromethane from65 to 965 dibromochloromethane from 57 to 905 and tribromomethanefrom 61 to 92 depending on the type of membrane applied (Waniek et al2002) Another study investigating the effectiveness of removing THMs by meansof NF with the use of NF200 and DS5 Osmonics membranes (Bodzek 2013 UyakKoyuncu Oktem Cakmakci amp Toroz 2008) (Figure 1512) showed that the operatingpressure did not affect THM retention whereas the initial concentration of THM had anoticeable influence on capacity and retention The NF200 membrane removed THMmore effectively than the DS5 membrane The most effectively removed compoundwas dibromochloromethane which resulted from the higher molecular weight ofbromine and in the greater size of the molecule

NF is also suggested for the removal of halogenated acetic acids (chloro- dichloro-and trichloroacetic acid and bromo- and dibromoacetic acid) from water (ChalatipChawalit amp Nopawan 2009) The high reduction in HAA content compared withan open negatively charged sulfonated polysulfone NTR7410 membrane and a neutralNTR729HF polyvinyl alcohol membrane (all membranes by Nitto Denco CorpJapan) was found for dense negatively charged ES10 aromatic polyamide membranesEffective separation was caused by repulsion forces (Donnan effect) and a sieving ef-fect The ES10 membrane removed HAAs in 90e100 even at the low operating pres-sure of 01 MPa and the change in linear velocity did not influence membraneperformance (Chalatip et al 2009) The increase in the concentration of acids resultedin a decrease in the removal rate in all investigated membranes according to the greaterconcentration polarization effect which was the driving force for HAA anion diffusionthrough the membrane

There are also studies on the removal of HAAs from water in bioreactors withimmobilized enzymatic UF membranes (Kowalska Dudziak amp Bohdziewicz2011) Enzymes isolated from strains of bacteria from activated sludge were used inthe immobilization process Trials have shown that after 8 h of degradation 37 of

Table 156 Retention coefficients of THMs for RO and NF

Osmonicsmembranes

Concentrationin raw water(mgL) CHCl3 CHBrCl2 CHBr2Cl CHBr3

NF-MQ16 10e100 83e87 885e965 905 92

RO-SS10 10e100 67e81 65e81 57e65 61e80

Note NF nanofiltration RO reverse osmosis THMs trihalomethanes

Membrane technologies for the removal of micropollutants in water treatment 493

monochloroacetic acid 35 of monobromoacetic acid and 484 of dichloroaceticacid were removed (Kowalska et al 2011)

Studies suggest that NF is the best available technology for removing THMs andHAAs from water

1542 Endocrine-activedisrupting compounds

Recent investigations focus especially on EACs as groups of micropollutants thatappear more often in natural waters and wastewaters even ones biologically purified(Biłyk amp Nowak-Piechota 2004) According to the definition those are chemicals thatmay interfere directly or indirectly with the endocrine system and affect target organsor tissues Depending on the dose of EAC and the destination physiology this effectmay (but not necessarily) have a side effect In the case of negative consequences forthe health of the organism its progeny or (sub)population compounds are classifiedaccording to the definition of the International Program on Chemical Safety asEDCs (Bodzek 2013) These behave similarly to natural (17b-estradiol estriol andestrone) and synthetic estrogens (ethinylestradiol and diethylstilbestrol) and in the

100

80

60

40

20

0

100

90

80

70

60

501 2 3 4

10 15 20Transmembrane pressure (bar)

Transmembrane pressure (bar)

THM

reje

ctio

n (

)TH

M re

ject

ion

()

25

20 μgL40 μgL80 μgL200 μgL

CHBr2Cl

CHBrCl2CHCl3

Figure 1512 Influence of pressure concentration and type of THM on retention coefficients ofTHMs in the NF process (Bodzek 2013) THM trihalomethane NF nanofiltration

494 Advances in Membrane Technologies for Water Treatment

body may mimic endogenous estrogens (produced within the body) antagonize theaction of estrogens and disturb the synthesis of estrogen receptors and the metabolismof endogenous hormones (Bodzek 2013) The EDC group includes endogenic hor-mones natural organic compounds produced by fungi (including toxins ie mycoes-trogenes) and plants (phytoestrogenes) and a wide range of anthropogenicmicropollutants among which the most important are

1 Polycyclic aromatic hydrocarbons2 Surfactants3 Plant protection products (pesticides herbicides and insecticides)4 Phthalates5 Halo-organic compounds including dioxins furans and polychlorinated biphenyls6 Phenol compounds (alkylphenols and bisphenols)

Major sources of EDCs for humans are both food and drinking water pollution isintroduced into them by chemicals in rain landfill leachate and industrial wastewaterEndocrine-disrupting compounds are present in natural waters in concentrationsranging from nanograms per liter to micrograms per liter

Phytoestrogens are found in plants and are used for therapeutic and cosmetic pur-poses The most important are these compounds are genistein daidzein formononetinbiochanin glicitein puerarin coumestrol and equol as a metabolite of daidzein Theirchemical structure is similar to 17b-estradiol and therefore they have estrogenic activ-ity These compounds enter water bodies as a result of the decomposition of plants intowastewaters Research has focused on removing phytoestrogens in water treatmentprocesses including membrane filtration Removal of biochanin daidzein genisteinand coumestrol in RO amounted to 97 69 92 and 86 respectively and forNF 86 68 71 and 72 respectively (Dudziak and Bodzek 2010a 2010b)During membrane filtration of water also containing NOM and inorganic compounds(salts of calcium sodium and bicarbonates) the relative permeability of the mem-branes was less than unity which confirmed the existence of fouling or scalingphenomena

Mycoestrogens are natural organic compounds that contaminate grain crops whenwashed by rain they can contaminate ground and surface waters They are toxic andreveal estrogenic activity The presence of mycoestrogens in the aquatic environmentcreates a need to remove them in water treatment processes Dudziak (2011) studiedthe efficiency of removing selected mycoestrogens from water in coagulation sorptionon activated carbon and NF Coagulation removed 34 of mycoestrogens sorptionwith PAC gave gt80 whereas NF gave from 70 to 88 depending on the typeof compound tested Integration of NF with sorption or coagulation improved theremoval of mycoestrogens

One of the main anthropogenic pollutants present in drinking water sources is poly-cyclic aromatic hydrocarbons (PAHs) These pollutants are harmful to human healthbecause most are carcinogenic eg benzo(a)phyrene so their permissible concentra-tion in drinking water cannot exceed 0010 mgL the total amount of benzo(b)fluoran-thene benzo(k)fluoranthene benzo(ghi)perylene and ideno(123-cd)pyrene may beonly 01 mgL Table 157 shows results obtained during studies focused on removing

Membrane technologies for the removal of micropollutants in water treatment 495

Table 157 Comparison of retention coefficients of PAHs removed during RO and NF (membranes fromOsmonics USA)

PAH nameConcentration inraw water ngL

Retention coefficient ()

UF HP-09RO-SS10 NF-SF10 NF-MQ16

Fluorantene 50 396 459 899 66e886

Benzo(b)fluorantene 60 644 978 859

Benzo(a)pirene 50 628 964 992

Benzo(ghi)perylene 70 968 911 933

Note PAH polycyclic aromatic hydrocarbons NF nanofiltration RO reverse osmosis

496Advances

inMem

braneTechnologies

forWater

Treatm

ent

PAHs by means of RO and NF at similar compound concentrations (Bodzek 2013Bodzek amp Konieczny 2010 Luks-Betlej Bodzek amp Waniek 2001) The most effec-tive membrane used during the studies was MQ16 (the retention coefficient of PAHswas in the range of 859 to 99 independent of the molecular weight of the com-pound) For other membranes the retention coefficient increased with an increase inthe molecular weight of the removed compound Ultrafiltration membranes used inthe research removed xenobiotics to a high level even though the molecular weightsof these compounds were smaller than the cutoff and the radius of the UF membranepores (Bodzek 2013 Luks-Betlej et al 2001) The likely cause of this phenomenonwas the adsorption of PAHs onto the surface of the UF membranes (Bodzek 2013)

Surface active agents (SAAs) are a specific group of anthropogenic water pollut-ants in particular detergents complexing and bleaching substances inhibitors stabi-lizers optical whiteners and others They affect wastewater treatment plantperformance mainly because of the toxic action on activated sludge the formationof foam the simulation of solubility of many hazardous substances etc The useful-ness of conventional methods (coagulation foaming sorption ion exchange andoxidation) is limited because of the variety of chemical structures of SAAs and theirchanges in concentration Pressure-driven membrane techniques are alternativemethods for removal of SAAs from water whereas the effectiveness and type of pro-cess depend on the concentration of the SAA (Bodzek 2013) When the concentrationis below critical micelle concentration (cmc) the application of NF membraneseventually RO is proposed It was shown that NF membrane Desal 5K eliminatedSAAs in 90e96 when the concentration was below cmc whereas for a concentrationhigher than the cmc the removal rate varied from 92 to 99 (Kowalska 2008)However when the concentration of the pollutant in water is greater than cmc UFcan be used even though the cutoff of applied membranes is greater than the molecularweight of the eliminated compounds Membranes with a cutoff of 5000e30000 Daare able to remove SAAs in the range of 30 to gt90 depending on membranecompactness and the type of membrane material (Kowalska 2008) An importantparameter in determining the effectiveness of the method is the concentration of theSAAs initially the retention ratio decreases with an increase in concentration andthen above the cmc the retention starts to increase (Bodzek 2013) Hybrid methodsare also proposed to remove anionic SAAs eg integrated UF and ion exchangewith an MIEX and other anionic resins (Kowalska 2010) Application of MIEX

resin in the amount of 20 cm3L of solution at a contact time of 20 min removed95 of the contaminant polyetherosulfone membranes of various densities wereused (Kowalska 2010)

Plant protection products (pesticides herbicides and insecticides) which belongto xenoestrogenes appear in surface and ground waters Pesticides are a group of arti-ficially synthesized substances used to fight pests and improve agricultural productionHowever they are generally toxic to living organisms and difficult to degrade becausetoxic agents have persistent bioaccumulative effects The use of pesticides also consti-tutes a risk for water quality in agricultural areas because these components may passthrough the soil and subsoil and pollute natural surface waters Regulations defining thequality of drinking water establish permissible concentrations of particular compounds

Membrane technologies for the removal of micropollutants in water treatment 497

or their sum at levels at 01 and 05 mgL These are substances with low molecularweight thus they can be effectively removed from water (above 90) during NF orby integrated systems with low pressure-driven membrane processes (MF or NF)and activated carbon adsorption (powdered or granulated) (Taylor amp Wiesner2000) Since the 1990s in many European countries including Poland studies havebeen performed on removing pesticides from natural waters using NF (Bodzek2013 Bodzek amp Konieczny 2005 Taylor amp Wiesner 2000) several pilot-scale andindustrial installations are already working Table 158 presents data from the literatureon removing selected pesticides from water by means of RO and NF (Bodzek 2013BodzekampKonieczny 2005 Taylor ampWiesner 2000) Nanofiltration membranes elim-inate pesticides with a molecular weight above 190 Da to an amount below the limit ofdetection generally the retention coefficient varies from 50 to 100 depending onthe molecular weight and the concentration of pesticides in water as well as on the pres-ence of organic and inorganic compounds (Bodzek 2013 Taylor amp Wiesner 2000)The formation of complexes of organic matter especially humic acids with moleculesof pesticides causes an increase in the retention of those compounds (Bodzek 2013Zhang Van der Bruggen Chen Braeken amp Vandecasteele 2004) However the

Table 158 Pesticide removal in RO and NF (data published from 1967to 2001)

Membrane process (membrane) Compound Retention ()

ROecellulosic membrane DDT 999

ROecellulosic membrane DDT 999

ROeTFC (aromatic polyamide) DDT 995

NF(NFe270 PVD1 PZ SUe610)

Simazine 66e94

Atrazine 79e99

Diuron 45e92

Other 38e100

NF(CAe50 BQe01 Desal 5eDKNTCe20 NTCe60 PVDe1NTRe7250)

Simazine atrazine 0e80

Diuron 5e90

Other 5e96

RO and i NF(20 types of membranes studied)

Symazine 14e95

Atrazine 41e99

Diuron 15e83

Other 0e99

NF (SFe10 STe10) Atrazine 25e67

Note NF nanofiltration RO reverse osmosis

498 Advances in Membrane Technologies for Water Treatment

presence of inorganic substances decreases the negative zeta potential of a membraneand causes the destruction of complexes of pesticides with humic acids resulting inthe release of micropollutants which finally leads to a decrease in retention (TaylorampWiesner 2000) In France near Paris a pilot installation is operating with a capacityof 2800 m3d based on Filmtec membranes (NF-70 and NF-200B) which are charac-terized by the high removal of atrazine and simazine up to 90 and 85 (concentrationin treated water drops from 1e2 gL to 01 gL) (Mallavialle Odendaal amp Wiesner1996) In the course of the study an increase in the retention rate of pesticides withan increase in organic carbon content in the raw water was found

Research on applying UF to the separation of atrazine from water solutions has beencarried out by several scientists (Majewska-Nowak Kabsch-Korbutowicz amp Dodz2001 Sarkar Venkateswralu Nageswara Bhattacharjee amp Kale 2007) The effi-ciency of the process depends on the type of membrane material and membranecompactness The best separation properties are exhibited by membranes with a cutoffof about 1e2 kDa (retention rate of about 60) (Majewska-Nowak et al 2001) Anincrease in efficiency up to 85e95 can be obtained during UF in the presence ofNOM andor cationic polyelectrolyte Hybrid systems combining coagulation adsorp-tion on activated carbon and NF are often used in pesticide removal (Sarkar et al2007) For example 98e99 removal of isoproturon (herbicide) was obtained inthe process of sorption and introduction of NF to the process protected treated wateragainst pesticide intrusion even for the exhaustion sorption bed

The presence of phthalates in the environment is caused by the massive productionof plastics mainly polyvinylchloride in which they are used as plasticizers Because oftheir negative effects on living organisms the concentration of phthalates in differentparts of the environment should be controlled especially in water Polish regulationsestablish the permissible concentration of di-n-butyl phthalate at 20 mgL A surpris-ingly high retention of phthalates was observed during both RO and NF processes(initial concentration 40 mgL) (Table 159) (Bodzek amp Konieczny 2010 BodzekDudziak amp LukseBetlej 2004) Retention rates achieved for diethyl phthalate di-n-butyl and di-2-ethylhexyl were very high and were from 897 (UF) to 999(RO and NF) Results obtained during the removal of phthalates with a molecularweight of 222e391 Da revealed that the molecular weight of a compound did not in-fluence the effectiveness of removal

Phenolic xenoestrogenes (octylphenol nonylphenol bisphenol A and bisphenolF) can be removed from water by means of NF Both the retention coefficient andthe rate of adsorption of xenoestrogenes strongly depend on the type of compoundthat is removed (Table 1510) as well as on the type of membrane (Bodzek 2013)During the membrane filtration of water containing a mixture of xenoestrogeneschanges in volumetric permeate flux (Jv) were not observed and relative volumepermeate flux (a) was close to 1 High retention of octylphenol and nonylphenol inthe range of 61 to 73 was observed for SF-10 and DS-5-DK membranes whereasfor bisphenol A DS-5-DK (69) and MQ-16 (75) the membranes were more effi-cient (Dudziak amp Bodzek 2008) With an increase in the concentration of xenoestro-genes in filtered water a decrease in their retention was observed as a result of theprogressive saturation of the membrane surface with these compounds Nanofiltration

Membrane technologies for the removal of micropollutants in water treatment 499

separation is often accompanied by the phenomenon of adsorption which greatly af-fects the elimination of pollutants and is directly correlated with their retention Thismay impede separation and cause the release of adsorbed organic micropollutants inthe course of the NF For UF membranes with concentrated compounds in deionizedwater at a level of 40 mgL the removal of bisphenol F bisphenol A 4-tert-octylophe-nol and 4-nonylphenol for GM membranes was 19 67 28 and 52 respec-tively whereas for the more compact DS-GE membrane it was 72 56 88and 100 respectively (Dudziak amp Bodzek 2008) A clear impact of the presenceand concentration of the NOM and the presence of inorganic salts as well as sub-stances causing concentration polarization on the retention of xenoestrogens wasfound During filtration in the presence of macromolecular substances the relativepermeability of membranes (a) was significantly less than unity which confirmedthe existence of the fouling phenomenon

A large amount of toxic halogenated aromatic hydrocarbons including chloro-benzenes and polychlobiphenyls (PCBs) chlorophenols and dioxins (polychlorodi-benzo-p-dioxins and dibenzofurans) is introduced into the environment Thesecompounds are insoluble in water They are characterized by high thermal chemicaland biochemical stability and are harmful to humans when they are deposited in adiposetissue They damage the liver and kidneys and interfere with the action of the humanenzyme system Polychlobiphenyls chlorobenzenes and chlorophenols are used invarious industries and enter the environment via wastewater from the chemical industrythrough the production of plastics and dyes from petroleum plants and plants producingplant protection substances and others Effective methods of removing chloro-organiccompounds from industrial wastewater include thermocatalytic oxidation strippingwith air inert gas or steam solvent extraction and adsorption on activated carbonor synthetic resins ( _Zarczynski Stopczyk Zaborowski Gorzka amp Kazmierczak2010) They can be removed from wastewater using a conventional activated sludge

Table 159 Removal of phthalates with RO NF and UF (membranesfrom Osmonics USA)

PhthalatesMolecularweight Da

Concentrationin raw watermgL

Process (membrane)

RO(DSe3eSE)

NF(DSe5eDK)

Retention coefficient

Diethylphthalate

2222 40 951 999

Dienebutylphthalate

2783 951 999

2-ethylhexylphthalate

3906 999 999

Note RO reverse osmosis NF nanofiltration

500 Advances in Membrane Technologies for Water Treatment

Table 1510 Comparison of retention coefficients and degrees of adsorption of phenolic xenoestrogens andrelative permeate flux of investigated NF membranes (Osmonics)

Compound

Nanofiltration membrane

SFe10 DSe5eDK MQe16 DSe51eHL

Retentionadsorption

4eterteoctylphenol 718522 727514 470179 480195

4enonylphenol 605680 703680 500525 435573

Bisphenol A 458525 688693 750750 607334

Bisphenol F e 75e78 e e

Relative permeate flux a 092 099 099 098

Mem

branetechnologies

forthe

removal

ofmicropollutants

inwater

treatment

501

process however the presence of suspended solids in the effluent significantly reducesthe removal rate Thus a better solution is the application of MBRs in which MF or UFmodules are applied instead of secondary settlers (Bolzonella Fatone Pavan amp Cecchi2010) This ensures the complete removal of suspended solids and extended retentiontimes in bioreactors which contributes to the high removal of halogenated aromatic hy-drocarbons from wastewaters Examples include the removal of chloro-dibenzo-p-dioxin which was 61e99 and chloro-dibenzo-p-furans which was 915e995depending on the type of dioxin and the concentration of biomass in the bioreactor (Bol-zonella et al 2010) In the case of natural waters in which the concentration of thehalogenated aromatic hydrocarbons is low one can use adsorption on activated carbonor other sorbents and photochemical oxidation with TiO2 In the latter case for the pho-tocatalyst separation membrane filtration is often used In addition to the removal of thisgroup of compounds NF and RO are proposed so one can get over 995 of themremoved Hydrophobic pervaporation with the use of polydimethylsiloxane membranescan also be used It revealed a high removal rate of contaminants that increased withincreasing vapor pressure and therefore did not depend on the molecular weight of xe-nobiotics The studies covered both PCBs and polychlorinated dioxins (YoonKoyanagi Asano Hara amp Higuchi 2002)

The appearance of compounds that affect hormone production processes in livingorganisms is often observed in surface waters Among these compounds naturaland synthetic hormones are specified Natural estrogens (17b-estradiol estroneand estriol) are present in the environment as a result of their natural excretion by an-imals and people Recently an increase in concentration of synthetic hormone (a-ethi-nylestradiol mestranol and diethylstilbestrol) resulting from the discharge of largeamounts of expired pharmaceuticals from households and from wastewater and hospi-tal waste as well as from pharmaceutical plants has been observed It was shown thatthis type of pollutant could be eliminated from water by means of membrane processes(Bodzek amp Dudziak 2006) Considering the relatively low molecular weight of thosepollutants dense membranes (RO or NF) must be applied Reverse osmosis mem-branes totally eliminate particular hormones retention coefficients obtained for NFand UF membranes were lower (Bodzek amp Dudziak 2006) For natural estrogensthe concentration of micropollutants (10e1000 ngL) does not affect the effectivenessof separation whereas for synthetic estrogens an increase in concentration causes anincrease in retention (Bodzek amp Dudziak 2006) Separation of hormones by meansof NF and UF strongly depends on the hydrophobicity and molecular weight of a com-pound Natural hormones ie estrone estriol and estradiol are removed less effi-ciently compared with their synthetic equivalents ethinylestradiol and mestranol(greater hydrophobicity) (Table 1511) (Bodzek 2013 Bodzek amp Konieczny2010) In addition instead of single-process elimination of hormones from water ahybrid system of coagulation and NF could be used (Bodzek amp Dudziak 2006) Mem-brane bioreactors are also proposed for the removal of hormones from wastewatersThe effectiveness of operating an MBR pilot installation (polyvinylidene difluoridemembrane with a pore diameter of 01 and 02 mm) was studied comparing theobtained results with the conventional installation working on a full-scale basis(Zuehlke Duennbier Lesjean Gnirss amp Buisson 2006) The ability to remove a

502 Advances in Membrane Technologies for Water Treatment

Table 1511 Retention of synthetic and natural hormones in pressure-driven membrane processes(concentration in water 1 mgL) (membranes from Osmonics USA)

Process(membrane)

Hormones(estrogens)

Natural Synthetic

Estrone 17beestradiol Estriol Mestranol17aeethynylEstradiol

DiethylStilbestrol

Retention coefficient

UF (DSGM) 368 353 281 685 553 701

NF (DSe5eDK) 630 767 711 100 904 861

RO (DSe3eSE) 100 100 100 100 100 100

Note RO reverse osmosis NF nanofiltration UF Ultrafiltration

Mem

branetechnologies

forthe

removal

ofmicropollutants

inwater

treatment

503

selected group of estrogenous hormones (estradiol estrone and ethinyl estradiol) wasmonitored More than 90 of natural hormones (estradiol and estrone) and approxi-mately 80 of synthetic ones (ethinylestradiol) were removed with conventional treat-ment In the case of MBR estradiol and estrone were removed in 99 andethinylestradiol in 95

1543 Pharmaceutically active compounds

One of the most important and specific anthropogenic groups of substances affectingthe environment are compounds called pharmaceutical and personal care products(PPCPs) This group includes compounds with pharmaceutical activity as well as sub-stances used by people to maintain personal hygiene (Heberer amp Feldmann 2008)Pharmaceutical and personal care products significantly affect wastewaters and otheraquatic environments (surface water and groundwater which constitute a source ofdrinking water) Main sources of aqueous environment pollution by pharmaceuticalsare households and hospitals as well as diagnostic units pharmaceutical plants andlivestock farms Medicines used by sick people do not totally metabolize and areremoved in urea and feces finally reaching wastewater treatment plants The occur-rence of pharmaceutically active compounds and personal care products and their bio-logically active metabolites in water can generate serious genetic mutations andencourage the formation of drug-resistant bacteria cultures They may lead to a situa-tion in which the human body will be resistant to the action of the drugs These chem-icals can also accumulate in the tissues of organisms which poses a threat to health andeven life Therefore increasing numbers of countries around the world have intro-duced monitoring of these compounds in water and their impact on ecosystems andthe aquatic environment (Heberer amp Feldmann 2008)

Studies on the comparative efficiency of removing drugs in wastewater treatmentplants have shown that biological methods are not always sufficient (Bodzek 2013)Methods to remove medicines from water and wastewater are advanced oxidationactivated carbon adsorption on granulated beds membrane processes such as NFand RO (Snyder et al 2007) and in the case of wastewater treatment MBRs (Claraet al 2005 Heberer amp Feldmann 2008)

The first results of studies performed at municipal wastewater treatment plants dur-ing which MBRs equipped with MF or UF modules were used revealed that theremoval of trace amounts of pollutants was comparable to conventional treatmentmethods (Clara et al 2005) These results attest to the fact that MF and UF membranesare too open to remove biologically nondegradable micropollutants in wastewatertreatment plants On the other hand the higher age of activated sludge and elongatedcontact time achieved in MBR improves biological degradation and the removal ofPhACs and EDCs Membrane bioreactors with immersed modules have been checkedfor the removal of selected pharmaceuticals (clofibric acid diclofenac ibuprofenketoprofen mefenamic acid and naproxen) (Kimura Hara amp Watanabe 2005) Inthe experiments high rates of removal of ketoprofen and naproxen for MBR havebeen observed which were not been found with a conventional treatment systemRemoval rates of phenazone propyphenazone and formylamino-antipyrine were

504 Advances in Membrane Technologies for Water Treatment

also less in conventional installation (15) than with MBR (60e70) (Zuehlke et al2006) Also the effectiveness of removing pharmaceuticals using MBR depended onthe structure of the PhAC molecules eg the number of aromatic rings A higherremoval rate of pharmaceutical substances was observed under low pH conditionsowing to their adsorption on activated sludge flocks (Zuehlke et al 2006)

In most cases installations that use MBR to treat wastewater improved the effi-ciency of organic micropollutant removal compared with conventional wastewatertreatment plants This was because of the extension of retention time and increasingage of the biomass but also because of the increase in its concentration and the adsorp-tion ability of micropollutants on the much larger flocks of activated sludge Thus theywere retained during filtration through MFUF membranes even though these micro-pollutants were often several hundred times smaller than the pores of the membranesRadjenovic Petrovoc and Barcelo (2009) observed significant improvement in the ef-ficiency of removing regulators of lipids and cholesterol statin drugs (gemfibrozilbezafibrate clofibric acid and pravastatin) b-blockers (atenolol and metoprolol) an-tibiotics (ofloxacin and erythromycin) and some painkillers and anti-inflammatorydrugs in MBRs Data from the literature indicate a high and stable rate of removalof clofibric acid and diclofenac in plants equipped with MBR The efficiency ofremoval for clofibric acid usually amounted to 50e70 and for diclofenac 51(Radjenovic et al 2009) during conventional wastewater treatment Other data indi-cate a low removal of diclofenac in typical wastewater treatment plants (10e30)This illustrates how inconsistently the data are presented in the literature and confirmsthe need to conduct further research on the removal of pharmaceutical residues fromwastewater (Radjenovic et al 2009)

Two-month performance monitoring was carried out in MBRs to examine the long-term stability of the system and the effect of retention time on the efficiency ofremoving residues of pharmaceuticals from treated wastewater (Barcelo Petrovic ampRadjenovic 2009) In general the pharmaceuticals were removed to a higher extentby MBR than by a conventional wastewater treatment process In some cases theremoval efficiency was similar and equally high for both cases (eg ibuprofen nap-roxen acetaminophen paroxetine and hydrochlorothiazide) Carbamazepine wasnot removed by the installation with MBR or by the wastewater treatment plantNevertheless wastewater coming from the MBR was characterized by low Chemicaloxygen demand (COD) and total organic carbon (TOC) values and a small content ofammonium nitrogen and total suspended solids The results of monitoring summarizedin Table 1512 (Barcelo et al 2009 Bodzek 2013) show a distinct advantage ofMBRs over the processes in typical wastewater treatment plants Membrane bioreac-tors enable the much more effective removal of residues of pharmaceuticals and othermicropollutants For many PPCPs the removal rate obtained by MBR is virtually100 Thus the use of bioreactors results in treated wastewater of a very high qualityso that the load of pollutants introduced into surface waters is less than that for waste-waters coming from conventional treatment plants

High-pressure membrane technology ie NF and RO used to purify wastewaterand natural waters along with other pollutants can also be used to remove residuesof PPCPs (Heberer amp Feldmann 2008 Yoon Westerhoff Snyder Wert amp Yoon

Membrane technologies for the removal of micropollutants in water treatment 505

2007) The NF membrane exhibited relatively low retention (40) for polar PhACslow volatile and low hydrophobicity In the case of polar organic compounds reten-tion significantly depended on the dipole moment and pH (Kimura Toshima Amy ampWatanabe 2004) Test results showed that negatively charged and ionic compoundssuch as the analgesic diclofenac could be removed in more than 90 regardless ofother physicochemical properties mainly according to electrostatic repulsion

Table 1512 Efficiency of removal of pharmaceuticals in installationwith MBR as well as in conventional wastewater treatment plant

PharmaceuticalEfficiency of removalwith MBR

Efficiency of removal inconventional wastewatertreatment plant

Naproxen 993 851

Ketoprofen 919 515

Ibuprofen 998 825

Diclofenac 874 501

Indomethacin 466 234

Acetaminophen 996 984

Mefenamowy acid 748 294

Propyfenazon 646 427

Ranitidine 950 422

Carbamazepine No elimination No elimination

Paroxetine 897 906

Ofloxacin 94 238

Sulfamethoxazole 605 556

Erythromycin 673 238

Atenolol 655 No elimination

Metoprolol 587 No elimination

Hydrochlorothiazide 663 763

Glibenclamide 473 445

Gemfibrozil 896 388

Bezafibrate 958 484

Klofibric acid 718 277

Pravastatin 908 618

Note MBR membrane bioreactor

506 Advances in Membrane Technologies for Water Treatment

Retention of other ionized drugs exceeded 95 for NF membranes 90 XLE andTFC-HR for the NF-200 membrane it was about 90 (Xu et al 2005) For neutralcompounds retention takes place according to molecular exclusion and adsorptionFor example the neutrally charged antipyretic drug phenacetin or anti-inflammatoryand anti-rheumatic drug ibuprofen show a lower retention rate (for phenacetin onlymore than 20) because they are significantly adsorbed onto membranes with rela-tively high hydrophobicity (Nghiem Scheuroafer amp Elimelech 2005) On the otherhand another neutral antipyretic medicament piramidon is always retained bymore than 70 which suggests that its retention is affected by other phenomena Inaddition the retention of pharmaceuticals in RO and NF is affected by the membranematerial (Kimura et al 2004) For example polyamide membranes had higher effi-ciency (57e91) than CA membranes In the case of polyamide membranes the mo-lecular weight of the compound could be used as a retention trend indicator (separationbased on molecular sieving) whereas the polarity predicted the retention of individualcompounds in the case of CA membranes Retention of pharmaceuticals also dependson the concentration (Kimura et al 2004) Experiments conducted at a concentrationof 100 ngl resulted in significantly lower retention (14e72 for NF and 50e80 forRO) compared with tests at a higher concentration which amounted to 100 mgl(19e93 for NF and 71e95 for RO) One can therefore conclude that the retentionof pharmaceuticals by a compact NF membrane is dominated by the spherical exclu-sion (size) mechanism whereas electrostatic repulsion and spherical exclusion governthe retention of ionized pharmaceuticals in the case of an open NF membraneThe United States evaluated the conventional drinking water treatment processesunder typical water treatment plant conditions for the removal of antibiotics (carbadoxsulfachlorpyridazine sulfamethoxazole sulfamerazine sulfamethazine sulfathiazoleand trimethoprim) (Adams Wang amp Meyer 2002) They showed a very highefficiency of RO in removing all antibiotics

Table 1513 Concentration of pharmaceuticals in water of TeltowCanal and in permeate after one step of RO

Compounds

Averageconcentration inraw water ngL

Averageconcentration inpermeate ngL

Retentioncoefficient

AMDOPH 290 lt1 gt99

Caffeine 429 lt1 gt99

Clofibric acid 155 lt1 gt99

Diclofenac 330 lt1 gt99

Ketoprofen 17 lt1 gt99

Naproxen 38 lt1 gt99

Propyfenazon 177 lt1 gt99

Note AMDOPH 1-Acetyl-1-methyl-2-dimethyl-oxamoyl-2-phenylhydrazide

Membrane technologies for the removal of micropollutants in water treatment 507

Table 1514 Average concentration of pharmaceuticals in biologically treated wastewater and permeate aftertreatment with two-stage RO system

Compound

Concentration ngL Retention coefficient

Raw water PermeateAfter preliminaryfiltration and UF After first RO stage

After second ROstage

AMDOPH 811 lt1 32 gt999 gt999

Bezafibrate 257 lt5 7 960 gt999

Carbamazepine 2282 lt1 13 gt999 gt999

Clofibric acid 178 lt1 20 gt994 gt994

Diclofenac 869 lt1 44 gt999 gt999

Fenofibric acid 705 lt1 22 970 gt999

Gemfibrozil 16 lt1 38 gt933 gt993

Ibuprofen 87 lt1 12 985 gt989

Indomethacin 46 lt1 0 920 gt978

Ketoprofen 99 lt1 20 gt990 gt990

Naproxen 224 lt1 0 982 gt995

Oxazepam 153 lt5 0 gt993 gt993

Primidone 734 lt1 0 gt999 gt999

Propyphenazone 309 lt1 46 993 gt997

Note AMDOPH 1-Acetyl-1-methyl-2-dimethyl-oxamoyl-2-phenylhydrazide RO reverse osmosis UF Ultrafiltration

508Advances

inMem

braneTechnologies

forWater

Treatm

ent

Pressure-driven membrane processes (MF UF NF and RO) were also tested toremove EDCs and PPCPs on a pilot scale and in industrial installations (Snyderet al 2007 Heberer amp Feldmann 2008)

Snyder et al (2007) performed pilot- and industrial-scale tests with MF UF NFand RO for the removal of EDCs and PPCPs from crude municipal wastewater withleachates after the first second and third treatment stages and saline groundwaterinto which specified micropollutants were introduced The study revealed that onlysome compounds were removed duringMF and UF whereas for NF and RO significantretention of all investigated compounds was observed However several compoundssuch as iopromide and pentoxifylline were detected in permeate in trace concentrations

Heberrer and Feldmann (2008) performed awide pilot study of PhAC removal using amobile installation for water treatment equipped with ROmodules normally used duringnatural disasters or military operations The substrate of the study was water from TeltowChannel (Berlin) and treated wastewater from the Ruhleben municipal wastewater treat-ment plant (Berlin) The prototypic three-stage installation with a capacity equal to10000 Lh included duplex bag filters with a particle separation less than 05 mm UFand RO RO could be performed as a one- or two-stage process The presence ofPhAC in treated water from Teltow Channel was not observed (Table 1513) (Bodzek2013 Bodzek amp Konieczny 2010) whereas in RO permeate obtained during treatedwastewater treatment the amount of pharmaceutical was below 10 ngl for both one-and two-stage configurations (Table 1514) (Bodzek 2013 BodzekampKonieczny 2010)

155 Conclusions

Properly selected membrane processes such as RO NF UF and MF in hybrid sys-tems DD ED and MBRs can be used to remove micropollutants from natural watersand wastewaters

High-pressure membrane techniques ie RO and NF can be used for directremoval of inorganic and organic micropollutants while low-pressure (MF and UF)can be used in integrated systems first of all into coagulation and adsorption and inMBR as well as after complexion with polymers or surfactants

Processes with ion-exchange membranes are suitable for micropollutants with anelectrical charge Because of this they are used in many large-scale applicationsincluding the separation of ions desalination and removal of ionic species

156 Final remarks

A number of inorganic and organic micropollutants have been found in potentiallyharmful concentrations in numerous water sources The maximum permissible levelof these compounds in drinking water set by the WHO and a number of countries isvery low (in the range of micrograms per liter to a few milligrams per liter) thusmost of them can be referred to as charged micropollutants Several common treatment

Membrane technologies for the removal of micropollutants in water treatment 509

technologies that are currently used to remove contaminants from natural water sup-plies represent serious exploitation problems

The use of membranes (NF RO and ED) to treat water sources containing anionicand metal micropollutants for drinking and industrial purposes can provide more orless selective removal of the target pollutants especially when the separation of mono-valent and multivalent ions is desired In NF it can be obtained by both ion size andcharge exclusion effects whereas in ED it results from the use of ion-exchange mem-branes with mono-anion permselectivity Nanofiltration and to some extent RO arealso suitable for removing organic micropollutants from water and wastewaters Themost important among them are DBPs pharmaceutical active compounds andEDCs which have high biological activity In the first case volatile THMs andnonvolatile compounds mainly HAAs are formed For this last groups of compoundsspecial attention in natural waters is paid to PAHs and surface-active substanceschlorinated pesticides phthalates alkylphenols polychlorinated biphenyls hormonessynthetic pharmaceuticals and other chemicals and substances produced by humansand disposed into the environment

The application of MF and UF in inorganic and organic micropollutant removal ispossible in integrated systems through coagulation adsorption complexion with poly-mers or surfactants and biological reactions In the last case three major membranebioprocesses have been developed pressure-driven MBRs biological membrane con-tactors and IEMBs The problem with operating low-pressure-driven membrane pro-cesses is membrane fouling

Drinking water containing biologically active substances ie viruses bacteriaprotozoa and other microorganisms is a significant health threat Ultrafiltration andMF can help improve the process of disinfecting water using traditional methodsbecause membranes are barriers to microorganisms Viruses can be retained by UFmembranes whereas bacteria and protozoa need UF and MF membranes

To remove NOM it is possible to successfully use either direct NF or integratedsystems combining UF or MF with coagulation adsorption on activated carbon andeven oxidation NOM and some other anthropogenic organic pollutants can be precur-sors of DBPs which is why it is very important to remove NOM from water

List of acronyms

AOP Advanced oxidation processAOX Adsorbable organic halidescmc Critical micelle concentrationCOD Chemical oxygen demandDBP Disinfection by-productDD Donnan dialysisDOC Dissolved organic carbonEAC Endocrine active compoundsED ElectrodialysisEDC Endocrine-disrupting compoundsEDI Electrodeionization

510 Advances in Membrane Technologies for Water Treatment

EDR Electrodialysis reversalEED Electro-electrodialysisEMBR-SRB Extractive membrane bioreactors with sulfate-reducing bacteriaEU European UnionHAA Haloacetic acidIEMB Ion-exchange membrane bioreactorMBR Membrane bioreactorMCR Membrane coagulation reactorMEUF Micellar enhanced ultrafiltrationMF MicrofiltrationNF NanofiltrationNOM Natural organic matterNTU Nephelometric turbidity unitPAC Powdered activated carbonPAH Polycyclic aromatic hydrocarbonPCB PolychlorobiphenylPEI PolyethyleneiminePEUF Polymer-enhanced ultrafiltrationPhAC Pharmaceutical active compoundPPCP Pharmaceutical and personal care productPVA Poly(vinyl alcohol)RO Reverse osmosisSAA Surface active agentTHM TrihalomethaneTOC Total organic carbonUF UltrafiltrationWHO World Health Organization

References

Adams Y Wang L K amp Meyer M (2002) Removal of antibiotics from surface and distilledwater in conventional water treatment processes Journal of Environmental Engineering128 253e260 Retrieved from httpdxdoiorg101061(ASCE)0733-9372(2002)1283(253)

Alvarado L Ramirez A amp Rodriacuteguez-Torres I (2009) Cr(VI) removal by continuouselectrodeionization Study of its basic technologies Desalination 249 423e428Retrieved from httpdxdoiorg101016jdesal200906051

Amy G Alleman C B amp Cluff C B (1990) Removal of dissolved organic matter bynanofiltration Journal of Environmental Engineering 116 200e205 Retrieved fromhttpdxdoiorg101061(ASCE)0733-9372(1990)1161(200)

Anonymous (2005) Microfiltration and ultrafiltration membranes for drinking water DenverCO American Water Works Association AWWA (USA)

Anonymous (2008) Remediation technologies for perchlorate contamination in water and soilWashington DC The Interstate Technology amp Regulatory Council Retrieved from httpwwwitrcweborgDocumentsPERC-2pdf

Bakalar T Bugel M amp Gajdosova L (2009) Heavy metal removal using reverse osmosisActa Montanistica Slovaca 14 250e253

Membrane technologies for the removal of micropollutants in water treatment 511

Barcelo D Petrovic M amp Radjenovic J (2009) Treating emerging contaminants (pharma-ceuticals) in wastewater and drinking water treatment plants technological perspectives forrational use of water resources in the Mediterranean Region Options Meacutediterraneacuteennes A88 133e140 Retrieved from httpomciheamorgompdfa8800801187

Bick A amp Oron G (2005) Post-treatment design of seawater reverse osmosis plants Boronremoval technology selection for potable water production and environmental controlDesalination 178 233e246 Retrieved from httpdxdoiorg101016jdesal200501001

Biłyk A amp Nowak-Piechota G (2004) Zanieczyszczenie srodowiska substancjami powo-dującymi zakłocenie funkcji endokrynologicznych organizmu (Environmental pollutionwith substances causing disturbance of the organism endocrine functions) OchronaSrodowiska 26(3) 29e35 (in Polish)

Bodzek M (1999) Membrane techniques in wastewater treatment In I M F A Goosen ampW H Shayya (Eds) Water purification Vol 2 Water management purification andconservation in arid climates (pp 121e184) Lancaster Basel Technomic Publishing

Bodzek M (2012) Usuwanie metali ze srodowiska wodnego za pomocą metod mem-branowych e stan wiedzy (Removal of metals from water environment using membranemethods e state of the art) Monografie Komitetu In_zynierii Srodowiska Polskiej AkademiiNauk 66 305e313 In Polish

Bodzek M (2013) Przegląd mo _zliwosci wykorzystania technik membranowych w usuwaniumikroorganizmow i zanieczyszczen organicznych ze srodowiska wodnego (An overviewof the possibility of membrane techniques application in the removal of microorganismsand organic pollutants from aquatic environment) In_zynieria i Ochrona Srodowiska 16(1)5e37 In Polish

Bodzek M amp Dudziak M (2006) Elimination of steroidal sex hormones by conventionalwater treatment and membrane processesDesalination 198 24e32 Retrieved from httpdxdoiorg101016jdesal200609005

Bodzek M Dudziak M amp LukseBetlej K (2004) Application of membrane techniques towater purification Removal of phthalates Desalination 162 121e128 Retrieved fromhttpdxdoiorg101016S0011-9164(04)00035-9

Bodzek M amp Konieczny K (2005) Zastosowanie procesow membranowych w uzdatnianiuwody (Application of membrane processes in water treatment) Bydgoszcz PolandOficyna Wydawnicza Projprzem-Eko In Polish

Bodzek M amp Konieczny K (2010) Wykorzystanie technik membranowych w uzdatnianiuwody do picia czII e usuwanie związkow organicznych (Utilization of membranetechniques in the treatmnent of drinking Water Part II e removal of organic compounds)Technologia Wody 2(04) 15e31 In Polish

Bodzek M amp Konieczny K (2011a) Membrane techniques in the removal of inorganicmicropollutants from water environment e state of the art Archives of EnvironmentalProtection 37(2) 15e29

Bodzek M amp Konieczny K (2011b) Usuwanie zanieczyszczen nieorganicznych zesrodowiska wodnego metodami membranowymi (Removal of inorganic micropollutantsfrom water environment by means of membrane methods) Warszawa WydawnictwoSeidel-Przywecki In Polish

Bodzek M Konieczny K amp Kwiecinska A (2011) Application of membrane processes indrinking water treatment e state of art Desalination and Water Treatment 35 164e184httpdxdoiorg105004dwt20122435

Bodzek M Korus I amp Loska K (1999) Application of the hybrid complexation e ultra-filtration process for removal of metal ions from galvanic wastewater Desalination 121117e121 Retrieved from httpdxdoiorg101016S0011-9164(99)00012-0

512 Advances in Membrane Technologies for Water Treatment

Bodzek M Płatkowska A Rajca M amp Komosinski K (2008) Fouling of membranesduring ultrafiltration of surface water (NOM) Ecological Chemistry and Engineering A16 107e119

Bolzonella D Fatone F Pavan P amp Cecchi F (2010) Poly-chlorinated dibenzo-p-dioxinsdibenzo-furans and dioxin-like poly-chlorinated biphenyls occurrence and removal inconventional and membrane activated sludge processes Bioresource Technology 1019445e9454 Retrieved from httpdxdoiorg101016jbiortech201007067

Bryjak M (2001) Procesy separacyjne a polimery O mo_zliwosciach nietypowego wykorzys-tania syntetycznych polimerow (Separation processes and polymers About the possibilitiesof an atypical use of synthetic polymers) Wrocław Poland Oficyna Wydawnicza Poli-techniki Wrocławskiej In Polish

Butler R Godley A Lytton L amp Cartmell E (2005) Bromate environmental contamina-tion review of impact and possible treatment Critical Reviews in EnvironmentalScience and Technology 35 193e217 Retrieved from httpdxdoiorg10108010643380590917888

Chalatip R Chawalit R amp Nopawan R (2009) Removal of haloacetic acids by nano-filtration Journal of Environmental Sciences 21 96e100

Clara M Strenn B Gans O Martinez E Kreuzinger N amp Kroiss H (2005) Removal ofselected pharmaceuticals fragrances and endocrine disrupting compounds in a membranebioreactor and conventional wastewater treatment plantsWater Research 39 4797e4807Retrieved from httpdxdoiorg101016jwatres200509015

Crespo J G Velizarov S amp Reis M A (2004) Membrane bioreactors for the removal ofanionic micropollutants from drinking water Current Opinion in Biotechnology 15463e468 Retrieved from httpdxdoiorg101016jcopbio200407001

Dilek C Ozbelge H O Bicak N amp Yilmaz L (2002) Removal of boron from aqueoussolution by continuous polymer enhanced-ultrafiltration by polyvinyl alcohol SeparationScience and Technology 37 1257e1271 Retrieved from httpdxdoiorg101081SS-120002610

Domany Z Galambos I Vatai G amp Bekassy-Molnar E (2002) Humic substances removalfrom drinking water by membrane filtration Desalination 145 333e337 Retrieved fromhttpdxdoiorg101016S0011-9164(02)00432-0

Dudziak M (2011) Usuwanie mikoestrogenow w procesie koagulacji sorpcji i nanofiltracji eprocesy pojedyncze i układy zintegrowane (Removal of mycoestrogens in the coagulationsorption and nanofiltration processes e a single and integrated processes) Nauka PrzyrodaTechnologie 5(4) 1e9 In Polish

Dudziak M amp Bodzek M (2008) Removal of xenoestrogens from water during reverseosmosis and nanofiltration e effect of selected phenomena on separation of organicmicropollutants Architecture Civil Engineering Environment 1(3) 95e101

Dudziak M amp Bodzek M (2010a) A study of selected phytoestrogens retention by reverseosmosis and nanofiltration membranes e the role of fouling and scaling Chemical Papers64(2) 139e146 Retrieved from httpdxdoiorg102478s11696-009-0072-0

Dudziak M amp Bodzek M (2010b) Removal of phytoestrogens from water solutions usingtubular nanofiltration membranes Ecological Chemistry and Engineering A 17 289e296

Frenzel I Holdik H Stamatialis D F Pourcelly G amp Wessling M (2005) Chromic acidrecovery by electro-electrodialysis Journal of Membrane Science 261 49e55 Retrievedfrom httpdxdoiorg101016jmemsci200503031

Hafiane A Lemordant D amp Dhahbi M (2000) Removal of hexavalent chromium bynanofiltration Desalination 130 305e312 Retrieved from httpdxdoiorg101016S0011-9164(00)00094-1

Membrane technologies for the removal of micropollutants in water treatment 513

Han B Runnells T Zimbron J amp Wickramasinghe R (2002) Arsenic removal fromdrinking water by flocculation and microfiltration Desalination 145 293e298 Retrievedfrom httpdxdoiorg101016S0011-9164(02)00425-3

Heberer T amp Feldmann D (2008) Removal of pharmaceutical residues from contaminatedraw water sources by membrane filtration In Klaus Keuroummerer (Ed) Pharmaceutical in theenvironment (pp 427e453) Berlin-Heidelberg Springer

Hu K amp Dickson J M (2006) Nanofiltration membrane performance on fluoride removalfrom water Journal of Membrane Science 279 529e538 Retrieved from httpdxdoiorg101016jmemsci200512047

Jacangelo J Aieta E M Carns K E Cummings E W amp Mallevialle J (1989) Assessinghollow-fiber ultrafiltration for particulate removal Journal AWWA 81(11) 68e75Retrieved from httpwwwjstororgstable41292731

Jacukowicz-Sobala I (2009) Wspołczesne metody usuwania chromu ze sciekow (Modernmethods of removal of chromium from wastewaters) Przemysł Chemiczny 88(1) 51e60In Polish

Kabay N Arar O Acar F Ghazal A Yuksel U amp Yuksel M (2008) Removal of boronfrom water by electrodialysis Effect of feed characteristics and interfering ions Desali-nation 223 63e72 Retrieved from httpdxdoiorg101016jdesal200701207

Kabsch-Korbutowicz M Biłyk A amp Mołczan M (2006) The effect of feed water pre-treatment on ultrafiltration membrane performance Polish Journal of EnvironmentalStudies 15 719e725

Kartinen E O amp Martin C J (1995) An overview of arsenic removal processes Desalina-tion 103 79e88 Retrieved from httpdxdoiorg1010160011-9164(95)00089-5

Kimura K Hara H amp Watanabe Y (2005) Removal of pharmaceutical compounds bysubmerged membrane bioreactors (MBRs) Desalination 178 135e140 Retrieved fromhttpdxdoiorg101016jdesal200411033

Kimura K Toshima S Amy G amp Watanabe Y (2004) Rejection of neutral endocrinedisrupting compounds (EDCs) and pharmaceutical active compounds (PhACs) by ROmembranes Journal of Membrane Science 245 71e78 Retrieved from httpdxdoiorg101016jmemsci200407018

Konieczny K Bodzek M amp Rajca M (2006) A coagulationeMF system for water treatmentusing ceramic membranes Desalination 198 100e109 Retrieved from httpdxdoiorg101016jdesal200609014

Korus I (2010) Removal of Pb(II) ions in ultrafiltration enhanced with polyelectrolytePolimery 55(2) 135e138

Korus I (2012) Wykorzystanie ultrafiltracji wspomaganej polimerami do separacji jonowmetali cię_zkich (The application of ultrafiltration enhanced with polymers for theseparation of heavy metal ions) Gliwice Poland Wydawnictwo Politechniki SląskiejIn Polish

Kowalska I (2008) Surfactant removal from water solutions by means of ultrafiltration and ion-exchange Desalination 221 351e357 Retrieved from httpdxdoiorg101016jdesal200701094

Kowalska I (2010) Usuwanie anionowych substancji powierzchniowo-czynnych z roztworowwodnych w hybrydowym układzie oczyszczania wymiana jonowa e ultrafiltracja(Removal of anionic surface active substances from aqueous solutions in a hybrid ionexchange-ultrafiltration system) Monografie Komitetu In_zynierii Srodowiska PAN 65271e277

Kowalska M Dudziak M amp Bohdziewicz J (2011) Biodegradacja kwasow halogen-ooctowych w bioreaktorze z poliamidową enzymatyczną membraną ultrafiltracyjną

514 Advances in Membrane Technologies for Water Treatment

(Biodegradation of haloacetic acids in bioreactor with polyamide enzymatic ultrafiltrationmembrane) In_zynieria i Ochrona Srodowiska 14 257e266

Kołtuniewicz A B amp Drioli E (2008) Membranes in clean technologies Weinheim Wiley-VchVerlag GmbH

Laine J-M Campos C Baudin I amp Janex M-L (2002) Understanding membrane foulingA review of over a decade of research In S Wodrich amp H Degeler-Koch (Eds)Proceedings of ldquoMembranes in drinking and industrial water production MDIW 2002rdquo(pp B37a 351e360) Mulheim an der Ruhr Germany ZENIT GmbH

Laine J Clark M M amp Mallevialle J (1990) Ultrafiltration of lake water Effect of pre-treatment on the partitioning of organics THMFP and flux Journal AWWA 82 12e82

Lee S Quyet N Lee E Kim S Lee S Jung Y D et al (2008) Efficient removals oftris(2-chloroethyl) phosphate (TCEP) and perchlorate using NF membrane filtrationsDesalination 221 234e237 Retrieved from httpdxdoiorg101016jdesal200702054

Luks-Betlej K Bodzek M amp Waniek A (2001) PAH removal from water by membraneprocesses In A Noworyta amp A Trusek-Hołowina (Eds) Using membranes to assist ofcleaner production (pp 61e67) Wrocław Poland Argi

Mack C Burgess J E amp Duncan J R (2004) Membrane bioreactors for metal recovery fromwastewater A review Water SA 30 521e532

Majewska-Nowak K Kabsch-Korbutowicz M amp Dodz M (2001) Herbicide separation bylow-pressure membrane process In A Noworyta amp A Trusek-Hołownia (Eds) Usingmembranes to assist of cleaner processes (pp 153e158) Wrocław Poland Argi

Mallavialle J Odendaal P E amp Wiesner M R (Eds) (1996) Water treatment membraneprocesses New York San Francisco Washington DC McGraw-Hill

Mavrov V Nikolov N D Islam M A amp Nikolova J D (1992) An investigation on theconfiguration of inserts in tubular ultrafiltration module to control concentration polari-zation Journal of Membrane Science 75 197e201 Retrieved from httpdxdoiorg1010160376-7388(92)80017-E

Mehiguene K Garba Y Taha S Gondrexon N amp Dorange G (1999) Influence ofoperating conditions on the retention of copper and cadmium in aqueous solutions bynanofiltration experimental results and modeling Separation and Purification Technology15 181e187 Retrieved from httpdxdoiorg101016S1383-5866(98)00096-3

Nawrocki J (2005) Uboczne produkty utlenienia i dezynfekcji wody (Oxidation and disin-fection by-products of water) Ochrona Srodowiska 27(4) 3e12 In Polish

Nghiem L D Scheuroafer A I amp Elimelech M (2005) Pharmaceutical retention mechanisms bynanofiltration membranes Environmental Science amp Technology 39 7698e7705Retrieved from httpdxdoiorg101021es0507665

Nguyen C M Bang S Cho J amp Kim K W (2009) Performance and mechanism of arsenicremoval from water by a nanofiltration membrane Desalination 245 82e94 Retrievedfrom httpdxdoiorg101016jdesal200804047

Owlad M Aroua M K Daud W A amp Baroutian S (2009) Removal of hexavalentchromium -contaminated water and wastewater A review Water Air Soil Pollution 20059e77 Retrieved from httpdxdoiorg101007s11270-008-9893-7

Pawlak Z Zak S amp Zabłocki L (2006) Removal of hazardous metals from groundwater byreverse osmosis Polish Journal of Environmental Studies 15 579e583

Prados-Ramirez M Ciba N amp Bourbigot M (1995) Available techniques for reducingbromate in drinking water Water Supply 13 61e70

Qdais H A amp Moussa H (2004) Removal of heavy metals from wastewater by membraneprocesses A comparative studyDesalination 164 105e110 Retrieved from httpdxdoiorg101016S0011-9164(04)00169-9

Membrane technologies for the removal of micropollutants in water treatment 515

Raczuk J (2010) Nitrogen compounds in well water as a factor of a health risk to theMaciejowice commune inhabitants (Mazowieckie Voivodeship) Archives of Environ-mental Protection 36(4) 31e39

Radjenovic J Petrovoc M amp Barcelo D (2009) Fate and distribution of pharmaceuticals inwastewater and sewage sludge of the conventional activated sludge (CAS) and advancedmembrane bioreactor (MBR) treatment Water Research 43 831e841 Retrieved fromhttpdxdoiorg101016jwatres200811043

Rajca M (2012) Wpływ wybranych czynnikow na usuwanie anionowych zanieczyszczenz wod w procesie wymiany jonowej MIEXDOC (The impact of selected factors onthe removal of anionic water pollutants in ion-exchange process of MIEX DOC)Archives of Environmental Protection 38 115e121 Retrieved from httpdxdoiorg102478v10265-012-0010-z

Religa P amp Gawronski R (2006) Oczyszczanie chromowych sciekow garbarskich e procesymembranowe (Treatment of tanning wastewaters e membrane processes) PrzeglądWłokienniczy e Włokno Odzie_z Skora 12 41e44 In Polish

Sarkar B Venkateswralu N Nageswara R Bhattacharjee C amp Kale V (2007) Treatmentof pesticide contaminated surface water for production of potable water by a coagulation eadsorption e nanofiltration approach Desalination 212 129e140 Retrieved from httpdxdoiorg101016jdesal200609021

Sehn P (2008) Fluoride removal with extra low energy reverse osmosis membranes Threeyears of large scale field experience in Finland Desalination 223 73e84 Retrieved fromhttpdxdoiorg101016jdesal200702077

Shih M-C (2005) An overview of arsenic removal by pressure-driven membrane processesDesalination 172 85e97 Retrieved from httpdxdoiorg101016jdesal200407031

Siddiqui M Amy G Ryan J amp Odem W (2000) Membranes for the control of naturalorganic matter from surface waterWater Research 34 3355e3370 Retrieved from httpdxdoiorg101016S0043-1354(00)00024-5

SnyderSAdhamSReddingACannonFDeCarolis JOppenheimer J et al (2007)Roleofmembranes and activated carbon in the removal of endocrine disruptors and pharmaceuticalsDesalination 202 156e181 Retrieved from httpdxdoiorg101016jdesal200512052

Sosnowski T Suchecka T amp Piątkiewicz W (2004) Penetracja komorki przez membranęmikrofiltracyjną (Penetration of the cell through the microfitration membrane)MonografieKomitetu In_zynierii Srodowiska PAN 22 359e367 In Polish

Tahaikt M Haddou A El Habbani R Amor Z Elhannouni F Taky M et al (2008)Comparison of the performances of three commercial membranes in fluoride removal bynanofiltration continuous operations Desalination 225 209e219 Retrieved from httpdxdoiorg101016jdesal200707007

Tan L amp Amy G (1991) Comparing ozonation and membrane separation for color removaland disinfection by-product control Journal AWWA 83(5) 74e79

Taylor J S ampWiesner M (2000) Membranes In R D Letterman (Ed)Membrane processesin water quality and treatment New York McGraw Hill

Thorsen T (1999) Membrane filtration of humic substances e state of art Water Science andTechnology 40(9) 105e112 Retrieved from httpdxdoiorg101016S0273-1223(99)00646-0

Uyak V Koyuncu I Oktem I Cakmakci M amp Toroz I (2008) Removal of trihalomethanesfrom drinking water by nanofiltration membranes Journal of Hazardous Materials 152789e794 Retrieved from httpdxdoiorg101016jjhazmat200707082

Van der Bruggen B amp Vandecasteele C (2003) Removal of pollutants from surface waterand ground water by nanofiltration Overview of possible applications in the drinking

516 Advances in Membrane Technologies for Water Treatment

water Environmental Pollution 122 435e445 Retrieved from httpdxdoiorg101016S0269-7491(02)00308-1

Velizarov S Crespo J G amp Reis M A (2004) Removal of inorganic anions fromdrinking water supplies by membrane bioprocesses Reviews in Environmental Sci-ence amp BioTechnology 3 361e380 Retrieved from httpdxdoiorg101007s11157-004-4627-9

Velizarov S Matos C Oehmen A Serra S Reis M amp Crespo J (2008) Removalof inorganic charged micropollutants from drinking water supplies by hybrid ionexchange membrane processes Desalination 223 85e90 Retrieved from httpdxdoiorg101016jdesal200701217

Wang C Lippincott L amp Meng X (2008) Kinetics of biological perchlorate reduction andpH effect Journal of Hazardous Materials 153 663e669 Retrieved from httpdxdoiorg101016jjhazmat200709010

Waniek A Bodzek M amp Konieczny K (2002) Trihalomethanes removal from water usingmembrane processes Polish Journal of Environmental Studies 11 171e178

Wilf M (2010) The guidebook to membrane technology for wastewater reclamationHopkinton MA Balaban Desalination Publications

Wisniewski J (2001) Electromembrane processes In A Noworyta amp A Trusek-Hołownia(Eds) Membrane separations (pp 147e179) Wrocław Poland Argi

Wisniewski J amp Kliber S (2010) Bromate removal from water in electrodialysis processMonografie Komitetu Inzynierii Srodowiska Polskiej Akademii Nauk 66 305e313

Xu P Drewes J E Bellona C Amy G Kim T U Adam M et al (2005) Rejection ofemerging organic micropollutants in nanofiltration-reverse osmosis membrane applica-tions Water Environment Research 77 40e48 Retrieved from httpdxdoiorg102175106143005X41609

Yoon B Koyanagi S Asano T Hara M amp Higuchi A (2002) Removal of endocrinedisruptors from aqueous solutions by pervaporation Journal of Membrane Science 198311e320 Retrieved from httpdxdoiorg101016S0376-7388(01)00671-8

Yoon Y Westerhoff P Snyder S Wert E amp Yoon J (2007) Removal of endocrinedisrupting compounds and pharmaceuticals by nanofiltration and ultrafiltration membranesDesalination 202 16e23 Retrieved from httpdxdoiorg101016jdesal200512033

Zakrzewska-Trznadel G (2003) Radioactive solution treatment by hybrid complexation-UFNF process Journal of Membrane Science 225 25e39 Retrieved from httpdxdoiorg101016S0376-7388(03)00261-8

_Zarczynski A Stopczyk A Zaborowski M Gorzka Z amp Kazmierczak M (2010) Usu-wanie związkow chloro-organicznych ze sciekow przemysłowych ze szczegolnym uwz-ględnieniem metody termo katalitycznego utleniania (Removal of chloro-organiccompounds from industrial wastewaters with special reference to the of thermo-catalyticoxidation method) Ochrona Srodowiska 32 49e54 In Polish

Zhang G Gao Y Zhang Y amp Gu P (2005) Removal of fluoride from drinking water by amembrane coagulation reactor (MCR) Desalination 177 143e155 Retrieved from httpdxdoiorg101016jdesal200412005

Zhang Y Van der Bruggen B Chen G X Braeken L amp Vandecasteele C (2004) Removalof pesticides by nanofiltration Effect of the water matrix Separation and PurificationTechnology 38 163e172 Retrieved from httpdxdoiorg101016jseppur200311003

Zuehlke S Duennbier U Lesjean B Gnirss R amp Buisson H (2006) Long-term com-parison of trace organics removal performances between conventional and membraneactivated sludge processes Water Environment Research 78 2480e2486 Retrieved fromhttpdxdoiorg102175106143006X111826

Membrane technologies for the removal of micropollutants in water treatment 517

Membrane technologies forwater treatment and reuse in thegas and petrochemical industries

16Y JiSchool of Resources and Environmental Engineering East China University of Scienceand Technology Shanghai PR China

161 Introduction

Petrochemicals can be defined as a large group of chemicals derived from natural gasand petroleum and further used for a variety of chemical purposes which areextremely important in modern civilization Nevertheless like most production activ-ities petroleum oil and gas production and further processing processes such as extrac-tion and refining are responsible for generating a huge volume of wastewater to bedischarged into the environment Because environmental policy is increasingly severewater contaminated with petroleum derivatives and processing additives should betreated to separate these derivatives from water before it can return to the environment

Wastewater generated in the petrochemical industry is a mixture of organic andinorganic materials containing many different chemical compositions depending onthe complexity of the refinery the existing processes and the type of petroleum oiland gas employed The effluents are mainly produced by extraction and physical sep-aration processes such as atmospheric and vacuum distillation deparaffinization andde-asphalting and also by processes involving chemical conversions by isomerizationalkylation etherification catalytic reform etc Therefore wastewater composition isqualitatively similar to petroleum oil andor gas production

The major compounds of the wastewater include (1) oil compounds (2) dissolvedformation minerals (3) production chemical compounds and (4) production solids(including formation solids corrosion and scale products bacteria waxes and asphal-tenes) Among pollutants present in effluents from petrochemical industries at higherconcentrations oilewater emulsions stand out Besides oilewater emulsions specificchemical concentrations of wastewaters vary considerably with the geographical loca-tion and refining processes Table 161 lists chemical compositions of typical wastewa-ters from petrochemical and gas production (Hansen amp Davies 1994 Li amp Lee 2009)

Oil is a mixture of hydrocarbons such as benzene toluene ethylbenzene andxylene naphthalene phenanthrene dibenzothiophene polyaromatic hydrocarbonsand phenols Oilewater mixtures are generated at different production stages Becausethe solubility of oil in water is generally very low most of the oil is dispersed in waterOil in these wastewater streams may exist in three forms free oil (separate oil globulesof sufficient size that they can rise as a result of buoyancy force generally larger than

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400016-2Copyright copy 2015 Elsevier Ltd All rights reserved

150 mm) dispersed oil (20e150 mm) and emulsified oil which has droplets typicallyless than 20 mm Stable oily emulsion is a dispersed system in which the phases areimmiscible or partially miscible liquids and difficult to be flocculated Wastewaterin petrochemical industry is currently treated by activated sludge process withpretreatment of oilewater separation However de-emulsifying these effluents withconventional processes including chemical dispersion breakup gravity settling centri-fugation air flotation fibrous or packed-bed coalescence and biological degradation isoften not economically feasible might cause secondary pollution does not haveappropriate efficiency with regard to separation or produces large amounts of mudthat also need treatment (Almeida Neto Silva Valenzuela-Diacuteaz amp Rodrigues 2006)

Furthermore with regard to the significant matter of environmental concern manycountries have implemented stringent regulatory standards for discharging thesewastewaters According to United States Environmental Protection Agency (USEPA)regulations the daily maximum limit of ldquooil and greaserdquo for petroleum oil and gas pro-duction wastewater is 42 mgL and the monthly average limit is 29 mgL (USEPA)

Table 161 Typical wastewater composition from petrochemical andgas production

Component Oil wastewater (mgL) Gas wastewater (mgL)

Organic composition

Aliphatic C2eC5 1 1

Aliphatic gtC5 5 10

Fatty acids C2eC5 300 150

Benzene 8 25

Naphthalenes 15 15

Phenols 5 5

Inorganic compositionHCO

3 15381 58703

H2S 225 65

Cl 130636 23895

SO24 45941 241

Nathorn 804212 41693

Kthorn 3986 35

Mgthorn 8941 19

Cathorn 43955 11

Srthorn 889 63

Fe2thorn 653 065

520 Advances in Membrane Technologies for Water Treatment

Besides the increasing need to reuse treated water has generated interest in treatingpetrochemical wastewater with the advanced physical membrane-based separationprocess

162 Membrane technologies for water treatmentand reuse in the gas and petrochemical industries

Generally membranes are defined essentially as a barrier in the form of thin syntheticorganic or inorganic films selectively separating fluid from its components andrestricting transport of various chemicals The membrane pressure-driven process re-lies on the pore size of the membrane to separate oily droplets according to their poresizes Membrane processes including microfiltration (MF) ultrafiltration (UF) nano-filtration (NF) and reverse osmosis (RO) are increasingly being applied to treat oilywastewater (wastewater containing oil) (Bhave amp Fleming 1988 Daiminger NitschPlucinski amp Hoffmann 1995) Microfiltration is mainly for the separation of sus-pended particles UF for macromolecules RO for dissolved and ionic componentsand NF for multivalent ions rather than for univalent ions Among these processesUF is especially useful for stable emulsions particularly water-soluble oily wastesin wastewaters from the gas and petrochemical industries

The membrane unit is usually operated in a semi-batch recycle as shown inFigure 161 The oilewater emulsion is fed into the separation tank at the same rateas treated permeate is withdrawn therefore maintaining a constant level in the tankThe retentate containing the oil is recycled to the process tank and allowed to concen-trate only when the oil concentration reaches a set level Generally the final concen-trate volume is only 3e5 of the initial volume of oily wastewater fed into the

Retentate

Membrane cell

PermeateFlowmeter

Cooling water

Pressure guage

Three way valve

Pump Feed tank

Water jacket

Water outlet

Figure 161 Schematic setup of membrane treatment of wastewaters from petrochemical andgas production

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 521

separation tank The recovered oil can be collected as a by-product or be further treatedusing other oxidation technologies

Membranes have many advantages over traditional techniques (Makki Al-AlawyAl-Hassani amp Rashad 2011) (1) They are more widely applicable across a widerange of industries (2) the quality of the treated water is more uniform regardless ofinfluent variations (3) no extra chemicals are added (4) membranes can be used in-process to allow recycling of selected waste streams within a plant (5) concentratesup to 40e70 oil can be obtained by UF or MF (6) the membrane equipment hasa smaller space requirement and offers a simple easy-to-operate low-maintenanceprocess option and (7) energy costs are lower compared with thermal treatments

Membrane processes also have the following limitations (1) Scale-up is almostlinear above a certain size and therefore the capital costs for large effluent volumescan be high and (2) polymeric membranes experience fouling and degradation duringuse which can increase operating costs significantly

Despite these disadvantages membrane separation is gaining wider acceptancebecause it consistently produces effluents of acceptable discharge quality and it isperceived to be a simple process from an operational viewpoint Therefore com-pounded with other methods membranes are a commercial success for oily wastewatertreatment with more than 3000 polymeric UFMF installations and over 75 inorganicceramic units worldwide (Bilstad amp Espedal 1996 Ciarapica amp Giacchetta 2003He amp Jiang 2008 Lee amp Frankiewicz 2005 Li Yan Xiang amp Hong 2006)

163 Integrating membrane processes into existingtreatment infrastructure

Currently wastewaters from gas and petroleum oil industries are generally treated basedon biodegradation by oxidation (and to a lesser extent reduction) worldwide Retrofit-ting such facilities with an entirely new approach not based on oxidation is rarelypossible Generally process integrations integrated with more advanced physicochem-ical technologies are accepted to be able to improve the sustainability of old treatmentfacilities and are typically necessary to minimize the overall environmental impactAmong these technologies membrane processes are thought to be ideal candidatesfor process integration because membrane technologies can be easily integrated intothe total treatment systems combining several processes The term ldquointegrated mem-brane systemrdquo (IMS) frequently refers to water treatment systems that incorporate mem-branes An IMS can be defined either as a system that integrates two or more membraneprocesses or a system combining a membrane process with other treatment processes Itis claimed that IMS has significant advantages for the treatment of wastewater streamscontaining oily substances halogenated organics or organic solvent (Scott 1995)Integrated membrane systems have gained increasing importance in treating oily waste-waters combined with a chemical or biological process or a conventional unit operationsuch as distillation or absorption An IMS with two or more separation processes ismost frequently employed to treat wastewater from the gas and petrochemical industriesto meet severe emission standards and reduce cost

522 Advances in Membrane Technologies for Water Treatment

1631 Permeate flux and concentration polarization

The capital and operational costs of membrane systems depend directly on membranepermeate flux Consequently the permeate flux is the central consideration indesigning a membrane process for water treatment and reuse in the gas and petrochem-ical industries

Generally if the concentration of the emulsified oil droplet and pressure are below acertain limit the permeate flux is directly proportional to the trans-membrane pressurewhich can be described as

J0w frac14 DP

h0Rm(161)

where J0w is the permeate flux of pure water DP is the trans-membrane pressure Rm theintrinsic resistance of the clean membrane and h0 is the water viscosity

During the membrane process the oil droplets accumulate on the membrane surfaceand a concentration difference between the membrane surface and bulk solution isformed resulting in oil droplets diffusing into the bulk solution backward and inincreasing hydraulic resistance to permeate flow until a balance is obtained concentra-tion polarization The concentration polarization layer results in an additional osmoticpressure therefore the effective driving force of membrane process as well as thefiltration flux and solute rejection are reduced correspondingly Consequently thepermeate flux declines in time and the following is the differential equation of masstransfer for steady state

JwdCdx

Dd2Cdx2

frac14 0 (162)

Integrating Eqn (162) gives the following equation

JwC DdCdx

frac14 C1 (163)

where D is the diffusion coefficient of oil droplets JwC is the solute flux ontomembrane and D dC

dx is the solute diffusion flux in the backward direction Theintegral constant C1 is equal to the oil droplet permeate flux which is a constant atsteady state

By integrating Eqn (163) we can obtain the following equation

Jw frac14 D

dlnCm Cf

Cb Cf(164)

where Cb is the oil droplet concentration in the bulk solution of feed Cm is the oildroplet concentration at the membrane surface Cf is the oil droplet concentration in thepermeate and d is the thickness of the boundary layer (polarization layer)

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 523

Increasing pressure can improve permeate flux of water and the oil droplet concen-tration at the membrane surface also goes up leading to more severe concentrationpolarization and higher flux of the solute diffusion backward to the bulk solution

1632 Membrane fouling

Besides concentration polarization another major challenge confronting membraneapplications in water treatment and reuse in the gas and petrochemical industries ismembrane fouling Concentration polarization decreases the driving force of fluxacross the membrane which is completely reversible and could be reduced by modi-fying the flow over the membrane (Asatekin Kang Elimelech amp Mayes 2007) How-ever membrane treatment of oily wastewater is economically limited by one factorloss of membrane flux owing to severe fouling Flux is often reduced by one to twoorders of magnitude severely affecting the economic viability of membrane treatmentof petrochemical industry wastewaters (Asatekin amp Mayes 2009)

As soon as the upper surface of the membrane comes into contact with the waste-water contaminants such as oil droplets and colloid particles adsorb at the membranesurface because of physiochemical interactions It is widely accepted that there are twomechanisms of membrane fouling pore blocking which is responsible for the initialsharp drop from the flux of pure water filtration and cake formation which is thereason for long-term gradual flux decline (Song 1998) The fundamental cause ofmembrane fouling is the nonequilibrium operation in which the applied pressure ismuch higher than the critical pressure that can be absorbed by the concentration polar-ization layer In such an operation the membrane pores will be quickly blocked anda cake layer will form to absorb the excessive pressure

There are four models of fouling that are categorized according to differentblockage mechanisms as follows (Kim amp DiGiano 2009) complete (solute particlesreach open pores of the membrane and block and seal the pore entrances completely)standard (solute particles enter the pores and are adsorbed or trapped inside the porewalls) intermediate pore blocking (solute particles occupy a fraction of the poreentrance leading to a reduction in the permeate flux without totally sealing the pores)and cake filtration (particle diameters are larger than those of the membrane pores sothe particles do not enter the pores) Hermia developed an empirical model to identifythe fouling mechanism by analysis of the characteristic curve (Hermia 1982)

d2tdV2 frac14 b

dtdV

n

(165)

where V is the cumulative volume of filtrate t is the time of operation and b is aconstant

The volumetric permeate flux can be expressed as

Jw frac14 1A

dVdt

(166)

524 Advances in Membrane Technologies for Water Treatment

Therefore the governing equation of the flux decline with time could be obtainedby substituting and integrating Eqn (166)

Jw frac14 1A

dJwdt

frac14 aJ3nw (167)

where a is a constant The value of n depends on the blockage mechanism n frac14 2 forcomplete pore blocking n frac14 15 for standard pore blocking n frac14 1 for intermediatepore blocking and n frac14 0 for cake formation

164 Improving process design operation monitoringand control

1641 Design considerations

Efforts have been made to improve permeate flux including

1 Membrane modification The separation behavior is strongly influenced by the membranematerials (Hamza Pham Matsuura amp Santerre 1997) and the surface properties of themembrane have a critical role in the determination of fouling resistance The widelyaccepted fact is that surface hydrophilic membrane is employed to treat an oily emulsionbecause the hydrophobic membranes are easily fouled owing to adsorption of oily sub-stances in water on and in the pores of the membranes (Nakatsuka Nakate amp Miyano1996) To achieve this goal membrane material can be modified or functionalized by(Ochoa Masuelli amp Marchese 2003 Ulbricht 2006) (1) synthesis of new surfacehydrophilic polymers (2) hydrophilic functionalization of polymeric membranes (3)preparation of homogenous or heterogenous hydrophilic blends starting from differentpolymeric materials or particles from organic or inorganic origin Recently polyvinylalcohol cellulose acetate and ceramicepolymeric composite membranes are beingused for oilewater emulsions separation because of their antifouling properties (MittalJana amp Mohanty 2011)

2 Pulsed flow The process of transporting oil droplets through a membrane boundary in asteady flow field is related to the classic Graetz problem that analyzes the concentrationprofile of a steadily flowing fluid that undergoes a step change on the boundary Super-imposing an oscillating flow to the steady flow will alter the flow profiles and thus alterthe concentration and mass transfer of the system The oscillations and unsteady flows canbe obtained by introducing pulsations into the feed or filtrate channels which can enhanceshear at the membrane surface to decrease concentration polarization Although pulsedflow decreases the effective operating time and results in a loss of permeate to the feedstream filtration performance was greatly improved in both tubular and flat-sheet mem-brane systems (Howell Field amp Wu 1993 Wu Howell amp Field 1993) in anothercase flux improvement of up to 300 was found when using periodically spaceddonut-shaped baffles in UF tubes together with pulsed flows with an oscillation frequencyup to 25 Hz (Finnigan amp Howell 1989)

3 Improving mass transfer by turbulence promoters Insertion of static turbulence promotersis a method for increasing shear stress at the membrane surface and is an effective technique

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 525

for reducing concentration polarization and membrane fouling Flux enhancement and fluxcontrol under laminar flow conditions can be achieved by generating well-defined secondary-flow structures by using baffles this is successful only when the radial velocities are highwhich leads to high Reynolds numbers and the flow becomes turbulent Bellhouse (1997)described designs of tubular membranes into which were placed concentric screw threadinserts which had a clearance with the tubular membranes to permit substantial leakageflow in the resulting annular gap The shape of the helical screw thread was semicircularto permit approximately 50 of the flow to pass along the helical path with a corkscrew vor-tex superimposed on the path to create radial mixing in the flow field (Wakeman ampWilliams2002) Different shapes of static turbulence promoters such as static rods spiral wire metalgrills and disc and donut-shaped inserts have been extensively constructed and placedconcentrically inside membrane tubes during MF and UF with or without superimposingthe pulsating flow (Gupta Howell Wu amp Field 1995 Holdich amp Zhang 1992) Howeverpressure loss induced by the insertion of the static turbulence promoter increased energyconsumption and might cause significant variation in trans-membrane pressure along themembrane length

4 Rotatingvibrating membranes In classical cross-flow filtration the shear stress at the mem-brane surface is increased by applying a tangential flow Therefore the shear stress and feedflow rate are interrelated because a higher shear stress implies a higher flow rate and subse-quently higher energy consumption as a result of the pressure drop In rotating filters theshear stress is independent of the flow rate because it relies on the speed of membrane rota-tion A high-shear stress can be developed at the membrane surface by rotating the surface athigh speed rather than pumping feed across the surface at a high cross-flow velocity(Wronski Molga amp Rudniak 1989) This rotating membraneehigh-shear (dynamic) filtra-tion can be implemented by rotating either the membrane or a baffle near the membrane Themagnitude of the shear stress can be varied independently of overpressure of the slurry in thefilter by varying the rotational speed of the rotating element Generally there are two types(Serra Wiesner amp Laicircneacute 1999) rotating cylinders or rotating disks Rotating cylindersreferred to as annular membranes consist of two concentric cylinders separated by a smallgap which take advantage of Taylor vortices when one of those cylinders is rotating Thelatter consist of two axial disks and take advantage of radial flow in the vicinity of the rotatingdisk to reduce particle deposition on the membrane as well as the centrifugal force and shearstress exerting on particles deposited on the membrane surface to drive them back into thebulk liquid

5 Incorporating force fields such as electric or ultrasonic The use of additional forces to aidfiltration has gained increasing attention in recent years Application of an electric field toimprove the efficiency of pressure-driven filtration processes called electro-filtration hasbeen practiced for a long time Besides the bulk flow tangential to the membrane in cross-flow filtration there also exists a convective flow into the porous surface leading to oil drop-lets being transported laterally toward the membrane By applying a direct current electricfield gradient to give oil droplets electrophoretic velocity the convective flow could be coun-terbalanced to a greater or lesser extent which might reduce membrane fouling and enhancefiltrate flux Two different configurations have been reported for electro-filtration An electricfield can be applied across the membrane with one electrode on either side of the membraneor the electric field may be applied between the membrane and another electrode In bothcases the performance of the membrane process is primarily improved owing to electropho-resis For electro-filtration to be successful a voltage higher than some critical value must beapplied (Henry Lawler amp Kuo 1977 Wakeman 1982) The critical voltage gradient definesthe voltage gradient at which the net particle migration toward the membrane is zero

526 Advances in Membrane Technologies for Water Treatment

The electrophoretic velocity (v) gained by an oil droplet could be obtained using the Henryformula as follows

v frac14 2ε0DdxE

3m(168)

where ε0 is the permittivity of a vacuum Dd is the dielectric constant x is the zetapotential E is the electric field gradient and m is the fluid viscosity

Huotari Huisman and Treuroagaringrdh (1999a) Huotari Treuroagaringrdh and Huisman (1999b)reported the effect of an electric field in the filtration of an oil emulsion in which thelimiting fluxes for low flow rate increased significantly using an electric field Thelimiting flux increase was affected by the electrophoretic mobility of the oil dropletsand the applied electric field strength In this work the permeate quality also improvedsignificantly and membranes with large pore sizes could be employed when the electricfield was present

The passage of ultrasound waves through a suspension can cause many phenomenaincluding particle dispersion viscosity reduction changes in particle surface proper-ties and cavitation (Kost amp Langer 1988) Generally ultrasound is characterizedby an ability to transmit substantial amounts of mechanical power through small me-chanical movements The passing of ultrasonic waves of a suitably high intensitythrough liquid media is accomplished by phenomena such as cavitation radiation pres-sure and acoustic streaming Cavitational mechanisms are considered important indetaching particles from the membrane surface whereas turbulence associated with ul-trasound has a role in transporting of particles away from the surface after detachment

Previous works demonstrate that higher particle concentrations produce greaterattenuation of the sound waves as they pass through the cross-flow suspension owingto increased acoustic impedance (Wakeman amp Tarleton 1991 Yunus amp Jones 1995)The degree of attenuation varies with different feed particles and processing condi-tions and is believed to be the controlling parameter for ultrasonic field efficiency Be-sides wastewater viscosity is a limiting factor as ultrasound is applied When viscositygoes up the flux enhancement decreases and no flux enhancements are found when theliquid viscosity is about 4 cp Experimental results showed that an ultrasound cleaningtechnique was applied to remove fouling of UF and MF membranes by cross-flowfiltration (Chai Kobayashi amp Fujii 1998) For each polymeric membrane made ofpolysulfone polyacrylonitrile and polyvinylidene fluoride cleaning experimentswere performed with three kinds of methods sonication water cleaning and watercleaning under sonication Results showed that water cleaning under sonication wasan effective method for the recovery of permeate flux

1642 Wastewater pretreatment

Pretreatment of wastewaters for the gas and petrochemical industries is an effective op-tion to enhance permeate flux and prevent membrane fouling therefore the use ofinnovative pretreatment can significantly reduce the treatment cost This techniqueis commonly used either to remove particles that may cause clogging in the membrane

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 527

pores or to prevent particles or macromolecules from reaching and depositing onto themembrane surface or to reduce the total oil emulsion load by breaking it Traditionalmethods for separating oil emulsion can be classified as physical chemical orcombined

Physical processes usually include prefiltration or centrifugation to remove sus-pended and colloidal solids that may plug the module or blind the membrane and me-chanical emulsion breaking based on the phenomenon of gravity (Adewumi Erb ampWatson 1992 Knudsen et al 2004) The efficiency of these methods mainly dependon the size of the oil droplets as well as the difference in density between water and oilAnother physical pretreatment method breaks the oil emulsion thermally by heatingthe wastewater leading to a significant increase in the oil droplet size (Aptel amp Clifton1986) This process requires a large amount of energy which makes it economicallyunfeasible

Chemical methods are most widely used in treating oily wastewater which are usu-ally directed toward destabilizing the dispersed oil droplets or destroying emulsifyingagents Chemical methods are primarily based on neutralizing detergents (emulsionrsquosstabilizers) resulting in the acceleration of a separation process owing to the coales-cence effect and a change in solution pH so that molecular or colloidal foulantswill be far from their isoelectric point thereby reducing the tendency to form a gellayer Chemical methods include precipitation coagulation or flocculation or theuse of proprietary antiscalants or disinfectants (Garbutt 1997 1999) Currently ferricand aluminum salts are the most widely used agents for demulsification The processusually consists of rapidly mixing the chemicals with the wastewater followed by floc-culation and flotation or settling The work has been reported for the application ofmembrane technology for oily emulsion stabilized by anionic surfactants (BelkacemMatamoros Cabassud Aurelle amp Cotteret 1995) By adding a reactive salt (CaCl2) ata very low concentration in the feed solution the permeate flux increased significantlyThe UF membrane behaved as efficient surface coalescer when the agent was addedwhich reduced polarization layer resistance

1643 Operation optimization

Optimizing the operation conditions may involve maintaining a high cross-flowvelocity limiting trans-membrane pressure manipulating wastewater temperatureand periodical hydraulic chemical andor mechanical cleaning etc

Pumping the feed at higher flow rates into the membrane can lead to increased shearon the membrane surface which will reduce concentration polarization and cake for-mation in commercial membrane modules in the same way turbulence promoters doWhereas steady flows often require cross-flow velocities in the turbulent regime un-steady flows can be effective in both the laminar (as for example Taylor and Deanvortex flows) and the turbulent regimes (Gekas amp Hallstreuroom 1987) These fluid insta-bilities could disturb foulants (Chung Brewster amp Belfort 1993 Winzeler 1990) andinduce fluid mixing at the membraneesolution interface (Jeffree Peakock Sobey ampBellhouse 1981) Fluid instabilities could substantially increase mass transfer ofsolutes away from the membrane therefore the performance of membrane processes

528 Advances in Membrane Technologies for Water Treatment

can be improved when unsteady fluid instabilities are superimposed on cross-flowvelocity (Thomas 1973 Winzeler amp Belfort 1993)

High cross-flow velocity reduces cake formation and polarization in membrane pro-cesses but the pressure drop on the feed side is generally high whereas the permeateside is often at or close to atmospheric pressure which means that the trans-membranepressure at the feed end of the membrane is greater than at the retentate discharge endcausing more cake formation (the extent of compaction depends on the properties ofthe feed) at the feed end Besides high pressure might induce other problems intooil-in-water emulsion by membrane technology when some surfactants are presentin emulsion It has been reported that for watereoilesurfactant emulsions hightrans-membrane pressure results in an increase in the permeability of the surfactantwithout a commensurate increase in the permeability of the water or oil (Sweet 1990)

Temperature is another important factor in cross-flow UF of oily emulsions Theseparation efficiency and membrane fouling depend on the oily droplet size distribu-tion which correlates strongly to the varying temperature With properly chosen mem-brane materials and pore sizes by manipulating the emulsion temperature below thecloud point of the least soluble component it is also possible to remove finelydispersed contaminant oils selectively without simultaneously losing active compo-nents from adequately formulated fluids (Misra amp Skold 1999)

After a certain period of use the membrane should be cleaned mechanically hy-draulically or chemically Cleaning-in-place procedures are generally recommendedto rejuvenate fouled membranes because they commonly involve shorter downtimesthan cleaning-out-of-place It is common practice to pump permeate back throughthe membrane periodically which is achieved by applying pressure on the permeateside of the membrane with the help of an automatic time switch or a microprocessorPermeated water is then forced in the reverse direction through the membrane therebylifting off the boundary layer and washing it out of the membrane surface Thepermeate flux could be significantly improved and the concentration polarizationand membrane fouling could be effectively controlled by periodic back-flushing Shortpulses (about 01 s or shorter) are particularly useful for oily wastewater with colloidalsuspensions

Besides periodic hydraulic cleaning and mechanical cleaning chemical cleaning isalso commonly employed Cleaning solutions are prepared with cleaning agents andare usually circulated with a pressure somewhat lower than that of normal filtrationto prevent deeper foulant penetration into the membrane The selection of cleaningagent is determined by factors such as the foulant type and the compatibility of themembrane with the solution A temporary adverse effect on the membrane rejectionis commonly observed after using many cleaning agents which can be attributableto membrane swelling during contact with the cleaning solution (Jonsson amp Johansen1989) Kim Sun Chen Wiley and Fane (1993) investigated the relationships betweenmembrane fouling and cleaning in terms of flow conditions trans-membrane pressurepH membrane properties and cleaning agents using a stirred batch-cell and aqueousalbumin solution Currently for a better cleaning effect combined processesie chemical agents with physical procedures are widely employed which includepretreatment pulsating gas back-washing adding chemicals in opposite direction

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 529

flushing the feed at high pressure and combining mechanical devices with chemicalcleaners

165 Energy consumption of membrane operationsin the gas and petrochemical industries

Although the membrane technology is widely accepted as a reliable way to treat waste-water with specific requirements the high operating energy consumption is one of themain constraints preventing it from increasing deployment in gas and petrochemicalindustries Generally the total cost of membrane process for wastewater treatment con-sists of pretreatment of original wastewater influents capital cost (typically includingmembrane pump and basic construction expenses) equipment maintenance oper-ating expenses and oily wastewater concentrate disposal cost

The OsloParis Convention for the Protection of the Marine Environment of theNorth-East Atlantic (OSPAR Commission) proposed a method for evaluating waste-water treatment costs in the gas and petrochemical industries Capital cost and oper-ating expenses were estimated based on market conformity The method was basedon three model situations

1 Small gas installation (based on 26 gas installations with small water discharges)2 Large gas installations (based on 27 gas installations with larger water discharges)3 Petroleum oil installations (based on seven oil installations)

Because of the high pressure required to overcome the trans-membrane osmoticpressure the operating expenses mainly energy consumption are the major partand can reach as high as 45 of the total cost (Busch amp Mickols 2004 Manth Gaboramp Oklejas 2003) Currently the energy consumption of membrane process has beenestimated using a phenomenological approach which does not explicitly consider themembrane properties and operating parameters Qi Wang Xu Wang and Wang(2012) proposed a method to theoretically calculate the energy consumption describedbelow According to the mass balance law the mass of oil in the feed solution equalsthe mass of oil in the retentate effluent plus that in the permeate which can beexpressed as

QfCf frac14 QpCp thorn QbCb (169)

where Qf represents the inflow rate Qp is the permeate flow rate and Qb is thevolumetric retentate outflow rate Cf Cp and Cb are the average oil concentrations ofinfluent permeate and retentate effluent respectively

The osmotic pressure difference at the exit of membrane module (ie Dpaexit) istherefore approximated by

Dpexit frac14 Dpmexit thorn Dpaexit frac14 p0Rt

1 YRtthorn Dpaexit (1610)

530 Advances in Membrane Technologies for Water Treatment

where p0 is the osmotic pressure of oily wastewater Dpm is the osmotic pressuredifference without concentration polarization Dpa is the osmotic pressure differencewith concentration polarization Rt is the observed rejection and Y is the targetrecovery rate

The pressure of wastewater to the treatment system should be higher than the os-motic pressure difference at the exit of membrane module in which DP is the appliedpressure and DPf is the pressure drop

DP DPf Dpexit frac14 p0Rt

1 YRtthorn Dpaexit (1611)

Here the average rejection is defined as

Rt frac14ZL

0

Rtdx=L (1612)

Equation (1612) is the thermodynamic limit for the cross-flow filtration processIt is shown that Dpexit would increase rapidly at high target recovery rates and so isthe required applied pressure The partial recovery rate Yx is defined as

Yx frac14 Y

Zx

0

jethxTHORNdxZL

0

jethxTHORNdx (1613)

Finally the rate of pump work or operating energy consumption of membrane pro-cess is normally calculated by

W frac14 Q DP

h(1614)

Here Q is the flow rate of pump and h is the efficiency of pump

166 Conclusions

Wastewater from the gas and petrochemical industries is widely treated via an acti-vated sludge process with oilewater separation Increasingly tightened environmentalregulations and the growing need to reuse treated water have generated interest in thetreatment of these wastewaters by the membrane process Integrated membrane sys-tems combined with different treatment technologies can help maximize water recov-ery achieve high water quality for water reuse and minimize life cycle costsConsequently it is clear that in the near future the use of membranes will growsubstantially for wastewater treatment from the gas and petrochemical industries

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 531

167 Future trends

For the gas and petrochemical industries the most significant waste stream is waterFor each barrel of oil produced 3e10 barrels of wastewater are generated If properlytreated about 95 of the water can be reinjected to enhance oil recovery However thefraction remaining is considerable consequently using cost-effective and efficienttechnology to reduce contaminants for water reuse or for discharge constitutes a chal-lenge for gas and petrochemical companies

To treat wastewater from the gas and petrochemical industries a suitable strategyfor the membrane process depends on the following major criteria

1 Source of wastewater and concentration of pollutants2 Final requirements for discharge recycle or reuse

Developing a fouling-resistant membrane will always be the core consideration forthis application

Nomenclature

A Membrane area (m2)C Solute concentration (ML)C1 Integral constant equal to the oil droplet permeate flux (Lm2 h)Cb Oil droplet concentration in the bulk solution of feed (vol )Cf Oil droplet concentration in permeate (vol )Cm Oil droplet concentration at the membrane surface (vol )

Cb Dimensionless form of average oil concentration of retentate effluent

Cf Dimensionless form of average oil concentration of influent

Cp Dimensionless form of average oil concentration of permeateD Diffusion coefficient of oil droplets (m2s)Dd Dielectric constantE Electric field gradient (Vm)J0w Permeate flux of pure water (Lm2 h)Jw Permeate flux of waste water (Lm2 h)n ConstantDP Applied pressure (bar)DPf Pressure drop (bar)Q Flow rate of pump (m3s)Qb Volumetric retentate outflow rate (m3s)Qf Inflow rate (m3s)Rm Intrinsic resistance of the clean membrane (Lm)Rt Observed rejection ()Rt Average rejection ()t Time of operation (s)v Electrophoretic velocity (mms)V Cumulative volume of filtrate (L)W Rate of pump work (KWh)

532 Advances in Membrane Technologies for Water Treatment

Y Target recovery rate ()Yx Partial recovery rate ()

Greek symbols

a Constantb Constantd Thickness of boundary layer (polarization layer) (m)ε0 Permittivity of vacuum (C2J m)h Efficiency of pumph0 Water viscosity (Nsm2)m Fluid viscosity (Pas)x Zeta potential (mV)p0 Osmotic pressure of oily wastewater (bar)Dpa Osmotic pressure difference with concentration polarization (bar)Dpm Osmotic pressure difference without concentration polarization (bar)

References

Adewumi M A Erb J E amp Watson R W (1992) Design considerations for a cost effectivetreatment of stripper oilwell produced water In J P Ray amp F R Engelhardt (Eds)Produced water TechnologicalEnvironmental issues and solutions (pp 511e523)New York Plenum Publishing Co

Almeida Neto A F Silva A A Valenzuela-Diacuteaz F R amp Rodrigues M G F (2006) Studyof organophilic clays in the adsorption of xylene and toluene In Proceedings of VIencontro Latino Americano de Pos-Graduaccedil~ao SP S~ao Joseacute dos Campos 2410 (inBrazilian)

Aptel P amp Clifton M (1986) Ultrafiltration In P M Bungay H K Lonsdale amp M N dePinho (Eds) Synthetic membrane Science engineering and applications DordrechtReidel Publishing Co

Asatekin A amp Mayes A M (2009) Oil industry wastewater treatment with fouling resistantmembranes containing amphiphilic comb copolymers Environmental Science and Tech-nology 43 4487e4492 httpdxdoiorg101021es803677k

Asatekin A Kang S Elimelech M amp Mayes A M (2007) Anti-fouling ultrafiltrationmembranes containing polyacrylonitrile-graft-poly (ethylene oxide) comb copolymeradditives Journal of Membrane Science 298(1e2) 136e146 httpdxdoiorg101016jmemsci200704011

Belkacem M Matamoros H Cabassud C Aurelle Y amp Cotteret J (1995) New results inmetal working wastewater treatment using membrane technology Journal of MembraneScience 106(3) 195e205 httpdxdoiorg1010160376-7388(95)00093-R

Bellhouse B J (1997) Membrane filters with corkscrew vortex generating means OxfordUnited Kingdom US Patent 5628909

Bhave R R amp Fleming H L (1988) Removal of oily contaminants in wastewater withmicroporous alumina membranes American Institute of Chemical Engineers SymposiumSeries 84(261) 19e27

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 533

Bilstad T amp Espedal E (1996) Membrane separation of produced water Water Science andTechnology 34 239e246 httpdxdoiorg101016S0273-1223(96)00810-4

Busch M amp Mickols W E (2004) Reducing energy consumption in seawater desalinationDesalination 165(0) 299e312 httpdxdoiorg101016jdesal200406035

Chai X Kobayashi T amp Fujii N (1998) Ultrasound effect on cross-flow filtrationof polyacrylonitrile ultrafiltration membranes Journal of Membrane Science 148(1)129e135 httpdxdoiorg101016S0376-7388(98)00145-8

Chung K Y Brewster M A amp Belfort G (1993) Dean vortices with wall flux in a curvedchannel membrane system IV Effect of vortices on permeation fluxes of suspensions inmicroporous membranes Journal of Membrane Science 81 139e150 httpdxdoiorg1010160376-7388(93)85038-X

Ciarapica F E amp Giacchetta G (2003) The treatment of produced water in offshore rigComparison between tradition installations and innovative systems In Fifth internationalmembrane science amp technology conference University of New SouthWales Sydney(in Australia)

Daiminger U Nitsch W Plucinski P amp Hoffmann S (1995) Novel techniques for oilwaterseparation Journal of Membrane Science 99(2) 197e203 httpdxdoiorg1010160376-7388(94)00218-N

Finnigan S M amp Howell J A (1989) The effect of pulsatile flow on ultrafiltration fluxes in abaffled tubular membrane system Transactions of the Institution of Chemical EngineersPart A 67 278e282

Garbutt C F (1997) Innovative treating processes allow steam flooding with poor quality oilfieldwater SPE annual technical conference and exhibition San Antonio TX (in USA)

Garbutt C F (1999)Water treatment process for reducing the hardness of an oilfield producedwater USA Marathon Oil Co US Patent 5879562

Gekas V amp Hallstreuroom B (1987) Mass transfer in the membrane concentration polarizationlayer under turbulent crossflow 1 Critical literature review and adaptation of existingSherwood correlations to membrane operations Journal of Membrane Science 30153e170 httpdxdoiorg101016S0376-7388(00)81349-6

Gupta B B Howell J A Wu D amp Field R W (1995) A helical baffle for crossflowmicrofiltration Journal of Membrane Science 102 31e42 httpdxdoiorg1010160376-7388(94)00241-P

Hamza A Pham V A Matsuura T amp Santerre J P (1997) Development of membraneswith low surface energy to reduce the fouling in ultrafiltration applications Journalof Membrane Science 131(1e2) 217e227 httpdxdoiorg101016S0376-7388(97)00050-1

Hansen B R amp Davies S R H (1994) Review of potential technologies for the removal ofdissolved components from produced water Chemical Engineering Research and Design72(2) 176e188

He Y amp Jiang Z W (2008) Technology review Treating oilfield wastewater Filter andSeparation 45(5) 14e16 httpdxdoiorg101016S0015-1882(08)70174-5

Henry J D Lawler L F amp Kuo C H A (1977) A solidliquid separation process based oncrossflow and electrofiltration American Institute of Chemical Engineers 23(6) 851e859httpdxdoiorg101002aic690230611

Hermia J (1982) Constant pressure blocking filtration laws Applications to power-law non Newtonian fluids Transactions of the Institution of Chemical Engineers60 183

Holdich R G amp Zhang G M (1992) Crossflow microfiltration incorporating rotational fluidflow Transactions of the Institution of Chemical Engineers Part A 70 527e536

534 Advances in Membrane Technologies for Water Treatment

Howell J A Field R W amp Wu D (1993) Yeast cell microfiltration Flux enhancementin baffled and pulsatile flow systems Journal of Membrane Science 80 59e71 httpdxdoiorg1010160376-7388(93)85132-G

Huotari H M Huisman I H amp Treuroagaringrdh G (1999a) Electrically enhanced crossflowmembrane filtration of oily waste waters using the membrane as a cathode Journal ofMembrane Science 156 49e60 httpdxdoiorg101016S0376-7388(98)00325-1

Huotari H M Treuroagaringrdh G amp Huisman I H (1999b) Crossflow membrane filtrationenhanced by an external DC electric field A review Chemical Engineering Research andDesign 77 461e468 httpdxdoiorg101205026387699526304

Jeffree M A Peakock J A Sobey I J amp Bellhouse B J (1981) Gel layer-limitedhemofiltration rates can be increased by vortex mixing Clinical and Experimental Dial-ysis and Apheresis 5 373e380 httpdxdoiorg10310908860228109076028

Jonsson G amp Johansen P L (1989) Selectivity of ultrafiltration membranes In J Yang ampC Yang (Eds) Indo-ECC membrane workshop New Delhi Department of Science andTechnology

Kim J amp DiGiano F A (2009) Fouling models for low-pressure membrane systemsSeparation and Purification Technology 68(3) 293e304 httpdxdoiorg101016jseppur200905018

Kim K J Sun P Chen V Wiley D E amp Fane A G (1993) The cleaning of ultrafiltrationmembranes fouled by protein Journal of Membrane Science 80 241e249 httpdxdoiorg1010160376-7388(93)85148-P

Knudsen B L Hjelsvold M Frost T K Grini P G Willumsen C F amp Torvik H (2004)Meeting the zero discharge challenge for produced water In Proceeding of the seventh SPEinternational conference on health safety and environment in oil and gas exploration andproduction Calgary Alberta (in Canada)

Kost J amp Langer R S (1988) Ultrasound enhancement of membrane permeability USAMassachusetts Institute of Technology US Patent 4780212

Lee J M amp Frankiewicz T (2005) Treatment of produced water with an ultrafiltration (UF)membrane-afieldtrial InSPEannual technicalconferenceandexhibitionDallasTX(inUSA)

Li L amp Lee R (2009) Purification of produced water by ceramic membranes Materialscreening process design and economics Separation Science and Technology 443455e3484 httpdxdoiorg10108001496390903253395

Li Y S Yan L Xiang C B amp Hong L J (2006) Treatment of oily wastewater byorganiceinorganic composite tubular ultrafiltration (UF) membranes Desalination 19676e83 httpdxdoiorg101016jdesal200511021

Makki H F Al-Alawy A F Al-Hassani M H amp Rashad Z W (2011) Membranesseparation process for oily wastewater treatment Journal of Engineering 17(2) 235e252

Manth T Gabor M amp Oklejas E (2003) Minimizing RO energy consumption under variableconditions of operation Desalination 157(13) 9e21 httpdxdoiorg101016S0011-9164(03)00377-1

Misra S K amp Skold R O (1999) Membrane filtration studies of inversely soluble modelmetalworking fluids Separation Science and Technology 34(1) 53e67 httpdxdoiorg101081SS-100100636

Mittal P Jana S amp Mohanty K (2011) Synthesis of low-cost hydrophilic ceramicepolymeric composite membrane for treatment of oily wastewater Desalination 28254e62 httpdxdoiorg101016jdesal201106071

Nakatsuka S Nakate I amp Miyano T (1996) Drinking water treatment by using ultrafiltrationhollow fiber membranes Desalination 106(1e3) 55e61 httpdxdoiorg101016S0011-9164(96)00092-6

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 535

Ochoa N A Masuelli M amp Marchese J (2003) Effect of hydrofilicity on fouling of anemulsified oil wastewater with PVDFPMMA membranes Journal of Membrane Science226 203e211 httpdxdoiorg101016jmemsci200309004

OSPAR Commission Background document concerning techniques for the management ofproduced water from offshore installations Retrieved from httpwwwosparorgdocumentsdbasepublicationsp00162Techniques20for20the20management20of20Produced20Waterpdf

Qi B Wang Y Xu S Wang Z amp Wang S (2012) Operating energy consumption analysisof RO desalting system Effect of membrane process and energy recovery device (ERD)performance variables Industrial and Engineering Chemistry 51 14135e14144 httpdxdoiorg101021ie300361e

Scott K (1995) Handbook of industrial membranes Oxford UK ElsevierSerra C A Wiesner M R amp Laicircneacute J M (1999) Rotating membrane disk filters Design

evaluation using computational fluid dynamics Chemical Engineering Journal 72 1e17httpdxdoiorg101016S1385-8947(98)00128-4

Song L (1998) Flux decline in crossflow microfiltration and ultrafiltration mechanisms andmodeling of membrane fouling Journal of Membrane Science 139(2) 183e200 httpdxdoiorg101016S0376-7388(97)00263-9

Sweet J R (1990) Pressure induced surfactant recovery during ultrafiltration of water-oilemulsions Florham Park NJ Exxon Research and Engineering Co US Patent 4892660

Thomas D G (1973) Forced convection mass transfer in hyperfiltration at high fluxesIndustrial and Engineering Chemistry Fundamentals 12 396e405 httpdxdoiorg101021i160048a002

Ulbricht M (2006) Advanced functional polymer membranes Polymer 47 2217e2262httpdxdoiorg101016jpolymer200601084

USEPA Website httpwwwepagovWakeman R J (1982) Effects of solids concentration and pH on electrofiltration Filtration amp

Separation 19 316Wakeman R J amp Tarleton E S (1991) An experimental study of electroacoustic

crossflow microfiltration Transactions of the Institution of Chemical Engineers Part A 69386e397

Wakeman R J amp Williams C J (2002) Additional techniques to improve microfiltrationSeparation and Purification Technology 26 3e18 httpdxdoiorg101016S1383-5866(01)00112-5

Winzeler H B (1990) Membran-filtration mit hoher Trennleistung und minimalen Ener-giebedarf CHIMIA International Journal for Chemistry 44(4) 288e291

Winzeler H B amp Belfort G (1993) Enhanced performance for pressure-driven membraneprocesses The argument for fluid instabilities Journal of Membrane Science 80 35e47httpdxdoiorg1010160376-7388(93)85130-O

Wronski S Molga E amp Rudniak L (1989) Dynamic filtration in biotechnology BioprocessEngineering 4 99e104 httpdxdoiorg101007BF00369757

Wu D Howell J A amp Field R W (1993) Pulsatile flow filtration of yeast cell debrisInfluence of preincubation on performance Bioengineering and Biotechnology 41998e1002 httpdxdoiorg101002bit260411011

Yunus R M amp Jones M (1995) Enhancement of tubular crossflow microfiltration of yeastsuspensions by ultrasonic force field In G Akay amp B J Azzopardi (Eds) Proceedings ofIst international conference on science engineering and technology of intensive processing(pp 189e192) Nottingham

536 Advances in Membrane Technologies for Water Treatment

Membrane technologiesfor water treatment and reusein the textile industry

17I Petrinic1 N Bajraktari2 C Heacutelix-Nielsen121University of Maribor Maribor Slovenia 2Technical University of DenmarkLyngby Denmark

171 Introduction

The textile industry is one of the largest consumers of water and chemicals for wet pro-cessing of textiles (Banat Nigam Singh amp Marchant 1996) This has led toincreasing environmental concerns thus control of water pollution is an importantissue Here we will review some aspects related to the treatment of textile wastewaterwith special emphasis on membrane processes

Textile processing is complex and includes sizing where various types of water-soluble polymers also called textile sizing agents such as modified starch polyvinylalcohol carboxymethyl cellulose and acrylates are used to increase the strength of theyarn for weaving scouring (eg detergent treatment) bleaching mercerizing (wheresodium hydroxide is added to provide lustrous appearance and strength to cotton)carbonizing (adding acid followed by baking and thereby removing (carbonized)impurities from wool dyeing and finishing) Consequently wastewater pollutants ariseboth from raw fabrics and a wide range of additives used to produce the finished prod-uct In textile wastewater treatment one therefore has to deal with pollutants spanninga wide range including nonbiodegradable highly persistent organics and pesticidesused in speciality textiles such as insect-proof fabrics

Organic matter represents the main emission load for textile wastewater which sug-gests treatment based on biological processes However the introduction of effectiveand sustainable water recycling techniques in this branch of production is often pre-vented by recalcitrant organic compounds and remaining dyes Because of the poorbiodegradability and sometimes even toxicity of the textile wastewater componentsadvanced treatment technologies are necessary Especially if reuse of treated waste-water is the objective extensive removal of organic contents as well as almost com-plete decolourization is required

Industrial wastewater streams can vary greatly in their composition within a plantand even during the same process over short periods of time For wastewater treatmentto be practical in this situation wide processing latitude is required to accommodateinherent variability The textile industry provides examples of this variability in batchprocesses such as dyeing printing finishing and washing as well as frequent changes

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400017-4Copyright copy 2015 Elsevier Ltd All rights reserved

in product runs In addition to this variability in water content many productionprocess reactions are incomplete leaving varying amounts of residue chemicals inthe processed water

When dyeingprinting textiles water serves two purposes First it ensures the trans-mission of the colour onto the fibre second it washes out excess amounts of dyes fromthe treated fabrics Of all dyedprinted textile fibres cellulose fibres stands out as themost prominent and more than 50 of production is dyedprinted with a special classof dyes the so-called reactive dyes Over 80000 tons of reactive dyes are producedand consumed each year which makes it possible to estimate the total pollution causedby their use (Allegre Moulin Maisseu amp Charbit 2006) They are adsorptive to thecellulose fibres and the hydrolysed dyestuff requires large amounts of water prefer-ably at high temperatures to be properly washed out Unfortunately this class ofdyes is also the most unfavourable from an ecological point of view because the ef-fluents produced are heavily coloured and contain high concentrations of salt andexhibit high biochemical oxygen demand (BOD) and chemical oxygen demand(COD) values (Allegre et al 2006)

172 Textile wastewater

A detailed source analysis of coloured wastewater released by a dyeprinting houseindicated that 15e30 of the applied dyestuff is released into the wastewater Themain portion corresponding to 50e80 of this amount results from the washingrinsing stages and thus has been diluted to average concentrations of 1e2 gl (Bechtoldamp Turcanu 2004) Wastewater containing reactive dyes is considered problematicbecause it is removed less efficiently compared with other dye classes in which waste-water can be processed by activated sludge sewage treatment (Pierce 1994) More-over fixation of the reactive dyes on the textile fabric is low 70 on averagecompared with other dye classes (over 90 on average)

In addition to reactive dyes the textile industries are dominated by the use of directdyes acidbasic dyes and disperse dyes depending on the material to be processedThus for example for polyester disperse dyes are most common whereas for blendedfabrics a mixture of reactive dyes and acid dyes is typically used For polyester andnylon mixtures disperse dyes and acid dyes are blended For nylon alone a mixtureof reactive dyes disperse dyes and acid dyes is used See Table 171 for a list of com-mon dyes found in textile wastewater

A particular problematic group of dyes is constituted by the so-called azo dyes(containing eNfrac14Ne bonds) because they and their metabolites may be mutagensand carcinogens (Chang et al 2001 Pandey Singh amp Lyengar 2007 _ZyłłaSojka-Ledakowicz Stelmach amp Ledakowicz 2006) Azo dyes commonly used inthe textile industry include reactive acid and direct dyes (You amp Teng 2009) Theyare aromatic compounds that make up the largest and most diverse group of syntheticdyes found in the wastewaters of dyefrac14 using industries such as textile paper printingfood and cosmetic industries

538 Advances in Membrane Technologies for Water Treatment

173 Treatment of textile wastewater

These wastewater streams are usually collected together and after eventual pH adjust-ment sent to communal wastewater treatment plants Methods for wastewater treat-ment have to focus on the cleaning of wastewater streams originating fromindividual textile processes In practice realization of this process is difficult Suitabletechnologies for the treatment of individual streams are used only when the dyeingprocess is well-defined andor when a wastewater stream contains materials that canbe separated out and reused in the finishing processes When treating textile waste-water for reuse by the industry colour removal as well reduction in total suspendedsolids (TSS) BOD COD and nonbiodegradable substances must be addressed inthe primary treatment stage

Therefore advanced treatment processes are required to improve the quality of thetreated wastewater up to reuse criteria (Feng Xu Li You amp Zhen 2010) Many treat-ment methods for textile wastewater have been investigated including (1) treatmentusing lime and alum This method generates large quantities of hazardous sludge and isgenerally ineffective in removing colour TSS BOD and COD (2) biological treat-ment with aeration to reduce BOD and COD levels (3) chlorination that successfullyremoves colour (eg as sodium hypochloride [NaOC])-based attack of dye moleculeamino bonds) Although this method reduces BOD and COD it produces chloro-organic compounds that are potentially carcinogenic and therefore not eco-friendly(4) ozonation with or without ultraviolet irradiation and (5) sorption usingH2O2eFe(II) salt and cucurbituril Other methods include adsorption (eg via acti-vated carbon peat wood chips fly ash and silica gels) ion exchange (for cationic

Table 171 Examples of dye components in textile wastewater

Dye class CI name Commercial name

Reactive Reactive Red 120 Suncion Red H-E3B

Reactive Blue 160 Sunicon Blue H-ERN

Reactive Yellow 84 Sunicon Yellow H-Z4RN

Acid Acid Red 57 Nylosan Red E-BL

Acid Blue 72 Nylosan Blue E-GL

Acid Yellow 256 Nylosan Yellow E-2RL

Disperse Disperse Red 60 PALANIL Red FD-BFY

Disperse Blue 56 DZANIX Blue E-R

Disperse Yellow 54 PALANIL Yellow 3GZ

CI Colour Index International is a reference database jointly maintained by the Society of Dyers and Colourists and theAmerican Association of Textile Chemists and ColouristsSource Partially adapted from Choi et al (2003)

Membrane technologies for water treatment and reuse in the textile industry 539

and anionic dyes) irradiation electron beams (combined with oxygenation) and elec-trokinetic coagulation (using added ferrous sulphate or ferric chloride) see (RobinsonMcmullan Marchant amp Nigam 2001) for a review of chemical and physicaltreatments

Because of their complex chemical structure dyes are generally resistant to fadingon exposure to light water and many chemicals When decolourization of waterpolluted with organic colorants occurs it takes place by reduction of eCfrac14Ce andeNfrac14Ne bonds and heterocyclicaromatic rings (Slokar amp Le Marechal 1998) Theazo (eNfrac14Ne) bonds (as well as sulfonic (eSO3) groups) are electron-withdrawinggroups and this generates electron deficiency within the molecule making the com-pound less susceptible to oxidative catabolism by bacteria (You amp Teng 2009)

Consequently decolouration of textile dye effluent is not normally observed whenthe textile wastewater is treated aerobically by municipal sewerage systems (Changet al 2001 Pandey et al 2007 _Zyłła et al 2006) Therefore anaerobic systemshave been used to cleave azo bonds in the treatment of textile wastewater (Dos SantosCervantes amp Van Lier 2007 Orsquoneill Hawkes Hawkes Esteves amp Wilcox 1999)and many bacterial groups possess enzymes (ie azo-reductases) capable of disruptingthe azo bonds under anaerobic conditions ( _Zyłła et al 2006) The anaerobic degrada-tion product is colourless aromatic amines that are carcinogenic but these aromaticamines can then be readily degraded via aerobic digestion by nonspecific enzymesthrough hydroxylation and ring opening of the aromatic compounds (Sponza amp Isik2005) Mineralization of the azo dyes is complete when the aromatic amines havebeen biodegraded to carbon dioxide (CO2) water (H2O) and ammonia (NH3) (Sponzaamp Isik 2005 Van Der Zee amp Villaverde 2005) Thus for complete mineralization ofazo dyes a combination of reductive (anaerobic) and oxidative (aerobic) steps arerequired (Dafale et al 2010 Kodam amp Gawai 2006 Kodam Soojhawon Lokhandeamp Gawai 2005)

Recently membrane bioreactor (MBR) technology has attracted interest for waste-water treatment (Badani Ait-Amar Si-Salah Brik amp Fuchs 2005 Banat et al1996 Brik Schoeberl Chamam Braun amp Fuchs 2006 Pierce Lloyd amp Guthrie2003) Conventional MBR is operated at aerobic conditions and therefore is not suit-able for dye degradation However anoxic or anaerobic MBR for dye wastewatertreatment has been investigated and shows some potential for a review onMBR-based textile wastewater treatment see Simonic (2013) However it hasalso been reported that the anoxic phase or low dissolved oxygen (DO) conditions(DO lt 03 mgl) have a negative effect on membrane permeability in the MBR pro-cess because low oxygen concentration leads to poorer flocculated activated sludge(Kang amp Lee 2004) Also biofouling is a major issue of concern in MBR processesbecause colony buildup on the membrane surface decreases water permeability(Lewandowski 2004)

A physical method gaining increasing general interest for wastewater treatment isdirect membrane separation because this can be used to recycle valuable components(and energy) as well as lower overall operating costs by lowering the volume of waste-water to be delivered to the wastewater treatment plant Membrane techniques char-acterized by their ability to clarify concentrate and continuously separate are

540 Advances in Membrane Technologies for Water Treatment

therefore potentially interesting for textile wastewater effluent treatment includingpotential recycling of dyes

1731 Membrane filtration in textile wastewater treatment

Processes using membranes provide possibilities for separating hydrolysed dyestuffsand auxiliaries thus simultaneously reducing coloration Over the past few yearstechnical and economical improvements have made treatment of wastewater bymembrane systems increasingly advantageous over conventional treatment processes(Porter 1999 Rozzi et al 1999 Sojka-Ledakowicz Koprowski Machnowski ampKnudsen 1998) The most notable outcome of the membrane treatment is the supe-rior quality of the produced water which is attained by adding fewer chemicals overconventional water treatment processes In addition membrane plants can be muchsmaller than conventional wastewater treatment plants because of the modularconfiguration of the membranes and the possible elimination of other processes(eg clarification) Traditional membrane processes studied in textile wastewatertreatment include the use of ultrafiltration (UF) nanofiltration (NF) and reverseosmosis (RO) membranes in which the selection of membrane technologies fortextile effluent relies on costs based on the balance between water flux and soluteretention

Ultrafiltration membranes have been successfully applied in many industries butthey have not been as widely accepted by the textile industry because they do notremove low-molecular-weight dyes There are examples of micelle-enhanced use ofUF membranes for dye removal (Ahmad amp Puasa 2007 Zaghbani Hafiane ampDhahbi 2007) but in general the rejection range from 30 to 90 makes the directuse of UF membranes impossible and further filtration is required by either RO orNF membranes In RO problems with fouling are present that result in low fluxesowing to the dense polymeric membrane used and poor separation Reverse osmosisalso becomes less effective when osmotic pressure caused by high salt concentrationin the feed wastewater becomes too high to obtain a reasonable transmembranepermeate flux without applying excess transmembrane hydraulic pressure In this sit-uation NF provides a possible alternative maintaining high dye rejections albeit withthe cost of lower rejection of electrolytes

Nanofiltration membranes have been used to recover salt from used dyeing baths(Erswell Brouchaert amp Buckley 1988 Gonzalvez-Zafrilla Sanz-Escribano Lora-Garciacutea amp Leon Hidalgo 2008 Petrinic Andersen SOstar-Turk amp Le Marechal2007 He et al 2009 Koyuncu 2003 Koyuncu Kural amp Topacik 2001) wherethe principle is that electrolytes will pass through the membrane as the dyes are rejectedHowever this principle requires the use of sufficiently small electrolytes For exampleNa2SO4 which often is used as electrolyte is rejected by the NF membrane limitingthe feasibility of this approach Also standard electrolytes (such as NaCl) are nothigh-value products An NF process for the treatment of mixed waste streams fromthe reactive dyeing process has been developed using this principle (Rautenbach ampMellies 1994) in which the retentate is further treated in a wet oxidation processThe effective desalination of the retentate by the NF membrane is desired because

Membrane technologies for water treatment and reuse in the textile industry 541

this diminishes electrolyte corrosion in the wet oxidation Nanofiltration-based dyeretention can be effective and retentions up to 99 with a permeate flux of 64 lm2 h have been obtained (Tegtmeyer 1993)

Reverse osmosis membranes have also been used in textile wastewater treatment(Suksaroj Heacuteran Allegre amp Persin 2005) One example of this used a combinationof RO membranes designed for brackish and seawater desalination (Treffry-GoatleyBuckley amp Groves 1983) Thus the brackish water RO membrane is used in the firststage and the seawater RO membrane is used in the second stage In this way the reten-tate is recycled in the second stage to obtain high water recovery and the cross-flowvelocity is kept high to minimise membrane fouling Using this two-stage RO processwater recovery is 85e95 with a mean permeate flux of 15 lm2 h

In a comparative study (Bonomo 1992) pilot plant tests with UF NF and RO treat-ment of wastewater from washing processes subsequent to reactive dyeing processesare described Ultrafiltration membrane treatment leaves the permeate stream colour-ized whereas NF membrane treatment results in efficient permeate decolourizationwith a flux of 70 lm2 h at 10 bar The RO membrane both decolourizes and desalinatesthe waste stream Interestingly the reactive dyes retention was somewhat lower than inthe NF process despite the use of the denser RO membrane Severe membrane foulingwas observed when the waste stream contained dispersed dyes together with reactivedyes which illustrates the important issue of membrane fouling when treating complexwastewaters

To elucidate fouling effects synthetic waste streams mimicking actual wastestreams can be analysed (Fritsch 1993) This approach would in principle make itpossible to relate the permeate flux decline to certain components or a combinationof component presents in the actual waste stream One could thus make a list of no-go components in dyeing and washing if the resulting wastewater is to be treated effi-ciently by membrane filtration processes In general pressure-driven processes such asUF NF and RO are all prone to fouling typically caused by the presence of naturalorganic matter (NOM) (Li amp Elimelech 2004) and biofouling (Vrouwenvelder ampVan Der Kooij 2001) With textile wastewater as a membrane feed stream this issuebecomes particularly important and it is therefore necessary to address this issue Thiscan be done in principle by making no-go list of components (ie components withstrong fouling propensity) Another more general strategy is to consider alternativesto pressure-driven processes

1732 Osmotic-based wastewater reduction and potentialdye recovery

In contrast to pressure-driven processes FO is less prone to fouling and FO-based sys-tems are attracting increasing interest in water treatmentengineering applications fora wide variety of aqueous solutions (Achilli Cath Marchand amp Childress 2009Cath Childress amp Elimelech 2006 Coday Yaffe Xu amp Cath 2014 Cornelissenet al 2008 Holloway Childress Dennett amp Cath 2007 Klaysom Cath Depuydtamp Vankelecom 2013 Teoh et al 2008) Thus FO has been used to treat industrialwastewaters (at bench-scale) to concentrate landfill leachate at pilot- and full-scale

542 Advances in Membrane Technologies for Water Treatment

(Beaudry Herron amp Peterson 1999 York amp Beaudry 1999) and to treat liquid foodsin the food industry at bench-scale (Dova Petrotos amp Lazarides 2007ab PetrotosLazarides Wolf Behsnilian amp Spiess 2001) Forward osmosis is also being evalu-ated for reclaiming wastewater for potable reuse in life support systems (atdemonstration-scale) for desalinating seawater and for purifying water in emergencyrelief situations for a detailed review see Cath et al (2006) Although no scientificreports on direct FO in the textile wastewater treatment have appeared so far CatalyxInc of Anaheim California have reported an FO-based system for recycling difficult-to-treat high-BOD and high-COD carpet-dyeing wastewater (Atkinson 2009) Thusthe FO technology can be seen as an addition to existing membrane processes such asUF NF and RO which are commonly used in textile wastewater treatment today

For FO there is no hydraulic pressure across the membrane For RO the appliedhydraulic pressure must exceed the osmotic pressure and convectively drive the waterfrom low to high water chemical potential For pressure-assisted osmosis (PAO) hy-draulic pressure is applied in the same direction as the water flow For PRO the hy-draulic pressure retards the FO process but the effective hydraulic pressure is stillless than the osmotic pressure In all cases the osmotic pressure difference acrossthe membrane can be approximated as the difference in osmotic pressure of each so-lution In ideal solutions the osmotic pressure p can be determined from the Morseequation p frac14 iMRT where i is the vanrsquot Hoff factor M is the molarity R is thegas constant and T is temperature Figure 171 schematically shows the four processesFO RO PAO and PRO

Forward osmosis operates by concentrating a feed solution (FS) and diluting a high-ly concentrated aqueous solution e the draw solution (DS) The larger osmotic pres-sure of the DS compared with the FS constitutes the driving force for the separationprocess Thus FO is an osmotic concentration process that in principle can operateat zero hydrostatic pressure providing a sustainable water treatment solution

Forward osmosis is not implemented on a large scale for several reasons There areat least three lsquomust-winrsquo battles to successfully overcome before FO becomes a large-scale technology comparable with established technologies such as RO First a newtype of membrane is needed that has to be very thin to minimise internal concentrationpolarization (Klaysom et al 2013) Second good DSs are needed the most studiedcurrently are ammonium bicarbonateebased DSs (Mccutcheon Mcginnis ampElimelech 2006) and their use poses several problems including unfavourable interac-tions with known (conventional) membrane materials Third a new system solutionan FO membrane cannot simply replace an RO membrane in conventional membranemodules (Gruber et al 2011 2012) Until good FO membranes and DSs are availablefor major industrial applications no system provider is likely to begin designing newFO-based systems

Recently a cellulose triacetate (CTA) FO membrane with an embedded supportscreen stabilizing a dense rejection layer (10e20 mm thick) and thin-film composite(TFC) membranes were commercialized by Hydration Technologies Inc (HTI) Sofar the use of these membranes has focused on low-volume nutrient drink production(Salter 2006) Thus a concentrated nutrient solution with a high osmotic pressure isused as DS where unsafe water as FS is purified through the FO membrane with a salt

Membrane technologies for water treatment and reuse in the textile industry 543

rejection between 93 and 95 However when operated in a high-volume applica-tion setup the HTI CTA membrane water flux is still low (lt 6 lm2 h) although theHTI TFC membrane seemingly has a flux that is double that of the HTI CTA mem-brane In comparison for RO membranes water fluxes can reach 75 lm2 h althoughtypical values are around 30 lm2 h (Xu Peng Tang Shiang Fu amp Nie 2010)However water flux and solute retention have to be evaluated together when evalu-ating membrane performance

One way to increase water flux across the membrane while preserving rejection ofsolutes is to enable facilitated water diffusion across the active layer This has beenstudied intensively over the last few years where in particular the use of naturersquosown selective water channels e aquaporin proteins e have attracted considerable in-terest for a review see Tang Zhao Wang Heacutelix-Nielsen and Fane (2013) and for ageneral review of the biomimetic approach to membrane technology see Nielsen(2009) Aquaporins constitute a large family of membrane spanning proteins for re-views see Fu and Lu (2007) Gonen and Walz (2006) and Ludewig and Dynowski(2009) Much has been revealed about this class of proteins since the purification ofa red blood cell membrane protein and subsequent heterologous expression of this pro-tein revealing rapid water diffusion along osmotic gradients

P

P

P

J J

JJ

Δ

Δ

Δ

(a) (b)

(d)(c)

Figure 171 Osmotic processes Water flux (J) versus hydraulic pressure (DP) in (a) forwardosmosis (FO) (b) reverse osmosis (RO) (c) pressure-assisted osmosis (PAO) and (d) pressure-retarded osmosis (PRO)

544 Advances in Membrane Technologies for Water Treatment

Recently a design was developed in which vesicles are embedded in thin (200 nm)films deposited on a porous support (Zhao et al 2012) Briefly a microporous poly-sulfone substrate was soaked with an m-phenylene-diamine aqueous solution that con-tained aquaporin vesicles The soaked substrate was subsequently exposed totrimesoyl chloride to form a three-dimensionally cross-linked polyamide layer inwhich the aquaporin vesicles are embedded The resulting membranes are made insheets up to 600 cm2 and are sufficiently stable to allow normal handling and shippingprocedures

The resulting TFC membrane has been characterized in cross-flow RO and FOsetups Reverse osmosis membranes were tested under applied pressures up to14 bar and benchmarked against commercially available RO membranes (Zhaoet al 2012) Compared with the control membranes (membranes with protein-freevesicles and membranes with protein vesicles in which the protein was mutated toan inactive form) the aquaporin TFC membranes achieved significantly higher waterpermeability (w4 lm2 h bar) with comparable NaCl rejection (w97) Their perme-ability was w40 higher compared with a commercial brackish water RO membrane(Dow Filmtec BW30) and an order of magnitude higher compared with a seawater ROmembrane (Dow Filmtec SW30HR) In FO the aquaporin membranes had greater than90 rejection of urea with a water flux of 10 lm2 h with 2 M NaCl as draw solutionThis clearly demonstrates the great potential of the aquaporin TFC membranes for in-dustrial RO and FO applications in 2014 the Danish Cleantech company AquaporinAS began commercializing membranes as aquaporin inside membranes (AIM)based on this design

Whether the FO membranes are to be used for wastewater volume reduction andorrecovery of dyes a key question is whether the reactive dyes can be processed by themembranes A simple test for this is to try and up-concentrate dyes using an FO mem-brane process Because Nylosan dyes are acid dyes applicable for polyamide we testedwhether this class of dye can be processed using the aquaporin polyamide TFC designas described without damaging the membrane

Specifically we tested two different dyes Nylosan Blue E-GL250 and Nylosan RedE-BL18 for up-concentration assays with FO AIM provided by Aquaporin AS (seeFigure 172) Fifty milligrams of the blue dye is solved in 100 ml milliQ water togenerate a stock solution of 500 mmml The stock solution is then diluted to encom-pass a dilution series from 200 to 5 mgml A broad range wavelength scan from 200 to800 nm is used to detect the optimal absorbing wavelength for the dye (620 nm forNylosan Blue E-GL250 and 513 nm for Nylosan Red E-BL18) The optical density(OD) value is measured for the different concentrations and standard curves are plottedrelating the OD value to the concentration

Because of the osmotic gradient over the membrane water from the dye solutionwill be extracted through the AIM membrane resulting in up-concentration of thedye The OD is then measured for the up-concentrated dye solution and the concentra-tion is calculated from the standard curves In a successful up-concentration experi-ment the up-concentration factor of the dye solution (light grey bars) follows thevolume reduction factor (dark grey bars) In none of the experiments was dye detectedin the draw solution The results are summarized in Figure 172

Membrane technologies for water treatment and reuse in the textile industry 545

174 Conclusions

In general wastewater represents challenging feed streams to be treated by membraneseparation In particular the large variability in composition and the presence of poten-tially reactive components makes textile industry wastewater a particularly difficulttask for any remediation technology including membrane-based methods To datemembrane technology for textile wastewater has been based on RONFUF-based sys-tems Also MBR technology has attracted considerable interest however the require-ments for low oxygen and the general issue of biofouling present problems forbioreactors to function properly Also the large variation in water composition eeven from the same textile process and plant e is a major obstacle in introducingMBR in textile wastewater treatment Recent technological developments of FO mem-branes have opened up the possibility of using this technology in industrial processesand wastewater treatment The inherent low fouling propensity of FO membranesmakes them an intriguing supplement to existing remediation methods Thus FOcan in principle be used to concentrate the wastewater e eg using seawater as adraw solution e thereby reducing the hydraulic load on the wastewater treatmentplant e with diluted seawater being the discharged water stream Forward osmosismay also be used in up-concentration of dyes directly as exemplified by biomimeticaquaporin-based FO membranes

Up-concentration of textile dyes10

9

8

7

6

5

4

3

2

1

0Vol Vol Vol Vol Vol VolConc Conc Conc Conc Conc Conc

Nylosan Red E-BL180Nylosan Blue E-GL250

Up-

conc

entr

atio

n fa

ctor

(x ti

mes

)

88

7

55

437

637

427 404435

56 556

4

48

Figure 172 Experimental results for up-concentration of Nylosan Blue E-GL and Nylosan RedE-BL (n frac14 3 for each dye) with starting concentrations of 10 and 20 mgml respectively Theup-concentration assay is carried with an FO membrane module The dye solution to be up-concentrated is placed in the reservoir well of the upper part of the module while on the bottompart an osmotic draw solution (here 1 M NaCl) is recirculated The module is connected to aperistaltic pump by tubing to ensure the recirculation of the draw solution at 50 mlmin Thevolume concentration factor (Vol) and concentration factor for the dye (Conc) reflect volumereduction and dye up-concentration factor respectively

546 Advances in Membrane Technologies for Water Treatment

List of abbreviations

AIM Aquaporin inside membraneBOD Biological oxygen demandCMC Carboxymethyl celluloseCOD Chemical oxygen demandCTA Cellulose triacetateDO Dissolved oxygenDS Draw solutionFO Forward osmosisFS Feed solutionMBR Membrane bioreactorMPD m-phenylene-diamineNF NanofiltrationNOM Natural organic matterOD Optical densityPAO Pressure-assisted osmosisPRO Pressure-retarded osmosisPVA Polyvinyl alcoholRO Reverse osmosisTFC Thin-film compositeTMC Trimesoyl chlorideTSS Total suspended solidsUF Ultrafiltration

References

AchilliACath TYMarchandEAampChildressAE (2009) The forwardosmosismembranebioreactor A low fouling alternative to MBR processes Desalination 239 10e21

Ahmad A L amp Puasa S W (2007) Reactive dyes decolourization from an aqueous solutionby combined coagulationmicellar-enhanced ultrafiltration process Chemical EngineeringJournal 132 257e265

Allegre C Moulin P Maisseu M amp Charbit F (2006) Treatment and reuse of reactivedyeing effluents Journal of Membrane Science 269 15e34

Atkinson S (2009) High BOD and COD carpetdyeing wastewater recycled using forwardosmosis Membrane Technology 2009 1e8

Badani Z Ait-Amar H Si-Salah A Brik M amp Fuchs W (2005) Treatment of textilewastewater by membrane bioreactor and re-use Desalination 185 411e417

Banat I M Nigam P Singh D amp Marchant R (1996) Microbial decolorization of textile-dye-containing effluents A review Bioresource Technology 58 217e227

Beaudry E G Herron J R amp Peterson S W (1999) Direct osmosis concentration of wastewater Final report Corvallis OR Osmotek Inc

Bechtold T amp Turcanu A (2004) Cathodic decolourisation of dyes in concentrates from nano-filtration and printing pastes Journal of Applied Electrochemistry 34 903e910

Bonomo L (1992) Nanofiltration and reverse osmosis treatment of textile dye effluentsRecents Progress en Genie des Precedes 6 327e336

Membrane technologies for water treatment and reuse in the textile industry 547

Brik M Schoeberl P Chamam B Braun R amp Fuchs W (2006) Advanced treatment oftextilewastewater towards reuse using a membrane bioreactor Process Biochemistry 411751e1757

Cath T Y Childress A E amp Elimelech M (2006) Forward osmosis Principles applicationsand recent developments Journal of Membrane Science 281 70e87

Chang J-S Chou C Lin Y-C Lin P-J Ho J-Y amp Hu T L L W R (2001) Kineticcharacteristics of bacterial azo-dye decolourization by Pseudomonas luteola WaterResearch 35(12) 2841e2850

Choi J-S Ahn S-J Ryu S-H Jun J-P Choi C-G Han B-S et al (2003) A study onthe removal of color in dyeing wastewater using electron beam irradiation In Proceedingsof a consultants meeting Status of industrial scale radiation treatment of wastewater andits future (pp 67e79) South Korea Daejon 13e16 October

Coday B D Yaffe B G Xu P amp Cath T Y (2014) Rejection of trace organic compoundsby forward osmosis membranes A literature review Environmental Science andTechnology 48 3612e3624

Cornelissen E R Harmsen D De Korte K F Ruiken C J Qin J J Oo H et al (2008)Membrane fouling and process performance of forward osmosis membranes on activatedsludge Journal of Membrane Science 319 158e168

Dafale N Agrawal L Kapley A Meshram S Purohit H amp Wate S (2010) Selection ofindicator bacteria based on screening of 16S rDNA metagenomic library from a two-stageanoxic-oxic bioreactor system degrading azo dyesBioresource Technology 101 476e484

Dos Santos A B Cervantes F J amp Van Lier J B (2007) Review paper on currenttechnologies for decolourisation of textile wastewaters Perspectives for anaerobictechnologies Bioresource Technology 98 2369e2385

Dova M I Petrotos K B amp Lazarides H N (2007a) On the direct osmotic concentration ofliquid foods Part I Impact of process parameters on process performance Journal of FoodEngineering 78 422e430

Dova M I Petrotos K B amp Lazarides H N (2007b) On the direct osmotic concentration ofliquid foods Part II Development of a generalized model Journal of Food Engineering78 431e437

Erswell A Brouchaert C J amp Buckley C A (1988) The reuse of reactive dye liquors usingcharged ultrafiltration membrane technology Desalination 70 157e167

Feng F Xu Z Li X You W amp Zhen Y (2010) Advanced treatment of dyeing wastewatertowards re-use by the combined Fenton oxidation and membrane bioreactor processJournal of Environmental Sciences 22 1657e1665

Fritsch J (1993) Untersuchungen der Aufbereitung von Abwassern aus Textilbleichern mittelsNanofiltration Aachen Aachner Membrane Kolloquium

Fu D amp Lu M (2007) The structural basis of water permeation and proton exclusion inaquaporins Molecular Membrane Biology 24 366e374

Gonen T amp Walz T (2006) The structure of aquaporins Quaterly Reviews Biophysics 39361e396

Gonzalvez-Zafrilla J M Sanz-Escribano D Lora-Garciacutea J amp Leon Hidalgo M C (2008)Nanofiltration of secondary effluent for wastewater reuse in the textile industry Desali-nation 222 272e279

Gruber M F Johnson C Tang C Y Jensen M H Yde L amp Heacutelix-Nielsen (2011)Computational Fluid Dynamics simulations of flow and concentration polarization inforward osmosis membrane systems Journal of Membrance Science 379 488e495

Gruber M Johnson C E Tang C Jensen M H Yde L amp Heacutelix-Nielsen C (2012)Validation and analysis of forward osmosis CFD model in complex 3D geometriesMembranes 2 764e782

548 Advances in Membrane Technologies for Water Treatment

He Y Li G Wang H Jiang Z Zhao J Su H amp Huang Q (2009) Experimental study onthe rejection of salt and dye with cellulose acetate nanofiltration membrane Journal ofTaiwan Institute of Chemical Engineers 40 289e295

Holloway R W Childress A E Dennett K E amp Cath T Y (2007) Forward osmosis forconcentration of anaerobic digester centrate Water Research 41 4005e4014

Kang I J amp Lee C H (2004) Effect of aerobic period on microfiltration performance in amembrane-coupled sequencing batch reactor Journal of Industrial and EngineeringChemistry 10 146e151

Klaysom C Cath T Y Depuydt T amp Vankelecom I F (2013) Forward and pressureretarded osmosis Potential solutions for global challenges in energy and water supplyChemical Society Reviews 42 6959e6989

Kodam K M amp Gawai K R (2006) Decolourisation of reactive red 11 and 152 azo dyesunder aerobic conditions Indian Journal of Biotechnology 5 422e424

Kodam K M Soojhawon I Lokhande P D amp Gawai K R (2005) Microbial decolour-isation of reactive azo dyes under aerobic conditions World Journal of Microbiology andBiotechnology 21 367e370

Koyuncu I (2003) Influence of dyes salts and auxiliary chemicals on nanofiltration of reactivedye baths Experimental observations and model verification Desalination 154 79e88

Koyuncu I Kural E amp Topacik D (2001) Pilot-scale nanofiltration membrane separation forwastewater management in the textile industryWater Science and Technology 43 233e240

Lewandowski Z (2004) Biofilms Their structure activity and effect on membrane filtrationProceedings of IWA Specialty Conference 2 417e431

Li Q amp Elimelech M (2004) Organic fouling and chemical cleaning of nanofiltrationmembranes Measurements and mechanisms Environmental Science and Technology 384683e4693

Ludewig U amp Dynowski M (2009) Plant aquaporin selectivity Where transport assayscomputer simulations and physiology meet Cellular and Molecular Life Sciences 663161e3175

Mccutcheon J R Mcginnis R L amp Elimelech M (2006) Desalination by a novelammoniaecarbon dioxide forward osmosis process Influence of draw and feed solutionconcentrations on process performance Journal of Membrane Science 278 114e123

Nielsen C H (2009) Biomimetic membranes for sensor and separation applications Analyticaland Bioanalytical Chemistry 395 697e718

Orsquoneill C Hawkes F R Hawkes D L Esteves S amp Wilcox S J (1999) Anaerobicaerobic biotreatment of simulated textile effluent containing varied ratios of starch and azodye Water Research 34 2355e2361

Pandey A Singh P amp Lyengar L (2007) Bacterial decolourization and degradation of azodyes International Biodeterioration Biodegradation 59 73e84

Petrinic I Andersen N P R SOstar-Turk S amp Le Marechal A M (2007) The removal ofreactive dye printing compounds using nanofiltration Dyes and Pigments 74 512e518

Petrotos K B Lazarides H N Wolf W Behsnilian D amp Spiess W (2001) Osmoticconcentration of liquid foods Journal of Food Engineering 49 201e206

Pierce J (1994) Colours in textile effluentse the origins of the problem Journal of The Societyof Dyers and Colourists 110 131e133

Pierce C I Lloyd J R amp Guthrie J T (2003) The removal of color from textile wastewaterusing whole bacterial cells A review Dyes Pigments 58 179e196

Porter J J (1999) Membrane filtration techniques used for recovery of dyes chemicals andenergy Textile Chemist and Colorist 22 21e25

Rautenbach R amp Mellis R (1994) Waste water treatment by a combination of bioreactor andnanofiltration Desalination 95 171e188

Membrane technologies for water treatment and reuse in the textile industry 549

Robinson T Mcmullan G Marchant R amp Nigam P (2001) Remediation of dyes in textileeffluent A critical review on current treatment technologies with a proposed alternativeBioresource Technology 77 247e255

Rozzi A Antonelli M amp Arcari M (1999) Membrane treatment of secondary textileeffluents for direct reuse Water Science and Technology 40 409e416

Salter R (2006) Forward osmosis Water Conditioning and Purification 48 36e38Simonic M (2013) Perspectives of textile wastewater treatment using MBR A review Textiles

and Light Industrial Science and Technology (TLIST) 2 71e77Slokar Y M amp Le Marechal A M (1998) Methods of decolouration of textile wastewaters

Dyes and Pigments 37 335e356Sojka-Ledakowicz J Koprowski T Machnowski W amp Knudsen H-H (1998) Membrane

filtration of textile dyehouse wastewater for technological water reuse Desalination 119 1e9Sponza D T amp Isik M (2005) Reactor performance and fate of aromatic amines through

decolourisation of Direct Black 38 dye under anaerobicaerobic conditions ProcessBiochemistry 40 35e44

Suksaroj C Heacuteran M Allegre C amp Persin F (2005) Treatment of textile plant effluent bynanofiltration andor reverse osmosis for water reuse Desalination 178 333e341

Tang C Y Zhao Y Wang R Heacutelix-Nielsen C amp Fane A G (2013) Desalination by bio-mimetic aquaporin membranes Review of status and prospects Desalination 308 34e40

Tegtmeyer D (1993) Moglichkeiten und chancen einer membrantechnischen abwasserbr-handlung in de textilfarberai Melliand Textiberichte 74 148e151

Teoh M M Wang K Bonyadi S amp Tai-Shung N (2008) Forward osmosis and membranedistillation proceses for freshwater production Innovation 8 15e17

Treffry-Goatley K Buckley C A amp Groves G R (1983) Reverse osmosis treatment andreuse of textile dyehouse effluents Desalination 47 313e320

Van Der Zee F P amp Villaverde S (2005) Combined anaerobic-aerobic treatment of azo dyesA short review of bioreactor studies Water Research 39 1425e1440

Vrouwenvelder J S amp Van Der Kooij D (2001) Diagnosis prediction and prevention ofbiofouling of NF and RO membranes Desalination 139 65e71

Xu Y Peng X Tang C Shiang Fu Q amp Nie S (2010) Effect of draw solution concen-tration and operating conditions on forward osmosis and pressure retarded osmosisperformance in a spiral wound module Journal of Membrane Science 348 298e309

York R TampBeaudry E (1999) Full scale experience of direct osmosis concentration applied toleachate management In T H Christensen R Cossu amp R Stegmann (Eds) Sardinia 99Seventh International Waste Management and Landfill Symposium 4-8 October Pro-ceedings CISA Environmental Sanitary EngineeringCentre Cagliari Italy (pp 359e366)Cagliari Sardinia Italy S Margherita di Pula

You S-J amp Teng J-Y (2009) Anaerobic decolourisation bacteria for the treatment of azo dyein a sequential anaerobic and aerobic membrane bioreactor Journal of Taiwan Institute ofChemical Engineers 40 500e504

Zaghbani N Hafiane A ampDhahbiM (2007) Separation ofmethylene blue from aqueous solutionby micellar enhanced ultrafiltration Separation and Purification Technology 55 117e124

ZhaoYQiuC LiXVararattanavechAWSTorres JHeacutelix-NielsenCWangRHuXFane A G amp Tang C Y (2012) Synthesizing Robust and high-performance aquaporinbased biomimetic membrane by interfacial polymerization - membrane preparation and ROperformance characterization Journal of Membrane Science 423e424 422e428

_Zyłła R Sojka-Ledakowicz J Stelmach E amp Ledakowicz S (2006) Coupling of membranefiltration with biological methods for textile wastewater treatment Desalination 198316e325

550 Advances in Membrane Technologies for Water Treatment

Membrane technologies forwater treatment and reuse in thefood and beverage industries

18A Cassano1 NK Rastogi2 A Basile131Institute on Membrane Technology ITM-CNR University of Calabria Rende (CS) Italy2Department of Food Engineering Central Food Technological Research Institute Councilof Scientific and Industrial Research Mysore India 3Ast-Engineering srl Rome Italy

181 Introduction

Water raw materials and energy are key resources used in the food-processingindustry In particular water is used as ingredient cleaning source and conveyor ofraw materials and to sanitize plant machinery and areas Subsequently effluentsfrom many agro-food industries are a hazard to the environment and require appro-priate management approaches

Wastewaters generated by different branches of the agro-food industry can bedivided into two classes (on the basis of plant or animal origin) and seven subclasses(Table 181)

The characteristics and volume of these effluents vary with the products and pro-duction procedures Typically they contain macropollutants such as chemical oxygendemand (COD) biochemical oxygen demand (BOD) total suspended solids (TSS)fats oils and nutrients (nitrogen and phosphorous) In addition some micropollutantsincluding hormones surfactants antibiotics and pesticides can be present However itis often difficult to predict the composition of food waste because of the seasonalnature of food processing and post-harvesting

The main parameters of typical food waste are given in Table 182 On the basis oftheir composition effluents from many agro-food industries produce negative effectswhen disposed into the environment and require appropriate management approachesConsequently extensive research has been devoted to coping with waste generated byagro-industries

Technological innovations including those in clean technologies and processesaim to introduce into food-processing factories advanced wastewater treatment prac-tices able to recycle spent process waters onsite and to reduce the amount of waste-water discharged into municipal sewage treatment plants Another target of greatinterest is the reduction of water and wastewater from the manufacturing process(closed-loopzero emission systems) and the reuse of treated waters in the food-processing industry

In addition food waste contains higheadded value compounds (ie phenols carot-enoids pectin hemicelluloses oligopeptides lactose proteins) that can be recovered

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400018-6Copyright copy 2015 Elsevier Ltd All rights reserved

and recycled inside the food chain as functional additives in different products To thispurpose conventional and emerging technologies offer interesting perspectives takinginto account the huge amounts of food-related materials discharged worldwide(Galanakis 2012)

Conventional technologies for the treatment of food-processing wastewatersinclude (1) physical and chemicophysical processes to remove suspended solids(screening systems sedimentation and dissolved air flotation) (2) biological treat-ment processes (anaerobic treatments activated sludge processes aerated lagoonsand land application) aimed at removing soluble pollutants and (3) tertiary treatmentsincluding membrane processes or other chemicophysical processes such as precipita-tion activated carbon and chelation for the removal of specific pollutants or forimproving water parameters (Bolzonella amp Cecchi 2007)

Membrane filtration processes offer interesting perspectives and key advantagesover conventional technologies in the treatment of wastewaters from food-processing industries

They can be combined with activated sludge processes to form membrane bioreac-tors (MBRs) to improve the capability of removing pollutants in biological treatmentprocesses (Stephenson Brindle Judd amp Jefferson 2000) In addition pressure-drivenmembrane operations such as microfiltration (MF) ultrafiltration (UF) nanofiltration(NF) and reverse osmosis (RO) can be used to treat high-strength wastewaters or at theend of conventional treatment systems to produce purified water for recycling or reuseand to recover valuable compounds (Moresi amp Lo Presti 2003 Muro Riera amp delCarmen Diaz 2012)

Table 181 Food waste and its origins

Source Waste origin Type of waste

Plant Cereals Rice bran wheat middling wheat straw wheat branoat mill waste malt dust breweryrsquos spent grains

Root and tubers Potato peel sugar beet molasses

Oil crops andpulses

Sunflower seed soybean oil waste soybeanwastewaters olive pomace olive mill wastewater

Fruit andvegetables

Citrus peel apple pomace apple skin peachpomace apricot kernel grape pomace grape skinwine lees banana peel tomato pomace tomatoskin

Animal Meat products Chicken by-products slaughterhouse by-productsbeef lung bovine blood

Fish and seafood Fish leftovers shrimp and crab shells surimiwastewater

Dairy products Cheese whey

Source Adapted from Galanakis (2012)

552 Advances in Membrane Technologies for Water Treatment

Table 182 Characteristics of agro-food wastewater

Industry BOD (mgL) COD (mgL) TSS (mgL)Total phosphorus(mgL)

Total nitrogen(mgL) References

Fruit juice 1580 3650 e 24 12 Noronha BritzMavrov Jankeand Chmiel(2002)

Fish and seafood e e Cros LignotJaouen andBourseau (2006)

Fish tradeactivities

400e2200 500e4500 3e35 e e Vandanjon CrosJaouenQueacutemeacuteneur andBourseau (2002)

Shrimpprocessingmdashthawing

650 1000 2 e e Walha et al (2011)

Shrimpprocessingmdashcooking

2000e10000 3000e20000 200e1200 e e

Shrimpprocessingmdashrinsing

650 1300 7 e e

Continued

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

553

Table 182 Continued

Industry BOD (mgL) COD (mgL) TSS (mgL)Total phosphorus(mgL)

Total nitrogen(mgL) References

Tuna cookingjuice

e 23500 2100

Food andbeverage

e 1800e6600 1000e7300 e e Chmiel KaschekBleuroocherNoronha andMavrov (2002)and Bleuroocher et al(2002)

Food 680 880 2480 e e Katayon et al2004

Dairy 800e1000 1400e2500 1100e1600 e e Gotmare Dhobleand Pittule(2011)

Dairy 650e6250 400e15500 250e2750 e 10e90 Passeggi Lopezand Borzacconi(2009)

554Advances

inMem

braneTechnologies

forWater

Treatm

ent

Dairy e 380e38500 31e796 e e Vourch BalannecChaufer andDorange (2008)

Poultryprocessing

858 1173 e e Lo Cao Argin-Soysal Wang ampHahm (2005)

Winery Valderrama et al(2012)

Harvesting 13448 1230 395 340

Harvesting andvinasse

e 3887 662 65 e

Vinasse e 3400 271 75 41

Process e 2323 178 50 400

Winery e 4728 320 35 60 Bolzonella FatonePavan andCecchi (2010)

Steamed soybeanwastewater

e 8400e8700 14500e15300 e e MatsubaraIwasakiNakajimaNabetani andNakao (1996)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

555

This chapter gives an overview of membrane-based processes for water reuse andenvironmental control in the treatment of wastewaters from food-processing indus-tries Applications involving the use of pressure-driven membrane operations electro-dialysis (ED) and MBRs as well as a combination of membrane operations in hybridsystems in the treatment of waste from different agro-food productions are analyzedand discussed

182 Wastewaters from food and beverage industry

In the food and beverage industries exhausted waters generated from different oper-ations (fruit processing cleaning of tanks and pipes and bottle washing) are mixedtogether before they are discharged into municipal sewage systems

These wastewaters can be defined as high-strength wastewaters because of theirhigh COD values and high content of biodegradable compounds such as nitrogen orphosphorous elements They can be discharged into the environment after specifictreatments to reduce polluting compounds according to standards defined by environ-ment regulations

The use of MBRs is a promising technology in treating high-strength wastewatersas an alternative to conventional activated sludge treatment Fundamentals configura-tions and typical applications of MBR systems are analyzed and discussed in Chapter6 As highlighted in this chapter the best performance of MBR can be producedthrough optimizing operating parameters such as hydraulic retention time solid reten-tion time (SRT) mixed liquor suspended solids (MLSS) and transmembrane pressure(TMP) Pretreatment systems physical and chemical cleaning and biofouling reducerssuch as powdered activated carbon are all systems that can be used to reduce foulingphenomena thus enhancing MBR performance (Katayon et al 2004 MutamimNoor Abu Hassan amp Olsson 2012)

A hybrid process for the production of drinking water from spent process waters offruit juice companies was developed by Bleuroocher et al (2002) on an industrial scaleafter preliminary studies on a pilot scale (Noronha Britz Mavrov Janke amp Chmiel2002) Spent waters from small and medium-sized enterprises were mixed in an equal-ization tank and clarified through a lamella clarifier to remove most solids The clar-ified effluent was treated in an MBR equipped with immersed tubular MFmembranes (pore size 004 mm) in which the active biomass and other particulate mat-ter were completely retained Although the organic loading rate of the spent water var-ied widely (between 1800 and 6600 mgL) COD and total organic carbon (TOC) werereduced by at least of 96 in this first step

The MF permeate was then submitted to a two-step NF process with integrated ul-traviolet (UV) disinfection The first NF step was operated with spiral-wound mem-brane modules characterized by low rejection for sodium chloride (on average55) ensuring a reduction of dissolved organics up to 97 The second filtrationstep was carried out using NF membrane modules with a rejection rate for sodiumchloride higher than 90 These membranes operated as desalting membranes with

556 Advances in Membrane Technologies for Water Treatment

a low fouling index reducing the salinity of the spent liquor more than 75 The finalCOD of the treated water was below the detection limit and TOC did not exceed thelimit value of 4 mgL Chemical and microbiological parameters of the final permeatewere within the water quality standard of the German Drinking Water Act The pro-posed process is illustrated in Figure 181 For a plant capacity of 5 m3h the overalltreatment cost for producing drinking water from spent process water was estimated tobe about 25e30 Vm3

The presence of oils and fats in spent process waters generated in margarine pro-duction creates several problems when these waters are submitted to biological treat-ment (ie high costs for aeration and sludge disposal flotation and coating in thetreatment plant and saponification of fats in the equalization tank) Treatment of theseeffluents with 02-mm ceramic MF membranes reduced the initial COD of5000e10000 mgL below 250 mgL The produced permeate could be mixedwith water of low and medium contamination and then submitted to biological treat-ment A concentrated product was recovered from the MF retentate and reused forsoap production after a skimming oil treatment (Chmiel Kaschek Bleuroocher Noronhaamp Mavrov 2002)

The Kubota submerged anaerobic membrane biological reactor process developedin the past decade by Kubota Membrane Technology (Hyogo Japan) is an interestingapplication of anaerobic MBRs in food-processing factories The process alsodescribed in Chapter 6 consists of a solubilization tank and a mesophilic or thermo-philic tank equipped with submerged membranes These membranes retain methano-genic bacteria while methane fermentation inhibitors such as ammonia are allowed topass in the permeate stream The generated biogas can be used to heat water viaboilers Permeate and sludge can be further treated in aerobic treatment facilities(Kanai Ferre Wakahara Yamamoto amp Moro 2010) The process has been success-fully implemented in food factory treatment plants stillage treatment plants forShouchu (a Japanese spirit made from sweet potato) and potato-processing sites

Ng Lin Panchangam Hong and Yang (2011) compared the performance of anovel bio-entrapped membrane reactor (BEMR) packed with bio-ball carrierswith that of a conventional MBR in the treatment of wastewater from a food andbeverageeprocessing plant The new reactor exhibited a longer SRT and lowerMLSS compared with the conventional system The BEMR produced also fewersoluble microbial products than the conventional system (34e48 less protein and16e29 less carbohydrate) owing to slow-growing microorganisms with long SRTFinally the new BEMR was able to operate at a constant permeate flux requiringless frequent chemical cleanings with consequent economic benefits

The technical feasibility of recovering and concentrating tartaric acid by ED fromfruit juice processing wastewater was assessed by Andreacutes Riera and Alvarez (1997)In particular the ED treatment of synthetic solutions simulating ionic exchange regen-eration waters obtained in grape juice processing increased five times the initial iontartrate concentration (from 1 to 10 kgm3 up to 532 kgm3) The energy consumptionwas estimated to be about 5 103 kJkg tartaric acid The purified acid can be reusedfor food and pharmaceutical applications

Membrane technologies for water treatment and reuse in the food and beverage industries 557

Water for reuse

NFMF

Spent processwater

UVdisinfection

Membrane bioreactorAir oroxygen

Excess sludgeNF

UVdisinfection

Retentateto be

dischargedSpent processwater Lamella

clarifier

Settled solids

Figure 181 Flow diagram of integrated membrane process for the recycling of spent process water from the food and beverage industriesAdapted from Noronha et al (2002)

558Advances

inMem

braneTechnologies

forWater

Treatm

ent

183 Wastewaters from fish and seafood industry

The fish-processing industry produces several effluents (ie wastewater generatedduring fishmeal production and wastewater generated by washing thawing rinsingand cooking treatments) exhibiting different characteristics The polluting load andthe flow rates of these effluents vary greatly according to the activity The COD andsalt content are in the range of 7e49 and 025e10 gL respectively Although thesewastewaters contain no toxic materials they cannot be released into the environmenttherefore depolluting treatments are needed in municipal or private treatment plantsIn addition fish industry wastewater contains potentially valuable molecules for thefood sector such as proteins flavor and aroma compounds and n-3 polyunsaturatedfatty acids whose recovery can lead to appreciable productivity gains (Masseacute et al2008)

Membrane technology has great potential for the treatment of fish-processing efflu-ents In particular key advantages of membrane processes over conventional technol-ogies such as coagulationflocculation and dissolved air flotation concern theproduction of good-quality permeate streams that can be disposed directly into thesea or recycled into the plant and the recovery of valuable compounds under mild con-ditions without using heat or chemicals An extensive review of the application ofpressure-driven membrane operations in the treatment of seafood-processing effluentswas reported by Afonso and Borquez (2002a) The authors also evaluated the perfor-mance of an integrated membrane process based on the use of MF and UF or NF torecover proteins from the effluents of a fishmeal plant Microfiltration pretreatmentreduced drastically the oil and grease content and the suspended matter improvingthe performance of the subsequent membrane treatment The selected UF ceramicmembrane (Carbosep M2 tubular 15 kDa molecular weight cutoff (MWCO)) reducedthe organic load of the MF permeate and allowed the recovery of valuable raw mate-rials including proteins The protein rejection ranged from 49 to 62 depending onthe operating conditions A ceramic NF membrane (Kerasep NanoN01A tubular1 kDa MWCO) produced a protein rejection of 66 when the MF permeate was pro-cessed In both cases the highest protein rejection was achieved at a TMP of 4 bar anda cross-flow velocity of 4 ms (Afonso amp Borquez 2002b Afonso Ferrer amp Borquez2004) A conceptual process for the treatment of 10 m3h of fishmeal effluent based onthe use of MF and UF membranes was designed (Figure 182) The plant wouldgenerate 1 m3h of concentrate containing 170 gL of solids and 112 gL of proteinsThe economic assessment for the integrated MFeUF process yielded a net worth ofUS$160 103 an interest rate of return of 17 and 8 yearsrsquo payback time indicatingthe feasibility of the process for protein recovery and pollution reduction

The UF treatment of fishery washing waters with polysulphone membranes of20 kDa and a multichannel ceramic membrane of 01 mm produced similar apparentrejections (70 and 80 respectively) toward proteins The process increased theprotein concentration in the feed solution from 5 to 35 gdm3 and reduced the BODby about 80 (Mameri et al 1996) Other applications related to the use ofpressure-driven membrane operations in the treatment of wastewater from surimi

Membrane technologies for water treatment and reuse in the food and beverage industries 559

production (Huang amp Morrissey 1998) menhaden bail water (Abu Rao Khan ampLiuzzo 1984) fish brine (Paulson Wilson amp Spatz 1984) and effluents dischargedfrom fish plants (Chao Asce amp Tojo 1987) have been investigated

An integrated process for the concentration of aroma compounds and the produc-tion of clean water from shrimp cooking juices was developed by Cros LignotJaouen and Bourseau (2006) The process is based on a clarification step to removesuspended solids followed by a desalination step by ED and a final concentrationstep by RO (Figure 183) The pre-filtered juice (pore size 500 mm) was treated byED and consisted of 20 compartments alternating cation-exchange and anion-exchange membranes for a total surface area of 0138 m2 The RO unit was equippedwith tubular polyethersulphone-polyamide membranes supplied by PCI (BeaupuyFrance) with an effective membrane area of 0033 m2 The performance of both sys-tems was evaluated for different juices containing from 20 to 200 gL of organic matterand from 4 to 40 gL of minerals Experimental results showed that the integration ofED and RO seems technically and economically feasible The payback time was eval-uated as less than 3 years

The size of the integrated process does not require a systematic evaluation of oper-ating and capital costs it can be evaluated by minimizing the total installed membranesurface area and energy consumption (Bourseau Masseacute Cros Vandanjon amp Jaouen

UF membranes carbosep M2Permeate

9 m3h70 kgh solids43 kgh prot78 gL solids48 gL prot

Concentrate

170 kgh solids1 m3h

112 kgh prot170 gL solids112 gL prot

210 kgh solids10 m3h

125 kgh proteins210 gL solids125 gL proteins

240 kgh solids10 m3h

155 kgh proteins240 gL solids155 gL proteins

(66 proteins dry basis)Rejection RUF () RMF + UF ()Total solids Total proteins

30 kgh solids30 kgh proteins

FeedRotary filter 5 μm

Feed tank

nabla

Pm = 4 bar v = 4 ms

6263 68

69

Figure 182 Integrated membrane process for the treatment of fishmeal effluent Reprinted fromAfonso et al (2004) with permission from Elsevier

560 Advances in Membrane Technologies for Water Treatment

2014) In the ED process the salt concentration can decrease from 20 to 28 gL withoutchanging the aromatic profile (Cros Lignot Bourseau Jaouen amp Prost 2005) How-ever a loss of volatile compounds under a critical salt concentration (23 gL) wasobserved This phenomenon was attributed to the salting-out of amino acids inducinga co-precipitation of hydrophobic aroma compounds and to the ionization of volatilecompounds and water splitting in the presence of a low concentration of ionic species

A desalination step before RO concentration is needed to avoid an increase in os-motic pressure in RO (RO membranes retain salt compounds) which limits the achiev-able extent of concentration This will increase the production cost of aromaconcentrates The use of NF membranes overcomes these problems The direct con-centration of aroma compounds from tuna cooking juices with NF tubular membranes(AFC30 PCI Ltd France) produced reasonable permeate fluxes (about 30 Lm2∙h)with retention factors of inorganic compounds between 70 and 76 The aromaproperties of the juice were slightly modified but the global characteristics of the juiceremained unchanged The MF pretreatment with ceramic multichannel membranes(Kerasep K01 Orelis) with a 01-mm pore size significantly improved NF permeationfluxes up to 90e100 Lm2 h (Walha et al 2011)

Integrated processes based on the use of UF as a pretreatment step followed by NFor RO for the concentration of aroma compounds from seafood cooking water werealso investigated by Vandanjon Cros Jaouen Queacutemeacuteneur and Bourseau (2002)

Shrimp cooking juice

Clean water

ED

RO

MF

Desalted juice

Clarified juice

Aromaconcentrate

Figure 183 Integrated membrane process for the production of clear water and aromaconcentrate from shrimp cooking juiceAdapted from Cros et al (2006)

Membrane technologies for water treatment and reuse in the food and beverage industries 561

RO membranes were more efficient in retaining aroma compounds from shrimp andbuckies cooking juices compared with 300-Da NF membranes and also had higher re-movals of COD (95 for shrimp and buckies and 85 for tuna juices)

184 Wastewater from dairy industry

Among the food industries the dairy industry is characterized by the production ofhuge quantities of polluted effluents (average of 02e10 L per liter of processed milk)

The pollution load of dairy industry wastewater can be defined by evaluatingdifferent parameters such as conductivity pH COD TOC TSS and residual hardness(Gotmare Dhoble amp Pittule 2011 Passeggi Lopez amp Borzacconi 2009) Vaporcondensates from evaporation and drying are considered to be low pollutant waters(Mavrov Chmiel amp Beacutelieres 2001) whereas end-pipe wastewaters are highly pollutedand require intense treatment to obtain clean water

Membrane treatment of these wastewaters including flushing water white waterand whey can give contribute greatly to reducing both total water consumption andthe volume of produced wastewater In addition the recovery of valuable compoundssuch as whey proteins using membrane technology is of great economical interestconsidering their nutritional biological and functional properties

NF and RO membranes have been shown to be useful for the concentration of milkconstituents from raw wastewater and to simultaneously produce treated water that canbe reused in the dairy industry (Koyuncu Turan Topacik amp Ates 2000) The perfor-mance of NF and RO membranes in the treatment of diluted skimmed milk used as aneffluent model solution (COD 36 gL) was investigated by Balannec Vourch Rabiller-Baudry and Chaufer (2005) Permeate flux and milk component rejections were eval-uated in dead-end filtration experiments performed in selected operating conditions(25 C and 14 bar for NF membranes and 25 C and 25 bar for RO membranes)up to a volume concentration ratio (VCR) of 3 Results of dead-end filtration experi-ments are summarized in Table 183 COD rejections were higher than 989 for allinvestigated membranes Cross-flow experiments performed with NF and RO spiral-wound membranes produced similar results (Balannec Geacutesan-Guiziou ChauferRabiller-Baudry amp Daufin 2002) The quality of produced permeates did not meetthe requirements of drinking water because of the high organic load of the effluentwhich suggests the use of a two-step RO process or a single step with a low chargedfeed for the production of reusable water Further studies performed by using modelprocess waters through one-stage and two-stage (NF plus RO and RO plus RO)spiral-wound membrane (Desal 5 DL Osmonics and TFC HR Koch Membrane Sys-tem) treatments indicated that after a single RO step or a combined NF plus RO pro-cess the final permeate could be reused as a replacement for cleaning heating orcooling and for boiler feed water More purified water with the typical requirementsof drinking water can be produced by a two-stage RO process (Vourch BalannecChaufer amp Dorange 2005) Similar results were obtained when dairy wastewaterwas treated through a single RO stage The process was carried out up to a recoveryfactor of 90e95 producing an average permeate flux of about 11 Lm2 h (Vourch

562 Advances in Membrane Technologies for Water Treatment

Table 183 Performance of nanofiltration and reverse osmosis membranes in the treatment of model dairyeffluent (initial COD 36 gL)

Membraneprocess

Membranetype Supplier

MWCO(kDa)

Membranematerial

Initialpermeate flux(Lm2 h)

PermeateCOD (mgL) RCOD ()

NF TFC S Koch membranesystems

PAPSPE 63 1095 9890

NF Desal 5 DL Osmonics 150e300 PAPS 79 300 9970

NF Desal 5 DK Osmonics 150e300 PAPS 72 960 9910

NF NF45 FilmTec 200 PAPSPE 68 1055 9900

NF NF200 FilmTec 200 PAPSPE 70 173 9980

RO Desal 3 SF Osmonics e PAPS 71 45 9996

RO TFC HR Koch membranesystems

e Composite PA 67 54 9995

RO BW 30 FilmTec e Composite PA 69 120 9988

MWCO molecular weight cutoff PA polyamide PS polysulphone PE polyesterSource Adapted from Balannec et al (2002)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

563

Balannec Chaufer amp Dorange 2008) According to the proposed scale-up a plantarranged with 18 spiral-wound 8-inch elements (for a total membrane surface areaof 540 m2) permits the recovery of 95 of water from 100 m3d of treated wastewater

Riera Suarez and Muro (2013) evaluated the effect of the main process parameterssuch as pressure temperature and VCR on the quality of permeate produced in asingle-step NF treatment of flash cooler condensates from direct ultraehigh tempera-ture processing The pilot plant was equipped with a spiral-wound membrane (SelROMPS-34 2540 B2X Koch Membrane Systems) with an MWCO of 200 Da As a gen-eral trend COD and TOC rejection increased by increasing the VCR (ie TOC rejec-tion increased from 676 at VCR 3 to 821 at VCR 15) Low-molecular-weightcompounds such as acetone acetoine and dimethylsulfide were partially retained bythe NF membrane Their increased rejection with VCR was attributed to the polariza-tion concentration layer on the membrane surface

In the investigated VCR values (between 1 and 15) average permeate fluxesbetween 100 and 110 Lm2 h were measured (at a TMP of 237 bar and a temperatureof 50 1 C) According to the experimental data an NF plant with 20 m3 h feedcapacity and 875 water recovery was designed The proposed plant was arrangedwith nine spiral-wound 8-inch elements (total membrane area 171 m2) distributedin three series of feed and bleed loops (Figure 184) Savings and operating costs ofthe designed NF plant were estimated at 2807 and 0777Vm3 respectively The ther-mal potential of permeate condensates suggested their reuse for heating purposes andin other miscellaneous services

A process combination based on the use of NF membranes for the reuse of vaporcondensate from milk processing was proposed by Chmiel Mavrov and Beacutelieres(2000) The process involves pretreatment with cartridge filtration and UV disinfectionfollowed by a two-stage NF process The demonstration plant was designed to treat15 m3h of feed and consisted of two membrane stages with spiral-wound membranemodules each with a membrane area of 40 m2 All of the parameters of the treated wa-ter met the requirements of drinking water (COD lt 10 mgL TOC lt 4 mgL andCa2thorn lt 04 mgL) as well as boiler makeup water

Whey is a co-product of cheese making with a low content of solids (up to 5e6)and a high BOD (30e50 gL for 1000 L of whey) which makes its disposal difficultand costly

Conventional processes in whey treatment include thermal evaporation and dryingThese processes are used to remove water from whey to diminish its volume but do notcontribute to the recovery of valuable compounds Anaerobic treatments are also usedto remove organic compounds from whey These processes are preferred over conven-tional aerobic treatments owing to the high COD of whey (about 60e80 gL) whichcan produce biomass granulation during biological treatment Other purification pro-cesses are based on the use of affinity chromatography cation-exchange resins andthermal precipitation (Pearce 1983 Uchida Sato Kawasaki amp Dosako 1996) How-ever these processes are not widely implemented on a large scale because of theircomplexity poor selectivity high cost and low product degradation

Whey processing is one of the most important applications in membrane technol-ogy in the dairy industry Whey concentration fractionation demineralization and

564 Advances in Membrane Technologies for Water Treatment

Feed pump25 bar

20 m3h

Recirculationpump

ΔP 14 bar342 m3h

Recirculationpump

ΔP 14 bar342 m3h

Recirculationpump

ΔP 07 bar171 m3h

Retentate25 m3h

80408040

80408040

80408040

8040

8040

8040

Permeate175 m3h

Figure 184 Multistage nanofiltration scheme for the treatment of flash cooler condensates from a dairy factory Reprinted from Riera et al (2013)with permission from Elsevier

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

565

purification can be achieved by using a combination of different membrane processesAt the same time the development of high value-added products from whey com-pounds is of great interest

The production of whey protein concentrates (WPCs) by UF is a well-establishedapplication in the dairy industry Ultrafiltration membranes separate lactose and min-erals from whey proteins producing a retentate stream that can be further processed byevaporation and spray-drying The lactose and mineral content in WPC can be furtherreduced by using a diafiltration (DF) step in which deionized water is continuallyadded to the retentate while lactose and minerals are continuously recovered in thepermeate stream By selecting a proper combination of UF and DF the protein contentin the WPC can be modified in the range of 35e85 The retentate can be used in avariety of beverages processed meats and baby foods or added to dairy products suchas yogurt and cottage cheese (Zydney 1998)

The concentration of whey andor its partial demineralization can be also achievedby NF NF membranes allow univalent ions (Nathorn Kthorn and Cl) to pass whereas largerions such as Cathornthorn or PO4

3 are retained Desalination degrees up to 40 can beachieved through a combination of NF and DF

The performance of UF NF and RO spiral-wound membrane modules for the re-covery of proteins and the production of clean water from white and curd cheese wheywas investigated by Yorgun Akmehmet Balcioglu and Saygin (2008) In particularthe performance of the selected membranes was evaluated according to a single-stageor multi-step operation involving different membrane modules in series Table 184summarizes the experimental results in terms of COD removal and permeate fluxfor the single-step process related to white cheese whey treatment The polysulphoneNF membrane module (200 Da as an MWCO) was considered the best choice whenthe effluent had to be further concentrated or treated by conventional treatmentsThis module exhibited an initial permeate flux of 24 Lm2 h when cheese whey wastreated at a TMP and a recirculation flow rate of 8 bar and 2500 Lh respectivelyAt the same time it produced permeate with a COD load of 2787 mgL with aCOD removal of 974 A further COD removal from the NF permeate required anadditional RO stage as a polishing step This combination allowed proteins to recoverseparately in the NF retentate while lactose was recovered in the second RO step withthe simultaneous production of a clean effluent

A combination of membrane-based cheese production was proposed by Atra VataiBekassy-Molnar and Balint (2005) to decrease the amount of waste in cheese produc-tion with a simultaneous increase in cheese yields through the incorporation of wheyproteins A flow diagram of the proposed process is depicted in Figure 185 The UF offresh milk and whey produces WPC (with a protein content of 12e14 and 8e10respectively) that can be used in cheese manufacturing improving the nutritional valueof the cheese UF permeates containing about 01e05 of proteins and 5 of lactoseare submitted to an NF process By selecting the proper operating conditions (ie atVCR 5 20 bar and 30 C) a concentrated solution containing 20e25 of lactosecan be obtained This solution can be reused in the dessert industry whereas thepermeate stream depleted in lactose can be reused for cleaning or irrigation or bedischarged into sewers

566 Advances in Membrane Technologies for Water Treatment

Table 184 Performance of ultrafiltration nanofiltration and reverse osmosis spiral-wound membranemodules in treatment of white cheese whey (initial COD w110 gL)

Membraneprocess Supplier

Membranematerial

Soluterejection ()

OperatingTMP (bar)

Initialpermeate flux(Lm2 h)

PermeateCOD (gL)

CODremoval ()

UF Microdyn Nadir PES e 3 225 54331 4280

NF Microdyn Nadir PES 25e40Na2SO4

5 27 43658 5850

NF Microdyn Nadir PES 80e95Na2SO4

8 17 37648 6402

NF Trisep Corp PA 95 MgSO4 8 25 23502 7761

NF Filmtec PS e 8 24 2787 9746

RO Trisep Corp PA 995 NaCl 12 146 3847 9257

PA polyamide PS polysulphone PES polyethersulphoneSource Adapted from Yorgun et al (2008)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

567

Most MBRs operate under aerobic conditions in which aeration is used to createcross-flow along the membrane to reduce fouling The use of anaerobic systems hasreceived great attention because of the energy balance achieved by biogas productionand the lower amount of produced sludge compared with aerobic MBRs (LiaoKraemer amp Bagley 2006) The performance of a bench-scale submerged anaerobicMBR in the treatment of a synthetic wastewater consisting of cheese whey and sucrosewas evaluated by Casu et al (2012) The results indicated that the maximum applicableorganic loading rates (OLRs) were in the range 6e10 g CODg L In this range thereactor showed a COD removal of 94 Higher OLRs produced high concentrationsof volatile fatty acids whereas the COD removal dropped to 33 The maximumbiomass concentration obtained in the system was of 40e50 g TSSL owing thelow filterability of the anaerobic sludge

NF

Cheese production

UF

Fresh milk(100 kg)

UF

20 kg

80 kg

Whey(25 kg)

Retentate(16 kg)

Permeate(64 kg)

Cheese(20 kg)

Permeate(60 kg)

Retentate(20 kg)

VRF 4

VRF 5

VRF 5

Retentate(5 kg)

Figure 185 Membrane-based process for the treatment of milk and whey in cheese productionAdapted from Atra et al (2005)

568 Advances in Membrane Technologies for Water Treatment

185 Wastewaters from meat industry

The meat-processing industry uses large volumes of water (approximately 62 Mm3y)generating polluting effluents for a total volume of about 80 of the freshwater inputThe produced effluents contain huge quantities of organic compounds and salts andrequire several treatments before their release into receiving waters or industrial reuseSedimentation coagulationflocculation and dissolved air flotation are typically usedas primary treatments to remove suspended solids and fat substances followed by aer-obic or anaerobic systems to achieve the removal of COD and BOD In general anaer-obic systems lead to higher BOD removal with lower cost and a smaller quantity ofproduced sludge compared with aerobic treatment In addition the generated methanecan be captured for use as a fuel (Johns 1995) Methods for microbial decontaminationinclude chemical (chlorine chlorine dioxide chloramines hydrogen peroxide ozoneand paracetic acid) and physical (membrane operations and UV) processes (CasaniRouhany amp Knochel 2005)

The selection of a proper treatment system is a main challenge in supplying water ofnecessary microbiological and chemical quality The treatment system should removeundesirable physical chemical and microbiological components and in some casesprevent the subsequent growth of pathogenic organisms

Membrane processes present some key advantages over conventional technologiesbecause they can be used to purify water and recover valuable compounds In additionthey are able to remove particles from wastewater preventing microbial regrowthphenomenon

Some integrated processes based on the use of membrane technology have beenimplemented in the meat-processing industry for the reuse of non-potable water withinthe plant

Kane and Osantowski (1981) described a pilot-plant study in which wastewater waspassed through chemical flocculationclarification and dual-media filtration beforefurther upgrading by ion exchange RO or ED The latter three processes producedmore than 90 reduction of total dissolved solids However RO exhibited lowercapital and operating costs compared with the other two processes

The treatment of meat wastewater in integrated systems including membrane op-erations such as coagulationeRO UFeRO and coagulationeUFeRO was investi-gated by Bohdziewicz and Sroka (2005) UF and RO were performed with differentplate-and-frame membrane modules produced by Osmonics Results indicated thatthe coagulation treatment similar to UF was not able to remove all pollutantsfrom wastewater and the produced effluent could not be discharged into the receivingwater The combination of coagulation UF and RO resulted in the satisfactoryremoval of pollutants in particular the highest removal degree of contaminantswas obtained in a sequence coagulation with PIX 113 (Fe2(SO4)3 Feog 128Fe2thorn 07 H2SO4 1) UF with a 15- to 30-kDa cellulose acetate membrane(DSCQ Osmonics) and RO with a cellulose acetate membrane (SS10 Osmonics)Analyses of polluting substances in each step of the hybrid system are reported inTable 185

Membrane technologies for water treatment and reuse in the food and beverage industries 569

In a previous study the authors demonstrated that in the biological treatment ofmeat wastewater applying the activated sludge method to a sequencing batch reactorproduced an effluent that could be discharged into the receiving water The combina-tion of biological treatment and the RO process obtained a higher degree of purifica-tion and the produced effluent could be reused in the production cycle of the plant(Sroka Kaminski amp Bohdziewicz 2004)

In the shower process after boiling sausage products are cooled by spraying withdrinking water The water generated in this process is commonly discharged into thesewage network Its reuse requires treatment able to produce drinking-quality water Ademonstration plant for the treatment of water from shower processes was installed in ameat-processing company at the end of 1997 (Feuroahnrich Mavrov amp Chmiel 1998)A flowchart of the plant based on the use of a two-step NF process is depicted inFigure 186 The flow rate of the demonstration plant was of 15e2 m3h correspond-ing to an average residence time of shower process water in the feed tank of about45 min TOC rejections were higher for the first NF membrane (956) comparedwith the second one (551) This was attributed to the presence of both dissolvedand undissolved organic substances in the solution fed to the first NF stage The orig-inal bacteria concentration in the feed tank of 1100000100 ml was reduced to 1600100 ml by UV irradiation in the pretreatment stage This step also allowed the reduc-tion of membrane biofouling After the second NF step the produced water metrequired drinking water regulations (lt100 bacteriamL at 37 C) The final UV disin-fection produced bacteria-free water

A similar approach was adopted by Mavrov et al (2001) to treat chiller shower waterin sausage production to reduce its salinity and hardness and achieve warm cleaningwater for reuse Polypiperazinamide NF membranes (NaCl rejection 85e90MgSO4 rejection 99) were used in both the treatment and posttreatment stages oper-ating at constant TMP values of 42 and 25 bar respectively Permeate fluxes were onthe order of 25e3 Lm2 h in the first stage and 5e6 Lm2 h in the second one For bothNF permeates the electrical conductivity was lower than 200 mScm In the second NFpermeate TOC and Ca2thorn were lower than 4 and 1 mgL respectively

Table 185 Performance of ultrafiltration (UF) and reverse osmosis(RO) membranes in treatment of meat wastewater

Pollutionindices(mgL)

Rawwastewater

UFpermeate

UFrejection()

ROpermeate

ROrejection()

COD 22840 3550 845 40 998

BOD 19000 3500 816 39 998

Total nitrogen 2850 400 860 25 991

Total phosphate 250 106 576 00 1000

Source Adapted from Bohdziewicz and Sroka (2005)

570 Advances in Membrane Technologies for Water Treatment

Water for reuse

NF

Spent processwater

UVdisinfection

PretreatmentNF UV

disinfection

Retentate to be discharged

Two-stage cartridgefiltration

Belt filtration

Figure 186 Flow diagram of a demonstration plant for the treatment of meat-processing wastewaterAdapted from Feuroahnrich et al (1998)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

571

The manufacture of cured hams requires several steps including the addition of saltsand subsequent desalting and washing with water This process generates polluted ef-fluents containing solved salts (mainly NaCl) and a variable amount of organic matterThese effluents are generally dumped with no treatment with consequent environ-mental problems A treatment process to recover solved salts from liquid effluentsof cured hams was proposed by Arnal Garciacutea-Fayos Sancho and Leon-Hidalgo(2013) The process is based on a pretreatment step to remove organic compoundsproducing a clarified liquid mainly composed of water and dissolved salts which isthen submitted to a membrane process (ie an RO unit) where dissolved salts canbe concentrated The concentrated stream is finally treated in a natural assisted evap-oration plant where it is concentrated into a solid state while the permeate stream canbe reused in the plant

Poultry processing wastewaters (PPWs) contain organic compounds such as pro-teins fats and carbohydrates resulting in high BOD and COD

Conventional depolluting methods of PPWs include electrical (electrical stimula-tion) optical (UV irradiation) physical (dissolved air flotation diatomaceous earthfiltration and MF) chemical (ozonation and chemical separation of organic matterby coagulation and flocculation) and biological (anaerobic filter or sequencing batchreactors) treatment However most existing commercial processes present some disad-vantages in terms of low clarification levels and low reduction of organic compounds(ie in UV treatment) precipitation of proteins when iron salts are used and degrada-tion of valuable compounds during biological treatment

The recovery of proteins from PPWs by UF was investigated by several authors(Lo Cao Argin-Soysal Wang amp Hahm 2005 Saravia Houston Toledo amp Nelson2005 Shih amp Kozink 1980 Zhang Kutowy Jumar amp Malcolm 1997) In the workof Lo et al (2005) PPWs were pretreated by dissolved air flotation to remove most fatsubstances The pretreated effluent was ultrafiltered using a polysulphone UF mem-brane (Minitan-S Millipore) in flat-sheet configuration with an MWCO of 30 kDaAlmost all crude proteins were retained by the UF membrane and the COD in theeffluent was reduced to less than 200 mgL The optimization of operating conditions(pH 674 flow rate of 683 mLmin and TMP of 096 bar) by response surface meth-odology improved the permeate flux from 100 Lm2 h to higher than 200 Lm2 h Aftera cleaning step with a commercial detergent containing 200 ppm sodium hypochloritethe UF membrane surface appeared to be free of a gel-layer deposit This step was ableto restore more than 90 of original water permeability indicating that the major fluxreduction in the process was reversible

In the UF process most total solids can be recovered as by-products avoiding thegeneration of solid sludge In addition a combination of UF and dehydration couldproduce a by-product containing up to 35 protein and up to 45 fat from PPWs(Avula Nelson amp Singh 2009)

Mannapperuna and Santos (2004) designed a membrane plant based on the use ofspiral-wound UF membranes for the treatment of 480 Lmin of poultry chiller overflowwith a production of 380 Lmin of reconditioned water at 80 recovery The total costof the system was estimated to be US$300000 and the total electrical power

572 Advances in Membrane Technologies for Water Treatment

requirement was 30 kW The system is able to replace 346 Lmin of freshwatermakeup to the chiller with additional advantages in terms of disposal costs and energysavings

186 Winery wastewater

Winery wastewater is typically generated from washing operations during grape har-vesting pressing and fermentation as well as from washing equipment and bottles

The wastewater contains huge amounts of biodegradable organic compoundstogether with small concentrations of phenolic compounds sugars organic acidsand nutrients COD values range typically between 800 and 12800 mgL The quantityof produced waters and their pollution load vary in relation to the working period andthe winemaking technologies used (Mulidzi 2010) Therefore depolluting treatmentsshould be highly flexible to counterbalance variations in both quality and quantity ofpollutants

In Europe activated sludge processes are commonly used to pretreat winery waste-water before release into sewage systems However some operational problems arisefrom the need to treat waters with high organic loads for relatively short periods duringharvesting and vintage The use of MBRs offers different advantages over conven-tional biological processes including reduced sludge production better flexibility ac-cording to influent loading low footprint high efficiency in COD reduction rapidstartup and complete suspended solids removal (Guglielmi Andreottola Foladoriamp Ziglio 2009 Judd 2011)

The performance of a full-scale MBR in the treatment of a winemaking facilityoperating in Italy was evaluated by Bolzonella Fatone Pavan and Cecchi (2010)The filtration unit consisted of plate-and-frame MF membranes (04 mm) with a totalsurface area of 276 m2 The plant was able to treat 110 m3d of wastewater producingpermeate of good quality and a relatively small amount of wasted sludge AverageCOD removal efficiency was about 95 for an organic loading rate up to2 kg CODm3 of bioreactor per day Energy consumption in the range of20e36 kWhm3 of treated wastewater or 1 kWhkg of COD removed was estimated

COD removal higher than 97 was also observed in a pilot-scale hollow-fiberMBR system in the treatment of simulated wastewater with a COD between 1000and 4000 mgL (Artiga Carballa Garrido amp Meacutendez 2007)

A comparison between an MBR pilot plant and a full-scale activated sludge systemin the treatment of winery wastewater was studied by Valderrama et al (2012) TheMBR plant which was equipped with flat-sheet membrane modules manufacturedby Kubota produced an average COD removal of 97 whereas for the conventionalsystem the removal was 95 The MBR permeate achieved most quality specificationsdefined by international guidelines for water reuse and reclamation A stable operationin terms of TMP and permeability was achieved despite the high variability in influent

An anaerobic MBR with an external MF module was tested on a laboratory scale totreat winery wastewater and compared with the performance of aerobic granulation

Membrane technologies for water treatment and reuse in the food and beverage industries 573

technology (Basset Lopez-Palau Dosta amp MataAlvarez 2014) The bioreactor wasstarted up for 230 days and produced up to 035 L CH4L d when 15 kg CODm3 dwas applied The treated effluent was of better quality compared with that producedin the aerobic granular sequencing batch reactor It was free of suspended solidswith a COD concentration lower than 100 mgL Average permeate fluxes were onthe order of 105 Lm2 h

The fractionation of phenolic compounds from winery sludge using UF membraneswas investigated by Galanakis Markouli and Gekas (2013) Hydro-ethanolic extractswere prepared from winery sludge and treated with UF membranes of different mate-rials and MWCOs Results indicated that polysulphone membranes of 20 and 100 kDawere not able to fractionate phenolic compounds except for the separation betweenpolymeric and monomeric anthocyanins Both membranes exhibited high rejection(more than 60) of polar compounds such as sugars and phenolic compounds In addi-tion the 100-kDa membrane showed a low rejection toward pectin and allowed it toseparate from phenolic compounds

For these membranes the solute rejection was mainly attributed to soluteadsorption onto the membrane surface instead of size exclusion The use of a nonpolarfluoropolymer membrane with an MWCO of 1 kDa produced good separation ofhydroxycinnamic acids from anthocyanins and flavonols because the observed rejec-tion toward acids was twofold higher than that observed for the other phenoliccompounds

187 Soybean wastewater

Soybeans are used to produce various oriental foods such as tofu (soybean curd) shoyu(soy sauce) miso (soybean paste) natto (fermented soybean) and soybean milk Ahuge amount of water (about 12e15 times the volume of soybeans) is used in the soak-ing process to clean the beans before further processing The produced wastewatercontains soluble peptides and carbohydrates such as glucose fructose and raffinosewith COD values up to 10 gL It is commonly forwarded to wastewater treatmentwith a consequent disposal of valuable compounds and water resources

An integrated membrane system for the recovery of water and soluble materialsfrom soybean soaking water was developed by Guu Chiu and Young (1997) Theprocess depicted in Figure 187 is based on the use of NF and RO membranes NFand RO retentates collected at weight concentration ratios of 7 and 6 respectivelywere further treated by fermentation to assess the possibility of producing lacticacid from fermenting soluble materials To this purpose NF and RO retentates wereinoculated with probiotic cultures of Lactobacillus acidophilus CCRC 10695 and Bifi-dobacterium longum CCRC 11847 Results revealed that a combination of bothselected cultures produced up to 75 gL organic acids mainly represented by lacticacid after 48 h fermentation at pH 55 and a temperature of 37 C After centrifugationand pasteurization the fermentation broth is suitable for the formulation of lactic acidbeverages whereas the RO permeate can be reused in the plant site for cleaning andsoaking

574 Advances in Membrane Technologies for Water Treatment

A membrane-based process to extract proteins oligosaccharides and isoflavonesfrom yellow bean product wastewater was patented by Jiang and Wang (2013) Theprocess involves a UF step to concentrate a soybean protein solution that can bethen spray-dried to obtain a pure soybean protein powder Soy isoflavones containedin the UF permeate are adsorbed onto weak polar macroporous resins and then elutedwith ethanol which is used in the production of soybean isoflavones NF membranesseparate soybean oligosaccharides from the resin effluent liquid and the concentratedliquid is used to prepare oligosaccharide powder Finally RO membranes removeinorganic salts from the NF permeate producing pure water

NF and ROmembranes were also used to concentrate oligosaccharides from steamedsoybean wastewater in tofu processing (Matsubara Iwasaki Nakajima Nabetani ampNakao 1996) The wastewater was pretreated by UF membranes that rejected high-molecular-weight proteins oligosaccharide components such as sucrose raffinoseand stachyose scarcely rejected by UF membranes were concentrated by spiral-woundNF (NTR-7250) and RO (NTR-7199) membranes manufactured by Nitto-Denko Con-centrations of oligosaccharides of 10 (wv) and 22 (wv) were obtained by RO andNF respectively operating according to a batch concentration configuration

188 Conclusions and future trends

The implementation of water reuse practices in the food industry presents a great chal-lenge for both companies and public health authorities regarding knowledge technicalexpertise and documentation

Soybean soaking water

Lactic acidfermentation

Probiotic culturesL acidophilus

B longum

Water for reuse

NF

RO

Lactic acidbeverage

Sedimentation

Centrifugation

Figure 187 Recovery of soluble compounds and water from soybean soaking waterAdapted from Guu et al (1997)

Membrane technologies for water treatment and reuse in the food and beverage industries 575

This chapter has given an overview of membrane-based processes for water reuseand environmental control in the treatment of wastewater from food-processing indus-tries High-strength wastewater can be successfully treated by MBRs The perfor-mance of these systems can be improved by optimizing operating parameters andimplementing methods to reduce membrane fouling Future trends in this area willbe devoted to enhancing performance reducing operational costs and prolongingthe lifetime of the membranes

Pressure-driven membrane operations and integrated membrane operations repre-sent useful approaches to the treatment of food-processing wastewaters for reducingsludge production and improving the final purified water quality Case studies referringto the treatment of individual wastewaters from agro-food production (dairy meat soy-bean fruit juices etc) underline the key advantages ofmembrane systems over conven-tional methodologies in water regeneration and various reuses Therefore continuousgrowth of the membrane market can be predicted in upcoming next years taking intoaccount the increasing cost of main water sources and effluent sewer disposal

List of acronyms

BEMR bio-entrapped membrane reactorBOD biochemical oxygen demandCOD chemical oxygen demandDF diafiltrationED electrodialysisMBR membrane bioreactorMF microfiltrationMLSS mixed liquor suspended solidsMWCO molecular weight cutoffNF nanofiltrationOLR organic loading ratePPW poultry-processing wastewaterRO reverse osmosisSRT solid retention timeTOC total organic carbonTSS total suspended solidsTMP transmembrane pressureUF ultrafiltrationVCR volume concentration ratioWPC whey protein concentrate

References

Abu M Y B Rao R M Khan M A amp Liuzzo J A (1984) Clarification of menhaden bailwater effluent by reverse osmosis Journal of Environmental Science and Health PartB-Pesticides Contaminants and Agricultural Wastes 19 67e82

576 Advances in Membrane Technologies for Water Treatment

Afonso M D amp Borquez R (2002a) Review of the treatment of a seafood processingwastewaters and recovery of proteins therein by membrane separation processes e pros-pects of the ultrafiltration of wastewaters from the fish meal industry Desalination 14229e45

Afonso M D amp Borquez R (2002b) Nanofiltration of wastewaters from the fish meal in-dustry Desalination 151 131e138

Afonso M D Ferrer J amp Borquez R (2004) An economic assessment of proteins recoveryfrom fish meal effluents by ultrafiltration Trends in Food Science and Technology 15506e512

Andreacutes L J Riera F A amp Alvarez R (1997) Recovery and concentration by electrodialysisof tartaric acid from fruit juice industries waste waters Journal of Chemical Technologyand Biotechnology 70 247e252

Arnal J M Garciacutea-Fayos B Sancho M amp Leon-Hidalgo M C (2013) Recovery of solvedsalts of the liquid effluents from the manufacture of cured hams Preliminary studyDesalination and Water Treatment 51 1922e1927

Artiga P Carballa M Garrido J M amp Meacutendez R (2007) Treatment of winery wastewatersin a membrane submerged bioreactor Water Science and Technology 56 63e69

Atra R Vatai G Bekassy-Molnar E amp Balint A (2005) Investigation of ultra- andnanofiltration for utilization of whey protein and lactose Journal of Food Engineering 67325e332

Avula R Y Nelson H M amp Singh R K (2009) Recycling of poultry process wastewater byultrafiltration Innovative Food Science and Emerging Technology 10 1e8

Balannec B Geacutesan-Guiziou G Chaufer B Rabiller-Baudry M amp Daufin G (2002)Treatment of dairy process waters by membrane operations for water reuse and milkconstituents concentration Desalination 147 89e94

Balannec B Vourch M Rabiller-Baudry M amp Chaufer B (2005) Comparative study ofdifferent nanofiltration and reverse osmosis membranes for dairy effluent treatment bydead-end filtration Separation and Purification Technology 42 195e200

Basset N Lopez-Palau S Dosta J amp Mata Alvarez L (2014) Comparison of aerobicgranulation and anaerobic membrane bioreactor technologies for winery wastewatertreatment Water Science and Technology 69 320e327

Bleuroocher C Noronha M Feurounfrocken L Dorda J Mavrov V Janke H D et al (2002)Recycling of spent process water in the food industry by an integrated process of biologicaltreatment and membrane separation Desalination 144 143e150

Bohdziewicz J amp Sroka E (2005) Treatment of wastewater from the meat industry applyingintegrated membrane systems Process Biochemistry 40 1339e1346

Bolzonella D amp Cecchi F (2007) Treatment of food processing wastewater In K Waldron(Ed)Handbook of waste management and co-product recovery in food processing (Vol 1pp 573e596) Abington Woodhead Publishing Ltd

Bolzonella D Fatone F Pavan P amp Cecchi F (2010) Application of a membrane bioreactorfor winery wastewater treatment Water Science and Technology 62 2754e2759

Bourseau P Masseacute A Cros S Vandanjon L amp Jaouen P (2014) Recovery of aromacompounds from seafood cooking juices by membrane processes Journal of Food Engi-neering 128 157e166

Casani S Rouhany M amp Knochel S (2005) A discussion paper on challenges and limita-tions to water reuse and hygiene in the food industry Water Research 29 1134e1146

Casu S Crispino N A Farina R Mattioli D Ferraris M amp Spagni A (2012) Wastewatertreatment in a submerged anaerobic membrane bioreactor Journal of Environmental

Membrane technologies for water treatment and reuse in the food and beverage industries 577

Science Health Part A-ToxicHazard Substance and Environmental Engineering 47204e209

Chao A C Asce M amp Tojo S (1987) Permeate quality of ultrafiltration process Journalof Environmental Engineering 113 383e394

Chmiel H Kaschek M Bleuroocher C Noronha M amp Mavrov V (2002) Concepts for thetreatment of spent process water in the food and beverage industries Desalination 152307e314

Chmiel H Mavrov V amp Beacutelieres E (2000) Reuse of vapour condensate from milkprocessing using nanofiltration Filtration and Separation 37 24e27

Cros S Lignot B Bourseau P Jaouen P amp Prost C (2005) Desalination of musselcooking juices by electrodialysis Effect on aroma profile Journal of Food Engineering69 425e436

Cros S Lignot B Jaouen P amp Bourseau P (2006) Technical and economical evaluationof an integrated membrane process capable both to produce an aroma concentrateand to reject clean water from shrimp cooking juices Journal of Food Engineering 77697e707

Feuroahnrich A Mavrov V amp Chmiel H (1998) Membrane processes for water reuse in the foodindustry Desalination 119 213e216

Galanakis C M (2012) Recovery of high added-value components from food wastesConventional emerging technologies and commercialized applications Trends in FoodScience and Technology 26 68e87

Galanakis C M Markouli E amp Gekas V (2013) Recovery and fractionation of differentphenolic classes from winery sludge using ultrafiltration Separation and PurificationTechnology 107 245e251

Gotmare M Dhoble R M amp Pittule A P (2011) Biomethanation of dairy waste waterthrough UASB at mesophilic temperature range International Journal of AdvancedEngineering Science and Technology 8 1e9

Guglielmi G Andreottola G Foladori P amp Ziglio G (2009) Membrane bioreactorsfor winery wastewater treatment Case-studies at full scaleWater Science and Technology60 1201e1207

Guu J K Chiu C H amp Young J K (1997) Processing of soybean soaking water witha NF-RO membrane system and lactic acid fermentation of retained solutes Journal ofAgricultural and Food Chemistry 45 4096e4100

Huang L amp Morrissey M T (1998) Fouling of membranes during microfiltration of surimiwash water Roles of pore blocking and surface cake formation Journal of MembraneScience 144 113e123

Jiang B Wang J (2013) Method for extracting soy protein oligosaccharide and isoflavonefrom soybean wastewater by one-step process Chinese patent CN103265614-A

Johns M R (1995) Developments in wastewater treatment in the meat processing industryBioresource Technology 54 203e216

Judd S (2011) The MBR Book Principles and applications of membrane bioreactors forwater and wastewater treatment (2nd ed) Oxford UK Elsevier Ltd

Kanai M Ferre V Wakahara S Yamamoto T amp Moro M (2010) A novel combination ofmethane fermentation and MBR e Kubota Submerged Anaerobic Membrane Bioreactorprocess Desalination 250 964e967

Kane J amp Osantowski R (1981) An evaluation for water reuse using advanced wastetreatment at a meat packing plant In Proc 35th Purdue industrial waste Conf (p 617) AnnArbor MI Ann Arbor Sci

578 Advances in Membrane Technologies for Water Treatment

Katayon S Megat Mohd Nool M J Ahmad J Abdul Ghani L A Nagaoka H amp Aya H(2004) Effects of mixed liquor suspended solid concentrations on membrane bioreactorefficiency for treatment of food industry wastewater Desalination 167 153e158

Koyuncu I Turan M Topacik D amp Ates A (2000) Application of low pressure nano-filtration membranes for the recovery and reuse of dairy industry effluents Water Scienceand Technology 41 213e221

Liao B Q Kraemer J T amp Bagley D M (2006) Anaerobic membrane bioreactorsApplications and research directions Critical Reviews in Environmental Science andTechnology 36 489e530

Lo Y M Cao D Argin-Soysal S Wang J amp Hahm T S (2005) Recovery of protein frompoultry processing wastewater using membrane ultrafiltration Bioresource Technology96 687e698

Mameri N Abdessemed D Belhocine D Lounici H Gavach C Sandeaux J et al(1996) Treatment of fishery washing water by ultrafiltration Journal of Chemical Tech-nology and Biotechnology 67 169e175

Mannapperuna J D amp Santos M R (2004) Reconditioning of poultry chiller overflow byultrafiltration Journal of Food Process Engineering 27 497e516

Masseacute A Vandanjon L Jaouen P Dumay J Kechaou E amp Bourseau P (2008)Upgrading and pollution reduction of fishing industry process-waters by membrane tech-nology In J P Bergeacute (Ed) Added value to Fisheries wastes (pp 81e99) KeralaTransworld Research Network

Matsubara Y Iwasaki K Nakajima M Nabetani H amp Nakao S (1996) Recovery ofoligosaccharides from steamed soybean waste water in Tofu processing by reverse osmosisand nanofiltration membranes Bioscience Biotechnology and Biochemistry 60 421e428

Mavrov V Chmiel H amp Beacutelieres E (2001) Spent process water desalination and organicremoval by membranes for water resuse in the food industry Desalination 138 65e74

Moresi M amp Lo Presti S (2003) Present and potential applications of membrane processingin the food industry Italian Journal of Food Science 15 3e34

Mulidzi A R (2010) Winery and distillery wastewater treatment by constructed wetland withshorter retention time Water Science and Technology 61 2611e2615

Muro C Riera F amp del Carmen Diaz M (2012) lsquoMembrane separation process in waste-water treatment of food industry In B Valdez (Ed) Food industrial processes - Methodsand equipment (pp 253e280) Rijeka InTech

Mutamim N S A Noor Z Z Abu Hassan M A amp Olsson G (2012) Application ofmembrane bioreactor technology in treating high strength industrial wastewater A per-formance review Desalination 305 1e11

Ng K K Lin C F Panchangam S C Hong P K A amp Yang P Y (2011) Reducedmembrane fouling in a novel bio-entrapped membrane reactor for treatment of food andbeverage processing wastewater Water Research 45 4269e4278

Noronha M Britz T Mavrov V Janke H D amp Chmiel H (2002) Treatment of spentprocess water from a fruit juice company for purposes and reuse Hybrid process conceptand on-site test operation of a pilot plant Desalination 143 183e196

Passeggi M Lopez I amp Borzacconi L (2009) Integrated anaerobic treatment of dairyindustrial wastewater and sludge Water Science and Technology 59 501e506

Paulson D J Wilson R L amp Spatz D D (1984) Crossflow membrane technology andits applications Food Technology 38 77e87

Pearce R J (1983) Thermal separation of beta-lactoglobulin and alpha-lactalbumin in bovinecheddar cheese whey New Zealand Journal of Dairy Science 15 13e22

Membrane technologies for water treatment and reuse in the food and beverage industries 579

Riera F A Suarez A amp Muro C (2013) Nanofiltration of UHT flash cooler condensatesfrom a dairy factory Characterisation and water reuse potential Desalination 309 52e63

Saravia H Houston J E Toledo R T amp Nelson H M (2005) Economic analysis ofrecycling chiller water in poultry processing plants using ultrafiltration membrane systemsJournal of Food Distribution Research 36 161e166

Shih J amp Kozink M B (1980) Ultrafiltration treatment of poultry processing wastewater andrecovery of a nutritional by-product Poultry Science 59 247e252

Sroka E Kaminski W amp Bohdziewicz J (2004) Biological treatment of meat industrywastewater Desalination 162 85e91

Stephenson T Brindle K Judd S amp Jefferson B (2000) Membrane bioreactors forwastewater treatments London UK IWA Publishing

Uchida T Sato K Kawasaki Y Dosako S (1996) Separation of lactoperoxidase secretorycomponent and lactoferrin from milk or whey with a cation exchange resin US Patent5516675

Valderrama C Ribera G Bahiacute Rovira M Gimeacutenez Nomen R et al (2012) Winerywastewater treatment for water reuse purpose Conventional activated sludge versusmembrane bioreactor (MBR) A comparative study Desalination 308 1e7

Vandanjon L Cros S Jaouen P Queacutemeacuteneur F amp Bourseau P (2002) Recovery bynanofiltration and reverse osmosis of marine flavours from seafood cooking watersDesalination 144 379e385

Vourch M Balannec B Chaufer B amp Dorange G (2005) Nanofiltration and reverseosmosis of model process waters from the dairy industry to produce water for reuseDesalination 172 245e256

Vourch M Balannec B Chaufer B amp Dorange G (2008) Treatment of dairy industrywastewater by reverse osmosis for water reuse Desalination 219 190e202

Walha K Ben Amar R Masseacute A Bourseau P Cardinal M Cornet J et al (2011)Aromas potentiality of tuna cooking juice concentrated by nanofiltration LWT FoodScience and Technology 44 153e157

Yorgun M S Akmehmet Balcioglu I amp Saygin O (2008) Performance comparison ofultrafiltration nanofiltration and reverse osmosis on whey treatment Desalination 229204e216

Zhang S Q Kutowy O Jumar A amp Malcolm I (1997) A laboratory study of poultryabattoir wastewater treatment by membrane technology Canadian Agricultural Engi-neering 39 99e105

Zydney A (1998) Protein separations using membrane filtration New opportunities for wheyfractionation International Dairy Journal 8 243e250

580 Advances in Membrane Technologies for Water Treatment

Membrane technologies forwater treatment and reusein the pulp and paper industries

19M Meuroantteuroari M Kallioinen M NystreuroomLappeenranta University of Technology Laboratory of Separation TechnologySkinnarilankatu Lappeenranta Finland

191 Introduction

Processes in the pulp and paper industry are based on the use of water and its proper-ties Although pulping processes can also be carried out using organic solvents wateris the dominating medium where the liberation of cellulose fibers from wooden mate-rial takes place Water is also needed to transport raw materials seal process equip-ment cool and heat wash and clean process equipment remove impurities andgenerate the necessary environment for the formation of the hydrogen-bondingnetwork between fibers and fillers which is the basic mechanism of paper formationTherefore a huge amount of water is necessary for pulp and paper productionprocesses

Water quality demands vary greatly A relatively low purity of water can be used inless demanding applications Therefore the pulp and paper industry has succeeded inreducing freshwater consumption or wastewater discharge significantly by increasingwater recirculation with no special purification processes For instance fiber recoveryfrom water discharged from a paper machine is made by flotation or filtration and theresidual water is typically reused in the process This kind of water has a low content ofsuspended solids but contains almost all dissolved compounds This water has a useeg in shower water in low-pressure showers on the paper machine However withoutadditional treatment further reuse of water causes severe problems because of theexponential accumulation of contaminants For instance dissolved impurities mightplug the nozzles of high-pressure showers that are used to clean paper machine fabricsThis would lead to production breaks on the paper machine Other detrimental influ-ences caused by insufficient process water quality are problems running the paper ma-chine or even the printing machine for end users It is obvious that water qualitysignificantly affects product quality For instance some residual organic compoundsin liquid packaging cardboard might cause an unpleasant smell or taste in foodsupplies

A modern paper machine consumes less than 10 m3 water per 1 ton of producedpaper This is 10 times less than some decades ago For instance in Finland thepulp and paper industry has succeeded in decreasing their environmental impact signif-icantly during the past 20 years by applying biological water treatment and by closing

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400019-8Copyright copy 2015 Elsevier Ltd All rights reserved

the water circulation As Table 191 shows the decrease in chemical oxygen demand(COD) for instance and absorbed organic halogen (AOX) load per ton of paper orpulp was 69 and 87 respectively between 1992 and 2012 The high reductionin AOX load resulted from changes in pulp bleaching processes to elementalchlorine-free bleaching in the beginning of the 1990s However as the emission valuesfrom 2012 show (Table 191) significant amounts of pollutants are left in the dischargewaters Many can be removed more efficiently if membranes are applied in the puri-fication processes as will be shown later in this chapter

1911 Driving forces for the use of membrane filtration

In Nordic countries water scarcity is not usually a reason to reduce water use in millsHowever the situation is totally different in central Europe or New Mexico forinstance where water scarcity has forced the McKinley cardboard mill to move to aliquid effluent-free operation (Pohjalainen 1999) Probably the most common causefor reducing water discharge comes from legislation and environmental demandsthat lead the mill to use advanced water treatment such as membranes for wastewatersSometimes a mill is situated close to a sensitive waterway such as the Artic Paper Mun-kedal paper mill in Sweden where in 1999 a tubular ultrafiltration unit was installed topurify 50 of the mill effluent (Hepp Joore Schonewille amp Futselaar 2005) Themill is located next to one of the finest salmon rivers in the country therefore thereis high demand for environmentally friendly paper production for example by closingthe water circulation In the future there might be limitations on how much water canbe used in the production of a specific product and the so-called ldquowater footprintrdquomight be a more important parameter when sustainability of different products are

Table 191 Total emission to waterways and reduction inenvironmental load related to amount of Finnish pulp cardboardand paper production between 1992 and 2012

Emission of pollutantsin 2012 ta

Reduction of emissionsbetween 1992 and 2012

Amount of wastewater 45

Suspended solids 10000 69

COD 133000 69

BOD 10000 87

Nitrogen 2175 47

Phosphorus 133 76

AOX 850 87

Reprinted from Anon (2013a) with permission from Elsevier

582 Advances in Membrane Technologies for Water Treatment

evaluated Therefore legislation and sometimes customer demand might lead com-panies to reduce water consumption and environmental emissions

Less often the reason for reducing water consumption comes from the economyespecially if water purification is the main reason for using membrane filtration How-ever this was the case in Albert Keuroohler Pappen in Gengenbach Germany where thelocal government increased the fee for wastewater sevenfold which led the companyto invest in purification and water recirculation technologies (Junk Dorfer Stratz ampLausch 2008)

Economically the most attractive applications for membrane processes are wheremembranes can be used to recover valuable raw materials from waste streams Agood example is all of the ultrafiltration processes that are used to recover coating pig-ments eg titanium dioxide from waste coating streams In these applications thepayback time might be less than 1 year for ultrafiltration (Anon 2013b)

1912 Barriers to membrane processes

There are also many barriers that restrict the use of membrane processes in the pulp andpaper industry Typically volumes that need to be treated are huge and contain manypossible foulants for membranes This makes it challenging to retain the filtrationcapacity and causes many challenges for membrane usability Obviously this also leadsto large membrane areas and causes the cost of the membrane filtration to be highSometimes the attitude toward the incompatibility of membrane filtration with pulpand paper industry streams is a difficult barrier to surpass In the case of old millsthe lack of space might also restrict the installation of membrane filters althoughthey usually use a small floor space efficiently (Nuortila-Jokinen 2005)

1913 Characteristic properties of waters

As mentioned the water quality requirements vary at different stages of pulp and papermanufacturing processes Naturally the characteristics of process and wastewatersalso differ significantly depending on the process stage from which they originateGenerally the waters contain different amounts of suspended solids such as fibersfillers and fines and dissolved wood-based compounds such as polysaccharides oligo-and monosaccharides lignin and other phenolic compounds such as lignins andlipophilic wood extractives Some such as dissolved bark compounds eg phenoliccompounds sterols or resin acids are known to be toxic to aquatic animals In addi-tion the waters contain chemicals or additives used in to process of raw materials ormanufacture end products It has been estimated that thousands of different com-pounds exist in pulp and paper mill process and wastewaters (Nuortila-JokinenMeuroantteuroari amp Nystreuroom 2003)

Moreover every mill and papermaking process has its own fingerprint related to theprocess and wastewater quality The content of the waters varies but the amount ofimpurities can also change remarkably even at the same production stage For instanceit has been reported that a more than 10 times variation in dissolved organic compoundconcentrations in the same paper machine circulation waters has occurred because of

Membrane technologies for water treatment and reuse in the pulp and paper industries 583

the breaks and different paper qualities (Meuroantteuroari amp Nystreuroom 2004) Therefore mem-branes are exposed to great variation regarding the amount and quality of impurities Inaddition if all of the pulp and paper manufacturing processes are taken into accountthere is great variation in temperature and pH Temperatures for instance vary fromvery low (external wastewater treatment (WWT)) to above 100 C (process waters andliquors in pulp plants) and pH varies from less than 2 to 14 (Anon 2010)

1914 Special demands for membranes and modules in pulpand paper capacity and stability

Process streams in the pulp and paper industry are huge as much as cubic meters persecond Therefore membrane permeability needs to be high and the flux stable withminimal operational breaks Unfortunately characteristic properties of waters and theirquantitative and qualitative variations seldom lead to stable filtration capacity iefouling leads to decline of capacity and to operational breaks and cleaning A highoperation temperature the existence of hard particles and a wide variety of foulantsas well as periodical cleaning processes might shorten the operational lifetime of amembrane

Generally the higher the capacity is the lower retention is Sometimes pluggedmembrane pores affect the flux of MF membranes more dramatically than UF mem-branes and the flux can be even higher with tighter UF membranes Therefore the se-lection of an optimal membrane cannot be based only on the membrane propertiesstated by the manufacturer Process and wastewaters have different compositionsand filtration experiments are the only means by which to judge the applicability ofmembrane processes for the cases in question Despite the challenging environmentin the pulp and paper industry it is possible to achieve stable capacity over yearsby selecting a correct hydrophilic membrane and an appropriate filter as the exampleof a paper mill in Lohja Finland proves (Section 193)

1915 Selectivity

Another requirement for a membrane is selectivity In WWT selectivity is not the mostcrucial requirement but if membranes aim to separate product compounds in futurebiorefinery applications selectivity will be an extremely important characteristicIn process and WWT selectivity is obviously needed but high and stable capacityovertime is an even more important property for the membrane

One important advantage offered by membrane is that separation efficiency (selec-tivity) can be tailored by selecting an appropriate membrane filtration process Asshown in Figure 191 the purified water is free from suspended solids when MF isused or it can be almost completely free from dissolved materials when reverseosmosis (RO) is used Depending on demands the most suitable membrane processesare chosen Using nanofiltration (NF) it is possible to retain metal ions such as bariumiron and manganese which are sparingly soluble or cause the higher consumption ofbleaching chemicals Nanofiltration is also efficient when sulfate ions need to beremoved However as will be discussed later chloride concentrations can be even

584 Advances in Membrane Technologies for Water Treatment

higher in permeate of NF than in the feed solution Therefore to remove monovalention RO electrodialysis (ED) or ion exchange is needed

1916 Module configurations

Because of a very demanding environment in which membranes are in the pulp andpaper industry special module configurations are commonly used In particular mod-ules in which high shear forces are generated on the membrane surface are commonlyapplied to prevent flux decline They can frequently be operated with minor pretreat-ment compared with conventional spiral-wound modules A drawback is that the shearmight cause a shorter lifetime for the membranes Although high shear rate modulesdominate industrial-scale applications all kinds of membrane modules are in use

A high shear rate on the membrane surface can be achieved in tubular modules byincreasing the pumping velocity but this strongly influences energy consumptionbecause under turbulent conditions power will vary with velocity up to a power of275 (Merry 1999) In addition it is estimated that in conventional cross-flow filtrationsystems only about 10 of energy is converted into shear on the membranes There-fore high shear rate modules have been developed to better use energy in generatingturbulent conditions Culkin Plotkin and Monroe (1998) claimed that the so-calledvibratory sheareenhanced processing (VSEP) filter allows nearly 99 of total energyused to be converted into shear at the membrane surface This is because the energy isdirected to create shear forces only into a thin zone near the membrane surface TheVSEP is a vertical plate-and-frame type construction in which membrane sheets are

Microfiltration

Ultrafiltration

Reverse osmosis

01ndash02 μm

Nanofiltration 100ndash150 gmol

50 gmol

1000 gmol

Algae

Bacteria

Giardia Turbidity

Galactoglucomannan

Sugars

Lignin

Suspended solids

Colloidal extractives

Glucoisosaccharinic acid

H2O

Phenols

Strerols

Lignans

Ca2+ Mg2+ Resin acids

Na+ Clndash

SO42ndash

Arabinoglucurono-xylan

Acetic acid

Figure 191 Separation scheme for pressure-driven membrane processes

Membrane technologies for water treatment and reuse in the pulp and paper industries 585

stacked on top of each other and the whole membrane stack is vibrated The VSEP pro-cess imposes an oscillatory motion on the whole module which generates a shear rateas high as 150000s on the membrane surface about 10 times that achievable in con-ventional cross-flow filtration

Similarly with the cross-rotational (CR) filter the rotor blade mixes only small vol-umes on the membrane surface Fouling control in the CR membrane unit (CR filterfrom Valmet Corp) is achieved by rotating rectangular plates between all membranesheets thus generating shear directly at the membranersquos surface In this constructionthe membrane itself does not move In industrial-scale applications the CR filter isthe most commonly used high shear rate filter The maximum pressure in the VSEPis 38 bar which is significantly higher than what can be achieved with CR filters(around 8 bar) Therefore the VSEP is an attractive choice especially for NF processesRecently several other membrane filters based on rotating membrane plates have beendeveloped Both polymeric and ceramic membranes can be applied in these filters butthey have not yet found a place in the pulp and paper industry (Jaffrin 2008)

Spiral-wound modules have also been used for several years to treat waters in papermills A prerequisite for their successful use is appropriate pretreatment which needsto remove suspended solids to prevent plugging of the feed channels and reduce theamount of foulants Therefore pretreatment consists of several processes includingtraditional physical and chemical separation processes (Lien amp Simonis 1995) A sec-ond membrane process such as UF has also been shown to be a sufficient pretreatmentfor NF with spiral-wound modules (Sutela 2008)

1917 Use of membranes in pulp and paper mills

Membranes are an excellent choice for purifying raw water recirculating processwater purifying effluents and recovering and purifying valuable compounds fromdifferent streams in the pulp and paper industry Figure 192 illustrates the use of mem-branes in water and WWT in pulp or paper mills as presented in this chapter

Simultaneous purification of process water and recovery of side product Section 194

Conventionalactivated sludge(CAS) treatment

Purification of processwaters for reuse Section 193

Purification of rawwater Section 195

Removal of nonbiodegradablecompounds prior to CAS treatment Section 19212

Direct membrane treatment to purify effluents Section 1922

MBR

Upgrading purificationlevel Section 19211

Section 19213

Figure 192 Simplified drawing of different options for using membranes related to pulp andpaper manufacturing

586 Advances in Membrane Technologies for Water Treatment

Membrane processes can be used as internal kidneys close to the place where waste-water is generated It might be beneficial to retain the purified water temperature andpH level equal to the process levels These advantages are achieved when eg papermachine process waters are recirculated (Section 193) In addition by keeping spe-cific water streams unmixed membrane processes can be focused on the most relevantstreams and thus only smaller volumes would need to be treated (as in the treatment ofevaporator condensate and coating wastewaters see Sections 1922 and 1941respectively) Today coating color recovery from waste coating streams is the mostcommon membrane filtration application in the pulp and paper industry Furthermoremembranes are applied to treat a wide variety of process streams and effluents such aspaper mill process water and bleaching effluents (Section 193) Membranes can oper-ate either alone or combined with biological or other chemical and physical processes(Sections 19211e19213)

192 Purification of wastewaters

1921 Membrane processes combined with biological WWT

Membrane processes are used to upgrade the purification results of biological WWTand before biological treatment to reduce the amount of scarcely biodegradable com-pounds in effluents In addition about 15 years ago some paper mills implementedmembrane bioreactors (MBRs) as an essential part of their wastewater purificationsystems

19211 Membrane processes to upgrade purificationresults of biological WWT

Membrane filtration makes it possible to upgrade existing WWT plant efficiency Forinstance the Eltmann newsprint mill of Papierfabrik Palm has used NF to improvethe quality of activated sludge process effluent since 1999 Sand filtration wasapplied to polish effluents before spiral-wound NF Nanofiltration succeeded inreducing about 90 of COD and color and about 60 of AOX As thought NFretained divalent ions excellently but the apparent retention of chloride ions was40 (Schirm Welt amp Ruf 2001)

Depending on the membrane filtration conditions amount of multivalent anionsand ratio of multivalent to monovalent ions NF can concentrate monovalent anions(chloride) into permeate because of the Donnan effect Therefore the apparent reten-tion of chloride ions can be negative even some as much as 100 This might limit thereusability of NF permeate When removal of monovalent ions such as chloride ion isneeded RO ED and ion exchange are the choices of technology

Electrodialysis is commonly defined as an electrochemical separation process inwhich electrically charged membranes and an electrical potential difference insteadof pressure are used to separate ionic species from an aqueous solution and other un-charged components In the pulp and paper industry ED is being studied for theremoval of chloride ions and other nonprocess elements before reuse of purified waters

Membrane technologies for water treatment and reuse in the pulp and paper industries 587

(Ferreira Amaral amp Machado 2004 Geraldes amp De Pinho 1995 Pfromm Tsa ampHenry 1999 Rapp amp Pfromm 1998)

In the Eltmann newsprint mill the membrane concentrate is recirculated back intothe activated sludge plant after lime precipitation The lime precipitation removes about99 of iron 60 of silicate and about 30 of sulfate ion In addition 40 of organiccompounds (measured as COD and AOX) and over 70 of colored compounds areremoved by this lime precipitation Therefore precipitation removes a significantamount of organic compounds in which biodegradability is not obvious In principlecompounds that have already been treated biologically (activated sludge process) areprobably not the most biodegradable and therefore their recirculation back into theactivated sludge process might not lead to their degradation (Schirm et al 2001)

Another alternative for treating membrane concentrate before recirculation backinto the activated sludge process is a mild oxidation which has been reported toenhance the biodegradability of NF concentrate (Meuroantteuroari Kuosa Kallas amp Nystreuroom2008 Mauchauffee Denieul amp Coste 2012) For instance ozonation was demon-strated to improve the biodegradability of NF concentrate although the amount of dis-solved organic carbon did not change Recently Panorel et al (2014) reported thatpulsed corona discharge treatment can oxidize lignin for example using about one-third of the energy needed in ozonation Therefore the reduced cost of oxidationprocesses enables the wider use of oxidative treatments in WWT and will help treatmembrane concentrates in the future

Mauchauffee et al (2012) tested different process alternatives for the treatment ofprinting paper mill effluents They concluded that the best process concept would be toupgrade existing anaerobic and aerobic treatment with suspended solids removal soft-ening to reduce the scaling potential of the effluent NF to remove organic compoundsand evaporation or oxidation to treat NF concentrate In addition softening by addinglime calcium and carbonate with a specific mixing reactor and settler significantlyimproved NF performance ie a higher recovery and better permeate quality wasachieved after the softening process Lime softening was also applied by MeuroantteuroariDaltrophe Oren Gilron and Nystreuroom (2001) to remove hardness from paper mill pro-cess waters

Several studies have also been published in which high shear rate CR NF orlow-pressure RO is studied directly as a polishing stage after biological treatmentFor instance a permeate flux of 150 L(m2h) at a volume reduction of 12 a pressureof 10 bar and a temperature of 40 C was achieved when discharge water from a pulpand paper mill WWT plant (activated sludge treatment) was nanofiltered (Meuroantteuroariet al 2008) The reported flux from spiral-wound NF in the Eltmann newsprint millwas significantly lower at 10e30 L(m2h) (Schirm et al 2001) It is clear that ahigh shear rate facilitates flux by reducing concentration polarization and fouling onthe membrane surface

Generally the permeate fluxes obtained from the filtration of biologically treatedeffluents are significantly higher than those obtained in the filtration of paper machineprocess waters (Meuroantteuroari amp Nystreuroom 2007) This is because of the lower amount ofimpurities left in the biologically treated water On the other hand heat recovery ismore difficult to performwhen biologically treated water is circulated back into themill

588 Advances in Membrane Technologies for Water Treatment

In the United States a closed cycle paper mill combines biological treatment mem-brane technology and evaporation to prevent the discharge of liquid effluent(McKinley Linerboard Paper Company New Mexico) There is no water recipientnear the mill for discharging even a minimal amount of effluent and raw water avail-ability is restricted because the mill is located in the desert of northwestern NewMexico Thus raw water consumption has been minimized to only 15 m3ton card-board product A waste stream of 33 m3ton cardboard produced is cleaned and finallyconcentrated using MF and RO membranes First flotation is used to separate fibersfines and stickers from the water then activated sludge treatment in sequenced batchreactors is carried out before membrane filtration Concentrated salts after RO treat-ment are crystallized by a tube-type falling film evaporator and its condensate is recir-culated back into the process (Durham 2000 Pohjalainen 1999) This example showsthat it is technically possible to recirculate all water but some fresh water is alwaysneeded because of evaporated process water during the manufacturing process

19212 Membrane processes to improve functioningof biological WWT

One of the most studied applications for membranes in the pulp and paper industry isthe purification of the strongly colored effluents from bleached kraft pulp mills Thefirst alkaline extraction stage effluent is a good example of a stream whose environ-mental impact is remarkably high compared with its volume For instance it hasbeen estimated that the first alkaline extraction stage effluent constitutes only5e10 of the total effluent volume of the mill but it contains about half of the colordischarge The strong color results from the high molar mass lignin molecules that aredifficult to biodegrade in conventional activated sludge treatment Also the COD andthe BOD loads of the first alkaline extraction stage effluent are high Fortunately thelarge sizes of the molecules and their high charge densities owing to high pH make thealkaline bleach plant effluents easier to filter using UF than the preceding chlorinationstage effluents containing smaller molar mass compounds (Jeuroonsson 1989 ZaidiBuisson Sourirajan amp Wood 1992) Therefore many researchers have studied mem-brane filtration with the aim of purifying the alkaline extraction stage effluents for reuseUltrafiltration membranes with cutoff values of some thousands of grams per mole havebeen shown to significantly decrease the color BOD COD and AOX loads of bleach-ing effluents and enable the use of the treated effluent for example for washing pur-poses Permeate of UF-treated bleaching effluent can also be more efficiently purifiedin biological treatment plants because UF removes slowly degrading high molarmass lignin compounds and decreases the amount of chlorinated compounds whichare resistant to attack by most microorganisms used in the biological treatment plantAccordingly the load on the treatment plant decreases and the average biodegradabilityof the remaining compounds increases The concentrate of the UF process is generallyburned in the recovery furnace where the cooking chemicals are recovered

In Sweden in the StoraEnso Nymeuroolla pulp mill UF has been used since 1995 toreduce the COD load of the mill effluent before treatment in the activated sludge plantThe mill produces pulp from both hardwood and softwood using the magnesium

Membrane technologies for water treatment and reuse in the pulp and paper industries 589

bisulfite process and oxygen bleaching The UF plant is based on tubular membraneswith a total membrane area of 4638 m2 (Greaves 1999) On average about 400 m3

effluent water is treated by the membrane plants in Nymeuroolla every hour The effluentof the oxygen bleaching stage on the pulping process has an average COD of around10 gL The aim for UF was to reduce 50 of the COD load in addition the aim was toconcentrate the organic compounds to the point where the concentrate could be incin-erated Therefore a high-volume reduction (50e60 times) was needed in UF toincrease the COD of the concentrate to 180 gL

Permeate is discharged to an activated sludge plant In this mill different tight UFmembranes were needed in the filtration of hardwood and softwood effluents becauseof variations in effluent composition The fluxes are about 60 and 70 L(m2h) at 7 and8 bar pressure for softwood and hardwood effluents respectively The high UF oper-ation temperature (up to 82 C) eliminates the need for rapid cooling before the mem-brane plant and decreases the fouling of the membrane caused by extractivesFurthermore the pH of the softwood effluents is controlled to keep it above 11This was also observed to reduce fouling of the membranes Reported energy con-sumption from the Nymeuroolla mill is approximately 39 and 15 kWm3 for hardwoodand softwood respectively (Anon 2013b Greaves 1999 Nordin amp Jeuroonsson 2008)

19213 Membrane bioreactors

Conventional aerobic WWT systems (conventional activated sludge [CAS]) are estab-lished as end-of-pipe technology in the paper industry It is estimated that the activatedsludge process is used in 60e75 of all biological effluent treatment plants in the pulpand paper industry The activated sludge plant consists of two main units the aerationbasin and the secondary clarifier (sedimentation basin) In the aeration basin theeffluent is treated with a mixture of microorganisms (activated sludge) which are pre-sent in high concentration The biomass (sludge) and water are separated by settlingbiomass in large clarifiers or by flotation after microbial degradation Generally theactivated sludge process achieves high treatment efficiencies However the biomassis vulnerable to disturbances such as spillages of concentrated liquor and operationalinstability and the purification efficiency varies somewhat

An MBR usually consists of an aerated bioreactor similar to the activated sludgeprocess combined with a membrane process to separate the biomass from the effluentIn an MBR a membrane replaces the settling or flotation stage in the conventional acti-vated sludge plant and separates completely suspended solids ie biomass In bothsystems dissolved organic components are converted by aerobic microorganisms toinorganic products such as carbon dioxide and water The filtered effluent from themembrane stage can be reused in the process while the separated biomass is recircu-lated into the bioreactor Sometimes surplus biomass is discharged Two basic MBRconfigurations exist one in which the membranes are immersed in the reactor andare an integral part of the biological reactor (internalsubmerged Section Paperie duRhin) and one in which the membranes are a separate unit process after the biologicalreactor (externalsidestream Section Ugchelen BV)

590 Advances in Membrane Technologies for Water Treatment

In principle there are several advantages of MBR processes over CAS treatmentsuch as a longer sludge age a higher biomass concentration (mixed liquor suspendedsolids (MLSS)) up to 30 gL a lower hydraulic retention time and a higher volumetricload In MBR complete retention of sludge by a membrane process makes it possibleto maintain high MLSS in the bioreactor which causes long sludge retention time anda low food-to-microorganism ratio The long sludge retention time also causes lesssludge production whereas a low food-to-microorganism ratio enables the hydraulicretention time to be reduced It has been pointed out that sludge production is inverselyproportional to the hydraulic retention time when MLSS is fixed Therefore the short-est hydraulic retention time and minimal sludge production cannot be achieved simul-taneously In addition the cost of aeration increases when sludge production isminimized and vice versa The high MLSS restricts oxygen transfer in the aerationtank and membrane scouring by air and increases membrane fouling Therefore thereis an optimum point at which the total operational cost is minimized and operating anMBR at very high MLSS is not common As a result the apparent excess sludge pro-duction is not much different from CAS although in principle even zero sludge pro-duction is possible with MBR (Stephenson Judd Jefferson amp Brindle 2000 YoonKim amp Yeom 2004)

The use of chlorine in the pulp bleaching process and the existence of slowlybiodegradable compounds in the waste and process waters may cause problems formicroorganisms in biological treatment The microbes in the MBR process operateat a high MLSS concentration and a long solids retention time is shown to be fasterwhen adapted for this kind of wastewater Therefore the purification results mightimprove with time as was shown after a 3-month operation period at VHP Securitypaper mill owned by Ugchelen BV The full-scale plant outperformed resultsachieved in pilot experiments The COD was reduced from 3500 to 600 mgL in pilotexperiments and to 450e500 mgL in the full-scale plant (Amaral Lange amp Borges2012 Hepp et al 2005 Ramaekers van Dijk Lumpe Verstraeten amp Joore 2001Simstich amp Oeller 2010)

Additional advantages are almost total retention of suspended solids high organicmatter removal and a low footprint which might sometimes be a critical demand whenpurification capacities of an existing plant are enlarged Membrane separation excludesthe sludge bulking problems often caused by unstable organic loading rate in CAS anMBR is therefore more tolerable to organic loading chock However in MBR a stableincoming load is needed to minimize membrane fouling When wastewater is purifiedfor reuse an important advantage and goal is bacteria- and suspended solidsefree wa-ter Typically MBR processes use membranes with pore sizes of 001e045 mmTherefore it can be assumed that all suspended solids and bacteria are removed bythe membrane filtration stage The high quality of the purified effluent makes MBRtechnology ideally suited for use as an internal water circuit treatment However dis-solved organic or inorganic compounds are not retained by the membrane and theirremoval efficiency depends on the functioning of the biological process In additionto water reuse an MBR process especially when applied at thermophilic conditionsenables the reuse of energy At thermophilic conditions an MBR is operated in the

Membrane technologies for water treatment and reuse in the pulp and paper industries 591

same temperature range as the paper machine (40e65 C) thus there is no need tocool or heat the process water

As in all membrane processes including MBR processes membrane fouling man-agement needs to be taken into account Depending on the MBR configuration this isdone by backflushing bubbling air close to the membrane surface and controllingpermeate flux Air is also consumed by microorganisms and typically air bubblingcauses more than 50 of operation costs In many cases membrane and operationalcosts are somewhat higher than in CAS processes but to evaluate total costs benefitssuch as water recirculation energy recovery operation at thermophilic conditions reli-ability of the process effluent quality achieved and possible reduced costs for sludgetreatment have to be taken into account (Anon 2013b) Helble and Meuroobius (2009)reported that total specific operation costs for MBR with submerged and with aeratedvertical tubular cross-flow membranes amount to 022 Vm3 Membrane bioreactorswith classical tubular cross-flow membranes consume slightly more energy and theoperation cost is around 033 Vm3 When capital costs are included the total annualcosts are in the range 056e059 Vm3

Paperie du RhinA paper roll mill in Paperie du Rhin in France installed an MBR process based onhollow-fiber membranes (Table 192) The mill uses recycled (not de-inked) paperas the raw material for the production of 40000 tons of paper rolls annually The biore-actor (1500 m3) is operated at an MLSS content of 12e16 gL The wastewater fromthe mill is first prescreened with drum screens then it is sent to an equalization basinfrom which it is pumped directly into the bioreactor The MBR process decreased theCOD from 4000 mgL to less than 200 mgL and the BOD from 1700 mgL to less than5 mgL Permeate is partly recycled as process water The main reasons for choosingMBR treatment were on-site space limitations and the need to recirculate the purifiedwater (Ramaekers et al 2001)

Ugchelen BVVHP security paper mill owned by Ugchelen BV located in Apeldoorn TheNetherlands produces bank notes and other security papers (Table 192) The papermill uses cotton as a raw material which it bleaches with hydrogen peroxide at atemperature of approximately 100 C and a pH between 11 and 12 The high pH ofthe wastewater makes purification a challenge The mill developed a wastewater puri-fication process in which dissolved carbon dioxide was used in a flotation process toremove fibers and debris and reduce the effluent pH from 11 to 82 before the MBRunit The MBR operates at thermophilic conditions to reduce the need to heat thepurified water (temperature around 55 C) The 8-mm tubular polyvinyl fluoridemembrane is installed outside the bioreactor (volume 250 m3) The MBR effluentCOD is stabilized to about 500 mgL (influent 3500 mgL) The MBR-treatedeffluent is recirculated with no detrimental effect on product quality This enablesthe mill to reduce the freshwater intake for bleaching by 80 and the mill wastewaterdischarge by 50 (Hepp et al 2005 Joore Wortel amp Bronold 2001 Ramaekerset al 2001)

592 Advances in Membrane Technologies for Water Treatment

Table 192 Examples of existing membrane bioreactors in pulp and paper industry

Keuroohler Pappen DE Ugchelen BV Paperie du Rhin

MBR type Hollow fibers submerged Tubular external Hollow fibers submerged

Amount of wastewater m3day 670 240 900

Pore size nm 40 40 40

Membrane area m2 5000 83

Average flux L(m2h) 8 120 15

Operating pressure bar 35 015

Cross-flow velocity ms e 35 e

Biomass concentration gL 10e12 12e16

Food to biomass ratiokg BODkg SS d

lt02

COD reduction 94 86 95

Adopted from Ramaekers et al (2001) Hepp et al (2005) Anon (2013b)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

pulpand

paperindustries

593

Albert Keuroohler PappenOne benefit of MBR compared with conventional activated sludge treatment is theusability of the MBR filtrate for further purification with spiral-wound membranesAn MBR was combined with downstream RO in a cardboard mill (Albert KeuroohlerPappen in Gengenbach Germany) (Table 192) The mill annually manufactures35000e40000 tons of high-quality cardboard on three paper machines Manydifferent grades are produced some of which are heavily colored Process waterwas taken from wells and before implementing the MBR the wastewater was dis-charged into the municipal sewer after sedimentation The main reason for investingin their own WWT was because of a decision by the local government to dramaticallyincrease wastewater fees from EUR 035 Vm3 up to EUR 205 Vm3 In addition themill has to pay for the use of well water Therefore the mill decided to close the waterloops by recirculating 600 m3day of treated water back into production This reducedwell water use to one-fourth (250 m3day) and significantly decreased the need forenergy to heat well water for the cardboard-making process The two-stage RO furthercleaned the filtrate by removing the remaining dissolved salts of the filtrate from theMBR plant To prevent possible scaling problems in RO calcium was reduced inthe decarbonization reactor Soda lime milk and iron (II) chloride and some acidsare added to the calcium-rich wastewater and mixed then microparticles of calciumcarbonate are formed After flocculation and sedimentation the suspension of removedcalcium carbonate (50e300 gL) is used as filler for cardboard grades By recirculatingthe filtrate from the MBR and by further treatment of the MBR filtrate (50) by ROthe original flow of the wastewater could be reduced by more than 90 The remainingflow (approximately 06 m3ton) of wastewater (the concentrate of the RO) is fed intothe municipal sewage treatment plant Chemical oxygen demand concentrations werereduced from 2600 to about 150 mgL in the MBR process and to 10 mgL by ROand BOD from 1300 mgL to less than 5 and 1 after MBR and RO respectively(Anon 2013b Junk et al 2008 Wagner 2010)

1922 Direct membrane filtration for wastewaters

In Canada a pulp mill in New Brunswick produced bleached kraft pulp without con-ventional biological WWT because of the limited land area In the effluents an evap-orator condensate stream was identified that caused significant amounts of BOD andtoxicity Therefore an RO plant was installed to purify the condensate streamPermeate of RO was recirculated into the bleaching process which led to a 40 reduc-tion in water consumption Compound identification of the RO process streamsshowed that the RO feed contained significant concentrations of low molar mass phe-nolics including phenols and guaiacols which were effectively removed and concen-trated by RO In addition RO is reported to remove compounds responsible forendocrine disruption in fish Although RO eventually exceeded the expected purifica-tion level permeate was still somewhat toxic and the BOD content was higher thanallowed Therefore a moving bed bioreactor was installed to reduce the BOD(Anon 2007 Webb 2002)

594 Advances in Membrane Technologies for Water Treatment

The mill achieved an extremely high water recovery of 99 in RO and thus only asmall amount of concentrate was incinerated in the bark boiler or was first sent to thehigh solids crystallizer to be subsequently burned in the recovery boiler (Table 193)Over 90 and 80 reduction was measured for COD and BOD respectively (DubeacuteMcLean MacLatchy amp Savage 2000) In RO one could assume even higher reten-tion for organic molecules A somewhat low retention probably resulted from ahigh-volume reduction in filtration Especially in solutiondiffusion type membraneprocesses such as RO and NF an increase in the feed concentration owing to theconcentration of impurities leads to lower permeate purity The permeate purity canbe improved by filtering permeate again

193 Membrane processes to recirculate process water

High shear rate modules such as CR filtration technology and VSEP tubular modulesand conventional spiral-wound modules have been used in several mills as internalkidneys to purify paper mill circulation waters such as white water and clear filtrates(Kreutzman amp Sutela 2004)

The only known industrial-scale example of the use of the VSEP in the pulp andpaper industry is from NF The Linpac recycle paper mill in Cowpens South Carolinahas a two stage tubular UF system and VSEP filters to remove impurities from watercirculation The UF systems (Koch membrane systems) treat the overflow from dis-solved air flotation (DAF) clarifiers Total suspended solids in the DAF units areimproved significantly by pressurized ozone injection before DAF To reduce theconcentrate (reject) volume from the UF system and improve the reused water qualitya VSEP NF system was installed to further concentrate the two-stage UF concentrateThis unconventional way of combining membrane processes produces an NF concen-trate with a solids content over 20 (Linpac 2006)

One of the best reported membrane filtration processes exists in a paper mill inLohja Finland When the fine paper machine was built in the 1990s the authoritieswould not accept an increase in effluent load Thus the mill was forced to findadvanced methods to reduce the environmental load By circulating the paper machine

Table 193 Reverse osmosis treatment for evaporator condensateof kraft pulp mill

Clean condensate RO concentratea RO permeate

Volume m3day 6000 100 5900

BOD mgL 560 41000 67

COD mgL 1067 78000 115

aCalculated from mass balancesAdopted from Dubeacute et al (2000)

Membrane technologies for water treatment and reuse in the pulp and paper industries 595

process waters efficiently after UF the mill succeeded in obtaining environmentalpermission During the 1990s 19-CR filters were installed to treat white water frompaper machines and recover coating color from the mill The membrane area installedfor white water treatment is 1428 m2 and for coating color treatment 336 m2 The finepaper machine membrane filtration plant operated in three stages recovering 94 ofthe feed into permeate (235 m3h) The permeate stream was used in paper machineshowers and for chemical dilution A part of UF permeate (50 m3h) was furtherpurified by spiral-wound NF Whereas UF removed only about 10 of dissolvedCOD NF removed about 85 at a water recovery of 70 The main benefit of UFis that it makes suspended solidsefree water in which the amount of anionic trash(extractives) has also been significantly reduced Ultrafiltration permeate has provensuitable for reuse in showers sealing waters and dilution of wet-end chemicalsBecause of the high purity of NF permeate it can be used to replace warm freshwateron the paper machine

Sutela (2008) reported a high average flux of 315 L(m2h) in UF at 08 bar and60 C for a 7-year filtration period Total operating costs for CR UF were about019 Vm3 in 2008 (used energy price 005 VkWh) Advanced water purificationenables the fine paper machine to operate with about 6 m3 freshwater intake perproduced ton of paper The high shear CR-filtration technology was also applied inthe newsprint mill of Holmen Paper in Madrid Spain and the UPM Kymmene millin Valkeakoski Finland Approximately 20e50 reduction in the use of freshwaterwas achieved in these mills (Sutela 2008)

Typically UF almost completely removes suspended solids (fibers) and bacteriaand partly organic dissolved compounds (lignin hemicellulose etc) but ions onlywhen they are bound for instance to fibers The removal of dissolved organic com-pounds depends on the process water and membrane used it is typically from 10to 40 in UF Membranes are typically needed when freshwater consumption needsto be reduced below 10 m3ton of paper Nanofiltration removes 70e90 of dissolvedorganic compounds (COD and TOC) color and lignin degradation products Veryhigh retention for multivalent ions has also been reported The retention efficiencyin NF depends on the filtration conditions and pH and naturally on the membraneproperties For instance increasing pH of slightly acidic paper machine process waterto neutral increased the retention of COD about 20

194 Simultaneous recovery of valuable by-productsand purification of process waters

1941 Recovery of coating color

Probably the most economical application for membrane processes in the paper indus-try is the recovery of coating effluents by UF especially when valuable coating pig-ments are used Effluents that contain coating color are generated during theflushing of coating equipment paper breaks and production changes in paper and

596 Advances in Membrane Technologies for Water Treatment

cardboard mill manufacturing coating grades (papers that are used in magazinescatalogs or books for example) (Lipnizki 2008)

Coating wastewaters create a lot of color in discharge water systems because theyare not easily treated by conventional treatments although their volumes are usuallynegligible compared with overall mill effluents (about 2e5 of total flow) Theheavy solids load and compounds that are sticky by nature in these wastewatersmay cause operating problems in treating effluent if discharged into sewers withoutappropriate pretreatment On the other hand pigments are expensive so the (partial)recovery of coating color for reuse is cost-effective in most cases Therefore theseparate treatment of coating wastewater is an attractive environmentally friendlyalternative to reducing color in the effluents at the same time the mill can benefitfrom reusing the coating material Diluted coating materials are recovered mostlyby UF to obtain a solid-free permeate stream and a retentate stream that containsthe coating materials preferably at a concentration suitable for recycling or dischargeIn UF the pore size of the membrane is sufficiently small to prevent pore pluggingand the permeability is still high The solid-free permeate stream can be either easilydischarged or recycled The permeate stream can be reused for example in coatingpreparation as washing water or as shower water for the paper machine Cross-rotational technology dominates new installations (more than 20 mills have begunto recover coating color by CR technology over the past 15 years) (Alho RoittoNygaringrd amp Hietanen 1998 Anon 2013b Jeuroonsson Jeuroonsson Teppler Tomani ampWeuroannstreuroom 1996 Singhet al 1999)

Payback time is typically around a year when treating valuable coating color (egwhen TiO2 pigments exist in coating wastewaters) High shear modules can recovercoating color from wastewater to higher dry solids content than traditional modulesOn an industrial scale effluent fed into the process typically contains 2e4 solidsand by UF its concentration is increased to 30e44 depending on the system Ahigh concentration is needed so that the concentrate can be added to fresh coating colorwithout overly diluting the coating color

1942 Recovery of by-product

Only about half of the wood material is converted to pulp in the pulping process therest of it is dissolved during the process Dissolved wood compounds eg galactoglu-komannan (GGM) can be recovered from thermomechanical pulp mill process waters(Figure 192) Other possible products are lignosulphonates and monosaccharides inwhich spent sulfite cooking liquors are rich Furthermore kraft lignin and hydroxyacids are possible valuable products in black liquor from the sulfate pulping processAll of these compounds are recoverable by using different membrane processes Mem-branes are used to recover compounds into concentrate (eg hemicelluloses or ligno-sulphonates) or into permeate (eg monosaccharides or vanillin) In SarpsbogNorway Borregaard Industries have concentrated lignosulphonates by UF since the1980s (Jeuroonsson amp Wimmerstedt 1985 Wagner 2000) Nanofiltration can purifyeg xylose into NF permeate As a result xylose purity can increase from 16 up

Membrane technologies for water treatment and reuse in the pulp and paper industries 597

to 65 (Heikkileuroa Meuroantteuroari Lindroos amp Nystreuroom 2005) When high molar mass com-pounds such GGM lignosulphonates and kraft lignin are recovered into the UFconcentrate stream diafiltration can be used to purify them All of these streams arewater streams and water itself can be used to carry away impurities It can be assumedthat the importance of membrane technology in the recovery and purification of valu-able compounds from different streams will increase in future

195 Purification of raw water

Membranes are used to purify process waters and effluents in the mills but also topurify incoming water Two examples of mills - Bahia Sul Celulose in Mucuri Braziland Stendal pulp mill at Arneburg near Stendal Germany - purify raw waters froma river using spiral-wound RO Both installations needed tailored and complicated pre-treatment systems to manage the seasonal variations of river water In the case of theBahia Sul Celulose mill complicated pretreatment including chlorination floccula-tion sedimentation sand filtration and filtration through activated carbon was not suf-ficient before RO because the standard BW30-365 membrane had high levels ofbiofouling that generated a high pressure drop on the system and demanded frequentcleaning After replacing the standard membrane with the more fouling-resistantBW30-365FR membrane (FilmTec currently Dow) and after optimizing the opera-tion (maximum flux 22 Lm2h) and cleaning conditions fouling was significantlyreduced and the cleaning interval doubled to 12 days Salt retention is 98 corre-sponding to a permeate conductivity of less than 6 mScm (Soalheiro 2000)

The Stendal pulp mill in Germany started to use RO to treat raw water from theElbe River in 2004 After multilevel pretreatments this water is led to RO The ROplant produces about 2500 m3h (feed 3100 m3h) of permeate which is used asprocess water and is further treated (300 m3h) with demineralized water Differencesin the quality of water taken from the Elbe River which result from seasonal andweather conditions are compensated for by a complicated pretreatment systemincluding different physical and chemical stages The RO removes 986 of saltsand the conductivity levels in permeate are about 15 mScm (Kremser DreshnerOtto amp Recknagel 2006) As these examples show spiral-wound modules needappropriate pretreatment so that their functionality can be ensured

196 Conclusion and future trends

This chapter reviewed membrane filtration related to water treatment in the pulp andpaper industry The need for water has not decreased in paper manufacturing pro-cesses but the need for freshwater and at the same time the amount of effluents canbe significantly decreased when advanced water purification technologies such asmembrane filtration are used The strongest driving force will also be legislationthat sets demands on effluent quality and how much effluent can be discharged The

598 Advances in Membrane Technologies for Water Treatment

Best Available Techniques (BAT) reference document for the production of pulppaper and cardboard is an excellent source of information on effluent treatment inthe pulp and paper industry it provides guidance to the industry member statesand the public regarding achievable emission and consumption levels when usingspecified BAT techniques

Several successful examples have shown membrane processes to improve the ma-terial energy and cost-efficiency of pulp and paper manufacturing processes anddecrease the environmental impact of mills They have also encouraged companiesto test membranes In the future the importance of membrane processes will increasefor water treatment purposes but also for the recovery and purification of valuableproducts from different liquors and water-based streams from pulp and paper millsBiorefineries based on lignocellulosic biomasses are under intensive developmentand the use of membranes is an essential issue in this Membranes will enable thesimultaneous recovery purification and concentration of monomeric oligomericand polymeric wood compounds from various process streams and extraction liquorsand they can also be used to dewater ethanol for biofuel use

The development of more resistant polymeric and cheaper ceramic membranes willenable the use of membranes under very alkaline or acidic conditions even at high tem-peratures which makes membrane processes an attractive alternative in pulp and papermill applications The need for water is increasing worldwide therefore purificationand reuse of process waters and effluents will increase in importance

197 Further information and advice

A comprehensive review on industrial-scale membrane filtration plants is presented byMeuroantteuroari and Nystreuroom (2009) The review consists of about 30 different industrialexamples on the use of membrane processes excluding coating color applicationsNuortila-Jokinen et al (2003) intensively discussed water use in pulp and paper mak-ing processes and their effluents Kallioinen Nystreuroom and Meuroantteuroari (2013) presentedrequirements and factors affecting the selection of membranes in pulp and paper appli-cations in which they deal with key properties of membranes to be taken into account

The BAT reference document for the production of pulp paper and cardboard is anexcellent source of information on effluent treatment in the pulp and paper industry itprovides guidance to the industry member states and the public on achievable emis-sion and consumption levels when using specified BAT techniques The documentalso reviews existing industrial-scale purification systems including membrane pro-cesses The last adopted document was in 2001 but the final draft of the new version(July 2013) was published and adopted in spring 2014

In the future membrane processes will probably be applied mostly in the fraction-ation and purification processes in biorefineries Nanofiltration is a promising fraction-ation and purification technology for biorefinery applications (Meuroantteuroari Van derBruggen amp Nystreuroom 2013) Almost all of the potential applications are water-based therefore water treatment is and will be an essential part of biorefineries

Membrane technologies for water treatment and reuse in the pulp and paper industries 599

Membrane Filtration Handbook Practical Hints and Tips (Wagner 2001) is rec-ommended as reading material when an industrial-scale membrane filtration process isplanned

List of acronyms

AOX Absorbed organic halogensBAT Best available techniquesBOD Biological oxygen demandCAS Conventional activated sludgeCOD Chemical oxygen demandCR Cross-rotationalDAF Dissolved air flotationED ElectrodialysisGGM GalactoglucomannanMBR Membrane bioreactorMF MicrofiltrationMLSS Mixed liquor suspended solidsNF NanofiltrationPCD Pulsed corona dischargePVDF Polyvinylidene difluorideRO Reverse osmosisTOC Total organic carbonUF UltrafiltrationVSEP Vibratory shear-enhanced processingWWT Wastewater treatment

References

Alho J Roitto I Nygaringrd S amp Hietanen S (1998) A review on coating effluent treatment byultrafiltration InProceedings of the2ndEcoPaperTechConference (pp 219e231) JyveuroaskyleuroaFinland The Finnish Pulp and Paper Research Institute and The Finnish Paper Association

Amaral M C S Lange L C amp Borges C P (2012) Treatment of bleach pulp mill effluentby MF-MBR Water Environmental Research 84(7) 547e553

Anon (2007) Factual record pulp and paper submission (SEM-02-003) Commission for Environ-mental Cooperation ofNorthAmerica Available fromhttpwww3cecorgislandoraenitem2825-north-american-environmental-law-and-policy-volume-22-enpdf Accessed 260214

Anon (2010) Water quality demands in paper chemical food and textile companies Aqua-Fit4Use (EU) Available from httpwwwaquafit4useeuuserdatafilePublic20resultsAquaFit4Use20-20Water20quality20demands20in20paper-chemical-food-textile20industrypdf Accessed 260214

Anon (2013a) Available from httpwww2metsateollisuusfitilastopalvelu2tilastokuviotYmparistoFormsDispFormaspxIDfrac1449ampRootFolderfrac142ftilastopalvelu22ftilastokuviot2fYmparisto2fJulkinen2dFIampSourcefrac14http3A2F2Fwww22Emetsateollisuus2Efi2Ftilastopalvelu22Ftilastokuviot2FYmparisto2FForms2FAllItems2EaspxAccessed 260214

600 Advances in Membrane Technologies for Water Treatment

Anon (2013b) Best available techniques (BAT) reference document for the production of pulppaper and board final draft july 2013 The European IPPC Bureau Available from httpeippcbjrceceuropaeureferenceBREFPP_BREF_FD_07_2013pdf Accessed 260214

Culkin B Plotkin A amp Monroe M (1998) Solve membrane fouling problems with highshear filtration Chemical Engineering Progress 94(1) 29e33

Dubeacute M McLean R MacLatchy D amp Savage P (August 2000) Reverse osmosis treat-ment effects on effluent quality Pulp amp Paper Canada

Durham B (2000) Case studies of wastewater re-use for the petrochemical power and paperindustry Special Publication Royal Society of Chemistry 249 (Membrane technology inwater and wastewater treatment) 241e247

Ferreira L M G A Amaral L amp Machado L (2004) Removal of chloride in the kraftchemical recovery cycle of pulp mills using the ion-exchange process Industrial ampEngineering Chemistry Research 43 7121e7128

Geraldes V amp De Pinho M N (1995) Process water recovery from pulp bleaching effluentsby an NFED hybrid process Journal of Membrane Science 102(1) 209e221

Greaves R (1999) The use of ultrafiltration for COD reduction in pulp mill effluent e A casestudy from Sweden In International Environmental Conference (pp 1167e1191)April 18e21 Nashville TN Tappi Press

Heikkileuroa H Meuroantteuroari M Lindroos M amp Nystreuroom M (2005) Recovery of xylose US Patent6872316 (B2) March 29 2005

Helble A amp Meuroobius C H (2009) Current experience with the use of membrane bioreactortechnology for the treatment of papermill effluent PTS Water amp Environment TechnologySymposium (p27) November 10e11 Munich Germany PTS

Hepp B Joore L Schonewille H amp Futselaar H (2005) Membrane filtration A sustainablewater treatment technology within modern papermaking concepts Papers Technology46(1) 41e48

Jaffrin M Y (2008) Dynamic shear-enhanced membrane filtration A review of rotating disksrotating membranes and vibrating systems Journal of Membrane Science 324 7e25

Jeuroonsson A-S (1989) Treatment of effluent from alkaline extraction with ultrafiltration andreverse osmosis Nordic Pulp Paper Research Journal 4(1) 33e37

Jeuroonsson A-S Jeuroonsson C Teppler M Tomani P amp Weuroannstreuroom S (1996) Recovery of dilutepaper coating colour effluents by ultrafiltration Filtration and Separation 33 453e457

Jeuroonsson A-S amp Wimmerstedt R (1985) The application of membrane technology in the pulpand paper industry Desalination 53 181e196

Joore LWortel N ampBronold N (2001)MBR inwater loop closure concepts inDutch recycledpaper mills e From pilot towards full-scale installations Paper Technology 42(7) 27e36

Junk H H Dorfer T Stratz K amp Lausch B (2008) Kohler Pappen installs the worldrsquos firstmembrane bioreactor with integrated reverse osmosis Allg Pap-Rundsch 132(4) 44e46

KallioinenM NystreuroomMampMeuroantteuroariM (2013)Membrane-based treatment of pulp and paperindustry process and waste waters In E M V Hoek amp V V Tarabara (Eds) Encyclopediaof membrane science and technology (pp 2156e2174) Hoboken NJ John Wiley amp Sons

Kremser U Dreshner G Otto G amp Recknagel V (2006) First operating experience with thetreatment of 3100 m3h of Elbe river water by means of reverse osmosis to produce processwater and demineralised water for use in the pulp industryDesalination 189(1e3) 53e58

Kreutzman E amp Sutela T (2004) Water management in the European paper industry IpptaJournal (Convention Issue) 15e22

Lien L amp Simonis D (1995) Case histories of two large nanofiltration systems reclaimingeffluent from pulp and paper mills for reuse In International Environmental Conference(pp 1023e1027) May 7e10 Atlanta GA Tappi Press

Membrane technologies for water treatment and reuse in the pulp and paper industries 601

Linpac (2006) Pressurized ozone membrane ultrafiltrationnanofiltration methodology for TDSremoval in paper mill process water for energy savings production efficiency and envi-ronmental benefits Available from httpwwwrobynrickertcomestrsitedocumentslinpacpdf Accessed 260214

Lipnizki F (2008) Opportunities and challenges of using ultrafiltration for the concentration ofdiluted coating materials Desalination 224 98e104

Meuroantteuroari M Daltrophe N Oren Y Gilron J amp Nystreuroom M (2001) Treatment of paper millprocess water with lime treatment MF and NF In Proceedings of the Engineering withMembranes (pp 1295e1299) June 3e6 Granada Spain Servicio de PublicacionesUniversidad de Oviedo

Meuroantteuroari M Kuosa M Kallas J amp Nystreuroom M (2008) Membrane filtration and ozonetreatment of biologically treated effluents from the pulp and paper industry Journal ofMembrane Science 309(1e2) 112e119

Meuroantteuroari M amp Nystreuroom M (2004) Ultrafiltration and nanofiltration in the pulp and paperindustry using cross-rotational (CR) filtersWater Science amp Technology 50(3) 229e238

Meuroantteuroari M amp Nystreuroom M (2007) Membrane filtration for tertiary treatment of biologicallytreated effluents from the pulp and paper industry Water Science amp Technology 55(6)99e107

Meuroantteuroari M amp Nystreuroom M (2009) Utilization of membrane processes in treating variouseffluents generated in pulp and paper Industry In A K Paddy S S H Rizvi ampA M Sastre (Eds) Handbook of membrane separations Chemical pharmaceutical andbiotechnological applications (pp 981e1006) Boca Raton USA CRS Press

Meuroantteuroari M Pekuri T amp Nystreuroom M (2004) NF-270 a new membrane having promisingcharacteristics and being suitable for treatment of dilute effluents from the paper industryJournal of Membrane Science 242 107e116

Meuroantteuroari M Van der Bruggen B amp Nystreuroom M (2013) Nanofiltration In S RamaswamyB Ramarao amp H Huang (Eds) Separation and purification technologies in biorefineries(pp 233e258) Chichester UK John Wiley amp Sons Ltd

Mauchauffee S Denieul M-P amp Coste M (2012) Industrial wastewater re-use Closure ofwater cycle in the main water consuming industries e The example of paper mills Envi-ronmental Technology 33(19) 2257e2262

Merry A (1999) The role of membranes in achieving ZLE Investigations Technical Paper36(142) 568e574

Nordin A-K amp Jeuroonsson A-S (2008) Optimisation of membrane area and energy requirementin tubular membrane modules Chemical Engineering Processing Process Intensification47(7) 1090e1097

Nuortila-Jokinen J (2005) Membranes in the pulp and paper applications - Only emptypromises PTS Symposium Water and Environmental Technology (pp 18-1e18-16) PTS

Nuortila-Jokinen J Meuroantteuroari M amp Nystreuroom M (2003) The pulp and paper industry InS Judd amp B Jefferson (Eds) Membranes for industrial wastewater recovery and reuseUK (pp 102e131) Elsevier Advanced Technology

Panorel I C Kaijanen L Kornev I Preis S Louhi-Kultanen M amp Sireacuten H (2014) Pulsedcorona discharge oxidation of aqueous lignin Decomposition and aldehydes formationEnvironmental Technology 35(2) 171e176

Pfromm P H Tsa i S-P amp Henry M P (1999) Electrodialysis for bleach effluent recyclingin kraft pulp production simultaneous control of chloride and other non-process elementsThe Canadian Journal of Chemical Engineering 77(6) 1231e1238

Pohjalainen T (1999) Case study of ldquoclosedrdquo board mill and application studies in FinlandInvestigacion y Tecnica del Papel 36(142) 637e647

602 Advances in Membrane Technologies for Water Treatment

Ramaekers H van Dijk L Lumpe C Verstraeten E amp Joore L (Feb 2001) Thermophilicmembarane bioreactors in the paper industrye A successful key to in-mill water treatmentPaper Technology 32e40

Rapp H J amp Pfromm P H (1998) Electrodialysis for chloride removal from the chemicalrecovery cycle of a kraft pulp mill Journal of Membrane Science 146 249e261

Schirm R Welt T amp Ruf G (2001) Nanofiltration Eine meurooglichkeit zur Kreizlaufs-chliebung Papierfabrik Palm Werk Eltmann IMPS Internationales Meurounchner Papier-symposium Meurounich Germany March 23

Simstich B amp Oeller H-J (2010) Membrane technology for the future treatment of paper milleffluents Chances and challenges of further system closure Water Science amp Technology62(9) 2190e2197

Singh S Matsuura T amp Ramamurthy P (1999) Treatment of coating plant effluent with anultrafiltration membrane Tappi Journal 82(4) 146e155

Soalheiro S C (2000) Membrane technology improves RO system for Bahia Sul CelulosePulp and Paper 74(10) 63e71

Stephenson T Judd S Jefferson B amp Brindle K (2000) Membrane bioreactors forwastewater treatment London IWA Publishing

Sutela T (2008) Membrantechnik in der Papierindustrie PTS Symposium (pp 27e28)May Meurounchen Germany PTS

Wagner J (2000) Membrane technology in wood pulp and paper industries Special Publi-cation Royal Society of Chemistry 249(Membrane technology in water and wastewatertreatment) 233e240

Wagner J (2001)Membrane filtration handbook practical hints and tips Osmonics Availablefrom httpgendocsrudocs3029820conv_1file1pdf Accessed 260214

Wagner R (2010) It pays to conserve and reuse water Paper 360 24e25Webb L (2002) Kidney technology brings success Pulp and Paper International 44(4)

28e32Yoon S-H Kim H-S amp Yeom I-T (2004) The optimum operational condition of mem-

brane bioreactor (MBR) Cost estimation of aeration and sludge treatmentWater Research38 37e46

Zaidi A Buisson H Sourirajan S ampWood H (1992) Ultra- and nano-filtration in advancedeffluent treatment schemes for pollution control in the pulp and paper industry WaterScience and Technology 25(10) 263e276

Membrane technologies for water treatment and reuse in the pulp and paper industries 603

Membrane technologies forwater treatment and reusein the power industries

20L Daal1 F de Vos1 J Soons2 T de Vries31DNV GL Energy Arnhem The Netherlands 2PWN Waterleidingbedrijf Noord HollandVelserbroek The Netherlands 3GDF SUEZ Energie Nederland Zwolle The Netherlands

201 Introduction

2011 General

In industry water is used for many purposes such as pure water for the watersteamcycle as a raw material for chemical reactions to extinguish fire and for cleaningand cooling In particular power- and energy-intensive industries are major consumersof water

2012 Water streams

When considering industrial and power plants one needs to recognize that most wateris used for cooling purposes According to the European Environment Agency (EEA)448 of total available freshwater is abstracted for cooling in energy production Incomparison the manufacturing industry consumes about 11 of water half of whichis used for processing and the remainder of which is for cooling (EEA 2010) In otherwords the total abstracted freshwater for cooling purpose accounts for approximatelyhalf of all water use across Europe Likewise in the United States the thermoelectricindustry consumes 46 of all water (Judd amp Jefferson 2005) Most industrial plantstypically choose a once-through cooling water system There cooling water is notconsumed but it is chemically and thermally treated and discharged into the environ-ment There are ways to minimize the impact on the environment for example bylimiting chemical use1 Cooling water is also used for evaporative cooling towersthe consumption of this water can be in total two-thirds or more of the total wateruse of industrial plants (fossil fuel and nuclear plants petroleum refinery plantsetc) More information about this subject and cooling water systems in general canbe found in the literature (Rajagopal Jenner amp Venugopalan 2012)

Aside from water consumption the industry needs demineralized (demin) water andproduces large sums of wastewater With regard to wastewater an important stream

1 Thermoshock is an alternative to biocidal dosing however a high energy penaltycost is associated with itsuse Also it is less effective than biocidal dosing against biofouling corrosion operational reliability etc

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400020-4Copyright copy 2015 Elsevier Ltd All rights reserved

arises from water used to clean flue gases which must be treated before discharge andor reuse This is usually done through physicalchemical processes In relation to futurelegislation the use of organics is expected

This chapter focuses on water treatment required for the production of demin waterused for the watersteam cycle in industrial plants First to better understand treatmentrequirements the water quality requirements for a watersteam cycle are explained

2013 Water quality

20131 Water quality requirements

The best way to understand water quality requirements is first to understand the watersteam cycle in an industrial plant The watersteam cycle can be considered as theblood circulation of the boilerturbine installation (Figure 201) because this is theheart of a power plant Here as with other living organisms the quality and healthof the blood circulation are key factors for the correct functioning of a boilerturbineinstallation The pure water (boiler water) ensures that the energy freed throughcombustion is transferred to steam which in turn drives a turbine The turbine thendrives a generator to produce electricity Just as in living organisms the watersteamcycle has different names or distinctions to identify where the blood or water in thiscase is within the system Giving a clear distinction of watersteam in the cycle helpsprevent misunderstanding Figure 201 shows the watersteam cycle with the distinc-tions makeup water feed water boiler feed water boiler water saturated steamsuperheated steam condensate and condensate return

Boiler feed water is normally a mixture of makeup water and condensate Thiscondensate is created after steam has passed the turbine Because losses occur alongthe way new water (makeup water) is needed The use of poor-quality water herewould result in serious problems for the boilerturbine installation Corroded boilerpipes in the watersteam cycle are shown in Figure 202 Hence the choice of a rawwater source and its treatment are essential to supply appropriate-quality makeupwater A main quality parameter of this makeup water is the sum conductivity whichhas a maximum value of 010 mScm In comparison theoretically pure water in whichno minerals are present has a conductivity of 0055 mScm

20132 Raw water source

For the production of demin water the following raw sources are used

1 Drinking water2 Well water3 Industry water (grey water)4 Surface water5 Brackish water and seawater

Because of costs and the need to involve authorities drinking water is used lessfrequently as a source of raw water Drinking water originates from surface water treat-ment and well water Well water (and drinking water where the source is well water) is

606 Advances in Membrane Technologies for Water Treatment

Figure20

1Schem

eof

thewater

steam

cycle

Membrane technologies for water treatment and reuse in the power industries 607

the least problematic when it comes to removing minerals these water sources onlypossess minerals but no organic material (humic acids) Minerals are relatively easyto remove compared with organic material

Surface water needs much more treatment for use as demin water Aside from saltsor minerals surface water has a lot of nondissolved substances that have to be removedIn other words pretreatment is necessary Also surface water contains natural organicmatter (NOM) the composition of which changes seasonally These compounds are notall removed during the demineralization process and hence influence the quality of theend product The demin water can be of different compositions during spring andautumn An example of the change in NOM of an industrial water sample (treated sur-face water) is shown in Figure 203 which shows examples in the spring and autumn

The height of the curve in the figure informs us about the concentration of organiccompounds Most the compounds are removed through ion exchange (IX) andmembranes The removal of polysaccharides which are found in higher concentrationsduring autumn can create a challenge for IX because a great deal of polysaccharideswill pass through the resins and end up in the demin water For membrane technology(reverse osmosis (RO)) these compounds can be prevented from passing through themembrane However these compounds cause unwanted fouling of the membranesAn illustration of the diversity and individual concentration of different organiccompounds in raw water such as surface water and drinking water at different loca-tions in The Netherlands is given in Figure 204 The composition of the total organiccarbon (TOC) is given in practise the TOC is often measured but not the individualcompounds

202 Water purification technologies

The most common technologies used to demineralize water are

1 IX technology2 Membrane technology3 Thermal processes

(a) (b)

Figure 202 (a) Corroded pipes in a combined heat and power plant (b) Cross-section of aboiler tube-fin with a thick corrosion layer

608 Advances in Membrane Technologies for Water Treatment

(a) (b)

Figure 203 Natural organic matter composition in the spring (a) and during autumn (b)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

power

industries609

A description of the two most common technologies is given below Thermal pro-cesses are primarily used in the Middle East as thermal desalination technologies fordrinking water (and industrial water) and are not described here For further reading onthis topic one may refer to the European Desalination Society

2021 Ion exchange technology

20211 General

An IX resin consists of plastic spheres with a diameter smaller than a millimetrePrimarily two different plastics are used one is based on polystyrene and the otheron polyacrylate Through chemical modification of the polymer an active group ismade on the spheres where the actual exchange takes place Figure 205 shows anexample of an IX resin The figure shows that the spheres have a uniform size andshape which is the current state of the art In the past different production processeswere used and resulted in spheres of different sizes and forms These nonuniformresins can still be found in older industrial plants

Because of their active groups there is a distinction between cation and anion resinsA salt that is dissolved in water dissociates in positive ions (cations) and negative ions(anions) A cation resin removes only the cations and the anion resin removes theanions For this reason a demin line normally consists of a cation and an anion filterIf the water quality is not according to specifications after leaving these two filters amixed bed (anion and cation resins in one tank) is used A simple representation isgiven in Figure 206

Figure 204 Total organic carbon (TOC) composition at different locations throughoutThe Netherlands

610 Advances in Membrane Technologies for Water Treatment

Figure 206 also shows a carbon dioxide (CO2) cascader or tower where CO2

is removed This is the result of acidic water coming from the cation filter and the hard-ness of the water Therefore it is not necessary to remove this hardness (present ascarbonate and bicarbonate) in the anion filter This results in savings in the amountof resin needed for the anion filter

Currently demin lines are run against current flow At a certain point the resins willbe fully loaded with ions and will have lost their capacity to demineralize To revert tonormal operation cation resins are treated with an acid such as hydrochloric acid andanion resins with sodium hydroxide The most effective way to have this treatmentdone is in a countercurrent flow

20212 Operational experience

In practise anion resins are less stable than cation resins This is primarily related tothe maximum operating temperature of 40 C for anion resins Above these tempera-tures the anion resin loses active groups and hence its functionality

Figure 205 Ion exchange resin with spheres of uniform size and shape

Cationfilter

Anionfilter

Mixedbed

Demintank

CO2

cascader

Figure 206 Demin line using ion exchange (IX) technology

Membrane technologies for water treatment and reuse in the power industries 611

The resins can be of a flexible gel or the lsquotougherrsquo macro-porous resin type Bothtypes consist of polymers As such the exchange groups in the resin network attracta lot of water from the outside A dry resin grain swells like a sponge in doing sowaterways are created inside the resin grain The macro-porous type resin also takesup water however it already has high porosity This porosity ensures a rapid exchangebut results in a lower capacity of the resin

As mentioned the resin grains take up a lot of water and thus swell If the grains dryout they shrink and cracks can form The grains still have the capacity to demineralizebut because of the cracks they could break into pieces This can lead to blockages in theresin bed and pressure buildup in the column An example of dried resin grains is shownin Figure 207 Aside from the many cracks visible on the grains the shape and form ofthe spheres are not similar to new IX resins The photo also shows an older resin

2022 Membrane technology

20221 General

Aside from the preparation of ultra-pure water for the power industry membraneprocess systems are used to treat different types of water such as wastewater and toproduce drinking water

In general membranes act as filters Depending on the pore size one can distin-guish among the following types (see also Figure 208)

1 Microfiltration (MF) with pore sizes of gt01 mm2 Ultrafiltration (UF) with pore sizes of 001e01 mm3 Nanofiltration (NF) with pore sizes roughly between 001 and 0001 mm4 RO membranes which are lt0001 mm

Figure 207 Dried-out resin

612 Advances in Membrane Technologies for Water Treatment

The actual pore sizes will differ from the theoretical ones In the literature a widevariety of classifications for different membrane types can be found

Microfiltration and UF membranes are normally used to separate particles whereasNF and RO change the chemical or ionic composition of the water because theyremove small molecules and ions from the water (source prime water Web site)Figure 208 shows a membrane filtration spectrum indicating the type of contaminantsthat can be removed by different membrane types

Under normal operation conditions membrane systems are easy to operate with lowchemical consumption and constant water quality which increases the reliability of thesystem The main drawback of membrane technology is the relatively high energyconsumption This is particularly true in areas where for example seawater has ahigh salt content such as in the Middle East There RO systems have become popularfor desalination purposes and for demin water production for the power industry

According to Kabsh-Korbutowicz (2006) the economic use of membrane filtrationsystems is often limited by fouling because this results in increased pressure drops thataffect energy consumption Hence there is an increase in the frequency of cleaningwhich affects the production rate of the membranes Therefore it is important toprevent the membranes from fouling This can be done by applying the right pretreat-ment using membrane materials that are less susceptible to fouling and ensuring goodcontrol and operation of the system

Over the years the energy consumption of membrane systems has been furtherreduced by the introduction of energy recovery systems that recover the pressure ofthe concentrate stream using this energy to increase the pressure of the feed flow(Avlonitis Kouroumbas amp Vlachakis 2003)

20222 RO membranes

Most RO membranes are constructed as a spiral-wound module as shown inFigure 209 There are hollow-fibre membrane modules but these are much less

Figure 208 Membrane filtration spectrum (Water treatment handbook 2007)

Membrane technologies for water treatment and reuse in the power industries 613

common The spiral-wound module consists of a membrane mesh paper (or spacer)and permeate tube The spacers are used to create flow channels within the module andensure equal distribution of the flow The membrane is glued on three sides and theopen side is connected to a central permeate tube around which the membrane sheetsare rolled (Figure 209)

RO membranes are made of polymers mostly cellulose acetate or compositepolyamide-type membranes

In practise individual membrane modules are called elements Multiple membranemodules (or elements) behind each other will form a train and several trains togetherform the system If it is a large system several trains can also form a stage and morestages are needed to complete the entire system Depending on whether the system isused to concentrate the brine product or to produce high-quality permeate the connec-tion between the modules will be of the concentrate or the permeate

203 Operational experience with membranes

2031 General

Most membranes for water treatment can withstand temperatures of up to 50 CHowever this should be verified by the manufacturerrsquos specifications becausesome membranes have a lower temperature limit (Bates 1998) Another importantparameter is pH Cellulose acetate membranes can be operated only within a smallpH range the pH should be kept between 4 and 6 On the other hand these mem-branes are resistant to oxidation by chlorine Thin-film composites membranes canbe operated within a large pH range 3e11 but they are sensitive to the presenceof chlorine When using these membranes steps have to be taken to ensure no residualchlorine will reach the RO modules To combat residual chlorine sodium meta-bisulphite can be added to the intake Intake pipes for desalination plants and coolingwater intake pipes can have free chlorine present to prevent biofouling In the power

Reverse osmosis

Permeate

Pressurizedfeed water

Permeate

Concentrate

Figure 209 Spiral-wound membrane (Judd amp Jefferson 2005)

614 Advances in Membrane Technologies for Water Treatment

industry demin plants typically extract their raw water source from the cooling watercircuit and discharge the brine there as well

Another method to reduce the risk of fouling and reduce energy consumption is toincrease the flow rate To increase the flow rate hydrophilic membranes are often usedWith these membranes water will easily pass through the membranes whereas hydro-phobic contaminants will be repelled reducing fouling Cellulose acetate membranesare most hydrophilic but have a lower salt rejection compared with polyamidemembranes

Another factor that determines fouling and the fluxes of the system is the surfacecharge of the membranes Cellulose acetate membranes are neutrally charged whereaspolyamide membranes can attract charged organic and colloidal material from the feedwater (Membrane Web site)

The most important fouling mechanisms will be discussed next together with waysto prevent fouling and how the effects of fouling can be minimized

2032 Fouling

One of the most important aspects of the operation of membrane systems is foulingFouling increases the pressure loss over the membrane surface resulting in higherenergy consumption and lower salt rejection Also higher fouling rates increase thecleaning frequency lowering the production rate (or the availability of a plant) andincreasing chemical consumption

Therefore it is essential to reduce fouling and minimize its effects The first step tocombat fouling is to determine what kind of fouling the system is dealing with becausedifferent types of fouling require differentmeasures Furthermore goodcontrol of the pro-cess and cleaning conditions is essential to prevent and overcome the effects of fouling

2033 Types of fouling

Different fouling sources can be described as follows

1 Fouling through concentration polarization2 Organic fouling3 Biological fouling4 Colloidal and suspended fouling5 Scaling

20331 Concentration polarization

This type of fouling occurs when salts and other rejected solutes concentrate near themembrane surface A laminar boundary layer will be present as the fluid adjacent tothe membrane moves slower than the main stream (Porter 1990) As a consequencethe salt rejection of the membrane decreases and therefore negatively affects the qual-ity of permeate Also the osmotic pressure will increase owing to the concentration ofthe salts This results in an increase in energy consumption

Membrane technologies for water treatment and reuse in the power industries 615

Concentration polarisation cannot be avoided The only way to combat thisphenomenon is to reduce the boundary layer by optimizing the hydraulic conditionsThis is done by increasing the flow rate across the membrane surface or introducingturbulence promoters into the feedreject stream To increase turbulence end spacersare designed in spiral-wound membrane modules to optimize hydraulic conditionswithin the module

20332 Organic fouling

Organic matter originating from feed water has different compositions throughoutthe world and its composition can change dramatically over time This makes it chal-lenging to combat organic fouling Organic fouling will increase the pressure dropover the membrane (trans-membrane pressure (TMP)) Figure 2010 shows a fouledRO membrane

Because most natural organic matter is charged it will bind to charged membranesurfaces from polyamide membranes In these situations organic matter will prefer themembrane over the water phase and will stick to the membrane causing fouling One ofthe most important compounds leading to organic fouling is humic acid in the feedwater which acts as a weak acid and retains metals such as iron Furthermore organicmatter can serve as a feeding source for bacteria and enhance biofouling

Also for organic fouling when coagulation and flocculation are applied as pretreat-ment the addition of too much flocculation chemical will lead to increased organicfouling The same is true for the addition of antiscalants

Organic fouling will take place over all membrane stages To combat organicfouling new membrane types with a neutrally charged surface have been developedIn this way the charged organic material will have fewer tendencies to attach to themembranes

Figure 2010 Fouled membrane photo taken near the collector of the membrane module

616 Advances in Membrane Technologies for Water Treatment

20333 Biofouling

Biofouling is a major concern for membrane systems Biofouling can be divided intomicrofouling and macrofouling Because macrofouling (mussel growth) occurs inintake pipes and cooling water systems it is not a direct threat to membrane operationsOn the other hand microfouling will occur on membranes and will have an effect onthe performance of the water treatment Microfouling refers to bacterial growth whichcan occur on the organic matter of the membrane surface and result in increasing TMPAlso bacteria can produce extracellular polymeric substances mostly polysaccha-rides which also result in fouling The formation of polysaccharides combined withbacterial growth makes cleaning measures less effective because these microorganismsare embedded with polysaccharides and hence are not easily removed

Within membrane modules lsquodead zonesrsquo should be avoided They lead to theincreased growth rate of microorganisms (Ho Altman Jones Khalsa amp McGrath2008) By applying equal flow conditions biofouling can be prevented Spacers ofspiral-wound membranes can also be a growth place for microorganisms augmentingbiofouling

To prevent the growth of macro- and microorganisms in the intake (pipe of theplant) and on the membranes installations are often disinfected This is often doneby applying free chlorine As already discussed the addition of chlorine can damagethe membranes but they also can potentially have negative effects on biofoulingOrganic matter can be broken down into bite-size pieces that can be readily takenup by bacteria present on the membrane surface

Biofouling typically occurs in the first membrane stages Biofouling can beobserved by following the flux and the salt rejection In this case the flux will decreasein the beginning with increasing salt rejection (AEDyR 2009) After this initial phasesalt rejection will also decrease

20334 Colloidal and suspended fouling

Excessive volumes of colloidal and suspended material will plug the RO element feedpath regardless of the membrane type Fortunately as with all other types of foulingthis type can easily be combated with proper pretreatment This can be done throughfiltration coagulation sedimentation flotation and decanters Typical levels ofcolloidal and suspended particles would be less than 10 NTU for turbidity and asilt density index value below 4 (AEDyR 2009)

20335 Scaling

From the information about concentration polarization it is clear that within thelaminar boundary layer of the membrane the concentration of rejected solutes stronglyincreases Salts will also be concentrated in this layer When the concentration exceedsthe solubility product salts will precipitate and can even form crystals on themembrane surface thus increasing the TMP and lowering the salt rejection

Known scaling compounds are calcium carbonate barium sulphate calcium phos-phate strontium sulphate and calcium fluoride

Membrane technologies for water treatment and reuse in the power industries 617

The scaling effect increases with the different stages when concentrate from theprevious stage is used as feed water for the next This is illustrated by the Langliersaturation index which increases with each membrane separation stage(Figure 2011)

According to Al-Shammiri and Al-Dawas (1997) four methods can be used toreduce the risk of scaling

1 Lowering the pH to remove carbonate from the system2 Adding antiscalant which will broaden the solubility limits of the salts3 Reducing the recovery rate so that the concentration on the outside of the membrane is

reduced4 Dehardening the feed water

Furthermore the addition of chemicals may be a source of fouling For examplewhen coagulant is added during pretreatment the membranes can be fouled withiron oxides if the coagulant addition is not controlled correctly

2034 Combating fouling

20341 Pretreatment

Pretreatment is required to suppress fouling andor clogging of membranes or toremove chemically aggressive constituents such as chlorine (Judd amp Jefferson2005) The objective is to clear the feed stream from everything potentially harmfulto the membrane performance andor lifetime Measures taken are

1 Mechanical prefiltration2 Acidification to reduce carbonate hardness followed if necessary by aeration to reduce CO2

3 Addition of antiscalants to keep divalent salts (sulphates) from precipitating

20

15

10

05

0Ca2+ aliment = 200 mgL HCO3

ndash = 150 mgL pH = 70

LSI = 165Conversion = 75

2nd stage1st stage

LSI

1 2 3 4 5 6 7 8 9 10 11 12

Figure 2011 Langlier saturation index with membrane steps (AEDyR 2009)

618 Advances in Membrane Technologies for Water Treatment

4 Chlorination (or alternative oxidation) to deactivate microorganisms usually followed bydechlorination to safeguard against membrane degradation (Beurooddeker 2008)

5 Removal of colloids and metals from the feed water by coagulation and flocculation

Pretreatment can consist of sand filtration dissolved air flotation and activatedcarbon filters as well as other membrane systems such as MF and UF This lastcombination (MFeUF followed by RO) has become increasingly popular

20342 Cleaning-in-place

Notwithstanding the measures applied to combat fouling it is inevitable that somewill occur In time the fouling rate will increase and should be removed or controlledto make sure fouling does not become irreversible Therefore it is important to cleanthe membranes when they are only lightly not heavily fouled Heavy fouling canimpair the effectiveness of the cleaning chemical by impeding the penetration ofthe chemical deep into the foulant and in the flushing of foulant out of the membraneelements (Technical Service Bulletin 10720 Hydranautics) According to the samesource some fouling is allowed as long as

1 Normalized permeate flow decrease is less than 102 Normalized permeate quality decrease is less than 103 Increase in normalized pressure drop as measured between the feed and concentrate headers

is less than 15

Fouling increases the TMP which increases pressure on the membranes increasingthe risk of mechanical damage to the membrane surface

By controlling the fouling rates the cleaning frequencies can be reduced resultingin a higher production rate and lower chemical consumption

RO membranes cannot be back-washed because of the high pressure that would beneeded which could potentially damage the permeate side of the membranes There-fore RO membranes are flushed from the feed to the concentrate side or from theconcentrate side to the feed Besides flushing so-called lsquocleaning-in-placersquo is appliedMembranes are soaked for several hours with a chemical solution and are flushedafterward to remove the chemicals

Organic fouling can be removed using high-pH cleaning for example with sodiumhydroxide Inorganic fouling can be removed with acid cleaning agents such as sulphu-ric acid or citric acid

Normally it is advised first to apply alkaline cleaning followed by acid clean-ing In the case of multistage systems it is recommended to clean every step sepa-rately to avoid fouling that would go through the whole system before it isremoved

Often the effectiveness of the cleaning increases with temperature in that casethe cleaning chemicals can be heated This option should be taken into considerationduring the design phase

Another important factor for cleaning is the flux Turbulent conditions will increasethe shear forces on the fouling and increase the removal rate

Membrane technologies for water treatment and reuse in the power industries 619

2035 Route cause analysis

In practise one can encounter poor membrane performance If the likely cause isassumed to be membrane fouling the following route cause steps can help identifythe type and cause of fouling

1 Check on process conditions2 Check on monitoring equipment3 Conduct visual inspection of pretreatment and water production installation4 Gather previous inspection reports and process condition data5 Conduct visual inspection of membrane modules from different stages6 Gather the fouled material and conduct a composition analysis

With respect to process conditions trends in flux TMP and permeate qualitynormally give a good indication of the type of fouling taking place This is shownin Table 201 where the effects of different types of fouling on process conditionsare given

Table 201 Troubleshooting matrix

Possible causePossiblelocation Pressure drop Feed pressure Salt passage

Metal oxidefouling (egFe Mn CuNi Zn)

First stage leadelements

Rapid increase Rapid increase Rapid increase

Colloidalfouling(organic andor inorganiccomplexes)

First stage leadelements

Gradualincrease

Gradualincrease

Slight increase

Mineral scaling(eg Ca MgBa Sr)

Last stage tailelements

Moderateincrease

Slight increase Markedincrease

Polymerizedsilica

Last stage tailelements

Normal toincreased

Increase Normal toincreased

Biologicalfouling

Any stageusually leadelements

Markedincrease

Markedincrease

Normal toincreased

Organic fouling(dissolvedNOM)

All stages Gradualincrease

Increase Decreased

Antiscalantfouling

Second stagemost severe

Normal toincreased

Increase Normal toincreased

Source Hydranautics

620 Advances in Membrane Technologies for Water Treatment

One may need to calibrate and check the monitoring equipment to make sure that itis operating correctly The manner of sampling is also important as is the processingand recording of data in the plantrsquos data collection system Operating personnel whohave many obligations have been known to fail to identify the need to pay attention tomonitoring equipment

This is also true when inspecting the operating water production installation Forexample the antiscalant or coagulant supply tank could be empty or the flow of theseunits could be incorrectly set Thus it is important to visually conduct a regular checkon the monitoring equipment and operating water production installation and pretreat-ment units

When adopting a route cause analysis vital pieces of information are the gathereddata and the process information from the supplier ie inspection reports operatingconditions performance trends age of the unit and the membranes With this historicdata one can compare the operating ranges with those of the supplier or during thecommissioning phase

Visual inspection of one or more membrane modules that have been taken out ofuse preferably of each stage gives valuable information on the type of fouling Forsome fouling types the formation of salt crystals versus organicbiofouling can easilybe distinguished Documentation through photographs is important

Samples can be gathered for further characterization by collecting them over thelength of the membranes to check for differences in fouling with the flow and alsobetween different membrane stages (Figure 2012) The samples can be analysed forinorganic and organic matter or through further analysis using for example scanningelectron microscopy with electron diffraction spectroscopy andor atomic absorptionspectroscopy

Alternatively a nondestructive technique is to conduct a leakage test over themembranes

Figure 2012 Fouling and sampling points of the membrane

Membrane technologies for water treatment and reuse in the power industries 621

204 Future trends

2041 Evaporated water capture

A hidden source of relatively clean water is the evaporated water present in manyindustrial processes In these processes water is produced andor liberated and escapesas lsquowastersquo water into the atmosphere This evaporated water can be captured using gasseparation membranes With a sufficiently selective membrane purified water can beproduced in a single process step Advantages of the proposed process compared withtraditional separation are

1 High energy efficiency no phase change is required to achieve separation2 Temperature neutral to the source which makes heat recirculation in industrial processes

interesting3 High reliability no moving parts4 Small footprint it generally easily fits in existing spaces factories etc5 Environmentally friendly no use of chemicals no waste streams6 Energy savings aside from recirculation reheating of flue gases is no longer necessary and

latent heat can be reused in the process7 Corrosion benefits removal of water vapour from flue gas streams helps mitigate corrosion

Considering these benefits the demin water produced with this technology cancompete with existing demin water technologies To this end the European Commis-sion funded the CapWa project to bring this technology a step closer to realizationMore information can be found in httpwwwwatercaptureeu

2042 Forward osmosis

In contrast to RO in which water is pushed through a semipermeable membraneforward osmosis needs almost no pressure to have the water flow to the other sideof the membrane The difference between both techniques is that in the case of forwardosmosis the water crosses the membrane from the lower osmotic pressure to the higherosmotic pressure side This process requires very little energy because it is a naturalprocess (see Figure 2013) RO osmosis uses a lot of energy to pressurize water toovercome osmotic pressure because the water needs to cross the membrane fromthe higher osmotic pressure to the lower osmotic pressure side

In forward osmosis the higher osmotic pressure is artificially created by addingsalts This addition takes place on the retentate side of the membrane rather than onthe permeate side Thus by creating a controlled saline water stream water from adirty stream (seawater or wastewater) will pass the membrane and leave pollutionbehind with almost no energy consumption The challenge of forward osmosis is torecover clean water from this artificially created saline water stream Therefore asecond process is required this could be physical separation a thermal process mem-brane separation or a combination of all three Also there are some applications inwhich a second step is not required such as makeup for cooling towers and lsquohydration

622 Advances in Membrane Technologies for Water Treatment

bagsrsquo In hydration bags high concentrations of sugars provide the difference insalinity by putting this bag into lsquodirtyrsquo water it will attract only clean water whichends up as a drinkable sugar solution (McCutcheon McGinnis amp Elimelech 2005Salter 2005)

205 Recommended reading

Journals and recommended reading are as followsJournals

1 Power Plant Chemistry2 Ultra Pure Water3 VGB Powertech4 Local journals for example in The Netherlands H2O Similar journals can be found in your

respective country

Conferences

1 European Desalination Society2 Chemie im KraftWerk3 Aquatech

Web sites

1 EDS2 Global Water Intelligence

Figure 2013 Principle of forward osmosis

Membrane technologies for water treatment and reuse in the power industries 623

List of acronymssymbols

CA Cellulose acetateIX Ion exchangeNF NanofiltrationNOM Natural organic matterRO Reverse osmosisSDI Silt density indexTOC Total organic carbonTMP Trans-membrane pressureUF Ultrafiltration

References

Al-Shammiri M amp Al-Dawas M (1997) Maximum recovery from seawater reverse osmosisplants in Kuwait Desalination 110 37e48

Avlonitis S A Kouroumbas K amp Vlachakis N (May 2003) Energy consumption andmembrane replacement cost for seawater RO desalination plants In European conferenceon desalination and the environment Fresh water for all Malta 4e8 2003 EuropeanDesalination Society International Water Association

Bates W (1998) Reducing the fouling rate of surface and waste water RO systems Hydra-nautics USA IWC

BeurooddekerKW (2008)Liquid separationswithmembranes Springer ISBN978-3-540-47451-7EEA (2010) The european environmente State and outlook httpwwwendresscomehhome

nsfpagewpower-energy-processes-coal-fired-power-plants-desalination (referenceFigure 6)

Escuela Superior de Ingenieros Agronomos de Madrid AEDyR (2009) Curso DesalacionAEDyR

Ho C K Altman S J Jones H D T Khalsa S S amp McGrath L K (2008) Analysisof micromixers to reduce biofouling on reverse-osmosis membranes EnvironmentalProgress 27(2) 195e203

Judd S amp Jefferson B (2005) Membranes for industrial wastewater recovery and re-useElsevier ISBN 1-8561-7-389-5

Kabsch-Korbutowicz M (2006) Removal of natural organic matter from water by in-linecoagulationultrafiltration process (presented at EUROMEMBRANE 2006 24e28September 2006 Giardini Naxos Italy) Desalination 200 421e423

McCutcheon J R McGinnis R L amp Elimelech M (2005) A novel ammoniamdashcarbondioxide forward (direct) osmosis desalination process Desalination 174 1e11 httpmembranescomdocspapers02_cleaningpdf

Porter M C (1990) Handbook of industrial membrane technology Noyes Publications ISBN0-8155-1205-8 wwwprimewatercom (reference Figure 8)

Rajagopal S Jenner H A amp Venugopalan V P (2012) Operational and environmentalconsequences of large industrial cooling water systems Springer SciencethornBusinessMedia LLC httpdxdoiorg101007978-1-4614-1698-2

Salter R J (2005) Forward osmosis Water Conditioning and Purification 48(4) 36e38Technical Service Bulletin 10720 Hydranautics

Water treatment handbook 7th ed Vol 1 Degreacutemont Suez (2007) 287

624 Advances in Membrane Technologies for Water Treatment

Index

Note Page numbers followed by ldquofrdquo and ldquotrdquo indicate figures and tables respectively

AAbsorbed organic halogen (AOX)

581ndash582AC See Activated carbonAcetone-butanol-ethanol fermentation

(ABE fermentation) 270ndash271Acid chloride monomers 7ndash8Acoustic sound test (AST) 368Acrylonitrilebutadienestyrene

heterogeneous AEMs 290Activated carbon (AC) 290Activated sludge process (ASP) 444Active layer facing draw solution (AL-DS)

295Active layer facing feed solution (AL-FS)

308ADMH See 3-allyl-55-dimethylhydantoinAdsorbable organic halides (AOX) 487Advanced oxidation process (AOP) 492AEL See Anion exchange layerAEM See Anion exchange membranesAeration process 460Aerobic membrane bioreactor (Aerobic

MBR) 160ndash161areas of application 161ndash162factors affecting membrane performance

162ndash165wastewater reuse 166 166f

background 166ndash167plant components 167results 167ndash168

AFM See Atomic force microscopyAFO See Amorphous ferric oxidesAGMD See Air gap membrane distillationAgro-food industry 551agro-food wastewater characteristics

553tndash555tAIM See Aquaporin inside membranes

Air bubbling 423Air flushing 69Air gap membrane distillation (AGMD)

258 431ndash432AL-DS See Active layer facing draw

solutionAL-FS SeeActive layer facing feed solutionAlbert KohlerPappen 594Aliphatic diamines 7ndash83-allyl-55-dimethylhydantoin (ADMH)

255Alum coagulant 424ndash425Aluminum dioxide nanoparticles (Al2O3

nanoparticles) 20ndash22Aluminum sulphate See Alum coagulantAM See Anion-selective membraneAmino acids 197ndash198Aminopropyltriethoxysilane (APTES)

18ndash19Ammonia (NH3) 540Amorphous ferric oxides (AFO) 358ndash359Anaerobic membrane bioreactor (AnMBR)

168ndash170areas of application 168ndash171factors affecting performance 173HRT and SRT 174membrane properties 174ndash175OLR 173ndash174temperature 173

treatment of high-strength industrialwastewater 175ndash177

Anion exchange layer (AEL) 292Anion exchange membranes (AEM) 192

288 290 472acrylonitrilebutadienestyrene

heterogeneous 290Anion removal 466ndash476Anion-selective membrane (AM) 195

AnMBR See Anaerobic membranebioreactor

Annular photocatalytic reactor (APR) 223Antiscalants 135AOP See Advanced oxidation processAOX See Absorbed organic halogen

Adsorbable organic halidesAPR See Annular photocatalytic reactorAPTES See AminopropyltriethoxysilaneAquaporin (AQP) 251Aquaporin inside membranes (AIM) 545Aquaporin Z (AQP-Z) 251Aromatic diamines See Aliphatic diaminesArsenic (As) 116ASP See Activated sludge processAST See Acoustic sound testAtomic force microscopy (AFM) 365Attenuated total reflectancendashFourier

transform infrared (ATR-FTIR) 364Availability of equipment 354ndash355Azo dyes 538

BBackwashing 69 457Bacteriophages 370Bathtub curve 353ndash354 354fBEMR See Bio-entrapped membrane

reactor13-benzenediamine See 13-

phenylenediamineBenzoyl peroxide initiator (BPO initiator)

11b-cyclodextrin (b-CD) 250ndash251b-cyclodextrin polyurethane (DABA) 8Bio-entrapped membrane reactor (BEMR)

557Bio-inspired membranes 26ndash27Bio-mimetic mineralization

See Bio-mineralizationBio-mineralization 26ndash27Biochemical oxygen demand (BOD)

448ndash450 538 551Biofouling 454 617Biological fouling 422Bipolar membrane (BPM) 292ndash293Bipolar membrane 193 198Bisphenol A (BPA) 213Blending 10ndash11BOD See Biochemical oxygen demand

Boiler feed water 606Boric acid (H3BO3) 469BP See Bucky-PaperBPA See Bisphenol ABPM See Bipolar membraneBPO initiator See Benzoyl peroxide initiatorBrackish water (BW) 411 413f See also

Seawater (SW)high-pressure membrane applications 342

Bromides (Brndash) 468Bucky-Paper (BP) 265Bulk membrane properties 293BW See Brackish water

CCA See Cellulose acetateCA-based NF hollow fiber membrane 297CAc See Cellulose acetate (CA)membranes 96 415

CAGR See Compound annual growth rateCake filtration 457CAM See Contact angle measurementsCapital recovery factor (CRF) 434Carbon dioxide (CO2) 540Carbon nanotubes (CNTs) 10ndash13 101 255Carbon oxygen demand (COD) 64CarmanndashKozeny equation 396CarmanndashKozeny relationship 47CAS See Conventional activated sludgeCASP See Conventional activated sludge

processCation exchange layer (CEL) 292Cation exchange membranes (CEM)

192ndash193 288 290 472PANI chemically modified

organiceinorganic hybrid 290ndash291Cation-selective membrane (CM) 195Cations See Co-ionsCavitational mechanism 527CB See Conduction bandCEL See Cation exchange layerCellulose acetate (CA) 4 244 297 481Cellulose triacetate (CTA) 244 543ndash544CEM See Cation exchange membranesCeramic membranes See also Polymeric

membranescleaning 68ndash70development and fabrication processes

44ndash58

626 Index

ceramic powder paste and suspensionpreparation 52ndash53

combined phase-inversion and sintering55ndash58

heat treatment 54layer deposition 54ndash55material and microstructure 47ndash50membrane characteristics and design 47membrane configurations 50ndash52shaping 53ndash54

housing sealing and operation 61ndash62MFUF 45tndash46tmodule and unit designs 58ndash60water treatment 43for water treatment 62ndash68

Chemical cleaning 457methods 69 423physical cleaning vs 458t

Chemical conditioning 94Chemical methods 528Chemical oxygen demand (COD) 448ndash450

538 551 581ndash582Chemical vapor deposition (CVD) 101Chitosan (CS) 270 290chitosan-based composites 15

Chlorination 4244-chlorophenol (4-CP) 220 223ndash224Chlorophenols 500ndash502Chromic acid (H2CrO4) 481ndash482Chromium removal 480ndash484CIP See Cleaning in-placeClay nanoparticles 13ndash15Cleaning in-place (CIP) 350combating fouling 619process 350

Cloisite grades 13CM See Cation-selective membranecmc See Critical micelle concentrationCMCNa See Sodium carboxymethyl

celluloseCNT-BP membranes 265CNTs See Carbon nanotubesCo-ions 189 475Coagulation 93 424ndash425adsorption process 93ndash94sedimentation process 93

Coating wastewaters 597COD See Carbon oxygen demand

Chemical oxygen demand

Colloidal fouling 421ndash422 617Combating fouling 618ndash619Commercial ceramic applications 66ndash68Complete blocking 455Composite 48Composite membranes 3ndash10 See also

Nanocomposite membranespreparation via blending of polymers 4ndash5studies on 5tndash6tTFC membranes 6ndash10

Compound annual growth rate (CAGR) 83Concentrate stream 27ndash28Concentration gradient driven membrane

processes See also Electric potentialgradient driven membrane processes

amine functionalized MWCNTs 313fforward osmosis 294ndash317ICP 294ndash295pressured retarded osmosis 294ndash317

Concentration polarization (CP) 134ndash135379 383ndash384 454ndash455 523ndash524615ndash616

Conduction band (CB) 207Contact angle measurements (CAM)

212ndash213 363ndash364Conventional activated sludge (CAS) 590Conventional activated sludge process

(CASP) 444Conventional membrane materials 95ndash96Conventional pretreatment for SWRO

423ndash425Cooling water 605Cost assessment membrane technology

459CP See Concentration polarization4-CP See 4-chlorophenolCR filter See Cross-rotational filterCRF See Capital recovery factorCritical micelle concentration (cmc) 497Critical voltage gradient 526ndash527Cross-linked ZrT chelating membranes

291Cross-rotational filter (CR filter) 586 595CS See ChitosanCSTiO2 nano-composite membranes 270CTA See Cellulose triacetateCTACA flat sheet membranes 297CVD See Chemical vapor depositionCylindrical membranes 51ndash52 59ndash60

Index 627

DDABA See b-cyclodextrin polyurethaneDAF See Dissolved air flotationDAF test See Diffusive air flow testDairy industry wastewaters from 562ndash568Darcyrsquos law 85DBP See Disinfection byproductDCF See DiclofenacDCMD See Direct contact membrane

distillationDD See Donnan dialysisDeionized water (DI water) 342Demin water production 606Dense membranes 6ndash7Depressurized membrane PRs 219ndash220Desalination 130 412ndash413DF See Diafiltration24-DHBA See 24-dihydroxybenzoic acidDI water See Deionized waterDiafiltration (DF) 566Dialysis coupling of 222Diclofenac (DCF) 228ndash229Dielectric exclusion effect 396Diffusive air flow test (DAF test) 36824-dihydroxybenzoic acid (24-DHBA)

222Dimethylacetamide (DMAc) 11Dioxins 500ndash502Dip coating 55Direct contact membrane distillation

(DCMD) 221 258ndash261performance of single and dual-layer

hollow fiber membranes 262tndash264tDirect potable reuse project (DPR project)

338Direct testing methods 367 See also

Indirect testing methodsadvantages and disadvantages 367tAST 368DAF test 368PDT 367ndash368VDT 368

Disinfection byproduct (DBP) 63 90 487492ndash494

Dissolved air flotation (DAF) 334ndash335 595Dissolved organic carbon (DOC) 490Dissolved oxygen (DO) 540DMAc See DimethylacetamideDMF See Dual media filtration

DO See Dissolved oxygenDOC See Dissolved organic carbonDonnan dialysis (DD) 465 471ndash472

472fDonnan effect 381ndash383exclusion effect 395

Donnan-Steric-Pore model (DSPM) 395Double-walled nanotubes (DWNT) 10DPR project See Direct potable reuse

projectDraw solution (DS) 543Drinking water production 62ndash63DS See Draw solutionDSPM See Donnan-Steric-Pore modelDual media filtration (DMF) 425Dual-layer hydrophobichydrophilic hollow

fiber membranes 260fDual-layer PVDF hollow fiber membranes

259DWNT See Double-walled nanotubesDye recovery 542ndash545Dyno rotating disk module 108f

EEAC See Endocrine active compoundsED See ElectrodialysisED reversal (EDR) 472EDC See Endocrine disturbing compoundEDI See ElectrodeionizationEDR See ED reversal Electrodialysis

reversalEDS See Energy dispersive X-ray

spectroscopyEEA See European Environment AgencyEED See Electro-electrodialysisEffluents 519 587Electric fields 70Electric potential gradient driven membrane

processes See also Concentrationgradient driven membrane processes

AEMs 290BPMs 292ndash293CEMs 290ndash291electrodialysis 288ndash294 289fRED 288 289f 293ndash294

Electro-electrodialysis (EED) 482ndash483Electro-filtration 526ndash527Electro-spun nanofibrous membrane

(ENM) 268f

628 Index

Electrochemical separation techniques482ndash483

Electrodeionization (EDI) 330 483 484fElectrodialysis (ED) 185ndash186 287ndash290

289f 330 414 465 478 484f 556584ndash585 587ndash588

advances in membranematerials 192ndash194modules and system configurations194ndash197

anti-fouling properties 291applications 197ndash198with bipolar membranes 293fcross-linked ZrT chelating membranes

291Fe3O4 NPs 291ndash292membrane monovalent selectivity 290system design 293ndash294for water treatment 187ndash192

Electrodialysis reversal (EDR) 288 330414

Electrospinning method 267Electrospun nanofibrous membrane (ENM)

265ndash267Electrostatic repulsion 455EMBR-SRB See Extractive MBRs with

sulphate-reducing bacteriaEmerging contaminants 460ndash461Endocrine active compounds (EAC)

465ndash466 494ndash504Endocrine disturbing compound (EDC)

443 491 494ndash504Energy dispersive X-ray spectroscopy

(EDS) 366Energy recovery device (ERD) 426Engineered osmosis (EO) 288ENM See Electro-spun nanofibrous

membrane Electrospun nanofibrousmembrane

EO See Engineered osmosisEPS See Extracellular polymeric substancesEquipment failure rates 353ndash354ERD See Energy recovery deviceEthanol (EtOH) pervaporation performance

in 272tndash273tEuropean Environment Agency (EEA) 605European Union (EU) 431Extracellular polymeric substances (EPS)

164ndash165

Extractive MBRs with sulphate-reducingbacteria (EMBR-SRB) 479ndash480480f

Extrusion 54

FF-MWCNTs See Functionalized MWCNTsFA See Fulvic acidFeed solution (FS) 543FESEM See Field-emission scanning

electron microscopyFiberglass reinforces plastic (FRP) 339Fickrsquos law 384Field-emission scanning electron

microscopy (FESEM) 252f 365Fillers See Inorganic particlesFiltration 93ndash94Fish and seafood industryintegrated membrane process 560fwastewaters from 559ndash562

Flat membranes 50 58ndash59Flat sheet membranes 265 362Flocculation 94 424ndash425Fluorescent particle challenge testing 371Fluorides (Fndash) 468ndash469Fluorosilanization mechanism 266fFO See Forward osmosisFO MBR See Forward osmosis membrane

bioreactorFood and beverage industries 65ndash66Food processing industriesfood waste and origins 552twastewaters 551from dairy industry 562ndash568from fish and seafood industry 559ndash562from food and beverage industry556ndash557

food-processing 552from meat industry 569ndash572soybean 574ndash575winery 573ndash574

Forward flushing 68Forward osmosis (FO) 131ndash132 288 294

295f 306f 542ndash543 622ndash623See also Reverse osmosis (RO)

Ag NPs 317CA 297CA-based NF hollow fiber membrane297

Index 629

Forward osmosis (FO) (Continued)coated hydrolyzed commercial CACTA

306CTACA flat sheet membranes 297desalination 146ndash148double-skinned LbL membrane fabrication

316felectrospun nano-fibrous supports 312fundamentals of water treatment 136ndash142hollow fiber membranes 306ndash308internal concentration polarizationconcentrative 136ndash139dilutive 140quantitative analysis 140ndash142

membrane fabrication 314ndash315membranes for 142ndash146PA TFC flat sheet membrane 308ndash309PAN-OH 315polymer nano-composites 317researches on 298tndash305tTFC membranes 308TFC-FO membranes 308ndash310TFI membrane 317TFN membranes 312ndash314water flux direction and energy

consumptionproduction 296fForward osmosis membrane bioreactor

(FO MBR) 177ndash178Fouling 27 64 165 381ndash383 542 615

combating 618ndash619SW and BW 417ndash426types 615ndash618

Fractionation 197ndash198FRP See Fiberglass reinforces plasticFS See Feed solutionFTCS See 1H 1H 2H 2H-

perfluorododecyltrichlorosilaneFulvic acid (FA) 219Functionalized MWCNTs (F-MWCNTs)

312Furosemide 225

GGain output ratio (GOR) 412Galactoglukomannan (GGM) 597ndash598g-methacryloxypropyl trimethoxy silane

(g-MPS) 292ndash293Gas industry 519 See also Petrochemicals

industry

Gemfibrozil (GEM) 225ndash226GGM See GalactoglukomannanGlobal membrane market 83GOR See Gain output ratioGraphene oxide (GO) 243Greenrsquo process 205Ground water low-pressure membrane

applications 336ndash337

HHagenndashPoiseuille law 396Haloacetonitrile (HAN) 117Halogenated acetic acids (HAA) 117 490Halogenated aromatic hydrocarbons

500ndash502Haloketone (HK) 117HClO See Hypochlorous acidHeavy metals 476ndash480HEMA See 2-hydroxyethyl methacrylateHermiarsquos model 398Heterogeneous membranes 192Heterogeneous photocatalysis 205High-concentrated salt solution 428High-performancedual-layer PBIPEI hollow fiber

membranes 269TFC PRO membranes 311

High-pressure membranes 332 See alsoLow-pressure membranes

applications for water treatment brackishwater seawaterocean water 342

nanofiltration 338ndash339NFRO element and system 340fplanning and designing 342ndash344process application 476ndash478reverse osmosis 338 340ndash342contaminants removal rates 341f

SWRO 342technology 505ndash507

High-rate anaerobic reactor (HRAR) 170HK See HaloketoneHollow-fiber membranes 60 306ndash308

358Homogeneous polyelectrolyte complex

membrane (HPECM) 271ndash273HPEI See Hyperbranched polyethylenimineHRAR See High-rate anaerobic reactorHRT See Hydraulic residence timeHTI-CTA membranes 310 312

630 Index

Hydration Technology Innovations (HTI)428ndash429 543ndash544

Hydraulic model of filtration resistance 397Hydraulic residence time (HRT) 163 174Hydrodynamic cleaning methods 423Hydrodynamic or pore model 386Hydrophilic host polymers 265Hydrophilic surface modifying

macromolecules (LSMM) 9Hydrophobicity 4552-hydroxyethyl methacrylate (HEMA)

174ndash175Hyperbranched polyethylenimine (HPEI)

246Hypochlorous acid (HClO) 358

IIbuprofen (IBU) 227ndash228IC See In-line coagulationICIC See 5-isocyanatoisophthaloyl chlorideICP See Internal concentration polarizationIEM See Ion-selective exchange membraneIEMB See Ion-exchange MBRImmersed membrane bioreactor (iMBR)

156 448IMS See Integrated membrane systemsIn-line coagulation (IC) 93Indirect potable reuse project (IPR project)

338Indirect testing methods 368ndash369 See also

Direct testing methodsadvantages and disadvantages 369tfluorescent and magnetic particles

challenge testing 371PAC challenge testing 371particle counting 369ndash370particle monitoring 369ndash370phage and spore challenge testing

370ndash371turbidity monitoring 370

Industrial wastewater treatment 64ndash65Inorganic micropollutant removal 466

See also Organic micropollutantremoval

anion removal 466ndash476chromium removal 480ndash484heavy metals 476ndash480

Inorganic particles 244Integral membrane 49ndash50

Integrated low-pressure membrane process478ndash480

Integrated membrane systems (IMS) 90332 344 522

concentration polarization 523ndash524membrane fouling 524ndash525permeate flux 523ndash524

Interfacial polymerization (IP) 24 248ndash249257f

Intermediate blocking 457Internal concentration polarization (ICP)

294ndash295Ion exchange (IX) 94demin line using 611fdried-out resin 612fmembrane process 471ndash474 478operational experience 611ndash612technology 608 610

Ion-exchange MBR (IEMB) 475 476fIon-selective exchange membrane (IEM)

287 290Ionic strength 455IP See Interfacial polymerizationIPA See IsopropanolIPC See Isophthaloyl chlorideIPR project See Indirect potable reuse

projectIron oxide (Fe3O4) 291ndash292nanoparticles 22ndash23

5-isocyanatoisophthaloyl chloride (ICIC)7ndash8

Isophthaloyl chloride (IPC) 7ndash8Isopropanol (IPA) 269pervaporation performance 272tndash273t

IX See Ion exchange

KKubota flat-plate membrane cartridges 175Kubota Membrane Technology 557

LLayer-by-layer assembly (LbL assembly)

253ndash255LbL assembly See Layer-by-layer assemblyLeaky membrane model 186ndash187Limiting current density 190Liquid entry pressure (LEP) 261LMWC See Low-molecular-weight

compounds

Index 631

Log removal values (LRV) 351Low-concentration salt solution 428Low-molecular-weight compounds

(LMWC) 177Low-pressure membranes 332 See also

High-pressure membranesapplications for water treatment surface

water and ground water 336ndash337flat plate MFUF immersed membrane

trainbankbasin 334fhollow fiber MFUF membrane fibers 334fmicrofiltration 332ndash335microorganism removal 484ndash487planning and designing 337ndash338technological process 336fultrafiltration 332ndash333 335ndash336

LRV See Log removal valuesLSMM See Hydrophilic surface modifying

macromolecules

Mm-phenylenediamine (MPD) 7ndash8 250Magnetic ion-exchange resin (MIEX

resin) 491Magnetic particle challenge testing 371Maintainability of membrane filtration 355Mathematical modeling

of membrane operations 379ndash401MFUF membranes 396ndash401NF membranes 393ndash396RO membranes 384ndash393 387tndash390twater treatment process and trend

379ndash380MBA See N N0-Methylenebis(acrylamide)MBR See Membrane bioreactorMCR See Membrane coagulation reactorMD See Membrane distillationMean time between failure (MTBF) 353Mean time to failure (MTTF) 353Mean time to repair (MTTR) 354Meat industry

demonstration plant for 571fwastewaters from 569ndash572

Mechanical cleaning 423MED See Multiple effect distillationMEDINA See Membrane-based

desalination integrated approachMEDIRAS See Membrane Distillation in

Remote Areas

Membrane ageing 350assessment tools 362 363fchemical and structural characteristics364

filtration characteristics 362ndash363mechanical and thermomechanicalcharacteristics 364ndash365

membrane integrity tests 366ndash371morphological characteristics 365ndash366surface characteristics 363ndash364

control methods 371membrane modification 372ndash373membrane train redundancies 371ndash372

effects 351fmonitoring methods 362

Membrane bioreactor (MBR) 43ndash44 95155 443 448ndash450 474ndash476 552587 590ndash594 See alsoPhotocatalytic membrane reactor(PMR)

aerobic 160ndash168anaerobic 168ndash177configurations 156ndash158conventional wastewater treatment vs

446ndash450 449textractive 475fforward osmosis 177ndash178fouling mechanisms in 455ndash457membrane material types and morphology

158ndash159membrane module types 160technology 540

Membrane coagulation reactor (MCR) 469Membrane distillation (MD) 216 220ndash221

258ndash267 430ndash434 See alsoPervaporation (PV)

Membrane Distillation in Remote Areas(MEDIRAS) 432 432f

Membrane failure 351ndash352due to chemical attack 358ndash359due to excessive movement 359ndash362due to faulty membrane module structure

359membrane module failure 361tmodes 355ndash362 356tndash357t

Membrane filtration (MF) 349f 485ndash486552 587

applications for water treatment 349fdriving forces for 582ndash583

632 Index

future trends 373ndash374maintainability 355membrane ageing 350

control methods 371ndash373monitoring methods 362ndash371

membrane failure 351ndash352modes 355ndash362 356tndash357t

microporous and semipermeable 349reliability 352ndash355resilience 355in textile wastewater treatment 541ndash542

Membrane fouling 165in WWT 454ndash457

Membrane integrity tests 366ndash367direct testing methods 367ndash368indirect testing methods 368ndash371

Membrane technologies 329 443 559612ndash614

energy consumption of 530ndash531filtration spectrum 613fmicropollutants removal 465

inorganic micropollutant removal466ndash484

microorganism removal 484ndash491NOM 484ndash491organic micropollutant removal491ndash509

for municipal wastewater treatment444ndash445

in natural waters treatment 465operational experience with 614ndash615

fouling 615spiral-wound membrane 614fin wastewaters treatment 465for water treatment 521ndash522 521f

614ndash615Membrane Technology and Research Inc

(MTR) 47Membrane-based desalination integrated

approach (MEDINA) 432ndash433Membrane-based separation technologies

239Membrane(s) 84 239 479ndash480cleaning 457desalination 130ndash131fabrication techniques 239ndash241fibers 333with innovative materials 239ndash241lifetime 460

modification 3ndash4 372ndash373 525modules 359 451pretreatment 425ndash426processes 84ndash85 586ndash587barriers to 583recirculate process water 595ndash596

in pulp and paper industry 586ndash587resistance 454separation 206ndash207 333 522processes for water treatment 240tndash241t

stability 211ndash212train redundancies 371ndash372types and configurations 330 332fand water treatment processes 331f

Memstill process 431Metal ions 476ndash477MF See Membrane filtration

MicrofiltrationMicellar enhanced UF (MEUF) 482Microbial challenge testing 370Microfiltration (MF) 43 241ndash243 330

332ndash335 420ndash421 443 465 521552 612 See also Nanofiltration(NF) Reverse osmosis (RO)Ultrafiltration (UF)

Cryptosporidium parvum deformation486f

low-pressure membranes 333ndash335process 85 86t

Microfouling 617Microorganism removal 484ndash491by low-pressure membrane process

484ndash487using UF 486f

Micropollutants 465ndash466Micropollutants removalinorganic micropollutant removal 466ndash484membrane techniques 465microorganism removal 484ndash491NOM 484ndash491organic micropollutant removal 491ndash509

MIEX resin See Magnetic ion-exchangeresin

Miso (soybean paste) 574Mixed liquor suspended solids (MLSS)

163ndash164 444 556 591Mixed matrix membrane (MMM) 239ndash241Mixed matrix membranes See Composite

membranes

Index 633

MLSS See Mixed liquor suspended solidsMMM See Mixed matrix membraneModified FTCSndashTiO2ndashPVDF membranes

265Module 160Molecular weight (MW) 116ndash117 451Molecular weight cut-off (MWCO) 85ndash87

160 248ndash249 363 559MPD See m-phenylenediamineMSD system See Multi-shaft disk systemMSF distillation See Multistage flash

distillationMT See Multi-tubularMTBF See Mean time between failureMTR See Membrane Technology and

Research IncMTTF See Mean time to failureMTTR See Mean time to repairMulti-shaft disk system (MSD system) 108

109fMulti-tubular (MT) 451Multi-walled carbon nanotube (MWCNT)

100ndash101 250ndash251 259 291ndash292carboxy-functionalized 256

Multi-walled nanotube (MWNT) 9 12fMultiple effect distillation (MED) 412Multistage flash distillation (MSF

distillation) 412Municipal wastewater 63ndash64Municipal wastewater treatment membrane

technologies for See alsoMembranetechnologies

drivers and barriers to 444ndash445membrane modules 451membrane processdesign operation and control 458ndash459optimisation 459ndash460

membrane-assisted processes andtechnologies 445ndash446

pressure-driven membrane process 445funit operation and process 447tWWTmembrane fouling in 454ndash457membrane technologies operationalfactors 453ndash454

membrane-assisted system in 446ndash451MW See Molecular weightMWCNT SeeMulti-walled carbon nanotubeMWCO See Molecular weight cut-off

MWNT See Multi-walled nanotubeMycoestrogens 495

NN N0-Methylenebis(acrylamide) (MBA)

255N-methyl-2-pyrrolidone (NMP) 308NaBH4 See Sodium borohydrideNano-enhanced membranes See

Nanocomposite membranesNanocomposite membranes 10ndash25

See also Composite membranesAl2O3 nanoparticles 20ndash22clay nanoparticles 13ndash15CNT 10ndash13iron oxide nanoparticles 22ndash23silver nanoparticles 15ndash16SiO2 nanoparticles 23ndash24TiO2 nanoparticles 16ndash19ZnO nanoparticles 19ndash20ZrO2 nanoparticles 25

Nanofiltration (NF) 83 88ndash90 241248ndash251 288 330 445ndash446465ndash468 521 541ndash542 552 563t567t 584ndash585 612 See alsoMicrofiltration (MF) Reverseosmosis (RO) Ultrafiltration (UF)

applications 89ndash90NOM 487ndash489pesticide removal in 498tphthalates removal 500t

characteristics 453tfor flash cooler condensates treatment 565fhigh-pressure membranes 338ndash339for seawater desalination 111ndash115

Nanoparticles (NPs) 243 291ndash292Naphthalene-136-trisulfonylchloride

(NTSC) 250ndash251Natto (fermented soybean) 574Natural hormones 502ndash504Natural organic matter (NOM) 63 90 215

422 454 465ndash466 487 542 608MF 489ndash491MF UF and NF comparative assessment

488tNF application 487ndash489 489tRO application 487ndash489UF 489ndash491

NavierndashStokes equations 186ndash187

634 Index

Nephelometric turbidity units (NTU) 370420ndash421 484ndash485

Nernst-Planck equation 394Net flux 458ndash459NF See NanofiltrationNHE See Normal hydrogen electrodeNitrates 4674-nitrophenol (4-NP) 212NMP See N-methyl-2-pyrrolidoneNOM See Natural organic matterNormal hydrogen electrode (NHE)

208ndash209Novel functionalized PS-based BPM

292Novel membranes 239ndash241materials 98ndash104

NPs See Nanoparticles4-NP See 4-nitrophenolNTSC See Naphthalene-136-

trisulfonylchlorideNTU See Nephelometric turbidity units

OOampM cost See Operation and maintenance

costOD See Optical densityOil 519ndash520Oilndashwater emulsion 521ndash522OLR See Organic loading rateOM See Optical microscopyOMMT See Organically modified

montmorilloniteOperation and maintenance cost (OampM

cost) 426Optical density (OD) 545Optical microscopy (OM) 211ndash212Organiccompounds 454fouling 616matter 537

Organic loading rate (OLR) 164ndash165173ndash174 568

Organic micropollutant removal 491See also Inorganic micropollutantremoval

DBP 492ndash494EAC 494ndash504EDC 494ndash504oxidation 492ndash494

pharmaceutically active compounds504ndash509

Organically modified montmorillonite(OMMT) 14

Organicndashinorganic nano-composite GOPVDF-blended UF membranes 246

Osmosis 131ndash132osmotic pressure 384ndash385osmotic-based wastewater reduction

542ndash545 544f

Pp-phenylenediamine (PPD) 7ndash8PA See PolyamidesPA membranes See Polyaniline membranesPA TFC flat sheet membrane 308ndash309PAA See Polyacrylic acidPAAPEI multilayer PEC films 269PAC See Powdered activated carbonPAH See Poly(allylamine hydrochloride)

Polycyclic aromatic hydrocarbonPAI See Polyamide-imidePall Corporation Membralox multi-

channeled alumina membranes 5151f

PAN See PolyacrylonitrilePAN membrane substrate (PAN-OH) 315PANPET fibrous scaffold See

Polyacrylonitrilepolyethyleneterephthalate fibrous scaffold

PANI See PolyanilinePAO See Pressure-assisted osmosisPaperie du Rhin 592Particle counting 369ndash370Particle monitoring 369ndash370Particulate components 454Particulate fouling 420ndash421PAS See PolyarylsulfonePBI See PolybenzimidazolePC See PolycarbonatePCB See PolychlobiphenylPCP See PentachlorophenolPDA See PolydopaminePDMC See Poly(2-methacryloyloxy ethyl

tri-methylammonium chloride)PDMPs See Pressure-driven membrane

processesPDMS See PolydimethylsiloxanePDT See Pressure decay test

Index 635

PEC See Polyelectrolyte complexPECH See PolyepichlorohydrinPEG See Polyethylene glycolPEI See PolyethyleneiminePentachlorophenol (PCP) 1631H 1H 2H 2H-

perfluorododecyltrichlorosilane(FTCS) 265

Permeate flux 523ndash524 529Permeated water 529Permselectivity 189Pervaporation (PV) 222ndash223 267ndash273

See alsoMembrane distillation (MD)coupling 222ndash224performance of PECMs and IPA and EtOH

272tndash273tPES See PolyethersulfonePesticides 116ndash117Petrochemicals industry 519

design considerations 525ndash527energy consumption of membrane

operations 530ndash531IMS 522ndash525membrane technologies for water

treatment 521ndash522 521foperation optimization 528ndash529reuse in 521ndash522wastewater composition 520twastewater pretreatment 527ndash528

PEUF See Polymer-enhanced UFPEVP See Poly (N-ethyl-4-

vinylpyridiniumbromide)PFU counting See Plaque forming unit

countingpH value 455PhACs See Pharmaceutical active

compoundsPhage and spore challenge testing 370ndash371Pharmaceutical active compounds (PhACs)

224 443 504ndash509 508tPharmaceutical and personal care product

(PPCP) 504Pharmaceuticals 117Phase-inversion 24 54ndash58 214 267Phenolic xenoestrogenes 499ndash50013-phenylenediamine 415Phosphomolybdic acid (PMA) 271Photocatalysis 205

coupling 220ndash224

membrane materials development anddesign 211ndash217

principles 207ndash211Photocatalyst 205ndash211Photocatalytic membrane reactor (PMR)

205ndash206 See also Membranebioreactor (MBR)

advances in membrane modules and systemconfigurations 217ndash224

advantages and limitations 230applications 224ndash229for water treatment 207ndash217

Photoreactor (PR) 205ndash206Phthalates 499Physical cleaning 457chemical cleaning vs 458tmethods 68ndash69

Phytoestrogens 495PI See PolyimidePiperazine (PIP) 7ndash8Pitzer equation 384ndash385Plant protection products 497ndash499Plaque forming unit counting (PFU

counting) 370Plate-and-frame modules 106PMA See Phosphomolybdic acidPMR See Photocatalytic membrane reactorPNIPAAm See Poly(N-isopropylacrylamide)Poly (N-ethyl-4-vinylpyridiniumbromide)

(PEVP) 271ndash273Poly (sodium 4-styrenesulfate) (PSS)

253ndash255Poly(1-vinylpyrrolidone) (PVP) 245ndash246Poly(2-methacryloyloxy ethyl tri-

methylammonium chloride)(PDMC) 271ndash273

Poly(allylamine hydrochloride) (PAH) 291Poly(N-isopropylacrylamide) (PNIPAAm)

255Poly(sodium 4-styrene sulfonate) (PSS)

291Poly(VBC-co-g-MPS) 292ndash293Polyacrylic acid (PAA) 214 269Polyacrylonitrile (PAN) 4 96 212

310ndash311nano-fibrous support 314f

Polyacrylonitrilepolyethylene terephthalatefibrous scaffold (PANPET fibrousscaffold) 243

636 Index

Polyamide-imide (PAI) 249Polyamides (PA) 244Polyaniline (PANI) 290ndash291Polyaniline membranes (PA membranes)

7ndash8Polyarylsulfone (PAS) 244Polybenzimidazole (PBI) 269Polycarbonate (PC) 244Polychlobiphenyl (PCB) 500ndash502Polycyclic aromatic hydrocarbon (PAH)

495ndash497retention coefficients comparison 496t

Polydimethylsiloxane (PDMS) 267ndash269Polydopamine (PDA) 251 310ndash311Polyelectrolyte complex (PEC) 269Polyelectrolyte membranes (PECMs)pervaporation performance 272tndash273t

Polyepichlorohydrin (PECH) 293Polyethersulfone (PES) 4 48 96 244 248f

335Polyethylene glycol (PEG) 253Polyethyleneimine (PEI) 243 307 479Polyimide (PI) 16 244Polymer nano-composites 317Polymer-enhanced UF (PEUF) 469Polymeric membranes 211 See also

Ceramic membranesapplications for water treatment 27ndash28bio-inspired membranes 26ndash27composite membranes 3ndash10nanocomposite membranes 10ndash25nanostructured membranes 25ndash26

Polymers 96 97tPolypropylene (PP) 96 212Polysulfone (PS) 96 243 292Polytetrafluoroethylene (PTFE) 212ndash213

259ndash261hollow fiber membrane 261f

Polyvinyl alcohol (PVA) 4 253 290 470Polyvinyl chloride (PVC) 189 244Polyvinylamine (PVAm) 243Polyvinylidene difluoride (PVDF) 4 96

244 248f 314ndash315ENMs 268ffluorosilanization mechanism 266f

Poultry processing wastewater (PPW) 572Powdered activated carbon (PAC) 117 490challenge testing 371

PP See Polypropylene

PPCP See Pharmaceutical and personal careproduct

PPD See p-phenylenediaminePPW See Poultry processing wastewaterPR See PhotoreactorPrefiltration 91ndash93Pressing 53Pressure decay test (PDT) 352

367ndash368Pressure Exchanger (PX) 427Pressure retarded osmosis (PRO) 287 294

295f 428 429felectrospun nano-fibrous supports 312high-performance TFC PRO membranes

311PA-based TFC membranes 310ndash311researches on 298tndash305twater flux direction and energy

consumptionproduction 296fPressure vessel (PV) 339Pressure-assisted osmosis (PAO) 543Pressure-driven membrane processes

(PDMPs) 241 288 466ndash471 475fSee also Vapor pressure gradientdriven membrane processes

characteristics 242tmicrofiltration 242ndash243nanofiltration 248ndash251reverse osmosis 251ndash258triangle-shape tri-bore hollow fiber

membranes 245fultrafiltration 244ndash246

Pressure-driven process 210Pressurized membrane PRs 217ndash219Pretreatmentcombating fouling 618ndash619requirements 90MBR 95pretreatment methods 91ndash94SW and BW 417ndash426

PRO See Pressure retarded osmosisProduced water 65PS See PolysulfonePSS See Poly (sodium 4-styrenesulfate)

Poly(sodium 4-styrene sulfonate)PTFE See PolytetrafluoroethylenePulp and paper industry 581demands for membranes and modules in

584

Index 637

Pulp and paper industry (Continued)driving forces for membrane filtration

582ndash583membranes process 586ndash587barriers to 583recirculate process water 595ndash596

module configurations 585ndash586pressure-driven membrane process 585fraw water purification 598selectivity 584ndash585total emission to waterways and reduction

582twastewaters purification 587ndash595watercharacteristic properties 583ndash584valuable byproducts recovery andpurification 596ndash598

Pulsed flow 525PV See Pervaporation Pressure vesselPVA See Polyvinyl alcoholPVAm See PolyvinylaminePVC See Polyvinyl chloridePVDF See Polyvinylidene difluoridePVDF-hexafluoropropylene (PVDF-HFP)

14PVDF-HFP See PVDF-

hexafluoropropylenePVDFMg(OH)2ndashMF hybrid membranes

243PVP See Poly(1-vinylpyrrolidone)PVP-grafted SiO2 NPs 245ndash246 247fPX See Pressure Exchanger

RRanitidine 225Raw water

purification 598source 606ndash608

RB5 dye See Reactive black 5 dyeRE See Reverse electrodialysisReactive black 5 dye (RB5 dye) 214Reactive dyes 538Reactive monomers 7ndash8Recirculate process water 594ndash595RED See Reverse electrodialysisReliability of membrane filtration 352ndash355

availability 354ndash355equipment failure rates 353ndash354MTTF and MTBF 353

Reverse electrodialysis (RE) 428ndash430RE-SGP investigations 430

Reverse electrodialysis (RED) 287membrane unit 288 289fperformances 293system design 293ndash294

Reverse osmosis (RO) 130ndash132 241251ndash258 288 295f 329 330445ndash446 465ndash468 521 541ndash542552 563t 567 584ndash585 608See also Forward osmosis (FO)Microfiltration (MF) Nanofiltration(NF) Ultrafiltration (UF)

characteristics 453tconventional and membrane pretreatment

135ndash136electroplating process line integration with

477ffundamentals of water treatment 132ndash135high-pressure membranes 338 340ndash342contaminants removal rates 341f

in meat wastewater treatment 570tmembrane process 329 330fmembranes 613ndash614NOM 487ndash489pesticide removal in 498tphthalates removal 500ttwo-stage system for boron removal 470fwater flux direction and energy

consumptionproduction 296fReversible fouling 397RO See Reverse osmosisRotating cylinders 526Rotating disk module systems 108Rotatingvibrating membranes 526

SSAA See Surface active agentSalinity gradient power (SGP) 287

429ndash430Scaling 454 617ndash618Scanning electron microscopy (SEM)

211ndash212 365SDBS See Sodium dodecylbenzene

sulfonateSDI See Silt density indexSeawater (SW) 411 413fdesalination 342plants 344

638 Index

energy from 427ndash433fouling 417ndash426high-pressure membrane applications

342MD economics 433ndash434pretreatment strategies 417ndash426product specifications of 419tRO 420f

energy requirements for 426ndash427membranes and modules 415ndash417principle 414

standard composition 413tSeawater reverse osmosis (SWRO) 342SEM See Scanning electron microscopySewage treatment 63ndash64Sewage treatment plants (STP) 224SGMD See Sweeping gas membrane

distillationSGP See Salinity gradient powerSHMP See Sodium hexametaphosphateShoyu (soy sauce) 574SHP model See Steric hindrance pore modelSiC SteriMem products 51 51fSide-stream membrane bioreactor (sMBR)

156 448Silica (SiO2) 243 245ndash246nanoparticles 23ndash24PVP-grafted 245ndash246

Silt density index (SDI) 92 423Silver ions 16Silver nanoparticles 15ndash16Single-walled carbon nanotubes (SWCNT)

101Single-walled nanotubes (SWNT) 10Sintering 54ndash58SiO2ndashGO nanohybridPS membrane 243SL See Sludge loadingSlip casting 53Slow sand filtration (SSF) 425Sludge loading (SL) 164ndash165Sludge retention time (SRT) 164 174sMBR See Side-stream membrane

bioreactorSMBS See Sodium metabisulphiteSMM See Surface modifying

macromoleculeSMP See Soluble microbial productsSMPR See Submerged membrane

photocatalytic reactor

Sodium borohydride (NaBH4) 261Sodium carboxymethyl cellulose (CMCNa)

271ndash273Sodium dodecylbenzene sulfonate (SDBS)

291Sodium hexametaphosphate (SHMP) 425Sodium hypochloride (NaOC) 539ndash540Sodium metabisulphite (SMBS) 425Sol-gel method 55Solids retention time (SRT) 444 556Soluble microbial products (SMP) 164Solute flux 384Solutiondiffusion mechanism 210 414Solvay Advanced Polymers See Torlon

4000T-MV PAISoybean wastewater 574ndash575 575fSparging See Air flushingSPEEK See Sulfonated

polyetheretherketoneSPEK polymer See Sulphonated poly(ether

ketone) polymerSPES See Sulfonated polyethersulfoneSpiegler-Kedem model 385Spin coating See Dip coatingSpinning parameters 56Spintek module 109fSpiral-wound module (SWM) 385

415ndash417 586SPPS membrane See Sulfonated

polyphenylenesulfone membraneSPTA See Sulfophthalic acidSRT See Sludge retention time Solids

retention timeSSF See Slow sand filtrationStable oily emulsion 519ndash520Standard blocking 457Steric effect 395Steric hindrance pore model (SHP model)

386STP See Sewage treatment plantsSubmerged MBR See Immersed membrane

bioreactor (iMBR)Submerged membrane bioreactor 156Submerged membrane photocatalytic

reactor (SMPR) 213 219Submerged membrane PRs See

Depressurized membrane PRsSulfonated polyetheretherketone (SPEEK)

293

Index 639

Sulfonated polyethersulfone (SPES)244ndash245 290

Sulfonated polyphenylenesulfonemembrane (SPPS membrane)309ndash310

Sulfophthalic acid (SPTA) 269ndash270Sulphonated poly(ether ketone) polymer

(SPEK polymer) 7ndash8 309Surface active agent (SAA) 497Surface hydrophilicity 363ndash364Surface modifying macromolecule (SMM)

265Surface topography modification 256ndash258Surface water low-pressure membrane

applications 336ndash337Suspended fouling 617SW See SeawaterSWCNT See Single-walled carbon

nanotubesSweeping gas membrane distillation

(SGMD) 258SWM See Spiral-wound moduleSWNT See Single-walled nanotubesSWRO See Seawater reverse osmosisSynthetic hormones 502ndash504

TTamoxifen (TAM) 225ndash226Tape casting method 53TDS See Total dissolved solidsTemperature 529TEMPO-oxidized cellulose nanofibrils

(TOCNs) 244Teorell-Meyer-Sievers model (TMS model)

386Tetraethoxysilane (TEOS) 23ndash24Textile industry 537

in batch process 537ndash538dyeingprinting textiles 538textile sizing agents 537

Textile processing 537Textile sizing agents 537Textile wastewater 538 539t

treatment 539membrane filtration in 541ndash542osmotic-based wastewater reduction542ndash545

potential dye recovery 542ndash545TFC See Thin-film composite

TFC RONF membranes 256ndash258TFI membrane See Thin-film inorganic

membraneTFN membranes See Thin-film

nanocomposite membranesTGA See Thermogravimetric analysisThermal desalination 130ndash131 412Thermal vapour compression (TVC) 412Thermogravimetric analysis (TGA) 365

366fThermolysis 54Thin-film composite (TFC) 95 415layer 248ndash249membranes 6ndash10 360ndash362 543ndash544RO membrane 254fTFC-FO membranes 7ndash8 308ndash310

Thin-film inorganic membrane (TFImembrane) 317

Thin-film nanocomposite membranes (TFNmembranes) 101 250ndash251312ndash314 313f

THM See TrihalomethaneThree-compartment EED 482ndash483 483fTiO2 nanoparticles See Titanium dioxide

nanoparticlesTitanium dioxide nanoparticles (TiO2

nanoparticles) 16ndash19TMC See Trimesoyl chlorideTMP See Transmembrane pressureTMS model See Teorell-Meyer-Sievers

modelTOC See Total organic carbonTOCNs See TEMPO-oxidized cellulose

nanofibrilsTofu (soybean curd) 574Torlon 4000T-MV PAI 269Total dissolved solids (TDS) 129 192ndash193

338 416ndash417Total organic carbon (TOC) 90 206

334ndash335 556 608Total suspended solids (TSS) 446 539 551Transmembrane pressure (TMP) 156

219ndash220 446 453ndash454 556 616Transport mechanisms 381ndash383Transport number of component 189Trihalomethane (THM) 93ndash94 485Trimesoyl chloride (TMC) 7ndash8 249 308TSS See Total suspended solidsTurbidity monitoring 370

640 Index

TVC See Thermal vapour compressionTwo cation-exchange membranes 483ndash484

UUF See UltrafiltrationUgchelen BV 592Ultrafiltration (UF) 43 83 85ndash88 86t 241

244ndash246 330 332ndash333 420ndash421443 465 521 541 552 567t 572612 See also Microfiltration (MF)Nanofiltration (NF) Reverseosmosis (RO)

fishery washing waters 559ndash560low-pressure membranes 335ndash336in meat wastewater treatment 570tphthalates removal 500t

Ultrapure water (UPW) 342 612Ultrasonic fields 70Ultrasound 527Ultraviolet irradiation (UV irradiation)

211ndash212 244ndash245 485 556ndash557Unconventional physical cleaning methods

69ndash70United States (US) 83United States Environmental Protection

Agency (USEPA) 520ndash521Unmodified montmorillonites 13UPW See Ultrapure waterUS See United StatesUSEPA See United States Environmental

Protection AgencyUV irradiation See Ultraviolet irradiation

VVacuum decay test (VDT) 368Vacuum membrane distillation (VMD)

258ndash261Vacuum-enhanced direct contact membrane

distillation (VEDCMD) 148Valence band (VB) 207Vanrsquot Hoff equation 384ndash385Vapor pressure gradient driven membrane

processes See also Pressure-drivenmembrane processes (PDMP)

membrane distillation 258ndash267pervaporation 267ndash273

VB See Valence bandVBC See Vinylbenzyl chlorideVCR See Volume concentration ratio

VDT See Vacuum decay testVEDCMD See Vacuum-enhanced direct

contact membrane distillationVeolia Water Ltd CeraMem element 51

51fVibrating module systems 108Vibrating shear-enhanced processing

(VSEP) 108 110f 585ndash586Vinylbenzyl chloride (VBC) 292ndash2934-vinylpyridine (4-VP) 290Viscous fingering 56ndash57VMD See Vacuum membrane distillationVolume concentration ratio (VCR)

562ndash564Volumetric permeate flux 5244-VP See 4-vinylpyridineVSEP See Vibrating shear-enhanced

processing

WWastewater 479ndash480 519 551compounds 519from dairy industry 562ndash568direct membrane filtration for 594ndash595from fish and seafood industry 559ndash562from food and beverage industry

556ndash557food-processing 552from meat industry 569ndash572pretreatment 527ndash528purificationdirect membrane filtration forwastewaters 594ndash595

membrane process 587ndash594textile 538ndash545

Wastewater treatment (WWT) 43ndash44583ndash584 See also Pulp and paperindustry

membrane fouling in 454ndash457membrane process with biological WWT

587improving functionality 589ndash590MBR 590ndash594 593tupgrade purification 587ndash589

membrane technologies operational factors453ndash454

membrane-assisted system 446conventional treatments vs MBR446ndash450

Index 641

Wastewater treatment (WWT) (Continued)NFRO after biological treatment450ndash451

Water (H2O) 411 540 551 581 605characteristic properties 583ndash584contamination 485flux 384ldquofootprintrdquo 582ndash583noncompliancy 355ndash358operational experience with membrane

614ndash615fouling 615

pollution 206purification 3hydration bag 144f

purification technologies 608ndash614quality 581raw water source 606ndash608requirements 606

recovery 564shortages 129stream 605ndash606cycle 605ndash606 607f

temperature 391turbidity 484ndash485valuable byproducts recovery and

purification 596ndash598water capture evaporation 622

Water permeation flux (WPF) 211ndash212Water treatment 43

advancesin membrane materials 95ndash104in polymeric membranes 3ndash27

applications 110membranes for groundwater treatment110ndash111

membranes for harvesting rainwater 116nanofiltration for seawater desalination111ndash115

specific contaminant removal 116ndash117surface water treatment 110

ceramic membranes 44concentration gradient driven membrane

processes 294ndash317electric potential gradient driven membrane

processes 288ndash294future trends 28 274 318ndash319 345global membrane market 83

high-pressure membranes 332applications 338ndash342

IMS 90integrated membrane systems 344low-pressure membranes 332applications 332ndash337planning and designing 337ndash338

membrane filtrationapplications 349 349ftechnology 84

membrane(s)modules and system configurations106ndash108

processes 84ndash85separation processes 240tndash241ttreatment combination 344ndash345types and configurations 330 332fand water treatment processes 331f

MF process in 43ndash44microfiltration process 85 86tNF 88ndash90PDMPs 241ndash258pretreatment requirements 90ndash95RO 132ndash135UF process 43ndash44 85ndash88 86tvapor pressure gradient driven membrane

processes 258ndash273Whey protein concentrate (WPC) 566Wilke-Chang equation 140ndash141Winery wastewater 573ndash574World Health Organization (WHO) 411

466WPC See Whey protein concentrateWPF See Water permeation fluxWWT See Wastewater treatment

ZZeolites 98Zinc oxide nanoparticles (ZnO

nanoparticles) 19ndash20Zirconium dioxide nanoparticles (ZrO2

nanoparticles) 25Zirconium tri-ethylene tetra-amine (ZrT)

291Zwitterionic materials 253

642 Index

  • Basile Copyrightspdf
    • Copyright
Page 2: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier

Woodhead Publishing is an imprint of Elsevier80 High Street Sawston Cambridge CB22 3HJ UK225 Wyman Street Waltham MA 02451 USALangford Lane Kidlington OX5 1GB UK

Copyright copy 2015 Elsevier Ltd All rights reserved

No part of this publication may be reproduced stored in a retrieval system or transmittedin any form or by any means electronic mechanical photocopying recording or otherwisewithout the prior written permission of the publisher

Permissions may be sought directly from Elsevierrsquos Science amp Technology RightsDepartment in Oxford UK phone (+44) (0) 1865 843830 fax (+44) (0) 1865 853333email permissionselseviercom Alternatively you can submit your request online byvisiting the Elsevier website at httpelseviercomlocatepermissions and selectingObtaining permission to use Elsevier material

NoticeNo responsibility is assumed by the publisher for any injury andor damage to personsor property as a matter of products liability negligence or otherwise or from any use oroperation of any methods products instructions or ideas contained in the material hereinBecause of rapid advances in the medical sciences in particular independent verificationof diagnoses and drug dosages should be made

British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library

Library of Congress Control Number 2014954883

ISBN 978-1-78242-121-4 (print)ISBN 978-1-78242-126-9 (online)

For information on all Woodhead Publishing publicationsvisit our website at httpstoreelseviercom

Typeset by TNQ Books and JournalswwwtnqcoinPrinted and bound in the United Kingdom

CONTENTS

List of contributors

WL Ang Research Centre for Sustainable Process Technology UniversitiKebangsaan Malaysia UKM Bangi Selangor Malaysia

A Antony The University of New South Wales Sydney NSW Australia

P Argurio Universita della Calabria Rende (CS) Italy

P Arribas Campus of International Excellence Moncloa Campus (UCM-UPM)Madrid Spain Department of Applied Physics I University Complutense of MadridAvda Complutense Madrid Spain

N Bajraktari Technical University of Denmark Lyngby Denmark

A Basile Institute on Membrane Technology ITM-CNR University of CalabriaRende (CS) Italy Ast-Engineering srl Rome Italy

M Bodzek Institute of Environmental Engineering of the Polish Academy ofSciences Zabrze Poland Silesian University of Technology Institute of Water andWastewater Engineering Gliwice Poland

SI Bouhadjar Institute of Applied Research (IAF) Karlsruhe University ofApplied Sciences Karlsruhe Germany

A Cassano Institute on Membrane Technology ITM-CNR University of CalabriaRende (CS) Italy

E Curcio University of Calabria (DIATIC-UNICAL) Cosenza Italy Institute onMembrane TechnologyndashNational Research Council of Italy (ITM-CNR) CosenzaItaly

L Daal DNV GL Energy Arnhem The Netherlands

SA Deowan Institute of Applied Research (IAF) Karlsruhe University of AppliedSciences Karlsruhe Germany

F de Vos DNV GL Energy Arnhem The Netherlands

T de Vries GDF SUEZ Energie Nederland Zwolle The Netherlands

G Di Profio Institute on Membrane TechnologyndashNational Research Council of Italy(ITM-CNR) Cosenza Italy

E Drioli University of Calabria (DIATIC-UNICAL) Cosenza Italy Institute onMembrane TechnologyndashNational Research Council of Italy (ITM-CNR) CosenzaItaly

E Fontananova Institute on Membrane TechnologyndashNational Research Council ofItaly (ITM-CNR) Cosenza Italy

VS Frenkel San Francisco CA USA

MC Garciacutea-Payo Department of Applied Physics I University Complutense ofMadrid Avda Complutense Madrid Spain

N Ghaemi Department of Chemical Engineering Kermanshah University ofTechnology Kermanshah Iran

L Gil School of Forest Engineering University Polytechnic of Madrid AvdaComplutense Madrid Spain

S Guclu Istanbul Technical University Civil Engineering Faculty EnvironmentalEngineering Department Istanbul Turkey National Research Center on MembraneTechnologies (MEM-TEK) Istanbul Turkey

C Heacutelix-Nielsen University of Maribor Maribor Slovenia Technical University ofDenmark Lyngby Denmark

J Hoinkis Institute of Applied Research (IAF) Karlsruhe University of AppliedSciences Karlsruhe Germany

Y Ji School of Resources and Environmental Engineering East China University ofScience and Technology Shanghai PR China

M Kallioinen Lappeenranta University of Technology Laboratory of SeparationTechnology Skinnarilankatu Lappeenranta Finland

M Khayet Department of Applied Physics I University Complutense of MadridAvda Complutense Madrid Spain Madrid Institute for Advanced Studies of Water(IMDEA Water Institute) Alcala de Henares Madrid Spain

I Koyuncu Istanbul Technical University Civil Engineering FacultyEnvironmental Engineering Department Istanbul Turkey National Research Centeron Membrane Technologies (MEM-TEK) Istanbul Turkey

M Lee Imperial College London London UK

GL Leslie The University of New South Wales Sydney NSW Australia

K Li Imperial College London London UK

SS Madaeni Membrane Research Centre Department of Chemical EngineeringRazi University Kermanshah Iran

M Meuroantteuroari Lappeenranta University of Technology Laboratory of SeparationTechnology Skinnarilankatu Lappeenranta Finland

AW Mohammad Research Centre for Sustainable Process Technology UniversitiKebangsaan Malaysia UKM Bangi Selangor Malaysia

R Molinari Universita della Calabria Rende (CS) Italy

xiv List of contributors

M Nystreuroom Lappeenranta University of Technology Laboratory of SeparationTechnology Skinnarilankatu Lappeenranta Finland

L Palmisano Universita di Palermo Palermo Italy

ME Pasaoglu Istanbul Technical University Civil Engineering FacultyEnvironmental Engineering Department Istanbul Turkey National Research Centeron Membrane Technologies (MEM-TEK) Istanbul Turkey

I Petrinic University of Maribor Maribor Slovenia

H Rajabi Membrane Research Centre Department of Chemical Engineering RaziUniversity Kermanshah Iran Department of Civil Engineering Razi UniversityKermanshah Iran

NK Rastogi Department of Food Engineering Central Food TechnologicalResearch Institute Council of Scientific and Industrial Research Mysore India

Seyed MK Sadr Centre for Environmental and Health Engineering (CEHE)Department of Civil and Environmental Engineering University of Surrey GuildfordSurrey United Kingdom

Devendra P Saroj Centre for Environmental and Health Engineering (CEHE)Department of Civil and Environmental Engineering University of Surrey GuildfordSurrey United Kingdom

R Sengur National Research Center on Membrane Technologies (MEM-TEK)Istanbul Turkey Istanbul Technical University Nanoscience and NanoengineeringDepartment Istanbul Turkey

J Soons PWN Waterleidingbedrijf Noord Holland Velserbroek The Netherlands

KH Tng The University of New South Wales Sydney NSW Australia

T Turken Istanbul Technical University Civil Engineering Faculty EnvironmentalEngineering Department Istanbul Turkey National Research Center on MembraneTechnologies (MEM-TEK) Istanbul Turkey

B Van der Bruggen KU Leuven Leuven Belgium

Y Wang The University of New South Wales Sydney NSW Australia

Z Wu Imperial College London London UK

List of contributors xv

Preface

Water is the most abundant and renewable resource in the world Unfortunately only asmall quantity is fit for use to sustain human life In addition population growthcoupled with industrialization and urbanization has led to the increased pollution ofexisting freshwater resources resulting in an increased demand for fresh water Atthe same time challenges related to water systems are expected to increase in thenear future requiring further investment and technological innovation to meet globalneeds

Currently water recycling is widely accepted as a sustainable option in response tothe general increase in the demand for fresh water and to water shortages and environ-mental protection According to this view industrial companies are increasingly inter-ested in recycling wastewater to reach an ideal zero-discharge condition

Membrane technology has become a significant separation technology in the fieldof water filtration over the past two decades providing effective alternatives to relatedtechnologies such as adsorption extraction distillation ion exchangers and sand fil-ters It enables desalination or obtaining drinking water from saltwater as well as puri-fication of groundwater or wastewater

Low-energy consumption continuous separation easy scale-up modularityremote control and no phase separation are well-recognized key advantages of mem-brane processes over conventional separation technologies

The growth of the global membranes market is mainly the result of the impressivedevelopment of materials used for membrane fabrication and modification improve-ments in membrane modules and the evolution of different related systems plantsand equipment

This book covers the most recent and applicable achievements regarding materialsprocesses and applications of membranes for water treatment

The book is split into three parts The first is related to both novel membrane mate-rials and advances in membrane operations The second part considers how to improvemembrane performance and the last part illustrates selected applications in water treat-ment In the following section each chapter is briefly introduced

Chapter 1 (Madeani Ghaemi and Rajabi) illustrates the recent development of newmaterials and methods for the fabrication and modification of polymeric membranesfor water treatment Chapter 2 (Lee Wu and Li) provides an extensive analysis con-cerning recent progress in ceramic membranes for drinking water production and in thetreatment of municipal and industrial wastewater produced water (waste stream gen-erated from oil and gas operations) and wastewater generated in the food and beverage

industry In Chapter 3 (Koyuncu Sengur Turken Guclu and Pasaoglu) after a gen-eral overview of the global membrane market and various membrane fabrication tech-niques advances in water treatment by membrane processes such as ultrafiltrationmicrofiltration and nanofiltration are extensively illustrated Water treatment byboth reverse and forward osmosis for the desalination of water is described in Chapter 4(Rastogi Cassano and Basile) Differences among various membrane processesand the fundamentals of water treatment by reverse osmosis and forward osmosisare also considered Chapter 5 (Deowan Bouhadjar and Hoinkis) introduces mem-brane bioreactor technology with particular attention to water treatment Both aero-bic and anaerobic reactors are described The various factors affecting membraneperformance in both reactors (membrane fouling hydraulic residence time waterflux decline and so on in aerobic reactors and temperature organic loadingrate membrane properties and so on in anaerobic reactors) are seen as importantissues in this application of technology For each reactor a case study is also pro-posed The state of the art in the use of electrodialysis and electrodialysis with bipo-lar membranes for water treatment is reported in Chapter 6 (Van der Bruggen) Inparticular after a general description of the operational mechanisms of electrodial-ysis progress in anion and cation exchange membranes and new developments inmodule configurations and process integration are described Finally a brief over-view of applications of electrodialysis for water treatment is given Chapter 7 (Moli-nari Argurio Palmisano and Grillone) discusses both the basic principles ofphotocatalysis and advantages related to its coupling with membrane separationin so-called photocatalytic membrane reactors (PMRs) Important aspects for appro-priate large-scale implementation are the types of membranes used their criteria ofselection PMR configuration and membrane operation Some case studies in watertreatment are also discussed evidencing possibilities drawbacks and future trendsChapter 8 (Arribas Khayet Garciacutea-Payo and Gil) describes pressure-driven mem-brane processes and significant progress achieved over the past few years regardingthe fabrication of novel membranes and their modification In particular the chapterfocuses on novel flat-sheet and hollow-fiber membranes made with innovative mate-rials and with improved properties suitable for specific applications In Chapter 9(Arribas Khayet Garciacutea-Payo and Gil) the authors of the previous chapter extendconsideration to the electric potential and concentration gradient membrane pro-cesses In particular in this chapter the authors focus on water treatment by electro-dialysis with forward osmosis Also special attention is dedicated to alternativetechnologies of emerging interests used to produce power such as reverse electro-dialysis and pressure-retarded osmosis able to generate electricity from salinity gra-dients Some critical challenges (eg concentration polarization membrane foulingreverse solute diffusion and draw solute design) are also discussed

Chapter 10 (Frenkel) introduces the importance of membrane technologies whenthe water supply is considered for the community industry or agricultural user Infact membrane technologies have entered every aspect of water and wastewater treat-ment such as municipal and industrial water advanced wastewater treatment andreuse and seawater and brackish water desalination This chapter pays attention tothe design of both low- and high-pressure membrane systems for water treatment

xxii Preface

Finally integrated membrane systems and a combination of membrane treatment andother technological processes are briefly considered After distinguishing betweenmembrane ageing and failure Chapter 11 (Tng Antony Wang and Leslie) describesmembrane ageing during water treatment with particular attention to the modes andmechanisms of failure The authors review possible monitoring and control techniquesnecessary for the early detection of membrane ageing They also suggest some meas-ures for mitigating membrane failure caused by ageing Chapter 12 shows the impor-tance of mathematical modeling in membrane operations for water treatment (Ang andMohammad) In particular this chapter provides useful data on designing the plant andhelpful prediction of the performance of the membrane water treatment plant Differenttransport mechanisms are involved in pressure-driven membrane operations Thus themathematical models necessary to predict their performance are also different Theauthors show that the selection of a particular model of membrane water treatmentplant is crucial because it leads to a better understanding of its long-term performanceChapter 13 (Curcio Di Profio Fontananova and Drioli) provides a general overviewof membrane operations currently in use in seawater and brackish water desalinationfor potable water production In this chapter reverse osmosis novel salinity gradientpower technologies (with emphasis on pressure-retarded osmosis and reverse electro-dialysis) and membrane distillation are treated as viable options in the logic of zeroliquid discharge After introducing a section on drivers and barriers to membrane tech-nologies for municipal wastewater treatment Chapter 14 (Sadr and Saroj) describesvarious membrane-assisted processes and technologies in wastewater treatmentAnother important part of the chapter is related to both applications of nanofiltra-tionreverse osmosis after biological treatment and the design operation and controlof membrane processes in municipal wastewater treatment The optimization of mem-brane processes in municipal wastewater treatment is also well described taking intoconsideration cost assessment energy efficiencies and operational costs In Chapter15 (Bodzek) an analysis of the main organic and inorganic micropollutants of watersources is presented Membrane processes such as reverse osmosis and nanofiltrationultrafiltration and microfiltration in integrated systems Donnan dialysis and electro-dialysis as well as membrane bioreactors and liquid membranes are presented as alter-native technologies for producing high-quality drinking water as well as purifiedwastewater that can be drained off into natural water sources Chapter 16 (Yang) high-lights key advantages of pressure-driven membrane operations and their integrationinto existing systems for water treatment and reuse in the gas and petrochemical indus-tries Methods to reduce concentration polarization and membrane fouling phenom-ena which mainly affect membrane system performance and directly determine thecapital and operational costs of membrane systems in this field are also presentedand discussed Membrane technologies for water treatment and reuse in the textileindustry are described in Chapter 17 (Petrinic Bajraktari and Heacutelix-Nielsen) Theauthors present various examples of reverse osmosisnanofiltrationultrafiltration-based systems and membrane bioreactor technology that have been investigated fortextile wastewater remediation Forward osmosis used to concentrate textile dyes isalso presented Chapter 18 (Cassano Rastogi and Basile) presents an overview ofmembrane-based processes for water reuse and the environmental control in the

Preface xxiii

treatment of wastewaters from food-processing industries Various applicationsinvolving the use of pressure-driven membrane operations electrodialysis membranebioreactors and integrated membrane systems are shown and discussed In particularthe authors illustrate typical applications for the treatment of process waters from thefruit and vegetables dairy fish meat soya and wine industries highlighting theiradvantages and drawbacks with respect to conventional technologies Chapter 19(Meuroantteuroari Kallioinen and Nystreuroom) focuses on the use of membrane technologiesto purify raw water and wastewaters circulate process waters and recover valuablematerials in the pulp and paper industry The driving forces to use membranes and bar-riers as well as their challenges are discussed in the introduction Chapter 20 (Daal)focuses on water treatment required for the production of demineralized wateremployed for the watersteam cycle in industrial plants Water purification technolo-gies including membrane technologies and operational experiences with membranesare presented and discussed

The editors wish to take this opportunity to thank all of the authors of the chaptersfor preparing developing and improving their text Special thanks to all of the staff ofWoodhead for their excellent help to both the authors and the editors

Angelo BasileAlfredo CassanoNavin K Rastogi

xxiv Preface

Related titles

Advanced membrane science and technology for sustainable energy and environmentalapplications

(ISBN 978-1-84569-969-7)

Handbook of water and energy management in food processing

(ISBN 978-1-84569-195-0)

Metropolitan sustainability Understanding and improving the urban environment

(ISBN 978-0-85709-046-1)

Woodhead Publishing Series in Energy

1 Generating power at high efficiency Combined cycle technology for sustainableenergy productionEric Jeffs

2 Advanced separation techniques for nuclear fuel reprocessing and radioactive wastetreatmentEdited by Kenneth L Nash and Gregg J Lumetta

3 Bioalcohol production Biochemical conversion of lignocellulosic biomassEdited by Keith W Waldron

4 Understanding and mitigating ageing in nuclear power plants Materials andoperational aspects of plant life management (PLiM)Edited by Philip G Tipping

5 Advanced power plant materials design and technologyEdited by Dermot Roddy

6 Stand-alone and hybrid wind energy systems Technology energy storage andapplicationsEdited by John K Kaldellis

7 Biodiesel science and technology From soil to oilJan C J Bart Natale Palmeri and Stefano Cavallaro

8 Developments and innovation in carbon dioxide (CO2) capture and storagetechnology Volume 1 Carbon dioxide (CO2) capture transport and industrialapplicationsEdited by M Mercedes Maroto-Valer

9 Geological repository systems for safe disposal of spent nuclear fuels and radioactivewasteEdited by Joonhong Ahn and Michael J Apted

10 Wind energy systems Optimising design and construction for safe and reliableoperationEdited by John D Soslashrensen and Jens N Soslashrensen

11 Solid oxide fuel cell technology Principles performance and operationsKevin Huang and John Bannister Goodenough

12 Handbook of advanced radioactive waste conditioning technologiesEdited by Michael I Ojovan

13 Membranes for clean and renewable power applicationsEdited by Annarosa Gugliuzza and Angelo Basile

14 Materials for energy efficiency and thermal comfort in buildingsEdited by Matthew R Hall

15 Handbook of biofuels production Processes and technologiesEdited by Rafael Luque Juan Campelo and James Clark

16 Developments and innovation in carbon dioxide (CO2) capture and storagetechnology Volume 2 Carbon dioxide (CO2) storage and utilisationEdited by M Mercedes Maroto-Valer

17 Oxy-fuel combustion for power generation and carbon dioxide (CO2) captureEdited by Ligang Zheng

18 Small and micro combined heat and power (CHP) systems Advanced design perfor-mance materials and applicationsEdited by Robert Beith

19 Advances in clean hydrocarbon fuel processing Science and technologyEdited by M Rashid Khan

20 Modern gas turbine systems High efficiency low emission fuel flexible powergenerationEdited by Peter Jansohn

21 Concentrating solar power technology Principles developments and applicationsEdited by Keith Lovegrove and Wes Stein

22 Nuclear corrosion science and engineeringEdited by Damien Feacuteron

23 Power plant life management and performance improvementEdited by John E Oakey

24 Electrical drives for direct drive renewable energy systemsEdited by Markus Mueller and Henk Polinder

25 Advanced membrane science and technology for sustainable energy and environ-mental applicationsEdited by Angelo Basile and Suzana Pereira Nunes

26 Irradiation embrittlement of reactor pressure vessels (RPVs) in nuclear power plantsEdited by Naoki Soneda

27 High temperature superconductors (HTS) for energy applicationsEdited by Ziad Melhem

28 Infrastructure and methodologies for the justification of nuclear power programmesEdited by Agustiacuten Alonso

29 Waste to energy conversion technologyEdited by Naomi B Klinghoffer and Marco J Castaldi

30 Polymer electrolyte membrane and direct methanol fuel cell technology Volume 1Fundamentals and performance of low temperature fuel cellsEdited by Christoph Hartnig and Christina Roth

31 Polymer electrolyte membrane and direct methanol fuel cell technology Volume 2In situ characterization techniques for low temperature fuel cellsEdited by Christoph Hartnig and Christina Roth

32 Combined cycle systems for near-zero emission power generationEdited by Ashok D Rao

33 Modern earth buildings Materials engineering construction and applicationsEdited by Matthew R Hall Rick Lindsay and Meror Krayenhoff

34 Metropolitan sustainability Understanding and improving the urban environmentEdited by Frank Zeman

35 Functional materials for sustainable energy applicationsEdited by John A Kilner Stephen J Skinner Stuart J C Irvine and Peter P Edwards

36 Nuclear decommissioning Planning execution and international experienceEdited by Michele Laraia

37 Nuclear fuel cycle science and engineeringEdited by Ian Crossland

xviii Woodhead Publishing Series in Energy

38 Electricity transmission distribution and storage systemsEdited by Ziad Melhem

39 Advances in biodiesel production Processes and technologiesEdited by Rafael Luque and Juan A Melero

40 Biomass combustion science technology and engineeringEdited by Lasse Rosendahl

41 Ultra-supercritical coal power plants Materials technologies and optimisationEdited by Dongke Zhang

42 Radionuclide behaviour in the natural environment Science implications andlessons for the nuclear industryEdited by Christophe Poinssot and Horst Geckeis

43 Calcium and chemical looping technology for power generation and carbon dioxide(CO2) capture Solid oxygen- and CO2-carriersPaul Fennell and E J Anthony

44 Materialsrsquo ageing and degradation in light water reactors Mechanisms andmanagementEdited by K L Murty

45 Structural alloys for power plants Operational challenges and high-temperaturematerialsEdited by Amir Shirzadi and Susan Jackson

46 Biolubricants Science and technologyJan C J Bart Emanuele Gucciardi and Stefano Cavallaro

47 Advances in wind turbine blade design and materialsEdited by Povl Broslashndsted and Rogier P L Nijssen

48 Radioactive waste management and contaminated site clean-up Processestechnologies and international experienceEdited by William E Lee Michael I Ojovan and Carol M Jantzen

49 Probabilistic safety assessment for optimum nuclear power plant life management(PLiM) Theory and application of reliability analysis methods for major powerplant componentsGennadij V Arkadov Alexander F Getman and Andrei N Rodionov

50 The coal handbook Towards cleaner production Volume 1 Coal productionEdited by Dave Osborne

51 The coal handbook Towards cleaner production Volume 2 Coal utilisationEdited by Dave Osborne

52 The biogas handbook Science production and applicationsEdited by Arthur Wellinger Jerry Murphy and David Baxter

53 Advances in biorefineries Biomass and waste supply chain exploitationEdited by Keith Waldron

54 Geological storage of carbon dioxide (CO2) Geoscience technologies environmentalaspects and legal frameworksEdited by Jon Gluyas and Simon Mathias

55 Handbook of membrane reactors Volume 1 Fundamental materials science designand optimisationEdited by Angelo Basile

56 Handbook of membrane reactors Volume 2 Reactor types and industrialapplicationsEdited by Angelo Basile

57 Alternative fuels and advanced vehicle technologies for improved environmental per-formance Towards zero carbon transportationEdited by Richard Folkson

Woodhead Publishing Series in Energy xix

58 Handbook of microalgal bioprocess engineeringChristopher Lan and Bei Wang

59 Fluidized bed technologies for near-zero emission combustion and gasificationEdited by Fabrizio Scala

60 Managing nuclear projects A comprehensive management resourceEdited by Jas Devgun

61 Handbook of Process Integration (PI) Minimisation of energy and water use wasteand emissionsEdited by Jiriacute J Klemes

62 Coal power plant materials and life assessmentEdited by Ahmed Shibli

63 Advances in hydrogen production storage and distributionEdited by Ahmed Basile and Adolfo Iulianelli

64 Handbook of small modular nuclear reactorsEdited by Mario D Carelli and Dan T Ingersoll

65 Superconductors in the power grid Materials and applicationsEdited by Christopher Rey

66 Advances in thermal energy storage systems Methods and applicationsEdited by Luisa F Cabeza

67 Advances in batteries for medium and large-scale energy storageEdited by Chris Menictas Maria Skyllas-Kazacos and Lim Tuti Mariana

68 Palladiummembrane technology for hydrogen production carbon capture and otherapplicationsEdited by Aggelos Doukelis Kyriakos Panopoulos Antonios Koumanakos andEmmanouil Kakaras

69 Gasification for synthetic fuel production Fundamentals processes and applicationsEdited by Rafael Luque and James G Speight

70 Renewable heating and cooling Technologies and applicationsEdited by Gerhard Stryi-Hipp

71 Environmental remediation and restoration of contaminated nuclear and NORMsitesEdited by Leo van Velzen

72 Eco-friendly innovation in electricity networksEdited by Jean-Luc Bessede

73 The 2011 Fukushima nuclear power plant accident How and why it happenedYotaro Hatamura Seiji Abe Masao Fuchigami and Naoto Kasahara Translated byKenji Iino

74 Lignocellulose biorefinery engineering Principles and applicationsHongzhang Chen

75 Advances in membrane technologies for water treatment Materials processes andapplicationsEdited by Angelo Basile Alfredo Cassano and Navin K Rastogi

76 Membrane reactors for energy applications and basic chemical productionEdited by Angelo Basile Luisa Di Paola Faisal Hai and Vincenzo Piemonte

xx Woodhead Publishing Series in Energy

Advances in polymericmembranes for water treatment 1SS Madaeni1 N Ghaemi2 H Rajabi131Membrane Research Centre Department of Chemical Engineering Razi UniversityKermanshah Iran 2Department of Chemical Engineering Kermanshah University ofTechnology Kermanshah Iran 3Department of Civil Engineering Razi UniversityKermanshah Iran

11 Introduction

As themost precious and renewable resource in the world water is an important aspect oflife Theworldrsquos population tripled in the twentieth century and it will increase by another40 to 50 within the next 50 years Population growth coupled with industrializationand urbanization has resulted in the rapidly increasing demand for fresh water Further-more some existing fresh water resources have gradually become polluted because ofhuman or industrial activities Problems with water are expected to grow in the comingdecades with water scarcity occurring globally even in regions currently consideredwater-rich Therefore many researchers have focused on suitablemethods to obtain freshwater by purifying and reusing water to support future generations Water purification isthe process of removing unpleasant agents such as chemicals organic and biologicalcontaminants and suspended solids from water to obtain satisfactory water

Owing to its low cost and high efficiency membrane technology has dominatedwater purification technologies Compared with the other types of membranes poly-meric membranes lead the membrane separation industries and markets because theyare economically and practically beneficial However limited chemical mechanicaland thermal resistance restricts their application Extensive efforts have been imple-mented to improve both flux and selectivity and reduce membrane fouling as the mostimportant problem in application of membranes To eliminate obstacles and decreasethe problems in membrane use much research and numerous studies have been conduct-ed to develop newmaterials and methods for fabricating and modifying polymeric mem-branes This chapter covers the most recent and applicable achievements regarding thepreparationmodification and performance of polymericmembranes for water treatment

12 Advances in polymeric membranes

121 Composite (mixed matrix) membranes

Sometimes when fabricating membranes structural modification is necessary toenhance overall performance as well as the mechanical chemical and thermal stability

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400001-0Copyright copy 2015 Elsevier Ltd All rights reserved

of the membrane Methods to overcome the challenges of membrane modification havebeen well established for polymeric membranes Much research on membrane scienceand technology has focused on the development of new membrane preparation tech-niques and material An alternate way to improve membrane performance includingpermeability and selectivity involves introducing second phases into the membranematrix Polymers and some nanofillers were mostly introduced as a second phaseinto polymeric membranes to prepare different kinds of composite membranes

1211 Composite membranes prepared via blendingof polymers

Blending of additives into the casting solution is one of the most applicable methods tochange the phase separation process and consequently membrane characteristicsPolymeric materials are applied considerably as additives into the dope solution(Musale Kumar amp Pleizier 1999 Ochoa et al 2001) Although certain polymerssuch as polyethersulfone (PES) and poly(vinylidenefluoride) (PVDF) possess excel-lent thermal and mechanical stability as well as acceptable film-forming propertiesthat make them ideal materials for membrane preparation their application is oftenrestricted because of their hydrophobic nature which results in low water permeationand high fouling On the other hand the membranes made of hydrophilic polymerssuch as poly(vinyl alcohol) (PVA) cellulose acetate (CAc) and polyacrylonitrile(PAN) are also applied for the fabrication of liquid separation membranes howeverthe thermal and mechanical resistance and chemical stability of these membrane arelow Blending of polymers in membrane fabrication has been widely investigatedbecause of the simplicity of procedure and high efficiency in developing newmembranes with elevated properties and performance

The main focus in blending polymers is to increase hydrophilicity and decreasemembrane fouling Rahimpour and Madaeni (2007) prepared PES membrane byblending different concentrations of CAP (20 30 and 40 wt) and PVP (2 4 and8 wt) as a pore former Contact angle measurements showed that the hydrophilicityof membranes was enhanced for all compositions because of numerous acidic andcarbonyl functional groups in the CAP structure Pure water flux milk water perme-ation and protein rejection also increased with an increase in PESCAP compositionsup to 8020 Moreover the antifouling property of PES membranes was improved byadding even small amounts of CAP into the casting solution In another study(Masuelli Marchese amp Ochoa 2009) a PVDF ultrafiltration membrane was modifiedby blending PVDF with PVP and sulfonated polycarbonate to enhance permeation fluxand reduce fouling Surprisingly the hydraulic permeability of the membrane wasreduced and fouling increased for composite membranes (Masuelli et al 2009)Composite polysulfone (PSf) membranes were synthesized by Adams NxumaloKrause Hoek and Mamba (2012) by blending PSf with different concentrations ofb-CPU (0e10) using a phase inversion technique Addition of 5 b-CPU to PSfmembrane greatly improved the hydrophilicity of composite membranes comparedwith higher amounts because fewer pores were created on the membrane surfaceand owing to the chemical interaction between OHNH and the sulfonyl backbone

4 Advances in Membrane Technologies for Water Treatment

of PSf Moreover it was revealed that a low concentration of b-CPU was effective inimproving flux without compromising membrane rejection (Adams et al 2012)Table 11 summarizes some studies on composite membranes and the main propertiesof blending polymers

Table 11 Studies on composite polymeric membranes

Materials Feed solution

Properties ofcomposite versusnascentmembrane References

CASPSf mdash Larger pore size MalaisamyMahendran andMohan (2002)

PVDFPMMA Effluent fromengine factory

Largermacrovoideshigherhydrophilicitylower fouling

Ochoa Masuelliand Marchese(2003)

PSPA Solution of CNeZn2thorn ZnethCN2

4 THORNGood chemicalstability lessmechanicalresistance goodselectivity

Amado GondranFerreiraRodrigues andFerreira (2004)

PESCAPPVP Milk Higherhydrophilicitymore pure waterflux milk waterpermeation andprotein rejection

Rahimpour andMadaeni (2007)

PESPIPVP Salt solution Higherhydrophilicitymore pure waterflux more saltrejection

MansourpanahMadaeni Adeliand Rahimpour(2009)

SPCPVDF Oilewateremulsion

Lower fouling Masuelli et al(2009)

PSfPAN Aqueous solution ofheavy metals

Decrease in meansurface-pore sizeoverall porosityand permeabilityhigh leadcadmium andchromiumrejection

Mbareck NguyenAlaoui andBarillier (2009)

Continued

Advances in polymeric membranes for water treatment 5

1212 Thin-film composite membranes

Dense membranes generally have low flux but high selectivity whereas porousmembranes have low selectivity but high permeability To increase flux through adense membrane with high selectivity the thickness of the membrane should bereduced as much as practically possible However the membrane should be

Table 11 Continued

Materials Feed solution

Properties ofcomposite versusnascentmembrane References

CAPU Aqueous solutionscontaining textiledye

Lower thermalstability

Zavastin et al(2010)

HPAAPSf BSA solutionaqueous solutioncontaining heavymetal

Higher water fluxhigher rejectionof BSA and Cd(II)

Han Yu et al(2012)

CNCPSf Papermakingeffluent

Decreasingmechanicalstrength byincreasing CNCcontent higherpermeation goodability inpapermakingeffluent filtration

Zhou Zhao BaiZhang and Tang(2012)

PVDFSPPO Ionic solution Higher watercontent and ion-exchangecapacitysuperiorperformance by60 SPPO and40 PVDF

Khodabakhshi et al(2012)

PSfb-CPU Solution of heavymetal

Higherhydrophilicitymore water fluxand rejectionlower porosityless mechanicalstrength

Adams et al (2012)

6 Advances in Membrane Technologies for Water Treatment

defect-free and possess adequate mechanical strength This may be achieved with theuse of thin-film composite (TFC) membranes

Such composite membranes often consist of two layers a thin dense selective toplayer supported by a porous substrate The main role of the porous support is to providemechanical strength whereas the thin skin layer is responsible for permselectivityA TFC membrane is usually formed by a two-step process formation of a thickporous and nonselective substrate followed by coating with an ultrathin skin layerAmong different methods for forming the top layer dip-coating (Lang SourirajanMatsuura amp Chowdhury 1996 Peng Huang Jawor amp Hoek 2010 Susanto ampUlbricht 2008) and interfacial polymerization (Kim Kim Yu amp Deng 2009 PrakashRao Desai amp Rangarajan 1997 Rahimpour Jahanshahi Mortazavian Madaeni ampMansourpanah 2010 Reddy et al 2005 Shao et al 2013 Verissimo Peinemann ampBordado 2005 Wu et al 2006) were widely used Of these interfacial polymerizationis particularly interesting taking into account the considerable amount of research inthis field

TFC membranes have had remarkable development since the concept of interfa-cial polymerization was introduced by Mogan in 1965 (Lau Ismail Misdan ampKassim 2012) In this technique polymerization reaction takes place between tworeactive monomers at the interface of two immiscible solvents First the pores ofa membrane used as the support are filled with liquid A then the support isimmersed in a bath containing a reactant for liquid A As the result of interfacialpolymerization reaction a dense highly cross-linked polymer layer is formed onthe surface of the membrane at the interface of two solutions Heat ultraviolet(UV) and plasma treatment are often applied to control and complete interfacialpolymerization The top skin layer is extremely thin (01 mm or less) so TFCmembrane permeability is high Also membrane selectivity is high as a result ofthe high cross-linking of polymers

Commonly used reactive monomers are aliphaticaromatic diamines such as piper-azine (PIP) m-phenylenediamine (MPDA) and p-phenylenediamine (PPD) and acidchloride monomers such as trimesoyl chloride (TMC) isophthaloyl chloride (IPC)and 5-isocyanatoisophthaloyl chloride (ICIC) Among these materials and preparedTFC membranes polyaniline (PA) membranes prepared by interfacial polymerizationof multifunctional amine and acyl chloride monomers (Han Chung et al 2012 KimHwang Gamal El-Din amp Liu 2012 Kim et al 2009 Maurya Parashuram SinghRay amp Reddy 2012 Rahimpour et al 2010 Shao et al 2013 Verissimo et al2005 Yu Liu Liu and Gao 2009 Wu et al 2006) are the most typical and successfulTFC membranes Rahimpour et al (2010) prepared a TFC PA nanofiltration mem-brane using interfacial polymerization of PDA with TMC The TFC polyamide mem-branes displayed a higher ability to soften water The composite membrane exhibitedwater permeability of 7 and 21 kgm2 h for salt solution containing NaCl (1 gl) andMgSO4 (1 gl) at 5 and 10 bar respectively Also rejection of the divalent saltMgSO4 (85 and 90) was high compared with the monovalent salt NaCl (64and 67) at 5 and 10 bar respectively In other research Han chang et al (2012)demonstrated that blending a certain amount of sulphonated poly(ether ketone)(SPEK) material into the PSf substrate of TFC forward osmosis (TFC-FO) membranes

Advances in polymeric membranes for water treatment 7

not only has a key role in forming a fully spongelike structure but also enhances mem-brane hydrophilicity and reduces structure parameters In this study MPDA and135-TMC were employed as monomers for the interfacial polymerization reactionto form a thin aromatic polyamide selective layer The TFC-FO membranes withthe most hydrophilic SPEK (50 wt) in the substrates exhibited the lowest membranethickness a fully spongelike structure and the highest water flux of 50 and 35 lm2 hwhen deionized water and 2 M NaCl were used as the feed and draw solutionrespectively

New synthesized monomers were also employed to prepare TFC membranes withnotable properties Li and Kim (2008) synthesized a series of isomeric tetra-functionalbiphenyl acid chloride (mm-BTEC om-BTEC and op-BTEC) to prepare TFC reverseosmosis membranes through an interfacial polymerization technique with MPDA asthe amine monomer in aqueous solution According to this study the organic phasereactants had a considerable impact on membrane performance compared with theaqueous phase reactant Experimental results showed that the membrane preparedfrom op-BTEC revealed the highest permeability (542 lm2 h) followed by mem-branes prepared from om-BTEC (500 lm2 h) and mm-BTEC (317 lm2 h) whentested using a 2000 ppm NaCl solution at 2 MPa The rougher and larger surfacearea of the op-BTEC membrane which led to greater contact with water moleculeswas reported as the reason for the flux enhancement of this membrane (Li ZhangZhang amp Zheng 2008) In another study Chen Li Zhang and Zhang (2008) synthe-sized a new class of polymeric amine named SPES-NH2 which was applied for thepreparation of TFC reverse osmosis membranes Polysulfone was used as substrateand TFC membrane was prepared through interfacial polymerization of TMC solu-tions and amine solutions containing SPES-NH2 and m-Phenylenediamine (MPDA)The salt rejection and water flux of the composite membrane prepared under the opti-mum condition (acyl chloride monomer frac14 10 ratio of MPDA to SPES-NH2 frac14 214 min contact time with organic solution) reached 973 and 512 lm2 h respectivelyThe improvement in water flux was due to the incorporation of hydrophilic SPES-NH2

to polyamides On the other hand the high salt rejection was related to the chain stiff-ness of the copolymer and the high degree of cross-linking A novel amine monomerb-cyclodextrin polyurethane (DABA) with three amino groups was synthesized andapplied along with MPDA in TFC membrane preparation by Wang Li Zhang andZhang (2010) to increase the hydrophilicity of a PAN nanofibrous substrate Withan increase in the DABA content in the aqueous phase from 0 to 025 (wv)the TFC membranes showed an increment in water flux from 375 to 554 lm2 h whilemaintaining high salt rejection (w98) in the filtration of a salt solution containing2000 ppm NaCl at 2 MPa

With respect to the fouling resistance Abu Seman Khayet and Hilal (2010 2011)reported on the preparation of TFC membranes with improved antifouling tendency bymeans of interfacial polymerization between BPA andor TMBPA with TMCIrreversible fouling of modified polyester TFC PES membranes decreased duringfiltration of solutions containing humic acid at different pH values The highly uniformtop polyester layer coupled with the negative charge of the composite membranewas introduced as the main reason for the lower fouling of the TFC membrane

8 Advances in Membrane Technologies for Water Treatment

Furthermore An Li Ji and Chen (2011) incorporated PVA into composite nanofiltra-tion membranes by adding different amounts of PVA into PIP during interfacialpolymerization with TMC to improve the antifouling performance of compositemembranes The incorporation of a hydrophilic PVA chain into the PA active layerhad beneficial effects on developing a smoother surface and increasing membranehydrophilicity that were effective in diminishing the fouling of protein over thelong run

The application of additives such as synthesized hydrophilic surface modifyingmacromolecules (Abu Tarboush Rana Matsuura Arafat amp Narbaitz 2008 RanaKim Matsuura amp Arafat 2011) was shown to be effective in altering TFC mem-brane performance Abu Tarboush et al (2008) prepared a TFC membrane with amore hydrophilic surface by incorporating the synthesized additive hydrophilicsurface modifying macromolecules (LSMM) into the active PA thin top layer Itwas observed that during in situ polymerization LSSMs could migrate toward thetop airepolymer interface rendering the membrane hydrophilic and producing acomposite membrane with improved flux stability over an extended operationalperiod compared with an LSMM-free composite membrane Another importantdevelopment in TFC membrane technology was the incorporation of nanoparticlesinto the TFC membrane structure (Kim Kwak Sohn amp Park 2003 Lee ImKim Kim amp Min 2008) Kim et al (2003) prepared a hybrid TFC reverse osmosismembrane by the self-assembly of anatase TiO2 nanoparticles through coordinationand H-bonding interaction with the COOH functional groups of an aromatic poly-amide thin-film layer to reduce membrane biofouling The photocatalytic bactericidalability of the hybrid TFC membrane was examined by determining the survival ratiosof Escherichia coli cells with and without UV light illumination Photocatalyticbactericidal efficiency was remarkably higher for the hybrid TFC membrane underUV light illumination than that without illumination and the neat TFC membranesLee et al (2008) also reported on a preparation of PA nanocomposite membranecontaining TiO2 nanoparticles synthesized via in situ interfacial polymerization un-der various curing temperatures and curing times The interfacial reaction occurredbetween the aqueous phase of MPDA and the organic phase of TMC in whichTiO2 nanoparticles were homogeneously dispersed The incorporation of TiO2 nano-particles into PA resulted in an increase in water flux owing to the enhancement ofhydrophilicity in the membranes When the concentration of TiO2 nanoparticleswas 50 wt the optimum membrane performance was obtained together withstrong mechanical properties In more concentration of TiO2 the permeation fluxincreased and salt rejection decreased significantly Moreover the decrease inmechanical strength of the membranes resulted in easier peeling-off of thePA-TiO2 layer from PES substrate after the filtration experiment These resultswere attributed to the fact that a lower degree of polymerization of PA occurs athigh TiO2 concentrations because of an increase in the interference of interfacialpolymerization by TiO2 nanoparticles The incorporation of zeolite-A nanoparticles(Jeong et al 2007) and multi-walled nanotubes (MWNTs) (Wu Tang amp Wu 2010)throughout the thin-film layer were also explored as a facile approach to producesuperior hydrophilic membranes with improved performance

Advances in polymeric membranes for water treatment 9

The addition of co-solvent into the organic phase is another alternative to improveTFC membrane performance (Kim Kwak amp Suzuki 2005 Kong KanezashiYamomoto Shintani amp Tsuru 2010) Kong et al (2010) applied this method andadded acetone as the co-solvent into the organic phase to synthesize TFC nanofiltra-tion membranes with controllable active layer thickness and effective nanopores Thepresence of acetone could eliminate the large immiscibility gap between waterand hexane therefore it caused the interfacial polymerization reaction zone tobe controllable Consequently the permeation flux increased noticeably from21 1012 m3m2 Pa s for membranes prepared by conventional interfacial polymer-ization to 80 1012 m3m2 Pa s for TFC membranes prepared by adding co-solvent

122 Nanocomposite membranes (nano-enhanced membranes)

In another approach to membrane development processes researchers focused onincorporating inorganic nanoparticles into polymeric materials which resulted in theformation of nanocomposite (nano-enhanced) membranes with improved mechanicaland physicochemical properties Various nanomaterials have been employed as fillersuch as carbon nanotubes (CNTs) nanoclay nanosilver and nanosized TiO2 ZnOAl2O3 Fe3O4 SiO2 and ZrO2 More details about developments in nanocompositemembranes and their performance in water treatment are presented in the followingsections

1221 Carbon nanotubes

Among the various nanomaterials studied CNTs have received a great deal of atten-tion With high hydrophilicity good chemical stability and high surface area CNTsinduce highly antibacterial properties and increase the porosity of nanocompositemembranes They are ideal for reinforcing membranes because of their high aspectratio and high axis strength (Daraei Madaeni Ghaemi et al 2013) The wide rangeof possible applications for CNTs has been a driving force for the production of high-quality single-walled (SW) double-walled (DW) and MW CNTs for incorporationinto CNTepolymer composites (Vatanpour Madaeni Moradian et al 2012)

Several methods have been applied to produce inorganic-polymer membranessuch as filtration of the solvent containing dispersed CNTs through the membraneand then in situ polymerization onto the membrane surface (Madaeni Zinadini ampVatanpour 2011a) dispersion of CNTs in the monomer solution and then interfacialpolymerization onto a membrane as substrate (Roy Addo Ntim Mitra amp Sirkar2011) and blending nanoparticles into the casting solution followed by immersioninto the coagulation bath (Celik Park Choi amp Choi 2011 Choi Jegal amp Kimb2006 Mansourpanah et al 2011) or evaporation (Tang Zhang Wang Fu andZhang 2009)

Blending has some advantages over other methods The method is simple and hasmild conditions reproducibility and capability for industrialization Also preparationthrough polymer solution casting permits the use of polymers which were previouslyfound not to be suitable for in situ polymerization (Vatanpour Madaeni Moradian

10 Advances in Membrane Technologies for Water Treatment

et al 2012) Previous studies by Choi et al (2006) showed that MWCNT-blended PSfmicrofiltration membranes had slightly higher flux and rejection rates than nascent PSfmembrane Also those authors found that MWCNT-blended membranes were morehydrophilic than PSf ones In a related work Qui et al (2009) showed thatMWCNT-blended PSf ultrafiltration membranes had higher flux and lower rejectionas well as lower protein adsorption compared with nascent PSf membrane

Although CNTs have excellent separation characteristics and electrical and me-chanical properties there are problems in preparing mixed matrix membranes usingthis material such as no suitable dispersion of synthesized CNTs in organic solventsand different polymers (Celik et al 2011 Shirazi Ahmadzadeh Tofighy andMohammadi 2011 Vatanpour Madaeni Moradian et al 2012) Thus surfacemodification of this material is necessary to fabricate a homogeneous nanocompositemembrane Recent studies showed that surface modification can increase thedispersing properties of CNTs Chemical modification and functionalization ofCNTs surfactant treatment and polymer wrapping are several methods that havebeen widely used for uniform dispersion of nanotubes in a polymer matrix and forenhancing CNT adhesion to the polymer (Choi et al 2006 Eitan Jiang DukesAndrews amp Schadler 2003 Islam Rojas Bergey Johnson amp Yodh 2003 OrsquoConnellet al 2001 Qu et al 2004 Yang Chen et al 2007) In this regard ShawkyChae Lin and Wiesner (2011) added different concentrations of MWCNTs tothe PA membrane casting solution to form a nanocomposite structure improvethe mechanical properties of these membranes and increase their ability to rejectsalts The MWCNTs were dispersed into a mixture of dimethylacetamide(DMAc) (solvent) and lithium chloride salts Benzoyl peroxide (BPO) initiatorwas added into the casting solution with the goal of forming free-radicals onboth CNTs and PA This process resulted in polymer-grafted nanotubes thatdispersed better throughout the casting solution and a more homogeneousMWCNTsePA composite membrane was formed Investigation of the hydrophilic-ity and mechanical strength of nanocomposite membranes revealed a decrease inhydrophilicity owing to the hydrophobic nature of nanomaterials and an increasein the mechanical strength of the membranes because of the strong interactionsbetween the PA matrix and MWCNTs and homogeneous dispersion of CNTs

The decrease in permeability from 32 to 28 lm2 h and increase in salt rejection from24 to 76 respectively for the PA and MWCNTsPA (15 mgg) composite mem-brane were attributed to this network structure In addition humic acid removal byMWCNT composite membranes increased from 54 to 90 as the MWCNT loadingincreased from 0 to 10 mgg (Shawky Chae Lin and Wiesner 2011)

The introduction of hydrophilic functional groups onto the surface of the CNTsusing chemical modification especially acid is one of the simplest most widelyused and least expensive methods for uniform dispersion of nanotubes in the polymermatrix (Balasubramanian amp Burghard 2005 Celik et al 2011 Eitan et al 2003Shirazi et al 2011 Vatanpour Madaeni Moradian Zinadini amp Astinchap 2011)Vatanpour et al (2011) fabricated nanocomposite membranes composed of PES andacid-treated functionalized MWCNTs using a solution of 3 M HNO3H2SO4 (13vv) Functionalized MWCNTs were embedded in PES matrix using the phase

Advances in polymeric membranes for water treatment 11

inversion method The treated MWCNTs exhibited good dispersion and compatibilitywith the polymer matrix The blending of MWCNTs into PES matrix resulted in anincrease in hydrophilicity and water flux along with a decrease in fouling of the nano-composite membrane caused by Bovine Serum Albomin (BSA) filtration

In another work the same author (Vatanpour Madaeni Moradian et al 2012)fabricated an anti-bifouling nanofiltration membrane by mixing PES with TiO2-coated functionalized MWCNTs They coated MWCNTs with TiO2 nanoparticlesto enhance the dispersion of CNTs in organic solvent and polymer and improvethe interaction between the CNTs and the polymer matrix To purify and functional-ize CNTs the MWCNTs were dispersed into a mixture of H2SO4 and HNO3 with aratio of 31 The functionalized MWCNTs could participate in a reaction with otherreagents as a result of the formation of carboxylic acid groups on the surface ofMWCNTs (Vatanpour Madaeni Moradian et al 2012) To better deposit TiO2

nanoparticles onto the surface of oxidized MWCNTs dendrimer polycitric acidwas grafted onto functionalized CNTs At the final step MWCNTs were coatedwith TiO2 nanoparticles A schematic of the preparation of TiO2-coated MWCNTsis presented in Figure 11

The TiO2-coated MWCNTs showed suitable compatibility with polymeric matrixresulting in a low agglomeration of MWCNTs Addition of the modified MWCNTsinfluenced the surface mean pore size and porosity of the nanocomposite membranes

31H2SO4HNO3

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

HOOC

COOH

COOHCOOH

COOH

COOHCOOHCOOH

COOH

COOHCOOHCOOH

COOH

HOOCCOOH

COOH

OH

COOHHOOC

HO

TiOC2H5

OC2H5

OC2H5

OC2H5

OC2H5

OC2H5C2H5OC2H5OC2H5O

C2H5OC2H5OC2H5O

Oxidized MWCNT

Monohydrate citric acid

Heated in vaccumfor 3h150 0C

Heated at 500 0C in N2 mediumfor 100 min

Polycitric acid-grafted MWCNTs

1) TiCI41 M HCI2) 5 M NH3stiring

for 3 h

Ti

O-Ti(OC2H5)(C2H5O)Ti-O

Ti

Anatase TiO2

TiO2-coated MWCNTS

Ti COOH

MWCNT

12 h reflux

Figure 11 Schematic showing coating of multi-walled carbon nanotubes (MWCNTs) withTiO2 nanoparticlesReprinted from Vatanpour Madaeni Moradian et al (2012) with permission from Elsevier

12 Advances in Membrane Technologies for Water Treatment

The prepared mixed matrix membranes showed higher hydrophilicity compared withnascent PES membrane which resulted in an increase in pure water flux Also theanti-biofouling characteristics of the nanoparticle-embedded membranes improvedas a result of increased hydrophilicity and decreased membrane surface roughness(Vatanpour Madaeni Moradian et al 2012) Daraei Madaeni Ghaemi Ahmadiet al (2013) and Daraei Madaeni Ghaemi Khadivi et al (2013) studied the effectsof blending polymer-modified MWCNTs and PES membranes and compared the re-sults with acid-functionalized MWCNTs They modified acid functionalizedMWCNTs using three hydrophilic polymers through an in situ polymerization reac-tion Citric acid acrylic acid and acryl amide were polymerized on acid-functionalized MWCNTs to achieve a higher number of functional groups onMWCNTs (Daraei Madaeni Ghaemi Khadivi et al 2013) The CNT-mixed mem-branes were fabricated using the phase inversion precipitation method Although thistreatment process caused a higher pure water flux with unchanged protein retention byadding a constant amount of PAA and PAAm-modified MWCNT into the membranematrix the best antifouling performance was shown by the membrane containingPCA-modified MWCNT The hyperbranched PCA caused an efficient dispersion ofMWCNTs because of good compatibility with PES This membrane also showedacceptable reusability and durability during three cycles of foulingewashing steps

1222 Clay nanoparticles

Clay nanoparticles are another inorganic additive for enhancing membrane perfor-mance Unmodified montmorillonites (NathornMMT) and Cloisite grades (modifiedMMT) are widely used nanofillers in the preparation of polymer nanocompositesMontmorillonite contains phyllosilicate groups and possesses an octahedral sheetsandwiched between two tetrahedral sheets forming a plate-shaped structure (withthe average diameter around 1 mm) (Abdollahi Rahmatpour Aalaie amp Khanbabae2008 Xie Tan Liao and Liu 2010) The layered structure of silicate has attractivehydrophilic properties and good thermal stability at high temperature (BebinCaravanier amp Galiano 2006) The most common methods used to prepare polymerclay nanocomposite technology are in situ polymerization melt intercalation andsolution dispersion In the latter method the clay mineral is exfoliated in single layersin the solvent medium and polymer chains are intercalated into these clay minerallayers The clay mineral platelets are joined by weak van der Waals forces and caneasily be dispersed in the solvent because of the increase in entropy caused by theirdisorganization Then polymer is adsorbed onto the delaminated clay mineral layersand the layers are reassembled after evaporation of the solvent and filled with polymerchains forming an intercalated nanocomposite (Anad~ao Sato Wiebeck Rolando ampDiaz 2010 Ghaemi Madaeni Alizadeh Rajabi amp Daraei 2011)

The clays most applied in polymer clay nanocomposite materials are generallythose containing clay minerals of the smectic group especially those containingMMT which are often employed for several innovative uses for example asabsorbers in the retention of pollutant gases in acid catalysis in sensors and as nano-fillers in nanocomposite preparation

Advances in polymeric membranes for water treatment 13

Many researchers have investigated the effects of adding clay particles on themorphology and thermal mechanical and hydrophilic properties as well as on theperformance of composite polymericmembranes Bebin et al (2006) prepared a compos-ite membrane containing clay particles Membranes were prepared by a recasting proce-dure using a Nafion solution mixed with Laponite particles comprising sulfonic acidgroups bonded to its surface The surface of clay particles was modified using plasmaactivation to bond styrenesulfonic moieties at their surface The dispersion of modifiedclay particles had a significant effect on the behavior of the Nafion membrane andenhanced both thewater retention and proton conductivity of nanocompositemembranesMonticelli Bottino ScandaleCapannelli andRusso (2007) reported on improvingwaterpermeability for PSf membranes blended with cationically modified clays The cationicclayePSf membranes showed the most flux and the least water contact angle (mosthydrophilicity) resulting in the enhancement of membrane performance Anad~ao et al(2010) also used modified clay as a PSf dopant and reported significant changes to themembrane morphology and thermal mechanical and hydrophilic properties

Another typical polymer used to prepare polymer clay composites is PVDFLi and Kim (2008) investigated the effect of adding modified clay (Closite Nathorn) onthe thermal properties of microporous PVDF membranes The authors reportedthat the thermal properties of PVDF nanocomposite membrane diminished afteradding modified clay nanoparticles In another work various kinds of clay particles(Closite Nathorn Closite 15A Closite 20A and Closite 30B) were incorporated intoPVDF membrane by a solution mixing method and PVDFeclay nanocomposite mem-branes were prepared by the phase inversion method (Hwang Kim Kim Hong ampNam 2011) Improved mechanical properties and thermal stability against shrinkagewere obtained by incorporating clay particles into the PVDF matrix In contrastKoh et al (2010) did not find considerable improvement in the mechanical propertiesof PVDFehexafluoropropylene (PVDFeHFP)eclay nanocomposite membranesbecause of the increased porosity of the nanocomposite membranes

Ghaemi et al (2011) synthesized PESorganically modified montmorillonite(OMMT) nanocomposites using Closite 15A and reported significant changes to themembrane skin layer and sublayer with increasing clay concentration in the casting so-lution They declared that the addition of OMMT can be effective in considerablyimproving membrane hydrophilicity and thermal and mechanical resistance as wellas pesticide retention capability at different solution conditions (acidic and neutral)In similar work Mierzwa Arieta Verlage Carvalho and Vecitis (2013) investigatedthe effect of incorporating unmodified clay nanoparticles (single platelet MMT) withand without sodium hexametaphosphate as a clay nanoparticle dispersant into the cast-ing solution on the morphology and performance of PES ultrafiltration membranesThey showed that clay additives have the ability to increase membrane permeabilityas a result of changes induced on the structure of the internal and surface pores ofthe membrane The addition of clay nanoparticles resulted in a reduction in hydrophi-licity and the negative charge of the membrane surface Surprisingly it was revealedthat although the clay membranes were more prone to fouling membrane permeabilityin the filtration of alginate solution was still greater than the nascent membrane(Mierzwa et al 2013)

14 Advances in Membrane Technologies for Water Treatment

Wan Ngah Teong and Hanafiah (2011) used chitosan-based composites containingMMT clay bentonite etc for dye removal from effluents Improvement of chitosanproperties and performance was considered the main achievement of fabricating suchnanocomposites An increase in mechanical and thermal strength as well as higher plas-ticity of chitosaneOMMT nanocomposite was also reported by researchers (Abdollahiet al 2008 Casariego et al 2009 Han Lee Choi amp Park 2010) Moreover manystudies were conducted on the adsorption of pollutants onto the chitosaneclay compos-ites in which the increment of the adsorption capacity of chitosan membranes wasproved as a result of adding clay nanoparticles (An ampDultz 2007 Bleiman ampMishael2010 Celis Adelino Hermosin amp Cornejo 2012 Chang amp Juang 2004 NesicVelickovic amp Antonovic 2012 Pandey amp Mishra 2011) For example Nesic et al(2012) tested the adsorption capability of chitosanMMT (Closite Nathorn) with BezactivOrange V-3RBO (BO) solution The effect of different amounts ofMMT on the adsorp-tion of BO was evaluated under different pHs and temperatures It was revealed thatchitosan in combination with clays produced a reliable adsorbent The main advantageof these membranes compared with similar systems is that these membranes possessedsignificantly higher adsorption capacity at low acidic conditions (pH above 6) There-fore the pretreatment of wastewater is not needed in real applications Despite relativelylong adsorption tests thesemembraneswere applicable as the result of a high adsorptioncapacity Thin-film composite membranes using chitosanenanoclay (Closite 15A and30B) coated onto the PVDF microfiltration membrane was fabricated by Daraei et al(2013) Insertion of organoclays with various percentages into the chitosan made itmore efficient for fabricating TFC membranes with the valuable ability to removedye (methylene blue and acid orange 7) from effluents

1223 Silver nanoparticles

Compared with other nanoparticles silver (Ag) is one of the first nanomaterials thatgained attention for fabricating composite membranes The bactericidal nature of silvernanoparticles brought them into the field of mixed matrix membranes Silver nanopar-ticles have a large surface-to-volume ratio thus they are used as a sustained local supplyfor Agthorn ions and provide a prolonged prevention of bacterial adhesion (Cao Tang LiuNie amp Zhao 2010 Martinez-Gutierrez et al 2012 Mollahosseini RahimpourJahamshahi Peyravi amp Khavarpour 2012) Silver is believed by some researchers(Danilczuk Lund Saldo Yamada amp Michalik 2006) to be nonallergic nontoxicand environmentally friendly Other researchers believe that silver is less harmful tohuman cells compared with bacteria (Taurozzi et al 2008) Research has shown thatincorporation of Ag nanoparticles onto the surface or in the matrix of membranes iseffective against the bacteria E coli Pseudomonas mendocina KR1 P aeruginosaand Staphylococcus aureus (Li Shao Zhou Li amp Zhang 2013 Liu Zhang HeZhao amp Bai 2010 Liu Rosenfield Hu ampMi 2013 Mollahosseini et al 2012 ZhangZhang Gusseme amp Verstraete 2012 Zodrow et al 2009) Also it was proved that theaddition of Ag nanoparticles into the membrane matrix not only makes the membranesbactericidal but also results in a significant improvement in virus removal (Zhang et al2012 Zodrow et al 2009) Chamakura Perez-Ballestero Luo Bashir and Liu (2011)

Advances in polymeric membranes for water treatment 15

described in detail the steps of the antibacterial mechanism including (1) generation ofreactive oxygen species indirectly (2) direct interaction of Ag with proteins and lipids inthe cellwall and alsoproteins in the cytoplasmicmembrane and (3) interactionwith deox-yribonucleic acid Some investigators (Koseoglu-Imer Kose Altinbas amp Koyuncu2013) suggested that Ag nanoparticles might pass through cell barriers and then releaseAgthorn ions Then Agthorn ions interact with the thiol groups of enzymes and cell proteinsdamage bacterial respiration and transport systems across the cell membrane

Silver ions were employed in membrane fabrication because of their low toxicity to-ward humans and their antibacterial ability In this regard researchers prepared mem-branes with silver ions to obtain a superior antifouling performance (Basri et al2010 Chou Yu amp Yang 2005) In contrast with silver ions silver nanoparticlesinduced long-lasting antibacterial and anti-adhesive effects and consequently consider-able resistance to biofouling in the membranes (Li et al 2013 Zodrow et al 2009) Totake advantage of Ag nanoparticles Ag does not necessarily need to be embedded intothe membrane structure during preparation It can be added to a commercial membraneand regenerated if needed However loss of antimicrobial and antiviral activity ofAg-coated membranes might occur as a result of depleting silver particles from themembrane surface and ineffectiveness against silver-resistant bacterial strains (Zodrowet al 2009) For this reason silver nanoparticles have received more attention in less-ening biofouling through embedding into the membrane backbone so far most studieson antifouling nanocomposite membranes have focused on incorporating silver nano-particles inside the membranes (Gusseme et al 2011 Li et al 2008 Sawada et al2012 Thomas et al 2009 Travan et al 2009 Zhang et al 2012 Zodrow et al2009) This way silver nanoparticles were added into the PAN (Yu et al 2003) poly(2-ethyl-2-oxazoline) (Kang Kim Char Won amp Kang 2006) PA (Lee et al 2007)polyimide (PI) (Deng Dang Zhou Rao amp Chen 2008) PES (Basri Ismail amp Aziz2011 Basri et al 2010 Cao et al 2010 Huang Arthanareeswaran et al 2012) CA(Barud et al 2011 Chou et al 2005) chitosan (Liu et al 2010 Zhu Bai Wee Liuamp Tang 2010) PVDF (Li et al 2013) and PSf (Zodrow et al 2009) compositemembranes Antibacterial experiments confirmed that bacterial growth was effectivelyinhibited and anti-biofouling performance rose in these kind of nanocompositemembranes

An increase in the hydrophilicity and selectivity of membranes blended with Agnanoparticles was also reported apart from the antibactericidal and antifouling proper-ties of silver (Basri et al 2011 Koseoglu-Imer et al 2013 Yong et al 2010 Zodrowet al 2009) Silver nanoparticles can be used as a suitable candidate for the simulta-neously improvement of membrane surface hydrophilicity and antifouling perfor-mance under proper conditions This phenomenon occurs because Ag particlesdiminish the surface tension of a pristine membrane and so water can easily spreadonto membrane surfaces (Li et al 2013)

1224 Titanium dioxide nanoparticles

Titanium dioxide (TiO2) is a special semiconductor that has been the focus ofnumerous investigations because of its excellent photocatalytic and hydrophilicity

16 Advances in Membrane Technologies for Water Treatment

properties in absorbing UV rays and its stability cheapness and commercial availabil-ity Therefore many researchers have prepared TiO2-mixed matrix membranes toimprove membrane performance by increasing hydrophilicity and reducing fouling(Madaeni amp Ghaemi 2007 Vatanpour Madaeni Khataee et al 2012 Yang ampWang 2006 Yang Zhang et al 2007)

Ebert Fritsch Koll and Tjahjawiguna (2004) investigated the influence of incorpo-rating TiO2 particles on the performance of PVDF and PAI membranes at elevatedpressures and temperatures Membranes fabricated by the phase inversion methodrevealed considerable thermal and mechanical stability In another work Yang andWang (2006) prepared a PSTiO2 organiceinorganic hybrid ultrafiltration membranewith high hydrophilicity and permeability and mechanical and thermal stability using asol-gel and phase inversion process The hybrid membranes exhibited extraordinaryhydrophilicity increased porosity and superior permeability without changingretention

The main benefit of using TiO2 nanoparticles in a mixture with polymeric mem-branes is the reduction of membrane fouling Much work has been conducted inblending TiO2 nanoparticles with different polymeric membranes to prepare compos-ite membranes with antifouling properties Table 12 lists some prepared polymericTiO2 composite membranes with antifouling properties

Regarding the photocatalytic bactericidal ability of TiO2 nanoparticles in recentyears heterogeneous photocatalysis UVeTiO2 systems have been also applied tosolve a variety of important environmental problems such as detoxifying water andproducing self-cleaning materials Damodar et al (2009) prepared PVDFeTiO2 com-posite membranes via the phase inversion method by mixing different amounts of TiO2nanoparticles (04 wt) into the PVDF casting solution The photocatalytic bacteri-cidal ability of composite PVDFeTiO2 membranes was tested using E coli (initialconcentration frac14 66 10thorn07 colony-forming unitsml) with and without the presenceof UV light (Figure 12)

These results were compared with a reference E coli solution that was kept indarkness Result showed that almost all E coli cells survived in the dark whereasabout 58 of cells survived on pristine PVDF membrane exposed to UV light for1 min The number of surviving E coli cells decreased by adding TiO2 particles andincreasing their content in the PVDFeTiO2 composite membrane and almost completeremoval of E coli occurred with a 4 TiO2ePVDF membrane during 1 min (Damodaret al 2009) In similar work with similar results Rahimpour Jahanshahi Rajaeian andRahimnejad (2012) induced bactericidal ability into a PVDFeSPES-blend membraneby incorporating TiO2 nanoparticles into the membrane to remove E coli

To increase homogeneous dispersion reduce agglomeration enhance nanofillerepolymer interaction and improve the stability of TiO2 nanoparticles chemicalapproaches have been applied to modify TiO2 nanoparticles (Li Zhu amp Zheng2007 Madaeni Zinadini amp Vatanpour 2011b Razmjou et al 2011) Li et al(2007) organically modified TiO2 nanoparticles with silane couple to overcomeaggregation and improve the dispersion of TiO2 nanoparticles in organic solventThe morphology and structure of PPESK ultrafiltration membrane indicated thatthe addition of TiO2 nanoparticles increased the thickness and porosity of the skin

Advances in polymeric membranes for water treatment 17

layer as well as the surface wettability and hydrophilicity of the membrane Thetensile mechanical strength of the membrane was also enhanced after the additionof TiO2 Moreover permeability and rejection tests showed that the pure waterflux and solute rejection of composite membranes were remarkably elevated whena small amount of TiO2 nanoparticles was added into the membrane structure

In other research Razmjou et al (2011) employed mechanical and chemical mod-ifications of TiO2 nanoparticles to improve their dispersion into the PES membranematrix For mechanical modification TiO2 nanoparticles with a volume of 50 cm3

Table 12 Some prepared polymericeTiO2 composite membraneswith antifouling properties

Polymer TiO2 (type) TiO2 (size nm) Reference

PSf-PVDF-PAN Degussa P25 20 Bae and Tak (2005)

PVDF Rutile 26e30 Cao et al (2010)

PVB Anatase 180 Fu Matsuyama and Nagai(2008)

PES Degussa P25 20 Rahimpour MadaeniTaheri and Mansourpanah(2008)

PES Rutile 30 Wu Gan Cui and Xu (2008)

PVDF Degussa P25 20 Damodar You and Chou(2009)

PVDF Degussa P25 20 Oh Kimb and Lee (2009)

PES Degussa P25 20 Li et al (2009)

PVDF Degussa P25 20 Yu Shen et al (2009)

PES Degussa P25 20 Hamid et al (2011)

CA Anatase 62 Abedini Mousavi andAminzadeh (2011)

PVDFSPES Degussa P25 20 Rahimpour et al (2011)

PVDF Degussa P25 25 Wei et al (2011)

PVDF Degussa(80 anataseand 20 rutile)

20 Madaeni Zinadini andVatanpour (2011b)

PES Degussa P25anatase

20 8 15e25 Vatanpour MadaeniKhataee et al (2012)

PVDF Anatase 20 Shi Ma Ma Wang and Sun(2012)

Reprinted from Vatanpour Madaeni Khataee et al (2012) with permission from Elsevier

18 Advances in Membrane Technologies for Water Treatment

were ground into fine powder until the volume decreased to 125 cm3 Afterward thepowder was dispersed in DMAc by sonication in a bath for 15 min followed by 10 minsonication by probe at an amplitude of 20 kHz The chemical modification of TiO2 wasalso carried out by surface modification of TiO2 nanoparticles with aminopropyltrie-thoxysilane (APTES) as silane coupling agent First 25 g of mechanically modifiedTiO2 nanoparticles was added into pure ethanol under nitrogen purging this was fol-lowed by 30 and 10 min sonication in bath and by probe respectively Differentamounts of APTES (2 20 50 and 80 wt) were added drop-wise to the mixture underan N2 atmosphere After stirring for 2 h at 65 C the particles were separated from thesolution by centrifuging at 10000 RPM for 10 min Finally the TiO2 particles weredried in an oven for 24 h at 50 C and then were ground into fine powder The com-bination of chemical and mechanical modifications was significantly effective for thefree energy and roughness of the surface pore size and protein absorption resistanceof the membrane surface as well as improved hydrophilicity of the membraneAlthough most researchers reported that an increase in hydrophilicity is the most likelyreason for decreased fouling Razmjou et al (2011) believed that the other parameterssuch as changes in the membrane morphology and local surface modifications mighthave a similar effect on the higher fouling resistance of TiO2-embedded membranes

1225 Zinc oxide nanoparticles

Another applicable nanoparticle used in modifying membranes is nano-zinc oxide(ZnO) As a multifunctional inorganic nanoparticle ZnO nanoparticles have recentlydrawn increasing attention owing to their prominent physical and chemical propertiessuch as high catalytic activity and effective antibacterial and bactericide capabilities(Balta et al 2012 Hong amp He 2012) Moreover ZnO nanoparticles are moreeconomical than some other nanoparticles such as TiO2 and Al2O3 nanoparticles

CFU0 = 66E+07 CFUml

Figure 12 Removal efficiency of Escherichia coli in water on the surface of differentpoly(vinylidenefluoride) (PVDF)TiO2 membranes with and without the radiation of UV lightReprinted from Damodar You and Chou (2009) with permission from Elsevier

Advances in polymeric membranes for water treatment 19

On the other hand ZnO nanoparticles are easily able to absorb hydrophilic hydroxylgroups (OH) (Shen et al 2012) Thus the supplementation of ZnO nanoparticlescan improve the hydrophilicity and mechanical and chemical properties of the polymermatrix (Hong amp He 2012 Lin et al 2009 Shen et al 2012)

Balta et al (2012) significantly reduced fouling of PES nanofiltration membranesafter blending with different concentrations of ZnO nanoparticles (0035 0070085 0125 0250 0375 0500 0750 1 2 and 4 wt) The ZnO-blended mem-branes showed a lower decline in flux and better permeability compared with pristinemembrane owing to the significantly higher hydrophilicity of nanocomposite mem-branes even at ultra-low concentrations of ZnO nanoparticles Also raising the nano-particle concentration to 0125 wt increased the relative flux of nanocompositemembranes but at higher concentrations no further increment was observed Further-more the addition of ZnO nanoparticles considerably improved the fouling resistanceof composite membranes during filtration of solutions containing humic acid This wasattributed to the reduction of adsorption of organic pollutants within the membranestructure as a result of increments of membrane hydrophilicity after the addition ofZnO nanoparticles Shen et al (2012) obtained similar results in fabricating aPESeZnO composite membrane Hydrophilicity thermal resistance porosity waterflux and antifouling capability of the nanocomposite membrane improved after addingZnO nanoparticles (Shen et al 2012)

In other work (Leo Cathie Lee Ahmad amp Mohammad 2012) ZnO nanoparticleswere added into a PSf ultrafiltration membrane to create antifouling properties not onlyon the membrane surface but also inside the pores Based on the results the addition ofZnO nanoparticles significantly increased the membrane hydrophilicity As a result ofincreasing the mean pore size and membrane hydrophilicity an increase as much as100 was observed in permeability The PSf membranes blended with ZnO nanopar-ticles also exhibited less fouling compared with nascent PSf membranes during filtra-tion of an aqueous solution containing oleic acid Moreover the composite membranesshowed improved thermal stability

In a study conducted by Liang Xiao Mo and Huang (2012) ZnO nanoparticleswith different concentrations were blended with PVDF polymer and applied for thefabrication of a composite PVDFeZnO membrane using the wet phase separationmethod Multi-cycle filtration tests demonstrated significant anti-irreversible foulingof the modified PVDF membrane Specifically all modified membranes reachedalmost 100 water flux recovery and maintained the initial fluxes constant in multi-cycle tests Similar to much other research this change was attributed to an increasein the surface hydrophilicity of the membrane

1226 Aluminum oxide nanoparticles

The stability availability hydrophilicity and suitable mechanical strength ofaluminum oxide (Al2O3) nanoparticles make this inorganic material another optionfor preparing of nanocomposite membranes By the aid of Al2O3 blending the mem-brane can combine the basic properties of these materials and display specific bene-fits with respect to thermal and chemical resistance separation performance and

20 Advances in Membrane Technologies for Water Treatment

adaptability to the severe water and wastewater conditions Much research has beendone in applying Al2O3 nanoparticles blending with a PVDF membrane to determinethe effect of Al2O3 particles on the hydrophilicity permeation flux morphologymechanical properties and antifouling performance of membranes

Various mixed matrix membranes of alumina (Al2O3) with CAc (Wara Francisand Velamakkani 1995) CAP (Mukherjee amp De 2013) PA (Saleh amp Gupt 2012)and PVDF (Yan Li amp Xiang 2005 Yan Li Xiang amp Xianda 2006 YanHong Li amp Li 2009) were prepared to change membrane properties such as hydro-philicity permeability and fouling resistance Yan et al (2005 2006) prepared aPVDFeAl2O3 nanocomposite membrane with different concentrations of Al2O3

(1 nm) using the phase inversion method The addition of nanosized Al2O3 particlesincreased membrane permeability with no change in the membrane pore size andnumber just by improving the surface hydrophilicity of the membrane The improve-ment in the hydrophilicity of the nanocomposite membrane also increased its anti-fouling performance in filtering oilewastewater solution from the oil field (Yanet al 2005) In another work the same authors prepared the phase inversion methodusing a nanocomposite tubular ultrafiltration PVDFeAl2O3 membrane (Yan et al2009) The flux of the modified membranes was always higher (about twice) thanthat of the unmodified membranes owing to the improvement of membrane hydro-philicity caused by adding nanosized alumina particles into the PVDF Interestinglythe permeation performance of the modified membrane increased significantlywithout sacrificing its retention properties All of these studies indicate that thepermeability and antifouling performance of the modified PVDF membranes wereconsiderably changed by incorporating Al2O3 nanoparticles into the membranematrix (Yan et al 2009 Yi et al 2011)

On the other hand Liu Moghareh Abed and Li (2011) used g-Al2O3 nanoparticlesThe authors tried to modify PVDF chains and impede segregation of nanoparticles by agrafting reaction between g-Al2O3 nanoparticles (containing a substantial amount ofhydroxyl groups [OH]) and the PVDF polymer catalyzed by some acid (H2SO4)The authors presented a mechanism for the reaction between g-Al2O3 and PVDFshown in Figure 13 The PVDFeg-Al2O3 nanocomposite membranes revealedhigh hydrophilicity and fouling resistance owing to their surface activity high adsorp-tive ability and surface enrichment of reactive functional hydroxyl groups

CF2 CF2

CF2

CH2 CH2

CH2

n

n

nn

OH-

CF CH

H+ FCH

FCH

CHCHγ -Al2O3-OH

γ -Al2O3-O

Basic γ -alumina

y

ndash

+

x

Figure 13 Schematic of the reaction between g-Al2O3 and poly(vinylidenefluoride) polymerReprinted from Liu Moghareh Abed and Li (2011) with permission from Elsevier

Advances in polymeric membranes for water treatment 21

In studies conducted by Maximous Nakhla Wan and Wong (2009) andMaximous Nakhla Wan et al (2010) PES membranes were modified by insertingdifferent concentrations of nanosized alumina (48 nm) particles inside the polymermatrix The increase in porosity and decrease in the hydrophobic interaction betweenmembrane surface and foulants changed the performance of the PES membrane afteradding Al2O3 nanoparticles into the casting solution As a result of the inducedchanges on the membrane after adding Al2O3 nanoparticles the nanocomposite mem-brane showed less flux decline compared with a pristine PES polymeric membrane(Maximous Nakhla Wan et al 2010 Maximous et al 2009)

1227 Iron oxide nanoparticles

Magnetic nanoparticles have gained much attention by researchers in recent yearsBecause of their inherent super paramagnetic properties magnetic nanoparticleshave been studied for various applications including drug and gene targeting cell sep-aration and hyperthermia (Ye Liu Wang Huang amp Xu 2009) Iron oxide (Fe3O4)has excellent thermal and chemical stability and good magnetic performance butalso good biocompatibility and biodegradation ability (Dudek et al 2012 Huanget al 2008) In this regard a PSfeFe3O4 composite ultrafiltration membrane wasfabricated by Fe3O4 nanoparticles (8e12 nm in size) wrapped in the oleic acid usingthe phase inversion method and the membrane performance in retaining lysozyme wasinspected under the magnetic field (Jian Yahui Yang amp Linlin 2006) Although thethermal stability and porosity of the PSf membrane increased after adding Fe3O4membrane hydrophilicity declined as the result of the hydrophobicity of Fe3O4 nano-particles which were wrapped in the oleic acid The rejection of lysozyme using PSfmembrane remained constant within and without the presence of the magnetic fieldHowever the rejection of the nanocomposite membrane was clearly reduced underthe magnetic field the retention recovered quickly when the magnetic field wasremoved On the other hand with the increase in magnetic intensity the decline inrejection was more noticeable The authors concluded that it is possible to separatesome substances using a PSfeFe3O4 nanocomposite membrane by altering themagnetic intensity

In various studies Huang Guo Guo and Zhang (2006) Huang Chen ChenZhang and Xu (2010) and Huang Zheng et al (2012) investigated the effects ofincorporating Fe3O4 nanoparticles on the performance of polymeric membranesThe authors showed that magnetization of a PAN membrane using Fe3O4 nanopar-ticles led to an increment of membrane permeation and antifouling performance inthe ultrafiltration of pig blood (Huang et al 2006) Moreover Fe3O4 nanoparticleswith different concentrations were applied in fabricating PSfeFe3O4 (Huang et al2010) and PVDFe Fe3O4 (Huang Zheng et al 2012) nanocomposite membranesThe composite membranes showed the best performance in terms of pure waterflux rejection and fouling resistance

Apart from improvements in membrane characteristics obvious benefits of ironoxide nanoparticles in the removal of arsenic (Sabbatini et al 2010 Sabbatini RossiThern amp Marajofsky 2009 Park amp Choi 2011) and adsorption of heavy metals

22 Advances in Membrane Technologies for Water Treatment

(Daraei et al 2012 Gholami Moghadassi Hosseini Shabani amp Gholami 2013Mansour Ossman amp Farag 2011) were proved in some research Daraei et al(2012) prepared Fe3O4ePA nanoparticles as adsorbent and used them in the PESmatrix to obtain a nanocomposite membrane with enhanced affinity for the removalof copper ions According to the experiments nanocomposite membranes indicatedhigher Cu(II) ion removal but lower pure water flux compared with pristine PESmembrane This was due to the surface pore blockage as a result of the presence ofnanoparticles in the superficial pores of the membrane during preparation (Figure 14)In other research conducted by Gholami et al (2013) iron oxide nanoparticles wereblended with polyvinyl chloride-blend cellulose membrane to apply the adsorbentproperties of Fe3O4 nanoparticles in the removal of lead from aqueous solution As ex-pected the permeability and rejection of lead rose in nanocomposite membranescompared with pristine membrane

1228 Silicon dioxide nanoparticles

Silicon dioxide (SiO2) is another convenient nanoparticle widely used in fabricatingnanocomposite membranes because of the mild reactivity and distinguished abilityin increasing hydrophilicity and improving the thermal and mechanical stability andfouling resistance of membranes (Jin Shi et al 2012 Jin Yu et al 2012 Ogoshi ampChujo 2005 Wu Xu amp Yang 2003) Silica was widely used with polymericmembranes such as PMMA (Zulfikar Mohammad amp Hilal 2006) PES (ShenRuan Wu amp Gao 2011 Wu et al 2003) PSf (Zhang Liu Lu Zhao amp Song2013) PA (Jin Shi et al 2012 Kim amp Lee 2001) PVA (Nagarale Shahi ampRangarajan 2005 Thanganathan Nishina Kimura Hayakawa amp Bobba 2012Yang James Li amp Liou 2011) and PVDF (Cho amp Sul 2001 Cui Liu Xiao amp

Figure 14 Field emission scanning electron microscopic image of cross-section of membraneprepared with 1 wt polyacrylonitrile (PAN)Fe3O4 nanoparticlesReprinted from Daraei et al (2012) with permission from Elsevier

Advances in polymeric membranes for water treatment 23

Zhang 2010 Liao Zhao Yu Tong amp Luo 2012 Yu Xu et al 2009 Zhang MaCao Li amp Zhu 2014) using sol-gel (Thanganathan et al 2012 Wu et al 2003)phase inversion (Cui Liu Xiao amp Zhang 2010 Liao Zhao Yu Tong amp Luo2012 Shen et al 2011 Zhang et al 2013) and interfacial polymerization (JinShi et al 2012 Namvar-Mahboub amp Pakizeh 2013) The sol-gel technique allowsthe formation of an inorganic framework under mild conditions and incorporation ofminerals into the polymers results in increased chemical mechanical and thermalstability without obviously decreasing the properties of the polymers (Kim andLee 2001 Wu et al 2003 Yu Xu et al 2009) Furthermore the hydrogen bondclusters remaining at the surface of the materials after the sol-gel reaction improvedmembrane hydrophilicity and enhanced the stability of composite materials (Cho ampSul 2001 Nagarale et al 2005 Yu Xu et al 2009) A simple method to obtain anorganiceSiO2 hybrid is to mix an organic polymer with a metal alkoxide such astetraethoxysilane (TEOS) followed by a sol-gel process involving hydrolysis andpolycondensation of TEOS (Wu et al 2003 Yu Xu et al 2009) Yu Xu et al(2009) synthesized organiceinorganic PVDFeSiO2 composite hollow fiber ultrafil-tration membranes using a sol-gel and wet-spinning process The microstructuremechanical property thermal stability hydrophilicity permeability and foulingresistance of composite membranes improved significantly by an appropriate choiceof TEOS concentration (3 wt)

The phase inversion process was also used by researchers as a simple and applicabletechnique to prepare polymeresilica-mixed matrix membranes The addition of hydro-philic SiO2 nanoparticles into the casting solution enhanced membrane hydrophilicity(Cui et al 2010 Shen et al 2011) On the other hand the permeability and anti-fouling ability of nanocomposite membranes also improved as the result of increasedhydrophilicity and the decreased adsorption of foulants on the membrane surface

Interfacial polymerization is another valuable method because the characteristics ofthe skin layer as a key factor in determining membrane performance can be optimizedseparately (Jin Shi et al 2012) Jin Yu et al (2012) and Jin Shi et al (2012)prepared a nanofiltration membrane with poly(amidoamine) (PAMAM) dendrimerand TMC containing SiO2 nanoparticles through an interfacial polymerization reactionon PSf ultrafiltration membrane The addition of nano-SiO2 in the skin layer improvedthermal stability and membrane hydrophilicity The results of raw water filtration bypristine PA membrane and PA-SiO2 membrane (1 wt SiO2 nanoparticles) are shownin Figure 15

As shown in the figure the flux of both PA and PA-SiO2 membranes was reducedduring the filtration time however the pristine PA membrane showed a greateramount of flux decline compared with the hydrophilic PA-SiO2 membrane Surfacewater typically contains three potential groups of foulants including microbial (bacte-ria viruses etc) organic and inorganic (humic acid and minerals) compounds Theaddition of SiO2 nanoparticles to the membrane significantly increased the antifoulingability of the PA membrane as the result of the presence of a huge number of hydroxylgroups on the surface of SiO2 nanoparticles This increased the negative charge on themembrane surface weakening the force between the negatively charged micelles andthe surface of the membrane (Jin Shi et al 2012)

24 Advances in Membrane Technologies for Water Treatment

1229 Zirconium oxide nanoparticles

Polymerezirconium dioxide (ZrO2) composite membranes are known to be chemi-cally more stable than titanium dioxide and aluminum oxide membranes and aremore suitable for liquid phase applications under rough conditions (MaximousNakhla Wan et al 2010) although a few studies have investigated the incorporationof ZrO2 into the membrane matrix Bottino Capannelli and Comite (2002) preparedZrO2ePVDF membranes using the phase inversion method Membrane performancedepended on the PVDF solvent (NMP or TEP) or ZrO2 concentration Other work con-ducted by Zheng Zou Nadeeshani Nanayakkara Matsuura and Paul Chen (2011)found that the addition of zirconia nanoparticles in PVDF membrane increased the hy-drophilicity and surface porosity of the membrane and resulted in an increment of fluxin the composite membrane It was proved that the ZrO2PVDF-blend membrane couldbe applied effectively to remove arsenate from an aqueous solution in a wide range ofpHs the optimal pH was 30e80

Furthermore Maximous Nakhla Wan et al (2010) found that ZrO2ePES mem-brane was stronger than pristine membrane and membranes blended with ZrO2 showedless flux decline and fouling resistance compared with unmodified PES membrane Onthe other hand Pang et al (2014) prepared ZrO2ePES hybrid ultrafiltration membranesby combining the ion-exchange process with the immersion precipitation technique toincrease membrane hydrophilicity and decrease membrane fouling The authors reportedthat the adsorption of foulants on the membrane surface decreased considerablycompared with pristine membranes because of an increase in membrane hydrophilicity

123 Nanostructured membranes

Based on the ISO definition membranes with pores in the range of 1e100 nm wouldevidently be considered nanostructured materials Hence ultrafiltration and most

PAPA-SiO2

Timeh

Flux

( L

sdot(m2

sdoth)-1

)

Figure 15 Flux of polyaniline (PA) and PA-SiO2 membranes versus filtration timeReprinted from Jin Shi et al (2012) with permission from Elsevier

Advances in polymeric membranes for water treatment 25

nanofiltration membranes that reject particles about 02e200 kDa corresponding to ananoscale diameter of around 1e100 nm should be classified as nanostructured mem-branes (Bhadra amp Mitra 2013 Muellera et al 2012) Generally membranes aredefined on the basis of the size of the particles that are rejected therefore the termldquonanordquo in ldquonanofiltrationrdquo does not refer to structural elements of the membranesuch as pore size (Bhadra amp Mitra 2013)

Rahimpour Madaeni Shockravi and Ghorbani (2009) added different concentra-tions of PSAm (2 5 10 and 15 wt) into the PES casting solution to prepare nano-structured ultrafiltration membranes Addition of PSAm not only resulted in theformation of an ultrafiltration membrane with nanopores it improved the hydrophilic-ity mechanical strength permeability and protein rejection of PES membranes More-over Mansourpanah and Momeni Habili (2013) employed the interfacialpolymerization technique to prepare a PA skin layer on the PES support using TMCand PIP as reagents Acrylic acid as a hydrophilic monomer and UV irradiation as aphysical procedure were used to modify the obtained thin layers The effect of UV irra-diation times (30 60 and 120 s) and acrylic acid concentration (1 5 and 10 wt)on the performance and morphology of modified TFC membranes was investigated bythe authors This modification technique resulted in the fabrication of a nanoporousmembrane by reducing the membrane pore size from 110 to 30 nm Meanwhile thehydrophilicity permeation flux rejection and antifouling ability of the modified mem-branes improved considerably

124 Bio-inspired membranes

Bio-inspired studies have drawn much attention as a potentially feasible approach toimprove current technologies In this method nature is considered a large database towhich its scientific rules might be applied in engineering applications as efficientsolutions for difficult problems In this way biological materials or natural biopoly-mers are considered for the fabrication of bio-inspired membranes because of theirwell-controlled structures and superior properties and the improvement of anyaspect of biological materials has the possibility of improving the structure and func-tion of bio-inspired membranes Moreover the conditions under which the mem-brane is fabricated are mild an aqueous solution controlled temperature moderatepressure and neutral or near neutral pH As a result of numerous advantages wideareas of application and high efficiency bio-inspired membranes have the chanceto be the next generation of membranes (Morones-Ramırez 2013 RawlingsBramble amp Staniland 2012)

Several bio-inspired platform methods such as bio-adhesion and bio-mimetic adhe-sion have been created (Li Liu et al 2009 Pan et al 2009) In addition a platformcalled bio-mineralization or bio-mimetic mineralization was developed from theformation process of bio-silica (Pan Jia Cheng amp Jiang 2010) Bio-inspired mem-branes have great benefits such as high permeability catalytic reactivity and foulingresistance and hence have the potential to be employed in water treatment processesPan et al (2010) proposed an innovative procedure to fabricate a polymereinorganicskin layer of a composite membrane by combining bio-mimetic mineralization and

26 Advances in Membrane Technologies for Water Treatment

polymer network structure manipulation In this work the silica nanoparticles showeduniform size and homogeneous distribution within the PVA structure The compositemembrane consisting of a PVAesilica skin layer and PSf hollow fiber support layershowed appropriate free volume properties

Inspired by the hierarchical structures in biology Xu et al (2011) proposed theconcept of vertically aligned nanotubes to emulate the biological channels within amembrane matrix As a result of the presence of nanopores inside the membranematrix the permeability selectivity and durability of bio-inspired membraneincreased Furthermore Balme et al (2011) conducted a research project focusingon bio-inspired membranes with biological ion channels These channels wereconfined inside the nanopores of solid-state materials The solvent had an effectiverole on membrane performance in terms of ion permeability and selectivity

Aside from the transport properties and membrane structure the development ofintelligent properties such as self-cleaning self-healing and stimuluseresponse inbio-inspired membranes are other concerns that have drawn the attention of someresearchers (Capadona Shanmuganathan Tyler Rowan amp Weder 2008 Madaeni ampGhaemi 2007 Wang Janout amp Regen 2011)

13 Applications for water treatment

Polymeric membranes are employed extensively for water treatment applications suchas desalination water softening purification of industrial and municipal wastewatersproduction of ultra-pure water and the food chemical and pharmaceutical industriesMembrane processes offer significant advantages such as operational simplicity andflexibility cost-effectiveness reliability low energy consumption good stabilityenvironment compatibility and easy control handling and scale-up under a widespectrum of operating conditions such as temperature pressure and pH Howeverthere are still unresolved problems regarding the employment of polymeric membranesunder more stringent applications Membrane fouling insufficient separation andrejection treatment of concentrates membrane lifetime and resistance to some chem-icals are the most important and well-known problems related to polymericmembranes

Fouling is the most important and well-known problem in membrane separationprocesses The urgent need for pretreatment cleaning limited recovery and short life-time are some negative results of fouling problems Membrane lifetime and chemicalresistance are also related to fouling and consequent cleaning as well as the conditionsunder which the membranes are employed Many researchers have concentrated onproposing efficient solutions and strategies to prolong the lifetime and chemical resis-tance of membranes improve membrane morphology increase hydrophilicitydecrease surface roughness and increase the degree of cross-linking of the polymerictop layer to decrease membrane fouling and increase the chemical resistance andlifetime of the membrane

Another inherent problem for pressure-driven membranes is the concentrate streamConcentrate is usually an unwanted by-product of water treatment using membrane

Advances in polymeric membranes for water treatment 27

technologies and needs to be further treated This treatment may include reuse furthertreatment by removal of contaminants and direct or indirect discharge into the surfacewater or groundwater and landfills

14 Concluding remarks and future trends

One of the most crucial problems facing the world in this century is the provision ofclean water with adequate quality from water resources Given the numerous privilegesof membranes such as relatively high selectivity and permeability low energyconsumption operational simplicity control scale-up and adaptability as well assatisfactory stability under various conditions over the years membranes have beenthe dominant technology in the water treatment industry Hence many studies havebeen conducted and much progress has been achieved in optimizing membrane char-acteristics and performance However some challenges still need to be addressed suchas decreasing membrane fouling increasing the membrane lifetime selectivity andpermeability improving thermal mechanical and chemical resistance and reducingenergy consumption

Some important incentives for the further development of polymeric membranes inwater treatment are fabrication of antifouling and self-cleaning membranes enhance-ment of membrane permselectivity an increase in membrane stability at extreme oper-ational conditions the production of new polymers with special properties for use incomposite membranes synthesis of novel nanomaterials for application in nanocom-posite membranes and the expansion of applications of bio-inspired and environmen-tally responsive membranes

Abbreviations

AA Acrylic acidAAm Acryl amideAPTES AminopropyltriethoxysilaneBPA Bisphenol ABO Bezactiv Orange V-3RCA Citric acidCAc Cellulose acetateCAP Cellulose acetate phthalateCNC Cellulose nanocrystallineCNTs Carbon nanotubesDABA b-Cyclodextrin polyurethaneDMAc DimethylacetamideDW Double-walledHPAA Hyperbranched poly(amidoamine)ICIC 5-Isocyanatoisophthaloyl chlorideIPC Isophthaloyl chloride

28 Advances in Membrane Technologies for Water Treatment

LSMM Hydrophilic surface modifying macromoleculesmm-BTEC 330550-biphenyl tetra acyl chlorideMMT MontmorilloniteMPDA m-PhenylenediamineMWCNT Multi-walled carbon nanotubeMWNTs Multi-walled nanotubesNMP N-methyl-2-pyrrolidoneom-BTEC 220440-biphenyl tetra acyl chlorideOMMT Organically modified montmorillonitesop-BTEC 220550-biphenyl tetra acyl chloridePA PolyanilinePAA Poly acrylic acidPAAm Poly acryl amidePAm PolyamidePAMAM Poly(amidoamine)PAI Poly(amide-imide)PAN PolyacrylonitrilePCA Polycitric acidPDA 13-PhenylenediaminePES PolyethersulfonePI PolyimidePIP PiperazinePMMA Poly(methyl methacrylate)PPD p-PhenylenediaminePPESK Poly(phthalazine ether sulfone ketone)PS PolystyrenePSAm Poly(sulfoxide-amide)PSf PolysulfonePU PolyurethanePVA Poly(vinyl alcohol)PVB Poly(vinyl butyral)PVDF Poly(vinylidenefluoride)PVP PolyvinylpyrrolidoneSEM Scanning electron microscopeSPC Sulfonated polycarbonateSPEK Sulphonated poly(ether ketone)SPES Sulfonated poly(ether sulfone)SPES-NH2 Sulfonated cardo poly(arylene ether sulfone)SPPO Sulfonated poly(26-dimethyl-14-phenylene oxide)SPSf Sulfonated polysulfoneSW Single-walledTEOS TetraethoxysilaneTEP TriethylphosphateTFC Thin-film compositeTFC-FO TFC forward osmosisTMBPA Tetramethyl bisphenol ATMC Trimesoyl chlorideTiO2 Titanium dioxide

Advances in polymeric membranes for water treatment 29

Greek symbol

b-CPU b-Cyclodextrin polyurethane

References

Abdollahi M Rahmatpour A Aalaie J amp Khanbabae G (2008) Preparation and evaluationof the microstructuer and properties of natural rubbersodiumemontmorillonite nano-composites Iran Polymer Journal 17 519e529

Abedini R Mousavi S M amp Aminzadeh R (2011) A novel cellulose acetate (CA) mem-brane using TiO2 nanoparticles Preparation characterization and permeation studyDesalination 277 40e45

Abu Seman M N Khayet M amp Hilal N (2010) Nanofiltration thin-film composite polyesterpolyethersulfone-based membranes prepared by interfacial polymerization Journal ofMembrane Science 348 109e116

Abu Seman M N Khayet M amp Hilal N (2011) Development of antifouling properties andperformance of nanofiltration membranes modified by interfacial polymerization Desali-nation 273 36e47

Abu Tarboush B J Rana D Matsuura T Arafat H A amp Narbaitz R M (2008)Preparation of thin film composite polyamide membranes for desalination using novelhydrophilic surface modifying marcromolecules Journal of Membrane Science 325166e175

Adams F V Nxumalo E N Krause R W M Hoek E M W amp Mamba B B (2012)Preparation and characterization of polysulfonecyclodextrin polyurethane compositenanofiltration membranes Journal of Membrance Science 405e406 291e299

Amado F D R Gondran E Ferreira J Z Rodrigues M A S amp Ferreira C A (2004)Synthesis and characterisation of high impact polystyrenepolyaniline composite mem-branes for electrodialysis Journal of Membrance Science 234 139e145

Anad~ao P Sato L F Wiebeck H Rolando F amp Diaz V (2010) Montmorillonite as acomponent of polysulfone nanocomposite membranes Applied Clay Science 48 127e132

An J amp Dultz S (2007) Adsorption of tannic acid on chitosanemontmorillonite as a functionof pH and surface charge properties Applied Clay Science 36 256e264

An Q Li F Ji Y amp Chen H (2011) Influence of polyvinyl alcohol on the surfacemorphology separation and anti-fouling performance of the composite polyamide nano-filtration membranes Journal of Membrane Science 367 158e165

Bae T H amp Tak T M (2005) Effect of TiO2 nanoparticles on fouling mitigation of ultra-filtration membranes for activated sludge filtration Journal of Membrane Science 2491e8

Balasubramanian K amp Burghard M (2005) Chemically functionalized carbon nanotubesSmall 1 180e192

Balme S Janot J M Dejardin P Beacuterardo L Henn F Bonhenry D et al (2011) Ionicdiffusion through a bio-inspired membrane Basic Principle of Diffusion Theory Experi-ment and Application 16(31) 1e2

Balta S Sotto A Luis P Benea L Van der Bruggen B amp Kim J (2012) A new outlookon membrane enhancement with nanoparticles The alternative of ZnO Journal ofMembrane Science 389 155e161

30 Advances in Membrane Technologies for Water Treatment

Barud H S Regiani T Marques R F C Lustri W R Messaddeq Y amp Ribeiro S J L(2011) Antimicrobial bacterial cellulose-silver nanoparticles composite membranesJournal of Nanomaterials 2011 1e8

Basri H Ismail A F amp Aziz M (2011) Polyethersulfone (PES)esilver composite UFmembrane Effect of silver loading and PVP molecular weight on membrane morphologyand antibacterial performance Desalination 273 72e80

Basri H Ismail A F Aziz M Nagai K Matsuura T Abdullah M S et al (2010) Silver-filled polyethersulfone membranes for antibacterial applications-effect of PVP and TAPaddition on silver dispersion Desalination 261 264e271

Bebin P Caravanier M amp Galiano H (2006) Nafionclay-SO3H membrane for protonexchange membrane fuel cell application Journal of Membrane Science 278 35e42

Bhadra M amp Mitra S (2013) Nanostructured membranes in analytical chemistry Trends inAnalytical Chemistry 45 248e263

Bleiman N amp Mishael Y G (2010) Selenium removal from drinking water by adsorption tochitosaneclay composites and oxides Batch and columns tests Journal of HazardousMaterials 183 590e595

Bottino A Capannelli G amp Comite A (2002) Preparation and characterization of novelporous PVDFeZrO2 composite membranes Desalination 146 35e40

Cao X Tang M Liu F Nie Y amp Zhao C (2010) Immobilization of silver nanoparticlesonto sulfonated polyethersulfone membranes as antibacterial materials Colloids andSurfaces B 81 555e562

Capadona J R Shanmuganathan K Tyler D J Rowan S J amp Weder C (2008) Stimuli-responsive polymer nanocomposites inspired by the sea cucumber dermis Science 3191370e1374

Casariego A Souza B W S Cerqueira M A Teixeira J A Cruz L Diaz R et al (2009)Chitosanclay films properties as affected by biopolymer and clay micronanoparticlesconcentrations Food Hydrocolloids 23 1895e1902

Celik E Park H Choi H amp Choi H (2011) Carbon nanotube blended polyethersulfonemembranes for fouling control in water treatment Water Resources 45 274e282

Celis R Adelino M A Hermosin M C amp Cornejo J (2012) Montmorilloniteechitosanbionanocomposites as adsorbents of the herbicide clopyralid in aqueous solution and soilwater suspensions Journal of Hazardous Materials 209e210 67e76

Chamakura K Perez-Ballestero R Luo Z Bashir S amp Liu J (2011) Comparison ofbactericidal activities of silver nanoparticles with common chemical disinfectants Colloidsand Surfaces B 84 88e96

Chang M amp Juang R (2004) Adsorption of tannic acid humic acid and dyes from waterusing the composite of chitosan and activated clay Journal of Colloid and InterfaceScience 278 18e25

Chen G Li S Zhang X amp Zhang S (2008) Novel thin-film composite membranes withimproved water flux from sulfonated cardo poly(arylene ether sulfone) bearing pendantamino groups Journal of Membrane Science 310 102e109

Choi J H Jegal J amp Kimb W N (2006) Fabrication and characterization of multi-walledcarbon nanotubespolymer blend membranes Journal of Membrane Science 284 406e415

Cho J W amp Sul K I (2001) Characterization and properties of hybrid composites preparedfrom poly(vinylidene fluoride-tetrafluoroethylene) and SiO2 Polymer 42 727e736

Chou W L Yu D G amp Yang M C (2005) The preparation and characterization of silverloading cellulose acetate hollow fiber membrane for water treatment Polymers forAdvanced Technologies 16(8) 600e607

Advances in polymeric membranes for water treatment 31

Cui A Liu Z Xiao C amp Zhang Y (2010) Effect of micro-sized SiO2-particle on the per-formance of PVDF blend membranes via TIPS Journal of Membrane Science 360259e264

Damodar R A You S J amp Cho H H (2009) Study the self cleaning antibacterial andphotocatalytic properties of TiO2 entrapped PVDF membranes Journal of HazardousMaterials 172 1321e1328

Danilczuk M Lund A Saldo J Yamada H ampMichalik J (2006) Conduction electron spinresonance of small silver particles Spectrochimica Acta Part A 63 189e191

Daraei P Madaeni S S Ghaemi N Ahmadi Monfared H amp Khadivi M A (2013)Fabrication of PES nanofiltration membrane by simultaneous use of multi-walled carbonnanotube and surface graft polymerization method Comparison of MWCNT and PAAmodified MWCNT Separation and Purification Technology 104 32e44

Daraei P Madaeni S S Ghaemi N Khadivi M A Astinchap B amp Moradian R (2013)Enhancing antifouling capability of PES membrane via mixing with various types of polymermodified multi-walled carbon nanotube Journal of Membrane Science 444 184e191

Daraei P Madaeni S S Ghaemi N Salehi E Khadivi M A Moradian R et al (2012)Novel polyethersulfone nanocomposite membrane prepared by PANIFe3O4 nanoparticleswith enhanced performance for Cu(II) removal from water Journal of Membrane Science415e416 250e259

Daraei P Madaeni S S Salehi E Ghaemi N Sadeghi Ghari H Khadivi M A et al(2013) Novel thin film composite membrane fabricated by mixed matrix nanoclaychitosanon PVDF microfiltration support Preparation characterization and performance in dyeremoval Journal of Membrane Science 436 97e108

Deng Y Q Dang G D Zhou H W Rao X H amp Chen C H (2008) Preparation andcharacterization of polyimide membranes containing silver nanoparticles in pores distrib-uting on one side Materials Letters 62 1143e1146

Dudek G Turczyn R Strzelewicz A Rybak A Krasowska M amp Grzywn Z J (2012)Preparation and characterization of iron oxidesepolymer composite membranes Separa-tion Science and Technology 47 1390e1394

Ebert K Fritsch D Koll J amp Tjahjawiguna C (2004) Influence of inorganic fillers on thecompaction behavior of porous polymer based membranes Journal of Membrane Science233 71e78

Eitan A Jiang K Dukes D Andrews R amp Schadler L S (2003) Surface modification ofmultiwalled carbon nanotubes Toward the tailoring of the interface in polymer compositesChemistry of Materials 15 3198e3201

Fu X Matsuyama H amp Nagai H (2008) Structure control of asymmetric poly(vinyl butyral)-TiO2 composite membrane prepared by nonsolvent induced phase separation Journal ofApplied Polymer Science 108 713e723

Ghaemi N Madaeni S S Alizadeh A Rajabi H amp Daraei P (2011) Preparation char-acterization and performance of polyethersulfoneorganically modified montmorillonitenanocomposite membranes in removal of pesticides Journal of Membrane Science 382135e147

Gholami A Moghadassi A R Hosseini S M Shabani S amp Gholami F (2013) Prepa-ration and characterization of polyvinyl chloride based nanocomposite nanofiltrationmembrane modified by iron oxide nanoparticles for lead removal from water Journal ofIndustrial and Engineering Chemistry 20(4) 1517e1522

Gusseme B D Hennebel T Christiaens E Saveyn H Verbeken K Fitts J P et al(2011) Virus disinfection in water by biogenic silver immobilized in polyvinylidenefluoride membranes Water Resources 45 1856e1864

32 Advances in Membrane Technologies for Water Treatment

Hamid N A A Ismail A F Matsuura T Zularisam A W Lau W J Yuliwati E et al(2011) Morphological and separation performance study of polysulfonetitaniumdioxide (PSFTiO2) ultrafiltration membranes for humic acid removal Desalination 27385e92

Han G Chung T S Toriida M amp Tamai S (2012) Thin-film composite forward osmosismembranes with novel hydrophilic supports for desalination Journal of MembraneScience 423e424 543e555

Han Y S Lee S H Choi K H amp Park I (2010) Preparation and characterization ofchitosaneclay nanocomposites with antimicrobial activity Journal of Physics andChemistry of Solids 71 464e467

Han K N Yu B Y amp Kwak S Y (2012) Hyperbranched poly(amidoamine)polysulfonecomposite membranes for Cd(II) removal from water Journal of Membrane Science 39683e91

Hong J amp He Y (2012) Effects of nano sized zinc oxide on the performance of PVDFmicrofiltration membranes Desalination 302 71e79

Huang J Arthanareeswaran G amp Zhang K (2012) Effect of silver loaded sodium zirconiumphosphate (nanoAgZ) nanoparticles incorporation on PES membrane performanceDesalination 285 100e107

Huang Z Q Chen L Chen K Zhang Z amp Xu H T (2010) A novel method for controllingthe sublayer microstructure of an ultrafiltration membrane The preparation of thePSF-Fe3O4 ultrafiltration membrane in a parallel magnetic field Journal of AppliedPolymer Science 117 1960e1968

Huang Z Q Chen K C Li S N Yin X T Zhang Z amp Xu H T (2008) Effect offerrosoferric oxide content on the performances of polysulfoneeferrosoferric oxide ultra-filtration membranes Journal of Membrane Science 315 164e171

Huang Z Q Guo X P Guo C L amp Zhang Z (2006) Magnetization influence on theperformance of ferrosoferric oxide Polyacrylonitrile membranes in ultrafiltration of pigblood solution Bioprocess and Biosystems Engineering 28 415e421

Huang Z Q Zheng F Zhang Z Xu H T amp Zhou K M (2012) The performance of thePVDF-Fe3O4 ultrafiltration membrane and the effect of a parallel magnetic field usedduring the membrane formation Desalination 292 64e72

Hwang H Y Kim D J Kim H J Hong Y T amp Nam S Y (2011) Effect of nanoclay onproperties of porous PVDF membranes Transactions of Nonferrous Metals Society ofChina 21 141e147

Islam M F Rojas E Bergey D M Johnson A T amp Yodh A G (2003) High weightfraction surfactant solubilization of single-wall carbon nanotubes in water Nano Letters3 269e273

Jeong B H Hoek E M V Yan Y Subramani A Huang X Hurwitz G et al (2007)Interfacial polymerization of thin film nanocomposites A new concept for reverse osmosismembranes Journal of Membrane Science 294 1e7

Jian P Yahui H Yang W amp Linlin L (2006) Preparation of polysulfoneeFe3O4 com-posite ultrafiltration membrane and its behavior in magnetic field Journal of MembraneScience 284 9e16

Jin L Shi W Yu S Yi X Sun N Ma C et al (2012) Preparation and characterization ofa novel PA-SiO2 nanofiltration membrane for raw water treatment Desalination 29834e41

Jin L Yu S L Shi W X Yi X S Sun N Ge Y L et al (2012) Synthesis of a novelcomposite nanofiltration membrane incorporated SiO2 nanoparticles for oily wastewaterdesalination Polymer 53 5295e5303

Advances in polymeric membranes for water treatment 33

Kang S W Kim J H Char K Won J amp Kang Y S (2006) Nanocomposite silverpolymer electrolytes as facilitated olefin transport membranes Journal of MembraneScience 285 102e107

Khodabakhshi A R Madaeni S S Xu TW Wu L Wu C Li C et al (2012) Preparationoptimization and characterization of novel ion exchange membranes by blending of chem-ically modified PVDF and SPPO Separation and Purification Technology 90 10e21

Kim E S Hwang G Gamal El-Din M amp Liu Y (2012) Development of nanosilver andmulti-walled carbon nanotubes thin-film nanocomposite membrane for enhanced watertreatment Journal of Membrane Science 394e395 37e48

Kim E S Kim Y J Yu Q amp Deng B (2009) Preparation and characterization of poly-amide thin-film composite (TFC) membranes on plasma-modified polyvinylidene fluoride(PVDF) Journal of Membrane Science 344 71e81

Kim S H Kwak S Y Sohn B H amp Park T H (2003) Design of TiO2 nanoparticles self-assembled aromatic poylamide thin-film composite (TFC) membrane as an approach tosolve biofouling problem Journal of Membrane Science 211 157e165

Kim S H Kwak E Y amp Suzuki T (2005) Positron annihilation spectroscopic evidence todemonstrate the flux-enhancement mechanism in morphology-controlled thin film com-posite (TFC) membrane Environmental Science and Technology 39 1764e1770

Kim J H amp Lee Y M (2001) Gas permeation properties of poly(amide-6-b-ethylene oxide)-silica hybrid membranes Journal of Membrane Science 193 209e225

Koh M J Hwang H Y Kim D J Kim H J Hong Y T amp Nam S Y (2010) Preparationand characterization of porous pvdf-HFPclay nanocomposite membranes Journal ofMaterials Science and Technology 26(7) 633e638

Kong C Kanezashi M Yamomoto T Shintani T amp Tsuru T (2010) Controlled synthesisof high performance polyamide membrane with thin dense layer for water desalinationJournal of Membrane Science 362 76e80

Koseoglu-Imer D Y Kose B Altinbas M amp Koyuncu I (2013) The production of pol-ysulfone (PS) membrane with silver nanoparticles (AgNP) Physical properties filtrationperformances and biofouling resistances of membranes Journal of Membrane Science428 620e628

Lang K Sourirajan S Matsuura T amp Chowdhury G (1996) A study on the preparation ofpolyvinyl alcohol thin-film composite membranes and reverse osmosis testing Desalina-tion 104 185e196

Lau W J Ismail A F Misdan N amp Kassim M A (2012) A recent progress in thin filmcomposite membrane A review Desalination 287 190e199

Lee H S Im S J Kim J H Kim J P amp Min B R (2008) Polyamide thin film nano-filtration membranes containing TiO2 nanoparticles Desalination 219 48e56

Lee S Y Kim H J Patel R Im S J Kim J H amp Min B R (2007) Silver nanoparticlesimmobilized on thin film composite polyamide membrane Characterization nanofiltrationantifouling properties Polymers for Advanced Technologies 18 562e568

Leo C P Cathie Lee W P Ahmad A L amp Mohammad A W (2012) Polysulfonemembranes blended with ZnO nanoparticles for reducing fouling by oleic acid Separationand Purification Technology 89 51e56

Liang S Xiao K Mo Y amp Huang X (2012) A novel ZnO nanoparticle blended poly-vinylidene fluoride membrane for anti-irreversible fouling Journal of Membrane Science394e395 184e192

Liao C Zhao J Yu P Tong H amp Luo Y (2012) Synthesis and characterization of lowcontent of different SiO2 materials composite poly (vinylidene fluoride) ultrafiltrationmembranes Desalination 285 117e122

34 Advances in Membrane Technologies for Water Treatment

Li B Liu W P Jiang Z Y Dong X Wang B Y amp Zhong Y R (2009) Ultrathin andstable active layer of dense composite membrane enabled by poly (dopamine) Langmuir25 7368e7374

Li H amp Kim H (2008) Thermal degradation and kinetic analysis of PVDFmodified MMTnanocomposite membranes Desalination 234 9e15

Li J B Zhu J W amp Zheng M S (2007) Morphologies and properties of poly(phthalazinoneethersulfoneketone) matrix ultrafiltration membranes with entrapped TiO2 nanoparticlesJournal of Applied Polymer Science 103 3623e3629

Li J F Xu Z L Yang H Yu L Y amp Liu M (2009) Effect of TiO2 nanoparticles on thesurface morphology and performance of microporous PES membrane Applied SurfaceScience 255 4725e4732

Li J H Shao X S Zhou Q Li M Z amp Zhang Q Q (2013) The double effects of silvernanoparticles on the PVDF membrane Surface hydrophilicity and antifouling perfor-mance Applied Surface Science 265 663e670

Li Q L Mahendra S Lyon D Y Brunet L Liga M V Li D et al (2008) Antimicrobialnanomaterials for water disinfection and microbial control Potential applications andimplication Water Resources 42(18) 4591e4602

Lin W Xu Y Huang C C Ma Y Shannon K B Chen D R et al (2009) Toxicity ofnano- and micro-sized ZnO particles in human lung epithelial cells Journal of Nano-particle Research 11 25e39

Liu C X Zhang D R He Y Zhao X S amp Bai R (2010) Modification of membranesurface for anti-biofouling performance Effect of anti-adhesion and anti-bacteriaapproaches Journal of Membrane Science 346 121e130

Liu F Moghareh Abed M R amp Li K (2011) Preparation and characterization ofpoly(vinylidene fluoride) (PVDF) based ultrafiltration membranes using nano g-Al2O3Journal of Membrane Science 366 97e103

Liu Y Rosenfield E Hu M amp Mi B (2013) Direct observation of bacterial deposition onand detachment from nanocomposite membranes embedded with silver nanoparticlesWater Resources 47 2949e2958

Madaeni S S amp Ghaemi N (2007) Characterization of self-cleaning RO membranes coatedwith TiO2 particles under UV irradiation Journal of Membrane Science 303 221e233

Madaeni S S Zinadini S amp Vatanpour V (2011a) Convective flow adsorption of nickelions in PVDF membrane embedded with multi-walled carbon nanotubes and PAA coatingSeparation and Purification Technology 80 155e162

Madaeni S S Zinadini S amp Vatanpour V (2011b) A new approach to improve antifoulingproperty of PVDF membrane using in situ polymerization of PAA functionalized TiO2nanoparticles Journal of Membrane Science 380 155e162

Malaisamy R Mahendran R amp Mohan D (2002) Cellulose acetate and sulfonated poly-sulfone blend ultrafiltration membranes II Pore statistics molecular weight cutoff andmorphological studies Journal of Applied Polymer Science 84(2) 430e444

Mansour M S Ossman M E amp Farag H A (2011) Removal of Cd (II) ion from waste waterby adsorption onto polyaniline coated on sawdust Desalination 272 301e305

Mansourpanah Y Madaeni S S Adeli M Rahimpour A amp Farhadian A (2009) Surfacemodification and preparation of nanofiltration membrane from polyethersulfonepolyimideblend e use of a new material (polyethyleneglycol-triazine) Journal of Applied PolymerScience 112(5) 2888e2895

Mansourpanah Y Madaeni S S Rahimpour A Adeli M Hashemi Y amp Moradian M R(2011) Fabrication new PES-based mixed matrix nanocomposite membranes usingpolycaprolactone modified carbon nanotubes as the additive Property changes andmorphological studies Desalination 277 171e177

Advances in polymeric membranes for water treatment 35

Mansourpanah Y amp Momeni Habili E (2013) Preparation and modification of thin film PAmembranes with improved antifouling property using acrylic acid and UV irradiationJournal of Membrane Science 430 158e166

Martinez-Gutierrez F Thi E P Silverman J M Camargo de Oliveira C Svensson S LVanden Hoek A et al (2012) Antibacterial activity inflammatory response coagulationand cytotoxicity effects of silver nanoparticles Nanomedicine Nanotechnology 8 328e336

Masuelli M Marchese J amp Ochoa N A (2009) SPCPVDF membranes for emulsified oilywastewater treatment Journal of Membrane Science 326(2) 688e693

Maurya S K Parashuram K Singh P S Ray P amp Reddy A V R (2012) Preparation ofpolysulfoneepolyamide thin film composite hollow fiber nanofiltration membranes andtheir performance in the treatment of aqueous dye solutions Desalination 304 11e19

Maximous N Nakhla G Wan W amp Wong K (2009) Preparation characterization andperformance of Al2O3PES membrane for wastewater filtration Journal of MembraneScience 341 67e75

Maximous N Nakhla G Wan W amp Wong K (2010b) Performance of a novel ZrO2PESmembrane for wastewater filtration Journal of Membrane Science 352 222e230

Maximous N Nakhla G Wong K amp Wan W (2010) Optimization of Al2O3PESmembranes for wastewater filtration Separation and Purification Technology 73294e301

Mbareck C Nguyen Q T Alaoui O T amp Barillier D (2009) Elaboration characterizationand application of polysulfone and polyacrylic acid blends as ultrafiltration membranes forremoval of some heavy metals from water Journal of Hazardous Materials 171(1e3)93e101

Mierzwa J C Arieta V Verlage M Carvalho H amp Vecitis C D (2013) Effect of claynanoparticles on the structure and performance of polyethersulfone ultrafiltration mem-branes Desalination 314 147e158

Mollahosseini A Rahimpour A Jahamshahi M Peyravi M amp Khavarpour M (2012) Theeffect of silver nanoparticle size on performance and antibacteriality of polysulfoneultrafiltration membrane Desalination 306 41e50

Monticelli O Bottino A Scandale I Capannelli G amp Russo S (2007) Preparation andproperties of polysulfoneeclay composite membranes Journal of Applied PolymerScience 103 3637e3644

Morones-Ramırez J R (2013) Bioinspired synthesis of optically and thermally responsivenanoporous membranes NPG Asia Materials 5 1e9

Muellera N C Bruggen B Keuterc V Luis P Melin T Pronk W et al (2012)Nanofiltration and nanostructured membranes should they be considered nanotech-nology or not Journal of Hazardous Materials 211e212 275e280

Mukherjee R amp De S (2013) Adsorptive removal of phenolic compounds using celluloseacetate phthalate alumina nanoparticle mixed matrix membrane Journal of HazardousMaterials 265 8e19

Musale D A Kumar A amp Pleizier G (1999) Formation and characterization of polyacrylonitrile)Chitosan composite ultrafiltration membranes Journal of Membrane Science154 163e173

Nagarale R K Shahi V K amp Rangarajan R (2005) Preparation of polyvinyl alcoholesilicahybrid heterogeneous anion-exchangemembranes by solegelmethod and their character-ization Journal of Membrane Science 248 37e44

Namvar-Mahboub M amp Pakizeh M (2013) Development of a novel thin filmcomposite membrane by interfacial polymerization on polyetherimidemodified SiO2 supportfor organic solvent nanofiltration Separation and Purification Technology 119 35e45

36 Advances in Membrane Technologies for Water Treatment

Nesic A R Velickovic S J amp Antonovic D G (2012) Characterization of chitosanmontmorillonite membranes as adsorbents for Bezactiv Orange V-3R dye Journal ofHazardous Materials 209e210 256e263

Ochoa A Masuelli M amp Marchese J (2003) Effect of hydrophilicity on fouling of anemulsified oil wastewater with PVDFPMMA membranes Journal of Membrane Science226 203e211

Ochoa N A Pradanos P Palacio L Pagliero C Marchese J amp Hernandez A (2001)Pore size distributions based on AFM imaging and retention of multidisperse polymersolutes characterisation of polyethersulfone UF membranes with dopes containing differentPVP Journal of Membrane Science 187 227e237

OrsquoConnell M J Boul P Ericson L M Huffman C Wang Y H Haroz E et al (2001)Reversible water-solubilization of single-walled carbon nanotubes by polymer wrappingChemical Physics Letters 342 265e271

Ogoshi T amp Chujo Y (2005) Synthesis of poly(vinylidene fluoride)(PVDF)silica hybridshaving interpenetrating polymer network structure by using crystallization between PVDFchains Journal of Polymer Science A Polymer Chemistry 43 3543e3550

Oh S J Kimb N amp Lee Y T (2009) Preparation and characterization of PVDFTiO2organiceinorganic composite membranes for fouling resistance improvement Journal ofMembrane Science 345 13e20

Pan F Jia H Cheng Q amp Jiang Z (2010) Bio-inspired fabrication of composite membraneswith ultrathin polymeresilica nanohybrid skin layer Journal of Membrane Science 362119e126

Pan F Jia H Qiao S Jiang Z Wang J Wang B et al (2009) Bioinspired fabrication ofhigh performance composite membranes with ultrathin defect-free skin layer Journal ofMembrane Science 341 279e285

Pandey S amp Mishra S B (2011) Organiceinorganic hybrid of chitosanorganoclaybionanocomposites for hexavalent chromium uptake Journal of Colloid and InterfaceScience 361 509e520

Pang R Li X Li J Lu Z Sun X amp Wang L (2014) Preparation and characterization ofZrO2PES hybrid ultrafiltration membrane with uniform ZrO2 nanoparticles Desalination332 60e66

Park H amp Choi H (2011) As (III) removal by hybrid reactive membrane process combinedwith ozonation Water Resources 45 1933e1940

Peng F Huang X Jawor A amp Hoek E M V (2010) Transport structural and interfacialproperties of poly (vinyl alcohol)epolysulfone composite nanofiltration membranesJournal of Membrane Science 353 169e176

Prakash Rao A Desai N V amp Rangarajan R (1997) Interfacially synthesized thin filmcomposite RO membranes for seawater desalination Journal of Membrane Science 124263e272

Qui S Wu L Pan X Zhang L Chen H amp Gao C (2009) Preparation and properties offunctionalized carbon nanotubePSF blend ultrafiltration membranes Journal of Mem-brane Science 342 165e172

Qu L Lin Y Hill D E Zhou B Wang W Sun X et al (2004) Polyimide-functionalizedcarbon nanotubes Synthesis and dispersion in nanocomposite films Macromolecules37 6055e6060

Rahimpour A Jahanshahi M Mortazavian N Madaeni S S amp Mansourpanah Y (2010)Preparation and characterization of asymmetric polyethersulfone and thin-film compositepolyamide nanofiltration membranes for water softening Applied Surface Science 2561657e1663

Advances in polymeric membranes for water treatment 37

Rahimpour A Jahanshahi M Rajaeian B amp Rahimnejad M (2011) TiO2 entrapped nano-composite PVDFSPES membranes Preparation characterization antifouling andantibacterial properties Desalination 278 343e353

Rahimpour A amp Madaeni S S (2007) Polyethersulfone (PES)cellulose acetate phthalate(CAP) blend ultrafiltration membranes Preparation morphology performance and anti-fouling properties Journal of Membrane Science 305 299e312

Rahimpour A Madaeni S S Shockravi A amp Ghorbani S (2009) Preparation and char-acterization of hydrophile nano-porous polyethersulfone membranes using synthesizedpoly(sulfoxide-amide) as additive in the casting solution Journal of Membrane Science334 64e73

Rahimpour A Madaeni S S Taheri A H amp Mansourpanah Y (2008) Coupling TiO2nanoparticles with UV irradiation for modification of polyethersulfone ultrafiltrationmembranes Journal of Membrane Science 313 158e169

Rana D Kim Y Matsuura T amp Arafat A H (2011) Development of antifouling thin-filmcomposite membranes for seawater desalination Journal of Membrane Science 367110e118

Rawlings A E Bramble J P amp Staniland S S (2012) Innovation through imitationBiomimetic bioinspired and biokleptic research Soft Matter 8 2675e2679

Razmjou A Mansouri J amp Chen V (2011) The effects of mechanical and chemicalmodification of TiO2 nanoparticles on the surface chemistry structure and fouling per-formance of PES ultrafiltration membranes Journal of Membrane Science 378 73e84

Reddy A V R Trivedi J J Devmurari C V Mohan D J Singh P Rao A P et al (2005)Fouling resistantmembranes in desalination andwater recoveryDesalination 183 301e306

Roy S Addo Ntim S Mitra S amp Sirkar K K (2011) Facile fabrication of superiornanofiltration membranes from interfacially polymerized CNT-polymer compositesJournal of Membrane Science 375 81e87

Sabbatini P Rossi F Thern G amp Marajofsky A (2009) Iron oxide adsorbers for arsenicremoval A low cost treatment for rural areas and mobile applications Desalination 248184e192

Sabbatini P Yrazu F Rossi F Thern G Marajofsky A amp Fidalgo de Cortalezzi M M(2010) Fabrication and characterization of iron oxide ceramic membranes for arsenicremoval Water Resources 44 5702e5712

Saleh T A amp Gupt V K (2012) Synthesis and characterization of alumina nano-particlespolyamide membrane with enhanced flux rejection performance Separation and Purifi-cation Technology 89 245e251

Sawada I Fachrul R Ito T Ohmukai Y Maruyama T amp Matsuyama H (2012) Develop-ment of a hydrophilic polymer membrane containing silver nanoparticles with both organicantifouling and antibacterial properties Journal of Membrane Science 387e388 1e6

Shao L Cheng X Q Liu Y Quan S Ma J Zhao S Z et al (2013) Newly developednanofiltration (NF) composite membranes by interfacial polymerization for Safranin O andAniline blue removal Journal of Membrane Science 430 96e105

Shawky H A Chae R Y Lin S amp Wiesner M R (2011) Synthesis and characterization ofa carbon nanotubepolymer nanocomposite membrane for water treatment Desalination272 46e50

Shen L Bian X Lu X Shi L Liu Z Chen L et al (2012) Preparation and character-ization of ZnOpolyethersulfone (PES) hybrid membranes Desalination 293 21e29

Shen J Ruan Wu L amp Gao C (2011) Preparation and characterization of PESeSiO2organiceinorganic composite ultrafiltration membrane for raw water pretreatmentChemical Engineering Journal 168 1272e1278

38 Advances in Membrane Technologies for Water Treatment

Shi F Ma Y Ma J Wang P amp Sun W (2012) Preparation and characterization of PVDFTiO2 hybrid membranes with different dosage of nano-TiO2 Journal of MembraneScience 389 522e531

Shirazi Y Ahmadzadeh Tofighy M ampMohammadi T (2011) Synthesis and characterizationof carbon nanotubespoly vinyl alcohol nanocomposite membranes for dehydration ofisopropanol Journal of Membrane Science 378 551e561

Susanto H amp Ulbricht M (2008) High-performance thin-layer hydrogel composite mem-branes for ultrafiltration of natural organic matter Water Resources 42 2827e2835

Tang C Zhang Q Wang K Fu Q amp Zhang C (2009) Water transport behavior of chi-tosan porous membranes containing multi-walled carbon nanotubes (MWNTs) Journal ofMembrane Science 337 240e247

Taurozzi J S Arul H Bosak V Z Burban A F Voice T C Bruening M L et al(2008) Effect of filler incorporation route on the properties of polysulfoneesilvernanocomposite membranes of different porosities Journal of Membrane Science 32558e68

Thanganathan U Nishina Y Kimura K Hayakawa S amp Bobba R (2012) Character-ization of hybrid composite membrane based polymerprecursorSiO2 Materials Letters81 88e91

Thomas V Yallapu M M Sreedhar B amp Bajpai S K (2009) Fabrication characterizationof chitosannanosilver film and its potential antibacterial application Journal of Bio-materials Science-Polymer E 20(14) 2129e2144

Travan A Pelillo C Donati I Marsich E Benincasa M Scarpa T et al (2009) Non-cytotoxic silver nanoparticle-polysaccharide nanocomposites with antimicrobial activityBiomacromolecules 10(6) 1429e1435

Vatanpour V Madaeni S S Khataee A R Salehi E Zinadini S amp Ahmadi Monfared H(2012) TiO2 embedded mixed matrix PES nanocomposite membranes Influence ofdifferent sizes and types of nanoparticles on antifouling and performance Desalination292 19e29

Vatanpour V Madaeni S S Moradian R Zinadini S amp Astinchap B (2011) Fabricationand characterization of novel antifouling nanofiltration membrane prepared from oxidizedmultiwalled carbon nanotubepolyethersulfone nanocomposite Journal of MembraneScience 375 284e294

Vatanpour V Madaeni S S Moradian R Zinadini S amp Astinchap B (2012) Novelantibifouling nanofiltration polyethersulfone membrane fabricated from embeddingTiO2 coated multiwalled carbon nanotubes Separation and Purification Technology90 69e82

Verissimo S Peinemann K V amp Bordado J (2005) Thin-film composite hollow fibermembranes An optimized manufacturing method Journal of Membrane Science 26448e55

Wan Ngah W S Teong L C amp Hanafiah M A K M (2011) Adsorption of dyes and heavymetal ions by chitosan composites A review Carbohydrate Polymers 83 1446e1456

Wang M Janout V amp Regen S L (2011) Hyper-thin organic membranes with exceptionalH2CO2 permeation selectivity Importance of ionic crosslinking and self-healingChemical Communications 47 2387e2389

Wang H Li L Zhang X amp Zhang S (2010) Polyamide thin-film composite membranesprepared from a novel triamine 35-diamino-N-(4-aminophenyl)-benzamide monomer andm-phenylenediamine Journal of Membrane Science 353 78e84

Wara N M Francis L F amp Velamakkani B V (1995) Addition of alumina to celluloseacetate membranes Journal of Membrane Science 104 43e49

Advances in polymeric membranes for water treatment 39

Wei Y ChuHQ Dong B Z Li X Xia S J ampQiang ZM (2011) Effect of TiO2 nanowireaddition on PVDF ultrafiltration membrane performance Desalination 272 90e97

Wu G Gan S Cui L amp Xu Y (2008) Preparation and characterization of PESTiO2composite membranes Applied Surface Science 254 7080e7086

Wu H Tang B amp Wu P (2010) MWNTsPolyester thin film nanocomposite membrane Anapproach to overcome the trade-off effect between permeability and selectivity Journal ofPhysical Chemistry C 114 16395e16400

Wu C Xu T amp Yang W (2003) A new inorganiceorganic negatively charged membraneMembrane preparation and characterizations Journal of Membrane Science 224 117e125

Wu C Zhang S Yang D Wei J Yan C amp Jian X (2006) Preparation characterizationand application in wastewater treatment of a novel thermal stable composite membraneJournal of Membrane Science 279 238e245

Xie Y Tan S Liao M amp Liu R (2010) Structure and antibacterial activity of modifiedmontmorillonite Chemical Research in Chinese Universities 26 509e513

Xu T Zhao N Ren F Hourani R Lee M T Shu J Y et al (2011) Subnanometer porousthin films by the co-assembly of nanotube subunits and block copolymers ACS Nano 51376e1384

Yan L Hong S Li M L amp Li Y S (2009) Application of the Al2O3ePVDF nano-composite tubular ultrafiltration (UF) membrane for oily wastewater treatment and itsantifouling research Separation and Purification Technology 66 347e352

Yan L Li Y S amp Xiang C B (2005) Preparation of poly(vinylidene fluoride)(pvdf)ultrafiltration membrane modified by nano-sized alumina (Al2O3) and its antifoulingresearch Polymer 46 7701e7706

Yan L Li Y S Xiang C B amp Xianda S (2006) Effect of nano-sized Al2O3-particleaddition on PVDF ultrafiltration membrane performance Journal of Membrane Science276 162e167

Yang C C James Li Y J amp Liou T H (2011) Preparation of novel poly(vinyl alcohol)SiO2 nanocomposite membranes by a solegel process and their application on alkalineDMFC Desalination 276 366e372

Yang Y amp Wang P (2006) Preparation and characterizations of a new PSTiO2 hybridmembranes by solegel process Polymer 47 2683e2688

Yang Y Zhang H Wang P Zheng Q amp Li J (2007) The influence of nano-sized TiO2fillers on the morphologies and properties of PSF UF membrane Journal of MembraneScience 288 231e238

Yang Z Chen X H Chen C S Li W H Zhang H Xu L S et al (2007) Noncovalent-wrapped sidewall functionalization of multiwalled carbon nanotubes with polyimidePolymer Composites 28 36e41

Ye X Y Liu Z M Wang Z G Huang X J amp Xu Z K (2009) Preparation and char-acterization of magnetic nanofibrous composite membranes with catalytic activity Mate-rials Letters 63 1810e1813

Yi X S Yu S L Shi W X Sun N Jin L M Wang S et al (2011) The influence ofimportant factors on ultrafiltration of oilwater emulsion using PVDF membrane modifiedby nano-sized TiO2Al2O3 Desalination 281 179e184

Yong Ng L Wahab Mohammad A Peng Leo C amp Hilal N (2010) Polymeric membranesincorporated with metalmetal oxide nanoparticles A comprehensive review Desalination308 15e33

Yu D G Teng M Y Chou W L amp Yang M C (2003) Characterization and inhibitoryeffect of antibacterial PANbased hollow fiber loaded with silver nitrate Journal of Mem-brane Science 225 115e123

40 Advances in Membrane Technologies for Water Treatment

Yu L Y Shen H M amp Xu Z L (2009b) PVDF-TiO2 composite hollow fiber ultrafiltrationmembranes prepared by TiO2 solegel method and blending method Journal of AppliedPolymer Science 113 1763e1772

Yu L Y Xu Z L Shen H M amp Yang H (2009a) Preparation and characterization ofPVDFeSiO2 composite hollow fiber UF membrane by solegel method Journal ofMembrane Science 337 257e265

Yu S Liu M Liu X amp Gao C (2009) Performance enhancement in interfacially synthe-sized thin-film composite polyamide-urethane reverse osmosis membrane for seawaterdesalination Journal of Membrane Science 342 313e320

Zavastin D Cretescu I Bezdadea M Bourceanu M Driagan M Lis G et al (2010)Preparation characterization and applicability of cellulose acetateepolyurethane blendmembrane in separation techniques Colloids and Surfaces A Physicochemical andEngineering Aspects 370(1e3) 120e128

Zhang Y Liu Lu Y Zhao L amp Song L (2013) Investigation of phosphorylatedTiO2eSiO2 particlespolysulfone composite membrane for wastewater treatment Desa-lination 324 118e126

Zhang F Ma X Cao C Li J amp Zhu Y (2014) Poly(vinylidene fluoride)SiO2composite membranes prepared by electrospinning and their excellent properties fornonwoven separators for lithium-ion batteries Journal of Power Sources 251423e431

Zhang M Zhang K S Gusseme B D amp Verstraete W (2012) Biogenic silver nano-particles (bio-Ag0) decrease biofouling of bio-Ag0PES nanocomposite membranesWaterResources 46 2077e2087

Zheng Y M Zou S W Nadeeshani Nanayakkara K G Matsuura T amp Paul Chen J(2011) Adsorptive removal of arsenic from aqueous solution by a PVDFzirconia blend flatsheet membrane Journal of Membrane Science 374 1e11

Zhou Y Zhao H Bai H Zhang L amp Tang H (2012) Papermaking effluent treatment Anew cellulose nanocrystallinepolysulfone composite membrane Procedia EnvironmentalSciences 16 145e151

Zhu X Y Bai R Wee K H Liu C amp Tang S L (2010) Membrane surfaces immobilizedwith ionic or reduced silver and their anti-biofouling performances Journal of MembraneScience 363 278e286

Zodrow K Brunet L Mahendra S Li D Zhang A Li Q et al (2009) Polysulfoneultrafiltration membranes impregnated with silver nanoparticles show improved biofoulingresistance and virus removal Water Resources 43 715e723

Zulfikar M A Mohammad A W amp Hilal N (2006) Preparation and characterization ofnovel porous PMMA-SiO2 hybrid membranes Desalination 192 262e270

Advances in polymeric membranes for water treatment 41

Advances in ceramic membranesfor water treatment 2M Lee Z Wu K LiImperial College London London UK

21 Introduction

211 Water treatment

Water is the most abundant natural resource on our planet but only a small percentageis accessible and fit for use in sustaining human life Many areas of the world have noaccess to safe and clean drinking water and are in urgent need of economical reliableand effective methods of treating local raw water sources In addition the global waterconsumption rate continues to increase because of the rapid rise in population andincreased industrialization and agricultural needs The strain placed on the limitedclean water supply will lead to rises in water price which can significantly increasethe operating costs in many industries where water is used extensively and in largevolumes Furthermore regulations on the quality of drinking ground surface andwastewater qualities are becoming increasingly stringent and thus effective watermanagement is of paramount importance more than ever Many industriesrsquo ideal statewould be to recycle all of their wastewater and reach a lsquozero-dischargersquo conditionSignificant developments have been made over the past half-century in the water treat-ment field in particular in the development of cost-effective low-pressure membraneprocesses such as microfiltration (MF) and ultrafiltration (UF) (Judd 2010 Staff2011 Van Der Bruggen et al 2003)

212 Micro- and ultrafiltration processes in water treatment

The commercialization of cost-effective MFUF membranes may be of the most sig-nificant changes in water and wastewater treatment since the 1960s MF and UF arelow pressure-driven separation processes that are less energy-intensive than traditionaltreatment methods The two processes can separate components by a sieving mecha-nism without the need for chemical or physical pre- or post-treatment Hence they arewidely used in many applications for a range of different purposes such as removingsuspended solids bacteria and viruses and heavy metals achieving oil and water sep-aration and pretreating desalination (Lens et al 2001 Mallada amp Meneacutendez 2008)MFUF membranes are porous with pore sizes ranging from microns to nanometresthey can be easily incorporated into existing processes as a standalone unit or com-bined with other technologies

A hybrid system that has broadened the use of MFUF in wastewater treatment isthe membrane bioreactor (MBR) It combines the biological treatment of wastewater

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400002-2Copyright copy 2015 Elsevier Ltd All rights reserved

with a membrane filtration process and is commonly used to treat industrial and munic-ipal wastewater (Judd 2008 2010 Meng et al 2009) However fouling and replace-ment costs of polymeric membranes still challenge the widening and large-scale useof MBRs Although the capital costs of ceramic membranes are higher their robust-ness higher resistance to microorganisms and ease of cleaning lead to lower main-tenance and replacement requirements cutting down long-term operating costs andoffering a competitive alternative to polymeric systems (Gander Jefferson amp Judd2000 Judd 2008)

213 Ceramic membranes in water treatment

Ceramic membranes may be an alternative material for use in MFUF applications inthe place of polymeric membranes Because of their superior chemical thermal and me-chanical properties they can be backwashed cleaned with harsh cleaning agents andsterilized at high temperatures offering reliable performance over longer periods oftime Ceramic membranes have found commercial success in applications in whichthe operating conditions are harsh such as at high temperatures and in aggressive chem-icals (solvents and highly acidic or caustic solutions) Examples of successfulcommercial-scale plants that use MFUF ceramic membranes include purifying andconcentrating valuable components such as enzymes and (Krstic et al 2007) clarifyingfermentation broths in biotechnology industries (Finley 2005 Sondhi Bhave amp Jung2003) clarification of fruit or sugar cane juices (Daufin et al 2001 Girard FukumotoampSefa Koseoglu 2000 Sondhi et al 2003) and treatment of highly oily wastewaterand degreasing baths (Cheryan amp Rajagopalan 1998 Majewska-Nowak 2010)

In contrast ceramic membranes are much less commonly used in water and waste-water treatment such as for the production of drinking water and treatment of munic-ipal wastewater This has historically been because of their high fabrication costscompared with commercially available polymeric membranes Common configura-tions of ceramic membranes include flat-sheet tubular and monolith elements asshown in Table 21 They are normally thicker than polymeric hollow-fibremembranes leading to lower packing densities They are also intrinsically brittleand therefore more expensive to pack and seal

However as the result of sustainable developments in ceramic membranescheaper more effective higher-performing and more compact ceramic systems canbe formed potentially allowing the widening of their applications Table 21 listssome current major international ceramic MFUF membrane suppliers Tubularmonolithic and flat-sheet ceramic membranes currently dominate over hollow-fibremembranes with great water permeation fluxes

22 Development in ceramic membranes and theirfabrication processes

Amembrane can be defined as a semi-permeable active or passive barrier which whenplaced under a certain driving force separates one or more selected species or

44 Advances in Membrane Technologies for Water Treatment

Table 21 List of commercially available ceramic membranes for MFUF

Company Product Material

Technical specifications

Pore size (mm)

Channeldiameterouterdiameter(mm)

Packingdensity(m2m3)

Purewater flux(L(m2hbar))

Flat sheet ItN NanovationAG

CFM Systems

(Itn-nanovation waterfiltration Itn-nanovation Filtrationrack Itn-nanovationT-series)

Substratea-Al2O3

Selectivelayera-Al2O3ZrO2

02 30e 918 e

MeidenshaCorporation

Ceramic membrane unit(Ceramic membraneunit 2013)

a-Al2O3 01 e 361 1670

LiqTechInternationalInc

Silicon carbide flat sheetmembrane (Liqtech)

SiC 02 e 377 e

Flat disc LiqTechInternationalInc

Silicon carbideFlat disc membrane(Liqtech Dynamic)

SiC 004 01 10 e e 3000 400010000

Tubularmonolith

Tami Industries CeacuteRAM (Inside ceacuteram)ISOFLUX (Isoflux)

e MF 014e14UF MWCO1 kDae150 kDa

e e e

AtechInnovationsGmbH

Ceramic membranes(Atech-innovations)

MF a-Al2O3

UF TiO2

MF 01e12UF up to 005and MWCO5 kDa

25e80100e520

e e

Continued

Table 21 Continued

Company Product Material

Technical specifications

Pore size (mm)

Channeldiameterouterdiameter(mm)

Packingdensity(m2m3)

Purewater flux(L(m2hbar))

LiqTechInternationalInc

SteriMem (LiqTech SiCSteriMem) CoMem(COMEM) CoMemConduit (COMEM

CONDUIT) andAquasolution(AQUASOLUTION)

SiC 004 01 10 30e170250e1460

e e

Pall Corporation Membralox (Pall

MembraloxMembralox)

Substrate Al2O3

Selective layerMF Al2O3 orZrO2

UF TiO2

MF 01e50UF 002e01and MWCO1e5 kDa

30e60e 285 e

Veolia WaterLtd

Ceramem

(TundrasolutionsCeraMem Full-sizemembrane modules2013 Veoliawaterst ampCERAMEM)

MF a-Al2O3SiC TiO2

UF SiC SiO2TiO2

MF 01e05UF 0005e005

20e501420 782 MF 400e1200UF 200e800

Hollowfibre

Hyflux Ltd InoCep (Inocepmembrane InoCep)

a-Al2O3 002e14 3040 157 250e4500

Media andProcessTechnologyInc

MPT hollow-fibremembranes (Mediaand process)

a-Al2O3 0004e02 10e35e 502 e

components of a liquid mixture whilst the rest is rejected (Mulder 1996) Micro- andultrafiltration are low pressure-driven processes in which physical separation ofthe different-sized feed components is achieved via a sieving mechanism across themembrane with a specific pore size

In 1989 the Membrane Technology and Research Inc (MTR) performed a studyaddressing the research priorities in the membrane separation industry (Ruutenhuch1992) For MF and UF the highest priority research topics include fouling-resistantlong-life membranes that are high temperature solvent wide pH and oxidant resistantlow-cost membrane modules and low energy module designs Although the study wasperformed more than 20 years ago many of the issues still remain as importantresearch areas today The development of cheap asymmetric inorganic membraneswith high packing densities can be seen as a possible solution to most of the challengeslisted above Significant progresses have been made in recent years regarding theceramic membranes and their fabrication processes

221 Desirable membrane characteristics and their design

To understand the type of membrane properties desired for pressure-driven membraneprocesses it is important to understand the membrane transport mechanisms Transportmodels can help identify the structural parameters that affect the membrane perfor-mance Different pore geometries exist depending on the fabrication processes andhence different models can be used to describe the transport through these different ge-ometries For example the pores can be depicted as parallel cylinders or a network oftightly packed spheres For pores formed from voids between tightly packed spheresthe CarmaneKozeny relationship can be used to describe membrane flux assumingno interaction exists between the fluids and surface of the membrane (Mulder 1996)

J frac14 ε3

khS2eth1 εTHORN2Dp

Dx(21)

where J is the membrane flux (m3(m2 s)) k is the CarmaneKozeny constant(depending on pore shape and tortuosity) ε is the porosity S is the specific surface area(m2m3) h is the permeate viscosity (N sm2) Dp is the pressure difference (Nm2) andDx is the membrane thickness (m) Membrane selectivity and permeation flux aremajor indicators of membrane performance Eqn (21) shows that structural parameterssuch as high porosity narrow pore size distribution and thin membrane thickness arealways desirable for improved membrane performance The different characteristics ofthe membrane can be designed and tailored using different fabrication techniques andcontrolling the related fabricating parameters during the course of production

222 Material and microstructure

Various membrane materials are available for MFUF processes The choice of themembrane material affects the practicality and sustainability of the filtration operationand hence can be chosen based on the specific application requirements

Advances in ceramic membranes for water treatment 47

Examples of ceramic materials include alumina (g-Al2O3 and a-Al2O3) zirconia(ZrO2) titania (TiO2) glass (SiO2) and silicon carbide (SiC) Ceramic membranesoffer superior temperature and chemical tolerances leading to an extensive range ofapplications across many industries They can be an important and environmentallyfriendly component in helping companies achieve a lsquozero-dischargersquo state Howeverthe main drawback of using ceramic membranes for water treatment is their highcapital cost hence large-scale membrane applications or less challenging water puri-fication processes are still dominated by polymeric membranes As shown in Table21 commercial ceramic membranes for MFUF processes consist mainly ofa-Al2O3 as the substrate and a-Al2O3 TiO2 or ZrO2 as the selective separation layerAccording to experiments in the literature there is a general consensus that chemicalstability (in highly acidic or basic environments) decreases with the following trendTiO2gt ZrO2gt a-Al2O3gt g-Al2O3gt SiO2 (Hofman-Zeurouter 1995 Mallada ampMeneacuten-dez 2008 Van Gestel et al 2003) Generally inorganic membranes can withstandorganic solvents chlorine and other oxidants are less susceptible to microbial attackthan polymeric membranes and can be used at pH values close to 0 and up to 14 (TiO2and a-Al2O3) (Hsieh 1996 Mallada amp Meneacutendez 2008)

Ceramic membranes are generally accepted to have high mechanical strengthBecause of this they can be backwashed at elevated pressures and operated over alonger period of time compared with polymer membranes (Guerra Pellegrino ampDrewes 2012 Sondhi amp Bhave 2001) However a disadvantage of ceramic mem-branes is their brittleness hence they must be handled with care and the choice ofhousing and sealing should be carefully considered The pressure required to driveMF is 01e2 bar and much higher for UF (Van Der Bruggen et al 2003) Themaximum operating pressure specified by a hollow-fibre ceramic membrane manufac-turer is 6 bar (Hyfluxmembranes InoCep) much higher than the 25-bar maximumallowable for polyethersulphone (PESf) membranes (Hyfluxmembranes Kristal)

As mentioned in Section 21 the microstructure across the membrane cross-sectionand surfaces is a key property that dictates the performance and usability of amembrane for a certain applications A membrane can be categorized into symmetricand asymmetric structures A symmetric membrane has a uniform cross-sectionthroughout whereas an asymmetric membrane does not as shown in Figure 21(a)and (b) (or Figure 21(c)) respectively

For MF and UF processes asymmetric membranes consisting of a thin skin layer ontop of a porous sub-layer are desired The top layers of UF membranes are much denserthan MF membranes hence they require higher trans-membrane pressures and gener-ally have lower permeability The asymmetric structures are associated with higherpermeation flux because the effective membrane thickness can be much thinnerthan in symmetric membranes The porous sub-layer acts to provide adequate mechan-ical strength This type of structure combines high selectivity of the skin layer withgood permeation fluxes

An asymmetric membrane can be integral or made of several layers known as acomposite The top and porous layers of an integral asymmetric membrane are normallymade of the same material (Figure 21(c)) and for composite membranes the top skinlayer and the porous sub-layer can be made of different materials (Figure 21(b))

48 Advances in Membrane Technologies for Water Treatment

A composite membranersquos properties and performance can be tailored usingdifferent materials in different layers Some disadvantages of composite membranesinclude the high complexity of the membrane fabrication process which requiresmany steps and the possibility of membrane failure owing to delamination of theseparation layer which occurs during sintering or variations in filtration pressures(wang Jerome Morris amp Kesting 1999) Integral membranes are homogeneous incomposition but can also be highly structurally varied in layers or distinct regionsdepending on their fabrication methods

As shown in Figure 21(c) and (b) the cross-sectional microstructure of the integralmembrane and the composite membrane vary significantly even though both are asym-metric membranes The integral membrane in Figure 21(c) is normally achieved viathe combined phase inversionsintering method (Li 2007) whereas the composite inFigure 21(b) is made by skin deposition on top of a multi-layer substrate supportThe integral membrane consists of two different types of sub-structures sponge-likeand finger-like The sponge-like structure can provide the membrane with the desiredselectivity and the finger-like structures can reduce the overall membrane resistance to

Figure 21 Scanning electron micrograph of the cross-section of (a) a symmetric aluminasubstrate (Reprinted from Kingsbury and Li (2009) with permission from Elsevier) (b) a three-layered alumina membranesupport composite (Reprinted from Hsieh Bhave and Fleming(1988) with permission from Elsevier) and (c) an asymmetric integral alumina membrane(Reprinted from Kingsbury et al (2010) with permission from Elsevier)

Advances in ceramic membranes for water treatment 49

permeate flow On the other hand the composite membrane consists of pores formedby voids between the particle packing only and the membrane selectivity is providedby the finer particles at the top layer and at a lower magnification the entire cross-section will appear to have a sponge-like structure

Integral and composite ceramic membranes can be made via different fabricationmethods the choice of method will largely depend on the membrane configurationand microstructures that are desired

223 Membrane configurations

There is a wide variety of membrane geometries available depending on the shapeformation technique chosen in the fabrication process Ceramic membranes exist intwo main types of element configurations ie flat and cylindrical The choice of mem-brane configuration depends largely on the application such as the required operatingand feed conditions

2231 Flat membranes

Flat ceramic membranes can come in a disc or sheet form The packing density of discmembranes is generally low and hence they are limited to use in small-scale industrialmedical and laboratory applications Commercial ceramic flat-sheet membranes mayhave thicknesses of around 6 mm and can be multi-channelled across their cross-section as shown in Table 21 and Figure 22 Flat-sheet membranes are easy toreplace when packed in modules and can handle high-turbidity feeds Mechanicalcleaning of ceramic flat-sheet membranes is also versatile it can withstand air scrub-bing backwashing and high-pressure water jet cleaning

Figure 22 Product photographof a commercial multi-channelledalumina flat-sheet membrane(CFM Systems)From ItN Nanovation AG(CFM-Flyer) (Reproduced bypermission of ItN NanovationAG)

50 Advances in Membrane Technologies for Water Treatment

2232 Cylindrical membranes

Single-channel tubular membranes generally have diameters of between 10 and25 mm shown in Table 21 and Figure 23 They are more suitable for separating feedsthat have high turbidity and large amounts of suspended solids Because of their largerdiameters and robustness they can be more easily cleaned mechanically and highcross-flow velocities can also be used to control fouling To further improve the pack-ing density of the tubular membranes they can be fabricated as multi-channel tubescalled monoliths with a surface area to volume ratio up to 782 m2m3 as shown inTable 21 In an effort to improve the packing density hexagonal monoliths werealso developed by Pall Corporation (Pall Membralox) (Figure 23(a)) Monolithmembranes offer the same advantages as singular tubular membranes Howeverwhen running in the inside-out configuration the pressure drop of the permeateflow across the monolith could be high as a result of the long and tortuous path ithas to travel to reach the outer surface of the monolith which limits the size of theouter diameter that can be used The patented CeraMem from Veolia Water Ltd (Tun-drasolutions) solves this problem by adding multiple conduits across the monoliththrough which permeate will flow through and then be collected at the end of the mod-ule (Figure 23(c))

Ceramic hollow-fibre membranes have diameters of 20e40 mm (Han et al 2011Kingsbury amp Li 2009 Liu Li amp Hughes 2003 Tan Liu amp Li 2001) (Figure 24)which means that compact modules with highly effective membrane surface areas can

(a) (b)

(c)

Figure 23 Product photograph of (a) Pall Corporation Membralox multi-channelled aluminamembranes (Pall Membralox) (Image courtesy of Pall Corporation) (b) LiqTech Interna-tional Incrsquos SiC SteriMem products (LiqTech SiC SteriMem) (Reproduced by permission ofLiqTech International AS) and (c) Veolia Water Ltd CeraMem element (Tundrasolutions)(Reproduced by permission of Veolia Water Technologies)

Advances in ceramic membranes for water treatment 51

be achieved Furthermore Fraunhofer IGB Ltd stated that ceramic hollow fibres withan outer diameter as low as 05 mm have been fabricated via combined phase inversionand sintering (Ceramic capillary membranes) potentially increasing the packingdensity that can be further achieved In addition they require lower trans-membranepressures to drive permeate flow because of the thinner membrane and can be cleanedeasily using methods such as backwashing and forward flushing

224 Fabrication techniques

Fabrication of composite ceramic membranes is generally a multi-step process It cangenerally be broken down into three different stages preparation of the ceramicpowder paste or suspension shaping of the ceramic powder into the desired geometryand heat treatment which includes calcination and sintering (Li 2007) After thesemain steps additional layer deposition followed by further heat treatment steps cantailor membrane selectivity as well as other membrane properties The choice ofmethod for each step depends on the desired membrane configuration qualitymorphology mechanical and chemical stability and selectivity of the final membranesHowever the fabrication method should also be economical and easy to replicatewithout compromising the quality of the final membrane

2241 Ceramic powder paste and suspension preparation

The ceramic powder preparation stage processes the raw inorganic material intothe shape and size distribution desired for membrane fabrication This can be in the

Figure 24 Product photograph of hollow-fibre alumina membranes from Hyflux Ltd(InoCep) (Reproduced by permission from Hyflux Ltd)

52 Advances in Membrane Technologies for Water Treatment

form of milling or chemical particle preparation Often the ceramic powder is madeinto a paste or suspension so that shape formation is possible During this step addi-tives can also be introduced to the ceramic material The choice of suspension mediumadditives and powder is important and affects the membranersquos microstructure andquality Deflocculants or dispersants often in the form of various fatty acids and esterscan be added to stabilize the ceramic particles in suspension to achieve high particleloadings and continuously high-quality ceramic membranes (Calvert et al 1986 Li2007 Sushumna Gupta amp Ruckenstein 1992 Zeurourcher amp Graule 2005) Magnesiumoxide has been used as a sintering additive to lower the sintering temperature requiredto form alumina hollow-fibre membranes via a combined phase-inversion and sinter-ing method (Choi et al 2006) Other additives such as the polymer binder are used tomaintain the shape of the ceramic membrane precursor and plasticizers can be usedto increase flexibility and ease of handling of the suspensions for tape casting or extru-sion methods (Burggraaf amp Cot 1996)

2242 Shaping

The shaping step is the physical process whereby the ceramic material is transformedfrom a suspension or powder paste form into the membrane geometry Methods thatcan create ceramic membranes and substrates include pressing tape casting slip cast-ing extrusion phase inversion foam techniques and leaching techniques

Pressing is a simple and quick method for producing flat ceramic membranes (Silvaet al 2012 Wang et al 2008a Xin et al 2007) A force is applied over an area ofceramic powder (varying from 10 to 100 MPa (Drioli amp Giorno 2010)) until the parti-cles are consolidated This method produces membranes of a symmetric structure owingto the uniform force applied across the area of ceramic material and are commonly usedto make disc membranes Meanwhile this method is not flexible in fine-tuning micro-structures and there is a limitation on the thickness to diameter ratio of the membranethat can be achieved In addition it is a batch fabrication process and has been usedprimarily to make membranes for use in laboratories rather than commercially

The tape casting method is used to form flat-sheet ceramic membranes (Das ampMaiti 2009 Das et al 1996 Lindqvist amp Lideacuten 1997) A tape cast suspension is firstprepared with the ceramic material a liquid-dispersing medium and organic additivesto provide the suspension with pseudo-plastic behaviour Then the suspension is trans-ferred into a reservoir controlled by a blade that can be height adjusted over a mobilecarrier film Subsequently the suspension film is dried in a controlled environmentTape casting is a more flexible method that can make flat-sheet membranes as wellas coat layers onto membrane supports

Slip casting uses a porous mould to form the shape of the ceramic membrane(Falamaki amp Beyhaghi 2009 Lin amp Tsai 1997) When the ceramic suspension ispoured into the mould the solvent is extracted into the pores of the mould as a resultof the capillary force leaving ceramic particles on the surface of the mould Slip cast-ing is commonly used to form tubular membranes with high surface quality densityand uniformity Important factors that affect the final quality of the membranes createdvia this method include slip density and viscosity

Advances in ceramic membranes for water treatment 53

Extrusion is a method popular for fabricating tubular monolith and hollow-fibrecapillary membranes (Castillon amp Laveniere 1995 Feenstra Terpstra amp Van Eijk1998 Smid et al 1996 Terpstra Bonekamp amp Veringa 1988 Wang et al 1998)It is a process in which an inorganic stiff paste is forced through an orifice of adesigned shape and compacted by applying high pressure The paste must have plasticproperties to form and maintain the shape of the membrane precursors hence addi-tives are added to the ceramic powder The paste is then forced through a die athigh pressure (around 20 MPa) to produce hollow tubes

Combined phase-inversionsintering (Kingsbury amp Li 2009 Liu et al 2003 Tanet al 2001) is a relatively new method for fabricating microstructured ceramic hollow-fibre membranes Solventenon-solvent exchange-induced precipitation of the poly-meric binder and viscous fingering phenomenon occur during membrane fabricationwhich distinguishes this method from conventional ram extrusion and will be furtherintroduced in Section 25

2243 Heat treatment

After the forming step the ceramic membrane precursors are produced They are thendried and treated with heat This heat treatment step consists of three main steps (Li2007) pre-sintering thermolysis and final sintering with the purpose of removingcomponents other than the ceramic material to strengthen the membrane and consol-idate the microstructure and dimensions of the final membrane

Presintering occurs at around 200 C Presintering is used to remove water from themembrane precursors which may be in the form of water chemically bonded to theceramic particle surfaces or as crystallized water within the inorganic phases Thermol-ysis or the calcination step is the process by which all organic components in the mem-brane precursor are removed The sintering stage is where the major changes to theporosity and pore size occur the final shape of the ceramic membrane is consolidatedand mechanical strength is improved In general the higher the sintering temperaturethe higher the mechanical strength but the porosity of the final membrane is lowered

Important parameters that affect thermal stability of ceramic membranes are sinteringactivity and phase transformation of the membrane material and the support (Mallada ampMeneacutendez 2008) During sintering the ceramic material is kept at a certain temperaturelong enough for the material to approach its equilibrium structure The membrane struc-ture can be maintained for temperatures up to 100e150 C below the sintering temper-ature which is normally extremely high (over 1000 C) (Burggraaf amp Cot 1996)

2244 Layer deposition for composite membranes

Additional layer deposition can be used to alter or enhance the ceramic membraneproperties for example by changing the membrane selectivity porosity hydrophilic-ity conductivity permeability biocompatibility etc

To form composite membranes layer deposition methods are required to add layersonto a symmetric substrate Each layer normally consists of ceramic particles ofdifferent sizes to achieve a gradient pore structure across the membrane cross-section Multiple layers are normally required to reach the desired selectivity at the end

54 Advances in Membrane Technologies for Water Treatment

Dip or spin coating is the most commonly used method for layer deposition onto asupport (Babaluo et al 2004 Gu amp Meng 1999 Lindqvist amp Lideacuten 1997) Dipcoating is when a support is dipped into and then withdrawn from a ceramic powdersuspension Upon withdrawal from the suspension the liquid will be sucked into thesupport pores because of capillary forces along with the ceramic particles if they aresmall enough in size Spin coating rotates the substrate while the suspension is depos-ited over the substrate surface

Sol-gel method can be used to fabricate membranes with high selectivity with poresfrom 100 nm down to a few nanometres and is commonly used to form ceramic UFmembranes (Agoudjil Kermadi amp Larbot 2008 Das amp Maiti 2009 Hao et al2004 Kim amp Lin 1998 Larbot et al 1988 Wu amp Cheng 2000) A colloidal (consistsof alkoxide) or polymeric solution is first deposited over a membrane substrate bymeans of dip coating whilst it is converted into a gel form by hydrolysis and conden-sation or polymerization Afterward it is heat treated to form a thin and uniform skinover the membrane

There are many other coating techniques such as chemical vapour depositionneutron sputtering and plasma details about these can be found elsewhere(Burggraaf amp Cot 1996 Hsieh 1996 Li 2007)

225 Combined phase-inversion and sintering fabricationtechnique

As described in the previous section the traditional and common method for pro-ducing hollow-fibre membranes is to use extrusion followed by sintering Howeverthis would give rise to symmetric membranes and additional layer deposition andheat treatment steps are required to produce the required selectivity with a gradientpore size along the membrane cross-section as shown in Figure 21(b) An alter-native and innovative method for producing ceramic hollow-fibre membranes isthe combined phase-inversion and sintering technique (Choi et al 2006 Kings-bury amp Li 2009 Kingsbury Wu amp Li 2010 Koonaphapdeelert amp Li 2007Liu et al 2003 Tan et al 2001 Wang et al 2008b Wang et al 2009 Weiet al 2008) It is a flexible technique that can produce both symmetric ceramicmembranes and a wide range of asymmetric ones in a single step for both flat-sheet and hollow-fibre geometries as shown in Figure 21(a) and (c) Because ofthe presence of large finger-like structures they can reduce mass transfer resistancefor permeation fluxes competitive to the membranes formed via conventionalmethods

A suspension consisting of ceramic particles and polymer binder in a solvent is firstprepared and then through solventenon-solvent exchange induced phase inversion ofthe polymer binder the ceramic particles are immobilized in their desired geometry bycasting (flat membrane) or spinning (hollow-fibre membrane) This method can easilytailor and form membrane precursors with various specific morphologies Thensimilar to all other ceramic fabrication methods the membrane precursors undergo aheat treatment session (Section 243) to remove all organics as well as consolidatethe final membrane structure and mechanical strength

Advances in ceramic membranes for water treatment 55

Preparation of the ceramicesolventepolymer suspension solution is a step that hasa major impact on the properties of the final membrane The particle size and particlesize distribution of the ceramic components can affect the pore size and selectivity ofthe membrane as well as the suspension rheology Porous alumina hollow-fibremembranes developed using this method have selectivity in the MF range when1-mm particles are used (Kingsbury amp Li 2009) and in the UF range when mixturesof 001- and 1-mm particles are used (Tan et al 2001) Yttria-stabilized zirconia(YSZ) porous membranes have pore sizes in the UF range when polydispersed YSZparticles (01 and 002 mm) are used (Wei et al 2008) Other factors such as theceramic to polymer binder ratio can affect the mechanical strength and quality ofthe sintered membrane and a ratio of up to 10 has been suggested (Kingsbury ampLi 2009 Tan et al 2001)

Although the process of spinning ceramic hollow-fibre membranes is similar tospinning polymeric ones the rules and optimization of the polymeric spinning systemcannot be applied directly to the ceramic spinning process because of the significantlydifferent composition of the spinning suspension The presence of a large amount ofceramic particles also changes the mechanisms behind the formation of the differentmembrane sub-structures Two basic sub-structures have been achieved within themembrane cross-section sponge-like denser structures and finger-liker structuresthat can be isolated or micro-channels as shown from Figure 25 The positioningand dimensions of these different sub-structures can be tailored mainly by changingthe parameters during spinning

Improved understanding of spinning parameters such as the air gap bore fluidchoice and bore fluid flow rate on the alumina membrane morphology was achievedby Kingsbury and Li (Kingsbury amp Li 2009 Kingsbury et al 2010) The designingand engineering of the two types of sub-structures led to distinctively differentmembrane morphologies (Figure 25) and generated a string of potential applicationsThese applications include hollow-fibre membrane micro-reactors membrane contac-tors solid-oxide fuel cells gas separation etc (Kanawka et al 2011 Kingsburyet al 2010 Koonaphapdeelert Wu amp Li 2009 Othman et al 2012 Rahman et al2011) In particular the morphology consisting of one sponge-like skin layer on topof a layer of finger-like micro-channels (Figure 25(d)) is expected to dramaticallyreduce the trans-membrane resistance to permeate flow The single thin separation layerprovides the membrane with its selectivity and the finger-like micro-channels canreduce the mass transfer resistance significantly This morphology is expected to excelin aqueous MFUF applications compared with conventional composite asymmetricceramic membranes

Current research has made significant progress in understanding the effects ofdifferent process parameters on membrane morphology and properties but the scientificmechanisms behind the formation of different sub-structures need further researcheffort In recent years the common viscous fingering phenomenon has been appliedto explain formation of the finger-like structures in the ceramicepolymeresolventand non-solvent systems (Kingsbury amp Li 2009 Kingsbury et al 2010 Wang ampLai 2012) Viscous fingering is a hydrodynamic phenomenon in which a less viscousfluid displaces a more viscous fluid forming finger-like patterns Important factors that

56 Advances in Membrane Technologies for Water Treatment

affect the initiation propagation and termination of these finger-like structures includeviscosity difference density difference moving interface velocity and polymer precip-itation rate Finger-shielding coalescing and spitting of the finger-like structures havealso been observed (Wang amp Lai 2012) A clearer understanding of the mechanismsbehind the formation of the unique sub-structures would allow easier and moreadvanced designing of the different morphologies and engineering of the productionprocess

The combined phase-inversion and sintering technique has been successfullyapplied to a wide range of ceramics as well as metals with a range of different pore sizes(Liu et al 2003 Luiten-Olieman et al 2011 2012 Yang Tan amp Ma 2008 Zhanget al 2009b 2012) However a compromise always has to be made between theporosity and mechanical strength when a high sintering temperature is involved Astudy suggested the use of a controlled sintering process by using PESf as not just apolymer binder but also a pore structure lsquostabilizerrsquo (Wu et al 2013) By thermallytreating the membrane precursors the PESf is not completely removed during the firststage of heat treatment Instead some of the PESf is converted to carbon at 1450 C inan environment devoid of oxygen which allows mechanical strengthening of thealumina membranes without losing significant porosity

Figure 25 Scanning electron micrograph of (a) cross-section morphology of a symmetricalumina hollow fibre and (bed) different asymmetric alumina hollow fibres formed by combinedphase-inversion and sintering (Reprinted from Kingsbury amp Li (2009) with permission fromElsevier Reprinted from Kingsbury et al (2010) with permission from Elsevier Reprinted fromTan et al (2011) with permission from Elsevier)

Advances in ceramic membranes for water treatment 57

As a result the combined phase-inversion and sintering method can potentiallycreate the opportunity to use ceramic membranes in large-scale water and wastewatertreatments by offering a hugely reduced fabrication process cost and great flexibilitiesin microstructure design However further improvements are required before thismethod can be fully commercialized for example to improve surface porosity andpure water permeation without sacrificing its mechanical strength and to have a betterfundamental understanding of the microstructure formation mechanisms to enablereliable and reproducible fabrication process on a large scale

23 Development in membrane modules and units

The design of the membrane module is important for achieving the highest packingdensity possible for the particular membrane element whilst offering effective filtra-tion The different membrane elements are packed in a unit called a module and thesemodules are often arranged and connected in a specific way to form a unit offeringgreat efficiency The unit(s) is then integrated with other components such as pumpspipes control systems etc to form a membrane system and part of the water or waste-water treatment plant The following section describes the ceramic MFUF modulesand units available commercially

231 Module and unit designs

Many different module designs are available for the different ceramic membranes andtheir choice depends largely on the application the demand of the process and anyspatial limitations and economical factors The arrangement and packing of themembrane elements can be divided into two main types ie flat membranes andcylindrical membranes

The membrane elements may be contained in pressure vessels or immersed in afluid medium at atmospheric pressure For the contained modules the ceramicmembranes are packed and fitted inside a pressure vessel and trans-membrane pressureis applied at one end of the vessel with the feed The immersed unit allows easierreplacement of the membrane elements or modules and is also more flexible to tailorto specific needs and demands Furthermore it enables air sparging in the unit toimprove permeation and reduce fouling by promoting turbulence Both flat-sheetand cylindrical membranes can be packed in this way and this type of system requiresless energy to operate than contained units

2311 Flat membranes

Ceramic flat membranes can come in the form of flat sheets or flat discs as described inSection 231 and can both be packed into plate-and-frame modules The containedplate-and-frame configuration consists of stacking the flat membranes on top of oneanother with porous spacers in between The size of the spacing depends on the amountand size of suspended solids in the feed The feed enters the module from one end and is

58 Advances in Membrane Technologies for Water Treatment

collected at the membrane support plates Such a module is easy to operate and mem-brane defects can be detected and replaced simply However their packing density islow and so most of the time they are limited to use for small-scale applications

Flat-sheet membranes with multiple channels can be stacked next to each other andform an immersed module as shown in Figure 26 These flat-sheet membranes are con-nected at the two ends to permeate collector(s) and then packed together and supportedby a metal framework that is then immersed into the feed medium Permeate enters fromthe membranersquos outer surface into the channels inside the flat sheets and is thencollected at the end(s) of the membrane These modules can then be further stackedtogether to easily increase productivity The energy consumption of the immersed mod-ule is lower than that of the contained module because of the lower pressureedrivingforce requirements The membranes can also be replaced easily because they are pro-duced and sealed sheet by sheet In addition their ability to handle feeds with a highcontent of suspended solids means that they are commonly used inMBRs to treat waste-water Packing densities of about 918 m2m3 are reached using the CFM Systems

from ItN Nanovation AG by stacking units on top of each other (Table 21) Howeverthis is still significantly lower than the packing densities offered by polymeric flat-sheetmembranes that are spiral wound (700e1000 m2m3) (Crittenden et al 2012)

2312 Cylindrical membranes

Tubular membranes are often packed as a bundle inside a casing which could be a con-tained vessel (Figure 27) or an open vessel The feed solution may be fed though the

(a) (b)

Figure 26 Product photograph of (a) a ceramic flat-sheet module from ItN Nanovation AG(Itn-nanovation) (Reproduced by permission of ItN Nanovation AG) and (b) a ceramic flat sheetsystem from Meidensha Corporation (Ceramic membrane unit 2013) (Reproduced bypermission of Meidensha Corporation)

Advances in ceramic membranes for water treatment 59

centre of the tubular or monolith membranes and permeate is collected outside the tubein the module casing This operating mode requires high operating flow rates and thepressure drop can be large hence energy consumption is highest compared with othermodule designs However because of the relatively large channel diameters of tubularand monolith membranes they are suitable for feed streams with larger particles andcleaning these membranes is also more facile The tubular or monolith membranescan also be packed and supported by a partly open housing support and operated byimmersion into the feed solution similar to the immersed flat-sheet modules offeringsimilar advantages and disadvantages The immersed tubular modules are commonlyused in MBRs for larger-scale applications and also to treat harsh feed streams

Hollow-fibre membranes can also be packed in a similar way in their modules asshown in Figure 24 Ceramic hollow-fibre membranes are generally packed togetherand immobilized at both ends and then placed in a cylindrical housing The fullycontained module is more suited to small-scale applications such as domestic-scaledrinking water treatment Hollow-fibre modules can potentially offer a much higherpacking density and form more compact systems saving space and improving produc-tivity As shown in Table 21 the packing density offered by commercial ceramichollow-fibre modules is not as competitive (502 m2m3 offered by Media and ProcessTechnology Inc) as some of the multi-channel tubular module designs (up to 782 m2m3 offered by Ceramem module from Veolia Water Ltd) This is mainly because ofthe relatively large ceramic hollow-fibre outer diameters from most of the suppliers(3e4 mm from Table 21) Furthermore their intrinsic brittleness makes it more diffi-cult to pack them into bundles and it limits their length Hence cassette-style modulesfor ceramic hollow-fibre membranes are not available in which the hollow fibres aresupported at the top and bottom only and are immersed fully into the feed solutionwith no housing In addition the lack of open vessel designs for hollow-fibre mem-brane elements means that their application in immersed MBR is limited

Figure 27 Product photograph of a containedmodule from Pall Corporation (Pall

Membralox IC) (Image courtesy of PallCorporation)

60 Advances in Membrane Technologies for Water Treatment

232 Housing sealing and operation

Membrane modules consist of the housing sealing materials and membrane The typeof housing used for the membrane varies depending on the membrane and module typeand operating configuration For contained cylindrical membranes the membrane ispacked and enclosed in a vessel shown in Figure 28 For outside-in feed configurationor immersed cylindrical membranes the housing may have openings that exposecertain areas of the membrane element Flat-sheet ceramic membranes are normallysealed at the top and bottom to a permeate collector They are then stacked togetherand supported by a stainless-steel frame into modules such as the Meidensha Corpo-rationrsquos ceramic membrane unit (Ceramic membrane unit 2013) and ItN NanovationAGrsquos CFM System (Itn-nanovation) (Figure 26)

Typical module housing materials include stainless steel titanium and plasticStainless steel is most commonly used because of its good chemical and thermalstability as well as great robustness Although plastic housing is a cheaper option itoften limits the conditions within which the membranes can operate

The type of seal used on the membranes varies depending on the membrane andmodule type They are important because they prevent contaminant leakage into thepermeate stream Mostly O-rings and gaskets are used to cover the perimeter of themembrane ends where both the feed and permeates are exposed The material usedto seal the membranes depends on the required operating conditions of the MFUFwhich will change depending on the application Typical sealing material includesrubber silicon polytetrafluoroethylene and poly(vinyl chloride)

There are many different module designs for flat-sheet and tubular (single andmulti-channel) ceramic membranes However because of the much larger dimensionsof the flat-sheet and tubular elements their packing density is lower than the polymericmembrane modules offered which makes them less competitive for large-scale appli-cations or when space is limited in a treatment plant Hollow-fibre membrane moduleshave the potential to improve the packing density significantly but most of the onesoffered on the market have relatively large outer diameters leading to lower packing

Figure 28 Product photograph of the CeraMem contained module and housing from VeoliaWater LtdReproduced by permission of Veolia Water Technologies (Tundrasolutions)

Advances in ceramic membranes for water treatment 61

densities Commercially available hollow-fibre modules are limited for example thereare limited open-vessel modules and no cassette-style ceramic hollow-fibre modulesfor large-scale immersion applications which is a problem for their application tosmall-scale MFUF applications

24 Ceramic membranes for water treatment

Because of the high chemical and thermal stability and robustness of ceramicmembranes they have been commonly applied in applications for which polymericmembranes cannot be used because of their lower stability For example ceramicscan be used in harsh environments such as at high temperatures and in aggressivechemicals (solvents highly acidic or caustic solutions) and oily water Unlike poly-meric membranes ceramic membranes do not swell in solvent and can be treatedwith strong cleaning agents and sterilized at high temperatures and can withstandhigh pressures for backwashing All of these advantages have made long-termflux stability possible for ceramic membranes to be used on a commercial scale(Mallada ampMeneacutendez 2008) Recently ceramic membranes have garnered increasingattention for applications in milder operating conditions in which polymericmembranes dominate because of the increase in the packing density of the membranemodules and reductions in capital costs

241 Drinking water production

MF and UF membranes are used extensively in producing drinking water and canhandle both small- and large-scale capacities (Staff 2011) Small-scale MFUF appli-cations include portable membrane systems and in large-scale applications MFUFmembranes can be used as stand-alone or hybrid systems in a water treatment processtrain This market has been and is still currently dominated by polymeric membranesbut recently the incorporation of ceramic membranes to produce drinking water hasbeen increasing (Bottino et al 2001 Li et al 2011 Mahesh Kumar Madhu ampRoy 2007 Muhammad et al 2009) Water sources used to produce drinking watercan vary considerably from groundwater lakes and rivers to municipal wastewaterand seawater The final water that is safe to drink must fulfil standards set by the WorldHealth Organisation or by the European Union and be free of suspended solidsmicroorganisms and harmful chemicals

Small-scale ceramic membrane MFUF systems can serve several purposes such asto improve the quality of tap water reduce the volume or recycle household waste-water provide safe drinking water in remote areas with limited resources such as dur-ing camping or hiking and provide safe drinking water in developing nations or duringhumanitarian crises

To produce drinking water from surface water for a large community e in otherwords for municipal use e large systems are required The water purification processwill consist of a process train of different steps Because the design of the process

62 Advances in Membrane Technologies for Water Treatment

depends on the feed quality and the final water quality preparing drinking water fromsurface water is much more expensive because it requires more purification steps Atypical process train for purifying surface water consists of a pre-filtration unit addi-tion of chemicals natural filtration disinfection fine filtration and preservation andstorage Ceramic MFUF membrane units may be used to replace conventional particleremoval units such as coagulation and sedimentation as well as disinfection unit(s)Furthermore the ability to reject microorganisms bacteria and viruses can reducethe amount of chemicals required to be added to drinking water saving considerablespace overall For the production of drinking water from seawater ceramic MFUFunits may be used to provide pre-treatment to reverse osmosis

Studies in literature have shown that ceramic MFUF membranes alone can providepermeate turbidity low enough for drinking standards and are effective in removingmicroorganisms organic matter and disinfection byproduct (DBP) precursors (Bottinoet al 2001 Harman et al 2010 Muhammad et al 2009) Because of the hydrophilicand inorganic characters of the ceramic membranes they are less affected by organicfouling compared with polymeric membranes (Hofs et al 2011) However high-turbidity water (up to 80 NTU) can lead to membrane fouling and significant permeateflux declination which can be recovered via chemical cleaning The membrane poresize also appears to affect the rate of flux decline because Harman et al suggestedthat the smaller 4-nm pore-size membrane fouls mainly by forming a cake layerwhereas pore clogging may dominate in the larger 10-nm pore-size membrane(Harman et al 2010)

To minimize the effect of fouling much research has been carried out to analyse theperformance of hybrid ceramic membrane systems such as the combination of ceramicmembrane MFUF with activated carbon for natural organic matter (NOM) removal(Karnik et al 2005b Konieczny amp Klomfas 2002 Lee Park amp Yoon 2009 Stoquartet al 2012) coagulation for reducing organics and viruses (Fiksdal amp Leiknes 2006Konieczny Bodzek amp Rajca 2006 Lerch et al 2005 Matsushita et al 2005) photo-catalytic reactions (Alem Sarpoolaky amp Keshmiri 2009 Chin et al 2007 Mozia2010) and ozonation to remove NOM (Karnik et al 2005a Kim et al 2008) andsubsequent formation of DBPs (Karnik et al 2005b) The use of the coagulationand MFUF hybrid system is preferred from an economic point of view

242 Municipal wastewatersewage treatment

Treatment and recycling of municipal wastewater is common and a highly importantpart of todayrsquos water management Municipal wastewater consists of household com-mercial and institutional wastewater A typical sewage treatment plant consists of thefollowing steps pre-treatment to remove large and heavy debris followed by primarytreatment used to remove the suspended inorganic and some organic particles and thensecondary treatment for the biological conversion of dissolved and colloidal organicsinto biomass and finally tertiary treatment for the further removal of suspended solidsor nutrients and disinfection

MFUF can be incorporated in the treatment train as stand-alone processes or com-bined with the activated sludge process to form hybrid systems such as the MBR

Advances in ceramic membranes for water treatment 63

This can reduce the steps in secondary and tertiary treatment for example eliminatingthe need for sedimentation and secondary disinfection saving space as well as reducingwaste such as DBPs that need to be treated and disposed of Ceramic membranes can beused to replace the traditional polymeric membranes for sewage treatment because thequick fouling of polymeric membranes limits them to short operating lifetimes Theycan be cleaned under harsher cleaning conditions and therefore offer longer andmore reliable operation as well as less servicing and maintenance reducing long-term operating costs Flat-sheet and cylindrical membrane elements are suitable forbeing combined with MBRs and the modules can be operated in the immersed modeor as a separate external unit The immersed mode consists of the membrane moduleimmersed in the aeration basin and permeate is extracted via suctioning The externalconfiguration consists of pumping the mixed liquor at high pressure through themembrane from one surface Because of the higher trans-membrane pressure requiredfor the external configuration their permeate flux is also generally higher (Marrot et al2004) However the energy and space consumption of the immersed configurationtends to be lower which makes them more suited to large-scale wastewater treatment

Many studies have been carried out to analyse the effectiveness of ceramic MBRsystems to treat municipal wastewater (Waeger Delhaye amp Fuchs 2010 Xinget al 2000 Xu et al 2003 Zhang et al 2009a) Xing et al (2000) looked at usingexternal cross-flow ceramic UF MBRs for urban wastewater reclamation The systemprovided high removal efficiency removing carbon oxygen demand (COD) of anaverage of 97 and the reclaimed water could be reused directly for municipal orindustrial purposes after additional treatment (Xing et al 2000) The lab-scaleimmersed ceramic MBR offered COD removal of more than 92 during the courseof a prolonged sludge retention time (142 days) to treat simulated high-strength waste-water (consisting of glucose and protein) (Sun Zeng amp Tay 2003) Using longersludge retention times can reduce the amount of sludge produced and cut down onthe cost of sludge treatment

Fouling was mainly affected by the membranersquos microstructure surface roughnessand pore sizes in immersed ceramic bioreactor systems (Jin Ong amp Ng 2010) Theceramic membrane with the roughest surface and largest pore size (03 mm) has thehighest fouling potential whereas the membrane with the smoothest surface and small-est pore size (008 mm) fouls the least Air sparging has been found to be an effectivesimple and economical method to improve permeate flux and reduce concentrationpolarization and fouling in external-loop air-lift ceramic MBRs and the immersedceramic MBR (Fan et al 2006 Sun et al 2003 Zhang et al 2009a) AnaerobicMBRs may have lower energy consumption (Liao Kraemer amp Bagley 2006) How-ever inorganic fouling in anaerobic MBRs by struvite has been observed in ceramicmembranes (Kang Yoon amp Lee 2002) and requires periodic alkaline backflushingto recover permeate flux

243 Industrial wastewater treatment

The composition of industrial wastewater varies dramatically across the industries andthe choice of membrane technology will vary according to the contaminants Because

64 Advances in Membrane Technologies for Water Treatment

of increasingly stringent regulations on waste discharge and the increasing cost ofclean water industries are more motivated to treat and recycle wastewater whichcan potentially save significant operating costs

Typical contaminants in industrial wastewater are suspended solids particulatescolloids bacteria and viruses dissolved inorganics such as heavy metals salts nuclearwastes acids or alkalis volatile organics such as aromatics aliphatics alcohols andhalogenated hydrocarbons and non-volatile organics such as phenolics polyaromaticcompounds pesticides insecticides surfactants and dyes Similar to sewage treatmentMBRs are a popular treatment unit in the treatment train Upstream and downstreamtreatment units will vary depending on the desired quality of the final effluent(ultra-pure water process water etc) Ceramic MBRs are commonly used for small-scale treatment of high-strength industrial wastewater because they are robust stableand reliable

244 Produced water

Produced water is the largest waste stream generated from oil and gas operations MFUF is a promising technology for use to treat produced water because it is a low-energyconsumption process and can cut down on the amount of harsh and expensive chem-icals required to treat the wastewater Polymeric membranes have been commonlyused to remove organic contaminants as well as suspended particles before desalina-tion so that the water can be reused However because the feed has a high compositionof organic contaminants oil and grease the polymeric membranes can be degradedand fouled easily requiring regular replacement Ceramic membranes offer higherstability in such conditions and may prolong the lifetime of the membrane and canalso be cleaned more easily

Many studies have been carried out to investigate the performance of ceramicmembranes in oilewater treatment in the laboratory or on a pilot scale (AshaghiEbrahimi amp Czermak 2007 Chen et al 1991 Ebrahimi et al 2010 Li amp Lee2009) Studies showed that using MFUF ceramic membranes gives permeate streamsof very high quality with less than 6 ppm total hydrocarbons and perform better thanpolymeric membranes However an important limitation is permeate flux decline as aresult of fouling by waxes and asphaltenes Backwashing is a useful cleaning methodto prevent permeate flux decline (Abadi et al 2011)

245 Food and beverage industries

MF and UF are important processes in the food and beverage industries They can beused to achieve clarification sterilization concentration and purification of the finalproduct in place of multiple traditional process units For the dairy industry MF canbe used to clarify cheese whey (Skrzypek amp Burger 2010) and to concentrate anddefat milk and sterilize it by rejecting microorganisms (Fernandez Garciacutea AlvarezBlanco amp Riera Rodriacuteguez 2013) In the sugar-refining and beverages industryMF and UF membranes are used to clarify products such as maple syrup wine

Advances in ceramic membranes for water treatment 65

beer juice and vinegar (Ceramic membranes 2000 Fukumoto Delaquis amp Girard1998 Gan et al 1999 Hinkova et al 2002 van der Horst amp Hanemaaijer 1990Li et al 2010) Wastewater generated in these industries can also be recycled withthe help of MFUF membranes to save operating costs Ceramic porous MFUFmembranes have demonstrated success in the food and beverage industries offeringsuperior long-term performance in these applications over polymeric membranes

246 Commercial ceramic applications

Ceramic membranes have been implemented commercially in the industriesmentioned in Sections 41e45 to treat aqueous feeds In terms of producing drinkingwater there are far fewer portable ceramic membrane drinking production systemsthan polymeric ones mainly owing to their high capital costs However Veolia WaterLtd developed a mobile ceramic UF system for providing emergency drinking water(Veoliawaterst Berkefeld) The system consists of a treatment train in the order ofcoagulation adsorption pre-filtration and UF using ceramic monolith elements andultraviolet and chlorination disinfection providing up to 360 m3day permeate flowfit for drinking purposes

For large-scale drinking water production the cost of ceramic membranes can berecuperated by their reliable performance and long operating lifetimes for examplea ceramic MF system by Metawater Co Ltd has been operating for 15 years(Metawater) Metawater Co Ltdrsquos systems typically consist of coagulation dead-end MF using ceramic monolith elements followed by disinfection with chlorineand have the treatment capacity of 1000e100000 m3day for the treatment of clearraw water

Because of the superior stability and operating lifetimes of ceramic MFUFmembranes they can also be used as a pre-treatment step before reverse osmosis fordesalination A drinking water plant in Qassim replaced polymeric UF pre-treatmentmembranes with ceramic flat-sheet ones which reduced the membrane replacementfrequency dramatically and has a treatment capacity of 42000 m3day (Itn-nanovationGround water)

For the treatment of municipal wastewater or sewage the performance of ceramicMBRs is highly competitive compared with polymeric systems Similar to drinkingwater production plants implementation of ceramic membranes is limited mainly bytheir high cost There are examples of commercial ceramic MBR systems being imple-mented in small-scale wastewater treatments such as in a school and an airport byLikuid Nanotek (Likuid-CBR) They use an external cross-flow configuration to treatdomestic wastewater with capacities ranging from 38 to 50 m3day and permeate flux isrecovered solely by periodic chemical cleaning For larger-scale wastewater treatmentthe ceramic immersed MBR is more commonly used for example ItN NanovationAG installed immersed ceramic flat-sheet membrane modules with a capacity to treat150 and 1300 m3day of sewage feed in two different sewage treatment plants(Itn nanovationMBR Itn nanovationMBCR) No membrane servicing or maintenancehas been required since operation began in 2011 for one of the plants and chemicalcleaning is used once a year (oxidant and chelating agent) to maintain permeation flux

66 Advances in Membrane Technologies for Water Treatment

Ceramic membranes have found more frequent use in the treatment of industrialwastewater because they are normally more challenging to treat An example of aceramic MBR includes an external MBR using ceramic tubular membranes fromLikuid Nanotech to treat industrial waste of 3e300 m3day which has been commer-cially used in olive oil wine and narcotics production plants For all of their ceramicMBRs the quality of the final effluent is clean enough to be directly discharged(Likuid-CBR) Another application includes the ceramic MBR installed for treatmentand recycling of up to 1400 m3day of highly pigmented wastewater by Pall Corpora-tion (Membralox pall) Complete retention of insoluble pigments is achieved usingmonolith ceramic membranes running in external configuration and up to 50 ofwastewater can be recycled A larger-scale ceramic MBR has been scheduled forinstallation in a demonstration plant by Meidensha Corporation to treat and recycleup to 4550 m3day of industrial wastewater by combining up-flow anaerobic sludgeblanket technology with the 01-mm alumina flat-sheet MBR system (Singaporecollaborate on ceramic membrane MBR demonstration plant 2012)

The commercial operation of ceramic membranes in produced water treatment ismuch more limited compared with other application areas such as in the food andbeverage industry and industrial wastewater treatment To treat produced water theceramic membranes typically run in cross-flow configuration (Elshorbagy 2013)An example is the full-scale facility in Colorado which uses ceramic membranes asone of the units to treat oily wastewater (Aqwatec) The process train consists ofdissolved air floatation pre-filtration ceramic MF and activated carbon adsorptionand then the water is supplied to a reverse osmosis plant providing municipal drinkingwater In addition Veolia Water Ltd has developed a system consisting of ceramicmonolith membranes to treat produced water which so far has been installed at 60locations (Veoliawaterst CeraMem) Their typical performance includes removalof 987 turbidity and effluent has less than 1 ppm oil and grease (Veoliawaterstna)Furthermore a ceramic (SiC) membrane module will be installed for commercial usein Columbia and Venezuela after the trial period offered consistent reductions of oilconcentration from 20e100 ppm to less than 5 ppm (Success for LiqTech ceramicmembranes in oil amp gas trial 2012)

Ceramic membranes are most commonly used in the food and beverage industry(Fernandez Garciacutea et al 2013) One commercial system for the removal of bacteriaand spores from milk using MF is the Tetra Alcross Bactocatch The raw milk is firstseparated into skim milk and cream and then the former undergoes MF leaving theconcentration of bacteria in permeate to be less than 05 of the original value(Peinemann Nunes amp Giorno 2011) Ceramic membranes were also chosen andinstalled by Atech Innovations GmbH over polymeric membranes in a commercialcitrus fruit juice production plant because of their high performance as well as resis-tance to essential oils from the fruit skins Another example of commercializationincludes the use of tubular ceramic monolith membranes in a high-velocity cross-flowconfiguration in a glucose production plant to minimize gel layer formation which isable to produce 180 m3day of glucose (Bolduan amp Latz 2005)

Ceramic MFUF membranes have been used across a wide range of different ap-plications involving water and wastewater treatment They are most commonly

Advances in ceramic membranes for water treatment 67

used in the food and beverage industry and in the small-scale treatment of industrialwastewater Laboratory pilot and some commercial case studies have shown poten-tial and advantages of using ceramic membranes for large-scale municipal waste-water treatment and the provision of safe drinking water As a result of the manybenefits offered by ceramic membranes their global incorporation into more drink-ing water treatment plants is anticipated Promising developments include theinstallation of ceramic flat-sheet membranes from ItN Nanovation AG in Saudi Ara-bia to pre-treat seawater in 2013 (Itn nanovation receives significant orders fromSaudi Arabia 2013) In addition three pilot plants using ceramic membrane hybridsystems with suspended ion exchange and ozone for drinking water treatment plantswill be installed in the United Kingdom Australia and Singapore by PWN Technol-ogies (Pwntechnologies) The incorporation of ceramic membranes in MBRs alsoclearly offers many advantages including ease of maintenance and long-term reli-ability High capital membrane costs along with energy consumption from contin-uous aeration contribute to a large proportion of the MBRrsquos operating costs andboth deter the growth of ceramic MBRs for large-scale sewage treatment There-fore further research and optimization of the immersed MBR is anticipated towiden the use of ceramic membranes The main overriding limitation to the com-mercial implementation of ceramic membranes for most large-scale water treat-ments is their high capital cost despite their overall longer lifetime and ease ofmaintenance

25 Ceramic membrane cleaning

Over time permeate flux of the ceramic membrane will inevitably decrease which issame as for their polymeric counterparts To recover as much as the initial flux aspossible many different cleaning methods are available The choice of the cleaningmethod(s) depends on the reversibility of the fouling the foulant(s) characteristicsthe membrane material and the membrane element and module design

251 Physical cleaning methods

Physical cleaning methods remove reversible foulants from the membrane surface viamechanical forces Examples of physical cleaning include forward and reverse flush-ing back-pulsingbackwashing use of turbulence promoters air flushing rinsing andsponge ball cleaning

Forward flushing is achieved by using high cross-flow velocities at the feedside to loosen and then remove foulants from the membrane surface The directionof the flush is often reversed for a few seconds to improve the effectiveness of thecleaning which is called reverse flushing Rinsing the membrane can also beused to dislodge and remove fouling layers One study found that rinsing withwater alone for 15 min could recover 90 of the original membrane flux ofmulti-channel tubular membranes fouled by whey proteins (Cabero Riera ampAlvarez 1999)

68 Advances in Membrane Technologies for Water Treatment

Backwashing is when a larger pressure is applied on the permeate side causing thereverse flow of permeate into the feed side and can help flush membrane pores as well(Laitinen et al 2001 Mugnier Howell amp Ruf 2000) For MF tubular ceramicmembranes fouled during treatment of oily wastewater over 95 recovery of the orig-inal flux or prevention of flux decline was achieved by periodic backwashing (Abadiet al 2011) However once permeate flux has dropped to 40e50 of the originalvalue chemical cleaning is required

Air flushingsparging can be used during MFUF to reduce the rate and extent offouling or it can be used periodically to clean the membrane surfaces (Cui Bellaraamp Homewood 1997 Matis et al 2004 Mercier-Bonin Lagane amp Fonade 2000)It can also increase permeate flux when used during filtration because the air bub-bles on the feed side can increase turbulence in the stream but increase energy con-sumption for the entire process Sponge ball cleaning scrubs foulants from themembrane surfaces and is suitable for use in cleaning large-diameter tubular mem-branes fouled by high-turbidity feed streams such as industrial wastewater (Psoch ampSchiewer 2006)

Forward flushing backwashing and air sparging can be combined because back-washing can loosen the fouling cake layer and forward flushing and air spargingcan sweep the foulants away

252 Chemical cleaning methods

Chemical cleaning methods are required to remove physically irreversible fouling bydissolving foulants without damaging the membrane A wide range of chemicals canbe used to clean the membranes their choice depends mainly on the type of foulant aswell as the membrane material For example acids may be used to treat inorganicfouling (Yoon Kang amp Lee 1999) and alkalis are commonly used to remove organicfouling (for membranes fouled by organic contaminants in surface water (Zondervanamp Roffel 2007) and whey protein (Bartlett Bird amp Howell 1995)) Ozone andoxidants have also been used to improve the removal of organic fouling (Changet al 1994) The chemical cleaning cycle normally consists of several steps andfactors such as cleaning temperature chemical concentration pH pressure and flowrates and time all of which can affect the cleaning efficiency (Bartlett et al 1995Bird amp Bartlett 2002) The cleaning agent can be introduced into the membrane chan-nels or the membranes can be immersed into cleaning agents

Often physical cleaning and chemical cleaning methods are combined for betterfouling control and shorter membrane cleaning time Using mechanical rinsing orbackflushing with caustic soda (NaOH) and oxidation (H2O2) leads to fast and effec-tive cleaning in which 87 of permeate flux is recovered within 8 min for ceramicmembrane fouled during beer filtration (Gan et al 1999)

253 Unconventional physical cleaning methods

The use of chemical cleaning methods generates undesired additional waste streams andconventional physical cleaning removes only reversible fouling Unconventional or

Advances in ceramic membranes for water treatment 69

developing techniques targeted for efficient and more environmentally friendly means toremove fouling material include the use of ultrasonic electric or magnetic fields

Ultrasonic fields can be used to aid in cleaning membranes Cavitation caused byultrasound can prevent the membranes from clogging when applied during operationand has the potential to improve permeation flux (Kylleuroonen et al 2006) They work byfirst loosening particles of the cake layer and then transporting them away by acousticstreaming (Lamminen Walker amp Weavers 2004) The same research found that fre-quencies between 70 and 620 kHz could be used without damaging the alumina mem-branes However damage to the membrane has been observed when it is placed withinthe cavitation region of the system (Chen Weavers amp Walker 2006) Furthermorethis may be an expensive method because the cost of energy to implement this maybe high and can potentially be used to remove foulants periodically instead

Electric fields can be used to clean membranes or enhance MFUF processesbecause they can provide an additional driving force to the filtration system Chargedsolids or species on the membrane can be moved as a result of the electric field appliedto the membrane surface thus reducing the effects of concentration polarization aswell (Jagannadh amp Muralidhara 1996) When electric fields are applied to the mem-brane fouling that is irreversible and resistant to physical cleaning methods canbecome physically reversible especially for membranes that are fouled by proteinsMagnetic fields can also potentially be applied to remove or reduce the extent of inor-ganic membrane fouling (Baker Judd amp Parsons 1997) This is because magneticfields change the calcium carbonate scale from its calcite form to the less solubleform aragonite and hence enhance the crystallization of CaCO3 preventing its forma-tion on membrane surfaces (Zaidi et al 2013)

There is a lot of freedom in choosing the cleaning method for ceramic membranesowing to their high thermal chemical and mechanical stabilities Fouling can beremoved effectively via a combination of physical and chemical cleaning methodsbut the use of chemicals to clean introduces new potentially hazardous wastes thatmay then need further treatment Unconventional methods such as using ultrasonicelectric and magnetic fields can potentially be useful in aiding membrane cleaningand reducing the need for chemical cleaning agents However the available literatureregarding the performance and mechanisms of these methods in realistic situations islimited and does not provide adequate evidences to prove their feasibility in improvingmembrane lifetime

26 Prospects and challenges

From a technical viewpoint the outstanding robustness and integrity of ceramic mem-branes have secured their positions in dealing with wastewater systems where at leastan aggressive environment is involved and contribute to sustainable and strong growthtoward wider applications Technical innovations in promoting separation performanceand engineering designs keep driving the development of ceramic membrane products

70 Advances in Membrane Technologies for Water Treatment

toward an application-oriented pattern In particular new membrane fabrication tech-niques such as the combined phase-inversion and sintering methods are expected tosee wider applications in membrane production facilities They offer a much simplerfabrication cycle and can make highly microstructurally varied membrane morphol-ogies that can be tailored according to the application In terms of membrane designthe presence of hollow-fibre membranes is expected to grow in the ceramic membranemarket to offer much greater treatment capacities for larger-scale applications Thepotential of a wider range of ceramic materials other than the commonly used aluminamembranes and membrane substrates is also expected In terms of applications there isa trend toward the increasing use of ceramic membranes for larger-scale wastewatertreatments especially in MBRs because the cost of ceramic membranes is reducedAnticipated cheaper ceramic membrane prices combined with higher packing densitiesof hollow-fibre configuration will increase applications in municipalities and morespace-efficient module designs especially for hollow-fibre membranes are expectedto penetrate the market to meet the higher demands

The widespread use of ceramic MFUF membranes in water treatment is limited bymany problems A key challenge is to reduce the capital cost of ceramic membraneswhich can be met by reducing the steps in the fabrication process and lowering the sin-tering temperature The emergence of cheaper fabrication processes such as the com-bined phase-inversion and sintering method can potentially reduce the fabricationcosts of ceramic membranes However further research and development are requiredto reduce the sintering temperature and maintain a continuously high-quality mem-brane The performance of the porous membranes formed by this method needs tobe improved so that both good mechanical strength and high porosity can be achievedImproved fundamental understanding of the formation mechanisms of ceramic mem-brane microstructures can help improve the reliability and reproducibility of the fabri-cation process which is particularly useful when producing membranes from differentceramic materials and when production is scaled up Furthermore challengesregarding the up-scaling of the combined phase-inversion and sintering processinclude developing a continuous fabrication and sintering process To meet the de-mands for large-scale treatment capacities more space-effective module and unit de-signs would also be required to cut down the costs of housing material as well asimprove productivity Hollow-fibre membrane elements may offer much higher pack-ing densities but improvements in element and module designs will be required suchas creating smaller-diameter hollow fibres and improving their mechanical strengthIn terms of fouling the mechanism varies from case to case depending on the appli-cation Although a combination of physical and chemical cleaning of ceramic mem-branes can be easily achieved this leads to additional waste products that requiretreatment and disposal hence more environmentally friendly approaches to mem-brane cleaning are desired This means that challenges arising in this area include bet-ter understanding of fouling mechanisms in ceramic membranes particularly theinteractions between ceramic membranes and the different foulants to ensure thatthe right choice of cleaning methods is made for reliable long-term operation

Advances in ceramic membranes for water treatment 71

Abbreviations

COD Carbon oxygen demandDBP Disinfectant byproductMBR Membrane bioreactorMF MicrofiltrationNOM Natural organic matterUF Ultrafiltration

Acknowledgements

The authors gratefully acknowledge the research funding provided by EPSRC in the UnitedKingdom (Grant no EPJ0149741)

References

Abadi S R H Sebzari M R Hemati M Rekabdar F amp Mohammadi T (2011) Ceramicmembrane performance in microfiltration of oily wastewater Desalination 265(1e3)222e228 Retrieved from httpdxdoiorg101016jdesal201007055

Agoudjil N Kermadi S amp Larbot A (2008) Synthesis of inorganic membrane by solegelprocess Desalination 223(1e3) 417e424 Retrieved from httpdxdoiorg101016jdesal200701187

Alem A Sarpoolaky H amp Keshmiri M (2009) Sol-gel preparation of titania multilayermembrane for photocatalytic applications Ceramics International 35(5) 1837e1843

AQUASOLUTION MEMBRANE [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileAQS-80mmpdf

Ashaghi K S Ebrahimi M amp Czermak P (2007) Ceramic ultra- and nanofiltration mem-branes for oilfield produced water treatment A mini review The Open EnvironmentalJournal 1 1e8

Babaluo A A Kokabi M Manteghian M amp Sarraf-Mamoory R (2004) A modified modelfor alumina membranes formed by gel-casting followed by dip-coating Journal of theEuropean Ceramic Society 24(15e16) 3779e3787 Retrieved from httpdxdoiorg101016jjeurceramsoc200401007

Baker J S Judd S J amp Parsons S A (1997) Antiscale magnetic pretreatment of reverseosmosis feedwater Desalination 110(1e2) 151e165 Retrieved from httpdxdoiorg101016S0011-9164(97) 00094e5

Bartlett M Bird M R amp Howell J A (1995) An experimental study for the developmentof a qualitative membrane cleaning model Journal of Membrane Science 105(1e2)147e157 Retrieved from httpdxdoiorg1010160376-7388(95)00052-E

Bird M R amp Bartlett M (2002) Measuring and modelling flux recovery during the chemicalcleaning of MF membranes for the processing of whey protein concentrate Journal ofFood Engineering 53(2) 143e152 Retrieved from httpdxdoiorg101016S0260-8774(01) 00151e0

Bolduan P amp Latz M (2005) Filtration by means of ceramic membranes - practical examplesfrom the chemical and food industries Germany Atech innovations gmbh

72 Advances in Membrane Technologies for Water Treatment

Bottino A Capannelli C Del Borghi A Colombino M amp Conio O (2001) Water treatmentfor drinking purpose Ceramic microfiltration application Desalination 141(1) 75e79Retrieved from httpdxdoiorg101016S0011-9164(01) 00390e3

Burggraaf A J amp Cot L (1996) Fundamentals of inorganic membrane science and tech-nology Amsterdam The Netherlands Elsevier Science

Cabero M L Riera F A amp Alvarez R (1999) Rinsing of ultrafiltration ceramic membranesfouled with whey proteins Effects on cleaning procedures Journal of Membrane Science154(2) 239e250 Retrieved from httpdxdoiorg101016S0376-7388(98) 00294e4

Calvert P D Lalanandham R R Parish M V Fox J Lee H Pober R L et al (1986)Dispersion of ceramic particles in organic liquids (Vol 73) MRS Online ProceedingsLibrary Retrieved from httpdxdoiorg101557PROC-73-579 p 579

Castillon R amp Laveniere J P (1995) Monolithic ceramic supports for filtration membranesUS Patent No 5415775 Washington DC US Patent and Trademark Office

CeraMem Full-size membrane modules 2013 [cited 2013 2108] Retrieved from httpwwwveoliawaterstcomceramemenfullsizemodulesceramemhtm

CeraMem Ceramic Membrane Technology Technology brief [cited 2014 1001] Retrievedfrom httpwwwtundrasolutionscafilesTechnologyBriefVWSCeramicMembranespdf

Ceramic capillary membranes [cited 2014 1001] Retrieved from httpwwwigbfraunhoferdeencompetencesinterfacial-materialsmembranescapillary-membraneshtml

Ceramic flat membrane ItN water filtration [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomfileadminuser_uploadpdf-downloadsTechnologyDataSheet_CFMpdf

Ceramic membrane filtration system Drinking water treatment [cited 2014 1001] Retrievedfrom httpwwwmetawatercojpengproductdrinkingmembrane_clarifylocationhtml

Ceramic membrane unit 2013 [cited 2014 0402] Retrieved from httpwater-solutionmeidenshacojpdownloadimgbb60-3163pdf

Ceramic membranes and their application in food and beverage processing Filtration amp Separation37(3) (2000) 36e38 Retrieved from httpdxdoiorg101016S0015-1882(00)88497e9

Ceramic membrane modules - existing and planned sizes CeraMem Ceramic Membranes[cited 2014 1101] Retrieved from httpwwwveoliawaterstcomceramemenceramemelementsizeshtm

Chang I-S Choo K H Lee C H Pek U H Koh U C Kim S W et al (1994)Application of ceramic membrane as a pretreatment in anaerobic digestion of alcohol-distillery wastes Journal of Membrane Science 90(1e2) 131e139 Retrieved fromhttpdxdoiorg1010160376-7388(94) 80040e5

Chen A Flynn J T Cook R G amp Casaday A L (1991) Removal of oil grease andsuspended solids from produced water with ceramic crossflow microfiltration SPE Pro-duction Engineering 6(2) 131e136

Chen D Weavers L K amp Walker H W (2006) Ultrasonic control of ceramic membranefouling by particles Effect of ultrasonic factors Ultrasonics Sonochemistry 13(5)379e387 Retrieved from httpdxdoiorg101016jultsonch200507004

Cheryan M amp Rajagopalan N (1998) Membrane processing of oily streams Waste-water treatment and waste reduction Journal of Membrane Science 151(1) 13e28Retrieved from httpdxdoiorg101016S0376-7388(98) 00190e2

Chin S S Lim T M Chiang K amp Fane A G (2007) Factors affecting the performanceof a low-pressure submerged membrane photocatalytic reactor Chemical EngineeringJournal 130(1) 53e63 Retrieved from httpdxdoiorg101016jcej200611008

Choi I-H Kim I C Min B R amp Lee K H (2006) Preparation and characterization ofultrathin alumina hollow fiber microfiltration membrane Desalination 193(1e3)256e259 Retrieved from httpdxdoiorg101016jdesal200507051

Advances in ceramic membranes for water treatment 73

COMEM [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileCoMem-OD25mm-monotubepdf

COMEM CONDUIT [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileCoMem-Conduit-OD146mm C3983pdf

Crittenden J C Trussell R R Hand D W Howe K J amp Tchobanoglous G (2012)MWHrsquos water treatment Principles and design New Jersey Wiley

Cui Z F Bellara S R amp Homewood P (1997) Airlift crossflow membrane filtration mdash Afeasibility study with dextran ultrafiltration Journal of Membrane Science 128(1) 83e91Retrieved from httpdxdoiorg101016S0376-7388(96) 00280e3

Das N Bandyopadhyay S Chattopadhyay D amp Maiti H S (1996) Tape-cast ceramicmembranes for microfiltration application Journal of Materials Science 31(19)5221e5225 Retrieved from httpdxdoiorg101007BF00355928

Das N amp Maiti H S (2009) Ceramic membrane by tape casting and solegel coating formicrofiltration and ultrafiltration application Journal of Physics and Chemistry of Solids70(11) 1395e1400 Retrieved from httpdxdoiorg101016jjpcs200908016

Daufin G Escudier J P Carrere H Beacuterot S Fillaudeau L amp Decloux M (2001) Recentand emerging applications of membrane processes in the food and dairy industry Food andBioproducts Processing 79(2) 89e102 Retrieved from httpdxdoiorg101205096030801750286131

Drioli E amp Giorno L (2010) Comprehensive membrane science and engineering OxfordUnited Kingdom Elsevier Science

Dynamic cross flow filtration silicon carbide membrane discs Future filtration [cited 2014 1001] Retrieved from httpliqtechcomimguserfileSiC-Disc-Sheet_V1pdf

Ebrahimi M Willershausen D Ashaghi K S Engel L Placido L Mund P et al (2010)Investigations on the use of different ceramic membranes for efficient oil-field producedwater treatment Desalination 250(3) 991e996 Retrieved from httpdxdoiorg101016jdesal200909088

Elshorbagy W (2013) Water treatment Rijeka Croatia IntechEmergency mobile drinking water News amp media [cited 2014 1001] Retrieved from http

wwwveoliawaterstcomnews-mediacase-studiesemergency-mobile-water-germanyhtmFalamaki C amp Beyhaghi M (2009) Slip casting process for the manufacture of tubular

alumina microfiltration membranes Materials Science-Poland 27(2) 427e441Fan Y B Li G Wu L L Yang W B Dong C S Xu H F et al (2006) Treatment and

reuse of toilet wastewater by an airlift external circulation membrane bioreactor ProcessBiochemistry 41(6) 1364e1370 Retrieved from httpdxdoiorg101016jprocbio200601023

Feenstra F K Terpstra R A amp Van Eijk J P G M (1998) Method for the production ofceramic hollow fibres US Patent No 5707584 Washington DC US Patent andTrademark Office

Fernandez Garciacutea L Alvarez Blanco S amp Riera Rodriacuteguez F A (2013) Microfiltrationapplied to dairy streams Removal of bacteria Journal of the Science of Food and Agri-culture 93(2) 187e196 Retrieved from httpdxdoiorg101002jsfa5935

Fiksdal L amp Leiknes T (2006) The effect of coagulation with MFUF membrane filtration forthe removal of virus in drinking water Journal of Membrane Science 279(1e2) 364e371Retrieved from httpdxdoiorg101016jmemsci200512023

Filtration module T-series ItN water filtration [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomfileadminuser_uploadpdf-downloadsProductDataSheet_FiltrationModulepdf

74 Advances in Membrane Technologies for Water Treatment

Filtration module T-series Components [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomdeproductscomponentsfiltration-module-t-serieshtml

Filtration rack Product program [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomindexphpidfrac1421

Finley J (2005) Ceramic membranes A robust filtration alternative Filtration amp Sepa-ration 42(9) 34e37 Retrieved from httpdxdoiorg101016S0015-1882(05)70695e9

Fukumoto L R Delaquis P amp Girard B (1998) Microfiltration and ultrafiltrationceramic membranes for apple juice clarification Journal of Food Science 63(5) 845e850Retrieved from httpdxdoiorg101111j1365-26211998tb17912x

Gan Q Howell J A Field R W England R Bird M R amp Mckechinie M T (1999)Synergetic cleaning procedure for a ceramic membrane fouled by beer microfiltrationJournal of Membrane Science 155(2) 277e289 Retrieved from httpdxdoiorg101016S0376-7388(98)00320e2

Gander M Jefferson B amp Judd S (2000) Aerobic MBRs for domestic wastewater treatmentA review with cost considerations Separation and Purification Technology 18(2)119e130 Retrieved from httpdxdoiorg101016S1383-5866(99)00056e8

Girard B Fukumoto L amp Sefa Koseoglu S (2000) Membrane processing of fruit juices andbeverages A review Critical Reviews in Biotechnology 20(2) 109e175

Ground water replacement of polymer ultra filtration system Case studies [cited 2014 1001]Retrieved from httpwwwitn-nanovationcomdeapplicationscase-studiespre-filtration-of-deep-ground-waterhtml

Gu Y amp Meng G (1999) A model for ceramic membrane formation by dip-coating Journalof the European Ceramic Society 19(11) 1961e1966 Retrieved from httpdxdoiorg101016S0955-2219(99)00013e8

Guerra K Pellegrino J amp Drewes J E (2012) Impact of operating conditions on permeateflux and process economics for cross flow ceramic membrane ultrafiltration of surfacewater Separation and Purification Technology 87(0) 47e53 Retrieved from httpdxdoiorg101016jseppur201111019

Han L-F Xu Z L Cao Y Wei Y M amp Xu H T (2011) Preparation characterization andpermeation property of Al2O3 Al2O3eSiO2 and Al2O3ekaolin hollow fiber membranesJournal of Membrane Science 372(1e2) 154e164 Retrieved from httpdxdoiorg101016jmemsci201101065

Hao Y X Li J S Yang X J Wang X amp Lu L D (2004) Preparation of ZrO2eAl2O3

composite membranes by solegel process and their characterization Materials Scienceand Engineering A 367(1e2) 243e247 Retrieved from httpdxdoiorg101016jmsea200310321

Harman B I Koseoglu H Yigit N O Sayilgan E Beyhan M amp Kitis M (2010) Theremoval of disinfection by-product precursors from water with ceramic membranes WaterSci Technol 62(3) 547e555 Retrieved from httpdxdoiorg102166wst2010260

Hinkova A Bubnık Z Kadlec P amp Pridal J (2002) Potentials of separation membranes inthe sugar industry Separation and Purification Technology 26(1) 101e110 Retrievedfrom httpdxdoiorg101016S1383-5866(01)00121e6

Hofman-Zeurouter J M (1995) Chemical and thermal stability of (modified) mesoporous ceramicmembranes

Hofs B Ogier J Vries D Beerendonk E F amp Cornelissen E R (2011) Comparison ofceramic and polymeric membrane permeability and fouling using surface water Separationand Purification Technology 79(3) 365e374 Retrieved from httpdxdoiorg101016jseppur201103025

Advances in ceramic membranes for water treatment 75

van der Horst H C amp Hanemaaijer J H (1990) Cross-flow microfiltration in the food in-dustry State of the art Desalination 77(0) 235e258 Retrieved from httpdxdoiorg1010160011-9164(90) 85028e9

Hsieh H P Bhave R R amp Fleming H L (1988) Microporous alumina membranes Journalof Membrane Science 39(3) 221e241 Retrieved from httpdxdoiorg101016S0376-7388(00)80931-X

Hsieh H P (1996) Inorganic membranes for separation and reaction Oxford UnitedKingdom Elsevier Science

InoCep ceramic hollow fibre membrane [cited 2014 0402] Retrieved from httpwwwhyfluxmembranescompdfbrochuresinoceppdf

InoCep ceramic hollow fibre membrane [cited 2014 1101] Retrieved from httpwwwhydrasystcomwp-contentuploadsHydrasyst Inoceppdf

Module Specifications InoCep [cited 2014 1001] Retrieved from httpwwwhyfluxmembranescominocep_modulehtml

Inside ceacuteram Industrial products [cited 2013 1001] Retrieved from httpwwwtami-industriescomINSIDE-CeRAM-TM1090html

Isoflux Industrial products [cited 2013 1001] Retrieved from httpwwwtami-industriescomIsoflux-TM1110html

ItN nanovation receives significant orders from Saudi ArabiaMembrane Technology 2013(10)(2013) 2e3 Retrieved from httpdxdoiorg101016S0958-2118(13) 70196e4

Jagannadh S N amp Muralidhara H (1996) Electrokinetics methods to control membranefouling Industrial amp Engineering Chemistry Research 35(4) 1133e1140

Jin L Ong S L amp Ng H Y (2010) Comparison of fouling characteristics in different pore-sized submerged ceramic membrane bioreactors Water Research 44(20) 5907e5918Retrieved from httpdxdoiorg101016jwatres201007014

Judd S (2008) The status of membrane bioreactor technology Trends in Biotechnology 26(2)109e116 Retrieved from httpdxdoiorg101016jtibtech200711005

Judd S (2010) The MBR book Principles and applications of membrane bioreactors for waterand wastewater treatment Oxford United Kingdom Elsevier Science

Kanawka K Othman M H D Wu Z T Droushiotis N Kelsall G amp Li K (2011) A duallayer NiNi-YSZ hollow fibre for micro-tubular SOFC anode support with a current col-lector Electrochemistry Communications 13(1) 93e95 Retrieved from httpdxdoiorg101016jelecom201011022

Kang I-J Yoon S-H ampLeeC-H (2002) Comparison of thefiltration characteristics of organicand inorganic membranes in a membrane-coupled anaerobic bioreactor Water Research36(7) 1803e1813 Retrieved from httpdxdoiorg101016S0043-1354(01) 00388e8

Karnik B S Davies S H R Chen K C Jaglowski D R Baumann M J amp Masten S J(2005a) Effects of ozonation on the permeate flux of nanocrystalline ceramic membranesWater research 39(4) 728e734

Karnik B S Davies S H Baumann M J amp Masten S J (2005b) The effects of combinedozonation and filtration on disinfection by-product formation Water Research 39(13)2839e2850 Retrieved from httpdxdoiorg101016jwatres200504073

Kim J H Davies S H R Baumann M J Tarabara V V amp Masten S J (2008) Effect ofozone dosage and hydrodynamic conditions on the permeate flux in a hybrid ozona-tioneceramic ultrafiltration system treating natural waters Journal of Membrane Science311(1) 165e172

Kim J amp Lin Y S (1998) Sol-gel synthesis and characterization of yttria stabilized zirconiamembranes Journal of Membrane Science 139(1) 75e83 Retrieved from httpdxdoiorg101016S0376-7388(97) 00250e0

76 Advances in Membrane Technologies for Water Treatment

Kingsbury B F K amp Li K (2009) A morphological study of ceramic hollow fibre mem-branes Journal of Membrane Science 328(1e2) 134e140 Retrieved from httpdxdoiorg101016jmemsci200811050

Kingsbury B F K Wu Z amp Li K (2010) A morphological study of ceramic hollow fibremembranes A perspective on multifunctional catalytic membrane reactors Catalysis Today156(3e4) 306e315 Retrieved from httpdxdoiorg101016jcattod201002039

Konieczny K amp Klomfas G (2002) Using activated carbon to improve natural water treat-ment by porous membranes Desalination 147(1e3) 109e116 Retrieved from httpdxdoiorg101016S0011-9164(02) 00584e2

Konieczny K Bodzek M amp Rajca M (2006) A coagulationeMF system for water treatmentusing ceramic membranes Desalination 198(1e3) 92e101 Retrieved from httpdxdoiorg101016jdesal200609014

Koonaphapdeelert S amp Li K (2007) Preparation and characterization of hydrophobicceramic hollow fibre membrane Journal of Membrane Science 291(1e2) 70e76Retrieved from httpdxdoiorg101016jmemsci200612039

Koonaphapdeelert S Wu Z amp Li K (2009) Carbon dioxide stripping in ceramic hollow fibremembrane contactors Chemical Engineering Science 64(1) 1e8 Retrieved from httpdxdoiorg101016jces200809010

Krstic D M Antov M G Pericin D M Heurooflinger W amp Tekic M N (2007) The pos-sibility for improvement of ceramic membrane ultrafiltration of an enzyme solutionBiochemical Engineering Journal 33(1) 10e15 Retrieved from httpdxdoiorg101016jbej200608016

Kylleuroonen H Pirkonen P Nystreuroom M Nuortila-Jokinen J amp Greuroonroos A (2006)Experimental aspects of ultrasonically enhanced cross-flow membrane filtration of indus-trial wastewaterUltrasonics Sonochemistry 13(4) 295e302 Retrieved from httpdxdoiorg101016jultsonch200504006

Laitinen N Luonsi A Leveuroanen E amp Nystreuroom M (2001) Effect of backflushing conditionson ultrafiltration of board industry wastewaters with ceramic membranes Separation andPurification Technology 25(1e3) 323e331 Retrieved from httpdxdoiorg101016S1383-5866(01) 00059e4

Lamminen M O Walker H W amp Weavers L K (2004) Mechanisms and factors influencingthe ultrasonic cleaning of particle-fouled ceramic membranes Journal of Membrane Science237(1e2) 213e223 Retrieved from httpdxdoiorg101016jmemsci200402031

Larbot A Fabre J P Guizard C amp Cot L (1988) Inorganic membranes obtained by sol-geltechniques Journal of Membrane Science 39(3) 203e212 Retrieved from httpdxdoiorg101016S0376-7388(00) 80929e1

Lee H C Park J Y amp Yoon D-Y (2009) Advanced water treatment of high turbidsource by hybrid module of ceramic microfiltration and activated carbon adsorptionEffect of organicinorganic materials Korean Journal of Chemical Engineering 26(3)697e701

Lens P Zeeman G amp Lettinga G (2001) Decentralised sanitation reuse Concepts systemand implementation Oxford United Kingdom Taylor amp Francis Group

Lerch A Panglisch S Buchta P Tomita Y Yonekawa H Hattori K et al (2005) Directriver water treatment using coagulationceramic membrane microfiltration Desalination179(1e3) 41e50 Retrieved from httpdxdoiorg101016jdesal200411054

Li M S Zhao Y J Zhou S Y amp Xing W H (2010) Clarification of raw rice wine byceramic microfiltration membranes and membrane fouling analysis Desalination256(1e3) 166e173 Retrieved from httpdxdoiorg101016jdesal201001018

Advances in ceramic membranes for water treatment 77

Li M Y Wu G X Guan Y T amp Zhang X H (2011) Treatment of river water by a hybridcoagulation and ceramic membrane process Desalination 280(1e3) 114e119 Retrievedfrom httpdxdoiorg101016jdesal201106059

Li L amp Lee R (2009) Purification of produced water by ceramic membranes Material screeningprocess design and economics Separation Science and Technology 44(15) 3455e3484

Li K (2007) Ceramic membranes for separation and reaction Chichester United KingdomWiley

Liao B-Q Kraemer J T amp Bagley D M (2006) Anaerobic membrane bioreactors ap-plications and research directions Critical Reviews in Environmental Science and Tech-nology 36(6) 489e530 Retrieved from httpdxdoiorg10108010643380600678146

Likuid-CBRfiltration systems for MBRS [cited 2014 1001] Retrieved from httpdioxide

com20130916_Likuid_CBR_ENpdfLin P-K amp Tsai D-S (1997) Preparation and analysis of a silicon carbide composite

membrane Journal of the American Ceramic Society 80(2) 365e372 Retrieved fromhttpdxdoiorg101111j1151-29161997tb02839x

Lindqvist K amp Lideacuten E (1997) Preparation of alumina membranes by tape casting and dipcoating Journal of the European Ceramic Society 17(2e3) 359e366 Retrieved fromhttpdxdoiorg101016S0955-2219(96) 00107e0

LiqTech SiC SteriMem [cited 2014 1001] Retrieved from httpwwwliqtechdkimguserfileLiqTech SiC SteriMem Ceramic Membranespdf

Liu S Li K amp Hughes R (2003) Preparation of porous aluminium oxide (Al2O3) hollow fibremembranes by a combined phase-inversion and sintering method Ceramics International29(8) 875e881 Retrieved from httpdxdoiorg101016S0272-8842(03) 00030e0

Luiten-Olieman M W J Raaijmakers M J T Winnubst L Wessling M Nijmeijer A ampBenes N E (2011) Porous stainless steel hollow fibers with shrinkage-controlled smallradial dimensions Scripta Materialia 65(1) 25e28 Retrieved from httpdxdoiorg101016jscriptamat201103023

Luiten-Olieman M W J Raaijmakers M J T Winnubst L Bor T C Wessling MNijmeijer A et al (2012) Towards a generic method for inorganic porous hollow fiberspreparation with shrinkage-controlled small radial dimensions applied to Al2O3 Ni SiCstainless steel and YSZ Journal of Membrane Science 407e408(0) 155e163 Retrievedfrom httpdxdoiorg101016jmemsci201203030

Mahesh Kumar S Madhu G M amp Roy S (2007) Fouling behaviour regeneration optionsand on-line control of biomass-based power plant effluents using microporous ceramicmembranes Separation and Purification Technology 57(1) 25e36 Retrieved from httpdxdoiorg101016jseppur200703002

Majewska-Nowak K M (2010) Application of ceramic membranes for the separation of dyeparticles Desalination 254(1e3) 185e191 Retrieved from httpdxdoiorg101016jdesal200911026

Mallada R amp Meneacutendez M (2008) Inorganic membranes Synthesis characterization andapplications Oxford United Kingdom Elsevier Science

Marrot B Barrios-Martinez A Moulin P amp Roche N (2004) Industrial wastewater treatmentin a membrane bioreactor A review Environmental Progress 23(1) 59e68 Retrieved fromhttpdxdoiorg101002ep10001

Matis K A Peleka E N Zamboulis D Erwe T amp Mavrov V (2004) Air spargingduring the solidliquid separation by microfiltration application of flotation Separa-tion and Purification Technology 40(1) 1e7 Retrieved from httpdxdoiorg101016jseppur200312017

78 Advances in Membrane Technologies for Water Treatment

Matsushita T Matsui Y Shirasaki N amp Kato Y (2005) Effect of membrane pore sizecoagulation time and coagulant dose on virus removal by a coagulation-ceramic micro-filtration hybrid system Desalination 178(1e3) 21e26 Retrieved from httpdxdoiorg101016jdesal200411026

Membralox ceramic membrane bio-reactor for industrial wastewater treatment Water pro-cessing [cited 2014 1001] Retrieved from httpjapanesepallcompdfCSMEMBRALOXENpdf

Membralox Ceramic membrane products Products [cited 2014 1101] Retrieved fromhttpwwwpallcommainfood-and-beverageproductpageidfrac1441052

Membrane specifications [cited 2013 2108] Retrieved from httpwwwhyfluxmembranescominocep_membranehtml

Meng F Chae S R Drews A Kraume M Shin H S amp Yang F L (2009) Recentadvances in membrane bioreactors (MBRs) Membrane fouling and membrane materialWater Research 43(6) 1489e1512 Retrieved from httpdxdoiorg101016jwatres200812044

Mercier-Bonin M Lagane C amp Fonade C (2000) Influence of a gasliquid two-phase flowon the ultrafiltration and microfiltration performances Case of a ceramic flat sheet mem-brane Journal of Membrane Science 180(1) 93e102 Retrieved from httpdxdoiorg101016S0376-7388(00) 00520e2

Mobile drinking water treatment TWA 15 UF Berkefeld Retrieved from httpwwwberkefeldcomberkefeldressourcesdocuments313300Mappe_ENpdf

Module Specifications Kristal [cited 2014 1001] Retrieved from httpwwwhyfluxmembranescomkristal_modulehtml

Mozia S (2010) Photocatalytic membrane reactors (PMRs) in water and wastewater treatmentA review Separation and Purification Technology 73(2) 71e91 Retrieved from httpdxdoiorg101016jseppur201003021

MPT hollow fiber ceramic membranes [cited 2013 1604] Retrieved from httpwwwmediaandprocesscomproductsproducts01html

Mugnier N Howell J A amp Ruf M (2000) Optimisation of a back-flush sequence for zeolitemicrofiltration Journal of Membrane Science 175(2) 149e161 Retrieved from httpdxdoiorg101016S0376-7388(00) 00412e9

Muhammad N Sinha R Krishnan E R amp Patterson C L (2009) Ceramic filter for smallsystem drinking water treatment Evaluation of membrane pore size and importance ofintegrity monitoring Journal of Environmental Engineering 135(11) 1181e1191

Mulder M (1996) Basic principles of membrane technology The Netherlands SpringerOthman M H D Droushiotis N Wu Z T Kelsall G amp Li K (2012) Dual-layer hollow

fibres with different anode structures for micro-tubular solid oxide fuel cells Journal of PowerSources 205(0) 272e280 Retrieved from httpdxdoiorg101016jjpowsour201201002

Pall Membralox Ceramic Membranes and modules [cited 2014 1001] Retrieved fromhttpwwwpallcompdfsFuels-and-ChemicalsPIMEMBRAENpdf

Membralox IC Pall Membralox IC ceramic membranes and modules [cited 2014 1101]Retrieved from httpwwwpallcompdfsFood-and-BeveragePIMEMBRAICENpdf

Peinemann K V Nunes S P amp Giorno L (2011)Membrane technology Vol 3 Membranesfor food applications Weinheim Germany Wiley

Produced water beneficial use case studies Case studies [cited 2014 1001] Retrieved fromhttpaqwatecmineseduproduced_waterassessbucase

Projects Innovative designs for sustainable advanced water treatment [cited 2014 1001]Retrieved from httpwwwpwntechnologiesnlprojectsindexhtml - six-ceramac-pilot-south-west-water-united-kingdom

Advances in ceramic membranes for water treatment 79

Psoch C amp Schiewer S (2006) Direct filtration of natural and simulated river water with airsparging and sponge ball application for fouling control Desalination 197(1e3)190e204 Retrieved from httpdxdoiorg101016jdesal200511027

Rahman M A Garciacutea-Garciacutea F R Irfan Hatim M D Kingsbury B F K amp Li K(2011) Development of a catalytic hollow fibre membrane micro-reactor for high purityH2 production Journal of Membrane Science 368(1e2) 116e123 Retrieved fromhttpdxdoiorg101016jmemsci201011025

Ruutenhuch R (1992) Membrane separation systems - recent developments and future di-rections Von R W Baker ua Noyes Data Corp Park Ridge 1991 XV 451 S zahlrAbb u Tab geb US-$64 Chemie Ingenieur Technik 64(6) 584 Retrieved from httpdxdoiorg101002cite330640633

Sewage treatment plant ceramicMBR Case studies [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomapplicationscase-studiessewage-treatment-plant-ceramic-mbrhtml

Sewage treatment plant MBCR Case studies [cited 2014 1001] Retrieved from httpwwwitn-nanovationcomapplicationscase-studiessewage-treatment-plant-mbcrhtml

Silva L L O Vasconcelos D C L Nunes E H M Caldeira L Costa V C Musse A Pet al (2012) Processing structural characterization and performance of alumina supportsused in ceramic membranes Ceramics International 38(3) 1943e1949 Retrieved fromhttpdxdoiorg101016jceramint201110025

PUB and Meiden Singapore collaborate on ceramic membrane MBR demonstration plantMembrane Technology 2012(9) (2012) 1e16 Retrieved from httpdxdoiorg101016S0958-2118(12) 70171e4

Skrzypek M amp Burger M (2010) Isoflux ceramic membranes mdash practical experiencesin dairy industry Desalination 250(3) 1095e1100 Retrieved from httpdxdoiorg101016jdesal200909116

Smid J Avci C G Geurounay V Terpstra R A amp Van Eijk J P G M (1996) Preparationand characterization of microporous ceramic hollow fibre membranes Journal ofMembrane Science 112(1) 85e90 Retrieved from httpdxdoiorg1010160376-7388(95)00274-X

Sondhi R amp Bhave R (2001) Role of backpulsing in fouling minimization incrossflow filtration with ceramic membranes Journal of Membrane Science 186(1)41e52 Retrieved from httpdxdoiorg101016S0376-7388(00) 00663e3

Sondhi R Bhave R amp Jung G (2003) Applications and benefits of ceramic membranesMembrane Technology 2003(11) 5e8 Retrieved from httpdxdoiorg101016S0958-2118(03) 11016e6

Staff A (2011) Microfiltration and ultrafiltration membranes for drinking water (M53)Denver Colorado American Water Works Association

Stoquart C Servais P Beacuterubeacute P R amp Barbeau B (2012) Hybrid membrane processes usingactivated carbon treatment for drinking water A review Journal of Membrane Science411e412(0) 1e12 Retrieved from httpdxdoiorg101016jmemsci201204012

Submersible silicon carbide flat sheet membranes Future filtration [cited 2014 1001] Retrievedfrom httpliqtechcomimguserfileSiC Ceramic Flat Sheet Membranepdf

Success for LiqTech ceramic membranes in oil amp gas trial Filtration Industry Analyst2012(11) (2012) 4 Retrieved from httpdxdoiorg101016S1365-6937(12) 70350e7

Sun D Zeng J amp Tay J (2003) A submerged tubular ceramic membrane bioreactor for highstrength wastewater treatment Water Science amp Technology 47(1) 105e111

SURVEY Technical data of atech Al2O3 membranes [cited 2014 1001] Retrieved fromhttpwwwatech-innovationscomfileadmindownloadatech_product_data_en_080206_01pdf

80 Advances in Membrane Technologies for Water Treatment

Sushumna I Gupta R amp Ruckenstein E (1992) Effective dispersants for concentratednonaqueous suspensions Journal of Materials Research-Pittsburgh- 7 2884e2893Retrieved from httpdxdoiorg101557JMR19922884

Tan X Liu N Meng B amp Liu S M (2011) Morphology control of the perovskitehollow fibre membranes for oxygen separation using different bore fluids Journal ofMembrane Science 378(1e2) 308e318 Retrieved from httpdxdoiorg101016jmemsci201105012

Tan X Liu S amp Li K (2001) Preparation and characterization of inorganic hollow fibermembranes Journal of Membrane Science 188(1) 87e95 Retrieved from httpdxdoiorg101016S0376-7388(01) 00369e6

Terpstra R A Bonekamp B C amp Veringa H J (1988) Preparation characterization andsome properties of tubular alpha alumina ceramic membranes for microfiltration and as asupport for ultrafiltration and gas separation membranesDesalination 70(1e3) 395e404Retrieved from httpdxdoiorg1010160011-9164(88) 85069e0

The ROSS System Produced water treatment [cited 2014 1001] Retrieved from httpwwwveoliawaterstnacomnews-resourcesinformation-filesROSSproducedwaterhtm

The Ross System Produced water treatment CeraMem Ceramic Membranes[cited 2014 1001] Retrieved from httpwwwveoliawaterstcomceramemen

Van Der Bruggen B Vandecasteele C Van Gestel T Doyen W amp Leysen R (2003) Areview of pressure-driven membrane processes in wastewater treatment and drinking waterproduction Environmental Progress 22(1) 46e56 Retrieved from httpdxdoiorg101002ep670220116

Van Gestel T Vandecasteele C Buekenhoudt A Dotremont C Luyten J Van derBruggen B et al (2003) Corrosion properties of alumina and titaniaNFmembranes Journalof Membrane Science 214(1) 21e29 Retrieved from httpdxdoiorg101016S0376-7388(02) 00517e3

Wang B amp Lai Z (2012) Finger-like voids induced by viscous fingering during phaseinversion of aluminaPESNMP suspensions Journal of Membrane Science 405e406(0)275e283 Retrieved from httpdxdoiorg101016jmemsci201203020

Waeger F Delhaye T amp Fuchs W (2010) The use of ceramic microfiltration and ultrafil-tration membranes for particle removal from anaerobic digester effluents Separation andPurification Technology 73(2) 271e278 Retrieved from httpdxdoiorg101016jseppur201004013

Wang H T Liu X Q Chen F L Meng G Y amp Soslashrensen O T (1998) Kinetics andmechanism of a sintering process for macroporous alumina ceramics by extrusion Journalof the American Ceramic Society 81(3) 781e784 Retrieved from httpdxdoiorg101111j1151-29161998tb02412x

Wang I-F D Jerome F Morris Richard A amp Kesting Robert (1999) Highly asymmetricultrafiltration membranes US Patent No 5958989 Washington DC US Patent andTrademark Office

Wang T Zhang Y Z Li G F amp Li H (2009) Preparation and characterization of aluminahollow fiber membranes Frontiers of Chemical Engineering in China 3(3) 265e271Retrieved from httpdxdoiorg101007s11705-009-0010-2

Wang Y H Cheng J G Liu X Q Meng G Y amp Ding Y W (2008a) Preparation andsintering of macroporous ceramic membrane support from titania sol-coated aluminapowder Journal of the American Ceramic Society 91(3) 825e830 Retrieved from httpdxdoiorg101111j1551-2916200702207x

Wang Z Yang N T Meng B Tan X Y amp Li K (2008b) Preparation andoxygen permeation properties of highly asymmetric La06Sr04Co02Fe08O3a Perovskite

Advances in ceramic membranes for water treatment 81

hollow-fiber membranes Industrial amp Engineering Chemistry Research 48(1) 510e516Retrieved from httpdxdoiorg101021ie8010462

Water filtration by ceramic flat membranes e CFM ItN water filtration [cited 2014 1101]Retrieved from httpwwwitn-nanovationcomfileadminuser_uploadpdf-downloadsCFM-Flyerpdf

Wei C C Chen O Y Liu Y amp Li K (2008) Ceramic asymmetric hollow fibre mem-branesmdashone step fabrication process Journal of Membrane Science 320(1e2) 191e197Retrieved from httpdxdoiorg101016jmemsci200804003

Wu J C-S amp Cheng L-C (2000) An improved synthesis of ultrafiltration zirconia mem-branes via the solegel route using alkoxide precursor Journal of Membrane Science167(2) 253e261 Retrieved from httpdxdoiorg101016S0376-7388(99)00294-X

Wu Z Faiz R Li T Kingsbury B F K amp Li K (2013) A controlled sintering process formore permeable ceramic hollow fibre membranes Journal of Membrane Science 446(0)286e293 Retrieved from httpdxdoiorg101016jmemsci201305040

Xin X S Lu Z Zhu Q S Huang X Q amp Su W H (2007) Fabrication of dense YSZ electro-lyte membranes by a modified dry-pressing using nanocrystalline powders Journal of Mat-erials Chemistry 17(16) 1627e1630 Retrieved from httpdxdoiorg101039B615548K

Xing C H Tardieu E Qian Y ampWen X H (2000) Ultrafiltration membrane bioreactor forurban wastewater reclamation Journal of Membrane Science 177(1e2) 73e82 Retrievedfrom httpdxdoiorg101016S0376-7388(00)00452-X

Xu N Xing W H Xu N P amp Shi J (2003) Study on ceramic membrane bioreactor withturbulence promoter Separation and Purification Technology 32(1e3) 403e410Retrieved from httpdxdoiorg101016S1383-5866(03)00073-X

Yang N Tan X amp Ma Z (2008) A phase inversionsintering process to fabricate nickelyttria-stabilized zirconia hollow fibers as the anode support for micro-tubular solid oxidefuel cells Journal of Power Sources 183(1) 14e19 Retrieved from httpdxdoiorg101016jjpowsour200805006

Yoon S H Kang I J amp Lee C H (1999) Fouling of inorganic membrane and fluxenhancement in membrane-coupled anaerobic bioreactor Separation Science and Tech-nology 34(5) 709e724 Retrieved from httpdxdoiorg10108001496399908951140

Zaidi N S Sohaili J Muda K amp Sillanpeuroaeuroa M (2013) Magnetic field application and itspotential in water and wastewater treatment systems Separation amp Purification Reviews43(3) 206e240 Retrieved from httpdxdoiorg101080154221192013794148

Zhang F Jing W H Xing W H amp Xu N P (2009a) Experiment and calculation offiltration processes in an external-loop airlift ceramic membrane bioreactor ChemicalEngineering Science 64(12) 2859e2865 Retrieved from httpdxdoiorg101016jces200902046

Zhang J W Fang H Hao L Y Xu X amp Chen C S (2012) Preparation of silicon nitridehollow fibre membrane for desalination Materials Letters 68(0) 457e459 Retrievedfrom httpdxdoiorg101016jmatlet201111041

Zhang X Fang D Lin B Dong Y C Meng G Y amp Liu X Q (2009b) Asymmetric porouscordierite hollow fiber membrane for microfiltration Journal of Alloys and Compounds487(1e2) 631e638 Retrieved from httpdxdoiorg101016jjallcom200908028

Zondervan E amp Roffel B (2007) Evaluation of different cleaning agents used for cleaningultra filtration membranes fouled by surface water Journal of Membrane Science304(1e2) 40e49 Retrieved from httpdxdoiorg101016jmemsci200706041

Zeurourcher S amp Graule T (2005) Influence of dispersant structure on the rheological propertiesof highly-concentrated zirconia dispersions Journal of the European Ceramic Society25(6) 863e873 Retrieved from httpdxdoiorg101016jjeurceramsoc200405002

82 Advances in Membrane Technologies for Water Treatment

Advances in water treatmentby microfiltration ultrafiltrationand nanofiltration

3I Koyuncu12 R Sengur23 T Turken12 S Guclu12 ME Pasaoglu121Istanbul Technical University Civil Engineering Faculty Environmental EngineeringDepartment Istanbul Turkey 2National Research Center on Membrane Technologies(MEM-TEK) Istanbul Turkey 3Istanbul Technical University Nanoscience andNanoengineering Department Istanbul Turkey

31 Introduction

In 2012 access to safe drinking water became the first millennium developmentgoal to be met by the international community (Url-1) The original aim set in2000 was to halve by 2015 the proportion of the population without sustainable ac-cess to safe drinking water and basic sanitation (UN 2010 pp 58e60) This encour-aging achievement should underscore the progress that can be made through thedevelopment of often simple and cheap technologies in low-income economies Atthe same time it can be expected that challenges related to water systems willcontinue to increase requiring further investment and technological innovation tomeet global needs Access to clean water is a simple human need and an importantdriver of social and economic development (UN Water 2006) Predictable andconsistent access to clean drinking water is globally seen as a core function of statesbecause it is crucial to a societyrsquos public health economic vitality and national secu-rity (Elimelech amp Phillip 2011)

311 Global membrane market

The global membrane market for microfiltration (MF) products used in liquidseparations was estimated to be $16 billion in 2013 It was projected to rise at a com-pound annual growth rate (CAGR) of 100 during the next 5 years to reach$26 billion in 2018 (Url-2)

The US market for ultrafiltration (UF) technologies was worth $882 million in2009 and reached $932 million at the end of 2010 By 2015 the market is estimatedto be valued at $12 billion a CAGR of 57 (Url-3)

The global market for nanofiltration (NF) membranes increased from$1728 million in 2012 to 1902 million in 2013 at the end of 2014 and 2019 it is esti-mated to reach $2156 million and 4451 million respectively CAGR will be 156during 2014e2019 (Url-4)

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400003-4Copyright copy 2015 Elsevier Ltd All rights reserved

312 Membrane filtration technology for water treatment

Membrane technology has become a significant separation technology over the past2 decades Continuing advances in regulatory constraints and aesthetic criteria forconsumer water quality have driven the water community to seek new technologiesMembrane technology is one of those new technologies In this technology mem-branes are used as filters in separation processes in various applications They pro-vide effective alternatives to related technologies such as adsorption ionexchangers and sand filters Major uses of this technology are water filtration(including desalination) and purification (including groundwater and wastewater)as well as industries such as food and beverages and biotechnology (Kurt KoseogluDizge Chellam amp Koyuncu 2012 Ozgun et al 2012) It also has medical uses suchas in dialysis

313 Membrane processes

A membrane is defined as a selective barrier between two homogenous phases Inprinciple membranes can carry out most of the separation processes and can com-plement or form an alternative for chemical processes such as distillation extractionfractionation and adsorption Some advantages of membrane filtration are lowenergy consumption the possibility of continuous separation and simpleup-scaling (Baker 2004)

The membrane process is not suitable for every fluid stream because of the contentof feed and product requirements as well as the nature of the membrane process and themembrane designed for that process There are four developed industrial membraneprocesses for water treatment The main difference in these processes is the poresize of the membranes Membrane processes are

1 Microfiltration2 Ultrafiltration3 Nanofiltration4 Reverse osmosis (RO)

RO is beyond the scope of this chapter but the other processes will be covered hereThe schematic separation spectrum given for membrane processes is shown inFigure 31 (Baker 2004)

1Aring 10 Aring 100 AringPore diameter

Reverseosmosis

UltrafiltrationMicrofiltration

Conventionalfiltration

1000 Aring 1 microm 10 microm 100 microm

Figure 31 Schematic spectrum for membrane processes and conventional filtrationReprinted from Baker (2004) Overview of membrane science and technology p 7

84 Advances in Membrane Technologies for Water Treatment

Membrane processes can be used for various applications There are variousguidelines for selecting the proper membrane process For example if particlesgt02 mm are removed the process becomes MF if dissolved contaminants can beprecipitated or coagulated the proper process may be MF or UF In the NF processit is possible to remove both organic and inorganic ions however if monovalentions exist or total dissolved solids removal of 3000 mgL is achieved the RO processis required (AWWA 2007)

General comparisons between MF UF and NF membranes can be found in Table 31

32 Water treatment by MF UF and NF

321 Microfiltration process

The MF and UF processes are commonly used for water treatment systems Af-ter a sand filter or cartridge filter MF can be applied to groundwater and surfacewaters In RO systems generally MF is in the pretreatment section of the treat-ment plant

The pore size of MF typically varies from 01 to 10 mm However the separationmechanism is not simple because particles of sizes are smaller than the pore sizeflow freely through the pore while the larger particles are rejected

Volume flow through MF membranes can be described by Darcyrsquos law where fluxJ through the membrane is directly proportional to the applied pressure (DP)

J frac14 A$DP

where permeability constant A contains structural factors such as the porosity and poresize distribution (Mulder 1996)

MF is used in a wide variety of industrial applications where particles of a sizegt01 mm have to be retained from a suspension The most important applicationsare still based on dead-end filtration using cartridges However for larger-scale appli-cations dead-end filtration will slowly be replaced by cross-flow filtration One of themain industrial applications is the sterilization and clarification of all kinds ofbeverages and pharmaceuticals industries Other applications are summarized below(Eykamp 1995 Mir Micheals Goel amp Kaiser 1992 Mulder 1996)

bull Ultrapure water in the semiconductorbull Drinking water treatmentbull Clarification of fruit juice wine and beerbull Wastewater treatmentbull Pretreatment

322 Ultrafiltration process

For UF pore sizes generally range from 001 to 005 mm (nominally 001 mm) orless UF membranes have the ability to retain larger organic macromolecules

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 85

Table 31 Characteristic features of MF and UF membranes

Microfiltration (MF) Ultrafiltration (UF) Nanofiltration (NF)

Operation mode Cross-flow and dead-endoperation

Cross-flow and dead-endoperation

Cross-flow operation

Operating pressure 01e3 bar (Transmembrane) 05e10 bar (Transmembrane) 2e40 bar (Transmembrane)

Separating mechanism Separation based on particle size Separation based on basedparticle size

Separation based on differencesin solubility and diffusivity

Molecular separation size Solids gt01 mmSeparation of particles

Colloids 20000e200000 DaSolids gt05 mmSeparation of macromolecules

Dissolved matter200e20000 Dasolids gt0001 mmSeparation of low-MW solutes(salt glucose lactose micro-pollutants)

Membrane types Predominantly symmetricpolymer or ceramic membranes

Asymmetric polymer compositeor ceramic membrane

Asymmetric polymer orcomposite membrane

Module types Spiral-wound hollow-fiber andtube modules plate or cushionmodules

Spiral-wound hollow-fiber andtube modules plate or cushionmodules

Spiral-wound tube and cushionmodules

Osmotic pressure negligible Osmotic pressure negligible Osmotic pressure negligible Osmotic pressure high(1e25 bar)

Thickness of separating layer Symmetric frac14 10e150 mmAsymmetric frac14 1 mm

01e10 mm 01e10 mm

Source Adapted from Pinnekamp and Friedrich (2006) volume 2 2nd edition

86Advances

inMem

braneTechnologies

forWater

Treatm

ent

they have been historically characterized by a molecular weight cutoff (MWCO)rather than by a particular pore size (Membrane Filtration Guidance Manual2005) Both UF and MF membranes can be considered porous membranes in whichrejection is determined mainly by the size and shape of the solutes relative to thepore size in the membrane In fact MF and UF involve similar membrane processeswith the same separation principle However an important difference is that UFmembranes have an asymmetric structure with a much denser top layer (smallerpore size and lower surface porosity) and consequently much higher hydrodynamicresistance (Mulder 1996)

There are two different operation modes for MF and UF systems Figure 32 showsthe cross-flow configuration in which the feed water is pumped tangential to the mem-brane Clean water passes through the membrane while the water that is rejected isrecirculated as concentrate and combined with additional feed water In dead-end ordirect filtration all of the feed water passes through the membrane Therefore recoveryis almost 100 and a small fraction is periodically used for backwash in the system(2e15) (Jacangelo et al 1997)

Permeate

Backwash waste

Recycle

Permeate

Air or liquidbackwash

Air or liquidbackwash

Recirculation pumpPre-screen

Pre-screen

Feed pump

Feed pump

Rawwater

Rawwater

(a)

(b)

Figure 32 (a) Cross-flow configuration MF and (b) dead-end filtration for microfiltration (MF)Reprinted from Jacangelo Trussell and Watson (1997) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 87

NowadaysmostMFUFplants operate in dead-endfiltrationmode because the energyrequired is lower compared with cross-flow systems as the high cross-flow velocityrequired to prevent fouling results in increased head loss and energy consumption

323 Nanofiltration process

NF membranes have applications in several areas (Koyuncu amp Cakmakci 2010) Themain applications of NF are in water treatment for drinking water production as well aswastewater treatment and also reuse (Debik Kaykioglu Coban amp Koyuncu 2010)NF can be used to treat all kinds of water including groundwater surface water andwastewater or as a pretreatment for desalination (Cakmakci Baspinar BalabanKoyuncu amp Kinaci 2009 Koyuncu Arikan Weisner Mark amp Rice 2008 UyakKoyuncu Oktem Cakmakci amp Toreurooz 2008) The introduction of NF as a pretreat-ment is considered a breakthrough in the desalination process NF membranes haveability to remove turbidity microorganisms and hardness as well as a fraction ofthe dissolved salts This results in a significantly lower operating pressure and providesa much more energy-efficient process compared with RO (Hilal Al-Zoubi DarwishMohammad amp Abu Arabi 2004)

These membranes which fall into a transition region between pure RO membranesand pure UF membranes are called loose RO low-pressure RO or more commonlyNF membranes Typically NF membranes have sodium chloride rejections between20 and 80 andMWCOs for dissolved organic solutes of 200e1000 Da These prop-erties are intermediate between RO membranes with a salt rejection of more than 90andMWCOof less than 50 andUFmembranes with a salt rejection of less than 5 Theneutral NF membrane rejects various salts in proportion to their molecular size so theorder of rejection is simply Na2SO4 gt CaCl2 gt NaCl (Baker 2004)

Many researchers have studies the softening of groundwater using NF Scheap et al(1998) used different NF membranes and their experimental results showed that60e70 ofmultivalent ions can be removed byNFmembranes Sombekke Voorhoeveand Hiemstrap (1997) compared NF membranes with activated carbon adsorptionAccording to the results both processes had goodperformanceHoweverNFmembraneshad some advantages in terms of investment costs (Hilal et al 2004 Schaep et al 1998Sombekke et al 1997)

NF membranes are used for their ion selectivity The retention of a dissolved salt isdetermined by the valence of the anions Therefore most salts with monovalent anions(eg Cl) can pass through the membrane whereas multivalent anions (eg SO2)are retained The separation spectrum for NF membranes is given in Figure 33

Some parameters are crucial for the operation of an NF unit solvent permeabilityflux through the membrane rejection of solutes and yieldrecovery Similar to otherpressure-driven membrane processes the flux J or the permeability (flux per unitof applied pressure) of a membrane is a crucial parameter Most NF membranes arehydrophilic except some used for solvent applications

Rejection in NF is mainly determined by molecular size hydrophobicity andcharge but the effects of the molecular shape and dipole moment for example mighthave an important role as well The porevoid dimensions are statistically distributed

88 Advances in Membrane Technologies for Water Treatment

and can be described by a log-normal distribution (Bowen amp Welfoot 2005) Thisexplains the smooth transition from no rejection to complete rejection in a typicalS-shaped curve when molecular size is varied The MWCO value is often used to indi-cate the lower limit of molecules that are (almost completely) retained similar to UFmembranes For NF membranes with MWCO values between 150 and 1000 (but oftenin the range 150e300) this concept should be used with care Hydrophobic moleculeslarger than the MWCO for example often have a low rejection The pH of the solutionmight change the membranersquos surface charge as well as the charge of the solute so therejection of this solute can be higher or lower than expected

Another parameter is the recovery or yield which is generally used for the design ofan industrial application rather than a membrane characteristic The recovery is theratio of the permeate stream to the feed stream values range from 40 to 90

3231 Applications of NF membranes

NF membranes can reduce the ionic strength of the solution Moreover hardnessorganics and particulate contaminants can be removed by NF membranes Manyresearchers have used NF to achieve those objectives

Some researchers have investigated the softening of groundwater using NFsystems All of the results gave good data Retentions higher than 90 were foundfor multivalent ions whereas monovalent ions were about 60e70 (Hilal et al2004 Scheap et al 1998) NF membranes with pellet softening and granular activatedcarbon for softening water were compared Although all methods had good results NFmembranes had several advantages from the point of health and lower investmentcosts The advantage of NF softening is that a smaller stream of water can be softenedbecause NF membranes remove essentially all hardness cations In municipal watertreatment works it is not necessary to reduce hardness to very low values and there-fore the use of NF membranes allows for side-stream treatment This involves sending

Reverse

osmosis

region

Nano-

filtration

region

100 105

104

103

102

10

80

60

40

20

0001 10 10 10001

Ultrafiltration

region

Water pressure-normalized flux

(m3 m2 middot bar middot day)

Mole

cula

r w

eig

ht cuto

ff

(90

rete

ntion

)

NaC

l re

jection (

)

Figure 33 Separation permeability spectrum of nanofiltration and other processesReprinted from Baker (2004) Membrane transport theory p 83

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 89

only a portion of the flow to be softened to the membranes and permeate is thenblended with the bulk flow stream to obtain a target blended value In contrast precip-itated lime softening cannot reduce hardness to below approximately 50 mgL CaCO3and therefore side-stream treatment is generally not practical

A typical NF membrane system consists of three separate subsystems pretreatmentmembrane processes and posttreatment

The primary application of NF membranes is desalting of saline surface orgroundwater Surface waters often have unsettled chemistry or composition owingto seasonal changes or after dilution with rain NF is a reliable option for surface watertreatment although the focus is on removing organics rather than on softening (Hilalet al 2004 Van der Bruggen amp Vandecasteele 2003)

Disinfection by-products (DBPs) are a significant regulatory concern NFmembranes are increasingly applied to remove DBP precursors such as natural organicmatter (NOM) which can react with various disinfectants used in the water treatmentprocess to form potential carcinogens NOM removal is an important water treatmenttarget for many utilities NF as a standalone process has been shown in many cases toreduce total organic carbon (TOC) to less than 05 mgL (AWWA 2007)

NF is also more effective than RO for lime softening removing naturally occurringcolor and DBP precursors both consist primarily of organic carbon

Semipermeable NF membranes are not porous they have the ability to screenmicroorganisms and particulate matter in the feed water This ability has been verifiedin a number of studies such as one that demonstrated that NF membranes providebetween 4 and 5 log removal of viruses

324 Integrated membrane systems

For acquiring regulation standards for drinking water NF and low pressure ROprocesses are considered however they are too sensitive to fouling and advanced pre-treatment processes like UF and MF are used to increase the productivity of systemsThese integrated systems are called as integrated membrane system (IMS) and theirpurpose is to reduce and control fouling

33 Pretreatment requirements

Pretreatment is typically applied to the feed water before entering the membranesystem to minimize membrane fouling However in some cases it may be used toaddress other water quality concerns or treatment objectives Pretreatment is mostoften used to remove foulants optimize recovery and system productivity and extendmembrane life Pretreatment may also be used to prevent physical damage to themembranes

Different types of pretreatment can be used in conjunction with any givenmembrane type Pilot testing can be used to compare various pretreatment optionsoptimize pretreatment andor demonstrate pretreatment performance (Membrane

90 Advances in Membrane Technologies for Water Treatment

Filtration Guidance Manual 2005) The feed water may contain various concentra-tions of dissolved matter and suspended solids depending on the source Suspendedsolids may include inorganic particles colloids and biological debris such as micro-organisms and algae Dissolved matter may consist of highly soluble matterssuch as chlorides soluble salts and sparingly soluble salts such as carbonate andsulfates

Depending on the raw water quality the pretreatment process may follow stepssuch as

bull Removal of large particles using a coarse strainerbull Water disinfection with chlorinebull Clarification with or without flocculationbull Clarification and hardness reduction using lime treatmentbull Media filtrationbull Reduction of alkalinity by pH adjustmentbull Addition of scale inhibitorbull Reduction of free chlorine using sodium bisulfite or activated carbon filtersbull Water sterilization using ultraviolet (UV) radiationbull Final removal of suspended particles using cartridge filters (Membrane Fouling

Considerations 2001)

331 General pretreatment methods

Membranes can be fouled by organic or inorganic substances Therefore pretreatmentof the feed stream is required to control colloidal organic and biological fouling aswell as scaling For low-pressure membranes a number of pretreatment methods arecurrently used (Abdelrasoul Doan amp Lohi 2013)

UF can sufficiently produce disinfected water directly from surface water fordifferent applications MF can also be used for disinfection although not all virusesare removed Because direct membrane filtration is limited by fouling it leads to acontinuous increase in transmembrane pressure during constant flux filtration(Kennedy et al 2008)

3311 Prefiltration

Prefiltration involving screening or coarse filtration is a common means ofpretreatment for membrane filtration systems that is designed to remove large particlesand debris Prefiltration can be applied to the membrane filtration system as a wholeand to each membrane unit separately The particular pore size associated with theprefiltration process varies depending on the type of membrane filtration system andthe feed water quality Generally hollow-fiber MF and UF systems are designedspecifically to remove suspended solids large particulate matter that can damage orclog the membranes fibers Use of these types of filtration system depend on theinfluent water quality and manufacturer specifications the pore sizemicron rating ofa chosen prefiltration process may range from as small as 100 mm to 3000 mm orhigher Because of this hollow-fiber MFUF membrane systems that operated in an

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 91

inside-out mode are more suitable to fiber clogging and thus may require prefiltration(Membrane Filtration Guidance Manual 2005)

NF and RO are nonporous membranes that cannot be backwashed and are mostcommonly designed in a spiral-wound configuration for municipal water treatment ap-plications NF and RO systems must use finer prefiltration to minimize membraneexposure of particulates of any size At this point spiral-wound membrane modulesare highly sensitive to particulate fouling that can reduce system productivity andreduce membrane life (Membrane Filtration Guidance Manual 2005) Table 32 listsrequired prefiltration systems for NFRO according to the silt density index (SDI) value

In cartridge filtration technology applications prefiltration is not required inhigh-quality source water treatment

Typical prefiltration requirements associated with various types of membranefiltration are presented in Table 33

In some cases one type of membrane filtration may be used as prefiltration foranother This type of treatment scheme is known as an IMS Generally this involvesMFUF use as pretreatment for NFRO applications that require the removal ofparticulates and microorganisms as well as some dissolved contaminants such as hard-ness iron and manganese or DBP precursors The most significant advantages of an

Table 32 Required prefiltration systems for NFRO according to SDIvalue

Feed water SDI value Proposed prefiltration Rating ranges

5 Cartridge filters 5e20 mm

gt5 MFUF 01e001 mm

Source Membrane Filtration Guidance Manual (2005)

Table 33 Typical membrane system prefiltration requirements

Membrane system Prefiltration requirements

Classification Configuration Size (mm) Type(s)

Membrane cartridgefiltrationa

Cartridge 300e3000 Strainersbag filters

MFUF Hollow-fiberinside-out

100e300 Strainersbag filters

Hollow-fiberoutside-in

300e3000 Strainersbag filters

NFRO Spiral-wound 5e20 Cartridge filters

aPrefiltration is not necessarily required for membrane cartridge filtration systemsSource Membrane Filtration Guidance Manual (2005)

92 Advances in Membrane Technologies for Water Treatment

IMS treatment scheme is that MFUF filtrate is of consistently high quality with respectto particulate matter and maintains stable operation by reducing the rate of membranefouling (Membrane Filtration Guidance Manual 2005)

3312 Coagulation and filtration

Coagulation as a pretreatment process can substantially reduce the concentration ofbiodegradable organic matter found in raw water thus it can decrease the potentialfor fouling and enhance membrane rejection However this method can be a problembecause coagulant residuals and increased solids loading can reduce membrane fluxesand increase cleaning requirements Generally coagulation is required for MF pro-cesses in water treatment Some research suggested that flocs need to reach a certaincritical floc size before MF on the contrary pores of MF membranes are irreversiblyfouled by small particles (Judd amp Hillis 2001)

3313 In-line coagulation

In-line coagulation (IC) involves the use of coagulants without the removal ofcoagulated solids After that coagulated water is given to MF or UF Conventionalcoagulation and IC are different from each other in terms of initial membrane fluxdecline IC has better results than conventional coagulation for initial membraneflux (Escobar project report)

The IC (without settling)UF process improves membrane performance and waterquality for surface water treatment Employing coagulation before UF increasedpermeate quality to the extent that dissolved organic matter removal is controlled bythe coagulation step (Guigui Rouch Durand-Bourlier Bonnelye amp Aptel 2002)

Antelmi Cabane Meireles and Aimar (2001) reported that aggregates producedunder sweep floc conditions are more compressible than for charge neutralization con-ditions resulting in compaction when the membrane filtration system is pressurizedThey thought that cake resistance is lower than the resistance resulting from theunsettled flocs and the noncoagulated organics

3314 Coagulationesedimentation process

In coagulation and sedimentation processes a coagulant is applied to form flocs thatare settled out by sedimentation After sedimentation the supernatant is fed to themembranes If coagulation and sedimentation are applied before UF UF membranesare less fouled Experimental studies showed that membrane life can be increased as aresult of coagulationesedimentation processes (Kruithof Nederlof Hoffmanamp Taylor 2004 Minegishi Jang Watanabe Hirata amp Ozawa 2001)

3315 Coagulationeadsorption process

Some research showed that membrane fouling can be minimized by pretreatmentNOM in feed water can be caused trihalomethane (THM) formation in the disinfectionstep Although coagulation and MF are a good flowchart for water treatment THM

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 93

precursors cannot be removed by the MF process When pre-adsorption is used forNOM the removal of THM precursors or NOM is improved (Beacuterube MavinicHall Kenway amp Roett 2002 Carroll King Gray Bolto amp Booker 2000 MaartensSwarta amp Jacobs 1999)

3316 Flocculation and filtration

Colloids can be removed by co-precipitation with Al(III) Fe(III) or Si(IV)hydroxides The negatively charged colloids are surrounded by the metal cationsand thus form a nucleus for their precipitation The same thing happens when limeis used for softening When polymer is added for coagulation the long chains canact as bridges linking colloidal particles and aiding in floc formation

Flocculation and filtration processes are used to achieve three objectiveseliminating the penetration of colloidal particles into the membrane pores increasingthe critical flux and modifying the characteristics of the deposits (Abdelrasoul et al2013 Kennedy et al 2008)

3317 Ion exchange

Some dissolved salts or divalent cations in feed water can cause scaling on themembrane surface To overcome this problem softening of feed water is requiredIon exchange process can be used for this purpose

The softening approach uses cationic resins to replace the calcium ions (or other diva-lent cations) with sodium ions which do not form insoluble salts with carbonate ion Ionexchange is well-suited for incorporation into an RO system Depending on the salinityand pH the RO concentrate may be used as a regenerate solution Cation exchange resinscan be adequately regenerated at lower concentrations than 10 with lower flow ratesand longer regeneration cycles (Wilbert Leitz Abert Boegli amp Linton 1998)

3318 Chemical conditioning

Chemical conditioning is used for various pretreatment purposes such as pHadjustment disinfection biofouling control scale inhibition and coagulation Sometype of chemical conditioning is almost always used with NFRO systems most oftenthe addition of an acid or proprietary scale inhibitor recommended by the membranemanufacturer to prevent the precipitation of sparingly soluble salts such as calciumcarbonate (CaCO3) barium sulfate (BaSO4) strontium sulfate (SrSO4) or silica spe-cies (eg SiO2) (Membrane Filtration Guidance Manual 2005)

A number of different chemicals can be added to MF or UF systems as apretreatment related to treatment objectives However as with NF and ROmembranesapplied pretreatment chemicals must be compatible with the particular membrane ma-terial used An MFUF system may be able to operate efficiently with the in-line addi-tion of lime or coagulants On the other hand presettling in association with thesepretreatment processes can enhance membrane flux and increase system efficiency(Membrane Filtration Guidance Manual 2005)

94 Advances in Membrane Technologies for Water Treatment

332 Pretreatment requirements for membrane bioreactors

The first generation of membrane bioreactors (MBR) in the 1970 and 1980s were builtwith large-diameter tubular membranes and were primarily used for small-scale indus-trial effluents containing little waste Pretreatment to MBR first became an issue whenhollow fibers and plate-immersed membranes were introduced in the 1990s forapplication to municipal wastewater

Today municipal MBR systems capacities are up to 50000 m3d and much largersystems are under construction or in the planning stages Current research goals are toreduce the cost of technology and increase the packing density These improvementsmake it significantly important to install adequate pretreatment to protect the mem-branes at the core of an MBR Possible negative effects of poor pretreatment on themembranes themselves include

bull Buildup of trash hair lint and other fibrous materialsbull Increased risk of sludge accumulationbull Eventually damage to the membrane (Co

ˇ

teacute Brink amp Adnan 2006)

34 Advances in membrane materials for watertreatment by MF UF and NF

Membrane technology is used to improve water quality treat wastewater and reuseprocesses for years The surge of interest in membrane separations increased owingto two developments high-flux defect-free membranes and high-surface-areaeconomical modules Membranes range from porous structures to nonporous onesand can be asymmetric or symmetric They are used for removal from macropollutantsup to ions Because pressure-driven membranes consist of selective barriers pore char-acteristics are important Macrofiltration UF and NF processes are classified by theirpore structure (pore size pore size distribution and porosity) Hydrophilicity surfacecharge roughness etc should also be considered The membrane material has greatsignificance An appropriate membrane material should resist chemical and thermalattack and should be robust thin defect-free and cheap (Baker 2004 Fane Tangamp Wang 2011)

For membrane materials polymers are generally preferred because they areinexpensive and easily formpore structures In additionmetallic ceramic andcompositematerials are used These materials are now thought of as conventional Recently mem-brane materials have improved Some novel membrane materials exist such as nano-structured reactive bioinspired membranes (Ng Mohammad Leo amp Hilal 2010Pendergast amp Hoek 2011)

341 Conventional membrane materials

Conventional membranes include polymeric ceramic and thin-film composite (TFC)membranes in general

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 95

Polymers are by far the most popular membrane material used for membranefabrication A good polymer material should resist thermal and chemical attack andhave good mechanical strength and the ability to form flat-sheet or hollow-fiberconfigurations easily Mostly polymeric membranes are fabricated with the phaseinversion technique Commonly used polymeric membrane materials are cellulose ac-etate (Chou amp Yang 2005 Saljoughi Amirilargani amp Mohammadi 2010) polyviny-lidene fluoride (PVDF) (Han Xu Yu Wei amp Cao 2010 Li Liu Xiao Ma amp Zhao2012) polyacrylonitrile (PAN) polypropylene (PP) polyethersulfone (PES) (ChenLi Han Xu amp Yu 2010 Loh Wang Shi amp Fane 2011 Xu Leurou Zhen Ku amp Yi2008) and polysulfone (PS) (Ohya Shiki amp Kawakami 2009 Rugbani 2009) Poly-meric membranes have varying process uses they can be applied from MF to ROCommercial UFMF membranes can be fabricated from both hydrophilic and hydro-phobic polymers Both polymers have some pros and cons because hydrophilic mem-branes lower the attachment of bacteria owing to adsorption but they are less robustthan hydrophobic polymers Table 34 shows commonly used polymeric materialsand their properties

Cellulose acetate membranes have good permeability and rejection characteristicsare susceptible to hydrolysis have limited pH resistance and low chlorine toleranceand are resistant to fouling On the other hand PES PVDF PS and PAN can be modi-fied as a blend to improve their limited abilities They show good permeability flex-ibility and high strength PP polymer has limited blending capacity and is prone tooxidation (Fane et al 2011)

Ceramic membranes are better than polymeric membranes because of their narrowpore size distribution higher porosity separation characteristics mechanical and chem-ical stability and lower fouling Typical ceramic membranes are fabricated using thesol-gel process and are asymmetric in structure Generally materials used for ceramicmembranes are zirconia silica alumina mullite oxide mixtures and sintered metals(Harman Koseoglu Yigit Beyhan amp Kitis 2010 Hofs Ogier Vries Beerendonkamp Cornelissen 2011 Mohammadi amp Maghsoodloorad 2013 Pendergast amp Hoek2011) They are well-suited for water treatment because they have higher stabilitiesFlux decrease can be easily recovered after fouling because they can resist destructivecleaning conditions so their lifetime is extended However they are expensive inindustry and owing to their inexpensiveness polymeric membranes are preferred

TFC membranes are asymmetric in structure therefore support and selectivelayers can be independently selected for optimization they are generally fabricatedthrough interfacial polymerization or coating and then cross-linking By changingthe properties of cross-linking thin-film structure stability selectivity and perme-ability can be changed Generally used TFC membranes are polyurea polyamideand polyurea-amide (Lau Ismail Misdan amp Kassim 2012 Pendergast amp Hoek2011) The support part of the membrane can be fabricated from PES PS PANetc The film structure is important for TFC membranes By changing monomers sur-factants and additives within the film composition different types of structure can beobtained (Lau et al 2012) TFC membranes are used to obtain high flux and highselectivity in desalination Also these kinds of membranes are used to desalt brackishwater and for water reclamation water softening and removing dissolved organics

96 Advances in Membrane Technologies for Water Treatment

Table 34 Commonly used polymeric materials and their properties

Polymer material Specifications

Cellulose acetate Cellulose acetate and its blends are widelyused for MF and UF membranes Celluloseacetate is susceptible to hydrolysis andmicrobial attacks and has a stable pHbetween 4 and 65

Polysulfone Polysulfone is an amorphous polymer It hasexcellent chemical and thermal stability It ismainly used for UF and MF membranes andas a support layer for NF and ROmembranes Polysulfone membranes have awide range of pore sizes and their modulescan be capillary flat-sheet and hollow-fiber

Polyethersulfone Polyethersulfone membranes have highchemical and thermal stability They aremainly used for UF and MF Flat-sheet orhollow-fiber module configurations exist

Polyacrylonitrile Polyacrylonitrile possesses superior resistanceto hydrolysis and oxidation It is mainlyused to prepare UF membranes and poroussupports of composite membranes

Polyamide Polyamide has good thermal and mechanicalstability It is resistant to organic solventattacks However it is susceptible tochlorine attacks It is used as a thin layer forRO and NF

Polyimide Polyamides exhibit excellent thermal andchemical stability because of their high glasstransition temperature They are used tomake NF membranes

Polycarbonate Polycarbonate is a transparent thermoplasticwith high-performance properties It hasgood mechanical strength and can be used tomake UF and MF membranes by the phaseinversion process

Polyvinylidene fluoride Polyvinylidene fluoride is semicrystalline witha low glass transition temperature It isresistant to chemical and thermal attacks aswell as to most inorganic and organicsolvents It can tolerate a wide range of pH

Source Adapted from Fane et al (2011) and Gupta (2013)

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 97

342 Novel membrane materials

Novel membrane materials can be defined as nanotechnology based membranesThese materials can be zeolite-coated ceramic membranes reactivecatalytic mem-branes nanocomposite membranes which can be either mixed matrix or TFC andbiologically inspired membranes that are aquaporin vertically aligned carbon nano-tube or block copolymer membranes (Pendergast amp Hoek 2011)

Zeolites are naturally occurring alumina silicate minerals that have high uniformityand nanometer-scale crystallinity People prefer zeolite-coated ceramic membranesbecause by using them one can obtain permeability in the range of UF membranesand also selectivity in the range of NF or higher Typical zeolite membranes are fabri-cated by hydrothermal layer-by-layer crystallization etc synthesis methods withamorphous silicate aluminosilicate which is inert and has good thermal and chemicalstability Zeolite crystals are tetrahedral frameworks that consist of cross-linked (SiAl)O4 (Figure 34) (Georgiev Bogdanov Angelova Markovska amp Hristov 2009) Waterpermeability and ion selectivity are primarily affected by the ore and framework den-sity of zeolite particles On the other hand the SiAl ratio is the most important factorfor obtaining chemical stability and hydrophilic properties They can be applied toboth polymers and ceramic membranes (Pendergast amp Hoek 2011) Dahe Teotiaand Bellare (2012) fabricated nanozeolitepolysulfone composite membranes for UFpurposes They found that the addition of nanozeolite increased water permeabilityup to 22 Lm2 h bar and also increased the MWCO value from 9500 to 54000 Da

Other novel membranes are reactive catalytic ones Reactive catalytic membranesactivate semiconductor-based membranes by sunlight or UV to degrade organiccontaminants Semiconductors are characterized by a filled valence band and anempty conduction band When photon energy (hn) exceeds band gap energy an elec-tron leaps from the valence band to the conduction band (Figure 35) This excitedstate of bands can recombine or dissipate input energy as heat and can get trappedin metastable surface states or react with electro-donors and acceptors that areadsorbed on the surface of semiconductors or within the electrical double layer ofcharged particles If there is a surface defect this defect can trap an electron orhole so that the band cannot recombine subsequently a redox reaction mayoccur Valence bands are good oxidants whereas conduction bands are goodreductants For interactions in bulk semiconductors an electron or hole is available

HOxygen

Silicon or Aluminum

Si Al

Ondash

Figure 34 (Left) Chemical structure of zeolite (Right) Building unit of a zeolite structureReprinted from Georgiev Bogdanov Angelova Markovska and Hristov (2009)

98 Advances in Membrane Technologies for Water Treatment

nanomaterials allow highly efficient interactions owing to their surfaces Organicphoto-degradation requires oxidizing and reducing species This degradation couldbe by indirect or direct oxidation With semiconductors contaminants such asalkanes phenols polychlorinated biphenyls alkenes alkanes surfactants and pes-ticides as well as heavy metals such as chromium(VI) can be removed (HoffmannMartin Choi amp Bahnemannt 1995)

Titanium zinc oxide and ferric oxide are the most commonly used semi-conductor-based membranes (Chong Jin Chow amp Saint 2010) The performance of this kind ofmembrane for degrading contaminants and inactivating complex dense cell wall struc-tures is limited Also these types of membranes have a high cost and low packing den-sity (Pendergast amp Hoek 2011) Crock Rogensues Shan and Tarabara (2013)fabricated exfoliated graphite nano-platelets decorated with Au nanoparticles(Figure 36) The resulting membrane was catalytic with UF properties When nano-platelets and the amount of Au were changed different catalytic activities wereobtained Ma Zhang Quan Fan and Zhao (2010) fabricated photocatalytic MF mem-branes with Ag-TiO2hydroxyapatiteAl2O3 to treat surface water According to theirresults humic acid removal synergistically affected filtration and photocatalysis Theantifouling ability of the membrane comes mainly from photocatalytic activityZhu et al (2011) fabricated MF ceramic membranes combined with titaniumoxide and alumina with ozonation for water treatment They obtained a fluxes of79 Lm2 h and 90 Lm2 h with alumina and titanium oxide respectively

Nanocomposite membranes are advantageous because of their low cost easyfabrication and high mechanical stability and because they show both polymericand inorganic material properties Typically used nanoparticles are silver- magne-sium- iron- aluminum- silica- zirconium- and titanium-based as well as carbonnanotubes and graphenes Nanoparticles can be formed by sol-gel processes ion sput-tering spray pyrolysis pulsed laser ablation laser pyrolysis mechanical alloyingmill-ing electrodeposition and so forth (Buonomenna 2013 Goh Ismail amp Ng 2013Mishra amp Ramaprabhu 2011 Ng et al 2010 Pendergast amp Hoek 2011)

Reduction

hv

∆EEnergy

Oxidation

Conductionband

Valenceband

Figure 35 Schematic of photocatalysisReprinted from Pendergast and Hoek (2011) with permission from Royal Society of Chemistry

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 99

Many applications exist for these kinds of membranes in water treatmentapplications Nanoparticles used within these types of membranes enhanced mem-brane selectivity and pore connectivity inhibit macro void formation and increase sur-face to volume ratios Attention is given to nanoparticles because of their ability todisinfect adsorb and degrade organics (Akar Asar Dizge amp Koyuncu 2013 Koseo-glu Kose Altinbas amp Koyuncu 2013) In this manner for example silver nanopar-ticles can be used to decrease fouling and increase antibacterial properties RazmjouResosudarmo Holmes and Li (2012) studied the effects of TiO2 nanoparticles on PEShollow fiber (HF) membranes They used both mechanically modified and chemicallyand mechanically modified TiO2 Higher thermal resistance permeability hydrophi-licity porosity and pore size and lower elasticity and tensile strength were foundfor chemically and mechanically modified TiO2 Han et al (2010) spun hollow-fibermembranes by adding aluminum silica and titanium oxide nanoparticles at thesame dope solution with different concentrations They observed high flux valuesand high tensile strength values Bovine serum albumin (BSA) rejection changeddiscordantly Morphology changed from a macroporous to an asymmetric structureDenser top layers were obtained and the most obvious effect on membranemorphology was on the inner surface Liang Xiao Mo and Huang (2012) fabricateda novel ZnO nanoparticle-blended PVDF membrane for anti-irreversible fouling Theaddition of ZnO nanoparticle increased the hydrophilicity of the membranes and 100water flux recovery was observed Permeability values were doubled compared withpristine membranes In addition they found that adding ZnO increased the mechanicalstability of the membranes Sengur (2013) fabricated PES hollow-fiber membranes

2nd functional nanoparticles

1st ˝carrier mats˝exfoliated graphite nanoplatelets

Hierarchy level

Nanocomposite membraneMembrane casting mixture

PolymerPhase inversion

Hierarchicalnanofiller

Solvent

Porogen

ReactantsProducts

-15 microm -12 nm

-30 nm

Catalyticreaction

Figure 36 Catalytic nanocomposite membrane fabricated with exfoliated graphitenanoplatelets and Au nanoparticlesReprinted from Crock et al (2013) with permission from Elsevier

100 Advances in Membrane Technologies for Water Treatment

with UF properties with both hydroxylated and carboxylated multi-walled carbonnanotube (MWCNT) The effects of different MWCNTs were different Fabricatedcarboxylated MWCNT membranes had antifouling ratios and better water recoveryratios whereas hydroxylated MWCNT membranes had higher permeabilities Turken(2013) fabricated PESAg-nanocomposite UF hollow-fiber membranes According totheir results the membranes showed improved antibacterial properties antifoulingand mechanical stability

Thin-film nanocomposite (TFN) membranes are fabricated through interfacialpolymerization by incorporating nanomaterials into the active layer of TFC mem-branes via doping into casting solutions or by surface modification their advantagesare enhanced separation reduced fouling antimicrobial activity and some other novelproperties For TFN membranes the particles most used are zeolites carbon nano-tubes TiO2 silica and silver (Buonomenna 2013 Kim Hwang El-Din amp Liu2012 Pendergast amp Hoek 2011 Qu Alvarez amp Li 2013) Tiraferri Vecitis andElimelech (2011) used covalently bonded single-walled carbon nanotubes (SWCNT)to a TFC membrane With that method they used a tiny amount of nanomaterials Theresulting membrane had improved antibacterial properties and potentially decreasedfouling In the literature TFN membranes are generally used for RO so there is littleliterature containing NF UF or MF applications

On the other hand biologically inspired membranes offer huge potential andimproved membrane properties However they are far from commercialization becausethere are some difficulties in scaling Aquaporin-based membranes one of the biolog-ically inspired membranes are highly productive and selective but not cost-effectiveAquaporins are protein channels that have the ability to control water flux within mem-branes Their ability to transport to water is higher than any kind of commercial ROmembrane Their water permeability is in the order of glucose glycerol salt andurea (Pendergast amp Hoek 2011 Qu et al 2013 Tang Zhao Wang Heacutelix-Nielsenamp Fane 2013 Zhong Chung Jeyaseelan amp Armugam 2012) Generally they areapplied in desalination and water reuse Table 35 shows studies from the literature

Another kind of biologically inspired membrane is vertically aligned carbonnanotubes (CNTs) (Figure 37) Water transport within CNTs is as high as aquaporinsSelectivity of the vertically aligned CNT membranes is described in Corry (2008)CNTebased membranes also have excellent mechanical properties Aligned CNTsare generally fabricated by chemical vapor deposition (CVD) such as microwaveplasma-enhanced CVD catalytic CVD spray pyrolysis and self-assembly (Pender-gast amp Hoek 2011) Vertically aligned CNT membranes can be used to remove micro-bial contaminants from drinking water They are superior to conventional membranesbecause they can be cleaned by ultrasonication or autoclaving whereas conventionalmembranes should be disposed of at the end of their limited life which is affected byfouling (Pendergast amp Hoek 2011)

The last type is block copolymer membranes These are macromolecules thathave the ability to self-assemble into highly ordered structures when added intothe proper solvent Their densely packed cylindrical pores are ideal for waterseparation In the literature there are many studies using block copolymers tofabricate UF membranes Wandera Himstedt Marroquin Wickramasingh and

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 101

Table 35 Examples of biomimetic membranes designed for water reuse and desalination Performance dataare presented as water permeability (WP) (lm2 h bar) NaCl rejection (RNaCl) () membrane area (A)(cm2) and maximal external pressure applied (Pmax) (bar) when operated in RO CA cellulose acetatePC polycarbonate

Approach WP (lm2 h bar) RNaCl () Area (cm2)Pmax

(bar) Upscaling issues Remarks

Charged lipid mixturevesicles depositionsonto NF membranes

083 nda 35 10 Difficult to producelarge defect-freemembranes

No aquaporinincluded

Vesicle fusionfacilitated byhydraulic pressure onhydrophilic NFmembranes coatedwith positivelycharged lipids

36 02 35 8 126 1 Difficult to producelarge defect-freemembranes

Low RNaCl Onlysuitable for NF

Membranes acrossmultiple micron-scaleapertures asfreestanding lipid orpolymer membranes

nda nda 4 nda Nanofabricationrequired Lowrobustness

WPRNaCl not testedNot suitable forRO

Membranes acrossmultiple micron-scaleapertures andstabilized byhydrogelencapsulation

12e40 nda 35 2 Nanofabricationrequired Highrobustness

Characterization withgramicidinchannels Noaquaporinincluded

102Advances

inMem

braneTechnologies

forWater

Treatm

ent

Aquaporin containingpolymersomes onmethacrylatefunctionalized CAmembranes

342 69 329 91 007 5 Medium robustness Small area High WPbut low RNaClOnly suitable forNF

Detergent-stabilizedHis-tagged aquaporinadded to monolayerswith nickel-chelatinglipids

nda nda nda nda Complex fabricationLow robustness

WPRNaCl not testedMay be notsuitable fordesalination

Proteopolymersomedeposition onto gold-functionalized PCtrack-etchedsubstrates

nda nda 0096 nda Complex fabricationLow robustness

Small areaRelatively highWP in FO No ROdata

Interfacialpolymerizationmethod withembeddedproteoliposomes

4 04 963 13 gt200 14 Simple fabricationHigh robustness

Combined high WPand RNaClSuitable for RO

and not definedSource Adapted from Tang et al (2013) Copyright (2013) with permission from Elsevier

Advances

inwater

treatment

bymicro

filtrationultrafiltrationand

nanofiltration

103

Husson (2012) modified low-MWCO cellulose UF membranes with block copol-ymer nanolayers They used poly(N-isopropylacrylamide)-block-poly([polyethyleneglycol] methacrylate) (PNIPAAm-b-PPEGMA) nanolayers and investigated therole of polymer on the performance of the membrane According to their resultsthe nanolayer structure affected fouling Optimization resulted in high stable fluxThe coating chemistry and structural properties of coating affected antifouling prop-erties Fabricated Ps-b-PMMA films showed unique porous morphology (Figure 38)(Kim Yang Lee amp Kim 2010) Nanopores were observed only at the bottom andtop membrane surfaces The structure had high resistance to all organic solvents andshowed great dimensional stability after filtration tests In another study (Zhao SuChen Peng amp Jiang 2011) the block-like copolymer poly(butyl methacrylate)-b-poly(methacrylic acid)-b-poly(hexafluorobutyl methacrylate) (PBMA-b-PMAA-b-PHFBM) material which has hydrophobic hydrophilic and fluorine-containingsegments was used Copolymer was added into the PES membrane matrix Accord-ing to the results the membrane showed excellent pH-responsive permeability anddesirable fouling release properties To increase the hydrophilicity of PS membranesRoux Jacobs van Reenen Morkel and Meincken (2006) used branchedPEO-block-PS copolymers and incorporated them into the membrane matrix Fluxand rejection data showed that the membrane morphology was changed after itwas modified with copolymer Figure 39 compares conventional and novel-basedmembranes

Figure 37 Carbon nanotube membrane simulationReprinted from Corry (2008) with permission from American Chemical Society

104 Advances in Membrane Technologies for Water Treatment

Figure 38 Scanning electron microscopy image for block copolymer film with mixedorientationReprinted from Kim Yang Lee and Kim (2010) with permission from Elsevier

ZeoliteTFNs

NanoparticleTFNs

NanostructuredceramicmembranesInorganic-organicmembranesBiologicallyinspiredmembranes

Blockcopolymers

Reactivecatalyticsurfaces

Mixedmatrices

Zeoliticfilms

Conventionalmembranes

Potential commercial viability

Pote

ntia

l per

form

ance

enh

ance

men

t

Aquaporins

Alignedcarbon nanotubes

Far

None

Evolutionary

Revolutionary

Near Immediate

Figure 39 Conventional and novel membrane current statusReprinted from Pendergast and Hoek (2011) with permission from Royal Society of Chemistry

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 105

35 Advances in membrane modules and systemconfigurations for water treatmentby MF UF and NF

Industrial membrane plants require a large amount of membrane area to performseparation on a useful scale If membranes are to be used on an industrial scale effi-cient packaging methods are required These packages are called membrane modulesBetween 1960 and the 1970s commercial membrane processes had a significant break-through with the development of low-cost membrane modules The earliest designswhich were tubular plate and frame hollow-fiber and spiral wound were mainly builton basic filtration technology including flat sheet membranes in a type of filter pressBecause of this these systems are called plate-and-frame modules At the same time1- to 3-cm-diameter tubes were developed These designs are still used but becauseof their relatively high cost in most applications two other designs have been largelydisplaced the spiral wound and hollow fiber modules Conventional membranemodules can be seen in Table 36

351 Recent advances in membrane modules

Liu Xu Zhao and Yang (2010) carried out research using a helical membrane moduleunit A terylene filter cloth without modification and with a pore size around 22 nm hadbeen used in the filtration test as a filter membrane Two pieces of membrane sheets(6 18 2 cm total area 0022 m2) were supported on a plastic spacer The fishboneor broom-like structured spacer is shown in the middle in Figure 310(a-1) and (a-3)resembling a deoxyribonucleic acid helix (Figures 310(a-4)) The cover membraneforms an empty sleeve outside the spacer once it is sealed around the edge(Figure 311) It has a tubing outlet at one end of the membrane to conduct thepermeate water The plastic spacer is flexible for helical rotation and its final total rota-tion angle together with the membrane sleeve can be kept at a certain value by fixingthe top and bottom edges The top end of the membrane can be fixed at a final angleto the bottom end while maintaining a certain helical rotation Several short pieces ofhelical membrane or extensions of membrane length can form modules with morehelixes (Figure 310(a-1))

Table 36 Membrane and module forms

Tubular Flat

Conventional membranemodules

Tube module Spiral-wound module

Capillary module Cushion module

Hollow-fiber module Plate module

Disc-tube module

106 Advances in Membrane Technologies for Water Treatment

Figure 310 Helical membrane module support spacer and final helical anglesReprinted from Liu et al (2010) with permission from Elsevier

Cross view of

the module

Mounting

of the

module in

filtration

chamberb

Water

permeation

Spacer

Permeate

Cross flow

Shearing

force

from

bubbles

Membrane

peeled openHold the two pieces

together with

thread

Seal with glue

Figure 311 Cross-view of helical membrane and its mount in a filtration chamberReprinted from Liu et al (2010) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 107

The long and rectangular new membrane modules are narrower thinner and lighterthan conventional wide flat-sheet membrane modules The helical membrane mayenhance vortex mixing just like a static stirrer in liquid phase Liu et al (2010) showedthat the higher the cross-flow the better the mixing

3511 Rotating disk module systems

Rotating disk module systems including a larger area and capacity module led to theintroduction of multi-disk systems mounted on a single shaft and rotating betweenfixed circular membranes This module is used for biotechnological applications andhas an area of 2 m2 Dyno manufactured by Bokela GmbH (Karlsruhe Germany)has a similar system design This system has a diameter of 137e85 cm and a totalmembrane area from 013 to 12 m2 This system is available with both polymericand ceramic membranes (Figure 312)

Another multi-disk system is produced by Spintek (Huntington CA) with rotatingmembranes of 23 m2 Initially it was available with organic membranes currently it isproduced with mineral membranes (Figure 313)

In Germany multi-shaft systems with overlapping rotating membranes per modulearea are common For example the multi-shaft disk (MSD) system has a diameter of312 cm in several ceramic membrane units All rotating disks turn at the same timethe Hitachi model (Japan) is available at up to a 150- and 100-m2 membrane area atparallel axes at the same time (Figure 314)

3512 Vibrating module systems

Vibrating module systems use an original concept called Vibratory Shear EnhancedProcessing System (VSEP) including a set of circular organic membranes separatedby gaskets and permeate collectors (Figure 315) The most important parameter isthe maximum azimuthal displacement of the membrane rim (Jaffrin 2008)

Figure 312 Dyno rotating disk module (Bokela Germany)Reprinted from Jaffrin (2008) with permission from Elsevier

108 Advances in Membrane Technologies for Water Treatment

Figure 314 Industrial multi-disk shaft module with eight parallel shafts and 31-cm ceramicdisksCourtesy of Westfalia Separator Reprinted from Jaffrin (2008) with permission from Elsevier

Figure 313 Spintek moduleReprinted from Jaffrin (2008) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 109

36 Applications of water treatment by MF UF and NF

Typically there are four main water sources for drinking and potable water supply sur-face water groundwater seawater and rainwater Different membrane technologiesare applicable to these sources because of their chemical and physical characteristicsFigure 316 shows a schematic describing water sources and possible membrane stepsto safe water For instance surface water can be converted into safe water using an MFUF MF plus UF plus an auxiliary or NF membrane Groundwater has generally highhardness and metal concentrations so MF and UF will not be efficient alone They needan auxiliary system

361 Applications for surface water treatment

Macrofiltration UF and NF membranes can be used in surface water treatmentalone or with an auxiliary system They are becoming popular in surface watertreatment because of their high efficiency Macrofiltration and UF process are effec-tive in removing turbidity particles bacteria and cysts If a high organic content ofwater exists MF and UF may not be used to obtain high water quality On the otherhand the NF process is able to treat many water contaminants such as DBPs andsynthetic organic compounds (Glucina Alvarez amp Laicircneacute 2000) Table 37 listsstudies concerning the use of the MF UF and NF membrane process to treatsurface water

362 Membranes for groundwater treatment

Owing to limited rainfall in some places surface water is scarce In these types of pla-ces groundwater sources become important Although they are variable in nature

Figure 315 Industrial VSEP vibrating modulesReprinted from Jaffrin (2008) with permission from Elsevier

110 Advances in Membrane Technologies for Water Treatment

groundwater sources generally contain calcium magnesium carbonatealkalinity andsilica If these ion concentrations reach high concentrations that exceed mineral solu-bility limits precipitation starts This precipitation forms deposits at the end andscales Scale formation can be problematic To solve this problem membrane technol-ogies are effective (Kinsela Jones Collins amp Waite 2012) Table 38 summarizesstudies applying MF UF and NF to groundwater treatment

363 Nanofiltration for seawater desalination

MWCO values of NF membranes are between 200 and 2000 Da They reject 98 ofdivalent ions and 30e85 of monovalent ions NF membranes have higher perme-ability than RO membranes which gives them an advantage in energy consumptionA flow diagram of dual-step NF is given in Figure 317 There is disagreement

Nanofiltration

Drinking water

MF+UF+auxillary

Surfacewater

MF+UF

Rainharvesting

Seawater

Groundwater

Figure 316 Water sources and applicable membrane steps to achieve potable water

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 111

Table 37 Studies related to microfiltration (MF) ultrafiltration (UF) and nanofiltration (NF) for thetreatment of surface waters

Process used and module type Approach Remarks References

Integrated membrane system wasused (UF thorn RO) spiral-woundand hollow-fiber configuration

Low-salinity water was used toevaluate efficiency of IMS

UF process found to be effective in controllingRO fouling UF reduced SDI

Glucina et al (2000)

MF and UF tubular and ceramicmembranes

Membrane permeability andfouling properties of ceramicand polymeric membraneswere compared

Increase TMP rate owing to fouling inverselyfollows the measured pore size Higherdegree of fouling on the polymericmembranes results from the lower volumearea ratio Aggressive methods are neededto clean non-purgeable organic carbon

Hofs et al (2011)

NF capillary and flat-sheetmembranes

New capillary NF membranewas compared with flat-sheetmembranes to find foulingproperties and pretreatmentrequirements

In capillary membranes flux decline can beincreased by forward flushing and airflushing Water permeability of capillarymembranes was 3e15 times higher thanflat-sheet membranes

Van der BruggenHawrijkCornelissen andVandecasteele(2003)

UF-MF Capillary membranes Application of UF polymericmembranes in the disinfectionand treatment of surfacewaters was investigated

Membranes were able to remove ironturbidity bacteria Escherichia coli organiccompounds and mesophilic bacteria

Konieczny (1998)

UF Carbosep M8 tubularinorganic membrane

Different kinds of surface waterswere tested for disinfection byUF membranes Differenthardnesses and organic loadswere tested

UF was a reliable method for disinfectingsurface waters

Di Zio Prisciandaroand Barba (2005)

112Advances

inMem

braneTechnologies

forWater

Treatm

ent

PVDF MF PVDF and PES UF Effects of different magnetic ionexchanges (MIEXs)pretreatment on low-pressuremembrane filtration wereinvestigated by using differentfeed water qualitiesmembrane properties andMIEX doses

Decrease in total and irreversible fouling wasobserved for PVDF MF and PES UF afterMIEX treatment Fouling of PVDF UFmembrane was not decreased after MIEXtreatment which showed the importance ofmembrane properties MIEX treatment waseffective

Huang Cho Schwaband Jacangelo(2012)

UF rotating membrane diskmodule

Irreversible fouling caused byconstituents in surface waterinvestigated

Evolution of irreversible fouling was due topolysaccharide-like organic matterpresumably iron and manganese contributedto some extent

Kimura HaneWatanabe Amyand Ohkuma(2004)

MFUF Irreversible membrane fouling inan MF membrane wasinvestigated Feed watercontaining humic acid ororganic matter was coagulatedwith polyaluminum chloride

Coagulation conditions (dosage) wereeffective for irreversible fouling Acidicconditions enhanced the treated waterquality and increased irreversible fouling

Kimura MaedaYamamura andWatanabe (2008)

NF UF MF spiral wound Efficiency of NF modules for therejection of DBPs from low-turbidity surface waters wasinvestigated

Dissolved organic carbon (DOC)trihalomethane formation potential(THMFP) haloacetic acid formationpotential (HAAFP) and chloral hydrateformation potential (CHFP) rejections werehigher than 86 in NF MF was moderatelyeffective in particle removals UF did notshow significant changes in operationalconditions

Siddiqui Amy Ryanand Odem (2000)

Continued

Advances

inwater

treatment

bymicro

filtrationultrafiltrationand

nanofiltration

113

Table 37 Continued

Process used and module type Approach Remarks References

NF flat-sheet Study aimed to treat surfacewater contaminated withpesticides

NF membranes were able to reduce hardnessCOD and TOC and remove microbialcontent completely

Sarkar et al (2007)

UF hollow-fiber Performance of UF membraneswas investigated by using rawwater from the Bin XianReservoir

Before UF use of coagulation increasedpermeate flux and retarded membrane fluxdecline UF was able to remove turbiditycoliform bacteria iron manganese andaluminum

Xia Nan Liu and Li(2004)

UF hollow-fiber PVDF UF membranes weretested for the treatment ofsurface waters

Permeate quality was stable regardless ofdifferent surface waters TMP should bebelow 1 bar to decrease irreversible fouling

Guo Zhang Fangand Su (2009)

114Advances

inMem

braneTechnologies

forWater

Treatm

ent

concerning whether it is possible to desalinate seawater by using dual-step NF at alower cost than RO In the dual-step NF process seawater is fed to the first NF mem-brane and then the collected permeate is fed to the second NF membrane Finallypotable water is obtained Concentrates are pumped into the NF feed tank optionallyThe energy requirement for seawater desalination using dual-stage NF is proportionalto the salinity of the permeate More energy is needed for lower permeate salinity(AlTaee amp Sharif 2011)

Table 38 Microfiltration (MF) ultrafiltration (UF) andnanofiltration (NF) groundwater applications

Process used andmodule type Approach Remarks References

Electro-ultrafiltration(EUF)

Effectiveness ofEUF system wasdetermined forarsenic removal

Arsenic removalincreased from1 to 14 toover 79

Hsieh WengHuang and Li(2008)

NF piperazinemembrane

Different hardnessand salinityvalues were used

High hardnessretentioncoefficients(70e76)satisfactorypermeate fluxesand high mineralfouling resistancebut low salinityremoval wereobtained

GalanakisFountoulis andGekas (2012)

NF polyamidemembrane

Ozonation slowsand filtrationand NF processeswere combined toremove dissolvedorganic matter(DOM) fromgroundwater

NF was able toremove aromatichumic acid andfulvic acid-likesubstances andDOM

Linlin Xuan andMeng (2011)

NF flat-sheetmembrane module

For fluorideremoval fromcontaminatedgroundwater NFmoduleperformance wasmodeled andsimulated

NF membrane wasable to removefluoride and dropthe level of pH ofgroundwater tothe desired level

Chakrabortty Royand Pal (2013)

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 115

364 Membranes for harvesting rainwater

Harvested rainwater is preferred for irrigation purposes On the other hand there isgrowing interest in harvesting rainwater for drinking and other indoor uses Rainwatercan be filtered by MF UF and NF according to the desired quality MF treatment issuitable for gray water production UF and NF treatment can be used for the drinkingwater supply Home size water treatment units can be used in drinking water produc-tion UF provides a good option for disinfection to remove viruses and bacteriaA number of companies supply UV granulated activated carbon and membranefiltration systems for rainwater purification

365 Applications of membranes for specific contaminantremoval

Arsenic (As) exists in natural water sources in both organic and inorganic forms Long-term exposure to arsenic causes cancer The World Health Organization limits thepresence of As in water to less than 001 mgL Removal of As with membranes is suc-cessful and is popular nowadays There is both pilot and lab-scale research in the liter-ature Nguyen Vigneswaran Ngo Shon and Kandasamy (2009) used both MF andNF NF membranes are more efficient for the removal of As than MF membraneswhich have bigger pores Sato Kang Kamei and Magara (2002) also evaluated Asremoval efficiency using NF and a rapid sand filtration inter-chlorination systemNF membranes with 996 NaCl rejection capacity removed 95 of As(V) and75 of As(III) with no chemical addition under low pressure Floch and Hideg(2004) conducted a study with 200e300 mgL As containing deep well water UsingZenon ZW 1000 hollow-fiber membranes they achieved As concentration less than10 mgL

Pesticides are used to control pests such as weeds and insects They are beneficial inpreventing disease and are used for food production Unfortunately they have anadverse effect on water quality and may have negative effects on human and aquatic

Figure 317 Dual-stage desalination processReprinted from AlTaee and Sharif (2011) with permission from Elsevier

116 Advances in Membrane Technologies for Water Treatment

life Chen Taylor Mulford and Norris (2004) proved that NF membranes can rejectpesticides from 46 up to 100 They found that the rejection rate is directly propor-tional to the molecular weight (MW) of the pesticide When the MW increased therejection rate also increased They also revealed rejection could be increased by adjust-ing the operational flux and recovery Van der Bruggen Schaep Maes Wilms andVandecasteele (1998) researched the removal of pesticides with membrane filtrationsystems that showed good efficiency of membranes in pesticide removal They triedNF membranes and obtained approximately 95 rejection of arsenic with an NF-70membrane

Disinfection is used in the final step of drinking water treatment to deactivate bio-logical agents However NOM in water reacts with disinfectants and causes DBPs toform such as THMs halogenated acetic acids (HAAs) haloacetonitriles (HANs) andhaloketones (HKs) which are detrimental to human health Lee and Lee (2007) usedNF membranes to remove NOMs from surface water and researched the effect ofmembrane pretreatment and membrane material They found that membraneswith an MWCO less than 200 Da were better for controlling NOM in surface waterHydrophobic and positively charged membranes fouled more than hydrophilic andnegatively charged membranes They also revealed that ozone pretreatment wasinefficient for preventing NF fouling but powdered activated carbon (PAC) or UFpretreatment was efficient

Pharmaceuticals have gained attention recently owing to their effects on biologicalactivities Pharmaceutical emissions to the environment should be controlled Radje-novic Petrovic Ventura and Barcelo (2008) studied the removal of pharmaceuticalsin a full-scale NF and RO drinking water treatment plant using groundwater An 85rejection rate was obtained using NF and RO Boleda Galceran and Ventura (2011)studied pharmaceuticals in a full-scale drinking water treatment plant treatment con-sisted of dioxychlorination coagulationflocculation and sand filtration units Aftersand filtration the system was split into two parallel lines conventional (ozonationand carbon) and advanced (UF and RO) treatment A flow diagram of the plant isshown in Figure 318 To remove pharmaceuticals an advanced system was moreeffective than a conventional system

RemineralizationReverseosmosisUVUltrafiltration

CoagulationFloculationSettling

Sandfiltration

Groundwater

Blending Finishedwater

CI2Ozonization GAC

filtration

Riverwater

CIO2

Figure 318 Treatment scheme of drinking water treatment plantReprinted from Boleda et al (2011) with permission from Elsevier

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 117

37 Future trends

Water has been a main problem of mankind for years and will continue to be problem-atic Membrane technology has a significant role in the water industry In the futurenovel membrane materials processes and modules will be used so that we cancome closer to obtaining an optimum membrane structure Membrane technologyhas some shortcomings such as higher energy requirements and fouling Todayrsquos tech-nology related to research on this subject consists of fabricating new membrane mate-rials designing modules calculating hydrodynamics and finding new operationmodes to decrease energy requirements or application setups to treat water or waste-water more effectively Future trends will be the reuse of process waters recoveryof valuable compounds creation of new technologies such as pervaporation and for-ward osmosis monitoring of fouling in real time improvement of new fouling analysismethods and fabrication of tailored novel membranes and developments ofmembranes can be used under extreme conditions

As these aims are realized cost capacity and selectivity should optimized and theirenvironmental impact such as concentrate handling and minimized chemical con-sumption should also be considered

As novel membrane materials are investigated the future lies in block copolymersand biomimetic and patterned membranes such as vertically aligned CNs Thesematerials show great potential because they have greater permeability rates and higherselectivity however commercialization is still a problem If they are commercializedin near future we will obtain lower energy consumption and thus the treatment cost ofpollutants will also decrease The ultimate challenge is extreme conditions such as hightemperatures On this point developments in ceramic membranes are promising(Abetz et al 2006 Url-5 Url-6)

Another problem is housing the membranes Hollow-fiber and spiral wound mod-ule geometry are the main membrane housings as already mentioned in this chapterMembrane module design focuses on mechanical considerations such as pressure butalso on how to limit concentration polarization According to studies on membranesurface there is a valley that causes roughness on membranes surface because ofthat a concentration of rejected species occurs To resolve these problems futureresearch will need to resolve them with fluid mechanical and mass transfer ap-proaches Also designing new membrane modules can decrease the cost and energyrequirements of the membranes For example when the transmembrane pressure islow high fluxes can be obtained Using novel membrane module technologies suchas vibrational modules can decrease the effect of fouling on the membrane surface(Fane et al 2011 Url-7)

Membrane processes are also significant With an improvement in membrane pro-cesses and materials it will become easier to use some new applications for instancepervaporation forward osmosis and new MBR systems Anaerobic MBRs use anaer-obic bacteria to degrade organic substances In this system it is possible to use biogasinstead of air in the submerged reactor Anaerobic MBR systems are better thanconventional systems because of their lower energy consumption Anaerobic MBR

118 Advances in Membrane Technologies for Water Treatment

systems are promising because they can sustain high organic loadings high biomassconcentration can be maintained energy and organic acid are recovered and sludgeproduction is low Another new technology is microbial fuel cells which are a noveltype of MBR Decentralized treatment systems can be used to lower cost and increasesanitation and reuse in wastewater systems (Abetz et al 2006 Fane et al 2011)

In this century great challenges will need to be overcome such as energy waterand a clean environment Membrane technology and its development have an impor-tant role in solving these problems efficiently with new research and development andinnovations in process designs

38 Sources of further information and advice

In the future we will see membranes much more in the water treatment sector Highperformance and low fouling membranes are the main targets in all membrane researchdevelopments and applications Membrane materials module configurations and pro-cesses are becoming more important for improving membrane system performance anddecreasing membrane fouling They will have a critical role in the future performance ofmembranes Interdisciplinary studies should be increased to improve performance basedon materials configurations and processes

39 Conclusion

This chapter summarizes MF UF and NF membranes for water treatment New mem-brane materials have improved membrane technology by enhancing permeability andselectivity As a result of these improvements in membrane performance concentra-tion polarization and fouling phenomena have become important factors in deter-mining membrane performance Membrane modules improve fluid flow so thatfouling and concentration polarization problems decrease In this chapter novel mem-brane materials and module design to increase membrane performance were summa-rized Applications of MF UF and NF membranes were also provided They may beapplied to treat surface water groundwater and seawater desalination and to harvestrainwater Many specific contaminants can be removed efficiently with thesemembrane processes

List of acronyms

AMBR Anaerobic membrane bioreactorCA Cellulose acetateCAGR Compound annual growth rateCHFP Chloral hydrate formation potentialCNT Carbon nanotube

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 119

COD Chemical oxygen demandCVD Chemical vapor depositionDBP Disinfection by-productsED ElectrodialysisEDR Electrodialysis reversalFO Forward osmosisGAC Granulated Activated CarbonHAA Halogenated acetic acidsHAAFP Haloacetic acid formation potentialHAN HaloacetonitrileHK HaloketoneIC In-line coagulationIMS Integrated membrane systemMBR Membrane bioreactorMCF Membrane cartridge filtrationMSD Multi-shaft diskMF MicrofiltrationMIEX Magnetic ion exchangeMWCNT Multi-walled carbon nanotubesMWCO Molecular weight cutoffNF NanofiltrationNOM Natural organic matternZVI Nano zero valent ironPAC Powdered activated carbonPAN PolyacrylonitrilePBMA-B-PMAA-B-PHFBM Poly(butyl methacrylate)-b-poly(methacrylic

acid)-b-poly(hexafluorobutyl methacrylate)PC PolycarbonatePES PolyethersulfonePI PolyimidePNIPAAm-B-PPEGMA poly(N-isopropylacrylamide)-block-poly([polyethylene

glycol] methacrylate)PP PolypropylenePS PolysulfonePS-B-PMMA Polysulfone-b-polymethylmethacrylatePVDF Polyvinylidene fluorideRO Reverse osmosisSDI Silt density indexSWCNT Single-walled carbon nanotubeTDS Total dissolved solidsTFC Thin-film compositeTFN Thin-film nanocompositeTHM TrihalomethanesTHMFP Trihalomethane formation potentialTMP Transmembrane pressureTOC Total organic carbonUF UltrafiltrationUV UltravioletWP Water permeability

120 Advances in Membrane Technologies for Water Treatment

List of symbols

A Membrane areaDa DaltonE Band gap energyhn Photon energyJ Membrane fluxDP Applied pressure

References

Abdelrasoul A Doan H amp Lohi A (2013) Fouling in membrane filtration and remediationmethods Retrieved from httpdxdoiorg10577252370

Abetz V Brinkmann T Dijkstra M Ebert K Fritsch D Ohlrogge K et al (2006)Developments in membrane research From material via process design to industrial appli-cation Advanced Engineering Materials 8(5) httpdxdoiorg101002adem200600032

Akar N Asar B Dizge N amp Koyuncu I (2013) Investigation of characterization andbiofouling properties of PES membrane containing selenium and copper nanoparticlesJournal of Membrane Science 437 216e226 httpdxdoiorg101016jmemsci201302012

AlTaee A amp Sharif A O (2011) Alternative design to dual stage NF seawater desalinationusing high rejection brackish water membranes Desalination 273 391e397 httpdxdoiorg101016jdesal201101056

Antelmi D Cabane B Meireles M amp Aimar P (2001) Cake collapse in pressure filtrationLangmuir 17 7137e7144 httpdxdoiorg101021la0104471

AWWA (2007) Reverse osmosis and nanofiltration (2nd ed) Denver American Water WorksAssociation ISBN 9781583214916

Baker W R (2004) Membrane technology and applications (2nd ed) John Wiley and SonsLtd httpdxdoiorg1010020470020393

Beacuterube P R Mavinic D S Hall E R Kenway S E amp Roett K (2002) Evaluation ofadsorption and coagulation as membrane pretreatment steps for the removal of organicmaterial and disinfection-by-product precursors Journal of Environmental Engineeringand Science 1(6) 465e476

Boleda M R Galceran M T amp Ventura F (2011) Behavior of pharmaceuticals and drugs ofabuse in a drinking water treatment plant (DWTP) using combined conventional andultrafiltration and reverse osmosis (UFRO) treatments Environmental Pollution 1591584e1591 httpdxdoiorg101016jenvpol201102051

Bowen W R amp Welfoot J S (2005) Modelling the performance of nanofiltration mem-branes In A I Schafer A G Fane amp T D Waite (Eds) Nanofiltration Principles andapplications (pp 119e146) Oxford Elsevier

Buonomenna M G (2013) Nano-enhanced reverse osmosis membranes Desalination 31473e88 httpdxdoiorg101016jdesal201301006

Cakmakci M Baspinar A B Balaban U Koyuncu I amp Kinaci C (2009) Comparison ofnanofiltration and adsorption techniques to remove arsenic from drinking water Desali-nation and Water Treatment 9 149e154 httpdxdoiorg105004dwt2009765

Carroll T King S Gray S R Bolto B A amp Booker N A (2000) The fouling ofmicrofiltration membranes by NOM after coagulation treatment Water Research 342861e2868 httpdxdoiorg101016S0043-1354(00)00051-8

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 121

Chakrabortty S Roy M amp Pal P (2013) Removal of fluoride from contaminated ground-water by cross flow nanofiltration Transport modeling and economic evaluation Desali-nation 313 115e124 httpdxdoiorg101016jdesal201212021

Chen G E Li F J Han L F Xu Z L amp Yu L Y (2010) Preparation of microporouspolyethersulfone hollow fiber membranes using non-solvent vapour induced phase sepa-ration Iranian Polymer Journal 19(11) 863e873

Chen S Taylor J Mulford L A amp Norris C D (2004) Influences of molecular weightmolecular size flux and recovery for aromatic pesticide removal by nanofiltration mem-branes Desalination 160 103e111 httpdxdoiorg101016S0011-9164(04)90000-8

Chong M N Jin B Chow C W K amp Saint C (2010) Recent developments in photo-catalytic water treatment technology A reviewWater Research 44 2997e3027 httpdxdoiorg101016jwatres201002039

Chou W L amp Yang M C (2005) Effect of take-up speed on physical properties andpermeation performance of cellulose acetate hollow fibers Journal of Membrane Science250 259e267 httpdxdoiorg101016jmemsci200410030

Corry B (2008) Designing carbon nanotube membranes for efficient water desalinationJournal of Physical Chemistry B 112 1427e1434 httpdxdoiorg101021jp709845u

Crock C A Rogensues A R Shan W amp Tarabara V V (2013) Polymer nanocompositeswith graphene-based hierarchical fillers as materials for multifunctional water treatmentmembranes Water Research 47(12) 3984e3996 httpdxdoiorg101016jwatres201210057

Co

ˇ

teacute P Brink D amp Adnan A (2006) Pretreatment requirements for membrane bioreactorsZENON membrane solutions Water Environment Foundation httpdxdoiorg102175193864706783750169

Dahe G Teotia R S amp Bellare J (2012) The role of zeolite nanoparticles additive onmorphology mechanical properties and performance of polysulfone hollow fiber mem-branes Chemical Engineering Journal 197 398e406 httpdxdoiorg101016jcej201205037

Debik E Kaykioglu G Coban A amp Koyuncu I (2010) Reuse of anaerobically andaerobically pre-treated textile wastewater by Uf and Nf membranes Desalination256(1e3) 174e180 httpdxdoiorg101016jdesal201001013

Di Zio A Prisciandaro M amp Barba D (2005) Disinfection of surface waters with UFmembranes Desalination 179 297e305 httpdxdoiorg101016jdesal200411075

Elimelech M amp Phillip W A (2011) The future of seawater desalination Energy technol-ogy and the environment Science 33 712e717 httpdxdoiorg101126science1200488

Eykamp W (1995) Microfiltration and ultrafiltration In R D Noble amp S A Stern (Eds)Membrane separation technology Principles and applications Amsterdam ElsevierISBN 0 444 81633 X

Fane A G Tang C Y amp Wang R (2011) Membrane technology for water Microfiltrationultrafiltration nanofiltration and reverse osmosis Reference Module in Earth Systems andEnvironmental Sciences Treatise on Water Science 4 301e335 Water-Quality Engi-neering httpdxdoiorg101016B978-0-444-53199-500091-9

Floch J ampHidegM (2004) Application of ZW-1000membranes for arsenic removal fromwatersources Desalination 162 75e83 httpdxdoiorg101016S0011-9164(04)00029e3

Galanakis C M Fountoulis G amp Gekas V (2012) Nanofiltration of brackish groundwaterby using a polypiperazine membrane Desalination 286 277e284 httpdxdoiorg101016jdesal201111035

122 Advances in Membrane Technologies for Water Treatment

Georgiev D Bogdanov B Angelova K Markovska I Hristov Y (2009) Synthetic zeolites -structure clasification current trends in zeolite synthesis review International ScienceConference 4e5 June Stara Zagora Bulgaria

Glucina K Alvarez A amp Laicircneacute J M (2000) Assessment of an integrated membrane systemfor surface water treatment Desalination 132 73e82 httpdxdoiorg101016S0011-9164(00)00137e5

Goh P S Ismail A F amp Ng B C (2013) Carbon nanotubes for desalination performanceevaluation and current hurdles Desalination 308 2e14 httpdxdoiorg101016jdesal201207040

Guigui C Rouch J C Durand-Bourlier L Bonnelye V amp Aptel P (2002) Impact ofcoagulation conditions on the in-line coagulationUF process for drinking water produc-tion Desalination 147 95e100 httpdxdoiorg101016S0011-9164(02)00582e9

Guo X Zhang Z Fang L amp Su L (2009) Study on ultrafiltration for surface water by apolyvinylchloride hollow fiber membrane Desalination 238 183e191 httpdxdoiorg101016jdesal200711064

Gupta V K (2013) Water treatment by membrane filtration techniques Environmental Waterhttpdxdoiorg101016B978-0-444-59399-300005-2

Han L F Xu Z L Yu L Y Wei Y M amp Cao Y (2010) Performance of PVDFmul-tinanoparticles composite hollow fibre ultrafiltration membranes Iranian Polymer Journal19(7) 553e565

Harman B I Koseoglu H Yigit N O Beyhan M amp Kitis M (2010) The use of ironoxide-coated ceramic membranes in removing natural organic matter and phenol fromwaters Desalination 261 27e33 httpdxdoiorg101016jdesal201005052

Hilal N Al-Zoubi H Darwish N A Mohammad A W amp Abu Arabi M (2004)A comprehensive review of nanofiltration membranes Treatment pretreatment modellingand atomic force microscopy Desalination 170 281e308 httpdxdoiorg101016jdesal200401007

Hoffmann M R Martin S T Choi W amp Bahnemannt D W (1995) Environmentalapplications of semiconductor photocatalysis Chemical Reviews 95 69e96 httpdxdoiorg101021cr00033a004

Hofs B Ogier J Vries D Beerendonk E F amp Cornelissen E R (2011) Comparison ofceramic and polymeric membrane permeability and fouling using surface water Sepa-ration and Purification Technology 79 365e374 httpdxdoiorg101016jseppur201103025

Hsieh L C Weng Y Huang C amp Li K (2008) Removal of arsenic from groundwater byelectro-ultrafiltration Desalination 234 402e408 httpdxdoiorg101016jdesal200709110

Huang H Cho H Schwab K J amp Jacangelo J G (2012) Effects of magnetic ion exchangepretreatment on low pressure membrane filtration of natural surface waterWater Research46 5483e5490 httpdxdoiorg101016jwatres201207003

Jacangelo J G Trussell R R amp Watson M (1997) Role of membrane technology indrinking water treatment in the United States Desalination 113(2e3) 119e127 httpdxdoiorg101016S0011-9164(97)00120e3

Jaffrin M Y (2008) Dynamic shear-enhanced membrane filtration A review of rotating disksrotating membranes and vibrating systems Journal of Membrane Science 324 7e25httpdxdoiorg101016jmemsci200806050

Judd S J amp Hillis P (2001) Optimisation of combined coagulation and microfiltration forwater treatment Water Research 35(12) 2895e2904 httpdxdoiorg101016S0043-1354(00)00586-8

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 123

Kennedy M D Kamanyi J Salinas Rodriguez S G Lee N H Schippers J C ampAmy G (2008) Water treatment by microfiltration and ultrafiltration In N N LiA G Fane W S Winston Ho amp T Matsuura (Eds) Advanced membranetechnology and applications (pp 131e165) John Wiley and Sons Inc ISBN 978-0-471-73167-2

Kim E-S Hwang G El-Din M G amp Liu Y (2012) Development of nanosilver and multi-walled carbon nanotubes thin film nanocomposite membrane for enhanced water treatmentJournal of Membrane Science 394e395 37e48

Kim J K Yang S Y Lee Y amp Kim Y (2010) Functional nanomaterials based on blockcopolymer self-assembly Progress in Polymer Science 35(11) 1325e1349 httpdxdoiorg101016jprogpolymsci201006002

Kimura K Hane Y Watanabe Y Amy G amp Ohkuma N (2004) Irreversible membranefouling during ultrafiltration of surface water Water Research 38 3431e3441 httpdxdoiorg101016jwatres200405007

Kimura K Maeda T Yamamura H amp Watanabe Y (2008) Irreversible membrane foulingin microfiltration membranes filtering coagulated surface water Journal of MembraneScience 320 356e362 httpdxdoiorg101016jmemsci200804018

Kinsela A S Jones A M Collins R N amp Waite T D (2012) The impacts of low-costtreatment options upon scale formation potentialin remote communities reliant on hardgroundwaters A case study Northern Territory Australia Science of the Total Environ-ment 416 22e31 httpdxdoiorg101016jscitotenv201112005

Konieczny K (1998) Treatment of natural waters using capillary membranes Polish Journal ofEnvironmental Studies 7(4) 213e220

Koseoglu D Y Kose B Altinbas M amp Koyuncu _I (2013) The production of polysulfone(PS) membrane with silver nanoparticles (AgNP) Physical properties filtration perfor-mances and biofouling resistances of membranes Journal of Membrane Science 428620e628 httpdxdoiorg101016jmemsci201210046

Koyuncu I Arikan O Wiesner M R amp Rice C (2008) Removal of hormones and anti-biotics by nanofiltration membranes Journal of Membrane Science 309 94e101 httpdxdoiorg101016jmemsci200710010

Koyuncu _I amp Cakmakci M (2010) Nanofiltration for water and wastewater treatmentNanotechnology in water treatment applications Horizon Press ISBN 978-1-904455-66-0

Kruithof J C Nederlof M M Hoffman J A M H amp Taylor J S (2004) Integratedmembrane systems Elbert CO AWWA Research Foundation and American Water WorksAssociation

Kurt E Koseoglu D Y Dizge N Chellam S amp Koyuncu _I (2012) Pilot-scaleevaluation of nanofiltration and reverse osmosis for process reuse of segregatedtextile dyewash wastewater Desalination 302 24e32 httpdxdoiorg101016jdesal201205019

Lau W J Ismail A F Misdan N amp Kassim M A (2012) A recent progress in thin filmcomposite membrane A review Desalination 287 190e199 httpdxdoiorg101016jdesal201104004

Lee S amp Lee C (2007) Effect of membrane properties and pretreatment on flux and NOMrejection in surface water nanofiltration Separation and Purification Technology 56 1e8httpdxdoiorg101016jseppur200701007

Li X Liu H Xiao C Ma S amp Zhao X (2012) Effect of take-up speed on polyvinylidenefluoride hollow fiber membrane in a thermally induced phase separation process Journal ofApplied Polymer Science httpdxdoiorg101002app37919

124 Advances in Membrane Technologies for Water Treatment

Liang S Xiao K Mo Y amp Huang X (2012) A novel ZnO nanoparticle blended poly-vinylidene fluoride membrane for anti-irreversible fouling Journal of Membrane Science394e395 184e192 httpdxdoiorg101016jmemsci201112040

Linlin W Xuan Z amp Meng Z (2011) Removal of dissolved organic matter in municipaleffluent with ozonation slow sand filtration and nanofiltration as high quality pre-treatmentoption for artificial groundwater recharge Chemosphere 83 693e699 httpdxdoiorg101016jchemosphere201102022

Liu L Xu X Zhao C amp Yang F (2010) A new helical membrane module for increasingpermeate flux Journal of Membrane Science 360 142e148 httpdxdoiorg101016jmemsci201005014

Loh C H Wang R Shi L amp Fane A G (2011) Fabrication of high performance poly-ethersulfone UF hollow fiber membranes using Pluronic block copolymers as pore formingadditives Journal of Membrane Science 380 111e123 httpdxdoiorg101016jmemsci201106041

Ma N Zhang Y Quan X Fan X amp Zhao H (2010) Performing a microfiltration integratedwith photocatalysis using an Ag-TiO2HAPAl2O3 composite membrane for water treat-ment evaluating effectiveness for humic acid removal and anti-fouling properties WaterResearch 44(20) 6104e6114 httpdxdoiorg101016jwatres201006068

Maartens A Swarta P amp Jacobs E P (1999) Feed-water pretreatment Methods to reducemembrane fouling by natural organic matter Journal of Membrane Science 163 51e62httpdxdoiorg101016S0376-7388(99)00155e6

Membrane Filtration Guidance Manual (November 2005) United States EnvironmentalProtection Agency(EPA) Office of Water(4601) EPA 815-R-06e009

Membrane Fouling Considerations (January 2001) Hydranautics high performance membraneproducts technical paper

Minegishi S Jang N-Y Watanabe Y Hirata S amp Ozawa G (2001) Fouling mechanismof hollow fibre ultrafiltration membrane with pre-treatment by coagulationsedimentationprocess Water Science and Technology Water Supply 1(4) 49e56

Mir L Micheals S L Goel V amp Kaiser R (1992) Crossflow microfiltration Applicationsdesign and cost membrane handbook New York Van Nostrand Reinhold httpdxdoiorg101007978-1-4615-3548-5_35

Mishra A K amp Ramaprabhu S (2011) Functionalized graphene sheets for arsenic removaland desalination of sea water Desalination 282 39e45 httpdxdoiorg101016jdesal201101038

Mohammadi T amp Maghsoodloorad H (2013) Synthesis and characterization of ceramicmembranes (W-type zeolite membranes) International Journal of Applied CeramicTechnology 10(2) 365e375 httpdxdoiorg101111j1744-7402201102749x

Mulder M (1996) Basic principles of membrane technology (2nd ed) Kluwer AcademicPublishers ISBN 978-94-009-1766-8

Ng L Y Mohammad A W Leo C P amp Hilal N (2010) Polymeric membranes incor-porated with metalmetal oxide nanoparticles A comprehensive review Desalinationhttpdxdoiorg101016jdesal201011033

Nguyen V T Vigneswaran S Ngo H H Shon H K amp Kandasamy J (2009) Arsenicremoval by a membrane hybrid filtration system Desalination 236 363e369 httpdxdoiorg101016jdesal200710088

Ohya H Shiki S amp Kawakami H (2009) Fabrication study of polysulfone hollow fibermicrofiltration membranes Optimal dope viscosity for nucleation and growth Journal ofMembrane Science 326 293e302 httpdxdoiorg101016jmemsci200810001

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 125

Ozgun H Ersahin M E Erdem S Atay B Kose B Kaya R et al (2012) Effects of thepre-treatment alternatives on the treatment of oil-gas field produced water by nanofiltrationand reverse osmosis membranes Journal of Chemical Technology and Biotechnologyhttpdxdoiorg101002jctb4007

Pendergast M T M amp Hoek E M V (2011) A review of water treatment membranenanotechnologies Energy and Environmental Science 4 1946e1971 httpdxdoiorg101039C0EE00541J

Pinnekamp J amp Friedrich H (2006) Municipal water and waste management Membranetechnology for wastewater treatment Aachen FIW Verlag ISBN 3-939377-01-5

Qu X Alvarez P J J amp Li Q (2013) Applications of nanotechnology in water andwastewater treatment Water Research 47(12) 3931e3946 httpdxdoiorg101016jwatres201209058

Radjenovic J Petrovic M Ventura F amp Barcelo D (2008) Rejection of pharmaceuticals innanofiltration and reverse osmosis membrane drinking water treatment Water Research42 3601e3610 httpdxdoiorg101016jwatres200805020

Razmjou A Resosudarmo A Holmes R L amp Li H (2012) The effect of modified TiO2

nanoparticles on the polyethersulfone ultrafiltration hollow fiber membranes Desalination287 271e280 httpdxdoiorg101016jdesal201111025

Roux S P Jacobs E P van Reenen A J Morkel C amp Meincken M (2006) Hydro-philisation of polysulphone ultrafiltration membranes by incorporation of branchedPEO-block-PSU copolymers Journal of Membrane Science 276(1e2) 8e15 httpdxdoiorg101016jmemsci200509025

Rugbani A (2009) Investigating the influence of fabrication parameters on the diameter andmechanical properties of polysulfone ultrafiltration hollow-fibre membranes (MScthesis) University of Stellenbosch

Saljoughi E Amirilargani M amp Mohammadi T (2010) Effect of PEG additive andcoagulation bath temperature on the morphology permeability and thermalchemical sta-bility of asymmetric CA membranes Desalination 262 72e78 httpdxdoiorg101016jdesal201005046

Sarkar B Venkateshwarlu N Nageswara Rao R Bhattacharjee C amp Kale V(2007) Potable water production from pesticide contaminated surface watermdashAmembrane based approach Desalination 204 368e373 httpdxdoiorg101016jdesal200602041

Sato Y Kang M Kamei T amp Magara Y (2002) Performance of nanofiltration for arsenicremoval Water Research 36 3371e3377 httpdxdoiorg101016S0043-1354(02)00037e4

Schaep J Van der Bruggen B Uytterhoeven S Croux R Vandecasteele C Wilms Det al (1998) Removal of hardness from groundwater by nanofiltration Desalination 119295e302 httpdxdoiorg101016S0011-9164(98)00172e6

Sengur R (2013) Fabrication and characterization of polyethersulfone (pes)multiwalledcarbon nanotube hollow fiber ultrafiltration membranes (MSc thesis) Istanbul TechnicalUniversity

Siddiqui M Amy G Ryan J amp Odem W (2000) Membranes for the control of naturalorganic matter from surface watersWater Research 34(13) 3355e3370 httpdxdoiorg101016S0043-1354(00)00024-5

Sombekke H D M Voorhoeve D K amp Hiemstrap P (1997) Environmental impactassessment of groundwater treatment with nanofiltration Desalination 113 293e296httpdxdoiorg101016S0011-9164(97)00144-6

126 Advances in Membrane Technologies for Water Treatment

Tang C Y Zhao Y Wang R Heacutelix-Nielsen C amp Fane A G (2013) Desalination bybiomimetic aquaporin membranes Review of status and prospects Desalination 30834e40 httpdxdoiorg101016jdesal201207007

Tiraferri A Vecitis C amp Elimelech M (2011) Covalent binding of single-walled carbonnanotubes to polyamide membranes for antimicrobial surface properties ACS AppliedMaterials amp Interfaces 3 2869e2877 httpdxdoiorg101021am200536p

Turken T (2013) Nanocomposite hollow fiber membrane fabrication with silver nanoparticlescharacterization and application (MSc thesis) Istanbul Technical University

UN (2010) The millennium development goals report (pp 58e60)UN-Water United Nations Educational Scientific and Cultural Organisation (2006) Water a

shared responsibility The united nations world water development report 2 World WaterAssessment Programme

Url-1 httpwwwwhointmediacentrenewsreleases2012drinking_water_20120306en Accessed231114

Url-2 httpwwwbccresearchcommarket-researchmembrane-and-separation-technologymembrane-microfiltration-mst028ehtml Accessed 241114

Url-3 httpwwwbccresearchcommarket-researchmembrane-and-separation-technologyultrafiltration-membrane-markets-mst044chtml Accessed 231114

Url-4 httpwwwbccresearchcommarket-researchnanotechnologynanofiltration-nan045bhtml Accessed 231114

Url-5 httpwwwceicunsweduaucentersmembraneimstec03contentpapersplenaryfellpdf Dateretrieved 231114

Url-6 httpwwwvttfifilesnews2011future_water_technologiesmari_kallioinen_future_rd_needs_in_membrane_technologiespdf Date retrieved 231114

Url-7 httplinkspringercomchapter1010072F978-1-59745-278-6_1page-39 Date retrieved231114

Uyak V Koyuncu I Oktem I Cakmakci M amp Toreurooz I (2008) Removal of tri-halomethanes from drinking water by nanofiltration membranes Journal of HazardousMaterials 152 789e794 httpdxdoiorg101016jjhazmat200707082

Van der Bruggen B Hawrijk I Cornelissen E amp Vandecasteele C (2003) Direct nano-filtration of surface water using capillary membranes Comparison with flat sheet mem-branes Separation and Purification Technology 31 193e201 httpdxdoiorg101016S1383-5866(02)00184e3

Van der Bruggen B Schaep J Maes W Wilms D amp Vandecasteele C (1998) Nano-filtration as a treatment method for the removal of pesticides from ground waters Desa-lination 117 139e147 httpdxdoiorg101016S0011-9164(98)00081e2

Van der Bruggen B amp Vandecasteele C (2003) Removal of pollutants from surface water andgroundwater by nanofiltration Overview of possible applications in the drinking waterindustry Environmental Pollution 122 435e445 httpdxdoiorg101016S0269-7491(02)00308e1

Wandera D Himstedt H Marroquin M Wickramasingh S R amp Husson S M (2012)Modification of ultrafiltration membranes with block copolymer nanolayers for producedwater treatment the roles of polymer chain density and polymerization time on perfor-mance Journal of Membrane Science 403e404 250e260 httpdxdoiorg101016jmemsci201202061

Wilbert C M Leitz F Abert E Boegli B amp Linton K (July 1998) The desalting andwater treatment membrane manual (2nd ed) Denver CO Water Treatment Engineeringand Research R-98e5

Advances in water treatment by microfiltration ultrafiltration and nanofiltration 127

Xia S Nan J Liu R amp Li G (2004) Study of drinking water treatment by ultrafiltration ofsurface water and its application to China Desalination 170 41e47 httpdxdoiorg101016jdesal200403014

Xu P D Leurou S L Zhen W X Ku B K amp Yi X Y (2008) Effect of coagulation bathtemperature on the structure and performance of polyerthersulfone hollow fiber membranesby drywet process Journal of Clinical Rehabilitative Tissue Engineering Research 125381e5384

Zhao X Su Y Chen W Peng J amp Jiang Z (2011) pH-responsive and fouling-releaseproperties of PES ultrafiltration membranes modified by multi-functional block-likecopolymers Journal of Membrane Science 382(1e2) 222e230 httpdxdoiorg101016jmemsci201108014

Zhong P S Chung T-S Jeyaseelan K amp Armugam A (2012) Aquaporin-embeddedbiomimetic membranes for nanofiltration Journal of Membrane Science 407e40827e33 httpdxdoiorg101016jmemsci201203033

Zhu B Hu Y Kennedy S Milne N Morris G Jin W et al (2011) Dual functionfiltration and catalytic breakdown of organic pollutants in wastewater using ozonationwith titania and alumina membranes Journal of Membrane Science 378(1e2) 61e72httpdxdoiorg101016jmemsci201011045

128 Advances in Membrane Technologies for Water Treatment

Water treatment by reverse andforward osmosis 4NK Rastogi1 A Cassano2 A Basile231Department of Food Engineering Central Food Technological Research InstituteCouncil of Scientific and Industrial Research Mysore India 2Institute on MembraneTechnology ITM-CNR University of Calabria Rende (CS) Italy 3Ast-Engineering srlRome Italy

41 Introduction

Water shortages have plagued many communities and humans have long searched fora solution to Earthrsquos limited freshwater supplies Less than 1 of the total water avail-able on the earth is considered freshwater Almost 965 of Earthrsquos water is located inthe seas and oceans 17 is present in icebergs and the remaining percentage is madeup of brackish water (Gleick 1996 Greenlee Lawler Freeman Marrot amp Moulin2009) The population explosion and the expansion of cities have made the productionof potable water undependable and have led to an increase in demand compared withavailability Today the production of potable water has become a worldwide concernfor many communities the projected population growth and demand exceed availableconventional water resources

Over the years purified water standards have become more stringent Watercontaining less than 1000 mgL of salts or total dissolved solids (TDS) is referred asfreshwater above this concentration properties such as taste color corrosion propen-sity and odor are adversely affected (Sandia 2003) Many countries have adoptednational drinking water standards for specific contaminants as well as for TDS butthe standard limits vary from country to country or from region to region within thesame country The World Health Organization and Gulf Drinking Water standardsAustralia recommend a drinking water standard of 1000 mgL TDS (FritzmannLowenberg Wintgens amp Melin 2007) Most desalination facilities are designed toachieve a TDS of 500 mgL or less (Gaid amp Treal 2007 Xu et al 2007) Desalinatedwater used for other purposes such as crop irrigation may have a higher TDS concen-tration Depending on the salinity of the feed water it can be divided into two typessuch as brackish water (often groundwater sources 1000e10000 mgL TDS) andseawater (30000e45000 mgL TDS) (Mickley 2001) The type of feed water decidesthe use of pretreatment method the design of the treatment plant the waste disposalmethod and the recovery of water

The expanding global population increasing water pollution and increasing stan-dard of living have put relentless pressure on water and energy resources Low-costmethods of purifying freshwater and desalting seawater are required to contend withthis destabilizing trend Hence the need for water is increasing rapidly and current

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400004-6Copyright copy 2015 Elsevier Ltd All rights reserved

freshwater resources may not be able to meet all requirements Desalination of sea (orsaline) water has been practiced regularly for over 50 years and is a well-establishedmeans to obtain a water supply in many countries In the 1970s exploration beganinto using membranes for water desalination Proving successful at producing purifiedwater from saltwater membranes became a viable alternative to evaporation-basedtechnologies in the water treatment market Over the years purified water standardshave become more stringent However membranes have risen to the challenge andcontinue to perform efficiently and effectively (Rastogi amp Nayak 2011)

42 Thermal or membrane desalination

Membrane and distillation processes equally share current desalination productioncapacity worldwide However reverse osmosis (RO) will emerge as the leader infuture desalination installations and will be the key to increasing water supplies fordrinking water production RO technology can now produce freshwater (fromseawater) at one-half to one-third the cost of distillation (Miller 2003) Brackish waterRO membranes typically have higher permeate flux and lower salt rejection andrequire lower operating pressures whereas seawater RO membranes have highersalt rejection and lower permeate fluxes and membrane permeability and requirehigher operating pressures to compensate for the higher osmotic pressure of seawaterBrackish water desalination is even less expensive than seawater desalination

The demand for additional freshwater production can be met by adopting waterreuse or desalination (Sauvet-Goichon 2007) Water reuse can be used for irrigationpower plant cooling and groundwater recharge (Focazio et al 2008) Desalination hasbeen identified as a potential source for producing drinking water Desalination is ageneral term for the process of separating salt from saline water for the productionof freshwater Thermal and membrane desalination both the processes are beingused for the recovery of water (Gleick 2006)

Middle East countries initiated the use of seawater thermal desalination and todaytheir share is more than 50 of the worldrsquos desalination capacity (Henthorne 2003Van der Bruggen amp Vandecasteele 2002) Membrane processes have rapidly devel-oped since the 1960s (Drsquosouza amp Mawson 2005 Loeb amp Sourirajan 1963) andnow surpass thermal processes in new plant installations (75 of new production ca-pacity) The advent of such membranes with high retention of low-molecular-weightorganic compounds and good physical and chemical stability has enabled RO to beused more widely on a commercial scale RO membrane technology has been devel-oped for both brackish and seawater applications RO membranes however are able toreject monovalent ions (sodium and chloride) Currently RO membranes are made sothat these can reject more than 99 salts (Brehant Bonnelye amp Perez 2003Reverberi amp Gorenflo 2007)

Membrane and distillation processes equally share current desalination productioncapacity worldwide RO has emerged as the leader in future desalination installationsRO will be the key to increasing water supplies for drinking water productionthroughout the world Although wealthy Middle Eastern countries have been able to

130 Advances in Membrane Technologies for Water Treatment

afford distillation processes RO technology can now produce freshwater (fromseawater) at one-half to one-third the cost of distillation (Miller 2003) Brackish waterdesalination is even less expensive than seawater desalination

Membranes have risen to the challenge of supplying desalinated water and continueto perform efficiently and effectively Another membrane process forward osmosis(FO) can be used to desalinate saline water sources at a notably reduced cost Itinvolves the use of a draw solution of aluminum sulfate or ammonium sulfate whichis used to transport water from saline water These draw solutions on chemical treat-ment or heating result in freshwater (Chanukya Patil amp Rastogi 2013 Frank 1972)This new athermal membrane process has been developed as a possible alternative todesalination It employs a semipermeable dense hydrophilic membrane that separatestwo aqueous solutions (feed and osmotic agent solution) with different osmoticpressures The difference in osmotic pressure acts as a driving force An osmoticpressure-driven process operates on the principle of osmotic transport of water acrossa semipermeable hydrophilic membrane from a dilute feed solution into a concentratedosmotic agent or draw solution (Nayak amp Rastogi 2010) Recently FO concentrationis gaining importance for concentrating liquid foods and natural colors (BabuRastogi amp Raghavarao 2006 Bolin amp Salunke 1971 Garcia-Castello Mccutcheonamp Elimelech 2009 Gusti amp Wrolstad 1996 Loeb amp Bloch 1973 MartinettiChildress amp Cath 2009 Popper et al 1966 Rodriguez-Saona Giusti Durst ampWrolstad 2001) generating electricity (Kravath amp Davis 1975) treating wastewater(Holloway Childress Dennett amp Cath 2007) and desalinating seawater(Mccutcheon Mcginnis amp Elimelech 2006)

43 Difference between osmosis RO and FO

Osmosis is the movement of solvent molecules through a selectively permeable mem-brane into a region of higher solute concentration with the aim of equalizing the soluteconcentrations on both sides The net movement of the solvent from a less concen-trated (hypotonic) to a more concentrated (hypertonic) solution tends to reduce the dif-ference in concentrations When a semipermeable membrane separates two solutionswater always diffuses from the solution with the lower osmotic potential to the onewith the higher osmotic potential This diffusion-driven motion of water through amembrane is termed osmosis It is the tendency of fluids to pass through a membraneso that equal concentrations are achieved on both sides (Figure 41(a)) RO is apressure-driven membrane process that entails forcing fluids through a membrane Itis a separation technique that can be used to concentrate or purify liquids without aphase change The RO process uses hydraulic pressure as the driving force for sepa-ration which serves to counteract the osmotic pressure gradient that would otherwisefavor water flux from the permeate to the feed (Figure 41(b)) FO is an osmotic pro-cess that like RO uses a semipermeable membrane to effect separation of water fromdissolved solutes The driving force for this separation is an osmotic pressure gradientsuch that a draw solution of high concentration (relative to that of the feed solution) isused to induce a net flow of water through the membrane into the draw solution thus

Water treatment by reverse and forward osmosis 131

effectively separating the feed water from its solutes FO uses the osmotic pressure dif-ferential (Dp) across the membrane as the driving force for transport of water throughthe membrane rather than the hydraulic pressure differential (similar to RO) The FOprocess results in the concentration of feed solution and the dilution of draw solution(Figure 41(c)) (Cath Childress amp Elimelech 2006 Rastogi amp Nayak 2011)

44 Fundamentals of water treatment by RO

Osmosis is the basis for RO When a semipermeable membrane separates a dilutesolution from a concentrated solution the solvent (water) crosses from the dilute solu-tion side to the concentrated solution side of the membrane to equalize concentrations onboth sides this process is known as osmosis The flow of solvent can be prevented byapplying an opposing hydrostatic pressure to the concentrated solution The magnitudeof the pressure required to completely impede the flow of water is defined as the osmoticpressure In the case of RO a hydrostatic pressure greater than the osmotic pressure isapplied for water to move from a high-solute to a low-solute concentration(Figure 41(b)) It necessitates high-pressure requirements The positive difference inpressure creates a chemical potential difference (concentration gradient) across the mem-brane that drives the liquid through the membrane against the natural direction ofosmosis (the movement of water molecules from an area of high concentration to anarea of low concentration) while the salts are retained and concentrated on the influentsurface of the membrane Some salt passage through the membrane occurs salt passagefor the same membrane increases with the salt concentration and temperature

The RO process requires high operating pressures ranging from 2300 to 3500 kPafor seawater and 100 to 300 kPa for brackish water to overcome the osmotic pressureof feed water (Perry amp Green 1997 Sagle amp Freeman 2004)

The dominant mechanism governing transport through RO membranes can beexplained as solution-diffusion which involves preferential dissolution of solvent

Feed

Feed

Feed

Feed

Wat

er

Wat

er

Wat

er

Dra

w s

olut

ion

(a) (b) (c)

Force( P)

nabla

Figure 41 Migration of water during (a) osmosis (b) reverse osmosis and (c) forward osmosisThe arrows indicate the direction of mass transfer DP is the hydraulic pressureReprinted from Rastogi (in press) with permission of Taylor amp Francis LLC (httpwwwtandfonlinecom)

132 Advances in Membrane Technologies for Water Treatment

(water) in the membrane and its transport through diffusion Water transport across anRO membrane occurs in three separate steps absorption onto the membrane surfacediffusion through the thickness of the membrane and desorption from the permeatesurface of the membrane Once a water molecule has absorbed onto the membranesurface the water concentration gradient (of the water-membrane system) across themembrane causes the water molecules to diffuse down the concentration gradient tothe permeate side of the membrane The water molecule then desorbs from the mem-brane and becomes part of the bulk permeate (Lonsdale Merten amp Riley 1965 Paul2004)

The equation that gives the water flux through a membrane as a function of pressuredifference during RO can be written in a simple form (Mulder 1996 p 298)

Jw frac14 AwethDp DpTHORN (41)

where Aw is the water permeability coefficient Dp is the transmembrane pressure andDp is the difference in the osmotic pressures of feed and permeate

The permeate flux during the course of RO decreases rapidly owing to reversibleand irreversible fouling of the membrane that significantly affects the process effi-ciency (Kwang-Sup Joo-Heon Dong-Ho Seok-Joong amp Soon-Dong 2004) Thepermeate fluxes are primarily affected by the phenomena of concentration polariza-tion (ie solute buildup) and fouling (eg microbial adhesion gel layer formationand solute adhesion) at the membrane surface Fouling is generally caused by thedeposition of colloidal particles inorganic and organic compounds and microbeson the surface of the membrane (Chien-Hwa Lung-Chen Shaik Khaja Chung-Hsin amp Cheng-Fang 2010) It is considered a group of physical chemical and bio-logical effects leading to irreversible loss of membrane permeability (Chien-Hwaet al 2010 Sablani Goosen AL-Belushi amp Wilf 2001) Concentration polariza-tion is mainly limited to the buildup of retained solute ie accumulation of matteron the surface of the membrane It is considered to be reversible and can becontrolled in a membrane module by means of velocity adjustment pulsation(back flush) ultrasound or an electric field (Vladisavljevic Vukosavljevic ampBukvic 2003)

Considering a situation in which a solution consisting of solvent and solute is sub-jected to a pressure-driven membrane process such as RO the solute is preferentiallyretained on the membrane surface whereas solvent permeates through the membraneAs solvent is removed from the feed the difference in the osmotic pressure (Dp)increases which in turn results in a decrease in flux At the same time a concentrationgradient is developed owing to the rejection of solute with the passage of solventthrough the membrane (Figure 42) The solvent flux through the membrane increaseswith an increase in the applied pressure until the concentration of solute on the mem-brane surface reaches a critical concentration which is referred to as the gel concen-tration (CG) Further increases in pressure do not change the solute concentration atthe membrane surface however they result in a thicker and compacted gel layerAt equilibrium the rate of solvent transport through the membrane (flux) can be calcu-lated on the basis of the convective transport of solutes to the membrane surface

Water treatment by reverse and forward osmosis 133

ethJw$CTHORN by the solvent which is equal to the sum of the diffusive back transport of

soluteD$

dCdx

and permeate flow ethJw$CpTHORN ie

Jw$C frac14D

dCdx

thorn Jw$Cp (42)

where D is the diffusion coefficient for solute transport through solvent C is the soluteconcentration retained on the membrane Cp is the solute concentration in permeate (inthe case of RO the solute is completely retained by the membrane ie Cp frac14 0) anddCdx

is the solute concentration gradient

The integration of Eqn (42) with appropriate boundary conditions (x frac14 0 C frac14 CGx frac14 x C frac14 CB) results in the following equation

Jw frac14 D

d$ln

CG

CB

frac14 k$ln

CG

CB

(43)

where d is the thickness of the boundary layer k is mass transfer coefficient CB and CG

are the bulk and gel layer solute concentrations and CGCB

is the concentration polari-zation modulus Equation (43) shows that at this juncture the flux through themembrane is independent of the transmembrane pressure drop or permeability anddepends only on the solute characteristics (D and CG) and boundary layer thickness(d) Concentration polarization is a reversible fluid dynamic phenomenon If CB

reaches CG solutes will start to precipitate or deposit on the membrane forming a gel

Figure 42 Formation of concentration gradient near the surface of the membrane

134 Advances in Membrane Technologies for Water Treatment

layer which leads to the permanent loss of flux known as fouling (Echavarria TorrasPagan amp Ibarz 2011)

45 Conventional and membrane pretreatmentfor RO feed water

The primary goal of any RO pretreatment system is to lower the fouling propensity ofthe water in the RO membrane system Conventional pretreatment typically consists ofchemical additions including acid coagulant and flocculent that prepare the feedwater for granular media filtration (Isaias 2001 Sauvet-Goichon 2007) Acid treat-ment reduces the pH of the feed water (typical pH range 5e7) which increases thesolubility of calcium carbonate the key potential precipitate in many feed waters(Bonnelye et al 2004) Coagulants are typically small positively charged moleculesthat effectively neutralize like charges (on aqueous particulate and colloidal matter)and allow the suspended solids to group together in flocs (large groups of looselybound suspended particles) Inorganic coagulants are commonly iron or aluminumsalts such as ferric chloride or aluminum sulfate whereas organic coagulants are typi-cally cationic low-molecular-weight (lt500000 Da) polymers (ie dimethyldially-lammonium chloride or polyamines) Granular media filtration includes materialssuch as sand anthracite pumice gravel and garnet (Bonnelye et al 2004) often acombination of materials is used in layers in the filtration bed to reduce the feed watersilt density index (Morenski 1992) Cartridge filtration (filter cartridges are usually1e10 mm) acts as a final polishing step to remove larger particles that passed throughmedia filtration in conventional RO pretreatment (Morenski 1992 Petry et al 2007)

Antiscalants are primarily used as pretreatment typically performed after granularmedia filtration either before or after cartridge filtration (Sauvet-Goichon 2007)Disinfection is achieved by adding a strong oxidant such as ozone chlorine (gaschlorine dioxide or sodium hypochlorite) chloramine or potassium permanganate(Morenski 1992)

A new trend in pretreatment has been the movement toward using larger pore-sizemembranes (microfiltration (MF) ultrafiltration (UF) and nanofiltration (NF)) to useRO as a pretreatment to feed water that avoids the passage of colloids and suspendedparticles contributing to RO membrane fouling (Brehant et al 2003) The mem-branes act as a defined barrier between the RO system and any suspended particlesThey can reduce silt density index as well as turbidity of the feed water (Pearce 2007Vedavyasan 2007) MF membranes are an appropriate choice for the removal oflarger particulate matter whereas NF membranes are used to remove dissolved con-taminants as well as particulate and colloidal material UF membranes represent thebest balance between the removal of contaminants and permeate production of theother three membrane types Typical final permeate fluxes for a UF-RO systemwere reported to be in the range of 15e24 Lm2 h (Kamp Kruithof amp Folmer2000) whereas the permeate flux exiting the UF pretreatment stage was within60e150 Lm2 h (Brehant et al 2003)

Water treatment by reverse and forward osmosis 135

Membrane pretreatment reduces the general aging and destruction of RO mem-branes by feed water components membrane replacement and the frequency of chem-ical (acid or base) cleaning However the RO system can be operated at a higherpermeate flux Membrane pretreatment systems are decreasing in capital cost andare becoming more cost-competitive with conventional systems The risk of membranefouling prevents general operation at high permeate flux especially for feed waters withimpurities such as hydrocarbons (oil) and cellular or extracellular material (frombacteria) (Jian Kitanaka Nishijima Baes amp Okada 1998 Williams amp Edyvean1998) Fouling results in membrane damage and flux decline requires membranereplacement every 5e10 years (Pearce 2007)

46 Fundamentals of water treatment by FO

FO can be considered a technique for the recovery of the water from saline water Itemploys an asymmetric semipermeable dense hydrophilic membrane that separatestwo aqueous solutions (feed and draw solution) with different osmotic pressuresThe osmotic pressure gradient is the sole driving force for the transport of water Con-centration polarization is a significant problem in pressure-driven membrane processessuch as RO It reduces permeate flow as a result of buildup of the retained moleculesleading to enhanced osmotic pressure at the membrane surface The FO phenomenonwith a dense symmetric membrane can result in the occurrence of concentration polar-ization on both sides of the membrane The solute is concentrated and diluted on thefeed and permeate sides leading to concentrative and dilutive external concentrationpolarization respectively (Figure 43(a)) The standard flux equation for forward equa-tion is given by the following equation

Jw frac14 Aethpd pf THORN (44)

where pd and pf are the bulk osmotic pressures of draw and feed solutions respec-tively Jw is the water flux and A is the pure water permeability coefficient

The asymmetric membrane employed in the case of FO consists of a dense activemembrane layer (active layer) and a loosely bound support layer (porous support layer)(Figure 43 Nayak amp Rastogi 2010) The membrane can be placed between the feedand the osmotic agent solutions in two different ways such that they feed toward thesupport layer (normal mode) and toward the active layer (reverse mode) which arereferred as modes I (Figure 43(b)) and II (Figure 43(c)) respectively (GrayMccutcheon amp Elimelech 2006 Nayak amp Rastogi 2010)

461 Modeling of flux when feed toward support layer(internal concentration polarization concentrative)

When the feed (05 M NaCl solution) is placed against a porous support layer and adraw solution is kept on the active layer side (mode I) water is diffused into the poroussupport layer and traversed to the draw solution side through the active layer of mem-brane as a result of the osmotic pressure gradient across the membrane The use of

136 Advances in Membrane Technologies for Water Treatment

sodium chloride solution results in buildup of salt within the porous support layer dueto the diffusion of water to the draw solution side Subsequently it results in a signif-icant internal concentration polarization (concentrative) and negligible external con-centration polarization At the same time permeation of water to the draw solutionside results in external concentration polarization (dilutive) But internal concentrationpolarization may not be highly significant Both the internal (concentrative) andexternal (dilutive) concentration polarization phenomena are responsible for the reduc-tion in the effective osmotic driving force The internal concentration polarization oc-curs within the porous support layer and it cannot be lessened by hydrodynamics suchas turbulence (since it is occurring within the pores of the support layer) leading todrastic reduction of effective osmotic driving force (McCutcheon amp Elimelech2007 Tang amp Ng 2008) The extent of external polarization is much less than the in-ternal concentration polarization during forward osmosis when permeate water fluxesare relatively low (Cath et al 2006 McCutcheon et al 2006)

The concentration profile across asymmetric FO membrane for concentrative inter-nal concentration polarization is illustrated in Figure 43(b) Assuming negligibleexternal concentration polarization at the outer surfaces of the membrane the waterand salt flux (Jw Js) across the membrane is given by

Jw frac14 AethDpeffTHORN frac14 Aethpd pf THORN (45)

Figure 43 Mechanism of forward osmosis indicating water transport (a) with a densesymmetric membrane and with asymmetric membrane (b) feed toward the support layer (mode I)and (c) feed toward active layer (mode II) pd and pf are the bulk osmotic pressures of draw andfeed solutions respectively p

d and pf the osmotic pressures on the membrane surface of draw

and feed solutions respectively p0f and p0

d are the osmotic pressures of the feed and drawsolutions on the inside of the active layer within the porous support for concentrative internalconcentration polarization on the feed side and dilutive internal concentration polarization on thedraw side for modes I and II respectively Dp1 Dp2 and Dp3 are the corresponding effectivedriving forces in (a) (b) and (c) situations respectively ECP and ICP refer to external andinternal concentration polarizations respectivelyReprinted from Rastogi (in press) with permission of Taylor amp Francis LLC (httpwwwtandfonlinecom)

Water treatment by reverse and forward osmosis 137

JS frac14 BethC2 C3THORN (46)

where A and B are the water and solute permeation coefficients respectively pd and pf

are the bulk osmotic pressure of draw and feed solutions respectively at the mem-brane surface and the corresponding solute concentrations are C2 and C3 Because pf

is not known this quantity can be obtained by the following analysis provided byMehta and Loeb (1978) The diffusion of solute is considered to be in the oppositedirection of water flux and hence it was taken as negative The salt flow consists oftwo components acting in opposite directions a diffusive part caused by diffusiondown the salt concentration gradient and a convective part caused by bulk flow ofwater through the membrane The salt flux across the porous support layer can thus bewritten as per the following equation

Js frac14 DεdCdx

JwC (47)

where ε and D are the porosity of the substrate and diffusion coefficient of the salt inthe membrane porous substrate respectively The distance x is measured fromthe membraneesolution interface on the porous support layer Substituting the valueof Js from Eqn (42) to Eqn (43) results in the following equation

BethC2 C3THORN frac14 DεdCdx

JwC

Boundary conditions x frac14 0 C frac14 C4 x frac14 st C frac14 C3

(48)

On rearranging

Z frac14 dCdx

frac14 JwC

Dεthorn BethC2 C3THORN

Dε Boundary conditions

x frac14 0 Z1 frac14 JwC4

Dεthorn BethC2 C3THORN

Dε x frac14 st Z2 frac14 JwC3

Dεthorn BethC2 C3THORN

Dε(49)

where t and s are the thickness and tortuosity of the support layer respectivelySolving Eqn (47) with the boundary conditions above yields Eqn (49)Differentiating Eqn (49) with respect to x results in the following equation

dZdx

frac14 JwDε

dCdx

(410)

Integrating Eqn (49) results in the following equation

Jw

ZZ2

Z1

1ZdZ frac14

Zst

0

dx orDε

Jwfrac12ln ZZ1

Z2frac14 st (411)

138 Advances in Membrane Technologies for Water Treatment

or lnJwC3 thorn BethC2 C3THORNJwC4 thorn BethC2 C3THORN frac14 st

DεJw frac14 KDJw (412)

where stDε is defined as a membrane (support and active layer) resistivity (KD) (sm or

dm)

orJwC3 thorn BethC2 C3THORNJwC4 thorn BethC2 C3THORN frac14 expethKDJwTHORN (413)

On rearranging Eqn (413)

C3

C2frac14 B

eKDJw 1

thorn JwC4C2eKDJw

BetheKDJw 1THORN thorn Jwor

1 C3

C2frac14 ethC2 C3THORN

C2frac14

1thorn C4

C2eKDJw

1thorn B

JwetheKDJw 1THORN

(414)

pd pf

pdfrac14

1 p

f

pdeKDJw

1thorn B

JwetheKDJw 1THORN

(415)

Substituting the values of (p2 p3) from Eqn (415) to Eqn (41)

Jw frac14 Apd pf

frac14Ap2

1 p

f

pdeKDJw

1thorn B

JwetheKDJw 1THORN

(416)

The rearrangement of Eqn (416) results in the following equation

Jw frac14

1KD

lnethApd thorn B JwTHORN

Bthorn Apf

(417)

where pd and pf are the bulk osmotic pressures at the draw side and osmotic pressures

on membrane surface at the feed side respectivelyFor low water flux pd and p

f can be replaced with bulk osmotic pressures of drawand feed sides (pd and pf) respectively Hence Eqn (417) becomes

Jw frac14

1KD

ln

Apd thorn B Jw

Bthorn Apf

(418)

The value of KD can be inferred from the plot of Jw versus lnApdthornBJwBthornApf

Water treatment by reverse and forward osmosis 139

462 Modeling of flux when feed is toward active layer(internal concentration polarization dilutive)

When the feed (05-M NaCl solution) is placed against the active layer and the drawsolution on the support layer side the water from the feed is diffused into the activelayer which in turn is diffused to the porous support layer and then to the bulk throughthe boundary layer resulting in dilutive internal concentration polarization on the drawsolution side (Figure 43(c)) The external and internal concentration polarizationstoward the feed side are considered negligible The osmotic solute from the drawsolution may penetrate the porous support layer before flux can occur As water fluxcrosses the active layer and enters into the porous support layer it results in dilutionof the draw solution owing to convection The solute diffuses back to the interiorsurface A steady state is quickly reached but the concentration at the interior surfaceof the active layer is far lower than in the bulk draw solution (Gray et al 2006) Thecombined effect of both the diffusion of water through the active layer and thediffusion of the draw solute into the support layer results in dilutive internal concen-tration polarization The extent of external concentration polarization is negligiblecompared with the internal concentration polarization which has a dominant role ina situation when the draw solution in placed against the support layer (Gray et al2006 Tan amp Ng 2008)

Similar to the analysis provided in the above section for concentrative internal con-centration polarization the equation for the dilutive internal concentration polarizationcan be written as

Jw frac14

1KC

ln

Bthorn Apd

Bthorn ApF thorn Jw

(419)

The value of KC can be inferred from the plot Jw versus ln BthornApdBthornApFthornJw

Constants A (0019 matmday) and B (0023 matmday) refer to the water andsolute permeability coefficients of the active layer of the membrane respectively(Gray et al 2006 Loeb Titelman Korngold amp Freiman 1997) and the valueswere determined as per Eqns (45) and (46) respectively based on the data presentedfor the ammonium bicarbonate draw solution by Achilli et al (2012)

463 Quantitative analysis of internal concentrationpolarization

Studies on the effect of draw solution concentration and temperature on transmem-brane flux in the case of modes I and II indicate that transmembrane flux for mode Iwas higher compared with mode II for all values of the draw solution concentrationAt the same time the transmembrane flux in modes I and II increased with an increasein feed temperature from 30 C to 45 C (Figure 44(a) and (b)) The increase in trans-membrane flux with temperature can be explained using the WilkeeChang equation(Treybal 1982) according to which the diffusion coefficient is proportional to theabsolute temperature divided by the viscosity of the solvent The increase in

140 Advances in Membrane Technologies for Water Treatment

temperature reduces the viscosity of solution and increases the diffusion coefficientswhich results in an increase in transmembrane flux (Holloway et al 2007Mccutcheon amp Elimelech 2006)

The severity of concentration polarizations in modes I and II can be inferred fromthe resistance to diffusion within the membrane porous layer (KD and KC values)

(Figure 44(c) and (d)) The values of Jw were plotted against lnApdthornBJw

BthornApf

and

ln BthornApdBthornApFthornJw

as per Eqns (418) and (419) respectively to determine the values of

KD and KC The relevant values are reported in Figure 44(c) and (d) which indicatesthat the predicted values are in good agreement with the experimental values(R2 gt 090) Higher values indicate a higher internal concentration polarization result-ing in lower flux

The low concentration of solute in the feed solution and draw solution results in ahigher effective driving force in mode I compared with mode II (Dpeff1 gt Dpeff2)hence in this situation mode I is most desirable for desalination to have a higher waterflux than mode II In the case of mode I external concentration polarization on both the

25

25

20

2020

15

15

10

10

05

0500

00

252015100500

25

20

15

10

05

00

25

20

15

10

05

00

25

20

15

10

05

00

00 10 30 40 50

2000 10 30 40 50

(a)

(b) (d)

(c)

Mode IIMode II

Mode I Mode I

Draw solution concentration (M)

Draw solution concentration (M)

Temp (degC) KC (dm)

Temp (degC)

Tran

smem

bran

e flu

xx

10ndash6

(m3 m

2 s)Tr

ansm

embr

ane

flux

x 10

ndash6 (m

3 m2 s)

Tran

smem

bran

e flu

xx

10ndash6

(m3 m

2 s)Tr

ansm

embr

ane

flux

x 10

ndash6 (m

3 m2 s)

KD (dm)30354045

30354045

1692 plusmn 032 1445 plusmn 027

1354 plusmn 0321168 plusmn 0261043 plusmn 012

1478 plusmn 022

1251 plusmn 033 1108 plusmn 018

In((B + Aπd ndashJw)(B + Aπf))

d fIn((B + Aπ )(B + Aπ + Jw))

Figure 44 (a b) Effect of the draw solution concentration at different temperatures on

transmembrane flux (c d) Plot of Jw versus lnBthornApdJw

BthornApF

and Jw versus ln

BthornApdBthornApFthornJw

as per

Eqns (418) and (419) respectively Modes I and II refer to the membrane orientation in whichthe feed was toward the support layer and active layer respectively (A 30 C 35 C- 40 C bull 45 C)Reprinted from Chanukya et al (2013) with permission from Elsevier

Water treatment by reverse and forward osmosis 141

feed and draw solution sides as well as internal concentration polarization on the drawside can be considered insignificant whereas internal concentration polarization(concentrative) toward the feed side will be the only dominant concentration polariza-tion Conversely in the case of mode II internal concentration polarization (dilutive)toward the draw side will be the most dominant concentration polarization which willbe higher because of the higher concentration of draw solution

The orientation of the asymmetric membrane had a significant effect on the perfor-mance of the membrane The feed toward the support layer (mode I) was the bestoption to maximize the flux owing to less concentrative internal concentration polar-ization compared with higher dilutive internal concentration polarization in the othercase when the feed was toward the active layer (mode II) The high agreement betweenthe experimental and predicted values indicated that the proposed model was a good fitand can be used to predict flux at variable conditions

Nayak and Rastogi (2010) and Nayak Valluri and Rastogi (2011) described themechanism of water transport in FO in a situation in which feed solution was a mixtureof low-and high-molecular-weight compounds When the solution of low-molecular-weight compounds was taken as a feed mode I was most desirable However whenthe solution of high-molecular-weight compounds was taken as a feed mode IIgave a higher driving force that in turn led to a higher transmembrane flux Mi andElimelech (2008 2010) also indicated that these high-molecular-weight compoundsmay be deposited within the porous structure of the membrane leading to cake layerformation owing to the lack of shear force as well as hindered back diffusion in theporous structure Fouling of the FO membrane as a result of alginate was reportedto be almost fully reversible after a simple water rinse with no chemical cleaningreagents It was attributed to the less compact formation of the fouling layer owingto the lack of hydraulic pressure Zhao and Zou (2011a b) and Zhao Zou Chuyanget al (2012) demonstrated that internal concentration polarization in the support layerstrongly depended on the physicochemical properties of the solution facing the supportlayer In a situation in which the feed was facing active layer it resulted in a more sta-ble and higher water flux than that of the situation in which support layer was towardthe feed

47 Membranes for FO

Membranes for FO should have high water flux high solute rejection minimumporosity high hydrophilicity reduced fouling and high mechanical strength Thesemembranes are different from standard RO membranes that typically consist of athin active layer (less than 10 mm) and a thick porous support layer Any dense nonpo-rous selectively permeable material commonly used for RO can also be used as amembrane for FO However the presence of a thick support layer results in the occur-rence of concentration polarization within the membrane support structure which mayrequire large osmotic driving forces to sustain adequate water flux (Dova Petrotos ampLazarides 2007ab Gray et al 2006 Mccutcheon Mcginnis amp Elimelech 2005Mcginnis Mccutcheon amp Elimelech 2007)

142 Advances in Membrane Technologies for Water Treatment

A special membrane for FO made of cellulose triacetate was developed by MsHydration Technologies Inc USA (thickness less than 50 mm) (Figure 45(a) and(b)) in which the support layer was embedded in a polyester mesh to provide mechan-ical support (Mccutcheon et al 2005) A scanning electron microscope image of thecross-section of the cellulose acetate polyamide composite and cellulose triacetatemembrane is presented in Figure 46 (Ng Tang amp Wong 2006)

FO membranes can also be made as hydration bags that can be used to recover water(Figure 47) They are double-lined bags The internal bag is made of a FO membraneand is filled with draw solution (eg flavored sucrose) and the external bag is a sealedplastic bag Upon immersing the bag in an aqueous solution water diffuses into the bagbecause of the osmotic pressure difference and slowly dilutes the draw solution Theconcept of a hydration bag was developed for military recreational and emergencyrelief situations in which reliable drinking water was scarce or not available Thehydration bag is one of the few commercial applications of FO (Cath et al 2006)

(a)

(b)

Figure 45 Scanning electron microscope images of cross-sections of cellulosic forwardosmosis membrane (CA) A polyester mesh is embedded within the polymer material formechanical support The membrane thickness is less than 50 mmReprinted from Garcia-Castello et al (2009) and Mccutcheon et al (2005) with permissionfrom Elsevier

Water treatment by reverse and forward osmosis 143

Figure 46 Scanning electron microscope images of the cross-section of (a) cellulose acetate(CA) membrane (b) polyamide composite (AD) membrane (c) forward osmosis (FO)membrane and (d) FO membrane at higher resolution where 1 is the dense selective layer and2 is the support layerReprinted with permission from Ng et al (2006) Copyright 2006 American Chemical Society

Figure 47 Water purification hydration bagReprinted from Cath et al (2006) with permission from Elsevier

144 Advances in Membrane Technologies for Water Treatment

With a view to reducing internal concentration polarization Wang Ong et al(2010) designed a cellulose acetate FO membrane composed of a highly poroussublayer sandwiched between two selective skin layers by using the phase inversiontechnique It prevented salt and other solutes in the draw solution from penetratinginto the membrane porous support It also resulted in higher water flux and lowersalt transport Zhang et al (2010) developed a double dense membrane structure usingphase inversion of cellulose acetate that produced low salt leakage and resulted in lessinternal concentration polarization in the FO process

A novel dual-layer hollow-fiber NF membrane suitable for FO using co-extrusiontechnology was developed consisting of an ultra-thin selective skin (around 10 mm)with a fully open-cell water channels underneath and a micro-porous sponge-like sup-port structure which could achieve high throughput and high salt rejection (YangWang amp Chung 2009ab) Later Wang et al (2010) fabricated a polyethersulfonethin-film composite hollow-fiber membrane for FO using a dry-jet wet spinning pro-cess with an ultra-thin RO-like skin layer (300e600 nm) on either surface of a poroushollow-fiber substrate by interfacial polymerization The active layers presented excel-lent intrinsic separation properties with a hydrophilic rejection layer and good mechan-ical strength A high-flux and high-rejection FO membrane for water reuse andseawater desalination was developed by fabricating polybenzimidazole NF hollow-fiber membranes with a thin wall and desired pore size by nonsolvent induced phaseinversion which was chemically modified by cross-linking with p-xylylene dichloride(Wang Yang Chung amp Rajagopalan 2009) Cross-linking finely tuned the mean poresize and enhanced the salt selectivity Furthermore Su Yang Teo and Chung (2010)developed cellulose acetate NF hollow-fiber membranes suitable for FO processes bysubjecting them to a two-step heat treatment (60 C 60 min and 95 C 20 min) whicheffectively shrank the membrane pores on the membrane surface with a denser outerskin layer (mean pore radius reduced from 063 to 030 nm) The resultant fiber hasa high rejection to NaCl and MgCl2 and low pure water permeability Chou et al(2010) developed a FO hollow-fiber membrane fabricated by the dry-jet wet spinningprocess The outer UF skin was made by increasing the air gap in the spinning processand the inner RO skin layer was made by interfacial polymerization using anm-phenylenediamine aqueous solution and trimesoyl chloride hexane solution Thedeveloped membrane showed excellent intrinsic separation properties with a waterflux of 426 Lm2h Yip Tiraferri Phillip Schiffman and Elimelech (2010) made ahigh-performance thin-film composite membrane consisting of a selective polyamideactive layer formed by interfacial polymerization on top of a polysulfone support layerfabricated by phase separation onto a thin (40 mm) polyester nonwoven fabric

Jia Li Wang Wu and Hu (2010) demonstrated the suitability of carbon nanotubemembranes for seawater desalination using FO The membrane could achieve theoptimal salt rejection property but also the largest water flux which broke the limitof the tradeoff effect between selectivity and permeability existing in traditional liquidseparation membranes The antifouling ability and good mechanical strength renderedit more suitable for FO According to a rough estimation carbon nanotube mem-branes can achieve a higher water flux far in excess of existing commercial FOmembranes

Water treatment by reverse and forward osmosis 145

Qiu Qi and Tang (2011) successfully fabricated FO membranes using layer-by-layer assembly of polyallylamine hydrochloride and polysodium 4-styrene-sulfonate on a porous polyacrylonitrile substrate The chemical cross-linking oflayer-by-layer polyelectrolyte layers was performed with glutaraldehyde The cross-linked and non-cross-linked membranes both had relatively high water permeabilityHowever the cross-linked membranes showed better MgCl2 rejection which clearlydemonstrated the potential of layer-by-layer membranes for high-flux FO applicationsLater Qiu Setiawan Wang Tang and Fane (2012) fabricated high-performance flat-sheet FO membranes using polyamide-imide materials via phase inversion followedby polyelectrolyte polyethyleneimine after treatment to form an NF-like rejection layerwith positive charges Polyamide-imide micro-porous substrate was embedded with awoven fabric the enhanced mechanical strength of the membrane made it possible toreduce the thickness of the substrate to 55 mm and the resultant membranes was able toreach a water flux of 2965 and 192 Lm2h when the active layer was facing draw orfeed solutions respectively

48 Desalination by FO

Research has been reported on the desalination of seawater by FO FO can be used effi-ciently and effectively to desalinate water FO using semipermeable polymeric mem-branes may be a viable alternative to RO as a lower-cost and more environmentallyfriendly desalination technology

Frank (1972) described a method of FO using a solution of aluminum sulfate as anosmotic agent which upon treatment with calcium hydroxide resulted in a precipitateof aluminum hydroxide and calcium sulfate which was removed by standard methodsleaving freshwater Mccutcheon et al (2006) reported FO desalination as a lower-costand more environmentally friendly technology The driving force was provided by adraw solution composed of highly soluble gases ammonia and carbon dioxide Waterfluxes ranging from 36 to 360 Lm2h for a wide range of draw and feed solution con-centrations were reported Ammonium bicarbonate was used as a draw solution toextract water from saline feed water by Mccutcheon Mcginnis and Elimelech(2009) and Chanukya et al (2013) in a FO desalination process High osmotic pres-sures generated by the highly soluble ammonium bicarbonate draw solute yieldedhigh water fluxes leading to high feed water recoveries The ammonium bicarbonatesolution was used as an osmotic solution (Jung et al 2011 Mccutcheon et al2005) that can be decomposed into ammonia and carbon dioxide gases at about60 C The water transferred from the feed side (seawater) to the osmotic solutioncan be obtained by distillation methods (Cath et al 2006 Ng Tang amp Wong2006) and the separated gases can then be recycled to use as a draw solution again(Jung et al 2011) Mcginnis and Elimelech (2007) presented a schematic diagramof the ammonia carbon dioxide FO desalination process to recover freshwater(Figure 48) Similarly Low (2009) studied the performance of FO with respect todifferent ammoniaecarbon dioxide draw solutions and membranes The internalconcentration polarization resulted in lowering of the flux The draw solution used

146 Advances in Membrane Technologies for Water Treatment

for desalination using FO should be highly soluble highly recoverable nontoxicnonreactive with membranes easily separable from water and economically feasible

Kravath and Davis (1975) described a process of seawater desalination by FOacross a cellulose acetate membrane using glucose as the draw solute Upon dilutionsalinity was reduced to a level where ingestion would be possible for short-term con-sumption The performance of flat-sheet cellulose acetate membranes was reported tobe poor in terms of salt rejection Stache (1989) used a semipermeable membrane bagfilled with concentrated fructose solution to desalinate small volumes of seawaterwhile simultaneously creating a nutritious drink Yaeli (1992) used a concentratedglucose solution as a draw solution and water was extracted from seawater by osmosisThe diluted glucose solution was fed to an RO unit in which a low-pressure RO mem-brane separated potable water from the glucose draw solution

An integrated FO process consisting of an RO process to generate potable waterwas proposed FO was used to generate significant hydraulic pressure used to drivingthe RO process in which it could separate salt from seawater to generate potable waterfrom water with a high salt content (Lampi Beaudry amp Herron 2007) BamagaYokochi and Beaudry (2009) designed an integrated desalination unit consisting ofa closed FO and RO process in which RO brine was used as the osmotic draw solutionand thus the chemical energy stored in the RO brine was recovered and used by the FOmembrane process Also Choi et al (2009 2010) investigated systems combining FOand RO for seawater desalination Pilot-scale combined systems with FO resulted inhigher recovery with higher quality and fluxes than conventional RO-based desalina-tion systems Similarly Valladares Yangali Li and Amy (2011) focused on rejecting13 selected micropollutants employing a clean or fouled FO membrane using Red Seawater as a draw solution The resulting effluent was then desalinated at low pressurewith an RO membrane to produce a high-quality permeate Tan and Ng (2010) pro-posed a hybrid FOeNF process for seawater desalination The process achievedgood-quality product water that met the recommended drinking water total dissolvedsolids guideline (500 mgL) Zhao Zou and Mulcahy (2012) designed a hybrid

Salinewater

Membrane

Product water

Brine

DrawsolutionNH3CO2

Soluterecovery system

Figure 48 Schematic diagram of the ammoniaecarbon dioxide forward osmosis desalinationprocessReprinted from Mcginnes and Elimelech (2007) with permission from Elsevier

Water treatment by reverse and forward osmosis 147

FOeNF system designed for brackish water desalination and compared it with a stand-alone RO process Lay et al (2010) examined possible factors for the slower decline offlux in the FO process The transmission of draw solutes from the draw solution intothe feed had significant effect on performance Yangali Li Valladares Li and Amy(2011) indicated that FO coupled with low-pressure RO used for indirect desalinationconsumed only half of the energy used for high-pressure seawater RO desalination andproduced good-quality water extracted from the impaired feed water A cost analysisrevealed that FO is a viable and promising technology

A comparison of vacuum-enhanced direct contact membrane distillation(VEDCMD) and FO for the desalination of brackish water indicated that water recov-ery in FO was higher (90) than with VEDCMD (81) (Martinetti et al 2009) Lingand Chung (2011) developed a potentially sustainable integrated FOeUF system forwater reuse During FO water was transferred from the salt solution to the draw solu-tion (containing super hydrophilic nanoparticles) which was regenerated from thedraw solution using UF

49 Conclusion

Membrane processes for water desalination are becoming increasingly interesting Theyallow improvements in quality enhanced process efficiency and profitability Theexpanding capabilities of membrane processes will certainly continue to benefit the in-dustry in future to obtain the required product quality purity yield and throughputalong with economic viability The use of RO and FO on an industrial scale will beeven more lucrative in the future if membranes with high selectivity improved fluxrobustness and greater chemical and mechanical stability are developed

List of symbols

A or Aw Water permeability coefficientB Solute permeation coefficientsCB Bulk layer solute concentrationCG Gel layer solute concentrationC Solute concentration retained on membraneCp Solute concentration in permeateD Diffusion coefficient for solute transport through solventdCdx

Solute concentration gradient

K Mass transfer coefficientpd and pf Bulk osmotic pressures of draw and feed solutionsJw and Js Water and salt fluxeskd and kf Mass transfer coefficients on draw and feed solution sidesDp Difference in the osmotic pressures of feed and permeateDp Transmembrane pressureD Thickness of the boundary layerε Porosity of the substrate

148 Advances in Membrane Technologies for Water Treatment

x Distance measured from membraneesolution interface on porous support layert Thickness of the support layers Tortuosity of the support layer

Abbreviations

TDS Total dissolved solidsRO Reverse osmosisFO Forward osmosisUF UltrafiltrationMF MicrofiltrationNF Nanofiltration

References

Achilli A Cath T Y amp Childress A E (2010) Selection of inorganic-based draw solutionsfor forward osmosis applications Journal of Membrane Science 364 233e241

Babu B R Rastogi N K amp Raghavarao K S M S (2006) Effect of process parameter ontransmembrane flux during direct osmosis Journal of Membrane Science 280 185e194

Bamaga O A Yokochi A amp Beaudry E G (2009) Application of forward osmosisin pretreatment of seawater for small reverse osmosis desalination units Desalination andWater Treatment 5 183e191

Bolin H R amp Salunke D K (1971) Physicochemical and volatile flavor changes occurringin fruit juices during concentration and foam-mat drying Journal of Food Science 36665e668

Bonnelye V Sanz M A Durand J P Plasse L Gueguen F amp Mazounie P (2004)Reverse osmosis on open intake seawater Pre-treatment strategy Desalination 167191e200

Brehant A Bonnelye V amp Perez M (2003) Assessment of ultrafiltration as a pretreatmentof reverse osmosis membranes for surface seawater desalination Water Science andTechnology Water Supply 3(5e6) 437e445

Cath T Y Childress A E amp Elimelech M (2006) Forward osmosis Principles applica-tions and recent developments Journal of Membrane Science 281 70e87

Chanukya B S Patil S amp Rastogi N K (2013) Influence of concentration polarization onflux behavior in forward osmosis during desalination using ammonium bicarbonateDesalination 312 39e44

Chien-Hwa Y Lung-Chen F Shaik Khaja L Chung-Hsin W amp Cheng-Fang L (2010)Enzymatic treatment for controlling irreversible membrane fouling in cross-flow humicacid-fed ultrafiltration Journal of Hazardous Materials 177 1153e1158

Choi Y J Choi J S Oh H J Lee S Yang D R amp Kim J H (2009) Toward a combinedsystem of forward osmosis and reverse osmosis for seawater desalination Desalination247 239e246

Choi J S Kim H Lee S Hwang T M Oh H Yang D R et al (2010) Theoreticalinvestigation of hybrid desalination system combining reverse osmosis and forwardosmosis Desalination and Water Treatment 15 114e120

Water treatment by reverse and forward osmosis 149

Chou S Shi L Wang R Tang C Y Qiu C amp Fane A G (2010) Characteristics andpotential applications of a novel forward osmosis hollow fiber membrane Desalination261 365e372

Dova M I Petrotos K B amp Lazarides H N (2007a) On the direct osmotic concentration ofliquid foods Part I Impact of process parameters on process performance Journal of FoodEngineering 78 422e430

Dova M I Petrotos K B amp Lazarides H N (2007b) On the direct osmotic concentration ofliquid foods Part II Development of a generalized model Journal of Food Engineering78 431e437

Drsquosouza N amp Mawson A J (2005) Membrane cleaning in the dairy industry A reviewCritical Reviews in Food Science and Nutrition 45(2) 125e134

Echavarria A Torras P C Pagan J amp Ibarz A (2011) Fruit juice processing and membranetechnology application Food Engineering Reviews 3 136e158

Focazio M J Kolpin D W Barnes K K Furlong E T Meyer M T Zaugg S D et al(2008) A national reconnaissance for pharmaceuticals and other organic wastewatercontaminants in the United States e (II) untreated drinking water sources Science of theTotal Environment 402(2e3) 201e216

Frank B S (1972) Desalination of sea water US Patent No 3670897 WI USAFritzmann C Lowenberg J Wintgens T amp Melin T (2007) State of-the-art of reverse

osmosis desalination Desalination 216 1e76Gaid K amp Treal Y (2007) Reverse osmosis desalination The experience of Veacute olia water

Desalination 203 1e14 (original language French)Garcia-Castello E M Mccutcheon J R amp Elimelech M (2009) Performance evaluation of

sucrose concentration using forward osmosis Journal of Membrane Science 338 61e66Gleick P H (1996) In S H Schneider (Ed) Water resources in encyclopedia of climate and

weather (Vol 2 pp 817e823) New York University PressGleick P H (2006) The worldrsquos water 2006e2007 the biennial report on freshwater

resources Chicago IL Island PressGray G T Mccutcheon J R amp Elimelech M (2006) Internal concentration polarization in

forward osmosis Role of membrane orientation Desalination 197 1e8Greenlee L F Lawler D F Freeman B D Marrot B amp Moulin P (2009) Reverse

osmosis desalination Water sources technology and todayrsquos challenges Water Research43 2317e2348

Gusti M M amp Wrolstad R E (1996) Radish anthocyanin extract as a natural red colorantfrom maraschino cherries Journal of Food Science 61 688e694

Henthorne L (2003) Desalination today Southwest Hydrology 12e13Holloway R W Childress A E Dennett K E amp Cath T Y (2007) Forward osmosis for

concentration of anaerobic digester centrate Water Research 41 4005e4014Isaias N P (2001) Experience in reverse osmosis pretreatment Desalination 139 57e64Jia Y X Li H L Wang M Wu L Y amp Hu Y D (2010) Carbon nanotube Possible

candidate for forward osmosis Separation and Purification Technology 75 55e60Jian W Kitanaka A Nishijima W Baes A U amp Okada M (1998) Removal of oil

pollutants in seawater as pretreatment of reverse osmosis desalination process WaterResearch 33(8) 1857e1863

Jung D H Lee J Kim D Y Lee Y G Park M Lee S et al (2011) Simulation offorward osmosis membrane process Effect of membrane orientation and flow direction offeed and draw solutions Desalination 277 83e91

Kamp P C Kruithof J C amp Folmer H C (2000) UFRO treatment plant Heemskerk Fromchallenge to full scale application Desalination 131 27e35

150 Advances in Membrane Technologies for Water Treatment

Kravath R E amp Davis J A (1975) Desalination of seawater by direct osmosis Desalination16 151e155

Kwang-Sup Y Joo-Heon H Dong-Ho B Seok-Joong K amp Soon-Dong K (2004)Effective clarifying process of reconstituted apple juice using membrane filtration withfilter-aid pretreatment Journal of Membrane Science 228 179e186

Lampi K Beaudry E amp Herron J (2007) Forward osmosis pressurized device and processfor generating potable water US Patent No 7303674 B2 Arizona USA

Lay W C L Chong T H Tang C Y Fane A G Zhang J amp Liu Y (2010) Foulingpropensity of forward osmosis Investigation of the slower flux decline phenomenonWaterScience and Technology 61 927e936

Ling M M amp Chung T S (2011) Desalination process using super hydrophilic nanoparticlesvia forward osmosis integrated with ultrafiltration regeneration Desalination 278194e202

Loeb S amp Bloch M R (1973) Counter current flow osmotic processes for the productionof solutions having a high osmotic pressure Desalination 13 207e215

Loeb S amp Sourirajan S (1963) Seawater dimineralization by means of an osmotic membraneAdvances in Chemistry Series 38 117e132

Loeb S Titelman L Korngold E amp Freiman J (1997) Effect of porous support fabric onosmosis through a Loeb-Sourirajan asymmetric membrane Journal of Membrane Science129 243e249

Lonsdale H K Merten U amp Riley R L (1965) Transport properties of cellulose acetateosmotic membranes Journal of Applied Polymer Science 9 1341e1362

Low S C (2009) Preliminary studies of seawater desalination using forward osmosisDesalination and Water Treatment 7 41e46

Martinetti C R Childress A E amp Cath T Y (2009) High recovery of concentrated RObrines using forward osmosis and membrane distillation Journal of Membrane Science331 31e39

Mccutcheon J R amp Elimelech M (2006) Influence of concentrative and dilutive concen-tration polarization on flux behavior in forward osmosis Journal of Membrane Science284 237e247

Mccutcheon J R amp Elimelech M (2007) Modeling water flux in forward osmosis Impli-cations for improved membrane design AIChE Journal 53 1736e1744

Mccutcheon J R Mcginnis R L amp Elimelech M (2005) A novel ammoniaecarbon dioxideforward (direct) osmosis desalination process Desalination 174 1e11

Mccutcheon J R Mcginnis R L amp Elimelech M (2006) Desalination by ammonia-carbondioxide forward osmosis Influence of draw and feed solution concentrations on processperformance Journal of Membrane Science 278 114e123

Mccutcheon J R Mcginnis R L amp Elimelech M (2009) A novel ammonia-carbon dioxideforward (direct) osmosis desalination process Desalination 174 1e11

McGinnis R L amp Elimelech M (2007) Energy requirements of ammoniaecarbon dioxideforward osmosis desalination Desalination 207 370e382

Mcginnis R L Mccutcheon J R amp Elimelech M (2007) A novel ammonia-carbon dioxideosmotic heat engine for power generation Journal of Membrane Science 305 13e19

Mehta G D amp Loeb S (1978) Internal polarization in the porous substructure of asemi-permeable membrane under pressure-retarded osmosis Journal of MembraneScience 4 261

Mickley M C (2001) Membrane concentrate disposal Practices and regulation Report No69 US Department of the Interior Bureau of Reclamation Boulder CO Mickley ampAssociates

Water treatment by reverse and forward osmosis 151

Mi B amp Elimelech M (2008) Chemical and physical aspects of organic fouling of forwardosmosis membranes Journal of Membrane Science 320 292e302

Mi B amp Elimelech M (2010) Organic fouling of forward osmosis membranes Foulingreversibility and cleaning without chemical reagents Journal of Membrane Science 348144e151

Miller J E (2003) Review of water resources and desalination technologies Sandia NationalLaboratories Available from httpwwwprodsandiagovcgi-bintechlibaccess-controlpl2003030800pdf Retrieved on 05012015

Morenski F (1992) Current pretreatment requirements for reverse osmosis membrane appli-cations In Official proceedings of the 53rd international water conference (pp 325e330)

Mulder M (1996) Basic principles of membrane technology The Netherlands KluwerAcademic Publisher

Nayak C A amp Rastogi N K (2010) Forward osmosis for concentration of anthocyanin fromKokum (Garcinia indica Choisy) Separation and Purification Technology 71 144e151

Nayak C A Valluri S S amp Rastogi N K (2011) Effect of high or low molecular weight ofcomponents of feed on transmembrane flux during forward osmosis Journal of FoodEngineering 106 48e52

Ng H Y Tang W amp Wong W S (2006) Performance of forward (direct) osmosis processMembrane structure and transport phenomenon Environmental Science and Technology40 2408e2413

Paul D R (2004) Reformulation of the solution-diffusion theory of reverse osmosis Journalof Membrane Science 241 371e386

Pearce G K (2007) The case for UFMF pretreatment to RO in seawater applicationsDesalination 203 285e295

Perry R H amp Green D W (Eds) (1997) Perryrsquos chemical engineersrsquo handbook New YorkMcGraw Hill

Petry M Sanz M A Langlais C Bonnelye V Durand J P Guevara D et al (2007)The El Coloso (Chile) reverse osmosis plant Desalination 203 141e152

Popper K Camirand W M Nury F amp Stanley W L (1966) Dialyzer concentratesbeverages Food Engineering 38 102e104

Qiu C Qi S amp Tang C Y (2011) Synthesis of high flux forward osmosis membranesby chemically crosslinked layer-by-layer polyelectrolytes Journal of Membrane Science381 74e80

Qiu C Setiawan L Wang R Tang C Y amp Fane A G (2012) High performance flat sheetforward osmosis membrane with an NF-like selective layer on a woven fabric embeddedsubstrate Desalination 287 266e270

Rastogi N K Opportunities and challenges in application of forward osmosis in foodprocessing Critical Reviews in Food Science and Nutrition (in press)

Rastogi N K amp Nayak C A (2011) Membranes for direct osmosis In A Basile ampS P Nunes (Eds) Advanced membrane science and technology for sustainable energyand environmental applications (pp 680e717) Cambridge UK Woodhead Publisher

Reverberi F amp Gorenflo A (2007) Three year operational experience of a spiral-woundSWRO system with a high fouling potential feed water Desalination 203 100e106

Rodriguez-Saona L E Giusti M M Durst R W amp Wrolstad R E (2001) Developmentand process optimization of red radish concentrate extract as potential natural red colourantJournal of Food Processing Preservation 25 165e182

Sablani S Goosen M AL-Belushi R amp Wilf M (2001) Concentration polarization inultrafiltration and reverse osmosis A critical review Desalination 141(3) 269e289

152 Advances in Membrane Technologies for Water Treatment

Sagle A amp Freeman B (2004) Fundamentals of membranes for water treatment InJ A Arroyo (Ed) The future of desalination in Texas (vol II pp 137e153) AustinTX Texas Water Development Board

Sandia (2003) Desalination and water purification Roadmap e a report of the executivecommittee DWPR Program Report 95 US Department of the Interior Bureau ofReclamation and Sandia National Laboratories Available from httpwrrinmsuedutbndrcroadmapreportpdf (accessed 260814)

Sauvet-Goichon B (2007) Ashkelon desalination plante a successful challenge Desalination203 75e81

Stache K (1989) Apparatus for transforming sea water brackish water polluted water or thelike into a nutritious drink by means of osmosis US Patent No 4879030

Su J Yang Q Teo J F amp Chung T S (2010) Cellulose acetate nanofiltration hollow fibermembranes for forward osmosis processes Journal of Membrane Science 355 36e44

Tan C H amp Ng H Y (2008) Modified models to predict flux behavior in forward osmosis inconsideration of external and internal concentration polarizations Journal of MembraneScience 324 209e219

Tan C H amp Ng H Y (2010) A novel hybrid forward osmosisenanofiltration (FO-NF)process for seawater desalination Draw solution selection and system configurationDesalination and Water Treatment 13 356e361

Tang W amp Ng H Y (2008) Concentration of brine by forward osmosis Performance andinfluence of membrane structure Desalination 224 143e153

Treybal R E (1982) Mass transfer operations (3rd ed) New Delhi McGraw-Hill ChemicalEngineering Series

Valladares L R Yangali Q V Li Z amp Amy G (2011) Rejection of micropollutants byclean and fouled forward osmosis membrane Water Research 45 6737e6744

Van der Bruggen B amp Vandecasteele C (2002) Distillation vs membrane filtration Over-view of process evolutions in seawater desalination Desalination 143 207e218

Vedavyasan C V (2007) Pretreatment trends e and overview Desalination 203 296e299Vladisavljevic G T Vukosavljevic P amp Bukvic B (2003) Permeate flux and fouling

resistance in ultrafiltration of depectinized apple juice using ceramic membranes Journal ofFood Engineering 60 241e247

Wang K Y Ong R C amp Chung T S (2010) Double-skinned forward osmosis membranesfor reducing internal concentration polarization within the porous sublayer IndustrialEngineering and Chemistry Research 49 4824e4831

Wang R Shi L Tang C Y Chou S Qiu C amp Fane A G (2010) Characterization ofnovel forward osmosis hollow fiber membranes Journal of Membrane Science 355158e167

Wang K Y Yang Q Chung T S amp Rajagopalan R (2009) Enhanced forward osmosisfrom chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membraneswith a thin wall Chemical Engineering Science 64 1577e1584

Williams C J amp Edyvean R G (1998) An investigation of the biological fouling in thefiltration of seawater Water Science and Technology 38(8e9) 309e316

Xu J Ruan G Chu X Yao Y Su B amp Gao C (2007) A pilot study of UF pretreatmentwithout any chemicals for SWRO desalination in China Desalination 207 216e226

Yaeli J (1992) Method and apparatus for processing liquid solutions of suspensions partic-ularly useful in the desalination of saline water US Patent No 5098575

Yang Q Wang K Y amp Chung T S (2009a) A novel dual-layer forward osmosis membranefor protein enrichment and concentration Separation and Purification Technology 69269e274

Water treatment by reverse and forward osmosis 153

Yang Q Wang K Y amp Chung T S (2009b) Dual-Layer hollow fibers with enhanced fluxas novel forward osmosis membranes for water production Environmental Science andTechnology 43 2800e2805

Yangali Q V Li Z Valladares R Li Q amp Amy G (2011) Indirect desalination of RedSea water with forward osmosis and low pressure reverse osmosis for water reuseDesalination 280 160e166

Yip N Y Tiraferri A Phillip Schiffman J amp Elimelech M (2010) High performancethin-film composite forward osmosis membrane Environmental Science and Technology44 3812e3818

Zhang S Wang K Y Chung T S Chen H Jean Y C amp Amy G (2010) Well-constructed cellulose acetate membranes for forward osmosis Minimized internalconcentration polarization with an ultra-thin selective layer Journal of Membrane Science360 522e535

Zhao S amp Zou L (2011a) Relating solution physicochemical properties to internalconcentration polarization in forward osmosis Journal of Membrane Science 379459e467

Zhao S amp Zou L (2011b) Effects of working temperature on separation performancemembrane scaling and cleaning in forward osmosis desalination Desalination 278157e164

Zhao S Zou L Chuyang T Y amp Mulcahy D (2012) Recent developments in forwardosmosis Opportunities and challenges Journal of Membrane Science 396 1e21

Zhao S Zou L amp Mulcahy D (2012) Brackish water desalination by a hybrid forwardosmosis-nanofiltration system using divalent draw solute Desalination 284 175e181

154 Advances in Membrane Technologies for Water Treatment

Membrane bioreactors for watertreatment 5SA Deowan SI Bouhadjar J HoinkisInstitute of Applied Research (IAF) Karlsruhe University of Applied SciencesKarlsruhe Germany

51 Introduction

Water is another synonym of life According to the World Health Organization themost dangerous threat to the health of mankind emerging within the next few years ispolluted water In underdeveloped countries the shortage of clean freshwater will bethe most important cause of death for children under 5 years The low quantities offreshwater for industrial agricultural and municipal use have to be well preserved byefficient sustainable and cost-effective technologies Water contaminated fromindustry and agriculture with heavy metal ions pesticides organic compoundsendocrine disruptive compounds nutrients (phosphates nitrates and nitrites) hasto be efficiently treated to protect humans from being intoxicated with these com-pounds or with bacteria Furthermore incidental sludge from industrial wastewatertreatment facilities is commonly highly contaminated with toxic compounds(BioNexGen 2013)

Clean water as a basis for health and good living conditions is too far out of reachfor most of the world population Thus neither sustainable consumption nor reinforce-ment of governmental regulations is an effective driver to force the industry to adoptsustainability policies Although polluted water and water shortages demand sustain-able water use and recycling of wastewater the barriers are high for adopt them(BioNexGen 2013)

Water recycling is widely accepted as a sustainable option to respond to the generalincrease in water shortages and the demand for freshwater and for environmentalprotection Water recycling is commonly seen as one of the main options to providea remedy for water shortage caused by the increase in the demand for water anddraughts as well as a response to some economical and environmental drivers Themain options for wastewater recycling are industrial irrigation aquifer rechargeand urban reuse (Pidou 2006)

Membrane bioreactor (MBR) technology is recognized as a promising technologyto provide water with reliable quality for reuse Today MBRs are robust simple tooperate and even more affordable They take up little space need modest technicalsupport and can remove contaminants in one step This makes it practical to providesafely reusable water for nonpotable use

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400005-8Copyright copy 2015 Elsevier Ltd All rights reserved

52 Fundamentals

MBR technology is a combination of the conventional biological sludge process awastewater treatment process characterized by a suspended growth of biomass anda microfiltration (MF) or ultrafiltration (UF) membrane system (Judd 2011) Thebiological unit is responsible for the biodegradation of waste compounds and themembrane module for the physical separation of treated water from the mixed liquorThe pore diametre of the membranes is in the range between 001 and 01 mm so thatparticulates and bacteria can be kept out of permeate and the membrane systemreplaces the traditional gravity sedimentation unit (clarifier) in the biological sludgeprocess Hence MBR offers the advantage of higher product water quality andlow footprint Because of its advantages MBR technology has great potential inwide-ranging applications including municipal and industrial wastewater treatmentand process water recycling By 2006 around 100 municipal full-scale plants(gt500 population equivalent) and around 300 industrial large-scale plants (gt20 m3day) were in operation in Europe (Lesjean amp Huisjeslow 2008) MBR installation ca-pacity grew in 2007 but declined in 2008 and 2009 The market was affected by lowerindustrial spending because of the economic downturn However there was an in-crease in demand for large plants during the past 2e3 years Installations of MBRincreased significantly in the years of 2010 and early 2011 (GIA 2013)

The main industrial applications are in the food and beverage chemical pharma-ceutical and cosmetics and textile industries as well as in laundries The technicalfeasibility of this technology has been demonstrated through a large number of small-and large-scale applications

521 MBR configurations

According to MBR configurations both aerobic and anaerobic MBRs can be dividedinto two classes as side-stream MBR (sMBR) and submerged or immersed MBR(iMBR) (Figure 51)

In side-stream MBRs the membrane module is placed outside the MBR Thesludge from the MBR is pumped into the membrane module which creates cross-flow at the membrane surface and thus permeate is generated The concentratedsludge rejected by the membrane is recycled to the MBR This is a pressure-drivenmembrane filtration process In the early development of stream MBRs both thetransmembrane pressure (TMP) and cross-flow velocity were generated by the recir-culation pump However a few modifications were made to reduce the high-energyconsumption associated with the side-stream configuration Therefore a suctionpump was added to the recirculation pump on the permeate side which increasedoperation flexibility and decreased the cross-flow rate and energy consumption(Shimizu Okuno Uryu Ohtsubo amp Watanabe 1996) The latest side-stream MBRseven introduced air flow into the membrane module which intensified turbulenceon the feed side of the membrane and reduced the fouling and operational costs(Jiang 2007)

156 Advances in Membrane Technologies for Water Treatment

In submerged MBRs the membrane module is directly submerged in the reactor Asuction or vacuum pump is needed to create a TMP difference for permeate produc-tion In this case no circulation pump is needed because cross-flow is created by aera-tion This concept was first developed by Yamamoto Hiasa Mahmood and Matsuo(1989) to reduce energy consumption compared with side-stream MBR configurationIn some cases (eg MF membrane and very low filtration fluxes) the permeate side isplaced in a lower position and gravity itself is the only driving force for the filtration(Ueda amp Hata 1999)

Table 51 compares the side-stream and submerged MBRs The submerged MBRhas a simpler configuration because it needs less equipment The coarse bubbleaeration in the membrane tank is multifunctional In addition to membrane fouling con-trol it supplies oxygen to the biological process (although the efficiency of oxygen useis low) The biggest advantage of submerged over side-stream configuration is energysavings using coarse bubble aeration instead of the high-rate recirculation pump in side-stream MBRs The capillary and hollow-fibre membranes used in many submergedMBRs have high packing density and low cost which make it feasible to use moremembranes However typical tubular membranes used in side-stream MBRs havelow packing density and are more expensive Gander Jefferson and Judd (2000)reviewed four side-stream and four submerged MBR systems and concluded thatside-stream MBRs have higher total energy cost by up to two orders of magnitudemainly owing to the high recycle flow velocity (1e3 ms) and head loss within themembrane module In addition the submerged MBRs experienced fouling and couldbe cleaned more easily than the side-stream MBRs (Gander et al 2000)

However side-stream MBRs have the advantages of more robust physicalstrength and more flexible cross-flow velocity control and hydraulic loading They

Return sludge

InfluentInfluent

EffluentEffluent

AerationAeration

Bioreactor BioreactorExtra sludge

Extra sludge

Side-stream MBR Submerged MBR

Figure 51 Configuration of side-stream and submerged MBRsModified from Jiang (2007)

Membrane bioreactors for water treatment 157

are mostly used in industrial wastewater treatment and small-scale wastewater treat-ment plants where influent flow rate and composition have larger variation andoperational conditions are tough (eg high-temperature conditions) (Jiang 2007)Furthermore both MBR systems can be applied as aerobic (in the presence of anaeration system for the module) and anaerobic (in the absence of an aeration systemfor the module)

522 Membrane material types and morphology

Membrane materials and pore size are important criteria for MBR application Thereare two different types of membrane materials polymeric and ceramic Metallicmembrane filters exist but these have specific applications that do not relate toMBR technology To be made useful the membrane material must then be formed(or configured) to allow water to pass through it In MBRs a dense MF or a looseUF membrane is often applied (average pore size around 05e005 mm)

A number of different polymeric and ceramic materials are used to formmembranes but they are nearly always composed of a thin surface layer that providesthe required permselectivity on top of a more open thicker porous support thatprovides mechanical stability A classical membrane is thus anisotropic in structurewith symmetry only in the plane orthogonal to the membrane surface Polymericmembranes are also usually fabricated to have high surface porosity or percent totalsurface pore cross-sectional area and narrow pore size distribution so as to provideas high throughput and as selective a degree of rejection as possible The membranemust also be mechanically strong (ie have structural integrity) Finally the materialwill normally have some resistance to thermal and chemical attacks (ie extremes of

Table 51 Comparison of side-stream MBRs and submerged MBRs

Parameters Side-stream Submerged

Complexity Complicated Simple

Flexibility Flexible Less flexible

Robustness Robust Less robust

Flux High (40e100 Lm2 h) Low (10e30 Lm2 h)

Fouling reducing methods bull Cross-flowbull Airliftbull Backwashingbull Chemical cleaning

bull Air bubble agitationbull Backwashing (notalways possible)

bull Chemical cleaning

Membrane packing density Low High

Energy consumption withfiltration

High (2e10 kW hm3) Low (02e04 kW hm3)

Source Jiang (2007 p 11)

158 Advances in Membrane Technologies for Water Treatment

temperature pH andor oxidant concentrations that normally arise when the membraneis chemically cleaned) and should ideally offer some resistance fouling (Judd 2006)

In principle any polymer can be used to form a membrane only a limited numberof materials are suitable for the duty of membrane separation the most common ofwhich are

bull Polyvinylidene difluoride (PVDF)bull Polyethylsulphone (PES)bull Polyethylene (PE)bull Polypropylene (PP)bull Polysulphone (PS)

The membrane materials most often used in MBRs are organic polymers eg PEPP and PVDF (Judd 2006) Some are blended with other materials to change their sur-face charge or hydrophobicity (Mulder 1996) Ceramic materials have been shown tobe suitable for MBR technology because of their thermal chemical and mechanicalstability

Through specific manufacturing techniques all of these polymers can be formedinto membrane materials with desirable physical properties and each has reasonablechemical resistance (Judd 2011) Based on the common membrane materials the prin-ciple types of membrane are shown in Figure 52 which describes the typicalmorphology of membranes in MBR technology isotropic and anisotropic micropo-rous membranes are usually applied The two other types of membrane representthe morphology of dense membranes applied in reverse osmosis (RO) and nanofiltra-tion (NF)

Figure 52 Principle types of membranesModified from Baker (2004 p 4)

Membrane bioreactors for water treatment 159

523 Membrane module types

The configuration of the membrane ie its geometry and the way it is mounted andoriented in relation to the flow of water is crucial in determining overall processperformance (Judd 2011) Large membrane areas are normally required whenmembranes have to be applied on an industrial scale The smallest unit into whichthe membranes are packed is called a module (Mulder 1996) Three types ofmembrane modules such as flat sheet (FS) hollow fibre (HF) and multi-tubular(MT) are available that are suited to MBR technologies (Judd 2011) Two populartypes of modules are shown in Figure 53

Flat-sheet capillary and HF membranes are applied in iMBR and typical tubularmembranes are used in sMBR (Gander et al 2000) The geometric structure of amembrane is valuable if it is capable of minimizing fouling during the filtration processand if its module has good specific surface where for lsquospecific surfacersquo meansthe filtering surface per unity of occupied volume Structural simplicity managementflexibility and modularity are also important when deciding whether a membranemodule is valuable An important parameter often taken into account while consid-ering the membrane filtration process is the molecular weight of the compound thatcan be retained by the membrane This is called the molecular weight cutoff it refersto the molecular weight cutoff the solute at which 90 rejection takes place and isexpressed in daltons (Manigas 2008)

53 Aerobic MBR

Aerobic MBR is an MBR configuration associated with aeration systems In thisregard aeration has two functions (1) it supplies oxygen to microorganisms in thebioreactor and (2) it scours the membrane surface to create cross-flow which keeps

(a) (b)

Figure 53 Membrane bioreactor (MBR) module types (a) flat sheet (from Kubota Japan)(b) hollow fibre (from Motian China)

160 Advances in Membrane Technologies for Water Treatment

the membrane surface comparatively clean Normally air is supplied through an airdiffusion system The diffusion rate of oxygen from air to water depends on the airbubble size generated by the diffuser Coarse air bubbles are preferred for betterscouring whereas fine air bubbles are preferred for higher oxygen mass transferinto the water phase

531 Areas of application

Generally aerobic MBR is applied for low- to intermediate-level strength organicload-oriented wastewater such as municipal wastewater (low organic load) industrialwastewater and textile wastewater (organic load of intermediate level) Some aerobicMBR applications for treating wastewater are

bull Municipal wastewaterbull Textile wastewaterbull Agriculture wastewaterbull Wastewater from slaughterhousesbull Fisheriesbull Food processing industry

According to Lesjean et al (2009) and Zheng Zhou Chen Zheng and Zhou(2010) the growth of MBR applications in the European and Chinese marketsis increasing almost exponentially (Figures 54 and 55) Figures 54 and 55 indicatethat the application of MBRs in European countries is more in the industrial sectorswhereas in China it is more in the municipal field Globally there is also a pro-nounced upward trend in plant size as well as in the diversity of technology

0

100

200

300

400

500

600

1990ndash1998

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Num

ber o

f pla

nts

(cum

val

ues)

30 new refsyear

45 new refsyear

65 new refsyearIndustrial (capacity gt20m3d)

Municipal (capacity gt20m3d)

Total municipal in EuropeAbout 2 millions ep (05 population)

Figure 54 Development of industrial andmunicipalMBRmarket inEurope (Lesjean et al 2009)

Membrane bioreactors for water treatment 161

providers - although the largest MBRs are predominantly fitted with GE Zenon Tech-nology (Judd 2011) In 2010 GE Zenon provided more than 40 of the total globalinstalled capacity from MBR treatment (Judd 2011) In 2014 the United States wasthe country with the largest number of large-scale MBR plants (over 50 MLD) world-wide (The MBR Site 2014)

532 Factors affecting membrane performance

MBRs use a membrane filtration process based on pressure gradient The process isaffected by the following factors

bull Intrinsic resistance of the membranebull TMPbull Hydrodynamic regime at the interface between the membrane and the solution to be filteredbull Fouling

Among these factors hydraulic geometry including microbiological aspects ofMBR and fouling of the membranes are the most important

Microbiological species of MBR are influenced by several common parameterssuch as

bull Hydraulic residence time (HRT)bull Mixed liquor suspended solids (MLSS)bull Sludge retention time (SRT)bull Sludge loading (SL) or organic loading rate (OLR)

An overview of these most common influencing parameters is been provided in thefollowing sections

Figure 55 Capacity development of industrial and municipal MBR markets in China (Zhenget al 2010)

162 Advances in Membrane Technologies for Water Treatment

5321 Hydraulic residence time

The HRT indicates the duration in hours that the feed solution remains in the MBRbefore it is processed as permeate by the membrane The formula for HRT is

HRT ethhTHORN frac14 Hydraulic volume ethLTHORNPermeate flow ethL=hTHORN (51)

From Eqn (51) it is evident that HRT depends on the hydraulic volume of thereactor and the permeate flow If HRT is high it is easier for bacterial biocenosis toacclimate to reactor conditions but low HRT affects conditions inversely

HRT is an important operating parameter in aerobic MBR operation (Le ClechChen amp Faine 2006 Meng et al 2009) Lower HRT values result in higher OLRwhich result in a reduction of reactor volumes required to achieve a specified removalperformance On the other hand higher HRTs usually result in better removal perfor-mance Qin Oo Tao and Kekre (2007) reported that for the operation of a submergedMBR for treatment of petrochemical wastewater the use of HRTs in the range13e19 h results in effluents that have acceptable qualities Chang et al (2006) founda negligible effect of HRT in the range of 12e30 h on the removal performanceof MBR used to treat the wastewater of an acrylonitrileebutadieneestyrene unitVisvanathan Thu Jegatheesan and Anotai (2005) reported similar chemical oxygendemand (COD) and pentachlorophenol removal performance at HRTs in the range of12e24 h in an MBR used to treat synthetic wastewater Decreased HRT has also beenreported to result in an increase in the rate of membrane fouling in MBRs although itseffect seems to be mostly indirect rather than direct (Chang et al 2006 Meng ShiYang amp Zhang 2007 Meng et al 2009 Qin et al 2007)

5322 Mixed liquor suspended solids

MLSS are the concentration of suspended solids in mixed liquor usually expressedin grams per litre (Wateronline 2011) Mixed liquor is a mixture of raw or settledwastewater and activated sludge contained in an aeration basin in the activated sludgeprocess MLSS are used to control the wastewater treatment plant in the suspendedgrowth process

According to Lousada-Ferreira et al (2010) MLSS are a critical operational param-eter for aerobic MBR The possibility of using high solid contents results in a reducedfootprint that is considered one of the biggest advantages of MBR technologyHowever the influence of MLSS on fouling is not consistent and sometimes is contra-dictory MLSS concentrations have a direct impact on viscosity (Hasar Kinaci euroUnleurouTogrul amp Ipek 2004 Rosenberger Kruger Witzig Manz Szewyk amp Kraume2002) According to Hasar et al (2004) suspensions with higher viscosity requirehigher cross-flow velocities to create turbulent regimes If the cross-flow is not enoughto scour the solids away from the membrane it is reasonable that the fouling layer willbuild up faster on the membrane surface

Membrane bioreactors for water treatment 163

Therefore the theoretical explanation suggests that increasing concentrations ofsolids result in increasing fouling However some authors report no effect of solidson TMP (Harada Momonoi Yamazaki amp Takizawa 1994) or permeate quality(Rosenberger Kubin amp Kraume 2002) and demonstrate a decrease in TMP for sam-ples with higher MLSS concentrations (Defrance amp Jaffrin 1999 Le Clech Jeffersonamp Judd 2003) One explanation for these apparently contradictory results is that theeffect of MLSS concentration on filtration resistance varies according to the appliedMLSS range in the MBR operation (Lousada-Ferreira et al 2010)

5323 Sludge retention time

SRT indicates how frequently sludge is taken away from the MBR It also means theage of the sludge Laeraa Polliceb Saturnob Giordanob and Sandullia (2009)observed a significant correlation between the SRT and the OLR That study suggestedthat the biomass activity is weakly affected by the age of the sludge Membrane clean-ing requirements also appear to depend slightly on the SRT

According to Ahmed Cho Lim Song and Ahn (2007) the SRT affects the mixedliquor characteristics and induces changes in the physiological state of microorganismsthus variations in membrane fouling substances such as extracellular polymeric sub-stances (EPS) and soluble microbial products (SMP) can occur (Chang amp Lee 1998Masse Sperandio amp Cabassud 2006) However contradictory reports exist in the liter-ature regarding the effects of SRT on membrane biofouling Several studies demon-strated that EPS increases as SRT increases (Chang amp Lee 1998 Cho 2004 Masseet al 2006) others have shown the opposite trend (Lee Kang amp Shin 2003Ng amp Hermanowicz 2005)

5324 Sludge loading or organic loading rate

The SL or ratio of feed to microorganism (FM) is an important design parameter in theMBR process Generally the MBR process can operate at higher FM ratios comparedwith an activated sludge plant (Robinsion 2003) It is defined as kilograms of CODdivided by kilograms of MLSS times days It can also be expressed as kilograms ofCOD divided by cubic metres times days

The OLR has an important role in the treatment of wastewater by MBRs Anincreased OLR decreases the filterability of the MBR Kornboonraksa and Lee (2009)reported that an increase in influent COD biological oxygen demand (BOD) andNH4eN from 1150 to 2050 mgL 683 to 1198 mgL and 154 to 248 mgL respec-tively resulted in a decrease in the removal efficiency of COD BOD and NH4eNTrussell Merlo Hermanowicz and Jenkins (2006) reported increased membranefouling with higher OLR They reported that steady-state membrane fouling ratesincreased 20-fold over a fourfold increase in FM Khoshfetrat Nikakhtari Sadeghifarand Khatibi (2011) found a reduction of COD removal efficiency from 90 to 74when OLR increased from 1 to 25 kg CODm3 day Shen Zhou Mahendran Bagleyand Liss (2010) reported a higher degradation of organics (glucose) of 98 at OLRs

164 Advances in Membrane Technologies for Water Treatment

of 13 g CODL day or less compared with an OLR of 30 g CODL day which had adegradation of about 70

In the biochemical stage of wastewater treatment organic carbon and nutrients areremoved from wastewater by microbes These microbes live and grow enmeshed inEPS that bind them into discrete micro-colonies forming three-dimensional aggre-gated microbial structures called flocs The ability of microorganisms to form flocsis vital for the activated sludge treatment of wastewater The floc structure enablesthe adsorption of soluble substrates but also the adsorption of colloidal matter andmacromolecules found in wastewaters (Liwarska-Bizukojc amp Bizukojc 2005Michael amp Fikret 2002) The diversity of microbial community in activated sludgeis large containing prokaryotes (bacteria) eukaryotes (protozoa nematodes androtifers) and viruses In this complex microsystem bacteria dominate the microbialpopulation and have a critical role in the degradation process (Michael amp Fikret2002)

5325 Fouling

When treating organic solutions (such as macromolecule solutions) the solute concen-tration at the membrane surface can attain a high value and a maximum concentration(the gel concentration) may be reached The formation of a gel layer on the membranesurface is often seen as fouling which causes a decrease in the permeate flux orincrease in TMP during a membrane process The gel concentration depends on thesize shape chemical structure and degree of solvation but is independent of thebulk concentration

Generally membrane fouling can be caused by a variety of constituents amongwhich are bacteria suspended solids and colloids as well as dissolved inorganicand organic compounds (Hilal Kochkodan Al-Khatib amp Levadna 2004)In MBRs fouling can be attributed to pore blocking (deposition within the pores)or to cake layer formation on the membrane surface (Jiang Kennedy van der MeerVanrolleghem amp Schippers 2003) (Figure 56) Colloidal and soluble foulants(SMP) can cause pore blocking and irreversible fouling because of their small size

Soluble microbial products(SMP)Colloids

Extracellular polymericsubstances (EPS)Polysaccarides proteinsnatural organic matter

Floc characteristics Size Structure

Biomass characteristics

Pore blocking Cake formationFigure 56 Biomass characteristics and biofouling

Membrane bioreactors for water treatment 165

533 Case study wastewater reuse by aerobic MBR in acommercial laundry

In addition to municipal wastewater treatment aerobic MBR is widely used in indus-trial wastewater treatment There are a multitude of industrial sectors such as laundrytannery textile wheat starch dairy beverage palm oil and pharmaceutical (Hoinkiset al 2012 Mutamim Noor Hassan Yuniarto amp Olsson 2013)

Several operational factors need to be considered such as HRT MLSS SRT andOLR to achieve high water quality and high water flux (ie to reduce the foulingeffect) The hydraulic performance indicates the productivity of the process in termsof water permeability or flux water quality is usually expressed in terms of COD inpermeate Section 5331 presents a typical case study on the treatment and reuse oflaundry textile wastewater

5331 Background

The process applied in the case study was developed through cooperation betweenthe Karlsruhe University of Applied Sciences and Textile Service KlingelmeyerDarmstadt Germany The wastewater was treated in a two-step process and wasrecycled in the laundryrsquos washing and rinsing process (Figure 57) After coarsescreening using a vibrating sieve to retain suspended particles the wastewater wascollected in a storage tank (WW) Subsequently the wastewater was treated in anMBR as the principal cleaning unit Air was injected into the reactor to scour themembranes and drive the biological treatment The MF permeate was stored in ancollecting tank (TWW) It was free of turbidity and considerably reduced in microbesSome of the MF permeate was treated in a second step by a low-pressure RO unit withspiral-wound modules to retain salts as well as organic residues The MF and RO

TWWTWWWWWW

Rain-Rain-waterwater SurplusSurplus

sludgesludge

SewageSewagetreatmenttreatmentplantplant

Mixed water

MBR ROTWWWWScreen

Sewagetreatmentplant

Surplussludge

Rain-water

MWMWMWMW

Figure 57 Schematic of the water reuse process (WW wastewater TWW treated wastewaterMW mixed wastewater)

166 Advances in Membrane Technologies for Water Treatment

permeates were mixed in a tank (MW) and were used for washing and rinsing Theratio of mixing (RO permeate to MBR permeate) lies between 21 and 11 dependingon the salt level of the MBR permeate Before storage the MBR and RO permeateswere treated with a small amount of chlorine dioxide to prevent the growth of germsBecause rainwater did not meet the water quality criteria for the process it wascollected in the wastewater collecting tank The integrated process generated twokinds of waste that needs to be disposed The surplus sludge was stored in a separatetank and was collected by commercial waste management enterprises The concentratefrom the RO treatment was drained into the municipal treatment plant (Hoinkis et al2012)

5332 Plant components

A commercial-scale MBR plant consists of

bull Vibrating sieve (Sweco) with a mesh size of 200 mmbull An MBRbull An RO unitbull Three storage tanks (wastewater WW MBR permeate TWW mixed MBR plus RO

permeate MW)

The MBR contained a submerged Kubota Type 510 MF plate and frame mem-branes (single plate 08 m2) with 04-mm pore size made of chlorinated polyethyleneThe MBR tank had a total volume of 126 m3 It was separated by a barrier into twocompartments connected by a spill One compartment was designed only for biodeg-radation the other was for biodegradation and membrane filtration This gavemaximum flexibility for adjusting aeration to the needs of the filtration and biodegra-dation process The biomass was circulated between compartments every other dayThe filtration compartment contained two double-deck Kubota stacks (SystemEK300) with 600 plate and frame modules (total membrane area of 480 m2) TheRO unit was fitted with six 8040 spiral-wound modules (Dow LE) The plant wascomposed of three collecting tanks (wastewater MBR drain and MBR plus RO drain)the first with an enamel steel collecting tank of 400 m3 for wastewater and two 200 m3

tanks for the MBR and MBR plus RO drains

5333 Results

The results of the case study are shown in Figures 58 through 510 Average flux wasaround 15 L(m2 h) at a permeability between 300 and 1000 L(m2 h bar) (Figure 58)After 1 year of operation without chemical cleaning the flux was lowered to 12 L(m2 h) at an average permeability of 150e300 L(m2 h bar) as can be seen inFigure 59 Figure 510 shows the COD values in feed and permeate as well as theelimination rate over more than 2 years of operation The feed COD started at600e800 mgL and increased to more than 1000 mgL whereas the COD in permeateremained at values below 100 mgL and the elimination rate was higher than 90The aeration rate in the filtration compartment of the MBR tank was 52 m3minThe biodegradation compartment was intermittently aerated by a fine diffuser at

Membrane bioreactors for water treatment 167

72 m3min The flux rate does not represent full flow capacity the plant was designedfor an eventual flux rate of 12e15 Lm2 h The concentration of MLSS in the reactorincreased from 3 to 10e15 kgm3 The COD sludge loading decreased from 014to 004 kg CODkg MLSS day The average yield factor for biomass growth wascalculated to 013 kg MLSSkg COD degraded The surplus sludge was collected ina storage tank and delivered to a commercial sludge processing unit

Typical water quality parameters of the MBR unit are shown in Table 52 whichdemonstrates that the COD removal efficiency was high (94) and the total N conver-sion rate was also relatively high (72)mdashindications of good permeate quality

54 Anaerobic MBRs

541 Areas of application

Because anaerobic digestion in wastewater treatment combines pollution reductionand energy production it is the most interesting process for industrial effluent

30FL

ux

L(m

2 h)

Per

mea

bilit

y L

(m2

h ba

r)

25

20

15

10

5

0

3000

2500

2000

1500

1000

500

0

0 7 14 21 28Time days

0 7 14TIme days

21 28

Figure 58 Permeate flux and permeability of the MBR treatment plant during a typicaloperation period of 28 days after start-up

168 Advances in Membrane Technologies for Water Treatment

30

25

20

15

10

5

0

400

350

300

250

200

150

100

50

0

0 7 14 21 28

Time days

0 7 14 21 28

Time days

Per

mea

bilit

y L

(m2

h ba

r)FL

ux

L(m

2 h)

Figure 59 Permeate flux and permeability of the MBR treatment plant during a typicaloperation period of 28 days after 1 year of operation

0 0

20

40

60

80

100

200400600800

10001200140016001800

Removal

Feed

Permeate

Timedate

230

620

0623

08

2006

231

020

06

231

220

06

230

220

07

230

420

0723

06

2007

230

820

07

231

020

07

231

220

0723

02

2008

230

420

08

230

620

08

231

020

0823

08

2008

CO

D

mg

L

CO

D re

mov

al

Figure 510 COD values in MBR feed permeate and COD removal efficiency

Membrane bioreactors for water treatment 169

treatment Historically anaerobic processes have been mainly employed for industrialhigh strength wastewater and less for municipal wastewater because (1) it is difficult toretain slow-growth anaerobic microorganisms with short HRT for the treatment oflow-strength wastewater and (2) anaerobic digestion rarely meets discharge standards(Lin et al 2013)

Similar to aerobic MBRs (see Section 53) AnMBRs combine biodegradation withthe MF and UF membrane process which provides solideliquid separation The mostsalient features of AnMBRs compared with aerobic MBRs are no need of oxygensupply biogas (methane) production and lower sludge yield which significantlylowers the operating costs

Compared with conventional anaerobic digestion AnMBRrsquos most important aspectis its ability to offer complete biomass retention owing to membrane filtration Thisprovides sufficient SRT for the methanogens Conventional anaerobic biodegradationshows relatively poor settling properties of the biomass and hence results in the loss ofbiomass into the effluent (Lin et al 2013) In conventional systems only the strategyof biofilm or granule formation in modern high-rate anaerobic reactors offers highbiomass retention but at the cost of a long start-up period and complex process con-ditions (Lin et al 2013) Many industrial wastewater characterized by hightemperature high fat oil and grease content toxicity high salinity or drastic changesin OLR eg have a negative impact on the sludge granulation process and eventuallycould lead to degranulation (Dereli Ersahin et al 2012) Table 53 compares the mainfeatures of conventional anaerobic treatment (CAT) and AnMBR treatment in whichAnMBR treatment shows better effluent quality than conventional anaerobic treat-ment but also total pretreatment and complete biomass retention Because of its ben-efits such as complete biomass retention enhanced effluent water quality andpotential net energy production AnMBR is becoming increasingly interesting formunicipal wastewater treatment (Lew Tarre Beliavski Dosoretz amp Green 2009)

Similar to aerobic MBRs two configurations are used side-stream and submerged(see Section 521) In a side-stream configuration the membrane filtration module isplaced outside the reactor and after filtration the biomass is recirculated into the

Table 52 Typical water quality parameters of the MBR unit

Parameter UnitFeeda

(wastewater)Permeatea

(microfiltrate) Removal rate ()

BOD5 mgL 390 lt9 gt97

COD mgL 1120 67 94

NeNO3 mgL 77 21 73

NeNH4thorn mgL 15 01 93

Total N mgL 160 45 72

PePO43 mgL 14 13 7

aTypically average values based on several measurements

170 Advances in Membrane Technologies for Water Treatment

reactor This offers high fluxes but at the cost of frequent cleaning and high energyconsumption around 10 kW hm3 (Le Clech et al 2006)

In addition high cross-flow velocity has a negative impact on biomass activities(Choo amp Lee 1996 Ghyoot amp Verstraete 1997) In submerged MBR the membranesare placed inside the reactor Because air cannot be used to provide cross-flow on themembranes as in aerobic MBR maintaining high permeability is more difficult inAnMBRs In many cases gas sparging with generated biogas is used to scour themembranes (Smith Stadler Love Skerlos amp Raskin 2012) Most laboratory researchor small-scale pilot trials have been conducted with side-stream AnMBRs Howeveron a large or full scale submerged systems are preferred for their lower energyconsumption

Most research work was done at laboratory and on a small pilot scale only a fewstudies have been conducted with large-scale AnMBR (Dereli Ersahin et al 2012)Although laboratory-scale studies provide invaluable information on treatabilityand membrane fouling mechanisms with scientific insight hydraulics and shear forcesacting on a small membrane module will significantly differ from a full-scale mem-brane module (Dereli Ersahin et al 2012) Table 54 shows treatment performanceon a large pilot and full scale for various industrial wastewaters All of these studiesused submerged membrane configurations

Table 53 Comparison of conventional anaerobic treatment (CAT)and anaerobic membrane bioreactor (AnMBR)

Feature CAT AnMBR

Organic removal efficiency thorn thornEffluent quality o thornOrganic loading rate thorn thornSludge production Footprint thorno Biomass retention Complete

Nutrient requirement Alkalinity requirement thorn For certain industrial

streamsthorno

Energy requirement Temperature sensitivity o o

Start-up time 2e4 months lt2 weeks

Bioenergy recovery Yes Yes

Mode of treatment Primarily pretreatment Total or pretreatment

thornthorn Excellent thorn high o moderate lowpoorModified from Lin et al (2013)

Membrane bioreactors for water treatment 171

Table 54 Treatment performance of various industrial wastewaters

Reactorvolumem3

temperatureCOLRkgCODm3 day HRTdays TSSgL

CODremoval

MembranetypePore sizeFluxLm2 hTMPbar Reference

Food processing 870033

12 29 23 994 Flat sheet04 mm25e42003

Christian et al(2011)

Potato processing 3335

2e12 35e14 40 99 Flat sheet04 mm083e5003e004

Singh Burkeand Grant(2010)

Stillage from tequilaproduction

1337

48 124 e 95 Flat sheetee

Grant ChristianVite andJuarez (2010)

Snack factory 07635

51 e 79e104 97 Hollow fibre04 mm65e8e

Diez Ramosand Cabezas(2012)

Ethanol thin stillage 1237

45e7 16 24 98 Flat sheet008 mm43 1101e02

Dereli Urbanet al (2012)

Modified from Dereli Urban et al (2012)

172Advances

inMem

braneTechnologies

forWater

Treatm

ent

542 Factors affecting performance

Regarding aerobic MBRs membrane fouling presents one of the main bottlenecks forAnMBR application (Dereli Ersahin et al 2012) Because of the fouling of organicand inorganic compounds permeate flux through the membrane can be significantlyreduced Compared with aerobic MBRs AnMBRs show lower permeate fluxes as aresult of less flocculation of the sludge and hence increased concentrations of fineparticles and colloidal solids at the membrane surface Cake layer formation was identi-fied as themost important foulingmechanism inAnMBRs (Dereli Ersahin et al 2012)

5421 Temperature

Regarding process temperature anaerobic digestion basically falls into one ofthe following categories (Rajeshwari Balakrishnan Kansal Lata amp Kishore 2000)psychrophilic (0e20 C) mesophilic (20e42 C) or thermophilic (ca 42e75 C) InAnMBRs a higher temperature can increase membrane flux owing to reducedviscosity and higher membrane permeability This is advantageous for loweringenergy requirements With lower sludge viscosity lower shear rates will be requiredto obtain the same shear stress (Jeison amp van Lier 2006) Because of higher membranepermeability the same water flux can be achieved at a lower TMP (Smith et al 2012)Higher temperatures in thermophilic operations proved to be advantageous only in short-term experiments in the long-term theywere disadvantageous (JeisonampvanLier 2007)

Jeison and van Lier (2007) showed that permeate water flux in a thermophilic oper-ation was two to three times lower compared with water flux in a mesophilic operationHence it was concluded that in the long-term adverse temperature effects on the prop-erties and composition of the sludge were more important than the beneficial influenceof membrane filtration These findings are in line with the results of Lin et al (2009)who investigated the influence of sludge properties on membrane fouling in sub-merged AnMBRs treating kraft evaporation condensate The AnMBRs were operatedunder similar hydrodynamic conditions and MLSS concentrations under both meso-philic and thermophilic conditions In the long-term the permeate water flux of themesophilic system was significantly higher than that for the thermophilic system(74 L(m2 h) versus 18 L(m2 h) respectively) (Lin et al 2009) This was attributedto the increased formation of small particles under thermophilic conditions whichresulted in a more compact and less porous cake layer on the membrane in the caseof thermophilic operation In addition Lin et al (2009) found that the concentrationof bound EPS and protein in the cake layer was higher under thermophilic conditionswhich might be because of the increased decay rate of bacteria at elevated tempera-tures Furthermore the permeate water quality of the mesophilic system was consid-erably better than that of the thermophilic reactor

5422 Organic loading rate

In theory a high OLR and short HRT can be employed in AnMBRs However OLRshould always be evaluated together with SRT and sludge activity (Dereli Ersahinet al 2012) A variety of experimental studies carried out up to very high OLR still

Membrane bioreactors for water treatment 173

showed high COD removal efficiency Treatment of simulated wastewater from thepetrochemical industry demonstrated high COD removal efficiency at OLR up to25 kg CODm3day (van Zyl Wenzel Ekama amp Riedel 2008) Similar high treat-ment efficiency has been shown for slaughterhouse and palm oil wastewater aswell at ORL up to 133 and 11 kg CODm3day respectively (Abdurraham Rosli ampAzhari 2011 Saddoud amp Sayadi 2007)

5423 Hydraulic residence time and SRT

The performance of AnMBR and membrane fouling is affected by HRT and SRTGenerally speaking a low HRT is preferred because it reduces tank volume and hencethe overall footprint of the system A high SRT is required to achieve better treatmentperformance especially at lower temperatures (OFlaherty Collins amp Mahony 2006)However increasing the SRT causes higher SMP and EPS production and results in ahigher propensity for membrane fouling Moreover increasing the SRT under constantHRT increases the biomass concentration resulting in lower permeate flux (Smith et al2012) A variety of publications are concerned with the study of treatment performanceon HRT An insignificant decrease in COD removal efficiency (ca 5) was observedby Hu and Stuckey when they studied the treatment of simulated domestic wastewaterat mesophilic temperatures (35 C) lowering HRT from 48 h down to 3 h (Hu ampStuckey 2006) Even at an HRT of 3 h COD removal efficiency was higher than90 Several other studies similarly concluded that HRT had little effect on AnMBRpermeate quality (Smith et al 2012) Those studies suggested that adequate AnMBRperformance may be obtained at relatively short HRTs even at lower temperaturesbut that a lower limit on HRT may exist primarily owing to concerns regarding mem-brane fouling (Smith et al 2012) For AnMBR SRT is an easily controllable opera-tional parameter because membrane separation allows complete retention of biomassHuang et al studied low-strength domestic wastewater and observed better treatmentperformance at a longer SRT but at the cost of increased membrane fouling as a resultof higher biomass concentrations and SMP production (Huang Ong amp Ng 2011)Despite this many publications observed that EPS is a major contributor to directfouling However the role of EPS quantity and characteristics in membrane foulingas a function of SRT is not well understood in AnMBRs (Smith et al 2012)

5424 Membrane properties

Fouling in AnMBRs is very much affected by membrane properties such as materialspore size and surface characteristics Although hydrophobic membrane materials aremore durable under harsh chemical and thermal conditions hydrophilic membranesare typically favoured because they are less prone to fouling (Dereli Urban et al2012) Membrane materials used for AnMBRs can be classified into three major cat-egories ceramic metallic and polymeric In early experimental studies ceramic wasthe most widely used material for AnMBRs (Lin et al 2013) In AnMBRs metallicmembranes have also been applied because of their better hydraulic performance bet-ter fouling recovery and better tolerance to oxidation and high temperature (Kim ampJung 2007 Zhang et al 2005) However because of economic constraints in

174 Advances in Membrane Technologies for Water Treatment

commercial applications cheaper polymeric materials have gained more interestTypically materials such as PVDF PES PE and PP are applied with pore sizes inthe MF or UF range (003e1 mm) and in hollow fibre flat sheet or tubular configu-rations In general preferred polymeric membrane materials for MBRs are PVDFand PES which account for around 75 of total products on the market including9 of the 11 commercially most important products (Santos amp Judd 2010) Becauseof the high fouling propensity modification of the hydrophobic membrane surfaceby hydrophilic coating is a main goal in reducing fouling propensity Choo et al(2000) modified the surface of an organic membrane by grafting with2-hydroxyethyl methacrylate (HEMA) which resulted in 35 flux increase A135 flux increase was reported by Sainbayar Kim Jung Lee and Lee (2001)who modified the surface of a PP membrane material by 70 grafting withHEMA Kochan Wintgens Melin and Wong (2009) studied surface coating viathe adsorption of surfactants in which different UF flat-sheet membranes were coatedwith branched poly(ethyleneimine) poly(diallyldimethyl ammonium chloride) andpoly(allylamine chloride) and filtered with sludge supernatant The experimentsshowed lower fouling but also low physical tolerance and chemical stability underMBR conditions To overcome this drawback Asatekin et al (2006) developed aself-assembling technique by coating commercial PVDF UF membranes with theamphophilic graft copolymer PVDFegraft-polyoxyethylene methacrylate

543 Case study treatment of high-strength industrialwastewater using a full-scale AnMBR

Most AnMBR research has been carried out at the laboratory or small pilot scale onlya few studies have been concerned with large- or full-scale applications Most full-scale AnMBR installations were established in Japan Kanai reported about 14large-scale AnMBR implementations in the food and beverage industries in Japan(Kanai Ferre Wakahara Yamamoto amp Moro 2010)

A typical case study on the treatment of high-strength industrial wastewater using afull-scale AnMBR is presented here

The study is the first AnMBR installation in North America and the largest AnMBRinstallation in the world It was built at Kenrsquos Foods in Massachusetts (ChristianGrant McCarthy Wilson amp Mills 2011)

Due to lack of space positive economics and the ability to provide additional ca-pacity for flow and organic load the system was converted from Kenrsquos Foodsrsquo existinganaerobic process to AnMBR in July 2008 It provides waste treatment but also a largegain in energy production from salad dressing and barbeque sauce wastewater

The process uses Kubota flat-plate membrane cartridges (with nominal pore size of04 mm) that are submerged directly into the anaerobic biomass and completely blockall suspended solids from escaping to the effluent Figure 511 shows a general processflow diagram of the AnMBR process

The design of this AnMBR system has an effluent flow rate of 475 m3day with39000 mgL COD 18000 mgL BOD and 12000 mgL total suspended solids(TSS) under mesophilic conditions ensured by an average operating temperature of

Membrane bioreactors for water treatment 175

33 C for all four anaerobic membrane tanks a pH of 69 01 for anaerobic sludgeacclimatization an operating volumetric flux rate in the range of 006e010 m3m2

day and a TMP fluctuating between 0005 and 01 bar Once the TMP reaches01 bar membrane cleaning is required (three of four membrane compartments werecleaned once during the first 20 months of operation) Table 55 presents the rawwastewater characteristics and average effluent quality after 20 months of runningthe pilot test

In Table 55 this AnMBR process consistently provides an effluent with undetect-able TSS concentrations and COD and BOD concentrations of 209 39 and16 5 mgL corresponding to COD and BOD removals of 994 and 999 respec-tively By dint of biogas scouring across the membrane surface a very low rate ofmembrane fouling is an important result in this study because membrane foulingunder anaerobic conditions is a considerable issue for the AnMBR process

Anaerobic MBR

Biogas

Feed

Methanefermentation

tank

Separation tankwith submerged

membrane

Wastewatertreatmentequipment

Powergenerating

facility

Sludgedehydrationequipment

Pretreatmentequipment

Optional

Figure 511 General process flow diagram of the AnMBR processModified from Christian et al (2011)

Table 55 Raw wastewater and AnMBR effluent characteristics(July 2008 to April 2010)

Parameter Raw wastewater AnMBR effluent Removals

Flow rate m3day 300 300 e

BOD mgL 18000 20 999

COD mgL 33500 210 994

TSS mgL 10900 lt1 100

pH e 705 e

176 Advances in Membrane Technologies for Water Treatment

Upgrading the existing anaerobic treatment system to an AnMBR demonstratedthe simplicity and suitability of the process for a wastewater treatment system that pre-viously experienced difficulty with solids management and sludge settling ability(Christian et al 2011)

This installation at Kenrsquos Foods can be considered an ideal technology forthe development of renewable energy from waste especially when containing ahigh suspended solids concentration

55 Forward osmosis MBRs

The combination of FO and activate sludge treatment is a relatively new process FO isa natural process driven by the osmotic pressure difference that retains solutes but al-lows water to permeate through a semipermeable membrane (Cath Childress ampElimlech 2006) FO is attractive because of the high rejection efficiency of its mem-branes hence the drawback of conventional MF and UF MBRs can be overcomewhich are limited in the retention of low-molecular-weight compounds (LMWC)To increase efficiency in LMWC removal conventional MBRs need to be combinedwith downstream RONF units which results in high capital cost and energy consump-tion (Alturki et al 2010)

In FO-MBRs treated water is drained without a pump by osmotic pressure into adraw solution with higher solute concentration than the feed solution this results indilution of the draw solution Therefore the draw solution needs to be concentratedby either mechanical (RO) or thermal processes (distillation) In doing so the treatedclean water can be drained off the system Figure 512 shows a schematic of theprocess FO-MBR offers the possibility of high cleaning efficiency in wastewatertreatment and reuse Achilli Cath Marchand and Childress (2009) reported morethan 99 of organic carbon and more than 98 of NH4eN removal combining thebiological and FO processes using flat-sheet cellulose triacetate FO membranes(Achilli et al 2009) With this process the draw solution is reconcentrated by RO

Draw solution

Reconcentration

Treated water

MBR

Feed

Figure 512 Schematic of FO-MBR system

Membrane bioreactors for water treatment 177

Most research work on FO-MBRs was conducted on the laboratory scale There areonly a few examples of larger pilot-scale studies Quin et al (2009) studied optimi-zation of an FO-MBR on the pilot scale using NaCl and MgSO4 salts in draw solu-tions The NaCl performed at much higher efficiency than MgSO4 as an osmoticagent owing to a greater solute diffusion coefficient

Chen et al (2014) combined a submerged AnMBR with an FO membrane to treatsynthetic low-strength wastewater The FO-AnMBR showed greater than 96 carbonremoval and 100 of total phosphorous and 62 of NH4eN removal This was betterremoval efficiency than for the conventional AnMBR The most salient feature ofFO-AnMBR is its ability to provide biogas that can be used as an energy source todrive the combined process

56 Conclusion and perspectives

Over the past 2 decades the development of MBRs has made great progress In partic-ular the application of aerobic MBRs showed rapid growth in many municipal andindustrial large-scale implementations This is mainly because of their potential forrecycling and reusing grey water and industrial effluents Major improvements havebeen achieved for aerobic MBRs (Brepols 2011)

bull Improved module hydraulics and optimized process control helped reduce energy consump-tion for air scouring

bull Advances in membrane production led to improvement in materials stability and resiliencewhereas market prices have come down

bull In terms of investment cost todayrsquos MBR plants are not necessarily more expensive thancomparable conventional activated sludge plants

MBR technology is expected to grow in the near future because of the increasingscarcity of water worldwide which makes wastewater reclamation necessary Thiswill be further aggravated by climate change Based on the estimated global MBRmarket of US$8382 million in 2011 the MBR market is projected to grow at anaverage rate of 224 reaching a total market size of US$344 billion in 2018(WaterWorld 2012) The Chinese market is expected to grow at an even higher rateof 289 with the key drivers of high economic growth rate increased confidencein technology and public awareness as well as a strong need for wastewater reclama-tion (Sartorius Walz amp Orzanna 2013)

Besides China the MBR market in Middle Eastern and North African countries isexpected to witness a high growth trajectory in the next 5e10 years because of a largenumber of projects commissioned in medium and large range plants with capacitiesranging between 5000 and 50000 m3day (Frost amp Sullivan 2012)

Future research and development should focus on further lowering energy demands(operating costs) and membrane costs (capital costs) as well as FO-MBRs because oftheir advantages regarding the high rejection of low-molecular-weight contaminantsand their lower fouling propensity

178 Advances in Membrane Technologies for Water Treatment

List of abbreviations

AnMBR Anaerobic MBRBOD Biological oxygen demandCAT Conventional anaerobic treatmentCOD Chemical oxygen demandEPS Extracellular polymeric substancesFS Flat sheetFM Feed to microorganismsHF Hollow fibreHRARs High-rate anaerobic reactorsHRT Hydraulic residence timeiMBR Immersed MBRLMWC Low molecular-weight compoundsMBR Membrane BioreactorMF MicrofiltrationMT Multi-tubularMLD Million liter per dayMLSS Mixed liquor suspended solidsMW Mixed wastewaterOLR Organic loading ratePCP PentachlorophenolPE Polyethylenepe Population equivalentPP PolypropylenePES PolyethylsulphonePS PolysulphonePVDF Poly vinylidene diflurideRO Reverse osmosisSL Sludge loadingSMP Soluble microbial productssMBR Side-stream MBRSRT Sludge retention timeTMP Transmembrane pressureTSS Total suspended solidsTWW Treated wastewaterUF UltrafiltrationWW Wastewater

References

Abdurraham N H Rosli Y M amp Azhari N H (2011) Development of a membraneanaerobic system (MAS) for palm oil mill effluent treatment (POME) Desalination 266208e212

Achilli A Cath T Y Marchand E A amp Childress A E (2009) The forward osmosis mem-brane bioreactor A low fouling alternative to MBR processes Desalination 239 10e21

Membrane bioreactors for water treatment 179

Ahmed Z Cho J Lim B-R Song K-G amp Ahn K-H (2007) Effects of sludge retentiontime on membrane fouling and microbial community structure in a membrane bioreactorJournal of Membrane Science 287 211e218

Alturki A A Tadkaew N McDonald J A Khan S J Price W E et al (2010) CombiningMBR and NFRO membranes filtration fort the removal of trace organics in indirect potablewater reuse applications Journal of Membrane Science 365 206e215

Asatekin A Menniti A Kang S Elimelech M Morgenroth E amp Mayes A M (2006)Antifouling nanofiltration membranes for membrane bioreactors from self-assembling graftcopolymers Journal of Membrane Science 285 81e89

Baker R W (2004) Membrane technology and applications (2nd ed) New York WileyBioNexGen (2013) Development of the next generation membrane bioreactor system www

bionexgeneu Accessed 60913Brepols C (2011) Operating large scale membrane bioreactors for municipal wastewater

treatment London UK IWA PublishingCath T Y Childress A E amp Elimlech M (2006) Forward osmosis Principles applications

and recent developments Journal of Membrane Sciences 281 70e87Chang I-S amp Lee C-H (1998) Membrane filtration characteristics in membrane coupled

activated sludge systemmdashthe effect of physiological states of activated sludge on mem-brane fouling Desalination 120 221e233

Chang J S Chang CY Chen A C Erdei L ampVigneswaran S (2006) Long term operationof submerged membrane bioreactor for the treatment of high strength acrylonitrile-butadiene-styrene (ABS) wastewater Effect of hydraulic retention time Desalination 19145e51

Chen L Gu Y Cao C Zhang J Ng J W amp Tang C (2014) Performance of a submergedanaerobic membrane bioreactor with forward osmosis membrane for low-strength waste-water treatement Water Research 50 114e123

Cho J (2004) Model development for a submerged membrane bioreactor with the effect ofextracellular polymeric substances Seoul Seoul National University

Choo K H Kang I J Joon S H Park H Kim J H Adia S et al (2000) Approaches tomembrane fouling control in anaerobic membrane bioreactors Water Science Technology41 363e371

Choo K H amp Lee C H (1996) Membrane fouling mechanisms in the membrane coupledanaerobic bioreactor Water Research 30 1771e1789

Christian S Grant S McCarthy P Wilson D ampMills D (2011) The first two years of full-scale anaerobic membrane bioreactor (AnMBR) operation treating high-strength industrialwastewater Proceedings of IWA 12th world congress on anaerobic digestion GuadalajaraMexico

Defrance L amp Jaffrin M Y (1999) Reversibility of fouling formed in activated sludgefiltration Journal of Membrane Science 157 73e84

Dereli R K Ersahin M E Ozgun H Ozturk I Jeison D van der Zee F et al (2012)Potentials of anaerobic membrane bioreactors to overcome treatment limitations induced byindustrial wastewaters Bioresource Technology 122 160e170

Dereli R K Urban D R Heffernan B Jordan J A Ewing J Rosenberger G T et al(2012) Performance evaluation of a pilot scale anaerobic membrane bioreactor (AnMBR)treating ethanol thin stillage Environmental Technology 33 1511e1516

Diez V Ramos C amp Cabezas J L (2012) Treating wastewater with high oil and greasecontent using an anaerobic membrane bioreactor (AnMBR) filtration and cleaning assaysWater Science and Technology 65(10) 1847e1853

180 Advances in Membrane Technologies for Water Treatment

Frost amp Sullivan (2012) The Middle East and North Africa membrane bioreactor market to growat a CAGR of 1777 per cent by 2015 httpwwwfrostcomprodservletpress-releasepagdocidfrac14251074704 Accessed 07012015 at 1132h

Gander M Jefferson B amp Judd S (2000) Aerobic MBRs for domestic wastewater treatment Areview with cost considerations Separation and Purification Technology 18(2) 119e130

Ghyoot W R amp Verstraete W H (1997) Coupling membrane filtration to anaerobic primarysludge digestion Environmental Technology 18 569e580

GIA Global Industrial Analysts Inc (2013) Global membrane bioreactors market to reachUS$888 million by 2017 httpwwwprwebcomreleasesmembrane_bioreactorsMBRprweb8973361htm Accessed 221113

Grant S Christian S Vite E amp Juarez V (2010) Anaerobic membrane bioreactor(AnMBR) pilot-scale treatment of stillage from tequila production Proceedings of IWA12th world congress on anaerobic digestion Guadalajara Mexico

Harada H Momonoi K Yamazaki S amp Takizawa S (1994) Application of anaerobic UFmembrane reactor for treatment of a wastewater containing high strength particulate or-ganics Water Science and Technology 30(12) 307e319

Hasar H Kinaci C euroUnleurou A Togrul H amp Ipek U (2004) Rheological properties ofactivated sludge in a sMBR Biochemical Engineering Journal 20 1e6

Hilal N Kochkodan V Al-Khatib L amp Levadna T (2004) Surface modified polymericmembranes to reduce (bio) fouling A microbiological study using E coli Desalination167 293e300

Hoinkis J Deowan S A Panten V Figoli A Huang R R amp Drioli E (2012) Membranebioreactor (MBR) technology e a promising approach for industrial water reuse ProcediaEngineering 33 234e241

Hu A Y amp Stuckey D C (2006) Treatment of dilute wastewaters using a novel sub-merged anaerobic membrane bioreactor Journal of Environmental Engineering 132190e198

Huang Z Ong S L amp Ng H Y (2011) Submerged anaerobic membrane bioreactor for low-strength wastewater treatment Effect of HRT and SRT on treatment performance andmembrane fouling Water Research 45 705e713

Jeison D amp van Lier J B (2006) Cake layer formation in anaerobic submerged membranebioreactors (AnSMBR) for wastewater treatment Journal of Membrane Science 284227e236

Jeison D amp van Lier J B (2007) Thermophilic treatment of acidified and partially acidifiedwastewater using anaerobic submerged MBR Factors governing long-term operationalflux Water Research 41 3868e3879

Jiang T (2007) Characterization and modelling of soluble microbial products in membranebioreactors (PhD thesis) (pp 241e248) Ghent University Belgium

Jiang T Kennedy M D van der Meer W G J Vanrolleghem P A amp Schippers J C(2003) The role of blocking and cake filtration in MBR fouling Desalination 157(1e3)335e343

Judd S (2006) The MBR book Principles and applications of membrane bioreactors for waterand wastewater treatment Cranfield University UK Elsevier ISBN 978-1-85617-481-7

Judd S (2011) The MBR book Principles and applications of membrane bioreactors for waterand wastewater treatment Cranfield University UK Elsevier

Kanai M Ferre V Wakahara S Yamamoto T amp Moro M (2010) A novel combinationof methane fermentation and MBR-Kubota submerged anaerobic membrane bioreactorprocess Desalination 250 960e967

Membrane bioreactors for water treatment 181

Khoshfetrat A B Nikakhtari H Sadeghifar M amp Khatibi M S (2011) Influence of organicloading and aeration rates on performance of a lab-scale upflow aerated submerged fixed-film bioreactor Process Safety and Environmental Protection 89 193e197

Kim J O amp Jung J T (2007) Performance of membrane-coupled organic acid fermenter fortthe resource recovery from municipal sewage sludge Water Science and Technology 55245e252

Kochan J Wintgens T Melin T amp Wong J (2009) Characterisation and filtrationperformance of coating-modified polymeric membranes used in membrane bioreactorsChemical Papers 63 152e157

Kornboonraksa T amp Lee S H (2009) Factors affecting the performance of membranebioreactor for piggery wastewater treatment Bioresource Technology 100 2926e2932

Laeraa G Polliceb A Saturnob D Giordanob C amp Sandullia R (2009) Influence ofsludge retention time on biomass characteristics and cleaning requirements in a membranebioreactor for municipal wastewater treatment Desalination 236 104e110

Le Clech P Chen V amp Faine T A G (2006) Fouling in membrane bioreactors usedin wastewater treatment Journal of Membrane Science 284 17e53

Le Clech P Jefferson B amp Judd S J (2003) Impact of aeration solids concentration andmembrane characteristics on the hydraulic performance of a membrane bioreactor Journalof Membrane Science 218 117e129

Lee W Kang S amp Shin H (2003) Sludge characteristics and their contribution to micro-filtration in submerged membrane bioreactors Journal of Membrane Science 216217e227

Lesjean B Ferre V Vonghia E amp Moeslang H (2009) Market and design considerationsof the 37 larger MBR plants in Europe Desalination and Water Treatment 6 227

Lesjean B amp Huisjeslow E H (2008) Survey of the European MBR market Trends andperspectives Desalination 231 71e81

Lew B Tarre S Beliavski M Dosoretz C amp Green M (2009) Anaerobic membranebioreactor (AnMBR) for domestic wastewater treatment Desalination 243 251e257

Lin H Peng W Zhang M Chen J Hong H amp Zhang Y (2013) A review on anaerobicmembrane bioreactors Applications membrane fouling and future perspectives Desali-nation 314 169e188

Lin H J Xie K Mahedran B Bagley D M Leung K T Liss S N et al (2009) Sludgeproperties and their effects in submerged anaerobic membrane bioreactors (SAnMBR)Water Research 43 3827e3837

Liwarska-Bizukojc E ampBizukojcM (2005) Digital image analysis to estimate the influence ofsodium dodecyl sulphate on activated sludge flocs Process Biochemistry 40 2067e2072

Lousada-Ferreira M Geilvoet S Moreau A Atasoy E Krzeminski P vanNieuwenhuijzen A et al (2010) MLSS concentration Still a poorly understoodparameter in MBR filterability Desalination 250 618e622

Manigas L (2008) Use of membrane bioreactor for the bioremediation of groundwaterpolluted by chlorinated compounds (PhD thesis) University of Cagliari Italy

Masse A Sperandio M amp Cabassud C (2006) Comparison of sludge characteristics andperformance of a submerged membrane bioreactor and an activated sludge process at highsolids retention time Water Research 40 2405e2415

The MBR Site (2014) Immersed anaerobic MBRs are they viable wwwthembrsitecomAccessed 150314

Meng F Chae S R Drews A Kraume M Shin H S amp Yang F (2009) Recent advancesin membrane bioreactors (MBRs) Membrane fouling and membrane material WaterResearch 43 1489e1512

182 Advances in Membrane Technologies for Water Treatment

Meng F Shi B Yang F amp Zhang H (2007) Effect of hydraulic retention time on membranefouling and biomass characteristics in submerged membrane bioreactors Bioprocess andBiosystems Engineering 30 359e367

Meng F amp Yang F (2007) Fouling mechanisms of deflocculated sludge normal sludge andbulking sludge in membrane bioreactor Journal of Membrane Science 305 48e56

Michael L S amp Fikret K (2002) Bioprocess engineering Basic concepts (2nd ed) UpperSaddle River NJ Prentice Hall

Mulder M (1996) Basic principles of membrane technology (2nd ed) Boston KluwerAcademic ISBN 0-7923-4248

Mutamim N S A Noor Z Z Hassan M A A Yuniarto A amp Olsson G (2013)Membrane bioreactor Applications and limitations in treating high strength industrialwastewater Chemical Engineering Journal 225 109e119

Ng H Y amp Hermanowicz S W (2005) Membrane bioreactor operation at short solidsretention times Performance and biomass characteristics Water Research 39 981e992

OFlaherty V Collins G amp Mahony T (2006) The microbiology and biochemistry ofanaerobic bioreactors with relevance to domestic sewage treatment Reviews in Environ-mental Science and Biotechnology 5 39e55

Pidou M (2006)Hybrid membrane processes for water reuse (PhD thesis) School of AppliedScience Department of Sustainable Systems Centre for Water Science CranfieldUniversity UK

Qin J J Oo H M Tao G Cornelissen E R Ruiken C J de Korte K F et al (2009)Optimization of operating conditions in forward osmosis for osmotic membrane bioreactorOpen Chemical Engineering Journal 3 27e32

Qin J J Oo M H Tao G amp Kekre K A (2007) Feasibility study on petrochemicalwastewater treatment and reuse using submerged MBR Journal of Membrane Science293 161e166

Rajeshwari K V Balakrishnan M Kansal A Lata K amp Kishore V V N (2000) State-of-the-art of anaerobic digestion technology for industrial wastewater treatment Renewableand Sustainable Energy Reviews 4 135e156

Robinsion T (2003) The MBR for industrial effluent Wakefield UK CIWEM amp Aqua EnviroConference

Rosenberger S Kruger U Witzig R Manz W Szewyk U amp Kraume M (2002) Per-formance of a bioreactor with submerged membranes for aerobic treatment of municipalwaste water Water Research 36 413e420

Rosenberger S Kubin K amp Kraume M (2002) Rheology of activated sludge in membranebioreactors Engineering in Life Sciences 2 269e275

Saddoud A amp Sayadi S (2007) Application of acidogenic fixed bed reactor prior to anaerobicmembrane bioreactor for sustainable slaughterhouse wastewater treatment Journal ofHazardous Materials 149 700e706

Sainbayar A Kim J S Jung W J Lee Y S amp Lee C H (2001) Application of surfacemodified polypropylene membranes to an anaerobic membrane bioreactor EnvironmentalTechnology 22(9) 1035e1042

Santos A amp Judd S (2010) The commercial status of membrane bioreactors for municipalwastewater Separation Science and Technology 45 850e857

Sartorius C Walz R amp Orzanna R (2013) Lead market for membrane bioreactor (MBR)technologyeChinarsquos second-mover strategy for the development and exploitation of its leadmarket potential Karlsruhe Fraunhofer Institute for Systems and Innovation Research ISIhttpkooperationenzewdefileadminuser_uploadRedaktionLead_MarketsWerkstattberichteWB_11_MBR_Sartorius_et_alpdf Accessed 010314

Membrane bioreactors for water treatment 183

Shen L Zhou Y Mahendran B Bagley D M amp Liss S N (2010) Membrane fouling in afermentative hydrogen producing membrane bioreactor at different organic loading ratesJournal of Membrane Science 360(1) 226e233

Shimizu Y Okuno Y Uryu K Ohtsubo S ampWatanabe A (1996) Filtration characteristicsof hollow fiber microfiltration membranes used in MBR for domestic wastewater treatmentWater Research 30(10) 2385e2392

Singh K Burke D amp Grant S (2010) Anaerobic flat sheet membrane bioreactor treating foodprocessing wastewater Pilot-scale performance Proceedings of IWA 12th world congresson anaerobic digestion Guadalajara Mexico

Smith A L Stadler L B Love N G Skerlos S J amp Raskin L (2012) Perspectiveson anaerobic membrane bioreactor treatment of domestic wastewater A critical reviewBioresource Technology 122 149e159

Trussell R S Merlo R P Hermanowicz S W amp Jenkins D (2006) The effect of organicloading on process performance and membrane fouling in a submerged membrane biore-actor treating municipal wastewater Water Research 40 2675e2683

Ueda T amp Hata K (1999) Domestic wastewater treatment by a submerged membranebioreactor with gravitational filtration Water Research 33(12) 2888e2892

Visvanathan C Thu L N Jegatheesan V amp Anotai J (2005) Biodegradation of penta-chlorophenol in a membrane bioreactor Desalination 183 455e464

Wateronline (2011) Mixed liquor suspended solids in wastewater httpwwwwateronlinecomarticlemvcMixed-Liquor-Suspended-Solids-In-Wastewater-0002 Accessed 230211

WaterWorld (2012) Membrane multiplier MBR set for global growth e water world wwwwaterworldcomarticleswwiprintvolume-27issue2regularscreative-financemembrane-multiplier-mbr-html Accessed 010314

Yamamoto K Hiasa M Mahmood T amp Matsuo T (1989) Direct solid-liquid separationusing hollow fiber membrane in an activated-sludge aeration tank Water Science andTechnology 21 43e54

Zhang S QuY Liu Y Yang F ZhangX FurukawaK et al (2005) Experimental study ofdomestic sewage treatment with a metal membrane bioreactor Desalination 177 83e93

Zheng X Zhou Y Chen S Zheng H amp Zhou C (2010) Survey of MBR market Trendsand perspectives in China Desalination 250 609e612

van Zyl P J Wenzel M C Ekama G A amp Riedel K J (2008) Design and start-up of ahigh rate anaerobic membrane bioreactor for the treatment of a low pH high strengthdissolved organic wastewater Water Science and Technology 57(2) 291e295

184 Advances in Membrane Technologies for Water Treatment

Advances in electrodialysis forwater treatment 6B Van der BruggenKU Leuven Leuven Belgium

61 Introduction

Electrodialysis is a membrane process driven by a difference in electrical potentialover a membrane stack in which charged compounds are removed from a feed solu-tion It is a process with a relatively long history with several papers published in the1950s on applications such as the demineralization of sugar solutions (Anderson ampWylam 1956) desalination (Dewhalley 1958) and protein separation (Laurence1956) which are still among applications of interest more than half a century laterWhat is remarkable is that although the direction has not substantially changed the in-terest in electrodialysis has boomed during the past decade The number of publica-tions on electrodialysis has doubled in 10 years and has increased by a factor of 10in 30 years Moorersquos law seems to be valid for electrodialysis as well This is partlythe result of the global tendency to publish more and more papers not necessarilyof higher or even the same quality Nevertheless it is interesting to observe thechanges in research interest over the years The most conservative conclusion fromthe numbers is that electrodialysis has remained a process of particular interest in termsof its potential for separation as well as in terms of applications over 6 decades It wasalready considered a mature process in 1972 (Solt 1972) and it is not surprising thatthe research topics have only partially shifted since the early days Scaling problemsfor example were reported in one of the earliest publications on electrodialysis(Cooke 1958) and are still on the research agenda today Examples include the devel-opment of pretreatment methods such as pre-softening with a pellet reactor (TranJullok Meesschaert Pinoy amp Van der Bruggen 2013) and the use of electrochemicalprocesses to remove scaling from membranes (Zaslavschi Shemer Hasson amp Semiat2013) The separation of proteins was already understood in earlier days to have po-tential (Laurence 1956) although the breakthrough in this area came much latermany applications today are in the dairy industry for whey protein concentrationmilk protein standardization etc (Daufin et al 2001) Applications and methodshowever are much more advanced today Electrodialysis with ultrafiltration mem-branes for example allows for advanced separation of peptides by exploiting the com-bined effect of charge and size separation by fine-tuning the pH and cutoff of themembrane (Firdaous et al 2009 Roblet Doyen Amiot amp Bazinet 2013) Electrodi-alysis in that context would touch the performance of a nanofiltration membranealthough the potential for specific separations is different (Langevin Roblet MoresoliRamassamy amp Bazinet 2012) Coupling nanofiltration and electrodialysis (with

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400006-XCopyright copy 2015 Elsevier Ltd All rights reserved

ultrafiltration membranes) in a single process line would optimize the overall separa-tion performance and allow the production of more specific peptide fractions The prin-ciple of electrodialysis can be further extended in view of the improved separation ofpeptides In the electrophoretic membrane contactor a porous membrane is used toestablish contact across two flowing liquids between which an electrically drivenmass transfer takes place (Galier amp Roux-de Balmann 2011)

In terms of applications comparison with the early days yields more surprisesUrine separation is currently a topic of considerable interest Historically the use ofelectrodialysis for salt separation was described in 1960 in a publication that appearedin Nature (Wood 1960) At that moment it did not attract much interest (it was citedan impressive three times) but today urine separation has been revived Scientific in-terest has shifted and the separation needed today is more challenging than only theremoval of salts the focus is rather on recycling of nutrients while micropollutantsshould be kept out of the eventual product (Pronk Biebow amp Boller 2006) Electro-dialysis is probably a critical process to achieve this although none of the processessuggested for urine separation including electrodialysis have so far advanced beyondthe laboratory stage a combination of solutions may be needed to meet the require-ments (Maurer Pronk amp Larsen 2006) A combination of electrodialysisprecipitation and evaporation has perspectives of application in developing countriesthis can be linked to local business development which is an important prerequisitefor the implementation of new technologies in developing countries (Pronk ampKone 2009)

Despite the continuous presence of electrodialysis on the separations scene it is byno means a static process Apart from the logical shift in attention for various applica-tions the main advances in electrodialysis are related to the breakthrough of electro-dialysis with bipolar membranes (which allows for integrated reactions in situcombination of fermentation and electrodialysis and in general the conversion ofsalts to their corresponding acids and base in a wide range of applications) and theuse of non-classical membrane materials and configurations for advanced separationsThese are described in more detail in this chapter Other advances are the integration ofelectrodialysis with traditional unit operations and other membrane separations in thechemical biochemical food and pharmaceutical industries (Xu amp Huang 2008) thedevelopment of reverse electrodialysis to capture renewable energy from mixing saltand freshwater (Vermaas et al 2013) and ionic liquideassisted electrodialysis forconcentrating acidifying and removing organic salts from aqueous solution(Lopez amp Hestekin 2013) or for the selective recovery of lithium from seawater(Hoshino 2013)

In addition even after over half a century the fundamental understanding ofall phenomena related to electrodialysis is still a point of attention For examplemechanisms for overlimiting current and concentration polarization are not yet well un-derstood and only recently was a first-principles model involving the NernstePlanckePoisson equations fully coupled with the NaviereStokes equations proposed(Urtenov et al 2013) At the same time the leaky membrane model was proposed as asimplified model based on the NernstePlanck equation (Dydek amp Bazant 2013) Otherefforts aim to translate the process fundamentals to a simulation model (Tanaka 2013)

186 Advances in Membrane Technologies for Water Treatment

which surprisingly has not yet converged for electrodialysis To understand the flow inan electrodialysis stack computational fluid dynamics can be used (Tamburini La Bar-bera Cipollina Ciofalo amp Micale 2012)

This chapter describes the fundamentals of electrodialysis in brief with the aim ofunderstanding the process principles (for a more in-depth analysis of the fundamentalsthe reader is referred to the publications mentioned above) followed by a review of theadvances of electrodialysis in water treatment as stated previously

62 Fundamentals of electrodialysis for water treatment

Two kinds of membranes are used in electrodialysis anion exchange and cationexchange These two membrane types are alternated in a membrane stack so that arepeating unit is obtained consisting of a compartment with an anion exchangemembraneon the left side and a cation exchange membrane on the right followed by anothercompartment with an anion exchange membrane on the right side and a cation exchangemembrane on the left

Over this membrane stack a difference in electrical potential is applied using elec-trodes at both ends of the stack The feed solution is pumped through the stack Cationsmigrate in the direction of the negatively charged cathode and are allowed to migratethrough the first cation exchange membrane The next membrane is an anion exchangemembrane so that the cation cannot migrate further Anions migrate in the direction ofthe positively charged anode and can migrate through the first anion exchange mem-brane The next membrane is a cation exchange membrane so that the anion cannotmigrate further (Figure 61) The membranes are in principle not permeable for wateralthough osmosis and electro-osmosis are known to occur in an electrodialysis stack

Cathode(ndash)

Anode(+)

+

ndash ndash ndash ndash ndash

+ + + + +

Electrode rinse

ConcentrateDiluate

Figure 61 Ion migration in a salt solution through the membrane stack

Advances in electrodialysis for water treatment 187

In this way positive as well as negative ions are removed from the feed solutionwhereas the neighboring compartments are concentrated

The flow through the feed compartments is usually denoted as the diluate streamthe flow with increasing concentration is denoted as the concentrate stream

The combination of a series of cells (consisting of an anion exchange and a cationexchange membrane and a diluate compartment and a concentrate compartment) isnecessary to decrease the time needed to purify a given stream (in a batch configurationwith recycling) or decrease the size of the membranes in the system (in a flow-throughsystem)

Because of the flow of ions through the stack the electrical current is transferredThe extent to which the electrical current is effectively used for migration of ionsthat should be removed determines the efficiency of electrodialysis

Apart from the diluate and concentrate flow an electrode rinse solution is generallyapplied The electrodes are positioned in separate compartments to protect the elec-trode material At the cathode hydrogen gas and hydroxyl ions may be formed owingto the dissociation of water (after application of a voltage) The hydroxyl ions maypossibly damage the electrode when the electrode material is not carefully selectedAn acid is usually added to the rinse liquid of the cathode to prevent damage

At the anode the electrode material is at risk because of the formation of metal ox-ides at the electrode surface (corrosion) which can then dissolve in an acid environ-ment Possible materials with sufficient resistance are graphite stainless steel nickelalloys or a Platinum coating Reactions with a metal M are

Mthorn xOH5MethOHTHORNx thorn xe

2Mthorn 2xOH5M2Ox thorn xH2Othorn 2xe

Because of the consumption of OH hydrogen ions are left which make the solu-tion more acidic This dissolves metal ions

MethOHTHORNx thorn xHthorn5Mxthorn thorn xH2O

M2Ox thorn xHthorn52Mxthorn thorn xH2O

H2 Cl2 and O2 may be formed as a result of oxidation reactions at the anode Thesecause negative effects Therefore it is important to make sure that negative ions (suchas Cl) do not have access to the electrode compartments For the cathode this is notproblematic because it repels anions but the anode needs sufficient protection Thiscan be achieved by using two cation exchange membranes The electrode rinse solu-tion usually contains SO2

4 which would not cause problems at the anodeMembranes are often exposed to aggressive compounds Furthermore because of

the electrical resistance the temperature may increase Many feed flows (eg surfacewater) contain suspended solids These may damage the membrane as the result of fric-tion and scouring The chemical thermal and mechanical resistance of the membranesis therefore an important parameter to consider

188 Advances in Membrane Technologies for Water Treatment

Between the membranes a spacer is positioned that is usually made of a polymer(polyethylene polyvinylchloride (PVC) or specialty polymers) The spacers providemechanical support to the membranes They are made in a maze configuration thatensures the membranes are not pressed onto each other They also provide goodflow dynamics by promoting turbulence

When the membranes are brought into the solution a chemical potential differencearises between the solution and the inner structure of the membrane This brings ionsof the same sign as the fixed ions into the membrane These are called co-ions For thesame reason counter-ions migrate from the membrane to the bulk of the solutionThen a dominant charge emerges in the membrane (co-ions and fixed ions have ahigher concentration and the same charge) giving rise to an electrical potential thatopposes the chemical potential This electrical potential (the Donnan potential) limitsthe co-ion concentration in the membrane and the removal of counter-ions from themembrane

When the electrical potential difference is applied over the electrodes a current willarise in which the counter-ions and co-ions take part Mainly counter-ions are trans-ported because their concentration is higher

This also demonstrates that there cannot be an ideally selective membrane becausetransport of ions always starts with the transport of co-ions The co-ion concentrationin the membrane is never zero at the startup This selectivity is described by the perm-selectivity and therefore also by the transport number

The selectivity of ion exchange membranes for anions or cations is related to thecharge which is in turn due to the presence of specific functional groups Anion ex-change membranes contain positively charged groups (typically quaternary ammo-nium salts) that attract anions Cations on the other hand are repelled Cationexchange membranes contain negatively charged groups (sulfonic acid or carboxylicacid groups) that attract cations Anions on the other hand are repelled

The selectivity of the membranes is determined by the transport number andpermselectivity A transport number of 1 for a cation exchange membrane meansthat it permeates all cations and retains all anions and vice versa for an anionexchange membrane In practice membranes with a transport number of 09 areconsidered good

The transport number ti of a component c is defined as

tc frac14 jci

(61)

where jc is the ion flow density and i is the current density

The permselectivity Pthorn is Pthorn frac14 tthorn tthorn1 tthorn

(62)

where tthorn is the value in the middle of the membrane The permselectivity is con-centration dependent when the concentration in the electrolyte solution is high moreco-ions end up in the membrane

Advances in electrodialysis for water treatment 189

The electrical resistance of a membrane largely determines the current losses occur-ring in the stack The lower this resistance is the less the temperature in the stack willincrease and therefore the fewer losses will occur Thus the electrical resistance of themembranes should be kept as low as possible to limit losses because the resistance ofthe flows through the stacks cannot be changed The order of magnitude of the elec-trical resistance of a membrane is 2e10 ohmcm2

When the electrical potential of the process is increased the current density in-creases as well More ions are transported This may lead to a total depletion ofions in the boundary layer at the diluate side of the membrane Then the current densitycannot increase further because no ions are left to transport the electrical current Thisis called the limiting current density At this point the efficiency of the process hasbecome low The electrical energy is consumed to split water into its ions whichcan transport the electrical charge and maintain the potential difference and currentdensity The electrical resistance has enormously increased It is important not toexceed this limiting current density The limiting current density can be determinedexperimentally using the method of Cowan and Brown which involves measuringelectrical resistance R as a function of the reciprocal current I 1 (Figure 62) Theintersection of the two lines tangential to the legs of the curves determines the limitingcurrent (from which the limiting current density can be calculated)

Another phenomenon that may occur is back-diffusion This occurs when thedriving force of the concentration difference between the diluate and the concentratecompartment has increased so much that ions diffuse from the concentrate compart-ment back to the diluate compartment against the electrical flow This should be taken

1I (Andash1)

R (VA)

Limiting current

Figure 62 Determination of the limiting current and the limiting current density inelectrodialysis

190 Advances in Membrane Technologies for Water Treatment

into account when applying concentrated solutions to an electrodialysis unit Electro-dialysis allows one to obtain a concentration factor up to ca 200e250

At the diluate side the ion concentration in the boundary layer (close to the mem-brane) is lower than in the bulk of the flow At the concentrate side the ion concentra-tion in the boundary layer (close to the membrane) is higher than in the bulk of theflow This is the result of diffusion Both concentrations can be calculated as

cm frac14 cb tm tbl

$i$d

z$F$Dethfor the diluate sideTHORN (63)

cm frac14 cb thorntm tbl

$i$d

z$F$Dethfor the concentrate sideTHORN (64)

The limiting current density in the boundary layer can be calculated from (eg atthe diluate side)

ilim frac14 z$D$F$ethcb cmTHORNd$tm tbl

(65)

where cb is the bulk concentration of the solute at a distance d from the membrane cmis the concentration of the solute near the membrane F is the Faradayrsquos constant(96487 Cmol) D is the diffusion coefficient (ms) z is the valence of the ion d isthe thickness of the boundary layer (m) tm is the transport number of the ion in themembrane and tbl is the transport number of the ion in the boundary layer

The limiting current density is reached when cm goes to zero The above equationfor the current density for cm frac14 0 (limiting current density) is

ilim frac14 z$D$F$cbd$tm tbl

It has been experimentally demonstrated that the limiting current density of a solu-tion increases linearly with temperature

ilim frac14 Athorn 4$T

where A is the limiting current density (ilim) at 0 C T is the temperature and 4 is thetemperature coefficient for the limiting current density

A and 4 are constants for a given concentration and a given species The concen-tration dependency for a given compound is linear as well

The temperature in the stack increases during electrodialysis so that during the pro-cess the limiting current density increases The flow velocity also increases themaximal current

Membrane fouling however will decrease the limiting current density All of thisshould be taken into account to ensure that the limiting current density is not exceeded

Advances in electrodialysis for water treatment 191

The limiting current density of the cation exchange and anion exchange membranesfor a solution with a single salt is not necessarily the same It is only the same when thecation and the anion have the same transport number If not the transport number ofthe cation is usually smaller than that of the anion and in that case the limiting currentdensity will first be attained at the cation-selective membrane In the ReI1 curve twoseparate minima are then visible for the two types of membranes

For solutions containing several solutes or a mixture of ions each compound willhave its own limiting current density

63 Advances in membrane materials for electrodialysisfor water treatment

Electrodialysis membranes are dense membranes that can be either heterogeneous orhomogeneous Heterogeneous membranes are made of an ion exchange resin whichis milled to a small grain size and then mixed with a solution of binding polymers(PVC rubber styrenedivinylbenzene copolymer etc) The ratio of resin grains andbinding polymer determines the electrical and mechanical properties of the membraneMore binding polymer improves the mechanical strength but also increases the elec-trical resistance Heterogeneous membranes have a limited mechanical strength and ahigh electrical resistance in general

Homogeneous membranes are synthesized by adding ionizable functional groups toa polymeric film The polymers that are used have to

bull induce a uniform charge distributionbull have good mechanical stability and low electrical resistancebull be cross-linked to reduce swelling when applied in water

The more charges are introduced the better is the conductivity but this leads toswelling because the material becomes more hydrophilic Cross-linking anchors thepolymeric chains in the polymer by chemically linking the chains to one anotherthis reduces swelling

Homogeneous membranes are thinner than heterogeneous membranes which re-duces their resistance They are mechanically stronger because they are directlymade as a film (unlike heterogeneous membranes)

The charge density of typical membranes is 1e2 mEqg (dry polymer)The membrane material contains functional groups that enable ion transport The

charged groups remaining on the membrane surface are the fixed ions the ions thatare dissociated from their functional group are the counter-ions Both are hydratedwhen an aqueous feed is applied Anion exchange membranes often contain quater-nary ammonium groups as fixed ions cation exchange membranes contain sulfonylor carboxyl groups Anion exchange membranes can be recognized by their trans-parent white color Cation exchange membranes vary in color from amber-brown towhite depending on the type

Regular ion exchange membranes are not selective However some anion exchangemembranes have been developed with selectivity for monovalent ions (such as the

192 Advances in Membrane Technologies for Water Treatment

ACS series of anion exchange membranes of Eurodia Industrie SA (WissousFrance)) This allows for the selective removal of eg nitrates compared with (diva-lent) sulfates This is important to manage the total dissolved solids (TDS) of the prod-uct stream which should not be too low for most applications including potable waterwhereas nitrates should be removed to a larger extent A typical outcome is a reductionof the nitrate concentration by 84 with a reduction in TDS by 49 The advantage ofthis is that remineralization after nitrate removal is no longer necessary

Whereas the number of ion-exchange membranes was limited until a decade agoresearch efforts have resulted in a much wider range of polymeric membranes (eventhough these are generally not commercially available) Synthesis of anion exchangemembranes includes poly(vinyltrimethoxysilane-co-2-(dimethylamine)ethylmethacry-late) copolymer (Chakrabarty Prakash amp Shahi 2013) membranes composed of4-vinylbenzyl chloride styrene and ethylmethacrylate (Koo Kwak amp Hwang2012) cross-linked polystyrene (Sachdeva Ram Singh amp Kumar 2008) acryloni-trilebutadienestyrene with activated carbon and silver fillers (Zendehnam RobarmiliHosseini Arabzadegan amp Madaeni 2013) and aliphatic-hydrocarbonebased anionexchange membranes prepared from glycidyl methacrylate and divinylbenzene(Tanaka Nagase amp Higa 2011) to name just a few Such membranes may be appli-cable in other electromembrane applications such as fuel cells (Merle Wessling ampNijmeijer 2011)

Cation exchange membranes include polystyrene and polyaniline blends (AmadoGondran Ferreira Rodrigues amp Ferreira 2004) heterogeneous polyvinylchloridestyreneebutadieneerubber blends (Hosseini Madaeni Heidari amp Moghadassi2011) and monovalent selective membranes made of blends of sulfonated poly(ethersulfone) with sulfonated poly(ether ether ketone) (Gohil Nagarale Binsu amp Shahi2006) Furthermore ceramic cation exchange membranes synthesized by impregna-tion of microporous ceramic supports with zirconium phosphate have been developedfor aggressive wastewater applications (Marti-Calatayud Garcia-Gabaldon Perez-Herranz Sales amp Mestre 2013) and phosphotungstic acidebased membranes ongraphite support intended for use as electrolyte-filled separators for batteries andsuper-capacitors (Seepana Pandey amp Shukla 2012)

This shows the large potential of various materials as anion exchange or cationexchange membranes although commercialization today is still limited

A bipolar membrane consists of a combination of a cation exchange and an anionexchange membrane (Figure 63) Between the two membranes a water film is presentfrom which water is dissociated the bipolar membrane is a source of anions (OH) aswell as cations (Hthorn) although they end up in different compartments on both sides ofthe bipolar membrane

Development and application of bipolar membranes have emerged especially in thepast decade Research on synthesis has resulted in eg sulfonated polystyrene ethylenebutylene polystyrene-poly(vinyl alcohol)equaternized polystyrene ethylene butylenepolystyrene bipolar membranes (Venugopal amp Dharmalingam 2013) poly(vinyl alco-hol)esodium alginate chitosan with TiO2 and ZnO (Chen Hu Chen Chen amp Zheng2011) and poly(vinyl alcohol)epoly(anetholesulfonic acid sodium salt) (cation selec-tive) and poly(vinyl alcohol)epoly(diallyldiethylammonium bromide) (anion selective)

Advances in electrodialysis for water treatment 193

bipolar membranes (Espinoza-Gomez Flores-Lopez Rogel-Hernandez amp Martinez2009) Several more examples can be found in the literature

64 Advances in membrane modules and systemconfigurations for electrodialysis for watertreatment

The classical stacked module is still the standard configuration Advances in moduledesign are primarily related to the use of spacers in the stack Spacers increase the elec-trical resistance which translates into higher power consumption Optimization of thefluid dynamics within the channels is still a problem as demonstrated by computa-tional fluid dynamics simulations to predict the fluid flow field inside a single channelinside an electrodialysis stack (Tamburini et al 2012) An appropriate choice of netspacer material can influence the slipno-slip condition of the flow on the spacer wiresthus significantly affecting the channel fluid dynamics in terms of pressure drops(Gurreri Tamburini Cipollina amp Micale 2012) A conducting spacer instead of thetraditional non-conducting spacer may help overcome electrical resistance (ZhangWang amp Goa 2012) whereas fluid dynamics and electrical resistance may beimproved simultaneously when using ion exchange membranes in which the spaceris formed directly on the membrane surface (Balster Stamatialis amp Wessling2010) so that it is no longer a separate entity

Further innovations are related to the stack configuration The use of bipolar mem-branes as described above yields a four-compartment membrane stack which is anextension of the classical three-compartment approach Such configuration is alsoapplied in selectrodialysis a process using a four-compartment stack without bipolar

Cathode

OHndash

H+

H2O

Bipolar membrane

Anode

Figure 63 Representation of a bipolar membrane for electrodialysis

194 Advances in Membrane Technologies for Water Treatment

membranes but with a combination of selective and nonselective membranes toachieve fractionation of ions so that for example phosphates can be selectivelyremoved from a feed stream (Zhang Paepen Pinoy Meesschaert amp Van der Bruggen2012) This is shown in Figure 64

A feed solution containing cations monovalent anions and divalent anions ispumped through the first compartment which is sealed by a cation exchangemembrane (CM) and an anion exchange-selectivemembrane (AM) The cationsmigrateunder the influence of the applied electrical potential difference toward the cathodepassing the CM The anions monovalent as well as bivalent migrate toward the anodeand thus pass theAMThus the solution of themiddle compartment the product will beenriched with anions At the same time monovalent ions available in this productcompartment migrate toward the anode passing the AMV This compartment iswhere the selection of the monovalent versus bivalent ions occurs and is denoted asthe selector This compartment is enriched in bivalent anions monovalent ions areremoved The third compartment (brine compartment) is enriched by the migratingmonovalent anions This process was shown to be feasible for concentrating phosphateions selectively from wastewater (Zhang et al 2013)

Other innovations relate to the flow through electrodialysis stacks A co-current hy-draulic flow mode of the salt solutions through the compartments of the stack is oftenapplied which requires a series of separation modules This can be improved bychanging the classical co-current hydraulic flow mode into a mixed flow mode inwhich the internal hydraulic flow of diluate and concentrate is co-current in the stackcompartments but is externally counter-current over the total series of stacks (Braunset al 2012)

Integrated processes may further extend the range of applications for water treat-ment As an example the separation of Co2thorn and Ni2thorn is discussed two cations

AM AMV CM

ProductFeed Brine

Clndash

ERS

SO42ndash

Na+

Na+

CM

Clndash

SO42ndash

Na+Na+Clndash

Clndash

Figure 64 Selectrodialysis stack for ion fractionation ERS electrode rinse solutionCM cation exchange membrane AM anion exchange membrane (nonselective) AMV anionexchange membrane (selective for monovalent ions)

Advances in electrodialysis for water treatment 195

with the same charge and approximately the same size (Xu 2001) Separation can beachieved by two electrodialysis stacks in series the first one of which is a conventionalelectrodialysis unit followed by an electrodialysis unit with bipolar membranes(Figure 65)

A wastewater stream containing a mixture of Co2thorn and Ni2thorn is supplied to compart-ment 1 The positive ions in this case Co2thorn and Ni2thorn migrate through the cationexchange membrane to compartment 2 In this compartment a complexing agent ispresent denoted as HR This agent selectively forms a complex with one of the twocations according to the reactions

Co2thorn thorn 2R Kc

CoR2

Ni2thorn thorn 2R Kc

NiR2

For the separation considered here Kc is much larger for Ni2thorn than for Co2thorn so thatonly the nickel complex is formed The cobalt ions are not complexed and can there-fore migrate through the two consecutive cation exchange membranes to compartment4 There they combine with an anion to the corresponding metal salt This concentratestream contains only the cobalt salt and no nickel

Nickel occurs now as a neutral complex in the solution and therefore cannot migrateto another compartment

++++++ +

++++++ +

++++++ +

++++++ +

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

ndashndashndashndashndashndashndashndash

++++++ +

Ni2+

Co2+

Clndash

Co2+

Ni2+

Co2+Co2+

Clndash

CoCl2

ClndashH+

Ni2+ Ni2+

NiCl2

OHndash

1 2 3 4

5 6 7

Ni2+

Co2+

Clndash

8

HR

Figure 65 Separation of ions with the same charge and similar size using electrodialysis andelectrodialysis with bipolar membranes (EDBM)

196 Advances in Membrane Technologies for Water Treatment

The solution in compartment 2 is fed to compartment 7 of the EDBM system In thiscompartment there is an excess of Hthorn ions so that the pH is sufficiently low for thefollowing reaction to occur

NiR2 thorn 2Hthorn Kc

Ni2thorn thorn 2HR

At low pH the Ni2thorn ions are exchanged for protons and are again released The pro-tons come from the bipolar membrane The free nickel ions can further migratethrough the cation exchange membrane to compartment 8 where they can be separatedas a metal salt

The complexing agents from compartment 5 are recycled to compartment 2together with the hydroxyl ions that are released in compartment 6 to increase thepH again to a neutral value These hydroxyl ions are also generated by the bipolarmembrane

The net result is that the Co2thorn ions accumulate in compartment 4 and the Ni2thorn ionsare collected in compartment 8

The concentration difference between Ni2thorn and Co2thorn ions in the correspondingcompartments can reach up to 120

65 Applications of electrodialysis for water treatment

The dominant application of electrodialysis is still in desalination This is a well-established application that can be readily applied Emerging applications are thereforein (1) the use of electrodialysis for alternative feed waters (2) ion fractionation and (3)the use of bipolar membranes in a wide range of production or conversion processes

A typical example of alternative feed water is concentrated brine from an reverseosmosis (RO) plant in which electrodialysis is used as a technology to prevent damageto marine ecosystems (Jiang Wang Zhang amp Xu 2014) Similarly the concentrateresulting from RO of treated wastewater is applied to reduce the volume of salty waterdischarge (Zhang Ghyselbrecht Meesschaert Pinoy amp Van der Bruggen 2011)Electrodialysis was found to be a viable technology but scaling may be a problembecause of the enhanced concentration of carbonates after wastewater treatmentIndustrial wastewater applications have been considered as well (Silva Poiesz ampvan der Heijden 2013) electrodialysis is feasible in terms of the separation of mono-valent and divalent ions with energy requirements ranging from 6 to 11 kW hm3 offeed stream depending on the water reclamation rate

Fractionation using electrodialysis has main applications for amino acids Aminoacids can be transported selectively across a double membrane system composed of acation exchange and an anion exchange membrane via pH adjustment of the sourcephase solution (Tsukahara Nanzai amp Igawa 2013) Electrodialysis with commerciallyavailable ion exchange membranes was applied to isolate the basic amino acids L-lysine(Lys) and L-arginine (Arg) (Readi Girones Wiratha amp Nijmeijer 2013) This has evenmore potential when electrodialysis is applied with ultrafiltration membranes This wasdemonstrated in several applications such as the separation of a pepsinepancreatin soy

Advances in electrodialysis for water treatment 197

protein isolate hydrolysate (Roblet et al 2013) and to recover and concentrate the activeantibacterial fraction of a snow crab by-products hydrolysate which is the result of apeptide with a molecular weight of about 800 Da (Doyen Saucier Beaulieu Pouliotamp Bazinet 2012) The attraction of using ultrafiltration membranes for electrodialysisapplications is in the possibility of fine-tuning the separation on the basis of either chargeseparation or size exclusion which allows for specific separation of charged organiccompounds typically related to peptides

However selective removal of other ions is also interesting One example is the useof monovalent permselective membranes for selective removal of arsenic and mono-valent ions from brackish water RO concentrate (Xu Capito amp Cath 2013) Mono-valent permselective anion exchange membranes have high selectivity in removingmonovalent anions over di- and multivalent anions In general transport of monova-lent and divalent ions is different because of steric effects and different charge inter-actions for example a removal rate of more than 70 for monovalent ions mightcorrespond to a removal rate below 50 for divalent ions (Silva et al 2013) Thiscan be exploited and optimized for eg the removal of nutrients from wastewater

The use of bipolar membranes has been considered in many studies The moststraightforward one is when concentrates from seawater desalination are used asfeed This yields a mixture of sulfuric acid and hydrochloric acid on the one sideand sodium hydroxide on the other A concentration of 1 molL can be obtained inrealistic conditions with a good prospect for long-term operation (Shen Huanget al 2013) Similar observations were made for industrial saline water mainlycomposed of NaCl and KCl which yielded an acid and a base stream with a concen-tration of around 2 molL (Ghyselbrecht et al 2013) Bipolar membranes were used inanother application on a pilot scale to recover glyphosate and the production of baseacid with high concentration in view of the zero discharge of wastewater (Yang GaoFan Fu amp Gao 2014) Electrodialysis with bipolar membranes may be coupled withdiffusion dialysis for two-step recovery with electrodialysis as the second step torecover the remaining concentrations of acid (Zhuang et al 2013) More applicationsinclude the production of morpholine (Jiang Wang amp Xu 2013) the separation oflithium and cobalt in view of the recycling of waste lithiumeion batteries in a similarapproach as described above for nickel and cobalt (Iizuka Yamashita NagasawaYamasaki amp Yanagisawa 2013) the production of tetrapropyl ammonium hydroxideon a pilot scale with a perspective for full-scale industrial application (Shen YuHuang amp Van der Bruggen 2013) and the production of L-ascorbyl-2-monophosphate a stable substitute of vitamin C (Song et al 2012) Many moreapplications have been reported which indicates the potential of electrodialysis withbipolar membranes as a versatile process A complete overview however is beyondthe scope of this chapter

66 Future trends

Electrodialysis has been of interest for the past 5 decades although for a limited rangeof applications such as the desalination of brackish water This will not substantially

198 Advances in Membrane Technologies for Water Treatment

change in years to come although an increase in these applications is not expectedbecause of competition with more cost-effective processes (at higher salt concentra-tions) such as RO and membrane distillation Other applications related to selectiveremoval of one or more ions however may become attractive when membrane mate-rials are developed with better selectivity (eg for nitrate specific peptides or phos-phate) or when alternative stack configurations are applied in which a fractionationeffect can be obtained

Since the turn of the century bipolar membranes have been increasingly studiedand applied This opens up a new range of applications related to combined reactionand purification owing to the acidebase splitting effect Numerous applications canbe based on this feature and many more are on the agenda to be further developedin coming years This will in turn stimulate the availability of bipolar membraneswith a further positive effect on the application market

One question remains for electrodialysis which is related to the sustainability of thesystem Although the process is claimed to be a green technology this may be arguedfrom an energetic point of view particularly when taking the exergetic value of therequired electrical energy into account Therefore more attention to this aspect is crit-ical Combined systems based on renewable energy may overcome this issue whichthen will allow for example remote applications of electrodialysis

Sources of further information and advice

Tanaka Y (2013) Ion exchange membrane electrodialysis Fundamentals desalination sep-aration (Water resource planning development and management series) New YorkNova

Bernardes A Siqueira Rodrigues M A amp Zoppas Ferreira J (Eds) (2014) Electrodialysisand water Reuse Berlin Heidelberg Springer

Strathmann H (2011) Introduction to membrane science and technology WeinheimGermany Wiley

Sata T (2004) Ion exchange membranes Preparation characterization modification andapplication London Royal Society of Chemistry

Strathmann H (2004) Ion-exchange membrane separation processes New York Elsevier

References

Amado F D R Gondran E Ferreira J Z Rodrigues M A S amp Ferreira C A (2004)Synthesis and characterisation of high impact polystyrenepoly aniline composite mem-branes for electrodialysis Journal of Membrane Science 234(1e2) 139e145

Anderson A M amp Wylam C B (1956) Ion exchange electrodialysis for demineralisation ofsugar solutions Chemistry and Industry 12 191e192

Balster J Stamatialis D F ampWessling M (2010) Membrane with integrated spacer Journalof Membrane Science 360(1e2) 185e189

Brauns E Bossaer J Toye S Mijnendonckx K Pinoy L amp Van der Bruggen B (2012) Astudy of electrodialysis operating with mixed flow mode Separation and PurificationTechnology 98 356e365

Advances in electrodialysis for water treatment 199

Chakrabarty T Prakash S amp Shahi V K (2013) End group cross-linked 2-(dimethylamino)ethylmethacrylate based anion exchange membrane for electrodialysis Journal of Mem-brane Science 428 86e94

Chen R Y Hu Y Y Chen Z Chen X amp Zheng X (2011) Preparation and char-acterization of bipolar membranes modified using photocatalyst nano-TiO2 and nano-ZnO Journal of Applied Polymer Science 122(2) 1245e1250

Cooke B A (1958) Scaling problems in electrodialysis using permselective membranesChemistry and Industry 19 555e556

Daufin G Escudier J P Carrere H Berot S Fillaudeau L amp Decloux M (2001) Recentand emerging applications of membrane processes in the food and dairy industry Food andBioproducts Processing 79(C2) 89e102

Dewhalley C H (1958) Desalting of water by electrodialysis Chemistry and Industry 18e13

Doyen A Saucier L Beaulieu L Pouliot Y amp Bazinet L (2012) Electroseparation of anantibacterial peptide fraction from snow crab by-products hydrolysate by electrodialysiswith ultrafiltration membranes Food Chemistry 132(3) 1177e1184

Dydek E V amp Bazant M Z (2013) Nonlinear dynamics of ion concentration polarization inporous media The leaky membrane model AIChE Journal 59(9) 3539e3555

Espinoza-Gomez H Flores-Lopez L Z Rogel-Hernandez E amp Martinez M (2009)Preparation and characterization of PVAPASA-PVAPDDAB bipolar membrane Journalof the Brazilian Chemical Society 20(7) 1294e1301

Firdaous L Dhulster P Amiot J Gaudreau A Lecouturier D Kapel R et al (2009)Concentration and selective separation of bioactive peptides from an alfalfa white proteinhydrolysate by electrodialysis with ultrafiltration membranes Journal of Membrane Science329(1e2) 60e67

Galier S amp Roux-de Balmann H (2011) The electrophoretic membrane contactor A mass-transfer-based methodology applied to the separation of whey proteins Separation andPurification Technology 77(2) 237e244

Ghyselbrecht K Huygebaert M Van der Bruggen B Ballet R Meesschaert B amp Pinoy L(2013) Desalination of an industrial saline water with conventional and bipolar membraneelectrodialysis Desalination 318 9e18

Gohil G S Nagarale R K Binsu V V amp Shahi V K (2006) Preparation and charac-terization of monovalent cation selective sulfonated poly(ether ether ketone) and poly(ethersulfone) composite membranes Journal of Colloid and Interface Science 298(2)845e853

Gurreri L Tamburini A Cipollina A amp Micale G (2012) CFD analysis of the fluid flowbehavior in a reverse electrodialysis stack Desalination and Water Treatment 48(1e3)390e403

Hoshino T (2013) Preliminary studies of lithium recovery technology from seawater byelectrodialysis using ionic liquid membrane Desalination 317 11e16

Hosseini S M Madaeni S S Heidari A R amp Moghadassi A R (2011) Preparation andcharacterization of polyvinyl chloridestyrene butadiene rubber blend heterogeneous cationexchange membrane modified by potassium perchlorate Desalination 279(1e3)306e314

Iizuka A Yamashita Y Nagasawa H Yamasaki A amp Yanagisawa Y (2013) Separationof lithium and cobalt from waste lithium-ion batteries via bipolar membrane electrodialysiscoupled with chelation Separation and Purification Technology 113 33e41

Jiang C X Wang Y M amp Xu T W (2013) An excellent method to produce morpholineby bipolar membrane electrodialysis Separation and Purification Technology 115 100e106

200 Advances in Membrane Technologies for Water Treatment

Jiang C X Wang Y M Zhang Z H amp Xu T W (2014) Electrodialysis of concentratedbrine from RO plant to produce coarse salt and freshwater Journal of Membrane Science450 323e330

Koo J S Kwak N S amp Hwang T S (2012) Synthesis and properties of an anion-exchangemembrane based on vinylbenzyl chloride-styrene-ethyl methacrylate copolymers Journalof Membrane Science 423 293e301

Langevin M E Roblet C Moresoli C Ramassamy C amp Bazinet L (2012) Comparativeapplication of pressure- and electrically-driven membrane processes for isolation ofbioactive peptides from soy protein hydrolysate Journal of Membrane Science 40315e24

Laurence D J R (1956) Separation of proteins by electrodialysis through filter-paper mem-branes Biochemical Journal 62(3) 36

Lopez A M amp Hestekin J A (2013) Separation of organic acids from water using ionicliquid assisted electrodialysis Separation and Purification Technology 116 162e169

Marti-Calatayud M C Garcia-Gabaldon M Perez-Herranz V Sales S amp Mestre S(2013) Synthesis and electrochemical behavior of ceramic cation-exchange membranesbased on zirconium phosphate Ceramics International 39(4) 4045e4054

Maurer M Pronk W amp Larsen T A (2006) Treatment processes for source-separated urineWater Research 40(17) 3151e3166

Merle G Wessling M amp Nijmeijer K (2011) Anion exchange membranes for alkaline fuelcells A review Journal of Membrane Science 277(1e2) 1e35

Pronk W Biebow M amp Boller M (2006) Electrodialysis for recovering salts from a urine so-lution containing micropollutants Environmental Science amp Technology 40(7) 2414e2420

Pronk W amp Kone D (2009) Options for urine treatment in developing countries Desali-nation 248(1e3) 360e368

Readi O M K Girones M Wiratha W amp Nijmeijer K (2013) On the isolation of singlebasic amino acids with electrodialysis for the production of biobased chemicals Industrialand Engineering Chemistry Research 52(3) 1069e1078

Roblet C Doyen A Amiot J amp Bazinet L (2013) Impact of pH on ultrafiltration membraneselectivity during electrodialysis with ultrafiltration membrane (EDUF) purification of soypeptides from a complex matrix Journal of Membrane Science 435 207e217

Sachdeva S Ram R P Singh J K amp Kumar A (2008) Synthesis of anion exchangepolystyrene membranes for the electrolysis of sodium chloride AIChE Journal 54(4)940e949

Seepana M M Pandey J amp Shukla A (2012) Synthesis and characterization of PWA basedinorganic ion-exchange membrane Separation and Purification Technology 98 193e198

Shen J N Huang J Liu L F Ye W Y Lin J Y amp Van der Bruggen B (2013) The useof BMED for glyphosate recovery from glyphosate neutralization liquor in view of zerodischarge Journal of Hazardous Materials 260 660e667

Shen J Yu C Huang J amp Van der Bruggen B (2013) Preparation of highly purified tet-rapropyl ammonium hydroxide using continuous bipolar membrane electrodialysisChemical Engineering Journal 220 311e319

Silva V Poiesz E amp van der Heijden P (2013) Industrial wastewater desalination using elec-trodialysis Evaluation and plant design Journal of Applied Electrochemistry 43(11)1057e1067

Solt G (1972) Electrodialysis comes of age Effluent and Water Treatment Journal 12(6) 293Song S Tao Y F Shen H Q Chen B Q Qin P Y amp Tan T W (2012) Use of bipolar

membrane electrodialysis (BME) in purification of L-ascorbyl-2-monophosphate Separationand Purification Technology 98 158e164

Advances in electrodialysis for water treatment 201

Tamburini A La Barbera G Cipollina A Ciofalo M amp Micale G (2012) CFD simulationof channels for direct and reverse electrodialysis Desalination and Water Treatment48(1e3) 370e389

Tanaka Y (2013) Development of a computer simulation program of batch ion-exchangemembrane electrodialysis for saline water desalination Desalination 320 118e133

Tanaka N Nagase M amp Higa M (2011) Preparation of aliphatic-hydrocarbon-based anion-exchange membranes and their anti-organic-fouling properties Journal of MembraneScience 384(1e2) 27e36

Tran A T K Jullok N Meesschaert B Pinoy L amp Van der Bruggen B (2013) Pelletreactor pre-treatment A feasible method to reduce scaling in bipolar membrane electro-dialysis Journal of Colloid and Interface Science 401 107e115

Tsukahara S Nanzai B amp Igawa M (2013) Selective transport of amino acids across adouble membrane system composed of a cation- and an anion-exchange membraneJournal of Membrane Science 448 300e307

Urtenov M K Uzdenova A M Kovalenko A V Nikonenko V V Pismenskaya N DVasilrsquoeva V I et al (2013) Basic mathematical model of overlimiting transfer enhancedby electroconvection in flow-through electrodialysis membrane cells Journal of MembraneScience 447 190e202

Venugopal K amp Dharmalingam S (2013) Fundamental studies on a new series ofSPSEBS-PVA-QPSEBS bipolar membrane Membrane preparation and characterizationJournal of Applied Polymer Science 127(6) 4983e4990

Vermaas D A Veerman J Yip N Y Elimelech M Saakes M amp Nijmeijer K (2013)High efficiency in energy generation from salinity gradients with reverse electrodialysisACS Sustainable Chemistry and Engineering 1(10) 1295e1302

Wood T (1960) Desalting of urine by electrodialysis Nature 186(4725) 634e635Xu T W (2001) Development of bipolar membrane based processes Desalination 140(3)

247e258Xu P Capito M amp Cath T Y (2013) Selective removal of arsenic and monovalent ions from

brackish water reverse osmosis concentrate Journal of Hazardous Materials 260885e891

Xu T W amp Huang C (2008) Electrodialysis-based separation technologies A critical reviewAIChE Journal 54(12) 3147e3159

Yang Y Gao X L Fan A Y Fu L L amp Gao C J (2014) An innovative beneficial reuseof seawater concentrate using bipolar membrane electrodialysis Journal of MembraneScience 449 119e126

Zaslavschi I Shemer H Hasson D amp Semiat R (2013) Electrochemical CaCO3 scaleremoval with a bipolar membrane system Journal of Membrane Science 445 88e95

Zendehnam A Robarmili N Hosseini S M Arabzadegan M amp Madaeni S S (2013)Fabrication of novel (acrylonitrile butadiene styreneactivated carbonsilver nanoparticles)heterogeneous anion exchange membrane Physico-chemical and antibacterial character-istics Journal of the Taiwan Institute of Chemical Engineers 44(4) 670e677

Zhang Y Desmidt E Van Looveren A Pinoy L Meesschaert B amp Van der Bruggen B(2013) Phosphate separation and recovery from wastewater by novel electrodialysisEnvironmental Science amp Technology 47(11) 5888e5895

Zhang Y Ghyselbrecht K Meesschaert B Pinoy L amp Van der Bruggen B (2011)Electrodialysis on RO concentrate to improve water recovery in wastewater reclamationJournal of Membrane Science 378(1e2) 101e110

202 Advances in Membrane Technologies for Water Treatment

Zhang Y Paepen S Pinoy L Meesschaert B amp Van der Bruggen B (2012) Selec-trodialysis Fractionation of divalent ions from monovalent ions in a novel electrodialysisstack Separation and Purification Technology 88 191e201

Zhang K Wang M amp Gao C J (2012) Ion conductive spacers for the energy-saving pro-duction of the tartaric acid in bipolar membrane electrodialysis Journal of MembraneScience 387 48e53

Zhuang J X Chen Q Wang S Zhang W M Song W G Wan L J et al (2013) Zerodischarge process for foil industry waste acid reclamation Coupling of diffusion dialysisand electrodialysis with bipolar membranes Journal of Membrane Science 432 90e96

Advances in electrodialysis for water treatment 203

Photocatalytic membranereactors for water treatment 7R Molinari1 P Argurio1 L Palmisano21Universita della Calabria Rende (CS) Italy 2Universita di Palermo Palermo Italy

71 Introduction

Heterogeneous photocatalysis is an advanced oxidation process (AOP) based on theuse of a semiconductor (the photocatalyst) It has been extensively studied for aboutfour decades when Fujishima and Honda (1972) discovered the photocatalytic split-ting of water on TiO2 electrodes It has been object of a large amount of studies relatedto environment recovery by the total degradation to innocuous substances of organicand inorganic pollutants (Hoffmann Martin Choi amp Bahnemann 1995) and for syn-thesis (Molinari Caruso amp Poerio 2009 Palmisano et al 2010) It is a discipline thatincludes a large variety of reactions (Molinari Argurio amp Lavorato 2013) partial ortotal oxidations dehydrogenation hydrogenation (eg hydrogen transfer) metal depo-sition water detoxification gaseous pollutant removal bactericidal action etc

The main advantages of photocatalysis making it a very promising lsquogreenrsquo processconsist in the mild operating conditions and the possibility to abate refractoryvery toxic and nonbiodegradable molecules (Molinari Caruso amp Palmisano 2010Palmisano Augugliaro Pagliaro amp Palmisano 2007) Besides photocatalysis (1)avoids the use of environmentally and unhealthy dangerous heavy metal catalystsby using safer photocatalysts (mainly TiO2) (2) uses mild oxidants (O2 in some casesfrom the air) (3) needs few auxiliary additives (4) does not produce harmful chemi-cals (5) offers a good alternative to the energy-intensive conventional treatmentmethods and (6) can be combined with other physical and chemical technologies(eg membrane separations)

Because the photocatalyst is generally used as a powder suspended in a liquidmedium the catalyst-recovering step from the reaction environment is a pivotal stagein view of large-scale applications Photocatalytic membrane reactors (PMRs) repre-sent a promising approach to overcome this limitation A PMR can be defined as a de-vice existing in various configurations that combines a photocatalyst and a membraneto produce chemical transformations A PMR improves the potentialities of classicalphotoreactors (PRs) and those of membrane processes with a synergy of both technol-ogies thus minimizing environmental and economic impacts (Molinari CarusoArgurio amp Poerio 2008 Molinari et al 2009) The membrane permits continuousoperation in systems in which the recovery of the photocatalyst (immobilized or in sus-pension) the reaction and the product separation simultaneously occurs resulting in adevice that is competitive with other separation technologies in terms of material

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400007-1Copyright copy 2015 Elsevier Ltd All rights reserved

recovery energy costs reduction of the environmental impact and selective removalof the components Higher energy efficiency modularity and easy scale-up are someother advantages of PMRs compared to conventional PRs

Water treatment by removing both organic and inorganic pollutants represents themain use of the photocatalytic techniques Water pollution caused by hazardousorganic chemicals used in industry and agriculture is a serious problem Environ-mental laws are severe and they will become more and more restrictive in the nextyears Furthermore various directives suggest the use of green chemistry conceptsand clean technologies inside the manufacturing processes to protect the environmentTraditional chemical and biological treatments (eg adsorption on active carbonchemical oxidation and aerobic biological treatments) to clean-up water often failto remove most organic pollutants because of the high resistance of these compoundsresulting in high concentrations discharged in treated effluents On the basis of this inthe last years the attention of the international scientific community has been focusedon the development of alternative methods In this context photocatalytic processesrepresent a promising alternative green process (Huo et al 2013 Mozia amp Morawski2006 2012 Mozia Tomaszewska amp Morawski 2005 2007) because as a conse-quence of the highly unselective reactions involved in the photocatalytic processesa wide range of organic pollutants can be totally degraded (ie mineralized) into smalland harmless species (carbon to carbon dioxide hydrogen to water nitrogen to nitrateetc) without using chemicals avoiding sludge production and its disposal

In the pertinent literature different studies in which photocatalysis is coupled withpressure-driven membrane techniques such as nanofiltration (NF) and ultrafiltration(UF) for the degradation of organic pollutants are reported (Molinari Borgese DrioliPalmisano amp Schiavello 2002 Molinari Palmisano Drioli amp Schiavello 2002Patsios Sarasidis amp Karabelas 2013 Zhang et al 2013) Membrane fouling is oneof the main drawbacks of these systems On the basis of this some authors proposedto couple photocatalysis with (1) membrane distillation (Huo et al 2013 Mozia ampMorawski 2006 Mozia amp Morawski 2012 Mozia Tomaszewska amp Morawski2007) obtaining an almost complete total organic carbon (TOC) removal butrequiring energy to activate the evaporation phenomenon (2) dialysis (AzragueAimar Benoit-Marquieacute amp Maurette 2007) to mineralize organic compounds con-tained in artificial turbid water operating at ambient temperature and (3) pervaporation(Camera-Roda amp Santarelli 2007 Camera-Roda et al 2011) improving the detoxi-fication efficiency of wastewater containing organic pollutants at low concentrationlevels

In this chapter the basic principles of photocatalysis and PMRs are reportedwith the advantages related to their coupling thanks to the synergistic effectsThe importance in making a correct choice of membrane (type and material) is evi-denced discussing the choices made in literature and the criteria used for selectionMoreover a classification of the PMRs based both on their configuration (pressurizedand depressurizedsubmerged) and on the particular membrane separation with photo-catalysis (pressure-driven membrane separation membrane distillation dialysis andpervaporation) is also presented providing evidence that the opportune choice ofPMR configuration and membrane separation is a key step to limit membrane fouling

206 Advances in Membrane Technologies for Water Treatment

Finally some applications of PMRs for water treatment in particular for pharmaceu-ticals removal are reported with evidence of the potentialities the drawbacks and thefuture trends

72 Fundamentals of PMRs for water treatment

721 Basic principles of photocatalysis and typesof photocatalysts and membranes

The main difference of photocatalysis compared to conventional catalysis is the pho-tonic activation mode of the catalyst which replaces the thermal activation (Herrmann2005) The electronic structure of a semiconductor is characterized by a valence band(VB) and a conduction band (CB) which are separated by an energy band gap (Eg)When a semiconductor particle is excited by irradiation with photons of energy (hn)equal or higher than its energy band gap (Eg) valence electrons (e) are promotedfrom VB to CB thus leaving a positive hole (hthorn) in the VB For semiconductorTiO2 this step is expressed as

TiO2 thorn hvTiO2e thorn hthorn

(71)

In the absence of suitable electron andor hole scavengers the photo-generated elec-trons and holes can recombine in bulk or on the surface of the semiconductor within ashort time releasing energy in the form of heat or photons Electrons and holes thatmigrate to the surface of the semiconductor without recombination can reduce andoxidize respectively the substrates adsorbed on the semiconductor A schematizationof both the photonic activation of the photocatalyst and the photocatalytic oxidationand reduction reactions that take place onto a photo-activated semiconductor particleis reported in Figure 71

The process in Figure 71 can be divided in four steps

1 Absorption of light followed by the separation of the electronehole couple2 Adsorption of the reagents3 Redox (reduction and oxidation) reaction4 Desorption of the products

The redox reactions involving the species adsorbed onto the semiconductor surfaceoccur only if the potentials of the redox couple to which the substrates belong (E0

1 E02)

are compatible with both the VB and CB potentials (EVB ECB) In particular the redoxpotential of the species to be oxidized E0

2 should be less positive than EVB so that thephoto-produced holes hthorn can oxidize the reduced form of this species (red2 ox2 seeFigure 71) At the same time the redox potential of the species to be reduced E0

1should be more positive than ECB so that the photo-produced electrons ee can reducethe oxidized form of this species (ox1 red1 see Figure 71) Only if both E0

2 lt EVB

and E01 lt ECB conditions are met both reduction and oxidation are thermodynami-

cally favoured and the overall photocatalytic process takes place

Photocatalytic membrane reactors for water treatment 207

The redox reactions that take place onto the semiconductor surface represent thebasic mechanisms of photocatalytic waterair purification and photocatalytic hydrogenproductionsubstrate hydrogenation respectively In the VB photo-generated holescan oxidize surface hydroxyl groups into hydroxyl radical in the aqueous reactingenvironment

OH thorn hthornOH (72)

As widely accepted hydroxyl radicals are the primary oxidants that attack thesubstrates to be degraded by reducing them to their elemental form

In the CB photo-promoted electrons can reduce the molecular oxygen dissolved inthe aqueous phase to superoxide radical metal ions to their lower oxidation states orHthorn ions to H

O2 thorn eO2 (73)

Menthorn thorn eMeethn1THORNthorn (74)

Hthorn thorn eH (75)

The so-generated hydrogen radicals can follow two main fates combination forH2 production or hydrogenation of adsorbed substrate

Thanks to (1) the favourable energetics of its band structure (2) its relatively highquantum yield (3) its stability under irradiation and (4) its low cost and availabilityTiO2 represents the archetypical photocatalyst a virtual synonym for photocatalysis

Eg

endash

h+

ox1Red1

ox2Red2

CB

VB

Light

Figure 71 Schematization of the photocatalytic process that occurs on a photo-activatedsemiconductor particle ox1 red1 ox2 and red2 represent respectively the oxidized and thereduced species of two different redox couples indicated as 1 and 2

208 Advances in Membrane Technologies for Water Treatment

Nevertheless this material does not present photo-response under visible light illumi-nation because of its wide band gap taking advantage of only less than 6 of the solarenergy Thus its potential as a green technology cannot be entirely fulfilled Conse-quently in the last years a great number of new photocatalysts have been synthesizedand tested as possible alternatives to TiO2 (Di Paola Garciacutea-Lopez Marcigrave ampPalmisano 2012 Hernandez-Alonso Fresno Suarez amp Coronado 2009) particularlyin view of the solar application The most important requirements that such a materialshould possess are a suitable band gap chemical and physical stability nontoxic na-ture good availability and low cost The most common materials used are oxidesor sulfides which redox potentials for the VBs and the CBs range are betweenthorn40 and 15 V versus a normal hydrogen electrode (NHE) Their photocatalyticproperties depend mainly on the position of the energetic level and on the band gapTable 71 summarizes the most common semiconductors used as photocatalystsreporting their band gap and wavelength of the radiation needed for the activation

The photoactivity of a semiconductor depends also on the mobility and lifetimeof the photo-produced electronhole couples on the light absorbance coefficientand on the method used to prepare the photocatalytic powder which affects manyphysicochemical properties of the semiconductor such as surface area distributionof particle size and crystallinity

Despite the photocatalytic process offering interesting advantages with respect toother catalytic process (eg milder operating conditions use of safer catalyst etc)its use in the industry is still limited for three different reasons (Ni Leung Leungamp Sumathy 2007) (1) recombination of photo-generated electronhole pairs that dissi-pate their energy as heat (2) fast backward reaction and (3) difficulty to use visiblelight which limits the effectiveness of the use of solar energy

Table 71 Band gaps and wavelengths of the most commonsemiconductors used as photocatalysts

Photocatalyst Band gap (eV) Wavelength (nm)

SnO2 38 318

TiO2 anatase 32 387

TiO2 rutile 30 380

WO3 28 443

Fe2O3 22 560

ZnO 32 387e390

ZnS 37 335e336

CdS 25 496e497

CdSe 17 729e730

GaAs 14 886e887

Photocatalytic membrane reactors for water treatment 209

To solve these problems continuous efforts have been made to enhance the photo-catalytic activity and promote the visible light response

A simple approach consists in the addition of electron donors or electron scaven-gers able to react irreversibly with the photo-generated VB holes or CB electronsrespectively Practically electron scavengers or electron donors can be reduced byCB electrons or oxidized by VB holes respectively the remaining strong oxidizingVB holes or strong reducing CB electrons can oxidizereduce the substrate Operatingin this way the electronhole recombination can be suppressed or reduced and higherquantum efficiency can be achieved

Another way to suppress or to reduce the recombination of photo-generatedelectronhole pairs consists in doping the semiconductor with a noble metal like PtAu Pd Rh Ni Cu and Ag By using this method photo-promoted electrons canbe transferred from CB of the semiconductor to metal particles deposited on its surfacewhile photo-generated VB holes remain on the photocatalyst Thus the possibility ofelectronehole recombination is greatly reduced resulting in an enhancement of photo-catalytic efficiency (Ara~na et al 2008 Chen et al 2008 Colmenares AramendiacuteaMarinas Marinas amp Urbano 2006 Rosu Suciu Lazar amp Bratu 2013 Wu et al2008 Yang et al 2013) A combined effect of metal ion doping consists in the reduc-tion of the band gap energy of the photocatalyst thus shifting the radiation absorptiontowards higher wavelengths permitting the use of visible light (Ge 2008 Ling Sunamp Zhou 2008) The same effect also can be obtained by doping the catalyst with an-ions such as N F C S and B (Collazzo Foletto Jahn amp Villetti 2012 Di Valentin ampPacchioni 2013)

Other ways to overcome previous limitations consist in dye sensitization compositesemiconductors metal-ion implantation etc

PMRs are hybrid systems in which photocatalysis is coupled with a membrane sep-aration In general a membrane can be defined as a barrier that separates two phasescontrolling the mass transport between them

The most important classification of membranes is based on their morphologicalproperties In particular a membrane can be porous allowing the permeation throughits pores and then the transport mechanisms (sieving mechanism andor Knudsendiffusion) depend on the pore size or dense in which the mass transport takes placeby the so-called solutiondiffusion mechanism ie dissolution of the permeationspecies in the membrane phase and diffusion across the membrane thickness

Another morphological classification of membrane distinguishes symmetric andasymmetric membranes In a symmetric membrane structural and transport proper-ties are the same throughout its section and the thickness of the entire membrane de-termines the flow In asymmetric membranes consisting of a dense thin layersupported by a porous layer that acts as mechanical support of the fragile skin layerstructural and transport properties change along the membrane thickness In this waythe high selectivity of a dense membrane is combined with the high permeation rateof a thin layer membrane Asymmetric membranes are mainly used in membrane sep-aration processes that use hydrostatic pressure as the driving force (the so-calledpressure-driven processes) reverse osmosis (RO) NF UF and microfiltration(MF) (Mulder 1996)

210 Advances in Membrane Technologies for Water Treatment

In a PMR system the appropriate choice of the membrane (material and type) andmembrane module configuration is mainly determined by the type of photocatalyticreaction Indeed the membrane can assume many roles The main purpose in couplinga membrane process with a photocatalytic reaction is the necessity to recover and reusethe catalyst So it is important to choose a membrane (type and material) with com-plete catalyst rejection thus maintaining it in the reaction environment Besideswhen the process is used for the degradation of organic pollutants the membranemust be able to reject the substrates and their intermediate products which otherwisepass in the permeate For example when the photocatalytic process is used as asynthetic pathway the main objective can be the selective separation of the producteg minimizing its successive oxidation which leads to undesirable byproducts

In this context the rejection (R) is a useful parameter that expresses the ability ofthe membrane to maintain the substrate and its intermediates in the reactiveenvironment

R frac14 Cf Cp

Cf frac14 1

CpCf

(76)

in which Cf and Cp are the solute concentrations in the feed and permeate respectivelyThe retention of the substrates and degradation byproducts is important also to con-

trol the residence time of substrates in the photocatalytic system This parameterstrongly influences the efficiency of photodegradation Longer retention times usuallyobtained by reducing the permeate flux results in higher pollutant degradation dueto the greater contact time between the molecules to be degraded and the catalystHowever since the PMR must be able to offer a high water permeate flux it is impor-tant to find a good compromise among the permeate flux and the residence time toachieve a system for application purpose

722 Membrane materials development and designfor photocatalysis

Because the main problem encountered when the photocatalytic process is coupled to apressure-driven process such as MF and UF (which requires porous membranes) is thedecrease of permeate flux caused by concentration polarization and fouling the choiceof membrane material is strongly determined by the need to limit these phenomena andby the chemical and thermal stability of the materials

Polymeric membranes are generally used in photocatalysis although inorganicones which generally present higher chemical and thermal stability are attractivefor PMR applications But they have the disadvantage of a significantly higher costcompared to polymeric ones (Chin Chiang amp Fane 2006 Moritz Benfer Arki ampTomandl 2001) In view of this economic factor suitable polymeric membranesshould be sought for this application

Molinari et al (2000) reported an investigation of the stability under ultraviolet(UV) irradiation of some eligible commercial membranes composed by variousmaterials Tests of photo-resistance under UV light were carried out by irradiating

Photocatalytic membrane reactors for water treatment 211

the membranes immersed in distilled water Samples were periodically withdrawn andanalysed by TOC optical microscopy (OM) and scanning electron microscopy (SEM)to verify any damage to the membrane surface Membrane stability was also deter-mined by measuring the changes in pure water permeation flux (WPF) before and afterUV irradiation Table 72 shows the main characteristic of the 11 commercialmembranes used in the UV irradiation tests

Membranes made of polyacrylonitrile (PAN) fluoride thorn polypropylene (PP) andpolysulphone thorn PP seemed to be stable to UV light over a 24-h period of irradiationPAN membrane was chosen to carry out some photo-reactivity experiments because itshowed the highest permeate flux which was constant in the time TiO2 was immobi-lized on the flat sheet membrane by ultrafiltrating TiO2 suspensions in water (600 mL)at 005 01 02 and 03 gL the amounts of immobilized TiO2 were respectively076 204 408 and 612 mgcm2 of membrane The best uniform coverage was givenby loading 408 mgcm2 although the best results for the photocatalytic reaction wereobtained in a suspended TiO2 system 4-nitrophenol (4-NP) was used as model mole-cule and 80 degradation was obtained in around 5 h by using 05 gL of suspendedTiO2 whereas degradation around 51 was obtained with the same irradiation time inthe system with deposited TiO2 regardless of the amount of catalyst

Some years later Chin et al (2006) reported a study focused on the selection ofpolymeric membranes for PMR applications providing a protocol similar to that

Table 72 Types of commercial membranes used in the UV irradiationtest

Type of membrane Pore size Polymer Supplier

MPPS 0000 u002 15 kDa Polysulphone Separem

MPPS 0000 u006 40 kDa Polysulphone Separem

MPPS 0000 u20 25 kDa Polyamide Separem

MPPS 0000 u25 20 kDa Polyamide Separem

P-12-10 e PEEK Homemade

FS 50 PP 50 kDa Fluoride thorn PP Dow

PES 40 kDa Polyethersulphone TechSep

PVDF 01 mm Polyvinyldenefluoride

TechSep

GR 51 PP 50 kDa Polysulphone thorn PP TechSep

PAN 40 kDa Polyacrylonitrile TechSep

CA 600 PP 20 kDa Cellulose acetate-PP

Dow

Note PP polypropyleneSource Molinari et al (2000)

212 Advances in Membrane Technologies for Water Treatment

one proposed byMolinari et al (2000) for testing the stability of polymeric membranesbefore using them with photocatalytic reactions Membrane stability was characterizedby (1) changes in WPF before and after UV irradiation (2) release of TOC in the50 mL of Milli-Q water in which the membrane were immersed before and afterthe predefined time of UV exposure and (3) SEM to observe the surface morphologyof the membranes before and after the exposure to UV light The overall change in sur-face hydrophobicity or hydrophilicity of the membranes was determined by contactangle measurements (CAM) Ten types of polymeric membranes (Table 73) were sub-jected to the initial UV screening test Polytetrafluoroethylene (PTFE) hydrophobicpolyvinylidene fluoride (PVDFphobic) and PAN membranes were stable after30 days of UV illumination However in a study of the oxidative stability of mem-branes (under UV hydrogen peroxide [H2O2] and combined UVH2O2 conditions)it was found that the stability of PAN membrane declined considerably when it wasexposed to 10 days of 200 mM H2O2UV conditions Then the author concludedthat on the basis of their UV and oxidative screening tests PTFE and hydrophobicPVDF are the better choice for photocatalytic applications

Different papers reported in the literature suggest the use of PVDF for PMRs Fu JiWang Jin and An (2006) successfully used a submerged membrane photocatalyticreactor (SMPR) in which the MF module was made of PVDF hollow fibre membranes(pore size frac14 02 mm filtration area frac14 02 m2) for the degradation of fulvic acid bynanostructured TiO2 Chin Lim Chiang and Fane (2007) studied a low-pressurePVDF submerged hollow fibre membrane module to retain the TiO2 particles in thephotodegradation of bisphenol A (BPA) used as a model pollutant

Table 73 Types of commercial membranes used in the UV irradiationtest

Type of membrane Pore size Suppliers

Polyvinyldene fluoride(PVDF)

022 mm Millipore

PVDF-MP 022 mm Millipore

PVDF-Pall 01 mm Pall filtration

Polycarbonate (PC) 01 mm Millipore

Polysulphone (PS) 600 kDa Osmonics

Polytetrafluoroethylene(PTFE)

02 mm Cole Parmer

Polypropylene (PP) 01 mm Osmonics

Polyacrylonitrile (PAN) 40 kDa Cleanseas

Polyethersulphone (PES) 50 kDa Millipore

Cellulose acetate (CA) 02 mm MFS

Source Chin et al (2006)

Photocatalytic membrane reactors for water treatment 213

Despite all the properties that make PVDF one of the most extensively applied UFmembrane materials (eg antioxidation good thermal and hydrolytic stabilities aswell as good mechanical and membrane-forming properties) the hydrophobic natureof PVDF often results in severe membrane fouling and permeability decline sinceorganic contaminants (hydrophobic) deposition on this materials results favoureddue to chemical affinity This has become a conspicuous drawback for their applicationin water treatment (Lang Xu Yang amp Tong 2007) Many methods have been testedto improve the membrane performances Among these ones blending with inorganicmaterials especially nanoparticles has attracted great attention owing to the relativelyeasy preparation by the method of phase inversion which is carried out under mildconditions (Shon et al 2010 Wei et al 2011) On the basis of this DamodarYou and Chou (2009) reported a study on the self-cleaning antibacterial and photo-catalytic properties of TiO2-entrapped PVDF membranes The modified PVDF mem-branes were prepared by using the phase inversion method adding different amountsof TiO2 particles (0e4 wt) into the casting solution The TiO2ePVDF membraneswere tested for their antibacterial property by using Escherichia coliform photoactiveproperty using reactive black 5 (RB5) dye and self-cleaning (antifouling) propertiesusing 1 Bovine Serum Albumin (BSA) solution Obtained results evidenced thatthe hydrophilicity and pore size of composite PVDFTiO2 membranes were variedby addition of different amounts of TiO2 This also improves the permeability of modi-fied PVDFTiO2 membrane The PVDFTiO2 membrane showed better bactericidalability as compared to neat PVDF membrane under UV light The rate of RB5 removalwas higher as compared to neat PVDF membrane Among the tested membranes theones with 2e4 PVDFTiO2 showed better antifoulingself-cleaning ability ascompared to neat PVDF membrane

On the same topic Wei et al (2011) proposed a new PVDFeTiO2 nanowire hybridUF membrane prepared via phase inversion by dispersing TiO2 nanowires in PVDFcasting solutions Obtained results showed that the microstructure mechanical prop-erty thermal stability hydrophilicity permeation and antifouling performance ofhybrid membranes were improved significantly by addition of hydrophilic inorganicTiO2 nanowires

In a recent work You Semblante Lu Damodar andWei (2012) evaluated the anti-fouling and photocatalytic properties of a membrane in which polyacrylic acid (PAA)was plasma-grafted on commercial PVDF membrane to introduce functional groupson the membrane surface that can support the TiO2 nanoparticles Obtained resultsshowed that the membrane hydrophilicity was tremendously enhanced by the self-assembly of TiO2 following a direct proportionality to TiO2 loading However greaterhydrophilicity did not necessarily implicate better antifouling properties since exces-sive nanoparticles plugged membrane pores The membrane with 05 TiO2 loadingmaintained the highest pure water flux and the best antifouling property Beyond thisconcentration a significant permeate flux decline was observed The TiO2-modifiedmembranes were able to remove 30e42 of 50 mgL aqueous RB5 dye and thedegradation reaction was highly dependent on TiO2 amount The overall resultsevidenced that the fabricated membranes are good candidates for use in membranereactors with high hydrophilicity fouling mitigation and photocatalytic capability

214 Advances in Membrane Technologies for Water Treatment

Chin et al (2006) demonstrated that PTFE (a highly crystalline polymer thatexhibits excellent thermal stability and high chemical resistance) membranes arealso good candidates for PMR applications On the basis of this Damodar and You(2010) proposed a PMR assembled by integrating a novel flat plate PTFE membranemodule that was placed at the centre of the tank and surrounded by two UV lamps (seeFigure 72)

The performance of the assembled PMR was evaluated in the mineralization ofRB5 and the efficiency of catalyst recycling and reuse was studied using batchand long-term continuous experiments The obtained data showed that during contin-uous long-term operations the membrane module was able to maintain the catalysteffectively within the reactor and the catalyst was also reused without much loss indye degradation efficiency Indeed the catalyst that gradually deposited on mem-brane surface during continuous operation was effectively recycled by using simpleand quick cleaning method after which the original behaviour of the membrane andRB5 degradation performance were restored The performance of the reactor wasstable with nearly 75e82 TOC removal and 85e90 chemical oxygen demand(COD) removal and showed similar trend for about five to six days after eachmembrane-cleaning step

Raja et al (2007) studied the discolouration of orange II on synthesized PTFECo3O4 films under visible light irradiation An innovative way to prepare PTFECo3O4 supported catalyst by a suitable thermal treatment of the PTFE film in contactwith the Co3O4 colloid was presented The so prepared catalyst allowed the accelerateddiscolouration of orange II

Another hydrophobic polymer largely used in PMR is PP PP hollow fibre mem-branes were used by Erdim Soyer Tasiyici and Koyuncu (2009) to study the effectof natural organic matter (NOM) fouling Synthetic and natural raw waters wereused in their photocatalytic experiments The experimental data showed that the in-crease in NOM concentration increased the pressure while raw water experimentsshowed a higher pressure increase and lower removal efficiencies compared to thatof synthetic water

Magnetic stirrer

Feed

Permeate

Air inlet

UV lampsMembrane module

Air diffuser

Figure 72 Schematization of the assembled photocatalytic membrane reactor (PMR)Adapted from Damodar and You (2010)

Photocatalytic membrane reactors for water treatment 215

Because of their hydrophobic nature PP membranes can be used in MD (Mozia ampMorawski 2006 Mozia Morawski Toyoda amp Tsumura 2010)

Many works are reported in literature on the coupling of the photocatalytic processwith NF membranes which have the advantage of retaining low molecular weightmolecules better in comparison to low-pressure MF and UF modules

Different NF membranes were tested in the photodegradation of different pharma-ceuticals by Molinari Pirillo Loddo and Palmisano (2006) Table 74 reports the maincharacteristic of these NF membranes

Obtained results evidenced that membrane retention depended on both the pH of theaqueous solution to be treated and on the chemical characteristics of the particularpharmaceutical compound to be degraded NF PES 10 at alkaline pHs NTR 7410at neutral and alkaline pHs and N 30 F at acidic pHs were the membranes that showed

Table 74 Main characteristics of commercial membranes tested

Type of membrane Material Characteristics Manufacturer

NTR 7410 Sulfonatedpolysulfone

Rejection 10 with02 NaCl at49 bar 25 Cand pH 65

Nitto DenkoTokyo

PAN GKSS HV3T Polyacrylonitrile Cut-off frac14 30 kDawater flux4231 Lhm2 at2 bar and8462 Lhm2 at4 bar

GKSS Germany

N 30 F Modifiedpolysulfone

Rejection 25e35with 02 NaCland 85e95with 05 ofNa2SO4 waterflux 40e70 Lhm2 at 40 bar and20 C

Hoechst CelgardGermany

NF PES 10 Polyethersulfone Rejection 10e20with 05 NaCland 40e70with 05 ofNa2SO4 waterflux 200e400 Lhm2 at 40 barand 20 C

Hoechst CelgardGermany

Source Molinari et al (2006)

216 Advances in Membrane Technologies for Water Treatment

the best rejection percentages for furosemide at pressures of 4e8 bar NTR 7410 wasthe best membrane for ranitidine rejection over the whole pH range although its rejec-tion at 8 bar was lower than that found for NF PES 10

In another work (Molinari et al 2002) NF PES 10 and NTR 7410 membraneswere tested for the photocatalytic removal of 4-NP and benzoic acid from aqueoussolutions TiO2 P25 Degussa was used as the catalyst both suspended and depositedon the polymeric membranes Obtained results showed that the treatment of 4-NPsolution in acidic medium allowed the total removal of the substrate by using a contin-uous system NTR 7410 was also an efficient NF membrane for separating two dyesCongo red and direct blue from aqueous solutions (Molinari Pirillo Falco Loddoamp Palmisano 2004)

73 Advances in membrane modules and systemconfigurations for PMRs for water treatment

Despite the important advantages of the photocatalytic processes with respect to thetraditional ones their application at industrial level is limited by different drawbacksrelated to the involved reactions and reactor configuration

With regard to the configuration of the reactor and in particular by considering thephotocatalyst two operative configurations can be identified the first one in whichthe photocatalyst is suspended in the aqueous reacting phase and another one withthe photocatalyst immobilized on a support

Slurry photocatalytic reactors in which the catalyst is suspended in the aqueousreacting phase have been widely used In these reactors the nondegraded moleculesor their byproducts are freely transported in the final stream Photocatalyst recoveryand recycle is another problem The coupling with pressure-driven membrane separa-tions in PMRs can solve these problems

731 Pressurized membrane PRs

Different types of PMRs were built with the purpose of obtaining an easy separation ofthe catalyst from the reaction environment and an efficient removal of pollutants fromaqueous media The most studied configurations were pressurized systems in whichpressure-driven membrane processes such as MF UF and NF were combined tothe photocatalytic process In these systems the catalyst used both in the suspendedconfiguration and immobilized on the membrane is confined in the pressurized sideof the permeation cell

In 2002 Molinari et al (2002) reported some experimental results obtained byusing two different pressurized PMR configurations for the degradation of 4-NPIn particular the configurations studied were (1) a first one in which the irradiationof the catalyst was performed in the permeation cell containing the membrane withthree sub-cases (a) catalyst in suspension (b) catalyst deposited on the membrane(c) catalyst entrapped in the membrane and (2) a second one in which the irradiation

Photocatalytic membrane reactors for water treatment 217

of the suspended catalyst was performed in the recirculation tank The results showedthat the second configuration appeared to be the most interesting for industrial appli-cations in terms of irradiation efficiency and membrane permeability For example inreactor optimization high irradiation efficiency high membrane permeate flow rateand selectivity can be obtained by sizing separately the lsquophotocatalytic systemrsquo andthe lsquomembrane systemrsquo and taking advantage of all the best research results for eachsystem

In a successive work the same group Molinari et al (2004) studied the photodegra-dation process of two commercial azo dyes ie Congo red (C32H22N6Na2O6S2) andpatent blue (C27H31N2NaO6S2) in a membrane PR by using TiO2 Degussa P25 asthe photocatalyst and an NF membrane Two different PR configurations a cylindricalone with an external lamp and an annular one with an immersed lamp in the axial po-sition (Figure 73) were studied and the influence of some operational parameterssuch as the pressure in the membrane cell and the initial concentration of the substrateswas determined A comparison between suspended and entrapped TiO2 was also done

The rate of pollutant photodegradation was strongly affected by the UV irradiationmode In particular the rate of photodegradation with the immersed lamp resulted 50times higher than that of suspended one (0274 versus 000548 mgmin) although thepower of the last was four times greater Congo red was photodegraded with higherrate under the same experimental conditions probably due to its higher adsorptiononto the catalyst surface The reactor containing the suspended photocatalyst wassignificantly more efficient than the reactor containing the catalyst entrapped intothe membrane as also found by other authors (Mascolo et al 2007) The observed

(5)

(2)

(6)

(3)

(1)(1)

(2)

(3)

(6)

(5)

(4)(4)

Figure 73 Scheme of the batch system with external lamp and with immersed lamp used in theexperimental runs without membrane with the suspended catalyst (1) oxygen cylinder (2)cylindrical reactor with cooling jacket (3) thermostatic baths with cooling water (4) powersupplies (5) medium pressure Hg lamp (6) magnetic stirrer (Reprinted from Molinari et al(2004) with permission from Elsevier)

218 Advances in Membrane Technologies for Water Treatment

reduction of photoactivity was probably due to the lower available active surface area ofthe catalyst compared to the suspended immobilized system The results evidenced thatit was possible to treat successfully highly concentrated solutions (500 mgL) of bothdyes by means of a continuous process obtaining good values of permeate fluxes(30e70 Lm2h) this could be interesting for industrial applications

732 Depressurized (submerged) membrane PRs

The main problem observed by coupling photocatalysis with a pressure-driven mem-brane process is the decrease of permeate flux caused by membrane fouling due tocatalyst deposition on the membrane Submerged membrane systems represent oneof the different approaches proposed to overcome this limitation In this configurationthe catalyst is suspended in an open-air reaction environment the membrane isimmersed in the batch and the permeate is sucked by means a vacuum pump

Fu et al (2006) reported the degradation of FA by using synthesized nanostructuredTiO2silica gel catalyst particles in a submerged membrane photocatalytic reactor(SMPR) schematized in Figure 74 It was found that the photocatalyst at 05 gLand airflow at 006 m3h were the optimal conditions for the removal of FA The resultsshowed a reduction of fouling phenomena when nanostructured TiO2 was used as thephotocatalyst

An additional way to prevent photocatalyst deposition and then reduce membranefouling consists in controlling the hydrodynamic conditions near the membrane sur-face In this context gas sparging at the bottom of the membrane represents a prom-ising strategy On this basis Chin et al (2007) studied the removal of BPA in waterby using low-pressure submerged module and they observed that the aeration allow-ing a mechanical agitation reduced the fouling of the membrane and maintained theTiO2 well suspended in the solution In addition in this study another strategy toreduce membrane fouling was proposed an intermittent membrane filtration whichpermitted to maintain high flux at low aeration rate Practically when suction across

(1)

(2)

Feed

(3)

(4)

Submerged membrane module

Permeate

Aeration

Cooling water

(5)

Figure 74 Schematic diagram of the submerged membrane photocatalytic reactor (SMPR)system (1) feed tank (2) feed pump (3) thermostated jacket protoreactor (4) UV lamp(5) suction pumpReprinted from Fu et al (2006) with permission form Elsevier

Photocatalytic membrane reactors for water treatment 219

the membrane was stopped the aeration could shear the membrane surface facilitatingthe detachment of catalyst particles The results summarized in Figure 75 showedthat TOC photomineralization by operating with intermittent operation was similarto that ones obtained with continuous operation ie 94 BPA reduction at250 min Moreover it was found that with the intermittent mode the transmembranepressure (TMP) of the system decreased by five times compared to the continuousoperation Because TMP is proportional to the filtration energy cost intermittentoperation would reduce the operating cost of the continuous SMPR

The advantages of this approachwere also studied byHuangMeng Liang andQian(2007) They demonstrated that sedimentation of the suspended semiconductor can becontrolled by applying fine-bubble aeration and intermittent membrane filtration

Choi (2006) used the same intermittent approach studying the performance of apilot-scale SMPR in the degradation of 4-Chlorophenol (4-CP) The results evidenceda complete degradation of the pollutant in 2 h Besides in continuous runs no mem-brane fouling was observed when the intermittent operation was used

Therefore the SMPR with fine-bubble aeration and intermittent membrane filtra-tion can be potentially applied in the photocatalytic oxidation process during drinkingwater treatment

733 Coupling of photocatalysis and membrane distillation

Coupling of photocatalysis and MD could avoid fouling problems related to the use ofpressure-driven membrane separations MD is a separation process based on the prin-ciple of vapoureliquid equilibrium The nonvolatile components (eg ions macromol-ecules etc) are retained on the feed side whereas the volatile components passthrough a porous hydrophobic membrane and then they condense in a cold distillate(usually distilled water)

0

20

40

60

80

100

120

140

Continuous membranefiltration

Intermittent membranefiltration

Perc

enta

ge (

)

Change in TMPEfficiency of TOC degradationEfficiency of production of water

Figure 75 Comparison of the transmembrane pressure (TMP) change total organic carbon(TOC) degradation and production of water between continuous and intermittent permeationoperationReprinted from Chin et al (2007) with permission from Elsevier

220 Advances in Membrane Technologies for Water Treatment

The possibility on the way to use a PMR obtained by coupling photocatalysis anddirect contact MD (DCMD) for degradation of azo dyes (acid red 18 acid yellow 36and direct green 99) in aqueous solution was investigated by Mozia et al (2007) Theinitial concentration of a dye was equal to 30 mgL and the catalyst (TiO2 Aeroxide

P25 Degussa Germany) loadings amounted to 01 03 and 05 gL The resultsshowed that the MD process was very effective in separation of photocatalyst particlesIndeed after 5 h of the experiment the turbidity of distillate was similar to thatmeasured for ultrapure water regardless of the TiO2 amount in the reacting phaseThe highest effectiveness of photodecomposition was obtained in the case of acidred 18 and the most difficult compound to be degraded was acid yellow 36 havingthe lowest molecular weight among all the dyes used (Figure 76)

A complete rejection of the dye and other nonvolatile compounds (organic mol-ecules and inorganic ions) was achieved Some volatile compounds crossed themembrane as indicated by the measurements of TOC concentration into the distil-late However the amount of these substances remained in the range 04e10 mgL so that it can be concluded that the product (distillate) was practically pure waterA permeate flux of 034 m3m2d was obtained similarly to those obtained during theprocess in which ultrapure water was used regardless of the TiO2 amount This resultevidenced that MD permitted to avoid the significant fouling observed whenpressure-driven membrane processes were coupled with photocatalysis althoughthe higher energetic consumption of MD represents an important disadvantage

Thus the hybrid process coupling the photocatalysis and DCMD is a promisingmethod for the removal of organic compounds such as azo dyes from water becausethe MD membrane is a very effective barrier for the catalysts particles and the nonvol-atile compounds present in the feed solution

0

25

50

75

100

Acid red 18 Acid yellow 36 Direct green 99

Deg

rada

tion

()

01 gL03 gL05 gL

Figure 76 Photodegradation of Acid red 18 Acid yellow 36 and Direct green 99 in the PMRobtained by coupling photocatalysis and direct contact membrane distillation (DCMD) usingdifferent TiO2 concentration in the reacting phase (evaluated on the basis of dyes concentrationin the feed phase after 5 h of illumination)Data from Mozia et al (2007)

Photocatalytic membrane reactors for water treatment 221

734 Coupling of photocatalysis and dialysis

The results summarized in the previous section show that only the combination ofphotocatalysis and MD avoids fouling but it needs energy to reach evaporationphenomena

On this basis Azrague et al (2007) proposed the combination of dialysis and photo-catalysis to mineralize organic compounds (24-dihydroxybenzoic acid [24-DHBA]was used as a model pollutant) contained in artificial turbid waters obtained by usinga natural clay named bentonite In this PMR configuration the dialysis membraneused as a membrane contactor permits to separate the polluted turbid water fromthe PR compartment (Figure 77)

Operating in this way the membrane acts as a barrier for the photocatalyst particlesand it allows to extract the organic compounds from the turbid water thanks to theconcentration difference between the turbid polluted compartment and the one inwhich the photocatalytic reaction takes place The absence of TMP avoids the forma-tion of fouling even in case of highly turbid water Besides the membrane permits (1)to maintain the TiO2 in the PR compartment avoiding a final filtration stage and (2) tokeep the bentonite away from the PR thus avoiding the loss of efficient irradiationsdue to the scattering by bentonite particles

All these advantages combined with the complete removal of a high 24-DHBAconcentration demonstrate the effectiveness of the proposed PMR combiningphotocatalysis and dialysis These results should lead to the design of a PMR workingin a continuous mode

735 Coupling of photocatalysis and pervaporation

Recently it has been demonstrated that the integration of photocatalysis with PV is apromising method to improve the efficiency of the detoxification of water streams con-taining recalcitrant organic pollutants at a low concentration (Camera-Roda amp Santar-elli 2007) as the integration of the two processes generates a synergistic effect In PVseparation is not based only on the relative volatility of the components in the mixture

(1)

(2)

(3)

(4)

(5) (6)

(7)

(8)

Figure 77 Schematization of the experimental set-up of the integrated photocatalysiseMDprocess (1) magnetic stirrer (2) feed (artificial turbid water) tank (3) and (4) circulation pumps(5) hollow fibre module or flat sheet membrane (6) thermostated photoreactor (7) pressureregulation valve (8) oxygen cylinderAdapted from Azrague et al (2007)

222 Advances in Membrane Technologies for Water Treatment

but also depends on the relative affinity of the components with the membrane Thusthe choice of membrane material is important to obtain a selective separation of themolecules

The experimental apparatus used for the integrated photocatalysis-PV process isschematically represented in Figure 78 The liquid is continuously recycled by a mem-brane pump to an annular photocatalytic reactor (APR) and kept at a constant temper-ature after passing through a small tank immersed in a thermostatic bath Oxygen iscontinuously supplied inside the tank to maintain a constant concentration of8 mg L1 in the system At the exit of the APR the water passes through one ortwo plane PV modules (membrane surface area frac14 160 cm2) through which the compo-nents permeate selectively thanks to the vacuum (6 mbar) that is kept downstream

The results (Figure 79) showed that the rate of disappearance of a model pollutant(4-chlorophenol [4-CP]) is highly improved by using the integrated system as the

(1)

(2)

(3)

(4)Permeate

Retentate

Figure 78 Schematization of the experimental set-up utilized for the integrated photocatalysis-PV process (1) termostated feed tank (2) membrane pump (3) annular photocatalytic reactor(APR) (4) plane pervaporation moduleAdapted from Camera-Roda and Santarelli (2007)

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35Time (h)

4-C

P re

mov

ed (

)

IntegrationPC+PV no integrationOnly photocatalysisOnly pervaporation

Figure 79 Percentage of 4-chlorophenol (4-CP) removed versus time in the integratedphotocatalysis-PV processAdapted from Camera-Roda and Santarelli (2007)

Photocatalytic membrane reactors for water treatment 223

membrane was efficient in continuously eliminating some intermediate productsthat could slow down the rate of the photocatalytic reaction and concurrently thephotocatalysis transforms the weakly permeable 4-CP into organic compounds thatPV can remove at a high rate

Process intensification by synergistic effect depends on the optimization of the ratiobetween the characteristic rates of the photocatalytic and PV processes

Recently the use of a highly selective membrane allowed to recover somechemical products with high added value as vanillin starting from trans-ferulic acid(Camera-Roda et al 2013)

74 Applications of PMRs for water treatment

In the last years the interest in the presence of pharmaceutical active compounds(PhACs) and their metabolites in waterways has increased significantly (JonesVoulvoulis amp Lester 2002 Kasprzyk-Hordern Dinsdale amp Guwy 2008) Largeamount of PhACs in terms of thousands of tons are annually used for therapeuticpurposes or in animal farming in each European country and may be excreted bothas unmetabolized and as active metabolites thus reaching the aquatic environmentBesides improper disposal of industrial waste may also contribute to their occurrencein aquatic environment The wastewater is generally treated in sewage treatment plants(STP) that often fail to remove the majority of PhACs resulting in high concentrationsdischarged in treated effluents (Braga Smythe Schafer amp Feitz 2005 Carballa et al2004 Castiglione et al 2006 Colpin et al 2002 Comeau Surette Brun amp Losier2008) so PhACs are detectable in the aquatic environment with concentration levelsup to the mgL These amounts are much lower than maximum concentrations reportedfor typical industrial contaminants but their toxicological chronic effects on aquaticenvironment due to the continuous exposure to mixtures of pharmaceuticals areunknown

On this basis the demand for developing efficient systems alternative to the tradi-tional purification methods to remove PhACs from water has assumed a great researchinterest PMRs could represent a useful solution to this problem

The photodegradation of different pharmaceuticals (furosemide ranitidine (hydro-chloride) ofloxacine phenazone naproxen carbamazepine and clofibric acid)contained in aqueous medium at various pHs by using a batch PR and a PMR workingin recirculation regime was studied by Molinari et al (2006) The experimental testswere performed by using polycrystalline TiO2 as the photocatalyst determining theperformances of different commercial membranes mainly of the NF type (Table 74)in the PMR To analyse the results of the photodegradation experiments in the PMRthe main factors involved in the overall performance of the PR were separately studiedby carrying out the following tests (1) adsorption tests on the TiO2 particles (2) degra-dation tests in the absence of the membrane (3) membrane rejection by changing theoperating pressures and (4) degradation tests in the PMR The results evidenced thatthe adsorption of the substrates onto the catalyst is affected by the pH owing to theinfluence of this operating parameter on the hydrophilichydrophobic character of

224 Advances in Membrane Technologies for Water Treatment

the photocatalyst All the seven considered molecules were successfully photode-graded in the batch reactor (without the membrane) with pseudo-first order kinetics

Furosemide and ranitidine were selected to carry out the study of rejection and pho-todegradation in the PMR During the photocatalytic tests in the PMR the permeateflux through the NTR 7410 membrane had an average value of 45 Lhm2 at bothacidic and alkaline pHs Rejection values were in the range 10e60 for furosemideand 5e30 for ranitidine in the dark (without photoreaction) but a net decreasedown to zero was observed in the contemporary presence of light photocatalystand oxygen Then the degradation results in the PMR (Figure 710) showed that rejec-tion measured in the presence of photocatalyst and oxygen both in the dark and underirradiation conditions was almost zero so that the membrane in this case was benefi-cial only because it allowed the confinement of the photocatalyst

In a successive work the same group Molinari et al (2008) reported the degradationof two pharmaceuticals (Gemfibrozil [GEM] and Tamoxifen [TAM]) selected astarget molecule using suspended TiO2 as catalyst in two configurations of PMRs(pressurized and depressurized) operated in both batch and continuous mode Thelatter mode consisted in the continuous withdrawn of the permeate from the reactorand its replacing by an equal volume of polluted water until reaching a steady state(approximately 190 min) in terms of flux and rejection values of intermediates Theobjective of these tests was to simulate the continuous photodegradation processthat could be applied at industrial level The experimental plant consisted of an annularPR with an immersed UV lamp connected to the permeation cell in which a pressurizedflat sheet membrane or a submerged membrane module was located The effects of pa-rameters such as pH of the aqueous TiO2 suspensions pump flow rate and membraneclean-up on the efficiency of the PMR were studied Closed and continuous

0

4

8

12

16

20

0 50 100 150 200Time (min)

Con

cent

ratio

n (m

gL)

Figure 710 Substrate concentrations versus time for runs carried out by using the hybridsystem with the NTR 7410 membrane at initial pH 3 (TiO2 frac14 1 gL O2 frac14 22 ppm immersedlamp 125 W) Furosemide (A) retentate (gt) permeate Ranitidine (-) retentate ()permeateReprinted from Molinari et al (2006) with permission from Elsevier

Photocatalytic membrane reactors for water treatment 225

procedures were used to investigate the behaviour of the pressurized PMRs The dataobtained for the closed membrane system showed complete photodegradation of GEMand TAM with an abatement of 99 after 20 min and mineralization higher than 90after approximately 120 min

Regard to the pressurized system the membrane used (commercial flat sheet NFmembrane NTR 7410 Nitto Denko Tokyo) allowed to maintain the drug and the cata-lyst in the reaction environment but it was not able to reject significantly the degrada-tion intermediates which were also found in the permeate A good operating stabilitywas observed by operating in continuous mode reaching a steady state for approxi-mately 120 min (Figure 711) with a complete abatement of the drug and values ofmineralization (60) and permeate flux (386 Lhm2) that remained constant untilthe end of a run A TOC rejection of about 62 at steady state confirmed the needto identify a membrane with higher rejection to the intermediate products Catalystdeposition on the membrane surface and fouling caused a flux decline during the pho-tocatalytic process

The depressurized system in which the submerged membrane module was locatedseparately from the PR and the oxygen was bubbled on the membrane surface couldbe of interest both to separate the photocatalytic zone from the separation zone and toreduce membrane fouling thanks to oxygen sparging The UF membrane (PES com-mercial capillary membrane 005e01 mm average pore size) used in the submergedsystem showed retention of only the catalyst in the reaction environment whileGEM and its oxidation products moved in the permeate However the submergedPMR permitted to obtain a steady-state flux of 651 Lhm2 higher than those obtainedoperating with the pressurized module resulting it interesting for application purposes

Retentate

Permeate

0 50 100 150 200 250 3000

Time (min)

TOC

(mg

L)

2

4

6

8

10

Figure 711 Total organic carbon (TOC) values versus the time in the degradation ofGemfibrozil (GEM) in the continuous submerged membrane photoreactor (continuous feed ofGEM at concentration of 10 mgL Reprinted from Molinari et al (2008) with permission fromElsevier)

226 Advances in Membrane Technologies for Water Treatment

The overall results reported by Molinari et al (2006) and Molinari et al (2008)confirmed that PMRs can be of interest in the removal of organic pollutants from waterbecause they allowed the recovery and reuse of the catalyst permitted to achieve acontinuous process and if a suitable membrane is found it is possible to retain thepollutant and its degradation products in the reaction environment

With regard to the possibility of using solar radiation to activate the photocatalystin 2005 Augugliaro et al studied lincomycin (a common antibiotic) degradation inaqueous suspensions of polycrystalline TiO2 Degussa P25 irradiated by sunlight Ahybrid system consisting of a solar PR coupled with a membrane module was testedwith the aim to improve system sustainability and performance The results of prelim-inary tests without the membrane separation step showed that lincomycin was success-fully oxidized in the pilot plant solar PR The presence of the membrane whichconfined both photocatalyst and pollutants in the reaction environment allowed oper-ation in continuous mode The data collected by using the hybrid system both in totalrecycle (batch) and in continuous mode (Figure 712) indicated that the presence of themembrane allows the reduction of both the substrate and intermediates down to lowconcentration levels

Benotti Stanford Wert and Snyder (2009) reported a study on the use of a PMRpilot system using UVTiO2 photocatalysis in the removal of 32 PhACs from waterThe results showed that concentrations of all compounds decreased during the treat-ment In particular removal efficiency higher than 70 was obtained for 29 of thetargeted compounds while a removal efficiency lower than 50 was achieved foronly three compounds During the treatment of all the considered PhACs no oestro-genically active transformation products were formed Thus the PMR developed inthis work is a useful technology for water treatment as determined by pharmaceuticaland endocrine-disrupting compound destruction as well as the removal of oestrogenicactivity

In 2012 Mozia and Morawski on the basis of their previous encouraging resultsobtained in dye removal from water compared the efficiency of photodegradationof ibuprofen (IBU) sodium salt present in tap water in a PMR using DCMD under a

90(a) (b)8070605040302010

00 1 2 3 0

E [einstein]E [einstein]

C [μ

M]

C [μ

M]

0

5

10

15

20

25

1 2 3 4

Figure 712 Lincomycin concentrations versus the cumulative photon energy E for runscarried out in (a) total recirculation regimens and (b) in continuous regimen by using the hybridsystem at different initial lincomycin concentrations Full symbol retentate open symbolpermeateReprinted from Augugliaro et al (2005) with permission from Elsevier

Photocatalytic membrane reactors for water treatment 227

batch and continuous operation The results revealed that the influence of the operationmode on the effectiveness of IBU decomposition and mineralization and on the prod-uct (distillate) quality was not significant The permeate did not contain IBU regard-less of the process conditions Despite that the authors recommended the operation ofthe PMR in the continuous mode due to its higher potential for a large-scaleapplication

Membrane scaling during a long-term process was also studied The results sum-marized in Figure 713 showed a decline of permeate flux during the long-term exper-iments In particular after 54 h of the PMR continuous operation the flux was lowerby approximately 7 compared to pure water flux (272 Lm2d versus 294 Lm2d)whereas after 188 h an 86 flux decline was detected The deposit layer formed ona membrane surface had a composite structure on a thin porous TiO2 layer the calciteand aragonite crystals were present The application of cleaning with HCl solutionallowed to dissolve the CaCO3 scale deposit and to recover the flux However about70 h after washing with HCl solution the flux started decreasing with a similar rate asbefore cleaning

In a successive work the same authors (Mozia Darowna Przepiorski amp Moraw-ski 2013) reported the removal of a nonsteroidal anti-inflammatory drug (diclofenacsodium salt [DCF]) from water in two hybrid systems coupling photolysis or photoca-talysis with DCMD The results are summarized in Figure 714 in terms of TOCamounts in distillate (permeate) at the end of various experiments in comparisonwith the initial and final amounts of organic carbon in feed solutions A completeDCF decomposition in the feed was obtained in both processes In the case of the pho-tolysiseDCMD hybrid system the effectiveness of TOC mineralization after 5 h ofirradiation ranged from 273 to 487 depending on the DCF initial concentrationThe addition of TiO2 allowed the improvement of the efficiency of TOC removal Af-ter 5 h of the hybrid photocatalysiseDCMD process the mineralization efficiency was

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300Time (h)

Perm

eate

fulx

(Lm

2 d)

HCl cleaning

Figure 713 Changes of permeate flux during long-term operation of photocatalytic membranereactor (PMR) using direct contact membrane distillation (DCMD) in continuous modeAdapted from Mozia and Morawski (2012)

228 Advances in Membrane Technologies for Water Treatment

in the range of 825e100 the highest for the lowest DCF concentration Applicationof DCMD in the hybrid systems ensured high efficiency of separation of DCF as wellas the products of its degradation Indeed regardless of the process applied distillatewas high purity water DCF was not detected TOC concentration did not exceed08 mgdm3 and conductivity was lower than 16 mScm

The results obtained by Mozia and Morawski (2012) and Mozia et al (2013)showed that because the MD efficiently separated not only TiO2 particles but alsoorganic contaminants present in feed solution the PMR using DCMD represents apromising method for treatment of waters containing pharmaceuticals Low permeate(distillate) flux assured relatively long residence time of contaminants which resultedin high effectiveness of their photodegradation

The overall results reported in this section confirm that PMRs can be of interest inthe removal of organic pollutants (eg pharmaceuticals) from water because the mem-brane (1) separates TiO2 particles efficiently thus permitting the recovery and reuse ofthe catalyst (2) permits the realization of a continuous process and (3) allows theretention of organic pollutants and their degradation products thus avoiding theirrelease in the permeate and controlling the residence time of contaminants in the reac-tion environment Then PMRs can be considered a useful technology for water treat-ment as determined by PhACs destruction and the removal of oestrogenic activity Animportant issue to take into consideration in developing photocatalysisemembranehybrid processes is membrane fouling mainly due to photocatalyst deposition onthe membrane feed side In this context the approach proposed by Mozia et al inwhich MD is coupled with photocatalysis seems to be promising because MD allowsto obtain the points (1) (2) and (3) previously reported and also permits the avoidanceof the significant fouling observed when a pressure-driven membrane process is usedalthough the higher energetic consumption of MD could represent a limitation of thishybrid process

642 640

00

627

377

05

640

110

0700

100

200

300

400

500

600

700

Feed 0 Feed 5 h Permeate 5 h

TOC

(mg)

DCMD

Photolysis - DCMDPhotocatalysis - DCMD

Figure 714 Comparison of TOC amounts in distillate (permeate) after 5 h of direct contactmembrane distillation (DCMD) photolysiseDCMD and photocatalysiseDCMD processeswith the initial and final total organic carbon (TOC) amounts in feed solutionsData from Mozia et al (2013)

Photocatalytic membrane reactors for water treatment 229

75 Advantages and limitations of PMRs in watertreatment

Based on the results summarized in the previous sections the use of PMRs can be pro-posed as an attractive green process because it is effective in abating harmful andrecalcitrant substances present in aqueous effluents

The main advantages related to the use of the PMRs to degrade pollutants are

1 Possibility to be applied to a wide range of compounds in aqueous gaseous and solid phase2 Short reaction times and mild experimental conditions usually ambient temperature and pressure3 Generally only oxygen from air without any additional additive is necessary4 Effectiveness with low concentration of pollutant(s)5 Possibility to destroy a variety of hazardous molecules with the formation of innocuous prod-

ucts solving the disposal pollutant problem associated to the conventional wastewatertreatment methods

6 Possibility to convert toxic metal ions in their nontoxic forms which can be recovered andreused

7 Synergistic effects by coupling the potentialities of classical PRs and those of membraneprocesses ie catalyst recovery and reuse (immobilized or in suspension) rejection of thesubstrate andor separation of degradation products thus allowing to perform the reactionof interest and the separation of the desired product(s) simultaneously in continuous mode

8 Possibility to control the residence time of substrates in the photocatalytic system thus verifyingthe contact time between the molecules to be degraded and the catalyst and then the photocata-lytic degradatione this feature is very important when the process is used for synthetic purposes

9 Possibility to use sunlight

Despite these important advantages the application of the photocatalytic process at in-dustrial level is limited by different drawbacks mainly related to the membrane fouling

As reported in previous sections the choice of the membrane is a key step forachieving a successful application of PMRs For example Molinari et al (2006) andMollinari et al (2008) demonstrated the potentialities of PMR applications in both pres-surized and submerged configurations in water detoxification because they allowed therecovery and reuse of the catalyst and permitted the achievement of a continuous pro-cess while the membrane rejection towards the pollutants was not very satisfactoryThese results show the necessity to identify a membrane selective to intermediate prod-ucts to retain the pollutant and its degradation products in the reaction environment

76 Conclusion

All the results reported in this chapter on coupling the photocatalytic process withmembrane separations show numerous advantages derived from a synergistic effectof these two techniques In particular it has been shown that PMRs can be considereda useful technology for the removal of organic pollutants (eg pharmaceuticals) fromwater thanks to PhAC destruction and the removal of oestrogenic activity

An important limitation related to photocatalysisemembrane coupling is related tothe decrease of permeate flux caused by concentration polarization and membrane

230 Advances in Membrane Technologies for Water Treatment

fouling mainly due to photocatalyst deposition on membrane surface This drawbackcan be limited by appropriately choosing membrane material which must also ensureadequate chemical and thermal stability and type and PMRs configuration

The ideal membrane process to be coupled with photocatalysis should possess thesefeatures (1) complete retention of the catalyst and controlled fouling and (2) goodrejection of the substrates and of degradation byproducts to avoid the release ofdangerous substances in the treated water and to assure a residence time in the photo-catalytic system sufficient for obtaining complete pollutant degradation and minerali-zation Longer residence times are usually obtained by reducing the permeate flux so itis important to find a good compromise among the permeate flux and the residencetime to achieve a system for application purpose In other words the process intensi-fication by synergistic effect depends on the optimization of the ratio between the char-acteristic rates of the photocatalytic and membrane separation processes

Many methods have been tested to improve the membrane performances Amongthese blending with inorganic materials (eg immobilization of TiO2) to increasethe hydrophilic character of the membrane surface exposed to the reacting environ-ment of TiO2 is a promising approach that produces photocatalytic membranes withantifoulingself-cleaning ability The so-prepared membranes are good candidatesfor use in membrane reactors for wastewater treatment and reuse processes

Considering PMR configuration the use of SMPRs with fine-bubble aeration andintermittent membrane filtration can be potentially applied in the photocatalytic oxida-tion process during drinking water treatment because this approach significantly re-duces membrane fouling

The hybrid process obtained by coupling photocatalysis with MD seems very prom-ising for the removal of organic pollutants from waters because it possesses the idealfeaturespreviously reported In particular this couplingavoids fouling but it needs energyto obtain evaporation On the basis of this the combination of dialysis and pervaporationwith photocatalysis has been also reported showing that this coupling also possesses thefeatures of the ideal membrane process to be coupled with photocatalysis

77 Future trends

The use of submerged membrane systems operated with fine-bubble aeration in theintermittent membrane filtration mode and the coupling of photocatalysis with MDdialysis and pervaporation represent some promising approaches for overcomingthe limitation related to membrane fouling In particular the coupling with DCMDseems to be more promising asMD (1) separates TiO2 particles efficiently (2) permitsthe retention of organic pollutants and their degradation byproducts (the MDdistillate is practically high purity water) (3) permits the realization of a continuousprocess and (4) allows the avoidance of membrane fouling although the higherenergetic consumption of MD could represent a limitation of this hybrid process

On this basis it is foreseen that hybrid system photocatalysisemembranes will havea significant impact in designing processes for the abatement of organic pollutantscontained in waters

Photocatalytic membrane reactors for water treatment 231

78 Sources of further information

An exhaustive reference book on the fundamentals and applications of heterogeneousphotocatalysis that was recently published is Clean by light irradiation Practicalapplications of supported TiO2 by Augugliaro V Loddo V Pagliaro M PalmisanoG amp Palmisano L (2010) Cambridge (UK) RCS Publishing

Fundamentals of photocatalysis and some interesting information about membranePR regarding membrane materials and some operational issues can be found inChapter 6 - Photocatalytic membrane reactors Fundamentals membrane materialsand operational issues by Mozia S Morawski AW Molinari R Palmisano Lamp Loddo V (2013) In A Basile (Ed) Handbook of membrane reactors - volume2 Reactor types and industrial applications (pp 236e295) Cambridge (UK) Wood-head Publishing Limited ISBN 978-0-85709-415-5

Other interesting information about configuration and performance of PMRs and anexample of this integrated technology in water treatment and chemical production canbe found in Chapter 21 - Photocatalytic membrane reactors Configurations perfor-mance and applications in water treatment and chemical production by MolinariR Palmisano L Loddo V Mozia S amp Morawski AW (2013) In A Basile(Ed) Handbook of membrane reactors - volume 2 Reactor types and industrialapplications (pp 808e845) Cambridge (UK) Woodhead Publishing LimitedISBN 978-0-85709-415-5

List of symbols

Cf Solute concentration in the feedCp Solute concentration in the permeateeL Photogenerated electronEg Energy band gaph Plankrsquos constanthD Photogenerated holen Frequency of light radiation

List of acronyms

E01 Redox potential of the species to be reduced

E02 Redox potential of the species to be oxidized

24-DHBA 24-dihydroxybenzoic acid4-CP 4-Chlorophenol4-NP 4-NitrophenolAOP Advanced oxidation processAPR Annular photocatalytic reactorBPA Bisphenol ACAM Contact angle measurementCB Conduction band

232 Advances in Membrane Technologies for Water Treatment

COD Chemical oxygen demandDCF DiclofenacDCMD Direct contact membrane distillationECB Redox potential of the conduction bandEVB Redox potential of the valence bandFA Fulvic acidGEM GemfibrozilIBU IbuprofenMD Membrane distillationMF MicrofiltrationNF NanofiltrationNHE Normal hydrogen electrodeNOM Natural organic matterOM Optical microscopyPAA Polyacrylic acidPAN PolyacrylonitrilePES PolyethersulfonePhAC Pharmaceutical active compoundPMR Photocatalytic membrane reactorPP PolypropylenePR PhotoreactorPTFE PolytetrafluoroethylenePV PervaporationPVDF Polyvinylidene fluorideR Membrane rejectionRB5 Reactive black 5 dyeRO Reverse osmosisSEM Scanning electron microscopySMPR Submerged membrane photocatalytic reactorSTP Sewage treatment plantsTAM TamoxifenTOC Total organic carbonUF UltrafiltrationUV Ultraviolet irradiationVB Valence bandWPF Water permeation flux

References

Ara~na J Pe~na Alonso A Do~na Rodriacuteguez J M Herrera Melian J A G Diacuteaz O amp PeacuterezPe~na J (2008) Comparative study of MTBE photocatalytic degradation with TiO2 andCu-TiO2 Applied Catalysis B-Evironmental 78 355e363 Retrieved from httpdxdoiorg101016japcatb200709023

Augugliaro V Garciacutea-Lopez E Loddo V Malato-Rodriacuteguez S Maldonado I Marcigrave Get al (2005) Degradation of lincomycin in aqueous medium Coupling of solar photo-catalysis and membrane separation Solar Energy 79 402e408 Retrieved from httpdxdoiorg101016jsolener200502020

Photocatalytic membrane reactors for water treatment 233

Azrague K Aimar P Benoit-Marquieacute F amp Maurette M T (2007) A new combination of amembrane and a photocatalytic reactor for the depollution of turbid water AppliedCatalysis B-Environmental 72 197e204 Retrieved from httpdxdoiorg101016japcatb200610007

Benotti M J Stanford B D Wert E C amp Snyder S A (2009) Evaluation of a photo-catalytic reactor membrane pilot system for the removal of pharmaceuticals and endocrinedisrupting compounds from waterWater Research 43 1513e1522 Retrieved from httpdxdoiorg101016jwatres200812049

Braga O Smythe G A Schafer A amp Feitz A J (2005) Fate of steroid estrogens inAustralian inland and coastal wastewater treatment plants Environmental Science ampTechnology 39 3351e3358 Retrieved from httpdxdoiorg101021es0501767

Camera-Roda G Augugliaro V Cardillo A Loddo V Palmisano G amp Palmisano L (2013)A pervaporation photocatalytic reactor for the green synthesis of vanillin Chemical Engi-neering Journal 224 136e143 Retrieved from httpdxdoiorg101016jcej201210037

Camera-Roda G amp Santarelli F (2007) Intensification of water detoxification by integratingphotocatalysis and pervaporation Journal of Solar Energy Engineering 129 68e73Retrieved from httpdxdoiorg10111512391204

Camera-Roda G Santarelli F Augugliaro V Loddo V Palmisano G Palmisano L et al(2011) Photocatalytic process intensification by coupling with pervaporation CatalyisToday 161 209e213 Retrieved from httpdxdoiorg101016jcattod201010052

Carballa M Omil F Lema J Llompart M Garcia-Jares C Rodriguez I et al (2004)Behaviour of pharmaceuticals cosmetics and hormones in a sewage treatment plant WaterResearch 38 2918e2926 Retrieved from httpdxdoiorg101016jwatres200403029

Castiglione S Magnati R Fanelli R Pomati F Calamari D amp Zuccato E (2006)Removal of pharmaceuticals in sewage treatment plants in Italy Environmental Scienceand Technology 40 357e363 Retrieved from httpdxdoiorg101021es050991m

Chen C Wang Z Ruan S Zou B Zhao M amp Wu F (2008) Photocatalyticdegradation of CI Acid Orange 52 in the presence of Zn-doped TiO2 prepared by a stearicacid gel method Dyes and Pigments 77 204e209 Retrieved from httpdxdoiorg101016jdyepig200705003

Chin S S Chiang K amp Fane A G (2006) The stability of polymeric membranes in a TiO2

photocatalysis process Journal of Membrane Science 275 202e211 Retrieved fromhttpdxdoiorg101016jmemsci200509033

Chin S S Lim T M Chiang K amp Fane A G (2007) Hybrid low-pressure submergedmembrane photoreactor for the removal of bisphenol A Desalination 202 253e261Retrieved from httpdxdoiorg101016jdesal200512062

Choi W (2006) Pure and modified TiO2 photocatalysts and their environmental applicationsCatalysis Surveys from Asia 10 16e28 Retrieved from httpdxdoiorg101007s10563-006-9000-2

Collazzo G C Foletto E L Jahn S L amp Villetti M A (2012) Degradation of Direct Black38 dye under visible light and sunlight irradiation by N-doped anatase TiO2 as photo-catalyst Journal of Environmental Management 98 107e111 Retrieved from httpdxdoiorg101016jjenvman201112029

Colmenares J C Aramendiacutea M A Marinas A Marinas J M amp Urbano F J (2006)Synthesis characterization and photocatalytic activity of different metal-doped titaniasystems Applied Catalysis A-General 306 120e127 Retrieved from httpdxdoiorg101016japcata200603046

Colpin D W Furlon E T Meyer M T Thurman E M Zaugg S D Barber L B et al(2002) Pharmaceuticals hormones and other organic wastewater contaminants in US

234 Advances in Membrane Technologies for Water Treatment

streams 1999e2000 A national reconnaissance Environmental Science amp Technology36 1202e1211 Retrieved from httpdxdoiorg101021es011055j

Comeau F Surette C Brun G L amp Losier R (2008) The occurrence of acidic drugs andcaffeine in sewage effluents and receiving waters from three coastal watersheds in AtlanticCanada Science of the Total Environment 396 132e146 Retrieved from httpdxdoiorg101016jscitotenv200802031

Damodar R A amp You S J (2010) Performance of an integrated membrane photocatalyticreactor for the removal of the reactive Black 5 Separation and Purification Technology 7144e49 Retrieved from httpdxdoiorg101016jseppur200910025

Damodar R A You S J amp Chou H H (2009) Study the self cleaning antibacterial andphotocatalytic properties of TiO2 entrapped PVDF membranes Journal of HazardousMaterials 172 1321e1328 Retrieved from httpdxdoiorg101016jjhazmat200907139

Di Paola A Garciacutea-Lopez E Marcigrave G amp Palmisano L (2012) A survey of photocatalyticmaterials for environmental remediation Journal of Hazardous Materials 3e69211e212 Retrieved from httpdxdoiorg101016jjhazmat201111050

Di Valentin C amp Pacchioni G (2013) Trends in non-metal doping of anatase TiO2 B C Nand F Catalysis Today 206 12e18 Retrieved from httpdxdoiorg101016jcattod201111030

Erdim E Soyer E Tasiyici S amp Koyuncu I (2009) Hybrid photocatalysissubmergedmicrofiltration system for drinking water treatment Desalination and Water Treatment 9165e174 Retrieved from httpdxdoiorg105004dwt2009767

Fu J Ji M Wang Z Jin L amp An D (2006) A new submerged membrane photocatalysisreactor (SMPR) for fulvic acid removal using a nano-structured photocatalyst Journal ofHazardous Materials 131 238e242 Retrieved from httpdxdoiorg101016jjhazmat200509039

Fujishima A amp Honda K (1972) Electrochemical photolysis of water at a semiconductorelectrode Nature 238 37e38 Retrieved from httpdxdoiorg101038238037a0

Ge L (2008) Novel visible-light-driven PtBiVO4 photocatalyst for efficient degradation ofmethyl orange Journal of Molecular Catalysis A-Chemical 282 62e66 Retrieved fromhttpdxdoiorg101016jmolcata200711017

Hernandez-Alonso M D Fresno F Suarez S amp Coronado J M (2009) Development ofalternative photocatalysts to TiO2 Challenges and opportunities Energy amp EnvironmentalScience 2 1231e1257 Retrieved from httpdxdoiorg101039b907933e

Herrmann J M (2005) Heterogeneous photocatalysis State of the art and present applicationsTopics in Catalysis 34 49e65 Retrieved from httpdxdoiorg101007s11244-005-3788-2

Hoffmann M R Martin S T Choi W amp Bahnemann D W (1995) Environmentalapplication of semicondutor photocatalysis Chemical Reviews 95 69e96 Retrieved fromhttpdxdoiorg101021cr00033a004

Huang X Meng Y Liang P amp Qian Y (2007) Operational conditions of a membranefiltration reactor coupled with photocatalytic oxidation Separation and PurificationTechnology 55 165e172 Retrieved from httpdxdoiorg101016jseppur200611018

Huo Y Xie Z Wang X Li H Hoang M amp Caruso R A (2013) Methyl orange removalby combined visible-light photocatalysis and membrane distillation Dyes and Pigments98 106e112 Retrieved from httpdxdoiorg101016jdyepig201302009

Jones Q A H Voulvoulis N amp Lester J N (2002) Aquatic environmental assessment of thetop 25 English prescription pharmaceuticals Water Research 36 5013e5022

Kasprzyk-Hordern B Dinsdale RM ampGuwy A J (2008) The occurrence of pharmaceuticalspersonal care products endocrine disruptors and illicit drugs in surface water in SouthWales

Photocatalytic membrane reactors for water treatment 235

UK Water Research 42 3498e3518 Retrieved from httpdxdoiorg101016jwatres200804026

Lang W Z Xu Z L Yang H amp Tong W (2007) Preparation and characterization ofPVDFePFSA blend hollow fiber UF membrane Journal of Membrane Science 288123e131 Retrieved from httpdxdoiorg101016jmemsci200611009

Ling Q Sun J amp Zhou Q (2008) Preparation and characterization of visible-light-driventitania photocatalyst co-doped with boron and nitrogen Applied Surface Science 2543236e3241 Retrieved from httpdxdoiorg101016japsusc200711001

Mascolo G Comparelli R Curri M L Lovecchio G Lopez A amp Agostiano A (2007)Photocatalytic degradation of methyl red by TiO2 Comparison of the efficiency of immo-bilized nanoparticles versus conventional suspended catalyst Journal of Hazardous Mate-rials 142 130e137 Retrieved from httpdxdoiorg101016jjhazmat200607068

Molinari R Argurio P amp Lavorato C (2013) Review on reduction and partial oxidation oforganics in photocatalytic (membrane) reactors Current Organic Chemistry 172516e2537 Retrieved from httpdxdoiorg10217413852728113179990063

Molinari R Borgese M Drioli E Palmisano L amp Schiavello M (2002) Hybrid processescoupling photocatalysis and membranes for degradation of organic pollutants in waterCatalysis Today 75 77e85

Molinari R Caruso A Argurio P amp Poerio T (2008) Degradation of the drugs Gemfibroziland Tamoxifen in pressurized and de-pressurized membrane photoreactors using sus-pended polycrystalline TiO2 as catalyst Journal of Membrane Science 319 54e63Retrieved from httpdxdoiorg101016jmemsci200803033

Molinari R Caruso A amp Palmisano L (2010) Photocatalytic processes in membrane re-actors In E Drioli amp L Giorno (Eds) Comprehensive membrane science and engineering(Vol 3 pp 165e193) Oxford Elsevier Science BV

Molinari R Caruso A amp Poerio T (2009) Direct benzene conversion to phenol in a hybridphotocatalytic membrane reactor Catalysis Today 144 81e86 Retrieved from httpdxdoiorg101016jcattod200902034

Molinari R Mungari M Drioli E Di Paola A Loddo V Palmisano L et al (2000) Studyon a photocatalytic membrane reactor for water purification Catalysis Today 55 71e78

Molinari R Palmisano L Drioli E amp Schiavello M (2002) Studies on various reactorconfigurations for coupling photocatalysis and membrane processes in water purificationJournal of Membrane Science 206 399e415

Molinari R Pirillo F Falco M Loddo V amp Palmisano L (2004) Photocatalytic degra-dation of dyes by using a membrane reactor Chemical Engineering and Processing 431103e1114 Retrieved from httpdxdoiorg101016jcep200401008

Molinari R Pirillo F Loddo V amp Palmisano L (2006) Heterogeneous photocatalyticdegradation of pharmaceuticals in water by using polycrystalline TiO2 and ananofiltration membrane reactor Catalysis Today 118 205e213 Retrieved from httpdxdoiorg101016jcattod200511091

Moritz T Benfer S Arki P amp Tomandl G (2001) Investigation of ceramic membranematerials by streaming potential measurements Colloids and Surfaces A 195 25e33

Mozia S Darowna D Przepiorski J amp Morawski A W (2013) Evaluation of performanceof hybrid photolysis-DCMD and photocatalysiseDCMD systems utilizing UV-C radiationfor removal of diclofenac sodium salt from water Polish Journal of Chemical Technology15(1) 51e60

Mozia S amp Morawski A W (2006) Hybridization of photocatalysis and membrane distil-lation for purification of wastewater Catalysis Today 118 181e188 Retrieved fromhttpdxdoiorg101016jcattod200512003

236 Advances in Membrane Technologies for Water Treatment

Mozia S amp Morawski A W (2012) The performance of a hybrid photocatalysis-MD systemfor the treatment of tap water contaminated with ibuprofen Catalysis Today 193213e220 Retrieved from httpdxdoiorg101016jcattod201203016

Mozia S Morawski A W Toyoda M amp Tsumura T (2010) Integration of photo-catalysis and membrane distillation for removal of mono- and poly-azo dyes from waterDesalination 250 666e672 Retrieved from httpdxdoiorg101016jdesal200906075

Mozia S Tomaszewska M amp Morawski A W (2005) A new photocatalytic membranereactor (PMR) for removal of azo-dye Acid Red 18 from water Applied CatalysisB-Environmental 59 131e137 Retrieved from httpdxdoiorg101016japcatb200501011

Mozia S Tomaszewska M amp Morawski A W (2007) Photocatalytic membrane reactor(PMR) coupling photocatalysis and membrane distillationmdasheffectiveness of removal ofthree azo dyes from water Catalysis Today 129 3e8 Retrieved from httpdxdoiorg101016jcattod200706043

Mulder M (1996) Basic principles of membrane technology AH Dordrecht The NetherlandsKluwer Academic Publishers

Ni M Leung M K H Leung D Y C amp Sumathy K (2007) A review and recent de-velopments in photocatalytic water-splitting using TiO2 for hydrogen productionRenewable and Sustainable Energy Reviews 11 401e425 Retrieved from httpdxdoiorg101016jrser200501009

Palmisano G Augugliaro V Pagliaro M amp Palmisano L (2007) Photocatalysis Apromising route for 21st century organic chemistry Chemical Communications3425e3437 Retrieved from httpdxdoiorg101039b700395c

Palmisano G Garcıa-Lopez E Marcigrave G Loddo V Yurdakal S Augugliaro V et al(2010) Advances in selective conversions by heterogeneous photocatalysis ChemicalCommunications 46 7074e7089 Retrieved from httpdxdoiorg101039c0CC02087g

Patsios S I Sarasidis V C amp Karabelas A J (2013) A hybrid photocatalysis-ultrafiltrationcontinuous process for humic acids degradation Separation and Purification Technology104 333e341 Retrieved from httpdxdoiorg101016jseppur201211033

Raja P Bensimon M Klehm U Albers P Laub D Kiwi-minsker L et al (2007) Highlydispersed PTFECo3O4 flexible films as photocatalyst showing fast kinetic performance fordiscoloration of azo-dyes under solar irradiation Journal of Photochemistry and Photo-biology 187 332e338 Retrieved from httpdxdoiorg101016jjphotochem200610033

Rosu M C Suciu R C Lazar M D amp Bratu I (2013) The influence of alizarin andfluorescein on the photoactivity of Ni Pt and Ru-doped TiO2 layersMaterials Science andEngineering B 178 383e390 Retrieved from httpdxdoiorg101016jmseb201301001

Shon H K Puntsho S Vigneswaran S Kandasamy J Kim J B Park H J et al (2010)PVDF-TiO2 coated microfiltration membranes Preparation and characterization Mem-brane Water Treatment 1(3) 193e206

Wei Y Chu H Q Dong B Z Li X Xia S J amp Qiang Z M (2011) Effect of TiO2

nanowire addition on PVDF ultrafiltration membrane performance Desalination 27290e97 Retrieved from httpdxdoiorg101016jdesal201101013

WuG Chen T SuW ZhouG ZongX Lei Z et al (2008)H2 productionwith ultra-lowCOselectivity viaphotocatalytic reformingofmethanol onAuTiO2 catalyst International Journalof Hydrogen Energy 33 1243e1251 Retrieved from httpdxdoiorg101016jijhydene200712020

Photocatalytic membrane reactors for water treatment 237

Yang D Zhao J Liu H Zheng Z Adebajo M O Wang H et al (2013) Enhancingphotoactivity of TiO2(B)anatase core-shell nanofibers by selectively doping cerium ionsinto the TiO2(B) core Chemistry-A European Journal 19 5113e5119 Retrieved fromhttpdxdoiorg101002chem201202719

You S J Semblante G U Lu S C Damodar R A amp Wei T C (2012) Evaluation of theantifouling and photocatalytic properties of poly(vinylidene fluoride) plasma-grafted pol-y(acrylic acid) membrane with self-assembled TiO2 Journal of Hazardous Materials237e238 10e19 Retrieved from httpdxdoiorg101016jjhazmat201207071

Zhang J W Wang L Zhang G L Wang Z Y Xu L S amp Fan Z (2013) Influence of azodye-TiO2 interactions on the filtration performance in a hybrid photocatalysisultrafiltrationprocess Journal of Colloid and Interface Science 389 273e283 Retrieved from httpdxdoiorg101016jjcis201208062

238 Advances in Membrane Technologies for Water Treatment

Novel and emerging membranesfor water treatment byhydrostatic pressure and vaporpressure gradient membraneprocesses

8

P Arribas12 M Khayet23 MC Garciacutea-Payo2 L Gil41Campus of International Excellence Moncloa Campus (UCM-UPM) Madrid Spain2Department of Applied Physics I University Complutense of Madrid Avda ComplutenseMadrid Spain 3Madrid Institute for Advanced Studies of Water (IMDEA Water Institute)Alcala de Henares Madrid Spain 4School of Forest Engineering University Polytechnic ofMadrid Avda Complutense Madrid Spain

81 Introduction

Membrane-based separation technologies are environmentally friendly separation pro-cesses that are designed to provide effective and economic solutions to a wide varietyof environmental issues related to water and energy use including climate change andglobal warming The growth of membrane science and technology is mainly due to theimpressive developments in materials used for membrane fabrication and modifica-tion improvements in membrane modules and the evolution of related systemsplants and equipment

In general membranes are semipermeable barriers used for selective permeation ofthe desired species in liquid or gaseous phases by means of an appropriate drivingforce(s) One of the provided classifications of membrane separation processes isaccording to the nature of the membrane and the applied transmembrane driving forceEach membrane process exhibits its advantages and drawbacks and as consequence ithas its fields of applications Providing that this chapter is focused on water treatmentTable 81 summarizes the common considered membrane separation processes in thisfield with the corresponding driving forces and their applications

It is worth mentioning that membranes of different forms and characteristics aregenerally made from a wide variety of chemically and thermally stable polymersBoth single polymers and polymer blends are considered Other materials such asceramics metals and glasses are also used and mixed matrix membranes (MMMs)are fabricated Various membrane fabrication techniques are being proposed andimproved (ie phase inversion sintering stretching track-etching electrospinningetc) In addition various methods have been developed for membrane modification(ie chemical modification surface coating grafting etc) to improve its performance

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400008-3Copyright copy 2015 Elsevier Ltd All rights reserved

Table 81 Membrane separation processes used for water treatmentwith their driving force and main fields of applications

Membraneprocess

Transmembranedriving force Main fields of applications

Microfiltration(MF)

Hydrostaticpressure gradient

Pre-treatment for other processesClarification and biological stabilization in thebeverage industry

AnalysisSterilization in food and pharmaceuticalindustries

Removal of bacteria clarification

Ultrafiltration(UF)

Hydrostaticpressure gradient

Pre-treatment for other processesSeparation of oilwater emulsionDewaxingDeasphaltingElectrophoretic paintRemoval of macromolecules and virus

Nanofiltration(NF)

Hydrostaticpressure gradient

Drinking water productionRemoval of ions and small organicsChemical and pharmaceutical industryConcentrationdewateringWater softeningFractionation of monovalent and divalentcations

Reverse osmosis(RO)

Hydrostaticpressure gradient

Sea and brackish water desalinationDrinking water productionWastewater treatment (industrial andmunicipal pulp and paper textile)

Petroleum industry

Membranedistillation(MD)

Vapor pressuregradient(temperaturegradientdownstreampressure)

Desalination and concentration of brinesUltrapure water productionNear 100 separation of nonvolatile solutespresent in water

Extraction of volatile organic compoundsRecovery of valuable compoundsFood medical radioactive wastewaters

Pervaporation(PV)

Vapor pressuregradient(downstreampressure)

Dehydration of organic solventsRemoval of organics from waterOrganicorganic separation

Electrodialysis(ED)

Electric potentialgradient

Sea and brackish water desalinationUltrapure water productionDemineralization of food productsTable salt productionConcentration of brines

240 Advances in Membrane Technologies for Water Treatment

Novel membranes with innovative materials and improved properties suitable forspecific applications and compact module designs with better hydrodynamic flowchannels and new areas of applications are continuously reported Besides the highprocess performance of a given membrane that includes both the high liquid or vaporproduction rate and selectivity or separation efficiency there are other basic propertiesthat must be taken into account such as operational simplicity high energy efficiencylow cost good stability under wide operating conditions long-term durability lessfouling and scaling susceptibility environment compatibility customizable and adap-tive between different membrane operations in integrated systems easy control of itsstructure and scale-up

82 Pressure-driven membrane processes

In general pressure-driven membrane processes (PDMPs) include microfiltration(MF) ultrafiltration (UF) nanofiltration (NF) and reverse osmosis (RO) These filtra-tion processes can be distinguished by the size of the particles or molecules that thecorresponding membrane is capable of retaining or passing through (Porter 1988)This is roughly related to the membrane pore size which is the main responsibleparameter dictating the field of the process applications

The membranes fabricated for each of the PDMPs exhibit specific characteristicsaccording to the operating conditions and the subjected application A commoncharacteristic of the PDMP membranes is the high mechanical property to bear theapplied hydrostatic pressure especially for NF and RO In the following sections

Table 81 Continued

Membraneprocess

Transmembranedriving force Main fields of applications

Reverseelectrodialysis(RED)

Electric potentialgradient

Power generationSea and brackish water desalination

Osmoticdistillation(OD)

Vapor pressuregradient(concentrationgradient)

Near 100 separation of non-volatile solutespresent in water

Recovery of valuable compoundsFood wastewaters

Forward osmosis(FO)

Concentrationgradient

Sea and brackish water desalinationDrinking water production

Pressure retardedosmosis(PRO)

Concentrationgradient

Power generationSea and brackish water desalination

Novel and emerging membranes for water treatment 241

the recent progress made in each individual PDMP is thoroughly described with itsnovel and emerging membranes proposed for water treatment

821 Microfiltration

As shown in Table 82 the pore size of anMFmembrane ranges between 01 and 10 mmThe MF membranes must have a high porosity and a pore size distribution as narrow aspossibleA large number ofmaterialswere considered for fabrication ofMFmembranesboth organic (hydrophilic or hydrophobic polymers) and inorganic materials (ceramicsmetals glasses) Some of the fabrication techniques such as sintering stretching track-etching and phase inversion were used for fabrication of polymeric MF membranes

Table 82 Characteristics of the different pressure-driven membraneprocesses

Microfiltration(MF)

Ultrafiltration(UF)

Nanofiltration(NF)

Reverseosmosis (RO)

Pore size(nm)

100e10000 1e100 05e2 lt05

MWCOa

(Da)gt5$105 2e5$105 5$102e2$103 lt5$102

Pressure(MPa)

01e2 1e10 10e30 15e30(brackish)

40e80(seawater)

Permeability(kgm2 s)

lt278 25e278 05e85 lt05

Membranematerialsb

CeramicPS PESPVDF CA

Ceramic PSPES PVDFCA TF

CA TF CA TF

Rejection ParticlesBacteria

MacromoleculesProteinsVirusColloids

High Mwcompounds

Multivalentions

Glucose

High and lowMwcompounds

Monovalentions

Inorganic ionsAmino acids

Separationmechanism

Sieving Sieving Sievingchargeeffectsdiffusion

Solutiondiffusion

aMWCO frac14Molecular weight cut-off of the membrane (corresponding solute rejection 90)bPS polysulfone PES Polyethersulfone PVDF polyvinylidene fluoride CA cellulose acetate TF thin-film

242 Advances in Membrane Technologies for Water Treatment

The main problems of MF are the concentration polarization and fouling phe-nomena Both reduce the water production rate and the efficiency of the whole pro-cess Therefore MF membranes are designed or modified taking into considerationboth phenomena and MF modules are cleaned periodically It must be pointed outthat the selection of a suitable material for MF is an important factor because sol-ute(s) adsorption phenomenon also plays an important role in irreversible foulingeffects

Dong et al (2012) used hydrophilic Mg(OH)2 nanoparticles (NPs) as inorganicfillers to prepare polyvinylidene fluoride PVDFMg(OH)2 MF hybrid membraneswith enhanced antifouling property Due to the addition of Mg(OH)2 NPs a largeamount of hydroxyl (eOH) groups were formed This results in an increase of thehydrophilicity of the prepared hybrid membrane reducing the permeate flux lossescaused by membrane biofouling of Escherichia coli and bovine serum albumin(BSA)

Wu Tang and Wu (2014) developed a novel silica (SiO2)egraphene oxide(GO) nano-hybridpolysulfone (PS) membrane which exhibited excellent anti-fouling ability and improved water permeability maintaining a high rejectionfactor to egg albumin These results were attributed to the specific properties ofSiO2eGO nanohybrid such as the high hydrophilicity and the good dispersionderived from SiO2 NPs

Wang Guan et al (2013) developed novel nanofibrous MF composite mem-branes consisting of a two-layered electrospun polyacrylonitrile (PAN)polyeth-ylene terephthalate (PET) fibrous scaffold infused with oxidized or modifiedcellulose nanofibers which were subsequently grafted by amine such as polyvinyl-amine (PVAm) polyethyleneimine (PEI) or ethylenediamine (see Figure 81) Thesemembranes have a web-like structure with high charge density high porosity andlarge surface area per unit volume These characteristics enabled the membranes tosimultaneously remove bacteria viruses andor toxic heavy metal ions maintaininga good permeation flux

PAN layer CNF in PAN layer Cellulose nanofibers

Figure 81 SEM images of electrospun polyacrylonitrilepolyethylene terephthalate(PANPET) membrane (a) electrospun polyacrylonitrilepolyethylene terephthalate (PANPET) membrane (cross-section) and (b) PANPET membrane infused with polyvinylamine(PVAm) grafted CNF (top view) (c) TEM image taken at a small section of the cellulosenetwork containing pores and individual polymer chains with spaghetti-like configurationReprinted from Wang Guan et al (2013) with permission from Elsevier

Novel and emerging membranes for water treatment 243

822 Ultrafiltration

UF is a PDMP placed between MF and NF However MF and UF both ivolve similarmembrane processes based on the same separation principle being the differencebetween both the structure of the membrane which is asymmetric for UF membranewith a much denser top layer and consequently a much higher hydrodynamic resis-tance than MF UF is commonly used to retain macromolecules and colloids fromaqueous solutions and to remove un-dissolved suspended or emulsified solids fromwater Cellulose acetate (CA) and polyelectrolytes are among the first syntheticpolymers used for UF membranes Today UF membranes are made from awide variety of chemically and thermally stable synthetic polymers including PSPAN polyethersulfone (PES) polyvinyl chloride (PVC) polycarbonate (PC)aliphatic and aromatic polyamides (PA) polyimides (PI) polyarylsulfone (PAS)and PVDF

Kong et al (2014) studied the effect of adding hydrophilic TEMPO-oxidizedcellulose nanofibrils (TOCNs) as a modifying agent on the structure and performanceof cellulose triacetate (CTA) UF membranes The obtained results showed that theincorporation of TOCNs to CTA membranes enhanced its mechanical properties(tensile strength and breakeelongate ratio) and its hydrophilicity resulting in higherpermeate fluxes and better antifouling performance

Another innovative and interesting study was performed by Wang Luo and Chung(2014) who developed tri-bore UF hollow fiber membranes made from Matrimid

and PES polymers with round-shape bore channels and a regular triangle-shape outergeometry Figure 82 shows the mechanism of formation of these UF membranestogether with their scanning electron microscopy (SEM) cross-section images Thisparticular geometry is claimed to be advantageous in terms of uniform mechanicalstrength and enhanced permeation properties due to the evenly distributed membranewall thickness

Recently a variety of inorganic particles or fillers such as SiO2 (Wu Mansouri ampChen 2013 Yu Zhang Zhang Liu amp Zhang 2013 ZhangWang et al 2014) silver(Ag) (Li et al 2013) ferrous ferric oxide (Fe3O4) alumina (Al2O3) (Arsuaga et al2013) zirconia (ZrO2) (Arsuaga et al 2013 Arthanareeswaran amp Thanikaivelan2010 Pang et al 2014) titania (TiO2) (Arsuaga et al 2013 Hamid et al 2011Razmjou Mansouri amp Chen 2011 Razmjou Resosudarmo et al 2012 Zhang Luet al 2013 Zhao Wang Wang Sun amp Zhang 2012) zinc oxide (ZnO) (Hong ampHe 2014) and zeolites (Leo Ahmad Kamil Junaidi Kamal amp Ahmad 2013) havebeen used to develop novel UF MMMs or organiceinorganic hybrid membraneswith improved permeabilities mechanical strengths and fouling resistant ability

Among the different inorganic NPs blended with polymeric membranes TiO2 hasalso been used in numerous studies due to its superhydrophilic photocatalytic andantibacterial properties under ultraviolet (UV) irradiation Rahimpour JahanshahiMollahosseini and Rajaeian (2012) performed an approach to improve the propertiesstructure and performance of PVDFsulfonated polyethersulfone (SPES) blend UFmembranes by using self-assembly of TiO2 NPs on the membrane surface followedby UV irradiation to activate their photocatalytic property The water contact angle

244 Advances in Membrane Technologies for Water Treatment

measurements showed that the hydrophilicity of PVDFSPES membranes wasstrongly improved by TiO2 deposition and UV irradiation The initial permeate fluxesof both pure water and BSA aqueous solutions were lower for the TiO2 depositedmembranes compared to the PVDFSPES membranes However the fouling propen-sity (bacterial activity) was significantly reduced and the long-term permeate fluxstability was enhanced

As was mentioned previously SiO2 is another common NP used for membranemodification SiO2 has the advantage to improve the membrane mechanical proper-ties and membrane porosity Yu et al (2013) used modified SiO2 NPs graftedwith N-Halamine to develop novel hydrophilic PES UF membranes By SEM imageanalysis and contact angle measurements it was confirmed that the additionof this modified SiO2 exerted a slight influence on the microstructure of the PESmembrane but significantly improved its surface hydrophilicity and permeability

Spinneret exit

Color change at air gap region

Externalcoagulant

Uponextrusion

Die swelleffect

Nascent fiber with ablossom geometry

Immediate phaseinversion at the

inner surface

Counterforce

Stretching to from atriangle shape

DF 3 mlmin DF 4 mlmin DF 5 mlmin

DF Dope flowrate

(a)

(b)

1mm

1mm

05mm

05mm

Figure 82 (a) Mechanisms of formation of triangle-shape tri-bore hollow fiber membranes(b) SEM images ofMatrimid tri-bore hollow fiber membranes using different dope compositionsAdapted from Wang et al (2014) with permission from Elsevier

Novel and emerging membranes for water treatment 245

Song and Kim (2013) prepared PS composites UF membranes with poly(1-vinylpyrrolidone) (PVP)-grafted SiO2 NPs (PVP-g-SiO2) by phase inversion method(see Figure 83) The resulted UF membranes exhibited higher water permeate fluxthan PS membranes without scarifying the solute rejection factors when the amountof PVP-g-SiO2 was less than or equal to 5 wt in the casting solution The hydro-philicity of the PVP-g-SiO2 membranes was increased with increasing PVP-g-SiO2

content and the PVP-g-SiO2 membranes exhibited enhanced fouling resistance to-ward non-ionic surfactants

Multifunctional inorganic ZnO NP has also attracted a significant attention due toits outstanding physical and chemical properties including promising catalytic activ-ity and efficient antibacterial and bactericidal capabilities ZnO as an additive NP ismore economical than TiO2 and Al2O3 (Liang Xiao Mo amp Huang 2012) Hong andHe (2014) successfully prepared PVDF UF membrane blended with ZnO NP viaphase inversion method The photocatalysis tests clearly showed that the modifiedPVDF membranes had significant photocatalysis self-cleaning capability whichwas due to the addition of nano-ZnO on the inner surface of the membrane (iethe pore wall) The water permeate flux of nano-ZnOPVDF blend membranes washigher than that of single PVDF membrane decreasing the membrane foulingresistance

Mehrparvar Rahimpour and Jahanshahi (2014) prepared novel modified PES UFmembrane for humic acid removal by blending different concentrations of twohydrophilic organic monomers 35-diaminobenzoic acid (DBA) and gallic acid(GA) with PES Experimental results showed that the different component ratios ofeach monomer affected the structural property of the blended membranes and thetop surface roughness As can be seen in Figure 84 with the addition of DBA andGA the size of the macrovoids became smaller and a denser surface was formed atthe top membrane surface The addition of DBA and GA monomers in the castingsolution increased the water content and the hydrophilicity of the membranes More-over the modified membranes exhibited better antifouling properties and the bestmembrane was prepared with 8 wt DBA and 6 wt GA

During the last 5 years GO nanosheets a two-dimensional carbon material havereceived tremendous attentions thanks to its fantastic properties such as good hydro-philicity easy to be modified and its ability to be dispersed in water yielding to aprolonged and stable suspension Wang et al (2012) used GO nanosheets to developnovel organiceinorganic nanocomposite GOPVDF-blended UF membranes TheGO addition played an important role in the membrane microstructure due to the af-finity of GO with many types of hydrophilic groups which increase the rapid masstransfer between the solvent and non-solvent during phase inversion When the GOcontent increased up to 030 wt lateral pore structures appeared within theGO-blended PVDF membranes (Figure 85) These features enhanced the hydro-philicity mechanical properties and water permeate flux recovery ratio comparedto the PVDF membrane Yu Zhang Zhang Liu Zhang amp Song (2013) also devel-oped a novel hyperbranched polyethylenimine (HPEI)-GOPES blend UF membranewith enhanced antifouling and antibacterial performance via the phase inversionmethod

246 Advances in Membrane Technologies for Water Treatment

NaOH 05molL

Water70ordmC 24h

Silica

SiO2

1-vinyl 2-pyrrolidone

Ethanol + AIBN70ordmC 3h

γ-MPSO

OO

Si O

O

HOHO

HOHO

OHOHOH

OHOH

OH

Silica-OH

(3-methacryloxypropyltrimethoxysilane)

OHOH

OHHO

HO

HOHO

OO

OSi O

O

ON

nPVP-g-silica

SiO2

Methanol + Water70ordmC 24h

NO

SiO2

SiO2

OHOH

OH

HOHO

HOHO

OO

OSi

Silica-MPS

O

O

Figure 83 Reaction procedure for preparation of PVP grafted silica nanoparticles (PVP-g-SiO2)Reprinted from Song and Kim (2013) with permission from Elsevier

Novel

andem

ergingmem

branesfor

water

treatment

247

823 Nanofiltration

NF is a PDMP using semipermeable membranes with a molecular weight cut-off(MWCO) in the range of 05e2 kDa and pore sizes in the range of 05e20 nm (seeTable 82) The origin of NF dates back to 1970s when efforts started to be madedeveloping RO membranes with reasonable water permeate fluxes at relatively lowpressures (Li Fane Ho Matsuura et al 2008) The NF process exhibits separationcharacteristics between RO and UF The specific features of NF membranes are mainlythe combination of very high rejection factors for multivalent ions (99) with low tomoderate rejection factors for monovalent ions (0e70) and high rejection factors(90) for organic compounds with molecular weights above that of the membraneMWCO The major separation mechanisms of NF involve a steric (ie size exclusion)effect and an electrostatic partitioning interaction (ie Donnan exclusion) between agiven NF membrane and a feed aqueous solution (Sun Hatton Chan amp Chung2012) In general the traditional materials used for fabrication of NF membranesare polymers using the phase inversion or the interfacial polymerization (IP)techniques The phase inversion membranes are homogeneous and asymmetric andthey are often made of CA or PES while the NF membranes made by IP are

(a) (b) (c)

Figure 84 SEM cross-section images of (a) neat polyethersulfone (PES) membrane and PESmembrane with (b) 15 wt diaminobenzoic acid (DBA) and (c) 15 wt gallic acid (GA)Reprinted from Mehrparvar et al (2013) with permission from Elsevier

(b)(a)

Figure 85 SEM cross-section images of the GO-blended polyvinylidene fluoride (PVDF)membranes with (a) 0 and (b) 03 wt graphene oxide (GO)Reprinted from Wang et al (2012) with permission from Elsevier

248 Advances in Membrane Technologies for Water Treatment

heterogeneous consisting of a thin-film composite (TFC) layer on the top of an UFsubstrate Typically used polymers are (aromatic) PA PI PS PES sulfonated PSand poly(piperazine amide) among others

Recently there has been a growing interest in developing novel NF hollow fibermembranes because of their flexibility and they are self-supporting and easy to packin modules with high membrane area per unit module volume (Nunes amp Peinemann2001 Yu Cheng et al 2013) Most NF membranes have a TFC structure because ofvarious key advantages compared to asymmetric membranes Sun et al (2012) devel-oped a TFC NF dual-layer hollow fiber membrane via IP of HPEI and isophthaloylchloride on a Torlon polyamide-imide (PAI) dual-layer hollow fiber substrateThis NF membrane exhibited a double repulsion effect a negatively charged substrateand a positively charged selective layer resulting in superior rejection factors (gt99)for both positively and negatively charged dye molecules This type of membrane wassuggested to recycle valuable products and reuse water for textile pharmaceutical andother industries Fang Shi and Wang (2013) prepared TFC NF hollow fiber mem-branes for water softening under low operating pressure (lt2 bar) using IP of PEIand trymesoyl chloride (TMC) on the inner surface of a PES UF membrane substrateThe prepared membrane showed a pure water permeability (PWP) of about17 Lm2 h bar an MWCO of around 500 Da (ie effective pore radius of about065 nm) an MgCl2 rejection factor of 967 and an MgSO4 rejection factor of806 Wei Kong Sun and Chen (2013) prepared also TFC NF hollow fiber mem-branes by IP of piperazine (PIP) and TMC on PSPES UF supporting membranes Thefabricated composite NF hollow fiber membranes had a relatively hydrophilic surfacewith an MWCO of approximately 520 Da a PWP of 119 Lm2 h bar and rejectionfactors of 398 and 962 to NaCl and Na2SO4 respectively Zheng et al (2013)followed the dip-coating method to prepare positively charged TFC NF hollow fibermembranes for cationic dyes removal using polypropylene (PP) hollow fiber MFmembrane as support PVA and polyquaternium-10 as coating materials and glutaral-dehyde (GLA) as a crosslinking agent The prepared membrane had an MWCO of 650Da a PWP of 86 Lm2 h bar and rejection factors of 928 and 350 to CaCl2 andNaCl respectively

Not only hollow fiber membranes have been proposed for NF but also flat sheetmembranes Guan Zhang Han Zhang and Jian (2013) developed TFC NF flat sheetmembranes with improved thermal stability and high performance by coating sulfo-nated copoly (phthalazinone biphenyl ether sulfone SPPBES) on poly(phthalazinoneether sulfone ketone) UF membranes used as support The prepared SPPBES compos-ite membranes exhibited a PWP of 73 Lm2 h bar and 84 Na2SO4 rejection factorTFC NF flat sheet membranes were also prepared by Han (2013) followingthe IP of melamine and TMC on a PEI UF membrane reinforced on PP non-wovenfabric as a backing material The membranes prepared under the optimum preparationconditions achieved a PWP of 34 Lm2 h bar and a rejection factor to Na2SO4 of778

As occurred with membranes designed for UF different polymers and inorganicNPs have been used to improve the NF performance of TFC membranes For instanceto solve the biofouling problem Ag NPs were used Kim Hwang Gamal El-Din and

Novel and emerging membranes for water treatment 249

Liu (2012) used Ag NPs to enhance the antifouling and antibacterial property ofthe surface of NF membranes Recently a stable Ag-doped fly ashpolyurethane(Ag-FAPU) nanocomposite multifunctional spider-web-like membrane was preparedby Pant et al (2014) via one-step electrospinning process using fly ash particles It wassuggested that the direct reduction of the Ag metal precursor (AgNO3) into Ag NPscaused by the solvent of PU (NN-dimethylformamide) in the blend solution couldbe the responsible of the simultaneous formation of spider-web-like nanonets anddeposition of Ag NPs on the surface of the fibers during electrospinning (Figure 86)These features enhanced absorption capacity to remove carcinogenic arsenic and toxicorganic dyes with the antibacterial properties reducing biofouling of the membrane

Mollahosseini and Rahimpour (2014) tried to improve the antibacterial and anti-fouling property of TFC NF membranes by first coating TiO2 NPs on an UF PS mem-brane support followed by the IP of m-phenylenediamine (MPD) and TMC monomerson the coated TiO2 layer With increasing TiO2 content in TFC membranes smootherand thicker surfaces appeared on the selective PA layer reducing the probability ofmembrane fouling by macromolecules

A novel b-cyclodextrin (b-CD)polyester TFC NF membrane was prepared by WuTang and Wu (2013b) via in situ IP of TMC and triethanolamine (TEOA) in presenceof b-CD By adding an appropriate amount of b-CD the membrane NF performancewas improved in terms of water permeability hydrophilicity water permeate fluxrejection factor and antifouling property To enhance acid stability of TFC NFmembranes Yu Zhou et al (2013) followed the IP of TMC and naphthalene-136-trisulfonylchloride (NTSC) and PIP to modify a PS UF membrane used as sup-port It was observed that the increase of the NTSC content in TMC-organic solutionresulted in a more hydrophilic and negatively charged membrane surface with an in-crease of both MWCO and PWP up to 660 Da and 106 Lm2 h bar respectively WuTang and Wu (2013a) performed an improved process to develop high-performancethin-film nanocomposite (TFN) membranes using IP of TEOA and TMC on PS UFsupporting membrane in presence of multiwalled carbon nanotubes (MWCNTs) By

Figure 86 Field-emission scanning electron microscopy (FESEM) images of AgFAPU (M1)mat (obtained from 1 h stirring solution) at different magnifications (a) lower magnification(b) higher magnification (inset is FESEM EDX of AgFAPU (M1) mat)Reprinted from Pant et al (2014) with permission from Elsevier

250 Advances in Membrane Technologies for Water Treatment

using an adequate amount of MWCNTs an appropriate surfactant and a proper reac-tion time MWCNTspolyester nanocomposite membranes can be fabricated with bothhigh permeation flux and excellent selectivity

A novel antifouling mixed matrix PES NF membrane was prepared by ZinadiniZinatizadeh Rahimi Vatanpour and Zangeneh (2014) by embedding GO nano-plates in PES matrix The modified GOPES membranes showed a wider finger-likestructure in comparison to those of the unmodified PES membrane with a significantlyhigher water permeate flux higher hydrophilicity higher dye removal capacity andhigher retention factor In addition it was found that the membrane prepared with05 wt GO exhibited the best antibiofouling property with the highest mean poresize porosity and therefore the greater water permeate flux

Recently positively charged composite NF membranes were prepared via cross-linking modification with an active PEI layer and a PAN substrate (Feng Xu LiTang amp Gao 2014) The PANPEI membrane with a PEI layer crosslinked with120 wt epichlorohydrin at 65 C for 15 h exhibited an optimum NF performancewith relatively high salt rejection factor and a high permeate flux (ie salt rejectionfactors of 9282 6976 and 6131 for feed aqueous solutions containing2000 mgL of MgCl2 MgSO4 and NaCl respectively with the correspondingPWP 163 160 and 179 Lm2 h bar)

Another type of NF membranes aquaporin (AQP)-based biomimetic membranehas attracted increasing attention during the last two years because of its potentialapplication for water purification and seawater desalination attributed to the excep-tionally high permeability and selectivity of AQPs In late 2013 Li et al (2014) intro-duced a novel and simple method to prepare an aquaporin Z (AQP-Z)-basedbiomimetic NF membrane consisting first on the deposition of polydopamine(PDA)-coated proteoliposomes on the surface of a substrate and then crosslinkingPEI with the PAI substrate to encapsulate these deposited proteoliposomes(Figure 87) The resultant AQP-Z-based membrane prepared under the optimal con-ditions achieved 95 MgCl2 rejection factor and a PWP of 37 Lm2 h bar (50higher than the control membrane with inactive AQPs) This type of membrane couldpreserve its activity even under harsh environmental conditions such as a high thermaltreatment at 343 K for 2 h (Li et al 2014)

824 Reverse osmosis

RO is a PDMP used to separate dissolved solids such as ions high and low molecularweight compounds and amino acids from water-based solutions More details on ROmembrane and process applications are summarized in Tables 81 and 82 CurrentlyRO is the most important desalination technology Different types of membranes wereproposed for the RO process but the most common ones are CA membranes andaromatic PA composite membranes The first was an asymmetric CA-based ROmembrane invented by Loeb and Sourirajan in 1960 (Hasson 2010) Today TFCmembranes are the most used in RO applications However the main drawbacksof RO membranes are the ldquotrade-offrdquo between permeability and salt rejectionfactors the membrane fouling and the chlorination problem resulting in a significant

Novel and emerging membranes for water treatment 251

membrane degradation by the presence of chlorine in feed water solutions (Xu Wangamp Li 2013) As a consequence research studies considered these three obstacles indeveloping novel suitable membranes for different RO applications (Misdan Lauamp Ismail 2012)

Innovative RO membrane engineering is still required because of the continuousincreasing demands of desalination and membrane wastewater treatments withenhanced water production rates greater salt rejection factors and overall higher resis-tance to fouling (Li amp Wang 2010) Various strategies have been explored to tacklethese needs among which surface modifications (eg surface coating) and incorpora-tion of specific additives nanoparticles andor co-solvents in the aqueousorganicphase during the IP have been identified to be the most effective (Xu et al 2013)

Wang Dai Zhang Li and Zhang (2013) prepared TFC RO membranes through IPof TMC 24406-biphenyl tetraacyl chloride 2304506-biphenyl pentaacyl chlorideand 220440660-biphenyl hexaacyl chloride with MPD The RO membrane skin layerbecame more negatively charged thinner and smoother as the functionality of the acid

AQPs (LPR 400) Mutants (LPR 400)

(A) (B)

(a) (b)

Figure 87 FESEM images (A and B scale bar 100 nm) and confocal fluorescence microscopyimages (a and b scale bar 50 mm) of different membranes with AQP-Z incorporated membrane(called LPR 400)Reprinted from Li et al (2014) with permission from Elsevier

252 Advances in Membrane Technologies for Water Treatment

chloride monomer increased The lower permeate flux of the highly functional acidchloride-based membrane owing to the greater extent of carboxylic acid groups onthe membrane surface lower surface roughness and lower mobility of the crosslinkedPA chains was observed A novel high permeability PA TFC RO membrane wassynthesized by Zhao Chang and Ho (2013) by introducing four different hydrophilicadditives (o-aminobenzoic acid-triethylamine salt m-aminobenzoic acid-triethylaminesalt 2-(2-hydroxyethl) pyridine and 4-(2-hydroxyethyl) morpholine) in the MPDaqueous solution for IP The obtained optimum membrane exhibited a stable desalina-tion performance over a one-month test with a salt rejection factor of 988 and apermeate flux of 1072 Lm2 h

Functionalized polyethylene glycol (PEG)-based polymers also have been synthe-sized and used to modify the PA TFC RO membrane surface to enhance its antifoulingproperties A comb-like amphiphilic copolymer methylmethacrylate-hydroxypoly(oxyethylene) methacrylate was synthesized by Choi Park Tak and Kwon (2012)via free-radical polymerization and used to modify the surface of the PA TFC ROmembrane by the dip-coating method In addition to introduce antifouling qualityin RO membranes without compromising their separation properties a new type ofpolymer coating made from hydrophilic dendritic polymers was used to modify thesurface of PA TFC RO membrane rendering it more hydrophilic (Sarkar et al2010) As it can be seen in Figure 88 the hydrophilic dendritic polymers were cross-linked to form a network and this was modified with hydrophilic linear chains (egPEG polyvinyl alcohol (PVA) and polyacrylamide) to form polymer brushes whichcan help to prevent formation of biofilm Moreover antimicrobial metal ions such asAg Zn or potassium could be chelated into the polymer network to further preventbiofouling Examples of dendritic polymers are hyperbranched polymers or den-drimers The chosen dendrimers were NH2-terminated PAMAM (PAMAM G2) andPAMAM G2-PEG Both dendrimers polymers can be crosslinked with glycidylether-functionalized au-telechelic PEG to from the PAMAM G2-PEG networkswhich were then used as hydrophilic coating layers

Zwitterionic materials can bind water molecules more strongly than other hydro-philic materials via electrostatically induced hydration Therefore zwitterionic-basedmaterials have been developed as promising candidates for preparation of antifoulingsurfaces (Xu et al 2013) In this sense Azari and Zou (2012) incorporated red-oxfunctional amino acid 3-(34-dihydroxyphenyl)-L-alanine onto commercial PA TFCRO membranes to create a zwitterionic surface resistant to membrane foulingIt was found that the coated membranes exhibited remarkably improved hydrophilic-ity which resulted in an increase of the membrane water permeability preserving thesalt rejection factor

For the purpose of improving the antifouling properties of ROmembranes Ishigamiet al (2012) used the layer-by-layer (LbL) assembly to modify their surfaces by poly(sodium 4-styrenesulfate) (PSS) and poly(allylamine hydrochloride) forming a thinpolyelectrolyte coating layer This antifouling capability increased with increasingthe number of layers due to the enhanced hydrophilicity and smoothness of the mem-brane surface The obtained optimal layer number based on the highest obtained waterpermeability when BSA was used as a foulant solute in water was found to be four

Novel and emerging membranes for water treatment 253

+

Ultra-purewater layer

Organiccontaminant

Bacteria NN NH

N

N

N

N

N

N

N

NH

N

NHN

N

NN

OH

HO OH

OH

OH

HO

OHOH

HO

HO

NH 8

8

8

8

8

8

5

5

6

6

7

N

N

NH

OH

HO

8(NH2)

16(NH2)

HN

O

O))

) )

Hydrophilicbrushes

Dendriticpolymercoating

PAMAMG2

PAMAMG2

PAMAM G2 (dendrimer)

PAMAM G2-PEG (dendrimer)

PAMAM G2-PEG network

AgRO membraneactive layer

Membranesupport

DGE-PEG

O

OO

O

O

O

O

OO OOn

O

O

OO

OO

O

))

)

)

)

)

))

)

)PAMAM

G2

PAMAMG2

PAMAMG2

PAMAMG2

PAMAMG2

PEG network chain segments

Figure 88 Schematic illustration of hydrophilic coating with dendritic polymers on the polyamide (PA) active layer of thin-film composite reverseosmosis (TFC RO) membraneReprinted from Xu et al (2013) and Sarkar et al (2010) with permission from Elsevier

254Advances

inMem

braneTechnologies

forWater

Treatm

ent

It was concluded that LbL assembly on a membrane surface could reduce fouling notonly by electrostatic repulsion between foulant and membrane surface but also byelectrostatic attraction due to the fact that the surface charge could be controlled byalternatively choosing the outer polyelectrolyte

As was pointed out previously chlorination is another trade-off for PA TFC ROmembranes Several researchers focused their studies to enhance chlorine toleranceof PA TFC RO membranes For instance Zhang Wang Wang and Wang (2013)modified a commercial TFC aromatic PA RO membrane (RE2521-TL WoongjinChemical Co Ltd Korea) via free-radical graft polymerization of 3-allyl-55-dimethylhydantoin (ADMH) followed by crosslinking by NN0-methylenebis(a-crylamide) (MBA) After graft polymerization it was observed that the ADMHMBA modified membrane was more hydrophilic with higher salt rejection factorsbut lower permeate flux than the unmodified membrane Recently Ni Meng Liand Zhang (2014) synthesized a novel hydrophilic random terpolymer poly(methyla-cryloxyethyldimethyl benzyl ammonium chloride-r-acryl-amide-r-2-hydroxyethylmethacrylate) via simple free-radical copolymerization using as a coating material acommercial PA TFC RO membranes (LCLE and BW30 DOW Chemical Co LtdMinneapolis USA) to improve their membrane antifouling performance and chlorineresistance (Figure 89) This innovative membrane modification method was demon-strated to be an effective way to render the PA TFC RO membrane more hydrophilicwith antimicrobial properties and more resistance to chlorine and fouling

The introduction of NPs with multifunctionalities in RO TFC membranes couldlead to another breakthrough in membrane desalination by further enhancing waterpermeability without scarifying the salt rejection factors (Misdan et al 2012)Recently a number of organiceinorganic TFC nanocomposite membranes con-taining NPs such as zeolite (Kim Hyeon Chun Chun amp Kim 2013 Liu ampChen 2013) SiO2 (Bao Zhu Wang Wang amp Gao 2013 Park Kim ChunChun amp Kim 2012) Ag (Nisola Park Beltran amp Chung 2012) TiO2 (KimKwak Sohn amp Park 2003) ZnO (Schwartz et al 2012) organo-selenium com-pounds (Vercellino et al 2013) and carbon nanotubes (CNTs) (Baro~na LimChoi amp Jung 2013 Zhao et al 2014) have been investigated for their potentialuse in RO applications Hydrophilic polyether-block-polyamide copolymer solu-tions with different contents of Ag NPs were used to prepare dense films andcoating layers to improve the biofouling resistance of commercial PS UF mem-branes (Nisola et al 2012) ZnO NPs in biocompatible poly(N-isopropylacryla-mide) (PNIPAAm) hydrogel layers were used by Schwartz et al (2012) toprepare novel antimicrobial composite membranes via mixing the PNIPAAm pre-polymer with ZnO NPs followed by spin-coating and photocrosslinking It wasalso found that these ZnOhydrogel nanocomposite coated films exhibited differen-tial toxicity between bacterial and cellular species which qualified them as prom-ising candidates for novel biomedical device coatings

It must be pointed out that different types of zeolite NPs such as NaA zeolite(Huang Qu Dong Zhang amp Chen 2013) NaX zeolite (Fathizadeh Aroujalian ampRaisi 2011) and A zeolite (Pendergast Ghosh amp Hoek 2013) have been added inPA active layer of TFC RO membranes to improve their RO performance

Novel and emerging membranes for water treatment 255

Carboxy-functionalized MWCNTs were incorporated by Zhao et al (2014) in PATFC RO membranes via IP of MPD and TMC to improve their RO performance Thedeveloped nanocomposite membranes were more negatively charged than theMWCNTs-free PA membrane and the increase of MWCNT concentration inthe membrane resulted in a higher permeate flux (50 higher) with almost the samesolute rejection factor

Surface topography modification of TFC RO membranes has been shown tobe another potential approach for fouling mitigation Functional TFC RO mem-brane with well-controlled surface patterns was reported by Maruf GrenbergPellegrino and Ding (2014) As it shown in Figure 810 this membrane fabricationprocedure consisted on the formation of a dense PA layer via IP with TMC and

Figure 89 Schematic diagram for synthesis of the terpolymer P(MDBAC-r-Am-r-HEMA)(a) and surface modification of reverse osmosis (RO) membranes (b)Reprinted from Ni et al (2014) with permission from Elsevier

256 Advances in Membrane Technologies for Water Treatment

NH2

NH2

Trimesoyl chloride O

O

O OO

O

CI

CI

CI

N

NH NH

NH

H

Crosslinked polyamide

m-phenylenediamine

(a)

(b) (c)

Figure 810 (a) Schematic diagram of the interfacial polymerization process used to fabricatethe patterned thin-film composite (TFC) membranes The monomers m-phenylenediamine andtrymesoyl chloride (TMC) react to form a highly crosslinked polyamide (PA) layer at top of thepatterned polyethersulfone (PES) ultrafiltration (UF) membrane used as a support SEM imagesof the non-patterned (b) and patterned (c) TFC membrane surface after 24 h of CaSO4 filtrationexperimentReprinted from Maruf et al (2014) with permission from Elsevier

Novel and emerging membranes for water treatment 257

MPD solutions on a nano-imprinted commercial PES UF support membrane (PWGE Water and Infrastructure) The results showed that the patterned TFC membranehad a separation performance comparable to the current commercial TFC RONFmembranes (ie commercial TFC RO membranes XLE-440 (DOW Filmtec)CPA 3 (Hydranautics) ACM 2 (Trisep) TM-700 (Toray) and commercial TFCNF membranes NF 270 (Hydranautics) and ES-10 (Nitto Denko)) It is importantto note that the surface patterns induced hydrodynamic secondary flow at themembrane-feed interface which is an effective way to decrease concentrationpolarization and reduce scaling effects

83 Vapor pressure gradient driven membraneprocesses

831 Membrane distillation

In contrast to the previous reported PDMPs (MF UF NF and RO) technology whichis isothermal membrane distillation (MD) is a non-isothermal separation process inwhich only molecules in the vapor phase are transported from the feed to the permeatethrough a porous hydrophobic membrane being the driving force the transmembranevapor pressure (Alkhudhiri Darwish amp Hilal 2012 Khayet amp Matsuura 2011)Simultaneous heat and mass transfer occur in MD and different MD configurationscan be used to establish the driving force The difference between the MD configura-tions is localized only in the permeate side of the membrane module In direct contactMD (DCMD) sweeping gas MD (SGMD) and air gap MD (AGMD) the temperaturedifference induces the necessary vapor pressure difference There is also anotherconfiguration termed vacuum MD (VMD) in which the permeate side of the mem-brane is kept at lower pressure by a vacuum pump to establish the transmembranevapor pressure

MD is applied in different fields (desalination treatment of wastewaters containingnon-volatile contaminants including radioactive wastes recovery of valuable com-pounds production of distilled and ultrapure water food medical etc) Comparedto RO separation process MD does not require the application of a high hydrostaticpressure (atmospheric pressure is enough) can process very high salinity brinesincluding those generated by RO and produce water with very high quality whichmeans almost total rejection factors of non-volatile contaminants Moreover MDcan be combined with other processes in integrated systems such as MF UF NFRO and forward osmosis among others making MD promising for various industrialapplications (Khayet amp Matsuura 2011) However MD technology also suffers somedrawbacks such as the low membrane permeability low thermal efficiency high waterproduction cost temperature and concentration polarization effects risk of membranepore wetting fouling and scaling phenomena (Alkhudhiri et al 2012 Khayet ampMatsuura 2011)

MD membranes are porous with a high porosity (void volume fractions) low poretortuosity low thermal conductivity and hydrophobic More details of the membrane

258 Advances in Membrane Technologies for Water Treatment

requirements for an effective MD application were outlined by Khayet (2011) Themost common used techniques for preparation of MD membranes are phase inversionstretching track-etching sintering drywet spinning or wet spinning electrospinningor membrane surface modification by physical or chemical techniques such as coatinggrafting and plasma polymerization Most of the MD membranes are made via phaseinversion methods because of its simplicity

Some authors focused their MD membrane engineering toward the preparation ofdual-layered membranes Wang Teoh and Chung (2011) investigated the morpholog-ical architecture of dual-layer PVDF hollow fiber membranes consisting of a fullyfinger-like macrovoid inner-layer and a totally sponge-like outer-layer Edwie andChung (2012) also designed novel hollow fiber membranes with improved wettingresistances for desalination and salt recovery from highly concentrated NaCl aqueoussolution by DCMD and crystallization Three types of hollow fiber membraneswere fabricated single-layer PVDF dual-layer hydrophobicehydrophobic PVDFand dual-layer hydrophobicehydrophilic PVDFPAN membranes The single-layerPVDF membrane had a superior wetting resistance compared to other types of dual-layer membranes in addition to the smallest reduction of membrane permeability(177) and the highest purity of product water (11e13 mScm)

Su Teoh Wang Su and Chung (2010) performed experimental and theoreticalstudies to investigate the effect of the inner-layer thermal conductivity on theDCMD permeate flux of hydrophobicehydrophilic dual-layer hollow fiber mem-branes prepared by drywet spinning technique Graphite particles and MWCNTswere embedded in the inner hydrophilic layer (Figure 811) It was found that incor-porating graphite alone led to only a minor improvement of the thermal conductivitybut using both graphite and MWCNT the thermal conductivity was increased from059 to 130 Wm K This enhancement of the thermal conductivity was attributedto the network formed by the MWCNT which bridges the polymer nodules As aconsequence of the improved thermal conductivity of the inner-layer a higher vaporpressure difference was established between both sides of the hydrophobic porouslayer (see Figure 811(b) and (c)) and therefore a significant increase of the DCMDpermeate flux was observed from 412 to 669 kgm2 h when using an inlet feed tem-perature of 804 C

Polytetrafluoroethylene (PTFE) is an attractive membrane material for MD due toits superior hydrophobicity chemical resistance thermal stability and mechanicalstrength compared to PP and PVDF It has also excellent stability in many organicand inorganic solvents Teoh Chung and Yeo (2011) prepared PVDFPTFE dual-layer composite hollow fiber membranes for seawater desalination by DCMD Theincorporation of PTFE particles in the PVDF spinning solution could efficiently sup-press the formation of macrovoids and enhance the outer surface hydrophobicity ofthe membranes Recently Zhu et al (2013) also used PTFE for the preparation ofnovel PTFE hydrophobic hollow fiber membranes for VMD by a cold pressingmethod including extrusion stretching and sintering It was observed that thePTFE hollow fiber membranes with four stretching ratios (120 160 180and 220) showed microstructures of nodes interconnected by fibrils (Figure 812)and achieved salt rejection factors of 999 The increase of the stretching ratio

Novel and emerging membranes for water treatment 259

(1)

(2)

(3)

R1

R3

R2

Tf

Tf

T1

T1rsquo

T2rsquoT3rsquo

T2

T3Td

Feed

FeedFeed

FeedDistillate

Distillate

Hydrophobic layerHydrophilic layer

Fillers with highthermal conductivity

(a)

(b)

Nodule

Graphite

Cloisite NA+

MWCNT

Td

Figure 811 (a) Schematic dual-layer hydrophobichydrophilic hollow fiber membranes(1) Cross-section of dual-layer hollow fiber membranes (2) temperature distribution acrossdual-layer hydrophobichydrophilic membranes and (3) temperature distribution across dual-layer hydrophobichydrophilic membranes filled with high thermal conductivity fillers blendedinto the inner-layer (b) SEM images of the inner-layer filled with graphite Cloisite NAthorn andMWCNTReprinted from Su et al (2010) with permission from Elsevier

260 Advances in Membrane Technologies for Water Treatment

significantly increased the pore size and porosity and therefore improved thepermeate flux but decreased the water entry pressure in the pores and reduced themechanical property of the membrane

It is well known that ceramic membranes exhibit excellent chemical structural andthermal stabilities Therefore it would be interesting to explore this type of membranesin MD applications Fang Gao Wang and Cheng (2012) developed a novel hydro-phobic porous alumina ceramic hollow fiber membrane by phase inversion and sinter-ing method for desalination by VMD process When using a feed salt aqueous solution(4 wt NaCl) at 80 C and a vacuum pressure of 4 kPa applied in the lumen side of thehollow fibers a water permeate flux as high as 429 Lm2 h was achieved with a saltrejection factor over 995 which was comparable to polymeric membranes

Yang Wang Shi Fane and Debowski (2011) proposed plasma or chemical modi-fication of the surface of PVDF hollow fiber-based membranes The plasma coatinginvolved a surface activation by exposing the membrane to a continuous plasmaand a polymerization with the vapor of activated monomer On the other hand thechemical modification involved the hydroxylation of the PVDF membrane by anaqueous lithium hydroxide solution and successive reduction with an organic sodiumborohydride (NaBH4) solution followed by crosslinking with a perfluoro-compound ofperfluoropolyether containing ethoxysilane terminal groups Compared to the unmod-ified PVDF hollow fiber membrane both modified membranes showed a greaterhydrophobicity higher liquid entry pressure (LEP) values better mechanicalstrengths smaller maximum pore sizes and narrower pore size distributions withreasonably high DCMD permeate fluxes over a long-term operation (one month) aswell as a high water quality Wei et al (2012) also used plasma surface modificationapproach to develop suitable membranes for MD The surface of asymmetric hydro-philic PES flat sheet and hollow fiber membranes were modified by CF4 plasma poly-merization to form a hydrophobic layer with a water contact angle up to 120 DCMDresults proved that these plasma-modified PES membranes were good membranes forMD with high water permeate fluxes up to 667 kgm2 h using 4 wt NaCl as feedaqueous solution and the salt rejection factors were as high as 9997 A comparativecompilation of DCMD performance for different novel hollow fiber membranes issummarized in Table 83

Figure 812 SEM images of the polytetrafluoroethylene (PTFE) hollow fiber membraneprepared by a stretching ratio of 220 (a) X27 cross-section (b) X1000 inner-surface and(c) X1000 outer-surfaceReprinted from Zhu et al (2013) with permission from Elsevier

Novel and emerging membranes for water treatment 261

Table 83 Direct contact membrane distillation (DCMD) performance of different single and dual-layer hollow fibermembranes fabricated in the literature

Membrane(reference)

Thickness(mm)

Hollow fiberporosity()

Mean poresize (mm)

Feed parameters Distillate parameters

DCMD flux(kgm2 h)Solution

Inlettemperature(C)

Flow rate(ms)

Inlettemperature(C)

Flow rate(ms)

Accurel PP S62a

(Gryta 2007)400 730 022 Concentrated

tap water90 096 20 029 340

PVDF single-layer HFb

(Teoh andChung 2009)

140 860 016 35 wt NaCl 795 19 175 09 461

PVDF single-layer HF(Wang et al2009)

180 867 e 35 wt NaCl 813 18 175 12 792

PVDF single-layer HF (Yanget al 2011)

275 830 0145 35 wt NaCl 70 e 25 e 540

PVDF single-layer HF(Edwie andChung 2012)

1275 696 023c 35 wt NaCl 80 07 17 07 351

PVDF single-layer HF (Houet al 2009)

130 797 028 35 wt NaCl 818 05 20 015 405

PVDF single-layer HF(Song et al2012)

180 719 028 35 wt NaCl 800 e 20 004 275

PVDF single-layer HF(Bonyadiet al 2009)

120 800 044 35 wt NaCl 799 16 194 08 543

PVDF single-layer HF(Drioli et al2013)

230 834 032 Distillatewater

70 e 25 e 220

Si3N4 single-layer HF(Zhang Fanget al 2014)

e 50 074 4 wt NaCl 80 e 20 e 108

PES single-layerHF (Wei et al2012)

210 790 lt007 4 wt NaCl 738 2 20 068 667

PVDFPANdual-layer HF(Bonyadi andChung 2007)

340 800 041 35 wt NaCl 782 16 166 08 374

Continued

Table 83 Continued

Membrane(reference)

Thickness(mm)

Hollow fiberporosity()

Mean poresize (mm)

Feed parameters Distillate parameters

DCMD flux(kgm2 h)Solution

Inlettemperature(C)

Flow rate(ms)

Inlettemperature(C)

Flow rate(ms)

PVDFPAN dual-layer HF (Suet al 2010)

271 700 041 35 wt NaCl 804 18 153 07 669

PVDFPANdual-layer HF(Edwie Teohand Chung2012)

153 754 047c 35 wt NaCl 80 14 17 07 834

PVDFPTFEdual-layer HF(Wang et al2011)

141 840 e 35 wt NaCl 798 14 17 07 986

PVDFPTFEdual-layer HF(Teoh et al2011)

145 825 026c 35 wt NaCl 80 19 175 09 509

aAccurel PP S62 Commercial membrane from GmbH GermanybHF frac14 hollow fibercMaximal pore size others are mean pore size

Novel and emerging flat sheet membranes were also developed for MD KhayetMengual and Matsuura (2005) proposed for the first time the use of double-layeredporous hydrophobichydrophilic composite membranes for DCMD using fluorinatedsurface modifying macromolecules (SMMs) and the phase inversion method Thispromising type of membrane exhibited a thin hydrophobic layer of about 10 mmhigher permeate flux than the commonly used commercial membranes and veryhigh salt rejection factors Then a series of studies were performed using differenttypes of SMMs and hydrophilic host polymers such as PES and PS (Essalhi amp Khayet2012 Khayet 2013 Khayet amp Matsuura 2011 Peng et al 2013 Qtaishat RanaKhayet amp Matsuura 2009 Suk Matsuura Park amp Lee 2010) Recently Khayet(2013) used this type of membrane in nuclear technology for the treatment of low-and intermediate-level radioactive liquid wastes

Dumeacutee Sears Finn Duke and Gray (2010) explored the possibility of developingnovel self-supporting CNT Bucky-Paper (BP) membranes via vacuum filtration forDCMD desalination CNTs have exceptional mechanical electrical and thermal prop-erties It was reported that the CNT-BP membranes exhibited a high water contactangle (113) a high porosity (90) and relatively low thermal conductivity (ie27 kWm2 h) However a decline of the DCMD permeate flux and delamination ofBP membranes due to the formation of micro-cracks were observed To optimizethis type of BP membrane Dumeacutee Sears Scheuroutz et al (2010) developed novelCNT-BP-based composite and supported membranes with significantly improvedMD performance Furthermore the same researchers also coated the CNT-BP mem-branes with a thin layer of PTFE to enhance their hydrophobicity and improve theirmechanical stability without drastically changing their average pore size and porosity(Dumeacutee et al 2011)

Various studies have been focused on the preparation of more hydrophobic mem-branes for MD to reduce the risk of pore wetting A variety of techniques such asplasma treatment lithography sol-gel technology NP deposition on both smoothand rough substrates fluoroalkylsilane coatings and phase separation of a multicom-ponent mixture were considered for fabrication of superhydrophobic surfaces (iewater contact angles higher than 150) Razmjou Arifin Dong Mansouri andChen (2012) prepared a superhydrophobic PVDF membrane for MD applicationswith a 163 water contact angle by generating a hieralchical structure with multilevelroughness and reducing the surface free energy of the membranes via TiO2 coatingthrough a low-temperature hydrothermal process followed by fluorosilanizationof the surface with 1H 1H 2H 2H-perfluorododecyltrichlorosilane (FTCS)(Figure 813) The multilevel hierarchical structure was attributed to the templatingagent which was found to be decisive in the final wettability of the membrane surfaceMoreover TiO2 coating layer on the membrane provided sites for covalent bondingwith hydrolyzed silane coupling agents The modified FTCSeTiO2ePVDF mem-branes showed good thermal and mechanical resistance while both the LEP and watercontact angle of the membrane were increased

During last five years novel flat sheet nanofibrous membranes prepared by electro-spinning were proposed for MD because of their attractive characteristics for MDsuch as the high void volume fraction high hydrophobicity high roughness high

Novel and emerging membranes for water treatment 265

surface-to-mass (volume) ratio interconnected open space between nanofibers lowthermal conductivity etc (Khayet amp Garciacutea-Payo 2011) Self-sustained electro-spun nanofibrous membranes (ENMs) were prepared varying the PVDF concentra-tions in the solvent mixture acetone (Ac)NN-dimethylacetamide from 15 to30 wt and the electrospinning time (Essalhi amp Khayet 2013a Essalhi amp Khayet2014) The optimum PVDF concentration and electrospinning time for ENM forma-tion was found to be 25 wt and 2 h respectively This ENM exhibited a DCMDpermeate flux of 1215 103 kgm2 s and the NaCl rejection factor was higherthan 9999 The permeate flux of the ENMs was lower for longer electrospinningtime Essalhi and Khayet (2013b) developed a novel theoretical model that considered

Figure 813 Mechanism for the fluorosilanization on the surface of polyvinylidene fluoride(PVDF) membranes with and without TiO2 (a) Hydrolyzation of 1H 1H 2H2Heperfluorododecyltrichlorosilane (FTCS) (b) interaction of the hydroxyl groups with thesurface of TiO2 can form covalent bonds of SieOeTi (c) the intermolecular crosslinkingbetween the tri-silanols can lead to a 2D network of polysiloxane (d) condensation of tri-silanolsin the solution in absence of TiO2 coating and (e) surface SEM image of FTCSePVDFmembraneReprinted from Razmjou Arifin et al (2012) with permission from Elsevier

266 Advances in Membrane Technologies for Water Treatment

the gas transport mechanisms through the inter-fiber space of ENMs to predict theDCMD permeate flux of ENMs

Maab et al (2012) used both the phase inversion technique and the electrospinnigmethod to prepare a novel flat sheet porous membrane for MD based on hydrophobicsynthesized aromatic fluorinated polyoxadiazoles and polytriazoles By combining thehigh polymer hydrophobicity (ie 162 water contact angle) the high void volumefraction and the LEP of about 09 bar the salt rejection factors of these membraneswere as high as 9995 and the water permeate fluxes were as high as 85 Lm2 hfor a feed temperature of 80 C and a permeate temperature of 22 C Similarly Princeet al (2012) developed novel ENMs consisting of PVDF blended with clay nano-composite for DCMD An increase of the surface hydrophobicity with the additionof clay nanocomposite was also observed and the prepared PVDF-clay ENMs showedgood DCMD performance

Lalia Guillen-Burrieza Arafat and Hashaikeh (2013) also prepared ENMsfor MD using the copolymer polyvinylidene fluoride-co-hexafluoropropylene(PVDF-HFP) To fuse the fibers together and enhance the ENMs structural integritywith the mechanical properties the ENMs were hot pressed Among all preparedENMs the one fabricated with 10 wt PVDF-HFP in the electrospinning solutionhad the optimum properties for MD application with 026 mm mean pore size 58porosity 125 water contact angle and a LEP value of 1317 kPa

To further improve the hydrophobicity of the PVDF ENMs used in MD the electro-spinning technique was followed by surface modification (Liao Wang amp Fane 2013)As shown in Figure 814 this procedure included PDA surface activation to improvethe adhesive force between the fibers and Ag NPs Ag NP deposition to optimize themorphology and roughness of the membrane and hydrophobic treatment with1-dodecanethiol Compared to the unmodified ENM the integrally-modified mem-brane could achieve a stable MD permeate flux of 316 Lm2 h using a 35 wtNaCl feed aqueous solution at 60 C and permeate temperature of 20 C

To enhance the MD performance of the ENMs Prince AnbharasiShanmugasundaram and Singh (2013) prepared PVDF ENM on a porous PVDFsupported membrane fabricated by the immersion precipitation method and used itfor desalination by AGMD configuration The addition of the nanofiber layer on thePVDF supported membrane was found to increase the permeate flux the salt rejectionfactor and the AGMD long-term performance

832 Pervaporation

PV is a membrane process in which an organic solventwater mixture or an organicsolvent mixture can be selectively separated by a dense membrane placed betweenthe liquid feed mixture and a downstream permeate maintained by a vacuum pumpPV technology is similar to VMD the difference being the characteristics of the mem-brane used which is porous and hydrophobic for VMD There is also a similaritybetween PV and SGMDwhen PV is carried out by gas stripping Both a solution diffu-sion model and a pore flowmodel were considered in PV in which the phase change ofthe diffused species takes place inside the membrane and the desorption step occurs at

Novel and emerging membranes for water treatment 267

Integral modification

(1)

(1)

(2)

(2)

(3)

(3)

I-PVDF

S-PVDFSurface modification

PVDFnanofibers

(a1) (a2)

(b2)

(c2)

(b1)

(c1)

(b)

(a)

Figure 814 (a) Schematic method used for preparation of superhydrophobic polyvinylidenefluoride electrospun nanofibrous membranes (PVDF ENMs) ((1) PDA-modification (2) silvernanoparticle coating (3) 1-dodecanethiol hydrophobic modification) (b) SEM images of un-modified PVDF ENMs ((a1) (a2)) integral modified PVDF ENMs (I-PVDF (b1) (b2)) andsurface modified PVDF ENMs (S-PVDF (c1) (c2))Reprinted from Liao et al (2013) with permission from Elsevier

268 Advances in Membrane Technologies for Water Treatment

the permeate side of the membrane There are mainly two PV applications thoseinvolving hydrophilic membranes used for the dehydration of organicwater mixturessuch as PVA and NaA zeolite membranes (Liu Wei Jin amp Xu 2012) and thoseinvolving hydrophobic membranes used to extract organic solvents or volatile organiccompounds from water such as polydimethylsiloxane (PDMS) and silicalite-1 mem-branes (Liu et al 2012)

Zuo Wang Sun and Chung (2012) developed high-performance hollow fibermembranes for PV dehydration of isopropanol (IPA) consisting of a TFC PA selectivelayer and a porous Torlon 4000T-MV PAI (Solvay Advanced Polymers) substrateprepared via IP of MPD or HPEI with TMC The TFC membrane prepared fromHPEI showed a higher hydrophilicity and fractional free volume than that madefrom MPD which exhibited a better permeability The TFC membrane fabricated un-der the optimum IP conditions from HPEI having a molecular weight of 2 kgmolshowed the best selectivity (ie 624) with a total permeate flux of 13 kgm2 h anda permeate water concentration of 991 wt using a feed composition of 8515 wtIPAwater at 50 C

Wang Gruender and Chung (2010) developed high-performance dual-layer poly-benzimidazole (PBI)PEI hollow fiber membranes for ethylene glycol dehydration byPV process Three types of membranes were prepared PBI flat sheet dense mem-branes which had the lowest PV separation performance due to its severe swellingPBI single-layer hollow fiber membranes which showed better PV separation perfor-mance but had very low tensile strains and PBIPEI dual-layer hollow fiber mem-branes which exhibited the best PV separation performance An enhancement ofthe separation performance of PBIPEI dual-layer hollow fiber membrane afterexposing it to 75 C thermal treatment was also detected A novel approach to preparemultilayered membranes with excellent PV dehydration of different solventwatermixtures has been performed by Zhang Dai and Ji (2011) This approach is basedon a dynamic pressure-driven LbL technique to obtain a covalent assembly ofGLA-crosslinked PEI multilayers on the inner surfaces of PAN hollow fiber poroussubstrate membranes The dynamic pressure-driven LbL assembly was demonstratedto be an effective way to fabricate a defect-free selective layer only on a single side ofthe hollow fiber which has the advantage of reducing the membrane transport resis-tance compared to the membranes made with traditional LbL process Zhang SongJi Wang and Liu (2008) prepared novel polyacrylic acid (PAA)PEI multilayer poly-electrolyte complex (PEC) films on the inner side of hydrolyzed PAN hollow fibermembranes by the dynamic negative pressure LbL technique Others papers also pro-posed an electric field enhanced method to fabricate multilayered PEC membranes byusing modified PA RO membranes as supports and poly(diallyl dimethylammonium-chloride) (PDDA) PEI PSS PAA as assembly components (Yin et al 2010 ZhangQian et al 2008 2009 Zhao An Ji Qian amp Gao 2011) Zhao Qian An and Sun(2010) used charged PEC colloidal aggregates as novel LbL building blocks to prepareLbL multilayered membranes for PV dehydration

As mentioned previously the hydrophilicity of the PV membrane is necessary forthe dehydration of organic solvents The more hydrophilic the membrane is the higherare the water sorption selectivity and water permselectivity To improve the membrane

Novel and emerging membranes for water treatment 269

hydrophilicity many polymer materials were modified using different methods such assulfonation quaternization grafting etc However an increase of the mem-brane hydrophilicity might increase the membrane swelling excessively leading toa membrane with an open structure which reduces the membrane strengthCrosslinking with an organic chemical reagent such as GA PAA maleic acidformaldehyde or fumaric acid is an effective way to reduce membrane swelling ZhangLiu Zhu Xiong and Ren (2009) synthesized quaternized PVA by grafting with(23-epoxypropyl) trimethylammonium chloride to enhance the hydrophilicity andthen crosslinked by GLA to restrict its swelling in an aqueous ethanol solutionRachipudi Kariduraganavar Kittur and Sajjan (2011) also developed PV membranesfor IPA dehydration by crosslinking sulfonated-PVA membranes with sulfophthalicacid (SPTA) The membrane prepared with 15 wt of SPTA showed the highest waterseparation selectivity of 3452 with a total permeate flux of 351102 kgm2 h

Novel chitosan (CS)TiO2 nanocomposite membranes were prepared by Yang LiJiang Lu and Chen (2009) using an in situ solegel process using tetrabutyl titanate asprecursor and acetyl acetone as chelating agent controlling the forming rate of TiO2NPs Compared to CS and CSTiO2 blended membranes CSTiO2 nanocompositemembranes exhibited better PV performance for ethanol dehydration CS-wrappedMWCNTs incorporated in sodium alginate membranes were prepared by SajjanJeevan Kumar Kittur and Kariduraganavar (2013) for the separation of waterIPAmixtures CS was chosen to wrap MWCNTs to improve their hydrophilicity ThePV membranes containing the highest amount of CS-wrapped MWCNTs (2 wt)showed a water selectivity of 6419 and a permeate flux of 2176102 kgm2 h at30 C and 10 wt of water in the feed solution

UVO3 surface modification technology was used by Lai et al (2012) to developPDMS PV membranes for the treatment of 90 wt aqueous ethanol mixture Watercontact angle measurements demonstrated that the hydrophilicity of PDMS mem-branes surface was significantly improved due to the change in its chemical structurefrom siloxane to silica PV results indicated that both the treatment time and the work-ing distance during the UVO3 treatment were important variables affecting the PVperformance of the PDMS membrane

To improve the PV permeate flux of polymeric membranes Xiangli Chen Jin andXu (2007) prepared PDMSceramic composite membrane by depositing uniformly acrosslinked PDMS layer on the top of tubular non-symmetric ZrO2Al2O3 porousceramic supports The resulted PDMSceramic composite membranes exhibited a totalpermeate flux of 195 kgm2 h and an ethanol selectivity of 57 when using a 43 wtethanol feed aqueous mixture Liu Hou Wei Xiangli and Jin (2011) used thesePDMSceramic composite membrane for butanol removal from its dilute aqueoussolution and obtained a total permeate flux of 0457 kgm2 h with an acceptablebutanol selectivity of 261 using a 1 wt butanol in the feed solution at 40 C Becauseof the good long-term stability of these PDMSceramic composite membranes LiuWei et al (2011) decided to use them for recovering biobutanol from biomassacetone-butanol-ethanol (ABE) fermentation broth exhibiting a high average totalflux of 0670 kgm2 h and an applicable ABE selectivity of 167 The performanceof PDMSceramic composite PV membranes was improved by a homogeneous

270 Advances in Membrane Technologies for Water Treatment

dispersion of ZSM-5 zeolite in PDMS via a surface graftcoating approach (LiuXiangli Wei Liu amp Jin 2011) Lue Chien and Mahesh (2011) also prepared aheterogeneous PDMS MMMs containing 10 mm sized zeolite (TZP-9023 TricateZeolites Bitterfeld Germany) for PV of ethanolwater solutions

Zhu Xia Liu and Jin (2010) synthesized hydrophilic crosslinked PVACSlayers on tubular asymmetric ZrO2Al2O3 ceramic supports and demonstrated thatthese ceramic-supported PVACS composite membranes were suitable candidatesfor PV dehydration of alcoholwater and esterwater mixtures The compositemembrane exhibited excellent PV performance achieving a permeate flux of125 kgm2 h and a water selectivity larger than 10000 for 35 wt ethyl acetatewater mixture

To achieve higher membrane stability and improve the PV performance variousattempts have been made to develop blend membranes of PVA with other poly-mers Mixed matrix blend membranes of PVAPVP loaded with phosphomolybdicacid (PMA) were prepared for ethanol dehydration by Magalad Gokavi Raju andAminabhavi (2010) It was demonstrated that the extent of PMA loaded in themembrane affected the PV performance 4 wt of PMA particles in PVAPVPblended matrix resulted in an enhancement of the PV performance but higherPMA amounts (8 and 12 wt) did not result in any improvement of PVperformance

It is worth mentioning that there are few research studies on homogeneous poly-electrolyte complex membranes (HPECMs) although these membranes exhibitgood PV performance for dehydration of different organic aqueous solutions contain-ing IPA ethanol Ac etc The required PECs to prepare HPECMs were synthesized byPAA sodium carboxymethyl cellulose (CMCNa) as anionic polyelectrolyte andPDDA CS poly(2-methacryloyloxy ethyl tri-methylammonium chloride) (PDMC)and poly(N-ethyl-4-vinylpyridiniumbromide) (PEVP) as cationic polyelectrolyteFor example the PECs were first synthesized in aqueous hydrochloric acid Thenthe obtained solid PECs were dissolved in aqueous NaOH and subsequently theHPECMs were made by casting the solution on a clean and smooth porous PS UFmembrane All the fabricated HPECMs from CMCNaePDDA PECs (Zhao QianAn Yang amp Zhang 2008 Zhao Qian An Gui et al 2009) PAAePDDA PECs(Zhao Qian An Yang amp Gui 2009) CMCNaeCS PECs (Zhao Qian An Gaoet al 2009) CMCNaePDMC (Zhao An et al 2010) and CMCNaePEVP (JinAn Zhao Qian amp Zhu 2010) were used in PV dehydration of aqueous IPA or ethanolsolutions and showed very high water selectivity and high permeability (see Table 84)Attempts were also made to improve the mechanical properties of the HPECMsby modification using inorganic SiO2 (Zhao Qian Zhu An Xu et al 2009) andMWCNTs (Zhao Qian Zhu amp An 2009) but even under the optimal membranefabrication conditions the elongations at break were maintained low whereas the ten-sile strengths increased In addition CMCNaePDDA PEC (Zhao Qian An Zhuet al 2009) PDDAePAANa PEC (Zhu Qian Zhao An amp Li 2010) andCMCNaePDMC PEC (Zhu et al 2011) were blended with the commercial PVA toincrease both the mechanical properties and the PV performance of the HPECMs Itwas found that the PECPVA blended membrane with PVA content of 30 wt

Novel and emerging membranes for water treatment 271

Table 84 Pervaporation performance of various polyelectrolytemembranes (PECMs) for dehydration of isopropanol (IPA) andethanol (EtOH) at 70 C

Membrane Feed solutionWaterselectivity

Permeationflux (kgm2 h) Reference

CMCNa-PDDAHPECM55

10 wt waterIPA

960 247 Zhao et al (2008)

CMCNa-PDDAHPECM26

10 wt waterIPA

1791 192 Zhao et al (2008)

CMCNa-PDDAHPECM019

10 wt waterIPA

1049 247 Zhao Qian AnGui et al(2009)

CMCNa-PDDATPECM

10 wt waterIPA

1484 149 Zhao Qian AnGui et al(2009)

PDMC-CMCNaPECM046

10 wt waterIPA

1641 425 Zhao An et al(2010)

PDMC-CMCNaPECM036

10 wt waterIPA

1641 385 Zhao An et al(2010)

CMCNa-PDDA5 wt SiO2

10 wt waterIPA

2186 21 Zhao Qian ZhuAn Xu et al(2009)

CMCNa-PDDA5 wtMWCNTs

10 wt waterIPA

2565 235 Zhao Qian Zhuamp An (2009)

PDDA-PAANa30 wt PVA

10 wt waterIPA

978 236 Zhu Qian et al(2010)

CMCNa-PDMC30 wt PVA

10 wt waterIPA

2084 212 Zhu et al (2011)

CS-CMCNaHPECM039

10 wt waterIPA

1657 217 Zhao Qian AnYang et al(2009)

PERVAP 2510a 10 wt waterIPA

810 075 Chapman et al(2008)

CMCNa-PDDATPECM

10 wt waterEtOH

188 049 Zhao Qian AnGao et al(2009)

CS-CMCNaHPECM0025

10 wt waterEtOH

1062 114 Zhao Qian AnGao et al(2009)

272 Advances in Membrane Technologies for Water Treatment

(PECPVA70-30) achieved the best mechanical properties with a tensile strengthYoungrsquos modulus and elongation at break of about 15 36 and 14 times those ofthe original HPECM respectively

84 Conclusions

The growth of membrane science and technology for water treatment is mainly due tothe developments of materials used for membrane fabrication and for their modifica-tion A wide variety of innovative materials such as chemically and thermally stablepolymers ceramics metallics etc are used for preparing novel membranes ofdifferent configurations and characteristics Moreover various membrane fabricationtechniques are being proposed and improved (ie phase inversion sintering stretch-ing track-etching drywet spinning or wet spinning electrospinning LbL assemblylithography sol-gel etc) and various methods have been developed for membranemodification (ie IP chemical modification surface coating grafting crosslinkingplasma polimerization polymer sulfonation or quaternization nanoparticles (NPs)deposition etc) to improve both the properties of the membranes and theperformance of the specific processes and their applications

It has been observed that the incorporation of different additives polymers andinorganic NPs or fillers (ie zeolite organo-selenium compounds SiO2 Fe3O4Al2O3 ZrO2 TiO2 ZnO CNTs MWCNTs GO TOCNs b-CD zwitterionic mate-rials etc) on the MF UF NF and RO membranes has improved their antifoulingand antibacterial ability has increased their hydrophilicity and water permeability pre-serving or improving the solute rejection factors and in some cases has enhancedmembrane mechanical properties porosity and thermal stability

In contrast to PDMP technology MD is a non-isothermal separation process whichuses porous hydrophobic membranes for water treatment In general there is agrowing interest on MD membrane engineering In particular various researchersare developing composite hollow fiber membranes for MD with a dual-layered config-uration (hydrophobicehydrophobic or hydrophobicehydrophilic) to reduce mem-brane pore wetting temperature and concentration polarization effects fouling and

Table 84 Continued

Membrane Feed solutionWaterselectivity

Permeationflux (kgm2 h) Reference

PECM0284 10 wt waterEtOH

1419 093 Jin et al (2010)

PECM0440 10 wt waterEtOH

782 132 Jin et al (2010)

aPERVAP 2510 commercial membrane from Sulzer Chemtech GmbH Linden Germany

Novel and emerging membranes for water treatment 273

scaling phenomena The addition of different materials and NPs (ie graphite parti-cles PTFE Al2O3 ZrO2 TiO2 ZnO CNTs MWCNTs SMMs etc) resulted ingreater membrane hydrophobicity and thermal conductivity higher LEP values waterquality and long-term operation and also better mechanical strengths permeatefluxes and salt rejections

High permeate fluxes and water selectivities were achieved when ceramic-supported composite membranes and HPECMs have been used for PV dehydrationof organic alcoholwater and esterwater mixtures containing solvents such as IPAethanol Ac etc Some attempts were made to improve the mechanical properties ofHPECMs using inorganic SiO2 and MWCNTs or blending their PEC with PVA

85 Future trends

Although the current use of membrane technology for water treatment is constantlygrowing thanks to the discovery and development of novel and advanced materialsfor membrane fabrication and modification there are still some involved phenomenawith effects that need to be reduced further (eg temperature and concentration polar-ization phenomena membrane fouling long-term operation etc)

Innovative membrane engineering is required because of the still continuousincreasing demands of desalination and treatments of different and emerging typesof wastewaters with improved water production rates greater salt rejection factorsand higher resistance to fouling

PMDPs and MD technologies can be adequately integrated for water productionoffering a wide range of industrial water treatment applications

List of acronyms

b-CD b-cyclodextrinABE Acetone-butanol-ethanolAc AcetoneADMH 3-allyl-55-dimethylhydantoinAg SilverAGMD Air gap membrane distillationAl2O3 AluminaAQP AquaporinAQP-Z Aquaporin ZBP Bucky-PaperBSA Bovine serum albuminCA Cellulose acetateCMCNA Sodium carboxymethyl celluloseCNTs Carbon nanotubesCS ChitosanCTA Cellulose triacetate

274 Advances in Membrane Technologies for Water Treatment

DBA 35-diaminobenzoic acidDCMD Direct contact MDEDX Energy-dispersive X-ray spectroscopyENMs Electrospun nanofibrous membranesFA Fly ashFe3O4 Ferrous ferric oxideFESEM Field-emission scanning electron microscopyFTCS 1H 1H 2H 2H-perfluorododecyltrichlorosilaneGA Gallic acidGLA GlutaraldehydeGO Graphene oxideHPECMs Homogeneous polyelectrolyte complex membranesHPEI Hyperbranched polyethylenimineIP Interfacial polymerizationIPA IsopropanolLbL Layer-by-layerLEP Liquid entry pressureMBA NN0-methylenebis(acrylamide)MD Membrane distillationMF MicrofiltrationMMMs Mixed matrix membranesMPD m-phenylenediamineMWCNTs Multiwalled carbon nanotubesNaBH4 Sodium borohydrideNF NanofiltrationNPs NanoparticlesNTSC Naphthalene-136-trisulfonylchloridePA PolyamidesPAA Polyacrylic acidPAH Poly (allylamine hydrochloride)PAI Polyamide-imidePAMAM G2 NH2-terminated PAMAMPAMAM Amine-functional polyamidoaminePAN PolyacrylonitrilePAS PolyarylsulfonePBI PolybenzimidazolePC PolycarbonatePDA PolydopaminePDDA Poly(diallyl dimethylammoniumchloride)PDMC Poly(2-methacryloyloxy ethyl tri-methylammonium chloride)PDMS PolydimethylsiloxanePEC Polyelectrolyte complexPEG Polyethylene glycolPEI PolyethyleneiminePES PolyethersulfonePET Polyethylene terephthalatePEVP Poly(N-ethyl-4-vinylpyridiniumbromide)PI PolyimidesPIP Piperazine

Novel and emerging membranes for water treatment 275

PMA Phosphomolybdic acidPNIPAAm Poly(N-isopropylacrylamide)PP PolypropylenePS PolysulfonePSS Poly(sodium 4-styrenesulfate)PTFE PolytetrafluoroethylenePU PolyurethanePVA Polyvinyl alcoholPVAm PolyvinylaminePVC Polyvinyl chloridePVDF Polyvinylidene fluoridePVDF-HFP Polyvinylidene fluoride-co-hexafluoropropylenePVP Poly(1-vinylpyrrolidone)PWP Pure water permeabilityRO Reverse osmosisSEM Scanning electron microscopySGMD Sweeping gas MDSiO2 SilicaSMMs Fluorinated surface modifying macromoleculesSPES Sulfonated polyethersulfoneSPPBES Sulfonated copoly (phthalazinone biphenyl ether sulfone)SPTA Sulfophthalic acidTEOA TriethanolamineTFC Thin-film compositeTFN Thin film nano-compositetio2 TitaniaTMC Trymesoyl chloridetocns TEMPO-oxidized cellulose nano-fibrilsUF UltrafiltrationVMD Vacuum MDZnO Zinc oxideZrO2 Zirconia

References

Alkhudhiri A Darwish N amp Hilal N (2012) Membrane distillation A comprehensivereview Desalination 287 2e18

Arsuaga J M Sotto A Del Rosario G Martiacutenez A Molina S Teli S B et al (2013)Influence of the type size and distribution of metal oxide particles on the properties ofnanocomposite ultrafiltration membranes Journal of Membrane Science 428 131e141

Arthanareeswaran G amp Thanikaivelan P (2010) Fabrication of cellulose acetateezirconiahybrid membranes for ultrafiltration applications Performance structure and foulinganalysis Separation and Purification Technology 74 230e235

Azari S amp Zou L (2012) Using zwitterionic amino acid l-DOPA to modify the surface of thinfilm composite polyamide reverse osmosis membranes to increase their fouling resistanceJournal of Membrane Science 401e402 68e75

276 Advances in Membrane Technologies for Water Treatment

Bao M Zhu G Wang L Wang M amp Gao C (2013) Preparation of monodispersedspherical mesoporous nanosilicaepolyamide thin film composite reverse osmosismembranes via interfacial polymerization Desalination 309 261e266

Baro~na G N B Lim J Choi M amp Jung B (2013) Interfacial polymerization of polyamide-aluminosilicate SWNT nanocomposite membranes for reverse osmosis Desalination 325138e147

Bonyadi S amp Chung T S (2007) Flux enhancement in membrane distillation by fabricationof dual layer hydrophilicehydrophobic hollow fiber membranes Journal of MembraneScience 306 134e146

Bonyadi S Chung T S amp Rajagopalan R (2009) A novel approach to fabricate macrovoid-free and highly permeable PVDF hollow fiber membranes for membrane distillationAIChE Journal 55 828e833

Chapman P D Oliveira T Livingston A G amp Li K (2008) Membranes for the dehy-dration of solvents by pervaporation Journal of Membrane Science 318 5e37

Choi H Park J Tak T amp Kwon Y N (2012) Surface modification of seawater reverseosmosis (SWRO) membrane using methyl methacrylate-hydroxy poly(oxyethylene) meth-acrylate (MMA-HPOEM) comb-polymer and its performance Desalination 291 1e7

Dong C He G Li H Zhao R Han Y amp Deng Y (2012) Antifouling enhancement ofpoly(vinylidene fluoride) microfiltration membrane by adding Mg(OH)2 nanoparticlesJournal of Membrane Science 387e388 40e47

Drioli E Ali A Simone S Macedonio F Al-Jlil S A Al Shabonah F S et al (2013)Novel PVDF hollow fiber membranes for vacuum and direct contact membrane distillationapplications Separation and Purification Technology 115 27e38

Dumeacutee L Campbell J L Sears K Scheuroutz J Finn N Duke M et al (2011) The impact ofhydrophobic coating on the performance of carbon nanotube bucky-paper membranesin membrane distillation Desalination 283 64e67

Dumeacutee L Sears K Finn N Duke M amp Gray S (2010) Carbon nanotube based compositemembranes for water desalination by membrane distillation Desalination Water Treat-ment 17 72e79

Dumeacutee L F Sears K Scheuroutz J Finn N Huynh C Hawkins S et al (2010) Charac-terization and evaluation of carbon nanotube Bucky-Paper membranes for direct contactmembrane distillation Journal of Membrane Science 351 36e43

Edwie F amp Chung T S (2012) Development of hollow fiber membranes for water and saltrecovery from highly concentrated brine via direct contact membrane distillation andcrystallization Journal of Membrane Science 421e422 111e123

Edwie F Teoh M M amp Chung T S (2012) Effects of additives on dual-layer hydro-phobicehydrophilic PVDF hollow fiber membranes for membrane distillation andcontinuous performance Chemical Engineering Science 68 567e578

Essalhi M amp Khayet M (2012) Surface segregation of fluorinated modifying macro-molecule for hydrophobichydrophilic membrane preparation and application in air gapand direct contact membrane distillation Journal of Membrane Science 417e418163e173

Essalhi M amp Khayet M (2013a) Self-sustained webs of polyvinylidene fluoride electrospunnanofibers at different electrospinning times 1 desalination by direct contact membranedistillation Journal of Membrane Science 433 167e179

Essalhi M amp Khayet M (2013b) Self-sustained webs of polyvinylidene fluoride electrospunnanofibers at different electrospinning times 2 theoretical analysis polarization effects andthermal efficiency Journal of Membrane Science 433 180e191

Novel and emerging membranes for water treatment 277

Essalhi M amp Khayet M (2014) Self-sustained webs of polyvinylidene fluoride electrospunnano-fibers Effects of polymer concentration and desalination by direct contact membranedistillation Journal of Membrane Science 455 133e143

Fang H Gao J F Wang H T amp Chen C S (2012) Hydrophobic porous alumina hollowfiber for water desalination via membrane distillation process Journal of MembraneScience 403e404 41e46

Fang W Shi L ampWang R (2013) Interfacially polymerized composite nanofiltration hollowfiber membranes for low-pressure water softening Journal of Membrane Science 430129e139

Fathizadeh M Aroujalian A amp Raisi A (2011) Effect of added NaX nano-zeolite intopolyamide as a top thin layer of membrane on water flux and salt rejection in a reverseosmosis process Journal of Membrane Science 375 88e95

Feng C Xu J Li M Tang Y amp Gao C (2014) Studies on a novel nanofiltration membraneprepared by cross-linking of polyethyleneimine on polyacrylonitrile substrate Journal ofMembrane Science 451 103e110

Gryta M (2007) Influence of polypropylene membrane surface porosity on the performance ofmembrane distillation process Journal of Membrane Science 287 67e78

Guan S Zhang S Han R Zhang B amp Jian X (2013) Preparation and properties of novelsulfonated copoly (phthalazinone biphenyl ether sulfone) composite nanofiltrationmembrane Desalination 318 56e63

Hamid N A A Ismail A F Matsuura T Zularisam A W Lau W J Yuliwati E et al(2011) Morphological and separation performance study of polysulfonetitanium dioxide(PSFTiO2) ultrafiltration membranes for humic acid removal Desalination 273 85e92

Han R (2013) Formation and characterization of (melamineeTMC) based thin film compositeNF membranes for improved thermal and chlorine resistances Journal of MembraneScience 425e426 176e181

Hasson D (2010) In memory of Sidney Loeb Desalination 261 203e204Hong J amp He Y (2014) Polyvinylidene fluoride ultrafiltration membrane blended with nano-

ZnO particle for photo-catalysis self-cleaning Desalination 332 67e75Hou D Wang J Qu D Luan Z amp Ren X (2009) Fabrication and characterization of

hydrophobic PVDF hollow fiber membranes for desalination through direct contactmembrane distillation Separation and Purification Technology 69 78e86

Huang H Qu X Dong H Zhang L amp Chen H (2013) Role of NaA zeolites in theinterfacial polymerization process towards a polyamide nanocomposite reverse osmosismembrane RSC Advances 3 8203e8207

Ishigami T Amano K Fujii A Ohmukai Y Kamio E Maruyama T et al (2012)Fouling reduction of reverse osmosis membrane by surface modification via layer-by-layerassembly Separation and Purification Technology 99 1e7

Jin H An Q Zhao Q Qian J amp Zhu M (2010) Pervaporation dehydration of ethanol byusing polyelectrolyte complex membranes based on poly (N-ethyl-4-vinylpyridiniumbromide) and sodium carboxymethyl cellulose Journal of Membrane Science 347183e192

Khayet M (2011) Membranes and theoretical modeling of membrane distillation A reviewAdvances in Colloid and Interface Science 164 56e88

Khayet M (2013) Treatment of radioactive wastewater solutions by direct contact membranedistillation using surface modified membranes Desalination 321 60e66

Khayet M amp Garciacutea-Payo M C (2011) Nanostructured flat membranes for direct contactmembrane distillation PCTES2011000091

278 Advances in Membrane Technologies for Water Treatment

Khayet M amp Matsuura T (2011) Membrane distillation Principles and applicationsThe Netherlands Elsevier

Khayet M Mengual J I amp Matsuura T (2005) Porous hydrophobichydrophilic compositemembranes Journal of Membrane Science 252 101e113

Kim E S Hwang G Gamal El-Din M amp Liu Y (2012) Development of nanosilver andmulti-walled carbon nanotubes thin-film nanocomposite membrane for enhanced watertreatment Journal of Membrane Science 394e395 37e48

Kim S G Hyeon D H Chun J H Chun B H amp Kim S H (2013) Nanocompositepoly(arylene ether sulfone) reverse osmosis membrane containing functionalzeolite nanoparticles for seawater desalination Journal of Membrane Science 44310e18

Kim S H Kwak S Y Sohn B H amp Park T H (2003) Design of TiO2 nanoparticle self-assembled aromatic polyamide TFC membrane as an approach to solve bio-foulingproblem Journal of Membrane Science 211 157e165

Kong L Zhang D Shao Z Han B Lv Y Gao K et al (2014) Superior effect ofTEMPO-oxidized cellulose nanofibrils (TOCNs) on the performance of cellulose triacetate(CTA) ultrafiltration membrane Desalination 332 117e125

Lai C L Fu Y J Chen J T An Q F Liao K S Fang S C et al (2012) Pervaporationseparation of ethanolwater mixture by UVO3-modified PDMS membranes Separationand Purification Technology 100 15e21

Lalia B S Guillen-Burrieza E Arafat H A amp Hashaikeh R (2013) Fabrication andcharacterization of polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) electro-spun membranes for direct contact membrane distillation Journal of Membrane Science428 104e115

Leo C P Ahmad Kamil N H Junaidi M U M Kamal S N M amp Ahmad A L (2013)The potential of SAPO-44 zeolite filler in fouling mitigation of polysulfone ultrafiltrationmembrane Separation and Purification Technology 103 84e91

Li D amp Wang H (2010) Recent developments in reverse osmosis desalination membranesJournal of Materials Chemistry 20 4551e4566

Li N N Fane A G Ho W S W amp Matsuura T (2008) Advanced membrane technologyand applications New Jersey John Wiley amp Sons Inc

Li X Pang R Li J Sun X Shen J Han W et al (2013) In situ formation of Agnanoparticles in PVDF ultrafiltration membrane to mitigate organic and bacterial foulingDesalination 324 48e56

Li X Wang R Wicaksana F Tang C Torres amp Fane A G (2014) Preparation of highperformance nanofiltration (NF) membranes incorporated with aquaporin Z Journal ofMembrane Science 450 181e188

Liang S Xiao K Mo Y amp Huang X (2012) A novel ZnO nanoparticle blended poly-vinylidene fluoride membrane for anti-irreversible fouling Journal of Membrane Science394e395 184e192

Liao Y Wang R amp Fane A G (2013) Engineering superhydrophobic surface onpoly(vinylidene fluoride) nanofiber membranes for direct contact membrane distillationJournal of Membrane Science 440 77e87

Liu Y amp Chen X (2013) High permeability and salt rejection reverse osmosis by a zeolitenano-membrane Physical Chemistry Chemical Physics 15 6817e6824

Liu G Hou D Wei W Xiangli F amp Jin W (2011) Pervaporation separation of butanol-water mixtures using polydimethylsiloxaneceramic composite membrane ChineseJournal of Chemical Engineering 19 40e44

Novel and emerging membranes for water treatment 279

Liu G Wei W Jin W amp Xu N (2012) Polymerceramic composite membranes and theirapplication in pervaporation processChinese Journal of Chemical Engineering 20 62e70

Liu G Wei W Wu H Dong X Jiang M amp Jin W (2011) Pervaporation performance ofPDMSceramic composite membrane in acetone butanol ethanol (ABE) fermentationePVcoupled process Journal of Membrane Science 373 121e129

Liu G Xiangli F Wei W Liu S amp Jin W (2011) Improved performance of PDMSceramic composite pervaporation membranes by ZSM-5 homogeneously dispersed inPDMS via a surface graftcoating approach Chemical Engineering Journal 174495e503

Lue S J Chien C F amp Mahesh K P O (2011) Pervaporative concentration of etha-nolewater mixtures using heterogeneous polydimethylsiloxane (PDMS) mixed matrixmembranes Journal of Membrane Science 384 17e26

Maab H Francis L Al-Saadi A Aubry C Ghaffour N Amy G et al (2012) Synthesisand fabrication of nanostructured hydrophobic polyazole membranes for low-energy waterrecovery Journal of Membrane Science 423e424 11e19

Magalad V T Gokavi G S Raju K V S N amp Aminabhavi T M (2010) Mixed matrixblend membranes of poly(vinyl alcohol)epoly(vinyl pyrrolidone) loaded with phospho-molybdic acid used in pervaporation dehydration of ethanol Journal of Membrane Science354 150e161

Maruf S H Greenberg A R Pellegrino J amp Ding Y (2014) Fabrication and character-ization of a surface-patterned thin film composite membrane Journal of MembraneScience 452 11e19

Mehrparvar A Rahimpour A amp Jahanshahi M (2014) Modified ultrafiltration membranesfor humic acid removal Journal of the Taiwan Institute of Chemical Engineers 45275e282

Misdan N Lau W J amp Ismail A F (2012) Seawater reverse osmosis (SWRO) desalinationby thin-film composite membranemdashcurrent development challenges and future prospectsDesalination 287 228e237

Mollahosseini A amp Rahimpour A (2014) Interfacially polymerized thin film nanofiltrationmembranes on TiO2 coated polysulfone substrate Journal of Industrial and EngineeringChemistry 20 1261e1268

Ni L Meng J Li X amp Zhang Y (2014) Surface coating on the polyamide TFC ROmembrane for chlorine resistance and antifouling performance improvement Journal ofMembrane Science 451 205e215

Nisola G M Park J S Beltran A B amp Chung W J (2012) Silver nanoparticles in apolyether-block-polyamide copolymer towards antimicrobial and antifouling membranesRCS Advances 2 2439e2448

Nunes S P amp Peinemann K V (2001) Membrane technology in the chemical IndustryWeinheim Wiley-VCH Verlag GmbH

Pang R Li X Li J Lu Z Sun X amp Wang L (2014) Preparation and characterization ofZrO2PES hybrid ultrafiltration membrane with uniform ZrO2 nanoparticles Desalination332 60e66

Pant H R Kim H J Joshi M K Pant B Park C H Kim J I et al (2014) One-stepfabrication of multifunctional composite polyurethane spider-web-like nanofibrous mem-brane for water purification Journal of Hazardous Materials 264C 25e33

Park S Y Kim S G Chun J H Chun B H amp Kim S H (2012) Fabrication andcharacterization of the chlorine-tolerant disulfonated poly(arylene ether sulfone)hyperbranched aromatic polyamide-grafted silica composite reverse osmosis membraneDesalination and Water Treatment 43 221e229

280 Advances in Membrane Technologies for Water Treatment

Pendergast M M Ghosh A K amp Hoek E M V (2013) Separation performance andinterfacial properties of nanocomposite reverse osmosis membranes Desalination 308180e185

Peng Y Dong Y Fan H Chen P Li Z amp Jiang Q (2013) Preparation of polysulfonemembranes via vapor-induced phase separation and simulation of direct-contact membranedistillation by measuring hydrophobic layer thickness Desalination 316 53e66

Porter M C (Ed) (1988) Handbook of industrial membrane technology Westwood NJNoyer Publications

Prince J A Anbharasi V Shanmugasundaram T S amp Singh G (2013) Preparation andcharacterization of novel triple layer hydrophilicehydrophobic composite membrane fordesalination using air gap membrane distillation Separation and Purification Technology118 598e603

Prince J A Singh G Rana D Matsuura T Anbharasi V amp Shanmugasundaram T S(2012) Preparation and characterization of highly hydrophobic poly(vinylidene fluoride)eclay nanocomposite nanofiber membranes (PVDFeclay NNMs) for desalination usingdirect contact membrane distillation Journal of Membrane Science 397e398 80e86

Qtaishat M Rana D Khayet M amp Matsuura T (2009) Preparation and characterization ofnovel hydrophobichydrophilic polyetherimide composite membranes for desalination bydirect contact membrane distillation Journal of Membrane Science 327 264e273

Rachipudi P S Kariduraganavar M Y Kittur A A amp Sajjan A M (2011) Synthesis andcharacterization of sulfonated-poly(vinyl alcohol) membranes for the pervaporationdehydration of isopropanol Journal of Membrane Science 383 224e234

Rahimpour A Jahanshahi M Mollahosseini A amp Rajaeian B (2012) Structural andperformance properties of UV-assisted TiO2 deposited nano-composite PVDFSPESmembranes Desalination 285 31e38

Razmjou A Arifin E Dong G Mansouri J amp Chen V (2012) Superhydrophobicmodification of TiO2 nanocomposite PVDF membranes for applications in membranedistillation Journal of Membrane Science 415e416 850e863

Razmjou A Mansouri J amp Chen V (2011) The effects of mechanical and chemicalmodification of TiO2 nanoparticles on the surface chemistry structure and fouling per-formance of PES ultrafiltration membranes Journal of Membrane Science 378 73e84

Razmjou A Resosudarmo A Holmes R L Li H Mansouri J amp Chen V (2012) Theeffect of modified TiO2 nanoparticles on the polyethersulfone ultrafiltration hollow fibermembranes Desalination 287 271e280

Sajjan A M Jeevan Kumar B K Kittur A A amp Kariduraganavar M Y (2013) Novelapproach for the development of pervaporation membranes using sodium alginate andchitosan-wrapped multiwalled carbon nanotubes for the dehydration of isopropanolJournal of Membrane Science 425e426 77e88

Sarkar A Carver P I Zhang T Merrington A Bruza K J Rousseau J L et al (2010)Dendrimer-based coatings for surface modification of polyamide reverse osmosis mem-branes Journal of Membrane Science 349 421e428

Schwartz V B Theacutetiot F Ritz S Peuroutz S Choritz L Lappas A et al (2012) Antibacterialsurface coatings from zinc oxide nanoparticles embedded in poly(N-isopropylacrylamide)hydrogel surface layers Advanced Functional Materials 22 2376e2386

Song H J amp Kim C K (2013) Fabrication and properties of ultrafiltration membranescomposed of polysulfone and poly(1-vinylpyrrolidone) grafted silica nanoparticlesJournal of Membrane Science 444 318e326

Song Z Xing M Zhang J Li B amp Wang S (2012) Determination of phase diagram of aternary PVDFg-BLDOP system in TIPS process and its application in preparing hollow

Novel and emerging membranes for water treatment 281

fiber membranes for membrane distillation Separation and Purification Technology 90221e230

Su M Teoh M M Wang K Y Su J amp Chung T S (2010) Effect of inner-layer thermalconductivity on flux enhancement of dual-layer hollow fiber membranes in direct contactmembrane distillation Journal of Membrane Science 364 278e289

Suk D E Matsuura T Park H B amp Lee Y M (2010) Development of novel surfacemodified phase inversion membranes having hydrophobic surface-modifying macromol-ecule (nSMM) for vacuum membrane distillation Desalination 261 300e312

Sun S P Hatton T A Chan S Y amp Chung T-S (2012) Novel thin-film compositenanofiltration hollow fiber membranes with double repulsion for effective removal ofemerging organic matters from water Journal of Membrane Science 401e402152e162

Teoh M M amp Chung T S (2009) Membrane distillation with hydrophobic macrovoid-freePVDFePTFE hollow fiber membranes Separation and Purification Technology 66229e236

Teoh M M Chung T S amp Yeo Y S (2011) Dual-layer PVDFPTFE composite hollowfibers with a thin macrovoid-free selective layer for water production via membranedistillation Chemical Engineering Journal 171 684e691

Vercellino T Morse A Tran P Song L Hamood A Reid T et al (2013) Attachment oforgano-selenium to polyamide composite reverse osmosis membranes to inhibit biofilmformation of S aureus and E coli Desalination 309 291e295

Wang K Y Foo S W amp Chung T S (2009) Mixed matrix PVDF hollow fiber membraneswith nanoscale pores for desalination through direct contact membrane distillationIndustrial amp Engineering Chemistry Research 48 4474e4483

Wang P Luo L amp Chung T S (2014) Tri-bore ultra-filtration hollow fiber membranes witha novel triangle-shape outer geometry Journal of Membrane Science 452 212e218

Wang P Teoh M M amp Chung T S (2011) Morphological architecture of dual-layer hollowfiber for membrane distillation with higher desalination performance Water Research 455489e5500

Wang R Guan S Sato A Wang X Wang Z Yang R et al (2013) Nanofibrousmicrofiltration membranes capable of removing bacteria viruses and heavy metal ionsJournal of Membrane Science 446 376e382

Wang T Dai L Zhang Q Li A amp Zhang S (2013) Effects of acyl chloride monomerfunctionality on the properties of polyamide reverse osmosis (RO) membrane Journal ofMembrane Science 440 48e57

Wang Y Gruender M amp Chung T S (2010) Pervaporation dehydration of ethylene glycolthrough polybenzimidazole (PBI)-based membranes 1 Membrane fabrication Journal ofMembrane Science 363 149e159

Wang Z Yu H Xia J Zhang F Li F Xia Y et al (2012) Novel GO-blended PVDFultrafiltration membranes Desalination 299 50e54

Wei X Kong X Sun C amp Chen J (2013) Characterization and application of a thin-filmcomposite nanofiltration hollow fiber membrane for dye desalination and concentrationChemical Engineering Journal 223 172e182

Wei X Zhao B Li X M Wang Z He B Q He T et al (2012) CF4 plasma surfacemodification of asymmetric hydrophilic polyethersulfone membranes for direct contactmembrane distillation Journal of Membrane Science 407e408 164e175

Wu H Mansouri J amp Chen V (2013) Silica nanoparticles as carriers of antifouling ligandsfor PVDF ultrafiltration membranes Journal of Membrane Science 433 135e151

282 Advances in Membrane Technologies for Water Treatment

Wu H Tang B ampWu P (2013a) Optimization characterization and nanofiltration propertiestest of MWNTspolyester thin film nanocomposite membrane Journal of MembraneScience 428 425e433

Wu H Tang B amp Wu P (2013b) Preparation and characterization of anti-foulingb-cyclodextrinpolyester thin film nanofiltration composite membrane Journal ofMembrane Science 428 301e308

Wu H Tang B amp Wu P (2014) Development of novel SiO2eGO nanohybridpoly-sulfone membrane with enhanced performance Journal of Membrane Science 45194e102

Xiangli F Chen Y Jin W amp Xu W (2007) Polydimethylsiloxane (PDMS)eceramic com-posite membrane with high flux for pervaporation of ethanol-water mixtures Industrail ampEngineering Chemistry Research 46 2224e2230

Xu G R Wang J N amp Li C J (2013) Strategies for improving the performance of thepolyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes Surfacemodifications and nanoparticles incorporations Desalination 328 83e100

Yang D Li J Jiang Z Lu L amp Chen X (2009) ChitosanTiO2 nanocompositepervaporation membranes for ethanol dehydration Chemical Engineering Science 643130e3137

Yang X Wang R Shi L Fane A G amp Debowski M (2011) Performance improvement ofPVDF hollow fiber-based membrane distillation process Journal of Membrane Science369 437e447

Yin M Qian J An Q Zhao Q Gui Z amp Li Y (2010) Polyelectrolyte layer-by-layer self-assembly at vibration condition and the pervaporation performance of as-sembly multilayer films in dehydration of isopropanol Journal of Membrane Science358 43e50

Yu H Zhang X Zhang Y Liu J amp Zhang H (2013) Development of a hydrophilic PESultrafiltration membrane containing SiO2N-Halamine nanoparticles with both organicantifouling and antibacterial properties Desalination 326 69e76

Yu L Zhang Y Zhang B Liu J Zhang H amp Song C (2013) Preparation and charac-terization of HPEI-GOPES ultrafiltration membrane with antifouling and antibacterialproperties Journal of Membrane Science 447 452e462

Yu S Cheng Q Huang C Liu J Peng X Liu M et al (2013) Cellulose acetate hollowfiber nanofiltration membrane with improved permselectivity prepared through hydrolysisfollowed by carboxymethylation Journal of Membrane Science 434 44e54

Yu S Zhou Q Shuai S Yao G Ma M amp Gao C (2013) Thin-film compositenanofiltration membranes with improved acid stability prepared from naphthalene-136-trisulfonylchloride (NTSC) and trimesoyl chloride (TMC) Desalination 315 164e172

Zhang G Dai L amp Ji S (2011) Dynamic pressure-driven covalent assembly of inner skinhollow fiber multilayer membrane AIChE Journal 57 2746e2754

Zhang G Lu S Zhang L Meng Q Shen C amp Zhang J (2013) Novel polysulfone hybridultrafiltration membrane prepared with TiO2-g-HEMA and its antifouling characteristicsJournal of Membrane Science 436 163e173

Zhang J W Fang H Wang J W Hao L Y Xu X amp Chen C S (2014) Preparation andcharacterization of silicon nitride hollow fiber membranes for seawater desalinationJournal of Membrane Science 450 197e206

Zhang Q G Liu Q L Zhu A M Xiong Y amp Ren L (2009) Pervaporation performanceof quaternized poly(vinyl alcohol) and its crosslinked membranes for the dehydration ofethanol Journal of Membrane Science 335 68e75

Novel and emerging membranes for water treatment 283

Zhang P Qian J An Q Liu X Zhao Q amp Jin H (2009) Surface morphology andpervaporation performance of electric field enhanced multilayer membranes Journal ofMembrane Science 328 141e147

Zhang P Qian J Yang Y An Q Liu X amp Gui Z (2008) Polyelectrolyte layer-by-layerself-assembly enhanced by electric field and their multilayer membranes for separatingisopropanolewater mixtures Journal of Membrane Science 320 73e77

Zhang G Song X Ji S Wang N amp Liu Z (2008) Self-assembly of inner skin hollow fiberpolyelectrolyte multilayer membranes by a dynamic negative pressure layer-by-layertechnique Journal of Membrane Science 325 109e116

Zhang S Wang R Zhang S Li G amp Zhang Y (2014) Treatment of wastewater containingoil using phosphorylated silica nanotubes (PSNTs)polyvinylidene fluoride (PVDF) com-posite membrane Desalination 332 109e116

Zhang Z Wang Z Wang J amp Wang S (2013) Enhancing chlorine resistances and anti-biofouling properties of commercial aromatic polyamide reverse osmosis membranes bygrafting 3-allyl-55-dimethylhydantoin and NN0-Methylenebis(acrylamide) Desalination309 187e196

Zhao L Chang P C Y amp Ho W S W (2013) High-flux reverse osmosis membranesincorporated with hydrophilic additives for brackish water desalination Desalination 308225e232

Zhao Q An Q F Ji Y Qian J amp Gao C (2011) Polyelectrolyte complex membranes forpervaporation nanofiltration and fuel cell applications Journal of Membrane Science 37919e45

Zhao Q An Q Sun Z Qian J Lee K R Gao C et al (2010) Studies on structures andultrahigh permeability of novel polyelectrolyte complex membranes The Journal ofPhysical Chemistry B 114 8100e8106

Zhao Q Qian J An Q Gao C Gui Z amp Jin H (2009) Synthesis and characterization ofsoluble chitosansodium carboxymethyl cellulose polyelectrolyte complexes and thepervaporation dehydration of their homogeneous membranes Journal of MembraneScience 333 68e78

Zhao Q Qian J An Q Gui Z Jin H amp Yin M (2009) Pervaporation dehydrationof isopropanol using homogeneous polyelectrolyte complex membranes ofpoly(diallyldimethylammonium chloride)sodium carboxymethyl cellulose Journal ofMembrane Science 329 175e182

Zhao Q Qian J An Q amp Sun Z (2010) Layer-by-layer self-assembly of polyelectrolytecomplexes and their multilayer films for pervaporation dehydration of isopropanol Journalof Membrane Science 346 335e343

Zhao Q Qian J An Q Yang Q amp Gui Z (2009) Synthesis and characterization ofsolution-processable polyelectrolyte complexes and their homogeneous membranes ACSApplied Materials amp Interfaces 1 90e96

Zhao Q Qian J W An Q F Yang Q amp Zhang P (2008) A facile route for fabricatingnovel polyelectrolyte complex membrane with high pervaporation performance in iso-propanol dehydration Journal of Membrane Science 320 8e12

Zhao Q Qian J An Q Zhu M Yin M amp Sun Z (2009) Poly(vinyl alcohol)poly-electrolyte complex blend membrane for pervaporation dehydration of isopropanolJournal of Membrane Science 343 53e61

Zhao Q Qian J Zhu C An Q Xu T Zheng Q et al (2009) A novel method forfabricating polyelectrolyte complexinorganic nanohybrid membranes with high iso-propanol dehydration performance Journal of Membrane Science 345 233e241

284 Advances in Membrane Technologies for Water Treatment

Zhao Q Qian J Zhu M amp An Q (2009) Facile fabrication of polyelectrolyte com-plexcarbon nanotube nanocomposites with improved mechanical properties and ultra-high separation performance Journal of Materials Chemistry 19 8732e8740

Zhao H Qiu S Wu L Zhang L Chen H amp Gao C (2014) Improving the performance ofpolyamide reverse osmosis membrane by incorporation of modified multi-walled carbonnanotubes Journal of Membrane Science 450 249e256

Zhao S Wang P Wang C Sun X amp Zhang L (2012) Thermostable PPESKTiO2

nanocomposite ultrafiltration membrane for high temperature condensed water treatmentDesalination 299 35e43

Zheng Y Yao G Cheng Q Yu S Liu M amp Gao C (2013) Positively charged thin-filmcomposite hollow fiber nanofiltration membrane for the removal of cationic dyes throughsubmerged filtration Desalination 328 42e50

Zhu H Wang H Wang F Guo Y Zhang H amp Chen J (2013) Preparation and propertiesof PTFE hollow fiber membranes for desalination through vacuum membrane distillationJournal of Membrane Science 446 145e153

Zhu M Qian J Zhao Q An Q amp Li J (2010) Preparation method and pervaparationperformance of polyelectrolyte complexPVA blend membranes for dehydration of iso-propanol Journal of Membrane Science 361 182e190

Zhu M Qian J Zhao Q An Q Song Y amp Zheng Q (2011) Polyelectrolyte complex(PEC) modified by poly(vinyl alcohol) and their blend membranes for pervaporationdehydration Journal of Membrane Science 378 233e242

Zhu Y Xia S Liu G amp Jin W (2010) Preparation of ceramic-supported poly(vinylalcohol)echitosan composite membranes and their applications in pervaporation dehy-dration of organicwater mixtures Journal of Membrane Science 349 341e348

Zinadini S Zinatizadeh A A Rahimi M Vatanpour V amp Zangeneh H (2014) Prepa-ration of a novel antifouling mixed matrix PES membrane by embedding graphene oxidenanoplates Journal of Membrane Science 453 292e301

Zuo J Wang Y Sun S P amp Chung T S (2012) Molecular design of thin film composite(TFC) hollow fiber membranes for isopropanol dehydration via pervaporation Journal ofMembrane Science 405e406 123e133

Novel and emerging membranes for water treatment 285

Novel and emerging membranesfor water treatment by electricpotential and concentrationgradient membrane processes

9

P Arribas12 M Khayet 23 MC Garciacutea-Payo2 L Gil41Campus of International Excellence Moncloa Campus (UCM-UPM) Madrid Spain2Department of Applied Physics I University Complutense of Madrid Avda ComplutenseMadrid Spain 3Madrid Institute for Advanced Studies of Water (IMDEA Water Institute)Alcala de Henares Madrid Spain 4School of Forest Engineering University Polytechnic ofMadrid Avda Complutense Madrid Spain

91 Introduction

Recently salinity gradient power (SGP) has been recognized as a renewable andsustainable alternative technology for energy generation This approach is able toconvert osmotic pressure difference of salt solutions (ie high-concentrated andless-concentrated salt solutions) into mechanical or electrical energy by using selectivemembranes (Brauns 2009) The worldwide availability of SGP is considered to be ahuge energy resource with an estimated potential power of 24e26 TWwhen the totaldischarge of all rivers in the world is taken into account (Hong Zhang Luo amp Chen2013) Each cubic meter of water in the river can generate 15 MJ of energy whenmixed with equal amounts of seawater (comparable to 05 molL NaCl) and morethan 169 MJ when mixed with brine solution (5 molL NaCl) (Post Hamelers ampBuisman 2008) Pressure retarded osmosis (PRO) and reverse electrodialysis (RED)are the most frequently studied membrane-based processes for energy conversion ofsalinity gradient energy (Hong et al 2013) While PRO is a mechanical processthat uses water selective membranes and turbines to produce electrical energy REDis an electrochemical process that uses ionic selective membranes and electrodes forelectricity production (Burheim Seland Pharoah amp Kjelstrup 2012) FurthermoreRED is often considered to be more favorable for power generation because of itsgreater energy efficiency and reduced sensitivity to membrane fouling comparedwith PRO (Post et al 2007)

Electrodialysis (ED) is an electrochemical process in which ions migrate throughion-selective exchange membranes (IEMs) as a result of their attraction to two electri-cally charged electrodes ED is able to remove most charged dissolved ions and is usedto produce potable water from saline aqueous solutions

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400009-5Copyright copy 2015 Elsevier Ltd All rights reserved

The interest in osmotically driven membrane processes such as forward osmosis(FO) and PRO has increased during last decade (Alsvik amp Heuroagg 2013a) Both pro-cesses belong to the emerging platform technology known as engineered osmosis(EO) that has the potential to sustainably produce clean drinking water and electricpower (Huang Bui Meyering Hamlin amp Mccutcheon 2013) Unlike the pressure-driven membrane processes (PDMPs) EO offers the possibility to use osmoticpressure gradients in a wide range of applications These include FO for water desali-nation PRO for electric power generation and direct osmotic concentration fordewatering (Arena Mc Closkey Freeman amp Mc Cutcheon 2011)

92 Electric potential gradient driven membraneprocesses EDRED

A typical ED system includes a membrane stack with a number of cell pairs each con-sisting of cation and anion exchange membranes (CEM and AEM respectively)stacked in an alternating pattern between a cathode and an anode (see Figure 91(a))The compartments between the membranes are alternately filled with a concentratedsalt aqueous solution and a diluted salt aqueous solution The electrodes are continuallyflushed to reduce fouling or scaling Some of the advantages of ED compared with othermembrane processes such as reverse osmosis (RO) and nanofiltration (NF) include thehigh water recovery the long useful life of the membranes due to their high chemicalmechanical stability the possibility to operate at temperatures up to 50 C and theachievement of higher brine concentrations ED technology is also used for the treat-ment of industrial effluents and the removal of fluoride nitrate and heavy metalsfrom water sources (Mulyati Takagi Fujii Ohmukai amp Matsuyama 2013) Whenthe polarity of the electrodes is regularly reversed the process is called electrodialysisreversal (EDR) This variation on the ED process uses electrode polarity reversal toclean automatically the membrane surfaces increasing membrane life This processminimizes the effect of inorganic scaling and fouling by converting product streamsinto waste streams and allows running at higher recovery rates (Valero amp Arbos2010) However EDR requires additional plumbing and electrical controls

A typical RED membrane unit consists of an alternating series of CEM and AEMsituated between two electrodes (see Figure 91(b)) The salinity gradient between bothsolutions induces an electrochemical potential difference through each membraneThis electrochemical potential difference causes the transport of ions through the mem-branes from the concentrated solution to the diluted solution At the electrodes theionic species accumulate and induce electron current via red-ox reactions whichcan be used to power on an external device (Hong et al 2013) To optimize bothED and RED processes various research studies were focused on the improvementof the IEMsrsquo performance including their physicochemical (eg thickness andswelling degree) and electrochemical (eg area resistance ie electrical membraneresistance (U cm2) permselectivity and charge density) characteristics (Geurouler ElizenVermaas Saakes amp Nijmeijer 2013)

288 Advances in Membrane Technologies for Water Treatment

When the ED process is used to produce NaCl (table salt) from high-salinity brinethe salt rejection factor (or membrane selectivity) to monovalent and multivalent ionsis important to avoid the possible salt precipitation taking placing in the concentrating

Figure 91 Schematic diagrams (a) Electrodialysis unit with five cell pairs and (b) Reverseelectrodialysis unit

Novel and emerging membranes for water treatment 289

compartments (Wang Jia Yao amp Wang 2013) It is worth noting that high processcost and low selectivity efficiency and durability of IEMs are still important issuesin ED technology (Kumar Khan Alothman amp Siddiqui 2013) Many researchersare investigating to develop specific selective membranesmaterials to overcome theseproblems

Chakrabarty et al (2011) developed thermally and chemically cross linked stableIEMs in an aqueous medium for water desalination by ED CEM was prepared by sul-fonation of poly (ether sulfone) (SPES) while AEM was fabricated by using polyvinylalcohol (PVA) and 4-vinylpyridine (4-VP) in three steps (1) solegel process (2)chemical cross linking and (3) quaternization The membrane electrochemical proper-ties and stabilities could be controlled by either the degree of sulfonation of SPES (inthe case of CEM) or chemical cross linking (in the case of AEM) Both CEM and AEMshowed excellent electro-transport properties and a good ED performance and energyconsumption (429 kWhkg of NaCl removed) for water desalination

Zendehnam Robatmili Hosseini Arabzadegan and Madaenic (2013) preparedacrylonitrilebutadienestyrene heterogeneous AEMs using anion exchange resin pow-der as functional group agents and tetrahydrofuran as a solvent In addition a silver(Ag) nanolayer was deposited on the prepared membrane surface using the magnetronsputtering method Activated carbon (AC) was also used as an inorganic filler additiveto create adsorptive active sites in the membrane matrix The results showed amaximum of the membrane permselectivity for 2 wt AC concentration in the castingsolution Both the ionic permeability and permeate flux were enhanced by increasingthe AC amount up to 05 wt and then they declined with further increase of AC con-centration from 05 to 4 wt The modified membranes showed good ability inEscherichia coli removal due to the increase of the coating thickness of Agnanolayer which reduced the growth rate of E coli

To improve the ED membrane monovalent selectivity Wang et al (2013) per-formed a promising modification method consisting on a photo-induced covalentimmobilization and self-crosslinking of a chitosan (CS) layer on a conventionalCEM surface This modification resulted in both chemical and morphological mem-brane surface changes such as the formation of chemical bonds between the basemembrane and the covalently immobilized and self-crosslinked CS layer The EDexperimental results with respect to NathornMg2thorn and HthornZn2thorn systems showed thatthe modified CEMs achieved a superior monovalent selectivity after the immobiliza-tion of CS layer The Zn2thorn and Mg2thorn leakage of the modified membrane were reducedby 274 and 624 respectively whereas the diffusion coefficient of Nathorn electricalresistance and limiting current density were not declined remarkably after the modi-fication by CS immobilization

Other research studies have demonstrated that the modification of CEMs with poly-aniline (PANI) is an efficient approach for improving the stability and selectivity ofIEMs toward monovalent ions For example Kumar et al (2013) developed PANIchemically modified organiceinorganic hybrid CEMs by in situ polymerization of an-iline in an HCl aqueous solution using ferric chloride (FeCl3) as an oxidizing agentThe PANI modified membranes were thermally stable in ED separation of Nathorn

from binary mixtures of (NathornZn2thorn and NathornAl3thorn) in aqueous solutions The water

290 Advances in Membrane Technologies for Water Treatment

uptake ion exchange capacity cation transport number in the membrane phase andequivalent membrane conductivity of the modified membranes were improved for a001 M NaCl aqueous solution The cation transport number value for Zn2thorn andAl3thorn (040 and 034 respectively) of the PANI modified membranes were lowerthan the cation transport number value for Nathorn (092) which indicated that the modi-fied membranes were more selective for Nathorn in comparison to Zn2thorn and Al3thorn ions

Mulyati et al (2012) improved the ED anti fouling properties of the commercialAEM (NEOSEPTA AMX Astom Corp Tokyo Japan) by surface modificationwith poly(sodium 4-styrene sulfonate) (PSS) Antifouling potential of the AEM wasevaluated based on the elapsed time before fouling took place using sodium dodecyl-benzene sulfonate (SDBS) as a model organic foulant It was observed an enhancedantifouling property of the modified membrane attributed to the increase of the nega-tive charge density and hydrophilicity of the membrane surface However the mono-valent anion selectivity was not improved by the deposition of a single layer of PSS Ayear later the same research group developed a new approach to simultaneouslyimprove the monovalent anion selectivity and antifouling properties of commercialAEMs (Mulyati et al 2013) The method was based on the generation of a high nega-tive charge on the membrane surface using layer-by-layer (LbL) deposition of differentpolyelectrolyte solutions in which PSS was used as a polyanion while poly(allylaminehydrochloride) (PAH) was used as a polycation A commercial AEM (NEOSEPTAAMX membrane Astom Corp Tokyo Japan) was modified via alternating contactwith the PSS and PAH solutions for 30 min The results showed that the increase ofthe number of layers resulted in better monovalent anion selectivity and anti foulingcharacter

Cross-linked zirconium tri-ethylene tetra-amine (ZrT) chelating membranes wereprepared by solegel method for Cu2thorn removal in the presence of other bivalent metalions (Chakrabarty Shah Srivastava Shahi amp Chudasamab 2013) The incorporationof ZrT in the PVA polymer matrix ensures the formation of homogeneous andinterconnected polymer network The developed ZrT membrane exhibited good ther-mal mechanical and chemical stabilities with a controlled pore size ED studiesrevealed high Cu2thorn permeate flux (55$107 molm2 s at 10 mAcm2 applied currentdensity) of ZrT membranes in comparison with other bivalent metal cations(15e2$107 molm2 s for Ni2thorn Zn2thorn and Mn2thorn) The selective recovery of Cu2thorn

was attributed to the hydrophilic structural membrane morphology having many aminogroups and highly cross linked The separation factor was estimated from the ratio ofCu2thorn permeate flux (JCu2thorn ) and other bivalent cation permeate flux (JCu2thorn=JM2thorn ) inequimolar solution metal ion mixtures The obtained high separation factor(30e40) for separating Cu2thornNi2thorn Cu2thornZn2thorn and Cu2thornMn2thorn suggested the appli-cation of ZrT chelating membranes for Cu2thorn recovery from industrial wastewaters

Hosseini Askari Koranian Madaeni and Moghadassia (2014) and Hosseini et al(2013) investigated the effects of the concentration of different additives iron oxide(Fe3O4) nanoparticles (NPs) and multiwalled carbon nanotubes (MWCNTs) on thephysicochemical and electrochemical properties of polyvinylchloride (PVC)-basedED CEM An increase of the water content (from 22 to 259) and the ion exchangecapacity (from 143 to 172 meqg) of the CEM with the increase of Fe3O4 NPs from

Novel and emerging membranes for water treatment 291

0 to 2 wt followed by a decline of both parameters for high NPs concentrations wasobserved The same behavior was observed for the ionic permeability for sodium andbarium ions achieving high values of 355$107 and 337$107 ms respectively at2 wt Fe3O4 content The membrane permselectivity was enhanced with the increaseof the additive content from 0 to 4 wt in sodium (790e860) and barium chloride(364e425) ionic solutions These results suggested that the prepared membraneswere less selective to bivalent ions (Ba2thorn) compared to monovalent ions (Nathorn) ForMWCNTs the prepared membrane water content also showed a maximum of283 for 4 wt MWCNT concentration in the casting solution The increase ofMWCNTsrsquo loading ratio also resulted in an increase of the permeability for monova-lent ions (Nathorn) from 2398$107 to 2420$107 ms while the permeability for bivalentions (Ba2thorn) did not show a straightforward relationship with MWCNTsrsquo loading ratio

ED was also carried out using bipolar membranes (BPMs) which are compositeIEMs consisting of a layered ion exchange structure composed of a cation exchangelayer (CEL) and an anion exchange layer (AEL) with a hydrophilic intermediate layerin between (Venugopal amp Dharmalingam 2012 Xu 2005) This composition ofanionic and cationic exchange layers exhibits various advantages in ED such as theseparation of monovalent and divalent ions antideposition antifouling water dissoci-ation into OH and Hthorn ions increase of reusability and recyclability of waste throughchemical production (acidic and alkaline solutions) low initial cost and no electro-chemical reactions (oxidation andor reduction species) that may produce undesirableproducts etc (Kariduraganavar Nagarale Kittur amp Kulkarni 2006) Today syntheticBPMs are receiving much attention because of their potential for application indifferent industries such as chemical production and separation industry biochemicalengineering (ie producing inorganic acidbase from the corresponding salts recov-eryproduce organic from fermentation broth etc) environmental conservation puri-fication or separation in food industries (ie inhabitation of polyphenol oxidase inapple juice) etc When applied to treat salt-containing wastewater BPM ED can pro-duce acids and bases due to its ability to split water into OH and Hthorn ions and over-come salt pollution and be discharged without treatment (see Figure 92) Venugopaland Dharmalingam (2012) developed a novel functionalized polysulfone (PS)-basedBPM with an intermediate layer of PVA and investigated its ED performance forseawater desalination and recovery of acid and alkali The prepared BPM possessedexcellent mechanical and chemical stabilities due to its unique ply structures in bothAEL and CEL forms The PS-based BPM showed higher current efficiency (ie18) lower power consumption (ie 8) greater salt rejection factor and higherprocess efficiency for the production of acid and alkali than those of the commercialBPM made of gel polystyrene crosslinked with divinylbenzene (PSDVB) (Arun Elec-tro chemicals Chennai)

Wang Peng et al (2010) developed a hybrid BPM for high temperature applica-tions The CEL was prepared by hybridizing sulfonated poly(26-dimethyl-14-phenylene oxide) with (3-aminopropyl) triethoxysilane (A1100) while the AELwas prepared from a hybrid anion exchange material poly(VBC-co-g-MPS) (vinyl-benzyl chloride (VBC) and g-methacryloxypropyl trimethoxy silane (g-MPS)) andPVA Palygorskite (a silicate mineral) and FeCl3 were added in the intermediate layer

292 Advances in Membrane Technologies for Water Treatment

as catalysts to further enhance water dissociation improving the generation of Hthorn andOH although the voltage drop across the BPM was detected By incorporatinginorganic silane (A1100 and g-MPS) in both the AELCEL the BPM showed higherthermal stability dimensional stability and catalytic effect on water dissociation in therange 25e80 C

Not only the improvement of the membrane properties is necessary to achieve highED and RED performances but it is also important to consider the scale-up and designof the EDRED unit and the optimization of the electrode systems Geurouler et al (2013)successfully constructed a RED unit completely built with tailor-made IEMs in whichCEMs were fabricated by sulfonated polyetheretherketone (SPEEK) and AEMs withpolyepichlorohydrin (PECH) The bulk membrane properties (ie area resistancepermselectivity and charge density) of both series of commercially available mem-branes and tailor-made ones were investigated and correlated to the obtained RED per-formance Experimental and theoretical statistical results showed that increasing thearea resistance resulted in an increase of the power density in RED whereas permse-lectivity did not show any straightforward relationship with the power densityFurthermore the performance of the tailor-made RED unit exhibited a higher powerdensity (128 Wm2) than other RED units based on the commercially consideredmembranes Fumatech FKSFAS (111 Wm2) Tukuyama CMXAMX (107 Wm2)Qianqui CEMAEM (083 Wm2) or Ralex CMHAMH (060 Wm2)

For the design of a typical system of both RED and ED processes metal oxide cat-alysts are commonly used to convert the electronic current to ionic current This conver-sion results from the red-ox reaction that occurs in the electrodes of the system Burheimet al (2012) studied the performance of electrode systems for RED and ED separation

Figure 92 Schematic diagram of electrodialysis with bipolar membranes cell to treat salt-containing wastewater

Novel and emerging membranes for water treatment 293

processes by testing two different electrode materials and red-ox salts demonstratingthat these electrochemical reactions were controlled by mass transfer in the electrolyterather than by the electro-catalytic properties of the electrode material It was concludedthat relatively cheap carbon materials (graphite and glassy carbon) with FeCl2FeCl3could act as good electrodes in a red-ox system with lower electrode concentration over-potential The power losses (ie dissipated energy) in the electrode compartments werereduced by increasing the concentration of the electroactive species Vermaas Saakesand Nijmeijer (2011) developed a RED unit using membranes with a specific labora-tory-made profile (profiled membranes) and evaluated its performance comparing itto that of RED unit of commercial IEMs (Ralex CMH and AMH Mega as CzechRepublic) separated by non-conductive spacers This new morphology resulted in aslight reduction in permselectivity (from 89 to 87) a significant decrease in arearesistance (from 73 to 27 U cm2) a large increase in conductivity (from 91 to177 mScm) and a slightly higher maximum power density (from 069 to 080 Wm2)

93 Concentration gradient driven membrane processesFO and PRO

In the case of FO a high-concentration solution (ie draw solution) is separated froma low-concentration solution by a water-selective semipermeable membrane As it isshown in Figure 93 the concentration gradient between both the feed and drawsolutions results in a transmembrane osmotic pressure Consequently water flowsspontaneously through the membrane from the low-concentration side to the draw-solution side PRO and FO are similar separation processes except for the additionalback pressure applied on the draw solution for PRO In both processes water flowsfrom the low-concentration side of the membrane to the high-concentration side aslong as the applied pressure is lower than the transmembrane osmotic pressureWhen the applied pressure is greater than the osmotic pressure difference the direc-tion of the water flux is reversed leading to the well-known RO separation process(Figure 94) Unlike RO in which mechanical energy is used for pumping the feedsaline aqueous solution through a water-selective membrane to overcome the trans-membrane osmotic pressure PRO converts the chemical potential (osmotic energy)of a salt-concentrated aqueous solution into mechanical energy (Xu Peng TangFu amp Nie 2010)

It must be pointed out that the membranes used in FO and PRO are not ideal andreverse solute(s) permeate fluxes also occur through the membrane opposite to the di-rection of water permeate flux This causes solute(s) concentration polarization insidethe membrane known as internal concentration polarization (ICP) phenomenon (Xuet al 2010) ICP is one of the most severe drawbacks in the osmotic membrane pro-cesses because it significantly reduces the membrane water permeability (Achilli ampChildress 2010 Chou et al 2012) Therefore preparation of specific membranes isessential for the development of FO and PRO technologies In this case three main

294 Advances in Membrane Technologies for Water Treatment

challenges must be addressed ICP weak mechanical strength of the membranes andmembrane fouling propensity (Chou et al 2012)

An ideal FOPROmembrane should be a semipermeable membrane with a high wa-ter permeability and a high solute rejection factor a small resistance toward solutediffusion high chemical stability low ICP using thin and highly porous supportswith low mass transfer resistance high mechanical strength to support high hydraulicpressure when used in PRO applications low susceptibility to fouling (ie hydrophilicmembrane to get high permeate fluxes and reduce membrane fouling) and low struc-tural parameter (S) defined as the ratio of the pore tortuosity and porosity multiplied bythe thickness of the membrane (S frac14 thickness tortuosityporosity) (Cath Childressamp Elimelech 2006 Chou et al 2010 Han Zhang et al 2013 Sivertsen HoltThelin amp Brekke 2013 Zhang et al 2010) In addition the surface structure ofthe FO membrane facing the feed aqueous solution is critical because it is directlyassociated with fouling tendency while a relatively dense substrate surface is desirablefor a membrane with an active layer facing draw solution (AL-DS)

For the preparation of FO and PRO membranes different polymers are usedincluding cellulose acetate (CA) (Herron 2008) cellulose triacetate (CTA) (HTI2013) PS (Yip Tiraferri Phillip Schiffman amp Elimelech 2010) polyethersulfone(PES) (Yu Seo Kim amp Lee 2011) polybenzimidazole (PBI) (Wang Chung ampQin 2007) polyamide (PA) (Alsvik amp Heuroagg 2013b) and poly(amide-imide) (PAI)(Setiawan Wang Li amp Fane 2011) These FO and PRO membranes were designedas thin-film composite (TFC) flat sheet membranes using different types of supportsand hollow fiber membranes

Until now three methods have been adopted to prepare polymeric FO membranesthe non-solvent phase inversion method developed by Loeb and Sourirajan (Loeb ampSourirajan 1963) the interfacial polymerization (IP) on porous substrates inventedby Cadotte (Cadotte 1981) to prepare TFC membranes and the LbL deposition ofnanometer thick polycations and polyanions on porous charged substrates (Qi Qiu

Initial nonequilibriumosmotic state

FO ( P = 0)∆∆ PRO ( P lt π)∆ ∆∆ RO ( P gt π)∆ ∆∆

Figure 93 Illustration of forward osmosis (FO) reverse osmosis (RO) and pressure retardedosmosis (PRO) processes (a) Initial non-equilibrium osmotic state (b) FO process in whichno pressure is applied on the draw solution (c) PRO process in which a hydrostatic pressurelower than the transmembrane osmotic pressure is applied on the draw solution (d) RO processused for desalination of a saline feed solution by applying a hydrostatic pressure greater than thetransmembrane osmotic pressure

Novel and emerging membranes for water treatment 295

amp Tang 2011) Fully integrated asymmetric FO membranes made of CTA (Herron2008) PBI (Wang et al 2007 Wang Goh et al 2009 Yang Wang amp Chung2009) CA (Su amp Chung 2011 Su Yang Teo amp Chung 2010) and PES (Yuet al 2011) are typical examples of the first method while FO membranes made of

Figure 94 (a) Water flux direction and (b) energy consumptionproduction in forward osmosis(FO) pressure retarded osmosis (PRO) and reverse osmosis (RO) using a selectivesemipermeable membrane

296 Advances in Membrane Technologies for Water Treatment

PA via IP on PS-based substrates (Wang Shi et al 2010 Yip et al 2010) sulfonatedsubstrates (Wang Chung amp Amy 2012 Widjojo Chung Weber Maletzko ampWarzelhan 2011) cellulose acetate propionate substrates (Li Wang Helmer ampChung 2012) and nanofibrous supports (Bui Lind Hoek amp Mc Cutcheon 2011)belong to the second method A comparison of the performance of membranes appliedin FOPRO process is listed in Table 91

It is worth noting that CA has been widely used to prepare FO membranes via phaseinversion because of its relatively high hydrophilicity that favors high water perme-ability and low fouling propensity good mechanical strength wide availability andgood resistance to degradation by various compounds including chlorine (ZhaoZou Tang amp Mulcahy 2012) The company Hydration Technology Innovations(HTI Albany OR USA) has provided asymmetric cellulose-based membranes forFO for nearly 25 years This company developed flat sheet membranes using celluloseesters exclusively for FO applications In 2008 HTI patented commercial asymmetricCACTA FO membranes composed of a thin skin layer for salt separation (10e20 mm)and a thicker porous scaffold layer (about 100 mm thick) with a woven or non-wovenmesh embedded within it (Herron 2008) These membranes exhibit high permeate fluxand salt rejection factors low resistance to water diffusion lack of defects and goodstructural integrity It was claimed that these membranes have far superior permeatefluxes than other commercially available composite membranes such as cellulose esterblend RO membrane (Osmonics now GE Water Systems) used in FO

Recently Nguyen Yun Kim and Kwon (2013) prepared CTACA flat sheet mem-branes with enhanced FO performance by immersion precipitation using different cast-ing compositions and support layers (Figure 95) The optimized membrane (WF1Figure 95(a)) was prepared by casting 63 wt CTA 126 wt CA 499 wt14-dioxane 172 wt acetone 37 wt maleic acid and 103 wt methanol to athickness of 250 mm on a porous woven support layer with a subsequent evaporationfor 30 s at 25 C and 70 relative humidity and then annealing at 85 C The opti-mized membrane showed a more hydrophilic and smoother surface than the commer-cial CTA FO membrane (090128-NW-1 HTI) with lower fouling the highest waterpermeate flux (9270 Lm2 h for a draw solution of 1 M NaCl) 99533 NaCl rejec-tion factor and a reverse salt permeate flux of 0248 mol Brm2 h

To develop FO membranes with a high salt rejection factor Su et al (2010) fabri-cated a CA-based NF hollow fiber membrane modified by heat treatment The heat-treated hollow fiber membrane at 95 C resulted in a significant shrinkage of poresat the membrane surface with a denser outer skin layer but a low FO performancewith increasing saline concentration in the feed solution due to the more severe ICPeffect One year later Su and Chung (2011) carried out both experimental and theoret-ical studies using different CA hollow fiber membranes prepared with different borefluid compositions via a dryjet wet spinning technique It was observed that the inter-nal membrane structure did not exert any apparent influence on the membraneperformance used in PRO mode whereas it affected significantly the concentrationpolymerization and the FO performance It was also claimed that the preferred internalsublayer of a hollow fiber for FO should have a high porosity low tortuosity and smallthickness to enhance the water permeate flux

Novel and emerging membranes for water treatment 297

Table 9 1 Overview of recent researches on forward osmosispressure retarted osmosis (FOPRO) process withdifferent membranes

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

CA NF HF 047 967 7350 052e PROFO DI water 2 M MgCl2 22e25 Su et al (2010)

CA HF 097 7416 36383 1010 PROFO DI water 2 M MgCl2 e Su and Chung(2011)

CA double denselayer FS

017 990 173103 1208 PROFO DI water 2 M MgCl2 22 Zhang et al (2010)

920 11378 4438 PROFO DI water 2 M NaCl 22

CA double-skinned FS

078 790 255168 4625 PROFO DI water 2 M MgCl2 22 Wang Ong et al(2010)

CA HTIc FS e e 45 27 FO DI water 15 MMgSO4

20 Cornelissen et al(2008)

CA HTIc FS e e 432181 e PROFO DI water 15 M NaCl 20 Mc Cutcheon andElimelech (2008)

CTA HTIc FS 068 e 196124 8862 PROFO DI water 15 M NaCl 25 Bui and McCutcheon (2013)

CTA HTIc FS e 910 119 55 FO DI water 2 M NaCl 20e25 You et al (2013)

CTA HTIc FS(CTA-W)

033 819 65550 4829 PROFO 10 mMNaCl

05 M NaCl 23 Wei Qiu TangWang and Fane(2011)229121 e PROFO 10 mM

NaCl2 M NaCl 23

Asymmetric PBINF HF

05 481 38 e PRO DI water 2 M NaCl 225 Wang et al (2007)

865 9053 e PROFO DI water 2 M MgCl2 225

PBI NF HF(original)

243 762 250126 e PROFO DI water 2 M MgCl2 230 Wang Yang et al(2009)

PBI NF HF(2h modified)

153 856 221112 e PROFO DI water 2 M MgCl2 230 Wang Yang et al(2009)

PBI-PESPVPdual-layer NFHF

174 872 195148 e PROFO DI water 2 M MgCl2 230 Yang et al (2009)

Positively chargedPAI single-layer HF

225 927 13284 9926 PROFO DI water 05 MMgCl2

230 Setiawan et al(2011)

179132 17549 PROFO DI water 2 M MgCl2 230

PAIPES dual-layer HF

159 890 155275 83755 PROFO DI water 05 MMgCl2

230 Setiawan WangShi Li and Fane(2012)

Positively chargedPAI with PETsubstrate FS

756 875 239192 36692 PROFO DI water 05 MMgCl2

22e25 Qiu SetiawanWang Tang andFane (2012)325275 107

333PROFO DI water 2 M MgCl2 22e25

PES with PETsubstrate FS

e e 314 82 FO DI water 3 M NaCl 200 Yu et al (2011)

Continued

Table 9 1 Continued

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

Cellulosic ROc

withoutPET FS GEOsmonics

e e 360186 e PROFO DI water 15 M NaCl 200 Mc Cutcheon andElimelech (2008)

TFC-PA-PES HF(A-FO)

095 780 12950 5021 PROFO DI water 05 M NaCl 230 Wang et al (2010)

25986 e PROFO DI water 2 M NaCl 230

TFC-PA-PES HF(B-FO)

222 910 32214 3518 PROFO DI water 05 M NaCl 230 Wang et al (2010)

450225 4425 PROFO DI water 2M NaCl 230

TFC-PA-PES HF(C-FO)

35 900 426187 4016 PROFO DI water 05 M NaCl 230 Chou et al (2010)

680295 5826 PROFO DI water 2 M NaCl 230

TFC-PA- PESwaterHF

118 8795 256225 3228 PROFO DI water 05 M NaCl 20-25 Sukitpaneenit andChung (2012)571321 6961 PROFO DI water 2 M NaCl 20-25

TFC-PA-PESwaterNMPPEG

HF

183 8152 651345 12399 PROFO DI water 2 M NaCl 20-25 Sukitpaneenitand Chung(2012)

TFC-PA-PES HF 19 878 383 106 PRO DI water 1 M NaCl e Han Wang et al(2013)

TFC-PA-sPPSUHF

199 909 494225 11055 PROFO DI water 05 M NaCl 23 Zhong Fu ChungWeber andMaletzko (2013)

TFC-PA-PS FS 178 934 205120 5949 PROFO 10 mMNaCl

05 M NaCl 23 Wei et al (2011)

543222 e PROFO 10 mMNaCl

2 M NaCl 23

TFC-PA-PS FS 31 700 376249 7532 PROFO 10 mMNaCl

2 M NaCl 23 Amini Jahanshahiand Rahimpour(2013)

TFC-PA-PS FS e e 325141 14453 PROFO DI water 2 M NaCl e Emadzadeh LauMatsuura Ismailand Rahbari-Sisakht (2014)

TFC-PA-PS withPET substrate FS

19 986 250 e FO DI water 1 M NaCl 23 Tiraferri YipPhillipSchiffman andElimelech (2011)

TFC-PA-PS withPET substrate FS

144 984 167 e FO DI water 1 M NaCl 25 Hoover Schiffmanand Elimelech(2013)

TFC-PA-PSSPEK FS

075 895 201161 4533 PROFO DI water 05 M NaCl 23 Han ChungToriida andTamai (2012)

500350 9070 PROFO DI water 2 M NaCl 23

Continued

Table 9 1 Continued

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

TFC-PA-SPPSUFS

323 841 322300 4752 PROFO DI water 05 M NaCl e Widjojo ChungWeberMaletzko andWarzelhan(2013)

540480 8876 PROFO DI water 2 M NaCl e

TFC-PA-CPSFFS

e e 275179 7348 PROFO DI water 1 M MgCl2 25 Cho Han HanGuiver and Park(2013)

TFC-PA-PESsulfonatedpolymersubstrate FS

073 910 162153 2730 PROFO DI water 05 M NaCl 20e25 Widjojo et al(2011)

330210 2822 PROFO DI water 2 M NaCl 20e25

TFC-PA-PESSPSf FS

077 935 241130 4536 PROFO DI water 05 M NaCl 20e25 Wang et al (2012)

475260 12483 PROFO DI water 2 M NaCl 20e25

TFC-PA-PVDF FS 082 e 217150 10278 PROFO DI water 05 M NaCl 20-25 Wang et al (2012)

360233 183112

PROFO DI water 2 M NaCl 20e25

TFC-PA-CAP FS 182 892 15578 0809 PROFO DI water 05 M NaCl 20e25 Li et al (2012)

35175 19518 PROFO DI water 2 M NaCl 20e25

TFC-PA-nylon66 MF FS

092 958 21962 0807 PROFO DI water 15 M NaCl 20 Huang et al (2013)

TFC-PA-Matrimid FS

100 e 891 154 PRO DI water 1 M NaCl 25 Han Zhang et al(2013)

TFC-PA PSnanofiber withPET substrate FS

174 e 260 23 FO DI water 15 M NaCl 23 Bui et al (2011)

TFC-PA-PESnanofiber FS

17 970 637576 e PROFO DI water 15 M NaCl 23 Song Liu and Sun(2011)

TFC-PA-PVDFnanofiber FS

315 844 621365 281169

PROFO DI water 15 M NaCl 23 Tian Qiu LiaoChou and Wang(2013)

TFC-PA-PANnanofiber FS

204 e 619350 5284 PROFO DI water 15 M NaCl 25 Bui and McCutcheon (2013)

TFC-PA-PANCAnanofiber FS

18 e 548301 42106 PROFO DI water 15 M NaCl 25 Bui and McCutcheon (2013)

TFC NF FS(TS80)Trisep

e e 11 004 FO DI water 15 MMgSO4

200 Cornelissen et al(2008)

TFC RO FS(SWC1)Hydranautics

e e 04 001 FO DI water 15 MMgSO4

200 Cornelissen et al(2008)

TFC-PA RO PSwith PET FS(SW30 XLE)Dow FilmTec

e e 8136 e PROFO DI water 15 M NaCl 200 Mc Cutcheon andElimelech (2008)

Continued

Table 9 1 Continued

Membrane(material-support-shape(commercialname))

Waterpermeability(Lm2 h bar)

Saltrejection()

FO performance Testing conditions

References

Waterflux (Lm2 h)

Saltflux (gm2 h)

Membraneorientation

Feedsolution

Drawsolution

Temperature(C)

TFC-PA HTIc FS e e 490200 e PROFO DI water 1 M NaCl 23 HTI (2013)

TFN-PAF-MWCNT-PSFS

447 730 951390 5229 PROFO 10 mMNaCl

2 M NaCl 23 Amini et al (2013)

TFN-PATiO2

ePS FS299 774 391225 208

102PROFO DI water 05 M NaCl e Emadzadeh et al

(2014)

751374 438233

PROFO DI water 2 M NaCl e

LbLnanocompositePVAMMt-TALiCl FS

e e 189100 01003 PROFO DI water 05M NaCl 230 Pardeshi andMungray (2014)

377255 028005

PROFO DI water 2 M NaCl 230

LbLnanocompositeNF-PANPSSAg FS

e 950 422178 3028 PROFO 10 mMNaCl

05 MMgCl2

260 Liu et al (2013)

LbLTFI-SSMsilica xerogelsTEOS FS

e 920 603598 106105

PROFO DI water 2 M NaCl 20e25 You et al (2013)

LbL double-skinned PANPAH-PSS FS

16 955 354766 119214

PROFO DI water 05 MMgCl2

22e23 Qi Qiu Zhao andTang (2012)

5011061

203516

PROFO DI water 2 M MgCl2 22e23

Note HF Hollow fiber FS flat sheet The superscript ldquocrdquo refers to commercial and PROFO refers to such membrane that the bottom layer faces the draw solution in the PRO mode and the top layer faces drawsolution in the FO mode

Recently Alsvik and Heuroagg (2013b) coated hydrolyzed commercial CACTA (CAfrom Alfa Laval and CTA from HTI) support membranes with a PA layer by amodified IP method forming a covalent bond between the active layer and the supportThe prepared membranes displayed salt rejection factors up to 97 and waterpermeate fluxes varying from 076 to 47 Lm2 s at transmembrane pressure of13$106 Pa (RO mode)

During the last eight years several studies have been published on the formation ofhollow fiber membranes specially designed for osmotically driven processes (Alsvik ampHeuroagg 2013a) Wang Yang et al (2009) fabricated hollow fiber membranes for FOapplications by the dryjet phase inversion method using PBI and modified via cross-linking using p-xylylene dichloride To improve the FO performance Yang et al

Figure 95 Images of supports (first row) and SEM cross-sectional images of forward osmosismembranes (second row) fabricated on the corresponding support layers Three woven fabricslabeled WF1 (a) WF2 (b) andWF3 (c) and three non-woven fabrics labeled NWF1 (d) NWF2(e) and NWF3 (f) were used as support layers for the cellulose triacetatecellulose acetate(CTACA)-based membranes Two commercial membranes were used to compare a cartridgeCTA-based membrane (090128-NW-1 HTI1 (g)) and a pouch CTA-based membrane(081118-SS-2 HTI2 (h))Reprinted from Nguyen et al (2013) with permission from Elsevier

306 Advances in Membrane Technologies for Water Treatment

(2009) developed a dual-layer PBIePES hollow fiber membrane via a co-extrusiontechnique This membrane consisted on an ultrathin selective skin layer fully porouswater channels underneath and a microporous sponge-like support structure The pre-pared PBIePESpolyvinylpyrrolidone (PVP) dual-layer membrane achieved a purewater permeability (PWP) of 174 Lm2 h bar and an MgCl2 rejection factor of872 The obtained water permeate fluxes in FO and PRO mode using 2 M MgCl2as a draw solution at 23 C (148 and 195 kgm2 h respectively) were higher thanthose of the commercial RO membranes (AG GE Osmonics 25 kgm2 h and ADGE Osmonics 11 kgm2 h) (Miller amp Evans 2006) but comparable to most commer-cial HTI FO flat sheet membranes (ie 129 kgm2 h for FO experiment and 85 kgm2 h for PRO experiment (Cornelissen et al 2008))

Setiawan et al (2011) fabricated hollow fiber membranes with a positively chargedlayer (ie NF-like skin layer) using asymmetric microporous hollow fibers made ofTorlon PAI material as substrates followed by chemical crosslinking using polyethy-leneimine (PEI) The PAI hollow fiber membranes exhibited a PWP of 219e225Lm2 h bar and a high MgCl2 rejection factor more than 911 under a pressure of1 bar By using 1 M MgCl2 draw solution better FO water permeate fluxes(104e110 kgm2 h) than those of previously reported PBI NF modified hollow fibers(Wang Yang et al 2009) prepared with 4 and 9 h of crosslinking time (50 and17 kgm2 h respectively) and CA-based NF hollow fiber (31 kgm2 h) (Su et al2010) However it was noted that the chemical crosslinking of the PAI hollow fibermembranes resulted in a denser substrate which adversely affected the water permeateflux To overcome this problem Setiawan et al (2012) developed asymmetric micro-porous PAIPES dual-layer hollow fiber membranes that consisted of an external layermade from PAI polymer and an internal layer made of PES Subsequently PEI poly-electrolyte modification was carried out on the outer PAI layer to produce an NF-likethin layer while the PES porous inner layer remained intact because PES is inert toPEI The developed PAIPES dual-layer hollow fiber membranes achieved a PWPof 159 Lm2 h bar and high MgCl2 rejection factors up to 89 In FO process thedual-layer hollow fiber exhibited a water permeate flux of 275 Lm2 h by using05 M MgCl2 as draw solution and deionized water as feed at room temperature

Fang Wang Chou Setiawan and Fane (2012) also fabricated novel compositedouble-skinned PAI hollow fiber membranes for FO In this case two selective skinlayers were integrated in each side of an ultrafiltration (UF) hollow fiber substratevia IP and chemical modification to yield a PA RO-like inner skin layer and a posi-tively charged NF-like outer skin layer The hydrophilic nature of the two skin layersreduced the contact angle of the membrane from 80 for PAI hollow fiber substrate to46 for the composite FO membrane The prepared double-skinned composite hollowfiber membrane exhibited a high PWP of 205 Lm2 h bar and 85 NaCl rejection at1 bar pressure Furthermore compared to commercial HTI FO flat sheet membranes(water flux of 186 kgm2 h (Mc Cutcheon Mc Ginnis amp Elimelech 2006)) and otherdouble-selective layer membranes reported in the literature (195 kgm2 h for dual-layer PBIePES hollow fiber membrane (Yang et al 2009)) the prepared double-skinned composite hollow fiber membrane presented higher water permeate flux of413 kgm2 h and a low salt fluxwater flux (JsJw) ratio of 0126 when using distilled

Novel and emerging membranes for water treatment 307

water and 2 M NaCl as feed and draw solution respectively the active layer faced theAL-DS orientation (PRO mode)

Compared to the conventional asymmetric membranes (ie CA-based membranes)made by the non-solvent induced phase inversion TFC membranes made by IP onporous support layers have several advantages such as a higher PWP greater soluterejection factors higher chemical stability and mechanical strength (Han et al2012) In addition TFC membranes have more design flexibility by separately tuningselective skins and sub-layers with the aid of using specific designed substrates TFCmembranes are widely used in RO process separation with high performance espe-cially in desalination and high energy efficiency However these RO TFC membraneshave poor permeate water fluxes when used in FO mainly due to the thick and densersupport layer that results in high ICP effect (Yip et al 2010) In fact the porous sup-port layer acts as a diffusive boundary layer which severely reduces the osmotic pres-sure difference across the active layer (Mc Cutcheon amp Elimelech 2006) Thereforean enhancement of this support layer is essential to minimize the ICP effect It wasdemonstrated that the additional resistance to mass transfer of this boundary layer isproportional to the thickness of the support layer and it is inversely proportional toits porosity (Mc Cutcheon amp Elimelech 2007 Yip et al 2010) Consequently thesupport layer for FO membranes must be as thin as possible with a high porosityand a minimal resistance for osmotically driven water transport across the membrane(Widjojo et al 2011)

It is also believed that the membrane performance limiting effects can be reduced bymodifying the support layer of the FO membranes (Alsvik amp Heuroagg 2013a) Wei et al(2011) synthesized flat sheet TFC-FO membranes based on a PS substrate witha straight finger-like structure under a thin sponge-like skin layer The PA selectivelayers were prepared by IP of trimesoyl chloride (TMC) and N-methyl-2-pyrrolidone (NMP) The obtained FO membranes had relatively small structural pa-rameters (S 670e710 mm) as a result of the thin cross-section (728e761 mm) lowtortuosity and high porosity (77e82) of the membrane substrates In addition thesemembranes had high PWP (115e178 Lm2 h bar) and NaCl rejection factors(934e945) in the RO testing mode Compared to the commercial CTA-basedasymmetric FO membranes (HTI Albany) and the brackish water RO membrane(BW30 Dow FilmTec Minneapolis MN) both prepared TFC membranes exhibitedsuperior FO performance achieving FO water permeate flux from 181 to 205 Lm2 hin the AL-DS orientation and water permeate flux from 953 to 120 Lm2 h in theactive layer facing feed solution (AL-FS) orientation when using 05 M NaCl drawsolution Moreover the TFC-FO membranes achieved high water permeate flux main-taining relatively low JsJw (29$10

4e35$104) as a result of their excellent rejectionlayer selectivity (ie their low salt permeabilitywater permeability ratio)

Tiraferri et al (2011) prepared PA TFC flat sheet membrane with PS support layerby casting different polymer solution concentrations and confirmed that the optimalFO membrane consisted of a mixed structure support layer in which a thin sponge-like layer was formed on top of a highly porous macrovoids structure The authorsconcluded that both the active layer transport properties and the support layer structuralcharacteristics needed to be optimized to fabricate a high-performance FO membrane

308 Advances in Membrane Technologies for Water Treatment

Water permeate fluxes of 25 Lm2 h with a consistently high salt rejection factor(gt955) were produced using 1 M NaCl aqeous solution as a draw solution anddeionized water as feed

To improve the FO membrane performance by reducing and delaying the foulingeffect Tiraferri Kang Giannelis and Elimelech (2012) fabricated a highly hydrophil-ic PA TFC-FO flat sheet membrane by surface functionalization with tailored silica(SiO2) NPs The surface of SiO2 NPs was functionalized by coating with two differentsuper-hydrophilic cationic ligands ((3-aminopropyl)trimethoxysilane and N-trime-thoxysilylpropyl-NNN-trimethylammonium chloride) to produce either quaternaryammonium or amine functional groups which were used to irreversibly bind theNPs to the native carboxylic groups of PA FO membranes Lower adhesion forceswere obtained when using 2000 mgL model organic foulant solution bovine serumalbumin and the hydrophilic surfaces compared to the unmodified PA membranesindicating an increase of membrane fouling resistance

With the purpose to prepare high hydrophilic flat sheet TFC membranes fordesalination by FO with a reduced thickness and a sponge-like structure instead of afinger-like structure Han et al (2012) prepared a super-hydrophilic support using sul-fonated poly(ether ketone) (SPEK) polymer It was observed that the TFC-FO mem-branes with the most hydrophilic support exhibited the lowest membrane thickness afully sponge-like structure morphology and the highest water permeate fluxes 50 Lm2 h and 35 Lm2 h tested under PRO and FO modes respectively when usingdistilled water as feed and 2 M NaCl as draw solution The highest water permeateflux of this type of membranes was 22 Lm2 h when tested under PRO mode with amodel seawater solution (35 wt NaCl) used as feed and 2 M NaCl as draw solutionMoreover a reduced S value of the membrane and ICP effects were observed whenblending a hydrophilic material in the membrane support

The FO performance of TFC-FO membranes was found to be further enhanced ifthe hydrophilicity of the substrates was increased as reported by Wang et al(2012) By blending 3 wt of hydrophilic sulfonated PS and PES into the membranesubstrates the resultant TFC-FO flat sheet membranes showed a water permeate fluxas high as 475 Lm2 h in the PRO mode with a salt permeate flux up to 124 gm2 husing 2 M NaCl as draw solution An enhancement of FO performance can be realizedby either increasing the hydrophilicity of the membrane substrate or fabricating mem-brane substrates with finger-like structures to enhance water transport through themembranes

Widjojo et al (2013) also used a sulfonated polyphenylenesulfone (SPPS) mem-brane as a support to prepare FO membranes Compared to TFC-FO membranesmade of hydrophobic non-sulfonated PPS supports those prepared with the hydrophilicSPPS supports comprising 25 mol of sulfonated monomer 330-di-sodiumdisulfate-440-dichlorodiphenyl sulfone achieved 44-fold increment of water permeate flux upto 54 Lm2 h with 88 gm2 h salt reverse permeate flux in PRO mode using 2 MNaCl as draw solution Surprisingly the newly developed TFC-FOmembranes showeda much smaller difference in water permeate flux between PRO and FO modescompared to previous studies indicating much lower ICP effects particularly at lowdraw solution concentrations (ie 05e2 M NaCl) When tested for seawater

Novel and emerging membranes for water treatment 309

desalination using 35 wt NaCl as feed and 2 M NaCl as a draw solution these mem-branes showed the highest water permeate flux ever reported for PRO process (ie22 Lm2 h)

Zhong et al (2013) also developed TFC-FO hollow fiber membranes using SPPSsupports The obtained water permeate fluxes were 306 and 820 Lm2 h for FOand PRO modes respectively using distilled water as feed and 2 M NaCl as a drawsolution while the salt reverse fluxes were maintained below 127 gm2 h The S ofthese membranes was reduced 45 times when the membrane support was changedfrom a non-sulfonated to a sulfonated one

Sukitpaneenit and Chung (2012) assumed that the existing macrovoids in the mem-brane support were undesirable because of their mechanically weak points whichcould cause membrane failure under continuous vibration and backwashing opera-tions In addition a macrovoid-free hollow fiber with a highly sponge-like structurecould reduce the ICP effects and enhance the water permeate flux In this sense novelhigh performance TFC-FO hollow fiber membranes with a high porous structure andmacrovoid-free were prepared As expected this structure enhanced the mechanicalproperties of the membranes which had an S value in the range 219e261 mm and ahigher permeate flux than the membrane prepared using a support containingmacrovoids (Chou et al 2010)

Wang et al (2010) prepared two types of TFC-FO hollow fibers with an ultrathinlayer PA-based RO-like skin layer on either the outer surface (A-FO with a skin layerthickness of 300 nm) or inner surface (B-FO 600 nm) of a porous PES hollow fibersubstrate It was observed that the B-FO hollow fiber membrane had an S parametercomparable to that of pouch-type HTI or cartridge-type HTI FO flat sheet membranes(Figure 96) The A-FO membrane had less water permeate flux and salt rejection fac-tor than the B-FO membrane which showed a water permeate flux of 322 Lm2 h fora draw solution of 05 M NaCl at 23 C Wang et al (2010) finally suggested that theoptimal FO membrane structure should exhibit a small portion of sponge-like layer in athin and a highly porous substrate

Last year the company HTI announced the production of a new highly durable anddimensionally stable TFC flat sheet membrane (the OsMem FO membrane line)designed by HTI (2013) The new TFC membrane has a high permeability and ahigh rejection factor and it is pH tolerant in the range 20e120 with a permeateflux of 20 Lm2 h in FO mode and 49 Lm2 h in PRO mode when tested using 1 MNaCl draw solution and distilled water as feed solution at 23 C The salt rejection fac-tor was 993 Comparatively HTIrsquos CTA FO membrane (HTI-CTA) has a permeateflux of 9 Lm2 h The tested new membrane has a power rate of 35 Wm2 for PRO at10 C and 10 bar

Various research studies were performed to improve the characteristics of the sup-port of PRO membranes PA-based TFC membranes over a polyacrylonitrile (PAN)support were studied by Zhang Fu and Chung (2013) It was revealed that the me-chanical strength pore structure and hydrophilicity of the support could be tailoredby increasing PAN concentration pre-compressing the substrate and coating withpolydopamine (PDA) By increasing the PAN polymer concentration in the supportbetter mechanical strength smaller and more uniform pore sizes and increased

310 Advances in Membrane Technologies for Water Treatment

hydrophilicity were obtained The resultant TFC membranes in PRO tests showed anincreased burst pressure from05 to 8 bar and a power density from almost 0 to 13 Wm2Much higherwater permeateflux andmechanical stabilitywere achieved after immersingthe TFCmembranes in methanol and ethanol It was proved that the ethanol-treated TFCmembrane could support a hydraulic pressure of 10 bar and exhibited a power density of26 Wm2

High-performance TFC PRO membranes with excellent mechanical strength andpower density were designed for osmotic power generation by Han Zhang et al(2013) These PRO membranes consisted of an aromatic PA selective layer formedby IP on the top of a porous polyimide (Matrimid 5218) microporous membrane sup-port The support layer showed a fully sponge-like structure with a small S and excel-lent mechanical properties while the PA selective layer was chemically modified usingpost-fabrication procedures The membranes not only exhibited an excellent PWP ofabout 10 Lm2 h bar and an outstanding power density of 7e12 Wm2 depending onthe feed and water salinity but they also could withstand a hydraulic pressure of15 bar The obtained superior PRO performance is a combinative result of the robustsupport layer with small S and highly permeable PA active layer with a moderate saltpermeability

(a)

(c) (d)

(b)

Figure 96 Cross-section SEM images of forward osmosis (FO) membranes (a) A-FO hollowfiber at X5000 (b) B-FO hollow fiber at X5000 (c) Cartridge-type HTI flat sheet at X300(d) Pouch-type HTI flat sheet at X300Reprinted from Wang Shi et al (2010) with permission from Elsevier

Novel and emerging membranes for water treatment 311

Thin-film nanocomposite (TFN) membranes were also prepared by incorporatingdifferent amounts of titanium dioxide (TiO2) NPs (ranging from 0 to 090 wt) ina PS substrate to reduce the ICP effect (Emadzadeh et al 2014) The results revealedthat both the hydrophilicity and porosity of the substrate were increased and a largenumber of finger-like macrovoids were formed leading to an enhancement of themembrane PWP The TFN membrane prepared with 060 wt TiO2 NPs (designatedas TFN 060) exhibited the best FO performance tested at AL-FS orientation withdistilled water as feed and 05 M NaCl as a draw solution with no significant changein reverse solute flux (ie a water permeate flux of 1881 Lm2 h which is 97 higherthan that of the TFC membrane prepared without TiO2) The enhancement of the waterpermeate flux was attributed to the decrease of the S (039 mm) mainly due to the for-mation of the finger-like macrovoids throughout the substrate and the reduced tortuos-ity It was also observed that a further increase of TiO2 NPs content to 090 wtincreased the membrane PWP but the FO performance of these membranes wascompromised by the significant increase in the reverse solute permeate flux

Amini et al (2013) used functionalized MWCNTs (F-MWCNTs) to synthesizenovel TFN FO flat sheet membranes Amine F-MWCNTs were used as additive inan aqueous solution of 13-phenylendiamine (MPD) to enhance the FO membrane per-formance Different concentrations of F-MWCNTs (001 005 and 01 wt) wereadded and dispersed in the MPD aqueous solution via sonication for 4 h at 30 C(Figure 97) The PA active layer was formed by IP on the top of a cast PS substrateThe obtained water permeate flux of these membranes (in both AL-FS and AL-DSmodes) and their salt rejection factors were simultaneously improved The highest wa-ter permeate flux was 957 Lm2 h which is nearly 160 greater than that of TFCmembranes These improvements were in accordance with the increase of the rough-ness and hydrophilicity of the TFN membranes when F-MWCNTs were incorporatedin the PA selective layer

Electrospun nanofibrous supports were also used to prepare FO and PRO mem-branes because of their superior void volume fraction (ie porosity) and pore intercon-nectivity which results in reduced ICP effects A novel flat sheet PA compositemembrane supported by a non-woven web of electrospun nanofibers was preparedby Bui et al (2011) This TFC membrane comprises an electrospun polymeric nano-fiber support layer and a PA skin layer formed by in situ polymerization It wasobserved that these membranes exhibited greater water permeate fluxes two to fivetimes higher than those of the commercial HTI-CTA membrane Recently Bui andMc Cutcheon (2013) used different materials to develop hydrophilic nanofibrous sup-ports by electrospinning different blends of CA at different ratios and PAN(Figure 98) In this study PA selective layer was formed on the PANCA nanofibroussupports by IP between MPD and TMC The prepared membranes exhibited excellentpermselectivity a reduced resistance to mass transfer low S and high water perme-abilities two to three times greater than HTI-CA membranes (2036 Lm2 h bar forPAN nanofibrous supports and 0683 Lm2 h bar for HTI-CA membranes)

Hoover et al (2013) prepared TFC membranes composed of an electrospun tere-phthalate (PET) nanofibrous support a PS phase inversion microporous layer and aPA selective layer formed by IP The obtained PWP was 113 Lm2 h bar the salt

312 Advances in Membrane Technologies for Water Treatment

(a)

(c) (d)

(b)

Figure 97 Conceptual model of amine functionalized MWCNTs in 13-phenylendiamine(MPD) solution used to prepare novel thin-film nanocomposite (TFN) membranes for forwardosmosis process SEM micrographs displaying the top surface and cross-section of conventionalthin-film composite (TFC) membranes (a and c) and TFNmembranes with 001 wtvol (b andd) respectivelyReprinted from Amini et al (2013) with permission from Elsevier

Novel and emerging membranes for water treatment 313

permeability was 023 Lm2 h and the S value was 0651 mm It was detected that theuse of electrospun fibers in the support layer enhanced the membrane resistance todelamination at high cross-flow velocities

It is worth noting that most supports used for the fabrication of FO membranes arehydrophilic mainly because of the concerns of higher fouling tendency of the morehydrophobic supports However hydrophobic materials such as polyvinylidene fluo-ride (PVDF) normally possess strong chemical resistance which could extend the useof FO process to some harsh environments with chemical wastes such as aromatic hy-drocarbons ketones ethers and esters Tian et al (2013) used electrospun PVDF

(a) (b)

(d)

(e)

(c)

Figure 98 SEM images of thin-film composite membranes supported on a polyacrylonitrile(PAN) nanofibrous support Cross-sectional (a) X1500 and (b) X2500 Top surface (c) X10 000and (e) X40 000 Bottom surface (d) X20 000 and zoom-in image showing the pores that wereformed on the bottom side of the polyamide (PA) selective layer when a fiber was removed fromthis layerReprinted with permission from Bui and Mc Cutcheon (2013) Copyright 2012 AmericanChemical Society

314 Advances in Membrane Technologies for Water Treatment

nanofibrous supports followed by IP to prepare high-performance TFC-FO mem-branes The S value of the TFC membrane was found to be as low as 0315 mm whichis better than most of the FO membranes reported in the literature As a result a waterpermeate flux of 304 Lm2 h was obtained when using 1 M NaCl as a draw solutionand distilled water as feed in ALeDS orientation

LbL assembly method was used for the fabrication of high-FO-performance mem-branes because of the formed ultrathin layers For instance LbL method was used toproduce ultrathin barrier layers assembled by oppositely charged polyelectrolytes(Pardeshi amp Mungray 2014) NaOH treated PAN membrane substrate (PAN-OH)is immersed in a polycation solution (1 gL PAH05 M NaCl solution) and a poly-anion solution (1 gL PSS05 M NaCl solution) following an alternative sequenceThis type of membranes exhibits high PWP and good retention against divalentions which makes them suitable candidates for FO membranes In addition LbLpolyelectrolyte layers generally have high solvent resistance (except in some ternarysolvent mixtures) and high thermal stability (eg no deterioration under 200 Cannealing temperature) (Qi et al 2011)

By using the LbL assembly method Qi et al (2011) synthesized a novel NF-likeFO membrane with good magnesium chloride retention factors The membrane sub-strate was tailored (high porosity finger-like pores thin cross-section and high hydro-philicity) to achieve a small S of 05 mm It was observed that the increased number ofpolyelectrolyte layers from one to six improved the selectivity but reduced the PWPSevere solute reverse transport was also detected for the ALeDS orientation Incontrast the ALeFS orientation showed remarkable FO performance (water permeatefluxes of 15 20 and 28 Lm2 h at 01 05 and 10 M MgCl2 respectively for themembrane 3LbL using distilled water as feed solution) superior to other NF-likeFO membranes reported in the literature (Setiawan et al 2011 Su et al 2010Wang et al 2007 Wang Yang et al 2009 Yang et al 2009) (see Table 91)

With the aim to investigate and compare the FO performance and fouling behaviorof double-skinned and single-skinned FO membranes Qi et al (2012) synthesizednovel membranes following the LbL assembly method as shown in Figure 99 TheLbL rejection skin on the top surface was formed by soaking only the top substratein PAH solution and then in PSS solution Three polyelectrolyte layers were depositedfor the top rejection skin The bottom LbL rejection skin was similarly prepared byexposing only the bottom surface of the substrate during the soaking steps and theeffects of the number of polyelectrolyte layers (from 0 to 3) on the FO membrane per-formance were studied The results revealed that both the top and bottom skins contrib-uted to the overall water resistance of the double-skinned LbL membranes Howeverthe overall salt rejection factor was mainly determined by the top skin layer Thedouble-skinned LbL FO membranes achieved excellent FO water permeate fluxesup to 501 and 1061 Lm2 h when the bottom skin layer was faced the draw solution(DS-PROmode) or the feed solution (FSeFOmode) respectively and low JsJw ratios(0405 and 0487 gL for PRO and FO mode respectively) when using 2 M MgCl2 asdraw solution at 23 C and distilled water as feed Furthermore the double-skinnedLbL membranes demonstrated much better antifouling performance compared to thesingle-skinned counterpart

Novel and emerging membranes for water treatment 315

(1) Formation of top selective layer

PAH polycation PSS polyanion

Top surface of PAN

Bottom surface of PAN

Negative charged PAN substrate

Step 1b coating substrate top surface with PSS

Step 1a coating substrate top surface with PAH

Step 2b coating substrate bottom surface with PSS

Steps 2a and 2b can be repeated to form multiple PAHPSS layers on the bottom surface ifneeded

Step 2a coating substrate bottom surface with PAH

Steps 1a and 1b can be repeated to form multiple PAHPSS layers on the surface if needed

(2) Formation of bottom selective layer

Figure 99 Conceptual illustrations of double-skinned LbL membrane fabrication and SEMcross-section of the PAN-OH supports of a single-skinned forward osmosis (FO) membrane(1 a) and a double-skinned FO membrane (2 b)Figure 99a reprinted with permission from Qi et al (2011) Copyright 2011 American ChemicalSociety and Figure 99b reprinted from Qi et al (2012) with permission from Elsevier

316 Advances in Membrane Technologies for Water Treatment

To reduce biological fouling and enhance the performance of the membranes inFO applications Liu et al (2013) added Ag NPs to the top surface of the membranesupports The LbL assembly method was used to fabricate novel Ag nanocomposite(LbL-Ag) NF and FO membranes It was observed that the surface roughnessincreased with the amount of Ag NPs The incorporation of Ag NPs also increasedthe hydrophilicity of the membrane surface (ie the contact angle decreased from691 to 513) The experimental results indicated that the small amount of AgNPs incorporated in the LbL-Ag FO membranes had little effect on the membranestructure and thus maintaining their original separation properties Around001 wt was chosen as the optimal Ag NPs concentration to obtain LbL-Ag mem-branes with good FO performance (MgCl2 rejection factor of 95 and waterpermeate fluxes of 422 and 178 Lm2 h in PRO and FO mode respectively using10 mM NaCl as feed and 05 M MgCl2 as draw solution at 23 C) MoreoverLbL-Ag membranes exhibited excellent antibacterial properties against Gram-positive (Bacillus subtilis) and Gram-negative bacteria (E coli)

Pardeshi and Mungray (2014) used polymer nanocomposites to tailor membranesupport and develop FO LbL self-assembled membranes with appropriate transportcharacteristics Nanocomposite of PVA lithium chloride (LiCl) and montmoril-lonite clay (surface modified with 25e30 wt methyl dihydroxyethyl hydrogenat-ed tallow ammonium MMt-TA) were used to synthesize the substrate of the FOmembrane (PVAMMt-TALiCl nanocomposite substrate) This type of substratesshowed a spongy structure a high porosity (81) an average thickness of about2643 mm and a high hydrophilicity The active layer of the membrane was pre-pared by LbL assembly of polyelectrolytes (CS as a polycation and polyacrylicacid as a polyanion) Three layers of polyelectrolyte were applied on PVAMMt-TALiCl substrate The resultant membranes (PVAMMt-TALiCl 3LbL) had athin sponge-like skin layer (about 3 mm) which was responsible for the observedlow reverse salt diffusion (0281 and 0051 gm2 h for PRO and FO mode respec-tively) The high hydrophilic nature of the PVAMMt-TALiCl support enhancedthe water permeate flux up to 3765 Lm2 h (PRO mode) and 255 Lm2 h (FOmode) when distilled water was used as feed and 2 M NaCl solution as drawsolution at 26 C

You et al (2013) developed a thin-film inorganic (TFI) membrane by LbL depo-sition of microporous SiO2 xerogels immobilized onto a stainless steel mesh supportIt was observed that the quasi-symmetry TFI microporous structure of the SiO2 mem-brane was responsible for the low ICP effect enhancing the water permeate flux dur-ing the FO process The TFI membrane showed a good NaCl rejection factor of 92and high water permeate fluxes of 603 Lm2 h and 598 Lm2 h for PRO and FOmode respectively when using distilled water as feed and 2 M NaCl solution asdraw solution at ambient temperature Particularly by increasing the temperatureto 70 C the water permeate flux was increased to 8502 Lm2 h at pH 6 It wasclaimed that the ability of the TFI membrane to sustain FO process without any curl-ing wrinkling cracking deformation or dissolution under harsh conditions also sug-gested a superior mechanical strength and thermal and chemical stability of thesemembranes over polymeric FO membranes

Novel and emerging membranes for water treatment 317

94 Conclusions

This chapter focuses on water treatment by ED and FO with special attention to thealternative technologies of emerging interests RED and PRO used for energy generationthrough a salinity-gradient difference Although membranes typically used for ED andRED processes are IEMs (AEMs and CEMs) BPMs are also reviewed due to their ad-vantages (eg separation of monovalent and divalent ions antideposition antifoulingwater dissociation into OHe and Hthorneions increase of reusability and recyclability ofwaste through chemical production low initial cost etc) Most of the research studieshave been focused on the improvement of the performance of these membranesincluding their physicochemical and electrochemical properties to optimize both EDand RED processes Various membrane-based polymers (SPES PS PVC PVASPEEK PECH etc) have been used and different membrane modification techniqueshave been applied such as thermal and chemical crosslinking quaternization sulfona-tion photo-induced covalent immobilization in situ polymerization addition of NPs orinorganic fillers as functional groups or additives etc Not only is the improvement ofthe membrane properties necessary to achieve high ED and RED performances butit is also important to consider the scale-up and design of the EDRED unit and theoptimization of the electrode systems

For the preparation of FO and PRO membranes different polymers were usedincluding CA CTA PS PES PBI PA PAI PVP PAN and PET Three differentmethods have been adopted to prepare polymeric FOPRO membranes (non-solventphase inversion IP on porous substrates and the LbL deposition) IP is the most-used technique TFC membrane structure either in flat sheet or hollow fiberconfiguration exhibits high water permeability solute rejection factor chemical stabilityand mechanical strength and good design flexibility by separately tuning the selectiveskins and sub-layers

Improved membrane characteristics and performance were achieved using differentmodification techniques such as chemical or thermal post-treatment chemical cross-linking surface functionalization via coating pre-compressing and coating the substrateincorporating different amounts of additives or fillers etc

95 Future trends

Membrane technologies experienced significant development during the last decadesdriven by available advanced materials novel technologies changes of environmentalregulations increasing demand of water supply and sanitation etc The availability ofnovel tailored membranes with specific properties and new membrane processes offersimportant tools for the design of alternative production systems appropriate for a sus-tainable growth

Researchers have made sufficient progress in the development of new membranematerials modifying the membrane surface to improve their performance detectingnew application fields and emerging membrane technologies etc Furthermore theintegration of different membrane processes was also explored because it potentially

318 Advances in Membrane Technologies for Water Treatment

allows the possibility to redesign important industrial processes with enhanced benefitsin terms of product quality quantity energy efficiency and cost

Some technologies especially the emerging ones are still far from fulfilling all thedeposited expectations on them However they are still in continuous improvementtrying to overcome the many challenges and barriers to extend their field of industrialapplications

List of acronyms

g-MPS g-methacryloxypropyl trimethoxy silane4-VP 4-vinylpyridineA1100 (3-aminopropyl) triethoxysilaneAC Activated carbonAEL Anion exchange layerAEM Anion exchange membraneAg SilverAL-DS Active layer facing draw solutionAL-FS Active layer facing feed solutionBPM Bipolar membraneCA Cellulose acetateCEL Cation exchange layerCEM Cation exchange membraneCS ChitosanCTA Cellulose triacetateED ElectrodialysisEDR Electrodialysis reversalEO Engineered OsmosisFe3O4 Iron oxideFeCl3 Ferric chlorideF-MWCNTs Functionalized MWCNTsFO Forward osmosisHTI Hydration Technology InnovationsICP Internal concentration polarizationIEMs Ion-exchange membranesIP Interfacial polymerizationLbL Layer-by-layerLiCl Lithium chlorideMMt-TA Methyl dihydroxyethyl hydrogenated tallow ammoniumMPD 13-phenylendiamineMWCNTs Multiwalled carbon nanotubesNF NanofiltrationNMP N-methyl-2-pyrrolidoneNPs NanoparticlesPA PolyamidePAH Poly(allylamine hydrochloride)PAI Poly(amide-imide)PAN PolyacrylonitrilePANI Polyaniline

Novel and emerging membranes for water treatment 319

PBI PolybenzimidazolePDA PolydopaminePECH PolyepichlorohydrinPEI PolyethyleneiminePES PolyethersulfonePET TerephthalatePRO Pressure retarded osmosisPS PolysulfonePSS Poly(sodium 4-styrene sulfonate)PVA Polyvinyl alcoholPVC PolyvinylchloridePVDF Polyvinylidene fluoridePVP PolyvinylpyrrolidoneRED Reverse electrodialysisRO Reverse osmosisSDBS Sodium dodecylbenzene sulfonateSGP Salinity gradient powerSiO2 SilicaSPEEK Sulfonated polyetheretherketoneSPEK Sulfonated poly(ether ketone)SPES Sulfonated poly(ether sulfone)SPPS Sulfonated polyphenylenesulfoneTFC Thin-film compositeTFI Thin-film inorganicTFN Thin-film nanocompositeTiO2 Titanium dioxideTMC Trimesoyl chlorideUF UltrafiltrationVBC Vinylbenzyl chlorideZrT Zirconium tri-ethylene tetra-amine

List of symbols

JM2D Bivalent cation permeate fluxJCu2D Cu2thorn permeate fluxJS Saltsolute permeate fluxJW Water permeate fluxPWP Pure water permeabilityS Structural parameter

References

Achilli A amp Childress A E (2010) Pressure retarded osmosis From the vision of SidneyLoeb to the first prototype installationmdashreview Desalination 261 205e211

Alsvik I amp Heuroagg M B (2013a) Pressure retarded osmosis and forward osmosis membranesMaterials and methods Polymers 5 303e327

320 Advances in Membrane Technologies for Water Treatment

Alsvik I L amp Heuroagg M B (2013b) Preparation of thin film composite membranes withpolyamide film on hydrophilic supports Journal of Membrane Science 428 225e231

Amini M Jahanshahi M amp Rahimpour A (2013) Synthesis of novel thin film nano-composite (TFN) forward osmosis membranes using functionalized multi-walled carbonnanotubes Journal of Membrane Science 435 233e241

Arena J T Mc Closkey B Freeman B D amp Mc Cutcheon J R (2011) Surface modi-fication of thin film composite membrane support layers with polydopamine Enablinguse of reverse osmosis membranes in pressure retarded osmosis Journal of MembraneScience 375 55e62

Brauns E (2009) Salinity gradient power by reverse electrodialysis Effect of modelparameters on electrical power output Desalination 237 378e391

Bui N N Lind M L Hoek E M V amp Mc Cutcheon J R (2011) Electrospun nanofibersupported thin film composite membranes for engineered osmosis Journal of MembraneScience 385e386 10e19

Bui N N amp Mc Cutcheon J R (2013) Hydrophilic nanofibers as new supports for thin filmcomposite membranes for engineered osmosis Environmental Science and Technology47 1761e1769

Burheim O S Seland F Pharoah J G amp Kjelstrup S (2012) Improved electrode systemsfor reverse electro-dialysis and electro-dialysis Desalination 285 147e152

Cadotte J E (1981) Interfacially synthesized reverse osmosis membrane US Patent 4277344Cath T Childress A amp Elimelech M (2006) Forward osmosis Principles applications and

recent developments Journal of Membrane Science 281 70e87Cornelissen E R Harmsen D de Korte K F Ruiken C J Qin J J Oo H et al (2008)

Membrane fouling and process performance of forward osmosis membranes on activatedsludge Journal of Membrane Science 319 158e168

Chakrabarty T Rajesh A M Jasti A Thakur A K Singh A K Prakash S et al(2011) Stable ion-exchange membranes for water desalination by electrodialysisDesalination 282 2e8

Chakrabarty T Shah B Srivastava N Shahi V K amp Chudasamab U (2013) Zirconiumtri-ethylene tetra-amine ligand-chelator complex based cross-linked membrane forselective recovery of Cu2thorn by electrodialysis Journal of Membrane Science 428462e469

Cho Y H Han J Han S Guiver M D amp Park H B (2013) Polyamide thin-filmcomposite membranes based on carboxylated polysulfone microporous support mem-branes for forward osmosis Journal of Membrane Science 445 220e227

Chou S Shi L Wang R Tang C Y Qiu C amp Fane A G (2010) Characteristics andpotential applications of a novel forward osmosis hollow fiber membrane Desalination261 365e372

Chou S Wang R Shi L She Q Tang C amp Fane A G (2012) Thin-film compositehollow fiber membranes for pressure retarded osmosis (PRO) process with high powerdensity Journal of Membrane Science 389 25e33

Emadzadeh D Lau W J Matsuura T Ismail A F amp Rahbari-Sisakht M (2014)Synthesis and characterization of thin film nanocomposite forward osmosis membranewith hydrophilic nanocomposite support to reduce internal concentration polarizationJournal of Membrane Science 449 74e85

Fang W Wang R Chou S Setiawan L amp Fane A G (2012) Composite forwardosmosis hollow fiber membranes Integration of RO- and NF-like selective layers toenhance membrane properties of anti-scaling and anti-internal concentration polarizationJournal of Membrane Science 394e395 140e150

Novel and emerging membranes for water treatment 321

Geurouler E Elizen R Vermaas D A Saakes M amp Nijmeijer K (2013) Performance-determining membrane properties in reverse electrodialysis Journal of Membrane Science446 266e276

HTI (2013) HTIrsquos new thin film forward osmosis membrane in production Retrieved fromwwwhtiwatercom

Han G Chung T S Toriida M amp Tamai S (2012) Thin-film composite forward osmosismembranes with novel hydrophilic supports for desalination Journal of MembraneScience 423-424 543e555

Han G Wang P amp Chung T S (2013) Highly robust thin-film composite pressureretarded osmosis (PRO) hollow fiber membranes with high power densities for renewablesalinity-gradient energy generation Environmental Science and Technology 478070e8077

Han G Zhang S Li X amp Chung T S (2013) High performance thin film compositepressure retarded osmosis (PRO) membranes for renewable salinity-gradient energy gen-eration Journal of Membrane Science 440 108e121

Herron J (2008) Asymmetric forward osmosis membranes US Patent 7445712 B2Hong J G Zhang W Luo J amp Chen Y (2013) Modeling of power generation from the

mixing of simulated saline and freshwater with a reverse electrodialysis system The effectof monovalent and multivalent ions Applied Energy 110 244e251

Hoover L A Schiffman J D amp Elimelech M (2013) Nanofibers in thin-film compositemembrane support layers Enabling expanded application of forward and pressure retardedosmosis Desalination 308 73e81

Hosseini S M Askari M Koranian P Madaeni S S amp Moghadassia A R (2014)Fabrication and electrochemical characterization of PVC based electrodialysis heteroge-neous ion exchange membranes filled with FE3O4 nanoparticules Journal of Industrialand Engineering Chemistry 20 2510e2520

Hosseini S M Koranian P Gholami A Madaeni S S Moghadassi A R Sakinejad Pet al (2013) Fabrication of mixed matrix heterogeneous ion exchange membrane bymultiwalled carbon nanotubes Electrochemical characterization and transport properties ofmono and bivalent cations Desalination 329 62e67

Huang L Bui N N Meyering M T Hamlin T J amp McCutcheon J R (2013) Novelhydrophilic nylon 66 microfiltration membrane supported thin film composite membranesfor engineered osmosis Journal of Membrane Science 437 141e149

Kariduraganavar M Y Nagarale R K Kittur A A amp Kulkarni S S (2006) Ion-exchangemembranes Preparative methods for electrodialysis and fuel cell applications Desalina-tion 197 225e246

Kumar M Khan M A Alothman Z A amp Siddiqui M R (2013) Polyaniline modifiedorganiceinorganic hybrid cation-exchange membranes for the separation of monovalentand multivalent ions Desalination 325 95e103

Li X Wang K Y Helmer B amp Chung T S (2012) Thin-film composite membranes andformation mechanism of thin-film layers on hydrophilic cellulose acetate propionate sub-strates for forward osmosis processes Industrial and Engineering Chemistry Research 5110039e10050

Liu X Qi S Li Y Yang L Cao B amp Tang C Y (2013) Synthesis and characterization ofnovel antibacterial silver nanocomposite nanofiltration and forward osmosis membranesbased on layer-by-layer assembly Water Research 47 3081e3092

Loeb S amp Sourirajan S (1963) Sea water demineralization by means of an osmoticmembrane In A I Chemistry (Ed) Saline water conversion-II American ChemicalSociety

322 Advances in Membrane Technologies for Water Treatment

Mc Cutcheon J R amp Elimelech M (2006) Influence of concentrative and dilutive internalconcentration polarization on flux behavior in forward osmosis Journal of MembraneScience 284 237e247

Mc Cutcheon J R amp Elimelech M (2007) Modeling water flux in forward osmosis Impli-cations for improved membrane design AIChE Journal 53 1736e1744

Mc Cutcheon J R amp Elimelech M (2008) Influence of membrane support layer hydro-phobicity on water flux in osmotically driven membrane processes Journal of MembraneScience 318 458e466

Mc Cutcheon J R Mc Ginnis R L amp Elimelech M (2006) Desalination by ammo-niaecarbon dioxide forward osmosis Influence of draw and feed solution concentrationson process performance Journal of Membrane Science 278 114e123

Miller J E amp Evans L R (2006) Forward osmosis A new approach to water purificationand desalination United States of America Sandia National Laboratories

Mulyati S Takagi R Fujii A Ohmukai Y Maruyama T amp Matsuyama H (2012)Improvement of the antifouling potential of an anion exchange membrane by surfacemodification with a polyelectrolyte for an electrodialysis process Journal of MembraneScience 417-418 137e143

Mulyati S Takagi R Fujii A Ohmukai Y amp Matsuyama H (2013) Simultaneousimprovement of the monovalent anion selectivity and antifouling properties of an anionexchange membrane in an electrodialysis process using polyelectrolyte multilayer depo-sition Journal of Membrane Science 431 113e120

Nguyen T P N Yun E T Kim I C amp Kwon Y N (2013) Preparation of cellulosetriacetatecellulose acetate (CTACA)-based membranes for forward osmosis Journal ofMembrane Science 433 49e59

Pardeshi P ampMungray A A (2014) Synthesis characterization and application of novel highflux FO membrane by layer-by layer self-assembled polyelectrolyte Journal of MembraneScience 453 202e211

Post J W Hamelers H V M amp Buisman C J N (2008) Energy recovery from controlledmixing salt and fresh water with a reverse electrodialysis system Environmental Scienceand Technology 42 5785e5790

Post J W Veerman J Hamelers H V M Euverink G J W Metz S J Nymeijer K et al(2007) Salinity-gradient power Evaluation of pressure-retarded osmosis and reverseelectrodialysis Journal of Membrane Science 288 218e230

Qi S Qiu C Q amp Tang C Y (2011) Synthesis and characterization of novel forwardosmosis membranes based on layer-by-layer assembly Environmental Science andTechnology 45 5201e5208

Qi S Qiu C Q Zhao Y amp Tang C Y (2012) Double-skinned forward osmosis membranesbased on layer-by-layer assemblymdashFO performance and fouling behavior Journal ofMembrane Science 405-406 20e29

Qiu C Setiawan L Wang R Tang C Y amp Fane A G (2012) High performance flat sheetforward osmosis membrane with an NF-like selective layer on a woven fabric embeddedsubstrate Desalination 287 266e270

Setiawan L Wang R Li K amp Fane A G (2011) Fabrication of novel poly(amideeimide)forward osmosis hollow fiber membranes with a positively charged nanofiltration-likeselective layer Journal of Membrane Science 369 196e205

Setiawan L Wang R Shi L Li K amp Fane A G (2012) Novel dual-layer hollow fibermembranes applied for forward osmosis process Journal of Membrane Science 421-422238e246

Novel and emerging membranes for water treatment 323

Sivertsen E Holt T Thelin W amp Brekke G (2013) Pressure retarded osmosis efficiency fordifferent hollow fibre membrane module flow configurations Desalination 312 107e123

Song X Liu Z amp Sun D D (2011) Nano gives the answer breaking the bottleneck ofinternal concentration polarization with a nanofiber composite forward osmosis membranefor a high water production rate Advanced Materials 23 3256e3260

Su J amp Chung T S (2011) Sublayer structure and reflection coefficient and their effects onconcentration polarization and membrane performance in FO processes Journal ofMembrane Science 376 214e224

Su J Yang Q Teo J F amp Chung T S (2010) Cellulose acetate nanofiltration hollow fibermembranes for forward osmosis processes Journal of Membrane Science 355 36e44

Sukitpaneenit P amp Chung T S (2012) High performance thin-film composite forwardosmosis hollow fiber membranes with macrovoid-free and highly porous structure forsustainable water production Environmental Science and Technology 46 7358e7365

Tian M Qiu C Liao Y Chou S amp Wang R (2013) Preparation of polyamide thin filmcomposite forward osmosis membranes using electrospun polyvinylidene fluoride (PVDF)nanofibers as substrates Separation and Purification Technology 118 727e736

Tiraferri A Kang Y Giannelis E P amp Elimelech M (2012) Highly hydrophilic thin-filmcomposite forward osmosis membranes functionalized with surface-tailored nanoparticlesACS Applied Materials and Interfaces 4 5044e5053

Tiraferri A Yip N Y Phillip W A Schiffman J D amp Elimelech M (2011) Relatingperformance of thin-film composite forward osmosis membranes to support layer formationand structure Journal of Membrane Science 367 340e352

Valero F amp Arbos R (2010) Desalination of brackish river water using electrodialysisreversal (EDR) Desalination 253 170e174

Venugopal K amp Dharmalingam S (2012) Desalination efficiency of a novel bipolar mem-brane based on functionalized polysulfone Desalination 296 37e45

Vermaas D A Saakes M amp Nijmeijer K (2011) Power generation using profiled mem-branes in reverse electrodialysis Journal of Membrane Science 385-386 234e242

Wang A Peng S Wu Y Huang C amp Xu T (2010) A hybrid bipolar membrane Journalof Membrane Science 365 269e275

Wang K Y Chung T S amp Amy G (2012) Developing thin-film-composite forwardosmosis membranes on the PESSPSf substrate through interfacial polymerization AIChEJournal 58 770e781

Wang K Y Chung T S amp Qin J J (2007) Polybenzimidazole (PBI) nanofiltration hollowfiber membranes applied in forward osmosis process Journal of Membrane Science 3006e12

Wang K Y Ong R C amp Chung T S (2010) Double-skinned forward osmosis membranesfor reducing internal concentration polarization within the porous sublayer Industrial andEngineering Chemistry Research 49 4824e4831

Wang K Y Yang Q Chung T S amp Rajagopalan R (2009) Enhanced forward osmosisfrom chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membraneswith a thin wall Chemical Engineering Science 64 1577e1584

Wang M Jia Y X Yao T T amp Wang K K (2013) The endowment of monovalentselectivity to cation exchange membrane by photo-induced covalent immobilization andself-crosslinking of chitosan Journal of Membrane Science 442 39e47

Wang R Shi L Tang C Y Chou S Qiu C amp Fane A G (2010) Characterization ofnovel forward osmosis hollow fiber membranes Journal of Membrane Science 355158e167

324 Advances in Membrane Technologies for Water Treatment

Wang Y Goh S H Chung T S amp Na P (2009) Polyamide-imidepolyetherimidedual-layer hollow fiber membranes for pervaporation dehydration of C1eC4 alcoholsJournal of Membrane Science 326 222e233

Wei J Qiu C Tang C Y Wang R amp Fane A G (2011) Synthesis and characterization offlat-sheet thin film composite forward osmosis membranes Journal of Membrane Science372 292e302

Widjojo N Chung T S Weber M Maletzko C amp Warzelhan V (2011) The role ofsulphonated polymer and macrovoid-free structure in the support layer for thin-filmcomposite (TFC) forward osmosis (FO) membranes Journal of Membrane Science 383214e223

Widjojo N Chung T S Weber M Maletzko C amp Warzelhan V (2013) A sulfonatedpolyphenylenesulfone (sPPSU) as the supporting substrate in thin film composite (TFC)membranes with enhanced performance for forward osmosis (FO) Chemical EngineeringJournal 220 15e23

Xu T (2005) Ion exchange membranes state of their development and perspective Journal ofMembrane Science 263 1e29

Xu Y Peng X Tang C Y Fu Q S amp Nie S (2010) Effect of draw solution concentrationand operating conditions on forward osmosis and pressure retarded osmosis performance ina spiral wound module Journal of Membrane Science 348 298e309

Yang Q Wang K Y amp Chung T S (2009) Dual-layer hollow fibers with enhanced flux asnovel forward osmosis membranes for water production Environmental Science andTechnology 43 2800e2805

Yip N Y Tiraferri A Phillip W A Schiffman J D amp Elimelech M (2010) High per-formance thin-film composite forward osmosis membrane Environmental Science andTechnology 44 3812e3818

You S Tang C Yu C Wang X Zhang J Han J et al (2013) Forward osmosis with anovel thin-film inorganic membrane Environmental Science and Technology 478733e8742

Yu Y Seo S Kim I C amp Lee S (2011) Nanoporous polyethersulfone (PES) membranewith enhanced flux applied in forward osmosis process Journal of Membrane Science 37563e68

Zendehnam A Robatmili N Hosseini S M Arabzadegan M amp Madaenic S S (2013)Fabrication of novel (acrylonitrile butadiene styrene-activated carbon-silver nano-particules) heterogeneous anion exchange membrane Physico-chemical and antibacterialcharacteristics Journal of the Taiwan Institute of Chemical Engineering 44 670e677

Zhang S Fu F amp Chung T S (2013) Substrate modifications and alcohol treatment onthin film composite membranes for osmotic power Chemical Engineering Science 8740e50

Zhang S Wang K Y Chung T S Chen H Jean Y C amp Amy G (2010)Well-constructed cellulose acetate membranes for forward osmosis Minimized internalconcentration polarization with an ultra-thin selective layer Journal of MembraneScience 360 522e535

Zhao S Zou L Tang C Y amp Mulcahy D (2012) Recent developments in forwardosmosis Opportunities and challenges Journal of Membrane Science 396 1e21

Zhong P Fu X Chung T S Weber M amp Maletzko C (2013) Development of thin-filmcomposite forward osmosis hollow fiber membranes using direct sulfonatedpolyphenylenesulfone (sPPSU) as membrane substrates Environmental Science and Tech-nology 47 7430e7436

Novel and emerging membranes for water treatment 325

Planning and designof membrane systems forwater treatment

10VS FrenkelSan Francisco CA USA

101 Introduction

Population and industry growth and limits to the current water supply are driving theneed to find new sources of water develop the more sustainable use of current watersources and improve water reuse Membrane technologies are playing a vital role inall these areas in increasing the available water supply portfolio for communitiesindustry or agricultural users As a confirmation membrane projects are demon-strating significant growth of membrane technology applications by increasing capac-ities of new membrane projects and upgrading existing facilities with membranesMembrane technologies have entered every corner of water and wastewater treatmentsuch as municipal and industrial water advanced wastewater treatment and reuseand sea and brackish water desalination The major reasons are the unique featuresthat membrane technologies can provide for solving water shortages which is in closeassociation with global climate change This trend accelerated the growth of themembrane market in past years and fuels the expected growth for the future

Because membrane technologies are separation technologies the simplified sche-matic of the membrane separation process is shown using the example of the reverseosmosis (RO) membrane process in Figure 101

The membrane process comprises three major streams

bull Feedbull Permeate (product water)bull Concentrate (reject or brine)

The mass balance for the entire system can be represented as follows

Qf Cf frac14 Qc Cc thorn Qp Cp

in which

bull Qf - feed flow (gpm or m3hr)bull Cf - salt concentration in feed water (mgL or ppm)bull Qc - concentrate flow (gpm or m3hr)bull Cc - salt concentration in concetrate (mgL or ppm)bull Qp - product flow (gpm or m3hr)bull Cp - salt concentration in product water (mgL or ppm)

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400010-1Copyright copy 2015 Elsevier Ltd All rights reserved

The membrane technology mass and hydraulic balance is a cross-check that allowsone to perform validation of the process integrity

102 Membrane types and configurations forwater treatment

Membranes are represented by four major membrane types categorized by the rate oftreatment and are in commercial use at present (Design of Municipal Waste 2009Frenkel 2011)

bull Microfiltration (MF) - screens particles from 01 to 05 mmbull Ultrafiltration (UF) - screens particles from 0005 to 005 mmbull Nanofiltration (NF) - screens particles from 00005 to 0001 mmbull RO - ranging molecular size down to 10 MWCO

Figure 102 demonstrates the relative size of different membrane types compared tothe conventional treatment processes and constituents of concern when treating water

MF and UF membranes were commercialized for drinking water treatment justabout 15 years ago Because they provide significant technical benefits and havebecome cost-competitive membrane technologies are rapidly replacing traditionalprocesses verified by the centuries

The differences in membrane shape and the type of membrane process drivingforces can be categorized as shown in Figure 103

Membrane shape type Spiral wound hollow fiber flat sheetMembrane type depending on driven pressure

bull Pressure-driven (low-pressure MF UF and high-pressure NF and RO)bull Immersed vacuum driven (low-pressure MF UF only)

The electrical current can drive membrane treatment as well and it is used inelectrodialysis (ED) electrodialysis reversal (EDR) and electrodeionization (EDI)membrane treatment processes

Membrane

Concentrate

Reject

Brine

Feed

Raw water

Qf cf

QC Cc

Qp Cp

Recovery = QpQf

Rejection = CcCf

Permeate

Treated water

Figure 101 Simplified diagram of reverse osmosis (RO) process major RO streams

330 Advances in Membrane Technologies for Water Treatment

Figure 102 Membranes and water treatment processesCourtesy of Val S Frenkel

Planning

anddesign

ofmem

branesystem

sfor

water

treatment

331

103 Low- and high-pressure membranes

As shown in Figure 102 membranes are broken down to two major categories

bull Low-pressure membranes represented by MF and UF membranes andbull High-pressure membranes represented by NF and RO membranes

One of the key difference between high- and low-pressure membranes is that thehigh-pressure membranes were developed to remove dissolved matter from the waterwhile they are not tolerant of suspended and colloidal matter The low-pressure mem-branes are opposite having high tolerance and high efficiency in the removal of sus-pended and organic matter while dissolved matter passes through the membranes Anumber of techniques were developed for numerous applications to convert certain dis-solved ions to the solid phase followed by removal using low-pressure membranesDue to the different treatment properties between low- and high-pressure membranesthe integrated membrane systems (IMS) found a niche in numerous applications whenhigh-pressure membranes are following low-pressure membranes in the treatmenttrain using low-pressure membranes as a pretreatment for high-pressure membranes

104 Low-pressure membrane applications

Low-pressure membranes are represented by MF and UF membranes

1041 Microfiltration and ultrafiltration

Membrane technologies include MF and UF membranes These membranes canremove particles and colloidal matter and are often selected over conventionalgranular-media filters based on their high removal efficiencies for Giardia cysts Cryp-tosporidium oocysts bacteria and viruses and the consistently high-quality water

Flat

Membrane type depending on driven power1 Pressure driven (MF UF NF and RO)2 Vacuum driven (MF and UF only)3 High voltage current (EDR and EDI)4 Osmotic power (FO and PRO)

Hollow fiber Spiral wound

Figure 103 Membranes shape type configuration and driven forces

332 Advances in Membrane Technologies for Water Treatment

produced by membranes independent from the source water quality variation andoperator skill (Frenkel amp Mourato 1998)

Membrane separation is a well-developed technology that is becoming a standardpractice in water treatment Membrane separation provides a physical barrier to path-ogens and can produce high-quality safe drinking water at a reasonable cost

1042 Microfiltration

MF is the ldquoloosestrdquo membrane and it screens particles in the range 01e05 mmremoving bacteria protozoan pathogens (Cryptosporidium oocysts Giardia cystsand some viruses) silt colloids and precipitates

MF is a pressure-driven or vacuum-driven (immersed type) membrane separationprocess that separates particulate matter from a fluid (water wastewater or industrialprocess fluid) by physical straining MF membranes have demonstrated more than6-log removal of particles and are credited by regulatory agencies up to 4-log removalfor Giardia and Cryptosporidium MF membranes remove some viruses and arecredited by regulatory agencies up to 05e25-log removal for viruses dependingon the brand and model

The MF membrane filtration surface is a thin synthetic polymer manufactured into ahollow fiber It can be supported or not supported The membrane surface can be on theoutside of the fiber (ldquooutside-inrdquo flow path) or on the inside of the fiber (ldquoinside-outrdquoflow path) Most MF membranes have an outside-in flow configuration in which thefeed water is on the outside surface of the fiber and treated water is collected in theinside of the fiber This outside-in configuration typically permits treating waterwith greater solids loading MF membranes can be also operated either in a cross-flow or in a dead-end flow mode In the dead-end mode all the source water passesthrough the membrane and periodically by batches is discharged on solid concentra-tion around membranes In the cross-flow mode a portion of the source water is dis-charged or recycled back to the inlet of the system continuously The cross-flow modecan accommodate higher solids loading but it may require more energy

Most MF membranes are manufactured from the polymers that are hydrophilic innature such as polyvinylidene fluoride (PVDF) polysulfone (PSF) polytetrafluoro-ethylene (PTFE) polypropylene (PP) and nylon The newer version of Teflon mem-branes were introduced to the market within last few years Most of the membranes areresistant to oxidants such as chlorine with the exception of PP Special agents are oftenadded to the membranes during the fabrication process to reduce fouling of the mem-branes by dissolved organics

The MF filtration system typically consists of membrane modules cassettes unitsand trains as shown in Figure 104

Membrane fibers are grouped together and secured into a single common moduleThe membrane module is repairable and replaceable Multiple membrane modules aresupported and manifolded together with common piping valves and instrumentationto form a complete integrated unit pressure MF skids or immersed MF units in basinsThe membrane unit has independent flow control and is backwashed cleaned andintegrity-tested as a complete unit Multiple membrane units are manifolded together

Planning and design of membrane systems for water treatment 333

into trains or banks to meet the overall capacity requirements for a system as shown inFigure 105

MF systems consistently provide high-quality low-turbidity filtered water (typi-cally below 01 NTU) independently of the source water turbidity fluctuations andoperator skills Depending on the source water characteristics most MF membraneapplications do not require pretreatment In some applications coagulant can be addedto the water to form flocs increasing the membrane treatment efficiency reduce mem-brane fouling andor to adsorb and to allow increasing removal efficiency of dissolvedtotal organic carbon (TOC) from the water In applications with high source watersolids a clarification process or dissolved air flotation (DAF) ahead of the MF system

(a) (b)

Figure 104 Hollow fiber microfiltrationultrafiltration membrane fibers (a) and cassette withmodules (b)

Figure 105 Flat plate microfiltrationultrafiltration immersed membrane trainbankbasin

334 Advances in Membrane Technologies for Water Treatment

may help reduce the membrane system capital and operating costs Depending on thewater chemistry and operational parameters the average MF recovery range is90e95 When coagulant is used the higher recovery of 95e98 can be achievedMF systems typically operate with feed pressures of 25e40 psi

1043 Ultrafiltration

UF screens particles from 0005 to 005 mm and removes most viruses and pathogensin addition to the particles removed by an MF system

Similarly to MF the UF is a pressure-driven or vacuum-driven (immersed type)membrane separation process that separates particulate matter from a fluid (waterwastewater or industrial process fluid) by physical straining UF membranes have ahigh removal efficiency for particles greater than approximately 005 mm includingbacteria pathogens (Cryptosporidium oocysts Giardia cysts) and viruses UF mem-branes have demonstrated removal of more than 6-log for particles and are credited byregulatory agencies with 4-log removal for Giardia and Cryptosporidium UF mem-brane systems also remove most viruses and are credited by regulatory agencieswith 2- to 4-log removal of viruses

Similarly to MF the UF membrane filtration surface is a thin synthetic polymermanufactured into a hollow fiber Many pressure UF membranes have an inside-outflow configuration in which the source water is on the inside surface of the fiberand filtered water is collected on the outside of the fiber This inside-out configurationpermits improved hydrodynamics at the membrane surface to minimize membranefouling and also permits higher pressure across the membrane for greater flux ratesHowever the inside-out configuration requires more energy and cannot handle ashigh a solid loading as the outside-in configuration The inside-out configurationcan be operated in the pressurized mode only not allowing the use of theimmersedvacuum concept The pressurized UF membranes can be also operatedeither in a cross-flow or in a dead-end flow mode In the dead-end mode all the sourcewater passes through the membrane In the dead-end mode all the source water passesthrough the membrane and periodically by batches is discharged on solid concentra-tion around the membranes In the cross-flow mode a portion of the source water isdischarged or recycled back to the inlet of the system continuously The cross-flowmode can accommodate higher solids loading but may require more energy UF mem-branes typically operate in a cross-flow mode on the high solid water

Similarly to MF most UF membranes are manufactured from the polymers that arehydrophilic in nature such as PVDF PSF polyethersulfone (PES) and PTFE MostUF membranes are resistant to oxidants such as chlorine Specific agents are oftenadded to the membranes during the fabrication process to reduce fouling of the mem-branes by dissolved organics

Like MF the UF filtration system typically consists of membrane modules unitsand trains Hollow fiber membranes are grouped together and secured into a singlecommon module This membrane module is repairable and replaceable Multiplemembrane modules are supported and manifolded together with common pipingvalves and instrumentation to form a complete integrated unit pressure UF skids

Planning and design of membrane systems for water treatment 335

or immersed UF units in basins The membrane unit has independent flow controland is backwashed cleaned and integrity-tested as a complete unit Multiple mem-brane units are manifolded together into trains or banks to meet the overall capacityrequirements for a system

UF systems provide consistent high-quality low-turbidity filtered water (typicallybelow 01 NTU) independent of the source water turbidity variations and operatorskills Depending on the source water characteristics UF membrane applicationsmay not require pretreatment In some applications coagulant can be added to the wa-ter to form floc particles to increase the membranersquos filtration efficiency andor toadsorb and reduce dissolved TOC in the water In applications with high source watersolids a clarification process ahead of the UF system may help reduce the capital andoperating costs of the membrane system Depending on the water chemistry and oper-ational parameters the average UF recovery range is 85e95 When coagulant isused the higher recovery of 95e98 can be achieved UF systems typically operatewith feed pressures of 35e50 psi

105 Applications of low-pressure membranes for watertreatment surface water and groundwater

When introduced to the market the low-pressure membranes MF and UF were analternative technology to the media filtration as illustrated schematically inFigure 106 (Frenkel amp Mourato 1998)

Conventional water treatment process

Sedimentation

Sedimentation

Surfacewater

Surfacewater

Coagulation

Coagulation

Media filtration

Membrane filtration

Membrane filtration treatment process

Figure 106 Example of one of the technological process using low-pressure membranes

336 Advances in Membrane Technologies for Water Treatment

In applications in which the solideliquid separation is required the low-pressuremembranes performed providing treated water with the quality superior compared tothe media filtration in most cases

Most applications were related to the surface water treatment replacing mediafiltration Due to the low-pressure membranesrsquo relatively high tolerance to the sus-pended solids applications of MFUF membranes allowed the removal of the clari-fication step in the treatment process for many projects providing significantreduction in the project cost and overall footprint of the plant This concept hasbeen called direct membrane filtration MFUF membranes were successfully appliedfor iron and manganese removal from the groundwater similarly to greensand filtersBecause low-pressure membranes are tolerant to suspended solids they are used as apretreatment for the high-pressure membranes NFRO as highlighted in clause twoabove compiling the IMS process Low-pressure membranes attracted significant in-terest by the wastewater industry and were successfully applied as a tertiary treatmenttechnology and as a basic technology for MBRs (Cui Muralidhara amp Frenkel 2010Frenkel Reardon Shlater Gharagozian amp Kondo 2011 Using Reclaimed Water2008)

106 Planning and designing low-pressure membranetreatment

Similarly to any water-treatment technology planning the low-pressure membraneproject needs careful planning and administration The major differences in the low-pressure membrane project compared to the basic conventional technology such asmedia filtration are

bull Membranes can tolerate higher solids loadbull Membranes can produce higher quality water compared to the conventional processesbull Most of the membrane plants are designed for continuous reject flow rather than batch filtra-

tion compared to the batch operation of the medial filters In this case the overall recovery ofthe membrane plant may be lower To improve membrane plant recovery the secondarystage of the membrane treatment train concentrating reject from the major treatment traincan be applied

bull When water is coagulated membranes may need smaller size flocs and less flocculation timeto achieve similar or better performance compared to the conventional processes

bull Because membranes provide higher-quality product water fewer UV doses andor a lowerchlorine injection rate are required

Because low-pressure membranes are still not standardized across the industry theyare manufacturer specific and not replaceable widely by the other suppliers This sit-uation complicates the membrane planning process and most of the membrane plantsthat were using the design-bid-build conventional procurement process are using thetwo-step procurement process During the first step the membrane suppliers are pre-qualified and preselected or membranes are prepurchased during the second step thegeneral contractor is selected This concept extends the overall project schedule

Planning and design of membrane systems for water treatment 337

requiring more time for the project procurement Because low-pressure membranes areshowing signs of standardization this situation may change in the future

The design of low-pressure membranes depends on the source water quality localconditions project size project preferences and requirements for the treated waterquality Depending on the solid load in the source water the low-pressure membranescan be designed to be operated in the dead-end filtration mode or cross-flow filtrationmode The dead-end filtration mode is limited by the solid content in the source waterwhile it provides higher overall system recovery and lower reject flow rate as a resultThe cross-flowmode is the opposite The system design needs to account the followingmajor plant components and parameters

bull Pretreatment requirements including fine screens chemical injection and clarification ifrequired

bull System recovery rate the ratio of the product flow to the feed flow expressed in percentbull Membrane active filtration area which is a function of the flow load on the membranes per

membrane area which is called membrane flux and expressed in gallonssquare feetday(GFD) or literhourmeter square (LHM)

bull Energy requirementsbull Posttreatment requirementsbull Solids treatment

Good design practice accommodates the maximum system recovery at the lowestenergy consumption and the best possible project economics both capital andoperational

107 High-pressure membrane applications

High-pressure membranes are represented by NF and RO membranes

1071 Nanofiltration and reverse osmosis

Membrane technology for groundwater treatment to remove color andor total dis-solved solids (TDS) includes NF and RO membranes These membrane-separationprocesses have a tighter membrane than MF and UF membranes which allowsthem to remove dissolved matter from the water organic and inorganic in nature

NF and RO also have been used as finishing processes in recycled water projectsremoving salt and constituents of concern being an integrated part of any indirectpotable reuse (IPR) or direct potable reuse (DPR) project

1072 Nanofiltration

NF separates particles in the range of 00005e0001 mm and is effective in removinghardness some TDS and TOC

NF is a pressure-driven membrane separation process that separates sparinglysoluble salts and large organic molecules from a fluid (water wastewater or industrial

338 Advances in Membrane Technologies for Water Treatment

process fluid) NF membranes have a high removal efficiency for multivalent ions suchas calcium and magnesium (hardness) but will also remove partially monovalent saltssuch as sodium and chloride depending on the size cutoff of the NF membrane

The NF membrane separation surface is a thin synthetic polymer manufactured intoa flat sheet and then spiral wound to form a membrane element The source water ispressurized and passed through the membrane module As the pressurized sourcewater passes along the membrane surface water molecules pass through the NF mem-brane and the larger salt ions and organic molecules are rejected and concentrated inthe water passing along the membrane

The NF system produces a high-quality (low TDS) permeate and a concentratedhigh salinity reject

The first generation of the NF membranes were manufactured from cellulose acetate(CA) the newer generation of NF membranes are manufactured from polyamide thinfilm composites (TFC) The CA material is resistant to strong oxidants while havinglower permeability and needing higher operational pressure as a result compared tothe TFC membranes The TFC material operates at lower pressures while it has rela-tively low tolerance to the oxidizing agents in the water and it can be damaged byoxidants Hydrophilic agents are often added to the membranes during the fabricationprocess to reduce fouling of the membranes by dissolved organics

An NF separation system typically consists of membrane elements pressure vessels(PVs) units and trains The membrane element is repairable and replaceable NFmembrane elements are loaded into PVs that are fabricated mainly from fiberglassreinforced plastic (FRP) or stainless steel The PVs can be different sizes and lengthsto accommodate from one to eight membrane elements While MF and UF membraneelements are not standardized across the industry NF membrane elements have stan-dard diameters of 25 4 and 8 inches and standard element lengths of 40 and 60inches This standardization permits flexibility in designing and operation of the NFsystem Currently the large-diameter RO elements in the range of 16e185 incheswere used for numerous RO facilities while they are not standardized across the indus-try at this time Groups of parallel PVs are supported and manifolded together withcommon piping valves and instrumentation to form a complete integrated NF unitor skids

The NF unit has independent flow control and is chemically cleaned and operated asa complete unit Multiple NF units are manifolded together into trains or banks to meetthe overall capacity requirements for a system as shown in Figure 107

Because NF membranes do not tolerate suspended and colloidal matter in the waterthey require pretreatment ahead of the membranes to protect them from solids and toprevent fouling of the membrane surface Because the spiral-wound NF membranescannot be backwashed the suspended solids must be removed from the NF feed waterDepending on the source water quality MF andor other filtration technologies aretypically used to protect membranes from the large particles Acids andor antiscalentsalso can be added to the feed water to reduce scale formation on the membrane surfaceDepending on the water chemistry and system operational parameters the average NFrecovery range is 75e85 Depending on the source water TDS NF systems typicallyoperate with feed pressures in the range 70e150 psi (5e10 Bar-g)

Planning and design of membrane systems for water treatment 339

1073 Reverse osmosis

RO separates ions and molecules down to less than 10 molecular weight units andis effective in removing TDS hardness TOC constituents of concern such as endo-crine disruptors pharmaceutically active compounds and personal care products(Frenkel 2009)

Similarly to NF RO is a pressure-driven membrane separation process that separatessoluble salts and organic molecules from a fluid (water wastewater or industrial pro-cess fluid) Osmosis is a natural process in which water passes through a semipermeablemembrane from low TDS concentration to high TDS concentration (Bartels FranksRybar Schierach amp Wilf 2005) The RO process is a reverse of the natural osmosisprocess which is the pressure-driven process in which the high TDS source water ispressurized and water then passes through the semipermeable membrane RO mem-branes have high removal efficiency for monovalent ions such as sodium and chlorideand will also remove organic molecules depending on the size and charge of the mole-cule Typical RO salt rejection is up to 998 by one single element at standard con-ditions However the overall RO system rejection rate is lower because RO elementsare operated in series within the PVs which results in the increased salt concentration inthe feed to each element as water moves along the PV Some rejections rates by one ROsingle membrane element at the standard conditions are shown in Figure 108

Similarly to NF the RO membrane separation surface is a thin synthetic polymermanufactured into a flat sheet and then spiral wound to form a membrane elementThe source water is pressurized and passed through the membrane module As thepressurized source water passes along the membrane surface water molecules passthrough the RO membrane and the salt ions and organic molecules are rejected andconcentrated in the water passing along the membrane The RO system produces ahigh-quality (low TDS) permeate and a concentrated (high TDS) reject

(a) (b)

Figure 107 High-pressure membrane nanofiltrationreverse osmosis element (a) and system (b)

340 Advances in Membrane Technologies for Water Treatment

The first generation of the RO membranes were manufactured from CA the newergeneration of NF membranes are manufactured from polyamide TFCs The CA mate-rial is resistant to strong oxidants while having lower permeability and needing higheroperational pressure as a result compared to the TFC membranes The TFC materialoperates at lower pressures while it has relatively low tolerance to the oxidizing agentsin the water and it can be damaged by oxidants Hydrophilic agents are often added tothe membranes during the fabrication process to reduce fouling of the membranes bydissolved organics

An RO separation system typically consists of membrane elements PVs units andtrains The membrane element is repairable and replaceable RO membrane elementsare loaded into the PVs fabricated mainly from the FRP or stainless steel The PVs canbe different sizes and lengths to accommodate from one to eight membrane elements(Frenkel 2011 Liberman amp Wilf 2005) While MF and UF membrane elements arenot standardized across the industry RO membrane elements have standard diametersof 25 4 and 8 inches and standard element lengths of 40 and 60 inches This standard-ization permits flexibility in designing and operation of the RO system Currently thelarge-diameter RO elements in the range of 16e185 inches were used for numerousRO facilities while they are not standardized across the industry at this time Groups ofparallel PVs are supported and manifolded together with common piping valves and

Contaminant Contaminant Nominal rejection Nominal rejection

Aluminum Ammonium

Bacteria

Boron

Cadmium

Copper

Chloride

Fluoride

Iron

Manganese

Mercury

Nitrate

Phosphate

Potassium

Silica

Silver

Sulfate

Zinc

96-98

99+

50-70

93-97

96-98

96-98

93-96

93-97

96-98

96-98

96-98

93-97

92-95

92-98

96-98

95-98

80-90

80-90

96-98

96-98

96-98

94-97

90-95

90-95

95-98

92-95

Borate

Bromide

Calcium

Chromate

Cyanide

Hardness Ca amp Mg

Lead

Magnesium

Nickel

Orthophosphate

Polyphosphate

Radioactivity

Silicate

Sodium

Thoisulfate

93-97

92-95

30-50

85-95

93-98

93-98

85-95

Figure 108 Typical contaminants removal rates from the water by reverse osmosis system

Planning and design of membrane systems for water treatment 341

instrumentation to form a complete integrated RO unit or skids The RO unit has in-dependent flow control and is chemically cleaned and operated as a complete unitMultiple RO units are manifolded together into trains or banks to meet the overall ca-pacity requirements for a system

RO membranes require pretreatment ahead of the membranes to protect them fromsolids and to prevent fouling of the membrane surface Because the spiral-wound ROmembranes cannot be backwashed suspended solids must be removed from the ROfeed water Depending on the source water quality MF andor other filtration technol-ogies are typically used to protect membranes from the large particles Acids andorantiscalants are also added to the feed water to reduce scale formation on the mem-brane surface Depending on the water chemistry and system operational parametersthe average brackish water RO recovery range is 75e85 Seawater RO (SWRO) usu-ally operates with a recovery of 40e60 Depending on the source water TDS ROsystems typically operate with feed pressures in the 150e1200 psi (10e83 Bar-g)range

1074 Seawater reverse osmosis

Membrane technology to remove salt from seawater to provide an alternative drinkingwater source can be designed with MF or UF pretreatment ahead of SWRO mem-branes This process currently represents a small segment of the US market but isexpected to see future growth in Florida Texas California and numerous other costalplaces where there is no other drinking water source (Desalination of Seawater 2011Stevens Kowal Herd Wilf amp Bates 2003 Wilf et al 2006)

108 Applications of high-pressure membranes forwater treatment brackish water seawateroceanwater

High-pressure membranes are widely applied to treat groundwater to reduce saltcontent nitrates and specific contaminants of concerns RO membranes became thedominant technology for seawater desalination providing beneficial process eco-nomics compared to thermal desalination processes RO membranes are becomingthe integrated part of the process in the water reuse and in IPR and DPR which areattracting attention lately and in light of the global warming and climate changesparticularly Another niche for the high-pressure membranes is preparation of thedeionized (DI) water and ultrapure water (UPW) of which many industries are in need

109 Planning and designing high-pressure membranetreatment

Similarly to low-pressure membrane planning the high-pressure membrane projectsneed careful planning and administration The major differences in the high-pressure

342 Advances in Membrane Technologies for Water Treatment

membrane projects compared to the low-pressure membrane projects and conventionaltechnologies are

bull Membranes cannot tolerate high suspended and colloidal solids load while being efficient inremoving dissolved matter from the water to be treated

bull Reliable pretreatment is required to reduce particular matter and colloids load prior to treat-ing water by high-pressure membranes

bull As membranes provide higher-quality product water the fewer ultraviolet doses andor lowerchlorine injection rate are required compared to the conventional processes

Because high-pressure membranes are well standardized across the industrythey are not manufacturer-specific and are replaceable by other suppliers(Frenkel amp Wilf 2009) The current status in the industry simplifies the high-pressure membrane planning process and most of the conventionally procuredmembrane plants are using a one-step procurement process the opposite ofthe low-pressure membrane procurement process The one-step procurementprocess reduces the project schedule compared to the low-pressure membraneprocurement process

Similarly to low-pressure membranes the design of high-pressure membranesdepends on the source water quality local conditions project preferences and require-ments of the treated water quality Because high-pressure membranes do not toleratesuspended and colloidal matter in the water design and performance of the high-pressure membranes depend on design and performance of pretreatment either con-ventional or low-pressure membranes Since development most of the engineeringand design efforts were directed to design high-pressure membranes in the continuousoperation The continuous operation has certain benefits and negatives as highlightedbelow

Benefits of RO operation in continuous mode

bull All membranes are operated continuously allowing a relatively simple system fittings andpiping arrangements

bull Equipment fittings and components are not cycling periodically increasing the lifetime ofequipment

bull Energy recovery devices can be easily added reducing overall energy demand by thesystem

bull There are number of techniques developed allowing system operation to be flexible such asconcentrate recycling and hybrid design

Within the last few years RO operation in a semibatch mode was proposed whichbrings the following benefits compared to the continuous RO operation

bull Flux can be better balanced between RO membrane elements within the PVbull Higher overall system recovery can be achieved at the same conditions compared to the

continuous RO operationbull Less potential membrane fouling may be achieved due to the change in the salt load within

each cycle

Planning and design of membrane systems for water treatment 343

The high-pressure membrane system design needs to account for the followingmajor plant components and parameters

bull Pretreatment requirements including chemical injection clarification when required filtra-tion using conventional processes or low-pressure membranes

bull System recovery rate the ratio of the product flow to the feed flow expressed in percentbull Membrane active filtration area which is a function of the flow load on the membranes per

membrane area which is called membrane flux and is expressed in GFD or LHMbull Energy requirementsbull Posttreatment requirements due to the low alkalinity of the product water and water aggres-

siveness as a resultbull Concentrate dischargemanagementbull Treatmentmanagement solids from pretreatment

Good design practice accommodates the maximum system recovery at the lowestenergy consumption and the best possible project economics both capital and opera-tional (Desalination of Seawater 2011)

1010 Integrated membrane systems

As described above low-pressure mmbranes were designed to remove suspendedmatter from the water similarly to media filtration or other solids-water separationtechnology High-pressure membranes are not tolerant of suspended and colloidal mat-ter while being designed to remove dissolved matter from the water similarly to theion exchange resins or water evaporators IMS found their application in a numberof industries and in municipal applications

A number of seawater desalination plants were designed by applying the IMSconcept when low-pressure membranes are followed by high-pressure membranesSurface water treatment adopted the IMS concept in which dissolved matter inorganicor organic in nature needs to be removed from the water Many industries adoptedIMS design when preparing to make up DI or UPW or when treating industrial effluentfor reuse As IPR is gaining popularity and DPR is knocking on the door the IMSconcept is becoming the gold standard for these applications

1011 Combination of membrane treatment with othertechnological processes

Membrane technologies have number of beneficial features allowing for rapidlyexpanding market shares such as

bull Absolute barrier for treatmentremovalbull Smaller footprintlayoutbull Product water is not affected by the feed water hydraulic and contaminant overloads spikes

and fluctuationsbull Less or no chemicals requiredbull Minimal or no pretreatment requiredbull Single-step processbull Modular expandability (for future expansion)

344 Advances in Membrane Technologies for Water Treatment

bull Less volume of discharged wastes (including sludge and chemicals)bull Simplicity of operation with remote monitoringbull Lower postdisinfection demand in chlorine UV intensity

Also membrane technologies have certain limitations such as

bull Prompt to foulbull Needs pretreatmentbull Have low rejection rate of non-ionized ionsbull Have low rejection rate of dissolved gases

Depending on the application feed water quality and criteria of the treated watermembrane technologies can be successfully combined with conventional processesGood examples could be

bull Using clarification upstream of low-pressure membranes to reduce suspended matter load tothe membranes

bull Using DAF to minimize low-pressure membrane fouling caused by the colloidal matter fineorganics and algae

bull Applying chemicals similarly to the conventional processes to form flocs coagulate waterand change water pH

bull Polish permeate from high-pressure membranes by activated carbonbull Add decarbonators to remove CO2 and balance pH in the product from high-pressure

membranesbull Use advanced oxidation concept to destruct constituents of concert and low molecular weight

organics that may pass through the high-pressure membranes

1012 Conclusions future trends in membranetreatment development for water treatment

Membranes are gaining popularity and market growth While traditionally membranetechnologies started to develop in the United States Europe and Japan the latesttrends are that more membranes companies are being established in different partsof the world including Korea and China Besides traditional membrane technologysuppliers there is a good number of players showing up on the market Competitiondrives improvements in membrane technology developments finding newer applica-tions improving technical features of membranes and reducing cost

Several trends in membrane technology developments can be identified

bull Improvements of membrane properties such as increase of permeability eg higher flux atlower pressure

bull Fouling minimizationbull Overall system energy reductionbull Minimization of the treatment plant footprint by applying larger-size treatment trains com-

mon headers and large-diameter membrane elements (RO)bull Newer membrane technology developments such as forward osmosis pressure retarded

osmosis membrane distillation and combinations of the newer processes with the estab-lished technologies

As the membrane market grows sooner or later membrane technology will be oneof the preferred choices for projects

Planning and design of membrane systems for water treatment 345

List of acronyms

BWRO Brackish water reverse osmosisC Concentration ppm or mgLCA Cellulose acetateDPR Direct potable reuseFRP Fiberglass reinforced plasticgpm Gallons per minute (US units of flow)IMS Integrated membrane systemIPR Indirect potable reusem3hr Cubic meter per hour (metric units of flow)mgL Milligram per liter (metric units of concentration)MBR Membrane bioreactorMF MicrofiltrationMWCO Molecular weight cut offNF NanofiltrationNTU Nephelometric turbidity unitsppm Part per million (fractional units of concentration equal to mgL)PV Pressure vesselQ Flow gpm or m3hrRO Reverse osmosisSWRO Seawater reverse osmosisTDS Total dissolved solidsTFC Thin film compositeTOC Total organic carbonUCLA University of California at Los AngelesUF UltrafiltrationUPW Ultrapure water

References

Bartels C Franks R Rybar S Schierach M amp Wilf M (2005) The effect of feed ionicstrength on salt passage through reverse osmosis membranes Desalination 184 185e195

Cui Z F Muralidhara H S amp Frenkel V (June 2010) Chapter 8 Membranetechnologies for food processing waste treatment A practical guide to membranetechnology and applications in food and bioprocessing Oxford United KingdomButterworth-Heinemann Elsevier Publisher

Desalination of Seawater (May 2011) Chapter 3 M61 In Treatment approaches (1st ed)Denver CO American Water Works Association (AWWA)

Design of municipal wastewater treatment plants (October 2009) Chapter 16 WEF MOP8 In Water environmental federation (5th ed) New York WEF Press and McGraw-Hill

Frenkel V amp Wilf M (2009) Using the flexibility of RO system configuration In Worldcongress on desalination and water reuse international desalination associationNovember 07e12 2009 Dubai UAE

Frenkel V (March 2011) Chapter 6 Seawater desalination trends and technologies InDesalination trends and technologies Vienna Austria INTECH

346 Advances in Membrane Technologies for Water Treatment

Frenkel V Reardon R Shlater N Gharagozian A amp Kondo (2011) Chapters 5 and 6WEF MOP 36 In Membrane bioreactors (1st ed) Alexandria VA Water environmentalfederation

Frenkel V (2009) Reverse osmosis How it began and where it is now Chennai India WaterToday Magazine MayeJune 2009

Frenkel V amp Mourato D (1998) Application of immersed microfiltration membranes fordrinking water treatment In NSF international conference Washington DC

Liberman B amp Wilf M (2005) Evolution of configuration of RO seawater desalinationsystems In Proceedings of IDA water desalination conference Singapore

Stevens L Kowal J Herd K Wilf M amp Bates W (2003) Tampa Bay seawater desali-nation facility start to finish In Proceedings of IDA water desalination conferenceBahamas

Using reclaimed water to augment potable water resources (2008) Alexandria and DenverA special publication by WEF and AWWA

Wilf M Bartels C Awerbuch L Mickley M Pearce G amp Voutchkov N (2006) Theguidebook to membrane desalination technology Reverse osmosis nanofiltration andhybrid systems Process design and applications Italy Balaban Desalination Publications

Planning and design of membrane systems for water treatment 347

Membrane ageing during watertreatment mechanismsmonitoring and control

11KH Tng A Antony Y Wang GL LeslieThe University of New South Wales Sydney NSW Australia

111 Introduction

Microporous and semipermeable membrane filtration processes are used to efficientlyand reliably achieve consistent product water quality and quantity on a range of watersources (see Figure 111) In general membrane processes are less complex comparedto conventional water treatment processes that use chemical flocculation clarificationand chlorination Product water quality can be easily monitored using a range of tech-niques that check for membrane integrity Similarly the capacity to maintain productquantity can be assessed by online monitoring of membrane permeability One chal-lenge unique to drinking water plants using membrane technology is anticipatingand scheduling activities to renew the inventory of membranes in service

The prorated warranty provided by membrane manufacturers can range from 3 to10 years However experience teaches that some plantsrsquo effective membrane lifecan either exceed or fall short of the manufacturerrsquos expectations Moreover it isnot uncommon to have significant variability in the integrity and productivity of

Application

Membrane type

Function

Surface water

Water treatment

Wastewater Seawater Groundwater

MFUF MFUF + RO MFUF + RO NFRO

Removes solids and pathogens

Removes solids and pathogens

+ removal of salts and

divalent ions

Removes colloids

+ removes

salts divalent ions and organics

Removes salts divalent

ions and organics

Figure 111 Typical membrane filtration applications in the water treatment industry

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400011-3Copyright copy 2015 Elsevier Ltd All rights reserved

membrane modules on site at any given time The capacity of an individual membraneelement or module can range from 42000 L per day for a microporous MFUF mem-brane to 21600 L per day for a semipermeable reverse osmosis (RO) membraneConsequently operators of plants with a treatment capacity of 50 MLD would needto manage a membrane inventory of several thousand membranes

The paramount operating objective is to avoid any failure that could compromisequality and restrict capacity Developing a strategy that relies exclusively on manufac-turerrsquos warranty to estimate membrane lifespan and replacement schedules is fraughtwith uncertainty

Membrane ageing and failure occurs throughout the membranersquos operational life-time The literature has been silent with regard to the understanding and predictionof membrane failure and has largely been focused on ageing due to exposure to strongoxidants such as sodium hypochlorite This chapter reviews the mechanisms andmodes of membrane failure approaches and methods used to monitor and the controlmembrane ageing and integrity in the water treatment industry

1111 Membrane ageing and failure

Membrane ageing is usually the main cause behind overall membrane failure as amembrane reaches the end of its lifespan (Prulho Therias Rivaton amp Gardette2013) This section would make a clear distinction between ageing and failure andfurther discuss how membrane ageing can lead to a membrane that is more susceptibleto failure

11111 Membrane ageing

Membrane ageing is defined as the deterioration of the surface layer and sublayers ofcomposite membranes due to irreversible deposition of foulants or by frequent expo-sure to chemical cleaning agents (Antony Fudianto Cox amp Leslie 2010 Benaventeamp Vazquez 2004 Thominette Farnault Gaudichet-Maurin Machinal amp Schrotter2006) Membrane productivity and removal efficiency are undermined by the retentionof dissolved salts organics microorganisms and suspended solids after extendedoperation also known as fouling (see Figure 112(a) (b) and (d)) Membrane foulingis the central bottleneck for all membrane filtration processes therefore the industryuses routine chemical cleaning protocols In some cases strong oxidants such assodium hypochlorite are used to control fouling Regrettably repeated chemicalcleaning exacerbates membrane aging

During the cleaning in place (CIP) process chemicals are intermittently applied tothe fouled membranes at specific concentrations temperatures and extended timesThe combination of these factors can lead to ageing of the membrane with mem-branes becoming discoloured over time (see Figure 112(c)) Prolonged filtrationand cleaning cycles not only have an adverse effect on membrane integrity butcan also lead to internal fouling of membranes which is irreversible and detrimentalto membrane performance (see Figure 112(b)) This also reduces the lifespan of themembrane leading to a higher likelihood of failure

350 Advances in Membrane Technologies for Water Treatment

11112 Membrane failure

Membrane failure can be defined as the loss of membrane mechanical integrity leadingto the inability to achieve rated log removal values (LRV) (Childress Le-ClechDaugherty Chen amp Leslie 2005 Gijsbertsen-Abrahamse Cornelissen amp Hofman2006 Mallevialle et al 1996) Membrane failure can occur during two phases ofthe membranersquos operational lifespan Membrane fibres can be damaged before andduring installation and also during membrane filtration Failure before and duringinstallation is often caused by inconsistent manufacturing and fabrication techniquesand installation This issue is kept in check via implementation of more rigorous qual-ity control methods and integrity testing of membrane modules before commissioning

Age

ing

Failure

(a)

(b)

(c)

(e)

(f)

(g)

(h)

(d)

Figure 112 Effects of membrane ageing and failure (a) Foulant accumulation (b) Membraneinternal fouling (c) Membrane fibre discolouration (d) Membrane surface fouling (e) Surfacepunctures (f) Fibre embrittlement (g) Surface delamination (h) Surface scratches and scores

Membrane ageing during water treatment mechanisms monitoring and control 351

Membrane failure during the filtration process can largely be attributed tooperating parameters and maintenance protocols (Johnson amp Maccormick 2003)During operation the likelihood of damage to the membrane is high given theastringent nature of operating protocols such as vigorous mechanical cleaning chem-ical cleaning using strong oxidants and high-pressure backwashes Although thisensures that the membranersquos performance is maintained it indirectly puts a strain onthe membranersquos integrity leading to accelerated membrane aging and subsequentfailure According to Childress et al (2005) failure results from physical damage tothe membrane module structure The damage maybe caused as a result of a suite offactors actions by chemicals excessive external forces scores scratches and punc-tures due to the presence of foreign bodies (see Figure 112(h)) all of which are exac-erbated by faulty membrane module structures and designs Membrane fibre breakagedue to chemical attack leads to embrittlement of membrane fibres leading to bothdiscolouration and breakage of membrane fibres (see Figure 112(f)) Membrane dam-age and integrity compromise can also be caused by unexpected water quality fluctu-ations or failure of pretreatment processes leading to inadequate removal of material(Gijsbertsen-Abrahamse et al 2006) These foreign bodies coupled with the effectsof strong aeration can puncture the membrane resulting in a rapid pressure loss anddetection of bubbles in a pressure decay test (PDT) (Cui Chang amp Fane 2003)(see Figure 112(e))

Although membrane ageing and failure are closely related a distinction should bemade between these two aspects Ageing results in membrane degradation and theonset of these adverse effects in turn leads to membrane failure Subsequently mem-brane failure results in loss of process removal efficiency reduction in product waterthroughput and product water noncompliancy

112 Reliability maintainability and resilience

Many communities rely on hollow-fibre membranes to remove pathogens from drink-ing water The resilience of water treatment plants using hollow-fibre membranes isdefined as the ability to meet a specified log reduction in pathogen concentration inroutine as well as in unexpected circumstances The reliability of a membrane filtra-tion system is therefore critical to ensuring that treated water meets regulatory require-ments Maintainability of the system is also important because that would determinethe systemrsquos downtime before being put back into service once the failure has beenrectified Therefore the reliability and maintainability of an asset are two factorsthat are crucial in evaluation of the assetrsquos resilience

1121 Reliability

The reliability of a membrane filtration process unit is an essential factor in maintain-ing the continuous compliance with specific performance criteria such as environ-mental discharge consent requirements and water quality parameters The evaluationof the reliability of such process units is an important part of its design and operation

352 Advances in Membrane Technologies for Water Treatment

However this has always been difficult to assess and quantify and often has been basedon the number of redundancies andor backup facilities (Eisenberg Soller Sakaji ampOlivieri 2001)

11211 Mean time to failure and mean time between failure

Process equipment is said to be completely reliable if there is no failure in the processperformance and it meets the required effluent discharge standards and targets Equip-ment reliability can be measured in terms of mean time to failure (MTTF) and meantime between failure (MTBF) (Stanley 2011) Although MTTF and MTBF can beused to quantify equipment reliability there is a distinct difference between thesetwo terms MTTF can only be applied to nonrepairable components and equipmentwhile MTBF is applied to repairable equipment (Kagan 2004) MTTF is the averagetime equipment remains functional until its failure and can be calculated by dividingthe total operation time of equipment by the number of units of equipment Formean time to repair (MTTR) to be accurate this statistical value should be measuredfor a long period and over a large number of units (Stanley 2011)

MTTF frac14 Cumulative operational time of equipment ethhoursTHORNNumber of equipment

(111)

In the case of repairable components MTBF is used instead of MTTF MTBF isthe average time equipment remains in service until it fails and can be calculated bythe following equation (Smith amp Mobley 2008)

MTBF frac14 Cumulative time in service ethhoursTHORNNumber of failures

(112)

For example MTTF could be applied to irreparable failure events of RO mem-branes in which delamination or damage to the membrane housing had occurreddue to excessive backwash pressure whereas MTBF would apply to repairable faultssuch as sealing of detected leaks in compromised hollow-fibre membranes beforebeing returned to service

11212 Failure rates

Equipment failure rates (eventstime) also can be used to quantify reliability A higherfailure rate or a greater number of failure incidences will directly translate to less-reliable equipment The failure rate of any given piece of equipment can be describedby a ldquobathtubrdquo curve (see Figure 113) The bathtub curve is divided into three sec-tions The first section is known as the ldquowearing in periodrdquo During this period thefailure rates are high due to infant mortality failures caused by defective componentsand improper quality control measures prior to operation An example in a membranesystem would be a failure that occurs during the commissioning stages when poorinstallation manufacturing defects and incorrect membrane preconditioning proto-cols can result in an early failure of the membrane units (Johnson amp Maccormick

Membrane ageing during water treatment mechanisms monitoring and control 353

2003) The failure rate then decreases rapidly as the equipment and its componentsare worn in until it reaches the second section the ldquointrinsic failure periodrdquoThis period is when most of the equipmentrsquos lifespan remains and throughout thislong period the equipment has a constant failure rate due to random failures Failureevents that occur during this period could be a result of a pretreatment processrsquoineffective removal of gross particles or unintentional operator error leading todamage and failure of the membranes (Yang Cicek amp Ilg 2006) The last sectionis the ldquowearing out periodrdquo In this period the failure rate increases again becauseof cumulative damage caused by wear and mechanical fatigue over time (KlutkeKiessler amp Wortman 2003) This period occurs toward the end of the membranersquoslifespan and would be replaced when it eventually fails to maintain removalefficiency and process integrity The typical lifespan of a membrane usually rangesfrom 5 to 10 years and varies with material type and manufacturers (LesjeanRosenberger Schrotter amp Recherche 2004)

11213 Availability

The availability of an equipment or component is defined as the proportion of time thatit is functioning properly and is available for operation Availability is the ratio of thetotal operational time to the sum of operational time and repair times Repair times arequantified via the equipmentrsquos MTTR This is the average time required for repairsto be made to restore the equipment back to its operational state The equipmentrsquosavailability can be calculated via the equation below

Availability frac14 MTBFMTBFthornMTTR

(113)

To maximise availability a balance between component reliability and mainte-nance has to be achieved Downtime is inevitable because both scheduled preventa-tive maintenance and repairs require time and cause disruptions to the systemrsquosoperation (Marshall amp Chapman 2002) Implementation of different design

Failu

re ra

te (λλ

)

Time (t)

Constant (random) failurerate

Wearoutfailures

Infant mortality failures

Figure 113 Bathtub curve describing equipmentrsquos failure rates with time

354 Advances in Membrane Technologies for Water Treatment

approaches for example having multiple smaller systems integrated to form a largercomplete system working with an optimised maintenance protocol can result in ahigher system reliability and availability

1122 Maintainability

Maintainability of a membrane filtration system is defined as the probability of thefailed system returning back to an operable condition using the recommended proce-dures in a specific period (Sutton 2010a)

Conventional maintenance can be divided into three categories repair condition-based maintenance and scheduled maintenance Repair and condition-based mainte-nance are performed when the process equipment has either failed or starts showingsigns of imminent failure with the only difference being repairs are usually donewithout equipment shutdown and condition-based are done with a shutdown In amembrane system an example of repair and condition-based maintenance would beisolating and replacing membrane modules on detection of a compromise in membraneintegrity Scheduled maintenance is regular maintenance performed regardless of con-dition or performance during operation Routine chemical backwashing is an exampleof scheduled maintenance that is used to restore membrane flux and control foulingduring membrane filtration To reduce process equipment downtime and labour costsreliability centred maintenance (RCM) was developed RCM uses a risk-basedapproach to prioritise process equipment so that equipment that is critical to processintegrity is inspected and maintained more frequently (Sutton 2010b)

1123 Resilience

A systemrsquos resilience is defined as the ability for the system to tolerate the distur-bance and return back to its steady-state following the perturbation (Gunderson ampPritchard 2002) In the case of membrane filtration systems the resilience isdescribed as how robust the system is in recovering from a failure event and canbe defined by the duration of the failure occurrence (Zhang Achari Sadiq Langfordamp Dore 2012) For example having only one operator responsible for an entire treat-ment system would result in the operator requiring a longer time to isolate and reme-diate the failing process leading to a longer downtime and deeming the process to beless resilient Therefore the resilience of the membrane system plays a critical role inensuring that continuous process throughput is maintained while the treated waterstill remains compliant with strict water discharge guidelines upholding public healthand safety

113 Membrane failure modes

There are two categories of membrane failure failure during installation and failureduring operation (see Table 111) Of the two aspects failure during operation ismore critical because it could lead to product water noncompliancy which is a threat

Membrane ageing during water treatment mechanisms monitoring and control 355

Table 111 Common failure modes of membranes and modules

Failure modeFailurelocation Cause Incidence of failure Consequences

Membranetypes

Manufacturingdefects

Module ormembrane

Accidental Installation oroperation

Poor removal efficiencyabnormal differential pressures

All

Cracks andruptures

Module Hydraulic shock accidentalhigh pressure or shearstress abrasion orbackwash pressure

Operation start-upsshutdowns

Abnormal differential pressures All

O-ring andseal failures

Module Accidental Operation Poor removal efficiencyabnormal differential pressures

All

Mechanicaldamage

Module Accidental Installation oroperation

Abnormal differential pressures All

Damage ofactive layer

Membrane Pretreatment failure presenceof crystalline or abrasiveparticles

Operation Poor removal efficiencyabnormally high permeate flux

All

Oxidativedamage ofmembrane

Membrane Use of strong oxidants Prolonged operation Poor removal efficiencyabnormally high permeate flux

All

356Advances

inMem

braneTechnologies

forWater

Treatm

ent

Colloidal orinorganicfouling

Membrane Pretreatment failure Prolonged operation Permeate flux decline high TMP All

Organicfouling

Membrane High organic loading of feedwater

Prolonged operation Permeate flux decline high TMP All

Internalfouling(lumen-side)

Membrane Prolonged operation Prolonged operation Permeate flux decline high TMP Hollow fibre

Fractures andcleavages

Membrane Hydraulic shock accidentalhigh pressure or shearstress

Operation start-upsshutdowns

Poor removal efficiencyabnormally high permeate flux

Hollow fibre

Delaminationof activelayer

Membrane High backwash pressure Operation shutdowns Poor removal efficiency Flat sheet

Compaction Membrane High operation pressure andsudden pressure surges

Operation Low permeate flux Flat sheet

Mem

braneageing

duringwater

treatment

mechanism

smonitoring

andcontrol

357

to public health Failure during installation is less critical given that it can be easilyovercome by having more rigorous inspections prior to commissioning Thereforethis section will focus on failure modes of membrane systems during operation

Hollow-fibre membranes are widely used in municipal and industrial wastewatertreatment (Chang 2011 Cheryan 1998 Oschmann Nghiem amp Scheuroafer 2005)Large bundles of hollow-fibre membranes are often either encapsulated in a pressurevessel forming a module or potted into large curtains for submerged filtration inwastewater (Gijsbertsen-Abrahamse et al 2006) Fibre failure can occur via fourdifferent mechanisms however only three are related to membrane ageing that leadsto its subsequent failure chemical attack excessive fibre movement and impropermembrane module design The fourth aspect presence of foreign bodies can beattributed to poor removal efficiency of pretreatment processes and thus does notdirectly contribute to membrane ageing

1131 Failure due to chemical attack

The removal efficiency of both microporous and semiporous membranes is optimalonly when membrane fouling is kept to the minimum while maintaining overallintegrity Therefore to control the fouling on the membrane surface frequentin-situ backwash regimens using strong oxidants are implemented Oxidativedamages are largely caused by the chemical incompatibility of the chemicals usedand the membrane material itself (Childress et al 2005) Due to this exposure toharsh chemicals the membrane properties would be altered resulting in membranedegradation (Antony amp Leslie 2011) Oxidants are the main causes behindmembrane integrity deterioration with sodium hypochlorite being the most commoncleaning agent used and studied However it should be noted that sodium hypochlo-rite is not universally used given the health and environmental impacts of thechlorinated organic by-products and the low chlorine tolerance of certain membranetypes (Kang et al 2007 Kwon amp Leckie 2006) From the equilibria equationsbelow sodium hypochlorite dissociates into hypochlorous acid HClO when itcomes in contact with water and further dissociates into hypochlorite ions ClOThe pH largely affects the stoichiometric ratio of hypochlorous acid dissociatedwith a low pH favouring a higher dissociation of the stronger oxidant HClO (RouaixCausserand amp Aimar 2006)

NaClOthorn H2O4HClOthorn NaOH (114)

HClO4Hthorn thorn ClO (115)

An example of the chemical incompatibility between cleaning reagents and mem-branes is the unexpected internal fouling of membranes in the presence of iron speciesIn Australia iron salts are dosed in wastewater treatment plants with the aim to aidphosphorous removal and odour control The presence of iron salts coupled with theoxidative nature of hypochlorite can lead to formation of amorphous ferric oxides(AFO) that could accumulate in the lumen side of the hollow-fibre membranes

358 Advances in Membrane Technologies for Water Treatment

causing internal fouling and sudden unexpected fibre failure (Tng Wang Waite ampLeslie 2013)

1132 Failure due to faulty membrane module structure

Membrane module design is usually correlated to the efficiency of membrane foulingprevention Current membrane modules consist of up to 20000 hollow fibres heldtogether with either an epoxy or urethane resin Depending on the manufacturing pro-cess the resin can be cured under static or dynamic conditions In static conditions theresin is allowed to cure without heat or external forces acting on it This method isslower than the dynamic curing method that uses centrifugal forces under elevatedtemperatures Each method would produce varying results and thus would havedifferent mechanical tensile strengths

Membranes that are potted statically would have the resin wick up the fibrersquos edgedue to the effects of capillary forces This leads to a development of a sharp edge thatcan cause fibre breakage (Figure 114(a)) Application of an elastomer overlay is addedto minimise the sharp edges (Figure 114(b)) However only the dynamic cured resinscan almost negate the development of these sharp edges (Figure 114(c)) (Childresset al 2005) With the addition of air scouring the probability of fibre breakage dueto the type of potting method increases

Membrane filtration and routine backwashes carried out at pressures higher thanthe manufacturerrsquos recommendations can lead to membrane failure via delaminationof membrane sheets (see Table 112(f)) damage to membrane module housing (seeTable 112(a)) and degradation of membrane module seals (see Table 112(c))Consequently the tolerable stress load on a membrane module will depend on thetype of membranes the way the membrane is packed into the module and themethod used to cure the resin that holds the membrane in place

The optimal membrane module design would have to find a balance between stressimposed on the membrane fibre and the amount of force required to hold the mem-brane fibres firmly in place Presently there is a lack of fundamental data on stressesexperienced by fibres during the filtration and cleaning cycles in the presence of airscouring (Regula et al 2014) This coupled with the difficulty in accuratelymeasuringcalculating stresses in multiple fibre systems has significantly limited thedevelopment of better-designed membrane modules This underlines the need forboth a better understanding in membrane potting methods and stressestrain forcesacting on the membrane fibres for better membrane module design

1133 Failure due to excessive movement

The advantage of submerged membranes is that the hydrostatic pressure generateddoes away with the need for the membrane modules to be pressurised For such con-figurations air scouring or bubbling is used to provide a shear force along the mem-brane surface to help alleviate the fouling phenomena (Cui Chang amp Fane 2003) Thehigher the shear force on the membrane surface the more efficient the removal of fou-lants however the excessive membrane movement due to the higher shear force can

Membrane ageing during water treatment mechanisms monitoring and control 359

also lead to fibre breakage (Wicaksana 2006) This phenomenon coupled with degra-dation of membrane fibres due to ageing could lead to a higher occurrence of fibrefailure

Flat sheet thin film composite (TFC) membranes are widely used in desalinationand water recycling applications via an RO process (Cadotte John 1985 CadotteJohn amp Petersen Robert 1981 Prakash Rao Desai amp Rangarajan 1997) TFC mem-branes consist of a polyamide active top layer on top of a polysulfone microporoussubstrate support layer on a woven or nonwoven polyester reinforcing backing to pro-vide additional mechanical strength (Antony amp Leslie 2011) These membranes areusually used in submerged or tubular module configurations TFC membranes witha polyamide active layer are able to operate at high recovery rates and wide pH rangeshowever similar to hollow-fibre membranes they are highly susceptible to chemicalattack by chlorine (Antony et al 2010 Glater Hong amp Elimelech 1994) To mitigatebiofouling chlorine disinfection is often introduced through upstream dosing before

Hollow fibre

Mold

Mold

Mold

Potting resin

Potting resin

Potting resin

(a)

(b)

(c)

Hollow fibre

Hollow fibre

Figure 114 (a) Static conditions (b) static with elastomer overlay and (c) dynamic conditionsAdapted from Childress et al (2005)

360 Advances in Membrane Technologies for Water Treatment

Table 112 Failure of membrane modules

2(a) Cracks in module housing

2(b) Cracks in module end caps

2(c) Module seal failure 2(d) Improper seal installation

Membrane ageing during water treatment mechanisms monitoring and control 361

the RO membrane system and excess residual chlorine is removed via the dosing ofsodium bisulfate However due to unexpected changes in the quality of the feed watera higher than tolerable amount of free chlorine is present in the RO system thus lead-ing to the degradation of membrane integrity by chemical attack

Flat sheet membranes are also more prone to delamination during routine back-washing When cake layer fouling occurs on the membrane surface the hydraulicresistance increases resulting in a decrease in membrane flux As a way to restorethe flux a backwash is used The backwash entails pumping either permeate wateror compressed air in the reverse direction from the permeate side to the feed sideThis would dislodge caked particles from the membrane surface back into the bulkfeed water (Ratnayaka Brandt amp Johnson 2009) Conventional backwash fre-quencies range from once every 30e90 min with a backwash duration of 30e90 s(Howe Hand Crittenden Trussell amp Tchobanoglous 2012) Backwash pressuresshould be performed according to the membrane manufacturerrsquos specifications andshould also take into account site-specific considerations to prevent delamination ofmembrane sheets formation of hairline cracks in the membrane module and mem-brane module seal failure all of which can result in membrane failure and subsequentcontamination of product water

114 Membrane ageing monitoring methods

Membrane ageing affects the performance of membranes via three different aspectsAs the membrane ages the permeate quality flux restoration after cleaning and themechanical strength are all adversely affected Membrane ageing also presents itselfas degradation in the membranersquos functional properties and characteristics Becausemembranes are extensively used in the production of drinking water integrity breachescan result in an increase in microbial contamination of the permeate (AntonyBlackbeard amp Leslie 2012) and can also lead to a public health compromise shouldthe pathogens and viruses not be removed prior to distribution (Gitis Haught ClarkGun amp Lev 2006) Therefore to monitor the effects of membrane ageing monitoringmethods are used to detect and assess the impacts of membrane ageing

1141 Membrane ageing assessment tools

Multiple analytical techniques are used to assess membrane ageing and are categorisedbased on five different membrane aspects They range from filtration characteristics tomorphological characteristics (see Figure 115) These techniques are well establishedand have been used by many researchers in the field of membrane characterisation Theprinciples behind these techniques will be briefly covered in the sections below

11411 Filtration characteristics

Permeability membrane resistance and solute rejection are filtration characteristicsthat can provide useful real-time information regarding the membranersquos filtration

362 Advances in Membrane Technologies for Water Treatment

properties These methods are also nondestructive and are fundamental in principlethus are usually the first tools used to monitor membrane ageing

Membrane permeability and resistance provides a direct measurement of the mem-brane flux restoration after a cleaning cycle The membrane is said to have undergonedegradation if the flux restored is greater than the initial membrane flux (Yadav ampMorison 2010) Although membrane permeability is a clear and distinctive way todetect membrane degradation it is often too late because it only occurs when a grossintegrity loss has happened and thus is not a reliable tool for real-time monitoring ofmembrane ageing

Solute rejection is determined by the molecular weight cut-off (MWCO) of themembrane Changes in the membranersquos pore size and subsequent rejection can bedetected via solute rejection tests Molecular weight markers or molecules with spe-cific known molecular weights are used to test the membranersquos rejection capabilities(Arkhangelsky Kuzmenko amp Gitis 2007) This method is superseded by other moreaccurate analytical techniques such as pore size distribution measurements based onbubble point and gas permeation methods Despite the limitations of these filtrationcharacteristic assessment tools they still provide the most distinct and fundamental in-formation about membrane aging and degradation in real time

11412 Surface characteristics

Two critical parameters that affect fouling on the membrane surface are membranehydrophilicity and surface charge After multiple cleaning cycles the membranesurface properties are altered due to the exposure to harsh cleaning chemicalsTherefore two analytical techniques are used to measure changes of these twoparameters

For surface hydrophilicity contact angle measurements are conducted via thesessile drop technique and the angle obtained determines the nature of the membranesurface Streaming potential is an electrokinetic measurement used to characterise themembrane surfacersquos zeta potential (see Figure 116) Membranes that were exposed tochlorine became more hydrophilic due to leaching of polymeric additives resulting information of larger pores With chain scission the membranersquos surface charge was also

Membrane ageing assessment tools amp techniques

Filtration characteristics

Surface characteristics

Chemical amp structural characteristics

Morphological characteristics

Mechanical characteristics

Membrane flux measurements

Solute rejection amp

MWCO

Contact angle measurements

Streaming potential

ATR-FTIR measurements

Elemental amp chemical

composition

Membrane mechanical properties

Thermogravimetric analysis

Morphological microscopy

(AFM SEM amp FESEM)

Figure 115 Membrane ageing assessment tools and techniques

Membrane ageing during water treatment mechanisms monitoring and control 363

altered resulting in a more hydrophilic membrane surface (Arkhangelsky et al 2007Wang Wang Wu Zhou amp Yang 2010)

11413 Chemical and structural characteristics

To assess the membranersquos chemical and structural properties two techniques arewidely used Attenuated total reflectanceeFourier transform infrared(ATReFTIR) is used to identify the membranersquos functional groups and shifts intransmission peaks would mean that the membrane chemical structure was altered(see Figure 117) X-ray photoelectron spectroscopy (XPS) measures the elementalcomposition and chemical binding of the membrane surface For both techniquescomparison of the results obtained from the virgin and aged membranes wouldprovide a definitive conclusion as to whether the membrane was missing certainfunctional groups or there were chemical depositions on the membrane surface(Antony et al 2010 Arkhangelsky et al 2007 Puspitasari Granville Le-Clechamp Chen 2010 Rouaix et al 2006) ATReFTIR is a qualitative measure of changewhile XPS is quantitative and thus these two techniques are complementary to oneanother

Exposure to harsh chemical cleaning regimes can cause membrane polymer chainscission and breaking reactions resulting in an ageing membrane that has lost its func-tional groups thus making it more susceptible to failure

11414 Mechanical and thermomechanical characteristics

Mechanical properties of the membrane such as the ultimate tensile strength breakingforce yield stress and Youngrsquos modulus are measured to determine whether ageinghas occurred Physical ageing of the membrane would result in an increase in yieldstress and Youngrsquos modulus and a decrease in tensile strength and breaking force indi-cating that the membrane has become stiffer more brittle and mechanically weaker(Arkhangelsky et al 2007 Rouaix et al 2006) It should be noted that results from

-40

-30

-20

-10

0

10

20

30

40

2 3 4 5 6 7 8 9 10

Zeta

-pot

entia

l (m

V)

pH

001mM

005mM

010mM

Figure 116 Streaming potential graph of membranes with varying additive concentrations

364 Advances in Membrane Technologies for Water Treatment

each mechanical property have to be cross-referenced before a sound conclusion canbe drawn with regard to the membranersquos mechanical integrity

Thermogravimetric analysis (TGA) is also used to detect loss of membrane materialdue to ageing (see Figure 118) TGA detects changes in the mass of the membranesample as a function of both temperature and time It is based on the principle thateach polymeric material has a unique degradation temperature and disappearancesof polymeric peaks at specific temperatures would indicate an alteration to the mem-branersquos mechanical properties (Yadav Morison amp Staiger 2009)

11415 Morphological characteristics

To have a better understanding of the membranersquos surface morphology microscopicvisualisation techniques are used Atomic force microscopy (AFM) scanning electronmicroscopy (SEM) and field emission scanning electron microscopy (FESEM) arevisualisation techniques that can provide accurate high-resolution images of variousmembrane characteristics

AFM is widely used to determine surface morphology and roughness via a preci-sion tip that is dragged along the membrane surface The repulsive interaction betweenthe surface and the tip is measured and a micrograph based on the force is measuredThe micrograph provides information on characteristics such as pore size distributionsurface roughness and membrane surface charge interactions (Arkhangelsky et al2007 Hilal Johnson Bowen amp Williams 2009) By comparing micrographs of thevirgin and aged membrane samples changes in the membranersquos morphological char-acteristics can be detected and could help with assessing and predicting membraneageing and failure

20

30

40

50

60

70

80

90

100

700 900 1100 1300 1500 1700

Abs

orba

nce

Wavelength (cm-1)

Figure 117 Typical Fourier transform infrared spectra for chemical functional groupcomparison

Membrane ageing during water treatment mechanisms monitoring and control 365

SEM and FESEM are able to capture high-resolution images of the membrane sur-face and can provide detailed information that can aid in the understanding of degra-dation on the membrane surface Through the captured high-resolution imagescharacterisation of the membranersquos pore size thickness membrane symmetry andphysical damage that has occurred on the membrane surface can be performedChanges in these parameters would indicate membrane ageing or failure SEM is com-bined with energy dispersive X-ray spectroscopy (EDS) to characterise the chemicalcomposition of the foulant on the membrane surface or the membrane itself (seeFigure 119)

1142 Membrane integrity tests

Membrane failure leads to the compromise of membrane integrity resulting in patho-gens being able to breach the membrane system and increase the microbial contami-nation risk of the treated water and subsequently pose a serious threat to publichealth and safety (Phattaranawik Fane amp Wong 2008) Therefore continuous

0

20

40

60

80

100

0 100 200 300 400 500 600

Wei

ght (

)

Temperature (degC)

Figure 118 Typical thermogravimetric analysis thermogram profile of weight loss as a functionof temperature

(a) (b)

Figure 119 (a) Cross-sectional scanning electron microscopy image and (b) energy dispersiveX-ray spectroscopy elemental map of a hollow-fibre membrane

366 Advances in Membrane Technologies for Water Treatment

integrity monitoring and testing are required to ensure that pathogens are completelyremoved and the product water meets the regulatory guidelines Membrane integritytesting can be divided into two groups direct and indirect testing methods (GuoWyart Perot Nauleau amp Moulin 2010)

11421 Direct testing methods

Direct integrity testing methods refer to tests conducted on the membrane or membranemodule directly and are the most obvious ways to determine membrane integrityTable 113 below summarises the advantages and limitations of the conventional directtesting methods (Guo et al 2010)

Pressure decay testA PDT is a pressure-driven test that is widely used and accepted in the water industryas a way to evaluate the integrity of a membrane During a PDT one side of the

Table 113 Advantages and disadvantages of direct integrity tests

Direct integrity test Advantages Disadvantages

Pressure decay test (PDT) bull Independent of feed waterquality

bull Ease of applicationbull High sensitivitybull High reliabilitybull Low maintenance of testequipment

bull Well-establishedtechnique

bull Performed offlinebull Limited by membranersquosbubble point

bull Requires a large range ofpressures

bull No information of filtratequality

Diffusive air flow (DAF) test bull Independent of feed waterquality

bull Higher sensitivity thanPDT

bull Ease of application

bull Performed offlinebull No information of filtratequality

Vacuum decay test (VDT) bull Independent of feed waterquality

bull Higher sensitivity thanPDT

bull Performed offlinebull No information of filtratequality

bull Difficult for large-scalesystems

Acoustic sound test (AST) bull High failure detectionaccuracy

bull Online operationbull Simple andnondestructive

bull No information of filtratequality

bull Dependent on back-ground noise andinterferences

bull Requires competentoperator training

Membrane ageing during water treatment mechanisms monitoring and control 367

membrane is drained and pressurised up to the test pressure which is set below themembranersquos bubble point The pressure is held for a specific duration and the pressuredecay is monitored It is normal for minor pressure decay (05e15 kPa) due to airdiffusion across the membrane however a faster decrease in pressure would indicatethat the membranersquos integrity has been compromised (ASTM 2013)

PDT is a reliable membrane integrity monitoring technique because it is sensitiveto leak detection and integrity breaches but can only be performed offline resulting inmembrane system downtime Because the membrane is subjected to pressure duringthe PDT and with the effects of membrane ageing or the membrane being not wettedproperly membrane breakage can occur during PDTs and thus may yield a false-positive result (USEPA 2005)

Diffusive air flow testThe diffusive air flow (DAF) test is based on the same principle as the PDT Instead ofmeasuring the pressure decay rate in the PDT DAF tests measure the rate of liquiddisplaced by the diffusive air flow DAF is also limited by the same disadvantagesas the PDT but is more sensitive when detecting integrity changes at levels of greaterthan six LRV Leaks in the additional pipework required for DAF tests could affect thesensitivity of the integrity tests and thus might not be feasible for routine use in largescale plants

Vacuum decay testThe vacuum decay test (VDT) is very similar to the PDT but instead of pressurising thedrained side a vacuum is applied and the vacuum pressure decay is measured Thismethod is more sensitive than a PDT because it negates the effect of air diffusionthrough the membrane and can also detect points of leakage and is nondestructive How-ever this method is rarely used in large-scale membrane systems (Guo et al 2010)

Acoustic sound testA more novel approach to direct integrity monitoring is the acoustic sound test (AST)This technique entails the use of an accelerometer to detect the vibrations generated byair leaks in the membrane module This process is time-consuming and in practice isused in conjunction with a PDT PDT is first used to detect any breaches in the moduleand AST is then used to accurately pinpoint the location of the defect so the membranecan be isolated for replacement or repairs (Johnson 1998) The advantage that ASThas over other direct integrity tests is that it can be performed online while membraneoperation is on thus cutting down on the plantrsquos downtime However ASTrsquos acousticdetection is hampered significantly by background noises and high-process flow ratestherefore it has yet to be implemented in a large-scale system (Laicircne GlucinaChamant amp Simonie 1998)

11422 Indirect testing methods

Indirect integrity testing methods often involve measuring a specific parameter ofthe product water and is used to represent the integrity of the membrane The

368 Advances in Membrane Technologies for Water Treatment

sensitivity of the chosen test should be relatively high so as to detect minor fluctuationsin a measured parameter This would ensure that the treated water achieves the targetedLRV and meets regulatory requirements Table 114 summarises the pros and cons ofindirect testing methods used by industry (Guo et al 2010)

Particle counting and monitoringParticle counting and monitoring is a laser-based light scattering technique usedto count the number of particles of a specific size in the feed and filtrate It is an

Table 114 Advantages and disadvantages of indirect integrity tests

Indirect integrity test Advantages Disadvantages

Particle counting bull Ease of applicationbull Independent of membraneconfigurations

bull Online operation

bull Low detection sensitivitybull Dependent on feed waterquality and operatingconditions

bull Relatively high cost toinstall and maintain

Particle monitoring bull As per particle countersbull Cheaper than particlecounting

bull More sensitive thanturbidity monitors

bull As per particle countersbull Not widely used in waterindustry

Turbidity monitoring bull As per particle monitoringbull Well-established tech-nique in water industry

bull As per particle counters

PhageSpore challengetesting

bull Online operationbull High sensitivitybull High accuracybull Provides actual logremoval value rates

bull Long preparation timefor microbial cultivationand analysis

bull Does not provide real-time integrity results

Powdered activated carbon(PAC) challenge testing

bull Online operationbull High sensitivity

bull High PAC feed concen-tration required

bull Difficult to ensure uni-form PAC particle size

bull May cause membranefouling

FluorescentMagneticparticles challenge testing

bull Independent of feed waterquality

bull Online operationbull High sensitivitybull Can detect virus-sizedbreaches

bull May cause membranefouling

bull Not a well-establishedtechnique

bull Not tested on industrialscale

Membrane ageing during water treatment mechanisms monitoring and control 369

in situ monitoring technique and can be applied to membrane systems of varying con-figurations The measurement sensitivity of the particle counter is directly related to thesize or size distribution of the particles measured and increases as the particle measure-ment threshold is reduced (Guo et al 2010) Therefore the particle counter shouldhave a low threshold that suits its application because the more sensitive the counteris the more expensive it becomes as well

Particle counters do suffer from a number of distinct disadvantages They can onlymeasure particles of a specific size and thus have no selectivity in particle size mea-surements and would produce false readings when micro air bubbles are present inthe permeate stream In a full-scale plant study carried out by Landsness in which fi-bres were progressively cut and the particle count measured the particle count mea-surements were inconsistent thus suggesting that particle counting might not besuitable for full-scale membrane plants (Landsness 2001)

Particle monitoring uses the same principle as particle counters except that itprovides a qualitative assessment of the particle size distribution of the feed orfiltrate It is therefore cheaper than particle counting but is less sensitive (BanerjeeLambertson amp Carlson 1999)

Turbidity monitoringTurbidity is described as the opaqueness of a fluid due to the presence of suspendedsolids and is measured in terms of nephelometric turbidity units (NTU) The turbidityof the feed and filtrate is monitored and a noncompromised membrane should be ableto reduce the turbidity by at least 90 This is cheaper than particle counting andmonitoring however even treated water with a turbidity less than 01 NTU could stillhave bacterial contamination (Banerjee Lambertson Lozier amp Colvin 2001)In the same study carried out by Landsness an insignificant change in turbidity(0024e0037 NTU) was observed when 200 fibres were intentionally cut (Landsness2001) Consequently turbidity monitoring has limited sensitivity for detection mem-brane breaches

Phage and spore challenge testingPhage and spore challenge tests are microbial integrity tests that are spiked into thefeed water and subsequently measured in the permeate Microbial tests are easy toimplement can be done online in situ with membrane system operation and arenondestructive Depending on the application and site-specific considerations thecorrect surrogate should be chosen for the challenge tests

Bacteriophages are virus-infected bacteria surrogates that are used in regulatoryrequired challenge tests to determine membrane integrity and LRV of treatment plantsMS2 bacteriophage is the most common surrogate given its similarly to enteric viruses(Antony et al 2012) Despite the advantages of bacteriophage and spore challengetesting there are also disadvantages Microbial challenge testing requires the longlead time for preparation and cultivation of the surrogate phage It also entails a lengthyanalysis after sampling due to the complexity of plaque forming unit (PFU) countingthus bacteriophage challenge testing cannot provide real-time membrane integrityinformation (Gitis et al 2006)

370 Advances in Membrane Technologies for Water Treatment

With microbial testing it is difficult to distinguish whether microbial reduction wasdue to biological inactivation or retention on the membrane surface Not only are thesephages prone to contamination from other viruses they can also accumulate in thepermeate piping system and lead to false-positive membrane breach detection (Guoet al 2010)

Powdered activated carbon challenge testingAn alternative that mitigates the disadvantages of microbial challenge testing ispowdered activated carbon (PAC) challenge testing It is based on the same principleas its microbial counterpart with the only difference being small controlled doses ofPAC are spiked into the system instead of bacteriophage or spore surrogates The PACparticle size has to be in the similar size range as Giardia and Cryptosporidium so as tomimic microbes (Van Hoof Broens Nahrstedt Panglisch amp Gimbel 2003) Thismethod relies on particle counters and thus suffers from the drawbacks of particlecounting In addition the sensitivity of the test is largely affected by the particlesize distribution of PAC and could lead to membrane fouling if not monitoredproperly

Fluorescent and magnetic particles challenge testingAnother novel surrogate challenge testing option is to either tag particles with fluores-cent or magnetic materials Fluorescent tagged particles can be easily detected bymeasuring the intensity of fluorescence A high fluorescent intensity indicates a largeamount of particles It should be noted that the mass of the particle should be below1 mg so as to maintain the linear relationship between mass and fluorescence Likewiseparticles tagged with magnetic materials such as iron can be easily detected andcollected after the testing (Choi Yang Suh amp Cho 2011) Notwithstanding these ad-vantages fluorescent and magnetic surrogates do experience similar disadvantages asthe other challenge testing methods and thus are not widely used in the water industry

115 Membrane ageing control methods

Membrane ageing and failure are the main challenges faced by water treatment plantsthat use membrane systems for water treatment and recycling Membrane degradationand failure increases the rate at which the membranes would need to be replaced andthus makes membrane filtration more costly Given that membrane ageing eventuallyleads to membrane failure more emphasis should be placed on controlling membraneageing so as to limit the occurrence of membrane failure

1151 Membrane train redundancies

The traditional ldquobelt and bracesrdquo approach in engineering relies on implementation ofmultiple process redundancies Redundancies can be either active or standby In thewater treatment industry active redundant membrane systems reduce the load on

Membrane ageing during water treatment mechanisms monitoring and control 371

one particular membrane train by sharing the overall processing load over multipleredundant trains when a surge in influent flow is detected Standby trains on the otherhand do not come into operation until a failure has occurred and the redundancy iscalled into service to maintain the water treatment systemrsquos functionality and treatedwater quality Therefore having standby redundancies would maintain the membranefiltration unitrsquos efficiency and performance but it will also lead to a higher capital andoperational expenditure thus highlighting the need for membrane process reliabilitymodelling

1152 Membrane modification

Polymeric membranes are often used in various chemical-based environments and arehighly susceptible to membrane degradation due to chemical exposure Therefore oneeffective way to mitigate this issue is to develop new polymeric membranes with sur-face modifications The chemistry of the surface properties of microporous and semi-porous membranes are changed via a surface coating These coatings would render themembranes fouling resistant antimicrobial and chlorine resistant (Geise et al 2010Mansouri Harrisson amp Chen 2010)

From studies conducted it has been proven that membranes become fouling resis-tant after different modifications An increase in the membrane surfacersquos hydrophilic-ity does decrease fouling because this prevents hydrophobic organic foulants frombeing attracted onto the membrane surface Changing the surface charge of the mem-brane can also aid the membrane in becoming more antifouling Similar to increasinghydrophilicity changing the surface charge would generate a repulsive force betweenthe membrane surface and the charged ions of the foulant thus preventing foulantdeposition (Rana amp Matsuura 2010)

Formation of biofilms or membrane biofouling has adverse effects on both mem-brane filtration flux and the membranersquos lifespan Biofouling is unlike other formsof fouling that can be reduced by effective pretreatment of the feedwater due to theself-replicating nature of microbial organisms Biofouling starts with the initial depo-sition of a film of organic molecules and is followed by bacterial colonisation As thebiofilm matures a fouling layer builds up and thus leads to a decline in membrane fluxIt has also been reported that biofouling in the feed channel can lead to a severe in-crease in internal pressure drop and in some cases result in deformation and damageto the membrane module (Mansouri et al 2010)

To control biofouling chlorine is often used as a disinfectant but it suffers from thenegative side effects of chlorine on membrane surfaces Thus chlorine resistance andsurface modification are highly favoured modifications given the high cost involved inthe dechlorinationerechlorination process and replacement of membranes in watertreatment plants

More recently nanoclay nanocomposites have been added to flat sheet membranesto increase the membranersquos abrasion resistance The study concluded that the mem-brane with 1 wt nanoclay showed superior abrasive resistance with the membranelasting two times longer than a normal membrane without the nanoclay addition How-ever the nanoclay concentration would require further optimisation work because an

372 Advances in Membrane Technologies for Water Treatment

increase in the concentration resulted in a decrease in the membranersquos permeability andadverse changes in the membranersquos essential mechanical properties (Lai Groth Grayamp Duke 2014)

116 Conclusion

Currently there are no standard protocols for assessing the membranersquos mechanicalintegrity after prolonged membrane operation and although there are multiple modesand mechanisms that can result in membrane failure membrane ageing and degrada-tion due to chemical attack via strong oxidants is the most common With better char-acterisation of the effects and quantification of membrane ageing at different stages ofa membranersquos lifespan membrane ageing can be mitigated thus prolonging the life-span of the membrane while still maintaining its resilience and reliability With theever-improving membrane modifications being developed the effects of membraneageing can be further controlled thus making membranes more robust cost-effective and efficient for water treatment processes

117 Future trends

The current state-of-the-art of membrane integrity monitoring tools is limited to detect-ing compromises via a variety of in situ and ex situ techniques and tools Despiteextensive research performed on membrane failure mechanisms and their resultant ef-fects these studies are often based on ex situ analytical techniques and can only pro-vide information when a serious breach in membrane integrity is detected Thereforethis highlights the need for the development of nondestructive computer-aided model-ling techniques to predict and quantify membrane ageing at various stages of mem-brane operation through to the end of the membranersquos lifespan

1171 Membrane failure prediction

Apart from monitoring membrane ageing and detecting integrity breaches and failureanother method to limit and control membrane degradation is membrane failure pre-diction Prediction of failure in membrane systems is achieved via a finite elementmethod known as finite element analysis (FEA) FEA is a computer-aided modellingtechnique that can perform mechanical analyses on structures to compute displace-ments from applied loads and is a tool that is widely used by structural and mechanicalengineers (Nicholson 2003) It has also been used by biomedical engineers to predictstress distribution within teeth for tooth fracture prediction (Xie Swain amp Hoffman2009)

FEA can determine stress strain and displacements in complicated shapes by firstdividing the complicated structure into smaller elements and this process is known asdiscretisation Simple equations are then used to solve each element Once all the

Membrane ageing during water treatment mechanisms monitoring and control 373

smaller elements are solved the equation for the whole structure can then be solvedand thus generating the stresses strains and displacements on the entire structureThrough FEA stresses at the locations where they are most likely to cause failurecan be determined Such analyses would aid in design of membrane modules and opti-misation of operation protocols FEA can also be diagnostic by providing supportiveinterpretations via simulation at similar operation conditions when performingautopsies on failed membranes and modules FEA with ageing monitoring tools willyield a more comprehensive understanding of membrane aging and failure and theirmechanisms as well as allow for better process efficiency through improved moduledesign

1172 Membrane reliability modelling

The evaluation of a membrane process unitrsquos reliability should be an important part ofits design and operation However this has traditionally been difficult to assess andquantify and as a consequence its management has largely been ignored Reliabilitymodelling can be used throughout the membrane modulersquos life cycle to predict the fail-ure and the subsequent process shortfalls This would also yield significant savings oncapital and operating costs via the implementation of better strategies derived from thesimulationrsquos results while enabling utilities and plant designers to effectively manageand quantify the risk of noncompliance due to membrane failure With the use ofreliability modelling membrane process performance is no longer just limited tomembrane fouling but can now encompass membrane ageing and failure

List of acronyms

AST Acoustic sound testAFO Amorphous ferric oxideAFM Atomic force microscopyATReFTIR Attenuated total reflectanceeFourier transform infraredCIP Cleaning in placeDAF Diffusive air flowEDS Energy dispersive X-ray spectroscopyFESEM Field emission scanning electron microscopyFEA Finite element analysisLRV Log removal valuesMF MicrofiltrationMLD Megaliter per dayMTBF Mean time between failureMTTF Mean time to failureMTTR Mean time to repairMWCO Molecular weight cut-offNTU Nephelometric turbidity unitsPFU Plaque forming unitPAC Powdered activated carbon

374 Advances in Membrane Technologies for Water Treatment

PDT Pressure decay testRCM Reliability centred maintenanceRO Reverse osmosisSEM Scanning electron microscopyTGA Thermogravimetric analysisTFC Thin film compositeUF UltrafiltrationVDT Vacuum decay testXPS X-ray photoelectron spectroscopy

References

Antony A Blackbeard J amp Leslie G (2012) Removal efficiency and integrity monitoringtechniques for virus removal by membrane processes Critical Reviews in EnvironmentalScience and Technology 42 891e933

Antony A Fudianto R Cox S amp Leslie G (2010) Assessing the oxidative degradation ofpolyamide reverse osmosis membranemdashaccelerated ageing with hypochlorite exposureJournal of Membrane Science 347 159e164

Antony A amp Leslie G (2011)Degradation of polymeric membranes in water and wastewatertreatment Advance membrane Woodhead Publishing Limited

Arkhangelsky E KuzmenkoDampGitisV (2007) Impact of chemical cleaning onproperties andfunctioning of polyethersulfone membranes Journal of Membrane Science 305 176e184

ASTM (2013) Standard practice for pressure decay leak test method ASTM E2930 WestConshohocken PA ASTM International

Banerjee A Lambertson M amp Carlson K (1999) Sub-micron particles in drinking water andtheir role in monitoring the performance of filtration processes In AWWA water qualitytechnology conference proceedings October 31eNovember 4 Tampa FL

Banerjee A Lambertson M Lozier J amp Colvin C (2001) Monitoring membrane integrityusing high sensitivity laser turbidimetry Water Supply 1 273e276

Benavente J amp Vazquez M (2004) Effect of age and chemical treatments on characteristicparameters for active and porous sublayers of polymeric composite membranes Journal ofColloid and Interface Science 273 547e555

Cadotte John E (1985) Evolution of composite reverse osmosis membranes In ACS symposiumseries (Vol 269 pp 273e294) Oxford University Press

Cadotte John E amp Petersen Robert J (1981) Thin-film composite reverse-osmosismembranes Origin development and recent advances [Water purification] In ACSsymposium series (USA)

Chang S (2011) Application of submerged hollow fiber membrane in membrane bioreactorsfiltration principles operation and membrane fouling Desalination 283 31e39

Cheryan M (1998) Ultrafiltration and microfiltration handbook Lancaster PA TechnomicPublishing Company

Childress A E Le-Clech P Daugherty J Chen C amp Leslie G L (2005)Mechanical analysisof hollow fiber membrane integrity in water reuse applications Desalination 180 5e14

Choi S H Yang J Suh C amp Cho J (2011) Use of fluorescent silica particles for checkingthe integrity of microfiltration membranes Journal of Membrane Science 367 306e313

Cui Z F Chang S amp Fane A G (2003) The use of gas bubbling to enhance membraneprocesses Journal of Membrane Science 221 1e35

Membrane ageing during water treatment mechanisms monitoring and control 375

Eisenberg D Soller J Sakaji R amp Olivieri A (2001) A methodology to evaluate water andwastewater treatment plant reliability Water Science and Technology A Journal of theInternational Association on Water Pollution Research 43 91e99

Geise G M Lee H S Miller D J Freeman B D Mcgrath J E amp Paul D R (2010)Water purification by membranes The role of polymer science Journal of Polymer SciencePart B Polymer Physics 48 1685e1718

Gijsbertsen-Abrahamse A J Cornelissen E R amp Hofman J A M H (2006)Fiber failure frequency and causes of hollow fiber integrity loss Desalination 194251e258

Gitis V Haught R C Clark R M Gun J amp Lev O (2006) Application of nanoscaleprobes for the evaluation of the integrity of ultrafiltration membranes Journal ofMembrane Science 276 185e192

Glater J Hong S-K amp Elimelech M (1994) The search for a chlorine-resistant reverseosmosis membrane Desalination 95 325e345

Gunderson L H amp Pritchard L (2002) Resilience and the behavior of large-scale systemsWashington DC Island Press

Guo H Wyart Y Perot J Nauleau F amp Moulin P (2010) Low-pressure membraneintegrity tests for drinking water treatment A review Water Research 44 41e57

Hilal N Johnson D Bowen W R amp Williams P M (2009) Chapter 2eMeasurement ofparticle and surface interactions using force microscopy In W R Bowen amp N Hilal(Eds) Atomic force microscopy in process engineering Oxford Butterworth-Heinemann

Howe K J Hand D W Crittenden J C Trussell R R amp Tchobanoglous G (2012)Principles of water treatment Hoboken NJ Wiley

Johnson W T (1998) Predicting log removal performance of membrane systems using in-situintegrity testing Filtration amp Separation 35 26e29

Johnson W amp Maccormick T (2003) Issues of operational integrity in membrane drinkingwater plants Water Supply 3 73e80

Kagan A (2004) Example 3-Mean time between failures (MTBF) In A Kagan (Ed) Excel byexample Burlington Newnes

Kang G-D Gao C-J Chen W-D Jie X-M Cao Y-M amp Yuan Q (2007) Study onhypochlorite degradation of aromatic polyamide reverse osmosis membrane Journal ofMembrane Science 300 165e171

Klutke G-A Kiessler P C amp Wortman M (2003) A critical look at the bathtub curve IEEETransactions on Reliability 52 125e129

Kwon Y-N amp Leckie J O (2006) Hypochlorite degradation of crosslinked polyamidemembranes I Changes in chemicalmorphological properties Journal of MembraneScience 283 21e26

Lai C Y Groth A Gray S amp Duke M (2014) Preparation and characterization of poly(vinylidene fluoride)nanoclay nanocomposite flat sheet membranes for abrasion resistanceWater Research 57 56e66

Laicircne J M Glucina K Chamant M amp Simonie P (1998) Acoustic sensor A noveltechnique for low pressure membrane integrity monitoring Desalination 11973e77

Landsness L B (2001) Accepting MFUF technology-making the final cut In AWWAMembrane technology conference proceedings March 4e7 2001 Texas San Antonio

Lesjean B Rosenberger S Schrotter J-C amp Recherche A (2004) Membrane-aided bio-logical wastewater treatmentean overview of applied systems Membrane Technology2004(8) 5e10

376 Advances in Membrane Technologies for Water Treatment

Mallevialle J Odendaal P E Foundation A R Wiesner M R Eaux-Dumez L D ampCommission S A W R (1996) Water treatment membrane processes New York NYMcGraw-Hill

Mansouri J Harrisson S amp Chen V (2010) Strategies for controlling biofouling inmembrane filtration systems Challenges and opportunities Journal of Materials Chemistry20 4567e4586

Marshall G amp Chapman D (2002) Resilience reliability and redundancy Retrieved fromhttpadmincopperallianceeudocslibrariesprovider5power-quality-and-utilisation-guide41-resilience-reliability-and-redundancypdfsfvrsn=4ampsfvrsn=4

Nicholson D W (2003) Finite element analysis Thermomechanics of solids Boca Raton FLCRC Press

Oschmann N Nghiem L D amp Schafer A (2005) Fouling mechanisms of submerged ul-trafiltration membranes in greywater recycling Desalination 179(1) 225e233

Phattaranawik J Fane A G amp Wong F (2008) Novel membrane-based sensor for onlinemembrane integrity monitoring Journal of Membrane Science 323 113e124

Prakash Rao A Desai N V amp Rangarajan R (1997) Interfacially synthesized thin filmcomposite RO membranes for seawater desalination Journal of Membrane Science 124263e272

Prulho R Therias S Rivaton A amp Gardette J-L (2013) Ageing of polyethersulfonepolyvinylpyrrolidone blends in contact with bleach water Polymer Degradation andStability 98 1164e1172

Puspitasari V Granville A Le-Clech P amp Chen V (2010) Cleaning and ageing effect ofsodium hypochlorite on polyvinylidene fluoride (PVDF) membrane Separation andPurification Technology 72 301e308

Rana D amp Matsuura T (2010) Surface modifications for antifouling membranes ChemicalReviews 110 2448e2471

Ratnayaka D D Brandt M J amp Johnson M (2009)Water Supply Burlington WA ElsevierScience

Regula C Carretier E Wyart Y Geacutesan-Guiziou G Vincent A Boudot D et al (2014)Chemical cleaningdisinfection and ageing of organic UF membranes A review WaterResearch 56 325e365

Rouaix S Causserand C amp Aimar P (2006) Experimental study of the effects of hypo-chlorite on polysulfone membrane properties Journal of Membrane Science 277137e147

Smith R amp Mobley R K (2008) Chapter 17eMTBF user guide Measuring mean timebetween failures In R Smith amp R K Mobley (Eds) Rules of thumb for maintenance andreliability engineers Burlington WA Butterworth-Heinemann

Stanley S (2011)MTBF MTTR MTTFamp FIT Explanation of terms Tech Rep IMC NetworksAvailable httpwww imcnetworks comAssetsDocSupportWP-MTBF-0311 pdf

Sutton I (2010a) Chapter 7-Reliability availability and maintainability In I Sutton (Ed)Process risk and reliability management Oxford William Andrew Publishing

Sutton I (2010b) Chapter 8eOperations maintenance and safety In I Sutton (Ed) Processrisk and reliability management Oxford William Andrew Publishing

Thominette F Farnault O Gaudichet-Maurin E Machinal C amp Schrotter J-C (2006)Ageing of polyethersulfone ultrafiltration membranes in hypochlorite treatment Desali-nation 200 7e8

Tng K H Wang Y Waite D amp Leslie G (2013) Unexpected iron fouling during mem-brane cleaning in wastewater treatment process 8th International Membrane Science andTechnology Conference (IMSTEC) conference proceedings November 25e29

Membrane ageing during water treatment mechanisms monitoring and control 377

USEPA (2005) Membrane filtration guidance manual EPA 815-R-06-009 Washington DCUnited States Environmental Protection Agency

Van Hoof S Broens L Nahrstedt A Panglisch S amp Gimbel R (2003) Development ofa new integrity testing system Water Supply 3 101e108

Wang P Wang Z Wu Z Zhou Q amp Yang D (2010) Effect of hypochlorite cleaningon the physiochemical characteristics of polyvinylidene fluoride membranes ChemicalEngineering Journal 162 1050e1056

Wicaksana F (2006) Submerged hollow fibre membranes in bubbling systems (PhD thesis)The University of New South Wales Sydney NSW

Xie Z Swain M V amp Hoffman M J (2009) Structural integrity of enamel Experimentaland modeling Journal of Dental Research 88 529e533

Yadav K amp Morison K R (2010) Effects of hypochlorite exposure on flux through poly-ethersulphone ultrafiltration membranes Food and Bioproducts Processing 88 419e424

Yadav K Morison K amp Staiger M P (2009) Effects of hypochlorite treatment on thesurface morphology and mechanical properties of polyethersulfone ultrafiltration mem-branes Polymer Degradation and Stability 94 1955e1961

Yang W Cicek N amp Ilg J (2006) State-of-the-art of membrane bioreactors Worldwideresearch and commercial applications in North America Journal of Membrane Science270 201e211

Zhang K Achari G Sadiq R Langford C H amp Dore M H I (2012) An integratedperformance assessment framework for water treatment plants Water Research 461673e1683

378 Advances in Membrane Technologies for Water Treatment

Mathematical modeling ofmembrane operations for watertreatment

12WL Ang AW MohammadResearch Centre for Sustainable Process Technology Universiti Kebangsaan MalaysiaUKM Bangi Selangor Malaysia

121 Introduction

This chapter will review the mathematical modeling used in water treatment plants thatincorporate membranes in the operation processes Recently more and more watertreatment plants have chosen membranes as the alternative process in producing cleanand potable water due to the processrsquo advantages over conventional treatment pro-cesses Hence a short review about the different mathematical equations used in watertreatment processes with different types of membranes should be carried out The firstsection will briefly introduce the current development trend in the water treatmentsector and the reasons behind the change The second section will focus on the math-ematical models used in membrane water treatment processes It reveals the mainmechanisms of transport in membranes introduces the fundamentals of membranefouling elaborates the phenomenon of concentration polarization (CP) and the deri-vation of the equation The design equation used in membranes processes accordingto the type of membranes will be briefly covered too The following sections willcover the design equations used in nanofiltration (NF) and reverse osmosis (RO) mem-branes and discuss the derivation and use of mathematical equations for microfiltration(MF)ultrafiltration (UF) membranes under different conditions The last part of thischapter provides information about the importance of mathematical modeling in mem-brane operations for water treatment plants and will look into the future trends andchallenges

1211 Water treatment process and its trend

Water scarcity has becomes a worldwide problem that threatens our daily activitiesand sustainable developments One of the main factors that contributed to this prob-lem is the reduction in clean water resources due to pollution Pollution especiallyfrom industry and agriculture has introduced toxins pesticides herbicides heavymetals and deleterious chemicalsresidues into our watercourse Conventional watertreatment plants that use chemical and physical processes are not able to removethose contaminants and are unable to produce consumable water with required

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400012-5Copyright copy 2015 Elsevier Ltd All rights reserved

qualities (Gibs et al 2007 Harisha Hosamani Keri Nataraj amp Aminabhavi 2010Radjenovic Petrovic Ventura amp Barcelo 2008 Saitua Giannini amp Padilla 2012Sarkar Venkateshwarlu Rao Bhattacharjee amp Kale 2007)

Besides the limited clean water resources several other challenges are alsocreating tension in potable water supply such as high blooming population and rapidurbanization stringent regulations for potable water uncertainty in climate changesoveruse and improper management of water resources All these factors coupledwith the underperformance of conventional water treatment processes have led tothe search for new technologies for a better safer and stable potable water supplyOne of the most popular alternatives is the membrane process in drinking water pro-duction plants In recent years membrane technology has emerged as one of the mainprocesses to resolve the problem of water scarcity The membrane process is veryversatile and it has been used for desalting softening and the removal of dissolvedorganics color particles and microbes Its performance has been proven to be betterthan conventional water treatment methods Hence the shortcomings of conven-tional water treatment processes and the strengths of membrane technology havebeen the reasons that contribute to the trend of membrane processes for watertreatment

Basically four types of membranes MF UF NF and RO have been widely usedin the drinking water industry A number of water treatment plants have alreadyimplemented membrane-based processes and the outcomes were encouragingwith the performances of membrane filtration better than those of conventionalprocesses Hence the focus now is on the track to optimize the membrane filtrationprocess and reduce the fouling problems that might affect a membranersquos rejectioncapabilities

122 Mathematical modeling

Modeling of membranes is very important because it will allow users to obtain usefulinformation especially on a membranersquos ability in retaining certain solutes and allow-ing the permeation of particular substances The mechanism of permeation and rejec-tion of membrane is a complicated process Thus a good predictive model will enablethe performance of the membrane to be predicted accurately without involving tediousand complicated procedures to obtain raw data for prediction and enhance theefficiency of the process by optimizing it A reliable modeling will result in a smallernumber of experiments and consequently a reduction in cost and time (HilalAl-Zoubi Darwish Mohammad amp Arabi 2004) Normally in the membrane processtwo aspects of performance will be predicted by using modeling flux prediction andrejection prediction (Van der Bruggen Meuroantteuroari amp Nystreuroom 2008) Several theoriesand models have been proposed for membrane transport mechanisms to derive anacceptable model The models used for each membrane might be different due tothe difference in membranes properties Several types of fouling also affect the compli-cation of the models Further details will be elaborated in the following section

380 Advances in Membrane Technologies for Water Treatment

1221 Transport and fouling mechanisms for membranes

Transport mechanisms of solutesolvent molecules through membranes are shown inFigure 121 Generally there are four types of transport mechanisms (Seader ampHenley 1998)

1 Bulk flow through pores2 Diffusion through pores3 Restricted diffusion through pores4 Solution-diffusion through dense membranes

Different types of membranes will have different transport mechanisms applied onthem For example an RO membrane is a dense membrane so the transport of compo-nents through the membrane will be a solution-diffusion type while for microporousmembranes such as MF and UF the transport mechanisms will involve the pore sizeof membranes NF membranes show a behavior between dense and microporous mem-branes In addition size exclusion and electrostatic interaction are the two fundamentalphenomena that govern the solute rejection by RONF The transport mechanism willdetermine how the performance (flux and rejection) of membranes are being modeledin the water treatment process Figure 122 shows a simple classification of transportmodels for the four membranes discussed in this chapter and the factors that affect thetype of transfermodels to be used inwater treatment (Mulder 1996 ShonVigneswaranKandasamy amp Shim 2008 Wiesner amp Buckley 1996 Williams 2003)

From Figure 122 it can be seen that the transport models used to predict anddescribe the water treatment process depend on the membranes used and the foulantsin the raw water Membrane class is further separated into porous and nonporous typeseach one having its own suitable equationstheories for mathematical modelingFor foulants its characteristic will determine which model is the most suitable and ac-curate in describing the retention mechanism Indeed transport mechanisms rely on acombination of several principles including size exclusion and charge or dielectricexclusion (DE) (Yaroshchuk amp Staude 1992) For uncharged solutes sieving effector steric hindrance will be the main rejection mechanism Solutes with larger molecularweight cutoff than the membrane will be retained Besides that the transport ofuncharged solutes is also contributed by convection due to pressure difference and

Figure 121 Transport mechanisms in membranes (Flow is downward) (a) Bulk flow throughpores (b) Diffusion through pores (c) Restricted diffusion through pores (d) Solution-diffusionthrough dense membranesSource Adapted from Seader and Henley (1998)

Mathematical modeling of membrane operations for water treatment 381

Transport models

Solutes(foulants)

Nonchargedcolloids

Chargedcolloids

Generalorganicmatter

Ions

Membranes

Porousmembranes

Nonporous (dense)membranes

CP relationshipconvection and diffusionNernstndashPlanck equationresistance in series and

cake filtration theory

CP relationshipthermodynamic modeldiffusivity resistance in

series and adsorption layers

NF

RO

MF

UF

Basic models-HagenndashPoiseulle equation

-KozenyndashCarman relationship

Homogeneous membrane models-Solution-diffusion

-Extended solution-diffusion-Solution-diffusion-imperfection

Convection and diffusion Donnanexclusion extended NernstndashPlanckequation resistance in series and

cake filtration theory

Donnan exclusion andextended NernstndashPlanck

equation

Pore based models-Preferential sorption-capillary flow

-Finely porous and surface force-pore flow

Knudsen flow

Friction model

Concentration polarization (CP)model

Resistance in series modelosmotic pressure model and

mechanistic interpretation

Irreversible thermodynamics models-KedemndashKatchalsky

-SpeiglerndashKedem

Figure 122 Classification of transport models according to the type of membranes and foulantsSource Adapted from Williams (2003) Mulder (1996) Shon et al (2008) and Wiesner and Buckley (1996)

382Advances

inMem

braneTechnologies

forWater

Treatm

ent

diffusion through a concentration gradient across the membrane The main transportmechanism of charged solutes (ions) is charged exclusion or the Donnan effect whichinvolves the interaction between the rejection of co-ions and the fixed electric chargesattached to the membrane matrix (Hassan Ali Abdull amp Ismail 2007) Some of thecommonly used transport models will be discussed in the following sections It shouldbe noted that so far there is not any mathematical modeling that is valid for wide-range applications Most of the established models are only applicable for certain andspecific conditions

Fouling is a major obstacle for membranes to be used widely Fouling may exist indifferent forms (Field 2010)

1 Adsorptionmdashoccurs when there are specific interactions between the membrane and foulantsolute in the solution

2 Pore blockagemdashfoulantsparticles block and clog the pores of membrane3 Depositionmdashdeposit of particles that grows layer by layer at the membrane surface (known

as cake resistance fouling as well)4 Gel formationmdashCP leads to the formation of a gel layer in the immediate vicinity of the

membrane surface

Fouling will affect membrane flux and rejection of unwanted components in waterHence modeling of membrane performance in water treatment should take into ac-count membrane fouling because fouling phenomena is unavoidable for current stage

1222 Concentration polarization

CP is a process of accumulation of retained solutes in the membrane boundary at thefeed side It is a natural consequence of membrane selectivity (Field 2010) CP com-plicates the modeling of the membrane filtration unit because the wall concentration ofsolute is not the same as the bulk feed concentration It is difficult to determine the so-lute wall concentration The boundary layer film model has been used to describe thisphenomenon Under steady-state conditions the convective flow of solute to themembrane surface is equal to the solute that permeates through the membrane deductwith diffusion of solute back to the bulk feed solution (as shown in Eqn (121))

J$C frac14 J$Cp DjidCdz

(121)

Integration of Eqn (121) with the following boundary conditions

z frac14 0 C frac14 Cm

z frac14 lbl C frac14 Cb

will yield Eqn (122)

J frac14Dij

lbl

ln

Cm Cp

Cb Cp

(122)

Mathematical modeling of membrane operations for water treatment 383

At the end this equation derived from film theory model will be used to determinethe solute concentration at the membrane surface Rearranging Eqn (122) yields

Cm frac14 ethCb CpTHORNexp J$lblDij

(123)

Solute concentration at the membrane surface is very important because it will beused in many membrane transport models

Usually the term Dij=lb in Eqns (122) and (123) will be described as a mass trans-fer coefficient kib and it can be determined from conventional chemical engineeringcorrelations such as the Sherwood number (Sh) Reynolds number (Re) Schmidtnumber (Sc) and Peclet number (Pe) (Baker 2000 Field 2010) The bulk andpermeate concentrations can be determined by using analytical instruments

CP might have some negative effects on the performance of a membrane filtrationunit It will decrease the water flux and rejection of undesired solute cause precipitationdue to high surface concentration that exceeds the solubility limit change the membraneseparation properties and enhance other fouling such as colloidal or particulate materialsthat will block the membrane surface Hence the design of the membrane module andoperating conditions are important to prevent and reduce the impact of CP

1223 Mathematical modeling for RO membranes

RO is a process especially applied in desalination that uses membranes only perme-able to water but impermeable to salt and other impurities Many mathematicalmodels have been proposed for the solute and solvent transport mechanism andthe most acceptable and widely applied is solution-diffusion transport mechanismThe water transport across the membrane can be expressed by Fickrsquos law (Baker2000) With some assumptions and further derivation the equation is reduced to aformula in which the water flux is linked to pressure and concentration gradientsacross the membrane For solute flux it depends on salt concentration at the feedside and permeate side

Design equations for RO membranes will be based on the solution-diffusiontransport mechanism Water flux and solute flux are expressed as (Baker 2000)

Jw frac14 PwethDp DpTHORN (124)

Js frac14 PsethC1 C2THORN (125)

One of the considerations when deciding on the operating pressure for RO is theosmotic pressure of the liquid feed Osmotic pressure is being defined as the pressurerequired to be applied to a solution to prevent the inward flow of water across the mem-brane For small to minimum concentration of solute osmotic pressure p is directlyproportional to the concentration of the solute and temperature according to the

384 Advances in Membrane Technologies for Water Treatment

experimental data done by other researchers (Senthilmurugan Ahluwalia amp Gupta2005) Osmotic pressure can be calculated by using the formula proposed by VanrsquotHoff (Geankoplis 2003) or using the Pitzer equation (Hu Wu amp Gao 1999) How-ever the calculation steps of the Pitzer equation are complicated as shown in the refer-ence cited So here is the easier form of Vanrsquot Hoff equation

p frac14 n

VmRGT (126)

However this equation is suitable for dilute water solutions For solutions with highconcentration of solutes modifications have to be made For concentration of dis-solved solids in the range of 20000e50000 ppm the osmotic pressure can be calcu-lated from the equation modified by (Kaghazchi Mehri Ravanchi amp Kargari 2010)

p frac14 09524C2 thorn 81633C 236143 (127)

Hence the osmotic pressure gradient is

Dp frac14 pm pp frac14 09524C2m C2

p

thorn 81633

Cm Cp

23614 (128)

in which the concentration of a solute at the membrane surface could be obtained fromthe CP correlation

An industrial seawater RO desalination plant with a spiral-wound module wassimulated using the solution-diffusion model and the model was found to be ableto predict the steady-state behavior of the plant with good accuracy Tables 121and 122 show the comparison between the actual results from the industrial unitand calculated data from the solution-diffusion model It can be concluded that themathematical model has a good accuracy of prediction for that particular seawaterRO desalination plant (Kaghazchi et al 2010)

Besides the well-known solution-diffusion model (under the category of nonporousor homogeneous membrane models as depicted in Figure 122) RO transport modelscan be derived from one of two main groups irreversible thermodynamics models andporous models (Gambier Krasnik amp Badreddin 2007) Table 123 presents a sum-mary of available transport models and basic equations for determining the soluteand solvent fluxes for RO membranes (Malaeb amp Ayoub 2011) Details of derivationcan be found in the reference cited

Models based on irreversible thermodynamics treat the membrane as a blackbox One of the irreversible thermodynamics models is the SpieglereKedem modelThis black box approach allows the performance of the membranes to be character-ized in terms of salt permeability Ps and the reflection coefficient s (LevensteinHasson amp Semiat 1996 Schirg amp Widmer 1992 Xu amp Spencer 1997)No particular mechanism of solute transport and structure of membrane arerequired

Mathematical modeling of membrane operations for water treatment 385

There are several assumptions being made for the classical hydrodynamic or poremodel It is assumed that (Nakao 1994 Zhao Zhou amp Yue 2000)

1 The membrane is crossed by cylindrical pores with uniform radius and length2 Solute molecules are simulated as rigid spheres moving slowly inside the pores3 Poiseuille flow applies in the pores of the solvent4 Steady-state flow occurs and5 Solute concentration is so small that there is no interaction among solute molecules inside

the pores

Membrane is being considered as a charged porous layer by steric hindrance pore(SHP) model and TeorelleMeyereSievers (TMS) model The partitioning effects aredescribed by steric hindrance and electrostatics and mass transfer through the mem-brane is based on the extended NernstePlanck equation Space charge models ofSpiegler-Kedem provide a relatively stable numerical solution but are computation-ally expensive (Malaeb amp Ayoub 2011)

Agriculture and industry the two largest water consumption sectors have producedand released a lot of new contaminants into our various drinking water sources Pes-ticides herbicides insecticides pharmaceutical products and heavy metals are a fewof the emerging trace contaminants that currently receive more attention in water treat-ment plants With the health threats from the emerging and newly discovered trace

Table 121 Simulation results of the first industrial unit

Parameter Industrial unit Calculated Error ()

Permeate flow rate(m3s)

830 105 753 105 93

Permeateconcentration(kgm3)

061 060 11

Concentrate flowrate (m3s)

225 103 223 103 09

Concentrateconcentration(kgm3)

6411 6472 09

Source Kaghazchi et al (2010)

Table 122 Performance comparison between actual and simulatedfirst unit

Parameter Industrial unit Calculated Error ()

Recovery 00259 00233 003

Rejection percent 09902 09905 003

Source Kaghazchi et al (2010)

386 Advances in Membrane Technologies for Water Treatment

Table 123 Available transport models for reverse osmosis membrane

Models Model reference Basic featuresequations

Models based on irreversiblethermodynamics

Kedem and Katchalsky (KK) model bull Describes the flow of solution and solute in which perfor-mance is measured through the dissipation function and doesnot address the mechanism of rejectionJv frac14 LpethDP sDpTHORNJs frac14 Psethcm cpTHORN thorn eth1 sTHORNJv

KedemeKatchalskyeZelman model bull Proposed for the multiple solute system in membranefiltration

bull Considers the differential equations for the transport ofmultiple solutes and involves the usage of finite-differenceequations

SpieglereKedem model bull Accounts for the variability of the concentration profile atlarge fluxes and high concentration gradients

bull Transport through membrane is characterized by solvent andsolute permeability and reflection coefficient

bull Calculated based on the average concentration inside themembrane

bull Mostly used in single-solute systems

Js frac14 P0dcdx

thorn eth1 sTHORNJv

Extended SpieglereKedem model bull A one-dimensional model for multiple solutes incorporatingsoluteesolute interactions

bull Characterized by parameters estimated using theLevenbergeMarquardt method coupled with theGausseNewton algorithm and based on experimental datafrom the literature

Continued

Mathem

aticalmodeling

ofmem

braneoperations

forwater

treatment

387

Table 123 Continued

Models Model reference Basic featuresequations

Stefan-Maxwell model Peppas amp Meadows (1983)Roberson amp Zydney (1988)

bull Have shown to be equivalent to models based on irreversiblethermodynamics

Js frac14 D2CxsdlnethysxsTHORN

dz thorn D2D1

JvCxs

xs is the solute mole fraction ys is the solute activitycoefficient C is the total molar concentration and D1 and D2

are overall transfer coefficients given in terms of the binaryStefan-Maxwell diffusivities

Teorell-Meyer-Sievers (TMS) model(Hassan et al 2007)

bull Describes the membrane electrical properties in terms ofeffective charge density and electrostatic effects

bull Assumes a uniform radial distribution of fixed charges andmobile species

ssalt frac14 1 2

eth2a 1THORNzthorn ethz2 thorn 4THORN1=2

Psalt frac14 Dseth1 ssaltTHORNAk

Dx

Space charge model

bull Suggests a radial distribution of the potential and concen-tration gradient across the pores

bull Ions are treated as point charges so steric effects of the size ofions are neglected

388Advances

inMem

braneTechnologies

forWater

Treatm

ent

bull The NernstePlanck equation is used for ion transport thenonlinear PoissoneBoltzmann equation for ionconcentration and radial distribution of electric potential andthe NaviereStokes equation for the force balance in narrowpores relative to pore length

Hydrodynamic or pore models Pappenheimer (1953) Solute flux due to diffusion onlyJds frac14 Dof ethqTHORNSDAkdC=dx DeffAkdC=dxSD steric factor restricting the entrance of the molecule intothe poref(q) viscous drag at the wall once the molecule has enteredthe poreDo and Deff diffusion coefficients in a free solution and in apore respectivelyAk corresponds to the membrane surface porositySD frac14 eth1 qTHORN2f ethqTHORN frac14 1=eth1thorn 24qTHORN

Renkin (1954) Solute flux is given in terms of both diffusion flow andconvection flowJs frac14 DoethqTHORNSDAkethCm Cf THORN thorn f ethqTHORNScJvCm

The restriction factor Sc for the convection flow isintroducedSc frac14 2eth1 qTHORN2 eth1 qTHORN4f ethqTHORN frac14 1 2104qthorn 209q3 095q5

Verniory DuBois Decoodt Gasseeamp Lambert (1973)

bull Modified the above classical pore models by adopting awall correction factor and relating it to the treatment withthermodynamic and frictional forcesJs frac14 Dof ethqTHORNSDAkDCs=Dxthorn gethqTHORNScJvCs

bull Introduced the convective friction forces function g(q) inaddition to f(g) f ethqTHORN frac14 eth1 2105q2 thorn 2865q3

17068q5 thorn 072603THORN=eth1 075857q5THORNgethqTHORN frac14 eth1 2=3q2 020217q5THORN=eth1 075857q5THORN

Continued

Mathem

aticalmodeling

ofmem

braneoperations

forwater

treatment

389

Table 123 Continued

Models Model reference Basic featuresequations

Steric hindrance pore (SHP) model bull Modified pore model by eliminating the wall correctionfactors used to predict pore radius and the ratio of membraneporosity to thickness

bull Particularly used for the permeation of a single neutral soluteand not suitable for salt retention application

Ji frac14 viki

HFiuxc HDiDi

dcdx thorn c ziFdf

RTdx

bull The HF and HD parameters are for steric hindrance andfrictional forces that impede convective and diffusivetransport respectively

Source Malaeb and Ayoub (2011)

390Advances

inMem

braneTechnologies

forWater

Treatm

ent

contaminants in natural water resources membrane technology (RONF) has been sug-gested and accepted as the most appropriate method to remove them Thus mathemat-ical modeling of the rejection of those trace contaminants is very useful in predictingthe removal of deleterious substances in water

The issue of boron in drinking water has received more attention judging from theincreasing number of scientific investigations on the removal of boron by RONFmembranes (Tu Nghiem amp Chivas 2010) Because boron exists in a solution inthe form of boric acid and borate salts the currently widely accepted solution-diffusion model can be used to explain the transport mechanism of boron throughRONF membranes Another model used to describe the transport of boron is the irre-versible thermodynamics model developed by Kedem and Katchalsky (Kedem ampKatchalsky 1958) The transport equations of solution-diffusion and irreversible ther-modynamics models have been presented above and in Table 123

The detection of pesticides and endocrine compounds in natural water is of greatconcern to the public and especially potable water production plants (CornelissenVerdouw Gijsbertsen-Abrahamse amp Hofman 2005) Pesticide removal by RONF isa complicated process However in general there is ample evidence that the mainmechanism that determines the retention of pesticides is size exclusion (sieving mecha-nism) (Plakas amp Karabelas 2012) For charged pesticides both size exclusion and elec-trostatic interaction are the twomechanisms that are responsible in controlling the degreeof separation Few models have been applied to predict the trace organic rejection andTable 124 shows the pros and cons of different models applied for modeling andpredicting trace organic rejection by NFRO membranes (Plakas amp Karabelas 2012)

In membrane water treatment processes water temperature is an important factorthat must be considered when operating the plants Higher temperature will requirelower operating pressure to produce the desired production capacity and the reverseis true for low-temperature raw water By assuming all the factors affecting perfor-mance of a membrane remain constant the permeate flow at any temperature relativeto flow at 25 C can be estimated by (AWWA amp ASCE 2012)

QT frac14 Q25C 103ethT25THORN (129)

This equation is applicable for both RO and NF membranesThe selectivity of RO membranes normally will be measured as solute rejection

coefficient as (AWWA amp ASCE 2012)

R frac14 Cb Cp

Cb 100 frac14

1 Cp

Cb

100 (1210)

Due to the high rejection of solute for RO membranes the concentration of solutebeing retained at the membrane surface (feed side) will be very high This leads to theproblem of CP The solute concentration at the membrane surface (feed side) will bedifferent from bulk concentration Hence the film theory model is used to determinethe solute wall concentration (as shown in the previous section) The solute wallconcentration is required to obtain the real rejection percentage of the RO membrane

Mathematical modeling of membrane operations for water treatment 391

Table 124 Main advantages and disadvantages of the models applied for modeling andor predicting traceorganic rejection by nanofiltrationreverse osmosis membranes

Models Advantages Disadvantages

Models based on irreversiblethermodynamics (SpieglereKedemmodel combined film theory-SpieglereKedem model models withand without convection)

bull No particular mechanism of solutetransport and structure of membraneis specified (membrane treated as aldquoblack boxrdquo)

bull Suitable for predicting theperformance of multiple solutes innanofiltrationreverse osmosissystems

bull Highly dependant on the driving forces (pressure andconcentration gradients) which restricts their practicalapplication

bull A number of assumptions made which in many cases areunrealistic

bull The system should not be too far from equilibrium inorder for the model to be applicable

bull Valid for high rejection membranes

Mass transport models (solution-diffusion models porous modelsnonporous or homogeneousmembrane models etc)

bull Simple models providing estimateseven for technically demandingseparations

bull The linearization of these modelsfacilitates rapid calculations

bull Variation of the solute mass transfer coefficients withdifferent water qualities and operating conditions intrin-sically membrane physicochemical properties constrainsthe model application from one system to another

bull Mainly applicable to single-solute systemsbull Solute mass transfer coefficients depend on the test unitscale (as different operating conditions may exist in theseunits) limiting the model accuracy in membrane scale-up

Artificial neural network models inconjunction (or not) with quantitativestructure activity relationship models

bull Easy to usebull Do not apply any physical laws andtransport phenomena thus over-coming the problems of complexity

bull More accurate estimates than exist-ing models

bull Valid models regardless of rejectionperformance of the membranes tested

bull Specific applicable in the range of experimental condi-tions employed for their development

bull Changes of membrane properties as a result of fouling orswelling influence the accuracy of models

Source Plakas amp Karabelas (2012)

392Advances

inMem

braneTechnologies

forWater

Treatm

ent

The model equations for water and solute flux also will be changed after taking the CPeffect into consideration Concentration of solute at membrane surface could beobtained from the final derivation shown in previous subsection

For rejection

RCP frac14 Cm Cp

Cm 100 frac14

1 Cp

Cm

100 (1211)

The CP effect will be included in modeling for more precise prediction An exampleis the incorporation of the CP ratio for tubular membranes in the turbulent region thathas been derived out as shown below (Wiesner amp Buckley 1996)

Cm

Cbfrac14 1

Drthorn1 1

Dr

expethkTHORN (1212)

Dr frac14 Cb

Cp

jd frac14 0023Re017

By incorporating the CP ratio into the solution-diffusion transport equations forwater and solute flux the following equation could be obtained

Jw frac14 kw

Dp Dp

Cm

Cb

thorn Dp

Dr

(1213)

Js frac14 kiCb

Cm

Cb 1Dr

(1214)

These equations allow the performance of RO membranes to be estimated andpredict what the effect of CP would be on the given operating conditions

1224 Mathematical modeling for NF membranes

NF has been defined by many as a process between UF and RO Indeed NF is a verycomplex process Generally NF is a charged membrane and the modeling mustconsider the interaction between the charged membrane and ionic solute Manycharged membrane transport theories have been proposed that account for electrostaticeffects as well as diffusive and convective flow to describe the solute separationIndeed NF and RO membranes both share most of the same models but under thissubsection a few models that are widely accepted for NF membrane will be discussedOne of them is the solution diffusion model which has been depicted in the previoussubsection However the most popular mathematical model for NF is the extendedNernstePlanck equation It has been widely adopted for NF membrane modeling

Mathematical modeling of membrane operations for water treatment 393

This equation consists of a few different terms that accounted for the different transportphenomena Donnan effect and dieletric exclusion are included in this model

The most commonly adopted form of the extended NernstePlanck equation (TsuruNakao amp Kimura 1991) is

Ji frac14 KicciJv Dipdcidx

ziciDip

RGTFdjdx

(1215)

The first term in Eqn (1215) represents the solute flux contribution due to convectionthe second term accounts for solute transport due to diffusion and the last term describesthe solute flux due to the Donnan potential (Williams 2003) This extendedNernstePlanck equation will be the base model for other models When a chargedmembrane is brought into contact with an electrolyte solution the concentrationpartition of co-ions and counter-ions occurs at the membraneesolution interfaces onboth the feed and permeate sides The potential differences associated at these boundariesare calledDonnan potentials andDonnan potentials exist tomaintain the electrochemicalequilibrium (Nguyen Bang ChoampKim 2009) TheDonnan potential helps in repellingions where co-ions are rejected because of the potential at the membrane-feed interfacewhereas counter-ions are attracted (Greenlee Lawler FreemanMarrotampMoulin 2009)

For uncharged solute transport through the membrane the Donnan effect will notbe considered so the third term in Eqn (1215) will be zero (Luo amp Wan 2011)The application of the modified extended NernstePlanck equation for unchargedsolutes can be obtained elsewhere (Bowen amp Welfoot 2005 2002) and Figures123 and 124 show the good agreement between the predicted and experimentaldata for organic solute (iminodiacetic acid IDA and glutamic acid Glu) rejectionby NF 270 membrane (Luo amp Wan 2011)

10

08

06

04

02

0000 50x10-6 10x10-5 15x10-5 20x10-5 25x10-5

Flux (ms)

0 M NaCl05 M NaCl10 M NaCl20 M NaClBest fitting 05 M NaClPrediction 10 M NaCl

Prediction 20 M NaCl

Rin

t

Figure 123 Measured and predicted iminodiacetic acid retentions for NF 270Reprinted from Luo and Wan (2011) with permission from Elsevier

394 Advances in Membrane Technologies for Water Treatment

Various studies have used a model termed the Donnan-Steric-Pore model (DSPM)to predict the behavior of ionic rejections in NF membranes (Bowen amp Mohammad1998 Bowen Mohammad amp Hilal 1997) DSPM is a model developed based onthe extended NernstePlanck equation in conjunction with the Donnan equilibriumIt has been widely accepted as one of the most effective models for NF membranesin predicting the rejection of ionic compounds (Mohammad 2008) The potentialgradient is

djdx

frac14Pn

ifrac14 1 ziJvDip

Kicci Cip

ethF=RGTTHORN

Pnifrac14 1 z

2i ci

(1216)

With the inclusion of the steric effect (4) and Donnan exclusion effect (Dj)

gicigoi Ci

frac14 4 exp

ziF

RGTDjD

(1217)

The DSPM model has been further modified to include the DE effect for chargedions (Mohammad Hilal Al-Zoubib Darwish amp Ali 2007) and this model hasbeen termed the DSPM-DE model The DSPM-DE model differs from the DSPMmodel due to the inclusion of the DE effect in the partitioning coefficients of eachion as follows

ciCi

frac14 4 exp

ziF

RGTDjD

exp

DWi

kBT

(1218)

10

08

06

04

02

00000 750x10-6 150x10-5 225x10-5 300x10-5

Flux (ms)

0 M NaCl05 M NaCl10 M NaCl20 M NaClPrediction 05 M NaClPrediction 10 M NaClBest fitting 20 M NaCl

Rin

t

Figure 124 Measured and predicted glutamic acid retentions for NF 270Reprinted from Luo and Wan (2011) with permission from Elsevier

Mathematical modeling of membrane operations for water treatment 395

The DE effect is represented by the Born solvation energy barrier The electro-static interactions between the ions of the solutions with the polarization chargesinduced by ions at the interfaces between the media of different dielectricconstants (in this case a membrane matrix and a solvent) will create DE (Bandiniamp Vezzani 2003 Yaroshchuk 2000) The derivations and the applications of theabove equations are not within the scope of this chapter and they could be obtainedfrom the references cited

1225 Mathematical modeling for MFUF membranes

Both MF and UF membranes are porous membranes which indicate that the basicmechanism of rejection will be the sieving mechanism Molecules with a greatersize than the pores of membranes will be rejected Hence the pore flow model canbe used to describe the flux through the membranes According to Darcyrsquos law fluxis proportional to applied pressure difference across the membrane as shown in Eqn(1219) (Baker 2000)

J frac14 P$ethpf ppTHORN frac14 P$Dp (1219)

This equation is the basic design equation used to model the performance of MFUF(clean membranes) in water treatment processes Unlike RONF membranes the os-motic pressure of macromolecules (solutes being rejected from passing through MFUF) is very low and can be neglected So the osmotic pressure effect is not beingconsidered for MFUF (Geankoplis 2003) The permeability constant P dependson the membrane structure (pore size distribution and porosity) and permeate quality(viscosity) There are two approaches normally used to define the permeability con-stant The first approach is using the Hagen-Poiseuille law in which the membranestructure can be assumed to be uniform capillaries (Seader amp Henley 1998)

v frac14 D2

32mLethpf ppTHORN (1220)

By combining the HagenePoiseuille equation the porosity of membrane 3 and thetortuosity of the pores s the flux can be described by

J frac14 εD2

32msDp

L(1221)

In real porous membranes the pores might not be cylindrical and straight so anotherapproach is assuming the membrane is an arrangement of near-spherical particles inwhich CarmaneKozeny equation can be applied to obtain the flux as (Field 2010)

J frac14 ε3

KmS2eth1 εTHORN2Dp

L(1222)

396 Advances in Membrane Technologies for Water Treatment

However both of the above two equations are idealized equations because the realstructure of the membrane deviates from the assumptions Thus usually a morecommonly accepted equation will be used to describe the pure water flux of MFUF known as the osmotic pressure model (Ahmad Chong amp Bhatia 2006 Karode2001)

J frac14 Dp Dp

mRmfrac14 Dp

mRm(1223)

Because the osmotic effect for MFUF membranes usually is very small this termwill be neglected To have a better prediction on the membrane performance thefouling effect has to be taken into consideration when treating the real water samplewhich might contain foulants Equation (1223) will be modified to include thepossible fouling resistance when the membranes are being used to treat nonpure wa-ter This leads to the development of a widely used mathematical model known asthe hydraulic model of filtration resistance (resistance in series model) (Konieczny2002 Rajca Bodzek amp Konieczny 2009 Shengji Juanjuan amp Naiyun 2008) Thismodel is based on the equation that describes the correlation between permeate fluxand pressure taking into account the hydraulic resistance fluid meets flowingthrough a membrane By looking at the equation below it can be seen that the liquidflowing through the membrane will not only encounter the resistance from mem-brane itself but also reversible and irreversible resistances ariseing due to foulingphenomena

J frac14 Dp

methRm thorn RtTHORN frac14 Dp

methRm thorn Rrev thorn RirrTHORN (1224)

Reversible fouling is a fouling process where the membrane capability can berecovered by either backwash or chemical cleaning methods while irreversible foulingis the permanent loss of a membranersquos productivity that could not be recovered by acleaning method The ways to obtain the values of resistance are shown elsewhere(Rajca et al 2009) Figure 125 depicts the comparison between volume water fluxobtained experimentally and calculated using Eqn (1224) under different operatingconditions It was shown that this resistance model is capable of characterizing thewater treatment process by UF membrane

Another simple mathematical model that has been tried out to calculate the fluxfrom the UF membrane water treatment process is the filtration model in a nonsta-tionary process (relaxation model) (Konieczny 2002) It uses the mass transportbalance equation during membrane filtration in which the decrease in the permeateflux is proportional to its value

ddtethJ JNTHORN thorn 1

t0ethJ JNTHORN frac14 0 (1225)

Mathematical modeling of membrane operations for water treatment 397

for t frac14 0 J frac14 J0

for t frac14 N J frac14 JN

After integration with the above boundary conditions

Jt frac14 ethJ0 JNTHORNe tt0 thorn JN (1226)

Figure 126 shows that the model curve (relaxation model) did not fit with the filtra-tion results (feed water from raw water reservoir) initially which might indicate thatthe system has not reached equilibrium yet The model adequately fits into themembrane water treatment process

In reality natural water for the potable water treatment process might containvarious contaminantsfoulants So to understand and describe the fouling mechanism(pore blocking) more precisely a mathematical model that can give a clue on whichpore blocking mechanisms should be developed and used Such a model has beendeveloped and it is known as Hermiarsquos model

Most of the fouling mechanisms for porous membranes like MF and UF are relatedto their pores As shown in Figure 127 porous membrane fouling mechanisms can bedivided into four categories (Field 2010)

J momentary experimental4

3

2

1

4

3

2

1

4

3

2

1

4

3

2

10 50 100 150 200 250 300 0 50 100 150 200 250 300

0 50 100 150 200 250 3000 50 100 150 200 250 300

Time (min) Time (min)

Time (min) Time (min)

J momentary theoreticalJ momentary experimentalJ momentary theoretical

J momentary experimentalJ momentary theoretical

J momentary experimentalJ momentary theoretical

J x

105 (m

3 m2 s)

J x

105 (m

3 m2 s)

J x

105 (m

3 m2 s)

J x

105 (m

3 m2 s)

(a)

(c) (d)

(b)

Figure 125 Comparison of experimental and theoretical volume flux for ceramic ultrafiltration(UF) membrane (a) Direct UF (b) Coagulation FeCl3-UF (c) Coagulation Al2(SO4)3-UF(d) Coagulation PAX-25-UFReprinted from Rajca et al (2009) with permission from Elsevier

398 Advances in Membrane Technologies for Water Treatment

The transport equations for each case have been derived from Hermiarsquos equationand the results can be seen in Table 125 (Field 2010 Field amp Wu 2011 FieldWu Howell amp Gupta 1995) Those equations could be used to diagnose thetype of fouling and predict the causes of it Originally these equations are

2

10 50 100 150 200 250

T (min) T (min)

T (min) T (min)

2

3

4

5

6

0 50 100 150 200 250 300 0 50 100 150 200 250 300

3

2

1

1

2

3

4

0 100 200 300 400 500 600

J experimental fluxJ theoretical flux

J experimental fluxJ theoretical flux

J experimental fluxJ theoretical flux

J experimental fluxJ theoretical flux

J v x

105 (

m3 m

2 s)

J v x

105 (

m3 m

2 s)

J v x

105 (

m3 m

2 s)

J v x

105 (

m3 m

2 s)

(a) (b)

(d)(c)

Figure 126 Comparison of experimental and theoretical volumetric flux (relaxation model)for MF membranes (a) Membrane 01 mm (01 MPa) (b) Membrane 02 mm (01 MPa)(c) Membrane 02 mm (02 MPa) (d) Membrane 045 mm (01 MPa)Source Reprinted from Konieczny (2002) with permission from Elsevier

Figure 127 Fouling mechanisms of porous membranes (a) Complete pore blocking(b) Internal pore blocking (c) Partial pore blocking (d) Cake filtrationSource Adapted from Field (2010) and Konieczny (2002)

Mathematical modeling of membrane operations for water treatment 399

Table 125 Fouling mechanisms phenomenological background and transport equations

Foulingmechanism n Phenomenological background Flux equation for dead-end Flux equation for crossflow

Complete poreblocking

2 Particles larger than the pore sizecompletely block pores

J frac14 J0 expethKbtTHORN J frac14 ethJ0 JTHORNexpethk2tTHORN thorn J

Internal poreblocking

15 Particles smaller than pore sizeenter the pores and get eitheradsorbed or deposited onto thepore walls this restricts theflow of permeate

J frac14 J0$

1thorn 1

2$Ks$ethA$J0THORN05$t2

J frac14 J0$

1thorn 1

2$Ks$ethA$J0THORN05$t2

Particle poreblocking

1 Particles reaching surface mayseal a pore or bridge a pore orpartially block it or adhere oninactive regions

J frac14 J0$eth1thorn Ki$ethA$J0THORN$tTHORN1 J frac14 J1

J0JJ0

exp

Jk1t

Cake filtration 0 Formation of a cake on themembrane surface by particlesthat neither enter the pores norseal the pores

J frac14 J0$eth1thorn 2$Kc$ethA$J0THORN2$tTHORN12 k0t frac14 1

J2

ln

JJ0$ethJ0JTHORNethJJTHORN

J

1J 1

J0

Note J - critical flux ki - constant in a crossflow fouling equation (i frac14 012)Source Field and Wu (2011) Field (2010) Field et al (1995)

400Advances

inMem

braneTechnologies

forWater

Treatm

ent

applicable to dead-end filtration but with some allowance for crossflow made itcan be applied to both modes of filtration

Besides than the fouling effect temperature will affect the flux performance ofmembranes as well For MF and UF systems the flow of permeate at any temperaturerelative to the flow at 20 C can be estimated by using (AWWA amp ASCE 2012)

QT frac14 Q20C

e00239ethT20THORN (1227)

This approximation is very useful and important because the effect from the fluctu-ation of raw water temperature can be minimized and the production of potable watercan be controlled

Another term used to define the performance of membranes is the removal percent-age of unwanted solute (foulants) from the raw water The solute rejection equationwill be the same as the one being used in NFRO membranes

R frac14 Cb Cp

Cb 100 frac14

1 Cp

Cf

100 (1228)

If the CP effect is to be taken into consideration then the concentration of solute atthe membrane surface should be used instead of the concentration of solute in bulksolution

123 Future work

Understanding the transport models and fouling mechanisms is very important andessential especially for reliable plant performance With better and accurate mathe-matical modeling membrane water treatment plants can be controlled monitoredand operated easily when the performance of the plants can be predicted preciselyThis will be very beneficial to automated plants in which the systems are controlledby sophisticated automation systems Without reliable mathematical modeling theautomated plants are vulnerable to membrane fouling because this problem couldnot be predicted properly in the initial stage and it will be too late to prevent thefouling problem when it is discovered Hence study about mathematical modelingfor the membrane water treatment process should be carried out more thoroughly Itis hoped that a predictive model that takes into account the effect of fouling andlong-term process operation could be developed because the main problem encoun-tered by the membrane process is membrane fouling

The challenge now is the ability to develop the mathematical models that canconvey the fundamental understanding and simple quantification of the governing phe-nomena in a way that has the potential for industrial application An accurate and pre-cise mathematical modeling not only will ease the design stage of the membrane watertreatment plant but also will smooth the operation of the plant because the fouling pro-pensity could be diagnosed earlier and preventive measures could be taken to curb it

Mathematical modeling of membrane operations for water treatment 401

Thus the models developed should be validated with real industrial data so that theapplicability and validation of the models could be tested With such a comparisonthe weakness of the mathematical modeling can be identified and improved

As shown in this chapter currently more and more new substances that might proveto be detrimental to our health and environment have been discovered Studies aboutthe removal of pesticides have been carried out and several models have been used topredict their retention by membranes However with the emerging deleterious compo-nents being discovered from time to time it is unsure whether the currently availablepredictive models could be used for membrane rejection performance Furthermore itseems like the mathematical model used by the membrane water treatment plant doesnot only depend solely on the membrane used but also the quality and foulant in theraw water will affect the suitability of the model used Until now there has not beenany mathematical modeling that could be applied to all the membranes and sourcewater Hence to have a better prediction on the membrane performance severalmodels might be required and the computational steps might be tedious Thus worksdeveloping a simpler and compact model should be focused to benefit all membraneapplications in the water treatment process

124 Conclusion

Process modeling plays a very important role in membrane operations for water treat-ment applications It allows users to obtain reliable prediction results that can be veryhelpful in membrane water treatment plants from the design stage toward the commis-sioning implementation and maintenance phases Mathematical modeling ensuresthat the fundamentals of the separation phenomena during the water treatment processof membranes can be understood With that specific preventative methods could beapplied to avoid the fouling problems In the earlier stage of designing a good predic-tive model will result in a smaller number of experiments and subsequently save timeand money With the appropriate design equation for the membrane the size of thewater treatment system as well as the area of membrane required to meet certainproduction rate could be determined Besides that mathematical modeling can beincorporated into the control system to predict the fouling potential of the membranesystem and thus suitable measures can be taken to reduce and mitigate the problem ofmembrane fouling Hence it can be concluded that with a good predictive modelingfor the membrane process the problem of water scarcity could be mitigated withthe wide acceptance of membranes in the water industry because the water treatmentplant can be controlled and operated stably

Nomenclature

ci Concentration of ion i within pore (kg molm3)C Solute concentration (kgm3 kg molm3)Cb Feed solute concentration (kgm3 kg molm3)Ci Ionic solute bulk solution concentration (kg molm3)

402 Advances in Membrane Technologies for Water Treatment

Cip Ionic solute bulk permeate concentration (kg molm3)Cm Membrane surface solute concentration (kgm3 kg molm3)Cp Permeate solute concentration (kgm3 kg molm3)CP Concentration polarizationD Pore diameter (m)Dij Diffusion coefficient of solute (m2s)Dip Pore diffusion coefficient of ion i (m2s)Dr Desalination ratio (CbCp)DE Dielectric exclusionDSPM Donnan-Steric-Pore-modelF Faraday constant (96487) (Cmol)jd Chilton-Coburn factorJ Volumetric flux (m3s m2)Ji Molar flux of solute (kg mols m2)J0 Initial flux (m3s m2)Js Solute flux (kgs m2)Jt Permeate flux at time t (m3s m2)Jv Solvent velocity (ms)Jw Pure water permeate flux (m3s m2)JN Equilibrium flux (m3s m2)k Mass transfer coefficient (ms)kib Mass transfer coefficient for concentration polarization (ms)kB Boltzmann constant (138066 1023) (JK)ki Membrane permeability coefficient for solute (ms)kw Mass transfer coefficient for water (ms atm)K Constant for CarmaneKozeny equationKic Hindrance factor for convection of ion ilbl Thickness of the mass transfer boundary layerL Length of pore (m)MF Microfiltrationn Number of kg mol of soluteNF Nanofiltrationpf Feed pressure (atm)pp Permeate pressure (atm)P Permeability coefficient (m3s m2 atm)Ps Solute permeability coefficient (ms)Pw Water permeability coefficient (m3s m2 atm)Q20 C Permeate flow at 20 C (m3s)Q25 C Permeate flow at 25 C (m3s)QT Permeate flow at temperature T (m3s)R Solute rejectionRe Reynolds numberRCP Solute rejection (after taking into CP effect)RG Gas law constant (82057 103) (m3 atmkg mol K)Rirr Resistance due to irreversible fouling (1m)Rm Membrane resistance (1m)Rrev Resistance due to reversible fouling (1m)Rt Resistance from foulants (total) (1m)RO Reverse osmosis

Mathematical modeling of membrane operations for water treatment 403

S Specific area (m2m3)Sc Schmidt numberSHP Steric hindrance poreT Temperature (K oC)TMS TeorelleMeyereSieversUF Ultrafiltrationv Flow velocity (ms)Vm Volume of pure solvent water in m3 associated with n kg mol of solute (m3)x Axial position within the pore (m)z Thickness of boundary layer (m)zi Valence of ion i

Greek letters

s Tortuosity of membrane3 Porosity of membranem Viscosity of liquid (kgs m)gi Activity coefficient of ion i within poregio Bulk activity coefficient of ion i

j Potential within the pore (V)DjD Donnan potential (V)DWi Born solvation energy barrier (J)Dp Transmembrane pressure (atm)Dp Transmembrane osmotic pressure (atm)p Osmotic pressure (atm)pm Osmotic pressure at membrane surface (atm)pp Osmotic pressure at permeate side (atm)

References

Ahmad A L Chong M F amp Bhatia S (2006) Ultrafiltration modeling of multiple solutes systemfor continuous cross-flow process Chemical Engineering Science 61(15) 5057e5069Retrieved from httplinkinghubelseviercomretrievepiiS0009250906001795

AWWA amp ASCE (2012) Water treatment plant design (5th ed) United States of AmericaMcGraw-Hill

Baker R W (2000) Membrane technology and applications United States of AmericaMcGraw-Hill

Bandini S amp Vezzani D (2003) Nanofiltration modeling The role of dielectric exclusion inmembrane characterization Chemical Engineering Science 58(15) 3303e3326 Retrievedfrom httplinkinghubelseviercomretrievepiiS0009250903002124

Bowen W R amp Mohammad A W (1998) Characterisation and prediction of nanofiltrationmembrane performancemdasha general assessment Transaction IChemE 76A 885e893

Bowen W R Mohammad A W amp Hilal N (1997) Characterisation of nanofiltrationmembranes for predictive purposesmdashuse of salts uncharged solutes and atomic forcemicroscopy Journal of Membrane Science 126 91e105

404 Advances in Membrane Technologies for Water Treatment

Bowen W R amp Welfoot J S (2002) Predictive modelling of nanofiltration Membranespecification and process optimisation Desalination 147(1e3) 197e203 Retrieved fromhttplinkinghubelseviercomretrievepiiS0011916402005349

Bowen W R amp Welfoot J S (2005) Modelling the performance of nanofiltrationmembranes In Nanofiltration principles and applications Great Britain Elsevier Ltd

Cornelissen E R Verdouw J Gijsbertsen-Abrahamse A J amp Hofman J A M H (2005) Ananofiltration retention model for trace contaminants in drinking water sources Desali-nation 178(2005) 179e192

Field R (2010) Fundamentals of fouling In Membranes for water treatment Great BritainWiley-VCH Verlag GmbH amp Co KGaA

Field R W Wu D Howell J A amp Gupta B B (1995) Critical flux concept for micro-filtration fouling Journal of Membrane Science 100(3) 259e272 Retrieved from httplinkinghubelseviercomretrievepii037673889400265Z

Field R W amp Wu J J (2011) Modelling of permeability loss in membrane filtrationRe-examination of fundamental fouling equations and their link to critical fluxDesalination 283 68e74 Retrieved from httplinkinghubelseviercomretrievepiiS0011916411003596

Gambier A Krasnik A amp Badreddin E (11e13 July 2007) Dynamic modeling of a simplereverse osmosis desalination plant for advanced control purposes In American controlconference New York Institute of Electrical and Electronics Engineers Inc

Geankoplis C J (2003) Transport processes and separation process principles (4th ed)United States of America Pearson Education Inc

Gibs J Stackelberg P E Furlong E T Meyer M Zaugg S D amp Lippincott R L (2007)Persistence of pharmaceuticals and other organic compounds in chlorinated drinking water asa function of time Science of the Total Environment 373(1) 240e249 Retrieved from httpwwwncbinlmnihgovpubmed17188338

Greenlee L F Lawler D F Freeman B D Marrot B amp Moulin P (2009) Reverseosmosis desalination Water sources technology and todayrsquos challenges Water Research43(9) 2317e2348 Retrieved from httpwwwncbinlmnihgovpubmed19371922

Harisha R S Hosamani K M Keri R S Nataraj S K amp Aminabhavi T M (2010)Arsenic removal from drinking water using thin film composite nanofiltration membraneDesalination 252(1e3) 75e80 Retrieved from httplinkinghubelseviercomretrievepiiS0011916409012600

Hassan A R Ali N Abdull N amp Ismail A F (2007) A theoretical approach on membranecharacterization The deduction of fine structural details of asymmetric nanofiltrationmembranes Desalination 206(1e3) 107e126 Retrieved from httplinkinghubelseviercomretrievepiiS0011916406014056

Hilal N Al-Zoubi H Darwish N A Mohammad A W amp Arabi M A (2004) Acomprehensive review of nanofiltration membranes Treatment pretreatment modellingand atomic force microscopy Desalination 170(3) 281e308 Retrieved from httplinkinghubelseviercomretrievepiiS0011916404800328

Hu Z-A Wu H-Y amp Gao J-Z (1999) Calculation of osmotic pressure differenceacross membranes in hyperfiltration Desalination 121(2) 131e137 Retrieved fromhttplinkinghubelseviercomretrievepiiS0011916499000144

Kaghazchi T Mehri M Ravanchi M T amp Kargari A (2010) A mathematical modeling oftwo industrial seawater desalination plants in the PersianGulf regionDesalination 252(1e3)135e142 Retrieved from httplinkinghubelseviercomretrievepiiS0011916409012211

Karode S K (2001) Unsteady state flux response A method to determine the nature of thesolute and gel layer in membrane filtration Journal of Membrane Science 188(1) 9e20Retrieved from httplinkinghubelseviercomretrievepiiS037673880000644X

Mathematical modeling of membrane operations for water treatment 405

Kedem O amp Katchalsky A (1958) Thermodynamics analysis of the permeability ofbiological membranes to non-electrolytes Biochimica et Biophysica Acta 27 229e246

Konieczny K (2002) Modelling of membrane filtration of natural water for potable purposesDesalination 143(2) 123e139 Retrieved from httplinkinghubelseviercomretrievepiiS0011916402002345

Levenstein R Hasson D amp Semiat R (1996) Utilisation of the Donnan effect for improvingelectrolyte separation with nanofiltration membranes Journal of Membrane Science 11677e92

Luo J amp Wan Y (2011) Effect of highly concentrated salt on retention of organic solutes bynanofiltration polymeric membranes Journal of Membrane Science 372(1e2) 145e153Retrieved from httplinkinghubelseviercomretrievepiiS0376738811000871

Malaeb L amp Ayoub G M (2011) Reverse osmosis technology for water treatment State ofthe art review Desalination 267(1) 1e8 Retrieved from httplinkinghubelseviercomretrievepiiS0011916410006351

Mohammad A W (16e19 November 2008) Nanofiltration membranes in desalinationmdashfromfundamental to applications In The 3rd international conference on water resources andarid environments and the 1st Arab water forum Riyadh Saudi Arabia Prince SultanInstitute for Environmental Water amp Desert Research King Saud University

Mohammad A W Hilal N Al-Zoubib H Darwish N A amp Ali N (2007) Modelling theeffects of nanofiltration membrane properties on system cost assessment for desalinationapplications Desalination 206(1e3) 215e225 Retrieved from httplinkinghubelseviercomretrievepiiS0011916406014184

Mulder M (1996) Basic principles of membrane technology (2nd ed) Boston Kluwer Aca-demic Publishers

Nakao S (1994) Determination of pore size and pore size distribution 3 Filtration membranesJournal of Membrane Science 96 131e165

Nguyen C M Bang S Cho J amp Kim K W (2009) Performance and mechanism of arsenicremoval from water by a nanofiltration membrane Desalination 245(1e3) 82e94Retrieved from httplinkinghubelseviercomretrievepiiS0011916409003282

Pappenheimer J (1953) Passage of molecules through capillary walls Physiological Reviews33 387e423

Peppas N amp Meadows D (1983) Macromolecular structure and solute diffusion in mem-branes An overview of recent theories Journal of Membrane Science 16 361e377

Plakas K V amp Karabelas A J (2012) Removal of pesticides from water by NF and ROmembranesmdasha review Desalination 287 255e265 Retrieved from httplinkinghubelseviercomretrievepiiS0011916411006874

Radjenovic J Petrovic M Ventura F amp Barcelo D (2008) Rejection of pharmaceuticals innanofiltration and reverse osmosis membrane drinking water treatment Water Research42(14) 3601e3610 httpwwwncbinlmnihgovpubmed18656225

Rajca M Bodzek M amp Konieczny K (2009) Application of mathematical models to thecalculation of ultrafiltration flux in water treatment Desalination 239(1e3) 100e110Retrieved from httplinkinghubelseviercomretrievepiiS0011916409000253

Renkin E (1954) Filtration diffusion and molecular sieving through porous cellulosemembranes The Journal of General Physiology 38 225e243

Roberson B amp Zydney A (1988) A Stefan-Maxwell analysis of protein transport in porousMembranes Separation Science and Technology 23 1799e1811

Saitua H Giannini F amp Padilla A P (2012) Drinking water obtaining by nanofiltration fromwaters contaminated with glyphosate formulations Process evaluation by means of toxicitytests and studies on operating parameters Journal of Hazardous Materials 227e228204e210 Retrieved from httpwwwncbinlmnihgovpubmed22664256

406 Advances in Membrane Technologies for Water Treatment

Sarkar B Venkateshwarlu N Rao R N Bhattacharjee C amp Kale V (2007) Potable waterproduction from pesticide contaminated surface watermdasha membrane based approachDesalination 204(1e3) 368e373 Retrieved from httplinkinghubelseviercomretrievepiiS0011916406013415

Schirg P ampWidmer F (1992) Characterisation of nanofiltration membranes for the separationof aqueous dye-salt solutions Desalination 89 89

Seader J D amp Henley E J (1998) Separation process principles United States of AmericaJohn Wiley amp Sons Inc

Senthilmurugan S Ahluwalia A ampGupta SK (2005)Modeling of a spiral-woundmodule andestimation of model parameters using numerical techniquesDesalination 173(3) 269e286Retrieved from httplinkinghubelseviercomretrievepiiS0011916404007234

Shengji X Juanjuan Y amp Naiyun G (2008) An empirical model for membrane fluxprediction in ultrafiltration of surface water Desalination 221(1e3) 370e375 Retrievedfrom httplinkinghubelseviercomretrievepiiS0011916407007163

Shon H K Vigneswaran S Kandasamy J amp Shim W G (2008) Ultraflitration of waste-water with pretreatment Evaluation of flux decline models Desalination 231(1e3)332e339 Retrieved from httplinkinghubelseviercomretrievepiiS0011916408003779

Tsuru T Nakao S amp Kimura S (1991) Calculation of ion rejection by extended Nernst-Planck equation with charged reverse osmosis membranes for single and mixedelectrolyte solutions Journal of Chemical Engineering of Japan 24 511e517

Tu K L Nghiem L D amp Chivas A R (2010) Boron removal by reverse osmosis mem-branes in seawater desalination applications Separation and Purification Technology 75(2)87e101 Retrieved from httplinkinghubelseviercomretrievepiiS1383586610003114

Van der Bruggen B Meuroantteuroari M amp NystreuroomM (2008) Drawbacks of applying nanofiltrationand how to avoid them a review Separation and Purification Technology 63(2) 251e263Retrieved from httplinkinghubelseviercomretrievepiiS1383586608002104

Verniory A DuBois R Decoodt P Gassee J amp Lambert P (1973) Measurement of thepermeability of biological membranes application to the glomerular wall The Journal ofGeneral Physiology 62 489e507

Wiesner M R amp Buckley C A (1996) Principles of rejection in pressure-driven membraneprocesses In Water treatment membrane processes United States of AmericaMcGraw-Hill

Williams M E (2003) A review of reverse osmosis theory Retrieved from httpwwweetcorpcomheepmRO_TheoryEpdf

Xu X amp Spencer H G (1997) Dye-salt separations by nanofiltration using weak acidpolyelectrolyte membranes Desalination 114 129e137

Yaroshchuk A E (2000) Dielectric exclusion of ions from membranes Advances in Colloidand Interface Science 85(2e3) 193e230 Retrieved from httpwwwncbinlmnihgovpubmed10768481

Yaroshchuk A amp Staude E (1992) Charged membranes for low-pressure reverse osmosisproperties and applications Desalination 86 115e134

Zhao C Zhou X amp Yue Y (2000) Determination of pore size and pore size distribution onthe surface of hollow-fiber filtration membranes A review of methods Desalination129(2) 107e123 Retrieved from httplinkinghubelseviercomretrievepiiS0011916400000540

Mathematical modeling of membrane operations for water treatment 407

Membrane technologiesfor seawater desalinationand brackish water treatment

13E Curcio12 G Di Profio2 E Fontananova2 E Drioli121University of Calabria (DIATIC-UNICAL) Cosenza Italy 2Institute on MembraneTechnologyeNational Research Council of Italy (ITM-CNR) Cosenza Italy

131 Introduction

In past decades the number of countries experiencing water scarcity has increasedsignificantly owing to steady demographic expansion and the amplified demand forwater in industrial activities in agriculture and for municipal (including domestic)purposes In particular agriculture accounts for about 70 of global freshwaterwithdrawal (FAO Water Report 2012) Average consumption per capita of water perday spans from 150 L in Western countries to about 20 L on the African continentthe latter value dramatically approaches the lower limit fixed by the World HealthOrganization which is sufficient to guarantee basic needs such as drinking personal hy-giene and food preparation The demand for water is expected to increase by 50 in thenext 40 years driving about 39 billion people under water stress (Mountford 2011)

Paradoxically water is one of the most abundant resources on earth (the estimatedamount in the ocean is 14 109 km3 (Bengtsson 2010)) Seawater (SW) representsabout 967 of total available water the remaining part is underground and surfacewaters mostly frozen in glaciers Only 07 of the total amount (12 107 km3) isavailable in lakes rivers and aquifers (Figure 131)

Water is classified primarily according to its salinity content Freshwater hassalinity up to 1500 ppm brackish water (BW) has a saline content in the range of1500e10000 ppm and SW salinity is between 10000 and 45000 ppm Forreference the average salinity of SW is conventionally normalized at 35000 ppm(lsquostandard SWrsquo is arbitrarily defined on the basis of certain samples taken from NorthAtlantic surface water as first proposed by Martin Knudsen at the InternationalConference for the Exploration of the Sea held in Stockholm in 1899 (Knudsen1903)) The main ionic constituents of SW are sodium (30) and chloride (55)Table 131 lists the composition of standard SW

To date SW and BW desalination represents the most reliable and economicallysustainable way to produce drinking water for human consumption The total globaldesalination capacity is currently around 664 million m3day and is expected to reachabout 100 million m3day by 2015 the annual market growth is about 55 SWrepresents the main source for the desalination industry (about 589) whereas BWaccounts for 212 (Global Water Intelligence)

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400013-7Copyright copy 2015 Elsevier Ltd All rights reserved

Thermal desalination processes dominate in the Gulf region (more than 90 of totalproduction) where water is generated together with electricity in large cogenerationplants There steam drives turbines and acts as a source for SW evaporation Multi-stage flash (MSF) distillation is the prevalent desalination technology in the MiddleEast with more than 80 of installed capacity followed by multiple effect distillation(MED) (IDA Media Analytics Ltd 2007)

MSF consumes a larger amount of total energy than other desalination processes(around 17e18 kWhm3) with a gain output ratio (GOR) of 8e10 kg of distillate per ki-logram of steam however its highly reliable performance (early plants began operationin 1978 with an expected life of over 30 years) makes MSF competitive in the MiddleEasteNorth Africa region MSF plants are generally built to be large The Jebel Ali MSFplant in Dubai contracted by Fisia and officially opened in 2013 has a productivity of626400 m3day and 2060 MWday of generated power (Borsani amp Ghiazza 2012)

MED plants are generally designed for operative temperature below 70 C to limitscale formation on the outside surface of evaporator tubes total energy consumption is6e7 kWhm3 for a GOR of 8e16 kg of distillate per kilogram of steam In recentyears the productivity of MED integrated with thermal vapour compression (TVC)units has increased exponentially For example the MEDeTVCMarafiq Jubail (SaudiArabia) desalination plant (27 units) completed in 2010 by Veoliarsquos subsidiarySidem produces a total of 800000 m3day of desalted water with a GOR of 984kg of distillate per kilogram of steam Huge MED plants are in operation at FujairahUnited Arab Emirates (463000 m3day) Ras Laffan Qatar (286000 m3day) and AlHidd Bahrain (272000 m3day) (sidem-desalinationcom 2014)

Developed in the 1980s mechanical vapour compression units have a small capac-ity with respect to MSF and MED (usually lower than 5000 m3day) and an averageenergy consumption of around 8 kWhm3 of electrical power (Lokiec amp Ophir 2007)

Desalination processes are classified according to the type of separation Conven-tionally two groups are identified membrane systems and thermal technologies

Atmosphere 0001

00132

00158

169

174 9654

200 40Amount ()

Water source

60 80 100

Lakes amp rivers

Groundwater

Oceans seas amp bays

Ground ice amp permafrost

Ice caps glaciers amp permanent snow

Figure 131 Rough estimate of global water distributionData elaborated from Shiklomanov (1993)

412 Advances in Membrane Technologies for Water Treatment

(Figure 132) The first group includes reverse osmosis (RO) which currentlydominates desalination technology the second is electrodialysis Both membraneoperations require electrical energy

Currently the largest SWRO plant with a productivity of 624000 m3day isinstalled in Sorek Israel and is operated by IDE Technologies The SWRO plant inAshkelon Israel operated by Veolia Water since 2005 reaches a daily productivityof 320000 m3day Feed water passes through 32 modules that decrease salt

Table 131 Standard seawater composition

Ion Concentration (ppm) Total salt content ()

Chloride Cl 19345 5503

Sodium Nathorn 10752 3059

Sulphate SO24 2701 768

Magnesium Mg2thorn 1295 368

Calcium Ca2thorn 416 118

Potassium Kthorn 390 111

Bicarbonate HCO3 145 041

Bromide Br 66 019

Borate BO33 27 008

Strontium Sr2thorn 13 004

Fluoride F 1 0003

Source Millero Feistel Wright and McDougall (2008)

Desalination technology

Membrane processes

Reverse osmosis (RO)

Electrodialysis (ED)

Thermal processes

Multiple effect distillation (MED)

Multistage flash (MSF)

Thermal vapour compression (TVC)

Mechanical vapour compression (MVC)

Figure 132 Classification of major technologies currently in use for seawater and brackishwater desalination

Membrane technologies for seawater desalination and brackish water treatment 413

concentration down to 30 mgL with a cost of 050 Eurom3 The SWRO plantinstalled in Perth Australia designed and built in only 18 months by MultiplexDegreacutemont Joint Venture in 2006 produces 144000 m3day of desalinated water(Clemente amp Mercer 2011)

Electrodialysis and electrodialysis reversal (EDR) are electrochemical separationprocesses in which ions are transferred through ion exchange membranes under directcurrent both are typically operated for BW desalination purposes One of the majorfacilities installed in Europe is the 57000-m3day EDR plant operated in Sant Boide Llobregat Spain (Segarra Iglesias Peacuterez amp Salas 2009)

132 Principle of RO

RO allows dissolved ions to be separated from feed water using semipermeablemembranes operated under the driving force of a difference in chemical potential(function of pressure concentration and temperature) From a phenomenologicalpoint of view RO separation is based on countering the natural osmotic processby applying hydrostatic pressure to the side contacted by SW thus driving thesolvent flux in the opposite direction with respect to that established by naturalosmosis

The value of osmotic pressure P (defined as the equilibrium pressure at which thenet flux of solvent stops) depends on the salt concentration ci according to thefollowing equation (Fell 1995)

P frac14 RTXi

nici (131)

The osmotic pressure of SW is typically around 23 MPa As long as the appliedhydrostatic pressure DP is higher than the osmotic pressure difference DPbetween the feed and permeate solutions the solvent (water) will flow from themore concentrated solution (feed) to the dilute solution (permeate) and the trans-membrane flux will reverse from the direction of natural osmosis as illustrated inFigure 133

The solution-diffusion model is frequently adopted with the aim of describing thetransport phenomenon in RO (Merten 1966) It is assumed that the volumetric flux ofwater (Jv) and the flux of solutes (Js) both of which occur by diffusing through themembrane are related to their mobility driving force (effective pressure differenceof DP DP) and salt concentration gradient

Jv frac14 kwDwVw

RT

DP DP

d

(132)

Js frac14 ksDs

d

c fs cps

(133)

414 Advances in Membrane Technologies for Water Treatment

133 RO membranes and modules

The RO membrane market is essentially based on thin-film composite (TFC) poly-amide membranes generally consisting of a polyester web used as a support(120e150 mm thick) a microporous interlayer usually made of polysulphonic polymer(40e50 mm) and a top ultrathin barrier layer with selectivity properties and low resis-tance to mass transfer of permeate (w02 mm) The selective layer which is generallyable to provide salt rejection higher than 995 to NaCl is commonly made of13-phenylenediamine (also known as 13-benzenediamine) and tri-acid chloride ofbenzene (Figure 134) (Lee Arnot amp Mattia 2011) Historically RO technologystarted with cellulose acetate (CA) membranes Although they are characterized byhigher resistance to chlorine (extensively used as a disinfectant to prevent bacterialgrowth on membranes) asymmetric CA or triacetate hollow-fibre modules are muchless frequently installed in RO plants because of their lower rejection ability Amongthe unresolved challenges the boron rejection of any commercially available mem-brane is still insufficient (w93) to meet WHO water drinking standards by one-pass RO process (Kumano amp Fujiwara 2008)

With few exceptions RO membranes are prepared in the flat-sheet form and areassembled in spiral-wound module (SWM) configuration with a high specific mem-brane surface area (the packing density is about 500e800 m2m3) and low replacementcost (Pearce 2007) In SWM two rectangular flat-sheet membranes are placed back toback and sealed on three sides to form an envelope One or multiple envelopes arewound around a collector tube connected to the fourth side which remains open

P

Nat

ural

osm

osis

Rev

erse

osm

osis

Applied pressure

ΔP gt Δ Fl

ux o

f sol

vent

0

Π

ΔP lt Δ Π

ΔP = Δ Π

Figure 133 Trans-membrane flux of solvent through an ideally semipermeable membrane as afunction of applied hydrostatic pressure

Membrane technologies for seawater desalination and brackish water treatment 415

Feed water enters tangentially in the module and the permeate goes through the mem-brane and flows perpendicularly in the collector tube while the retentate leaves themodule at the opposite end

Advances in membrane desalination (innovation in membrane materials optimiza-tion of module fluid dynamics and improvement in process design pretreatment andenergy recovery systems) resulted in progressive enhancement of membrane rejectionand a decrease in overall energy consumption as illustrated in Figure 135

Currently some major suppliers of RO membrane modules are Dow (Filmtech)Toray Hydranautics (Nitto Group) and Koch Membrane Systems Standard modulesfor current SWRO desalination plants are 8 inches in diameter However recent devel-opments in module design and hydrodynamics optimization are moving towards largermodules (Yun Gabelich Cox Mofidi amp Lesan 2006) Tables 132 and 133 summa-rize the main characteristics of eight modules commercialized by these companies

SWMs are contained in pressure vessels consisting of a cylindrical housing eachhosting typically six to eight modules From a technical point of view each groupof parallel connected vessels forms a lsquostagersquo Connection in parallel leads to an in-crease in productivity A configuration ratio of 21 representing the ratio betweenthe number of pressure vessels from one stage to the next is generally adopted inRO plants SWRO plants are typically composed of two stages to increase the total wa-ter recovery factor to 50e60 at an operating pressure of 50e70 bar The number oflsquopassesrsquo identifies the number of times that permeate is treated in the system Addi-tional passes are necessary whenever high permeate quality is requested A single-pass RO plant typically guarantees a total dissolved solids (TDS) content around

H2N NH2 H2N NH2

COClOClC

COCl

COClOClC

COCl

HN NHOC

CO

CO HN NHOC CO

COOH

nm

Trimesoyl chloride in hexane

m-Phenylenediaminein water

PolymerizationInterfacial

Figure 134 Sample scheme of interfacial polymerization for the preparation of the top layer ofa thin-film composite fully aromatic polyamide membrane

416 Advances in Membrane Technologies for Water Treatment

500 mgL whereas a two-pass configuration decreases TDS below 300 mgL Stagesinterconnected in series form a lsquotrainrsquo SWRO plants are generally composed ofseveral trains Typical examples of RO flow sheets are given in Figure 136(a) and (b)

134 Fouling and pretreatment strategies

Composition and characteristics of BW and SW used as a feed in desalination plantsdirectly affect the efficiency of membrane processes (El-Manharawy amp Hafez 2001)The presence of sparingly soluble salts colloids and suspended matters organic com-pounds or microorganisms if not appropriately controlled might result in a severeimpact of fouling phenomena on the performance of RO plants leading to irreversibledamage to membranes and a significant decrease in their lifetime (see Figure 137 foran overview)

Membrane damage primarily results from oxidation and hydrolysis of the polymericmaterial In general membranes cannot tolerate residual chlorine concentrations whichare used extensively in desalination processes to prevent biological growth Adjust-ment of the pH to recommended operational values is therefore required to fit optimaloperation protocols and mitigate scaling (acidification is usually made by adding sul-phuric acid) Moreover oxidizing agents and dissolved oxygen must be removed byadding appropriate reducing compounds such as sodium thiosulphate or sodium bisul-phite More details on pretreatment procedures are provided in paragraph 1541

Scaling refers to the precipitation of sparingly soluble salts onto the membrane sur-face often exacerbated by concentration polarization In fact owing to the progressive

Figure 135 Improvement in salt rejection () and energy consumption (kWhm3) of SWROtechnologyData from Lee Arnot and Mattia (2011)

Membrane technologies for seawater desalination and brackish water treatment 417

Table 132 Product specifications of selected brackish water desalination modules

Element modelDowtrade FilmtectradeBW30-365a

Toray StandardBWRO TM720-370b

NittoHydranauticsESPA1c

Koch MembraneSystemsFluidSystemsreg TFCreg-FR400-34d

Active area (m2) 34 34 371 372

Permeate flow rate (m3day) 36 36 454 416

Stabilized salt rejection () 995 997 993 9955

Diameter (inch) 8 8 8 8

Membrane type Polyamide thin-filmcomposite

Cross-linked fullyaromatic polyamidecomposite

Composite polyamide TFC polyamide

NoteaTest conditions 2000 ppm NaCl 153 bar 25 C 15 recovery pH 8bTest conditions 2000 ppm NaCl 155 MPa 25 C 15 recovery pH 7cTest conditions 1500 ppm NaCl 105 MPa 25 C 15 recovery pH 65e7dTest conditions 2000 ppm NaCl 155 MPa 25 C 15 recovery pH 75

418Advances

inMem

braneTechnologies

forWater

Treatm

ent

Table 133 Product specifications of selected seawater desalination modules

Element model Filmtectrade SW30HR-380aToray StandardSWRO TM820C-400b

NittoHydranauticsSWC4-LDc

Koch MembraneSystemsFluidSystemsreg

TFCreg-SW 400-34d

Active area (m2) 35 37 371 372

Permeate flow rate (m3day) 23 246 246 272

Stabilized salt rejection () 997 9975 998 9975

Diameter (inch) 8 8 8 8

Applied pressure (bar) 55 55 55 55

Membrane type Polyamide thin-filmcomposite

Cross-linked fully aromaticpolyamide composite

Composite polyamide TFC polyamide

NoteaTest conditions 32000 ppm NaCl 55 bar 25 C 8 recovery pH 8bTest conditions 32000 ppm NaCl 552 MPa 25 C 15 recovery pH 7cTest conditions 32000 ppm NaCl 55 MPa 25 C 10 recovery pH 65e7dTest conditions 32800 ppm NaCl 552 MPa 25 C 7 recovery pH 75

Mem

branetechnologies

forseaw

aterdesalination

andbrackish

water

treatment

419

removal of solvent through the membrane the solubility limit of some componentsdissolved in the feed (typically calcium carbonate magnesium carbonate calcium sul-phate silica barium sulphate strontium sulphate and calcium fluoride) may beexceeded (van de Lisdonk Rietman Heijman Sterk amp Schippers 2001)

The scaling propensity of a given feed water is usually evaluated by the Langeliersaturation index for BW (Patzay Stahl Karman amp Kalman 1998) and by the Stiffand Davis stability index for SW (Al-Shammiri amp Al-Dawas 1997) Scaling doesnot occur for negative values of these indexes

Typical countermeasures to limit scaling problems are to

bull reduce the water recovery factor to operate below solubility limitsbull decrease pH by adding acids to regulate the calcium carbonate speciation (moving solubility

equilibrium towards the formation of carbonates and bicarbonates into carbon dioxide)bull add inhibitors or antiscalants that delay the induction time of precipitationbull eliminate calcium and magnesium to limit the risk of calciummagnesium carbonate precip-

itation (softening)bull use ion exchange resins to eliminate undesirable ions

Particulate fouling is caused by particles and suspended colloidal matter present insolution Clogging can be mitigated by limiting the amount of particles by conven-tional coagulationeflocculation (a critical issue is the appropriate dosage of

FeedDischarged

brine

Permeate

1st Stage 2nd Stage

Retentate(a)

Figure 136 Reverse osmosis train configuration (a) single-passtwo stages Example TampaBay SWRO plant United States (b) two-passtwo stages per pass Example Point Lisas SWROplant Trinidad

420 Advances in Membrane Technologies for Water Treatment

coagulanteflocculants that might damage membranes) or by pressure-drivenmembrane operations (microfiltration (MF) or ultrafiltration (UF)) (Ning amp Troyer2007) To quantify the potential of particulate fouling a gravimetric procedure isnormally used to express the concentration of particles in terms of total suspendedsolids In addition turbidity measurements expressed in nephelometric turbidity units(NTU) provide quick and easy measurements for low solid concentrations

Colloidal fouling is caused by the accumulation of colloids on the membrane sur-face leading to the formation of a cake layer As a result the permeate flux decreases

FeedReject to

waste

Permeate1st pass(fed to

2nd pass)

1st Stage 2nd Stage

Retentate

Permeate2nd pass

Recycle

1st Stage 2nd Stage

1st Pass

2nd Pass

(b)

Figure 136 Continued

Membrane technologies for seawater desalination and brackish water treatment 421

because of the additional cake layer resistance moreover the hindered back-diffusionof salt ions within the deposit layer increases the ion concentration at the membranesurface thus enhancing the osmotic pressure and decreasing the net driving force

Biological fouling originates from the growth of colonies of bacteria or algae on thesurface of the membrane (Nguyen Roddick amp Fan 2012) Washing with biocidesmay be necessary to prevent the development of biomass for membranes resistantto chlorine shock chlorination is the preferred option

Natural organic matter (NOM) is considered a major foulant among all species pre-sent in natural water (Pressman et al 2012) NOM is a complex mixture of both inor-ganic and organic components characterized by a wide range of molecular weight andfunctional groups (phenolic hydroxyl carbonyl groups and carboxylic acid) origi-nated by allochthonous (terrestrial and vegetative debris) and autochthonous input(algae) Particularly aggressive fouling is caused by dissolved organic mattercomposed of humic substances polysaccharides amino acids proteins fatty acidsphenols carboxylic acids quinines lignins carbohydrates alcohols etc (ZularisamIsmail amp Salim 2006) Fouling mechanisms of NOM typically include preliminaryadsorption on the surface followed by the formation of a continuous gel The structureof the gel layer depends on both chemical conditions (pH ionic strength and the pres-ence of multivalent cations) and physical conditions (permeate flux and cross-flowvelocity) The presence of inorganic ions in solution exacerbates the fouling problem(for example through NOMecalcium complexation) resulting in the formation of adense and highly resistant fouling layer (Lee Cho amp Elimelech 2005)

Cleaning procedures partially restore the efficiency of a membrane process As arule membrane elements should be cleaned whenever a critical performance parameter(usually permeate flux salt rejection or trans-membrane pressure) changes by at least10e15 Cleaning methods are usually classified into four groups mechanicalhydrodynamic airewater cleaning and chemical

Fouling

Scaling

Precipitation ofsparingly soluble

compounds(calcium

magnesiumcarbonate

calciumbariumStrontium

sulphate calciumfluoride

magnesiumhydroxide silica etc)

Particulate fouling

Deposition of suspended

solidscolloidal mater

algae nongrowing

microorganismsMonitored by

silt densityindex (SDI) test

modifiedfouling index(MFI-UF) etc

Inorganicfouling

Deposition ofinorganic particles(aluminum silicate

clays andcolloids of

ironndashiron oxidealuminum oxide

silica)

Organicfouling

Biologicalfouling

Formation ofbiofilm due to

bacteria algaefungi viruses

protozoabacterial cell wall

fragments

Due to naturalorganic matter

(NOM)proteins

carbohydratesfats oil

tannins aromaticacids such as humic

acid

Figure 137 Qualitative classification of fouling phenomena

422 Advances in Membrane Technologies for Water Treatment

Mechanical cleaning is accomplished by promoting high shear forces at the mem-brane surface by mechanical action (for example using sponge balls for cleaningtubular membranes or using ultrasound waves causing the cavitation of fluids andthe consequent increase in turbulence and promotion of shear forces at the mem-brane surface) mechanical cleaning is not frequently applied on an industrial scale(Al-Amoudi amp Lovitt 2007)

Hydrodynamic cleaning methods consist in a temporary increase of cross-flow ve-locity in a pulsed feed flow or in a temporary reversal of the flow through the mem-brane elements In particular periodic back-washing of membranes is an effective andcommonly used method to remove accumulated cake although it is energeticallyexpensive (Sagiv amp Semiat 2010) Air bubbling (periodic injection of compressedair) also increases turbulence and results in high shear forces at the membrane surface(Cornelissen et al 2007)

Chemical cleaning methods aim to dissolve complexate oxidize inactivatesolubilize hydrolyze and denature membrane fouling (Madaenl Mohamamdi ampMoghadam 2001 Zondervan amp Roffel 2007) Common cleaning agents are

1 acid cleaning agents used to dissolve inorganic precipitates caused by scaling (CaCO3FeSO4 FeO FeOH Al2(SO4)3 BaSO4 SrSO4 CaSO4 etc) or the inorganic matrixin a biofilm Most frequently used chemicals are citric acid sulphuric acid and phosphoricacid

2 alkaline cleaning agents used to dissolve organic deposits Typically used chemicals areNaOH andor Na2CO3

3 complexing or anti-precipitating agents used to remove metals (mostly bivalent ions) andother precipitating ions from the solution For example ethylenediaminetetraacetic acidremoves Ca2thorn and Mg2thorn ions

4 biocides used to inactivate microorganisms (for example chlorine chloramines organic per-oxides glutaraldehyde sodium bisulphite)

5 detergents or surfactants that reduce the surface tension of the water resulting in betterhydration and solubility of the fouling layer

6 enzymatic cleaning agents aiming at hydrolyzing the extra polymeric substances formed bymicroorganisms

7 chaotrophic cleaning agents that induce denaturation of proteins resulting in the bettersolvability of organic compounds

1341 Conventional pretreatment

Conventional pretreatment operations for an SWRO plant usually include (1) screensfor preliminary coarse prefiltration (2) chlorination and acidification steps (3) addi-tion of flocculation agents and coagulationflocculation units (4) single or doublemedia filtration (5) dechlorination and addition of antiscalants and (6) cartridgefiltration before RO trains Main disadvantages of conventional pretreatment systemsinclude high sensitivity to fluctuations of feed characteristics difficulties in supplyingfeed a constant silt density index (SDI) less than 30 and large footprint owing to slowfiltration velocities A schematic representation of a conventional pretreatment systemis illustrated in Figure 138

Membrane technologies for seawater desalination and brackish water treatment 423

Screens are used to protect water pumps from particle clogging and remove coarsefloating solids from the feed (used for both BW and SW) To limit the environmentalimpact screens are designed to reduce the risk of impingement on marine organismsTraditional travelling water screens are equipped with revolving wire mesh panels with6- to 95-mm openings

Chlorination is a standard disinfection method aiming at destroying or inactivatingpathogenic microorganisms (bacteria amoebic cysts algae spores and viruses)In general sodium hypochlorite is dispersed in SW where the following reactionoccurs

NaOClthorn H2OHOClthorn NaOH

In principle chlorine gas can be injected directly into the feed stream it readily dis-solves in water to a maximum concentration of 3500 mgL and reacts as

Cl2 thorn H2OHOClthorn HCl

However direct injection is not a common practice in large desalination plantsIn solution hypochlorous acid dissociates to hydrogen and hypochlorite ionsThe sum of Cl2 NaOCl HOCl and OCl is indicated as free residual chlorinethis value should be maintained within 05e10 mgL along the pretreatmentline to prevent biofouling Contact or detention times of 10e120 min may berequired which depend on the level of residual chlorine (Shams El Din Arain ampHammoud 2000)

Coagulationflocculation is applied to remove fine suspended solids (size range of1 nm to 10 mm) soluble organic and toxic substances and trace metals Coagulantssuch as aluminum sulphate (or alum) ferric sulphate or ferric chloride quicklimeand synthetic cationicanionicnonionic polymers are efficiently dispersed in floccula-tion chambers by diffuser grids chemical jets or in-line blender systems Flocculationis achieved through slow mixing using paddles or propellers Usually several floccu-lation chambers are built in series with successively decreasing mixing velocitiesAlum is the most commonly used primary coagulant theoretically 1 mgL of alumwill consume approximately 050 mgL of alkalinity (as CaCO3) and produce

Intake pump

SeawaterScreen

ChlorinationFlocculants

pH adj

Flocculation chambers

Clarifier

Dual media filtration

Antiscalingdechlorination

Cartridgefiltration

To RO trains

Figure 138 Typical conventional SWRO pretreatment system

424 Advances in Membrane Technologies for Water Treatment

044 mgL of carbon dioxide If the natural alkalinity of the water is not sufficient toreact with the alum and buffer the pH alkalinity is increased by adding lime orsoda ash (coagulant aids)

After the coagulationflocculation stage simple and inexpensive slow sand filtra-tion (SSF) can be successfully applied to treat feed with a turbidity of less than 50NTU SSF consists of the filtration of BW or SW through a bed of fine sand at lowvelocity which causes the retention of organic and inorganic suspended matter inthe upper 05e2 cm of the filter bed Slow sand filters are also appropriate forremoving pathogenic organisms that are eventually present in surface waters Scrapingoff the top layer cleans the filter and restores its original efficiency Although sludgehandling is negligible and close control by an operator is not strictly necessaryslow sand filters require a large footprint huge quantities of filter medium and exten-sive labour for manual cleaning

Dual media filtration (DMF) more efficiently removes suspended solids and path-ogens and reduces the turbidity of the RO feed water to about 04 NTU with an SDItypically around 25 or slightly less DMF consists of coarse anthracite coal over a bedof fine sand (Zouboulis Traskas amp Samaras 2007) Cleaning is usually required whenwater head loss through the filter exceeds 15e25 m

Before entering the cartridge filters the pH value of feed water has to be reduced atmoderate values to prevent calcium carbonate scaling and damage to RO membranesSulphuric acid is typically injected to adjust the pH to around 75 The addition of anti-scaling agents is also requested for SWRO systems operated with a recovery greaterthan 35 (Hasson Drak amp Semiat 2003) In past decades sodium hexametaphos-phate (SHMP) was extensively used as an antiscalant today it has been replacedby polymeric compounds such as polyphosphates and polyacrylates because of theeutrophicating properties of SHMP and associated disposal problems Dechlorinationhas to be performed before the RO stage to avoid oxidation damage by residual chlo-rine in the feed water (Saeed 2002) Commonly sodium metabisulphite (SMBS) isused for dechlorination owing to its high cost effectiveness 30 mg of SMBS isused to remove 10 mg of free chlorine

Cartridge filters with a pore size of 5e10 mm represent the last pretreatment stagebefore RO trains they are used to capture contaminants and particles throughout thewhole thickness of the filtering medium

1342 Membrane pretreatment

Interest in pretreatment operations based on membrane technology has recentlyincreased MF is a low energy-consuming membrane unit commonly used to removesuspended solids reduce the chemical oxygen demand below 25 mgL and achieve anSDI less than 5 UF is a versatile separation process able to retain suspended solidsbacteria macromolecules and colloids turbidity is also significantly decreased (lessthan 04 NTU) and SDI is below 2 in the permeate stream The main benefits of inte-grated MFUF pretreatment technologies are (Buscha Chub Kolbe Meng amp Li2009 Vial amp Doussau 2002) (1) the potential for higher RO flux and water recoveryfactor (2) a low footprint with respect to the conventional coagulationflocculation

Membrane technologies for seawater desalination and brackish water treatment 425

DMF method (3) improved membrane lifetime and (4) a significant reduction inchemical dosing

Although the capital cost of membrane pretreatment still exceeds that of conven-tional processes by about 10 (for instance membranes are about twice as expensiveas dual media filters) this is compensated for by the reduction of operation and main-tenance (OampM) costs in subsequent RO trains Whereas a typical annual replacementrate for RO membranes operated with a conventional pretreatment system is 15e20it is reduced to 10e15 when MFUF pretreatment technology is used The frequencyof RO cleaning is also shortened As the desalination industry gains long-term expe-rience with membrane pretreatment systems MF and UF are expected to become thestandard for the next generation of BWRO and SWRO plants (operational scheme inFigure 139) (Voutchkov 2010)

135 Energy requirements for RO plant

The energy consumption of modern large SWRO desalination plants is currentlyaround 4 kWhm3 which makes membrane desalination the most energy-efficienttechnology for drinking water production (Darwish Hassabou amp Shomar 2013)Because of the lower salinity of the treated feed BWRO requires less energy input(015e08 kWhm3) than a corresponding SWRO plant About 80 of the total energyinput is absorbed by high-pressure pumps that pressurize the feed entering RO trainstherefore increasing of energy efficiency of both BWRO and SWRO trains is a criticalissue According to this perspective various energy recovery devices (ERDs) such asthe Francis turbine and Pelton wheel and the turbochargers DWEER and PressureExchanger have been used over the past 15 years

The goal of Pelton wheels and Francis turbines is to recover the energy of ROretentate (pressurized at 60e70 MPa) in the form of mechanical energy (Figure 1310)

Intake pump

Seawater

Screen

ChlorinationFlocculants

pH adj

Antiscalingdechlorination

To RO trains

Air bubbling

MFUF

Figure 139 Seawater pretreatment based on submerged MFUF unit (Di Profio Ji Curcio ampDrioli 2011) Integration of standard MFUF modules is also frequently applied

426 Advances in Membrane Technologies for Water Treatment

Pelton wheels and Francis turbines (usually denoted as Class III ERD) convert thehydraulic energy of the reject stream into rotational energy which is delivered in theform of mechanical shaft power Although these systems can reach 80e88 efficiencyin converting hydraulic energy into rotational mechanical power a second conversionis needed to obtain useful hydraulic energy Overall the real net transfer efficienciesfall to 63e76 (MacHarg 2001)

Hydraulically driven pumps such as hydraulic turbochargers Pelton-drive pumpsand hydraulic pressure boosters are centrifugal in nature and belong to the secondclass of ERDs their hydraulic energy transfer efficiency is less than Class III devices

Class I energy recovery technologies use the principle of positive displacementEnergy is transferred directly from the reject stream to an incoming SW stream thatcombines with the total feed stream to the RO membranes (operational principles ofDesalcorsquos Work Exchanger Energy Recovery (DWEER) system and EnergyRecovery Incrsquos Pressure Exchanger (PX) are illustrated in Figure 1311(a) and (b))Positive displacement devices achieve net energy transfer efficiencies between91 and 96 (Clemente amp Mercer 2011) Theoretically Class I devices areable to decrease the energy consumption of SWRO plants to about 2 kWhm3

(MacHarg 2001)

136 Energy from SW

The sea is more than just a potentially unlimited source of drinking water Thermody-namic considerations based on evaluation of the energy of mixing suggest that a hugeamount of energy can be potentially generated when waters of different salinities aremixed together (salinity gradient power generation) Vermaas et al (2013) showed thatthe theoretical obtainable Gibbs free energy of mixing typical SW (30 gL NaCl) andriver water (1 gL NaCl) both at a flow rate of 1 m3s is 139 MW (Vermaas et al2013)

The global potential for salinity gradient power is reported to be 1650 TWhyear Inthe United States with a total flow of rivers into the ocean of about 1700 km3year this

M

Turbine

Feed

Brine

Permeate

Retentate

60 bar 1 bar

58 bar

Figure 1310 Scheme of an SWRO desalination unit with a Pelton wheel energy recoverydevice (ERD)

Membrane technologies for seawater desalination and brackish water treatment 427

technology could generate about 55 GW assuming an energy conversion efficiency of40 (Thorsen amp Holt 2009)

Theoretical calculations using the vanrsquot Hoff equation (Eqn (131)) show that themaximum extractable energy from mixing freshwater with SW is 075 kWhm3

(assuming 055 M NaCl concentration) this value increases to 15 kWhm3 whenconsidering SWRO brine from a desalination plant operating at a 50 recovery factor(Helfer Lemckert amp Anissimov 2014)

To date pressure retarded osmosis (PRO) and reverse electrodialysis (RE) are themost investigated technologies to recover energy from saline gradients

In PRO a semipermeable membrane separates a low-concentration and a high-concentrated salt solution (also called a draw solution) Under the difference ofosmotic pressure water flows from the low-concentration compartment to the oppositeside thus increasing the volume of the concentrate flow A turbine is coupled to thepipe containing the increased pressure flow to generate power In the scheme ofFigure 1312 PRO is used to recover the osmotic energy of SWRO brine by operatingwith SW

The performance of PRO strictly depends on the properties of the membrane Sofar membranes specifically developed for forward osmosis and PRO are almostexclusively commercialized by Hydration Technology Innovations (HTI) althoughthe market is now accelerating driven by renewed interest in osmotic processesPRO laboratory tests using commercial flat-sheet cellulose triacetate forward osmosis(FO) membranes from HTI resulted in the generation of a power density of 22 and27 Wm2 membrane area when operating with SWBW and SWpure water

Brine

PistonBarrier

Feed

Permeate

High pressureretentatePistonBarrier

Feed Permeate

Low pressurereject

PX

High pressurepump

High pressureretentate

(a)

(b)

Figure 1311 Operational schemes of (a) DWEER system (Ashkelon SWRO plant Israel)and (b) PXs (Qingdao SWRO plant China)

428 Advances in Membrane Technologies for Water Treatment

respectively (Achilli Cath amp Childress 2009) When using SWRO brine (6 NaCl)lab-made TFC hollow fibres specifically developed for PRO resulted in a power den-sity higher than 10 Wm2 (Wang Tang amp Fane 2012)

The first osmotic power plant prototype with a designed capacity to generate10 kW of electricity was constructed by the Norwegian state-owned power companyStatkraft in 2009 It is currently operated by Sintef Energy Research a research divi-sion of the Sintef Group (Melanson 2014)

RE is an emerging technology with the potential to generate energy from salinitygradients power (SGP) In a typical SGP-RE module cation exchange membranesand anion exchange membranes are stacked alternately in a module (Figure 1313)

Turbine

Generator

Water

Pretreatedseawater

PX

Pressureexchanger

To RO train

SWRO brine

Diluted brinedischarge

Figure 1312 A possible scheme of pressure retarded osmosis (PRO) system to recover osmoticpower from SWRO brine

Load

CEM AEM

SWR

O

SWR

O

brin

e

brin

e

SWR

Obr

ine

Seaw

ater

Seaw

ater

Seaw

ater

AEM AEMCEM CEM CEM

ndash ndash ndash+++ +

Electron flow

Recirculating electrolyte solution

Ele

ctro

deE

lectrode

Figure 1313 Scheme of an reverse electrodialysis (RE) unit operated with SWRO brine andseawater

Membrane technologies for seawater desalination and brackish water treatment 429

Driven by a concentration gradient the diffusive flux of ions generates an electrochem-ical membrane potential recorded as a voltage across electrodes (Tedesco CipollinaTamburini van Baak amp Micale 2012)

RE-SGP investigations carried out with aqueous NaCl solutions mimicking SW andriver water salinity reached a power density of about 2 Wm2 (Dlugolecki GambierNijmeijer amp Wessling 2009 Post et al 2010 Vermaas Saakes amp Nijmeijer2011) and energy efficiency around 50 Daniilidis Vermaas Herber and Nijmeijer(2014) achieved a power density of 67 Wm2 of total membrane area using 001 MNaCl solution against 5 M at 60 C in general the power density increased monoton-ically for high-concentrated feed solutions (Daniilidis et al 2014)

Theoretical predictions on a 12-cell stack equipped with Fujifilm ion exchangemembranes and operated with 05 M54 M NaCl diluteconcentrate solutions resultedin a maximum gross power density of 24 Wm2 (Veerman Saakes Metz amp Harmsen2009)

1361 Environmental impact of membrane desalination plants

Coastal and near-shore constructions (including intake and outfall structures) use oflarge quantity of SW causing impingement and entrainment of marine organismsand disposal of large amount of brines and chemicals severely impact the environment

Open intakes (the most common option in large desalination plants) and single openoutfall or diffuser systems when placed above the seafloor may cause wave refrac-tions and a change in current patterns thus interfering with marine sediment The localincrease of turbidity results in an increased level of pollutants or a reduced level ofdissolved oxygen burying benthic flora and fauna Moreover structures above the sea-floor might provide a substrate to which algae anemones or mussels might attachthese species attract echinoderms and crustaceans and ultimately result in a significantalteration in the marine community (Latterman amp Hopner 2008) Intake screensrepresent a high-mortality source for larger marine organisms and fish owing toimpingement (causing suffocation starvation or exhaustion) for these reasons theintake velocity of SW should be reduced as much as possible

However the highest impact on the marine environment is caused by the rejectedSWRO concentrate stream A typical plant operating at 50 recovery factor producesa brine with a salinity of about 70 that has a density of 1053 kgL (higher than the SWdensity of 1025 kgL) at room temperature The brine spread through multi-portdiffuser systems over the seafloor affects benthic communities Studies on Posidoniaoceanica showed that salinity around 45 causes about 50 mortality in 15 days(Latorre 2005)

1362 Membrane distillation

Membrane distillation (MD) is a membrane contactor technology with the potential tosignificantly reduce the amount of RO concentrate to be discharged In MD a micro-porous hydrophobic membrane contacts a heated solution on one side (lsquofeedrsquo or lsquoreten-tatersquo) The hydro-repellent nature of the membrane avoids the permeation of any liquid

430 Advances in Membrane Technologies for Water Treatment

while sustaining a vapoureliquid interface at the entrance of each pore There waterevaporates (whereas nonvolatile solutes are retained) diffuses across the membraneand condenses on the opposite side (lsquodistillatersquo) of the module (Figure 1314)

The specific method used to activate the vapour pressure gradient across the mem-brane (driving force) has four major MD configurations In the most common andsimplest arrangement direct contact MD the permeate side of the membrane consistsof condensing pure water Alternatively the water vapour can be extracted by vacuumrecovered on a condensing metallic surface separated from the membrane by an air gap(AGMD) or removed by a sweep gas

Ideally MD guarantees the complete rejection of nonvolatile solutes such as mac-romolecules colloidal species and ions Low-temperature gradients are generally suf-ficient to establish an acceptable trans-membrane flux (1e20 kgm2h) typical feedtemperatures vary in the range of 50e80 C permitting the efficient recycle of low-grade or waste heat streams as well as the use of alternative energy sources (solarwind or geothermal) An interesting advantage with respect to RO is that MD doesnot have the limitations of concentration polarization therefore it can be applied toRO brines to increase the water recovery factor and decrease the amount of disposedbrine

Currently no MD systems have reached a large industrial scale or are available onthe market most installations are at the pilot stage The Swedish company ScarabDevelopment provides flat-plate MD modules Production rates of 10e20 kgh arereported for high-temperature gradients across the membrane These modules werealso tested within European Union (EU)-funded project MEDESOL (SW desalinationby innovative solar-powered MD system) (psa 2014)

The Memstill process was developed by TNO (The Netherlands) for SW desali-nation using air gap MD carried out in a countercurrent flow configuration Cold SWflows through a condenser with nonpermeable walls through a heat exchanger andfrom there into the membrane evaporator The wall of the evaporator is a microporoushydrophobic membrane through which water vapour diffuses and liquid salted water isretained (Hanemaaijer et al 2006)

Seawater

Pure water (DCMD)Vacuum (VMD)

Sweep gas (SGMD)Air gap (AGMD)

Tfeed Vapour

Vapour

Vapour

Microporous hydrophobicmembrane

Figure 1314 Principle of membrane distillation

Membrane technologies for seawater desalination and brackish water treatment 431

Within the EU-funded project MEDIRAS (Membrane Distillation in RemoteAreas) a two-loop MD system with a nominal production of 5 m3day was installedin an 8-MW diesel power plant on Pantelleria island Italy The system which usesthermal energy (20) from 40 m2 of solar collectors and waste heat (80) at 90 Cfrom the refrigeration of engines is an example of a prototypal solar MD unit(Figure 1315)

Air gap MD modules integrated with an appropriate heat recovery system weredeveloped by SolarSpring GmbH a Fraunhofer spin-off company The module setupconsists of three channels condenser evaporator and distillate (Figure 1316)Condenser and distillate channels are separated by a metallic foil whereas a micropo-rous hydrophobic membrane is interposed between the evaporator and the distillatechannels The hot SW (typically at 80 C) is directed in the evaporator channel therewater vapour diffuses across the membrane and condenses at the metallic foil surfacewhere the heat of evaporation is partially recovered Cold feed water (around 20 C)enters in the distillate channel (in countercurrent with respect to the flow directionof the evaporator stream) to increase the temperature when in contact with the conden-sate foil (Koschikowski Wieghaus amp Rommel 2009)

The concept of integrated membrane desalination systems with MD operated on theRO retentate to increase the water recovery factor and reduce the volume of discharged

(a) (b)

Figure 1315 MEDIRAS project Membrane Distillation (MD) pilot plant installed inPantelleria Italy (a) Solar thermal collectors (b) multi-module MD systemFrom MEDIRAS Project website (2014) with kind permission

Metallic foil

Membrane

Condenser channel

Evaporator channelDistillate channelHeat

exchanger

Condenser inlet(feed at 20 degC)

Condenser outlet(ca 70 degC)

Evaporator inlet(80 degC)

Evaporator outlet(ca 30 degC)

Distillate outlet(ca 25 degC)

Figure 1316 Principle of AGMD module with integrated heat recovery developed bySolarSpring GmbH

432 Advances in Membrane Technologies for Water Treatment

brine (thus approaching the concept of zero liquid discharge) was developed within theEU-funded project MEDINA (membrane-based desalination an integrated approach)(Al Obaidani et al 2008 Macedonio Curcio amp Drioli 2007) The possibility ofdriving MD towards concentrations overcoming the saturation levels of salts dissolvedin solution (MDecrystallization) led to the recovery of pure crystallized salts (sodiumchloride epsomite etc) from SW brine (Drioli Criscuoli amp Curcio 2005 Ji et al2010)

137 Economics of membrane desalination

Over the past 3 decades the unit cost of water produced by SWRO desalinationprocesses has progressively decreased (Figure 1317) In particular the economicsof membrane desalination was found to be sensitive to the plant capacity Despitea higher initial capital investment plants with large capacities reduce the unitcost of water to 05e07 $m3 Table 134 reports the estimated unit water cost pro-duced in some large industrial SWRO desalination plants On the other hand thecost of desalinated water unit produced from BW by RO plants with a capacityless in 1000 m3day might range between 06 and 1 $m3 (Karagiannis amp Soldatos2008)

The unit cost of water ($m3) is obtained by dividing the total annual cost ($year)and the annual yield (m3year)

The annual yield is determined by multiplying the maximum daily water production(m3day) and the annual plant utility (number of days on-line per year percentage ofdaily plant capacity)

0 05 1 15 2

1982

1992

2002

2010

Unit water cost ($m3)

Yea

r

Electric power

Maintenance

Capex charges

Figure 1317 Historical trend of unit cost of drinking water produced by SWRO desalinationData from Water Reuse Association (2012)

Membrane technologies for seawater desalination and brackish water treatment 433

The total annual cost is determined by (1) the annual cost of debt service on capitalitems ($year) and (2) the annual operating and maintenance cost ($year)

The annual cost of debt service on capital items ($year) is composed of (11) theannual debt service on water conveyance ($year) and (12) the annual debt service ofwater production ($year) (11) is calculated by multiplying the total capital cost ofconveyance ($) by the capital recovery factor (CRF) (12) is calculated by multiplyingthe total capital cost of concerns and treatment ($) by the CRF

The total capital cost of conveyance refers to the cost of constructing pipelines andany accessories and turnout on the pipeline route including water storage tanks Thetotal capital cost of concerns and treatment includes both the cost of the contract asso-ciated with the delivery of the desalination plant and the cost of the engineering legaland administrative tasks associated with developing the contract documentation andexecuting the contract

The CRF is calculated on the basis of a net present value of the asset defined for agiven discount rate (usually 6) and a series of future payments over a defined periodof time (usually serviced over 25 years)

The annual OampM costs which emerge after plant commissioning and during plantoperation include (21) the cost of energy (in RO plants primarily electrical powertypically in the range of 35e5 KWhm3) (22) chemical costs (typically chlorinefor disinfection acid against calcium carbonate precipitation antiscaling agents coag-ulants and flocculants caustic soda etc) (23) membranes and filtration mediareplacement (24) maintenance costs covering all activities and consumables associ-ated with scheduled and emergency servicing of mechanical equipment calibratingand servicing instrumentation data acquisition and electrical systems and monitoring(collecting analysing and reporting on water quality data) and (25) labor costs

A rough breakdown of total capital costs and OampM costs is provided inFigure 1318(a) and (b)

Table 134 Unit water cost of some large SWRO plants

SWRO plant Start-up Productivity (m3day) Unit water cost ($m3)

Ashkelon (Israel) 2001 320000 052

Palmachim(Israel)

2005 83000 078

Perth (Australia) 2006 144000 075

Carlsbad(California)

2006 189000 076

Skikda (Algeria) 2008 100000 073

Hamma (Algeria) 2008 200000 082

Hadera (Israel) 2010 348000 063

Source Ghaffour Missimer and Amy (2013) Pankratz (2009)

434 Advances in Membrane Technologies for Water Treatment

138 Conclusions

Driven by RO membrane science has exponentially grown over the past 40 years tobecome the leader in technology for BW and SW desalination Despite this enormoussuccess many technological challenges still need to be addressed

The recent development of ERDs has resulted in a drastic improvement in theenergetic efficiency of desalination plants however the large energetic potential ofconcentrated streams remains unexploited In this regard emerging technologies

3 210

20

2Testing and

commissioning35

Mechanical andprocess works

5 2 1

Civilworks20

Electrical works

Control andinstrumentation

Structural works

Architectural and landscape

General and preliminariesExternal

works

Maintenance and spares

under warranty

(a)

(b)

10

10

12

8

Energy60

Maintenance and monitoring

Membrane replacement

Labour

Chemicals

Figure 1318 Percent breakdown of (a) capital costs elements and (b) OampM cost elementsAfter UNESCO Centre for Membrane Science and Technology (2008)

Membrane technologies for seawater desalination and brackish water treatment 435

such as PRO and RE promise a considerable reduction in the energy input andultimately the unit water costs

Further advances are expected to come from new RO membrane materialsand module designs and in particular from larger-diameter SWMs and high-fluxmembranes with enhanced selectivity

Driven by rapid technological development MFUF operations are expected to in-crease in acceptance as standard pretreatment methods in the near future with majorbenefits in terms of improvedwater quality and a lower ROmembrane replacement rate

Today extensive expansion in the number and capacity of coastal desalination plantsexacerbates the negative impact of rejected concentrate on the fauna and flora of the sur-rounding seas Although far from being fully implemented on an industrial scale MDand related operations (such as membrane crystallization) have emerged as an inter-esting answer to the brine disposal problem in the logic of zero liquid discharge

In general considering the strategic relevance of the desalination industry formany countries continuous multidisciplinary research efforts are mandatory tomake BWRO and SWRO affordable worldwide

List of symbols

Italic font

c Molar concentrationD Diffusion coefficientJs Solute molar fluxJv Volumetric fluxk Partition coefficientR Ideal gas constantT Absolute temperatureV Partial molar volume

Greek font

d Membrane thicknessn Vanrsquot Hoff coefficientP Osmotic pressure

Superscripts

f Feedp Permeate

Subscripts

i ith ions Solutew Water

436 Advances in Membrane Technologies for Water Treatment

List of acronyms

AEM Anion exchange membraneAGMD Air gap membrane distillationBW Brackish waterCA Cellulose acetateCEM Cation exchange membraneCOD Chemical oxygen demandCRF Capital recovery factorDCMD Direct contact membrane distillationDMF Dual media filtrationDOM Dissolved organic matterED ElectrodialysisEDR Electrodialysis reversalEDTA Ethylenediaminetetraacetic acidERD Energy recovery devicesGOR Gain output ratioLSI Langelier saturation indexMD Membrane distillationMED Multiple effect distillationMENA Middle East and North AfricaMF MicrofiltrationMSF Multistage flashMVC Mechanical vapour compressionNOM Natural organic matterNTU Nephelometric turbidity unitsOampM Operating and maintenance (costs)PRO Pressure retarded osmosisPX Pressure exchangerRE Reverse electrodialysisRO Reverse osmosisSDI Silt density indexSampDSI Stiff and Davis stability indexSHMP Sodium hexametaphosphateSMBS Sodium metabisulphiteSGMD Sweep gas membrane distillationSGP Salinity gradient powerSSF Slow sand filtrationSW SeawaterSWM Spiral-wound moduleTCA Cellulose triacetateTDS Total dissolved solidsTFC Thin-film compositeTSS Total suspended solidsTVC Thermal vapour compressionUF UltrafiltrationVMD Vacuum membrane distillationWHO World Health Organization

Membrane technologies for seawater desalination and brackish water treatment 437

References

Achilli A Cath T Y amp Childress A E (2009) Power generation with pressure retardedosmosis An experimental and theoretical investigation Journal of Membrane Science343 42e52

Al Obaidani S Curcio E Macedonio F Di Profio G Al Hinai H amp Drioli E (2008)Potential of membrane distillation in seawater desalination Thermal efficiency sensitivitystudy and cost estimation Journal of Membrane Science 323 85e98

Al-Amoudi A amp Lovitt W L (2007) Fouling strategies and the cleaning system of NF mem-branes and factors affecting cleaning efficiency Journal of Membrane Science 303 4e28

Al-Shammiri M amp Al-Dawas M (1997) Maximum recovery from seawater reverse osmosisplants in Kuwait Desalination 110 37e48

Bengtsson L (2010) The global atmospheric water cycle Environmental Research Letters5(2) 025202

Borsani R amp Ghiazza E (8e11 April 2012) New development in MSF technology for highperformances plant In Proceedings of water desalination conference in Arab countriesARWADEX Riyad Saudi Arabia

Buscha M Chub R Kolbe U Meng Q Q amp Li S J (2009) Ultrafiltration pretreatment toreverse osmosis for seawater desalination mdash three years field experience in the WangtanDatang power plant Desalination and Water Treatment 10 1e20

Clemente R amp Mercer G (4-9 September 2011) A five year lifecycle analysis of the Perthseawater desalination plant In Proceedings of IDA World Congress Perth Australia

Cornelissen E R Vrouwenvelder J S Heijman S G J Viallefont X D Van Der Kooij D ampWessels L P (2007) Periodic airwater cleaning for control of biofouling in spiral woundmembrane elements Journal of Membrane Science 287 94e101

Daniilidis A Vermaas D A Herber R amp Nijmeijer K (2014) Experimentally obtainableenergy from mixing river water seawater or brines with reverse electrodialysis RenewableEnergy 64 123e131

Darwish M Hassabou A H amp Shomar B (2013) Using seawater reverse osmosis(SWRO) desalting system for less environmental impacts in Qatar Desalination 309113e124

Di Profio G Ji X Curcio E amp Drioli E (2011) Submergedhollow fiber ultrafiltration asseawater pretreatment in the logic of integrated membrane desalination systems Desali-nation 128e135

Dlugolecki P Gambier A Nijmeijer K amp Wessling M (2009) The practical potential ofreverse electrodialysis as process for sustainable energy generation Environmental Scienceand Technology 43 6888e6894

Drioli E Criscuoli A amp Curcio E (2005) Membrane contactors Fundamentals applica-tions and potentialities Amsterdam Elsevier Science Ltd

El-Manharawy S amp Hafez A (2001) Water type and guidelines for RO system designDesalination 139 97e113

FAO Water Report (2012) Coping with water scarcity Rome FAO Sales and MarketingGroup ISSN 1020e1203

Fell C J D (1995) Membrane separations technology mdash principles and applicationsMembrane Science and Technology 2 113e142

Ghaffour N Missimer T M amp Amy G L (2013) Technical review and evaluation of theeconomics of water desalination Current and future challenges for better water supplysustainability Desalination 309 197e207

438 Advances in Membrane Technologies for Water Treatment

GlobalWater Intelligence (GWIIDADesalData) (2013)Market profile and desalination markets2009e2012 yearbooks and GWI website Retrieved from httpwwwdesaldatacom

Hanemaaijer J H van Medevoort J Jansen A E Dotremont C Van Sonsbeek EYuan T et al (2006) Memstill membrane distillationmdasha future desalination technologyDesalination 199 175e176

Hasson D Drak A amp Semiat R (2003) Induction times induced in an RO system byantiscalants delaying CaSO4 precipitation Desalination 157 193e207

Helfer F Lemckert C amp Anissimov Y (2014) Osmotic power with pressure retarded osmosistheory performance and trends e a review Journal of Membrane Science 453 337e358

IDA Media Analytics Ltd (2007) The 20th IDA worldwide desalting plant inventory OxfordUK

Ji X Curcio E Al Obaidani S Di Profio G Drioli E amp Fontananova E (2010)Membrane distillation-crystallization of seawater reverse osmosis brines Separation andPurification Technology 71 76e82

Karagiannis I C amp Soldatos P G (2008) Water desalination cost literature Review andassessment Desalination 223 448e456

Knudsen M (1903) On the standard-water used in the hydrographical research until July1903 Conseil permanent international pour lrsquoexploration de la mer Publications decirconstance no 2 Copenhagen

Koschikowski J Wieghaus M amp Rommel M (2009) Membrane distillation for solardesalination In A Cipollina G Micale amp L Rizzuti (Eds) Seawater desalination BerlinHeidelberg Springer-Verlg

Kumano A amp Fujiwara N (2008) Cellulose triacetate membranes for reverse osmosis InA G Fane N Li W S W Ho amp T Matsuura (Eds) Advanced membrane technologyand application Hoboken NJ John Wiley amp Sons

Latorre M (2005) Environmental impact of brine disposal on Posidonia seagrasses Desali-nation 182 517e524

Latterman S amp Hopner T (2008) Impacts of seawater desalination plants on the marineenvironment of the Gulf In A H Abuzinada H J Barth F Krupp et al (Eds) Protectingthe Gulfrsquos marine ecosystems for pollution Basel Birkhauser

Lee S Cho J amp Elimelech M (2005) Combined influence of natural organic matter (NOM)and colloidal particles on nanofiltration membrane fouling Journal of Membrane Science262 27e41

Lee K P Arnot T C amp Mattia D (2011) A review of reverse osmosis membrane materialsfor desalinationmdash development to date and future potential Journal of Membrane Science370 1e22

van de Lisdonk C A C Rietman B M Heijman S G J Sterk G R amp Schippers J C(2001) Prediction of supersaturation and monitoring of scaling in reverse osmosis andnanofiltration membrane systems Desalination 138 259e270

Lokiec F amp Ophir A (21e26 October 2007) The mechanical vapor compression 38 yearsof experience In Proceedings of IDA world congress Maspalomas Gran Canaria Spain

Macedonio F Curcio E amp Drioli E (2007) Integrated membrane systems for seawaterdesalination Energetic and exergetic analysis economic evaluation experimental studyDesalination 203 260e276

MacHarg J P (2001) The evolution of SWRO energy-recovery systemsDesalination ampWaterReuse 11(3) 49e53

Madaenl S S Mohamamdi T amp Moghadam M K (2001) Chemical cleaning of reverseosmosis membranes Desalination 134 77e82 Retrieved from httpwwwmediraseuindexphpidfrac14121html

Membrane technologies for seawater desalination and brackish water treatment 439

Melanson D Norwayrsquos statkraft kick-starts worldrsquos first osmotic power plant EngadgetRetrieved from httpwwwengadgetcom20091125norways-statkraft-kick-starts-worlds-first-osmotic-power-plant

Merten U (1966) Transport properties of osmotic membranes In U Merten (Ed) Desali-nation by reverse osmosis Cambridge MA The MIT Press

Millero F J Feistel R Wright D G amp McDougall T J (2008) The composition ofstandard seawater and the definition of the reference-composition salinity scale deep searesearch part I Oceanographic Research Papers 55(1) 50e72

Mountford H (25e26 October 2011) Water The environmental outlook to 2050 In Pro-ceedings of OECD global forum on environment Paris Making Water Reform Happen

Nguyen T Roddick F A amp Fan L (2012) Biofouling of water treatment membranes Areview of the underlying causes monitoring techniques and control measuresMembranes2 804e840

Ning R Y amp Troyer T L (2007) Colloidal fouling of RO membranes following MFUF inthe reclamation of municipal wastewater Desalination 208 232e237

Pankratz T (13e16 September 2009) The total water cost of seawater desalination In Pro-ceedings of the 24th water reuse symposium Seattle Washington

Patzay G Stahl G Karman F H amp Kalman E (1998) Modeling of scale formation andcorrosion from geothermal water Electrochimica Acta 43 137e147

Pearce G (2007) Water and wastewater filtration Membrane module format Filtration ampSeparation 44 31e33

Post J W Goeting C H Valk J Goinga S Veerman J Hamelers H V M et al (2010)Towards implementation of reverse electrodialysis for power generation from salinitygradients Desalination and Water Treatment 16 182e193

Pressman J G McCurry D L Parvez S Rice G E Teuschler L K Miltner R J et al(2012) Disinfection byproduct formation in reverse-osmosis concentrated andlyophilized natural organic matter from a drinking water source Water Research 46(16)5343e5354 Retrieved from httpwwwpsaeswebengprojectsmedesolresultsphp

Saeed M O (2002) Effect of dechlorination point location and residual chlorine on thebiofouling in a seawater reverse osmosis plant Desalination 143 229e235

Sagiv A amp Semiat R (2010) Parameters affecting backwash variables of RO membranesDesalination 261(3) 347e353

Segarra J Iglesias A Peacuterez J amp Salas J (2009) Construccion de la planta con mayorcapacidad de produccion mundial con tecnologiacutea EDR para agues regeneradas Tecnologiacuteadel Agua 309 56e62

Shams El Din A M Arain R A amp Hammoud A A (2000) On the chlorination of seawaterDesalination 129 53e62

Shiklomanov I (1993) World fresh water resources In P H Gleick (Ed) Water in crisis Aguide to the worldrsquos fresh water resources New York Oxford University Press Retrievedfrom httpwwwsidem-desalinationcomsidemressourcesfiles116543Sidem-Company-Profile-Dec-2011pdf

Tedesco M Cipollina A Tamburini A van Baak W amp Micale G (2012) Modelling thereverse electrodialysis process with seawater and concentrated brine Desalination andWater Treatment 49 404e424

Thorsen T amp Holt T (2009) The potential for power production from salinity gradients bypressure retarded osmosis Journal of Membrane Science 335 103e110

UNESCO Centre for Membrane Science and Technology (October 2008) Emerging trends indesalination A review In Waterlines report series 9 University of New South WalesNational Water Commission Canberra (Australia)

440 Advances in Membrane Technologies for Water Treatment

Veerman J Saakes M Metz S J amp Harmsen G J (2009) Reverse electrodialysisPerformance of a stack with 50 cells on the mixing of sea and river water Journal ofMembrane Science 327 136e144

Vermaas D A Saakes M amp Nijmeijer K (2011) Doubled power density from salinitygradients at reduced intermembrane distance Environmental Science amp Technology 457089e7095

Vermaas D A Veerman J Yip N Y Elimelech M Saakes M amp Nijmeijer K (2013)ACS Sustainable Chemistry amp Engineering 1 1295e1302

Vial D amp Doussau G (2002) The use of microfiltration membranes for seawaterpre-treatment prior to reverse osmosis membranes Desalination 153 141e147

Voutchkov N (2010) Considerations for selection of seawater filtration pretreatment systemDesalination 261 354e364

Wang R Tang C amp Fane A G (2012) Development of pressure retarded osmosis (PRO)membranes with high power density for osmotic power harvesting In Proceedings of the3rd osmosis membrane summit statkraft Barcelona Spain

Water Reuse Association (2012) Seawater desalination costs Retrieved from httpswwwwatereuseorgsitesdefaultfilesu8WateReuse_Desal_Cost_White_Paperpdf

Yun T I Gabelich C J Cox M R Mofidi A A amp Lesan R (2006) Reducing costs forlargescale desalting plants using large-diameter reverse osmosis membranesDesalination189 141e154

Zondervan E amp Roffel B (2007) Evaluation of different cleaning agents used for cleaningultra filtration membranes fouled by surface water Journal of Membrane Science 30440e49

Zouboulis A Traskas G amp Samaras P (2007) Comparison of single and dual mediafiltration in a full-scale drinking water treatment plant Desalination 213 334e342

Zularisam A W Ismail A F amp Salim R (2006) Behaviours of natural organic matter inmembrane filtration for surface water treatment mdash a review Desalination 194 211e231

Membrane technologies for seawater desalination and brackish water treatment 441

Membrane technologiesfor municipal wastewatertreatment

14Seyed MK Sadr Devendra P SarojCentre for Environmental and Health Engineering (CEHE) Department of Civiland Environmental Engineering University of Surrey Guildford Surrey United Kingdom

141 Introduction

1411 Membrane technologies for advanced wastewatertreatment

Membrane technology is increasingly becoming popular for the advanced treatmentof municipal wastewater This is mainly because of growing concerns about waterquality and pollution trends in relation to more complex global challenges such asrapid urbanisation and increasing water demands in the domestic and industrialsectors In the past few decades wastewater treatment and reuse has gained interestand so has advanced wastewater treatment technologies Among these new technol-ogies membrane-assisted ones offer consistently high-quality treatment of effluentMembrane technologies have also been shown to be promising in the removal ofemerging compounds such as endocrine disturbing compounds (EDCs) and phar-maceutically active compounds (PhACs) It is projected that membrane-assistedtechnologies will be among the most reliable systems for water reclamation in com-ing decades (Shannon et al 2008) Membrane technologies encompass a widerange of membrane processes depending on the desired quality of the effluentFor instance by itself microfiltration (MF) can remove particulate and colloidalforms of contaminants whereas as a part of a membrane bioreactor (MBR) MFforms an integral part of a biological treatment system Various membrane-assisted configurations for wastewater treatment exist all of which have theirown advantages and disadvantages depending on various factors such as effluentquality energy consumption and system complexity Often membrane technolo-gies are employed in a combination of physical chemical and biological processesresulting in an efficient process configuration for a particular scenario of wastewatertreatment For example MBR technology combines activated sludge processes(ASPs) or an anaerobic biodegradation process with MF or ultrafiltration (UF)and MF or UF is also integrated as a posttreatment for tertiary treatment of munic-ipal wastewater to achieve high effluent quality

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400014-9Copyright copy 2015 Elsevier Ltd All rights reserved

1412 Drivers and barriers to membrane technologiesfor municipal wastewater treatment

14121 Advantages

Membrane technologies for municipal wastewater treatment particularly MBRs havebeen considered a reliable option for applications requiring a smaller footprint andorhigher effluent quality In most cases of domestic wastewater treatment in developedurban areas carbon (usually indicated by biochemical oxygen demand [BOD]) andnitrogen (NH4-N and total nitrogen (TN)) removal are achieved using biologicalaerobic (BOD oxidation and nitrification) and anoxic treatment (denitrification) aspart of the ASP The conventional activated sludge process (CASP) is normallydesigned and operated at a mixed liquor suspended solids (MLSS) concentration ofless than 4 gL and a lower range of solids retention times (SRTs) to maintain theMLSS In MBRs however the typical MLSS range between 8 and 15 gL allowsthe intensification of microbial suspended growth and raises the possibility of reusingexisting units to increase the plantrsquos capacity with little or no increase in the footprint(Kraemer et al 2012) In general an advantage of membrane technology is the capitalcosts of constructioninstallation which are similar to or lower than those of conven-tional technologies although membrane cost can have an important role depending onthe market trend in coming years Current membrane technologies generally demand ahigh level of automation because of their need for continuous management of foulingConsequently membrane-assisted technologies can be controlled by computerisedmonitoring and control systems This means that they can also be widely applied indecentralised and household systems in the coming decade

14122 Disadvantages

Clear disadvantages of MBRs can be seen in regions where conventional secondarywastewater treatment plants have already established In this regard although it wouldbe possible to use existing bioreactors or clarifiers for the membrane basins majorretrofit modifications and reconstruction are required to meet the requirements of pro-cess geometry the number of basins and provisions for high mixed liquor recycle flowrates Regarding retrofitting it might be possible to use the clarifiers for other pur-poses eg sludge storage In the case of posttreatment membrane technologies (MFor UF units) the cost of membrane modules and operation are compared against theresulting high effluent quality after tertiary treatment

In addition there are limitations to the widespread application of membrane tech-nologies in municipal wastewater treatment eg energy consumption membrane costand process complexity Moreover the scarcity of operational and equipment stan-dards is evident Although standardisation was contemplated in the European regionthrough the European Commissionrsquos Amadeus project (de Wilde Richard Lesjeanamp Tazi-Pain 2007) this has not been widely considered successful so far Membranemanufacturers have their own membrane module configurations and features and theyalso differ in recommended process unit geometry and sizes (Kraemer et al 2012)Other operational disadvantages have been observed eg the limited peak flow

444 Advances in Membrane Technologies for Water Treatment

capacity and performance abilities compared with conventional clarifier-based sys-tems As a result of high energy consumption and in some cases chemical consump-tion the operational costs of membrane technologies are still higher than those ofconventional technologies although the trend of energy consumption has recentlydecreased based on some new process modifications and the use of new materials

142 Process fundamentals and indicators

1421 Membrane-assisted processes and technologies

A membrane can be defined as a barrier that allows some components either physicalor chemical to pass more freely through it than others As normally applied to waterand wastewater treatment membranes are perm-selective Main components in theprocess of membrane filtration are

1 The permeate that passes through the membrane2 The retentate that is rejected by the membrane

Membranes can be classified depending on their pore size applied pressure molec-ular weight cutoff and permeability Commonly accepted classifications in the field ofwater and wastewater treatment include MF UF nanofiltration (NF) and reverseosmosis (RO) Coarser membranes are associated with MF and the most selectivemembranes are associated with RO processes As shown in Figure 141 the first twomembranes operated at low pressures (01e5 bar) are normally used in MBR systemsThey are capable of retaining bacteria pathogens and large fraction of viruses the NFand RO membranes operated at higher pressures (3e100 bars) are able to reject soluble

Figure 141 Various pressure-driven membrane processes

Membrane technologies for municipal wastewater treatment 445

organic compounds EDCs and PhACs Reverse osmosis can also remove monovalentions eg sodium (Nathorn) These well-established capabilities of various types of mem-brane processes are used in the design and operation of wastewater treatment systems

There are several commonly observed operational issues with membrane processesin wastewater treatment The rejected constituents in the retentate tend to accumulate atthe membrane surface This leads to various phenomena and a reduction in the waterflow rate at a given transmembrane pressure (TMP) or conversely an increase in theTMP for a given flux (Judd 2011) These phenomena are collectively referred to asfouling A number of physicochemical and biological mechanisms are related to anincreased deposition of fouling materials onto the membrane structure Importantfactors in the type and the extent of fouling are the membrane material feed watercomposition and flux through the membrane

1422 Membrane-assisted systems in wastewater treatment

Because water quality in wastewater treatment and reuse applications is crucialadvanced treatment technologies are used to achieve the desired level of effluentquality Principal unit operations and processes as well as constituent classes arelisted in Figure 141 As suggested by Asano Burton Leverenz Tsuchihashi andTchobanoglous (2007) an almost endless number of treatment processes can beapplied in water reuse applications to improve the quality of treatment effluent forvarious purposes such as different water reuse scenarios Table 141 shows differentprocesses and their capability of removing various classes of contaminants Mostestablished wastewater treatment processes employ biological treatment to removeBOD total suspended solids (TSS) and even for total nitrogen and phosphorus Inmembrane-assisted processes membranes have an important role in removing resid-ual suspended solids and improving the effectiveness of disinfection

14221 Conventional treatments versus MBRs

The main aerobic biological processes of municipal wastewater treatment applicationscan be categorised into three groups

bull Suspended growth biological treatment processes In these processes microorganisms aremaintained in liquid suspension by mixing and aerating The ASP is one of the most success-fully applied processes for biological wastewater treatment Various reactor types are used inthe design of suspended growth processes for municipal wastewater treatment such ascompletely mixed reactor and sequencing batch reactor

bull Attached growth processes A medium eg a rotating disc or fixed packing is used to whichmicroorganisms attach and form a biofilm Then the biofilm microorganisms come in contactwith wastewater and oxidise the organic matters

bull Hybrid processes These use a combination of attached growth and suspended growth reac-tors to meet different conditions An example of such processes is moving biofilm bioreactortechnology

These processes form the fundamental components of widely applicable biologicalwastewater treatment In conventional treatment systems these processes are applied

446 Advances in Membrane Technologies for Water Treatment

Table 141 Unit operation and processes used to remove various constituents in wastewater

Unitprocess

Suspendedsolids

Colloidalsolids

Particulateorganicmatter

Dissolvedorganicmatter Nitrogen

Phosp-horous

Traceconstituents

Totaldissolvedsolids Bacteria

Protozoancysts andoocysts Viruses

Secondarytreatment

Secondary thornnutrientremoval

Depthfiltration

Surfacefiltration

Micro-filtration

Ultrafiltration

Dissolved airflotation

Nanofiltration

Reverseosmosis

Electro-dialysis

Carbonadsorption

Ion exchange

Advancedoxidation

Disinfection

Source Asano et al (2007)

Mem

branetechnologies

formunicipal

wastew

atertreatm

ent447

combined with well-established solideliquid separation unit operations such as sedi-mentation tanks or clarifiers The major advantage of applying these conventionaltreatment processes is that they are well understood therefore coping with the oper-ation and maintenance is relatively simple The other benefit is that automation of theseprocesses is possible to a certain extent However conventional systems may not bemost suitable especially in an area with a lack of sufficient land The effluent qualityis also relatively lower than that of advanced membrane technologies Table 142compares conventional processes and MBRs

Combined with conventional biological treatment processes membrane processescan form robust membrane technologies offering a higher level of treatment Forexample MBR technology which combines membrane technology and the high-rate biological process forms a unique technology for municipal wastewater treatment(Stephenson Judd Jeferson amp Brindle 2000) Membrane bioreactors use two mainconfigurations for solideliquid separation

bull Side-stream MBR (sMBR) In this configuration the membrane module is separated fromthe main reactor (Figure 142(a)) The mixed liquor in the bioreactor is pumped into a mem-brane module and a concentrated stream is retained by the membrane and returned to thebioreactor Two major developments have been made in this configuration A suctionpump was added on the permeate side to increase flexibility and simultaneously decreasethe cross-flow rate and energy consumption

bull Submerged or immersed MBR (iMBR) This configuration was introduced by YamamotoHissa Mahmood and Matsuo (1989) with the aim of reducing energy consumption associ-ated with the recirculation pump in the side-stream configuration In this configuration amembrane is directly immersed in the reactor (Figure 142(b)) As a result only a suctionpump is applied on the permeate side to create the TMP Table 143 compares sMBR andiMBR

Membrane bioreactors produce high effluent quality with a greater reuse potentialTable 144 compares the effluent quality of conventional treatments with a typicalMBR system In addition the footprint of an MBR is much smaller than a conventionaltreatment process mainly because of the higher SRT and higher MLSS in the biore-actor and the small footprint of the membrane separation units The Nordkanal plantin Germany eg has five main parts the sludge mechanical dewatering processlidded sludge the sludge liquor holding tanks a grit chamber the fine screen thecoarse screen the MBR with nitrification and denitrification tanks and processcontrol The plant has consistently achieved acceptable purification results eg thechemical oxygen demand (COD) removal is about 97 The biochemical oxygen de-mand (BOD) detected in effluent is below 3 mgL when the average BOD in raw wateris 300 mgL The elimination rate of TSS is 100 In addition to this plant and othercommissioned plants various pilot studies have shown that MBR technologies are reli-able for water reuse andor can be applied to decentralised and household-scale waste-water treatment systems It is evident that wastewater treatment plants that employMBRs can produce effluent (Table 144) that can meet various requirements for reusestandards eg landscape and agricultural irrigation and surface water discharge Forexample the Urban Wastewater Treatment Directive in Europe provides mandatoryminimum design rules for sewerage systems as well as treatment plants (minimum

448 Advances in Membrane Technologies for Water Treatment

Table 142 Advantages and disadvantages of conventional treatmentprocesses versus MBRs

Advantages Disadvantages

Conventional wastewater treatment processes

Technologies are well understood Greater sludge production

Process potentials are universally accepted More bio-solids handling and costs required

Different configurations allow the processto be designed to maximise contact timebetween macromolecules andmicroorganisms

Clarifier performance is reduced owing todevelopment of filamentous organisms orpoor settling sludge in aeration process

Energy requirement is less Limited suspended solid removal thatrequires a high level of disinfection

Slow rate of kinetic reaction Large footprint

Skilled operation and maintenancepersonnel are available

Subsequent filtration is needed for effectivedisinfection

MBRs

Very high and stable effluent quality High capital and operation costs

High potential for water reuse scenarios More energy consumption

Smaller footprint and compact design More extensive pretreatment required

Low sludge production More chemical cleaning

Possibility of growth of specificmicroorganisms

Inevitable membrane fouling formation

Low suspended solid concentration andremoval of large particles leads to moreeffective disinfection

Fouling mechanism and control still underinvestigation

Lower effluent production capacity

Possible to add nutrient removal processes Low oxygen transfer efficiency

Effluent quality independence from influentquality based on buffering effect of highMLSS values

Pilot scale often needed for full-scale design

Membrane replacement is relativelyexpensive

Adaptable to decentralised and satellitetechnologies

Complicated control systems

Automation is fairly achievable No standard configuration is available

High rate of nitrification owing to longerretention of nitrifying bacteria

Source Adapted from Asano et al (2007)

Membrane technologies for municipal wastewater treatment 449

design requirement is the highest maximum weekly average load throughout the year)European regulations state that regardless of water reusewastewater treatmentpurposes effluent from wastewater treatment plants in Europe must not exceed25 mgL BOD and 125 mgL COD (Bloch 2005)

14222 Emerging membrane-assisted technologies applicationof NFRO after biological treatment

After the conventional secondary or MBR-based treatment the level of treatment canbe further improved by using membranes with tighter pore sizes When an advancedlevel of removal of dissolved organics and inorganics is desired membrane

Figure 142 Configurations of (a) side-stream and (b) submerged MBRs

Table 143 Comparison of sMBRs and iMBRs

Side-stream MBR Immersed MBR

Complexity High Fair

Flexibility High Low

Robustness High Fair

Flux High (40e100 Lm2$h) Low (10e30 Lm2$h)

Fouling Cross-flow Air bubble agitation

Air lift Back-washing (not alwayspossible eg flat-sheet[FS] membranes)

Chemical cleaning Chemical cleaning

Membrane packing density Low High

Energy consumption High (2e10 kWhm3) Low (02e04 kWhm3)

450 Advances in Membrane Technologies for Water Treatment

technologies such as NF and RO can be applied The process of removing dissolvedconstituents can be accomplished by a pressure-driven separation process Nanofiltra-tion and RO require hydrostatic pressure to overcome the osmotic pressure of the feedstream whereas MF and UF separations are based on the pore size and porosity of themembranes and the size of the contaminant constituents Osmotic pressure can be seenwhere two solutions with different solute concentrations are separated by a thin semi-permeable tissue eg a membrane If a difference in chemical potential exists acrossthe membrane water will diffuse through the membrane from the lower concentratedside (higher chemical potential) to the higher concentrated side (lower chemical poten-tial) until a potential equilibrium occurs (the concentrations on both sides are similar)

Nanofiltration and RO are very similar in terms of rejection mechanisms and oper-ation However some fundamental differences make these two technologies distin-guishable from each other for wastewater treatment applications Nanofiltration andRO remove particles with a molecular weight (MW) of 300e1000 gmol and lowerthan 300 gmol respectively Reverse osmosis is capable of removing monovalentions eg sodium and chloride from 98 to 100 whereas NF can reject theseions in the 50e90 range They are also different in terms of water reuse applicationNF is usually used for water softening and reducing the concentration of TDS inreclaimed water whereas RO is used to desalinate seawater and brackish water Thecharacteristics and main applications of each technology are presented in Table 145

1423 Membrane modules

All commercial membrane modules have a particular membrane geometry and orien-tation in relation to the water flow All membrane designs permit modularisation andprovide limited economy scale with respect to membrane costs these are directly pro-portional to the membrane area that correlates directly with the flow (Judd 2011) Theother factor is promoting turbulence which results in a significant increase in energycosts and is adversely affected by high packing densities A lower packing densitywould be preferred for promoting turbulence and hence reducing fouling On the otherhand low packing densities can lead to high membrane unit costs For an efficientmodule narrowing the retentate flow channels is preferred to produce a high mem-brane packing density Six types of membrane modules are commonly applied onan industrial scale

bull Flat sheet (FS)bull Hollow fibre (HF)bull Multi-tubular (MT)bull Capillary tube (CT)bull Pleated filter cartridge (FC)bull Spiral wound (SW)

Flat sheet HF and MT are suitable for MBR technologies owing to the reasonsmentioned above as well as for effective cleaning Modules SW and HF are normallyused in NF and RO technologies mainly because of their high packing densities andsmall pores

Membrane technologies for municipal wastewater treatment 451

Table 144 Typical range of influent and effluent quality after CASPs and MBRs

Constituent Unit Untreated waterConventionalactivated sludge

Activated sludge withbiological nutrientremoval (BNR) MBR

TSS mgL 120e400 50e250 50e200 pound10

BOD mgL 110e350 50e250 50e150 lt10e50

COD mgL 250e800 40e80 200e400 lt100e300

Total organic carbon mgL 80e260 100e400 80e200 05e50

Ammonia nitrogen mg NL 12e45 10e100 10e30 lt10e50

Nitrate nitrogen mg NL 0 to trace 100e300 20e80 lt100a

Nitrite nitrogen mg NL 0 to trace 0 to trace 0 to trace 0 to trace

Total nitrogen mg NL 20e70 150e350 30e80 lt100a

Total phosphorous mg PL 4e12 40e100 10e20 05e20a

Turbidity NTU lt15 20e150 20e80 pound10

Volatile organiccompounds

mgL 100e400 100e400 100e200 100e200

Metals mgL 15e25 10e15 10e15 Trace

Surfactants mgL 40e100 05e20 01e10 01e05

TDS mgL 270e860 500e700 500e700 500e700

Trace constituents mgL 100e500 50e400 50e300 05e200

Total coliforms No100 mL 106e109 104e105 104e105 lt100

Protozoan cystsand oocysts

No100 mL 101e104 101e102 00e100 00e10

Viruses Plaqueeformingunits100 mL

101e104 101e103 101e103 100 to lt103

NoteaWith BNR processSource Adapted from Asano et al (2007)

452Advances

inMem

braneTechnologies

forWater

Treatm

ent

1424 Operational factors of membrane technologiesin wastewater treatment

As one of the most important operational factors flux (J) or permeate is the quantityof fluid passing through a unit area of membrane per unit area (m3m2$s or Lm2$h)The regular flux unit used in wastewater applications is metres per day (md) or litresper metre square per hour (Lm2$h or LMH) Membrane bioreactors are normallyoperated at 0025e0400 md of permeate Transmembrane pressure is another

Table 145 Characteristics of NF and RO applications

Factor Nanofiltration Reverse osmosis

Membrane driving force Hydrostatic pressuredifference

Hydrostatic pressuredifference

Separation mechanisms Sieve electrostatic repulsionsolutiondiffusionexclusion

Electrostatic repulsionsolutiondiffusionexclusion

Pore size (nm) Microspores (lt20) Dense (lt20)

Operating range (mm) 0001e001 00001e0001

Molecular weightcutoff (Da)

300e1000 lt300

Typical removedconstituents

Small molecules colourhardness bacteria virusesproteins multivalent ions

Very small moleculescolour hardness bacteriaviruses proteins nitratesodium multivalent andmonovalent ions

Operating pressure (bar)a 35e55 120e180

Energy consumption(kWhm3)a

06e12 15e25

Membrane configuration Spiral wound (SW) hollowfibre (HF)

SW HF

Typical application Water softening (to reduce theconcentration ofmultivalent ions leading towater hardness) and waterreuse (used for both non-potable and potable waterreuse applications)

Desalination (removingdissolved organics andinorganics for bothseawater and brackishwater) water reuse (usedfor both nonpotable andpotable water reuseapplications)

NoteaBased on treating reused water with a TDS concentration in the range of 1000e2500 mgL It is widely believed that higheroperating pressures are needed for seawaterSource Adapted from Asano et al (2007)

Membrane technologies for municipal wastewater treatment 453

important operational parameter it defines the driving force for solideliquid separa-tion in MBRs or MFUF applications as posttreatment

Other parameters are used to describe the operational characteristics of membraneprocesses in municipal wastewater treatment For example resistance (R) is the ratio ofthe pressure difference (DP) to the flux and viscosity (h) It is inversely correlated tothe permeability (K) The units normally used for resistance and permeability are me1

and LMHbar respectively The resistance in membrane processes for municipalwastewater treatment consists of different components

1 Membrane resistance This component mainly depends on membrane characteristics such asmaterial pore size and surface porosity

2 Resistance of the fouling layer This is normally correlated with filtration mechanismsdepending on feed constituents andor microbial products

3 Solution interfacial region This component is associatedwith concentration polarisation (CP)

143 Membrane fouling in wastewater treatment

Membrane fouling refers to the adsorption and deposition of constituents on a mem-brane surface or in the membrane pores Consequently fouling leads to a reductionin membrane permeability Fouling in general is divided into two subgroups

bull Reversible fouling usually formed on the membrane surface It can be removed by physicalcleaning

bull Irreversible fouling which designates internal fouling in the membrane pores and can beremoved only by chemical cleaning

1431 Characteristics of membrane fouling

Common compounds and materials (foulants) causing membrane fouling can becategorised into four groups (Table 146)

bull Particulate components Small particles can accumulate on the membrane surface conse-quently forming a filter cake This type of fouling is common in MBRs using MF and UF

bull Organic compounds Adsorption of dissolved organics on membrane surface results inmembrane fouling Natural organic matters (NOMs) eg humic substances in drinkingwater filtration processes have a significant role In membrane processes for wastewater treat-ment organics remaining after biodegradation also can contribute to fouling

bull Biofouling This refers to the adhesion and growth of microorganisms on the membranesurface It results in a loss of membrane performance Membrane processes other than MFand UF commonly used in MBRs and posttreatment after conventional ASP NF and ROmay have more biofouling (Jiang 2007)

bull Scaling This occurs when dissolved salts exceed their solubility product This phenomenonis of main concern in the operation of NF and RO with regard to the deposition of salts suchas CaCO4 CaSO4 BaSO4 SrSO4 MgCO3 and SiO2 (Baker 2012)

The interaction between foulants and membrane mainly concerns the phenomenoninvolving colloidal and macromolecular organic matter rather than the particulatesA number of factors can affect this complex interaction (Table 146)

454 Advances in Membrane Technologies for Water Treatment

14311 Electrostatic repulsion

If a colloid or microorganism contains a similar charge to a membrane surface it willbe repelled by the membrane surface as a result of electrostatic forces As a conse-quence the adsorption will be much less Therefore manufacturers develop membranemodules with appropriate membrane surface properties

14312 pH

Various organics compounds present in a wastewater matrix will be more negativelycharged at higher pH conditions because of the proton deficiency This increases thedissociation of protons into the solution In other words pH is likely to influenceelectrostatic repulsion

14313 Hydrophobicity

Opposite hydrophobicity in the microorganisms and the membrane surface also leadsto hydrophobic repulsion this also causes adsorption Many membranes are made ofhydrophilic materials (or coated) which is advantageous in terms of high permeabilityand low affinity with various NOMs

14314 Ionic strength

Adsorption of microorganisms and colloids to the membrane is reduced by the lowionic strength of the feed water For example in the filtration of proteins andNOMs screening of the charges is decreased at a low ionic strength As a result thesemolecules repel each other at the membrane surface

1432 Concentration polarisation

Concentration polarisation relates to the continuous transport of polluted influent to themembrane surface and the selective retention of some constituents that leads to theaccumulation of some solutes on or near the membrane surface Over the operationtime their concentration increases consequently a boundary layer of higher concen-tration is created This layer contains near-stagnant fluid and the velocity at the mem-brane surface is zero It means that the only transport mode within this layer isdiffusion The concentration build-up causes a particle back-transport flux into thebulk Cross-flow filtration can improve particle back-transport and reduce foulingbecause higher flux leads to higher diffusion

1433 Fouling mechanisms in MBRs

Fouling mechanisms observed in MBRs can be divided into four different groups

14331 Complete blocking

Complete blocking refers to the situation in which each particle upon arriving at themembrane surface participates in blocking some pore with no superposition of parti-cles These particles have sizes comparable to the membrane pore sizes

Membrane technologies for municipal wastewater treatment 455

Table 146 Characteristics of different types of foulants

Particulate fouling Organic fouling Biofouling Scaling

Foulants Colloid suspended solids Organic matters Microorganisms Salts metal cations

Major factors affectingfouling

Concentration particle sizedistributioncompressibility ofparticles

Concentration chargehydrophobicity pH ionicstrength calcium

Temperature nutrients Temperatureconcentration pH

Fouling predictionindicator

Silt density indexModified fouling indexspecific resistance tofouling

Dissolved organic carbon (DOC)ultraviolet254 (UV254) specificultraviolet adsorption (SUVA)

Assimilable organiccarbon biofilmformation rate

Solubility

Feed water pretreatment Coagulation MF and UF Adjustment of pH coagulation Sand filtration biofiltercoagulationflocculation MF UF

Acid antiscalant

Source Jiang (2007)

456Advances

inMem

braneTechnologies

forWater

Treatm

ent

14332 Standard blocking

This mechanism refers to conditions under which particles are deposited onto the in-ternal pore walls This leads to a decrease in pore volume

14333 Cake filtration

Cake filtration is defined as a phenomenon in which each particle locates on the otherdeposited particles It implies that there is no room for particles to directly obstruct themembrane area

14334 Intermediate blocking

Intermediate blocking is pronounced when each particle can either settle on other par-ticles that have already arrived or directly block some membrane area It may beconsidered an intermediate step between complete blocking and cake filtration(Bowen Calvo amp Hernandez 1995)

1434 Fouling control chemical and physical cleaning

Membrane cleaning is achieved by physical and chemical cleaning Physical cleaningis usually accomplished by backwashing and relaxation in wastewater treatment bymembrane-assisted technologies Backwashing is simply referred to reversing theflow toward membranes whereas relaxation is defined as ceasing permeation to scourthe membrane with aeration (air bubbles) On the other hands chemical cleaning isachieved with some mineral and organic acids caustic soda and sodium hypochloriteSometimes the cleaning process can be carried out with backwashing with the additionof a lower concentration of a chemical agent (chemically enhanced backwash) Table147 compares various cleaning methods

In most membrane-assisted technologies fouling control is determined by consid-ering the balance between flux physical and chemical cleaning and CP control Con-trolling and reducing CP-related fouling can be divided into two methods (Judd 2011)

bull Promoting turbulence This reduces the thickness of the boundary layer Promoting turbu-lence in iMBRs and sMBRs can be achieved by increasing membrane aeration andincreasing cross-flow velocity respectively

bull Reducing flux This decreases fouling formation on the membrane surface

A successful MBR project the cleaning method at the Nordkanal wastewatertreatment plant in Germany is summarised (Blastakova Engelheardt Drensla ampBondik 2009)

bull Physical cleaning by employing air scouring backwashing and relaxation of filters duringthe time of low inflow when the installed capacity is reduced by 125

bull Chemical cleaning by using backwashing with chemical cleaning agents for maintenancecleaning in place in biomass andor on air and occasional intensive cleaning out of place

bull Additional mechanical cleaning to remove debris from the membrane modules after COPwhen necessary

Membrane technologies for municipal wastewater treatment 457

144 Design operation and control of membraneprocesses in municipal wastewater treatment

Various process components of the entire technology need to be considered whendesigning membrane-assisted technology Wastewater characteristics and the pur-pose of wastewater treatment are important factors in the design of membranetechnologies

The required membrane surface area is a function of the membrane flux and hy-draulic load The net flux is an important parameter that characterises the averageflow rate including the relaxation and backwash phases (Li Fane Ho amp Matsuura2008) With the help of net flux the treatment capacity of the whole plant is esti-mated The normal range for the maximum fluxes of iMBRs in municipal waste-water treatment is 25e30 L(m2$h) with a net flux about 20 lower In termsof the optimal operation of a pilot-scale plant it is usually recommended to recordthe initial flux and test different cleaning strategies to reconcile fouling controlmeasures cleaning procedures and required flux Estimation of recycle ratio andan appropriate flow regime and filtration tank are important steps in the designand operation of membrane technologies Some important parameters and theirvalue ranges for NF and RO are summarised in Table 145 Regarding operationalissues the membrane lifetime is important It is directly correlated to operation andmaintenance costs eg repair replacement and operation efficiencies Operatingefficiencies can be considered a consequence of the membrane lifetime and perfor-mance stability (Asano et al 2007) The following factors have a high impact on

Table 147 Comparison between physical and chemical cleaning

Physical cleaning Chemical cleaning

Methods Backwashing without air Base (eg caustic sodacitric oxalic)

Backwashing with air Acid (eg hydrochloricsulphuric citricoxalic)

Relaxation Oxidant (eg hydrogenperoxide hypochlorite)

Advantages Simpler and less complex Much higher cleaningefficiencies (generally)

No chemical neededconsequently no chemicalwaste

Capable of returning flux tooriginal or betterconditions

No membrane degradation Capable of removingtenacious materials frommembrane surface

Capable of removing gross solids

458 Advances in Membrane Technologies for Water Treatment

the operational efficiency of all membrane technologies in municipal wastewatertreatment (Celenza 2000)

bull Consistent membrane fouling involving frequent and long regeneration timesbull Membrane failure and then replacementbull Failure of high-pressure pumpsbull Failure of membranes and pumps as a result of abrasive waste materials and components

145 Optimisation of membrane processes in municipalwastewater treatment

1451 Cost assessment

Cost assessment in most membrane technology projects is divided into capital costs(CAPEX) and operation and maintenance (OPEX) costs Generally it is challengingto obtain an appropriate cost assessment It is evident that membrane prices have grad-ually decreased and are still slowly dropping Judd (2011) reported that the prices ofMBRs in the United Kingdom decreased from 320 to 80 Vm2 membrane surface areafrom 1992 to 2000 However the other parts of these systems (eg aeration devicescontrol systems cleaning devices and pipes) are almost at the same prices Moreoverit is reported that at different wastewater treatment plants with MBRs eg the plant atNordkanal Germany the space requirement could be significantly reduced comparedwith conventional design capacity planning (Blastakova et al 2009 Henze vanLoosdrecht Ekama amp Brdjanovic 2008) Consequently capital costs would be sub-stantially decreased Investment costs for the Nordkanal MBR wastewater treatmentplant amounted to V215 million (including VAT) In addition approxV32 million was spent for engineering special consults acquisition of land andcharges for environmental compensation (Blastakova et al 2009) Life cycle costanalysis which can be defined as a sensitivity analysis on uncontrollable expendituresshows that although the capital cost often needs enormous investment a more capitalintensive technology might be selected when the OampM costs are more reasonable andcontrollable (Li et al 2008)

1452 Energy efficiencies and operational costs

There are a number of equations and evaluation methods for energy efficiency in waterreuse technologies but according to Li et al (2008) most of these formulas whichwere developed a few decades ago have not been updated and reconsidered properlyTherefore it is necessary to revisit these evaluation methods especially because of thedevelopment of new technologies with different materials and methods of construc-tion Various factors are associated with energy consumption and operational costsHydraulic factors have an important role in improving energy efficiency Aging infra-structures and redundant equipment should also be taken into consideration Otherimportant factors for this evaluation are the appropriate adaptation and replacement

Membrane technologies for municipal wastewater treatment 459

of membranes and other parts of membrane-assisted technologies to ensure acceptableenergy efficiency

The aeration process may be considered a major part of total energy demand andoperational costs The energy consumption of aeration in MBRs in a normal waste-water treatment plant is about 04 kWhm3 effluent whereas in CASPs it is in the rangeof 025e040 kWhm3 (Krause 2005) Fouling control is another main part of energyconsumption The cost of chemical cleaning regardless of the energy demand is about02e10 Vm2 membrane surface area per year (Li et al 2008) Based on a biologicalactivated sludge model study of the Schilde MBR the energy consumption of theentire MBR is 063 kWhm3 with a yearly average permeate production of 220 m3h Therefore the energy cost can be determined as 220 m3h 24 hd 365 dyr 063 kWhm3 008VkWfrac14 97130Vyr In this evaluation the energy consump-tion for coarse bubble aeration compressors warming of the permeate for cleaningmixing energy and pretreatment are 352 31 66 70 and 26 respec-tively for a total of 540 of the total energy when the system is operated at220 m3h (Greenlee Lawler Freeman Marrot amp Moulin 2009) Blastakova et al(2009) reported that with the Nordkanal wastewater treatment plant at full capacityspecific energy consumption ranges between 04 and 08 kWhm3 wastewater Onaverage the energy demands of membrane air scouring process aeration bioreactormixing permeate suction and biomass circulation are 49 121 115 27and 13 respectively The remaining 232 is consumed by pumping stations pre-treatment dewatering units and miscellaneous process units (Blastakova et al 2009Judd 2011)

Membrane lifetime is also an important factor in cost assessment Studies haveshown that membrane lifetime relates to the composition and pretreatment of thewastewater membrane material module construction and cleaning strategies (Liet al 2008) Moreover toward the end of an effective membrane lifetime energy con-sumption can increase to 170 owing to the reduced flow rate (Fenu et al 2012)

146 Future trends and conclusion

Emerging global issues such as rapid urbanisation increasing water pollution andclimate change have resulted in water scarcity in many regions of the world As aresult improvement in water quality treatment technologies and a move toward waterreuse are increasingly being adapted to satisfy growing water demand From a sus-tainability point of view wastewater treatment and reuse will be essential placingresultant responsibility on wastewater treatment companies to provide clean waterto suite end users Membrane-assisted technologies are an undisputed part of high-quality wastewater treatment and reuse systems However there are still variouschallenges and issues eg high CAPEX and OPEX costs low flow rate andoperational complexities In looking to develop new approaches it is importantto be able to meet both existing and new water reuse regulations and guidelinesconsistently Regarding future regulations and guidelines the additional issue is toconsider removing micropollutants and emerging contaminants such as PhACs

460 Advances in Membrane Technologies for Water Treatment

endocrine-disruptive compounds and personal care products legislation shouldclearly require their removal

Furthermore development of new membrane technologies is needed that can beless expensive in terms of investment and OPEX andor more effective in terms of wa-ter quality New membranes have been successfully developed using different mate-rials but they still need improvement For example according to Howell (2004) it ispossible to make HF membranes with different materials the membranes can beconcentric leaving an annular gap that can be filled by microorganisms so as to createan MBR in which feed streams and product streams can be totally separated or wheredifferent nutrients can be supplied from two different streams Various ongoing devel-opments may lead to the emergence of cost-effective and energy-efficient membranetechnologies that can transform municipal wastewater treatment practices for higheffluent-quality production with a high potential of water reuse

List of acronyms and abbreviations

AnMBR Anaerobic biodegradation processASM Activated sludge modelASP Activated sludge processBOD Biochemical oxygen demandCAPEX Capital costsCASP Conventional activated sludge processCIP Cleaning in placeCOD Chemical oxygen demandCOP Cleaning out of placeCP Concentration polarisationCT Capillary tubeDOC Dissolved organic carbonEDCs Endocrine disturbing compoundsFC Pleated filter cartridgeFS Flat sheetHF Hollow fibreiMBR Immersed membrane bioreactorK PermeabilityMBBR Moving biofilm bioreactorMBR Membrane bioreactorMF MicrofiltrationMLSS Mixed liquor suspended solidsMT Multi-tubularMW Molecular weightMWCO Molecular weight cutoffNF NanofiltrationNOMs Natural organic mattersOPEX Operation and maintenance costsPCPs Personal care productsPhACs Pharmaceutically active compounds

Membrane technologies for municipal wastewater treatment 461

R ResistanceRO Reverse osmosisRSS Residual suspended solidssMBR Side-stream MBRSOCs Soluble organic compoundsSRT Solids retention timeSUVA Specific ultraviolet adsorptionSW Spiral woundTMP Transmembrane pressureTN Total NitrogenTSS Total suspended solidsUF UltrafiltrationUV254 Ultraviolet254h ViscosityDP Pressure difference

References

Asano T Burton F L Leverenz H L Tsuchihashi R amp Tchobanoglous G (2007) Waterreuse Issues technologies and applications New York Metcalf amp Eddy Inc

Baker R W (2012) Membrane technology and applications (3rd ed) Chichester New YorkJ Wiley

Blastakova A Engelheardt N Drensla K amp Bondik I (2009) Operation of the biggestmembrane waste water treatment plant in Europe In The 36th international conference ofSlovak society of chemical engineering Slovak University of Technology in BratislavaISBN 978-80-227-3072-3

Bloch H (2005) European Union legislation on wastewater treatment and nutrients removal(pp 1e8) Marlow UK European Commission Directorate General Environment Foun-dation for Water Research

Bowen W R Calvo J I amp Hernandez A (1995) Steps of membrane blocking in flux declineduring protein microfiltration Journal of Membrane Science 101(1e2) 153e165 httpdxdoiorg1010160376-7388(94)00295-A

Celenza G J (2000) Industrial waste treatment process engineering Specialized treat-ment system (vol III) Lancaster Basel PA Technomic Publication Co Inc

de Wilde W Richard M Lesjean B amp Tazi-Pain A (2008) Towards standardisation of theMBR technology Desalination 231(1) 156e165

Fenu A DeWildeWGaertnerMWeemaesM deGueldre G ampVanDe Steene B (2012)Elaborating the membrane life concept in a full scale hollow-fibers MBR Journal ofMembrane Science 421e422 349e354 httpdxdoiorg101016jmemsci201208001

Greenlee L F Lawler D F Freeman B D Marrot B amp Moulin P (2009) Reverseosmosis desalination Water sources technology and todayrsquos challenges Water research43(9) 2317e2348 httpdxdoiorg101016jwatres200903010

Henze M van Loosdrecht M C M Ekama G A amp Brdjanovic D (2008) Biologicalwastewater treatment Principles modelling and design (pp 1e528) London UK IWAPublishing

Howell J A (2004) Future of membranes and membrane reactors in green technologies and forwater reuseDesalination 162(0) 1e11 httpdxdoiorg101016S0011-9164(04)00021-9

462 Advances in Membrane Technologies for Water Treatment

Jiang T (2007) Characterization and modelling of soluble microbial products in membranebioreactors (p 241) Belgium Ghent University

Judd S (2011) The MBR book principles and applications of membrane bioreactors in waterand wastewater treatment (2nd ed) Oxford UK Elsevier Ltd

Kraemer J T Menniti A L Erdal Z K Constantine T A Johnson B R amp Daigger G T(2012) A practitionerrsquos perspective on the application and research needs of membranebioreactors for municipal wastewater treatment Bioresource Technology 122 2e10httpdxdoiorg101016jbiortech201205014

Krause S (2005) Undersuchungen zum Energiebedarf von MembranelebungsanlagenUnpublished PhD Technische Universitaet Darmstadt

Li N N Fane A G Ho W S W amp Matsuura T (2008) Advanced membrane technologyand applications Hoboken New Jersery USA John Wiley amp Sons Inc ISBN9780471731672

Shannon M A Bohn P W Elimelech M Georgiadis J G Mari~nas B J amp Mayes A M(2008) Science and technology for water purification in the coming decades Nature452(7185) 301e310

Stephenson T Judd J Jeferson B amp Brindle K (2000) Membrane bioreactors forwastewater treatment (1st ed) London IWA Publishing ISBN 1 900222 07 8

Yamamoto K Hissa M Mahmood T amp Matsuo T (1989) Direct solid liquid separationusing hollow fibre membrane in an activated sludge aeration tank Water Science ampTechnology 21 43e54

Membrane technologies for municipal wastewater treatment 463

Membrane technologies for theremoval of micropollutants inwater treatment

15M BodzekInstitute of Environmental Engineering of the Polish Academy of Sciences Zabrze PolandSilesian University of Technology Institute of Water and Wastewater EngineeringGliwice Poland

151 Introduction

In the treatment of natural water for drinking and household needs and industrialwastewaters pressure-driven membrane techniques are principally applied Otherprocesses are taken into consideration as well such as electrodialysis (ED) and electro-deionization (EDI) Donnan dialysis (DD) and diffusion dialysis membrane contac-tors and bioreactors The choice of an appropriate membrane process depends onthe scope of removed effluents and admixtures present in water They can be usedto remove effluents as independent processes or be combined with unit complementaryprocesses forming a treatment process line Potential membrane techniques in thetreatment of natural waters and wastewaters are

bull Reverse osmosis (RO) which retains monovalent ions and most low-molecular organic com-pounds - principally desalination of waters and removal of inorganic and organicmicropollutants

bull Nanofiltration (NF) which retains colloids low-molecular organic compounds and bivalentions - softening and removal of micropollutants from water

bull Ultrafiltration (UF) and microfiltration (MF) clarification methods for the removal ofturbidity retention of suspended substances and microorganisms and disinfection

bull Hybrid processes covering membrane techniques especially UF and MF with coagulationadsorption onto activated carbon and in bioreactors and treatment of drinking water andwastewaters

bull Processes with ion-exchange membranes (ED and EDI and DD and diffusion dialysis) toremove inorganic pollutants

bull Membrane bioreactors (MBRs) for the removal of organics and to some extent inorganics

Increasingly numerous micropollutants occur in the degenerated water environmentmainly in surface waters but also in underground waters Micropollutants in surfacewaters come from rainfall sewage industrial wastewaters and landfill leachate aswell as earth flow from the drainage area The concentration of micropollutants in sur-face waters depends on their source and the pollution grade of the drainage area andsewage Pollutants and organic additives present in natural waters are mainly dispersedsubstances and microorganisms organic compounds including natural organic matter

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400015-0Copyright copy 2015 Elsevier Ltd All rights reserved

(NOM) endocrine active compounds (EAC) and pharmaceutical residues and personalcare products as well as inorganic substances such as heavy metals and toxic anions

152 Inorganic micropollutant removal

A number of inorganic compounds including anions (nitrate (V) chlorate (VII) (V)and (III) bromate (V) arsenate (III) and (V) borate and fluoride) and heavy metalshave been found at potentially harmful concentrations in natural water sourcesand wastewaters (Bodzek amp Konieczny 2011a 2011b Bodzek Konieczny ampKwiecinska 2011 Crespo Velizarov amp Reis 2004 Velizarov Crespo amp Reis2004 Velizarov et al 2008) Some of these compounds are highly soluble in waterand dissociate completely resulting in the formation of ions that are chemically stableat normal water conditions The maximum permissible levels of these compounds indrinking water and wastewaters discharged to environment set by the World HealthOrganization (WHO) and a number of countries are very low (in the range of micro-grams per liter to a few milligrams per liter) Thus most of them can be referred to ascharged micropollutants

Pollution of the aquatic environment with metals and anions may be of either nat-ural or anthropogenic origin Several common treatment technologies includingcoagulationesedimentationefiltration chemical precipitation adsorption ion-exchange classical solvent extraction evaporation and biological methods whichare currently used to remove inorganic contaminants from natural waters or wastewa-ters represent serious exploitation problems (Bodzek amp Konieczny 2011a 2011bCrespo et al 2004 Velizarov et al 2004 2008) Increasingly membrane processesare applied to remove inorganic micropollutants from the aquatic environment Pri-marily RO NF UF and MF in hybrid systems DD and ED as well as these com-bined with extraction (liquid membranes) and bioreactors are used (Bodzek ampKonieczny 2011a 2011b Bodzek et al 2011 Crespo et al 2004 Velizarov et al2004 2008)

1521 Anion removal

15211 Pressure-driven membrane processes

The RO process is highly efficient in directly removing inorganic anions during drink-ing water production In addition it guarantees safe detoxification However completedesalination is undesirable because of possible corrosion problems and remineraliza-tion requirements (Kołtuniewicz amp Drioli 2008) Water with a hardness below50 mgL is corrosive to copper iron zinc and other metals (Bodzek amp Konieczny2011a 2011b Bodzek et al 2011) As a result other processes suitable for selectiveremoval of toxic anions and moderate desalination are desired Nanofiltration fulfillssuch requirements because it enables selective desalination ie the separation of poly-valent ions from monovalent ions with the higher capacity obtained for lower trans-membrane pressures compared with RO process Asymmetric membranes used in

466 Advances in Membrane Technologies for Water Treatment

NF have a negative electrical charge in neutral and alkaline solutions Thus the sepa-ration of anions consists of the difference in the rate of transport through a membranebut also the electrostatic repulsion between anions and the membrane surface chargewhich is greater for polyvalent ions than for monovalent anions (Velizarov et al 2004)Charge of the surface of NF membranes results in the presence of functional groupspossessing an electrical charge but also in the adsorption of anions from water Hencethe charge of a membrane surface depends on the concentration of anions in the solu-tion (Velizarov et al 2004) and varies from negative values to zero in the isoelectricpoint of a membrane up to positive values in an acidic environment (usually pH lt 4)when the adsorption of cations takes place The NF process is much more sensitive tothe ionic strength and pH of raw water than RO hence the selection of proper processconditions is crucial to its application Many studies considering the removal of toxicanions from natural waters and purified wastewaters by means of RO and NF have beenperformed Promising results were obtained in a significant part of them (Bodzek ampKonieczny 2011a 2011b Velizarov et al 2004)

The pollution of natural waters with nitrates (V) is a result of the application of ni-trogen fertilizers and the disposal of municipal and industrial solid and liquid wastesinto the environment (Bodzek amp Konieczny 2011a 2011b) Ion exchange RO EDand biological denitrification are the methods most often used to remove excessiveamounts of nitrates (Bodzek amp Konieczny 2011a 2011b Kołtuniewicz amp Drioli2008) Nitrates can have several adverse effects on human health the most notableare methemoglobinemia gastric cancer and non-Hodgkinrsquos lymphoma (Raczuk2010) The RO process allows the amount of NO

3 in drinking water to be decreasedto the level established in regulations (10 mg NL) Reverse osmosis membranes arecharacterized by high values for the retention coefficient of inorganic salts Thusthe required decrease in NO

3 concentrations in drinking water can be achieved bymixing permeate and raw water (Bodzek amp Konieczny 2011a Kołtuniewicz amp Drioli2008) Nitrates as monovalent ions are not totally retained by NF for example theretention coefficient of NO

3 for an NF-70 membrane (DowFilmTec) is equal to76 which is lower than for an RO membrane (Van der Bruggen amp Vandecasteele2003) Nanofiltration can be also used as a first step in the NO

3 removal process incombination with RO or ion exchange (Bodzek amp Konieczny 2011a Kołtuniewiczamp Drioli 2008) However the presence of sulfates decreases the retention coefficientof NO

3 ions during NF Under such conditions NF membranes practically do noteliminate NO

3 nevertheless they retain multivalent ions (Ca and Mg) which has apositive effect on RO and ion-exchange performance Relative purification costs ofboth processes are comparable with the costs of ion exchange and ED including thecosts of disposing the concentrate

Reverse osmosis and NF membranes used to remove nitrates from water are twiceas expensive as membranes applied in low-pressure membrane processes Moreovertheir application is much more energy-consuming because they require a much higherpressure Hence alternative methods consisting of UF membranes and surfactants orpolymers complexing nitrate ions are applied (Kołtuniewicz amp Drioli 2008) Com-plexes or micelles containing nitrate ions can be retained by UF membranes Forthe application of UF membranes at a surfactant concentration below the critical

Membrane technologies for the removal of micropollutants in water treatment 467

concentration of micelle formation the rate of removal of nitrate ions exceeds 79depending on the type and dose of surfactant used (Kołtuniewicz amp Drioli 2008)

Contamination of drinking water with bromates (V) ethBrO3 THORN is usually associated

with the formation of disinfection by-products (DBP) during ozonation of waters con-taining bromides (Bre) The concentration of BrO

3 in natural waters varies between 15and 200 mgL whereas the larger content appears in the groundwater Removal ofBrO3

in the NF process reaches up to 75100 with an initial content of 285 mgLwhereas for the RO process an average retention coefficient of 97 is obtained (ButlerGodley Lytton amp Cartmell 2005) Prados-Ramirez Ciba and Bourbigot (1995)observed 77 removal of BrO

3 and 63 of Bre using NF membranes to treat riverwater at the initial concentration of BrO

3 amounting to 300 mgL They found thatthe NF was more economical in terms of cost mainly as a result of the lower pressureapplied Disadvantages of these techniques include the deep deionization of permeatewhich requires remineralization and the formation of a waste stream ie retentate(concentrate) which needs to be treated before discharge into the environment

Because of widespread use high mobility in natural waters and a low tendency todegrade chlorates (VII) constitute a serious environmental problem mainly because oftheir toxicity and negative impact on the development and function of the human or-ganism Studies have shown that RO and NF can be applied to remove ClO

4 fromaqueous solutions (Bodzek amp Konieczny 2011b Lee et al 2008) For NF ClO

4retention amounts are up to 75e90 whereas for RO it is 96 at an initial concen-tration of 100 mg ClO4L (Bodzek amp Konieczny 2011a 2011b) High-pressure ROmembranes allow even 999 of ClO

4 ions to be removed for low-pressure ROmem-branes the retention coefficient of ClO

4 is lower (95) (Anonymous 2008) Hencein some cases additional treatment of permeate before its introduction into the waternetwork may be required eg by means of ion exchange or adsorption on activatedcarbon or in bioreactors (Anonymous 2008) In principle RO can be used as a stand-alone technology to remove chlorates (VII) during the production of drinking wateronly at low ClO

4 concentrations Because RO and NF are not destructive processesretentate contains chlorate (VII) and other pollutants that must be removed beforedischarge into the environment In general biological treatment and evaporation aretaken into consideration (Anonymous 2008)

The appearance of fluorides (F) in natural waters is a result of their presence in thelithosphere and anthropogenic industrial activity According to the WHO themaximum fluoride concentration in drinking water is established at 15 mgL(Kołtuniewicz amp Drioli 2008 Velizarov et al 2004) Adsorption coagulation withsedimentation ion exchange and membrane processes ie RO NF and ED arethe main methods proposed to remove fluorides from water (Bodzek amp Konieczny2011a 2011b) The application of RO to fluoride removal is connected with the partialdemineralization of water which is the main disadvantage of the process(Kołtuniewicz amp Drioli 2008) Reverse osmosis membranes for water desalinationallow the removal of 9899 of salts which results in the almost total retention offluorides eg below 003 mgL compared with the initial content range of13e18 mgL (Sehn 2008) During the treatment of water characterized by a highfluoride content the application of NF is beneficial because the remineralization of

468 Advances in Membrane Technologies for Water Treatment

permeate is not always required The final concentration of F ions in permeate ob-tained for commercially available NF membranes ie NF-90 and NF-270 (FilmTec)and TR-60 (Toray) was in the range of 005e40 mgL depending on the initial con-centration and membrane type (Tahaikt et al 2008) Results obtained during similarstudies confirmed the possibility of producing drinking water from brackish water witha high fluorides content using other commercial NF membranes ie NTR-7250NTR-7450 F-70 (FilmTec) Desal-5-DL and Desal 51-HL (Osmonics) MT-08(PCI) and SR-1 (Koch) (Hu amp Dickson 2006) Analysis of the retention of monova-lent ions for NF membranes indicates that smaller ions (fluorides) are retained moreefficiently than other halogen ions (eg chlorides) The difference in selectivity resultsfrom differences in the hydration energy of particular ions because higher energycauses better retention (a hydration energy of F equals 515 kJmol whereas for Cl

it is 381 kJmol) (Hu amp Dickson 2006) This explains the possibility of selective desa-lination of brackish water containing F using NF and allows drinking water to be pro-duced less expensively than when RO is applied

Besides RO and NF a membrane coagulation reactor (MCR) ie a combination ofcoagulation and MF can be used to remove fluorides during drinking water production(Zhang Gao Zhang amp Gu 2005) In the MCR aluminum salt is used as the coagulantand its hydroxide is the adsorbent Sodium hydroxide can be added to provide hydrox-ide ions and adjust the pH during coagulation and adsorption Hydrolysis (Eqn (151))coprecipitation (Eqn (152)) and adsorption (Eqn (153)) may occur when A12(SO4)3and NaOH are simultaneously added into raw water The primary fluoride removalmechanism results in the low solubility constant of Al(OH)3 (solubility product19 1033) and hard dissolution of the aluminumefluoride complex Thus theyare precipitated out of the solution or can be separated by the MF membrane

Al3thorn thorn 3OHAlethOHTHORN3Y (151)

Al3thorn thorn 3 x

OH thorn xFAlethOHTHORN3xFxY (152)

AlethOHTHORN3 thorn xFAlethOHTHORN3xFxYthorn xOH (153)

Boron appears in the environment mainly in the form of boric acid (H3BO3) and itssalts (Bick amp Oron 2005 Kołtuniewicz amp Drioli 2008) At a lower pH the hydrationof boric acid does not occur which causes its low retention during membrane separa-tion The dissociated form of the contaminant is totally hydrated and is characterizedby a greater diameter and negative ion charge resulting in higher retention (Bick ampOron 2005) In the European Union the permissible concentration of boron in drink-ing water is 10 mgL whereas for industrial wastewater disposed to sewage it is10 mgL (Bick amp Oron 2005) Boron is removed from the environment mainly bymeans of coagulation and electrocoagulation adsorption and ion exchange as wellas membrane processes ie RO NF ED and polymer-enhanced UF (PEUF) (Bickamp Oron 2005 Bodzek amp Konieczny 2011a 2011b Bodzek et al 2011) Howeveronly two of those methods are used in the industry ie RO at high pH conditions andion exchange (Bick amp Oron 2005)

Membrane technologies for the removal of micropollutants in water treatment 469

The removal of boron compounds from natural waters by means of RO is especiallyimportant because any of the conventional desalination methods (distillation or ED)are capable of reducing boron content to a permissible level The retention of boronat low or neutral pH varies from 40 to 60 which is insufficient to obtain a permis-sible level for drinking water but also for seawater desalination or water disposed intothe environment On the other hand high pH process conditions lead to fouling andscaling which are mainly caused by the precipitation of calcium and magnesium com-pounds Thus RO permeate is alkalized to pH c 95 and once more treated by RO orion exchange (Figure 151) (Bick amp Oron 2005 Bodzek amp Konieczny 2011a 2011bKołtuniewicz amp Drioli 2008) The cost of boron removal via the two-step process ishigh usually multistep (34 steps) RO processes are applied (Kołtuniewicz amp Drioli2008) Hence second- and third-stage RO membranes are operated at lower concen-trations and pressure Currently studies are focusing on developing and testing novelRO membranes that can be applied in a one-step process

UF and MF can also be used to remove boron from water An interesting solution isthe hybrid process of sorption-membrane separation used in boron removal fromseawater or the permeate after seawater desalination with RO Boron is removed byion-exchange resins (eg Dowex XUS 43594 Dow Chemicals Diaion CRB01Mitsubishi) of very small grain size (20 mm) and after the sorption the resin is sepa-rated by means of MF The small size of grains of resin causes the boron content todecrease after 2 min from 2 mgL to 02430124 mgL depending on the dose ofion exchanger (025e10 gL) (Dilek Ozbelge Bicak amp Yilmaz 2002) Other studieshave focused on removing boron from water solutions using PEUF usually withpoly(vinyl alcohol) (PVA) or other specially synthesized polymers (Dilek et al2002) The process consists of two stages the complexation of boron with a polymerand the separation of complexes by a capillary UF membrane (Dilek et al 2002)However a decrease in the boron retention coefficient is observed during the process(starting from values close to 1) as the number of active centers of the chelating poly-mer decreases The retention also depends on pH and boron and polymer concentra-tions in the feed

Inorganic arsenic occurs in water in anionic forms as As(III) and As(V) and alower-oxidation stage dominates in groundwater and a higher one in surface watersAt a pH close to neutral As(III) occurs in the form of inert molecules H3AsO3 andAs(V) as H2AsO

4 HAsO24 and AsO3

4 The form of As(V) ions has a direct impact

Raw water1st stage RO 2nd stage RO

2nd stagepermeate

Brine

Ionexchange

Cleanwater

NaOH

Figure 151 Two-stage RO system for boron removal (Bodzek amp Konieczny 2011a 2011b)RO reverse osmosis

470 Advances in Membrane Technologies for Water Treatment

on the choice and effectiveness of the treatment method To decrease arsenic content indrinking water RO and NF membranes as well as a hybrid process of coagula-tioneMFUF are applied (Bodzek amp Konieczny 2011a 2011b Shih 2005) Reverseosmosis membranes eg TFC-ULP (Koch) allow 99 of arsenic to be removed fromgroundwater (a decrease from 60 to 09 mgL) whereas DK2540F membranes (Desal)retain 8896 of the pollutant (Shih 2005) The amount of As(III) removed is alwayslower than for As(V) and oxidizing conditions during the process are recommended(Pawlak Zak amp Zabłocki 2006) The pH and the content of dissolved organic matterhave a great influence on arsenic removal The rate of As(V) removal at pH 3 reaches80 whereas it can be up to 95 at pH 5e10 (NTR-729HF membrane) A higherremoval of arsenic(V) (90) is observed for waters with a lower organic matter con-tent whereas compared with a higher concentration of organics it is equal to 80(Pawlak et al 2006) Other laboratory and pilot research on arsenic removal usingRO membranes has been performed (Bodzek amp Konieczny 2011a 2011b) NF mem-branes can be also applied for As removal For NF-70 FilmTec membrane 97removal of As(V) is obtained and for NF-45 membrane it varies from 45 to 90depending on the initial concentration of the pollutant in water (Nguyen BangCho amp Kim 2009) In the case of As(III) as for RO retention coefficients aremuch lower and decrease from 20 to 10 with an increase in the pollutant concen-tration in water The rate of removal of As(V) with the use of NF-45 membrane signif-icantly increases with an increase in pH (Shih 2005) according to the difference in Asion hydration An influence of pH in the range of 4e8 on the retention coefficient ofAs(III) was not observed which indicates that the mechanism of arsenic removal usingNF membranes is based on both sieving separation and electrostatic repulsion betweenions and the charged membrane surface Microfiltration and UF can be also used toremove arsenic from water but mainly by means of integrated systems with coagula-tion (Han Runnells Zimbron amp Wickramasinghe 2002 Shih 2005) For examplefrom water with an As content equal to 40 mgL water containing less than 2 mgLAs can be obtained using ferric coagulants and membranes with a pore size of 022and 122 mm (Shih 2005) In the integrated process As removal is caused by theadsorption of As on coagulation flocks and the separation of those flocks by the MFmembrane In such a case the removal of As(III) is also less effective than that ofAs(V) and preliminary oxidation of As(III) to As(V) is often required

15212 Ion-exchange membrane processes

Donnan dialysis is a process that uses an ion-exchange membrane without applying anexternal electric potential difference across the membrane (Velizarov et al 2004Wisniewski 2001) For anion removal anion-exchange membranes are used whereasfor cation removal cation-exchange membranes are employed (Figure 152) Mem-branes separate two solutions ie raw solution and stripping solution (concentrate)that differ in both composition and concentration The type of operation such as DDrequires the addition of a so-called driving counter-ion to the stripping solution (usu-ally an NaCl solution of 01e1 M concentration is used) which is transported in theopposite direction of the target anion or cation to maintain electroneutrality

Membrane technologies for the removal of micropollutants in water treatment 471

(Figure 152) (Bodzek amp Konieczny 2011b Wisniewski 2001) The ions which arepermeable to the membrane equilibrate between the two solutions until the Donnanequilibrium is obtained Because the concentration differences and their ratios deter-mine the Donnan equilibrium DD allows the charged micropollutants to be transportedagainst their concentration gradients which is important for drinking water suppliesbecause they usually contain only trace amounts of polluting ions As a result of itsproperties DD has received attention in the removal of inorganic ions from drinkingwater especially nitrates (V) and fluorides and some cations (Velizarov et al 2004)

Because the mechanism of ion transport in DD is governed solely by the Donnanequilibrium principle the ion fluxes achieved may be low for certain applicationsIn ED the transport of ions is accelerated owing to an externally applied electric po-tential difference which allows one to obtain higher anion fluxes than those in DD Inthis process anion-exchange and cation-exchange membranes are applied alternatelywhich allows solutions of varying concentration (diluate and concentrate) to be ob-tained (Bodzek amp Konieczny 2011b Velizarov et al 2004) The ED systems are usu-ally operated in the so-called ED reversal (EDR) mode to prevent membrane foulingand scaling Because most known toxic anions are monovalent the use of monovalentanion permselective exchange membranes is especially attractive (Velizarov et al2004) The suitability of ED depends strongly on the ionic composition of contami-nated water Thus the process appears to be less applicable to waters of very lowsalinity (conductivity less than 05 mS) for which DD can be a better solution In casesin which low-molecular-weight non-charged compounds besides ion removal is neces-sary pressure-driven membrane processes may be preferable Successful applicationsof ED and EDR include the removal of various anions eg nitrates (V) bromates (V)chlorates (VII) arsenic (V) boron and fluorides as well as various heavy metals(Velizarov et al 2004 Wisniewski 2001) The brine discharge or treatment remainsimportant for all of these separation processes

The use of a monovalent anion permselective membrane in the ED process provedsuccessful in a full-scale ED plant located in Austria which was designed to removenitrates (V) from groundwater (Velizarov et al 2004 Wisniewski 2001) The NO

3concentration in the raw water was 120 mg NO3L and the removal efficiency

Anion exchangemembrane

Cation exchangemembrane

Raw water(water+NaA)

Raw water(water+CaSO4)

Stripping solutioneg NaCl solution

Stripping solutioneg NaCl solution

AndashClndash

Andash

Na+ Na+

Na+

SO42ndash SO4

2ndash

Kn+

Kn+

Figure 152 Scheme of Donnan dialysis process (A target anion Knthorn target cation) (Bodzek ampKonieczny 2011b)

472 Advances in Membrane Technologies for Water Treatment

(66) was adjusted to obtain a product concentration of 40 mg NO3L at a desalinationrate of c 25

ED and EDR are also proposed to remove bromates from water (Bodzek ampKonieczny 2011a 2011b Wisniewski amp Kliber 2010) Studies on ED with anion-exchange membranes (Neosepta AMX) resulted in BrO

3 removal efficiencies of8687 and with the use of mono-anion-selective membranes (Neosepta ACS) upto 99 at a current density of 20 Am2 The removal rates of other anions werefrom 80 (HCO

3 ) to 93 (NO3 ) (Wisniewski amp Kliber 2010) This means that

the ED of water with an initial concentration of BrO3 of 100 mgL causes a decrease

in the final concentration to approximately 1 mgl which is significantly below thelimit value of drinking water (for BrO

3 10 mgL) The increase in power densityfor ED with standard anion-exchange membranes results in an increase in the aniontransport rate of 36

Investigations were also carried out on chlorate (VII) ion removal by ED and EDRand at high concentrations of silica (approximately 80 mgL) Regardless of the pres-ence of SiO2 and its concentration water recovery in the EDR installations was notaffected Pilot studies have shown that the removal of ClO

4 varied in the range of70e97 depending on the initial concentration of the anion and the number of stepsin the configuration of the EDR system (Anonymous 2008) During removal ofchlorate (VII) ions using the EDR method the retention coefficients of other anionswith similar valence (eg nitrate) are also important

ED can be applied to fluoride removal from water that contains a significant amountof this contaminant The removal rate of F is often higher than that obtained for ROand it increases with an increase in the electrical potential difference temperature andflow rate (Velizarov et al 2004 Wisniewski 2001) To minimize the precipitation ofsalts of bivalent ions (sulfates and carbonates) in the concentrate chambers prelimi-nary removal of bivalent ions is proposed using two-step ED with the application ofvarious ED membranes in each step or by chemical methods followed by conventionalED (Bodzek amp Konieczny 2011b) The content of fluorides generally decreases from30 to 063 mgL for the first configuration and to 081 mgL for the second one whichallows water of municipal quality to be obtained The first method is preferred becauseof its simplicity and the elimination of the need to add other chemicals

Similar to RO electrodialytic removal of boron from water and wastewater requiresa high pH because boric ions are transported through an anion-exchange membrane(Bick amp Oron 2005 Kabay et al 2008) The main advantage of ED comparedwith RO is the lesser sensitivity of ion-exchange membranes to pH and foulingHigh pH values also prevent the precipitation of Mg(OH)2 and CaCO3 Howevereven for such a high pH (910) chlorides are preferably transported and sulfatesare removed in an extent similar to boron (Bick amp Oron 2005 Kabay et al 2008)The low mobility of boric ions compared with others is the main disadvantage ofED because boron can be transported only after a significant decrease in other salt con-tents in diluate (Kabay et al 2008) To omit high demineralization of the diluate amonopolar membrane at alkali process conditions (pH 910) should be applied(Bick amp Oron 2005)

Membrane technologies for the removal of micropollutants in water treatment 473

Studies on arsenic removal fromwater by EDhave shown that it is possible to removeAswith an efficiency exceeding 80 for As(V) and 50 for As(III) (KartinenampMartin1995) with a water recovery of 85 In other studies with EDR a concentration ofarsenic in eluate was decreased to 0003 mgL (its initial level was 0021 mgl) whichcorresponded to a retention coefficient of 86 (Bodzek amp Konieczny 2011b)

15213 Membrane bioreactors

The main disadvantage of pressure-driven membrane processes and ED is the produc-tion of a concentrate highly loaded with anions Thus the use of MBRs to removemicropollutants from RO NF and ED concentrates as well as natural water and waste-waters is proposed The concentration of pollutants can be decreased to a value corre-sponding to drinking water quality (Bodzek amp Konieczny 2011a 2011b Crespo et al2004 Velizarov et al 2004 2008)

The biological degradation of oxyanions (NO3 ClO

4 and BrO

3 ) is based on their

reduction to harmless substances (N2 Cl and Br) at anaerobic conditions the pres-

ence of microorganisms (heterotrophic or autotrophic bacteria) and proper electrondonors (ethanol methanol and acetates for heterotrophic conditions and sulfur com-pounds and hydrogen for autotrophic ones) (Bodzek amp Konieczny 2011ab Crespoet al 2004 Velizarov et al2004) The kinetic of the reaction depends on the kind ofmicroorganism and the biodegradation process conditions (pH and anion concentra-tion) (Crespo et al 2004) The advantage of autotrophic degradation is the lower pro-duction of excess sludge however the process runs slowly (Kołtuniewicz amp Drioli2008) When heterotrophic process is applied the removal of dissolved organiccarbon (DOC) and biomass from treated water is required (Velizarov et al2004) Dis-advantages of conventional biological anion biodegradation can be eliminated byapplying an MBR which ensures the total retention of biomass The configurationof MBR processes can be arranged as a system with pressure-driven membrane mod-ules (MF and UF) (Figure 153) (Bodzek amp Konieczny 2011a 2011b) or as extractiveMBRs (membrane contactors) (Figure 154) (Bodzek amp Konieczny 2011a 2011bCrespo et al 2004)

In the case of an MBR with a pressure-driven membrane process an MF or UFmembrane may be placed inside or outside the bioreactor because the retention ofions and low-molecular-mass compounds (electron donors and some metabolicby-products) by porous membranes is generally insufficient therefore either processmodifications or water posttreatments are necessary The solution is an extractiveMBR (Figure 154) in which water with anions is supplied to the inside (lumenside) of hollow-fiber membranes and anions diffuse to the outside (shell side) Thereexisting microorganisms use anionic micropollutants as an electron donor for thereduction process (Bodzek amp Konieczny 2011a 2011b) Under these conditionsboth electron donor and biomass are separated from the water by a membrane

Biological degradation of oxyanions may also be used to remove nitrates (V) bro-mates (V) and chlorates (VII) Studies have shown their full reduction to nitrogenbromides and chlorides by the same bacterial cultures that are used for nitrate (V)reduction (Wang Lippincott amp Meng 2008)

474 Advances in Membrane Technologies for Water Treatment

A new membrane bioprocess for the removal and bioconversion of ionic micropol-lutants from water streams is the ion-exchange MBR (IEMB) (Crespo et al 2004Velizarov et al 2004) In this process the ionic micropollutant is transported fromthe water stream through a nonporous ion-exchange membrane into a biologicalcompartment There it is simultaneously converted into a harmless product by a suit-able microbial culture in the presence of an adequate carbon source and other requirednutrients The mechanism of anion pollutant transport through the membrane is thesame as in DD (Figure 155) (Bodzek amp Konieczny 2011a) The co-ions (cations)are excluded from the positively charged membrane and the target anion(s) transportis combined with its bioconversion In addition the bioconversion of the pollutant inthe IEMB keeps its concentration at low levels which guarantees an adequate drivingforce for transport

This concept was first demonstrated in the example of synthetic waters preparedfor the removal and bioconversion of nitrate to harmless nitrogen gas using a Neo-septa ACS mono-anion permselective membrane and ethanol as the carbon source(Velizarov et al 2004) Because of its very low diffusion coefficient (three ordersof magnitude lower than that in water) carbon source penetration into the treatedwater was avoided by employing this nonporous type of membrane and thedevelopment of an ethanol-consuming biofilm on the membrane surface contacting

Recirculation Water withoutnitrates

Water withoutnitrates

GasSludge to

waste

Sludge towaste

Electron donornutrient

Electron donornutrient

Bioreactor

Bioreactor

Water containingnitrates

Water containingnitrates

Reactionmixture Capillary

Water withoutnitrates

Biofilm

Figure 153 Membrane bioreactors with pressure-driven membrane module (Bodzek ampKonieczny 2011a 2011b)

Bioreactor Recirculation

Sludge towaste

Electron donornutrient

Water withoutnitrates

Water withnitrates

Biofilm

Capillary

Figure 154 Extractive membrane bioreactor (Bodzek amp Konieczny 2011a 2011b)

Membrane technologies for the removal of micropollutants in water treatment 475

the biocompartment Chloride ions were used as major counterions in IEMB for oxy-anion removal Within the concentration relevant to nitrate polluted water(50e350 mg NO

3 L) complete denitrification was achieved without the accumula-tion of NO

3 and NO2 ions in the biocompartment (Velizarov et al 2004)

1522 Heavy metals

Heavy metals are one of the most dangerous impurities present in natural waters andwastewaters Because natural waters are the main source of drinking water it ispossible that heavy metals will appear in them When the daily monthly or annualconsumption of water is considered the danger resulting from the presence of heavymetals in water is significant Metals such as lead mercury selenium iron nickelmanganese copper cobalt cadmium zinc and chromium are present in drinking wa-ter The permissible concentration for only part of them is established in each countryrsquosregulations regarding tapwater Except for iron manganese and aluminum in Polishregulations permissible concentrations of the following metals are specifiedantimony 0005 mgL arsenic 0010 mgL chromium 0050 mgL cadmium005 mgL nickel 0020 mgL copper 20 mgL lead 0025 mgL mercury0001 mgL selenium 0010 mgL and silver 0010 mgL (Bodzek amp Konieczny2011b) Conventional methods such as precipitation extraction and ion exchangehave many shortcomings especially with respect to the processing of large volumesof water containing a low concentration of metal ions Nowadays these contaminantsare most frequently precipitated as hydrated metal oxides hydroxides or sulfides withthe use of flocculation or coagulation A major problem pertaining to the precipitationprocess involves the formation of substantial quantities of sludge containing metals(Bodzek 1999) Often the concentration of metal ions in the filtrate after the finalfiltration process is still above the level of several milligrams per liter Membranetechniques such as RO NF UF and ED are more often applied to remove heavymetals from water solutions on an industrial scale (Bodzek 2012)

15221 Application of high-pressure membrane processes

Metal ions can be successfully removed from water solutions by means of RO or NFbecause the membranes applied in those processes are able to retain dissolved salts of

BiofilmAnion exchange

membrane

BioreactorCations

Electron donornutrients

Nontoxicproducts

Rawwater

Anionicmicropollutants

Clndash

Xndash

Xndash

Clndash

Purified water

Figure 155 Schematic diagram of ion transport mechanism in the ion-exchange membranebioreactor (Bodzek amp Konieczny 2011a)

476 Advances in Membrane Technologies for Water Treatment

molecular sizes as small as a few nanometers as shown in a number of studies(Bakalar Bugel amp Gajdosova 2009 Mehiguene Garba Taha Gondrexon ampDorange 1999 Qdais amp Moussa 2004)

The application of RO in the removal of heavy metals from solutions can be shownin the example of wastewater treatment in the electroplating industry The wastewaterconsists mainly of effluent from product-washing processes after electroplatingcoating in electroplating baths The concentration of metal ions in such wastewaterranges from 0025 to 1 mgL (Bodzek 1999) Frequently electroplating effluentscontain Cr Cu Cd Zn Ni Pb and Ag ions and because the metal-coating technol-ogies are based to a great extent on cyanide solutions the presence of toxic cyanideanion is also important The RO process allows the recovery of water at a very highpurity level which in many cases can be directly returned to the technological processwithout additional treatment The concentrated solution (retentate) may be reused tofill up the electroplating bath (Bodzek 1999) Figure 156 presents a typical diagramof the installation operating in a closed cycle applied to such a process (Bodzek 1999Bodzek amp Konieczny 2011b)

A series of investigations were conducted on the removal of heavy metals fromaqueous solutions using RO technology For example Bakalar et al (2009) presentedthe results of removing copper nickel and zinc using composite polyamide membraneTW30-1812-50 (Dow Filmtec) They determined the effect of the accompanying an-ions (co-ions) the concentration of cations and the transmembrane pressure on theseparation efficiency In turn Qdais and Moussa (2004) tested removing Cu2thorn andCd2thorn ions by means of RO and NF Results showed that the removal efficiency of in-dividual heavy metals by RO was high and amounted to 98 for copper and 99 forcadmium whereas for NF it was above 90 In the case of a solution containing bothmetals RO membranes reduced the concentration of ions from 500 to about 3 mgL(removal rate of 994) whereas the rejection efficiency of NF amounted to anaverage of 97 These studies showed that NF was also an appropriate technique toremove heavy metals from wastewater to a level acceptable according to

Chemicals

Metalproducts

Galvanic bathsConcentrate

Preliminary filtration

Reverse osmosis

Washing system

Water

Metalproducts

Deionized water

Figure 156 Diagram of electroplating process line integrated with reverse osmosis (Bodzek ampKonieczny 2011b)

Membrane technologies for the removal of micropollutants in water treatment 477

environmental regulations In addition as with RO it was possible to reuse permeatefor rinsing purposes and to recycle the retentate containing heavy metals Retention ofthe cations in the process strongly depends on the energy of hydration the type andvalence of co-ions passing through the NF membrane and the applied pressure andpH For example the retention of Cu2thorn and Cd2thorn ions is greater for the higher co-ion valence and higher cation hydration energy (Mehiguene et al 1999) The obtainedretention coefficients of copper and cadmium sulfates are close to 100 independentof pressure In the case of chlorides and nitrates the retention rates increase with pres-sure to specific values that depend on the nature of the co-ions Heavy metal retentionduring NF also strongly depends on the pH In a highly acidic environment a high con-centration of hydrogen ions in solution causes gradual neutralization of the negativeactive centers on the membrane surface so the impact of the membrane charge oncation and anion retention is significantly reduced Under such conditions nitrateand chloride ions easily pass through a membrane and to maintain the electrostaticbalance of the solution through the membrane protons also penetrate it Thereforecopper and cadmium ions are retained in retentate

15222 Ion-exchange membrane processes

Electrodialysis is particularly useful and often applied to treat rinsing effluents andother wastewaters from electroplating plants (Bodzek 1999) The diagram of installa-tion is similar to Figure 156 but instead of RO ED is applied The retentate which isa concentrated solution of metal ions is used to fill up the electroplating bath whereasthe dialysate is returned to the washing installation Hence practically the entire quan-tity of water and salts present in washing effluents can be used (Bodzek 1999)Recently the application of ED to recover metals for electroplating with such metalsas Au Pt Ni Ag Pd Cd Zn and SnPb from diluted electroplating wastewaters hasgained attention (Bodzek 1999) The solution of metal salt can be concentrated to alevel corresponding to the componentsrsquo content in the electroplating bath eg forNi from 1 to 60 gL (Bodzek 1999) which is much greater than with the applicationof RO The principal disadvantage of ED is the inability to simultaneously remove thenon-ionic substances (eg organic compounds) from the dilute stream which can bedone using RO

15223 Integrated low-pressure membrane processes

An interesting solution to removing heavy metals from aqueous solutions is the PEUF(Bodzek Korus amp Loska 1999 Korus 2012) It combines UF with metal complex-ation using water-soluble polymers The formed complexes are sufficiently large to beretained by a UF membrane Permeate is deprived of metal ions and retentate can un-dergo regeneration to recover both the metal and polymer

The process was applied to deactivate radioactive liquid waste containing metalions ie cesium cobalt strontium antimony and technetium isotopes themajor components of radioactive wastewater and to separate the lanthanides(140La 152Eu and 169Y) (Zakrzewska-Trznadel 2003) A significant reduction inpermeate radioactivity was observed

478 Advances in Membrane Technologies for Water Treatment

Mavrov Nikolov Islam and Nikolova (1992) carried out investigations into theremoval of Cu(II) Ni(II) and Co(II) ions from synthetic aqueous solutions with aninitial metal concentration of 104 molL using the hybrid PEUF method with polyac-rylonitrile membranes (UF-25-PAN) (cutoff of 25 kDa) Polyvinyl alcohol(50000 Da) and polyethyleneimine (PEI) (30000e40000 Da) were used as complex-ing agents The optimal concentration of PEI was two to six times higher comparedwith the stoichiometric concentration and retention rates of formed complexes whichranged within 85e99 The highest retention rate was obtained for PVA complexes(97e99) at a ratio of metal concentration to polymer concentration ranging from 14to 18 (Mavrov et al 1992)

Korus (2010 2012) conducted studies on the removal of heavy metals (Ni Cu andZn) from synthetic and galvanic wastewater by applying the hybrid complexationeUFprocess Poly(vinyl alcohol) (50000 Da) PEI (30000e40000 Da) polyacrylic acidand sodium polyacrylate as complexing agents were used in connection with polysul-fone and polyamide membranes The efficiency reached 85e97 for polyamide mem-brane depending on the polymer to the metal ratio pH and kind of metal A highremoval efficiency of zinc and nickel ions (97e99) was obtained for polysulfonemembrane The decomplexing process enabled metal to be recovered from the concen-trated solution to an extent suitable for its reuse

Sodium poly(styrene sulfonate) a water-soluble anionic polymer with strongcation-exchange groups was used as a complexing agent for lead ion complexing(Korus 2010) The high rate of metal removal (85e99) depended on the ratio ofmetals to polymer the pH of the solution and the operating UF conditions obtainedfor the polysulfone membrane It was possible to obtain the retentate with a concentra-tion of Pb 20 times higher than the concentration of the feed solution which contained50 mg PbL The main process parameters were a fivefold excess of polymer in rela-tion to metal as well as a pH of 6 and a pressure of 01 MPa The decomplexationeUFprocess involved breaking the polymeremetal bond and allowed it to recover 85of metal whereas diafiltration conducted with a sufficient volume of water enabledfive- to 15-fold reduction of the concentration of metal remaining in retentate sothe recovery and reuse of the polymer were possible

The use of membrane separation combined with the biological removal of metalsfrom a solution (MBRs) is of a great interest Wastewaters with a high load of metalsusually contain compounds that may be toxic for microorganisms or inhibit theirgrowth they often have a high salinity or pH Therefore it is often impossible to carryout conventional biological removal of metals from wastewater owing to the inactiva-tion of microorganisms The solution may be extractive MBRs with sulfate-reducingbacteria (EMBR-SRB) which eliminate these restrictions because of the physical sep-aration of biomass from effluents (Figure 157) (Bodzek amp Konieczny 2011b MackBurgess amp Duncan 2004) Membranes which are usually made of silicone polymersperform two functions they separate two water phases and enable H2S transport fromthe phase containing biomass to wastewater where the precipitation of metal sulfide(s)takes place Study of zinc removal from synthetic wastewater using EMBR-SRBMBRs showed that the reaction rate between H2S and Zn ions was high owing tothe large concentration gradient of H2S on both sides of the membrane When the

Membrane technologies for the removal of micropollutants in water treatment 479

pH of the biological mixture decreased the quantity of nondissociated H2S grewincreasing its concentration gradient More than 90 removal of Zn ions from solu-tions containing 250 mgL of this metal was obtained The transport rate of H2Salso depends on the membrane thickness On the side of wastewater a thin layer ofzinc sulfide formed on the membrane surface constituting significant resistance toH2S transport This problem can be solved by changing the hydrodynamic conditionsof the water stream or using pulse flow

1523 Removal of chromium

A separate discussion on chromium is associated with the fact that in the natural envi-ronment chromium most commonly occurs in the third oxidation state as cation (Crthorn3)and sixth Cr(VI) in the form of anions Chromium (VI) is a strong oxidant easilyreduced to Cr(III) (Jacukowicz-Sobala 2009) Chromium (III) which is naturally pre-sent in the environment is an essential nutrient whereas chromium (VI) is formed inindustrial processes and enters the environment as anthropogenic pollution Chromium(VI) and chromium (III) compounds are widely used in many industries because of thedurability of the metal and its aesthetic effects One can mention the galvanic industrythe production of dyes and pigments and textile and leather articles tanneries andwood maintenance That is why chromium compounds are increasingly found inwastewaters groundwater or soil Chromium (VI) compounds are soluble in waterand at pH 1e6 they appear as HCrO

4 and Cr2O27 ions whereas at pH gt 6 CrO2

4ions are formed The influence of chromium compounds on living organisms dependson the oxidation state of chromium the solubility and the method of entry into thebody Chromium (III) is trace element essential to the proper functioning of plants an-imals and humans (Bodzek amp Konieczny 2011b) whereas Cr(VI) is highly toxic toliving organisms so their permissible concentration in drinking water amounts to005 mgL including 3 mgL for Cr(VI) The traditional way to remove and recoverchromium salts from contaminated water and wastewater is to reduce Cr(VI) to Cr(III)and then precipitate Cr(III) hydroxide and in the final stages filter the suspension

Biofilm Wastewater

Membrane

Heavy metalsacids bases andsalts

Metal sulfidesdrain as asuspension

H2S

H2S

Figure 157 Scheme of bioreactor with sulfate-reducing bacteria EMBR SRB (Bodzek ampKonieczny 2011b)

480 Advances in Membrane Technologies for Water Treatment

(Owlad Aroua Daud amp Baroutian 2009) For Cr(III) the reduction stage is omittedFor chromium removal several other methods are also proposed such as adsorptionand biosorption ion exchange (used on an industrial scale) solvent extraction andelectrochemical methods (Owlad et al 2009) Membrane processes both high-pres-sure and low-pressure membrane processes enhanced with surfactants and polymersare very important to the recovery and disposal of chromium (Bodzek amp Konieczny2011b Kołtuniewicz amp Drioli 2008 Owlad et al 2009) Application has also beenfound for liquid membranes and processes based on ion-exchange membranesincluding ED EDI and membrane electrolysis (Bodzek 2012)

Reverse osmosis and NF permit the direct separation of chromium compoundsfrom the solutions and find practical application in this respect (Bodzek 2012Kołtuniewicz amp Drioli 2008 Owlad et al 2009) To remove Cr(III) and Cr(VI)both inorganic membranes and polymer membranes can be used Studies carried outon Cr(VI) removal from water involved RO using Osmonics membranes Sepa-Stype and membranes made of cellulose acetate (CA) (Bodzek et al 2011Kołtuniewicz amp Drioli 2008 Owlad et al 2009) It was found that the CAmembranesretained 96 of Cr(VI) ions whereas Osmonics membranes retained 8096depending on the membrane compactness (Bodzek amp Konieczny 2011a) Applicationof RO for the treatment of chromium tanning wastewater is limited by chloride andsulfate ion concentration High concentrations require the use of high transmembranepressure This causes removal of chromium to become economically justifiable only ifthe salt concentration does not exceed 5 gL and the chromium concentration 1 gLHowever to treat galvanic wastewater with a concentration of chromium amountingto 2 gL the RO process can be successfully applied (Bodzek 2012) In this casepermeate with a concentration of 00017 mg CrL suitable for reuse can beobtained as well as concentrated chromic acid anhydride (concentration of Cr 5 gL)(Jacukowicz-Sobala 2009)

It seems that NF is a better solution for the removal of chromium from water(tannery and galvanic wastewaters) The obtained filtrate is then without chromiumbut it contains a significant amount of salt that can be used to prepare etching bathsAs for the retentate a concentrated solution of chromium after further concentrationhydroxide is precipitated and then dehydrated sludge is dissolved in sulfuric acid Theresulting solution can be used directly in the process of tanning (Religa amp Gawronski2006) For NF the retention coefficient of Cr increases with an increase in pH but theeffect is more pronounced for membranes with lower separation capacity (eg from47 to 945 for Osmonics membranes) compared with more compact membranes(eg from 84 to 997 for Osmonics membranes) (Hafiane Lemordant amp Dhahbi2000) The dependence of the retention coefficient on the concentration of Cr in feedwas also observed for NF membranes (Hafiane et al 2000) but the range of the effectalso depended on the pH In an acidic solution at higher concentrations of Cr in feed ahigher retention was found whereas at pH 65e11 the nature of this relationship wasthe opposite ie lower retention was obtained for higher concentrations of Cr Thisphenomenon is important because Cr(VI) changes its ionic form with a change inpH In the highly acidic environment Cr(VI) occurs in the form of no dissociated chro-mic acid (H2CrO4) and when the pH is changed to 65 HCrO4

e ions are formed the

Membrane technologies for the removal of micropollutants in water treatment 481

concentration of which increases with an increase in the parameter A furtherincreasing in pH above 7 causes the formation of CrO2

4 ions the concentration ofwhich also depends on pH Cr2O2

7 ions are also present in the solution and their con-centration depends on the initial concentration of the contaminant in the feed and pHThis ion is usually dominant at high concentrations of Cr and in a strongly acidic envi-ronment (pH 17) but its concentration decreases with an increase in pH (Bodzek ampKonieczny 2011a 2011b Hafiane et al 2000)

Characteristics of membranes used in UF and MF processes do not allow chromiumions to be retained directly in the retentate That is why low-pressure membrane pro-cesses are used to remove Cr in an integrated process In this respect the followingpossibilities can be identified (Bodzek 2012 Kołtuniewicz amp Drioli 2008 Owladet al 2009)

bull Preliminary MFUF before further treatment with conventional or membrane processesbull Modification of UF membranes to reduce pore size or ion-exchange propertiesbull Polymer-enhanced UF or surfactantmicellar-enhanced UF (MEUF)

The first method was used in the initial stages of tanning and galvanic wastewatertreatment MicrofiltrationUF removes suspended solids fats and emulsions from theaqueous phase (without added chemicals) which makes it easier and improves the per-formance of subsequent purificationprocess separation (Religa amp Gawronski 2006)The main methods of introducing the charge on the surface and inside the pores of UFmembranes are sulfonation of polysulfone membranes and the introduction of aminoand carboxylic groups Modification of UF membranes extends their separation prop-erty by giving them ion-exchange properties (Bryjak 2001) Polymer-enhanced UF orMEUF allows separation of metal ions including chromium Polymer-enhanced UFhas been successfully applied to remove chromate (VI) from groundwater usingcomplexing agents such as 1-hexa-decylopiridine chloride sodium polyacrylatepoly(dimethyldiallylammonium) chloride chitosan and pectin (Bodzek amp Konieczny2011b) Polyethylenimine (PEI) is used for the concentration and recovery of chro-mium (III)

Electrochemical separation techniques are an alternative method of removing chro-mium from the water environment This toxic metal is present in various streams pro-duced by a number of industrial processes which also contain other substances(mainly metals) that should be separated from chromium Therefore electrochemicaltechnology is more flexible than other membrane techniques and is applied to recoverchromic acid (VI) from the bath coating metal parts (a large concentration of chro-mium) or as a method of disposal and recovery of chromium from wastewater derivedfrom washing these elements In most cases among others in the plating industry so-called three-compartment electro-electrodialysis (EED) is applied It is based on elec-trolysis reactions running on electrodes and the ED process (Bodzek amp Konieczny2011b Frenzel Holdik Stamatialis Pourcelly amp Wessling 2005) (Figure 158) Itcan simultaneously manage three different tasks removal of impurities chromicacid recovery and purification of rinse water The treated solution feeds the centerchamber of the device which is separated from the anolite chamber by the anion-exchange membrane and from the catolite chamber by the cation-exchange membrane

482 Advances in Membrane Technologies for Water Treatment

(Frenzel et al 2005) The anolite chamber is supplied with water whereas the catolitechamber is supplied with sulfuric acid Chromium (VI) ions migrate to the anolitewhere they form chromic acid (VI) with protons formed on the anode In turn metalcations permeate to catolite chamber where sulfuric acid neutralizes the hydroxideions formed on the cathode so in this part of the device soluble metal sulfates (VI)are formed

Both the ED and EDI processes can be applied to remove and separate metal ionsand their mixtures including chromium In ED the electrical resistance in dialysatechambers increases in time as the ions are removed from the diluted solution to theconcentrate chamber which causes higher energy consumption and decreases theefficiency of the process One solution to this problem is the EDI process in whichthe dilute solution chamber is filled with an ion-exchange resin (Bodzek amp Konieczny2011b) The applied voltage improves the migration of ions to the respectiveelectrodes and thus to concentrated stream and causes water dissociation into Hthorn

and OH ions which regenerate the ion-exchange resin Alvarado Ramirez andRodriacuteguez-Torres (2009) assessed the feasibility of EDI and ED continuous processesfor the removal of chromium (VI) from synthetic solutions at pH 5 The EDEDIinstallation consisted of electrodes and two acrylic separation plates between whichan anion-exchange membrane manufactured by Neosepta was placed (Figure 159)(Alvarado et al 2009 Bodzek amp Konieczny 2011b)

Two cation-exchange membranes by the same producer separated the electrodesfrom the separation plates In this way two chambers with diluate and concentratedsolution were formed Synthetic wastewater containing 100 mgL Cr(VI) was treatedDuring the EDI process a chamber with diluted solution was filled with a mixed

Collectingsolution

AEM

Chromicacid

Regeneratedsolution

(eg rinse water)

Metalsulfates

O2

Cr2O72ndash

Cr3+

Ni2+

Cu2+

Fe2+3+

CrO42ndash

SO42ndash

H2O

H2

H+

H+

+ ndash

CEM

H2SO4 dil

Figure 158 Principles of three-compartment electro-electrodialysis for chromic (Bodzek ampKonieczny 2011b) acid recovery AEM anion-exchange membrane CEM cation-exchangemembrane

Membrane technologies for the removal of micropollutants in water treatment 483

ion-exchange resin In the ED process the removal of Cr amounted to 98 during625 h at an energy consumption of approximately 12 kWhm3 and at a maximumlimited current (Ilim) of 85 In the EDI process with the use of a mixed bed at thesame Ilim 998 removal of Cr(VI) was reached within 13 h (energy consump-tion frac14 0167 kWhm3)

153 Removal of microorganisms and NOM

1531 Removal of dispersed substances and microorganismsby low-pressure membrane processes

The turbidity of water is caused by the presence of suspended mineral and organic mol-ecules of different sizes (colloids and coarse and fine suspensions) Usually MF or UFis applied to decrease water turbidity to the level below 1 nephelometric turbidity unit(NTU) ie the value that corresponds to regulations for drinking water Only severalstudies discussed in the literature focused on turbidity removal by means of membraneprocesses although it is proven that the use of those techniques enables the productionof water with a turbidity below 1 NTU from water with an initial turbidity of 100 NTUand greater (Taylor amp Wiesner 2000) It is accepted that UF and MF can also be usedfor water clarification (Bodzek amp Konieczny 2005) The study of application of a UFAquasource membrane (France) revealed that from waters of different turbidityranging from 01 to 115e248 NTU drinking water of a turbidity of 003e004NTU could be obtained (Taylor amp Wiesner 2000) The publication (Anonymous2005) summarizes the results of a series of studies carried out on membrane filtrationin 1989e2001 which showed that the use of MF and UF allowed for maximumremoval of turbidity regardless of raw water turbidity the kind of membrane and

A

V

V

Concentrate

CEM

H+

H+ OHndash

HCrO4O2

O2

K+

CEM

Diluate

ndash+

AEM

Figure 159 Diagram of apparatus for electrodialysiselectrodeionization processes AEManion-exchange membrane CEM cation-exchange membrane (Bodzek amp Konieczny 2011b)

484 Advances in Membrane Technologies for Water Treatment

its producer as well as the application of precoagulation The average value of thefiltrate turbidity was 0097 NTU at a standard deviation of 006 for 72 measurementsSimilar results were obtained for various membrane modules during studies in theUnited States France and other countries (Taylor amp Wiesner 2000) Sometimeswhen turbidity is caused by colloidal fraction membrane filtration is preceded bycoagulation to obtain flocks of a greater size (Bodzek amp Konieczny 2005) Reverseosmosis and NF also can eliminate these types of impurities and organic admixturesbut those processes are not applied because of the fouling phenomenon Table 151summarizes the percent removal of turbidity and NOM by various membrane tech-niques (Bodzek 2013)

Water and wastewater that contain microorganisms ie viruses bacteria and pro-tozoa (fungi algae snails worms and Crustacea) may have many negative health ef-fects (Anonymous 2005 Taylor amp Wiesner 2000) Polish regulations regarding thequality of drinking water establish the maximum permissible content of Escherichiacoli and Enterococcus and as additional requirements the amount of Coli bacteriagroup the total number of microorganisms and the amount of Clostridium perfringens(Bodzek amp Konieczny 2005) Water contamination can occur at its source at the siteof its intake or treatment and directly in the water supply system Various methods canbe applied to water disinfection each of which has some advantages and disadvan-tages Sand filters remove 99e999 of bacteriophages whereas commercial watertreatment devices based on ultraviolet (UV) and ozonation do not guarantee theremoval of all pathogenic microorganisms Chlorination causes the formation of tri-halomethanes (THMs) and is ineffective in the case of microorganisms associatedwith suspension Some microorganisms (eg Cryptosporidium) are resistant to its ac-tion (Taylor amp Wiesner 2000)

Membrane filtration (MF and UF) may significantly improve the disinfection pro-cess because it almost completely eliminates viruses bacteria and protozoa The sizeof viruses varies from 20 to 80 nm whereas the pore size of UF membranes is less than10 nm Thus at least theoretically the elimination of microorganisms is possible On theother hand bacteria (05e10 mm) cysts and oocytes (3e15 mm) are larger and thusthey can be totally eliminated during MF (Bodzek amp Konieczny 2005 Taylor ampWiesner 2000) A comparison of the pore sizes of UF and MF membranes with thesize of microorganisms indicates that the UF process can be successfully used for water

Table 151 Turbidity and NOM removal using membrane techniques

Process Pressure kPaTurbidityremoval

NOMremoval

Waterwastage

Microfiltration lt100 gt97 lt2 5e10

Ultrafiltration lt100 gt99 lt10 10e15

Nanofiltration lt500 gt99 gt90 15e30

Note NOM natural organic matter

Membrane technologies for the removal of micropollutants in water treatment 485

disinfection (Bodzek amp Konieczny 2005) Figure 1510 shows the rates of removal ofviruses bacteria and protozoa for different UF membranes (Bodzek amp Konieczny2010 Taylor amp Wiesner 2000) The obtained retention for all types ofmicroorganisms was greater than 4 log ie 9999

However it has been shown in practice that UF membranes are not always able toeliminate bacteria and viruses completely from water This is mainly connected to im-perfections in membranes and membrane modules and the secondary growth of bac-teria in water after its passage through a membrane In commercial membranes adiscontinuous skin layer through which microorganism can pass takes place In addi-tion the design of the modules often requires the raw stream to be sealed off from thepermeate stream which is not always appropriate The most efficient disinfection isobtained using capillary modules in which isolation of raw water from permeate iseasier than in the spiral-wound and hollow-fiber modules (Bodzek amp Konieczny2005) Furthermore cells of microorganisms could penetrate membrane pores with di-ameters much smaller than the dimensions of the cells themselves owing to pressuredeformation with the filtration of intracellular fluid but tonus of the cellular membraneremains unchanged (Figure 1511) (Bodzek 2013 Bodzek amp Konieczny 2010

8

6

4

2

0Viruses

Red

uctio

n (lo

g)

Bacteria GiardiaWater I

63

7271

74

47

51

Water II

Level of disinfection expressedas reduction in logarithmic scale1 log = 90 of inactivation2 log = 99 of inactivation3 log = 999 of inactivation4 log = 9999 of inactivation

Figure 1510 Removal of microorganisms using UF (Bodzek amp Konieczny 2010) UFultrafiltration

Figure 1511 Deformation of Cryptosporidium parvum in the microfiltration process (Bodzek2013 Bodzek amp Konieczny 2010)

486 Advances in Membrane Technologies for Water Treatment

Sosnowski Suchecka amp Piątkiewicz 2004) In addition it was demonstrated that theshape of microorganisms could be a key factor determining the efficiency of bacteriaremoval via a membrane For example bacteria or viruses of a slim elongated shapewere removed to a greater extent than ones of more compact shape (Bodzek 2013)

1532 Natural organic matter

NOM present in aqueous ecosystems is the mixture of many compounds characterizedby various chemical structure and properties Fulvic acids soluble in water(MW 2000 Da) more hydrophobic humic acids (MW 2000e5000 Da) andinsoluble humic fraction (humins) of bituminous character are part of NOM (Bodzek2013 Domany Galambos Vatai amp Bekassy-Molnar 2002) Humic substances usu-ally appear in water as dissolved compounds colloids and non-dissolved admixturesusually the appearance of a given form strongly depends on the water pH The dis-solved NOM fraction in natural water is equal to c 80e90 of the total NOM contentHumic substances cause intensive coloration of water from brown to black In addi-tion complexation reactions of humic substances with heavy metals or adsorptionof toxic organic substances creates many health hazards Humic substances are alsodisinfection by-product (DBP) precursors (Domany et al 2002) These are the mainreasons for the need to remove NOM from water

The elimination of NOM is one of the most important processes in water treatmenttechnology The main advantage of applying membrane techniques in water treatmentis to remove DBP precursors including part of NOM (Taylor amp Wiesner 2000 Wilf2010) As one of the most popular disinfection methods chlorination results in the for-mation of adsorbable organic halides (AOX) including THMs halogenated aceticacids halogenated aldehydes and ketones halogenated acetonitriles amines and otherDBPs (Bodzek 2013 Bodzek amp Konieczny 2005) The introduction of pressure-driven membrane processes to water treatment allows the formation of DBP to becontrolled as semipermeable membranes retain NOM including DBP precursors(Van der Bruggen amp Vandecasteele 2003) The removal of NOM also decreasesthe amount of chlorine required for disinfection which results in a reduction of the bio-logical activity of water in the distribution system (Bodzek 2013 Bodzek ampKonieczny 2005) According to a very wide molecular size distribution of NOM(from c 1 nm to c 045 mm) the effectiveness of its removal depends on propertiesof the applied membranes (Bodzek 2013) Table 152 compares the effectiveness ofNF UF and MF processes in NOM content control in natural waters (Bodzek2013 Bodzek amp Konieczny 2010)

15321 Application of RO and NF

By introducing NF or RO systems to water treatment one can directly control forma-tion of the DBP because semipermeable membranes retain NOM including the precur-sors of DBP Nanofiltration membranes are particularly important for removing NOMand DBP precursors because they are an effective barrier against organic compounds iftheir molecular weight (particle diameter) is greater than the cutoff of the membrane

Membrane technologies for the removal of micropollutants in water treatment 487

Nanofiltration membranes are able to retain 90 of DBP precursors from naturalwaters because they have a cutoff of 200e500 Da (eg Filmtec NF-50 and NF-70)(Bodzek 2013 Taylor amp Wiesner 2000 Thorsen 1999 Van der Bruggen ampVandecasteele 2003) The obtained permeate is high-quality drinking water with alow amount of DBP and a small risk of secondary bacteria growth after chlorinationwhich precedes water distribution to the network The results of removing DBP pre-cursors are given in Table 153 (Bodzek 2013 Bodzek amp Konieczny 2010 TaylorampWiesner 2000) High removal rates of DBP precursors are obtained for both surfaceand groundwater However because of greater fouling mainly caused by the high con-tent of colloids and suspensions surface waters are more difficult to clean using mem-brane methods As a consequence to keep appropriate membrane flux more advancedpretreatment or a combination of NF and low-pressure membrane techniques isrequired

Long-term research on DBP precursor content in Flagler Beach Florida (ground-water) and Punta Gorda Florida (surface water) treatment stations compared theeffectiveness of groundwater and surface water purification using RO and NF (Tayloramp Wiesner 2000) Although satisfactory levels of THM precursor removal wereachieved permeate flux was low for surface water and the system required adequateregeneration A pilot study of water treatment from Florida River using NF showeda 95 reduction in THM precursor content (Siddiqui Amy Ryan amp Odem 2000)In addition RO membranes (cutoff of 100 Da) were significantly more effective inremoving THM precursors (98) than NF ones with a cutoff of 400 Da (96)(Siddiqui et al 2000)

Table 152 Comparative assessment of MF UF and NF processes forNOM removal

Parameters MF UF NF

NOM removal lt10 0 30 gt80

Removal ofsuspensions andcolloids

20 40 70 90 gt95

DBP removal No 50 THM 32HAA

gt80

Requirements forcleaning

Required back-washing

Cyclical cleaningrequired

Cyclical cleaningrequired

Performanceproblems

Moderate fouling Fouling Fouling clogging

Pretreatment In-line coagulationor other process

In-line coagulationor other process

No

Note MF microfiltration UF Ultrafiltration NF nanofiltration NOM natural organic matter HAA haloacetic acidsTHM trihalomethane DBP disinfection by-product

488 Advances in Membrane Technologies for Water Treatment

Amy Alleman and Cluff (1990) conducted laboratory- pilot- and full-scalestudies of the NF treatment of water from the Colorado River A relatively low reduc-tion in the content of THM precursors (65e70) was associated with their small mo-lecular weight (a significant amount of compounds of a molecular weight lt 500 Da)Tan and Amy (1991) compared ozonation and NF used in color and DBP precursorremoval and found that membranes were much more effective Laine Clark andMallevialle (1990) and Jacangelo Aieta Carns Cummings amp Mallevialle (1989) pro-posed the use of UFMF as water pretreatment before NF and observed that MF mem-branes with a high cutoff (eg 100000 Da) were effective only in removing fineparticles of suspended solids in the range of 005e2 mm whereas UF membraneswith a lower cutoff (eg 10000e50000 Da) caused the retention of a certain groupof DBP precursors

15322 Microfiltration and UF

Aside from for NF and RO processes low pressure-driven membrane filtration is alsowidely used in water treatment (Thorsen 1999) Ultrafiltration and MF membraneseffectively remove colloids and ionic and non-ionic organic compounds of sizesthat correspond to the nominal molecular weight cutoff of UF or MF membranesThus single-step UFMF can be directly used to remove greater fractions of NOMfrom water including part of high-molecular-weight DBP precursors whereasmedium- and low-molecular-weight compounds can be eliminated in integratedsystems (Bodzek 2013 Thorsen 1999) To eliminate humic substances from waterdirect UF with modules equipped with dense membranes (eg c 1000 Da) or hybrid

Table 153 Natural organic matter (NOM) removal by nanofiltration(NF) (NF-50 and NF-70 membranes from Filmtec)

Water type Pretreatment

Raw water Purified water

Removal NOM content mgL

Ground Antiscalant 961 28e32 97

Preliminaryfiltration

961 31e39 96e97

Surface Preliminaryfiltration

157e182 55e84 49e70

Ground Preliminaryfiltration

259 39 85

Ground Preliminaryfiltration

120 6 95

Surface Preliminaryfiltration

40e460 NA 30e90

Note NA data not available

Membrane technologies for the removal of micropollutants in water treatment 489

systems of UF or MF with coagulation activated carbon adsorption or oxidation(ozonation or photocatalysis) can be applied (Bodzek 2013)

For the application of powdered activated carbon (PAC) the removal rate dependson the concentration of DOC the concentration of an adsorbate on the surface of anadsorbent and adsorbent dose pH temperature and contact time For direct UFMFremoval of DOC precursors of AOX including precursors of THM and haloaceticacids (HAA) do not exceed 20 On the other hand retention obtained for combina-tion with activated carbon increases to values between 7 and 82 for DOC20e85 for AOX precursors including 0e97 for THM precursors and 26e81for HAA precursors (Bodzek 2013 Bodzek amp Konieczny 2010) (Table 154) Hybridsystems are effective in view of the extended contact time and a greater concentrationof adsorbent in a membrane system

Results on the efficiency of hybrid systems using coagulation and MFUF(aluminum and iron (III) coagulants) indicate the removal rates between 12 and83 for DOC 30 and 88 for THM precursors 39 and 92 for HAA precursorsand 20 and 85 for precursors of AOX (Anonymous 2005) Retention rates are afunction of the dose and type of coagulant pH temperature and time and speed formixing the reaction mixture Organic pollutants are adsorbed onto coagulation flocksand these in turn are retained by the MFUF membrane In the coagula-tionesedimentationeUFMF (ceramic membrane and capillary) integrated processremoval of organic compounds was approximately 90 (DOC and UV254) in the firststage of the purification process whereas in the second it increased almost to 100(Bodzek amp Konieczny 2005) In coagulationemembrane filtration the removal oforganic compounds increases among other things because of the increased retentiontime of flocks in the reaction system (Anonymous 2005) Membrane flux observed inan integrated system also increased with reference to single-step UF This was accord-ing to the removal of organic compounds and thus the intensity of NOM foulingreduction but it depended on the coagulation mode used in the integrated system(Bodzek amp Konieczny 2005 Konieczny Bodzek amp Rajca 2006) Processes conduct-ed with coagulation and sedimentation exhibit relative permeability values close tounity but in the case of in-line hybrid processes relative permeability amounts to

Table 154 Characterization of NOM removal processes using UFMF

Process Direct UFMF UFMF-PAC process

Diameter of membrane pores nm 1e5 10e100

Transmembrane pressure MPa 02e08 01e04

Permeate flux Lm2 h 15e25 50e200

Removal of NOM Partial (10e20) 60e80

Removal of particles bacteria andviruses

Yes Yes

Note UF Ultrafiltration MF microfiltration NOM natural organic matter PAC powdered activated carbon

490 Advances in Membrane Technologies for Water Treatment

083e089 for ceramic membranes and 074e078 for capillary ones (Bodzek ampKonieczny 2005 Konieczny et al 2006) This is caused by a reduction in the foulingsubstance penetration of the membrane pores and the creation of a filter cake charac-terized by much greater porosity and smaller hydraulic resistance compared with oneformed during direct UFMF Such a process increases the lifetime of membranes andreduces the frequency of back-washing and chemical cleaning

Recently an ion-exchangeeUFMF integrated process was proposed for NOMremoval especially with the use of magnetic ion-exchange (MIEX) resin(Kabsch-Korbutowicz Biłyk and Mołczan 2006 Rajca 2012) The effectiveness ofNOM removal from water with the ion-exchange process is 30e90 (Kabsch-Korbutowicz et al 2006) and depends on the properties of water and the mode ofprocess conduction Application of MIEX resins before UFMF allows the filtrationcycle to be extended and water with better parameters than in the case of directmembrane filtration to be obtained However fine resin particles present in the watercould cause the membrane surface to be blocked Therefore an integrated processie the use of ion exchange as water pretreatment before MFUF is a more usefulsolution (Kabsch-Korbutowicz et al 2006) Interesting comparative studies conductedby Kabsch-Korbutowicz et al (2006) showed the superiority of an ion-exchangeeUFover a coagulationeUF system

The problem with the membrane filtration of surface water and groundwater is adrop in permeate flux caused by membrane fouling especially in the case of MFUF membranes (Laine Campos Baudin amp Janex 2002) It is known that NOMand in particular its hydrophobic fraction is the primary substance that causes fouling(Bodzek 2013) A symptom of this phenomenon is the formation of a brown gel on themembrane surface which can cause a decrease in flux by up to 75 over 2000 h ofoperation (Bodzek 2013) To determine the role of natural organic substances andtheir properties in membrane fouling many studies have been carried out (BodzekPłatkowska Rajca amp Komosinski 2008) However their results are often contradic-tory possibly because of the number of factors affecting this phenomenon Foulingdepends on the characteristics of both filtered water and the membrane used Adsorp-tive properties connected with membrane hydrophobicity pore sizes cutoff surfacecharge performance or surface roughness have a significant impact on fouling Inthe case of water properties the ionic strength of the solution is important in partic-ular the content of calcium cations which affects the solubility of organic substancesand influences the distribution of NOM molecular weight type of organic matter andpH of the water

154 Organic micropollutant removal

The following organic micropollutants can be found in water and wastewater (Bodzek2013)

1 DBPs2 EACs and endocrine-disrupting compounds (EDCs)3 PhACs

Membrane technologies for the removal of micropollutants in water treatment 491

Both secondary DBPs and residues of pharmaceuticals in the aquatic environmentmay exhibit properties of compounds with estrogenic biological activity Organicmicropollutants have strong carcinogenic and mutagenic properties The presence ofNOM in water especially humic substances may change the chemical properties ofmicropollutants and contribute to their migration to a significant distance It hasbeen shown that humic substances can hydrophobically bind water additives throughcovalent bonds hydrogen bonds and van der Waals forces (Nawrocki 2005) Theycan also increase the water solubility of nonpolar compounds cause hydrolysis ofsome pesticides photodegrade organic substances and restrict the bioaccessibilityof aquatic organisms (Nawrocki 2005) These properties significantly depend onthe form of the organic micropollutants ie whether they are a free state or areadsorbed onto other substances The removal of micropollutants during water treat-ment is usually performed using activated carbon sorption or advanced oxidation pro-cesses (AOPs) The first method is economically unattractive when the amount ofNOM in water is high whereas for AOPs the possibility exists of forming by-productsof undefined biological activity (Bodzek 2013) This results in the need to developnew separation processes among which pressure-driven membrane processes seemto be a good solution In addition they can be performed as independent processesas well as be a part of integratedhybrid systems with coagulation or sorption on activecarbon or in MBRs (Bodzek 2013 Bodzek amp Konieczny 2005)

1541 Oxidation and DBPs

Disinfection and oxidation by-products constitute a group of undesirable substancesformed as a result of the reaction of disinfectants and other strong oxidants with waterpollutants and admixtures Table 155 shows the number of DBPs among which themost important are THMs and HHAs (Bodzek 2013)

Reverse osmosis and NF are most often applied to remove THMs halogenated ace-tic acids and other halogenated hydrocarbons from water In Poland permissible con-centrations of THMs in water are established as follows total THM lt100 mgLchloroform 30 mgL and bromodichloromethane 15 mgL (Bodzek et al 2011)

Table 155 Organic water disinfection and oxidation by-products ofcontaminants and impurities present in natural waters

Disinfectant Organic by-products

Chlorine Trihalomethanes haloacetic acids halocetonitriles haloaldehydeshaloketones halopicrates nitroso-dimethylamine 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX)

Chlorine dioxide Aldehydes carboxylic acids

Ozone Aldehydes carboxylic acids aldo- and ketoacids

492 Advances in Membrane Technologies for Water Treatment

A study in which RO and NF Osmonics membranes (SS10 and MQ16) wereapplied for the removal of THMs revealed that the retention depended on the mem-brane capacity ie the higher permeate flux the lower retention coefficient (Bodzek2013 Waniek Bodzek amp Konieczny 2002) (Table 156) The increase in molecularweight of the halogenated compound resulted in an increase of the retention coefficientaccording to the following series CHCl3 lt CHBrCl2 lt CHBr3 lt CHBr2Cl Theremoval rate of chloroform varied from 67 to 87 bromodichloromethane from65 to 965 dibromochloromethane from 57 to 905 and tribromomethanefrom 61 to 92 depending on the type of membrane applied (Waniek et al2002) Another study investigating the effectiveness of removing THMs by meansof NF with the use of NF200 and DS5 Osmonics membranes (Bodzek 2013 UyakKoyuncu Oktem Cakmakci amp Toroz 2008) (Figure 1512) showed that the operatingpressure did not affect THM retention whereas the initial concentration of THM had anoticeable influence on capacity and retention The NF200 membrane removed THMmore effectively than the DS5 membrane The most effectively removed compoundwas dibromochloromethane which resulted from the higher molecular weight ofbromine and in the greater size of the molecule

NF is also suggested for the removal of halogenated acetic acids (chloro- dichloro-and trichloroacetic acid and bromo- and dibromoacetic acid) from water (ChalatipChawalit amp Nopawan 2009) The high reduction in HAA content compared withan open negatively charged sulfonated polysulfone NTR7410 membrane and a neutralNTR729HF polyvinyl alcohol membrane (all membranes by Nitto Denco CorpJapan) was found for dense negatively charged ES10 aromatic polyamide membranesEffective separation was caused by repulsion forces (Donnan effect) and a sieving ef-fect The ES10 membrane removed HAAs in 90e100 even at the low operating pres-sure of 01 MPa and the change in linear velocity did not influence membraneperformance (Chalatip et al 2009) The increase in the concentration of acids resultedin a decrease in the removal rate in all investigated membranes according to the greaterconcentration polarization effect which was the driving force for HAA anion diffusionthrough the membrane

There are also studies on the removal of HAAs from water in bioreactors withimmobilized enzymatic UF membranes (Kowalska Dudziak amp Bohdziewicz2011) Enzymes isolated from strains of bacteria from activated sludge were used inthe immobilization process Trials have shown that after 8 h of degradation 37 of

Table 156 Retention coefficients of THMs for RO and NF

Osmonicsmembranes

Concentrationin raw water(mgL) CHCl3 CHBrCl2 CHBr2Cl CHBr3

NF-MQ16 10e100 83e87 885e965 905 92

RO-SS10 10e100 67e81 65e81 57e65 61e80

Note NF nanofiltration RO reverse osmosis THMs trihalomethanes

Membrane technologies for the removal of micropollutants in water treatment 493

monochloroacetic acid 35 of monobromoacetic acid and 484 of dichloroaceticacid were removed (Kowalska et al 2011)

Studies suggest that NF is the best available technology for removing THMs andHAAs from water

1542 Endocrine-activedisrupting compounds

Recent investigations focus especially on EACs as groups of micropollutants thatappear more often in natural waters and wastewaters even ones biologically purified(Biłyk amp Nowak-Piechota 2004) According to the definition those are chemicals thatmay interfere directly or indirectly with the endocrine system and affect target organsor tissues Depending on the dose of EAC and the destination physiology this effectmay (but not necessarily) have a side effect In the case of negative consequences forthe health of the organism its progeny or (sub)population compounds are classifiedaccording to the definition of the International Program on Chemical Safety asEDCs (Bodzek 2013) These behave similarly to natural (17b-estradiol estriol andestrone) and synthetic estrogens (ethinylestradiol and diethylstilbestrol) and in the

100

80

60

40

20

0

100

90

80

70

60

501 2 3 4

10 15 20Transmembrane pressure (bar)

Transmembrane pressure (bar)

THM

reje

ctio

n (

)TH

M re

ject

ion

()

25

20 μgL40 μgL80 μgL200 μgL

CHBr2Cl

CHBrCl2CHCl3

Figure 1512 Influence of pressure concentration and type of THM on retention coefficients ofTHMs in the NF process (Bodzek 2013) THM trihalomethane NF nanofiltration

494 Advances in Membrane Technologies for Water Treatment

body may mimic endogenous estrogens (produced within the body) antagonize theaction of estrogens and disturb the synthesis of estrogen receptors and the metabolismof endogenous hormones (Bodzek 2013) The EDC group includes endogenic hor-mones natural organic compounds produced by fungi (including toxins ie mycoes-trogenes) and plants (phytoestrogenes) and a wide range of anthropogenicmicropollutants among which the most important are

1 Polycyclic aromatic hydrocarbons2 Surfactants3 Plant protection products (pesticides herbicides and insecticides)4 Phthalates5 Halo-organic compounds including dioxins furans and polychlorinated biphenyls6 Phenol compounds (alkylphenols and bisphenols)

Major sources of EDCs for humans are both food and drinking water pollution isintroduced into them by chemicals in rain landfill leachate and industrial wastewaterEndocrine-disrupting compounds are present in natural waters in concentrationsranging from nanograms per liter to micrograms per liter

Phytoestrogens are found in plants and are used for therapeutic and cosmetic pur-poses The most important are these compounds are genistein daidzein formononetinbiochanin glicitein puerarin coumestrol and equol as a metabolite of daidzein Theirchemical structure is similar to 17b-estradiol and therefore they have estrogenic activ-ity These compounds enter water bodies as a result of the decomposition of plants intowastewaters Research has focused on removing phytoestrogens in water treatmentprocesses including membrane filtration Removal of biochanin daidzein genisteinand coumestrol in RO amounted to 97 69 92 and 86 respectively and forNF 86 68 71 and 72 respectively (Dudziak and Bodzek 2010a 2010b)During membrane filtration of water also containing NOM and inorganic compounds(salts of calcium sodium and bicarbonates) the relative permeability of the mem-branes was less than unity which confirmed the existence of fouling or scalingphenomena

Mycoestrogens are natural organic compounds that contaminate grain crops whenwashed by rain they can contaminate ground and surface waters They are toxic andreveal estrogenic activity The presence of mycoestrogens in the aquatic environmentcreates a need to remove them in water treatment processes Dudziak (2011) studiedthe efficiency of removing selected mycoestrogens from water in coagulation sorptionon activated carbon and NF Coagulation removed 34 of mycoestrogens sorptionwith PAC gave gt80 whereas NF gave from 70 to 88 depending on the typeof compound tested Integration of NF with sorption or coagulation improved theremoval of mycoestrogens

One of the main anthropogenic pollutants present in drinking water sources is poly-cyclic aromatic hydrocarbons (PAHs) These pollutants are harmful to human healthbecause most are carcinogenic eg benzo(a)phyrene so their permissible concentra-tion in drinking water cannot exceed 0010 mgL the total amount of benzo(b)fluoran-thene benzo(k)fluoranthene benzo(ghi)perylene and ideno(123-cd)pyrene may beonly 01 mgL Table 157 shows results obtained during studies focused on removing

Membrane technologies for the removal of micropollutants in water treatment 495

Table 157 Comparison of retention coefficients of PAHs removed during RO and NF (membranes fromOsmonics USA)

PAH nameConcentration inraw water ngL

Retention coefficient ()

UF HP-09RO-SS10 NF-SF10 NF-MQ16

Fluorantene 50 396 459 899 66e886

Benzo(b)fluorantene 60 644 978 859

Benzo(a)pirene 50 628 964 992

Benzo(ghi)perylene 70 968 911 933

Note PAH polycyclic aromatic hydrocarbons NF nanofiltration RO reverse osmosis

496Advances

inMem

braneTechnologies

forWater

Treatm

ent

PAHs by means of RO and NF at similar compound concentrations (Bodzek 2013Bodzek amp Konieczny 2010 Luks-Betlej Bodzek amp Waniek 2001) The most effec-tive membrane used during the studies was MQ16 (the retention coefficient of PAHswas in the range of 859 to 99 independent of the molecular weight of the com-pound) For other membranes the retention coefficient increased with an increase inthe molecular weight of the removed compound Ultrafiltration membranes used inthe research removed xenobiotics to a high level even though the molecular weightsof these compounds were smaller than the cutoff and the radius of the UF membranepores (Bodzek 2013 Luks-Betlej et al 2001) The likely cause of this phenomenonwas the adsorption of PAHs onto the surface of the UF membranes (Bodzek 2013)

Surface active agents (SAAs) are a specific group of anthropogenic water pollut-ants in particular detergents complexing and bleaching substances inhibitors stabi-lizers optical whiteners and others They affect wastewater treatment plantperformance mainly because of the toxic action on activated sludge the formationof foam the simulation of solubility of many hazardous substances etc The useful-ness of conventional methods (coagulation foaming sorption ion exchange andoxidation) is limited because of the variety of chemical structures of SAAs and theirchanges in concentration Pressure-driven membrane techniques are alternativemethods for removal of SAAs from water whereas the effectiveness and type of pro-cess depend on the concentration of the SAA (Bodzek 2013) When the concentrationis below critical micelle concentration (cmc) the application of NF membraneseventually RO is proposed It was shown that NF membrane Desal 5K eliminatedSAAs in 90e96 when the concentration was below cmc whereas for a concentrationhigher than the cmc the removal rate varied from 92 to 99 (Kowalska 2008)However when the concentration of the pollutant in water is greater than cmc UFcan be used even though the cutoff of applied membranes is greater than the molecularweight of the eliminated compounds Membranes with a cutoff of 5000e30000 Daare able to remove SAAs in the range of 30 to gt90 depending on membranecompactness and the type of membrane material (Kowalska 2008) An importantparameter in determining the effectiveness of the method is the concentration of theSAAs initially the retention ratio decreases with an increase in concentration andthen above the cmc the retention starts to increase (Bodzek 2013) Hybrid methodsare also proposed to remove anionic SAAs eg integrated UF and ion exchangewith an MIEX and other anionic resins (Kowalska 2010) Application of MIEX

resin in the amount of 20 cm3L of solution at a contact time of 20 min removed95 of the contaminant polyetherosulfone membranes of various densities wereused (Kowalska 2010)

Plant protection products (pesticides herbicides and insecticides) which belongto xenoestrogenes appear in surface and ground waters Pesticides are a group of arti-ficially synthesized substances used to fight pests and improve agricultural productionHowever they are generally toxic to living organisms and difficult to degrade becausetoxic agents have persistent bioaccumulative effects The use of pesticides also consti-tutes a risk for water quality in agricultural areas because these components may passthrough the soil and subsoil and pollute natural surface waters Regulations defining thequality of drinking water establish permissible concentrations of particular compounds

Membrane technologies for the removal of micropollutants in water treatment 497

or their sum at levels at 01 and 05 mgL These are substances with low molecularweight thus they can be effectively removed from water (above 90) during NF orby integrated systems with low pressure-driven membrane processes (MF or NF)and activated carbon adsorption (powdered or granulated) (Taylor amp Wiesner2000) Since the 1990s in many European countries including Poland studies havebeen performed on removing pesticides from natural waters using NF (Bodzek2013 Bodzek amp Konieczny 2005 Taylor amp Wiesner 2000) several pilot-scale andindustrial installations are already working Table 158 presents data from the literatureon removing selected pesticides from water by means of RO and NF (Bodzek 2013BodzekampKonieczny 2005 Taylor ampWiesner 2000) Nanofiltration membranes elim-inate pesticides with a molecular weight above 190 Da to an amount below the limit ofdetection generally the retention coefficient varies from 50 to 100 depending onthe molecular weight and the concentration of pesticides in water as well as on the pres-ence of organic and inorganic compounds (Bodzek 2013 Taylor amp Wiesner 2000)The formation of complexes of organic matter especially humic acids with moleculesof pesticides causes an increase in the retention of those compounds (Bodzek 2013Zhang Van der Bruggen Chen Braeken amp Vandecasteele 2004) However the

Table 158 Pesticide removal in RO and NF (data published from 1967to 2001)

Membrane process (membrane) Compound Retention ()

ROecellulosic membrane DDT 999

ROecellulosic membrane DDT 999

ROeTFC (aromatic polyamide) DDT 995

NF(NFe270 PVD1 PZ SUe610)

Simazine 66e94

Atrazine 79e99

Diuron 45e92

Other 38e100

NF(CAe50 BQe01 Desal 5eDKNTCe20 NTCe60 PVDe1NTRe7250)

Simazine atrazine 0e80

Diuron 5e90

Other 5e96

RO and i NF(20 types of membranes studied)

Symazine 14e95

Atrazine 41e99

Diuron 15e83

Other 0e99

NF (SFe10 STe10) Atrazine 25e67

Note NF nanofiltration RO reverse osmosis

498 Advances in Membrane Technologies for Water Treatment

presence of inorganic substances decreases the negative zeta potential of a membraneand causes the destruction of complexes of pesticides with humic acids resulting inthe release of micropollutants which finally leads to a decrease in retention (TaylorampWiesner 2000) In France near Paris a pilot installation is operating with a capacityof 2800 m3d based on Filmtec membranes (NF-70 and NF-200B) which are charac-terized by the high removal of atrazine and simazine up to 90 and 85 (concentrationin treated water drops from 1e2 gL to 01 gL) (Mallavialle Odendaal amp Wiesner1996) In the course of the study an increase in the retention rate of pesticides withan increase in organic carbon content in the raw water was found

Research on applying UF to the separation of atrazine from water solutions has beencarried out by several scientists (Majewska-Nowak Kabsch-Korbutowicz amp Dodz2001 Sarkar Venkateswralu Nageswara Bhattacharjee amp Kale 2007) The effi-ciency of the process depends on the type of membrane material and membranecompactness The best separation properties are exhibited by membranes with a cutoffof about 1e2 kDa (retention rate of about 60) (Majewska-Nowak et al 2001) Anincrease in efficiency up to 85e95 can be obtained during UF in the presence ofNOM andor cationic polyelectrolyte Hybrid systems combining coagulation adsorp-tion on activated carbon and NF are often used in pesticide removal (Sarkar et al2007) For example 98e99 removal of isoproturon (herbicide) was obtained inthe process of sorption and introduction of NF to the process protected treated wateragainst pesticide intrusion even for the exhaustion sorption bed

The presence of phthalates in the environment is caused by the massive productionof plastics mainly polyvinylchloride in which they are used as plasticizers Because oftheir negative effects on living organisms the concentration of phthalates in differentparts of the environment should be controlled especially in water Polish regulationsestablish the permissible concentration of di-n-butyl phthalate at 20 mgL A surpris-ingly high retention of phthalates was observed during both RO and NF processes(initial concentration 40 mgL) (Table 159) (Bodzek amp Konieczny 2010 BodzekDudziak amp LukseBetlej 2004) Retention rates achieved for diethyl phthalate di-n-butyl and di-2-ethylhexyl were very high and were from 897 (UF) to 999(RO and NF) Results obtained during the removal of phthalates with a molecularweight of 222e391 Da revealed that the molecular weight of a compound did not in-fluence the effectiveness of removal

Phenolic xenoestrogenes (octylphenol nonylphenol bisphenol A and bisphenolF) can be removed from water by means of NF Both the retention coefficient andthe rate of adsorption of xenoestrogenes strongly depend on the type of compoundthat is removed (Table 1510) as well as on the type of membrane (Bodzek 2013)During the membrane filtration of water containing a mixture of xenoestrogeneschanges in volumetric permeate flux (Jv) were not observed and relative volumepermeate flux (a) was close to 1 High retention of octylphenol and nonylphenol inthe range of 61 to 73 was observed for SF-10 and DS-5-DK membranes whereasfor bisphenol A DS-5-DK (69) and MQ-16 (75) the membranes were more effi-cient (Dudziak amp Bodzek 2008) With an increase in the concentration of xenoestro-genes in filtered water a decrease in their retention was observed as a result of theprogressive saturation of the membrane surface with these compounds Nanofiltration

Membrane technologies for the removal of micropollutants in water treatment 499

separation is often accompanied by the phenomenon of adsorption which greatly af-fects the elimination of pollutants and is directly correlated with their retention Thismay impede separation and cause the release of adsorbed organic micropollutants inthe course of the NF For UF membranes with concentrated compounds in deionizedwater at a level of 40 mgL the removal of bisphenol F bisphenol A 4-tert-octylophe-nol and 4-nonylphenol for GM membranes was 19 67 28 and 52 respec-tively whereas for the more compact DS-GE membrane it was 72 56 88and 100 respectively (Dudziak amp Bodzek 2008) A clear impact of the presenceand concentration of the NOM and the presence of inorganic salts as well as sub-stances causing concentration polarization on the retention of xenoestrogens wasfound During filtration in the presence of macromolecular substances the relativepermeability of membranes (a) was significantly less than unity which confirmedthe existence of the fouling phenomenon

A large amount of toxic halogenated aromatic hydrocarbons including chloro-benzenes and polychlobiphenyls (PCBs) chlorophenols and dioxins (polychlorodi-benzo-p-dioxins and dibenzofurans) is introduced into the environment Thesecompounds are insoluble in water They are characterized by high thermal chemicaland biochemical stability and are harmful to humans when they are deposited in adiposetissue They damage the liver and kidneys and interfere with the action of the humanenzyme system Polychlobiphenyls chlorobenzenes and chlorophenols are used invarious industries and enter the environment via wastewater from the chemical industrythrough the production of plastics and dyes from petroleum plants and plants producingplant protection substances and others Effective methods of removing chloro-organiccompounds from industrial wastewater include thermocatalytic oxidation strippingwith air inert gas or steam solvent extraction and adsorption on activated carbonor synthetic resins ( _Zarczynski Stopczyk Zaborowski Gorzka amp Kazmierczak2010) They can be removed from wastewater using a conventional activated sludge

Table 159 Removal of phthalates with RO NF and UF (membranesfrom Osmonics USA)

PhthalatesMolecularweight Da

Concentrationin raw watermgL

Process (membrane)

RO(DSe3eSE)

NF(DSe5eDK)

Retention coefficient

Diethylphthalate

2222 40 951 999

Dienebutylphthalate

2783 951 999

2-ethylhexylphthalate

3906 999 999

Note RO reverse osmosis NF nanofiltration

500 Advances in Membrane Technologies for Water Treatment

Table 1510 Comparison of retention coefficients and degrees of adsorption of phenolic xenoestrogens andrelative permeate flux of investigated NF membranes (Osmonics)

Compound

Nanofiltration membrane

SFe10 DSe5eDK MQe16 DSe51eHL

Retentionadsorption

4eterteoctylphenol 718522 727514 470179 480195

4enonylphenol 605680 703680 500525 435573

Bisphenol A 458525 688693 750750 607334

Bisphenol F e 75e78 e e

Relative permeate flux a 092 099 099 098

Mem

branetechnologies

forthe

removal

ofmicropollutants

inwater

treatment

501

process however the presence of suspended solids in the effluent significantly reducesthe removal rate Thus a better solution is the application of MBRs in which MF or UFmodules are applied instead of secondary settlers (Bolzonella Fatone Pavan amp Cecchi2010) This ensures the complete removal of suspended solids and extended retentiontimes in bioreactors which contributes to the high removal of halogenated aromatic hy-drocarbons from wastewaters Examples include the removal of chloro-dibenzo-p-dioxin which was 61e99 and chloro-dibenzo-p-furans which was 915e995depending on the type of dioxin and the concentration of biomass in the bioreactor (Bol-zonella et al 2010) In the case of natural waters in which the concentration of thehalogenated aromatic hydrocarbons is low one can use adsorption on activated carbonor other sorbents and photochemical oxidation with TiO2 In the latter case for the pho-tocatalyst separation membrane filtration is often used In addition to the removal of thisgroup of compounds NF and RO are proposed so one can get over 995 of themremoved Hydrophobic pervaporation with the use of polydimethylsiloxane membranescan also be used It revealed a high removal rate of contaminants that increased withincreasing vapor pressure and therefore did not depend on the molecular weight of xe-nobiotics The studies covered both PCBs and polychlorinated dioxins (YoonKoyanagi Asano Hara amp Higuchi 2002)

The appearance of compounds that affect hormone production processes in livingorganisms is often observed in surface waters Among these compounds naturaland synthetic hormones are specified Natural estrogens (17b-estradiol estroneand estriol) are present in the environment as a result of their natural excretion by an-imals and people Recently an increase in concentration of synthetic hormone (a-ethi-nylestradiol mestranol and diethylstilbestrol) resulting from the discharge of largeamounts of expired pharmaceuticals from households and from wastewater and hospi-tal waste as well as from pharmaceutical plants has been observed It was shown thatthis type of pollutant could be eliminated from water by means of membrane processes(Bodzek amp Dudziak 2006) Considering the relatively low molecular weight of thosepollutants dense membranes (RO or NF) must be applied Reverse osmosis mem-branes totally eliminate particular hormones retention coefficients obtained for NFand UF membranes were lower (Bodzek amp Dudziak 2006) For natural estrogensthe concentration of micropollutants (10e1000 ngL) does not affect the effectivenessof separation whereas for synthetic estrogens an increase in concentration causes anincrease in retention (Bodzek amp Dudziak 2006) Separation of hormones by meansof NF and UF strongly depends on the hydrophobicity and molecular weight of a com-pound Natural hormones ie estrone estriol and estradiol are removed less effi-ciently compared with their synthetic equivalents ethinylestradiol and mestranol(greater hydrophobicity) (Table 1511) (Bodzek 2013 Bodzek amp Konieczny2010) In addition instead of single-process elimination of hormones from water ahybrid system of coagulation and NF could be used (Bodzek amp Dudziak 2006) Mem-brane bioreactors are also proposed for the removal of hormones from wastewatersThe effectiveness of operating an MBR pilot installation (polyvinylidene difluoridemembrane with a pore diameter of 01 and 02 mm) was studied comparing theobtained results with the conventional installation working on a full-scale basis(Zuehlke Duennbier Lesjean Gnirss amp Buisson 2006) The ability to remove a

502 Advances in Membrane Technologies for Water Treatment

Table 1511 Retention of synthetic and natural hormones in pressure-driven membrane processes(concentration in water 1 mgL) (membranes from Osmonics USA)

Process(membrane)

Hormones(estrogens)

Natural Synthetic

Estrone 17beestradiol Estriol Mestranol17aeethynylEstradiol

DiethylStilbestrol

Retention coefficient

UF (DSGM) 368 353 281 685 553 701

NF (DSe5eDK) 630 767 711 100 904 861

RO (DSe3eSE) 100 100 100 100 100 100

Note RO reverse osmosis NF nanofiltration UF Ultrafiltration

Mem

branetechnologies

forthe

removal

ofmicropollutants

inwater

treatment

503

selected group of estrogenous hormones (estradiol estrone and ethinyl estradiol) wasmonitored More than 90 of natural hormones (estradiol and estrone) and approxi-mately 80 of synthetic ones (ethinylestradiol) were removed with conventional treat-ment In the case of MBR estradiol and estrone were removed in 99 andethinylestradiol in 95

1543 Pharmaceutically active compounds

One of the most important and specific anthropogenic groups of substances affectingthe environment are compounds called pharmaceutical and personal care products(PPCPs) This group includes compounds with pharmaceutical activity as well as sub-stances used by people to maintain personal hygiene (Heberer amp Feldmann 2008)Pharmaceutical and personal care products significantly affect wastewaters and otheraquatic environments (surface water and groundwater which constitute a source ofdrinking water) Main sources of aqueous environment pollution by pharmaceuticalsare households and hospitals as well as diagnostic units pharmaceutical plants andlivestock farms Medicines used by sick people do not totally metabolize and areremoved in urea and feces finally reaching wastewater treatment plants The occur-rence of pharmaceutically active compounds and personal care products and their bio-logically active metabolites in water can generate serious genetic mutations andencourage the formation of drug-resistant bacteria cultures They may lead to a situa-tion in which the human body will be resistant to the action of the drugs These chem-icals can also accumulate in the tissues of organisms which poses a threat to health andeven life Therefore increasing numbers of countries around the world have intro-duced monitoring of these compounds in water and their impact on ecosystems andthe aquatic environment (Heberer amp Feldmann 2008)

Studies on the comparative efficiency of removing drugs in wastewater treatmentplants have shown that biological methods are not always sufficient (Bodzek 2013)Methods to remove medicines from water and wastewater are advanced oxidationactivated carbon adsorption on granulated beds membrane processes such as NFand RO (Snyder et al 2007) and in the case of wastewater treatment MBRs (Claraet al 2005 Heberer amp Feldmann 2008)

The first results of studies performed at municipal wastewater treatment plants dur-ing which MBRs equipped with MF or UF modules were used revealed that theremoval of trace amounts of pollutants was comparable to conventional treatmentmethods (Clara et al 2005) These results attest to the fact that MF and UF membranesare too open to remove biologically nondegradable micropollutants in wastewatertreatment plants On the other hand the higher age of activated sludge and elongatedcontact time achieved in MBR improves biological degradation and the removal ofPhACs and EDCs Membrane bioreactors with immersed modules have been checkedfor the removal of selected pharmaceuticals (clofibric acid diclofenac ibuprofenketoprofen mefenamic acid and naproxen) (Kimura Hara amp Watanabe 2005) Inthe experiments high rates of removal of ketoprofen and naproxen for MBR havebeen observed which were not been found with a conventional treatment systemRemoval rates of phenazone propyphenazone and formylamino-antipyrine were

504 Advances in Membrane Technologies for Water Treatment

also less in conventional installation (15) than with MBR (60e70) (Zuehlke et al2006) Also the effectiveness of removing pharmaceuticals using MBR depended onthe structure of the PhAC molecules eg the number of aromatic rings A higherremoval rate of pharmaceutical substances was observed under low pH conditionsowing to their adsorption on activated sludge flocks (Zuehlke et al 2006)

In most cases installations that use MBR to treat wastewater improved the effi-ciency of organic micropollutant removal compared with conventional wastewatertreatment plants This was because of the extension of retention time and increasingage of the biomass but also because of the increase in its concentration and the adsorp-tion ability of micropollutants on the much larger flocks of activated sludge Thus theywere retained during filtration through MFUF membranes even though these micro-pollutants were often several hundred times smaller than the pores of the membranesRadjenovic Petrovoc and Barcelo (2009) observed significant improvement in the ef-ficiency of removing regulators of lipids and cholesterol statin drugs (gemfibrozilbezafibrate clofibric acid and pravastatin) b-blockers (atenolol and metoprolol) an-tibiotics (ofloxacin and erythromycin) and some painkillers and anti-inflammatorydrugs in MBRs Data from the literature indicate a high and stable rate of removalof clofibric acid and diclofenac in plants equipped with MBR The efficiency ofremoval for clofibric acid usually amounted to 50e70 and for diclofenac 51(Radjenovic et al 2009) during conventional wastewater treatment Other data indi-cate a low removal of diclofenac in typical wastewater treatment plants (10e30)This illustrates how inconsistently the data are presented in the literature and confirmsthe need to conduct further research on the removal of pharmaceutical residues fromwastewater (Radjenovic et al 2009)

Two-month performance monitoring was carried out in MBRs to examine the long-term stability of the system and the effect of retention time on the efficiency ofremoving residues of pharmaceuticals from treated wastewater (Barcelo Petrovic ampRadjenovic 2009) In general the pharmaceuticals were removed to a higher extentby MBR than by a conventional wastewater treatment process In some cases theremoval efficiency was similar and equally high for both cases (eg ibuprofen nap-roxen acetaminophen paroxetine and hydrochlorothiazide) Carbamazepine wasnot removed by the installation with MBR or by the wastewater treatment plantNevertheless wastewater coming from the MBR was characterized by low Chemicaloxygen demand (COD) and total organic carbon (TOC) values and a small content ofammonium nitrogen and total suspended solids The results of monitoring summarizedin Table 1512 (Barcelo et al 2009 Bodzek 2013) show a distinct advantage ofMBRs over the processes in typical wastewater treatment plants Membrane bioreac-tors enable the much more effective removal of residues of pharmaceuticals and othermicropollutants For many PPCPs the removal rate obtained by MBR is virtually100 Thus the use of bioreactors results in treated wastewater of a very high qualityso that the load of pollutants introduced into surface waters is less than that for waste-waters coming from conventional treatment plants

High-pressure membrane technology ie NF and RO used to purify wastewaterand natural waters along with other pollutants can also be used to remove residuesof PPCPs (Heberer amp Feldmann 2008 Yoon Westerhoff Snyder Wert amp Yoon

Membrane technologies for the removal of micropollutants in water treatment 505

2007) The NF membrane exhibited relatively low retention (40) for polar PhACslow volatile and low hydrophobicity In the case of polar organic compounds reten-tion significantly depended on the dipole moment and pH (Kimura Toshima Amy ampWatanabe 2004) Test results showed that negatively charged and ionic compoundssuch as the analgesic diclofenac could be removed in more than 90 regardless ofother physicochemical properties mainly according to electrostatic repulsion

Table 1512 Efficiency of removal of pharmaceuticals in installationwith MBR as well as in conventional wastewater treatment plant

PharmaceuticalEfficiency of removalwith MBR

Efficiency of removal inconventional wastewatertreatment plant

Naproxen 993 851

Ketoprofen 919 515

Ibuprofen 998 825

Diclofenac 874 501

Indomethacin 466 234

Acetaminophen 996 984

Mefenamowy acid 748 294

Propyfenazon 646 427

Ranitidine 950 422

Carbamazepine No elimination No elimination

Paroxetine 897 906

Ofloxacin 94 238

Sulfamethoxazole 605 556

Erythromycin 673 238

Atenolol 655 No elimination

Metoprolol 587 No elimination

Hydrochlorothiazide 663 763

Glibenclamide 473 445

Gemfibrozil 896 388

Bezafibrate 958 484

Klofibric acid 718 277

Pravastatin 908 618

Note MBR membrane bioreactor

506 Advances in Membrane Technologies for Water Treatment

Retention of other ionized drugs exceeded 95 for NF membranes 90 XLE andTFC-HR for the NF-200 membrane it was about 90 (Xu et al 2005) For neutralcompounds retention takes place according to molecular exclusion and adsorptionFor example the neutrally charged antipyretic drug phenacetin or anti-inflammatoryand anti-rheumatic drug ibuprofen show a lower retention rate (for phenacetin onlymore than 20) because they are significantly adsorbed onto membranes with rela-tively high hydrophobicity (Nghiem Scheuroafer amp Elimelech 2005) On the otherhand another neutral antipyretic medicament piramidon is always retained bymore than 70 which suggests that its retention is affected by other phenomena Inaddition the retention of pharmaceuticals in RO and NF is affected by the membranematerial (Kimura et al 2004) For example polyamide membranes had higher effi-ciency (57e91) than CA membranes In the case of polyamide membranes the mo-lecular weight of the compound could be used as a retention trend indicator (separationbased on molecular sieving) whereas the polarity predicted the retention of individualcompounds in the case of CA membranes Retention of pharmaceuticals also dependson the concentration (Kimura et al 2004) Experiments conducted at a concentrationof 100 ngl resulted in significantly lower retention (14e72 for NF and 50e80 forRO) compared with tests at a higher concentration which amounted to 100 mgl(19e93 for NF and 71e95 for RO) One can therefore conclude that the retentionof pharmaceuticals by a compact NF membrane is dominated by the spherical exclu-sion (size) mechanism whereas electrostatic repulsion and spherical exclusion governthe retention of ionized pharmaceuticals in the case of an open NF membraneThe United States evaluated the conventional drinking water treatment processesunder typical water treatment plant conditions for the removal of antibiotics (carbadoxsulfachlorpyridazine sulfamethoxazole sulfamerazine sulfamethazine sulfathiazoleand trimethoprim) (Adams Wang amp Meyer 2002) They showed a very highefficiency of RO in removing all antibiotics

Table 1513 Concentration of pharmaceuticals in water of TeltowCanal and in permeate after one step of RO

Compounds

Averageconcentration inraw water ngL

Averageconcentration inpermeate ngL

Retentioncoefficient

AMDOPH 290 lt1 gt99

Caffeine 429 lt1 gt99

Clofibric acid 155 lt1 gt99

Diclofenac 330 lt1 gt99

Ketoprofen 17 lt1 gt99

Naproxen 38 lt1 gt99

Propyfenazon 177 lt1 gt99

Note AMDOPH 1-Acetyl-1-methyl-2-dimethyl-oxamoyl-2-phenylhydrazide

Membrane technologies for the removal of micropollutants in water treatment 507

Table 1514 Average concentration of pharmaceuticals in biologically treated wastewater and permeate aftertreatment with two-stage RO system

Compound

Concentration ngL Retention coefficient

Raw water PermeateAfter preliminaryfiltration and UF After first RO stage

After second ROstage

AMDOPH 811 lt1 32 gt999 gt999

Bezafibrate 257 lt5 7 960 gt999

Carbamazepine 2282 lt1 13 gt999 gt999

Clofibric acid 178 lt1 20 gt994 gt994

Diclofenac 869 lt1 44 gt999 gt999

Fenofibric acid 705 lt1 22 970 gt999

Gemfibrozil 16 lt1 38 gt933 gt993

Ibuprofen 87 lt1 12 985 gt989

Indomethacin 46 lt1 0 920 gt978

Ketoprofen 99 lt1 20 gt990 gt990

Naproxen 224 lt1 0 982 gt995

Oxazepam 153 lt5 0 gt993 gt993

Primidone 734 lt1 0 gt999 gt999

Propyphenazone 309 lt1 46 993 gt997

Note AMDOPH 1-Acetyl-1-methyl-2-dimethyl-oxamoyl-2-phenylhydrazide RO reverse osmosis UF Ultrafiltration

508Advances

inMem

braneTechnologies

forWater

Treatm

ent

Pressure-driven membrane processes (MF UF NF and RO) were also tested toremove EDCs and PPCPs on a pilot scale and in industrial installations (Snyderet al 2007 Heberer amp Feldmann 2008)

Snyder et al (2007) performed pilot- and industrial-scale tests with MF UF NFand RO for the removal of EDCs and PPCPs from crude municipal wastewater withleachates after the first second and third treatment stages and saline groundwaterinto which specified micropollutants were introduced The study revealed that onlysome compounds were removed duringMF and UF whereas for NF and RO significantretention of all investigated compounds was observed However several compoundssuch as iopromide and pentoxifylline were detected in permeate in trace concentrations

Heberrer and Feldmann (2008) performed awide pilot study of PhAC removal using amobile installation for water treatment equipped with ROmodules normally used duringnatural disasters or military operations The substrate of the study was water from TeltowChannel (Berlin) and treated wastewater from the Ruhleben municipal wastewater treat-ment plant (Berlin) The prototypic three-stage installation with a capacity equal to10000 Lh included duplex bag filters with a particle separation less than 05 mm UFand RO RO could be performed as a one- or two-stage process The presence ofPhAC in treated water from Teltow Channel was not observed (Table 1513) (Bodzek2013 Bodzek amp Konieczny 2010) whereas in RO permeate obtained during treatedwastewater treatment the amount of pharmaceutical was below 10 ngl for both one-and two-stage configurations (Table 1514) (Bodzek 2013 BodzekampKonieczny 2010)

155 Conclusions

Properly selected membrane processes such as RO NF UF and MF in hybrid sys-tems DD ED and MBRs can be used to remove micropollutants from natural watersand wastewaters

High-pressure membrane techniques ie RO and NF can be used for directremoval of inorganic and organic micropollutants while low-pressure (MF and UF)can be used in integrated systems first of all into coagulation and adsorption and inMBR as well as after complexion with polymers or surfactants

Processes with ion-exchange membranes are suitable for micropollutants with anelectrical charge Because of this they are used in many large-scale applicationsincluding the separation of ions desalination and removal of ionic species

156 Final remarks

A number of inorganic and organic micropollutants have been found in potentiallyharmful concentrations in numerous water sources The maximum permissible levelof these compounds in drinking water set by the WHO and a number of countries isvery low (in the range of micrograms per liter to a few milligrams per liter) thusmost of them can be referred to as charged micropollutants Several common treatment

Membrane technologies for the removal of micropollutants in water treatment 509

technologies that are currently used to remove contaminants from natural water sup-plies represent serious exploitation problems

The use of membranes (NF RO and ED) to treat water sources containing anionicand metal micropollutants for drinking and industrial purposes can provide more orless selective removal of the target pollutants especially when the separation of mono-valent and multivalent ions is desired In NF it can be obtained by both ion size andcharge exclusion effects whereas in ED it results from the use of ion-exchange mem-branes with mono-anion permselectivity Nanofiltration and to some extent RO arealso suitable for removing organic micropollutants from water and wastewaters Themost important among them are DBPs pharmaceutical active compounds andEDCs which have high biological activity In the first case volatile THMs andnonvolatile compounds mainly HAAs are formed For this last groups of compoundsspecial attention in natural waters is paid to PAHs and surface-active substanceschlorinated pesticides phthalates alkylphenols polychlorinated biphenyls hormonessynthetic pharmaceuticals and other chemicals and substances produced by humansand disposed into the environment

The application of MF and UF in inorganic and organic micropollutant removal ispossible in integrated systems through coagulation adsorption complexion with poly-mers or surfactants and biological reactions In the last case three major membranebioprocesses have been developed pressure-driven MBRs biological membrane con-tactors and IEMBs The problem with operating low-pressure-driven membrane pro-cesses is membrane fouling

Drinking water containing biologically active substances ie viruses bacteriaprotozoa and other microorganisms is a significant health threat Ultrafiltration andMF can help improve the process of disinfecting water using traditional methodsbecause membranes are barriers to microorganisms Viruses can be retained by UFmembranes whereas bacteria and protozoa need UF and MF membranes

To remove NOM it is possible to successfully use either direct NF or integratedsystems combining UF or MF with coagulation adsorption on activated carbon andeven oxidation NOM and some other anthropogenic organic pollutants can be precur-sors of DBPs which is why it is very important to remove NOM from water

List of acronyms

AOP Advanced oxidation processAOX Adsorbable organic halidescmc Critical micelle concentrationCOD Chemical oxygen demandDBP Disinfection by-productDD Donnan dialysisDOC Dissolved organic carbonEAC Endocrine active compoundsED ElectrodialysisEDC Endocrine-disrupting compoundsEDI Electrodeionization

510 Advances in Membrane Technologies for Water Treatment

EDR Electrodialysis reversalEED Electro-electrodialysisEMBR-SRB Extractive membrane bioreactors with sulfate-reducing bacteriaEU European UnionHAA Haloacetic acidIEMB Ion-exchange membrane bioreactorMBR Membrane bioreactorMCR Membrane coagulation reactorMEUF Micellar enhanced ultrafiltrationMF MicrofiltrationNF NanofiltrationNOM Natural organic matterNTU Nephelometric turbidity unitPAC Powdered activated carbonPAH Polycyclic aromatic hydrocarbonPCB PolychlorobiphenylPEI PolyethyleneiminePEUF Polymer-enhanced ultrafiltrationPhAC Pharmaceutical active compoundPPCP Pharmaceutical and personal care productPVA Poly(vinyl alcohol)RO Reverse osmosisSAA Surface active agentTHM TrihalomethaneTOC Total organic carbonUF UltrafiltrationWHO World Health Organization

References

Adams Y Wang L K amp Meyer M (2002) Removal of antibiotics from surface and distilledwater in conventional water treatment processes Journal of Environmental Engineering128 253e260 Retrieved from httpdxdoiorg101061(ASCE)0733-9372(2002)1283(253)

Alvarado L Ramirez A amp Rodriacuteguez-Torres I (2009) Cr(VI) removal by continuouselectrodeionization Study of its basic technologies Desalination 249 423e428Retrieved from httpdxdoiorg101016jdesal200906051

Amy G Alleman C B amp Cluff C B (1990) Removal of dissolved organic matter bynanofiltration Journal of Environmental Engineering 116 200e205 Retrieved fromhttpdxdoiorg101061(ASCE)0733-9372(1990)1161(200)

Anonymous (2005) Microfiltration and ultrafiltration membranes for drinking water DenverCO American Water Works Association AWWA (USA)

Anonymous (2008) Remediation technologies for perchlorate contamination in water and soilWashington DC The Interstate Technology amp Regulatory Council Retrieved from httpwwwitrcweborgDocumentsPERC-2pdf

Bakalar T Bugel M amp Gajdosova L (2009) Heavy metal removal using reverse osmosisActa Montanistica Slovaca 14 250e253

Membrane technologies for the removal of micropollutants in water treatment 511

Barcelo D Petrovic M amp Radjenovic J (2009) Treating emerging contaminants (pharma-ceuticals) in wastewater and drinking water treatment plants technological perspectives forrational use of water resources in the Mediterranean Region Options Meacutediterraneacuteennes A88 133e140 Retrieved from httpomciheamorgompdfa8800801187

Bick A amp Oron G (2005) Post-treatment design of seawater reverse osmosis plants Boronremoval technology selection for potable water production and environmental controlDesalination 178 233e246 Retrieved from httpdxdoiorg101016jdesal200501001

Biłyk A amp Nowak-Piechota G (2004) Zanieczyszczenie srodowiska substancjami powo-dującymi zakłocenie funkcji endokrynologicznych organizmu (Environmental pollutionwith substances causing disturbance of the organism endocrine functions) OchronaSrodowiska 26(3) 29e35 (in Polish)

Bodzek M (1999) Membrane techniques in wastewater treatment In I M F A Goosen ampW H Shayya (Eds) Water purification Vol 2 Water management purification andconservation in arid climates (pp 121e184) Lancaster Basel Technomic Publishing

Bodzek M (2012) Usuwanie metali ze srodowiska wodnego za pomocą metod mem-branowych e stan wiedzy (Removal of metals from water environment using membranemethods e state of the art) Monografie Komitetu In_zynierii Srodowiska Polskiej AkademiiNauk 66 305e313 In Polish

Bodzek M (2013) Przegląd mo _zliwosci wykorzystania technik membranowych w usuwaniumikroorganizmow i zanieczyszczen organicznych ze srodowiska wodnego (An overviewof the possibility of membrane techniques application in the removal of microorganismsand organic pollutants from aquatic environment) In_zynieria i Ochrona Srodowiska 16(1)5e37 In Polish

Bodzek M amp Dudziak M (2006) Elimination of steroidal sex hormones by conventionalwater treatment and membrane processesDesalination 198 24e32 Retrieved from httpdxdoiorg101016jdesal200609005

Bodzek M Dudziak M amp LukseBetlej K (2004) Application of membrane techniques towater purification Removal of phthalates Desalination 162 121e128 Retrieved fromhttpdxdoiorg101016S0011-9164(04)00035-9

Bodzek M amp Konieczny K (2005) Zastosowanie procesow membranowych w uzdatnianiuwody (Application of membrane processes in water treatment) Bydgoszcz PolandOficyna Wydawnicza Projprzem-Eko In Polish

Bodzek M amp Konieczny K (2010) Wykorzystanie technik membranowych w uzdatnianiuwody do picia czII e usuwanie związkow organicznych (Utilization of membranetechniques in the treatmnent of drinking Water Part II e removal of organic compounds)Technologia Wody 2(04) 15e31 In Polish

Bodzek M amp Konieczny K (2011a) Membrane techniques in the removal of inorganicmicropollutants from water environment e state of the art Archives of EnvironmentalProtection 37(2) 15e29

Bodzek M amp Konieczny K (2011b) Usuwanie zanieczyszczen nieorganicznych zesrodowiska wodnego metodami membranowymi (Removal of inorganic micropollutantsfrom water environment by means of membrane methods) Warszawa WydawnictwoSeidel-Przywecki In Polish

Bodzek M Konieczny K amp Kwiecinska A (2011) Application of membrane processes indrinking water treatment e state of art Desalination and Water Treatment 35 164e184httpdxdoiorg105004dwt20122435

Bodzek M Korus I amp Loska K (1999) Application of the hybrid complexation e ultra-filtration process for removal of metal ions from galvanic wastewater Desalination 121117e121 Retrieved from httpdxdoiorg101016S0011-9164(99)00012-0

512 Advances in Membrane Technologies for Water Treatment

Bodzek M Płatkowska A Rajca M amp Komosinski K (2008) Fouling of membranesduring ultrafiltration of surface water (NOM) Ecological Chemistry and Engineering A16 107e119

Bolzonella D Fatone F Pavan P amp Cecchi F (2010) Poly-chlorinated dibenzo-p-dioxinsdibenzo-furans and dioxin-like poly-chlorinated biphenyls occurrence and removal inconventional and membrane activated sludge processes Bioresource Technology 1019445e9454 Retrieved from httpdxdoiorg101016jbiortech201007067

Bryjak M (2001) Procesy separacyjne a polimery O mo_zliwosciach nietypowego wykorzys-tania syntetycznych polimerow (Separation processes and polymers About the possibilitiesof an atypical use of synthetic polymers) Wrocław Poland Oficyna Wydawnicza Poli-techniki Wrocławskiej In Polish

Butler R Godley A Lytton L amp Cartmell E (2005) Bromate environmental contamina-tion review of impact and possible treatment Critical Reviews in EnvironmentalScience and Technology 35 193e217 Retrieved from httpdxdoiorg10108010643380590917888

Chalatip R Chawalit R amp Nopawan R (2009) Removal of haloacetic acids by nano-filtration Journal of Environmental Sciences 21 96e100

Clara M Strenn B Gans O Martinez E Kreuzinger N amp Kroiss H (2005) Removal ofselected pharmaceuticals fragrances and endocrine disrupting compounds in a membranebioreactor and conventional wastewater treatment plantsWater Research 39 4797e4807Retrieved from httpdxdoiorg101016jwatres200509015

Crespo J G Velizarov S amp Reis M A (2004) Membrane bioreactors for the removal ofanionic micropollutants from drinking water Current Opinion in Biotechnology 15463e468 Retrieved from httpdxdoiorg101016jcopbio200407001

Dilek C Ozbelge H O Bicak N amp Yilmaz L (2002) Removal of boron from aqueoussolution by continuous polymer enhanced-ultrafiltration by polyvinyl alcohol SeparationScience and Technology 37 1257e1271 Retrieved from httpdxdoiorg101081SS-120002610

Domany Z Galambos I Vatai G amp Bekassy-Molnar E (2002) Humic substances removalfrom drinking water by membrane filtration Desalination 145 333e337 Retrieved fromhttpdxdoiorg101016S0011-9164(02)00432-0

Dudziak M (2011) Usuwanie mikoestrogenow w procesie koagulacji sorpcji i nanofiltracji eprocesy pojedyncze i układy zintegrowane (Removal of mycoestrogens in the coagulationsorption and nanofiltration processes e a single and integrated processes) Nauka PrzyrodaTechnologie 5(4) 1e9 In Polish

Dudziak M amp Bodzek M (2008) Removal of xenoestrogens from water during reverseosmosis and nanofiltration e effect of selected phenomena on separation of organicmicropollutants Architecture Civil Engineering Environment 1(3) 95e101

Dudziak M amp Bodzek M (2010a) A study of selected phytoestrogens retention by reverseosmosis and nanofiltration membranes e the role of fouling and scaling Chemical Papers64(2) 139e146 Retrieved from httpdxdoiorg102478s11696-009-0072-0

Dudziak M amp Bodzek M (2010b) Removal of phytoestrogens from water solutions usingtubular nanofiltration membranes Ecological Chemistry and Engineering A 17 289e296

Frenzel I Holdik H Stamatialis D F Pourcelly G amp Wessling M (2005) Chromic acidrecovery by electro-electrodialysis Journal of Membrane Science 261 49e55 Retrievedfrom httpdxdoiorg101016jmemsci200503031

Hafiane A Lemordant D amp Dhahbi M (2000) Removal of hexavalent chromium bynanofiltration Desalination 130 305e312 Retrieved from httpdxdoiorg101016S0011-9164(00)00094-1

Membrane technologies for the removal of micropollutants in water treatment 513

Han B Runnells T Zimbron J amp Wickramasinghe R (2002) Arsenic removal fromdrinking water by flocculation and microfiltration Desalination 145 293e298 Retrievedfrom httpdxdoiorg101016S0011-9164(02)00425-3

Heberer T amp Feldmann D (2008) Removal of pharmaceutical residues from contaminatedraw water sources by membrane filtration In Klaus Keuroummerer (Ed) Pharmaceutical in theenvironment (pp 427e453) Berlin-Heidelberg Springer

Hu K amp Dickson J M (2006) Nanofiltration membrane performance on fluoride removalfrom water Journal of Membrane Science 279 529e538 Retrieved from httpdxdoiorg101016jmemsci200512047

Jacangelo J Aieta E M Carns K E Cummings E W amp Mallevialle J (1989) Assessinghollow-fiber ultrafiltration for particulate removal Journal AWWA 81(11) 68e75Retrieved from httpwwwjstororgstable41292731

Jacukowicz-Sobala I (2009) Wspołczesne metody usuwania chromu ze sciekow (Modernmethods of removal of chromium from wastewaters) Przemysł Chemiczny 88(1) 51e60In Polish

Kabay N Arar O Acar F Ghazal A Yuksel U amp Yuksel M (2008) Removal of boronfrom water by electrodialysis Effect of feed characteristics and interfering ions Desali-nation 223 63e72 Retrieved from httpdxdoiorg101016jdesal200701207

Kabsch-Korbutowicz M Biłyk A amp Mołczan M (2006) The effect of feed water pre-treatment on ultrafiltration membrane performance Polish Journal of EnvironmentalStudies 15 719e725

Kartinen E O amp Martin C J (1995) An overview of arsenic removal processes Desalina-tion 103 79e88 Retrieved from httpdxdoiorg1010160011-9164(95)00089-5

Kimura K Hara H amp Watanabe Y (2005) Removal of pharmaceutical compounds bysubmerged membrane bioreactors (MBRs) Desalination 178 135e140 Retrieved fromhttpdxdoiorg101016jdesal200411033

Kimura K Toshima S Amy G amp Watanabe Y (2004) Rejection of neutral endocrinedisrupting compounds (EDCs) and pharmaceutical active compounds (PhACs) by ROmembranes Journal of Membrane Science 245 71e78 Retrieved from httpdxdoiorg101016jmemsci200407018

Konieczny K Bodzek M amp Rajca M (2006) A coagulationeMF system for water treatmentusing ceramic membranes Desalination 198 100e109 Retrieved from httpdxdoiorg101016jdesal200609014

Korus I (2010) Removal of Pb(II) ions in ultrafiltration enhanced with polyelectrolytePolimery 55(2) 135e138

Korus I (2012) Wykorzystanie ultrafiltracji wspomaganej polimerami do separacji jonowmetali cię_zkich (The application of ultrafiltration enhanced with polymers for theseparation of heavy metal ions) Gliwice Poland Wydawnictwo Politechniki SląskiejIn Polish

Kowalska I (2008) Surfactant removal from water solutions by means of ultrafiltration and ion-exchange Desalination 221 351e357 Retrieved from httpdxdoiorg101016jdesal200701094

Kowalska I (2010) Usuwanie anionowych substancji powierzchniowo-czynnych z roztworowwodnych w hybrydowym układzie oczyszczania wymiana jonowa e ultrafiltracja(Removal of anionic surface active substances from aqueous solutions in a hybrid ionexchange-ultrafiltration system) Monografie Komitetu In_zynierii Srodowiska PAN 65271e277

Kowalska M Dudziak M amp Bohdziewicz J (2011) Biodegradacja kwasow halogen-ooctowych w bioreaktorze z poliamidową enzymatyczną membraną ultrafiltracyjną

514 Advances in Membrane Technologies for Water Treatment

(Biodegradation of haloacetic acids in bioreactor with polyamide enzymatic ultrafiltrationmembrane) In_zynieria i Ochrona Srodowiska 14 257e266

Kołtuniewicz A B amp Drioli E (2008) Membranes in clean technologies Weinheim Wiley-VchVerlag GmbH

Laine J-M Campos C Baudin I amp Janex M-L (2002) Understanding membrane foulingA review of over a decade of research In S Wodrich amp H Degeler-Koch (Eds)Proceedings of ldquoMembranes in drinking and industrial water production MDIW 2002rdquo(pp B37a 351e360) Mulheim an der Ruhr Germany ZENIT GmbH

Laine J Clark M M amp Mallevialle J (1990) Ultrafiltration of lake water Effect of pre-treatment on the partitioning of organics THMFP and flux Journal AWWA 82 12e82

Lee S Quyet N Lee E Kim S Lee S Jung Y D et al (2008) Efficient removals oftris(2-chloroethyl) phosphate (TCEP) and perchlorate using NF membrane filtrationsDesalination 221 234e237 Retrieved from httpdxdoiorg101016jdesal200702054

Luks-Betlej K Bodzek M amp Waniek A (2001) PAH removal from water by membraneprocesses In A Noworyta amp A Trusek-Hołowina (Eds) Using membranes to assist ofcleaner production (pp 61e67) Wrocław Poland Argi

Mack C Burgess J E amp Duncan J R (2004) Membrane bioreactors for metal recovery fromwastewater A review Water SA 30 521e532

Majewska-Nowak K Kabsch-Korbutowicz M amp Dodz M (2001) Herbicide separation bylow-pressure membrane process In A Noworyta amp A Trusek-Hołownia (Eds) Usingmembranes to assist of cleaner processes (pp 153e158) Wrocław Poland Argi

Mallavialle J Odendaal P E amp Wiesner M R (Eds) (1996) Water treatment membraneprocesses New York San Francisco Washington DC McGraw-Hill

Mavrov V Nikolov N D Islam M A amp Nikolova J D (1992) An investigation on theconfiguration of inserts in tubular ultrafiltration module to control concentration polari-zation Journal of Membrane Science 75 197e201 Retrieved from httpdxdoiorg1010160376-7388(92)80017-E

Mehiguene K Garba Y Taha S Gondrexon N amp Dorange G (1999) Influence ofoperating conditions on the retention of copper and cadmium in aqueous solutions bynanofiltration experimental results and modeling Separation and Purification Technology15 181e187 Retrieved from httpdxdoiorg101016S1383-5866(98)00096-3

Nawrocki J (2005) Uboczne produkty utlenienia i dezynfekcji wody (Oxidation and disin-fection by-products of water) Ochrona Srodowiska 27(4) 3e12 In Polish

Nghiem L D Scheuroafer A I amp Elimelech M (2005) Pharmaceutical retention mechanisms bynanofiltration membranes Environmental Science amp Technology 39 7698e7705Retrieved from httpdxdoiorg101021es0507665

Nguyen C M Bang S Cho J amp Kim K W (2009) Performance and mechanism of arsenicremoval from water by a nanofiltration membrane Desalination 245 82e94 Retrievedfrom httpdxdoiorg101016jdesal200804047

Owlad M Aroua M K Daud W A amp Baroutian S (2009) Removal of hexavalentchromium -contaminated water and wastewater A review Water Air Soil Pollution 20059e77 Retrieved from httpdxdoiorg101007s11270-008-9893-7

Pawlak Z Zak S amp Zabłocki L (2006) Removal of hazardous metals from groundwater byreverse osmosis Polish Journal of Environmental Studies 15 579e583

Prados-Ramirez M Ciba N amp Bourbigot M (1995) Available techniques for reducingbromate in drinking water Water Supply 13 61e70

Qdais H A amp Moussa H (2004) Removal of heavy metals from wastewater by membraneprocesses A comparative studyDesalination 164 105e110 Retrieved from httpdxdoiorg101016S0011-9164(04)00169-9

Membrane technologies for the removal of micropollutants in water treatment 515

Raczuk J (2010) Nitrogen compounds in well water as a factor of a health risk to theMaciejowice commune inhabitants (Mazowieckie Voivodeship) Archives of Environ-mental Protection 36(4) 31e39

Radjenovic J Petrovoc M amp Barcelo D (2009) Fate and distribution of pharmaceuticals inwastewater and sewage sludge of the conventional activated sludge (CAS) and advancedmembrane bioreactor (MBR) treatment Water Research 43 831e841 Retrieved fromhttpdxdoiorg101016jwatres200811043

Rajca M (2012) Wpływ wybranych czynnikow na usuwanie anionowych zanieczyszczenz wod w procesie wymiany jonowej MIEXDOC (The impact of selected factors onthe removal of anionic water pollutants in ion-exchange process of MIEX DOC)Archives of Environmental Protection 38 115e121 Retrieved from httpdxdoiorg102478v10265-012-0010-z

Religa P amp Gawronski R (2006) Oczyszczanie chromowych sciekow garbarskich e procesymembranowe (Treatment of tanning wastewaters e membrane processes) PrzeglądWłokienniczy e Włokno Odzie_z Skora 12 41e44 In Polish

Sarkar B Venkateswralu N Nageswara R Bhattacharjee C amp Kale V (2007) Treatmentof pesticide contaminated surface water for production of potable water by a coagulation eadsorption e nanofiltration approach Desalination 212 129e140 Retrieved from httpdxdoiorg101016jdesal200609021

Sehn P (2008) Fluoride removal with extra low energy reverse osmosis membranes Threeyears of large scale field experience in Finland Desalination 223 73e84 Retrieved fromhttpdxdoiorg101016jdesal200702077

Shih M-C (2005) An overview of arsenic removal by pressure-driven membrane processesDesalination 172 85e97 Retrieved from httpdxdoiorg101016jdesal200407031

Siddiqui M Amy G Ryan J amp Odem W (2000) Membranes for the control of naturalorganic matter from surface waterWater Research 34 3355e3370 Retrieved from httpdxdoiorg101016S0043-1354(00)00024-5

SnyderSAdhamSReddingACannonFDeCarolis JOppenheimer J et al (2007)Roleofmembranes and activated carbon in the removal of endocrine disruptors and pharmaceuticalsDesalination 202 156e181 Retrieved from httpdxdoiorg101016jdesal200512052

Sosnowski T Suchecka T amp Piątkiewicz W (2004) Penetracja komorki przez membranęmikrofiltracyjną (Penetration of the cell through the microfitration membrane)MonografieKomitetu In_zynierii Srodowiska PAN 22 359e367 In Polish

Tahaikt M Haddou A El Habbani R Amor Z Elhannouni F Taky M et al (2008)Comparison of the performances of three commercial membranes in fluoride removal bynanofiltration continuous operations Desalination 225 209e219 Retrieved from httpdxdoiorg101016jdesal200707007

Tan L amp Amy G (1991) Comparing ozonation and membrane separation for color removaland disinfection by-product control Journal AWWA 83(5) 74e79

Taylor J S ampWiesner M (2000) Membranes In R D Letterman (Ed)Membrane processesin water quality and treatment New York McGraw Hill

Thorsen T (1999) Membrane filtration of humic substances e state of art Water Science andTechnology 40(9) 105e112 Retrieved from httpdxdoiorg101016S0273-1223(99)00646-0

Uyak V Koyuncu I Oktem I Cakmakci M amp Toroz I (2008) Removal of trihalomethanesfrom drinking water by nanofiltration membranes Journal of Hazardous Materials 152789e794 Retrieved from httpdxdoiorg101016jjhazmat200707082

Van der Bruggen B amp Vandecasteele C (2003) Removal of pollutants from surface waterand ground water by nanofiltration Overview of possible applications in the drinking

516 Advances in Membrane Technologies for Water Treatment

water Environmental Pollution 122 435e445 Retrieved from httpdxdoiorg101016S0269-7491(02)00308-1

Velizarov S Crespo J G amp Reis M A (2004) Removal of inorganic anions fromdrinking water supplies by membrane bioprocesses Reviews in Environmental Sci-ence amp BioTechnology 3 361e380 Retrieved from httpdxdoiorg101007s11157-004-4627-9

Velizarov S Matos C Oehmen A Serra S Reis M amp Crespo J (2008) Removalof inorganic charged micropollutants from drinking water supplies by hybrid ionexchange membrane processes Desalination 223 85e90 Retrieved from httpdxdoiorg101016jdesal200701217

Wang C Lippincott L amp Meng X (2008) Kinetics of biological perchlorate reduction andpH effect Journal of Hazardous Materials 153 663e669 Retrieved from httpdxdoiorg101016jjhazmat200709010

Waniek A Bodzek M amp Konieczny K (2002) Trihalomethanes removal from water usingmembrane processes Polish Journal of Environmental Studies 11 171e178

Wilf M (2010) The guidebook to membrane technology for wastewater reclamationHopkinton MA Balaban Desalination Publications

Wisniewski J (2001) Electromembrane processes In A Noworyta amp A Trusek-Hołownia(Eds) Membrane separations (pp 147e179) Wrocław Poland Argi

Wisniewski J amp Kliber S (2010) Bromate removal from water in electrodialysis processMonografie Komitetu Inzynierii Srodowiska Polskiej Akademii Nauk 66 305e313

Xu P Drewes J E Bellona C Amy G Kim T U Adam M et al (2005) Rejection ofemerging organic micropollutants in nanofiltration-reverse osmosis membrane applica-tions Water Environment Research 77 40e48 Retrieved from httpdxdoiorg102175106143005X41609

Yoon B Koyanagi S Asano T Hara M amp Higuchi A (2002) Removal of endocrinedisruptors from aqueous solutions by pervaporation Journal of Membrane Science 198311e320 Retrieved from httpdxdoiorg101016S0376-7388(01)00671-8

Yoon Y Westerhoff P Snyder S Wert E amp Yoon J (2007) Removal of endocrinedisrupting compounds and pharmaceuticals by nanofiltration and ultrafiltration membranesDesalination 202 16e23 Retrieved from httpdxdoiorg101016jdesal200512033

Zakrzewska-Trznadel G (2003) Radioactive solution treatment by hybrid complexation-UFNF process Journal of Membrane Science 225 25e39 Retrieved from httpdxdoiorg101016S0376-7388(03)00261-8

_Zarczynski A Stopczyk A Zaborowski M Gorzka Z amp Kazmierczak M (2010) Usu-wanie związkow chloro-organicznych ze sciekow przemysłowych ze szczegolnym uwz-ględnieniem metody termo katalitycznego utleniania (Removal of chloro-organiccompounds from industrial wastewaters with special reference to the of thermo-catalyticoxidation method) Ochrona Srodowiska 32 49e54 In Polish

Zhang G Gao Y Zhang Y amp Gu P (2005) Removal of fluoride from drinking water by amembrane coagulation reactor (MCR) Desalination 177 143e155 Retrieved from httpdxdoiorg101016jdesal200412005

Zhang Y Van der Bruggen B Chen G X Braeken L amp Vandecasteele C (2004) Removalof pesticides by nanofiltration Effect of the water matrix Separation and PurificationTechnology 38 163e172 Retrieved from httpdxdoiorg101016jseppur200311003

Zuehlke S Duennbier U Lesjean B Gnirss R amp Buisson H (2006) Long-term com-parison of trace organics removal performances between conventional and membraneactivated sludge processes Water Environment Research 78 2480e2486 Retrieved fromhttpdxdoiorg102175106143006X111826

Membrane technologies for the removal of micropollutants in water treatment 517

Membrane technologies forwater treatment and reuse in thegas and petrochemical industries

16Y JiSchool of Resources and Environmental Engineering East China University of Scienceand Technology Shanghai PR China

161 Introduction

Petrochemicals can be defined as a large group of chemicals derived from natural gasand petroleum and further used for a variety of chemical purposes which areextremely important in modern civilization Nevertheless like most production activ-ities petroleum oil and gas production and further processing processes such as extrac-tion and refining are responsible for generating a huge volume of wastewater to bedischarged into the environment Because environmental policy is increasingly severewater contaminated with petroleum derivatives and processing additives should betreated to separate these derivatives from water before it can return to the environment

Wastewater generated in the petrochemical industry is a mixture of organic andinorganic materials containing many different chemical compositions depending onthe complexity of the refinery the existing processes and the type of petroleum oiland gas employed The effluents are mainly produced by extraction and physical sep-aration processes such as atmospheric and vacuum distillation deparaffinization andde-asphalting and also by processes involving chemical conversions by isomerizationalkylation etherification catalytic reform etc Therefore wastewater composition isqualitatively similar to petroleum oil andor gas production

The major compounds of the wastewater include (1) oil compounds (2) dissolvedformation minerals (3) production chemical compounds and (4) production solids(including formation solids corrosion and scale products bacteria waxes and asphal-tenes) Among pollutants present in effluents from petrochemical industries at higherconcentrations oilewater emulsions stand out Besides oilewater emulsions specificchemical concentrations of wastewaters vary considerably with the geographical loca-tion and refining processes Table 161 lists chemical compositions of typical wastewa-ters from petrochemical and gas production (Hansen amp Davies 1994 Li amp Lee 2009)

Oil is a mixture of hydrocarbons such as benzene toluene ethylbenzene andxylene naphthalene phenanthrene dibenzothiophene polyaromatic hydrocarbonsand phenols Oilewater mixtures are generated at different production stages Becausethe solubility of oil in water is generally very low most of the oil is dispersed in waterOil in these wastewater streams may exist in three forms free oil (separate oil globulesof sufficient size that they can rise as a result of buoyancy force generally larger than

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400016-2Copyright copy 2015 Elsevier Ltd All rights reserved

150 mm) dispersed oil (20e150 mm) and emulsified oil which has droplets typicallyless than 20 mm Stable oily emulsion is a dispersed system in which the phases areimmiscible or partially miscible liquids and difficult to be flocculated Wastewaterin petrochemical industry is currently treated by activated sludge process withpretreatment of oilewater separation However de-emulsifying these effluents withconventional processes including chemical dispersion breakup gravity settling centri-fugation air flotation fibrous or packed-bed coalescence and biological degradation isoften not economically feasible might cause secondary pollution does not haveappropriate efficiency with regard to separation or produces large amounts of mudthat also need treatment (Almeida Neto Silva Valenzuela-Diacuteaz amp Rodrigues 2006)

Furthermore with regard to the significant matter of environmental concern manycountries have implemented stringent regulatory standards for discharging thesewastewaters According to United States Environmental Protection Agency (USEPA)regulations the daily maximum limit of ldquooil and greaserdquo for petroleum oil and gas pro-duction wastewater is 42 mgL and the monthly average limit is 29 mgL (USEPA)

Table 161 Typical wastewater composition from petrochemical andgas production

Component Oil wastewater (mgL) Gas wastewater (mgL)

Organic composition

Aliphatic C2eC5 1 1

Aliphatic gtC5 5 10

Fatty acids C2eC5 300 150

Benzene 8 25

Naphthalenes 15 15

Phenols 5 5

Inorganic compositionHCO

3 15381 58703

H2S 225 65

Cl 130636 23895

SO24 45941 241

Nathorn 804212 41693

Kthorn 3986 35

Mgthorn 8941 19

Cathorn 43955 11

Srthorn 889 63

Fe2thorn 653 065

520 Advances in Membrane Technologies for Water Treatment

Besides the increasing need to reuse treated water has generated interest in treatingpetrochemical wastewater with the advanced physical membrane-based separationprocess

162 Membrane technologies for water treatmentand reuse in the gas and petrochemical industries

Generally membranes are defined essentially as a barrier in the form of thin syntheticorganic or inorganic films selectively separating fluid from its components andrestricting transport of various chemicals The membrane pressure-driven process re-lies on the pore size of the membrane to separate oily droplets according to their poresizes Membrane processes including microfiltration (MF) ultrafiltration (UF) nano-filtration (NF) and reverse osmosis (RO) are increasingly being applied to treat oilywastewater (wastewater containing oil) (Bhave amp Fleming 1988 Daiminger NitschPlucinski amp Hoffmann 1995) Microfiltration is mainly for the separation of sus-pended particles UF for macromolecules RO for dissolved and ionic componentsand NF for multivalent ions rather than for univalent ions Among these processesUF is especially useful for stable emulsions particularly water-soluble oily wastesin wastewaters from the gas and petrochemical industries

The membrane unit is usually operated in a semi-batch recycle as shown inFigure 161 The oilewater emulsion is fed into the separation tank at the same rateas treated permeate is withdrawn therefore maintaining a constant level in the tankThe retentate containing the oil is recycled to the process tank and allowed to concen-trate only when the oil concentration reaches a set level Generally the final concen-trate volume is only 3e5 of the initial volume of oily wastewater fed into the

Retentate

Membrane cell

PermeateFlowmeter

Cooling water

Pressure guage

Three way valve

Pump Feed tank

Water jacket

Water outlet

Figure 161 Schematic setup of membrane treatment of wastewaters from petrochemical andgas production

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 521

separation tank The recovered oil can be collected as a by-product or be further treatedusing other oxidation technologies

Membranes have many advantages over traditional techniques (Makki Al-AlawyAl-Hassani amp Rashad 2011) (1) They are more widely applicable across a widerange of industries (2) the quality of the treated water is more uniform regardless ofinfluent variations (3) no extra chemicals are added (4) membranes can be used in-process to allow recycling of selected waste streams within a plant (5) concentratesup to 40e70 oil can be obtained by UF or MF (6) the membrane equipment hasa smaller space requirement and offers a simple easy-to-operate low-maintenanceprocess option and (7) energy costs are lower compared with thermal treatments

Membrane processes also have the following limitations (1) Scale-up is almostlinear above a certain size and therefore the capital costs for large effluent volumescan be high and (2) polymeric membranes experience fouling and degradation duringuse which can increase operating costs significantly

Despite these disadvantages membrane separation is gaining wider acceptancebecause it consistently produces effluents of acceptable discharge quality and it isperceived to be a simple process from an operational viewpoint Therefore com-pounded with other methods membranes are a commercial success for oily wastewatertreatment with more than 3000 polymeric UFMF installations and over 75 inorganicceramic units worldwide (Bilstad amp Espedal 1996 Ciarapica amp Giacchetta 2003He amp Jiang 2008 Lee amp Frankiewicz 2005 Li Yan Xiang amp Hong 2006)

163 Integrating membrane processes into existingtreatment infrastructure

Currently wastewaters from gas and petroleum oil industries are generally treated basedon biodegradation by oxidation (and to a lesser extent reduction) worldwide Retrofit-ting such facilities with an entirely new approach not based on oxidation is rarelypossible Generally process integrations integrated with more advanced physicochem-ical technologies are accepted to be able to improve the sustainability of old treatmentfacilities and are typically necessary to minimize the overall environmental impactAmong these technologies membrane processes are thought to be ideal candidatesfor process integration because membrane technologies can be easily integrated intothe total treatment systems combining several processes The term ldquointegrated mem-brane systemrdquo (IMS) frequently refers to water treatment systems that incorporate mem-branes An IMS can be defined either as a system that integrates two or more membraneprocesses or a system combining a membrane process with other treatment processes Itis claimed that IMS has significant advantages for the treatment of wastewater streamscontaining oily substances halogenated organics or organic solvent (Scott 1995)Integrated membrane systems have gained increasing importance in treating oily waste-waters combined with a chemical or biological process or a conventional unit operationsuch as distillation or absorption An IMS with two or more separation processes ismost frequently employed to treat wastewater from the gas and petrochemical industriesto meet severe emission standards and reduce cost

522 Advances in Membrane Technologies for Water Treatment

1631 Permeate flux and concentration polarization

The capital and operational costs of membrane systems depend directly on membranepermeate flux Consequently the permeate flux is the central consideration indesigning a membrane process for water treatment and reuse in the gas and petrochem-ical industries

Generally if the concentration of the emulsified oil droplet and pressure are below acertain limit the permeate flux is directly proportional to the trans-membrane pressurewhich can be described as

J0w frac14 DP

h0Rm(161)

where J0w is the permeate flux of pure water DP is the trans-membrane pressure Rm theintrinsic resistance of the clean membrane and h0 is the water viscosity

During the membrane process the oil droplets accumulate on the membrane surfaceand a concentration difference between the membrane surface and bulk solution isformed resulting in oil droplets diffusing into the bulk solution backward and inincreasing hydraulic resistance to permeate flow until a balance is obtained concentra-tion polarization The concentration polarization layer results in an additional osmoticpressure therefore the effective driving force of membrane process as well as thefiltration flux and solute rejection are reduced correspondingly Consequently thepermeate flux declines in time and the following is the differential equation of masstransfer for steady state

JwdCdx

Dd2Cdx2

frac14 0 (162)

Integrating Eqn (162) gives the following equation

JwC DdCdx

frac14 C1 (163)

where D is the diffusion coefficient of oil droplets JwC is the solute flux ontomembrane and D dC

dx is the solute diffusion flux in the backward direction Theintegral constant C1 is equal to the oil droplet permeate flux which is a constant atsteady state

By integrating Eqn (163) we can obtain the following equation

Jw frac14 D

dlnCm Cf

Cb Cf(164)

where Cb is the oil droplet concentration in the bulk solution of feed Cm is the oildroplet concentration at the membrane surface Cf is the oil droplet concentration in thepermeate and d is the thickness of the boundary layer (polarization layer)

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 523

Increasing pressure can improve permeate flux of water and the oil droplet concen-tration at the membrane surface also goes up leading to more severe concentrationpolarization and higher flux of the solute diffusion backward to the bulk solution

1632 Membrane fouling

Besides concentration polarization another major challenge confronting membraneapplications in water treatment and reuse in the gas and petrochemical industries ismembrane fouling Concentration polarization decreases the driving force of fluxacross the membrane which is completely reversible and could be reduced by modi-fying the flow over the membrane (Asatekin Kang Elimelech amp Mayes 2007) How-ever membrane treatment of oily wastewater is economically limited by one factorloss of membrane flux owing to severe fouling Flux is often reduced by one to twoorders of magnitude severely affecting the economic viability of membrane treatmentof petrochemical industry wastewaters (Asatekin amp Mayes 2009)

As soon as the upper surface of the membrane comes into contact with the waste-water contaminants such as oil droplets and colloid particles adsorb at the membranesurface because of physiochemical interactions It is widely accepted that there are twomechanisms of membrane fouling pore blocking which is responsible for the initialsharp drop from the flux of pure water filtration and cake formation which is thereason for long-term gradual flux decline (Song 1998) The fundamental cause ofmembrane fouling is the nonequilibrium operation in which the applied pressure ismuch higher than the critical pressure that can be absorbed by the concentration polar-ization layer In such an operation the membrane pores will be quickly blocked anda cake layer will form to absorb the excessive pressure

There are four models of fouling that are categorized according to differentblockage mechanisms as follows (Kim amp DiGiano 2009) complete (solute particlesreach open pores of the membrane and block and seal the pore entrances completely)standard (solute particles enter the pores and are adsorbed or trapped inside the porewalls) intermediate pore blocking (solute particles occupy a fraction of the poreentrance leading to a reduction in the permeate flux without totally sealing the pores)and cake filtration (particle diameters are larger than those of the membrane pores sothe particles do not enter the pores) Hermia developed an empirical model to identifythe fouling mechanism by analysis of the characteristic curve (Hermia 1982)

d2tdV2 frac14 b

dtdV

n

(165)

where V is the cumulative volume of filtrate t is the time of operation and b is aconstant

The volumetric permeate flux can be expressed as

Jw frac14 1A

dVdt

(166)

524 Advances in Membrane Technologies for Water Treatment

Therefore the governing equation of the flux decline with time could be obtainedby substituting and integrating Eqn (166)

Jw frac14 1A

dJwdt

frac14 aJ3nw (167)

where a is a constant The value of n depends on the blockage mechanism n frac14 2 forcomplete pore blocking n frac14 15 for standard pore blocking n frac14 1 for intermediatepore blocking and n frac14 0 for cake formation

164 Improving process design operation monitoringand control

1641 Design considerations

Efforts have been made to improve permeate flux including

1 Membrane modification The separation behavior is strongly influenced by the membranematerials (Hamza Pham Matsuura amp Santerre 1997) and the surface properties of themembrane have a critical role in the determination of fouling resistance The widelyaccepted fact is that surface hydrophilic membrane is employed to treat an oily emulsionbecause the hydrophobic membranes are easily fouled owing to adsorption of oily sub-stances in water on and in the pores of the membranes (Nakatsuka Nakate amp Miyano1996) To achieve this goal membrane material can be modified or functionalized by(Ochoa Masuelli amp Marchese 2003 Ulbricht 2006) (1) synthesis of new surfacehydrophilic polymers (2) hydrophilic functionalization of polymeric membranes (3)preparation of homogenous or heterogenous hydrophilic blends starting from differentpolymeric materials or particles from organic or inorganic origin Recently polyvinylalcohol cellulose acetate and ceramicepolymeric composite membranes are beingused for oilewater emulsions separation because of their antifouling properties (MittalJana amp Mohanty 2011)

2 Pulsed flow The process of transporting oil droplets through a membrane boundary in asteady flow field is related to the classic Graetz problem that analyzes the concentrationprofile of a steadily flowing fluid that undergoes a step change on the boundary Super-imposing an oscillating flow to the steady flow will alter the flow profiles and thus alterthe concentration and mass transfer of the system The oscillations and unsteady flows canbe obtained by introducing pulsations into the feed or filtrate channels which can enhanceshear at the membrane surface to decrease concentration polarization Although pulsedflow decreases the effective operating time and results in a loss of permeate to the feedstream filtration performance was greatly improved in both tubular and flat-sheet mem-brane systems (Howell Field amp Wu 1993 Wu Howell amp Field 1993) in anothercase flux improvement of up to 300 was found when using periodically spaceddonut-shaped baffles in UF tubes together with pulsed flows with an oscillation frequencyup to 25 Hz (Finnigan amp Howell 1989)

3 Improving mass transfer by turbulence promoters Insertion of static turbulence promotersis a method for increasing shear stress at the membrane surface and is an effective technique

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 525

for reducing concentration polarization and membrane fouling Flux enhancement and fluxcontrol under laminar flow conditions can be achieved by generating well-defined secondary-flow structures by using baffles this is successful only when the radial velocities are highwhich leads to high Reynolds numbers and the flow becomes turbulent Bellhouse (1997)described designs of tubular membranes into which were placed concentric screw threadinserts which had a clearance with the tubular membranes to permit substantial leakageflow in the resulting annular gap The shape of the helical screw thread was semicircularto permit approximately 50 of the flow to pass along the helical path with a corkscrew vor-tex superimposed on the path to create radial mixing in the flow field (Wakeman ampWilliams2002) Different shapes of static turbulence promoters such as static rods spiral wire metalgrills and disc and donut-shaped inserts have been extensively constructed and placedconcentrically inside membrane tubes during MF and UF with or without superimposingthe pulsating flow (Gupta Howell Wu amp Field 1995 Holdich amp Zhang 1992) Howeverpressure loss induced by the insertion of the static turbulence promoter increased energyconsumption and might cause significant variation in trans-membrane pressure along themembrane length

4 Rotatingvibrating membranes In classical cross-flow filtration the shear stress at the mem-brane surface is increased by applying a tangential flow Therefore the shear stress and feedflow rate are interrelated because a higher shear stress implies a higher flow rate and subse-quently higher energy consumption as a result of the pressure drop In rotating filters theshear stress is independent of the flow rate because it relies on the speed of membrane rota-tion A high-shear stress can be developed at the membrane surface by rotating the surface athigh speed rather than pumping feed across the surface at a high cross-flow velocity(Wronski Molga amp Rudniak 1989) This rotating membraneehigh-shear (dynamic) filtra-tion can be implemented by rotating either the membrane or a baffle near the membrane Themagnitude of the shear stress can be varied independently of overpressure of the slurry in thefilter by varying the rotational speed of the rotating element Generally there are two types(Serra Wiesner amp Laicircneacute 1999) rotating cylinders or rotating disks Rotating cylindersreferred to as annular membranes consist of two concentric cylinders separated by a smallgap which take advantage of Taylor vortices when one of those cylinders is rotating Thelatter consist of two axial disks and take advantage of radial flow in the vicinity of the rotatingdisk to reduce particle deposition on the membrane as well as the centrifugal force and shearstress exerting on particles deposited on the membrane surface to drive them back into thebulk liquid

5 Incorporating force fields such as electric or ultrasonic The use of additional forces to aidfiltration has gained increasing attention in recent years Application of an electric field toimprove the efficiency of pressure-driven filtration processes called electro-filtration hasbeen practiced for a long time Besides the bulk flow tangential to the membrane in cross-flow filtration there also exists a convective flow into the porous surface leading to oil drop-lets being transported laterally toward the membrane By applying a direct current electricfield gradient to give oil droplets electrophoretic velocity the convective flow could be coun-terbalanced to a greater or lesser extent which might reduce membrane fouling and enhancefiltrate flux Two different configurations have been reported for electro-filtration An electricfield can be applied across the membrane with one electrode on either side of the membraneor the electric field may be applied between the membrane and another electrode In bothcases the performance of the membrane process is primarily improved owing to electropho-resis For electro-filtration to be successful a voltage higher than some critical value must beapplied (Henry Lawler amp Kuo 1977 Wakeman 1982) The critical voltage gradient definesthe voltage gradient at which the net particle migration toward the membrane is zero

526 Advances in Membrane Technologies for Water Treatment

The electrophoretic velocity (v) gained by an oil droplet could be obtained using the Henryformula as follows

v frac14 2ε0DdxE

3m(168)

where ε0 is the permittivity of a vacuum Dd is the dielectric constant x is the zetapotential E is the electric field gradient and m is the fluid viscosity

Huotari Huisman and Treuroagaringrdh (1999a) Huotari Treuroagaringrdh and Huisman (1999b)reported the effect of an electric field in the filtration of an oil emulsion in which thelimiting fluxes for low flow rate increased significantly using an electric field Thelimiting flux increase was affected by the electrophoretic mobility of the oil dropletsand the applied electric field strength In this work the permeate quality also improvedsignificantly and membranes with large pore sizes could be employed when the electricfield was present

The passage of ultrasound waves through a suspension can cause many phenomenaincluding particle dispersion viscosity reduction changes in particle surface proper-ties and cavitation (Kost amp Langer 1988) Generally ultrasound is characterizedby an ability to transmit substantial amounts of mechanical power through small me-chanical movements The passing of ultrasonic waves of a suitably high intensitythrough liquid media is accomplished by phenomena such as cavitation radiation pres-sure and acoustic streaming Cavitational mechanisms are considered important indetaching particles from the membrane surface whereas turbulence associated with ul-trasound has a role in transporting of particles away from the surface after detachment

Previous works demonstrate that higher particle concentrations produce greaterattenuation of the sound waves as they pass through the cross-flow suspension owingto increased acoustic impedance (Wakeman amp Tarleton 1991 Yunus amp Jones 1995)The degree of attenuation varies with different feed particles and processing condi-tions and is believed to be the controlling parameter for ultrasonic field efficiency Be-sides wastewater viscosity is a limiting factor as ultrasound is applied When viscositygoes up the flux enhancement decreases and no flux enhancements are found when theliquid viscosity is about 4 cp Experimental results showed that an ultrasound cleaningtechnique was applied to remove fouling of UF and MF membranes by cross-flowfiltration (Chai Kobayashi amp Fujii 1998) For each polymeric membrane made ofpolysulfone polyacrylonitrile and polyvinylidene fluoride cleaning experimentswere performed with three kinds of methods sonication water cleaning and watercleaning under sonication Results showed that water cleaning under sonication wasan effective method for the recovery of permeate flux

1642 Wastewater pretreatment

Pretreatment of wastewaters for the gas and petrochemical industries is an effective op-tion to enhance permeate flux and prevent membrane fouling therefore the use ofinnovative pretreatment can significantly reduce the treatment cost This techniqueis commonly used either to remove particles that may cause clogging in the membrane

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 527

pores or to prevent particles or macromolecules from reaching and depositing onto themembrane surface or to reduce the total oil emulsion load by breaking it Traditionalmethods for separating oil emulsion can be classified as physical chemical orcombined

Physical processes usually include prefiltration or centrifugation to remove sus-pended and colloidal solids that may plug the module or blind the membrane and me-chanical emulsion breaking based on the phenomenon of gravity (Adewumi Erb ampWatson 1992 Knudsen et al 2004) The efficiency of these methods mainly dependon the size of the oil droplets as well as the difference in density between water and oilAnother physical pretreatment method breaks the oil emulsion thermally by heatingthe wastewater leading to a significant increase in the oil droplet size (Aptel amp Clifton1986) This process requires a large amount of energy which makes it economicallyunfeasible

Chemical methods are most widely used in treating oily wastewater which are usu-ally directed toward destabilizing the dispersed oil droplets or destroying emulsifyingagents Chemical methods are primarily based on neutralizing detergents (emulsionrsquosstabilizers) resulting in the acceleration of a separation process owing to the coales-cence effect and a change in solution pH so that molecular or colloidal foulantswill be far from their isoelectric point thereby reducing the tendency to form a gellayer Chemical methods include precipitation coagulation or flocculation or theuse of proprietary antiscalants or disinfectants (Garbutt 1997 1999) Currently ferricand aluminum salts are the most widely used agents for demulsification The processusually consists of rapidly mixing the chemicals with the wastewater followed by floc-culation and flotation or settling The work has been reported for the application ofmembrane technology for oily emulsion stabilized by anionic surfactants (BelkacemMatamoros Cabassud Aurelle amp Cotteret 1995) By adding a reactive salt (CaCl2) ata very low concentration in the feed solution the permeate flux increased significantlyThe UF membrane behaved as efficient surface coalescer when the agent was addedwhich reduced polarization layer resistance

1643 Operation optimization

Optimizing the operation conditions may involve maintaining a high cross-flowvelocity limiting trans-membrane pressure manipulating wastewater temperatureand periodical hydraulic chemical andor mechanical cleaning etc

Pumping the feed at higher flow rates into the membrane can lead to increased shearon the membrane surface which will reduce concentration polarization and cake for-mation in commercial membrane modules in the same way turbulence promoters doWhereas steady flows often require cross-flow velocities in the turbulent regime un-steady flows can be effective in both the laminar (as for example Taylor and Deanvortex flows) and the turbulent regimes (Gekas amp Hallstreuroom 1987) These fluid insta-bilities could disturb foulants (Chung Brewster amp Belfort 1993 Winzeler 1990) andinduce fluid mixing at the membraneesolution interface (Jeffree Peakock Sobey ampBellhouse 1981) Fluid instabilities could substantially increase mass transfer ofsolutes away from the membrane therefore the performance of membrane processes

528 Advances in Membrane Technologies for Water Treatment

can be improved when unsteady fluid instabilities are superimposed on cross-flowvelocity (Thomas 1973 Winzeler amp Belfort 1993)

High cross-flow velocity reduces cake formation and polarization in membrane pro-cesses but the pressure drop on the feed side is generally high whereas the permeateside is often at or close to atmospheric pressure which means that the trans-membranepressure at the feed end of the membrane is greater than at the retentate discharge endcausing more cake formation (the extent of compaction depends on the properties ofthe feed) at the feed end Besides high pressure might induce other problems intooil-in-water emulsion by membrane technology when some surfactants are presentin emulsion It has been reported that for watereoilesurfactant emulsions hightrans-membrane pressure results in an increase in the permeability of the surfactantwithout a commensurate increase in the permeability of the water or oil (Sweet 1990)

Temperature is another important factor in cross-flow UF of oily emulsions Theseparation efficiency and membrane fouling depend on the oily droplet size distribu-tion which correlates strongly to the varying temperature With properly chosen mem-brane materials and pore sizes by manipulating the emulsion temperature below thecloud point of the least soluble component it is also possible to remove finelydispersed contaminant oils selectively without simultaneously losing active compo-nents from adequately formulated fluids (Misra amp Skold 1999)

After a certain period of use the membrane should be cleaned mechanically hy-draulically or chemically Cleaning-in-place procedures are generally recommendedto rejuvenate fouled membranes because they commonly involve shorter downtimesthan cleaning-out-of-place It is common practice to pump permeate back throughthe membrane periodically which is achieved by applying pressure on the permeateside of the membrane with the help of an automatic time switch or a microprocessorPermeated water is then forced in the reverse direction through the membrane therebylifting off the boundary layer and washing it out of the membrane surface Thepermeate flux could be significantly improved and the concentration polarizationand membrane fouling could be effectively controlled by periodic back-flushing Shortpulses (about 01 s or shorter) are particularly useful for oily wastewater with colloidalsuspensions

Besides periodic hydraulic cleaning and mechanical cleaning chemical cleaning isalso commonly employed Cleaning solutions are prepared with cleaning agents andare usually circulated with a pressure somewhat lower than that of normal filtrationto prevent deeper foulant penetration into the membrane The selection of cleaningagent is determined by factors such as the foulant type and the compatibility of themembrane with the solution A temporary adverse effect on the membrane rejectionis commonly observed after using many cleaning agents which can be attributableto membrane swelling during contact with the cleaning solution (Jonsson amp Johansen1989) Kim Sun Chen Wiley and Fane (1993) investigated the relationships betweenmembrane fouling and cleaning in terms of flow conditions trans-membrane pressurepH membrane properties and cleaning agents using a stirred batch-cell and aqueousalbumin solution Currently for a better cleaning effect combined processesie chemical agents with physical procedures are widely employed which includepretreatment pulsating gas back-washing adding chemicals in opposite direction

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 529

flushing the feed at high pressure and combining mechanical devices with chemicalcleaners

165 Energy consumption of membrane operationsin the gas and petrochemical industries

Although the membrane technology is widely accepted as a reliable way to treat waste-water with specific requirements the high operating energy consumption is one of themain constraints preventing it from increasing deployment in gas and petrochemicalindustries Generally the total cost of membrane process for wastewater treatment con-sists of pretreatment of original wastewater influents capital cost (typically includingmembrane pump and basic construction expenses) equipment maintenance oper-ating expenses and oily wastewater concentrate disposal cost

The OsloParis Convention for the Protection of the Marine Environment of theNorth-East Atlantic (OSPAR Commission) proposed a method for evaluating waste-water treatment costs in the gas and petrochemical industries Capital cost and oper-ating expenses were estimated based on market conformity The method was basedon three model situations

1 Small gas installation (based on 26 gas installations with small water discharges)2 Large gas installations (based on 27 gas installations with larger water discharges)3 Petroleum oil installations (based on seven oil installations)

Because of the high pressure required to overcome the trans-membrane osmoticpressure the operating expenses mainly energy consumption are the major partand can reach as high as 45 of the total cost (Busch amp Mickols 2004 Manth Gaboramp Oklejas 2003) Currently the energy consumption of membrane process has beenestimated using a phenomenological approach which does not explicitly consider themembrane properties and operating parameters Qi Wang Xu Wang and Wang(2012) proposed a method to theoretically calculate the energy consumption describedbelow According to the mass balance law the mass of oil in the feed solution equalsthe mass of oil in the retentate effluent plus that in the permeate which can beexpressed as

QfCf frac14 QpCp thorn QbCb (169)

where Qf represents the inflow rate Qp is the permeate flow rate and Qb is thevolumetric retentate outflow rate Cf Cp and Cb are the average oil concentrations ofinfluent permeate and retentate effluent respectively

The osmotic pressure difference at the exit of membrane module (ie Dpaexit) istherefore approximated by

Dpexit frac14 Dpmexit thorn Dpaexit frac14 p0Rt

1 YRtthorn Dpaexit (1610)

530 Advances in Membrane Technologies for Water Treatment

where p0 is the osmotic pressure of oily wastewater Dpm is the osmotic pressuredifference without concentration polarization Dpa is the osmotic pressure differencewith concentration polarization Rt is the observed rejection and Y is the targetrecovery rate

The pressure of wastewater to the treatment system should be higher than the os-motic pressure difference at the exit of membrane module in which DP is the appliedpressure and DPf is the pressure drop

DP DPf Dpexit frac14 p0Rt

1 YRtthorn Dpaexit (1611)

Here the average rejection is defined as

Rt frac14ZL

0

Rtdx=L (1612)

Equation (1612) is the thermodynamic limit for the cross-flow filtration processIt is shown that Dpexit would increase rapidly at high target recovery rates and so isthe required applied pressure The partial recovery rate Yx is defined as

Yx frac14 Y

Zx

0

jethxTHORNdxZL

0

jethxTHORNdx (1613)

Finally the rate of pump work or operating energy consumption of membrane pro-cess is normally calculated by

W frac14 Q DP

h(1614)

Here Q is the flow rate of pump and h is the efficiency of pump

166 Conclusions

Wastewater from the gas and petrochemical industries is widely treated via an acti-vated sludge process with oilewater separation Increasingly tightened environmentalregulations and the growing need to reuse treated water have generated interest in thetreatment of these wastewaters by the membrane process Integrated membrane sys-tems combined with different treatment technologies can help maximize water recov-ery achieve high water quality for water reuse and minimize life cycle costsConsequently it is clear that in the near future the use of membranes will growsubstantially for wastewater treatment from the gas and petrochemical industries

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 531

167 Future trends

For the gas and petrochemical industries the most significant waste stream is waterFor each barrel of oil produced 3e10 barrels of wastewater are generated If properlytreated about 95 of the water can be reinjected to enhance oil recovery However thefraction remaining is considerable consequently using cost-effective and efficienttechnology to reduce contaminants for water reuse or for discharge constitutes a chal-lenge for gas and petrochemical companies

To treat wastewater from the gas and petrochemical industries a suitable strategyfor the membrane process depends on the following major criteria

1 Source of wastewater and concentration of pollutants2 Final requirements for discharge recycle or reuse

Developing a fouling-resistant membrane will always be the core consideration forthis application

Nomenclature

A Membrane area (m2)C Solute concentration (ML)C1 Integral constant equal to the oil droplet permeate flux (Lm2 h)Cb Oil droplet concentration in the bulk solution of feed (vol )Cf Oil droplet concentration in permeate (vol )Cm Oil droplet concentration at the membrane surface (vol )

Cb Dimensionless form of average oil concentration of retentate effluent

Cf Dimensionless form of average oil concentration of influent

Cp Dimensionless form of average oil concentration of permeateD Diffusion coefficient of oil droplets (m2s)Dd Dielectric constantE Electric field gradient (Vm)J0w Permeate flux of pure water (Lm2 h)Jw Permeate flux of waste water (Lm2 h)n ConstantDP Applied pressure (bar)DPf Pressure drop (bar)Q Flow rate of pump (m3s)Qb Volumetric retentate outflow rate (m3s)Qf Inflow rate (m3s)Rm Intrinsic resistance of the clean membrane (Lm)Rt Observed rejection ()Rt Average rejection ()t Time of operation (s)v Electrophoretic velocity (mms)V Cumulative volume of filtrate (L)W Rate of pump work (KWh)

532 Advances in Membrane Technologies for Water Treatment

Y Target recovery rate ()Yx Partial recovery rate ()

Greek symbols

a Constantb Constantd Thickness of boundary layer (polarization layer) (m)ε0 Permittivity of vacuum (C2J m)h Efficiency of pumph0 Water viscosity (Nsm2)m Fluid viscosity (Pas)x Zeta potential (mV)p0 Osmotic pressure of oily wastewater (bar)Dpa Osmotic pressure difference with concentration polarization (bar)Dpm Osmotic pressure difference without concentration polarization (bar)

References

Adewumi M A Erb J E amp Watson R W (1992) Design considerations for a cost effectivetreatment of stripper oilwell produced water In J P Ray amp F R Engelhardt (Eds)Produced water TechnologicalEnvironmental issues and solutions (pp 511e523)New York Plenum Publishing Co

Almeida Neto A F Silva A A Valenzuela-Diacuteaz F R amp Rodrigues M G F (2006) Studyof organophilic clays in the adsorption of xylene and toluene In Proceedings of VIencontro Latino Americano de Pos-Graduaccedil~ao SP S~ao Joseacute dos Campos 2410 (inBrazilian)

Aptel P amp Clifton M (1986) Ultrafiltration In P M Bungay H K Lonsdale amp M N dePinho (Eds) Synthetic membrane Science engineering and applications DordrechtReidel Publishing Co

Asatekin A amp Mayes A M (2009) Oil industry wastewater treatment with fouling resistantmembranes containing amphiphilic comb copolymers Environmental Science and Tech-nology 43 4487e4492 httpdxdoiorg101021es803677k

Asatekin A Kang S Elimelech M amp Mayes A M (2007) Anti-fouling ultrafiltrationmembranes containing polyacrylonitrile-graft-poly (ethylene oxide) comb copolymeradditives Journal of Membrane Science 298(1e2) 136e146 httpdxdoiorg101016jmemsci200704011

Belkacem M Matamoros H Cabassud C Aurelle Y amp Cotteret J (1995) New results inmetal working wastewater treatment using membrane technology Journal of MembraneScience 106(3) 195e205 httpdxdoiorg1010160376-7388(95)00093-R

Bellhouse B J (1997) Membrane filters with corkscrew vortex generating means OxfordUnited Kingdom US Patent 5628909

Bhave R R amp Fleming H L (1988) Removal of oily contaminants in wastewater withmicroporous alumina membranes American Institute of Chemical Engineers SymposiumSeries 84(261) 19e27

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 533

Bilstad T amp Espedal E (1996) Membrane separation of produced water Water Science andTechnology 34 239e246 httpdxdoiorg101016S0273-1223(96)00810-4

Busch M amp Mickols W E (2004) Reducing energy consumption in seawater desalinationDesalination 165(0) 299e312 httpdxdoiorg101016jdesal200406035

Chai X Kobayashi T amp Fujii N (1998) Ultrasound effect on cross-flow filtrationof polyacrylonitrile ultrafiltration membranes Journal of Membrane Science 148(1)129e135 httpdxdoiorg101016S0376-7388(98)00145-8

Chung K Y Brewster M A amp Belfort G (1993) Dean vortices with wall flux in a curvedchannel membrane system IV Effect of vortices on permeation fluxes of suspensions inmicroporous membranes Journal of Membrane Science 81 139e150 httpdxdoiorg1010160376-7388(93)85038-X

Ciarapica F E amp Giacchetta G (2003) The treatment of produced water in offshore rigComparison between tradition installations and innovative systems In Fifth internationalmembrane science amp technology conference University of New SouthWales Sydney(in Australia)

Daiminger U Nitsch W Plucinski P amp Hoffmann S (1995) Novel techniques for oilwaterseparation Journal of Membrane Science 99(2) 197e203 httpdxdoiorg1010160376-7388(94)00218-N

Finnigan S M amp Howell J A (1989) The effect of pulsatile flow on ultrafiltration fluxes in abaffled tubular membrane system Transactions of the Institution of Chemical EngineersPart A 67 278e282

Garbutt C F (1997) Innovative treating processes allow steam flooding with poor quality oilfieldwater SPE annual technical conference and exhibition San Antonio TX (in USA)

Garbutt C F (1999)Water treatment process for reducing the hardness of an oilfield producedwater USA Marathon Oil Co US Patent 5879562

Gekas V amp Hallstreuroom B (1987) Mass transfer in the membrane concentration polarizationlayer under turbulent crossflow 1 Critical literature review and adaptation of existingSherwood correlations to membrane operations Journal of Membrane Science 30153e170 httpdxdoiorg101016S0376-7388(00)81349-6

Gupta B B Howell J A Wu D amp Field R W (1995) A helical baffle for crossflowmicrofiltration Journal of Membrane Science 102 31e42 httpdxdoiorg1010160376-7388(94)00241-P

Hamza A Pham V A Matsuura T amp Santerre J P (1997) Development of membraneswith low surface energy to reduce the fouling in ultrafiltration applications Journalof Membrane Science 131(1e2) 217e227 httpdxdoiorg101016S0376-7388(97)00050-1

Hansen B R amp Davies S R H (1994) Review of potential technologies for the removal ofdissolved components from produced water Chemical Engineering Research and Design72(2) 176e188

He Y amp Jiang Z W (2008) Technology review Treating oilfield wastewater Filter andSeparation 45(5) 14e16 httpdxdoiorg101016S0015-1882(08)70174-5

Henry J D Lawler L F amp Kuo C H A (1977) A solidliquid separation process based oncrossflow and electrofiltration American Institute of Chemical Engineers 23(6) 851e859httpdxdoiorg101002aic690230611

Hermia J (1982) Constant pressure blocking filtration laws Applications to power-law non Newtonian fluids Transactions of the Institution of Chemical Engineers60 183

Holdich R G amp Zhang G M (1992) Crossflow microfiltration incorporating rotational fluidflow Transactions of the Institution of Chemical Engineers Part A 70 527e536

534 Advances in Membrane Technologies for Water Treatment

Howell J A Field R W amp Wu D (1993) Yeast cell microfiltration Flux enhancementin baffled and pulsatile flow systems Journal of Membrane Science 80 59e71 httpdxdoiorg1010160376-7388(93)85132-G

Huotari H M Huisman I H amp Treuroagaringrdh G (1999a) Electrically enhanced crossflowmembrane filtration of oily waste waters using the membrane as a cathode Journal ofMembrane Science 156 49e60 httpdxdoiorg101016S0376-7388(98)00325-1

Huotari H M Treuroagaringrdh G amp Huisman I H (1999b) Crossflow membrane filtrationenhanced by an external DC electric field A review Chemical Engineering Research andDesign 77 461e468 httpdxdoiorg101205026387699526304

Jeffree M A Peakock J A Sobey I J amp Bellhouse B J (1981) Gel layer-limitedhemofiltration rates can be increased by vortex mixing Clinical and Experimental Dial-ysis and Apheresis 5 373e380 httpdxdoiorg10310908860228109076028

Jonsson G amp Johansen P L (1989) Selectivity of ultrafiltration membranes In J Yang ampC Yang (Eds) Indo-ECC membrane workshop New Delhi Department of Science andTechnology

Kim J amp DiGiano F A (2009) Fouling models for low-pressure membrane systemsSeparation and Purification Technology 68(3) 293e304 httpdxdoiorg101016jseppur200905018

Kim K J Sun P Chen V Wiley D E amp Fane A G (1993) The cleaning of ultrafiltrationmembranes fouled by protein Journal of Membrane Science 80 241e249 httpdxdoiorg1010160376-7388(93)85148-P

Knudsen B L Hjelsvold M Frost T K Grini P G Willumsen C F amp Torvik H (2004)Meeting the zero discharge challenge for produced water In Proceeding of the seventh SPEinternational conference on health safety and environment in oil and gas exploration andproduction Calgary Alberta (in Canada)

Kost J amp Langer R S (1988) Ultrasound enhancement of membrane permeability USAMassachusetts Institute of Technology US Patent 4780212

Lee J M amp Frankiewicz T (2005) Treatment of produced water with an ultrafiltration (UF)membrane-afieldtrial InSPEannual technicalconferenceandexhibitionDallasTX(inUSA)

Li L amp Lee R (2009) Purification of produced water by ceramic membranes Materialscreening process design and economics Separation Science and Technology 443455e3484 httpdxdoiorg10108001496390903253395

Li Y S Yan L Xiang C B amp Hong L J (2006) Treatment of oily wastewater byorganiceinorganic composite tubular ultrafiltration (UF) membranes Desalination 19676e83 httpdxdoiorg101016jdesal200511021

Makki H F Al-Alawy A F Al-Hassani M H amp Rashad Z W (2011) Membranesseparation process for oily wastewater treatment Journal of Engineering 17(2) 235e252

Manth T Gabor M amp Oklejas E (2003) Minimizing RO energy consumption under variableconditions of operation Desalination 157(13) 9e21 httpdxdoiorg101016S0011-9164(03)00377-1

Misra S K amp Skold R O (1999) Membrane filtration studies of inversely soluble modelmetalworking fluids Separation Science and Technology 34(1) 53e67 httpdxdoiorg101081SS-100100636

Mittal P Jana S amp Mohanty K (2011) Synthesis of low-cost hydrophilic ceramicepolymeric composite membrane for treatment of oily wastewater Desalination 28254e62 httpdxdoiorg101016jdesal201106071

Nakatsuka S Nakate I amp Miyano T (1996) Drinking water treatment by using ultrafiltrationhollow fiber membranes Desalination 106(1e3) 55e61 httpdxdoiorg101016S0011-9164(96)00092-6

Membrane technologies for water treatment and reuse in the gas and petrochemical industries 535

Ochoa N A Masuelli M amp Marchese J (2003) Effect of hydrofilicity on fouling of anemulsified oil wastewater with PVDFPMMA membranes Journal of Membrane Science226 203e211 httpdxdoiorg101016jmemsci200309004

OSPAR Commission Background document concerning techniques for the management ofproduced water from offshore installations Retrieved from httpwwwosparorgdocumentsdbasepublicationsp00162Techniques20for20the20management20of20Produced20Waterpdf

Qi B Wang Y Xu S Wang Z amp Wang S (2012) Operating energy consumption analysisof RO desalting system Effect of membrane process and energy recovery device (ERD)performance variables Industrial and Engineering Chemistry 51 14135e14144 httpdxdoiorg101021ie300361e

Scott K (1995) Handbook of industrial membranes Oxford UK ElsevierSerra C A Wiesner M R amp Laicircneacute J M (1999) Rotating membrane disk filters Design

evaluation using computational fluid dynamics Chemical Engineering Journal 72 1e17httpdxdoiorg101016S1385-8947(98)00128-4

Song L (1998) Flux decline in crossflow microfiltration and ultrafiltration mechanisms andmodeling of membrane fouling Journal of Membrane Science 139(2) 183e200 httpdxdoiorg101016S0376-7388(97)00263-9

Sweet J R (1990) Pressure induced surfactant recovery during ultrafiltration of water-oilemulsions Florham Park NJ Exxon Research and Engineering Co US Patent 4892660

Thomas D G (1973) Forced convection mass transfer in hyperfiltration at high fluxesIndustrial and Engineering Chemistry Fundamentals 12 396e405 httpdxdoiorg101021i160048a002

Ulbricht M (2006) Advanced functional polymer membranes Polymer 47 2217e2262httpdxdoiorg101016jpolymer200601084

USEPA Website httpwwwepagovWakeman R J (1982) Effects of solids concentration and pH on electrofiltration Filtration amp

Separation 19 316Wakeman R J amp Tarleton E S (1991) An experimental study of electroacoustic

crossflow microfiltration Transactions of the Institution of Chemical Engineers Part A 69386e397

Wakeman R J amp Williams C J (2002) Additional techniques to improve microfiltrationSeparation and Purification Technology 26 3e18 httpdxdoiorg101016S1383-5866(01)00112-5

Winzeler H B (1990) Membran-filtration mit hoher Trennleistung und minimalen Ener-giebedarf CHIMIA International Journal for Chemistry 44(4) 288e291

Winzeler H B amp Belfort G (1993) Enhanced performance for pressure-driven membraneprocesses The argument for fluid instabilities Journal of Membrane Science 80 35e47httpdxdoiorg1010160376-7388(93)85130-O

Wronski S Molga E amp Rudniak L (1989) Dynamic filtration in biotechnology BioprocessEngineering 4 99e104 httpdxdoiorg101007BF00369757

Wu D Howell J A amp Field R W (1993) Pulsatile flow filtration of yeast cell debrisInfluence of preincubation on performance Bioengineering and Biotechnology 41998e1002 httpdxdoiorg101002bit260411011

Yunus R M amp Jones M (1995) Enhancement of tubular crossflow microfiltration of yeastsuspensions by ultrasonic force field In G Akay amp B J Azzopardi (Eds) Proceedings ofIst international conference on science engineering and technology of intensive processing(pp 189e192) Nottingham

536 Advances in Membrane Technologies for Water Treatment

Membrane technologiesfor water treatment and reusein the textile industry

17I Petrinic1 N Bajraktari2 C Heacutelix-Nielsen121University of Maribor Maribor Slovenia 2Technical University of DenmarkLyngby Denmark

171 Introduction

The textile industry is one of the largest consumers of water and chemicals for wet pro-cessing of textiles (Banat Nigam Singh amp Marchant 1996) This has led toincreasing environmental concerns thus control of water pollution is an importantissue Here we will review some aspects related to the treatment of textile wastewaterwith special emphasis on membrane processes

Textile processing is complex and includes sizing where various types of water-soluble polymers also called textile sizing agents such as modified starch polyvinylalcohol carboxymethyl cellulose and acrylates are used to increase the strength of theyarn for weaving scouring (eg detergent treatment) bleaching mercerizing (wheresodium hydroxide is added to provide lustrous appearance and strength to cotton)carbonizing (adding acid followed by baking and thereby removing (carbonized)impurities from wool dyeing and finishing) Consequently wastewater pollutants ariseboth from raw fabrics and a wide range of additives used to produce the finished prod-uct In textile wastewater treatment one therefore has to deal with pollutants spanninga wide range including nonbiodegradable highly persistent organics and pesticidesused in speciality textiles such as insect-proof fabrics

Organic matter represents the main emission load for textile wastewater which sug-gests treatment based on biological processes However the introduction of effectiveand sustainable water recycling techniques in this branch of production is often pre-vented by recalcitrant organic compounds and remaining dyes Because of the poorbiodegradability and sometimes even toxicity of the textile wastewater componentsadvanced treatment technologies are necessary Especially if reuse of treated waste-water is the objective extensive removal of organic contents as well as almost com-plete decolourization is required

Industrial wastewater streams can vary greatly in their composition within a plantand even during the same process over short periods of time For wastewater treatmentto be practical in this situation wide processing latitude is required to accommodateinherent variability The textile industry provides examples of this variability in batchprocesses such as dyeing printing finishing and washing as well as frequent changes

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400017-4Copyright copy 2015 Elsevier Ltd All rights reserved

in product runs In addition to this variability in water content many productionprocess reactions are incomplete leaving varying amounts of residue chemicals inthe processed water

When dyeingprinting textiles water serves two purposes First it ensures the trans-mission of the colour onto the fibre second it washes out excess amounts of dyes fromthe treated fabrics Of all dyedprinted textile fibres cellulose fibres stands out as themost prominent and more than 50 of production is dyedprinted with a special classof dyes the so-called reactive dyes Over 80000 tons of reactive dyes are producedand consumed each year which makes it possible to estimate the total pollution causedby their use (Allegre Moulin Maisseu amp Charbit 2006) They are adsorptive to thecellulose fibres and the hydrolysed dyestuff requires large amounts of water prefer-ably at high temperatures to be properly washed out Unfortunately this class ofdyes is also the most unfavourable from an ecological point of view because the ef-fluents produced are heavily coloured and contain high concentrations of salt andexhibit high biochemical oxygen demand (BOD) and chemical oxygen demand(COD) values (Allegre et al 2006)

172 Textile wastewater

A detailed source analysis of coloured wastewater released by a dyeprinting houseindicated that 15e30 of the applied dyestuff is released into the wastewater Themain portion corresponding to 50e80 of this amount results from the washingrinsing stages and thus has been diluted to average concentrations of 1e2 gl (Bechtoldamp Turcanu 2004) Wastewater containing reactive dyes is considered problematicbecause it is removed less efficiently compared with other dye classes in which waste-water can be processed by activated sludge sewage treatment (Pierce 1994) More-over fixation of the reactive dyes on the textile fabric is low 70 on averagecompared with other dye classes (over 90 on average)

In addition to reactive dyes the textile industries are dominated by the use of directdyes acidbasic dyes and disperse dyes depending on the material to be processedThus for example for polyester disperse dyes are most common whereas for blendedfabrics a mixture of reactive dyes and acid dyes is typically used For polyester andnylon mixtures disperse dyes and acid dyes are blended For nylon alone a mixtureof reactive dyes disperse dyes and acid dyes is used See Table 171 for a list of com-mon dyes found in textile wastewater

A particular problematic group of dyes is constituted by the so-called azo dyes(containing eNfrac14Ne bonds) because they and their metabolites may be mutagensand carcinogens (Chang et al 2001 Pandey Singh amp Lyengar 2007 _ZyłłaSojka-Ledakowicz Stelmach amp Ledakowicz 2006) Azo dyes commonly used inthe textile industry include reactive acid and direct dyes (You amp Teng 2009) Theyare aromatic compounds that make up the largest and most diverse group of syntheticdyes found in the wastewaters of dyefrac14 using industries such as textile paper printingfood and cosmetic industries

538 Advances in Membrane Technologies for Water Treatment

173 Treatment of textile wastewater

These wastewater streams are usually collected together and after eventual pH adjust-ment sent to communal wastewater treatment plants Methods for wastewater treat-ment have to focus on the cleaning of wastewater streams originating fromindividual textile processes In practice realization of this process is difficult Suitabletechnologies for the treatment of individual streams are used only when the dyeingprocess is well-defined andor when a wastewater stream contains materials that canbe separated out and reused in the finishing processes When treating textile waste-water for reuse by the industry colour removal as well reduction in total suspendedsolids (TSS) BOD COD and nonbiodegradable substances must be addressed inthe primary treatment stage

Therefore advanced treatment processes are required to improve the quality of thetreated wastewater up to reuse criteria (Feng Xu Li You amp Zhen 2010) Many treat-ment methods for textile wastewater have been investigated including (1) treatmentusing lime and alum This method generates large quantities of hazardous sludge and isgenerally ineffective in removing colour TSS BOD and COD (2) biological treat-ment with aeration to reduce BOD and COD levels (3) chlorination that successfullyremoves colour (eg as sodium hypochloride [NaOC])-based attack of dye moleculeamino bonds) Although this method reduces BOD and COD it produces chloro-organic compounds that are potentially carcinogenic and therefore not eco-friendly(4) ozonation with or without ultraviolet irradiation and (5) sorption usingH2O2eFe(II) salt and cucurbituril Other methods include adsorption (eg via acti-vated carbon peat wood chips fly ash and silica gels) ion exchange (for cationic

Table 171 Examples of dye components in textile wastewater

Dye class CI name Commercial name

Reactive Reactive Red 120 Suncion Red H-E3B

Reactive Blue 160 Sunicon Blue H-ERN

Reactive Yellow 84 Sunicon Yellow H-Z4RN

Acid Acid Red 57 Nylosan Red E-BL

Acid Blue 72 Nylosan Blue E-GL

Acid Yellow 256 Nylosan Yellow E-2RL

Disperse Disperse Red 60 PALANIL Red FD-BFY

Disperse Blue 56 DZANIX Blue E-R

Disperse Yellow 54 PALANIL Yellow 3GZ

CI Colour Index International is a reference database jointly maintained by the Society of Dyers and Colourists and theAmerican Association of Textile Chemists and ColouristsSource Partially adapted from Choi et al (2003)

Membrane technologies for water treatment and reuse in the textile industry 539

and anionic dyes) irradiation electron beams (combined with oxygenation) and elec-trokinetic coagulation (using added ferrous sulphate or ferric chloride) see (RobinsonMcmullan Marchant amp Nigam 2001) for a review of chemical and physicaltreatments

Because of their complex chemical structure dyes are generally resistant to fadingon exposure to light water and many chemicals When decolourization of waterpolluted with organic colorants occurs it takes place by reduction of eCfrac14Ce andeNfrac14Ne bonds and heterocyclicaromatic rings (Slokar amp Le Marechal 1998) Theazo (eNfrac14Ne) bonds (as well as sulfonic (eSO3) groups) are electron-withdrawinggroups and this generates electron deficiency within the molecule making the com-pound less susceptible to oxidative catabolism by bacteria (You amp Teng 2009)

Consequently decolouration of textile dye effluent is not normally observed whenthe textile wastewater is treated aerobically by municipal sewerage systems (Changet al 2001 Pandey et al 2007 _Zyłła et al 2006) Therefore anaerobic systemshave been used to cleave azo bonds in the treatment of textile wastewater (Dos SantosCervantes amp Van Lier 2007 Orsquoneill Hawkes Hawkes Esteves amp Wilcox 1999)and many bacterial groups possess enzymes (ie azo-reductases) capable of disruptingthe azo bonds under anaerobic conditions ( _Zyłła et al 2006) The anaerobic degrada-tion product is colourless aromatic amines that are carcinogenic but these aromaticamines can then be readily degraded via aerobic digestion by nonspecific enzymesthrough hydroxylation and ring opening of the aromatic compounds (Sponza amp Isik2005) Mineralization of the azo dyes is complete when the aromatic amines havebeen biodegraded to carbon dioxide (CO2) water (H2O) and ammonia (NH3) (Sponzaamp Isik 2005 Van Der Zee amp Villaverde 2005) Thus for complete mineralization ofazo dyes a combination of reductive (anaerobic) and oxidative (aerobic) steps arerequired (Dafale et al 2010 Kodam amp Gawai 2006 Kodam Soojhawon Lokhandeamp Gawai 2005)

Recently membrane bioreactor (MBR) technology has attracted interest for waste-water treatment (Badani Ait-Amar Si-Salah Brik amp Fuchs 2005 Banat et al1996 Brik Schoeberl Chamam Braun amp Fuchs 2006 Pierce Lloyd amp Guthrie2003) Conventional MBR is operated at aerobic conditions and therefore is not suit-able for dye degradation However anoxic or anaerobic MBR for dye wastewatertreatment has been investigated and shows some potential for a review onMBR-based textile wastewater treatment see Simonic (2013) However it hasalso been reported that the anoxic phase or low dissolved oxygen (DO) conditions(DO lt 03 mgl) have a negative effect on membrane permeability in the MBR pro-cess because low oxygen concentration leads to poorer flocculated activated sludge(Kang amp Lee 2004) Also biofouling is a major issue of concern in MBR processesbecause colony buildup on the membrane surface decreases water permeability(Lewandowski 2004)

A physical method gaining increasing general interest for wastewater treatment isdirect membrane separation because this can be used to recycle valuable components(and energy) as well as lower overall operating costs by lowering the volume of waste-water to be delivered to the wastewater treatment plant Membrane techniques char-acterized by their ability to clarify concentrate and continuously separate are

540 Advances in Membrane Technologies for Water Treatment

therefore potentially interesting for textile wastewater effluent treatment includingpotential recycling of dyes

1731 Membrane filtration in textile wastewater treatment

Processes using membranes provide possibilities for separating hydrolysed dyestuffsand auxiliaries thus simultaneously reducing coloration Over the past few yearstechnical and economical improvements have made treatment of wastewater bymembrane systems increasingly advantageous over conventional treatment processes(Porter 1999 Rozzi et al 1999 Sojka-Ledakowicz Koprowski Machnowski ampKnudsen 1998) The most notable outcome of the membrane treatment is the supe-rior quality of the produced water which is attained by adding fewer chemicals overconventional water treatment processes In addition membrane plants can be muchsmaller than conventional wastewater treatment plants because of the modularconfiguration of the membranes and the possible elimination of other processes(eg clarification) Traditional membrane processes studied in textile wastewatertreatment include the use of ultrafiltration (UF) nanofiltration (NF) and reverseosmosis (RO) membranes in which the selection of membrane technologies fortextile effluent relies on costs based on the balance between water flux and soluteretention

Ultrafiltration membranes have been successfully applied in many industries butthey have not been as widely accepted by the textile industry because they do notremove low-molecular-weight dyes There are examples of micelle-enhanced use ofUF membranes for dye removal (Ahmad amp Puasa 2007 Zaghbani Hafiane ampDhahbi 2007) but in general the rejection range from 30 to 90 makes the directuse of UF membranes impossible and further filtration is required by either RO orNF membranes In RO problems with fouling are present that result in low fluxesowing to the dense polymeric membrane used and poor separation Reverse osmosisalso becomes less effective when osmotic pressure caused by high salt concentrationin the feed wastewater becomes too high to obtain a reasonable transmembranepermeate flux without applying excess transmembrane hydraulic pressure In this sit-uation NF provides a possible alternative maintaining high dye rejections albeit withthe cost of lower rejection of electrolytes

Nanofiltration membranes have been used to recover salt from used dyeing baths(Erswell Brouchaert amp Buckley 1988 Gonzalvez-Zafrilla Sanz-Escribano Lora-Garciacutea amp Leon Hidalgo 2008 Petrinic Andersen SOstar-Turk amp Le Marechal2007 He et al 2009 Koyuncu 2003 Koyuncu Kural amp Topacik 2001) wherethe principle is that electrolytes will pass through the membrane as the dyes are rejectedHowever this principle requires the use of sufficiently small electrolytes For exampleNa2SO4 which often is used as electrolyte is rejected by the NF membrane limitingthe feasibility of this approach Also standard electrolytes (such as NaCl) are nothigh-value products An NF process for the treatment of mixed waste streams fromthe reactive dyeing process has been developed using this principle (Rautenbach ampMellies 1994) in which the retentate is further treated in a wet oxidation processThe effective desalination of the retentate by the NF membrane is desired because

Membrane technologies for water treatment and reuse in the textile industry 541

this diminishes electrolyte corrosion in the wet oxidation Nanofiltration-based dyeretention can be effective and retentions up to 99 with a permeate flux of 64 lm2 h have been obtained (Tegtmeyer 1993)

Reverse osmosis membranes have also been used in textile wastewater treatment(Suksaroj Heacuteran Allegre amp Persin 2005) One example of this used a combinationof RO membranes designed for brackish and seawater desalination (Treffry-GoatleyBuckley amp Groves 1983) Thus the brackish water RO membrane is used in the firststage and the seawater RO membrane is used in the second stage In this way the reten-tate is recycled in the second stage to obtain high water recovery and the cross-flowvelocity is kept high to minimise membrane fouling Using this two-stage RO processwater recovery is 85e95 with a mean permeate flux of 15 lm2 h

In a comparative study (Bonomo 1992) pilot plant tests with UF NF and RO treat-ment of wastewater from washing processes subsequent to reactive dyeing processesare described Ultrafiltration membrane treatment leaves the permeate stream colour-ized whereas NF membrane treatment results in efficient permeate decolourizationwith a flux of 70 lm2 h at 10 bar The RO membrane both decolourizes and desalinatesthe waste stream Interestingly the reactive dyes retention was somewhat lower than inthe NF process despite the use of the denser RO membrane Severe membrane foulingwas observed when the waste stream contained dispersed dyes together with reactivedyes which illustrates the important issue of membrane fouling when treating complexwastewaters

To elucidate fouling effects synthetic waste streams mimicking actual wastestreams can be analysed (Fritsch 1993) This approach would in principle make itpossible to relate the permeate flux decline to certain components or a combinationof component presents in the actual waste stream One could thus make a list of no-go components in dyeing and washing if the resulting wastewater is to be treated effi-ciently by membrane filtration processes In general pressure-driven processes such asUF NF and RO are all prone to fouling typically caused by the presence of naturalorganic matter (NOM) (Li amp Elimelech 2004) and biofouling (Vrouwenvelder ampVan Der Kooij 2001) With textile wastewater as a membrane feed stream this issuebecomes particularly important and it is therefore necessary to address this issue Thiscan be done in principle by making no-go list of components (ie components withstrong fouling propensity) Another more general strategy is to consider alternativesto pressure-driven processes

1732 Osmotic-based wastewater reduction and potentialdye recovery

In contrast to pressure-driven processes FO is less prone to fouling and FO-based sys-tems are attracting increasing interest in water treatmentengineering applications fora wide variety of aqueous solutions (Achilli Cath Marchand amp Childress 2009Cath Childress amp Elimelech 2006 Coday Yaffe Xu amp Cath 2014 Cornelissenet al 2008 Holloway Childress Dennett amp Cath 2007 Klaysom Cath Depuydtamp Vankelecom 2013 Teoh et al 2008) Thus FO has been used to treat industrialwastewaters (at bench-scale) to concentrate landfill leachate at pilot- and full-scale

542 Advances in Membrane Technologies for Water Treatment

(Beaudry Herron amp Peterson 1999 York amp Beaudry 1999) and to treat liquid foodsin the food industry at bench-scale (Dova Petrotos amp Lazarides 2007ab PetrotosLazarides Wolf Behsnilian amp Spiess 2001) Forward osmosis is also being evalu-ated for reclaiming wastewater for potable reuse in life support systems (atdemonstration-scale) for desalinating seawater and for purifying water in emergencyrelief situations for a detailed review see Cath et al (2006) Although no scientificreports on direct FO in the textile wastewater treatment have appeared so far CatalyxInc of Anaheim California have reported an FO-based system for recycling difficult-to-treat high-BOD and high-COD carpet-dyeing wastewater (Atkinson 2009) Thusthe FO technology can be seen as an addition to existing membrane processes such asUF NF and RO which are commonly used in textile wastewater treatment today

For FO there is no hydraulic pressure across the membrane For RO the appliedhydraulic pressure must exceed the osmotic pressure and convectively drive the waterfrom low to high water chemical potential For pressure-assisted osmosis (PAO) hy-draulic pressure is applied in the same direction as the water flow For PRO the hy-draulic pressure retards the FO process but the effective hydraulic pressure is stillless than the osmotic pressure In all cases the osmotic pressure difference acrossthe membrane can be approximated as the difference in osmotic pressure of each so-lution In ideal solutions the osmotic pressure p can be determined from the Morseequation p frac14 iMRT where i is the vanrsquot Hoff factor M is the molarity R is thegas constant and T is temperature Figure 171 schematically shows the four processesFO RO PAO and PRO

Forward osmosis operates by concentrating a feed solution (FS) and diluting a high-ly concentrated aqueous solution e the draw solution (DS) The larger osmotic pres-sure of the DS compared with the FS constitutes the driving force for the separationprocess Thus FO is an osmotic concentration process that in principle can operateat zero hydrostatic pressure providing a sustainable water treatment solution

Forward osmosis is not implemented on a large scale for several reasons There areat least three lsquomust-winrsquo battles to successfully overcome before FO becomes a large-scale technology comparable with established technologies such as RO First a newtype of membrane is needed that has to be very thin to minimise internal concentrationpolarization (Klaysom et al 2013) Second good DSs are needed the most studiedcurrently are ammonium bicarbonateebased DSs (Mccutcheon Mcginnis ampElimelech 2006) and their use poses several problems including unfavourable interac-tions with known (conventional) membrane materials Third a new system solutionan FO membrane cannot simply replace an RO membrane in conventional membranemodules (Gruber et al 2011 2012) Until good FO membranes and DSs are availablefor major industrial applications no system provider is likely to begin designing newFO-based systems

Recently a cellulose triacetate (CTA) FO membrane with an embedded supportscreen stabilizing a dense rejection layer (10e20 mm thick) and thin-film composite(TFC) membranes were commercialized by Hydration Technologies Inc (HTI) Sofar the use of these membranes has focused on low-volume nutrient drink production(Salter 2006) Thus a concentrated nutrient solution with a high osmotic pressure isused as DS where unsafe water as FS is purified through the FO membrane with a salt

Membrane technologies for water treatment and reuse in the textile industry 543

rejection between 93 and 95 However when operated in a high-volume applica-tion setup the HTI CTA membrane water flux is still low (lt 6 lm2 h) although theHTI TFC membrane seemingly has a flux that is double that of the HTI CTA mem-brane In comparison for RO membranes water fluxes can reach 75 lm2 h althoughtypical values are around 30 lm2 h (Xu Peng Tang Shiang Fu amp Nie 2010)However water flux and solute retention have to be evaluated together when evalu-ating membrane performance

One way to increase water flux across the membrane while preserving rejection ofsolutes is to enable facilitated water diffusion across the active layer This has beenstudied intensively over the last few years where in particular the use of naturersquosown selective water channels e aquaporin proteins e have attracted considerable in-terest for a review see Tang Zhao Wang Heacutelix-Nielsen and Fane (2013) and for ageneral review of the biomimetic approach to membrane technology see Nielsen(2009) Aquaporins constitute a large family of membrane spanning proteins for re-views see Fu and Lu (2007) Gonen and Walz (2006) and Ludewig and Dynowski(2009) Much has been revealed about this class of proteins since the purification ofa red blood cell membrane protein and subsequent heterologous expression of this pro-tein revealing rapid water diffusion along osmotic gradients

P

P

P

J J

JJ

Δ

Δ

Δ

(a) (b)

(d)(c)

Figure 171 Osmotic processes Water flux (J) versus hydraulic pressure (DP) in (a) forwardosmosis (FO) (b) reverse osmosis (RO) (c) pressure-assisted osmosis (PAO) and (d) pressure-retarded osmosis (PRO)

544 Advances in Membrane Technologies for Water Treatment

Recently a design was developed in which vesicles are embedded in thin (200 nm)films deposited on a porous support (Zhao et al 2012) Briefly a microporous poly-sulfone substrate was soaked with an m-phenylene-diamine aqueous solution that con-tained aquaporin vesicles The soaked substrate was subsequently exposed totrimesoyl chloride to form a three-dimensionally cross-linked polyamide layer inwhich the aquaporin vesicles are embedded The resulting membranes are made insheets up to 600 cm2 and are sufficiently stable to allow normal handling and shippingprocedures

The resulting TFC membrane has been characterized in cross-flow RO and FOsetups Reverse osmosis membranes were tested under applied pressures up to14 bar and benchmarked against commercially available RO membranes (Zhaoet al 2012) Compared with the control membranes (membranes with protein-freevesicles and membranes with protein vesicles in which the protein was mutated toan inactive form) the aquaporin TFC membranes achieved significantly higher waterpermeability (w4 lm2 h bar) with comparable NaCl rejection (w97) Their perme-ability was w40 higher compared with a commercial brackish water RO membrane(Dow Filmtec BW30) and an order of magnitude higher compared with a seawater ROmembrane (Dow Filmtec SW30HR) In FO the aquaporin membranes had greater than90 rejection of urea with a water flux of 10 lm2 h with 2 M NaCl as draw solutionThis clearly demonstrates the great potential of the aquaporin TFC membranes for in-dustrial RO and FO applications in 2014 the Danish Cleantech company AquaporinAS began commercializing membranes as aquaporin inside membranes (AIM)based on this design

Whether the FO membranes are to be used for wastewater volume reduction andorrecovery of dyes a key question is whether the reactive dyes can be processed by themembranes A simple test for this is to try and up-concentrate dyes using an FO mem-brane process Because Nylosan dyes are acid dyes applicable for polyamide we testedwhether this class of dye can be processed using the aquaporin polyamide TFC designas described without damaging the membrane

Specifically we tested two different dyes Nylosan Blue E-GL250 and Nylosan RedE-BL18 for up-concentration assays with FO AIM provided by Aquaporin AS (seeFigure 172) Fifty milligrams of the blue dye is solved in 100 ml milliQ water togenerate a stock solution of 500 mmml The stock solution is then diluted to encom-pass a dilution series from 200 to 5 mgml A broad range wavelength scan from 200 to800 nm is used to detect the optimal absorbing wavelength for the dye (620 nm forNylosan Blue E-GL250 and 513 nm for Nylosan Red E-BL18) The optical density(OD) value is measured for the different concentrations and standard curves are plottedrelating the OD value to the concentration

Because of the osmotic gradient over the membrane water from the dye solutionwill be extracted through the AIM membrane resulting in up-concentration of thedye The OD is then measured for the up-concentrated dye solution and the concentra-tion is calculated from the standard curves In a successful up-concentration experi-ment the up-concentration factor of the dye solution (light grey bars) follows thevolume reduction factor (dark grey bars) In none of the experiments was dye detectedin the draw solution The results are summarized in Figure 172

Membrane technologies for water treatment and reuse in the textile industry 545

174 Conclusions

In general wastewater represents challenging feed streams to be treated by membraneseparation In particular the large variability in composition and the presence of poten-tially reactive components makes textile industry wastewater a particularly difficulttask for any remediation technology including membrane-based methods To datemembrane technology for textile wastewater has been based on RONFUF-based sys-tems Also MBR technology has attracted considerable interest however the require-ments for low oxygen and the general issue of biofouling present problems forbioreactors to function properly Also the large variation in water composition eeven from the same textile process and plant e is a major obstacle in introducingMBR in textile wastewater treatment Recent technological developments of FO mem-branes have opened up the possibility of using this technology in industrial processesand wastewater treatment The inherent low fouling propensity of FO membranesmakes them an intriguing supplement to existing remediation methods Thus FOcan in principle be used to concentrate the wastewater e eg using seawater as adraw solution e thereby reducing the hydraulic load on the wastewater treatmentplant e with diluted seawater being the discharged water stream Forward osmosismay also be used in up-concentration of dyes directly as exemplified by biomimeticaquaporin-based FO membranes

Up-concentration of textile dyes10

9

8

7

6

5

4

3

2

1

0Vol Vol Vol Vol Vol VolConc Conc Conc Conc Conc Conc

Nylosan Red E-BL180Nylosan Blue E-GL250

Up-

conc

entr

atio

n fa

ctor

(x ti

mes

)

88

7

55

437

637

427 404435

56 556

4

48

Figure 172 Experimental results for up-concentration of Nylosan Blue E-GL and Nylosan RedE-BL (n frac14 3 for each dye) with starting concentrations of 10 and 20 mgml respectively Theup-concentration assay is carried with an FO membrane module The dye solution to be up-concentrated is placed in the reservoir well of the upper part of the module while on the bottompart an osmotic draw solution (here 1 M NaCl) is recirculated The module is connected to aperistaltic pump by tubing to ensure the recirculation of the draw solution at 50 mlmin Thevolume concentration factor (Vol) and concentration factor for the dye (Conc) reflect volumereduction and dye up-concentration factor respectively

546 Advances in Membrane Technologies for Water Treatment

List of abbreviations

AIM Aquaporin inside membraneBOD Biological oxygen demandCMC Carboxymethyl celluloseCOD Chemical oxygen demandCTA Cellulose triacetateDO Dissolved oxygenDS Draw solutionFO Forward osmosisFS Feed solutionMBR Membrane bioreactorMPD m-phenylene-diamineNF NanofiltrationNOM Natural organic matterOD Optical densityPAO Pressure-assisted osmosisPRO Pressure-retarded osmosisPVA Polyvinyl alcoholRO Reverse osmosisTFC Thin-film compositeTMC Trimesoyl chlorideTSS Total suspended solidsUF Ultrafiltration

References

AchilliACath TYMarchandEAampChildressAE (2009) The forwardosmosismembranebioreactor A low fouling alternative to MBR processes Desalination 239 10e21

Ahmad A L amp Puasa S W (2007) Reactive dyes decolourization from an aqueous solutionby combined coagulationmicellar-enhanced ultrafiltration process Chemical EngineeringJournal 132 257e265

Allegre C Moulin P Maisseu M amp Charbit F (2006) Treatment and reuse of reactivedyeing effluents Journal of Membrane Science 269 15e34

Atkinson S (2009) High BOD and COD carpetdyeing wastewater recycled using forwardosmosis Membrane Technology 2009 1e8

Badani Z Ait-Amar H Si-Salah A Brik M amp Fuchs W (2005) Treatment of textilewastewater by membrane bioreactor and re-use Desalination 185 411e417

Banat I M Nigam P Singh D amp Marchant R (1996) Microbial decolorization of textile-dye-containing effluents A review Bioresource Technology 58 217e227

Beaudry E G Herron J R amp Peterson S W (1999) Direct osmosis concentration of wastewater Final report Corvallis OR Osmotek Inc

Bechtold T amp Turcanu A (2004) Cathodic decolourisation of dyes in concentrates from nano-filtration and printing pastes Journal of Applied Electrochemistry 34 903e910

Bonomo L (1992) Nanofiltration and reverse osmosis treatment of textile dye effluentsRecents Progress en Genie des Precedes 6 327e336

Membrane technologies for water treatment and reuse in the textile industry 547

Brik M Schoeberl P Chamam B Braun R amp Fuchs W (2006) Advanced treatment oftextilewastewater towards reuse using a membrane bioreactor Process Biochemistry 411751e1757

Cath T Y Childress A E amp Elimelech M (2006) Forward osmosis Principles applicationsand recent developments Journal of Membrane Science 281 70e87

Chang J-S Chou C Lin Y-C Lin P-J Ho J-Y amp Hu T L L W R (2001) Kineticcharacteristics of bacterial azo-dye decolourization by Pseudomonas luteola WaterResearch 35(12) 2841e2850

Choi J-S Ahn S-J Ryu S-H Jun J-P Choi C-G Han B-S et al (2003) A study onthe removal of color in dyeing wastewater using electron beam irradiation In Proceedingsof a consultants meeting Status of industrial scale radiation treatment of wastewater andits future (pp 67e79) South Korea Daejon 13e16 October

Coday B D Yaffe B G Xu P amp Cath T Y (2014) Rejection of trace organic compoundsby forward osmosis membranes A literature review Environmental Science andTechnology 48 3612e3624

Cornelissen E R Harmsen D De Korte K F Ruiken C J Qin J J Oo H et al (2008)Membrane fouling and process performance of forward osmosis membranes on activatedsludge Journal of Membrane Science 319 158e168

Dafale N Agrawal L Kapley A Meshram S Purohit H amp Wate S (2010) Selection ofindicator bacteria based on screening of 16S rDNA metagenomic library from a two-stageanoxic-oxic bioreactor system degrading azo dyesBioresource Technology 101 476e484

Dos Santos A B Cervantes F J amp Van Lier J B (2007) Review paper on currenttechnologies for decolourisation of textile wastewaters Perspectives for anaerobictechnologies Bioresource Technology 98 2369e2385

Dova M I Petrotos K B amp Lazarides H N (2007a) On the direct osmotic concentration ofliquid foods Part I Impact of process parameters on process performance Journal of FoodEngineering 78 422e430

Dova M I Petrotos K B amp Lazarides H N (2007b) On the direct osmotic concentration ofliquid foods Part II Development of a generalized model Journal of Food Engineering78 431e437

Erswell A Brouchaert C J amp Buckley C A (1988) The reuse of reactive dye liquors usingcharged ultrafiltration membrane technology Desalination 70 157e167

Feng F Xu Z Li X You W amp Zhen Y (2010) Advanced treatment of dyeing wastewatertowards re-use by the combined Fenton oxidation and membrane bioreactor processJournal of Environmental Sciences 22 1657e1665

Fritsch J (1993) Untersuchungen der Aufbereitung von Abwassern aus Textilbleichern mittelsNanofiltration Aachen Aachner Membrane Kolloquium

Fu D amp Lu M (2007) The structural basis of water permeation and proton exclusion inaquaporins Molecular Membrane Biology 24 366e374

Gonen T amp Walz T (2006) The structure of aquaporins Quaterly Reviews Biophysics 39361e396

Gonzalvez-Zafrilla J M Sanz-Escribano D Lora-Garciacutea J amp Leon Hidalgo M C (2008)Nanofiltration of secondary effluent for wastewater reuse in the textile industry Desali-nation 222 272e279

Gruber M F Johnson C Tang C Y Jensen M H Yde L amp Heacutelix-Nielsen (2011)Computational Fluid Dynamics simulations of flow and concentration polarization inforward osmosis membrane systems Journal of Membrance Science 379 488e495

Gruber M Johnson C E Tang C Jensen M H Yde L amp Heacutelix-Nielsen C (2012)Validation and analysis of forward osmosis CFD model in complex 3D geometriesMembranes 2 764e782

548 Advances in Membrane Technologies for Water Treatment

He Y Li G Wang H Jiang Z Zhao J Su H amp Huang Q (2009) Experimental study onthe rejection of salt and dye with cellulose acetate nanofiltration membrane Journal ofTaiwan Institute of Chemical Engineers 40 289e295

Holloway R W Childress A E Dennett K E amp Cath T Y (2007) Forward osmosis forconcentration of anaerobic digester centrate Water Research 41 4005e4014

Kang I J amp Lee C H (2004) Effect of aerobic period on microfiltration performance in amembrane-coupled sequencing batch reactor Journal of Industrial and EngineeringChemistry 10 146e151

Klaysom C Cath T Y Depuydt T amp Vankelecom I F (2013) Forward and pressureretarded osmosis Potential solutions for global challenges in energy and water supplyChemical Society Reviews 42 6959e6989

Kodam K M amp Gawai K R (2006) Decolourisation of reactive red 11 and 152 azo dyesunder aerobic conditions Indian Journal of Biotechnology 5 422e424

Kodam K M Soojhawon I Lokhande P D amp Gawai K R (2005) Microbial decolour-isation of reactive azo dyes under aerobic conditions World Journal of Microbiology andBiotechnology 21 367e370

Koyuncu I (2003) Influence of dyes salts and auxiliary chemicals on nanofiltration of reactivedye baths Experimental observations and model verification Desalination 154 79e88

Koyuncu I Kural E amp Topacik D (2001) Pilot-scale nanofiltration membrane separation forwastewater management in the textile industryWater Science and Technology 43 233e240

Lewandowski Z (2004) Biofilms Their structure activity and effect on membrane filtrationProceedings of IWA Specialty Conference 2 417e431

Li Q amp Elimelech M (2004) Organic fouling and chemical cleaning of nanofiltrationmembranes Measurements and mechanisms Environmental Science and Technology 384683e4693

Ludewig U amp Dynowski M (2009) Plant aquaporin selectivity Where transport assayscomputer simulations and physiology meet Cellular and Molecular Life Sciences 663161e3175

Mccutcheon J R Mcginnis R L amp Elimelech M (2006) Desalination by a novelammoniaecarbon dioxide forward osmosis process Influence of draw and feed solutionconcentrations on process performance Journal of Membrane Science 278 114e123

Nielsen C H (2009) Biomimetic membranes for sensor and separation applications Analyticaland Bioanalytical Chemistry 395 697e718

Orsquoneill C Hawkes F R Hawkes D L Esteves S amp Wilcox S J (1999) Anaerobicaerobic biotreatment of simulated textile effluent containing varied ratios of starch and azodye Water Research 34 2355e2361

Pandey A Singh P amp Lyengar L (2007) Bacterial decolourization and degradation of azodyes International Biodeterioration Biodegradation 59 73e84

Petrinic I Andersen N P R SOstar-Turk S amp Le Marechal A M (2007) The removal ofreactive dye printing compounds using nanofiltration Dyes and Pigments 74 512e518

Petrotos K B Lazarides H N Wolf W Behsnilian D amp Spiess W (2001) Osmoticconcentration of liquid foods Journal of Food Engineering 49 201e206

Pierce J (1994) Colours in textile effluentse the origins of the problem Journal of The Societyof Dyers and Colourists 110 131e133

Pierce C I Lloyd J R amp Guthrie J T (2003) The removal of color from textile wastewaterusing whole bacterial cells A review Dyes Pigments 58 179e196

Porter J J (1999) Membrane filtration techniques used for recovery of dyes chemicals andenergy Textile Chemist and Colorist 22 21e25

Rautenbach R amp Mellis R (1994) Waste water treatment by a combination of bioreactor andnanofiltration Desalination 95 171e188

Membrane technologies for water treatment and reuse in the textile industry 549

Robinson T Mcmullan G Marchant R amp Nigam P (2001) Remediation of dyes in textileeffluent A critical review on current treatment technologies with a proposed alternativeBioresource Technology 77 247e255

Rozzi A Antonelli M amp Arcari M (1999) Membrane treatment of secondary textileeffluents for direct reuse Water Science and Technology 40 409e416

Salter R (2006) Forward osmosis Water Conditioning and Purification 48 36e38Simonic M (2013) Perspectives of textile wastewater treatment using MBR A review Textiles

and Light Industrial Science and Technology (TLIST) 2 71e77Slokar Y M amp Le Marechal A M (1998) Methods of decolouration of textile wastewaters

Dyes and Pigments 37 335e356Sojka-Ledakowicz J Koprowski T Machnowski W amp Knudsen H-H (1998) Membrane

filtration of textile dyehouse wastewater for technological water reuse Desalination 119 1e9Sponza D T amp Isik M (2005) Reactor performance and fate of aromatic amines through

decolourisation of Direct Black 38 dye under anaerobicaerobic conditions ProcessBiochemistry 40 35e44

Suksaroj C Heacuteran M Allegre C amp Persin F (2005) Treatment of textile plant effluent bynanofiltration andor reverse osmosis for water reuse Desalination 178 333e341

Tang C Y Zhao Y Wang R Heacutelix-Nielsen C amp Fane A G (2013) Desalination by bio-mimetic aquaporin membranes Review of status and prospects Desalination 308 34e40

Tegtmeyer D (1993) Moglichkeiten und chancen einer membrantechnischen abwasserbr-handlung in de textilfarberai Melliand Textiberichte 74 148e151

Teoh M M Wang K Bonyadi S amp Tai-Shung N (2008) Forward osmosis and membranedistillation proceses for freshwater production Innovation 8 15e17

Treffry-Goatley K Buckley C A amp Groves G R (1983) Reverse osmosis treatment andreuse of textile dyehouse effluents Desalination 47 313e320

Van Der Zee F P amp Villaverde S (2005) Combined anaerobic-aerobic treatment of azo dyesA short review of bioreactor studies Water Research 39 1425e1440

Vrouwenvelder J S amp Van Der Kooij D (2001) Diagnosis prediction and prevention ofbiofouling of NF and RO membranes Desalination 139 65e71

Xu Y Peng X Tang C Shiang Fu Q amp Nie S (2010) Effect of draw solution concen-tration and operating conditions on forward osmosis and pressure retarded osmosisperformance in a spiral wound module Journal of Membrane Science 348 298e309

York R TampBeaudry E (1999) Full scale experience of direct osmosis concentration applied toleachate management In T H Christensen R Cossu amp R Stegmann (Eds) Sardinia 99Seventh International Waste Management and Landfill Symposium 4-8 October Pro-ceedings CISA Environmental Sanitary EngineeringCentre Cagliari Italy (pp 359e366)Cagliari Sardinia Italy S Margherita di Pula

You S-J amp Teng J-Y (2009) Anaerobic decolourisation bacteria for the treatment of azo dyein a sequential anaerobic and aerobic membrane bioreactor Journal of Taiwan Institute ofChemical Engineers 40 500e504

Zaghbani N Hafiane A ampDhahbiM (2007) Separation ofmethylene blue from aqueous solutionby micellar enhanced ultrafiltration Separation and Purification Technology 55 117e124

ZhaoYQiuC LiXVararattanavechAWSTorres JHeacutelix-NielsenCWangRHuXFane A G amp Tang C Y (2012) Synthesizing Robust and high-performance aquaporinbased biomimetic membrane by interfacial polymerization - membrane preparation and ROperformance characterization Journal of Membrane Science 423e424 422e428

_Zyłła R Sojka-Ledakowicz J Stelmach E amp Ledakowicz S (2006) Coupling of membranefiltration with biological methods for textile wastewater treatment Desalination 198316e325

550 Advances in Membrane Technologies for Water Treatment

Membrane technologies forwater treatment and reuse in thefood and beverage industries

18A Cassano1 NK Rastogi2 A Basile131Institute on Membrane Technology ITM-CNR University of Calabria Rende (CS) Italy2Department of Food Engineering Central Food Technological Research Institute Councilof Scientific and Industrial Research Mysore India 3Ast-Engineering srl Rome Italy

181 Introduction

Water raw materials and energy are key resources used in the food-processingindustry In particular water is used as ingredient cleaning source and conveyor ofraw materials and to sanitize plant machinery and areas Subsequently effluentsfrom many agro-food industries are a hazard to the environment and require appro-priate management approaches

Wastewaters generated by different branches of the agro-food industry can bedivided into two classes (on the basis of plant or animal origin) and seven subclasses(Table 181)

The characteristics and volume of these effluents vary with the products and pro-duction procedures Typically they contain macropollutants such as chemical oxygendemand (COD) biochemical oxygen demand (BOD) total suspended solids (TSS)fats oils and nutrients (nitrogen and phosphorous) In addition some micropollutantsincluding hormones surfactants antibiotics and pesticides can be present However itis often difficult to predict the composition of food waste because of the seasonalnature of food processing and post-harvesting

The main parameters of typical food waste are given in Table 182 On the basis oftheir composition effluents from many agro-food industries produce negative effectswhen disposed into the environment and require appropriate management approachesConsequently extensive research has been devoted to coping with waste generated byagro-industries

Technological innovations including those in clean technologies and processesaim to introduce into food-processing factories advanced wastewater treatment prac-tices able to recycle spent process waters onsite and to reduce the amount of waste-water discharged into municipal sewage treatment plants Another target of greatinterest is the reduction of water and wastewater from the manufacturing process(closed-loopzero emission systems) and the reuse of treated waters in the food-processing industry

In addition food waste contains higheadded value compounds (ie phenols carot-enoids pectin hemicelluloses oligopeptides lactose proteins) that can be recovered

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400018-6Copyright copy 2015 Elsevier Ltd All rights reserved

and recycled inside the food chain as functional additives in different products To thispurpose conventional and emerging technologies offer interesting perspectives takinginto account the huge amounts of food-related materials discharged worldwide(Galanakis 2012)

Conventional technologies for the treatment of food-processing wastewatersinclude (1) physical and chemicophysical processes to remove suspended solids(screening systems sedimentation and dissolved air flotation) (2) biological treat-ment processes (anaerobic treatments activated sludge processes aerated lagoonsand land application) aimed at removing soluble pollutants and (3) tertiary treatmentsincluding membrane processes or other chemicophysical processes such as precipita-tion activated carbon and chelation for the removal of specific pollutants or forimproving water parameters (Bolzonella amp Cecchi 2007)

Membrane filtration processes offer interesting perspectives and key advantagesover conventional technologies in the treatment of wastewaters from food-processing industries

They can be combined with activated sludge processes to form membrane bioreac-tors (MBRs) to improve the capability of removing pollutants in biological treatmentprocesses (Stephenson Brindle Judd amp Jefferson 2000) In addition pressure-drivenmembrane operations such as microfiltration (MF) ultrafiltration (UF) nanofiltration(NF) and reverse osmosis (RO) can be used to treat high-strength wastewaters or at theend of conventional treatment systems to produce purified water for recycling or reuseand to recover valuable compounds (Moresi amp Lo Presti 2003 Muro Riera amp delCarmen Diaz 2012)

Table 181 Food waste and its origins

Source Waste origin Type of waste

Plant Cereals Rice bran wheat middling wheat straw wheat branoat mill waste malt dust breweryrsquos spent grains

Root and tubers Potato peel sugar beet molasses

Oil crops andpulses

Sunflower seed soybean oil waste soybeanwastewaters olive pomace olive mill wastewater

Fruit andvegetables

Citrus peel apple pomace apple skin peachpomace apricot kernel grape pomace grape skinwine lees banana peel tomato pomace tomatoskin

Animal Meat products Chicken by-products slaughterhouse by-productsbeef lung bovine blood

Fish and seafood Fish leftovers shrimp and crab shells surimiwastewater

Dairy products Cheese whey

Source Adapted from Galanakis (2012)

552 Advances in Membrane Technologies for Water Treatment

Table 182 Characteristics of agro-food wastewater

Industry BOD (mgL) COD (mgL) TSS (mgL)Total phosphorus(mgL)

Total nitrogen(mgL) References

Fruit juice 1580 3650 e 24 12 Noronha BritzMavrov Jankeand Chmiel(2002)

Fish and seafood e e Cros LignotJaouen andBourseau (2006)

Fish tradeactivities

400e2200 500e4500 3e35 e e Vandanjon CrosJaouenQueacutemeacuteneur andBourseau (2002)

Shrimpprocessingmdashthawing

650 1000 2 e e Walha et al (2011)

Shrimpprocessingmdashcooking

2000e10000 3000e20000 200e1200 e e

Shrimpprocessingmdashrinsing

650 1300 7 e e

Continued

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

553

Table 182 Continued

Industry BOD (mgL) COD (mgL) TSS (mgL)Total phosphorus(mgL)

Total nitrogen(mgL) References

Tuna cookingjuice

e 23500 2100

Food andbeverage

e 1800e6600 1000e7300 e e Chmiel KaschekBleuroocherNoronha andMavrov (2002)and Bleuroocher et al(2002)

Food 680 880 2480 e e Katayon et al2004

Dairy 800e1000 1400e2500 1100e1600 e e Gotmare Dhobleand Pittule(2011)

Dairy 650e6250 400e15500 250e2750 e 10e90 Passeggi Lopezand Borzacconi(2009)

554Advances

inMem

braneTechnologies

forWater

Treatm

ent

Dairy e 380e38500 31e796 e e Vourch BalannecChaufer andDorange (2008)

Poultryprocessing

858 1173 e e Lo Cao Argin-Soysal Wang ampHahm (2005)

Winery Valderrama et al(2012)

Harvesting 13448 1230 395 340

Harvesting andvinasse

e 3887 662 65 e

Vinasse e 3400 271 75 41

Process e 2323 178 50 400

Winery e 4728 320 35 60 Bolzonella FatonePavan andCecchi (2010)

Steamed soybeanwastewater

e 8400e8700 14500e15300 e e MatsubaraIwasakiNakajimaNabetani andNakao (1996)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

555

This chapter gives an overview of membrane-based processes for water reuse andenvironmental control in the treatment of wastewaters from food-processing indus-tries Applications involving the use of pressure-driven membrane operations electro-dialysis (ED) and MBRs as well as a combination of membrane operations in hybridsystems in the treatment of waste from different agro-food productions are analyzedand discussed

182 Wastewaters from food and beverage industry

In the food and beverage industries exhausted waters generated from different oper-ations (fruit processing cleaning of tanks and pipes and bottle washing) are mixedtogether before they are discharged into municipal sewage systems

These wastewaters can be defined as high-strength wastewaters because of theirhigh COD values and high content of biodegradable compounds such as nitrogen orphosphorous elements They can be discharged into the environment after specifictreatments to reduce polluting compounds according to standards defined by environ-ment regulations

The use of MBRs is a promising technology in treating high-strength wastewatersas an alternative to conventional activated sludge treatment Fundamentals configura-tions and typical applications of MBR systems are analyzed and discussed in Chapter6 As highlighted in this chapter the best performance of MBR can be producedthrough optimizing operating parameters such as hydraulic retention time solid reten-tion time (SRT) mixed liquor suspended solids (MLSS) and transmembrane pressure(TMP) Pretreatment systems physical and chemical cleaning and biofouling reducerssuch as powdered activated carbon are all systems that can be used to reduce foulingphenomena thus enhancing MBR performance (Katayon et al 2004 MutamimNoor Abu Hassan amp Olsson 2012)

A hybrid process for the production of drinking water from spent process waters offruit juice companies was developed by Bleuroocher et al (2002) on an industrial scaleafter preliminary studies on a pilot scale (Noronha Britz Mavrov Janke amp Chmiel2002) Spent waters from small and medium-sized enterprises were mixed in an equal-ization tank and clarified through a lamella clarifier to remove most solids The clar-ified effluent was treated in an MBR equipped with immersed tubular MFmembranes (pore size 004 mm) in which the active biomass and other particulate mat-ter were completely retained Although the organic loading rate of the spent water var-ied widely (between 1800 and 6600 mgL) COD and total organic carbon (TOC) werereduced by at least of 96 in this first step

The MF permeate was then submitted to a two-step NF process with integrated ul-traviolet (UV) disinfection The first NF step was operated with spiral-wound mem-brane modules characterized by low rejection for sodium chloride (on average55) ensuring a reduction of dissolved organics up to 97 The second filtrationstep was carried out using NF membrane modules with a rejection rate for sodiumchloride higher than 90 These membranes operated as desalting membranes with

556 Advances in Membrane Technologies for Water Treatment

a low fouling index reducing the salinity of the spent liquor more than 75 The finalCOD of the treated water was below the detection limit and TOC did not exceed thelimit value of 4 mgL Chemical and microbiological parameters of the final permeatewere within the water quality standard of the German Drinking Water Act The pro-posed process is illustrated in Figure 181 For a plant capacity of 5 m3h the overalltreatment cost for producing drinking water from spent process water was estimated tobe about 25e30 Vm3

The presence of oils and fats in spent process waters generated in margarine pro-duction creates several problems when these waters are submitted to biological treat-ment (ie high costs for aeration and sludge disposal flotation and coating in thetreatment plant and saponification of fats in the equalization tank) Treatment of theseeffluents with 02-mm ceramic MF membranes reduced the initial COD of5000e10000 mgL below 250 mgL The produced permeate could be mixedwith water of low and medium contamination and then submitted to biological treat-ment A concentrated product was recovered from the MF retentate and reused forsoap production after a skimming oil treatment (Chmiel Kaschek Bleuroocher Noronhaamp Mavrov 2002)

The Kubota submerged anaerobic membrane biological reactor process developedin the past decade by Kubota Membrane Technology (Hyogo Japan) is an interestingapplication of anaerobic MBRs in food-processing factories The process alsodescribed in Chapter 6 consists of a solubilization tank and a mesophilic or thermo-philic tank equipped with submerged membranes These membranes retain methano-genic bacteria while methane fermentation inhibitors such as ammonia are allowed topass in the permeate stream The generated biogas can be used to heat water viaboilers Permeate and sludge can be further treated in aerobic treatment facilities(Kanai Ferre Wakahara Yamamoto amp Moro 2010) The process has been success-fully implemented in food factory treatment plants stillage treatment plants forShouchu (a Japanese spirit made from sweet potato) and potato-processing sites

Ng Lin Panchangam Hong and Yang (2011) compared the performance of anovel bio-entrapped membrane reactor (BEMR) packed with bio-ball carrierswith that of a conventional MBR in the treatment of wastewater from a food andbeverageeprocessing plant The new reactor exhibited a longer SRT and lowerMLSS compared with the conventional system The BEMR produced also fewersoluble microbial products than the conventional system (34e48 less protein and16e29 less carbohydrate) owing to slow-growing microorganisms with long SRTFinally the new BEMR was able to operate at a constant permeate flux requiringless frequent chemical cleanings with consequent economic benefits

The technical feasibility of recovering and concentrating tartaric acid by ED fromfruit juice processing wastewater was assessed by Andreacutes Riera and Alvarez (1997)In particular the ED treatment of synthetic solutions simulating ionic exchange regen-eration waters obtained in grape juice processing increased five times the initial iontartrate concentration (from 1 to 10 kgm3 up to 532 kgm3) The energy consumptionwas estimated to be about 5 103 kJkg tartaric acid The purified acid can be reusedfor food and pharmaceutical applications

Membrane technologies for water treatment and reuse in the food and beverage industries 557

Water for reuse

NFMF

Spent processwater

UVdisinfection

Membrane bioreactorAir oroxygen

Excess sludgeNF

UVdisinfection

Retentateto be

dischargedSpent processwater Lamella

clarifier

Settled solids

Figure 181 Flow diagram of integrated membrane process for the recycling of spent process water from the food and beverage industriesAdapted from Noronha et al (2002)

558Advances

inMem

braneTechnologies

forWater

Treatm

ent

183 Wastewaters from fish and seafood industry

The fish-processing industry produces several effluents (ie wastewater generatedduring fishmeal production and wastewater generated by washing thawing rinsingand cooking treatments) exhibiting different characteristics The polluting load andthe flow rates of these effluents vary greatly according to the activity The COD andsalt content are in the range of 7e49 and 025e10 gL respectively Although thesewastewaters contain no toxic materials they cannot be released into the environmenttherefore depolluting treatments are needed in municipal or private treatment plantsIn addition fish industry wastewater contains potentially valuable molecules for thefood sector such as proteins flavor and aroma compounds and n-3 polyunsaturatedfatty acids whose recovery can lead to appreciable productivity gains (Masseacute et al2008)

Membrane technology has great potential for the treatment of fish-processing efflu-ents In particular key advantages of membrane processes over conventional technol-ogies such as coagulationflocculation and dissolved air flotation concern theproduction of good-quality permeate streams that can be disposed directly into thesea or recycled into the plant and the recovery of valuable compounds under mild con-ditions without using heat or chemicals An extensive review of the application ofpressure-driven membrane operations in the treatment of seafood-processing effluentswas reported by Afonso and Borquez (2002a) The authors also evaluated the perfor-mance of an integrated membrane process based on the use of MF and UF or NF torecover proteins from the effluents of a fishmeal plant Microfiltration pretreatmentreduced drastically the oil and grease content and the suspended matter improvingthe performance of the subsequent membrane treatment The selected UF ceramicmembrane (Carbosep M2 tubular 15 kDa molecular weight cutoff (MWCO)) reducedthe organic load of the MF permeate and allowed the recovery of valuable raw mate-rials including proteins The protein rejection ranged from 49 to 62 depending onthe operating conditions A ceramic NF membrane (Kerasep NanoN01A tubular1 kDa MWCO) produced a protein rejection of 66 when the MF permeate was pro-cessed In both cases the highest protein rejection was achieved at a TMP of 4 bar anda cross-flow velocity of 4 ms (Afonso amp Borquez 2002b Afonso Ferrer amp Borquez2004) A conceptual process for the treatment of 10 m3h of fishmeal effluent based onthe use of MF and UF membranes was designed (Figure 182) The plant wouldgenerate 1 m3h of concentrate containing 170 gL of solids and 112 gL of proteinsThe economic assessment for the integrated MFeUF process yielded a net worth ofUS$160 103 an interest rate of return of 17 and 8 yearsrsquo payback time indicatingthe feasibility of the process for protein recovery and pollution reduction

The UF treatment of fishery washing waters with polysulphone membranes of20 kDa and a multichannel ceramic membrane of 01 mm produced similar apparentrejections (70 and 80 respectively) toward proteins The process increased theprotein concentration in the feed solution from 5 to 35 gdm3 and reduced the BODby about 80 (Mameri et al 1996) Other applications related to the use ofpressure-driven membrane operations in the treatment of wastewater from surimi

Membrane technologies for water treatment and reuse in the food and beverage industries 559

production (Huang amp Morrissey 1998) menhaden bail water (Abu Rao Khan ampLiuzzo 1984) fish brine (Paulson Wilson amp Spatz 1984) and effluents dischargedfrom fish plants (Chao Asce amp Tojo 1987) have been investigated

An integrated process for the concentration of aroma compounds and the produc-tion of clean water from shrimp cooking juices was developed by Cros LignotJaouen and Bourseau (2006) The process is based on a clarification step to removesuspended solids followed by a desalination step by ED and a final concentrationstep by RO (Figure 183) The pre-filtered juice (pore size 500 mm) was treated byED and consisted of 20 compartments alternating cation-exchange and anion-exchange membranes for a total surface area of 0138 m2 The RO unit was equippedwith tubular polyethersulphone-polyamide membranes supplied by PCI (BeaupuyFrance) with an effective membrane area of 0033 m2 The performance of both sys-tems was evaluated for different juices containing from 20 to 200 gL of organic matterand from 4 to 40 gL of minerals Experimental results showed that the integration ofED and RO seems technically and economically feasible The payback time was eval-uated as less than 3 years

The size of the integrated process does not require a systematic evaluation of oper-ating and capital costs it can be evaluated by minimizing the total installed membranesurface area and energy consumption (Bourseau Masseacute Cros Vandanjon amp Jaouen

UF membranes carbosep M2Permeate

9 m3h70 kgh solids43 kgh prot78 gL solids48 gL prot

Concentrate

170 kgh solids1 m3h

112 kgh prot170 gL solids112 gL prot

210 kgh solids10 m3h

125 kgh proteins210 gL solids125 gL proteins

240 kgh solids10 m3h

155 kgh proteins240 gL solids155 gL proteins

(66 proteins dry basis)Rejection RUF () RMF + UF ()Total solids Total proteins

30 kgh solids30 kgh proteins

FeedRotary filter 5 μm

Feed tank

nabla

Pm = 4 bar v = 4 ms

6263 68

69

Figure 182 Integrated membrane process for the treatment of fishmeal effluent Reprinted fromAfonso et al (2004) with permission from Elsevier

560 Advances in Membrane Technologies for Water Treatment

2014) In the ED process the salt concentration can decrease from 20 to 28 gL withoutchanging the aromatic profile (Cros Lignot Bourseau Jaouen amp Prost 2005) How-ever a loss of volatile compounds under a critical salt concentration (23 gL) wasobserved This phenomenon was attributed to the salting-out of amino acids inducinga co-precipitation of hydrophobic aroma compounds and to the ionization of volatilecompounds and water splitting in the presence of a low concentration of ionic species

A desalination step before RO concentration is needed to avoid an increase in os-motic pressure in RO (RO membranes retain salt compounds) which limits the achiev-able extent of concentration This will increase the production cost of aromaconcentrates The use of NF membranes overcomes these problems The direct con-centration of aroma compounds from tuna cooking juices with NF tubular membranes(AFC30 PCI Ltd France) produced reasonable permeate fluxes (about 30 Lm2∙h)with retention factors of inorganic compounds between 70 and 76 The aromaproperties of the juice were slightly modified but the global characteristics of the juiceremained unchanged The MF pretreatment with ceramic multichannel membranes(Kerasep K01 Orelis) with a 01-mm pore size significantly improved NF permeationfluxes up to 90e100 Lm2 h (Walha et al 2011)

Integrated processes based on the use of UF as a pretreatment step followed by NFor RO for the concentration of aroma compounds from seafood cooking water werealso investigated by Vandanjon Cros Jaouen Queacutemeacuteneur and Bourseau (2002)

Shrimp cooking juice

Clean water

ED

RO

MF

Desalted juice

Clarified juice

Aromaconcentrate

Figure 183 Integrated membrane process for the production of clear water and aromaconcentrate from shrimp cooking juiceAdapted from Cros et al (2006)

Membrane technologies for water treatment and reuse in the food and beverage industries 561

RO membranes were more efficient in retaining aroma compounds from shrimp andbuckies cooking juices compared with 300-Da NF membranes and also had higher re-movals of COD (95 for shrimp and buckies and 85 for tuna juices)

184 Wastewater from dairy industry

Among the food industries the dairy industry is characterized by the production ofhuge quantities of polluted effluents (average of 02e10 L per liter of processed milk)

The pollution load of dairy industry wastewater can be defined by evaluatingdifferent parameters such as conductivity pH COD TOC TSS and residual hardness(Gotmare Dhoble amp Pittule 2011 Passeggi Lopez amp Borzacconi 2009) Vaporcondensates from evaporation and drying are considered to be low pollutant waters(Mavrov Chmiel amp Beacutelieres 2001) whereas end-pipe wastewaters are highly pollutedand require intense treatment to obtain clean water

Membrane treatment of these wastewaters including flushing water white waterand whey can give contribute greatly to reducing both total water consumption andthe volume of produced wastewater In addition the recovery of valuable compoundssuch as whey proteins using membrane technology is of great economical interestconsidering their nutritional biological and functional properties

NF and RO membranes have been shown to be useful for the concentration of milkconstituents from raw wastewater and to simultaneously produce treated water that canbe reused in the dairy industry (Koyuncu Turan Topacik amp Ates 2000) The perfor-mance of NF and RO membranes in the treatment of diluted skimmed milk used as aneffluent model solution (COD 36 gL) was investigated by Balannec Vourch Rabiller-Baudry and Chaufer (2005) Permeate flux and milk component rejections were eval-uated in dead-end filtration experiments performed in selected operating conditions(25 C and 14 bar for NF membranes and 25 C and 25 bar for RO membranes)up to a volume concentration ratio (VCR) of 3 Results of dead-end filtration experi-ments are summarized in Table 183 COD rejections were higher than 989 for allinvestigated membranes Cross-flow experiments performed with NF and RO spiral-wound membranes produced similar results (Balannec Geacutesan-Guiziou ChauferRabiller-Baudry amp Daufin 2002) The quality of produced permeates did not meetthe requirements of drinking water because of the high organic load of the effluentwhich suggests the use of a two-step RO process or a single step with a low chargedfeed for the production of reusable water Further studies performed by using modelprocess waters through one-stage and two-stage (NF plus RO and RO plus RO)spiral-wound membrane (Desal 5 DL Osmonics and TFC HR Koch Membrane Sys-tem) treatments indicated that after a single RO step or a combined NF plus RO pro-cess the final permeate could be reused as a replacement for cleaning heating orcooling and for boiler feed water More purified water with the typical requirementsof drinking water can be produced by a two-stage RO process (Vourch BalannecChaufer amp Dorange 2005) Similar results were obtained when dairy wastewaterwas treated through a single RO stage The process was carried out up to a recoveryfactor of 90e95 producing an average permeate flux of about 11 Lm2 h (Vourch

562 Advances in Membrane Technologies for Water Treatment

Table 183 Performance of nanofiltration and reverse osmosis membranes in the treatment of model dairyeffluent (initial COD 36 gL)

Membraneprocess

Membranetype Supplier

MWCO(kDa)

Membranematerial

Initialpermeate flux(Lm2 h)

PermeateCOD (mgL) RCOD ()

NF TFC S Koch membranesystems

PAPSPE 63 1095 9890

NF Desal 5 DL Osmonics 150e300 PAPS 79 300 9970

NF Desal 5 DK Osmonics 150e300 PAPS 72 960 9910

NF NF45 FilmTec 200 PAPSPE 68 1055 9900

NF NF200 FilmTec 200 PAPSPE 70 173 9980

RO Desal 3 SF Osmonics e PAPS 71 45 9996

RO TFC HR Koch membranesystems

e Composite PA 67 54 9995

RO BW 30 FilmTec e Composite PA 69 120 9988

MWCO molecular weight cutoff PA polyamide PS polysulphone PE polyesterSource Adapted from Balannec et al (2002)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

563

Balannec Chaufer amp Dorange 2008) According to the proposed scale-up a plantarranged with 18 spiral-wound 8-inch elements (for a total membrane surface areaof 540 m2) permits the recovery of 95 of water from 100 m3d of treated wastewater

Riera Suarez and Muro (2013) evaluated the effect of the main process parameterssuch as pressure temperature and VCR on the quality of permeate produced in asingle-step NF treatment of flash cooler condensates from direct ultraehigh tempera-ture processing The pilot plant was equipped with a spiral-wound membrane (SelROMPS-34 2540 B2X Koch Membrane Systems) with an MWCO of 200 Da As a gen-eral trend COD and TOC rejection increased by increasing the VCR (ie TOC rejec-tion increased from 676 at VCR 3 to 821 at VCR 15) Low-molecular-weightcompounds such as acetone acetoine and dimethylsulfide were partially retained bythe NF membrane Their increased rejection with VCR was attributed to the polariza-tion concentration layer on the membrane surface

In the investigated VCR values (between 1 and 15) average permeate fluxesbetween 100 and 110 Lm2 h were measured (at a TMP of 237 bar and a temperatureof 50 1 C) According to the experimental data an NF plant with 20 m3 h feedcapacity and 875 water recovery was designed The proposed plant was arrangedwith nine spiral-wound 8-inch elements (total membrane area 171 m2) distributedin three series of feed and bleed loops (Figure 184) Savings and operating costs ofthe designed NF plant were estimated at 2807 and 0777Vm3 respectively The ther-mal potential of permeate condensates suggested their reuse for heating purposes andin other miscellaneous services

A process combination based on the use of NF membranes for the reuse of vaporcondensate from milk processing was proposed by Chmiel Mavrov and Beacutelieres(2000) The process involves pretreatment with cartridge filtration and UV disinfectionfollowed by a two-stage NF process The demonstration plant was designed to treat15 m3h of feed and consisted of two membrane stages with spiral-wound membranemodules each with a membrane area of 40 m2 All of the parameters of the treated wa-ter met the requirements of drinking water (COD lt 10 mgL TOC lt 4 mgL andCa2thorn lt 04 mgL) as well as boiler makeup water

Whey is a co-product of cheese making with a low content of solids (up to 5e6)and a high BOD (30e50 gL for 1000 L of whey) which makes its disposal difficultand costly

Conventional processes in whey treatment include thermal evaporation and dryingThese processes are used to remove water from whey to diminish its volume but do notcontribute to the recovery of valuable compounds Anaerobic treatments are also usedto remove organic compounds from whey These processes are preferred over conven-tional aerobic treatments owing to the high COD of whey (about 60e80 gL) whichcan produce biomass granulation during biological treatment Other purification pro-cesses are based on the use of affinity chromatography cation-exchange resins andthermal precipitation (Pearce 1983 Uchida Sato Kawasaki amp Dosako 1996) How-ever these processes are not widely implemented on a large scale because of theircomplexity poor selectivity high cost and low product degradation

Whey processing is one of the most important applications in membrane technol-ogy in the dairy industry Whey concentration fractionation demineralization and

564 Advances in Membrane Technologies for Water Treatment

Feed pump25 bar

20 m3h

Recirculationpump

ΔP 14 bar342 m3h

Recirculationpump

ΔP 14 bar342 m3h

Recirculationpump

ΔP 07 bar171 m3h

Retentate25 m3h

80408040

80408040

80408040

8040

8040

8040

Permeate175 m3h

Figure 184 Multistage nanofiltration scheme for the treatment of flash cooler condensates from a dairy factory Reprinted from Riera et al (2013)with permission from Elsevier

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

565

purification can be achieved by using a combination of different membrane processesAt the same time the development of high value-added products from whey com-pounds is of great interest

The production of whey protein concentrates (WPCs) by UF is a well-establishedapplication in the dairy industry Ultrafiltration membranes separate lactose and min-erals from whey proteins producing a retentate stream that can be further processed byevaporation and spray-drying The lactose and mineral content in WPC can be furtherreduced by using a diafiltration (DF) step in which deionized water is continuallyadded to the retentate while lactose and minerals are continuously recovered in thepermeate stream By selecting a proper combination of UF and DF the protein contentin the WPC can be modified in the range of 35e85 The retentate can be used in avariety of beverages processed meats and baby foods or added to dairy products suchas yogurt and cottage cheese (Zydney 1998)

The concentration of whey andor its partial demineralization can be also achievedby NF NF membranes allow univalent ions (Nathorn Kthorn and Cl) to pass whereas largerions such as Cathornthorn or PO4

3 are retained Desalination degrees up to 40 can beachieved through a combination of NF and DF

The performance of UF NF and RO spiral-wound membrane modules for the re-covery of proteins and the production of clean water from white and curd cheese wheywas investigated by Yorgun Akmehmet Balcioglu and Saygin (2008) In particularthe performance of the selected membranes was evaluated according to a single-stageor multi-step operation involving different membrane modules in series Table 184summarizes the experimental results in terms of COD removal and permeate fluxfor the single-step process related to white cheese whey treatment The polysulphoneNF membrane module (200 Da as an MWCO) was considered the best choice whenthe effluent had to be further concentrated or treated by conventional treatmentsThis module exhibited an initial permeate flux of 24 Lm2 h when cheese whey wastreated at a TMP and a recirculation flow rate of 8 bar and 2500 Lh respectivelyAt the same time it produced permeate with a COD load of 2787 mgL with aCOD removal of 974 A further COD removal from the NF permeate required anadditional RO stage as a polishing step This combination allowed proteins to recoverseparately in the NF retentate while lactose was recovered in the second RO step withthe simultaneous production of a clean effluent

A combination of membrane-based cheese production was proposed by Atra VataiBekassy-Molnar and Balint (2005) to decrease the amount of waste in cheese produc-tion with a simultaneous increase in cheese yields through the incorporation of wheyproteins A flow diagram of the proposed process is depicted in Figure 185 The UF offresh milk and whey produces WPC (with a protein content of 12e14 and 8e10respectively) that can be used in cheese manufacturing improving the nutritional valueof the cheese UF permeates containing about 01e05 of proteins and 5 of lactoseare submitted to an NF process By selecting the proper operating conditions (ie atVCR 5 20 bar and 30 C) a concentrated solution containing 20e25 of lactosecan be obtained This solution can be reused in the dessert industry whereas thepermeate stream depleted in lactose can be reused for cleaning or irrigation or bedischarged into sewers

566 Advances in Membrane Technologies for Water Treatment

Table 184 Performance of ultrafiltration nanofiltration and reverse osmosis spiral-wound membranemodules in treatment of white cheese whey (initial COD w110 gL)

Membraneprocess Supplier

Membranematerial

Soluterejection ()

OperatingTMP (bar)

Initialpermeate flux(Lm2 h)

PermeateCOD (gL)

CODremoval ()

UF Microdyn Nadir PES e 3 225 54331 4280

NF Microdyn Nadir PES 25e40Na2SO4

5 27 43658 5850

NF Microdyn Nadir PES 80e95Na2SO4

8 17 37648 6402

NF Trisep Corp PA 95 MgSO4 8 25 23502 7761

NF Filmtec PS e 8 24 2787 9746

RO Trisep Corp PA 995 NaCl 12 146 3847 9257

PA polyamide PS polysulphone PES polyethersulphoneSource Adapted from Yorgun et al (2008)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

567

Most MBRs operate under aerobic conditions in which aeration is used to createcross-flow along the membrane to reduce fouling The use of anaerobic systems hasreceived great attention because of the energy balance achieved by biogas productionand the lower amount of produced sludge compared with aerobic MBRs (LiaoKraemer amp Bagley 2006) The performance of a bench-scale submerged anaerobicMBR in the treatment of a synthetic wastewater consisting of cheese whey and sucrosewas evaluated by Casu et al (2012) The results indicated that the maximum applicableorganic loading rates (OLRs) were in the range 6e10 g CODg L In this range thereactor showed a COD removal of 94 Higher OLRs produced high concentrationsof volatile fatty acids whereas the COD removal dropped to 33 The maximumbiomass concentration obtained in the system was of 40e50 g TSSL owing thelow filterability of the anaerobic sludge

NF

Cheese production

UF

Fresh milk(100 kg)

UF

20 kg

80 kg

Whey(25 kg)

Retentate(16 kg)

Permeate(64 kg)

Cheese(20 kg)

Permeate(60 kg)

Retentate(20 kg)

VRF 4

VRF 5

VRF 5

Retentate(5 kg)

Figure 185 Membrane-based process for the treatment of milk and whey in cheese productionAdapted from Atra et al (2005)

568 Advances in Membrane Technologies for Water Treatment

185 Wastewaters from meat industry

The meat-processing industry uses large volumes of water (approximately 62 Mm3y)generating polluting effluents for a total volume of about 80 of the freshwater inputThe produced effluents contain huge quantities of organic compounds and salts andrequire several treatments before their release into receiving waters or industrial reuseSedimentation coagulationflocculation and dissolved air flotation are typically usedas primary treatments to remove suspended solids and fat substances followed by aer-obic or anaerobic systems to achieve the removal of COD and BOD In general anaer-obic systems lead to higher BOD removal with lower cost and a smaller quantity ofproduced sludge compared with aerobic treatment In addition the generated methanecan be captured for use as a fuel (Johns 1995) Methods for microbial decontaminationinclude chemical (chlorine chlorine dioxide chloramines hydrogen peroxide ozoneand paracetic acid) and physical (membrane operations and UV) processes (CasaniRouhany amp Knochel 2005)

The selection of a proper treatment system is a main challenge in supplying water ofnecessary microbiological and chemical quality The treatment system should removeundesirable physical chemical and microbiological components and in some casesprevent the subsequent growth of pathogenic organisms

Membrane processes present some key advantages over conventional technologiesbecause they can be used to purify water and recover valuable compounds In additionthey are able to remove particles from wastewater preventing microbial regrowthphenomenon

Some integrated processes based on the use of membrane technology have beenimplemented in the meat-processing industry for the reuse of non-potable water withinthe plant

Kane and Osantowski (1981) described a pilot-plant study in which wastewater waspassed through chemical flocculationclarification and dual-media filtration beforefurther upgrading by ion exchange RO or ED The latter three processes producedmore than 90 reduction of total dissolved solids However RO exhibited lowercapital and operating costs compared with the other two processes

The treatment of meat wastewater in integrated systems including membrane op-erations such as coagulationeRO UFeRO and coagulationeUFeRO was investi-gated by Bohdziewicz and Sroka (2005) UF and RO were performed with differentplate-and-frame membrane modules produced by Osmonics Results indicated thatthe coagulation treatment similar to UF was not able to remove all pollutantsfrom wastewater and the produced effluent could not be discharged into the receivingwater The combination of coagulation UF and RO resulted in the satisfactoryremoval of pollutants in particular the highest removal degree of contaminantswas obtained in a sequence coagulation with PIX 113 (Fe2(SO4)3 Feog 128Fe2thorn 07 H2SO4 1) UF with a 15- to 30-kDa cellulose acetate membrane(DSCQ Osmonics) and RO with a cellulose acetate membrane (SS10 Osmonics)Analyses of polluting substances in each step of the hybrid system are reported inTable 185

Membrane technologies for water treatment and reuse in the food and beverage industries 569

In a previous study the authors demonstrated that in the biological treatment ofmeat wastewater applying the activated sludge method to a sequencing batch reactorproduced an effluent that could be discharged into the receiving water The combina-tion of biological treatment and the RO process obtained a higher degree of purifica-tion and the produced effluent could be reused in the production cycle of the plant(Sroka Kaminski amp Bohdziewicz 2004)

In the shower process after boiling sausage products are cooled by spraying withdrinking water The water generated in this process is commonly discharged into thesewage network Its reuse requires treatment able to produce drinking-quality water Ademonstration plant for the treatment of water from shower processes was installed in ameat-processing company at the end of 1997 (Feuroahnrich Mavrov amp Chmiel 1998)A flowchart of the plant based on the use of a two-step NF process is depicted inFigure 186 The flow rate of the demonstration plant was of 15e2 m3h correspond-ing to an average residence time of shower process water in the feed tank of about45 min TOC rejections were higher for the first NF membrane (956) comparedwith the second one (551) This was attributed to the presence of both dissolvedand undissolved organic substances in the solution fed to the first NF stage The orig-inal bacteria concentration in the feed tank of 1100000100 ml was reduced to 1600100 ml by UV irradiation in the pretreatment stage This step also allowed the reduc-tion of membrane biofouling After the second NF step the produced water metrequired drinking water regulations (lt100 bacteriamL at 37 C) The final UV disin-fection produced bacteria-free water

A similar approach was adopted by Mavrov et al (2001) to treat chiller shower waterin sausage production to reduce its salinity and hardness and achieve warm cleaningwater for reuse Polypiperazinamide NF membranes (NaCl rejection 85e90MgSO4 rejection 99) were used in both the treatment and posttreatment stages oper-ating at constant TMP values of 42 and 25 bar respectively Permeate fluxes were onthe order of 25e3 Lm2 h in the first stage and 5e6 Lm2 h in the second one For bothNF permeates the electrical conductivity was lower than 200 mScm In the second NFpermeate TOC and Ca2thorn were lower than 4 and 1 mgL respectively

Table 185 Performance of ultrafiltration (UF) and reverse osmosis(RO) membranes in treatment of meat wastewater

Pollutionindices(mgL)

Rawwastewater

UFpermeate

UFrejection()

ROpermeate

ROrejection()

COD 22840 3550 845 40 998

BOD 19000 3500 816 39 998

Total nitrogen 2850 400 860 25 991

Total phosphate 250 106 576 00 1000

Source Adapted from Bohdziewicz and Sroka (2005)

570 Advances in Membrane Technologies for Water Treatment

Water for reuse

NF

Spent processwater

UVdisinfection

PretreatmentNF UV

disinfection

Retentate to be discharged

Two-stage cartridgefiltration

Belt filtration

Figure 186 Flow diagram of a demonstration plant for the treatment of meat-processing wastewaterAdapted from Feuroahnrich et al (1998)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

foodand

beverageindustries

571

The manufacture of cured hams requires several steps including the addition of saltsand subsequent desalting and washing with water This process generates polluted ef-fluents containing solved salts (mainly NaCl) and a variable amount of organic matterThese effluents are generally dumped with no treatment with consequent environ-mental problems A treatment process to recover solved salts from liquid effluentsof cured hams was proposed by Arnal Garciacutea-Fayos Sancho and Leon-Hidalgo(2013) The process is based on a pretreatment step to remove organic compoundsproducing a clarified liquid mainly composed of water and dissolved salts which isthen submitted to a membrane process (ie an RO unit) where dissolved salts canbe concentrated The concentrated stream is finally treated in a natural assisted evap-oration plant where it is concentrated into a solid state while the permeate stream canbe reused in the plant

Poultry processing wastewaters (PPWs) contain organic compounds such as pro-teins fats and carbohydrates resulting in high BOD and COD

Conventional depolluting methods of PPWs include electrical (electrical stimula-tion) optical (UV irradiation) physical (dissolved air flotation diatomaceous earthfiltration and MF) chemical (ozonation and chemical separation of organic matterby coagulation and flocculation) and biological (anaerobic filter or sequencing batchreactors) treatment However most existing commercial processes present some disad-vantages in terms of low clarification levels and low reduction of organic compounds(ie in UV treatment) precipitation of proteins when iron salts are used and degrada-tion of valuable compounds during biological treatment

The recovery of proteins from PPWs by UF was investigated by several authors(Lo Cao Argin-Soysal Wang amp Hahm 2005 Saravia Houston Toledo amp Nelson2005 Shih amp Kozink 1980 Zhang Kutowy Jumar amp Malcolm 1997) In the workof Lo et al (2005) PPWs were pretreated by dissolved air flotation to remove most fatsubstances The pretreated effluent was ultrafiltered using a polysulphone UF mem-brane (Minitan-S Millipore) in flat-sheet configuration with an MWCO of 30 kDaAlmost all crude proteins were retained by the UF membrane and the COD in theeffluent was reduced to less than 200 mgL The optimization of operating conditions(pH 674 flow rate of 683 mLmin and TMP of 096 bar) by response surface meth-odology improved the permeate flux from 100 Lm2 h to higher than 200 Lm2 h Aftera cleaning step with a commercial detergent containing 200 ppm sodium hypochloritethe UF membrane surface appeared to be free of a gel-layer deposit This step was ableto restore more than 90 of original water permeability indicating that the major fluxreduction in the process was reversible

In the UF process most total solids can be recovered as by-products avoiding thegeneration of solid sludge In addition a combination of UF and dehydration couldproduce a by-product containing up to 35 protein and up to 45 fat from PPWs(Avula Nelson amp Singh 2009)

Mannapperuna and Santos (2004) designed a membrane plant based on the use ofspiral-wound UF membranes for the treatment of 480 Lmin of poultry chiller overflowwith a production of 380 Lmin of reconditioned water at 80 recovery The total costof the system was estimated to be US$300000 and the total electrical power

572 Advances in Membrane Technologies for Water Treatment

requirement was 30 kW The system is able to replace 346 Lmin of freshwatermakeup to the chiller with additional advantages in terms of disposal costs and energysavings

186 Winery wastewater

Winery wastewater is typically generated from washing operations during grape har-vesting pressing and fermentation as well as from washing equipment and bottles

The wastewater contains huge amounts of biodegradable organic compoundstogether with small concentrations of phenolic compounds sugars organic acidsand nutrients COD values range typically between 800 and 12800 mgL The quantityof produced waters and their pollution load vary in relation to the working period andthe winemaking technologies used (Mulidzi 2010) Therefore depolluting treatmentsshould be highly flexible to counterbalance variations in both quality and quantity ofpollutants

In Europe activated sludge processes are commonly used to pretreat winery waste-water before release into sewage systems However some operational problems arisefrom the need to treat waters with high organic loads for relatively short periods duringharvesting and vintage The use of MBRs offers different advantages over conven-tional biological processes including reduced sludge production better flexibility ac-cording to influent loading low footprint high efficiency in COD reduction rapidstartup and complete suspended solids removal (Guglielmi Andreottola Foladoriamp Ziglio 2009 Judd 2011)

The performance of a full-scale MBR in the treatment of a winemaking facilityoperating in Italy was evaluated by Bolzonella Fatone Pavan and Cecchi (2010)The filtration unit consisted of plate-and-frame MF membranes (04 mm) with a totalsurface area of 276 m2 The plant was able to treat 110 m3d of wastewater producingpermeate of good quality and a relatively small amount of wasted sludge AverageCOD removal efficiency was about 95 for an organic loading rate up to2 kg CODm3 of bioreactor per day Energy consumption in the range of20e36 kWhm3 of treated wastewater or 1 kWhkg of COD removed was estimated

COD removal higher than 97 was also observed in a pilot-scale hollow-fiberMBR system in the treatment of simulated wastewater with a COD between 1000and 4000 mgL (Artiga Carballa Garrido amp Meacutendez 2007)

A comparison between an MBR pilot plant and a full-scale activated sludge systemin the treatment of winery wastewater was studied by Valderrama et al (2012) TheMBR plant which was equipped with flat-sheet membrane modules manufacturedby Kubota produced an average COD removal of 97 whereas for the conventionalsystem the removal was 95 The MBR permeate achieved most quality specificationsdefined by international guidelines for water reuse and reclamation A stable operationin terms of TMP and permeability was achieved despite the high variability in influent

An anaerobic MBR with an external MF module was tested on a laboratory scale totreat winery wastewater and compared with the performance of aerobic granulation

Membrane technologies for water treatment and reuse in the food and beverage industries 573

technology (Basset Lopez-Palau Dosta amp MataAlvarez 2014) The bioreactor wasstarted up for 230 days and produced up to 035 L CH4L d when 15 kg CODm3 dwas applied The treated effluent was of better quality compared with that producedin the aerobic granular sequencing batch reactor It was free of suspended solidswith a COD concentration lower than 100 mgL Average permeate fluxes were onthe order of 105 Lm2 h

The fractionation of phenolic compounds from winery sludge using UF membraneswas investigated by Galanakis Markouli and Gekas (2013) Hydro-ethanolic extractswere prepared from winery sludge and treated with UF membranes of different mate-rials and MWCOs Results indicated that polysulphone membranes of 20 and 100 kDawere not able to fractionate phenolic compounds except for the separation betweenpolymeric and monomeric anthocyanins Both membranes exhibited high rejection(more than 60) of polar compounds such as sugars and phenolic compounds In addi-tion the 100-kDa membrane showed a low rejection toward pectin and allowed it toseparate from phenolic compounds

For these membranes the solute rejection was mainly attributed to soluteadsorption onto the membrane surface instead of size exclusion The use of a nonpolarfluoropolymer membrane with an MWCO of 1 kDa produced good separation ofhydroxycinnamic acids from anthocyanins and flavonols because the observed rejec-tion toward acids was twofold higher than that observed for the other phenoliccompounds

187 Soybean wastewater

Soybeans are used to produce various oriental foods such as tofu (soybean curd) shoyu(soy sauce) miso (soybean paste) natto (fermented soybean) and soybean milk Ahuge amount of water (about 12e15 times the volume of soybeans) is used in the soak-ing process to clean the beans before further processing The produced wastewatercontains soluble peptides and carbohydrates such as glucose fructose and raffinosewith COD values up to 10 gL It is commonly forwarded to wastewater treatmentwith a consequent disposal of valuable compounds and water resources

An integrated membrane system for the recovery of water and soluble materialsfrom soybean soaking water was developed by Guu Chiu and Young (1997) Theprocess depicted in Figure 187 is based on the use of NF and RO membranes NFand RO retentates collected at weight concentration ratios of 7 and 6 respectivelywere further treated by fermentation to assess the possibility of producing lacticacid from fermenting soluble materials To this purpose NF and RO retentates wereinoculated with probiotic cultures of Lactobacillus acidophilus CCRC 10695 and Bifi-dobacterium longum CCRC 11847 Results revealed that a combination of bothselected cultures produced up to 75 gL organic acids mainly represented by lacticacid after 48 h fermentation at pH 55 and a temperature of 37 C After centrifugationand pasteurization the fermentation broth is suitable for the formulation of lactic acidbeverages whereas the RO permeate can be reused in the plant site for cleaning andsoaking

574 Advances in Membrane Technologies for Water Treatment

A membrane-based process to extract proteins oligosaccharides and isoflavonesfrom yellow bean product wastewater was patented by Jiang and Wang (2013) Theprocess involves a UF step to concentrate a soybean protein solution that can bethen spray-dried to obtain a pure soybean protein powder Soy isoflavones containedin the UF permeate are adsorbed onto weak polar macroporous resins and then elutedwith ethanol which is used in the production of soybean isoflavones NF membranesseparate soybean oligosaccharides from the resin effluent liquid and the concentratedliquid is used to prepare oligosaccharide powder Finally RO membranes removeinorganic salts from the NF permeate producing pure water

NF and ROmembranes were also used to concentrate oligosaccharides from steamedsoybean wastewater in tofu processing (Matsubara Iwasaki Nakajima Nabetani ampNakao 1996) The wastewater was pretreated by UF membranes that rejected high-molecular-weight proteins oligosaccharide components such as sucrose raffinoseand stachyose scarcely rejected by UF membranes were concentrated by spiral-woundNF (NTR-7250) and RO (NTR-7199) membranes manufactured by Nitto-Denko Con-centrations of oligosaccharides of 10 (wv) and 22 (wv) were obtained by RO andNF respectively operating according to a batch concentration configuration

188 Conclusions and future trends

The implementation of water reuse practices in the food industry presents a great chal-lenge for both companies and public health authorities regarding knowledge technicalexpertise and documentation

Soybean soaking water

Lactic acidfermentation

Probiotic culturesL acidophilus

B longum

Water for reuse

NF

RO

Lactic acidbeverage

Sedimentation

Centrifugation

Figure 187 Recovery of soluble compounds and water from soybean soaking waterAdapted from Guu et al (1997)

Membrane technologies for water treatment and reuse in the food and beverage industries 575

This chapter has given an overview of membrane-based processes for water reuseand environmental control in the treatment of wastewater from food-processing indus-tries High-strength wastewater can be successfully treated by MBRs The perfor-mance of these systems can be improved by optimizing operating parameters andimplementing methods to reduce membrane fouling Future trends in this area willbe devoted to enhancing performance reducing operational costs and prolongingthe lifetime of the membranes

Pressure-driven membrane operations and integrated membrane operations repre-sent useful approaches to the treatment of food-processing wastewaters for reducingsludge production and improving the final purified water quality Case studies referringto the treatment of individual wastewaters from agro-food production (dairy meat soy-bean fruit juices etc) underline the key advantages ofmembrane systems over conven-tional methodologies in water regeneration and various reuses Therefore continuousgrowth of the membrane market can be predicted in upcoming next years taking intoaccount the increasing cost of main water sources and effluent sewer disposal

List of acronyms

BEMR bio-entrapped membrane reactorBOD biochemical oxygen demandCOD chemical oxygen demandDF diafiltrationED electrodialysisMBR membrane bioreactorMF microfiltrationMLSS mixed liquor suspended solidsMWCO molecular weight cutoffNF nanofiltrationOLR organic loading ratePPW poultry-processing wastewaterRO reverse osmosisSRT solid retention timeTOC total organic carbonTSS total suspended solidsTMP transmembrane pressureUF ultrafiltrationVCR volume concentration ratioWPC whey protein concentrate

References

Abu M Y B Rao R M Khan M A amp Liuzzo J A (1984) Clarification of menhaden bailwater effluent by reverse osmosis Journal of Environmental Science and Health PartB-Pesticides Contaminants and Agricultural Wastes 19 67e82

576 Advances in Membrane Technologies for Water Treatment

Afonso M D amp Borquez R (2002a) Review of the treatment of a seafood processingwastewaters and recovery of proteins therein by membrane separation processes e pros-pects of the ultrafiltration of wastewaters from the fish meal industry Desalination 14229e45

Afonso M D amp Borquez R (2002b) Nanofiltration of wastewaters from the fish meal in-dustry Desalination 151 131e138

Afonso M D Ferrer J amp Borquez R (2004) An economic assessment of proteins recoveryfrom fish meal effluents by ultrafiltration Trends in Food Science and Technology 15506e512

Andreacutes L J Riera F A amp Alvarez R (1997) Recovery and concentration by electrodialysisof tartaric acid from fruit juice industries waste waters Journal of Chemical Technologyand Biotechnology 70 247e252

Arnal J M Garciacutea-Fayos B Sancho M amp Leon-Hidalgo M C (2013) Recovery of solvedsalts of the liquid effluents from the manufacture of cured hams Preliminary studyDesalination and Water Treatment 51 1922e1927

Artiga P Carballa M Garrido J M amp Meacutendez R (2007) Treatment of winery wastewatersin a membrane submerged bioreactor Water Science and Technology 56 63e69

Atra R Vatai G Bekassy-Molnar E amp Balint A (2005) Investigation of ultra- andnanofiltration for utilization of whey protein and lactose Journal of Food Engineering 67325e332

Avula R Y Nelson H M amp Singh R K (2009) Recycling of poultry process wastewater byultrafiltration Innovative Food Science and Emerging Technology 10 1e8

Balannec B Geacutesan-Guiziou G Chaufer B Rabiller-Baudry M amp Daufin G (2002)Treatment of dairy process waters by membrane operations for water reuse and milkconstituents concentration Desalination 147 89e94

Balannec B Vourch M Rabiller-Baudry M amp Chaufer B (2005) Comparative study ofdifferent nanofiltration and reverse osmosis membranes for dairy effluent treatment bydead-end filtration Separation and Purification Technology 42 195e200

Basset N Lopez-Palau S Dosta J amp Mata Alvarez L (2014) Comparison of aerobicgranulation and anaerobic membrane bioreactor technologies for winery wastewatertreatment Water Science and Technology 69 320e327

Bleuroocher C Noronha M Feurounfrocken L Dorda J Mavrov V Janke H D et al (2002)Recycling of spent process water in the food industry by an integrated process of biologicaltreatment and membrane separation Desalination 144 143e150

Bohdziewicz J amp Sroka E (2005) Treatment of wastewater from the meat industry applyingintegrated membrane systems Process Biochemistry 40 1339e1346

Bolzonella D amp Cecchi F (2007) Treatment of food processing wastewater In K Waldron(Ed)Handbook of waste management and co-product recovery in food processing (Vol 1pp 573e596) Abington Woodhead Publishing Ltd

Bolzonella D Fatone F Pavan P amp Cecchi F (2010) Application of a membrane bioreactorfor winery wastewater treatment Water Science and Technology 62 2754e2759

Bourseau P Masseacute A Cros S Vandanjon L amp Jaouen P (2014) Recovery of aromacompounds from seafood cooking juices by membrane processes Journal of Food Engi-neering 128 157e166

Casani S Rouhany M amp Knochel S (2005) A discussion paper on challenges and limita-tions to water reuse and hygiene in the food industry Water Research 29 1134e1146

Casu S Crispino N A Farina R Mattioli D Ferraris M amp Spagni A (2012) Wastewatertreatment in a submerged anaerobic membrane bioreactor Journal of Environmental

Membrane technologies for water treatment and reuse in the food and beverage industries 577

Science Health Part A-ToxicHazard Substance and Environmental Engineering 47204e209

Chao A C Asce M amp Tojo S (1987) Permeate quality of ultrafiltration process Journalof Environmental Engineering 113 383e394

Chmiel H Kaschek M Bleuroocher C Noronha M amp Mavrov V (2002) Concepts for thetreatment of spent process water in the food and beverage industries Desalination 152307e314

Chmiel H Mavrov V amp Beacutelieres E (2000) Reuse of vapour condensate from milkprocessing using nanofiltration Filtration and Separation 37 24e27

Cros S Lignot B Bourseau P Jaouen P amp Prost C (2005) Desalination of musselcooking juices by electrodialysis Effect on aroma profile Journal of Food Engineering69 425e436

Cros S Lignot B Jaouen P amp Bourseau P (2006) Technical and economical evaluationof an integrated membrane process capable both to produce an aroma concentrateand to reject clean water from shrimp cooking juices Journal of Food Engineering 77697e707

Feuroahnrich A Mavrov V amp Chmiel H (1998) Membrane processes for water reuse in the foodindustry Desalination 119 213e216

Galanakis C M (2012) Recovery of high added-value components from food wastesConventional emerging technologies and commercialized applications Trends in FoodScience and Technology 26 68e87

Galanakis C M Markouli E amp Gekas V (2013) Recovery and fractionation of differentphenolic classes from winery sludge using ultrafiltration Separation and PurificationTechnology 107 245e251

Gotmare M Dhoble R M amp Pittule A P (2011) Biomethanation of dairy waste waterthrough UASB at mesophilic temperature range International Journal of AdvancedEngineering Science and Technology 8 1e9

Guglielmi G Andreottola G Foladori P amp Ziglio G (2009) Membrane bioreactorsfor winery wastewater treatment Case-studies at full scaleWater Science and Technology60 1201e1207

Guu J K Chiu C H amp Young J K (1997) Processing of soybean soaking water witha NF-RO membrane system and lactic acid fermentation of retained solutes Journal ofAgricultural and Food Chemistry 45 4096e4100

Huang L amp Morrissey M T (1998) Fouling of membranes during microfiltration of surimiwash water Roles of pore blocking and surface cake formation Journal of MembraneScience 144 113e123

Jiang B Wang J (2013) Method for extracting soy protein oligosaccharide and isoflavonefrom soybean wastewater by one-step process Chinese patent CN103265614-A

Johns M R (1995) Developments in wastewater treatment in the meat processing industryBioresource Technology 54 203e216

Judd S (2011) The MBR Book Principles and applications of membrane bioreactors forwater and wastewater treatment (2nd ed) Oxford UK Elsevier Ltd

Kanai M Ferre V Wakahara S Yamamoto T amp Moro M (2010) A novel combination ofmethane fermentation and MBR e Kubota Submerged Anaerobic Membrane Bioreactorprocess Desalination 250 964e967

Kane J amp Osantowski R (1981) An evaluation for water reuse using advanced wastetreatment at a meat packing plant In Proc 35th Purdue industrial waste Conf (p 617) AnnArbor MI Ann Arbor Sci

578 Advances in Membrane Technologies for Water Treatment

Katayon S Megat Mohd Nool M J Ahmad J Abdul Ghani L A Nagaoka H amp Aya H(2004) Effects of mixed liquor suspended solid concentrations on membrane bioreactorefficiency for treatment of food industry wastewater Desalination 167 153e158

Koyuncu I Turan M Topacik D amp Ates A (2000) Application of low pressure nano-filtration membranes for the recovery and reuse of dairy industry effluents Water Scienceand Technology 41 213e221

Liao B Q Kraemer J T amp Bagley D M (2006) Anaerobic membrane bioreactorsApplications and research directions Critical Reviews in Environmental Science andTechnology 36 489e530

Lo Y M Cao D Argin-Soysal S Wang J amp Hahm T S (2005) Recovery of protein frompoultry processing wastewater using membrane ultrafiltration Bioresource Technology96 687e698

Mameri N Abdessemed D Belhocine D Lounici H Gavach C Sandeaux J et al(1996) Treatment of fishery washing water by ultrafiltration Journal of Chemical Tech-nology and Biotechnology 67 169e175

Mannapperuna J D amp Santos M R (2004) Reconditioning of poultry chiller overflow byultrafiltration Journal of Food Process Engineering 27 497e516

Masseacute A Vandanjon L Jaouen P Dumay J Kechaou E amp Bourseau P (2008)Upgrading and pollution reduction of fishing industry process-waters by membrane tech-nology In J P Bergeacute (Ed) Added value to Fisheries wastes (pp 81e99) KeralaTransworld Research Network

Matsubara Y Iwasaki K Nakajima M Nabetani H amp Nakao S (1996) Recovery ofoligosaccharides from steamed soybean waste water in Tofu processing by reverse osmosisand nanofiltration membranes Bioscience Biotechnology and Biochemistry 60 421e428

Mavrov V Chmiel H amp Beacutelieres E (2001) Spent process water desalination and organicremoval by membranes for water resuse in the food industry Desalination 138 65e74

Moresi M amp Lo Presti S (2003) Present and potential applications of membrane processingin the food industry Italian Journal of Food Science 15 3e34

Mulidzi A R (2010) Winery and distillery wastewater treatment by constructed wetland withshorter retention time Water Science and Technology 61 2611e2615

Muro C Riera F amp del Carmen Diaz M (2012) lsquoMembrane separation process in waste-water treatment of food industry In B Valdez (Ed) Food industrial processes - Methodsand equipment (pp 253e280) Rijeka InTech

Mutamim N S A Noor Z Z Abu Hassan M A amp Olsson G (2012) Application ofmembrane bioreactor technology in treating high strength industrial wastewater A per-formance review Desalination 305 1e11

Ng K K Lin C F Panchangam S C Hong P K A amp Yang P Y (2011) Reducedmembrane fouling in a novel bio-entrapped membrane reactor for treatment of food andbeverage processing wastewater Water Research 45 4269e4278

Noronha M Britz T Mavrov V Janke H D amp Chmiel H (2002) Treatment of spentprocess water from a fruit juice company for purposes and reuse Hybrid process conceptand on-site test operation of a pilot plant Desalination 143 183e196

Passeggi M Lopez I amp Borzacconi L (2009) Integrated anaerobic treatment of dairyindustrial wastewater and sludge Water Science and Technology 59 501e506

Paulson D J Wilson R L amp Spatz D D (1984) Crossflow membrane technology andits applications Food Technology 38 77e87

Pearce R J (1983) Thermal separation of beta-lactoglobulin and alpha-lactalbumin in bovinecheddar cheese whey New Zealand Journal of Dairy Science 15 13e22

Membrane technologies for water treatment and reuse in the food and beverage industries 579

Riera F A Suarez A amp Muro C (2013) Nanofiltration of UHT flash cooler condensatesfrom a dairy factory Characterisation and water reuse potential Desalination 309 52e63

Saravia H Houston J E Toledo R T amp Nelson H M (2005) Economic analysis ofrecycling chiller water in poultry processing plants using ultrafiltration membrane systemsJournal of Food Distribution Research 36 161e166

Shih J amp Kozink M B (1980) Ultrafiltration treatment of poultry processing wastewater andrecovery of a nutritional by-product Poultry Science 59 247e252

Sroka E Kaminski W amp Bohdziewicz J (2004) Biological treatment of meat industrywastewater Desalination 162 85e91

Stephenson T Brindle K Judd S amp Jefferson B (2000) Membrane bioreactors forwastewater treatments London UK IWA Publishing

Uchida T Sato K Kawasaki Y Dosako S (1996) Separation of lactoperoxidase secretorycomponent and lactoferrin from milk or whey with a cation exchange resin US Patent5516675

Valderrama C Ribera G Bahiacute Rovira M Gimeacutenez Nomen R et al (2012) Winerywastewater treatment for water reuse purpose Conventional activated sludge versusmembrane bioreactor (MBR) A comparative study Desalination 308 1e7

Vandanjon L Cros S Jaouen P Queacutemeacuteneur F amp Bourseau P (2002) Recovery bynanofiltration and reverse osmosis of marine flavours from seafood cooking watersDesalination 144 379e385

Vourch M Balannec B Chaufer B amp Dorange G (2005) Nanofiltration and reverseosmosis of model process waters from the dairy industry to produce water for reuseDesalination 172 245e256

Vourch M Balannec B Chaufer B amp Dorange G (2008) Treatment of dairy industrywastewater by reverse osmosis for water reuse Desalination 219 190e202

Walha K Ben Amar R Masseacute A Bourseau P Cardinal M Cornet J et al (2011)Aromas potentiality of tuna cooking juice concentrated by nanofiltration LWT FoodScience and Technology 44 153e157

Yorgun M S Akmehmet Balcioglu I amp Saygin O (2008) Performance comparison ofultrafiltration nanofiltration and reverse osmosis on whey treatment Desalination 229204e216

Zhang S Q Kutowy O Jumar A amp Malcolm I (1997) A laboratory study of poultryabattoir wastewater treatment by membrane technology Canadian Agricultural Engi-neering 39 99e105

Zydney A (1998) Protein separations using membrane filtration New opportunities for wheyfractionation International Dairy Journal 8 243e250

580 Advances in Membrane Technologies for Water Treatment

Membrane technologies forwater treatment and reusein the pulp and paper industries

19M Meuroantteuroari M Kallioinen M NystreuroomLappeenranta University of Technology Laboratory of Separation TechnologySkinnarilankatu Lappeenranta Finland

191 Introduction

Processes in the pulp and paper industry are based on the use of water and its proper-ties Although pulping processes can also be carried out using organic solvents wateris the dominating medium where the liberation of cellulose fibers from wooden mate-rial takes place Water is also needed to transport raw materials seal process equip-ment cool and heat wash and clean process equipment remove impurities andgenerate the necessary environment for the formation of the hydrogen-bondingnetwork between fibers and fillers which is the basic mechanism of paper formationTherefore a huge amount of water is necessary for pulp and paper productionprocesses

Water quality demands vary greatly A relatively low purity of water can be used inless demanding applications Therefore the pulp and paper industry has succeeded inreducing freshwater consumption or wastewater discharge significantly by increasingwater recirculation with no special purification processes For instance fiber recoveryfrom water discharged from a paper machine is made by flotation or filtration and theresidual water is typically reused in the process This kind of water has a low content ofsuspended solids but contains almost all dissolved compounds This water has a useeg in shower water in low-pressure showers on the paper machine However withoutadditional treatment further reuse of water causes severe problems because of theexponential accumulation of contaminants For instance dissolved impurities mightplug the nozzles of high-pressure showers that are used to clean paper machine fabricsThis would lead to production breaks on the paper machine Other detrimental influ-ences caused by insufficient process water quality are problems running the paper ma-chine or even the printing machine for end users It is obvious that water qualitysignificantly affects product quality For instance some residual organic compoundsin liquid packaging cardboard might cause an unpleasant smell or taste in foodsupplies

A modern paper machine consumes less than 10 m3 water per 1 ton of producedpaper This is 10 times less than some decades ago For instance in Finland thepulp and paper industry has succeeded in decreasing their environmental impact signif-icantly during the past 20 years by applying biological water treatment and by closing

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400019-8Copyright copy 2015 Elsevier Ltd All rights reserved

the water circulation As Table 191 shows the decrease in chemical oxygen demand(COD) for instance and absorbed organic halogen (AOX) load per ton of paper orpulp was 69 and 87 respectively between 1992 and 2012 The high reductionin AOX load resulted from changes in pulp bleaching processes to elementalchlorine-free bleaching in the beginning of the 1990s However as the emission valuesfrom 2012 show (Table 191) significant amounts of pollutants are left in the dischargewaters Many can be removed more efficiently if membranes are applied in the puri-fication processes as will be shown later in this chapter

1911 Driving forces for the use of membrane filtration

In Nordic countries water scarcity is not usually a reason to reduce water use in millsHowever the situation is totally different in central Europe or New Mexico forinstance where water scarcity has forced the McKinley cardboard mill to move to aliquid effluent-free operation (Pohjalainen 1999) Probably the most common causefor reducing water discharge comes from legislation and environmental demandsthat lead the mill to use advanced water treatment such as membranes for wastewatersSometimes a mill is situated close to a sensitive waterway such as the Artic Paper Mun-kedal paper mill in Sweden where in 1999 a tubular ultrafiltration unit was installed topurify 50 of the mill effluent (Hepp Joore Schonewille amp Futselaar 2005) Themill is located next to one of the finest salmon rivers in the country therefore thereis high demand for environmentally friendly paper production for example by closingthe water circulation In the future there might be limitations on how much water canbe used in the production of a specific product and the so-called ldquowater footprintrdquomight be a more important parameter when sustainability of different products are

Table 191 Total emission to waterways and reduction inenvironmental load related to amount of Finnish pulp cardboardand paper production between 1992 and 2012

Emission of pollutantsin 2012 ta

Reduction of emissionsbetween 1992 and 2012

Amount of wastewater 45

Suspended solids 10000 69

COD 133000 69

BOD 10000 87

Nitrogen 2175 47

Phosphorus 133 76

AOX 850 87

Reprinted from Anon (2013a) with permission from Elsevier

582 Advances in Membrane Technologies for Water Treatment

evaluated Therefore legislation and sometimes customer demand might lead com-panies to reduce water consumption and environmental emissions

Less often the reason for reducing water consumption comes from the economyespecially if water purification is the main reason for using membrane filtration How-ever this was the case in Albert Keuroohler Pappen in Gengenbach Germany where thelocal government increased the fee for wastewater sevenfold which led the companyto invest in purification and water recirculation technologies (Junk Dorfer Stratz ampLausch 2008)

Economically the most attractive applications for membrane processes are wheremembranes can be used to recover valuable raw materials from waste streams Agood example is all of the ultrafiltration processes that are used to recover coating pig-ments eg titanium dioxide from waste coating streams In these applications thepayback time might be less than 1 year for ultrafiltration (Anon 2013b)

1912 Barriers to membrane processes

There are also many barriers that restrict the use of membrane processes in the pulp andpaper industry Typically volumes that need to be treated are huge and contain manypossible foulants for membranes This makes it challenging to retain the filtrationcapacity and causes many challenges for membrane usability Obviously this also leadsto large membrane areas and causes the cost of the membrane filtration to be highSometimes the attitude toward the incompatibility of membrane filtration with pulpand paper industry streams is a difficult barrier to surpass In the case of old millsthe lack of space might also restrict the installation of membrane filters althoughthey usually use a small floor space efficiently (Nuortila-Jokinen 2005)

1913 Characteristic properties of waters

As mentioned the water quality requirements vary at different stages of pulp and papermanufacturing processes Naturally the characteristics of process and wastewatersalso differ significantly depending on the process stage from which they originateGenerally the waters contain different amounts of suspended solids such as fibersfillers and fines and dissolved wood-based compounds such as polysaccharides oligo-and monosaccharides lignin and other phenolic compounds such as lignins andlipophilic wood extractives Some such as dissolved bark compounds eg phenoliccompounds sterols or resin acids are known to be toxic to aquatic animals In addi-tion the waters contain chemicals or additives used in to process of raw materials ormanufacture end products It has been estimated that thousands of different com-pounds exist in pulp and paper mill process and wastewaters (Nuortila-JokinenMeuroantteuroari amp Nystreuroom 2003)

Moreover every mill and papermaking process has its own fingerprint related to theprocess and wastewater quality The content of the waters varies but the amount ofimpurities can also change remarkably even at the same production stage For instanceit has been reported that a more than 10 times variation in dissolved organic compoundconcentrations in the same paper machine circulation waters has occurred because of

Membrane technologies for water treatment and reuse in the pulp and paper industries 583

the breaks and different paper qualities (Meuroantteuroari amp Nystreuroom 2004) Therefore mem-branes are exposed to great variation regarding the amount and quality of impurities Inaddition if all of the pulp and paper manufacturing processes are taken into accountthere is great variation in temperature and pH Temperatures for instance vary fromvery low (external wastewater treatment (WWT)) to above 100 C (process waters andliquors in pulp plants) and pH varies from less than 2 to 14 (Anon 2010)

1914 Special demands for membranes and modules in pulpand paper capacity and stability

Process streams in the pulp and paper industry are huge as much as cubic meters persecond Therefore membrane permeability needs to be high and the flux stable withminimal operational breaks Unfortunately characteristic properties of waters and theirquantitative and qualitative variations seldom lead to stable filtration capacity iefouling leads to decline of capacity and to operational breaks and cleaning A highoperation temperature the existence of hard particles and a wide variety of foulantsas well as periodical cleaning processes might shorten the operational lifetime of amembrane

Generally the higher the capacity is the lower retention is Sometimes pluggedmembrane pores affect the flux of MF membranes more dramatically than UF mem-branes and the flux can be even higher with tighter UF membranes Therefore the se-lection of an optimal membrane cannot be based only on the membrane propertiesstated by the manufacturer Process and wastewaters have different compositionsand filtration experiments are the only means by which to judge the applicability ofmembrane processes for the cases in question Despite the challenging environmentin the pulp and paper industry it is possible to achieve stable capacity over yearsby selecting a correct hydrophilic membrane and an appropriate filter as the exampleof a paper mill in Lohja Finland proves (Section 193)

1915 Selectivity

Another requirement for a membrane is selectivity In WWT selectivity is not the mostcrucial requirement but if membranes aim to separate product compounds in futurebiorefinery applications selectivity will be an extremely important characteristicIn process and WWT selectivity is obviously needed but high and stable capacityovertime is an even more important property for the membrane

One important advantage offered by membrane is that separation efficiency (selec-tivity) can be tailored by selecting an appropriate membrane filtration process Asshown in Figure 191 the purified water is free from suspended solids when MF isused or it can be almost completely free from dissolved materials when reverseosmosis (RO) is used Depending on demands the most suitable membrane processesare chosen Using nanofiltration (NF) it is possible to retain metal ions such as bariumiron and manganese which are sparingly soluble or cause the higher consumption ofbleaching chemicals Nanofiltration is also efficient when sulfate ions need to beremoved However as will be discussed later chloride concentrations can be even

584 Advances in Membrane Technologies for Water Treatment

higher in permeate of NF than in the feed solution Therefore to remove monovalention RO electrodialysis (ED) or ion exchange is needed

1916 Module configurations

Because of a very demanding environment in which membranes are in the pulp andpaper industry special module configurations are commonly used In particular mod-ules in which high shear forces are generated on the membrane surface are commonlyapplied to prevent flux decline They can frequently be operated with minor pretreat-ment compared with conventional spiral-wound modules A drawback is that the shearmight cause a shorter lifetime for the membranes Although high shear rate modulesdominate industrial-scale applications all kinds of membrane modules are in use

A high shear rate on the membrane surface can be achieved in tubular modules byincreasing the pumping velocity but this strongly influences energy consumptionbecause under turbulent conditions power will vary with velocity up to a power of275 (Merry 1999) In addition it is estimated that in conventional cross-flow filtrationsystems only about 10 of energy is converted into shear on the membranes There-fore high shear rate modules have been developed to better use energy in generatingturbulent conditions Culkin Plotkin and Monroe (1998) claimed that the so-calledvibratory sheareenhanced processing (VSEP) filter allows nearly 99 of total energyused to be converted into shear at the membrane surface This is because the energy isdirected to create shear forces only into a thin zone near the membrane surface TheVSEP is a vertical plate-and-frame type construction in which membrane sheets are

Microfiltration

Ultrafiltration

Reverse osmosis

01ndash02 μm

Nanofiltration 100ndash150 gmol

50 gmol

1000 gmol

Algae

Bacteria

Giardia Turbidity

Galactoglucomannan

Sugars

Lignin

Suspended solids

Colloidal extractives

Glucoisosaccharinic acid

H2O

Phenols

Strerols

Lignans

Ca2+ Mg2+ Resin acids

Na+ Clndash

SO42ndash

Arabinoglucurono-xylan

Acetic acid

Figure 191 Separation scheme for pressure-driven membrane processes

Membrane technologies for water treatment and reuse in the pulp and paper industries 585

stacked on top of each other and the whole membrane stack is vibrated The VSEP pro-cess imposes an oscillatory motion on the whole module which generates a shear rateas high as 150000s on the membrane surface about 10 times that achievable in con-ventional cross-flow filtration

Similarly with the cross-rotational (CR) filter the rotor blade mixes only small vol-umes on the membrane surface Fouling control in the CR membrane unit (CR filterfrom Valmet Corp) is achieved by rotating rectangular plates between all membranesheets thus generating shear directly at the membranersquos surface In this constructionthe membrane itself does not move In industrial-scale applications the CR filter isthe most commonly used high shear rate filter The maximum pressure in the VSEPis 38 bar which is significantly higher than what can be achieved with CR filters(around 8 bar) Therefore the VSEP is an attractive choice especially for NF processesRecently several other membrane filters based on rotating membrane plates have beendeveloped Both polymeric and ceramic membranes can be applied in these filters butthey have not yet found a place in the pulp and paper industry (Jaffrin 2008)

Spiral-wound modules have also been used for several years to treat waters in papermills A prerequisite for their successful use is appropriate pretreatment which needsto remove suspended solids to prevent plugging of the feed channels and reduce theamount of foulants Therefore pretreatment consists of several processes includingtraditional physical and chemical separation processes (Lien amp Simonis 1995) A sec-ond membrane process such as UF has also been shown to be a sufficient pretreatmentfor NF with spiral-wound modules (Sutela 2008)

1917 Use of membranes in pulp and paper mills

Membranes are an excellent choice for purifying raw water recirculating processwater purifying effluents and recovering and purifying valuable compounds fromdifferent streams in the pulp and paper industry Figure 192 illustrates the use of mem-branes in water and WWT in pulp or paper mills as presented in this chapter

Simultaneous purification of process water and recovery of side product Section 194

Conventionalactivated sludge(CAS) treatment

Purification of processwaters for reuse Section 193

Purification of rawwater Section 195

Removal of nonbiodegradablecompounds prior to CAS treatment Section 19212

Direct membrane treatment to purify effluents Section 1922

MBR

Upgrading purificationlevel Section 19211

Section 19213

Figure 192 Simplified drawing of different options for using membranes related to pulp andpaper manufacturing

586 Advances in Membrane Technologies for Water Treatment

Membrane processes can be used as internal kidneys close to the place where waste-water is generated It might be beneficial to retain the purified water temperature andpH level equal to the process levels These advantages are achieved when eg papermachine process waters are recirculated (Section 193) In addition by keeping spe-cific water streams unmixed membrane processes can be focused on the most relevantstreams and thus only smaller volumes would need to be treated (as in the treatment ofevaporator condensate and coating wastewaters see Sections 1922 and 1941respectively) Today coating color recovery from waste coating streams is the mostcommon membrane filtration application in the pulp and paper industry Furthermoremembranes are applied to treat a wide variety of process streams and effluents such aspaper mill process water and bleaching effluents (Section 193) Membranes can oper-ate either alone or combined with biological or other chemical and physical processes(Sections 19211e19213)

192 Purification of wastewaters

1921 Membrane processes combined with biological WWT

Membrane processes are used to upgrade the purification results of biological WWTand before biological treatment to reduce the amount of scarcely biodegradable com-pounds in effluents In addition about 15 years ago some paper mills implementedmembrane bioreactors (MBRs) as an essential part of their wastewater purificationsystems

19211 Membrane processes to upgrade purificationresults of biological WWT

Membrane filtration makes it possible to upgrade existing WWT plant efficiency Forinstance the Eltmann newsprint mill of Papierfabrik Palm has used NF to improvethe quality of activated sludge process effluent since 1999 Sand filtration wasapplied to polish effluents before spiral-wound NF Nanofiltration succeeded inreducing about 90 of COD and color and about 60 of AOX As thought NFretained divalent ions excellently but the apparent retention of chloride ions was40 (Schirm Welt amp Ruf 2001)

Depending on the membrane filtration conditions amount of multivalent anionsand ratio of multivalent to monovalent ions NF can concentrate monovalent anions(chloride) into permeate because of the Donnan effect Therefore the apparent reten-tion of chloride ions can be negative even some as much as 100 This might limit thereusability of NF permeate When removal of monovalent ions such as chloride ion isneeded RO ED and ion exchange are the choices of technology

Electrodialysis is commonly defined as an electrochemical separation process inwhich electrically charged membranes and an electrical potential difference insteadof pressure are used to separate ionic species from an aqueous solution and other un-charged components In the pulp and paper industry ED is being studied for theremoval of chloride ions and other nonprocess elements before reuse of purified waters

Membrane technologies for water treatment and reuse in the pulp and paper industries 587

(Ferreira Amaral amp Machado 2004 Geraldes amp De Pinho 1995 Pfromm Tsa ampHenry 1999 Rapp amp Pfromm 1998)

In the Eltmann newsprint mill the membrane concentrate is recirculated back intothe activated sludge plant after lime precipitation The lime precipitation removes about99 of iron 60 of silicate and about 30 of sulfate ion In addition 40 of organiccompounds (measured as COD and AOX) and over 70 of colored compounds areremoved by this lime precipitation Therefore precipitation removes a significantamount of organic compounds in which biodegradability is not obvious In principlecompounds that have already been treated biologically (activated sludge process) areprobably not the most biodegradable and therefore their recirculation back into theactivated sludge process might not lead to their degradation (Schirm et al 2001)

Another alternative for treating membrane concentrate before recirculation backinto the activated sludge process is a mild oxidation which has been reported toenhance the biodegradability of NF concentrate (Meuroantteuroari Kuosa Kallas amp Nystreuroom2008 Mauchauffee Denieul amp Coste 2012) For instance ozonation was demon-strated to improve the biodegradability of NF concentrate although the amount of dis-solved organic carbon did not change Recently Panorel et al (2014) reported thatpulsed corona discharge treatment can oxidize lignin for example using about one-third of the energy needed in ozonation Therefore the reduced cost of oxidationprocesses enables the wider use of oxidative treatments in WWT and will help treatmembrane concentrates in the future

Mauchauffee et al (2012) tested different process alternatives for the treatment ofprinting paper mill effluents They concluded that the best process concept would be toupgrade existing anaerobic and aerobic treatment with suspended solids removal soft-ening to reduce the scaling potential of the effluent NF to remove organic compoundsand evaporation or oxidation to treat NF concentrate In addition softening by addinglime calcium and carbonate with a specific mixing reactor and settler significantlyimproved NF performance ie a higher recovery and better permeate quality wasachieved after the softening process Lime softening was also applied by MeuroantteuroariDaltrophe Oren Gilron and Nystreuroom (2001) to remove hardness from paper mill pro-cess waters

Several studies have also been published in which high shear rate CR NF orlow-pressure RO is studied directly as a polishing stage after biological treatmentFor instance a permeate flux of 150 L(m2h) at a volume reduction of 12 a pressureof 10 bar and a temperature of 40 C was achieved when discharge water from a pulpand paper mill WWT plant (activated sludge treatment) was nanofiltered (Meuroantteuroariet al 2008) The reported flux from spiral-wound NF in the Eltmann newsprint millwas significantly lower at 10e30 L(m2h) (Schirm et al 2001) It is clear that ahigh shear rate facilitates flux by reducing concentration polarization and fouling onthe membrane surface

Generally the permeate fluxes obtained from the filtration of biologically treatedeffluents are significantly higher than those obtained in the filtration of paper machineprocess waters (Meuroantteuroari amp Nystreuroom 2007) This is because of the lower amount ofimpurities left in the biologically treated water On the other hand heat recovery ismore difficult to performwhen biologically treated water is circulated back into themill

588 Advances in Membrane Technologies for Water Treatment

In the United States a closed cycle paper mill combines biological treatment mem-brane technology and evaporation to prevent the discharge of liquid effluent(McKinley Linerboard Paper Company New Mexico) There is no water recipientnear the mill for discharging even a minimal amount of effluent and raw water avail-ability is restricted because the mill is located in the desert of northwestern NewMexico Thus raw water consumption has been minimized to only 15 m3ton card-board product A waste stream of 33 m3ton cardboard produced is cleaned and finallyconcentrated using MF and RO membranes First flotation is used to separate fibersfines and stickers from the water then activated sludge treatment in sequenced batchreactors is carried out before membrane filtration Concentrated salts after RO treat-ment are crystallized by a tube-type falling film evaporator and its condensate is recir-culated back into the process (Durham 2000 Pohjalainen 1999) This example showsthat it is technically possible to recirculate all water but some fresh water is alwaysneeded because of evaporated process water during the manufacturing process

19212 Membrane processes to improve functioningof biological WWT

One of the most studied applications for membranes in the pulp and paper industry isthe purification of the strongly colored effluents from bleached kraft pulp mills Thefirst alkaline extraction stage effluent is a good example of a stream whose environ-mental impact is remarkably high compared with its volume For instance it hasbeen estimated that the first alkaline extraction stage effluent constitutes only5e10 of the total effluent volume of the mill but it contains about half of the colordischarge The strong color results from the high molar mass lignin molecules that aredifficult to biodegrade in conventional activated sludge treatment Also the COD andthe BOD loads of the first alkaline extraction stage effluent are high Fortunately thelarge sizes of the molecules and their high charge densities owing to high pH make thealkaline bleach plant effluents easier to filter using UF than the preceding chlorinationstage effluents containing smaller molar mass compounds (Jeuroonsson 1989 ZaidiBuisson Sourirajan amp Wood 1992) Therefore many researchers have studied mem-brane filtration with the aim of purifying the alkaline extraction stage effluents for reuseUltrafiltration membranes with cutoff values of some thousands of grams per mole havebeen shown to significantly decrease the color BOD COD and AOX loads of bleach-ing effluents and enable the use of the treated effluent for example for washing pur-poses Permeate of UF-treated bleaching effluent can also be more efficiently purifiedin biological treatment plants because UF removes slowly degrading high molarmass lignin compounds and decreases the amount of chlorinated compounds whichare resistant to attack by most microorganisms used in the biological treatment plantAccordingly the load on the treatment plant decreases and the average biodegradabilityof the remaining compounds increases The concentrate of the UF process is generallyburned in the recovery furnace where the cooking chemicals are recovered

In Sweden in the StoraEnso Nymeuroolla pulp mill UF has been used since 1995 toreduce the COD load of the mill effluent before treatment in the activated sludge plantThe mill produces pulp from both hardwood and softwood using the magnesium

Membrane technologies for water treatment and reuse in the pulp and paper industries 589

bisulfite process and oxygen bleaching The UF plant is based on tubular membraneswith a total membrane area of 4638 m2 (Greaves 1999) On average about 400 m3

effluent water is treated by the membrane plants in Nymeuroolla every hour The effluentof the oxygen bleaching stage on the pulping process has an average COD of around10 gL The aim for UF was to reduce 50 of the COD load in addition the aim was toconcentrate the organic compounds to the point where the concentrate could be incin-erated Therefore a high-volume reduction (50e60 times) was needed in UF toincrease the COD of the concentrate to 180 gL

Permeate is discharged to an activated sludge plant In this mill different tight UFmembranes were needed in the filtration of hardwood and softwood effluents becauseof variations in effluent composition The fluxes are about 60 and 70 L(m2h) at 7 and8 bar pressure for softwood and hardwood effluents respectively The high UF oper-ation temperature (up to 82 C) eliminates the need for rapid cooling before the mem-brane plant and decreases the fouling of the membrane caused by extractivesFurthermore the pH of the softwood effluents is controlled to keep it above 11This was also observed to reduce fouling of the membranes Reported energy con-sumption from the Nymeuroolla mill is approximately 39 and 15 kWm3 for hardwoodand softwood respectively (Anon 2013b Greaves 1999 Nordin amp Jeuroonsson 2008)

19213 Membrane bioreactors

Conventional aerobic WWT systems (conventional activated sludge [CAS]) are estab-lished as end-of-pipe technology in the paper industry It is estimated that the activatedsludge process is used in 60e75 of all biological effluent treatment plants in the pulpand paper industry The activated sludge plant consists of two main units the aerationbasin and the secondary clarifier (sedimentation basin) In the aeration basin theeffluent is treated with a mixture of microorganisms (activated sludge) which are pre-sent in high concentration The biomass (sludge) and water are separated by settlingbiomass in large clarifiers or by flotation after microbial degradation Generally theactivated sludge process achieves high treatment efficiencies However the biomassis vulnerable to disturbances such as spillages of concentrated liquor and operationalinstability and the purification efficiency varies somewhat

An MBR usually consists of an aerated bioreactor similar to the activated sludgeprocess combined with a membrane process to separate the biomass from the effluentIn an MBR a membrane replaces the settling or flotation stage in the conventional acti-vated sludge plant and separates completely suspended solids ie biomass In bothsystems dissolved organic components are converted by aerobic microorganisms toinorganic products such as carbon dioxide and water The filtered effluent from themembrane stage can be reused in the process while the separated biomass is recircu-lated into the bioreactor Sometimes surplus biomass is discharged Two basic MBRconfigurations exist one in which the membranes are immersed in the reactor andare an integral part of the biological reactor (internalsubmerged Section Paperie duRhin) and one in which the membranes are a separate unit process after the biologicalreactor (externalsidestream Section Ugchelen BV)

590 Advances in Membrane Technologies for Water Treatment

In principle there are several advantages of MBR processes over CAS treatmentsuch as a longer sludge age a higher biomass concentration (mixed liquor suspendedsolids (MLSS)) up to 30 gL a lower hydraulic retention time and a higher volumetricload In MBR complete retention of sludge by a membrane process makes it possibleto maintain high MLSS in the bioreactor which causes long sludge retention time anda low food-to-microorganism ratio The long sludge retention time also causes lesssludge production whereas a low food-to-microorganism ratio enables the hydraulicretention time to be reduced It has been pointed out that sludge production is inverselyproportional to the hydraulic retention time when MLSS is fixed Therefore the short-est hydraulic retention time and minimal sludge production cannot be achieved simul-taneously In addition the cost of aeration increases when sludge production isminimized and vice versa The high MLSS restricts oxygen transfer in the aerationtank and membrane scouring by air and increases membrane fouling Therefore thereis an optimum point at which the total operational cost is minimized and operating anMBR at very high MLSS is not common As a result the apparent excess sludge pro-duction is not much different from CAS although in principle even zero sludge pro-duction is possible with MBR (Stephenson Judd Jefferson amp Brindle 2000 YoonKim amp Yeom 2004)

The use of chlorine in the pulp bleaching process and the existence of slowlybiodegradable compounds in the waste and process waters may cause problems formicroorganisms in biological treatment The microbes in the MBR process operateat a high MLSS concentration and a long solids retention time is shown to be fasterwhen adapted for this kind of wastewater Therefore the purification results mightimprove with time as was shown after a 3-month operation period at VHP Securitypaper mill owned by Ugchelen BV The full-scale plant outperformed resultsachieved in pilot experiments The COD was reduced from 3500 to 600 mgL in pilotexperiments and to 450e500 mgL in the full-scale plant (Amaral Lange amp Borges2012 Hepp et al 2005 Ramaekers van Dijk Lumpe Verstraeten amp Joore 2001Simstich amp Oeller 2010)

Additional advantages are almost total retention of suspended solids high organicmatter removal and a low footprint which might sometimes be a critical demand whenpurification capacities of an existing plant are enlarged Membrane separation excludesthe sludge bulking problems often caused by unstable organic loading rate in CAS anMBR is therefore more tolerable to organic loading chock However in MBR a stableincoming load is needed to minimize membrane fouling When wastewater is purifiedfor reuse an important advantage and goal is bacteria- and suspended solidsefree wa-ter Typically MBR processes use membranes with pore sizes of 001e045 mmTherefore it can be assumed that all suspended solids and bacteria are removed bythe membrane filtration stage The high quality of the purified effluent makes MBRtechnology ideally suited for use as an internal water circuit treatment However dis-solved organic or inorganic compounds are not retained by the membrane and theirremoval efficiency depends on the functioning of the biological process In additionto water reuse an MBR process especially when applied at thermophilic conditionsenables the reuse of energy At thermophilic conditions an MBR is operated in the

Membrane technologies for water treatment and reuse in the pulp and paper industries 591

same temperature range as the paper machine (40e65 C) thus there is no need tocool or heat the process water

As in all membrane processes including MBR processes membrane fouling man-agement needs to be taken into account Depending on the MBR configuration this isdone by backflushing bubbling air close to the membrane surface and controllingpermeate flux Air is also consumed by microorganisms and typically air bubblingcauses more than 50 of operation costs In many cases membrane and operationalcosts are somewhat higher than in CAS processes but to evaluate total costs benefitssuch as water recirculation energy recovery operation at thermophilic conditions reli-ability of the process effluent quality achieved and possible reduced costs for sludgetreatment have to be taken into account (Anon 2013b) Helble and Meuroobius (2009)reported that total specific operation costs for MBR with submerged and with aeratedvertical tubular cross-flow membranes amount to 022 Vm3 Membrane bioreactorswith classical tubular cross-flow membranes consume slightly more energy and theoperation cost is around 033 Vm3 When capital costs are included the total annualcosts are in the range 056e059 Vm3

Paperie du RhinA paper roll mill in Paperie du Rhin in France installed an MBR process based onhollow-fiber membranes (Table 192) The mill uses recycled (not de-inked) paperas the raw material for the production of 40000 tons of paper rolls annually The biore-actor (1500 m3) is operated at an MLSS content of 12e16 gL The wastewater fromthe mill is first prescreened with drum screens then it is sent to an equalization basinfrom which it is pumped directly into the bioreactor The MBR process decreased theCOD from 4000 mgL to less than 200 mgL and the BOD from 1700 mgL to less than5 mgL Permeate is partly recycled as process water The main reasons for choosingMBR treatment were on-site space limitations and the need to recirculate the purifiedwater (Ramaekers et al 2001)

Ugchelen BVVHP security paper mill owned by Ugchelen BV located in Apeldoorn TheNetherlands produces bank notes and other security papers (Table 192) The papermill uses cotton as a raw material which it bleaches with hydrogen peroxide at atemperature of approximately 100 C and a pH between 11 and 12 The high pH ofthe wastewater makes purification a challenge The mill developed a wastewater puri-fication process in which dissolved carbon dioxide was used in a flotation process toremove fibers and debris and reduce the effluent pH from 11 to 82 before the MBRunit The MBR operates at thermophilic conditions to reduce the need to heat thepurified water (temperature around 55 C) The 8-mm tubular polyvinyl fluoridemembrane is installed outside the bioreactor (volume 250 m3) The MBR effluentCOD is stabilized to about 500 mgL (influent 3500 mgL) The MBR-treatedeffluent is recirculated with no detrimental effect on product quality This enablesthe mill to reduce the freshwater intake for bleaching by 80 and the mill wastewaterdischarge by 50 (Hepp et al 2005 Joore Wortel amp Bronold 2001 Ramaekerset al 2001)

592 Advances in Membrane Technologies for Water Treatment

Table 192 Examples of existing membrane bioreactors in pulp and paper industry

Keuroohler Pappen DE Ugchelen BV Paperie du Rhin

MBR type Hollow fibers submerged Tubular external Hollow fibers submerged

Amount of wastewater m3day 670 240 900

Pore size nm 40 40 40

Membrane area m2 5000 83

Average flux L(m2h) 8 120 15

Operating pressure bar 35 015

Cross-flow velocity ms e 35 e

Biomass concentration gL 10e12 12e16

Food to biomass ratiokg BODkg SS d

lt02

COD reduction 94 86 95

Adopted from Ramaekers et al (2001) Hepp et al (2005) Anon (2013b)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

pulpand

paperindustries

593

Albert Keuroohler PappenOne benefit of MBR compared with conventional activated sludge treatment is theusability of the MBR filtrate for further purification with spiral-wound membranesAn MBR was combined with downstream RO in a cardboard mill (Albert KeuroohlerPappen in Gengenbach Germany) (Table 192) The mill annually manufactures35000e40000 tons of high-quality cardboard on three paper machines Manydifferent grades are produced some of which are heavily colored Process waterwas taken from wells and before implementing the MBR the wastewater was dis-charged into the municipal sewer after sedimentation The main reason for investingin their own WWT was because of a decision by the local government to dramaticallyincrease wastewater fees from EUR 035 Vm3 up to EUR 205 Vm3 In addition themill has to pay for the use of well water Therefore the mill decided to close the waterloops by recirculating 600 m3day of treated water back into production This reducedwell water use to one-fourth (250 m3day) and significantly decreased the need forenergy to heat well water for the cardboard-making process The two-stage RO furthercleaned the filtrate by removing the remaining dissolved salts of the filtrate from theMBR plant To prevent possible scaling problems in RO calcium was reduced inthe decarbonization reactor Soda lime milk and iron (II) chloride and some acidsare added to the calcium-rich wastewater and mixed then microparticles of calciumcarbonate are formed After flocculation and sedimentation the suspension of removedcalcium carbonate (50e300 gL) is used as filler for cardboard grades By recirculatingthe filtrate from the MBR and by further treatment of the MBR filtrate (50) by ROthe original flow of the wastewater could be reduced by more than 90 The remainingflow (approximately 06 m3ton) of wastewater (the concentrate of the RO) is fed intothe municipal sewage treatment plant Chemical oxygen demand concentrations werereduced from 2600 to about 150 mgL in the MBR process and to 10 mgL by ROand BOD from 1300 mgL to less than 5 and 1 after MBR and RO respectively(Anon 2013b Junk et al 2008 Wagner 2010)

1922 Direct membrane filtration for wastewaters

In Canada a pulp mill in New Brunswick produced bleached kraft pulp without con-ventional biological WWT because of the limited land area In the effluents an evap-orator condensate stream was identified that caused significant amounts of BOD andtoxicity Therefore an RO plant was installed to purify the condensate streamPermeate of RO was recirculated into the bleaching process which led to a 40 reduc-tion in water consumption Compound identification of the RO process streamsshowed that the RO feed contained significant concentrations of low molar mass phe-nolics including phenols and guaiacols which were effectively removed and concen-trated by RO In addition RO is reported to remove compounds responsible forendocrine disruption in fish Although RO eventually exceeded the expected purifica-tion level permeate was still somewhat toxic and the BOD content was higher thanallowed Therefore a moving bed bioreactor was installed to reduce the BOD(Anon 2007 Webb 2002)

594 Advances in Membrane Technologies for Water Treatment

The mill achieved an extremely high water recovery of 99 in RO and thus only asmall amount of concentrate was incinerated in the bark boiler or was first sent to thehigh solids crystallizer to be subsequently burned in the recovery boiler (Table 193)Over 90 and 80 reduction was measured for COD and BOD respectively (DubeacuteMcLean MacLatchy amp Savage 2000) In RO one could assume even higher reten-tion for organic molecules A somewhat low retention probably resulted from ahigh-volume reduction in filtration Especially in solutiondiffusion type membraneprocesses such as RO and NF an increase in the feed concentration owing to theconcentration of impurities leads to lower permeate purity The permeate purity canbe improved by filtering permeate again

193 Membrane processes to recirculate process water

High shear rate modules such as CR filtration technology and VSEP tubular modulesand conventional spiral-wound modules have been used in several mills as internalkidneys to purify paper mill circulation waters such as white water and clear filtrates(Kreutzman amp Sutela 2004)

The only known industrial-scale example of the use of the VSEP in the pulp andpaper industry is from NF The Linpac recycle paper mill in Cowpens South Carolinahas a two stage tubular UF system and VSEP filters to remove impurities from watercirculation The UF systems (Koch membrane systems) treat the overflow from dis-solved air flotation (DAF) clarifiers Total suspended solids in the DAF units areimproved significantly by pressurized ozone injection before DAF To reduce theconcentrate (reject) volume from the UF system and improve the reused water qualitya VSEP NF system was installed to further concentrate the two-stage UF concentrateThis unconventional way of combining membrane processes produces an NF concen-trate with a solids content over 20 (Linpac 2006)

One of the best reported membrane filtration processes exists in a paper mill inLohja Finland When the fine paper machine was built in the 1990s the authoritieswould not accept an increase in effluent load Thus the mill was forced to findadvanced methods to reduce the environmental load By circulating the paper machine

Table 193 Reverse osmosis treatment for evaporator condensateof kraft pulp mill

Clean condensate RO concentratea RO permeate

Volume m3day 6000 100 5900

BOD mgL 560 41000 67

COD mgL 1067 78000 115

aCalculated from mass balancesAdopted from Dubeacute et al (2000)

Membrane technologies for water treatment and reuse in the pulp and paper industries 595

process waters efficiently after UF the mill succeeded in obtaining environmentalpermission During the 1990s 19-CR filters were installed to treat white water frompaper machines and recover coating color from the mill The membrane area installedfor white water treatment is 1428 m2 and for coating color treatment 336 m2 The finepaper machine membrane filtration plant operated in three stages recovering 94 ofthe feed into permeate (235 m3h) The permeate stream was used in paper machineshowers and for chemical dilution A part of UF permeate (50 m3h) was furtherpurified by spiral-wound NF Whereas UF removed only about 10 of dissolvedCOD NF removed about 85 at a water recovery of 70 The main benefit of UFis that it makes suspended solidsefree water in which the amount of anionic trash(extractives) has also been significantly reduced Ultrafiltration permeate has provensuitable for reuse in showers sealing waters and dilution of wet-end chemicalsBecause of the high purity of NF permeate it can be used to replace warm freshwateron the paper machine

Sutela (2008) reported a high average flux of 315 L(m2h) in UF at 08 bar and60 C for a 7-year filtration period Total operating costs for CR UF were about019 Vm3 in 2008 (used energy price 005 VkWh) Advanced water purificationenables the fine paper machine to operate with about 6 m3 freshwater intake perproduced ton of paper The high shear CR-filtration technology was also applied inthe newsprint mill of Holmen Paper in Madrid Spain and the UPM Kymmene millin Valkeakoski Finland Approximately 20e50 reduction in the use of freshwaterwas achieved in these mills (Sutela 2008)

Typically UF almost completely removes suspended solids (fibers) and bacteriaand partly organic dissolved compounds (lignin hemicellulose etc) but ions onlywhen they are bound for instance to fibers The removal of dissolved organic com-pounds depends on the process water and membrane used it is typically from 10to 40 in UF Membranes are typically needed when freshwater consumption needsto be reduced below 10 m3ton of paper Nanofiltration removes 70e90 of dissolvedorganic compounds (COD and TOC) color and lignin degradation products Veryhigh retention for multivalent ions has also been reported The retention efficiencyin NF depends on the filtration conditions and pH and naturally on the membraneproperties For instance increasing pH of slightly acidic paper machine process waterto neutral increased the retention of COD about 20

194 Simultaneous recovery of valuable by-productsand purification of process waters

1941 Recovery of coating color

Probably the most economical application for membrane processes in the paper indus-try is the recovery of coating effluents by UF especially when valuable coating pig-ments are used Effluents that contain coating color are generated during theflushing of coating equipment paper breaks and production changes in paper and

596 Advances in Membrane Technologies for Water Treatment

cardboard mill manufacturing coating grades (papers that are used in magazinescatalogs or books for example) (Lipnizki 2008)

Coating wastewaters create a lot of color in discharge water systems because theyare not easily treated by conventional treatments although their volumes are usuallynegligible compared with overall mill effluents (about 2e5 of total flow) Theheavy solids load and compounds that are sticky by nature in these wastewatersmay cause operating problems in treating effluent if discharged into sewers withoutappropriate pretreatment On the other hand pigments are expensive so the (partial)recovery of coating color for reuse is cost-effective in most cases Therefore theseparate treatment of coating wastewater is an attractive environmentally friendlyalternative to reducing color in the effluents at the same time the mill can benefitfrom reusing the coating material Diluted coating materials are recovered mostlyby UF to obtain a solid-free permeate stream and a retentate stream that containsthe coating materials preferably at a concentration suitable for recycling or dischargeIn UF the pore size of the membrane is sufficiently small to prevent pore pluggingand the permeability is still high The solid-free permeate stream can be either easilydischarged or recycled The permeate stream can be reused for example in coatingpreparation as washing water or as shower water for the paper machine Cross-rotational technology dominates new installations (more than 20 mills have begunto recover coating color by CR technology over the past 15 years) (Alho RoittoNygaringrd amp Hietanen 1998 Anon 2013b Jeuroonsson Jeuroonsson Teppler Tomani ampWeuroannstreuroom 1996 Singhet al 1999)

Payback time is typically around a year when treating valuable coating color (egwhen TiO2 pigments exist in coating wastewaters) High shear modules can recovercoating color from wastewater to higher dry solids content than traditional modulesOn an industrial scale effluent fed into the process typically contains 2e4 solidsand by UF its concentration is increased to 30e44 depending on the system Ahigh concentration is needed so that the concentrate can be added to fresh coating colorwithout overly diluting the coating color

1942 Recovery of by-product

Only about half of the wood material is converted to pulp in the pulping process therest of it is dissolved during the process Dissolved wood compounds eg galactoglu-komannan (GGM) can be recovered from thermomechanical pulp mill process waters(Figure 192) Other possible products are lignosulphonates and monosaccharides inwhich spent sulfite cooking liquors are rich Furthermore kraft lignin and hydroxyacids are possible valuable products in black liquor from the sulfate pulping processAll of these compounds are recoverable by using different membrane processes Mem-branes are used to recover compounds into concentrate (eg hemicelluloses or ligno-sulphonates) or into permeate (eg monosaccharides or vanillin) In SarpsbogNorway Borregaard Industries have concentrated lignosulphonates by UF since the1980s (Jeuroonsson amp Wimmerstedt 1985 Wagner 2000) Nanofiltration can purifyeg xylose into NF permeate As a result xylose purity can increase from 16 up

Membrane technologies for water treatment and reuse in the pulp and paper industries 597

to 65 (Heikkileuroa Meuroantteuroari Lindroos amp Nystreuroom 2005) When high molar mass com-pounds such GGM lignosulphonates and kraft lignin are recovered into the UFconcentrate stream diafiltration can be used to purify them All of these streams arewater streams and water itself can be used to carry away impurities It can be assumedthat the importance of membrane technology in the recovery and purification of valu-able compounds from different streams will increase in future

195 Purification of raw water

Membranes are used to purify process waters and effluents in the mills but also topurify incoming water Two examples of mills - Bahia Sul Celulose in Mucuri Braziland Stendal pulp mill at Arneburg near Stendal Germany - purify raw waters froma river using spiral-wound RO Both installations needed tailored and complicated pre-treatment systems to manage the seasonal variations of river water In the case of theBahia Sul Celulose mill complicated pretreatment including chlorination floccula-tion sedimentation sand filtration and filtration through activated carbon was not suf-ficient before RO because the standard BW30-365 membrane had high levels ofbiofouling that generated a high pressure drop on the system and demanded frequentcleaning After replacing the standard membrane with the more fouling-resistantBW30-365FR membrane (FilmTec currently Dow) and after optimizing the opera-tion (maximum flux 22 Lm2h) and cleaning conditions fouling was significantlyreduced and the cleaning interval doubled to 12 days Salt retention is 98 corre-sponding to a permeate conductivity of less than 6 mScm (Soalheiro 2000)

The Stendal pulp mill in Germany started to use RO to treat raw water from theElbe River in 2004 After multilevel pretreatments this water is led to RO The ROplant produces about 2500 m3h (feed 3100 m3h) of permeate which is used asprocess water and is further treated (300 m3h) with demineralized water Differencesin the quality of water taken from the Elbe River which result from seasonal andweather conditions are compensated for by a complicated pretreatment systemincluding different physical and chemical stages The RO removes 986 of saltsand the conductivity levels in permeate are about 15 mScm (Kremser DreshnerOtto amp Recknagel 2006) As these examples show spiral-wound modules needappropriate pretreatment so that their functionality can be ensured

196 Conclusion and future trends

This chapter reviewed membrane filtration related to water treatment in the pulp andpaper industry The need for water has not decreased in paper manufacturing pro-cesses but the need for freshwater and at the same time the amount of effluents canbe significantly decreased when advanced water purification technologies such asmembrane filtration are used The strongest driving force will also be legislationthat sets demands on effluent quality and how much effluent can be discharged The

598 Advances in Membrane Technologies for Water Treatment

Best Available Techniques (BAT) reference document for the production of pulppaper and cardboard is an excellent source of information on effluent treatment inthe pulp and paper industry it provides guidance to the industry member statesand the public regarding achievable emission and consumption levels when usingspecified BAT techniques

Several successful examples have shown membrane processes to improve the ma-terial energy and cost-efficiency of pulp and paper manufacturing processes anddecrease the environmental impact of mills They have also encouraged companiesto test membranes In the future the importance of membrane processes will increasefor water treatment purposes but also for the recovery and purification of valuableproducts from different liquors and water-based streams from pulp and paper millsBiorefineries based on lignocellulosic biomasses are under intensive developmentand the use of membranes is an essential issue in this Membranes will enable thesimultaneous recovery purification and concentration of monomeric oligomericand polymeric wood compounds from various process streams and extraction liquorsand they can also be used to dewater ethanol for biofuel use

The development of more resistant polymeric and cheaper ceramic membranes willenable the use of membranes under very alkaline or acidic conditions even at high tem-peratures which makes membrane processes an attractive alternative in pulp and papermill applications The need for water is increasing worldwide therefore purificationand reuse of process waters and effluents will increase in importance

197 Further information and advice

A comprehensive review on industrial-scale membrane filtration plants is presented byMeuroantteuroari and Nystreuroom (2009) The review consists of about 30 different industrialexamples on the use of membrane processes excluding coating color applicationsNuortila-Jokinen et al (2003) intensively discussed water use in pulp and paper mak-ing processes and their effluents Kallioinen Nystreuroom and Meuroantteuroari (2013) presentedrequirements and factors affecting the selection of membranes in pulp and paper appli-cations in which they deal with key properties of membranes to be taken into account

The BAT reference document for the production of pulp paper and cardboard is anexcellent source of information on effluent treatment in the pulp and paper industry itprovides guidance to the industry member states and the public on achievable emis-sion and consumption levels when using specified BAT techniques The documentalso reviews existing industrial-scale purification systems including membrane pro-cesses The last adopted document was in 2001 but the final draft of the new version(July 2013) was published and adopted in spring 2014

In the future membrane processes will probably be applied mostly in the fraction-ation and purification processes in biorefineries Nanofiltration is a promising fraction-ation and purification technology for biorefinery applications (Meuroantteuroari Van derBruggen amp Nystreuroom 2013) Almost all of the potential applications are water-based therefore water treatment is and will be an essential part of biorefineries

Membrane technologies for water treatment and reuse in the pulp and paper industries 599

Membrane Filtration Handbook Practical Hints and Tips (Wagner 2001) is rec-ommended as reading material when an industrial-scale membrane filtration process isplanned

List of acronyms

AOX Absorbed organic halogensBAT Best available techniquesBOD Biological oxygen demandCAS Conventional activated sludgeCOD Chemical oxygen demandCR Cross-rotationalDAF Dissolved air flotationED ElectrodialysisGGM GalactoglucomannanMBR Membrane bioreactorMF MicrofiltrationMLSS Mixed liquor suspended solidsNF NanofiltrationPCD Pulsed corona dischargePVDF Polyvinylidene difluorideRO Reverse osmosisTOC Total organic carbonUF UltrafiltrationVSEP Vibratory shear-enhanced processingWWT Wastewater treatment

References

Alho J Roitto I Nygaringrd S amp Hietanen S (1998) A review on coating effluent treatment byultrafiltration InProceedings of the2ndEcoPaperTechConference (pp 219e231) JyveuroaskyleuroaFinland The Finnish Pulp and Paper Research Institute and The Finnish Paper Association

Amaral M C S Lange L C amp Borges C P (2012) Treatment of bleach pulp mill effluentby MF-MBR Water Environmental Research 84(7) 547e553

Anon (2007) Factual record pulp and paper submission (SEM-02-003) Commission for Environ-mental Cooperation ofNorthAmerica Available fromhttpwww3cecorgislandoraenitem2825-north-american-environmental-law-and-policy-volume-22-enpdf Accessed 260214

Anon (2010) Water quality demands in paper chemical food and textile companies Aqua-Fit4Use (EU) Available from httpwwwaquafit4useeuuserdatafilePublic20resultsAquaFit4Use20-20Water20quality20demands20in20paper-chemical-food-textile20industrypdf Accessed 260214

Anon (2013a) Available from httpwww2metsateollisuusfitilastopalvelu2tilastokuviotYmparistoFormsDispFormaspxIDfrac1449ampRootFolderfrac142ftilastopalvelu22ftilastokuviot2fYmparisto2fJulkinen2dFIampSourcefrac14http3A2F2Fwww22Emetsateollisuus2Efi2Ftilastopalvelu22Ftilastokuviot2FYmparisto2FForms2FAllItems2EaspxAccessed 260214

600 Advances in Membrane Technologies for Water Treatment

Anon (2013b) Best available techniques (BAT) reference document for the production of pulppaper and board final draft july 2013 The European IPPC Bureau Available from httpeippcbjrceceuropaeureferenceBREFPP_BREF_FD_07_2013pdf Accessed 260214

Culkin B Plotkin A amp Monroe M (1998) Solve membrane fouling problems with highshear filtration Chemical Engineering Progress 94(1) 29e33

Dubeacute M McLean R MacLatchy D amp Savage P (August 2000) Reverse osmosis treat-ment effects on effluent quality Pulp amp Paper Canada

Durham B (2000) Case studies of wastewater re-use for the petrochemical power and paperindustry Special Publication Royal Society of Chemistry 249 (Membrane technology inwater and wastewater treatment) 241e247

Ferreira L M G A Amaral L amp Machado L (2004) Removal of chloride in the kraftchemical recovery cycle of pulp mills using the ion-exchange process Industrial ampEngineering Chemistry Research 43 7121e7128

Geraldes V amp De Pinho M N (1995) Process water recovery from pulp bleaching effluentsby an NFED hybrid process Journal of Membrane Science 102(1) 209e221

Greaves R (1999) The use of ultrafiltration for COD reduction in pulp mill effluent e A casestudy from Sweden In International Environmental Conference (pp 1167e1191)April 18e21 Nashville TN Tappi Press

Heikkileuroa H Meuroantteuroari M Lindroos M amp Nystreuroom M (2005) Recovery of xylose US Patent6872316 (B2) March 29 2005

Helble A amp Meuroobius C H (2009) Current experience with the use of membrane bioreactortechnology for the treatment of papermill effluent PTS Water amp Environment TechnologySymposium (p27) November 10e11 Munich Germany PTS

Hepp B Joore L Schonewille H amp Futselaar H (2005) Membrane filtration A sustainablewater treatment technology within modern papermaking concepts Papers Technology46(1) 41e48

Jaffrin M Y (2008) Dynamic shear-enhanced membrane filtration A review of rotating disksrotating membranes and vibrating systems Journal of Membrane Science 324 7e25

Jeuroonsson A-S (1989) Treatment of effluent from alkaline extraction with ultrafiltration andreverse osmosis Nordic Pulp Paper Research Journal 4(1) 33e37

Jeuroonsson A-S Jeuroonsson C Teppler M Tomani P amp Weuroannstreuroom S (1996) Recovery of dilutepaper coating colour effluents by ultrafiltration Filtration and Separation 33 453e457

Jeuroonsson A-S amp Wimmerstedt R (1985) The application of membrane technology in the pulpand paper industry Desalination 53 181e196

Joore LWortel N ampBronold N (2001)MBR inwater loop closure concepts inDutch recycledpaper mills e From pilot towards full-scale installations Paper Technology 42(7) 27e36

Junk H H Dorfer T Stratz K amp Lausch B (2008) Kohler Pappen installs the worldrsquos firstmembrane bioreactor with integrated reverse osmosis Allg Pap-Rundsch 132(4) 44e46

KallioinenM NystreuroomMampMeuroantteuroariM (2013)Membrane-based treatment of pulp and paperindustry process and waste waters In E M V Hoek amp V V Tarabara (Eds) Encyclopediaof membrane science and technology (pp 2156e2174) Hoboken NJ John Wiley amp Sons

Kremser U Dreshner G Otto G amp Recknagel V (2006) First operating experience with thetreatment of 3100 m3h of Elbe river water by means of reverse osmosis to produce processwater and demineralised water for use in the pulp industryDesalination 189(1e3) 53e58

Kreutzman E amp Sutela T (2004) Water management in the European paper industry IpptaJournal (Convention Issue) 15e22

Lien L amp Simonis D (1995) Case histories of two large nanofiltration systems reclaimingeffluent from pulp and paper mills for reuse In International Environmental Conference(pp 1023e1027) May 7e10 Atlanta GA Tappi Press

Membrane technologies for water treatment and reuse in the pulp and paper industries 601

Linpac (2006) Pressurized ozone membrane ultrafiltrationnanofiltration methodology for TDSremoval in paper mill process water for energy savings production efficiency and envi-ronmental benefits Available from httpwwwrobynrickertcomestrsitedocumentslinpacpdf Accessed 260214

Lipnizki F (2008) Opportunities and challenges of using ultrafiltration for the concentration ofdiluted coating materials Desalination 224 98e104

Meuroantteuroari M Daltrophe N Oren Y Gilron J amp Nystreuroom M (2001) Treatment of paper millprocess water with lime treatment MF and NF In Proceedings of the Engineering withMembranes (pp 1295e1299) June 3e6 Granada Spain Servicio de PublicacionesUniversidad de Oviedo

Meuroantteuroari M Kuosa M Kallas J amp Nystreuroom M (2008) Membrane filtration and ozonetreatment of biologically treated effluents from the pulp and paper industry Journal ofMembrane Science 309(1e2) 112e119

Meuroantteuroari M amp Nystreuroom M (2004) Ultrafiltration and nanofiltration in the pulp and paperindustry using cross-rotational (CR) filtersWater Science amp Technology 50(3) 229e238

Meuroantteuroari M amp Nystreuroom M (2007) Membrane filtration for tertiary treatment of biologicallytreated effluents from the pulp and paper industry Water Science amp Technology 55(6)99e107

Meuroantteuroari M amp Nystreuroom M (2009) Utilization of membrane processes in treating variouseffluents generated in pulp and paper Industry In A K Paddy S S H Rizvi ampA M Sastre (Eds) Handbook of membrane separations Chemical pharmaceutical andbiotechnological applications (pp 981e1006) Boca Raton USA CRS Press

Meuroantteuroari M Pekuri T amp Nystreuroom M (2004) NF-270 a new membrane having promisingcharacteristics and being suitable for treatment of dilute effluents from the paper industryJournal of Membrane Science 242 107e116

Meuroantteuroari M Van der Bruggen B amp Nystreuroom M (2013) Nanofiltration In S RamaswamyB Ramarao amp H Huang (Eds) Separation and purification technologies in biorefineries(pp 233e258) Chichester UK John Wiley amp Sons Ltd

Mauchauffee S Denieul M-P amp Coste M (2012) Industrial wastewater re-use Closure ofwater cycle in the main water consuming industries e The example of paper mills Envi-ronmental Technology 33(19) 2257e2262

Merry A (1999) The role of membranes in achieving ZLE Investigations Technical Paper36(142) 568e574

Nordin A-K amp Jeuroonsson A-S (2008) Optimisation of membrane area and energy requirementin tubular membrane modules Chemical Engineering Processing Process Intensification47(7) 1090e1097

Nuortila-Jokinen J (2005) Membranes in the pulp and paper applications - Only emptypromises PTS Symposium Water and Environmental Technology (pp 18-1e18-16) PTS

Nuortila-Jokinen J Meuroantteuroari M amp Nystreuroom M (2003) The pulp and paper industry InS Judd amp B Jefferson (Eds) Membranes for industrial wastewater recovery and reuseUK (pp 102e131) Elsevier Advanced Technology

Panorel I C Kaijanen L Kornev I Preis S Louhi-Kultanen M amp Sireacuten H (2014) Pulsedcorona discharge oxidation of aqueous lignin Decomposition and aldehydes formationEnvironmental Technology 35(2) 171e176

Pfromm P H Tsa i S-P amp Henry M P (1999) Electrodialysis for bleach effluent recyclingin kraft pulp production simultaneous control of chloride and other non-process elementsThe Canadian Journal of Chemical Engineering 77(6) 1231e1238

Pohjalainen T (1999) Case study of ldquoclosedrdquo board mill and application studies in FinlandInvestigacion y Tecnica del Papel 36(142) 637e647

602 Advances in Membrane Technologies for Water Treatment

Ramaekers H van Dijk L Lumpe C Verstraeten E amp Joore L (Feb 2001) Thermophilicmembarane bioreactors in the paper industrye A successful key to in-mill water treatmentPaper Technology 32e40

Rapp H J amp Pfromm P H (1998) Electrodialysis for chloride removal from the chemicalrecovery cycle of a kraft pulp mill Journal of Membrane Science 146 249e261

Schirm R Welt T amp Ruf G (2001) Nanofiltration Eine meurooglichkeit zur Kreizlaufs-chliebung Papierfabrik Palm Werk Eltmann IMPS Internationales Meurounchner Papier-symposium Meurounich Germany March 23

Simstich B amp Oeller H-J (2010) Membrane technology for the future treatment of paper milleffluents Chances and challenges of further system closure Water Science amp Technology62(9) 2190e2197

Singh S Matsuura T amp Ramamurthy P (1999) Treatment of coating plant effluent with anultrafiltration membrane Tappi Journal 82(4) 146e155

Soalheiro S C (2000) Membrane technology improves RO system for Bahia Sul CelulosePulp and Paper 74(10) 63e71

Stephenson T Judd S Jefferson B amp Brindle K (2000) Membrane bioreactors forwastewater treatment London IWA Publishing

Sutela T (2008) Membrantechnik in der Papierindustrie PTS Symposium (pp 27e28)May Meurounchen Germany PTS

Wagner J (2000) Membrane technology in wood pulp and paper industries Special Publi-cation Royal Society of Chemistry 249(Membrane technology in water and wastewatertreatment) 233e240

Wagner J (2001)Membrane filtration handbook practical hints and tips Osmonics Availablefrom httpgendocsrudocs3029820conv_1file1pdf Accessed 260214

Wagner R (2010) It pays to conserve and reuse water Paper 360 24e25Webb L (2002) Kidney technology brings success Pulp and Paper International 44(4)

28e32Yoon S-H Kim H-S amp Yeom I-T (2004) The optimum operational condition of mem-

brane bioreactor (MBR) Cost estimation of aeration and sludge treatmentWater Research38 37e46

Zaidi A Buisson H Sourirajan S ampWood H (1992) Ultra- and nano-filtration in advancedeffluent treatment schemes for pollution control in the pulp and paper industry WaterScience and Technology 25(10) 263e276

Membrane technologies for water treatment and reuse in the pulp and paper industries 603

Membrane technologies forwater treatment and reusein the power industries

20L Daal1 F de Vos1 J Soons2 T de Vries31DNV GL Energy Arnhem The Netherlands 2PWN Waterleidingbedrijf Noord HollandVelserbroek The Netherlands 3GDF SUEZ Energie Nederland Zwolle The Netherlands

201 Introduction

2011 General

In industry water is used for many purposes such as pure water for the watersteamcycle as a raw material for chemical reactions to extinguish fire and for cleaningand cooling In particular power- and energy-intensive industries are major consumersof water

2012 Water streams

When considering industrial and power plants one needs to recognize that most wateris used for cooling purposes According to the European Environment Agency (EEA)448 of total available freshwater is abstracted for cooling in energy production Incomparison the manufacturing industry consumes about 11 of water half of whichis used for processing and the remainder of which is for cooling (EEA 2010) In otherwords the total abstracted freshwater for cooling purpose accounts for approximatelyhalf of all water use across Europe Likewise in the United States the thermoelectricindustry consumes 46 of all water (Judd amp Jefferson 2005) Most industrial plantstypically choose a once-through cooling water system There cooling water is notconsumed but it is chemically and thermally treated and discharged into the environ-ment There are ways to minimize the impact on the environment for example bylimiting chemical use1 Cooling water is also used for evaporative cooling towersthe consumption of this water can be in total two-thirds or more of the total wateruse of industrial plants (fossil fuel and nuclear plants petroleum refinery plantsetc) More information about this subject and cooling water systems in general canbe found in the literature (Rajagopal Jenner amp Venugopalan 2012)

Aside from water consumption the industry needs demineralized (demin) water andproduces large sums of wastewater With regard to wastewater an important stream

1 Thermoshock is an alternative to biocidal dosing however a high energy penaltycost is associated with itsuse Also it is less effective than biocidal dosing against biofouling corrosion operational reliability etc

Advances in Membrane Technologies for Water Treatment httpdxdoiorg101016B978-1-78242-121-400020-4Copyright copy 2015 Elsevier Ltd All rights reserved

arises from water used to clean flue gases which must be treated before discharge andor reuse This is usually done through physicalchemical processes In relation to futurelegislation the use of organics is expected

This chapter focuses on water treatment required for the production of demin waterused for the watersteam cycle in industrial plants First to better understand treatmentrequirements the water quality requirements for a watersteam cycle are explained

2013 Water quality

20131 Water quality requirements

The best way to understand water quality requirements is first to understand the watersteam cycle in an industrial plant The watersteam cycle can be considered as theblood circulation of the boilerturbine installation (Figure 201) because this is theheart of a power plant Here as with other living organisms the quality and healthof the blood circulation are key factors for the correct functioning of a boilerturbineinstallation The pure water (boiler water) ensures that the energy freed throughcombustion is transferred to steam which in turn drives a turbine The turbine thendrives a generator to produce electricity Just as in living organisms the watersteamcycle has different names or distinctions to identify where the blood or water in thiscase is within the system Giving a clear distinction of watersteam in the cycle helpsprevent misunderstanding Figure 201 shows the watersteam cycle with the distinc-tions makeup water feed water boiler feed water boiler water saturated steamsuperheated steam condensate and condensate return

Boiler feed water is normally a mixture of makeup water and condensate Thiscondensate is created after steam has passed the turbine Because losses occur alongthe way new water (makeup water) is needed The use of poor-quality water herewould result in serious problems for the boilerturbine installation Corroded boilerpipes in the watersteam cycle are shown in Figure 202 Hence the choice of a rawwater source and its treatment are essential to supply appropriate-quality makeupwater A main quality parameter of this makeup water is the sum conductivity whichhas a maximum value of 010 mScm In comparison theoretically pure water in whichno minerals are present has a conductivity of 0055 mScm

20132 Raw water source

For the production of demin water the following raw sources are used

1 Drinking water2 Well water3 Industry water (grey water)4 Surface water5 Brackish water and seawater

Because of costs and the need to involve authorities drinking water is used lessfrequently as a source of raw water Drinking water originates from surface water treat-ment and well water Well water (and drinking water where the source is well water) is

606 Advances in Membrane Technologies for Water Treatment

Figure20

1Schem

eof

thewater

steam

cycle

Membrane technologies for water treatment and reuse in the power industries 607

the least problematic when it comes to removing minerals these water sources onlypossess minerals but no organic material (humic acids) Minerals are relatively easyto remove compared with organic material

Surface water needs much more treatment for use as demin water Aside from saltsor minerals surface water has a lot of nondissolved substances that have to be removedIn other words pretreatment is necessary Also surface water contains natural organicmatter (NOM) the composition of which changes seasonally These compounds are notall removed during the demineralization process and hence influence the quality of theend product The demin water can be of different compositions during spring andautumn An example of the change in NOM of an industrial water sample (treated sur-face water) is shown in Figure 203 which shows examples in the spring and autumn

The height of the curve in the figure informs us about the concentration of organiccompounds Most the compounds are removed through ion exchange (IX) andmembranes The removal of polysaccharides which are found in higher concentrationsduring autumn can create a challenge for IX because a great deal of polysaccharideswill pass through the resins and end up in the demin water For membrane technology(reverse osmosis (RO)) these compounds can be prevented from passing through themembrane However these compounds cause unwanted fouling of the membranesAn illustration of the diversity and individual concentration of different organiccompounds in raw water such as surface water and drinking water at different loca-tions in The Netherlands is given in Figure 204 The composition of the total organiccarbon (TOC) is given in practise the TOC is often measured but not the individualcompounds

202 Water purification technologies

The most common technologies used to demineralize water are

1 IX technology2 Membrane technology3 Thermal processes

(a) (b)

Figure 202 (a) Corroded pipes in a combined heat and power plant (b) Cross-section of aboiler tube-fin with a thick corrosion layer

608 Advances in Membrane Technologies for Water Treatment

(a) (b)

Figure 203 Natural organic matter composition in the spring (a) and during autumn (b)

Mem

branetechnologies

forwater

treatment

andreuse

inthe

power

industries609

A description of the two most common technologies is given below Thermal pro-cesses are primarily used in the Middle East as thermal desalination technologies fordrinking water (and industrial water) and are not described here For further reading onthis topic one may refer to the European Desalination Society

2021 Ion exchange technology

20211 General

An IX resin consists of plastic spheres with a diameter smaller than a millimetrePrimarily two different plastics are used one is based on polystyrene and the otheron polyacrylate Through chemical modification of the polymer an active group ismade on the spheres where the actual exchange takes place Figure 205 shows anexample of an IX resin The figure shows that the spheres have a uniform size andshape which is the current state of the art In the past different production processeswere used and resulted in spheres of different sizes and forms These nonuniformresins can still be found in older industrial plants

Because of their active groups there is a distinction between cation and anion resinsA salt that is dissolved in water dissociates in positive ions (cations) and negative ions(anions) A cation resin removes only the cations and the anion resin removes theanions For this reason a demin line normally consists of a cation and an anion filterIf the water quality is not according to specifications after leaving these two filters amixed bed (anion and cation resins in one tank) is used A simple representation isgiven in Figure 206

Figure 204 Total organic carbon (TOC) composition at different locations throughoutThe Netherlands

610 Advances in Membrane Technologies for Water Treatment

Figure 206 also shows a carbon dioxide (CO2) cascader or tower where CO2

is removed This is the result of acidic water coming from the cation filter and the hard-ness of the water Therefore it is not necessary to remove this hardness (present ascarbonate and bicarbonate) in the anion filter This results in savings in the amountof resin needed for the anion filter

Currently demin lines are run against current flow At a certain point the resins willbe fully loaded with ions and will have lost their capacity to demineralize To revert tonormal operation cation resins are treated with an acid such as hydrochloric acid andanion resins with sodium hydroxide The most effective way to have this treatmentdone is in a countercurrent flow

20212 Operational experience

In practise anion resins are less stable than cation resins This is primarily related tothe maximum operating temperature of 40 C for anion resins Above these tempera-tures the anion resin loses active groups and hence its functionality

Figure 205 Ion exchange resin with spheres of uniform size and shape

Cationfilter

Anionfilter

Mixedbed

Demintank

CO2

cascader

Figure 206 Demin line using ion exchange (IX) technology

Membrane technologies for water treatment and reuse in the power industries 611

The resins can be of a flexible gel or the lsquotougherrsquo macro-porous resin type Bothtypes consist of polymers As such the exchange groups in the resin network attracta lot of water from the outside A dry resin grain swells like a sponge in doing sowaterways are created inside the resin grain The macro-porous type resin also takesup water however it already has high porosity This porosity ensures a rapid exchangebut results in a lower capacity of the resin

As mentioned the resin grains take up a lot of water and thus swell If the grains dryout they shrink and cracks can form The grains still have the capacity to demineralizebut because of the cracks they could break into pieces This can lead to blockages in theresin bed and pressure buildup in the column An example of dried resin grains is shownin Figure 207 Aside from the many cracks visible on the grains the shape and form ofthe spheres are not similar to new IX resins The photo also shows an older resin

2022 Membrane technology

20221 General

Aside from the preparation of ultra-pure water for the power industry membraneprocess systems are used to treat different types of water such as wastewater and toproduce drinking water

In general membranes act as filters Depending on the pore size one can distin-guish among the following types (see also Figure 208)

1 Microfiltration (MF) with pore sizes of gt01 mm2 Ultrafiltration (UF) with pore sizes of 001e01 mm3 Nanofiltration (NF) with pore sizes roughly between 001 and 0001 mm4 RO membranes which are lt0001 mm

Figure 207 Dried-out resin

612 Advances in Membrane Technologies for Water Treatment

The actual pore sizes will differ from the theoretical ones In the literature a widevariety of classifications for different membrane types can be found

Microfiltration and UF membranes are normally used to separate particles whereasNF and RO change the chemical or ionic composition of the water because theyremove small molecules and ions from the water (source prime water Web site)Figure 208 shows a membrane filtration spectrum indicating the type of contaminantsthat can be removed by different membrane types

Under normal operation conditions membrane systems are easy to operate with lowchemical consumption and constant water quality which increases the reliability of thesystem The main drawback of membrane technology is the relatively high energyconsumption This is particularly true in areas where for example seawater has ahigh salt content such as in the Middle East There RO systems have become popularfor desalination purposes and for demin water production for the power industry

According to Kabsh-Korbutowicz (2006) the economic use of membrane filtrationsystems is often limited by fouling because this results in increased pressure drops thataffect energy consumption Hence there is an increase in the frequency of cleaningwhich affects the production rate of the membranes Therefore it is important toprevent the membranes from fouling This can be done by applying the right pretreat-ment using membrane materials that are less susceptible to fouling and ensuring goodcontrol and operation of the system

Over the years the energy consumption of membrane systems has been furtherreduced by the introduction of energy recovery systems that recover the pressure ofthe concentrate stream using this energy to increase the pressure of the feed flow(Avlonitis Kouroumbas amp Vlachakis 2003)

20222 RO membranes

Most RO membranes are constructed as a spiral-wound module as shown inFigure 209 There are hollow-fibre membrane modules but these are much less

Figure 208 Membrane filtration spectrum (Water treatment handbook 2007)

Membrane technologies for water treatment and reuse in the power industries 613

common The spiral-wound module consists of a membrane mesh paper (or spacer)and permeate tube The spacers are used to create flow channels within the module andensure equal distribution of the flow The membrane is glued on three sides and theopen side is connected to a central permeate tube around which the membrane sheetsare rolled (Figure 209)

RO membranes are made of polymers mostly cellulose acetate or compositepolyamide-type membranes

In practise individual membrane modules are called elements Multiple membranemodules (or elements) behind each other will form a train and several trains togetherform the system If it is a large system several trains can also form a stage and morestages are needed to complete the entire system Depending on whether the system isused to concentrate the brine product or to produce high-quality permeate the connec-tion between the modules will be of the concentrate or the permeate

203 Operational experience with membranes

2031 General

Most membranes for water treatment can withstand temperatures of up to 50 CHowever this should be verified by the manufacturerrsquos specifications becausesome membranes have a lower temperature limit (Bates 1998) Another importantparameter is pH Cellulose acetate membranes can be operated only within a smallpH range the pH should be kept between 4 and 6 On the other hand these mem-branes are resistant to oxidation by chlorine Thin-film composites membranes canbe operated within a large pH range 3e11 but they are sensitive to the presenceof chlorine When using these membranes steps have to be taken to ensure no residualchlorine will reach the RO modules To combat residual chlorine sodium meta-bisulphite can be added to the intake Intake pipes for desalination plants and coolingwater intake pipes can have free chlorine present to prevent biofouling In the power

Reverse osmosis

Permeate

Pressurizedfeed water

Permeate

Concentrate

Figure 209 Spiral-wound membrane (Judd amp Jefferson 2005)

614 Advances in Membrane Technologies for Water Treatment

industry demin plants typically extract their raw water source from the cooling watercircuit and discharge the brine there as well

Another method to reduce the risk of fouling and reduce energy consumption is toincrease the flow rate To increase the flow rate hydrophilic membranes are often usedWith these membranes water will easily pass through the membranes whereas hydro-phobic contaminants will be repelled reducing fouling Cellulose acetate membranesare most hydrophilic but have a lower salt rejection compared with polyamidemembranes

Another factor that determines fouling and the fluxes of the system is the surfacecharge of the membranes Cellulose acetate membranes are neutrally charged whereaspolyamide membranes can attract charged organic and colloidal material from the feedwater (Membrane Web site)

The most important fouling mechanisms will be discussed next together with waysto prevent fouling and how the effects of fouling can be minimized

2032 Fouling

One of the most important aspects of the operation of membrane systems is foulingFouling increases the pressure loss over the membrane surface resulting in higherenergy consumption and lower salt rejection Also higher fouling rates increase thecleaning frequency lowering the production rate (or the availability of a plant) andincreasing chemical consumption

Therefore it is essential to reduce fouling and minimize its effects The first step tocombat fouling is to determine what kind of fouling the system is dealing with becausedifferent types of fouling require differentmeasures Furthermore goodcontrol of the pro-cess and cleaning conditions is essential to prevent and overcome the effects of fouling

2033 Types of fouling

Different fouling sources can be described as follows

1 Fouling through concentration polarization2 Organic fouling3 Biological fouling4 Colloidal and suspended fouling5 Scaling

20331 Concentration polarization

This type of fouling occurs when salts and other rejected solutes concentrate near themembrane surface A laminar boundary layer will be present as the fluid adjacent tothe membrane moves slower than the main stream (Porter 1990) As a consequencethe salt rejection of the membrane decreases and therefore negatively affects the qual-ity of permeate Also the osmotic pressure will increase owing to the concentration ofthe salts This results in an increase in energy consumption

Membrane technologies for water treatment and reuse in the power industries 615

Concentration polarisation cannot be avoided The only way to combat thisphenomenon is to reduce the boundary layer by optimizing the hydraulic conditionsThis is done by increasing the flow rate across the membrane surface or introducingturbulence promoters into the feedreject stream To increase turbulence end spacersare designed in spiral-wound membrane modules to optimize hydraulic conditionswithin the module

20332 Organic fouling

Organic matter originating from feed water has different compositions throughoutthe world and its composition can change dramatically over time This makes it chal-lenging to combat organic fouling Organic fouling will increase the pressure dropover the membrane (trans-membrane pressure (TMP)) Figure 2010 shows a fouledRO membrane

Because most natural organic matter is charged it will bind to charged membranesurfaces from polyamide membranes In these situations organic matter will prefer themembrane over the water phase and will stick to the membrane causing fouling One ofthe most important compounds leading to organic fouling is humic acid in the feedwater which acts as a weak acid and retains metals such as iron Furthermore organicmatter can serve as a feeding source for bacteria and enhance biofouling

Also for organic fouling when coagulation and flocculation are applied as pretreat-ment the addition of too much flocculation chemical will lead to increased organicfouling The same is true for the addition of antiscalants

Organic fouling will take place over all membrane stages To combat organicfouling new membrane types with a neutrally charged surface have been developedIn this way the charged organic material will have fewer tendencies to attach to themembranes

Figure 2010 Fouled membrane photo taken near the collector of the membrane module

616 Advances in Membrane Technologies for Water Treatment

20333 Biofouling

Biofouling is a major concern for membrane systems Biofouling can be divided intomicrofouling and macrofouling Because macrofouling (mussel growth) occurs inintake pipes and cooling water systems it is not a direct threat to membrane operationsOn the other hand microfouling will occur on membranes and will have an effect onthe performance of the water treatment Microfouling refers to bacterial growth whichcan occur on the organic matter of the membrane surface and result in increasing TMPAlso bacteria can produce extracellular polymeric substances mostly polysaccha-rides which also result in fouling The formation of polysaccharides combined withbacterial growth makes cleaning measures less effective because these microorganismsare embedded with polysaccharides and hence are not easily removed

Within membrane modules lsquodead zonesrsquo should be avoided They lead to theincreased growth rate of microorganisms (Ho Altman Jones Khalsa amp McGrath2008) By applying equal flow conditions biofouling can be prevented Spacers ofspiral-wound membranes can also be a growth place for microorganisms augmentingbiofouling

To prevent the growth of macro- and microorganisms in the intake (pipe of theplant) and on the membranes installations are often disinfected This is often doneby applying free chlorine As already discussed the addition of chlorine can damagethe membranes but they also can potentially have negative effects on biofoulingOrganic matter can be broken down into bite-size pieces that can be readily takenup by bacteria present on the membrane surface

Biofouling typically occurs in the first membrane stages Biofouling can beobserved by following the flux and the salt rejection In this case the flux will decreasein the beginning with increasing salt rejection (AEDyR 2009) After this initial phasesalt rejection will also decrease

20334 Colloidal and suspended fouling

Excessive volumes of colloidal and suspended material will plug the RO element feedpath regardless of the membrane type Fortunately as with all other types of foulingthis type can easily be combated with proper pretreatment This can be done throughfiltration coagulation sedimentation flotation and decanters Typical levels ofcolloidal and suspended particles would be less than 10 NTU for turbidity and asilt density index value below 4 (AEDyR 2009)

20335 Scaling

From the information about concentration polarization it is clear that within thelaminar boundary layer of the membrane the concentration of rejected solutes stronglyincreases Salts will also be concentrated in this layer When the concentration exceedsthe solubility product salts will precipitate and can even form crystals on themembrane surface thus increasing the TMP and lowering the salt rejection

Known scaling compounds are calcium carbonate barium sulphate calcium phos-phate strontium sulphate and calcium fluoride

Membrane technologies for water treatment and reuse in the power industries 617

The scaling effect increases with the different stages when concentrate from theprevious stage is used as feed water for the next This is illustrated by the Langliersaturation index which increases with each membrane separation stage(Figure 2011)

According to Al-Shammiri and Al-Dawas (1997) four methods can be used toreduce the risk of scaling

1 Lowering the pH to remove carbonate from the system2 Adding antiscalant which will broaden the solubility limits of the salts3 Reducing the recovery rate so that the concentration on the outside of the membrane is

reduced4 Dehardening the feed water

Furthermore the addition of chemicals may be a source of fouling For examplewhen coagulant is added during pretreatment the membranes can be fouled withiron oxides if the coagulant addition is not controlled correctly

2034 Combating fouling

20341 Pretreatment

Pretreatment is required to suppress fouling andor clogging of membranes or toremove chemically aggressive constituents such as chlorine (Judd amp Jefferson2005) The objective is to clear the feed stream from everything potentially harmfulto the membrane performance andor lifetime Measures taken are

1 Mechanical prefiltration2 Acidification to reduce carbonate hardness followed if necessary by aeration to reduce CO2

3 Addition of antiscalants to keep divalent salts (sulphates) from precipitating

20

15

10

05

0Ca2+ aliment = 200 mgL HCO3

ndash = 150 mgL pH = 70

LSI = 165Conversion = 75

2nd stage1st stage

LSI

1 2 3 4 5 6 7 8 9 10 11 12

Figure 2011 Langlier saturation index with membrane steps (AEDyR 2009)

618 Advances in Membrane Technologies for Water Treatment

4 Chlorination (or alternative oxidation) to deactivate microorganisms usually followed bydechlorination to safeguard against membrane degradation (Beurooddeker 2008)

5 Removal of colloids and metals from the feed water by coagulation and flocculation

Pretreatment can consist of sand filtration dissolved air flotation and activatedcarbon filters as well as other membrane systems such as MF and UF This lastcombination (MFeUF followed by RO) has become increasingly popular

20342 Cleaning-in-place

Notwithstanding the measures applied to combat fouling it is inevitable that somewill occur In time the fouling rate will increase and should be removed or controlledto make sure fouling does not become irreversible Therefore it is important to cleanthe membranes when they are only lightly not heavily fouled Heavy fouling canimpair the effectiveness of the cleaning chemical by impeding the penetration ofthe chemical deep into the foulant and in the flushing of foulant out of the membraneelements (Technical Service Bulletin 10720 Hydranautics) According to the samesource some fouling is allowed as long as

1 Normalized permeate flow decrease is less than 102 Normalized permeate quality decrease is less than 103 Increase in normalized pressure drop as measured between the feed and concentrate headers

is less than 15

Fouling increases the TMP which increases pressure on the membranes increasingthe risk of mechanical damage to the membrane surface

By controlling the fouling rates the cleaning frequencies can be reduced resultingin a higher production rate and lower chemical consumption

RO membranes cannot be back-washed because of the high pressure that would beneeded which could potentially damage the permeate side of the membranes There-fore RO membranes are flushed from the feed to the concentrate side or from theconcentrate side to the feed Besides flushing so-called lsquocleaning-in-placersquo is appliedMembranes are soaked for several hours with a chemical solution and are flushedafterward to remove the chemicals

Organic fouling can be removed using high-pH cleaning for example with sodiumhydroxide Inorganic fouling can be removed with acid cleaning agents such as sulphu-ric acid or citric acid

Normally it is advised first to apply alkaline cleaning followed by acid clean-ing In the case of multistage systems it is recommended to clean every step sepa-rately to avoid fouling that would go through the whole system before it isremoved

Often the effectiveness of the cleaning increases with temperature in that casethe cleaning chemicals can be heated This option should be taken into considerationduring the design phase

Another important factor for cleaning is the flux Turbulent conditions will increasethe shear forces on the fouling and increase the removal rate

Membrane technologies for water treatment and reuse in the power industries 619

2035 Route cause analysis

In practise one can encounter poor membrane performance If the likely cause isassumed to be membrane fouling the following route cause steps can help identifythe type and cause of fouling

1 Check on process conditions2 Check on monitoring equipment3 Conduct visual inspection of pretreatment and water production installation4 Gather previous inspection reports and process condition data5 Conduct visual inspection of membrane modules from different stages6 Gather the fouled material and conduct a composition analysis

With respect to process conditions trends in flux TMP and permeate qualitynormally give a good indication of the type of fouling taking place This is shownin Table 201 where the effects of different types of fouling on process conditionsare given

Table 201 Troubleshooting matrix

Possible causePossiblelocation Pressure drop Feed pressure Salt passage

Metal oxidefouling (egFe Mn CuNi Zn)

First stage leadelements

Rapid increase Rapid increase Rapid increase

Colloidalfouling(organic andor inorganiccomplexes)

First stage leadelements

Gradualincrease

Gradualincrease

Slight increase

Mineral scaling(eg Ca MgBa Sr)

Last stage tailelements

Moderateincrease

Slight increase Markedincrease

Polymerizedsilica

Last stage tailelements

Normal toincreased

Increase Normal toincreased

Biologicalfouling

Any stageusually leadelements

Markedincrease

Markedincrease

Normal toincreased

Organic fouling(dissolvedNOM)

All stages Gradualincrease

Increase Decreased

Antiscalantfouling

Second stagemost severe

Normal toincreased

Increase Normal toincreased

Source Hydranautics

620 Advances in Membrane Technologies for Water Treatment

One may need to calibrate and check the monitoring equipment to make sure that itis operating correctly The manner of sampling is also important as is the processingand recording of data in the plantrsquos data collection system Operating personnel whohave many obligations have been known to fail to identify the need to pay attention tomonitoring equipment

This is also true when inspecting the operating water production installation Forexample the antiscalant or coagulant supply tank could be empty or the flow of theseunits could be incorrectly set Thus it is important to visually conduct a regular checkon the monitoring equipment and operating water production installation and pretreat-ment units

When adopting a route cause analysis vital pieces of information are the gathereddata and the process information from the supplier ie inspection reports operatingconditions performance trends age of the unit and the membranes With this historicdata one can compare the operating ranges with those of the supplier or during thecommissioning phase

Visual inspection of one or more membrane modules that have been taken out ofuse preferably of each stage gives valuable information on the type of fouling Forsome fouling types the formation of salt crystals versus organicbiofouling can easilybe distinguished Documentation through photographs is important

Samples can be gathered for further characterization by collecting them over thelength of the membranes to check for differences in fouling with the flow and alsobetween different membrane stages (Figure 2012) The samples can be analysed forinorganic and organic matter or through further analysis using for example scanningelectron microscopy with electron diffraction spectroscopy andor atomic absorptionspectroscopy

Alternatively a nondestructive technique is to conduct a leakage test over themembranes

Figure 2012 Fouling and sampling points of the membrane

Membrane technologies for water treatment and reuse in the power industries 621

204 Future trends

2041 Evaporated water capture

A hidden source of relatively clean water is the evaporated water present in manyindustrial processes In these processes water is produced andor liberated and escapesas lsquowastersquo water into the atmosphere This evaporated water can be captured using gasseparation membranes With a sufficiently selective membrane purified water can beproduced in a single process step Advantages of the proposed process compared withtraditional separation are

1 High energy efficiency no phase change is required to achieve separation2 Temperature neutral to the source which makes heat recirculation in industrial processes

interesting3 High reliability no moving parts4 Small footprint it generally easily fits in existing spaces factories etc5 Environmentally friendly no use of chemicals no waste streams6 Energy savings aside from recirculation reheating of flue gases is no longer necessary and

latent heat can be reused in the process7 Corrosion benefits removal of water vapour from flue gas streams helps mitigate corrosion

Considering these benefits the demin water produced with this technology cancompete with existing demin water technologies To this end the European Commis-sion funded the CapWa project to bring this technology a step closer to realizationMore information can be found in httpwwwwatercaptureeu

2042 Forward osmosis

In contrast to RO in which water is pushed through a semipermeable membraneforward osmosis needs almost no pressure to have the water flow to the other sideof the membrane The difference between both techniques is that in the case of forwardosmosis the water crosses the membrane from the lower osmotic pressure to the higherosmotic pressure side This process requires very little energy because it is a naturalprocess (see Figure 2013) RO osmosis uses a lot of energy to pressurize water toovercome osmotic pressure because the water needs to cross the membrane fromthe higher osmotic pressure to the lower osmotic pressure side

In forward osmosis the higher osmotic pressure is artificially created by addingsalts This addition takes place on the retentate side of the membrane rather than onthe permeate side Thus by creating a controlled saline water stream water from adirty stream (seawater or wastewater) will pass the membrane and leave pollutionbehind with almost no energy consumption The challenge of forward osmosis is torecover clean water from this artificially created saline water stream Therefore asecond process is required this could be physical separation a thermal process mem-brane separation or a combination of all three Also there are some applications inwhich a second step is not required such as makeup for cooling towers and lsquohydration

622 Advances in Membrane Technologies for Water Treatment

bagsrsquo In hydration bags high concentrations of sugars provide the difference insalinity by putting this bag into lsquodirtyrsquo water it will attract only clean water whichends up as a drinkable sugar solution (McCutcheon McGinnis amp Elimelech 2005Salter 2005)

205 Recommended reading

Journals and recommended reading are as followsJournals

1 Power Plant Chemistry2 Ultra Pure Water3 VGB Powertech4 Local journals for example in The Netherlands H2O Similar journals can be found in your

respective country

Conferences

1 European Desalination Society2 Chemie im KraftWerk3 Aquatech

Web sites

1 EDS2 Global Water Intelligence

Figure 2013 Principle of forward osmosis

Membrane technologies for water treatment and reuse in the power industries 623

List of acronymssymbols

CA Cellulose acetateIX Ion exchangeNF NanofiltrationNOM Natural organic matterRO Reverse osmosisSDI Silt density indexTOC Total organic carbonTMP Trans-membrane pressureUF Ultrafiltration

References

Al-Shammiri M amp Al-Dawas M (1997) Maximum recovery from seawater reverse osmosisplants in Kuwait Desalination 110 37e48

Avlonitis S A Kouroumbas K amp Vlachakis N (May 2003) Energy consumption andmembrane replacement cost for seawater RO desalination plants In European conferenceon desalination and the environment Fresh water for all Malta 4e8 2003 EuropeanDesalination Society International Water Association

Bates W (1998) Reducing the fouling rate of surface and waste water RO systems Hydra-nautics USA IWC

BeurooddekerKW (2008)Liquid separationswithmembranes Springer ISBN978-3-540-47451-7EEA (2010) The european environmente State and outlook httpwwwendresscomehhome

nsfpagewpower-energy-processes-coal-fired-power-plants-desalination (referenceFigure 6)

Escuela Superior de Ingenieros Agronomos de Madrid AEDyR (2009) Curso DesalacionAEDyR

Ho C K Altman S J Jones H D T Khalsa S S amp McGrath L K (2008) Analysisof micromixers to reduce biofouling on reverse-osmosis membranes EnvironmentalProgress 27(2) 195e203

Judd S amp Jefferson B (2005) Membranes for industrial wastewater recovery and re-useElsevier ISBN 1-8561-7-389-5

Kabsch-Korbutowicz M (2006) Removal of natural organic matter from water by in-linecoagulationultrafiltration process (presented at EUROMEMBRANE 2006 24e28September 2006 Giardini Naxos Italy) Desalination 200 421e423

McCutcheon J R McGinnis R L amp Elimelech M (2005) A novel ammoniamdashcarbondioxide forward (direct) osmosis desalination process Desalination 174 1e11 httpmembranescomdocspapers02_cleaningpdf

Porter M C (1990) Handbook of industrial membrane technology Noyes Publications ISBN0-8155-1205-8 wwwprimewatercom (reference Figure 8)

Rajagopal S Jenner H A amp Venugopalan V P (2012) Operational and environmentalconsequences of large industrial cooling water systems Springer SciencethornBusinessMedia LLC httpdxdoiorg101007978-1-4614-1698-2

Salter R J (2005) Forward osmosis Water Conditioning and Purification 48(4) 36e38Technical Service Bulletin 10720 Hydranautics

Water treatment handbook 7th ed Vol 1 Degreacutemont Suez (2007) 287

624 Advances in Membrane Technologies for Water Treatment

Index

Note Page numbers followed by ldquofrdquo and ldquotrdquo indicate figures and tables respectively

AAbsorbed organic halogen (AOX)

581ndash582AC See Activated carbonAcetone-butanol-ethanol fermentation

(ABE fermentation) 270ndash271Acid chloride monomers 7ndash8Acoustic sound test (AST) 368Acrylonitrilebutadienestyrene

heterogeneous AEMs 290Activated carbon (AC) 290Activated sludge process (ASP) 444Active layer facing draw solution (AL-DS)

295Active layer facing feed solution (AL-FS)

308ADMH See 3-allyl-55-dimethylhydantoinAdsorbable organic halides (AOX) 487Advanced oxidation process (AOP) 492AEL See Anion exchange layerAEM See Anion exchange membranesAeration process 460Aerobic membrane bioreactor (Aerobic

MBR) 160ndash161areas of application 161ndash162factors affecting membrane performance

162ndash165wastewater reuse 166 166f

background 166ndash167plant components 167results 167ndash168

AFM See Atomic force microscopyAFO See Amorphous ferric oxidesAGMD See Air gap membrane distillationAgro-food industry 551agro-food wastewater characteristics

553tndash555tAIM See Aquaporin inside membranes

Air bubbling 423Air flushing 69Air gap membrane distillation (AGMD)

258 431ndash432AL-DS See Active layer facing draw

solutionAL-FS SeeActive layer facing feed solutionAlbert KohlerPappen 594Aliphatic diamines 7ndash83-allyl-55-dimethylhydantoin (ADMH)

255Alum coagulant 424ndash425Aluminum dioxide nanoparticles (Al2O3

nanoparticles) 20ndash22Aluminum sulphate See Alum coagulantAM See Anion-selective membraneAmino acids 197ndash198Aminopropyltriethoxysilane (APTES)

18ndash19Ammonia (NH3) 540Amorphous ferric oxides (AFO) 358ndash359Anaerobic membrane bioreactor (AnMBR)

168ndash170areas of application 168ndash171factors affecting performance 173HRT and SRT 174membrane properties 174ndash175OLR 173ndash174temperature 173

treatment of high-strength industrialwastewater 175ndash177

Anion exchange layer (AEL) 292Anion exchange membranes (AEM) 192

288 290 472acrylonitrilebutadienestyrene

heterogeneous 290Anion removal 466ndash476Anion-selective membrane (AM) 195

AnMBR See Anaerobic membranebioreactor

Annular photocatalytic reactor (APR) 223Antiscalants 135AOP See Advanced oxidation processAOX See Absorbed organic halogen

Adsorbable organic halidesAPR See Annular photocatalytic reactorAPTES See AminopropyltriethoxysilaneAquaporin (AQP) 251Aquaporin inside membranes (AIM) 545Aquaporin Z (AQP-Z) 251Aromatic diamines See Aliphatic diaminesArsenic (As) 116ASP See Activated sludge processAST See Acoustic sound testAtomic force microscopy (AFM) 365Attenuated total reflectancendashFourier

transform infrared (ATR-FTIR) 364Availability of equipment 354ndash355Azo dyes 538

BBackwashing 69 457Bacteriophages 370Bathtub curve 353ndash354 354fBEMR See Bio-entrapped membrane

reactor13-benzenediamine See 13-

phenylenediamineBenzoyl peroxide initiator (BPO initiator)

11b-cyclodextrin (b-CD) 250ndash251b-cyclodextrin polyurethane (DABA) 8Bio-entrapped membrane reactor (BEMR)

557Bio-inspired membranes 26ndash27Bio-mimetic mineralization

See Bio-mineralizationBio-mineralization 26ndash27Biochemical oxygen demand (BOD)

448ndash450 538 551Biofouling 454 617Biological fouling 422Bipolar membrane (BPM) 292ndash293Bipolar membrane 193 198Bisphenol A (BPA) 213Blending 10ndash11BOD See Biochemical oxygen demand

Boiler feed water 606Boric acid (H3BO3) 469BP See Bucky-PaperBPA See Bisphenol ABPM See Bipolar membraneBPO initiator See Benzoyl peroxide initiatorBrackish water (BW) 411 413f See also

Seawater (SW)high-pressure membrane applications 342

Bromides (Brndash) 468Bucky-Paper (BP) 265Bulk membrane properties 293BW See Brackish water

CCA See Cellulose acetateCA-based NF hollow fiber membrane 297CAc See Cellulose acetate (CA)membranes 96 415

CAGR See Compound annual growth rateCake filtration 457CAM See Contact angle measurementsCapital recovery factor (CRF) 434Carbon dioxide (CO2) 540Carbon nanotubes (CNTs) 10ndash13 101 255Carbon oxygen demand (COD) 64CarmanndashKozeny equation 396CarmanndashKozeny relationship 47CAS See Conventional activated sludgeCASP See Conventional activated sludge

processCation exchange layer (CEL) 292Cation exchange membranes (CEM)

192ndash193 288 290 472PANI chemically modified

organiceinorganic hybrid 290ndash291Cation-selective membrane (CM) 195Cations See Co-ionsCavitational mechanism 527CB See Conduction bandCEL See Cation exchange layerCellulose acetate (CA) 4 244 297 481Cellulose triacetate (CTA) 244 543ndash544CEM See Cation exchange membranesCeramic membranes See also Polymeric

membranescleaning 68ndash70development and fabrication processes

44ndash58

626 Index

ceramic powder paste and suspensionpreparation 52ndash53

combined phase-inversion and sintering55ndash58

heat treatment 54layer deposition 54ndash55material and microstructure 47ndash50membrane characteristics and design 47membrane configurations 50ndash52shaping 53ndash54

housing sealing and operation 61ndash62MFUF 45tndash46tmodule and unit designs 58ndash60water treatment 43for water treatment 62ndash68

Chemical cleaning 457methods 69 423physical cleaning vs 458t

Chemical conditioning 94Chemical methods 528Chemical oxygen demand (COD) 448ndash450

538 551 581ndash582Chemical vapor deposition (CVD) 101Chitosan (CS) 270 290chitosan-based composites 15

Chlorination 4244-chlorophenol (4-CP) 220 223ndash224Chlorophenols 500ndash502Chromic acid (H2CrO4) 481ndash482Chromium removal 480ndash484CIP See Cleaning in-placeClay nanoparticles 13ndash15Cleaning in-place (CIP) 350combating fouling 619process 350

Cloisite grades 13CM See Cation-selective membranecmc See Critical micelle concentrationCMCNa See Sodium carboxymethyl

celluloseCNT-BP membranes 265CNTs See Carbon nanotubesCo-ions 189 475Coagulation 93 424ndash425adsorption process 93ndash94sedimentation process 93

Coating wastewaters 597COD See Carbon oxygen demand

Chemical oxygen demand

Colloidal fouling 421ndash422 617Combating fouling 618ndash619Commercial ceramic applications 66ndash68Complete blocking 455Composite 48Composite membranes 3ndash10 See also

Nanocomposite membranespreparation via blending of polymers 4ndash5studies on 5tndash6tTFC membranes 6ndash10

Compound annual growth rate (CAGR) 83Concentrate stream 27ndash28Concentration gradient driven membrane

processes See also Electric potentialgradient driven membrane processes

amine functionalized MWCNTs 313fforward osmosis 294ndash317ICP 294ndash295pressured retarded osmosis 294ndash317

Concentration polarization (CP) 134ndash135379 383ndash384 454ndash455 523ndash524615ndash616

Conduction band (CB) 207Contact angle measurements (CAM)

212ndash213 363ndash364Conventional activated sludge (CAS) 590Conventional activated sludge process

(CASP) 444Conventional membrane materials 95ndash96Conventional pretreatment for SWRO

423ndash425Cooling water 605Cost assessment membrane technology

459CP See Concentration polarization4-CP See 4-chlorophenolCR filter See Cross-rotational filterCRF See Capital recovery factorCritical micelle concentration (cmc) 497Critical voltage gradient 526ndash527Cross-linked ZrT chelating membranes

291Cross-rotational filter (CR filter) 586 595CS See ChitosanCSTiO2 nano-composite membranes 270CTA See Cellulose triacetateCTACA flat sheet membranes 297CVD See Chemical vapor depositionCylindrical membranes 51ndash52 59ndash60

Index 627

DDABA See b-cyclodextrin polyurethaneDAF See Dissolved air flotationDAF test See Diffusive air flow testDairy industry wastewaters from 562ndash568Darcyrsquos law 85DBP See Disinfection byproductDCF See DiclofenacDCMD See Direct contact membrane

distillationDD See Donnan dialysisDeionized water (DI water) 342Demin water production 606Dense membranes 6ndash7Depressurized membrane PRs 219ndash220Desalination 130 412ndash413DF See Diafiltration24-DHBA See 24-dihydroxybenzoic acidDI water See Deionized waterDiafiltration (DF) 566Dialysis coupling of 222Diclofenac (DCF) 228ndash229Dielectric exclusion effect 396Diffusive air flow test (DAF test) 36824-dihydroxybenzoic acid (24-DHBA)

222Dimethylacetamide (DMAc) 11Dioxins 500ndash502Dip coating 55Direct contact membrane distillation

(DCMD) 221 258ndash261performance of single and dual-layer

hollow fiber membranes 262tndash264tDirect potable reuse project (DPR project)

338Direct testing methods 367 See also

Indirect testing methodsadvantages and disadvantages 367tAST 368DAF test 368PDT 367ndash368VDT 368

Disinfection byproduct (DBP) 63 90 487492ndash494

Dissolved air flotation (DAF) 334ndash335 595Dissolved organic carbon (DOC) 490Dissolved oxygen (DO) 540DMAc See DimethylacetamideDMF See Dual media filtration

DO See Dissolved oxygenDOC See Dissolved organic carbonDonnan dialysis (DD) 465 471ndash472

472fDonnan effect 381ndash383exclusion effect 395

Donnan-Steric-Pore model (DSPM) 395Double-walled nanotubes (DWNT) 10DPR project See Direct potable reuse

projectDraw solution (DS) 543Drinking water production 62ndash63DS See Draw solutionDSPM See Donnan-Steric-Pore modelDual media filtration (DMF) 425Dual-layer hydrophobichydrophilic hollow

fiber membranes 260fDual-layer PVDF hollow fiber membranes

259DWNT See Double-walled nanotubesDye recovery 542ndash545Dyno rotating disk module 108f

EEAC See Endocrine active compoundsED See ElectrodialysisED reversal (EDR) 472EDC See Endocrine disturbing compoundEDI See ElectrodeionizationEDR See ED reversal Electrodialysis

reversalEDS See Energy dispersive X-ray

spectroscopyEEA See European Environment AgencyEED See Electro-electrodialysisEffluents 519 587Electric fields 70Electric potential gradient driven membrane

processes See also Concentrationgradient driven membrane processes

AEMs 290BPMs 292ndash293CEMs 290ndash291electrodialysis 288ndash294 289fRED 288 289f 293ndash294

Electro-electrodialysis (EED) 482ndash483Electro-filtration 526ndash527Electro-spun nanofibrous membrane

(ENM) 268f

628 Index

Electrochemical separation techniques482ndash483

Electrodeionization (EDI) 330 483 484fElectrodialysis (ED) 185ndash186 287ndash290

289f 330 414 465 478 484f 556584ndash585 587ndash588

advances in membranematerials 192ndash194modules and system configurations194ndash197

anti-fouling properties 291applications 197ndash198with bipolar membranes 293fcross-linked ZrT chelating membranes

291Fe3O4 NPs 291ndash292membrane monovalent selectivity 290system design 293ndash294for water treatment 187ndash192

Electrodialysis reversal (EDR) 288 330414

Electrospinning method 267Electrospun nanofibrous membrane (ENM)

265ndash267Electrostatic repulsion 455EMBR-SRB See Extractive MBRs with

sulphate-reducing bacteriaEmerging contaminants 460ndash461Endocrine active compounds (EAC)

465ndash466 494ndash504Endocrine disturbing compound (EDC)

443 491 494ndash504Energy dispersive X-ray spectroscopy

(EDS) 366Energy recovery device (ERD) 426Engineered osmosis (EO) 288ENM See Electro-spun nanofibrous

membrane Electrospun nanofibrousmembrane

EO See Engineered osmosisEPS See Extracellular polymeric substancesEquipment failure rates 353ndash354ERD See Energy recovery deviceEthanol (EtOH) pervaporation performance

in 272tndash273tEuropean Environment Agency (EEA) 605European Union (EU) 431Extracellular polymeric substances (EPS)

164ndash165

Extractive MBRs with sulphate-reducingbacteria (EMBR-SRB) 479ndash480480f

Extrusion 54

FF-MWCNTs See Functionalized MWCNTsFA See Fulvic acidFeed solution (FS) 543FESEM See Field-emission scanning

electron microscopyFiberglass reinforces plastic (FRP) 339Fickrsquos law 384Field-emission scanning electron

microscopy (FESEM) 252f 365Fillers See Inorganic particlesFiltration 93ndash94Fish and seafood industryintegrated membrane process 560fwastewaters from 559ndash562

Flat membranes 50 58ndash59Flat sheet membranes 265 362Flocculation 94 424ndash425Fluorescent particle challenge testing 371Fluorides (Fndash) 468ndash469Fluorosilanization mechanism 266fFO See Forward osmosisFO MBR See Forward osmosis membrane

bioreactorFood and beverage industries 65ndash66Food processing industriesfood waste and origins 552twastewaters 551from dairy industry 562ndash568from fish and seafood industry 559ndash562from food and beverage industry556ndash557

food-processing 552from meat industry 569ndash572soybean 574ndash575winery 573ndash574

Forward flushing 68Forward osmosis (FO) 131ndash132 288 294

295f 306f 542ndash543 622ndash623See also Reverse osmosis (RO)

Ag NPs 317CA 297CA-based NF hollow fiber membrane297

Index 629

Forward osmosis (FO) (Continued)coated hydrolyzed commercial CACTA

306CTACA flat sheet membranes 297desalination 146ndash148double-skinned LbL membrane fabrication

316felectrospun nano-fibrous supports 312fundamentals of water treatment 136ndash142hollow fiber membranes 306ndash308internal concentration polarizationconcentrative 136ndash139dilutive 140quantitative analysis 140ndash142

membrane fabrication 314ndash315membranes for 142ndash146PA TFC flat sheet membrane 308ndash309PAN-OH 315polymer nano-composites 317researches on 298tndash305tTFC membranes 308TFC-FO membranes 308ndash310TFI membrane 317TFN membranes 312ndash314water flux direction and energy

consumptionproduction 296fForward osmosis membrane bioreactor

(FO MBR) 177ndash178Fouling 27 64 165 381ndash383 542 615

combating 618ndash619SW and BW 417ndash426types 615ndash618

Fractionation 197ndash198FRP See Fiberglass reinforces plasticFS See Feed solutionFTCS See 1H 1H 2H 2H-

perfluorododecyltrichlorosilaneFulvic acid (FA) 219Functionalized MWCNTs (F-MWCNTs)

312Furosemide 225

GGain output ratio (GOR) 412Galactoglukomannan (GGM) 597ndash598g-methacryloxypropyl trimethoxy silane

(g-MPS) 292ndash293Gas industry 519 See also Petrochemicals

industry

Gemfibrozil (GEM) 225ndash226GGM See GalactoglukomannanGlobal membrane market 83GOR See Gain output ratioGraphene oxide (GO) 243Greenrsquo process 205Ground water low-pressure membrane

applications 336ndash337

HHagenndashPoiseuille law 396Haloacetonitrile (HAN) 117Halogenated acetic acids (HAA) 117 490Halogenated aromatic hydrocarbons

500ndash502Haloketone (HK) 117HClO See Hypochlorous acidHeavy metals 476ndash480HEMA See 2-hydroxyethyl methacrylateHermiarsquos model 398Heterogeneous membranes 192Heterogeneous photocatalysis 205High-concentrated salt solution 428High-performancedual-layer PBIPEI hollow fiber

membranes 269TFC PRO membranes 311

High-pressure membranes 332 See alsoLow-pressure membranes

applications for water treatment brackishwater seawaterocean water 342

nanofiltration 338ndash339NFRO element and system 340fplanning and designing 342ndash344process application 476ndash478reverse osmosis 338 340ndash342contaminants removal rates 341f

SWRO 342technology 505ndash507

High-rate anaerobic reactor (HRAR) 170HK See HaloketoneHollow-fiber membranes 60 306ndash308

358Homogeneous polyelectrolyte complex

membrane (HPECM) 271ndash273HPEI See Hyperbranched polyethylenimineHRAR See High-rate anaerobic reactorHRT See Hydraulic residence timeHTI-CTA membranes 310 312

630 Index

Hydration Technology Innovations (HTI)428ndash429 543ndash544

Hydraulic model of filtration resistance 397Hydraulic residence time (HRT) 163 174Hydrodynamic cleaning methods 423Hydrodynamic or pore model 386Hydrophilic host polymers 265Hydrophilic surface modifying

macromolecules (LSMM) 9Hydrophobicity 4552-hydroxyethyl methacrylate (HEMA)

174ndash175Hyperbranched polyethylenimine (HPEI)

246Hypochlorous acid (HClO) 358

IIbuprofen (IBU) 227ndash228IC See In-line coagulationICIC See 5-isocyanatoisophthaloyl chlorideICP See Internal concentration polarizationIEM See Ion-selective exchange membraneIEMB See Ion-exchange MBRImmersed membrane bioreactor (iMBR)

156 448IMS See Integrated membrane systemsIn-line coagulation (IC) 93Indirect potable reuse project (IPR project)

338Indirect testing methods 368ndash369 See also

Direct testing methodsadvantages and disadvantages 369tfluorescent and magnetic particles

challenge testing 371PAC challenge testing 371particle counting 369ndash370particle monitoring 369ndash370phage and spore challenge testing

370ndash371turbidity monitoring 370

Industrial wastewater treatment 64ndash65Inorganic micropollutant removal 466

See also Organic micropollutantremoval

anion removal 466ndash476chromium removal 480ndash484heavy metals 476ndash480

Inorganic particles 244Integral membrane 49ndash50

Integrated low-pressure membrane process478ndash480

Integrated membrane systems (IMS) 90332 344 522

concentration polarization 523ndash524membrane fouling 524ndash525permeate flux 523ndash524

Interfacial polymerization (IP) 24 248ndash249257f

Intermediate blocking 457Internal concentration polarization (ICP)

294ndash295Ion exchange (IX) 94demin line using 611fdried-out resin 612fmembrane process 471ndash474 478operational experience 611ndash612technology 608 610

Ion-exchange MBR (IEMB) 475 476fIon-selective exchange membrane (IEM)

287 290Ionic strength 455IP See Interfacial polymerizationIPA See IsopropanolIPC See Isophthaloyl chlorideIPR project See Indirect potable reuse

projectIron oxide (Fe3O4) 291ndash292nanoparticles 22ndash23

5-isocyanatoisophthaloyl chloride (ICIC)7ndash8

Isophthaloyl chloride (IPC) 7ndash8Isopropanol (IPA) 269pervaporation performance 272tndash273t

IX See Ion exchange

KKubota flat-plate membrane cartridges 175Kubota Membrane Technology 557

LLayer-by-layer assembly (LbL assembly)

253ndash255LbL assembly See Layer-by-layer assemblyLeaky membrane model 186ndash187Limiting current density 190Liquid entry pressure (LEP) 261LMWC See Low-molecular-weight

compounds

Index 631

Log removal values (LRV) 351Low-concentration salt solution 428Low-molecular-weight compounds

(LMWC) 177Low-pressure membranes 332 See also

High-pressure membranesapplications for water treatment surface

water and ground water 336ndash337flat plate MFUF immersed membrane

trainbankbasin 334fhollow fiber MFUF membrane fibers 334fmicrofiltration 332ndash335microorganism removal 484ndash487planning and designing 337ndash338technological process 336fultrafiltration 332ndash333 335ndash336

LRV See Log removal valuesLSMM See Hydrophilic surface modifying

macromolecules

Mm-phenylenediamine (MPD) 7ndash8 250Magnetic ion-exchange resin (MIEX

resin) 491Magnetic particle challenge testing 371Maintainability of membrane filtration 355Mathematical modeling

of membrane operations 379ndash401MFUF membranes 396ndash401NF membranes 393ndash396RO membranes 384ndash393 387tndash390twater treatment process and trend

379ndash380MBA See N N0-Methylenebis(acrylamide)MBR See Membrane bioreactorMCR See Membrane coagulation reactorMD See Membrane distillationMean time between failure (MTBF) 353Mean time to failure (MTTF) 353Mean time to repair (MTTR) 354Meat industry

demonstration plant for 571fwastewaters from 569ndash572

Mechanical cleaning 423MED See Multiple effect distillationMEDINA See Membrane-based

desalination integrated approachMEDIRAS See Membrane Distillation in

Remote Areas

Membrane ageing 350assessment tools 362 363fchemical and structural characteristics364

filtration characteristics 362ndash363mechanical and thermomechanicalcharacteristics 364ndash365

membrane integrity tests 366ndash371morphological characteristics 365ndash366surface characteristics 363ndash364

control methods 371membrane modification 372ndash373membrane train redundancies 371ndash372

effects 351fmonitoring methods 362

Membrane bioreactor (MBR) 43ndash44 95155 443 448ndash450 474ndash476 552587 590ndash594 See alsoPhotocatalytic membrane reactor(PMR)

aerobic 160ndash168anaerobic 168ndash177configurations 156ndash158conventional wastewater treatment vs

446ndash450 449textractive 475fforward osmosis 177ndash178fouling mechanisms in 455ndash457membrane material types and morphology

158ndash159membrane module types 160technology 540

Membrane coagulation reactor (MCR) 469Membrane distillation (MD) 216 220ndash221

258ndash267 430ndash434 See alsoPervaporation (PV)

Membrane Distillation in Remote Areas(MEDIRAS) 432 432f

Membrane failure 351ndash352due to chemical attack 358ndash359due to excessive movement 359ndash362due to faulty membrane module structure

359membrane module failure 361tmodes 355ndash362 356tndash357t

Membrane filtration (MF) 349f 485ndash486552 587

applications for water treatment 349fdriving forces for 582ndash583

632 Index

future trends 373ndash374maintainability 355membrane ageing 350

control methods 371ndash373monitoring methods 362ndash371

membrane failure 351ndash352modes 355ndash362 356tndash357t

microporous and semipermeable 349reliability 352ndash355resilience 355in textile wastewater treatment 541ndash542

Membrane fouling 165in WWT 454ndash457

Membrane integrity tests 366ndash367direct testing methods 367ndash368indirect testing methods 368ndash371

Membrane technologies 329 443 559612ndash614

energy consumption of 530ndash531filtration spectrum 613fmicropollutants removal 465

inorganic micropollutant removal466ndash484

microorganism removal 484ndash491NOM 484ndash491organic micropollutant removal491ndash509

for municipal wastewater treatment444ndash445

in natural waters treatment 465operational experience with 614ndash615

fouling 615spiral-wound membrane 614fin wastewaters treatment 465for water treatment 521ndash522 521f

614ndash615Membrane Technology and Research Inc

(MTR) 47Membrane-based desalination integrated

approach (MEDINA) 432ndash433Membrane-based separation technologies

239Membrane(s) 84 239 479ndash480cleaning 457desalination 130ndash131fabrication techniques 239ndash241fibers 333with innovative materials 239ndash241lifetime 460

modification 3ndash4 372ndash373 525modules 359 451pretreatment 425ndash426processes 84ndash85 586ndash587barriers to 583recirculate process water 595ndash596

in pulp and paper industry 586ndash587resistance 454separation 206ndash207 333 522processes for water treatment 240tndash241t

stability 211ndash212train redundancies 371ndash372types and configurations 330 332fand water treatment processes 331f

Memstill process 431Metal ions 476ndash477MF See Membrane filtration

MicrofiltrationMicellar enhanced UF (MEUF) 482Microbial challenge testing 370Microfiltration (MF) 43 241ndash243 330

332ndash335 420ndash421 443 465 521552 612 See also Nanofiltration(NF) Reverse osmosis (RO)Ultrafiltration (UF)

Cryptosporidium parvum deformation486f

low-pressure membranes 333ndash335process 85 86t

Microfouling 617Microorganism removal 484ndash491by low-pressure membrane process

484ndash487using UF 486f

Micropollutants 465ndash466Micropollutants removalinorganic micropollutant removal 466ndash484membrane techniques 465microorganism removal 484ndash491NOM 484ndash491organic micropollutant removal 491ndash509

MIEX resin See Magnetic ion-exchangeresin

Miso (soybean paste) 574Mixed liquor suspended solids (MLSS)

163ndash164 444 556 591Mixed matrix membrane (MMM) 239ndash241Mixed matrix membranes See Composite

membranes

Index 633

MLSS See Mixed liquor suspended solidsMMM See Mixed matrix membraneModified FTCSndashTiO2ndashPVDF membranes

265Module 160Molecular weight (MW) 116ndash117 451Molecular weight cut-off (MWCO) 85ndash87

160 248ndash249 363 559MPD See m-phenylenediamineMSD system See Multi-shaft disk systemMSF distillation See Multistage flash

distillationMT See Multi-tubularMTBF See Mean time between failureMTR See Membrane Technology and

Research IncMTTF See Mean time to failureMTTR See Mean time to repairMulti-shaft disk system (MSD system) 108

109fMulti-tubular (MT) 451Multi-walled carbon nanotube (MWCNT)

100ndash101 250ndash251 259 291ndash292carboxy-functionalized 256

Multi-walled nanotube (MWNT) 9 12fMultiple effect distillation (MED) 412Multistage flash distillation (MSF

distillation) 412Municipal wastewater 63ndash64Municipal wastewater treatment membrane

technologies for See alsoMembranetechnologies

drivers and barriers to 444ndash445membrane modules 451membrane processdesign operation and control 458ndash459optimisation 459ndash460

membrane-assisted processes andtechnologies 445ndash446

pressure-driven membrane process 445funit operation and process 447tWWTmembrane fouling in 454ndash457membrane technologies operationalfactors 453ndash454

membrane-assisted system in 446ndash451MW See Molecular weightMWCNT SeeMulti-walled carbon nanotubeMWCO See Molecular weight cut-off

MWNT See Multi-walled nanotubeMycoestrogens 495

NN N0-Methylenebis(acrylamide) (MBA)

255N-methyl-2-pyrrolidone (NMP) 308NaBH4 See Sodium borohydrideNano-enhanced membranes See

Nanocomposite membranesNanocomposite membranes 10ndash25

See also Composite membranesAl2O3 nanoparticles 20ndash22clay nanoparticles 13ndash15CNT 10ndash13iron oxide nanoparticles 22ndash23silver nanoparticles 15ndash16SiO2 nanoparticles 23ndash24TiO2 nanoparticles 16ndash19ZnO nanoparticles 19ndash20ZrO2 nanoparticles 25

Nanofiltration (NF) 83 88ndash90 241248ndash251 288 330 445ndash446465ndash468 521 541ndash542 552 563t567t 584ndash585 612 See alsoMicrofiltration (MF) Reverseosmosis (RO) Ultrafiltration (UF)

applications 89ndash90NOM 487ndash489pesticide removal in 498tphthalates removal 500t

characteristics 453tfor flash cooler condensates treatment 565fhigh-pressure membranes 338ndash339for seawater desalination 111ndash115

Nanoparticles (NPs) 243 291ndash292Naphthalene-136-trisulfonylchloride

(NTSC) 250ndash251Natto (fermented soybean) 574Natural hormones 502ndash504Natural organic matter (NOM) 63 90 215

422 454 465ndash466 487 542 608MF 489ndash491MF UF and NF comparative assessment

488tNF application 487ndash489 489tRO application 487ndash489UF 489ndash491

NavierndashStokes equations 186ndash187

634 Index

Nephelometric turbidity units (NTU) 370420ndash421 484ndash485

Nernst-Planck equation 394Net flux 458ndash459NF See NanofiltrationNHE See Normal hydrogen electrodeNitrates 4674-nitrophenol (4-NP) 212NMP See N-methyl-2-pyrrolidoneNOM See Natural organic matterNormal hydrogen electrode (NHE)

208ndash209Novel functionalized PS-based BPM

292Novel membranes 239ndash241materials 98ndash104

NPs See Nanoparticles4-NP See 4-nitrophenolNTSC See Naphthalene-136-

trisulfonylchlorideNTU See Nephelometric turbidity units

OOampM cost See Operation and maintenance

costOD See Optical densityOil 519ndash520Oilndashwater emulsion 521ndash522OLR See Organic loading rateOM See Optical microscopyOMMT See Organically modified

montmorilloniteOperation and maintenance cost (OampM

cost) 426Optical density (OD) 545Optical microscopy (OM) 211ndash212Organiccompounds 454fouling 616matter 537

Organic loading rate (OLR) 164ndash165173ndash174 568

Organic micropollutant removal 491See also Inorganic micropollutantremoval

DBP 492ndash494EAC 494ndash504EDC 494ndash504oxidation 492ndash494

pharmaceutically active compounds504ndash509

Organically modified montmorillonite(OMMT) 14

Organicndashinorganic nano-composite GOPVDF-blended UF membranes 246

Osmosis 131ndash132osmotic pressure 384ndash385osmotic-based wastewater reduction

542ndash545 544f

Pp-phenylenediamine (PPD) 7ndash8PA See PolyamidesPA membranes See Polyaniline membranesPA TFC flat sheet membrane 308ndash309PAA See Polyacrylic acidPAAPEI multilayer PEC films 269PAC See Powdered activated carbonPAH See Poly(allylamine hydrochloride)

Polycyclic aromatic hydrocarbonPAI See Polyamide-imidePall Corporation Membralox multi-

channeled alumina membranes 5151f

PAN See PolyacrylonitrilePAN membrane substrate (PAN-OH) 315PANPET fibrous scaffold See

Polyacrylonitrilepolyethyleneterephthalate fibrous scaffold

PANI See PolyanilinePAO See Pressure-assisted osmosisPaperie du Rhin 592Particle counting 369ndash370Particle monitoring 369ndash370Particulate components 454Particulate fouling 420ndash421PAS See PolyarylsulfonePBI See PolybenzimidazolePC See PolycarbonatePCB See PolychlobiphenylPCP See PentachlorophenolPDA See PolydopaminePDMC See Poly(2-methacryloyloxy ethyl

tri-methylammonium chloride)PDMPs See Pressure-driven membrane

processesPDMS See PolydimethylsiloxanePDT See Pressure decay test

Index 635

PEC See Polyelectrolyte complexPECH See PolyepichlorohydrinPEG See Polyethylene glycolPEI See PolyethyleneiminePentachlorophenol (PCP) 1631H 1H 2H 2H-

perfluorododecyltrichlorosilane(FTCS) 265

Permeate flux 523ndash524 529Permeated water 529Permselectivity 189Pervaporation (PV) 222ndash223 267ndash273

See alsoMembrane distillation (MD)coupling 222ndash224performance of PECMs and IPA and EtOH

272tndash273tPES See PolyethersulfonePesticides 116ndash117Petrochemicals industry 519

design considerations 525ndash527energy consumption of membrane

operations 530ndash531IMS 522ndash525membrane technologies for water

treatment 521ndash522 521foperation optimization 528ndash529reuse in 521ndash522wastewater composition 520twastewater pretreatment 527ndash528

PEUF See Polymer-enhanced UFPEVP See Poly (N-ethyl-4-

vinylpyridiniumbromide)PFU counting See Plaque forming unit

countingpH value 455PhACs See Pharmaceutical active

compoundsPhage and spore challenge testing 370ndash371Pharmaceutical active compounds (PhACs)

224 443 504ndash509 508tPharmaceutical and personal care product

(PPCP) 504Pharmaceuticals 117Phase-inversion 24 54ndash58 214 267Phenolic xenoestrogenes 499ndash50013-phenylenediamine 415Phosphomolybdic acid (PMA) 271Photocatalysis 205

coupling 220ndash224

membrane materials development anddesign 211ndash217

principles 207ndash211Photocatalyst 205ndash211Photocatalytic membrane reactor (PMR)

205ndash206 See also Membranebioreactor (MBR)

advances in membrane modules and systemconfigurations 217ndash224

advantages and limitations 230applications 224ndash229for water treatment 207ndash217

Photoreactor (PR) 205ndash206Phthalates 499Physical cleaning 457chemical cleaning vs 458tmethods 68ndash69

Phytoestrogens 495PI See PolyimidePiperazine (PIP) 7ndash8Pitzer equation 384ndash385Plant protection products 497ndash499Plaque forming unit counting (PFU

counting) 370Plate-and-frame modules 106PMA See Phosphomolybdic acidPMR See Photocatalytic membrane reactorPNIPAAm See Poly(N-isopropylacrylamide)Poly (N-ethyl-4-vinylpyridiniumbromide)

(PEVP) 271ndash273Poly (sodium 4-styrenesulfate) (PSS)

253ndash255Poly(1-vinylpyrrolidone) (PVP) 245ndash246Poly(2-methacryloyloxy ethyl tri-

methylammonium chloride)(PDMC) 271ndash273

Poly(allylamine hydrochloride) (PAH) 291Poly(N-isopropylacrylamide) (PNIPAAm)

255Poly(sodium 4-styrene sulfonate) (PSS)

291Poly(VBC-co-g-MPS) 292ndash293Polyacrylic acid (PAA) 214 269Polyacrylonitrile (PAN) 4 96 212

310ndash311nano-fibrous support 314f

Polyacrylonitrilepolyethylene terephthalatefibrous scaffold (PANPET fibrousscaffold) 243

636 Index

Polyamide-imide (PAI) 249Polyamides (PA) 244Polyaniline (PANI) 290ndash291Polyaniline membranes (PA membranes)

7ndash8Polyarylsulfone (PAS) 244Polybenzimidazole (PBI) 269Polycarbonate (PC) 244Polychlobiphenyl (PCB) 500ndash502Polycyclic aromatic hydrocarbon (PAH)

495ndash497retention coefficients comparison 496t

Polydimethylsiloxane (PDMS) 267ndash269Polydopamine (PDA) 251 310ndash311Polyelectrolyte complex (PEC) 269Polyelectrolyte membranes (PECMs)pervaporation performance 272tndash273t

Polyepichlorohydrin (PECH) 293Polyethersulfone (PES) 4 48 96 244 248f

335Polyethylene glycol (PEG) 253Polyethyleneimine (PEI) 243 307 479Polyimide (PI) 16 244Polymer nano-composites 317Polymer-enhanced UF (PEUF) 469Polymeric membranes 211 See also

Ceramic membranesapplications for water treatment 27ndash28bio-inspired membranes 26ndash27composite membranes 3ndash10nanocomposite membranes 10ndash25nanostructured membranes 25ndash26

Polymers 96 97tPolypropylene (PP) 96 212Polysulfone (PS) 96 243 292Polytetrafluoroethylene (PTFE) 212ndash213

259ndash261hollow fiber membrane 261f

Polyvinyl alcohol (PVA) 4 253 290 470Polyvinyl chloride (PVC) 189 244Polyvinylamine (PVAm) 243Polyvinylidene difluoride (PVDF) 4 96

244 248f 314ndash315ENMs 268ffluorosilanization mechanism 266f

Poultry processing wastewater (PPW) 572Powdered activated carbon (PAC) 117 490challenge testing 371

PP See Polypropylene

PPCP See Pharmaceutical and personal careproduct

PPD See p-phenylenediaminePPW See Poultry processing wastewaterPR See PhotoreactorPrefiltration 91ndash93Pressing 53Pressure decay test (PDT) 352

367ndash368Pressure Exchanger (PX) 427Pressure retarded osmosis (PRO) 287 294

295f 428 429felectrospun nano-fibrous supports 312high-performance TFC PRO membranes

311PA-based TFC membranes 310ndash311researches on 298tndash305twater flux direction and energy

consumptionproduction 296fPressure vessel (PV) 339Pressure-assisted osmosis (PAO) 543Pressure-driven membrane processes

(PDMPs) 241 288 466ndash471 475fSee also Vapor pressure gradientdriven membrane processes

characteristics 242tmicrofiltration 242ndash243nanofiltration 248ndash251reverse osmosis 251ndash258triangle-shape tri-bore hollow fiber

membranes 245fultrafiltration 244ndash246

Pressure-driven process 210Pressurized membrane PRs 217ndash219Pretreatmentcombating fouling 618ndash619requirements 90MBR 95pretreatment methods 91ndash94SW and BW 417ndash426

PRO See Pressure retarded osmosisProduced water 65PS See PolysulfonePSS See Poly (sodium 4-styrenesulfate)

Poly(sodium 4-styrene sulfonate)PTFE See PolytetrafluoroethylenePulp and paper industry 581demands for membranes and modules in

584

Index 637

Pulp and paper industry (Continued)driving forces for membrane filtration

582ndash583membranes process 586ndash587barriers to 583recirculate process water 595ndash596

module configurations 585ndash586pressure-driven membrane process 585fraw water purification 598selectivity 584ndash585total emission to waterways and reduction

582twastewaters purification 587ndash595watercharacteristic properties 583ndash584valuable byproducts recovery andpurification 596ndash598

Pulsed flow 525PV See Pervaporation Pressure vesselPVA See Polyvinyl alcoholPVAm See PolyvinylaminePVC See Polyvinyl chloridePVDF See Polyvinylidene difluoridePVDF-hexafluoropropylene (PVDF-HFP)

14PVDF-HFP See PVDF-

hexafluoropropylenePVDFMg(OH)2ndashMF hybrid membranes

243PVP See Poly(1-vinylpyrrolidone)PVP-grafted SiO2 NPs 245ndash246 247fPX See Pressure Exchanger

RRanitidine 225Raw water

purification 598source 606ndash608

RB5 dye See Reactive black 5 dyeRE See Reverse electrodialysisReactive black 5 dye (RB5 dye) 214Reactive dyes 538Reactive monomers 7ndash8Recirculate process water 594ndash595RED See Reverse electrodialysisReliability of membrane filtration 352ndash355

availability 354ndash355equipment failure rates 353ndash354MTTF and MTBF 353

Reverse electrodialysis (RE) 428ndash430RE-SGP investigations 430

Reverse electrodialysis (RED) 287membrane unit 288 289fperformances 293system design 293ndash294

Reverse osmosis (RO) 130ndash132 241251ndash258 288 295f 329 330445ndash446 465ndash468 521 541ndash542552 563t 567 584ndash585 608See also Forward osmosis (FO)Microfiltration (MF) Nanofiltration(NF) Ultrafiltration (UF)

characteristics 453tconventional and membrane pretreatment

135ndash136electroplating process line integration with

477ffundamentals of water treatment 132ndash135high-pressure membranes 338 340ndash342contaminants removal rates 341f

in meat wastewater treatment 570tmembrane process 329 330fmembranes 613ndash614NOM 487ndash489pesticide removal in 498tphthalates removal 500ttwo-stage system for boron removal 470fwater flux direction and energy

consumptionproduction 296fReversible fouling 397RO See Reverse osmosisRotating cylinders 526Rotating disk module systems 108Rotatingvibrating membranes 526

SSAA See Surface active agentSalinity gradient power (SGP) 287

429ndash430Scaling 454 617ndash618Scanning electron microscopy (SEM)

211ndash212 365SDBS See Sodium dodecylbenzene

sulfonateSDI See Silt density indexSeawater (SW) 411 413fdesalination 342plants 344

638 Index

energy from 427ndash433fouling 417ndash426high-pressure membrane applications

342MD economics 433ndash434pretreatment strategies 417ndash426product specifications of 419tRO 420f

energy requirements for 426ndash427membranes and modules 415ndash417principle 414

standard composition 413tSeawater reverse osmosis (SWRO) 342SEM See Scanning electron microscopySewage treatment 63ndash64Sewage treatment plants (STP) 224SGMD See Sweeping gas membrane

distillationSGP See Salinity gradient powerSHMP See Sodium hexametaphosphateShoyu (soy sauce) 574SHP model See Steric hindrance pore modelSiC SteriMem products 51 51fSide-stream membrane bioreactor (sMBR)

156 448Silica (SiO2) 243 245ndash246nanoparticles 23ndash24PVP-grafted 245ndash246

Silt density index (SDI) 92 423Silver ions 16Silver nanoparticles 15ndash16Single-walled carbon nanotubes (SWCNT)

101Single-walled nanotubes (SWNT) 10Sintering 54ndash58SiO2ndashGO nanohybridPS membrane 243SL See Sludge loadingSlip casting 53Slow sand filtration (SSF) 425Sludge loading (SL) 164ndash165Sludge retention time (SRT) 164 174sMBR See Side-stream membrane

bioreactorSMBS See Sodium metabisulphiteSMM See Surface modifying

macromoleculeSMP See Soluble microbial productsSMPR See Submerged membrane

photocatalytic reactor

Sodium borohydride (NaBH4) 261Sodium carboxymethyl cellulose (CMCNa)

271ndash273Sodium dodecylbenzene sulfonate (SDBS)

291Sodium hexametaphosphate (SHMP) 425Sodium hypochloride (NaOC) 539ndash540Sodium metabisulphite (SMBS) 425Sol-gel method 55Solids retention time (SRT) 444 556Soluble microbial products (SMP) 164Solute flux 384Solutiondiffusion mechanism 210 414Solvay Advanced Polymers See Torlon

4000T-MV PAISoybean wastewater 574ndash575 575fSparging See Air flushingSPEEK See Sulfonated

polyetheretherketoneSPEK polymer See Sulphonated poly(ether

ketone) polymerSPES See Sulfonated polyethersulfoneSpiegler-Kedem model 385Spin coating See Dip coatingSpinning parameters 56Spintek module 109fSpiral-wound module (SWM) 385

415ndash417 586SPPS membrane See Sulfonated

polyphenylenesulfone membraneSPTA See Sulfophthalic acidSRT See Sludge retention time Solids

retention timeSSF See Slow sand filtrationStable oily emulsion 519ndash520Standard blocking 457Steric effect 395Steric hindrance pore model (SHP model)

386STP See Sewage treatment plantsSubmerged MBR See Immersed membrane

bioreactor (iMBR)Submerged membrane bioreactor 156Submerged membrane photocatalytic

reactor (SMPR) 213 219Submerged membrane PRs See

Depressurized membrane PRsSulfonated polyetheretherketone (SPEEK)

293

Index 639

Sulfonated polyethersulfone (SPES)244ndash245 290

Sulfonated polyphenylenesulfonemembrane (SPPS membrane)309ndash310

Sulfophthalic acid (SPTA) 269ndash270Sulphonated poly(ether ketone) polymer

(SPEK polymer) 7ndash8 309Surface active agent (SAA) 497Surface hydrophilicity 363ndash364Surface modifying macromolecule (SMM)

265Surface topography modification 256ndash258Surface water low-pressure membrane

applications 336ndash337Suspended fouling 617SW See SeawaterSWCNT See Single-walled carbon

nanotubesSweeping gas membrane distillation

(SGMD) 258SWM See Spiral-wound moduleSWNT See Single-walled nanotubesSWRO See Seawater reverse osmosisSynthetic hormones 502ndash504

TTamoxifen (TAM) 225ndash226Tape casting method 53TDS See Total dissolved solidsTemperature 529TEMPO-oxidized cellulose nanofibrils

(TOCNs) 244Teorell-Meyer-Sievers model (TMS model)

386Tetraethoxysilane (TEOS) 23ndash24Textile industry 537

in batch process 537ndash538dyeingprinting textiles 538textile sizing agents 537

Textile processing 537Textile sizing agents 537Textile wastewater 538 539t

treatment 539membrane filtration in 541ndash542osmotic-based wastewater reduction542ndash545

potential dye recovery 542ndash545TFC See Thin-film composite

TFC RONF membranes 256ndash258TFI membrane See Thin-film inorganic

membraneTFN membranes See Thin-film

nanocomposite membranesTGA See Thermogravimetric analysisThermal desalination 130ndash131 412Thermal vapour compression (TVC) 412Thermogravimetric analysis (TGA) 365

366fThermolysis 54Thin-film composite (TFC) 95 415layer 248ndash249membranes 6ndash10 360ndash362 543ndash544RO membrane 254fTFC-FO membranes 7ndash8 308ndash310

Thin-film inorganic membrane (TFImembrane) 317

Thin-film nanocomposite membranes (TFNmembranes) 101 250ndash251312ndash314 313f

THM See TrihalomethaneThree-compartment EED 482ndash483 483fTiO2 nanoparticles See Titanium dioxide

nanoparticlesTitanium dioxide nanoparticles (TiO2

nanoparticles) 16ndash19TMC See Trimesoyl chlorideTMP See Transmembrane pressureTMS model See Teorell-Meyer-Sievers

modelTOC See Total organic carbonTOCNs See TEMPO-oxidized cellulose

nanofibrilsTofu (soybean curd) 574Torlon 4000T-MV PAI 269Total dissolved solids (TDS) 129 192ndash193

338 416ndash417Total organic carbon (TOC) 90 206

334ndash335 556 608Total suspended solids (TSS) 446 539 551Transmembrane pressure (TMP) 156

219ndash220 446 453ndash454 556 616Transport mechanisms 381ndash383Transport number of component 189Trihalomethane (THM) 93ndash94 485Trimesoyl chloride (TMC) 7ndash8 249 308TSS See Total suspended solidsTurbidity monitoring 370

640 Index

TVC See Thermal vapour compressionTwo cation-exchange membranes 483ndash484

UUF See UltrafiltrationUgchelen BV 592Ultrafiltration (UF) 43 83 85ndash88 86t 241

244ndash246 330 332ndash333 420ndash421443 465 521 541 552 567t 572612 See also Microfiltration (MF)Nanofiltration (NF) Reverseosmosis (RO)

fishery washing waters 559ndash560low-pressure membranes 335ndash336in meat wastewater treatment 570tphthalates removal 500t

Ultrapure water (UPW) 342 612Ultrasonic fields 70Ultrasound 527Ultraviolet irradiation (UV irradiation)

211ndash212 244ndash245 485 556ndash557Unconventional physical cleaning methods

69ndash70United States (US) 83United States Environmental Protection

Agency (USEPA) 520ndash521Unmodified montmorillonites 13UPW See Ultrapure waterUS See United StatesUSEPA See United States Environmental

Protection AgencyUV irradiation See Ultraviolet irradiation

VVacuum decay test (VDT) 368Vacuum membrane distillation (VMD)

258ndash261Vacuum-enhanced direct contact membrane

distillation (VEDCMD) 148Valence band (VB) 207Vanrsquot Hoff equation 384ndash385Vapor pressure gradient driven membrane

processes See also Pressure-drivenmembrane processes (PDMP)

membrane distillation 258ndash267pervaporation 267ndash273

VB See Valence bandVBC See Vinylbenzyl chlorideVCR See Volume concentration ratio

VDT See Vacuum decay testVEDCMD See Vacuum-enhanced direct

contact membrane distillationVeolia Water Ltd CeraMem element 51

51fVibrating module systems 108Vibrating shear-enhanced processing

(VSEP) 108 110f 585ndash586Vinylbenzyl chloride (VBC) 292ndash2934-vinylpyridine (4-VP) 290Viscous fingering 56ndash57VMD See Vacuum membrane distillationVolume concentration ratio (VCR)

562ndash564Volumetric permeate flux 5244-VP See 4-vinylpyridineVSEP See Vibrating shear-enhanced

processing

WWastewater 479ndash480 519 551compounds 519from dairy industry 562ndash568direct membrane filtration for 594ndash595from fish and seafood industry 559ndash562from food and beverage industry

556ndash557food-processing 552from meat industry 569ndash572pretreatment 527ndash528purificationdirect membrane filtration forwastewaters 594ndash595

membrane process 587ndash594textile 538ndash545

Wastewater treatment (WWT) 43ndash44583ndash584 See also Pulp and paperindustry

membrane fouling in 454ndash457membrane process with biological WWT

587improving functionality 589ndash590MBR 590ndash594 593tupgrade purification 587ndash589

membrane technologies operational factors453ndash454

membrane-assisted system 446conventional treatments vs MBR446ndash450

Index 641

Wastewater treatment (WWT) (Continued)NFRO after biological treatment450ndash451

Water (H2O) 411 540 551 581 605characteristic properties 583ndash584contamination 485flux 384ldquofootprintrdquo 582ndash583noncompliancy 355ndash358operational experience with membrane

614ndash615fouling 615

pollution 206purification 3hydration bag 144f

purification technologies 608ndash614quality 581raw water source 606ndash608requirements 606

recovery 564shortages 129stream 605ndash606cycle 605ndash606 607f

temperature 391turbidity 484ndash485valuable byproducts recovery and

purification 596ndash598water capture evaporation 622

Water permeation flux (WPF) 211ndash212Water treatment 43

advancesin membrane materials 95ndash104in polymeric membranes 3ndash27

applications 110membranes for groundwater treatment110ndash111

membranes for harvesting rainwater 116nanofiltration for seawater desalination111ndash115

specific contaminant removal 116ndash117surface water treatment 110

ceramic membranes 44concentration gradient driven membrane

processes 294ndash317electric potential gradient driven membrane

processes 288ndash294future trends 28 274 318ndash319 345global membrane market 83

high-pressure membranes 332applications 338ndash342

IMS 90integrated membrane systems 344low-pressure membranes 332applications 332ndash337planning and designing 337ndash338

membrane filtrationapplications 349 349ftechnology 84

membrane(s)modules and system configurations106ndash108

processes 84ndash85separation processes 240tndash241ttreatment combination 344ndash345types and configurations 330 332fand water treatment processes 331f

MF process in 43ndash44microfiltration process 85 86tNF 88ndash90PDMPs 241ndash258pretreatment requirements 90ndash95RO 132ndash135UF process 43ndash44 85ndash88 86tvapor pressure gradient driven membrane

processes 258ndash273Whey protein concentrate (WPC) 566Wilke-Chang equation 140ndash141Winery wastewater 573ndash574World Health Organization (WHO) 411

466WPC See Whey protein concentrateWPF See Water permeation fluxWWT See Wastewater treatment

ZZeolites 98Zinc oxide nanoparticles (ZnO

nanoparticles) 19ndash20Zirconium dioxide nanoparticles (ZrO2

nanoparticles) 25Zirconium tri-ethylene tetra-amine (ZrT)

291Zwitterionic materials 253

642 Index

  • Basile Copyrightspdf
    • Copyright
Page 3: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 4: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 5: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 6: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 7: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 8: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 9: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 10: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 11: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 12: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 13: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 14: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 15: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 16: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 17: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 18: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 19: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 20: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 21: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 22: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 23: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 24: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 25: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 26: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 27: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 28: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 29: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 30: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 31: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 32: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 33: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 34: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 35: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 36: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 37: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 38: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 39: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 40: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 41: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 42: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 43: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 44: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 45: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 46: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 47: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 48: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 49: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 50: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 51: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 52: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 53: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 54: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 55: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 56: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 57: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 58: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 59: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 60: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 61: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 62: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 63: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 64: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 65: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 66: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 67: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 68: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 69: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 70: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 71: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 72: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 73: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 74: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 75: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 76: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 77: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 78: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 79: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 80: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 81: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 82: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 83: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 84: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 85: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 86: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 87: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 88: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 89: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 90: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 91: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 92: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 93: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 94: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 95: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 96: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 97: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 98: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 99: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 100: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 101: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 102: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 103: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 104: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 105: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 106: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 107: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 108: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 109: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 110: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 111: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 112: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 113: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 114: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 115: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 116: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 117: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 118: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 119: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 120: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 121: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 122: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 123: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 124: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 125: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 126: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 127: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 128: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 129: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 130: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 131: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 132: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 133: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 134: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 135: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 136: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 137: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 138: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 139: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 140: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 141: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 142: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 143: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 144: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 145: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 146: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 147: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 148: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 149: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 150: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 151: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 152: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 153: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 154: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 155: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 156: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 157: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 158: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 159: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 160: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 161: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 162: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 163: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 164: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 165: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 166: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 167: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 168: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 169: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 170: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 171: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 172: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 173: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 174: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 175: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 176: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 177: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 178: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 179: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 180: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 181: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 182: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 183: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 184: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 185: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 186: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 187: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 188: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 189: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 190: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 191: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 192: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 193: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 194: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 195: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 196: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 197: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 198: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 199: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 200: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 201: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 202: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 203: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 204: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 205: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 206: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 207: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 208: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 209: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 210: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 211: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 212: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 213: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 214: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 215: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 216: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 217: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 218: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 219: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 220: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 221: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 222: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 223: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 224: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 225: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 226: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 227: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 228: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 229: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 230: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 231: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 232: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 233: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 234: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 235: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 236: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 237: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 238: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 239: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 240: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 241: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 242: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 243: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 244: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 245: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 246: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 247: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 248: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 249: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 250: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 251: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 252: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 253: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 254: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 255: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 256: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 257: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 258: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 259: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 260: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 261: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 262: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 263: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 264: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 265: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 266: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 267: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 268: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 269: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 270: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 271: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 272: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 273: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 274: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 275: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 276: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 277: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 278: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 279: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 280: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 281: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 282: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 283: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 284: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 285: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 286: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 287: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 288: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 289: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 290: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 291: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 292: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 293: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 294: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 295: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 296: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 297: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 298: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 299: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 300: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 301: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 302: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 303: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 304: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 305: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 306: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 307: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 308: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 309: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 310: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 311: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 312: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 313: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 314: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 315: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 316: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 317: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 318: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 319: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 320: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 321: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 322: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 323: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 324: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 325: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 326: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 327: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 328: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 329: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 330: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 331: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 332: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 333: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 334: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 335: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 336: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 337: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 338: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 339: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 340: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 341: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 342: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 343: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 344: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 345: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 346: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 347: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 348: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 349: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 350: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 351: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 352: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 353: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 354: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 355: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 356: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 357: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 358: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 359: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 360: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 361: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 362: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 363: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 364: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 365: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 366: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 367: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 368: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 369: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 370: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 371: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 372: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 373: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 374: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 375: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 376: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 377: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 378: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 379: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 380: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 381: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 382: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 383: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 384: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 385: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 386: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 387: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 388: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 389: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 390: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 391: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 392: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 393: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 394: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 395: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 396: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 397: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 398: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 399: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 400: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 401: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 402: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 403: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 404: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 405: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 406: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 407: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 408: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 409: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 410: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 411: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 412: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 413: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 414: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 415: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 416: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 417: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 418: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 419: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 420: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 421: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 422: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 423: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 424: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 425: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 426: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 427: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 428: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 429: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 430: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 431: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 432: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 433: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 434: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 435: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 436: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 437: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 438: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 439: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 440: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 441: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 442: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 443: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 444: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 445: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 446: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 447: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 448: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 449: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 450: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 451: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 452: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 453: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 454: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 455: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 456: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 457: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 458: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 459: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 460: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 461: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 462: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 463: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 464: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 465: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 466: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 467: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 468: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 469: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 470: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 471: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 472: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 473: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 474: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 475: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 476: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 477: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 478: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 479: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 480: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 481: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 482: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 483: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 484: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 485: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 486: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 487: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 488: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 489: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 490: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 491: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 492: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 493: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 494: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 495: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 496: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 497: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 498: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 499: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 500: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 501: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 502: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 503: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 504: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 505: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 506: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 507: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 508: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 509: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 510: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 511: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 512: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 513: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 514: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 515: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 516: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 517: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 518: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 519: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 520: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 521: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 522: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 523: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 524: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 525: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 526: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 527: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 528: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 529: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 530: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 531: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 532: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 533: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 534: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 535: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 536: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 537: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 538: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 539: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 540: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 541: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 542: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 543: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 544: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 545: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 546: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 547: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 548: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 549: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 550: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 551: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 552: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 553: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 554: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 555: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 556: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 557: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 558: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 559: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 560: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 561: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 562: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 563: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 564: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 565: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 566: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 567: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 568: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 569: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 570: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 571: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 572: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 573: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 574: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 575: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 576: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 577: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 578: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 579: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 580: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 581: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 582: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 583: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 584: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 585: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 586: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 587: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 588: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 589: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 590: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 591: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 592: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 593: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 594: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 595: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 596: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 597: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 598: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 599: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 600: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 601: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 602: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 603: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 604: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 605: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 606: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 607: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 608: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 609: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 610: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 611: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 612: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 613: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 614: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 615: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 616: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 617: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 618: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 619: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 620: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 621: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 622: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 623: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 624: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 625: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 626: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 627: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 628: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 629: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 630: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 631: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 632: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 633: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 634: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 635: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 636: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 637: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 638: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 639: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 640: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier
Page 641: Advances in Membrane Technologies for Water Treatment – Materials, Processes and Applications; Volume 75 of Woodhead Series in Energy - Elsevier