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Separation and Purification Technology 62 (2008) 249–263

Review

Research and applications of membrane bioreactorsin China: Progress and prospect

Zhiwei Wang a,∗, Zhichao Wu a, Suihai Mai b, Caifeng Yang c,Xinhua Wang a, Ying An a, Zhen Zhou a

a State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering,Tongji University, Shanghai 200092, PR China

b Operation and Management of Wastewater of South Shanghai Municipality Co., Ltd., Shanghai 201203, PR Chinac Shanghai Bailonggang Wastewater

Treatment Plant, Shanghai 201201, PR China

Received 21 September 2007; received in revised form 16 December 2007; accepted 27 December 2007

bstract

In the past 15 years, remarkable progress has been achieved on the research and commercial applications of membrane bioreactor (MBR)echnology in China. The objective of this paper is then to critically review the research achievements and to specifically present commercialpplications of MBR in China. A total of 722 scientific papers published in peer-reviewed journals (600 Chinese papers and 122 English papers)ritten by Chinese authors from 1991 to 2006 and 254 full-scale MBR plants constructed in China were used as the analysis database. The numberf articles published in journals together with organizations involved in MBR research saw a significant increase from 2001 to 2006, and muchesearch progress was made during this period. From geographic distribution of these studies, it was found that the majority of the studies werearried out in North China, East China and North-East China. The research mainly focused on biomass separation MBR (BSMBR) with limitedtudies on extractive MBR (EMBR) and membrane aeration bioreactor (MABR), etc., and research contents included MBR configuration and type,embrane material and module, membrane fouling and control, characteristics of various wastewater treatment and other aspects like gas removal

nd microbial fermentation, etc. For commercial applications in China, a total of 254 MBR plants for municipal and industrial wastewater treatmentere constructed by a lot of home-grown companies such as Tianjin Motimo Membrane Technology Co., Ltd. and Beijing Origin Water Technology

o., Ltd. and overseas-funded companies like Toray (Japan), Zenon (Canada), Mitsubishi-Rayon (Japan), etc. MBR plants with large treatmentapacity will be built in future especially in North China due to the great need of water reclamation and reuse. Potential areas of MBR applicationnclude surface/drinking water treatment, gas diffusion and removal, membrane assisted fermentation for biological substance transformation androduction, etc.

2008 Elsevier B.V. All rights reserved.

eywords: Membrane bioreactor (MBR); Wastewater treatment; Drinking water treatment; Critical review; Commercial application

ontents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2502. Research of MBR technology in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250

2.1. Chronological distribution of these studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2502.2. Geographic distribution of these studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2512.3. Organizations involved in MBR research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

2.4. Research areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.4.1. Fundamental information of these studies . . . . . . . . . .2.4.2. Research contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.5. Comparison of research characteristics in China and those in t

∗ Corresponding author. Tel.: +86 21 65980400; fax: +86 21 65980400.E-mail addresses: zhiweiwang tongji@yahoo.com.cn (Z. Wang), wuzhichao@ma

383-5866/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2007.12.014

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254he world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256

il.tongji.edu.cn (Z. Wu).

250 Z. Wang et al. / Separation and Purification Technology 62 (2008) 249–263

3. Commercial applications in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2573.1. MBR providers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2573.2. MBR plants in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

3.2.1. Geographic distribution of MBR plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2573.2.2. Distribution of MBR plant scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

3.3. MBR commercial application in future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2583.4. Comparison of commercial application of MBR in China and that in the world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

4. Future prospect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2584.1. Existing challenges of the technology in China . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

4.1.1. MBR market share . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2594.1.2. MBR standardization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2594.1.3. Membrane fouling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2594.1.4. Membrane lifespan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2594.1.5. Cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2594.1.6. Large-scale MBR operational experiences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

4.2. Resolution measure analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2594.3. Future development trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

5. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. Introduction

In recent years, membrane bioreactor (MBR) process hasained worldwide attraction and popularity for the treatmentf municipal/domestic wastewater [1], industrial wastewater [2]nd surface/drinking water [3]. MBR are considered as a goodntegration of conventional activated sludge (CAS) system anddvanced membrane separation, thus enabling the independentontrol of sludge retention time (SRT) and hydraulic retentionime (HRT) and retaining a high concentration of sludge biomassn the reactors. Compared with CAS processes, MBR processas great advantages including a smaller footprint, less sludgeroduction and better effluent quality [4,5].

China’s research on MBR technology started in 1991. Chen6] published the first paper on MBR technology in Chinese jour-als and introduced the application of MBR for the treatmentf wastewater in other countries. Since then, some universitiesnd research institutes have involved in MBR research includ-ng Tongji University, Tsinghua University, Chinese Academyf Sciences, Tianjin University, Zhejiang University and Harbinnstitute of Technology, etc. In order to promote developmentnd application of MBR in wastewater treatment and reclama-ion, Ministry of Science and Technology (MOST) of Chinanancially supported Research and Development Project onBR from 1996 under the national 9th “5-year-plan” and from

002 under the national high-tech development plan (“863”roject). During this period, a number of home-grown andverseas-funded companies emerged and dedicated their effortso the MBR application in Chinese market. To date, muchrogress has been achieved both on research and practical appli-ations of MBR in China.

With the rapid development of MBR technology, a detailed

nalysis and review of past academic research progress could bealuable. Furthermore, the analysis of development trend androspect of China’s MBR technology can also be of interest tondividuals and companies involved in MBR sector. This paper

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

s then expected to provide the recent research and applicationrogress and future development trend of MBR technology inhina by critically reviewing the research achievements and by

pecifically presenting commercial applications in China.

. Research of MBR technology in China

Eight online databases including Web of Science, Elsevier,luwer Online, Taylor & Francis, Proquest, American Chem-

cal Society (ACS) and John Wiley were searched for Englishapers written by Chinese researchers and two Chinese onlineatabases, National Knowledge Infrastructure of China (CNKI)nd Vip Information Periodical (VIP), used for the search ofhinese papers on MBR study. A total of 722 scientific papersublished in peer-reviewed journals from 1991 to 2006, includ-ng 600 Chinese papers and 122 English papers, were collectednd used as the analysis database. It should be pointed out thathis collection of papers might not be complete despite the inten-ive efforts by the authors to locate all relevant publications on

BR research in China.

.1. Chronological distribution of these studies

The chronological distribution of published Chinese andnglish peer-reviewed articles written by Chinese authors isresented in Figs. 1 and 2, respectively. It can be seen fromig. 1 that there were very few Chinese journal papers publishedntil the late 1990s although the MBR concept was developedy USA Dorr-Oliver Inc. as early as 1966 [2]. Three differ-nt stages could be observed in the Chinese article variations:rom 1991 to 1995, it is an entry-level stage during which fewapers, mostly review papers, were published to introduce the

BR concept; the intermediate level stage, from 1996 to 2000,as featured by an increase in the paper outputs and by the

mergence of original research papers probably attributed toesearch and Development Project on MBR initiated by China

Z. Wang et al. / Separation and Purification Technology 62 (2008) 249–263 251

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ig. 1. Chronological distribution of peer-reviewed Chinese journal articles onBR research.

OST under the national 9th “5-year-plan”; the MBR researchn China underwent a rapid development in the third stage from001 to 2006 with a significant increase in the number of arti-les published in journals. In the year of 2005, the number ofhinese articles surprisingly reached 141, as shown in Fig. 1,

ncluding 111 research papers and 30 review papers.The first English research paper [7] written by Chinese

uthors, which studied a MBR system comprising a fermenternd a flat pervaporation module for continuous ethanol fer-entation by Saccharomyces cerevisiae, was published in the

eer-reviewed journal, Biotechnology Techniques, in 1995. Alight increase can be observed after 1998, and in 2003 theumber of English articles on MBR research totaled 15. A sig-ificant jump occurred between 2004 and 2005, and the numberf English articles reached 35–40 in the last 2 years whereas itas just in the range of 1–7 before 2005 except for 15 in 2003.nother characteristic different from the published Chinese arti-

les is that only one article of 2006 is a review paper while theest 121 papers are all original research papers.

The chronological distribution of the published articles indi-ates that MBR technology has drawn more and more attentionf individuals and research organizations in China in recentears. The large number of publications is also a good indi-ator of a great many highly qualified personnel currently being

nvolved and trained in the field of MBR technology. If theumber of articles continues to climb, significant progress inpplication areas could be expected.

ig. 2. Chronological distribution of peer-reviewed English journal articles writ-en by Chinese authors.

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Fig. 3. Geographic distribution of the studies on MBR.

.2. Geographic distribution of these studies

The distribution of English papers, Chinese papers and theotal numbers in eight regions according to Chinese Adminis-ration Division (CAD) is shown in Fig. 3. It can be observedhat the seven regions of mainland and the Special Administra-ive Regions (SARs, including Hongkong, Macao and Taiwanrovince) all have been involved in MBR research; however,ver 80% of all the studies were carried out in North ChinaNC), East China (EC) and North-East China (NEC) while theublications of the rest five regions (Central China (CC), South-est China (SWC), North-West China (NWC), South China

SC) and SARs) only accounted for less than 20% of the total.In China, water resources are rich in the south and east and

oor in the north and west [8], and 400 cities out of 669 areuffering the shortage of water due to the extremely unevenegional distribution. The geographic distribution of the stud-es on MBR, as shown in Fig. 3, indicates that a great numberf scientists and researchers in the North and the North-Easthina, where are undergoing the shortage of water resources,ave dedicated their efforts to MBR research attributed to therocess’s prominent advantages in water reclamation and reuse.lthough in East China it is not short of water resources, inten-

ive efforts were also made to the study of MBR technologyor wastewater treatment in numerous cities, mostly developedostal cities, due to the increasingly stringent effluent standardsequired by the local government, the soaring price of tap water,nd the improvement of citizen’s environment protection con-ciousness. It is worth pointing out that the research obviouslyagged behind and more financial support and human resourcesre needed in the vast underdeveloped areas of West China whereave been facing the severe crisis of water resources.

.3. Organizations involved in MBR research

Fig. 4 shows the variation of universities, companies andnstitutes involved in the study on MBR technology. It can beeen that the variation of organizations involved in MBR studys similar to that of published Chinese journal papers as shown

n Fig. 1. It can be also observed that universities were dominantmong the organizations, and after 1999 a number of companiesnd institutes, such as Tianjin Motimo Membrane Technologyo., Ltd., Tianjin Tsinghua Daring Co., Ltd., Beijing Origin

252 Z. Wang et al. / Separation and Purification Technology 62 (2008) 249–263

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armixed liquor turbulence, was developed by Wu and Wang in2004 [14]. The schematic diagram of the SAMBR is shownin Fig. 7. Since 2004, many efforts [15–19] have been dedi-

Fig. 4. Variations of organizations involved in these studies.

ater Technology Co., Ltd., Chinese Academy of Sciences andangzhou Development Center of Water Treatment Technol-gy, etc. joined in the research and dedicated their efforts to theevelopment of MBR technology.

.4. Research areas

The 722 total publications are classified into two groupshich are 174 critical review papers and 548 original researchapers. The 548 research papers are then analyzed and reviewedrom two major perspectives: (1) to analyze and discuss theundamental information of these studies through investigat-ng the MBR configuration, MBR type and membrane materialnd module of these studies; (2) to characterize the researchontents by grouping them into membrane fouling and control,BR for different water and wastewater treatment and other

spects which include microbial fermentation, gas removal andiffusion, etc.

.4.1. Fundamental information of these studies

.4.1.1. MBR configuration. MBR systems are generallyomprised of two configurations: submerged (immersed or inte-rated) MBRs and side-stream (recirculated or external) MBRs.amamoto et al. [9] were the first to put forward the conceptf submerged MBRs by introducing submerged membranes inn aeration tank for solid/liquid separation in 1989. SubmergedBRs consume much less power than side-stream MBRs due to

he absence of a high-flow recirculation pump. Compared withide-stream MBR, submerged MBR is more popular in water andastewater treatment because of its lower operational cost. It isorth noting that a modified side-stream MBR (also called as

irlift external circulation MBR, AEC-MBR) as schematicallyhown in Fig. 5, which has both the advantages of submergedBRs and side-stream MBRs, was developed in China by Fan et

l. [10–13] through replacing the recirculation pump by H-typeecycling pipe.

Fig. 6 presents the distribution of these original researchapers on different MBR configurations. Before 1995, the pub-

ished articles are all review papers and thus not shown in Fig. 6.t can be seen that the study of side-stream MBRs was domi-ant before 2001 while afterwards submerged MBRs were moreopular among the studies. Since 2003, the AEC-MBR has been

Fig. 6. Distribution of these studies on three MBR configurations.

ell studied for the treatment of toilet wastewater and municipalastewater by the study team led by professor Fan of Chinesecademy of Sciences. In general, among these studies sub-erged MBRs were mostly utilized for municipal wastewater

reatment while the side-stream MBRs were commonly appliedor particular industrial wastewater treatment.

Another innovative submerged anaerobic membrane biore-ctor (SAMBR), in which membrane fouling was controlled byecirculating the biogas produced by the bioreactor to induce

Fig. 7. Diagram of a novel SAMBR.

Z. Wang et al. / Separation and Purificati

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Fig. 8. Distribution of these studies on different MBR types.

ated to the study of membrane material selection, proper suctionode and membrane fouling properties of this SAMBR for the

reatment of high-strength alcohol-distillery wastewater.

.4.1.2. MBR type. MBR types are generally divided into fourategories based on the purpose of membrane usage [20,21]:1) biomass separation membrane bioreactor (BSMBR), (2)embrane aeration bioreactor (MABR), (3) extractive mem-

rane bioreactor (EMBR) and (4) another newly developedon exchange membrane bioreactor (IEMBR) [22]; however, inhina, the research was mainly conducted on the first three typeshile IEMBR remains unexplored. Fig. 8 shows the distribu-

ion of the total 548 research papers on the first three types. Itan be observed that the majority of these studies focused onhe application of BSMBRs, where the membranes were usedor solid–liquid separation. From 2001 to 2006, a few studiesere conducted with regard to the MABR and EMBR; how-

ver, unlike BSMBRs, there was no obvious increase of studiesver time on these two MBR types. It indicates that the currentesearch in China is mainly involved in wastewater treatmentnd reclamation by employing BSMBR with its success in com-ercial applications; while MABR and EMBR, due to their

xpense and immaturity, still need a long period to achieveommercial success and thus the research on these two typesagged behind. These two types still have their own potential tottract researchers’ attention for specific applications. MABRs,n which the membranes are used to diffuse oxygen or other gasesnd/or to realize bubbleless aeration in the reactor for wastewaterreatment, have several advantages such as high gas transferringfficiency, low energy consumption and so on [23–29]. Toxicrganic wastewaters [30–32] and surface/drinking water [33]re two basic areas for the application of EMBRs. In China,wo other innovative processes, membrane enzyme bioreactorMEBR) for hydrolysis of special organic substances such aslive oil and whey protein [34,35] and membrane pervaporationioreactor (MPBR) for volatile organic wastewater treatment36], were also investigated. It has to be pointed out that althoughhe study of all the types of MBR was carried out, the BSM-Rs have been successively achieved commercial applicationsnd the rest types of MBR are still at the level of lab-scale

esearch.

In future, experimental study and real applications ofSMBR will continue to grow. With the development of mem-rane manufacturing technology, the research on MABR and

wccc

on Technology 62 (2008) 249–263 253

MBR as well as MEBR and MPBR will be expected to increaseue to their specific characteristics for water treatment and forther purposes. IEMBR, which incorporates pollutant transporthrough an ion exchange membrane by Donnan dialysis withiological removal of the pollutant [22], will also present itsigh potential for use in drinking water treatment to draw atten-ion of researchers in China. It has to be admitted that there istill a long way to go before successful commercial applicationsf MABR, EMBR, MEBR, MPBR and IEMBR can be achievedn China.

.4.1.3. Membrane materials and modules. A number of mem-rane materials and modules were used in these studies andeveral typical kinds are summarized in Table 1. The home-ade hollow fiber membranes were mainly produced by Tianjinotimo Membrane Technology Co., Ltd. and Zheda Hyfluxualv Membrane Technology Co., Ltd. The main-stream prod-cts of Tianjin Motimo are polyvinylidene fluoride (PVDF)bers with 0.2 �m pore size though polysulfone (PS), polyether-ulfone (PES), polyethylene (PE) and other materials are alsosed to manufacture hollow fibers in this company, and Zhedayflux Hualv Membrane Technology Co., Ltd. is basically

nvolved in the production of polypropylene (PP) hollow fiberembranes. Several other membrane materials including PE,ES produced by overseas companies and polyvinylidene chlo-ide (PVC), PS made by Chinese institutes were also applied inhese studies and their characteristics of wastewater treatmentn MBRs were well investigated.

The two more popular kinds of flat-sheet membranes areade of PVDF and PES compared with the rest PP and poly-

crylonitrile (PAN) materials, which are produced by Shanghaiizheng Environmental Technology Co., Ltd. and Shanghai

nstitute of Applied Physics, respectively. Among these orig-nal research papers, the vast majority of them focused on thetudy of hollow fiber membranes for wastewater treatment whileat-sheet membranes were only intensively studied by Tongjiniversity and few institutes in China.Ceramic membranes, as shown in Table 1, were also

esearched in MBR process in China due to their special qual-ties including the resistance against extreme pH, temperaturend pressures and the tolerance of rigorous cleaning with acid,lkali and hot water, etc. Another novel process, self-formingynamic MBR (SFDMBR) using cheap coarse mesh as sup-orting material to form self-forming dynamic membranes, waslso studied for municipal wastewater and simulated distilleryastewater treatment.Table 2 is a summary comparison of membrane properties and

BR performance of several companies. The referenced mem-ranes in Table 2 are produced by the current leaders in MBR,hich include home-grown companies and overseas-funded

ompanies. Blank spaces mean that the data in literatures was not

as not compared, but a general conditions still can be con-luded, i.e., membranes made by home-grown companies haveomparatively lower price than those made by overseas-fundedompanies.

254 Z. Wang et al. / Separation and Purification Technology 62 (2008) 249–263

Table 1Membrane materials used in these studies

Materiala Module Pore size (�m) Flux (L/(m2 h)) Manufacturer

PE [37,38] Hollow fiber 0.1–0.4 10–20 DAIKI, Japan; Mitsubishi Rayon, JapanPP [39–42] Hollow fiber 0.06–0.27 3.5–10/35–50b Zheda Hyflux Hualv, ChinaPVC [43] Hollow fiber 0.2 3–8.5 Donghua Univ., ChinaPVDF [44,45] Hollow fiber 0.2 6–16 Tianjin Motimo, ChinaPES [46] Hollow fiber 0.02 5–14 Membrane GmbH Company, GermanyPS [47] Hollow fiber 10–50 kc 40–80b Hohai Univ., ChinaPVDF [8,48] Flat-sheet 0.1–0.4 20–30 Liaoning Univ. of Petrol. Chem. Technol., China; Toray, JapanPP [39,40] Flat-sheet 0.06–0.14 35–50b Zheda Hyflux Hualv, ChinaPAN [8] Flat-sheet 20–70 kc 10–20 Tongji Univ., ChinaPES [49,50] Flat-sheet 0.2 20–30 Shanghai Zizheng Environm., ChinaCeramic [51,52] Tubular 0.2 70–175b Nanjing Univ. of Technol., China

InorganicFlat-sheet: metal [53] – 18.6

Dalian Univ. of Technol., China; HitachiMetals, Japan; Tsinghua Univ., China

Stainless-steel [54] 0.2 8–38Dacron mesh [55] 100 14.8–33.3

a PE: polyethylene; PP: polypropylene; PVC: polyvinylidene chloride; PVDF: polyvinylidene fluoride; PES: polyether-sulfone; PS: polysulfone; PAN: polyacry-l

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onitrile.b Pressurized side-stream MBR.c Molecular weight cut-off, MWCO.

.4.2. Research contents

.4.2.1. Membrane fouling and control. It is well known thatembrane fouling is a major obstacle for wide application

f MBRs. Membrane fouling results in severe flux decline,igh-energy consumption and frequent membrane cleaning oreplacement and has been investigated from various perspectivesuch as the causes, mechanisms, characteristics and model-ng of fouling. A number of researchers dedicated their effortso the study of causes and mechanisms of membrane foulingrom the following aspects: soluble microbial products (SMPs)56–59], extracellular polymeric substance (EPS) [60–62], bulk-

ng sludge [37,63], sludge components [16,64], sludge cakeayer [65,66], low temperature operation [49], influent charac-eristics [67], sludge concentration [68] and other perspectives

ais

able 2ummary comparison of membranes used in full-scale MBRs and MBR performance

tems Zenon Mitsubishi Rayo

1) Membrane module propertiesPolymer PVDF PEFiltration type UF MFModule Hollow fiber Hollow fiberHydrophilic Yes YesOutside diameter (mm) 1.95Inside diameter (mm) 0.92Fiber length (mm) 1650 663.5Pore size (�m) 0.04 0.4Surface area (m2) 23/module 105/moduleNormal flux (L/(m2 h)) 25.5 10.3–16.7

2) MBR performanceMLSS (g/L) 12–30Aeration per module (m3/h) 14 57–73SRT (d) 10–100Sludge yield (kg MLSS/kg BOD) 0.1–0.3BOD effluent (mg/L) <2 2–6NH3 effluent (mg/L) <0.3

a Although Kubota was not found very active in China, it was still referenced herther countries.

69] while other authors focused on the fouling characteristics70–72] and the modeling of fouling [73,74]. Based on thesetudies, a general understanding of membrane fouling could bestablished: (1) SMP and EPS, which are easily adhered to mem-rane surface to form gel layer, have significant correlations withembrane fouling; (2) sludge cake layer has strong effects onembrane permeability; (3) bulking sludge or other abnormal

erformance such as low temperature operation is detrimentalo membrane filtration; (4) a proper sludge concentration shoulde maintained to facilitate MBR performance; (5) other param-ters like influent water characteristics, sludge components, etc.

ll have correlations, to some extent, with membrane fouling. Its worth noting that disagreements still remain on some aspect,uch as the effect of sludge concentration on membrane fouling,

n Tianjin Motimo Kubotaa Shanghai Zizheng

PVDF PE PVDFMF MF MFHollow fiber Flat-sheet Flat-sheetYes Yes Yes1.00 490 (width) 460 (width)0.65 1000 (height) 1010 (height)1010 6 (thickness) 7 (thickness)0.20 0.4 0.220/module 0.8/panel 0.7/panel15 25.5 20–30

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ue to different influent water quality, various reactor configura-ion and diverse operational conditions among the studies. Morefforts should be dedicated to the membrane fouling mechanismn order to further establish a consensus of such kind of problems.

Based on the understanding of fouling mechanisms and char-cteristics, a great many researchers studied and developedffective and applicable measures to prevent and control mem-rane fouling. Three following aspects of attempts have beenade to control and reduce membrane fouling in MBRs.2.4.2.1.1. To improve antifouling property of membrane

aterials. Membranes antifouling properties can be enhancedy changing physical and/or chemical characteristics of mem-ranes. Several measures were applied among these studieso improve antifouling property of membranes: one wasurface modification by the sequential photoinduced graft poly-erization of acrylic acid [39], by the immobilization of

oly(N-vinyl-2-pyrrolidone) on membrane surface [40], bylasma-induced tethering of sugar moieties [75], by NH3 plasmareatment [76], by CO2 plasma treatment [77] and by otherlasma treatment [78]; another was to add precoating layern membrane surface, such as powdered activated carbonPAC)-precoated membrane [53] and ferric hydroxide-precoatedembrane [79]; Another method reported by Xu et al. [51,52]

hat the antifouling property was improved by enwinding turbu-ence promoter on tubular ceramic membranes when the ceramic

BR process was applied for municipal wastewater treatment.2.4.2.1.2. To enhance the filterability of mixed liquors.

owdered and porous materials such as powdered activated car-on (PAC) and zeolite were added into MBRs to modify thelterability of mixed liquors. It was found that membrane foulingas reduced after PAC addition among many studies [44,80–82]ainly due to the decrease the content of EPS in microbial cells,

he reduction of cake resistance, the increase of floc size distri-ution and the mitigation of apparent viscosity of mixed liquors.imilar effects were achieved with zeolite addition in MBRs byther researchers [83,84], which were attributed to the increasef microbial activity, the scouring of membrane surface broughty zeolite particles, and the decrease of supernatant organicatters of mixed liquors.Some kinds of coagulants including Al2(SO4)3, FeCl3, poly-

eric aluminum chloride and polymeric ferric sulfate (PFS)ere also used in MBRs for membrane fouling control. It was

ound that polymeric coagulants had a better effect in filterabil-ty enhancement and PFS was the most effective in reducing

embrane fouling [38,50] probably owing to three functions:estraining the formation of gel layer, decelerating the devel-pment of foulants and removing adhered foulants from theembrane surfaces.A lot of other innovative attempts were also made for mem-

rane fouling control, such as MBRs seeded with granular sludge42] and MBRs coupled suspended carriers [85,86]. The mainoal of MBRs seeded with granular sludge was to reduce theouling caused by fine particles in the system while MBRs cou-

led suspended carrier could obtain better hydraulic conditionshrough the carrier’s movement induced by aeration and thusnhanced the filterability of mixed liquors. Interesting resultsere also reported that the application of ozone into mixed liquor

mimi

on Technology 62 (2008) 249–263 255

ould improve sludge filterability due to the oxidization of cellurface EPS, the increase of sludge floc size and the reduction ofupernatant organic substances and viscosity of mixed liquors87].

2.4.2.1.3. To optimize operational conditions and parame-ers. Operational conditions play a key role in MBR process,nd optimized operational conditions and parameters are veryonducive to reduce and control membrane fouling. It has beenell recognized that critical flux is an important concept in sub-erged MBRs, below which the increase of trans-membrane

ressure (TMP) or the decline of flux with time does not occurnd above that level fouling is observed [5]. Many researchers88–91] focused on the study of critical flux in MBR and iden-ified that sub-critical operation was suitable for the submerged

BRs. Under sub-critical operation, MBRs could achieve long-erm, stable operation without frequent membrane cleaning.

Operational parameters including DO concentration in MBR92], aeration intensity [66], the ratio of suction and non-suctionime (intermittent filtration) [66], sludge retention time (SRT)59,71], hydraulic retention time (HRT) [93,94], filtration modes95], sludge concentration [66,94,96] and temperature [96], etc.ere investigated in order to reach better understanding of theperational characteristics and to optimize these factors foreducing membrane fouling.

In aerobic MBRs, air-sparging or air-scouring, which cannduce a shearing stress upon membrane surfaces by upliftingir bubbles, plays an important role in controlling membraneouling. The air-scouring can reduce the biofouling substancesdhered or deposited on membrane surfaces; furthermore, theffectiveness of air-scouring can be significantly improved underntermittent suction operation due to the absence of trans-

embrane pressure (TMP) during non-suction time. It is alsoell known that the effect of air-scouring, generally expressed

s cross-flow velocity (CFV), is mainly dependent on the aera-ion intensity and the structural hydrodynamics of the reactors.n order to achieve a higher CFV in submerged MBRs at a certaineration intensity, structural modification of reactors was carriedut including increasing reactor height, decreasing the ratio ofiser surface area and down-comer surface area and enhancinghe distance of membrane modules from bottom, etc. [97,98]. A

odified submerged MBR [99] based on the hydraulic researchas applied for the treatment of municipal wastewater and a bet-

er effect of membrane fouling control was achieved comparedith a conventional submerged MBR.Although the measures mentioned above can effectively con-

rol membrane fouling to some extent, the decrease of membraneermeability is inevitable attributed to pore clogging, biofouling,tc. Once operational pressure increases dramatically to a certainalue, membrane cleaning procedure is needed to recover theembrane permeability. Back-flushing is an effective way for

igh-pressure-resistance membranes [100], such as hollow fibernd ceramic membranes, to remove the particles and biofoul-ng substances clogged in membrane pores and/or adhered onto

embrane surfaces. In general, back-flushing consists of revers-ng the filtration direction for 5–30 s every 30–60 min. Other

echanical cleaning methods were also studied and developedn China. Xu and Fan [101] developed a hollow fiber mem-

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rane module with enhanced self-mechanical-cleaning functionhich was suitable for high sludge concentration and flux oper-

tion, and Sun et al. [102] adopted sponge scouring to removehe fouling in a submerged flat-sheet MBR. It was also foundhat the application of ultrasound could effectively reduce mem-rane fouling in a side-stream anaerobic MBR for high-strengthynthetic wastewater treatment [103].

Chemical cleaning has been intensively studied and exten-ively used for removing membrane fouling and recoveringembrane permeability. A variety of chemical agents were

pplied in membrane cleaning, such as acids (hydrochloric acid,ulfuric acid, citric acid, etc.), alkali (sodium hydroxide), oxi-ants (sodium hypochlorite, perhydrol, etc.), and their effectsn foulants removal were identified [104–110]. A general con-lusion that could be drawn from these studies is that acids canffectively removal inorganic foulants while alkaline solutionnd oxidants perform well in removing organic substances andiofouling. Much higher cleaning efficiency could be reached bymploying multi-step chemical cleaning, for instance, sodiumypochlorite cleaning followed by acid cleaning and/or alkalineleaning.

Membrane fouling and control strategy are two closely inter-elated hot topics of the research on MBR technology. Theltimate goal of the research on membrane fouling is to proposeorresponding fouling control methods and to facilitate MBRtable operation. With the deep understanding of membraneouling mechanism in MBRs, more effective, efficient and con-enient control strategy could be developed in future. Anotherssue that should be addressed is that the fouling control strat-gy in full-scale MBR plants, especially large-scale MBRs, isnsufficient in China. Fouling control measures mentioned aboveere proposed just based on lab-scale or pilot-scale MBRs, and

heir fouling control efficiency in full-scale MBRs needs to beurther verified.

.4.2.2. MBR for various water and wastewater treatment. Theotal 548 original research papers were grouped into four cate-ories based on various water and wastewater that were treated inhese studies: (1) municipal/domestic wastewater treatment; (2)

ndustrial wastewater treatment; (3) surface/drinking water treat-ent; (4) others which include landfill leachates, gas removal,

as diffusion, microbial fermentation, etc. The chronologicalistribution of these studies on the four groups is shown in Fig. 9.

Fig. 9. Research distribution on various wastewater treatment.

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on Technology 62 (2008) 249–263

It can be seen from Fig. 9 that a larger number of studies werearried out for the purpose of municipal/domestic wastewaterreatment and reclamation compared with the studies on indus-rial wastewater and other kinds of water treatment. Anotherrend that can be observed is that the number of papers onndustrial wastewater treatment increased annually, which indi-ated that MBR process was increasingly popular in industrialastewater treatment particularly toxic and refractory wastew-

ter due to its advantages as mentioned earlier. According tohe characteristics of wastewater to be treated and the effluentuality required, the MBR process could be diversified as A/Or A/A/O MBR [111], sequencing batch MBR (SBMBR) [112],ybrid MBR [113] and other biological and/or physical and/orhemical process coupled with MBRs [114–116].

Studies on the application of MBR technology for surfaceater treatment in China, which just totaled 8 out of 548 researchapers, were much less than those of municipal and indus-rial wastewater treatment; however, in China the surface waterollution is very severe and more than half the watersheds ofhina have been contaminated by industrial, farm and house-old wastes [117]. Therefore, more research efforts are neededn order to ensure drinking water safety, and MBR, as an innova-ive and promising process, will play an increasingly importantole in surface water treatment in vast areas of China in future.

.4.2.3. Other research aspects. As shown in Fig. 9, MBRsere also applied for other purposes. Landfill leachate treatmentas well studied by employing MBR coupled other biological

nd/or physical/chemical process [116,118,119]. MBR pro-ess was also used in microbial fermentation for productionf ethanol, dihydroxyacetone and ganoderma lucidum exo-olysaccharide, etc. [7,120–123] while other purposes of MBRpplication were reported such as gas diffusion [23–29], gasemoval [124] and so on [47].

Although various areas of MBR process were studied, muchf the published information on MBRs focused on lab-scaler pilot-scale studies during short-term operation and very fewublications were reported on full-scale studies for long-termperation. Besides, MBR research on surface/drinking waterreatment still lagged behind. In the future, the research of MBRrocess on surface/drinking water treatment will gain muchore momentum attributed to the severe pollution of the water-

heds in China. The application of MBR technology in industrialastewater will continue to be boosted, and the full-scale MBR

tudy on municipal/domestic wastewater is also needed in ordero obtain operational experiences especially on large-scale MBRlants.

.5. Comparison of research characteristics in China andhose in the world

MBR research of the whole world mainly experienced threetages: (1) From 1966 to 1980, it was the entry-level stage dur-

ng which lab-scale research was mainly conducted. Membranesf the time had low flux and short lifespan due to the unde-eloped membrane manufacturing technology. (2) From 1980o 1995, MBR technology was well investigated especially in

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Z. Wang et al. / Separation and Pur

apan, Canada and USA. During this stage, new membraneaterial development, MBR configuration design and MBR

peration were critically studied by employing external MBR,nd the research efforts, to a great extent, promoted the tech-ology development including treatment scale enlargement andpplication area extension. Submerged MBR concept by intro-ucing submerged membranes in aeration tanks for solid/liquideparation was put forward by Japanese researchers [9] in 1989.3) From 1995 till now, MBR technology underwent a rapidevelopment which was featured by deep understanding of theechnology’s properties in research communities and the instal-ation of full-scale MBRs.

Compared with MBR research of the world, China’s researchn MBR technology did not start until the early 1990s, and theapid research development has been achieved mainly in the lastyears. Chinese researchers have played an important role inBR research in recent years, and the contribution rate of peer-

eviewed English publications of Chinese researchers to those ofhe whole world was in the range of 1/10–1/4. It is worth notinghat the research of newly developed MBR in China lags behindhat of the world especially in Europe and Japan, for example,EMBR has been studied for the treatment of drinking water toemove nitrate and heavy metals in France while it still remainsnexplored in China.

. Commercial applications in China

Although the original research began in the mid 1990s, therst MBR project for municipal wastewater treatment and recla-ation [125] was installed in Dalian city of East-North China in

998 by DAIKI Project Environmental Protection (Dalian) Co.,td. Following this, a number of MBR systems were constructed

n China for municipal and industrial wastewater treatment andeclamation. In East and South China, the constructed MBRsere mostly involved in high-strength industrial wastewater

reatment while in North China MBRs mainly focused on munic-pal wastewater treatment and reuse.

.1. MBR providers

A lot of MBR providers were found according to our statis-ics, which include famous overseas companies such as Zenonnvironmental Inc. (Canada), Mitsubishi-Rayon (Japan), Toray

Japan), NOVO Environmental Technology (Singapore) and X-low (Netherlands), Japan-based companies like Dalian DAIKInd Shanghai Renyuan, America-based providers like Omexnvironmental Engineering Co., Ltd. and CNC (Sai-En-Si-Te)ater Technology Co., Ltd., and numerous home-grown com-

anies including Tianjin Motimo Membrane Technology Co.,td., Zheda Hyflux Hualv Co., Ltd., Tianjin Tsinghua Daringo., Ltd., Beijing Origin Water Technology Co., Ltd., Shang-ai Zizheng Environmental Technology Co., Ltd. and Shanghainstitute of Applied Physics, etc. A total of 33 companies or insti-

utes were found to have involved in MBR installations in China.mong these MBR providers, only 3 companies, Toray, Shang-ai Zizheng Environmental Technology Co., Ltd. and Shanghainstitute of Applied Physics, supplied the flat-sheet membranes

on Technology 62 (2008) 249–263 257

hereas the rest were all hollow fiber membrane providers.urprisingly, the worldwide renowned flat-sheet membranerovider, Kubota (Japan), was not found very active in Chineseembrane market.

.2. MBR plants in China

A total of 254 MBR plants have been constructed in ChinaMBR plants in SARs of China were not counted), whichonsist of 117 MBRs for industrial wastewater (including land-ll leachate) treatment and 137 MBRs for municipal/domesticastewater treatment and reclamation. It should be pointed out

hat this collection of MBR plants might not be complete despitehe intensive efforts by the authors to search and survey existing

BR plants in China.Among these MBR providers mentioned earlier, the company

ith the largest number of MBR plants constructed is Tian-in Motimo (47 plants), then followed by Shanghai Renyuan40 plants), Tianjin Tsinghua Daring (20 plants), Beijing Origin

ater (19 plants), Tianjin Spring Environmental Technology (18lants), Beijing Yongxin Environmental Protection (12 plants),OVO Environmental Technology (9 plants), Toray (9 plants)

nd so on. The MBR projects constructed are conducive to mit-gate water crisis, to control water pollution and to improvenvironmental conditions in China.

.2.1. Geographic distribution of MBR plantsThe geographic distribution of the 254 MBR plants in seven

egions according to Chinese Administration Division is shownn Fig. 10. It can be observed that the majority of the MBRlants were located in North China and East China, then fol-owed by North-East China, South China, South-West China,entral China and North-West China. The distribution of theBR plants is closely related to the geographic distribution of

riginal research on MBR technology (shown in Fig. 3), whichndicates that the commercial interest correspondingly followshe research field. It can be also found that in North China the

BR plants mainly focused on municipal/domestic wastewaterreatment and reuse while in East and South China the major-

Fig. 10. Geographic distribution of MBR plants.

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hina where are not short of water resources and many devel-ped coastal cities located, the pollution of industrial sectoras strictly monitored and controlled mainly attributed to the

tringent effluent standards required by local government.

.2.2. Distribution of MBR plant scaleAlthough 254 MBR plants were constructed in China, most of

he pants in operation, as shown in Fig. 11, are medium-scale ormall-scale in terms of treatment capacity. The number of plantsith treatment capacity below 1000 m3 per day totals 225, andnly 29 plants each exceed a capacity of 1000 m3 per day inhich 10 plants each have a capacity over 10,000 m3 per day.The largest MBR plant with a capacity of 80,000 m3 per day

or municipal wastewater treatment and reuse, Beijing Qingheastewater Treatment and Reuse Plant, was jointly constructed

n Beijing by Zenon Environmental Inc., Omex Environmentalngineering Co., Ltd. and CNC Water Technology Co., Ltd. The

argest MBR plant for industrial wastewater treatment locatedn Guangdong Huizhou Dayawan Petrochemical Industrial ParkGuangdong Province, China) was installed by NOVO Environ-ental Technology Inc., which has a capacity of 25,000 m3 per

ay.

.3. MBR commercial application in future

Among the 254 MBR plants in China, just 13 of them weremployed with flat-sheet membrane modules; however, over halff the total MBR plants were flat-sheet MBRs worldwide [2].ith the development of membrane market in China, flat-sheetembrane modules will draw increasing attention due to its

pecial characteristics. Compared with hollow fiber membraneodule, flat-sheet membrane module generally has higher flux

nd its hydraulic condition is also better than that of hollowber membrane module. Thus, flat-sheet MBRs, in most cases,ave lower operational pressure, higher membrane flux, higherLSS concentration and slower fouling rates than hollow-fiberBRs. It has to be admitted that flat-sheet membrane mod-

le also has its demerits such as higher price per filtrationrea, lower loading density of modules and intolerance of back-ushing, etc. Science and Technology Commission of Shanghai

unicipality (STCSM) has successively supported Shanghai

nstitute of Applied Physics [126] and Shanghai Zizheng Envi-onmental Technology Co., Ltd. for the research and applicationf flat-sheet MBRs in the last 3 years. The three flat-sheet

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on Technology 62 (2008) 249–263

embrane providers, Shanghai Institute of Applied PhysicsChina), Shanghai Zizheng Environmental Technology (China)nd Toray (Japan) that are now active in China will install morend more flat-sheet MBR plants in future.

Since MBR technology is becoming increasingly popular inhina, the capacity of MBR plant will be larger and larger for the

reatment of municipal/domestic wastewater especially in Northhina and industrial wastewater in South and East China. As

eported by Beijing Origin Water Technology Co., Ltd. [127],he company had inked a contract of constructing the Sunyiincheng Water Resources Reuse Project by employing MBR

echnology in 2007, which has a capacity of 100,000 m3 per day.everal other large MBR plants are also planning to be installed

n China in the near future.Another trend in China’s MBR commercial application is that

BR technology for municipal/domestic wastewater treatmentnd reclamation in South and East China will be pushed forwardradually due to the stringent effluent standards required and theoaring price of tap water. The vast areas of North-West Chinaill be another hot spot for the application of MBRs with the

upport of Chinese government in future.

.4. Comparison of commercial application of MBR inhina and that in the world

In the worldwide application, flat-sheet membrane modulesroduced by Kubota were employed in about 68% of the totallants according to the research conducted by Yang et al. [2];owever, in China, according to our research, no more than% of the total 254 plants were installed with flat-sheet mem-rane modules. It is necessary to promote the application ofat-sheet membrane modules in China to balance the devel-pment of MBR application. The current application status alsoresents a significant opportunity for institutes and enterprises totrengthen flat-sheet membrane module development and to pro-ote flat-sheet MBR application. Another difference betweenhina’s application and worldwide application is the distribu-

ion of municipal wastewater MBRs and industrial wastewaterBRs. Based on the database collected by Yang et al. [2], the

otal 2259 plants were comprised of 1527 municipal wastewaterBRs and 732 industrial wastewater MBRs, i.e., the number

f municipal wastewater plants was over twice of industrialastewater plants. In China, the total 254 MBR plants included37 municipal wastewater MBRs and 117 industrial wastewaterBRs, and the number of industrial wastewater MBRs was close

o that of municipal wastewater MBRs. It is mainly attributed tohe fact that in North China municipal wastewater MBRs are pre-ominant while in South China and South-East China industrialastewater MBRs dominate the market.

. Future prospect

.1. Existing challenges of the technology in China

Although much progress has been achieved both on researchnd commercial applications in China, MBR technology is cur-ently facing some research and development challenges. If these

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hallenges are well solved, it could lead to a more competi-ive and mature market for application in China. Some of thesehallenges are shown as follows [8,128,129].

.1.1. MBR market shareMBR market in China is currently dominated by foreign

ompanies which have skilled membrane manufacturing tech-ology and comparatively high filtration quality though a lot ofome-grown membrane companies have appeared in mainland.n one hand, the introduction of foreign membrane technol-gy can promote the development of Chinese MBR market; onhe other hand, it might have negative influences on Chinesewn membrane companies especially small and medium-sizednterprises.

.1.2. MBR standardizationThere are too many MBR filtration products with diverse

eometries, module capacities and operational modes in Chi-ese membrane market. Although it is a normal situation in aompetitive market, this fragmentation of MBR products coulde detrimental to the acceptance of the technology as “state-of-he-art” process and thus cause concern to potential clients ornd-users. MBR standardization is needed mainly for the fol-owing aspects: to increase the comparability and transparencyf products and to promote the end-user’s confidence in them bytandardizing acceptance and monitoring tests; to improve thend-user’s reinvestment opportunities and to decrease the MBRltration module investment costs by specifying guidelines toacilitate interchangeability of MBR filtration systems.

.1.3. Membrane foulingAlthough intensive efforts have been dedicated to the study

n membrane fouling mechanisms and control, it is necessary toevelop more effective and easier methods to control and mini-ize membrane fouling especially in large-scale applications.

.1.4. Membrane lifespanNumerous membrane materials and modules have been

eveloped in China, but the lifespan of the membranes stilleeds improving. Further study on how to increase membrane’sechanical and chemical stability is very essential to extendembrane lifespan.

.1.5. CostThe cost of MBR technology mainly lies in the membrane

odule cost, maintenance and cleaning cost, the cost of mem-rane replacement, energy requirements and labor requirements,tc. The solution or improvement of the three challenges men-ioned above will be very conducive to reduce the cost of MBRrocess to some extent. Other technology innovations in futureesearch and application such as the development of efficientleaning methods and the enhancement the oxygen transferringate of the mixed liquor, etc. are also necessary to lower the cost.

.1.6. Large-scale MBR operational experiencesDespite many full-scale MBRs that have been installed

n China, the design and operation experiences especially on

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arge-scale MBR plants are still insufficient. The skilled manage-ent and optimized operation of large-scale MBRs are further

eeded, through which MBR technology will become more cost-ffective.

.2. Resolution measure analysis

One effective measure to solve the existing problems men-ioned above is the continuous support including finance andolicy regulation from Chinese government. Ministry of Sciencend Technology (MOST) should give more financial supporto universities and research institutes (including companies)o carry out further research on existing challenges. Related

embrane companies of China can also strengthen technol-gy innovation to improve their competitive edge in virtue ofavorable development policy offered by local government. Ifhe home-grown companies could further improve their productuality such as membrane flux, lifespan, material strength andoughness, etc., the share of Chinese companies in MBR marketill undoubtedly increase. It is very vital that the increase of the

hare of Chinese companies in MBR market will well resolve thexisting problems with MBR technology of China. In addition,esearch institutes should further verify the efficiency of mem-rane fouling control measures, which were developed throughab-scale or pilot-scale studies, in full-scale or large-scale MBRlants to obtain practical operation experiences.

.3. Future development trend

MBR process becomes more and more attractive for munici-al/domestic wastewater treatment when a compact technologys required due to a lack of space or the high cost of additionaland in urban areas, or when high effluent quality is requiredor water reuse or pretreatment for reverse osmosis (RO) orano-filtration (NF) processes [2]. The increasingly stringentischarge standards and the great need of water reclamationnd reuse will further push forward the application of MBRsor ever-larger municipal wastewater treatment plants in China,specially in North China where is now suffering the shortagef water resources. In vast areas of North-West China subjecto severe water crisis, the application will also be promoted inuture.

The application of MBR process in industrial wastewaterreatment is also gaining popularity in China. Original researchn MBR technology for various industrial wastewater treat-ent is becoming a hot topic, and the application areas include

ood-processing wastewater, petrochemical wastewater, hospi-al wastewater, printing and dyeing wastewater, slaughterhouseastewater, etc. [8,21]. It is worth noting that the application

n landfill leachate treatment is also promising. Over 15 MBRlants for landfill leachate treatment have been installed in Chinan the last 5 years. MBR systems combined with pretreatmentnaerobic biological process and/or with post-treatment steps

ike nano-filtration (NF) was commonly used in landfill leachatereatment in order to achieve good effluent quality [130].

Another area for MBR application is surface/drinking waterreatment for nitrate removal [33,131] and organic substances

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emoval [132]. It is worth pointing out that studies on the appli-ation of MBR technology for surface/drinking water treatmentbviously lagged behind the research on municipal/domesticnd industrial wastewater treatment; however, in China the sur-ace water pollution is very severe and more than half of theatersheds have been contaminated. Therefore, in the future,

he research and application of MBR process in surface/drinkingater treatment will be boosted profoundly in China.

. Concluding remarks

In the past 15 years, remarkable progress has been made onhe research and commercial application of MBR technology inhina, and the following conclusions could be drawn:

1) Research progress: A great number of peer-reviewed paperswere published in Chinese and English journals. Throughthese studies, a profound understanding of MBR technol-ogy was achieved including the characteristics of MBR forvarious wastewater treatment, the membrane fouling mech-anisms and control, membrane cleaning, etc. The academicresearch, to a great extent, pushed forward the commercialapplication of this technology in vast areas of China.

2) Application progress: A total of 254 full-scale MBR plantshave been constructed in China for the treatment of indus-trial wastewater and municipal/domestic wastewater byhome-grown and overseas-funded MBR providers since1998. As MBR technology is becoming more and more pop-ular in China, the capacity of MBR plant will be larger andlarger due to the increasingly stringent discharge standardsand the great need of water reclamation and reuse especiallyin North China.

3) Future development trend: Besides current applications inmunicipal/domestic and industrial wastewater treatment,other potential areas of MBR application include sur-face/drinking water treatment, gas diffusion and removal,membrane assisted fermentation for biological substancetransformation and production, etc.

4) Research and development challenges: MBR technology isalso facing several research and development challenges inChina, such as MBR market share, MBR standardization,membrane fouling, membrane life-span, costs and large-scale MBR operational experiences. If these challengescould be well resolved by the research community andorganizations, MBRs will undoubtedly achieve much widerapplication.

cknowledgement

This study was financially supported by Science and Tech-ology Commission of Shanghai Municipality (STCSM) underrant No. 062312023.

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