problems in seawater industrial desalination processes and potential sustainable solutions: a review

REVIEWS

Problems in seawater industrial desalination processesand potential sustainable solutions: a review

S. Liyanaarachchi • L. Shu • S. Muthukumaran •

V. Jegatheesan • K. Baskaran

� Springer Science+Business Media Dordrecht 2013

Abstract Seawater desalination has significantly

developed towards membrane technology than phase

change process during last decade. Seawater reverse

osmosis (SWRO) in general is the most familiar

process due to higher water recovery and lower energy

consumption compared to other available desalination

processes. Despite major advancements in SWRO

technology, desalination industry is still facing sig-

nificant amount of practical issues. Therefore, the

potentials and problems faced by current SWRO

industries and essential study areas are discussed in

this review for the benefit of desalination industry. It is

important to consider all the following five compo-

nents in SWRO process i.e. (1) intake (2) pre-

treatment (3) high pressure pumping (4) membrane

separation (performance of membranes and brine

disposal) and (5) product quality. Development of

higher corrosion resistant piping materials or coating

materials, valves, and pumps is believed to be in

higher research demand. Furthermore, brine

management, that includes brine disposal and resource

recovery need further attention. Pre-treatment sludge

management and reduced cleaning in place flush

volume will reduce the capital costs associated with

evaporation ponds and the maintenance costs associ-

ated with disposal and transportation reducing the unit

cost of water.

Keywords Desalination � Reverse osmosis �Sludge disposal � Brine management � Corrosion

1 Introduction

Desalination, removal of salt and minerals from

seawater, brackish water and wastewater effluent, is

becoming one of the promising solutions for increas-

ing fresh water demand in the world. In 2005,

approximately 98 % of domestic water supply in

UAE were satisfied by desalted water (Mohamed et al.

2005). Hoang et al. (2009) predicted that seawater

desalination capacity in Australia will increase over

450 GL/year by 2013. This will be 10 times larger

compared to the capacity in 2006. There are two types

of desalination processes available to date, viz phase

change process which includes multistage flash

(MSF), multiple effect distillation (MED) and vapour

compression (VC) and membrane process which

includes reverse osmosis (RO) and electro-dialysis

reversal (EDR). Table 1 illustrates installed capacity,

unit cost, water recovery and energy demand of the

S. Liyanaarachchi (&) � L. Shu � V. Jegatheesan �K. Baskaran

School of Engineering, Deakin University, Waurn Ponds,

VIC 3216, Australia

e-mail: [email protected]

V. Jegatheesan

e-mail: [email protected]

S. Muthukumaran

College of Engineering and Science, Victoria University,

Melbourne, VIC 8001, Australia

123

Rev Environ Sci Biotechnol

DOI 10.1007/s11157-013-9326-y

available desalination processes. From the total

installed production capacity worldwide, seawater

desalination plant capacity is nearly 59 %. Current

seawater reverse osmosis (SWRO) plants consume

around 3–6 kWh electricity to produce one cubic

meter of product water. Phase change processes are

more expensive as large amount of energy is required.

Energy demand for MSF and MED processes are

10–16 and 6–12 kWh/m3, respectively. Unit produc-

tion cost (UPC) of water using MSF and MED

processes are 0.6–1.97 and 0.60–1.17 US$ respec-

tively. Interestingly, UPC for RO is 0.45–0.95 US$

with a combined energy demand (demand for both

heat (thermal) and electricity (pumping) require-

ments) of 3–6 kWh/m3. The production costs signif-

icantly vary with the plant capacity. Obviously, large

scale desalination plants’ water cost is comparatively

smaller. Water recovery from single stage RO process

lies from 40 to 60 %.

Out of all the discussed desalination processes RO

is the most potential and robust technology for large

scale seawater desalination since it produces well

purified water with a lower unit product cost (Nooijen

and Wouters 1992; Ebrahim and Abdel-Jawad 1994;

Abou Rayan and Khaled 2003; Semiat 2008; El-Sadek

2010) as well as simpler to operate and maintain

compared to other desalination processes (Misdan

et al. 2012). Coupled with lower unit product cost and

lower energy demand (refer Table 1), global SWRO

production capacity has increased drastically in few

years time. As per the Table 1, desalination produc-

tion capacity using RO process technology in the

world is 44 % (Greenlee et al. 2009), and it is used by

majority of Australian desalination plants (Hoang

et al. 2009). A list of large scale SWRO plants

available and under construction in Australia is given

in Table 2. Four large scale plants are currently in

operation and others are under construction or being

commissioned. All the large scale plants use RO

technology. Interestingly, large scale RO plants have

the highest potential for further improvements com-

pared to other available processes (Blank et al. 2007).

Therefore, this paper describes the potentials and

problems in the SWRO industry only.

RO membrane technology employs semi permeable

membranes which allow saline water to separate into

two streams; (1) permeate or purified water which passes

through the membrane and (2) concentrate or brine

which contains concentrated salts and other minerals.

However, the resource needs to undergo several treat-

ment processes before and after RO membrane treat-

ment in order to make SWRO process economical and

environmental friendly. Thus, a typical SWRO plant

could be divided into five major steps (Fig. 1):

1. Intake,

2. Feed water pre-treatment,

3. High pressure pumping,

4. Membrane separation (or desalting process)

4.1. Performance of membranes,

4.2. Concentrate disposal/resource recovery,

and

5. Product quality

In this review, problems encountered in each step

have been surveyed. Furthermore, existing solutions

and drawbacks of them have been discussed. In

addition, authors suggest solutions for the current

Table 1 Desalination capacity, unit cost, energy demand and recovery of available large scale desalination processes

Desalination process World’s installed desalination capacitya (%) UPCb (US$) Combined energy demandc (kWh/m3)

MSF 40 0.62–1.97 10–16

MED 3 0.60–1.17 6–12

VC 5 Only small scale plants are available

RO 44 0.45–0.95 3–6

ED 6 Only small scale plants are available

a As at 2002; 2 % uses desalination processes other than mentioned

b UPC = Unit production cost =ðCapital cost/Plant life) + Annual operating cost

Plant capacity�Plant availabilityc Equivalent energy (for heat and electricity requirements) in terms of electrical energy

(Blank et al. 2007; Karagiannis and Soldatos 2008; Semiat 2008; Wittholz et al. 2008; Greenlee et al. 2009)


123

drawbacks and highlight the mandatory research areas

in seawater desalination. Table 3 summarises the

issues in each process with existing solutions and

suggestions. These issues and solutions are discussed

in detail in Sect. 2.

2 Treatment process

2.1 Intake

Place of intake is not vital, however objectives of a

proper intake system should be to maintain constant

seawater characteristics (temperature and salinity) and

avoid suspended and dissolved organic matter, bio-

logical activity and heavy metals and scaling

compounds in the source. In most circumstances place

of intake depends on the selection of site for the

desalination plant. Place of intake affects the intake

type (i.e. open sea intake, beach well intake or

horizontal directional drilling), intake infrastructure,

pump requirements and ultimately the necessity of

pre-treatment.

Entrainment of small marine organisms in intake

infrastructure is a major problem that desalination

plants faced, as it influences the inflow rate and it is a

threat to marine organisms (Morton et al. 1997). At

present, intake pipes undergo periodical shock chlo-

rination to remove entrained marine organisms, but the

operational cost is higher (NCED 2010). Impingement

of marine fauna in intake filters is another environ-

mental concern (Morton et al. 1997). Therefore,

Table 2 Large scale desalination plants available in Australia (Palmer 2012)

Location Owner Process Capacity (MLD) Status Completion date

Kwinana, WA WCWA MMF/RO 145 Operating 2006

Bunbury, WA WCWA UF/RO 150 Operating 2011

Karratha, WA CITIC iron UF/RO 140 Under construction 2012

Adelaide, SA SA water UF/RO 300 Being commissioned 2011

Whyalla, SA BHP billiton – 280 Planning 2014

Wonthaggi, VIC DSE MMF/RO 450 Standby mode 2012

Kurnell, NSW Sydney water MMF/RO 250 Operating 2010

Gold coast, QLD SEQ water MMF/RO 125 Operating 2009

Total 1,840

(1) (2)

(4.1)

(3)

(5)

(4.2)

Fig. 1 Schematic of a typical SWRO plant (Kim et al. 2009). ERD, HP and LP denote energy recovery device, high pressure and low

pressure, respectively


123

Table 3 Key issues in seawater desalination, current solutions and suggestions for overcoming drawbacks

SWRO step Associated problems Existing solutions Essential study areas

Intake 1. Rust and valve problems 1. Shock chlorination to remove

entrained marine organisms in

intake pipes

1. Development of higher corrosion

resistant piping materials/coating

materials, valves

2. Entrainment and Impingement of

small marine organisms

2. Use corrosion resistant pumps 2. Alternative for shock chlorination

3. Threat to marine environment as

pipe lines acts as artificial reefs

3. Proper intake systems in a way that it

minimizes disturbing coastal hydrology

4. Pipe lines disturb the seafloor; surf

zone hence changes coastal

hydrology

Pre-treatment

(low pressure

membrane)

1. MF-UF cleaning (Cost of cleaning

exceeds cleaning costs associated

with RO membranes)

1. Land disposal 1. Alternatives for UF/MF (current ISIa

research)

2. Replacing and transportation cost

(increase the cost of water

production)

2. Conventional pre-treatment with novel

chemicals

3. MF-UF cartridge discharge 3. Development of longer life cartridge

filters (NCED suggestion and Siemens

carrying out a research)

Pre-treatment

(chemical)

1. Pre-treated sludge disposal 1. Landfill disposal 1. Alternative coagulants for sludge

reduction

2. Amount of sludge generated 2. Recycling of ferric sludge

3. Higher chemical usage 3. Sludge volume reduction (Deakinb

research)

High pressure

pumping

1. Corrosion in pumps 1. Offset with renewable energy 1. Use of alternative membranes such as

lower hydraulic pressure membranes

2. Carbon emission from the

desalination plant

2. Use corrosion resistant pumps 2. Corrosion resistance coating to pumps

Membrane

separation

1. Brine disposal on land has a

significant adverse effect on aquifer

1. Concentrated brine diffuses to

land or sea

1. Reduce brine volume

2. Brine discharge to sea cause impacts

on marine fauna and flora

2. Metal recovery before

discharging (research stage)

2. Brine management guidelines (current

ISIa research)

3. Low water recovery (30–50 %) 3. High recovery of RO brines

using FO and membrane

distillation (research stage)

3. Improvements in high recovery

4. RO fouling (Chemical cleaning

agents increase the cost of water

production)

4. Alternative membranes (e.g. FO

still in research stage)

4. Development of better membranes

5. Disposal of used RO 5. Proper pre-treatment methods

6. Assessment of alternatives to disposal of

used RO membranes (current ISIa

research)

Product quality 1. Higher concentration of Br- in

product water

1. Boron removal using ion

exchange, multi stage RO, EDR,

and electro-coagulation

1. Proper boron removal method

2. Treatment of Br- and I- (DBFs) 2. Proper guidelines for limits

3. Boron removal

a ISI—Institute for Sustainability and Innovation, Australia

b Deakin—Deakin University, Australia

(Morton et al. 1997; Latorre 2005; Mohamed et al. 2005; Elimelech 2007; Jacob 2007; Tularam and Ilahee 2007; Vedavyasan 2007; Sarp et al.

2008; Agus et al. 2009; Jeppesen et al. 2009; Martinetti et al. 2009; Ji et al. 2010; NCED 2010; Vollprecht 2013)


123

further improvements in this area are needed. How-

ever, Gary Amy (2013) reports that impingement and

entrainment of marine organisms is not an issue with

beach well intake system. However life span of beach

well intake system is shorter compared to direct intake

systems. Figure 2 shows pictures of surface (open sea)

intake system and deep well intake system. As Fig. 2a

illustrates, open sea intake gives a negative visual

impact on seashore.

As per the literature survey and personnel commu-

nications, it was found that most of the Australian

desalination industries face significant corrosion

issues in the intake piping, pumps and valves (Harris

2012). Major corrosion resistant materials currently

use in desalination industry are (Valdez and Schorr

2010):

1. Ni containing alloys (Ni based alloys, Cu–Ni

alloys and stainless steel)

2. Titanium and aluminium alloys (UNS 95052)

Further, for piping and storage vessels following

non-metallic materials and composites are being used

(Habib and Fakhral-Deen 2001; Johnson et al. 2013):

1. Polyethelene (PE)

2. Polypropylene (PP)

3. Polyvinylchloride (PVC)

4. Fiber reinforced plastic (FRP) (e.g. fiber rein-

forcement in a polymer resin)

Figure 3 shows a cross section of a pump where

attention is needed for corrosion resistant as well for

high pressure resistant (during desalting process).

Manifold includes ports which direct seawater by

suction to discharge ports. Valve body plate, pump

body and spacer body are also in contact with flowing

seawater, therefore they need to be made up of high

corrosion resistant materials (Johnson et al. 2013).

Most of the pumps are designed with composites as

mentioned above (e.g. FRP). However, intake piping,

pumps and valves still associated with severe corro-

sion attacks. Figure 4 shows chloride induced stress

corrosion cracking (SCC) in a 316L vent system

caused by chlorides and crevice corrosion under

victaulic coupling in high pressure piping. Intake

and pre-treatment process (Sect. 2.2) line face more

severe corrosive conditions than high pressure desalt-

ing process (Sect. 2.4) due to presence of residual

chlorine (Olsson 2005). Therefore, development of

cost effective higher corrosion resistant piping mate-

rials or coating materials in salt environment may be a

competitive research area in desalination. Pumps,

valves and other machinery parts are in a need of

proper corrosion resistant layer treatments.

2.2 Feed water pre-treatment

Pre-treatment is the most integral part in SWRO as it

will lead to the reduction in membrane fouling, higher

recovery, longer membrane life and higher quality

product water. Intake seawater is pre-treated to filter

debris, suspended particles, dissolved organics, and

micro-organisms providing significant operational

benefits such as lower RO replacement rates and

reduced backwash frequencies. Pre-treatment meth-

ods may vary depending on the influent water qualities

such as suspended solids (SS) concentration and silt

Fig. 2 a Deep sea water intake system and b horizontal directional drilled beach wells (Alvarado 2008)


123

density index (SDI), investment cost, and environ-

mental impact assessments. Table 4 shows character-

istics of intake seawater at Perth Seawater

Desalination Plant (PSDP), Australia (Vollprecht

2013). Drawing water contains 35,000–37,000 mg/L

salinity.

Blank et al. (2007) has summarised most R&D

needed areas in each large scale desalination process.

According to the report, pre-treatment is one of the

most R&D needed areas in large scale RO desalination

process (Blank et al. 2007). Intake seawater is being

pre-treated using (1) chemical treatments (conven-

tional coagulation and filtration) and/or (2) low

pressure membrane treatment (microfiltration/ultrafil-

tration). Conventional pre-treatment needs more space

and improved sludge management options, but

requires lower investment cost and lower energy

requirements compared to low pressure membrane

treatment (NCED 2010). The surface seawater SDI of

13–25 was reduced below 1 through ultrafiltration pre-

treatment whereas conventional pre-treatment failed

to reduce SDI below 2.5 (Brehant et al. 2002). Even

though SDI below 3 is typically acceptable for RO

systems, much lower SDI reduces the RO flushing

frequency (Kremen and Tanner 1998). RO cleaning

frequency with conventional pre-treatment (coagula-

tion ? 2 stage sand filtration) is 4–12 times per year

whereas only 1–2 times per year with UF membrane

pre-treatment (Kim et al. 2009). The issues in two

Fig. 3 Parts of the pump which must withstand corrosive

environment as well as high pressures for the durability of the

equipment (Johnson et al. 2013)

Fig. 4 a, b Chloride

induced stress corrosion

cracking (SCC) in a 316L

vent system and crevice

corrosion under victaulic

coupling in high pressure

piping made of c 316L

(Jeddah) d 904L (Spain)

(Olsson 2005)


123

pre-treatment processes are discussed in Sects. 2.2.1

and 2.2.2, separately.

2.2.1 Conventional treatment

In general, chemical pre-treatment is more often used

technique in current operating SWRO plants (Hoang

et al. 2009). Large scale SWRO plants (Plant in Perth,

Australia and worlds’ largest desalination plant in

Fujairah, UAE which produce 144 and 170 ML/day,

respectively) pre-treat their seawater using chemical

treatment methods. Furthermore, among 32 desalina-

tion plants surveyed by CSIRO, Australia, approxi-

mately half of plants use conventional pre-treatment

options (Hoang et al. 2009). FeCl3, FeSO4 and Alum

are the most commonly used coagulants and use

additional chemicals as coagulant aids, disinfectants

and scaling control agents.

Generated sludge needs to be disposed in a way that

it minimize the negative effects to the environment.

However, major issue in sludge management is

transportation and disposal which takes more than

75 % of total sludge treatment Operation and main-

tenance (O&M) cost (Vollprecht 2013). Figure 5

shows a cost analysis for sludge treatment (These

values have calculated considering one particular

day). Chemicals and power take only 1.9 and 1.4 %

of the total O&M cost, respectively. Transportation

and disposal take 18.4 and 78.3 %, respectively, which

is significantly a higher amount. Therefore, it is

evident that reduced sludge volume could significantly

reduce transportation and disposal expenses associ-

ated with conventional treatment.

2.2.2 Low pressure membrane treatment

This technology is superior solid removers, smaller in

plant size, less sensitivity to changes in influent, and

simpler to operate compared to conventional pre-

treatment (NCED 2010). However, membrane foul-

ing, and large capital (up to 25 % higher) and

operational (energy, cleaning, disposal and replace-

ment of cartridge) costs are becoming vital industrial

Table 4 Intake seawater properties as in July 2012 at PSDP

(Vollprecht 2013)

Parameter Concentration (mg/L)

pH 8.17

Conductivity at 25 �C 5100 mS/m

Total filtered solids 36,500

Suspended solids 30

Total alkalinity 116

Alkalinity as HCO3 139

Carbonate \1

Calcium—unfiltered 420

Magnesium—unfiltered 1,342

Hardness as CaCO3 6,590

Aluminium—unfiltered \0.16

Manganese—unfiltered \0.04

Potassium—unfiltered 175

Sodium—unfiltered 11,300

Strontium—unfiltered 7.5

Boron—unfiltered 4.9

Sulphate—unfiltered 2,889

Sulphur—unfiltered 964

Barium—unfiltered \0.004

Silicon (as SiO2) by DA \0.2

Nitrogen–ammonia \0.005

Nitrogen—Kjeldahl \0.02

Nitrogen—NO2 ? NO3 0.010

Nitrogen—NO2 \0.002

Nitrogen—NO3 0.010

Total nitrogen \0.02

Total iron \0.06

Phosphorous—total 0.016

Chloride 20,510

Bromide 72.6

Fluoride 0.70

Total organic carbon (TOC) 0.9

Fig. 5 Operating and maintenance cost analysis for sludge

treatment (Vollprecht 2013)


123

issues, as they increase the water cost per unit

(Vedavyasan 2007). Table 5 summarises the specific

energy comparison of conventional and membrane

process. Specific energy consumption of conventional

pre-treatment is *0.07 kWh/m3 of effluent whereas

membrane technology consumes *0.1 kWh/m3.

Typical life time of UF membrane is 5–10 years

where as life time of conventional pre-treatment

system (coagulation ? 2 stage sand filtration system)

is 20–30 years. Increasing issue in low pressure

membrane pre-treatment is disposal of cartridge.

Literature explains that cost of low pressure mem-

brane cleaning exceeds cleaning costs associated with

RO membranes (NCED 2010). Therefore, it is

suggested that development of longer life membranes

(NCED 2010), development of alternative low pres-

sure membrane technology, and development of better

chemical treatment options may enhance the quality of

pre-treatment technology.

2.3 High pressure pumping

SWRO desalting process requires electric power to

drive pumps that increases the pressure of the seawater

to a required value. One of the environmental concerns

is that SWRO plants can be noisy due to use of high

pressure pumps (Tularam and Ilahee 2007). The

required pressure depends on the salt concentration

of saline solution and it is normally around 70 bar for

seawater desalination (Charcosset 2009) accounting

*50 % of total operational costs. When salinity varies

from 18,000 to 45,000? mg/L, typical pressure

requirement vary from 44.8 to 82.7 bar. In general,

for every 1,000 mg/L increment in seawater salinity,

pressure requirement is increased by 0.76 bar to

produce equivalent amount of permeate (Water Reuse

Association 2011). Previous SWRO plants consume

up to *10 kWh of electric energy to produce one

cubic meter of fresh water from seawater (Colombo

et al. 1999; Semiat 2008). Interestingly, with techno-

logical developments and new membrane materials,

recent SWRO plants consume as low as 4 kWh/m3 of

product water (Blank et al. 2007). In most of the

SWRO plants, energy recovery devices recover the

residual pressure of brines. Pelton wheel turbines

(PWT), pressure exchangers (PX) and hydraulic

turbochargers (HTC) are the energy recovery devices

available in SWRO systems. Perth, Australia desali-

nation plant recovers around 25 bars using PX, which

is then transferred to the feed flow of seawater with an

efficiency rate of 95 %.

Lee et al. (2010) reports that an average of 4 kWh

electric energy to produce one cubic meter of purified

water from seawater resulting in emission of 1.78 kg

of CO2 (Lee et al. 2010). Lower the energy consump-

tion lower the relevant emissions associated with RO.

When energy consumptions are reduced from 4 to

2 kWh/m3, CO2 emission has dropped from 1.78 to

0.92 kg/m3 of desalted water, which is nearly 50 %

lower (Raluy et al. 2006). Consequently, most of the

desalination plants use renewable energy sources to

supply their energy demand. Desalination plant in

Gold Coast, Australia offset with solar, wind and

hydro energy and PSDP in Perth, Australia, consume

wind energy in order to reduce the greenhouse gas

Table 5 Percentage cost and specific energy comparison at each SWRO step

SWRO step Cost/total

water price (%)

Specific energy

(kWhea/m3 of product)

Energy/total power

requirement (%)

Intake 0.79b

Pre-treatment

Conventional 4.1 (chemicals) 0.07c 8–12

Membrane 0.10c

High pressure pumping 25.4 (energy) 2.83d 65–85

Desalting process 5.4

Post treatment 1.8 \2

ae-Electric, b intake ? raw water supply ? feed booster, c kWh/m3 of effluent, d Pumps ? turbine ? motors ? auxiliary ? lighting

(Wilf and Klinko 1998; Dreizin 2006; Semiat 2008; Charcosset 2009; Water Reuse Association 2011)


123

emission. Use of energy efficient pump could be

another solution to minimize the energy consumption.

Since most of the plants are not affluent with

renewable energy sources and high pressure RO

membranes generally leads to serious membrane

fouling, it is required to seek membranes which need

lower hydraulic pressures. Forward osmosis (FO) is

such alternative technology which operates at low or

no hydraulic pressure with lower electrical consump-

tion (Elimelech 2007).

2.4 Desalting process

RO membrane separates pre-treated seawater into two

streams; permeate and concentrate under a hydraulic

pressure higher than the osmotic pressure, therefore

higher energy requirement (65–85 %) compared to

other SWRO steps (Refer Table 5). Permeate requires

further treatment before distribution to communities.

Concentrate or brine needs further management

options before discharge. Properties of permeate and

brine depend on the performance of membrane unit.

Membrane fouling, which leads to poor membrane

performance, is the major factor that limits use of RO

technology to treat seawater. (Luo and Wang 2001).

Therefore, under desalting process (1) performance of

membrane and (2) brine management/resource recov-

ery will be discussed separately in Sects. 2.4.1 and

2.4.2 respectively.

2.4.1 Performance of membranes

Maintaining a stable performing membrane process

is one of the most R&D needed areas in large scale

RO desalination process (Blank et al. 2007). Foul-

ing of RO membrane is a huge problem faced by

SWRO industries worldwide (Sheikholeslami and

Tan 1999; Yang et al. 2010; Alhadidi et al. 2012).

Four types of fouling in the order of significance are

bio-fouling, scaling, organic fouling and fouling due

to particles (Pandey et al. 2012). Luo and Wang

(2001) believed that the adsorption of colloids and

organics would be the vital factors which acceler-

ates fouling tendency (Luo and Wang 2001).

Furthermore, they report that the preferential

order of essential fouling agents is silica colloids [adsorbed organic compounds [ particulate matter

(iron and aluminium colloids) [ microorganisms [

metallic oxides. As a result, numerous researches

are being conducted for proper pre-treatment tech-

niques since properties of feed water to the mem-

brane affects RO membrane fouling. Sequential

membrane cleaning (backwash flashing) is also

required to prevent from foulants.

Bio-fouling is due to unwanted growth and depo-

sition of biofilms which leads to higher operating

pressure, lower recovery, more frequent chemical

cleaning, and shorter membrane life (Matin et al.

2011). Factors affecting microorganisms’ adhesion to

membrane surfaces are (Nguyen et al. 2012);

1. Microorganisms (species, population density,

their nutrient status, hydrophobicity, charges,

physiological responses etc.),

2. Properties of membrane surface (chemical com-

position, surface charge, surface tension, hydro-

phobicity, conditioning film, roughness, porosity

etc.) and

3. Characteristics of feed seawater (temperature, pH,

dissolved organic matter, dissolved organics,

suspended matter, viscosity, shear forces, bound-

ary layer, flux etc.)

Bio fouling can be minimized by controlling

bacterial and viral characteristics in feed sea water

stream (such as plankton, bacteria, fungi, algae).

Chlorination deactivates these microorganisms in the

feed stream. Thus, it has been used in SWRO

industries to decrease membrane bio-fouling prob-

lems. However, membrane must be chlorine resistant

(e.g. CTA membrane, however their application is

limited to waters of relatively low salinity). In order to

increase the life of the chlorine resistant membrane,

sodium metabisulphite (NaHSO3) should be added

prior to RO or chlorination dose should be optimised

as excessive injection promotes membrane degrada-

tion (Fujiwara and Matsuyama 2008). Furthermore,

surface modification of RO membrane to protect the

chlorine sensitive sites of the membrane using surface

coating method have also been successfully investi-

gated in lab scale (Kwon et al. 2012). UV, sand

filtration, NH2Cl, ClO2 and ozone are other the

physical and chemical disinfectants used for bio-

fouling control of SWRO membranes (Matin et al.

2011). However, all these disinfectants have merits

and demerits. Consequently, requirement of chemical

agents/cleaning agents leads to increase the water

production cost.


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2.4.2 Concentrate disposal/resource recovery

Currently, Brine is discharge back to the sea (diffuses at

a specific rate at which they get blend with seawater),

land (ground infiltration, evaporation basin, discharge to

beach, Zero liquid discharge) and dispose to sewer lines

(Morton et al. 1997; Ahmed et al. 2001; Sadhwani et al.

2005). Evaporation ponds and zero liquid discharge

(brine concentrators) are the most expensive options due

to statutory groundwater regulations and energy require-

ments, respectively (Greenlee et al. 2009).

Post treatment of brine take up a significant

percentage of the total cost of desalination. Therefore,

recent research focus on reducing brine volume which

will reduce the operational and maintenance cost.

Brine volume can be reduced by further concentrating

it (Martinetti et al. 2009), applying alternative mem-

branes for RO (Elimelech 2007) and increasing

recovery of RO unit. Currently, these options have

attracted a lot of research interest and pilot scale plants

have been used. Brine disposal on land has a

significant adverse effect on aquifer (Mohamed et al.

2005). On the other hand by discharging back to the

sea there can be impacts on marine fauna and flora

(Latorre 2005) and algae formation near the beach

(Ahmed et al. 2001). Many of the disinfection by-

products (DBPs) formed during pre-treatment and post

treatment (a result from reactions between organic and

inorganic matter in water with chemical disinfection

agents such as bromide, ozone, Cl2 etc.) will be

discharged with the brine and they could affect marine

ecosystems if they are not diluted sufficiently after

discharge (Agus et al. 2009). On the contrary, from a

4 year continuous monitoring results by University of

Western Australia, Palmer reports that (Palmer 2012)

there is no any impact on marine fauna and flora.

However, there could be an impact on the marine

system as Palmer 2012 reports from a research that

was conducted only for a short period of time. Authors

suggest that implementing national level guidelines

and standards for brine discharge (either to sea or land)

could be a better initiative to control impacts on

environment.

2.5 Product quality

Most importantly final product should meet statutory

water quality standards and this process involves pH

adjustment, disinfection, boron removal, addition of

corrosion inhibitors. Higher concentration of bromide

in product water is a vital issue. Bromide concentra-

tion in intake of Perth seawater treatment plant is

72.6 mg/L (refer Table 3). Higher concentration of

bromide enhances the production of brominated DBFs

during chlorination (Agus et al. 2009). Fortunately,

bromoform (CHBr3), and other brominated trihalo-

methanes and haloacetic acids formed during pre-

treatment, which could be present in permeate, are

expected to be below regulatory standards. However,

compounds such as bromophenols and brominated

analogs of mutagen X compounds (MX) may also be

formed during continuous chlorination. Further inves-

tigations are necessary to assess the formation of these

compounds and their toxicity levels (Agus et al. 2009).

Desalination water production cost significantly

depends on the boron reduction method. According to

World Health Organization (WHO) maximum boron

concentration level for drinking water was 0.5 mg/L

for many years. Unfortunately, many of the existing

SWRO plants are struggling to meet this WHO

restricted level. However recent WHO drinking water

regulation allows boron concentration up to 2.4 mg/L.

This limit based on human health concerns only.

When consider irrigation purposes, higher boron

concentrations have an adverse effect on some plant

species. Australian Drinking Water Guidelines by

National Health and Medical Research Council

(NHMRC) declare boron limit to be\4 mg/L.

Boron rejection by RO membranes is affected by

permeate flux, operating temperature, operating pres-

sure and largely depend on pH. Current applied

SWRO systems’ boron removal efficiency is

85–90 % at nominal conditions, however largely

depend on the membrane type. In RO desalting

system, higher the salt concentration higher the boron

removal efficiency is (Sarp et al. 2008). Ion exchange

resins demonstrate a significant benefit for removing

boron in RO desalination process (Jacob 2007). Other

than that, multi stage RO, electro-coagulation and

electro dialysis are available options for boron reduc-

tion to national permissible level (Bick and Oron

2005). However, more research is needed in this area.

3 Future perspective

Pressure retarded osmosis (PRO)/FO is a novel

emerging technology which supports to improve the


123

SWRO process by increasing plant’s recovery. FO is

being used to concentrate the brine (Martinetti et al.

2009), to dewater pre-treatment sludge (Liyanaarach-

chi et al. 2013) and to replace the second stage of two

staged RO system etc. Kim (2013) suggests a sustain-

able seawater desalination process i.e. a hybrid system

combined with RO (e.g. MD–PRO or RO–PRO)

which will eventually achieve following three goals.

(1) Volume reduction using MD (30 % volume

reduction), (2) Recovery of osmotic energy (PRO)

and (3) Valuable resource recovery (e.g. Li to be used

in batteries, composite of materials to blend with

construction materials such as concrete). However,

FO/PRO applications are still in laboratory scale and

pilot plant scale (McCutcheon et al. 2006; Elimelech

2007) due to various incompetence facts such as

significantly lower flux, higher bio-fouling tendency,

and complexity of regeneration of draw solution from

product water. Therefore numerous researches are

being conducted on the application of FO in SWRO

and this is the competitive research area to date in the

field of desalination.

4 Conclusions

This review explains the potentials and problems of

current SWRO industry. The study has shown that pre-

treatment and desalting process associated more issues

compared to other processes. Furthermore, following

areas need further attention;

1. Corrosion in intake piping materials and other

equipment

2. Brine management and

3. Boron and bromide level management in product

water.

Acknowledgments The authors would like to acknowledge

the financial support of the VU-CRGS grant from Victoria

University. Authors would like to thank Robert Vollprecht,

Degremont PTY LTD for supplying valuable data throughout

the study.

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