Chung-FO Technologies and Challenges for Clean Water and Clean Energy-COCHE 2012

8/13/2019 Chung-FO Technologies and Challenges for Clean Water and Clean Energy-COCHE 2012

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FO membranes and cost-effectively recyclable draw

solutes. However, for direct fertigation [22] and osmotic

power generation, fertilizer and seawater are natural draw

solutes, respectively. Therefore, molecular design of FO

membraneswith high flux and power density has received

major attention in the R & D of these two applications.

For osmotic membrane bioreactor (MBR), the requiredmembrane performance may not be as stringent as those

for osmotic power and desalination [23,24], but finding

low cost and easy recyclable draw solutes for osmotic

MBR is still quite challenging unless RO retentate is

readily available to be used as the draw solute as RO

retentatemay provide adequate osmotic pressure and can

be obtained at low or no cost if available.

Although the fouling behavior of FO membranes is more

reversible than RO membranes [25,26,27], the removal

of foulants in the former is more complicated than thelatter because of the internal concentration polarization

when the feed stream faces the porous sublayer [24,28

32]. In addition, owing to the high hydraulic pressure in

the high-pressure compartment, it is believed that the

Current forward osmosis technology development Chung et al. 247

Figure 1

Diluted draw

solution

Draw solution

Fresh water

Feed

Concentrated

feed

FO

membrane

Draw solution

regeneration

Retentate of

recycled water

Clean

water

Seawater

River water

Seawater

Pressure

exchanger

TurbineDiluted

seawater

Membrane

Pressure

exchanger

Turbine

Diluted

seawater

Membrane

(a) (b)

RO

Current Opinion in Chemical Engineering

Schematic diagrams of(a) a typical forward osmosis (FO) process and (b) osmotic power generation from the mixing of seawater and freshwater (top)

and from the mixing of RO and recycled water retentates (bottom).

Table 1

Benefits and challenges of different applications of FO

Applications of FO Benefits Challenges

Desalination Low energy consumption for water transport

across the semi-permeable membrane

Ineffective membranes; lack of cost effective draw solutes

Direct fertigation Fertilizers are natural draw solutes; diluted

draw solution is useful for irrigation

Limited application sites

Osmotic power generation Seawater is a natural draw solute Pretreatments of seawater and river water;

complicated fouling phenomenon owing to thehigh pressure in the seawater compartment

Osmotic membrane bioreactor Low fouling and low energy consumption Need to find low cost and easy recyclable draw solutes

www.sciencedirect.com Current Opinion in Chemical Engineering 2012, 1:246257


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fouling behavior during osmotic power generation may bequite different from that in low-pressureFO processes.So

far, apart from Statkraft patents [21], almost no academic

studies have touched this interesting subject. Table 1

summarizes benefits and challenges for each application

ofFO. Table 2 and Figure 2 show a comparison ofFO and

RO processes.

The state-of-the-art FO membranes for lowpressure processesThe desired FO membranes must have (i) high salt

retention and high water flux; (ii) low concentrationpolarization; and (iii) resistance to chlorine and wide

range of pH plus long-term stability in separation per-

formance and mechanical strength [6]. Up to the pre-

sent, four approaches have been adopted to prepare

polymeric FO membranes by using (i) the non-solvent

phase inversion method developed by Loeb and Sourir-

ajan [33]; (ii) the thin-film composition (TFC) method via

interfacial polymerization on porous substrates invented

by Cadotte [34]; (iii) the layer-by-layer (LbL) depositionof nanometer-thick polycations and polyanions on porous

charged substrates [35]; and (iv) aquaporin (Aqp) incorp-

orated biomimetic membranes [36]. Wholly integrated

asymmetric FO membranes made of cellulose triacetate

(CTA) [37,38], polybenzimidazole (PBI) [3942], cellu-

lose acetate [43,44,45,46] and polyethersulfone [47] are

typical examples of the 1st approach (as shown in

Figure 3(a)(d)), while FO membranes made of polya-

mide via interfacial polymerization on polysulfone basedsubstrates [48,49], sulfonated substrates [50,51], cel-

lulose acetate propionate (CAP) substrates [52] and nano-

fibers [53,54] belong to the second approach (as shown

in Figure 3(e), (f)). Examples of LbL FO membranes can

be found elsewhere [55,56].

Usually, membranes derived from the phase inversion

method have relatively low fluxes compared to those

membranes made from TFC approach. In addition totheir inherent differences in water permeability and salt

248 Energy and environmental engineering

Table 2

A comparison of FO and RO processes

Process Advantages Disadvantages Challenges

FO Less energy intensive for water transport acrossthe semi-membranes; more reversible fouling

Permeate water 6 product;requires a second separation step

Ineffective membranes; lack of costeffective draw solutes; limited studies

on foulingRO Permeate water = high quality product High energy consumption; some

irreversible fouling

How to improve energy recovery efficiency;

How to mitigate membrane fouling

Figure 2

Seawater(feed)

Osmotic pressure gradient (FO)No hydraulic pressure gradient

RO vs. FO

Seawater(feed)

Draw solution

NaCl

NaCl

The RO membrane is densified underhigh pressures

The FO membrane is loose underno or low pressures

Hydraulic pressure gradient(RO)

Water = Product Water Product

Reverse flux of

draw solutes

Thick sub-layer Thin sub-layer


A comparison of (a) RO and (b) FO processes.

Current Opinion in Chemical Engineering 2012, 1:246257 www.sciencedirect.com


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rejection [57,58,59], the phase inversion membrane also

tends to have a greater sublayer resistance and internal

concentration polarization (ICP) owing to the difficulties

in controlling the selective skin and sublayer morphology

simultaneously during the rapid phase inversion process,while the TFC membrane has more design flexibility by

separately tuning selective skins and sublayers with the

aid of using more porous or less tortuous membranes as

the TFC substrates. Furthermore, by applying the dual-

layer co-extrusion technology or electrospun nano-fibers,

one may

have

greater

capabilities

to

effectively

manip-ulate the sublayer morphology and significantly mitigate

the low flux issue [42,45,53,54].

To reduce the ICP effects, Wang et al. were the first in

inventing double-skinned FO membranes consisting of a

less selective nano-filtration (NF) skin layer, a fully porous

cross-section, and a highly selective RO skin layer [43].

Subsequent theoretical and experimental works have con-

firmed the unique characteristics and advantages of this

type ofmembranemorphology suchas low fouling and low

ICP [60,61]. In addition, Fang et al. [62] and Su et al. [63]

also extended the basic principle of double skins to fab-

ricate double-skinFO hollow fibers consisting of a NF and

a RO skins. On the contrary, Wang et al. [50] and Widjojo

et al. [51] adopt another scheme to circumvent the ICP.

They reported that the hydrophilicity of porous substratesplays an important role on TFC FO membranes. TFC

membranes that are interfacially polymerized on hydro-

philic porous substrates not only showreduced ICP effects

butalso have a very high water flux (as shown in Figure 4).

So far, 22 LMH (L m2 h1) is the highest ever reported

water

flux for

TFC

FO

membranes

in

seawater

desalina-tionusing2.0 MNaCl as thedraw solution (DS) byWidjojo

et al. [64].Consistent with Wang et al. [50] andWidjojo et al.

[51]observation, Arena et al. surface modified the support

layers ofcommercially availableROTFCmembranes with

polydopamine (PDA) to improve the membranes hydro-

philicity forpressure retarded osmosis (PRO) [65].Follow-

ing the similar principle, Han et al. [66] surface modified

hydrophobic polysulfone (PSf) substrates with polydopa-

minebefore conducting interfacial polymerization. Results

show effective enhancements in both water flux and salt

rejection of the resultant TFC membranes.


Figure 3

Single-layer PBImembrane

40

Dual Layer PBI/PESmembrane

CA flat sheet membrane

Thin-film interfacial polymerized flat-sheet FO membrane

HTI CTA membrane Thin-film interfacialpolymerized FO hollow fiber

(a) (b)OL

(c)

(d) (e) (f)

200 m

1.53m

10.61m

1 m


Some of typical FO membranes for water reuse and desalination. (a) Single-layer polybenzimidazole (PBI) membrane1; (b) Dual Layer PBI/polyethersulfone (PES) membrane2; (c) CA flat sheet membrane3; (d) Hydration Technology Innovations (HTI) CTAmembrane; (e) Thin-film interfacial

polymerized flat-sheet FO membrane4; and (f) Thin-film interfacial polymerized FO hollow fiber5.1 Reprinted from ref. [40] with permission from Elsevier.2 Adapted from ref. [42] with permission from Elsevier.3 Adapted with permission from ref. [43]. Copyright (2010) American Chemical Society.4 Reprinted from ref. [50] with permission from John Wiley and Sons.5 Reprinted with permission from ref. [111]. Copyright (2012) American Chemical Society.



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So far, FO membranes made from LbL have shown a

trade-off between the water fluxes and the reverse salt

leakages. LbL membranes reported either have low

reverse salt leakages but low water fluxes (for the

cross-linkedones) [56] or high water fluxesbutwith high

reverse salt leakages (for the un-cross-linked ones) [55].Since most data were obtained by using MgCl2 as the

draw solute, no experimental data have proven that FO

membranes prepared from LbL have good rejections to

NaCl. A better design of LbL morphology and appro-

priate choices of electrolytes and cross-linkers are essen-

tial to advance LbL FOmembranes for real applications

in water reuse and desalination. FO membranes madefrom TFC/nano-fibers [53,54] also show significant

differences in performance; observed water fluxes of

66 vs. 26 LMH have been reported using 1.5 M NaCl

as the draw solution.Abetter understandingof the causes

of the differences is essential for the advancement of this

technology.

Novel

Aquaporin

(Aqp)

incorporated biomi-metic FOmembranes have recently been developed by

Wang et al. [36]. The membranes were prepared by

rupturing the AqpZ-embedded triblock copolymer

vesicles on the acrylate-functionalized polycarbonate

tracked-etched (PCTE) substrates. The planar pore-

spanning biomimetic membrane displays the highest

water flux of 142 LMH ever reported with very low

reverse salt leakage using 2.0 M NaCl as the draw

solution. However, the Aqp embedded membranes are

not mechanically strong because the selective layer is

only 10 nm in thickness.

FOmembranes for osmotic energy under PROTheoretically, the hydraulic pressure difference in the

seawater compartment during the mixing of river water

and seawater across a semi-permeable membrane under

PRO is preferred to operate at about 13.5 bars for sea-

water consisting of 3.5 wt% NaCl in order to generate themaximal energy output [19,20,21]. Since most conven-

tional FO membranes are designed for no-pressure or

low-pressure operation environments, currently available

FO membranes are likely to be damaged under this high

pressure condition.For example, based on a recent visit to

Statkraft, the latest membranes used in Statkraft are only

operated at about 6 bar because of membrane limitations[67]. Han et al. have recently developed flat asymmetric

membranes with osmotic power density in the range of 6

10W/m2 that can withstand up to 15 bar using model

seawater (0.59 M NaCl) and DI water [68,69,70]. To the

best of our knowledge, among the available membranes

for

osmotic

power

generation [19

,20,21,68

,7174], this

isthe first FO membrane that can withstand a hydraulic

pressure difference over 13.5 bar and also produce a high

energy output. It is worth mentioning that the exper-

iments to estimate membranes power density must be

conducted in actual PRO setup in which the hydraulic

pressure varies in the high pressure compartment. As the

real power density usually deviates a lot from the power

density calculated from an extrapolation of water flux vs.

pressure from the initial water flux under no hydraulic

pressure difference. As a result, any conclusion derived

from ideal theoretical predictions could be misleading.


Figure 4

20 mCross section

Porousbottomsurface

Sponge-likecross-section

Macrovoid free

Hydrophilic substrate by usingBASF materials

Draw solution concentration, NaCl (M)

Waterflux(LMH)

(a) (b)

0 1 210

20

30

40

50

60

3 4 5

Pressure retardedosmosis (PRO) mode

Forward osmosis(FO) mode

Feed (DI water): flux 33 LMH (DS: 2 M NaCl), salt reverse flux 3.6 gMHSeawater (3.5 wt% NaCl): 15 LMH (DS: 2 M NaCl)

Cross section 40k


thin film

TFCFOmembrane with macrovoid-free substrate. (a)Water flux as a function of draw solution concentration, and (b) SEM images of TFCmembrane.

Adapted from ref. [51] with permission from Elsevier.



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Although an increase in membrane thickness and poly-mer concentration during casting or spinning may

improve membranes mechanical strengths, it also results

in a much lower water flux and power density. Therefore,

the FO membrane design for power generation under

high salinity

gradients

will

be

significantly different fromthose used in conventional low-pressure environments.

One must consider membranes physicochemical proper-

ties in the wet state as well as their changes under tensile,

elongation, compression, and bending stresses [75,76].

If RO retentate is to be used as the draw solution while

retentate of recycled water (i.e. retentate fromwastewater

reclamation processes) as the feed solution as proposed

elsewhere [6] and shown inFigure 1(b), as the salinity of

RO retentate is much greater than that of seawater (about

7.98.5 vs. 3.5 wt%), it will then increase the salinity

gradient and generate higher power output. The former

can result in a much higher osmotic pressure (about 7077

vs. 28 bar at 22.5 8C) and osmotic energy than the latter,

but also create tremendous challenges for membrane

scientists to design high flux FO membranes with superhigh mechanical strengths. However, if osmotic power

generation and RO plants can be successfully integrated,

not only can it make seawater desalination less energy

dependent and more sustainable, but also significantly

alleviate the disposal and environmental issues of wasteRO retentate. In addition, since the RO retentate has

been well pre-treated in its previous processes, it can

significantly reduce the membrane fouling in the high

pressure compartment. As a result, the integration may

save some

of

expensive pre-treatment

costs

originallyrequired for seawater before PRO. In addition, the integ-

ration of RO and osmotic power generation will signifi-

cantly alleviate the disposal of highly concentrated brine

back to ocean. Therefore, from the environmental stand-

point, the integration may provide a better ecosystem for

habitats and species, water composition, and landscape.

The development of draw solutesCompared to FO membranes, the progress in draw

solutes is much slower. This is owing to the fact that it

is not trivial to design draw solutes with characteristics of

(i) good water solubility; (ii) high osmotic pressures; (iii)

low leakages or reverse fluxes; (iv) easy recovery; and (v)

membrane compatibility and (vi) zero toxicity.

Since the 1960s, many efforts have been devoted to

discover suitable draw solutes such as sulfur dioxide[77], aluminum sulfate [78], glucose [79,80], fructose

[80,81], sucrose [63], fertilizers [22], and inorganic salts

[3856,6062,82]. Prof. Elimelech and his colleagues at


Figure 5

Fe(acac)3+2-pyrrolidine245C

reflux

Fe(acac)3+triethylene glycol280C

reflux

Fe(acac)3+triethylene glycol+ polyacrylic acid

280C

reflux

2-Pyrol-MNP:

TREG-MNP:

PAA-MNP:

Structure of Tris(acetylacetonato) Iron: Fe(acac)3

OO

O

O

O

O

Fe


Schematic diagram of syntheses of water soluble magnetic nano-particles (MNP): 2-Pyrol-MNP, TREG-MNP, and PAA-MNP.Reprinted with permission from ref. [86]. Copyright (2010) American Chemical Society.



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Yale University developed the first generation of drawsolution from water and ammonium bicarbonate

(NH4HCO3) mixtures for desalination in the early

2000s. The draw solute of NH4HCO3 decomposes to

ammonia and carbon dioxide upon heating at about

65 8C and

it

can

be

regenerated

by

re-dissolution[2,83]. However, using compounds with small mol-

ecules as draw solutes may not be economic and practical

because of high energy consumption in their recycles and

significant reverse fluxes in FO processes. Small molecu-

lar salts may also induce clogging in the supporting layer

and lead to severe fouling and internal concentration

polarization [30,31,84,85].

By taking advantages of the characteristics of high surface

area and high osmotic pressure, hydrophilic magnetic

nanoparticles were developed by Ling et al. [86] and

Ge et al. [87] as draw solutes. The original idea was to

produce pure water as well as to recapture nanoparticles

by using a magnetic separator. Figure 5 shows syntheses

of water soluble magnetic nano-particles [86] and

Figure 6 illustrates the draw solution regeneration ofwater soluble magnetic nano-particles in FO processes.

However, the nanoparticles gradually clumped together

owing to the strongmagnetic field.As a result, the osmotic

pressure of draw solutions reduced after regeneration and

so did the yield of fresh water. Ling and Chung demon-

strated that the use of an ultrafiltration (UF) process can

eliminate the magnetic field induced agglomeration [88].

To enhance the separation efficiency of nanoparticles

from water and minimize the loss of nanoparticles during

the UF recycle process, Ling et al. designed the nano-

particles comprising an outer layer of a temperaturesensitive amphiphilic polymer [89]. Below 34 8C, the

nanoparticles performed as draw solutes because of stronghydrogen bonding interactions with water, while above

37 8C, the nanoparticles clumped together as hydro-

phobic globules, making them easier to be captured by

means of UF.

Recently, a series of novel draw solutes based on poly-

electrolytes of PAA-Na salts were developed by Ge et al.

[90]. The characteristics of high solubility in water and

flexibility in structural configuration enable this type of

draw solutes to generate high water fluxes yet with

insignificant reverse salt fluxes in the FO process. These

unique properties not only ensure high efficiency in water

reclamation and high quality in water product, but also

lower the replenishment cost of draw solutes. In addition,

PAA-Na salts have good stability and show repeatable

performance after many recycles. Figure 7 shows some

common draw solutes and preparation of poly(acrylic acid

sodium) (PAA-Na).

Integrated systems for clean water productionand draw solute regenerationSustainable integrated systems for water production and

draw solute recycle must be developed in order to suc-

cessfully market FO technologies. For seawater desalina-

tion, researchers have proposed the integration of FO and

RO/NF processes for draw solute recovery and clean

water production [9193]. They are technically feasiblebut economically and industrially unpractical because of

high energy costs to operate RO and NF for draw solute

recycles. If waste heat or cold energy is available, anintegratedFOMD (forward osmosismembrane distilla-

tion) system (as shown in Figure 8(a)) is a promisingprocess for seawater desalination [94]. The cold energy


Figure 6

Diluted drawsolution

Concentrated drawsolution

Feed(seawater)

Concentrated brine

FO membrane

Draw solution regeneration

N SProduct water

Magnetic field

Magnetic nano-particlesrecycled back to FO


Schematic diagram of water soluble magnetic nano-particles draw solutes for FO processes.



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refers to the heat absorption effect from the ambient

surrounding when liquefied natural gas (LNG) is re-

gasified at the LNG terminals [95]. However, the pro-

vision of low-cost waste heat for MD is the pre-condition

for the success of the integrated FOMDprocess [96,97].

By using highly hydrophilic nano-particles as draw

solutes, one may minimize the fouling issues including

scaling and crystallization in MD. Several attempts have

been made. Yen et al. [98] and Wang et al. [99] were one of

the firsts demonstrating the FOMD process for water

reuse and protein enrichment applications, respectively.

Su et al. extended their works by using a novel CAP

polymer as the FO membrane material and 0.5 M MgCl2as the draw solution for wastewater reclamation [100],

while Ge et al. developed a polyelectrolyte-promoted

FOMD hybrid system for the recycle of wastewater


Figure 7

C CC

O OH

n

NaOH

H

H

H

C CC

O O-Na+

n

H

H

H

PAA PAA-Na

Mg2+Cl2

Na+Cl

NH4HCO3or NH3/CO2

O

OH

OH

OHO CH2OH

CH2OH

CH2OH

OH

OHO

Sucrose

(b)

(a)

Magnetic nanoparticlesSalts


(a) Some common draw solutes and (b) preparation of poly(acrylic acid sodium) (PAA-Na).

Figure 8

Drawsolution

feedsolution

(a) (b)

Drawsolution

Drawsolution MD

FeedClean water

FO MD

feedsolution

Drawsolution

Drawsolution

Feed

Clean water

FO RO


Integrated (a) FOMD and (b) FORO systems to regenerate the draw solution and produce water.



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and an acid dye [101]. High performance home-made

polyvinylidene fluoride (PVDF) membranes [102104]

were used in their studies to recycle draw solute and

produce product water. Many useful design principles

and membrane modifications for MD can be found else-

where

[105

107].

However,

to

the

best

of

our

knowledge,no demonstration of FOMD process is available for

seawater desalination. This is owing to the fact that we

still lack (1) high performance FO membranes with high

fluxes and high salt rejections; and (2) cost effective draw

solutes with high osmotic pressures and minimal reverse

fluxes.

For water reuse, FOUF, FONF, FOMD and FORO

integrated systemsmay have great potential depending on

thequalityof feed solutions, physicochemical properties of

draw solutions, and applications [63,99,100,101,108,109].

UF is the most preferred because it is a well-established

low energy filtration process compared to RO and NF

[110]. In addition, various types of UF membranes and

modules are commercially available.As a result, theoverall

system development and operation cost for FOUF areeasier and more affordable compared to other integrated

systems.On the contrary, ifwastebutcleanRO retentate is

employed as the draw solute, a FORO integrated system

(as shown in Figure 8(b)) is recommended to remove

mono-valent ions. A combined system comprising FO,

UF and magnetic separators may be also a good choice

for water reuse. However, most existingmagnetic separa-

tors possesshighmagneticfieldsbecause they aredesigned

for other purposes. To avoid particle aggregation, tailored

magnetic separators with tunable magnetic strengths are

needed to recycle different magnetic nanoparticles in theFO process.

ConclusionIt took about 40 years (from about 1960 to about 2000) for

RO to surpass thermal multi-effect evaporation technol-

ogies as the dominant technology in seawater desalina-

tion. Technology evolutions on both RO membranes andprocess design have been continuously taking place to

increase membrane performance and achieve better

energy efficiency and mitigate fouling. Similarly, FO

technologies may appear promising but are still in the

infancy stage. Time andmoreR &D efforts are needed in

order to

have

significant breakthroughs on

FO

mem-branes, draw solutes and their regeneration methods so

that the FO technologies can compete effectively with

the well-established RO technologies for seawater desa-

lination. Commercialization of FO for fertigation appears

promising,while cost effective and easily recyclable draw

solutes must be found for water reuse. The use of RO

retentate as the draw solute for water reuse may lower the

operation cost and bring FO closer to commercialization.

A successful integration of osmotic power generation

and RO desalination plants will entirely revolutionizethe future power and desalination industries. However,

membrane scientists must overcome the challenges todesign high flux FO membranes with extremely robust

mechanical properties to withstand the operating pressure

in the high pressure PRO process. Encouragingly, a few

breakthroughs on high flux and high strength FO mem-

branes, draw

solutes with

high

osmotic

pressures, andadvanced integrated systems for water production and

draw solute recycle have been recently demonstrated.

AcknowledgementsThis research was funded by the Singapore National Research Foundationunder its Competitive Research Program for the project entitled,Advanced FO Membranes and Membrane Systems for WastewaterTreatment, Water Reuse and Seawater Desalination (grant numbers: R-279-000-336-281 and R-279-000-339-281). The authors also thank Miss SuiZhang, Dr. Jincai Su, Dr. NataliaWidjojo, Miss Sicong Chen, Miss Yue Cuifor their help and suggestions. Special thanks are due to BASF, EastmanChemicals and Mitsui Chemicals for their financial supports as well as Prof.Donald R. Paul, University of Texas at Austin, Dr. J.J. Qin, Public UtilitiesBoard (PUB, Singapore), Prof. D. Bhattacharyya, University of Kentucky,Dr. Subhas Sikdar, National Risk Management Research Laboratory, USEPA, Prof. Gary Amy, KAUST as well as the editorial team ofCOCHE

(Prof. Sirkar and Prof. Agrawal) for their valuable suggestions.

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of special interest

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PhuntshoS, Shon HK,Hong S,LeeS, VigneswaranS:A novel lowenergyfertilizer drivenforward osmosis desalination for directfertigation: evaluating the performance of fertilizer drawsolutions. J Membr Sci2011, 375:172-181.

This paper covers forward osmosis applications from a different per-spective and provides the study of a highly relevant application forforward osmosis in agricultural industry.

23. CornelissenER,HarmsenD,deKorteKF,RuikenCJ,Qin JJ,Oo H,Wessels LP:Membrane fouling and process performance offorwardosmosismembranesonactivatedsludge.J Membr Sci2008, 319:158-168.

24. Achilli A, Cath TY, Marchand EA, Childress AE: The forwardosmosis membrane bioreactor: a low fouling alternative toMBR processes. Desalination 2009, 239:10-21.

25. Mi B, Elimelech M: Chemical and physical aspects of organicfouling of forward osmosis membranes. J Membr Sci2008,320:292-302.

26.

Mi B, Elimelech M: Gypsum scaling and cleaning in forwardosmosis:measurements andmechanisms. Environ Sci Technol2010, 44:2022-2028.

The authors presented innovative methods for in-depth studies of fouling

behavior in forward osmosis.27. Mi B, Elimelech M: Organic fouling of forward osmosis

membranes: fouling reversibility and cleaning withoutchemical reagents. J Membr Sci2010, 348:337-345.

28. Lee S, Boo C, Elimelech M, Hong S: Comparison of foulingbehavior in forward osmosis (FO) and reverse osmosis (RO).J Membr Sci2010, 365:34-39.

29. Tang CY, She Q, Lay WCL, WangR,FaneAG:Coupledeffects ofinternal concentration polarization and fouling on fluxbehavior of forward osmosis membranes during humic acidfiltration. J Membr Sci2010, 354:123-133.

30. Zhao SF, Zou L: Relating solution physicochemical propertiesto internal concentration polarization in forward osmosis.J Membr Sci2011, 379:459-467.

31. Shibutani T, Kitaura T, Ohmukai Y, Maruyama T, Nakatsuka S,Watabe T, Matsuyama H:Membrane fouling properties ofhollow fiber membranes prepared from cellulose acetatederivatives. J Membr Sci2011, 376:102-109.

32. McCutcheon JR, Elimelech M: Influence of membrane supportlayer hydrophobicity on water flux in osmotically drivenmembrane processes. J Membr Sci2008, 318:458-466.

33. Loeb S, Sourirajan S: Sea water demineralization by means ofan osmoticmembrane, SalineWaterConversion-II. Chapter 9.Adv Chem Ser1963, 38:117-132.

34. Cadotte JE: Interfacially synthesized reverse osmosismembrane. US Patent 4,277,344; 1981.

35. Podsiadlo P, Kaushik AK, Arruda EM, Waas AM, Shim BS, Xu J,NandivadaH, Pumplin BG, Lahann J, Ramamoorthy A, Kotov NA:Ultrastrong and stiff layered polymer nanocomposites.Science 2007, 318:80-83.

36.

Wang HL, Chung TS, Tong YW, Jeyaseelan K, Armugam A,Chen ZC, Hong MH, Meier W: Highly permeable and selectivepore-spanning biomimetic membrane embedded withAquaporin Z. Small2012, 8:1185-1190.

This study reported a very high water flux for biomimetic membranes inforward osmosis and demonstrated the use of such membranes inforward osmosis.

37. Herron J:Asymmetric forward osmosis membranes. USPatent7,445,712 B2; 2008 and http://www.htiwater.com.

38. Ong RC, Chung TS: Fabrication and positron annihilationspectroscopy (PAS) characterization of cellulose triacetatemembranes for forward osmosis. J Membr Sci2012, 394395:230-240.

39. Wang KY, Chung TS, Qin JJ: Polybenzimidazole (PBI)nanofiltration hollow fiber membranes applied in forwardosmosis process. J Membr Sci2007, 300:6-12.

40. Wang KY, Yang Q, ChungTS,Rajagopalan R: Enhanced forwardosmosis from chemically modified polybenzimidazole (PBI)nanofiltration hollow fiber membranes with a thin wall. ChemEng Sci2009, 64:1577-1584.

41. Hausman R, Digman B, Escobar IC, Coleman M, Chung TS:Functionalization of polybenzimidizole membranes to impartnegative charge and hydrophilicity. J Membr Sci2010,363:195-203.

42. Yang Q, Wang KY, Chung TS: Dual-layer hollow fibers withenhanced fluxas novel forwardosmosismembranes forwaterreclamation. Environ Sci Technol2009, 43:2800-2805.

43.

WangKY, Ong RC,Chung TS:Double-skinned forwardosmosismembranes for reducing internal concentration polarizationwithin the porous sublayer. Ind Eng Chem Res 2010,49:4824-4831.

This is the first work on the invention of double skinned forward osmosismembranes.

44. Su JC, Yang Q, Teo JF, Chung TS: Cellulose acetatenanofiltration hollow fiber membranes for forward osmosisprocesses. J Membr Sci2010, 355:36-44.

45.

SuJC, Chung TS: Sublayer structure and reflection coefficientandtheir effects on concentration polarization andmembraneperformance in FO processes. J Membr Sci2011, 376:214-224.

This paper covers a holistic study on the effects of membrane structuralparameters on the forward osmosis performance.

46. Zhang S, Wang KY, Chung TS, Jean YC, Chen HM:Moleculardesign of the cellulose ester-based forward osmosismembranes for desalination. Chem EngSci2011, 66:2008-2018.

47. YuY, Seo S,KimIC,LeeS:Nanoporous polyethersulfone (PES)membrane with enhanced flux applied in forward osmosisprocess. J Membr Sci2011, 375:63-68.

48.

Yip NY, Tiraferri A, Phillip WA, Schiffman JD, Elimelech M: Highperformance thin-film composite forwardosmosis. Environ SciTechnol2010, 44:3812-3818.

This study is one of the firsts to report the achievement of highwater fluxby inventing thin film composite membranes specially designed forforward osmosis.


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49.

Wang R, Shi L, Tang CY, Chou S, Qiu C, Fane AG:Characterization of novel forward osmosis hollow fibermembranes. J Membr Sci2010, 355:158-167.

This study is one of the firsts to report the achievement of highwater fluxby inventing thin film composite hollow fiber membranes speciallydesigned for forward osmosis.

50. Wang KY, Chung TS, Amy G: Developing thin-film-composite

forward

osmosis membranes based

on the PES/SPSfsubstrate through interfacial polymerization. AIChE J2012,58:770-781.

51.

Widjojo N, Chung TS, Weber M, Maletzko C, Warzelhan V: Therole of sulphonated polymer and macrovoid-free structure inthe support layer for thin-film composite (TFC) forwardosmosis (FO) membranes. J Membr Sci2011, 383:214-223.

This study reported the highest water flux performance for forwardosmosis desalination to date.

52. Li X, Wang KY, Helmer B, Chung TS: Thin-film compositemembranes and formation mechanism of thin-film layers onhydrophilic cellulose acetate propionate substrates forforward osmosis processes. Ind Eng Chem Res, http://dx.doi.org/10.1021/ie2027052.

53.

Song X, Liu Z, Sun DD: Nano gives the answer: breaking thebottleneck of internal concentration polarization with ananofiber composite forward osmosis membrane for a high

water production rate.

Adv Mater2011, 23:3256-3260.This study is one of the firsts to report using a very porous nanofibermembrane as the support for TFC membranes with reduced ICP.

54.

Bui NN, Lind ML, Hoek EMV, McCutcheon JR: Electrospunnanofiber supported thin film composite membranes forengineered osmosis. J Membr Sci2011, 385386:10-19.

This study is one of the firsts to report using a very porous nanofibermembrane as the support for TFC membranes.

55. QiS,QiuCQ, Tang CY: Synthesis andcharacterization of novelforward osmosis membranes based on layer-by-layerassembly. Environ Sci Technol2011, 45:5201-5208.

56. Qiu C, Qi S, Tang CY: Synthesis of high flux forward osmosismembranes by chemically crosslinked layer-by-layerpolyelectrolytes. J Membr Sci2011, 381:74-80.

57. Sagle A, Freeman B: Fundamentals of membranes for watertreatment.The Future of Desalination in Texas. Austin, TX:Texas Water Development Board; 2004: 137154.

58.

Geise GM, Lee HS, Miller DJ, Freeman BD, McGrath JE, Paul DR:Water purification by membrane: the role of polymer science.J Polym Sci Part B: Polym Phys 2010, 48:1685-1718.

This paper is an in-depth study on polymer science to relate how thepolymer basic characteristics affect membranes water transport proper-ties.

59. Zhang S, Zhang RW, Jean YC, Paul DR, Chung TS: Celluloseesters for forward osmosis: characterization of water andsalttransport properties and free volume. Polymer2012,53:2664-2672.

60. Zhang S,Wang KY, Chung TS, ChenHM, JeanYC, Amy G:Well-constructed cellulose acetate membranes for forwardosmosis: minimized internal concentration polarization withan ultra-thin selective layer. J Membr Sci2010,360:522-535.

61. Tang CY, She Q, LayWCL,Wang R,Field R,FaneAG: Modelingdouble-skinned FO membranes. Desalination 2011,283:178-183.

62. Fang W, Wang R, Chou S, Setiawan L, Fane AG: Compositeforward osmosis hollow fiber membranes: integration of RO-andNF-like selective layers to enhancemembrane propertiesof anti-scaling and anti-internal concentration polarization. JMembr Sci2012, 394395:140-150.

63. Su JC, Chung TS, Helmer BJ, de Wit JS: Enhanced double-skinnedFOmembraneswithinner dense layer forwastewatertreatment andmacromolecule recycle using Sucrose as drawsolute. J Membr Sci2012, 396:92-100.

64. Widjojo N, Chung TS, Weber M, Maletzko C, Warzelhan V: Asulfonated polyphenylenesulfone (sPPSU) as the supportingsubstrate in thin film composite (TFC) membranes with

enhanced performance for forward osmosis (FO), submitted forpublication.

65. Arena JT, McCloskey B, Freeman BD, McCutcheon JR: Surfacemodification of thin film composite membrane support layerswith polydopamine: enabling use of reverse osmosismembranes in pressure retarded osmosis. J Membr Sci2011,375:55-62.

66.

Han G, Zhang S, Li X,Widjojo N,ChungTS: Thin film compositeforward osmosis membranes based on polydopaminemodified polysulfone substrates with enhancements in bothwater flux and salt rejection. Chem Eng Sci2012, 80:219-231.

This paper demonstrates the improvement of separation performance ofthin-film composite FO membranes.

67. Chung TS: Personal communication during a recent visit toStatkraft in Oct 13, 2011.

68.

Han G, Zhang S, Li X, Chung TS: High performance pressureretarded membranes: break the power output bottleneck ofharvesting renewable osmotic power from nature salinity-gradient resources, in preparation.

The membranes show a very high power density and can withstand highpressures that may provide important insights to the design of mem-branes for osmotic power generation.

69. Li X, Zhang S, Han G, Sun S, Chung TS: Molecular design ofmembranes for osmotic power generation. 22nd AnnualMeeting 2012; North American Membrane Society, New Orleans:2012.

70. Zhang S, Li X, Han G, Sun S, Sukitpaneenit P, Chung TS:Membrane development for osmotic power generation atNational University of Singapore (NUS). 3rd Osmosis Summit2012; Barcelona: 2012.

71. McGinnis RL, McCutcheon JR, Elimelech M: A novel ammonia-carbon dioxide osmotic heat engine for power generation. JMembr Sci2007, 305:13-19.

72. Achilli A,CathTY,ChildressAE:Powergenerationwith pressureretarded osmosis: an experimental and theoreticalinvestigation. J Membr Sci2009, 343:42-52.

73. Yip NY, Elimelech M: Performance limiting effects in powergeneration from salinity gradients by pressure retardedosmosis. Environ Sci Technol2011, 45:10273-10282.

74. Chou S, Wang R, Shi L, She Q, Tang CY, Fane AG: Thin-filmcomposite hollow fiber membranes for pressure retardedosmosis (PRO) process with high power density. J Membr Sci2012, 389:25-33.

75. Zhang S,Fu FJ, Chung TS: Substratemodificationsand alcoholtreatment on thin film composite membranes for osmoticpower, submitted for publication.

76. Li X, Zhang S, Fu FJ, Chung TS: Deformation and reinforcementof thin-film composite (TFC) polyamide-imide (PAI)membranes for osmotic power generation, submitted forpublication.

77. Batchelder GW: Process for the demineralization of water. USPatent 3,171,799; 1965.

78. Frank BS:Desalination of seawater. USPatent3,670, 897; 1972.

79. Kravath RE, Davis JA: Desalination of sea-water by direct

osmosis.

Desalination 1975, 16:151-155.80. Kessler JO, Moody CD: Drinking-water from seawater by

forward osmosis. Desalination 1976, 18:297-306.

81. Stache K: Apparatus for transforming seawater, brackishwater, polluted water or the like into a nutritious drink bymeans of osmosis. US Patent 4,879,030; 1989.

82. Achilli A, Cath TY, Childress AE: Selection of inorganic-baseddrawsolutions for forward osmosis applications.J Membr Sci2010, 364:233-241.

83.

McCutcheon JR, McGinnis RL, Elimelech M: A novel ammonia-carbondioxide forward(direct) osmosis desalinationprocess.Desalination 2005, 174:1-11.

This paper reported an ammonium bicarbonate solution as the drawsolution that can be a viable desalination process.


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84. Hancock NT, Cath TY: Solute coupled diffusion in osmoticallydriven membrane processes. Environ Sci Technol2009,43:6769-6775.

85. Phillip WA, Yong JS, Elimelech M: Reverse draw solutepermeation in forward osmosis: modeling and experiments.Environ Sci Technol2010, 44:5170-5176.

86.

Ling MM, Wang KY, Chung TS: Highly water soluble magneticnanoparticles as novel draw solutes in forward osmosis forwater reuse. Ind Eng Chem Res 2010, 49:5869-5876.

The application of highly water-soluble magnetic nanoparticles as drawsolutes was reported for the first time in the work.

87.

Ge QC, Su JC, Chung TS, Amy G: Hydrophilicsuperparamagnetic nanoparticles: synthesis,characterization, and performance in forward osmosisprocesses. Ind Eng Chem Res 2011, 50:382-388.

Thepapergivesan investigation forthe synthesisof PEGbasedmagneticnanoparticles and their application in FO process. The draw solutesexhibited high osmotic pressures and good recovery behavior.

88. Ling MM, Chung TS: Desalination process using superhydrophilic nanoparticles via forward osmosis integratedwithultrafiltration regeneration. Desalination 2011, 278:194-202.

89. LingMM,Chung TS, LuXM:Facile synthesis of thermosensitivemagnetic nanoparticles as smart draw solute in forwardosmosis. Chem Commun 2011, 47:10788-10790.

90.

GeQC,Su JC, AmyG,ChungTS:Explorationofpolyelectrolytesas draw solutes in forward osmosis processes. Water Res2012, 46:1318-1326.

This paper firstly explored polyelectrolytes as draw solutes with low saltleakages, high salt rejection, repeatable recycling performance, noaggregation problems.

91. Yaeli J:Method and apparatus for processing liquid solutionsof suspensions particularly useful in the desalination of salinewater. US Patent 5,098,575; 1992.

92. Choi YJ, Choi JS, Oh HJ, Lee S, Yang DR, Kim JH: Toward acombined systemof forwardosmosis andreverse osmosis forseawater desalination. Desalination 2009, 247:239-246.

93. Hancock NT, Black ND, Cath TY: A comparative life cycleassessment of hybrid osmotic dilution desalination andestablished seawater desalination and wastewaterreclamation processes. Water Res 2012, 46:1145-1154.

94. Riziero Martinetti C, Childress AE, Cath TY: High recovery ofconcentrated RO brines using forward osmosis andmembrane distillation. J Membr Sci2009, 331:31-39.

95. MiyazakiT, KangYT,Akisawa A,KashiwagiT:A combined powercycle using refuse incineration and LNG cold energy. Energy2000, 25:639-655.

96. Song L, Li B, Sirkar KK, Gilron JL: Direct contact membranedistillation-based desalination: novel membranes, devices,larger-scale studies and a model. Ind Eng Chem Res 2007,46:2307-2323.

97. Al-Obaidani S, Curcio E, Macedonio F, Di Profio G, Al-Hinai H,Drioli E: Potential of membrane distillation in seawaterdesalination: thermal efficiency, sensitivity study and costestimation. J Membr Sci2008, 323:85-98.

98. Yen SK, Haja NFM, SuML, Wang KY, Chung TS: Study of drawsolutes using2-methylimidazolebasedcompounds in forwardosmosis. J Membr Sci2010, 364:242-252.

99. Wang KY, Teoh MM, Nugroho A, Chung TS: Integrated forwardosmosis-membranedistillation (FO-MD) hybrid systemfor theconcentration of protein solutions. Chem Eng Sci2011,66:2421-2430.

100. Su JC, Ong RC, Wang P, Chung TS, Helmer BJ, de Wit JS:Advanced FO membranes from newly synthesized CAPpolymer for wastewater reclamation through an integratedFO-MD hybrid system. AIChE J, in press.

101

. GeQC, Wang P,Wan CF, Chung TS: Polyelectrolyte-promotedforward osmosis-membrane distillation (FO-MD) hybridprocess for dye wastewater treatment. Environ Sci Technol2012, 46:6236-6243.

This paper firstly demonstrates the concept of a polyelectrolyte-pro-moted FOMD system. The wastewater was efficiently dehydrated andhybrid technology showed potential in other separation processes.

102.Su ML, Teoh MM, Wang KY, Su JC, Chung TS: Effect of inner-layer thermal conductivity on flux enhancement of dual-layerhollow fiber membranes in direct contact membranedistillation. J Membr Sci2010, 364:278-289.

103. TeohMM, ChungTS, YeoYS:Dual-layer PVDF/PTFEcompositehollow fibers with a thin macrovoid-free selective layer forwater production viamembrane distillation. Chem Eng J2011,171:684-691.

104. Wang P, Teoh MM, Chung TS: Morphological architecture ofdual-layer hollow fiber for membrane distillation with higherdesalination performance. Water Res 2011, 45:5489-5500.

105. SongL, MaZ, Liao X, Kosaraju PB, Irish JR, Sirkar KK: Pilot plantstudies of novel membranes and devices for direct contactmembrane distillation-based desalination. J Membr Sci2008,323:257-270.

106. Gilron J, Song L, Sirkar KK: Design for cascade of crossflowdirect contact membrane distillation. Ind Eng Chem Res 2007,46:2324-2334.

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Zhao S, Zou L, Mulcahy D: Brackish water desalination by ahybrid forward osmosis-nanofiltration system using divalentdraw solute. Desalination 2012, 284:175-181.

109. Lutchmiah K, Cornelissen ER, Harmsen DJH, Post JW, Lampi K,Ramaekers H, Rietveld LC, Roest K:Water recovery fromsewage using forward osmosis. Water Sci Technol2011,64:1443-1449.

110. Zeman LJ,Zydney AL:Microfiltration and Ultrafiltration: Principlesand Applications. Marcel Dekker, Inc.; 1996.

111

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This paper presents well-constructed thin-film composite (TFC) hollowfiber membranes with high-performance.



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Chung-FO Technologies and Challenges for Clean Water and Clean Energy-COCHE 2012