IICPIlraqi Journal ot Chemical and Petroleum EngineeringVol.10 No.3 (Septembef 2009) 5'l-56 I S S N : 1 9 9 7 4 8 8 4 A Study of Forward Osmosis Using Various Drawing Agents Adit A. Al-Hemiri-, Adil O. Sharil"and Mustrfa Hussein 'Chemical Eneinee ng Departnent - Cotlege of Engineenng - Uniwrsity of Bashdad - Ituq " Center for osnosis Research & Awlications, UniwrcW of Suwy UK Abstract This rcseqtch was ained to st1.t4, the osmotic elJiciency afthe droo solutions and the factors alfecting the perfomance of forya osnosis process. The dftr,,r' solutions 6ed 'ere masnesiun sufate hy.hate (MqSO4.7H2O), patassiun chloride (KCl), calciun chlotide (CaCl2), and amnoniun bicarbonate (NH4HC)3). It v,as found that wqtet tltx in.reases vith increasing *ate solution concentrution, and feed solution flow tate and dec rcases w ith incrcasing dnlr solution fow rate and feed solution concentration. And also found that the efrciency of the .lrN solutions is in the Caclr> KCI > Nr!HCO3> MgSOa.TH,O relrdrdr: Forward Osmosis, Draw solution, Desalination lntroduction Desalination refers to the wide range of processes designed to remove salts from waters of different qualiti€s Desalination technolog/ is in use throughout the world for a wide range ofpurposes, including providing potable ftesh water for domestic and municipal pur?oses, treated water for industrial processes, and emergency water for r€fugees or military operations Because of growing conc€ms about water scarcity and quality, and disputes over allocations of scarce water resourc€s, a tremendous amount of effort has been devoted to developing technologres to desalinate the vast quantiiies of seawater available n l. To reduce the cost of existing desalination technologies, it is prudent to focus on what makes current technologies so expensive. Energy is indisputably the most significant contributor to the cost of desalination. Hence, reduction in energJ usage is the primary objective io making desalination nore affordable [2]. Forward (or direct) osmosis (FO) is a process thal may be able to desalinate saline water sources at a notably reduced cost. In lorward osmosis, like RO, water transDofs across a semi-Dermeabl€ membrane that is impeirn*bl€ ro sah. However, instead ofusing hydraulic pressure ro create tbe driving force for water transport throueh the nenbrane, the FO process utilizes an osmotic pressure gradient. A "dra 'solution having a significantly higher osnotic pressure than the saline feed warer flows along the permeate side of the membrane, and water naturally transports across rhe membrane by osmosis. osmotic driving forces in FO can be significantly greater than hydraulic driving forces in RO, potentially leading to higher water flux rates and recoveries. The lack of hydraulic pressure may make the process less expensive than RO, while the minimization of brine discharge reduces the environmenial impact of the desalination process [3]. Previors forward osmosis efforts In 1965, Batchelder [a] described a process of adding volatile solut€s, such as sultut dioxide, to seawater or fteshwater io create a solution which may be used in a forward osmotic process to extmct wat€r from seawater. The suggested membrane to be used in this process was cellulosic in nature. Other exampl€s in the palent I J c P E V o l . 1 0 N o . 3 ( S e p t e m b e r 2 0 0 9 ) d e s c r i b e d r h e x . e o f c a n o r r o o r a s a m e m b r d n e m a r e r i a l . c a f i i e d o u r u n r i t r h e d r a $ s o t u r i o n i s s u r n c r e n f l y d r t u t e . a r t r h i c h p o i n t l h e \ o t a r i t e j o t u r e i j removed by heat;ng and/or a; srripDins. In 1472. Frant [5] descrjbed ; m;rhod or rorward o s m o s i s u s i n g a p r e c i p i t a b t e s a t r . i n r h i s c a s e a t u m i n u m s u f a r e . a s r h e _ d r a w 5 0 t u t i o n s o t u t e . j - o o s i n g o s m o s i s o f w a r e r a c r o s \ l h e m e m b r a n e . r h e d i t u r e d d r a $ s o r u U o n \ r a s d o s e d . q i l h c d l c i u m h y d r o x i d e . t e s d i n g r o r h e p r e c r p a n o n o t a t L ' m i n u m h y d r o x i d e a n d c a t c ; u m ( u t f a r e . _l-i.f*;"'"1e is remo!ed b) srandard merhods reavins rne rresh producl waler. Ercess caJciu,n hydrorjde from rne.precrprtalion s,ep can be removed by dosing wirh s u l l u r i c a c i d o r c a r b o n d i o r i d e . t { h i c h p r o d u J c , ( a r c r u m s u r l a t e a n d c a l c i u m c a r b o n a r e p r e c i p i t a r e s . r e s p e c r i v e t ) . l h r s s t e p r e q L i r e d a d d i t i o n a l s o t i d r e m o \ a l a n d t e d t o neutral pH in the product waaer. The mernbrane used rn the patenr was cetlulose acerate membrane. In i975, Kravath and Davis t6l described a process of seawater desalination achieved by forM.d osnosis of water across a cellutose acetate menbrane. Initial tests were run wirh a dialys;" ce wirh gtucose as the draw sorule a1d sea$ arer as the feed. Additional lesN $(re run with glucose dissolved in seawater as a drarv soruron. E&ergency lifeboars w€re considered as apossible use of rn-e. process in $trch seawarer was broughr abodrd a I r e b o a t a n d g t u - o s e w a s d d d e d . A d d i l i o n a l s e a $ a r e , ! r a s p a s s e d r h r o u g n a d , J t y < i s u n i r t e a d i n g r o o s m o . t a n d a o l u u o n o t l h e . e J $ a l e r g l u c o s e d r a $ " o t u l i o n . U p o nd j l u t i o n . t h e . . , . i n i r y w a s r e d u c e d r o a t e v e l t \ h e r e rngestron wa: po.sible for shon tem conrumplion. The rrar sneet cettLiose dcelate membranes did nol pertorm weil in terms satr rejeciion. Hollow fiber membran€s were also tried and resutrs improved. Draw sorure r€moval was nor considered because the sorute was intended for ingestion. In 1994 Herron t7l were awarded a parenr on a membrane mod|]e and a method to concenrrate ftufu Jurces and wrnes. In the summary ofthe inv€ntion, the rnventors reconnlended rhe us€ of 50_85 w1. %o sugar solut'on as the drarv sotution. In 2002, Mccinnis [8] described a merhod of forward osmosis using a combination of draw sotutions across several senr-pcmeable membranes. This parent c o m b i n e d t h e o - r s o f d m s s o t u l i o n r c c y c t e w l n a n osmo!icalll el.i -11 draw solurion lo increase , c(oveD . The two-stage IO prccess takes advantage of the t€nperalure dependent solubilities ofthe solut€s, in this case potassium ilrele (KNO3) and sutturdioxide (SO2). seawater was he.red and led to the FO membrane unit where a heated solution of saturated potassium nitrare s€rved as the dfaw solution. The diluted draw soruuon was sent !o a nerv chamber where it was cooled by i n c o m i n g s e " \ . , . . s h i c h w a s s i m u t t a n e o u s t y h e a t e d r o l h e a p p r o p n J l ( f - e d r e m p e m t u r e . U p o n c o o l i n g . . " i g n i f i c a n r p o r ' i I o i l h e K N O 3 p , e c i p i r a t e s o u r o t s o l r ' l i o n . r e d u c i n g l h e o s m o | | c p r e s s u r e . \ e n . r h e d i t u l e o d r . s o h e d . S O 2 _ a c r e d a s r h e d r a w s o t u l i o n . T h e d i t L r r e ^ r \ u r i s o r L l r o n h a d a t o w o s m o r i c p r e s s u r e i l c o n p a r i s o l wrrn Ine saturated SOj soturion. and waler diftused a c r o s s r h e m e m b r d n e $ h i t e r h e K \ O j $ d s r c j e c r e d . t h e surtur d'oxid€_$as rhen remored rhroLrgh sraniard mean., r e a \ r n g p o t a b l e q a r e r . A s o t u l e s $ e r e r e c l c l e d i n l h € In 2005 Jeffrey I2l desc.ibed a forwaro osmosrs process ror seawarerand brackish warer desalinarion. The process used a.rl'x-onium bicarbonate dmw solulion ro extract waler ftom saline feed water across a semi_ permeable polymeric membrane. Very larsc osmolc presslre5 gener,red by rhe hj8hty sotubte ammonium b i c a r b o n d l e d m $ s o l u r l o n ) i e t d h i g h t \ a l e r f l u r e s a n d c o u l d r e s u t l j n \ e r y l r i g h t e e d w d r e r r e c o \ e r i e s . L p o n moderate heating, ammonium bicarbonate decomposed into ammonia and carbon dioxide $ses thai could be sepamted and recycled as draw solutes, teaving the fresh p r o d u c J . . w a r e r . F x p e r i m e n r s $ : r h a t a b o r d r o r y _ s c a t e F O u n i l u l i l i T i n g a n r t s h e e r c e t J u t o s e l r i , a c e r a l e , . , e m o r m e demonstmted hiSh produd ware. flux and relativety high ^rl _2!0q. a novet osmoriL membrane b;oreacror t u . M B R I L p r e s e n t e d b y . n d r e r [ q l . I h e s y s r e r u t i l i T e J a subTerged foflard osmo)is (FO) membrane modute r n s r d e a b r o r e a c l o r . T h r o u g h o s m o s i s . w d r e r i s r r d n s p o n e d rom lhe mixed liquor across a semi_per.l1eabte membrane, and into a draw soturion (DS) wirh a highef o s m o l j c p r e s s u r e . t o p r o d u c e p o r a b t e $ a r e r . t h e d i t u r e d u 5 , r s r r e a l e d I n a r e v e h e o s m o s i s ( R O j u n i r : r h e b ) , proouo rs a reconcentrared DS for reuse in the FO p r o c e 5 s . M e m b r a n e t o u t i n g u a . L o n r r o e d $ i r h o s m o r ' c backl\a:hing. The FO membrdne was found r^ ,-r-- eseo oforeanic carbon ana ro;" "r "^.""i,nl_" -,"Ji", t h e O s \ 4 B R p r o c e s . r b i o r e a c r o r a n d I O m e m b m n e ) ; a s lound to remove greaier than 99% oforeanic carbon and o 8 o ; o f a m n o n i u m { i r r o g e n . r e s p e c r , , e l l : . u g e e s r n g a b e u e r c o m p a t i b i l i r y o f r h e O s M B R \ ^ i r h d o $ n ; r r e d m K o sysrems than convenrional membrane bioreacrors. The ideal drarying rgenr for forward osmosh ' f h e d m w i n g a g e n r s m u s r h a \ e a h i g h o s m o r i c e f l ; c i e n c ) . n a m e l y h i g h s o l u b i t i r y i n s a l e r a n d r e t a r i ! e t y t o $ m o l e c u l a r w e i g j r l , w h i c h c a n t e a d r o h i a h o s n o r i c pressures [21. . R . " g a r d r e s s o t t h e a p p t ; c a r i o n . o s m o l ; c a g e n t . s h o u t d r 0 e a r r y b e r n e n . s l a b l e . o f n e L r r a l o r n e a r n e u ! r u t p H . a n d n o n . l o x i c . T h e l s h o u t d n o r d e g , a d e t h e m e m b r a n e c h e m r L d l l ) f r h r o u g h r e a c r i o n . d i s s o t u r i o n . o r a d s u r p . r o n / o r p h y . i c d l l ) { f o u l i n g ) a n d s h o u t d h a v e m i n i m a t e f f e c r s on the environm€nt or human healrh. Theyshoutd also be Inexpensrve! very sotuble, and provide a hish osnotrc IJCPE Vol.'10 No.3 (September 2OO9) 52 A.til A. Al-Henii, Adil o.sha4f and pressure. For specifio applications, additional criteria will apply, e.g. in desalination concept requires the dmwing agent to be easily (both ftom a physical and enereeric standpoint) and completely recoverable ftom warer [10]. Experimental Work Figures I and 2 describes the apparatus used in laboratory-scale FO experiments Fig. I Sohematic Diagram ofspiml wound forward osmosis process Fig. 2 Sohematic Diagram offlat sheet forward osmosis Process UCPE Vol.10 No.3 (September 2009) 53 a ShJ) aJ I atuad Osnat, lj:ing yatiau, DruwtaB ̂ Aea6 The Experinental work consists of two parts. The first paft is to show the effecr of operating conditions on the $ a e r i r L x n I h e t f ( . H R m e r b m r e c o n s t r J c t e d a s spiral wound module and the second part is to show ihe efficiency of different draw soluiions in TFC-ULP membrane constructed as flat sheet module [] 11. The Experimental Procedure is a- Draw and feed solutions w€re pr€pared in the eVF glass vessels by dissolving rhe solid salt in 25 lite. of b- The oullet valve ofthe feed vessels lvas open to le! rhe solutions fi1lthe whole pipes ofthe sysiem. c- The feed solurion drawn ffon rhe feed vesselby rn€ans of a centrifugal pump to pass rhrough filrers (5 l1n) to rcmove macromolecules, colloids and suspended solids d- Then the feed solution is introduced into the permeator (onthe feed side) by neans ofahigh pressure pump e- The draw solution 's fed tothe forward osnosis unit on f- lhe feed and draw solurion flow tangential to rhe membrane in the sane direction (co-curent flow). g-The sieady - state operation took between I to 1.5 hr to achieve. During this time the conductivitjes (concentariono ofthe feed solution, draw sotution. feed solution outlet concentration and draw solution outtet concentration were measured bylhe conducrivity merer. h- A*er recording the results, the solution was drained through a drain valve. The whole sysren was washed by deionized water. Now, the system is ready for rhe next Results and Discussion TX'C-HR membrane Effect of feed solution flow rate otr lyater flux Figure 3 shows the effect of sodiun chloride feed solulion flow rate on water flux, for nagnesium sulfate hydrate draw solution at different concentrations of MgSO4.7H2O. Increasing the flow rare of feed solution caused decreasing the concentratio! buildup in the vicinity of the membran€ surface, which leads to decr€asing in osnotic pressure in the feed solution side a r d r h e n r e \ u l r i n g i n i r c r e a . i n s r h e d r i v i n g f o r c e r ^ n ) . Le. increasing th€ potent water flux Fig. 3 water flux with feed solulion flolv rare ar ditrerent draw solution concentrarion D|aw solution rate = I l,4rr and feed solunor concentrarion = 2.5g/l Effect of draw solution flow rate on waterflux Figure 4 represenls the effecr of draw solution flow rare on water flux, decreasing ofthe d.a!v solulion flow rate caused inc.easing the concentrarion buildup in the v r c i n i r ) o f t h e m e m b r a n e ' u r f a c e . f t i s l e a d s r o i r c r e a s i n g the osmotic pressure in the draw solution side and lhen increasing the water fl ux. : - g s DesolutionflowRalo Fig.4 water flux w;th drawsolution flow rate at differen! draw solution concentrarion Feed solution flow ratF60l/hr and feed solution concentratjon : 2.5 g/l U C P E V o l . 1 0 N o . 3 ( S e p t e m b e r 2 0 0 9 ) Ad A. AI_H".trt, A Effect of feed solution conceDtration on water flux Figure 5 illustrate tbe effect ol feed soruuon concentration on water flux, increasing the feed solutjon concenlration leads to decreasing the driving force and tben decreasing the wate. flux as shown in figure 5. TFC-ULP membrane Effecf ofthe Type ofDraw Solution The draw solution solute must have high osnotic efficiency, meaning that it has ro be highly soluble in water and have a low molecular weight in order to generate a high osmotic pressure. Higher osmoric pressure leads to higher water flux and feed water Using diferent rypes of draw solurions in order to find ihe best one which has the higb€st osmotic pressure to eive hieh warer flux, it was found that the order of higher J. rc"crr>J" ccrr>J- rrn rsco)>J. @sso.rruo) Calcium chloride (caclt has ahigh water flux because ir has highesl osnotic pressure (driving force) than other mat€rial studied. This is shown in figur€ ?. Tabl rysical properties ofthe draw solution solut€ 25oC&90 g! I t 0 9 9 5 9 5 2 KCl 7,1.56 21.(f 53.907 ) NrllHCOT l 5 7 l l 4 1 8 4 6 MgSOr?HrO 1 0 r 5 9 ! = Fig. 5 lvater nux with feed solution concentration for different draw solution concentration Draw solution rate =3 l/hrand feed solurion flov rate = 601/hr Eff€ct ofdraw solution concentrrtion on water llux Increasing rhe drus solution concenrrurion will increase the driving force (An) and then increasing the water flux, this is shown in figure 6. ore so dion lon.ed€uon q\ F i g . 6 $ a r e r n u x s i l h d r a $ s o l u r i o n c o n c e n l r u l i o n a l different draw solution flow rates Feed solulion flow rare - 60l,hr and feed soluli!,' concentrarion = 2.5 g/l Dftu soubm ccrced?tiln g\t Fig.7 water flux with draw solution concentration for difierent draw solurions D'at\ solulion rare - 3 l/hrand, solurion flow mte - 601,ftr and feed solution concentration = 2.5 g,4 IJCPE Vol.'10 No.3 (September 2009) t i A Sludr oJ Fotuar.l Oshosis Usihg ra, ous Conclusions The foilowing conclusions could be drawn 1iom the present research Il ll: i- Forward osmosis can be us€d to sepa.ate water rrom a concentrated slream (e.e. saljne watet that contains water and satt where rhE war€r transfer fio|n low concenrrarion (feed solution) to high concentration (d.aw soluiion) 2- The water flux produced from the osmosis cell increases by incr€asjDglbe conc€nrrarion or draw solutions and increasing the flow rare of feed solution and decreases by jncreasing the concentration of feed sotution and increasing the flow rare of draw solutions. Some results for M g S O " . 7 H ? O i n " p i r a t $ o u n d m o d u , e a r e g i v e n in the followingtable. cr Ff Cd J* 60 9 0 3 6 . 4 6 1 60 90 l 6.089 t2 9 0 l 3.562 0 . 5 6 0 1 0 3 3 . 8 3 8 0 . 5 6 0 9 0 l 5 4.623 l- Spiral-wound membrane which is normally used in reverse osmosis process can be modified and a p p l l e d a " a g o o d a l r e r n a r i \ e i n d i r e c r o 5 m o , t 4- The best draw solulion was the sotution that gives higher warer flux. It was found thar lhe order ofwaier flux for the reagenrs used !vas: CaCI2 > KCI> NH4HCO3 > MsSO4.7H2O Cd Draw solution concentrafion dl Cr Feed sotution concentralion tl fd Dmw sollrion now rare I hr F, feed solurion flow rare I hr J* watef flux L,lr.m? r Osmotic pressure ba, TFC Thin film composite HR High rejecrion ULP Ultra low pressure References l) .Heath€r Cool€y. peter H. cleick, and ca.) Wolff, (2006), Desalination, wfth a grain oi salt" Alonzo printing Co., tnc. p 9. 2 , , : f t l , * - R o b e n . 1 . . a n d M e n d c h e m . r . , (2005)," A novet nnronia_carbon dioxide forward (dnect) osmosis desaljnation process " D e s a l i n a t i o n , 1 7 4 , p . 1 - l t . 3) l:F"v, n., Robert, 1., and Menachen, E., (2006),', Desalination by anmonia,carbon dioxide forward osmosis: lnfllence of draw and feed soturion concentrations on process peribnnance,,, Journal of Membrane Science, 2 7 8 , P . 1 1 4 " 1 2 3 . 4) Batchelder, c.w., (1965) .,process for the D-emineralization of Watef'; US patenr 3, 171, 799. s ) F r a n k , B . S . , ( r 9 7 2 ) . , D e s a t i n a t i o n o f S e a Water", US patent 3, 670. 897. 6) Kravarh, R.E., and Davis, J.A., (1975)," Desalination of seawaler by directs osmosis,,, D e s a l i n a t i o n , 1 6 . p . 1 5 l - 1 6 i . ? J H € r o n . J . R . . B e a u d D . t . u . . J o c h u . r s . c . E . . a n d \ 4 e d , n a 1 . E . . 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