Fouling in Whey Reverse Osmosis - ACS Symposium Series (ACS

4 Fouling in Whey Reverse Osmosis B. R. SMITH

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 27, 1981 | doi: 10.1021/bk-1981-0154.ch004

CSIRO Division of Chemical Technology, P.O. Box 310, South Melbourne, Australia 3205

Reverse osmosis, although originally developed f o r water desalination ( 1 ) , has been a p p l i e d to numerous pollution c o n t r o l and c o n c e n t r a t i o n problems, i n c l u d i n g industrial (2) and m u n i c i p a l (3) wastewaters, pulp and paper waste streams ( 4 ) , food processing liquids ( 5 ) , and d a i r y wastes ( 6 ) . Whey is a highly polluting waste stream (BOD5 about 40,000 ppm) from cheese and casein manufacture. Historically, whey has been disposed of by feeding it to p i g s , by u s i n g it as a fertiliser, or by dumping it in sewers and watercourses. With i n c r e a s i n g environmental c o n t r o l s , there is now more i n t e r e s t in whey utilization. For whey c o n c e n t r a t i o n , reverse osmosis is attractive i n that the process operates a t ambient temperatures, so that the f u n c t i o n a l p r o p e r t i e s of the whey p r o t e i n s are l e s s a f f e c t e d and, of course, the energy consumption is lower than f o r alternative processes. One of the important f a c t o r s determining the process economics is the f l u x d e c l i n e that is caused by a b u i l d - u p of whey components a t the membrane s u r f a c e . It is the aim of t h i s paper t o review the a p p l i c a t i o n of reverse osmosis to whey p r o c e s s i n g , and in particular, to d i s c u s s the problem of membrane f o u l i n g . Whey P r o p e r t i e s There a r e two types of whey, c l a s s i f i e d (7) according t o source: ( i ) "sweet" whey, which i s d e r i v e d from the manufacture of products i n which rennet-type enzymes a r e used t o coagulate m i l k (e.g. Gouda and Cheddar cheeses), and which has a minimum pH of 5.6, and ( i i ) " a c i d " whey, which i s d e r i v e d from acid-induced coa g u l a t i o n (e.g. cottage cheese and c a s e i n ) , and which has a maximum pH o f 5.1. T y p i c a l concentrations of the major c o n s t i t u e n t s i n each type of whey a r e l i s t e d i n Table I (8) :

0097-6156/81/0154-0037$05.00/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Table I


HC1 c a s e i n whey

l a c t o s e , g/1 p r o t e i n , g/1 non-protein N, g/1 c i t r i c a c i d , g/1 calcium, g/1 phosphorus, g/1 pH

Cheddar cheese whey

51.4 7.3 0.18 1.93 1.11 0.78 4.47

48.7 6.5 0.23 1.56 0.47 0.54 6.25

The osmotic pressure of whey i s approx. 0.6 MPa (6) Whey P r o d u c t i o n The s c a l e of whey production i s i l l u s t r a t e d i n Table I I (summarized from reference 9 ) , which l i s t s the q u a n t i t i e s of whey produced i n v a r i o u s c o u n t r i e s i n 1977 : Table I I ( U n i t s : k i l o t o n n e s )

Country

U.S.A. Canada Australia New Zealand E.E.C.

Sweet whey

A c i d whey

Total

1,920 158 420 1,282 2,200*

15,640 1,368 1,208 2,067 25,000*

13,720 1,210 788 785 22,800*

*1978 f i g u r e s , approximate only In A u s t r a l i a , New Zealand and I r e l a n d , where d a i r y c a t t l e a r e pasture-fed, whey production i s h i g h l y seasonal; the peak monthly production may be up to twice the average monthly p r o d u c t i o n . This r e s u l t s i n a lower p l a n t u t i l i z a t i o n i n whey processing i n these c o u n t r i e s , and consequently greater emphasis on process efficiency. Membrane Processing of Whey The development of commercial u l t r a f i l t r a t i o n equipment has made recovery of the whey p r o t e i n s economically f e a s i b l e , and a number of uses f o r the remaining l a c t o s e (the p r i n c i p a l BOD source)



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have been suggested i n an attempt to achieve complete u t i l i z a t i o n of the whey s o l u t e s . Concentration of the whey (or whey u l t r a f i l t r a t e ) i s g e n e r a l l y necessary at some stage, perhaps p r i o r to t r a n s p o r t to a c e n t r a l processing f a c i l i t y , or p r i o r to evaporati o n , or to produce a concentrate which can be used d i r e c t l y . S e v e r a l commercial whey reverse osmosis i n s t a l l a t i o n s are i n ope r a t i o n (10), notably i n Northern Europe where e s c a l a t i o n i n f u e l costs has been a major f a c t o r , de Boer et a l . (11) have shown that reverse osmosis i s more economic than evaporation up to a volume r e d u c t i o n of 75%. Reverse osmosis was f i r s t proposed as a method f o r the conc e n t r a t i o n of l i q u i d foods some f i f t e e n years ago (12), and s i n c e that time, numerous s t u d i e s have been reported on aspects of the u l t r a f i l t r a t i o n and reverse osmosis of whey. A common observati o n has been the d e c l i n e i n f l u x r a t e through the membrane that occurs during operation due to the accumulation of f o u l i n g l a y e r s on the membrane surface. Membrane F o u l i n g Studies on Whey Lim et a l . (13) s t u d i e d the reverse osmosis of cottage cheese whey and showed that only part of the f o u l i n g l a y e r could be removed w i t h f l u i d shear, and that c a s e i n was the major component of that which remained. The l a t t e r f i n d i n g was a s c r i b e d to the lower d i f f u s i o n c o e f f i c i e n t of c a s e i n r e l a t i v e to the other s o l u t e s . The f l u x r a t e s under v a r i o u s c o n d i t i o n s were used to c a l c u l a t e the h y d r a u l i c r e s i s t a n c e s of the v a r i o u s l a y e r s , f o l l o w i n g the approach of Markley et a l . ( 1 4 ) ; these c a l c u l a t i o n s showed that the r e s i s t a n c e of the f o u l i n g l a y e r was f i v e times the r e s i s t a n c e of the membrane at low feed v e l o c i t i e s (Reynold s Number = 1500), whereas i t was l e s s than the r e s i s t a n c e of the membrane at higher feed v e l o c i t i e s (Reynold's Number = 5,900). The authors pointed out that f o u l i n g of the membrane surface would r e t a r d d i f f u s i o n of the m i c r o s o l u t e s , and so increase the m i c r o s o l u t e c o n c e n t r a t i o n p o l a r i z a t i o n . F o u l i n g thus reduced f l u x r a t e s by c o n t r i b u t i n g an added h y d r a u l i c r e s i s t a n c e , and by reducing the e f f e c t i v e d r i v i n g f o r c e f o r water permeation through the membrane. In an attempt to d i r e c t l y measure the amount of m a t e r i a l i n the f o u l i n g l a y e r , Dejmek et a l . (15) studied the u l t r a f i l t r a t i o n of 1^1 i - l a b e l l e d c a s e i n . A very slow accumulation a t the membrane surface was observed, superimposed on the expected changes due to feed flow r a t e , a p p l i e d pressure, e t c . Lee and Merson (16) s t u d i e d the e f f e c t s of chemical t r e a t ments of cottage cheese whey on membrane f o u l i n g i n u l t r a f i l t r a t i o n . By examining the deposits obtained w i t h scanning e l e c t r o n microscopy, they were able to c o r r e l a t e f l u x r a t e s w i t h the nature of the deposits on the membrane. Calcium s e q u e s t r a t i o n gave increased f l u x r a t e s , as d i d r a i s i n g the i o n i c s t r e n g t h of the whey; these r e s u l t s i n d i c a t e d that f o u l i n g could be minimised by d i s p e r s i n g the whey p r o t e i n s , and so preventing t h e i r d e p o s i t i o n on the membrane. !



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More r e c e n t l y , Hiddink et a l . ( 6 ) , s t u d i e d the reverse osmosis of Gouda cheese whey, and concluded that the f l u x - l i m i t ing f a c t o r s were the osmotic pressure of the feed, and membrane f o u l i n g . F o u l i n g by p r o t e i n was observed w i t h d e i o n i z e d whey, 'and w i t h whey that had been adjusted to pH 4.6; i n both cases, the f o u l i n g was seen as a consequence of the lower s t a b i l i t y of the whey p r o t e i n s r e s u l t i n g i n aggregation a t the membrane s u r f a c e . Calcium phosphate d e p o s i t i o n was a l s o noted i f Gouda whey (pH 6.6) was concentrated at 30 C over a concentration r a t i o of 1.6 : 1. This source of f o u l i n g could be removed e i t h e r by exchanging the calcium i n the whey f o r sodium, or by s l i g h t l y lowering the pH of the whey. As noted by Matthews (17), the s t u d i e s on membrane f o u l i n g published so f a r would suggest that some of the p r o t e i n components causing f o u l i n g are a f f e c t e d by such f a c t o r s as pH, i o n i c s t r e n g t h and i o n i c composition ( p a r t i c u l a r l y calcium c o n c e n t r a t i o n ) . I n t e r a c t i o n s between the v a r i o u s s o l u t e s are a l s o important, as shown by P e r i and Dunkley (18). Their r e s u l t s on the reverse osmosis of s o l u t i o n s of whey components showed l i t t l e i n d i c a t i o n of f o u l i n g ; only whole whey gave a steady d e c l i n e i n f l u x r a t e w i t h time. Whey Pretreatments t o Reduce F o u l i n g The p o s s i b i l i t y of p r e t r e a t i n g the whey before membrane processing to reduce f o u l i n g may be commercially a t t r a c t i v e , provided that the product p r o p e r t i e s , such as the f u n c t i o n a l i t y of the p r o t e i n s , a r e not d e t r i m e n t a l l y a f f e c t e d . For whey u l t r a f i l t r a t i o n , pretreatment methods have been developed t o remove the l i p i d f r a c t i o n (19, 20) which i n v o l v e f l o c c u l a t i o n and g r a v i t y settling. Hayes et a l . (21) s t u d i e d the e f f e c t s of pH v a r i a t i o n on the u l t r a f i l t r a t i o n of Cheddar cheese and HC1 c a s e i n wheys. Their e a r l i e r work had shown that both wheys gave low f l u x r a t e s a t pH 4.1 - 4.4, and high f l u x r a t e s below pH 3. F l u x r a t e s improved f o r Cheddar cheese whey above pH 5, but there was l i t t l e improvement w i t h HC1 c a s e i n whey. Heat treatment (80 C f o r 15 seconds) of the c a s e i n whey followed by pH adjustment to an optimum between 5.2 and 5.9 r e s u l t e d i n marked decrease i n f o u l i n g . Demineraliza t i o n o f , or EDTA a d d i t i o n t o , HC1 c a s e i n whey a l s o gave higher f l u x r a t e s . These r e s u l t s were explained i n terms of a balance between ( i ) a heat-induced i n t e r a c t i o n of c a s e i n w i t h $ - l a c t o g l o b u l i n and calcium, which formed aggregates which d i d not f o u l the membrane, and ( i i ) i n c r e a s i n g calcium phosphate p r e c i p i t a t i o n as the pH was r a i s e d , which would lead to lower f l u x r a t e s . Smith and MacBean (22) a p p l i e d the pretreatments developed by Hayes e t a l . (21) t o the reverse osmosis of HC1 c a s e i n and Cheddar cheese wheys, but found that an i n c r e a s e i n f o u l i n g occurred com-



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pared to untreated whey. I t was a l s o found that the r a t e of f l u x d e c l i n e decreased i f the whey was demineralized and increased i f sodium c h l o r i d e was added. The r a t e of f l u x d e c l i n e was much higher f o r HC1 c a s e i n whey than f o r Cheddar whey. These r e s u l t s have been supported by those of Matthews et a l . (23) f o r the reverse osmosis of u l t r a f i l t r a t e s from p r e t r e a t e d whey. Hickey ( 8 ) , f o l l o w i n g on from the e a r l i e r A u s t r a l i a n work (21, 22), c a r r i e d out d e t a i l e d l a b o r a t o r y s t u d i e s on the reverse osmosis and u l t r a f i l t r a t i o n of HC1 c a s e i n and Cheddar cheese wheys i n order t o c h a r a c t e r i z e the membrane f o u l i n g i n these systems. Again, pretreatments i n v o l v i n g combinations of heat, pH a d j u s t ments, and calcium or c i t r a t e a d d i t i o n s l e d t o e s s e n t i a l l y oppos i t e e f f e c t s i n reverse osmosis compared to u l t r a f i l t r a t i o n . This was p a r t i c u l a r l y evident w i t h HC1 c a s e i n whey. For untreated HC1 c a s e i n whey, a minimum occurs i n the curve of permeation r a t e versus pH. This l i k e l y to r e f l e c t the i s o e l e c t r i c p o i n t of the f o u l i n g p r o t e i n s , as under these c o n d i t i o n s the p r o t e i n s a r e l e a s t s o l u b l e , and hence l i k e l y to form denser l a y e r s w i t h higher hydr a u l i c r e s i s t a n c e . A s i m i l a r f l u x minimum at the i s o e l e c t r i c p o i n t has been reported f o r the u l t r a f i l t r a t i o n of g e l a t i n s o l u t ions by Akred et a l . (24). I n the reverse osmosis experiments, the f l u x minimum occurred a t a higher pH than i n the u l t r a f i l t r a t i o n experiments; t h i s can be explained i n terms of the higher i o n i c s t r e n g t h and/or l o c a l calcium concentration i n the reverse osmosis boundary l a y e r causing a s h i f t i n the i s o e l e c t r i c p o i n t of the f o u l i n g p r o t e i n s to a more a l k a l i n e pH value. Membrane F o u l i n g Models Merten et a l . (25) found that the simple r e l a t i o n s h i p A ( l o g f l u x r a t e ) = constant x A ( l o g time )

(1)

described the f l u x d e c l i n e due to membrane compaction. The same r e l a t i o n s h i p has been used s a t i s f a c t o r i l y to express f l u x d e c l i n e r a t e s due to membrane f o u l i n g i n the reverse osmosis of such feed streams as r i v e r water (26, 27) , decondary sewage e f f l u e n t (_3, 28) and whey (22). I n s e v e r a l t h e o r e t i c a l s t u d i e s of membrane f o u l i n g k i n e t i c s , equations c o n t a i n i n g exponential forms have been deri v e d ; i t i s l i k e l y that equation (1) i s simply an e m p i r i c a l approximation to these more complex r e l a t i o n s h i p s . B l a t t et al.(29) developed what has become known as the " g e l p o l a r i z a t i o n " theory f o r u l t r a f i l t r a t i o n , i n which the amount of macromolecular m a t e r i a l i n the f o u l i n g l a y e r i s c o n t r o l l e d by i t s b a c k - d i f f u s i o n r a t e i n t o the feed stream. The gradual d e c l i n e i n f l u x observed i n some p r a c t i c a l systems was explained i n terms of an i r r e v e r s i b l e c o n s o l i d a t i o n of the g e l l a y e r w i t h time, l e a d i n g to a r e d u c t i o n i n the l a y e r ' s p e r m e a b i l i t y . Kimura and Nakao (2) used B l a t t ' s approach to model the f o u l i n g of reverse osmosis



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membranes by the suspended s o l i d s i n i n d u s t r i a l wastewater, and were a b l e to -correlate t h e i r experimental r e s u l t s w i t h the d e r i v e d equations. More r e c e n t l y , Gutman (30) extended the "turbulence b u r s t " model f o r p a r t i c l e re-entrainment from a smooth impermeable w a l l to f o u l i n g of reverse osmosis membranes. Both of these a n a l yses showed that the f l u x d e c l i n e depended on the f l u x of the unf o u l e d membrane, the mass t r a n s f e r c o e f f i c i e n t of the f o u l a n t and i t s c o n c e n t r a t i o n , the feed v e l o c i t y , and the d e n s i t y and s p e c i f i c h y d r a u l i c r e s i s t a n c e of the f o u l i n g l a y e r . An e f f e c t not considered i n the above models i s the added r e s i s t a n c e , caused by f o u l i n g , to s o l u t e b a c k - d i f f u s i o n from the boundary l a y e r . F o u l i n g thus increases c o n c e n t r a t i o n p o l a r i z a t i o n e f f e c t s and r a i s e s the osmotic pressure of the feed adjacent to the membrane s u r f a c e , so reducing the d r i v i n g f o r c e f o r permeati o n . T h i s f a c t o r was explored e x p e r i m e n t a l l y by Sheppard and Thomas (31) by covering reverse osmosis membranes w i t h uniform, permeable p l a s t i c f i l m s . These authors a l s o developed a p r e d i c t i v e model to c o r r e l a t e t h e i r r e s u l t s . C a r t e r et a l . (32) have s t u d i e d the c o n c e n t r a t i o n p o l a r i z a t i o n caused by the build-up of r u s t f o u l i n g l a y e r s on reverse osmosis membranes but assumed (and confirmed by experiment) that the r u s t l a y e r had n e g l i g i b l e hydraulic resistance. A f u r t h e r c o m p l i c a t i o n a r i s e s when the f o u l a n t c a r r i e s a f i x e d charge, such as whey p r o t e i n i n s o l u t i o n s w i t h pH s i g n i f i c a n t l y d i f f e r e n t from the i s o e l e c t r i c p o i n t . Under these c o n d i t i o n s , the f o u l i n g l a y e r a c t s as a p o l y e l e c t r o l y t e membrane i n s e r i e s w i t h the reverse osmosis membrane, and changes i n the s a l t c o n c e n t r a t i o n at the surface of the reverse osmosis membrane would be expected. Conclusions Membrane f o u l i n g i n the reverse osmosis of whey i s c l e a r l y a complex phenomenon, because of the range of s o l u t e s present p r o t e i n s , l a c t o s e and s a l t s - and t h e i r i n t e r a c t i o n s w i t h each other. Few d e t a i l e d s t u d i e s have been reported, and although some i n s i g h t s can be gained from work on f o u l i n g i n u l t r a f i l t r a t i o n , a d d i t i o n a l f a c t o r s must be considered. The c o n d i t i o n s i n the foul i n g l a y e r are, of course, somewhat d i f f e r e n t i n reverse osmosis than i n u l t r a f i l t r a t i o n . The a p p l i e d pressure i s an order of magnitude g r e a t e r , and t h i s may a f f e c t p r o t e i n i n t e r a c t i o n s ( 3 3 ) . Probably more s i g n i f i c a n t l y , the i o n i c s t r e n g t h i n the f o u l i n g l a y e r w i l l be considerably higher because of the r e j e c t i o n of low molecular weight s o l u t e s by the membrane and the r e d u c t i o n i n the d i f f u s i o n r a t e away from the membrane surface caused by the presence of the f o u l i n g l a y e r . I n p a r t i c u l a r , more h i g h l y r e j e c t e d s o l u t e s such as calcium, phosphate, and l a c t o s e w i l l have higher concentrations i n the f o u l i n g l a y e r r e l a t i v e to l e s s w e l l r e j e c t e d s o l u t e s such as monovalent i o n s . P r e c i p i t a t i o n of calcium phosphate i n the f o u l i n g l a y e r i s t h e r e f o r e a p o s s i b l e e x p l a n a t i o n f o r



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the observed f o u l i n g (22), p a r t i c u l a r l y w i t h HC1 c a s e i n whey because o f i t s higher calcium content. A l t e r i n g the s t a t e of aggregation of the f o u l i n g m a t e r i a l by pretreatment of the whey caused l i t t l e change i n the reverse osmos i s f l u x r a t e s . This r e s u l t , together w i t h the e f f e c t s of demine r a l i z a t i o n or s a l t a d d i t i o n mentioned above, would suggest that the f l u x - d e t e r m i n i n g process i n the reverse osmosis of whey i s the c o n c e n t r a t i o n p o l a r i z a t i o n which i s increased by the presence of the f o u l i n g l a y e r . The aggregates formed by the pretreatment procedure, w h i l s t forming a more water-permeable f o u l i n g l a y e r as shown by the u l t r a f i l t r a t i o n r e s u l t s , do not lead to a s i g n i f i c a n t l y greater b a c k - d i f f u s i o n r a t e of s o l u t e from the membrane surface. I t seems t h e r e f o r e , that the e s t a b l i s h e d procedures i n v o l v i n g h i g h feed v e l o c i t y across the membrane s u r f a c e , a d d i t i o n a l t u r b u l ence promotion, e t c . , need to be a p p l i e d and optimized. There i s a need f o r a model f o r f o u l i n g i n reverse osmosis which i n c o r p o r ates such f a c t o r s as the added concentration p o l a r i z a t i o n caused by the f o u l i n g l a y e r , and Donnan e x c l u s i o n e f f e c t s due to charged f o u l a n t s . C l e a r l y there i s scope f o r more d e t a i l e d experimental work i n t h i s area. Literature 1.

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Cited

Loeb, S.; and S o u r i r a j a n , S; Sea water d e s a l i n a t i o n by means of a semi-permeable membrane U.C.L.A. Dept. of Eng. Report No. 60-60, 1960. Kimura, S.; and Nakao, S-I.; D e s a l i n a t i o n , 1975, 17, 267. W i n f i e l d , B.A.; Water Research, 1979, 13, 561. Jonsson, G.; and K r i s t e n s e n , S.; D e s a l i n a t i o n , 1980, 32, 327. Kennedy, T.J.; Monge, L.E.; McCoy, B.J.; and Merson, R.L.; A.I.Ch.E. Symposium S e r i e s , 1973, 69, (132), 81. Hiddink, J . ; de Boer, R.; and Nooy, P.F.C.; J. D a i r y Science 1980, 63, 204. I n t e r n a t i o n a l Dairy Federation; Standards of identity f o r whey powders, Report D-Doc. 1978, 49. Hickey, M.W.; Hill, R.D.; and Smith, B.R.; N.Z.J. D a i r y . Sci. Tech., 1980, 15, 109. Z a l l , R.R.; Kuipers, A.; M u l l e r , L.L.; and M a r s h a l l , K.R.; N.Z.J. D a i r y Science and Technology, 1979, 14 ( 2 ) , 79. E r i k s s o n , P.; Nordeuropaesk Mejertidsskrift, 1977, 43, 238. de Boer, R.; de Wit, J.N.; and Hiddink, J . ; J. Soc. D a i r y Technol., 1977, 30, 112. Morgan, A.J.; Lowe, E.; Merson, R.L.; Durkee, E.L.; Food Technol., 1965, 19, 52. Lim, T.H.,; Dunkley, W.L.; and Merson, R.L.; J . Dairy Sci., 1971, 54(3), 306. Markley, L.L.; Cross, R.A.; Bixler, H.J.; Hunter, J.A.; G i l l m a n , W.S.; and Johnson, S.; U.S. Dept. of the Interior, O f f i c e of S a l i n e Water, Res. Dev. Report No. 281, 1967.


44 15. 16. 17. 18. 19.


20. 21. 22. 23. 24.

25.

26. 27. 28. 29.

30. 31. 32. 33.

SYNTHETIC MEMBRANES:

HF

AND

UF

USES

Dejmek, P.; H a l l s t r o n , B.; K l i m a , A.; and Winge, L; Lebensm.-Wiss. u. Technol., 1973, 6 (1), 26. Lee, D.N.; and Merson, R.L.; J . Food Science, 1976, 41, 778. Matthews, M.E.; N.Z.J. D a i r y Sci. and Technol., 1979, 14(2), 86. P e r i , C.; and Dunkley, W.L.; J . Food Science, 1971, 36, 25. de Wit, J.N.; Klarenbeck, G.; de Boer, R.; Proc. 20th I n t . D a i r y Congress 1978, E, 919. A t t e b e r y , J.M.; U.S. Patent 3 560 219, (2/2/71). Hayes, J.F.; Dunkerley, J.A.; M u l l e r , L.L.; and Griffin, A.T.; Aust. J . D a i r y Technol., 1974, 29, 132. Smith, B.R.; and MacBean, R.D.; Aust. J . D a i r y Technol., 1978 33(2), 57. Matthews, M.E.; Doughty, R.K.; and Short, J.L.; N.Z.J. D a i r y S c i . Tech., 1978, 13, 216. Akred, A.R.; Fane, A.F.; and F r i e n d , J.P.; Proc. A.C.S. Symposium on Ultrafiltration membranes and a p p l i c a t i o n s , Washington, 1979. ( i n p r e s s ) . Merten, U.; Lonsdale, H.K.; R i l e y , R.L.; and Voss, K.O.; U.S. Dept. of the Interior, O f f i c e of S a l i n e Water, Res. Dev. Report No. 265, 1967. Sheppard, J.D.; Thomas, D.G.; and Channabasappa, K.C.; D e s a l i n a t i o n , 1972, 11, 385. K u i p e r , D.; van Hezel, J.L.; and Bom, C.A.; D e s a l i n a t i o n , 1977, 15(2), 193. Wechsler, R.; Water Research, 1977, 11, 379. B l a t t , W.F.; D r a v i d , A.; M i c h a e l s , A.S.; and Nelson, L.; i n Membrane Science and Technology, ed. J.E. Flinn, Plenum Press p.47, 1970. Gutman, R.G.; The Chemical Engineer, 1977 No. 322, 510. Sheppard, J.D.; and Thomas, D.G.; A.I.Ch.E. J o u r n a l , 1971, 17(4), 910. C a r t e r , J.W.; and Hoyland, G.; Proc. 5th I n t . Symp. Fresh Water from the sea, 1976, 4, 21. Payens, T.A.J.; and Heremans, K.; Biopolymers, 1969, 8, 335.

RECEIVED

December 30,

1980.


Fouling in Whey Reverse Osmosis - ACS Symposium Series (ACS

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