Synthetic Membranes: Volume I - American Chemical Society

20 Reverse-Osmosis Research in India: Scope and Potentialities

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D. J. MEHTA and A. V. RAO Central Salt and Marine Chemicals Research Institute, Bhavnagar 364002, India

The supply of good-quality potable water to the community i s a measure of the degree of civilization which a society can reach, and i t i s the c i v i c r e s p o n s i b i l i t y of those i n power to ensure a continued supply of good-quality potable water to the masses. There are many large areas i n our country which are d e f i c i e n t i n potable water* The most extensive a r i d and semi-arid regions are i n the western and northwestern parts and i n the central Deccan Plateau of India where drinking water problems due to s a l i n i t y are acute. Most of the regions along the coastal b e l t also do not have good q u a l i t y drinking water resources. India, receives an average r a i n f a l l of 93 • 5 x 10' with roughly 30 per cent of i t as ground water which should prove s u f f i c i e n t to meet the requirements of the people for a g r i c u l t u r e , industry and drinking purposes. However, due to the v a s t ness and topography of the country and the scattered i n t e n s i t y of the r a i n - f a l l pattern, the task of f i n d i ng and transporting good q u a l i t y water to the people i n the isolated and remote areas of the vast arid and semi-arid regions of the country i s , i n i t s e l f , a s t u pendous and formidable one. It i s p r e c i s e l y i n this background that this Institute has embarked upon a systematic research programme on the desalination of brackish and sea water. Intensive research and development studies on the d i s t i l l a t i o n processes during s i x t i e s led to the development of proto-type plants based on flash d i s t i l l a t i o n , humidification-dehumidif i c a t i o n and solar d i s t i l l a t i o n . The main concern i n a l l the d i s t i l l a t i o n processes with the sole exception of s o l a r - d i s t i l l a t i o n i s that the energy cost i s so incredibly large that i t forbids their adoptability to meet the drinking water needs of the community. 1

0097-6156/81/0153-0293$05.00/0 © 1981 American Chemical Society

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

SYNTHETIC


294

MEMBRANES:

DESALINATION

The s u c c e s s f u l development of asymmetric c e l l u l o s e a c e t a t e membranes by Loeb and S o u r i r a j a n i n the e a r l y s i x t i e s , a t the U n i v e r s i t y of C a l i f o r n i a , Los Angel e s , has been p r i m a r i l y r e s p o n s i b l e f o r the r a p i d development of Reverse Osmosis (RO) technology f o r b r a c k i s h / s e a water d e s a l i n a t i o n . Reverse Osmosis approaches a r e v e r s i b l e p r o c e s s when the p r e s s u r e b a r e l y exceeds the o s m o t i c p r e s s u r e and hence the energy c o s t s are q u i t e low. Theenergy requirement to p u r i f y one l i t r e o f water by RO i s o n l y 0.003 as a g a i n s t 0 . 7 KW r e q u i r e d j u s t to s u p p l y the v a p o r i s a t i o n energy to change the phase o f one l i t r e o f water from l i q u i d to vapour by e v a p o r a t i o n . Thus RO has an i n h e r e n t c a p a b i l i t y to c o n v e r t b r a c k i s h water to p o t a b l e water a t economic c o s t and thus c o n t r i b u t e e f f e c t i v e l y to the h e a l t h and p r o s p e r i t y o f a l l humanity. The promise of a b r i g h t f u t u r e f o r RO made p o s s i b l e by the i n t e n s e p u r s u i t of Loeb and S o u r i r a j a n has i n s p i r e d a s m a l l group of r e s e a r c h workers i n t h i s L a b o r a t o r y t o i n i t i a t e R&D e f f o r t s i n t h i s new and d e v e l o p i n g s c i e n c e , i n the l a t e s i x t i e s . The work of Loeb and S o u r i r a j a n has been and c o n t i n u e s to be the f o u n t a i n head of a l l the i n s p i r a t i o n and e n c o u ragement and has become a g u i d i n g t o r c h i n our p u r s u i t o f R&D e f f o r t s to d e v e l o p a s u i t a b l e i n d i g e n o u s t e c h n o l o g y f o r b r a c k i s h / s e a water d e s a l i n a t i o n . The p r e s e n t paper d e s c r i b e s , at l e n g t h , the v a r i o u s R&D a c t i v i t i e s i n Reverse Osmosis a t the C e n t r a l S a l t and Marine C h e m i c a l s R e s e a r c h I n s t i t u t e , i n p a r t i c u lar. An attempt i s a l s o made to p r o j e c t the R&D achievements of other r e s e a r c h o r g a n i z a t i o n s i n the country. Development

of C e l l u l o s i c P o l y m e r s :

S y s t e m a t i c i n v e s t i g a t i o n s were c a r r i e d out f o r the p r e p a r a t i o n o f c e l l u l o s e a c e t a t e o f D . S . 2.65 and o t h e r mixed e s t e r s which i n c l u d e d c e l l u l o s e a c e t a t e propionate, cellulose acetate-butyrate, cellulose a c e t a t e - b e n z o a t e and c e l l u l o s e ace t a t e - m e t h a c r y l a t e . The e x p e r i m e n t a l c o n d i t i o n s were o p t i m i s e d f o r m a x i mum y i e l d of the e s t e r . F l a t o s m o t i c membranes were d e v e l o p e d from these e s t e r s and c h a r a c t e r i s e d f o r t h e i r o s m o t i c and t r a n s p o r t p r o p e r t i e s . The membranes were e v a l u a t e d i n a r e v e r s e osmosis l a b o r a t o r y t e s t - c e l l u s i n g 5000 ppm sodium c h l o r i d e s o l u t i o n at 40 b a r s p r e s s u r e . Table 1 p r e s e n t s the t y p i c a l performance d a t a o f these membranes. Of these e s t e r s , C A - M e t h a c r y l a t e was found to



40000-60000

15-20 20-25 40-42 7-12

acetyl, Benzyl,

acetyl, Mejhacry-

CA-Benzoate

CA-Methacrylate

50000-55000

30000-50000

10-15 35-40

acetyl, Butyl,

30000-50000

1500

1700

1400

1300

1700

40000-60000

CA-Butyrate

CA-Propionate

1200

Tensile strength psi.

30000-60000

Mole weight

acetyl 10-15 Propionyl 30-35

41.6-41.7

acetyl

CA.D.S.

2.65

39.7-39.9

%Substitution

acetyl

the E s t e r

C A . D . S . 2.5 (Commercial)

Name o f

90-92

93-95

93-94

93-94

95-96

90-92

% S.R.

CHARACTERISATION AND PERFORMANCE OP CA MIXED ESTERS

TABLE I


15-18

15-20

12-13

1 2 - 13

1 1 - 15

10- 12

P r o d u c t water flux gfd.


296

SYNTHETIC

MEMBRANES:

DESALINATION

p o s s e s s f a i r l y h i g h r e j e c t i o n f o r u r e a and b o r i c a c i d ; 55 and 50 per c e n t r e s p e c t i v e l y as compared to 20 per cent o r l e s s f o r CA membranes. I t was a l s o observed e a r l i e r t h a t CA-PMMA b l e n d membrane a l s o gave 75-80 per c e n t urea and 60 per cent b o r i c a c i d r e j e c t i o n (1). Thus i t seems r e a s o n a b l e to assume t h a t i n t r o d u c t i o n o f m e t h a c r y l a t e group i n CA m o l e c u l e a l t e r s the c h e m i c a l n a t u r e o f the s u r face o f CA membrane and thus improves i t s r e j e c t i o n e f f i c i e n c y f o r u r e a and b o r i c a c i d . T u b u l a r membranes o f 8' l o n g were p r e p a r e d from b l e n d c o m p o s i t i o n c o n s i s t i n g o f CA and PMMA and p e r formance d a t a f o r one month o p e r a t i o n was c o l l e c t e d . These d a t a s show h i g h p r o d u c t water f l u x ( 1 8 - 2 0 g f d . ) w i t h low f l u x d e c l i n e s l o p e . However, i t was o b s e r ved t h a t these membranes i n i t i a l l y showed " f o u n t a i n s " which d i s a p p e a r e d i n about 30 minutes t i m e . This was a t t r i b u t e d t o the p e c u l i a r membrane r h e o l o g y and o r i e n t a t i o n o f PMMA m o l e c u l e w i t h r e s p e c t t o CA molecule. T h i s needed f u r t h e r study f o r c o n f i r m a t i o n . Development o f N o n - C e l l u l o s i c P o l y m e r s : S y n t h e s i s o f P o l y s u l f o n e : The i n t e r m e d i a t e s r e q u i r e d i n the s y n t h e s i s o f p o l y s u l f o n e namely ( i ) c h l o r o benzene s u l f o n y l c h l o r i d e and ( i i ) d i c h l o r o d i p h e n y l s u l f o n e were p r e p a r e d by the r e a c t i o n o f c h l o r o b e n zene w i t h c h l o r o s u l f o n i c a c i d under c o n t r o l l e d c o n d i tions. These were c h a r a c t e r i s e d by the m e l t i n g p o i n t d e t e r m i n a t i o n and e l e m e n t a l a n a l y s i s . Poly sulfone was o b t a i n e d by the c o n d e n s a t i o n o f s u l f o n e w i t h b i s - p h e n o l - A sodium s a l t i n D i m e t h l s u l f o x i d e . The polymer thus o b t a i n e d was c h a r a c t e r i s e d by ( i ) e l e mental a n a l y s i s , ( i i ) s o f t e n i n g p o i n t and ( i i i ) r e duced v i s c o s i t y . Membranes p r e p a r e d from the l a b o r a t o r y - s y n t t e s i s e d p r o d u c t gave 2 5 gfd water f l u x a t 50 p s i g . 'vYhen t e s t e d w i t h 0 . 5 per cent d e x t r a n s o l u t i o n these f i l m s gave more than 9 8 per cent d e x t r a n r e j e c t i o n w i t h 10 g f d p r o d u c t - w a t e r f l u x a t 50 p s i g . thus showing promise o f i t s use i n ultrafiltration applications. PAN.PMMA and Copolymer of AN/MMA: C o n d i t i o n s were optimised for homo-polynierisation of a c r y l o n i t r i l e and methyl m e t h a c r y l a t e monomers and c o p o l y m e r i s a t i o n o f AN/MMA. The c h a r a c t e r i s t i c s o f these polymers are g i v e n i n Table I I .


20.

MEHTA

A N D RAO

RO

Research

in India

297

TABLE I I CHARACTERISTICS OF ACRYLIC POLYMERS


Name of polymer

the

Mole weight

Softening point °C

% Nitrogen 23.0 23.1

to

Poly(acrylonitrile)

130,000 to 135,000

245 260

Poly(Me t h y l m e t h a crylate)

600,000 to 700,000

280

-

AN/MMA co-polymer

153,000 to 150,000

-

1.85

to

F l a t membranes from these polymers were t e s t e d f o r d e s a l i n a t i o n and found to be of low s a l t r e j e c t i n g type. However, the copolymer was found to p o s s e s s more than 90 per c e n t r e j e c t i o n f o r 1 per c e n t d e x t r a n s o l u t i o n w i t h 10.0 gfd water f l u x a t 200 p s i thus i n d i c a t i n g the p o s s i b i l i t y o f a p p l i c a t i o n o f these membranes i n u l t r a f i l t r a t i o n and h e m o d i a l y s i s . Reverse Osmosis i n Water D e s a l i n a t i o n and R u r a l lopment :

Deve-

Reverse osmosis d e s a l i n a t i o n p l a n t s c o n s i s t i n g o f 8 l o n g t u b u l a r membranes prepared from commercial CA of D . S . 2.5 were s e t up f o r s u p p l y o f d r i n k i n g water and b o i l e r feed water a t two d i f f e r e n t l o c a t i o n s . Table I I I g i v e s t y p i c a l performance d a t a o f the RO p l a n t s e t up i n a v i l l a g e to s u p p l y d r i n k i n g water to the v i l l a g e p e o p l e . The p l a n t was o p e r a t e d f o r over s i x months. f

TABL13 I I I PERFORMANCE DATA OF RO PLANT OF 3000 g a l / d a y CAPACITY ( O p e r a t i n g c o n d i t i o n s : Feed r a t e , 3 g a l / m i n ; O p e r a t i n g p r e s s u r e , 600 p s i ; Feed s a l i n i t y , 5000 ppm Solvent f l u x (gfd) 8-9

Salt rejection % 80-85

Recovery % 50-55

Feed^temp. °C 25-28


298

SYNTHETIC

MEMBRANES:

DESALINATION

The performance d a t a o f the RO p l a n t s e t up and o p e r a t e d f o r 21 days i n a t e x t i l e m i l l i n n o r t h I n d i a f o r the supply o f b o i l e r feed water are g i v e n i n Table IV TAB LB IV


PERFORMANCE DATA OF RO PLANT OF 2,500 G a l / D a y CAPACITY FOR SUPPLY OF BOILER FEED WATER.

Feed water s a l i n i t y Feed flow r a t e Operating Pressure

Solvent flux tefd)

: : :

2850 ppm 3 gal/min. 600 p s i

Salt rejection %

8.5

Recovery %

95-97

52

Remarks

The p l a n t was o p e r a ted w i t h o u t any p r e treatment #

I t was observed t h a t the p l a n t gave a t r o u b l e f r e e s e r v i c e d u r i n g the 21 day p e r i o d . However, f l u s h i n g o f the membranes w i t h feed water was r e s o r t e d to o n l y once a f t e r 15 days of c o n t i n u o u s o p e r a t i o n . A f t e r 21 d a y s , the p l a n t showed s i g n s o f d e c l i n e i n s a l t r e j e c t i o n which dropped to 8 8 per c e n t . At t h i s stage the membranes were f l u s h e d w i t h o x a l i c a c i d . The f o u l i n g of the membranes was observed to be somewhat r a p i d . A t the end o f the continuous o p e r a t i o n , the p l a n t was shut down and the s l i m y m a t e r i a l c o l l e c t e d from w i t h i n the membranes was a n a l y s e d (Table V) TABLE V ANALYSIS OF SLIMS COLLECTED FROM WITHIN THE RO MEMBRANES. Constituents Fe

as P e ° 3

Al

as

% by weight 1

2

Ca as

A1 0 ,

*

2

1

1 H 0

20.50

CaSO^, 2 H 0

8.70

2

5

2

2

Insolubles

5.51

O r g a n i c matter

63.50



20.

MEHTA A N D RAO

RO

Research

in India

299

The o r g a n i c matter was assumed to be due to ( i ) o i l c o n t a m i n a t i o n from the p i s t o n pump and ( i i ) the p r e s e nce o f l a r g e q u a n t i t y o f m i c r o o r g a n i s m i n the feed water (106000 per m l ) . The a n a l y s i s i n d i c a t e d t h a t e x h a u s t i v e p r e t r e a t m e n t c o n s i s t i n g of sand f i l t e r , a c i d d o s i n g , c h l o r i n a t i o n and SKMP d o s i n g i s e s s e n t i a l f o r p r o l o n g e d s u c c e s s f u l o p e r a t i o n o f the RO p l a n t on natural well waters. Based on the performance of 500 g a l / d a y c a p a c i t y RO s p i r a l p l a n t which was o p e r a ted c o n t i n u o u s l y f o r 3 0 days (2) a 2500 g a l / d a y c a p a c i t y p l a n t was designed and f a F r i c a t e d to be s e t up i n a v i l l a g e " A r n e j " 120 km. from B h a v n a g a r . The p l a n t was r u n c o n t i n u o u s l y r o u n d - t h e - c l o c k f o r 3 months i n the i n s t i t u t e p r o c e s s i n g 1200 ppm bore w e l l w a t e r . The feed water was f i l t e r e d i n a sand f i l t e r and the pH was a d j u s t e d to 5.5 by a c i d d o s i n g b e f o r e i t e n t e r e d the s p i r a l modules. The performance of the p l a n t at the s t a r t was 7 gfd f l u x w i t h 85 per cent S . R . which g r a d u a l l y d e c l i n e d to a b o u t 75 per oent when the modul e s were c l e a n e d thoroughly and the o p e r a t i o n was c o n tinued f u r t h e r . Reverse O s m o s i s / U l t r a f i l t r a t i o n i n I n d u s t r y : E x p l o r a t o r y s t u d i e s were a l s o u n d e r t a k e n to examine the t e c h n i c a l f e a s i b i l i t y o f a p p l i c a t i o n o f RO/UF i n i n d u s t r i a l p r o c e s s e s such as waste treatment f o r r e c o v e r y o f c h e m i c a l s a n d / o r reuse o f w a t e r , and i n p o l l u tion control. Some of the t y p i c a l problems which were i n v e s t i g a t e d e a r l i e r have a l r e a d y been r e p o r t e d ( 3 ) » Other a p p l i c a t i o n s which were s t u d i e d f u r t h e r are"" b r i e f l y d e s c r i b e d here: ( i ) C o n c e n t r a t i o n of V i t a m i n B - 1 2 : E x p l o r a t o r y e x p e r i ments on the c o n c e n t r a t i o n o f V i t . B - 1 2 u s i n g c e l l u l o s e a c e t a t e membranes were c a r r i e d o u t . F l a t membranes having an a r e a of about 5 s q . i n c h e s are used i n an UF t e s t k i t . The e f f e c t of parameters l i k e polymer s o l u t i o n c o m p o s i t i o n , e v a p o r a t i o n time and s h r i n k a g e temperature were s t u d i e d f o r the t a i l o r making o f the membranes. The commercial r e q u i r e m e n t f o r the c o n c e n t r a t i o n i s h i k i n g o f c o n c e n t r a t i o n from 20 m g / l to 10 g / l . The f e a s i b i l i t y o f the p r o c e s s was a s s e s s e d by experiments i n three s t a g e s ( i ) 19 m g / l to 122 m g / l ( i i ) 96 m g / l to 0.75 g / l and ( i i i ) 1.03 g / l to 10.5 s / l a l l a t 85 p s i g . The f l u x ranged from 4 . 2 - 5 . 6 g f d , and i s independent o f f e e d c o n c e n t r a t i o n and the r e j e c t i o n v a r i e d from 98.6 to 99.5 per c e n t , i n d i c a t i n g t e c h n i c a l f e a s i b i l i t y o f c o n c e n t r a t i o n , w i t h o u t the a t t e n d a n t d e c r e a s e i n f l u x due to the i n c r e a s e d feed c o n c e n t r a -


300

SYNTHETIC

tion. Improvements of are under way,

MEMBRANES:

the membranes f o r b e t t e r

DESALINATION

flux


( i i ) C o n c e n t r a t i o n o f Skim M i l k and Whole M i l k ; A few t r i a l s on c o n c e n t r a t i o n o f skim m i l k and whole m i l k r e s p e c t i v e l y to 5 and 3.5 times were c a r r i e d out a t an o p e r a t i n g p r e s s u r e of 65 p s i g w i t h c e l l u l o s e a c e tate membranes. The permeates i n b o t h the cases were extremely c l e a r and the f l u x e s were about 6 and 3 gfd f o r skim m i l k and whole m i l k r e s p e c t i v e l y , ( i i i ) Treatment o f C u t t i n g O i l Waste E m u l s i o n : C l e a r permeate, low i n o i l c o n t e n t a n d BOD was o b t a i n e d d u r i n g u l t r a f i l t r a t i o n of c u t t i n g - o i l waste a t 35 p s i g o p e r a t i n g p r e s s u r e w i t h c e l l u l o s e a c e t a t e membranes a t a f l u x o f about 6-8 g f d . F u r t h e r experiments are c o n t i n u e d on l a r g e s c a l e to e s t a b l i s h the economic f e a s i b i l i t y o f RO/UF f o r the c o n c e n t r a t i o n of these s u b s t a n c e s on a commercial l e v e l Economics o f D e s a l i n a t i o n by RO: The c o s t o f a 10 m V d a y t u b u l a r RO p l a n t i s e s t i mated a t Rs.8,500/m3 and the water c o s t i s R s . 1 0 / m 3 . For the same c a p a c i t y w i t h s p i r a l c o n f i g u r a t i o n the c o s t i s c a l c u l a t e d to be R s . 6 , 0 0 0 / n K w i t h a water c o s t o f R s . 6 / n r . F o r c a p a c i t i e s o f over 100 m? per d a y , the treatment c o s t i s expected to be b r o u g h t down to an a c c e p t a b l e l e v e l o f R s . 5 / m ^ . Table VI shows p r o j e c t e d c o s t f o r t u b u l a r R0 p l a n t s o f d i f f e r e n t c a p a cities. R&D a c t i v i t i e s o f other Research O r g a n i z a t i o n s i n Reverse Osmosis: (a) A t Bhabha Atomic R e s e a r c h Centre (BARC) ( £ ) , Bombay, s t u d i e s on r e v e r s e osmosis p r i m a r i l y aim a t d e v e l o p i n g the technology on a commercial s c a l e f o r the d e s a l i n a t i o n o f b r a c k i s h water and sea w a t e r . A 10 n r / d a y p i l o t p l a n t based on c e l l u l o s e a c e t a t e memb r a n e s ( t u b u l a r module) was designed and f a b r i c a t e d i n the m i d - s e v e n t i e s . The s u p p o r t tubes used were o f a l u m i n i u m . The p l a n t i s s t i l l i n o p e r a t i o n w i t h about 10-20 gfd f l u x and 90-98 per cent r e j e c t i o n far a feed c o n t a i n i n g 5,000 ppm d i s s o l v e d s a l t s . P r e s e n t l y , development work i s g o i n g on to r e p l a c e A l . tubes w i t h FRP porous tubes to improve the economics, r e l i a b i l i t y and to overcome c o r r o s i o n p r o b l e m s . Membrane l i f e has been found to be about one y e a r . Enough o p e r a t i o n a l d a t a have been c o l l e c t e d to d e s i g n l a r g e capacity R.O. plants. B e s i d e s t h i s , development o f



' SiblTI Xtillllllul)

^>

000

33,000 17,000

1 10

8

67,000 20,000

2 25

4 125

5 250

6 500

TDS 700 to

1000ppn

1

5

5

9

1,33,000 3 , 3 1 , 0 0 0 6 , 5 8 , 0 0 0 1 3 , 0 4 , 0 0 0 32,000 60,000 1,20,000 2,25,000

3 50

TDS - 5000 ppm; P r o d u c t water

1. Energy c o s t 1.15 2 . Labour and s u p e r v i s i o n 5.00 3 . Maintenance (2% o f CI) 0.38 4 . Depreciation a) On p l a n t 8% 0.70 b) On pump 12# 0.50 c) On membrane 200% 1.70 d) Chemical p r e t r e a t m e n t 0.32 cost. -z Cost of p r o d u c t water per nTRs.9.75

5

1.15 1.00 0.24 0.30 0.26 1.86 0.30 5.60

1.15 2.00 0.26 0.81 0.32 1.86 0.31 6.71

5.20

0.79 0.19 1.86 0.32

1.15 0.66 0.23

4.90

0.79 0.19 1.86 0.35

1.15 0.33 0.23

4.70

0.78 0.18 1.86 0.31

1.15 0.20 0.22

'°°° '°°° '°°° 78,000 1,53,000 4 . P r e - t r e a t m e n t assembly 22,000 40,000 80,OOP 1,00.000 1 , 1 5 , 0 0 0 3,20,000 Total 85,000 1,35.000 2 , 6 0 . 0 0 0 5 , 3 0 . 0 0 0 1000.000 2 0 . 0 0 . 0 0 0 OPERATING COST PER C o s t o f Power R s . 0 . 2 0 / k w h ; Labour charges 9 Rs.500/month p e r persoi 3 persons f o r 1 & 2 , 5 p e r s o n s f o r 3 & 4 and 6 p e r s o n s f o r 5 & 6 Plant capacity, m /day K L 25 50 125 2£0 £00

3

, Plant capacity, m V d a y C a p i t a l Investment: 1. Modules and Membranes 2 . Pump

Raw water

5

TABLB VI COST ESTIMATES FOR REVERSE OSMOSIS PLANTS OF-DIFFERENT CAPACITIES RANGING FROM 10 M TO 500


302

SYNTHETIC MEMBRANES: DESALINATION

compact modules which can be f a b r i c a t e d by s m a l l industries is in progress.

scale


(b) A t defence l a b o r a t o r y , Jodhpur (4) s u i t a b l e f l a t and t u b u l a r semi-permeable membranes y i e l d i n g h i g h f l o w r a t e and s a l t r e j e c t i o n have been developed* A p i l o t p l a n t of c a p a c i t y 5,000 l p d based on f l a t type membranes has been c o m p l e t e d . A similar capacity p l a n t based on t u b u l a r type membranes has a l s o been developed. (c) BEERI, Nagpur (4) i s engaged i n r e s e a r c h and development work r e l a t e d to use o f r e v e r s e osmosis p r o c e s s f o r t r e a t n e n t of waste w a t e r s . Preliminary f i e l d s t u d i e s have been conducted u t i l i s i n g s m a l l R.O. units. I t i s planned to s c a l e up these s t u d i e s and a l s o extend i t s a p p l i c a t i o n towards c o n v e r s i o n of b r a c k i s h waters. P r e s e n t S t a t u s and F u t u r e

Perspective:

The emphasis i n RO i s more on the improvement of the q u a l i t y and l i f e of the membranes. Investigations are i n p r o g r e s s to improve upon the p e r f o r mance o f CA membranes by i n t r o d u c i n g e l a b o r a t e p r e treatment methods and m o d i f y i n g the membrane s t r u c t u r e e i t h e r c h e m i c a l l y or by admixture o f the c a s t i n g s o l u tion with c e r t a i n additives. In the f u t u r e programme, development o f n o n - c e l l u l o s i c polymers such as aromat i c p o l y a m i d e s , PBIL e t c . and CTA f i b r e s and u l t r a t h i n f i l m s i n the composite membrane are g i v e n due consideration. F a b r i c a t i o n and s e t t i n g up o f s p i r a l p l a n t s i n v i l l a g e s i n a phased programme w i l l be c a r r i e d out to meet the needs o f r u r a l communities w i t h p o p u l a t i o n o f 1 to 2 thousand. More s t r e s s i s g i v e n to the development o f Hollow f i n e f i b r e t e c h n o l o g y and adequate f i n a n c e s are a l l o c a t e d f o r the same. Work i s a l s o i n i t i a t e d to f a b r i c a t e one m o b i l e u n i t o f 10 m'/day f o r d e m o n s t r a t i o n o f the p r o c e s s i n the v i l l a g e s and a l s o t r e a t d i f f e r e n t q u a l i t y feed waters. Conclusion: The economics o f Reverse Osmosis P r o c e s s w i l l be h i g h l y f a v o u r a b l e p r o v i d e d the d e s a l i n a t i o n i n d u s t r y i s taken up i n a b i g way b r i n g i n g down the c a p i t a l investment. Water manageiaent and d i s t r i b u t i o n p a r t i c u l a r l y the water s u p p l y i n the r u r a l a r e a s must be g i v e n top p r i o r i t y and s h o u l d be under the d i r e c t c o n t r o l o f c e n t r a l and f e d e r a l government a g e n c i e s ; and i n t h i s endeavour r e v e r s e osmosis has a p o t e n t i a l


20.

M E H T A A N D RAO

RO

Research

in'India

303

r o l e to p l a y i n b r i n g i n g r e l i e f to the s e c t i o n o f the people who a r e a f f l i c s t t e d w i t h b r a c k i s h water p r o b l e ms and thereby p r o j e c t i n g the advantages and b e n e f i t s o f R&D e f f o r t s to the s o c i e t y .


ABSTRACT Reverse Osmosis has emerged as a major breakthrough i n the realm of water d e s a l i n a t i o n . Its s i m p l i c i t y of operation and lower c a p i t a l costs as compared to other desalination techniques are i t s a t t r a c t i v e features. Research work carried out i n this Institute i n the early seventies to develop useful osmotic membranes from the indigenously a v a i lable commercial cellulose acetate resulted i n membranes with fairly satisfactory performance of 7 to 8 gfd. flux and 85 to 90 per cent s a l t r e j e c t i o n . The studies on s o l u t i o n - s t r u c t u r e and evaporation rate led to the modified composition of membranes which gave 12 to 15 gfd. f l u x and 93 to 95 per cent S.R. Cellulose acetate mixed e s t e r s were then prepared and membranes developed from these e s t e r s , i n general, gave fairly high s a l t r e j e c t i o n (95 to 96 per cent) with moderate water flux (8-12 g f d ). Blend compos i t i o n s of CA-CTA and CA-PMMA were developed which gave high product water flux of 20-30 gfd. and s a l t r e j e c t i o n of 90-97 per cent. The paper describes the Research and Development e f f o r t s and projects the relevance of RO i n as much as i t s a b i l i t y to meet the drinking water needs of the r u r a l community and unfolds the unlimited i n d u s t r i a l p o t e n t i a l i t i e s . Literature Cited: 1.

2. 3. 4.

Narola, B.J.; Chandorikar, M.V.; Rao, A . V . Paper presented at 2nd Symposium on "Synthetic Membranes i n Science and Industry", Tubingen, September 17-19, 1979. Mehta, D.J.; Rao, A . V . ; Govindan, K . P . Desalinat i o n , 1979, 30, 325. Mehta, D.J.; Pandya, V.P.; Rao, A . V . D e s a l i n a t i o n , 1977, 20, 403. Thomas, K . T . CSMCRI S i l v e r Jubilee Souvenir, 1979, 37.

RECEIVED

December 4, 1980.


Synthetic Membranes: Volume I - American Chemical Society

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