combination filter purifier
TRANSCRIPT
N e w s a n d V i e w s
Engineering, 33, 3, pp 416--425, J u l y 1993 (a t r a n s l a t i o n from Chemle-lngenieur-Technlk, 62, 3, pp 175-182). The ecological p r o b l e m s of a m m o n i a a n d a m m o n i u m sa l t s in wastewater , a n d the a d v a n t a g e s a n d d i s a d v a n t a g e s of the va r ious recovery m e t h o d s are a lso d i scus sed .
I n d u s t r i a l was t ewa te r s c o n t a i n i n g res idua l a m o u n t s of a m m o n i a have u p un t i l now b e e n rega rded as hav ing little re levance as far as the e n v i r o n m e n t is conce rned . Over the las t few years , however, ecological knowledge ha s a d v a n c e d to the s ta te where a m m o n i u m - c o n t a i n i n g was tewate r is a n a l y s e d to have the po ten t i a l to c ause e n v i r o n m e n t a l damage .
Methods which are avai lable for overcoming the p rob lem of a m m o n i u m in was tewate r i nc lude recovery of the a m m o n i u m a n d conver s ion of the a m m o n i u m n i t rogen in to mo lecu l a r n i t rogen .
A m m o n i a c a n be conver ted to a r e u s a b l e form u s i n g a l iquid m e m b r a n e . The process u s e s a n organic l iquid m e m b r a n e wh ich is bu i l t u p as a ba r r i e r be tween two a q u e o u s phases . In this case it is be tween the was tewa te r a n d the p roduc t phases . E m u l s i o n m e m b r a n e s have p roven to be pa r t i cu la r ly use fu l for i n d u s t r i a l pu rposes . These are p r o d u c e d by b r i n g i n g a n a q u e o u s so lu t ion (the acceptor phase) in to a n organic p h a s e (the m e m b r a n e phase) in s u c h a way as to form a wa te r - in -o i l emuls ion . The acceptor p h a s e u s u a l l y employed in the recovery of a m m o n i a is d i lu te s u l p h u r i c acid. The a m m o n i a which is p r o d u c e d w h e n the pH is ra i sed di f fuses t h r o u g h the organic m e m b r a n e a n d is conver ted to a m m o n i u m s u l p h a t e in the aeceptor phase . This is i n so lub le in the m e m b r a n e .
The biggest p rob lem h a m p e r i n g the deve lopment of th i s t e c h n i q u e is the s tab i l i ty of the emuls ion . It c a n be s tabi l ized b y a d d i n g a tensible , b u t t h e n s u b s e q u e n t b r e a k i n g at a la ter s tage c a n be uneconomic . A c o m p r o m i s e h a s to be reached.
Ano the r use fu l t e c h n i q u e is reverse osmosis . Most of the exper ience tha t h a s b e e n ga ined re la t ing to the s epa ra t i on of a m m o n i a ha s b e e n wi th the t r e a t m e n t of g r o u n d inf i l t ra t ion water. Sepa ra t i on efficiencies of 90% have b e e n ach ieved with feed c o n c e n t r a t i o n s of approx ima te ly 400 m g / l i t r e NH4+, wi th a water yield of 80%. In the pur i f i ca t ion of i n d u s t r i a l wastewater , the l iml t ing va lues of reverse osmos i s (the osmotic p r e s s u r e a n d the s a t u r a t i o n c o n c e n t r a t i o n of c r u s t - f o r m i n g s u b s t a n c e s ) c a n exert a greater in f luence t h a n t ha t of g r o u n d inf i l t ra t ion water. T h u s a l imit exis ts to the degree of c o n c e n t r a t i o n of a m m o n i u m t h a t c a n be achieved, due to the assoc ia ted inc rease in osmot ic p ressure .
As a p rocess for s epa ra t i ng electrolytes from a q u e o u s so lu t ions , e lec t rodia lys is is also use fu l for the recovery of a m m o n i u m ions from was tewaters . Sepa ra t i on a n d s i m u l t a n e o u s fo rma t ion of a c o n c e n t r a t e d a m m o n i n m - s a l t so lu t ion can be achieved wi th a n i on -exchange m e m b r a n e in c o n j u n c t i o n wi th a n electr ical field. The degree of d e s a l i n a t i o n t ha t is achieved by electrodialysis is de t e rmined , essent ia l ly , by the c u r r e n t be tween the ca thode a n d a n o d e a n d the avai lable su r face of the m e m b r a n e .
Further information from: Prof. Dipl.-Ing. Dr. Rolf Marr, Instltut f u r Thermische Verfahrenstechnik und Umwekttechnlk, Technische Universltat Graz, Inffeldgasse 25, A-8010 Graz, Austria.
Combinat ion f i l ter purifier A c o m b i n a t i o n filter purif ier h a s b e e n developed for u l t r apur i f i ca t ion of gases at the Univers i ty of Arizona, Tucson , USA. A commerc ia l u n i t will be avai lable in two years from Pall Corp.
Normal ly f i l t ra t ion a n d pur i f i ca t ion are done separate ly , b u t th is l imits pur i ty . O r d i n a r y filters p roduce some ga se ous c o n t a m i n a n t s t h r o u g h adso rp t ion a n d desorpt ion , while fr ict ion in packed -bed pur i f iers p r o d u c e s part icles .
The un ive r s i ty ' s m e t h o d avoids th is by u s i n g ceramic or me ta l m e m b r a n e s be a r i ng propr ie ta ry react ive me ta l s i tes tha t scavenge gaseous c o n t a m i n a n t s to the pa r t s per tr i l l ion level. S i mu l t a ne ous l y , the m e m b r a n e s filter par t ic les as smal l as 0.01 micrometer . Because the m e m b r a n e filter e l imina t e s the need for a p a c k e d - b e d purifier, the c o m b i n a t i o n will be only 10-12% the size of a s t a n d a r d two-un i t sys tem.
Reverse o s m o s i s m e m b r a n e deve loped from aromat ic po lyamide A reverse osmos i s m e m b r a n e fabr ica ted from aromat ic po lyamide c a n be u s e d wi thou t p r e t r e a t m e n t to purify tap water, c la ims m a n u f a c t u r e r Toyobo Co. The O s a k a - b a s e d s p i n n i n g firm says the ma te r i a l is also chlor ine- a n d ac id - res i s t an t .
Toyobo is c u r r e n t l y p r o d u c i n g a b o u t four t o n n e s of the m e m b r a n e every m o n t h , b u t will en te r full- scale p r o d u c t i o n in 1994.
Further information from: Toyobo Co Ltd, 2-2-8, Dojimahama, Klta-ku, Osaka 530, Japan. Tel: +81 6 348 3111. Fax: +81 6 348 3192.(c)
2 M e m b r a n e Techno logy No. 40