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Simultaneous Separation of Suspended Solids, Ammonium and Phosphate Ions from Waste Water by Modified Clinoptilolite
H.G. Karge, J. Weitkamp (Editors), Zeolites as Catalysts, Sorbents and Detergent Builders
0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
S I M U L T A N E O U S S E P A R A T I O N OF S U S P E N D E D S O L I D S , A M M O N I U M A N D P H O S P H A T E IONS FROM WASTE WATER B Y M O D I F I E D C L I N O P T I L O L I T E
J. O L A H Y 1 J. PAPP,2 A.MESZAROS-KIS,’
G Y . MUCSI’ and D.
KALL02
‘ R e s e a r c h C e n t r e f o r W a t e r R e s o u r c e s D e v e l o p m e n t , 1453 B u d a p e s t , P.O.Box 2 7 ( H u n g a r y ) n
L Central Research I n s t i t u t e f o r C h e m i s t r y , H u n g a r i a n A c a d e m y o f S c i e n c e , H - 1 5 2 5 Budapest, P.O.Box 17 ( H u n g a r y )
ABSTRACT A municipal s e w a g e t r e a t m e n t t e c h n o l o g y has been d e v e l o p e d based o n t h e r e c o g n i t i o n t h a t ( i ) z e o l i t e - c o n t a i n i n g p o w d e r (i.e. c r u s h e d z e o l i t i c r o c k ) o f a p p r o p r i a t e g r a i n s i z e a d d e d t o w a s t e w a t e r i n c r e a s e s the biological a c t i v i t y o f the s l u d g e , ( i i ) removal o f s u s p e n d e d s o l i d s is i n c r e a s e d a n d ( i i i ) t h e p h o s p h a t e removal e f f i c i e n c y o f t r i v a l e n t c a t i o n s ( F e 3 + , A l J + ) is h i g h e r in the presence o f zeolite. A f t e r biological t r e a t m e n t t h e r e m a i n i n g a m m o n i u m and dissolved or c o l l o i d o r g a n i c s u b s t a n c e s c a n be removed in a c o l u m n f i l l e d w i t h z e o l i t e (e.g. c l i n o p t i l o l i t e ) s e l e c t i v e f o r a m m o n i u m ions, INTRODUCTION A f t e r biological t r e a t m e n t w i t h a c t i v a t e d s l u d g e t h e o u t l e t sewage mostly c o n t a i n s c o n t a m i n a n t s in u n a c c e p t a b l e a m o u n t s . In o r d e r t o r e m o v e t h e r e m a i n i n g i m p u r i t i e s chemical m e t h o d s a r e usually a p p l i e d , e.g. s u s p e n d e d s o l i d s can be c o a g u l a t e d by adding a l u m i n i u m s u l f a t e or a s y n t h e t i c p o l y e l e c t r o l y t e s ; p h o s p h o r u s a s p h o s p h a t e s a r e precipitated w i t h a l u m i n i u m o r i r o n s a l t s o r w i t h l i m e ; a m m o n i u m removal proceeds via i o n - e x c h a n g e o r t h r o u g h n i t r i f i c a t i o n f o l l o w e d by d e n i t r i f i c a t i o n (ref. 1). C o n s i d e r i n g t h e p u b l i c a t i o n s o f p r o c e s s e s a p p l i e d it s e e m s t h a t the i m p r o v e m e n t o f s e w a g e t r e a t m e n t t e c h n o l o g i e s is still o f c u r r e n t interest. As a r e s u l t s o f t h e a b o v e t r e a t m e n t s with e x p e n s i v e c h e m i c a l s , w a s t e s a r e f o r m e d wich c o n t a m i n a t e t h e e n v i r o n m e n t . T h e u s e o f natural m a t e r i a l s 1 ike z e o l i t e s a s i o n - e x c h a n g e r s a n d / o r adsorbents s e e m s r a t h e r promising, s i n c e they a r e much c h e a p e r and t h e i m p u r i t i e s a r e r e m o v e d in l e s s h a z a r d o u s forms.
712
Among n a t u r a l z e o l i t e s , c l i n o p t i l o l i t e o c c u r s m o s t frequently, e.g.
i n U.S.A.,
Japan,
t h e S o v i e t U n i o n and Hungary ( r e f . 2 ) .
Ames was t h e f i r s t o b s e r v t h e s e l e c t i v e ammonium i o n - e x c h a n g e f o r c l i n o p t i l o l i t e (ref. 3);
thereafter the a p p l i c a b i l i t y o f
c l i n o p t i l o l i t e f o r ammonium r e m o v a l f r o m r a w a n d w a s t e w a t e r s was extensively investigated.
Koon a n d Kaufmann s t u d i e d i n d e t a i l
t h e ammonium r e m o v a l w i t h c l i n o p t i l o l i t e i n a f i x e d - b e d c o l u m n and d e t e r m i n e d t h e r e g e n e r a t i o n c o n d i t i o n s ( r e f . 4 ) . experts found t h a t p h i l l i p s i t e i s applicable, o f ammonium f r o m w a t e r b y i o n - e x c h a n g e ( r e f .
too,
5).
Italian
f o r removal
Union Carbide
p r o d u c e d a z e o l i t e s p e c i a l l y s e l e c t i v e f o r ammonium i o n s ( r e f . 6 ) . Similarly,
i n f i x e d - b e d o p e r a t i o n L i b e r t i and c o - w o r k e r s
(ref.
7,8) u t i l i z e d c l i n o p t i l o l i t e f o r ammonium r e m o v a l a n d an a n i o n - e x c h a n g e r e s i n f o r p h o s p h a t e r e m o v a l i n sewage t r e a t m e n t p i l o t p l a n t s o f 10 a n d 240 m 3 / d c a p a c i t i e s . When z e o l i t e A ,
came i n t o u s e as a d e t e r g e n t b u i l d e r i t s r o l e
i n sewage t r e a t m e n t was i n v e s t i g a t e d . N e i t h e r C a r r o n d o e t a l . ( r e f . 91, n o r Holman a n d H o p p i n g ( r e f .
10,
1 1 ) f o u n d any u n f a -
vourable e f f e c t o f z e o l i t e A during the treatment o f laundry effluents. I s h i i and K a j i p u b l i s h e d ( r e f . 1 2 1 , t h e e q u a t i o n s o f a d s o r p t i o n i s o t h e r m s o f ammonium a n d p h o s p h a t e i o n s on s u s p e n d e d c l i n o p t i l o l i t e doped w i t h a l u m i n i u m s u l f a t e . The authors have succeeded i n i n c r e a s i n g t h e r e m o v a l o f s u s p e n d e d solids,
p h o s p h a t e a n d t o some e x t e n t ammonium i o n s f r o m m u n i c i p a l
sewage b y t h e u s e o f c l i n o p t i l o l i t e s u s p e n d e d i n c o n c e n t r a t e d aqueous s o l u t i o n o f a F e 3 + s a l t .
The r e m a i n i n g o f t h e ammonium
c a n t h e r e a f t e r be removed b y i o n - e x c h a n g e i n a f i x e d - b e d c o l u m n f i l l e d w i t h c l i n o p t i l o l i t e . The a i m o f o u r f u r t h e r i n v e s t i g a t i o n s was t o c o n f i r m t h e e a r l i e r r e s u l t s t h r o u g h l a r g e - s c a l e experiments a n d f u r t h e r m o r e t o c l a r i f y up t h e i n f l u e n c e o f a c l i n o p t i l o l i t e s u s p e n s i o n on t h e a c t i v i t y a n d p r o p e r t i e s o f a c t i v a t e d s l u d g e . EXPERIMENT Materials
A 6 3 - 1 8 0 I.cm f r a c t i o n o f a r h y o l i t e t u f f c o n t a i n i n g a b o u t 5 0 % c l i n o p t i l o l i t e ( f r o m R a t k a , T o k a j H i l l s , H u n g a r y ) was s u s p e n d e d i n d i f f e r e n t a m o u n t s o f aqueous i r o n c h l o r o - s u l f a t e s o l u t i o n c o n t a i n i n g 200 g F e 3 + / l . S u s p e n s i o n s w i t h d i f f e r e n t c l i n o p t i l o l i t e / /Fe3+ r a t i o s were used.
713
The o p t i m a l g r a i n s i z e o f t h e t u f f was e x p e r i m e n t a l l y determined: ( i ) t h e s m a l l e s t p a r t i c l e s must n o t escape t h e s e t t l i n g t a n k , ( i i ) the e f f i c i e n c y o f t h e l a r g e s t p a r t i c l e s should n o t essent i a l l y decrease because o f t h e s h o r t e r s e t t l i n g t i m e and t h e slower d i f f u s i o n - c o n t r o l l e d processes, To e n s u r e f a v o u r a b l e o p e r a t i n g c o n d i t i o n s , 0 . 5 - 2 . 0
mm g r a i n
s i z e f r a c t i o n o f t h e a b o v e t u f f was u s e d i n t h e i o n - e x c h a n g e column. The c l i n o p t i l o l i t e - c o n t a i n i n g t u f f i s c h a r a c t e r i z e d as f o l l ows. C l i n o p t i l o l i t e c r y s t a l s o f s i z e 1 - 1 0 ,urn a r e i r r e g u l a r l y embedded i n t h e r o c k , w h i c h c o n t a i n s q u a r t z , montmorillonite,
crystobalite,
f e l s p a r a n d some 1 0 % v o l c a n i c g l a s s . The
minerals form a texture w i t h a convenient pore-size d i s t r i b u t i o n .
No s w e l l i n g i s o b s e r v a b l e i n w a t e r , i . e . t h e s i z e o f p a r t i c l e s The m a i n p h y s i c a l - c h e m i c a l d a t a o f t h e u s e d t u f f a r e summarized i n T a b l e 1.
does n o t change.
TABLE 1 The p r o p e r t i e s o f t h e c l i n o p t i l o l i t e - c o n t a i n i n g r o c k Chemical Composition i n w t . % : Si02
2'3
69.50
11.65
Fe203
Na20
K20
MgO
CaO
loss ign.
1.06
0.44
4.44
0.59
1.83
10.53
Pore-size d i s t r i b u t i o n r
1.6 10
d1.6
-= r PP .= 1 0
-
Volume o f p o r e s i n f u n c t i o n o f p o r e s i z e s
nm
0.1 c m 3 / g
nm
0.1
cm3/g
<
r ~ 7 5 0 0nm 0.5 c m 3 / g P P o r o s i t y : 40-50 % ( t h e r a t i o o f t h e t o t a l p o r e volume and t h e
volume o f t h e p o r o u s m a t e r i a l ) S u r f a c e a r e a f r o m benzene a d s o r p t i o n : 20-30 mz/g S u r f a c e a r e a f r o m n i t r o g e n a d s o r p t i o n : 400-500 mz/g I o n - e x c h a n g e c a p a c i t y : 1.1 meq/g The c h a r a c t e r i s t i c s o f sewages a r e l i s t e d i n T a b l e 2 t o g e t h e r w i t h t h e mean v a l u e s o f e x p e r i m c n t a l d a t a ,
s i n c e d i f f e r e n t sewages
w e r e f e d i n d i f f e r e n t p l a n t s . The a m o u n t o f s u s p e n d e d s o l i d s ,
COD
( C h e m i c a l O x y g e n Demand) t o t a l p h o s p h o r u s a n d o r t h o - p h o s p h a t e , ammonium a n d n i t r a t e c o n t e n t s w e r e d e t e r m i n e d , M o h l m a n n i n d e x ( a datum f o r c h a r a c t e r i z i n g t h e s e d i m e n t a t i o n p r o p e r t i e s o f t h e suspended s o l i d s ) and b i o l o g i c a l a c t i v i t y o f t h e s l u d g e were m e a s u r e d , a s we1 1 .
714 TABLE 2 The m a i n p a r a m e t e r s o f sewage t r e a t m e n t s i n d i f f e r e n t p l a n t s Location, Year (Type 1
Amount o f sewage
m3 /d
Biological 1oadi ng
Age o f sludge
kg BOD d
k g - l d-’ D u n a k e s z i , 1985
48
0.25
2.3
1850
0.08
15.5
0.04
25
( p i l o t plant)
Zalaegerszeg,
1987
(large scale) Bal atonbereny , 1987 (large scale)
,
Character o f sewage
municipal 50%+canning f a c t o r y 50%
municipal 60% food i n d u s t r y 40% m u n i c ip a l
Equipment and Methods C o n t i n u o u s e x p e r i m e n t s were c a r r i e d o u t i n a p i l o t p l a n t and i n l a r g e - s c a l e p l a n t s . T y p i c a l t e c h n i c a l d a t a o f sewage treatment a r e g i v e n i n Table 3. The a r r a n g e m e n t o f t h e t e c h n o l o g i c a l u n i t s ( s c r e e n , g r i t chamber, a e r a t o r ,
s e c o n d a r y s e t t l i n g t a n k ) w e r e t h e same f o r a l l
i n s t a l l a t i o n s . The z e o l i t e s u s p e n s i o n was a d d e d t o t h e sewage i n t h e c h a n n e l j u s t b e f o r e t h e a e r a t o r , w h e r e a p e r f e c t m i x i n g was achieved. loading,
The t e c h n o l o g i c a l p a r a m e t e r s ( e . g . etc.)
residence time,
and t h e s i z e o f equipment were i d e n t i c a l f o r b o t h
t h e e x p e r i m e n t a l a n d c o n t r o l l i n e s . The p i l o t p l a n t ( i n D u n a k e s z i ) operated w i t h high loading,
t h e o t h e r s i n a t o t a l o x i d a t i o n mode.
RESULTS A N D D I S C U S S I O N A v e r a g e s o f a g r e a t amount o f e x p e r i m e n t a l d a t a d e t e r m i n e d b o t h i n p i l o t p l a n t and i n l a r g e - s c a l e p l a n t s a r e summarized i n T a b l e 3 . The l a t t e r p l a n t s a r e l o c a t e d i n t h e w e l l p r o t e c t e d a r e a o f Lake-Balaton.
W
c,
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c,
mc1 E a J
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L
0
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0
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mii m 11
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715
716 Removal o f P h o s p h o r u s D e p e n d i n g on t h e amount o f c o n t a m i n a n t s 15-30 mg F e 3 + a n d
30-100 mg p o w d e r e d c l i n o p t i l o l i t e c o n t a i n i n g r o c k i s a d d e d t o one l i t r e o f sewage. The r e m o v a l o f p h o s p h o r u s i n t h e p i l o t p l a n t ( i n D u n a k e s z i ) as a f u n c t i o n o f t i m e on f l o w i s i l l u s t r a t e d i n Fig.
1. I n most p r o t e c t e d d i s t r i c t s o f Hungary (around t h e g r e a t
l a k e s ) t h e p e r m i t t e d l i m i t o f p h o s p h o r u s c o n t e n t i n emmissions i s
1.8 mg P/1 (5,5 mg P O i - / l ) ,
w h i c h c a n r e l i a b l y be a t t a i n e d w i t h
t h i s treatment.
5
10
15
20
25
50
30
55 60 time, day
F i g . 1. O r t h o - p h o s p h a t e c o n c e n t r a t i o n as a f u n c t i o n o f t i m e on f l o w i n t h e s e t t l e d sewage i n l e t (l), i n t h e c o n t r o l sewage o u t l e t ( w i t h o u t additives, 2 ) , w i t h a d d i t i o n o f a suspension c o n t a i n i n g 18.3 mg F e 3 + / l + 65 mg z e o l i t e / l ( 3 ) On a d d i n g 1.16-1.95 i r o n i o n s t o g e t h e r , z e o l i t i c r o c k t o 1 atom phosphorus, P/1 c a n be g u a r a n t e e d .
w i t h the suspension o f
a d e p h o s p h o r i z a t i o n t o 1.8 mg
W i t h o u t z e o l i t e a d d i t i v e 1.7-2.5
i r o n ions
a r e needed f o r c o m p a r a b l e p u r i f i c a t i o n . Our o b s e r v a t i o n s , p o r t e d by t h e f i n d i n g o f I s h i i and K a j i ( r e f .
sup-
12), a r e s i m i l a r
f o r A12(S04)3 a d d i t o n w i t h and w i t h o u t z e o l i t e s . Consequently, t h e e f f i c i e n c y o f phosphate removal w i t h t r i v a l e n t c a t i o n s increases i n the presence o f z e o l i t e ; 1 g o f z e o l i t i c rock i t s e l f removes 6 . 4
mg p h o s p h o r u s o w i n g t o t h e m o b i l e Ca a n d Mg ( F e ) i o n s
i n t h e z e o l i t e phase which f o r m phosphate p r e c i p i t a t e
717
a f t e r e x c h a n g e f o r ammonium i o n s f r o m t h e sewage. The o b s e r v e d e f f e c t o f c l i n o p t i l o l i t e i s 3-6 times g r e a t e r t h a n t h e v a l u e o f 6.4 mg/g.
A f t e r an o p e r a t i o n p e r i o d f o r some weeks t h e p h o s p h a t e
removal e f f i c i e n c y
i s preserved i n the z e o l i t e containing aerator,
when t h e dosage i s s t o p p e d e v e n f o r o n e d a y . The r e a s o n f o r t h i s e f f e c t i s t h e r e t e n t i o n o f i r o n i n t h e z e o l i t i c r o c k i n t h e a e r a t o r . The r e s i d e n c e t i m e o f z e o l i t i c r o c k w i t h i r o n s a l t occluded i n the pores o f d i f f e r e n t s i z e i s l o n g e r t h a n t h a t o f n o n - f i x e d i r o n s o l u t i o n . The r e t a r d e d d e s o r p t i o n o f i r o n during a longer residence time r e s u l t s i n a b e t t e r utilization o f t h e Fe3+ introduced. This i s i n q u a n t i t a t i v e c o r r e l a t i o n w i t h the experimental findings. Removal o f Suspended S o l i d s I n each case t h e c o n t e n t o f suspended s o l i d s i n t h e e f f l u e n t i s l e s s when t h e b i o l o g i c a l t r e a t m e n t o f t h e sewage i s c a r r i e d out with z e o l i t e / i r o n - s a l t addition than without i t (c.f. " e x p e r i m e n t a l " a n d " c o n t r o l " d a t a i n T a b l e 3 ) : e.g.
i n a large
s c a l e p l a n t ( Z a l a e g e r s z e g ) t h e e f f l u e n t c o n t a i n e d 35 m g / l s u s p e n d e d s o l i d s w h i c h d e c r e a s e d t o 18 m g / l b y z e o l i t e / i r o n - s a l t addition.
The z e o l i t e p a r t i c l e s p r e f e r a b l y a d s o r b c o l l o i d s ,
and
c o a g u l a t i o n s e e d s a r e t h u s f o r m e d . The h y d r o x i d e s o f m e t a l s f o r m e d f r o m t h e i n t r o d u c e d s a l t s e x e r t an a d d i t i o n a l c o a g u l a t i o n effect
.
As a r e s u l t o f z e o l i t e t r e a t m e n t ( i ) t h e d e n s i t y o f a c t i v a t e d s l u d g e i n c r e a s e s f r o m 1 5 g / l t o 30 g / 1 i n t h e s e c o n d a r y s e t t l i n g tank,
( i i ) the d e w a t e r a b i l i t y improves, i . e .
the
c a p i l l a r y s u c t i o n t i m e decreases f r o m 30 s t o 10-15 s , and ( i i i ) t h e Mohlmann i n d e x d i m i n i s h e s s i g n i f i c a n t l y . The E f f e c t o f Z e o l i t e on t h e B i o l o g i c a l A c t i v i t y o f t h e S l u d g e An i n c r e a s e d b i o l o g i c a l a c t i v i t y i s r e f l e c t e d b y t h e C O D v a l u e s o f t h e f i l t e r e d e f f l u e n t s ( T a b l e 3 ) s i n c e w i t h t h e same residence times,
they are r e g u l a r l y lower a f t e r z e o l i t e treatment
than i n the c o n t r o l l i n e . The d i g e s t i o n a c t i v i t y o f t h e s l u d g e c a n be b e t t e r e x p r e s s e d i n terms o f COD g - l h - l
. Pilot
p l a n t experiments (Dunakeszi,
showed an a c t i v i t y o f 52 C O D 9 - l h - l g-'h-'
i n t h e case o f z e o l i t e i n t r o d u c t i o n .
v a l u e s i n an o p e r a t i n g p l a n t ( B a l a t o n b e r e n y , 44 C O D g - l h - ' ,
respectively.
1986)
i n t h e c o n t r o l l i n e and 65 COD The c o r r e s p o n d i n g 1 9 8 7 ) w e r e 35 a n d
These e x a m p l e s ( a n d a s e r i e s o f
o t h e r d a t a ) p o i n t t o an i n c r e a s e o f t h e b i o l o g i c a l a c t i v y b y a b o u t 2 5 % due t o z e o l i t e i n t r o d u c t i o n .
Upon z e o l i t e a d d i t i o n a s i g n i f i c a n t i n c r e a s e o f n i t r i f i c a t i o n has b e e n o b s e r v e d a s w e l l . a b o u t 60%, i . e . i n the effluents
For instance,
i n Zanka ( 1 9 8 6 ) i t was
53 m g / l a n d 85 m g / l n i t r a t e c o n t e n t s w e r e f o u n d o f c o n t r o l and e x p e r i m e n t a l l i n e s r e s p e c t i v e l y .
The c o r r e s p o n d i n g v a l u e s i n B a l a t o n b e r e n y ( 1 9 8 7 ) w e r e 24 m g / l a n d 57 m g / l ,
respectively.
The i n c r e a s e o f b i o l o g i c a l a c t i v i t y e f f e c t e d t r o u g h z e o l i t i c a d d i t i v e c a n be e x p l a i n e d as f o l l o w s : ( i ) Z e o l i t e p a r t i c l e s a r e seeds f o r b a c t e r i a f l o c k s . F l o c k s a r e t h u s f o r m e d i n g r e a t e r number a n d o f s m a l l e r s i z e t h a n i n t h e absence o f z e o l i t i c g r a i n s . s m a l l e r t h a n 0.3 mm; a n d 2 mm.
With z e o l i t e s the f l o c k s are
w i t h o u t z e o l i t e s t h e i r s i z e i s b e t w e e n 0.4
The t r a n s p o r t o f o x y g e n a n d n u t r i e n t s i s f a s t e r i n t h e
s m a l l e r f l o c k s t h a n i n l a r g e r ones. ( i i ) Z e o l i t e p a r t i c l e s s o r b ammonia w h i c h i s a c c e s s i b l e f o r n i t r i f i c a t i o n b a c t e r i a c o n c e n t r a t e d on z e o l i t e c r y s t a l s ,
thus the
n i t r i f i c a t i o n accelerates. ( i i i ) The b i o l o g i c a l c o m p o s i t i o n o f a c t i v a t e d s l u d g e c h a n g e s f a v o u r a b l y i n t h e p r e s e n c e o f z e o l i t e . The " p r e d a t o r c i l i a t e s " (Litonotus, Loxophillum,
Vorticella,
Convallaria,
Opercularia,
C o a r e t a t a ) m u l t i p l y . Nematodes a l s o a p p e a r i n t h e s l u d g e .
These
a n i m a l s f e e d on t h e f r e e - s w i m m i n g b a c t e r i a i n l i q u i d phase. ( i v ) The b i o l o g i c a l s t a b i l i t y o f t h e s e p a r a t e d a n d z e o l i t e containing sludge i s greater than without z e o l i t e : observable a n a e r o b i c d i g e s t i o n proceeds w i t h i n f i v e days i n t h e absence o f z e o l i t e w h e r e a s t h e s l u d g e r e m a i n s u n c h a n g e d e v e n f o r t h r e e weeks u n d e r t h e same c o n d i t i o n s ,
i f i t c o n t a i n s z e o l i t e . The phenomenon
i s being investigated i n d e t a i l . ( v ) Contrary t o usual sludges, the desiccated sludge c o n t a i n i n g z e o l i t e i s o f h i g h v a l u e because a f t e r composting i t c a n be u s e d a s a f e r t i l i z e r o f s u f f i c i e n t n u t r i e n t v a l u e s . When i n s t e a d o f i r o n s a l t an a l u m i n i u m s a l t i s u s e d f o r t h e treatment, h o w e v e r , t h e s l u d g e c a n h a r d l y be u t i l i z e d i n a g r i c u l t u r e . F i n a l Treatment A f t e r b i o l o g i c a l treatment o f increased a c t i v i t y the r e s t o f t h e ammonium c a n be r e m o v e d c o n v e n t i o n a l l y b y i o n - e x c h a n g e w i t h zeolite,
p r e f e r a b l y w i t h c l i n o p t i l o l i t e because o f i t s h i g h
s e l e c t i v i t y f o r ammonium.
The ammonium c o n t e n t i n t h e o u t l e t c a n be
kept below 4 mg/l. The o p e r a t i o n p a r a m e t e r s f o r o u r p i l o t p l a n t w e r e o p t i m i z e d . The f i l l i n g c a n be r e p e a t e d l y r e g e n e r a t e d w i t h a 2 w t . %
719 KCl/NaCl
s o l u t i o n o f pH
=-
1 0 . The ammonia was r e m o v e d e i t h e r b y
s t r i p p i n g w i t h a i r and a b s o r b i n g , solution,
e.g.
i n a phosphoric a c i d
o r b y p r e c i p i t a t i o n i n t h e f o r m o f MgNH4P04. We
observed t h a t t h e f i r s t s e c t i o n o f ion-exchanger works as a filter,
where d i s s o l v e d o r c o l l o i d ( m a i n l y o r g a n i c ) c o n t a m i n a n t s
n o t a l r e a d y removed a r e bound. A f t e r t h e c o u n t e r c u r r e n t r e g e n e r a t i o n they can be s e t t l e d from t h e r e g e n e r a t i n g s o l u t i o n . REFERENCES 1
Water T r e a t m e n t Handbook, V . E d i t i o n , Degremont 1979, pp. 57-74, 141-144. 2 Y . M u r a k a m i , A . I i j i m a a n d J.W. Ward ( E d i t o r s ) : New Development i n Z e o l i t e Science and Technology. E l s e v i e r S c i e n t i f i c P u b l . Co. A m s t e r d a m , 1 9 8 6 . 3 L . L . Ames: Amer. M i n e r a l o g i s t 4 5 ( 1 9 6 0 ) 6 8 9 - 7 0 0 . 4 J.H. Koon a n d W.J. K a u f m a n : O p t i m a t i o n o f Ammonia Removal b y I o n E x c h a n g e U s i n g C l i n o p t i l o l i t e . U S R e p o r t f o r t h e EPA, 1 9 7 1 . 5 P. C i a m b e l l i , P . C o r b o , C . P o r c e l l i a n d A . R i m o l i : Z e o l i t e s 5 ( 1 9 8 5 ) 184-187. 6 US P a t e n t 3 723 3 0 8 7 L. L i b e r t i , G. B o a r i a n d R. P a s s i n o : Wat. S u p p l y 1 ( 1 9 8 3 ) , 169-176. 8 L . L i b e r t i , N. L i m o n i , A . L o p e z , R . P a s s i n o a n d G . B o a r i : Water Research 20 ( 1 9 8 6 ) 735-739. 9 M.J.T. C a r r o n d o , R . P e r r y a n d J.N. L e s t e r : J. Wat. P o l l u t . C o n t r o l Fed. 52 ( 1 9 8 0 ) 2 7 9 6 - 2 8 0 6 . 1 0 W.F. H o l m a n a n d W.D. H o.p.p i n q- : J. W a t . P o l l u t . C o n t r o l F e d . 52 (1980) 2887-2905. 1 1 J.E. K i n g , D.W. H o p p i n g a n d F.W. H o l m a n : I . J . Wat. P o l l u t . C o n t r o l Fed. 52 ( 1 9 8 0 1 2 8 7 5 - 2 8 8 6 . 1 2 M . I s h i i a n d K. K a j i : . G y p s u m a t L i m e 186 ( 1 9 8 3 ) 8 - 1 6 .
0 1989 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
S I M U L T A N E O U S S E P A R A T I O N OF S U S P E N D E D S O L I D S , A M M O N I U M A N D P H O S P H A T E IONS FROM WASTE WATER B Y M O D I F I E D C L I N O P T I L O L I T E
J. O L A H Y 1 J. PAPP,2 A.MESZAROS-KIS,’
G Y . MUCSI’ and D.
KALL02
‘ R e s e a r c h C e n t r e f o r W a t e r R e s o u r c e s D e v e l o p m e n t , 1453 B u d a p e s t , P.O.Box 2 7 ( H u n g a r y ) n
L Central Research I n s t i t u t e f o r C h e m i s t r y , H u n g a r i a n A c a d e m y o f S c i e n c e , H - 1 5 2 5 Budapest, P.O.Box 17 ( H u n g a r y )
ABSTRACT A municipal s e w a g e t r e a t m e n t t e c h n o l o g y has been d e v e l o p e d based o n t h e r e c o g n i t i o n t h a t ( i ) z e o l i t e - c o n t a i n i n g p o w d e r (i.e. c r u s h e d z e o l i t i c r o c k ) o f a p p r o p r i a t e g r a i n s i z e a d d e d t o w a s t e w a t e r i n c r e a s e s the biological a c t i v i t y o f the s l u d g e , ( i i ) removal o f s u s p e n d e d s o l i d s is i n c r e a s e d a n d ( i i i ) t h e p h o s p h a t e removal e f f i c i e n c y o f t r i v a l e n t c a t i o n s ( F e 3 + , A l J + ) is h i g h e r in the presence o f zeolite. A f t e r biological t r e a t m e n t t h e r e m a i n i n g a m m o n i u m and dissolved or c o l l o i d o r g a n i c s u b s t a n c e s c a n be removed in a c o l u m n f i l l e d w i t h z e o l i t e (e.g. c l i n o p t i l o l i t e ) s e l e c t i v e f o r a m m o n i u m ions, INTRODUCTION A f t e r biological t r e a t m e n t w i t h a c t i v a t e d s l u d g e t h e o u t l e t sewage mostly c o n t a i n s c o n t a m i n a n t s in u n a c c e p t a b l e a m o u n t s . In o r d e r t o r e m o v e t h e r e m a i n i n g i m p u r i t i e s chemical m e t h o d s a r e usually a p p l i e d , e.g. s u s p e n d e d s o l i d s can be c o a g u l a t e d by adding a l u m i n i u m s u l f a t e or a s y n t h e t i c p o l y e l e c t r o l y t e s ; p h o s p h o r u s a s p h o s p h a t e s a r e precipitated w i t h a l u m i n i u m o r i r o n s a l t s o r w i t h l i m e ; a m m o n i u m removal proceeds via i o n - e x c h a n g e o r t h r o u g h n i t r i f i c a t i o n f o l l o w e d by d e n i t r i f i c a t i o n (ref. 1). C o n s i d e r i n g t h e p u b l i c a t i o n s o f p r o c e s s e s a p p l i e d it s e e m s t h a t the i m p r o v e m e n t o f s e w a g e t r e a t m e n t t e c h n o l o g i e s is still o f c u r r e n t interest. As a r e s u l t s o f t h e a b o v e t r e a t m e n t s with e x p e n s i v e c h e m i c a l s , w a s t e s a r e f o r m e d wich c o n t a m i n a t e t h e e n v i r o n m e n t . T h e u s e o f natural m a t e r i a l s 1 ike z e o l i t e s a s i o n - e x c h a n g e r s a n d / o r adsorbents s e e m s r a t h e r promising, s i n c e they a r e much c h e a p e r and t h e i m p u r i t i e s a r e r e m o v e d in l e s s h a z a r d o u s forms.
712
Among n a t u r a l z e o l i t e s , c l i n o p t i l o l i t e o c c u r s m o s t frequently, e.g.
i n U.S.A.,
Japan,
t h e S o v i e t U n i o n and Hungary ( r e f . 2 ) .
Ames was t h e f i r s t o b s e r v t h e s e l e c t i v e ammonium i o n - e x c h a n g e f o r c l i n o p t i l o l i t e (ref. 3);
thereafter the a p p l i c a b i l i t y o f
c l i n o p t i l o l i t e f o r ammonium r e m o v a l f r o m r a w a n d w a s t e w a t e r s was extensively investigated.
Koon a n d Kaufmann s t u d i e d i n d e t a i l
t h e ammonium r e m o v a l w i t h c l i n o p t i l o l i t e i n a f i x e d - b e d c o l u m n and d e t e r m i n e d t h e r e g e n e r a t i o n c o n d i t i o n s ( r e f . 4 ) . experts found t h a t p h i l l i p s i t e i s applicable, o f ammonium f r o m w a t e r b y i o n - e x c h a n g e ( r e f .
too,
5).
Italian
f o r removal
Union Carbide
p r o d u c e d a z e o l i t e s p e c i a l l y s e l e c t i v e f o r ammonium i o n s ( r e f . 6 ) . Similarly,
i n f i x e d - b e d o p e r a t i o n L i b e r t i and c o - w o r k e r s
(ref.
7,8) u t i l i z e d c l i n o p t i l o l i t e f o r ammonium r e m o v a l a n d an a n i o n - e x c h a n g e r e s i n f o r p h o s p h a t e r e m o v a l i n sewage t r e a t m e n t p i l o t p l a n t s o f 10 a n d 240 m 3 / d c a p a c i t i e s . When z e o l i t e A ,
came i n t o u s e as a d e t e r g e n t b u i l d e r i t s r o l e
i n sewage t r e a t m e n t was i n v e s t i g a t e d . N e i t h e r C a r r o n d o e t a l . ( r e f . 91, n o r Holman a n d H o p p i n g ( r e f .
10,
1 1 ) f o u n d any u n f a -
vourable e f f e c t o f z e o l i t e A during the treatment o f laundry effluents. I s h i i and K a j i p u b l i s h e d ( r e f . 1 2 1 , t h e e q u a t i o n s o f a d s o r p t i o n i s o t h e r m s o f ammonium a n d p h o s p h a t e i o n s on s u s p e n d e d c l i n o p t i l o l i t e doped w i t h a l u m i n i u m s u l f a t e . The authors have succeeded i n i n c r e a s i n g t h e r e m o v a l o f s u s p e n d e d solids,
p h o s p h a t e a n d t o some e x t e n t ammonium i o n s f r o m m u n i c i p a l
sewage b y t h e u s e o f c l i n o p t i l o l i t e s u s p e n d e d i n c o n c e n t r a t e d aqueous s o l u t i o n o f a F e 3 + s a l t .
The r e m a i n i n g o f t h e ammonium
c a n t h e r e a f t e r be removed b y i o n - e x c h a n g e i n a f i x e d - b e d c o l u m n f i l l e d w i t h c l i n o p t i l o l i t e . The a i m o f o u r f u r t h e r i n v e s t i g a t i o n s was t o c o n f i r m t h e e a r l i e r r e s u l t s t h r o u g h l a r g e - s c a l e experiments a n d f u r t h e r m o r e t o c l a r i f y up t h e i n f l u e n c e o f a c l i n o p t i l o l i t e s u s p e n s i o n on t h e a c t i v i t y a n d p r o p e r t i e s o f a c t i v a t e d s l u d g e . EXPERIMENT Materials
A 6 3 - 1 8 0 I.cm f r a c t i o n o f a r h y o l i t e t u f f c o n t a i n i n g a b o u t 5 0 % c l i n o p t i l o l i t e ( f r o m R a t k a , T o k a j H i l l s , H u n g a r y ) was s u s p e n d e d i n d i f f e r e n t a m o u n t s o f aqueous i r o n c h l o r o - s u l f a t e s o l u t i o n c o n t a i n i n g 200 g F e 3 + / l . S u s p e n s i o n s w i t h d i f f e r e n t c l i n o p t i l o l i t e / /Fe3+ r a t i o s were used.
713
The o p t i m a l g r a i n s i z e o f t h e t u f f was e x p e r i m e n t a l l y determined: ( i ) t h e s m a l l e s t p a r t i c l e s must n o t escape t h e s e t t l i n g t a n k , ( i i ) the e f f i c i e n c y o f t h e l a r g e s t p a r t i c l e s should n o t essent i a l l y decrease because o f t h e s h o r t e r s e t t l i n g t i m e and t h e slower d i f f u s i o n - c o n t r o l l e d processes, To e n s u r e f a v o u r a b l e o p e r a t i n g c o n d i t i o n s , 0 . 5 - 2 . 0
mm g r a i n
s i z e f r a c t i o n o f t h e a b o v e t u f f was u s e d i n t h e i o n - e x c h a n g e column. The c l i n o p t i l o l i t e - c o n t a i n i n g t u f f i s c h a r a c t e r i z e d as f o l l ows. C l i n o p t i l o l i t e c r y s t a l s o f s i z e 1 - 1 0 ,urn a r e i r r e g u l a r l y embedded i n t h e r o c k , w h i c h c o n t a i n s q u a r t z , montmorillonite,
crystobalite,
f e l s p a r a n d some 1 0 % v o l c a n i c g l a s s . The
minerals form a texture w i t h a convenient pore-size d i s t r i b u t i o n .
No s w e l l i n g i s o b s e r v a b l e i n w a t e r , i . e . t h e s i z e o f p a r t i c l e s The m a i n p h y s i c a l - c h e m i c a l d a t a o f t h e u s e d t u f f a r e summarized i n T a b l e 1.
does n o t change.
TABLE 1 The p r o p e r t i e s o f t h e c l i n o p t i l o l i t e - c o n t a i n i n g r o c k Chemical Composition i n w t . % : Si02
2'3
69.50
11.65
Fe203
Na20
K20
MgO
CaO
loss ign.
1.06
0.44
4.44
0.59
1.83
10.53
Pore-size d i s t r i b u t i o n r
1.6 10
d1.6
-= r PP .= 1 0
-
Volume o f p o r e s i n f u n c t i o n o f p o r e s i z e s
nm
0.1 c m 3 / g
nm
0.1
cm3/g
<
r ~ 7 5 0 0nm 0.5 c m 3 / g P P o r o s i t y : 40-50 % ( t h e r a t i o o f t h e t o t a l p o r e volume and t h e
volume o f t h e p o r o u s m a t e r i a l ) S u r f a c e a r e a f r o m benzene a d s o r p t i o n : 20-30 mz/g S u r f a c e a r e a f r o m n i t r o g e n a d s o r p t i o n : 400-500 mz/g I o n - e x c h a n g e c a p a c i t y : 1.1 meq/g The c h a r a c t e r i s t i c s o f sewages a r e l i s t e d i n T a b l e 2 t o g e t h e r w i t h t h e mean v a l u e s o f e x p e r i m c n t a l d a t a ,
s i n c e d i f f e r e n t sewages
w e r e f e d i n d i f f e r e n t p l a n t s . The a m o u n t o f s u s p e n d e d s o l i d s ,
COD
( C h e m i c a l O x y g e n Demand) t o t a l p h o s p h o r u s a n d o r t h o - p h o s p h a t e , ammonium a n d n i t r a t e c o n t e n t s w e r e d e t e r m i n e d , M o h l m a n n i n d e x ( a datum f o r c h a r a c t e r i z i n g t h e s e d i m e n t a t i o n p r o p e r t i e s o f t h e suspended s o l i d s ) and b i o l o g i c a l a c t i v i t y o f t h e s l u d g e were m e a s u r e d , a s we1 1 .
714 TABLE 2 The m a i n p a r a m e t e r s o f sewage t r e a t m e n t s i n d i f f e r e n t p l a n t s Location, Year (Type 1
Amount o f sewage
m3 /d
Biological 1oadi ng
Age o f sludge
kg BOD d
k g - l d-’ D u n a k e s z i , 1985
48
0.25
2.3
1850
0.08
15.5
0.04
25
( p i l o t plant)
Zalaegerszeg,
1987
(large scale) Bal atonbereny , 1987 (large scale)
,
Character o f sewage
municipal 50%+canning f a c t o r y 50%
municipal 60% food i n d u s t r y 40% m u n i c ip a l
Equipment and Methods C o n t i n u o u s e x p e r i m e n t s were c a r r i e d o u t i n a p i l o t p l a n t and i n l a r g e - s c a l e p l a n t s . T y p i c a l t e c h n i c a l d a t a o f sewage treatment a r e g i v e n i n Table 3. The a r r a n g e m e n t o f t h e t e c h n o l o g i c a l u n i t s ( s c r e e n , g r i t chamber, a e r a t o r ,
s e c o n d a r y s e t t l i n g t a n k ) w e r e t h e same f o r a l l
i n s t a l l a t i o n s . The z e o l i t e s u s p e n s i o n was a d d e d t o t h e sewage i n t h e c h a n n e l j u s t b e f o r e t h e a e r a t o r , w h e r e a p e r f e c t m i x i n g was achieved. loading,
The t e c h n o l o g i c a l p a r a m e t e r s ( e . g . etc.)
residence time,
and t h e s i z e o f equipment were i d e n t i c a l f o r b o t h
t h e e x p e r i m e n t a l a n d c o n t r o l l i n e s . The p i l o t p l a n t ( i n D u n a k e s z i ) operated w i t h high loading,
t h e o t h e r s i n a t o t a l o x i d a t i o n mode.
RESULTS A N D D I S C U S S I O N A v e r a g e s o f a g r e a t amount o f e x p e r i m e n t a l d a t a d e t e r m i n e d b o t h i n p i l o t p l a n t and i n l a r g e - s c a l e p l a n t s a r e summarized i n T a b l e 3 . The l a t t e r p l a n t s a r e l o c a t e d i n t h e w e l l p r o t e c t e d a r e a o f Lake-Balaton.
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715
716 Removal o f P h o s p h o r u s D e p e n d i n g on t h e amount o f c o n t a m i n a n t s 15-30 mg F e 3 + a n d
30-100 mg p o w d e r e d c l i n o p t i l o l i t e c o n t a i n i n g r o c k i s a d d e d t o one l i t r e o f sewage. The r e m o v a l o f p h o s p h o r u s i n t h e p i l o t p l a n t ( i n D u n a k e s z i ) as a f u n c t i o n o f t i m e on f l o w i s i l l u s t r a t e d i n Fig.
1. I n most p r o t e c t e d d i s t r i c t s o f Hungary (around t h e g r e a t
l a k e s ) t h e p e r m i t t e d l i m i t o f p h o s p h o r u s c o n t e n t i n emmissions i s
1.8 mg P/1 (5,5 mg P O i - / l ) ,
w h i c h c a n r e l i a b l y be a t t a i n e d w i t h
t h i s treatment.
5
10
15
20
25
50
30
55 60 time, day
F i g . 1. O r t h o - p h o s p h a t e c o n c e n t r a t i o n as a f u n c t i o n o f t i m e on f l o w i n t h e s e t t l e d sewage i n l e t (l), i n t h e c o n t r o l sewage o u t l e t ( w i t h o u t additives, 2 ) , w i t h a d d i t i o n o f a suspension c o n t a i n i n g 18.3 mg F e 3 + / l + 65 mg z e o l i t e / l ( 3 ) On a d d i n g 1.16-1.95 i r o n i o n s t o g e t h e r , z e o l i t i c r o c k t o 1 atom phosphorus, P/1 c a n be g u a r a n t e e d .
w i t h the suspension o f
a d e p h o s p h o r i z a t i o n t o 1.8 mg
W i t h o u t z e o l i t e a d d i t i v e 1.7-2.5
i r o n ions
a r e needed f o r c o m p a r a b l e p u r i f i c a t i o n . Our o b s e r v a t i o n s , p o r t e d by t h e f i n d i n g o f I s h i i and K a j i ( r e f .
sup-
12), a r e s i m i l a r
f o r A12(S04)3 a d d i t o n w i t h and w i t h o u t z e o l i t e s . Consequently, t h e e f f i c i e n c y o f phosphate removal w i t h t r i v a l e n t c a t i o n s increases i n the presence o f z e o l i t e ; 1 g o f z e o l i t i c rock i t s e l f removes 6 . 4
mg p h o s p h o r u s o w i n g t o t h e m o b i l e Ca a n d Mg ( F e ) i o n s
i n t h e z e o l i t e phase which f o r m phosphate p r e c i p i t a t e
717
a f t e r e x c h a n g e f o r ammonium i o n s f r o m t h e sewage. The o b s e r v e d e f f e c t o f c l i n o p t i l o l i t e i s 3-6 times g r e a t e r t h a n t h e v a l u e o f 6.4 mg/g.
A f t e r an o p e r a t i o n p e r i o d f o r some weeks t h e p h o s p h a t e
removal e f f i c i e n c y
i s preserved i n the z e o l i t e containing aerator,
when t h e dosage i s s t o p p e d e v e n f o r o n e d a y . The r e a s o n f o r t h i s e f f e c t i s t h e r e t e n t i o n o f i r o n i n t h e z e o l i t i c r o c k i n t h e a e r a t o r . The r e s i d e n c e t i m e o f z e o l i t i c r o c k w i t h i r o n s a l t occluded i n the pores o f d i f f e r e n t s i z e i s l o n g e r t h a n t h a t o f n o n - f i x e d i r o n s o l u t i o n . The r e t a r d e d d e s o r p t i o n o f i r o n during a longer residence time r e s u l t s i n a b e t t e r utilization o f t h e Fe3+ introduced. This i s i n q u a n t i t a t i v e c o r r e l a t i o n w i t h the experimental findings. Removal o f Suspended S o l i d s I n each case t h e c o n t e n t o f suspended s o l i d s i n t h e e f f l u e n t i s l e s s when t h e b i o l o g i c a l t r e a t m e n t o f t h e sewage i s c a r r i e d out with z e o l i t e / i r o n - s a l t addition than without i t (c.f. " e x p e r i m e n t a l " a n d " c o n t r o l " d a t a i n T a b l e 3 ) : e.g.
i n a large
s c a l e p l a n t ( Z a l a e g e r s z e g ) t h e e f f l u e n t c o n t a i n e d 35 m g / l s u s p e n d e d s o l i d s w h i c h d e c r e a s e d t o 18 m g / l b y z e o l i t e / i r o n - s a l t addition.
The z e o l i t e p a r t i c l e s p r e f e r a b l y a d s o r b c o l l o i d s ,
and
c o a g u l a t i o n s e e d s a r e t h u s f o r m e d . The h y d r o x i d e s o f m e t a l s f o r m e d f r o m t h e i n t r o d u c e d s a l t s e x e r t an a d d i t i o n a l c o a g u l a t i o n effect
.
As a r e s u l t o f z e o l i t e t r e a t m e n t ( i ) t h e d e n s i t y o f a c t i v a t e d s l u d g e i n c r e a s e s f r o m 1 5 g / l t o 30 g / 1 i n t h e s e c o n d a r y s e t t l i n g tank,
( i i ) the d e w a t e r a b i l i t y improves, i . e .
the
c a p i l l a r y s u c t i o n t i m e decreases f r o m 30 s t o 10-15 s , and ( i i i ) t h e Mohlmann i n d e x d i m i n i s h e s s i g n i f i c a n t l y . The E f f e c t o f Z e o l i t e on t h e B i o l o g i c a l A c t i v i t y o f t h e S l u d g e An i n c r e a s e d b i o l o g i c a l a c t i v i t y i s r e f l e c t e d b y t h e C O D v a l u e s o f t h e f i l t e r e d e f f l u e n t s ( T a b l e 3 ) s i n c e w i t h t h e same residence times,
they are r e g u l a r l y lower a f t e r z e o l i t e treatment
than i n the c o n t r o l l i n e . The d i g e s t i o n a c t i v i t y o f t h e s l u d g e c a n be b e t t e r e x p r e s s e d i n terms o f COD g - l h - l
. Pilot
p l a n t experiments (Dunakeszi,
showed an a c t i v i t y o f 52 C O D 9 - l h - l g-'h-'
i n t h e case o f z e o l i t e i n t r o d u c t i o n .
v a l u e s i n an o p e r a t i n g p l a n t ( B a l a t o n b e r e n y , 44 C O D g - l h - ' ,
respectively.
1986)
i n t h e c o n t r o l l i n e and 65 COD The c o r r e s p o n d i n g 1 9 8 7 ) w e r e 35 a n d
These e x a m p l e s ( a n d a s e r i e s o f
o t h e r d a t a ) p o i n t t o an i n c r e a s e o f t h e b i o l o g i c a l a c t i v y b y a b o u t 2 5 % due t o z e o l i t e i n t r o d u c t i o n .
Upon z e o l i t e a d d i t i o n a s i g n i f i c a n t i n c r e a s e o f n i t r i f i c a t i o n has b e e n o b s e r v e d a s w e l l . a b o u t 60%, i . e . i n the effluents
For instance,
i n Zanka ( 1 9 8 6 ) i t was
53 m g / l a n d 85 m g / l n i t r a t e c o n t e n t s w e r e f o u n d o f c o n t r o l and e x p e r i m e n t a l l i n e s r e s p e c t i v e l y .
The c o r r e s p o n d i n g v a l u e s i n B a l a t o n b e r e n y ( 1 9 8 7 ) w e r e 24 m g / l a n d 57 m g / l ,
respectively.
The i n c r e a s e o f b i o l o g i c a l a c t i v i t y e f f e c t e d t r o u g h z e o l i t i c a d d i t i v e c a n be e x p l a i n e d as f o l l o w s : ( i ) Z e o l i t e p a r t i c l e s a r e seeds f o r b a c t e r i a f l o c k s . F l o c k s a r e t h u s f o r m e d i n g r e a t e r number a n d o f s m a l l e r s i z e t h a n i n t h e absence o f z e o l i t i c g r a i n s . s m a l l e r t h a n 0.3 mm; a n d 2 mm.
With z e o l i t e s the f l o c k s are
w i t h o u t z e o l i t e s t h e i r s i z e i s b e t w e e n 0.4
The t r a n s p o r t o f o x y g e n a n d n u t r i e n t s i s f a s t e r i n t h e
s m a l l e r f l o c k s t h a n i n l a r g e r ones. ( i i ) Z e o l i t e p a r t i c l e s s o r b ammonia w h i c h i s a c c e s s i b l e f o r n i t r i f i c a t i o n b a c t e r i a c o n c e n t r a t e d on z e o l i t e c r y s t a l s ,
thus the
n i t r i f i c a t i o n accelerates. ( i i i ) The b i o l o g i c a l c o m p o s i t i o n o f a c t i v a t e d s l u d g e c h a n g e s f a v o u r a b l y i n t h e p r e s e n c e o f z e o l i t e . The " p r e d a t o r c i l i a t e s " (Litonotus, Loxophillum,
Vorticella,
Convallaria,
Opercularia,
C o a r e t a t a ) m u l t i p l y . Nematodes a l s o a p p e a r i n t h e s l u d g e .
These
a n i m a l s f e e d on t h e f r e e - s w i m m i n g b a c t e r i a i n l i q u i d phase. ( i v ) The b i o l o g i c a l s t a b i l i t y o f t h e s e p a r a t e d a n d z e o l i t e containing sludge i s greater than without z e o l i t e : observable a n a e r o b i c d i g e s t i o n proceeds w i t h i n f i v e days i n t h e absence o f z e o l i t e w h e r e a s t h e s l u d g e r e m a i n s u n c h a n g e d e v e n f o r t h r e e weeks u n d e r t h e same c o n d i t i o n s ,
i f i t c o n t a i n s z e o l i t e . The phenomenon
i s being investigated i n d e t a i l . ( v ) Contrary t o usual sludges, the desiccated sludge c o n t a i n i n g z e o l i t e i s o f h i g h v a l u e because a f t e r composting i t c a n be u s e d a s a f e r t i l i z e r o f s u f f i c i e n t n u t r i e n t v a l u e s . When i n s t e a d o f i r o n s a l t an a l u m i n i u m s a l t i s u s e d f o r t h e treatment, h o w e v e r , t h e s l u d g e c a n h a r d l y be u t i l i z e d i n a g r i c u l t u r e . F i n a l Treatment A f t e r b i o l o g i c a l treatment o f increased a c t i v i t y the r e s t o f t h e ammonium c a n be r e m o v e d c o n v e n t i o n a l l y b y i o n - e x c h a n g e w i t h zeolite,
p r e f e r a b l y w i t h c l i n o p t i l o l i t e because o f i t s h i g h
s e l e c t i v i t y f o r ammonium.
The ammonium c o n t e n t i n t h e o u t l e t c a n be
kept below 4 mg/l. The o p e r a t i o n p a r a m e t e r s f o r o u r p i l o t p l a n t w e r e o p t i m i z e d . The f i l l i n g c a n be r e p e a t e d l y r e g e n e r a t e d w i t h a 2 w t . %
719 KCl/NaCl
s o l u t i o n o f pH
=-
1 0 . The ammonia was r e m o v e d e i t h e r b y
s t r i p p i n g w i t h a i r and a b s o r b i n g , solution,
e.g.
i n a phosphoric a c i d
o r b y p r e c i p i t a t i o n i n t h e f o r m o f MgNH4P04. We
observed t h a t t h e f i r s t s e c t i o n o f ion-exchanger works as a filter,
where d i s s o l v e d o r c o l l o i d ( m a i n l y o r g a n i c ) c o n t a m i n a n t s
n o t a l r e a d y removed a r e bound. A f t e r t h e c o u n t e r c u r r e n t r e g e n e r a t i o n they can be s e t t l e d from t h e r e g e n e r a t i n g s o l u t i o n . REFERENCES 1
Water T r e a t m e n t Handbook, V . E d i t i o n , Degremont 1979, pp. 57-74, 141-144. 2 Y . M u r a k a m i , A . I i j i m a a n d J.W. Ward ( E d i t o r s ) : New Development i n Z e o l i t e Science and Technology. E l s e v i e r S c i e n t i f i c P u b l . Co. A m s t e r d a m , 1 9 8 6 . 3 L . L . Ames: Amer. M i n e r a l o g i s t 4 5 ( 1 9 6 0 ) 6 8 9 - 7 0 0 . 4 J.H. Koon a n d W.J. K a u f m a n : O p t i m a t i o n o f Ammonia Removal b y I o n E x c h a n g e U s i n g C l i n o p t i l o l i t e . U S R e p o r t f o r t h e EPA, 1 9 7 1 . 5 P. C i a m b e l l i , P . C o r b o , C . P o r c e l l i a n d A . R i m o l i : Z e o l i t e s 5 ( 1 9 8 5 ) 184-187. 6 US P a t e n t 3 723 3 0 8 7 L. L i b e r t i , G. B o a r i a n d R. P a s s i n o : Wat. S u p p l y 1 ( 1 9 8 3 ) , 169-176. 8 L . L i b e r t i , N. L i m o n i , A . L o p e z , R . P a s s i n o a n d G . B o a r i : Water Research 20 ( 1 9 8 6 ) 735-739. 9 M.J.T. C a r r o n d o , R . P e r r y a n d J.N. L e s t e r : J. Wat. P o l l u t . C o n t r o l Fed. 52 ( 1 9 8 0 ) 2 7 9 6 - 2 8 0 6 . 1 0 W.F. H o l m a n a n d W.D. H o.p.p i n q- : J. W a t . P o l l u t . C o n t r o l F e d . 52 (1980) 2887-2905. 1 1 J.E. K i n g , D.W. H o p p i n g a n d F.W. H o l m a n : I . J . Wat. P o l l u t . C o n t r o l Fed. 52 ( 1 9 8 0 1 2 8 7 5 - 2 8 8 6 . 1 2 M . I s h i i a n d K. K a j i : . G y p s u m a t L i m e 186 ( 1 9 8 3 ) 8 - 1 6 .