Appl. Environ. Microbiol. 1983 Bancroft 683 8

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    46(3):683.

    1983,Appl. Environ. Microbiol.I H Suffet and W O PipesK Bancroft, S W Maloney, J McElhaney,activated carbon contactors.carbon removal on granular

    growth and total organicAssessment of bacterial

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    A P P L I E D AND E N V I R O N M E N T A L M I C R O B I O L O G Y , S e p t . 1 9 8 3 , p . 6 8 3 - 6 8 80 0 9 9 - 2 2 4 0 / 8 3 / 0 9 0 6 8 3 - 0 6 0 2 . 0 0 / 0C o p y r i g h t 1 9 8 3 , A m e r i c a n S o c i e t y f o r M i c r o b i o l o g yV o l . 4 6 , N o . 3

    A s s e s s m e n t o f B a c t e r i a l G r o w t h a n d T o t a l O r g a n i c CarbonR e m o v a l on G r a n u l a r A c t i v a t e d C a r b o n C o n t a c t o r sK . BANCROFT,1 S . W. MALONEY,1 J . McELHANEY,2 I . H. S U F F E T , 1 * AND W 0. PIPES1E n v i r o n m e n t a l S t u d i e s I n s t i t u t e , D r e x e l U n i v e r s i t y , 1 and C i t y o f P h i l a d e l p h i a Water D e p a r t m e n t , 2P h i l a d e l p h i a , P e n n s y l v a n i a 1 9 1 0 4

    R e c e i v e d 2 5 O c t o b e r 1 9 8 2 / A c c e p t e d 2 3 Ma y 1 9 8 3T h e o v e r a l l g r o w t h r a t e o f b a c t e r i a on g r a n u l a r a c t i v a t e d c a r b o n ( G A C )c o n t a c t o r s a t t h e P h i l a d e l p h i a T o r r e s d a l e W a t e r T r e a t m e n t P i l o t P l a n t f a c i l i t y wasf o u n d t o d e c r e a s e u n t i l s t e a d y s t a t e was r e a c h e d . T h e g r o w t h r a t e was f o u n d t of l u c t u a t e b e t w e e n 6 . 9 4 x 1 0 - 3 a n d 8 . 6 8 x 1 0 - 4 d o u b l i n g s pe r h . The m i c r o b i o l o g i -c a l r e m o v a l o f t o t a l o r g a n i c c a r b o n ( T O C ) was c a l c u l a t e d b y c o n s i d e r i n g t h e GACc o n t a c t o r s a s s e m i c l o s e d c o n t i n u o u s c u l t u r e systems a n d u s i n g g r o w t h y i e l df a c t o r s d e t e r m i n e d i n l a b o r a t o r y e x p e r i m e n t s . A f t e r o z o n a t i o n , t h e a v e r a g e TOCe n t e r i n g t h e c o n t a c t o r s was 1 , 4 8 8 I A g / l i t e r , a n d t h e average e f f l u e n t TOC was 4 9 7, u g / l i t e r . M i c r o b i o l o g i c a l TOC r e m o v a l was f o u n d t o av er ag e 2 4 0 , u g / l i t e r on GACc o n t a c t o r s , w h i c h was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m m i c r o b i o l o g i c a l TOC ( 2 2 0, u g / l i t e r r e m o v a l across a p a r a l l e l s a n d c o n t a c t o r w h e r e n o a d s o r p t i o n t o o k p l a c e .T h u s , GAC d i d n o t appear t o e n h a n c e b i o l o g i c a l TOC r e m o v a l . B a c t e r i a l g r o w t ha n d m a i n t e n a n c e was r e s p o n s i b l e f o r a p p r o x i m a t e l y 24 o f t h e TOC r e m o v a l onGAC u n d e r t h e c o n d i t i o n s o f t h i s s t u d y .

    T h e i d e n t i f i c a t i o n o f p o t e n t i a l l y h a r m f u l o r -g a n i c c h e m i c a l s i n d r i n k i n g w a t e r h a s l e d t o a ni n t e r e s t i n t h e u s e o f g r a n u l a r a c t i v a t e d c a r b o n( G A C ) a s a p r o c e s s f o r t h e i r r e m o v a l ( 2 2 ) . T h ep u r p o s e o f GAC i n w a t e r t r e a t m e n t i s r e m o v a l o ft o x i c o r g a n i c s u b s t a n c e s ; h o w e v e r , r e m o v a l o fo t h e r b a c k g r o u n d o r g a n i c c o m p o u n d s a s m e a -s u r e d b y t o t a l o r g a n i c c a r b o n ( T O C ) i s a l s o a ni m p o r t a n t c o n s i d e r a t i o n b e c a u s e i s o m e o ft h e m ( e . g . , h u m i c a c i d s ) may a c t a s p r e c u r s o r si n t h e f o r m a t i o n o f c h l o r i n a t e d c o m p o u n d sw h i c h may b e t o x i c ( 2 , 1 7 ) , i i t h e r e may b ec o m p e t i t i o n b e t w e e n c o m p o u n d s o f h e a l t h c o n -c e r n a n d b a c k g r o u n d o r g a n i c s f o r a d s o r p t i o ns i t e s ( 9 , 2 1 ) , a n d i i i t o x i c o r g a n i c s may a s s o -c i a t e w i t h more p o o r l y a d s o r b e d h u m i c a c i d s ( 7 ,1 5 ) a n d b e c a r r i e d t h r o u g h t h e c a r b o n c o l u m n .O n e m e c h a n i s m o f b a c k g r o u n d o r g a n i c r e -m o v a l i s b i o l o g i c a l d e g r a d a t i o n . T h e o c c u r r e n c eo f l a r g e n u m b e r s o f b a c t e r i a o n GAC f i l t e r s i sw e l l d o c u m e n t e d ( 1 , 8 ) ; c o n s e q u e n t l y , b a c t e r i a lTOC r e m o v a l h a s b e e n s t u d i e d a s a m e c h a n i s mb y w h i c h m o r e a d s o r p t i o n s i t e s o n GAC c o u l db e m a d e a v a i l a b l e f o r t h e r e m o v a l o f n o n - b i o d e -g r a d a b l e c o m p o u n d s ( 4 ) , t h u s e x t e n d i n g t h e b e dl i f e o f GAC c o l u m n s a n d r e d u c i n g o p e r a t i n gc o s t s .T h e a c c u m u l a t i o n o f l a r g e n u m b e r s o f b a c t e r i ai n GAC c o n t a c t o r s f o l l o w s a s i g m o i d a l c u r v et h a t h a s b e e n i n t e r p r e t e d a s a g r o w t h c u r v e ( 6 ,1 3 ) . T h e b a c t e r i a l a c c u m u l a t i o n i s w e l l d o c u -

    m e n t e d ( 1 , 6 , 1 9 , 2 6 ) , a n d t h e maximum n u m b e r sa t t a i n e d h a v e b e e n d e s c r i b e d a s a f u n c t i o n o fs u b s t r a t e a v a i l a b i l i t y a n d i n f l u e n t b a c t e r i a l n u m -b e r s 1 . A l t h o u g h much e f f o r t h a s b e e n e x p e n d -e d o v e r t h e l a s t f e w y e a r s t o a s s e s s t h e d e n s i t y ,c o m p o s i t i o n , a n d a c t i v i t y o f b a c t e r i a l p o p u l a -t i o n s a s s o c i a t e d w i t h GAC c o n t a c t o r s ( 5 , 1 2 ,1 3 ) , l i t t l e c o n s i d e r a t i o n h a s b e e n g i v e n t o t h ea c t u a l d e t e r m i n at i o n o f t h e g r o w t h k i n e t i c s . A c -c u m u l a t i o n o f b a c t e r i a t h a t a r e n o t a c t i v e i nr e m o v i n g o r g a n i c s i s p o s s i b l e a n d c o u l d b e ac o n f u s i n g f a c t o r i n a t t e m p t s t o d e t e r m i n e m i c r o -b i o l o g i c a l r e m o v a l o f TOC i n a GAC c o l u m n .C o m p a r i n g r a t e s o f TOC r e m o v a l o n s a n d a n dGAC, E b e r h a r d t ( 8 ) c o n c l u d e d t h a t GAC e n -h a n c e d t h e r a t e o f b i o d e g r a d a t i o n . E n h a n c e db i o d e g r a d a t i o n w as p r o p o s e d t o o c c u r a s a r e s u l to f s t o r a g e b y a d s o r p t i o n o f r e c a l c i t r a n t o r g a n i cm a t e r i a l o n t h e s u r f a c e o f t h e c a r b o n p a r t i c l e s .S t o r a g e was p o s t u l a t e d t o p r o v i d e a l o n g e r c o n -t a c t t i m e , w h i c h c o u l d p r o m o t e a c c l i m a t i o n ( 2 7 ) .H o w e v e r , i t i s n o t c l e a r t h a t o r g a n i c c o m p o u n d ss t o r e d b y a d s o r p t i o n w o u l d b e a v a i l a b l e t om i c r o o r g a n i s m s g r o w i n g i n t h e c o l u m n .I m p r o v e d b i o d e g r a d a b i l i t y o f n a t u r a l l y o c c u r -r i n g TOC h a s b e e n o b s e r v e d a f t e r o z o n a t i o n 3 ,2 0 ) . T h e s o - c a l l e d b i o l o g i c a l a c t i v a t e d c a r b o np r o c e s s h a s b e e n b a s e d i n p a r t o n t h i s o b s e r v a -t i o n a n d i n p a r t on E b e r h a r d t ' s 8 d a t a . I t h a sb e e n p r o p o s e d t h a t i n t h e b i o l o g i c a l a c t i v a t e dc a r b o n p r o c e s s , c a r b o n b e d l i f e c a n b e p r o -

    6 8 3

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    6 8 4 BANCROFT ET A L .l o n g e d b y c o n v e r t i n g a p o r t i o n o f t h e r e c a l c i -t r a n t o r g a n i c s t o b i o d e g r a d a b l e o r g a n i c s b yp r e o z o n a t i o n . T h e m i c r o o r g a n i s m s a t t a c h e d t ot h e GAC t h e n c o n v e r t t h e b i o d e g r a d a b l e p o r t i o nt o b i o m a s s , c a r b o n d i o x i d e , a n d w a s t e p r o d u c t sb e f o r e t h a t m a t e r i a l c a n o c c u p y a d s o r p t i o n s i t e so n t h e GAC. I t h a s a l s o b e e n h y p o t h e s i z e d t h a ti n c r e a s e d b i o d e g r a da t i o n i n GAC c o l u m n s o c -c u r s d u e t o t h e l a r g e r s u r f a c e a r e a p r o v i d e d b yt h e c a r b o n p a r t i c l e s f o r a t t a c h m e n t a n d g r o w t ho f b a c t e r i a ( 1 ) .E x i s t i n g d a t a d o n o t s h o w c o n c l u s i v e l y t h a te x t e n d e d s e r v i c e t i m e o f GAC b e d s i s a r e s u l t o fe n h a n c e d b i o d e g r a d a t i o n . S l o w a d s o r p t i o n k i -n e t i c s ( 1 0 , 1 4 ) c o u l d a l s o e x p l a i n l o n g - t e r m TOCr e m o v a l . W h e t h e r GAC p r o v i d e s a m o r e f a v o r -a b l e e n v i r o n m e n t f o r b a c t e r i a l g r o w t h a n d a t -t a c h m e n t t h a n o t h e r m e d i a i s o p e n t o q u e s t i o n .T h e a p p r o a c h t a k e n i n t h i s s t u d y w as t oc o n s i d e r t h e GAC c o n t a c t o r a s a b l a c k box i nw h i c h h e t e r o t r o p h i c m i c r o o r g a n i s m s f u n c t i o nf o r i n d i v i d u a l m a i n t e n a n c e a n d t o p r o d u c e n e wc e l l s a t t h e e x p e n s e o f e n e r g y a n d c a r b o ns o u r c e s e n t e r i n g t he c o n t a c t o r . We n e e d s m a l lGAC c o n t a c t o r s t o e x a m i n e b a c t e r i a l g r o w t hr a t e s d u r i n g t h e i n i t i a l i n c r e a s e i n t h e b a c t e r i a lp o p u l a t i o n s . L a r g e r c o n t a c t o r s c o n t a i n i n g GACo r s a n d w e r e u s e d t o m e a s u r e g r o w t h r a t e s a n db a c t e r i a l TOC r e m o v a l d u r i n g l o n g - t e r m p s e u d o -s t e a d y s t a t e TOC r e m o v a l .

    MATERIALS AND METHODSGA C c o l u m n s . Tw o s i z e s o f c o l u m n s w e r e u s e d i nt h e s e s t u d i e s . C o l u m n s u s e d t o a s s e s s i n i t i a l b a c t e r i a lg r o w t h r a t e s i n s h o r t t e r m e x p e r i m e n t s w e r e c o n -s t r u c t e d o f s e g m e n t e d T e f l o n w i t h s i d e p o r t s f o rr e m o v i n g c a r b o n s a m p l e s w i t h o u t t a k i n g t h e c o l u m n so u t o f s e r v i c e . T h e T e f l o n s e g m e n t s ( S a v i l l e x C o r p . ,M i n n e t o n k a , M i n n . ) w e r e 4 . 7 5 i n . ( c a . 1 1 . 9 c m ) l o n gw i t h a n i n s i d e d i a m e t e r o f 1 . 6 i n . ( c a . 4 c m ) . F i v es e g m e n t s w e r e c o u p l e d t o g e t h e r f o r a n o v e r a l l l e n g t h

    o f a p p r o x i m a t e l y 2 5 i n . ( c a . 6 3 . 5 c m ) . W a t e r t o o n ec o l u m n ( d e s i g n a t e d a s c o l u m n A ) w a s p a s s e d t h r o u g ha 0 . 2 2 - j L j m m e m b r a n e f i l t e r ( M i l l i p o r e C o r p . , B e d f o r d ,M a s s . ) w h i c h r e d u c e d , b u t d i d n o t e n t i r e l y e l i m i n a t e ,b a c t e r i a l l o a d i n g b e f o r e t h e GAC c o l u m n . T h e c o l u m nt h a t r e c e i v e d w a t e r t h a t w a s n o t p r e f i l t e r e d w a s d e s i g -n a t e d a s c o l u m n B . F i g u r e 1 i s a d i a g r a m o f t h ec o l u m n s s h o w i n g s a m p l e p o r t s .C o l u m n s o f s i m i l a r c o n s t r u c t i o n , b u t 4 0 i n . ( c a . 1 m )i n l e n g t h a n d c o n t a i n i n g c a . 1 , 0 0 0 g o f GAC w e r e u s e df o r t h e l o n g e r - t e r m e x p e r i m e n t o n p s e u d o - s t e a d y s t a t eg r o w t h . F o r t h e s e e x p e r i m e n t s a s i m i l a r c o l u m n c o n -t a i n i n g s a n d w a s r u n i n p a r a l l e l t o a s s e s s b a c t e r i a lTOC r e m o v a l i n t h e a b s e n c e o f a d s o r p t i o n . T h e s a n dw a s s i e v e d t o g i v e t h e s a m e p a r t i c l e s i z e r a n g e a s t h ec a r b o n .W a t e r s o u r c e . T h e s o u r c e o f i n f l u e n t w a t e r f o r t h e s es t u d i e s w a s t h e P i l o t P l a n t a t t h e P h i l a d e l p h i a T o r r e s -d a l e w a t e r t r e a t m e n t f a c i l i t y l o c a t e d o n t h e D e l a w a r eR i v e r . T h e P i l o t P l a n t h a s b e e n d e s c r i b e d e l s e w h e r e( 1 6 ) . T h e r a w w a t e r i s p u m p e d f r o m t h e r i v e r i n t o ab a s i n a n d t h e n t o a n u p f l o w c l a r i f i e r w i t h c h e m i c a l

    INFLUENT

    EFFLUENT Gl GAC *R cT 0 * GAC SAMPLING PORTo NM T 0 . 2 5 1 n . TUBE FITTINGE AT CE T0R R

    F I G . 1 . D i a g r a m o f a c o l u m n u s e d a s a c o n t a c t o rf o r t h e s t u d i e s . C o l u m n s u s e d f o r t h e g r o w t h r a t es t u d i e s w e r e 2 5 i n . l o n g . C o l u m n s u s e d f o r p s e u d o -s t e a d y s t a t e e x p e r i m e n t s ( i n c l u d i n g t h e s a n d c o l u m n )w e r e 4 0 i n . l o n g .a d d i t i o n ( F e C l 3 a n d N a O H ) . A f t e r t h e c l a r i f i e r , t h ew a t e r p a s s e s t h r o u g h a r a p i d s a n d f i l t e r a n d a n o z o n ec o n t a c t o r ( o z o n e d o s e , 1 . 2 m g / l i t e r ) t o a r e t e n t i o n t a n k( 3 0 m i n ) f o r d i s s i p a t i o n o f r e s i d u a l o z o n e . From t h er e t e n t i o n t a n k t h e w a t e r i s p u m p e d t o t h e GAC c o n t a c -t o r s . T h e c o n t a c t t i m e s i n t h e GAC c o n t a c t o r s w e r e7 . 5 a n d 1 5 m i n f o r t h e s h o r t - t e r m a n d l o n g - t e r me x p e r i m e n t s , r e s p e c t i v e l y .B a c t e r i a l e n u m e r a t i o n . I n f l u e n t a n d e f f l u e n t w a t e rs a m p l e s w e r e c o l l e c t e d i n s t e r i l e 5 0 0 - m l N a l g e n e b o t -t l e s . To d e t e r m i n e b a c t e r i a l n u m b e r s i n t h e c o n t a c t o r s ,1 - g c a r b o n s a m p l e s w e r e t a k e n f r o m t h e p o r t s l o c a t e di n t h e c o l u m n s w i t h a s t e r i l e s p a t u l a . T h e s a m p l e sw e r e s u s p e n d e d i n 1 0 m l o f s t e r i l e w a t e r i n t e s t t u b e sa n d p l a c e d i n a s o n i c a t o r f o r 3 0 m i n b y t h e m e t h o d o fM c E l h a n e y a n d McKeon ( 1 2 ) . A l l s a m p l e s w e r e t h e nd i l u t e d i n s t e r i l e b u f f e r e d w a t e r f o r p l a t e c o u n t a n a l y -s i s . T r i p l i c a t e p l a t e s o f s o i l e x t r a c t a g a r w e r e p r e p a r e df o r e a c h d i l u t i o n . T h e p l a t e s w e r e i n c u b a t e d f o r 7 d a y sa t 2 8 C b e f o r e c o u n t i n g .O r g a n i c c a r b o n . S a m p l e s f o r TOC a n a l y s i s w e r ec o l l e c t e d i n 2 5 0 - m l a m b e r b o t t l e s s e a l e d w i t h c a p s w i t hT e f l o n l i n e r s . B o t t l e s h a d b e e n p r e v i o u s l y w a s h e dw i t h d e t e r g e n t , a n d r i n s e d w i t h t a p w a t e r , d i l u t e H C I ,d i s t i l l e d w a te r , a c e to n e , a n d h e x a n e ( t h r e e t i m e se a c h ) . A f t e r t h e h e x a n e r i n s e t h e b o t t l e s w e r e a i rd r i e d . A p p r o x i m a t e l y 2 5 0 m l o f s a m p l e w a s a c i d i f i e dw i t h 1 m l o f c o n c e n tr a t e d p h o s p h o r i c a c i d a n d s t o r e da t 4 C u n t i l a n a l y s i s ( 1 1 ) . A Dohrman 5 4 - D l o w - l e v e lTOC a n a l y z e r w a s e m p l o y e d t o m e a s u r e TOC.

    RESULTST h e t o t a l n u m b e r s o f b a c t e r i a o n t h e GAC a n dt h e t o t a l b a c t e r i a p e r d a y i n t h e i n f l u e n t s a n de f f l u e n t s f o r t h e p r e f i l t e r e d ( c o l u m n A ) a n dn o n f i l t e r e d ( c o l u m n B ) c o n t a c t o r s a r e p r e s e n t e di n F i g . 2 a n d 3 , r e s p e c t i v e l y . T h e s e n u m b e r sw e r e c a l c u l a t e d f r o m b a c t e r i a l d e n s i t i e s o n t h ec a r b o n t i m e s t h e a m o u n t o f c a r b o n i n t h e c o n -t a c t o r s a n d t h e a v e r a g e i n f l u e n t a n d e f f l u e n t

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    F I G . 2 . B a c t e r i a l n u m b e r s f o r c o l u m n A ( p r e f i l -t e r e d ) . T h e n u m b e r o f b a c t e r i a i n t h e i n f l u e n t ( O )i n c r e a s e d f r o m 1 0 6 p e r d a y t o m o r e t h a n 1 0 8 p e r d a y .T h e n u m b e r o f b a c t e r i a i n t h e e f f l u e n t ( A ) i n c r e a s e df r o m 1 0 1 t o 1 0 9 p e r d a y . T h e t o t a l n u m b e r o f b a c t e r i a i nt h e c o n t a c t o r ( O ) s h o w s a n e x p o n e n t i a l i n c r e a s e f o l -l o w e d b y a l e v e l i n g o f f .d e n s i t i e s t i m e s t h e f l o w r a t e . A v e r a g e i n f l u e n td e n s i t i e s t o c o l u m n A ( F i g . 2 ) i n c r e a s e d f r o m1 . 4 7 x 1 0 2 c e l l s p e r m l t o 3 . 3 2 x 1 0 3 c e l l s p e r m lo v e r t h e f i r s t 2 5 d a y s . A v e r a g e i n f l u e n t b a c t e r i a l

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    DAYS ON L I N EF I G 3 . B a c t e r i a l n u m b e r s f o r c o l u m n B ( n o n f i l -t e r e d ) . T h e n u m b e r o f b a c t e r i a p e r d a y i n t h e i n f l u e n t( 0 ) a n d e f f l u e n t ( A ) r e m a i n e d r e l a t i v e l y c o n s t a n t , b u tt h e t o t a l n u m b e r o f b a c t e r i a i n t h e c o n t a c t o r ( O )i n c r e a s e d f r o m 1 0 8 t o more t h a n 1 0 1 0 .

    d e n s i t i e s t o c o l u m n B ( F i g . 3 ) w e r e f o u n d t o b ef a i r l y c o n s t a n t ( x i = 7 . 4 3 x 1 0 3 c e l l s p e r m l ) f o rt h e d u r a t i o n o f t h e e x p e r i m e n t . E f f l u e n t b a c t e r i -a l d e n s i t i e s f o r b o t h c o n t a c t o r s w e r e f o u n d t o b er e l a t i v e l y c o n s t a n t . H o w e v e r , t h e a v e r a g e e f f l u -e n t b a c t e r i a l d e n s i t y f o r c o l u m n A ( x e = 2 . 9 4 x1 0 4 c e l l s p e r m l ) w a s 56 o f t h e a v e r a g e f o rc o l u m n B ( M = 5 . 1 8 x 1 0 4 c e l l s p e r m l ) t h r o u g h -o u t t h e s t u d y p e r i o d .F i g u r e s 2 a n d 3 s h o w t h a t g r o w t h a n d a c c u m u -l a t i o n o f b a c t e r i a o n b o t h f i l t e r e d a n d n o n f i l t e r e dc a r b o n c o n t a c t o r s e x hi b i t e d t he t y p i c a l i n c r e a s ef o l l o w e d b y a c o n s t a n t d e n s i t y , w h i c h h a s b e e no b s e r v e d i n b a t c h c u l t u r e a n d o t h e r GAC e x p e r i -m e n t s ( 6 ) . T h e t i m e t o r e a c h p s e u d o - s t e a d y s t a t eb a c t e r i a l c o n c e n t r a t i o n s f o r p r e f i l t e r e d c o l u m nA ( 7 . 2 1 x 1 0 7 c e l l s p e r g o f c a r b o n ) w a s a p p r o x i -m a t e l y 5 0 d a y s c o m p a r e d w i t h 2 0 d a y s f o rn o n f i l t e r e d c o l u m n B ( 7 . 3 9 x 1 0 7 c e l l s p e r g o fc a r b o n ) . O c c a s i o n a l f l u c t u a t i o n s i n b a c t e r i a ld e n s i t i e s o n t h e c a r b o n a n d l o s s o f b a c t e r i a w e r en o t e d . T h e d e c r e a s e s i n GAC b a c t e r i a l d e n s i t i e sw e r e n o t a c c o m p a n i e d b y o b v i o u s i n c r e a s e s i ne f f l u e n t b a c t e r i a l d e n s i t i e s .T h e n e t c h a n g e i n t h e n u m b e r o f o r g a n i s m s i nt h e c o n t a c t o r w i t h t i m e c a n b e d e t e r m i n e d b yt h e r e l a t i v e r a t e s o f i n p u t , g r o w t h , a n d w a s h o u ta s f o l l o w s :R a t e o f c h a n g e = i n p u t + g r o w t h - w a s h o u tM ( d X / d t ) = Q X i + pXM - QXe 1

    w h e r e X i s t h e b a c t e r i a l d e n s i t y p e r g r a m o fc a r b o n , X i i s t h e i n f l u e n t d e n s i t y p e r m l , X e i st h e e f f l u e n t d e n s i t y , M i s t h e m a s s o f c a r b o n i nt h e c o n t a c t o r , Q i s t h e f l o w r a t e , a n d , u i s t h es p e c i f i c g r o w t h r a t e . A t p s e u d o - s t e a d y s t a t e :d X / d t = 0 a n d pX M = Q ( X e X , ) ( 2 )

    o r u = [ Q ( X e - X , ) ] / M X ( 3 )P r i o r t o p s e u d o - s t e a d y s t a t e , d X / d t > 0 a n d t h es p e c i f i c g r o w t h r a t e c a n b e c a l c u l a t e d b y i t e r a -t i v e s o l u t i o n o f :

    I A X M = ( X e - X i ) Q e ' - ( X e - X i ) Q ( 4 )E q u a t i o n 4 was d e r i v e d f r o m e q u a t i o n 1 b yi n t e g r a t i o n . F o r m a k i n g t h e c a l c u l a t i o n s , XM i st h e t o t a l n u m b e r o f b a c t e r i a i n a c o n t a c t o rc a l c u l a t e d f r o m t h e n u m b e r p e r g r a m t i m e s t h eg r a m s o f c a r b o n i n t h e c o n t a c t o r , a n d t h e t e r m( X e - X j ) Q i s o b t a i n e d b y m u l t i p l y i n g t h e f l o wr a t e t i m e s t h e d i f f e r e n c e b e t w e e n t h e e f f l u e n ta n d i n f l u e n t d e n s i t i e s .T h e s e c a l c u l a t i o n s w e r e p e r f o r m e d f o r t h ef i l t e r e d a n d n o n f i l t e r e d 2 5 - i n . GAC c o n t a c t o r s .No s t a t i s t i c a l d i f f e r e n c e w as f o u n d b y a t - t e s t ( a= 0 . 0 5 ) i n c a l c u l a t e d g r o w t h r a t e s ; t h e r e f o r e , t h ea v e r a g e s o f t h e two a r e p r e s e n t e d i n F i g . 4 . T h er e s u l t s i n d i c a t e a d e c r e a s e i n t h e g r o w t h r a t e o f

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    DAYS ON L I N EF I G . 4 . T h e s p e c i f i c g r o w t h r a t e o f t h e p o p u l a t i o n so n t h e 2 5 - i n . c o n t a c t o r s d e c r e a s e d e x p o n e n t i a l l y f o rt h e f i r s t 4 0 d a y s a n d r e m a i n e d c o n s t a n t t h e r e a f t e r .

    b a c t e r i a u n t i l p s e u d o - s t e a d y s t a t e i s a t t a i n e d .D u r i n g p s e u d o - s t e a d y s t a t e , f l u c t u a t i o n s i ng r o w t h r a t e o c c u r w i t h t h e mean p o p u l a t i o nd o u b l i n g t i m e b e i n g a p p r o x i m t e l y 6 d a y s .T h e a v e r a g e b a c t e r i a l d e n s i t i e s o n t h e GACa n d i n t h e e f f l u e n t f o r t h e 4 0 - i n . GAC c a r b o nc o l u m n s w e r e 5 . 2 7 x 1 0 7 c e l l s p e r g o f c a r b o na n d 1 . 5 5 x 1 0 4 c e l l s p e r m l , r e s p e c t i v e l y , d u r i n gt h e p s e u d o - s t e a d y s t a t e e x p e r i m e n t . T h e g r o w t hr a t e s o f b a c t e r i a l p o p u l a t i o n s i n t h e 4 0 - i n . GACc o n t a c t o r s d u r i n g p s e u d o - s t e a d y s t a t e w e r e a l s oc a l c u l a t e d ( F i g . 5 . T h e r e s u l t s , w h i l e s h o w i n gc o n s i d e r a b l e f l u c t u a t i o n , i n d i c a t e a m ean d o u -b l i n g t i m e o f a p p r o x i m a t e l y 2 0 d a y s f o r t h ep e r i o d u p t o 1 8 0 d a y s . T h e r e a f t e r , t h e p o p u l a -t i o n d o u b l i n g t i m e i n c r e a s e d , f o l l o w e d b y a

    s o r40

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    o n t h e 4 0 - i n . c o n t a c t o r s f l u c t u a t e d b e t w e e n 1 0 - 4 a n d 5x 1 0 - 4 pe r h f r o m d a y 6 0 t o d a y 2 6 0 .

    g r a d u a l d e c r e a s e . T h e a v e r a g e d o u b l i n g t i m ed u r i n g t h i s s e c o n d p e r i o d ( d a y 1 8 0 t o 2 5 0 ) w a sf o u n d t o b e a p p r o x i m a t e l y 5 0 d a y s .T o t a l TOC r e m o v a l ( t h e sum o f b i o l o g i c a l

    r e m o v a l a n d a d s o r p t i o n ) f o r t h i s 4 0 - i n . GACc o n t a c t o r a n d TOC r e m o v a l o n a p a r a l l e l s a n dc o n t a c t o r a r e p r e s e n t e d i n F i g . 6 . TOC r e m o v a lf o r t h e GAC c o n t a c t o r e x h i b i t e d a n i n i t i a l r a p i dd e c r e a s e a s a d s o r p t i o n s i t e s w e r e o c c u p i e d ,f o l l o w e d b y p s e u d o - s t e a d y s t a t e r e m o v a l a p p a r -e n t l y d u e t o s l o w a d s o r p t i o n a n d b a c t e r i a l r e -m o v a l . T h e s a n d c o l u m n e x h i b i t e d a m o r e g r a d -u a l c h a n g e i n i t i a l l y a n d a n a v e r a g e TOC r e m o v a lo f 2 2 0 , u g o f c a r b o n p e r l i t e r d u r i n g t h e p s e u d o -s t e a d y s t a t e p e r i o d . W e i n t e r p r e t t h e t w o b r i e fp e r i o d s o f n o TOC r e m o v a l o n t h e s a n d c o l u m n sa s i n d i c a t i n g i n h i b i t o r y s u b s t a n c e s i n t he i n f l u -e n t . TOC r e m o v a l o n t h e GAC c o l u m n s c o n t i n -u e d d u r i n g t h e s e p e r i o d s d u e t o a d s o r p t i o n .

    DISCUSSIONT h e u s e o f t h e 0 . 2 2 - , u m M i l l i p o r e f i l t e r c a r -t r i d g e t o p r e v e n t i n t r o d u c t i o n o f b a c t e r i a t o t h eGAC c o n t a c t o r s w a s f o u n d t o b e u n s a t i s f a c t o r y .T h i s a p p a r e n t l y w a s t h e r e s u l t o f g r o w - t hr o u g h .T h e r a t e o f g r o w t h o f b a c t e r i a o n t h e c o n t a c t o r sw a s t h e r e f o r e d e t e r m i n e d b y m a t h e m a t i c a l l ye l i m i n a t i n g t h e b a c t e r i a a p p l i e d t o t h e c o n t a c t o r s

    i n t h e i n f l u e n t w a t e r a s o u t l i n e d a b o v e ( e q u a t i o n4 ) . A c c u m u l a t i o n a n d g r o w t h o f b a c t e r i a o n GACs h o w s t h e t y p i c a l s i g m o i d a l c u r v e c o m m o n l yo b s e r v e d ( 6 , 1 3 ) . H o w e v e r , t h e p r o p o s e d i n -c r e a s e i n g r o w t h r a t e ( 6 ) w a s n o t o b s e r v e dd u r i n g t h i s s t u d y . U s i n g t h e n o n - s t e a d y s t a t ee q u a t i o n t o c a l c u l a t e g r o w t h r a t e s , w e f o u n d ad e c r e a s e i n g r o w t h r a t e w h i c h l e v e l s o f f a s GACa n d e f f l u e n t b a c t e r i a l d e n s i t i e s b e c o m e s t a b l e ,16001 4 0 012001 0 0 0J o 8 0 0 r

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    F I G . 6 . T h e t o t a l TOC r e m o v a l o n t h e 4 0 - i n . GACc o n t a c t o r ( O ) a v e r a g e d 9 9 2 , u g / l i t e r f r o m d a y 6 0 t o d a y2 6 0 , w h e r e a s t h e b a c t e r i a l TOC r e m o v a l o n t h e s a n dc o n t a c t o r ( A ) a v e r a g e d 2 2 0 , u g / l i t e r f o r t h e s a m ep e r i o d .

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    BACTERIAL GROWTH AND TOC REMOVAL ON GAC 6 8 7s i m i l a r t o a c o n t i n u o u s c u l t u r e a p p a r a t u s w i t h -o u t a t t a c h m e n t s u r f a c e s . I n t h i s c a s e h o w e v e rt h e r e a c t o r ( 4 0 - i n . c o l u m n ) c e l l d e n s i t y ( x =5 . 2 7 x 1 0 7 c e l l s p e r g o f c a r b o n o r a p p r o x i m a t e l y1 0 5 4 x 1 0 7 c e l l s p e r m l ) i s much g r e a t e r t h a n t h ee f f l u e n t c e l l d e n s i t y ( x = 1 . 5 5 x 1 0 4 c e l l s p e r m l )d u e t o a t t a c h m e n t o f b a c t e r i a o n t h e c a r b o n .T h i s t y p e o f c o n ti n u o u s c u l t u r e h a s b e e nd e s c r i b e d b y R o s e ( 1 8 ) a s a s e m i c l o s e d c o n t i n u -o u s c u l t u r e s y s t e m w h e r e t h e d e v i a t i o n f r o m an o r m a l o p e n s y s t e m c a n b e d e s c r i b e d b y t h ec l o s u r e i n d e x ( C ) :

    C = 1 0 0 [ 1 X e ) l X c I ( 5 )w h e r e X e i s t h e e f f l u e n t c e l l d e n s i t y a n d X c i s t h er e a c t o r c e l l d e n s i t y . From t h i s e q u a t i o n i t i st h e r e f o r e p o s s i b l e t o d e t e r m i n e c e l l p r o d u c t i o n i fo n e k n o w s t h e a v e r a g e e f f l u e n t a n d GAC c e l ld e n s i t i e s . S i n c e b i o m a s s p r o d u c t i o n i s a f u n c t i o no f s u b s t r a t e ( T O C ) a v a i l a b i l i t y , i t i s p o s s i b l e t od e t e r m i n e t h e b i o l o g i c a l TOC r e m o v a l o n t h eGAC c o n t a c t o r s i f t h e a v e r a g e g r o w t h y i e l d( c e l l s p e r g o f T O C ) i s k n o w n .Van d e r K o o i j e t a l . ( 2 3 - 2 5 ) h a v e r e p o r t e dy i e l d f a c t o r s f o r s e v e r a l s p e c i e s o f b a c t e r i aw h i c h a r e t h e o r g a n i s m s c o m m o n l y i s o l a t e df r o m GAC c o n t a c t o r . F o r c o n c e n t r a t i o n r a n g e so f 2 5 , u g t o 1 . 0 m g o f g l u c o s e c a r b o n p e r l i t e r ,a v e r a g e y i e l d f a c t o r s f o r a F l a v o b a c t e r i u m s p . ,t w o P s e u d o m o n a s s p p . , a n d A e r o m o n a s h y d r o -p h i l a w e r e 4 . 7 x 1 0 , 5 . 0 x 1 0 3 , a n d 3 . 8 x 1 0 3C F U / m l p e r , u g o f c a r b o n p e r l i t e r , r e s p e c t i v e l y .I n o u r l a b o r a t o r y w e r e p r o d u c e d t h e s e r e s u l t sw i t h a n i s o l a t e o f P s e u d o m o n a s a e r u g i n o s af r o m t h e T o r r e s d a l e w a t e r t r e a t m e n t p l a n t t od e t e r m i n e a g r o w t h y i e l d f a c t o r ( K . B a n c r o f t ,W. 0 . P i p e s , S . W. M a l o n e y , G . B u r l i n g a m e ,I . H . S u f f e t , J . M c E l h a n e y , a n d J . S a n t o , A b s t r .A n n u . M e e t i n g Am. S o c . M i c r o b i o l . 1 9 8 2 , Q 3 1 ,p . 2 1 5 ) b y t h e t e c h n i q u e o f Va n d e r K o o i j a n dH i j n e n ( 2 4 ) . An a v e r a g e v a l u e d e t e r m i n e d w a s4 . 0 5 x 1 0 3 c e l l s p e r m l p e r , u g o f g l u c o s e c a r b o np e r l i t e r . U s i n g t h i s v a l u e a n d t h e c l o s u r e i n d e x ,w e d e t e r m i n e d b i o l o g i c a l TOC r e m o v a l on t h eGAC c o n t a c t o r w i t h t h e f o l l o w i n g e q u a t i o n :

    B a c t e r i a l TOC r e m o v a l = ( 1 / c l o s u r e i n d e x )x ( e f f l u e n t c e l l / m l ) / y i e l d f a c t o r ( 6 )

    I t s h o u l d b e n o t e d t h a t t h e b a c t e r i a l TOC r e m o v -a l c a n b e c a l c u l a t e d f r o m e q u a t i o n 6 w i t h o u tk n o w i n g t h e n u m b e r o f b a c t e r i a i n t h e c o n t a c t o r .O v e r t h e d u r a t i o n o f t h e e x p e r i m e n t n o s t a t i s -t i c a l d i f f e r e n c e t t e s t , a = 0 . 0 5 ) was f o u n db e t w e e n t h e GAC m i c r o b i a l TOC r e m o v a l a n dt h e a v e r a g e r e m o v a l a c r o s s s a n d , w h i c h i s i na g r e e m e n t w i t h t h e r e s u l t s d e t e r m i n e d b y M a -l o n e y e t a l . ( 1 1 ) a t t h e T o r r e s d a l e W a t e r T r e a t -m e n t P l a n t . M o r e o v e r , b y u s i n g t h e me a n s a n dTOC r e m o v a l a n d t h e a v e r a g e GAC b a c t e r i a ld e n s i t i e s , t h e g r o w t h y i e l d f a c t o r d e t e r m i n e d b y

    r e v e r s e c a l c u l a t i o n , w a s f o u n d t o b e 4 . 7 0 5 x 1 0 3c e l l s p e r m l p e r , u g o f c a r b o n p e r l i t e r . M o r ei m p o r t a n t l y , i n a s e m i c l o s e d s y s t e m s u c h a s t h a td e s c r i b e d h e r e , t h e b a c t e r i a l p o p u l a t i o n s c a n b eh e t e r o g e n e o u s o r p l u g f l o w ( 1 8 ) , a c o n d i t i o nf r e q u e n t l y e n c o u n t e r e d i n GAC c o n t a c t o r s ( 6 ,1 2 ) , w h i c h u n t i l n o w h a s made d i s c u s s i o n o fg r o w t h c h a r a c t e r i s t i c s d i f f i c u l t . U s i n g t h e m o d i -f i e d c o n t i n u o u s c u l t u r e a p p r o a c h w e h a v e b e e na b l e t o e x p l a i n t h e o p e r a t i o n o f t h e s e c o n t a c t o r sa n d t o d e t e r m i n e b i o l o g i c a l TOC r e m o v a l . T h ec a l c u l a t e d mean b i o l o g i c a l TOC r e m o v a l o n t h eGAC c o l u m n w a s f o u n d t o b e 2 4 0 , u g o f c a r b o np e r l i t e r c o m p a r e d w i t h s a n d r e m o v a l o f 2 2 0 , go f c a r b o n p e r l i t e r . T h e a v e r a g e i n f l u e n t TOCw a s 1 , 4 8 8 j i g o f c a r b o n p e r l i t e r , a n d t h e a v e r a g ee f f l u e n t TOC w a s 4 9 7 , u g o f c a r b o n p e r l i t e r ;t h u s , 2 4 o f t h e TOC r e m o v a l w a s a t t r i b u t e d t ob i o l o g i c a l a c t i v i t y . More i m p o r t a n t l y s i n c e t h eb i o l o g i c a l r e m o v a l w a s n o t s i g n i f i c a n t l y d i f f e r e n tf r o m t h e s a n d r e m o v a l i t a p p e a r s t h a t i n t h e s ec o l u m n s GAC d i d n o t e n h a n c e b i o d e g r a d a t i o n .T h i s f i n d i n g i s i n a g r e e m e n t w i th a n i n d e p e n d e n ts t u d y c o n d u c t e d a t t h e s a m e w a t e r t r e a t m e n tf a c i l i t y b y M a l o n e y e t a l . ( 1 1 ) . T h e g e n e r a l i t y o ft h e r e s u l t s o b t a i n e d a t t h i s l o c a t i o n c a n b ec he c k e d b y a p p l y i n g e q u a t i o n 6 t o r e s u l t s f r o mo t h e r l o c a t i o n s .

    ACKNOWLEDGMENTST h i s r e s e a r c h w a s c o m p l e t e d u n d e r a c o o p e r a t i v e p r o g r a m( C R 8 0 6 2 5 - 0 2 ) b e t w e e n t h e C i t y o f P h i l a d e l p h i a W a t e r D e p a r t -m e n t , W i l l i a m M a r a z z o , C o m m i s s i o n e r a n d D r e x e l U n i v e r s i -t y , P h i l a d e l p h i a , P a . , s u p p o r t e d b y t h e U . S . E n v i r o n m e n t a lP r o t e c t i o n A g e n c y , C i n c i n n a t i , O h i o , P r o j e c t O f f i c e r K e i t hC a r s w e l l .W e a l s o t h a n k J . S a n t o a n d G . B u r l i n g a m e f o r s a m p l ec o l l e c t i o n a n d a n a l y s i s .

    LITERATURE C I T E D1 . A m e r i c a n W a t e r W o r k s A s s o c i a t i o n . 1 9 8 1 . An a s s e s s m e n t

    o f m i c r o b i a l a c t i v i t y o n G A C . J . Am . W a t e r W o r k s A s s o c .7 3 : 4 4 7 - 4 5 4 .2 . B e l l a r , T . A . , J . J . L k c h t e n b e r g , a n d R . C . K r o n e r . 1 9 7 4 .T h e o c c u r e n c e o f o r g a n o h a l i d e s i n c h l o r i n a t e d d r i n k i n gw a t e r . J . Am. W a t e r W o r k s A s s o c . 6 6 : 7 0 3 - 7 0 6 .3 . B e n e d e k , A . 1 9 7 9 . O z o n e a n d a c t i v a t e d c a r b o n a d s o r p -t i o n : m e c h a n i s t i c a n a l y s i s o f w a t e r t r e a t m e n t d a t a . O z o n -e w s 6 : 1 - 64 . B e n e d e k , A . 1 9 8 0 . S i m u l t a n e o u s b i o d e g r a d a t i o n a n d a c t i -v a t e d c a r b o n a d s o r p t i o n , p . 2 7 3 - 3 0 2 . I n M. J . M c G u i r ea n d I . H . S u f f e t ( e d . ) , A c t i v a t e d c a r b o n a d s o r p t i o n o fo r g a n i c s f r o m t h e a q u e o u s p h a s e , v o l . 2 . An n A r b o rS c i e n c e , An n A r b o r , M i c h .5 . B r e w e r , W. S . , a n d W. W. C a r m i c h a e l . 1 9 7 9 . M i c r o b i o -l o g i c a l c h a r a c t e r i z a t i o n o f g r a n u l a r a c t i v a t e d c a r b o n f i l t e rs y s t e m s . J . Am . W a t e r W o r k s A s s o c . 7 1 : 7 3 8 - 7 4 0 .6 . C a i r o , P . R . , J . M c E l h a n e y , a n d I . H . S u f f e t . 1 9 7 9 . P i l o tp l a n t t e s t i n g o f a c t i v a t e d c a r b o n a d s o r p t i o n s y s t e m s . J .Am . W a t e r W o r k s A s s o c . 7 1 : 6 6 0 - 6 7 3 .7 . C a r t e r , C . W . , a n d I . H . S u f f e t . 1 9 8 2 . B i n d i n g o f DDT t od i s s o l v e d h u m i c m a t e r i a l s . E n v i r o n . S c i . T e c h n o l . 1 6 : 7 3 5 -7 4 0 .8 . E b e r h a r d t , M. 1 9 7 6 . E x p e r i e n c e w i t h t h e u s e o f b i o l o g i -c a l l y e f f e c t i v e a c t i v a t e d c a r b o n , p . 3 3 1 - 3 4 7 . I n H . S o n t h -e i m e r ( e d . ) , R e p o r t s o n s p e c i a l p r o b l e m s i n w a t e r t e c h n o l -

    V O L . 4 6 , 1 9 8 3

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    6 8 8 BANCROFT ET A L .o g y ( t r a n s l a t i o n ) , v o l . 9 , A d s o r p t i o n , E P A - 6 0 0 / 9 - 7 6 - 0 3 0 .U . S . E n v i r o n m e n t a l P r o t e c t i o n A g e n c y , C i n c i n n a t i , O h i o .9 . F r i c k , B . , R . B a r t z , H . S o n t h e i m e r , a n d F . A . D i G i a n o .1 9 8 0 . P r e d i c t i n g c o m p e t i t i v e a d s o r p t i o n e f f e c t s o n g r a n u -l a r a c t i v a t e d c a r b o n f i l t e r s , p . 2 2 9 - 2 4 2 . I n I . H . S u f f e t a n dM . J . M c G u i r e ( e d . ) , A c t i v a t e d c a r b o n a d s o r p t i o n o fo r g a n i c s f r o m t h e a q u e o u s p h a s e , v o l . 1 . An n A r b o rS c i e n c e , An n A r b o r , M i c h .1 0 . M a l l e v i a l i e , J . 1 9 7 9 . T r a n s f o r m a t i o n s o f h u m i c a c i d s b yo z o n e , p . 2 9 1 - 3 0 8 . I n W. Kuhn a n d H . S o n t h e i m e r ( e d . ) ,O x i d a t i o n t e c h n i q u e s i n d r i n k i n g w a t e r , E P A - 5 7 0 / 9 - 7 9 -0 2 0 . U . S . E n vi r o n m e n t a l P r o t e c t i o n A g e n c y , C i n c i n n a t i ,O h i o .1 1 . M a l o n e y , S . W . , K . B a n c r o f t , W. 0 . P i p e s , a n d I . H .S u f f e t . 1 9 8 2 . B a c t e r i a l TOC r e m o v a l o n s a n d a n d GAC, p .6 0 0 - 6 0 8 . I n P r o c e e d i n g s 1 9 8 2 ASCE N a t i o n a l C o n f e r e n c eo n E n v i r o n m e n t a l E n g i n e e r i n g . A m e r i c a n S o c i e t y o f C i v i lE n g i n e e r s , Ne w Y o r k .1 2 . M c E l h a n e y , J . , a n d W. R . M c K e o n . 1 9 7 8 . E n u m e r a t i o na n d i d e n t i f i c a t i o n o f b a c t e r i a i n g r a n u l a r a c t i v a t e d c a r b o nc o l u m n s , p . 6 3 - 6 8 . I n P r o c e e d i n g s o f t h e 6 t h A n n u a lA m e r i c a n W a t e r W o r k s A s s o c i a t i o n W a t e r Q u a l i t y T e c h -n o l o g y C o n f e r e n c e . A m e r i c a n W a t e r W o r k s A s s o c i a t i o n ,D e n v e r , C o .1 3 . P a r s o n s , F . , P . R . W o o d , a n d J . D e M a r c o . 1 9 8 0 . B a c t e r i aa s s o c i a t e d w i t h g r a n u l a r a c t i v a t e d c a r b o n c o l u m n s , p .2 7 1 - 2 . I n P r o c e e d i n g s o f t h e 8 t h A n n u a l A m e r i c a nW a t e r W o r k s A s s o c i a t i o n W a t e r Q u a l i t y T e c h n o l o g yC o n f e r e n c e . A m e r i c a n W a t e r W o r k s A s s o c i a t i o n , D e n -v e r , C o .1 4 . P e e l , R . G . , a n d A . B e n e d e k . 1 9 8 0 . D u a l r a t e k i n e t i c m o d e lo f f i x e d b e d a d s o r b e r s . J . E n v . E n g i n . D i v . Am . S o c . C i v i lE n g r s . 1 0 6 : 7 9 7 - 8 1 3 .1 5 . P i r b a z a r i , M . , a n d W. J . W e b e r . 1 9 8 2 . R e m o v a l o f d i e l -d r i n f r o m w a t e r b y a c t i v a t e d c a r b o n , p . 5 0 6 - 5 1 3 . I nP r o c e e d i n g s 1 9 8 2 A m e r i c a n S o c i e t y o f C i v i l E n g i n e e r sN a t i o n a l C o n f e r e n c e o n C i v i l E n g i n e e r i n g . A m e r i c a n S o -c i e t y o f C i v i l E n g i n e e r s , Ne w Y o r k .1 6 . R a d z i u l , J . V . 1 9 7 7 . P h i l a d e l p h i a s a d v a n c e d w a t e r t r e a t -m e n t p l a n t . W a t e r S e w . W o r k s . 1 2 4 : 7 6 - 7 8 .

    1 7 . R o o k , J . J . 1 9 7 4 . F o r m a t i o n o f h a l o f o r m s d u r i n g c h l o r i n a -t i o n o f n a t u r a l w a t e r s . J . W a t e r T r e a t m e n t E x m i n a t i o n2 3 : 2 5 4 - 2 5 9 .1 8 . R o s e , A . H . 1 9 7 6 . C h e m i c a l m i c r o b i o l o g y : a n i n t r o d u c t i o nt o m i c r o b i a l p h y s i o l o g y . P l e n u m P u b l i s h i n g C o r p . , Ne wY o r k .1 9 . S c h a l e k a m p , M. 1 9 7 9 . T h e u s e o f GA C f i l t r a t i o n t o e n s u r eq u a l i t y i n d r i n k i n g w a t e r f r o m s u r f a c e w a t e r s . J . Am .W a t e r W o r k s A s s o c . 7 1 : 6 3 8 - 6 4 7 .2 0 . S c h a l e k a m p , M. 1 9 7 9 . E x p e r i e n c e s i n S w i t z e r l a n d w i t ho z o n e , p a r t i c u l a r l y i n c o n n e c t i o n w i t h h y g i e n i c a l l y u n d e -s i r a b l e e l e m e n t s p r e s e n t i n w a t e r . O z o n e w s 7 : 1 - 8 .2 1 . S n o e y i n k , V . L . , J . J . M c C r e a r y , a n d C . J . M u r i n . 1 9 7 7 .A c t i v a t e d c a r b o n a d s o r p t i o n o f t r a c e o r g a n i c c o m p o u n d s ,E P A - 6 0 0 / 2 - 7 7 - 2 2 3 . U . S . E n v i r o n m e n t a l P r o t e c t i o n A g e n -c y , C i n c i n n a t i , O h i o .2 2 . S u f f e t , I . H . 1 9 8 0 . An e v a l u a t i o n o f a c t i v a t e d c a r b o n f o rd r i n k i n g w a t e r t r e a t m e n t : a N a t i o n a l A c a d e m y r e p o r t . J .Am . W a t e r W o r k s A s s o c . 7 2 : 4 1 - 5 0 .2 3 . V a n d e r K o o i j , D . 1 9 7 8 . D r i n k i n g w a t e r , ( t e c h n i c a l r e p o r t1 1 / 7 8 ) . T h e N e t h e r l a n d s W a t e r w o r k s T e s t i n g a n d R e -s e a r c h I n s t i t u t e , KIWA L t d . , R i j s w i j k , N e t h e r l a n d s .2 4 . V a n d e r K o o l J , D . , a n d W. A . M. H l n e n . 1 9 8 1 . U t i l i z a t i o no f l o w c o n c e n t r a t i o n s o f s t a r c h b y a F l a v o b a c t e r i u ms p e c i e s i s o l a t e d f r o m t a p w a t e r . A p p l . E n v i r o n . M i c r o b i -o l . 4 1 : 2 1 6 - 2 2 1 .2 5 . Van d e r K o o J J , D . , A . V i s s e r , a n d W. A . N . H i j n e n . 1 9 8 0 .G r o w t h o f A e r o m o n a s h y d r o p h i l a a t l o w c o n c e n t r a t i o n so f s u b s t r a t e s a d d e d t o t a p w a t e r . A p p l . E n v i r o n. M i c r o b i-o l . 3 9 : 1 1 9 8 - 1 2 0 4 .2 6 . W e b e r , W. J . , M. P i r b a z a r l , a n d G . L . N e l s o n . 1 9 7 8 .B i o l o g i c a l g r o w t h o n a c t i v a t e d c a r b o n : An i n v e s t i g a t i o nb y s c a n n i n g e l e c t r o n m i c r o s c o p y . E n v i r o n . S c i . T e c h n o l .1 2 : 8 1 7 - 8 1 9 .2 7 . Y i n g , W . , a n d W. J . W e b e r . 1 9 7 9 . B i o p h y s i c a l c h e m i c a la d s o r p t i o n s y s t e m s f o r w a s t e w a t e r t r e a t m e n t : P r e d i c t i v em o d e l l i n g f o r d e s i g n a n d o p e r a t i o n , p . 1 28 - 1 3 6. I n P r o -c e e d i n g s o f t h e 3 3 r d I n d u s t r i a l W a s t e C o n f e r e n c e , P u r d u eU n i v e r s i t y . An n A r b o r S c i e n c e , An n A r b o r , M i c h .

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