anaerobic degradation of the various fractions

7/30/2019 Anaerobic Degradation of the Various Fractions

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Biological Wastes 23 (1988) 117-142

A n a e r o b ic D e g r a d a t i o n o f th e V a r io u s F r a c t io n s o fS l a u g h t e r h o u s e W a s t e w a t e r

Sam eh Sayed, Jos van der Zanden, R en6 W ijf fe ls & G atze LettingaAgricu l tu ra l Unive rs i ty o f Wageningen , Dep ar tment o f W ate r Po l lu t ion Cont ro l ,De Drei jen 12, 6702 BC Wa g en i n g en , Th e N e th er l a n d s

(Received 1 Ap ril 1987; revi sed v ers ion rece ived 26 Ma y 1987; accep ted 26 Ma y 1987)

A B S T R A C TThe ma in objectives o f the pre sent invest igations w ere to determine them ax im um ex ten t o f anaerobic b io logica l degradation o f the so luble , co lloidaland Coarse Susp ended So l ids f rac t ion s o f s laughterhouse wastewater , inorder to e lucidate the mechanisms involved in the removal of these organicpol lu tan t f rac t io ns an d to de termine the ra te -l imi t ing s teps in the degradat iono f each f rac t ion o f the w astewater , and to assess the e ffec ts o f the rac t io ns onthe methanogenic act iv i ty of the sludge.

T he e x pe r ime n t s w e re pe r fo rm e d w i th me mbrane - f i lt e re d w as te w a te r( wa s tewater , , : ) , paper- f i l te red wastew ater (wa s tew aterp :) and the whole( to ta l ) w as tew a te r. T he e x pe r ime n ta l a r range me n t s c ons is t e d o f a c o lumnconta in ing granular s ludge , through which the te s t was tewater wasrecireulated. The biodegradabil i ty tests with the Coarse Sus pen ded Solidsf rac t ion o f t he w as te w a te r w e re pe r fo rm e d w i th g ranu lar an d f l oe e u le n ts ludge in convent ional s ti rred batch d igesters. A l l e xper im ents werepe r fo rme d a t 30C and 20C .The m ax im um biodegradabi li ties ( i. e. convers ion in to m e t ha ne ) fo un d a t3 0 C w e re 7 5 % f o r w a s t ew a t er ,. :, 6 1 % f o r w a s t ew a t e rp : a n d 6 7 % f o rwastewatertotoo w hi le a t 20C these va lues w e re 72% , 49% and 51% ,respec tive ly . The max im um biodegradabi li ty o f the Coarse Suspended Sol idsf r a c t io n o f t h e w a s te w a s 5 0 % a t 3 0 C a n d 4 5 % a t 20 C .The resu l t s ind ica te tha t an important mechanism in the removal o f thesoluble , an d especial ly the colloidal , fra ct io ns o f the w astew ater is adsorption.Par t icu lar ly a t impo sed h igh s ludge loads o f approx im ate ly 0"17g co lloidal-C O D g - : V S S the lim i ting ra t e o f l ique fac tion o f t he absorbed c ompoundsm ay resu l t in a ser ious drop in the me thanogenic ac t iv ity o f the s ludge .

11 7Biological Wastes 0269-7483/88/$03-50 Elsevier Appl i ed Science Publishers L td, England,1988. Printed in G rea t Bri ta in


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118 S a m e h S a yed , J o s va n d e r Z a n d en , R en b W i f f fe l s , Ga t z e L e t t in g a

The e xten t, as we ll as the rate, of the liquefaction o f the adsorbed insolublesubs trate m ateria l o f the wastewater are the controlling fac to rs with respectto loading pote ntials o f the process, and consequently temperature is a fa ct oro f pred om inan t importance. T he methanogenic activ ity o f the granular sludgedeteriorates because o f the relatively high degree o f adsorption o f the colloidalfrac t ion o f the wastewater to the surface o f the s ludge and i ts high fa t content.

I N T R O D U C T I O NA n a e r o b i c p r o c e s s e s a r e a l t ra c t i v e f o r th e t r e a t m e n t o f w a s t e w a t e r s v a r y i n gw i d e l y i n s tr e n g t h a n d c o m p o s i t i o n (M c C a r t y , 198 1). T h e a d v a n t a g e s o f th ea n a e r o b i c t r e a t m e n t a r e t h a t i t c o u p l e s th e r e m o v a l o f o r g a n ic p o l l u t a n t s o ft h e w a s t e w i th t h e p r o d u c t i o n o f e n e r g y in t h e f o r m o f m e t h a n e , w h i le e xc es ss l u d g e p r o d u c t i o n i s l o w c o m p a r e d t o a e r o b i c p r o c e s s e s . M o r e o v e r , t h ee x c e ss s l u d g e is h i g h l y s t a b i l i s e d a n d g e n e r a l l y i t s d e w a t e r a b i l i t y i s e x c e ll e n t.

T h e n a t u r e a n d c o m p o s i t i o n o f t h e w a s te w a t e r s f r o m t h e f o o d i n d u s t r yh a v e b e e n d i s c u s s e d i n d e ta i l b y I s a a c & A n d e r s o n (19 74). T h e y r e p o r t t h a tm o s t e f f lu e n ts f r o m f o o d i n d u s t r ie s t e n d t o b e h e a v i ly p o l l u t e d a n d c o n t a i n ah i g h c o n c e n t r a t i o n o f b i o d e g r a d a b l e o r g a n i c m a t e r ia l s. T h e r e f o r e , th ed i s c h a r g e o f s u c h e f f lu e n t s t o a s e w e r o r a w a t e r c o u r s e w i ll e x e r t a s u b s t a n t i a lo x y g e n d e m a n d .F o r s l a u g h te r h o u s e s , w h i c h c o n s t i tu t e a n i m p o r t a n t b r a n c h o f th e f o o di n d u s t r y , i t is , o f c o u r s e , e s s e n ti a l , a n d n o r m a l , p r a c t i c e t o p u r i f y e f fl u e n tsb e f o r e d is c h a r g e t o a s e w e r o r a w a t e r c o u r s e . A m o n g s t t h e s e ve r al a n a e r o b i ct r e a t m e n t p r o c e s s e s , t h e u p f l o w a n a e r o b i c s l u d g e b l a n k e t ( U A S B ) p r o c e s sa p p e a r s t o b e a n a t t ra c t i v e s y s t e m fo r t h e t r e a t m e n t o f f o o d i n d u s t r y w a s t e s( P e t t e & V e r s p r il l e, 1 98 1). R e c e n t s t u d i e s h a v e s h o w n t h e f e a s i b il i ty o f u s i n gt h e U A S B p r o c e ss f o r a o n e - s ta g e a n a e r o b i c t r e a t m e n t o f s la u g h t e r h o u s ew a s t e w a t e r ( S a y ed et aL, 1984; 1987).I n a p r e v i o u s p a p e r ( S a y e d et al. , 1 9 8 7 ) w e r e p o r t e d t h a t , a p a r t f r o mt h e p o o r r e m o v a l o f t h e C o a r s e S u s p e n d e d S o li d s fr a ct io n , t h e p e r f o r m a n c eo f a o n e - s ta g e g r a n u l a r s lu d g e U A S B w i t h r e s p ec t t o t h e r e m o v a l o f t h es o l u b l e a n d c o l l o i d a l C O D o f t h e w a s t e w a t e r w a s q u i t e s a t is f a c to r y , e v e nu n d e r h i g h l o a d i n g c o n d i t i o n s ( u p t o 19 k g C O D m - 3 d a y - 1 a t 3 0 C a n d11 k g C O D m - 3 d a y - 1 a t 2 0 C).

H o w e v e r , a t t h e s a m e t i m e , t h e r e w a s a d r a m a t i c d e t e r i o r a t i o n i n t h ee ff ic ie n c y o f t h e s y s t e m i n t h e c o n v e r s i o n o f t h e r e m o v e d p o l l u t a n t s p r e s e n ti n t h e f i l t r a t e i n t o m e t h a n e u n d e r t h e h i g h l o a d i n g c o n d i t i o n s .T h e r e f o re , t h e m e c h a n i s m o f th e r e m o v a l o f t h e o r g a n i c p o l l u t a n t s f r o mt h e f il tr a te f r a c t i o n o f t h e w a s t e w a t e r is a m a t t e r o f c o n c e r n . I t is n e c e s s a ry t oe l u c id a t e th e m e c h a n i s m i n v o l v e d in t h e r e m o v a l o f t h e se c o m p o u n d s ,


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Anaerob ic digestion o f slaughterhouse w astewater 119p a r t i c u l a r l y i f i t m i g h t i n d u c e s i g n i fi c a n t r e t a r d a t i o n o f t h e l i q u e f a c t i o n o ft h e m a t e r i a l s ( S a y e d et al. , 1 98 7) a n d c o n s e q u e n t l y o f th e i r c o n v e r s i o n i n t om e t h a n e . T h e l i q u e f a c t i o n o f i n s o l u b l e b i o d e g r a d a b l e i n g r e d i e n t s i sg e n e r a l l y t h e r a t e - l i m i t in g s te p i n t h e d i g e s t i o n p r o c e s s ( G u j e r & Z e h n d e r ,1 9 8 3 ; S t a f f o r d , 1 9 8 3 ) . T h e r e f o r e , t h e m a i n o b j ec t i v e s o f t h e p r e s en ti n v e s t i g a t i o n s w e r e t o d e t e r m i n e t h e m a x i m u m e x t e n t o f t h e a n a e r o b i cd e g r a d a t i o n o f t h e so l u b le , c o l l o i d a l a n d c o a r s e S u s p e n d e d S o l id s fr a c t i o n so f t h e s l a u g h t e r h o u s e w a s t e w a t e r; t o e l u c i d a te t h e m e c h a n i s m s i n v o l v e d i nt h e r e m o v a l o f th e o r g a n i c p o l l u t a n t s o f t h e f il tr a te o f t h e w a s t e , a n d t o a ss es st h e r a t e - li m i t i n g st e ps i n t h e d e g r a d a t i o n o f e a c h f r a c t i o n o f t h e w a s t e w a t e r ,a s we l l a s t o a s s e ss t h e e f fec ts o f t h e f r ac t i o n s o n t h e m e t h an o g en i c ac t i v i ty o ft h e s l u d g e .

M E T H O D SSludgeT w o d i f f e r e n t t y p e s o f a n a e r o b i c s l u d g e w e r e u s e d i n t h e s e e x p e r i m e n t s ,g r a n u l a r a n d f lo c c u le n t. T h e g r a n u l a r s l u dg e w a s o b t a in e d f r o m a U A S B -p l a n t a t a p o t a t o p r o c e ss i n g fa c t o r y ( A V I K O , S t e e n d er e n , T h e N e t h e rl a n d s ).T h e T o t a l S u s p e n d e d S o li ds (T S S ) c o n t e n t o f th is s lu d g e w a s 9 .2 % a n d t h eV o l a t i le S u s p e n d e d S o l id s (V S S ) c o n t e n t , 6 . 4 % . T h e f l o c c u l e n t sl u d g e w a s ad i g e st e d s e w a g e s lu d g e, o b t a i n e d f r o m t h e m u n i c i p a l s e w a g e t r e a t m e n t p l a n ta t R e n k u m , T h e N e t h e r l a n d s . T h e T S S c o n t e n t w a s 2 . 9 % a n d t h e V S Sc o n t e n t w a s 1 . 8 % .AnalysesC h e m i c a l O x y g e n D e m a n d ( C O D ), B i o c he m i c a l O x y g e n D e m a n d (B O D ) ,t o t a l n i t r o g e n , p h o s p h a t e , a m m o n i a n i t r o g e n ( N H ~ - N ) , D r y S u s p e n d e dS o l i d s ( D S S ) a n d V o l a t i l e S u s p e n d e d S o l i d s ( V S S ) w e r e d e t e r m i n e da c c o r d i n g t o s t a n d a r d m e t h o d s ( S t a n d a r d M e t h o d s , 1 9 8 0 ). P r o t e i n w a sd e t e r m i n e d a c c o r d i n g to t h e m e t h o d s d e s c r ib e d b y L o w r y et al . (1951) andf at s w e r e d e t e r m i n e d a c c o r d i n g t o t h e D u t c h N o r m a l is e d S t a n d a r d M e t h o d s(1 96 9). V o l a t i le F a t t y A c i d s (V F A ) c o n c e n t r a t i o n s w e r e d e t e r m i n e d b y g a sc h r o m a t o g r a p h y u s i n g a P a c k a r d B e c k e r M o d e l 4 1 7 e q u i p p e d w i t h a6 m x 2 m m g la ss c o l u m n a n d a f la m e i o n i sa t i o n d e te c t o r. T h e c o l u m n w a sp a c k e d w i t h C h r o m o s o r b 101 ( 6 0- 8 0 m e s h) . F l o w r a t e o f t h e c a rr i e r g a s,n i t r o g e n s a t u r a t e d w i t h f o r m i c a c id , w a s 18 m l m i n - 1 . T h e c o l u m n w a sm a i n t a i n e d a t a t e m p e r a t u r e o f 2 10 C a n d t h e in j e c ti o n p o r t w a s a t 2 3 0 C .


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1 2 0 Sam eh Sayed, Jo s van der Zanden, Renb Woffels, Ga tze Lett inga

T A B L E 1O u t l i n e o f t h e P r o c e d u r e A p p l i e d i n P r e p a r i n g t h e V a r i o u s W a s t e F r a c t i o n s

Distinguished wastewater fra ctio ns Separation Size limits o fprocedure f ract ion remove d( R a w w a s t e w a t e r )

W a s t e w a t e r t o t ~ ~= C o a r s e S u s p e n d e d S o li d s +c o l l o i d a l + s o l u b l e f r a c t i o n

W a s t e w a t e r p f " = c o l l o i d a l + s o l u b l e f r a c t i o n

1W a s t e w a t e r m ~ = s o l u b l e f r a c t i o n

S c r e e n

F i l t r a t i o np a p e r f i l t e rF i l t r a t i o nm e m b r a n e f i l t e r

C o a r s e S u s p e n d e dS o l i d s : 1 m m - 7 .4 p mC o l l o i d a l :7 .4 - 0 - 4 5 p m

a W as te w at er pf = wa stew aterpa pe r filtered'b W a s t e w a t e r m f = w a s t e w a te r m e m b . . . nJtered; t h i s f r a c t i o n i s a r b i t r a r i l y d e f i n e d a s s o l u b l e .

Prep aration o f the wastew ater fractionsW a s t e w a t e r o r i g i n a t i n g f r o m s l a u g h t e r i n g a r e a s w a s c o l l e c t e d . T h e r a ww a s t e w a t e r w a s s e p a r a t e d i n t o t h r e e d i f f e r e n t f r a c t i o n s a c c o r d i n g t o t h ep r o c e d u r e p r e s e n t e d in T a b l e 1.Exp er imenta l se t-upA l l e x p e r i m e n t s w e r e p e r f o r m e d a t t e m p e r a t u r e s o f 3 0 C a n d 2 0 C . T w ot y p e s o f e x p e r i m e n t w e r e e m p l o y e d d e p e n d i n g o n t h e s p ec if ic p u r p o s e o f t h ee x p e r i m e n t . R e c i r c u l a t i o n e x p e r i m e n t s w i t h w a s te w a t e rm r , w a s t e w a t er p f a n dw i t h w a s te w a te rt ot a ~ w e r e p e r f o r m e d i n t h e r e c i r c u la t e d b a t c h d i g e s t e rs y s t e m s h o w n i n F i g . 1 . T h e e x p e r i m e n t a l a r r a n g e m e n t c o n s i s t e d o f ac o l u m n c o n t a i n i n g a g r a n u l a r s lu d g e t h r o u g h w h i c h t h e 5 -6 l it re s w a s t e w a t e rp r e s e n t i n th e c o n t a i n e r w a s r e c i r c u l a t e d a t a s u p e r f i ci a l v e l o c i t y o f 3"5 m h - ~T h e 5"3 c m d i a m e t e r c o l u m n s w e re 6 0 c m i n h e i g ht , t h e t o t a l v o l u m e o f t h ed i g e s t e r c o l u m n w a s 1 -3 2 l it re s w i t h a w o r k i n g v o l u m e o f 1 .2 0 l it re s. N om e c h a n i c a l m i x i n g w a s a p p l i e d . I n a ll e x p e r i m e n t s 2 6"7 g V S S g r a n u l a rs l u d g e p e r l i tr e re a c t o r v o l u m e w a s u s e d i n t h e d i g e s t i o n c o l u m n .T h e r e a s o n s f o r u s i n g th i s ty p e o f b a t c h r e c i r c u l a ti o n e x p e r i m e n t i n s t e a do f t h e c o n v e n t i o n a l s t i r r e d - t a n k b a t c h e x p e r i m e n t s w e r e: l it tl e, i f a n y ,e r o s i o n o f t h e g r a n u l a r s l u d g e o c c u r s; th e p r a c t ic a l o p e r a t i n g c o n d i t i o n s o fg r a n u l a r s l u d g e b e d r e a c t o r s a r e a p p r o a c h e d b e t t e r i n t h i s e x p e r i m e n t a la r r a n g e m e n t ; a s a t i s f a c t o r y c o n t a c t b e t w e e n w a s t e w a t e r a n d s l u d g e i s


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Anaerobic d igestion o f slaughterhouse wastewater 121

G

I r e c y c l e5

E2g t l S

~oo

, t .. . , ., / ,t/" / /" J /, ' 1 "

Fig . 1 . Schem at ic d iagram of the convent io na l ba tch fed d iges te r ( le f t) and the rec i rcula teddigester ( r ight) used in these experiments . Left : 1, Digester . 2, St i r rer . 3, Headspace. 4,Sam pling points . 5, G as o ut let . 6, M ario t te f lask. Right : 1, Inf luen t vessel . 2, Dig ester colum n.3, Granular s ludge. 4, Inf luent inlet points . 5, Gas out let . 6, Sampling points . 7, Magnet icst i r r ing device. 8. Mariot te f lask.

p r o v i d e d i n th e c o l u m n ; in f o r m a t i o n i s o b t a i n e d a b o u t t h e e x t e n t a n d t h er a t e o f e l i m i n a t i o n o f th e v a r i o u s w a s t e w a t e r f r a c ti o n s .T h e r e c i r c u l a t i o n e x p e r i m e n t s p r o v i d e , t h e r e f o r e , r e a l i s t i c i n f o r m a t i o na b o u t t h e m a x i m u m e x t e n t a n d r a te o f th e d e g r a d a t i o n o f t h e su b s t ra t em a t e r i a l s a n d t h e m e c h a n i s m s i n v o l v e d i n t h e r e m o v a l o f t h e s u b s t r a t em a t e r i a l s .T h e d e g r a d a t i o n e x p e r im e n t s w i t h t h e C o a r s e S u s p e n d e d S o li ds fr a c t io no f t h e w a s t e w a t e r w e r e p e r f o r m e d i n c o n v e n t i o n a l s t ir re d b a t c h d i ge s te rs( F i g . 1 ) b ec au s e r e c i r cu l a t i o n ex p e r i m en t s a r e l e ss i n f o r m a t i v e i n t h i s c a se ,an d i t wa s d i ff icu l t t o p e r f o r m w i t h a s u s p e n s i o n o f co a r s e s o li d s. A l l t h ec o n v e n t i o n a l b a t c h e x p e r i m e n t s w e r e p e r f o r m e d i n i n t e r m i t t e n t l y s t i r r e d( 30 s a t 1 40 r p m ev e r y 3 m i n ) 3 -1 itre d i g e s te r s , u s i n g a w o r k i n g v o l u m e o f 2"5l it re s . B o t h t y p es o f sl u d g e w e r e i n v es t i g a t ed i n t h e s e ex p e r i m e n t s u s i n g , i na l l c a se s , a n i n it ia l s lu d g e c o n c e n t r a t i o n o f 5 g V S S p e r l i tr e w o r k i n g v o l u m e .T h e C H 4 ga s p r o d u c t i o n w a s m e a s u r e d u s i n g a l i q u id d i s p l a c e m e n ts y s te m ( M a r i o t t e f la sk ), c a r b o n d i o x i d e b e i n g r e m o v e d f r o m t h e b i o g a s b yh a v i n g a 1 % w / v N a O H s o l u ti o n in th e v ess els .T h e d e g r a d a t i o n e x p e r i m e n t s w e r e p e r f o r m e d t w i c e f o r w a s t e w a t e r m r ,f o u r t i m es f o r was t ew a t e r p f an d o n c e f o r was t ewa t e rt o ta ~ T ab l e 2 ). A f t e r e a chs e r i e s o f e x p e r i m e n t s , t h e c o l u m n o f t h e r e c i r c u l a t e d b a t c h d i g e s t e r w a ss e e d e d w i t h a f re s h a m o u n t (2 6.7 g l i t re - 1 ) o f t h e g r a n u l a r s lu d g e .T h e d e g r a d a t i o n e x p e r i m e n t s w i th t h e C o a r s e S u s p e n d e d S o li ds fr a c t io no f t h e w a s t e w a t e r w e r e p e r f o r m e d o n c e a t 3 0 C a n d o n c e a t 2 0 C w i t h


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122 Sameh Sayed, Jos van der Zanden, Ren~ Wiff fels, Gatze Lett inga

T A B L E 2Rec i r cu l a t i on Ba t ch Expe r imen t s Con duc t ed w i th t he Va r ious Was t ew a te r F r ac t i ons and t heS ludge Ac t iv i t y Tes ts Pe r fo rm ed .Wa stewater Experime nt Type of experiments

W as tew a te rm f A S ludge ac t i v it y meas u rem en t s (VFA- feed , F ig. 3 )B Reci rcu la t ion exper im ents , t es t 1C Reci rc u la t ion exper im ents , t es t 2D S ludge ac t i v it y measu remen t sE S ludge ac t i v it y me asu rem nt sF Reci rcu la t ion exper im ents , t es t 1G Reci rcu la t ion exper im ents , t es t 2H S ludge ac t iv i t y me asu rem en t sI Rec i rcu la t ion exper im ents , t es t 3J Rec i rcu la t ion exper im ents , t es t 4K S ludge ac t i v it y mea su rem en t sL S ludge ac t i v it y mea su rem en t sM Reci rcu la t ion exper ime nts , t es t 1N S ludge ac t i v it y mea su rem en t s

Was t ewa te rv f

Wastewatertotal

(Fig. 2)(VFA-feed , F ig . 3)(VFA- feed )(Figs 4 and 5)(VFA- feed )

(VFA- feed )(VFA- feed )(Figs 7, 8 and 9)(VFA- feed )

g r a n u l a r s l u d ge ; w i t h d i g e s t e d se w a g e s l u d g e o n e s er ie s o f e x p e r i m e n t s w a sp e r f o r m e d ( T a b le 3). A l l t h e b a t c h e x p e r i m e n t s w e r e p e r f o r m e d a tc o n s e c u t i v e l o a d s i n o r d e r t o a ss e ss i f a n y s l u d g e a d a p t a t i o n o c c u r r e d , a sw e ll a s to d e t e r m i n e t h e m a x i m u m e x t e n t o f t h e s u b s tr a te d e g r a d a t i o n i nr e l a t i o n t o t h e a p p l i e d l o a d s . T h e d i g e s t e rs w e r e s ee d e d w i t h a f r e s h b a t c h o fg r a n u l a r o r d i g e s t e d s e w a g e s l u d g e a f te r e a c h s er ie s o f e x p e r im e n t s .

T h e e x p e r i m e n t s w e r e t e r m i n a t e d a f t e r t h e g a s p r o d u c t i o n c e a s e d a s th i si n d i c a t e d t h e c o m p l e t e e l i m i n a t io n o f t h e b i o d e g r a d a b l e C O D . T h e C O Dr e m a i n i n g i n t h e s y s te m c a n b e c o n s i d e r e d as n o n - b i o d e g r a d a b l e . T h ed i g e s t i o n p r o c e s s w a s f o l l o w e d b y m e a s u r i n g t h e C H 4 p r o d u c t i o n a n d b ya n a l y s i n g t h e l i q u i d p h a s e f o r V F A a n d C O D .T h e s l u d g e a c t i v i t y m e a s u r e m e n t s w e r e p e r f o r m e d b o t h i n t h e r e -c i r c u l a t e d b a t c h e x p e r i m e n t s a n d i n t h e c o n v e n t i o n a l b a t c h d i g es te r . As l u d g e c o n c e n t r a t i o n o f 2 6-7 g l i tr e - 1 w a s u s e d i n t h e r e c i r c u la t e d b a t c he x p e r i m e n t s w h i l e 5 g l i t re - 1 w a s a p p l i e d i n a ll t h e c o n v e n t i o n a l b a t c he x p e r i m e n t s . A m i x t u r e o f a ce t a te , p r o p i o n a t e a n d b u t y r a t e , a t a n i n it ia lc o n c e n t r a t i o n o f 0 . 6 g l i t r e - 1 e a c h , w a s u s e d a s s u b s t ra t e , t h e p H w a sb e t w e e n 6 "5 a n d 7 "5 . I n a d d i t i o n t o t h e s u b s t r a t e s t h e f o l l o w i n g n u t r i e n t sw e r e s u pp l ie d : 1 7 4 m g N H 4 C 1, 28 .3 m g K H E P O 4 a n d 5 3 0 m g N a 2 S O , a n dI m l t r a c e e l e m e n t s o l u t i o n a c c o r d i n g t o Z e h n d e r ( 1 97 6) ; i n a ll c a s e s p e r li t rew o r k i n g v o l u m e . B e f o r e s ta r t i n g t h e e x p e r i m e n t s th e r e a c t o r s w e r e f lu s h e dw i t h n i t r o g e n g a s i n o r d e r t o r e m o v e o x y g e n f r o m t h e l i qu i d a n d f r o m t h eh e a d s p a c e .


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Anaerobic d igestion o f slaughterhouse wastewater 123

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8/26

124 Sameh Sayed, Jos van der Zanden, Renb Wi~els, Gatze LettingaT h e m e t h a n e p r o d u c t i o n w a s m e a s u r e d s e v e r a l t i m e s a d a y a n d a l s o

v a r i o u s s a m p l e s w e r e ta k e n d u r i n g t h e d a y f o r d e t e r m i n i n g t h e V F A -c o n c e n t r a t i o n s . T h e m a x i m u m s pe ci fi c m e t h a n o g e n i c a c t iv i ty o f t h e s l u d g ew a s c a lc u la t ed f r o m t h e m a x i m u m s lo p e o f a g r a p h o f th e m e t h a n ep r o d u c t i o n w i t h t im e . G e n e r a l l y , th e r e s ul ts o f t h e s e c o n d V F A - f e e d w e r eu s e d f o r c a lc u l at io n , b e c a u se t h e m e t h a n e p r o d u c t i o n r a te o b t a i n e d i n t h es e c o n d f e e d w a s s i g n i fi c a n t ly h i g h e r t h a n i n t h e f i rs t fe e d w h i l e it w a s c l o s e t ot h a t o f t h e t h i r d f ee d . T h e s p ec if ic a c ti v it y is e x p re s s e d a s g C H 4 - C O D g - 1V S S d a y - 1.

T h e a d s o r p t i o n e x p e r i m e n t s w e re c o n d u c t e d a s fo ll ow s . A c e r t a i n a m o u n to f g r a n u l a r s lu d g e w a s r in s e d w i t h t a p w a t e r s a t u r a t e d w i t h o x y g e n in o r d e rt o i n h i b i t t h e m e t h a n o g e n i c a c ti v it y o f th e s l u d g e a n d t o r e m o v e a l l t h e f in e lyd i s p e r s e d m a t e r i a l s f r o m t h e s l u d g e . T h e a d s o r p t i o n e x p e r i m e n t w a sp e r f o r m e d u s i n g 0 .5 l i tr e s l u d g e ( 6 4 g s l u d g e - V S S p e r l it re ) w i t h 2 .5 l i t re sw a s t e w a t e r p r i n a f la s k. T h e w a s t e w a t e r p f c o n s i s t e d o f 5 0 % s o l u b l e a n d 5 0 %c o l lo i d a l m a t t e r a n d i ts i n it ia l C O D - v a l u e w a s 2 . 2 g C O D l it re - 1 ,c o r r e s p o n d i n g t o a s l u d g e l o a d o f 0"17 g C O D g - 1 V S S . I m m e d i a t e l y a f te rt h e a d d i t i o n o f t h e s l u d g e a n d w a s t e w a t e r t o t h e f la sk , m e c h a n i c a l s h a k i n g o ft h e m i x t u r e w a s s t a r te d . A f t e r f ix e d ti m e i n t e r v a ls t h e f l as k w a s t a k e n f r o mt h e s h a k i n g m a c h i n e a n d t h e m i x t u r e w a s a l l o w e d t o s et tl e f o r I m i n . T h e n as a m p l e w a s d r a w n f r o m t h e s u p e r n a t a n t s o l u t i o n f o r d e t e r m i n i n g t h e to t a lC O D a n d CODmf.D e f i n i t i o n s a n d c a l c u l a t i o n sDef in i t ions o f t he var ious f rac t ion sF o r t h e p u r p o s e o f th e i n t e r p r e t a t i o n o f t h e e x p e r im e n t a l r e su l ts a n u m b e r o ff r a c t i o n a l f a c t o r s , a l l b a s e d o n C O D - e q u i v a l e n t , h a v e b e e n d e f i n e d :

F r a c t i o n m e t h a n o g e n i s e d (F M )% = 1 00 x M / T oF r a c t i o n a c i d i f i e d ( F A ) % = 1 00 x ( M + f A ) / T oF r a c t i o n l i q u e fi e d ( F L )% = 1 00 x ( M + f A + f N As ) / T oF r a c t i o n c o l l o i d a l ( F c )% = 1 00 x C / T oF r a c t i o n r e t a i n e d ( FR )% = 1 00 x (1 - - ( M + T x )/ To )

i n w h i c h : M = C O D r e m o v e d v i a m e t h a n e g a s ( g l i t r e - 1); 1 l it re C H 4 ( 3 0 Ca n d 7 20 m m H g ) i s e q u a l t o 2 .4 85 g C H 4 - C O D ; 1 l it re C H 4 ( 20 C a n d 7 20 m mH g ) is e q u a l t o 2 .6 2 0 g C H 4 - C O D ; fA = C O D c o r r e s p o n d i n g t o t h e V F Ac o n c e n t r a t i o n ( g l i t re - 1 ) i n t h e l i q u id p h a s e ; fN AS = C O D o f n o n - a c i d i fi e ds o l u b l e f r a c t i o n ( g l i tr e - 1 ) in t h e l i q u i d p h a s e ; C = C O D o f t h e c o ll o i d a lf r a c t i o n (g l i t r e - 1) i n t h e li q u i d p h a s e ; T o, T x = t o t a l C O D o f t h e w a s t e w a t e ra t t i m e t = 0 a n d t i m e t = x ( g l i t r e - 1 ) i n t h e l i q u i d p h a s e .


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A n a ero b i c d i g e st io n o f s l a u g h te rh o u se w a s t ew a t e r 12 5

C a l c u l a t i o n o f th e c o n t a c t t i m e i n t h e r e c ir c u l a ti o n e x p e r i m e n t sw o r k i n g v o l u m e o f t h e d i g e s t e r c o l u m n ( l i t r e s )

C o n t a c t t im e ( h ) = v o l u m e o f t h e w a s t e w a t e r (litre s)x r e c i r c u l a t i o n t i m e (h )R E S U L T S

Wastewater compos i t ionT h e c o m p o s i t i o n o f t h e s l a u g h t e r h o u s e w a s t e w a t e r , fo r t h e t h r e e f r a c ti o n se x p r e s s e d a s a p e r c e n t a g e o f t h e t o t a l C O D , i s p r e s e n t e d i n T a b l e 4 . T h er e s u lt s i n T a b l e 5 p r e s e n t t h e c o m p o s i t i o n o f t h e C o a r s e S u s p e n d e d S o l i d sa n d c o l l o i d a l f r a c t i o n s o f t h e w a s t e w a t e r in t e r m s o f C O D t o t a I a n d C O D r a t sa n d C O D p r o t e t n. T h e r e s u l ts i n T a b l e 5 i n d i c a t e t h a t t h e c o m p o s i t i o n s o f t h e

T A B L E 4W a s t e w a t e r C o m p o s i t io n

F r a c ti o n A s % o f C O D - t o t a lC o a r s e S u s p e n d e d S o l id s 4 5 - 5 5C o l l o i d a l 2 0 - 3 0S o l u b l e 2 0 - 3 0T o t a l 2 87 0 m g C O D l i t r e - ~ 1 00

T A B L E 5T h e C o m p o s i t i o n o f t h e C o a r s e S u s p e n d e d S o l id s a n d C o l l o i d a l F r a c t i o n s o f th e W a s t e w a t e r

P a ra m e t e r F ra c t i o n sC o a r se A s % o f C O D C o ll oi da l A s % o f C O D

S S S SA sh (% ) 18"3 17"2CO Dtotat (g g - 1 VSS)O 1"63 100 1.78 100F a t s ( g f a t s -C O D g - 1 V S S )b 1.10 67.5 1-20 67-4P r o t e in ( g p r o t e i n - C O D g - ~ V S S )b 0"30 18-4 0-40 22"5Re st (g C O D g - 1 VSS ) 0 .23 14-1 0-18 10-1

I g f a t s is e q u a l t o 2 .9 1 g C O D ( K r o l et al . , 1977).1 g p r o t e i n i s e q u a l t o 1 - 1 5 g C O D ( B u n g a a r d et al . , 1980). A v e r a g e o f e i g h t a n a l y s e s ; s t a n d a r d d e v i a t i o n _+ 0 "1 0 g g - 1 V S S .b A v e rag e o f t h r e e ana l y s e s ; s t a nd a rd dev i a t i on ___ 0"10g f a t s C O D pe r g -x V S S , _ __ if02gp r o t e in C O D g - 1 V S S .


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126 Sameh Sayed , Jos van der Zanden, Renb Wi j f fe l s , Gatze Le t t inga

TABLE 6Results of the Rec irculation Experiments B and C after 20 Hours' Contact Time.

Expe r imen t s Tes t Con tac t I n it ia l CODmf CODmt CODmt conver t edNo. a No. t ime concentra tion reduct ion in to me thane(h) (g l i tre - ~) (% ) (% )

At a process temperature of 30CB 1 20"0 1.42 74 74C 2 20.2 1'50 75 75At a process temperature of 20CB 1 20.0 1.42 70 70C 2 20.2 1.50 72 72 For explanation: See Table 2.

C o a r s e S u s p e n d e d S o l i d s a n d t h e c o l l o i d a l f r a c t i o n s a re si m i l ar ; t h e f a tsc o n c e n t r a t i o n i s s i g n if i c an t l y h i g h e r t h a n t h e p r o t e in c o n c e n t r a t i o n f o r b o t hfra c t io ns .E x p e r i m e n t s w i t h w a s t e w a t e r ( m e m b r a , e f i l t e r e d )T h e r e s u l ts o f t h e r e c i r c u l a t i o n e x p e r i m e n t s w i t h w a s te w a te r m r ( i.e. t h es o l u b l e f r a c t i o n o f th e w a s t e w a t e r ) a f t e r 2 0 h c o n t a c t t i m e a r e p r e s e n t e d i nT a b l e 6 . D e t a i l s o f e x p e r i m e n t C ( T a b l e 2 ) a r e s h o w n i n F i g . 2. A s i m i l a rF i g u r e w a s o b t a i n e d f o r e x p e r i m e n t B .

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/ ocontoct t ime VFA-COD( h ) (mgl-II ~>0 179 t~1 1 1 5 0 wL~IL, 1109S 220.0 2~0 80r e c i r c u [ a f i o n t i m e ( h )

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8./* 16B 0 8/* 168c o n t o c t t i m e ( h ) c o n t a c t t im e ( h )Results of recircu lation experiment C with wastewatermr at 30C and 20C. (Q) CODremoved; (O) COD converted into methane -COD (CODt= o = 1"50 g litr-1).


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A naerobi c digest ion of slau ghterhou se wastewater 127

CH ~product ion ( L I r 1VF A-conce nfra t ion (g.[71)1.2 0.6-

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0 . ~ - o.~ ~i~\o/ \ ,,X00 10 20 3Orec i r cu ta t ion t ime (h )

~ 1 i . 2 6'.3 8'.~c on t a c t tim e ( h }

Fig. 3. Resu l ts o f the s ludge act iv i ty exper iments A (left ) and D (right ) (Table 2), using therec irculated batch d igester at 30C. O = CH4 , = C2, [ ] = C3, A = C4 acids.

T h e l e f t - h a n d a x i s o f t h e F i g u r e r e p r e s en t s t h e i n i t i a l C O D s o ~.c o n c e n t r a t i o n o f t h e w a s t ew a t e r . T h e p e r c e n t a g es s h o w n i n t h e ce n t r ec o l u m n r e p re se n t t h e m a x i m u m p e r c en t ag e c o n v er s io n i n t o m e t h a n e - C O Do f th e s u p p l i ed C O D ( t r ea t m e n t e ff ic ie n c y) a n d C O D r e m o v e d .

T h e r e s u l ts o f t h e sl u d g e a c t iv i t y e x p e r i m e n t s A a n d D a t 3 0 C w i t h th er e c i r c u l a t e d b a t c h p r o c e d u r e a r e s h o w n i n F i g . 3 . A s i m i l a r p i c t u r e w a so b t a i n e d f o r t h e t e s t s p e r f o r m e d a t 2 0 C . T h e c a l c u l a t e d s p e c i f i c s l u d g ea c t i v i t i e s p r i o r t o , a n d a f t e r , r e c i r c u l a t i o n e x p e r i m e n t s ( A , D ) w i t hwa s tewa term f a re p res ented in Ta b le 7 .

T a b l e 8 s h o w s t h e C O D v a l u e s o f th e in f l u e n t a n d t h e e ff lu e n t s o l u t i o ni n te r m s o f C O D t o t a l, C O D f a t s , C O D p r o te i n a n d CO Dreductio n o f e x p e r i m e n t Cp e r f o r m e d a t 3 0 C . T h e f a t s f r a c t io n o f b o t h t h e i n f l u e n t a n d e f fl u e n t i si n s i g n i f i c a n t , w h i l e t h e p r o t e i n f r a c t i o n o f b o t h l i q u i d s i s r e l a t i v e l y h i g h .

T A B L E 7Th e C a l cu la ted S p ec if ic M eth a n o g en i c A c t i v i ty f ro m th e R ec i rcu la t i o n B a tch

S y s tem w i th V F A - M i x t u r e ( E x p e r i m e n t s A a n d D )Tempe r a t u r e S p e ci fi c s l ud g e a c t iv i ty ( k g C O D 4 - C O D k g - 1 V S S d a y - 1)

( C) Exp. Exp . aA D

30 0"30 0"6020 0-20 0"38

F o r ex p l a n a t i o n : S ee Ta b l e 2.


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128 Sameh Sayed, Jos van der Zanden, Renb Wijffels, Gatze L ett in ga

TABLE 8Th e C om posit ion of the Inf luent and Eff luent in E xperiment C Performed at 3 0C and theC alculated Degrad ation PercentagesComposi ti on I n f l u en t E f f l u e n t Degr a da ti o n

( m g l it r e - 1 ) As % o f CO D ( m g l it r e - 1 ) As % o f CO DCOD 1 500 100 375 100 75Fats 15"0 1.0 8-0 1"6 47Protein 570 38.0 75 20 86-8Rest 915 61.0 292 78 68.11 g fats i s equal to 2.91 gC OD (Krol et al., 1977).1 g protein is equal to 1.15 gC OD (Bungaard et al., 1980).

E x p e r i m e n t s w i t h w a s t e w a t e r ( p a p ~ r f i l t e r e d )T a b l e 9 s u m m a r i s e s t h e r e s u lt s o b t a i n e d f r o m t h e r e c i rc u l a ti o n e x p e r i m e n t sw i t h w a s t e w a t e r p r M o r e d e t a i le d r e s u l ts o f e x p e r i m e n t G ( T a b l e 2 ) a r es h o w n i n F i g . 4 . V e r y s i m i l a r F i g u r e s w e r e o b t a i n e d f o r t h e o t h e re x p e r i m e n t s . T h e r e s u l t s i n F i g . 4 i n d i c a t e t h a t , a t t h e t e r m i n a t i o n o f t h ee x p e r i m e n t s , a f te r a c o n t a c t t i m e o f 2 0 h , a p a r t o f th e e li m i n a t e d C O D h a sn o t b e e n c o n v e r t e d i n t o m e t h a n e . T h i s is r e p r e s e n te d b y t h e a r ea b e t w e e n t h eu p p e r a n d t h e l o w e r c u r v e s in t h e F ig u r e . T h e r e m o v a l e f fi c ie n c y a m o u n t s t o8 6 % a t 3 0 C ; o n l y 6 1 % o f th e i m p o s e d C O D l oa d h a s b ee n c on v e r te di n t o m e t h a n e a f te r th is 2 0 h c o n t a c t t im e , c o r r e s p o n d i n g t o 7 1 % o f t h eC O D , ,m o v ~ . T h e r e t a i n ed C O D , c o m p r i s i n g 2 9 % o f th e C O D rem ove~ ,a p p a r e n t l y h a s b e e n e l i m i n a t e d i n a d i ff e re n t w a y . A t a p r o c e s s t e m p e r a t u r eo f 20 C 3 9 % o f th e CODremoved c a n n o t b e a c co u n t e d f o r a s m e t h a n e - C O D .

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