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UBC Theses and Dissertations

A two-phase anaerobic digestion process (UASB-UASB) for simulated sewage sludge 1992

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A T W O - P H A S E A N A E R O B I C D I G E S T I O N P R O C E S S ( U A S B - U A S B ) F O R S I M U L A T E D S E W A G E S L U D G E b y P R A Y O O N F O N G S A T I T K U L B . S c . ( S a n i t a t i o n ) , M a h i d o l U n i v e r s i t y , 1 9 7 5 M . S c . ( E n v i r o n m e n t a l T e c h n o l o g y a n d M a n a g e m e n t ) , A s i a n I n s t i t u t e o f T e c h n o l o g y , 1 9 7 8 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y i n T H E F A C U L T Y O F G R A D U A T E S T U D I E S ( D e p a r t m e n t o f C i v i l E n g i n e e r i n g ) W e a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R T Y O F B R I T I S H C O L U M B I A A p r i l 1 9 9 2 © P R A Y O O N F O N G S A T I T K U L , 1 9 9 2 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s m a y b e g r a n t e d b y t h e h e a d o f m y d e p a r t m e n t o r b y h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t m y w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f C i v i l E n g i n e e r i n g T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r , C a n a d a D a t e / D E - 6 ( 2 1 8 8 ) A B S T R A C T T h e o b j e c t i v e s o f t h i s r e s e a r c h p r o g r a m w e r e t o d e m o n s t r a t e t h e f e a s i b i l i t y a n d e f f e c t i v e n e s s o f a “ t w o - p h a s e ” a n a e r o b i c s e w a g e s l u d g e s t a b i l i z a t i o n ( U A S B - U A S B ) p r o c e s s . A b e n c h - s c a l e e x p e r i m e n t , c o n s i s t i n g o f t w o c o m p l e t e l y m i x e d s e a l e d u p f l o w a n a e r o b i c ( A - U A S B a n d M - U A S B ) r e a c t o r s , d e s i g n e d t o o p e r a t e i n s i d e a w a l k - i n t e m p e r a t u r e c o n t r o l l e d r o o m a t 3 5 0 C , w a s e m p l o y e d . T h e s y s t e m w a s f i r s t s e e d e d a n d a c c l i m a t i z e d , a n d t h e n u s e d i n a s e r i e s o f d i f f e r e n t e x p e r i m e n t a l r u n s , e m p h a s i z i n g t h e e f f e c t s o f i n f l u e n t S l u d g e R a t i o ( S R ) o f p r i m a r y t o s e c o n d a r y s l u d g e s a n d R e c y c l e R a t i o ( R R ) o f f l u i d i z e d s l u d g e f r o m s l u d g e b l a n k e t p o r t i o n o f t h e r e a c t o r , o n p r o c e s s p e r f o r m a n c e . T h e v i c i n i t y o f “ b e s t k n o w n ” r u n n i n g c o n d i t i o n w a s l o c a t e d b y a n a p p l i c a t i o n o f 2 b y 2 f a c t o r i a l d e s i g n a n d R e s p o n s e S u r f a c e M e t h o d ( R S M ) . M a x i m u m s y s t e m l o a d i n g c a p a c i t y , o p t i m u m o p e r a t i n g c o n d i t i o n s , a n d s y s t e m f a i l u r e / r e c o v e r y p r o c e s s w e r e f u r t h e r i n v e s t i g a t e d . T h e r e s u l t s o f t h i s r e s e a r c h s t u d y s h o w e d t h a t a t w o - p h a s e U A S B - U A S B p r o c e s s a p p e a r e d t o b e f e a s i b l e a n d e f f e c t i v e i n s t a b i l i z i n g s e w a g e s l u d g e a t h i g h o r g a n i c l o a d i n g r a t e s , w h i l e m a i n t a i n i n g a n a c c e p t a b l e l e v e l o f s u p e r n a t a n t q u a l i t y a n d C H4 g a s p r o d u c t i o n . T h e s y s t e m h a d a h i g h p o t e n t i a l t o r e c o v e r e f f e c t i v e l y , a f t e r a s e r i o u s f a i l u r e , b y a p p l y i n g a s t e p - l o a d i n g r e d u c t i o n a n d i n t e r n a l r e c i r c u l a t i o n ( R R ) a p p r o a c h . T h e “ T w o - p h a s e ” c o n c e p t h a s p r o v e d t o b e s u c c e s s f u l i n t r e a t i n g s e w a g e s l u d g e . H y d r o l y s i s a c i d i f i c a t i o n p r e d o m i n a t e d i n t h e A - U A S B , w h i l e a c e t o g e n e s i s - m e t h a n o g e n e s i s 1 1 d o m i n a t e d i n t h e M - U A S B . M o s t o f t h e r e a c t i o n s o c c u r r e d a t t h e l o w e r p a r t s ( s l u d g e b l a n k e t a n d b e d ) o f b o t h r e a c t o r s . A c o m b i n a t i o n o f s y s t e m h y d r a u l i c a n d o r g a n i c o v e r l o a d i n g i n t h e M - U A S B reactor w a s a m a j o r c a u s e o f p r o c e s s f a i l u r e . T h i s w a s i n d i c a t e d b y a w a s h o u t o f M L V S S , a n i n c r e a s e i n t h e t o t a l V F A c o n c e n t r a t i o n , a r e d u c t i o n i n t h e s y s t e m r e m o v a l e f f i c i e n c y , a c e s s a t i o n o f CH4 g a s p r o d u c t i o n , a d r o p o f p H , a n d a n i n c r e a s e i n t o t a l V F A / a l k a l i n i t y r a t i o . A p p l y i n g a t w o - s t e p approach t o i n c r e a s e t h e HRT o f t h e M - U A S B b y 1 . 5 a n d 5 . 8 t i m e s t h a t o f t h e p r o c e s s f a i l u r e HRT ( M - U A S B ) , t h e s y s t e m C O D ( s o l ) r e m o v a l e f f i c i e n c y r e c o v e r e d e x p o n e n t i a l l y w i t h a n i n c r e a s e i n H R T , w h i l e t h e CH4 g a s p r o d u c t i o n r e c o v e r e d l o g a r i t h m i c a l l y(r2=O.81-O.99). T h e o p t i m u m o p e r a t i n g HRTs f o r t h e M U A S B , r e g a r d i n g C O D ( s o l ) r e m o v a l e f f i c i e n c y a n d CH4 g a s p r o d u c t i o n , w e r e 2 a n d 2 . 7 d a y s d u r i n g t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d , r e s p e c t i v e l y . F o r d e s i g n p u r p o s e s , t h e o p t i m u m o p e r a t i n g HRTs o f 1 a n d 2 d a y s a s w e l l a s RR o f 2 a n d 3 t i m e s that o f t h e i n t l u e n t f l o w r a t e are r e c o m m e n d e d f o r t h e A - a n d M - U A S B r e a c t o r s , r e s p e c t i v e l y . A reactor d i a m e t e r t o h e i g h t r a t i o o f 1 : 8 t o 1 : 1 0 , a n d a n o r g a n i c l o a d i n g rate o f 1 9 k g COD(total)/m3-d a t 3 5 ° C , w i t h t h e f e e d s l u d g e r a t i o o f 4 t o 1 ( 8 0 / 2 0 ) a r e a l s o r e c o m m e n d e d . M o d i f i e d d e s i g n c r i t e r i a , s t a r t - u p a n d a c c l i m a t i z a t i o n p r o c e s s e s , a n d s y s t e m o p e r a t i o n , f o r t h e t w o - p h a s e a n a e r o b i c d i g e s t i o n o f s e w a g e s l u d g e (UASB U A S B ) , w e r e f i n a l l y d e v e l o p e d . 1 1 1 • V I I • x l i • x • x v i i .1 .1 .2 .6 .6 .9 • 1 1 • 2 1 • 2 1 • 2 6 • 2 8 • 3 3 3 3 3 3 3 5 3 5 3 6 3 9 3 9 3 9 4 1 4 6 T A B L E O F C O N T E N T S A B S T R A C T i i T A B L E O F C O N T E N T S i v L I S T O F T A B L E S L I S T O F F I G U R E S A C K N O W L E D G E M E N T S L I S T O F A B B R E V I A T I O N S 1 . I N T R O D U C T I O N 1 . 1 R e s e a r c h N e e d s a n d B a c k g r o u n d 1 . 2 R e s e a r c h O b j e c t i v e s a n d A p p r o a c h 2 . B A C K G R O U N D A N D B R I E F L I T E R A T U R E R E V I E W 2 . 1 A n a e r o b i c S l u d g e D i g e s t i o n 2 . 2 O p e r a t i n g P a r a m e t e r s a n d R e s p o n s e s 2 . 3 A n a e r o b i c P r o c e s s D e v e l o p m e n t 3 . S Y S T E M S E T - U P A N D O P E R A T I O N 3 . 1 R a t i o n a l e a n d D e s i g n C r i t e r i a 3 . 2 E x p e r i m e n t a l A p p a r a t u s a n d O p e r a t i o n 3 . 3 S y n t h e t i c S l u d g e P r e p a r a t i o n 4 . E X P E R I M E N T A L P R O G R A M S 4 . 1 A c c l i m a t i z a t i o n P r o c e s s 4 . 1 . 1 S y s t e m S e e d i n g a n d S t a r t u p L o a d i n g 4 . 1 . 2 S y s t e m O p e r a t i n g C o n d i t i o n s 4 . 2 E x p e r i m e n t a l D e s i g n 4 . 2 . 1 O p t i m u m “ B e s t k n o w n ” O p e r a t i n g C o n d i t i o n s 4 . 2 . 2 M a x i m u m L o a d i n g R a t e a n d R e c o v e r y P e r i o d s 4 . 2 . 3 S a m p l i n g P r o g r a m a n d A n a l y t i c a l T e c h n i q u e s 4 . 2 . 3 . 1 S a m p l i n g P r o g r a m 4 . 2 . 3 . 2 A n a l y t i c a l T e c h n i q u e s 4 . 2 . 4 D a t a a n d S t a t i s t i c a l A n a l y s i s i v 5 . 2 . 2 . 3 5 . 2 . 2 . 4 4 7 4 7 4 7 4 8 4 9 5 0 5 6 5 8 6 0 6 0 6 1 6 6 6 9 7 9 8 0 8 3 8 3 9 1 9 3 9 4 9 9 1 0 4 1 1 1 1 2 2 6 . C O N C L U S I O N S A N D R E C O M M E N D A T I O N S 1 3 3 6 . 1 C o n c l u s i o n s 6 . 2 R e c o m m e n d a t i o n s R E F E R E N C E S 1 3 9 A P P E N D I X A 1 4 7 S y n t h e t i c S l u d g e P r e p a r a t i o n a n d S y s t e m S e t - u p 1 4 7 5 . R E S U L T S A N D D I S C U S S I O N 5 . 1 A c c l i m a t i z a t i o n p r o c e s s 5 . 1 . 1 D e v e l o p m e n t o f t h e A c c l i m a t i z a t i o n P r o c e s s 5 . 1 . 1 . 1 B e h a v i o u r a n d R e s p o n s e 5 . 1 . 1 . 2 A c c l i m a t i z a t i o n A l t e r n a t i v e s ( a ) W a s h o u t P h e n o m e n o n ( b ) S y s t e m P e r f o r m a n c e 5 . 1 . 2 C o n c l u s i o n s 5 . 2 E x p e r i m e n t a l D e s i g n 5 . 2 . 1 O p t i m u m “ b e s t k n o w n ” O p e r a t i n g C o n d i t i o n 5 . 2 . 1 . 1 E f f e c t s a n d I n t e r a c t i o n o f S l u d g e R a t i o ( S R ) a n d R e c y c l e R a t i o ( R R ) 5 . 2 . 1 . 2 “ B e s t K n o w n ” R u n n i n g C o n d i t i o n 5 . 2 . 1 . 3 T w o - p h a s e S e p a r a t i o n ( U A S B - U A S B ) 5 . 2 . 1 . 4 C o n c l u s i o n s 5 . 2 . 2 M a x i m u m L o a d i n g C a p a c i t y a n d R e c o v e r y P r o c e s s 5 . 2 . 2 . 1 M a x i m u m L o a d i n g C a p a c i t y ( a ) P r o c e s s F a i l u r e ( b ) M a x i m u m L o a d i n g R a t e 5 . 2 . 2 . 2 R e c o v e r y P r o c e s s ( a ) R e c o v e r y P e r i o d ( b ) S y s t e m R e c o v e r y B a s i c E x p e r i m e n t a l K i n e t i c s O p t i m u m L o a d i n g C a p a c i t y ( a ) C a s e 1 : O v e r a l l S y s t e m L o a d i n g C a p a c i t y ( b ) C a s e 2 : O p t i m u m L o a d i n g C a p a c i t y o f A M - U A S B s 5 . 2 . 2 . 5 C o n c l u s i o n s 1 1 1 a n d 1 1 6 1 1 8 5 . 2 . 3 D e v e l o p m e n t o f S y s t e m D e s i g n C r i t e r i a 5 . 2 . 3 . 1 O p t i m u m S y s t e m P e r f o r m a n c e a n d F e a s i b i l i t y 1 2 2 5 . 2 . 3 . 2 M o d i f i c a t i o n o f D e s i g n C r i t e r i a a n d O p e r a t i o n 1 2 5 1 3 3 1 3 6 V APPENDIX B.160 Acclimatization Process 160 APPENDIX C 182 Optimum “best known” Operating Condition 182 APPENDIX D 264 Maximum Loading Capacity and Recovery Process 264 vi LIST OF TABLES Table Page 3.1 Comparative Characteristics of Prepared Synthetic Sludge And Actual Primary and Secondary Sludges 31 4.1 Characteristics of Anaerobic Sludge Used in Seeding the System (Anaerobic Sludge Digestor/Lion’s Gate Treatment Plant) 34 4.2 Experimental Running Conditions During the Optimum “Best known” Operating Condition, Maximum Loading Capacity and Recovery Period . . 37 5.1 Summary of Effects (SR and RR) /Interaction (SR*RR) Change in mean During Sequence 1, 2, and 3 Experiments 63 5.2 Summary of Average Responses Under Pseudo Steady-state of the Different Designed Running Conditions (Sequence 1, 2, and 3 Experiments) 70 5.3 Performance of A Two-phase Anaerobic Sludge Digestion (UASB-UASB) Process 72 5.4 Statistical Constants and Kinetics During the Maximization and Recovery Period 110 5.5 Summary of Average Responses at the Optimum System Operating Condition Under Pseudo Steady-State Conditions 123 5.6 Recommended Design Criteria/Start-up and Acclimatization/System Operation of the Two-phase UASB-UASB Process 130 A1.1 Summary of Research Problems/Remedial Actions/Scope and Approach vii M o d i f i c a t i o n s. 1 4 8 A 2 . 1 : S y s t e m S e e d i n g a n d L o a d i n g R a t e 1 5 0 A 2 . 2 : F i n a l C o n s t i t u e n t s o f P r i m a r y a n d S e c o n d a r y S y n t h e t i c S l u d g e s a n d C h e m i c a l A n a l y s i s o f D o g F o o d s 1 5 0 A 3 . 1 D e t a i l e d S i z i n g o f A c i d - a n d M e t h a n e - P h a s e R e a c t o r s ( U A S B - U A S B ) ... 1 5 1 A 3 . 2 : S p r e a d - s h e e t f o r S i z i n g o f t h e A c i d - a n d M e t h a n e - P h a s e R e a c t o r s ( U A S B - U A S B ) 1 5 2 A 4 . 1 D e v e l o p m e n t o f A S m a l l - S c a l e ( 1 - L i t r e ) S y n t h e t i c S l u d g e P r e p a r a t i o n ... 1 5 3 A 4 . 2 : D e v e l o p m e n t o f A S c a l e - U p ( 3 0 - L i t r e ) S y n t h e t i c S l u d g e P r e p a r a t i o n . . . . 1 5 4 A 5 . 1 : M o n i t o r i n g t h e C h a r a c t e r i s t i c s o f P r i m a r y S y n t h e t i c S l u d g e P r e p a r e d T h r o u g h o u t t h e E x p e r i m e n t 1 5 6 A 5 . 2 : M o n i t o r i n g t h e C h a r a c t e r i s t i c s o f S e c o n d a r y S y n t h e t i c S l u d g e P r e p a r e d T h r o u g h o u t t h e E x p e r i m e n t 1 5 8 B 1 . 1 : A v e r a g e S y s t e m E f f l u e n t Q u a l i t y a n d R e m o v a l E f f i c i e n c y a t P s e u d o S t e a d y - s t a t e U n d e r D i f f e r e n t A l t e r n a t i v e s D u r i n g t h e A c c l i m a t i z a t i o n . . . 1 6 1 B 2 . 1 R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 1 U n d e r D i f f e r e n t A c c l i m a t i z a t i o n A l t e r n a t i v e s 1 6 4 B 2 . 2 R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 2 U n d e r D i f f e r e n t A c c l i m a t i z a t i o n A l t e r n a t i v e s 1 6 6 B 2 . 3 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 3 U n d e r D i f f e r e n t A c c l i m a t i z a t i o n A l t e r n a t i v e s 1 6 8 B 2 . 4 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 4 U n d e r D i f f e r e n t v i i i A c c l i m a t i z a t i o n A l t e r n a t i v e s. B 2 . 5 R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered A c c l i m a t i z a t i o n A l t e r n a t i v e s B 2 . 6 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered A c c l i m a t i z a t i o n A l t e r n a t i v e s B 2 . 7 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered A c c l i m a t i z a t i o n A l t e r n a t i v e s B 2 . 8 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered A c c l i m a t i z a t i o n A l t e r n a t i v e s C 1 . 1 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 C 1 . 2 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 C 1 . 3 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t N u m b e r e d R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 C 1 . 4 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 C 1 . 5 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 C 1 . 6 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered 6 Under D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 E x p e r i m e n t C 1 . 7 : R e s p o n s e Data o f t h e S a m p l i n g P o i n t Numbered 7 Under D i f f e r e n t i x 5 Under D i f f e r e n t 6 Under D i f f e r e n t 7 Under D i f f e r e n t 8 Under D i f f e r e n t 1 Under D i f f e r e n t E x p e r i m e n t 2 Under D i f f e r e n t E x p e r i m e n t 3 Under D i f f e r e n t E x p e r i m e n t 4 Under D i f f e r e n t E x p e r i m e n t 5 Under D i f f e r e n t E x p e r i m e n t 1 7 0 • 1 7 2 1 7 4 1 7 6 • 1 7 8 • 1 8 3 • 1 8 8 • 1 9 3 1 9 8 • 2 0 3 2 0 8 R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 E x p e r i m e n t 2 1 3 C 1 . 8 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 8 U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e S e q u e n c e 1 , 2 , a n d 3 E x p e r i m e n t 2 1 8 C 2 . 1 C a l c u l a t i o n o f t h e e f f e c t s ( S R a n d R R ) , I n t e r a c t i o n , P h a s e m e a n s , C h a n g e i n m e a n s , o n t h e R e s p o n s e P a r a m e t e r s d u r i n g t h e A c c l i m a t i z a t i o n ( S e q u e n c e 1 a n d 2 E x p e r i m e n t s ) 2 2 3 C 3 . 1 : p H o f A - a n d M - U A S B s D u r i n g t h e S e q u e n c e 2 a n d 3 E x p e r i m e n t s a s w e l l a s t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 6 0 C 3 . 2 : N a O H ( 0 . 1 N ) A d d i t i o n D u r i n g t h e S e q u e n c e 1 E x p e r i m e n t 2 6 2 D 1 . 1 S u m m a r y o f A v e r a g e S y s t e m P e r f o r m a n c e a n d R e m o v a l E f f i c i e n c y a t P s e u d o S t e a d y - s t a t e D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 6 4 D 2 . 1 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 1 D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 6 6 D 2 . 2 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 2 D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 6 8 D 2 . 3 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 3 D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 7 0 D 2 . 4 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 4 D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 7 2 D 2 . 5 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 5 D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 7 4 D 2 . 6 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 6 D i f f e r e n t R u n n i n g x C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 7 6 D 2 . 7 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 7 D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 7 8 D 2 . 8 : R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 8 D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 8 0 D 2 . 9 : A v e r a g e R e s p o n s e D a t a o f t h e S a m p l i n g P o i n t N u m b e r e d 1 t h r o u g h 8 a t P s e u d o S t e a d y - s t a t e U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 8 2 D 3 . 1 : C a l c u l a t i o n o f t h e T h e o r e t i c a l C H4 P r o d u c t i o n 2 8 7 D 4 . 1 : A M - U A S B s S y s t e m R e c o v e r y a t P s e u d o S t e a d y - s t a t e U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n s ( C H ,m3/m-d) 2 8 8 D 4 . 2 : A M - U A S B s S y s t e m R e c o v e r y a t P s e u d o S t e a d y - s t a t e U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n s ( C O D ( s o l . ) R e m o v a l E f f i c i e n c y , % ) 2 8 8 D 5 . 1 : R e s p o n s e D a t a o f G a s c o m p o s i t i o n , P r o d u c t i o n , L o a d i n g R a t e ( A - a n d M - U A S B s ) D u r i n g t h e A c c l i m a t i z a t i o n P r o c e s s 2 8 9 D 5 . 2 : R e s p o n s e D a t a o f G a s c o m p o s i t i o n , P r o d u c t i o n , L o a d i n g R a t e ( A - a n d M - U A S B s ) D u r i n g S e q u e n c e 1 , 2 , a n d 3 E x p e r i m e n t s 2 9 1 D 5 . 3 : R e s p o n s e D a t a o f G a s c o m p o s i t i o n , P r o d u c t i o n , L o a d i n g R a t e ( A U A S B ) D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 9 5 D 5 . 4 R e s p o n s e D a t a o f G a s c o m p o s i t i o n , P r o d u c t i o n , L o a d i n g R a t e ( M U A S B ) D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 2 9 7 x i L I S T O F F I G U R E S F i g u r e p a g e 1 . 1 R e s e a r c h S t r a t e g y a n d A p p r o a c h 4 2 . 1 P a t h w a y o f A n a e r o b i c B i o d e g r a d a t i o n t o s i m p l e c o m p o u n d s a n d o r g a n i c a c i d s 7 3 . 1 S c h e m a t i c F l o w D i a g r a m o f A T w o - p h a s e A n a e r o b i c S l u d g e D i g e s t i o n ( U A S B - U A S B ) P r o c e s s 2 4 3 . 2 D e t a i l e d D i m e n s i o n s o f U A S B R e a c t o r s U s e d i n t h e E x p e r i m e n t 2 4 3 . 3 P h o t o g r a p h s o f A B e n c h S c a l e T w o - p h a s e A n a e r o b i c S l u d g e D i g e s t i o n ( U A S B - U A S B ) P r o c e s s 2 5 3 . 4 C h a r a c t e r i s t i c s o f P r i m a r y S y n t h e t i c S l u d g e 3 0 3 . 5 C h a r a c t e r i s t i c s o f S e c o n d a r y S y n t h e t i c 3 0 3 . 6 C h a r a c t e r i s t i c s o f P r i m a r y S y n t h e t i c S l u d g e M o n i t o r e d T h r o u g h o u t t h e E x p e r i m e n t a l P r o g r a m 3 2 3 . 7 C h a r a c t e r i s t i c s o f S e c o n d a r y S y n t h e t i c S l u d g e M o n i t o r e d T h r o u g h o u t t h e E x p e r i m e n t a l P r o g r a m 3 2 4 . 1 A S c h e m a t i c F l o w D i a g r a m o f E x p e r i m e n t a l D e s i g n s 3 6 4 . 2 S a m p l i n g P r o g r a m : R e s p o n s e P a r a m e t e r s , S a m p l i n g P o i n t , a n d F r e q u e n c y , P r e s e r v a t i o n a n d S t o r a g e 3 8 5 . 1 A n A c c l i m a t i z a t i o n W a s h o u t P h e n o m e n o n 5 2 5 . 2 S y s t e m R e m o v a l E f f i c i e n c y D u r i n g A c c l i m a t i z a t i o n 5 2 x i i 5.3 VFA Removal Efficiency of the M-UASB 54 5.4 Effluent VFAs of the M-UASB 54 5.5 Surface Responses of Sequence 1 Experiment 65 5.6 NaOH (0.1 N) Addition During the Sequence 1 Experiment 67 5.7 System Responses and Performance of Sequence 1 Experiment 68 5.8 COD (soluble) Profiles Along the Reactor Height Under Different Running Conditions 76 5.9 Total VFA Profiles Along the Reactor Height Under Different Running Conditions 77 5.10 MLVSS Profiles Along the Reactor Height Under Different Running Conditions 78 5.11 A M-UASB Step-loading and Removal Efficiency During the System Maximization 86 5.12 Aciddogenic Phase of Glucose Formation under Low and High H2 Partial Pressure to form Acetic Acids, Propionic Acids, H, Gas, and CO2 87 5.13 A M-UASB System Effluent Qualities During the System Maximization 88 5.14 A M-UASB Nutrients and MLVSS During the System Maximization 89 5.15 System Optimum Operating Region and Maximum Capacity 92 5.16 A M-UASB Step-loading and Removal Efficiency During the System Recovery 96 5.17 A M-UASB System Recovery Process 97 5.18 A M-UASB Nutrients and MLVSS During the System Recovery 98 xiii 5 . 1 9 A M - U A S B S y s t e m R e c o v e r y a t P s e u d o S t e a d y - s t a t e C O D ( s o l u b l e ) r e m o v a l e f f i c i e n c y 1 0 1 5 . 2 0 A M - U A S B S y s t e m R e c o v e r y a t P s e u d o S t e a d y - s t a t e ( C H4 G a s P r o d u c t i o n ) 1 0 2 5 . 2 1 A P r e d i c t e d M - U A S B S y s t e m R e c o v e r y W i t h D i f f e r e n t R u n n i n g C o n d i t i o n s 1 0 3 5 . 2 2 A n E s t i m a t i o n o f E x p e r i m e n t a l K i n e t i c s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 1 0 8 5 . 2 3 A P r e d i c t e d O p t i m u m O p e r a t i n g H R T D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 1 1 2 5 . 2 4 A N A - U A S B S y s t e m E f f l u e n t Q u a l i t i e s D u r i n g t h e M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 1 1 7 5 . 2 5 C o m p a r i s o n o f T o t a l V F A A l o n g t h e H e i g h t o f M - U A S B D u r i n g t h e A c c l i m a t i z a t i o n 1 2 7 5 . 2 6 C O D ( s o l . ) P r o f i l e o f a T w o - p h a s e U A S B - U A S B P r o c e s s D u r i n g M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 1 2 9 5 . 2 7 p H V a r i a t i o n o f A - U A S B a n d M - U A S B D u r i n g t h e S e q u e n c e 2 / 3 E x p e r i m e n t s a n d M a x i m i z a t i o n a n d R e c o v e r y P e r i o d 1 3 2 B 1 . 1 : E f f l u e n t Q u a l i t i e s o f t h e M - U A S B ( C O D , M L V S S , PO4-P, T K N I T P ) U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n s D u r i n g t h e A c c l i m a t i z a t i o n 1 8 0 B 2 . 1 : S y s t e m G a s P r o d u c t i o n a n d L o a d i n g R a t e U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n D u r i n g t h e A c c l i m a t i z a t i o n 1 8 1 x i v D1.1 : An A-UASB Step-loading and Removal Efficiency (COD,P04-P) Under Different Running Conditions During the Maximization and Recovery Period 299 D2.1 : An A-UASB System Nutrients and MLVSS Under Different Running Conditions During the Maximization and Recovery Period 300 xv A C K N O W L E D G E M E N T S I w i s h t o t a k e t h i s o p p o r t u n i t y t o e x p r e s s m y s i n c e r e t h a n k s f o r t h e m o r a l e , e n c o u r a g e m e n t , a n d u n d e r s t a n d i n g r e c e i v e d f r o m m y w i f e , L a d d a a n d m y parents t h r o u g h o u t t h e c o m p l e t i o n o f m y r e s e a r c h . I a l s o w o u l d l i k e t o e x t e n d m y a p p r e c i a t i o n t o t h e f o l l o w i n g , w h o e n t h u s i a s t i c a l l y supported a n d e n c o u r a g e d m e i n o n e w a y o r another D r . D . S . M a v i n i c , m y a d v i s o r a n d Head o f t h e E n v i r o n m e n t a l E n g i n e e r i n g G r o u p , U . B . C . a n d D r . V . L o , C o - a d v i s o r a n d Head o f t h e B i o - R e s o u r c e E n g i n e e r i n g , U . B . C . f o r t h e i r c r i t i c a l t e c h n i c a l a d v i c e a n d f a i t h f u l s u p p o r t t h r o u g h o u t t h e c o m p l e t i o n o f t h e r e s e a r c h . D r . W . K . O l d h a m , H e a d o f t h e C i v i l E n g i n e e r i n g Department a n d D r . K . H a l l , W a s t e w a t e r R e s e a r c h C e n t r e f o r t h e i r i n v a l u a b l e c o m m e n t s a n d a d v i c e d u r i n g t h e preparation o f t h e r e s e a r c h p r o p o s a l a n d t h e s i s . S u s a n L i p t a k , M a n a g e r o f t h e E n v i r o n m e n t a l E n g i n e e r i n g L a b o r a t o r y , U . B . C . , P a u l a P a r k i n s o n a n d R o m y L o f o r t h e i r u n d e r s t a n d i n g , a s s i s t a n c e , a n d g u i d a n c e o f a l l a n a l y s i s i n v o l v e d i n t h e r e s e a r c h . x v i G u y K i r s c h , C i v i l E n g i n e e r i n g W o r k s h o p T e c h n i c i a n , f o r h i s s u g g e s t i o n a n d a s s i s t a n c e i n b u i l d i n g a n d f i x i n g a l l t h e c o m p o n e n t s o f t h e e x p e r i m e n t a l s y s t e m r e a c t o r s . P a n a g i o t i s ( T a k i s ) E l e f s i n i o t i s , P h . D c a n d i d a t e i n t h e E n v i r o n m e n t a l E n g i n e e r i n g G r o u p , U . B . C . f o r h i s t r u e f r i e n d s h i p , e n c o u r a g e m e n t , a n d t e c h n i c a l a s s i s t a n c e . F i n a l l y , I w o u l d l i k e t o s i n c e r e l y t h a n k m y s p o n s o r s h i p , C a n a d i a n I n t e r n a t i o n a l D e v e l o p m e n t A g e n c y ( C I D A ) a n d m y e m p l o y e r , T h a i l a n d N a t i o n a l E n v i r o n m e n t a l B o a r d ( N E B ) . W i t h o u t t h e s e s p o n s o r s , t h i s r e s e a r c h w o u l d n o t h a v e b e e n p o s s i b l e . x v i i L I S T O F A B B R E V I A T I O N S U A S B - U A S B A T w o - p h a s 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 P r o c e s s A - U A S B A c i d - p h a s 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 R e a c t o r M - U A S B M e t h a n e - p h a s 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 R e a c t o r R R I n t e r n a l R e c y c l e R a t i o S R F e e d S l u d g e R a t i o H R T / € H y d r a u l i c R e t e n t i o n T i m e S R T S o l i d s R e t e n t i o n T i m e R S M R e s p o n s e S u r f a c e M e t h o d M L G H M u l t i p l e L i n e a r R e g r e s s i o n H y p o t h e s i s I n N a t u r a l l o g a r i t h m C O D C h e m i c a l O x y g e n D e m a n d M L V S S M i x e d L i q u e u r V o l a t i l e S u s p e n d e d S o l i d s T S T o t a l S o l i d s T V S T o t a l V o l a t i l e S o l i d s T S S T o t a l S u s p e n d e d S o l i d s T V S S T o t a l V o l a t i l e S u s p e n d e d S o l i d s T P T o t a l P h o s p h o r u s x v i i i TKN Total Kjeldahl Nitrogen P04-P Ortho-Phosphorus NH4-N Ammonia Nitrogen VFA Volatile Fatty Acid HAc Acetic acid HPr Propionic acid HBu Butyric acid HVr Valeric acid mg/L Part per million hrs. Hours ml vfil1i—litre Lid Litre per day OHPA Obligate Hydrogen Producing Acetogens Rh Hydrolysis rate Kh First-order hydrolysis constant F Effluent Particulate COD concentration, mass/vol. Fo Influent Particulate COD concentration, mass/vol. k Maximum rate of substrate utilization per unit weight of microorganisms, time1 Ks Half velocity coefficient, mass/vol, equal to substrate concentration when BL/St = (1/2)k L Influent Substrate mass concentration, mass/vol. xix Le Effluent Substrate mass concentration, mass/vol. 6S/6t Net growth rate of microorganisms, mass/vol-time a Growth yield coefficient, mass/mass 6L/6t Substrate utilization rate, mass/vol-time b Microorganisms decay coefficient, time1 S Microbial mass concentration, mass/vol. V Reactor Volume Q Flow rate RCOD System COD (sol.) removal efficiency, % System P04-P removal efficiency, % RCH4 CH4 gas production, m31-d HRTAUB Hydraulic retention time of A-UASB HRTMUASB Hydraulic retention time of M-UASB HRTSY,ICA1 Hydraulic retention time of system xx C H A P T E R O N E I N T R O D U C T I O N L i R E S E A R C H N E E D S A N D B A C K G R O U N D M a n y w a s t e w a t e r t r e a t m e n t p r o c e s s e s , w h e t h e r p r i m a r y o r s e c o n d a r y , y i e l d l a r g e q u a n t i t i e s o f w a s t e m a t e r i a l s i n t h e f o r m o f a d i l u t e s o l i d m i x t u r e , k n o w n a s s l u d g e ; t h i s s l u d g e u s u a l l y c o n t a i n s a s i g n i f i c a n t a m o u n t o f o r g a n i c w a s t e s . T r e a t m e n t a n d d i s p o s a l o f t h i s s l u d g e i s r e c o g n i z e d a s o n e o f t h e m o s t c r i t i c a l a r e a s o f w a t e r p o l l u t i o n c o n t r o l , a n d a c c o u n t s f o r a l m o s t 4 0 - 5 0 % o f t h e t o t a l c a p i t a l a n d o p e r a t i n g c o s t s a t a 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 t . ( U . S . E P A 1 9 7 9 ; G l o y n a , 1 9 8 2 ; B e n e f i e l d , 1 9 8 0 ) . A n a e r o b i c s l u d g e s t a b i l i z a t i o n i s o n e o f t h e m o s t s u c c e s s f u l a n d p r o m i s i n g t r e a t m e n t p r o c e s s e s , e x h i b i t i n g s e v e r a l s i g n i f i c a n t a d v a n t a g e s o v e r a e r o b i c s t a b i l i z a t i o n : r e d u c t i o n o f p a t h o g e n i c o r g a n i s m s a n d s l u d g e p r o d u c t i o n , s a v i n g o n a i r s u p p l y , p r e v e n t i o n o f n u i s a n c e - o d o u r c o n d i t i o n s a f t e r d i g e s t i o n , a n d f o r m a t i o n o f h i g h m e t h a n e c o n t e n t i n t h e g a s p r o d u c t i o n ( P o h l a n d , 1 9 7 5 ) . W i t h a n i n c r e a s e i n w o r l d w i d e e n e r g y c o s t s d u r i n g t h e l a s t 2 0 y e a r s , t h e a d v a n t a g e o f p r o d u c i n g h i g h l y r e c o v e r a b l e m e t h a n e ( s e r v i n g a s a n a d d i t i o n a l e n e r g y s o u r c e ) h a s a t t r a c t e d a g r e a t d e a l o f r e s e a r c h e f f o r t , m a i n l y t o i n c r e a s e t h e a b i l i t y a n d r e l i a b i l i t y o f t h i s p r o c e s s . H o w e v e r , m a n y u n a n s w e r e d p r o b l e m s s t i l l e x i s t i n s t a b i l i z i n g s e w a g e s l u d g e a n a e r o b i c a l l y , e s p e c i a l l y u s i n g c o n v e n t i o n a l , t w o - s t a g e , c o m p l e t e l y - m i x e d d i g e s t e r s . T h e s e i n c l u d e p o o r s u p e r n a t a n t q u a l i t y , w h i c h g e n e r a l l y r e q u i r e s f u r t h e r t r e a t m e n t , a n d t h e r e l a t i v e l y l o w l e v e l o f m e t h a n e p r o d u c t i o n p o s s i b l e u n d e r t h i s c o n v e n t i o n a l t w o - s t a g e t r e a t m e n t . T o h e l p s o l v e t h e s e p r o b l e m s , t w o b r o a d a p p r o a c h e s c a n b e e m p l o y e d : ( i ) 2 increase bacterial activity by creating optimum digester operating conditions and ensuring an adequate supply of all known essential nutrients; (ii) increase the density of bacterial populations in the digesters ( Callander, 1983 ). The former approach incorporates the basic mechanism of anaerobic sludge stabilization, which is, in fact, a di-phasic process - acidogenesis and methanogenesis. Therefore, providing an optimal environmental conditions ( adequate supply of nutrients ) for each predominant group of bacteria in the two-phase system is expected to enhance both the methane yield and increase the process performance and reliability (Pohiand and Ghosh, 1971a; Massey, 1978; Cohen, 1979; and Bull, 1984). The second approach aims at maintaining or increasing the hiomass and retaining it within the digester for a longer period of time, while undergoing stabilization. This can be achieved by a careful design of the floe-based digester with an appropriate sludge recycle ratio (RR). The Upflow Anaerobic Sludge Blanket (UASB) process is one of the most promising processes of the floe-based system digesters. With careful design, it can retain and increase biomass within the digester, without any additional mixing requirements. The purpose of this research was to initiate a feasibility study for enhancing the efficiency of anaerobic sludge stabilization and increase the quality level of the final supernatant through development of a modified design criteria, start-up process, and operation of a two-phase, upflow anaerobic sludge stabilization (UASB-UASB) process. 1.2 RESEARCH OBJECTIVES AN]) APPROACH The principle goals were to evaluate the feasibility, effectiveness, and suitability 3 of this two-phase, UASB-UASB process for anaerobic sludge stabilization. The primary objectives were to achieve superior supernatant quality and to maximize % methane content and production, through a two-phase separation (UASB-UASB) process. Secondary objectives included identifying the optimum operating conditions, examining the effects of influent Sludge Ratio (SR) of primary to secondary sludges and Recycle Ratio (RR) of fluidized sludge from sludge blanket portion of the reactor on process performance and gas production, and investigating the maximum acceptable loading rate and associated system recovery. Time permitting, other objectives included developing a set of system design criteria and determining effective and reliable parameters for indicating process failure and system steady state conditions. It is generally recognized that a research approach must be developed in the context of a particular situation. A” point-in-time statement “with a continuous flow of information (data sets of response parameters) as shown in Figure 1.1, represents a specific discrete work effort, which must be achieved prior to permitting continuance of further work tasks. As shown in Figure 1.1, emphasis was initially placed on the preparation of a realistic research proposal. It covered the whole range of problem identification, rationale, research objectives and approach, experimental program, as well as work schedule and cost estimation. After approval of the research proposal, two major tasks - synthetic sludge preparation and system design and construction, were carried out simultaneously; this was followed by system seeding and acclimatization requiring at least 40-60 days to reach steady-state conditions. The sampling program and response parameters were undertaken as shown in Figure 4.2. Along with each sequence of the •. .0..oKJ ..c: •::•::•::::: •s...o•.. .c-v••-•• £2. 11 CD -‘ CD CD Cr) CD C) CI) -I CD CD D 0 -o 0 C) •x... :..:......: •0... •‘<• g N .0 ...cD..:....:...D::: CD 0 •. •.. Cd) - G12 :::•::m:::::: •17 5experimental run, data analysis and results interpretation were made, using a spreadsheet software program (Symphony Version 1.2), Response Surface Method (RSM) and Yate’s Algorithm Method. The best known optimum operating condition that generated the maximum % methane content and production, with superior supernatant quality, was then identified ; whereas, system maximum loading capacity and the recovery process were carried out afterward. Finally, the feasibility and effectiveness of this two-phase UASB-UASB process, to stabilize the sludge anaerobically, together with the difficulties and problems faced throughout the experiment and their remedial actions ( shown in Table A1.1 of appendix A ), were conclusively evaluated and reported on. The details of each task are discussed in Chapter 4. 6CHAPTER TWO BACKGROUND AND BRIEF LITERATURE REVIEW The purpose of this chapter is to briefly overview and update theoretical concepts on anaerobic sludge digestion and process development. The review will be used as background to formulate a framework for further investigation and the experimental program. In case of any particular references that are closely related to the result of the research, they will be discussed separately in the main text of Chapter 5 - Results and Discussion. 2.1 ANAEROBIC SLUDGE DIGESTION (Biochemistry and Rate Liniitirig Step) The overall anaerobic conversion of biodegradable organic solids to the end products of carbon dioxide (C02) and methane (CH4) is initially believed to involve 3 processes which occur simultaneously: hydrolysis of insoluble biodegradable polymers; the production of fatty acids from smaller soluble organic molecules; and CH4 generation (Stronach, 1986). But Gujer and Zehnder (1983) proposed a six-step system in the anaerobic conversion of high molecular weight degradable organics to CH4 and CO2 as shown in Figure 2.1. Two groups of bacteria, acid- and methane- producing bacteria, are, in principle, responsible for the overall anaerobic conversion of biodegradable organics. Acid-producing bacteria are responsible for converting heterogeneous substrate into fatty acids. The primary acids produced during acid fermentation are acetic, propionic, and 7PROTEINS CARBOHYDRATES LIPIDS 1A lB 1C AMINO ACIDS HIGHER FATTY SUGARS ALCOHOLS 2 3 INTERMEDIARY PRODUCTS PROPIONATE BUTYRATE ETC 4 ACETATE HYDROGEN rMETHANE 6 1. Hydrolysis 2. Fermentation 3. Anaerobic (3) Oxidation 4. Anaerobic Oxidation 5. Decarboxylation of Acetate CH3 COO+ H2O —+ CH4 + HCO3 6. Hydrogen Oxidation CO+ 4H—+ CH4+ 2HzO Figure 2.1 Pathway of anaerobic biodegradation Source : After Gujer arid Zehnder, 1983 8 butyric; however, smaller quantities of formic, valeric, iso-valeric, and caproic acids are also frequently found (Malina, 1980). These acids are subsequently decomposed by methane-producing bacteria, resulting in the production of methane. Approximately 85% of the CH4 results from the fermentation of acetic and propionic acids with the remainder generated from primarily butyric and formic acids, as well as the reduction of CO2 by H2; some CH4 is generated from the fermentation of long-chain fatty acids via anaerobic (j3) oxidation (Stronach, 1986). The pathways for the formulation of CR4 are mostly dependent on the nature of influent substances and fall into three subgroups : lower fatty acids (C1-6,ie. formic, acetic, propionic, butyric etc.); normal or iso-alcohols (C1-5, ie. methanol, ethanol, propanol, butanol etc.); and inorganic compounds (ie. H2, CO, C02). The biochemistry of these basic reactions can be summarized as follows: (1) Biochemical decomposition of lower fatty acids: (1.1) Acetic acid decomposition CH3OOH — CH4 + CO2 (1) (1.2) Propionic acid decomposition Two-step requirement: 4CH3C2OOH + 2H0 — — 4CH3COOH + CO2 + 3CH4 (2) 4CH3COOH 4CR + 4C02 (3) Overall: 4CH3C2OOH + 2H0 5CO2 + 7CR4 (4) (1.3) Butyric acid decomposition Two-step requirement: 92CH3COOH + 2H0 + C O2 - — — b 4CH3COOH + CR4. ( 5 ) 4CH3COOH — 4 C R + 4 C 02 ( 6 ) O v e r a l l : 2CH3COOH + 2H0 —b 3 C O + 5 C R4 ( 7 ) ( 1 . 4 ) M i c r o b i a l r e d u c t i o n o f C O2 f o r m e d f r o m r e d u c t i o n C O + H20 — C O2 + H2 ( 8 ) C O2 + 4 H2 C H4 + 2H0 ( 9 ) C O + 2 H — C R4 + H2O ( 1 0 ) 4C2H5COOH + 8H2O — b 4CH3COOH + 4 C O2 + 2 4 H ( 1 1 ) 3 C O2 + 2 4 H — — - p 3 C H4 + 6H20 ( 1 2 ) 4C2H5COOH + 2RO - — - - - * 4CH3COOH + C O2 + 3 C H4 ( 1 3 ) CH3OOH — . C H + C O , ( 1 4 ) C o n v e r s i o n o f v o l a t i l e f a t t y a c i d s ( V F A s ) t o t h e p r o d u c t i o n o f C H4 i s c o n s i d e r e d t o b e a r a t e - l i m i t i n g s t e p f o r s o l u b l e o r g a n i c m a t t e r , w h e r e a s h y d r o l y s i s o f i n s o l u b l e o r g a n i c s i s b e l i e v e d t o b e a r a t e - l i m i t i n g s t e p f o r p a r t i c u l a t e m a t t e r ( E a s t m a n , 1 9 8 1 ; C o h e n , 1 9 8 3 ; a n d P a v l o s t a t h i s , 1 9 8 6 ) . 2 . 2 O P E R A T I N G P A R A M E T E R S A N D R E S P O N S E S A n a e r o b i c s t a b i l i z a t i o n i s r e c o g n i z e d a s a s e q u e n t i a l , d i - p h a s i c p r o c e s s : h y d r o l y s i s a n d a c i d o g e n e s i s , f o l l o w e d b y m e t h a n o g e n e s i s . P h a s e s e p a r a t i o n i s t h e n a l o g i c a l c h o i c e t o s t i m u l a t e t h e g r o w t h o f t h e s e t w o g r o u p s o f b a c t e r i a . A c i d - a n d m e t h a n e - p r o d u c i n g b a c t e r i a a r e s t r i c t a n a e r o b e s a n d e x t r e m e l y s e n s i t i v e t o c h a n g e s i n t e m p e r a t u r e a n d p H . 1 0 T h e s e b a c t e r i a a r e a c t i v e i n t w o temperature z o n e s : m e s o p h i l i c r a n g e ( 3 0 - 3 5 C ) a n d t h e r m o p h i l i c r a n g e ( 5 0 - 6 0 0 C ) . T h e o p t i m u m p H r a n g e f o r m e t h a n e - p r o d u c i n g b a c t e r i a i s 6 . 4 - 7 . 2 , w h e r e a s i t i s 5 . 5 f o r a c i d - p r o d u c i n g b a c t e r i a . A b o v e pH 8 o r b e l o w 6 , t h e g r o w t h o f methane f o r m e r s f a l l s r a p i d l y . A s u d d e n c h a n g e i n e n v i r o n m e n t a l c o n d i t i o n s a n d / o r a n i n t r o d u c t i o n o f t o x i c s u b s t a n c e s i n t o t h e s y s t e m , m a y c a u s e t h e i m b a l a n c e d g r o w t h rate o f t h e s e t w o g r o u p s o f b a c t e r i a . O n c e t h e b a l a n c e i s u p s e t , i n t e r m e d i a t e o r g a n i c a c i d s a c c u m u l a t e a n d t h e p H d r o p s . A s a r e s u l t , t h e m e t h a n o g e n s a r e f u r t h e r i n h i b i t e d a n d t h e p r o c e s s e v e n t u a l l y f a i l s , u n l e s s c o r r e c t i v e m e a s u r e s a r e t a k e n . T h i s i m b a ’ a n c e c a n b e i n d i c a t e d b y v a r i o u s p a r a m e t e r s : a n i n c r e a s e i n % CO2 c o n t e n t o f t h e g a s p r o d u c e d a n d a c o r r e s p o n d i n g d e c r e a s e i n % CH4 c o n t e n t ; a d e c r e a s e i n t h e pH a n d t o t a l d a i l y q u a n t i t y o f g a s p r o d u c e d ; a n i n c r e a s e i n t h e c o n c e n t r a t i o n o f V F A s ; a n o v e r a l l d e c r e a s e i n t h e e f f i c i e n c y o f w a s t e s t a b i l i z a t i o n ; a n d t h e r a t i o o f v o l a t i l e a c i d s / a l k a l i n i t y > 0 . 5 (Graef a n d A n d r e w s , 1 9 7 4 a / b ; U S . E P A , 1 9 7 9 ) . T o x i c m a t e r i a l s a n d other m a t t e r s c a n a l s o u p s e t t h e s y s t e m ; t h e s e i n c l u d e o x y g e n , v o l a t i l e a c i d s ( 2 , 0 0 0 m g / L ) , t o t a l NH3-N ( 1 , 5 0 0 - 3 , 0 0 0 m g / L a t p H 7 . 4 - 7 . 6 o r > 3 , 0 0 0 m g / L a t a n y pH v a l u e s ) , a n d s o l u b l e m e t a l s e g . 3 m g / L C r , 2 m g / L N i , 1 m g / L Z n , a n d 0 . 5 m g / L C u . H o w e v e r , i f s u f f i c i e n t t i m e i s a v a i l a b l e , m e t h a n e - p r o d u c i n g b a c t e r i a c a n a c c l i m a t i z e t o t h e t o x i c m a t e r i a l s ( S t r o n a c h , 1 9 8 6 ; M a l i n a , 1 9 8 0 ; C a p r i , 1 9 7 5 ; Z i e k e f o o s e , 1 9 7 6 ; K u j e l m a n , 1 9 8 1 ; G r a e f , 1 9 7 4 ; C o r t i n o v i s , 1 9 8 4 ; U S . E P A , 1 9 7 9 ; C h i u - y u e , 1 9 8 6 ) . I n a t y p i c a l a n a e r o b i c s l u d g e d i g e s t e r , a p p r o x i m a t e l y 7 2 % o f t h e m e t h a n e p r o d u c e d e v o l v e s t h r o u g h a c e t a t e s p l i t t i n g , a n d t h e remainder c o m e s f r o m t h e r e d u c t i o n o f C O , w i t h H2 ( J e r i s a n d M c C a r t y , 1 9 6 5 ) . H y d r o g e n i s t h e n a n important i n t e r m e d i a t e 11 in methanogenesis and a build up of hydrogen may alter the electron flow during fermentation of carbohydrates and other polymers. Accumulation of hydrogen further inhibits other important intermediates being formed during anaerobic sludge digestion, such as propionate and butyrate (Scheifinger and Wolin, 1972; Chung, 1976; Kasper and Wuhrmann, 1978). Therefore, Mosey, (1983a) has suggested that hydrogen gas might be a simpler and more effective prime indicator for monitoring the anaerobic digestion process. However, Hickey, (1987) concluded that there appeared to be some limitations on the potential of using hydrogen as a prime indicator of process upset, resulting from the application of organic toxicants. He found that severe inhibition of methane production occurred at high organic loading rates, resulting in an accumulation of hydrogen and VFA’s; however, at lower loading rates, inhibition was less severe and hydrogen accumulation was slightly above controls. He finally recommended monitoring hydrogen, in consert with other conventional process indicators, would provide an effective indication of process upset due to toxic shocks. 2.3 ANAEROBIC PROCESS DEVELOPMENT (Stability/Performance/Kinetics) Anaerobic process development has recently advanced in two directions: improvement of the gas yield and satisfactory substrate removal efficiency, while, at the same time, minimizing the system capital and operating costs. A thorough investigation of the best “system operating condition” is necessary to achieve the goals of process development. 1 2 A r a p i d e s c a l a t i o n e n e r g y s h o r t a g e s a n d h e i g h t e n e d e n v i r o n m e n t a l a w a r e n e s s h a v e i n c r e a s e d t h e p r e s s u r e t o i m p r o v e a n a e r o b i c d i g e s t i o n p e r f o r m a n c e w h e r e a p p l i c a b l e a n d f e a s i b l e . T w o b r o a d a p p r o a c h e s a r e g e n e r a l l y e m p l o y e d - o n e p r o v i d i n g p r e f e r a b l y o p t i m u m e n v i r o n m e n t a l c o n d i t i o n s f o r e a c h g r o u p o f b a c t e r i a a n d t h e other c o n c e r n e d w i t h i n c r e a s i n g b a c t e r i a p o p u l a t i o n d e n s i t y a n d r e t a i n i n g i t w i t h i n t h e d i g e s t e r . T h e f o r m e r approach c a n b e a c h i e v e d t h r o u g h t h e u s e o f t w o - p h a s e a n a e r o b i c d i g e s t i o n , w i t h a n adequate s u p p l y o f n u t r i e n t s . T h e latter o n e c a n a l s o b e a c c o m p l i s h e d t h r o u g h a n i n c r e a s e i n t h e s y s t e m S R T b y m e a n s o f s o l i d - l i q u i d s e p a r a t i o n a n d appropriate s l u d g e r e c y c l e . Either f l o c - b a s e d ( suspension) o r a n a t t a c h e d - f i x e d f i l m s y s t e m c a n i n c r e a s e d i g e s t i o n p e r f o r m a n c e a n d p r o v i d e s p r o m i s i n g r e s u l t s ( C a l l a n d e r , 1 9 8 3 ) . T w o - p h a s e a n a e r o b i c s t a b i l i z a t i o n i s c a p a b l e o f p r o v i d i n g t h e o p t i m u m c o n d i t i o n s f o r t h e g r o w t h o f b o t h a c i d - a n d m e t h a n e - f o r m e r s , t h e latter p r e f e r r i n g w i d e l y d i f f e r e n t e n v i r o n m e n t a l c o n d i t i o n s f r o m t h e f o r m e r . T h e m e r i t s o f t h i s p r o c e s s a r e a n i n c r e a s e i n t h e p r o d u c t i o n rate o f CH4, m a x i m u m l o a d i n g r a t e s f o r t h e m e t h a n e - p h a s e r e a c t o r , a d e c r e a s e i n r e c o v e r y t i m e a f t e r s h o c k l o a d i n g , a n d e n h a n c e m e n t o f p r o c e s s e f f i c i e n c y a n d r e l i a b i l i t y ( P o h i a n d a n d G h o s h , 1 9 7 1 ; C o h e n , 1 9 7 9 ; M a s s e y e t a l . , 1 9 7 8 ) . A l t h o u g h a two p h a s e s t a b i l i z a t i o n p r o c e s s s e e m s b e s t s u i t e d f o r t h e treatment o f s o l u b l e - t y p e w a s t e w a t e r s p r o d u c i n g a h i g h p o t e n t i a l f o r v o l a t i l e a c i d s a c c u m u l a t i o n ( P i p y n e t a l . , 1 9 7 9 ; G h o s h e t a l . , 1 9 8 1 ; G h o s h e t a l . , 1 9 8 3 a ) , s u p e r i o r p e r f o r m a n c e h a s a l s o b e e n d e m o n s t r a t e d f o r p a r t i c u l a t e - t y p e s u b s t r a t e s s u c h a s s e w a g e s l u d g e a n d a g r i c u l t u r a l w a s t e s ( G h o s h , 1 9 8 3 b ; K e e n a n , 1 9 7 6 ; N o r m a n n , 1 9 7 7 ; R i j k e n s , 1 9 8 1 ; Datta, 1 9 8 1 ; C o l l e r a n , 1 9 8 3 ) . 1 3 T h e l i m i t i n g s t e p i n a n a e r o b i c s t a b i l i z a t i o n o f c o m p l e x o r g a n i c m a c r o m o l e c u l e s , s u c h a s c o n t a i n e d i n s e w a g e s l u d g e , i s h y d r o l y s i s - a c i d i f i c a t i o n , w h e r e a s f o r s t a b i l i z a t i o n o f s h o r t e r c h a i n s o l u b l e o r g a n i c s w a s t e w a t e r , i t i s m e t h a n o g e n e s i s . P h a s e - s e p a r a t e d d i g e s t i o n ( h y d r o l y s i s - a c i d i f i c a t i o n i n d e p e n d e n t o f m e t h a n o g e n e s i s ) h a s d e m o n s t r a t e d s e v e r a l p r a c t i c a l a d v a n t a g e s : b e t t e r s t a b i l i z a t i o n o f t h e s l u d g e a n d a g r e a t e r q u a n t i t y o f g a s , r e d u c e d d i g e s t i o n t i m e a n d r e d u c e d r e a c t o r s i z e ( G h o s h , 1 9 8 7 ; D i c h t l , 1 9 8 7 ) . P e r o t , ( 1 9 8 9 ) c o n c l u d e d t h a t t w o “ o p t i m i z e d ” s t e p s h a d s e v e r a l a d v a n t a g e s o v e r a s i n g l e - p h a s e d i g e s t e r : s t a r t - u p p e r i o d w a s n o t a s l o n g ( 4 5 d a y s i n s t e a d o f 7 5 f o r a s i n g l e - s t e p p r o c e s s ) ; h i g h e r v o l a t i l e m a t t e r d e g r a d a t i o n y i e l d ( 6 0 % i n s t e a d o f 4 0 % ) ; a n d t h e H R T c o u l d b e h a l f o f t h a t o f t h e s i n g l e - s t e p p r o c e s s , w i t h o u t r i s k i n g t h e s y s t e m g a s p r o d u c t i o n a n d p e r f o r m a n c e . H e a l s o i n d i c a t e d t h a t g a s p r o d u c t i o n w a s l i n k e d p r i m a r i l y t o t h e q u a n t i t y 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 t e r . A n o t h e r p r o m i s i n g a p p r o a c h t o e n h a n c e t h e a n a e r o b i c s l u d g e s t a b i l i z a t i o n p r o c e s s i s t o i n c r e a s e t h e d e n s i t y o f b a c t e r i a i n t h e s y s t e m a n d r e t a i n i t w i t h i n t h e d i g e s t e r , w i t h a d e q u a t e s u p p l y o f n u t r i e n t s . T h i s c a n b e d o n e b y a n a p p r o p r i a t e d e s i g n a n d s e l e c t i o n o f a p r o p e r a n a e r o b i c s t a b i l i z a t i o n p r o c e s s a n d r e c y c l e r a t i o . O n e o f t h e m a i n c r i t i c i s m s o f a n a e r o b i c w a s t e t r e a t m e n t i s t h e d i f f i c u l t y o f r e t a i n i n g a s u f f i c i e n t a m o u n t o f a c t i v e a n a e r o b i c s l u d g e u 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 s i n g t h e p r e s e n t a n a e r o b i c t r e a t m e n t t e c h n o l o g y . R e c e n t l y , t h i s d i f f i c u l t y h a s b e e n a d d r e s s e d t h r o u g h t h e d e v e l o p m e n t o f 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 s ( H o l s o f f - P o l e t a l . , 1 9 8 6 ) . 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 ) t e c h n o l o g y i s c r e d i t e d a s a n e f f e c t i v e p r o c e s s i n s t a b i l i z i n g s o l u b l e o r g a n i c w a s t e , a s w e l l a s p r o d u c i n g s u p e r i o r s u p e m a t a n t 1 4 q u a l i t y w i t h o u t a n y m i x i n g r e q u i r e m e n t s . I t a l s o p r o v i d e s t h e a d v a n t a g e o f d e v e l o p i n g a n d r e t a i n i n g a h i g h l y s e t t l e a b l e b i o m a s s w i t h i n t h e d i g e s t e r k n o w n a s “ s l u d g e b l a n k e t ” ; t h i s i s a g r a n u l a r s l u d g e m e d i a , w i t h h i g h s e t t l e a b i l i t y a n d m e t h a n o g e n i c a c t i v i t y . T h i s b i o m a s s d e c o m p o s e s t h e V F A ’ s g e n e r a t e d f r o m h y d r o l y s i s - a c i d o g e n e s i s f o r t h e p r o d u c t i o n o f C H4,C02, a n d s m a l l a m o u n t s o f N2,H2, e t c . T h e r i s i n g g a s e s a n d i n f l u e n t f l o w r a t e a r e s i g n i f i c a n t f a c t o r s i n m a i n t a i n i n g b i o m a s s g r a n u l e s a n d f l o c s i n m o r e - o r - l e s s f l u i d i z e d s t a t e s , a n d t h e r e s u l t i n g t u r b u l e n c e a l s o a i d s i n d e t a c h i n g g a s b u b b l e s f r o m f l o c s i n t h e u p p e r p a r t o f t h e d i g e s t e r . T h e b i o g a s i s r e m o v e d b y a t h r e e - p h a s e , g a s / l i q u i d s / s o l i d s s e p a r a t o r ( G S S - d e v i c e ) a t t h e t o p o f t h e r e a c t o r ( F i g u r e s 3 . 1 - 3 . 2 ) , w h o s e m a i n f u n c t i o n s a r e t o r e t a i n a h i g h l y s e t t l e a b l e b i o m a s s w i t h i n d i g e s t e r a n d a l s o t o p r o v i d e a n e f f e c t i v e s e p a r a t i o n o f t h e g a s p r o d u c e d d u r i n g s t a b i l i z a t i o n a s w e l l a s t o r e t u r n t h e d i s p e r s e d s l u d g e b a c k t o t h e s l u d g e b e d s i t u a t e d b e l o w t h e G S S - d e v i c e ( w i t h t h e h e l p o f 5 0 w a l l o f t h e s e t t l e r ) . A g a s - f r e e z o n e a b o v e t h e c o l l e c t o r a l l o w s f o r t h e s e t t l i n g o f f i n e l y - d i s p e r s e d s o l i d s t o t h e r e a c t o r b o t t o m , w h i l e c l a r i f i e d e f f l u e n t e x i t s f r o m t h e t o p . A s i m p l e b a f f l e a r r a n g e m e n t c a n a s s i s t i n r e t a i n i n g b i o m a s s w i t h i n t h e d i g e s t e r , t h r o u g h t h e c r e a t i o n o f a q u i e s c e n t r e g i o n ; a s s u c h , e n t r a i n e d f l o c s s e p a r a t e f r o m t h e l i q u i d b e f o r e i t l e a v e s t h e d i g e s t e r v i a a n u m b e r o f w e i r s . ( L e t t i n g a , 1 9 8 0 ) . T o d a t e , i t i s n o t k n o w n w h i c h f a c t o r s t r i g g e r t h e g r o w t h a n d d e v e l o p m e n t o f g r a n u l a r s l u d g e , i n c l u d i n g h o w a n d w h e n t h i s b i o m a s s w i l l d e v e l o p . D o l f i n g , ( 1 9 8 6 ) s u g g e s t e d t h a t a c e t o c l a s t i c M e t h a n o t h r i x - l i k e o r g a n i s m s p l a y a n i m p o r t a n t r o l e i n d e t e r m i n i n g w h i c h t y p e o f s l u d g e w o u l d d e v e l o p u n d e r m e t h a n o g e n i c c o n d i t i o n s . H e a l s o s u g g e s t e d t h a t e x t r a c e l l u l a r m a t e r i a l u n d o u b t e d l y p l a y e d a m a j o r r o l e a s a m a t r i x , w h i c h 1 5 k e p t t h e c e l l t o g e t h e r . P h o s p h o r u s a n d s o d i u m m a y a l s o i n f l u e n c e t h e f i l a m e n t l e n g t h o f M e t h a n o t h r i x - l i k e o r g a n i s m s a s t h e y h a v e o n t h e f i l a m e n t l e n g t h o f M e t h a n o s p i r i l l u m h u n g a t e i ( P a t e l , 1 9 7 9 ) . T h e s l u d g e g r a n u l a t i o n p r o c e s s g e n e r a l l y i n v o l v e s 3 s e q u e n t i a l p r o c e s s e s : s t a r t - u p , s a y w i t h a l o a d i n g r a t e u p t o 5 k g C O D / m3-d; t h e n g r a n u l a t i o n s l u d g e a p p e a r a n c e a n d f l o c - f o r m e d s l u d g e w a s h o u t p r o c e s s ; a n d f i n a l l y c o n t i n u e d f o r m a t i o n o f g r a n u l e s u n d e r a v o l u m e t r i c l o a d i n g r a t e u p t o 1 6 k g C O D / m3-d ( L e t t i n g a , 1 9 8 6 ; W u , 1 9 8 5 ) . C u l t i v a t i o n o f t h e g r a n u l a r s l u d g e c a n b e o b t a i n e d t h r o u g h a c a r e f u l s e l e c t i o n o f o r g a n i c s , w i t h a n o p t i m u m C O D : N r a t i o o f b e t w e e n 3 0 t o 5 5 : 1 . A d d i t i o n s o f N i , C o , M o , a n d Z n S O4 i n t o t h e d i g e s t e r a l s o y i e l d e d p o s i t i v e e f f e c t s ( H u l s o f f - P o l , 1 9 8 6 ; W u , 1 9 8 5 ) . T h e g r a n u l a r s l u d g e b e g i n s t o a p p e a r a t a C O D l o a d i n g r a t e o f a p p r o x i m a t e l y 0 . 6 k g C O D / k g V S S - d o r h i g h e r , a f t e r w h i c h t h e g r a n u l a t i o n p r o c e s s d e v e l o p s v e r y q u i c k l y . T h e o p t i m u m c o n d i t i o n s f o r c u l t i v a t i o n c a n b e a c h i e v e d u n d e r e l e v a t e d m e s o p h i l i c c o n d i t i o n s ( 3 0 - 5 0 C C ) , a p H i n e x c e s s o f 6 . 5 - 7 . 2 , s u f f i c i e n t b u f f e r i n g c a p a c i t y , a n d t h e a b s e n c e o f i n h i b i t o r y a n d t o x i c s u b s t a n c e s s u c h a s N a , K , a n d NH3-N; t h e s e s u b s t a n c e s s h o u l d b e l o w e r t h a n 3 , 5 0 0 , 2 , 5 0 0 , a n d 1 , 7 0 0 m g / L r e s p e c t i v e l y ( W u , 1 9 8 5 ) . W i e g a n t ( 1 9 8 5 ) a l s o s t r e s s e d t h a t a s u p e r f i c i a l b i o g a s l o a d i n g r a t e ( b i o g a s v e l o c i t y , m / h r ) w a s a n i m p o r t a n t f a c t o r i n t h e g r a n u l a t i o n a n d s e l e c t i o n p r o c e s s . A p p r o p r i a t e s t a r t - u p l o a d i n g r a t e s p l u s t h e a d d i t i o n o f C a + h a v e a l s o p r o v e n t o b e b e n e f i c i a l t o t h e s l u d g e f l o c c u l a t i o n a n d t h i c k e n i n g p r o c e s s . C a i l a n d B a r f o r d ( 1 9 8 6 ) s t a t e d t h a t t h e p r e s e n c e o f C a i n t h e r a n g e o f u p t o 1 5 0 m g / L s t i m u l a t e d s l u d g e g r a n u l e f o r m a t i o n a n d t h i c k e n i n g . A l s o , M a h o n e y ( 1 9 8 7 ) f o u n d t h a t t h e s l u d g e g r a n u l e s f o r m e d i n s i d e t h e r e a c t o r w i t h c a l c i u m a d d i t i o n , s e t t l e d 3 - 4 t i m e s f a s t e r t h a n t h a t w i t h o u t 1 6 c a l c i u m a d d i t i o n . A h i g h r a t e o f b i o m a s s a c c u m u l a t i o n w a s a l s o e v i d e n t i n t h e c a l c i u m - p o s i t i v e r e a c t o r . A n o p t i m u m s t a r t - u p p r o c e s s , i n v o l v i n g f a v o u r a b l e c o n d i t i o n s f o r t h e f l o c c u l a t i o n / g r o w t h / h i g h s e t t l e a b i l i t y a n d s p e c i f i c a c t i v i t y o f t h e b i o m a s s s l u d g e , a r e t h e m a i n p r e r e q u i s i t e s i n a c h i e v i n g s u c c e s s f u l t r e a t m e n t w i t h h i g h l o a d i n g r a t e s i n t h e U A S B p r o c e s s . T h e l o a d i n g p o t e n t i a l o f a U A S B c a n b e m a x i m i z e d t h r o u g h a c a r e f u l c o n s i d e r a t i o n o f a n a p p r o p r i a t e d e s i g n f o r u n i f o r m f e e d i n l e t s , a 5 0 0 a n g l e i n c l i n e d - w a l l s e t t l e r , w i t h a s u r f a c e l o a d i n g v e l o c i t y o f l e s s t h a n 0 . 7 m / h r , a n d a n a v e r a g e f l o w t h r o u g h t h e a p e r t u r e b e t w e e n g a s c o l l e c t o r s b e l o w 2 . 0 r n / h r ( L e t t i n g a , 1 9 8 3 c ; S c h w a r t z , 1 9 8 2 ) . A l s o r e c o m m e n d e d i s p e r i o d i c w a s t i n g o f s m a l l a m o u n t s o f s l u d g e , t o m a i n t a i n a c o n s t a n t l e v e l o f b i o m a s s s l u d g e w i t h i n t h e r e a c t o r ( L e t t i n g a , 1 9 7 9 b ) . H o w e v e r , c o n v e n t i o n a l s e p a r a t i o n c a n b e i n a d e q u a t e f o r t h e b u o y a n t , f l o c c u l a n t s l u d g e . I t i s s o m e t i m e s r e p l a c e d b y a l t e r n a t i v e s l i k e s u r f a c e c l a r i f i c a t i o n ( H a m o d a , 1 9 8 4 ) , u l t r a f i l t r a t i o n ( C h o a t e , 1 9 8 2 ) , a n d c o a g u l a n t s ( C a i l , 1 9 8 6 ) . D L A I n c . ( O l t h o f , 1 9 8 2 ) h a v e p l a c e d t h e b i o f i l t e r m e d i a i n t h e u p p e r z o n e o f t h e r e a c t o r o f a c o n v e n t i o n a l U A S B p r o c e s s , t o i n c r e a s e t h e s y s t e m S R T a n d t o d a m p e n t h e s h o r t c i r c u i t i n g ; t h i s p r o c e d u r e h a s a l s o i m p r o v e d g a s / s o l i d s / l i q u i d s e p a r a t i o n , a s w e l l a s p r o v i d e d a s u r f a c e f o r t h e a t t a c h m e n t o f b i o m a s s . T h i s s y s t e m h a s w o r k e d v e r y w e l l a n d i s m a r k e t e d u n d e r t h e t r a d e n a m e “ A n h y b r i d ” . F u r t h e r , O l e s z k i e w i c z ( 1 9 8 8 ) h a s d e m o n s t r a t e d t h a t a r e a c t o r , w i t h r a n d o m m e d i a i n t h e u p p e r 4 0 % o f t h e v o l u m e , s h o w e d b e t t e r C O D r e m o v a l e f f i c i e n c y a n d g a s g e n e r a t i o n , a s w e l l a s l e s s w a s h o u t o f t h e f l o c c u l a n t s l u d g e t h r o u g h s h o r t c i r c u i t i n g , t h a n t h o s e r e a c t o r s w i t h m e d i a o r i e n t e d v e r t i c a l l y a n d / o r n o m e d i a . D e v e l o p m e n t o f a n a e r o b i c r e a c t o r s u s i n g a t t a c h e d b i o m a s s , s u c h a s t h e f l u i d i z e d 1 7 b e d a n d t h e a n a e r o b i c f i l t e r , h a s r e s u l t e d i n t h e a b i l i t y t o i n c r e a s e t h e l o a d i n g r a t e f r o m 2 0 t o 5 0 k g C O D I m3-d a n d f r o m 1 0 t o 3 0 k g C O D / m3-d r e s p e c t i v e l y . H o w e v e r , p r o b l e m s w i t h a t t a c h e d b i o m a s s s y s t e m s i n c l u d e c l o g g i n g a n d h i g h o p e r a t i n g c o s t s , d u e t o e x t e r n a l e n e r g y r e q u i r e m e n t s ( M a a t , 1 9 8 7 ) . H e a l s o f o u n d t h a t t h e U A S B o v e r c a m e m a n y o f t h e s e l i m i t a t i o n s b y i n t r o d u c i n g g r a n u l a t e d s u s p e n d e d b i o m a s s a n d t h e G S S - d e v i c e . T h i s s y s t e m c o u l d a c h i e v e 7 5 - 9 4 % r e m o v a l e f f i c i e n c y , w i t h a s l u d g e c o n c e n t r a t i o n o f 8 - 1 3 % d r y s o l i d s a t t e m p e r a t u r e s r a n g i n g f r o m 2 0 - 4 0 0 C ( e v e n i f t h e r e a c t o r l o a d i n g i s 3 0 k g C O D / m3-d o r h i g h e r ) . T h e U A S B r e a c t o r h a s b e e n s u c c e s s f u l l y c o m m e r c i a l i z e d a s t h e B I O P A Q w a s t e w a t e r t r e a t m e n t s y s t e m . T h e d e s i g n l o a d i n g f o r s e v e r a l B I O P A Q i n s t a l l a t i o n s i s a b o u t 1 0 k g COD/ni3-d, w h i l e a c t u a l c a p a c i t y l i m i t s f o r v o l u m e t r i c l o a d i n g h a v e e x c e e d e d 2 0 - 3 0 k g C O D / m3-d ( M a a t , 1 9 8 7 ) . C u r r e n t d e s i g n p r a c t i c e s f o r U A S B r e a c t o r s , a r e e f f e c t i v e f o r s e v e r a l t y p e s o f w a s t e w a t e r s , r e g a r d l e s s o f w h e t h e r i t i s s e w a g e o r i n d u s t r i a l w a s t e w a t e r s ( w i t h e i t h e r d i l u t e o r c o n c e n t r a t e d w a s t e s ) . T h e r e a r e t h r e e b a s i c c o n s i d e r a t i o n s f o r t h e d e s i g n o f t h e U A S B r e a c t o r : v o l u m e t r i c o r g a n i c l o a d a p p l i e d , l i q u i d v e l o c i t y o n t h e s e t t l e r s u r f a c e , a n d r e a c t o r h e i g h t . B a s e d o n a s p e c i f i c s t u d y o f a t y p i c a l U A S B p r o c e s s , S o u z a ( 1 9 8 6 ) r e c o m m e n d e d t h a t m a x i m u m s a f e d e s i g n v a l u e s b e a b o u t 1 5 - 2 0 k g COD/m3-d, 1 . 2 - 1 . 5 m / h r , a n d a h e i g h t o f l e s s t h a n 6 . 0 m e t r e s , r e s p e c t i v e l y . M i n i m u m a n d m a x i m u m s u p e r f i c i a l g a s r e l e a s e r a t e s w e r e r e c o m m e n d e d t o b e 1 a n d 3 - 5 m3 gas/m2-hr, r e s p e c t i v e l y . I t w a s a l s o s u g g e s t e d t h a t t h e f e e d i n l e t d i s t r i b u t i o n a r e a b e 7 - 1 0 m2/inlet. L e t t i n g a e t a l . ( 1 9 8 3 a n d 1 9 8 6 ) a t t e m p t e d t o i n c r e a s e t h e s u p e r f i c i a l l i q u i d v e l o c i t y u p t o 5 - 1 5 m / h r , b y i n c r e a s i n g t h e s l u d g e l o a d i n g r a t e a n d r e c y c l i n g t h e e f f l u e n t b a c k t o t h e s y s t e m u s i n g t h e e x p a n d e d g r a n u l a r s l u d g e b e d r e a c t o r s ( E G S B ) . T h e 1 8 a t t e m p t a p p e a r e d t o b e f e a s i b l e . S l u d g e r e c i r c u l a t i o n h e l p s i n o c u l a t e t h e f r e s h s l u d g e i n s i d e t h e d i g e s t e r a n d a l s o i n c r e a s e t h e s y s t e m S R T . F i n a l l y , D o l d ( 1 9 8 7 ) u s e d a U A S B t o t r e a t a p p l e j u i c e w a s t e , a t t h e t e m p e r a t u r e l e s s t h a n o p t i m u m ( 2 5 a n d 3 0 ° C ) a n d a m a x i m u m l o a d i n g o f 1 2 - 1 6 k g C O D / m3-d. H e c o n c l u d e d t h a t t h e U A S B s y s t e m w o r k e d v e r y w e l l , e v e n a t a l o w t e m p e r a t u r e o f 2 5 C a n d t h e m a x i m u m l o a d i n g r a t e e m p l o y e d . A n a p p l i c a t i o n o f t w o - p h a s e s e p a r a t i o n , t o t r e a t p a r t i c u l a t e m a t e r i a l s ( s u c h a s c r o p r e s i d u a l s , m a n u r e , a n d m u n i c i p a l r e f u s e ) w h e r e i n h y d r o l y s i s i s t h e r a t e - l i m i t i n g s t e p , i s a l s o s h o w i n g p r o m i s e . A v a r i e t y o f a p p r o a c h e s h a s b e e n p r o p o s e d , s u c h a s u s i n g t h e U A S B a s a m o d i f i e d a c i d r e a c t o r ( Z o e t e m e i j e r e t a l . , 1 9 8 2 ; T h e r k e l s e n , 1 9 7 9 ) , t o a c c e l e r a t e t h e r a t e o f h y d r o l y s i s a n d a c i d o g e n e s i s . H o w e v e r , f o r s l u r r i e s l i k e s e w a g e s l u d g e a n d 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 h e a p p l i c a t i o n o f p h a s e s e p a r a t i o n , u s i n g U A S B i s s t i l l q u e s t i o n a b l e i n t e r m o f r e a l b e n e f i t s , w h e n c o m p a r e d t o a s i n g l e - U A S B p r o c e s s ( L e t t i n g a , 1 9 8 3 a ) . G h o s h , ( 1 9 8 4 ) , h o w e v e r , r e p o r t e d t h a t a t w o - p h a s e U A S B p r o c e s s w a s v e r y e f f e c t i v e i n s t a b i l i z i n g s e w a g e s l u d g e . T h e m e t h a n e y i e l d w a s n e a r l y 7 7 % o f t h e o r e t i c a l v a l u e s a t a n H R T o f 5 . 5 a n d 5 . 9 d a y s , i n t h e s e q u e n t i a l r e a c t o r s ; t h e o p t i m u m H R T ’ s f o r t h e a c i d - a n d m e t h a n e - p h a s e r e a c t o r s w e r e 0 . 9 - 1 . 5 a n d 4 . 0 - 5 . 0 d a y s , r e s p e c t i v e l y . S e v e r a l m o d e l s h a s b e e n i n i t i a t e d t o e x p l a i n a n d p r e d i c t t h e m e c h a n i s m a n d p e r f o r m a n c e o f a n a e r o b i c d i g e s t i o n . A r b i t r a r i l y , t h e m o d e l s c a n b e c l a s s i f i e d i n t o 4 g r o u p s : M o n o d , s u b s t r a t e i n h i b i t i o n k i n e t i c s , f i r s t - o r d e r k i n e t i c s , a n d C o n t o i s - d e r i v e d k i n e t i c s . C o n c e p t u a l c o m p a r i s o n s a m o n g t h e s e m o d e l s i s w e l l d o c u m e n t e d w i t h M o n o d k i n e t i c s b e i n g t h e m o s t p o p u l a r a n d a c c e p t e d a m o n g r e s e a r c h e r s , t o e x p l a i n t h e 19 anaerobic digestion process (Mosey, 1983b; Ripley, 1983). For example, Monod kinetics are frequently used to explain the mechanism of anaerobic digestion of sewage sludge and particulate materials (Pavlostathis, 1986; Massey, 1987). In addition, a mathematical model for the UASB, serving as methane-phase reactor only, is well established. The principle element of the model involves dynamic behaviour and distribution of the fluid pattern, anaerobic sludge in the reactor, kinetic conversion of organic wastes, and formulation of bacterial end products and CH4.The use of a mass balance for substrate, CH4, and bacterial end products in the system, is carefully made in formulating a mathematical model for the UASB process (Buijis, 1981; Buijis, 1982; Heertjes, 1978/1982; and Van Der Meer, 1983). An indepth review of these kinetic models is beyond the scope of this project and the reader is referred to the literature as cited above. From this brief literature review, it is apparent that there have been several major studies completed, with the basic goal of enhancing the efficiency of anaerobic sludge digestion using the two-phase separation and/or the UASB process. However, very few have taken full advantage of combining these two concepts, to enhance the overall effectiveness of anaerobic stabilization. To maximize the benefits, it appeared logical to evaluate the feasibility and effectiveness of using a two-phase UASB-UASB process, one with an internal recycle of fluidized sludge known as sludge blanket in order to enhance the efficiency of anaerobic sludge stabilization. The basic idea was to take advantage of the di-phasic phenomenon of anaerobic stabilization by using phase separation to provide a preferred environment for growth stimulation of the two different groups of bacteria. 2 0 B y u s i n g t h e U A S B p r o c e s s a n d i n t e r n a l s l u d g e b l a n k e t r e c y c l e c o n c e p t s , i t w a s h o p e d t o i n c r e a s e t h e c o n t a c t b e t w e e n m i c o o r g a n i s m s a n d s u b s t r a t e s a s w e l l a s t o i n c r e a s e t h e s y s t e m b u f f e r r i n g c a p a c i t y . T h u s t h e s y s t e m c a n r e t a i n t h e g r a n u l a r b i o m a s s w i t h i n t h e d i g e s t e r , w i t h o u t a n y m i x i n g r e q u i r e m e n t s a n d p r o v i d e a p r o m i s i n g s y s t e m p e r f o r m a n c e a n d s t a b i l i t y . T h e r e s e a r c h p r o g r a m w a s i n i t i a t e d a n d f o r m u l a t e d a l o n g t h e s e l i n e s . 2 1 C H A P T E R T H R E E S Y S T E M S E T - U P A N D O P E R A T I O N 3 . 1 R A T I O N A L E A N D D E S I G N C R i T E R I A T h e p r i n c i p l e g o a l s o f t h i s r e s e a r c h w e r e t o e v a l u a t e t h e f e a s i b i l i t y , e f f e c t i v e n e s s , a n d s u i t a b i l i t y o f u s i n g a t w o - p h a s e , U A S B - U A S B p r o c e s s t o e n h a n c e t h e e f f i c i e n c y o f a n a e r o b i c s l u d g e s t a b i l i z a t i o n . T o a c h i e v e t h e s e g o a l s , a s c h e m a t i c f l o w d i a g r a m o f e x p e r i m e n t a l d e s i g n s w a s d e l i n e a t e d a s s h o w n i n F i g u r e 4 . 1 . T h e r a t i o n a l e a n d d e s i g n c r i t e r i a w e r e t h e n c o n c e p t u a l l y f o r m u l a t e d . T o e n h a n c e t h e e f f i c i e n c y o f a n a e r o b i c s t a b i l i z a t i o n , t w o b r o a d a p p r o a c h e s a r e g e n e r a l l y e m p l o y e d - o n e p r o v i d i n g p r e f e r a b l y o p t i m u m e n v i r o n m e n t a l c o n d i t i o n s f o r e a c h g r o u p o f b a c t e r i a a n d t h e o t h e r c o n c e r n e d w i t h i n c r e a s i n g b a c t e r i a p o p u l a t i o n d e n s i t y a n d r e t a i n i n g i t w i t h i n t h e d i g e s t e r . T h e f o r m e r a p p r o a c h c a n b e a c h i e v e d t h r o u g h t h e u s e o f t w o - p h a s e a n a e r o b i c d i g e s t i o n , w i t h a n a d e q u a t e s u p p l y o f n u t r i e n t s . A t w o - p h a s e U A S B - U A S B p r o c e s s w a s s e l e c t e d t o t r e a t a s y n t h e t i c s l u d g e , u n d e r t h e s p e c i f i c c o n t r o l o f t e m p e r a t u r e a t 3 5 ° C a n d p H ’ s o f 5 a n d 7 f o r t h e a c i d - p h a s e ( A - U A S B ) a n d m e t h a n e - p h a s e ( M - U A S B ) r e a c t o r s r e s p e c t i v e l y . B y c o n t r o l l i n g t h e t e m p e r a t u r e a n d p H , a s w e l l a s s e p a r a t i n g t h e i r e n v i r o n m e n t s , t h e a c i d o g e n s a n d m e t h a n o g e n s w e r e e x p e c t e d t o d o m i n a t e t h e m i x e d c u l t u r e s o f b a c t e r i a w i t h i n t h e A - U A S B a n d M - U A S B u n i t s , r e s p e c t i v e l y ; i t w a s a l s o e x p e c t e d t h a t t h e r e w o u l d b e a r a p i d u t i l i z a t i o n o f o r g a n i c m a t t e r , a n e f f e c t i v e p r o d u c t i o n o f v o l a t i l e f a t t y a c i d s ( V F A s ) a n d f i n a l l y m e t h a n e p r o d u c t i o n . T o e n h a n c e t h e 2 2 s t a b i l i z a t i o n p r o c e s s a n d m e t h a n e g a s f o r m a t i o n , n u t r i e n t r e q u i r e m e n t s m u s t b e s u f f i c i e n t . V a r i a t i o n i n f e e d s l u d g e r a t i o ( S R ) o f p r i m a r y t o s e c o n d a r y s y n t h e t i c s l u d g e s , m e a n s a s i g n i f i c a n t d i f f e r e n c e i n f e e d s l u d g e c h a r a c t e r i s t i c s ( C O D / V S S , T K N , T P , e t c . a s s h o w n i n T a b l e 3 . 1 ) . S i n c e i t i s k n o w n t h a t p r i m a r y s l u d g e c o n t a i n s m o s t l y o r g a n i c s w h i l e s e c o n d a r y s l u d g e c o n t a i n s o r g a n i c s , n u t r i e n t s ( N a n d P ) a n d b a c t e r i a l c e l l s . T h i s w o u l d s t r o n g l y a f f e c t t h e s y s t e m p e r f o r m a n c e s a n d m e t h a n e f o r m a t i o n . A c a r e f u l c o m b i n a t i o n o f t h e s e t w o s l u d g e s , w i t h a n o p t i m u m S R , c o u l d r e s u l t i n a m a x i m i z a t i o n o f C H4 g a s p r o d u c t i o n a n d r e m o v a l e f f i c i e n c y . T h i s w o u l d b e o f p a r t i c u l a r i n t e r e s t t o t h o s e w a s t e t r e a t m e n t p l a n t s t h a t p r o d u c e b o t h a p r i m a r y a n d s e c o n d a r y w a s t e s l u d g e r e q u i r i n g f u r t h e r s t a b i l i z a t i o n . T h e l a t t e r a p p r o a c h c a n b e a c c o m p l i s h e d t h r o u g h a n a p p r o p r i a t e d e s i g n o f U A S B s y s t e m c o n f i g u r a t i o n t o h e l p k e e p t h e b i o m a s s i n s i d e t h e r e a c t o r w i t h t h e o p t i m u l r e c y c l e r a t i o ( R R ) . N e w t e c h n o l o g i e s h a v e i n c o r p o r a t e d c h a n g e s , w h i c h a l l o w S R T a n d H R T t o b e v a r i e d i n d e p e n d e n t l y . T y p i c a l l y , t h e s o l i d s i n t h e r e a c t o r e f f l u e n t a r e a l l o w e d t o s e t t l e a n d r e c y c l e b a c k t o t h e r e a c t o r i n f l u e n t i n o r d e r t o i n c r e a s e t h e r a t i o o f S R T I H R T ( C h r i s t e n s e n , 1 9 8 4 ) . S e v e r a l o t h e r f a c t o r s ( f e e d c h a r a c t e r i s t i c s , s e e d s l u d g e a n d s t a r t - u p p r o c e s s , o p e r a t i n g c o n d i t i o n ( S R , R R , m i x i n g , w a s t i n g , e t c . ) , a n d p r o c e s s c o n f i g u r a t i o n ) a r e a l s o s e p a r a t e l y c o n s i d e r e d t o i m p r o v e t h e s y s t e m p e r f o r m a n c e s i n t h i s e x p e r i m e n t . I n p r i n c i p l e , U A S B c o m p o s e s o f 3 m a i n c o m p o n e n t s ( s l u d g e b e d , s l u d g e b l a n k e t , a n d s e t t l e r ) . A v e r y c o n c e n t r a t e d s l u d g e b e d d e v e l o p s n e a r t h e b o t t o m o f t h e r e a c t o r . T h e b l a n k e t v a r i e s f r o m v e r y d e n s e a n d g r a n u l a r p a r t i c l e s w i t h h i g h s e t t l i n g v e l o c i t i e s n e a r t h e b o t t o m , t o t h e l i g h t e r , m o r e d i f f u s e p a r t i c l e s a t h i g h e r l e v e l o f t h e b l a n k e t . M o s t o f 23 the reactions occurs throughout the entire sludge bed and blanket zones. The system is mixed by hydraulic upflow and rising gas bubbles. The potential of UASB reactor, are mainly dictated by the amount of sludge that can be retained in the reactor. In the internal settler, a quiescent zone is created to enable the sludge particle released from the blanket to settle rather than being washed out. Sludge separated by settling is recirculated into the reactor and thus being retained in the system. To help increase this sludge retaining ability, internal recycling ratio (RR) of this fluidized sludge known as sludge blanket back to the reactor influent can significantly enhance the system performance. Increasing the RR means an increase in not only the contact between microorganisms and substrates but also the system bufferring capacity, which finally can lead to the improvement of system stability and removal efficiency; however; too high an RR can break down the sludge bed and seriously damage the system performance. The success of system performance depends not only on the optimal level of operating conditions such as loading rate, RR, and SR, but also on the system configuration. Since the UASB-UASB process is quite new, detailed microbial and kinetic data are not yet available. Conceptual and preliminary designs of this two-phase configuration have to be made through a modification of existing design criteria of UASB process and theoretical conceptual ideas. Overall schematic diagrams of the system configuration are shown in Figures 3.1 and 3.2, respectively. The detailed sizing of the system components is shown in Table A3.1 of Appendix A. As shown in Figure 3.1, the diameter of the settling section is double that of the sludge bed and blanket sections, and 4° C r n 1j -iEEi___ A - U A S B I M - U A S B L e g e n d s : ( 1 ) S l u d g e b l e n d e r ( 2 ) M e r s ( 3 ) A c I d - p h a s e r e a c t o r N o t e : U q u i d f l o w ( 4 ) S t o r a g e t a n k ( 5 ) M e t h a n e - p h a s e r e a c t o r ( 6 ) G a s t r a p ( w a t e r ) G a s f i o w W e t g a s h o w m e t e r s ( 8 ) P u m p c o n t r o l l e r s ( 9 ) p H c o n t r o l l e r s ( 0 ) T I m e r S o l i d s f l o w F i g u r e 3 . 2 D e t a i l e d D i m e n s i o n s o f U A S B R e a c t o r s u s e d i n t h e e x p e r i m e n t A I F - B - H - I — 5 — H V N o t e : 5 0 d e g r e e I n c l I n e d w a l l M i x e r @ A - U A S B 1 . 2 7 c m s . I n d l a . @ I n & o u t l e t A - U A S B M - U A S _ _ A F i g u r e 3 . 1 S c h e m a t i c F l o w D i a g r a m o f a M o d i f i e d T w o - p h a s e A n a e r o b i c S l u d g e D i g e s t i o n ( U A S B - U A S B ) P r o c e s s 2 4 V g a s 3 5 L e g e n d A - U A S B M - U A S B ( e m s ) ( e m s ) A 2 0 2 5 B 1 0 1 5 C 2 0 3 0 D 5 0 5 0 E 5 0 5 0 ( A , B ) = D i a m e t e r , c m s ( C , D , E ) = H e i g h t , e m s (b) 2 6 h a s a 5 0 0 i n c l i n e d - w a l l ; i t w a s d e s i g n e d t o r e d u c e t h e u p f l o w v e l o c i t y a n d h e l p s e t t l e t h e s o l i d s b a c k t o t h e l o w e r p a r t s . T h i s a l s o r e d u c e s s i g n i f i c a n t l y t h e a m o u n t o f supernatant s o l i d s , e s p e c i a l l y i n t h e A - U A S B r e a c t o r . T o o h i g h a c o n c e n t r a t i o n ( > 5 0 0 m g / L S S ) , c a n a f f e c t t h e M - U A S B p e r f o r m a n c e a d v e r s e l y ( C h r i s t e n , 1 9 8 4 ). T o e n s u r e a h o m o g e n e o u s f e e d s l u d g e a n d a l s o t o p r e v e n t t h e p o t e n t i a l s t a b i l i z a t i o n o f t h e i n f l u e n t f e e d b e f o r e e n t e r i n g t h e s y s t e m , m i x e d p r i m a r y a n d s e c o n d a r y s l u d g e s w e r e m i x e d c o n t i n u o u s l y ( a t 6 0 r p m ) i n s i d e a 3 0 - l i t r e , p l e x i - g l a s s s t o r a g e v e s s e l , i n s t a l l e d i n a w a l k - i n temperature c o n t r o l l e d r o o m , a t 4 - 6 0 C . I n a d d i t i o n , m a x i m u m s y s t e m l o a d i n g c a p a c i t y a n d s y s t e m f a i l u r e a n d r e c o v e r y a r e a l s o w o r t h i n v e s t i g a t e d . A c c i d e n t a l s h o c k l o a d (and/or o v e r l o a d i n g ) a n d / o r t e m p o r a r y s y s t e m c e s s a t i o n (stoppage ) m a y r e d u c e t h e s y s t e m p e r f o r m a n c e o r e v e n b e a m a j o r c a u s e o f a c o m p l e t e s y s t e m f a i l u r e . Appropriate p r i m e i n d i c a t o r s o f s y s t e m f a i l u r e m u s t b e i d e n t i f i e d a n d q u a n t i f i e d a n d t h e n s y s t e m r e c o v e r y a l t e r n a t i v e s c a n b e f o r m u l a t e d . T h e s e a d d i t i o n a l i n f o r m a t i o n a n d r e s u l t s w i l l b e u s e d a s a part o f a f i n a l r e c o m m e n d a t i o n o n s y s t e m d e s i g n a n d o p e r a t i o n o f t h e t w o - p h a s e a n a e r o b i c d i g e s t i o n p r o c e s s ( U A S B - U A S B ) f o r s e w a g e s l u d g e . 3 . 2 EXPERIMENTAL A P P A R A T U S A N D OPERATION A s a l a b s c a l e e x p e r i m e n t , t w o c o m p l e t e l y s e a l e d u p f l o w a n a e r o b i c ( A - U A S B a n d M - U A S B ) r e a c t o r s w e r e d e s i g n e d t o operate i n s i d e a w a l k - i n temperature c o n t r o l l e d r o o m a t 3 5 C . T h e i r h e i g h t a n d c a p a c i t y w e r e 1 . 3 m e t e r s , w i t h 2 0 a n d 2 5 l i t r e s f o r A - 2 7 U A S B , a n d M - U A S B , r e s p e c t i v e l y , a s s h o w n i n F i g u r e 3 . 2 . W h e n e v e r t h e m e a s u r e d p H w a s under t h e s e t p o i n t v a l u e s o f 5 a n d 7 f o r t h e A - a n d M - U A S B r e a c t o r s , a s i g n a l w a s s e n t t o t h e c o n t r o l l e r , w h i c h s u b s e q u e n t l y d i r e c t e d t h e d i a p h r a g m p u m p t o s t a r t p u m p i n g a 0 . 1 - 0 . 2 N NaOH s o l u t i o n i n t o t h e d i g e s t e r t o m a i n t a i n t h e p H a t t h e s e t v a l u e s . A s s h o w n i n F i g u r e s 3 . 1 a n d 3 . 2 , t h e i n f l u e n t s y n t h e t i c p r i m a r y a n d s e c o n d a r y s l u d g e s w e r e m i x e d w i t h i n a 3 0 - l i t r e s t o r a g e v e s s e l l o c a t e d i n a w a l k - i n temperature c o n t r o l l e d r o o m o f 4 - 6 0 C ; t h e m i x t u r e w a s s u b s e q u e n t l y p u m p e d t o t h e b o t t o m o f t h e A - U A S B reactor b y a p e r i s t a l t i c p u m p . T h e l i q u i d p a s s e d t h r o u g h s l u d g e b e d , b l a n k e t , a n d s e t t l e r , a n d f i n a l l y l e f t t h e reactor v i a t h e w e i r . T h e e f f l u e n t f r o m t h e A - U A S B reactor w a s t h e n p u m p e d t o t h e M - U A S B r e a c t o r , v i a p e r i s t a l t i c p u m p s . T h e l i q u i d t h e n f o l l o w e d a s i m i l a r pattern t o t h a t o f A - U A S B a n d i t e v e n t u a l l y o v e r f l o w e d a s t h e s y s t e m f i n a l e f f l u e n t . C o n c u r r e n t l y , t h e f l u i d i z e d s l u d g e b l a n k e t o f b o t h r e a c t o r s w a s r e c y c l e d b a c k i n t o t h e d i g e s t e r . T h e g a s p r o d u c e d f r o m b o t h r e a c t o r s w a s entrained i n a g a s c a p t u r e f a c i l i t y attatched t o t h e upper p a r t o f e a c h r e a c t o r . T h e g a s w a s t h e n m o n i t o r e d b y t w o w e t g a s f l o w m e t e r s v i a w a t e r t r a p f l a s k s . T o e n s u r e t h a t there w a s n o l e a k a g e o f g a s a n d / o r f l u i d , rubber 0 - r i n g s a n d o n e - i n c h b o l t s w e r e p l a c e d a r o u n d t h e d i g e s t e r c o v e r s . A 1 . 2 7 c m ( I D ) f o o d a n d b e v e r a g e t u b e , w i t h s t r a i g h t c o n n e c t e r s a n d m e t a l c l a m p s , w a s u s e d , w h e r e n e c e s s a r y , t h r o u g h o u t t h e s y s t e m t o p r e v e n t c l o g g i n g a n d / o r f l u i d s p i l l a g e . A l s o , a t w o - w e e k s c h e d u l e o f t i g h t e n i n g t h e c l a m p s w a s i m p l e m e n t e d . A f t e r t h e c o m p l e t i o n o f t h e s y s t e m s e t u p , a t e s t r u n w i t h t a p w a t e r w a s m a d e t o c h e c k t h e p o s s i b i l i t y o f a n y l i q u i d l e a k i n g a n d / o r improper o p e r a t i n g e q u i p m e n t . A g a s l e a k i n g t e s t , u s i n g n i t r o g e n g a s a t 2 - 3 p s i a n d f o a m i n g a g e n t s , w a s a l s o 2 8 c a r r i e d o u t s e v e r a l t i m e s t o e n s u r e t h a t t h e r e w a s n o g a s l e a k a g e s f r o m w i t h i n t h e d i g e s t e r . 3 . 3 S Y N T H E T I C S L U D G E P R E P A R A T I O N T o a v o i d p o t e n t i a l p r o b l e m s o f t o x i c i t y f r o m a c t u a l w a s t e w a t e r s l u d g e a n d s u p p l y r e l i a b i l i t y f o r b o t h p r i m a r y a n d s e c o n d a r y s l u d g e s , a s y n t h e t i c s l u d g e m i x t u r e w a s u s e d . T h e i n i t i a l c o n s t i t u e n t s o f s y n t h e t i c p r i m a r y s l u d g e w e r e p a r t l y b a s e d o n t h o s e r e p o r t e d i n t h e l i t e r a t u r e ( T h e r k e l s e n , 1 9 7 9 ) . T h e m a i n c o n s t i t u e n t s , b a s e d o n p e r c e n t a g e b y w e i g h t o f t o t a l d r y s o l i d s ( % b y w t o f d r y s o l i d s ) , w e r e c o m p o s e d o f d o g f o o d ( 7 6 % ) , s o a p ( 4 % ) , c o r n o i l ( 6 % ) , C a C O3 ( 2 % ) , a n d M g C O3 ( 2 % ) . T h e c h e m i c a l a n a l y s i s o f d o g f o o d ( “ N o N a m e ” - S p e c i a l - d i n n e r f o r D o g s ) u s e d i n t h e p r e p a r a t i o n o f b o t h p r i m a r y a n d s e c o n d a r y s y n t h e t i c s l u d g e s , i s s h o w n i n T a b l e A 2 . 2 ( b ) o f t h e A p p e n d i x A . T h e p r o p o r t i o n o f t h e s e i n g r e d i e n t s w a s f u r t h e r m o d i f i e d b y u s i n g n u m e r o u s t r i a l - a n d - e r r o r t e c h n i q u e s t o e n s u r e t h a t t h e c h a r a c t e r i s t i c s o f p r e p a r e d s y n t h e t i c s l u d g e w e r e i n t h e t y p i c a l r a n g e o f a c t u a l p r i m a r y a n d s e c o n d a r y s l u d g e s , r e s p e c t i v e l y . T h e f i n a l m o d i f i e d c o n s t i t u e n t s o f p r i m a r y a n d s e c o n d a r y s y n t h e t i c s l u d g e s a r e s h o w n i n T a b l e A 2 . 2 ( a ) o f A p p e n d i x A . T h e a m o u n t o f e a c h i n g r e d i e n t w a s c a l c u l a t e d b a s e d o n i t s p r o p o r t i o n , t o t a l l i q u i d v o l u m e ( 3 0 a n d 2 4 l i t r e s ) , a n d t o t a l d r y s o l i d s ( 4 a n d 2 % b y w e i g h t ) f o r p r i m a r y a n d s e c o n d a r y s y n t h e t i c s l u d g e s , r e s p e c t i v e l y . T o e n s u r e s u f f i c i e n t m i x i n g a n d s o l u b i l i t y o f t h e p r e p a r e d m i x t u r e a s w e l l a s c o n s i s t e n c y o f t h e p r e p a r e d s l u d g e c h a r a c t e r i s t i c s , s e v e r a l d e s i g n e d p r e p a r a t i o n 2 9 t e c h n i q u e s w e r e d e v e l o p e d a n d m o d i f i e d . T h e s y n t h e t i c s l u d g e w a s p r e p a r e d i n s i d e a 6 0 - l i t r e p l e x i - g l a s s r e a c t o r w i t h a m e c h a n i c a l m i x e r . T h e f i n e - g r o u n d , d o g f o o d , t o g e t h e r w i t h a l l o t h e r i n g r e d i e n t s , w a s d i s s o l v e d w i t h t a p w a t e r t o m a k e t h e t o t a l v o l u m e o f 1 2 l i t r e s a n d w a s m i x e d c o n t i n u o u s l y a t 9 0 - 9 5 r p m f o r 2 h o u r s ; i t w a s t h e n l e f t o v e r n i g h t i n s i d e t h e w a l k - i n t e m p e r a t u r e c o n t r o l l e d r o o m a t 4 C . A f t e r t h a t , t h e p r e p a r e d s l u d g e w a s t r a n s f e r r e d t o s e v e r a l 1 . 4 - l i t r e b e a k e r s a n d w a r m e d u p t o 6 5 - 7 0 C i n s i d e a w a t e r b a t h f o r 1 . 5 h o u r s ; i t w a s t h e n m i x e d a t 9 0 - 9 5 r p m f o r a f u r t h e r 1 h o u r a n d s e t t l e d f o r 1 0 m i n u t e s . A f t e r s e t t l i n g , a p o r t i o n o f t h e s e t t l e d s o l i d s w a s w a s t e d , t o e n s u r e t h a t t h e r e m a i n i n g s o l i d s l e v e l w e r e a t t h e a s s i g n e d l e v e l o f P a n d S f o r p r i m a r y a n d s e c o n d a r y s y n t h e t i c s l u d g e s , r e s p e c t i v e l y ; a n d f i n a l l y , t h e v o l u m e s w e r e m a d e u p t o 3 0 a n d 2 4 l i t r e s , f o r p r i m a r y a n d s e c o n d a r y s y n t h e t i c s l u d g e s , r e s p e c t i v e l y . A s e r i e s o f s m a l l s c a l e ( 1 - l i t r e ) a n d s c a l e u p ( 3 0 - l i t r e ) e x p e r i m e n t a l e v a l u a t i o n s w a s c a r r i e d o u t , t o d e t e r m i n e t h e c h a r a c t e r i s t i c s o f t h e p r e p a r e d s l u d g e , a n d t o c o m p a r e w i t h t h o s e o f a c t u a l d o m e s t i c w a s t e w a t e r s l u d g e . A s s h o w n i n F i g u r e 3 . 4 a n d 3 . 5 , a s e r i e s o f r u n - a n d - c o m p a r e e x p e r i m e n t s w e r e u n d e r t a k e n f o r m o r e t h a n t h r e e m o n t h s , b e f o r e t h e c h a r a c t e r i s t i c s o f t h e s y n t h e t i c s l u d g e c o r r e s p o n d e d r e a s o n a b l y t o t h o s e o f a c t u a l s a n i t a r y w a s t e s l u d g e s . D u r i n g t h e s c a l e - u p e x p e r i m e n t , a n a d d i t i o n o f u r e a a n dNa2H P O4 w a s n e c e s s a r y t o i n c r e a s e t h e c o n c e n t r a t i o n o f T K N a n d T P u p t o t h e a c t u a l r a n g e f o r s e c o n d a r y s l u d g e . N u m e r o u s t r i a l - a n d - e r r o r e f f o r t s w e r e s p e n t o n w a s t i n g o f s e t t l e d s o l i d s , i n s u c h a w a y t h a t t h e C O D / V S S r a t i o o f b o t h p r i m a r y a n d s e c o n d a r y s l u d g e s w a s i n t h e t y p i c a l r a n g e f o r a c t u a l s l u d g e . A c o m p a r a t i v e s u m m a r y o f t h e b a s i c c h a r a c t e r i s t i c s o f s y n t h e t i c a n d t y p i c a l “ a c t u a l ” d o m e s t i c s l u d g e s i s i l l u s t r a t e d i n T a b l e 3 . 1 . RA 11 O % TS % TS II % TS I I I - ‘ — - . 4 0 - C ) - ‘ 4 Co (D C) C)’ 0 0 0 0 0 C3 0 (1) . 1 I I I li ii I I I I Cn R A TI O O R % TS % TS % TS CD % TS 0 - C. ) (J ,- .r ’. ) C. ) O ( D 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 — ‘ I I II Co Y( L J - : rz. G) C m C) 0 - U c I) 8 c Cl ) (I) C) z — I m — I C) C,) 1 C EJ G) m 0 . a ’ - 1 m . Co 0 ) a ) - • 1 1 C/) > I a) Co 0 F rn I-U m m z 0 0 - 1 m 0 Co / / - U I 1 0 / \ - u Co /z ‘ z \ 0 I Co - U , , x 0 C C o 2 z , r — . ‘ — — i— i — — G) C m c) — I 0 CO 0 > c m ‘ ii d c, ) z - n a - a 0 CO CO C o z H m -1 0 C, ) I C C) m I’ ) (0 (3 ) 1 LFI C. ) - U I C z I - Cl ) Z 0 -I 0 m - 4 AC TU AL NO RM AL RA NG E, RA TI O OR % DR Y DR Y SO IJ D S - ‘ - 0) 0 - . . . c n a ) - 1 . t.. C0 0) C. ) . r ) - ‘ AC TU AL NO RM AL RA NG E, RA TI O OR % DR Y DR Y SO LI DS 31 Table 3 1 Comparative Characteristics of Prepared Synthetic Sludge and Actual Primary and Secondary Sludges Charact. US.EPA (1979) Synthetic Sludges Typical Range # Primary Secondary Primary Secondary mgIL wgt % of TS mgIL wgt % of TS COD 32900 25470TS [3—7] [1—2] 33370 3.35 19980 1.99VSS 17300 0.50 11780 0.59VS [64—93] [59—88] 30330 91.00 17600 88.14COD/VSS 11.2—1.6] 2.17 1.90 ‘ 2.16TKN [1.5—4.01 [2.4—6.7] 3.95 5.84TP [0.35—1.2] [1.3—1.6] 1.10 1.52PROTEIN [20—30] [32—41] 25.00 36.55CARBO. [17—26] 20.00 26.49TOC [17—441 41.00 33.44 NOTE: # = Selected Parameters, percent by weight of dry solids (%TS) Throughout the experimental program, monitoring of key parameters of the prepared sludge was undertaken at least once a month; this monitoring showed that the constituents and characteristics of the sludge used in the experiment were maintained within 10-15 % variation. As shown in Figure 3.6 and 3.7, throughout the Sludge monitoring period of 620 days, the characteristics of the prepared sludge were very consistent and fell into the typical range of both actual primary and secondary sludges. 3 2 1 0 0 . 0 0 8 0 . 0 0 : 6 0 , 0 0 — 4 0 . 0 0 : 2 0 . 0 0 : 0 . 0 0 C o 6 . 0 0 — 0 ) E 4 . 0 0 — 0 ) - 9 3 . 0 0 - 6 4 . 0 0 C o 3 0 . 0 0 — 2 0 . 0 0 4 . 0 0 0 C : I 1 . 2 0 - - 8 8 5 9 - 4 1 — 3 2 : : : I 1 . 6 0 1 . 3 0 1 4 . 6 0 0 0 , C C o 3 . 5 0 0 C C o 2 . 1 7 < 1 0 0 . 0 0 8 0 . 0 0 6 0 . 0 0 4 0 . 0 0 C o 2 0 . 0 0 I 0 . 0 0 0 4 . 0 0 3 . 0 0 — 2 . 0 0 — 1 . 0 0 — 0 . 0 0 1 . 8 0 — . 2 1 . 5 0 - 1 . 2 0 - 0 . 9 0 — 0 . 6 0 — 0 . 3 0 — 0 . 0 0 T a - . . ‘ . j . . 1 r t e i a . . . . . . . - — — z P f f l O . . . . Y S z z z z : Y _ — J L i i J J J J J J i I k I - - - - - T K N — — T P ‘ , E E S T K N X X T P - A C O D N S S - ç 4 9 1 2 6 2 0 3 3 0 8 3 7 1 4 4 8 4 9 7 5 6 1 6 1 8 T i m e , d a y s F i g u r e 3 . 6 C h a r a c t e r i s t i c s o f P r i m a r y S y n t h e t i c S l u d g e m o n i t o r e d t h r o u g h o u t t h e e x p e r i m e n t a l p r o g r a m : ( a ) P r o t e i n , V S ; ( b ) T K N , T P ; ( c ) C O D I V S S N P N P ( b ) c c - C / N — — C c ) \ \ c c - — - - - C O D N S S C d ) 0 C O 2 . 0 0 — 0 . 0 0 - 1 2 . 0 0 : 8 . 0 0 - 4 . 0 0 0 . 0 0 2 . 4 0 1 . 6 0 - 0 . 8 0 - 0 . 0 0 1 4 9 1 2 6 2 0 3 3 0 8 3 7 1 4 4 8 4 9 7 5 6 1 6 1 8 T i m e , d a y s F i g u r e 3 . 7 C h a r a c t e r i s t i c s o f S e c o n d a r y S y n t h e t i c S l u d g e m o n i t o r e d t h r o u g h o u t t h e e x p e r i m e n t a l p r o g r a m : ( a ) P r o t e i n , V S ; ( b ) T K N , T P ; ( c ) C / N ; ( d ) C O D N S S 33 CHAPTER FOUR EXPERIMENTAL PROGRAMS This chapter presents details of system seeding and acclimatization, followed by a series of experimental designs emphasizing the effects of influent feed sludge ratio (SR) and recycle ratio (RR) on the process performance. Maximum system loading capacity and the recovery process after a complete failure, are further investigated. An overview of the sampling program, analytical techniques, and data I statistical analysis complete the chapter. 4.1 ACCLIMATIZATION PROCESS Acclimatization is an important step in determining the success or failure of the process. A careful seeding and start up of the system is required. 4.1.1 System Seeding and Start up Loading In April 1988, sludge taken from the anaerobic primary sludge digester of the Lion’s Gate treatment plant (whose characteristics are shown in Table 4.1) in North Vancouver, B.C., was used to seed both reactors with a ratio of 1:1 for seed sludge and tap water. Following the seeding, the system was fed initially at a flow rate of 2 litres/day, with a ratio of primary and secondary synthetic sludges of about 80:20 (by volume); this was approximately equivalent to a sludge loading rate of 0.1 gCOD/gVSS/d and a 34 Table 4.1 Characteristics of Anaerobic Sludge used in Seeding the System [Anaerobic sludge digester/Lion’s Gate treatment plant] Characteristics Concentration mg/L %Dsolids pH 7.2 Total Alkalinity, 2740 mg/L as CaCo3 COD Total COD 12490 Soluble COD 3150 Solids TS 9300 TVS 6900 74 SS 8100 VSS 6100 75 Nitrogens NH4—N 600 NOX 0.25 TKN 800 5 Phosphorus P04-P 65 TP 80 2.5 Volatile acids HAc 45 volumetric loading rate of 1.2 gCOD/L/d, as recommended by Zeeuw, (1980). ‘The calculations of seed sludge volume and starting loading rate are shown in Table A2.1 of Appendix A. The loading rate was not increased unless more than 80% of the influent soluble COD was digested. After the system stabilized, the flow rate was increased to 5 L/day and loading optimization was started. 3 5 4 . 1 . 2 S y s t e m O p e r a t i n g C o n d i t i o n s D u r i n g t h e a c c l i m a t i z a t i o n p r o c e s s , t h e s y s t e m w a s o p e r a t e d a t p H v a l u e s o f 5 a n d 7 f o r t h e A - U A S B a n d M - U A S B r e a c t o r s , r e s p e c t i v e l y . T h e A - U A S B r e a c t o r w a s e q u i p p e d w i t h a m e c h a n i c a l m i x e r , r u n n i n g f o r o n l y t h e f i r s t t w o w e e k s o f a c c l i m a t i z a t i o n a t t h e r a t e o f 2 0 r p m , t o e n s u r e s u f f i c i e n t c o n t a c t b e t w e e n b a c t e r i a a n d i n c o m i n g f e e d ; t h e s e t t l e d s l u d g e o f t h e s l u d g e b e d w a s w a s t e d d a i l y a t 5 - 1 0 % o f t h e i n f l u e n t f l o w r a t e , t o m a i n t a i n s u f f i c i e n t a c t i v e v o l u m e i n t h e r e a c t o r . H o w e v e r , n o s l u d g e w a s t i n g w a s n e c e s s a r y f o r t h e M - U A S B r e a c t o r . A l s o , t h e f l u i d i z e d s l u d g e b l a n k e t e f f l u e n t w a s r e c y c l e d c o n t i n u o u s l y b a c k t o t h e s l u d g e b e d ( R R ) a t t h e r a t e o f 4 a n d 7 t i m e s o f t h e i n f l u e n t f l o w r a t e f o r t h e A - U A S B a n d M - U A S B r e a c t o r s , r e s p e c t i v e l y . 4 . 2 E X P E R I M E N T A L D E S I G N T h e d e s i g n a i m e d t o a c c o m p l i s h t h e r e s e a r c h o b j e c t i v e s a s m e n t i o n e d e a r l i e r . T h e r e l a t i o n s h i p s o f e a c h c o m p o n e n t i n t h e e x p e r i m e n t a l d e s i g n a r e i l l u s t r a t e d i n F i g u r e 4 . 1 . T h e p r o c e s s e f f e c t i v e n e s s c a n b e e v a l u a t e d m a i n l y i n t e r m s o f t h e p r o c e s s p e r f o r m a n c e , a t d i f f e r e n t 2 b y 2 f a c t o r i a l d e s i g n r u n n i n g c o n d i t i o n s ( S R a n d R R ) a n d o p t i m a l o p e r a t i n g c o n d i t i o n ; w h e r e a s , t h e p r o c e s s s u i t a b i l i t y c a n a l s o b e a s c e r t a i n e d t h r o u g h t h e m a x i m u m s y s t e m l o a d i n g c a p a c i t y a n d r e c o v e r y p r o c e s s a f t e r a s e v e r e f a i l u r e . T h e p r o c e s s f e a s i b i l i t y a n d d e s i g n c r i t e r i a a r e f i n a l l y i n i t i a t e d . I t w a s a s s u m e d t h a t t h e s y s t e m r e a c h e d a p s e u d o s t e a d y - s t a t e c o n d i t i o n w h e n t h e g a s p r o d u c t i o n , % C H4 c o n t e n t , a n d e f f l u e n t C O D r e a c h e d a p p r o p r i a t e l y 36 steady values, with less than 10 % variation (about 2-3 system HRT). FIgute 4.iAShernatIc F!owPlagrarn:ol:ExPerImefltaI:DeSigflS:.: I System set-up I Synthetic sludge L Acclimatization L Experimental Runs Optlmai operating condition J Max. load / Recovery Effectiveness Feasibility Suitability Design Criteria rn 4.2.1 Optimum “Best known” Operating Conditions A 2 by 2 factorial design was applied to optimize the feed SR and RR within the A-UASB and M-UASB reactors. After the acclimatization process appeared to reach a pseudo steady-state at about 40-50 days, a number of different running conditions was commenced (as shown in Table 4.2), to maximize the gas production, % CH, and also to achieve a reasonable supernatant quality. Samples were taken and analyzed twice a week for COD, TKN, TP, TS, TVSS, ‘TSS, TVSS, NH4,P0 WA, and % gas components. The influent flow rate and gas production were recorded daily. The actual sampling program and schedules are shown in Figure 4.2. Each running condition was not changed, unless pseudo steady- state, with a minimum 2-3 system HRT and/or more than 80 % soluble COD removal efficiency ( 10-15 % variation in effluent soluble COD ) was achieved.For the first step in loading 37 Table 4.2 Experimental Running Conditions During the Optimal Operating Condition and Maximum Loading Capacity and Recovery Period ExperimentalRuns J Sludge Feed Ratio Recycle Ratio Flaw Ratè,lJd • (SR) (RR) (FR) Phase 1: Reference Condition (Acclimatization) 0 80/20 4/7 5-6 1 80/20 2/4 5—6 2 80/20 6/10 5-6 3 50/50 6/10 5—6 4 50150 214 5-6 Phase 2: Best known condition 5 70/30 3/6 5-6 6 70/30 5/8 5—6 7 60/40 5/8 5—6 8 60/40 3/6 5—6 9 80/20 5/8 5—6 Phase 3: Additional Runs — 10 80/20 4/7 5-6 11 90/10 5/8 5—6 12 90/10 3/6 5—6 Maximum Loading capacity: SR = Ratio of Primary/Secondary Sludges HRT. days 9.0, 4.5, 3.0, 2.25, 1.5 RR = Ratio of Qr/Qin Recovery Periods: where Qr, Qin = recycle and influent flow rate HRT, days @ 1.5, 2.25, 3.0, 4.5, 9.0 ie. 4/7, Qr = 4*Qin in the A-UASB and Qr = 7*Qin in the M-UASB ‘optimization, an arbitrary reference running condition (SR8O/20 and RR4/7), used in the acclimatization process, was adopted as an initial running condition for the design of the experimental runs. The first four running conditions followed and the response parameters for each one was monitored and analyzed continuously, until a pseudo steady-state was obtained. Fi gu re 4. 2 Sa m pl in g Pr og ra m s: R es po ns e Pa ra m et er s/ Sa m pl in g Po in ts a n d Fr eq ue nc y/ Pr es er va tio n a n d St or ag e Re sp on se Pr es er va tio n/ Sa m pl in g Po in ts an d Fr eq ue nc y Pa ra m et er s St or ag e 01 1 2 3 4 5 6 7 8 9 10 1. So lid s T S N o — — — — — — — — V S N o — — — — — — — SS N o : : = : = V SS N o 2. O rg an ic s To ta lC O D N o * * — — — — — — — — Fi lte rC O D N o * * — — — — — — — — 3. ln or ga ni cs N H 4- N Y es * * — — — — — — — — P0 4- P Y es * * — — — — — — — — TK N Y es * * — — — — — — — — TP Y es * * — — — — — — — — 4. V ol at ile A dd s H Ac Y es * * — — — — — — — — H Pr Y es * * — — — — — — — — lso -H Br Y es * * — — — — — — — — H Br Y es * * — — — — — — — — A- HV r Y es * * — — — — — — — — lso -H V r Y es * * — — — — — — — — HV r Y es * * — — — — — — — — H H e Y es * * — — — — — — — — 5. G as C om po si tio n N o — — Pr od uc tio n N o — — Y ie ld s N o — — 35 C Le ge nd :) Sa m pI in g Po in t L eg en ds : * = O np e a m o n th fo rP rim ar y/ Se co nd ar y Sy nt he tic Sl ud ge s (01 ,02 ) — = Iw ic e a n d/ or th re e tim es a w ee k Go 3 9 T h e a v e r a g e r e s p o n s e v a l u e s o f e a c h r u n n i n g c o n d i t i o n w e r e c a l c u l a t e d i n t e r m s o f m a i n e f f e c t s a n d i n t e r a c t i o n o f e a c h p a r a m e t e r , p h a s e m e a n , r e f e r e n c e m e a n , a n d c h a n g e i n m e a n r e s p o n s e b y a n a p p l i c a t i o n o f Y a t e ’ s a l g o r i t h m . W i t h t h e s e r e s u l t s , c o u p l e d w i t h 2 S E ( s t a n d a r d e r r o r s ) f o r e a c h i n d i v i d u a l a v e r a g e a n d a n a p p l i c a t i o n o f R e s p o n s e S u r f a c e M e t h o d ( R S M ) , i d e n t i f i c a t i o n o f t h e “ b e s t k n o w n ” r u n n i n g c o n d i t i o n t h a t g e n e r a t e d t h e m a x i m u m m e t h a n e g a s p r o d u c t i o n a n d g o o d s u p e r n a t a n t q u a l i t y w a s a c h i e v e d a n d t h e e f f e c t s o f S R a n d R R w e r e a l s o c a l c u l a t e d . T h i s b e s t k n o w n c o n d i t i o n w a s t h e n r e a s s i g n e d a s a n a r b i t r a r y r e f e r e n c e r u n n i n g c o n d i t i o n f o r t h e n e x t f o u r r u n s . 4 . 2 . 2 M a x i n i u m L o a d i n g R a t e a n d R e c o v e r y P e r i o d s T h e l o a d i n g r a t e i n c r e a s e d g r a d u a l l y , s t e p - b y - s t e p u n t i l t h e s y s t e m w a s o v e r l o a d e d , c a u s i n g V F A ’ s t o a c c u m u l a t e w i t h i n t h e s y s t e m . T h e p H d r o p p e d f r o m t h e d e s i r e d r a n g e , r e s u l t i n g i n a n i m b a l a n c e o f a c i d - a n d m e t h a n e - f o r m i n g p o p u l a t i o n ; t h i s s u b s e q u e n t l y l e d t o a s y s t e m u p s e t . B y i n c r e a s i n g t h e l o a d i n g r a t e f r o m t h e o p t i m u m c o n d i t i o n s o b t a i n e d f r o m t h e p r e v i o u s e x p e r i m e n t , t h e m a x i m u m l o a d i n g r a t e w a s d e t e r m i n e d . I n a d d i t i o n , t h e l o a d i n g r a t e w a s d e s i g n e d t o i n c r e a s e g r a d u a l l y s t e p - b y - s t e p , w h i l e t h e p H c o n t r o l l e r w a s o f f , u n t i l t h e s y s t e m c r a s h e d . T h e n t h e l o a d i n g r a t e w a s d e c r e a s e d g r a d u a l l y i n o r d e r t o r e c o v e r t h e s y s t e m a s s h o w n i n T a b l e 4 . 2 . 4 . 2 . 3 S a m p l i n g P r o g r a m a n d A n a l y t i c a l T e c h n i q u e s 4 . 2 . 3 . 1 S a m p l i n g P r o g r a m T h e s a m p l i n g p r o g r a m , a n a l y t i c a l t e c h n i q u e s , a n d d a t a i n t e r p r e t a t i o n w e r e 4 0 c a r e f u l l y d e s i g n e d t o e n s u r e r e l i a b l e a n d a c c u r a t e r e s u l t s , f o r e v a l u a t i o n o f t h e p r o c e s s p e r f o r m a n c e . A n e x t e n s i v e s a m p l i n g p r o g r a m w a s s e t u p t o c h a r a c t e r i z e a n d m o n i t o r t h e s y n t h e t i c s l u d g e a n d s y s t e m p e r f o r m a n c e , a s s h o w n i n F i g u r e 4 . 2 . T h e p r o p o s e d p r o g r a m w a s s t r i c t l y f o l l o w e d d u r i n g t h e a c c l i m a t i z a t i o n p r o c e s s a n d t h e f i r s t f o u r r u n n i n g c o n d i t i o n s ( S e q u e n c e 1 ) , h o w e v e r ; t h e s a m p l i n g p r o g r a m w a s m o d i f i e d s l i g h t l y t o “ s u i t t h e f a c t s ” o b t a i n e d d u r i n g t h e f i r s t f o u r r u n n i n g c o n d i t i o n s . T h e r e s u l t s o f t h e f i r s t f o u r r u n s i n d i c a t e d that t h e s y s t e m c o u l d r e a c h a p s e u d o s t e a d y - s t a t e c o n d i t i o n w i t h i n 2 - 3 H R T ’ s a n d t h a t there w a s v e r y l i t t l e c h a n g e i n t h e r e s p o n s e parameters d u r i n g t h e f i r s t f e w w e e k s o f e a c h r u n n i n g c o n d i t i o n . I t w a s t h e n f e l t j u s t i f i e d t o r e d u c e t h e s a m p l i n g f r e q u e n c y o f t h e n e x t f o u r r u n n i n g c o n d i t i o n s , t o o n c e a w e e k , f o r t h e f i r s t f e w w e e k s a f t e r c h a n g i n g t h e r u n n i n g c o n d i t i o n a n d t w i c e a w e e k a f t e r w a r d , u n t i l t h e s y s t e m r e a c h e d a p s e u d o s t e a d y - s t a t e c o n d i t i o n (more t h a n 8 0 % r e m o v a l e f f i c i e n c y , 2 - 3 H R T s , a n d / o r 5 - 1 0 % v a r i a t i o n o f t h e e f f l u e n t q u a l i t y ). H o w e v e r , m o n i t o r i n g o f t h e g a s p r o d u c t i o n , i n f l u e n t f l o w r a t e , a n d g a s c o n t e n t w e r e undertaken a s s c h e d u l e d , s o t h a t t h e y c o u l d b e u s e d a s i n d i c a t o r s t o p r e d i c t t h e p s e u d o s t e a d y - s t a t e c o n d i t i o n o f e a c h r u n . T h e s a m p l i n g p r o g r a m f u n c t i o n e d i n t w o m a j o r p a r t s ; that f o r a c c l i m a t i z a t i o n p e r i o d s , a n d t h a t f o r e x p e r i m e n t a l p e r i o d s . L i q u i d s a m p l e s w e r e t a k e n f r o m e i g h t d i f f e r e n t p o i n t s a l o n g t h e h e i g h t o f t h e A - U A S B a n d M - U A S B r e a c t o r s . T w o g a s s a m p l i n g r i g s w e r e u s e d . I n g e n e r a l , a l i q u i d s a m p l e o f 2 5 0 m l w a s c o l l e c t e d , p r e s e r v e d , a n d a n a l y z e d f o r v a r i o u s r e s p o n s e parameters t w i c e a w e e k . I n a d d i t i o n , s y s t e m m a i n t e n a n c e , t i g h t e n i n g o f a l l c l a m p s a n d r e a c t o r ’ s c o v e r , c h a n g i n g o f a l l t u b i n g l i n e s a n d p u m p h e a d s , a n d c h e c k i n g o f t h e w a t e r l e v e l a n d t u b i n g o f t h e g a s f l o w m e t e r s , e t c . , 4 1 w e r e c a r r i e d o u t r e g u l a r l y , t o e n s u r e t h a t p r o p e r s y s t e m o p e r a t i o n w a s m a i n t a i n e d a n d t o p r e v e n t a n y i n c i d e n t s o f l e a k i n g a n d / o r s p i l l a g e w h i c h m i g h t o c c u r d u r i n g t h e e x p e r i m e n t a l r u n s . 4 . 2 . 3 . 2 A n a l y t i c a l T e c h n i q u e s A n a l y t i c a l m e t h o d s f o r a l l r e s p o n s e p a r a m e t e r s w e r e i n a c c o r d a n c e w i t h S t a n d a r d M e t h o d s (i6th e d i t i o n , 1 9 8 5 ) , u n l e s s s p e c i f i c a l l y d e s c r i b e d s e p a r a t e l y . F o r s o l u b l e s a m p l e a n a l y s i s , s a m p l e p r e s e r v a t i o n a n d s t o r a g e w e r e r e q u i r e d p r i o r t o a n y f u r t h e r a n a l y s i s . A s a m p l e o f 1 5 0 m l c o l l e c t e d f r o m e a c h s a m p l i n g p o i n t w a s c e n t r i f u g e d a t 2 , 5 0 0 r p m . f o r a b o u t 1 5 m i n u t e s , i n a n I n t e r n a t i o n a l E q u i p m e n t C o m p a n y M o d e C S C e n t r i f u g e a n d t h e s u p e r n a t a n t w a s t h e n f i l t e r e d t h r o u g h a n o . 4 W h a t m a n f i l t e r . A f i l t r a t e a l i q u o t w a s a n a l y z e d f o r s o l u b l e C O D a n d t h e r e m a i n d e r w a s p r e s e r v e d a n d s t o r e d , a s s h o w n i n F i g u r e 4 . 2 , f o r f u r t h e r a n a l y s i s . A n a l y t i c a l m e t h o d s f o r e a c h r e s p o n s e p a r a m e t e r c a n b e s u m m a r i z e d a s f o l l o w s : C h e m i c a l O x y g e n D e m a n d ( C O D ) S a m p l e s i z e s o f 0 . 1 - 0 . 5 a n d 1 . 0 - 2 . 0 m l w e r e u s e d t o a n a l y z e f o r t o t a l a n d s o l u b l e C O D u s i n g t h e d i c h r o m a t e o x i d a t i o n r e f l u x m e t h o d a s o u t l i n e d i n t h e S t a n d a r d M e t h o d s . S o l i d s A s a m p l e o f 3 0 - 6 0 m l o f e a c h s a m p l i n g p o i n t w a s u s e d f o r t h e a n a l y s i s o f s o l i d s c o n t e n t a s f o l l o w s : 4 2 T S / T V S - A s a m p l e o f 1 0 - 3 0 m l c o l l e c t e d f r o m t h e s a m p l i n g p o i n t n u m b e r 1 , 2 , 3 , a n d 6 w a s p o u r e d s e p a r a t e l y i n t o t h e k n o w n w e i g h t o f e v a p o r a t i n g d i s h , w h i c h w a s h e a t e d f o r 2 h o u r s a t 5 5 0 ° C i n s i d e t h e m u f f l e f u r n a c e a n d t h e n w e i g h e d a f t e r c o o l i n g . S a m p l e s w e r e t h e n d r i e d o v e r n i g h t i n a F i s h e r i s o t e m p o v e n ( M o d e l 3 5 0 ) a t 1 0 4 ° C . A f t e r c o o l i n g t h e s a m p l e s i n s i d e a v a c u u m d e s i c c a t o r , t h e s a m p l e s w e r e t h e n w e i g h e d a n d b u r n t f o r a b o u t 2 h o u r s , f o r v o l a t i l e s o l i d s , i n a L i n b e r g m u f f l e o v e n a t 5 5 0 ° C . T h e s a m p l e s w e r e f i n a l l y c o o l e d i n s i d e a v a c u u m d e s i c c a t o r a n d w e i g h e d a g a i n . T S S I T V S S - A s a m p l e o f 1 0 - 2 0 m l c o l l e c t e d f r o m t h e s a m p l i n g p o i n t s n u m b e r e d 1 - 8 , w a s t r e a t e d s i m i l a r l y t o t h a t o f T S / T V S , e x c e p t t h a t a 9 3 4 - A H W h a t m a n g l a s s m i c r o f i b e r w a s u s e d t o f i l t e r t h e s a m p l e i n s t e a d o f u s i n g t h e e v a p o r a t i n g d i s h . C a l c u l a t i o n o f t h e w e i g h t a n d c o n c e n t r a t i o n o f s o l i d s w a s m a d e a 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 . T o t a l O r g a n i c C a r b o n ( T O C ) T h e f i l t e r e d s a m p l e s w e r e p r e s e r v e d a s d e s c r i b e d i n t h e C O D s e c t i o n , a n d a n a l y z e d i n a n a u t o m a t i c S h i m a d z u T o t a l O r g a n i c C a r b o n A n a l y z e r , T O C - 5 0 0 , u s i n g t h e c o m b u s t i o n - i n f r a r e d m e t h o d ( T O C - 5 0 0 I n s t r u c t i o n M a n u a l , S h i m a d z u S c i e n t i f i c I n s t r u m e n t s , I n c . ) . P r o t e i n s T h e c r u d e p r o t e i n c o n t e n t o f t h e s a m p l e s c a n b e d e t e r m i n e d f r o m t h e T K N v a l u e 4 3 b y m u l t i p l y i n g i t w i t h a f a c t o r o f 6 . 2 5 . T h i s i s b a s e d o n t h e a s s u m p t i o n s t h a t a l l t h e n i t r o g e n o f t h e o r g a n i c m a t t e r i s d u e t o p r o t e i n , a n d t h a t p r o t e i n c o n t a i n s 1 6 p e r c e n t n i t r o g e n o n a v e r a g e ( 1 0 0 / 1 6 = 6 . 2 5 ) . C a r b o h y d r a t e s T h e t o t a l s o l u b l e c a r b o h y d r a t e s w e r e d e t e r m i n e d b y t h e f e r r i c y a n i d e m e t h o d a s o u t l i n e d i n t h e H a n d b o o k o f M i c r o m e t h o d s f o r t h e B i o l o g i c a l S c i e n c e ( 1 9 7 4 ) . I n o r g a n i c / A c i d s A s o l u b l e s a m p l e , a f t e r b e i n g p r e s e r v e d a n d s t o r e d f o r u p t o a w e e k , w a s a n a l y z e d f o r NH4-N, P04-P, T K N R ’ P , a n d V F A s a s f o l l o w s : N H4-N - A l i q u o t s o f s o l u b l e s a m p l e s c o l l e c t e d f r o m t h e s a m p l i n g p o i n t s n u m b e r e d 1 - 8 w e r e a n a l y z e d f o r N H4-N, u s i n g t h e A u t o m a t e d P h e n a t e M e t h o d ( A . P . H . A . , 1 9 8 0 ) . A p p r o p r i a t e d i l u t i o n s r a n g i n g f r o m 1 / 5 0 - 1 / 1 0 0 w e r e m a d e p r i o r t o d e t e r m i n i n g t h e i n t e n s i t y o f t h e s a m p l e c o l o u r s u s i n g a T e c h n i c o n A u t o A n a l y z e r I I a n d t h e n c o m p a r e d w i t h t h o s e o f p r e p a r e d N H4-N s t a n d a r d s , r a n g i n g f r o m 1 . 0 - 3 . 0 m g / L i n o r d e r t o e s t i m a t e t h e c o n c e n t r a t i o n o f N H4-N i n t h e s a m p l e . P04-P - T h e a u t o m a t e d a s c o r b i c a c i d r e d u c t i o n m e t h o d ( T e c h n i c o n I n d u s t r i a l S y s t e m , 1 9 7 3 ) w a s u s e d t o a n a l y z e P04-P. I n a n a c i d m e d i u m , a m m o n i u m m o l y b d a t e a n d p o t a s s i u m a n t i m o n y l t a r t r a t e r e a c t w i t h P04-P t o f o r m a n a n t i m o n y - 4 4 p h o s p h o m o l y b d a t e c o m p l e x ; t h i s i s f u r t h e r r e d u c e d w i t h a s c o r b i c a c i d , y i e l d i n g a n i n t e n s e b l u e c o l o u r . T h e i n t e n s i t y o f t h e s a m p l e c o l o u r w a s d e t e r m i n e d b y a T e c h n i c o n A u t o A n a l y z e r I I . C a l c u l a t i o n o f P04-P c o n c e n t r a t i o n w a s m a d e b y c o m p a r i n g t h e s a m p l e r e s p o n s e s w i t h t h o s e o f p r e p a r e d s t a n d a r d s o f P04-P. T K N I T P - A s e r i e s o f k n o w n T K N / T P s t a n d a r d s , s o l u b l e s a m p l e s , a n d d r i e d s o l i d s s a m p l e s ( a f t e r b e i n g d r i e d a t 1 0 4 C ) w e r e d i g e s t e d i n t h e T e c h n i c o n B l o c k D i g e s t e r 4 0 w i t h c o n c e n t r a t e d H2S04 a n d K2S04T h i s p r o c e d u r e l i b e r a t e d a l l b o u n d o r g a n i c n i t r o g e n a n d p a r t i c u l a t e T P t o N H4-N a n d P04-P, r e s p e c t i v e l y . T h e T K N / T P c o n c e n t r a t i o n s o f t h e s a m p l e s a n d s t a n d a r d s w e r e m e a s u r e d c o l o r i m e t r i c a l l y , u s i n g t h e T e c h n i c o n A u t o A n a l y z e r I I a n d c a l c u l a t e d b y c o m p a r i n g t h e r e s p o n s e s o f b o t h s a m p l e s a n d s t a n d a r d s . V o l a t i l e f a t t y a c i d s ( V F A ) S a m p l e s t a k e n f r o m s a m p l i n g p o i n t s n u m b e r e d 1 - 8 w e r e f i l t e r e d u s i n g n o . 4 W h a t m a n f i l t e r s a n d f r o z e n i n s e a l e d p l a s t i c p i p e t s . A f t e r t h e t i m e o f a n a l y s i s , t h e s a m p l e s w e r e t h a w e d a t r o o m t e m p e r a t u r e a n d d i l u t e d 1 : 1 0 w i t h d i s t i l l e d w a t e r . A 1 . 0 1t d s a m p l e , a f t e r b e i n g a c i d i f i e d b y a d r o p o f 1 % s o l u t i o n o f p h o s p h o r i c a c i d t o b r i n g t h e p H b e l o w 3 . 0 , w a s i n j e c t e d i n t o a c o m p u t e r - c o n t r o l l e d H e w l e t t P a c k a r d 5 8 8 0 A g a s c h r o m a t o g r a p h e q u i p p e d w i t h a f l a m e i o n i z a t i o n d e t e c t o r ( F I D ) , u s i n g h e l i u m a s t h e c a r r i e r g a s . T o a c h i e v e a c c u r a t e a n d r e l i a b l e r e s u l t s , m i c r o s y r i n g e s ( H a m i l t o n M o d e l 7 0 i N , 1 0 L l ) a n d a H e w l e t t P a c k a r d a u t o - s a m p l e r ( M o d e l 7 6 7 2 A ) w e r e u s e d . T h e g l a s s 4 5 c o l u m n ( 0 . 9 1 m l o n g w i t h a 6 . 0 m m ( O D ) a n d 2 . 0 m m ( I D ) ) p a c k e d w i t h 0 . 3 % C a r b o w a x / 0 . 1 % H3P04 o n S u p e l c o C a r b o p a k C ( s u p p l i e d b y S u p e l c o I n c . ) , w a s c o n d i t i o n e d a c c o r d i n g t o t h e p r o c e d u r e o u t l i n e d i n t h e S u p e l c o B u l l e t i n 7 5 1 E ( 1 9 8 1 ) . T h e o p e r a t i n g c o n d i t i o n s f o r t h e c h r o m a t o g r a p h w e r e m a i n t a i n e d a s f o l l o w s : I n j e c t i o n p o r t t e m p e r a t u r e = 1 5 0 o C D e t e c t i o n p o r t t e m p e r a t u r e = 2 0 0 ° C I s o t h e r m a l o v e n t e m p e r a t u r e 1 2 0 ° C F l o w r a t e o f c a r r i e r g a s ( h e l i u m ) = 2 0 m i / m m T h e r e s p o n s e p e a k s o f e a c h s a m p l e w e r e q u a n t i f i e d b y c o m p a r i n g w i t h e x t e r n a l s t a n d a r d m e t h o d s , u s i n g r e a g e n t g r a d e s t a n d a r d s . G a s c o n t e n t G a s s a m p l e s w e r e e x t r a c t e d f r o m s a m p l i n g p o i n t s 9 a n d 1 0 ( S e e F i g u r e 4 . 2 ) u s i n g a 1 - m I H a m i l t o n S y r i n g e . T h e i n j e c t i o n s y r i n g e w a s f l u s h e d t w i c e , b e f o r e t h e i n j e c t i o n s a m p l e w a s t a k e n . T h e p l u n g e r w a s d e p r e s s e d t o e x p e l t h e e x c e s s g a s p r i o r t o i n s e r t i n g t h e s y r i n g e n e e d l e t h r o u g h t h e d i a p h r a g m o f t h e s a m p l e i n j e c t i o n p o r t o f t h e F i s h e r M o d e l 2 9 G a s P a r t i t i o n e r . T h e s a m p l e w a s t h e n r a p i d l y i n j e c t e d a n d a m i x t u r e o f g a s w a s s w e p t t h r o u g h t w o c h r o m a t o g r a p h i c c o l u m n s , p a c k e d w i t h a l i q u i d p h a s e i s o n a s o l i d s u p p o r t k n o w n a s D E H S a n d 4 2 - 6 0 m e s h M o l e c u l a r S i e v e f o r c o l u m n 1 a n d 2 r e s p e c t i v e l y , b y a c o n t i n u o u s f l o w o f t h e h e l i u m c a r r i e r g a s . T h e g a s c o m p o n e n t s w e r e s e p a r a t e d a n d e l u t e d f r o m t h e s y s t e m a t d i f f e r e n t r e t e n t i o n t i m e s . A t h e r m a l c o n d u c t i v i t y d e t e c t o r t h e n s e n s e d t h e d i f f e r e n c e s i n c o n d u c t i v i t y o f t h e s e p a r a t e d c o m p o n e n t s , w h i c h 46 was amplified and integrated for quantification. The retention time elapsed from the point of injection to the emergence of a peak is characteristic of a particular gas. The area of a peak is also proportional to the concentration of the gas. Calculation of the gas concentration was made by comparing the peak areas of measurable samples and the standard. 4.2.4 Data and Statistical Analysis All data in this research were analyzed and plotted by using an integrated software program, Symphony version 1.2 and Lotus version 2.2 with an add-in program (Aliways ). Some of the graphics were imported into the Freelance software program, version 3.0, for further modifications. For the report preparation and statistical analysis, a Word Perfect 5.1 program and Systat/Sygraph programs were used. 4 7 C H A P T E R F I V E R E S U L T S A N D D I S C U S S I O N T h i s c h a p t e r d e a l s w i t h t w o m a i n s e c t i o n s : ( i ) t h e a c c l i m a t i z a t i o n m o d e ; a n d ( i i ) t h e e x p e r i m e n t a l m o d e . T h e d e v e l o p m e n t o f t h e a c c l i m a t i z a t i o n p r o c e s s a n d a c o m p a r i s o n o f d i f f e r e n t a c c l i m a t i z a t i o n a l t e r n a t i v e s i s f o l l o w e d b y t h e e f f e c t s a n d i n t e r a c t i o n o f S l u d g e R a t i o ( S R ) a n d R e c y c l e R a t i o ( R R ) o n t h e r e s p o n s e s a n d p r o c e s s p e r f o r m a n c e , m a x i m u m l o a d i n g c a p a c i t y , a n d s y s t e m r e c o v e r y p r o c e s s . S y s t e m f e a s i b i l i t y , d e s i g n c r i t e r i a , a n d e f f e c t i v e a n d r e l i a b l e s y s t e m i n d i c a t o r s a r e a l s o d i s c u s s e d . 5 . 1 A C C L I M A T I Z A T I O N P R O C E S S I t h a s l o n g b e e n r e c o g n i z e d t h a t t h e a c c l i m a t i z a t i o n p r o c e s s h a s a g r e a t i m p a c t o n t h e s u c c e s s o r f a i l u r e o f s y s t e m o p e r a t i o n . U n d e r s t a n d i n g t h e c o n c e p t u a l d e v e l o p m e n t o f t h e p r o c e s s a n d a c c l i m a t i z i n g t h e s y s t e m p r o p e r l y a r e e x t r e m e l y i m p o r t a n t , i n o r d e r t o a c h i e v e t h e d e s i r e d l e v e l o f t h e s y s t e m p e r f o r m a n c e . 5 . 1 . 1 D e v e l o p m e n t o f t h e A c c l i m a t i z a t i o n P r o c e s s O n e o f t h e m a i n d i f f i c u l t i e s i n t h e t r e a t m e n t o f s e w a g e s l u d g e a p p e a r s t o b e i n t h e d e v e l o p m e n t o f s u i t a b l e a n d e f f i c i e n t m i x t u r e s o f m i c r o b i a l c u l t u r e s t o t r e a t t h i s p a r t i c u l a r t y p e o f w a s t e i n t h i s t y p i c a l r e a c t o r . T o a l l e v i a t e t h i s p r o b l e m , i t i s n e c e s s a r y 4 8 t o u n d e r s t a n d t h e p r i n c i p l e / b e h a v i o u r / r e s p o n s e o f t h e U A S B p r o c e s s u n d e r d i f f e r e n t o p e r a t i n g c o n d i t i o n s . 5 . 1 . 1 . 1 B e h a v i o u r a n d R e s p o n s e T h e U A S B i s a s u s p e n d e d - g r o w t h b i o m a s s s y s t e m c o m p o s e d o f t h r e e m a i n p o r t i o n s : ( i ) s l u d g e b e d ; ( i i ) s l u d g e b l a n k e t ; a n d ( i i i ) s e t t l e r . M o s t o f t h e r e a c t i o n s o c c u r i n t h e l o w e r p a r t o f t h e s y s t e m ( s l u d g e b e d a n d b l a n k e t ) . I n t h e t w o - p h a s e U A S B - U A S B p r o c e s s , c o m p l e x i n f l u e n t s u b s t r a t e s s u c h a s c a r b o h y d r a t e s , p r o t e i n s , a n d l i p i d s a r e f i r s t h y d r o l y s e d a n d a c i d i f i e d i n s i d e t h e A - U A S B r e a c t o r b y a p r e d o m i n a n t l y a c i d o g e n i c b a c t e r i a p o p u l a t i o n ; t h i s p r o d u c e s s i m p l e c o m p o u n d s s u c h a s v o l a t i l e f a t t y a c i d s ( V F A s ) . T h e s e V F A s t h e n p a s s t h r o u g h t h e M - U A S B r e a c t o r , w h e r e t h e y a r e s u b s e q u e n t l y c o n v e r t e d t o C H4 a n d C O2 g a s e s b y p r e d o m i n a n t l y m e t h a n o g e n i c b a c t e r i a . S m a l l a m o u n t s o f N2 g a s a n d o t h e r b y - p r o d u c t s a r e a l s o p r o d u c e d . U s i n g a s t e p - l o a d i n g a p p r o a c h r a t h e r t h a n c o n t i n u o u s ( c o n s t a n t ) l o a d i n g f o r s y s t e m s t a r t - u p , t h e s y s t e m w a s c a r e f u l l y a c c l i m a t i z e d w i t h a n i n c r e a s e i n i n f l u e n t l o a d i n g t o k e e p p a c e , a s c l o s e a s p o s s i b l e , w i t h a n i n c r e a s e i n s y s t e m b i o m a s s ( B u l l e t a l . , 1 9 8 3 ) . T h e i n f l u e n t s u b s t r a t e w a s , t h e r e f o r e , s t a r t e d a n d m a i n t a i n e d i n i t i a l l y a t a l o w l o a d i n g r a t e ( s u b - c r u c i a l l e v e l ) t o e n s u r e g r e a t e r c o n v e r s i o n a n d b i o m a s s g r o w t h r a t e s t h a n w a s h o u t o n e . T h e s y s t e m l o a d i n g r a t e w a s n o t i n c r e a s e d u n t i l m o r e t h a n 8 0 % r e m o v a l e f f i c i e n c y o f t h e s y s t e m i n f l u e n t C O D h a d b e e n a c h i e v e d . O v e r - o r - u n d e r h y d r a u l i c a n d / o r o r g a n i c l o a d i n g a U A S B c a n a d v e r s e l y a f f e c t t h e s t a r t u p p r o c e s s . O v e r - l o a d i n g t e n d s t o 4 9 p r o d u c e e x c e s s i v e g a s , c a u s i n g a g a s - l i f t i n t h e r e a c t o r , f l o a t a t i o n o f t h e s l u d g e s o l i d s , a n d f i n a l l y , a s y s t e m w a s h o u t p r o c e s s . U n d e r - l o a d i n g r e s u l t s i n t h e f o r m a t i o n o f a m a s s i v e c o m p a c t e d s l u d g e , t h u s r e d u c i n g t h e e f f i c i e n c y o f t h e s y s t e m s i g n i f i c a n t l y ( H u l s o f f - P o l e t a l . , 1 9 8 3 ) . I n i t i a l l y , t h e s t a r t u p o f n o n - a t t a c h e d b i o m a s s p r o c e s s e s , l i k e U A S B , r e l y i n g h e a v i l y o n s u s p e n d e d b i o m a s s a n d a t t a c h e d m i c r o f l o r a , a p p e a r s t o i n d u c e a “ w a s h o u t p h e n o m e n o n . L a r g e q u a n t i t i e s o f t h e U A S B b i o m a s s w e r e w a s h e d o u t o f t h e s y s t e m d u r i n g t h e f i r s t c o u p l e o f w e e k s o f t h i s r e s e a r c h , f o l l o w e d b y d e v e l o p m e n t o f s m a l l g r a n u l e s o r p e l l e t s . T h e n , t h e r e m a i n i n g b i o m a s s s h o w e d b e t t e r s e t t l e a b i l i t y a n d s e r v e d a s a s u r f a c e m e d i u m f o r a c t i v e m i c r o b i a l m a s s g r o w t h . M i n i m i z a t i o n o f b i o m a s s w a s h o u t i s , t h e r e f o r e , c r u c i a l t o r e a c t o r a c t i v i t y d u r i n g t h e s t a r t u p p r o c e s s . A s u i t a b l e t y p e o f s e e d s l u d g e , s e e d i n g r a t i o a n d a c c l i m a t i z a t i o n , s e e m t o b e e f f e c t i v e i n c o m p e n s a t i n g f o r t h e s o l i d s w a s h o u t p h e n o m e n a . P r e c i p i t a t i o n o f s a l t s o f C a C O3 a n d P0;3 i n s i d e t h e r e a c t o r i s a l s o c r e d i t e d f o r a n i n c r e a s e i n s l u d g e s e t t l e a b i l i t y , a s t h e s e s a l t s w e i g h d o w n t h e p e l l e t s , a n d i n c r e a s e t h e s e t t l i n g c a p a c i t y ( K l a p w i j k e t a l . , 1 9 8 1 ) . C o n s i d e r i n g a l l t h e s e p o i n t s a n d b e h a v i o u r s , a c a r e f u l s y s t e m s e e d i n g a n d s t a r t u p o f t h e U A S B - U A S B p r o c e s s w a s s e l e c t e d a s o u t l i n e d i n C h a p t e r 3 . 5 . 1 . 1 . 2 A c c l i m a t i z a t i o n A l t e r n a t i v e s T o d e v e l o p a n e f f e c t i v e s t a r t u p a n d a c c l i m a t i z a t i o n p r o c e s s , t h e s y s t e m w a s s e e d e d w i t h a h i g h r a t i o o f s e e d s l u d g e t o t a p w a t e r ( 1 : 1 b y v o l u m e ) , t o c o m p e n s a t e f o r 5 0 t h e s o l i d s w a s h o u t p r o b l e m . I n a d d i t i o n , t h r e e a c c l i m a t i z a t i o n a l t e r n a t i v e s w e r e i n v e s t i g a t e d i n d e t a i l ; s a m p l e s w e r e t a k e n r e g u l a r l y a n d a n a l y z e d f o r s e v e r a l p a r a m e t e r s , a s s h o w n i n F i g u r e 4 . 2 . T h e s e a l t e r n a t i v e s w e r e : ( A ) S e e d i n g b o t h A - a n d M - U A S B s w i t h s l u d g e f r o m t h e L i o n ’ s Gate treatment p l a n t a n a e r o b i c s l u d g e d i g e s t e r a n d u s i n g a s t e p - l o a d i n g a p p r o a c h ; ( B ) S e e d i n g b o t h r e a c t o r s w i t h a c c l i m a t i z e d s y n t h e t i c s e e d s l u d g e a n d u s i n g a c o n s t a n t - l o a d i n g a p p r o a c h ; ( C ) S e e d i n g t h e A - U A S B w i t h a c c l i m a t i z e d s y n t h e t i c s e e d s l u d g e , b u t t h e M - U A S B w i t h s l u d g e f r o m t h e L i o n ‘ s Gate a n a e r o b i c s l u d g e d i g e s t e r , u s i n g a s t e p - l o a d i n g a p p r o a c h . T h e r e s u l t s o f t h i s i n v e s t i g a t i o n a r e s u m m a r i z e d a s f o l l o w s : ( a ) W a s h o u t P h e n o m e n o n I n s u s p e n d e d - g r o w t h b i o m a s s s y s t e m s l i k e U A S B , w h e r e t h e treatment p o t e n t i a l i s d i c t a t e d b y t h e d u a l parameters o f t h e b i o m a s s q u a l i t y r e t a i n a b l e i n t h e s y s t e m a n d t h e s p e c i f i c a c t i v i t y o f b i o m a s s ( s u c h a s m e t h a n e p r o d u c t i o n a n d s e t t l e a b i l i t y ), a n i n o c u l a t i o n o f a b o u t 3 0 - 5 0 % reactor v o l u m e o f a c t i v e s l u d g e i s r e q u i r e d . S t a r t - u p a n d a c c l i m a t i z a t i o n o f U A S B r e a c t o r s r e q u i r e s a b o u t 4 - 8 w e e k s t o d e v e l o p a n a c t i v e m i c r o b i a l m a s s s l u d g e (Lettinga, 1 9 7 9 ; Z e e u w , 1 9 8 0 ) . S t a r t - u p , t h e r e f o r e , i s d e p e n d e n t u p o n a n e q u i l i b r i u m b e t w e e n l o a d i n g a n d w a s h o u t a s w e l l a s t h e s e l e c t i o n o f a s u i t a b l e s e e d s l u d g e , w a s t e w a t e r c h a r a c t e r i s t i c s , a n d c a r e f u l m a n a g e m e n t . I n i t i a l l y , l a r g e p o r t i o n s o f b i o m a s s a r e w a s h e d o u t o f t h e s y s t e m ; l a t e r , t h e m i c r o s t r u c t u r a l g r a n u l e s o r p a l l e t s a r e d e v e l o p e d w i t h t h e h e l p o f p r e c i p i t a t e d s a l t s o f c a r b o n a t e a n d p h o s p h a t e . T h e s e 5 1 w e i g h d o w n t h e p e l l e t s , i n c r e a s i n g t h e s e d i m e n t a t i o n c a p a c i t y . A s s h o w n i n F i g u r e 5 . 1 , t h e s y s t e m w i t h t h e s t e p l o a d i n g r a t e o f 0 . 1 0 - 0 . 2 1m3/m-d, d e m o n s t r a t e s t h e w a s h o u t p h e n o m e n o n o f t h e M L V S S ( p o i n t s 1 , 2 , a n d 3 ) a t d a y 2 3 - 4 5 , 1 - 1 5 a n d 1 - 7 f o r a l t e r n a t i v e s A , B , a n d C , r e s p e c t i v e l y . A c t i v e b i o m a s s s e t t l e s a t t h e s l u d g e b l a n k e t ( s a m p l i n g p o i n t n o . 6 , 5 0 e m s f r o m t h e b o t t o m ) o f t h e M - U A S B , t h e n s t a r t s t o b u i l d u p t o a c o n c e n t r a t i o n o f 5 7 5 0 , 1 2 6 5 , a n d 2 5 8 0 m g / L o f M L V S S f o r a l t e r n a t i v e s A , B , C , r e s p e c t i v e l y . I t i s b e l i e v e d t h a t d e v e l o p m e n t o f g r a n u l e s l u d g e a n d p e l l e t i z a t i o n d o o c c u r a t t h e s l u d g e b e d . A c c i d e n t a l l y , t h e r e w a s a c a s e o f s l u d g e s p i l l a g e d u e t o c l o g g i n g i n s i d e t h e r e c y c l e l i n e d u r i n g t h e e x p e r i m e n t a l p r o g r a m . F o r t u n a t e l y , t h e r e w a s s t i l l s u f f i c i e n t b i o m a s s r e m a i n i n g a t t h e b o t t o m o f t h e r e a c t o r ; t h i s w a s c h a r a c t e r i z e d b y v e r y h a r d a n d d e n s e p e l l e t s . A l s o , J i n g - Q i n g Y a n ( 1 9 9 1 ) s t u d i e d a s l u d g e c o n c e n t r a t i o n p r o f i l e a l o n g t h e h e i g h t o f U A S B a n d i n d i c a t e d t h a t t h e r e w e r e 2 d i s t i n c t l a y e r s o f s l u d g e c o n c e n t r a t i o n p r o f i l e s . T h e s e i n c l u d e d a d e n s e s l u d g e b e d ( f r o m 0 - 3 0 c m s . ) w i t h 1 8 - 5 8 g / L V S S a n d a s l u d g e b l a n k e t ( a b o v e 3 7 c m s . ) w i t h 2 - 1 0 g / L V S S . T h e a u t h o r a l s o m e n t i o n e d t h a t s y s t e m s t a r t - u p p r o c e s s w i t h a s l u d g e l o a d i n g r a t e o f l e s s t h a n 0 . 2 k g C O D / k g V S S - d w a s c r u c i a l f o r a s u c c e s s f u l d e v e l o p m e n t o f p e l l e t i z a t i o n . A s m e n t i o n e d e a r l i e r , t h e s t a r t - u p s l u d g e l o a d i n g r a t e i n t h e p r e s e n t c a s e ( U A S B - U A S B ) w a s a b o u t 0 . 1 k g C O D / k g V S S - d a n d t h e c o n c e n t r a t i o n o f M L V S S a t s l u d g e b l a n k e t l e v e l ( 5 0 c m s . h e i g h t ) w a s i n t h e r a n g e o f 1 3 0 0 - 5 8 0 0 m g / L . S i n c e s i m i l a r p a t t e r n s o f s t a r t - u p p r o c e s s a n d M L V S S c o n c e n t r a t i o n r a n g e w e r e o b s e r v e d i n t h e p r e s e n t s t u d y , i t i s b e l i e v e d t h a t d e v e l o p m e n t o f s l u d g e c o n c e n t r a t i o n p r o f i l e ( p e l l e t i z a t i o o n ) d i d o c c u r i n t h e s y s t e m . I t i s q u i t e c l e a r t h a t a c i d o g e n i c a n d m e t h a n o g e n i c b a c t e r i a p l a y a n i m p o r t a n t r o l e 5 2 ( a ) ( b ) ( C ) 5 I 4 - E f f l u e n t M L V S S . R e a c t o r M L V S S 4 3 I I I I I _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 0 2 0 4 0 6 0 0 2 0 4 0 6 0 0 2 0 4 0 6 0 l i m e , d a y s F i g u r e 5 . 1 A n A c c l i m a t i z a t i o n W a s h o u t P h e n o m e n o n U n d e r d i f f e r e n t r u n n i n g c o n d f t l o n s ( a , b , a n d c ) , M e n t i o n e d i n s e c t i o n 5 . 1 . 1 . 2 A c c l i m a t I z a t i o n A l t e r n a t i v e s 4 0 \ Y / ( a ) ( b ) ( C ) 3 0 — + c o o + S o L C O D 0 4 - P 2 0 I I . . , — I — I I I I I I I I I I 0 2 0 4 0 6 0 0 2 0 4 0 6 0 0 2 0 4 0 6 0 T i m e , d a y s F i g u r e 5 . 2 S y s t e m R e m o v a l E f f i c i e n c y D u r i n g A c c l i m a t i z a t i o n : U n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s ( a , b , a n d c ) , M e n t i o n e d i n s e c t i o n 5 . 1 . 1 . 2 A c c l i m a t I z a t i o n A l t e r n a t i v e s 53 in the initial wash out phenomenon. As shown in alternative A, Figures 5.1, it took approximately 23 days to develop active and sufficient amounts of acidogenic and methanogenic bacteria to dominate within A- and M-UASB reactors, respectively. As a result, influent substrate is hydrolysed and acidified in the A-UASB, producing low to medium molecular weight VFA’s such as HVr, HBu, HPr, HAc etc.; these are further broken down to CH4,C02, and H2 by methanogenic bacteria in the M-UASB. Figures 5.3-5.4 showed a decrease of influent total VFA from 4,070 to 1,120 mg/L with an HAcIHPr concentration ratio of 1:40, corresponding to an increase of VFA removal efficiency of the M-UASB up to 71 %. The produced gas (CH4,C02, H2, and etc.) then caused a gas-lift, solids sludge floatation, and finally, a system washout phenomenon in the M-UASB reactor at point (1) of the Figure 5.1. Conversely, alternatives B and C demonstrated the washout phenomenon immediately after day 1 (points 2 and 3, respectively), and it took only a week for alternative C to start up, compared to two weeks for alternative B; however, the acclimatization process was completed within 4 weeks for both alternatives. Lettinga (1978) found a similar result whereby, when he acclimatized a UASB at 30 C with 1250 mg/L HAc and 1000 mg/L HBu, a distinct granulation appeared 5 weeks after the start-up of the process. The time reduction, compared with alternative A, may result from the effectiveness of well acclimatized synthetic sludge seeded in A-UASBs, generating sufficient volume of VFAS ready for methanogenesis to proceed further in the M-UASB. Comparing alternatives B and C at day 20-30 (same range of loading rate in both alternatives as shown in Figure B2.1 of Appendix B), it is interesting to point out that 5 4 2 0 > . C . ) a ) C ) C ) 0 - 6 0 ( a ) 4 C ) I hL M1 1 0 0 6 0 / ( a ) ( b ) ( c ) — I I — I I — - 1 0 0 - 1 4 0 5 0 2 0 4 0 6 0 0 2 0 4 0 6 0 0 2 0 4 0 6 0 T i m e , d a y s F i g u r e 5 . 3 V F A R e m o v a l E f f i c i e n c y o f t h e M - U A S B : D u r i n g t h e a c c l i m a t i z a t i o n u n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s ( a , b , a n d c ) , M e n t i o n e d i n s e c t i o n 5 . 1 . 1 . 2 A c c l i m a t i z a t i o n A f t e r n a t i v e s ( b ) I 1 1 1 1 1 L I 5 ( C ) 4 3 - J - . - C , ) : I I I I I I I I 0 2 0 4 0 6 0 2 0 4 0 6 0 2 0 4 0 6 0 T i m e , d a y s F i c i u r e 5 . 4 E f l u e n t V F A s o f t h e M - U A S B : D u r i n g t J T e a c c l i m a t i z a t i o n u n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s ( a , b , a n d c ) , M e n t i o n e d i n s e c t i o n 5 . 1 . 1 . 2 A c c l i m a t i z a t i o n A l t e r n a t i v e s 5 5 a l t e r n a t i v e C h a d b e t t e r p e r f o r m a n c e s t h a n t h o s e o f a l t e r n a t i v e B i n t e r m s o f s y s t e m a n d V F A r e m o v a l e f f i c i e n c i e s a n d e f f l u e n t V F A a s s h o w n i n F i g u r e s 5 . 2 - 5 . 4 . T h i s m a y b e c a u s e d b y a m o r e d i v e r s i f i e d s t r u c t u r e o f b a c t e r i a l c o m m u n i t y d u e t o t h e s t e p - l o a d i n g a p p r o a c h ( s t a r t i n g f r o m l o w l o a d i n g r a t e w i t h s e e d s l u d g e f r o m L i o n ’ s G a t e a n a e r o b i c d i g e s t e r u s e d i n a l t e r n a t i v e C , c o m p a r e d w i t h a c o n s t a n t l o a d i n g s c h e m e ( h i g h l o a d i n g r a t e ) a n d a c c l i m a t i z e d s e e d s l u d g e i n a l t e r n a t i v e B . P a v o n i ( 1 9 7 2 ) a n d E n c i n a ( 1 9 8 7 ) i n d i c a t e d d u r i n g t h e s t a r t - u p p r o c e s s t h a t a l o w F / M r a t i o o f t h e i n f l u e n t h e l p e d p r o m o t e bc f o r m a t i o n a n d a l s o i n d u c e t h e g r e a t e s t w a s h o u t r a t e i n a t y p i c a l U A S B . T h e r e a s o n i s t h a t f l o c a n d g r a n u l e s c a n b e f o r m e d e f f e c t i v e l y i f s u b s t r a t e f e e d r a t e s a r e k e p t a s c l o s e a s p o s s i b l e t o t h a t o f b a c t e r i a l g r o w t h r a t e s . H o w e v e r , t h e r e a p p e a r e d t o b e a s u d d e n i n c r e a s e i n t o t a l e f f l u e n t V F A o f A - U A S B ( s a m p l i n g p o i n t n o . 5 ) b e y o n d d a y 3 0 , r a n g i n g f r o m 4 , 9 5 0 - 5 , 1 5 0 t o 5 , 2 0 0 - 6 , 2 0 0 m g / L a s H A c a s s h o w n i n T a b l e B 2 . 5 o f A p p e n d i x B . T h i s s u d d e n i n c r e a s e a s a s h o c k l o a d t o t h e M - U A S B r e s u l t e d i n a d e c r e a s e i n s y s t e m p e r f o r m a n c e s a s i l l u s t r a t e d i n F i g u r e s 5 . 1 - 5 . 4 . C o m b i n a t i o n o f a d i f f i c u l t y i n c o n t r o l l i n g t h e s y s t e m l o a d i n g r a t e b e y o n d d a y 3 0 a n d a n a t t e m p t t o m a i n t a i n t h e p H o f M - U A S B w h i c h d e s t r o y e d t h e s l u d g e b e d a n d b l a n k e t , w a s r e s p o n s i b l e f o r t h i s p a r t i c u l a r s i t u a t i o n . T h i s w a s h o u t p h e n o m e n o n d u r i n g t h e s t a r t - u p p r o c e s s w a s a l s o m e n t i o n e d b y s e v e r a l o t h e r r e s e a r c h e r s . Z e e u w ( 1 9 8 0 ) c o n c l u d e d t h a t t h e a c c l i m a t i o n p r o c e s s o f a n U A S B r e a c t o r i n c l u d e d r o u g h l y 3 s t a g e s o f a d a p t a t i o n : ( a ) a d a p t a t i o n o f s l u d g e t o t h e s u b s t r a t e c o m p o s i t i o n - a n i n i t i a l l o a d i n g r a t e s h o u l d b e k e p t c l o s e t o t h e m a x i m u m p o t e n t i a l o f s e e d s l u d g e ( 0 . 0 4 k g C O D / k g V S S I d a y ) i n o r d e r t o p r e v e n t a n i n h i b i t i o n o f t h e b r e a k d o w n o f H P r ; ( b ) i n c r e a s i n g o f t h e s p e c i f i c a c t i v i t y o f t h e s l u d g e a s a r e s u l t o f 5 6 b a c t e r i a l g r o w t h , retention t i m e a n d w a s h o u t p r o c e s s w h i c h o c c u r r e d i n t h e f i r s t w e e k o f o p e r a t i o n ; ( c ) s l u d g e p e l l e t i z a t i o n - appeared a p p r o x i m a t e l y 6 - 7 w e e k s after t h e start u p a n d t h e s l u d g e b e d c o n c e n t r a t i o n i n c r e a s e d f r o m 7 t o 1 8 k g VSS/m3. ( b ) S y s t e m P e r f o r m a n c e I n a c c o r d a n c e w i t h t h e s t a r t - u p o f d i f f e r e n t a c c l i m a t i z a t i o n p r o c e d u r e s , a s s h o w n i n F i g u r e s 5 . 1 - 5 . 4 , t h e r e s u l t s i n d i c a t e d t h a t a w e l l - a d a p t e d s l u d g e c o u l d f o r m w i t h i n a p e r i o d o f 4 - 5 w e e k s . T h e o r g a n i c l o a d i n g u p t o 1 . 0 - 3 . 4 a n d 0 . 5 6 - 1 . 8 k g COD.m31d, e q u i v a l e n t t o a h y d r a u l i c l o a d i n g u p t o 0 . 1 0 - 0 . 2 4 a n d 0 . 0 6 - 0 . 1 3m”m-d o r a n o r g a n i c l o a d i n g o f 0 . 3 6 - 0 . 6 0 a n d 0 . 2 0 - 0 . 3 3 k g C O D / k g V S S - d f o r t h e M - U A S B a n d t h e e n t i r e s y s t e m r e s p e c t i v e l y , c o u l d b e s u c c e s s f u l l y a c c o m m o d a t e d a t 3 5 0 C . T h i s r e s u l t s h a v e a g r e e d w i t h t h e s t u d i e s c a r r i e d o u t b y H u l s o f f - P o l e t . a l ( 1 9 8 3 ) o n t h e e f f e c t o f s l u d g e l o a d i n g rate o n g r a n u l a t i o n i n t h e U A S B s y s t e m . H e f o u n d that p e l l e t s f o r m e d o n l y a t l o a d i n g r a t e s i n e x c e s s o f 0 . 6 k g C O D / k g V S S - d , w h i l e a t 0 . 3 k g C O D / k g V S S - d , b u l k i n g a n d w a s h o u t o c c u r r e d . D u r i n g a c c l i m a t i z a t i o n , i t w a s i n t e r e s t i n g t o n o t e that there w a s a l a g p e r i o d o f a b o u t 2 w e e k s f o r a l t e r n a t i v e A , b e f o r e t h e s y s t e m s t a r t e d t o break d o w n t h e s u b s t r a t e , w h e r e a s n o l a g p e r i o d appeared i n e i t h e r a l t e r n a t i v e B o r C ( a s s h o w n i n F i g u r e 5 . 2 - 5 . 4 ) . T h e r e a s o n s e x p l a i n i n g t h i s l a g p e r i o d h a v e a l r e a d y b e e n n o t e d e a r l i e r . T h e s y s t e m appeared t o t a k e a b o u t 5 2 , 3 5 , a n d 3 0 - 5 2 d a y s f o r a l t e r n a t i v e A , B , a n d C t o r e a c h p s e u d o s t e a d y - s t a t e , a t a r e m o v a l e f f i c i e n c y o f 8 6 - 9 1 % s o l u b l e C O D a n d 9 4 - 1 0 0 % V F A 5 7 ( a s s h o w n i n F i g u r e 5 . 2 a n d 5 . 3 ) , r e s p e c t i v e l y . T h e a c c l i m a t i z a t i o n p e r i o d f o r a l t e r n a t i v e C t o o k a l m o s t t w o m o n t h s ( a p p r o x i m a t e l y 3 0 - 5 2 d a y s ) , l o n g e r t h a n e x p e c t e d . T h e p o s s i b l e m a j o r c a u s e s o f t h i s p a r t i c u l a r s i t u a t i o n a r e a s u d d e n i n c r e a s e i n s y s t e m l o a d i n g a n d / o r a d i s t u r b a n c e o f s l u d g e b e d a n d b l a n k e t a s m e n t i o n e d e a r l i e r . A r a p i d i n c r e a s e i n t h e H P r / H A c r a t i o , a s s h o w n i n F i g u r e 5 . 4 , i n d i c a t e d t h a t t h e s y s t e m w a s i n t e r r u p t e d a n d / o r u n d e r s t r e s s , c a u s i n g t h e a c c u m u l a t i o n o f H P r ( b e c a u s eH2- u t i l i z i n g b a c t e r i a , t o f o r m C H4, a r e i n h i b i t e d ) . A s s u c h , t h e e x c e s s o f r e d u c t i o n e q u i v a l e n t s i s d i v e r t e d i n t o l e s s f a v o u r a b l e b i o c h e m i c a l r o u t e s ( u s i n g o r g a n i c a c i d s a s a n e l e c t r o n s i n k ) r e s u l t i n g i n t h e a c c u m u l a t i o n o f H P r ( Z o e t e m e i j e r , 1 9 8 2 ) . H o w e v e r , i t t o o k o n l y a c o u p l e o f w e e k s f o r t h e s y s t e m t o r e c o v e r b y i t s e l f , n a t u r a l l y . D e s p i t e t h i s p r o b l e m , a l t e r n a t i v e C ( b e t w e e n d a y s 2 0 - 3 0 ) s e e m s t o b e s l i g h t l y b e t t e r t h a n a l t e r n a t i v e s A a n d B , i n t e r m s o f a v e r a g e s y s t e m r e m o v a l e f f i c i e n c y a n d e f f l u e n t q u a l i t y a s s h o w n i n T a b l e B 1 . 1 o f A p p e n d i x B . A p o s s i b l e e x p l a n a t i o n i s t h a t t h e A - U A S B o f t h e a l t e r n a t i v e C w a s p r o p e r l y a c c l i m a t i z e d a n d l o a d e d s t e p - w i s e , w i t h w e l l a d a p t e d s e e d s l u d g e . T h i s h e l p e d t o g e n e r a t e s u f f i c i e n t v o l u m e o f r e a d i l y b i o d e g r a d a b l e V F A ’ s f o r m e t h a n o g e n e s i s i n t h e M - U A S B ; w h i c h w a s s e e d e d w i t h s l u d g e f r o m t h e a n a e r o b i c d i g e s t e r o f L i o n ’ s G a t e t r e a t m e n t p l a n t . W i t h g r e a t e r v a r i e t i e s o f a c e t o g e n s a n d m e t h a n o g e n s i n t h i s t y p e o f d i g e s t e r s l u d g e , c o u p l e d w i t h a p r o p e r s t a r t - u p o f t h e A - U A S B , a l t e r n a t i v e C a p p e a r s t o a c c l i m a t i z e t h e s y s t e m m o r e e f f e c t i v e l y a n d e f f i c i e n t l y t h a n e i t h e r a l t e r n a t i v e A o r B . I n t e r m s o f n u t r i e n t r e q u i r e m e n t s , i t a p p e a r s t h a t e f f l u e n t l e v e l s a n d r e m o v a l e f f i c i e n c y o f P04-P t e n d t o f o l l o w t h e p a t t e r n s o f b o t h C O D a n d 5 8 V F A e f f l u e n t l e v e l s a n d r e m o v a l e f f i c i e n c y ; h o w e v e r , T K N s e e m e d t o h a v e n o r e l a t i o n s h i p a t a l l w i t h t h e s y s t e m r e m o v a l e f f i c i e n c y , a s s h o w n i n F i g u r e B 1 . 1 o f A p p e n d i x B . T h e s u m m a r y o f a v e r a g e s y s t e m p e r f o r m a n c e d u r i n g t h e a c c l i m a t i z a t i o n p r o c e s s , u n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s w a s i l l u s t r a t e d i n T a b l e B L 1 o f A p p e n d i x B . 5 . 1 . 2 C o n c l u s i o n s S y s t e m a c c l i m a t i z a t i o n i s o n e o f t h e m o s t c r u c i a l s t e p s t o s e c u r e a r e l i a b l e s y s t e m p e r f o r m a n c e . C a r e f u l a n d p r o p e r s y s t e m s t a r t - u p a n d a c c l i m a t i z a t i o n r e s u l t s i n t h e p r o d u c t i o n o f a n a c t i v e a n d e f f e c t i v e g r a n u l a r b i o m a s s s l u d g e ( p e l l e t s ) , w h i c h s u b s e q u e n t l y c r e a t e s a n e f f e c t i v e s y s t e m r e m o v a l e f f i c i e n c y a n d g e n e r a t e s s i g n i f i c a n t a m o u n t s o f C H4 g a s . A c c o r d i n g t o t h e r e s u l t s o b t a i n e d d u r i n g t h e a c c l i m a t i z a t i o n p r o c e s s , t h e f o l l o w i n g c o n c l u s i o n s c a n b e m a d e : ( 1 ) A s t e p - l o a d i n g s c h e m e , s t a r t i n g a t a s l u d g e l o a d i n g r a t e o f 1 . 2 g C O D I L - d w i t h a s e e d s l u d g e r a t i o o f 1 : 1 ( b y v o l u m e ) , a p p e a r s t o b e a n e f f e c t i v e m e a s u r e t o a c c l i m a t i z e t h e s y s t e m . S a l t s o f C a2 a n d P 043 s e e m t o p l a y a m a j o r p a r t i n t h e i n c r e a s e o f t h e s l u d g e s e t t l e a b i l i t y . ( 2 ) T h e “ w a s h o u t p h e n o m e n o n ” o c c u r s w i t h i n 2 w e e k s o f t h e p r o c e s s a c c l i m a t i z a t i o n , a t a s l u d g e l o a d i n g o f l e s s t h a n 1 . 2 g C O D / L - d o r 0 . 3 6 k g C O D / k g V S S - d . ( 3 ) A c c l i m a t i z a t i o n a l t e r n a t i v e C , s e e d i n g t h e A - U A S B w i t h a c c l i m a t i z e d s y n t h e t i c s e e d s l u d g e a n d t h e M - U A S B w i t h s l u d g e f r o m t h e L i o n ’ s G a t e a n a e r o b i c s l u d g e d i g e s t e r , i s t h e m o s t e f f e c t i v e a n d p r a c t i c a l m e t h o d t o a c c e l e r a t e t h e a c c l i m a t i z a t i o n 5 9 p r o c e s s , s i n c e a n a e r o b i c d i g e s t e r s e e d s l u d g e i s a l r e a d y a v a i l a b l e a t s u f f i c i e n t v o l u m e s f o r a t y p i c a l f u l l s c a l e U A S B p r o c e s s . T h e s y s t e m s t a r t s t o w a s h o u t t h e M L V S S i m m e d i a t e l y a f t e r a c c l i m a t i z a t i o n a n d c o m p l e t e s t h e p r o c e s s w i t h i n 4 - 5 w e e k s , w i t h 8 6 - 9 1 % C O D ( s o l . ) a n d 9 4 - 1 0 0 % t o t a l V F A r e m o v a l e f f i c i e n c i e s . 6 0 5 . 2 E X P E R I M E N T A L D E S I G N T h i s s e c t i o n d e s c r i b e s w i t h a s e a r c h f o r a n o p t i m u m “ b e s t k n o w n ” o p e r a t i n g c o n d i t i o n b y d e t e r m i n i n g t h e e f f e c t s a n d i n t e r a c t i o n o f S R a n d R R o n t h e r e s p o n s e s a n d p r o c e s s p e r f o r m a n c e u n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s . T h e r e s u l t s a r e t h e n u s e d t o l o c a t e t h e “ b e s t k n o w n ” r u n n i n g c o n d i t i o n , w h i c h p r o v i d e s s u p e r i o r s u p e r n a t a n t q u a l i t y a n d r e a s o n a b l e m e t h a n e g a s p r o d u c t i o n , b y a n a p p l i c a t i o n o f Y a t e ’ s a l g o r i t h m a n d R e s p o n s e S u r f a c e M e t h o d ( R S M ) ( B o x , 1 9 6 9 ) . T h e s e a p p l i c a t i o n t e c h n i q u e s o f e x p e r i m e n t a l d e s i g n s a r e i n i t i a l l y u s e d a s m a j o r t o o l s t o h e l p d i r e c t t h e n e x t a p p r o p r i a t e a n d e f f e c t i v e m o v e s o f t h e e x p e r i m e n t a l d e s i g n t o w a r d t h e o p t i m a l “ b e s t k n o w n ” o p e r a t i n g c o n d i t i o n . T h e e f f e c t i v e n e s s o f a t w o - p h a s e a n a e r o b i c d i g e s t i o n ( U A S B - U A S B ) s y s t e m t o s t a b i l i z e t h e p a r t i c u l a t e s u b s t r a t e u n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s i s t h e n e v a l u a t e d . S t e p - l o a d i n g r a t e e x p e r i m e n t s a r e f u r t h e r u n d e r t a k e n t o l o c a t e t h e o p t i m u m a n d m a x i m u m s y s t e m h y d r a u l i c a n d / o r o r g a n i c l o a d i n g c a p a c i t i e s . F u r t h e r m o r e , t h e e x p e r i m e n t s s h o u l d p r o v i d e i n f o r m a t i o n o n t h e r e q u i r e d r e c o v e r y p e r i o d , a f t e r a s e r i o u s w a s h o u t o f t h e a c t i v e b i o m a s s h a s o c c u r r e d . E v a l u a t i o n o f b a s i c k i n e t i c s i s a l s o m a d e . T h e f e a s i b i l i t y o f t h i s t w o - p h a s e ( U A S B - U A S B ) p r o c e s s c a n t h e n b e e v a l u a t e d i n t e r m s o f s y s t e m e f f e c t i v e n e s s ( a c c l i m a t i z a t i o n a n d p e r f o r m a n c e ) a n d s y s t e m s u i t a b i l i t y ( m a x i m u m a n d o p t i m u m h y d r a u l i c a n d / o r o r g a n i c l o a d i n g c a p a c i t y a n d s y s t e m r e c o v e r y ) . M o d i f i c a t i o n s t o d e s i g n c r i t e r i a a n d o p e r a t i o n p r o c e d u r e s a r e p r o p o s e d a t t h e e n d o f t h i s s e c t i o n . 5 . 2 . 1 O p t i m u m “ b e s t k n o w n ” O p e r a t i n g C o n d i t i o n 6 1 T h e t e r m “ b e s t k n o w n’ i n t h i s p a r t i c u l a r s i t u a t i o n , i s d e f i n e d a s a r u n n i n g c o n d i t i o n t h a t p r o v i d e s t h e m a x i m u m s y s t e m C O D r e m o v a l e f f i c i e n c y a n d C H4 g a s p r o d u c t i o n u n d e r a c e r t a i n r e g i m e o f p H , t e m p e r a t u r e , a n d i n f l u e n t f l o w r a t e . T o l o c a t e t h e o p t i m u m “ b e s t k n o w n ” o p e r a t i n g c o n d i t i o n , r e g a r d i n g S R a n d R R , a p r e v i o u s l y s u c c e s s f u l r u n n i n g c o n d i t i o n , d u r i n g t h e a c c l i m a t i z a t i o n p r o c e s s , w a s u s e d a s a s t a r t i n g c o n d i t i o n ; a l s o , a n o t h e r s e t o f r u n n i n g c o n d i t i o n s , a s s h o w n i n T a b l e 4 . 2 o f S e c t i o n 4 . 2 . 1 , w a s a l s o i m p l e m e n t e d . T h e r e s p o n s e s a n d e f f i c i e n c y o f e a c h r u n n i n g c o n d i t i o n w e r e u s e d t o e v a l u a t e t h e e f f e c t s o f S R / R R o n s y s t e m p e r f o r m a n c e , t h e e f f e c t i v e n e s s o f t h e t w o - p h a s e ( U A S B - U A S B ) c o n c e p t , a n d t h e l o c a t i o n o f t h e “ b e s t k n o w n ” r u n n i n g c o n d i t i o n . 5 . 2 . 1 . 1 E f f e c t s a n d I n t e r a c t i o n o f S l u d g e R a t i o ( S R ) a n d R e c y c l e R a t i o ( R R ) T o o h i g h a n R R c a n d e s t r o y t h e s l u d g e b e d a n d w a s h o u t t h e a c t i v e b i o m a s s f r o m t h e s y s t e m , b u t t o o l o w a n R R c a n a l s o r e d u c e t h e s y s t e m r e m o v a l e f f i c i e n c y b y r e d u c i n g t h e c h a n c e s o f b e t t e r c o n t a c t b e t w e e n m i c r o o r g a n i s m s a n d s u b s t r a t e s a n d d e c r e a s i n g t h e s y s t e m b u f f e r i n g c a p a c i t y . E q u a l l y i m p o r t a n t , t o o - h i g h a n d - l o w a n S R c a n s i g n i f i c a n t l y a f f e c t t h e s y s t e m p e r f o r m a n c e , s i n c e t h e p r i m a r y a n d s e c o n d a r y s l u d g e s a r e c o m p o s e d o f e x t r e m e l y d i f f e r e n t n u t r i e n t c o n c e n t r a t i o n s , t h u s a f f e c t i n g o r g a n i c l o a d i n g c a p a c i t y . T h e e f f e c t s a n d i n t e r a c t i o n o f b o t h R R a n d S R , a s w e l l a s t h e i n i t i a l o p t i m u m r a n g e o f t h e s e t w o i n f l u e n t i a l c o n t r o l p a r a m e t e r s , m u s t b e a n a l y z e d a n d i d e n t i f i e d p r i o r t o p r o c e e d i n g a n y f u r t h e r t o w a r d o p t i m u m a n d m a x i m u m l o a d i n g c a p a c i t y o f t h e U A S B 6 2 U A S B s y s t e m . I n t h i s p a r t i c u l a r s i t u a t i o n t h a t o n l y t h e a c c l i m a t i z a t i o n r u n n i n g c o n d i t i o n i s k n o w n , a n “ E v o l u t i o n a r y O p e r a t i o n P r o c e s s ( E O P ) ” u s i n g Y a t e ’ s a l g o r i t h m s w i t h 2 s t a n d a r d e r r o r s ( S . E . ) i s a n e f f e c t i v e t e c h n i q u e t o l e a d t h e e x p e r i m e n t a l d e s i g n t o w a r d t h e o p t i m a l “ b e s t k n o w n ” r u n n i n g c o n d i t i o n p r o v i d i n g s u p e r i o r s u p e m a t a n t q u a l i t y a n d r e a s o n a b l e s y s t e m r e m o v a l e f f i c i e n c y . A t e a c h s t e p o f E O P , a r e f e r e n c e r u n n i n g ( b e s t k n o w n ) c o n d i t i o n w i t h a n o t h e r f o u r a p p r o p r i a t e r u n n i n g c o n d i t i o n s i s d e s i g n e d a n d i m p l e m e n t e d . C a l c u l a t i o n s o f e f f e c t , i n t e r a c t i o n , p h a s e m e a n , a n d c h a n g e i n m e a n o f t h e s e d a t a a r e m a d e a n d a n a l y z e d w i t h a n a p p l i c a t i o n o f S t e e p e s t A s c e n t t e c h n i q u e . I f n e c e s s a r y , a n o t h e r s e t o f e x p e r i m e n t a l d e s i g n ( b e s t k n o w n r u n n i n g c o n d i t i o n o f t h e p r e v i o u s s e t p l u s a n o t h e r f o u r d e s i g n e d r u n n i n g c o n d i t i o n s ) h a s t o b e s e t u p i f m a g n i t u d e s o f e f f e c t a n d c h a n g e i n m e a n a r e s i g n i f i c a n t , c o m p a r e d w i t h 2 S . E . . O n t h e o t h e r h a n d , i f t h e s e m a g n i t u d e s a r e n o t s i g n i f i c a n t c o m p a r e d w i t h 2 S . E . , i t m e a n s t h e r e f e r e n c e b e s t k n o w n c o n d i t i o n i s c l o s e d t o t h e v i c i n i t y o f t h e o p t i m a l s y s t e m o p e r a t i n g c o n d i t i o n . B y a p p l y i n g a Y a t e ’ s a l g o r i t h m w i t h t w o s t a n d a r d e r r o r s ( B o x , 1 9 6 9 ) o n t h e s e l e c t e d p a r a m e t e r s o f S e q u e n c e 1 a n d 2 e x p e r i m e n t s , t h e e f f e c t , i n t e r a c t i o n , p h a s e m e a n , a n d c h a n g e i n m e a n w e r e c a l c u l a t e d a n d s u m m a r i z e d i n T a b l e 5 . 1 . A d e t a i l e d c a l c u l a t i o n o f t h e a b o v e s t a t i s t i c a l p a r a m e t e r s , b a s e d o n t h e r e p l i c a t e d v a l u e s a t p s e u d o s t e a d y - s t a t e c o n d i t i o n o f e a c h r u n n i n g c o n d i t i o n i n S e q u e n c e 1 a n d 2 e x p e r i m e n t s , i s d e m o n s t r a t e d i n T a b l e C 2 . 1 o f A p p e n d i x C . F r o m T a b l e 5 . 1 , i t i s a p p a r e n t , a p a r t f r o m t h e e f f e c t o f 2 s t a n d a r d e r r o r s , t h a t S R a n d R R h a v e a s i g n i f i c a n t e f f e c t o n t h e e f f l u e n t J a l e : 5 . 1 S I . i r T 1 u T 1 a r ’ f . . è f f é i t s ( S R . a i i i l l / c h a n g e i n m e a n d u r i n g t h e s e q u e n c e 1 a n d 2 e x p e r i m e n t s . R s p o n s e . : p a r a m e t e r s • l n t é r a - t i o n : . • : : P h a S e : S e q u e n c e 1 E f f l u e n t , m g I L o r m g i L a s H A c C 0 D ( s o l . ) 1 4 5 4 - 3 4 6 0 4 8 6 3 2 0 7 2 3 5 7 1 8 6 / 1 6 7 V F A ( t o t . ) 1 2 6 2 - 1 1 9 6 - 8 0 2 1 9 6 5 1 7 3 4 1 4 4 1 / 1 2 8 8 P 0 4 - P 8 5 - 2 1 3 - 8 1 4 2 1 2 2 7 2 . 3 3 / 6 4 . 6 4 S y s t e m R e m . , % C 0 D ( s o L ) - 2 4 . 4 6 5 9 . 7 5 - 1 . 4 5 2 . 9 3 - 3 0 . 5 6 6 . 4 2 / 5 . 7 5 P 0 4 - P - 5 1 . 5 2 8 1 . 2 8 1 6 . 9 9 2 4 . 2 8 - 6 0 . 3 1 2 1 . 7 6 / 1 9 . 4 4 C H 4 g a s % C H 4 - 7 . 4 9 5 . 3 1 - 5 . 3 1 6 7 . 9 1 6 . 3 2 . 7 9 / 2 . 5 Y i e l d s 0 . 7 7 - 0 . 6 1 0 . 0 4 1 . 7 7 0 . 0 6 1 . 0 5 / . 9 5 S e q u e n c e 2 E f f l u e n t , m g I L o r m g / I . a s H A c C O D ( s o l . ) - 3 6 - 1 5 - 8 4 4 3 0 - 1 4 6 1 7 3 / 1 5 5 V F A ( t o t . ) - 1 3 . 5 6 3 . 5 - 1 3 . 5 8 3 - 2 0 5 1 9 7 / 1 7 6 P 0 4 - P - 4 3 . 5 - 7 8 . 5 4 0 . 5 3 9 3 3 3 8 . 4 9 / 3 4 . 4 S y s t e m R e m . , % C O D ( s o l . ) 1 . 0 1 - 0 . 8 3 1 . 1 5 9 3 . 8 1 2 . 4 6 2 . 0 7 / 1 . 8 5 P 0 4 - P 1 0 . 3 1 2 9 . 2 1 - 8 . 5 4 8 3 . 8 3 - 1 0 . 2 1 1 . 2 7 / 1 0 . 0 7 C H 4 g a s % C H 4 - 3 . 0 9 - 0 . 3 8 - 1 . 8 1 7 2 . 6 2 0 0 . 9 8 / 0 . 8 8 Y i e l d s 0 . 2 7 - 0 . 3 4 - 0 . 5 3 1 . 9 4 0 . 1 0 . 2 9 / 0 . 2 7 N o t e : 1 . = 2 s t a n d a r d Ø f t o o f . é f f é c t , i h t é r ä c t i o n . p h ã s e m e a r 2 # = 2 s t a n d a r d e r r o r s o f c h a n g e i n m e a n N e g a t i v e ( — y e ) r e s p o n s e m a g n i t u d e , i f s i g n i f i c a n t , c o m p a r e d w i t h 2 S E m e a n b e t t e r p e r f o r m a n c e c a n b e a c h i e v e d b y d e c r e a s i n g S R , R R , a n d l o r a c o m b i n a t i o n o f b o t h D e t a i l e d c a l c u l a t i o n w a s i l l u s t r a t e d i n T a b l e C 2 1 o f A p p e n d i x C 6 3 64 and removal efficiency of COD(sol.) and P04-P in the Sequence 1 experiment. However, the effect of SR appears to be of a greater magnitude than that of RR and only the interaction (SR*RR) of effluent COD is significant. This may suggest that the system COD removal efficiency is probably governed by the anaerobic stabilization processes and depends largely on the SR and RR factors to increase the contact between microorganisms and substrates, bufferring capacity, and nutrient requirements; whereas, the removal of P04-P, without any interaction, is mostly a chemical reaction, affected strongly by the influent TP in the feed SR, thus resulting in the precipitation of Ca2 and P043 salts inside the reactor. The large relative magnitudes of the main effect, interaction, and change in means on most of the responses in the effluent and removal efficiency, compared with 2 SE. in the Sequence 1 experiment, indicated that the optimum “best known” running condition was still not reached. An additional sequence of running conditions was needed to move toward the optimum condition. Under these circumstances, a “steep ascent” method is the most effective preliminary procedure to direct the next appropriate move of the experimental operation and thus approaches the optimum running condition. Once the linear effect becomes small, further application of the method is unprofitable (Box et a], 1969). A graphical contour plot, using data from each pseudo steady-state of the Sequence 1 experiment, was made, as shown in Figure 5.5. The sequence 2 experimental operation was then made by assigning the “best known” condition in sequence 1 experiment as a reference running condition, plus another 4 different running conditions YMAX.81.5 65 I o.86Io3101 z (a) 2400 32o0r 000 V MIN. 48.5 V MAX.. 81.5 8773D552 z x C b) 72 72 56 V M(N-48.5 Figure 5.5 Surface Responses of Phase I Experiment:(a) Effluent COD (sol.);(b) COD Removal EfficiencAt Pseudo Steady-state under Different Running Conca’ions Note: x = Recycle Ratio (RR); y = Sludge Ratio (SR) 6 6 a s s h o w n i n T a b l e 4 . 2 . T h e d e t a i l s o f t h i s “ b e s t k n o w n ” c o n d i t i o n w i l l b e d i s c u s s e d i n t h e n e x t s e c t i o n . C o m p a r i n g t h e p h a s e m e a n s o f b o t h S e q u e n c e 1 a n d 2 e x p e r i m e n t s , t h e s y s t e m p e r f o r m e d m u c h b e t t e r i n t e r m s o f e f f l u e n t q u a l i t y , C O D r e m o v a l e f f i c i e n c y , a n d C H4 g a s c o n t e n t a n d y i e l d , i n t h e S e q u e n c e 2 e x p e r i m e n t ( a s s h o w n i n T a b l e 5 . 1 ) . T h e r e w a s a l s o n o s i g n i f i c a n t e f f e c t o f S R a n d R R o n a l l t h e r e s p o n s e s , w h e n c o m p a r e d w i t h 2 S . E . . T h e s e c o m b i n a t i o n s i n d i c a t e d t h a t t h e s y s t e m w a s n o w i n t h e v i c i n i t y o f t h e o p t i m u m “ b e s t k n o w n ” c o n d i t i o n p r o v i d i n g t h e m a x i m u m C O D r e m o v a l e f f i c i e n c y . H o w e v e r , t h e r e w e r e s t i l l s o m e e f f e c t s o f S R o n t h e c o n t e n t a n d r e m o v a l e f f i c i e n c y o f P04-P a n d t h e e f f e c t o f R R a n d i n t e r a c t i o n ( S R * R R ) o n t h e C H4 g a s c o n t e n t . A n a d d i t i o n a l r u n ( S e q u e n c e 3 e x p e r i m e n t a s s h o w n i n T a b l e 4 . 2 ) w a s t h e n c a r r i e d o u t t o e n s u r e t h a t t h e s y s t e m r e a l l y r e a c h e d t h e o p t i m u m ‘ b e s t k n o w n ” r u n n i n g c o n d i t i o n . 5 . 2 . 1 . 2 ‘ E e s t K n o w n ” R u n n i n g C o n d i t i o n B y a p p l y i n g t h e s t e e p a s c e n t t e c h n i q u e a s m e n t i o n e d e a r l i e r , a r e s p o n s e s u r f a c e o f t h e S e q u e n c e 1 e x p e r i m e n t a l r u n s a s s h o w n i n T a b l e 4 . 2 , w i t h r e s p e c t t o e f f l u e n t C O D ( s o l . ) a n d C O D r e m o v a l e f f i c i e n c y , i s i l l u s t r a t e d i n F i g u r e 5 . 5 . A s s h o w n , t h e c o n t o u r l i n e s o f b o t h C O D r e m o v a l e f f i c i e n c y a n d e f f l u e n t C O D t e n d t o m o v e t o w a r d s t h e b e s t k n o w n r u n n i n g c o n d i t i o n ( e x p e r i m e n t a l r u n n o . 0 : S R 8 O / 2 0 a n d R R 4 / 7 ) , w h e r e 8 6 . 0 9 % C O D ( s o l . ) r e m o v a l e f f i c i e n c y a n d 8 6 1 m g / L o f e f f l u e n t C O D ( s o ! . ) w e r e o b t a i n e d . I t i s q u i t e i n t e r e s t i n g t o n o t e t h a t t h e r u n n i n g c o n d i t i o n o f S R 5 O / 5 0 a n d R R 2 / 4 w a s t h e w o r s t 67 4- 3.5 - m—() :. 3 - Running Conditions SR RR (a) 80/20 2/4E 2.5- (b) 80/20 6/10 ( C ) 50/50 6/10 6° 2- (d) 50/50 214 I 1.5- IL H I A-UASB + M-UASB -0.5 - 1 10 19 28 37 46 55 64 73 82 91 100 Time, days - Figure 5.6 NaOH (0.1 N) Addition During the Sequence 1 Experiment scenario in the Sequence 1 experiment, with 8.81 % COD removal efficiency and the effluent (so!.) COD of 5950 mg/L. This may have been the result of a large volume of 0.1 N NaOH automatically pumped into the reactor to neutralize and maintain the pH ‘at 7.0-7.2 (as shown in Figure 5.6), thus destroying the sludge bed and diminishing the CH4 gas production and the system removal efficiency (as shown in Figure 5.7). It is speculated that a malfunction of the pH sensor in the M-UASB might have played a major role in this unusual situation. Although results of the worst running condition were suspected and even without considering them, the overall picture of sequence 1 Fi gu re 5. 7 Sy st em R es po ns es a n d Pe rf or m an ce o f S eq ue nc e 1 E xp er im en t: (a) CO D R em ov al Ef fid en cy ;(b )E ffl ue nt C O D ;(c ) C H 4 C on te nt ;(d ) C H 4 G as Pr od uc tio n 00 8 0 - 7 0 - 8 0 - 5 0 - 4 0 - 3 0 iii J f / J } % 70 50 30 1 0 80 40I I. I I E 4? r o a . N 04 •. L • i e 38 47 Tb n. , d .y 69 experiment still remained moving toward the acclimatization running condition (SR 80/20 and RR 4/7). Reseeding and repeating the acclimatization process of the M-UASB, using a new pH sensor, were made before starting the experiments in Sequences 2 and 3, as detailed in Table 4.2. A summary of average responses and system performance under different running conditions (Sequence 1-3) is shown in Table 5.2. As also shown, running condition no.7 (SR6O/40 and RR5/8) appeared to perform better in terms of better effluent quality and higher CH4 gas productivity than those of running condition no.10 (SR8O/20 and RR4/7); however; condition no.10 provided a better P04-P removal efficiency. Finally, as shown in Table 5.2, the choice of running condition no.9 (SR8O/20 and RR5/8) was the optimum “Best known” condition with respect to P04-P removal efficiency, specific CR4 gas productivity, and CH4 gas production, compared to all other running conditions. A summary of average responses and performance of the “best known” running condition is illustrated in Table 5.3. Under this “best known” condition, the system appears to provide a promising performance with 95, 99, and 90 % removal efficiencies of soluble COD, total COD, and P04-P, respectively. A low level of soluble effluent COD of 308 mg/L is also indicated. 5.2.1.3 Two-phase Separation (UASB-UASB) To avoid confusion between a conventional, completely mixed “two-stage” T ab le 5 2 Su m m ar y o f A ve ra ge R es po ns es U nd er P se ud o St ea dy — st at e o f th e D iff er en t D es ig ne d iu nn in g C on di tio ns (S eq ue nc e 1, 2, a n d 3 E xp er im en ts ) : : E xp er im en ta l R U A in gC on di tio na A ve ra ge R es po ns es S eq ue nc e 1 S eq ue nc e 2 S eq ue nc eS 11 21 31 4 51 61 71 8 91 10 1 1 1 12 L oa di ng R at e c u .m /c u. m — d 0. 10 0. 14 0. 10 0. 12 0. 12 0. 12 0. 08 0. 12 0. 09 0. 11 0. 09 0. 10 K g CO D( So l)I cu .m — d 0. 63 0. 97 0. 62 0. 76 0. 75 0. 78 0. 63 0. 91 0. 69 0. 59 0. 59 0. 62 K g C O D (T ota l)I cu .m — d 5. 70 6. 00 4. 50 6. 35 5. 60 4. 80 3. 95 4. 70 4. 30 4. 25 4. 25 3. 85 E ff lu en t Q ua lit y So lid s, m gI L TS 71 40 65 00 34 80 54 40 31 30 36 00 23 55 26 35 26 10 26 00 26 60 26 00 VS 40 30 42 00 13 00 26 45 90 0 14 30 81 5 11 75 10 50 62 0 93 0 88 0 TS S 27 0 58 0 19 0 28 0 21 0 20 0 23 0 73 0 30 0 30 0 34 0 23 0 TV SS 18 0 33 0 16 0 26 0 65 10 0 10 0 43 0 15 5 14 0 12 0 10 0 CO D ,m g! L CO D (T ota l) 27 80 33 80 51 35 64 80 49 0 40 0 42 0 44 5 47 0 40 0 42 5 40 0 C O D (S ol) 27 55 30 55 48 70 60 30 46 0 32 5 35 5 35 0 30 0 30 5 28 0 29 0 In or ga ni cs , m g/ L NH 4— N 27 0 36 0 42 5 40 5 45 5 40 0 52 5 51 5 51 0 41 0 39 0 42 5 TK N 30 0 38 5 43 5 46 6 45 9 42 0 49 2 48 3 48 9 38 7 55 7 42 0 TP 60 12 4 23 0 36 4 17 6 74 76 85 91 32 14 0 27 P0 4— P 20 91 23 0 34 0 9 6 34 74 20 23 11 11 To ta l V FA ,m g/ L HA G 14 60 20 50 17 80 35 07 80 50 0 0 0 0 0 20 Sy st em R em ov al Ef fic ie nc y So lid s, % TS 85 80 91 82 91 89 93 91 91 91 93 92 V S 91 80 96 90 97 95 97 95 96 97 97 97 TS S 99 98 99 99 99 99 99 96 99 99 99 99 TV SS 99 99 99 99 10 0 10 0 99 98 99 99 10 0 10 0 C O D ,% CO D (T ota l) 95 92 89 83 99 99 99 99 99 99 99 99 CO D (S ol) 54 57 23 4 93 95 95 95 96 94 96 95 In or ga ni cs , % TP 66 31 — 6 — 66 14 63 65 57 50 76 40 83 P0 4— P 85 40 33 — 94 95 97 81 58 91 88 94 92 M et ha ne G as Fl ow ,l /d To ta l G as 53 80 35 30 95 91 10 7 12 6 12 0 87 85 .0 0 83 CH 4 G as 34 46 14 10 60 58 62 .2 0 71 69 50 54 49 CH 4 Pr od uc tiv ity lId 34 46 14 10 60 58 62 71 69 50 54 49 cu .m /c u. m — d 0. 75 1. 00 0. 30 0. 20 1. 35 1. 30 1. 38 1. 60 1. 55 1. 10 1. 20 1. 10 cu .m /c u. m — d @ SC 0. 70 0. 90 0. 25 0. 20 1. 20 1. 15 1. 25 1. 40 1. 40 0. 90 1. 00 0. 95 c u .m /k gC O D (T ota l)a dd ed @ SC 0. 12 0. 15 0. 05 0. 03 0. 20 0. 25 0. 30 0. 30 0. 32 0. 25 0. 25 0. 25 N ot e Ex pe rim en ta l R un ni ng C on di tio ns SR = Sl ud ge R at io (P rim ary a n d Se co nd ar y Sl ud ge s) SR RR SR RR RR = R ec yc le R at io (R ec yc le a n d In flu en tf lo w) 1 80 /2 0 2/ 4 7 60 /4 0 5I 8 o pe ra te d © w alk — in co n tr ol le d ro o m te m pe ra tu re a t 35 o 2 80 /2 0 6/ 10 8 60 /4 0 3/ 6 a n d pH o f 5 .0— 5.3 a n d 7. 0— 7. 3 fo r A — a n d M — UA SB s 3 50 /5 0 6/ 10 9 80 /2 0 5/ 8 In tlu en t f ee d © 4— 5 o C 4 50 /5 0 2/ 4 10 80 /2 0 41 7 5 70 /3 0 3/ 6 11 90 /1 0 5/ 8 6 70 I3 0 5/ 8 12 90 11 0 3/ 6 :T hb le 53 Pe ifô rin an ce of A: Tw ó- ph as e A na ér ób k S! ud ge Di ge sti on : ( UA SB -U AS B) Pr óo es s O pe ra tin g Co nd iti on s I Pe rto rm an ce UA SB -U AS B Ru nn in g HR T, da ys 9- 10 Lo ad in g ra te , kg CO D (to tal )Ic u.m -d 5. 00 kg V S/ cu .m -d 2. 00 Su pe rn at an tq ua lit y, So lid s,m gI l TS 26 00 V S, (% TS ) 10 50 (40 ) SS 30 0 V SS ,(% TS ) 15 5(5 8) O rg an ic s,m gI l (T ota l) CO D 47 0 (Fi l.) CO D 31 0 ln or ga ni cs ,m g/ I NH 4- N 51 0 P0 4- P 20 TK N 49 0 TP 90 V ol ati le ac id s,m g/ l HA c nil H Pr nil lso -H Br nil HB r nil A- HV r nil lso -H Vr nil HV r nil H H e nil To ta lV FA ,m g/1 a s HA c nil :T ab ie S3 Pe rñ ia he of :A T* d’ ph as e A ra èr öb lc :S iL dg e O ist io n: (U AS BU A$ B) :pr oc ess : at 35 de gr ee C /9 da y H RT /S R 80 /2 0 /f iR 5/8 (c on t’d O pe ra tin g Co nd iti on s I Pe rf or m an ce UA SB -U AS B M et ha ne ga s CH 4 yi el ds cu .m /k g VS re m o v ed 0. 90 cu .m /k g CO D (T ota l) a dd ed 0. 32 CH 4 pr od uc tio n ra te cu .m /d 75 v o l/c ul tu re v o l-d 1. 70 % th eo re tic al CH 4 95 G as co m po sit io n, m ol % C 02 27 N2 1. 00 CH 4 72 Re m ov al Ef fic ie nc y, % O rg an ic s (T ota l) CO D 99 (Fi l) CO D 97 So lid s TS S 98 In or ga ni cs P0 4- P 87 TP 56 VF A 10 0 7 4 a n a e r o b i c d i g e s t i o n p r o c e s s a n d a “ t w o - p h a s e’ a n a e r o b i c d i g e s t i o n p r o c e s s , i t i s a p p r o p r i a t e t o c l e a r l y d i s t i n g u i s h t h e s e t w o c o n c e p t s . T h e “ t w o - s t a g e ” p r o c e s s c o n s i s t s o f t w o c o m p l e t e l y m i x e d r e a c t o r s c o n n e c t e d i n s e r i e s . T h e f i r s t r e a c t o r s e r v e s a s a f e r m e n t e r w h i l e t h e s e c o n d o n e a c t s m a i n l y a s a s e t t l e r a n d / o r a r e s e r v e d f e r m e n t e r , i n c a s e o f e m e r g e n c y o r f a i l u r e o f t h e f i r s t o n e . O f t e n , t h e s e c o n d d i g e s t e r p e r f o r m s p o o r l y a s a t h i c k e n e r , p r o d u c i n g d i l u t e s l u d g e a n d a h i g h s o l i d s s u p e r n a t a n t . T h i s m a y b e t h e r e s u l t o f a h i g h p r o p o r t i o n o f f i n e - s i z e d p a r t i c l e s i n t h e f i r s t d i g e s t e r . T h e y a r e p r o d u c e d g e n e r a l l y b y m i x i n g a n d n a t u r a l b r e a k d o w n o f p a r t i c l e s i z e t h r o u g h b i o l o g i c a l d e c o m p o s i t i o n , a n d b e c o m e s a t u r a t e d w i t h d i g e s t e r g a s . W h e n t h e g a s i s t r a n s f e r r e d i n t o t h e s e c o n d d i g e s t e r , i t w i l l c o m e O u t o f t h e s o l u t i o n , f o r m i n g s m a l l b u b b l e s ; t h e s e b e c o m e a t t a c h e d t o s l u d g e p a r t i c l e s a n d c r e a t e a b u o y a n t f o r c e t h a t h i n d e r s s e t t l i n g . T h e “ t w o - p h a s e ” c o n c e p t , o n t h e o t h e r h a n d , i s a n a t t e m p t t o t a k e a d v a n t a g e o f t h e d i - p h a s i c p h e n o m e n o n o f t h e a n a e r o b i c d i g e s t i o n p r o c e s s , b y k e e p i n g t h e r e a c t o r s s e p a r a t e d p h y s i c a l l y a n d p r o v i d i n g t h e o p t i m u m e n v i r o n m e n t a l c o n d i t i o n s t o s t i m u l a t e a n d / o r p r o m o t e t h e h y d r o l y s i s - a c i d i f i c a t i o n a n d a c e t o g e n e s i s - m e t h a n o g e n e s i s i n t h e f i r s t a n d s e c o n d r e a c t o r s r e s p e c t i v e l y . I n s h o r t , “ P h a s e ” s h o u l d b e u s e d f o r p r o c e s s e s w h e n d i f f e r e n t r e a c t i o n s o c c u r i n d i f f e r e n t r e a c t o r s a n d “ S t a g e ” s h o u l d b e a p p l i e d f o r t h e s a m e r e a c t i o n / p r o c e s s o c c u r r i n g i n t h e t w o c o n s e c u t i v e r e a c t o r s . I t i s a l s o a p p r o p r i a t e t o a v o i d t h e u s e o f t h e w o r d “ S t e p s ” , s i n c e i t i s u s u a l l y u s e d t o d e s c r i b e v a r i o u s t y p e s o f r e a c t i o n s i e . m e c h a n i s m s o f c h e m i c a l r e a c t i o n . T o d e t e r m i n e w h e t h e r a t w o - p h a s e ( U A S B - U A S B ) p r o c e s s d o e s o c c u r , 3 - d i m e n s i o n a l p l o t s o f e f f l u e n t p r o f i l e s o b t a i n e d a l o n g t h e h e i g h t o f b o t h A - U A S B a n d M 7 5 U A S B u n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s , w e r e m a d e . A s s h o w n i n F i g u r e 5 . 8 ( a ) , i t i s c l e a r t h a t h y d r o l y s i s - a c i d i f i c a t i o n p r e d o m i n a t e s i n t h e A - U A S B ; t h e a v e r a g e l o w c o n c e n t r a t i o n o f i n f l u e n t s o l u b l e C O D i n c r e a s e s g r a d u a l l y f r o m t h e b o t t o m u p t o t h e t o p o f t h e r e a c t o r u n d e r a l l t e s t e d r u n n i n g c o n d i t i o n s d u r i n g 1 4 5 d a y s o f t h e S e q u e n c e 2 e x p e r i m e n t . I n c o n t r a s t , t h e a v e r a g e h i g h C O D c o n c e n t r a t i o n o f t h e e f f l u e n t f r o m A - U A S B , f e d a t t h e b o t t o m o f M - U A S B , d e c r e a s e s r a p i d l y a s i t e n t e r s t h e s l u d g e b e d a n d b l a n k e t , b e f o r e l e a v i n g t h e s y s t e m a t t h e t o p o f t h e r e a c t o r ( a s s h o w n i n F i g u r e 5 . 8 ( b ) ) . T h i s m e a n s t h a t a c e t o g e n e s i s - m e t h a n o g e n e s i s d o m i n a t e s i n t h e M - U A S B a n d m o s t o f t h e r e a c t i o n s o c c u r s a t t h e l o w e r p a r t o f t h e r e a c t o r . T h i s r e s u l t a l s o a g r e e s w i t h t h e w o r k p r e s e n t e d b y G h o s h ( 1 9 8 4 ) . F i g u r e s 5 . 9 a n d 5 . 2 6 r e c o n f i r m a s i m i l a r s i t u a t i o n o f 3 - d i m e n s i o n a l p l o t s o f e f f l u e n t t o t a l V F A a n d C O D ( s o l ) p r o f i l e s , i n d i c a t i n g a f e a s i b i l i t y o f t w o - p h a s e ( U A S B - U A S B ) p r o c e s s p h e n o m e n o n d u r i n g b o t h “ b e s t k n o w n ” o p e r a t i n g c o n d i t i o n a n d m a x i m i z a t i o n a n d r e c o v e r y p e r i o d e x p e r i m e n t s , r e s p e c t i v e l y . I n a d d i t i o n , F i g u r e 5 . 1 0 s h o w s a s i g n i f i c a n t d i f f e r e n c e o f M L V S S c o n c e n t r a t i o n a t t h e s l u d g e b e d a n d b l a n k e t l e v e l s , c o m p a r e d w i t h t h o s e o f s e t t l i n g a n d e f f l u e n t l e v e l s . I n f l u e n t M L V S S c o n c e n t r a t i o n i n c r e a s e d s i g n i f i c a n t l y a t t h e s l u d g e b e d a n d b l a n k e t l e v e l s a n d t h e n r e m a i n e d a l m o s t c o n s t a n t a t t h e e f f l u e n t l e v e l o f A - U A S B . I n c o n t r a s t , t h e s e h i g h e f f l u e n t V S S c o n c e n t r a t i o n s o f A - U A S B d e c r e a s e d s h a r p l y a f t e r t h e s l u d g e b e d a n d b l a n k e t l e v e l s a n d r e m a i n e d a l m o s t u n c h a n g e d i n t h e e f f l u e n t o f M - U A S B . A l l t h e s e r e s u l t s a p p e a r t o i n d i c a t e t h e f e a s i b i l i t y a n d e f f e c t i v e n e s s o f t h e t w o - p h a s e a n a e r o b i c s t a b i l i z a t i o n ( U A S B U A S B ) p r o c e s s , i n w h i c h m o s t o f t h e r e a c t i o n s o c c u r r e d a t t h e l o w e r p a r t ( s l u d g e b e d 76 Sampllri point no. — Sp.1 So.3 Sp.4 Sp.2 I Sampling point no. Sp.8 Sp.7 Sp.6 50.5 (b) Lperimsntat running ccnditicnsj [Exper:men1aPenods-j SR RR Days 70/30 3/6 1-29 70/30 5/8 35.71 60/40 5/8 78-1 (c)60/40 3/6 107-145 Figure 5.8 COD (soluble) Profiles Along the Reactor Height: Under different runninq conditions (a) A-UASB; (b) M-UASB; (cYRunning Conditions Note: All sampling locations are illustrated in Fig.4.1 El fluent COO. mgJl llhousan) 0— I I 1 8 16 22 25 29 43 50 57 54 71 75 35 92 99102106113120130134141146 Time, days Effluent COO. mg/I (thousand) (a) A 1 8 16 22 25 29 43505754 71 75 86 92 99102106113120130134141146 Time, days 7 7 r: L 1 1 1 5 2 5 4 3 5 7 7 1 8 5 9 9 1 0 6 1 2 0 1 3 4 1 4 5 ( a ) L U T i m e , d a y s 6 g g0 0 0 0 0 1 7 ( 6 ) o o L 7 o o o c c f i o o o c / c 2 0 1 1 5 1 4 5 ( b ) L U T ’ r n e , d a y s _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ L n t e d o s 1 S R R R D a y s 7 0 / 3 0 3 / 6 1 - 2 9 7 0 / 3 0 5 / 8 3 6 - 7 1 6 0 / 4 0 5 / 8 7 8 - 1 0 6 ( c ) 6 0 / 4 0 3 / 6 1 0 7 - 1 4 5 F i g u r e 5 . 9 T o t a l V F A P r o f i l e s A l o n g t h e R e a c t o r H e i g h t : U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n s ( a ) A - U A S B ; ( b ) M - U A S B ; ( c ) R u n n i n g C o n d i t i o n s N o t e : A l l s a m p l i n g l o c a t i o n s a r e I l l u s t r a t e d I n F I g . 4 . 1 78 0 i 1 15 25 43 57 71 85 99 106 120 134 145 (a) Time, days (7) .J2 OOOOOOOOCCU/8) f 15 25 43 57 71 85 99 106120134145 Time, days (b [iiri.nring conditions. [€xperimentatP.erlàdsj SR RR Days 70/30 3/6 1-29 70/30 5/8 35-71 60/40 5/8 78-106 Cc)60/40 3/8 107-145 Figure 5.10 MLVSS Profiles Along the Reactor Height: Under Different Running Conditions (a) A-UASB; (b) M-UASB; (c) Running Conditions Note: All sampling locations are Illustrated in Fig.4.1 7 9 a n d b l a n k e t l e v e l s ) o f b o t h A - U A S B a n d M - U A S B . A s i n a r i ( 1 9 8 1 ) a n d H a r p e r ( 1 9 8 6 ) r e p o r t e d a s i m i l a r s i t u a t i o n w h e r e b y t h e c o n s t a n t p r o d u c t i o n o f H P r a n d / o r H B u a c i d s i n t h e f i r s t r e a c t o r w a s b e n e f i c i a l f o r t h e m e t h a n o g e n i c r e a c t o r , s i n c e i t e n a b l e d t h e d e v e l o p m e n t o f a h e a l t h y p o p u l a t i o n o f o b l i g a t e h y d r o g e n p r o d u c i n g a c e t o g e n i c , ( O H P A ) , b a c t e r i a a n d t h e a s s o c i a t e d h y d r o g e n - o x i d i z i n g m e t h a n o g e n s ; t h i s e n s u r e d t h e r a p i d a s s i m i l a t i o n o f t h e s e a c i d s i n t h e s e c o n d r e a c t o r . 5 . 2 . 1 . 4 C o n c l u s i o n s W i t h a n a p p l i c a t i o n o f a 2 b y 2 f a c t o r i a l d e s i g n e x p e r i m e n t a n d R e s p o n s e S u r f a c e M e t h o d ( R S M ) , t h e e f f e c t a n d i n t e r a c t i o n o f S R a n d R R o n t h e s y s t e m r e s p o n s e s a n d p e r f o r m a n c e w e r e c a l c u l a t e d . A n o p t i m u m “ b e s t k n o w n ” r u n n i n g c o n d i t i o n w a s l o c a t e d , w i t h a n i n t e r p r e t a t i o n o f t h e e f f e c t a n d i n t e r a c t i o n o f S R a n d R R o n t h e r e s p o n s e p a r a m e t e r s a t d i f f e r e n t s e q u e n c e s o f t h e e x p e r i m e n t . T h e r e s u l t s o f t h i s i n v e s t i g a t i o n c a n b e s u m m a r i z e d a s f o l l o w s : ( 1 ) A s t e e p a s c e n t t e c h n i q u e , o n e o f t h e m o s t p r o m i s i n g R S M a p p r o a c h e s , a p p e a r s t o b e a n e f f e c t i v e m e a s u r e i n d i r e c t i n g a n a p p r o p r i a t e s t e p o f t h e e x p e r i m e n t a l d e s i g n t o w a r d t h e o p t i m u m “ b e s t k n o w n ” r u n n i n g c o n d i t i o n , i n c a s e s w h e r e t h e s e c o n d i t i o n s a r e f a i r l y r e m o t e o r u n k n o w n , ( l i k e t h o s e o f t h e S e q u e n c e 1 e x p e r i m e n t ) . ( 2 ) T h e e f f e c t o f S R o n t h e e f f l u e n t C O D a n d P04-P w a s g r e a t e r t h a n t h a t o f R R a n d o n l y t h e i n t e r a c t i o n o f S R a n d R R o n t h e e f f l u e n t C O D w a s s i g n i f i c a n t i n t h e 8 0 S e q u e n c e 1 e x p e r i m e n t s . H o w e v e r , t h e r e w e r e n o s i g n i f i c a n t e f f e c t s a n d i n t e r a c t i o n s o f S R a n d R R a n y o f t h e r e s p o n s e p a r a m e t e r s i n t h e S e q u e n c e 2 e x p e r i m e n t s , w i t h t h e e x c e p t i o n o f S R o n t h e e f f l u e n t a n d r e m o v a l e f f i c i e n c y o f P 04- P , a n d R R o n t h e % C H4 c o n t e n t ( w h e r e a s l i g h t e f f e c t w a s d e t e c t e d ) . ( 3 ) T h e o p t i m u m “ b e s t k n o w n ” r u n n i n g c o n d i t i o n w a s S R 8 0 1 2 0 a n d R R 5 / 8 , w i t h r e s p e c t t o P 04- P r e m o v a l e f f i c i e n c y , s p e c i f i c C H4 g a s p r o d u c t i v i t y , a n d C H4 g a s p r o d u c t i o n . ( 4 ) T h e f e a s i b i l i t y o f t w o - p h a s e s e p a r a t i o n o f a n a e r o b i c d i g e s t i o n o f s e w a g e s l u d g e w a s c o n f i r m e d . H y d r o l y s i s - a c i d i f i c a t i o n a n d a c e t o g e n e s i s - m e t h a n o g e n e s i s d o m i n a t e i n t h e A - a n d M - U A S B s , r e s p e c t i v e l y . I n a d d i t i o n , i t i s q u i t e p r o b a b l e t h a t m o s t o f t h e r e a c t i o n s i n s i d e t h e M - U A S B o c c u r r e d a t t h e l o w e r p a r t o f t h e r e a c t o r ( s l u d g e b e d a n d b l a n k e t ) . 5 . 2 . 2 M a x i m u m L o a d i n g C a p a c i t y a n d R e c o v e r y P r o c e s s T h e c o n v e n t i o n a l a n a e r o b i c d i g e s t i o n p r o c e s s h a s , u n t i l r e c e n t l y , b e e n c o n s i d e r e d t o b e u n p o p u l a r a n d n o t f e a s i b l e f o r t r e a t m e n t o f a h i g h - s t r e n g t h o r g a n i c w a s t e ( s u c h a s s e w a g e s l u d g e ) u n d e r s h o r t r e t e n t i o n t i m e s , s i n c e i t i s t o o s e n s i t i v e t o v a r i o u s e x t r a n e o u s f a c t o r s a n d u n a b l e t o r e t a i n a s i g n i f i c a n t a m o u n t o f v i a b l e s l u d g e u 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 . H o w e v e r , i t i s n o w p o s s i b l e a n d f e a s i b l e t o i n s t a l l w e l l - f u n c t i o n i n g , f u l l - s c a l e a n a e r o b i c f a c i l i t i e s o p e r a t i n g a t h i g h l o a d i n g r a t e s . A l l m o d e r n “ h i g h r a t e ” a n a e r o b i c 8 1 p r o c e s s e s a r e b a s e d o n t h e p r i n c i p l e s o f h i g h v i a b l e b i o m a s s r e t e n t i o n a n d s l u d g e i m m o b i l i z a t i o n ( i e . f i x a t i o n ) . A t l e a s t t w o m e c h a n i s m s a r e i n v o l v e d h e r e : ( i ) t h e f o r m a t i o n o f h i g h l y s e t t l e a b l e s l u d g e a g g r e g a t e s , c o m b i n e d w i t h e a r l y g a s s e p a r a t i o n a n d s l u d g e s e t t l i n g ; a n d ( i i ) a t t a c h m e n t a n d e n t r a p m e n t o f b a c t e r i a a n d s l u d g e a g g r e g a t e s t o a h i g h d e n s i t y p a r t i c u l a t e c a r r i e r , o r p a c k i n g m a t e r i a l , s u p p l i e d t o t h e r e a c t o r ( L e t t i n g a , 1 9 8 3 a ) . T h e U A S B i s c o n s i d e r e d t o b e o n e o f t h e m o s t s u c c e s s f u l a n d p r o m i s i n g p r o c e s s e s o f t h e m o d e r n h i g h - r a t e a n a e r o b i c d i g e s t i o n c o n c e p t . I t h a s l o n g b e e n r e c o g n i z e d t h a t t h e U A S B p r o c e s s h a s s u p e r i o r f l o c c u l a t i o n a n d s e t t l i n g a b i l i t i e s , a s w e l l a s b e i n g a b l e t o m a i n t a i n a h i g h s o l i d s r e t e n t i o n t i m e , u n d e r a h i g h o r g a n i c l o a d i n g r a t e . L e t t i n g a ( 1 9 7 9 b ) s u g g e s t e d t h a t h i g h s e t t l e a b i l i t y a n d s p e c i f i c a c t i v i t y o f t h e a n a e r o b i c s l u d g e w e r e t h e m a i n p r e r e q u i s i t e s i n a c h i e v i n g h i g h l o a d i n g r a t e s . T o a c c o m p l i s h t h i s t a r g e t , a t l e a s t 3 c o n d i t i o n s m u s t b e a p p l i e d : ( a ) c a r e f u l s t a r t - u p o f t h e p r o c e s s ; ( b ) m a i n t e n a n c e o f f a v o u r a b l e c o n d i t i o n s f o r f l o c c u l a t i o n a n d g r o w t h ; a n d ( 3 ) p r o m o t i o n o f t h i c k e n i n g . U n d e r t h e s e r e q u i r e m e n t s , t h e s y s t e m w a s l o a d e d s t e p - w i s e l y , b y k e e p i n g t h e b e s t k n o w n r u n n i n g c o n d i t i o n ( S R 8 O / 2 0 a n d R R 5 / 8 ) f r o m t h e p r e v i o u s s e c t i o n a s a s t a r t i n g p o i n t . T h e s y s t e m l o a d i n g r a t e w a s n o t s t e p p e d u p u n t i l t h e s y s t e m w a s o p e r a t e d a s l o n g a s 2 - 3 s y s t e m H R T a n d / o r 8 0 % r e m o v a l e f f i c i e n c y w a s a c h i e v e d . P r i o r t o d i s c u s s i n g t h e r e s u l t s o f m a x i m i z a t i o n a n d r e c o v e r y p e r i o d , t h e f o l l o w i n g t e r m s a n d a p p r o a c h e s u s e d i n t h i s p a r t i c u l a r e x p e r i m e n t , s h o u l d b e c l e a r l y d e f i n e d : ( a ) M a x i m u m l o a d i n g c a p a c i t y - i s t h e p o i n t w h e r e t h e r e w a s n o s y s t e m r e m o v a l a t a l l , w i t h t h e i n f l u e n t a n d e f f l u e n t C O D c o n c e n t r a t i o n s b e i n g e q u a l . 8 2 ( b ) R e c o v e r y p r o c e s s - i s t h e a p p r o a c h t o r e c o v e r t h e s y s t e m b y r e d u c i n g t h e o r g a n i c l o a d i n g r a t e , s t e p - b y - s t e p , a n d a n a l y z i n g t h e p e r c e n t a g e o f s y s t e m r e c o v e r y a t e a c h s t e p o f l o a d i n g r e d u c t i o n a f t e r a c o m p l e t e s y s t e m f a i l u r e . ( c ) O p t i m u m o p e r a t i n g c o n d i t i o n - i s t h e o p t i m u m p o i n t o f S R a n d R R w h e r e t h e o p t i m i z a t i o n o f s y s t e m C O D r e m o v a l e f f i c i e n c y a n d m e t h a n e g a s p r o d u c t i o n w e r e a c h i e v e d . T h e r e s u l t s o f s y s t e m m a x i m i z a t i o n , p r o c e s s f a i l u r e , r e c o v e r y p e r i o d , s y s t e m r e c o v e r y , a n d o p t i m u m o p e r a t i n g c o n d i t i o n s a r e d i s c u s s e d i n t h e f o l l o w i n g s e c t i o n s . 8 3 5 . 2 . 2 . 1 M a x i m u m L o a d i n g C a p a c i t y A s t h e o r g a n i c l o a d i n g r a t e i n c r e a s e s s t e p - b y - s t e p a n d f i n a l l y o v e r l o a d s t h e s y s t e m , i t i s i m p o r t a n t t o m o n i t o r w h e t h e r t h e s y s t e m r e a c h e s t h e p o i n t o f c o m p l e t e f a i l u r e . S e v e r a l f a c t o r s h a v e t o b e c o n s i d e r e d , i n c l u d i n g h o w t o i d e n t i f y w h e t h e r t h e s y s t e m i s c l o s e t o t h e c r i t i c a l p o i n t ; w h a t p a r a m e t e r s s h o u l d b e m e a s u r e d ; w h a t o p t i o n s a r e a v a i l a b l e ; a n d h o w t o c o n t r o l t h e m . I n g e n e r a l , f e e d s t o p p a g e , i n f l u e n t l o a d i n g r e d u c t i o n , e f f l u e n t r e c y c l e , a n d a l k a l i n e a d d i t i o n a r e r e c o m m e n d e d f o r r e c o v e r i n g t h e s y s t e m a f t e r a s e r i o u s s h o c k l o a d a n d / o r f a i l u r e . A c o m b i n a t i o n o f s t e p - l o a d i n g r e d u c t i o n a n d r e c y c l e w a s s e l e c t e d a s a p r a c t i c a l a n d e f f e c t i v e a p p r o a c h t o t h i s p a r t i c u l a r c a s e . ( a ) P r o c e s s F a i l u r e A l t h o u g h t h i s t w o - p h a s e U A S B - U A S B p r o c e s s i s d e s i g n e d t o p r o v i d e o p t i m u m c o n d i t i o n s t o s t i m u l a t e t h e g r o w t h o f a c i d o g e n s a n d m e t h a n o g e n s i n t h e A - a n d M U A S B s r e s p e c t i v e l y , p r o c e s s f a i l u r e c a n s t i l l o c c u r , i f t h e s y s t e m i s c o n t i n u o u s l y a n d c o n s t a n t l y o v e r l o a d e d . T h i s c a n s l o w l y t u r n t h e M - U A S B i n t o a s i n g l e - s t a g e d i g e s t e r , w h e r e b o t h a c i d o g e n s a n d m e t h a n o g e n s c o m p e t e f o r s u b s t r a t e u t i l i z a t i o n a n d g r o w t h . I f o v e r l o a d i n g c o n t i n u e s w i t h o u t a n y e f f e c t i v e r e m e d i a l a c t i o n s t a k e n , t h e s y s t e m w i l l e v e n t u a l l y f a i l . B e t t e r u n d e r s t a n d i n g o f m i c r o b i o l o g i c a l a n d b i o c h e m i c a l r e a c t i o n s h a s l e a d t o s t a b i l i t y i m p r o v e m e n t o f t h e a n a e r o b i c d i g e s t i o n p r o c e s s . I t i s n o w k n o w n t h a t V F A s a n d 8 4 h y d r o g e n c a n b e f o r m e d m o r e r a p i d l y t h a n t h e y a r e r e m o v e d , u n d e r h i g h l o a d i n g r a t e a n d / o r a s u d d e n i n c r e a s e i n o r g a n i c l o a d i n g ( Z o e t e m e i j e r , 1 9 8 2 ) . U n d e r t h i s c o n d i t i o n , a c e t o g e n s ( e s p e c i a l l y O b l i g a t e H y d r o g e n P r o d u c i n g A c e t o g e n s , O H P A ) , r e s p o n s i b l e f o r c o n v e r t i n g I - I P r a n d o t h e r h i g h e r V F A s i n t o H A c , C 02, a n d H2 . a r e i n h i b i t e d i f t h e h y d r o g e n c o n c e n t r a t i o n e x c e e d s 0 . 0 1 % . A s a r e s u l t , t h e e x c e s s o f r e d u c t i o n e q u i v a l e n t s i s d i v e r t e d i n t o l e s s f a v o u r a b l e b i o c h e m i c a l r o u t e s , r e s u l t i n g i n a c c u m u l a t i o n o f H P r o r h i g h e r V F A p r o d u c t s ( Z o e t e m e i j e r , 1 9 8 2 ) . T h i s o b s e r v a t i o n c a n p a r t l y e x p l a i n t h e f e a s i b i l i t y o f u s i n g t h e t w o - p h a s e c o n c e p t t o s t a b i l i z e i n f l u e n t s u b s t r a t e a n a e r o b i c a l l y . H o w e v e r , i f s y s t e m o v e r l o a d i n g s t i l l c o n t i n u e s , h i g h c o n c e n t r a t i o n o f V F A s w i l l d e s t r o y t h e M - U A S B b u f f e r i n g c a p a c i t y , r e s u l t i n g i n a d r o p i n t h e d i g e s t e r p H a n d d i s c o u r a g i n g t h e g r o w t h o f m e t h a n o g e n s . T h i s s i t u a t i o n c o m b i n e d w i t h h i g h l o a d i n g a n d h i g h r e c y c l e r a t e s c a n l e a d t o a w a s h o u t o f t h e m e t h a n o g e n s f r o m t h e s y s t e m . I f t h e H R T e x c e e d s t h e m a x i m u m b a c t e r i a l g r o w t h r a t e , c e s s a t i o n o f C H4 p r o d u c t i o n a n d f i n a l l y p r o c e s s f a i l u r e m a y r e s u l t . D i f f e r e n t a p p r o a c h e s a n d m e t h o d s h a v e b e e n p r o p o s e d t o p r e d i c t w h e t h e r t h e s y s t e m h a s f a i l e d o r n o t . G r a e f a n d A n d r e w ( 1 9 7 4 a a n d 1 9 7 4 b ) s u g g e s t e d t h a t c e s s a t i o n o f C H4 p r o d u c t i o n r a t e , s u d d e n i n c r e a s e i n V F A c o n c e n t r a t i o n , a i n c r e a s e i n % C O2 c o n t e n t i n d r y g a s , a n d a d r o p i n p H , a s i n d i c a t o r s o f p r o c e s s f a i l u r e . M o r e o v e r , B e r g m a n ( 1 9 6 6 ) p r o p o s e d t h a t t h e r a t i o o f V F A l a l k a l i n i t y e x c e e d i n g 0 . 3 - 0 . 4 w a s a s i g n a l f o r p r o c e s s f a i l u r e . 8 5 A s s h o w n i n F i g u r e 5 . 1 1 a n d F i g u r e 5 . 1 3 - 5 . 1 4 , t h e s y s t e m ( M - U A S B ) , d u r i n g t h e m a x i m i z a t i o n s e q u e n c e , i n d i c a t e d s o m e s i g n s o f f a i l u r e a s t h e l o a d i n g r a t e i n c r e a s e d , b y s h o r t e n i n g t h e H R T f r o m 3 . 4 0 t o 1 . 2 0 d a y s ; i t f a i l e d c o m p l e t e l y a t a n H R T o f l e s s t h a n 1 . 0 d a y ( 0 . 9 8 ) , e q u i v a l e n t t o a s y s t e m h y d r a u l i c l o a d i n g o f 1 . 0m3/m-d. C O D ( s o l . ) a n d V F A r e m o v a l e f f i c i e n c i e s d e c l i n e d f r o m 9 0 % d o w n t o l e s s t h a n 1 0 % , a t t h e H R T o f 1 d a y , w i t h a c c u m u l a t i o n o f P04-P i n s i d e t h e s y s t e m ( a s s h o w n i n F i g u r e 5 . 1 1 ) . F i g u r e 5 . 1 3 c o n f i r m s t h i s s i t u a t i o n , w h e r e b y t h e t o t a l V F A c o n c e n t r a t i o n r o s e i n t h e r e a c t o r a t d a y 3 7 , a t a s y s t e m h y d r a u l i c l o a d i n g r a t e o f 0 . 3 5 m3/m-d. I n i t i a l l y , t h e c o n c e n t r a t i o n o f b o t h H A c a n d H P r i n c r e a s e d r a p i d l y t o 9 3 0 m g / L a n d 3 4 0 m g / L a t d a y 4 0 ; a p p r o x i m a t e l y 3 - 4 d a y s l a t e r , t h e 1 - l A c d i s a p p e a r e d a n d t o t a l V F A c o n c e n t r a t i o n r o s e t o 1 8 0 0 m g / L a s H A c , b y d a y 4 2 . A l s o , t h e p r e s e n c e o f H B u a n d o t h e r h i g h e r V F A S w a s n o t e d , f u r t h e r i n c r e a s i n g t h e c o n c e n t r a t i o n o f t o t a l V F A u p t o 2 8 1 5 m g / L a s H A c a t a n H R T o f 1 d a y ( o r p r o c e s s f a i l u r e ) . I t i s i n t e r e s t i n g t o n o t e t h a t t h e r e i s a n a c c u m u l a t i o n o f H P r a t a n H R T o f l e s s t h a n o n e d a y . U n d e r t h e s t r e s s o f a h i g h o r g a n i c l o a d i n g r a t e , t h e r e m a y b e a s h i f t i n t h e m e t a b o l i c p a t h w a y t o a l e s s f a v o u r a b l e o n e , i n s i d e t h e r e a c t o r . A s t h e M U A S B w a s l o a d e d u p s t e p - b y - s t e p , t h e r e w a s a s h i f t i n t h e r a t i o o f V F A p r o d u c e r s ( a c i d o g e n s a n d a c e t o g e n s ) a n d c o n s u m e r s ( m e t h a n o g e n s , S R B , a n d N R B ) i n s i d e t h e r e a c t o r . T h i s l e a d s t o t h e p r o d u c t i o n o f s i g n i f i c a n t a m o u n t s o f C O2 a n d H2. A s a r e s u l t , t h e p a r t i a l p r e s s u r e o f H2 i n s i d e t h e s y s t e m i n c r e a s e s u p t o c e r t a i n l e v e l ( h i g h e r t h a n 1 0 a t m ) c a u s i n g a s h i f t i n t h e m e t a b o l i c p a t h w a y a n d a c c u m u l a t i o n o f H P r , a s s h o w n i n F i g u r e 5 . 1 2 . A s a l s o s h o w n i n F i g u r e 5 . 1 3 ( a ) , t h e e f f l u e n t s o l u b l e C O D a n d V F A c o n c e n t r a t i o n s i n c r e a s e d g r a d u a l l y t o d a y 5 1 , w i t h a n i n c r e a s e i n l o a d i n g r a t e , a f t e r 8 6 F i g u r e 5 . 1 1 A T w o - p h a s e ( U A S B - U A S B ) S t e p - l o a d i n g A n d M - U A S B R e m o v a l E f f i c i e n c y D u r i n g t h e s y s t e m m a x i m i z a t i o n ( a ) H R T , K g C O D / c u m - d ; ( b ) R e m o v a l e f f i c i e n c y 2 4 - 2 0 - 1 6 - 1 2 - 8 - K g C O D ! c u . m - d 2 5 4 7 6 a 1 0 2 ] 1 M E , d a y s a 8 I 4 0 1 0 0 8 0 6 0 4 0 2 0 0 - 2 0 5 1 — I I I — ‘ III’I. 1 8 1 1 1 5 2 2 2 7 3 3 3 7 4 2 4 7 l i M E d a y s - _ \ \ , 4 / ’ • C O D ( R I . ) + P 0 4 - P - 4 0 - - 6 0 - - 8 0 1 6 1 1 1 5 2 2 2 7 3 3 3 7 4 2 4 7 l i m e , d a y s 5 1 87 (1) C9 2 NA&+ 2ADP + 2 p — 2 CHOOOH + 2 NADH + 2ATP PynMc add (2) 2 NADH —2 NAD . 2 H2 (2) CH OCOOH + 2 NADH + ADP + P (3)2 CH SOCOOH +2 NAD — CCI-COOH +2 NAD+ ATP + 2 CKoA + 2 C+ 2 NACH (3) CHOCOOH + NAD (4)2CHoA+2ADP+2P — CCoA+O2+NADH 2CHOOH+2ATP (4)CHoA+NADH COOH+H+NAD (I) Gft.jcose (1 Glucose ;NA1;7.r_aLa, I ___ 2’ I 2*0. (SI• I) 2*?’ (3g.. I MP c3 2PYR 2PYR(.32 : I c 2> CA) 2AcCoA t AcC0A !‘H?r - HO (5’.. 3)1 2NAc ‘ HAc I c.toc.C Aç•r;C SIc;. Ste;. SIc;. 1 cr1ict pr.ssur. () ;ç;-I ‘4a c’aI r•S%if• Overail: C2&.2H2+4ADP+4P %J+3AOP+3P 2CHOOH+2CO +4H24ATP CCCOOH+CCOOH+c ++3ATP Figure 5/2 Aciaogenic phase ofglucosefermentation under low andh:ghH2partid pressures to form acetic acid propionic acid ‘‘2 gas and CO2. (Abbreviations: EM? - Embden-Meyerhof pathway; PYR - pyruvic acid; AcCoA — acetyl coenzyme A; I-fPr — propionic acid; HAc — acetic (Source: Modified after PALNS et.aI, 1987) 14768102 — / 1 T i m e , d a y s 1 1 1 2 2 3 3 4 2 5 1 T I m e , d a y s — 1 - 0 . 8 - 0 . 4 - 0 . 2 0 8 8 • C H 4 , V d ÷ % C 0 2 C O D ( a ) I 2 6 0 2 4 0 2 2 0 2 0 0 1 8 0 1 6 0 - 1 4 0 - 1 2 0 - 1 0 0 - 8 0 - 6 0 - 4 0 - 2 0 0 7---..- I’ll I”II 1 0 - 9 — 6 - 8 5 - • 4 j 2 — i 0 4 - 3 . 5 - 3 2 . 5 0 . 5 M a 2 d n , n l o a d s U > 4 - 3 . 5 - 3 - 2 . 5 - 2 - 1 . 5 - 1 — 0 . 5 - 0 . - 1 . 8 - 1 . 4 1 . 2 2 5 4 7 6 6 T i m e , d a y s D V F N A L K • T o t . V F A — H A C 1 0 2 ( b ) 0 . 8 1 6 1 1 1 5 2 2 2 7 3 3 3 7 4 2 4 7 5 1 T I m e , d a y s F i g u r e 5 . 1 3 A M - U A S B S y s t e m E f f l u e n t Q u a l i t i e s : D u r i n g t h e p r o c e s s m a x i m i z a t i o n ( a ) C H 4 p r o d u c t l o n , % C 0 2 , E f f . C O D ; ( b ) T o t a l V F A , H A c / H P r , V F A / A l k a l l n I t y 89 1 0 .ooyp.flod 9 I E f f l u e n t MLV + M L V S S ( M . U A S B ) 8 7 A 1 2 5 47: 6 8 1 0 2 l i m e , d a y s (a) 0 • I 1 6 1 1 1 5 2 2 2 7 3 3 3 7 4 2 4 7 5 1 l i m e , d a y s T 1 < N ( M - I J A S 8 ) U i d n i t m , t o a d ’ R . o o . t y o e d o d 0 . 9 _____ T P ( M - U A S B ) - (b) 1 I 0 . 6 l i m e , d a y s itfttaftftftr l i m e , d a y s Figure 5.14 A M-UASB Nutrients and MLVSS: During the System Maximization (a) Effluent MLVSS,MLVSS(M-UASB); (b) TKNJP 9 0 s h o r t e n i n g t h e H R T ( M - U A S B ) t o 1 . 2 0 d a y s . T h e C O2 c o n t e n t i n t h e o f f g a s i n c r e a s e d f r o m a p p r o x i m a t e l y 3 1 . 0 3 ( d a y 3 7 ) t o 5 1 % ( d a y 5 1 ) , a s t h e l o a d i n g r a t e i n c r e a s e d , w h i l e C H4 g a s p r o d u c t i o n i n c r e a s e d a l m o s t l i n e a r l y w i t h a d e c r e a s e i n H R T ( M - U A S B ) d o w n t o 1 . 5 5 d a y s ; h o w e v e r , b e y o n d t h a t , t h e C H4 p r o d u c t i o n r a t e d e c r e a s e d w i t h a d e c r e a s e i n H R T . T h e V F A / a l k a l i n i t y r a t i o a l s o s h o w e d e v i d e n c e o f s y s t e m f a i l u r e a t a n H R T l o w e r t h a n 1 . 5 5 d a y s . T h e r a t i o s e e m s t o i n c r e a s e l i n e a r l y w i t h a d e c r e a s i n g H R T a n d i s a b o v e t h e c r i t i c a l l e v e l o f 0 . 3 - 0 . 4 r e c o m m e n d e d b y B e r g m a n ( 1 9 6 6 ) . T h e w a s h o u t p h e n o m e n o n ( a s s h o w n i n F i g u r e 5 . 1 4 ) , l e a d i n g t o s y s t e m f a i l u r e , c o r r e s p o n d e d t o a n i n c r e a s e i n e f f l u e n t V S S f r o m t h e s y s t e m . T h e c o n c e n t r a t i o n p r o f i l e o f M L V S S i n t h e M - U A S B , a s s h o w n i n F i g u r e 5 . 1 4 , i s s i m i l a r t o t h a t o f C R4 g a s p r o d u c t i o n , i l l u s t r a t e d i n F i g u r e 5 . 1 3 . A s s h o w n , t h e s y s t e m b e g a n t o w a s h o u t t h e M L V S S a n d t h e c o n c e n t r a t i o n o f M L V S S i n t h e r e a c t o r d e c l i n e d s h a r p l y a f t e r r e a c h i n g a n H R T ( M - U A S B ) o f 1 . 5 5 d a y s ; h o w e v e r , t h e M L V S S c o n c e n t r a t i o n d i d r e c o v e r s l i g h t l y a f t e r a b o u t 4 d a y s , a t a h y d r a u l i c l o a d i n g r a t e o f 1 . 8 0m3/m-d ( H R T o f 1 . 0 d a y ) . T h i s s i t u a t i o n m a y h a v e r e s u l t e d f r o m t o o h i g h a l o a d i n g r a t e c r e a t i n g a n u n s e t t l e d s i t u a t i o n a n d s e v e r e t u r b u l e n c e i n t h e l o w e r p a r t o f t h e r e a c t o r , t h u s p a r t l y d e s t r o y i n g t h e s l u d g e b e d . B e c a u s e t h e s a m p l e s w e r e t a k e n i n t h e m i d d l e o f t h e r e a c t o r ( S a m p l i n g p o i n t n o . 6 ) , i t i s p o s s i b l e t h a t a h i g h e r c o n c e n t r a t i o n o f M L V S S , r e s u l t i n g f r o m t h i s t u r b u l e n c e i n t h i s p a r t i c u l a r c a s e , c o u l d o c c u r . I t i s i n t e r e s t i n g a t t h i s p o i n t t o n o t e t h a t t h e m a i n c a u s e s o f p r o c e s s f a i l u r e w e r e t h e c o m b i n a t i o n o f h y d r a u l i c o v e r l o a d i n g , t h u s e x c e e d i n g t h e g r o w t h r a t e o f b o t h 9 1 a c i d o g e n s a n d m e t h a n o g e n s ( w a s h o u t p h e n o m e n o n ) , a n d t h e d e s t r u c t i o n o f t h e d y n a m i c b a l a n c e o f a c e t o g e n s a n d m e t h a n o g e n s i n s i d e t h e M - U A S B . T h e s y s t e m d e m o n s t r a t e d a n i n c r e a s e i n V F A c o n c e n t r a t i o n a n d % C O2 c o n t e n t , b u t a d e c r e a s e i n % C H4 c o n t e n t a n d p r o d u c t i o n , a s d i s c u s s e d e a r l i e r . T h i s o b s e r v a t i o n a l s o c o n f i r m e d t h a t t h e f a i l u r e w a s n o t c a u s e d b y a t o x i c e f f e c t , s i n c e t h e r e w a s n o s i g n o f a d e c r e a s e i n V F A c o n c e n t r a t i o n c o r r e s p o n d i n g t o a d e c r e a s e i n % C H4 c o n t e n t . I n t e r m o f n u t r i e n t r e q u i r e m e n t s d u r i n g t h e p r o c e s s f a i l u r e , o n l y t h e c o n c e n t r a t i o n o f T P i n s i d e t h e r e a c t o r a n d e f f l u e n t i n c r e a s e d s i g n i f i c a n t l y ; T K N i n c r e a s e d o n l y s l i g h t l y . ( b ) M a x i m u m L o a d i n g R a t e T h e s y s t e m c o m p l e t e l y f a i l e d a s t h e l o a d i n g r a t e w a s i n c r e a s e d a n d t h e H R T w a s s h o r t e n e d , i n s t e p w i s e f a s h i o n . A s s h o w n i n F i g u r e 5 . 1 5 , t h e s o l u b l e C O D r e m o v a l e f f i c i e n c y d e c l i n e d l i n e a r l y , a s t h e H R T d e c r e a s e d b e y o n d 1 . 5 d a y s . T o p r e d i c t t h e m a x i m u m l o a d i n g r a t e p r e c i s e l y , a s i m p l e l i n e a r r e g r e s s i o n w a s a p p l i e d , u s i n g t h e a v e r a g e v a l u e s o f e a c h s t e p l o a d i n g r a t e , a t p s e u d o s t e a d y - s t a t e c o n d i t i o n s a s f o l l o w s : Y = 1 2 9 . 2 8 1 - 3 . 2 1 4 X ( 1 5 ) w h e r e Y = % C O D ( s o l u b l e ) r e m o v a l e f f i c i e n c y X = I n f l u e n t f l o w r a t e , L i d 0 . 8 8 9 2 1 0 0 - 9 0 - 8 0 - 7 0 - 60- 5 0 - 4 0 - 3 0 - 2 0 - 1 0 0 ( a ) Y = 1 2 9 . 2 8 1 - 3 . 2 1 4 X y = % C O D R e m o v a l E f f i c i e n c y x = I n f l u e n t F l o w R a t e , l / d r2= 0 . 8 8 M a x . S y s t e m C a p a c i t y = 4 0 l / d O p e r a t i n g C o n d i t i o n s ; S R 8 0 / 2 0 , R R 5 / 8 T e m p . 3’ C N o p H C o n t r o l + % C O D R e m . E f f . • I n f l u e n t F l o w , l / d C r i t i c a l H R T s y s , d = 3 . 0 H R T m - u a s b = 1 . 5 - 1 0 0 - 9 0 - 8 0 - 7 0 -60 • 5 0 L . -40 - 3 0 - 2 0 - 1 0 0 a ) C . ) E a ) 0 C ) C 0 D - o 0 0 . I C ) 0 a ) - C 0 1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0 — I I I I I I — 0 . 5 1 . 5 2 . 5 3 . 5 4 . 5 M - U A S B H R T , d a y s ( b ) ./ S y s t e m H R T % T h e o C H 4 P r o d [ . . : ‘ : . . . : . . . ‘ . : . 1 . 7 7 3 6 . 4 7 I ...::.:...::.:. 2 . 1 8 6 0 . 1 1 / 2 . 8 0 7 3 . 2 1 I ..::...-...:::.: 4 . 8 0 9 7 . 9 9 I 6 . 0 7 8 3 . 7 0 L_J O p t i m a l O p e r a t i n g R e g i o n — I I I I 1 2 3 4 5 6 7 S y s t e m H R T , d a y s Figure 5.15 System Optimum Operating Region and Maximum Capacity: ( a ) O p t i m a l O p e r a t i n g R e g i o n ; ( b ) T h e o r e t i c a l C H 4 P r o d u c t i o n 9 3 B a s e d o n t h i s s i m p l e m o d e l , t h e m a x i m u m l o a d i n g r a t e ( d e f i n e d a s n o C O D r e m o v a l e f f i c i e n c y ) a s s h o w n i n F i g u r e 5 . 1 5 , w a s a b o u t 4 0 L I d ; t h i s w a s e q u i v a l e n t t o a s y s t e m h y d r a u l i c l o a d i n g o f 1 . 8 0m3/m-d, a t a s y s t e m H R T o f 1 . 1 2 5 d a y s ( 0 . 6 2 5 d a y f o r M - U A S B ) . T h e C H4 g a s p r o d u c t i o n a t t h i s p o i n t o f c o m p l e t e f a i l u r e w a s a b o u t 5 0 % o f t h e t h e o r e t i c a l v a l u e , w h i c h i s a c o m b i n a t i o n o f C H4 g a s p r o d u c t i o n f r o m b o t h A - a n d M - U A S B s . D e t a i l s o f c a l c u l a t i n g t h e t h e o r e t i c a l C H4 g a s p r o d u c t i o n ( b a s e d o n t h e a s s u m p t i o n t h a t t h e i n f l u e n t s u b s t r a t e i s 1 0 0 % g l u c o s e ) , a r e s h o w n i n T a b l e D 3 . 1 o f A p p e n d i x D . A t t h i s “ f a i l u r e l o a d i n g ” , t h e e f f l u e n t C O D ( s o l . ) w a s i n e x c e s s o f 9 5 4 0 m g / L , t o t a l V F A s w e r e a b o v e 3 , 7 5 0 m g / L a s H A c , t h e C O2 c o n t e n t w a s m o r e t h a n 4 5 % , a n d t h e V F A l a l k a l i n i t y r a t i o w a s o v e r 1 . 5 5 . O l e s z k i e w i c z ( 1 9 8 8 ) i n d i c a t e d t h a t t h e “ f a i l u r e l o a d i n g r a t e ” f o r a b i o f i l t e r u s i n g a U A S B r e a c t o r t o s t a b i l i z e s y n t h e t i c w a s t e w a t e r , w a s 2 0 k g COD/m3-d, w h i c h i s e q u i v a l e n t t o 5 0 L I d a t a n H R T o f 5 . 8 h r s . M o r e o v e r , B e r g m a n ( 1 9 6 6 ) p o i n t e d o u t t h a t h i s s y s t e m , b e i n g u s e d t o t r e a t s e w a g e s l u d g e , f a i l e d a t a n H R T o f 2 . 2 0 d a y s , a p H o f 4 . 6 0 , a n d a H A c : H P r : H B u r a t i o o f 2 . 0 : 2 . 5 : 1 . 0 , w i t h H P r o v e r 9 , 0 0 0 m g / L . A l t h o u g h t h e s e r e s u l t s a r e n o t d i r e c t l y c o m p a r a b l e , t h e r e i s s o m e s i m i l a r i t y i n t h e d a t a b a s e s f r o m t h e s e U A S B - U A S B s t u d i e s , w i t h r e c o g n i z a b l e p a t t e r n s a n d n u m e r i c a l i n d i c e s i n t h e s a m e g e n e r a l r a n g e . 5 . 2 . 2 . 2 R e c o v e r y P r o c e s s I n a n a e r o b i c t r e a t m e n t p r o c e s s e s , s h o r t t e r m h y d r a u l i c o v e r l o a d i n g i s a p r o b l e m d i f f i c u l t t o a v o i d a n d o p e r a t i o n a l f a i l u r e i s f r e q u e n t l y t h e o u t c o m e . A n e x t e n d e d r e a c t o r 9 4 r e c o v e i y p e r i o d i s u s u a l l y n e c e s s a r y . T h e p r o b l e m o f h y d r a u l i c o v e r l o a d i n g i s a g g r a v a t e d w h e r e n o r e c y c l e f a c i l i t y i s a v a i l a b l e , t o p r e v e n t t h e l o s s o f t h e s l o w g r o w i n g m e t h a n o g e n s f r o m t h e s y s t e m . T h e f o l l o w i n g s e c t i o n s d e a l w i t h t h e b e h a v i o u r a n d r e s p o n s e o f t h i s s y s t e m a f t e r c o m p l e t e f a i l u r e a n d t h e r e c o v e r y t o i n i t i a l n o r m a l i t y . P r i o r t o a d e t a i l e d d i s c u s s i o n , h o w e v e r , s o m e c l a r i f i c a t i o n s s h o u l d b e m a d e . T h e t e r m “ p r o c e s s f a i l u r e ” c a n b e e i t h e r t e m p o r a r y ( i e . a s u d d e n o r g a n i c s h o c k l o a d i n g ) o r r e l a t i v e l y p r o l o n g e d ( i e . a t o x i c s h o c k l o a d o r h y d r a u l i c o v e r l o a d i n g - c o m p l e t e w a s h o u t o f t h e a c t i v e b i o m a s s ) . S e v e r a l s t u d i e s h a v e d e a l t w i t h t e m p o r a r y f a i l u r e s , b u t r a r e l y w i t h a p e r m a n e n t o n e , e s p e c i a l l y t h a t o f h y d r a u l i c o v e r l o a d i n g . T h e f o l l o w i n g s e c t i o n s d e a l w i t h s y s t e m r e c o v e r y b a c k t o t h e i n i t i a l s t a g e , u s i n g a c o m b i n a t i o n o f R R a n d s t e p - d o w n l o a d i n g a p p r o a c h e s . ( a ) R e c o v e r y P e r i o d T h e w o r s t s c e n a r i o i n r e c o v e r i n g a s y s t e m a f t e r c o m p l e t e f a i l u r e i s t h e n e e d t o r e - s e e d a n d r e - a c c l i m a t i z e t h e s y s t e m . H o w e v e r , t h i s o p t i o n i s c o s t l y a n d n o t p r a c t i c a l i n t e r m s o f a f u l l - s c a l e o p e r a t i o n : t i m e - c o n s u m i n g p r o c e s s e s a n d h i g h - s k i l l e d m a n p o w e r a r e r e q u i r e d . A c o m b i n a t i o n o f s t e p - d o w n l o a d i n g r a t e a n d R R i s r e l a t i v e l y s i m p l e a n d q u i t e p r a c t i c a l , c o m p a r e d w i t h t h e o p t i o n o f r e s e e d i n g a n d a c c l i m a t i z a t i o n ( s t e p - u p l o a d i n g ) . H o w e v e r , s o m e q u e s t i o n s s t i l l e x i s t a s t o w h e t h e r t h i s a p p r o a c h i s m o r e e f f e c t i v e t h a n t h a t o f r e - a c c l i m a t i z a t i o n , a n d w h a t c h a n g e s t h e s y s t e m u n d e r g o e s d u r i n g t h e r e c o v e r y p r o c e s s , c o m p a r e d w i t h t h a t o f t h e i n i t i a l n o r m a l s t a g e . 9 5 A s s h o w n i n F i g u r e 5 . 1 6 - 5 . 1 8 , t h e s y s t e m a p p e a r e d t o b e g i n r e c o v e r i n g f r o m t h e s e r i o u s f a i l u r e a f t e r 1 9 d a y s o f d e c r e a s i n g t h e h y d r a u l i c l o a d i n g f r o m 0 . 4 0 t o 0 . 2 5m31m- d ; t h i s w a s a c c o m p l i s h e d b y p r o l o n g i n g t h e H R T ( M - U A S B ) f r o m 1 . 2 0 d a y u p t o 2 . 0 0 d a y s . T h e s y s t e m d e m o n s t r a t e d C O D a n d V F A r e m o v a l e f f i c i e n c i e s ( M - U A S B ) o f 4 3 a n d 4 5 % r e s p e c t i v e l y , w i t h 6 , 5 8 0 m g / L e f f l u e n t C O D , 4 7 % C O2 c o n t e n t , 6 8 L I d o f C H4 g a s p r o d u c t i o n , a n d a V F A l a l k a l i n i t y r a t i o o f 1 . 4 0 . T h e r e a f t e r , t h e s y s t e m s e e m e d t o r e c o v e r l i n e a r l y w i t h t i m e a n d r e c o v e r e d c o m p l e t e l y t o t h e i n i t i a l l e v e l o f o p e r a t i o n a t a p p r o x i m a t e l y d a y 4 3 , t h e r e b y s h o w i n g 9 7 % V F A a n d 9 2 % s o l u b l e C O D r e m o v a l e f f i c i e n c i e s . T h e e f f l u e n t C O D ( s o l u b l e ) w a s l e s s t h a n 1 , 0 0 0 ( 8 8 0 ) m g / L a n d t h e t o t a l V F A w a s 1 2 5 m g / L a s H A c , w i t h 3 2 % C O2 c o n t e n t , 6 2 L I d o f C H4 g a s p r o d u c t i o n , a n d V F A l a l k a l i n i t y r a t i o o f l e s s t h a n 0 . 1 ( 0 . 0 5 ) . T h e s y s t e m t h e n f o l l o w e d a “ d i m e n s i o n a l t i m e f r a m e ” , d e f i n e d a s t h e r a t i o o f t h e r e c o v e r y t i m e t o t h e H R T ; t h i s w a s e q u a l t o a p p r o x i m a t e l y 5 . 6 0 a n d 1 0 f o r t h e s y s t e m a n d t h e M - U A S B , r e s p e c t i v e l y . T h i s c o m p a r e d w e l l t o a r a t i o o f 5 - 1 0 f o r a n e x p a n d e d b e d a n a e r o b i c r e a c t o r ( U A S B w i t h e f f l u e n t r e c y c l e ) , o p e r a t e d a t a h i g h o r g a n i c l o a d i n g r a t e i n n o n - s t e a d y s t a t e c o n d i t i o n s r e p o r t e d e l s e w h e r e ( E n c i n a , 1 9 8 7 ) . B y d a y 3 0 , t h e a c t i v e b i o m a s s ( M L V S S ) o f t h e s l u d g e b l a n k e t , i n t h e m i d d l e o f t h e r e a c t o r , r e c o v e r e d a n d r e a c h e d a p e a k a t d a y 4 0 . T h i s m a y h a v e b e e n t h e r e s u l t o f t h e s y s t e m b e g i n n i n g t o r e c o v e r a n d p r o d u c i n g s m a l l g a s b u b b l e s , t h u s c r e a t i n g f l o c c u l a t i o n a t t h e s l u d g e b l a n k e t l e v e l , ( t h e r e w a s e v i d e n c e o f i n c r e a s i n g C H4 g a s p r o d u c t i o n a t d a y 3 0 , a s i l l u s t r a t e d i n F i g u r e 5 . 1 7 ( a ) ) . F o r t h e n e x t 1 0 d a y s ( d a y 3 8 - 4 3 ) , i t i s s p e c u l a t e d t h a t t h e g r a n u l a t i o n p r o c e s s p l a y e d a m a j o r r o l e i n a s s i s t i n g s u b s t r a t e s t a b i l i z a t i o n a n d s y s t e m r e c o v e r y ; t h e r e w a s a s h a r p i n c r e a s e i n C O D a n d V F A 9 6 2 2 - 2 0 - 1 8 - E - 1 8 - 0 - C . , _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 4 - 1 2 )10: 8 6 4 2 Ti’i’iii’ I 1 5 1 0 1 5 1 9 2 6 3 8 4 5 5 1 l i M E , d a y s 2 : - 1 0 - 3 0 - - 5 0 - - 7 0 /V M a ) * n , . , n l o a d s R e c o w t y p . i o d 1 2 5 4 7 6 8 1 0 2 l i m e , d a y s ‘ 4 - l i m e , d a y s ( a ) • H R T + K g C O D / c u m - d 1 1 0 1 9 3 8 5 1 l i m e , d a y s Figure 5.16 A Two-phase (UASB-UASB) Step-loading And M-UASB Removal Efficiency D u r i n g t h e s y s t e m r e c o v e r y ( a ) H R T , K g C O D / c u . m - d ; ( b ) R e m o v a l e f f i c i e n c y 9 7 1 9 — 1 9 0 - M a x i m u m L o a d s R e c o v e f y P e r i o d ( a ) • C H , C O D % C O 2 2 5 4 7 6 8 1 0 2 E 1 1 — j 1 1 0 T l m e , d a y s - . . _ _ _ . 1 0 _ _ _ _ _ : f l m e , d a y s 6 8 - \ A e c w y p . 1 o d ( b ) V F N A L K • T o t . V F A 3 5 : : H A c 1 3 Z 2 H P r 1 2 5 T i m e , d a y s 3 2 0 T i m e , d a y s F i g u r e 5 . 1 7 A M - U A S B S y s t e m R e c o v e r y P r o c e s s : ( a ) C H 4 p r o d u c t i o n , % C 0 2 , E f f . C O D ; ( b ) T o t a l V F A , H A c / H P r , V F N A k a l i n i t y 9 8 8 - ( a ) M s j d , m a i l o a d s E f f l u e n t M L V S S : M L V S S ( M . I J A S B ) 1 7 1 T I M E , d a y s T i m e , d a y s 1 . 2 ( b ) 1 . 1 T K N ( M - U A S B ) M a d m u m l o a d s P o c o v e r y p o t o d 1 T P ( M - U A S B ) • E f f l u e n t T K N i - E f f l u e n t T P 0 . 9 0 . 8 1 2 5 4 7 6 8 1 0 2 0 . 7 T I M E , d a y s E 0 . 8 0 . 5 0 . 4 0 . 3 0 . 2 0 . 1 0 I I 1 1 0 1 9 3 8 5 1 l i M E , d a y s F i g u r e 5 . 1 8 A S y s t e m N u t r i e n t s a n d M L V S S : D u r i n g t h e r e c o v e r y p r o c e s s ( a ) E f f l u e n t M L V S S , M L V S S ( M - U A S B ) ; ( b ) T K N , T P 9 9 r e m o v a l e f f i c i e n c i e s , a p p r o x i m a t e l y 9 1 - 9 7 % , a V F A / a l k a l i n i t y r a t i o l e s s t h a n 0 . 5 , a n d a s h a r p b u i l d u p i n b i o m a s s ( M L V S S ) i n t h e s l u d g e b l a n k e t , u p t o 1 , 7 0 0 m g / L . N u t r i e n t r e q u i r e m e n t s , m e a s u r e d a s C O D ( t o t a l ) : T K N : T P i n s i d e t h e r e a c t o r a t t h e s l u d g e b l a n k e t l e v e l ( s a m p l i n g p o i n t n o . 6 ) , w a s i n t h e r a t i o o f 3 6 : 4 : 1 . ( b ) S y s t e m R e c o v e r y A l t h o u g h t h e s y s t e m r e t u r n e d t o t h e i n i t i a l l e v e l o f o p e r a t i o n b y d a y 4 0 , i t i s q u i t e i n t e r e s t i n g t o n o t e t h a t a n a c c u m u l a t i o n o f H P r a n d a n i n c r e a s e i n t o t a l V F A o f t h e M U A S B o c c u r r e d , a s s h o w n i n F i g u r e 1 7 ( b ) ; t h i s i s i n a g r e e m e n t w i t h r e s u l t s r e p o r t e d b y Z o e t e m e i j e r e t a l , ( 1 9 8 2 ) . T h i s m i g h t s u g g e s t t h a t t h e s y s t e m m e t a b o l i c p a t h w a y s s h i f t e d t o a l e s s f a v o u r a b l e r o u t e ; h o w e v e r , t h e p a t h w a y s d i d s h i f t b a c k t o m o r e f a v o u r a b l e o n e s a f t e r a l m o s t 2 0 d a y s o f l o a d i n g r e d u c t i o n , a s a n i n c r e a s e i n C H4 g a s p r o d u c t i o n , % C H c o n t e n t , a n d a l i n e a r r e d u c t i o n o f T o t a l V F A a n d H P r c o n c e n t r a t i o n w e r e o b t a i n e d . R i n z e m a ( 1 9 8 8 ) i n d i c a t e d t h a t a s y s t e m u s i n g t h e U A S B p r o c e s s , i n o c u l a t e d w i t h g r a n u l a r s l u d g e t o s t a b i l i z e V F A i n t h e p r e s e n c e o fH2S c o n c e n t r a t i o n o v e r 1 0 0 m g / L S , h a d a s h a r p d r o p o f V F A r e m o v a l e f f i c i e n c y , b u t r e c o v e r e d w i t h i n 3 - 4 w e e k s . T o d e m o n s t r a t e h o w w e l l t h e s y s t e m r e c o v e r e d a t e a c h s t e p o f l o a d i n g r e d u c t i o n , c o m p a r e d w i t h t h e s a m e l o a d i n g r a t e d u r i n g t h e m a x i m i z a t i o n p r o c e s s , s o m e m o d i f i c a t i o n a n d f u r t h e r a n a l y s i s o f t h e e x p e r i m e n t a l r e s u l t s w e r e m a d e , a s s h o w n i n F i g u r e 5 . 1 9 a n d 5 . 2 0 . C O D ( s o l . ) r e m o v a l e f f i c i e n c y a n d C H4 g a s p r o d u c t i o n w e r e s e l e c t e d a s m a i n r e s p o n s e p a r a m e t e r s f o r t h i s i n v e s t i g a t i o n , s i n c e s u p e r i o r s u p e r n a t a n t q u a l i t y a n d 1 0 0 r e a s o n a b l e C H4 g a s p r o d u c t i o n a r e t h e t w o m a i n o b j e c t i v e s o f t h e a n a e r o b i c s t a b i l i z a t i o n p r o c e s s . F i g u r e s 5 . 1 9 ( c ) a n d 5 . 1 9 ( d ) s h o w t h e r e l a t i o n s h i p b e t w e e n t h e a c t u a l r u n n i n g H R T a n d % s o l u b l e C O D r e m o v a l e f f i c i e n c y d u r i n g t h e m a x i m u m l o a d i n g a n d r e c o v e r y p e r i o d . B a s e d o n t h e s e r e l a t i o n s h i p s , C O D r e m o v a l e f f i c i e n c y a t e a c h d i s c r e t e H R T s t a r t i n g f r o m 1 , 1 . 5 , . . . 4 . 5 d a y s c a n b e e s t i m a t e d d u r i n g t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d . S y s t e m r e c o v e r y e f f i c i e n c y , d e f i n e d a s a p e r c e n t a g e o f C O D r e m o v e d d u r i n g t h e r e c o v e r y p e r i o d o v e r t h a t o f m a x i m i z a t i o n a t t h e s a m e H R T , c a n t h e n b e c a l c u l a t e d a n d g r a p h e d , a s s h o w n i n F i g u r e s 5 . 1 9 ( a ) a n d 5 . 1 9 ( b ) . S i m i l a r l y , s y s t e m r e c o v e r y e f f i c i e n c y i n t e r m s o f C H4 g a s p r o d u c t i o n a t e a c h s p e c i f i c H R T d u r i n g t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d c a n a l s o b e e x p r e s s e d , a s s h o w n i n F i g u r e s 5 . 2 0 ( a ) - 5 . 2 0 ( d ) . P r e d i c t i v e m o d e l s f o r t h i s s y s t e m r e c o v e r y , w i t h a h i g h c o r r e l a t i o n(r2= O . 8 1 - 0 . 9 9 ) , a s s h o w n i n F i g u r e 5 . 2 1 , a r e f o r m u l a t e d a s f o l l o w s : Y = 2 5 . 3 7 e° ( 1 6 ) w h e r e Y = % C O D ( s o l . ) r e m o v a l e f f i c i e n c y X H R T ( M - U A S B ) , d a y s F o r t h e C H4 g a s p r o d u c t i o n , t h e p r e d i c t i v e m o d e l i s a s f o l l o w s : Y l = 9 . 2 5 + 6 4 . 0 1 l n X l ( 2 0 ) w h e r e Y l = C H4 g a s p r o d u c t i o n , L i d 80 > 0 E a: 4 0 0 C) 0 0 2 0 I _ _ i — _ _ _ j : : : : : I I I I . 7 — 80 .4 )0 :— : I I I I I I . 7 , • . 6 0 0 O 1 r r r P I 40 4) 0 20 00 - - fle co ve ty Pe rio d 0 04 1 . r r , Ir .. -. U 00 lO t) 20 4) 00 44 )0 5. 00 IU F . tl o y s Fi gu re 5. 19 A M -U AS B Sy ste m R ec ov er y at Ps eu do St ea dy -s ta te W ith di ffe re nt ru n n in g co n di tio ns % CO D (FI L) re m o v al 10 0 (a ) (b) IIR T. da ys % 00 0( 11 .) re m o v al M ax .L oa ds H ec ov er y Pe rio d % H ec ov er 1. 0 22 18 0 1. 5 88 37 41 2. 0 95 40 42 2. 5 97 50 52 3. 0 97 60 62 3. 5 98 71 72 4. 0 98 ° 81 83 4. 5 98 . 90 92 4. 7 98 . 96 98 N ot e° E st im at ed v a lu es 10 0 / 80 1’ . 6 0 f ‘ % R ec ov er y 4 0 R ec ov er y Pe rio d 20 / • M ad m ur n L oa ds a I I I I I 0 1. 0 1. 5 2. 0 2. 5 3. 0 3. 5 4 . 4. 5 4. 7 FI IT .d ay s 10 00 0 1 - - ’ ” - - - r — : (c) 1 6 0 0 0 1 : 6 0 .0 0 : I ! • I I I Li. . • 40 .0 0 : I M ax im um Lo ad s o • Il I o : I I I I 2O .O o I : : I I I I I I 0. 00 04 )0 0 0 44 )4) 45 0 20 4) 2 .0 10 0 35 0 II R I. J I l y s (d) 2 2 0 • 2 .0 0 C- ) 1. 80 Fi gu re 5. 20 A M -U AS B Sy ste m Re co ve ry at Ps eu do St ea dy -s ta te W ith di ffe re nt ru n n in g c o n di tio ns CH 4, cu .m /c u. m -d 5 4. 5 • 0 E 3. 5, E , 2. 5 C) 2 1 s I. (a ) • M ax im tz n Lo ad s 10 0 C? % R ec ov er y 80 60 4. 4. . . : + R ec ov er y Pe rio d 15 2. 0 2: 5 3. 5 H RT , d ay s 2. 60 1 4. 00 — I I :1 (C ) I I !Eh1 : M ax im um Lo ad s i o I I I I I I I I I I I I I I I I I I ‘ . 00 , . n m ’ j . , . . . , , , . I 3. 00 0. 50 1. 00 5 0 2. 00 2. 50 30 0 3 .0 H R T. da ys (b ) IJ T .d ay s. CH 4, cu .m /c u. m .d M ax Lo ad s R ec ov er y Pe rio d % R ec ov eq 1 2. 45 2. 46 0 1.5 3. 98 2. 25 57 2. 0 3. 65 1. 88 52 2. 5 3. 25 1. 78 55 3. 0 2. 55 1. 76 69 3. 5 1. 70 1. 74 10 2 I I I I I I I I I I I I I I I I I I I — — — — 4, : :c i j\ R ec ov er y Pe rio d I 40 . ‘ , Ir r, rf .. I.- . - - ,- .- j-,- . . I I, . 3.o O 1. 00 2. 00 3.C 0 4. 00 5. 00 H R T. d a s 24 0 1 0 3 F i g u r e 5 . 2 1 A P r e d i c t e d M - U A S B S y s t e m R e c o v e r y L U n d e r D i f f e r e n t R u n n i n g C o n d i t i o n s 1 2 0 — % C O D ( E l i . ) r e m o v a l 1 0 0 C H 4 , c m / c u . m - d / 8 0 - ( 2 ) / G ) > 0 C . ) 6 0 - . 4 0 , . ( 1 ) 2 0 - O . 2 9 X ( 1 ) Y = 2 5 . 3 7 e (r2= O . 9 9 ) ( 2 ) Y = 9 . 2 5 + 6 4 . 0 1 ( m x ) ( r2 0 . 8 1 ) 0 - I I I 0 1 2 3 4 5 H R T , d a y s 1 0 4 X l = H R T ( M - U A S B ) , d a y s T o m e e t t h e o b j e c t i v e s o f b o t h p o l l u t i o n c o n t r o l a n d m a x i m u m C H4 g a s p r o d u c t i o n , t h e o p t i m u m s y s t e m H R T o f 7 . 6 5 d a y s a n d 4 . 2 5 d a y s f o r t h e M - U A S B ( e q u i v a l e n t t o 4 3 d a y s o f r e c o v e r y p e r i o d a f t e r c o m p l e t e s y s t e m f a i l u r e ) w e r e i n i t i a t e d i n o r d e r t o p r o v i d e 9 2 a n d 1 0 0 % r e c o v e r y o f C O D r e m o v a l e f f i c i e n c y a n d C H4 g a s p r o d u c t i o n , r e s p e c t i v e l y . I t i s a l s o i n t e r e s t i n g t o p o i n t o u t t h a t t h e b r e a k t h r o u g h o f s y s t e m r e c o v e r y i s p r e d i c t e d a t a n H R T M U A S B o f 1 . 5 - 1 . 7 d a y s , r e s u l t i n g i n m o r e t h a n 4 0 % r e c o v e r y o f b o t h C O D r e m o v a l e f f i c i e n c y a n d C H4 g a s p r o d u c t i o n , ( a s s h o w n i n F i g u r e 5 . 2 1 ) . T h e s y s t e m t h e n r e c o v e r e d b a c k t o t h e i n i t i a l l e v e l a t a n H R T o f 4 . 2 5 d a y s . T h i s o b s e r v a t i o n l e a d s t o t h e c o n c l u s i o n t h a t a t w o - s t e p i n c r e a s e i n H R T b y 1 . 5 0 a n d 5 . 8 0 t i m e s t h a t o f t h e f a i l u r e v a l u e H R T M U A S B o f 0 . 6 2 5 d a y s , i s a m o s t e f f e c t i v e m e a s u r e f o r c o m p l e t e r e c o v e r y . 5 . 2 . 2 . 3 B a s i c E x p e r i m e n t a l K i n e t i c s S i n c e t h e a n a e r o b i c s t a b i l i z a t i o n p r o c e s s i s c o n s i d e r e d t o b e b i - p h a s i c i n n a t u r e , t h u s r e q u i r i n g a b a l a n c e b e t w e e n a c i d p r o d u c t i o n a n d u t i l i z a t i o n , p r o c e s s s t a b i l i z a t i o n a n d c o n t r o l m a y b e p o s s i b l y e n h a n c e d b y p h y s i c a l s e p a r a t i o n o f t h e s e t w o p h a s e s . F i g u r e 5 . 8 c o n f i r m e d t h e f e a s i b i l i t y o f t h e p h a s e s e p a r a t i o n c o n c e p t , a s d i s c u s s e d e a r l i e r . A l t h o u g h t h e s y s t e m a c h i e v e d p r o m i s i n g r e s u l t s , i t w o u l d b e i n t e r e s t i n g t o k n o w h o w t h e m i x e d c u l t u r e o f b a c t e r i a r e s p o n d e d d u r i n g b o t h t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d s . 1 0 5 O n e w a y t o a c h i e v e t h i s i s t o p r e d i c t t h e k i n e t i c r e s p o n s e g o v e r n i n g t h e a c i d - a n d m e t h a n e - p h a s e r e a c t o r s ( A - U A S B a n d M - U A S B ) , u n d e r t h e s e s i t u a t i o n s . T h i s p r e d i c t i o n a n d e s t i m a t i o n w e r e b a s e d o n t h e e x p e r i m e n t a l d a t a o b t a i n e d a t p s e u d o s t e a d y - s t a t e c o n d i t i o n s , w i t h a c o n t i n u o u s s t e p - l o a d i n g r a t e d u r i n g t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d s . I t i s i m p o r t a n t a t t h i s p o i n t t o m e n t i o n t h a t t h i s k i n e t i c e s t i m a t i o n i s s y s t e m d e p e n d e n t : p r o c e s s d e s i g n a n d c o n f i g u r a t i o n , r u n n i n g c o n d i t i o n s , f e e d c h a r a c t e r i s t i c s , s e e d s l u d g e a n d s t a r t - u p p r o c e d u r e , a n d e v a l u a t i o n p r o c e s s . A c o m p a r i s o n o f t h e s e k i n e t i c v a l u e s w i t h o t h e r s m u s t i n d e e d t a k e t h i s d e p e n d e n c y i n t o a c c o u n t . T h e b a s i c k i n e t i c r e s p o n s e s p r e d i c t e d h e r e a r e e x p e c t e d t o b e h i g h e r t h a n t h o s e c i t e d i n t h e l i t e r a t u r e , s i n c e s y n t h e t i c s u b s t r a t e a n d c o n t i n u o u s f e e d i n g ( i n s t e a d o f b a t c h f e e d i n g ) w e r e u s e d , a l o n g w i t h a p r o l o n g e d p e r i o d o f a c c l i m a t i z a t i o n a n d e x p e r i m e n t a l r u n n i n g o f a w e l l - a d a p t e d m i x e d c u l t u r e o f b a c t e r i a . B e c a u s e r e a c t o r k i n e t i c s g o v e r n i n g t h e a c i d p h a s e a n d m e t h a n e p h a s e a r e q u i t e d i f f e r e n t , a s a b i - p h a s i c p h e n o m e n o n , a n e s t i m a t i o n o f t h e k i n e t i c s m u s t b e m a d e a c c o r d i n g l y . T h e r a t e - l i m i t i n g s t e p i n t h e A - U A S B r e a c t o r i s t h e h y d r o l y s i s o f p a r t i c u l a t e f e e d t o s o l u b l e s u b s t r a t e s , w h i l e m e t h a n o g e n e s i s i s t h e p r e d o m i n a n t p r o c e s s i n t h e M U A S B . T h e f i r s t - o r d e r h y d r o l y s i s c o n s t a n t ( K h ) a n d p e r c e n t a g e o f p a r t i c u l a t e h y d r o l y s i s o f t h e A - U A S B , t h e y i e l d c o e f f i c i e n t ( a ) , d e c a y c o e f f i c i e n t ( b ) , m a x i m u m s p e c i f i c s u b s t r a t e u t i l i z a t i o n r a t e ( K ) , a n d h a l f - v e l o c i t y c o e f f i c i e n t ( K s ) o f t h e M - U A S B w e r e e s t i m a t e d , i n o r d e r t o p r o v i d e a b r o a d v i e w o f m i c r o b i a l r e s p o n s e u n d e r d i f f e r e n t s t r e s s e s . T h e h y d r o l y s i s r a t e ( R h ) f o l l o w s a n a p p r o x i m a t e f i r s t o r d e r r e a c t i o n , w i t h r e s p e c t 1 0 6 t o t h e c o n c e n t r a t i o n o f d e g r a d a b l e p a r t i c u l a t e C O D ( P a v l o s t a t h i s , 1 9 8 6 ) . R h = K h * F ( 1 7 ) w h e r e R h = h y d r o l y s i s r a t e K h = f i r s t - o r d e r h y d r o l y s i s c o n s t a n t F = p a r t i c u l a t e C O D c o n c e n t r a t i o n A M a s s b a l a n c e a r o u n d A - U A S B a t s t e a d y - s t a t e c o n d i t i o n s y i e l d s : Q ( F o F ) V * K h * F = 0 ( 1 8 ) w h e r e 0 = F l o w r a t e F o = I n f l u e n t p a r t i c u l a t e C O D c o n c e n t r a t i o n V R e a c t o r v o l u m e D i v i d i n g e q u a t i o n ( 2 2 ) b y Q a n d r e a r r a n g i n g y i e l d s : 0 = F o / ( F / 0 ) - 1 / K h ( 1 8 ) w h e r e 0 = H R T = V / Q , F = F o - F , a n d F * K h = B y p l o t t i n g 0 a g a i n s t 0 / S F , t h e i n t e r c e p t o f t h i s l i n e i s e q u a l t o l I K h , a s 1 0 7 i l l u s t r a t e d i n F i g u r e 5 . 2 2 ( c ) ; t h e v a l u e o f K h i s e q u a l t o 1 . 6 7 d a y1 ( r2 = 0 . 8 8 ) d u r i n g t h e m a x i m i z a t i o n p r o c e s s , c o m p a r e d w i t h 3 . 0 d a y1 r e p o r t e d b y E a s t m a n ( 1 9 8 1 ) . R a j a n ( 1 9 8 9 ) a l s o r e p o r t e d t h a t t h e p e r c e n t a g e o f p a r t i c u l a t e h y d r o l y s i s w a s a b o u t 4 5 % , d e f i n e d a s t h e p e r c e n t a g e o f e f f l u e n t s o l u b l e C O D o v e r t o t a l C O D . H o w e v e r , i n t h i s e v a l u a t i o n , 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 t a n d i n f l u e n t s o l u b l e C O D w a s u s e d t o c a l c u l a t e t h e p e r c e n t a g e o f p a r t i c u l a t e h y d r o l y s i s u n d e r d i f f e r e n t l o a d i n g c o n d i t i o n s , a s s h o w n i n F i g u r e 5 . 2 2 ( d ) . T h e r e l a t i o n s h i p b e t w e e n t h e r a t e o f m i c r o b i a l u t i l i z a t i o n o f t h e s u b s t r a t e a n d t h e r a t e o f b a c t e r i a l g r o w t h c a n b e e x p r e s s e d i n t e r m s o f a m a t h e m a t i c a l m o d e l d e v e l o p e d b y L a w r e n c e a n d M c C a r t y ( 1 9 7 0 ) : 6 S / & = a 6 L / 6 t - b S ( 1 9 ) w h e r e 6 S / 6 t = n e t g r o w t h r a t e o f m i c r o o r g a n i s m s , m a s s / v o l - t i m e a = g r o w t h y i e l d c o e f f i c i e n t , m a s s / m a s s 6 L / 6 t = s u b s t r a t e u t i l i z a t i o n r a t e , m a s s / v o l - t i m e b = m i c r o o r g a n i s m s d e c a y c o e f f i c i e n t , t i m e ’ S = m i c r o b i a l m a s s c o n c e n t r a t i o n , m a s s / v o l . D i v i d i n g e q u a t i o n ( 2 4 ) b y S a n d r e a r r a n g i n g y i e l d s : ( 6 L / 6 t ) / S = a ( 6 S / 6 t ) / S - b ( 2 0 ) 3. 5 15 1. 4 1. 3 1. 2 0 .7 0. 5 0. 4 0. 3 0. 2 0.1 8 M ax lm iza llo n r— R ec ov ey Pe rio d K = 1. 37 da y- i / K 0. 50 da y- 1 Ks = 40 0 m gI L / Ks = io, 55 o m gL A I, j • p p I I I I I I I 0 1 2 S 4 5 6 7 S 9 10 ii O b a u .4 EH M ax im iza tio n Re cc N el y Pe rio d 10 — . - . . . . . No te: Al l n in ni ng co n di tio ns a re Ill us tra ted . ln Fl gu ro 5. 22 (c ) C I I 4 5 8 10 a 1.5 0.5 Re co ve ry Pe rio d a = 3. 52 b = - 0. 93 da y- i r = 0. 84 4. . 0 2 0. 4 0. 6 0. 6 1 (61 .16 1)1 3, da y- i 1. 2 1. 4 1. 6 3 2. 5 0. 5 (c) 0 0 = 1 .6 7 da y- i 0 2 0. 4 0. 5 0. 6 1 1. 2 1. 4 1. 6 1. 8 2 0 2 Ol AF Ex pe iim en ta l R un ni ng co n di tio ns Fi gu re 5. 22 An Es tim at io n o f E xp er im en ta l K in et ic s D ur in g m ax im iz at io n an d re co v er y pe rio d (a) a an d b; (b) K an d Ks ; ( C) Kh ; ( d) Pa rti cu la te CO D H yd ro ly sis 1 0 9 B y p l o t t i n g ( c L I 5 t ) / S a g a i n s t ( 6 S / 6 t ) / S , a a n d b c a n b e o b t a i n e d a s t h e s l o p e a n d t h e i n t e r c e p t o f t h e l i n e , r e s p e c t i v e l y , a s s h o w n i n F i g u r e 5 . 2 2 ( a ) . T h e s u b s t r a t e u t i l i z a t i o n r a t e c a n a l s o b e r e l a t e d t o s u b s t r a t e a n d m i c r o o r g a n i s m s c o n c e n t r a t i o n s : 8 L / 6 t = ( k L e S ) / ( K s + L e ) ( 2 1 ) w h e r e k = m a x i m u m r a t e o f s u b s t r a t e u t i l i z a t i o n p e r u n i t w e i g h t o f m i c r o o r g a n i s m s , t i m e ’ K s = h a l f v e l o c i t y c o e f f i c i e n t , m a s s / v o l , e q u a l t o s u b s t r a t e c o n c e n t r a t i o n w h e n 8 L I 5 t = ( 1 / 2 ) k L e = e f f l u e n t s u b s t r a t e m a s s c o n c e n t r a t i o n , m a s s / v o l . L = i n f l u e n t s u b s t r a t e m a s s c o n c e n t r a t i o n , m a s s / v o l . R e a r r a n g i n g e q u a t i o n ( 2 6 ) : ( 6 L / 6 t ) / S = ( k L e ) / ( K s + L e ) B y a p p l y i n g t h e c l a s s i c p l o t ( M o n o d t y p e ) b e t w e e n ( 6 L / 6 t ) / S a g a i n s t L e , t h e k a n d K s v a l u e s c a n b e o b t a i n e d , a s s h o w n i n F i g u r e 5 . 2 2 ( b ) . I n T a b l e 5 . 4 a n d F i g u r e 5 . 2 2 ( a ) , t h e d a t a s h o w o n l y a m o d e r a t e c o r r e l a t i o n w i t h t h e l i n e ( r2 = 0 . 6 6 - 0 . 7 1 ) o b t a i n e d b y r e g r e s s i o n a n a l y s i s , w i t h “ a ” a n d “ b ” v a l u e s p a r t i c u l a r l y s u s p e c t . H o w e v e r , d e s p i t e t h e s e s h o r t c o m i n g s , o n e o f t h e k i n e t i c c o e f f i c i e n t s , i n p a r t i c u l a r , d o e s s h o w s o m e e v i d e n c e o f 110 what may be happening inside the M-UASB during maximization and recovery periods. During maximization, as the loading rate increases step-by-step, the k value is about 1.4 day’, compared with 0.50 day’ during the recovery period. Table5.4 Statistical Constants and Kinetics During the Maximization and Recovery Table 5.4 Statistical Constants and Kinetics L During maximization and recovery period Kinetics Coefficients ‘ A-LJASB MUASB and constants . . . .Maximization Recovery period Maximization Recovery period n 4 5.00 4.00 r 0.95 0.80 0.85 Kh 1.70 6x 0.75 1.70 a (1.80) 3.50 b 2.65 (0.95) K 1.40 0.50 Ks 400 10,550 %Par.COD Hydrolysi 14-29 3-26 Note: n = number of data point this tendency seems to reverse itself during the recovery period, as the loading rate is decreased step-by-step, (as shown in Figure 5.22 (b)). This result is in agreement with those reported by Chen (1978) where k was practically constant at low influent loadings ‘but it increased rapidly at high loading rates. Unfortunately, none of the other coefficients lend themselves to detinitive conclusions at this time and a more detailed “kinetic study” would be needed to advance any hypotheses further. Such an in-depth analysis could not be justified in this study. 1 1 1 5 . 2 . 2 . 4 O p t i m u m I o a d m g C a p a c i t y S i n c e t h i s p r o c e s s i s a t w o - p h a s e U A S B - U A S B s y s t e m , o p t i m u m l o a d i n g c a p a c i t y s h o u l d b e c o n s i d e r e d s e p a r a t e l y a s A - U A S B a n d M - U A S B . H o w e v e r , i f t h e s y s t e m i s c o n s i d e r e d a s a w h o l e , t h e o p t i m u m l o a d i n g c a p a c i t y o f t h e M - U A S B i s r e a l l y t h e s y s t e m l o a d i n g c a p a c i t y , b e c a u s e t h e m a x i m u m s p a c e l o a d i n g c a p a c i t y o f M - U A S B i s t h e r a t e - l i m i t i n g s t e p o f t h e w h o l e s y s t e m . H o w e v e r , t h e o p t i m u m l o a d i n g c a p a c i t y o f t h e M U A S B i s n o t n e c e s s a r i l y t h e o p t i m u m o n e f o r t h e A - U A S B . I n f a c t , t h e l a t t e r c a n h a n d l e a h i g h e r l o a d i n g r a t e b e c a u s e t h e g r o w t h r a t e o f a c i d o g e n s i s p r e d o m i n a n t a n d s i g n i f i c a n t l y g r e a t e r t h a n m e t h a n o g e n s . T o o p t i m i z e t h e s y s t e m l o a d i n g c a p a c i t y w i t h r e s p e c t t o p o l l u t i o n c o n t r o l a n d C H4 g a s p r o d u c t i o n , t h e f o l l o w i n g t w o p a r t i c u l a r c a s e s a r e p r e s e n t e d : ( a ) C a s e 1 : O v e r a l l S y s t e m L o a d i n g C a p a c i t y S y s t e m l o a d i n g c a p a c i t y i s d e p e n d e n t l a r g e l y o n s y s t e m c o n f i g u r a t i o n a n d o p e r a t i o n a l c o n d i t i o n s . D i f f e r e n c e s i n t h e c o n f i g u r a t i o n a n d o p e r a t i n g c o n d i t i o n s c a n a f f e c t t h e o p t i m u m s y s t e m l o a d i n g c a p a c i t y . F i g u r e 5 . 2 3 s h o w s t h e o p t i m u m o p e r a t i n g c o n d i t i o n a t 2 a n d 2 . 7 d a y s H R T s f o r t h e M - U A S B , r e s u l t i n g f r o m t w o p r e d i c t i v e m o d e l s o f C O D r e m o v a l e f f i c i e n c y a n d C H4 g a s p r o d u c t i o n d u r i n g t h e s y s t e m m a x i m i z a t i o n a n d r e c o v e r y p e r i o d s , r e s p e c t i v e l y . T h e s e m o d e l s a r e f o r m u l a t e d b a s e d o n t h e C O D ( s o l . ) r e m o v a l e f f i c i e n c y a n d C H4 g a s p r o d u c t i o n r e l a t i v e t o t h e H R T o f M - U A S B a s : >0 E a ) I U 0 0 C u > 0 E G ) 0 0 H R T , d a y s - 3 . 5 1 ? E C . ) E - 2 . 5 I 0 2 . 5 2 E D C . ) S C . ) 1 . 5 I 0 I // 1 1 2 - 4 . 5 - 4 — 3 ( a ) A % C O D ( F . ) r e m o v a l C H 4 , c u . i / c u . m - d A V ( 2 ) A ( 1 ) V = 8 8 . 1 3 + 7 . 2 7 I n X ( r2= 0 . 7 4 > ( 2 ) V = 5 . 2 9 - 2 . 5 9 I n X ( r 0 . 9 0 ) 1 2 0 1 0 0 8 0 6 0 4 0 2 0 0 1 0 0 8 0 6 0 4 0 2 0 0 0 1 2 3 4 5 — 2 — 1 . 5 3 % C O D ( F H . ) r e m o v a l C H 4 , C u / / , / / 9 / Z ( ) Q — . . . . . - - - . . - D \ I / f 4 ( 3 ) V = 1 . 2 7 8 + 1 9 . 9 1 X ( r2= 0 . 9 9 ) ‘ ‘ - 0 . 3 0 4 ( 4 ) Y = 2 . 4 4 X ( r = 0 . 9 3 ) / 0 1 2 3 4 5 1 F i g u r e 5 . 2 3 A P r e d i c t e d O p t i m a l O p e r a t i n g H R T ( a ) M a x i m i z a t i o n P r o c e s s ; ( b ) R e c o v e r y P e r i o d 1 1 3 D u r i n g t h e m a x i m i z a t i o n p r o c e s s : Y 2 = 8 8 . 1 3 + 7 . 2 7 i n X 2 ( 2 3 ) w h e r e Y 2 = % s o l u b l e C O D r e m o v a l e f f i c i e n c y X 2 H R T ( M - U A S B ) , d a y s 0 . 7 4 F o r C H4 g a s p r o d u c t i o n , t h e p r e d i c t i v e m o d e l i s a s f o l l o w s : Y 3 = 5 . 2 9 - 2 . 5 9 I n X 3 ( 2 4 ) w h e r e Y 3 = C H4 g a s p r o d u c t i o n , L i d X 3 H R T ( M - U A S B ) , d a y s r2 = 0 . 9 0 D u r i n g t h e r e c o v e r y p e r i o d : Y 4 = 2 . 4 4 X 4 °3 0 4 ( 2 5 ) w h e r e Y 4 = % s o l u b l e C O D r e m o v a l e f f i c i e n c y X 4 = H R T ( M - U A S B ) , d a y s r2 = 0 . 9 3 F o r C H4 g a s p r o d u c t i o n , t h e p r e d i c t i v e m o d e l i s a s f o l l o w s : Y 5 = 1 . 2 7 8 + 1 9 . 9 1 X 5 ( 2 6 ) 1 1 4 w h e r e Y 5 = C H4 g a s p r o d u c t i o n , L i d X 5 = H R T ( M - U A S B ) , d a y s r2 = 0 . 9 9 A s s h o w n i n F i g u r e 5 . 2 3 , t h e o v e r a l l o p t i m u m s y s t e m o p e r a t i n g c o n d i t i o n i s p r e d i c t e d a t a n H R T o f 2 . 0 d a y s , w i t h 9 0 % C O D ( s o l . ) r e m o v a l e f f i c i e n c y a n d 3 . 6 m3/m-d o f C H4 g a s p r o d u c t i o n . T h i s o p t i m u m H R T c o r r e s p o n d s t o t h e o p t i m u m p o i n t o b t a i n e d f r o m t h e C O2 a n d V F A j a l k a l i n i t y r a t i o d a t a a t H R T s f r o m 1 . 5 - 2 . 2 5 d a y s , a s s h o w n i n F i g u r e 5 . 1 3 a n d 5 . 1 4 . F i g u r e 5 . 1 5 i n d i c a t e s a n o p t i m u m f l o w r a t e o f 1 6 . 1 0 L i d , e q u i v a l e n t t o a n H R T o f 1 . 5 5 d a y s w i t h 9 5 % C O D r e m o v a l e f f i c i e n c y a n d a p p r o x i m a t e l y 7 5 - 8 0 % o f t h e t h e o r e t i c a l C H4 g a s p r o d u c t i o n . T h e o p t i m u m R R ’ s a r e t h e n c a l c u l a t e d a s 1 . 6 a n d 2 . 5 . G h o s h ( 1 9 8 4 ) s u g g e s t e d t h a t H R T s o f 0 . 9 - 1 . 5 a n d 4 . 0 - 5 . 0 d a y s a r e o p t i m u m f o r A - a n d M - U A S B s r e a c t o r s r e s p e c t i v e l y , a n d C h a n g e t a l . ( 1 9 8 9 ) r e p o r t e d t h a t a n H R T o f 2 d a y s w a s t h e o p t i m u m f o r t h e A - U A S B . A p p r o x i m a t e l y 7 7 % o f t h e t h e o r e t i c a l C H4 g a s p r o d u c t i o n ( 0 . 4 8 m3/ k g V S a d d e d a t s t a n d a r d t e m p e r a t u r e a n d p r e s s u r e ) w a s a c h i e v e d t h r o u g h t h e u s e o f a t w o - p h a s e U A S B - U A S B p r o c e s s a t H R T s o f 5 . 5 a n d 5 . 9 d a y s r e s p e c t i v e l y ( G h o s h , 1 9 8 4 ) . I n p r i n c i p l e , t h e m i n i m u m S R T f o r m e t h a n o g e n s i s i n t h e r a n g e o f 2 . 5 - 4 . 0 d a y s ( E a s t m a n , 1 9 8 1 ; A n d r e w s , 1 9 6 5 ; T o r p e y , 1 9 5 5 ; B e r g m a n , 1 9 6 6 ; a n d A n d e r s o n , 1 9 7 8 ) . U S . E P A ( 1 9 7 9 ) , r e c o m m e n d s t h a t t h e o p t i m u m S R T i s e q u a l t o t h e m i n i m u m S R T p l u s a s a f e t y f a c t o r o f 2 . 5 . A p p l y i n g t h e E P A r e c o m m e n d a t i o n t o t h i s p a r t i c u l a r c a s e , a s s u m i n g t h a t t h e m i n i m u m S R T ( z e r o r e m o v a l e f f i c i e n c y ) i s e q u i v a l e n t t o t h e m a x i m u m H R T , t h e o p t i m u m H R T i s t h e n e q u a l t o 1 1 5 a p p r o x i m a t e l y 1 . 6 d a y s , c o r r e s p o n d i n g t o a m a x i m u m f a i l u r e f l o w r a t e o f 4 0 . 2 2 L I d , c o n s i d e r a b l y h i g h e r t h a n f o u n d i n t h i s s t u d y . ( A s u m m a r y o f a v e r a g e r e s p o n s e s a n d p e r f o r m a n c e a t e a c h p s e u d o s t e a d y - s t a t e , u n d e r d i f f e r e n t r u n n i n g c o n d i t i o n s , i s s h o w n i n T a b l e D 1 . 1 o f A p p e n d i x D ) . C o n s i d e r i n g t h e o p t i m u m H R T o b t a i n e d f r o m t h i s e x p e r i m e n t a l r e s e a r c h ( 1 . 5 - 2 . 2 5 d a y s a s m e n t i o n e d e a r l i e r ) , t h e o p t i m u m H R T s c i t e d i n s e v e r a l p u b l i c a t i o n s , a s w e l l a s t h e o n e c a l c u l a t e d b a s e d o n t h e U S . E P A r e c o m m e n d a t i o n , i t i s r e a s o n a b l e a n d s a f e t o s u g g e s t t h a t t h e o p t i m u m o p e r a t i n g H R T ’ s f o r t h e M - U A S B a n d t h e o v e r a l l s y s t e m , a r e 2 . 0 a n d 4 . 0 d a y s r e s p e c t i v e l y . T h i s 2 - d a y H R T i s a s l i g h t l y l o w e r t h a n t h e m i n i m u m r a n g e o f 2 . 5 - 4 . 0 d a y S R T r e c o m m e n d e d f o r m e t h a n o g e n s m e n t i o n e d a b o v e ; h o w e v e r , i n t h i s c a s e , i t i s r e a s o n a b l e s i n c e t h e d e s i g n e d s y s t e m i s a t w o - p h a s e o n e , p r o v i d i n g t h e o p t i m u m e n v i r o n m e n t t o s t i m u l a t e t h e g r o w t h o f m e t h a n o g e n s . I t i s a l s o e q u i p p e d w i t h a r e c y c l e f a c i l i t y t o i n c r e a s e t h e c o n t a c t b e t w e e n m i c r o o r g a n i s m s a n d s u b s t r a t e a s w e l l a s t o i n c r e a s e t h e s y s t e m b u f f e r r i n g c a p a c i t y . M o r e o v e r , i t i s i n t e r e s t i n g t o n o t e t h a t t h i s o p t i m u m H R T o f 2 d a y s , p r e d i c t e d f r o m t h e e x p e r i m e n t a l r e s u l t s d u r i n g t h e m a x i m i z a t i o n p r o c e s s , i s s h o r t e r t h a n t h a t o f 2 . 7 d a y s H R T o b t a i n e d a t t h e r e c o v e r y p e r i o d , a s s h o w n i n F i g u r e 5 . 2 3 . T h i s m a y b e t h e r e s u l t o f a s h i f t i n t h e m i c r o b i a l s t r u c t u r e ( a c h a n g e i n p r e d o m i n a n t b a c t e r i a l c o m m u n i t i e s a n d t h e i r m i c r o e n v i r o n m e n t , a n d a d i f f e r e n c e i n b i o c h e m i c a l p a t h w a y s ) o f t h e a c e t o g e n i c a n d m e t h a n o g e n i c b a c t e r i a l c o m m u n i t y i n s i d e t h e M - U A S B . 1 1 6 ( b ) C a s e 2 : O p t i m u m L o a d i n g C a p a c i t y o f A - a n d M - U A S B s T h e o p t i m u m 2 - d a y H R T o f t h e M - U A S B , r e c o m m e n d e d e a r l i e r i n c a s e ( a ) , e q u i v a l e n t t o a f l o w r a t e o f a b o u t 1 6 L I d , i s n o t n e c e s s a r i l y t h e o p t i m u m o n e f o r t h e A U A S B , s i n c e t h e g r o w t h r a t e o f a c i d o g e n s i s p r e d o m i n a n t i n t h e A - U A S B . F r o m F i g u r e 5 . 2 4 a n d T a b l e D 1 . 1 o f A p p e n d i x D , i t c a n b e c o n c l u d e d t h a t r u n n i n g c o n d i t i o n n o . 4 , a t a n A - U A S B H R T o f 1 . 0 ( 0 . 9 7 ) d a y s a n d e q u i v a l e n t t o a f l o w r a t e o f 2 0 L I d , i s t h e o p t i m u m l o a d i n g c a p a c i t y . T h i s i s i n a g r e e m e n t w i t h t h e o p t i m u m r a n g e o f 0 . 9 - 1 . 5 d a y H R T f o r a c i d o g e n i c r e a c t o r s r e p o r t e d b y G h o s h ( 1 9 8 4 ) . A t t h i s o p t i m u m r u n n i n g c o n d i t i o n d u r i n g t h e m a x i m i z a t i o n p e r i o d , t h e A - U A S B g e n e r a t e d t h e h i g h e s t V F A / a l k a l i n i t y r a t i o o f 7 . 5 a t d a y 4 0 , w i t h e f f l u e n t C O D ( s o l . ) o f 1 1 , 0 5 5 m g / L a n d t o t a l V F A p r o d u c t i o n o f 5 , 3 0 0 m g / L a s H A c . T h e M L V S S c o n c e n t r a t i o n o f t h e A - U A S B a l s o i n c r e a s e d s i g n i f i c a n t l y u p t o 4 2 , 1 5 0 m g / L , b u t t h e r e w a s o n l y a s m a l l c h a n g e i n t h e e f f l u e n t T K N a n d T P c o n c e n t r a t i o n s , a s s h o w n i n F i g u r e D 1 . 1 a n d D 2 . 1 o f A p p e n d i x D . I t i s i n t e r e s t i n g t o n o t e t h a t t h e t o t a l V F A a n d t h e V F A l a l k a l i n i t y r a t i o o f t h e A - U A S B i n c r e a s e d s i g n i f i c a n t l y d u r i n g t h e r e c o v e r y p e r i o d , a s s h o w n i n F i g u r e 5 . 2 4 ( b ) . T h i s m a y b e t h e r e s u l t o f t h e a b i l i t y o f t h e A - U A S B t o t o l e r a t e s h o c k - l o a d s , a n d t o s t i m u l a t e t h e r e a c t o r ’ s a c t i v i t y ( L e t t i n g a , 1 9 7 9 a ) . T h e o p t i m u m H R T r a t i o s b e t w e e n A - a n d M - U A S B s , a n d a l s o b e t w e e n A - U A S B a n d t h e o v e r a l l s y s t e m , a r e a b o u t 0 . 6 0 a n d 0 . 4 0 , r e s p e c t i v e l y ( D e t a i l s i n T a b l e D 1 . 1 o f A p p e n d i x D ) . D i n o p o u l o u ( 1 9 8 9 ) r e p o r t e d t h a t t h e o p t i m u m v o l u m e o f t h e a c i d o g e n i c r e a c t o r w a s i n t h e r a n g e o f 1 2 - 2 5 % o f t h e o v e r a l l a c t i v e 1 1 7 2 0 — i 2 0 0 1 8 0 - + C H 4 , l / d ‘ % C 0 2 : ; C O D o 1 2 0 - T i m e , d a y s 1 4 - ’ 0 1 3 - i 1 0 0 - : T I m e , d a y s 6 - H A c H P r l i m e , d a y s / \ - 6 P : : I i f t [ 1 J I i t t f l Z T i m e , d a y s F i g u r e 5 . 2 4 A n A - U A S B S y s t e m E f f l u e n t Q u a l i t i e s : D u r i n g t h e p r o c e s s m a x i m i z a t i o n ( a ) C H 4 p r o d u c t i o n , % C 0 2 , E f f . C O D ; ( b ) T o t a l V F A , H A c / H P r , V F A ’ A l k a l i n i t y 1 1 8 v o l u m e i n a s t u d y , u s i n g a t w o - p h a s e a n a e r o b i c d i g e s t i o n s y s t e m w i t h C S T R a c i d o g e n i c r e a c t o r a n d a m e t h a n o g e n i c f l u i d i z e d b e d r e a c t o r t o s t a b i l i z e a s y n t h e t i c w a s t e w a t e r . T h e d i f f e r e n c e i n t h e H R T s r a t i o s i n t h i s c a s e m a y r e s u l t f r o m a l o n g e r h y d r o l y s i s r a t e o f t h e p a r t i c u l a t e s y n t h e t i c s l u d g e t a k i n g p l a c e i n t h e U A S B - U A S B p r o c e s s , c o m p a r e d w i t h t h e s h o r t e r h y d r o l y s i s r a t e f o r t h e s y n t h e t i c w a s t e w a t e r . 5 . 2 . 2 . 5 C o n c l u s i o n s F r o m b o t h s y s t e m p e r f o r m a n c e a n d k i n e t i c c o n s i d e r a t i o n s , i t a p p e a r s t h a t t h e U A S B - U A S B s y s t e m c a n r e c o v e r t o i t s o r i g i n a l p e r f o r m a n c e b y a p p l y i n g a s t e p - d o w n l o a d i n g a p p r o a c h . A l t h o u g h t h e p e r f o r m a n c e , i n t e r m s o f % C O D r e m o v a l e f f i c i e n c y a n d % C H c o n t e n t , r e c o v e r e d t o t h e o r i g i n a l v a l u e s , t h e t o t a l C H4 g a s p r o d u c t i o n w a s r e d u c e d a n d t h e o p t i m u m o p e r a t i n g p o i n t b e t w e e n C O D r e m o v a l e f f i c i e n c y a n d g a s p r o d u c t i o n w a s m o v e d a l i t t l e f u r t h e r . T h i s m e a n s t h a t t h e r e w a s a t o t a l s h i f t o f t h e s p e c i e s r a t i o a m o n g t h e m i x e d c u l t u r e o f a c e t o g e n s a n d m e t h a n o g e n s i n s i d e t h e M U A S B a f t e r t h e r e c o v e r y p r o c e s s . B a s e d o n t h e r e s u l t s o f t h e s e s t u d i e s , t h e f o l l o w i n g c o n c l u s i o n s c a n b e d r a w n : ( 1 ) A c o m b i n a t i o n o f h y d r a u l i c a n d o r g a n i c o v e r l o a d i n g o f t h e M - U A S B r e a c t o r w a s a m a j o r c a u s e o f p r o c e s s f a i l u r e ; t h i s c a n r e s u l t i n M L V S S w a s h o u t , i n c r e a s e i n t o t a l V F A c o n c e n t r a t i o n , r e d u c t i o n o f t h e s y s t e m r e m o v a l e f f i c i e n c y , a n d c e s s a t i o n o f C H4 g a s p r o d u c t i o n . 1 1 9 ( 2 ) A d r o p i n p H a n d a n i n c r e a s e i n t o t a l V F A / a l k a l i n i t y r a t i o , a r e d u c t i o n o f C H4 g a s p r o d u c t i o n , a n d a n i n c r e a s e i n t h e e f f l u e n t t o t a l V F A , w e r e a l s o i n d i c a t o r s o f t h e p r o c e s s f a i l u r e . ( 3 ) T h e m a x i m u m h y d r a u l i c l o a d i n g r a t e s w e r e 1 . 6 a n d 0 . 9 0m31 m- d , e q u i v a l e n t t o H R T s o f l e s s t h a n 1 . 1 2 5 a n d 0 . 6 2 5 d a y s , f o r t h e M - U A S B a n d t h e w h o l e s y s t e m , r e s p e c t i v e l y . T h e C H4 g a s p r o d u c t i o n w a s r e d u c e d t o l e s s t h a n 5 0 % o f t h e t h e o r e t i c a l v a l u e , w i t h e f f l u e n t C O D a n d t o t a l V F A o f 9 , 5 4 0 m g / L a n d 3 , 7 5 0 m g f L a s H A c , r e s p e c t i v e l y . ( 4 ) T h e M - U A S B r e c o v e r e d e x p o n e n t i a l l y w i t h a n i n c r e a s e i n H R T ( l o a d i n g r e d u c t i o n ) i n t e r m o f C O D r e m o v a l e f f i c i e n c y , b u t l o g a r i t h m i c a l l y w i t h r e s p e c t t o C H4 g a s p r o d u c t i o n , a s f o l l o w s : Y = 2 5 . 3 7 e o .2 9x Y l = 9 . 2 5 + 6 4 . 0 1 I n X l w h e r e Y = % s o l u b l e C O D r e m o v a l e f f i c i e n c y X = H R T ( M - U A S B ) , d a y s Y l = C H4 g a s p r o d u c t i o n , L i d X l = H R T ( M - U A S B ) , d a y s T h e s y s t e m d i d r e c o v e r b a c k t o i t s i n i t i a l s t a g e o f o p e r a t i o n b y a p p l y i n g a t w o - s t e p i n c r e a s e o f t h e H R T M . U A S B a t 1 . 5 a n d 5 . 8 t i m e s t h e f a i l u r e H R T , w i t h a d i m e n s i o n a l t i m e o f 5 . 6 0 a n d 1 0 f o r t h e M - U A S B a n d t h e o v e r a l l s y s t e m , r e s p e c t i v e l y . 1 2 0 ( 5 ) T h e s h o c k l o a d s a p p e a r e d t o s t i m u l a t e t h e A - U A S B ’ s a c t i v i t y d u r i n g s y s t e m r e c o v e r y , b u t i t a p p e a r e d t o h a v e n o e f f e c t a t a l l o n t h e M - U A S B , w h e n t h e s y s t e m f a i l e d c o m p l e t e l y . T h e r e c o v e r y a p p r o a c h , e m p l o y i n g t h e s t e p - l o a d i n g r e d u c t i o n a n d t h e i n t e r n a l R R , s e e m e d t o h a v e n o s i g n i f i c a n t b e n e f i c i a l e f f e c t , c o m p a r e d w i t h t h e r e a c c l i m a t i z a t i o n i n t e r m o f t i m e r e q u i r e m e n t ( b o t h n e e d e d 4 - 5 w e e k s t o c o m p l e t e t h e p r o c e s s e s ) . H o w e v e r , i t d i d p r o v i d e s o m e a d v a n t a g e s i n t e r m s o f e a s e o f o p e r a t i o n a n d a m o r e p r a c t i c a l a p p r o a c h f o r a p o t e n t i a l f u l l - s c a l e o p e r a t i o n . ( 6 ) T h e h y d r o l y s i s r a t e g o v e r n i n g t h e A - U A S B w a s a b o u t 1 . 7 0 d a y s . T h e s p e c i f i c v e l o c i t y k d u r i n g t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d s , w a s 1 . 4 0 a n d 0 . 5 0 d a y1, r e s p e c t i v e l y . T h e c o r r e s p o n d i n g s u b s t r a t e s a t u r a t i o n c o e f f i c i e n t ( h a l f v e l o c i t y c o n s t a n t , K s ) w a s f o u n d t o b e 4 0 0 a n d 1 0 , 5 5 0 m g / L d u r i n g t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d , r e s p e c t i v e l y . ( 7 ) T h e o p t i m u m H R T f o r t h e A - U A S B w a s 1 . 0 ( 0 . 9 7 ) d a y s , w h e r e a s , t h o s e f o r t h e M - U A S B , w i t h r e s p e c t t o C O D r e m o v a l e f f i c i e n c y a n d C H4 g a s p r o d u c t i o n , d u r i n g t h e m a x i m i z a t i o n a n d r e c o v e r y p e r i o d , w e r e 2 . 0 a n d 2 . 7 d a y s , r e s p e c t i v e l y . T h i s s e e m s t o i m p l y t h e r e w a s a r e s t r u c t u r i n g o f t h e b a c t e r i a l c o m m u n i t y i n s i d e t h e M - U A S B , d u r i n g t h e r e c o v e r y p e r i o d . F o r d e s i g n p u r p o s e s , t h e o p t i m u m o p e r a t i n g H R T ’ s o f 1 a n d 2 d a y s , a s w e l l a s t h e R R o f 1 . 6 a n d 2 . 5 t i m e s t h e i n f l u e n t f l o w r a t e , a r e r e c o m m e n d e d f o r A a n d M - U A S B s , r e s p e c t i v e l y , w i t h a c o n s e r v a t i v e o r g a n i c l o a d i n g r a t e o f 1 9 k g C O D ( t o t a l ) / m3-d ( e q u i v a l e n t t o 0 . 5 5m3/ m- d ) . 1 2 1 ( 8 ) T h e o p t i m u m H R T A U H R T M U B r a t i o w a s a b o u t 0 . 6 0 a n d t h e H R T A . u p s i / H R T s y s t e m w a s 0 . 4 0 , a s a p p l i e d t o t h e t w o - p h a s e a n a e r o b i c d i g e s t i o n o f s e w a g e s l u d g e ( U A S B - U A S B ) . 1 2 2 5 . 2 . 3 D e v e l o p m e n t o f S y s t e m D e s i g n C r i t e r i a T h e m a i n r e s e a r c h g o a l w a s t o e v a l u a t e t h e f e a s i b i l i t y o f t h e t w o - p h a s e a n a e r o b i c d i g e s t i o n ( U A S B - U A S B ) c o n c e p t , t o s t a b i l i z e a p a r t i c u l a t e s u b s t r a t e . T h e f o l l o w i n g s e c t i o n s , d e a l w i t h t h e s y s t e m e f f e c t i v e n e s s ( o r p e r f o r m a n c e ) , s y s t e m s u i t a b i l i t y ( o r l o a d i n g c a p a c i t y ) , a n d s y s t e m f e a s i b i l i t y , f o l l o w e d b y a m o d i f i c a t i o n o f d e s i g n c r i t e r i a a n d o p e r a t i o n p r o c e d u r e s . F i n a l l y , m a j o r s y s t e m c o n t r o l p a r a m e t e r s a r e e v a l u a t e d a n d d i s c u s s e d . 5 . 2 . 3 . 1 O p t i m u m S y s t e m P e r f o r m a n c e a n d F e a s i b i l i t y T h e o p t i m u m s y s t e m H R T o f 2 . 8 0 ( 1 . 2 4 + 1 . 5 5 ) d a y s e q u a t e s t o a h y d r a u l i c l o a d i n g r a t e o f 0 . 4 0 m3/ m- d . T h e o v e r a l l s o l u b l e a n d t o t a l C O D r e m o v a l e f f i c i e n c i e s w e r e 9 0 . 7 6 a n d 9 8 % , r e s p e c t i v e l y , w i t h 6 9 % C H4 c o n t e n t a n d 1 7 9 L I d o f C H4 g a s p r o d u c t i o n ( / e q u i v a l e n t t o 7 3 % o f t h e t h e o r e t i c a l v a l u e ) . A v e r a g e p s e u d o s t e a d y - s t a t e s y s t e m p e r f o r m a n c e a n d e f f l u e n t q u a l i t y , a t t h e o p t i m u m r u n n i n g c o n d i t i o n , a r e s u m m a r i z e d i n T a b l e 5 . 5 . I t i s i n t e r e s t i n g t o p o i n t o u t t h a t t h e r e w a s a c t u a l l y s o m e P 04- P ( a n d / o r T P ) r e m o v a l , b u t r a r e l y N H4- N ( a n d / o r T K N ) r e m o v a l a s s h o w n i n F i g u r e 5 . 1 4 . T h i s m a y b e d u e t o c h e m i c a l r e a c t i o n s f o r m i n g p r e c i p i t a t i n g s a l t s o f C a a n d / o r M g p h o s p h a t e . H o w e v e r , t h e r e w a s a s m a l l c h a n g e i n N H4- N ( a n d / o r T K N ) . c o n c e n t r a t i o n , s i n c e N H4- N c a n b e u s e d a s a r e l e a s e - a n d - a p p r e h e n d i o n t o m a i n t a i n t h e b a l a n c e o f b u f f e r c a p a c i t y 1 2 3 T a b l e 5 5 S u m m a r y o f A v e r a g e R e s p o n s e s a t t h e O p t i m a l S y s t e m O p e r a t i n g . s e d o S A v e r a g e R e s p o n s e s E x p e r i m e n t a l R u n n i n g C o n d i t i o n P r o c e s s e s 2 — p h a s e ( U A S B — U A S B ) R u n n i n g P e r i o d , d a y s 3 6 S l u d g e F e e d R a t i o ( S R ) 8 0 / 2 0 R e c y c l e R a t i o ( R R ) 2 / 3 I n f l u e n t F l o w , l / d 1 6 . 1 0 H R T , d a y s A - U A S B 1 . 2 5 M - U A S B 1 . 5 5 S y s t e m 2 . 8 0 L o a d i n g R a t e c u . m / c u . m — d 0 . 3 5 K g C O D ( s o l . ) / c u . m — d 2 . 1 5 E f f l u e n t Q u a l i t y S o l i d s , m g I L T S 2 8 5 0 V S 1 2 3 0 T S S 1 8 5 T V S S 1 1 0 C O D , m g I L T o t a l C O D 6 8 0 C O D ( s o l . ) 5 5 0 I n o r g a n i c s , m g / L N H 4 - N 3 0 0 T K N 4 0 0 T P 8 5 P 0 4 - P 1 5 V F A , m g / L H A c 4 0 H P r 6 5 l s o — H B r 0 H B r 5 A - H V r 0 l s o — H V r 0 H V r 0 H H e 0 T o t a l V F A m g / L a s H A c 9 5 1 2 4 T a b l e 5 5 S u m m a r y o f A v e r a g e R e s p o n s e s a t t h e O p t i m a l S y s t e m O p e r a t i n g L J n d e r . I ? S e U d o S I e á d y S t à t e Q n A v e r a g e R e s p o n s e s E x p e r i m e n t a l R u n n i n g C o n d i t i o n P r o c e s s e s 2 — p h a s e ( U A S B — U A S B ) A l k a l i n i t y , m g / L a s C a C O 3 A - U A S B 9 6 0 M - U A S B 2 5 2 0 T o t a l V F A / A l k A - U A S B 4 . 9 0 M - U A S B 0 . 0 5 S y s t e m R e m o v a l E f f i c i e n c y S o l i d s , % T S S 9 9 . 0 0 C O D , % C O D ( s o l . ) 9 1 . 0 0 T o t a l C O D 9 8 . 0 0 I n o r g a n i c s , % P 0 4 — P 8 8 . 0 0 T P 3 9 . 0 0 M e t h a n e G a s F l o w , l / d T o t a l G a s 3 1 0 . 0 0 C H 4 G a s 1 8 0 . 0 0 C H 4 P r o d u c t i v i t y l I d 1 8 0 . 0 0 c u . m l c u . m — d 4 . 0 0 c u . m l c u . m — d @ S C 3 . 5 0 c u . m / k g C O D ( T o t a l ) a d d e d @ S C 0 . 2 5 % o f t h e o r e t i c a l C H 4 P r o d u c t i o n 7 3 . 0 0 % C H 4 c o n t e n t 6 9 . 0 0 1 2 5 o f t h e M - U A S B , a s w e l l a s a b a s i c g r o w t h n u t r i e n t . I t i s d i f f i c u l t t o c o m p a r e t h e p e r f o r m a n c e o f d i f f e r e n t p r o c e s s e s , s i n c e e a c h p r o c e s s h a s i t s o w n u n i q u e c h a r a c t e r i s t i c s , c o n f i g u r a t i o n , a n d o p e r a t i n g c o n d i t i o n s . H o w e v e r , t h e o p t i m u m s y s t e m p e r f o r m a n c e a n d e f f l u e n t q u a l i t y c a n b e u s e d a s g u i d e l i n e s t o e v a l u a t e b o t h e f f e c t i v e n e s s a n d s u i t a b i l i t y , p o s s i b l y l e a d i n g t o a n e v a l u a t i o n o f s y s t e m f e a s i b i l i t y . A s s h o w n i n T a b l e 5 . 5 , i t i s c l e a r t h a t t h e t w o - p h a s e U A S B - U A S B c o n c e p t , a t a n e x t r e m e l y l o w o p e r a t i n g H R T ( 2 . 8 d a y s ) , p e r f o r m s r e a s o n a b l y w e l l w i t h C H4 g a s p r o d u c t i o n o f a b o u t 7 3 % t h e o r e t i c a l C H4 v a l u e , e f f l u e n t C O D o f 5 5 0 m g / L , a n d v o l a t i l e a c i d s o f 9 5 m g / L . T h e i n t e r n a l R R a p p e a r s t o p l a y a m a j o r r o l e i n c o n t r o l l i n g a n d m a i n t a i n i n g t h e s y s t e m p e r f o r m a n c e b y i n c r e a s i n g t h e c o n t a c t b e t w e e n m i c r o o r g a n i s m s a n d s u b s t r a t e s , r e d u c i n g t h e e f f e c t o f s h o c k l o a d i n g , a n d i n c r e a s i n g t h e s y s t e m b u f f e r i n g c a p a c i t y . C o m b i n i n g i n f l u e n t l o a d i n g r a t e c o n t r o l a n d a p p r o p r i a t e R R s , i t i s t h u s p o s s i b l e t o m a i n t a i n a g o o d s y s t e m p e r f o r m a n c e o r t o a s s i s t i n r e c o v e r i n g t h e s y s t e m , i n c a s e o f a n i n t e r r u p t i o n a n d / o r f a i l u r e . 5 . 2 . 3 . 2 M o d i f i c a t i o n o f D e s i g n C r i t e r i a a n d O p e r a t i o n D e v e l o p m e n t o f a n a e r o b i c d i g e s t i o n s y s t e m d e s i g n h a s r e c e n t l y m o v e d t o w a r d s “ h i g h r a t e ” d i g e s t i o n s y s t e m s . E a c h s y s t e m h a s i t s o w n m e r i t s , l i m i t a t i o n s , a n d p o t e n t i a l , a n d d e p e n d s l a r g e l y o n t h e l o c a l s i t u a t i o n , c h a r a c t e r i s t i c s o f t h e w a s t e s t o b e t r e a t e d , a n d 1 2 6 t h e p e r f o r m a n c e a n d s p e c i f i c e x p e r i e n c e o f e a c h s y s t e m d e s i g n e r i n e a c h t y p e o f s y s t e m c o n f i g u r a t i o n . A l t h o u g h t h e t w o - p h a s e a n a e r o b i c d i g e s t i o n c o n c e p t w o r k s e x c e p t i o n a l l y w e l l , c o m p a r e d w i t h a s i n g l e s t a g e o n e , t h e r e i s s t i l l n o u n i v e r s a l , t w o - p h a s e d i g e s t i o n c o n f i g u r a t i o n t h a t i s o p t i m u m f o r a l l s i t u a t i o n s . T h e c h o i c e o f t h e f e r m e n t e r t y p e d e p e n d s l a r g e l y o n t h e p h y s i c a l , c h e m i c a l a n d b i o l o g i c a l c h a r a c t e r i s t i c s o f t h e f e e d a n d t h e o b j e c t i v e o f t r e a t m e n t , i e . , w h e t h e r i t i s p o l l u t i o n c o n t r o l o r m a x i m i z a t i o n o f C H4 g a s p r o d u c t i o n . T h e d e s i g n o f t h e t w o - p h a s e U A S B - U A S B p r o c e s s m u s t e n s u r e a u n i f o r m d i s t r i b u t i o n o f i n f l u e n t f e e d a t t h e l o w e r p a r t o f t h e r e a c t o r , a s u f f i c i e n t c r o s s - s e c t i o n t o p r e v e n t b i o m a s s e n t r a i n m e n t , a n d a n e f f e c t i v e s e p a r a t i o n o f g a s , b i o m a s s , a n d l i q u i d . T h e k e y s t o t h e s u c c e s s f u l a n a e r o b i c s t a b i l i z a t i o n p r o c e s s e s a r e t o i n c r e a s e t h e c o n t a c t b e t w e e n m i c r o o r g a n i s m s a n d s u b s t r a t e s a s w e l l a s t o i n c r e a s e t h e s y s t e m b u f f e r r i n g c a p a c i t y . S l u d g e r e c y c l i n g a l s o p l a y s a m a j o r r o l e i n t h e s e a s p e c t s , w h i c h s u b s e q u e n t l y i m p r o v e s t h e p r o c e s s p e r f o r m a n c e a n d s t a b i l i t y . B a s e d o n t h e r e s u l t s o f t h i s s t u d y , o p t i m u m d e s i g n H R T ’ s f o r A - a n d M - U A S B ’ s r e a c t o r s a r e a b o u t 1 a n d 2 d a y s , w i t h R R s 2 a n d 3 t i m e s t h e i n f l u e n t f l o w r a t e , r e s p e c t i v e l y . M o s t o f t h e r e a c t i o n s s e e m t o o c c u r a t t h e l o w e r p a r t o f t h e r e a c t o r s ( s l u d g e b e d a n d b l a n k e t p o r t i o n ) . A s s h o w n i n F i g u r e 5 . 2 5 , t h e r e i s n o d i f f e r e n c e i n t h e e f f l u e n t V F A c o n c e n t r a t i o n p r o f i l e f r o m t h e b o t t o m t o t h e u p p e r p a r t o f t h e M - U A S B r e a c t o r . P o s s i b l e r e a s o n s f o r t h i s p h e n o m e n o n m a y b e d u e t o h i g h c o n c e n t r a t i o n s o f a c t i v e a n a e r o b i c s l u d g e i n t h e l o w e r p a r t o f t h e r e a c t o r , t h e e f f e c t i v e m i x i n g c r e a t e d b y t h e i n c o m i n g f l o w r a t e , t h e u p w a r d e s c a p e o f t h e p r o d u c e d g a s , a n d t h e r e c y c l e o f t h e e f f l u e n t f r o m t h e s l u d g e b l a n k e t . A l l t h e s e f a c t o r s 1 2 7 F i g u r e 5 . 2 5 C o m p a r i s o n o f T o t a l V F A A l o n g t h e H e i g h t o f M - U A S B : D u r i n g t h e A c c l i m a t i z a t i o n P r o c e s s S l u d g e b l a n k e t V F A 1 . 6 M A c H P r 2 1 . 2 - 0 . 8 I - - 0 . 4 0 I i I i 0 I I I 0 2 0 4 0 6 0 8 0 l i m e , d a y s 1 2 8 c o n t r i b u t e t o i n c r e a s e t h e r e m o v a l e f f i c i e n c y a t t h e l o w e r p a r t o f t h e r e a c t o r . C h r i s t e n s e n ( 1 9 8 4 ) f o u n d