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Effects on anaerobic digestion of employing polyelectrolytes and ferric chloride as aids to clarification… Warman, Robert W. 1975

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EFFECTS ON ANAEROBIC DIGESTION OF EMPLOYING POLYELECTROLYTES AND FERRIC CHLORIDE AS AIDS TO CLARIFICATION OF DOMESTIC SEWAGE by ROBERT W. WARMAN B.A.Sc, University of B r i t i s h Columbia, 1970 j A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of C i v i l Engineering We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1975 In 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 an 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 make 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 may be g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s 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 be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . n o n a p f n i i n t „ f CIVIL ENGINEERING Department or The 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 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 D a t e September 12, 1975 A B S T R A C T The advent of h i g h m o l e c u l a r weight p o l y e l e c t r o l y t e s has s t i m u l a t e d r e s e a r c h i n t o t h e i r use f o r BOD r e d u c t i o n i n primary and secondary treatment and as sludge dewatering a i d s i n vacuum f i l t r a t i o n and c e n t r i f u g a t i o n . Since many of these products have not been approved f o r use i n domestic water s u p p l i e s because of t h e i r p o s s i b l e t o x i c i t y t o humans, i t was f e l t t h a t they may be t o x i c t o the microorganisms i n anaerobic d i g e s t i o n , a c t i v a t e d sludge or o t h e r b i o l o g i c a l treatment p r o c e s s e s . T h i s r e s e a r c h e v a l u a t e s e f f e c t s on the anaerobic d i g e s t i o n p r o c e s s . Three c o n t i n u o u s l y mixed l a b o r a t o r y s c a l e a n a e r o b i c d i g e s t e r s were operated a t 32±1°C w i t h a 30 day h y d r a u l i c and s o l i d s r e t e n t i o n time. D i g e s t e r number one served as a c o n t r o l and r e c e i v e d sludge o b t a i n e d by sedime n t a t i o n of domestic sewage without the use o f c o a g u l a n t s ; number two r e c e i v e d sludge o b t a i n e d u s i n g 14 mg/l of a c a t i o n i c Hercules I n c o r p o r a t e d polymer, H e r e o f l o c 814.2, as the coagulant; and number t h r e e r e c e i v e d sludge o b t a i n e d u s i n g 30 mg/l of f e r r i c c h l o r i d e as the primary coagulant and 1 mg/l of H e r c o f l o c 836.2 as a coagulant a i d . Waste s t a b i l i z a t i o n c a l c u l a t i o n s , based on i n f l u e n t and e f f l u e n t BOD, COD, and VS r e s u l t s and on methane p r o d u c t i o n , f a i l e d t o i n d i c a t e any t o x i c i t y or p h y s i c a l i n a b i l i t y o f a n a e r o b i c microorganisms t o p e n e t r a t e the f l o e s formed as a r e s u l t o f the a d d i t i o n o f co a g u l a n t s as a i d s t o sewage s e d i -mentation. C a l c u l a t i o n s o f waste s t a b i l i z a t i o n from BOD,-/ BOD , COD, and VS r e s u l t s i n d i c a t e d treatment e f f i c i e n c i e s o f appro-x i m a t e l y 81, 70, 62 and 59 p e r c e n t , r e s p e c t i v e l y , f o r a l l t h r e e d i g e s t e r s . R e s u l t s o f pH, a l k a l i n i t y , and v o l a t i l e a c i d s t e s t i n g o f d i g e s t e r e f f l u e n t s and t o t a l gas p r o d u c t i o n from the d i g e s t e r s d i d not i n d i c a t e unbalanced treatment due t o the presence o f c o a g u l a n t s . pH and a l k a l i n i t y r e s u l t s were, however, c o n s i s -t e n t l y h i g h e r i n the d i g e s t e r s r e c e i v i n g c h e m i c a l l y c o a g u l a t e d sludge than i n the c o n t r o l d i g e s t e r , s i g n i f y i n g a g r e a t e r b u f f e r i n g c a p a c i t y a g a i n s t d i g e s t e r upset. The e f f l u e n t from d i g e s t e r number two was observed t o s e t t l e more r a p i d l y and l e a v e a c l e a r e r supernatant than e f f l u e n t from e i t h e r o f the o t h e r d i g e s t e r s . Subsequent Buchner f u n n e l vacuum f i l t r a t i o n t e s t s produced v a l u e s o f s p e c i f i c r e s i s t a n c e f o r e f f l u e n t s from d i g e s t e r s one and th r e e t h a t were 18 times g r e a t e r than the v a l u e s o b t a i n e d f o r the number two e f f l u e n t . Although the r e s u l t s were f o r the mixed d i g e s t e r c o n t e n t s r a t h e r than f o r t h e s e t t l e d p o r t i o n o f the e f f l u e n t , they i n d i c a t e t h a t l i t t l e o r no a d d i t i o n a l c o n d i t i o n i n g would be r e q u i r e d p r i o r t o vacuum f i l t r a t i o n dewatering o f e f f l u e n t from,, d i g e s t e r , number two. A l i m i t e d number o f j a r t e s t s and s e t t l i n g column t e s t s u s i n g a weak to medium s t r e n g t h domestic sewage, produced BOD^ and COD removal e f f i c i e n c i e s o f 50 t o 70 per c e n t u s i n g 30 mg/l of F e C l ^ i n combination w i t h 0.5-1.0 mg/l o f a n i o n i c H e r e o f l o c 836.2. S i m i l a r e f f i c i e n c i e s were achieved u s i n g 6-14 mg/l o f e i t h e r o f the c a t i o n i c H e r c o f l o c polymers, 812 or 814.2, as the s o l e c o a g u l a n t . i i i An economic a n a l y s i s was c a r r i e d out compar ing the t o t a l a n n u a l c o s t s o f p r i m a r y and a c t i v a t e d s l u d g e t r e a t m e n t methods. C a p i t a l c o s t s were a m o r t i z e d o v e r a t w e n t y - f i v e y e a r p e r i o d a t 10 p e r c e n t p e r annum and were added t o o p e r a t i o n and maintenance c o s t s t o o b t a i n t o t a l c o s t s . The r e s u l t s o f t h i s a n a l y s i s i n d i c a t e d t h a t the maximum economic dosages o f H e r e o f l o c 814.2 added c o n t i n u o u s l y t o p r i m a r y p l a n t s o p e r a t i n g a t c a p a c i t y a re 1 4 . 9 , 1 0 . 2 , and 6.6 m g / l f o r 1, 10, and 100 mgd p l a n t s , r e s p e c t i v e l y . S i m i l a r l y f o r f e r r i c c h l o r i d e and 0.5 m g / l o f H e r c o f l o c 836 .2 , t h e c o r r e s p o n d i n g economic dosages o f FeCl.3 a r e 51, 34, and 21.5 m g / l . These dosages a r e based on t h e a s s u m p t i o n t h a t an adequate degree o f t r e a t m e n t can be o b t a i n e d by c h e m i c a l p r e c i p i t a t i o n . W i t h i n the l i m i t a t i o n s o f the economic a n a l y s i s and based on j a r t e s t r e s u l t s , i t was c o n c l u d e d t h a t use o f H e r c o f l o c 814.2 as an a i d t o p r i m a r y c l a r i f i c a t i o n o f d o m e s t i c sewage i s not an e c o n o m i c a l l y a t t r a c t i v e a l t e r n a t i v e t o p r o v i d i n g a c t i v a t e d s l u d g e t r e a t m e n t u n l e s s an adequate degree o f t r e a t m e n t can be a c h i e v e d a t dosages somewhat l e s s t h a n 14 m g / l . On the o t h e r h a n d , use o f f e r r i c c h l o r i d e and H e r c o f l o c 836.2 was found t o be e c o n o m i c a l l y a t t r a c t i v e f o r p l a n t s i n the 1-10 mgd r a n g e . iv TABLE OF CONTENTS Page LIST OF TABLES v i i LIST OF FIGURES v i i i ACKNOWLEDGEMENT i x CHAPTER I INTRODUCTION 1 1.1 General 1 1.2 H i s t o r y o f Chemical Treatment 2 1.3 Theory of Chemical P r e c i p i t a t i o n 2 1.4 E f f i c i e n c y of Removal of Organics by Chemical P r e c i p i t a t i o n 5 1.5 Why Use Chemical P r e c i p i t a t i o n ? 6 1.6 Advantage of P o l y e l e c t r o l y t e s i n Chemical Treatment 7 1.7 O b j e c t i v e s o f the Research 7 CHAPTER I I EXPERIMENTAL METHODS 8 2.1 General 8 2.2 E v a l u a t i o n o f P o l y e l e c t r o l y t e s 8 2.3 E v a l u a t i o n o f E f f e c t s on Anaerobic D i g e s t i o n 10 2.4 S i g n i f i c a n c e o f D i g e s t i o n Parameters Monitored 11 2.5 S e l e c t i o n o f Coagulants f o r E v a l u a t i o n o f E f f e c t s on Anaerobic D i g e s t i o n 15 2.6 Procedure Used to Obtain Raw Sludge for- Anaerobic D i g e s t e r s 16 2.7 F i l t e r a b i l i t y o f Di g e s t e d Sludges 17 CHAPTER I I I RESULTS - POLYMER EVALUATIONS AND FILTERABILITY OF DIGESTED SLUDGES 19 3.1 E v a l u a t i o n o f P o l y e l e c t r o l y t e s 19 3.2 Problems w i t h A i r M i x i n g of Polymers and Sewage i n S e t t l i n g Columns 26 3.3 F i l t e r a b i l i t y o f Di g e s t e d Sludges 26 v Page CHAPTER IV RESULTS - ANAEROBIC DIGESTION 2 9 4.1 General 29 4.2 Problems During D i g e s t e r Start-Up 29 4.3 R e s u l t s of Long-Term BOD T e s t s o f Raw and D i g e s t e d Sludges 32 4.4 S t a b i l i z a t i o n of Organics C a l c u l a t e d from BOD, COD and V o l a t i l e S o l i d s R e s u l t s 33 4.5 S t a b i l i z a t i o n o f Organics C a l c u l a t e d from Methane P r o d u c t i o n 37 4.6 Comparison of R e s u l t s Obtained f o r Waste S t a b i l i z a t i o n 41 4.7 S i g n i f i c a n c e o f Other D i g e s t i o n Parameters Monitored 43 CHAPTER V ECONOMICS OF CHEMICAL TREATMENT 47 CHAPTER VI SUMMARY, CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE RESEARCH 55 6.1 Summary 55 6.2 C o n c l u s i o n s 58 6.3 Recommendations f o r Future Research 60 BIBLIOGRAPHY 62 APPENDIX A JAR TEST RESULTS - RAW SEWAGE FLOCCULATION 64 APPENDIX B DIGESTION PARAMETER TEST RESULTS 68 APPENDIX C RESULTS OF LONG-TERM BOD TESTS ON RAW AND DIGESTED SLUDGES 75 APPENDIX D SAMPLE CALCULATION OF THE MICROBIAL STABILIZATION OF VOLATILE SOLIDS, BOD OR COD IN A DIGESTER 8 2 v i LIST OF TABLES Table Page I BOD 5 AND COD REMOVAL EFFICIENCIES ACHIEVED IN SETTLING COLUMN TESTS 25 II VALUES OF SPECIFIC RESISTANCE IN S E C 2 / G OBTAINED FROM BUCHNER FUNNEL VACUUM FILTRATION TESTS ON DIGESTED SLUDGES 27 I I I RESULTS OF LONG-TERM, 20°C, BOD TESTS ON RAW AND DIGESTED SLUDGES 33 IV EFFICIENCY OF STABILIZATION OF SLUDGE ORGANICS CALCULATED FROM INFLUENT AND EFFLUENT BOD, COD AND VS RESULTS 36 V ESTIMATES OF EFFICIENCY OF STABILIZATION OF SLUDGE ORGANICS FROM METHANE PRODUCTION 4 0 VI COMPARISON OF THE EFFICIENCY OF STABILIZATION OF ORGANICS CALCULATED DIRECTLY FROM BOD, COD AND VS RESULTS AND INDIRECTLY FROM METHANE PRODUCTION 42 V l l LIST OF FIGURES F i g u r e Page 1 SCHEMATIC OF DIGESTER AND ANCILLARY APPARATUS 12 2 JAR TEST SUPERNATANT COD AS A FUNCTION OF DOSAGE OF CATIONIC ROHM AND HAAS "PRIMAFLOC C-7" PRECEDED BY 1.0 MG/L OF ANIONIC ALCHEM "D-17 9-M" 20 3 JAR TEST SUPERNATANT BOD AS A FUNCTION OF DOSAGE OF HERCULES INCORPORATED1S CATIONIC POLYELECTROLYTES "HERCOFLOC 812" AND "HERCOFLOC 814.2" 22 4 JAR TEST SUPERNATANT COD AND BOD AS FUNCTIONS OF DOSAGE OF CYANIMID'S CATIONIC POLYELECTROLYTE "MAGNIFLOC 560C" 23 5 JAR TEST SUPERNATANT BOD AS A FUNCTION OF DOSAGE OF FERRIC CHLORIDE AND HERCULES INCORPORATED1S ANIONIC POLYELECTROLYTE "HERCOFLOC 836.2" ' . ' 24 6 pH OF DIGESTERS 44 7 METHANE CONTENT OF DIGESTER GASES 45 8 U.S. ENVIRONMENTAL PROTECTION AGENCY SEWAGE TREATMENT PLANT CONSTRUCTION COST INDEX 4 9 9 U.S. DEPARTMENT OF LABOR - AVERAGE EARNINGS FOR NONSUPERVISORY WORKERS IN WATER, STEAM AND SANITARY SYSTEMS 50 10 CAPITAL COST, OPERATING AND MAINTENANCE COST, AND DEBT SERVICE vs. DESIGN CAPACITY FOR PRIMARY AND ACTIVATED SLUDGE PLANTS ADJUSTED TO AUGUST, 1975 51 11 ECONOMIC DOSAGES OF A CATIONIC POLYELECTROLYTE AND OF FERRIC CHLORIDE AND 0.5 MG/L OF ANIONIC POLYELECTORLYTE FOR PLANTS OPERATING AT DESIGN CAPACITY 52 v i i i A C K N O W L E D G E M E N T The a u t h o r wishes t o thank the f o l l o w i n g o r g a n i z a t i o n s and i n d i v i d u a l s f o r t h e i r a s s i s t a n c e : Canada Department o f E n e r g y , M i n e s and Resources who p r o v i d e d the f u n d i n g f o r t h i s r e s e a r c h . G r e a t e r Vancouver Sewerage and D r a i n a g e D i s t r i c t and M r . V i c T e r r y , former S u p e r i n t e n d e n t o f O p e r a t i o n s and M a i n t e n a n c e , f o r a l l o w i n g t h e a u t h o r a c c e s s to and use o f f a c i l i t i e s a t t h e L i o n s Gate Sewage Treatment P l a n t . Dayton & K n i g h t L t d . , C o n s u l t i n g E n g i n e e r s , f o r a l l o w i n g t ime t o complete the w r i t t e n p o r t i o n o f t h i s t h e s i s d u r i n g w o r k i n g hours and f o r making s e c r e t a r i a l s t a f f a v a i l a b l e . E l i z a b e t h McDonald f o r her a s s i s t a n c e i n the l a b o r a t o r y . C a r o l i n e Holm f o r t y p i n g o f the f i n i s h e d copy o f the t h e s i s ; E l e a n o r Foreman and P a u l i n e K l a s s e n f o r t y p i n g e a r l i e r d r a f t s . A l S i l v e r f o r h i s s k i l l w i t h d r a f t i n g i m p l e m e n t s . D r . R. D. Cameron f o r h i s g u i d a n c e and c o n s t r u c t i v e c r i t i c i s m t h r o u g h o u t . ix CHAPTER 1 INTRODUCTION 1.1 G e n e r a l The advent o f h i g h m o l e c u l a r . w e i g h t , l o n g - c h a i n p o l y e l e c -t r o l y t e s has s t i m u l a t e d r e s e a r c h i n t o t h e i r use i n sewage t r e a t m e n t f o r r e m o v a l o f o r g a n i c s o l i d s i n p r i m a r y and s e c o n -d a r y t r e a t m e n t and as s l u d g e d e w a t e r i n g a i d s i n vacuum f i l t r a -t i o n and c e n t r i f u g a t i o n . Polymers a r e a l s o under i n v e s t i g a t i o n as p r i m a r y c o a g u l a n t s or c o a g u l a n t a i d s f o r removal o f s o l i d s and o r g a n i c c o l o u r from water s u p p l i e s and i n water s o f t e n i n g . Because o f p o s s i b l e a d v e r s e p h y s i o l o g i c a l e f f e c t s t o humans stemming f r o m t h e use o f p o l y m e r s i n p u b l i c water s u p p l i e s , t h e U . S . E n v i r o n m e n t a l P r o t e c t i o n Agency approves some polymers f o r t h i s u s e , but s e t s l i m i t s upon dosages f o r t h o s e p o l y m e r s w h i c h a r e a p p r o v e d . The r e s e a r c h r e p o r t e d on h e r e i n stems from a c o n c e r n about p o s s i b l e t o x i c i t y t o m i c r o b i a l l i f e i n a n a e r o b i c d i g e s t e r s , a c t i v a t e d s l u d g e and t r i c k l i n g f i l t e r p l a n t s . C o a g u l a t i o n and s e t t l i n g t e s t s d u r i n g s t u d i e s on s l u d g e d e w a t e r i n g a t t h e U n i v e r s i t y o f Washington i n d i c a t e d t h a t p o l y e l e c t r o l y t e s had a t o x i c e f f e c t on t h e b a c t e r i a l l i f e i n t h e s u p e r n a t a n t l i q u o r [1]. The scope o f t h i s s t u d y was l i m i t e d t o d e t e r m i n a t i o n o f t h e e f f e c t s on the 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 o f t h e c h e m i c a l s l u d g e o b t a i n e d by t h e c o a g u l a t i o n and s e d i m e n t a t i o n o f a d o m e s t i c sewage e m p l o y i n g p o l y e l e c t r o l y t e s and f e r r i c c h l o r i d e as c o a g u l a n t s . 1 2 1.2 H i s t o r y o f Chemical Treatment The use o f che m i c a l s i n sewage treatment i s not a new concept, the advent of p o l y e l e c t r o l y t e s has merely served t o s t i m u l a t e i n t e r e s t i n t h e i r use. Chemical p r e c i p i t a t i o n was t r i e d i n P a r i s , France i n 1740 and was popular i n England between 18 57 and 1880/ when i n t e r e s t waned due t o the i n t r o d u c t i o n o f b i o l o g i c a l t r e a t m e n t . [ 2 ] . In the U n i t e d S t a t e s , chemical p r e c i p i t a t i o n was popular f o r about 35 y e a r s p r i o r t o 1910. I n t e r e s t waned between 1910 and 1928 and r e v i v e d around 192 9, a p p a r e n t l y due to development of the L a u g h l i n process [ 2 ] . The f o l l o w i n g statement by Enslow [3] i n 1935 a t t e s t s t o the p o p u l a r i t y o f c h e m i c a l treatment a t t h a t time: "Today t h e r e are 5 0 or more American p l a n t s completed, under c o n s t r u c t i o n , or d e f i n i t e l y planned, i n which chemical p r e c i p i t a t i o n alone o r i n combination w i t h b i o l o g i c a l p r o c e s s e s i s bei n g , or w i l l be, employed. In a d d i t i o n , t h e r e are not l e s s than 14 such p l a n t s proposed, 12 to employ chemical treatment alone and 2 to use i t f o r a s s i s t i n g b i o l o g i c a l p r o c e s s e s . " By 1959, the c o n s t r u c t i o n o f sewage treatment p l a n t s based s o l e l y on chemi c a l p r e c i p i t a t i o n had d e c l i n e d but chemical treatment as an a i d to ot h e r p r o c e s s e s was on the i n c r e a s e [2]. 1.3 Theory o f Chemical P r e c i p i t a t i o n Chemical p r e c i p i t a t i o n , o r p h y s i c a l - c h e m i c a l treatment as the p r o c e s s i s a l s o known, i s a process by which c l a r i f i c a t i o n o f sewage i s a t t a i n e d by the a d d i t i o n o f chemical substances t o 3 promote c o a g u l a t i o n and f l o c c u l a t i o n o f suspended c o l l o i d a l m a t t e r . In o r d e r t o u n d e r s t a n d c h e m i c a l p r e c i p i t a t i o n , i t i s n e c e s s a r y t o u n d e r s t a n d t h e n a t u r e o f sewage c o l l o i d s . The s i z e range o f c o l l o i d a l p a r t i c l e s i s a r b i t r a r i l y d e f i n e d as one m i l l i m i c r o n t o one m i c r o n . A d i s p e r s i o n o f such p a r t i c l e s i n a l i q u i d i s c a l l e d a " s o l " . A d i s p e r s i o n o f p a r t i c l e s o f l a r g e r s i z e , c a l l e d a " s u s -p e n s i o n " , w i l l c l a r i f y i t s e l f by g r a v i t y s e t t l i n g i n a r e a s o n -a b l e l e n g t h o f t i m e . A d i s p e r s i o n o f p a r t i c l e s o f s m a l l e r s i z e , c a l l e d a " s o l u t i o n " , i s - l i t t l e a f f e c t e d by c o a g u l a n t s . C o l l o i d s a r e e i t h e r h y d r o p h o b i c ( l i t t l e a f f i n i t y f o r water) o r h y d r o p h i l i c (great a f f i n i t y f o r w a t e r ) . G e n e r a l l y , i n o r -g a n i c c o l l o i d s a r e h y d r o p h o b i c and o r g a n i c c o l l o i d s a r e h y d r o -p h i l i c . The o r g a n i c c o l l o i d s found i n d o m e s t i c sewage a r e m a i n l y h y d r o p h i l i c . C o l l o i d s o f b o t h t y p e s a l s o p o s s e s s an e l e c t r i c a l c h a r g e . The c o l l o i d s u s u a l l y found i n wastewaters a r e c h a r a c t e r i z e d by a z e t a p o t e n t i a l o f -15 t o -2 0 m i l l i v o l t s [4 ] . The s t r o n g m u t u a l r e p u l s i o n i n d u c e d by a h i g h z e t a p o t e n t i a l c o n t r i b u t e s to t h e s t a b i l i t y o f poor s e d i m e n t a t i o n c h a r a c t e r i s t i c s o f a " s o l " . B e f o r e c o l l o i d s can be removed f rom the wastewater , t h e " s o l " must f i r s t be d e s t a b i l i z e d , f o l l o w e d by f l o c c u l a t i o n t o g e n e r a t e l a r g e p a r t i c l e s . D e s t a b i l i z a t i o n can be a c c o m p l i s h e d b y : 1 . The a d d i t i o n o f a s t r o n g c a t i o n i c e l e c t r o l y t e s u c h as f e r r i c c h l o r i d e t o lower the z e t a p o t e n t i a l , 4 p e r m i t t i n g the van der Waals a t t r a c t i v e f o r c e s to become e f f e c t i v e . 2. The a d d i t i o n o f c a t i o n i c e l e c t r o l y t e i n the presence of s u f f i c i e n t a l k a l i r e s u l t i n g i n the f o r m a t i o n of p o s i t i v e l y charged hydrous o x i d e s . These i n s o l u b l e complexes become adsorbed on the c o l l o i d s . 3. The a d d i t i o n of s u f f i c i e n t c a t i o n i c p o l y e l e c -t r o l y t e t o lower the z e t a p o t e n t i a l r e s u l t i n g i n the f o r c e s o f a t t r a c t i o n between the polymer and c o l l o i d s becoming l a r g e enough f o r b r i d g i n g to o c c u r . 4. Mutual c o a g u l a t i o n of c a t i o n i c and a n i o n i c p o l y -mers i n the system. 5. Agglomeration of n e g a t i v e c o l l o i d s w i t h an a n i o n i c or n o n i o n i c p o l y e l e c t r o l y t e . 6. Entrapment of wastewater c o l l o i d s and o t h e r sus-pended matter by the f l o e s formed by the above p r o c e s s e s . From the p r e c e d i n g d i s c u s s i o n i t may be i n f e r r e d t h a t c h e m i c a l p r e c i p i t a t i o n o f domestic sewage i s a w e l l understood s c i e n c e . In f a c t , the c o a g u l a t i o n p r o c e s s e s are not w e l l understood, and a " t r i a l - a n d - e r r o r " procedure - the j a r t e s t -i s s t i l l one of the most w i d e l y used methods of e v a l u a t i n g c o a g u l a n t s and d e t e r m i n i n g optimum dosages. Thus, i n - p l a n t c o n t r o l of chemical treatment i s p a r t i c u l a r l y d i f f i c u l t f o r domestic wastewaters, s i n c e both the s t r e n g t h and amount o f waste f l u c t u a t e throughout t h e day. 1.4 E f f i c i e n c y o f Removal o f Organics by Chemical P r e c i p i t a t i o n ' The c o n v e n t i o n a l methods o f treatment used i n r e c e n t y e a r s have been termed "primary" and "secondary" treatment. The e x p r e s s i o n "primary treatment" means removal o f sus-pended s o l i d s by g r a v i t y s e t t l i n g w i t h d i s c h a r g e of the l i q u i d p o r t i o n or supernatant. "Secondary treatment" c u s t o m a r i l y i n c l u d e s primary s e d i m e n t a t i o n p l u s a d d i t i o n a l a e r o b i c b i o l o -g i c a l treatment o f the supernatant and secondary sedimentation b e f o r e d i s c h a r g e of the e f f l u e n t supernatant. Treatment e f f i c i e n c i e s n o r m a l l y expected from primary s e d i m e n t a t i o n are 25-35 p e r c e n t removal o f 5-day, 20°C B i o -c h e m i c a l Oxygen Demand (BOD) and 50-60 p e r c e n t removal o f suspended s o l i d s (SS). For the most e f f i c i e n t b i o l o g i c a l p r o -c e s s e s , removal e f f i c i e n c i e s o f approximately 90 p e r c e n t o f both BOD and SS can be a c h i e v e d . As s o l u b l e o r g a n i c s are l i t t l e a f f e c t e d by c o a g u l a n t s , c h e m i c a l p r e c i p i t a t i o n can be expected to remove o n l y 65-85 p e r c e n t o f BOD [3,5], but SS removals approaching 90 p e r c e n t should be p o s s i b l e . However, h i g h e r BOD and SS removal e f f i -c i e n c i e s have been r e p o r t e d f o r chemical p r e c i p i t a t i o n p r o c e s s e s when f o l l o w e d by an e f f l u e n t p o l i s h i n g s t e p . One such p r o c e s s , the Guggenheim p r o c e s s , employed f e r r i c s u l p h a t e and l i m e as c o a g u l a n t s f o l l o w e d by z e o l i t e i o n ex-6 changers. BOD and SS removals a v e r a g i n g 90 p e r c e n t and 97 p e r -c e n t , r e s p e c t i v e l y , were r e p o r t e d [5]. E x c l u d i n g the i o n exchange s t e p , however, monthly average BOD r e d u c t i o n ranged between 76 and 8 6 p e r c e n t over a seven month p e r i o d . Chemical dosages were hi g h w i t h f e r r i c s u l p hate r a n g i n g from 19.5 t o 38.5 mg/l as Fe and l i m e from 31.6 to 52.9 mg/l as CaO. 1.5 Why Use Chemical P r e c i p i t a t i o n ? Although i t has been shown i n the p r e v i o u s s e c t i o n t h a t -chemical p r e c i p i t a t i o n i s capable o f a c h i e v i n g o n l y an " i n t e r -mediate" degree o f treatment, t h e r e are s e v e r a l i n s t a n c e s i n which i t s use may be advantageous. These a r e : 1. Where p l a i n s e d i m e n t a t i o n i s normally s u f f i c i e n t . but r e c e i v i n g water l i m i t a t i o n s n e c e s s i t a t e b e t t e r treatment a t times. 2. Where seasonal v a r i a t i o n s occur i n the volume o f sewage t r e a t e d and degree o f treatment r e q u i r e d . 3. Where an i n t e r m e d i a t e degree o f treatment between p l a i n s e d i m e n t a t i o n and secondary b i o l o g i c a l treatment i s a l l t h a t i s r e q u i r e d . 4. Where the area f o r p l a n t l o c a t i o n i s r e s t r i c t e d . 5. Where i t i s necessary t o help out an e x i s t i n g p l a n t , primary o r secondary, which i s o v e r l o a d e d . 6. Where i t i s n e c e s s a r y to t r e a t c e r t a i n i n d u s t r i a l wastes or domestic sewage c o n t a i n i n g a s i g n i f i c a n t p o r t i o n o f i n d u s t r i a l wastes which are i n h i b i t o r y t o b i o l o g i c a l p r o c e s s e s . 7 1.6 Advantage of P o l y e l e c t r o l y t e s i n Chemical Treatment  The p r i n c i p a l advantages i n u s i n g p o l y e l e c t r o l y t e s are the s i g n i f i c a n t r e d u c t i o n s i n the q u a n t i t y o f c h e m i c a l sludge which must be handled and i n the q u a n t i t y of chemical coagulant which must be handled. E a r l y i n v e s t i g a t o r s found t h a t q u a n t i t i e s of lime i n excess of 100 mg/l as CaO were o f t e n r e q u i r e d i n con-j u n c t i o n w i t h metal s a l t s to o b t a i n e f f i c i e n t treatment [5]. A f r a c t i o n o f a p a r t per m i l l i o n o f a n i o n i c p o l y e l e c t r o l y t e has been found to e f f e c t i v e l y r e p l a c e lime as a coagulant a i d . When used as primary c o a g u l a n t s , c a t i o n i c polymers have been found to be 10 t o 15 times as e f f e c t i v e as metal s a l t s f o r the d e s t a b i l i z a t i o n of sewage c o l l o i d s [4]. 1.7 O b j e c t i v e s o f the Research The p r i n c i p a l o b j e c t i v e of the r e s e a r c h undertaken was t o i n v e s t i g a t e the p o s s i b l e t o x i c i t y o f p o l y e l e c t r o l y t e s i n a n a erobic d i g e s t i o n . In a d d i t i o n , i t was a n t i c i p a t e d t h a t these coagulant a i d s might have a p h y s i c a l e f f e c t on a n aerobic d i g e s -t i o n e i t h e r through p h y s i c a l i n t e r f e r e n c e w i t h mixing due t o the s i z e and weight of the f l o c c u l a t e d p a r t i c l e s formed or through the i n a b i l i t y of the organisms to p e n e t r a t e and s t a -b i l i z e the l a r g e f l o e s formed. I t was i n t e n d e d , t h e r e f o r e , t h a t the r e s e a r c h l o o k a t both the p h y s i c a l and b i o l o g i c a l aspects o f the a n a e r o b i c d i g e s t i o n of c h e m i c a l l y p r e c i p i t a t e d wastes. C H A P T E R I I E X P E R I M E N T A L M E T H O D S 2.1 G e n e r a l T h e r e s e a r c h d e t a i l e d i n t h i s r e p o r t i n c l u d e s r e s u l t s o f t h e f o l l o w i n g l a b o r a t o r y i n v e s t i g a t i o n s : 1. J a r t e s t s w e r e p e r f o r m e d t o e v a l u a t e s e v e r a l p o l y m e r s a s p r i m a r y c o a g u l a n t s o r a s c o a g u l a n t a i d s f o r t h e c l a r i f i c a t i o n o f d o m e s t i c w a s t e -w a t e r . 2. T h r e e l a b o r a t o r y s c a l e , m o d e l d i g e s t e r s w e r e o p e r a t e d - o n e w i t h w a s t e w a t e r s o l i d s o b t a i n e d u s i n g n o c o a g u l a n t s , t h e s e c o n d w i t h w a s t e w a t e r s o l i d s o b t a i n e d u s i n g a c a t i o n i c p o l y m e r a s t h e c o a g u l a n t , a n d t h e t h i r d w i t h w a s t e w a t e r s o l i d s o b t a i n e d u s i n g f e r r i c c h l o r i d e a s t h e p r i m a r y c o a g u l a n t a n d a n a n i o n i c p o l y m e r a s a c o a g u l a n t a i d . 3. A B u c h n e r f u n n e l a s s e m b l y w a s u s e d t o e v a l u a t e t h e d e w a t e r a b i l i t y o f t h e d i g e s t e d s l u d g e s b y v a c u u m f i l t r a t i o n . 2.2 E v a l u a t i o n o f P o l y e l e c t r o l y t e s J a r t e s t s w e r e c o n d u c t e d u s i n g a P h i p p s - B i r d j a r t e s t a p p a r a t u s c a p a b l e o f s i m u l t a n e o u s l y s t i r r i n g s i x s a m p l e s a t s p e e d s u p t o 100 r e v o l u t i o n s p e r m i n u t e ( r p m ) . 8 9 Each polymer was prepared i n accordance w i t h the manufac-t u r e r ' s d i r e c t i o n s . A stock s o l u t i o n o f 1.0 or 0.5% was prepared and was s t a b l e f o r one or two weeks. From the stock s o l u t i o n a working s o l u t i o n o f 0.1 or 0.5% was prepared each day. A 1.0% working s o l u t i o n o f f e r r i c c h l o r i d e was used. One l i t e r samples o f f r e s h raw sewage were arranged i n the j a r t e s t apparatus w i t h one sample as a c o n t r o l . M i x i ng o f the c o n t e n t s a t 100 rpm was i n i t i a t e d b e f o r e the a d d i t i o n o f c o a g u l a n t s . F o l l o w i n g the a d d i t i o n o f coagulants a t v a r i o u s - c o n c e n t r a t i o n s , the system was mixed a t 100 rpm f o r one minute. When two c o a g u l a n t s were added, r a p i d mixing a t 100 rpm p r o -ceeded f o r one minute a f t e r each coagulant was added. The a d d i t i o n o f c o a g u l a n t s was f o l l o w e d by a f l o c c u l a t i o n p e r i o d o f t h r e e minutes w i t h mixing at 3 0 rpm. A f t e r f l o c c u l a t i o n , mixing was slowed t o 5 to 10 rpm f o r a dynamic s e t t l i n g p e r i o d . O b s e r v a t i o n s such as s i z e and type o f f l o e and t h e i r s e t t l i n g c h a r a c t e r i s t i c s were re c o r d e d . I n i t i a l l y , v i s u a l o b s e r v a t i o n s were used t o e v a l u a t e the v a r i o u s polymers and f e r r i c c h l o r i d e . However, a f t e r i t had been determined t h a t f e r r i c c h l o r i d e i n combination w i t h some a n i o n i c polymers and t h a t some c a t i o n i c polymers appeared t o y i e l d s a t i s f a c t o r y r e s u l t s , f i n a l s e l e c t i o n o f co a g u l a n t s and o f coa g u l a n t dosages was based on COD or BOD t e s t s o f the j a r supernatants a f t e r f i v e minutes o f s e t t l i n g . 10 2.3 E v a l u a t i o n o f E f f e c t s on 'Anaerobic D i g e s t i o n Three model d i g e s t e r s were c o n s t r u c t e d o f a c r y l i c p l a s t i c f o r use i n the l a b o r a t o r y . Low temperature h e a t i n g tapes wrapped around the d i g e s t e r s and switched on and o f f by means of a thermo-couple maintained the c o n t e n t s of the d i g e s t e r s a t 32+ 1"C. The d i g e s t e r c o n t e n t s were c o n t i n u o u s l y mixed by motor-driven s t a i n l e s s s t e e l paddles a t a r a t e s u f f i c i e n t t o keep o r g a n i c s o l i d s i n suspension. Some i n o r g a n i c p a r t i c l e s s e t t l e d out. During a d d i t i o n and withdrawal of sludge, the mixing speed was i n c r e a s e d t o suspend a l l s o l i d s . Raw sludge was added to each d i g e s t e r a t the r a t e of 250 ml per day, and d i g e s t e d sludge was withdrawn s i m u l t a n e o u s l y . The working c a p a c i t y of each d i g e s t e r was 7.5 l i t e r s , t h e r e f o r e h y d r a u l i c and s o l i d s r e t e n t i o n times were 3 0 days. A l l d i g e s t e r gases were passed through gas sampling tubes f i t t e d w i t h rubber n i p p l e s i n o r d e r t h a t samples c o u l d be w i t h -drawn f o r c o m p o s i t i o n a n a l y s i s by gas chromatography. Each gas sampling tube was f o l l o w e d by a simple bubbler apparatus which prevented p o s s i b l e backflow o f atmospheric a i r i n t o the samp-l i n g tubes and d i g e s t e r s . These were f o l l o w e d by h o r i z o n t a l a c r y l i c tubes f i l l e d w i t h water s a t u r a t e d w i t h d i g e s t e r gas which were used to measure the q u a n t i t y o f gas produced by di s p l a c e m e n t and c o l l e c t i o n of the water. The c o n f i g u r a t i o n o f the tubes was such t h a t the maximum back-pressure on the d i g e s -t e r was about 2-inches o f water. Towards the end o f the e x p e r i m e n t a l p e r i o d a s i n g l e Gallenkamp Model GF-052 wet gas meter was o b t a i n e d , and t h i s was used f o r both gas q u a n t i t y 11 measurements on a r o t a t i o n b a s i s and as a check a g a i n s t the water displacement method. F i g u r e 1 shows the l a y o u t o f a d i g e s t e r and a n c i l l a r y appa-r a t u s . The f o l l o w i n g d i g e s t i o n parameters were measured •. 1. I n f l u e n t raw sludge - t o t a l and v o l a t i l e s o l i d s , BOD, COD, t o t a l i r o n . 2. E f f l u e n t d i g e s t e d sludge - pH, v o l a t i l e a c i d s , a l k a l i n i t y , t o t a l and v o l a t i l e s o l i d s , BOD, COD, t o t a l i r o n . 3. D i g e s t e r gas - amount and c o m p o s i t i o n . Long-term BOD t e s t s were performed on samples o f i n f l u e n t and e f f l u e n t sludges to determine the r e l a t i o n s h i p between 5-day and u l t i m a t e carbonaceous b i o c h e m i c a l oxygen demand (BOD T). L a b o r a t o r y a n a l y s e s were performed a c c o r d i n g to p r o -cedures i n "Standard Methods" [6]. For gas chromatographic a n a l y s e s o f d i g e s t e r gas composition, a 16-foot by one-eighth i n c h diameter s t a i n l e s s s t e e l column was used, packed w i t h 8-f e e t of 50-80 mesh Poropack Q and 8-feet of 50-80 mesh Poro-pack R. The gas chromatograph was a Hewlett-Packard Model 5752B. 2.4 S i g n i f i c a n c e o f D i g e s t i o n Parameters Monitored  The p r e v i o u s l y l i s t e d d i g e s t i o n parameters measured were used to determine the e f f i c i e n c y of s t a b i l i z a t i o n o f o r g a n i c s 12 FIGURE I - SCHEMATIC OF DIGESTER AND ANCILLARY APPARATUS 13 and as i n d i c a t o r s o f u n b a l a n c e d t r e a t m e n t . Parameters w h i c h i n d i c a t e u n b a l a n c e d t r e a t m e n t a r e i n c r e a s e s i n v o l a t i l e a c i d s and i n CC>2 c o n t e n t o f d i g e s t e r gas and d e c r e a s e s i n p H , t o t a l gas p r o d u c t i o n and BOD, COD o r v o l a -t i l e s o l i d s r e d u c t i o n . E f f i c i e n c y o f o r g a n i c removal i s d e t e r m i n e d from measurements o f i n f l u e n t and e f f l u e n t COD, BOD and v o l a t i l e s o l i d s . Methane p r o d u c t i o n a l s o s e r v e s as a parameter f o r e s t i m a t i o n o f waste s t a b i l i z a t i o n . U n b a l a n c e d t r e a t m e n t can be e i t h e r o f a temporary n a t u r e o r p r o l o n g e d . F a c t o r s w h i c h may cause a temporary i m b a l a n c e are sudden changes i n t e m p e r a t u r e , o r g a n i c l o a d i n g , o r t h e n a t u r e o f t h e w a s t e . As t h e f i r s t two f a c t o r s were c o n t r o l l e d , t h e o n l y f a c t o r o f minor c o n c e r n was a change i n the n a t u r e o f t h e waste a t t h e s t a r t o f a d d i t i o n o f t h e e x p e r i m e n t a l s l u d g e . However, no problems were e x p e c t e d as any temporary i m b a l a n c e c o u l d be h a n d l e d by pH c o n t r o l and by r e d u c i n g f e e d i n g r a t e s t o a l l o w t i m e f o r t h e b a c t e r i a l p o p u l a t i o n t o a d j u s t . A p r o l o n g e d i m b a l a n c e may be caused by the i n t r o d u c t i o n o f t o x i c m a t e r i a l s t o t h e d i g e s t e r s , by an extreme d r o p i n p H , ' o r by s low b a c t e r i a l growth d u r i n g s t a r t u p . S i n c e pH c o u l d be c o n t r o l l e d by t h e a d d i t i o n o f l i m e o r sodium b i c a r b o n a t e , and s i n c e t h e ; : d i g e s t e r s were o p e r a t e d f o r s e v e r a l months b e f o r e the a d d i t i o n o f t h e e x p e r i m e n t a l s l u d g e s , a p r o l o n g e d i m b a l a n c e c o u l d be used as an i n d i c a t o r o f t o x i c i t y . I t was b e l i e v e d t h a t t h e p a r a m e t e r s measured would a l s o be s u f f i c i e n t t o d i f f e r e n t i a t e between m i c r o b i a l i n h i b i t i o n and 14 p h y s i c a l i n a b i l i t y o f m i c r o - o r g a n i s m s t o p e n e t r a t e and s t a b i l i z e t h e l a r g e f l o e s formed d u r i n g s e d i m e n t a t i o n . The b a c t e r i a l p o p u l a t i o n i n an a n a e r o b i c d i g e s t e r c o n s i s t s o f two main groups o f b a c t e r i a . These a r e a group o f f a c u l -t a t i v e and a n a e r o b i c b a c t e r i a known c o l l e c t i v e l y as " a c i d f o r m i n g b a c t e r i a " and a group o f o b l i g a t e anaerobes known c o l -l e c t i v e l y as "methane f e r m e n t i n g b a c t e r i a " . In the d i g e s t i o n p r o c e s s , t h e " a c i d f o r m e r s " m a i n l y c o n v e r t complex o r g a n i c s t o o r g a n i c f a t t y a c i d s ( v o l a t i l e a c i d s ) . The "methane f o r m e r s " c o n v e r t t h e s e o r g a n i c a c i d s m a i n l y t o methane and c a r b o n d i o x i d e . Of t h e two groups o f b a c t e r i a , t h e "methane f o r m e r s " are t h e most s e n s i t i v e t o changes i n t h e i r e n v i r o n m e n t . T h u s , when t o x i c i t y i s p r e s e n t , i t i s t h i s group w h i c h i s a f f e c t e d , r e s u l t i n g i n u n b a l a n c e d t r e a t m e n t . The " a c i d f o r m e r s " c o n t i n u e t o f u n c t i o n , r e s u l t i n g i n an i n c r e a s e i n v o l a t i l e a c i d s and a d e c r e a s e i n p H . The d e c r e a s e d a c t i v i t y o f t h e "methane f o r m e r s " r e s u l t s i n d e c r e a s e d waste s t a b i l i z a t i o n and a r e s u l t i n g d e c r e a s e i n methane p r o d u c t i o n . T h e r e f o r e t o t a l gas p r o d u c t i o n d e c r e a s e s and t h e r a t i o o f CO2 t o CH^ i n c r e a s e s . In the e v e n t o f a p h y s i c a l i n a b i l i t y o f m i c r o b e s t o p e n e -t r a t e t h e l a r g e f l o e s , i t was a n t i c i p a t e d t h a t the " a c i d f o r m e r s " would be a f f e c t e d , r e s u l t i n g i n a d e c r e a s e i n waste s t a b i l i z a t i o n and t o t a l gas p r o d u c t i o n w i t h o u t changes i n the o t h e r parameters w h i c h i n d i c a t e u n b a l a n c e d t r e a t m e n t . 15 2.5 S e l e c t i o n of Coagulants f o r E v a l u a t i o n o f E f f e c t s on Anaerobic D i g e s t i o n  For the f o l l o w i n g reasons i t was d e c i d e d t o use f e r r i c c h l o r i d e i n c o n j u n c t i o n w i t h an a n i o n i c polymer i n one d i g e s t e r and a c a t i o n i c polymer i n the o t h e r s 1. Only c a t i o n i c polymers were found t o be e f f e c t i v e as primary c o a g u l a n t s . Although a few c a t i o n i c polymers were r e a s o n a b l y e f f e c t i v e , a l l were b e l i e v e d t o be acrylamide-based polymers and without a d d i t i o n a l i n f o r m a t i o n about the f u n c -t i o n a l groups which account f o r t h e i r i o n i c n a t u r e , i t was f e l t t h a t no u s e f u l purpose would be served by t e s t i n g more than one o f them. 2. F e r r i c s a l t s were the most s u c c e s s f u l and most widely-used coagulants d u r i n g e a r l y experimenta-t i o n , w i t h chemical p r e c i p i t a t i o n [5]. At t h a t time t h e r e were c o n f l i c t i n g statements t h a t i r o n s a l t s both improve and r e t a r d a n a e r o b i c d i g e s t i o n , but l i t t l e c o n c r e t e data was pre s e n t e d to s u b s t a n t i a t e e i t h e r c l a i m [3,5]. 3. F e r r i c c h l o r i d e r e q u i r e d an' a n i o n i c polymer as a coa g u l a n t a i d f o r e f f e c t i v e agglomeration of the s m a l l f l o e s formed. The s m a l l q u a n t i t i e s o f polymer r e q u i r e d were not expected to be t o x i c as some a n i o n i c acrylamide-based polymers have been approved f o r use i n p u b l i c water s u p p l i e s a t dosages up to 1 mg/l. However, the p o s s i b i l i t y o f the polymer a c t i n g s y n e r g i s t i c a l l y w i t h f e r r i c c h l o r i d e or w i t h some o t h e r component o f sewage sludge c o u l d not be d i s c o u n t e d . On the b a s i s o f the j a r t e s t r e s u l t s , c a t i o n i c H e r c o f l o c 814.2 was s e l e c t e d f o r use as a primary c o a g u l a n t a t a dosage of 14 mg/l. 3 0 mg/l of f e r r i c c h l o r i d e as the primary coagu-l a n t f o l l o w e d by 1 mg/l of a n i o n i c H e r c o f l o c 83 6.2 as a coagulant a i d were a l s o s e l e c t e d . As the primary o b j e c t i v e o f the r e s e a r c h was the e v a l u a t i o n o f e f f e c t s on d i g e s t i o n , no attempt was made t o s e l e c t economi-c a l dosages o f c o a g u l a n t s . Dosages were s e l e c t e d t o be s l i g h t l y i n excess o f p r a c t i c a l requirements f o r e f f e c t i v e c o a g u l a t i o n . 2.6 Procedure Used t o O b t a i n Raw Sludge f o r Anaerobic D i g e s t e r s  In o r d e r to o b t a i n raw sludge f o r the l a b o r a t o r y d i g e s t e r s w i t h approximately the same c h a r a c t e r i s t i c s as c o u l d be expected from an o p e r a t i n g p h y s i c a l - c h e m i c a l p l a n t , two a c r y l i c s e t t l i n g columns were u t i l i z e d . Each was 12-inches i n diameter, 4 - f e e t h i g h , and had a working c a p a c i t y o f 80 l i t e r s . The bottom o f each was f i t t e d w i t h a c o n i c a l sludge hopper. S e v e r a l sampling p o r t s on the s i d e s allowed f o r withdrawal of super-n a t a n t . F r e s h barminuted raw sewage was pumped i n t o the columns and mixed w i t h the c o a g u l a n t s . A f l o c c u l a t i o n p e r i o d f o l l o w e d d u r i n g which the contents were s t i r r e d f o r s e v e r a l minutes. 17 F o l l o w i n g s e t t l i n g , s l u d g e was withdrawn from the bot tom o f t h e s l u d g e h o p p e r s . S ludge f o r t h e c o n t r o l d i g e s t e r was o b t a i n e d s i m u l t a n e o u s l y by s e t t l i n g sewage i n a l a r g e p o l y e t h y l e n e t a n k . I t became a p p a r e n t t h a t i t was n o t p o s s i b l e t o o b t a i n s u f -f i c i e n t s l u d g e i n a r e a s o n a b l e l e n g t h o f t i m e i f t h e s e t t l i n g columns were d r a i n e d c o m p l e t e l y each t ime c o a g u l a n t s were a d d e d . T h e r e f o r e , a f t e r t h e f i r s t a d d i t i o n o f c o a g u l a n t s and f l o c c u l a t i o n o f the sewage, t h e f l o e s were a l l o w e d t o s e t t l e p a s t t h e m i d - p o i n t o f t h e columns and 4 0 l i t e r s o f s u p e r n a t a n t were w i t h d r a w n . The columns were t h e n r e - f i l l e d , a d d i t i o n a l c o a g u l a n t s were added and t h e c o n t e n t s were remixed and s t i r r e d w h i l e f l o c c u l a t i o n took p l a c e . T h i s p r o c e s s was r e p e a t e d s e v e r a l t i m e s b e f o r e t h e columns were d r a i n e d . The u n t r e a t e d raw sewage was h a n d l e d i n a s i m i l a r manner f o r c o n s i s t e n c y . T h i s p r o c e d u r e a p p r o x i m a t e s t h e r e s u l t s w h i c h would be o b t a i n e d by r e t u r n i n g c h e m i c a l s l u d g e t o t h e head o f t h e p r i m a r y s e d i -m e n t a t i o n b a s i n i n a f u l l s c a l e p l a n t . V o l a t i l e s o l i d s c o n c e n t r a t i o n s o f s l u d g e s were a d j u s t e d by t h e a d d i t i o n o f s u p e r n a t a n t t o b r i n g a l l s l u d g e s t o a p p r o x i -m a t e l y e q u a l v a l u e s b e f o r e f e e d i n g t o t h e d i g e s t e r s . 2 .7 F i l t e r a b i l i t y o f D i g e s t e d S l u d g e s Based on o b s e r v a t i o n s o f uneven s e t t l i n g r a t e s f o r t h e d i g e s t e d s l u d g e s , i t appeared t h a t t h e c o a g u l a n t s had r e t a i n e d some v a l u e as s l u d g e d e w a t e r i n g a i d s . T h e r e f o r e , Buchner f u n n e l 18 vacuum f i l t r a t i o n t e s t s a t vacuums o f 375, 500 and 625 mm of mercury were conducted to determine the r e l a t i v e f i l t e r a b i l i t y . o f the t h r e e sludges as i n d i c a t e d by s p e c i f i c r e s i s t a n c e . The procedure has been d e s c r i b e d by R i c h [ 7 ] . CHAPTER I I I RESULTS - POLYMER EVALUATIONS AND FILTERABILITY OF DIGESTED SLUDGES 3.1 E v a l u a t i o n o f P o l y e l e c t r o l y t e s I n i t i a l j a r t e s t r e s u l t s were d i s c o u r a g i n g . As sewage c o l -l o i d s are mainly a n i o n i c , f i r s t e f f o r t s were d i r e c t e d towards f i n d i n g a s i n g l e c a t i o n i c polymer which would e f f e c t i v e l y a c t as a c o a g u l a n t . V i s u a l r e s u l t s were poor as e i t h e r no f l o c c u -l a t i o n o c c u r r e d o r very s m a l l f l o e s formed which s e t t l e d s l o w l y under s t a t i c c o n d i t i o n s and not a t a l l under dynamic c o n d i t i o n s a t dosages up t o 10 mg/l. S i m i l a r r e s u l t s were observed f o r s e v e r a l a n i o n i c polymers used a l o n e a t the same dosages. E a r l y i n the i n v e s t i g a t i o n some polymer samples were not a v a i l a b l e and a t t e n t i o n was d i r e c t e d towards f i n d i n g e f f e c t i v e combinations o f polymers. A number o f combinations of a n i o n i c polymer i n dosages o f about 1.0 mg/l f o l l o w e d by about 5 mg/l of c a t i o n i c polymer produced tough, r a p i d s e t t l i n g f l o e s . T y p i c a l r e s u l t s o f supernatant BOD t e s t s a f t e r the a d d i t i o n of an a n i o n i c , f o l l o w e d by a c a t i o n i c polymer are shown on F i g u r e 2. R e s u l t s o f some v i s u a l o b s e r v a t i o n s d u r i n g j a r t e s t i n g are t a b u l a t e d i n Appendix A. Among the l a s t polymers t o a r r i v e were pro d u c t s o f Herc u l e s I n c o r p o r a t e d and of Cyanamid o f Canada L i m i t e d . Two c a t i o n i c p r o d u c t s o f these companies, H e r e o f l o c 812 and Magni-f l o c 560C, r e s p e c t i v e l y , were found t o produce good f l o c -c u l a t i o n o f raw sewage s o l i d s when used alone. When more 19 20 2|0 1 1 : [— 1 1 o I 1 — _ L _ I — 1 .—. 0 . 1.0 2.0 3.0 4.0 5.0 DOSAGE OF PRIMAFLOC C-7 (MG/L) FIGURE 2 - JAR TEST SUPERNATANT COD AS A FUNCTION OF DOSAGE OF CATIONIC ROHM AND HAAS "PRIMAFLOC C -7 " PRECEEDED BY 1.0 MG/L OF ANIONIC ALCHEM "D-I79-M" 21 samples were r e c e i v e d from H e r c u l e s , c a t i o n i c H e r c o f l o c 814.2 was a l s o found t o produce good r e s u l t s . T y p i c a l r e s u l t s o f BOD and COD a n a l y s e s o f j a r t e s t supernatants f o r these p r o d u c t s are shown on F i g u r e s 3 and 4. Two manufacturers suggested t h e a d d i t i o n o f i n o r g a n i c s a l t s , such as f e r r i c c h l o r i d e , f o l l o w e d by a n i o n i c p o l y e l e c t r o l y t e f o r the e f f i c i e n t removal o f suspended s o l i d s and BOD i n a primary p l a n t . Subsequently j a r t e s t s were run u s i n g combi-n a t i o n s o f f e r r i c c h l o r i d e and a n i o n i c polymers. The r e s u l t s o f one such t e s t i n which twelve j a r s were dosed w i t h combi-n a t i o n s o f 5, 15, and 3 0 mg/l f e r r i c c h l o r i d e and 0, 0.5, 1.0, and 2.0 mg/l H e r c o f l o c 836.2 are pre s e n t e d as supernatant BOD "contours" on F i g u r e 5. R e s u l t s o f BOD and COD removal e f f i c i e n c i e s i n t e s t s u s i n g s e t t l i n g columns are presented i n Table I. In summary, the l i m i t e d number of j a r t e s t and s e t t l i n g column r e s u l t s p r e s e n t e d h e r e i n are i n c o n c l u s i v e r e g a r d i n g removal of BOD and COD f o r v a r i o u s dosages o f polymers and f e r r i c c h l o r i d e . They i n d i c a t e , however, f o r a weak to medium s t r e n g t h sewage, t h a t BOD and COD removal e f f i c i e n c i e s o f 50 to 70 p e r c e n t can be o b t a i n e d u s i n g 30 mg/l of F e C l ^ i n combi-n a t i o n w i t h 0.5-1.0 mg/l of a n i o n i c H e r c o f l o c 836.2. S i m i l a r e f f i c i e n c i e s were achieved u s i n g 6-14 mg/l of e i t h e r o f the c a t i o n i c H e r c o f l o c polymers, 812 or 814.2, as the s o l e c o a g u l a n t . 120 110 100 90 80 70 60 50 o \ > HE ?C0FL0C 8 2 HERCC )FL0C 814.: ?—— V o ( o 0 4 8 12 16 20 POLYELECTROLYTE CONCENTRATION (MG/L) FIGURE 3-JAR TEST SUPERNATANT BOD AS A FUNCTION OF DOSAGE OF HERCULES INCORPORATED'S CATIONIC POLYELECTROLYTES "HERCOFLOC 812" AND "HERCOFLOC 814.2". 23 350 300 250 200 150 100 50 0 -COD < —BOD L J L 0 2 4 6 8 10 DOSAGE OF MAGNIFLOC 560C (MG/L) FIGURE 4-JAR TEST SUPERNATANT COD AND BOD AS FUNCTIONS OF DOSAGE OF CYANIMID'S CATIONIC POLYELECTROLYTE "MAGNIFLOC 560C". 35 30 25 20 15 10 5 0 V 8 5 ^ ^-SUPERN/ TANT BOD , MG/L "90 "95 • 1 0 0 — — 110 \ '105***"*^ 0 0.5 1.0 1.5 2.0 2.5 DOSAGE OF HERCOFLOC 836.2 (MG/L) FIGURE 5- JAR TEST SUPERNATANT BOD AS A FUNCTION OF DOSAGE OF FERRIC CHLORIDE AND HERCULES INCORPORATED'S ANIONIC POLYELECTROLYTE "HERCOFLOC 836.2". TABLE I BOD 5 AND COD REMOVAL EFFICIENCIES ACHIEVED IN SETTLING COLUMN TESTS* February 11, 1971 Raw Sewage, mg/l Supernatant, mg/l % Removal No Coagulants 6 mg/l H e r c o f l o c 812 BODc 178 125 30 COD 390 260 33 BODt 152 70 54 COD 330 160 52 A p r i l 27, 1971 Raw Sewage, mg/l Supernatant, mg/l % Removal 30 mg/l F e C l 3 and 1 mg/l H e r c o f l o c 8 36.2 BOD,, COD 126 50 60 358 159 56 14 mg/l H e r c o f l o c 814.2 BODt 138 63 54 COD 374 175 53 June 16, 1971 Raw Sewage, mg/l Supernatant, mg/l % Removal No Coagulants BODr- COD 180 128 29 551 322 42 3 0 mg/l F e C l 3 and 1 mg/l H e r c o f l o c 836.2 BODc 180 49 73 COD 551 170 69 14 mg/l H e r c o f l o c 814.2 BODc 180 89 51 COD 551 224 59 * 15-minutes sedimentation to 26 3.2 Problems w i t h A i r M i x i n g of Polymers and Sewage i n S e t t l i n g Columns Large t e n a c i o u s f l o e s formed almost immediately when com-pressed a i r was used to p r o v i d e mixing o f raw sewage and 14 mg/l of H e r e o f l o c 814.2 i n the s e t t l i n g columns. A i r bubbles trapped i n the f l o e s caused them to r i s e , whereas i n o r g a n i c " g r i t " s e t t l e d . Only by s t i r r i n g the s u r f a c e i n a manner which c r e a t e d c o n s i d e r a b l e t u r b u l e n c e c o u l d the f l o e s be broken up s u f f i c i e n t l y t o a l l o w the trapped a i r t o escape and the f l o e s t o s e t t l e . T h i s o b s e r v a t i o n suggested a p o s s i b l e means o f s e p a r a t i n g o r g a n i c s from g r i t i n a p h y s i c a l - c h e m i c a l p l a n t u s i n g polymers. E l i m i n a t i o n of the c o n v e n t i o n a l s e d i m e n t a t i o n b a s i n may be p o s s i b l e by u s i n g a s i n g l e a e r a t e d b a s i n to achieve f l o t a t i o n o f o r g a n i c s and sedimentation o f g r i t . However f u r t h e r sludge dewatering may be r e q u i r e d to o b t a i n s o l i d s c o n c e n t r a t i o n s comparable t o those achieved u s i n g c o n v e n t i o n a l s e d i m e n t a t i o n b a s i n s , and the trapped a i r may p r e c l u d e anaerobic d i g e s t i o n , u n l e s s removed. 3.3 F i l t e r a b i l i t y o f D i g e s t e d Sludges E f f l u e n t from the d i g e s t e r c o n t a i n i n g l a r g e amounts of the c a t i o n i c polymer, H e r e o f l o c 814.2, p r e c i p i t a t e d more r a p i d l y than e f f l u e n t from the o t h e r two d i g e s t e r s . I t was hypothe-sized, t h e r e f o r e , t h a t the polymer s t i l l r e t a i n e d some p r o p e r t i e s as a coagulant a f t e r d i g e s t i o n . These o b s e r v a t i o n s l e d to an 27 i n v e s t i g a t i o n o f t h e f i l t e r a b i l i t y o f t h e d i g e s t e d s l u d g e s u s i n g t h e Buchner f u n n e l vacuum f i l t r a t i o n t e s t . R e s u l t s o f t h e Buchner f u n n e l f i l t r a t i o n t e s t s a r e p r e s e n -t e d i n T a b l e I I . TABLE II VALUES OF SPECIFIC RESISTANCE IN S E C 2 / G OBTAINED FROM BUCHNER FUNNEL VACUUM FILTRATION TESTS ON DIGESTED SLUDGES C o a g u l a n t ( s ) D i g e s t e r C o n t a i n e d Vacuum i n mm Hg Number i n Sludge 375 500 625 1 None 3 0 0 0 x l 0 7 2 7 0 0 x l 0 7 3 2 0 0 x l 0 7 2 H e r c o f l o c 814.2 1 6 5 x l 0 7 1 8 0 x l 0 7 2 0 5 x l 0 7 ( c a t i o n i c polymer) 3 F e C l 3 and 2 6 0 0 x l 0 7 2 7 5 0 x l 0 7 2 9 5 0 x l 0 7 H e r c o f l o c 836.2 ( a n i o n i c polymer) These r e s u l t s c l e a r l y i n d i c a t e d t h a t c a t i o n i c H e r c o f l o c 814.2 i n d i g e s t e r No. 2 r e t a i n e d some v a l u e as an a i d t o s l u d g e d e w a t e r i n g t h r o u g h o u t d i g e s t i o n , whereas the F e C l ^ and a n i o n i c polymer i n d i g e s t e r No. 3 had n o t . V a r i o u s a u t h o r s have p u b l i s h e d v a l u e s o f s p e c i f i c r e s i s -t a n c e f o r d o m e s t i c s l u d g e . Some o f t h e s e v a l u e s a r e : BOLTON AND KELIN [8] - D i g e s t e d 1 4 2 0 x l 0 7 s e c 2 / g 7 2 - D i g e s t e d and c o a g u l a t e d 24x10 sec / g - Maximum f o r s a t i s f a c t o r y vacuum f i l t r a t i o n 40x10 sec / g 28 ECKENFELDER [4] - D i g e s t e d c o n d i t i o n e d METC/ALF AND EDDY [9] - D i g e s t e d - D i g e s t e d and c o a g u l a t e d RICH [7] - D i g e s t e d (?) As e x p e c t e d , t h e t e s t v a l u e s o f s p e c i f i c r e s i s t a n c e from t h e c o n t r o l d i g e s t e r were h i g h e r t h a n p u b l i s h e d v a l u e s because t h e d i g e s t e d " s l u d g e s " t e s t e d were t h e mixed c o n t e n t s o f the d i g e s t e r s r a t h e r than t h e s e t t l e d o r e l u t r i a t e d s l u d g e s w h i c h would n o r m a l l y be dewatered by vacuum f i l t r a t i o n , and t h u s c o n t a i n e d excess c o l l o i d a l m a t t e r w h i c h h i n d e r s f i l t r a t i o n . A l t h o u g h t h e r e s u l t s a r e i n c o n c l u s i v e , t h e y i n d i c a t e t h a t a s e t t l e d s l u d g e from d i g e s t e r No. 2 c o u l d be s u c c e s s f u l l y dewatered by vacuum f i l t r a t i o n w i t h l i t t l e o r no a d d i t i o n a l c o n d i t i o n i n g . 1 0 . 5 x l 0 7 s e c 2 / g 1 0 0 - 6 0 0 x l 0 7 s e c 2 / g 3-4 0 x l 0 7 s e c 2 / g 9 0 0 x l 0 ^ ° s e c 2 / l b . mass (2000xl0 7 s e c V g ) CHAPTER IV RESULTS - ANAEROBIC DIGESTION 4.1 General In the ensuing d i s c u s s i o n s of the e f f e c t s on anaerobic d i g -e s t i o n , the d i g e s t e r s have been numbered f o r convenience. D i g e s t e r number one was the c o n t r o l d i g e s t e r and r e c e i v e d sludge o b t a i n e d by s e d i m e n t a t i o n without the use o f c o a g u l a n t s ; d i g e s t e r number two r e c e i v e d sludge o b t a i n e d u s i n g 14 mg/l o f H e r c o f l o c 814.2 as the coagulant; and d i g e s t e r number t h r e e r e c e i v e d sludge o b t a i n e d u s i n g 30 mg/l o f f e r r i c c h l o r i d e as the primary coagulant and 1 mg/l of H e r c o f l o c 836.2 as the coagulant a i d . The i n f l u e n t or raw sludges and the e f f l u e n t or d i g e s t e d sludges are g i v e n c o r r e s p o n d i n g numbers. The d i g e s t i o n parameters measured were d i s c u s s e d p r e -v i o u s l y . T a b u l a t e d r e s u l t s of the t e s t s performed are i n Appendix B. 4.2 Problems During D i g e s t e r S t a r t - u p The l a b o r a t o r y d i g e s t e r s were put i n t o o p e r a t i o n on September 8, 1970 and f i l l e d t o t h e i r working c a p a c i t y o f 7.5.1 w i t h d i g e s t e d sludge o b t a i n e d from the L i o n s Gate sewage t r e a t -ment p l a n t i n West Vancouver, B r i t i s h Columbia. On September 9, 1970, the f i r s t " f e e d i n g " o f 250 ml o f raw sludge from the same p l a n t was added to each d i g e s t e r . A d d i t i o n o f sludge c o n t i n u e d a t the r a t e o f 250 ml per day. By September 14, the pH o f the d i g e s t e r s had dropped t o 6.6 from 7.1 i n i t i a l l y . One day l a t e r , d i g e s t e r pH v a l u e s dropped t o a range o f 6.3 t o 6.4 and f u r t h e r a d d i t i o n o f sludge was h a l t e d . By September 28, w i t h no f u r t h e r a d d i t i o n s o f sludge, the pH v a l u e s had dropped f u r t h e r t o l e s s than 6.2. At t h i s p o i n t an a d d i t i o n a l 3 l i t e r s o f d i g e s t e d sludge was added t o each d i g e s t e r , and 3 l i t e r s o f the c o n t e n t s were removed. T h i s r a i s e d the pH of each d i g e s t e r to the 6.4 to 6.5 range. By October 5 t h e r e was no improvement i n the d i g e s t e r pH v a l u e s , even though no a d d i t i o n a l raw sludge had been added. I t was d e c i d e d , t h e r e f o r e , t o add lime t o the d i g e s t e r s to b r i n g the pH up to a f a v o r a b l e l e v e l f o r the methane b a c t e r i a . Lime was added t o d i g e s t e d sludge from the L i o n s Gate sewage t r e a t -ment p l a n t . T h i s mixture, when added to the l a b o r a t o r y d i g e s -t e r s a t the r a t e of 50 ml per day, added lime a t the r a t e of one pound o f c a l c i u m hydroxide per day per thousand c u b i c f e e t of d i g e s t e r c a p a c i t y . T h i s s l u d g e - l i m e mixture was added to each d i g e s t e r a t a r a t e o f 50 ml per day f o r f o u r days, r a i s i n g the pH o f the d i g e s t e r s t o the 6.6 t o 6.7 range by October 8. On October 17 the v o l a t i l e a c i d c o n t e n t o f the d i g e s t e r s was i n the range o f 500 t o 900 mg/l as a c e t i c . Because o f these hi g h v a l u e s , the f e e d i n g was reduced i n i t i a l l y t o 50 ml o f raw sludge per day, then g r a d u a l l y i n c r e a s e d . The d e s i r e d r a t e o f 25 0 ml per day was reached on November 12. The pH o f a l l t h r e e d i g e s t e r s was 6.9 on t h i s date. 31 The d i g e s t e r s operated w e l l a t the d e s i r e d r a t e of sludge a d d i t i o n f o r one week. During the n i g h t of November 18-19, however, the temperature c o n t r o l s on one d i g e s t e r m a l f u n c t i o n e d . On the morning of November 19, the temperature o f the d i g e s t e r was 35°C. A n e g a t i v e p r e s s u r e i n the d i g e s t e r i n d i c a t e d t h a t gas p r o d u c t i o n had f a l l e n o f f and t h a t the temperature was c o n t i n u i n g t o f a l l . When gas p r o d u c t i o n f a i l e d to r e t u r n to normal, sludge was exchanged between the h e a l t h y d i g e s t e r s and the upset one. Raw sludge a d d i t i o n to the upset d i g e s t e r was reduced f o r the next few days. In s p i t e of t h i s , the v o l a t i l e a c i d s content o f t h i s d i g e s t e r was 44 0 mg/l as a c e t i c on November 24 compared to 4 0 and 13 0 mg/l i n the o t h e r two. The pH was 6.8 on t h i s date, compared t o 6.9 f o r the other two d i g e s t e r s . The raw sludge a d d i t i o n r a t e o f 2 50 ml per day was resumed on November 25, 197 0 f o r a l l t h r e e d i g e s t e r s and no f u r t h e r problems o c c u r r e d u n t i l March 29, 1971 when the pH of a l l t h r e e d i g e s t e r s began t o f a l l . On March 31 the pH had dropped 0.2-0.3 u n i t s to v a l u e s of 6.6-6.7. T h e r e f o r e , raw sludge a d d i t i o n was d i s c o n t i n u e d f o r f o u r days. By A p r i l 5 the pH of a l l d i g e s t e r s was back t o 6.8 and sludge a d d i t i o n was resumed. No more problems were encountered and a d d i t i o n of the experimental sludge began on A p r i l 29. 4.3 R e s u l t s o f L o n g - T e r m BOD T e s t s o f Raw and D i g e s t e d S l u d g e s L o n g - t e r m BOD t e s t s were p e r f o r m e d on raw and d i g e s t e d s l u d g e s t o d e t e r m i n e the r a t i o o f BODg t o BOD^ i n o r d e r t h a t t h e removal o f BOD L by d i g e s t i o n c o u l d be e v a l u a t e d . The c l a s s i c f o r m u l a t i o n o f the BOD c u r v e i s a c o n t i n u o u s f i r s t o r d e r r e a c t i o n o f t h e form y = L Q (1 - e " K t ) . . . (1) where y i s t h e amount o f oxygen consumed o r BOD a f t e r any t ime t , L„ i s t h e u l t i m a t e c a r b o n a c e o u s BOD o r t h e t o t a l o amount o f oxygen consumed i n t h e r e a c t i o n , K i s t h e average r e a c t i o n - r a t e c o n s t a n t , e i s t h e base o f n a t u r a l l o g a r i t h m s , and t i s t ime o f i n c u b a t i o n i n d a y s . The BOD e x e r t e d by many complex w a s t e s , i n c l u d i n g d o m e s t i c sewage, conforms c l o s e l y t o t h i s e q u a t i o n . The t h r e e common methods o f d e t e r m i n i n g the v a l u e s o f L Q and K, t h e method o f moments, t h e l o g - d i f f e r e n c e method, and t h e g r a p h i c a l method, have been d e s c r i b e d by E c k e n f e l d e r [ 4 ] . A l l t h r e e methods were used and p r o d u c e d c o n s i s t e n t r e s u l t s f o r t h e raw s l u d g e s t e s t e d . A t t e m p t s t o use these methods f o r t h e d i g e s t e d s l u d g e s were u n s u c c e s s f u l , and i t i s b e l i e v e d t h a t t h e BOD e x e r t e d by d i g e s t e d s l u d g e cannot be f o r m u l a t e d by a f i r s t - o r d e r r e a c t i o n 33 curve. The BOD curves f o r the d i g e s t e d sludges were "eye-b a l l e d " , t h e r e f o r e , and the v a l u e s f o r L Q (BOD^) a r e based on j udgment. The p l o t t e d long-term BOD curves are presented i n Appendix C. The v a l u e s o f K and L are shown i n T a b l e I I I . o TABLE I I I RESULTS OF LONG-TERM, 2 0°C, BOD TESTS ON RAW AND DIGESTED SLUDGES Raw Sludges •1 2 3 K - l (day. i ) 0.31 0.44 0.36 L_ (BODT ) ° ( g / D L 10.5 13.2 12.2 BOD^ (g/i 5) 8.3 11.7 10.2 BOD L/ BOD, 1.27 1.12 1.20 Dige s t e d Sludges 1 NA 2 NA 3 NA 3.4 3.7 3.6 1.45 2 .30 1. 95 2.34 1. 61 1.85 NA - not a p p l i c a b l e , f i r s t o r d e r r e a c t i o n curve d i d not f i t d a t a . 4.4 S t a b i l i z a t i o n o f Organics C a l c u l a t e d from BOD, COD and V o l a t i l e S o l i d s R e s u l t s  The removal o f o r g a n i c s from the d i g e s t e r s i s achieved b i o l o g i c a l l y by c o n v e r s i o n t o more s t a b l e substances and gases, and p h y s i c a l l y d u r i n g withdrawal o f sludge. The purpose of t h i s study was to determine the e f f e c t s o f chemicals on b i o -l o g i c a l removal, thereby r e q u i r i n g the c a l c u l a t i o n o f p h y s i c a l removal t o account f o r i t i n the removal e f f i c i e n c y c a l c u l a t i o n s . 34 In a system which i s c o m p l e t e l y m i x e d , when s l u d g e a d d i t i o n and w i t h d r a w a l a re c o n t i n u o u s , and when i n f l u e n t s l u d g e s t r e n g t h i s c o n s t a n t , t h e c o n c e n t r a t i o n o f v o l a t i l e s o l i d s , BOD o r COD a t any t i m e assuming p h y s i c a l removal o n l y , can be d e t e r m i n e d f rom t h e f o l l o w i n g e q u a t i o n (see A p p e n d i x D ) : C = C e " K 2 t + ^ C r (1 - e " K 2 t ) . . . (2) o K 2 r where C i s t h e v o l a t i l e s o l i d s , BOD o r COD c o n c e n t r a t i o n i n t h e system a t any t i m e , C i s t h e i n i t i a l c o n c e n t r a t i o n i n the system a t o t i m e z e r o , C r i s t h e c o n c e n t r a t i o n i n the raw s l u d g e b e i n g a d d e d , e i s the base o f n a t u r a l l o g a r i t h m s , i s a r a t e c o n s t a n t e q u a l to the volume o f raw s l u d g e added p e r u n i t o f t i m e d i v i d e d by t h e volume i n the s y s t e m , K2 i s a r a t e c o n s t a n t e q u a l t o t h e volume o f d i g e s t e d s l u d g e removed per u n i t o f t ime d i v i d e d by t h e volume i n t h e . s y s t e m , and t i s t i m e . The c o n c e n t r a t i o n o f t h e raw s l u d g e added t o t h e d i g e s t e r s was n o t c o n s t a n t t h r o u g h o u t the l i f e o f t h e p r o j e c t but i t was n e a r l y c o n s t a n t f o r s e v e r a l days a t a t i m e . In a d d i t i o n , s l u d g e was not added and withdrawn c o n t i n u o u s l y but o c c u r r e d d u r i n g a few m i n u t e s o f each d a y . 3 5 The f i r s t p r o b l e m was overcome by u s i n g a s e q u e n t i a l c a l -c u l a t i o n . A c a l c u l a t i o n was made f o r each d i f f e r e n t s l u d g e u s i n g t h e " C " v a l u e o b t a i n e d f rom t h e p r e c e d i n g c a l c u l a t i o n as the " C 11 v a l u e i n t h e new c a l c u l a t i o n . The p r o b l e m o f a d d i t i o n and w i t h d r a w a l d u r i n g a -few m i n u t e s o f each day does n o t i n v a l i d a t e e q u a t i o n 2, as a d d i t i o n and w i t h d r a w a l o f s l u d g e o c c u r r e d s i m u l t a n e o u s l y w h i l e t h e system was t h o r o u g h l y m i x e d . A t ime u n i t o f one day was u s e d . The c a l c u l a t e d " C " v a l u e a t any t i m e t h e r e f o r e r e p r e s e n t s t h e t h e o r e t i c a l c o n c e n t r a t i o n ( v o l a t i l e s o l i d s , BOD, COD) i n t h e d i g e s t e r a t t h a t t ime assuming o n l y p h y s i c a l r e m o v a l . The v a l u e s o f t h e c o n s t a n t s and depend on t h e r a t e o f s l u d g e a d d i t i o n and r e m o v a l . Raw s l u d g e was added a t the r a t e o f 2 50 ml p e r day t o a d i g e s t e r volume o f 7.5 l i t e r s . The v a l u e o f K ^ , t h e r e f o r e , was 0.0333 p e r d a y . In o r d e r t o m a i n t a i n a c o n s t a n t volume o f 7.5 1 i n the d i g e s t e r s , i t was n e c e s s a r y t o remove l e s s t h a n 250 ml per day from each d i g e s t e r t o a c c o u n t f o r l o s s e s , m a i n l y e v a p o r a t i o n . The average r a t e o f s l u d g e removal was 243 ml p e r day from each d i g e s t e r . The v a l u e o f t h e r e f o r e was 0.0324 p e r d a y . I n f l u e n t and e f f l u e n t v o l a t i l e s o l i d s , BOD and COD r e s u l t s have been used i n c o n j u n c t i o n w i t h e q u a t i o n 2 t o c a l c u l a t e t h e e f f i c i e n c y o f removal o f o r g a n i c s by t h e a n a e r o b i c p r o c e s s . The r e s u l t s a r e p r e s e n t e d i n T a b l e I V . A sample c a l c u l a t i o n i s i n c l u d e d as A p p e n d i x D. TABLE IV EFFICIENCY OF STABILIZATION OF SLUDGE ORGANICS CALCULATED FROM INFLUENT AND EFFLUENT BOD, COD AND VS RESULTS V o l a t i l e S o l i d s (g/1) BOD 5(g/l) BOD L(g/l) COD (g/1) D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. June 11, 1971 Organic Loading by C a l c u l a t i o n Organics i n D i g e s t e r E f f l u e n t E f f i c i e n c y o f Removal by B a c t e r i a , % June 28, 1971 Organic Loading by C a l c u l a t i o n O rganics i n D i g e s t e r E f f l u e n t E f f i c i e n c y o f Removal by B a c t e r i a , % J u l y 4, 1971 Organic Loading by C a l c u l a t i o n Organics i n D i g e s t e r E f f l u e n t E f f i c i e n c y o f Removal by B a c t e r i a , % Average E f f i c i e n c y , % 1 2 3 1 2 3 1 2 3 1 2 3 27.0 26.6 27.0 8.35 10.7 9.97 10.7 12.0 11.9 45.6 49.7 48.8 10.8 11.2 10.3 1.55 1.77 1.55 3.6 2.8 2.9 17.6 19.7 17.5 60 58 62 81 83 84 66 77 76 61 60 64 26.5 26.1 26.6 8. 03 11.2 9.85 10.3 12.6 11.7 45.7 50.4 48.9 10.7 11.1 11.2 1.85 2.08 2.16 4.3 3.3 4.0 17.3 18.8 18.5 60 57 58 77 81 78 58 74 66 62 63 62 26.3 26.2 26.6 8.04 11.4 9.98 10.3 12.8 11.9 45.7 50.6 49.2 10.3 11.3 10.8 1.45 2.30 1. 95 3.4 3.7 3.6 17.1 19. 9 18.4 61 57 59 82 80 80 67 71 70 63 61 63 60 57 60 80 81 81 64 74 71 62 61 63 These r e s u l t s do n o t show any s i g n i f i c a n t d i f f e r e n c e i n the waste s t a b i l i z a t i o n a c h i e v e d by m i c r o b i a l a c t i o n i n t h e t h r e e d i g e s t e r s - A l t h o u g h a g r e a t e r r e m o v a l o f u l t i m a t e carbonaceous BOD i n t h e d i g e s t e r s r e c e i v i n g c h e m i c a l s l u d g e s i s i n d i c a t e d , t h i s parameter i s t h e l e a s t r e l i a b l e o f t h e f o u r because o f t h e d i f f i c u l t i e s e x p e r i e n c e d i n d e t e r m i n i n g BODT f o r t h e d i g e s t e d s l u d g e s . I t i s s i g n i f i c a n t a l s o t h a t t h e l o n g - t e r m BOD t e s t s were r u n on e f f l u e n t s l u d g e s o b t a i n e d on J u l y 4 and on the raw s l u d g e s used d u r i n g the p e r i o d o f June 18 t o J u l y 4. The r e s u l t s f o r J u l y 4, t h e r e f o r e , a r e c o n s i d e r e d t o be the most r e p r e -s e n t a t i v e o f t h e t r u e s t a b i l i z a t i o n o f BOD_. These r e s u l t s a r e i n c l o s e agreement w i t h i n t h e a c c u r a c y o f t h e e x p e r i m e n t a l methods and add f u r t h e r c r e d e n c e t o t h e c o n c l u s i o n t h a t t h e r e was no s i g n i f i c a n t d i f f e r e n c e i n t h e waste s t a b i l i z a t i o n a c h i e v e d by m i c r o b i a l a c t i o n i n t h e t h r e e d i g e s t e r s as e v i d e n c e d by t h e r e s u l t s f o r BOD^, v o l a t i l e s o l i d s , and COD. These r e s u l t s a l s o i n d i c a t e t h a t the c o a g u l a n t s used were not t o x i c and d i d not p h y s i c a l l y i n t e r f e r e w i t h t h e a b i l i t y o f t h e m i c r o - o r g a n i s m s t o p e n e t r a t e t h e f l o e s formed d u r i n g s e d i -m e n t a t i o n . 4 .5 S t a b i l i z a t i o n o f O r g a n i c s C a l c u l a t e d from Methane P r o d u c t i o n M c C a r t y [10] has shown s t o i c h i o m e t r i c a l l y t h a t 5.62 c u b i c f e e t o f methane a t s t a n d a r d t e m p e r a t u r e and. p r e s s u r e (STP) are p r o d u c e d p e r pound o f BODT ( u l t i m a t e carbonaceous BOD) or COD 38 s t a b i l i z e d (0.351 1/g). Thus, methane p r o d u c t i o n serves as a measure of the e f f i c i e n c y o f the s t a b i l i z a t i o n o f o r g a n i c s . E f f i c i e n c y i s c a l c u l a t e d a c c o r d i n g to the e q u a t i o n : where S i s the percentage o f added BOD or COD L i which i s s t a b i l i z e d , C i s l i t e r s o f methane produced per day, (STP), and F i s grams of B0D_ o r COD added per day. L i T o t a l gas p r o d u c t i o n was a l s o c o n s i d e r e d f o r use as an i n d i c a t o r o f d i g e s t e r e f f i c i e n c y but was r e j e c t e d . V a r i o u s authors [2,4,9] r e p o r t t h a t gas p r o d u c t i o n f o r a w e l l - o p e r a t i n g d i g e s t i o n tank i s 12 to 22 c u b i c f e e t per pound of VS d e s t r o y e d (0.75 to 1.37 1/g). T h i s wide range of r e p o r t e d v a l u e s renders t o t a l gas p r o d u c t i o n i m p r a c t i c a l as a measure of VS s t a b i l i -z a t i o n . When the s t r e n g t h and amount of the waste added to a d i g e s -t e r v a r i e s , as i t d i d i n t h i s study, a problem a r i s e s i n attempting to determine the percentage o f o r g a n i c s s t a b i l i z e d from the methane produced. Gas p r o d u c t i o n and composition on a p a r t i c u l a r day i s i n f l u e n c e d to a c o n s i d e r a b l e extent by the waste added w i t h i n a few days p r i o r t o gas measurement but both c o m p o s i t i o n and amount o f gas produced a l s o r e f l e c t t o some ex t e n t the s t r e n g t h and amount of raw sludge added weeks p r i o r to measurement and a n a l y s i s . Only a v e r y d e t a i l e d , c o m p l icated and t i m e - c o n s u m i n g e x p e r i m e n t c o u l d s o r t out the r e l a t i v e c o n -t r i b u t i o n s from t h e s l u d g e s added a t v a r i o u s t i m e s . F o r t h e p u r p o s e o f e s t i m a t i n g e f f i c i e n c y o f s t a b i l i z a t i o n o f o r g a n i c s , t h e o r g a n i c s t r e n g t h o f t h e s l u d g e added on the day t h e gas p r o d u c t i o n was m o n i t o r e d and c o m p o s i t i o n a n a l y z e d was assumed t o a c c o u n t f o r t o t a l methane p r o d u c t i o n f o r the d a y . E s t i m a t e s o f waste s t a b i l i z a t i o n based on methane p r o d u c -t i o n a r e p r e s e n t e d i n T a b l e V . The f o l l o w i n g o b s e r v a t i o n s are based on t h e s e r e s u l t s . 1 . The v a l u e s o f u l t i m a t e carbonaceous BOD removed f a r exceed 1 0 0 % s u g g e s t i n g t h a t the a e r o b i c BOD t e s t p r o v i d e s a poor measure o f t h e b i o d e g r a d a -b i l i t y a n a e r o b i c a l l y o f d o m e s t i c wastewater s l u d g e . A l t h o u g h t h e v a l i d i t y o f t h e s t o i c h i o m e t r i c a l l y d e t e r m i n e d r a t i o o f methane p r o d u c e d t o COD o r BOD L d e s t r o y e d can be q u e s t i o n e d , i t s v a l i d i t y has r e p o r t e d l y been shown t o be c o r r e c t f o r "a wide v a r i e t y o f wastes v a r y i n g f rom pure l a b o r a -t o r y s u b s t r a t e s t o complex waste s l u d g e " [ 1 0 ] . I t can be c o n c l u d e d , t h e r e f o r e , . tha t d o m e s t i c s l u d g e c o n t a i n s l a r g e q u a n t i t i e s o f o r g a n i c s u b -s t a n c e s w h i c h a r e b i o d e g r a d a b l e a n a e r o b i c a l l y d u r i n g c o n v e n t i o n a l d i g e s t e r d e t e n t i o n t i m e s , but w h i c h r e q u i r e l o n g e r p e r i o d s o f t ime o r a r e not s t a b i l i z e d a t a l l a e r o b i c a l l y . C e l l u l o s e i s such a s u b s t a n c e . TABLE V ESTIMATES OF EFFICIENCY OF STABILIZATION OF SLUDGE ORGANICS FROM METHANE PRODUCTION Reduction Methane i n Oxygen Gas Pro- Produc- Demand d u c t i o n Percent t i o n @ from COD BOD L @ STP*, Methane STP*, Methane Added, Added, Pe r c e n t Percei P e r i o d o f D i g e s t e r L i t e r s / by L i t e r s / Produced, Grams/ Grams/ COD BOD L O p e r a t i o n Number day Volume day Grams/day day day Reduced Redud June 4 1 3.94 58.2 2.2 9 6. 54 11.4 1. 99 57 330 to 2 4.04 63.6 2.57 7.33 12.5 3.00 59 240 June 17 3 3.81 62.2 2.37 6.75 11.2 2.30 60 290 June 18 1 3.38 59.2 2.00 5.70 11.0 2.49 52 230 to 2 3. 62 63.4 2.30 6.55 12.5 3.36 52 195 J u l y 4 3 3.21 62.9 2.02 5.76 12.2 3.07 47 190 *Standard temperature and p r e s s u r e o 41 2. No p a r t i c u l a r s i g n i f i c a n c e i s a t t a c h e d to the lower e f f i c i e n c i e s o b t a i n e d f o r the p e r i o d o f June 18-J u l y 4 than f o r the p e r i o d of June 4-17. One pos-s i b l e e x p l a n a t i o n f o r t h i s i s t h a t the sludges used d u r i n g the l a t t e r p e r i o d c o n t a i n e d a g r e a t e r r a t i o of o r g a n i c compounds which were slow t o degrade a n a e r o b i c a l l y , r e s u l t i n g from d i f f e r e n c e s i n the domestic sewage on the days the sludges were o b t a i n e d . 3. The d i f f e r e n c e s i n r e l a t i v e v a l u e s of waste s t a b i -l i z a t i o n parameters f o r the t hree d i g e s t e r s based on methane p r o d u c t i o n are not s i g n i f i c a n t . There-f o r e , n e i t h e r t o x i c i t y of c o a g u l a n t s nor p h y s i c a l i n a b i l i t y of micro-organisms to p e n e t r a t e the f l o c c u l a t e d p a r t i c l e s added to the d i g e s t e r s i s i n d i c a t e d . 4.6 Comparison o f R e s u l t s Obtained f o r Waste S t a b i l i z a t i o n by the Two Methods * A comparison o f o r g a n i c s t a b i l i z a t i o n e f f i c i e n c i e s c a l c u -l a t e d d i r e c t l y from i n f l u e n t and e f f l u e n t r e s u l t s and i n d i r e c t l y from methane p r o d u c t i o n i s p resented i n Table VI. The f o l l o w i n g a d d i t i o n a l comments are based on these r e s u l t s . 1. The r e s u l t s o b t a i n e d by d i r e c t c a l c u l a t i o n u s i n g i n f l u e n t and e f f l u e n t waste s t r e n g t h parameters are more r e l i a b l e . The problem w i t h c a l c u l a t i n g s t a b i l i z a t i o n e f f i c i e n c y from gas measurements, TABLE V I COMPARISON OF THE EFFICIENCY CALCULATED DIRECTLY FROM AND INDIRECTLY FROM OF STABILIZATION OF ORGANICS BOD, COD AND VS RESULTS METHANE PRODUCTION Date D i g e s t e r No. From Methane P r o d u c t i o n BOD, COD V S From C a l c u l a t i o n s BOD, BOD, COD June 4 t o June 17 1 2 3 330 240 290 57 59 60 60 58 62 81 83 84 66 77 76 61 60 64 June 18 to J u l y 4 1 2 3 230 195 190 52 52 47 60 57 58 80 80 79 62 72 68 62 62 62 t o 43 under t h e t e s t c o n d i t i o n s o f v a r y i n g i n f l u e n t s t r e n g t h , was t h e p r e v i o u s l y ment ioned d i f f i -c u l t y o f a s s i g n i n g r e p r e s e n t a t i v e BOD and COD v a l u e s t o t h e raw s l u d g e c o n t r i b u t i n g t o gas p r o d u c t i o n on any p a r t i c u l a r d a y . 2 . Comparisons o f BOD L and COD r e s u l t s i n d i c a t e t h a t COD i s a r e a s o n a b l y a c c u r a t e parameter f o r t h e d e t e r m i n a t i o n o f oxygen demand s a t i s -f i e d by a n a e r o b i c d i g e s t i o n . The a e r o b i c BOD t e s t c l e a r l y u n d e r e s t i m a t e d the oxygen demand o f t h e raw d o m e s t i c s l u d g e s used i n t h e e x p e r i -m e n t a l p r o g r a m . 4 . 7 S i g n i f i c a n c e o f Other D i g e s t i o n Parameters M o n i t o r e d  The r e s u l t s o f d e t e r m i n a t i o n s o f p H , a l k a l i n i t y , v o l a t i l e a c i d s , and CO2 c o n t e n t o f d i g e s t e r gas (Appendix B) d u r i n g t h e a d d i t i o n o f t h e t e s t s s l u d g e s a l l f a l l w i t h i n t h e l i m i t s f o r normal a n a e r o b i c t r e a t m e n t as i n d i c a t e d by M c C a r t y [ 1 0 ] . None o f t h e s e parameters i n d i c a t e d u n b a l a n c e d t r e a t m e n t . R e s u l t s o f d i g e s t e r pH and CH^ c o n t e n t o f d i g e s t e r gas a r e p l o t t e d on F i g u r e 6 and 7 . Throughout the t e s t p e r i o d d i g e s t e r No. 2 c o n s i s t e n t l y r e g i s t e r e d t h e h i g h e s t v a l u e s o f p H , a l k a -l i n i t y , and methane c o n t e n t o f g a s . No. 2 was f o l l o w e d c l o s e l y by No. 3 , and No. l , t h e c o n t r o l d i g e s t e r , c o n s i s t e n t l y r e g i s -t e r e d t h e l o w e s t v a l u e s f o r t h e s e p a r a m e t e r s . APRIL MAY JUNE PERCENTAGE METHANE BY VOLUME F I G U R E 7 - M E T H A N E C O N T E N T O F D I G E S T E R G A S E S 46 These r e s u l t s i n d i c a t e b e t t e r o p e r a t i n g c o n d i t i o n s f o r the d i g e s t e r s r e c e i v i n g c h e m i c a l l y c o a g u l a t e d sludge. The h i g h e r v a l u e s o f a l k a l i n i t y s i g n i f y a g r e a t e r b u f f e r i n g c a p a c i t y a g a i n s t a temporary d i g e s t e r imbalance due to changes i n the nature of the waste or o r g a n i c l o a d i n g . The h i g h e r methane content of the gas from No. 2 and No. 3 d i g e s t e r s i s important i n sewage treatment because o f the c a l o -r i f i c v a l u e o f methane. The t o t a l i r o n content of the raw sludges averaged 13 0 mg/l f o r sludge No. 1, 110 mg/l f o r sludge No. 2 and 630 mg/l f o r sludge No. 3. The maximum v a l u e o f t o t a l i r o n i n the e f f l u e n t from No. 3 d i g e s t e r was 500 mg/l. There was no apparent i m p a i r -ment of d i g e s t i o n e f f i c i e n c y as a r e s u l t o f t h i s i r o n concen-t r a t i o n nor, a p p a r e n t l y , d i d f e r r i c c h l o r i d e a c t s y n e r g i s t i c a l l y wi'th the a n i o n i c polymer t o c r e a t e t o x i c i t y . CHAPTER V ECONOMICS OF CHEMICAL TREATMENT As d i s c u s s e d i n C h a p t e r I , t h e r e a r e a number o f i n s t a n c e s i n w h i c h c h e m i c a l t r e a t m e n t o f sewage may be b e n e f i c i a l . U s u a l l y t h e c h o i c e o f t r e a t m e n t p r o c e s s e s i s governed by economic c o n -s i d e r a t i o n s , but i n two c a s e s , s p e c i f i c a l l y t h e use o f c o a g u -l a n t s t o a s s i s t an e x i s t i n g o v e r l o a d e d p l a n t o r when a waste c o n t a i n s components w h i c h a r e i n h i b i t o r y t o b i o l o g i c a l p r o c e s s e s , some form o f c h e m i c a l t r e a t m e n t may be mandatory t o meet e f f l u e n t r e q u i r e m e n t s . In a d d i t i o n , when t h e r e a r e s e a s o n a l v a r i a t i o n s i n the volume and s t r e n g t h o f sewage, when p l a i n s e d i m e n t a t i o n i s n o r m a l l y adequate but r e c e i v i n g water l i m i t a t i o n s a t t i m e s n e c e s s i t a t e b e t t e r t r e a t m e n t , o r when l a n d i s e x p e n s i v e , c h e m i -c a l c o a g u l a t i o n i n c o m b i n a t i o n w i t h p h y s i c a l t r e a t m e n t may be a p a r t i c u l a r l y a t t r a c t i v e a l t e r n a t i v e t o b i o l o g i c a l p r o c e s s e s . W h i l e i t i s r e c o g n i z e d t h a t p l a i n s e d i m e n t a t i o n a s s i s t e d by c h e m i c a l c o a g u l a t i o n cannot be e x p e c t e d t o a c h i e v e t h e BOD and s o l i d s removal e f f i c i e n c i e s o f b i o l o g i c a l t r e a t m e n t , the b a s i s o f c o s t c o m p a r i s o n s used h e r e i n i s t h e d i f f e r e n c e between t h e a m o r t i z e d c a p i t a l p l u s a n n u a l o p e r a t i o n and maintenance c o s t s f o r c o n v e n t i o n a l a c t i v a t e d s l u d g e v e r s u s p r i m a r y t r e a t m e n t . T h i s d i f f e r e n c e i s used to c a l c u l a t e t h e q u a n t i t i e s o f c o a g u -l a n t s and c o a g u l a n t a i d s w h i c h c o u l d e c o n o m i c a l l y be added b e f o r e i t becomes more e c o n o m i c a l to p r o v i d e b i o l o g i c a l t r e a t m e n t o f t h e s u p e r n a t a n t . C a p i t a l and o p e r a t i o n and maintenance c o s t s a r e e x t r a c t e d from a paper by Smith [11] and a r e r e p o r t e d to 47 48 i n c l u d e p r e l i m i n a r y expenses such as e n g i n e e r i n g and l e g a ' l f e e s , l a n d a c q u i s i t i o n , and i n t e r e s t d u r i n g c o n s t r u c t i o n , whereas a n c i l l a r y works such as i n t e r c e p t o r s , o u t f a l l s , o r pumping s t a t i o n s a r e e x c l u d e d . C o s t f i g u r e s p r e s e n t e d by Smith r e p r e s e n t J u n e , 1967 p r i c e s . C a p i t a l c o s t s have been a d j u s t e d to A u g u s t , 1975 p r i c e s u s i n g the U . S . E n v i r o n m e n t a l P r o t e c t i o n Agency Sewage Treatment P l a n t C o n s t r u c t i o n C o s t Index . T h i s i n d e x s t o o d a t 119.11 i n J u n e , 1967 and has been p r o j e c t e d t o 244 f o r A u g u s t , 1975 ( F i g u r e 8 ) . O p e r a t i o n and maintenance c o s t s r e f l e c t t h e wages p a i d to e m p l o y e e s , hence the U . S . Department o f Labour Average E a r n i n g s : f o r N o n s u p e r v i s o r y Workers i n Water , Steam and S a n i t a r y Systems was used t o a d j u s t a l l o p e r a t i n g and maintenance c o s t s t o t h e A u g u s t , 1975 l e v e l ( F i g u r e 9) [12] . The J u n e , 1967 v a l u e was $2.80 and t h e p r o j e c t e d A u g u s t , 1975 v a l u e i s $4 .94 . The updated c o s t e s t i m a t e s f o r p r i m a r y and f o r c o n v e n t i o n a l a c t i v a t e d s l u d g e t r e a t m e n t a re shown on F i g u r e 10. To b r i n g a l l c o s t s t o a common b a s e , c a p i t a l c o s t s were a m o r t i z e d o v e r a t w e n t y - f i v e y e a r p e r i o d a t t e n p e r c e n t i n t e r e s t and shown as d e b t s e r v i c e . O p e r a t i n g and maintenance c o s t s a re added t o d e b t s e r v i c e c o s t s t o o b t a i n t o t a l t r e a t m e n t c o s t s . F i g u r e 11 shows t h e economic dosages o f c a t i o n i c H e r c o f l o c 814.2 and o f f e r r i c c h l o r i d e used i n c o m b i n a t i o n w i t h 0.5 m g / l o f a n i o n i c H e r c o f l o c 836.2 v e r s u s d e s i g n c a p a c i t y . C o s t s used i n t h e a n a l y s i s were $0.40 per pound f o r anhydrous f e r r i c c h l o -r i d e , $1.4 0 p e r pound f o r t h e c a t i o n i c polymer and $1.2 0 per pound f o r the a n i o n i c p o l y m e r . Polymer c o s t s were s u p p l i e d by 4 9 O O O O O O O O O O O O CO CD ^ ( M O O O C O ^ t C M O r o c v i CM CM OJ CM —• — C O S T INDEX FIGURE 8-U.S. ENVIRONMENTAL PROTECTION AGENCY SEWAGE TREATMENT PLANT CONSTRUCTION COST INDEX. T 1 1 1 1 1 1 1 1 1 1 r o o o O O O O O O O O O O O o 00 CD st CM O CO CD st CM O CO CD st l 6 st st st st rO rd rd rd rd c\i cvi CO AVERAGE HOURLY EARNINGS IN DOLLARS FIGURE 9-U.S. DEPARTMENT OF LABOR - AVERAGE EARNINGS FOR NONSUPERVISORY WORKERS IN WATER, STEAM AND SANITARY SYSTEMS. 51 4 0 0 4 0 3 0 2 0 10 8 6 4 3 0.8 0 .6 0 . 4 0 .3 0 .2 \-co o o < Q_ o 8 10 2 0 3 0 4 0 C A P A C I T Y , M G D 0 . 100 I 2 3 4 6 D E S I G N C= C A P I T A L C O S T , $ M I L . A= D E B T S E R V I C E , IOOO G A L . ( I O % - 2 5 Y E A R S ) O & M - O P E R A T I N G A N D M A I N T E N A N C E C O S T , <t / IOOO G A L . T= T O T A L T R E A T M E N T C O S T , <t / IOOO G A L . P.T.= P R I M A R Y T R E A T M E N T A.S,T.= A C T I V A T E D S L U D G E T R E A T M E N T FIGURE 10-CAPITAL COST, OPERATING AND MAINTENANCE COST AND DEBT SERVICE VS. DESIGN CAPACITY FOR PRIMARY AND ACTIVATED SLUDGE PLANTS ADJUSTED TO AUGUST, 1975. 52 Q >-O <t a. < o o co LU Q rO O O O O O O O O O O C T ) CO CD lO O C D C O r - C D l O ^ f r O CM — ECONOMIC DOSAGE MG/L FIGURE 11-ECONOMIC DOSAGES OF CATIONIC POLYELECTROLYTE AND OF FERRIC CHLORIDE AND 0.5 MG/L OF ANIONIC POLYELECTROLYTE FOR PLANTS OPERATING AT DESIGN CAPACITY 53 H e r c u l e s I n c o r p o r a t e d i n A u g u s t , 1975. Economic dosages were o b t a i n e d on t h e b a s i s o f t h e d i f f e r e n c e i n t o t a l a n n u a l c o s t o f c o n v e n t i o n a l a c t i v a t e d s l u d g e and p r i m a r y t r e a t m e n t s . The c a p i t a l c o s t o f a polymer m i x i n g and f e e d i n g i n s t a l -l a t i o n i n c l u d i n g d i s p e r s i n g mechanisms, a u t o m a t i c c o n t r o l s , m i x e r s , t a n k s and t r a n s f e r pumps i s l e s s than $20,000 and was i g n o r e d as i t d i d not s i g n i f i c a n t l y a f f e c t t h e a n a l y s i s . T h i s c o s t would be s l i g h t l y h i g h e r i f f e r r i c c h l o r i d e and a polymer were u s e d . The a d d i t i o n a l c o s t o f manpower i n a p l a n t u t i l i -z i n g c h e m i c a l t r e a t m e n t was a l s o i g n o r e d as i t w a s n ' t documented and does not appear t o be s i g n i f i c a n t . Economic dosages were o b t a i n e d on t h e b a s i s o f d e s i g n c a p a -c i t y o f t h e two t y p e s o f p l a n t s c o n s i d e r e d . T h e r e f o r e , F i g u r e 11 p r e s e n t s economic dosages f o r p l a n t s o p e r a t i n g a t c a p a c i t y . N o r m a l l y t r e a t m e n t p l a n t s o p e r a t e below c a p a c i t y f o r a number o f y e a r s , and even h i g h e r c h e m i c a l dosages a r e e c o n o m i c a l under t h e s e c i r c u m s t a n c e s . The economic a n a l y s i s c o n s i d e r s t h e o v e r a l l c o s t o f t r e a t -ment r a t h e r t h a n t h e c o s t t o a m u n i c i p a l i t y o r r e g i o n a l sewerage a u t h o r i t y . U s u a l l y s e n i o r government f i n a n c i a l a s s i s t a n c e i s a v a i l a b l e f o r c a p i t a l e x p e n d i t u r e s i n t h e form o f g r a n t s o r debt f o r g i v e n e s s whereas no a s s i s t a n c e i s n o r m a l l y a v a i l a b l e toward o p e r a t i n g c o s t s . Such a s s i s t a n c e f a v o u r s b i o l o g i c a l t r e a t m e n t o v e r c h e m i c a l t r e a t m e n t . R e s u l t s o f the economic a n a l y s i s show t h a t maximum economic dosages o f t h e c a t i o n i c polymer H e r c o f l o c 814.2 added c o n t i n u -o u s l y t o p r i m a r y p l a n t s o p e r a t i n g a t c a p a c i t y a r e 1 4 . 9 , 1 0 . 2 , 54 and 6.6 mg/l f o r 1, 10, and 100 mgd p l a n t s , r e s p e c t i v e l y . S i m i -l a r l y , f o r f e r r i c c h l o r i d e and 0.5 mg/l of the a n i o n i c polymer H e r c o f l o c 836.2, the economic dosages of FeCl-j are 51, 34 and 21.5 mg/l, r e s p e c t i v e l y . For dosages g r e a t e r than these amounts, the a d d i t i o n of secondary a c t i v a t e d sludge treatment becomes more economical. Economic dosages were determined on the b a s i s o f the assump-t i o n t h a t the degree o f treatment a f f o r d e d by p h y s i c a l - c h e m i c a l treatment i s adequate t o meet r e q u i r e d r e c e i v i n g water q u a l i t y o b j e c t i v e s . The a d d i t i o n a l removal of o r g a n i c s o b t a i n a b l e u s i n g b i o l o g i c a l treatment i s c o n s i d e r e d t o be of no economic v a l u e i n t h i s a n a l y s i s . A comparison based on c o s t per pound o f BOD removed would f u r t h e r reduce these economic q u a n t i t i e s . When these r e s u l t s are combined w i t h the j a r and s e t t l i n g column t e s t r e s u l t s o f Chapter I I I , i t becomes apparent t h a t use of the c a t i o n i c polymer, H e r c o f l o c 814.2, as a primary c o a g u l a n t , would not l i k e l y be an e c o n o m i c a l l y f e a s i b l e a l t e r n a t i v e t o secondary treatment f o r p l a n t s o p e r a t i n g a t c a p a c i t y , u n l e s s p i l o t p l a n t t e s t s i n d i c a t e t h a t a dosage o f somewhat l e s s than 14 mg/l c o u l d achieve an a c c e p t a b l e degree of treatment. Use of f e r r i c c h l o r i d e as the primary coagulant i n combination w i t h a n i o n i c H e r c o f l o c 836.2 as a c o a g u l a n t a i d , however, appears to be an e c o n o m i c a l l y a t t r a c t i v e a l t e r n a t i v e t o secondary treatment f o r p l a n t s i n the 1 to 10 mgd s i z e range. An a d d i t i o n a l economic b e n e f i t , not c o n s i d e r e d here, would be the improved d e w a t e r a b i l i t y of the d i g e s t e d sludge when u s i n g H e r c o f l o c 814.2. CHAPTER V I SUMMARY, CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE RESEARCH 6.1 Summary 1. The advent o f h i g h m o l e c u l a r w e i g h t , l o n g - c h a i n p o l y -e l e c t r o l y t e s has s t i m u l a t e d r e s e a r c h i n t o t h e i r use i n sewage t r e a t m e n t f o r removal o f o r g a n i c s o l i d s i n p r i m a r y and secondary t r e a t m e n t and as s l u d g e d e w a t e r i n g a i d s i n vacuum f i l t r a t i o n and c e n t r i f u g a t i o n . 2. The r e s e a r c h r e p o r t e d on h e r e i n stems from a c o n c e r n about p o s s i b l e polymer t o x i c i t y t o m i c r o b i a l l i f e i n b i o l o g i c a l t r e a t m e n t p r o c e s s e s . 3. The scope o f t h i s s t u d y was l i m i t e d t o a d e t e r m i n a t i o n o f t h e e f f e c t s on 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 o f the c h e m i -c a l s l u d g e o b t a i n e d from t h e c o a g u l a t i o n and s e d i m e n t a t i o n o f a d o m e s t i c sewage e m p l o y i n g p o l y e l e c t r o l y t e s and f e r r i c c h l o r i d e as c o a g u l a n t s . 4. J a r t e s t s were p e r f o r m e d t o e v a l u a t e s e v e r a l p o l y m e r s as p r i m a r y c o a g u l a n t s o r as c o a g u l a n t a i d s f o r c l a r i f i c a t i o n o f d o m e s t i c w a s t e w a t e r . 5. E f f e c t s on a n a e r o b i c d i g e s t i o n were e v a l u a t e d u s i n g t h r e e l a b o r a t o r y s c a l e model d i g e s t e r s . D i g e s t e r c o n t e n t s were mixed c o n t i n u o u s l y and o p e r a t i n g t e m p e r a t u r e s were 32+ 1 ° C . D i g e s t e r s were " f e d " once per day on a f i l l and draw b a s i s . H y d r a u l i c and s o l i d s r e t e n t i o n t i m e s were 3 0 d a y s . 55 56 6. D i g e s t e r No. 1 served as a c o n t r o l and r e c e i v e d sludge o b t a i n e d by sedim e n t a t i o n without the use o f c o a g u l a n t s ; No. 2 r e c e i v e d sludge o b t a i n e d u s i n g 14 mg/l of H e r c o f l o c 814.2 as the coagulant; and No. 3 r e c e i v e d sludge o b t a i n e d u s i n g 3 0 mg/l of f e r r i c c h l o r i d e as the primary coagulant and 1 mg/l of Herco-f l o x 836.2 as a coagulant a i d . 7. A l i m i t e d number o f j a r t e s t s and s e t t l i n g column t e s t s were c a r r i e d out to determine BOD and COD r e d u c t i o n s w i t h the a i d o f c o a g u l a n t s . The r e s u l t s i n d i c a t e , f o r a weak to medium s t r e n g t h sewage, t h a t BOD and COD removal e f f i c i e n c i e s o f 5 0 t o 70% can be o b t a i n e d u s i n g 30 mg/l of F e C l ^ i n combination w i t h 0.5-1.0 mg/l of a n i o n i c H e r c o f l o c 836.2. S i m i l a r e f f i c i e n c i e s were achieved u s i n g 6-14 mg/l of e i t h e r of the c a t i o n i c Herco-f l o c polymers, 812 or 814.2, as the s o l e c o a g u l a n t . 8. V i s u a l o b s e r v a t i o n s of j a r t e s t s i n d i c a t e t h a t c e r t a i n combinations of a n i o n i c polymers f o l l o w e d by a c a t i o n i c polymer were cap a b l e o f produ c i n g tough, r a p i d - s e t t l i n g f l o e s . Dosages o f about 1 mg/l and 5 mg/l, r e s p e c t i v e l y , were r e q u i r e d . 9. The v a l u e o f s p e c i f i c r e s i s t a n c e o b t a i n e d from a Buchner f u n n e l vacuum f i l t r a t i o n t e s t o f the e f f l u e n t sludge from D i g e s t e r No. 1, the c o n t r o l d i g e s t e r , was 18 times as hi g h as the v a l u e o b t a i n e d f o r sludge from No. 2, the d i g e s t e r c o n t a i n i n g the c a t i o n i c polymer H e r c o f l o c 814.2, c l e a r l y i n d i c a t i n g t h a t the polymer r e t a i n e d some v a l u e as a sludge dewatering a i d throughout d i g e s t i o n . However, the sludge from No. 3, the d i g e s t e r c o n t a i n i n g FeCl-j a n < ^ a n i o n i c polymer, d i d not dewater more r e a d i l y than sludge from the c o n t r o l d i g e s t e r . 57 10. C a l c u l a t i o n s of waste s t a b i l i z a t i o n from BOD 5, B0D L, COD and VS r e s u l t s i n d i c a t e treatment e f f i c i e n c i e s o f a p p r o x i -mately 81, 70, 62 and 59 p e r c e n t , r e s p e c t i v e l y , f o r a l l t h r e e d i g e s t e r s . 11. Waste s t a b i l i z a t i o n c a l c u l a t i o n s , based on i n f l u e n t and e f f l u e n t BOD, COD, and VS r e s u l t s and on methane produc-t i o n , f a i l e d to i n d i c a t e any t o x i c i t y or p h y s i c a l i n a b i l i t y o f anaerobic micro-organisms t o p e n e t r a t e the f l o e s formed as a r e s u l t o f the a d d i t i o n o f c o a g u l a n t s and a i d s t o sewage s e d i -mentation. 12. E s t i m a t e s o f e f f i c i e n c y o f waste s t a b i l i z a t i o n based on methane p r o d u c t i o n i n c l u d e removal e f f i c i e n c i e s f o r BOD L r a n g i n g from 190 to 330% of the BOD^ added t o the d i g e s t e r s . I t was concluded, t h e r e f o r e , t h a t the c o n v e n t i o n a l a e r o b i c BOD t e s t i s a poor means o f measuring the ana e r o b i c b i o d e g r a d a b i l i t y of domestic sludge. 13. Measured v a l u e s o f COD removal corresponded c l o s e l y t o e s t i m a t e d v a l u e s based on methane p r o d u c t i o n . I t was c o n c l u -ded, t h e r e f o r e , t h a t the COD t e s t i s a re a s o n a b l y good method of d e t e r m i n i n g the oxygen demand s t a b i l i z e d by anaerobic d i g e s t i o n . 14. R e s u l t s o f pH, a l k a l i n i t y , and v o l a t i l e a c i d s t e s t i n g of d i g e s t e r e f f l u e n t s and t o t a l methane p r o d u c t i o n from the d i g e s t e r s d i d not i n d i c a t e unbalanced treatment due t o the presence o f co a g u l a n t s at any time. These v a l u e s a l l f e l l w i t h i n the p u b l i s h e d l i m i t s f o r normal anaerobic treatment. 58 15. pH and a l k a l i n i t y r e s u l t s were c o n s i s t e n t l y h i g h e r i n the d i g e s t e r s r e c e i v i n g c h e m i c a l l y c o a g u l a t e d sludge than i n the c o n t r o l d i g e s t e r , s i g n i f y i n g a g r e a t e r b u f f e r i n g c a p a c i t y a g a i n s t d i g e s t e r upset due t o changes i n the nature o f the waste or i n o r g a n i c l o a d i n g . 16. The average t o t a l i r o n content of the sludge added t o d i g e s t e r No. 3 was 630 mg/l. The maximum v a l u e o f t o t a l i r o n i n the d i g e s t e r was 5 00 mg/l. There was no impairment of d i g e s t e r e f f i c i e n c y as a r e s u l t of t h i s i r o n c o n c e n t r a t i o n nor d i d f e r r i c c h l o r i d e a c t s y n e r g i s t i c a l l y w i t h the a n i o n i c polymer to c r e a t e t o x i c i t y . 17. R e s u l t s o f an economic a n a l y s i s show t h a t the maximum economic dosages o f the c a t i o n i c polymer H e r c o f l o c 814.2 added c o n t i n u o u s l y t o primary p l a n t s o p e r a t i n g a t c a p a c i t y a re 14.9, 10.2, and 6.6 mg/l f o r 1, 10 and 100 mgd p l a n t s , r e s p e c t i v e l y . S i m i l a r l y , f o r f e r r i c c h l o r i d e and a 0.5 mg/l of the a n i o n i c polymer H e r c o f l o c 836.2, the economic dosages of F e C l ^ are 51, 34, and 21.5 mg/l, r e s p e c t i v e l y . For dosages g r e a t e r than these amounts, the a d d i t i o n o f secondary a c t i v a t e d sludge treatment becomes more economical. 6.2 C o n c l u s i o n s 1. Hercules I n c o r p o r a t e d ' s c a t i o n i c p o l y e l e c t r o l y t e , H e r c o f l o c 814.2, produced BOD^ and COD removal e f f i c i e n c i e s o f approximately 60% i n j a r t e s t s and s e t t l i n g column t e s t s u s i n g a weak to medium s t r e n g t h domestic sewage. The dosages r e q u i r e d were 6 t o 14 mg/l of polymer. 59 2. An economic a n a l y s i s which compared the t o t a l annual c o s t of treatment f o r primary and secondary a c t i v a t e d sludge p l a n t s showed t h a t the d i f f e r e n c e i n c o s t was e q u i v a l e n t t o dosages o f 14.9, 10.2 and 6.6 mg/l o f H e r c o f l o c 814.2, f o r 1, 10, and 100 mgd p l a n t s , r e s p e c t i v e l y . Thus i t was concluded t h a t the use of H e r c o f l o c 814.2 as an a i d to the primary c l a r i -f i c a t i o n o f domestic sewage i s not an e c o n o m i c a l l y a t t r a c t i v e a l t e r n a t i v e t o p r o v i d i n g a c t i v a t e d sludge treatment u n l e s s an adequate degree of treatment can be achieved a t dosages of somewhat l e s s than 14 mg/l. 3. -The c o a g u l a t e d sludge produced, u s i n g 14 mg/l o f H e r c o f l o c 814.2 added t o domestic sewage, n e i t h e r improved nor impaired the e f f i c i e n c y o f the anaerobic d i g e s t i o n process i n a l a b o r a t o r y d i g e s t e r . On the o t h e r hand, f o l l o w i n g d i g e s t i o n , t h i s sludge dewatered more r e a d i l y than non-coagulated sludge from a c o n t r o l d i g e s t e r . A p p a r e n t l y , l i t t l e o r no a d d i t i o n a l c o n d i t i o n i n g would be r e q u i r e d p r i o r t o vacuum f i l t r a t i o n o f such a d i g e s t e d sludge. 4. J a r t e s t s and s e t t l i n g column t e s t s u s i n g 30 mg/l of f e r r i c c h l o r i d e as a primary c o a g u l a n t i n combination w i t h 0.5-1.0 mg/l of a n i o n i c H e r c o f l o c 83 6.2 as a coagulant a i d produced BOD^ and COD removal e f f i c i e n c i e s of approximately 60% f o r a weak to medium s t r e n g t h domestic sewage. 5. Comparison of the t o t a l annual c o s t o f treatment f o r primary and secondary a c t i v a t e d sludge p l a n t s showed t h a t the d i f f e r e n c e i n c o s t was e q u i v a l e n t t o dosages of 51, 34 and 21.5 mg/l of f e r r i c c h l o r i d e f o r 1, 10, and 100 mgd p l a n t s , r e s p e c -t i v e l y , assuming a dosage o f 0.5 m g / l o f H e r c o f l o c 836.2 as t h e c o a g u l a n t a i d . Thus i t was c o n c l u d e d t h a t the use o f f e r r i c c h l o r i d e and a n i o n i c polymer as a i d s to t h e s e d i m e n t a t i o n o f d o m e s t i c sewage p r e s e n t e d an e c o n o m i c a l l y a t t r a c t i v e a l t e r n a t i v e t o s e c o n d a r y t r e a t m e n t f o r p l a n t s i n t h e 1-10 mgd r a n g e , p r o -v i d e d t h a t an adequate degree o f t r e a t m e n t c o u l d be o b t a i n e d . 6. The c o a g u l a t e d s l u d g e p r o d u c e d , u s i n g 3 0 m g / l o f F e C l ^ and 1 m g / l o f H e r c o f l o c 8 3 6.2 added t o d o m e s t i c sewage, n e i t h e r improved nor i m p a i r e d the e f f i c i e n c y 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 n a l a b o r a t o r y d i g e s t e r . A l s o t h e r e was no s i g n i f i c a n t d i f f e r e n c e i n t h e d e w a t e r a b i l i t y o f t h e d i g e s t e d s l u d g e when compared t o the n o n - c o a g u l a t e d s l u d g e from a c o n t r o l d i g e s t e r . 6.3 Recommendations f o r F u t u r e R e s e a r c h 1. T h i s r e s e a r c h has f a i l e d t o i n d i c a t e any a d v e r s e e f f e c t s on a n a e r o b i c d i g e s t i o n as a r e s u l t o f u s i n g H e r c o f l o c 814.2 as a p r i m a r y c o a g u l a n t o r H e r c o f l o c 83 6.2 as a c o a g u l a n t a i d i n c o m b i n a t i o n w i t h f e r r i c c h l o r i d e f o r t h e c l a r i f i c a t i o n o f d o m e s t i c w a s t e w a t e r . However, the q u e s t i o n o f polymer t o x i c i t y t o b i o -l o g i c a l p r o c e s s e s has not been answered. B e f o r e any f u r t h e r r e s e a r c h a l o n g t h e s e l i n e s i s begun, more i n f o r m a t i o n must be o b t a i n e d about t h e p o l y m e r s - s p e c i f i c a l l y t h e i r base compounds and t h e f u n c t i o n a l groups w h i c h a c c o u n t f o r t h e i r e l e c t r o l y t i c p r o p e r t i e s . O n l y t h e n c a n the p r o d u c t s o f v a r i o u s m a n u f a c t u r e r s be grouped a c c o r d i n g t o s p e c i f i c p r o p e r t i e s and d u p l i c a t i o n o f _ _ e f f o r t be p r e v e n t e d . 2. F u r t h e r r e s e a r c h a l o n g t h e l i n e s o f t h a t r e p o r t e d on h e r e i n c o u l d i n c l u d e an assessment o f t h e e f f e c t o f r e d u c i n g d i g e s t e r d e t e n t i o n t i m e s . 3 . F a v o u r a b l e r e s u l t s o f Buchner f u n n e l vacuum f i l t r a t i o n t e s t s on d i g e s t e d , c o a g u l a t e d s l u d g e s u g g e s t r e s e a r c h t o d e t e r -mine t h e f e a s i b i l i t y of u s i n g c a t i o n i c polymer f o r t h e d u a l p u r p o s e o f i n c r e a s i n g s o l i d s c a p t u r e d d u r i n g s e d i m e n t a t i o n and as an a i d t o d e w a t e r i n g o f t h e s l u d g e o b t a i n e d , w i t h or w i t h o u t an i n t e r m e d i a t e b i o l o g i c a l d i g e s t i o n p r o c e s s . Of p a r t i c u l a r i n t e r e s t would be a c o m p a r i s o n o f amount o f polymer r e q u i r e d when added j u s t p r i o r to the d e w a t e r i n g p r o c e s s v e r s u s the amount r e q u i r e d f o r optimum s l u d g e d e w a t e r i n g when a d d e d . t o the i n c o m i n g sewage o r a t some o t h e r s tage o f t r e a t m e n t . Any i n -c r e a s e i n t r e a t m e n t e f f i c i e n c y must be weighed a g a i n s t t h e i n c r e a s e i n c o a g u l a n t c o s t s . 4. Problems w i t h f l o t a t i o n o f t h e l a r g e t e n a c i o u s f l o e s formed when a i r m i x i n g o f c a t i o n i c polymer and sewage was a t tempted sugges ted f u r t h e r i n v e s t i g a t i o n o f t h i s as a means o f s e p a r a t i o n o f g r i t and o r g a n i c s o l i d s i n sewage t r e a t m e n t . Whereas s e p a r a t e g r i t t anks and s e d i m e n t a t i o n b a s i n s a r e now u s e d , i t may be p o s s i b l e to e l i m i n a t e the s e d i m e n t a t i o n b a s i n and employ one d u a l - p u r p o s e a e r a t e d b a s i n . 62 BIBLIOGRAPHY [ I ] Cameron, R . D . , Department o f C i v i l E n g i n e e r i n g , 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 , p r i v a t e communicat ion [2] "Sewage Treatment P l a n t D e s i g n " , WPCF Manual o f P r a c t i c e No. 8, Water P o l l u t i o n C o n t r o l F e d e r a t i o n , W a s h i n g -t o n , D . C . (1967) [3] E n s l o w , L . H . , " C h e m i c a l P r e c i p i t a t i o n P r o c e s s e s " , C i v i l E n g i n e e r i n g , V o l . 5, No. 4, p .235 (1935) [4] E c k e n f e l d e r , W.W. , "Water Q u a l i t y E n g i n e e r i n g f o r P r a c -t i c i n g E n g i n e e r s " , Barnes and N o b l e , I n c . , New Y o r k , N . Y . (1970) [5] Committee on Sewage D i s p o s a l , A m e r i c a n P u b l i c H e a l t h A s s o c i a t i o n , - " C h e m i c a l Treatment o f Sewage", Sewage Works J o u r n a l , V o . 7, No . 6, p .997 (1935) [6] " S t a n d a r d Methods f o r t h e E x a m i n a t i o n o f Water and Waste-w a t e r " , 12th E d i t i o n , A m e r i c a n P u b l i c H e a l t h A s s o c i a t i o n , New Y o r k , N . Y . (1960) [7] R i c h , L . G . , " U n i t O p e r a t i o n s o f S a n i t a r y E n g i n e e r i n g " , John W i l e y and S o n s , I n c . , New Y o r k , N . Y . (1961) [8] B o l t o n , R . L . and K l e i n , L . , "Sewage Treatment - B a s i c P r i n c i p l e s and T r e n d s " , 2nd E d i t i o n , Ann A r b o r S c i e n c e P u b l i s h e r s , I n c . , Ann A r b o r , M i c h i g a n (1971) [9] M e t c a l f and E d d y , I n c . , "Wastewater E n g i n e e r i n g : C o l l e c -t i o n , T r e a t m e n t , D i s p o s a l " , M c G r a w - H i l l , I n c . , New Y o r k , N . Y . (1972) [10] M c C a r t y , P . L . , " A n e r o b i c Waste Treatment F u n d a m e n t a l s , P a r t One : C h e m i s t r y and M i c r o b i o l o g y and P a r t Two: E n v i r o n m e n t a l Requirements and C o n t r o l " , P u b l i c Works (September and O c t o b e r , 1964) [ I I ] S m i t h , R . , " C o s t o f C o n v e n t i o n a l and Advanced Treatment o f Wastewater " , J o u r n a l Water P o l l u t i o n C o n t r o l F e d e r a t i o n , V o l . 40, No. 9, p .1546 (September 1968) [12] "Employment and E a r n i n g s and M o n t h l y Report on the L a b o r F o r c e " , U . S . Department o f L a b o r , Bureau o f Labor S t a t i s t i c s , V o l . 22, No . 1 ( J u l y 1975) APPENDICES 63 APPENDIX A J A R TEST RESULTS RAW SEWAGE FLOCCULATION 64 65 APPENDIX A JAR TEST RESULTS RAW SEWAGE FLOCCULATION T e s t P o l y e l e c t r o l y t e s Dosage Range No. U s e d * (mg/l) R e s u l t s  1 1 1-10 No a p p a r e n t f l o c c u l a t i o n 2 2 1-5 No a p p a r e n t f l o c c u l a t i o n 3 7 0 . 2 - 1 . 0 No a p p a r e n t f l o c c u l a t i o n 4 7 1-5 No a p p a r e n t f l o c c u l a t i o n 5 . 3 1 - 5 S m a l l f l o e s formed. Poor s e t t l i n g 6 7, 0 . 1 - 0 . 5 No a p p a r e n t f l o c c u l a t i o n t h e n 3 1-5 7 3, 1-5 L a c y f l o e s . Poor s e t -t h e n 7 0 . 1 - 0 . 5 t l i n g 8 3, t h e n 1 1-5 1-5 Good f l o e s . Rapid s e t -t l i n g . 2 m g / l o f each worked b e s t 9 3, t h e n 1 2 1-5 . Good f l o e s . R a p i d s e t -t l i n g . 5 m g / l o f #1 worked b e s t 10 3, t h e n 1 1-5 2 A l l c o m b i n a t i o n s appear e q u a l l y good 11 3, t h e n 1 0 . 5 - 2 . 5 5 A l l c o m b i n a t i o n s appear e q u a l l y good 12 3, t h e n 1 1 5-9 There i s no a p p a r e n t i m p-rovement a t c o n c e n t r a t i o n s o f #1 above 5 m g / l 13 3, t h e n 7 1 1-5 Medium f l o e s . Good s e t -t l i n g . 2 m g / l o f #7 appeared b e s t 14 5, t h e n 6 1-5 2 V e r y s m a l l f l o e s appeared to f o r m . Poor s e t t l i n g 66 T e s t No. P o l y e l e c t r o l y t e s U s e d * Dosage Range . (mg/l) R e s u l t s 15 4, t h e n 2 1-5 1-5 L a r g e f l o e s . Good s e t -t l i n g . 5 m g / l o f each appeared b e s t . 16 4, t h e n 6 1-5 1-5 Medium f l o e s . F a i r s e t -t l i n g . A c o n s i d e r a b l e number o f f i n e p a r t i c l e s remained i n s u s p e n s i o n 17 5, t h e n 2 1-5 1-5 Poor f l o c c u l a t i o n 18 3, t h e n 8 1 0 . 5 - 2 . 5 Large f l o e s . Good s e t -t l i n g . C o n c e n t r a t i o n s o f 2.0 and 2.5 m g / l o f #8 worked b e s t 19 3, t h e n 8 0 . 5 - 2 . 5 1.5 A l l c o m b i n a t i o n s appear e q u a l l y good 20 3, then 9 1 1-5 S m a l l f l o e s . Poor s e t -t l i n g 21 10, t h e n 8 1 1-5 L a r g e f l o e s . R a p i d s e t -t l i n g . 5 m g / l o f #8 worked b e s t 22 3, t h e n 8 1 1-5 L a r g e f l o e s . F a i r s e t -t l i n g . 4 and 5 m g / l o f #8 appeared s l i g h t l y b e t t e r 23 3, t h e n 8 1 , 1 , 1 , 2 , 2 , 2 3 , 4 , 5 , 3 , 4 , 5 A p p r o x i m a t e l y e q u a l r e s u l t ! 2 m g / l o f #3 and 5 m g / l o f #8 appeared t o p r o d u c e . t h e s t r o n g e s t , l e a s t l a c y , f l o e 24 4, . t h e n 8 2 1-5 Medium f l o e . F a i r s e t -t l i n g . F l o e s appeared " f l i m s y " I qned N o . * P o l y e l e c t r o l y t e Type 1 Alchem 603 C a t i o n i c 2 Alchem 607 C a t i o n i c 3 Alchem D -179-M A n i o n i c 4 Alchem D-176 A n i o n i c 5 Alchem 633-HD A n i o n i c 6 Alchem 636-HD C a t i o n i c 7 Rohm & Haas P r i m a f l o c C -7 C a t i o n i c 8 H e r c u l e s C o r p . H e r c o f l o c * 312 S l i g h t l y C a t i o n i c 9 Dow P u r i f l o c C -31 C a t i o n i c 10 Dow P u r i f l o c A-23 A n i o n i c APPENDIX B DIGESTION PARAMETER TEST RESULTS 68 RAW SLUDGE DATA T o t a l I r o n T o t a l S o l i d s V o l a t i l e S o l i d s BOD 5 COD Dates Sludge Number (mg/l) (g/1) (g/1) (g/D (g/D Used o f Days D i g e s t e r No D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. (1971) Used 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 P r i o r t o * * * * * * A p r i l 2 9 - - - 36.5 36.5 36.5 12.0 12.0 12.0 65.0 65.0 65.0 A p r i l 2 9 t o May 4 6 - 22.0 19.4 23.1 19.4 16.9 19.0 5.81 6.77 7.72 33.0 31.0 36.6 May 5 to May 11 7 160 88 643 24.5 23.9 29.0 21.3 20.8 23.9 5.81 8.79 8.68 36.2 39.3 42.2 May 12 to May 24 13 125 150 500 28.2 29.8 29.7 24.0 23.5 25.1 9.00 10.3 10.2 37.3 44.4 49.5 May 25 to June 3 10 112 102 675 25.5 25.4 25.6 21.7 22.0 20.9 6.65 10.2 10.0 33.7 40.8 35.1 June 4 t o June 17 14 105 110 640 30.0 28.9 30.1 26.0 24.8 24.7 6.26 10.7 7.65 45.5 49.9 45.0 June 18 to J u l y 4 17 150 112 666 30.7 36.9 41.1 24.7 25.3 25.7 7.84 12.0 10.2 44.2 49.9 48.9 *Estimated from v o l a t i l e s o l i d s vo DIGESTER EFFLUENT DATA T o t a l Iron T o t a l S o l i d s V o l a t i l e S o l i d s BOD5 COD (mg/l) ' (g/1) (g/1) (g/1) (g/1) Date D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. (1971) 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 A p r i l 12 - 29.6 23.6 26.5 15.8 15.2 15.5 2.18 2.05 1.85 -May 30 96 110 386 17.3 21.4 18.0 11.4 12.6 11.4 2.41 2.63 2.36 19.2 21.8 20.4 June 7 144 188 394 17.0 20.3 16.6 10.9 11.7 10.6 1.47 2.07 1.64 18.8 20.4 17.9 June 11 138 140 332 17.8 18.6 15.8 10.8 11.2 10.3 1.55 1.77 1.55 17.6 19.7 17.5 June 28 140 156 396 16.0 17.2 19.0 10.7 11.1 11.2 1.85* 2.08* 2.16* 17.3 18.8 18.5 J u l y 4 183 220 500 16.7 20.1 17.1 10.3 11.3 10.8 1.45 2.30 .1.95 17.1 19.9 18.4 *These BOD v a l u e s are not s t a t i s t i c a l l y sound as d i l u t i o n s were used which gave d i s s o l v e d oxygen d e p l e t i o n s l e s s than 2.0 mg/l 71 pH OF DIGESTER EFFLUENT A p r i l May June Day of D i g e s t e r No. D i g e s t e r No. D i g e s t e r No. Month 1 2 3 1 2 3 1 2 3 1 6.93 6.66 6.88 6.99 7.00 6.93 2 6.92 6.67 6.92 6.94 6.98 6.95 3 - - - - - - 6.86 6. 99 6. 98 4 - - - 6.99 6.99 7. 04 6.87 7.00 6. 98 5 6.83 6.79 6.83 - - - 6.86 7. 04 7. 00 6 6. 97 6. 90 6. 96 6.86 6. 93 6.86 6.86 7. 00 6. 96 7 6.89 6.83 6.88 6.86 6. 95 6.87 - - -8 - - - - - - 6.88 7.02 6.99 9 — — — 6. 92 6. 97 6. 93 - - -11 - 6.83 6.93 6.90 12 6.84 6.82 6.82 6.90 7.12 7.01 6.88 7.01 6.99 13 6.89 6.85 6.88 - 6.92 7.05 7.01 14 6.90 6.92 6.87 - -15 - 6.92 6.96 6.92 -16 6.93 6.89 6.91 - 6.85 7.00 6.98 17 - - - 6.86 6.93 6.90 -18 - _ - - _ _ _ 19 6.99 6.93 6.95 6.96 7.09 6.99 -20 6.97 6.90 7.00 6.87 7.04 6.97 6.88 7.09 6.99 21 6.87 6.88 6.86 - 6.86 7.04 7.01 22 6.91 6.90 6.89 6.99 7.04 7.05 -23 - 6.90 7.00 6.99 6.88 7.06 7.03 24 6.90 6.86 6.82 - - - -25 6.90 6.94 6.87 6.92 7.05 6.97 6.88 7.06 7.02 26 6.85 6.84 6.86 - - 6.88 7.06 7.01 27 - - 6.90 7.04 6.99 28 6.86 6.85. 6.90 - -29 6.90 6.87 6.91 6.84 6.96 6.98 6.91 7.08 7.02 30 6.99 6.99 6.97 - 6.90 7.04 7.02 31 - 6.88 7.00 6.98 - - -72 DIGESTER EFFLUENT VOLATILE ACIDS AND ALKALINITY Date  March 17 May 19 May 30 June 5 June 9 June 22 V o l a t i l e A c i d s , m g / l as A c e t i c D i g e s t e r No. 1 2 3 40 50 60 70 50 70 100 40 130 120 90 50 70 50 140 A l k a l i n i t y , m g / l as CaCO^ D i g e s t e r No. 1 2 3 160 170 170 1,675 1,650 1,620 1,510 1,780 1,790 1,940 1,960 1,830 2,480 1,770 1,890 1,890 1,770 2,150 7 3 GAS PRODUCTION FROM DIGESTERS LITERS/DAY AT STANDARD TEMPERATURE AND PRESSURE D i g e s t e r No. Date 1 2 A p r i l 28-29 5.52 5.98 6.51 June 5-6 3.86 3.96 3.85 June 7-8 4.11 4.10 3.73 June 9-10 3.85 4.06 3.85 June 19-20 3.17 3.40 3.10 June 20-21 - 3.78 June 22-23 3.78 June 24-25 - - 3.31 June 25-26 - 3.62 June 28-29 3.46 June 29-30 - - 3.22 June 30-July 1 - 3.71 J u l y 1-2 3.12 J u l y 2-3 - - 3.21 COMPOSITION OF DIGESTER GAS PERCENTAGE BY VOLUME 74 Date A p r i l 15 A p r i l 2 9 May 3 May 7 May 10 May 16 May 21 May 28 June 3 June 12 June 18 June 28 D i g e s t e r Number 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 H 2 S w m < tH U W E H W Q E H O 53 0.4 0.2 0.1 0.6 0.3 0.3 0.8 0.3 0.3 0.4 0.3 0.2 0.2 0.2 0.2 0.3 0.2 0.1 0.2 0.4 0.2 0.5 0.3 0.5 0.5 0.2 0.4 0.4 0.3 0.4 0.5 0.3 0.4 0.6 0.5 0.5 CH, CO, 57.3 58.5 56.7 58.8 58. 0 56. 6 60.1 62 .1 60.2 60.2 63. 6 62.7 61. 0 64.0 62. 0 59 .9 63.9 61. 6 61. 0 64.2 62. 0 60.2 64.1 62.3 61.4 65. 3 63.8 58.4 63.2 61.9 58 .1 63. 9 62.5 59.2 63.4 62.9 41.8 40.8 42.7 40 .1 41 .0 42 .0 38. 6 37. 0 38.7 38. 35. 36. 38, 35, 36, 39, 35, .7 4 4 ,2 ,1 ,7 ,1 ,2 36.8 38.2 34.8 36.8 38. 0 34.1 36.0 37.4 33.6 35.0 40.6 35.8 37.2 4 0.6 34. 9 36.2 39.4 35.1 35.8 H 2 0 0.5 0.5 0.5 0.5 0.7 1.1 0.5 0.6 0.8 0.7 0.7 0.7 0.6 0.7 1.1 0.7 0.7 1.5 0.6 0.6 1 .0 1.3 1.5 1.2 0.7 0.9 0.8 0.6 0.7 0.5 0.8 0.9 0.9 0.8 1.0 0.8 APPENDIX C RESULTS OF LONG-TERM BOD TESTS ON RAW AND DIGESTED SLUDGES 75 o 5 o o a o 9 DAY .5 G/L 3 G/L o o ( D o ^ 2 co ro «" " U Q Q » o o m m © G O o o o o c 0 c \ ° i \ o o m o m o m o CM CM — — B I O C H E M I C A L O X Y G E N D E M A N D ( G R A M S / L I T E R ) L O N G - T E R M BOD TEST RAW SLUDGE NO. I © G 3 o O G G O O G G G O 'DAY .2 G/L .7 G/L o o o o o o ^ = • 1 LO O Q Q " o o ^ CD GO v ty o © G G O o ©1 \ ° G \ GOV LO o m o m o CM CM — — BIOCHEMICAL OXYGEN DEMAND (GRAMS/L ITER) LONG-TERM BOD TEST RAW SLUDGE NO. 2 m ro 78 O ro Q O or LU CL o h-<I m Z> o IO CM o CM LO o LO BIOCHEMICAL OXYGEN DEMAND (GRAMS/LITER) L O N G - T E R M BOD TEST RAW SLUDGE NO. 3 o o O o < Vs D MG/L i MG/L \ o 11 II _1 LO o o CQ CD o o o o q o O 00 CD st OJ B IOCHEMICAL O X Y G E N DEMAND (GRAMS/L ITER ) L O N G - T E R M B O D T E S T E F F L U E N T S L U D G E N O . I o ro 80 LONG-TERM BOD TEST EFFLUENT SLUDGE NO. 2 LONG-TERM BOD TEST EFFLUENT SLUDGE NO. 3 APPENDIX D SAMPLE CALCULATION OF THE MICROBIAL STABILIZATION OF VOLATILE SOLIDS,. BOD OR COD IN A DIGESTER 82 83 APPENDIX D PROBLEM: To d e t e r m i n e t h e m i c r o b i a l s t a b i l i z a t i o n o f VS i n D i g e s t e r #1 on J u l y 4, 1971 SOLUTION: C a l c u l a t e t h e t h e o r e t i c a l c o n c e n t r a t i o n on J u l y 4 assuming o n l y p h y s i c a l removal and compare t h i s r e s u l t w i t h the a c t u a l VS c o n c e n t r a t i o n as measured i n t h e d i g e s t e r e f f l u e n t DERIVATION OF EQUATION 2: Where s l u d g e i s added t o a d i g e s t e r , t h e r a t e . o f change of t h e VS c o n c e n t r a t i o n i n t h e d i g e s t e r i s e x p r e s s e d by t h e e q u a t i o n a f = K I C R ••• { D 1 ) where : C i s t h e VS c o n c e n t r a t i o n i n the d i g e s t e r , C R i s t h e VS c o n c e n t r a t i o n i n t h e s l u d g e added t o the d i g e s t e r , i s a r a t e c o n s t a n t e q u a l t o t h e volume o f s l u d g e added p e r u n i t o f t i m e d i v i d e d by t h e volume i n t h e d i g e s t e r , and t i s t i m e . S i m i l a r l y , when s l u d g e i s removed from the d i g e s t e r , the r a t e o f change o f t h e VS c o n c e n t r a t i o n i n the d i g e s t e r i s e x p r e s -sed by t h e e q u a t i o n a r = - K 2 C ••• ( D 2 ) where : K 2 i s a r a t e c o n s t a n t e q u a l t o t h e volume o f s l u d g e removed p e r u n i t o f t i m e d i v i d e d by the volume i n t h e d i g e s t e r . Combining t h e two e q u a t i o n s §^ = K.CU - K 0 C . . . (D3) d t 1 R Z 84 The s t e a d y s t a t e s o l u t i o n o f t h i s e q u a t i o n i s o b t a i n e d by s e t t i n g dC d t = 0 T h e r e f o r e , C = K l C D R e a r r a n g i n g t e r m s , e q u a t i o n D3 becomes ' • • d t + K 2 C _ K 1 C R The g e n e r a l s o l u t i o n o f t h i s e q u a t i o n i s o b t a i n e d by s e t t i n g dC ~ + K„C - 0 d t 2 S o l v i n g f o r C y i e l d s ft ~ —K^t C = ae 2 where : a i s a c o n s t a n t , and e i s t h e base o f n a t u r a l l o g a r i t h m s Combining t h e s t e a d y s t a t e and g e n e r a l s o l u t i o n s , y i e l d s C = K l C D + a e " ^ 1 (D4) A t t ime t = 0 , C e q u a l s t h e i n i t i a l v o l a t i l e s o l i d s c o n c e n -t r a t i o n i n t h e d i g e s t e r , C Q . S u b s t i t u t i n g i n e q u a t i o n D4 and s o l v i n g f o r " a " y i e l d s a = C 0 - £ L C R 2 S u b s t i t u t i n g t h i s r e s u l t back i n t o e q u a t i o n D4 y i e l d s e q u a t i o n 2 C = C r , e " K 2 t + K l C D ( 1 - e " K 2 t ) . . . (2) ° The c a l c u l a t e d v a l u e s o f and K 2 a r e : 250 m l / d a y r, n->->-> J K l = 7,500 ml = 0-0333 p e r day K, = 2^3 m l / d a y = 0 . 0 3 2 4 p e r day 2 7,500 ml ^ J 85 SOLUTION: P r i o r t o A p r i l 29, 1971 Average VS c o n t e n t o f s l u d g e added = 36.5 m g / l A p r i l 29 - May 4 C Q = 3 6.5 m g / l C_. = VS c o n c e n t r a t i o n o f s l u d g e added = 19.4 m g / l R t = 6 days •K„t. C Q e - K 2 f c = K l K 2 C R (1 - e~ C = 30. 05 May 4 -• May 11 C 0 = 33.58 C R = 21.3 t = 7 C = 26. 55 May 11 — May 2 4 C 0 = 31.22 C R = 24.0 t = 13 C = 20.49 May 24 _ June 3 C 0 = 28. 98 C R 21.7 t 10 C 20. 96 27.14 m g / l 86 June 3 - June 17 C 0 = 27.14 C R = 26.0 t = 14 C = 17.24 June 17 -- J u l y 4 C 0 = 27. 00 C R = 24.7 t = 17 = 15.57 + 10.76 = 26.33 m g / l C = t h e o r e t i c a l VS c o n c e n t r a t i o n i n D i g e s t e r #1 on J u l y 4 assuming no m i c r o b i a l s t a b i l i z a t i o n Measured VS c o n c e n t r a t i o n i n D i g e s t e r #1 on J u l y 4 : 10.3 m g / l M i c r o b i a l VS S t a b i l i z a t i o n = 2 6 ' 1 ~ 0 1 0 ' ' 3 = 61% 26.3 T h i s method a l s o a p p l i e s t o BOD and COD removal e f f i c i e n c y d e t e r m i n a t i o n s . 

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