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Treatability of leachate from a sanitary landfill by anaerobic digestion Poorman, Basil Lloyd 1974

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c l TREATABILITY OF LEACHATE FROM A SANITARY LANDFILL BY ANAEROBIC DIGESTION by B a s i l L l o y d Poorman B . S c , I s r a e l i I n s t i t u t e of Technology, 1968 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 t h e s i s as conforming to the re q u i r e d standard The U n i v e r s i t y of B r i t i s h Columbia A p r i l , 1974 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree 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 olumbia, I agree 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 and s t u d y . I f u r t h e r agree 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 the Head o f my Department 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 . Department o f C i v i l E n g i n e e r i n g  The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date A p r i l 11, 1974 ABSTRACT P o l l u t i o n c o n t r o l a u t h o r i t i e s are becoming more and more con-cerned about the e f f e c t s of h i g h l y p o l l u t e d leachate from s o l i d waste l a n d f i l l s on r e c e i v i n g waters. C o n t r o l or treatment of such leachate i s thus becoming very important. This study was e s t a b l i s h e d to i n v e s t i g a t e the p o s s i b i l i t y of reducing the amounts of oxygen demanding m a t e r i a l i n the leachate by anaerobic d i g e s t i o n without any p r i o r removal of heavy metals which were contained i n i t . I t a l s o i n c l u d e d a study of the e f f e c t s of v a r i e d detention time and the changing c h a r a c t e r i s t i c s of the leachate. BOD,, removals ranging from 80 to 96 percent were achieved f o r detention times ranging from 5 to 20 days and i n f l u e n t BOD^'s ranging from 11,000 to 16,000 mg/1. C.O.D. removals ranged from 65 to 79 percent f o r i n f l u e n t values ranging from 23,000 to 33,000 mg/1. A v a r i e t y of metals i n c l u d i n g aluminum, cadmium, chromium, copper, l e a d , mercury, n i c k e l and z i n c were present i n the leachate. Their concentrations covered a broad range w i t h z i n c being the highest at 65 mg/1. The anaerobic d i g e s t i o n process was not adversely e f f e c t e d by these metals. Some of these metals, notably aluminum, cadmium, mercury, n i c k e l and z i n c were e s s e n t i a l l y completely a s s o c i a t e d w i t h the sludge, w h i l e the others were a s s o c i a t e d to a l e s s e r extent. Gas production ranged from 11.9 to 15.0 cubic fee t per pound of BOD,, destroyed, and methane production ranged from 5.8 to 6.8 cubic f e e t per pound of C.O.D. destroyed. From the r e s u l t s obtained the i n d i c a t i o n s are that leachate t r e a t -a b i l i t y by anaerobic d i g e s t i o n holds good prospects. Since at 20 days i i i d e t ention time 96 percent removal was achieved i t i s l i k e l y that detention times beyond 20 days would r e s u l t i n a greater percent removal. TABLE OF CONTENTS Page LIST OF TABLES • • • v • LIST OF FIGURES v i i ACKNOWLEDGEMENT v i i i CHAPTER I INTRODUCTION 1 I I RESEARCH RATIONALE 3 I I I GENERAL REVIEW OF ANAEROBIC DIGESTION 7 3-1 General Process D e s c r i p t i o n 7 3-2 R e l a t i o n s h i p Between Waste S t a b i l i z a t i o n and Gas Production 8 3-3 Factors A f f e c t i n g Anaerobic D i g e s t i o n . . . . . 9 3- 4 Conclusion 15 IV SYSTEM DESIGN AND EXPERIMENTAL PROCEDURE 16 4- 1 Design of Treatment System 16 4-2 Detention Time 18 4-3 Leachate Source and C h a r a c t e r i s t i c s 19 4-4 N u t r i e n t Balance 21 4-5 pH Co n t r o l 21 4-6 Metal Concentrations 22 4-7 A n a l y s i s Schedule and Procedure 22 4-8 S t a r t i n g up the Digesters 23 4- 9 Summary 25 V ANALYSIS OF RESULTS 26 5- 1 Removal of Oxygen Demanding M a t e r i a l 26 5-2 Gas Composition 35 5-3. Gas Production 39 5-4- S t a b i l i t y Parameters 46 5-5 Metal D i s t r i b u t i o n W ithin the E f f l u e n t . . . . 46 i i i i v Page VI CONCLUSIONS AND RECOMMENDATIONS . . . 57 6-1 Conclusions 57 6-2. Recommendations f o r Future Studies 60 VII REFERENCES 61 V I I I " APPENDICES 62 Appendix A I n f l u e n t and e f f l u e n t pH of d i g e s t e r contents . 62 Appendix B A c i d n e u t r a l i z i n g c a p a c i t y of d i g e s t e r contents 66 Appendix C S o l i d s i n d i g e s t e r e f f l u e n t 70 Appendix D Sample C a l c u l a t i o n s 74 LIST OF TABLES Table Page I LEACHATE COMPOSITION . 4 I I COMPOSITION OF TYPICAL LEACHATES 5 I I I GAS PRODUCTION AS RELATED TO COPPER CONCENTRATION 13 IV COMPOSITION OF LEACHATE FEED USED DURING STUDY 20 V BOD5:N:P RATIO USED IN STUDY 21 VI SAMPLING AND ANALYSIS SCHEDULE 22 VII OPERATING CONDITIONS FOR FULLY ESTABLISHED DIGESTERS 24 V I I I AVERAGE PERCENTAGE BOD5 REMOVAL 27 I5C, BOD5 AND HEAVY METAL CONCENTRATION OF EACH SUCCESSIVE BATCH OF FEED 29 X AVERAGE PERCENT REMOVAL BASED ON SETTLED EFFLUENT BOD5 30 XI PERCENTAGE COD REMOVAL 34 XII AVERAGE COMPOSITION OF DIGESTER GAS 36 X I I I BALANCE OF TOTAL AND AMMONIA-NITROGEN IN DIGESTER LIQUID 38 XIV AVERAGE GAS COMPOSITION AS A FUNCTION OF INFLUENT BOD5 40 XV GAS PRODUCTION IN RELATION TO DETENTION TIME AND BOD5 REMOVAL 41 XVI GAS PRODUCTION PER LITRE OF FEED IN RELATION TO HEAVY METAL CONCENTRATIONS 43 XVII METHANE PRODUCTION IN RELATION TO COD REMOVAL... 45 XVIII METAL DETERMINATION IN DIGESTER #1, DETENTION TIME = 5 DAYS, 2ND BATCH OF FEED 48 v v i Table Page XIX METAL DETERMINATION IN DIGESTER #3, DETENTION TIME = 20 DAYS, 2ND BATCH OF FEED 49 XX METAL DETERMINATION OF DIGESTER #1, DETENTION TIME = 5 DAYS, 3RD BATCH OF FEED 50 XXI METAL DETERMINATION IN DIGESTER #2, DETENTION TIME = 10 DAYS, 3RD BATCH OF FEED 51 XXII METAL DETERMINATION IN DIGESTER #3, DETENTION TIME = 20 DAYS, 3RD BATCH OF FEED 52 XXIII SUMMARY OF METAL PERCENTAGE IN THE DRY SLUDGE . . 54 LIST OF FIGURES FIGURE Page 1 LABORATORY ANAEROBIC DIGESTER 17 2 PERCENTAGE BOD5 REMOVAL VS. DETENTION TIME 33 3 INFLUENT AND EFFLUENT pH VS. TIME FOR DIGESTER #1 63 4 INFLUENT AND EFFLUENT pH VS. TIME FOR DIGESTER #2 64 5 INFLUENT. AND EFFLUENT pH VS. TIME FOR DIGESTER #3 65 6 ACID NEUTRALIZING CAPACITY (TO pH 4.5) OF EFFLUENT VS. TIME FOR DIGESTER #1 67 7 ACID NEUTRALIZING CAPACITY (TO pH 4.5) OF EFFLUENT VS.. TIME FOR DIGESTER #2 68 8 ACID NEUTRALIZING CAPACITY (TO pH 4.5) OF EFFLUENT VS. TIME FOR DIGESTER #3 69 9 SOLIDS VS. TIME FOR DIGESTER #1 71 10 SOLIDS VS. TIME FOR DIGESTER #2 72 11 SOLIDS VS. TIME FOR DIGESTER #3 73 v i i ACKNOWLEDGEMENT The author i s very g r a t e f u l to h i s s u p e r v i s o r Dr. R.D. Cameron f o r h i s guidance and encouragement during t h i s study. The author i s a l s o g r a t e f u l f o r the help and a s s i s t a n c e r e c e i v e d from h i s l o v i n g w i f e Joan E l i z a b e t h , Dr. D.S. Mavinic and Mrs. L i z a McDonald. v i i i CHAPTER I INTRODUCTION Over the years there has been a tremendous increase i n the volume of s o l i d waste being generated. Despite the problems created by t h i s l a r g e i n c r e a s e , s a n i t a r y l a n d f i l l s and garbage dumps have remained the most popular method of d i s p o s a l . One major concern about t h i s method of d i s p o s a l has been the f a c t that the water which flows through the s i t e e x t r a c t s a l a r g e number and o f t e n h i g h concentrations of s o l u b l e substances, and so ends up as a h i g h l y p o l l u t e d l i q u i d . This l i q u i d i s known as leachate and can be a very s e r i o u s source of r e c e i v i n g water p o l l u t i o n . The i d e a l l a n d f i l l s i t e i s one i n which the leachate does not f i n d i t s way i n t o nearby s u r f a c e or ground waters, or one i n which no leachate i s generated. However urban development has r e s u l t e d i n keen competition f o r the a v a i l a b l e lands by a l l p o t e n t i a l users and so l e s s than i d e a l s i t e s have o f t e n been chosen f o r l a n d f i l l s i t e s . This k i n d of competition i s l i k e l y to r e s u l t i n very c r i t i c a l problems i n the f u t u r e as the number of p o t e n t i a l land users i n c r e a s e . The problem i s f u r t h e r complicated by the f a c t that the p o p u l a t i o n has been i n c r e a s i n g at a r a p i d r a t e , and t h i s along w i t h i n c r e a s i n g a f f l u e n c e i s r e s u l t i n g i n tremendous increases i n the volume of waste being produced. With i n c r e a s i n g use of l e s s than i d e a l s i t e s there i s a greater p o s s i b i l i t y of r e c e i v i n g surface and ground waters being p o l l u t e d by leachate unless e f f e c t i v e methods of c o n t r o l l i n g leachate are developed. I n a d d i t i o n , many l a n d f i l l s i t e s are l o c a t e d i n areas where p r e c i p i t a t i o n r a t e s are 1 2. high and where a v a i l a b l e s o i l cover m a t e r i a l i s u n s u i t a b l e f o r s e a l i n g the l a n d f i l l against i n f i l t r a t i n g p r e c i p i t a t i o n . This speeds up the degradation process but al s o increases the r a t e of removal of l a r g e amounts of s o l u b l e substances. In many instances r a p i d degradation of the waste i s d e s i r a b l e from the standpoint that i t speeds up s t a b i l i z a -t i o n of the waste. This enables the e a r l y r e c l a mation f o r some other use but i s o f f s e t by the high concentrations found i n the leachate. Other d i s p o s a l a l t e r n a t i v e s have been t r i e d but are, i n ge n e r a l , l e s s acceptable than l a n d f i l l s . These i n c l u d e i n c i n e r a t i o n , ocean dump-i n g , composting, r e c y c l i n g , heat recovery and other l e s s common methods. The use of any of these methods i n s t e a d of s a n i t a r y l a n d f i l l i s u s u a l l y determined by some s i t u a t i o n p e c u l i a r to a p a r t i c u l a r l o c a l i t y . A number of f a c t o r s have c o n t r i b u t e d to t h e i r l i m i t e d use: (a) They are u s u a l l y very c o s t l y a l t e r n a t i v e s . (b) Some of them have adverse environmental e f f e c t s . (c) In some cases a backup s e r v i c e i s necessary i n case of breakdown or s e r v i c i n g . This i s u s u a l l y a l a n d f i l l s i t e . (d) Some are not r e a d i l y adaptable to expansion, m o d i f i c a t i o n or conversion. (e) Most of them r e s u l t i n some form of residue or by-product which has to be disposed of i n a l a n d f i l l . I t i s th e r e f o r e evident that l a n d f i l l s w i l l continue to be a very popular method of s o l i d waste d i s p o s a l . However, because the leachate produced can r e s u l t i n serious p o l l u t i o n problems there i s the need f o r e f f e c t i v e c o n t r o l methods that w i l l minimize p o t e n t i a l damage to the en v i r o n -ment. This study was th e r e f o r e e s t a b l i s h e d to i n v e s t i g a t e treatment of leachate as a means of reducing p o t e n t i a l r e c e i v i n g water degradation. CHAPTER I I RESEARCH RATIONALE I t i s apparent that leachate can create environmental hazards and t h e r e f o r e leachate c o n t r o l i s a subject r e q u i r i n g i n v e s t i g a t i o n . One aspect of c o n t r o l i s c o l l e c t i o n and treatment. This research i s d i r e c t e d towards leachate treatment w i t h s p e c i f i c reference to areas where r a i n f a l l r a tes are high and impervious cover m a t e r i a l cannot be plac e d , or to areas where i t i s f e l t d e s i r a b l e to r a p i d l y s t a b i l i z e a l a n d f i l l . One of the f i r s t things that must be assessed i s the chemical and p h y s i c a l character of the waste. Having done t h i s , then a treatment technique can be developed. I n the case of leachate the problem i s extremely complicated because i t s chemical composition can vary s i g n i f i c a n t l y . A number of f a c t o r s have c o n t r i b u t e d to the wide v a r i a t i o n i n i t s composi-t i o n - these i n c l u d e , l a r g e v a r i a t i o n i n the nature of s o l i d waste, c l i m a -t i c v a r i a t i o n , ground water f l u c t u a t i o n s , geographic l o c a t i o n , age of s i t e , depth of refuse and depth and nature of cover m a t e r i a l . Some of these f a c t o r s might be i n s i g n i f i c a n t i n one l o c a l i t y but s i g n i f i c a n t i n another. In a d d i t i o n , the a n a l y t i c a l methods used f o r determining the various c o n s t i t u e n t s may not be able to produce accurate or dependable r e s u l t s . Furthermore, the l a r g e number of substances and t h e i r p o s s i b l y high concen-t r a t i o n s can produce i n t e r f e r e n c e s , thus r e s u l t i n g i n e r r o r s . Although many f a c t o r s are known to a f f e c t the composition of leachate and the determination of the components, previous s t u d i e s have shown that . i n v a r i a b l y , leachate has very high BOD v a l u e s . TABLES I and I I i l l u s t r a t e the high concentrations of oxygen demanding m a t e r i a l s which 3 4. TABLE I  LEACHATE COMPOSITION DETERMINATION SOURCE1 (mg/1) I 2 2 2 3 3 4 3 5 3 6 3 pH 5.6 5. 9 8.3 T o t a l hardness (CaC0 3) 8,120 3,260 537 - 8,700 500 I r o n - T o t a l 305 336 219 1,000 - -Sodium 1,805 350 600 - - -Potassium 1,860 655 - - -S u l f a t e 630 1,200 99 - 940 24 Ch l o r i d e 2,240 300 2,000 1,000 220 N i t r a t e 5 18 - - -A l k a l i n i t y as CaCO^ 8,100 1,710 1,290 - - -Ammonia n i t r o g e n 845 141 - - - -Organic n i t r o g e n 550 152 - - -COD N.R. 7,130 750,000 - -BOD 32,400 7,050 720,000 - -T o t a l d i s s o l v e d s o l i d s — 9,190 2,000 - 11,254 2,075 "'"No age of f i l l s p e c i f i e d f o r Sources - o l d and 6 i s from 15-year-old f i l l . 1-3, Source 4 i s i n i t i a l , 5 i s 3-year .' Data from Los Angeles County (1968) 'Data from Emrich (1969) : 5. TABLE I I COMPOSITION OF TYPICAL LEACHATES [1] Constituent Concentration Range mg/1 I r o n Zinc Phosphate S u l f a t e C h l o r i d e Sodium Nitrogen Hardness (as CaCO^) COD T o t a l Residue N i c k e l Copper pH 200-1700 1-135 5-130 25-500 100-2400 100-3800 20-500 200-5250 100-51,000 1000-45,000 0.01-0.8 0.10-9.0 4.00-8.5 A l l values except that f o r pH are i n mg/l 6. have been reported f o r leachates. I n i t i a l a n a l y s i s of the leachate being produced i n an ongoing study a t the U n i v e r s i t y of B r i t i s h Columbia showed BOD,, and COD values as high as 25,500 and 35,406 mg/1 r e s p e c t i v e l y , as w e l l as numerous heavy metals of v a r y i n g c o n c e n t r a t i o n . Because of the presence of l a r g e amounts of oxygen demanding m a t e r i a l s , which i s of major concern, e s p e c i a l l y i n r i v e r s w i t h f i s h , i t was f e l t that f i r s t e f f o r t s should be d i r e c t e d at reducing BOD. As a r e s u l t some form of b i o l o g i c a l treatment was considered. However, the e f f e c t of heavy metals on the process, where they end up and the d i s p o s a l of the r e s u l t i n g sludge were a l l of v i t a l i n t e r e s t and would a l s o r e q u i r e i n v e s t i g a t i o n . A f t e r d e c i d i n g that b i o l o g i c a l treatment would be the f i r s t attempt, a d e c i s i o n had to be made as to what type of b i o l o g i c a l treatment was l i k e l y to be most e f f e c t i v e on a waste e x e r t i n g a high BOD. Consequently, aerobic and anaerobic d i g e s t i o n processes were evaluated i n attempting to decide which would be used. A f t e r c a r e f u l l y c o n s i d e r i n g the fe a t u r e s of both, as w e l l as the composition of the l e a c h a t e , i t was decided that anaerobic b i o l o g i c a l treatment showed greater promise. The main advantages-a t t r i b u t e d to an anaerobic system are: (a) Good treatment e f f i c i e n c y , e s p e c i a l l y w i t h waste of high BOD,can be achieved. (b) Treatment i s not l i m i t e d by an oxygen t r a n s f e r r a t e . (c) P r e l i m i n a r y work by Boyle and Ham f l ] i n d i c a t e d the s u i t a b i l i t y of anaerobic treatment f o r medium st r e n g t h l e a c h a t e . Therefore anaerobic d i g e s t i o n method was s e l e c t e d as the t r e a t -ment method f o r t h i s study. CHAPTER I I I GENERAL REVIEW OF ANAEROBIC DIGESTION 3-1 General Process D e s c r i p t i o n Anaerobic d i g e s t i o n i s a b i o l o g i c a l process i n which organic wastes are decomposed i n the absence of f r e e oxygen by micro-organisms to a more s t a b l e s t a t e . There are two stages of anaerobic decomposition, namely, l i q u e f a c t i o n and g a s i f i c a t i o n . Each stage i s c a r r i e d out by a very d i s t i n c t group of micro-organisms. (a) L i q u e f a c t i o n L i q u e f a c t i o n i n v o l v e s the conversion o f complex m a t e r i a l s such as f a t s , p r o t e i n s and carbohydrates to simple organic a c i d s . This b i o l o g i c a l conversion of s u b s t r a t e i n v o l v e s h y d r o l y s i s and fermentation, and i s brought about by f a c u l t a t i v e and anaerobic b a c t e r i a , commonly c a l l e d acid-formers. In the process s m a l l amounts of energy are r e l e a s e d f o r growth and a small p o r t i o n of the waste i s converted to new c e l l s . Although no waste s t a b i l i z a t i o n occurs during t h i s stage of treatment i t i s important i n that i t transforms the waste i n t o a d e s i r a b l e s t a t e i n p r e p a r a t i o n f o r the second stage of treatment. (b) G a s i f i c a t i o n G a s i f i c a t i o n i n v o l v e s the conversion of the organic acids i n t o gaseous end products, mainly methane and carbon d i o x i d e . I t i s i n t h i s stage that r e a l waste s t a b i l i z a t i o n occurs, because methane i s very i n s o l u b l e i n water and i t s l o s s to the system i s i r r e v e r s i b l e . Conversion i s c a r r i e d out by a s p e c i a l group 8. of b a c t e r i a c a l l e d methane formers. These b a c t e r i a are s t r i c t l y anaerobic and even s m a l l amounts of d i s s o l v e d oxygen can be harmful [ 2 ] . There are s e v e r a l d i f f e r e n t groups of methane formers, and each group i s c h a r a c t e r i z e d by i t s a b i l i t y to ferment a l i m i t e d number of organic compounds [ 2 ] . The most important methane formers l i v e on a c e t i c and p r o p i o n i c acids and grow q u i t e s l o w l y w h i l e c a r r y i n g out the major p o r t i o n of waste s t a b i l i z a t i o n . Their slow r a t e of growth and a c i d u t i l i z a t i o n represents the l i m i t i n g step around which anaerobic processes must be designed. [2] Very l i t t l e i s known of the b a s i c b i o -chemistry i n v o l v e d i n the conversion of organic acids to methane. However t r a c e r s t u d i e s have i n d i c a t e d the major sources of methane as: [3] (1) A c e t i c A c i d Cleavage CH3COOH -* CH 4 + C0 2 (1) (2) Carbon Dioxide Reduction 3-2 R e l a t i o n s h i p Between Waste S t a b i l i z a t i o n and Gas Production Waste s t a b i l i z a t i o n i n anaerobic treatment i s d i r e c t l y r e l a t e d to methane production. Buswell e t . a l . [4] developed a method to p r e d i c t the maximum q u a n t i t y of methane which could be produced from a knowledge of the waste during the complete anaerobic breakdown of an organic compound. C0 2 + 8H CH. + 2H„0 (2) (3) 9. I f i n s t e a d the waste i s s t a b i l i z e d a e r o b i c a l l y , the f o l l o w i n g r e a c t i o n would take p l a c e . Cn Ha°b + ( n + I " I> °2 * N C ° 2 + f H2° ( 4 ) From these two equations i t can be seen that one mole of methane i s produced f o r each two moles of oxygen demand s a t i s f i e d . I t can a l s o be shown that the u l t i m a t e oxygen demand of the waste i s equal to that of the methane produced during d i g e s t i o n . By c o n v e r t i n g to cubic f e e t of 3 methane per pound of oxygen a value of 5.62 f t at S.T.P. i s obtained. This provides a second method of p r e d i c t i n g methane production and that i s from an estimate of the COD or BOD ( u l t i m a t e ) s t a b i l i z a t i o n . L i Although d i g e s t e r gas i s predominantly carbon d i o x i d e and methane, sm a l l amounts of other gases have been found. McCarty [2] has suggested that f o r a healthy d i g e s t e r the percentage carbon d i o x i d e should f a l l between 25 and 45% w i t h the remainder being methane except f o r small amounts of I^S, ^ and water vapour. 3-3 Factors A f f e c t i n g Anaerobic D i g e s t i o n A p p l i c a t i o n and study over a number of years have demonstrated that c e r t a i n f a c t o r s may have favourable or unfavourable e f f e c t s on anaerobic d i g e s t i o n . Since the process i s c a r r i e d out by a h i g h l y mixed group of micro-organisms c e r t a i n optimum co n d i t i o n s must be maintained during d i g e s t i o n . The f a c t o r s most commonly assessed f o r these optimum c o n d i t i o n s are pH, a l k a l i n i t y , v o l a t i l e a c i d s , gas production and composition, n i t r o g e n , s o l i d s and temperature. Because an understanding of the f a c t o r s that e f f e c t the process was necessary i n order to design and operate the d i g e s t e r s , the most important ones were i n v e s t i g a t e d . 10. Temperature Because anaerobic d i g e s t i o n i s a b i o l o g i c a l process i t i s extremely temperature dependent. I t s a p p l i c a t i o n i s normally r e s t r i c t e d to what i s r e f e r r e d to as m e s o p h i l i c (29 - 38°C) and t h e r m o p h i l i c (48 - 56°C) ranges. In these ranges methane production as w e l l as treatment e f f i c i e n c y are higher than at lower temperatures. Although i t has been demonstrated that d i g e s t i o n r a t e s could be increased by employing t h e r m o p h i l i c d i g e s t i o n , mesophilic i s pr e f e r e d due to d i f f i c u l t y experienced i n m a i n t a i n i n g high t h e r m o p h i l i c temperatures and th e r m o p h i l i c s t a b i l i t y . [5,6]. pH, V o l a t i l e Acids and A l k a l i n i t y These three are grouped together because the pH of a l i q u o r undergoing anaerobic treatment i s r e l a t e d to s e v e r a l d i f f e r e n t acid-base chemical e q u i l i b r i a . T h e i r s i g n i f i c a n c e i n anaerobic d i g e s t i o n has been demonstrated i n many s t u d i e s . A low pH i n d i c a t e s that the 'gas formers" are under s t r e s s and the " a c i d formers" are t a k i n g over, thus r e s u l t i n g i n a b u i l d up of v o l a -t i l e a c i d s . S u f f i c i e n t a l k a l i n i t y should be present to b u f f e r the system against f a l l i n g pH and excess v o l a t i l e acids production. When d i g e s t i o n i s proceeding s a t i s f a c t o r i l y the pH should normally range from 6.6 - 7.6, a l k a l i n i t y from 1000 to 5000 mg/1 and v o l a t i l e a c i d s l e s s than 250 mg/1. N u t r i e n t Requirements In order f o r any b i o l o g i c a l process to f u n c t i o n p r o p e r l y , n u t r i e n t s r e q u i r e d by the micro-organisms must be present and 11. a v a i l a b l e . The n u t r i e n t s r e q u i r e d i n highest concentrations are n i t r o g e n and phosphorus. Since these m a t e r i a l s may be absent i n some wastes, i t i s important to know the amounts which may have to be added. Sawyer [7] e s t a b l i s h e d a r a t i o of n i t r o g e n to phosphorus to BOD^ which should be achieved i f the micro-organisms are to f u n c t i o n e f f e c t i v e l y . The r a t i o s are expressed as BOD,_:N and BOD^rP. The r a t i o s he c i t e d range from 17:1 to 32:1 f o r n i t r o g e n and 90:1 to 150:1 f o r phosphorus. These r a t i o s have been adjusted through usage to B0D^:N:P of 100:5:1 and have r e s u l t e d i n s a t i s f a c t o r y performance by the micro-organisms. N i t r a t e and n i t r i t e n i t r o g e n are u n a v a i l a b l e f o r b a c t e r i a l u t i l -i z a t i o n under anaerobic c o n d i t i o n s as they are reduced to elemen-t a l n i t r o g e n and escape as a gas. Ammonia n i t r o g e n and the p o r t i o n of organic n i t r o g e n released during waste degradation are the forms used by b a c t e r i a under anaerobic c o n d i t i o n s . As a r e s u l t , i f n i t r o g e n i s to be added i t should be i n one of these forms. In the case of phosphorus both organic and i n o r g a n i c forms are normally s u i t a b l e f o r b i o l o g i c a l use. Toxic M a t e r i a l There are many i n o r g a n i c and organic substances which may be t o x i c or i n h i b i t i n g to anaerobic d i g e s t i o n . According to McCarty [ 2 ] , "The term t o x i c i s r e l a t i v e , and the concentrations at which any substance i s t o x i c or i n h i b i t i n g may vary from a f r a c t i o n of a mg/1 to s e v e r a l thousand 12. mg/1. At some low co n c e n t r a t i o n , s t i m u l a t i o n of a c t i v i t y i s u s u a l l y achieved. This s t i m u l a t o r y c o n c e n t r a t i o n may range from a f r a c t i o n of a mg/1 f o r heavy metals to over one hundred mg/1 f o r sodium and calcium s a l t s . As the concentra-t i o n i s increased above s t i m u l a t o r y c o n c e n t r a t i o n s , the r a t e of b i o l o g i c a l a c t i v i t y begins to decrease. A p o i n t i s then reached where i n h i b i t i o n i s appar-ent and the r a t e of b i o l o g i c a l a c t i v i t y i s l e s s than t h a t achieved i n the absence of the substance. F i n a l l y at some high c o n c e n t r a t i o n the b i o l o g i c a l a c t i v i t y approaches zero. Micro-organisms u s u a l l y have the a b i l i t y to adapt, to some extent, to the i n h i b i t o r y c o n c e n t r a t i o n of most substances. The extent of adaptation i s r e l a -t i v e , and i n some cases the a c t i v i t y a f t e r a c c l i m a -t i o n may approach that obtained i n the absence of the i n h i b i t o r y substance, w h i l e i n other cases the acclima-t i o n may be much l e s s than t h i s . " Moore et a l [8, 9] conducted a comprehensive study on the e f f e c t s of heavy metals on a conventional a c t i v a t e d sludge process. However t h e i r study i n v o l v e d only four metals, namely chromium, copper, z i n c and n i c k e l . I t i n v o l v e d the a d d i t i o n of each metal at v a r y i n g concentrations to domestic sewage which was then t r e a t e d by the conventional a c t i v a t e d sludge process, followed by anaerobic d i g e s t i o n of the sludge generated. Each 13. was used i n a separate run so as to determine i t s i n d i v i d u a l e f f e c t . In a d d i t i o n , mixed doses of the four metals were a p p l i e d at d i f f e r e n t concentrations so as to i n v e s t i g a t e p o s s i b l e s y n e r g i s t i c e f f e c t s , ( i ) Chromium Concentrations of 50 mg/1 of chromium i n sludge fed to the d i g e s t e r on a d a i l y b a s i s caused gas production to f a l l and a f t e r 42 days only 75 mg/1/ day of v o l a t i l e s o l i d s were being removed. This i n d i c a t e s that at concentrations of 50 mg/1 or more there w i l l be system upset, ( i i ) Copper Two forms of copper were used, copper sulphate and of the d i g e s t e r s was measured by the l e v e l of gas production. From the r e s u l t s shown i n Table l i t ±t i evident that concentrations above 5 mg/1 copper can produce adverse e f f e c t s on the d i g e s t i o n process. a copper cyanide complex [Na^ Cu(CN)]. The performance TABLE I I I Gas Production as Related to Copper Concentration Copper i n Sewage mg/1 Primary Sludge Gas Production Combined Primary and Excess A c t i v a t e d Sludge .Gas Production 5 Normal Normal 10 Normal Subnormal 15 Subnormal Subnormal 25 Subnormal Subnormal 14. ( i i i ) Z i n c I t was found that a conc e n t r a t i o n of 20 mg/1 caused r a p i d slowing down of the d i g e s t i o n process. This i n d i c a t e s that z i n c i s very i n h i b i t o r y to anaerobic a c t i v i t y above 20 mg/1. ( i v ) N i c k e l Anaerobic d i g e s t i o n was found to be h i g h l y r e s i s t a n t to upset by n i c k e l . At a conc e n t r a t i o n of 40 mg/1 nor n o t i c e a b l e e f f e c t on the process was observed. I t was a l s o found that during d i g e s t i o n s o l u b l e n i c k e l was being converted to the i n s o l u b l e form. This was used to e x p l a i n the l a c k of upset. The combined e f f e c t of the four metals was s t u d i e d at low concentra-t i o n s . The .concentrations'iof" the heavy metals 0.4 mg/1 copper, 4.0 mg/1 chromium, 2.0 mg/1 n i c k e l and 2.5 mg/1 z i n c . At these concentrations there were no i n d i c a t i o n s of i n s t a b i l i t y . Detention Time Detention time has been shown to a f f e c t the e f f i c i e n c y of the treatment process. I t i s c l o s e l y r e l a t e d to lo a d i n g r a t e . As the detention time increases the lo a d i n g r a t e decreases, s i m i -l a r l y as the loa d i n g r a t e increases the dete n t i o n time decreases. Decreasing detention time r e s u l t s i n an i n c r e a s i n g percentage of b a c t e r i a being removed each day w i t h the e f f l u e n t . Even-t u a l l y a l i m i t i n g d etention time i s reached when the b a c t e r i a 15. are being removed from the system f a s t e r than they can reproduce themselves. McCarty [5] recommends that f o r p r a c t i c a l c o n t r o l and r e l i a b l e treatment, detention times should range from 10 to 30 days. However detention time of 5 days have been found to produce worthwhile l e v e l s of treatment. 3-4 Conclusions Anaerobic d i g e s t i o n i s s e n s i t i v e to a number of f a c t o r s and so should be designed w i t h these i n mind. Optimum n u t r i e n t requirements and operating temperatures f o r anaerobic micro-organisms have been w e l l e s t a b l i s h e d and can r e a d i l y be s a t i s -f i e d . pH was a l s o f e l t to be f a i r l y r e a d i l y c o n t r o l l a b l e through maintenance of proper l e v e l s of a l k a l i n i t y and v o l a t i l e a c i d s . This then l e f t the e f f e c t of detention time and t o x i c metal concentrations as the two main f a c t o r s to be examined. CHAPTER IV SYSTEM DESIGN AND EXPERIMENTAL PROCEDURE 4-1 Design of Treatment System The i n v e s t i g a t i o n of the theory of anaerobic d iges t ion provided the b a s i c informat ion needed to design the system. I t was decided that a s i n g l e stage bench sca le system was to be used because of i t s s i m p l i c i t y and ease of operat ion . A f t e r i n v e s t i g a t i n g previous models used i n s i m i l a r studies i t was decided to use three digesters each of 14 l i t r e s capac i ty . Th i s d e c i s i o n was based on the fac t that (1) they were r e a d i l y a v a i l a b l e i n the l a b o r a t o r y , (2) they were s u c c e s s f u l l y used i n a previous study and (3) leachate volumes a v a i l a b l e were i n s u f f i c i e n t to use l a r g e r d iges ters . The d igesters were made from transparent a c r y l i c and equipped with appur-tenances for monitoring gas product ion and composit ion, for temperature c o n t r o l and for mixing. A photograph of the laboratory set up i s shown i n F igure 1. Appurtenances (a) Temperature Controls I t was decided that the d iges ters would be operated at 35°C which f a l l s i n the mesophi l ic range (29 - 3 8 ° C ) . The operat ing temperature was maintained by the use of heat ing tapes which were regulated by a temperature c o n t r o l mechanism. With th i s arrangement the temperature of the contents w i t h i n the d igesters was kept f a i r l y constant and f luc tuated between 34.5 and 3 6 ° C . Ambient temperature was never as high as 35°C and so there was no need to consider the i n c l u s i o n of a coo l ing system. Tempera-16 FIGURE 1 LABORATORY ANAEROBIC DIGESTER 18. tures were read from thermometers suspended through the covers. The temperature c o n t r o l systems were t e s t e d w i t h water and adjusted to achieve the d e s i r e d temperature. Once set the c o n t r o l l e r s r e q u i r e d no a d d i t i o n a l adjustments. (b) Mixing Apparatus Mixing of the contents i n each d i g e s t e r was done by means of an e l e c t r i c motor d r i v e n paddle. This was considered necessary i n order to ensure uniform d i s t r i b u t i o n of food and micro-organisms. A l l three d i g e s t e r s were not operated at e x a c t l y the same mixing speed, because the degree of mixing was not being used as an operating parameter. However l i t t l e d i f f e r e n c e i n mixing c h a r a c t e r i s t i c s was observed. (c) Gas Production Monitoring System The gas produced i n the d i g e s t e r flowed through a gas vent i n the d i g e s t e r cover and then through a gas sampling tube and a f l a s k c o n t a i n i n g water then f i n a l l y through a gas meter. Passing the gas through water reduced the chances of malodourous H^S escaping i n t o the a i r and prevented p o s s i b l e d i f f u s i o n of oxygen i n t o the d i g e s t e r . 4-2 Detention Time In p r a c t i c e d etention times i n anaerobic d i g e s t i o n range from 10 to 30 days. Boyle and Ham [1] found that 5 days de t e n t i o n time gave a good degree of leachate treatment. As a r e s u l t i t was decided that i t would be worthwhile to i n c l u d e a 5 day detention time i n t h i s study. The other two d i g e s t e r s were operated at 10 and 20 days. With three detention times of 5, 10 and 20 days i t was f e l t that a good i n d i c a t i o n of the e f f e c t of 19. detention time would be obtained. 4-3 Leachate Source and C h a r a c t e r i s t i c s The leachate used as feed i n t h i s study was generated from a l y s i m e t e r which i s pa r t of a s o l i d waste p r o j e c t at the U n i v e r s i t y of B r i t i s h Columbia. D e t a i l s of the l y s i m e t e r are: (1) Dimensions - 14 feet deep, 4 f e e t i n diameter (2) Cover m a t e r i a l - 2 feet of sandy c l a y (3) Depth of garbage - 8 f e e t (4) R a i n f a l l r a t e - 90 inches per year (5) Wet density of garbage - 953 l b s . per cubic f e e t (6) Moisture content of garbage - 37% (7) Percentage composition of garbage Food waste - 11.8 Garden waste - 9.8 Paper products - 47.6 Cardboard - 5.4 T e x t i l e s - 3.6 Wood - 4.7 Metals - 8.7 Glass and Ceramics - 7.0 Ash, Rocks and D i r t - 1.4 T o t a l - 100 The composition of the leachate v a r i e d during the p e r i o d i t was used as feed. Table IV shows i t s composition during t h i s p e r i o d . Leachate was c o l l e c t e d on a weekly b a s i s and st o r e d f o r three weeks a f t e r which time TABLE IV COMPOSITION OF LEACHATE FEED USED DURING STUDY Component Concentration mg/1 1st - 4th day Concentration mg/1 5th - 25th day Concentration mg/1 26th - 47th day Concentration mg/1 48th - 64th day BOD 16,011 12,655 11,487 11,811 COD 32,562 27,870 23,571 21,146 T o t a l Carbon 11,140 9,500 ,8,500 7,300 Organic Carbon 11,140 9,500 8,500 7,300 T o t a l S o l i d s 15,880 14,015 11,245 10,303 V o l a t i l e S o l i d s 9,397 8,150 6,363 5,588 Di s s o l v e d S o l i d s 15,405 13,357 10,789 9,812 A l 3.4 2.3 1.6 1.2 Ba 0.44 0.20 0.31 0.11 Be 0.0 0.0 0.0 0.0 Ca 1,680 1,415 1,170 1,065 Cd 0.025 0.0 0.20 0.0 CI 1,060 1,014 851 620 Cr 0.40 0.20 0.16 0.12 Cu 0.055 0.037 0.04 0.03 Fe 560 628 588 620 Hg 0.0 0.01 0.006 0.0 K 710 585 480 350 Mg 156 128 100 84 Mn 20.6 24.6 13.5 12.8 N-Total 693 693 517 511 NH 3 624 494 454 401 Na 690 575 450 400 N i 0.27 0.19 0.21 0.15 P-Total 12.3 13.1 10.1 10.9 Pb 1.41 0.37 0.88 0.37 SO. 4 473 410 350 192 Zn 90 65 57 46 Tannin & L i g n i n 640 592 396 530 pH* 5.1 5.15 5.21 5.31 * not i n mg/1 21. i t was mixed to produce a composite sample. Storage was at 4°C so as to minimize b i o l o g i c a l a c t i v i t y before feeding. 4-4 N u t r i e n t Balance In order to maintain a BOD^:N:P r a t i o of 100:5:1 a d d i t i o n a l N or P was needed. A number of chemicals were considered f o r t h i s purpose. Di-ammonium phosphate [(NH^^HPO^] was s e l e c t e d because i t s u p p l i e d both N and P i n forms s u i t a b l e f o r u t i l i z a t i o n by anaerobic micro-organisms. An exact r a t i o of 5:1 f o r N:P could not be achieved because a s i n g l e com-pound was the source of both. Instead the 100:5 r a t i o of BOD to N was e s t a b l i s h e d w i t h the r e s u l t i n g phosphorus concentrations shown i n Table'V. TABLE y B0Dc:N:P RATIO USED IN STUDY Feed Batch B0D 5 N P 1 100 5 1.28 2 100 5 1.30 3 100 5 1.24 4 100 5 1.86 The s l i g h t excess of P was of l i t t l e concern as these small concentrations have not shown any d e t r i m e n t a l e f f e c t on d i g e s t i o n . 4-5 pH C o n t r o l Because the pH of the leachate was w e l l below 6.6 i t was f e l t that pH c o n t r o l might be necessary. I t was decided that i f t h i s was ever necessary calcium'hydroxide would be used on a t r i a l and e r r o r b a s i s . 22. 4-6 Metal Concentrations No attempt was made to modify metal concentrations. I t was f e l t that the best approach would be to use leachate as produced and observe the p o s s i b l e e f f e c t s of the metals on the d i g e s t i o n process. 4-7 A n a l y s i s Schedule and Procedure Table VI shows the sampling and a n a l y s i s schedule followed f o r the e f f l u e n t and gas. TABLE VI  SAMPLING AND ANALYSIS SCHEDULE A n a l y s i s Frequency T o t a l E f f l u e n t Centrifuged E f f l u e n t D i g e s t e r Gas BOD5 2/week X X pH d a i l y X A l k a l i n i t y d a i l y X Gas Production 1/3 days X Gas A n a l y s i s 2/week X V o l a t i l e Acids o c c a s i o n a l l y X C.O.D. o c c a s i o n a l l y X X N and P X X In the event that a n a l y s i s of the e f f l u e n t was delayed f o r one or more days, the samples were immediately r e f r i g e r a t e d at 4°C u n t i l the t e s t was per-formed. The a n a l y t i c a l techniques used are o u t l i n e d i n the 13th e d i t i o n of Standard Methods [10] and f u r t h e r explained i n Chemistry f o r Sa n i t a r y Engineers [11]. I n some cases i t was necessary to d i l u t e the samples 23. before a n a l y z i n g . A s e r i e s of t e s t s e s t a b l i s h e d the proper d i l u t i o n s which remained f a i r l y constant throughout the e n t i r e study. A complete a n a l y s i s of the composite i n f l u e n t sample was performed once every three weeks (Table I V ) . The composition of the d i g e s t e r gas was determined on a Research Gas Chromatograph equipped w i t h a Gas P a r t i t i o n e r . D e t a i l s of the Chromatograph and P a r t i t i o n e r are: (1) Chromatograph - Hewlett Packard 5750 (2) Gas P a r t i t i o n e r - F i s h e r Hamilton 29 - w i t h two 6 f e e t columns. Column 1 - 6' x 1/4" aluminum, packed w i t h 30% D.E.H.S. on 60 - 80 mesh Chromosorb. Column 2 - 6' x 3/6" Aluminum, packed w i t h 40 - 60 mesh molecular s i e v e 13X. 4-8 S t a r t i n g Up the Digesters In order to e s t a b l i s h the three d i g e s t e r s , seven l i t r e s of sludge from an anaerobic d i g e s t e r at a domestic sewage treatment p l a n t were i n t r o -duced i n t o each. The d i g e s t e r s were l e f t f o r a day to make c e r t a i n gas was being produced. In order to maintain and develop acclimated micro-organisms each d i g e s t e r was i n i t i a l l y fed 0.5 l i t r e s of feed per day and no wasting took place during t h i s feeding. The feeding of 0.5 l i t r e s to each d i g e s t -er was continued u n t i l they were a l l f i l l e d to 14 l i t r e s . When the d i g e s t e r s were f u l l y s t a b i l i z e d the t o t a l volume i n each was reduced to 10 l i t r e s . The r e s u l t i n g operating c o n d i t i o n s are shown i n Table V I I . 24. TABLE VII OPERATING CONDITIONS FOR FULLY ESTABLISHED DIGESTERS Digester # T o t a l Volume of d i g e s t e r contents ( l i t r e s ) Detention Time (Days) ! Feed Rate 1/day Wasting Rate 1/day 1 10 5 2.0 2.0 2 10 10 1.0 1.0 3 10 20 0.5 0.5 I t took a number of months to e s t a b l i s h a v i a b l e c u l t u r e i n the d i g e s t e r s . During these months numerous problems were encountered, however i n v a l u a b l e experience was gained i n operating an anaerobic d i g e s t i o n system. The pH of the sludge used to seed the d i g e s t e r s was 7.1. A f t e r feeding w i t h leachate, having a pH of 5.21, f o r a week the pH w i t h i n the d i g e s t e r s f e l l below 6.6. As a r e s u l t C a ^ H ^ - solution-was added to the feed i n s u f f i c i e n t q u a n t i t y to r a i s e the pH to w i t h i n the range of 6.6 - 7.6. This was c o n t i n -ued f o r three weeks but the pH w i t h i n the d i g e s t e r s s t i l l remained below 6.6„Ca(OH)2 s o l u t i o n was then added d i r e c t l y to the d i g e s t e r s i n s m a l l amounts on a d a i l y b a s i s . A f t e r 5 days of Ca(0H)2 a d d i t i o n the pH rose suddenly to 7.9. Further a d d i t i o n s were then suspended. Digesters 1 and 3 recovered sl o w l y from the h i g h pH and e v e n t u a l l y s t a b i l i z e d , w i t h no f u r t h e r lime a d d i t i o n , a t pH-'s of 7.35 and 7.45 r e s p e c t i v e l y . A f t e r t h i s the pH d i d not vary much f o r the duration of the study. D i g e s t e r 2 never recovered and e v e n t u a l l y gas production stopped. A second attempt to e s t a b l i s h i t a l s o f a i l e d . On the t h i r d attempt, e f f l u e n t from d i g e s t e r s 1 25. and 3 was used as seed and t h i s proved s u c c e s s f u l w i t h the d i g e s t e r s t a b i l i z i n g at a pH of 7.4. Other parameters besides pH were used as i n d i c a t i o n of s t a b i l i -z a t i o n . These i n c l u d e d a c i d n e u t r a l i z i n g ' c a p a c i t y , B.O.D.^, gas composi-t i o n and production and v o l a t i l e a c i d s . During the s t a r t i n g up p e r i o d , analyses were done on a more frequent b a s i s than that o u t l i n e d i n Table VI. A f t e r s t a b i l i z a t i o n d i g e s t e r s 1 and 3 were operated f o r 64 days and d i g e s t e r 2 f o r 34 days. 4-9 Summary Minor d i f f i c u l t i e s were encountered during the study but none of these changed the o b j e c t i v e s . Stable o p e r a t i o n was achieved 4 months a f t e r s t a r t i n g up. W e l l balanced and s t a b l e anaerobic d i g e s t i o n s t u d i e s were then conducted f o r periods of 34 and 64 days. As no i n o r g a n i c carbon i s present i n the leachate the carbonate system i s a l s o not present. Therefore, the term a c i d n e u t r a l i z i n g c apacity i s used because the term a l k a l i n i t y i m p l i e s the presence of the carbonate system. The r e s u l t s are reported i n m i l l i e q u i v a l e n t s per l i t r e so as to avoid having to r e f e r to the n o r m a l i t y and k i n d of a c i d . A l l m i l l i -e q u ivalents were determined by t i t r a t i n g to the a r b i t r a r y pH of 4.5. CHAPTER V ANALYSIS OF RESULTS 5-1 Removal of Oxygen Demanding M a t e r i a l (a) . BOD,. Removal Table V I I I shows percentage removal based on i n f l u e n t and e f f l u e n t BOD5. E f f l u e n t BOD i s the BOD5 of a completely mixed sample of the d i g e s t e r contents. I t can be seen t h a t h i g h l e v e l s of treatment were obtained ranging from 80 to 96 per cent. As the detention time was increased the per cent removal increased. Decreases i n the i n f l u e n t BOD,, d i d not a f f e c t t h i s p a t t e r n . The decrease i n i n f l u e n t BOD,, was accompanied by a decrease i n heavy metal concentration as shown i n Table IX. The only s i g n i f i c a n t exception was the lead c o n c e n t r a t i o n i n batch 3. This higher concentration of lead d i d not have any n o t i c e a b l e e f f e c t on d i g e s t e r performance. Batch 1 had the highest BOD,, and metal concentrations and a l s o r e s u l t e d i n the hi g h e s t amounts of BOD,, removal per l i t r e of feed. Consequently, there was no i n d i c a t i o n of the heavy metals having any e f f e c t on process performance. Table X shows per cent removal based on BOD,, of the i n f l u e n t and that of the c l a r i f i e d e f f l u e n t obtained a f t e r s e t t l i n g i n a 1000 ml graduated c y l i n d e r f o r h a l f an hour. This was done to determine whether or not s e t t l i n g would produce an e f f l u e n t q u a l i t y much higher than that of the completely mixed e f f l u e n t . These r e s u l t s along w i t h those f o r the completely mixed e f f l u e n t 26 TABLE V I I I AVERAGE PERCENTAGE BODr REMOVAL Batch 1, BOD of Feed = 16,011 mg/1 (a s i n g l e a n a l y s i s was done) Digester # Detention Time (Days) % Removal Average % Removal Average BOD5 Remaining (mg/1) 1 5 81.1 81.1 3020 2 10 3 20 92.8 92.8 1150 Batch 2, BOD of Feed = 12,655 mg/1 Digester # Detention Time (Days) Range of % Removal Average % Removal Average BOD5 Remaining (mg/1) 1 5 78.6-82.1 80.2 2,500 2 10 3 20 9 3 . 2 - 9 4 . 9 94.1 740 Batch 3, BOD- of Feed = 11,487 mg/1 Digester # Detention Time (Days) Range of % Removal Average % Removal Average BOD,. Remaining (mg/1) 1 5 78.1-81.5 79.9 2,300 2 10 87.1-89.7 88.7 1,300 3 20 94.6-95.8 95.3 540 28. TABLE V I I I - Cont'd Batch 4,.BOD 5.of.Feed = . 11,811 mg/1 Di g e s t e r •# Detention Time (Days) Range of % . Removal Average % . . Removal. Average BOD5 Remaining (mg/1) 81.2-81.7 81.5 2,180 10 87.6-90.3 89.2 1,250 20 95.6-96.9 96.2 440 *• 29. TABLE IX BOD5 AND HEAVY METAL CONCENTRATION OF EACH SUCCESSIVE BATCH OF FEED Component mg/1 Batch of Feed #1 #2 #3 #4 BOD5 16,011 12,655 11,487 11,811 AI 3.4 • 2.3 1.6 1.2 Cd 0.025 not detectable not detectable not detectable Cr 0.4 . . 0.2 0.16 0.12 Cu 0.055 0.037 0.04 0.03 Hg not detectable 0.01. 0.006 . not detectable N i 0.27 0.19 0.21 0.15 Pb 1.41 0.37 0.88 0.37 Zn 90 65 57 46 30. TABLE X AVERAGE PER CENT REMOVAL BASED ON SETTLED . EFFLUENTBOD,. Batch 1, BOD. of Feed = 16,011 mg/1 Digester # Retention Time (Days) Range of % Removal Average % Removal Average BOD5 Remaining (mg/1) 1 5 84.2 84.2 2,530 2 10 3 20 96.3 96.3 594 Batch 2, BOD5 of Feed = 12,655 mg/1 Digester # Retention Time (Days) Range of % Removal . Average % Removal Average BOD5 Remaining (mg/1) 1 5 81.1-85.1 82.9 2,165 2 10 3 20 96.1-97.1 96.7 415 31. TABLE X - Cont'd . . . . Batch 3, BOD of Feed = 11,487 mg/1 Dig e s t e r # Retention Time (Days) Range of % . Removal Average % Removal Average BOD5 Remaining.(mg/1) 1 5 81.5-83.7 82.3 1,992 2 10 90.2-92.0 91.1 1,005 3 20 96.4-97.7 96.9 541 Batch 4, BOD5 of Feed = 11,811 mg/1 Dige s t e r # Retention Time (Days) Range of % Removal Average % Removal Average BOD5 Remaining (mg/1) 1 5 83.3-84.3 83.9 1,897 2 10 92.5-92.9 92.7 865 3 20 98.0-98.9 98.4 188 32. are shown i n Figure 2 f o r d i f f e r e n t detention times. By comparing these p l o t s f o r the d i f f e r e n t batches of feed i t can be seen that s e t t l i n g increases the per cent BOD,, removal by 2 to 3 per cent. I t a l s o shows that a l a r g e percentage of the BOD,, remaining a f t e r d i g e s t i o n i s suspended. Although the 2 to 3 per cent removal achieved by s e t t l i n g appears i n s i g n i f i -cant, i t can be worthwhile, e s p e c i a l l y i n areas where d i s s o l v e d oxygen i n the r e c e i v i n g water i s important. Figure 2 a l s o shows that no optimum detention time was achieved i n t h i s study because, as detention time i n c r e a s e d , per cent removal increased at a decreasing r a t e . However the graphs i n d i c a t e that detention times of 25 to 30 days would r e s u l t i n a higher degree of treatment. C.O.D. Removal Because i t was decided that BOD,, would be used as the p r i n c i p a l method of e s t i m a t i n g the degree of treatment, COD removal was determined only once. These r e s u l t s are shown i n Table XI. The r e s u l t s show t h a t , as de t e n t i o n time i n c r e a s e d , the per cent removal increased. This followed a s i m i l a r p a t t e r n f o r BOD,. removal. However, the l e v e l of removal i s higher i n the case of BOD,, than i n the case of COD. This i s understandable because COD includes both chemically o x i d i z a b l e organics which are not a v a i l a b l e to the micro-organisms and those which are slowly o x i d i z e d by the micro-organisms. 33. 9 5 o > o !! 9 0 or i m Q O CD 85 80 A l B I b o t c h of f e e d - BOD B = 16,011 m g / l i t r e O 2 n d b o t c h o f f e e d - B 0 D 8 = I 2 , 6 5 5 m g / l i t r e m i x e d e f f l u e n t s e t t l e d e f f l u e n t I I 100 > o E or i i n Q O CD 90 80 h-77.5 3 r d b a t c h o f f e e d - B 0 D 8 = l l , 4 8 7 m g / l i t r e 4 ' " b a t c h of f e e d - B 0 D 8 = II, 811 mg / l i t r e m i x e d e f f l u e n t s e t t l e d e f f l u e n t 10 15 T i me - days 20 25 Figure 2 PERCENTAGE B0D 5 REMOVAL VS. DETENTION TIME-DAYS TABLE XI PERCENTAGE C.O.D. REMOVAL Batch 3 - I n f l u e n t COD = 23,571 mg/1 Digester Retention Time (Days) E f f l u e n t COD (mg/1) % Removal 1 5 8,250 65.0 2 10 7,324 68.9 3 20 4,875 79.3 35. 5-2 Gas Composition Table XII shows the average gas composition f o r the three d i g e s t e r s over the p e r i o d of o p e r a t i o n . I t can be seen that detention time has d e f i n i t e e f f e c t s on gas composition. With an i n c r e a s e i n deten-t i o n time there was an increase i n the percentage of n i t r o g e n and a corresponding decrease i n that of methane w h i l e that of carbon d i o x i d e remained f a i r l y constant. I n order to e x p l a i n t h i s , a balance of t o t a l n i t r o g e n and ammonia-nitrogen was performed on the i n f l u e n t and e f f l u e n t of each d i g e s t e r at the end of the study. These r e s u l t s are shown i n Table X I I I . I t i s evident that there was l i t t l e d i f f e r e n c e between the i n f l u e n t and e f f l u e n t concentrations of the ammonia-nitrogen i n a l l three d i g e s t e r s . However, i n the case of t o t a l n i t r o g e n the e f f l u e n t concentrations showed a d e f i n i t e decreasing trend w i t h i n c r e a s i n g detention time. I t i s there-f o r e apparent that d e n i t r i f i c a t i o n was t a k i n g p l a c e i n the d i g e s t e r s and that w i t h i n c r e a s i n g detention time n i t r i t e and n i t r a t e conversion to f r e e n i t r o g e n was i n c r e a s i n g . This r e s u l t e d i n increased amounts of n i t r o g e n i n the d i g e s t e r gas. The f a c t that the percentage decrease i n methane c o r r e s -ponded to the percentage increase i n n i t r o g e n i n d i c a t e s t h a t , w i t h increased detention time, there i s competition f o r s u b s t r a t e between methane forming and d e n i t r i f y i n g b a c t e r i a . I t i s to be noted that small q u a n t i t i e s of oxygen were present i n the gas samples. I t s presence i s a t t r i b u t e d to the d i f f u s i o n of small amounts of a i r i n t o the syringe c o n t a i n i n g samples f o r i n j e c t i o n i n t o the gas chromatograph. The average oxygen content found i n the samples ranged from 0.15 to 0.4 per cent. Based on the composition of a i r of 20 per cent oxygen to 80 per cent n i t r o g e n , d i f f u s i o n of a i r i n t o the syringe would 36. TABLE X I I AVERAGE COMPOSITION OF DIGESTER GAS Digester 1 Detention Time = 5 days, Feed Rate = 2.0 l i t r e s / d a y Gas Components Measured L i m i t s i n Per Cent Average Per Cent CH. 4 74.1-76.9 75.0 co 2 23.0-25.0 24.0 N 2 0.4-1.9 1.13 °2 0.0-0.3 0.15 Digester 2 Detention Time = 10 days, Feed Rate = 1.0 l i t r e s / d a y Gas Components Measured L i m i t s i n Per Cent Average Per Cent CH. 4 71.1-74.5 72.8 co 2 23.1-25.0 23.9 N 2 1.4-5.0 3.2 °2 0.0-0.3 0.15 37. TABLE X I I - Cont'd . . . . Dig e s t e r 3 Detention Time = 20 days, Feed Rate =0.5 l i t r e s / d a y Gas Measured L i m i t s Average Components i n Per Cent Per Cent CH. 4 67.3-70.7 69.0 co 2 23.1-25.6 24.4 N2 5.2-8.1 6.6 °2 0.0-0.8 0.4 38. TABLE X I I I BALANCE OF TOTAL AND AMMONIA-NITROGEN IN  DIGESTER LIQUID Digester # Detention Time (Days) T o t a l N i n Feed I n c l u d i n g N added (mg/1) T o t a l N i n E f f l u e n t (mg/1) 1 5 478.9 467.8 2 10 478.9 449.0 3 20 478.9 416.4 Dig e s t e r # Detention Time (Days) T o t a l NH 3-Nitrogen i n Feed i n c l u d -ing NH3-nitrogen added (mg/1) T o t a l NH 3-Nitrogen i n E f f l u e n t (mg/1) 1 5 396 398.0 2 10 396 400.5 3 20 396 394.0 39. th e r e f o r e i n c r e a s e the n i t r o g e n content by an average of 0.6 to 1.6 per cent. As these percentages are much lower than the percentage of ni t r o g e n found i n the d i g e s t e r gas i t remains evident that d e n i t r i f i -c a t i o n increases w i t h increased detention time. According to Buswell's [4] equation (equation 3, page 8) p r e d i c t i n g methane production, the r a t i o of methane to carbon d i o x i d e should be 1 to 1. However, from the r e s u l t s shown i n Table X I I , the r a t i o of methane to carbon d i o x i d e i s 3 to 1. Two major f a c t o r s are re s p o n s i b l e f o r t h i s d i f f e r e n c e : (1) methane i s completely i n s o l u b l e i n the l i q u i d whereas carbon d i o x i d e i s s o l u b l e to a c e r t a i n e x tent, (2) some of the carbon d i o x i d e produced i s reduced to methane as shown i n equation 5. C0 2 + 4H 2 + CH4+ + 2H 20 (5) Table XIV shows gas composition as a f u n c t i o n of i n f l u e n t BOD,.. From these r e s u l t s , i t can be seen that v a r i a t i o n i n feed BOD,, d i d not a f f e c t gas composition. I f the heavy metals had any e f f e c t on gas composi-t i o n , t h i s i s not evident from the r e s u l t s . 5-3 Gas Production Table XV shows the average gas production per l i t r e of feed and also per pound of BOD,, removed. From column 5 i t can be seen t h a t , as detention time was increas e d , the volume of gas produced per l i t r e of feed increased. I t i s al s o evident that a decrease i n the i n f l u e n t BOD,, di d not e f f e c t t h i s p a t t e r n . Table XVI shows the data presented i n column 5 of Table XV i n r e l a t i o n to heavy metal concentration i n the feed. As p r e v i o u s l y s t a t e d there i s no i n d i c a t i o n that the heavy metals a f f e c t e d the process. 40. TABLE XIV AVERAGE GAS COMPOSITION AS A FUNCTION OF INFLUENT BOD Digester #1 Detention Time = 5.days Di g e s t e r #2 Detention Time = 1 0 days Digester //3 Detention Time = 2 0 days BOD5 of Feed (mg/1) Gas Components Per Cent Per Cent Per Cent 16,011 CH. 4 74.6 69.8 c o 2 23.8 23.5 N 2 1.3 6.0 ° 2 0.3 0.53 12,655 CH. 4 74.8 ,74.9 e o 2 24.1 24.9 N 2 1.1 5.8 °2 0.0 0.47 11,487 CH. 4 76.0 73.1 69.1 c o 2 23.2 23.2 24.2 N 2 0.6 2.7 6.5 °2 0.03 0.11 0.12 11,811 CH. 4 76.3 72.4 69.2 c o 2 22.5 23.5 24.5 N 2 1.1 3.2 6.1 °2 0.03 0.13 0.11 41. TABLE XV GAS PRODUCTION IN RELATION TO DETENTION TIME AND BODc REMOVAL (See Appendix D f o r Sample C a l c u l a t i o n ) Batch 1, BOD of feed = 16,011 mg/l (1) (2) (3) (4) (5) (6) Digester # Feed Rate (1/day) E f f l u e n t BOD5 (mg/l) BOD5 Removal (mg/l of feed) Gas Production (l/l of feed) Gas Produced per l b BOD5 removed ( f t ^ ) 1 2.0 3019 12,992 9.7 11.9 2 1.0 3 0.5 1153 14,858 10.6 11.4 Batch 2, BOD of feed = 12,655 mg/l Digester // Feed Rate (1/day) E f f l u e n t BOD5 (mg/l) BOD5 Removal (mg/l of feed) Gas Production (£/£ of feed) Gas Produced per l b BOD5 removed ( f t 3 ) 1 2.0 2500 10,155 9.2 14.6 2 1.0 3 0.5 740 11,915 10.4 14.0 42. TABLE XV - Cont'd . . . . Batch 3, BOD. of feed = 11,487 mg/1 Digester # Feed Rate (1/day) E f f l u e n t BOD 5 (mg/1) B0D5 Removal (mg/1 of feed) Gas Production (l/l of feed) Gas Produced per l b BOD5 removed ( f t ^ ) 1 2.0 2304 9,183 8.6 15.0 2 1.0 1300 10,187 9.3 14.6 3 0.5 540 10,947 9.8 14 . 3 " ' Batch 4, BOD5 of feed = 11,811 mg/1 Digester # Feed Rate (1/day) E f f l u e n t B0D5 (mg/1) BOD,. Removal (mg/1 of feed) Gas Production (l/l of feed) Gas Produced per l b BOD. removed ( f t ^ ) 1 2.0 2177 9,634 9.1 15.0 2 1.0 1254 10,557 9.6 14.5 3 0.5 443 11,367 10.1 14.2 43. TABLE XVI .GAS PRODUCTION PER LITRE OF FEED IN RELATION TO HEAVY METAL CONCENTRATIONS Heavy Metal Component Concentration (mg/l) 5 days detention 10 days det e n t i o n 20 days detention time time time A l Cd Cr 3.4 0.025 0.4 I of gas produced/ l i t r e of feed . . 1 of gas produced/ l i t r e of feed £ of gas produced/ l i t r e of ... feed Cu 0.055 Hg 0.0 9.7 - 10.6 N i 0.27 Pb 1.41 Zn 90 Heavy Metal Component Concentration (mg/l) 5 days detention time 10 days detention time 20 days detention time A l Cd Cr 2.3 0.0 0.2 i of gas produced/ l i t r e of feed I of gas produced/ l i t r e of feed I of gas produced/ l i t r e of feed Cu Hg 0.037 0.01 9.2 - 10.4 N i 0.19 Pb 0.37 Zn 65 4 4 . Table XVI - Cont'd . . . . 1 Heavy Metal Component Concentration (mg/D 5 days det e n t i o n time 10 days detention time 20 days detention time AI Cd Cr Cu Hg N i Pb Zn 1.6 0.02 0.16 0.04 0.006 0.21 0.88 57 H of gas produced/ l i t r e of feed I of gas produced/ l i t r e of feed I of gas produced/ l i t r e of feed 8.6 8.8 9.8 Heavy Metal Component Concentration (mg/1) 5 days detention time 10 days detention time 20 days detention time AI Cd Cr Cu Hg N i Pb Zn 1.2 0.0 0.12 0.03 0.0 0.15 0.37 46 I of gas produced/ l i t r e of feed I of gas produced/ l i t r e of feed I of gas produced/ l i t r e of feed 8.6 9.0 10.1 45. Gas product ion was also inves t iga ted i n terms of BOD,, removal. From Table XV i t can be seen that BOD,, removal and gas product ion rates increased with detention time. However the BOD,, removal rates showed a greater increase than the gas product ion rate and so the volume of gas produced per pound of BOD,, removed decreased with increased detent ion time. This reduct ion i n gas product ion per pound of BOD^ removed i s to be expected because the d e n i t r i f y i n g b a c t e r i a have a greater growth y i e l d c o e f f i c i e n t and so produce new c e l l s at the expense of gas p r o -duct ion . Methane product ion was determined i n r e l a t i o n to C . O . D . removal for the t h i r d batch of feed. This was done on one occasion on ly . The r e s u l t s are shown i n Table XVII . TABLE XVII METHANE PRODUCTION IN RELATION TO COD REMOVAL Digester # Feed Rate (Jl/day) C . O . D . Removed (mg/1 of feed) Gas Product ion (£, /£ of feed) Methane Product ion (SL/SL of feed) Methane Product ion per lb of COD removed (ft^) 1 2.0 15,321 8.6 6.50 6.8 2 1.0 16,247 8.8 6.41 6.31 3 0.5 18,696 9.8 6.77 5.80 46. From the r e s u l t s , i t can be seen that the volume of methane produced 3 per pound of C.O.D. removed i s greater than the 5.62 f t per pound of C.O.D. removed at S.T.P. as i s reported by Buswell [4]. This d i f f e r e n c e i s a t t r i b u t e d to the r e d u c t i o n of a p o r t i o n of the carbon d i o x i d e to methane. 5-4 S t a b i l i t y Parameters A number of parameters were measured and used as i n d i c a t o r s of di g e s t e r s t a b i l i t y . These included a c i d n e u t r a l i z i n g c a p a c i t y , pH, sus-pended and v o l a t i l e suspended s o l i d s . A l l these parameters remained e s s e n t i a l l y constant throughout the study and so i n d i c a t e d the maintenance of s t a b l e operation. These parameters are i n c l u d e d i n Appendices A,B and C. During the e a r l y stages of s t a b l e o p e r a t i o n , the d i f f e r e n c e between i n f l u e n t and e f f l u e n t pH may have been achieved by the i n i t i a l lime feed-i n g , which r e s u l t e d i n a good b u f f e r c a p a c i t y w i t h i n the systems. Previous anaerobic d i g e s t i o n s t u d i e s have i n d i c a t e d the need f o r a bicarbonate-carbonate system to maintain adequate b u f f e r c a p a c i t y . However i n t h i s case no bicarbonate-carbonate system was present due to the absence of any i n o r g a n i c carbon i n the leachate. This shows that a bicarbonate-carbonate system i s not necessary i f other more complex b u f f e r i n g systems are capable of maintaining s t a b l e o p e r a t i o n . I t i s a l s o p o s s i b l e that the micro-organisms could c o n t r i b u t e to the more complex b u f f e r i n g system. 5-5 Metal D i s t r i b u t i o n With i i i the E f f l u e n t The d i s t r i b u t i o n of metals w i t h i n the e f f l u e n t was of s p e c i a l i n t e r e s t f o r three reasons. (1) I t can provide i n f o r m a t i o n needed to decide on a s a t i s f a c t o r y 47. method of sludge d i s p o s a l . (2) The need f o r a d d i t i o n a l treatment of the l i q u i d e f f l u e n t to remove the heavy metals can be i d e n t i f i e d . (3) Depending on where the heavy metals are concentrated, the p o s s i b i l i t y of t o x i c i t y can be assessed. In order to do t h i s , the concentrations of the v a r i o u s metals i n the mixed e f f l u e n t , as w e l l as the l i q u i d and dry f r a c t i o n s , were determined f o r a l l three d i g e s t e r s . This was done on two occasions and the analyses were performed on e f f l u e n t samples obtained on the l a s t day of feeding w i t h a p a r t i c u l a r batch of feed. For batches 2 and 3 t h i s was a f t e r 24 and 46 days of s t a b l e operation r e s p e c t i v e l y . The r e s u l t s along w i t h the i n f l u e n t concentrations are shown i n Tables X V I I I , XIX, XX, XXI and XXII. From columns 2 and 3 of the Tables i t can be seen t h a t , i n the case of some metals, there were b i g d i f f e r e n c e s between the i n f l u e n t and mixed e f f l u e n t concentrations. T h e o r e t i c a l l y these two concentrations should be equal because the e f f l u e n t samples used f o r a n a l y s i s were c o l l e c t e d a f t e r feeding w i t h a p a r t i c u l a r batch of feed f o r at l e a s t twenty days which i s equal to the longest detention time. The concentrations of calcium, i r o n and manganese i n the mixed e f f l u e n t were as much a s . f i f t y per cent lower than i n the i n f l u e n t s . These three metals are known to form a wide range of c h l o r i d e and sulphide com-pl e x e s , some of which are very s o l u b l e and some very i n s o l u b l e . Large amounts of both c h l o r i d e and sulphate were present i n the i n f l u e n t s . I t i s l i k e l y that the sulphate was reduced to sulphide :• and so i n s o l u b l e complexes of sulphides were formed w i t h calcium, i r o n and manganese. The TABLE XVIII METAL DETERMINATION IN DIGESTER #1, DETENTION TIME = 5 DAYS, 2ND BATCH OF FEED Mixed e f f l u e n t volume = 1 l i t r e s , L i q u i d f r a c t i o n = 0.966 l i t r e s . Dry weight of sludge = 29;000 CD (2) (3) (4) (5) (6) (7) Metal Component I n f l u e n t Concentration (mg/l) Mixed E f f l u e n t Concentration (mg/l) Centrifuged E f f l u e n t Concentration (mg/l) Concentration i n l i q u i d f r a c -t i o n (PPM) Concentration i n dry sludge (PPM) Percent of metal i n dry sludge Aluminum 2.3 2.5 0.4 0.4 72.9 84.5 Barium 0.2 0.31 0."l2 0.12 6.7 62.6 Cadmium not detectable 0.03 not detectable not detectable 1.03 100 Calcium 1415 748 580 580 23.9 25.1 Chromium 0.2 0.22 0.1 0.1 4.3 56.1 Copper 0.03 0.21 0.19 0.19 0.009 12.6 Iron 628 394 40 40 21.9 90.2 Lead 0.37 0.77 0.14 0.14 21.9 82.4 Magnesium 128 120 120 120 140 3.4 Manganese 24 13.4 3.9 3.9 332 71.9 Mercury 0.01 not detectable not detectable not detectable not detectable -N i c k e l 0.19 0.31 0.072 0.072 8.3 77.6 Potassium 585 624 624 624 730 0.17 Sodium 575 588 590 590 625 3.1 Zinc 65 68.0 0.42 0.42 2330 99.4 TABLE XIX METAL DETERMINATION IN DIGESTER #3, DETENTION TIME = 20 DAYS, 2ND BATCH OF FEED Mixed e f f l u e n t volume = 1 l i t r e ; L i q u i d f r a c t i o n = 0.954 l i t r e s , Dry weight of sludge = 23,700 mg (1) (2) (3) (4) (5) (6) (7) Metal Component I n f l u e n t Concentration (mg/1) Mixed E f f l u e n t Concentration (mg/1) Centrifuged E f f l u e n t Concentration (mg/1) Concentration i n l i q u i d f r a c t i o n (PPM) Concentration i n dry sludge (PPM) Percent of metal i n dry sludge Aluminum 2.3 3.1 0.4 0.4 80.5 87.7 Barium 0.2 0.19 not detectable not detectable 5.64 100 Cadmium not detectable 0.01 not detectable not detectable 0.29 100 Calcium 1415 610 314 314 9200 50.9 Chromium 0.2 0.26 0.1 0.1 4.9 63.5 Copper 0.03 0.27 0.04 0.04 6.83 85.2 Iron 628 440 12.0 12.0 12700 97.4 Lead 0.37 0.68 0.14 0.14 16.2 80.3 Magnesium 128 138 122 122 640 15.7 Manganese 24 12.4 1.7 1.7 319.5 86.9 Mercury 0.01 not detectable not detectable not detectable — — N i c k e l 0.19 0.28 0.077 0.077 6.14 73.9 Potassium 585 714 730 730 520 2.5 Sodium 575 682 684 684 875 4.3 Zinc 65 79 0.85 0.85 2330 79 TABLE XX Mixed E f f l u e n t volume = 1 l i t r e , L i q u i d f r a c t i o n = 0.974 l i t r e s ; Dry weight of sludge = 28,700 mg. (1) (2) (3) (4) (5) (6) (7) Metal Component I n f l u e n t concentration (mg/1) Mixed E f f l u e n t Concentration (mg/1) Centrifuged E f f l u e n t Concentration (mg/1) Concentration i n l i q u i d f r a c t i o n (PPM) Concentration i n dry sludge (PPM) Percent of metal i n dry sludge Aluminum 1.6 1.2 1 not detectable not detectable 41.81 100 Barium 0.31 0.20 not detectable not detectable 6.97 100 Cadmium 0.02 0.03 not detectable not detectable 1.07 100 Calcium 1170 570 398 398 6350 32 Chromium 0.16 0.08 0.07 0.07 0.42 15 Copper 0.04 0.22 0.12 0.12 3.59 46.8 Iron 588 222 19.5 19.5 7100 91.5 Lead 0.88 0.41 0.22 0.22 6.83 47.8 Magnesium 100 90 88 88 149.5 4.8 Manganese 13.5 5.3 1.5 1.5 133.5 72.5 Mercury 0.006 0.0032 not detectable not detectable 0.11 100 N i c k e l 0.208 0.17 0.01 0.01 5.58 94.2 Potassium 480 442 "452 452 61 0.4 Sodium 450 471 482 482 53.5 0.33 Zinc 57 37 0.35 0.35 1275 99.1 TABLE XXI METAL DETERMINATION IN DIGESTER 2, DETENTION TIME = 10 DAYS; 3RD BATCH OF FEED Mixed e f f l u e n t volume = 1 l i t r e , L i q u i d f r a c t i o n = 0.956 l i t r e s ; Dry weight of sludge = 31,300 mg. m (2) (3) (4) (5) (6) (7) Metal Component I n f l u e n t Concentration (mg/l) Mixed E f f l u e n t Concentration (mg/D Centrifuged E f f l u e n t Concentration (mg/l) Concentration i n l i q u i d f r a c t i o n (PPM) Concentration i n dry sludge (PPM) Percent of metal i n dry sludge Aluminum 1.6 1.2 not detectable not detectable 38.3 100 Barium 0.31 0.1 not detectable not detectable 3.19 100 Cadmium 0.02 not detectable not detectable not detectable — — Calcium 1170 476 388 388 335.5 22.1 Chromium 0.16 0.08 0.05 0.05 1.02 40.0 Copper 0.04 0.08 0.04 0.04 1.34 52.5 Iron 588 206 157 157 1785 27.1 Lead 0.88 0.32 0.21 0.21 3.8 37.2 Magnesium 100 98 88 88 443 14.2 Manganese 13.5 2.9 2.0 2.0 31.57 34.1 Mercury 0.006 0.0014 not detectable not detectable 0.045 100 N i c k e l 0.208 0.1 not detectable not detectable 3.19 100 Potassium 480 476 388 388 3350 22.1 Sodium 450 492 482 482 995 6.3 Zinc 57 31 0.29 0.29 950 99.1 TABLE XXII METAL DETERMINATION IN DIGESTER #3; DETENTION TIME = 20 DAYS; 3RD BATCH OF FEED Mixed e f f l u e n t volume = 1 l i t r e ; L i q u i d f r a c t i o n = 0.960 l i t r e s ; Dry weight of sludge - 32,900 mg. (1) (2) (3) (4) (5) (6) (7) Metal Component I n f l u e n t Concentration (mg/l) Mixed E f f l u e n t Concentration (mg/l) Centrifuged E f f l u e n t Concentration (mg/l) Concentration i n l i q u i d f r a c t i o n (PPM) Concentration i n dry sludge (PPM) Percent of metal i n dry sludge Aluminum 1.6 1.2 not detectable not detectable 36.45 100 Barium 0.31 0.11 not detectable not detectable 3.3 100 Cadmium 0.02 0.01 not detectable not detectable 0.3 100 Calcium 1170 422 338 338 2950 23.1 Chromium 0.16 0.13 0.07 0.07 1.91 48.5 Copper 0.04 0.23 0.05 0.05 0.33 4.8 Iron 588 242 8.7 8.7 6800 92.4 Lead 0.88 0.15 0.15 0.15 0.183 4.0 Magnesium 100 102 94 94 357.5 11.5 Manganese 13.5 7.5 1.8 1.8 175.5 76.9 Mercury 0.006 0.0014 not detectable not detectable 0.041 100 N i c k e l 0.208 0.13 0.02 0.02 3.37 85.4 Potassium 480 526 532 532 464.5 2.9 Sodium 450 540 538 538 715.0 4.4 Zinc 57 36 0.63 0.63 1075 98.3 53. increase i n pH when leachate was added to the d i g e s t e r s also undoubtedly caused the formation of i n s o l u b l e sulphide and c h l o r i d e complexes. Since these complexes are i n s o l u b l e , they would then p r e c i p i t a t e out. There was an accumulation of s o l i d s underneath the paddle i n the d i g e s t e r s and i t i s l i k e l y that some of the i n s o l u b l e complexes ended up here. Conse-quently, the concentrations of these metals i n the mixed e f f l u e n t were much lower than i n the i n f l u e n t . Copper concentrations i n the mixed e f f l u e n t s were greater than those i n the i n f l u e n t s by more than f i f t y per cent. I t i s p o s s i b l e that t h i s was caused by c o r r o s i o n of some of the brass f i t t i n g s i n the d i g e s t e r . This presumption i s at l e a s t p a r t l y supported by the s l i g h t l y higher con-c e n t r a t i o n s of z i n c i n d i g e s t e r e f f l u e n t s f o r the second batch of feed. Column 7 of the Tables shows the per cent of each metal i n the dry sludge i n terms of the concentration i n the mixed e f f l u e n t . These percentages are summarized i n Table X X I I I . For d i s c u s s i o n purposes, the metals are d i v i d e d i n t o groups, (a) A l k a l i Earth Metals This group 1 i n c l u d e s barium, calcium and magnesium. (1) Barium. I t s concentration i n the dry sludge was 100 per cent i n a l l but one e f f l u e n t sample which had 63 per cent. I t i s reasonable to s t a t e t h e r e f o r e that v i r t u a l l y a l l of the barium i s a s s o c i a t e d w i t h the sludge s o l i d s . (2) Calcium. The co n c e n t r a t i o n of calcium i n the sludge ranged from 22 to 51 per cent i n d i c a t i n g that calcium remains l a r g e l y d i s s o l v e d i n the l i q u i d f r a c t i o n of the e f f l u e n t t TABLE XXIII SUMMARY OF METAL PERCENTAGE IN DRY SLUDGE Metal Component Percentages of Metal i n the Dry Sludge Aluminum 84.5 87.7 100 100 100 Barium 62.6 100 100 100 100 'Cadmium 100 100 100 - 100 Calcium 25.1 50.9 32 22.1 23.1 Chromium 56.1 63.5 15 40 48.5 Copper 12.6 85.2 46.8 52.5 4.8 Iro n 90.2 97.4 91.5 27.1 92.4 Lead 82.4 80.3 47.8 37.2 4.0 Magnesium 3.4 15.7 4.8 14.2 11.5 Manganese 71.9 86.9 72.5 34.1 76.9 Mercury - - 100 100 100 N i c k e l 77.6 73.9 94.2 100 85.4 Potassium 0.17 2.5 0.4 22.1 2.9 Sodium 3.1 4.3 0.33 6.3 4.4 Zinc 99.4 79 99.1 99.1 98.3 55. (3) Magnesium. The concentration of magnesium i n the sludge ranged from 3 to 16 per cent. This shows th a t almost a l l of the i n f l u e n t magnesium w i l l be i n the l i q u i d f r a c t i o n of the e f f l u e n t . A l k a l i Metals T h i s group i n c l u d e s potassium and sodium. From Table X X I I I , i t can be seen that t h e i r concentrations a s s o c i a t e d w i t h the sludge s o l i d s range from 0.17 to 6.3 per cent except i n one d i g e s t e r sample which had 22.1 per cent. As might be expected, sodium and potassium are v i r t u a l l y completely a s s o c i a t e d w i t h the l i q u i d f r a c t i o n of the e f f l u e n t . I r o n and Manganese (1) Iron The concentration of i r o n a s s o c i a t e d w i t h the sludge s o l i d s was greater than 90 per cent i n a l l but one d i g e s t e r sample. This s i n g l e sample had 27.1 percent. (2) Manganese The co n c e n t r a t i o n of manganese a s s o c i a t e d w i t h the sludge s o l i d s was greater than 70 per cent i n a l l but one d i g e s t e r sample. This s i n g l e sample showed 34.1 per cent and was the same sample that showed low percentage of i r o n . At the time t h i s sample was taken, the d i g e s t e r content had a pH of 7.4 which was i t s highest value f o r the duration of the study. This could have r e s u l t e d i n both i r o n and manganese complexes s e t t l i n g out and ending up i n the 56. s o l i d s under the paddle. On the whole, the i n d i c a t i o n i s that both i r o n and manganese are r e a d i l y a s s o c i a t e d w i t h the sludge s o l i d s . Heavy Metals This group i n c l u d e s aluminum, chromium, copper, l e a d , mercury, n i c k e l and z i n c . Of t h i s group cadmium and mercury were 100 per cent a s s o c i a t e d w i t h the sludge s o l i d s . The a s s o c i a t i o n of aluminum, n i c k e l and z i n c w i t h the sludge s o l i d s ranged from 74 to 100 per cent. This i n d i c a t e s the strong tendency of these metals to become concentrated w i t h the sludge. Copper, chromium and l e a d showed l a r g e v a r i a t i o n s i n percentage a s s o c i a t e d w i t h the sludge s o l i d s . This ranged from 4 to 85 per cent. Chromium and l e a d tend to be s l i g h t l y concentrated w i t h the sludge s o l i d s w h i l e copper tends to remain s l i g h t l y more d i s s o l v e d w i t h i n the l i q u i d f r a c t i o n . On the whole, the greater p o r t i o n of these heavy metals seem to be r e a d i l y a s s o c i a t e d w i t h the sludge s o l i d s . However, i t i s not known whether the a s s o c i a t i o n i s due to b i o l o g i c a l c o n c e n t r a t i o n , or p h y s i c a l adsorption. CHAPTER VI CONCLUSIONS AND RECOMMENDATIONS 6-1 Conclusions (1) Anaerobic d i g e s t i o n of leachate w i t h BOD^ values ranging from 11,000 to 16,000 mg/1 w i l l r e s u l t i n 80 to 96 per cent removal f o r d etention times ranging from 5 to 20 days. Detention times greater than 20 days would r e s u l t i n somewhat higher l e v e l s of treatment but may be uneconomical. (2) The r e s i d u a l BOD,, can range from 400 to 3000 mg/1 and so ad d i -t i o n a l treatment to reduce these values to acceptable l e v e l s would be necessary. By s e t t l i n g the e f f l u e n t f o r h a l f an hour 13 to 57 per cent of the r e s i d u a l BOD,, w i l l be removed from the l i q u i d . , (3) For COD values ranging from 23,000 to 33,000 mg/1, 65 to 80 per cent removal w i l l be achieved f o r detention times ranging from 5 to 20 days. (4) : The d i g e s t e r gas contained 68 to 76 per cent methane w i t h the percentage decreasing w i t h increased detention time. This r e -duction i n per cent methane was accompanied by a corresponding increase i n n i t r o g e n gas. Gas production per pound of BOD,, or C.O.D. removed decreased w i t h increased d e t e n t i o n time. I t i s concluded that as detention times i n c r e a s e d e n i t r i f i c a t i o n w i l l occur. This w i l l reduce methane and t o t a l gas production per u n i t of su b s t r a t e removed and may s i g n i f i c a n t l y a f f e c t energy recovery from methane at detention times exceeding 20 days. 57 58. The volume of methane produced per pound of C.O.D. removed ranged from 5.8 to 6.8 cubic f e e t which i s greater than that expected t h e o r e t i c a l l y . This i s l i k e l y due to conversion of a p o r t i o n of the carbon d i o x i d e produced to methane. The a s s o c i a t i o n of the metals w i t h the l i q u i d and dry f r a c t i o n s of the sludge v a r i e d from metal to metal. (a) A l k a l i Metals Potassium and sodium showed v i r t u a l l y no a s s o c i a t i o n \^  w i t h the sludge. T h e i r d i s t r i b u t i o n i n the mixed e f f l u e n t was w i t h one exception, greater than 94 per cent d i s s o l v e d i n the l i q u i d f r a c t i o n and l e s s than 6 per cent i n the dry s o l i d s . (b) A l k a l i Earth Metals Of the a l k a l i metals i n the mixed e f f l u e n t , barium, w i t h one exception was completely a s s o c i a t e d w i t h the sludge s o l i d s . On the average, 30 per cent of the calcium i n the mixed e f f l u e n t was a s s o c i a t e d w i t h the s o l i d s . Magnesium averaged 10 per cent. (c) I r o n and Manganese I r o n , w i t h one exception, was 90 per cent concentrated w i t h the s o l i d f r a c t i o n of the e f f l u e n t . In the case of manganese, wi t h one exception, e s s e n t i a l l y 70 per cent of the t o t a l amount i n the mixed e f f l u e n t was a s s o c i a t e d w i t h the s o l i d f r a c t i o n . 59. (d) Heavy Metals Cadmium and mercury are 100 per cent a s s o c i a t e d w i t h the s o l i d f r a c t i o n of the e f f l u e n t . I n the case of aluminum, n i c k e l and z i n c 70 to 100 per cent was a s s o c i a t e d w i t h the s o l i d f r a c t i o n . Chromium and lead tend to be s l i g h t l y concentrated w i t h the s o l i d f r a c t i o n w h i l e copper tends to remain more d i s s o l v e d i n - the l i q u i d p o r t i o n of the e f f l u e n t . I t i s apparent that some of the metals ( p a r t i c u l a r l y heavy metals) are concentrated w i t h the sludge to a great extent during d i g e s t i o n . However, at the concentrations of the v a r i o u s heavy metals i n the leachate used i n t h i s study, there were no i n d i c a -t i o n s of i n s t a b i l i t y a t t r i b u t a b l e to them. This i n d i c a t e s t h a t , f o r a high strength waste, c o n t a i n i n g r e l a t i v e l y high concentra-t i o n s of metals, a b i o l o g i c a l community can be acclimated and r e s u l t i n a p r o p e r l y f u n c t i o n i n g system. Since a l l the heavy metals are not completely concentrated w i t h the sludge s o l i d s , i t i s evident the r e s t i s i n the l i q u i d f r a c t i o n A d d i t i o n a l treatment i s t h e r e f o r e necessary to remove the remain-der of the heavy metals. Because the greater p o r t i o n of the heavy metals i s a s s o c i a t e d w i t h the sludge, i t should be d i s -posed of i n a manner that w i l l minimize i t s p o l l u t i o n p o t e n t i a l . A bicarbonate-carbonate system was not present but other complex b u f f e r i n g systems maintained s t a b l e o p e r a t i o n . From t h i s i t can be concluded that a bicarbonate-carbonate system might not be necessary i n leachate d i g e s t i o n . 60. (8) BOD:N:P r a t i o s of 100 to 5 to 1 were maintained and proved to be adequate. However, i t was not known i f the N and P were i n excess of what was needed. 6-2 Recommendations -for Future Studies Since very l i t t l e work has been done on the use of anaerobic d i g e s t i o n as a method of t r e a t i n g leachate, a d d i t i o n a l s t u d i e s are nec-essary. These should i n c l u d e (1) An i n v e s t i g a t i o n of detention times beyond 20 days to see i f i t would r e s u l t i n much higher e f f l u e n t q u a l i t y . I n a d d i t i o n i t would provide a d d i t i o n a l i n f o r m a t i o n on the e f f e c t s of p o s s i b l e i n c r e a s i n g d e n i t r i f i c a t i o n . (2) An i n v e s t i g a t i o n i n t o methods of d i s p o s i n g the sludge so as to minimize the p o l l u t i o n p o t e n t i a l of the heavy metals. (3) A d d i t i o n a l treatment methods to reduce the heavy metals and r e s i d u a l oxygen demanding m a t e r i a l i n the l i q u i d f r a c t i o n of the e f f l u e n t . (4) An i n v e s t i g a t i o n of the n i t r o g e n and phosphorus requirements of anaerobic micro-organisms i n the d i g e s t i o n process. REFERENCES 1. Boyle, W.C. and Ham, R.K. , " T r e a t a b i l i t y of Leachate from S a n i t a r y L a n d f i l l s " Proc. 27th. Annual Purdue I n d u s t r i a l Waste Conference Purdue U n i v e r s i t y , L a f a y e t t e , Indiana, May 3, 1972. 2. McCarty, P.L., "Anaerobic Waste Treatment Fundamentals", P u b l i c Works Sept. - Dec. 1964. 3. Barker, H.A., " B i o l o g i c a l Fermentation of Methane", I n d u s t r i a l and Engineering Chemistry 48, 9, 1438, 1956. 4. Buswell, A.M. and S o l l o , F.W., "The Mechanism of Methane Fermentation", American Chemical So c i e t y J o u r n a l , 70, 1778 - 1780, 1948. 5. M a l i n a , J.E., "The E f f e c t of Temperature on High Rate D i g e s t i o n of A c t i v a t e d Sludge", Proc. 16th I n d u s t r i a l Waste Conference, Purdue U n i v e r s i t y 232 - 230, 1961. 6. F a i r , G.M. and Moore, E.W., "Time and Rate of Sludge D i g e s t i o n and Their V a r i a t i o n s w i t h Temperature", Sewage Works J o u r n a l , 6, 1, 3, 1934. 7. Sawyer, C.N., " B a c t e r i a N u t r i t i o n and S y n t h e s i s " , B i o l o g i c a l Treatment of Sewage and I n d u s t r i a l Waste, V o l . 1, Reinhold P u b l i s h i n g Company, New York, 1956. 8. Moore, W.R., McDermott, G.N., B a r t h , E.F., " I n t e r a c t i o n of Heavy Metals and B i o l o g i c a l Sewage Treatment Process P a r t I " , J o u r n a l Water P o l l u t i o n C o n t r o l Federation 33:54, Jan. 1961. 9. Moore, W.R., McDermott, G.N., B a r t h , E.F., " I n t e r a c t i o n of Heavy Metals and B i o l o g i c a l Sewage Treatment Process P a r t I I " , 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 , 35 - 227, Feb. 1963. 10. A.P.HA, A.W.W.A., W.P.C.F., Standard Methods f o r the Examination of Water and Wastewater (1971), American P u b l i c Health A s s o c i a t i o n , Inc. 13th E d i t i o n . 11. Sawyer, C.N. and McCarty, P.L., Chemistry f o r S a n i t a r y Engineers, McGraw H i l l Book Company, 2nd E d i t i o n , 1967. 61 APPENDIX A INFLUENT AND EFFLUENT pH OF DIGESTER CONTENTS 62 7.5 7.4 7.3 E f f l u e n t X 5.4 5.3 5.2 0 Dete n t i o n Time = 5 days Feed Rate = 2 litres per day Inf luent ± 8 12 16 2 0 24 2 8 32 36 4 0 Time - d a y s 4 4 48 52 56 6 0 6 4 1 ON ! LO Figure 3 INFLUENT AND EFFLUENT pH VS. TIME FOR DIGESTER #1 . 7.5 T i m e - d a y s Figure 4 INFLUENT AND EFFLUENT pH VS. TIME FOR DIGESTER #2. 7.6 7.5 7.4 X Q . 5.4 5.3 r-5.2 0 D e t e n t i o n Time = 2 0 d a y s Feed Rate =0.5 lit r e per day 28 32 36 40 Time - d a y s 48 52 56 6 0 64 Figure 5 INFLUENT AND EFFLUENT pH VS. TIME FOR DIGESTER #3. APPENDIX B ACID NEUTRALIZING CAPACITY OF DIGESTER CONTENTS 66. Figure 6 ACID NEUTRALIZING CAPACITY ( to pH 4 . 5 ) OF EFFLUENT VS. TIME FOR DIGESTER # I . 0 4 8 12 16 2 0 24 28 32 36 4 0 4 4 48 52 56 6 0 64 Time - da ys Figure 7 ACID NEUTRALIZING CAPACITY ( to pH 4 . 5 ) OF EFFLUENT VS.TIME FOR DIGESTER #2. 0 4 8 12 16 2 0 24 28 32 36 4 0 4 4 48 52 56 60 64 Ti me - d a y s Figure 8 ACID NEUTRALIZING CAPACITY (to pH 4 . 5 ) OF EFFLUENT VS. TIME FOR DIGESTER # 3 . APPENDIX C SOLIDS IN DIGESTER EFFLUENT 70 2 5 0 0 2 0 0 0 CO C P E CO O CO 7 0 0 /\ l O O O h V *N! S u s p e n d e d S o l i d s Detention Time = 5 days Feed Rate = 2 litres per day V o l a t i l e S u s p e n d e d Sol ids -0--0- «( . -.^  V V \ / o . / V J L J L J L J L 0 8 12 16 2 0 2 4 28 32 36 4 0 4 4 48 52 56 60 64 Time - days Figure 9 SOLIDS VS. TIME FOR DIGESTER # I 2 5 0 0 2 0 0 0 E •o o CO Detention Time = 10 days Feed Rate = I litre per day / \ 100 O N 7 0 0 _L S u s p e n d e d S o l i d s V o l a t i l e S u s p e n d e d So l ids 0 8 12 2 0 2 4 28 32 36 Time - days 4 0 4 4 4 8 52 56 6 0 64 Figure 10 SOLIDS VS. TIME FOR DIGESTER # 2 . 2 5 0 0 2 0 0 0 cn E CO •yj o CO \> -c 1 0 0 0 7 0 0 1 S u s p e n d e d S o l i d s Detention Time = 20 days Feed Rate = 0.5 litre per day -Vo la t i l e S u s p e n d e d So l ids A \ / \ / o-°. / 0 8 12 16 2 0 24 28 32 36 4 0 4 4 48 52 56 6 0 64 Time - da y s Figure II SOLIDS VS. TIME FOR DIGESTER # 3 APPENDIX D SAMPLE CALCULATION 74 75. GAS PRODUCTION PER POUND OF BOD5 REMOVED I n f l u e n t BOD„ E f f l u e n t BODP Feed Rate Volume of gas produced BOD,, removed Volume of gas ( f t ) Cubic f e e t of gas/lb, BOD,, removed 11487 mg/l 1300 mg/l 1 £/day 9.3 l i t r e / d a y = 9.3 ill of feed 10,187 mg (10,187 x 2.204 x 10~ 6) l b s . BOD 0.0225 l b s . B0D 5 9.3 x 0.035315 = 0.328 0.328 0.0225 = 14.6 

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