UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Aerobic biostabilization of a high-strength landfill leachate 1976

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1976_A7 U46.pdf [ 5.48MB ]
Metadata
JSON: 1.0062599.json
JSON-LD: 1.0062599+ld.json
RDF/XML (Pretty): 1.0062599.xml
RDF/JSON: 1.0062599+rdf.json
Turtle: 1.0062599+rdf-turtle.txt
N-Triples: 1.0062599+rdf-ntriples.txt
Citation
1.0062599.ris

Full Text

AEROBIC BIOSTABILIZATION OF A HIGH-STRENGTH LANDFILL LEACHATE by V i c t o r Charles U l o t h B.A.Sc, U n i v e r s i t y of Waterloo, 1973 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 r e 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 February, 1976 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r 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 . D e p a r t m e n t o f C i v i l Engineering 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 * e J " f H \ l 3 Q j MIL 11 ABSTRACT One p a r t i c u l a r l y u n d e s i r a b l e aspect of s o l i d waste d i s p o s a l on land i s the contamination of water passing through the l a n d f i l l s i t e . The p o t e n t i a l adverse environmental e f f e c t s of these " l e a c h a t e s " have been recognized to the extent that t h e i r c o n t r o l and treatment i s the subject of a great deal of cur r e n t research i n water p o l l u t i o n c o n t r o l . This study was i n i t i a t 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 a h i g h - s t r e n g t h l a n d f i l l l e a - chate by aerob i c b i o l o g i c a l methods, without any p r i o r removal of the heavy metals contained i n that leachate. The e f f e c t of v a r y i n g s o l i d s d e t e n t i o n time was a l s o i n v e s t i g a t e d and the d i s t r i b u t i o n of the heavy metals i n the e f f l u e n t s was examined. Using very h i g h mixed l i q u o r v o l a t i l e suspended s o l i d s concentra- t i o n s , 8,000 to 16,000 mg/1, and a combination of a i r and mechanical mixing, a n t i c i p a t e d foaming problems were c o n t r o l l e d and s t a b l e d i g e s t e r o p e r a t i o n was maintained at s o l i d s d e t e n t i o n times as low as 10 days. For i n f l u e n t COD concentrations between 44,000 and 52,000 mg/1, s e t t l e d e f f - luent COD removal increased m a r g i n a l l y from 96.8 to 99.2 percent, as the s o l i d s d e t e n t i o n time increased from 10 to 60 days. Mixed l i q u o r COD removal s i m i l a r l y increased from 51.5 to 75.7 percent. I n c r e a s i n g the s o l i d s d e t e n t i o n time from 10 to 20 days, s i g n i f i c a n t l y improved the q u a l i t y of the s e t t l e d e f f l u e n t w i t h respect to oxygen demanding m a t e r i a l . At s o l i d s d e t e n t i o n times greater than 20 days, and w i t h i n f l u e n t ' BOD^ between 32,000 and 38,000 mg/1, s e t t l e d e f f l u e n t B0D 5 averaged 58.1 mg/1, as opposed to s e t t l e d e f f l u e n t BOD5 greater than 125 mg/1 when the s o l i d s d e t e n t i o n time was 10 days or l e s s . The leachate feed used i n these s t u d i e s contained a v a r i e t y of heavy metals i n c l u d i n g aluminum (41.8 mg/l), cadmium (0.39 mg/l), chromium (1.9 mg/l), copper (0.24. mg/l), lead (1.44 mg/l), n i c k e l (0.65 mg/l), and z i n c (223 mg/l). Most of these metals i n c l u d i n g aluminum, cadmium, chromium, n i c k e l and z i n c were almost completely removed by the s e t t l i n g b i o l o g i c a l f l o e . Others were a s s o c i a t e d w i t h the sludge s o l i d s to a l e s s e r extent. A n a l y s i s of the k i n e t i c parameters a s s o c i a t e d w i t h the b i o s t a b i - l i z a t i o n process i n d i c a t e d that the h i g h heavy metal concentrations i n the mixed l i q u o r s i n h i b i t e d the a c t u a l b i o l o g i c a l removal of oxygen demand- ing m a t e r i a l i n the d i g e s t e r s t e s t e d . The s e t t l i n g b i o l o g i c a l f l o e was found, however, to remove greater than 97 percent of the mixed l i q u o r BOD,, and g r e a t e r than 96 percent of the mixed l i q u o r COD when s o l i d s d e t e n t i o n times were maintained greater than 20 days. Therefore, f o r best treatment r e s u l t s a s o l i d s d e t e n t i o n time of at l e a s t 20 days i s recommended and the food to micro-organism r a t i o should be kept below 0.15 lb.BOD^/lb.MLVSS/ day. i v TABLE OF CONTENTS Page ABSTRACT . . . . . . . . . . . . . . i i L I S T OF TABLES . . . . . . . . . . . . • v i LIST OF FIGURES ' * v i i ACKNOWLEDGMENT . . . . . '. i x CHAPTER 1 INTRODUCTION . '. . . . . . . . . • 1 2 GENERAL REVIEW OF AEROBIC BIOSTABILIZATION . . . 4 2-1 G e n e r a l P r o c e s s D e s c r i p t i o n 4 2-2 D e s i g n E q u a t i o n s . 7 2-3 F a c t o r s A f f e c t i n g A e r o b i c B i o s t a b i l i z a t i o n . . 8 2-4 Heavy M e t a l Removal by A c t i v a t e d S l u d g e . . . 14 2-5 P r e v i o u s S t u d i e s o f B i o l o g i c a l Treatment o f L a n d f i l l L e a c h a t e . . . . . . . . 17 2-6 Summary . ' 20 . 3 RESEARCH RATIONALE AND EXPERIMENTAL DESIGN . . . 22 4 SYSTEM DESIGN AND EXPERIMENTAL PROCEDURE . . . . 24 4-1 D e s i g n o f the Treatment System 24 4-2 L e a c h a t e Source and C h a r a c t e r i s t i c s . . . . 25 4-3 pH C o n t r o l 28 4-4 N u t r i e n t B a l a n c e 28 4-5 M e t a l C o n c e n t r a t i o n s . . . . . . . 31 4-6 A c c l i m a t i z a t i o n - M e t a l Removal Study . . . . 31 4-7 A e r o b i c B i o s t a b i l i z a t i o n E f f i c i e n c y S t u d i e s . . 34 4-8 Summary . . . . . . . . . . . . 37 V Page CHAPTER 5 DISCUSSION OF RESULTS 39 5-1 Removal o f Oxygen Demanding M a t e r i a l . . . . 39 5-2 V o l a t i l e Suspended S o l i d s 55 5-3 . M e t a l Removal and D i s t r i b u t i o n 58 5-4 S e t t l e d E f f l u e n t C h a r a c t e r i z a t i o n . . . . 71 5- 5 K i n e t i c Parameters and E f f i c i e n c y P r e d i c t i o n s . . ' 76 6 CONCLUSIONS AND RECOMMENDATIONS 80 6- 1 C o n c l u s i o n s . . . . . . . . . . . 80 6-2 Recommendations f o r F u t u r e S t u d i e s . . . . . 82 7 REFERENCES . . . . . . . . . . 84 8 APPENDICES 86 Appendix A S o l i d s T e s t s R e s u l t s D u r i n g S t u d i e s -. . 87 Appendix B BOD5 T e s t R e s u l t s D u r i n g S t u d i e s . . . 92 Appendix C pH o f E f f l u e n t s and Mixed L i q u o r s D u r i n g S t u d i e s . . . . . . . . . 98 Appendix D Oxygen Uptake R a t e s D u r i n g S t u d i e s . . 102 Appendix E D e t e r m i n a t i o n o f K i n e t i c Parameters From "Extended A e r a t i o n " E f f i c i e n c y Study Data . 106 LIST OF TABLES Page TABLE I COMPOSITION OF TYPICAL LEACHATES . ' .. . . . . . 2 I I DESIGN PARAMETERS FOR ACTIVATED SLUDGE PROCESSES . . 5 I I I CONTINUOUS DOSE OF METAL THAT WILL GIVE SIGNIFICANT REDUCTION IN AEROBIC TREATMENT EFFICIENCY . . . . 12 IV DISTRIBUTION OF METALS THROUGH THE ACTIVATED SLUDGE PROCESS (CONTINUOUS DOSAGE) . . . . . . . 15 V EFFECTS OF METALS ON MIXED LIQUOR SOLIDS . . . . 15 VI COMPOSITION OF LEACHATE FEED USED DURING STUDY . . 29 V I I NUTRIENT ADDITIONS AND BOD 5:N:P RATIOS DURING STUDY . 30 V I I I TYPICAL BOD 5 TEST RESULTS FOR MIXED LIQUOR EFFLUENTS FROM DIGESTERS A, B AND C, AND FOR LEACHATE FEED . . 42 IX COMPARISON OF BOD5 TEST RESULTS ON SETTLED EFFLUENTS USING UNSEEDED AND SEEDED BOD DILUTION WATER . . . 45 X ORGANIC CARBON REMOVAL DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY 55 XI METAL DISTRIBUTION AT END OF ACCLIMATIZATION-METAL REMOVAL STUDY . . 62 X I I METAL DISTRIBUTION AT END OF EFFICIENCY STUDIES . . 66 X I I I SUMMARY OF METAL REMOVAL BY SETTLING BIOLOGICAL FLOC DURING EFFICIENCY STUDIES . . . 69 XIV CHARACTERISTICS OF LEACHATE FEED AND SETTLED EFFLUENTS' FROM AEROBIC BIOSTABILIZATION EFFICIENCY STUDIES . . 72 XV KINETIC PARAMETERS DETERMINED FROM "EXTENDED AERATION" EFFICIENCY STUDY DATA . ' 77 XVI MIXED LIQUOR BOD 5 DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY 79 v i i LIST OF FIGURES Page FIGURE 1 SCHEMATIC OF LABORATORY AEROBIC DIGESTERS . . . . 26 2 BOD5 OF MIXED LIQUORS AND SETTLED EFFLUENTS vs SOLIDS DETENTION TIME 40 3 PERCENT BOD5 REMOVALS vs SOLIDS DETENTION TIME . . . 41 4 COD OF MIXED LIQUORS DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY 47 5 COD OF SETTLED EFFLUENTS DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY 48 6 COD OF MIXED AND SETTLED EFFLUENTS vs SOLIDS DETENTION TIME 49 7 PERCENT COD REMOVALS vs SOLIDS DETENTION TIME . . . 50 8 COD OF MIXED AND SETTLED EFFLUENTS vs FOOD TO MICRO- ORGANISM RATIO . 52 9 PERCENT COD REMOVALS vs FOOD TO MICRO-ORGANISM RATIO . 54 10 STEADY STATE MIXED LIQUOR VOLATILE SUSPENDED SOLIDS CONCENTRATIONS vs SOLIDS DETENTION TIME . . . . 57 11 EFFLUENT TOTAL SOLIDS CONCENTRATION DURING THE ACCLIMATIZATION-METAL REMOVAL STUDY 59 12 MIXED LIQUOR TOTAL SOLIDS CONCENTRATIONS vs TIME FROM STARTUP- 88 13 MIXED LIQUOR SUSPENDED SOLIDS CONCENTRATIONS vs TIME FROM START UP: 89 14 MIXED LIQUOR VOLATILE SUSPENDED SOLIDS CONCENTRATIONS vs TIME FROM START UP 90 15 SETTLED EFFLUENT TOTAL SOLIDS CONCENTRATION vs SOLIDS DETENTION TIME 91 16 BOD5 OF SETTLED EFFLUENTS DURING ACCLIMATIZATION STUDY . 93 17 . BOD5 OF SETTLED EFFLUENTS DURING EFFICIENCY STUDIES . . 94 18 BOD5 OF MIXED LIQUORS DURING EFFICIENCY STUDIES . . 95 19 BODs OF MIXED LIQUORS vs FOOD TO MICRO-ORGANISM RATIO . 96 V 111 Page FIGURE 20 PERCENT B0D5 REMOVAL vs FOOD TO MICRO-ORGANISM RATIO < 92 21 pH OF SETTLED EFFLUENTS DURING ACCLIMATIZATION STUDY . 99 22 pH OF MIXED LIQUORS DURING "EXTENDED AERATION" EFFICIENCY STUDY 100 23 pH OF MIXED LIQUORS DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY 101 24 OXYGEN UPTAKE RATES DURING ACCLIMATIZATION STUDY . . 103. 25 OXYGEN UPTAKE RATES DURING "EXTENDED AERATION" EFFICIENCY STUDY 104 26 OXYGEN"UPTAKE RATES DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY 105 27 DETERMINATION OF K AND K s USING BOD5 DATA FROM "EXTENDED AERATION" EFFICIENCY STUDY 108 28 DETERMINATION OF Y AND b USING BOD5 DATA FROM "EXTENDED AERATION" EFFICIENCY STUDY 110 ACKNOWLEDGMENT The author wishes to s i n c e r e l y thank h i s s u p e r v i s o r , Dr. D.S. Mavin i c , f o r h i s guidance, i n t e r e s t and encouragement during t h i s study. The author i s a l s o v e r y g r a t e f u l f o r the advice 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 , Susanne; Dr. R.D. Cameron; Mrs. E l i z a b e t h McDonald and the t e c h n i c i a n s i n the p o l l u t i o n c o n t r o l l a b o r a t o r y , Mary Mager and Susan Harper. The author would a l s o l i k e to thank the N a t i o n a l Research C o u n c i l , as he was supported d u r i n g t h i s study by a NRC Postgraduate S c h o l a r s h i p . Equipment f o r t h i s work was provided under NRC Research Grant Number A-8945. CHAPTER 1 INTRODUCTION Over the years there has been a s u b s t a n t i a l increase i n the volume of s o l i d waste being generated throughout the world. Although enormous amounts of money have been spent on the development of a l t e r n a t i v e d i s p o s a l methods such as i n c i n e r a t i o n , composting and r e c y c l i n g , s a n i t a r y l a n d f i l l s and garbage dumps remain the most popular method of d i s p o s a l f o r s o l i d wastes. One of the major problems presented by the op e r a t i o n of a s o l i d waste l a n d f i l l , p a r t i c u l a r l y i n high r a i n f a l l c l i m a t e s , i s the production of leach- ate. Leachate i s produced when surface or groundwater:, becomes contaminated as i t passes through the l a y e r s of refuse i n a l a n d f i l l . I f the leachate enters nearby surface or groundwaters, a se r i o u s p o l l u t i o n problem may r e s u l t . The magnitude of the p o l l u t i o n problem w i l l depend l a r g e l y on the stren g t h and q u a n t i t y of leachate produced, as w e l l as on the d i l u t i o n a f f o r d e d by r e c e i v i n g waters. Table I i l l u s t r a t e s the observed v a r i a b i l i t y of leachate s t r e n g t h (1). The q u a l i t y and q u a n t i t y of leachate depends on the amount and composition of the r e f u s e , the hydrogeology of the s i t e , the age of the l a n d f i l l , and the c l i m a t e . The d e l e t e r i o u s e f f e c t s of leachates on r e c e i v i n g waters has been w e l l documented i n the l i t e r a t u r e (1,2,3). With the recent p o p u l a r i t y of environmental matters, the importance of leachate as a p a r t i c u l a r l y u n d e s i r a b l e aspect of s o l i d waste d i s p o s a l on land has been recognized to such an extent that d i s p o s a l s i t e s are u s u a l l y chosen and designed to minimize leachate production. Design precautions e n t a i l d i v e r s i o n of surface water from the l a n d f i l l s i t e , prevention of groundwater contact w i t h r e f u s e , and s e a l i n g and s l o p i n g the sur f a c e to minimize or e l i m i n a t e p r e c i p i t a t i o n i n f i l t r a t i o n . This method of c o n t r o l i s very e f f e c t i v e i n a r i d or semi-arid c l i m a t e s where p r e c i p i t a t i o n i s minimal. TABLE I COMPOSITION OF TYPICAL LEACHATES Range of Values or Concentrations Parameter ( L a n d f i l l s and Test Lysimeters) BOD5 9 - 55,000 COD 0 - 90,000 T o t a l Carbon 715 22,350 T o t a l Organic Carbon 715 - 22,350 T o t a l S o l i d s •1,000 _ 45,000 T o t a l V o l a t i l e S o l i d s 1,000 - 23,157 T o t a l D i s s o l v e d S o l i d s 0 - 42,300 A c i d i t y 0 _ 9,560 A l k a l i n i t y 0 - 20,900 Aluminum 0 _ 122 Ar s e n i c 0 - 11.6 Bar ium 0 5.4 B e r y l l i u m 0 - 0.3 Calcium 5 - 4,000 Cadmium 0 - 0.19 C h l o r i d e 34 - 2,800 Chromium 0 - 33.4 Copper 0 - 10 Iron 0.2 - 5,500 Lead 0 - 5.0 Magnesium 165 - 15,600 Manganese 0.06 - 1,400 Mercury 0 - 0.064 Molybdenum 0 - 0.52 Nitr o g e n - t o t a l 0 - 2,406 - NH 3 0 - 1,106 N i c k e l 0.01 - 0.80 Phosphorus - t o t a l 0 - 154 Potassium 2.8 - 3,770 Sodium 0 - 7,700 Sulphates 1 - 1,826 Sulphides 0 - 0.13 Titanium 0 - 5.0 Vanadium 0 - 1.4 Zinc 0 - 1,000 PH 3.7 - 8.5 T a n n i n - l i k e compounds'L.. _.;.•>•> 78 - 1,278 Colour ( c h l o r o p l a t i n a t e ) 0 - 12,000 Odour not d e t e c t a b l e to ter: a l l values except those f o r pH, c o l o u r and odour are i n mg/1. 3 However, 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 rates are h i g h 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 a g a i n s t 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 . In a d d i t i o n , urban develop- ment 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 poten- t i a l users and so l e s s than i d e a l p a r c e l s of land have o f t e n been chosen for l a n d f i l l s i t e s . The p e r c o l a t i o n of water through the refuse g r e a t l y increases the r a t e of biochemical s t a b i l i z a t i o n of the l a n d f i l l and thus decreases the time r e q u i r e d f o r c o n s o l i d a t i o n and s e t t l i n g of the l a n d f i l l . Although such a l a n d f i l l s i t e may be used f o r b u i l d i n g c o n s t r u c t i o n or r e c r e a t i o n a l purposes much sooner than a sealed l a n d f i l l , the leachate produced i s h i g h l y contaminated and must t h e r e f o r e be c o l l e c t e d f o r subsequent treatment. C o l l e c t i o n of the leachate before i t enters ground or surface waters can be accomplished by c a r e f u l l a n d f i l l design and s i t e s e l e c t i o n . The development of s u i t a b l e treatment methods, however, remains the t o p i c of much current research. This study was i n i t i a t e d to i n v e s t i g a t e a e r o b i c b i o s t a b i l i z a t i o n of a h i g h - s t r e n g t h l a n d f i l l 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 p o l l u t i o n problems. CHAPTER 2 GENERAL REVIEW OF AEROBIC BIOSTABILIZATION 2-1 General Process D e s c r i p t i o n Aerobic processes i n c l u d e a c t i v a t e d sludge, t r i c k l i n g f i l t e r s and aerobic s t a b i l i z a t i o n ponds. The a c t i v a t e d sludge process i s used almost e x c l u s i v e l y i n la r g e c i t i e s . T r i c k l i n g f i l t e r s are o f t e n used i n s m a l l c i t i e s and for hi g h - s t r e n g t h , r e a d i l y biodegradable i n d u s t r i a l wastes. Aerobic ponds are used i n small c i t i e s where l a r g e land areas :lare . a v a i l a b l e . The p r i n c i p l e s _behind a l l three processes are s i m i l a r . However, s i n c e v a r i a t i o n s of the complete-mix a c t i v a t e d sludge system were used i n t h i s study, the f o l l o w i n g d i s c u s s i o n w i l l be d i r e c t e d to that process. The a c t i v a t e d sludge process was developed i n England i n 1914 and was so named because i t inv o l v e d the production of an a c t i v a t e d mass of micro-organisms capable of a e r o b i c a l l y s t a b i l i z i n g or decomposing an organic waste. The aerobic environment i n an a c t i v a t e d sludge a e r a t i o n b a s i n i s maintained by the use of d i f f u s e d or mechanical a e r a t i o n . The r e a c t o r con- tents are r e f e r r e d to as the mixed l i q u o r . A f t e r the waste i s t r e a t e d i n the r e a c t o r , the r e s u l t i n g b i o l o g i c a l mass:is separated from the l i q u i d i n a s e t t l i n g tank or c l a r i f i e r . A p o r t i o n of the s e t t l e d b i o l o g i c a l s o l i d s , i s u s u a l l y r e c y c l e d , the remaining mass i s wasted. A p o r t i o n of the micro- organisms must be wasted, otherwise the mass of micro-organisms would keep i n c r e a s i n g u n t i l the system could no longer c o n t a i n them. The l e v e l at which the b i o l o g i c a l mass should be kept depends on the d e s i r e d treatment e f f i c i e n c y and other c o n s i d e r a t i o n s r e l a t e d to growth k i n e t i c s . The micro- organism concentrations g e n e r a l l y maintained i n three types:of: a c t i v a t e d Sludge treatment systems., are l i s t e d i n Table. 11(4) . TABLE I I DESIGN PARAMETERS FOR ACTIVATED SLUDGE PROCESSES Process M o d i f i c a t i o n S o l i d s D e t e n t i o n Time,0 ,Days Food To Mi c r o - organism R a t i o , U, lb. BOD5/lb.MLVSS/Day Volumetric Loading, lb.BOD 5/1000 c u . f t . Mixed Liquor V o l a t i l e Suspended S o l i d s , mg/1iter Recycle R a t i o Conventional 5 - 15 0.2 - 0.4 20 - 40 1,200 - 2,400 0. 25 - 0.50 Complete Mix 5 - 15 0.2 - 0.6 50 - 120 2,400 - 4,800 0. 25 - 1.00 Extended A e r a t i o n 20 - 30 0.05 - 0.15 10 - 25 2,400 - 4,800 0. 75 - 1.50 To design and operate an a c t i v a t e d sludge system e f f i c i e n t l y , i t i s necessary to understand the importance of the micro-organisms i n the systems. In nature, the key r o l e of the b a c t e r i a i s to decompose organic matter produced by other l i v i n g organisms. In the a c t i v a t e d sludge process, the b a c t e r i a are the most important micro-organisms because they are r e - spons i b l e f o r the decomposition of the organic m a t e r i a l i n the i n f l u e n t . In the mixed l i q u o r .tank, a p o r t i o n of the organic waste matter i s used by aerobi c and f a c u l t a t i v e b a c t e r i a to o b t a i n energy f o r the sy n t h e s i s of the remainder of the organic m a t e r i a l i n t o new c e l l s . Thus, a p o r t i o n of the organic matter i s o x i d i z e d to low energy compounds such as NO^., SO^ and CC>2, Thfc remainder i s synthesized i n t o c e l l u l a r m a t e r i a l . While b a c t e r i a are the micro-organisms that a c t u a l l y degrade the organic waste i n the i n f l u e n t , the metabolic a c t i v i t i e s of other micro- organisms are a l s o important i n the ac t i v a t e d - sludge system. For example, protozoa and r o t i f e r s act as e f f l u e n t p o l i s h e r s . Protozoa consume d i s - persed b a c t e r i a that have not f l o c c u l a t e d , and r o t i f e r s consume any small b i o l o g i c a l f l o e p a r t i c l e s that have not s e t t l e d . F urther, w h i l e i t i s important that b a c t e r i a decompose the organic waste as q u i c k l y as p o s s i b l e , i t i s a l s o important that they form a s a t i s - f a c t o r y f l o e , which i s a p r e r e q u i s i t e f o r the e f f e c t i v e s e p a r a t i o n of the b i o l o g i c a l s o l i d s i n the s e t t l i n g u n i t . I t has been observed that as the s o l i d s d e t e n t i o n or mean c e l l residence time i s increased, the s e t t l i n g c h a r a c t e r i s t i c s of the b i o l o g i c a l f l o e are enhanced. The reason f o r t h i s i s t h a t , as the mean age of the c e l l s i n c r e a s e s , the su r f a c e charge i s r e - duced and the micro-organisms s t a r t to produce e x t r a c e l l u l a r polymers, even- t u a l l y becoming "encapsulated" i n a slime l a y e r . The presence of these polymers and the slime promotes the formation of f l o e p a r t i c l e s that can be removed r e a d i l y by g r a v i t y s e t t l i n g . T y p i c a l values of mean c e l l r e s i d e nce 7 or s o l i d s d e t e n t i o n time used i n the design and op e r a t i o n of a c t i v a t e d sludge processes are a l s o shown i n Table I I (4). 2-2 Design Equations : . In t h i s study the b i o l o g i c a l s o l i d s r e t e n t i o n time, 0 , arid the food to micro-organism r a t i o , U, were used as b a s i c design parameters. Lawrence and McCarty (5) have defined f o r completely mixed, no-recycle systems as the r e c i p r o c a l of the net s p e c i f i c growth r a t e as f o l l o w s : JL = Y K S - b (1) 0 C  K s + S where Y = growth y i e l d c o e f f i c i e n t , K = maximum r a t e of s u b s t r a t e u t i l i z a t i o n per u n i t weight of micro- organisms, ( T " l ) , S = c o n c e n t r a t i o n of s u b s t r a t e surrounding the micro-organisms, (M/L ), b = micro-organism decay or endogenous r e s p i r a t i o n c o e f f i c i e n t , (T ^) , K s = su b s t r a t e c o n c e n t r a t i o n when dS/dt = K , (M/L ) , X 2 dS = r a t e of m i c r o b i a l s u b s t r a t e u t i l i z a t i o n per u n i t volume, and •' dt X = m i c r o b i a l mass c o n c e n t r a t i o n or mixed l i q u o r v o l a t i l e suspended s o l i d , MLVSS, c o n c e n t r a t i o n , (M/L 3). An expression f o r the mixed l i q u o r m i c r o b i a l mass c o n c e n t r a t i o n , X, can be deri v e d f o r st e a d y - s t a t e c o n d i t i o n s by performing a s u b s t r a t e mass balance on the r e a c t o r . The equation i s as f o l l o w s : X =• Y ( S 0 - Sj) (2) i + be. c 3 where S Q = i n f l u e n t waste c o n c e n t r a t i o n , (M/L ), and S-]̂  = e f f l u e n t waste c o n c e n t r a t i o n , (M/L ). The parameters, Y, b, K and K s were determined us i n g the r e s u l t s of SL ... p r e l i m i n a r y "extended a e r a t i o n " e f f i c i e n c y study and then, equations 1 and 8 2 were used to p r e d i c t the performance of the u n i t s at lower s o l i d s d e t e n t i o n times. 2-3 Factors A f f e c t i n g Aerobic B i o s t a b i l i z a t i o n A p p l i c a t i o n and study of a e r o b i c treatment methods 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 un- favourable e f f e c t s on a e r o b i c 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 d i v e r s e group of micro-organisms, c e r t a i n optimum c o n d i t i o n s must be maintained during d i g e s t i o n . Among the f a c t o r s most o f t e n considered i n d esigning an aerobic s t a b i l i z a t i o n process are pH, temperature, oxygen requirements, n u t r i e n t requirements, and waste t o x i c i t y . Because an under- standing 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 s u c c e s s f u l l y operate the d i g e s t e r s , the most important f a c t o r s were examined. (a) pH and A l k a l i n i t y - To m a i n t a i n a s t a b l e , b i o l o g i c a l p o p u l a t i o n , the pH should be maintained between 6.5 and 9.0. Values o u t s i d e of t h i s recommended range may i n h i b i t the growth of a e r o b i c b a c t e r i a or even cause t h e i r d e s t r u c t i o n . As the organic waste i s decomposed and o x i d i z e d , SO^ , NO^ and CO2 may be formed r e s u l t i n g i n a pH drop. For t h i s reason i t i s recommended that the i n f l u e n t waste should c o n t a i n 0.5 l b . of a l k a l i n i t y per l b . of BOD5 to be removed. I f s u f f i c i e n t a l k a l i n i t y i s not .present i n the i n f l u e n t , i t may be necessary to add b u f f e r i n g agents to maintain the pH i n the d e s i r e d range. (b) Temperature - The temperature dependence of the b i o l o g i c a l r e a c t i o n - r a t e constant i s very important i n a s s e s s i n g the o v e r a l l e f f i c i e n c y of a b i o l o g i c a l treatment process. Temperature not only i n f l u e n c e s the metabolic a c t i v i t i e s of the m i c r o b i a l p o p u l a t i o n , but a l s o has a profound e f f e c t on such f a c t o r s as gas t r a n s f e r r a t e s and the s e t t l i n g c h a r a c t e r i s t i c s of the b i o l o g i c a l s o l i d s . The temperature e f f e c t on the r e a c t i o n r a t e of a b i o l o g i c a l process i s u s u a l l y ex- pressed i n the f o l l o w i n g form: Ky_ = * < T" 2 0> (3) K20 where K̂ , = r e a c t i o n r a t e at T°C, K 2 0 = r e a c t i o n r a t e at 20°C, <t> = t e m p e r a t u r e - a c t i v i t y c o e f f i c i e n t , and T = temperature, °C. For a c t i v a t e d sludge processes, <j> v a r i e s between 1.00 and 1.03. From these r e l a t i v e l y low values of the t e m p e r a t u r e - a c t i v i t y coef- f i c i e n t , i t i s evident that r e l a t i v e l y l a r g e temperature changes would be r e q u i r e d to s i g n i f i c a n t l y a f f e c t treatment e f f i c i e n c y . Oxygen Requirements - To maintain a e r o b i c c o n d i t i o n s i n the r e a c t o r , the d i s s o l v e d oxygen l e v e l must be kept above 1-2 m g / l i t r e . In a d d i t i o n , the a i r supply r a t e must be adequate to s a t i s f y the BOD of the waste, to s a t i s f y the endogenous r e s p i r a t i o n of the sludge o r - ganisms, and to provide adequate mixing. For food to micro-organ- ism r a t i o s greater than 0.3, the a i r requirements amount to 500 to 900 cubic f e e t per l b . of B O D 5 removed. At lower food to micro- organism r a t i o s , endogenous r e s p i r a t i o n , n i t r i f i c a t i o n and prolonged a e r a t i o n periods increase a i r use to 1,200 to 1,800 cubic f e e t per ' l b . of BOD^ removed. A minimum a i r flow of approximately 3 cubic f e e t per minute per foot of tank l e n g t h i s r e q u i r e d to m a i n t a i n adequate mixing and to a v o i d s o l i d s d e p o s i t i o n ( 4 ) . 10. (d) N u t r i e n t Requirements - I f any b i o l o g i c a l system i s 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 a v a i l - a b l e i n adequate amounts. N i t r o g e n and phosphorus". • are the n u t r i e n t s r e q u i r e d i n highest c o n c e n t r a t i o n s . 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 (6) 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 maintained i f a e r o b i c micro- organisms are to f u n c t i o n e f f e c t i v e l y . He c i t e d B0D^:N r a t i o s ranging from 17:1 to 32:1 and B O D r ^ P r a t i o s ranging from 90:1 to 150:1 as being adequate. These r a t i o s have been adjusted through usage to B0D5:N :P of 100:5:1 and have g e n e r a l l y r e s u l t e d i n s a t i s - f a c t o r y performance. (e) Waste T o x i c i t y - Because the incoming waste i s more or l e s s u n i - . formly dispersed i n a complete-mix r e a c t o r , i t can, i n comparison to the co n v e n t i o n a l , plug-flow, a c t i v a t e d sludge r e a c t o r , more e a s i l y withstand shock loads of organic and t o x i c m a t e r i a l s . For t h i s reason, a complete-mix r e a c t o r was chosen f o r t h i s study. The term t o x i c , however, i s very r e l a t i v e and the c o n c e n t r a t i o n at which any substance i s t o x i c or i n h i b i t i n g to aerob i c d i g e s t i o n may vary from a f r a c t i o n of a mg/l to s e v e r a l thousand mg/l. At some low con c e n t r a t i o n s , 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/l for heavy metals to over a hundred mg/l f o r sodium and ca l c i u m s a l t s . As the c o n c e n t r a 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 point i s then reached where i n h i b i t i o n i s apparent 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 may 11 approach zero. Micro-organisms 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, however, i s a l s o r e l a t i v e . In 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 z 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 l e v e l of a c t i v i t y w i l l remain much lower than that obtained i n the absence of I n h i b i - t o r y substances. Barth et a l . (7) 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, n i c k e l and z i n c . During each run, an experimental p i l o t - p l a n t u n i t and a c o n t r o l u n i t r e c e i v i n g no metal were compared. The metal was added c o n t i n u o u s l y to a constant sewage feed of the experimental u n i t . Two weeks of a c c l i m a t i o n were allowed before data on the q u a l i t y of the f i n a l e f f l u e n t were c o l l e c t e d . This time i n t e r v a l was r e q u i r e d f o r the metal c o n c e n t r a t i o n i n the a c t i v a t e d sludge to b u i l d up to a c o n d i t i o n of op e r a t i n g e q u i l i b r i u m . The f i n a l e f f l u e n t from both u n i t s was assayed d a i l y f o r BOD, COD, suspended s o l i d s and t u r b i d i t y . The run f o r any s e l e c t e d metal dosage was continued•for 60 days to o b t a i n s u f f i c i e n t data. The values f o r the two u n i t s were then compared as frequency d i s t r i b u t i o n curves and the c o n t i n - uous doses of each metal that w i l l g i v e s i g n i f i c a n t r e d u c t i o n i n aerobic treatment e f f i c i e n c y were thus determined. T h e i r r e s u l t s are summarized i n Table I I I (7). TABLE I I I CONTINUOUS DOSE OF METAL THAT WILL GIVE SIGNIFICANT REDUCTION IN AEROBIC TREATMENT EFFICIENCY Metal Concentration i n I n f l u e n t Waste mg/l Chromium (VI) 10 Copper 1 N i c k e l 1 to 2.5 Zinc 5 to 10 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 c o n c e n t r a t i o n s , 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 . The r e s u l t s of these s t u d i e s showed that the a c t i v a t e d sludge phase of a b i o l o g i c a l treatment p l a n t can t o l e r a t e , i n the i n f l u e n t sewage, chromium, copper, n i c k e l and z i n c , up to a t o t a l heavy metal con- c e n t r a t i o n of 10 mg/l.; E i t h e r s i n g l y or i n combination, heavy metal concentrations of t h i s magnitude caused ; o nly a 5 percent r e d u c t i o n i n o v e r a l l p l a n t e f f i c i e n c y (7). In a d d i t i o n Kampf (8) , a German researcher, has developed a 3- stage method fo r examining the e f f e c t of t o x i c compounds on a c t i - vated sludge. Based on measurements of oxygen consumption u s i n g the Warburg respirometer, stage 1 measures the d i r e c t . i n h i b i t i o n : o f r e s p i r a t i o n by t o x i c substances; Stage 2, which examines the recovery of the sludge and the d u r a t i o n and i n t e n s i t y of harmful e f f e c t s a f t e r the t o x i c load has been i n t e r r u p t e d , measures the i n h i b i t i o n of r e s p i r a t i o n i n sludge from a p a r a l l e l stage 1 sample a f t e r mixing w i t h f r e s h n u t r i e n t s o l u t i o n ; i.Stage 3, used':.to.indicate the..a t o x i c i t y of the s u b s t r a t e a f t e r contact w i t h the a c t i v a t e d sludge, 13 measures the i n h i b i t i o n of r e s p i r a t i o n i n f r e s h sludge when exposed to a t o x i c s o l u t i o n separated from a stage 1 sample by c e n t r i f u g - ing . The method has been used to examine the e f f e c t s of magnesium and aluminum. Only high concentrations of magnesium a f f e c t e d oxygen consumption. Concentrations of about 2,850 mg of magnesium c h l o r i d e per l i t r e were p r a c t i c a l l y harmless, w h i l e the highest c o n c e n t r a t i o n t e s t e d , 20,000 m g / l i t r e , i n h i b i t e d r e s p i r a t i o n by about 25 percent, and the o r i g i n a l r a t e of r e s p i r a t i o n was r e s t o r e d r a p i d l y when the sludge was separated and exposed to f r e s h n u t r i e n t s o l u t i o n . The r e s p i r a t i o n r a t e of a c t i v a t e d sludge was, however, i n h i b i t e d by aluminum (as sulphate) i n concentrations of 100 mg per l i t r e , but the micro-organisms became a c c l i m a t i z e d a f t e r s e v e r a l hours. In the second stage, even a f t e r long periods of contact, the separated sludge regained i t s r e s p i r a t o r y a c t i v i t y s l o w l y , provided the c o n c e n t r a t i o n of aluminum was not s i g n i f i c a n t l y higher than 160 mg per l i t r e . The highest c o n c e n t r a t i o n of aluminum t e s t e d , 320 mg per l i t r e , caused i r r e v e r s i b l e damage. Neufeld and Hermann (9) i n v e s t i g a t e d the e f f e c t of mercury, cadmium and z i n c on acclimated a c t i v a t e d sludge. Using shock doses of 30, 100, 300 and 1,000 mg/1 of each metal, they found that i t was p o s s i b l e to°maintain a t h r i v i n g c u l t u r e of a c t i v a t e d b i o t a i n ~ the presence of l e v e l s of mercury, cadmium and z i n c that are much higher than p r e v i o u s l y thought p o s s i b l e . K i n e t i c parameters were evaluated at s e v e r a l heavy metal c o n c e n t r a t i o n s . For cadmium and z i n c , the maximum r a t e of s u b s t r a t e u t i l i z a t i o n per u n i t weight of micro-organisms, K, was found to be v i r t u a l l y constant u n t i l a t h r e s h o l d c o n c e n t r a t i o n of metal i n the sludge, about 25 mg/1 of cadmium or 8 mg/1 of z i n c , was reached. Beyond t h i s t h r e s h o l d , K 14 decreased l i n e a r l y when p l o t t e d r e l a t i v e to metal i n the f l o e , mg/gm VSS, on l o g - l o g paper. No t h r e s h o l d e f f e c t was observed i n the case of mercury and i t was concluded that mercury a f f e c t s the metabolic r a t e i n a way that may be t o t a l l y counteracted by i n - c r e a s i n g the c o n c e n t r a t i o n of organic s u b s t r a t e , ( f ) Detention Time - D e t e n t i o n time, which i s c l o s e l y r e l a t e d to l o a d i n g r a t e expressed i n terms of the food to micro-organism r a t i o , has been shown to a f f e c t the e f f i c i e n c y of a e r o b i c b i o s t a b i l i z a t i o n . As d e t e n t i o n time decreases, the l o a d i n g r a t e increases. As the deten- t i o n time decreases, an i n c r e a s i n g percentage of b a c t e r i a i s removed each day w i t h the e f f l u e n t . E v e n t u a l l y a l i m i t i n g d e t e n t i o n time i s reached when the b a c t e r i a are being removed from the system a s . f a s t as . they can reproduce themselves. This minimum s o l i d s d e t e n t i o n time can be p r e d i c t e d , i f Y, b, K, K g and S Q are known usin g the equation (5) : 1 = Y K S 0 b (4) Q c min. K s + S D Using the r e s u l t s of a p r e l i m i n a r y study at " s a f e " c o n s e r v a t i v e d e t e n t i o n times, the minimum s o l i d s d e t e n t i o n time cari^ be pre- d i c t e d and d e t e n t i o n times i n the f i n a l e f f i c i e n c y study can then be set above the p r e d i c t e d minimum. 2-4 Heavy Metal Removal by A c t i v a t e d Sludge The completely mixed, aerobic b i o l o g i c a l treatment process has been shown to have a c a p a b i l i t y f o r long-term removal of heavy metal ions that i s s u p e r i o r to anaerobic processes ( 7 , 1 0 ) . Barth et a l . (7) i n v e s t i g a t e d the removal of chromium, copper, n i c k e l and z i n c by a c t i v a t e d sludge. T h e i r r e s u l t s are.. summarized i n Table IV ( 7 ) . I t was a l s o found that the e f f e c t s of the metals on the mixed l i q u o r are apparent even i n the 1 to 2 mg/1 range. During f i v e years, of study, no b u l k i n g was encountered i n the metal fed system. The f l o e i n the f i n a l s e t t l e r s e t t l e d q u i c k l y w h i l e c o n t r o l u n i t s f r e q u e n t l y bulked. Table V (7) shows the e f f e c t s , of a combination of the four metals on the v o l a t i l e s o l i d s content of the mixed l i q u o r . TABLE IV DISTRIBUTION OF METALS THROUGH THE ACTIVATED SLUDGE PROCESS (CONTINUOUS DOSAGE) Cr (VI) Cu N i Zn O u t l e t (15 mg/1) (10 mg/1) (10 mg/1) (10 mg/1) Primary Sludge 2.4 9 2.5 14 Excess A c t i v a t e d Sludge 27 55 15 63 Percent F i n a l E f f l u e n t 56 25 72 11 of Metal Unaccoun- Metal ted f o r 15 15 11 12 Fed Average E f f i c - iency of Pro- • cess i n Re- moving Metal 44-: 75 28 89 Range of Removal 'Ef-f i c l e n c i e s 18-58 50-80 12-76 74-97 TABLE V EFFECTS OF METALS ON MIXED LIQUOR SOLIDS Analys i s Mixed L i q u o r From C o n t r o l U n i t Metal M i x t u r e 8.9 mg/1 Metal M i x t u r e 4.9 mg/1 Metal M i x t u r e 2.0 mg/1 Percent V o l a t i l e S o l i d s 66.7 57.9 61.3 63.8 16 Moulton and Shumate (11) i n d i c a t e d t h a t over a long p e r i o d , an acclimated, a c t i v a t e d sludge system r e t a i n e d 80 to 85 percent of the i n - f l u e n t copper fed to i t at a c o n c e n t r a t i o n of 50 mg/l. Jackson et a l . (12) i n a survey of metals removal by a c t i v a t e d sludge, l i s t e d r e p o r t s of copper removals ranging from 54 to 93 percent, chromium removals from 10 to 100 percent, and z i n c removals from 60 to 100 percent. T o t a l i n f l u e n t metal concentrations f o r t h i s r e p o r t , however, were l e s s than 10 mg/l. Neufeld and Hermann (9) a l s o i n v e s t i g a t e d the uptake of mercury, cadmium and z i n c by a c c l i m a t e d a c t i v a t e d sludge. Using shock doses of 30, 100, 300 and 1000 mg/l of each metal, they i n v e s t i g a t e d the metal d i s t r i b u - t i o n between the s e t t l e d sludge and c l e a r supernatant versus time. Mercury, cadmium and z i n c were removed r a p i d l y from aqueous s o l u t i o n by the b i o l o g i - c a l f l o e . Although eventual e q u i l i b r i u m was achieved a f t e r about 2 weeks of contact, no s i g n i f i c a n t increase i n the percent metal removal could be observed a f t e r 3 hours of contact. At doses up to 300 mg/l, a f t e r 3 hours, 95 percent of the mercury, 73 percent of the cadmium, and 53 percent of the z i n c were removed oh the b i o l o g i c a l f l o e . Using s l u g doses up to 25 mg/l of cadmium, copper, lea d and n i c k e l . i n a s y n t h e t i c waste feed, Cheng et a l . (13) a l s o s t u d i e d the heavy metal uptake by acclimated sludge w i t h time. I t was found that under a e r o b i c c o n d i t i o n s , metal uptake by the biomass i s c h a r a c t e r i z e d by a very r a p i d phase of 3 to 10 minutes f o l l o w e d by a long-term, slow-phase, uptake. At lower metal c o n c e n t r a t i o n s , metal was concluded to be taken up by the b i o f l o c through the formation of metal-organic complexes. At higher metal co n c e n t r a t i o n s , metal i o n p r e c i p i t a t i o n from s o l u t i o n may occur i n a d d i t i o n to sludge uptake. The h i g h molecular weight e x o c e l l u l a r polymers of the b i o f l o c , which i n c l u d e p o l y s a c c h a r i d e s , p r o t e i n s , r i b o n u c l e i c a c i d , and 17 deoxyribonucleic a c i d , provide many f u n c t i o n a l groupings that may act as bin d i n g s i t e s f o r the metals. Cheng et a l . (13) found that metal uptake by the biomass depends on s e v e r a l f a c t o r s , i n c l u d i n g pH and the c o n c e n t r a t i o n of organic matter and metals present i n the system. Higher i n i t i a l concentrations of metal ions or mixed l i q u o r v o l a t i l e suspended s o l i d s increase the o v e r a l l uptake. In general, the uptake c a p a c i t y increases w i t h i n c r e a s i n g pH, up to a value at which metal hydroxide p r e c i p i t a t i o n occurs. Among the metals s t u d i e d , the p r e f e r r e d order of uptake by a c t i v a t e d sludge, w i t h average percent removal i n brackets, was found to be lead (90%) > copper (89%) > cadmium (80%) > n i c k e l (58%) at mixed l i q u o r v o l a t i l e suspended s o l i d s c oncentrations be- tween 1600 and 1800 mg/1. The l a r g e - s c a l e accumulation of heavy metals by a c t i v a t e d sludge, w i t h i t s subsequent removal i n the secondary c l a r i f i e r , would t h e r e f o r e appear to o f f e r a very promising method of t r e a t i n g l a n d f i l l leachate. 2-5 Previous Studies of B i o l o g i c a l Treatment of L a n d f i l l Leachate A study by Poorman (14) 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 leachate by anaerobic d i g e s t i o n without any p r i o r removal of heavy metals. The e f f e c t s of v a r i e d d e t e n t i o n time and changing c h a r a c t e r i s t i c s of the leachate were a l s o s t u d i e d . BOD^ removals ranging from 80 to 96 percent were achieved for d e t e n t i o n times ranging from 5 to 20 days and i n f l u e n t B0D5's ranging from 11,000 to 16,000 mg/1. COD 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, 1 lead, mercury, n i c k e l and z i n c were present i n the leachate. T h e i r 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 18 process was not a d v e r s e l y a f f e c t e d by these metals. Some of the 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 com- p l e t e l y a s s o c i a t e d w i t h the sludge, w h i l e others were p r i m a r i l y a s s o c i a t e d w i t h the s e t t l e d e f f l u e n t . Boyle and Ham (15) i n v e s t i g a t e d the b i o l o g i c a l t r e a t a b i l i t y of l a n d f i l l leachate w i t h t o t a l s o l i d s concentrations between 4,000 and 7,800 mg/l. Processes evaluated i n the l a b o r a t o r y included anaerobic and a e r o b i c b i o l o g i c a l treatment of leachate, a e r o b i c treatment of s e l e c t e d combinations of leachate and domestic wastewater i n a simulated a c t i v a t e d sludge t r e a t - ment p l a n t , and anaerobic followed by aerobic p o l i s h i n g treatment of leach- ate. Anaerobic treatment of raw leachate was most promising, p r o v i d i n g greater than 90 percent BOD r e d u c t i o n f o r h y d r a u l i c d e t e n t i o n times greater than 10 days at temperatures i n the range of 23° to 30°C. Temperature was found to g r e a t l y a f f e c t the anaerobic s t a b i l i z a t i o n of leachate i n the range of 23° to 11°C. A temperature c o e f f i c i e n t of 1.111 was estimated f o r BOD removal r a t e s i n l a b o r a t o r y v e s s e l s . A e r o b i c p o l i s h i n g of anaerobic e f f l u e n t s produced a more s t a b l e e f f l u e n t s u i t a b l e f o r s u r f a c e water d i s - charge. Aerobic treatment a l s o proved to be promising, r e s u l t i n g i n BOD removals i n excess of 90 percent and COD removals :greater than 80 percent at approximately 23°C and at loadings of l e s s than 30 lb.BOD^/day/1,000-cu. f t . BOD removal dropped to 80 percent as the l o a d i n g was increased to 87 l b .B0D5/day/l,000 c u . f t . and COD removal dropped to 74 percent at a food to micro-organism r a t i o of about 0.25 mg BOD^/mg MLVSS/day. Serious foam- ing problems were encountered throughout the study, even though an a n t i - foam s o l u t i o n was added to the aerobic u n i t s . When the food to micro- organism r a t i o exceeded 1.5, sludge b u l k i n g problems were a l s o encountered. No metal analyses were given and no e f f o r t was made to determine the metal d i s t r i b u t i o n i n the mixed l i q u o r e f f l u e n t s . A d d i t i o n a l l a b o r a t o r y s t u d i e s i n d i c a t e d that leachate could be added to domestic wastewater i n an "extended a e r a t i o n " a c t i v a t e d sludge pl a n t at a l e v e l up to 5 percent by volume (leachate COD ='.10,000 mg/1) without s e r i o u s l y i m p a i r i n g e f f l u e n t q u a l i t y . At gre a t e r than 5 per- cent by volume, leachate a d d i t i o n s r e s u l t e d . i n g r e a t l y increased e f f l u e n t BOD and COD, increased oxygen uptake r a t e s , and poorer mixed l i q u o r s e t t l i n g . Cook and Foree (16) i n v e s t i g a t e d a e r o b i c b i o s t a b i l i z a t i o n of a medium-strength (B0D 5 = 9,500 mg/1, COD = 17,500 mg/1) s a n i t a r y l a n d f i l l leachate. T h e i r study was designed to determine the s u s c e p t i b i l i t y to treatment of a t y p i c a l s a n i t a r y l a n d f i l l leachate by aerobic b i o l o g i c a l methods, to evaluate treatment processes f o r p o l i s h i n g of the e f f l u e n t s from aerobic b i o l o g i c a l treatment, and to perform a chemical and p h y s i c a l c h a r a c t e r i z a t i o n of the leachate and t r e a t e d e f f l u e n t s . To accomplish these o b j e c t i v e s , l a b o r a t o r y s c a l e treatment u n i t s (2 l i t r e volume) were operated under v a r i o u s organic lo a d i n g , n u t r i e n t a d d i t i o n and pH c o n d i t i o n s , and t h e i r performance was evaluated by a n a l y t i c a l t e s t i n g . The r e s u l t s of t h i s study i n d i c a t e d that aerobic b i o l o g i c a l treatment was a very e f f e c t i v e means of. s t a b i l i z i n g a " t y p i c a l " s a n i t a r y l a n d f i l l leachate. The best opera- t i o n a l c o n d i t i o n s were found to be a de t e n t i o n time of 10 days (COD l o a d i n g = 98.5 lb.COD/day/1,000 - c u . f t . ) , which r e s u l t e d i n a MLVSS c o n c e n t r a t i o n of 4,400 mg/1 or greater (food to micro-organism r a t i o = 0.216 lb.BOD^/lb. MLVSS/day) i n the completely mixed, no r e c y c l e , systems evaluated. With these two o p e r a t i o n a l c o n d i t i o n s , COD s t a b i l i z a t i o n e f f i c i e n c y of greater than 97 percent was accomplished. The BOD5 of the s e t t l e d e f f l u e n t was reduced to l e s s than 26 mg/1 (99.7 percent removal), i n d i c a t i n g almost, complete b i o l o g i c a l s t a b i l i z a t i o n . A s t a b l e m i c r o b i a l p o p u l a t i o n was e s t a b l i s h e d and maintained. The mixed l i q u o r was c h a r a c t e r i z e d by very 20 good s e t t l i n g p r o p e r t i e s and e f f i c i e n t n u t r i e n t removal was accomplished. The obnoxious odour of the raw leachate was completely removed and a pH above 7.6 was maintained i n each u n i t . Aerobic b i o l o g i c a l treatment u n i t s w i t h d e t e n t i o n times of 2 days and 5 days f a i l e d as i n d i c a t e d by s h a r p l y i n c r e a s i n g e f f l u e n t COD concentrations and s h a r p l y decreasing MLVSS con- c e n t r a t i o n s . This f a i l u r e was p r e d i c t e d by t h e o r e t i c a l determinations. The removal of only three metals was examined. The i r o n c o n c e n t r a t i o n -in the raw leachate was 240 mg/l. A l l of the 10 day u n i t s had l e s s than 10 mg/l of i r o n remaining i n t h e i r s e t t l e d e f f l u e n t . This l a r g e i r o n removal was a t t r i b u t e d mainly to chemical p r e c i p i t a t i o n at the h i g h pH maintained i n the 10 day u n i t s . The c a l c i u m c o n c e n t r a t i o n i n the raw feed was 1,200 mg/l. Less than 430 mg/l remained i n any of the s e t t l e d e f f l u e n t s from the 10 day u n i t s . As the pH i n these 10 day u n i t s increased from 7.6 to 8.4, the c a l c i u m c o n c e n t r a t i o n i n the s e t t l e d e f f l u e n t s dropped from 430 mg/l to 20 mg/l. The magnesium c o n c e n t r a t i o n i n the raw leachate was 170 mg/l. This c o n c e n t r a t i o n was not s i g n i f i c a n t l y reduced because the pH i n the b i o l o g i c a l treatment u n i t s was not h i g h enough to cause p r e c i p i t a t i o n of the magnesium as magnesium hydroxide. The e f f l u e n t p o l i s h i n g r e s u l t s showed th a t a c t i v a t e d carbon was very e f f e c t i v e i n reducing the r e s i d u a l COD (by approximately 40 p e r c e n t ) , organic carbon and c o l o u r . The use of bleach was e f f e c t i v e i n c o l o u r r e - moval, but had l i t t l e e f f e c t on COD. 2-6 Summary Aerobic 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 should t h e r e f o r e be designed w i t h these i n mind. Optimum n u t r i e n t requirements and s u i t a b l e o perating temperatures f o r a e r o b i c 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 may a l s o be c o n t r o l l e d through the a d d i t i o n of b u f f e r s and a c i d s or bases. Enough oxygen must b s u p p l i e d to keep the r e a c t o r s a e r o b i c . I f l o a d i n g r a t e s are kept low enough, aerobic b i o s t a b i l i z a t i o n i s a very e f f e c t i v e means of s t a b i l i z i n g medium-strength l a n d f i l l leachate. The e f f e c t of increased heavy metal concentrations i n a strong l a n d f i l l leachate, on the aerobic treatment e f f i c i e n c y at various d e t e n t i o n times, must, however, be examined and the degree t o which these heavy metals may be concentrated i n the s e t t l e d sludge must be determined. CHAPTER 3 ( RESEARCH RATIONALE AND EXPERIMENTAL DESIGN The development of methods of s a t i s f a c t o r i l y t r e a t i n g l a n d f i l l leachates i s a major goal of an on-going research program c u r r e n t l y being conducted at the U n i v e r s i t y of B r i t i s h Columbia. As part of that research program, anaerobic d i g e s t i o n , chemical treatment and peat treatment have been i n v e s t i g a t e d by research personnel i n the Department of C i v i l Engineer- ing . To complete the i n v e s t i g a t i o n of the most obvious treatment a l t e r n a - t i v e s , t h i s study was i n i t i a t e d to determine the t r e a t a b i l i t y of l a n d f i l l leachate by aerobic d i g e s t i o n . Although the composition of l a n d f i l l leachate v a r i e s w i d e l y , previous s t u d i e s have shown that i n v a r i a b l y , leachate has very h i g h BOD v a l u e s , as w e l l as numerous heavy metals of .varying c o n c e n t r a t i o n . Because the presence of l a r g e amounts of oxygen demanding m a t e r i a l s i s a 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 , BOD r e d u c t i o n must be the prime goal of any leachate treatment process. For t h i s reason a l l forms of b i o l o g i c a l treatment must be considered. The e f f e c t s of heavy metals on the process and t h e i r d i s t r i - b u t i o n i n the r e s u l t i n g sludge and l i q u i d e f f l u e n t s are a l s o of v i t a l i n t e r e s t and t h e r e f o r e r e q u i r e i n v e s t i g a t i o n . Although the presence of heavy metals i s g e n e r a l l y b e l i e v e d to cause more problems during aerobic d i g e s t i o n than during anaerobic d i g e s t i o n , advantages claimed f o r aerobic d i g e s t i o n as compared to anaerobic d i g e s t i o n i n c l u d e (4): (a) v o l a t i l e - s o l i d s r e d u c t i o n approximately equal to that obtained anaero- b i c a l l y ; (b) lower BOD concentrations i n supernatant l i q u o r ; (c) production of an odourless, humus-like, b i o l o g i c a l l y s t a b l e end product 23 that can be disposed of e a s i l y ; (d) production of a sludge w i t h e x c e l l e n t dewatering c h a r a c t e r i s t i c s ; (e) recovery of more of the b a s i c f e r t i l i z e r values i n the sludge; (f ) fewer o p e r a t i o n a l problems; and (g) lower c a p i t a l cost. The major disadvantage of the aerobic d i g e s t i o n process appears to be the higher power cost a s s o c i a t e d w i t h supplying the r e q u i r e d oxygen. The purposesof t h i s study were to determine the s u s c e p t i b i l i t y to treatment of a h i g h - s t r e n g t h , l a n d f i l l leachate by aerobic b i o l o g i c a l methods, to determine where and to what extent metals i n the leachate might be concentrated, and to c h a r a c t e r i z e the s e t t l e d e f f l u e n t s obtained from the aerobic b i o s t a b i l i z a t i o n process. The study was c a r r i e d out i n three phases. The a c c l i m a t i z a t i o n - m e t a l removal study was designed to produce an a c c l i m a t i z e d m i c r o b i a l p o p u l a t i o n f o r use i n the subsequent aero b i c b i o s t a b i l i z a t i o n e f f i c i e n c y s t u d i e s and to study the long-term, metal removal c a p a c i t y of the s e t t l i n g b i o l o g i c a l f l o e . The aerobic b i o s t a b i l i z a t i o n e f f i c i e n c y s t u d i e s were designed to determine the e f f e c t of i n c r e a s i n g s o l i d s d e t e n t i o n time and organic l o a d i n g on t r e a t - ment e f f i c i e n c y and metal removal. Based on estimates of the steady s t a t e mixed l i q u o r v o l a t i l e suspended s o l i d s l e v e l s , s o l i d s d e t e n t i o n times were s e l e c t e d to give organic loadings i n the range recommended f o r extended aera- t i o n . Using the r e s u l t s of t h i s "extended a e r a t i o n " e f f i c i e n c y study, the minimum s o l i d s d e t e n t i o n time f o r the system was p r e d i c t e d and the s o l i d s d e t e n t i o n times to be used i n the " s h o r t e r detention.time" e f f i c i e n c y study were then set above t h i s p r e d i c t e d minimum. At the c o n c l u s i o n of each phase of the study, s e t t l e d e f f l u e n t s were c o l l e c t e d f o r metal a n a l y s i s and sub- sequent c h a r a c t e r i z a t i o n . CHAPTER 4 SYSTEM DESIGN AND EXPERIMENTAL PROCEDURE 4-1 Design of the Treatment System The i n v e s t i g a t i o n of the theory of ae r o b i c b i o s t a b i l i z a t i o n and previous attempts at a e r o b i c a l l y t r e a t i n g l a n d f i l l leachate (15,16) provided the b a s i c i n f o r m a t i o n needed to design the system. I t was decided that a s i n g l e stage bench s c a l e system would be used to evaluate the aerob i c b i o s t a - b i l i z a t i o n of hi g h - s t r e n g t h l a n d f i l l l eachate, because of i t s s i m p l i c i t y and ease of operation.: 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 s t u d i e s , i t was decided to use three d i g e s t e r s each of 10 l i t r e s c a p a c i t y . This d e c i s i o n was based on the f a c t t h a t : (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) s i m i l a r u n i t s had s u c c e s s f u l l y been used i n previous s t u d i e s , 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 i g e s t e r s . The d i g e s t e r s were made from l a r g e glass b o t t l e s . The bottom of each b o t t l e was removed and the necks were f i t t e d w i t h l a r g e rubber stoppers. The stoppers were secured u s i n g heavy s t a i n l e s s s t e e l w i r e but no w i r e was allowed i n s i d e the d i g e s t e r s , thus preventing any unknown a d d i t i o n s of metal to the d i g e s t e r contents. A porous g l a s s , coarse-bubble, a i r d i f f u s e r was f i t t e d i n t h e bottom of each d i g e s t e r and a i r was provided f o r each u n i t from the l a b o r a t o r y compressed a i r system. Because of the high concentrations of metals i n the leachate feed, foaming problems were a n t i c i p a t e d . To c o n t r o l foaming, w h i l e m a i n t a i n i n g adequate mixing, i t was f e l t that a combination of a i r and mechanical mixing should be employed i n the d i g e s t e r s . Consequently, an a d j u s t a b l e clamp was placed on the a i r l i n e to each d i g e s t e r to c o n t r o l a i r flow and an e l e c t r i c d r i v e n s t i r r e r was provided i n each d i g e s t e r to ensure uniform d i s t r i b u t i o n of food and micro-organisms. M i x i n g speeds were set approximately equal i n 25 a l l three d i g e s t e r s and a i r flow r a t e s were adjusted to maintain a e r o b i c c o n d i t i o n s w h i l e minimizing foaming. A schematic of these d i g e s t e r s i s shown i n Figure 1. To c o n t a i n any foam which might be produced during the study, i t was decided to use only 4.5 l i t r e s of mixed l i q u o r , thus a l l o w i n g f o r about 8 inches of foam i n each d i g e s t e r . An antifoam agent* was a l s o t e s t e d f o r tox- c i t y to the b i o l o g i c a l system. Various doses of the antifoam agent were addled to t e s t u n i t s , but even i n very l a r g e doses the oxygen uptake r a t e s of t e s t and c o n t r o l u n i t s remained equal a f t e r s e v e r a l hours. Foaming problems, how- ever, never reached the proportions a n t i c i p a t e d and i t was necessary to add the antifoam agent to only the h i g h e s t loaded d i g e s t e r t e s t e d . Since the conventional a c t i v a t e d sludge process i s not s i g n i f i c a n t l y i n f l u e n c e d by small temperature changes, and s i n c e the r e a c t o r s were to be operated during the summer, i t was f e l t t hat temperature c o n t r o l s were not necessary. The temperature of the mixed l i q u o r s was measured f r e q u e n t l y o o throughout the study and found to v a r y between 21 and 25 C. The temperature of the mixed l i q u o r appeared to be a f f e c t e d more by the a i r f l o w r a t e through the d i g e s t e r than by the ambient a i r temperature, decreasing as the a i r flow- r a t e increased. 4-2 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 - meter constructed at the U n i v e r s i t y of B r i t i s h Columbia, as part of an on- going program to c h a r a c t e r i z e l a n d f i l l leachates and monitor v a r i a t i o n s i n t h e i r composition w i t h time, r a i n f a l l r a t e , cover m a t e r i a l and other para- meters., The program was i n i t i a t e d by Dr. R.D. Cameron, of the Department of *Dow Corning antifoam emulsion DB-31. E l e c t r i c motor V o l u m e t r i c g r a d u a t i o n ( o n m a s k i n g tape) P l a s t i c tubing Oil - free air • E l e c t r i c motor d r i v e n s t i r r e r 0 Porous , G l a s s , Coarse bubb le d i f fuser Ad ju s t ab le screw clamp R u b b e r stopper J3 F i g u r e 1 SCHEMATIC OF LABORATORY AEROBIC DIGESTERS C i v i l E n g i n e e r i n g , U.B 0C. D e t a i l s o f the l y s i m e t e r a r e : (1) Dimensions - 14 f e e t deep, 4 f e e t i n d i a m e t e r (2) Cover m a t e r i a l - 2 f e e t o f hog f u e l (3) T o t a l w e ight o f garbage - 3420 l b s . (4) Depth o f garbage - 8 f e e t (5) Weight ( d e n s i t y ) b e f o r e f i n a l c o v e r - 884 l b . / c u b i c y a r d (wet) (6) R a i n f a l l r a t e - 15 i n c h e s per y e a r (7) M o i s t u r e c o n t e n t - 34.77„ (8) P e r c e n t a g e c o m p o s i t i o n o f garbage: Food waste - 11.8 Garden waste - 9.8 Paper p r o d u c t s - 47.6 Cardboa r d - 5.4 T e x t i l e s - 3.6 Wood - 4.7 M e t a l s - 8.7 G l a s s and c e r a m i c s - 7.0 Ash, r o c k s and d i r t - 1.4 T o t a l - 100 L e a c h a t e from t h i s l y s i m e t e r was c o l l e c t e d weekly, r e t u r n e d o o to the l a b and s t o r e d a t 4 C. The 4 C temperature has been found adequate t o m i n i m i z e changes i n l e a c h a t e c o m p o s i t i o n . Samples were mixed e v e r y 4 weeks t o produce a composite sample, which was a n a l y s e d by t e c h n i c i a n s i n the l a b o r a t o r y as p a r t o f the l e a c h a t e c h a r a c t e r i z a - t i o n r e s e a r c h program. Composite samples were t h e n mixed f o r use o i n t h i s s t u d y and s t o r e d i n 20 1 p o l y e t h y l e n e b o t t l e s a t 4 C. 120 l i t r e s of h i g h - s t r e n g t h l a n d f i l l leachate were thus c o l l e c t e d over a f i v e month pe r i o d f o r use i n the aerobic b i o s t a b i l i z a t i o n study. One 20 l i t r e b o t t l e was s e l e c t e d f o r use i n the a c c l i m a t i z a t i o n - metal removal study. I t s composition i s shown i n Table VI. As the a c c l i m a t i z a t i o n - m e t a l removal study drew to an end, the remaining 100 1 of leachate were mixed to form a l a r g e composite which was used throughout the treatment e f f i c i e n c y s t u d i e s . The composite was pumped i n t o 20 1 poly- o ethylene b o t t l e s and again s t o r e d at 4 C to minimize b i o l o g i c a l a c t i v i t y before feeding. The composition of the composite leachate sample i s a l s o shown i n T a b l e V I . 4-3 pH C o n t r o l Because the pH of the leachate was w e l l below 6.5, i t was f e l t t hat pH c o n t r o l might be necessary. At the s t a r t of the a c c l i m a t i z a t i o n - m e t a l removal study, the pH of the leachate feed, prepared i n 2 l i t r e batches, was t h e r e f o r e adjusted to approximately 7.2 u s i n g calcium hydroxide. The pH of the mixed l i q u o r was monitored d a i l y . In 9 days the pH of a l l mixed l i q u o r s , rose from 7.2 to g r e a t e r than 8.3 and thus, pH adjustment of the leachate feed was stopped. From day 10 on i n the a c c l i m a t i z a t i o n study and a l l through the e f f i c i e n c y s t u d i e s , only n u t r i e n t s were added to the leachate feed and no attempt was made to c o n t r o l the pH of the mixed l i q u o r s . 4-4 N u t r i e n t Balance In order to maintain a B0D,_:N:P r a t i o of 100:5:1, a d d i t i o n a l n i t r o - gen and phosphorus ; were r e q u i r e d . S e v e r a l chemicals were considered f o r t h i s purpose. A mixture of mono-basic ammonium phosphate ((NH^H^PO^.) and di-ammonium phosphate ((OTI^)2HPO4) was s e l e c t e d because i t s u p p l i e d both n i t r o g e n and phosphorus.; 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 a e r o b i c 29 TABLE VI COMPOSITION OF LEACHATE FEED USED DURING STUDY Concentration Concentration mg/l mg/l Parameter During A c c l i m a t i z a t i o n - During E f f i c i e n c y Metal Removal Study Studies BOD5 42,000 36,000 COD 58,000 48,000 T o t a l Carbon 18,400 15,400 T o t a l Inorganic Carbon 16 11 T o t a l S o l i d s 34,900 26,600 T o t a l V o l a t i l e S o l i d s 21,500 17,800 T o t a l D i s s o l v e d S o l i d s 34,500 25,700 A c i d i t y 6,600 5,640 A l k a l i n i t y 10,200 7,640 Aluminum 60.2 41.8 A r s e n i c 4.1 3.6 Barium 1.3 0.7 B e r y l l i u m t r a c e t r a c e Boron 7.40 7.30 Calcium 1,924 1,394 Cadmium 0.43 0.39 C h l o r i d e 1,650 1,620 Chromium 2.3. 1.9 Copper 0.17 0.24 Iro n 1,260 960 Lead 1.79 1.44 Magnesium 378 310 Manganese 46.0 41.0 Mercury 0.012 0.012 . Nitr o g e n - t o t a l 1,370 1,080 - NH 3 938 725 N i c k e l 0.61 0.65 Phosphorus - t o t a l 22.2 19.8 Potassium 1,610 1,060 Sodium 1,720 1,250 Sulphates 1,020 1,070 Zinc 227 223 T a n n i n - l i k e compounds 943 578 * pH 5.09 5.02 *not i n mg/l 30 micro-organisms and i t was f e l t that pH of the leachate feed could be buffered around 7.2 by s e l e c t i o n !.o£ .the proper molar r a t i o s of these two s a l t s . An exact r a t i o of 5:1 f o r N:P could, however, not be achieved u s i n g these two s a l t s , so a B0D^:N r a t i o of 20:1 was aimed f o r i n e s t a b l i s h i n g r e q u i r e d n u t r i e n t a d d i t i o n s . Since the a n a l y s i s of the leachate feed used i n the a c c l i m a t i z a t i o n - m e t a l removal study was not complete when the study began, n u t r i e n t a d d i t i o n s were estimated from previous lab analyses on the 4-week composite samples. S i m i l a r l y , the a n a l y s i s of the composite leachate feed used i n the e f f i c i e n c y s t u d i e s was not complete when these' s t u d i e s began. Therefore, the same amounts of each s a l t were added during the f i r s t h a l f of the e f f i c i e n c y study ("extended a e r a t i o n " e f f i c i e n c y study). N u t r i e n t a d d i t i o n s were then reduced during the f i n a l h a l f of the e f f i c i e n c y study ("shorter d e t e n t i o n time" e f f i c i e n c y s t u d y ) . The r e s u l t i n g n u t r i e n t a d d i t i o n s and B0Dc:N:P r a t i o s are shown i n Table V I I . TABLE V I I NUTRIENT ADDITIONS AND B0Dc:N:P RATIOS DURING STUDY Study Phase Ammonium Phosphate A d d i t i o n , mg/1 Di-Ammonium Phosphate A d d i t i o n , mg/1 BOD :N:P R a t i o i n Leachate Feed A c c l i m a t i z a t i o n - M etal Removal Study 630 2 , 9 0 0 100:4.85:2.05' "Extended A e r a t i o n " E f f i c i e n c y Study 630 2 , 9 0 0 100:6.37:3.12 "Shorter Detention Time" E f f i c i e n c y Study 1,462 100:5:1.3 4-5 Metal Concentrations No attempt was made to modify metal c o n c e n t r a t i o n s . I t was f e l t that the best approach would be to use leachate as produced and observe the e f f e c t s of the very h i g h metal concentrations on the e f f i c i e n c y of the aerobic b i o s t a b i l i z a t i o n process. 4-6 A c c l i m a t i z a t i o n - M e t a l Removal Study This phase of the research program was designed to produce an a c c l i m a - t i z e d m i c r o b i a l p o p u l a t i o n f o r use i n the aerobic b i o s t a b i l i z a t i o n e f f i c i e n c y s t u d i e s and to study the long-term, metal removal c a p a c i t y of the s e t t l i n g b i o l o g i c a l f l o e . To set " s a f e " h y d r a u l i c d e t e n t i o n times f o r use i n t h i s study, i t was necessary to evaluate a number of co n v e n t i o n a l design parameters. Boyle and Ham (15) found aerobic treatment of l a n d f i l l l e a c h a t e promising when loadings were kept below 30 lb.BOD^/day/1,000 c u b i c . f e e t . Cook and Foree (16) found, however, that BOD removals were s t i l l e x c e l l e n t when loadings were increased to about 100 lb.COD/day/1,000 c u b i c f e e t , provided food to micro-organism r a t i o s were kept r e l a t i v e l y low (around 0.22 lb.BOD^/lb.MLVSS/ day). For t h i s reason, the vo l u m e t r i c BOD and COD loa d i n g r a t e s and food to micro-organism r a t i o s , assuming a MLVSS c o n c e n t r a t i o n of 4,000 mg/l, were evaluated at a number of convenient h y d r a u l i c d e t e n t i o n times. With a h y d r a u l i c d e t e n t i o n time of 45 days, COD loa d i n g was a n t i c i p a t e d to be about 81 lb.COD/day/1,000 cubic feet r e s u l t i n g i n an i n i t i a l food to micro- organism r a t i o of about 0.23 lb/BOD 5/lb.MLVSS/day. Thus, a 45 day hydrau- l i c d e t e n t i o n time was set f o r the highest loaded d i g e s t e r and h y d r a u l i c d e t e n t i o n times f o r the other two d i g e s t e r s were c o n v e n i e n t l y set at 60 and 90 days. Since no suspended s o l i d s were to be withdrawn during the a c c l i m a - t i z a t i o n study, the s o l i d s d e t e n t i o n times i n a l l three u n i t s were equal to the.length of that study.(56 days). (a) S t a r t Up - About 15 1 of waste a c t i v a t e d sludge were obtained from the C e n t r a l Sewage Treatment P l a n t i n Squamish, B.C., some 40 miles north of Vancouver. The Squamish Sewage Treatment P l a n t i s a "package a c t i v a t e d sludge treatment" p l a n t t r e a t i n g a mixture of domestic and l i g h t i n d u s t r i a l waste. A survey of "package a c t i v a t e d sludge treatment" p l a n t s i n the Vancouver area had shown i t to pro- duce the most s u i t a b l e a c t i v a t e d sludge f o r use i n t h i s study. • The mixed l i q u o r v o l a t i l e suspended s o l i d s c o n c e n t r a t i o n i n the sludge sample was determined and enough sludge was then placed i n each d i g e s t e r to provide 4.5 1 of mixed l i q u o r w i t h a v o l a t i l e suspended s o l i d s c o n c e n t r a t i o n of 3,960 mg/1. The r e q u i r e d volumes of leachate feed w i t h n u t r i e n t s added and pH adjusted to about 7.2 were then added to each d i g e s t e r : 100 ml to D i g e s t e r D j , 75 ml to D i g e s t e r E", and 50 ml to D i g e s t e r F". The t o t a l volume i n each d i g e s t e r was then adjusted to 4.5 1 u s i n g d i s t i l l e d water. A i r flow was i n i t i a t e d and adjusted i n each d i g e s t e r u s i n g the a d j u s t - able clamps on the a i r l i n e s . S t i r r e r s i n each d i g e s t e r were then turned on and s t i r r i n g speeds set approximately equal. (b) Digester Operation and T e s t i n g - At 24 h o u r : i n t e r v a l s the water l o s t by evaporation was replaced w i t h d i s t i l l e d water. The sides of the d i g e s t e r s and the s t i r r e r s i n each d i g e s t e r were scraped to remove a l l adhering micro-organisms, which were thus returned to the mixed l i q u o r and then the contents were completely mixed. The o * oxygen uptake r a t e i n each d i g e s t e r was then measured at 20 C u s i n g 3.0 ml of mixed l i q u o r , which was subsequently returned to the d i g e s - * u s i n g a YSI Model 53 B i o l o g i c a l Oxygen Monitor and a Haake Constant Temperature C i r c u l a t o r , Model FJ . t e r from which i t was obtained. A f t e r the oxygen uptake r a t e i n each d i g e s t e r had been determined, the a i r and s t i r r e r s i n a l l three d i g e s t e r s were shut o f f and the b i o l o g i c a l f l o e s were allowed to s e t t l e . The s e t t l i n g time r e q u i r e d to o b t a i n an adequate volume of c l e a r supernatant increased as b i o l o g i c a l s o l i d s accumulated i n the d i g e s t e r s , but the d i g e s t e r s were never allowed t o s i t more than an hour without a i r . A f t e r s e t t l i n g , the r e q u i r e d volume of c l e a r supernatant was withdrawn from each d i g e s t e r u s i n g v o l u m e t r i c p i p e t t e s : 100 ml from D i g e s t e r D 7 5 ml from D i g e s t e r E a n d 50 ml from D i g e s t e r F•". Volumes of leachate feed equal to the volumes removed were then added to each d i g e s t e r . A i r to the d i g e s t e r s was turned back on and the s t i r r i n g speeds were again set equal. The pH of the s e t t l e d e f f l u e n t from each d i g e s t e r was measured and recorded. Every 5 days the t o t a l s o l i d s concentrations i n the s e t t l e d e f f l u e n t s were determined. The BOD^'s of the s e t t l e d e f f l u e n t s were .determined every 7 days. As i n d i c a t e d , leachate feed f o r these u n i t s was prepared i n 2 l i t r e volumes and st o r e d at 4°C u n t i l needed. pH adjustment on the i n i t i a l feed caused a great p o r t i o n of the metals to s e t t l e out of the leachate feed. When the pH of a l l 3 u n i t s climbed t o gr e a t e r than 8.3 a f t e r 9 days of ope r a t i o n , the pH adjustment of the leachate feed was di s c o n t i n u e d . The a d d i t i o n o f n u t r i e n t s alone s t i l l caused a p o r t i o n of the metals to s e t t l e out of the leachate. Thus, throughout t h i s study, feed was brought out of the r e f r i g e r a t o r , allowed to warm up f o r about an hour t o reduce any temperature shock t the system and then thoroughly mixed j u s t p r i o r to the d a i l y feeding. A f t e r 56 days, 500 ml of mixed l i q u o r were withdrawn from each d i g e s t e r . 100 ml of each mixed l i q u o r were digested f o r metal a n a l y s i s f o l l o w i n g the recommended EPA method (17) and the balance: was allowed to s e t t l e . C l e a r supernatants were then withdrawn f o r metal a n a l y s i s . 4-7 Aerobic B i o s t a b i l i z a t i o n E f f i c i e n c y Studies S o l i d s t e s t s near the end of the a c c l i m a t i z a t i o n - m e t a l removal study i n d i c a t e d MLVSS l e v e l s i n Di g e s t e r s D", E', and F" of approximately 11,800, 10,900 and 7,600 mg/1 r e s p e c t i v e l y . While these MLVSS l e v e l s are g r e a t l y i n excess o f the recommended range f o r a c t i v a t e d sludge processes, no attempt was made to s i g n i f i c a n t l y reduce the b i o l o g i c a l s o l i d s concentra- t i o n s because: (1) the b i o l o g i c a l f l o e s s t i l l s e t t l e d w e l l , (2) the s e t t l e d e f f l u e n t s had very low BOD^ and g r e a t l y reduced metal c o n c e n t r a t i o n s , (3) Cook and Foree (16) c r e d i t e d t h e i r high MLVSS l e v e l s ( >4,400 mg/1) w i t h h e l p i n g c o n t r o l and reduce the foaming problem, and (4) i t was f e l t that the b i o l o g i c a l s o l i d s l e v e l s would drop to s u i t a b l e l e v e l s i f there was not enough food i n the leachate feed to maintain such high MLVSS co n c e n t r a t i o n s . Again, to set " s a f e " s o l i d s d e t e n t i o n times f o r use i n the f i r s t h a l f of these e f f i c i e n c y s t u d i e s , v o l u m e t r i c BOD and COD l o a d i n g r a t e s and a n t i c i p a t e d food to micro-organism ratios' were c a l c u l a t e d . Assuming a maximum MLVSS co n c e n t r a t i o n of 10,000 mg/1, a 30 day : s o l i d s d e t e n t i o n time r e s u l t e d . i n a food to micro-organism r a t i o of about 0.12, a BOD l o a d i n g r a t e of about 75 lb.BOD 5/day/l,000 cubic fee t and COD l o a d i n g of about 102 lb.COD/day/1,000 cubic f e e t . The COD l e a d i n g was t h e r e f o r e very c l o s e to the maximum recommended by Cook and Foree (16) and the food to micro- organism r a t i o was expected to remain i n the range recommended f o r extended 35 a e r a t i o n and below the range f o r conventional complete mix a c t i v a t e d sludge treatment (see Table I I ) . A s o l i d s d e t e n t i o n time of 30 days was there- for e set f o r the highest loaded d i g e s t e r , D i g e s t e r D, i n the f i r s t h a l f of the aerobic b i o s t a b i l i z a t i o n e f f i c i e n c y s t u d i e s . S o l i d s d e t e n t i o n times f o r D i g e s t e r s E and F were then set at 45 and 60 days r e s p e c t i v e l y , to cover the range of food to micro-organism r a t i o s recommended f o r extended a e r a t i o n , 0.05 to 0.15 lb.BOD^lb.MLVSS/day. (a) D i g e s t e r Operation and T e s t i n g - A t 24 hour i n t e r v a l s , the water l o s t by evaporation was replaced w i t h d i s t i l l e d water, the sides and s t i r r e r s i n each d i g e s t e r were scraped, and the oxygen uptake r a t e at 20°C was determined f o r each d i g e s t e r . The r e q u i r e d volumes of mixed l i q u o r were then withdrawn from each d i g e s t e r u s i n g l a r g e - t i p - opening', b a c t e r i o l o g i c a l p i p e t t e s : 150 ml from D i g e s t e r D, 100 ml from D i g e s t e r E, and 75 ml from D i g e s t e r F. Volumes of leachate feed equal to the volumes of mixed l i q u o r s . removed were then added to each d i g e s t e r . The pH of the mixed l i q u o r from each d i g e s t e r was measured and recorded. Every 3 or 4 days, the MLSS c o n c e n t r a t i o n , MLVSS c o n c e n t r a t i o n and t o t a l s o l i d s c o n c e n t r a t i o n i n the mixed l i q u o r e f f l u e n t were determined. The BOD5 of the mixed l i q u o r and s e t t l e d e f f l u e n t s were determined every 7 days. These parameters were used to determine when steady s t a t e o p e r a t i o n was achieved. A f t e r 30 days, s e t t l e d e f f l u e n t s from each d i g e s t e r were c o l l e c t e d d a i l y and composited f o r subsequent e f f l u e n t c h a r a c t e r i - z a t i o n . A f t e r 35 days, 200 ml of mixed l i q u o r were withdrawn from each d i g e s t e r . 100 ml of each mixed l i q u o r were wet-ash digested f o l l o w i n g the recommended EPA procedure (17). Small samples of each mixed l i q u o r were then withdrawn f o r COD a n a l y s i s and the balance of the samples was allowed t o s e t t l e . The s e t t l e d e f f l u e n t s 36 were then c o l l e c t e d f o r metal a n a l y s i s . The a n a l y t i c a l procedures employed f o r a l l t e s t s used i n t h i s study are o u t l i n e d i n the t h i r t e e n t h e d i t i o n of Standard Methods (18) and f u r t h e r explained i n Chemistry f o r S a n i t a r y Engineers (19). Metal concentrations were determined u s i n g a J a r r e l l - A s h MV 500 Atomic A d s o r p t i o n Spectrophotometer. (b) T r a n s i t i o n to "Shorter Detention Time" Study - A n a l y s i s of the MLVSS co n c e n t r a t i o n and mixed l i q u o r BOD^ data c o l l e c t e d d u r i ng the "extended a e r a t i o n " e f f i c i e n c y study, p r e d i c t e d a minimum s o l i d s d e t e n t i o n time of 6.46 days (see Appendix E). A c t i v a t e d sludge treatment p l a n t s are u s u a l l y designed w i t h s o l i d s d e t e n t i o n times 3 or 4 times the p r e d i c t e d minimum. Therefore, because con s i d e r - a b l e personal judgment was inv o l v e d i n the s e l e c t i o n of the k i n e t i c parameters used to determine the minimum s o l i d s d e t e n t i o n time, and because foaming problems were s t i l l a n t i c i p a t e d at s h o r t e r de- t e n t i o n times, a s o l i d s d e t e n t i o n time o f 10 days was set f o r the highest loaded d i g e s t e r . Detention times o f 20 and 30 days, approximately 3 and 4 times the p r e d i c t e d minimum, were then chosen f o r the remaining u n i t s . To minimize the shock to any u n i t , i t was decided to g r a d u a l l y increase the l o a d i n g on each and to make the highest loaded d oigester i n the "extended a e r a t i o n " e f f i c i e n c y study, the highest loaded d i g e s t e r i n the " s h o r t e r d e t e n t i o n time" e f f i c - iency study. Therefore, over the next 7 days, the volume of mixed l i q u o r withdrawn and leachate feed added t o each u n i t was g r a d u a l l y increased: from 150 ml per day to 450 ml per day f o r D i g e s t e r D, from 100 ml per day to 225 ml per day f o r D i g e s t e r E, and from 75 ml per day to 150 ml per day f o r D i g e s t e r F. 37 (c) "Shorter Detention Time" E f f i c i e n c y Study - The same d a i l y procedure used i n the "extended a e r a t i o n " e f f i c i e n c y study was employed during t h i s study. B r i e f l y , each day, a f t e r r e p l a c i n g water l o s t by evaporation and measuring the oxygen uptake r a t e i n each d i g e s t e r , the r e q u i r e d volumes of mixed l i q u o r were withdrawn from each d i g e s t e r : 450 ml from D i g e s t e r A, 225.ml from D i g e s t e r B, and 150 ml from D i g e s t e r C. Volumes of leachate feed equal to the volumes o f mixed l i q u o r withdrawn were then added to each d i g e s t e r . The pH of the mixed l i q u o r from each d i g e s t e r was measured and recorded d a i l y . Every 3 or 4 days the MLSS c o n c e n t r a t i o n , MLVSS co n c e n t r a t i o n and t o t a l s o l i d s c o n c e n t r a t i o n i n the mixed l i q u o r were determined. The BOD^ of the mixed and s e t t l e d e f f l u e n t s was. determined every 7 days. However, because there was some evidence of i n h i b i t i o n i n the mixed l i q u o r BOD5 t e s t s and because those t e s t r e s u l t s were very e r r a t i c , . ; , the COD of the mixed and s e t t l e d e f f l u e n t s was - determined every 3 or 4 days i n i t i a l l y , and every 7 days a f t e r steady s t a t e o p eration was achieved. ' A f t e r 35 days, 100 ml of each mixed l i q u o r was di g e s t e d f o r metal a n a l y s i s (17). One l i t r e of each mixed l i q u o r was then w i t h - drawn f o r s e t t l i n g t e s t s and the s e t t l e d e f f l u e n t s were c o l l e c t e d f o r metal a n a l y s i s and c h a r a c t e r i z a t i o n . 4-8 Summary A long, c a r e f u l , a c c l i m a t i z a t i o n p e r i o d produced mixed l i q u o r s w i t h very h i g h v o l a t i l e suspended s o l i d s c o n c e n t r a t i o n s . Prudent s e l e c t i o n of s o l i d s d e t e n t i o n times f o r the "extended a e r a t i o n " e f f i c i e n c y study r e s u l t e d i n s t a b l e o p e r a t i o n w i t h i n 3 weeks, as i n d i c a t e d by the mixed l i q u o r BOD^ and VSS c o n c e n t r a t i o n s . A short t r a n s i t i o n p e r i o d to s h o r t e r d e t e n t i o n 38 times r e s u l t e d again i n s t a b l e o p e r a t i o n , at these new d e t e n t i o n times, w i t h i n 3 weeks. W e l l balanced and s t a b l e a e r o b i c b i o s t a b i l i z a t i o n e f f i c i e n c y s t u d i e s were conducted f o r 35 days f o r these two sets of d i g e s t e r s . The h i g h suspended s o l i d s l e v e l s and the combination of a i r and mechanical mix- in g e f f e c t i v e l y c o n t r o l l e d foaming and only at the lowest (detention time t e s t e d was i t necessary to add a chemical antifoam agent. CHAPTER 5 DISCUSSION OF RESULTS 5-1 Removal of Oxygen Demanding M a t e r i a l (a) B O D c ; Removal - I t was o r i g i n a l l y intended to use B O D r j data through- out the study to i n d i c a t e the e f f i c i e n c i e s o f the u n i t s t e s t e d . * Figure 2 shows the BOD's of"the mixed l i q u o r s " a n d s e t t l e d e f f l u e n t s as a f u n c t i o n of the s o l i d s d e t e n t i o n time. Figure 3 shows the percent BOD,, removal as a f u n c t i o n of the s o l i d s d e t e n t i o n time. i From these two f i g u r e s , i t can be seen that the mixed l i q u o r BOD^ data were very / e r r a t i c j... v a r y i n g randomly from 2,040 to 3,680 mg/1. Throughout the study, the mixed l i q u o r BOD^ concentrations deter- mined, u s i n g the standard BOD^ t e s t , i n d i c a t e d BOD^ removals rang- i n g from 89.3 t o 93.7 percent. While such h i g h l e v e l s o f treatment would be very encouraging, the r e l i a b i l i t y of the BOD,, t e s t on a waste c o n t a i n i n g such h i g h heavy metal concentrations i s very questionable. Table V I I I shows t y p i c a l BOD^ t e s t r e s u l t s f o r the mixed l i q u o r e f f l u e n t s from D i g e s t e r s A, B and C, as w e l l as one set of BOD5 t e s t r e s u l t s f o r the leachate feed. As the d i l u t i o n f a c t o r decreases, the c a l c u l a t e d BOD5 of each sample decreases. This trend i s i n d i - c a t i v e o f b i o l o g i c a l i n h i b i t i o n . At d i l u t i o n s greater;than.2 .times the g r e a t e s t d i l u t i o n used f o r the determination of the mixed l i q u o r BOD,., the same i n h i b i t i o n may be observed i n the leachate feed r e s u l t s . Since metal concentrations i n the mixed l i q u o r s were very c l o s e to those i n the leachate feed, i t i s h i g h l y probable t h a t 180 160 140 „ 120 ^ I O O E I 80 « a O 60 CO 40 20 0 Settled effluents T i r Average for detention times over iOdays = 58. I mg/litre O J L _L 10 15 20 25 30 35 40 45 50 S o l i d s d e t e n t i o n t ime,0 C — d a y s 55 60 Mixed liquor effluents a> O m 3,800i 1 I I 1 1 1 I . I 1 1 . 1 i 3,600 O O 3,400 O — 3,200 — 3,000 — — 2,800 o — 2,600 — — 2,400 2,200 * Values shown on l a s t 14-21 days graphs are averages over of each run (see Appendix B) o - 2,000 I I I ! 1 1 1 1 0 1 1 1 5 10 15 20 S o l i d s 25 30 35 40 45 50 55 detent ion t i m e , 0 c ~ d a y s 60 F i g u r e 2 BOD OF MIXED LIQUORS AND SETTLED EFFLUENTS vs SOLIDS DETENTION TIME 41 100 99.8 99.6 99.4 ^ 99.2 o > o E 99.0 •o Q> . C o cx X UJ ° o' X / tr — — / C N Settled effluents to a o (D 9 5 r 93 9 I 89 • Mixed I i quor effluents • • 87 h 85 83 i . 1 1 10 20 30 40 50 60 Solids detention time, 0c - days 70 80 F i g u r e 3 PERCENT BOD REMOVALS v s SOLIDS DETENTION TIME TABLE V I I I ..-TYPICAL BOD5 TEST RESULTS FOR MIXED LIQUOR EFFLUENTS FROM DIGESTERS A, B AND C, AND FOR LEACHATE FEED D i s s o l v e d BOD 5 ML of Sample i n 300 ML Oxygen mg/1 Sample BOD B o t t l e ( D i l u t i o n ; D e p l e t i o n Accepted Source Factor i n Brackets) mg/1 Average 0.10 (3,000:1) 1.38 4,140 Mixed Liquor "0.'20 (1,500:1) 2.20 3,300 1 E f f l u e n t from 0.30 (1,000:1) 2.94 2,940 2,998 Dig e s t e r A 0.30 (1,000:1) 3.03 3,030 0 = 10 days 0.50 ( 600:1) 4.54 2,724 J c 0.70 ( 429:1) 5.40 2,320 0.10 (3,000:1) 1.47 4,410 Mixed Liquor 0.20 (1,500:1) 2.60 3,900 E f f l u e n t from 0.30 (1,000:1) 3.50 3,500 3,667 Di g e s t e r B 0.30 (1,000:1) 3.60 3,600 J 0 = 20 days 0.50 ( 600:1) 4.73 2,838 c 0.70 ( 429:1) 5.82 2,494 0.10 (3,000:1) 1.70 5,100 Mixed Liquor 0.20 (1,500:1) 2.52 3,780 i E f f l u e n t from 0.30 (1,000:1) 3.40 3,400 3,560 Dig e s t e r C 0.30 (1,000:1) 3.50 3,500 j 0 = 30 days 0.50 ( 600:1) 4.69 2,814 c 0.70 ( 429:1) 5.85 2,507 0.010 (30,000:1) 0.97 29,100 0.020 (15,000:1) 2.23 33,450 Leachate 0.020 (15,000:1) 2.28 35,100 •-34,580 Feed 0.030 (10,000:1) 3.52 35,200 0.040 ( 7,500:1) 3.72 27,900 0.050 ( 6,000:1) 3.96 23,600 43 heavy metal i n h i b i t i o n of b i o l o g i c a l a c t i v i t y r e s u l t e d i n the observed h i g h l y v a r i a b l e BOD5 t e s t r e s u l t s . Since the metals co n c e n t r a t i o n s and BOD5 of the s e t t l e d supernatants were v e r y low, i t was b e l i e v e d that the metals and a l a r g e percentage of the BOD5 of the mixed l i q u o r s , were bound to the b i o l o g i c a l f l o e . Since no method co u l d be found t o remove the i n h i b i t i n g heavy metals without removing b i o l o g i - c a l s o l i d s and hence BOD5, d i l u t i o n o f f e r e d the only f e a s i b l e method of o b t a i n i n g r e l i a b l e BOD5 t e s t r e s u l t s f o r the mixed l i q u o r s . In the standard BOD5 t e s t , an oxygen d e p l e t i o n of at l e a s t 0.50 mg/l i s r e q u i r e d f o r s t a t i s t i c a l r e l i a b i l i t y . Blanks of the BOD d i l u t i o n water used, g e n e r a l l y had oxygen d e p l e t i o n s between 0.15 and 0.30 mg/l a f t e r 5 days. Higher d i l u t i o n s of the mixed l i q u o r e f f l u e n t s r e s u l t e d i n h i g h l y v a r i a b l e r e s u l t s w i t h oxygen d e p l e t i o n s v e r y c l o s e to 0.50 mg/l. The hi g h v a r i a b i l i t y at these higher d i l u t i o n s may have been due to sampling v a r i a b i l i t y or to the oxygen d e p l e t i o n of the BOD d i l u t i o n water, as observed i n blank t e s t s . Nevertheless, s i n c e higher d i l u t i o n s d i d not gi v e c o n s i s - t e n t , s t a t i s t i c a l l y - r e l i a b l e r e s u l t s , and s i n c e the trend i n d i c a t e d i n Table V I I I was not always observed w i t h a l l mixed l i q u o r samples, the BOD,, values obtained u s i n g d i l u t i o n f a c t o r s between 1,000:1 and 1,500:1 were accepted f o r the mixed l i q u o r e f f l u e n t s . However, because of the problem i n o b t a i n i n g c o n s i s t e n t , s t a t i s t i c a l l y - r e l i a b l e B O D c j r e s u l t s , without any evidence of b i o l o g i c a l i n h i b i - t i o n , i t was decided that COD r e s u l t s would be used to i n d i c a t e the e f f i c i e n c y of the u n i t s t e s t e d . The BOD^ of the s e t t l e d e f f l u e n t s was very low; w i t h average e f f l u e n t BOD^'s ranging between 27.1 and 128.9 mg/l. S e v e r a l d i l u t i o n s of each s e t t l e d e f f l u e n t were used.in the BOD^ t e s t s 44 and no evidence of i n h i b i t i o n was apparent i n the r e s u l t s . I f the mixed liquor BOD5 results are accepted, the s e t t l i n g b i o l o g i c a l floe removed an average of 97.5 percent of the mixed liquor BOD5. The actual percent removal by the s e t t l i n g b i o l o g i c a l floe i s probably even, higher. Overall, better than 99.6 percent of the influent BOD5 was removed i n a l l settled effluents. As shown i n Figure 3, .two curves may.be drawn though the .percent BOD.,, removal data for settle d effluents. Curve 1 was the BOD^ data for settl e d effluents from Digesters D, E and F. During this study, the mixed liquor was allowed to s e t t l e for about a ha l f an hour before s e t t l e d effluent samples were withdrawn for BOD5 analysis. Curve 2 uses the BOD5 data for settled effluents from Digesters A, B and C. During this study, the mixed liquor was allowed to s e t t l e for at least an hour before sett l e d effluent samples were withdrawn for BOD^ and COD analysis. The extra time was required to obtain adequate volumes of set t l e d effluent for both test procedures; As can be seen in both Figures 2 and 3, the longer s e t t l i n g time resulted i n greater ov e r a l l BOD5 removal and lower se t t l e d effluent BOD5. For detention times over 20 days, the BOD^ of the settl e d effluents averaged"58.1 mg/1. Because the s e t t l i n g b i o l o g i c a l floe was observed to remove a very large percentage of both the mixed liquor BOD5 and s o l i d s , it was suspected that the very low settled effluent BOD,, might be due to an absence of micro-organisms in the se t t l e d effluent. For t h i s reason, BOD5 tests were p e r i o d i c a l l y conducted on settle d effluent samples using unseeded BOD d i l u t i o n water and BOD d i l u t i o n water seeded with enough domestic sewage to cause an oxygen depletion of 45 about 0.50 mg/l a f t e r 5 days. T y p i c a l r e s u l t s from these t e s t s are shown i n Table IX. As o n l y the BOD^ of s e t t l e d e f f l u e n t from Di g e s t e r A was s i g n i f i c a n t l y increased by seeding the BOD d i l u t i o n water, the BOD5 of a l l s e t t l e d e f f l u e n t s was determined u s i n g un- seeded BOD d i l u t i o n water. The values reported i n f o l l o w i n g t a b l e s and f i g u r e s and In Figures 2 and 3 are the r e s u l t s o f BOD t e s t s u s i n g unseeded BOD d i l u t i o n water. TABLE IX COMPARISON OF BOD5 TEST RESULTS ON SETTLED EFFLUENTS USING UNSEEDED AND SEEDED BOD DILUTION WATER S e t t l e d E f f l u e n t Source D i g e s t e r A 0 = c 10 days B 0 = c 20 days C 0 = c 30 days D 0 = c 30 days E 0 = c 45 days F 0 = c 60 days E f f l u e n t BOD5,mg/l - u s i n g unseeded BOD d i l u - t i o n water 162.6 32.4 27.1 83.2 65.9 77.0 - u s i n g seeded BOD d i l u - t i o n water 208.6 28.7 24.9 88.2 68.9 79.5 (b) COD Removal - Because i t was o r i g i n a l l y intended to use BOD5 data throughout the study to i n d i c a t e o p e r a t i o n a l s t a b i l i t y and removal e f f i c i e n c i e s , the COD of the mixed l i q u o r s and s e t t l e d e f f l u e n t s from D i g e s t e r s D, E and F was checked only at the end of the "extended a e r a t i o n " e f f i c i e n c y study. During the " s h o r t e r d e t e n t i o n 46 time" e f f i c i e n c y study, the COD of both the mixed l i q u o r s and s e t t l e d e f f l u e n t s from D i g e s t e r s A, B, and C was- monitored. F i g u r e s 4 and 5 show the COD of the mixed l i q u o r s and s e t t l e d e f f l u e n t s , r e s p e c t i v e l y , d u r i ng that study. From these f i g u r e s , i t can be seen that the COD r e s u l t s on mixed l i q u o r e f f l u e n t s were more v a r i a b l e than the COD r e s u l t s on s e t t l e d e f f l u e n t s . However, c o n s i d e r i n g the very h i g h mixed l i q u o r suspended s o l i d s l e v e l s i n these u n i t s (20,500 to 25,000 mg/1) and the r e s u l t i n g sampling problems, the observed v a r i a b i l i t y of the mixed l i q u o r COD t e s t r e s u l t s i s n e i t h e r s u r p r i s i n g nor e x c e s s i v e . The mixed l i q u o r and s e t t l e d e f f l u e n t COD r e s u l t s over the l a s t 14 to 17 days were averaged. COD t e s t s were a l s o conducted on the mixed l i q u o r and s e t t l e d e f f l u e n t s from D i g e s t e r s D, E, and F at the end of the "extended a e r a t i o n " e f f i c i e n c y study. F i g u r e 6 shows the COD of the mixed l i q u o r s and s e t t l e d e f f l u e n t s as a f u n c t i o n of the s o l i d s d e t e n t i o n time. The COD of the i n f l u e n t leachate averaged 48,250 mg/1. This h i g h COD was s u b s t a n t i a l l y reduced. The COD of both the mixed l i q u o r s and s e t t l e d e f f l u e n t s decreased w i t h i n - c r e a s i n g s o l i d s d e t e n t i o n time. The s e t t l i n g b i o l o g i c a l f l o e r e - moved an average of 96.4 percent of the mixed l i q u o r COD. At s o l i d s de- t e n t i o n times;.less 'than' 20 days, however, s e t t l e d e f f l u e n t COD rose • very s h a r p l y . S e t t l e d e f f l u e n t COD at s o l i d s d e t e n t i o n times gre a t e r than 20 days was l e s s than 600 mg/1. F i g u r e 7 shows the percent COD removal as a f u n c t i o n of the s o l i d s d e t e n t i o n time. Mixed l i q u o r COD removal increased from 51.5 to 75.7 percent as the s o l i d s d etention time was increased from 10 to 60 days. S e t t l e d e f f l u e n t COD removal increased s l i g h t l y from 96.8 1 47 25,000 23,000 21,000 E o o 19,000 17,000 I 5,000 13,000 Digester A 0 c = IOdays Digester C 0C= 30days Dotted lines indicate averages used in tables and on other graphs i _ J l _L 1 10 14 18 22 26 Time from start up - days 30 34 F i g u r e 4 COD OF MIXED LIQUORS DURING "SHORTER DETENTION TIME' E F F I C I E N C Y STUDY 48 2,400 2,000 1,600 a) E I 1,200 Q O O 800 400 Digester A 0c=IOdays Digester B ©c=20day Digester C |0c=3Odays Dotted lines indicate averages used in tables and on other graphs 8 12 16 20 24 Time from start up - days 28 32 36 F i g u r e 5 COD OF SETTLED EFFLUENTS DURING "SHORTER DETENTION TIME" E F F I C I E N C Y STUDY Mixed liquor effluents 2 4 , 0 0 0 21,000 £ I 8 , 0 0 0 h - 10 15 20 25 3 0 35 4 0 45 50 55 6 0 S o l i d s dete ntion t ime, © c - days F i g u r e 6 COD OF MIXED AND SETTLED EFFLUENTS v s SOLIDS DETENTION TIME 50 F i g u r e 7 PERCENT COD REMOVALS vs SOLIDS DETENTION TIME 51 to 99.2 percent as the s o l i d s d e t e n t i o n time increased from 10 to 60 days. At s o l i d s d e t e n t i o n time greater than 20 days, s e t t l e d e f f l u e n t COD removal was greater than 98.7 percent. I t has been g e n e r a l l y observed that the s e t t l i n g c h a r a c t e r i s t i c s of the b i o l o g i - c a l f l o e are enhanced as the s o l i d s d e t e n t i o n time increases ( 4 ) . As the mean age of the c e l l s i n each d i g e s t e r i n c r e a s e s , the micro- organisms i n the b i o l o g i c a l f l o e produce more e x t r a c e l l u l a r polymers and e v e n t u a l l y become, "encapsulated" i n a slime l a y e r . I t appears, t h e r e f o r e , that the presence of these e x t r a c e l l u l a r polymers and the slime l a y e r promote both BOD and COD removal, when very h i g h v o l a t i l e suspended s o l i d s l e v e l s are maintained. In the 10 day s o l i d s deten- t i o n time u n i t , the s e t t l i n g b i o l o g i c a l f l o e removed 93.5 percent of the mixed l i q u o r COD. I n the 20 day s o l i d s d e t e n t i o n time u n i t , the s e t t l i n g b i o l o g i c a l f l o e removed 97.0 percent of the mixed l i q u o r COD. A decrease of b e t t e r than 800 mg/1 i n s e t t l e d e f f l u e n t COD t h e r e f o r e r e s u l t e d from i n c r e a s i n g the s o l i d s d e t e n t i o n time from 10 to 20 days. Because very h i g h v o l a t i l e suspended s o l i d s c o ncentrations were maintained i n a l l s i x d i g e s t e r s , a look at COD removal as a f u n c t i o n of the food to micro-organism r a t i o i s d e s i r a b l e both f o r design purposes and f o r a comparison of the r e s u l t s w i t h those obtained by other researchers. Figure 8 shows the COD of the mixed l i q u o r and s e t t l e d e f f l u e n t s as a f u n c t i o n of the food to micro-organism r a t i o . The COD of the mixed l i q u o r and s e t t l e d e f f l u e n t s increases as the organic l o a d i n g or food to micro-organism r a t i o i n c r e a s e s . As. the food to micro-organism r a t i o i s increased, the incremental r i s e i n s e t t l e d e f f l u e n t COD i n c r e a s e s , w h i l e the incremental i n c r e a s e i n mixed l i q u o r COD decreases. These c o n t r a s t i n g curves probably Settled effluents 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 Food / micro - organism ra t io , lb. B O D 5 / l b . MLVSS/ .day Mixed liquor effluents a) £ I8,000H o> 15,000 E Q O O 0.02 0.04 0.06 0.08 0.10 0.12 0.i4 0.16 0.18 0.20 0.22 0.24 Food / m i c r o - o r g a n i s m ra t i o , lb. B 0 D 5 / l b . M L V S S / d a y F i g u r e 8 COD OF MIXED AND SETTLED EFFLUENTS v s FOOD TO MICRO-ORGANISM RATIO 53 i n d i c a t e that the q u a l i t y of the s e t t l e d e f f l u e n t i s a f f e c t e d more by the sludge age ( 0 ). than by the food to micro-organism r a t i o . c Figure 9 shows the percent COD removal f o r both the mixed l i q u o r and s e t t l e d e f f l u e n t s as a f u n c t i o n of the organic l o a d i n g . The' percent COD removal decreases w i t h i n c r e a s i n g food to micro-organism r a t i o . At food to micro-organism r a t i o s l e s s than 6.12 lb.BOD^/ lb.MLVSS/day, b e t t e r than 59 percent of the i n f l u e n t COD i s removed i n the mixed l i q u o r and b e t t e r than 98 percent of the i n f l u e n t COD i s removed i n the s e t t l e d e f f l u e n t . As the food to micro-organism r a t i o increases to greater than 0.20 lb.B0D5/lb.MLVSS/day, the per- cent COD removal decreases r a p i d l y . This trend was a l s o observed by Boyle and Ham (15) and Cook and Foree (16), even though lower s t r e n g t h l a n d f i l l leachates were used i n t h e i r s t u d i e s , (c) Organic Carbon Removal - T o t a l carbon i n the raw leachate averaged 15,400 mg/1, of which 15,389 mg/1 was organic carbon and 11 mg/1 was i n o r g a n i c carbon. The t o t a l carbon and t o t a l i n o r g a n i c carbon i n the s e t t l e d e f f l u e n t s from D i g e s t e r s A, B, and C were deter- mined* as part of the s e t t l e d e f f l u e n t c h a r a c t e r i z a t i o n program. The r e s u l t s are summarized i n Table X. From these r e s u l t s , i t i s apparent that a l a r g e amount of organic matter was .removed/from, the s e t t l e d e f f l u e n t s of a l l u n i t s . The removal of organic carbon increased r a p i d l y as the s o l i d s d e t e n t i o n time increased from 10 to 20 days. Removal of organic carbon was greater than 98 percent at s o l i d s d e t e n t i o n times, ( 0 ), greater than 20 days, and thus c confirmed the observed COD removal e f f i c i e n c i e s . u s i n g a Beckman Model 915-A. T o t a l Organic Carbon Analyser. 54 100 99 98 97 96 o o o (fl U o> -•c o Q. K £ 95" o 6 80r - 0) o o 75 70 65 60 55 50 45 Settled effluents Mixed liquor effluents J 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 Food to micro-organism ratio,lb.BODg/lb.MLVSS/day F i g u r e 9 PERCENT COD REMOVALS v s FOOD TO MICRO-ORGANISM RATIO 55 TABLE X ORGANIC CARBON REMOVAL DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY S e t t l e d E f f l u e n t Source S o l i d Detention Time, days Raw Leachate D i g e s t e r A 10 D i g e s t e r B 20 D i g e s t e r C 30 T o t a l Carbon, mg/1 T o t a l Organic Carbon, mg/1 .Total ..Inorganic .Carbon,mg/1. 15,400 15,389 .11 933 683 ,25.0 513 268 245 454 221 N 233 Percent Organic Carbon Removal 95.6 98.3 98.6 T o t a l i n o r g a n i c carbon i n the leachate feed was only 11 mg/1. T o t a l i n o r g a n i c carbon i n the s e t t l e d e f f l u e n t s , however, v a r i e d between 230 and 250 mg/1. This increase i n e f f l u e n t i n o r g a n i c carbon, r e s u l t s from the biodegradation of organic carbon to carbon d i o x i d e and water. As carbon d i o x i d e was formed by the d e s t r u c t i o n of organic m a t e r i a l s i n the leachate feed, a p o r t i o n of the re l e a s e d gas d i s s o l v e d i n the mixed l i q u o r water and was converted to carbonate and bicarbonate m e t a l l i c s a l t s . The high pH maintained i n these u n i t s (8.5 - 8.8) would promote both the formation of i n - s o l u b l e carbonates, such as calc i u m carbonate, and the r e l e a s e of gaseous carbon d i o x i d e to the atmosphere. I t i s t h e r e f o r e l i k e l y t h at t h i s narrow range of t o t a l i n o r g a n i c carbon concentrations i s caused by s a t u r a t i o n of the s e t t l e d e f f l u e n t s w i t h s o l u b l e carbonate and bicarbonate m e t a l l i c s a l t s . 5-2 V o l a t i l e Suspended S o l i d s The mixed l i q u o r t o t a l s o l i d s , t o t a l suspended s o l i d s , and v o l a t i l e suspended s o l i d s were monitored during the e f f i c i e n c y s t u d i e s . The r e s u l t s of those t e s t s are i l l u s t r a t e d i n Appendix A. A l l 3 parameters g e n e r a l l y reached steady s t a t e values w i t h i n 4 weeks of s t a r t u p . Although the sus- pended s o l i d s l e v e l s maintained i n a l l u n i t s were s e v e r a l times the recom- mended l e v e l s f o r a c t i v a t e d sludge systems, the mixed l i q u o r s s e t t l e d w e l l and the s e t t l i n g b i o l o g i c a l f l o e removed a l a r g e percentage of the mixed l i q u o r COD and BOD5. Steady s t a t e MLSS concentrations ranged from 14,500 mg/l .'"to 25,000 mg/l. An average 64 percent of these suspended s o l i d s were v o l a t i l e . The mixed l i q u o r s s e t t l e d q u i c k l y to produce sludges w i t h t o t a l suspended s o l i d s concentrations around 45,000 mg/l. S e t t l i n g was essen- t i a l l y complete a f t e r 2 hours. Figure 10 shows the steady s t a t e mixed l i q u o r v o l a t i l e suspended s o l i d s concentrations as a f u n c t i o n of the s o l i d s d e t e n t i o n time. The steady s t a t e MLVSS c o n c e n t r a t i o n decreases as the s o l i d s d e t e n t i o n time i n c r e a s e s . As p r e v i o u s l y d i s c u s s e d , i n c r e a s i n g the s o l i d s d e t e n t i o n time from 10 to 20 days increased the removal of mixed l i q u o r COD by the s e t t l i n g b i o l o g i c a l f l o e , from 93.5 to 97.0 percent. At s o l i d s d e t e n t i o n times gr e a t e r than 20 days, the s e t t l i n g b i o l o g i c a l f l o e c o n s i s t e n t l y removed between 96.5 and 97.5 percent of the mixed l i q u o r COD even though the MLVSS concentrations s t e a d i l y decreased. This f a c t supports the p r e v i o u s l y drawn c o n c l u s i o n that s o l i d s d e t e n t i o n time or sludge age i s very important i n determining s e t t l e d e f f l u e n t composition, and that i n c r e a s i n g the s o l i d s d e t e n t i o n time from 10 to 20 days s i g n i f i c a n t l y improves the q u a l i t y of the s e t t l e d e f f l u e n t . The v e r y low s e t t l e d e f f l u e n t organic carbon, COD, and BOD5 i n d i c a t e that h i g h l y s t a b i l i z e d m i c r o b i a l masses e x i s t e d i n a l l u n i t s . M i c r o s c o p i c examination of the mixed l i q u o r s confirmed the presence of v a r i o u s forms of b a c t e r i a , protozoa, fu n g i and r o t i f e r s i n a l l u n i t s . Fungal growth was 16,000 14,000 £ 12,000}- \ E I; 10,000 +-c Q> U o 8,000 o Ul in > 6,000 s 4 , 0 0 0 h 2 ,000h 0 10 15 20 25 30 35 40 Solids detention time,0 c-days 45 50 F i g u r e 10 STEADY STATE MIXED LIQUOR VOLATILE SUSPENDED SOLIDS CONCENTRATIONS v s SOLIDS DETENTION TIME 58 v e r y l i m i t e d and thus d i d not a d v e r s e l y a f f e c t the s e t t l i n g c h a r a c t e r i s t i c s of the b i o l o g i c a l f l o e s . . A l a r g e number of free-swimming c i l i a t e s were observed.- Since free-swimming c i l i a t e s use much more energy than f i x e d or s t a l k e d protozoa, and t h e r e f o r e r e q u i r e much more food, these m i c r o s c o p i c examinations conf i r m the observed h i g h mixed l i q u o r BOD^ and COD concentra- t i o n s . 5-3 'Metal Removal •and'Di'stribut i o n The metal d i s t r i b u t i o n w i t h i n the mixed l i q u o r e f f l u e n t was examined at the end of both sets of e f f i c i e n c y s t u d i e s . In a d d i t i o n , the o v e r a l l metal removal by the s e t t l i n g b i o l o g i c a l f l o e was examined during the a c c l i m a t i z a t i o n - m e t a l removal study. The d i s t r i b u t i o n of metals w i t h i n the mixed l i q u o r e f f l u e n t and the metal removal e f f i c i e n c y of the b i o l o g i c a l f l o e were of s p e c i a l i n t e r e s t f o r three reasons: (1) They can provide i n f o r m a t i o n heeded to decide .on a s a t i s f a c t o r y method of sludge d i s p o s a l . (2) Any need f o r a d d i t i o n a l treatment of the s e t t l e d e f f l u e n t s to remove 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. (a) A c c l i m a t i z a t i o n - M e t a l Removal Study - To study the long-term metal removal c a p a c i t y of the s e t t l i n g b i o l o g i c a l f l o e , the t o t a l s o l i d s c o n c e n t r a t i o n i n the s e t t l e d e f f l u e n t s was monitored. Since no b i o l o g i c a l s o l i d s were removed, h y d r a u l i c d e t e n t i o n time was used as the b a s i s of t h i s study. Figure 11 shows the t o t a l s o l i d s con- c e n t r a t i o n of the s e t t l e d e f f l u e n t s from the three d i g e s t e r s , as a f u n c t i o n of the time from s t a r t . u p . From Figure 11 i t i s evident that the t o t a l s o l i d s c o n c e n t r a t i o n i n the s e t t l e d e f f l u e n t s i n - 8,000h <y 7,000 E 6,000 I c Z 5 S 000J- O Digester D',hydraulic detention time 8 45days n — H — F 1 — I I — — n — — II — = 60 —"—> < ^ I I — f't — I I — — I I — — II — = 9 0 — " — 5 10 15 20 25 30 35 40 45 50 Time from start up — days F i g u r e 11 EFFLUENT TOTAL SOLIDS CONCENTRATION DURING ACCLIMATIZATION-METAL REMOVAL STUDY 55 VO 60 creases as the h y d r a u l i c d e t e n t i o n time decreases. S i m i l a r l y , i t was found that the BOD^ of the s e t t l e d e f f l u e n t s increased as the h y d r a u l i c d e t e n t i o n time decreased (see Appendix B) even though the MLVSS concentrations increased w i t h d e c r e a s i n g : h y d r a u l i c d e t e n t i o n time. A f t e r 30 days, the t o t a l s o l i d s concentrations i n the s e t t l e d e f f l u e n t s began to l e v e l o f f . A f t e r 56 days of ope r a t i o n , b i o l o g i c a l s o l i d s had accumulated i n the d i g e s t e r s to the extent that i t was d i f f i c u l t to o b t a i n the r e q u i r e d volumes of c l e a r supernatant from Diges t e r s D' and E'", even a f t e r one hour of s e t t l i n g . At t h i s time samples of the mixed l i q u o r s and s e t t l e d e f f l u e n t s from each d i g e s t e r were c o l l e c t e d f o r metal a n a l y s i s . The mixed l i q u o r samples were "wet-ash" dig e s t e d , f o l l o w i n g the recommended EPA procedure (17). However, when the di g e s t e d samples were f i l t e r e d p r i o r to metal a n a l y s i s , c o n s i d e r a b l e p a r t i c u l a t e matter was observed on t h e . f i l t e r s . To check the e f f i c i e n c y o f the d i g e s t i o n process f o r meta-1 recovery, and to check the accuracy of the subsequent metal a n a l y s i s , a m a t e r i a l balance was developed, u s i n g the r e s u l t s of the t o t a l s o l i d s c o n c e n t r a t i o n t e s t s on the s e t t l e d e f f l u e n t s . In developing t h i s m a t e r i a l balance, i t was assumed tha t : the net i n f l u e n t metal c o n c e n t r a t i o n metal c o n c e n t r a t i o n i n leachate feed metal c o n c e n t r a t i o n i n day 56 s e t t l e d e f f l u e n t X'. ^weighted average t o t a l s o l i d s c o n c e n t r a t i o n throughout study ' t o t a l s o l i d s concentra- t i o n i n day 56 ^ s e t t l e d e f f l u e n t The c o n c e n t r a t i o n of each metal i o n expected i n each mixed l i q u o r was then determined by m u l t i p l y i n g the net i n f l u e n t metal concentra- t i o n to each d i g e s t e r by 56 days and d i v i d i n g by the r e s p e c t i v e 61 d i g e s t e r s h y d r a u l i c d e t e n t i o n time. The r a t i o of the analysed mixed l i q u o r metal c o n c e n t r a t i o n to t h a t determined by t h i s mass balance was then used to check the metal a n a l y s i s and metal recovery u s i n g the "wet-ash" d i g e s t i o n process. ,- The l a r g e number of substances i n leachate and t h e i r p o s s i b l y h i g h c o n c e n t r a t i o n s , can produce i n t e r f e r e n c e s r e s u l t i n g i n e r r o r s i n the determination of i n f l u e n t metal c o n c e n t r a t i o n s . When the many i n s o l u b l e metal-sludge complexes which might be formed, are considered, the p o s s i b i l i t y of f u l l metal recovery by any sludge d i g e s t i o n process i s very s l i g h t . In l i g h t of these problems and the s i m p l i c i t y of the m a t e r i a l balance a p p l i e d , i t was decided that the metal d i s t r i b u t i o n r e s u l t s would be considered acceptable i f a p p l i c a t i o n of the m a t e r i a l balance accounted f o r between 90 and 110 percent of the i n f l u e n t metal. To meet t h i s c r i t e r i o n , i t was found necessary to use n i t r o u s oxide-acetylene flames f o r aluminum, calcium, i r o n , and manganese analyses. The a i r - a c e t y l e n e flame, normally employed i n atomic a b s o r p t i o n a n a l y s i s f o r metals, was used f o r a l l other metals. These procedural m o d i f i c a t i o n s f o r metal a n a l y s i s were s i m i l a r l y employed i n the metal analyses per- formed at the end of each e f f i c i e n c y study. The r e s u l t s of the metal analyses and the a p p l i c a t i o n of the simple m a t e r i a l balance, along w i t h i n f l u e n t c o n c e n t r a t i o n s , are shown i n Table XI. A p p l y i n g the a c c e p t a b i l i t y c r i t e r i o n p r e v i o u s l y mentioned, i t can be seen from the l a s t column i n Table XI that none of the averages f o r any metal l i e very f a r outside the acceptable range. Cadmium, chromium, i r o n , and magnesium recovery were, how- ever, r a t h e r low. When the d i g e s t e r s were taken apart at the end of the study, l a r g e clumps of metal were found s e t t l e d below the coarse- TABLE XI METAL DISTRIBUTION AT END OF ACCLIMATIZATION-METAL REMOVAL STUDY Percent of Concentration S e t t l e d Metal, Expected i n I n f l u e n t Mixed L i q u o r E f f l u e n t A s s o c i a t e d Mixed Liquor Percent of D i g - Concentration Concentration Concentration With ' (From; M a t e r i a l I n f l u e n t M e t a l Metal e s t e r mg/1 mg/1 mg/1 Sludge S o l i d s Balance) mg/1 Accounted For Aluminum 60.2 75.0 0.4 99.47 74.5 100.6 E r 58.0 0.0 100 56.2 103.2 F' 40.3 0.0 100 37.4 107.6 Cadmium 0.430 • 0.430 0.02 95.35 0.517 83.7 ET 0.360 0.01 97.22 0.395 91.3 F^ 0.240 0.00 100 0.267 89.9 Calcium 1,924 D" 2,140 194 90.93 2,224 96.5 E' 1,670 130 92.21 1,720 97.2 F* 1,140 127 88.86 1,138 100.1 Chromium 2.31. D' 2.43 0.07 97.11 2.81 86.4 Ef 1.85 0.05 97.29 2.12 87.1 F̂ - .1.30 0.04 96.92 1.42 91.7 I r o n 1,260 D'' ' 1,300 11.4 99.12 1,557 83.6 f: 940 11.7 98.75 1,168 80.6 F* 765 17.8 97.67 775 98.7 /continued.. TABLE XI continued Metal Dig- e s t e r I n f l u e n t C oncentration mg/l Mixed L i q u o r Concentrat ion mg/l S e t t l e d E f f l u e n t Concentration mg/l Percent of Metal A s s o c i a t e d With Sludge S o l i d s Concentration Expected i n Mixed Liquor (From M a t e r i a l Balance) mg/l Percent of I n f l u e n t Metal Accounted For Lead 1.79 D" 2.02 0.44 78.22 i.84 108.0 E: 1.58 0.39 75.32 i.42 110.0 F > 1.05 0.29 72.38 0.98 106.0 Magnesium 378 D* 276 159.0 42.39 33i.4 88.3 E? 240 115.4 51.92 277.2 89.5 F* 179 87.4 51.17 195.1 93.1 Manga- 46.0 56.1 nese D'" 50.4 1.3 97.48 90.1 E* 38.8 ' 0.7 98.20 42.5 91.5 F' 26.0 0.6 97.69 28.3 91.8 N i c k e l 0.61:- D" 0.667 0.090 86.51 6.674 99.1 E? 0.495 0.090 81.82 6.506 98.1 F-* 0.350 0.055 84.29 0.351 99.7 Potassium 1,610 Dr 1,043 1,020 2.21 l i 111 96.6 880 862 2.05 938 96.2 F* 678 662 2.06 698 98.0 Zinc 227 D' 252 7.6 96.19 275.8 91.6 E" 200 5.5 97.25 208.2 96.1 F" 142 7.7 94.57 137.7 103.0 bubble d i f f u s e r s . Tests w i t h a magnet i n d i c a t e d t h a t those clumps were p r i m a r i l y i r o n , but they probably a l s o contained other metal p r e c i p i t a t e s . This o b s e r v a t i o n could account f o r many of the low mixed l i q u o r metal concentrations determined i n t h i s phase of the study. Examination of Table XI i n d i c a t e s that most of the metals checked are a s s o c i a t e d w i t h the sludge s o l i d s . These metals may be p r e c i p i t a t e d , adsorbed to the b i o l o g i c a l f l o e , or 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 sludge, but they would be removed from the f i n a l c l a r i f i e r w i t h the s e t t l e d " sludge. B e t t e r than 95 percent of the mixed l i q u o r aluminum, cadmium, chromium, i r o n , manganese, and z i n c were removed by the s e t t l i n g b i o l o g i c a l f l o e s . Between 70 and 95 percent of the mixed l i q u o r calcium, l e a d , and n i c k e l were a s s o c i ated w i t h the sludge s o l i d s . Between 42 and 52 percent of the mixed l i q u o r magnesium was r e - moved by s e t t l i n g . I t i s l i k e l y t hat the h i g h pH maintained i n the three d i g e s t e r s caused a p o r t i o n of the i n f l u e n t magnesium s a l t s to p r e c i p i t a t e and subsequently to s e t t l e out of the mixed l i q u o r w i t h the s e t t l i n g b i o l o g i c a l f l o e s . Less than 3 percent of the mixed l i q u o r potassium was removed by the s e t t l i n g b i o l o g i c a l f l o e s . Potassium passes r i g h t through the b i o l o g i c a l treatment system. The mixed l i q u o r potassium remained v i r t u a l l y completely d i s s o l v e d and 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 mixed l i q u o r . S i m i l a r r e s u l t s would be expected f o r sodium. From the f i f t h column i n Table XI i t can a l s o be seen t h a t the c o n c e n t r a t i o n of any p a r t i c u l a r metal i n the s e t t l e d e f f l u e n t gener- a l l y decreases w i t h i n c r e a s i n g h y d r a u l i c d e t e n t i o n time. This trend 65 however, i s due to the decreasing mixed l i q u o r metal c o n c e n t r a t i o n s . The MLVSS concentrations i n d i g e s t e r s D E a n d F w e r e approx- imately 11,800, 10,900 and 7,600 mg/l r e s p e c t i v e l y . From the s i x t h column of Table XI i t i s evident that i n c r e a s i n g MLVSS conc e n t r a t i o n s d i d not increase the metal removal by the s e t t l i n g b i o l o g i c a l f l o e s and s i m i l a r l y , that i n c r e a s i n g h y d r a u l i c d e t e n t i o n time d i d not s i g - n i f i c a n t l y ..improve metal removal by the s e t t l i n g b i o l o g i c a l f l o e s . S o l i d s d e t e n t i o n times i n a l l u n i t s were equal 7as no b i o l o g i c a l s o l i d s were removed during t h i s study. These r e s u l t s are, t h e r e f o r e , c o n s i s t e n t w i t h the r e s u l t s observed i n the removal of oxygen demand- ing m a t e r i a l . From the f o u r t h column of Table XI i t may be noted that d a i l y s e t t l i n g r e s u l t e d i n mixed l i q u o r metal concentrations i n D i g e s t e r D' exceeding those i n the leachate feed. Since metal removal by the . s e t t l i n g b i o l o g i c a l f l o e s remained c o n s i s t e n t l y h i g h i n a l l of the u n i t s t e s t e d , no l i m i t could be set on the metal removal c a p a c i t y of the s e t t l i n g b i o l o g i c a l f l o e . I t i s c l e a r from these r e s u l t s , how- ever, that a s e t t l i n g , a c t i v a t e d sludge f l o e may e f f e c t i v e l y be used as a p h y s i c a l treatment method f o r good removal of very h i g h concentra- t i o n s of a number of metals. The f a c t that most heavy metals are concentrated i n the sludge means, however, that a great deal of care must be taken i n d i s p o s i n g of that sludge, (b) E f f i c i e n c y Studies - The concentrations of metals i n the mixed l i q u o r and s e t t l e d e f f l u e n t s from a l l three d i g e s t e r s were determined at the end of each set of e f f i c i e n c y s t u d i e s . Table X I I shows the r e s u l t s of those metal analyses along w i t h the i n f l u e n t leachate metal concent- r a t i o n s . From the f o u r t h column i t can be seen t h a t mixed l i q u o r TABLE X I I METAL DISTRIBUTION AT END OF EFFICIENCY STUDIES S e t t l e d Percent of I n f l u e n t Mixed L i q u o r E f f l u e n t M e t a l Removed Dig- Concentration Concentration Concentration By S e t t l i n g M e t a l e s t e r mg/1 mg/1 me/1 B i o l o g i c a l F l o e Aluminum 41.8 A 41.00 1.02 97.51 "B •40.60 0.64 98.42 C 36.60 0.31 99.15 D 38.40 0.31 99.19 E 38.40 0.00 100 F 37.60 0.00 100 Cadmium 0.39 A 0.384 0.012 96.88 B 0.388 0.009 97.68 C 0.352 0.005 98.58 D 0.374 0.010 97.33 E 0.369 0.008 97.83 F 0.334 0.005 98.50 Calcium 1,394 A 1,394 28.0 97.99 B 1,392 20.6 98.52 C 1,200 20.8 98.27 D 1,630 84.0 94.85 E 1,640 63.8 96.11 F 1,160 75.0 93.53 Chromium 1.9. A 1.87 0.14 92.51 B 1.85 0.06 96.76 C 1.78 0.06 96.63 D 1.85 0.06 96.76 E 1.78 0.04 97.75 F 1.38. 0.04 97.10 I r o n 960 A 980 13.6 98.61 B 973 2.9 99.70 C 887 1.45 99.84 D 888 1.45 99.84 E 847 0.50 99.94 F 782 0.10 99.99' /continued.. 67 TABLE X I I continued ... S e t t l e d Percent of I n f l u e n t Mixed L i q u o r E f f l u e n t M e t a l Removed Dig- Concentration Concentration Concentration ' By S e t t l i n g M e tal e s t e r me/1- mg/l mg/l B i o l o g i c a l F l o e Lead •1.44 A 1.39 0.28 79.85 B 1.22 0.20 83.61 C 1.10 0.16 85.45 D 1.35 0.22 83.70 ,E . -1.12 0.14 .87.. 50 F 1.06 0.11 89.62 Magnesium 310 A 306 139 54.57 B 289 91 68.51 C 244 85 65.16 D 278 112 59.71 E 244 96 60.65 F 193 98 49.22 Manganese 41.0 A 40.50 1.73 95.73 B 36.10 0.68 98.12 C 32.50 0.45 98.62 D 38.60 0.45 98.83 E 34.30 0.18 99.47 F 27.70 0.11 99.60 N i c k e l 0.65 A 0.640 0.190 70.31 B 0.640 0.180 71.87 C 0.640 0.120. 81.25 D 0.620 0.150 75.80 E 0.620 0.150 75.80 F 0.540 0.080 85.19 Potassium 1,'060 A • 828 690 16.67 B 792 715 9.72 C 710 660 7.58 D 744 680 8.60 E 716 615 14.11 F 762 570 15.18 Zinc 223 A 197.3 1.81 99.08 B 183.4 1.42 99.23 C 160.3 0.60 99.63 D 215.4 0.86 99.60 E 179.1 0.25 99.86 F 137.1 0.17 99.88 68 calcium concentrations at the end of the "extended aeration" e f f i c i e n c y study exceeded those i n the leachate feed. Those calcium concentrations, however, are less than those i n the leachate feed used i n the acclimatization-metal removal study (1,924 mg/1) and therefore, indicate that calcium concentrations i n the mixed liquor were dropping to approach those i n the new leachate feed. A l l other mixed liquor metal concentrations were less than or equal to those i n the leachate feed. In the highest loaded units i n each study, the mixed liquor metal concentrations were very close to those i n the leachate feed. As the loading rate decreases i n each set, the concentration of metal i n the mixed liquors decreases, • as would be expected. Since the same units were used i n each study, the metal concentrations i n each "shorter detention time" digester more closely approach the metal concentrations i n the leachate: feed, than do those i n the same digesters during the "extended aeration" e f f i c i e n c y study. Table X I I I summarizes the digester operating parameters and the resul t i n g metal removal e f f i c i e n c i e s . As i n the acclimatization- metal removal study, the s e t t l i n g b i o l o g i c a l floes removed better than 95 percent of the mixed liquor aluminum, cadmium, chromium, iron , manganese-and zinc. Mixed liquor calcium and lead removal e f f i c i e n c i e s increased s l i g h t l y i n most digesters during the e f f i c - iency studies, while average mixed liquor n i c k e l removal decreased s l i g h t l y . Between 49 and 68 percent of the mixed liquor magnesium was re- moved with the s e t t l i n g b i o l o g i c a l s o l i d s . I t i s very l i k e l y that the s l i g h t l y higher pH's maintained during the e f f i c i e n c y studies account for t h i s s l i g h t improvement i n magnesium removal over that TABLE X I I I SUMMARY OF METAL REMOVAL BY SETTLING BIOLOGICAL FLOC DURING EFFICIENCY STUDIES Digester S o l i d s Detention Time, Days A 10 B 20 C 30 . D 30 E 45 F 60 Steady-State MLSS Concentration,mg/l Steady-State MLVSS Concentration,mg/1 24,250 16,100 22,650 15,100 20,800 13,500 19,550 10,590 20,300 11,880 14,300 8,100 Percent of Mixed Li q u o r M e t a l Concentrations Removed by S e t t l i n g B i o l o g i c a l F l o e : Aluminum 97.51 98.42 99.15 99.19 100 100 Cadmium 96.88 97.68 98.58 97.33 97.83 98.50 Calcium 97.99 98.52 98.27 94.85 96.11 93.53 Chromium 92.51 96.76 96.63 . 96.76 97.75 97.10 Iro n 98.61 99.70 99.84 99.84 99.94 99.99 Lead 79.85 83,61 85.45 83.70 87.50 89.62 Magnesium 54.57 68.51 65.16 59.71 60,65 49.22 Manganese 95.73 98.12 98.62 98.83 99.47 99.60 N i c k e l 70.31 71.87 81.25 75.80 75.80 85.19 Potassium 16.67 9.72 7.58 8.60 14.11 15.18 Zinc 99.08 99.23 99.63 99.60 99.86 99.88 70 observed i n the a c c l i m a t i z a t i o n - m e t a l removal study. Table X I I I a l s o shows that only between 7.6 and 16.7 percent of the mixed l i q u o r potassium was a s s o c i a t e d w i t h the sludge s o l i d s . While potassium removal during the e f f i c i e n c y s t u d i e s increased over that observed i n the a c c l i m a t i z a t i o n - m e t a l removal study, the r e s u l t s s t i l l i n d i c a t e that potassium passes r i g h t through the a c t i v a t e d sludge, treatment process and th a t i t remains almost com- p l e t e l y 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 mixed l i q u o r . From the e f f i c i e n c y study r e s u l t s and those observed at the end of the a c c l i m a t i z a t i o n - m e t a l removal study, i t may be concluded that the order of mixed l i q u o r metalremoval by the s e t t l i n g b i o l o g i c a l f l o e , w i t h average percent removal i n b r a c k e t s , i s as f o l l o w s : aluminum (99.3) and i r o n (99.3) > z i n c (98.4) > manganese (98.2) > cadmium (97.7) > chromium (96.5) > c a l c i u m (94.6) > lead (81.7) > n i c k e l (79.2) > magnesium (55.9) > potassium (8.7). The percent removal f o r a l l metals i s g e n e r a l l y c o n s i d e r a b l y h i gher that that observed by other researchers (9,11,12,13). The higher pH and v o l a t i l e suspended s o l i d s l e v e l s used i n t h i s study could account f o r t h i s increased metal removal by the s e t t l i n g b i o l o g i c a l f l o e , although i t may be observed from Table X I I I that decreasing MLVSS concentrations from 16,100 to 8,100 mg/l d i d not a d v e r s e l y a f f e c t the mixed l i q u o r metal removal by the s e t t l i n g b i o l o g i c a l f l o e . Indeed, i t : may be observed t h a t i n most cases, the percent metal removal i n D i g e s t e r A represents the lowest v a l u e i n any u n i t t e s t e d . This trend again suggests that i n c r e a s i n g the s o l i d s deten- t i o n time from 10 to 20 days, or higher, s i g n i f i c a n t l y improves the s e t t l i n g c h a r a c t e r i s t i c s of the b i o l o g i c a l s o l i d s , w i t h subsequent higher BOD5, COD, organic carbon, and metal removal by the s e t t l i n g 71 b i o l o g i c a l f l o e . 5-4 S e t t l e d E f f l u e n t C h a r a c t e r i z a t i o n The leachate feed to a l l u n i t s d u r ing the e f f i c i e n c y study was v e r y dark green i n c o l o u r , w i t h a f a i r l y s t r o n g obnoxious odour. S e t t l e d e f f l u - ents from a l l the u n i t s t e s t e d was l i g h t brown to y e l l o w i n c o l o u r . The obnoxious odour of the raw leachate was almost completely removed. The s e t t l e d e f f l u e n t s from the e f f i c i e n c y study d i g e s t e r s are f u r t h e r charac- t e r i z e d i n Table XIV. A l s o shown i n Table XIV are the i n f l u e n t leachate concentrations and the proposed B.C. P o l l u t i o n C o n t r o l Board g u i d e l i n e s f o r s p e c i f i c discharges ( 1 ) . Where no numbers are shown f o r a s p e c i f i c s e t t l e d e f f l u e n t , the t e s t was not performed due. t o a shortage of the sample. (a) Oxygen Demanding M a t e r i a l - As p r e v i o u s l y discussed, the removal of oxygen demanding m a t e r i a l from the s e t t l e d e f f l u e n t s was e x c e l l e n t . I n c r e a s i n g the s o l i d s d e t e n t i o n time from 10 to 20 days, s i g n i f i - c a n t l y improved the q u a l i t y of the s e t t l e d e f f l u e n t w i t h respect to oxygen demanding m a t e r i a l . For s o l i d s d e t e n t i o n times gr e a t e r than 20 days, the BOD^ of the s e t t l e d e f f l u e n t s averaged 58.1 mg/1 and the COD of the s e t t l e d e f f l u e n t remained l e s s than 625 mg/1. I t i s evident from these r e s u l t s that the BOD5 of the s e t t l e d e f f l u e n t s may s a t i s f y r e g u l a t o r y agency requirements, i f adequate s e t t l i n g time i s allowed i n the f i n a l c l a r i f i e r . (b) S o l i d s - The t o t a l s o l i d s c o ncentrations i n the s e t t l e d e f f l u e n t s g e n e r a l l y decreased w i t h i n c r e a s i n g s o l i d s d e t e n t i o n time. Again, the t o t a l s o l i d s r e s u l t s i n d i c a t e that i n c r e a s i n g the s o l i d s d e t e n t i o n time from 10 to 20 days or h i g her s i g n i f i c a n t l y improves the e f f l u e n t q u a l i t y . Although the sample volumes obtained were TABLE XIV CHARACTERISTICS OF LEACHATE FEED AND SETTLED EFFLUENTS FROM AEROBIC BIOSTABILIZATION EFFICIENCY STUDIES ; 5 C h a r a c t e r i s t i c s ( a l l , except pH,in mg/1) Leachate Feed Di g e s t e r A Dig e s t e r B Digester C Dig e s t e r D Digester . E Digester F P.C.B» U-> Requirements BOD5 36,000 128.9 32.4 27.1". 90.8 65.7 74.9 45 COD 48,000 1,547 594.2 456.4 610.4 427.8 385.5 T o t a l Carbon 15,400 933 513 454 - - - T o t a l Organic Carbon 15,389 683 268 221 - - - T o t a l S o l i d s 26,600 6,050 5,200 4,980 5,160 4,870 4,450 pH 5.02 8.80 8.73 8.50 8.80 8.74 8.60 6.5-8.5 A c i d i t y 5,640 0.0 0.0 0.0 0.0 0.0 0.0 A l k a l i n i t y 7,640 1,320 1,210 1,080 857 728 542 Aluminum '41.8 1.02 0.64 0.31 0.31 0.00 0.00 0.5 Ar s e n i c 3.62 - - - 0.265 0.26 0.26 0.05 Cadmium 0.39 0.012 0.009 0.005 0.010 0.008 O.OOf 0.005 Calcium 1,394 28.0 20.6 20.8 84.0 63.8 75.0 Chromium 1.9, 0.14 0.06 0.06 0.06 0.04 , 0.04 0.10 Iron 960 13.6 2.9 1.45 1.45 0.50 0.10 0.3 Lead 1.44 0.28 0.20 0.16 0.22 0.14 0.11 0.05 Magnesium 310 119 91 85 112 96 98 150 Manganese 41.0 1.73 0.68 0.45 0.45 0.18 0.11 0.05 N i c k e l 0.65.:; 0.19:' 0.180 0.12t 0.15C- 0.15 0.08: 0.3 Potass ium 1,060 690 715 660 680 615 570 Selenium 0.450 - - - 0.036 - -Zinc 223 1.81 1.42 0.60 0.86 0.25 0.17 0.5 /continued... TABLE XIV continued... C h a r a c t e r i s t i c s ( a l l , except pH,in mg/1) Leachate Feed D i g e s t e r A D i g e s t e r B Digester C D i g e s t e r D D i g e s t e r E D i g e s t e r F P.CB. Requirements T o t a l N i t r o g e n * 1,770 1,390 29.4 23.9 13.4 70.4 39.4 22.9 15.0 T o t a l Phosphoruss* ' '868 ,362 12.0 5.46 3.11 32.4 25.8 20.3 4.5 * n u t r i e n t a d d i t i o n s to the leachate feed were decreased during the " s h o r t e r detention time" e f f i c i e n c y study. 74 not s u f f i c i e n t to a c c u r a t e l y determine the suspended s o l i d s concen- t r a t i o n s i n the s e t t l e d e f f l u e n t s , t e s t s showed that suspended s o l i d s c oncentrations i n a l l s e t t l e d e f f l u e n t s were low ( l e s s than 100 mg/l), but may, i n many cases, exceed P o l l u t i o n C o n t r o l Board r e - quirements. For t h i s reason some form of e f f l u e n t p o l i s h i n g may be necessary. (c) pH, A l k a l i n i t y and A c i d i t y - pH was checked d a i l y . The r e s u l t s are i l l u s t r a t e d i n Appendix C. Because pH f l u c t u a t e d c o n s i d e r a b l y , the values shown i n Table XIV are approximate averages over the l a s t 15 to 20 days of each study. The pH of the leachate feed was 5.02, probably p r i m a r i l y the r e s u l t of organic a c i d s produced i n the l a n d f i l l . The pH i n a l l d i g e s t e r u n i t s was maintained at gr e a t e r than 8.5. These r e l a t i v e l y h i g h pH values undoubtedly aided i n the p r e c i p i t a t i o n of many metals such as i r o n , c a l c i u m and magnesium. The a c i d i t y of the leachate feed was completely destroyed, i n - d i c a t i n g that the organic a c i d s were n e u t r a l i z e d . The a l k a l i n i t y of the leacha t e feed was a l s o s u b s t a n t i a l l y reduced. The a l k a l i n i t y of the s e t t l e d e f f l u e n t s decreases w i t h i n c r e a s i n g s o l i d s d e t e n t i o n time. This t r e n d i s probably caused by the a d s o r p t i o n of p r e c i p i - t a t e d metal carbonates by the b i o l o g i c a l f l o e (carbonate i s one form of a l k a l i n i t y ) and by the production of organic a c i d i n each d i g e s t e r . As the s o l i d s d e t e n t i o n time i n c r e a s e s , more of the organic matter i n the leachate feed should be u t i l i z e d and thus the a l k a l i n i t y of the s e t t l e d e f f l u e n t s should decrease w i t h i n c r e a s i n g s o l i d s d e t e n t i o n time, (d) Metals - The metal concentrations i n the leachate feed are s i g n i f i - 75 c a n t l y reduced, but the s e t t l e d e f f l u e n t s s t i l l do not s a t i s f y the e f f l u e n t requirements set by the P o l l u t i o n C o n t r o l Board. Metal concentrations i n the s e t t l e d e f f l u e n t g e n e r a l l y decrease w i t h i n - c r e a s i n g s o l i d s d e t e n t i o n time, as do the mixed l i q u o r metal concen- t r a t i o n s at the end of each study. A s o l i d s d e t e n t i o n time of only 10 days i s r e q u i r e d to s a t i s f y the P.C.B. e f f l u e n t requirements f o r • -magnesium and n i c k e l , w h i l e - s o l i d s d e t e n t i o n times of at l e a s t 30 days are r e q u i r e d to s a t i s f y those requirements f o r cadmium, chromium and z i n c . Even w i t h the sludge age as long as 60 days, and mixed l i q u o r metal concentrations s i g n i f i c a n t l y l e s s than those i n the leachate feed, the P o l l u t i o n C o n t r o l Board e f f l u e n t standards for a r s e n i c , lead and manganese cannot be met. For t h i s reason, some form of e f f l u e n t p o l i s h i n g should be developed. Carbon adsorp- t i o n or i o n exchange columns would appear t o be most promising f o r metal removal i n these low c o n c e n t r a t i o n ranges, (e) N u t r i e n t s - U s i n g the lower leachate feed c o n c e n t r a t i o n s i n Table XIV as a g u i d e l i n e , i t would appear that a s o l i d s d e t e n t i o n time of at l e a s t 30 days i s necessary to o b t a i n s e t t l e d e f f l u e n t n i t r o g e n and phosphorus concentrations l e s s than the maximums allowed by r e g u l a t i n g agencies. However, s i n c e the mixed l i q u o r BOD5 i n a l l u n i t s was s t i l l f a i r l y h i gh, micro-organisms i n those d i g e s t e r s were not given enough time to use a l l the n u t r i e n t s s u p p l i e d . Reducing n u t r i e n t a d d i t i o n s during the " s h o r t e r d e t e n t i o n time" e f f i c i e n c y study improved the q u a l i t y o f the s e t t l e d e f f l u e n t s w i t h respect to n u t r i e n t c o n c e n t r a t i o n s , without adversely a f f e c t i n g the b i o l o g i c a l e f f i c i e n c y of those d i g e s t e r s . I t may be concluded, t h e r e f o r e , that n u t r i e n t a d d i t i o n s to the leachate feed were exces- s i v e and that those a d d i t i o n s might be s u b s t a n t i a l l y reduced, thus 76 lowering the cost of leachate treatment. Cook and Foree (16) have shown that i t i s p o s s i b l e to a e r o b i - c a l l y t r e a t a medium-strength l a n d f i l l leachate w i t h a B0D5:N:P r a t i o of 100:3.95:0.18 without any s i g n i f i c a n t r e d u c t i o n i n a e r o b i c b i o - , s t a b i l i z a t i o n e f f i c i e n c y . Without n u t r i e n t a d d i t i o n s , the leachate feed used i n these e f f i c i e n c y s t u d i e s would have had a B0D5:N:P ...ratio of 100,: 2.,02:0.55. Since much of the ammonia i n the leachate feed may have been s t r i p p e d out of the h i g h pH mixed l i q u o r s by a i r bubbling, through the d i g e s t e r s , i t may have been necessary to add n i t r o g e n i n some form to the'leachate feed. However, s i n c e reduced n u t r i e n t a d d i t i o n s to the leachate feed might r e s u l t i n s a t i s f a c t o r y n i t r o g e n and phosphorus . l e v e l s i n the s e t t l e d e f f l u e n t s , without any s i g n i f i c a n t r e d u c t i o n i n treatment e f f i c i e n c y , the n i t r o g e n and phosphorusv requirements f o r a e r o b i c b i o s t a b i l i z a t i o n of such " n u t r i e n t - d e f i c i e n t " wastes should be more thoroughly i n v e s t i g a t e d . 5-5 K i n e t i c Parameters and E f f i c i e n c y P r e d i c t i o n s The r e s u l t s of the "extended a e r a t i o n " e f f i c i e n c y study were used to determine the k i n e t i c parameters a s s o c i a t e d w i t h a e r o b i c b i o s t a b i l i z a - • t i o n of t h i s h i g h - s t r e n g t h l a n d f i l l leachate. These k i n e t i c parameters were then used to p r e d i c t the minimum s o l i d s d e t e n t i o n time f o r leachate treatment (see Appendix E) and " s a f e " s o l i d s d e t e n t i o n times were then chosen f o r the " s h o r t e r d e t e n t i o n time" e f f i c i e n c y study. The k i n e t i c parameters thus determined are summarized i n Table XV. For comparison, the k i n e t i c - p a r a m e t e r s determined by Cook and Foree (16) f o r the treatment of a medium-strength l a n d f i l l leachate, and those commonly used i n sewage treatment p l a n t design (4) are a l s o presented. 77 TABLE XV KINETIC PARAMETERS DETERMINED FROM "EXTENDED AERATION" EFFICIENCY STUDY DATA K i n e t i c Para- meter Range of Values Normally Employed i n Sewage Treat- ment P l a n t Design (4) Value Determined For a Medium- Strength L a n d f i l l Leachate (16) Value Determined From This "Extended A e r a t i o n " E f f i c i e n c y Study Data Y 0.40-0.67 mgVSS/mgB0D5 0.4 mgVSS/mgCOD • , 0.332 mgVSS/mgBOD5 b 0.05-0.09 d a y - 1 0.05 d a y - 1 0.0025 day" 1 K 3.0-6.0 mgBOD5/mgVSS/day 0.60 mgCOD/mgVSS/day 0.75 mgBOD5/mgVSS/day K s 20-200 mgB0D 5/l 175 mgCOD/1 21,375 mgB0D 5/l Since the BOD^ data from the "extended a e r a t i o n " e f f i c i e n c y study showed a great deal of s c a t t e r , when p l o t t e d to determine these k i n e t i c para- meters, con s i d e r a b l e personal judgment was i n v o l v e d i n o b t a i n i n g the e s t i - mates shown i n Table XV. B i o l o g i c a l i n h i b i t i o n made accurate determination of mixed l i q u o r BOD,, impossible. However, that i n h i b i t i o n was not always evident i n the "extended a e r a t i o n " e f f i c i e n c y study BOD^ t e s t s . Attempts to analyse the COD data from the "extended a e r a t i o n " e f f i c i e n c y study proved even more u n s a t i s f a c t o r y , as even gre a t e r s c a t t e r prevented any r e l i a b l e e s t i m a t i o n of these k i n e t i c parameters. Thus, although the accuracy of the parameter values appearing i n Table XV i s somewhat questionable, an a n a l y s i s of those values should give some i n s i g h t i n t o what i s happening i n the d i g e s t e r s . The low growth y i e l d c o e f f i c i e n t , Y, i n d i c a t e s that only 0.332 mg of b i o l o g i c a l suspended s o l i d s were produced f o r each mg of BOD^ destroyed. This low value may be the r e s u l t of underestimating the mixed l i q u o r BOD^ or of b i o l o g i c a l i n h i b i t i o n caused by the high mixed liquor,heavy metal c o n c e n t r a t i o n s . 78 The endogenous r e s p i r a t i o n or a u t o - o x i d a t i o n c o e f f i c i e n t , b, i s a l s o very low. The micro-organisms i n the mixed l i q u o r enter the endogenous growth phase only when the food c o n c e n t r a t i o n i n the mixed l i q u o r i s too low to maintain l o g a r i t h m i c growth. During endogenous r e s p i r a t i o n , c e l l s u t i l i z e the protoplasm of s i m i l a r micro-organisms to o b t a i n energy f o r growth. The BOD,, of a l l mixed l i q u o r s i n the "extended a e r a t i o n " e f f i c i e n c y - study,, exceeded .2,000 mg/l and,,there f o r e , .there was no need f o r autp-oxida- t i o n to occur. This f a c t i s r e f l e c t e d by the very low value of b. The maximum r a t e of su b s t r a t e u t i l i z a t i o n per u n i t weight of micro- organisms, K, i s lower than normally observed i n domestic sewage treatment p l a n t s . The low value of K i n d i c a t e s b i o l o g i c a l i n h i b i t i o n , probably due to the very h i g h heavy metal concentrations i n the mixed l i q u o r . K g i n d i c a t e s the s u b s t r a t e (BOD5) c o n c e n t r a t i o n when the r a t e of sub s t r a t e u t i l i z a t i o n per u n i t weight of micro-organisms i s one h a l f the maximum, K. K s has been observed to vary w i t h the type of waste. As the complexity of the waste increases or as the b i o d e g r a d a b i l i t y of the waste decreases, K g increases. Here the very h i g h value again i n d i c a t e s b i o l o g i - c a l i n h i b i t i o n , and suggests that very h i g h MLVSS concentrations are neces- sary to get reasonable reductions i n the i n f l u e n t leachate B0D__. Although these estimates of the k i n e t i c parameters may not be very accurate, they may be used to p r e d i c t the behaviour of the d i g e s t e r s as the s o l i d s d e t e n t i o n time i s decreased. Use of these parameters i n equation ( 2 ) , as presented i n s e c t i o n 3-2, p r e d i c t s a maximum MLVSS c o n c e n t r a t i o n of 11,900 mg/l. The f a c t that a l l MLVSS concentrations i n t h e " s h o r t e r deten- t i o n time" e f f i c i e n c y study exceeded t h i s p r e d i c t e d maximum would i n d i c a t e that the p r e d i c t e d value of the growth y i e l d c o e f f i c i e n t i s low. Neverthe- l e s s , the k i n e t i c parameter estimates were then used i n equation ( 1 ) , to p r e d i c t the mixed l i q u o r B0D s. A comparison of the e x p e r i m e n t a l l y determined 79 and p r e d i c t e d mixed l i q u o r BOD5 values i s presented i n Table XVI. Using higher estimates of the growth y i e l d c o e f f i c i e n t would r e s u l t i n lower pre- d i c t e d mixed l i q u o r BOD5 c o n c e n t r a t i o n s . TABLE XVI MIXED LIQUOR B0D 5 DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY D i - gester S o l i d s Detention Time,Days Exp e r i m e n t a l l y Determined P r e d i c t e d Values Mixed L i q u o r BOD5 7o Removal Mixed Liquor BOD5 7o Removal A 10 2,805 mg/1 92.15 17,700 mg/1 50.5 B 20 3,676 mg/1 89.72 6,250 mg/1 82.5 C 30 3,582 mg/1 89.98 3,790 mg/1 89.3 The p r e d i c t e d mixed l i q u o r BOD5 i n D i g e s t e r C i s very c l o s e to the e x p e r i m e n t a l l y determined value. However, t h i s would be expected as data from a s i m i l a r 30 day s o l i d s d e t e n t i o n time u n i t was used to estimate the k i n e t i c parameters. As p r e v i o u s l y discussed, heavy metal i n h i b i t i o n pre- vented any accurate determination of mixed l i q u o r BOD^. The p r e d i c t e d values i n Table XVI, however, i n d i c a t e the general trend which should have been observed and the':.value-;.o.f^increasing the s o l i d s d e t e n t i o n time from 10 to 20 /days or higher.: Trends s i m i l a r tbathat -indicated by the p r e d i c t e d values of mixed l i q u o r BOD5 were observed i n the mixed l i q u o r COD and s e t t l e d e f f l u e n t B0D 5 and COD r e s u l t s . CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS 6-1 Conclusions (1) Aerobic b i o s t a b i l i z a t i o n i s an e f f e c t i v e means of s t a b i l i z i n g a hi g h - s t r e n g t h l a n d f i l l leachate. Using very h i g h mixed l i q u o r v o l a t i l e suspended s o l i d s concentrations (8,000 to 16,000 mg/1), s t a b l e d i g e s t e r o p e r a t i o n can be maintained at s o l i d s d e t e n t i o n times as short as 10 days, provided food to micro-organism r a t i o s are kept below 0.22 lb.BOD^lb.VSS/day. (2) For i n f l u e n t COD concentrations between 44,000 and 52,000 mg/1, s e t t l e d e f f l u e n t COD removal increases s l i g h t l y from 96.7 to 99.1 percent as the s o l i d s d e t e n t i o n time i s increased from 10 to 60 days. Mixed l i q u o r COD removal s i m i l a r l y increases from 51.5 to 75.7 percent as the food to the micro-organism r a t i o decreases from 0.22 to 0.06 lb.B0D 5/lb.VSS/day. (3) For i n f l u e n t B0D 5 concentrations between 32,000 and 38,000 mg/1, s e t t l e d e f f l u e n t BOD^ removal greater than 99.6 percent i s p o s s i b l e at s o l i d s d e t e n t i o n times g r e a t e r than 10 days. (4) For i n f l u e n t organic carbon concentrations between 15,250 and 15,550 mg/1, s e t t l e d e f f l u e n t removals of grea t e r than 95 percent may be expected when food to micro-organism r a t i o s are maintained l e s s than 0.22 lb.B0D 5/lb.VSS/day. (5) The s e t t l i n g b i o l o g i c a l f l o e removes gre a t e r than 97 percent of the mixed l i q u o r BOD5 and greater than 96 percent of the mixed l i q u o r COD when high v o l a t i l e suspended s o l i d s c o ncentrations (8,000 to 16,000 mg/1) are maintained i n the mixed l i q u o r . 81 (6) I n c r e a s i n g the s o l i d s d e t e n t i o n time from 10 to 20 days increases the removal of mixed l i q u o r COD by the s e t t l i n g b i o l o g i c a l f l o e from 93.5 to 97.0 percent and s i g n i f i c a n t l y improves the q u a l i t y of the s e t t l e d e f f l u e n t s w i t h respect to oxygen demanding m a t e r i a l . " At s o l i d s d e t e n t i o n times g r e a t e r than 20 days, s e t t l e d e f f l u e n t B0D 5 averaged 58.1 mg/l. (7) -Most of the .metals i n the mixed l i q u o r were removed by the s e t t l i n g b i o l o g i c a l f l o e . pH's g r e a t e r than 8.5 were maintained i n a l l u n i t s t e s t e d without any pH adjustment to the leachate feed. The h i g h pH values undoubtedly aided metal removal, as d i d the h i g h MLVSS co n c e n t r a t i o n s . B e t t e r than 95 percent of the mixed l i q u o r aluminum, cadmium, chromium, i r o n , manganese and z i n c were removed by the s e t t l i n g b i o l o g i c a l f l o e . B e t t e r than 90 percent of the mixed l i q u o r c a l - cium and around 80 percent of both the mixed l i q u o r l e a d and n i c k e l were 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, however, only 56 percent of the magnesium i n the mixed l i q u o r was removed by s e t t l i n g , and b e t t e r than 90 percent of mixed l i q u o r potassium remained i n the s e t t l e d e f f l u e n t s . Even though the leachate used i n t h i s study contained very h i g h concentrations of v a r i o u s heavy metals, there was no i n d i c a t i o n 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 these metals. This i n d i c a t e s t h a t , f o r a h i g h - s t r e n g t h waste, c o n t a i n i n g r e l a t i v e l y h i g h concentra- t i o n s of metals, a b i o l o g i c a l community can be a c c l i m a t e d and r e s u l t i n a s t a b l e system. Since a l l of the heavy metals are not completely concentrated i n the sludge s o l i d s , a d d i t i o n a l treatment i s necessary to remove 82 the metal remaining i n the s e t t l e d e f f l u e n t s . In a d d i t i o n , because a hi g h percentage of the metals i s ; a s s o c i a t e d w i t h the sludge, the l a t t e r should be disposed of i n a manner such that the p o l l u t i o n p o t e n t i a l of these metals i s minimized. (8) A n a l y s i s of k i n e t i c parameters i n d i c a t e s that the heavy metals i n the mixed l i q u o r s s e r i o u s l y i n h i b i t e d the b i o l o g i c a l e f f i c i e n c y of -the u n i t s tested-and .suggests t h a t very h i g h .mixed l i q u o r v o l a t i l e suspended s o l i d s concentrations may be necessary to o b t a i n reason- able mixed l i q u o r BOD5 r e d u c t i o n s . (9) . The very h i g h mixed l i q u o r metal concentrations i n h i b i t e d b i o l o g i - c a l a c t i v i t y i n the BOD5 t e s t s to the extent that i t was impossible to o b t a i n accurate mixed l i q u o r BOD5 r e s u l t s . For t h i s reason, COD removal and/or organic carbon removal should be used to ch a r a c t e r - i z e the e f f i c i e n c y of b i o l o g i c a l treatment processes, when the feed to such systems contains h i g h concentrations of i n h i b i t i n g heavy metals. (10) BOD^iNiP r a t i o s of 100:5:1 or b e t t e r were used i n the e f f i c i e n c y s t u d i e s and proved s a t i s f a c t o r y . Analyses of the n u t r i e n t s i n the s e t t l e d e f f l u e n t s i n d i c a t e d , however, that the n i t r o g e n and phos- phorus, a d d i t i o n s to the leachate feed were excessive and might be s u b s t a n t i a l l y reduced without a d v e r s e l y a f f e c t i n g treatment e f f i c i e n c y . 6-2 Recommendations f o r Future Studies Since very l i t t l e work has been done on the use of aer o b i c .bio- s t a b i l i z a t i o n as a method of t r e a t i n g l a n d f i l l leachate, a d d i t i o n a l s t u d i e s are necessary. These should i n c l u d e : (1) 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 of 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. (2) An i n v e s t i g a t i o n of a d d i t i o n a l treatment methods f o r e f f l u e n t p o l i s h i n g , to reduce the heavy metal concentrations and r e s i d u a l oxygen demanding m a t e r i a l i n the s e t t l e d e f f l u e n t s . (3) 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 aerobi c micro-organisms i n the d i g e s t i o n process. (4) An i n v e s t i g a t i o n of the e f f i c i e n c y of aerobic b i o s t a b i l i z a t i o n of a hi g h - s t r e n g t h l a n d f i l l leachate when much of the heavy metals are removed by p r i o r chemical treatment of the leachate. CHAPTER 7 REFERENCES 1. Cameron, R.D., "The E f f e c t s of S o l i d Waste L a n d f i l l Leachates on R e c e i v i n g Water", paper presented at the 1975 B r i t i s h Columbia Water and Waste A s s o c i a t i o n Conference, H a r r i s o n Hot Springs, B.C., 14 pages, A p r i l 1975. 2. Hughes, G., Tremblay, J . , Anger, H., D'Cruz, J . , " P o l l u t i o n of Ground- - water Due to M u n i c i p a l Dumps", T e c h n i c a l " B u l l e t i n No. 42, Inland Waters Branch, Department of Energy, Mines and Resources, Ottawa, Canada, 98 pages, 1971. 3. Zanoni, A.E., "Groundwater P o l l u t i o n from S a n i t a r y L a n d f i l l s and Refuse Dump Grounds - A C r i t i c a l Review", Department of N a t u r a l Resources7 Madison, Wisconsin, 43 pages, 1971. 4. M e t c a l f , L. and Eddy, H., Wastewater Engineering: C o l l e c t i o n , Treat- . ment, D i s p o s a l , McGraw-Hill Book Company, 1972. 5. Lawrence, A.W. and McCarty, P.L., "A U n i f i e d Basis f o r B i o l o g i c a l Treatment Design and Operation", J o u r n a l of the S a n i t a r y Engineering D i v i s i o n , Proceedings of the American S o c i e t y of C i v i l Engineers, • page 757, 1970. 6. 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, Volume 1, Reinhold P u b l i s h i n g Company, New York, 1956. 7. Barth, E.F., E t t i n g e r , M.B., S a l o t t o , B.V. and McDermott, G.N., "Summary Report on the E f f e c t s of Heavy Metals on the B i o l o g i c a l Treatment Processes", 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, V o l . 37, page 86, January 1965. 8. Water P o l l u t i o n A b s t r a c t s , e d i t e d by Department of the Environment, London, England, Volume 44, page 456, October 1971. 9. Neufeld, R.D. and Hermann, E.R., "Heavy Metal Removal by Acclimated A c t i v a t e d Sludge", 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 . ' 47, page 310, February 1975. 10. " 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 Processes", U.S. Department of He a l t h , Education and Welfare, P u b l i c H e a l t h , S e r v i c e P u b l i c a t i o n Number 999-WP-22, 1965. 11. Moulton, E. and Shumate, K., "The P h y s i c a l and B i o l o g i c a l E f f e c t s of Copper on Aerobic B i o l o g i c a l Waste Treatment Processes", Proceedings of the 18th I n d u s t r i a l Waste Conference, Purdue U n i v e r s i t y , Ext.Serv. 115,.West L a f a y e t t e , Indiana, page 602, 1963. 85 12. Jackson, S. and Brown, V., " E f f e c t of Toxic Wastes on Treatment Processes and Watercourses", Water P o l l u t i o n C o n t r o l , London, page 292, June 1970. 13. Cheng, M.H., P a t t e r s o n , J.W„ and Minear, R.A., "Heavy Metals Uptake by A c t i v a t e d Sludge", 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 . 47, page 362, February 1975. 14. Poorman, B.L. " T r e a t a b i l i t y of Leachate from a S a n i t a r y L a n d f i l l by Anaerobic D i g e s t i o n " , Master of A p p l i e d Science Thesis, Department of C i v i l Engineering, U n i v e r s i t y of B r i t i s h Columbia, 75 pages, A p r i l 1974. 15. Boyle, W.C. and Ham, R.K., " B i o l o g i c a l T r e a t a b i l i t y of L a n d f i l l Leachate", 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, V o l . 46, page 860, May 1974. 16. Cook, E.N. and Foree, E.G., "Aerobic B i o s t a b i l i z a t i o n of S a n i t a r y L a n d f i l l Leachate", 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, V o l . 46, page 380, February 1974. 17. "Methods f o r Chemical A n a l y s i s of Water and Wastes', U.S. Environmental P r o t e c t i o n Agency, Water Q u a l i t y Laboratory, C i n c i n n a t i , Ohio, 1971. 18. A.P.H.A., A.W.W.A., W.P.C.F., Standard Methods f o r the Examination of Water and Wastewater, American P u b l i c H e a l t h A s s o c i a t i o n , Inc., 13th E d i t i o n , 1971. 19. Sawyer, C.N. and McCarty, P.L., Chemistry f o r S a n i t a r y Engineers, McGraw-Hill Book Company, 2nd E d i t i o n , 1967. 86 CHAPTER 8 APPENDICES 87 APPENDIX A SOLIDS TESTS RESULTS DURING STUDIES 88 28,000h 18,000 I 6,000 12 16 20 Time from start up F i g u r e 12 MIXED LIQUOR TOTAL SOLIDS CONCENTRATIONS v s TIME FROM START UP 89 26,000 24,000 16,000 14,000* SOLIDS DIGESTER DETENTION DAYS O A 10 0 B 20 Q c 30 @ D 30 • E 45 ^ F 60 8 12 16 20 24 Time from start up — days F i g u r e 13 MIXED LIQUOR SUSPENDED SOLIDS CONCENTRATIONS v s TIME FROM START UP 90 18,000 I 6,000 2 14,000 8,000 6,000 SOLI DS DIGESTER DETENTION D A Y S O A 10 @ B 20 Q c 30 © D 30 • E 45 ^ F 60 Dotted lines indicate averages used to calculate F/M ratios J I I J L _ 8 12 16 20 24 Time from start up — days 28 32 36 F i g u r e 14 MIXED LIQUOR VOLATILE SUSPENDED SOLIDS CONCENTRATIONS v s TIME FROM START UP 8,000r- 10 15 20 25 30 35 40 45 Solids detention time, 0 C - days 50 55 60 F i g u r e 15 SETTLED EFFLUENT TOTAL' SOLIDS CONCENTRATION v s SOLIDS DETENTION TIME vo 92 APPENDIX B BODr TEST RESULTS DURING STUDIES F i g u r e 16 BOD c; OF S E T T L E D E F F L U E N T S DURING A C C L I M A T I Z A T I O N STUDY 9.4 240 200 160 • 20 80 40 SOLIDS DIGESTER DETENTION TIME, DAYS O A 10 ® 8 20 Q c 30 © D 30 • E 45 ^ F 60 * Dotted lines indicate averages used in tables and on other graphs 1 I I I I I 4 8 12 16 20 24 28 Time from start up - days 32 T i g u r e 17 BOD 5 OF SETTLED EFFLUENTS DURING E F F I C I E N C Y STUDIES 4.800H 9 5 4,000 3,200 a> E I 2,4 001 IO O O m 1,600 800 S O L I D S D I G E S T E R D E T E N T I O N T IME, D A Y S O A 1 0 ® B 2 0 Q C 3 0 © D 3 0 • £ 4 5 ^ F 6 0 * Dotted lines indicate averages used in tables and on other graphs 8 12 16 20 24 Time from start up-days 28 32 F i g u r e 18 BOD_ OF MIXED LIQUORS DURING EFFICIENCY STUDIES 2,200 2,000 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 Food / micro - organism ratio, lb. BOD 5/lb. MLVSS/day 0.22 0.24 VO ON F i g u r e 19 BOD _ OF MIXED LIQUORS v s FOOD TO MICRO-ORGANISM RATIO I O O I — 9 9 . 8 9 9 . 6 9 9 . 4 I 99.21 o > o E 9 9 . 0 " v U 9 5 i o o - in T3 <o X3 c ~ o cx UJ Q O CD 9 3 • • — Settled effluents \ \ • • Mixed liquor effluents \ \ 9 I 8 9 8 7 8 5 8 3 • • 1 0 . 0 3 0 . 0 6 0 . 0 9 0.12 0.15 0.18 0.21 0 . 2 4 Food / micro - organism ratio, lb. BOD 5/lb.MLVSS/day Figure 20 PERCENT B0D 5 REMOVAL vs FOOD TO MICRO-ORGANISM RATIO 98 • _ • APPENDIX C pH OF EFFLUENTS AND MIXED LIQUORS DURING STUDIES F i p u r p 71 nil OF SF.TTT.F.D EFFLUENTS DURING ACCLIMATIZATION STUDY 100 101 4 8 12 16 20 24 28 32 Time from start up -days F i g u r e 23 pH OF MIXED LIQUORS DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY APPENDIX D OXYGEN UPTAKE RATES DURING STUDIES Time from start up - days F i e u r e 24 OXYGEN UPTAKE RATES DURING ACCLIMATIZATION STUDY 104 F i g u r e 25 OXYGEN UPTAKE RATES DURING "EXTENDED AERATION" EFFICIENCY STUDY O Digester A, sol ids detention time = lOdays 4 8 12 16 20 24 28 32 Time from start up - days OXYGEN UPTAKE RATES DURING "SHORTER DETENTION TIME" EFFICIENCY STUDY 106 APPENDIX E DETERMINATION OF KINETIC PARAMETERS FROM "EXTENDED AERATION" EFFICIENCY STUDY DATA 10? Determining K and K Rate of food u t i l i z a t i o n It can be shown that: AS_ At AS At S - S o 1 0 C K X S 1 K + S s 1 [MONOD EQUATION] (AS/At) . K S. Rearranging the above equation: X K s K K + S, s 1 Vsij K or (AS/At) X I K 1 / Plotting (^g/At) v s g" should yield a straight li n e with slope _s_ and intercept 'K. K. DIGESTER 0 c days X mg VSS/1 S o mg/i S l m g / l AS/At mg/x V s , (10" 3)/( mg/^ X (AS/At) m g VSS/mg/day D 30 10,589 35,750 3,454 1,076 0.290 9.85 E 45 11,869 35,750 2,036 750 0.491 15.83 F 60 8,121 35,750 2,194 559 0.456 13.71 The above data i s plotted in Figure 27. From that graph i t was estimated that: K = 0.75 m g B0D5/mg VSS/day and K = 21,375 m g / l s Determining Y and b: A biological solids balance yields the equation: AX AS At YAt bX Dividing each side by X: l^U*! = Y _ b „JLUo 20 18 16 o ^ 14 o» E S 12 > cn E 10 co < 8 Slope K K s _ 28,500 K = 0.75.mg/mgVSS/day K s= 2l ,375mg/ l i t re Intercept = —=1.33 /. K = 0.75 mg/litre/day mg MLVSS/ l i tre 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1/S 10 -3 1 mg/litre F i g u r e 27 DETERMINATION OF K AND K s USING BOD5 DATA FROM "EXTENDED AERATION" E F F I C I E N C Y STUDY 109 A plot-of .̂ •^/At) vs. -^——^ should therefore y i e l d a straight l i n e with slope Y and intercept, -b. AS... S - S' /At = o 1 AX,... X. - X /At 1 o Assuming v o l a t i l e .suspended solids concentration i n the leachate feed are ne g l i g i b l e , X Q =0, then: A X / A t = X l and AX/At X 1 0 DIGESTER 0 c days AX/At = X days 1 1 0 c X mg VSS / ; L S o m g / l S l m g / 1 A S/At m g / l /day AS/At X m g /mg VSS/ day ,D 30 0.0333 10,589 35,750 3,454 1,076 0.107 E. 45 0.0222 11,869 35,750 2,036 750 0.063 F 60 0.0166 8,121 35,750 2,194 59 0.069 The above data i s plotted i n Figure 28. From that graph i t i s evident that the estimated values of Y and b depend a great deal on personal judgement. The "best" values estimated by the author are: Y = 0.332 mg VSS/mg B0D5 and b = 0.0025 day" 1 Estimation of Minimum Solids Detention Time: c min.. s o Therefore, minimum solids detention time, 0 ; ;. =6.46 days ' c mm. 0.04 0.03 0 . 0 2 h 0.01 Slope = Y = 0.332 mg VSS mg J L J L V. 0.0 -0.0! h -0.02 0.02 b =-0.0025 day 0.03 -I 0.04 0.05 0.06 0.07 0.08 A S v / A t . mg/mg VSS/day 0.09 0.10 0.03 F i g u r e 28 DETERMINATION OF Y AND b USING BOD 5 DATA FROM "EXTENDED AERATION" EFFICIENCY STUDY

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
China 7 0
United States 3 0
Japan 2 0
City Views Downloads
Beijing 7 0
Tokyo 2 0
Ashburn 2 0
Unknown 1 25

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}

Share

Share to:

Comment

Related Items