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Anoxic-aerobic digestion of waste activated sludge : a lab scale comparison to aerobic digestion with… Jenkins, Christopher Jay 1988

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ANOXIC-AEROBIC DIGESTION OF WASTE ACTIVATED SLUDGE A LAB SCALE COMPARISON TO AEROBIC DIGESTION WITH AND WITHOUT LIME ADDITION By CHRISTOPHER JAY JENKINS B.A.Sc.., The U n i v e r s i t y of B r i t i s h Columbia, 1986 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of C i v i l Engineering) ' We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA Ju l y 1988 Christopher Jay Jenkins, 1988 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of c i v i l Engineering The University of British Columbia Vancouver, Canada Date July 18, 1988 DE-6 (2/88) ABSTRACT A lab-scale study of anoxic-aerobic digestion of waste activ a t e d sludge was performed, using 6 l i t r e digesters, and operated i n a semi - continuous (fed-once-a-day) manner with s o l i d s retention times (SRTs) of 20, 15 and 10 days and mixed-liquor temperatures of 20 °C and 10 °C. Raw sludge was obtained from a p i l o t - s c a l e b i o l o g i c a l phosphorus removal f a c i l i t y operating at U.B.C. Fresh sludge was obtained d a i l y and digested by three d i f f e r e n t d i g e s t i o n modes: anoxic-aerobic, aerobic with lime addition and aerobic. Two aerobic c o n t r o l digesters were run i n p a r a l l e l with the anoxic-aerobic digesters. One of the aerobic digesters received a d a i l y dose of lime s l u r r y . A l l three digesters were operated under i d e n t i c a l conditions (except for the c y c l i n g of a i r supply to the anoxic-aerobic digesters) so that d i r e c t comparison could be made between the three d i g e s t i o n modes. Comparisons were made on the basis of f i v e main parameters r e l a t e d to: (1) di g e s t i o n k i n e t i c s , (2) digested sludge c h a r a c t e r i s t i c s , (3) supernatant q u a l i t y , (4) ORP monitoring, and (5) an o v e r a l l r a t i n g system. Percent v o l a t i l e suspended s o l i d s (VSS) reduction was used as one performance v a r i a b l e . Despite using only 42 percent of the a i r required by the two controls, anoxic-aerobic d i g e s t i o n showed comparable percent VSS reductions. A l l three digestion modes showed increased s o l i d s reduction with increasing SRT and temperature. There was a l i n e a r r e l a t i o n s h i p between percent TVSS and the product of SRT and temperature. A l l three d i g e s t i o n modes had a propensity to r e t a i n t h e i r percent nitrogen and phosphorus within t h e i r s o l i d s . However, with respect to r e t a i n i n g phosphorus, the aerobic controls were the l e a s t e f f e c t i v e . Anoxic-aerobic d i g e s t i o n maintained neutral mixed-liquor pH (MLpH) throughout. Lime controls were maintained at MLpH close to neutral. Aerobic digestion, i n general, r e s u l t e d i n MLpH l e v e l s below 5.0, however, there were periods when the MLpH of the aerobic digesters v a r i e d widely between 4.2 and 6.8. Supernatant q u a l i t y was superior for the anoxic-aerobic digesters. Due to the incorporation of non-aerated periods, there was almost 100 percent d e n i t r i f i c a t i o n of n i t r a t e s produced during the aerated time. This n i t r i f i c a t i o n - d e n i t r i f i c a t i o n resulted i n very low soluble nitrogen l e v e l s i n the e f f l u e n t , as well as considerable removal of nitrogen gas. Neither of the controls showed th i s a b i l i t y . The lime and aerobic controls produced high l e v e l s of e f f l u e n t n i t r a t e s , as well as occasional measurements of ammonia and n i t r i t e . Phosphorus l e v e l s were lowest f o r the lime c o n t r o l and anoxic-aerobic digesters. Presumably, due to reduced pH l e v e l s , the soluble phosphorus l e v e l s from the aerobic digesters were 2 to 3 times those i n the lime or anoxic-aerobic digesters. A l k a l i n i t y was conserved i n the anoxic-aerobic digesters as well as the lime c o n t r o l . However, the purely aerobic digesters consumed a l k a l i n i t y u n t i l very l i t t l e b u f f e r i n g capacity remained. Oxidation-reduction p o t e n t i a l (ORP) was used as a means of monitoring the anoxic-aerobic digesters on a r e a l time bas i s . ORP was p a r t i c u l a r l y useful during the non-aerated periods, due to the f a c t that, at those times, diss o l v e d oxygen was undetectable. C h a r a c t e r i s t i c r e a l time ORP p r o f i l e s were revealed. Slope changes c o r r e l a t e d well with events of t h e o r e t i c a l and engineering i n t e r e s t ; the' disappearance of ammonia and n i t r a t e s , as well as the (dis)appearance of detectable dissolved oxygen, could be predicted by these slope changes. As a r e s u l t of the findings, ORP may prove to be an i d e a l parameter for the control of the anoxic-aerobic d i g e s t i o n process. F i n a l l y , an o v e r a l l r a t i n g system was developed. The r e s u l t s of t h i s study suggest that, for the d i g e s t i o n of waste activ a t e d sludge, anoxic-aerobic di g e s t i o n out-performed both lime-control and conventional d i g e s t i o n modes. i v TABLE OF CONTENTS PAGE ABSTRACT i i LIST OF TABLES v i i LIST OF FIGURES ix ACKNOWLEDGEMENTS x i i I INTRODUCTION 1 II LITERATURE REVIEW 4 A - K i n e t i c s of Aerobic Digestion 4 B - Influence of Temperature on Digestion K i n e t i c s 7 C - ORP Monitoring 9 D - Previous Research i n Aerobic Digestion 11 E - Previous Research i n Anoxic-Aerobic Sludge Digestion 22 F - Need for Future Research 23 III MATERIALS AND METHODS 25 A - Experimental Apparatus 25 B - Experimental Design 27 C - General Procedures 30 D - A n a l y t i c a l Procedures 32 IV RESULTS AND DISCUSSION 38 A - Digestion K i n e t i c s 39 1. Solids Reduction 39 2. Endogenous Decay C o e f f i c i e n t s 49 B - Digested Sludge C h a r a c t e r i s t i c s 64 1. Daily TSS and TVSS Levels 64 2. Daily Mixed-Liquor pH Levels 74 3. Nitrogen Balance 81 4. Phosphorus Balance 85 5. A l k a l i n i t y Consumption and Production 91 6. Chemical Oxygen Demand 93 7. Q u a l i t a t i v e Observations 95 C - Supernatant C h a r a c t e r i s t i c s 97 1. Nitrogen 97 2. Phosphorus 113 3. COD 124 4. A l k a l i n i t y 126 D - Monitoring Results 130 E - O v e r a l l Rating System 135 V CONCLUSIONS 138 A - Digestion K i n e t i c s 138 B - Digested Sludge C h a r a c t e r i s t i c s 139 C - Supernatant C h a r a c t e r i s t i c s 140 D - Monitoring Results 142 E - Ove r a l l Rating System 143 F - Future Research 143 v TABLE OF CONTENTS (continued) PAGE REFERENCES 144 APPENDICES 150 A - Solids Data 151 B - Duplicate Solids Determinations 177 C - Nitrogen Data 185 D - Phosphorus Data 198 E - Real Time ORP P r o f i l e s 211 BIOGRAPHICAL INFORMATION 223 v i LIST OF TABLES TABLE PAGE 1. Summary of Percent TVSS Reduction Based on an Overa l l Mass Balance 42 2. Summary of Percent Reduction Based on Consecutive 1 Balance Periods 43 3. Median Endogenous Decay Coefficent Based on TVSS and TSS Measurements 54 4. Summary of Daily TSS and TVSS Levels f o r 20 day SRT 65 5. Summary of Daily TSS and TVSS Levels f o r 15 day SRT 66 6. Summary of Daily TSS and TVSS Levels f o r 10 day SRT 67 7. Average Nitrogen Levels Within Raw and Digested Sludge 83 8. Nitrogen Removal Data 86 9. Average Phosphorus Levels Within Raw and Digested Sludge 89 10. Phosphorus Balance 90 11. Average A l k a l i n i t y Levels Within Raw and Digested Sludge 92 12. Average COD Levels Within Raw and Digested Sludge 94 13. Average Supernatant Phosphorus Levels 114 14. Average Supernatant COD Levels 125 15. Summary of N i t r i f i c a t i o n and D e n i t r i f i c a t i o n Rates f o r Anoxic-aerobic Digesters 134 16. Summary of Rating Points f o r Comparison of Three Digestion Modes 137 A . l . Solids Data f o r 20 day SRT at 20°C 152 A.2. Solids Data f o r 20 day SRT at 10°C 158 A.3. Solids Data f o r 15 day SRT at 20°C 164 A.4. Solids Data for 15 day SRT at 10°C 168 A.5. Solids Data f o r 10 day SRT at 20°C 171 A. 6. Solids Data for 10 day SRT at 10°C 174 B. l . M u l t i p l e (n=9) Solids Determinations on a Single Sample f or November 20, 1987 178 B.2. M u l t i p l e (n=9) Solids Determinations on a Single Sample f o r February 4, 1988 178 B.3.Daily Duplicate Solids Determinations f o r Run #1 179 B.4. D a i l y Duplicate Solids Determinations f o r Run #2 ^ 181 B.5. Daily Duplicate Solids Determinations for Run #3 183 v i i LIST OF TABLES (continued) TABLE PAGE C . l . Nitrogen Data f or 20 day SRT at 20°C 186 C.2. Nitrogen Data f or 20 day SRT at 10°C 188 C.3. Nitrogen Data f or 15 day SRT at 20°C 190 C.4. Nitrogen Data for 15 day SRT at 10°C 192 C.5. Nitrogen Data for 10 day SRT at 20°C 194 C. 6. Nitrogen Data f or 10 day SRT at 10°C 196 D. l . Phosphorus Data f or 20 day SRT at 20°C 199 D.2. Phosphorus Data for 20 day SRT at 10°C 201 D.3. Phosphorus Data f or 15 day SRT at 20°C 203 D.4. Phosphorus Data f or 15 day SRT at 10°C 205 D.5. Phosphorus Data for 10 day SRT at 20°C 207 D.6. Phosphorus Data for 10 day SRT at 10°C 209 v i i i \ LIST OF FIGURES FIGURE PAGE 1. Schematic of Side-A Digesters 26 2. Schematic of Automated Monitoring Equipment 28 3. Solids Mass Balance i n Digesters 37 4. Performance Curve Based on Percent TVSS Reduction at Various Combinations of SRT and Temperature 44 5. Percent TVSS Reduction Versus SRT at 20°C and 10°C 45 6. Daily Endogenous Decay C o e f f i c i e n t s f o r 20 day SRT at 20°C 52 7. Endogenous Decay C o e f f i c i e n t s f o r 20 day SRT at 20°C - TVSS Basis 55 8. Endogenous Decay C o e f f i c i e n t s f o r 20 day SRT at 10°C - TVSS Basis 56 9. Endogenous Decay C o e f f i c i e n t s for 15 day SRT at 20°C - TVSS Basis 57 10. Endogenous Decay C o e f f i c i e n t s f o r 15 day SRT at 10°C - TVSS Basis 58 11. Endogenous Decay C o e f f i c i e n t s f o r 10 day SRT at 20°C - TVSS Basis 59 12. Endogenous Decay C o e f f i c i e n t s f o r 10 day SRT at 10°C - TVSS Basis 60 13. Temperature S e n s i t i v i t y C o e f f i c i e n t s f o r 20 day SRT 61 14. Temperature S e n s i t i v i t y C o e f f i c i e n t s f o r 15 day SRT 62 15. Temperature S e n s i t i v i t y C o e f f i c i e n t s for 10 day SRT 63 16. Daily TSS Levels for 20 day SRT at 20°C 68 17. Daily TVSS Levels f o r 20 day SRT at 20°C 68 18. Daily TSS Levels for 20 day SRT at 10°C 69 19. Daily TVSS Levels for 20 day SRT at 10°C 69 20. Daily TSS Levels f o r 15 day SRT at 20°C 70 21. Dai l y TVSS Levels for 15 day SRT at 20°C 70 22. Daily TSS Levels f o r 15 day SRT at 10°C 71 23. Dai l y TVSS Levels f o r 15 day SRT at 10°C 71 24. Daily TSS Levels f o r 10 day SRT at 20°C 72 25. D a i l y TVSS Levels f o r 10 day SRT at 20°C 72 26. Dai l y TSS Levels for 10 day SRT at 10°C 73 27. Dai l y TVSS Levels for 10 day SRT at 10°C 73 28. Dai l y Mixed-Liquor pH Levels f o r 20 day SRT at 20°C 75 29. D a i l y Mixed-Liquor pH Levels f o r 20 day SRT at 10°C 76 30. Daily Mixed-Liquor pH Levels for 15 day SRT at 20°C 77 ix LIST OF FIGURES (continued) FIGURE PAGE 31. Daily Mixed-Liquor pH Levels for 15 day SRT at 10°C 78 32. Daily Mixed-Liquor pH Levels f o r 10 day SRT at 20°C 79 33. Daily Mixed-Liquor pH Levels f o r 10 day SRT at 10°C 80 34. Nitrogen Balance During Anoxic-Aerobic and Aerobic Digestion 84 35. Supernatant Nitrogen Levels for 20 day SRT at 20°C 99 36. Supernatant Nitrogen Levels for 20 day SRT at 10°C 100 37. Supernatant Nitrogen Levels for 15 day SRT at 20°C 101 38. Supernatant Nitrogen Levels for 15 day SRT at 10°C 102 39. Supernatant Nitrogen Levels f o r 10 day SRT at 20°C 103 40. Supernatant Nitrogen Levels f o r 10 day SRT at 10°C 104 41. Nitrogen Forms and MLpH Within Aerobic Control f o r 20 day SRT at 20°C 107 42. Nitrogen Forms and MLpH Within Aerobic Control for 20 day SRT at 10°C 108 43. Nitrogen Forms and MLpH Within Aerobic Control for 15 day SRT at 20°C 109 44. Nitrogen Forms and MLpH Within Aerobic Control for 15 day SRT at 10°C 110 45. Supernatant Phosphorus Levels f o r 20 day SRT at 20°C 116 46. Supernatant Phosphorus Levels f o r 20 day SRT at 10°C 117 47. Supernatant Phosphorus Levels f o r 15 day SRT at 20°C 118 48. Supernatant Phosphorus Levels f o r 15 day SRT at 10°C 119 49. Supernatant Phosphorus Levels f o r 10 day SRT at 20°C 120 50. Supernatant Phosphorus Levels for 10 day SRT at 10°C 121 51. Relationship Between Phosphorus Release and MLpH 122 52. A l k a l i n i t y Consumption and Production Over a Single Cycle ^ f o r 20 day SRT at 20°C 128 53. A l k a l i n i t y Consumption and Production Over a Single Cycle for 20 day SRT at 10°C 129 54. Monitoring Results for 20 day SRT at 20°C on October 23 - 24, 1987 131 E . l . Monitoring Results for 20 day SRT at 20°C on October 2 - 3 , 1987 ' 212 E.2. Monitoring Results f o r 20 day SRT at 20°C on November 10 - 11, 1987 213 E.3. Monitoring Results for 20 day SRT at 10°C on December 17 - 18, 1987 214 x LIST OF FIGURES (continued) FIGURE PAGE E.4. Monitoring Results f o r 20 day SRT at 10°C on January 8 - 9 , 1988 215 E.5. Monitoring Results for 20 day SRT at 10°C on January 27 - 28, 1988 216 E.6. Monitoring Results for 10 day SRT at 20°C on September 30 - October 1, 1987 217 E.7. Monitoring Results for 10 day SRT at 20°C on October 9 - 1 0 , 1987 218 E.8. Monitoring Results f o r 10 day SRT at 20°C on October 17 - 18, 1987 219 E.9. Monitoring Results for 10 day SRT at 10°C on December 15 - 16, 1987 220 E.10. Monitoring Results for 10 day SRT at 10°C on January 5 - 6 , 1988 221 E . l l . Monitoring Results for 10 day SRT at 10°C on January 13 - 14, 1988 222 x i ACKNOWLEDGEMENTS The author wishes to thank the many in d i v i d u a l s who a s s i s t e d and supported him throughout the completion of t h i s research work. F i r s t , I would l i k e to acknowledge the tec h n i c a l , f i n a n c i a l and s p i r i t u a l support given by my wife, Carol. I am g r a t e f u l to three of my colleagues, Fred Koch, Craig Peddie and Bruce Anderson, f o r t h e i r t e c h n ical advice and general encouragement. I wish to express my sincere gratitude to Dr. D.S. Mavinic whose enthusiasm provided the impetus f o r t h i s undertaking. As well, I am indebted to him for h i s c r i t i c a l , yet f a i t h f u l , supervision. Fond thanks are also due to Susan Liptak, Lab Manager, and her s t a f f for th e i r valuable t e c h n i c a l assistance during the research p o r t i o n of my work. Las t l y , the author wishes to thank the Natural Sciences and Engineering Research Council of Canada f o r t h e i r f i n a n c i a l assistance i n support of t h i s work. x i i 1 I - INTRODUCTION Advances i n the treatment of wastewater have increasingly improved the q u a l i t y of sewage treatment plant e f f l u e n t s . Accordingly, regulations have, i n general, strengthened to the point where secondary treatment i s often required. Many of these secondary treatment f a c i l i t i e s r e l y on the production of waste activated sludge. As a r e s u l t , treatment schemes for waste activa t e d sludge have had to deal with a dual problem: increasing quantity combined with decreasing q u a l i t y . Statements such as, "Today, most a u t h o r i t i e s agree that sludge disposal i s the number-one problem i n water and wastewater treatment." (Haines, 1976) appear r e g u l a r l y i n the l i t e r a t u r e . Gloyna (1982) suggested one area that deserved increased research was sludge treatment methods and disposal. Aerobic d i g e s t i o n i s i d e a l l y s u i t e d to the treatment of most waste activated sludges, e s p e c i a l l y i n small plants. Carried out i n a separate reactor, aerobic d i g e s t i o n r e l i e s on extended aeration to "produce a b i o l o g i c a l l y stable end-product suitable for disposal or subsequent treatment i n a v a r i e t y of processes" (Adams and Eckenfelder, 1981). Not encumbered by the c a p i t a l cost and d e l i c a t e operation of anaerobic digestion, aerobic d i g e s t i o n has been the most su i t a b l e choice of wastewater systems t r e a t i n g small to medium discharges (Rich, 1977). At present, there are approximately 20 aerobic digesters operating i n B r i t i s h Columbia. Since, i n general, these digesters are located outside and are not heated, there i s a need for studies that also y i e l d low temperature r e s u l t s . 2 I t has been reported that aerobic d i g e s t i o n has a number of advantages. Adams and Eckenfelder (1981) summarized the advantages associated with aerobic d i g e s t i o n when compared to anaerobic digestion, c i t i n g improved supernatant q u a l i t y , formation of stable end-products, and equal v o l a t i l e s o l i d s reduction f o r secondary sludges. However, a disadvantage i s the higher energy costs associated with aerobic d i g e s t i o n because of i t s a i r (oxygen) requirements. Another p o t e n t i a l drawback to aerobic digestion i s the r e s u l t i n g drop i n mixed-liquor pH (MLpH). Levels as low as 3.8 have been reported i n the l i t e r a t u r e . While many researchers have maintained that these low MLpH le v e l s do not adversely a f f e c t s o l i d s reduction, Anderson and Mavinic (1984) demonstrated that maintaining neutral MLpH by lime b u f f e r i n g improved s o l i d s reduction considerably. Even i f th i s i s not the case, maintaining a low MLpH (besides sub-optimum conditions for micro-organisms' a c t i v i t y ) produces a number of p o t e n t i a l disadvantages r e l a t e d to digested sludge c h a r a c t e r i s t i c s and supernatant q u a l i t y . The concept of anoxic-aerobic d i g e s t i o n incorporates, at regular i n t e r v a l s , non-aerated periods during aerobic digestion of waste a c t i v a t e d sludge, to produce a digester which cycles between anoxic and aerobic conditions. The objective of t h i s study was to assess the a c c e p t a b i l i t y of anoxic-aerobic digestion, i n comparison to aerobic d i g e s t i o n with and without lime addition. I t was f e l t that c y c l i n g of the a i r would have at l e a s t two be n e f i t s : (1) less a i r consumption, and (2) maintenance of a neutral pH throughout d i g e s t i o n as a r e s u l t of a l k a l i n i t y consumption and production by way of n i t r i f i c a t i o n - d e n i t r i f i c a t i o n processes. The f i r s t b e n e f i t would tran s l a t e into lower operating costs, and the second b e n e f i t could r e s u l t i n better digested sludge c h a r a c t e r i s t i c s and supernatant q u a l i t y . 3 Since very l i t t l e research had been done on anoxic-aerobic digestion, i t was hoped that this work would demonstrate the acceptability, as well as the potential benefits, of this adaption to the aerobic digestion process. 4 II - LITERATURE REVIEW A - K i n e t i c s of Aerobic Digestion For micro-organisms to tr e a t wastewater, a e r o b i c a l l y or anaerobically, they must oxidize organic matter for energy and c e l l synthesis. The process of aerobic digestion can be represented i n the following equation: Organic Matter + O2 + NH3 > Sludge C e l l s + CO2 + H2O . .. .(1) In Equation 1, the sludge c e l l s can be represented by the empirical formula C5H7NO2 (Hoover, et a l . 1952). Thus, the stoichiometric presentation of Equation 1 becomes: 2(C xH y0 z) + 2(x + ^ - ? -5)0 2 + 2NH3  2C 5H 7N0 2 + 2(x - 5)C0 2 + (y - 4)H 20 ....(2) Under conditions of unlimited organic substrate (food), the mass of sludge c e l l s increases due to growth and c e l l d i v i s i o n . When substrate i s l i m i t i n g , production of c e l l material i s accompanied by auto-oxidation of c e l l material (Benefield and Randall, 1978).. It follows that, under aerobic conditions and no external source of food, micro-organisms are forced to consume t h e i r own c e l l u l a r material i n order to survive. Thus "when the substrate i s unable to supply s u f f i c i e n t organic matter for synthesis and energy and the rate of destruction exceeds the rate of growth, the micro-organisms obtain t h e i r energy by autodigestion of the c e l l s ' • protoplasm, and the b i o l o g i c a l l y degradable organic matter i n the sludge i s oxidized to carbon dioxide, water and ammonia" (Dreier, 1963). 5 Aerobic sludge di g e s t i o n can be represented i n the following s e r i e s of equations (Metcalf and Eddy, 1979): Sludge C e l l s + O2 —5> Non-biodegradable C e l l M a t erial + C0 2 + H 20 + N H 3 (3) or s t o i c h i o m e t r i c a l l y , C 5 H 7 N O 2 + 50 2 > 5C0 2 + 2H20 + NH3 ....(4) As aerobic d i g e s t i o n proceeds, the ammonia produced i n Equation 4 w i l l be oxidized, f i r s t to n i t r i t e and then to n i t r a t e , as follows: NH3 + 1.50 2 >• N0 2" + H + + H 20 ....(5) and N0 2" + 0.5O2 > N0 3" ....(6) Combining Equations 5 and 6 y i e l d s the o v e r a l l n i t r i f i c a t i o n equation: N H 3 + 20 2 > N O 3 " + H + + H 20 ....(7) Thus, under n i t r i f y i n g conditions (combining Equations 4 and 7), Equation 8 represents aerobic sludge digestion: C 5H 7N0 2 + 70 2 > 5C0 2 + 3H20 + N O 3 " + H + ....(8) From Equation 4, the t h e o r e t i c a l amount of oxygen required, when ammonia i s the f i n a l form of nitrogen, would be 1.42 kg 0 2/kg c e l l oxidized. From Equation 8, when a l l the ammonia has been converted to n i t r a t e , 1.98 kg 0 2 would be required to oxidize 1 kg of c e l l material. It has been found that, due to n i t r i f i c a t i o n i n h i b i t i o n at low pH, complete 1 n i t r i f i c a t i o n may not be achieved. B a r r i t t (1933), proposed that at pH below 5.5, a c y c l i c r eaction explained a continued drop i n pH without producing a d d i t i o n a l n i t r a t e s : 3HN02 > (H + + N0 3 -) + 2N0 + H 20 2N0 + H 20 + 1/2 0 2 > 2HN02 6 Therefore, i f the pH drops below 5.5, the n i t r i f i c a t i o n process w i l l be incomplete and the amount of oxygen required w i l l be between 1.42 and 1.98 kg 02/kg c e l l mass oxidized. Futhermore, i f n i t r i f i c a t i o n i s incomplete, there w i l l be a build-up of ammonia. Residual ammonia l e v e l s were found by Anderson (1988) at pH l e v e l s l e s s than 5.5, but not i n digesters where the pH (through lime addition) was maintained above 6.0. Several k i n e t i c models for the production of waste activ a t e d sludge e x i s t . Although d i f f e r e n t nomenclature has been given for various models, which mathematically p r e d i c t the amount of c e l l production as a function of substrate removal, the following equation i s presented (Stein et a l . , 1972a): Sludge accumulation ^ = K a - KdM ....(9) where: M = quantity of active mass i n the system (VSS), S = quantity of substrate removed from system (BOD), K a = f r a c t i o n of substrate removed, which i s synthesized into new active mass, and K d = f r a c t i o n of active mass i n the system, which i s consumed per day by endogenous r e s p i r a t i o n . In the absence of external substrate, Equation 9 becomes: dM g£ = " KdM or, upon integra t i o n : = e -K dt , or In ^ = -K dt ....(10) Equation 10 represents a f i r s t order reaction where K d i s the rate constant of auto-oxidation (Koers, 1979). K d i s also r e f e r r e d to as the endogenous decay c o e f f i c i e n t (Anderson, 1988). Equation 10 holds under batch or plug 7 flow conditions (Benedek et a l . , 1972). For continuous flow, completely mixed systems, a mass balance around the system y i e l d s the following expression (Benedek e l at, 1972): j*t - 1 (11) M 0 1+K dt' } Without recycle, t' i s equal to the hydraulic retention time; however, with rec y c l e , t' has been taken to be the average residence time of the sludge p a r t i c l e s , known as "sludge age" (Koers, 1979). It has been proposed (Anderson, 1988) that, f o r semi-continuous (fed-once-a-day) systems, Equation 10 can be used to determine K<j when t i s taken to be 1 day and new i n i t i a l conditions are found for each day. In other words, semi-continuous systems may be treated as a continual succession of d a i l y batches. B - Influence of Temperature on Digestion K i n e t i c s As temperature i s increased, biochemical a c t i v i t y i s correspondingly increased and v i c e versa. Since aerobic d i g e s t i o n i s a b i o l o g i c a l process, i t comes as l i t t l e surprise that, i n general, at higher temperatures, there i s greater a c t i v i t y leading to increased s o l i d s reduction. Most researchers reported increased s o l i d s reduction a elevated temperatures (Jaworski et a l . , 1960; Dreier 1963; and Randall et a l . , 1975). Work conducted (Koers and Mavinic, 1979 and Anderson and Mavinic, 1984) i n the low temperature ranges (below 20 °C) also report increases i n s o l i d s reduction as temperature was increased. A symbol often used f o r temperature dependence i s Qxo> a f a c t o r corresponding to how many times the rea c t i o n rate w i l l increase i f the temperature i s increased 10 °C. The "rule of the thumb" that a c t i v i t y 8 increases two-fold for every 10 °C increase i s often quoted. This temperature dependence should be reported between c e r t a i n l i m i t s . For example, Benedek et a l . (1972) concluded that the rate of b i o l o g i c a l a c t i v i t y i n the range of 5 - 40 °C increases with temperature according to the r e l a t i o n s h i p of van't Hoff-Arrhenius: dt RT 7 K J where: H = the heat of reaction or a c t i v a t i o n heat ( c a l ) , K = the equilibrium constant of the reaction, i . e . the r a t i o of the rate constants of the reactions, R = the u n i v e r s a l gas constant (1.986 c a l / K), and T = temperature i n degrees Kelvin. Upon integration, Equation 12 y i e l d s an expression s u i t a b l e f or use i n evaluating experimental data: log K = log A - 2303R * V T ....(13) where K d or K^ may be substituted for K, and A i s a constant. A p l o t of log K d or log K]-, versus temperature w i l l y i e l d a s t r a i g h t l i n e i f the Arrhenius r e l a t i o n s h i p i s followed. Randall et a l . (1982) concluded (from on-going studies) that the aerobic d i g e s t i o n c o e f f i c i e n t s , K d and K^ ,, apparently followed the Arrhenius r e l a t i o n s h i p from 5 to 20 °C. Above 20 °C, however, i t seemed that the r e l a t i o n s h i p does not hold for e i t h e r c o e f f i c i e n t . Droste and Sanchez (1986) concluded that an Arrhenius r e l a t i o n s h i p d i d not describe a c t i v i t y or decay c o e f f i c i e n t s i n semi-continuous reactors. 9 The S t r e e t e r - P h e l p s e m p i r i c a l formula i s f r e q u e n t l y used to describe the temperature dependency of biochemical r e a c t i o n s (Phelps, 1945): l& = 0 ( T 2 • T l ) ....(14) K d l where: K ^ i and K q 2 = the r a t e constants corresponding to temperatures Tj_ and T 2 r e s p e c t i v e l y . Eckenfelder and Englande (1970), concluded that the temperature c o e f f i c i e n t , 9, was g r e a t l y dependent upon the process c h a r a c t e r i s t i c . The range of 0 f o r a c t i v a t e d sludge, between the temperature l i m i t s of 5 and 45 °C, was found to be 1.000 - 1.041. Qio and 9 are r e l a t e d i n the f o l l o w i n g manner: l o g Q 1 0 = 10 l o g 9 ....(15) Thus, 9 = 1.072 corresponds to the " r u l e of thumb" th a t a c t i v i t y doubles f o r an increase i n temperature of 10 degrees c e l s i u s . Koers (1979) found that between 10 °C and 20 °C, 9 equaled 1.074 f o r both continuous and semi-continuous systems. A value of 1.120 was found f o r batch d i g e s t i o n systems over the same temperature range. Between 5 °C and 10 °C, 9 equaled 1.311, 1.156 and 1.113 f o r continuous, semi-continuous and batch d i g e s t i o n systems, r e s p e c t i v e l y . C - ORP M o n i t o r i n g The o x i d a t i o n - r e d u c t i o n p o t e n t i a l (ORP), or redox p o t e n t i a l , i s a measure of the a c t i v i t y of e l e c t r o n s i n o x i d a t i o n - r e d u c t i o n r e a c t i o n s w i t h i n an aqueous environment. While i n complex b i o l o g i c a l systems (e.g. wastewater treatment a p p l i c a t i o n s ) ORP cannot be i n t e r p r e t e d thermodynamically (Sawyer and McCarty, 1978), the observed ORP represents the net e l e c t r o n a c t i v i t y of a l l the r e a c t i o n s t a k i n g place. Thus, ORP i n d i c a t e s the general o x i d a t i v e s t a t e of the system (Kjaergaard, 1977; Koch and Oldham, 1985). 10 The potential of the platinum electrode can be expressed by general form of the Nernst equation: 0.059 (OXIDANT) _ o c Q_ Eh - Eo + — LOG at 25 °C where: Eh = The voltage difference between the oxidation-reduction electrode and the normal hydrogen electrode, the potential of which i i s zero by d e f i n i t i o n , Eo = A constant c h a r a c t e r i s t i c of the system i n question, N = The number of electrons reacting. The use of ORP for monitoring s t r i c t l y aerobic digestion has not been excessive. Previous work by Hood (1957) revealed that, under highly oxidized conditions, ORP reached +700 mV. In 1964, Malina reported ORP values under oxidizing conditions of +250 mV. Also noted was a drop to +25 mV during a 12 hour a i r pump f a i l u r e . Alherg and Boyko (1972) reported the use of ORP i n conjunction with dissolved oxygen and ni t r a t e levels i n a survey of aerobic digesters. They concluded that an ORP greater than +400 mV (combined with DO > 1.0 mg/L and NO3 > 10 mg/L) indicated conditions that were satisfactory for aerobic digestion. For aerobic systems, the a v a i l a b i l i t y of r e l i a b l e , commercial dissolved oxygen probes superceded ORP measurements (Koch and Oldham, 1985) . Nevertheless, recent advances i n wastewater treatment processes (which incorporate unaerated zones), especially sequencing batch operations and optimized oxygen usage, have renewed interest i n ORP as an operational tool. Sekine et a l . (1985) established a linea r relationship between n i t r i f i c a t i o n rate and ORP; Koch and Oldham (1985) noted that slope changes i n the real time ORP p r o f i l e corresponded to changing conditions within the system, such as the disappearance of measurable dissolved oxygen and n i t r a t e . ORP values 11 ranged from +300 to -300 mV for both these studies and i n d i c a t e d that the systems alternated between aerobic and anaerobic conditions. ORP has been u t i l i z e d over a wide range of oxidative conditions. I s h i z a k i et a l . (1974) used ORP to monitor and c o n t r o l anaerobic fermentation during beer, wine and saki production. Koch and Oldham (1985) found that methane production was optimized at ORP l e v e l s between -500 and -520 mV. A number of researchers found that ORP v a r i e d l i n e a r l y with the log of oxygen concentration, suggesting that ORP i s a much more s e n s i t i v e parameter at very low l e v e l s ( I s h i z a k i et a l . , 1974; Shibai et a l . , 1974 and Radjai et a l . , 1984). A recent p i l o t - s c a l e study of anoxic-aerobic digestion of waste activ a t e d sludge i n d i c a t e d that r e a l time ORP p r o f i l e s c o r r e l a t e d to s i g n i f i c a n t events within the digesters (Peddie and Mavinic, 1988). For example, the onset of aeration, dissolved oxygen breakthrough, f u l l y oxidized plateau, disappearance of DO ( a f t e r terminating aeration) and d e n i t r i f i c a t i o n could a l l be matched to slope changes along the ORP p r o f i l e . Thus, for the study of anoxic-aerobic sludge digestion, ORP presented i t s e l f as having the p o t e n t i a l to be an i d e a l monitoring and c o n t r o l parameter. D - Previous Research i n Aerobic Digestion More than h a l f a century has past since Heukelekian (1933) f i r s t reported that wastewater s o l i d s were s t a b i l i z e d a e r o b i c a l l y at a greater rate than during anaerobic digestion. In the l a s t 30 years, a great deal of research has been conducted on the subject of aerobic digestion. Kountz and Forney (1959) investigated the aerobic s t a b i l i z a t i o n of milk s o l i d s and found that high oxygen demand occurred immediately following the 12 addition of substrate. This indicated that energy was required to s t a b i l i z e organic substrate. They found that, during aerobic digestion, the nitrogen storage i n the sludge f e l l from a t h e o r e t i c a l maximum of 12.4 to 7.5 percent. They correspondingly predicted that 0.6 moles of ammonia released would be subsequently oxidized to n i t r a t e . They concluded that t o t a l endogenous oxidation was not possible within normal times and sizes of treatment f a c i l i t i e s . Barnhart (1960) conducted experiments i n aerobic d i g e s t i o n on f i v e d i f f e r e n t sludges: bio-chemical, mixed pulp and paper waste, domestic sewage, mixed domestic sewage, and, t e x t i l e and domestic sewage. While assuming the non-oxidizable VSS por t i o n of the sludge to be less than 5 percent of the differen c e between the i n i t i a l VSS and the minimum VSS remaining at the end of a sampling period, i t was found that, for domestic sewage, the endogenous decay c o e f f i c i e n t was between 0.23 and 0.275 days"-'-. The corresponding oxygen consumption rate was 3 - 7 mg/L of 02/hr/mg/L of VSS s t a b i l i z e d . The pH of the digesters tended to a range of 5.0 - 6.0 and, for aeration periods i n excess of 30 days, the pH dropped below 5.0. A drop i n a l k a l i n i t y was also noticed during the aeration period. Barnhart concluded that " i n p a r t i c u l a r cases, aerobic digestion may present an e f f e c t i v e and economical means of sludge dige s t i o n . " The aerobic d i g e s t i o n of night s o i l was investigated by Reyes and Kruse (1962) . The degree of s t a b i l i z a t i o n was found to vary d i r e c t l y with temperature and compare favourably with r e s u l t s reported for aerobic d i g e s t i o n of sewage s o l i d s . They recommended that, i n order to destroy pathogens, temperatures greater than 45 °C be used. At t h i s temperature, 40 - 50% reduction i n the VSS content of the night s o i l was achieved a f t e r 15 -20 days of aerobic digestion. 13 Dreier (1963) reported that, i n terms of VSS removed per c u . f t . of digester per day, i t appeared that the e f f i c i e n c y of d i g e s t i o n increased with increasing loading rates. This does not include other important factors such as supernatant q u a l i t y , or that higher VSS reduction on an o v e r a l l basis corresponded to lower loading rates. The apparent c o n t r a d i c t i o n disappeared when one considered the e f f e c t of d i v i d i n g by the digester volume. In a s e r i e s of papers presented i n 1963, various researchers, i n v e s t i g a t i n g the theory of endogenous metabolism i n bacteriology, helped explain the success of aerobic digestion through endogenous r e s p i r a t i o n . Lamanna (1963) defined "endogenous metabolism as the sum of a l l the chemical a c t i v i t i e s performed by organisms i n the absence of u t i l i z a b l e e x t r a c e l l u l a r materials serving as sources of energy and b u i l d i n g stones for a s s i m i l a t i o n and growth". He added that, when deprived of e s s e n t i a l nutrients such as nitrogen and/or phosphorus, the micro-organism immediately and e x c l u s i v e l y uses i n t e r n a l resources. Eventually the starving c e l l w i l l waste away and die, perhaps to become, i n a predacious environment, a source of food for others; i n the mean time, i n case external conditions change, the starving c e l l w i l l continue to metabolize, and the concept of "energy maintenance" to sustain v i a b i l i t y i s postulated. Marr et a l . (1963) suggested that t h i s " s p e c i f i c maintenance represents the consumption of the source of carbon and energy for purposes that are not a function of the rate of growth". While a greater understanding on a m i c r o b i o l o g i c a l l e v e l was being r e a l i z e d , researchers i n the wastewater f i e l d continued t h e i r i n v e s t i g a t i o n of aerobic sludge digestion. Malina (1964) found VSS reduction at two d i f f e r e n t loading rates (0.10 and 0.14 l b . VSS/day/cu.ft.) were 33.3 and 43.2 percent, r e s p e c t i v e l y , at a dig e s t i o n temperature of 35 °C. A change of a i r flow rate from 0.2 - 0.35 cu.ft./min. did not a f f e c t the percent VSS reduction. The f i r s t use of pure oxygen to replace a i r sparging was presented by Bruemmer (1966). This work concluded that normal a i r sparging rates were not e f f e c t i v e i n oxygenating high strength batch loads of primary sludge. Also, high oxygen tension was not adverse to removal of nitrogen and phosphorus. Under optimal conditions of oxygenation, the minimal time for processing raw primary sludge was 4 days at 30 °C. In 1970, R i t t e r observed the performance of aerobic d i g e s t i o n at three plants i n Pennsylvania. A few of the conclusions from the survey were: 1. The digesters of each plant produced a stable sludge which d r i e d r e a d i l y . 1 2. Manual decanting of supernatant produced a supernatant low i n BOD, but with increased l e v e l s of ortho-phosphate and n i t r a t e . These l e v e l s would be inconsistent with nutrient removal requirements. 3. Concentrating sludge p r i o r to feeding increased sludge residence time, r e s u l t i n g i n increased VSS destruction. Stein et a l . (1972b) compared a i r and pure oxygen aeration of waste ac t i v a t e d sludge from a brewery waste treatment system. U t i l i z i n g 10 bench-scale digesters, they investigated both batch and continuous feed systems using a i r sparging f or h a l f the digesters and oxygen for the remainder. A sing l e temperature of 30 °C was used and the i n i t i a l VSS l e v e l s were 6000 mg/L. The r e s u l t s showed that there was no s i g n i f i c a n t d i f f e r e n c e i n terms of s t a b i l i z a t i o n rates f or a i r and pure oxygen systems. Indeed, the optimum performance (63.5% VSS reduction) was achieved with an a i r system and a 10 day SRT. 15 That same year, Graves et a l . (1972) examined detention times of 2, 4, 8, 12, 18, 24, 30, and 36 days at a single temperature of 25 °C. The digesters were operated i n a semi-continuous (fed-once-a-day) mode under aerobic conditions using a i r . I t was concluded that "aerobic d i g e s t i o n of primary, mixed primary and secondary, and secondary waste sludges was f e a s i b l e , although r e s u l t s of some tests show great v a r i a t i o n " . The r e s u l t s showed that: only the 2 day detention time f a i l e d to produce an adequately s t a b i l i z e d sludge; maximum reduction i n TSS and VSS occurred at 4 to 36 day detention times; and, i n terms of o v e r a l l performance (dewaterability, supernatant q u a l i t y and s o l i d s s t a b i l i z a t i o n ) , sludge digested 4 to 12 days out-performed the r e s t . Ahlberg and Boyko (1972) reviewed the operation of aerobic digesters at seven treatment plants i n the Province of Ontario. Process performance was assessed on digester sludge c h a r a c t e r i s t i c s , v o l a t i l e s o l i d s reductions, supernatant c h a r a c t e r i s t i c s and f i e l d measurements. Most of the digesters operated at TS l e v e l s greater than 2 percent and noted that, at l e v e l s above 3 percent, d i f f i c u l t i e s with sludge s e t t l i n g and supernatant removal were encountered. In addition, " i t seemed that with long detention times, s e t t l e a b i l i t y of the sludge and supernatant q u a l i t y d e t e r i o r a t e s " . This could be c o r r e l a t e d with low r e s i d u a l DO (less than 1.0 mg/L DO) i n the digesters. In terms of r e c y c l i n g the supernatant to the head of the plant, they noted that aerobic digestion produced a supernatant of low-strength (when compared with anaerobic di g e s t i o n ) . The p o s s i b i l i t y f o r nitrogen removal due to d e n i t r i f i c a t i o n of the n i t r i f i e d supernatant was c i t e d . Ahlberg and Boyko generalized that i f the DO l e v e l , the ORP and the n i t r a t e l e v e l were a l l high (DO > 1.0 mg/L, ORP > 400mV, and NO3-N > 10 mg/L), then the process, i n general, was found to be performing s a t i s f a c t o r i l y . They suggested that, while VSS reduction did take place during aerobic digestion, 16 i t could not be used as a performance v a r i a b l e for continuous loading cases due to a gradual build-up of non-biodegradable v o l a t i l e s o l i d s . Benedek et a l . (1972) reported that, a f t e r studying both batch-fed and continuous-fed, plug flow aerobic digesters at various temperatures, f i r s t order k i n e t i c s and Van't Hoff-Arrhenius thermal r e l a t i o n s were observed. They found endogenous decay c o e f f i c i e n t s of 0.02 d"^ - and 0.06 d"^ at 10 °C and 20 °C r e s p e c t i v e l y . Also, i t was noted that the organic load (which hydr o l y s i s converts into b a c t e r i a l nutrients) influenced the on set of endogenous decomposition of c e l l s . Oxygen consumption per gram of organic matter decomposed ranged from 1.0 to 2.2 grams. Leclerc and Brouzes (1973) , while comparing the e f f i c i e n c y of various sludge treatments, noted that, with a p a r a l l e l decrease i n the mass that occurs with time, a large and gradual e l i m i n a t i o n of the t o t a l b a c t e r i a and enterobacteria also occurs. However, they observed that while the disappearance of Salmonella occurred i n 80 percent of the cases, and that the Salmonella could not adapt or multiply under aerobic conditions, the treatment could not be considered a s t e r i l i z a t i o n of pathogenic b a c t e r i a . In an e f f o r t to improve aerobic digestion, Singh and Patterson (1974) proposed s o l u b i l i z i n g the waste sludge. Waste sludge was s o l u b i l i z e d using concentrated s u l f u r i c a c i d and then digested a e r o b i c a l l y . A f t e r 4 days, a reduction i n VSS of 40 percent was achieved. Meanwhile the co n t r o l (no s o l u b i l i z a t i o n ) achieved VSS reduction of 16 percent. They admitted that the cost of pretreatment (and subsequent n e u t r a l i z a t i o n ) was high; however, the improved performance may o f f s e t t h i s cost. Also, i n an e f f o r t to enhance the aerobic di g e s t i o n process, B o k i l and Bewtra (1974) proposed mechanical blending of the sludge. Their work showed that, with increasing 17 energy of mixing, there was improved v o l a t i l e s o l i d s reduction and s e t t l i n g capacity within the digested sludge. Eikum et a l . (1974) investigated the f e a s i b i l i t y of using aerobic digesters for the treatment of mixed primary-chemical (alum) sludge. Aerobic digesters were operated on a semi-continuous (fed-once-a-day) basis, with detention times ranging from 5 to 35 days at temperatures of 7, 12, 18 and 25 °C. They concluded that: aerobic d i g e s t i o n of sludge from a primary-chemical treatment plant was possible; temperature influences on the reduction of v o l a t i l e s o l i d s were s l i g h t l y greater on the primary sludge alone; chemical oxygen demand (COD) was removed at approximately the same rate as v o l a t i l e s o l i d s reduction; although there were wide f l u c t u a t i o n s i n pH, the d i g e s t i o n process was never i n h i b i t e d ; and, a reduction i n the nitrogen content of the sludge ( s o l i d s and l i q u i d ) was noticed. In 1975, Randall et a l . determined the influence of temperature on the aerobic d i g e s t i o n of waste activated sludge. They conducted 15 day batch tests at 5, 10, 20, 30, 35 and 45 °C. Results showed that endogenous decay c o e f f i c i e n t s , (day"-'-), agreed with Van't Hoff-Arrhenius equation (9 = 1.05) for temperatures between 5 and 20 °C, but for temperatures greater, the measured K^'s remained well below the predicted values. They concluded that the 45 °C temperature was unsuitable for batch aerobic digestion. Furthermore, there appeared to be no p r a c t i c a l advantage to aerobic d i g e s t i o n temperatures i n excess of 20 °C. Hamoda and Ganczarczyk (1977) studied the aerobic d i g e s t i o n of lime p r e c i p i t a t e d sludge, using both batch and semi-continuous reactors. . Based on experiments conducted at 20 °C, with i n f l u e n t v o l a t i l e s o l i d s concentration of around 7000 mg/L, i t was reported that: aerobic digestion 18 of the lime sludge was f e a s i b l e , although at large lime doses, some adverse a f f e c t s were noticed; detention times of at l e a s t 15 days are required for adequate s t a b i l i z a t i o n ; and, i n terms of supernatant q u a l i t y and dewaterability, semi-continuous systems out-performed batch digesters. Pagoria (1977) presented a summary table of endogenous decay c o e f f i c i e n t s found i n the l i t e r a t u r e before 1977. Sludge type, di g e s t i o n temperature, parameter used to c a l c u l a t e K d (base e), dige s t i o n system and the references are a l l presented. In general, f o r temperatures between 5 and 45 °C, no matter which sludge was investigated or how the K was determined, K d ranged from 0.019 to 0.35 (day"-'-) . The majority of the references c i t e d used batch systems f o r digestion. For semi-continuous systems, reported K d's ranged from 0.023 to 0.205 d" 1. Pagoria and Drewry (1978) investigated continuous flow with s o l i d s recycle (CFWSR) aerobic sludge digesters. The digesters were operated at organic s o l i d s loading rates (OSLR) of 0.32, 1.6 and 3.2 kg v o l a t i l e solids/cu.m./day and s o l i d s r e t ention time (SRT) values of 13, 23 and 33 days. The temperature was maintained at 25 °C. Through analysis of variance techniques, they found that s t a b i l i z a t i o n rate c o e f f i c i e n t s , based on biodegradable v o l a t i l e suspended s o l i d s (BVSS), va r i e d with both OSLR and SRT. S i m i l a r l y , i t was shown that c o e f f i c i e n t s based on dissol v e d oxygen uptake rates (DOUR) and adenosine 5'-triphosphate (ATP), v a r i e d with OSLR but not SRT. Thus, Pagoria and Drewry f i r s t proposed the use of DOUR as a means of quantifying process performance and rate c o e f f i c i e n t values. Koers (1979) investigated the p o s s i b i l i t y of aerobic di g e s t i o n at low temperatures. Batch, continuous and semi-continuous aerobic digesters were employed at temperatures of 20, 10, and 5 °C. Good c o r r e l a t i o n was found 19 between the product of the temperature and sludge age and the percent VSS reduction. For a product below 250, the percent s o l i d s reduction increased with temperature-sludge age product; however, above 250, there appeared to be no further'improvement i n VSS reduction. C a l c u l a t i o n of endogenous decay c o e f f i c i e n t s followed the same trend. D i f f e r e n t K^'s were found above and below the 250 breakpoint. A s i g n i f i c a n t difference between k i n e t i c c o e f f i c i e n t s derived from batch and continuous systems was noted and the author cautioned that the two are not interchangeable. While low pH l e v e l s (3.5 - 5.0) were experienced i n a l l digesters, i t was concluded that these l e v e l s d i d not adversely a f f e c t that s o l i d s reduction. Appreciable n i t r i f i c a t i o n and d e n i t r i f i c a t i o n was shown to be possible i n a l l systems at a l l temperatures studied. Ganczarczyk et a l . (1980) found that increasing s o l i d s l e v e l s improved dig e s t i o n and, thus, was a more e f f e c t i v e way of u t i l i z i n g digester volume. This agrees with the findings of Randall et a l . (1969), Norman (1961) and Burton & Malina (1964), but disagrees with the findings of Tebbutt (1971) and Reynolds (1973). The l a t t e r two studies, as well as Randall et a l . (1969), used aerobic batch digesters; whereas, i n the other studies, semi-continuous aerobic digesters were employed. The authors concluded that batch d i g e s t i o n showed d i f f e r e n t performance c h a r a c t e r i s t i c s than semi-continuous digestion. Therefore, r e s u l t s obtained from batch di g e s t i o n experiments may not be applicable to the design of continuous flow aerobic digesters. This a s s e r t i o n agrees with Koers' (1979) findings. Adams and Eckenfelder (1981) reviewed aerobic di g e s t i o n of wastewater sludges and compiled l i s t s of advantages and disadvantages of aerobic digestion. The advantages, which are generally presented for aerobic digestion, include the following: 20 1. A b i o l o g i c a l l y s t a b l e end-product i s produced. 2. The s t a b l e end-product i s r e l a t i v e l y noxious, hence encouraging land d i s p o s a l by h o l d i n g lagoons or spray i r r i g a t i o n . 3. Due to s i m p l i c i t y of c o n s t r u c t i o n , c a p i t a l costs f o r the aerobic system are r e l a t i v e l y low when compared w i t h anaerobic d i g e s t i o n and other s o i l s - h a n d l i n g schemes. 4. A e r o b i c a l l y d i g e s t e d sludge g e n e r a l l y possesses good dewatering c h a r a c t e r i s t i c s . I t drains w e l l when placed on a sand bed and i s r e s i s t a n t to rewatering during r a i n f a l l . 5. V o l a t i l e s o l i d s r e d u c t i o n e q u i v a l e n t to anaerobic d i g e s t i o n r e s u l t s i s p o s s i b l e w i t h aerobic systems t r e a t i n g secondary sludges. 6. Supernatant l i q u o r s from aerobic d i g e s t i o n possess a lower BOD content than those from anaerobic d i g e s t i o n . The aerobic supernatant i n most a l l cases has been found to possess a BOD l e s s than 100 mg/L. This advantage i s s i g n i f i c a n t because many conventional b i o l o g i c a l treatment p l a n t s have been overloaded due to r e c y c l i n g of the high-BOD supernatant l i q u o r s from anaerobic d i g e s t e r s . 7. Fewer o p e r a t i o n a l problems e x i s t from aerobic d i g e s t i o n when compared w i t h the more complex anaerobic process, due to a higher s t a b i l i t y of the aerobic system. Therefore, lower maintenance costs can be expected and l e s s s k i l l e d labour r e q u i r e d w i t h an aerobic f a c i l i t y . 8. I t has been reported that the a e r o b i c a l l y d i g e s t e d sludge has a higher f e r t i l i z e r content than that r e s u l t i n g from anaerobic d i g e s t i o n . A few disadvantages of the process i n c l u d e the f o l l o w i n g : 1. There are higher power c o s t s , which generate higher o p e r a t i n g costs i n comparison' w i t h anaerobic d i g e s t i o n . The d i f f e r e n c e i n ope r a t i n g costs i s not s i g n i f i c a n t w i t h smaller treatment p l a n t s but i s important w i t h the l a r g e r f a c i l i t i e s . 21 2. Gravity thickening processes following aerobic di g e s t i o n tend to generate high s o l i d s concentrations i n the supernatant. 3. Some sludges which have been a e r o b i c a l l y digested have not been observed to dewater e a s i l y by the vacuum f i l t r a t i o n process. 4. Since the process i s aerobic, no methane gas i s produced for recovery as a by-product. 5. The s o l i d s reduction e f f i c i e n c y of the aerobic digester may vary with extreme changes i n ambient temperature, which subsequently a f f e c t s the aeration basin temperature. Work done by Tran and Gannon (1981), using deep-shaft high rate aerobic digesters, suggests an a l t e r n a t i v e to the t r a d i t i o n a l design of aerobic digesters. They found that organic loading rates of up to eight times the standard design values (EPA, 1979, C.A.P.D.E.T., 1979 and Brody, 0., 1979 recommend a VSS loading not to exceed 1.6 kg VSS/m^-day) could be achieved while s t i l l achieving a s t a b i l i z e d sludge (24 - 41% VSS reduction). Anderson and Mavinic (1984) studied aerobic di g e s t i o n with pH c o n t r o l . This preliminary i n v e s t i g a t i o n , using waste activa t e d sludge from two d i f f e r e n t sources, incorporated temperature runs at 20, 12 and 5 ° C , as well as SRTs of 5, 10, 12 and 15 days. The sludges investigated were obtained•from a high rate convention acti v a t e d sludge plant and a modified-Bardenpho process. Bench-scale (6L) aerobic digesters were operated on a semi-continuous, fill-and-draw basis with the ad d i t i o n of an appropriate amount of lime s l u r r y to achieve desired digester mixed-liquor pH. Results showed that, for both sludges, improved %VSS reduction was achieved through lime b u f f e r i n g . A future study was proposed whereby the scale would be increased to 150 l i t r e digesters. The r e s u l t s of that work have not been presented to date (Anderson, 1988). 22 Droste and Sanchez (1986) a e r o b i c a l l y digested waste activ a t e d sludge i n lab-scale reactors under batch and semi-continuous flow patterns. The reactors were monitored at three d i f f e r e n t temperatures: 10 , 20 and 30 ° C . No attempt was made to co n t r o l pH, and they report that f i n a l pH l e v e l s i n the batch digesters ranged from 4 . 4 to 5 . 5 , while i n the semi-continuous digesters the pH ranged from 4 . 5 to 6 . 4 . One of t h e i r conclusions confirms what previous researchers had noted, namely, that "decay c o e f f i c i e n t s , determined i n terms of degradable VSS from batch experiments, cannot be used to accurately p r e d i c t s o l i d s reductions i n semi-continuous u n i t s " . E - Previous Research i n Anoxic-Aerobic Sludge Digestion Very l i t t l e l i t e r a t u r e e x i s t s on the development of anoxic-aerobic sludge digestion. As f a r as the author i s able to discern, work conducted by Warner et a l . (1983) was the f i r s t use of regular, non-aerated periods, during aerobic d i g e s t i o n of waste activ a t e d sludge. Previous researchers may have, on occasion, experienced anoxic conditions during periods of s e t t l i n g f o r the purpose of manually decanting supernatant (Koers, 1 9 7 9 ) ; however, the condition was not reported as such. Warner et a l . (1985) discussed the a p p l i c a t i o n of the general a c t i v a t e d sludge model as set out by Dold et a l . (1980) and extended by van Haandel et a l . (1981) to anoxic-aerobic digestion of waste activ a t e d sludge. The laboratory experiments involved c y c l i n g of a i r to produce aerobic, then anoxic conditions, at regular time i n t e r v a l s for an extended time frame. Some of the conclusions drawn from t h i s work are: 1. Aerobic d i g e s t i o n of waste activated sludge with a l t e r n a t i n g periods of anoxic and aerobic conditions i s as e f f i c i e n t with regard to v o l a t i l e s o l i d s destruction as purely aerobic d i g e s t i o n provided: i ) the anoxic cycles do not constitute more than 50 to 60% of the t o t a l retention time, and i i ) the duration of a single anoxic cycle i s less than 3 hours. 2. For digesters with a 50% anoxic time, the n i t r a t e generated by n i t r i f i c a t i o n i n the aerobic cycle was d e n i t r i f i e d during the anoxic cycle. 3. By d e n i t r i f y i n g the n i t r a t e generated, the a l k a l i n i t y , and hence the pH, i n the digester remains stable. Dold et a l . (1985) further proposed that anoxic-aerobic digestion showed promise i n terms of cost savings, i n terms of approximately 20 percent les oxygen required over purely aerobic digestion. In addition, due to n i t r i f i c a t i o n - d e n i t r i f i c a t i o n cycling, a neutral pH was maintained, thus negating the need for chemical (e.g., lime) addition. Peddie and Mavinic (1988) reported VSS reduction to be the same (24% at 20 °C) for purely aerobic, aerobic with lime addition and anoxic-aerobic sludge digestion. Investigation were carried out at p i l o t - s c a l e (300 l i t r e s ) , u t i l i z i n g continuous flow-through reactors and incorporating a po thickening c l a r i f i e r with recycle. Anoxic-aerobic cycle times of 3 hours were used. A i r was used for mixing, consequently, a i r flow rates were 90 103 L/mJ min. , far exceeding the 20 - 40 L/m-1 min. recommended by Metcalf and Eddy, 1979. F - Need for Future Research In reviewing the previous research conducted into aerobic digestion, i t i s evident that considerable attention has been devoted to a better understanding of the varied processes involved. At f i r s t , primary, mixed primary-chemical and chemical sludges were investigated under a variety of 24 conditions. With the increase i n b i o l o g i c a l waste treatment f a c i l i t i e s came the need for digestion of waste activated sludges. These b i o l o g i c a l l y active sludges lent themselves i d e a l l y to aerobic digestion.and the need for an even greater understanding of the aerobic digestion process. Investigations into improvements and enhancements of the aerobic digestion process continued. The need for more research, i n terms of design and satisfactory operation of aerobic digesters, became evident. The idea that aerobic digestion could be made more desirable, through the incorporation of anoxic periods, deserved to be further investigated and became the focal point of this study. 25 I I I - METHODS AND MATERIALS A - Experimental Apparatus A bench top, lab scale experiment was carried out u t i l i z i n g s i x digesters. Each digester was a 1 0 - l i t r e , inverted, glass, b e l l - j a r whose bottom had been removed. Thus, the open end of the digester had a diameter of 20 cm; and since the digester volume was maintained at 6 l i t r e s , a freeboard of 15cm existed (see Figure 1). The b e l l end was stoppered with a bung that had been f i t t e d with a long stem, glass rod, porous ceramic a i r d i f f u s e r . A i r was supplied to each digester through 6 mm i.d. p l a s t i c tubing. Before reaching the ceramic diff u s e r s , the a i r coming out of the common l i n e at 825 kPa (120 psi) was passed through a regulator to maintain a constant supply at 35kPa (5 p s i ) . After leaving the regulator, the a i r passed through a moisture trap and was s p l i t into a c i r c u l a r loop. The a i r supply was e f f e c t i v e l y s p l i t into six equal flows by s i x control valves i n s t a l l e d along the loop. Each of these flows was, i n turn, monitored and regulated by Cole-Parmer PR034-FM032-15ST, adjustable, a i r flow meters (rated range 15-150 mL/min.). The DO i n each digester was p e r i o d i c a l l y checked and, i n general, exceeded 2.0 mg/L but was less than 4.5 mg/L. Although no analysis was conducted, the a i r supply was assumed to be o i l - f r e e . For those digesters which required the a i r to be turned on and off, i.e. cycled digesters, Mac 113-112CCAA a i r solenoids were i n s t a l l e d and connected to AMF/Paragon "Time Command 48" lamp timers. Oil Free Air Regu la to r to S i d e - B Elect r ic motor Daily L ime Dose Aerob ic Contro l 6 L Ce ramic Air Di f fuser C O I Contro l c o A n o x i c - A e r o b i d T imer A So leno id Valve Air flow meter Figure 1. Schemat i c of S i c i e - A Digesters ( S i d e - B ident ical ) as 27 Mechanical mixing was provided for each digester by Sargent-Welsh S c i e n t i f i c Company "Cone Drive S t i r r i n g Motor" driving a stainless s t e e l shaft and paddle. The blade design and revolutions per minute were such that there was complete mixing i n both horizontal and v e r t i c a l directions. For the purposes of frequent, continuous monitoring and continual monitoring, a number of e l e c t r i c a l devices were i n s t a l l e d . Broadly-James Corporation (BJC) platinum electrodes (Model 9176) were used to measure oxidation reduction potential (ORP) of the digesting sludge. Dissolved oxygen (DO) was monitored using a Yellow Springs Instrument (YSI) DO meter model 54ARC and YSI 5739 probe. A l l ORP probes were connected to an amplifier to strengthen the signal before being relayed to a DataElectronics Aust Pty Ltd. Datataker DT100. A "blue-box" LCD read-out was also connected i n p a r a l l e l to the amplifier, to allow r e a l v i s u a l monitoring of the ORP values within the digesters. Amplification of the DO meter response was not necessary and, consequently, i t could be relayed to the Datataker d i r e c t l y . Figure 2 shows a simple schematic of the monitoring devices. The Datataker was "dumped" to an IBM personal computer located within the lab, and the data was subsequently manipulated using Symphony database functions. B - Experimental Design The use of solids retention time (SRT) as a control parameter for sludge digestion was chosen because i t i s simple to maintain a constant value, i t i s easy for an operator to change the SRT to a pre-determinable value, and can be d i r e c t l y equated to loading rates. A constant value could be maintained since the digester volume remained unchanged and there was no D i g e s t e r s " O R P P r o b e s r\ r\ r~\ r\ r\ Blue Box "Oi o 6 ^ 2 G 7 o o o o o 0 3 0 8 Q O O O O - O 4 0 9 6 7 8 g 1 0 0 5 O 10 A m p l i f ie D.O. P r o b e D.O. Me te r to IBM P C D a t a t a k e r F igure 2. S c h e m a t i c of A u t o m a t e d M o n i t o r i n g E q u i p m e n t . 29 recycle, by wasting and then replacing with raw sludge, a set volume each day. Thus the SRT, i n days, can be expressed as the following: SRT- v ° l u m e °f digester volume wasted per day As w e l l , the merits of SRT control are oulined elsewhere (Smith, 1978). Two l i q u i d temperatures, 20 °C and 10 °C, were required i n order to investigate: (1) the influence of temperature on solids reduction and supernatant quality, and (2) the digestion process under both summer and winter operating conditions i n moderate North American climates. The experiment was performed incorporating three experimental runs, three SRTs, and two temperatures.. Six, 6 - l i t r e , completely mixed, digesters, as described above, were employed. This allowed for two SRTs to be run simultaneously. Except as noted, each run lasted at least three SRT's after an i n i t i a l start-up period of between 1 to 2 weeks. For the f i r s t run, a t o t a l of s i x digesters was employed: two control digesters, one being aerobic and one being aerobic with the addition of lime to maintain neutral pH, and four cycled digesters operated with a 15 day SRT at l i q u i d temperature of 20 + 0.5 °C. The four cycled digesters were so named because, based on an arbitrary t o t a l cycle time of s i x hours (see Chapter IV), the a i r was on for a portion of that time. Thus, four di f f e r e n t r a t ios of a i r off to a i r on, namely 4.0:2.0, 3.5:2.5, 3.0:3.0 and 2.5:3.5, were investigated. At the completion of the f i r s t run, the decision was made, based on overall performance (see Discussion), to proceed with the r a t i o of a i r off 3.5 hours and on 2.5 hours. The second run also employed s i x digesters s p l i t into two sides; each one consisted of one anoxic/aerobic (unaerated 3.5 hours, aerated 2.5 hours), 30 one lime control and one aerobic control digester. Side-A was operated at a 10 day SRT for 3 SRT's (30 days). Side-B was operated with a 20 day SRT for 60 days. In addition, after 30 days, the a i r to side-A was switched off (mixing was continued) and SRT's of 10, 15 and 20 days, using anoxic/anaerobic (no cover) digesters, were investigated. The l i q u i d temperature throughout run #2 was 20 + 0.5 °C. The t h i r d run was conducted i n a Bel-Par Industries environment chamber. This run replicated run #2, except that the l i q u i d temperature was 10 + 0.5 °C and, due to poor solids reduction and odour problems, the anoxic/anaerobic digesters were abandoned. In order to investigate a 15 day SRT at 10 °C, side-A was changed, after 3 SRT's, from a 10 to 15 day SRT. Ai r flow rates were maintained between 7.5 - 12 L/m^  min. This range i s somewhat lower than recommended by Metcalf and Eddy (1979); however, since mechanical mixing was provided, a i r was not required for mixing. In addition, DO levels were maintained above 2.0 mg/L at these flow rates. C - General Procedures Raw sludge was obtained d a i l y from the U.B.C. P i l o t Plant, located at the south end of the U.B.C. campus, Vancouver, B.C. This p i l o t scale, b i o l o g i c a l , phosphorus removal f a c i l i t y (bio-P Plant for short) treats 7220 l i t r e s of domestic sewage per day. A modified UTC process, the p i l o t plant has been operating for 4 years and, during the length of this study, maintained an average aerobic sludge age of 22 days. I t should be noted that A-side sludge was used exclusively. The A-side of the process has the addition of v o l a t i l e f a t t y acids (VFA's) by way of fermentation of the primary sludge. 31 Collection of raw sludge involved wasting from the aerobic basin of the process. The amount wasted depended on the desired SRT of the process, but was i n general 100 l i t r e s . This wastage was allowed to gravity s e t t l e u n t i l the sludge blanket interface reached the 40 l i t r e mark. The time for gravity s e t t l i n g to occur varied between 30 and 60 minutes. The thickened sludge was then collected i n a 4 l i t r e jug for transfer to the digesters set up i n the Environmental Engineering Laboratory located 2 kilometers north. In the lab, the raw sludge was allowed to gravity thicken a second time for between 30 and 90 minutes or u n t i l approximately 1 l i t r e of 'clear' supernatant could be siphoned off by a vacuum flask and hose arrangement. As a resu l t of the two-stage thickening, the raw sludge had a MLSS roughly three (3) times that of the aerobic basin and, more importantly, i t was possible to maintain MLSS levels of the raw sludge above those i n the digesters. Wasting from the digesters was accomplished using the same vacuum flask and hose arrangement. The amount wasted was governed by the desired SRT. Since the digesters a l l had an equal volume of s i x (6) l i t r e s , wastage of 300, 400 and 600 ml per day yielded SRTs of 20, 15 and 10 days respectively. The wasted volume was measured by volumetric cylinder and transferred to sample container for subsequent analysis. After wasting, the appropriate amount of raw sludge (shaken to ensure uniform MLSS levels) was added to maintain a constant volume of 6 l i t r e s i n each of the digesters. A portion of the raw sludge was saved for analysis. Liquid temperature and MLSS pH were recorded for each digester and the raw sludge. An aliquot of 80 g/L lime (Ca[0H]2) sl u r r y was added to the lime control digesters i n order to maintain a minimum pH of 6.8. The volume of the dai l y lime dose ranged 32 between 0 and 4 mL. The corresponding average doses were 28, 29 and 16 mg/L of lime/L of sludge/day f o r Runs 1, 2 and 3 re s p e c t i v e l y . In order to ensure that no s o l i d s were l o s t , the sides of the digesters were cleaned every 3 to 4 days. Any evaporation losses were compensated for by the add i t i o n of d i s t i l l e d water. D - A n a l y t i c a l Procedures The handling of the samples during c o l l e c t i o n , storage and analysis can have a s i g n i f i c a n t impact on both the accuracy and r e l i a b i l i t y of the r e s u l t s . Therefore, i t i s important to note that a n a l y t i c a l samples were c o l l e c t e d i n the following manner: 1. For d a i l y s o l i d s and twice weekly supernatant, 25 ml aliquots of MLSS were measured i n a graduated cy l i n d e r and poured into 50 mL centrifuge tubes; these were then transferred to a IEC International centrifuge and spun at 2500 rpm for approximately 15 minutes. A f t e r c e n t r i f u g i n g , the samples were poured onto washed, f i r e d and weighed Whatman 934AH glass microfibre 5.5 cm d i a . f i l t e r s , and vacuum f i l t e r e d . When soluble analyses followed, the centrate (supernatant) was ret r i e v e d , appropriately preserved, and kept i n a fridge at 4 °C. Care was taken to avoid possible cross contamination. 2. For twice weekly mixed l i q u o r TKN and TP, 20 ml of well mixed sample were tra n s f e r r e d to l a b e l l e d b o t t l e s , preserved with a few drop of cone. H2SO4, and kept i n the f r i d g e . 3. For twice weekly %N and %P of the s o l i d s , the p e l l e t s were scooped into glass v a i l s and drie d at 104 °C. A f t e r completely drying, the r e s i d u a l s o l i d s were scraped out of the v i a l s , ground to a f i n e powder, and tr a n s f e r r e d to a i r t i g h t p l a s t i c pouches. I t should be noted that the same procedures were used f o r the c o l l e c t i o n of the r e a l time samples 33 during the continual monitoring days, although i t was necessary to reduce the indiv i d u a l volumes i n order that the SRT of the digester not be altered too greatly. These samples were then spun i n an IEC C l i n i c a l centrifuge at 2000 rpm for 4 minutes. As a matter of course, a l l weights were determined on a Sartorius a n a l y t i c a l balance and, when available, a Technicon Autoanalyzer II was used for soluble chemical analyses. Solids Determinations Total suspended solids (TSS) and t o t a l v o l a t i l e suspended solids (TVSS) values were determined d a i l y on the wasted mixed liquor from each of the six digesters as well as the raw sludge. The Standard Methods approach was modified (see above) i n order to allow a larger volume of MLSS to be analyzed. Drying took place i n a Fisher isotemp oven, model 350, at 104 °C. Burning of v o l a t i l e material took place i n a Lindberg muffle oven at 550 °C. pH pH of the MLSS was measured using a Cole-Parmer Chemcadet model 5986-60 pH meter with automatic temperature compensation (ATC). The meter was calibrated, routinely using standard buffers of 4.00 and 7.01. Liquid temperatures were recorded using the same meter. Temperature c a l i b r a t i o n was confirmed by a mercury thermometer. TKN Samples, f i l t e r e d or un f i l t e r e d , were digested i n a Technicon block digester 40 and analyzed according to Technicon Industrial Method NO. 376-75W. 34 TP Samples, f i l t e r e d or u n f i l t e r e d , were digested i n a Technicon block digester 40 and analyzed according to Technicon Industrial Method No. 327-74W. %N Specific weights of f i n e l y ground solids were digested i n a Technicon block digester 40 and analyzed according to Technicon I n d u s t r i a l Method No. 376-75W. %P Specific weights of f i n e l y ground solids were digested i n a Technicon block digester 40 and analyzed according to Technicon Industrial Method No. 327-74W. N0 X Samples preserved with mercuric phenyl acetone were analyzed according to Technicon I n d u s t r i a l Method No. 100-70W. Note that the cadmium granules were replaced with a cadmium wire. NH3 Samples preserved with cone. H2SO4 to pH < 2.0 were analyzed according to EPA Method 350.1. P0 4 Samples preserved with mercuric phenyl acetone were analyzed according to Technicon I n d u s t r i a l Method No. 94-70W. A l k a l i n i t y The a l k a l i n i t y of MLSS and f i l t e r e d samples were determined according to Standard Methods. The t i t r a t i o n end-point used was pH 4.5. 35 COD Samples, f i l t e r e d and un f i l t e r e d , were preserved with cone. H2SO4 to a pH < 2.0 and analyzed according to Standard Methods. ORP As noted e a r l i e r , BJC ORP probes were used for measuring the oxidation state of the MLSS on monitoring days. Regular maintenance of the platinum electodes involved a thorough wiping with a paper towel. The probes were then returned to the digesters and allowed to equilibrate for a minimum of 3 hours before any subsequent reading. Dissolved oxygen Probe membrane and electrolyte were replaced on average every two weeks. The meter was calibrated using the Winkler Method as described i n Standard  Methods. Solids Balance Determination of da i l y solids levels allowed for a complete solids balance to be performed for both TSS and TVSS. This approach was outined elsewhere (Koers, 1979 and Anderson & Mavinic, 1984) and i s presented i n Equation 17: Overall change i n mass = Amount i n - Amount out + Net change within system (Feed) (Effluent) (Increase/decrease i n digester solids) . . . . ( 1 7 ) Figure 3 presents a schematic mass balance diagram for a digester as applied i n this research. Two' approaches were undertaken using the equations i n Figure 3. In the f i r s t case, the summation sign applies over an entire experimental run, that i s , lengths of 3 SRT's resulted i n 30, 45 or 60 measurements being considered. The second approach reduced the summation period to equal the SRT and calculate balances on a consecutive basis. 36 Therefore, for 20 day SRT, days 1 to 19 constitute the 1st balance period, days 2 to 20, the second, etc. As a res u l t , for a run of 60 days, 40 - 20 day balance periods were observed. The reason that the second approach was considered was that i t allowed for multiple determinations of percent solids reduction to be performed thoroughout each run. Thus, variations i n solids reduction performance, such as maximum and minimum values, were assessed. As seen i n Chapter IV, there was no s i g n i f i c a n t difference, i n terms of average solids reductions, between the two methods. Cp = Concentration of suspended solids i n feed sludge Vp = Daily volume of feed sludge C R = Concentration of suspended solids i n reactor sludge mass = Volume of reactor sludge (AC RxV R) = Change i n reactor sludge solids over sampling period (+) increase (-) decrease Cg = Concentration of suspended solids i n effluent Vp = Daily volume of effluent 2.(CF x V F) A(C R x V R) -7" Solids destroyed = 5_(Cp x Vp) - 5/CE x V E) - <&CR x V R) »/ T - J J J Solids destroyed 1 f t., A solids destroyed = — „ — x 100% (Cp x Vp) Figure 3. Solids Mass Balance i n Digesters (After Koers, 1979) 38 IV - RESULTS AND DISCUSSION The investigation of anoxic-aerobic sludge digestion was undertaken to determine the "acceptability" of the process, when compared d i r e c t l y to aerobic digestion, with and without lime addition, i n terms of a number of parameters: 1. Digestion k i n e t i c s , including solids reduction and determination of endogenous decay c o e f f i c i e n t s ; 2. Digested sludge c h a r a c t e r i s t i c s , including TSS and TVSS le v e l s , d a i l y pH values, nitrogen and phosphorus balances, a l k a l i n i t y destruction and production, chemical oxygen demand (COD) and q u a l i t a t i v e observations; 3. Supernatant c h a r a c t e r i s t i c s , including n i t r i f i c a t i o n , nitrogen forms and d e n i t r i f i c a t i o n , phosphorus forms, COD and a l k a l i n i t y ; 4. Application of continuous monitoring using ORP and DO to show n i t r i f i c a t i o n and d e n i t r i f i c a t i o n as well as the r e p r o d u c i b i l i t y of the ORP versus time p r o f i l e ; and 5. An o v e r a l l rating system. In an e f f o r t to determine a suitable r a t i o of a i r off to a i r on, the f i r s t experimental run was conducted using four (see Chapter III) anoxic-aerobic digesters of various non-aerated periods. Average percent TVSS reductions of 23.2, 20.9, 20.9 and 18.3 were found for ratios of 2.5:3.5, 3.0:3.0, 3.5:2.5 and 4.0:2.0 hours off to hours on, respectively. While the cycled digester with the longest aerated period showed the greatest percent TVSS reduction, i t was not considered for future study because increasing levels of n i t r a t e were found (up to 23.5 mg/L-N) i n the supernatant, as well as a gradual decrease i n the mixed-liquor pH (MLpH) levels was noted. These observations suggested that complete d e n i t r i f i c a t i o n could not be achieved 39 within this digester. In comparison, the remaining three digesters achieved complete d e n i t r i f i c a t i o n . The cycled digester with the shortest aerated period was rejected because i t showed the least promise i n terms of solids reduction. In addition, i t was observed that during the aerated period ( r e l a t i v e l y short) the break-through and subsequent maximum l e v e l of dissolved oxygen was retarded. Since there was a t i e between the two remaining cycled digesters, the cycled digester which used less a i r was chosen. Therefore, throughout the following results and discussion, anoxic-aerobic digester refers solely to non-aerated/aerated periods of 3.5:2.5 hours respectively, based on a s i x hour cycle and four cycles per day. A - Digestion Kinetics 1. Solids Reduction Using the approach outlined i n Figure 3, solids balances, i n terms of t o t a l suspended solids (TSS) and t o t a l v o l a t i l e suspended solids (TVSS), were calculated. Appendix A i s a detailed summary of a l l solids determinations for a l l experimental runs. The conundrum as to which parameters are most appropriate for the determination of digester performance has not been solved. In the past, researchers have used percent reduction of: t o t a l suspended s o l i d s , TSS (Randall et a l . , 1974 and D'Antonio, 1983); biodegradable v o l a t i l e suspended solids (BVSS) found by subtracting the asymptotic value of TVSS remaining at the end of a batch aeration test (Droste and Sanchez, 1983); and percent reduction i n TVSS (Koers, 1979 and Anderson and Mavinic, 1984). S t i l l , other researchers have used parameters 40 other than s o l i d s . Percent reduction i n BOD (Datar and Bhargava, 1986), dissolved oxygen uptake rate (DOUR), and ATP (Pagoria and Drewry, 1978) have also been proposed. The addition of solids to the lime control digester precluded the use of TSS for measuring the r e l a t i v e performance of the digesters. An appropriate correction technique was not available to account for the digestion of the t o t a l solids present before lime addition, versus that same f r a c t i o n digested after lime addition. In other words, were the t o t a l solids i n the sludge or the t o t a l solids introduced by lime addition being reduced? Since the digesters were a l l operated on a semi-continuous, daily fill-and-draw basis, there was no scope for the determination of the amount of non-biodegradable TVSS; hence, determination of percent of BVSS reduction was not possible. I n i t i a l conditions within semi-continuous (fed-once-a-day) digesters changed on a d a i l y basis; therefore, whichever parameter was chosen, i t would have to have been measured da i l y i n order to obtain meaningful results. Consequently, the use of d a i l y BOD was considered impractical. Since i t was hoped that this work would be applicable to future f u l l - s c a l e operations, the use of DOUR and ATP were also considered inappropriate. Mavinic and Koers (1977) noted that the i n i t i a l t o t a l TVSS i s a property of the sludge, independent of the decay rate, and can be used as a basis of comparison. Thus, i t s use allows these results to be compared to previous work. Therefore, for this work, r e l a t i v e performance of the digesters was determined using percent TVSS reduction. 41 I t should also be mentioned that the sludge's o r i g i n has important implications when discussing r e l a t i v e performance. Although not taken into account, the non-degradable v o l a t i l e f r a c t i o n of the sludge i s influenced by the SRT of the process i n which the activated sludge was grown (Reece et a l . , 1979). A system with a long SRT w i l l have a larger f r a c t i o n of non-degradable v o l a t i l e c e l l material and, as a consequence, performance i n terms of TVSS reduction ( i . e . , not taking into account the non-degradable fraction) w i l l appear to be reduced. The sludge used i n the study was from a single source which had a long t o t a l SRT (40 days). However, a comparison, i n r e l a t i v e terms, of the three digestion modes for various SRTs and temperatures was possible. Given that the a i r flow rates were approximately equal i n a l l the digesters, and that the re s u l t i n g dissolved oxygen levels remained above 2.0 mg/L (for the anoxic-aerobic reactors t h i s value was, i n general, reached or exceeded by the end of the aeration period), the only variables considered to have an affect on the performance of the digesters, i n terms of solids reduction, were the solids retention time (SRT), the mixed-liquor temperature and the res u l t i n g mixed-liquor pH (MLpH). Table 1 i s a summary of the percent reduction i n TVSS for a l l SRT's and temperatures. Figures 4 and 5 reveal the trends i n digester performance. The values i n Table 2 have been determined using a different approach than was the case for Table 1. Instead of the mass balance being calculated over the entire experimental runs, they were calculated continually on a moving average basis, where balance periods equal to the SRT were used. For example, for a 20 day SRT, days 1 to 19 Table 1. Summary of Percent TVSS Reduction  Based on an Overall(1) Mass Balance 20°C Tempe rature(2) 10°C SRT(3) SRT Mode 20 15 10 20 15 10 C(4) 23.9 18.8 14.6 18.0 14.8 7.0 L(5) 28.0 20.0 19.0 17.0 16.8 10.9 A(6) 28.3 18.4 19.1 13.2 12.2 6.7 (1) Single balance period equal to 3 SRTs. (2) Liquid temperature i n °C. (3) Solids retention time i n days. (4) Anoxic-aerobic digester. (5) Constant aeration with d a i l y lime slurry addition. (6) Constant aeration. 43 Table 2. Summary of Percent Reduction Based  on Consecutive(1) Balance Periods 20 °C Temperature(2) 10 °C SRT(3) SRT Mode 20 15 10 20 15 10 ave.(7) 24.1 20. 9 14.0 18. 9 15. 4 9.2 C(4) max.(8) 29.7 26. 6 18.1 27. 4 16. 2 15.4 min.(9) 17.8 11. 7 7.3 12. 4 14. 5 3.4 ave. 30.2 22. 2 18.6 18. 3 16. 6 13.5 L(5) max. 34.1 29. 5 22.8 21. 3 17 . 3 ' 20. 3 min. 25.9 16. 5 13.8 15. 9 15'. 8 8.8 ave. 24.2 21. 1 16.5 15. 0 12. 9 9.2 A(6) max. 44.9 27. 8 24.8 21. 7 13. 9 12.1 min. 16.0 8. 8 12.3 9. 9 11. 9 3.6 (1) Multiple balance periods per run based on SRT. (2) Liquid temperature i n °C. (3) Solids retention time i n days. (4) Anoxic-aerobic digester. (5) Constant aeration with d a i l y lime s l u r r y addition. (6) Constant aeration. (7) Based on a l l balance periods throughout run period. (8) Maximum % TVSS reduction experienced for single balance. (9) Minimum % TVSS reduction experienced for single balance. cz O ~o Z5 ~D CD CU 00 if) > c u CP CL 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 A A n o x i c — A e r o b i c 51 L i m e C o n t r o l V A e r o b i c C o n t r o l V X l i m e ^ a n o x / a e r o a e r o ^ o L i n e a r R e g r e s s i o n E g u a t i o n R S q u a r e d A n o x i c — A e r o b i c y = 0 . 0 4 7 5 3 x + 5 . 4 8 5 3 0 . 8 3 5 5 1 L i m e C o n t r o l y = 0 . 0 4 9 0 2 x + 7 . 6 0 0 9 0 . 9 0 6 7 5 A e r o b i c C o n t r o l y = 0 . 0 6 4 1 2 x + 1 . 8 9 0 6 0 . 8 8 0 4 5 0 100 200 300 4 0 0 500 Figure 4. Degree-Days ( C * days Performance Curve Based on Percent TVSS Reduction at Various Combinations of SRT and Temperature. 4^ c O ~ o ~D CD CO > cz CD cj ^ CD D _ 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 2 0 ° C 10 10 A n o x i c — A e r o b i c -A- L i m e C o n t r o l A' A e r o b i c C o n t r o l 15 20 30 Figure 5. Sol ids Re ten t ion T ime , SRT (days . Percent TVSS Reduction Versus SRT at 20 t and 10°C. constitute the f i r s t balance period, days 2 to 20 the second, etc. The advantage of this approach i s that the operator, by p l o t t i n g the point associated with each balance period d a i l y , has the a b i l i t y : (1) to re a l i z e that something has gone wrong, (2) to i d e n t i f y when the trouble started, (3) to pinpoint the cause of the trouble, and (4) to r e c t i f y the s i t u a t i o n (Berthouex and Hunter, 1981). Comparing the values i n Table 1 to Table 2, there i s obvious s i m i l a r i t y between the average of the percent TVSS reduction based on consecutive balance periods and based on an ove r a l l approach. The maximum and minimum values i n Table 2 indicated the range over which the digesters performed for each SRT and temperature. For Figure 4, the percent TVSS reduction has been calculated on an over a l l mass balance basis for the entire length of a given run and acts as the independent variable. The product of the SRT and the digestion temperature has been calculated and acts as the dependent variable. As expected, there i s an increase i n percent TVSS reduction with an increase i n the SRT-temperature product. This i s true for the experimental and both control digesters. While the anoxic-aerobic digester and the lime control show p a r a l l e l performance (lime s l i g h t l y above), the purely aerobic digester exhibits a greater rate of increase i n digestion of TVSS with increasing time and temperature. However, the aerobic digester lags behind both the anoxic-aerobic and the lime control u n t i l the SRT-temperature product exceeds 220 and 380, respectively. Over the range plotted, this relationship appeared to be lin e a r . 47 In an e f f o r t to separate the combined affects of temperature and SRT on the r e l a t i v e performance of the three digesters, Figure 5 i s presented. The slope of the curves show that there was improved performance, i n terms of percent TVSS reduction, with increasing SRT. As w e l l , there was greater percent reduction found at 20 °C than at 10 °C for a l l digesters at a l l SRTs. This was expected. I t was observed that the anoxic-aerobic digesters performed at approximately the same l e v e l as either of the controls. Therefore, i t appeared that cycling the a i r flow (3.5 hours off:2.5 hours on) did not greatly influence the percent TVSS reduction. As noted e a r l i e r , the same conclusion also applied to the other cycles investigated. A complete s t a t i s t i c a l approach was not undertaken; however, i t was possible to calculate the standard deviation of the d a i l y solids l e v e l s . From these values, as well as reducing the o v e r a l l solids reduction for each digester to a d a i l y figure, i t was possible to determine that, due to overlapping standard deviations, there was no r e a l difference between digestion modes, i n terms of solids reduction. Nevertheless, by v i s u a l observation of the r e s u l t s , i t was apparent that the lime controls consistently yielded the greatest percent TVSS reduction. In the absence of a more formal s t a t i s t i c a l analysis, the observed results act as a good indication that percent TVSS reductions, for the three digestion modes, were quantitatively d i f f e r e n t , yet q u a l i t a t i v e l y s i m i l a r . Moreover, cycling of the a i r supply had one major benefit, namely, a considerable savings i n the amount of a i r required for s t a b i l i z a t i o n . To i l l u s t r a t e this point, the percent TVSS reduction values presented 48 e a r l i e r have been divided by the amount of a i r sparged. For the lime and aerobic controls, the amount of a i r was assumed to be unity, while for the anoxic-aerobic digesters the amount of a i r was 0.42 unity. Thus, at 20°C and 10 °C, the percent TVSS reduction per unit a i r supplied for the anoxic-aerobic digester were 56.9, 44.7, and 34.8 and 43.0, 35.1 and 16.6, respectively. The lime and aerobic control values remained the same as presented i n Table 1. In a l l cases, based on a per unit of a i r supplied, the anoxic-aerobic digesters out performed either of the controls by 150 to 200 percent. Caution should be exercised when comparing the results i n this manner. The q u a l i t a t i v e observation remains that, on a mass balance basis, the lime controls exhibited the greatest percent TVSS reduction. In addition, the fact there was a 58 percent 'savings' i n the amount of a i r supplied does not necessarily imply there would a s i m i l a r cost savings. The anoxic-aerobic digesters required the i n s t a l l a t i o n of timers and a i r solenoids as well as mixing energy. A cost analysis was not performed; however, i t seems reasonable to assume that there could be s i g n i f i c a n t cost savings associated with anoxic-aerobic digestion. Warner et a l . (1985), estimated a potential cost saving of 30 percent for anoxic-aerobic digesters, having an on off r a t i o of 1:1, over conventional aerobic digesters. Based on the results obtained herein, t h i s estimate seems reasonable. At f i r s t , i t seemed counter i n t u i t i v e that roughly the same amount of s t a b i l i z a t i o n could be achieved using less a i r (and that, on a unit basis, the anoxic-aerobic would be vastly superior). Nevertheless, a couple of explanations are postulated. One explanation for the 49 comment that anoxic-aerobic digestion was as successful, i n terms of percent TVSS reduction, as either the lime or aerobic controls i s that the anoxic-aerobic digesters were more e f f i c i e n t i n use of the a i r supplied. That i s , when the a i r came on, the dissolved oxygen l e v e l i n the anoxic-aerobic digesters was very low and, thus, for the f i r s t portion of the aerated period ( u n t i l the residual DO exceeded 1.0 mg/L), the driving force was very high. I t was speculated that this high driving force p a r t i a l l y accounted for greater oxygen transfer e f f i c i e n c y during aerated periods. With the DO l e v e l i n both the controls being maintained above 2 . 0 mg/L, the driving force was not as great, and consequently a portion of the oxygen supplied was 'wasted'. A second, perhaps even more substantial, explanation was that, during the non-aerated periods, the d e n i t r i f i e r s were able to use nitrates produced during the aerated period for energy. Thus, there continued to be endogenous decay despite the absence of molecular oxygen. During aerated periods, while oxidation took place i n the absence of an external food source, micro-organisms were able to endogenously decay as expected. However, during non-aerated periods, while reduction took place, again i n the absence of an external food source, endogenous decay also occurred. 2 . Endogenous Decay Coefficients Using Equation 10 and TVSS levels ( i n mg/L), the endogenous decay co e f f i c i e n t s for a l l digesters, at a l l SRTs and temperatures, have been calculated. In general, K<j's are found by p l o t t i n g the r a t i o of the mass remaining at time, t, over the i n i t i a l mass versus t. The slope of the resu l t i n g straight l i n e i s the for that system. This 50 works well for batch experiments and continuous flow through systems (using Equation 10); however, i n the case of semi-continuous systems, the i n i t i a l conditions are being changed da i l y . This i s especially true when no attempt has been made to control the concentration of the raw sludge to be added daily. As a re s u l t , K d's for semi-continuous systems can be calculated by two means: (1) the average TVSS concentration of the wasted sludge (M t), the average TVSS concentration of the raw sludge added (MQ) and the length of the run, t, can be substituted i n Equation 10, or (2) Mt and MQ can be determined on a dai l y basis (t = 1.0) and substituted into Equation 10. Method (1) i s unsatisfactory for several reasons: (a) Only a single value of K d i s produced, hence i t s s t a t i s t i c a l relevance i s unknown, and (b) taking the overall average of the TVSS concentration smooths out any periods of poor or exceptional performance. Consequently, method (2) was adopted. Thus, for the purpose of determining endogenous decay c o e f f i c i e n t s , the semi-continuous digesters were treated as d a i l y batch systems. Equation 10 was evaluated using t equal to 1.0 day, Me determined at t equal to 1.0 day, and MQ determined at t equal to zero (previous day). The formula for MQ i s as follows: MQ - ( Mt.VR^ M FV F) .... ( 1 8 where: M t = mg/L TVSS of the wasted sludge, Mp - mg/L TVSS of the raw feed sludge, Vp = volume of sludge wasted/added da i l y ( l i t r e s ) , V R = volume of reactor minus Vp, and V T = Vp + V R. 51 When the re s u l t i n g endogenous decay co e f f i c i e n t s were plotted on a da i l y basis, i t was apparent that there was a great deal of v a r i a b i l i t y i n the da i l y values. In fact, Figure 6 revealed almost no usable information. This v a r i a b i l i t y , i n part, can be attributed to da i l y variations i n the raw feed sludge. While the use of such "noisy" data for the determination of li n e a r c o e f f i c i e n t s i s very l i m i t e d (Holmberg and Ranta, 1982 and Holmberg, 1982), an attempt to u t i l i z e these results i s presented herein. However, the author concurs with the statement that such variations "represent the r e a l , not ideal circumstance " (Pagoria, 1977). In order to present the K^'s i n a much more useful form, they have been ranked i n ascending order and plotted against a normalized abscissa. Before the coeff i c i e n t s were plotted, t h e i r standard deviations were calculated and found, i n general, to be larger than the means. Thus, the percentage variance of the endogenous decay co e f f i c i e n t s was often i n excess of 100%. Figures 7 - 1 2 provide information such as overall v a r i a b i l i t y ( s t i l l very large) and the r e l a t i v e difference between the three digesters. Of p a r t i c u l a r importance i s the a b i l i t y to use these curves for choosing design values of K^'s. The choice of endogenous decay co e f f i c i e n t s and the expected percent of time that that value can be achieved may prove useful during the design stage. For discussion purposes, the use of the 50 percent of time-less-than-y value i s suggested. In Figure 7, st a r t i n g at the 50 percent less -than-y-value on the x-axis, a v e r t i c a l l i n e was drawn u n t i l i t reached the curve denoting the type of digester of interest; from that intersect, a C CD 'u " C D o O o u 0 Q GO Z5 o c CD CD ' O "O C Time (days Figure 6. Daily Endogenous Decay Coefficients for 20 day SRT at 20°C. ho 53 horizontal projection to the y-axis yielded the anticipated endogenous decay c o e f f i c i e n t . This has been done for each digester. A summary of these results was presented i n Table 3 which revealed that the median endogenous decay coef f i c i e n t s for the anoxic-aerobic and lime control digesters, based on TVSS, were larger than those based on TSS. However, the opposite was true for the purely aerobic digesters. No trend with SRT was apparent. Figures 7 - 1 2 also provide information about the changes that occur due to changes i n SRT and digestion temperature. I t i s observed that the median values, as well as the maximum and minimum values for each of the three types of digesters, increased with increasing SRT and temperature. Also, the overlapping of the points indicated that 'equivalent' performance could be anticipated for the three digestion modes investigated. Using the 50-percent-less-than values provided i n Table 3, Streeter-Phelps temperature s e n s i t i v i t y c o e f f i c i e n t s were determined from the slope of the semi-logarithm plots (Figures 13 - 15). No explanation was found for the anomalous point i n Figure 14. No trend with SRT was noticed. Average temperature s e n s i t i v i t y c o e f f i c i e n t s of 1.046, 1.067 and 1.076 were calculated for the anoxic-aerobic, lime control and aerobic control digesters, respectively. This suggested that, over the temperature range examined, anoxic-aerobic digestion was least affected by temperature le v e l s . 54 Table 3. Median(l) Endogenous Decay Coefficent  Based on TVSS and TSS Measurements 20°C Temperature 10°C SRT SRT 20 15 10 20 15 10 C(2) TVSS TSS 0.0185 0.0161 0.0144 0.0133 0.0168 0.0093 0.0104 0.0072 0. 0. .0104 .0118 0. 0. .0106 .0072 L(3) TVSS TSS 0.0229 0.0145 0.0132 0.0091 0.0277 0.0175 0.0130 0.0083 0. 0, .0156 .0141 0. 0, .0135 .0094 A(4) TVSS TSS 0.0168 0.0192 0.0198 0.0165 0.0204 0.0232 0.0100 0.0092 0, 0, .0076 .0114 0, 0, .0099 .0108 (1) (2) (3) Value equal to or less-than 50 percent of the time Anoxic-aerobic digester. Constant aeration with d a i l y lime s l u r r y addition. (4) Constant aeration. • A n o x i c - A e r o b i c + Lime Control o Aerobic Control t-Hhi Figure 20 40 60 80 P e r c e n t of T ime less —than Y - V a l u e Endogenous Decay-"Coefficients for 20 day SRT at 20°C - TVSS Basis. 100 1 ^ CD CD O O D ( J CD Q 00 Z5 o C CD cn O X) c U J 0.1 1 0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 -0.01 -0.02 -0.03 -0.04 -0.05 -0.06 -0.07 -0.08 -0.09 -0.10 • Anoxic—Aerobic + Lime Contro l o Aerobic Cont ro l 0 20 40 60 80 P e r c e n t of T ime l e s s - t h c i n Y - V o l u e Figure 8. Endogenous Decay Coefficients for 20 day SR" at 10°C - TVSS Basis. 100 OS V c CD o CD O o >> o o CD Q CO Z5 o c CD CT> O "O C 0.14' 0.12 0.10 0.08 0.06 0.04 0.02 0.00 -0.02 -0.04 -0.06 -0.12 • A n o x i c - A e r o b i c + Lime Control o Aerob ic Control 0 20 40. 60 80 Percen t of T ime l e s s - t h a n Y—Va lue 100 Figure 9. Endogenous Decay Coefficients for 15 day SRT at 20°C - TVSS Basis. ~D 0.04 P e r c e n t of T i m e l e s s — t h a n Y — V a l u e Figure 10. Endogenous Decay Coefficients for 15 day SRT at 10°C - TVSS Basis. OO CD CJ CD O O D O CD Q CO Z3 o C CD c n O T) C L J 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 -0.01 -0.02 -0.03 -0.04 -0.05 -0.06 Anoxic—Aerobic Lime Contro l o Aerobic Contro l 0 20 40 60 80 P e r c e n t of T i m e l e s s - t h a n Y - V a l u e Figure 11. Endogenous Decay. Coefficients for'10 day SRT at 20°C - TVSS Basis. 100 X5 c CD CD O o o o CD Q 00 Z5 o c CD C7> O "O c LU 0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 -0.01 -0.02 -0.03 -0.04 -0.05 -0.06 -0.07 • A n o x i c - A e r o b i c + Lime Contro l o Aerob ic Contro l 0 20 40 60 80 Percent of Time l e s s - t h a n Y-Value Figure 12. Endogenous Decay Coefficients for 10 day SRT at 10°C - TVSS Basis. 100 O c CD U CD O CJ >.. D O CD O CO Z5 O GZ CD d> O C Ld 0.0316 0.0251 0.0200 0.0158 H 0.0126 H 0.0100 H 0.0079 H A X e = 1.05* 0.0063 - • Anoxic—Aerobic - A Lime Control Aerobic Control 20 T e m p e r a t u r e 10 Figure 13. Temperature Sensitivity Coefficients for 20 day SRT. 0.0251 0.0200 0.0158 H 0.0126 H 0.0100 0.0079 H 0.0063 • — A n o x i c - A e r o b i c — -A— - L ime Contro l * - Aerob ic Cont ro l ' e = 1 . 1 0 0 0 - 1 .033 20 10 Temperature (°C) Figure 14. Temperature Sensitivity Coefficients for 15 day SRT. CD O O ^ O o CD Q CO Z5 o C CD CT> O T J C LU 0.0398 0.0316 H 0.0251 H 0.0200 H 0.015^ 0 .0126 0.0100 0.0079 G = 1.075 -A-A n o x i c — A e r o b i c Lime C o n t r o l A e r o b i c C o n t r o l 9 = 1.047 20 10 T e m p e r a t u r e ( °C) Figure 15. Temperature Sensitivity Coefficients for 10 day SRT. ON 64 B - Digested Sludge Characteristics 1. Daily TSS and TVSS levels Appendix A contains the da i l y TSS and TVSS levels for a l l the digesters throughout the three experimental runs. Figures 16 - 27 show the d a i l y v a r i a t i o n i n the TSS and TVSS levels for the diff e r e n t digesters as well as the raw sludge. The average, standard deviation, maximum and minimum value for both TSS and TVSS levels were determined and are presented i n Tables 4 - 6. The precision of the method used to determine the solids levels i s presented i n Appendix B. In general, the method was very good; on two separate occasions, with a sample size of nine, the r e l a t i v e error i n the TVSS levels were 1.24% and 0.61%, respectively. In addition, the average, r e l a t i v e error of da i l y duplicate samples throughout a l l three runs was less then 1.4%. Since no e f f o r t was made to control the d a i l y raw sludge to a set value, i t i s not unexpected that there was considerable v a r i a b i l i t y i n the d a i l y TSS and TVSS levels. This was true for both the raw sludge and the digested sludge e x i t i n g the digesters on a d a i l y basis. After an i n i t i a l start-up period of 1 - 2 weeks, measurements were taken as outlined i n the previous chapter. Steady-state conditions were not a goal; however, as seen i n Figures 16 - 27, even though there was d a i l y v a r i a t i o n , the horizontal aspect of the median value revealed that the systems were operating under consistent conditions, with respect to so l i d s . 65 Table 4. Summary of Daily TSS and TVSS Levels for 20 day SRT Std. T Parameter Mode Ave. Dev. Max. Min. F(l) 7960 538 9268 6616 TSS C(2) 6349 218 6876 5884 mg/L L(3) 6251 191 6700 5900 A(4) 6131 438 6876 4772 F 6227 424 7340 5212 TVSS C 4819 156 5216 4440 mg/L L 4509 170 4968 4240 A 4886 324 5340 3808 F 0.78 0.01 0.80 0.76 TVSS/TSS C 0.76 0.01 0.79 0.74 L 0.72 0.01 0.76 0.69 A 0.80 0.01 0.82 0.78 F 8555 794 9984 6228 TSS C 7112 143 7508 6752 mg/L L 7267 164 7604 6956 A 7076 242 7540 6532 F 6587 616 7732 4784 TVSS C 5359 117 5668 5064 mg/L L 5401 139 5676 5132 A 5469 197 5844 5080 F 0.77 0.01 0.81 0.75 TVSS/TSS C 0.75 0.01 0.77 0.72 L 0.74 0.01 0.76 0. 73 A 0.77 0.00 0.78 0.76 (1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime s l u r r y addition. (4) Constant aeration. 66 Table 5. Summary of Daily TSS and TVSS Levels f o r 15 day SRT Std. T Parameter Mode Ave. Dev. Max. Min. F ( l ) 7538 1240 12584 5456 TSS C(2) 6207 126 6504 5904 mg/L L(3) 6464 210 7220 6120 A(4) 5856 183 6352 5484 F 5798 921 9640 4232 TVSS C 4660 107 4856 4384 mg/L L 4650 143 5052 4352 A 4597 147 5008 4312 F 0.77 0.01 0.79 0.75 TVSS/TSS C 0.75 0.01 0.76 0.73 L 0.72 0.01 0.74 0.69 A 0.79 0.00 0.79 0.77 F 8555 794 9984 6228 TSS C 7664 129 7824 7372 mg/L L 7568 135 7780 7300 A 7633 158 7852 7328 F 6587 616 7732 . 4784 TVSS C 5829 91 5968 5596 mg/L L 5704 100 5868 5500 A 5953 123 6116 5716 F 0.77 0.01 0.81 0.75 TVSS/TSS C 0.76 0.01 0.77 0.76 L 0.75 0.00 0. 76 0. 75 A 0.78 0.00 0.78 0.77 (1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime s l u r r y addition. (4) Constant aeration. 67 Table 6. Summary of Daily TSS and TVSS Levels for 10 day SRT Std. Parameter Mode Ave. Dev. Max. Min. F ( l ) 7960 538 9268 6616 TSS C(2) 6976 166 7368 6704 mg/L L(3) 6835 172 7096 6408 A(4) 6649 196 7056 6232 F 6227 424 7340 5212 TVSS C 5330 131 5616 5104 mg/L L 5078 135 5280 4800 A 5198 143 5492 4780 F 0.78 0.01 0.80 0.76 TVSS/TSS C 0.76 0.00 0.77 0.76 L 0.74 0.01 0.76 0.73 A 0.78 0.01 0.80 0.75 F 8555 794 9984 6228 TSS C 7706 173 8020 7348 mg/L L 7459 239 7856 6972 A 7552 162 7912 7296 F 6587 616 7732 4784 TVSS C 5819 157 6108 5516 mg/L L 5578 204 5936 5172 A 5760 134 6000 5520 F 0.77 0.01 0.81 0.75 TVSS/TSS C 0.76 0.01 0.77 0. 74 L 0.75 0.01 0.76 0.74 A 0.76 0.01 0.78 0.75 (1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime slurry addition. (4) Constant aeration. Figure 17. Doily TVSS Leve ls fo r 2 0 day SRT at 2 0 ° C Figure 19. Daily TVSS Leve ls fo r 2 0 day SRT at 10°C 13.0 0 10 20 30 40 Day F igure 2 0 . Dai ly TSS Leve ls fo r 15 day SRT at 2 0 ° C . F igu re 2 1 . Dai ly TVSS Leve ls for 15 day SRT at 20 °C 71 F igure 2 5 . Dai ly TVSS Leve ls f o r 10 day SRT at 20 °C 73 74 2. Daily Mixed-Liquor pH Levels Figures 28 - 33 r e f l e c t the dai l y mixed-liquor pH (MLpH) l e v e l i n each of the digesters as well as the raw sludge. No attempt was made to control the pH l e v e l i n the anoxic-aerobic digesters or the aerobic digesters. A d a i l y dose of lime s l u r r y was added to the lime control digester i n an attempt to maintain the pH l e v e l near 7.0. The values shown i n Figures 28 - 33 for this digester are the minimum d a i l y values; that i s , the pH reading was taken, then the lime added, and the next reading was not taken u n t i l the following day. This system was less rigorous than that employed by others (Anderson and Mavinic, 1984); however, i t was successful at maintaining a minimum pH l e v e l within the range considered optimum for a mixed population of microorganisms. The average MLpH le v e l i n the anoxic-aerobic digesters was 7.12 + 0.07. Thus, anoxic-aerobic digesters showed a remarkable a b i l i t y to 'naturally' control the pH l e v e l . This was the case for both temperatures (20 °C and 10 °C), as well as for the three SRT's investigated (20, 15, and 10 days). One benefit of this s e l f -regulating pH process was apparent during the discussions concerning the TVSS reduction, namely, that at lower SRT-temperature products, the anoxic-aerobic digester out-performed the aerobic control. The average minimum d a i l y MLpH l e v e l i n the lime control digesters was 6.81 + 0.12. While the standard deviation i s larger than that for the anoxic-aerobic digesters, i t can be explained as a function of operator r e l i a b i l i t y and dai l y slug dosing. M i x e d - L i q u o r pH (MLpH) Leve ls - £ » - £ - u i c n a i c n ^ - - j o o w O Ln O C n O In O C n O 8.0 7.5 7.0 6.5 6.0 5.5 5.0 -4.5 -4.0 X • A n o x i c — A e r o b i c + L i m e C o n t r o l o A e r o b i c C o n t r o l i i i i i i i r 1 0 - D e c 1 7 - D e c 2 4 - D e c 3 1 - D e c 0 7 - J a n 1 4 - J a n 2 1 - J a n 2 8 - J a n 0 4 - F e b Date Figure 29. Daily Mixed-Liquor pH Levels for 20 day SRT at 10°C. M i x e d - L i q u o r pH (MLpH) Leve ls Mixed-Liquor pH (MLpH) Levels 8.0 CO X ^ 4.5 -1 0 - D e c 1 7 - D e c 2 4 - D e c 3 1 - D e c 0 7 - J a n 1 4 - J a n Date Figure 33.. Daily Mixed-Liquor pH Levels for 10 day SRT at 10°C. 0 0 o 81 There was considerable v a r i a t i o n i n the MLpH levels i n the aerobic control digesters. For example, the average MLpH was 5.25 + 0.42 and ranged from 6.71 to 4.24. While the aerobic controls did not seem to suffer greatly i n terms of solids reduction, i t cannot be assumed that large fluctuations i n MLpH levels were completely tolerable. For example, sudden increases i n the MLpH levels within the aerobic control, as seen i n Figures 28 - 33, were associated with n i t r i t e build-up and lack of a l k a l i n i t y consumption due to i n h i b i t i o n of Nitrobacter. A more detailed account of this phenomenon appears l a t e r during the discussion of the supernatant c h a r a c t e r i s t i c s . An explanation of why the lime control out-performed, i n terms of solids reduction, both anoxic-aerobic and aerobic digesters cannot be founded solely on the basis of pH control. Additional benefits associated with a neutral digester pH are discussed l a t e r i n terms of supernatant quality. 3. Nitrogen Balance Appendix C contains a compilation of the nitrogen forms measured throughout the three experimental runs. This includes both the nitrogen associated with the digested sludge and the supernatant. Table 7 presents a summary of the average TKN and %N for the raw sludge and the digested sludges. In order to discuss and compare the res u l t s , the TKN values have also been expressed i n terms of TVSS. In a l l cases, there was a decrease i n the levels of TKN and the %N through digestion. Variations i n the TKN levels appeared not to 82 follow a trend with respect to SRT. However, the reduction i n TKN was greater for a l l digesters at 20 °C than at 10 °C. Average values of 0.086 and 0.094 g TKN/g TVSS were calculated for the raw sludge at 20°C and 10 °C, respectively and are within the range reported i n the l i t e r a t u r e (Koers, 1979). The unit values for a l l digesters were quite s i m i l a r , with overall averages at the two temperatures of 0.082 and 0.092 g TKN/g TVSS. These values represented decreases of only 4.1% and 2.1%; due to the r e l a t i v e errors associated with t h e i r determination, this was not considered s i g n i f i c a n t . In order to determine more closely the fate of nitrogen through the various digestion modes, the following mass balance equation was employed: ov e r a l l N balance = t o t a l N i n - t o t a l N out + change i n N i n digester .... (19) Figure 34 presents a schematic of the mass balance and the various forms of nitrogen measured. From t h i s , i t was possible to estimate the amount of nitrogen 'missing'. I t was assumed that any missing nitrogen represented a loss of nitrogen gas to the surroundings. The forms and quantity of the gases liberated during digestion were not measured. 83 Table 7. Average Nitrogen Levels Within Raw and Digested Sludge 20°C Temperature 10°C Parameter Mode SRT SRT 20 15 10 20 15 10 F( l ) 529 516 520 617 666 595 C(2) 403 325 443 470 544 526 ' TKN mg/L L(3) 443 347 425 526 537 506 A(4) 432 355 428 493 538 522 N(5) 494 498 492 - -F 6.68 6.31 6.35 7.15 7.53 6.91 C 6.23 6.21 6.39 7.09 7.53 6.79 %N L 5.71 5.46 6.05 6.89 7.34 6.85 A 6.42 6.14 6.42 7.08 7.46 6.86 N 7.04 6.88 6.79 - - -F 0.085 0 .089 0 .084 0.094 0.096 0 .093 C 0.084 0 .071 0 .083 0.088 0.093 0 .090 TKN/ TVSS L • 0.098 0 .075 0 .084 0.097 0.094 0 .091 A 0.088 0 .077 0 .082 0.090 0.090 0 .091 N 0.094 0 .094 0 .089 - - -(1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime slurry addition. (4) Constant aeration. (5) Non-aerated digesters. 84 Feed sludge TKN NH3-N NO3-N '\ Nitrogen gas l o s t M i n e r a l i z a t i o n N i t r i f i c a t i o n D e n i t r i f i c a t i o n Digested sludge TKN NH3-N NO3-N "7 Figure 34. Nitrogen Balance During Anoxic-aerobic and Aerobic Digestion ( a f t e r Koers, 1979) 85 While Koers (1979) found that there was considerable nitrogen removal, i t should be noted that the only route for nitrogen removal at this l e v e l of investigation was through d e n i t r i f i c a t i o n to N 2 gas. He observed that the process of turning o f f the a i r and d a i l y decanting "most assuredly resulted i n anoxic conditions"; thus, an explanation for the d e n i t r i f i c a t i o n could e a s i l y manifest i t s e l f . Table 8 presents the amount of nitrogen removal that can be expected for the digesters investigated. I t was found that almost a l l the nitrogen could be accounted for i n the lime and aerobic controls. Since the a i r was always on, i t i s speculated that there was very l i t t l e d e n i t r i f i c a t i o n taking place i n these digesters. On the other hand, since the anoxic-aerobic digesters experienced anoxic conditions on a regular basis, i t was not unreasonable to expect a s i g n i f i c a n t amount of d e n i t r i f i c a t i o n , and hence nitrogen removal, to take place. As such, nitrogen removals up to 30% may be anticipated through the use of anoxic-aerobic digestion. Note: I t was assumed that ammonification (the conversion of organic nitrogen) took place and soluble nitrogen f i r s t appeared as ammonia (and subsequently n i t r i f i e d ) . This i s discussed more f u l l y under "supernatant c h a r a c t e r i s t i c s " . 4. Phosphorus Balance Appendix D contains a compilation of a l l the phosphorus data, including those associated with the digested sludge and the supernatant, for a l l the digesters. Table 9 presents a summary of the average levels of t o t a l phosphorus (TP) within the raw and digested 86 Table 8. Nitrogend) Removal Data T SRT Mode N i n N o u t N i n-N o u t N0 X o u t N 2 Removal (2) (3) (4) (5) (f) (g) % C(6) 8994 6850 2144 27 2043 22.7 20 L(7) 8994 6663 2331 2533 -253 -2.8 A(8) 8994 7337 1657 1500 131 1.5 C 6708 4494 2214 24 2189 32.6 20°C 15 L 6708 4505 2203 1455 747 11.1 A 6708 4612 2096 1267 829 12.4 C 4678 3987 591 9.8 586 12.5 10 L 4678 3825 853 853 -43 -0.9 A 4678 3854 824 775 43 0.9 C 10482 7993 2489 39 2450 23.4 20 L 10482 8267 2215 1720 495 4.7 A 10482 8384 2098 1145 953 9.1 C 4666 3806 860 11 849 18.2 10°C 15 L 4666 3756 910 634 256 5.5 A 4666 3769 897 555 342 7.3 C 6542 5788 754 14 740 11.3 10 L 6542 5571 971 781 190 2.9 A 6542 5742 800 704 96 1.5 (1) Nitrogen expressed as mg/L as N. (2) Equals sum of both TKN and N0 X added. (3) Equals sum of TKN wasted. (4) Nitrogen gas evolution assumed to be (f) - (g). (5) Based on N 2/TKN i n x 100. (6) Anoxic-aerobic digester. (7) Constant aeration with d a i l y lime s l u r r y addition. (8) Constant aeration. 87 sludge. Results concerning the supernatant phosphorus are presented i n the section on "supernatant ch a r a c t e r i s t i c s " . Table 9 revealed that there was a decrease i n the TP content of the sludge for a l l digesters at both temperatures. This suggested that there was phosphorus release taking place during digestion. This was confirmed by the average percent P levels i n the digested sludge for the aerobic digesters. The %P levels i n the aerobically digested sludge were consistently less than those i n the raw sludge, constituting average decreases of 15.4 and 3.14 % at 20 and 10 °C. Moreover, the greatest decrease i n %P content of the sludge was found to be 19.9 percent for the aerobic digester having a 15 day SRT operating at 20 °C. In contrast, the average %P for the anoxic-aerobic and the lime controls increased during digestion. This can readily be explained for the lime controls by the formation of calcium phosphate, which i s insoluble and became a portion of the so l i d s . A s l i g h t increase i n the %P for the anoxic-aerobic digesters was apparent. Since d e n i t r i f i e r s have been shown to be responsible for phosphorus accumulation, one explanation existed. In addition, i t i s speculated that the continuation of anoxic-aerobic cycling (experienced i n the b i o l o g i c a l phosphorus removal process from which the sludge was obtained) promoted phosphorus retention within the digesting sludge. However, to confirm t h i s , more work i s necessary. The observation that the unit TP per unit TVSS (g TP/g TVSS) increased (when compared to the values for the raw sludge) for a l l the digesters 88 at both temperatures can be explained. During digestion, there was a decrease i n the l e v e l s of TP as well as a decrease i n the TVSS l e v e l s ; however, the decrease i n the TVSS content was greater than the decrease i n the TP content. This was an encouraging r e s u l t , since i t suggested that, during aerobic di g e s t i o n ( e s p e c i a l l y f or the anoxic-aerobic and lime control) there was an attempt made by the microorganisms to r e t a i n P. The short experimental run conducted without aeration showed that t h i s was not the case for the anoxic-anaerobic digesters, which exhibited an average drop, i n %P being retained i n the sludge, of 45%. A mass balance of phosphorus was conducted i n a manner s i m i l a r to that done for nitrogen. Equation 19 was employed, as well as using the approach presented i n Figure 34 ( s u b s t i t u t i n g relevant phosphorus forms for nitrogen forms). Table 10 i s a summary of those c a l c u l a t i o n s and reveals that, within experimental error, a l l the phosphorus can be accounted for with a recovery range of 77 - 99 percent. 89 Table 9. Average Phosphorus Levels Within Raw and Digested Sludge 20°C Temperature 10°C SRT SRT Parameter Mode 20 15 10 20 15 10 F ( l ) 296 305 305 299 305 300 C<2) TP mg/L L(3) 284 287 248 260 296 294 269 279 293 284 293 283 A(4) 285 253 283 277 280 282 N(5) 274 273 281 - - .' -F 3.65 3.86 3.84 3.44 3.25 3.56 C 3.85 3.88 3.87 3.66 3.64 3.72 %P L 4.24 4.07 4.09 3.75 3.63 3.82 A 2.94 3.09 3.56 3.24 3.06 3.64 N 2.17 2.11 2.12 - - -F 0.048 0.053 0.049 0.045 0.044 0.047 C TP/ TVSS L 0.059 0.064 0.055 0.056 0.056 0.058 0.050 0.052 0.050 0.050 0.050 0.051 A 0.058 0.055 0.054 0.051 0.047 0.049 N 0.052 0.051 0.051 - - -(1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime s l u r r y addition. (4) Constant aeration. (5) Non-aerated digesters. 90 Table 10. Phosphorus Balance P missing(2) T SRT Mode P in"^out(l) (absolute value) C(3) -121 7.35 20 L(4) -17 1.00 A(5) -47 2.82 C 167 10.52 20°C 15 L 102 6.46 A 86 5.45 C 23 1.38 10 L 163 9.90 A 151 9.17 C 236 15.63 20 L 36 2.34 A -65 4.29 C 128 15.18 10°C 15 L 116 13.77 A 192 22.75 C 47 2.92 10 L 164 10.21 A 217 13.54 (1) Sum of t o t a l phosphorus added minus sum of t o t a l phosphorus wasted i n milligrams. (2) Expressed as a percentage of t o t a l phosphorus added. (3) Anoxic-aerobic digester. (4) Constant aeration with daily lime s l u r r y addition. (5) Constant aeration. 91 5. A l k a l i n i t y Consumption and Production Table 11 shows the a l k a l i n i t y levels experienced i n the raw and digested sludges. The raw sludge contained, on average, 214 mg/L as CaCC>3 a l k a l i n i t y . In general, this value would be considered to be low; yet i n areas where there i s very l i t t l e natural a l k a l i n i t y i n the water supply, such as Vancouver, this value could be considered normal. In order to maintain favourable conditions within the p i l o t -plant, a l k a l i n i t y , i n the form of sodium bicarbonate, i s added. As with pH, no trends i n digested sludge a l k a l i n i t y were found for the anoxic-aerobic digesters, either with respect to SRT or temperature. The l e v e l s , on average, were approximately 20 percent less than those i n the raw sludge and, i n general, matched the levels maintained i n the lime controls. Ordinarily, a l k a l i n i t y i s consumed at the rate of 7.14 mg/L as CaC03 per mg/L of ammonia N oxidized to n i t r a t e . Yet, the f i r s t step, ammonification, results i n a gain of 3.57 mg/L of a l k a l i n i t y as CaC03 per mg/L of N ammonified (Warner et a l . , 1985). Therefore, when there i s no subsequent d e n i t r i f i c a t i o n , a net loss of a l k a l i n i t y , of 3.57 mg/L (as CaC03) per mg/L ammonia N, results. The outcome of this work indicated a s l i g h t l y lower net loss value of 3.07 mg/L of a l k a l i n i t y (as (CaC03) per mg/L ammonia N solubilized) could be expected. However, the a l k a l i n i t y data was not exhaustive and the author does not dispute the theoretical value. 92 Table 11. Average A l k a l i n i t y Levels Within Raw and Digested Sludge 20°C Temperature 10°C Parameter Mode SRT SRT 20 15 10 20 15 10 F ( l ) 226 248 207 191 - 200 A l k a l i n i t y C(2) 192 137 169 163 161 mg/L as CaC03 L(3) 300 224 172 139 149 A(4) 57 40 16 57 - 25 (1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime s l u r r y addition. (4) Constant aeration. 93 In the case when d e n i t r i f i c a t i o n does take place, such as with anoxic-aerobic digestion, an a l k a l i n i t y gain of 3.57 mg/L (as CaC03> per mg/L of n i t r a t e N reduced can be expected. Thus, over one complete cycle, there i s an a l k a l i n i t y gain of 3.57 mg/L (as CaCC^) during ammonification, a loss of 7.14 mg/L (as CaC0 3) during n i t r i f i c a t i o n , and a gain of 3.57 mg/L as CaCC>3 during d e n i t r i f i c a t i o n . Consequently, there i s no net loss of a l k a l i n i t y during anoxic-aerobic d i g e s t i o n provided there i s complete d e n i t r i f i c a t i o n . The aerobic controls consumed almost a l l the a l k a l i n i t y present i n the raw sludge. In general, the l e v e l s i n the aerobic c o n t r o l were very low, approximately one tenth those i n the raw sludge. The values presented i n Table 11 are o v e r a l l averages and r e f l e c t the f a c t that, on several occasions, there was incomplete conversion of n i t r i t e s to n i t r a t e s , r e s u l t i n g i n less a l k a l i n i t y being consumed. This i s discussed i n more d e t a i l i n the n i t r i f i c a t i o n s e ction of the "supernatant c h a r a c t e r i s t i c s " . 6. Chemical Oxygen Demand Raw and digested sludge chemical oxygen demand (COD) l e v e l s , as well as g COD/g TVSS values, were c a l c u l a t e d and are presented i n Table 12. Trends i n the COD l e v e l s matched those found f or percent TVSS reduction. However, since COD l e v e l s were measured only occasionally, any p a r a l l e l s are observational and may not withstand c l o s e r i n v e s t i g a t i o n . The lime control digesters were found to be most e f f e c t i v e at COD removal regardless of SRT or temperature. 94 Table 12. Average COD Levels Within  Raw and Digested Sludge 20°C Temperature 10°C Parameter Mode SRT SRT 20 15 10 20 15 10 F(l) 8400 8832 8329 9510 10193 8941 C(2) 6599 6059 7293 7784 9023 9027 COD mg/L L(3) 6116 6049 6926 7888 8331 8333 A(4) 6782 6417 6953 8117 9019 8552 N(5) 8189 8035 8529 - - -C 21.4 31.4 12.4 18.1 11.5 -1.0 % COD L 27.2 31.5 16.8 17.1 18.3 6.8 Removal A 19.3 27.3 16.5 14.6 11.5 4.4 N 2.5 9.0 -2.3 - - -F 1.35 1.52 1.34 1.44 1.47 1.40 C 1.37 1.33 1.37 1.45 1.55 1.55 COD/TVSS L 1.36 1.30 1.36 1.46 1.46 1.49 A 1.39 1.40 1.34 1.48 1.52 1.48 N 1.57 1.51 1.54 - - -(1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime s l u r r y addition. (4) Constant aeration. (5) Non-aerated digesters. 95 Averages of 1.42 and 1.43 g COD/g TVSS for the raw sludge and a l l digested sludge, respectively, were calcu l a t e d . The small difference confirmed the speculation that the COD reduction p a r a l l e l e d the TVSS reduction. This i s consistent i n f a c t , since the majority of the v o l a t i l e s o l i d s would be carbon compounds and COD i s an i n d i r e c t measure of the carbon content. The t r a d i t i o n a l C:N:P r a t i o of 100:5:1 (Metcalf and Eddy, 1979) was not observed. A r a t i o of 100:6.3:3.5 was found. This was not unusual considering the sludge's o r i g i n . Coming from a b i o l o g i c a l n u t r i e n t removal f a c i l i t y , i t seems predictable that the sludge would have higher portions of both N and P. Also, the r a t i o of N to P was decreased s i g n i f i c a n t l y , suggesting that there were high l e v e l s of P i n the sludge. Again, since the p i l o t - p l a n t was operating s u c c e s s f u l l y during t h i s study, i t was a n t i c i p a t e d that the sludge phosphorus would be high. 7. Q u a l i t a t i v e Observations Although no formal tests were c a r r i e d out to determine the following r e s u l t s , t h e i r i n c l u s i o n was warranted on the basis of c a r e f u l observation. No s o l i d s determination on the supernatant were conducted because c e n t r i f u g a t i o n was substituted f or gravity s e t t l i n g . Nevertheless, a r e l a t i v e idea of the c l a r i t y of the supernatant could be seen when the t o t a l s o l i d s determinations were made. That i s , the mixed l i q u o r s were spun, then the supernatant poured through the vacuum f i l t e r . At t h i s 96 point, the r e l a t i v e amount of residue on the f i l t e r was assessed v i s u a l l y . For the anoxic-aerobic and the lime c o n t r o l digesters, there was l i t t l e , i f any, detectable residue, thus i n d i c a t i n g a 'clear ' supernatant being achieved. In p r a c t i c e , the c l a r i t y of the supernatant would be a function of the l i q u i d s o l i d separation technique employed. In contrast, the purely aerobic digester supernatant l e f t a residue which was l i g h t brown i n colour. Foaming was experienced from time to time on a l l the digesters except the lime controls. This occurred at both 20 and 10 °C. The maximum thickness of any of the foam layers was approximately 2 centimeters. Since sampling and wasting were performed well below the mixed-liquor foam i n t e r f a c e , the presence of foam was considered benign. For the anoxic-aerobic digesters, a small blanket of foam could have the b e n e f i c i a l e f f e c t of reducing any surrounding a i r tran s f e r during the anoxic ( d e n i t r i f i c a t i o n ) periods. Colour changes i n the digested sludge were noted. The anoxic-aerobic and the lime c o n t r o l digested sludge were brown (the raw sludge was a darker brown). On the other hand, the aerobic c o n t r o l digested sludge was a l i g h t brown. Although of dubious p r a c t i c a l s i g n i f i c a n c e , the presence of sludge worms was observed i n the raw sludge. This was not always the case, but when they were present a couple of observations were made. Sludge worms survived the lime control digester; however, they were not present i n the e f f l u e n t of the anoxic-aerobic digester. I t i s speculated that the worms are unable to survive without oxygen, hence 97 they expire and become food f o r the b a c t e r i a . Sludge worms were not able to survive the pure aerobic d i g e s t i o n process e i t h e r . Since oxygen was always present, i t i s assumed that the worms were unable to adapt to the low pH l e v e l within the digester. None of the digesters produced a detectable odour. Even at 10 °C where the digesters were i n a r e l a t i v e l y small environment chamber, i was there no noticeable odour. A b r i e f experiment was conducted whereby sludge was digested at 20 °C without aeration (mixing with no cover). However, these digesters experienced odour problems and the experiment was not repeated. C - Supernatant C h a r a c t e r i s t i c s The supernatant from each of the digesters and the raw sludge was analyzed for soluble constituents of engineering i n t e r e s t . These included: nitrogen i n the forms of N0 X (N0 2 + NO3) and NH4+; t o t a l phosphorus and ortho-phosphate; chemical oxygen demand; and a l k a l i n i t y . 1. Nitrogen As noted e a r l i e r , Appendix C contains a l l the tabulated nitrogen information f o r a l l experimental runs. N i t r i f i c a t i o n A l l digesters showed that n i t r i f i c a t i o n took place during each run. This was not s u r p r i s i n g on two accounts: (1) The source of the sludge, and (2) past experience. The raw sludge was obtained from a modified UCT b i o l o g i c a l phosphorus removal p i l o t - p l a n t . The f a c i l i t y was operating s u c c e s s f u l l y throughout the sludge di g e s t i o n study period. In part, the successful 98 operation of the p i l o t - p l a n t r e l i e s on a healthy population of both n i t r i f i e r s and d e n i t r i f i e r s . Thus, when the raw sludge was obtained from the p i l o t - p l a n t , i t was assumed to contain both n i t r i f i e r s and d e n i t r i f i e r s . This assumption was corroborated by the r e s u l t s . The production of n i t r a t e s during aerobic d i g e s t i o n i s well understood. Dreier (1963) reported n i t r a t e l e v e l s as high as 600 mg/L. Koers (1979) reported l e v e l s around 200 mg/L. For the anoxic-aerobic digesters, the n i t r i f i c a t i o n that took place during the aerated periods was d e n i t r i f i e d during the non-aerated periods. Therefore, the l e v e l of n i t r a t e found, at any p a r t i c u l a r time, was a function of the sampling time. S i m i l a r l y , the TKN and NH4+ l e v e l s were a f f e c t e d by the sampling time frame. In order to assess the real-time TKN and NH4+ l e v e l s , a serie s of continuous monitoring experiments were conducted. The r e s u l t s are discussed i n greater d e t a i l i n Section D. During aerobic digestion, i t i s usu a l l y the case that any ammonia formed as a r e s u l t of the s t a b i l i z a t i o n of the v o l a t i l e s o l i d s present w i l l f i r s t be converted to n i t r i t e s by Nitrosomonas and then to n i t r a t e s by Nitrobacter. In general, n i t r i t e s are unstable and quickly converted to n i t r a t e . The production of n i t r a t e i s an i n d i c a t i o n that s t a b i l i z a t i o n has taken place. Figures 35 - 40 show the trends i n n i t r a t e production, over time, f o r the three digesters, for a l l SRTs and temperatures investigated. The ammonia l e v e l s within the aerobic c o n t r o l were also p l o t t e d at the same time. Figures 35 - 40, for the lime controls, suggest a steady 180 2 4 - S e p 0 1 - O c t 0 8 - O c t 1 6 - O c t 2 2 - O c t 2 9 - O c t 05 -Nov 12 -Nov D a t e Figure 35. Supernatant Nitrogen Levels for 20 day SRT at 20 °C. VO VD 130 1 0 - D e c 1 7 - D e c 2 4 - D e c 3 1 - D e c 0 7 - J a n 1 4 - J a n 2 1 - J a n 2 8 - J a n 0 4 - F e b D a t e Figure 36. Supernatant Nitrogen Levels for 20 day SRT at 10°C. o o S o l u b l e N i t r o g e n a s N ( m g / L ) o o o o o o o o o o o o o o o o CO O C CD cn O _CD _Q Z5 o CO 1 2 0 1 1 0 1 0 0 9 0 8 0 -7 0 6 0 5 0 4 0 3 0 2 0 10 0 • NOx A n o x i c - A e r o b i c + NOx L ime Control o NOx Aerob ic Control v N H 3 Nitrite not detected -v-i 2 4 - S e p 2 8 - S e p 0 1 - O c t 0 5 - 0 c t 0 8 - 0 c t 1 3 - 0 c t 1 6 - 0 c t 1 9 - 0 c t 2 2 - O c t D a t e Figure 39 . Supernatant Nitrogen Levels for 10 day SRT at 20 °C. o CD CO D C CD c n O _CD _Q Z5 "o CO 9 0 8 0 7 0 6 0 -5 0 -4 0 3 0 2 0 10 0 • NOx Anoxic—Aerobic + NOx Lime Contro l o NOx Aerob ic Contro l v N H 3 Nitrite not detec ted 1 0 - D e c 1 7 - D e c 2 4 - D e c 3 1 - D e c 0 7 - J a n 1 4 - J a n D a t e Figure 40. Supernatant Nitrogen Levels for 10 day SRT at 10°C. o 105 increase i n the l e v e l of ni t r a t e s , eventually l e v e l l i n g off; however, the aerobic controls experienced fluctuations i n thei r n i t r a t e production. Due to the n i t r i f i c a t i o n - d e n i t r i f i c a t i o n taking place within the anoxic-aerobic digesters, the peak n i t r a t e levels were found to be low. That i s , i n general, the maximum concentration of n i t r a t e found was less than 2.0 NO3-N mg/L. At 20 °C, the levels were 1.74, 1.98 and 1.20 NO3-N mg/L for SRTs 20, 15 and 10 days, respectively. At 10 °C, peak n i t r a t e levels were found to be 4.44, 1.74 and 1.60 N03-N mg/L for SRTs 20, 15 and 10 days, respectively. Supernatant n i t r a t e levels i n the lime control digesters were maximum at 20 °C, peaking at 174, 133 and 111 NO3-N mg/L for SRTs 20, 15 and 10 days, respectively. At 10 °C, peak ni t r a t e levels were found to be 126, 101 and 80.5 N03-N mg/L for SRTs 20, 15 and 10 days, respectively. Nitrate production, at 20 °C, i n the aerobic controls peaked at 97.6, 94.9 and 89.5 NO3-N mg/L and, at 10 °C, 81.4, 78.5 and 74.3 NO3-N mg/L for SRTs 20, 15 and 10 days, respectively. The magnitude of the peak levels for the lime controls and aerobic controls were consistent with the fact that n i t r i f i e r s prefer a s l i g h t l y a l k a l i n e pH. The conversion of ammonia to n i t r a t e consumes a l k a l i n i t y at the rate of 7.14 mg/L (as CaC03) per mg/L ammonia N oxidized (Warner et a l . 1984; among others), and i f the buffering capacity of the digesting sludge i s low, t h i s results i n a drop i n digester pH levels as n i t r i f i c a t i o n proceeds. For the anoxic-aerobic digesters, 106 d e n i t r i f i c a t i o n during the non-aerated periods produce a l k a l i n i t y and, consequently, there i s no drop i n digester pH. For the lime control digesters, the d a i l y addition of lime maintains the pH l e v e l and i n d i r e c t l y restores the a l k a l i n i t y l o s t due to n i t r i f i c a t i o n . As noted while discussing Figures 28 - 33, the pH control of the anoxic-aerobic units was excellent. The pH control by the addition of lime was adequate, but was li m i t e d by the d a i l y addition of a slug,, rather than through a continuous feed. The aerobic digesters, where pH was not controlled, showed that, i n general, the pH levels dropped to r e l a t i v e l y low levels (4.2 - 5.0). On several occasions, there was a sudden increase i n the aerobic digester pH, which can be p a r t i a l l y explained i n terms of n i t r i t e production. The presence of n i t r i t e s was not detected for the anoxic-aerobic nor the lime control digesters. However, on a number of occasions, n i t r i t e s were detected i n the aerobic digester supernatant. A measurable amount of n i t r i t e was noted i n a l l the aerobic control digesters for SRTs of 20 and 15 days at 20 and 10 °C. There was no measurable n i t r i t e i n the 10 day SRT digesters at either temperature. N i t r i t e build-up 'events' were characterized by. a sudden increase i n digester pH (a r i s e of 1.0-2.0 pH units over 2-4 days); a large -increase i n dissolved oxygen (from 3 to 7 mg/L); a drop i n ammonia le v e l s , and; a drop i n n i t r a t e levels. Figures 41 - 44 i l l u s t r a t e the apparent interplay between digester pH, DO and soluble nitrogen forms. Ordinarily, the conversion from n i t r i t e to n i t r a t e i s rapid and therefore residual amounts of n i t r i t e are not detected. Therefore, i t S o l u b l e N i t r o g e n a s N ( m g / L ) S o l u b l e N i t r o g e n a s N ( m g / L ) M i x e d - L i q u o r p H ( M L p H ) L e v e l 80T S o l u b l e N i t r o g e n a s N ( m g / L ) O M ^ b c o b r o ^ b c o b r o l ^ b c o b M i x e d - L i q u o r p H ( M L p H ) L e v e 601 S o l u b l e N i t r o g e n a s N ( m g / L ) b 4^ 4^ 4^ CO Cn b cn NO Cn 4^ cn b cn 00 b CD cn 4^ cn i x e d - L i q u o r p H ( M L p H ) L e v e l CO b o n 111 was assumed that there was no change i n the n i t r i t e production, but there was a decrease i n the conversion of n i t r i t e to n i t r a t e . In other words, at those times, environmental conditions i n h i b i t e d Nitrobacter but not Nitrosomonas. I t was f e l t that competition and low energy levels were a greater hinderance to Nitrobacter than Nitrosomonas. When the Nitrobacter population was incapable of converting the n i t r i t e to n i t r a t e at the normal rate, a 'residual' amount of n i t r i t e was detected. At 20 °C, the maximum l e v e l of n i t r i t e was 17.82 mg/L NO2-N for a 20 day SRT. Meanwhile, at 10 °C, the maximum levels were 13.2 and 5.39 mg/L NO2-N for 20 and 15 day SRTs, respectively. There were corresponding drops i n the n i t r a t e levels of 54% at 20 °C and 77% and 21% at 10 °C. Since there was less production of n i t r a t e , there was a corresponding decrease i n a l k a l i n i t y consumption, res u l t i n g i n increasing digester pH. The increase i n the DO levels i n the digesters i s explained by the i n a b i l i t y of the Nitrobacter to consume oxygen to form n i t r a t e . A s i g n i f i c a n t f r a c t i o n of the a i r sparging that was being used for n i t r a t e production was no longer being u t i l i z e d ; as a r e s u l t , there was an increase i n the residual dissolved oxygen. These events were self-correcting. Even though nothing changed, after a number of days the pH began to slowly drop to the previous l e v e l , D.O returned to normal, the n i t r i t e levels dropped and the n i t r a t e levels increased. One explanation i s that replacement of inactive 'digested' Nitrobacter with 'fresh' sludge, combined with the increased pH le v e l s , allowed for the re-establishment of a healthy Nitrobacter population. As a r e s u l t , 100% conversion of n i t r i t e to n i t r a t e was re-established. 112 I t was speculated that, with the restored conversion of n i t r i t e to n i t r a t e , there was a corresponding consumption of a l k a l i n i t y r e s u l t i n g i n steadily decreasing pH. Experimental runs were not long enough to say whether or not these events would repeat themselves within a single digester. However, i t i s l i k e l y that s i m i l a r events could occur over time during long-term digestion studies. This explanation was supported by the fact that no n i t r i t e was found i n the 10 day SRT aerobic controls. The addition of a larger volume of 'fresh' sludge prevented n i t r i t e build-up from occurring, despite a decrease i n MLpH. At the same time, Figures 41 - 44 reveal that the ammonia levels also dropped during the n i t r i t e 'events'. With increasing pH, the n i t r i f i e r s were no longer i n h i b i t e d and consequently there was increased conversion of ammonia to n i t r i t e . Ammonia levels I f samples were taken at the end of an aerated period, that i s under highly oxidized conditions, there tended to be very l i t t l e ammonia present. This was the case for the anoxic-aerobic and the lime control digesters. However, the aerobic digesters showed a s i g n i f i c a n t l y high build-up of ammonia. Supernatant ammonia levels i n the aerobic digesters were maximum at 20 °C, peaking at 30.5, 72.9 and 14.1 mg/L NH4+-N for SRTs 20, 15 and 10 days, respectively. At 10 °C, peak ammonia levels i n the aerobic digesters were found to be 23.9, 17.0 and 3.71 mg/L NH4+-N for SRTs 20, 15 and 10 days, respectively. With the one exception, there was a decreasing ammonia residual with decreasing SRT, as well as with temperature. The longer SRT allowed for a greater degree of 113 s o l u b i l i z a t i o n of nitrogen to form ammonia and, due to greater b i o l o g i c a l a c t i v i t y at higher temperatures, there was an increase i n the rate at which s o l u b i l i z a t i o n took place. A short experiment conducted under anoxic-anaerobic conditions (no aeration, mixing without covers) produced ammonia levels of 41.4, 51.8 and 39.3 mg/L NH4+-N for SRTs 20, 15 and 10 days, respectively. This run was conducted at 20 °C for 30 days. Observations made on the continuous monitoring dates revealed that the soluble TKN levels were approximately equal to the NH4+ l e v e l s . 2. Phosphorus Appendix D contains a summary of a l l the phosphorus data. Ortho-phosphate The levels of ortho-phosphate (PO4) observed are presented i n Figures 45 - 50. Table 13 reveals, i n terms of SRT and temperature, trends associated with the digesters investigated. I t was apparent that the average l e v e l of phosphate i n the supernatant increased with increasing SRT, as well as with increasing temperature. The addition of lime was assumed to produce an insoluble calcium phosphate, Ca3(P04), which remained with the so l i d s . As a resu l t , ignoring possible adsorption to CaC03 at high pH, i t was anticipated that the ortho-phosphate levels i n the supernatant of the lime control digesters would be a function of the amount of lime added. A l l digesters showed a tendency to have higher PO4 levels at longer SRTs and higher digestion temperatures. At 20 °C, average levels i n the anoxic-aerobic digesters were approximately 1.5 times those i n the 114 Table 13. Average Supernatant Phosphorus Levels 20°C Temperature 10°C SRT SRT Parameter Mode 20 15 10 20 15 10 F( l ) 0.3 6.4 0.3 1.4 2.6 0.8 PO4-P mg/L C(2) L(3) 42.5 24.7 41.9 29.8 34.8 23.5 26.0 26.1 20.2 21.1 13.5 17.2 A(4) 117.7 103.2 71.7 65.3 71.3 30.7 N(5) 148.4 152.4 152.1 - - -F - - - - - -TP mg/L C L 46.2 23.0 - 37.9 23.2 27.3 26.1 - 13.3 14.6 A 123.6 - 79.7 54.4 - 35.4 N - - - - - -(1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with daily lime s l u r r y addition. (4) Constant aeration. (5) Non-aerated digesters. 115 lime control; levels i n the aerobic control supernatant were 3 - 5 times those i n the lime control (or 2 - 3 times those i n the anoxic-aerobic) . Similar ratios were obtained at 10 °C. In addition, with an increase i n SRT from 10 to 20 days at 20 °C for both the anoxic-aerobic and the aerobic digesters, the PO4 levels increased 1.5 times and, at 10 °C, levels roughly doubled. Phosphorus levels i n the lime control supernatant exhibited the same trends, although not to the same extent. Results of the continuous monitoring revealed that no measurable phosphorus release and uptake occurred for the anoxic-aerobic digesters during a single cycle. The significance of the difference between the ortho-phosphate levels found i n the supernatant of the anoxic-aerobic and the aerobic digesters may be explained i n terms of digester pH. As shown i n previous studies, more P release occurred at lower pH levels. For the lime control, the a b i l i t y to maintain the lowest PO4 levels could be a function of both calcium phosphate formation and neutral pH. In a e f f o r t to show the relationship between pH and phosphorus release, Randall et a l . (1971) plotted phosphorus released per day versus digester pH. They found that, below pH 6.5, there was a large increase i n the release of phosphate during aerobic digestion. Figure 51 i s a s i m i l a r plot for this work and helps explain the di f f e r e n t PO4 levels i n the supernatants of the digesters. Clearly there was s i g n i f i c a n t l y greater release of soluble phosphorus per day at MLpH levels below 5.8. Thus, sim i l a r to previous findings (Hopson and Sack, 1973; among others), i t was observed that phosphorus 1 5 0 i l I I T I I 1 1 2 4 - S e p 0 1 - O c t 0 8 - O c t 1 6 - O c t 2 2 - O c t 2 9 - O c t 0 5 - N o v 1 2 - N o v 1 9 - N o v D a t e Figure 45. Supernatant Phosphorus Levels for 20 day SRT at 20°C. 1 2 0 1 1 0 ioo H 90 H 8 0 H 7 0 H 1 0 - D e c 1 7 - D e c 2 4 - D e c 3 1 - D e c 0 7 - J a n 1 4 - J a n 2 1 - J a n 2 8 - J a n 0 4 - F e b D a t e Figure 46. Supernatant Phosphorus Levels for 20 day SRT at 10°C. 1 3 0 0 2 - J u l 0 9 - J u l 1 6 - J u l 2 3 - J u l 3 0 - J u l 0 6 - A u g 1 3 - A u g D a t e Figure 47. Supernatant Phospho rus Levels for 15 day SRT at 20°C. cn Q_ I O D_ Q) _Q Z5 "o 00 10 D a t e Figure 48. Supernatant Phospho rus Levels for 15 day SRT at 10°C. 9 0 • Anox ic—Aerob ic + L ime Cont ro l o Aerob ic Contro l i i i i i n i 1 2 4 - S e p 2 8 - S e p 0 1 - O c t 0 5 - 0 c t 0 8 - 0 c t 1 3 - 0 c t 1 6 - 0 c t 1 9 - 0 c t 2 2 - 0 c t D a t e -Figure 49. Supernatant Phosphorus Levels for 10 day SRT at 20°C. ho O 55 1 0 - D e c 1 7 - D e c 2 4 - D e c 3 1 - D e c 0 7 - J o n 1 4 - J o n D a t e Figure 50. Supernatant Phospho rus Levels for 10 day SRT at 1 0 ° C . P h o s p h a t e R e l e a s e ( m g / L P 0 4 - P / d a y ) 4 * 4^ ft) 73 n O _> C / ) Q Q_ "O ZC 4^ 00 ~o I T Be Le r-t-Le CD < fD fD CD — T ) _X X OD O 00 C T3 __ Z3 —J O c CD 00 4^ X ) fD ft) Q 00 fD 00 123 release w i l l occur as a result of the on-set of unfavourable conditions such as low pH. I t i s also possible that adsorption/desorption reactions could be as important as direct p r e c i p i t a t i o n . Total phosphorus As seen i n Table 13, the levels of soluble t o t a l phosphorus i n the digester supernatants closely followed the ortho-phosphate l e v e l s . I t was assumed that, due to the r e l a t i v e errors associated with both determination methods, soluble TP and PO4 were about the same. Therefore, throughout the following discussion, t o t a l soluable phosphorus and ortho-phosphate are considered interchangeable. The importance of the PO4 levels obtained, after digestion of the raw sludge, can be considered to be a function of the sludge o r i g i n , effluent requirements and ultimate sludge disposal methods available. Sludge obtained from a b i o l o g i c a l phosphorus removal f a c i l i t y w i l l undoubtedly have a high phosphorus content. Although i t i s desirable to digest that sludge, i n order to s t a b i l i z e and reduce i t s volume, i t i s undesirable to release the phosphorus during digestion. Thus, i s was desirable to have a method of digestion which maintains s t a b i l i z a t i o n and allows for minimal phosphorus release. The anoxic-aerobic digesters were superior to aerobic digesters, i n terms of preventing phosphorus release. I f the effluent requirements are not very stringent, then the phosphorus levels found i n the supernatant after digestion are of no consequence. The supernatant may be combined with the plant effluent and discharged. However, i t i s more l i k e l y that there w i l l e xist effluent requirements that prohibit this course of action. Two 124 choices present themselves: (1) the supernatant from the digesters may be recycled to the head of the plant, or (2) the phosphorus may be removed by a separate treatment process before being discharged. The l a t t e r could be readily accomplished by a r e l a t i v e l y small chemical stri p p i n g basin (lime coagulation). The former option i s available i f the plant has excess capacity, but i t should be remembered that phosphorus must be 'physically' removed (presumably through sludge wasting) on a continual basis. The ultimate disposal method determines the appropriate sludge treatment. I f adequate land i s available for composting and sludge dewatering, then digestion may not be required at a l l , and the importance of phosphorus levels i n digester supernatant i s irrelevant. However, assuming that aerobic digestion takes place before ultimate disposal, then the phosphorus levels i n the supernatant are relevant. Again, i t i s desirable to re t a i n as high a percentage of phosphorus as possible i n the digested sludge s o l i d s , especially i f the dewatered digested sludge i s to be used as a f e r t i l i z e r or s o i l conditioner. 3. COD The soluble COD l e v e l for the various digesters, SRTs and temperatures are summarized i n Table 14. With the exception of the aerobic control digesters and the b r i e f experiment conducted under non-aerated conditions, there were no trends i n the measured CODs. 125 Table 14. Average Supernatant COD Levels 20°C Temperature 10°C SRT SRT Parameter Mode 20 15 10 20 15 10 F(D 30 28 28 29 29 28 C(2) 41 40 34 32 34 28 COD mg/L L(3) 53 36 36 31 29 32 A(4) 118 118 57 116 126 77 N(5) 184 181 174 - - -C 37 43 21 10 17 0 % COD L 77 29 29 7 0 14 increase(6) A 293 321 103 300 334 175 N 513 546 521 - - -(1) Raw sludge feed. (2) Anoxic-aerobic digester. (3) Constant aeration with d a i l y lime s l u r r y addition. (4) Constant aeration. (5) Non-aerated digesters. (6) Relative to raw sludge feed. 126 In general, for the anoxic-aerobic and the lime control digesters, the l e v e l of soluble COD i n the supernatant equalled that within the raw sludge. This suggested that any s o l u b i l i z a t i o n of carbon that occurred during digestion was readily consumed. On the other hand, the aerobic controls showed a deterioration i n th e i r a b i l i t y to maintain a low COD l e v e l i n the supernatant. Again, t h i s may be a function of low pH and a reduced capacity for the bacteria to u t i l i z e carbon under these conditions. I t may also be a function of the amount of c e l l l y s i s that takes place within the various types of digesters. I t was assumed that any dead c e l l u l a r material would act as food for the remaining micro-organisms; however, even i f that material was b i o l o g i c a l l y unavailable, i t may s t i l l exert a chemical oxygen demand. No BODs were measured so this can not be confirmed or denied. Also, during the b r i e f non-aerated experiment, the anoxic-anaerobic digesters showed an increase i n their l e v e l of supernatant COD over and above those experienced by the aerobic controls at 20 °C. There was an increase i n the soluble CODs of roughly 5 times over the anoxic-aerobic digesters and 1.5 - 3.0 times over the aerobic controls. 4. A l k a l i n i t y I t was assumed that the a l k a l i n i t y consumed and produced during the various digestion modes could be i n d i r e c t l y associated with the digester pH. For the most part, this assumption was correct on a day-to-day basis (see Chapter IV, Section B, Number 5). Two sets of 127 a l k a l i n i t i e s were determined for the 20 day anoxic-aerobic digester; one at 20 °C and the other at 10 °C. The results have been plotted along with nitrogen levels from a dif f e r e n t date. Figures 52 - 53 show that, after the a i r was introduced, a l k a l i n i t y was consumed while nitrates were produced, and during d e n i t r i f i c a t i o n , there was production of a l k a l i n i t y . Over an entire cycle, there was no net change i n the a l k a l i n i t y l e v e l . This confirms Warner et al.'s (1984) conclusion that anoxic-aerobic digestion does not consume a l k a l i n i t y . Figures 52 - 53 also confirm there i s 100% conversion of s o l u b i l i z e d ammonia to n i t r a t e , within the anoxic-aerobic digesters. For example, n i t r i f i c a t i o n continued after the detectable ammonia has disappeared, while at the same time a l k a l i n i t y consumption followed n i t r a t e production. The s p e c i f i c rates of a l k a l i n i t y consumption were 8.33 and 4.16 mg/L (as CaC03) per mg/L NH4+ consumed at 20 °C and 10 °C, respectively. These disagree with the theoretical value of 7.14 mg/L (as CaC03) per mg/L of NH4+ consumed. However, they are based on only two observations, consequently, more work would be required to confirm these values. A l k a l i n i t y a s m g / L C a C O ^ O N 0 4 ^ C n O O O M 4 ^ a > C O O M 4 ^ C n C » 0 o ^ w o j ^ u i o i v j a i f f l o - ^ M ^ ^ a i o i N i a j f f l o S o l u b l e N i t r o g e n a s N ( m g / L ) 8ZT A l k a l i n i t y a s m g / L C a C O p o o o p o o p o o - - - - - - ^ - - ^ - - ^ _ l _ i r o N i t r o g e n a s N ( m g / L ) 6ZI 130 D - Monitoring Results The following results were obtained from 12 continuous monitoring experiments. Oxidation-reduction potential (ORP) and dissolved oxygen (DO) readings were recorded every two minutes over a 24 hour period. For the f i r s t six-hour cycle, chemical parameters of interest were also measured. Readings from the anoxic-aerobic digesters were plotted and are presented i n Figure 54 and Figures E ; l - E . l l . contained i n Appendix E. Figure 54 i d e n t i f i e s a number of features. Peddie et a l . (1988) described these features i n more d e t a i l than i s presented below. However, a b r i e f overview, i d e n t i f y i n g t h e i r existence, i s appropriate. Feature (A) denotes a rapid slope change i n the ORP p r o f i l e with the onset of aeration. Feature (B) has been dubbed the "elbow" and occurs at the time when dissolved oxygen becomes measurable. Before this time, any oxygen introduced has presumably been u t i l i z e d for the production of n i t r a t e s , thus only combined oxygen i s present, and the "elbow" s i g n i f i e s the emergence of free oxygen. I t also corresponds to the time when a l l the ammonia l e f t over from the non-aerated period has been oxidized. The "elbow" occurred between 20 and 40 minutes after the onset of aeration, depending on the SRT and the digestion temperature. 10 11 12 13 14 15 16 T i m e ( h o u r s ) Figure 54. Monitoring Resul ts for 20 Day SRT at 20°C on October 2 3 - 2 4 , 1987. 132 Feature (C) i s the plateau value of the ORP value during the aerated period. I t corresponds to a f u l l y oxidized state or, at least, the time when the rate of oxidation equals the rate of aeration. Feature (D) i s the i n f l e c t i o n point after aeration has been stopped. Dubbed the "oxygen knee", i t corresponds to the disappearance of measurable DO. Note that, up to this point, the concentration of nitrates has been increasing and that, beyond, d e n i t r i f i c a t i o n takes place. Point D occurred between 14 and 56 minutes after aeration had been halted, depending on the SRT and digestion temperature. Feature (E) i s a second i n f l e c t i o n point. I t has been dubbed the "nitrate knee" and corresponds to complete d e n i t r i f i c a t i o n . The concentration of nitrates at this time was less than the detection l i m i t of 0.1 mg/L. Point (E) occurred between 96 and 206 minutes after aeration had been halted, depending on the SRT and digestion temperature. On two occasions, at 10 °C, for a 20 day SRT, the a i r came back on before d e n i t r i f i c a t i o n was complete. The r e p r o d u c i b i l i t y of the ORP p r o f i l e s and the ch a r a c t e r i s t i c features noted above can be seen i n Figures 54 and E.l - E . l l . Except as noted, each of the features i s present for each of the monitoring dates. In addition, the inset curve reveals the ORP and DO p r o f i l e s over a 24 hour period. Again, consistent results were obtained. The f i r s t cycle of the 24 hour inset i s the main figure. Further work r e l a t i n g to the a p p l i c a b i l i t y of ORP as a monitoring and control parameter for both anoxic-aerobic digesters and Sequencing Batch Reactors (SBR) has already begun at U.B.C. 133 One reason for the two occasions when complete d e n i t r i f i c a t i o n did not occur i s that, at 10 °C, there was not enough soluble carbon available for the d e n i t r i f i e r s . Since complete d e n i t r i f i c a t i o n took place within the 10 day SRT digester at 10 °C, the longer SRT also contributed to the lack of carbon available. I t should be noted that, on monitoring days, the digesters were not "fed" raw sludge u n t i l after 16:00 hours. This meant that fresh sludge was not introduced for up to 30 hours. Therefore, i t i s possible that a l l the readily available carbon needed for d e n i t r i f i c a t i o n had been depleted. However, i f d e n i t r i f i c a t i o n was not complete, there would have been a gradual increase i n the n i t r a t e l e v e l within the digester. This did not occur. Presumably, after fresh feed was introduced, there was s u f f i c i e n t carbon available for complete d e n i t r i f i c a t i o n to take place during subsequent cycles. This presumption was confirmed by the overnight ORP p r o f i l e , which showed that complete d e n i t r i f i c a t i o n took place on each of the cycles following the addition of raw sludge (inset Figures 54 - 67). Table 15 contains a summary of the calculated n i t r i f i c a t i o n and d e n i t r i f i c a t i o n rates found during monitoring. No clear trend i n n i t r i f i c a t i o n rates emerged with respect to SRT. However, the rate of n i t r i f i c a t i o n decreased, on average, 33 percent with a decrease i n temperature of 10 °C. S i m i l a r i l y , d e n i t r i f i c a t i o n rates dropped 56 and 36 percent for 20 and 10 day SRT, respectively, with decreasing temperature. In most cases, the rate of d e n i t r i f i c a t i o n exceeded the rate of n i t r i f i c a t i o n . This i s p a r t i c u l a r i l y true for 10 day SRT. For example, at 134 Table 15. Summary of N i t r i f i c a t i o n and D e n i t r i f i c a t i o n  Rates for Anoxic-aerobic Digesters T SRT 0(1) N i t r i f i c a t i o n ( 2 ) D e n i t r i f i c a t i o n ( 3 ) 1 0. ,646 0. 784 20 2 0, .524 0. 892 3 0. .561 0. 900 Ave. 0. .577 0. 858 1 0. .721 0. 633 20°C 15 2 0. .647 0. .808 3 0. .630 0. 756 Ave. 0. .666 0. 732 1 0. .684 1. ,328 10 2 0. .682 1. ,023 3 0. .527 1. ,121 Ave. 0, .631 1; ,187 1 0. .354 0. ,351 20 2 0. .397 0. ,416 3 0. .387 0. ,365 Ave. 0, .379 0. ,377 1 0. .422 0. ,608 10°C 10 2 0, .491 0. ,746 3 0, .453 0. .929 Ave. 0. .455 0. .761 (1) Observation number. (2) mg/L NO3-N produced per hour. (3) mg/L NO3-N reduced per hour. 135 20 °C, the rate of d e n i t r i f i c a t i o n exceeded the rate of n i t r i f i c a t i o n by 88 percent. E - Overall Rating System The main objective of this study was to assess the acceptability, i n terms of a number of accepted performance variables, of anoxic-aerobic digesters for the s t a b i l i z a t i o n of a waste activated sludge. In so doing, l o g i c a l comparisons have been drawn between anoxic-aerobic digesters and two diff e r e n t controls: aerobic digesters enhanced by lime addition and pure aerobic digesters. So far these comparisons have been dealt with i n d i v i d u a l l y . I t i s hoped that the following discussion w i l l help round out those ind i v i d u a l comparisons by presenting an ov e r a l l rating system and applying i t to this case. For each of the criterium presented i n Table 16, each of the digestion modes has been given a score. Each criterium has a t o t a l point value of 6; 3 available for the highest ranking; 2 for the next and 1 for the l a s t . In the event of a t i e , the combined points available for those two positions are divided equally between the two (or three). In addition to the t o t a l points awarded to each digestion mode being recorded, the number of f i r s t , second and t h i r d place finishes have also been recorded. I d e n t i f i c a t i o n of a p a r t i c u l a r digestion mode's strengths and weaknesses are then possible. Results suggested that anoxic-aerobic digestion was superior to either of the two controls. The lime control ranked above the aerobic control. While the system was somewhat arbitrary, i t i s f e l t that this approach had some merit by presenting a r a t i o n a l for comparing the dif f e r e n t digestions modes. 136 The system could be improved by u t i l i z i n g several independent evaluations. In addition, the r e l a t i v e importance of each category was not assessed, nor was a complete cost evaluation considered. 137 Table 16. Summary of Rating Points for Comparison of Three Digestion Modes Cr i t e r i o n % TVSS reduction MLpH control Nitrogen removal Phosphorus retention Lack of effluent n i t r a t e Lack of effluent ammonia Lack of effluent phosphorus Total COD removal Least increase i n soluble COD A b i l i t y to conserve a l k a l i n i t y A i r requirements Chemical cost Additional equipment required F u l l scale experience Potential for automation 1.5 3.0 1.5 3.0 2.0 1.0 3.0 1.5 1.5 2.5 2.5 1.0 3.0 1.0 2.0 2.5 2.5 1.0 2.0 3.0 1.0 1.5 3.0 1.5 2.5 2.5 1.0 3.0 2.0 1.0 3.0 1.5 1.5 2.5 1.0 2.5 1.0 2.0 3.0 1.5 1.5 3.0 3.0 .1.5 1.5 Total Number of highest rankings Number of 2nd place rankings Number of 3rd place rankings 35.5 10 4 1 30. 5 6 7 2 24.0 3 6 6 138 V - CONCLUSIONS Based on the results of this experimental work, u t i l i z i n g a single source of waste activated sludge, various digestion modes and two temperatures, the following conclusions can be drawn: A - Digestion Kinetics 1. Anoxic-aerobic digestion compared favourably to aerobic digestion, with and without lime addition. The use of non-aerated and aerated conditions i n the r a t i o of 3.5:2.5 hours per s i x hour cycle allowed for equal percent TVSS reduction when compared with aerobic digestion. Over the range of temperature and SRTs investigated, there i s a li n e a r relationship between the percent TVSS reduction achieved, and the product of SRT and temperature. 2. Lime control digesters consistently showed greater percent TVSS reduction. However, the differences between the three digestion modes, in terms of percent TVSS reduction, were within experimental error. I t i s concluded that anoxic-aerobic digestion i s as effective as aerobic digestion, with or without lime addition. 3. The incorporation of non-aerated periods during aerobic digestion resulted i n a s i g n i f i c a n t savings i n the amount of a i r required for comparable percent TVSS reduction. Anoxic-aerobic digestion consumed only 42 percent of the a i r required by either the lime or aerobic controls. 139 4. Variations of 200% i n the calculated endogenous decay c o e f f i c i e n t s (based on TVSS) can be expected when dai l y feed sludge concentrations are not controlled. However, a useful approach for comparing the endogenous coe f f i c i e n t s was presented. By p l o t t i n g the endogenous decay c o e f f i c i e n t s against the percent-time-exceeded, i t was possible to show p a r a l l e l performance between the digestion modes. 5. Temperature s e n s i t i v i t y was different for each digestion mode. Between 20 °C and 10 °C, temperature s e n s i t i v i t y c o e f f i c i e n t s of 1.046, 1.067 and 1.076 were found for anoxic-aerobic, lime control and aerobic digesters, respectively. This indicated that anoxic-aerobic digestion of bio-P sludge was less affected by temperature than would be predicted by the standard QIQ = 2 (0 = 1.072). B - Digested Sludge Characteristics 1. Anoxic-aerobic digesters showed an a b i l i t y to control the mixed-liquor pH (MLpH) levels that was superior to d a i l y lime dosing. Neutral MLpH conditions were maintained i n the anoxic-aerobic digesters, despite low a l k a l i n i t y levels i n the raw sludge. 2. Aerobic digestion afforded large drops i n MLpH which did not seem to i n h i b i t solids reduct ion. Low (generally 4.2 - 5.5) MLpH levels did, however, effect the o v e r a l l acceptability of the process. 3. A reduction i n t o t a l TKN content of the sludge can be expected, whichever digestion mode i s employed. There was no trend i n the amount of TKN reduction with respect to SRT; however, more reduction occurred at 20 °C than at 10 °C. The average levels of 0.086 and 0.094 g TKN/g 140 TVSS for the raw sludge at 20 °C and 10 °C, were maintained throughout digestion. 4. Anoxic-aerobic digestion showed an a b i l i t y through d e n i t r i f i c a t i o n to remove nitrogen as nitrogen gas. As much as 32 percent of the raw sludge nitrogen may be converted to nitrogen gas. In general, the amount of nitrogen removal can be expected to be 2 to 4 times that of the controls. 5. Phosphorus release took place during a l l three digestion modes. Anoxic-aerobic and aerobic digestion with lime addition showed the most promise with respect to retention of percent phosphorus within the so l i d s . 6. A l k a l i n i t y was consumed during aerobic digestion. The incorporation of regular non-aerated periods resulted i n the production of a l k a l i n i t y , such that there was no net loss of a l k a l i n i t y during anoxic-aerobic digestion. The d a i l y addition of lime i n d i r e c t l y maintained the a l k a l i n i t y l e v e l within the lime controls. 7. Reductions i n COD levels p a r a l l e l e d TVSS reductions. A r a t i o of 1.42 g COD/g TVSS was observed throughout digestion. The r a t i o of C:N:P was 100:6.3:3.5 before and after digestion. C - Supernatant Characteristics 1. Anoxic-aerobic digestion resulted i n superior supernatant quality over either of the controls. Soluble n i t r a t e levels within the anoxic-aerobic supernatant were generally less than 5.0 mg/L as N. In 141 contrast, n i t r a t e levels i n the lime control ranged between 80 and 175 mg/L as N, and levels within the aerobic control ranged between 75 and 100 mg/L as N. Soluble phosphorus levels within the anoxic-aerobic digesters were, depending on lime dose, approximately equal to the levels within the lime controls and were one-half to one-third the levels within the purely aerobic controls. 2. N i t r i f i c a t i o n took place within a l l digestion modes. Nitrate levels i n the lime controls were the highest. Due to low MLpH within the aerobic controls, there was some retardation of n i t r i f i c a t i o n , r e s u l t i n g i n lower levels of effluent n i t r a t e as well as an ammonium residual. Due to the incorporation of non-aerated periods, there was complete d e n i t r i f i c a t i o n within the anoxic-aerobic digesters. Consequently, nitrogen removal to N2 gas can be expected during anoxic-aerobic digestion. The rate of nitrogen removal was 2 to 3 times that of either of the controls. 3. Low MLpH (4.2 - 5.5) may have contributed to a 'build-up' of n i t r i t e s within the aerobic controls. I t did result i n s i g n i f i c a n t l y higher phosphate levels i n the aerobic control supernatant, when compared to either anoxic-aerobic or lime control digesters' supernatant. 4. Phosphorus supernatant levels were comparable within the anoxic-aerobic digesters and lime controls. Any differences could be attributed to lime dose and subsequent p r e c i p i t a t i o n of soluble phosphate. 142 5. Waste activated sludge generated by a b i o l o g i c a l removal of phosphorus f a c i l i t y may preclude the use of aerobic digestion without s u f f i c i e n t forethought as to the fate of phosphorus within the digester supernatant. Anoxic-aerobic or aerobic digestion with lime addition are more suited to this purpose and are therefore recommended. 6. Low soluble COD levels existed i n the supernatant of both the anoxic-aerobic and the lime control digesters. This was not the case for aerobic digestion, which tended to exceed the levels found i n the others by 3 times. 7. Over a single cycle within the anoxic-aerobic digesters, a l k a l i n i t y was consumed and produced such that there was no net loss of a l k a l i n i t y during digestion. D - Monitoring Results 1. ORP proved to be a valuable tool for the monitoring of anoxic-aerobic digesters. Similar features occurred on a l l r e a l time ORP p r o f i l e s which correlate to events of engineering and theoretical interest. The use of ORP as a control parameter shows great promise. 2. N i t r i f i c a t i o n and d e n i t r i f i c a t i o n rates were affected by temperature, although, i n general, there was s u f f i c i e n t time afforded within each cycle for both complete n i t r i f i c a t i o n and d e n i t r i f i c a t i o n to take place. 143 E - O v e r a l l Rating System 1. Based on an o v e r a l l r a t i n g system, anoxic-aerobic d i g e s t i o n rated higher than the lime control which, i n turn, rated higher than the aerobic c o n t r o l . There e x i s t s a need for a standardized r a t i n g system such that regulators, operators and designers can adequately compare various d i g e s t i o n schemes. F - Future Research As a r e s u l t of t h i s work, the author f e e l s that there are a number of areas of i n t e r e s t which could lead to important discoveries and cost savings. As a r e s u l t , the following topics are suggested: 1. Anoxic-aerobic d i g e s t i o n should continue to be investigated. Only one source of sludge was investigated during t h i s study. Anoxic-aerobic d i g e s t i o n of high-rate sludges, or the d i g e s t i o n of sludges which combine a r e l a t i v e l y small f r a c t i o n of primary sludge with a larger f r a c t i o n of secondary sludge, may prove i n t e r e s t i n g . 2. Considerable scope e x i s t s for the design of new digesters and r e t r o f i t of e x i s t i n g aerobic digesters to u t i l i z e the p o t e n t i a l benefits of anoxic-aerobic digestion. In p a r t i c u l a r , the incorporation of mechanical mixing and an a b i l i t y to 'cycle' the a i r supply come to mind. 3. 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Rich, L.G., (1977) "Rational Design of Aerobic Digestion Systems." Water and Sewage Works. 124. 94. 64. R i t t e r , L.E. (1970) "Design and Operating Experiences using Diffused Aeration for Sludge Digestion." Journal Water P o l l u t i o n Control  Federation. 42, 10, 1782-1791. 65. Sawyer, C.N. and McCarty, P.L., "Chemistry For Environmental Engineering." McGraw-Hill Book Company, 1978. 66. Sekine, T., Iwahori, K., Fujimoto, E. and Inamori, Y., "Advanced Control Strategies for the Activated Sludge Process." Inst, and Cont. of Wat. & Wastewater Treatment and Transport Systems, Proc. 4th IAWPRC Workshop, Houston & Denver, Ed. R.A.R. Drake, Pergamon Press, 1985. 67. Shibai, H., I s h i z a k i , A., Kobayashi, K., and Hirose, Y. (1974) "Simultaneous Measurement of Dissolved Oxygen and Oxidation -Reduction Potentials i n the Aerobic Culture." J. Agr. and B i o l .  Chemistry. 38, 12, 2407-2411. 68. Singh, T. and Patterson, J.W. (1974) "Improvement of aerobic sludge digestion process e f f i c i e n c y . " Journal Water P o l l u t i o n Control  Federation. 46, 1, 102-112. 69. Smith, D. (1978) "Wastage Rates Determined by SRT Method." Water and  Sewage Works. September, 68-77. 70. Standard Methods for the Examination of Water and Wastewater. 16th ed., American Public Health Association, Inc., New York, 1986. 149 71. Stein, R.M., Adams, C.E., Jewell, W.J. and Eckenfelder, W.W., J r . (1972b) "A Study of Aerobic Sludge Digestion Comparing Pure Oxygen and A i r . " Proceedings 27th In d u s t r i a l Waste Conference. Purdue University, Lafayette, Indiana, 492-500. 72. Stein, R.M., Adams, C.E., J r . and Eckenfelder, W.W., J r . (1972a) "A P r a c t i c a l Model of Aerobic Sludge S t a b i l i z a t i o n . " Proceedings. 3rd Annual Environmental Engineering and Science Conference. University of L o u i s v i l l e , L o u i s v i l l e , KY., 781. 73. Tebbutt, T.H.Y. (1971) "Further Studies on Aerobic Digestion." -L_ Inst. Publ. Health Engrs.. 70, 223-232. 74. Tran, F. and Gannon, D. (1981) "Deep Shaft High Rate Aerobic Digestion: Laboratory and P i l o t Plant Performance." Water P o l l . Res. J. Canada. 16, 71-89. 75. Van Haandel, A.C., Ekama, G.A. and Marais, G.v.R. (1981) "The Activated Sludge Process Part 3 - Single Sludge D e n i t r i f i c a t i o n . " Water  Research. 15, 1153-1152. 76. Warner, A.P.C., Ekama, G.v.R., and Marais, G.v.R. (1983) "Anoxic-Aerobic Digestion of Waste Activated Sludge." Res Rep W 48, Dept of C i v i l Eng, Univ of Cape Town. 77. Warner, A.P.C., Ekama, G.A. and Marais, G.v.R. (1985) "The Activated Sludge Process Part 4 - Application of the General Model to Anoxic-Aerobic Digestion of Waste Activated Sludge." Wat. Sci and Tech. 17, 8, 1475-1488. 150 APPENDICES APPENDIX A Solids Data 152 Table A . l . Solids Data f o r 20 Day SRT at 20°C. DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 9180 7076 0. 77 2 8264 6364 0. 77 3 8172 6308 0. 77 4 7560 5808 0. 77 5 7600 5932 0. 78 6 8672 6664 0. 77 7 8084 6200 0. 77 8 7432 5764 0. ,78 9 8344 6508 0. ,78 10 . 7308 5624 0. .77 11 7512 5812 0. .77 12 7276 5628 0. .77 13 8476 6548 0. .77 14 , 7620 5904 0. .77 15 7864 6000 0. .76 16 8436 6524 0. .77 17 7572 5868 0. .77 18 7196 5592 0, .78 19 8096 6284 0. .78 20 7380 5768 0. .78 21 8072 6312 0, .78 22 7940 6200 0, .78 23 8128 6368 0, .78 24 8248 6428 0, .78 25 8588 6756 0, .79 26 7520 5948 0. .79 27 8088 6372 0, .79 28 8100 6344 0. .78 29 7996 6256 0. ,78 30 8456 6616 0. ,78 31 8328 6540 0. ,79 32 7296 5764 0. ,79 33 6616 5212 0. 79 34 7560 6028 0. 80 35 8096 6344 0. 78 36 8576 6780 0. 79 37 8348 6712 0. 80 38 9268 7340 0. 79 39 7836 6248 0. 80 40 6904 5512 0. 80 41 7672 6144 0. 80 42 8288 6644 0. 80 43 8000 6348 0. 79 44 7804 6276 0. 80 45 7496 6024 0. 80 153 Table A . l . (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 46 7544 6020 0. .80 47 7020 5656 0. ,81 48 7832 6240 0. ,80 49 7800 6196 0. ,79 50 7368 5824 0. ,79 51 7252 5720 0. ,79 52 9044 7176 0. ,79 53 8644 6836 0. .79 54 7240 5704 0. .79 55 7704 6076 0, .79 56 8232 6496 0. .79 57 8332 6592 0. .79 58 7472 5868 0, .79 59 8684 6840 0, .79 AVERAGE 7923 6219 0.79 ST. DEV. 554 433 0.01 MAX. 9268 7340 0.81 MIN. 6616 5212 0.76 1 6876 5216 0. .76 2 6776 5140 0 .76 3 6652 5032 0 .76 4 6560 4972 0. .76 5 6556 4980 0, .76 6 6516 4920 0, .76 7 6484 4860 0, .75 8 6504 4896 0, .75 9 6556 4972 0. .76 10 6816 5132 0, .75 11 6596 4988 0. ,76 12 6332 4776 0. ,75 13 6360 4768 0. ,75 14 6536 4928 0. ,75 15 6360 4736 0. ,74 16 6696 4992 0. ,75 17 6636 5004 0. 75 18 6392 4780 0. 75 19 6324 4784 0. 76 20 6352 4740 0. 75 21 6432 4800 0. 75 22 6248 4692 .0. 75 23 6468 4900 0. 76 27.08 24.72 24.99 20.71 9924 9004 9089 7538 23.82 21.27 22.21 18.32 11293 10014 10435 8605 154 Table A . l . (cont'd.) • DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 24 6592 4948 0 .75 20 .48 7492 17 .03 8034 25 6648 5004 0 .75 19 .11 7036 16 .28 7727 26 6280 4728 0, .75 22, .33 8174 20 .09 9468 27 6380 4816 0, .75 21, .62 7927 19, .14 9020 28 6488 4876 0, .75 22, .27 8203 18 .78 8890 29 6164 4648 0, .75 28, .71 10553 26, .27 12407 30 6484 5116 0. .79 19. .38 7183 20, .20 9611 31 6596 5000 0. ,76 18. ,30 6822 15, .89 7600 32 6328 4828 0, .76 20, .99 7831 19, .62 9383 33 6276 4780 0. .76 23. .50 8675 21, .62 , 10218 34 6120 4604 0. ,75 ' 23. ,58 8713 21. .60 10205 35 6220 4676 0. .75 26. .82 9938 24, .80 11732 36 6240 4704 0. ,75 26. ,94 10006 24. ,14 11431 37 6228 4744 0. ,76 23. ,41 8753 21. ,84 10394 38 6376 4876 0. .76 22. .37 8480 20, .17 9725 39 6288 4784 0. ,76 23. , 11 8758 21. .51 10354 40 6224 4768 0. ,77 24. , 13 9128 23. .16 11113 41 6108 4660 0. ,76 24. ,14 9120 22. ,32 10682 C 42 6300 4848 0. .77 24. .60 9326 22. .80 10939 43 6344 4844 0. .76 25, .46 9649 23, .82 11418 44 6324 4852 0. .77 26, .21 9920 24, .73 11821 45 6240 4808 0, .77 22, .23 8368 20 .88 9912 46 6284 4816 0, .77 23, .48 8843 21, .60 10254 47 6208 4828 0, .78 23, .80 8912 23, .51 11089 48 6240 4808 0, .77 20, .46 7654 19, .00 8947 49 6204 4760 0. .77 28 .61 10698 23 .42 11012 50 6012 4600 0, .77 29, .28 10879 27 .09 12652 51 6056 4616 0, .76 26, .06 9620 22, .90 10619 52 5984 4584 0 .77 26, .84 10021 24 .24 11366 53 6088 4692 0, .77 23, .35 8831 22, .04 10471 54 5992 4596 0. .77 25, .83 9744 24, .45 11590 55 5884 4440 0. .75 28. .79 10838 26, .09 12341 56 6300 4844 0. .77 22, .70 8527 20, .45 9652 57 6040 4620 0. .76 28. .42 10664 25, .75 12151 58 6020 4588 0. ,76 26. ,83 9949 24, ,25 11311 59 6116 4680 0. .77 25. .52 9510 22, .72 10657 60 6244 4724 0. ,76 23. ,11 8611 19. ,59 9187 AVERAGE 6349 4819 0. ,76 24. ,15 8998 21. ,94 10384 ST. DEV. 218 156 0. 01 MAX. 6876 5216 0. 79 29. 28 10879 27. 09 12652 MIN. 5884 4440 0. 74 18. 30 6822 15. 89 7600 Table A . l . (cont'd.) f # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 6448 4824 0. .75 2 6700 4968 0 .74 3 6496 4788 0, .74 4 6516 4756 0 .73 5 6492 4788 0, .74 6 6596 4824 0, .73 7 6340 4584 0. .72 8 6516 4744 0. .73 9 6560 4804 0. .73 10 6524 4756 0. ,73 11 6436 4732 0. ,74 12 6368 4648 0. ,73 13 6420 4648 0. ,72 14 6512 4700 0. 72 15 6284 4448 0. ,71 16 6608 4736 0. ,72 17 6520 4672 0. ,72 18 6284 4480 0. ,71 19 6288 4516 0. 72 20 6268 4456 0. ,71 29, .19 10699 20 .54 9740 21 6288 4476 0. ,71 31. .07 11318 23 .04 10848 22 6196 4408 0. 71 29, .60 10765 21. .77 10230 23 6184 4424 0. ,72 29, .14 10604 22 .36 10502 24 6332 4528 0. ,72 28. .51 10427 20 .63 9732 25 6248 4480 0. ,72 30. .60 11270 23 .65 11230 26 6328 4544 0. ,72 25, .44 9316 18 .99 8948 27 6276 4488 0. ,72 29, .16 10692 21 .93 10337 28 6204 4416 0. .71 31, .92 11756 23 .93 11327 29 6088 4388 0. ,72 31, .79 11686 25 .08 11844 30 6116 4380 0. ,72 32, .38 12000 24 .42 11615 31 6400 4600 0. .72 27, .99 10434 20 .41 9758 32 6316 4544 0. ,72 29, .05 10842 22 .16 10596 33 6388 4588 0. .72 28, .46 10507 21 .51 10168 34 6096 4340 0. ,71 28. .76 10628 22 .56 10658 35 6056 4308 0. ,71 34, .25 12694 27 .43 12980 36 6076 4348 0. ,72 33. ,02 12263 26. .47 12534 37 6192 4436 0. ,72 29, .17 10907 22 .60 10753 38 6064 4320 0. ,71 32. .68 12391 25, .37 12233 39 6084 4384 0. ,72 30, .81 11676 24 .88 11976 40 5956 4268 0. ,72 32, .97 12472 26. .70 12815 41 6064 4624 0. 76 26. ,03 9833 24. .15 11562 42 6056 4360 0. 72 30. ,76 11660 24. .36 11684 43 6112 4368 0. 71 32. ,31 12247 25. .49 12220 44 6336 4540 0. 72 28. 74 10878 21. ,42 10237 45 6104 4424 0. 72 31. 23 11755 24. ,91 11825 46 6188 4432 0. 72 30. 34 11426 23. 29 11058 47 6104 4380 0. 72 29. 71 11124 23. 03 10861 156 Table A . l . (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 48 5996 4292 0. .72 30 .71 11490 22 .93 10795 49 6120 4396 0 .72 28 .88 10798 21 .59 10151 50 6056 4332 0, .72 33 .05 12278 25 .55 11930 51 6104 4392 0. .72 30 .88 11399 23 .51 10904 52 5996 4340 0 .72 33 .37 12460 26 .88 12605 53 6108 4448 0, .73 28 .70 10853 22 .89 10873 L 54 6248 4292 0, .69 30 .52 11514 20. .36 9652 55 , 5900 4240 0, .72 31 .89 12006 24 .93 11789 56 6212 4504 0, .73 28 .80 10818 22. .18 10469 57 6188 4480 0, .72 27 .23 10217 20. .86 9841 58 5960 4328 0, .73 29 .85 11069 23. .20 10822 59 5960 4340 0. .73 28, .16 10492 22, .06 10345 60 6192 4500 0. .73 31 .13 11598 20, .32 9530 AVERAGE 6251 4509 0. .72 30. .20 11250 23. . 18 10975 ST. DEV. 191 170 0. ,01 MAX. 6700 4968 0. .76 34. ,25 12694 27. 43 12980 MIN. 5900 4240 0. ,69 25. ,44 9316 - 18. 99 8948 1 6804 5312 0. 78 2 6768 5252 0. 78 3 6876 5340 0. 78 4 6604 5152 0. 78 5 6524 5124 0. 79 6 6784 5272 0. 78 7 6596 5132 0. 78 8 6524 5104 0. .78 9 6612 5200 0. 79 10 6720 5304 0. 79 11 6632 5240 0. 79 A 12 6240 4920 0. 79 13 6284 4948 0. 79 14 6272 4944 0. 79 15 6080 4768 0. .78 16 6412 5080 0. 79 17 6192 4924 0. 80 18 6200 4884 0. 79 19 6184 4940 0. 80 20 6008 4768 0. 79 25. ,74 9434 28. 25 13394 21 6024 4820 0. 80 23. ,83 8681 27. 58 12984 22 6140 4884 0. 80 24. .43 8886 27. 73 13027 23 6084 4876 0. 80 21. ,88 7963 25. 45 11956 24 6096 4856 0. 80 22. ,39 8190 24. 93 11762 25 6192 4932 0. 80 24. ,24 8927 27. 68 13142 157 Table A. 1. (conf d.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 26 6128 4892 0. ,80 22. .47 8226 25, .99 12250 27 6200 4980 0. .80 20, .80 7627 24, .41 11506 28 6240 4980 0. .80 22, .84 8414 25, .52 12079 29 6020 4820 0. .80 27, .30 10037 29 .90 14120 30 6292 5024 0. .80 23, .77 8810 26 .14 12433 31 6312 5052 0. .80 18 .77 6997 21 .55 10302 32 6296 5056 0. .80 19, .14 7141 22 .27 10651 33 6284 5052 0. ,80 18, .17 6709 21, .36 10093 34 6096 4884 0. .80 18, .18 6716 21 .39 10104 35 6292 5024 0. .80 20, .98 7775 23 .09 10926 36 6184 4968 0, .80 19, .62 7285 21 .89 10364 37 6164 4796 0. .78 22 .38 8369 22 .64 10774 38 6304 5112 0. .81 19 .16 7265 21 .63 10428 39 6344 5116 0. .81 16, .21 6145 18 .71 9006 40 6156 4984 0. .81 18, .79 7108 20 .93 10043 41 6212 5008 0. .81 19, .17 7241 21, .36 10226 42 6200 5044 0. .81 18, .63 7062 20, .95 10049 A 43 6328 5124 0. .81 16, .84 6382 19, .28 9241 44 6400 5180 0. ,81 16, .80 6359 19, .16 9161 45 6240 5080 0. .81 17, .15 6455 19, .79 9395 46 6176 5016 0. ,81 19, .52 7351 21, .49 10204 47 6108 4948 0. ,81 20', .17 7554 22, .39 10559 48 6200 5044 0. ,81 15, .95 5968 18, .31 8618 49 5900 4732 0. 80 24. .26 9072 25. ,58 12028 50 5812 4656 0. ,80 25. .75 9569 26. , 75 12493 51 5664 4568 0. 81 27. ,15 10020 28. ,37 13157 52 5200 4240 0. ,82 33. .84 12632 35. .66 16722 53 5492 4452 0. 81 29. .14 11020 30. ,92 14688 54 5332 4276 0. ,80 34. .46 13001 35. .77 16957 55 5252 4180 0. 80 35. ,63 13414 35. ,91 16984 56 5532 4396 0. 79 29. ,75 11172 32. ,37 15276 57 5460 4336 0. 79 36. ,06 13530 35. ,51 16754 58 5344 4272 0. 80 37. ,08 13748 37. ,39 17440 59 5044 4080 0. 81 39. ,18 14597 39. ,99 18756 60 ' 4772 3808 0. 80 44. ,89 16726 45. ,07 21139 AVERAGE 6131 4886 0. 80 24. .21 9014 26. ,37 12468 ST. DEV. 438 324 0. ,01 MAX. 6876 5340 0. ,82 44, .89 16726 45. .07 21139 MIN. 4772 3808 0. ,78 15, .95 5968 18, .31 8618 F = Raw sludge feed C = Anoxic-aerobic L = Lime control A = Aerobic control Table A.2. Solids Data for 20 Day SRT at 10°C. DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 8460 6428 0. 76 2 7456 5724 0. 77 3 8564 6552 0. 77 4 7476 5700 0. 76 5 6228 4784 0. 77 6 8692 6612 0. 76 7 8660 6592 0. 76 8 8512 6508 0. 76 9 8364 6392 0. 76 10 9148 6964 0. 76 11 9648 7380 0. 76 12 7256 5500 0. 76 13 9132 6916 0. 76 14 9180 6907 0. 75 15 8640 6468 0. 75 16 7188 5440 0. 76 17 7800 5964 0. 76 18 7048 5400 0. .77 19 8220 6320 0. ,77 20 7996 6112 0. ,76 21 7508 5728 0. ,76 22 8188' 6232 0, .76 23 8028 6132 0. .76 24 9236 7060 0. .76 25 8160 6256 0. .77 26 7988 6144 0, .77 27 9116 6976 0, .77 28 9360 7188 0. .77 29 8300 6552 0 .79 30 9352 7184 0 .77 31 8112 6216 0. .77 32 8152 6628 0 .81 33 6812 5384 0 .79 34 8680 6796 0 .78 35 7908 6224 0 .79. 36 8712 6820 0 .78 37 9276 7240 0, .78 38 8256 6440 0. .78 39 8660 6760 0, .78 40 9224 7220 0. .78 41 8572 6624 0, .77 42 9488 7324 0, .77 43 9932 7696 0, .77 44 9460 7284 0. .77 45 9984 7732 0, .77 159 Table A.2. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 46 8640 6704 0. ,78 47 8852 6868 0. .78 48 9216 7120 0. .77 49 8032 6212 0. .77 50 8968 6972 0. .78 51 8972 6996 0. .78 52 8204 6364 0, .78 53 8604 6644 0. .77 54 8284 6360 0. .77 55 9632 7356 0. .76 56 8500 6548 0. .77 57 9412 7232 0, .77 58 9720 7456 0, .77 59 9548 7280 0. .76 AVERAGE 8555 6587 0.77 ST. DEV. 794 616 0.01 MAX. 9984 7732 0.81 MIN. 6228 4784 0.75 1 7080 5384 0 .76 2 7060 5436 0. .77 3 7084 5440 0. .77 4 7136 5448 0 .76 5 7032 5404 0. .77 6 7008 5380 0 .77 7 6924 5236 0 .76 8 7152 5456 0 .76 9 7216 5484 0, .76 10 6948 5288 0, .76 11 7156 5468 0 .76 12 7220 5452 0, .76 13 6992 5308 0, .76 14 7100 5364 0, .76 15 7072 5244 0. .74 16 7332 5516 0. .75 17 7096 5360 0. ,76 18 7124 5400 0. 76 19 7076 5324 0. 75 20 7120 5360 0. 75 21 7112 5304 0. 75 22 7060 5240 0. 74 23 7096 5312 0. 75 13. .95 5217 12, .79 6282 15 .27 5679 12 .12 5915 16, .87 6298 13, .44 6590 15 , 66 5827 13. , 34 6522 160 Table A.2. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 24 7232 5376 0. .74 14 .91 5608 11 .30 5581 25 7204 5392 0. .75 15 .27 5814 12 .27 6133 26 7124 5320 0, .75 13. .87 5259 11, .78 5863 27 7000 5224 0. .75 19 .12 7274 16 .21 8089 28 6928 5168 0. .75 21 .10 8068 18 .39 9227 29 7176 5196 0, .72 17 .91 6859 12 .21 6124 30 7180 5376 0, .75 17 .98 6898 14 .62 7339 31 6972 5204 0 .75 19 .90 7564 17 .22 8566 32 7004 5248 0, .75 17 .83 6836 14 .68 7339 33 7144 5340 0. .75 16 .23 6151 12, .99 6406 34 7264 5452 0, .75 12 .41 4699 10, .82 5318 35 7204 5424 0. .75 16 .87 6372 14, .26 6979 36 7320 5492 0. .75 14, .27 5449 10, .78 5328 37 7176 5396 0. ,75 17, .20 6637 13. .60 6779 38 7168 5428 0. .76 16, .18 6293 13. .72 6888 39 7024 5284 0. ,75 19, .26 7517 16. ,22 8164 40 7152 5400 0. 76 17. ,29 6805 15. 20 7706 41 7064 5304 0. ,75 18. .34 7266 16. ,18 8256 42 7188 5412 0. 75 18. ,34 7326 15. 71 8080 43 7064 5320 0. .75 21. .60 8729 19. .66 10220 44 7088 5352 0. 76 21. ,51 8707 19. 25 10019 45 7280 5488 0. .75 19. .24 7873 16. ,94 8911 46 7380 5584 0. 76 16. ,57 6810 14. 56 7686 47 6776 5096 0. 75 22. ,91 9408 20. .61 10866 48 6752 5064 0. 75 23. .82 9779 23. 74 12508 49 7508 5668 0. 75 17. ,08 6991 14. 86 7816 50 7156 5396 0. 75 18. ,40 7522 16. 33 8572 51 7048 5348 0. 76 20. ,10 8264 18. 29 9647 52 7208 5460 0. 76 19. ,50 8002 17. .97 9481 53 7256 5452 0. 75 21. ,89 9066 19. 55 10417 54 7228 5460 0. 76 21. ,12 8717 19. 03 10117 55 6816 5152 0. 76 27. .38 11394 25. 92 13919 56 6972 5276 0. 76 24. ,21 10057 22. 67 12160 57 7092 5352 0. ,75 23. ,60 9804 21. .35 11458 58 6948 5224 0. 75 24. ,08 10074 22. 11 11963 59 7476 5596 0. .75 20. .48 8600 17 . 83 9694 60 6976 5228 0. .75 24. .49 10284 22. .47 12218 AVERAGE 7112 ST. DEV. 143 MAX. 7508 MIN. 6752 5359 0.75 18.88 117 0.01 5668 0.77 27.38 5064 0.72 12.41 7507 16.41 8467 11394 25.92 13919 4699 10.78 5318 161 Table A.2. (cont'd.) { # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 7532 5676 0 .75 2 7376 5640 0 .76 3 7352 5608 0 .76 4 7388 5592 0 .76 5 7108 5412 0 .76 6 7180 5440 0 .76 7 7024 5244 0 .75 8 7220 5464 0 .76 9 7188 5400 0 .75 10 7116 5352 0 .75 11 7368 5524 0 .75 12 7196 5356 0 .74 13 7192 5380 0 .75 14 7400 5520 0 .75 15 7276 5352 0 .74 16 7296 5424 0 .74 17 7184 5340 0. .74 18 7204 5364 0 .74 19 7164 5272 0. .74 20 7280 5396 0, .74 17 .25 6452 14 .46 7099 21 7160 52.92 0. .74 18 .19 6765 13 .74 6709 22 7180 5272 0. ,73 18 .63 6956 13. .71 6724 23 6956 5156 0. .74 20 .33 7566 16, .86 8242 24 6960 5132 0. ,74 19 .07 7176 14, .56 7194 25 7056 5192 0. ,74 19 . 68 7491 15. ,30 7645 26 7032 5188 0. ,74 16 .54 6274 13, .43 6686 27 7016 5180 0. ,74 20, .44 7777 16. ,23 8098 28 7024 5160 0. ,73 20, .42 7808 16. .29 8171 29 7088 5188 0. ,73 19. .49 7464 14. ,69 7366 30 7176 5256 0. 73 21. .33 8182 16. ,72 8393 31 7200 5308 0. 74 17. .31 6578 13. ,68 6806 32 7096 5248 0. 74 19, .44 7453 15. ,41 7705 33 7264 5360 0. 74 18. .92 7167 14. 66 7228 34 7160 5292 0. 74 17, .44 6602 14. ,30 7030 35 7096 5264 0. 74 18, .94 7156 15. 05 7368 36 7244 5356 0. 74 17 , .11 6534 12. ,71 6281 37 7228 5356 0. 74 18. .29 7056 13. 90 6926 38 7140 5328 0. 75 17. .99 6995 15. ,13 7596 39 7148 5264 0. ,74 21, .16 8257 16. ,65 8381 40 7180 5348 0. 74 19, .00 7476 15. ,51 7867 41 7108 5288 0. 74 20, .16 7986. 17. ,16 8754 42 7340 5436 0. ,74 16, .72 6680 12. ,37 6360 43 7324 5436 0. 74 17, .12 6922 13. ,35 6941 44 7352 5460 0. ,74 17, .55 7106 14. ,02 7298 45 7480 5560 0. ,74 16, .65 6815 12. ,94 6806 46 7548 5604 0. 74 15, .93 6546 12. ,01 6343 47 7484 5520 0. ,74 16 .55 6796 12. .43 6556 162 Table A.2. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 48 7416 5468 0 .74 17 .45 7163 13.64 7187 49 7496 5556 0 .74 16 .68 6830 13.37 7032 50 7396 5504 0 .74 17 .90 7316 14.47 7595 51 7484 5584 0 .75 16 .12 6628 12.54 6616 52 7384 5488 0 .74 18 .82 7724 15.45 8153 53 7504 5580 0 .74 17 .09 7076 13.65 7274 L 54 7440 5496 0 .74 17 .49 7220 13.30 7072 55 7364 5480 0 .74 19 .57 8143 16.49 8852 56 7464 5536 0 .74 18 .47 7672 14.97 8027 57 7420 5508 0 .74 18 .35 7624 14.43 7746 58 7396 5444 0 .74 18 .87 7894 15.34 8300 59 7568 5588 0 .74 18 .08 7592 13.98 7601 60 7604 5612 0 .74 16 .69 7009 12.55 6826 AVERAGE 7267 5401 0 .74 18 .27 7218 14.43 7387 ST. DEV. 164 139 0 .01 MAX. 7604 5676 0 .76 21 .33 8257 17.16 8852 MIN. 6956 5132 0 .73 15 .93 6274 12.01 6281 1 7084 5384 0. .76 2 6920 5308 0, .77 3 6960 5340 0. .77 4 6920 5296 0, .77 5 6916 5304 0. .77 6 6868 5296 0. , 77 7 8 6844 6992 5216 5380 0. 0. .76 77 9 7020 5392 0. 77 10 7040 5416 0. 77 11 6980 5400 0. 77 A 12 6948 5340 0. 77 13 7144 5508 0. 77 14 6956 5344 0. 77' 15 7036 5368 0. 76 16 7068 5408 0. 77 17 6888 5304 0. 77 18 6836 5312 0. 78 19 6688 5160 0. 77 20 6952 5368 0. 77 14. 55 5442 16.65 8174 21 6808 5240 0. 77 15. 02 5587 16.08 7852 22 6976 5352 0. 77 14. 05 5246 14.86 7286 23 6844 5268 0. 77 14. 46 5382 15.78 7712 24 6848 5292 0. 77 15. 14 5695 16.63 8214 25 6884 5312 0. 77 15. 67 5966 16.60 8299 163 Table A.2. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 26 6580 5112 0. .78 17, .41 6601 19, .80 9854 27 6576 5108 0, .78 20, .39 7756 22, .01 10984 28 6532 5080 0, .78 21, .68 8290 23, .54 11808 29 6988 5444 0 .78 16 .41 6283 18 .31 9182 30 6768 5256 0. .78 19, .37 7429 20. .49 10285 31 7012 5452 0. .78 14 .54 5528 16 .40 8159 32 7004 5456 0 .78 17 .77 6816 19 .27 9635 33 6984 5436 0 .78 14 .55 5514 16 .18 7979 34 7068 5516 0 .78 13 .45 5093 15 .81 7771 35 6996 5440 0 .78 15 .07 5694 16 .73 8188 36 7140 5536 0 .78 12 .75 4870 13 .52 6679 37 7156 5536 0 .77 13 .56 5231 13 .31 6634 38 7104 5512 0 .78 12 .12 4715 12 .63 6340 39 7096 5464 0 .77 16 .12 6292 15 .85 7981 40 7008 5400 0 .77 15 .83 6230 15 .77 7997 41 7108 5484 0 . 77 16 .64 6594 16 .92 8634 42 7216 5548 0 .77 14 .96 5975 14 .61 7512 A 43 7264 5608 0 .77 15 .16 6126 14 .80 7693 44 7308 5636 0 .77 14 .92 6042 14 .55 7574 45 7384 5696 0 .77 11 .75 4810 10 .82 5692 46 7472 5812 0 .78 9 .85 4048 9 .60 5068 47 7296 5624 0 .77 11 .74 4820 10 .55 5564 48 7480 5776 0 .77 14 .28 5863 13 .04 6869 49 7496 5808 0 .77 10 .58 4332 9 .92 5220 50 7288 5644 0 . 77 15 .44 6312 14 .60 7661 51 7480 5808 0 .78 13, .33 5479 12 .47 6578 52 7384 5736 0 .78 13 .72 5628 13 .15 6936 53 7268 5636 0. . 78 16. .97 7026 16. .12 8588 54 7172 5544 0, .77 16, .92 6983 16, .14 8582 55 7332 5716 0. .78 16. .30 6784 16. .58 8903 56 7344 5720 0. .78 15. .94 6623 16, .41 8802 57 7400 5752 0. ,78 14. ,97 6220 15. .13 8122 58 7392 5740 0. 78 14. 91 6240 15. 66 8474 59 7524 5828 0. 77 12. 80 5375 13. 41 7292 60 7540 5844 0. 78 13. 45 5650 14. 05 7637 AVERAGE 7076 5467 0. 77 14. 99 5917 15. 48 7913 ST. DEV. 242 197 0. 00 MAX. 7540 5844 0. 78 21. 68 8290 23. 54 11808 MIN. 6532 5080 0. 76 9. 85 4048 9. 60 5068 F = Raw sludge feed C = Anoxic-aerobic L = Lime c o n t r o l A = Aerobic c o n t r o l Table A. 3. Solids Data for 15 Day SRT at 20° C DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 8420 2 7872 3 7844 4 7984 5 7676 6 8620 7 6908 8 5456 9 5456 10 6800 11 7640 12 8440 13 7660 14 7412 15 7816 16 8428 17 5572 18 7364 19 . 8112 20 8296 21 7872 F 22 8180 23 8300 24 6700 25 6936 26 12584 27 7664 28 7828 29 8132 30 7544 31 5532 32 6912 33 8104 34 7372 35 8940 36 8804 37 7056 38 6396 39 5612 40 5668 41 6352 42 8500 43 8164 44 8248 AVERAGE 7572 ST. DEV. 1233 MAX. 12584 MIN. 5456 6500 0.77 5992 0.76 6152 0.78 6176 0.77 5888 0.77 6656 0.77 5336 0.77 4232 0.78 4232 0.78 5352 0.79 5952 0.78 6476 0.77 5848 0.76 5700 0.77 5996 0.77 6456 0.77 4328 0.78 5704 0.77 6232 0.77 6388 0.77 6024 0.77 6208 0.76 6284 0.76 5244 0.78 5296 0.76 9640 0.77 5836 0.76 5960 0.76 6172 0.76 5788 0.77 4272 0.77 5324 0.77 6232 0.77 5580 0.76 6840 0.77 6768 0.77 5376 0.76 4968 0.78 4432 0.79 4476 0.79 5008 0.79 6344 0.75 6216 0.76 6260 0.76 5821 0.77 918 0.01 9640 0.79 4232 0.75 165 Table A.3. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 6236 4704 0. .75 2 6128 4604 0. 75 3 6032 4592 0. ,76 4 6248 4716 0. 75 5 6304 4772 0. 76 6 6288 4768 0. 76 7 6504 4856 0. 75 8 6420 4828 0. 75 9 6392 4824 0. .75 10 6244 4716 0. 76 11 6080 4604 0. ,76 12 6128 4644 0. ,76 13 6200 4648 0. ,75 14 6196 4648 0. .75 15 6332 4764 0. .75 17. .09 5947 14. .86 6698 16 6276 4740 0. .76 15. ,59 5374 14. .03 6265 17 6376 4836 0, .76 11, .74 3967 9, .31 4070 18 6364 4812 0, .76 13, .65 4588 11, .74 5113 19 6236 4700 0. .75 16, .72 5625 14 .39 6273 20 6364 4820 0 .76 14, .96 5062 12, .85 5633 21 6252 4564 0. .73 20, .70 6954 16, .81 7317 C 22 6276 4668 0. .74 19 .41 6586 16 .50 7269 23 6116 4588 0. .75 22 .90 7959 20 .63 9320 24 6112 4608 0, .75 21 .85 7682 19 .84 9065 25 6204 4656 0 .75 19 .13 6724 16 .62 7600 26 6236 4684 0. .75 22, .11 7991 19 .74 9294 27 6240 4684 0. .75 21 .67 7743 20 .07 9348 28 6060 4524 0 .75 24 .52 9267 22 .52 11104 29 6348 4724 0, .74 23, .69 8532 21, .19 9960 30 6268 4704 0 .75 23 .51 8493 21 .37 10076 31 6056 4588 0. .76 25, .41 9038 23, .67 10985 32 6140 4636 0. .76 25, .26 9084 23, .51 11039 33 6260 4684 0. .75 23, .18 8387 20, .93 9889 34 6124 4572 0. .75 26, .64 9569 23, .90 11222 35 6056 4500 0. ,74 24. ,31 8774 24. ,02 11339 36 6028 4516 0, .75 26, .43 9619 25, .46 12113 37 6148 4580 0. ,74 23. ,45 8457 21. ,29 10035 38 6380 4808 0. .75 18, , 56 6595 16, .72 7751 39 6028 4504 0. ,75 23. ,92 8423 21. ,80 10014 40 5960 4464 0. ,75 24. 75 8580 22. ,64 10219 41 6204 4632 0. ,75 18. ,11 5957 15. ,44 6604 42 6132 4572 0. 75 17. 49 6158 15. 38 7064 43 6236 4656 0. 75 19. 26 6406 17. 56 7618 44 5940 4384 0. 74 24. 23 8111 20. 96 9151 45 6168 4592 0. 74 18. 54 6261 14. 87 6534 AVERAGE 6207 4660 0. 75 20. 93 7352 18. 73 8580 ST. DEV. 126 107 0. 01 MAX. 6504 4856 0. 76 26. 64 9619 25. 46 12113 MIN. 5940 4384 0. 73 11. 74 3967 9. 31 4070 166 Table A.3. (cont'd.) MAX. MIN. Y # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 6676 4908 0 .74 2 6784 4856 0. .72 3 6576 4740 0 .72 4 6668 4836 0. .73 5 6864 4940 0, .72 6 6704 4860 0. .72 7 7220 5052 0. .70 8 6660 4784 0. .72 9 6420 4652 0. .72 10 6296 4580 0. .73 11 6308 4608 0. .73 12 6420 4676 0. ,73 13 6288 4556 0. .72 14 6432 4664 0. ,73 15 6332 4588 0. ,72 23, .11 7995 16, .53 7406 16 6464 4672 0. .72 20, .98 7256 16. .41 7350 17 6488 4728 0. .73 16. .54 5610 11. .75 5157 18 6216 4520 0. .73 21 .77 7342 16 .69 7293 19 6252 4504 0. .72 24, .34 8218 19 .36 8470 20 6448 4632 0. .72 21. .48 7293 15 .34 6749 21 6660 4752 0, .71 22 .30 7515 18 .98 8291 22 6680 4816 0, .72 17 .52 5966 12 .52 5536 23 6120 4352 0. .71 25 .67 8952 19 .43 8810 24 6320 4504 0, .71 22 .88 8072 16 .15 7403 25 6264 4512 0 .72 23 .25 8197 17 .17 7878 26 6120 4400 0 .72 29 .50 10835 , 23 .96 11467 27 6420 4636 0 .72 23 .19 8459 18 .01 8565 28 6680 4612 0 .69 25 .39 9274 16 .33 7779 29 6608 4736 0 .72 22 .43 8234 16 .34 7829 30 6536 4724 0, .72 23 .68 8672 18 . 54 8862 31 6508 4716 0, .72 22 .84 8165 17 .15 7998 32 6444 4620 0, .72 21 .95 7934 15 .48 7304 33 6440 4616 0, .72 22 .10 8035 16 .32 7750 34 6268 4516 0, .72 25 .31 9138 20 .47 9656 35 6400 4616 0. .72 26 .03 9445 21 .95 10413 36 6400 4604 0. .72 28. .04 10258 23. .03 11010 37 6512 4652 0, .71 19 .09 6918 13 .92 6595 38 6152 4424 0. ,72 24, .20 8643 19, .70 9181 39 6280 4476 0. ,71 22. .79 8066 16, .59 7658 40 6200 4452 0. ,72 20. .63 7234 14, .88 6792 41 6416 4628 0. ,72 17. .01 5650 10, ,85 4685 42 6624 4632 0. ,70 17. .02 5686 12, .07 5250 43 6512 4696 0. 72 18. ,24 6115 13. ,04 5691 44 6428 4592 0. 71 20. 15 6760 13. 46 5882 45 6388 4612 0. 72 20. ,28 6847 14. ,30 6285 3E 6464 4650 0. 72 22. 25 7832 16. 67 7645 iV. 210 143 0. 01 7220 5052 0. 74 29. 50 10835 23. 96 11467 6120 4352 0. 69 16. 54 5610 10. 85 4685 Table A.3. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 5840 4612 0 .79 2 5916 4636 0 .78 3 5728 4504 0 .79 4 6016 4732 0 .79 5 6028 4700 0 .78 6 6096 4792 0 .79 7 5936 4624 0 .78 8 5892 4596 0. .78 9 5584 4384 0 .79 10 5728 4536 0. .79 11 5856 4608 0, .79 12 5532 4368 0, .79 13 5656 4420 0, .78 14 5664 4424 0. .78 15 5800 4560 0. ,79 21. .70 7509 22 .62 10133 16 6104 4792 0. .79 17, .85 6171 19 .33 8662 17 5804 4604 0. ,79 17. .26 5854 19. .28 8459 18 5868 4604 0. ,78 20, .76 7003 21, .87 9555 19 5796 4540 0. ,78 21. .61 7294 23. .31 10198 20 6032 4736 0. ,79 20, .19 6856 21. .45 9437 21 5840 4544 0. ,78 20. .31 6846 21. .59 9432 A 22 5820 4532 0. ,78 20, .96 7136 22. .27 9843 23 5928 4648 0. ,78 17, .11 5968 18. .68 8470 24 5768 4516 0. .78 22. .75 8024 23, .38 10718 25 5660 4444 0. ,79 25, .25 8902 26. .62 12216 26 5624 4412 0. .78 25. .07 .9208 26, .24 12558 27 5772 4556 0. .79 22, .82 8325 25, .25 12008 28 5864 4568 0. ,78 22. .63 8262 24. .12 11488 29 6116 4768 0. .78 21, .60 7930 22, .75 10899 30 6048 4780 0. ,79 24. .79 9078 27, .03 12923 31 6092 4828 0. ,79 18, .95 6774 20, .81 9706 32 5920 4664 0. ,79 22, .50 8133 24, .61 11611 33 5888 4612 0. .78 22, .74 8269 24, . 56 11659 34 6052 4768 0. ,79 22. .60 8157 24, .78 11693 35 5492 4312 0. .79 27, .81 10091 30, .30 14374 36 5900 4628 0. ,78 22, .93 8387 25, .42 12155 37 5888 4600 0. ,78 24, .53 8891 26, .18 12398 38 5884 4644 0. ,79 20. .47 7310 23. .00 10718 39 5612 4432 0. 79 22. ,21 7859 24, .54 11330 40 5668 4476 0. 79 20. .14 7062 22. .49 10267 41 6352 5008 0. 79 7. ,96 2643 9. ,89 4267 42 5884 4528 0. 77 17. ,39 5810 18. ,20 7917 43 6044 4772 0. 79 16. ,61 5566 19. 55 8531 44 5484 4312 0. 79 25. 68 8616 26. ,97 11782 45 6024 4760 0. 79 19. 06 6434 20. 68 9088 AVERAGE 5856 4597 0. 79 21. 10 7431 22. 83 10468 ST. DEV. 183 147 0. 00 MAX. 6352 5008 0. 79 27. 81 10091 30. 30 14374 MIN. 5484 4312 0. 77 7. 96 2643 9. 89 4267 168 Table A.4. Solids Data for 15 Day SRT at 10°C. DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg r 7600 5804 0. .76 2 7560 5772 0. .76 3 7372 5596 0. .76 4 7516 5768 0. .77 5 7520 5752 0. .76 6 7656 5800 0. .76 7 ' 7756 5896 0. .76 8 7804 5932 0, .76 9 7804 5928 0. .76 10 7728 5860 0, .76 11 7752 5856 0. .76 12 7824 5920 0. .76 13 7724 5868 0. .76 14 7616 5768 0. .76 15 7812 5968 0. .76 16 7572 5768 0. .76 17 7756 5892 0, .76 18 7760 5888 0. .76 19 7772 5916 0. .76 20 7700 5872 0. ,76 21 7720 5856 0. ,76 22 7872 5980 0. .76 23 7844 5916 0. ,75 24 7864 5940 0. .76 14, .49 6098 12. .77 6923 16. .22 6770 14. ,33 7706 11. .97 5003 10, .26 5534 13. ,88 5782 11. ,29 6069 13. ;22 5514 11. .28 6082 14. .37 5987 13. ,41 7229 15. ,85 6600 14. .20 7653 14. ,31 5942 12. ,82 6898 15. ,18 6307 13. ,16 7085 AVERAGE 7664 ST. DEV. 129 MAX. 7824 MIN. 7372 5829 0.76 15.36 91 0.00 5968 0.77 16.22 5596 0.76 14.49 6434 13.55 7314 6770 14.33 7706 6098 12.77 6923 169 Table A.4. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 7464 5620 0. .75 2 7404 5600 0, .76 3 7488 5632 0. .75 4 7424 5604 0. .75 5 7300 5500 0 .75 6 7616 5720 0. .75 7 8 7580 7528 5712 5696 0. 0. .75 .76 9 7660 5768 0. .75 10 7748 5864 0, .76 11 7656 5736 0. .75 L 12 7732 5804 0. .75 13 7780 5868 0. .75 14 7532 5688 0. ,76 15 7712 5816 0. .75 15, .80 6650 13, .42 7275 16 7468 5640 0. .76 17, .32 7227 14, .78 7949 17 7412 5600 0. ,76 18. .52 7741 16. ,55 8925 18 7444 5576 0. .75 18, .20 7579 15, .28 8216 19 7560 5696 0. ,75 14. .99 6253 12. .76 6885 20 7536 5684 0. ,75 18, .10 7541 16 , .33 8802 21 7520 5672 0. .75 18. .13 7547 16. .13 8690 22 7496 5624 0. ,75 18. .48 7678 15. ,75 8470 23 7788 5816 0. .75 16, .63 6909 13, .82 7442 24 7724 5780 0. ,75 AVERAGE 7568 5704 0. ,75 16, .56 6938 14. .10 7612 ST. DEV. 135 100 0. .00 MAX. 7780 5868 0. ,76 17, .32 7227 14. .78 7949 MIN. 7300 5500 0. .75 15, .80 6650 13 . 42 7275 170 Table A.4. (cont'd.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED in mg 1 7612 5916 0. .78 2 7496 5852 0. ,78 3 7368 5752 0. ,78 4 7328 5716 0. ,78 5 7416 5792 0. .78 6 7552 5852 0. .77 7 7704 6008 0. .78 8 7612 5948 0. .78 9 7852 6116 0. .78 10 7836 6112 0. .78 11 7800 6100 0. ,78 A 12 7752 6020 0. .78 13 7756 6052 0. .78 14 7660 5988 0. .78 15 7660 6004 0. .78 13 .92 5858 15 .06 8163 16 7720 6024 0. .78 11. .89 4960 12 .34 6635 17 7744 6020 0. .78 10, .52 4398 10 .69 5763 18 7600 5892 0. .78 11. .37 4734 11. .43 6144 19 7700 5984 0. .78 11. .00 4586 11, .28 6086 20 7772 6060 0. ,78 10, .44 4352 11. .69 6299 21 7684 5984 0. .78 13, .58 5654 14, .21 7656 22 7800 6064 0. 78 11. .30 4696 11. , 68 6285 23 7836 6056 0. 77 13. .74 5707 13. .85 7454 24 7932 6144 0. 77 AVERAGE 7633 5953 0. 78 12. ,90 5408.80 13 . 70 7399.20 ST. DEV. 158 123 0. 00 MAX. 7852 6116 0. 78 13. 92 5858 15. 06 8163 MIN. 7328 5716 0. 77 11. 89 4960 12. .34 6635 171 Table A.5. Solids Data for 10 Day SRT at 20 C, DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED in mg 1 7096 5492 0 .77 2 7136 5472 0. .77 3 7224 5540 0 .77 4 6992 5332 0. .76 5 6996 5388 0. .77 6 7040 5344 0 .76 7 6884 5216 0, .76 8 7368 5616 0 .76 9 7072 5444 0. .77 10 7292 5540 0, .76 11. .86 4430 9. .37 4534 11 7112 5456 0. .77 11. .14 4078 10, .22 4843 12 6852 5232 0, .76 15. .30 5532 13. .91 6509 13 6900 5244 0. .76 12. .49 4534 11, .09 5206 14 6992 5312 0. .76 12, .47 4531 10 .03 4714 C 15 6868 5200 0. .76 13, .99 5093 12, .63 5957 16 7160 5468 0. .76 7. .05 2558 6 , .50 3055 17 6920 5284 0. .76 16, .12 5822 15, . 14 7070 18 6928 5256 0. ,76 14. ,08 5071 11. .53 5369 19 6704 5144 0. .77 17. .74 6365 17, .46 8105 20 6780 5168 0. 76 16. ,76 6026 14. .89 6919 21 6708 5104 0. ,76 15. .38 5578 13, .61 6370 22 6804 5172 0. 76 15. , 36 5621 13. .79 6509 23 6880 5268 0. ,77 14, .61 5330 13, .64 6408 24 7116 5380 0. 76 11. ,57 4260 9. .61 4550 25 7128 5452 0. 76 15. ,40 5738 13. ,62 6509 26 6724 5188 0. .77 16. .36 6041 15. .25 7205 27 6924 5288 0. 76 14. ,97 5573 13. ,37 6360 28 6908 5276 0. .76 14. .37 5412 11. .78 5666 29 6816 5256 0. 77 14. .85 5592 13. .63 6547 30 6968 5368 0. ,77 12. .91 4925 11. .78 5736 AVERAGE 6976 5330 0. ,76 14. .04 5148 12, .52 5911 ST. DEV. 166 131 0. 00 MAX. 7368 5616 0. ,77 17, .74 6365 17, .46 8105 MIN. 6704 5104 0. ,76 7, .05 2558 6. .50 3055 Table A.5. (cont'd.) 172 DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED in mg REDUCED i n mg 1 6972 5272 0 .76 • 2 7036 5280 0, .75 3 7088 5264 0, .74 4 7016 5212 0 .74 5 6856 5096 0 .74 6 6980 5148 0 .74 7 8 6864 6912 5080 5092 0 0 .74 .74 9 7056 5272 0 .75 10 7096 5248 0. .74 16. .91 6314 11. .78 5700 11 6996 5236 0, .75 15, .57 5698 11, .97 5669 12 6860 5100 0, .74 16. .83 6084 13. .49 6310 13 6820 5056 0 .74 17, .37 6305 13, .76 6461 14 6816 5032 0 .74 16. .28 5918 12, .09 5681 L 15 6776 4968 0 .73 18 .50 6732 14, .57 6871 16 7012 5180 0. .74 13, .63 4949 9, .78 4598 17 6988 5152 0, .74 13, .70 4946 9, .95 4649 18 6924 5148 0. .74 16, .42 5914 12, .34 5748 19 6532 4876 0, .75 20, .92 7505 18. .33 8506 20 6584 4836 0. .73 22, .27 8006 17, .10 7944 21 6504 4828 0. .74 21. ,47 7783 17. ,61 8239 22 6480 4800 0, .74 22, .43 8210 18. . 58 8770 23 6712 5032 0. ,75 18. ,03 6581 15. .35 7210 24 6628 4904 0. ,74 19. ,99 7356 16. .81 7963 25 6744 5036 0. ,75 22. , 14 8249 19. .12 9137 26 6688 4988 0. ,75 22. ,05 8138 18. 99 8974 27 6772 5048 0. ,75 21. .82 8119 17. 93 8525 28 6832 5052 0. ,74 18. ,51 6972 13. 33 6410 29 6732. 5020 0. ,75 18. ,12 6821 14. 87 7142 30 6768 5084 0. 75 17. ,69 6749 14. 34 6982 AVERAGE 6835 5078 0. 74 18. 60 6826 14. 86 7023 ST. DEV. 172 135 0. ,01 MAX. 7096 5280 0. 76 22. ,43 8249 19. 12 9137 MIN. 6480 4800 0. ,73 13, .63 4946 9 . 78 4598 \ 173 Table A. 5 . ( con f d.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 6924 5348 0. ,77 2 6912 5340 0. ,77 3 6912 5340 0. ,77 4 6820 5268 0. ,77 5 6736 5244 0. ,78 6 6896 5316 0. .77 7 8 6720 7056 5212 5492 0. 0. .78 .78 9 6924 5416 0. .78 10 6792 5288 0, .78 15, .40 5750 16 .43 7946 11 6808 5344 0, .78 12, .60 4610 14, .46 6847 12 6436 5048 0, .78 16, .93 6120 18 .75 8772 13 6540 5128 0. .78 15, .10 5479 17, .04 8002 14 6600 5176 0 .78 14 .20 5160 15 .55 7306 A 15 6416 5008 0, .78 18, .64 6782 20 .61 9720 16 6680 5224 0. .78 13. .31 4834 15. .03 7068 17 6620 5212 0 .79 17 .69 6386 19, .69 9197 18 6576 5148 0, .78 17, .82 6418 18, .93 8815 19 6628 5240 0 .79 14, .13 5069 16, .68 7740 20 6492 5120 0. .79 17, .55 6312 19, .10 8875 21 6544 5160 0 .79 12 .98 4706 14 .59 6826 22 6436 5048 0, .78 16, .94 6202 18, .00 8496 23 6428 5116 0 .80 16 .39 5981 18 .65 8762 24 6496 5144 0, .79 13, .96 5138 16, .24 7690 25 6668 5284 0. .79 15, .79 5882 17, .84 8525 26 6676 5248 0, .79 15, .35 5666 16, .02 7570 27 6540 5148 0. .79 16, .72 6223 17, .83 8479 28 6620 5164 0. .78 18, .90 7121 18, .35 8827 29 6232 4932 0. ,79 21. ,14 7961 21. ,89 10517 30 6352 4780 0. .75 25. ,75 9826 22. .26 10838 AVERAGE 6649 5198 0. ,78 16. ,54 6077 17. ,81 8420 ST. DEV. 196 143 0. ,01 MAX. 7056 5492 0. ,80 25. ,75 9826 22. ,26 10838 MIN. 6232 4780 0. .75 12. ,60 4610 14. 46 6826 174 Table A.6. Solids Data for 10 Day SRT at 10 C. DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg ' 1 7984 6100 0. .76 2 7904 6052 0. ,77 3 7764 5956 0. ,77 4 7732 5896 0. ,76 5 7672 5884 0. ,77 6 7568 5680 0. .75 7 8 7592 7676 5736 5844 0. 0. .76 .76 9 7700 5836 0. .76 10 7712 5880 0. .76 8, .98 3355 8. .55 4186 11 7816 5928 0. .76 9 .11 . 3454 7. .85 3895 12 7804 5864 0, .75 8 .57 3240 6, .19 3067 13 7948 6008 0, .76 5 .80 2203 4, .49 2242 14 8020 6032 0, .75 6 .79 2630 4, .52 2299 15 7792 5796 0 .74 9 .77 3885 8 .44 4418 16 8012 5988 0, .75 5 .59 2181 4, .03 2074 17 7584 5716 0. .75 10 .59 4096 9, .10 4634 C 18 7572 5728 0 .76 8 .90 3381 8, .06 4034 19 7348 5516 0. .75 13 .35 5066 11. .16 5575 20 7564 5672 0 .75 10 .77 4031 8 .73 4301 21 7568 5644 0. .75 8 .21 2994 6. .40 3070 22 7568 5660 0 .75 11 .72 4324 9 .55 4634 23 7960 6108 0 .77 3 .43 1250 4, .27 2045 24 7396 5532 0. .75 10 .08 3682 9, .33 4469 25 7448 5556 0 .75 12 .93 4706 11. .33 5395 26 7452 5596 0, .75 9 .49 3492 7, .52 3619 27 7456 5580 0. .75 11 .62 4349 8, .98 4390 28 7696 5756 0. .75 7. .99 3077 5. .80 2918 29 7700 5776 0, .75 10 .03 3876 8, .00 4027 30 7672 . 5760 0. .75 11. .19 4394 9. .71 4968 31 7804 5868 0. ,75 10. .11 4001 8. , 54 4397 32 7880 5968 0. .76 15, .43 6142 11. .82 6084 33 7784 5880 0. 76 7. .37 2902 5. .23 2652 34 7740 5880 . 0. ,76 6. .83 2678 5. .33 2688 35 7892 5984 0. 76 5. ,15 2018 2. 75 1382 36 7728 5840 0. 76 7 , .69 3046 5. 24 2659 37 7600 5796 0. 76 11. ,06 4394 •9. 60 4877 AVERAGE 7706 5819 0. 76 9. 23 3530 7. 52 3750 ST. DEV. 173 157 0. 01 MAX. 8020 6108 0. 77 15. 43 6142 11. 82 6084 MIN. 7348 5516 0. 74 3. 43 1250 2. 75 1382 175 Table A. 6 . ( c o n f d. ) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED i n mg 1 7856 5936 0. .76 2 7800 5920 0 .76 3 7528 5716 0, .76 4 7748 5860 0. .76 5 7488 5708 0 .76 6 7312 5516 0. .75 7 7400 5532 0. .75 8 7396 5568 0, .75 9 7424 5560 0. .75 10 7404 5608 0 .76 13 .83 5167 13 .15 6434 11 7500 5632 0 .75 14. .98 5681 12, .99 6449 12 7776 5804 0. .75 8, .89 3360 6. .17 3055 13 7668 5768 0 .75 12 .17 4627 10 .59 5280 14 7752 5804 0 .75 10 .99 4257 8 .32 4236 15 7736 5720 0 .74 11, .60 4612 8 .74 4574 16 7764 5788 0 .75 8 .80 3434 7 .31 3761 17 7516 5592 0 .74 11 .41 4413 9 .11 4639 L 18 7396 5516 0 .75 11 .02 4187 9 .29 4649 19 7064 5224 0 .74 16 .82 6386 13 .31 6650 20 7144 5324 0 .75 14 .93 5589 12 .61 6211 21 7060 ' 5228 0 .74 17 .69 6448 15 .32 7351 22 7168 5312 0 .74 17 .52 6462 14 .38 6979 23 6972 5172 0 .74 20 .33 7406 17 .57 8414 24 7072 5240 0 .74 18 .96 6924 17 .03 8160 25 7128 5268 0 .74 20 .08 7308 16 .94 8069 26 7192 5340 0 .74 17 .36 6391 14 .59 7020 27 7264 5388 0, .74 17. .04 6377 13. .93 6809 28 7328 5448 0 .74 13 .97 5378 11, .66 5861 29 7544 5584 0, .74 13, .17 5086 9. .55 4805 30 7660 5680 0. .74 11. .11 4363 8 , .03 4109 31 7756 5800 0. .75 10, .35 4097 8. .01 4126 32 7584 5648 0. .74 10. .56 4205 7. ,21 3710 33 7588 5652 0. .74 9, .79 3852 6. .28 3187 34 7552 5656 0. , 75 9. ,15 3588 6. ,18 3118 35 7408 5572 0. 75 11. 03 4322 8. 05 4046 36 7564 5676 0. .75 10. ,59 4190 7. ,40 3754 37 7464 5620 0. 75 12. 34 4906 9. 28 4714 AVERAGE 7459 5578 0. 75 13. 45 5108 10. 82 5363 ST. DEV. 239 204 0. 01 MAX. 7856 5936 0. 76 20. 33 7406 17. 57 8414 MIN. 6972 5172 0. 74 8. 80 3360 6. 17 3055 176 Table A. 6 . (conf d.) DAY # TSS TVSS TVSS/TSS % TVSS TVSS % TSS TSS mg/L mg/L REDUCED i n mg REDUCED in mg 1 7828 5944 0 .76 2 7788 5952 0 .76 3 7496 5720 0, .76 4 7472 5680 0, .76 5 7532 5752 0. .76 6 7364 5628 0. .76 7 8 7364 7600 5520 5772 0, 0. .75 .76 9 7452 5660 0. ,76 10 7492 5736 0. ,77 11, .20 4183 11, .69 5719 11 7616 5820 0. ,76 11 .53 4373 11, .23 5575 12 7832 5916 0. ,76 6 .07 2292 4, .81 2381 .13 7724 5904 0. ,76 5, .87 2232 6, . 19 3089 14 7696 5828 0. ,76 9 .70 3755 8, .85 4505 15 7728 5800 0. ,75 10, .47 4161 8, .85 4634 16 7912 6000 0. ,76 3, .55 1386 4, .47 2299 17 7516 5708 0. .76 10 .76 4161 10 .77 5484 A 18 7456 5708 0. ,77 7 .53 2862 8 .32 4164 19 7376 5596 0. ,76 10 .50 3986 9, .69 4843 20 7380 5632 0. .76 10 .21 3825 10 .03 4939 21 7300 5528 0. .76 11 .55 4209 11 .71 5621 22 7396 5600 0. .76 11 .75 4334 10 .75 5218 23 7296 5564 0. ,76 10 .51 3827 10, .95 5244 24 7304 5572 0. .76 10 .56 3857 11 .81 5657 25 7472 5672 0. .76 12 .11 4406 11 .80 5618 26 7424 5656 0. .76 9 .18 3379 8 .95 4303 27 7488 5708 0. .76 9 .82 3674 8 .93 4366 28 7420 5644 0. .76 11 .69 4498 11 .34 5702 29 7764 5916 0. ,76 7 .84 3029 6 .91 3478 30 7676 5836 0, .76 8 .67 3406 8 .14 4162 31 7688 5908 0. ,77 8 .77 3470 9 .31 4795 32 7652 5880 0. ,77 8, .77 3492 8, .23 4236 33 7724 5960 0. 77 6, .03 2374 5, .65 2866 34 7540 5840 0. 77 8, .61 3374 8, .93 4502 35 7512 5828 0. 78 8. .26 3238 8. .37 4207 36 7536 5824 0. 77 9. ,80 3878 9. .50 4814 37 7612 5916 0. 78 7. .49 2976 7. ,82 3972 AVERAGE 7552 5760 0. 76 9. ,24 3523 9. .07 4514 ST. DEV. 162 134 0. 01 MAX. 7912 6000 0. 78 12. 11 4498 11. 81 5719 MIN. 7296 5520 0. 75 3. 55 1386 4. 47 2299 APPENDIX B Duplicate Solids Determinations 178 Table B . l . Multiple (n=9) Solids Determinations on  a Single Sample at 20°C. Date/Sample TSS TVSS TVSS/TSS mg/L mg/L November 20/anoxic-aerobic 6076 4680 0.77 6040 4628 0.77 5984 4608 0.77 6220 4752 0.76 6056 4620 0.76 6180 4712 0.76 6096 4676 0.77 6240 4792 0.77 6116 4680 0.77 average standard deviation maximum minimum 6112 81 6240 5984 4683 58 4792 4608 0.77 0.00 0.77 0.76 Table B.2. Multiple (n=9) Solids Determinations on E ^ a Single Sample at 10 C. Date/Sample TSS mg/L TVSS mg/L TVSS/TSS February 4/anoxic-aerobic 7400 5560 0.75 7492 5632 0.75 7400 5556 0.75 7424 5600 0. 75 7468 5608 0.75 7516 5668 0.75 7492 5640 0.75 7432 5592 0.75 7476 5596 0.75 average standard deviation maximum minimum 7456 40 7516 7400 5606 34 5668 5556 0.75 0.00 0.75 0.75 179 Table B.3. Daily Duplicate Solids Determinations for Samples Throughout Run #1. DUPLICATE VALUES kTE DIGESTOR TSS TVSS TSS TVSS (1) (2) (3) (4) [a] [b] [c] [d] TSS TVSS - # dig. # mg/L mg/L mg/L mg/L mg/L mg/L % % 1 5 6256 4748 6236 4704 20 44 0 .35 0 .84 2 4 6136 4600 6220 4676 84 76 1 .49 1 .47 3 3 6816 4908 6576 4740 240 168 3 .93 3 .11 4 4 6176 4672- 6248 4696 72 24 1 .26 0 .46 5 2 6400 4844 6284 4768 116 76 1 .99 1 .43 6 1 6264 4740 6296 4764 32 24 0 .55 0 .46 7 feed 6920 5316 6908 5336 12 20 0 .19 0 .34 8 1 6224 4680 6144 4600 80 80 1 .41 1 .56 9 2 6204 4692 6340 4772 136 80 2 .37 1 .52 10 3 6396 4632 6296 4580 100 52 1 .73 1 .01 11 4 6016 4528 6060 4552 44 24 0 .79 0 .48 12 5 6048 4564 6128 4644 80 80 1 .43 1 .56 13 . 6 5804 4548 5656 4420 148 128 2 .77 2 .63 14 feed 7388 5680 7412 5700 24 20 0 .35 0 .32 15 6 5712 4464 5800 4560 88 96 1 .65 1 .94 16 5 6144 4644 6276 4740 132 96 2 .32 1 . 84 17 4 6188 4664 6056 4568 132 96 2 . 34 1 .88 18 3 6072 4388 6216 4520 144 132 2 .59 2 .62 19 2 6132 4668 6180 4708 48 40 0 .85 0 .77 20 1 6256 4736 6392 4828 136 92 2 . 35 1 .73 21 feed 7788 5980 7872 6024 84 44 1 .16 0 .66 22 1 6200 4660 6076 4592 124 68 2 .20 1 .33 23 2 6492 4892 6484 4904 8 12 0 .13 0 .22 24 3 6300 4520 6320 4504 20 16 0 .35 0 .31 25 4 6336 4744 6372 4740 36 4 0 .62 0 .08 26 5 6276 4668 6236 4684 40 16 0 .70 0 .31 27 6 5760 4536 5772 4556 12 20 0 .22 0 .40 28 feed 7748 5896 7828 5960 80 64 1 .12 0 .98 29 6 6032 4708 6116 4768 84 60 1 . 50 1 .15 30 5 6360 4788 6268 4704 92 84 1 .58 1 .60 31 4 6440 4824 6400 4820 40 4 0 .68 0 .07 32 3 6224 4460 6444 4620 220 160 3 .85 3 .09 33 2 6268 4728 6216 4672 52 56 0 .91 1 .08 34 1 5896 4408 5828 4360 68 48 1 .26 0 . 99 35 feed 8848 6784 8940 6840 92 56 1 .12 0 .74 (1) Absolute difference between duplicate TSS values. (2) Absolute difference between duplicate TVSS values. (3) Percentage error for TSS values based on the average{([a]+[c])/2}. (4) Percentage error for TVSS values based on the average!([b]+[d])/2}. 180 Table B.3. (cont'd.) DUPLICATE VALUES DATE DIGESTOR TSS TVSS TSS TVSS (1) (2) (3) (4) [a] [b] [c] [d] TSS TVSS day # dig. # mg/L mg/L mg/L mg/L mg/L mg/L % % 36 1 5752 4308 5772 4332 20 24 0. .38 0. ,50 37 2 6516 4884 6440 4836 76 48 1. .28 0, .89 38 3 6296 4504 6152 4424 144 80 2. .55 1. ,59 39 4 6072 4536 6020 4468 52 68 0. .94 1, .36 40 5 5752 4312 5960 4464 208 152 3, .89 3. .09 41 6 6192 4888 6352 5008 160 120 2. ,75 2. ,22 42 feed 8616 6496 8500 6344 116 152 1. .47 2. .14 43 6 6020 4772 6044 4772 24 0 0. .43 0. ,00 44 5 6260 4628 5940 4384 320 244 5. , 70 4. ,90 45 4 6280 4652 6188 4596 92 56 1. ,61 1. ,09 AVERAGE 1.581 1.306 ST. DEV 1.159 0.992 MAX. 5.705 4.896 MIN. 0.134 0.000 (1) Absolute difference between duplicate TSS values. (2) Absolute difference between duplicate TVSS values. (3) Percentage error for TSS values based on the average{([a]+[c])/2). (4) Percentage error for TVSS values based on the average{([b]+[d])/2}. Table B.4. Daily Duplicate Solids Determinations for Samples Throughout Run #2 DUPLICATE VALUES DATE DIGESTOR TSS TVSS TSS TVSS (1) (2) (3) (4) [a] [b] [c] [d] TSS TVSS day # dig. # mg/L mg/L mg/L mg/L mg/L mg/L % % 1 5 6600 4924 6448 4824 152 100 2. 54 1. 85 2 4 6988 5288 6776 5140 212 148 3. 34 2. 58 3 3 6840 5308 6912 5340 72 32 1. 13 0. 55 4 2 6872 5080 7016 5212 144 132 2. 28 2. 29 5 1 7080 5436 6996 5388 84 48 1. .29 0. .81 6 feed 8616 6620 8672 6664 56 44 0. 70 0. .60 7 1 6916 5256 6884 5216 32 40 0. ,50 0. .69 8 2 7036 5200 6912 5092 124 108 1. ,94 1. ,88 9 3 6908 5412 6924 5416 16 4 0. .25 0. .07 10 4 6736 5068 6816 5132 80 64 1. ,29 1. ,13 11 5 6356 4692 6436 4732 80 40 1, .37 0, .76 12 6 6364 5008 6240 4920 124 88 2. .11 1. .63 13 feed 8528 6576 8476 6548 52 28 0, . 66 0 .39 14 6 6328 4992 . 6272 4944 56 48 0, .95 0. .89 15 5 6204 4408 6284 4448 80 40 1. .42 0 .79 16 4 6612 4940 6696 4992 84 52 1, .38 0 .94 17 3 6668 5224 6620 5212 48 12 0 .78 0 .21 18 2 6620 4808 6924 5148 304 340 4. .97 6 .04 19 1 6692 5120 6704 5144 12 24 0 .19 0 .42 20 feed 7500 5852 7380 5768 120 84 1. .74 1 .33 21 1 6912 5288 6708 5104 204 184 3 .24 3 .23 22 2 6524 4828 6480 4800 44 28 0. .74 0 .52 23 3 6488 5172 6428 5116 60 56 1. .00 1 .01 24 4 6528 4904 6592 4948 64 44 1. .07 0 .80 25 5 6340 4544 6248 4480 92 64 1, .61 1 .26 26 6 6172 4936 6128 4892 44 44 0. .77 0. .83 27 feed 8200 6436 8088 6372 112 64 1. .48 0 .92 28 6 6232 4972 6240 4980 8 8 0. .14 0. .15 29 5 6104 4404 6088 4388 16 16 0. ,29 0. .32 30 4 6396 4808 6484 5116 88 308 1. ,49 5. ,63 31 3 6952 5660 6840 5572 112 88 1. ,73 1. .46 32 2 6552 5444 6528 5428 24 16 0. ,39 0. ,28 33 1 6732 5448 6760 5500 28 52 0. ,44 0. .88 34 feed 7568 6056 7560 6028 8 28 0. 11 0. .43 (1) Absolute difference between duplicate TSS values. (2) Absolute difference between duplicate TVSS values. (3) Percentage error for TSS values based on the average{([a]+[c])/2). (4) Percentage error for TVSS values based on the average{([b]+[d])/2). 182 i Table B.4. (cont'd.) DUPLICATE VALUES iTE DIGESTOR TSS TVSS TSS TVSS (1) (2) (3) (4) [a] [b] [c] [d] TSS TVSS ' # dig. # mg/L mg/L mg/L mg/L mg/L mg/L % % 35 1 6616 5372 6628 5412 12 40 0 . 18 0 .74 36 2 6364 5300 6380 5292 16 8 0 .25 0 .15 37 3 6012 5052 6420 5228 408 176 6 .56 3 .42 38 4 6328 4908 6376 4876 48 32 0 .82 0 .59 39 5 6084 4400 6084 4384 0 16 0 .00 0 .32 40 6 6196 5020 6156 4984 40 36 0 .69 0 .67 41 feed 7732 6180 7672 6144 60 36 0 .83 0 .54 42 6 6192 5028 6200 5044 8 16 0 .14 0 .29 43 5 6212 4420 6112 4368 100 52 1 .79 1 .05 44 4 6288 4840 6324 4852 36 12 0 .62 0 .22 45 3 6248 5204 6224 5196 24 8 0 .41 0 .14 46 2 6312 5264 6428 5336 116 72 1 .93 1 .27 47 1 6832 5724 6788 5708 44 16 0 .68 0 .26 48 feed 7940 6308 7832 6240 108 68 1 .47 1 .00 49 1 6672 5576 6636 5564 36 12 0 .57 0 .20 50 2 6456 5388 6212 5176 244 212 4 .05 3 .79 51 3 6244 5172 6060 5000 184 172 3 .16 3 .18 52 4 5960 4576 5984 4584 24 8 0 .44 0 .16 53 5 6080 4396 6108 4448 28 52 0 .51 1 .04 54 6 5268 4256 5332 4276 64 20 1 .29 0 .43 55 feed 7656 6016 7704 6076 48 60 0 .67 0 .91 56 6 5568 4444 5532 4396 36 48 0 .69 1 .00 57 5 6228 4480 6188 4480 40 0 0 .71 0 .00 58 4 6008 4560 6020 4588 12 28 0 .22 0 .55 59 3 6324 5212 6332 5228 8 16 0 .13 0 .29 60 2 6408 5296 6420 5280 12 16 0 .20 0 .28 AVERAGE 1.242 1.165 ST. DEV 1.060 1.261 MAX. 4.969 6.043 MIN. 0.000 0.068 (1) Absolute difference between duplicate TSS values. (2) Absolute difference between duplicate TVSS values. (3) Percentage error for TSS values based on the average{([a]+[c])/2}. (4) Percentage error for TVSS values based on the average{([b]+[d])/2}. 183 Table B.5. Daily Duplicate Solids Determinations for Samples  Throughout Run #3. DUPLICATE VALUES LTE D I G E S T O R T S S T V S S T S S T V S S (1) (2) (3) (4) [a] [b] [c] [d] T S S T V S S ' # dig. # mg/L mg/L mg/L mg/L mg/L mg/L % % 1 4 7228 5512 7080 5384 148 128 2 .24 2 .14 2 3 7672 5832 7788 5952 116 120 1 .63 1 .84 3 2 7656 5824 7528 5716 128 108 1 .83 1 .70 4 1 7728 5892 7732 5896 4 4 0 .06 0 .06 5 feed 6248 4808 6228 4784 20 24 0 .35 0 .46 6 1 7592 5756 7568 5680 24 76 0 .34 1 .20 7 2 7364 5552 7400 5532 36 20 0 .53 0 .32 8 3 7540 5744 7600 5772 . 60 28 0 .86 0 .44 9 4 7112 5400 7216 5484 104 84 1 .58 1 .39 10 5 7436 5604 7116 5352 320 252 4 .76 4 .18 11 6 6896 5312 6980 5400 84 88 1 .31 1 .49 12 feed 7228 5484 7256 5500 28 16 0 .42 0 .26 13 6 7148 5512 7144 5508 4 4 0 .06 0 .07 14 5 7264 5348 7400 - 5520 136 172 2 .04 2 .82 15 4 7112 5292 7072 5244 40 48 0 .62 0 .82 16 3 7720 5844 7912 6000 192 156 2 .68 2 .37 17 2 7320 5428 7516 5592 196 164 2 .90 2 .65 18 1 7648 5760 7572 5728 76 32 1 .09 0 .50 19 feed 8540 6500 8220 6320 320 180 4 .13 2 .57 20 1 7396 5540 7564 5672 168 132 2 .46 2 .11 21 2 7080 5232 7060 5228 20 4 0 .31 0 .07 22 3 7384 5572 7396 5600 12 28 0 .18 0 .45 23 4 7236 5432 7096 5312 140 120 2 .13 2 .02 24 5 7012 5156 6960 5132 52 24 0 .82 0 .42 25 6 6836 5260 6884 5312 48 52 0 .76 0 .89 26 feed 8048 6208 7988 6144 60 64 0 .81 0 .94 27 6 6620 5128 6576 5108 44 20 0 .72 0 .36 28 5 6884 5064 7024 5160 140 96 2 .21 1 .67 29 4 7192 5436 7176 5196 16 240 0 .24 4 .04 30 3 7636 5836 7676 5836 40 0 0 .57 0 .00 31 2 7856 5956 7756 5800 100 156 1 .39 2 .40 32 1 7800 5892 7880 5968 80 76 1 .11 1 .16 33 feed 6700 5232 6812 5384 112 152 1 .79 2 .62 (1) Absolute difference between duplicate TSS values. (2) Absolute difference between duplicate TVSS values. (3) Percentage error for TSS values based on the average{([a]+[c])/2). (4) Percentage error for TVSS values based on the average{([b]+[d])/2}. 184 Table B.5. (cont'd.) DUPLICATE VALUES DATE DIGESTOR TSS TVSS TSS TVSS (1) (2) (3) (4) [a] [b] [c] [d] TSS TVSS day # dig. # mg/L mg/L mg/L mg/L mg/L mg/L % % 34 1 7720 5820 7740 5880 20 60 0. .28 0, .93 35 2 7580 5704 7408 5572 172 132 2, .49 2, .12 36 3 7628 5900 7536 5824 92 76 1. .31 1. .18 37 4 7160 5396 7176 5396 16 0 0, .24 0, .00 38 5 7228 5372 7140 5328 88 44 1. .34 0 .74 39 6 7120 5476 7096 5464 24 12 0. .37 0 .20 40 feed 9196 7168 9224 7220 28 52 0, .33 0 .66 41 6 7144 5516 7108 5484 36 32 0, .55 0. .53 42 5 7252 5344 7340 5436 88 92 1. .32 1. .52 43 4 7212 5460 7064 5320 148 140 2. .25 2. .35 44 3 7584 5908 7612 5948 28 40 0. .40 0. .62 45 2 7660 5768 7660 5768 0 0 0 .00 0, .00 46 1 7820 5940 7728 5860 92 80 l'. .28 1 .23 47 feed 8956 6952 8852 6868 104 84 1 .26 1 .11 48 1 7836 5916 7824 5920 12 4 0. .17 0 .06 49 2 7664 5768 7780 5868 " 116 100 1. .64 1. .55 50 3 7500 5852 7660 5988 160 136 2. .28 2. .09 51 4 6960 5264 7048 5348 88 84 1. .37 1. .43 52 5 7448 5528 7384 5488 64 40 0, .94 0, .65 53 6 7352 5708 7268 5636 84 72 1. .24 1. .16 54 feed 8184 6268 8284 6360 100 92 1. .32 1. ,32 55 6 7280 5624 7332 5716 52 92 0. .77 1. ,48 56 5 7448 5540 7464 5536 16 4 0. .23 0. ,06 57 4 7136 5384 7092 5352 44 32 0. .67 0. ,54 58 3 7784 6052 7800 6064 16 12 0. ,22 0. .18 59 2 7688 5720 7788 5780 100 60 1. ,42 0. 93 60 1 7932 5988 7864 5940 68 48 0. 94 0. 73 AVERAGE 1.193 1.197 ST. DEV 0.964 , 0.964 MAX. 4.763 4.183 MIN. 0.000 0.000 (1) Absolute diff e r e n c e between duplicate TSS values. (2) Absolute difference between duplicate TVSS values. (3) Percentage error for TSS values based on the average{([a]+[c])/2}. (4) Percentage error f o r TVSS values based on the average{([b] + [d])/2}. APPENDIX C Nitrogen Data 186 Table C . l . Nitrogen Data - 20 Day SRT at 20°C.  Nitrogen Forms as mg/L N. DATE TKN t o t a l NH3 NOx NO 2 NO 3 %N solids 24-Sep 455 0. ,1 0.1 0 0.1 6. .05 28-Sep 493 0. .1 0.1 0 0.1 6 .43 01-0ct 538 0. , 1 0.1 0 0.1 6 .87 05-Oct 538 0. .1 0.1 0 0.1 6 .72 08-Oct 429 0. .1 0.1 0 0.1 6 .41 13-0ct 539 0, .1 0.1 0 0.1 6 .47 16-Oct 552 0, .1 0.1 0 0.1 6 .84 F 19-0ct 547 0, .1 0.1 0 0.1 6 .67 22-Oct 587 0 .1 0.1 0 0.1 6 .61 26-Oct 552 0, .1 0.1 0 0.1 6 .78 29-Oct 513 0 .1 0.1 0 0.1 7 .41 02-Nov 513 0 .1 0.1 0 0.1 6 .74 05-Nov 546 0 .1 0.1 0 0.1 6 .61 09-Nov 507 0 .1 0.1 0 0.1 6 .53 12-Nov 552 0 .1 0.1 0 0.1 6 .85 19-Nov 552 0 .1 0.1 0 0.1 6 .71 average 529 0 .1 0.1 0.1 6 .68 std. dev. 40 0 .27 24-Sep 375 0. ,1 1.35 0 1.35 5 .82 28-Sep 401 0. .1 1.61 0 1.61 6 .51 01-0ct 398 0. , 1 1.54 0 1.54 6 .27 05-Oct 420 0. .1 1.26 0 1.26 6 .14 08-Oct 437 0. ,1 1.72 0 1.72 5, .77 13-0ct 393 0. ,1 1.57 0 1.57 5, .80 16-Oct 384 0. 1 1.34 0 1.34 5. .89 C 19-0ct 409 0. 1 1.40 0 1.40 6. .15 22-Oct 399 0. 1 1.63 0 1.63 5. ,95 26-Oct 409 0. 1 1.24 0 1.24 6. ,51 29-Oct 395 0. 1 1.70 0 1.70 6. ,29 02-Nov 372 0. 1 1.61 0 1.61 6. 42 05-Nov 356 0. 1 1.36 0 1.36 6. 46 09-Nov 378 0. 1 1.64 0 1.64 6. 53 12-Nov 448 0. 1 1.36 0 1.36 6. 36 19-Nov 448 0. 1 1.64 0 1.64 6. 52 average std. dev. 403 0.1 1.51 26 0.16 1.54 6.23 0.28 0.27 Table C.l. (cont'd) DATE TKN NH3 NOx NO 2 NO 3 %N t o t a l solids 24-Sep 383 0 .1 94.5 0 94.5 5 .68 28-Sep 378 0 .1 109 0 109 6 .26 01-0ct 385 0 .1 121 0 121 6 .41 05-Oct 385 0 .1 129 0 129 5 .49 08-Oct 363 0 .1 115 0 115 5 .87 13-0ct 412 0 .1 150 0 150 5 .40 L 16-Oct 384 0 .1 146 0 146 5 .48 19-0ct 389 0 .1 153 0 153 5 .78 22-0ct 384 0 .1 156 0 156 5 .50 26-Oct 394 0 .1 159 0 159 5 .42 29-Oct 367 0 .1 172 0 172 5 .55 02-Nov 372 0 .1 176 0 176 5 .61 05-Nov 367 0 .1 169 0 169 5 .42 09-Nov 389 0 .1 167 0 167 5 .62 12-Nov 453 0 .1 171 0 171 5 .86 19-Nov 434 0 .1 174 0 174 5 .87 average 443 0 .1 149 112 5 .71 std. dev. . 24 25 18 0 .28 24-Sep 418 9 .4 73.5 0 73.5 5 .93 28-Sep 442 18. .4 81.5 0 81.5 6 .35 01-0ct 445 21. .7 87.2 0 87.2 6 .19 05-0ct 420 28. .7 97.6 0 97.6 6. .69 08-Oct 366 29. .4 82.1 0 82.1 6, .27 13-0ct 437 30. ,5 90.9 0 90.9 6. .30 A 16-Oct 419 18. ,6 81.3 0 81.3 6. .22 19-Oct 419 16. 0 80.0 0 80.0 6. ,12 22-Oct 448 12. ,6 77.2 17.3 60.0 6. ,30 26-Oct 453 7. 8 68.9 17.8 51.1 6. 44 29-Oct . 434 7. 0 65.0 17.7 47.3 . 6. ,67 02-Nov 406 5. 7 57.6 15.4 42.3 6. 67 05-Nov 417 5. 4 55.5 13.8 41.7 6. 58 09-Nov 395 15. 0 47.5 0.7 46.8 6. 43 12-Nov 532 9. 7 66.9 0.2 66.7 6. 55 19-Nov 443 20. 0 62.3 0.1 62.2 6. 74 average 432 15. 7 72.5 10.4 74.3 6. 42 std. dev. 33 8. 0 13.4 7.9 13.8 0. 23 188 Table C.2. Nitrogen Data - 20 Day SRT at 10°C.  Nitrogen Forms as mg/L N. DATE TKN NH3 NOx N02 N03 %N t o t a l solids 10-Dec 510 0 .05 1, .36 0 1 .36 7 , .27 14-Dec 659 0, .05 0, .08 0 0 .08 6, .99 17-Dec 672 0. .05 0. .08 0 0, .08 6, .81 21-Dec 540 0, .05 0, .08 0 0 .08 7, .55 24-Dec 476 0 .05 0, .72 0 0 .72 6, .81 28-Dec 540 0, .05 0. .08 0 0 .08 6 .80 31-Dec 568 0, .24 1, .42 0 1 .42 6 .60 04-Jan 627 0, .05 0. .60 0 0, .60 6, .92 07-Jan 638 0, .33 0. ,05 0 0 .05 6, .64 11-Jan 589 0, .14 0. .05 0 0, .05 6, .53 14-Jan 723 0. .29 0. ,05 0 0. .05 7. .06 18-Jan 571 0, .05 0. .05 0 0, .05 6. .95 21-Jan 686 0. .62 0. .05 0 0, .05 7. .66 25-Jan 631 0, .51 0. .23 0 0, .23 7 , .86 28-Jan 592 0. .45 0. ,05 0 0, .05 7. , 60 01-Feb 710 0. ,11 0. ,28 0 0. .28 7. ,96 04-Feb 750 0. ,30 0. ,05 0 0, .05 7. .60 rage 617 0. ,20 0. 31 0 0. ,31 7. 15 dev. 76 0. 18 0. 44 0 0. 44 0. 45 10-Dec 553 0 .05 1, .50 0 1, .50 7 .28 14-Dec 491 0 .05 2, .88 0 2, .88 6 .94 17-Dec 516 0 .05 1, .48 0 1, .48 7 .05 21-Dec 370 0, .05 1, .82 0 1. .82 7 .47 24-Dec 437 0, .05 1. .11 0 1. , 11 6 .94 28-Dec 461 0, .05 1, .75 0 1. .75 6 .75 31-Dec 497 0, .05 1. ,72 0 1. ,72 6, .88 04-Jan 465 0, .05 4, .44 0 4. ,44 6 .95 07-Jan 465 0. .05 3. .31 0 3. ,31 6, .66 11-Jan 418 0. .05 2. ,57 0 2. 57 6, .10 14-Jan 499 0. .05 2. .72 0 2. ,72 7, .69 18-Jan 464 0. .05 3. ,25 0 ' 3. 25 6, .78 21-Jan 485 0. ,05 3. ,00 0 3. ,00 7, .40 25-Jan 438 0, .05 1. .84 0 1. ,84 7, .51 28-Jan 482 0. .05 1. ,56 0 1. .56 7, .75 01-Feb 470 0, .05 1. .56 0 1. ,56 7 .45 04-Feb 482 0. .05 1. .45 0 1. ,45 6, .95 average 470 0.05 2.23 0 2.23 7.09 std. dev. 39 0.88 0 0.88 0.41 Table C.2. (cont'd) DATE TKN NH3 NOx N02 N03 %N t o t a l solids 10-Dec 540 0, .05 54 .3 0 54 .3 7, .31 14-Dec 466 0, .05 66 .6 0 66 .6 6 .99 17-Dec 510 0 .05 70 .4 0 70 .4 7 .08 21-Dec 370 0. .05 81 .4 0 81 .4 6 .60 24-Dec 431 0 .05 86 .9 0 86 .9 6 .87 28-Dec 523 0 .05 90 .5 0 90 .5 6 .79 L 31-Dec 492 0 .05 97 .2 0 97 .2 6 .78 04-Jan 481 0 .05 106 0 106 6 .35 07-Jan 459 0 .05 110 0 110 6 .74 11-Jan 418 0 .05 120 0 120 5 .82 14-Jan 510 0 .05 117 0 117 6 .71 18-Jan 520 0 .05 116 0 116 6 .45 21-Jan 511 0 .05 116 0 116 7 .41 25-Jan 471 0 .05 118 0 118 7 .30 28-Jan 482 0 .05 118 0 118 7 . 37 01-Feb 533 0 .05 126 0 126 7 .40 04-Feb 550 0 .05 125 0 125 7 .21 average 526 0 .05 101 0 101 6 .89 std. dev. 46 22 0 22 0 .42 10-Dec 485 0. .07 54 .3 0 54 .3 7. .21 14-Dec 497 0. .55 61 .7 0 61 .7 7. .20 17-Dec 522 2. .79 68 .0 0 68 .0 7, .23 21-Dec 419 6. ,13 81 .4 0 81 .4 7. .41 24-Dec 504 7. .91 77 .1 0 77 .1 6. .83 28-Dec 523 8. .99 77 .7 0 77 .7 7. ,06 A 31-Dec 497 9. 20 77 .4 0. .45 77 .0 6. .54 04-Jan 503 19. 79 63 .8 13. .20 50 .6 6. 64 . 07-Jan 487 23. 91 37 .3 4. ,54 32 .8 6. 52 11-Jan 445 0. 05 18 .8 0. .05 18 .8 6. 32 14-Jan 499 0. 05 27 .5 0 27 .5 6. 91 18-Jan 509 0. 05 45 .9 0 45 .9 6. 72 21-Jan 500 0. 27 62 .3 0 62 .3 7. 62 25-Jan 520 0. 51 69 .8 0 69 .8 7. 60 28-Jan 476 5. 27 72 .7 0 72 .7 7. 37 01-Feb 453 6. 05 72 .7 0 72 .7 7. 74 04-Feb 545 6. 95 77 .8 0 77 .8 7. 45 average 493 6.85 61.5 4.56 60.47 7.08 std. dev. 30 7.31 18.2 5.29 18.75 0.42 190 Table C.3. Nitrogen Data for 15 Day SRT at 20°C,  Nitrogen Forms as mg/L N. DATE TKN t o t a l NH3 NOx N02 NO 3 %N solids 02-Jul 441 nd 0 .20 0 0 .20 6 .07 06-Jul 489 nd 0 .20 0 0 .20 5 .81 09-Jul 532 nd 3 .40 0 3 .40 5 .76 13-Jul 514 nd 1 .70 0 1 .70 6 .01 16-Jul 439 nd 1 .53 0 1 .53 6 .19 20-Jul 527 nd 0 .11 0 0 .11 6 .40 F 23-Jul 491 nd 10 .20 0 10 .20 6 .20 27-Jul 807 nd 4 .90 0 4 .90 6 .45 30-Jul 457 nd 3 .98 0 3 .98 6. .57 03-Aug 440 nd 1 .57 0 1 .57 6, .52 06-Aug 508 nd 3 .92 0 3, .92 6. .57 10-Aug 559 nd 2 .90 0 2, .90 6, .42 13-Aug 504 nd 3, .66 0 3, .66 7. .10 average 516 2. .94 2. .94 6. ,31 std. dev. 92 2. .60 2. .60 0. ,35 02-Jul 370 0.02 1. .34 0 1. ,34 5. 85 06-Jul 263 0.02 1. ,80 0 1. ,80 7 . ,78 09-Jul 330 0.02 1. ,67 0 1. ,67 6. ,77 13-Jul 373 0.44 1. ,10 0 1. ,10 5. 93 16-Jul 374 0.35 1. ,40 0 1. ,40 5. 93 20-Jul 355 1.09 1. ,84 0 1. ,84 5. 89 C 23-Jul 373 1.21 1. 60 0 1. 60 5. 89 27-Jul 418 0.36 1. ,64 0 1. 64 6. 36 30-Jul 287 0.18 1. ,35 0 1. 35 6. 03 03-Aug 287 0.20 1. ,87 0 1. .87 6. 29 06-Aug 355 0.25 1. ,40 0 1. 40 6. 03 10-Aug 347 0.35 1. 07 0 1. 07 5. 93 13-Aug 362 0.14 1. ,98 0 1. 98 5. 99 average 325 0.36 1. 54 1. 54 6. 21 std. dev. 42 0.36 0. 28 0. 28 0. 52 nd = not detected Table C.3. (cont'd) 191 DATE TKN NH3 NOx t o t a l NO 2 NO 3 %N solids 02-Jul 397 0 .20 71 .2 0 71 .2 5. .47 06-Jul 346 0 .02 87 .6 0 87 .6 5 .20 09-Jul 338 0 .02 96 .4 0 96 .4 5 .13 13-Jul 371 0, .20 95 .0 0 95 .0 5 .46 16-Jul 299 0, .40 109 0 109 5 .34 20-Jul 355 0, .90 116 0 116 5 .29 L 23-Jul 391 0. .11 131 0 131 5 .40 27-Jul 391 0, .08 126 0 126 5. .53 30-Jul 292 0, .06 123 0 123 5 .78 03-Aug 270 0, .18 117 0 117 5 .76 06-Aug 338 0, .14 117 0 117 5 .60 10-Aug 355 0, .14 131 0 131 5 .46 13-Aug 362 0. .15 133 0 133 5, .61 average 347 0. .20 112 112 5. .46 std. dev. 38 0. .22 18 18 0, .19 02-Jul 405 13. .70 62 .4 0 62 .4 6, .32 06-Jul 335 17. ,20 67 .3 0 67 .3 6. ,48 09-Jul 329 19. 80 83 .7 0 83 .7 5. 43 13-Jul 296 25. 60 84 .4 0 84 .4 5. ,81 16-Jul 384 26. 70 88 .6 0 88 .6 6. 28 20-Jul 391 32. 09 83 .5 0 83 .5 6. 12 A 23-Jul 346 30. 50 93 .8 0 93 .8 5. 90 27-Jul 373 39. 20 94 .9 0 94 .9 6. 48 30-Jul 338 79. 20 72 .4 0 72 .4 6. 00 03-Aug 304 10. 10 62 .7 0 62 . 7 6. 53 06-Aug 355 5. 10 59 .1 0 59 .1 6. 14 10-Aug 355 1. 31 57 .5 0 57 .5 5. 94 13-Aug 401 0. 52 55 .6 0 55 .6 6. 34 average std. dev. 355 24.97 74.3 34 23.57 13.8 74.3 6.14 13.8 0.30 192 Table C.4. Nitrogen Data for 15 Day SRT at 10°C.  Nitrogen Forms as mg/L N. DATE TKN t o t a l NH3 NOx N02 NO 3 %N solids 14-Jan 723 0. .29 0. 05 0 0. ,05 7. ,06 18-Jan 571 0. 05 0. 05 0 0. 05 6. ,95 21-Jan 686 0. ,62 0. 05 0 0. ,05 7. ,66 F 25-Jan 631 0. ,51 0. .23 0 0. .23 7. .86 28-Jan 592 0. ,45 0. ,05 0 0. .05 7. .60 01-Feb 710 0. .11 0. ,28 0 0. .28 7. .96 04-Feb 750 0. ,30 0. ,05 0 0. ,05 7, .60 average 666 0. .33 0. .11 0, .11 7. .53 std. dev. 64 0, .19 0. .09 0. .09 0. .35 14-Jan 536 0. .05 1. .31 0 1 .31 7 .37 18-Jan 565 0 .05 1, .44 0 1 .44 6 .91 21-Jan 575 0. .05 1. .54 0 1. .54 7 .64 C 25-Jan 509 0 .05 1, .74 0 1 .74 7 .60 28-Jan 532 0 .05 1 .45 0 1 .45 8 .23 01-Feb 533 0 .05 1. .43 0 1 .43 7 .64 04-Feb 556 0 .05 1 .53 0 1 .53 7 .30 average std. dev. 544 0.05 1.49 21 0.12 1.49 7.53 0.12 0.37 Table C.4. (cont'd) DATE TKN NH3 NOx N02 N03 %N t o t a l solids 14-Jan 552 0.05 78.0 0 78.0 7.00 18-Jan 537 0.05 86.6 0 86.6 6.66 21-Jan 543 0.05 92.1 0 92.1 7.83 L 25-Jan 509 0.05 94.5 0 94.5 7.80 28-Jan 548 0.05 99.3 0 99.3 7.67 01-Feb 545 0.05 102 0 102 7.57 04-Feb 522 0.05 101 0 101 6.87 average 537 0.05 93.4 93.4 7.34 std. dev. 14 8.0 8.0 0.45 14-Jan 574 1.03 68.1 0 68.1 7.06 18-Jan 571 3.65 76.8 0 76.8 6.49 21-Jan 543 5.50 78.4 0 78.4 7.23 A 25-Jan 543 9.65 79.7 4.65 75.1 8.11 28-Jan 471 16.97 67.7 5.39 62.3 8.36 01-Feb 562 8.10 67.7 4.97 62.7 7.67 04-Feb 505 6.80 65.1 3.44 61.7 7.31 average 538 7.39 71.9 4.61 69.3 7.46 std. dev. 35 4.72 5.6 0.73 6.8 0.59 194 Table C.5. Nitrogen Data - 10 Day SRT at 20°C,  Nitrogen Forms as mg/L N. DATE TKN t o t a l NH3 NOx NO 2 NO 3 %N solids 24-Sep 455 0. .1 0. .1 0 0. .1 6 .05 28-Sep 493 0. ,1 0. .1 0 0. .1 6 .43 Ol-Oct 538 0. .1 0. .1 0 0. .1 6 .87 05-0ct 538 0. ,1 0. .1 0 0. .1 6. .72 F 08-Oct 429 0. .1 0. ,1 0 0. ,1 6, .41 13-Oct 539 0. .1 0. .1 0 0. .1 6. .47 16-Oct 552 0. ,1 0. .1 0 0. ,1 6, .84 19-Oct 547 0. .1 0. ,1 0 0. ,1 6. .67 22-Oct 587 0. ,1 0. .1 0 0. .1 6 .61 average 520 0. ,1 0. .1 0. .1 6, .56. std. dev. 48 0. .24 24-Sep 373 0. .17 0. ,10 0 0. ,10 5. .59 28-Sep 424 0. .08 1. ,78 0 1. ,78 6. ,28 01-0ct- 430 0. .17 0. .59 0 0. ,59 6. .78 05-Oct 440 0. .05 1. ,18 0 1. ,18 6. .58 08-0ct 451 0. .05 1. ,20 0 1. ,20 5. .81 13-Oct 515 0, .06 1. .32 0 1. ,32 6. .36 16-Oct 433 0. .10 1. ,16 0 1. ,16 6. .58 19-Oct 453 0. .10 0. ,90 0 0. ,90 6. .70 22-Oct 468 0. .04 0. ,74 0 0. ,74 6. ,81 average std. dev. 443 0.09 1.00 36 0.05 0.46 1.00 6.39 0.46 6.39 Table C.5. (cont'd) DATE TKN NH3 NOx N02 N03 %N t o t a l solids 24-Sep 410 0.30 77.5 0 77.5 5.50 28-Sep 420 0.02 87.0 0 87.0 6.30 01-0ct 440 0.08 93.2 0 93.2 5.94 05-Oct 400 0.03 99.1 0 99.1 6.15 L 08-Oct 398 0.53 80.9 0 80.9 5.62 13-Oct 466 0.04 111.0 0 111.0 5.94 16-Oct 414 0.07 110.0 0 110.0 6.15 19-0ct 424 0.33 107.0 0 107.0 6.32 22-Oct 453 0.02 85.4 • 0 85.4 6.49 average 425 0.16 94.6 94.6 6.05 std. dev. 22 0.17 12.0 12.0 0.31 24-Sep 423 3.40 67.0 0 67.0 5.49 28-Sep 410 8.53 71.0 0 71.0 6.51 01-0ct 460 10.40 75.4 0 75.4 6.73 05-Oct 435 11.20 76.8 0 76.8 . 6.61 A 08-Oct 383 14.10 67.6 0 67.6 6.17 13-Oct 437 13.10 89.5 0 89.5 6.46 16-0ct 414 13.40 84.0 0 84.0 6.20 19-Oct 463 10.80 73.5 0 73.5 6.68 22-Oct 429 5.90 79.5 0 79.5 6.90 average std. dev. 428 10.09 76.0 23 3.38 7.0 76.0 6.42 7.0 0.40 Table C.6. Nitrogen Data for 10 Day SRT at 10°C.  Nitrogen Forms as mg/L N. 196 DATE TKN t o t a l NH3 NOx NO 2 NO 3 %N solids 10-Dec 510 0 .05 1. 36 0 1 .36 7 .27 14-Dec 659 0. .05 0. 08 0 0 .08 6. .99 17-Dec 672 0. .05 0. 08 0 0 .08 6. .81 21-Dec 540 0, .05 0. 08 0 0 .08 7. .55 24-Dec 476 0, .05 0. 72 0 0, .72 6. .81 28-Dec 540 0. .05 0. 08 0 0. .08 6. .80 F 31-Dec 568 0, .24 1. 42 0 1, .42 6. .60 04-Jan 627 0. .05 0.6 0 0. .60 6. .92 07-Jan 638 0. .33 0. 05 0 0. .05 6. .64 11-Jan 589 0. .14 0. 05 0 0. ,05 6, .53 14-Jan 723 0. ,29 0. 05 0 0. ,05 7. .06 average 516 0. ,12 2. 94 2. ,94 6. .31 std. dev. 92 0. 11 2. 60 2. 60 0. .35 10-Dec 578 0. 05 0. 99 0 0. ,99 6. .85 14-Dec 528 0. ,05 1. 38 0 1. ,38 6. ,92 17-Dec 541 0. ,05 1. 04 0 1. ,04 7. .19 21-Dec 546 0. 05 0. 89 0 0. 89 7. .01 24-Dec 498 0. ,05 1. 40 0 1. ,40 6, .78 28-Dec 473 0. 05 1. 40 0 1. 40 6. ,76 C 31-Dec 524 0. ,05 1. 60 0 1. .60 6. ,55 04-Jan 514 0. 05 1. 45 0 1. 45 6. ,38 07-Jan 535 0. ,05 1. 31 0 1. .31 6. .32 11-Jan 515 0. 05 0. 30 0 0. 30 6. ,64 14-Jan 536 • 0. 05 1. 31 0 1. 31 7 . , 37 average 526.1818 0.05 1.19 0 1.19 6.80 std. dev. 25.89425 0.35 0 0.35 0.31 Table 6. (cont'd) 197 DATE TKN t o t a l NH3 NOx NO 2 NO 3 %N solids 10-Dec 584 0 .05 55 .6 0 55 .6 7 .08 14-Dec 503 0 .05 59 .2 0 59 .2 6 .96 17-Dec 590 0 .05 58 .9 0 58 .9 6 .99 21-Dec 431 0 .05 68 .6 0 68 .6 7 .03 24-Dec 492 0 .05 75. .9 0 75 .9 6 .84 L 28-Dec 455 0 .05 74 .7 0 74 .7 6 .61 31-Dec 481 0 .05 73, .7 0 73 .7 6 .81 04-Jan 492 0 .05 74, .9 0 74 .9 6. .45 07-Jan 487 0, .05 80, .5 0 80 .5 6 .94 11-Jan 504 0. .05 80, .5 0 80, .5 6, .64 14-Jan 552 0, .05 78, .0 0 78 .0 7. .00 average 506 0. .05 71. ,0 71, .0 6, .85 std. dev. 48 8. .6 8, .6 0, .19 10-Dec 590 0. .05 43. ,3 0 43. .3 6. .89 14-Dec 578 0. ,05 53. .1 0 53. ,1 7. .03 17-Dec 565 3. ,71 56. .4 0 56. ,4 7. .05 21-Dec 400 0. 41 61. ,9 0 61. ,9 6. ,79 24-Dec 498 1. ,03 64. ,3 0 64. ,3 7. .75 A 28-Dec 504 0. 76 62. 5 0 62. .5 6. ,86 31-Dec 503 0. 82 66. ,2 0 66. ,2 6. ,54 04-Jan 492 0. 16 70. 0 0 70. ,0 6. .47 07-Jan 508 2. ,00 74. ,3 0 74. .3 6. ,65 11-Jan 530 1. 25 73. 1 0 73. .1 6. .39 14-Jan 574 1. ,03 68. 1 0 68. , 1 7. ,06 average std. dev. 522 1.02 63.0 52 1.02 8.8 63.0 6.86 8.8 0.36 APPENDIX D Phosphorus Data Table D.l. Phosphorus Data - 20 Day SRT at 20°C.  Phosphorus Forms as mg/L P. DATE TP TP P04 %P t o t a l soluble solids 24-Sep 273 0.31 3. .75 28-Sep 302 0.28 3. ,69 01-0ct 320 0.24 3. .88 05-0ct 325 0.50 3. ,95 08-0ct 299 0.17 4. ,03 13-0ct 309 0.18 3. ,87 16-0ct 298 0.41 3. .88 19-0ct 298 0.30 3. ,86 F 22-Oct 324 0.27 3. .68 26-Oct 291 0.25 3. ,43 29-Oct 283 0.43 3. .76 02-Nov 273 0.30 3. ,37 05-Nov 299 0.30 3. ,29 09-Nov 275 0.18 3. .31 12-Nov 275 0.14 3. .43 16-Nov 297 0.19 3. .41 19-Nov 289 0.24 3 .53 average 296 0.28 3 .65 std. dev. 16 0.10 0 .24 24-Sep 265 32.0 3 .89 28-Sep 275 35.5 3 .59 01-Oct 278 40 .9 38.4 3 .83 05-Oct 315 42.6 3 .82 08-Oct 280 44.4 3 .99 13-Oct 280 45.8 3 .92 16-Oct 283 44.5 4 .04 19-0ct 288 43.9 4 .10 C 22-Oct 283 50. .9 46.0 3, .77 26-Oct 283 46.0 4, .08 29-Oct 290 42.2 3. .78 02-Nov 283 44.1 3, .76 05-Nov 283 42.6 3. .96 09-Nov 299 46. .7 43.4 3. .99 12-Nov 272 43.4 3. ,66 16-Nov 282 43.4 3. .65 19-Nov 295 43.5 3. 70 average 284 46. 2 42.5 3. 85 std. dev. 11 4. 1 3.7 0. 15 Table D.l. (cont'd) DATE TP t o t a l TP soluble P04 %P solids 24-Sep 275 39, .0 3.86 28-Sep 268 22, .0 4.18 01-0ct 293 32.9 31. ,1 4.27 05-Oct 290 33. .5 4.09 08-Oct 275 26. ,0 4.65 13-Oct 316 25. ,3 4.62 16-Oct 278 26. .3 4.27 19-0ct 278 26. ,9 4.50 L 22-Oct 275 22.1 24, .8 4.21 26-Oct 286 28. .0 4.25 29-Oct 294 25. ,1 4.24 02-Nov 301 25. .0 4.20 05-Nov 295 12. .5 4.23 09-Nov 285 14.0 12. ,5 4.17 12-Nov 302 14, .8 4.25 16-Nov 289 21. .8 4.06 19-Nov 285 25. ,0 4.03 average 287 23.0 24. ,7 4.24 std. dev. 12 7.7 6. ,7 0.19 24-Sep 275 71. 0 3.55 28-Sep 290 88. 0 3.32 01-0ct 295 120 99. 6 3.18 05-Oct 298 114 3.33 08-Oct 272 127 3.31 13-Oct 300 145 2.95 16-Oct 281 129 2.84 19-0ct 278 126 2.92 A 22-Oct 288 131 123 2.82 26-Oct 240 126 2.84 29-Oct 287 126 2.84 02-Nov 283 116 2.75 05-Nov 288 123 2.76 09-Nov 287 120 112 2.65 12-Nov 316 127 2.59 16-Nov 275 124 2.68 19-Nov 292 125 2.64 average 285 124 118 2.94 std. dev. 15 5 17 0.28 201 Table D.2. Phosphorus Data - 20 Day SRT at 10°C.  Phosphorus Forms as mg/L P. DATE TP TP P04 %P t o t a l soluble solids 10-Dec 249 0. 11 3. .48 14-Dec 328 0. 14 3. ,67 17-Dec 333 0. 52 3. .51 21-Dec 289 1. 14 3. ,91 24-Dec 248 0. ,14 3. .65 28-Dec 286 0. ,29 3. .67 31-Dec 298 0. ,23 3. .53 04-Jan 319 0. ,34 3, .69 07-Jan 324 1. .25 3 .45 11-Jan 297 1. .62 3. .15 14-Jan 335 3, .11 3 .46 18-Jan 255 2. .26 3 .40 21-Jan 328 3, .20 3 .34 25-Jan 282 3, .64 3 .25 28-Jan 255 4, .81 2 .96 01-Feb 315 0 .57 3 .19 04-Feb 344 0. .69 3 .13 average 299 1.42 3.44 std. dev. 32 1.42 0.24 10-Dec 282 14 .5 3 .53 14-Dec 266 17, .6 3. .72 17-Dec 295 19 .2 19 .6 3. .81 21-Dec 215 20, .5 3. .99 24-Dec 254 20. .3 3, .79 28-Dec 270 21. .5 3. .75 31-Dec 286 24. .9 3, .79 04-Jan 278 28. .6 3. ,61 07-Jan 273 29. .7 31. .5 3 . 70 11-Jan 279 27. .2 3. ,36 14-Jan 285 29. .1 . 4. ,12 1,8-Jan 263 31. .2 3. ,69 21-Jan 275 31. .6 3. ,60 25-Jan 253 30. ,9 3. ,51 28-Jan 267 33. .0 33. .1 3. .56 01-Feb 261 31. ,9 3. ,44 04-Feb 268 28. 0 3. 30 269 27.3 26.0 3.66 17 5.9 5.7 0.20 average std. dev. 202 Table D.2. (cont'd) DATE TP TP P04 %P t o t a l soluble solids 10-Dec 282 18, .3 3. .71 14-Dec 266 20, .1 3. .95 17-Dec 284 19. .8 20, .3 3. .99 21-Dec 223 22. .3 3 . 73 24-Dec 248 21. .8 4, .04 28-Dec 292 25. .0 3. .92 31-Dec 293 25. .7 3, .98 04-Jan 288 29. .2 3. .57 07-Jan 278 28. ,0 28, .9 3, .98 11-Jan 299 25, .2 3, .43 14-Jan 291 26. .5 3, .82 18-Jan 272 27, .7 3, .69 21-Jan 299 29, .5 3. .71 25-Jan 280 30 .9 3 .62 28-Jan 270 30, .4 32, .1 3. .56 01-Feb 288 30, .9 3 .56 04-Feb 293 29 .7 3 .43 279 26.1 26.1 3.75 19 4.5 4.1 0.20 10-Dec 255 21. .3 3 .53 14-Dec 263 27 .2 3 .83 17-Dec 289 40 .5 37 .0 3 .73 21-Dec 232 48 .5 3 .72 24-Dec 281 56 .4 3. .53 28-Dec 292 62. .2 3. .53 31-Dec 288 66 .4 3 .21 04-Jan 288 96. . 5 3. .01 07-Jan 273 55. .0 110, .7 2, .73 11-Jan 297 98. .3 2, .79 14-Jan 275 76, .0 2, .87 18-Jan 263 64. .9 3. .15 21-Jan 287 •63. ,2 3. ,25 25-Jan 290 67. ,7 66. ,0 3. .17 28-Jan 267 68. 0 3. 14 01-Feb 278 72. .7 3. 04 04-Feb 285 74. 0 2. 85 average std. dev. average std. dev. 277 54.4 65.3 3.24 16 11.1 22.9 0.34 203 Table D.3. Phosphorus Data - 15 Day SRT at 20°C.  Phosphorus Forms as mg/L P. DATE TP TP P04 %P t o t a l soluble solids 02-Jul 243 1. .40 3. .73 06-Jul 268 1. .30 3. .77 09-Jul 241 1, .35 3. .66 13-Jul 308 2. .10 3. .64 16-Jul 258 3, .40 3. .68 20-Jul 294 4, .45 3. .76 23-Jul 294 4. .74 3. ,64 27-Jul 486 44. .10 3. .58 30-Jul 314 4. .20 4, .03 03-Aug 297 4. .50 3. ,91 06-Aug 305 3. .20 4. .04 10-Aug 338 2. .50 4. ,22 13-Aug 319 5. .66 4. ,56 323 1 J.5 3. ,94 std. dev. 61 12.6 0.30 02-Jul 243 34, .4 3. ,81 06-Jul 210 33. .9 3. ,75 09-Jul ' 233 38. .5 ,3. ,72 13-Jul 262 41, .6 3. ,75 16-Jul 252 37. .7 3. ,75 20-Jul 250 44. .5 3. ,79 23-Jul 259 46. ,9 3. 73 27-Jul 268 46. .3 4. ,07 30-Jul 239 43, .4 3. ,89 03-Aug 247 43. .5 4. ,06 06-Aug 247 44, .6 3. ,91 10-Aug 243 45, .8 4. ,18 13-Aug 265 43, .5 4. .09 average std. dev. 252 9 44.0 2.5 3.94 0.16 Table D.3. (cont'd) DATE TP TP P04 %P t o t a l soluble solids 02-Jul 243 22. .2 3.98 06-Jul 226 15. .7 4.05 09-Jul 242 16. .3 4.03 13-Jul 271 32. .7 3.87 16-Jul 266 32. .7 3.89 20-Jul 259 30. .6 3.98 23-Jul 285 36. .9 4.02 27-Jul 259 37, .7 4.11 30-Jul 289 29. .8 4.25 03-Aug 255 32. .4 4.22 06-Aug 255 32. .9 4.03 10-Aug 264 31. .2 4.20 13-Aug 265 36. .4 ' 4.27 average 266 33.4 4.11 std. dev. 12 2.7 0.13 02-Jul 243 70.0 3. .35 06-Jul 210 80.2 3 .11 09-Jul 287 86.5 3. .09 13-Jul 208 96.3 3. .03 16-Jul 252 95.1 3 .06 20-Jul 259 93.8 3. .19 23-Jul 250 102 3. .11 27-Jul 259 123 3. .19 30-Jul 297 123 2. ,94 03-Aug 255 118 3. 13 06-Aug 247 120 2. ,78 10-Aug 243 116 3. 03 13-Aug 274 118 3. 14 average std. dev. 260 16 112 11 3.06 0.13 205 Table D.4. Phosphorus Data - 15 Day SRT at 10 C.  Phosphorus Forms as mg/L P. DATE TP t o t a l TP soluble P04 %P solids 14-Jan 18-Jan 21-Jan 25-Jan 28-Jan 01-Feb 04-Feb 335 255 328 282 255 315 344 3.11 2.26 3.20 3.64 4.81 0.57 0.69 3.46 3.40 3.34 3.25 2.96 3.19 3.13 average std. dev. 302 35 2.61 1.44 3.25 0.16 14-Jan 18-Jan 21-Jan 25-Jan 28-Jan 01-Feb 04-Feb 307 289 304 290 280 288 290 13.1 16.3 18.6 23.5 25.2 24.0 20.8 3.86 3.73 3.75 3.56 3.82 3.44 3.33 average std. dev. 293 9 20.2 4.1 3 .64 0.19 Table D.4. (cont'd) DATE TP TP P04 %P t o t a l soluble solids 14-Jan 291 12.8 3.76 18-Jan 263 17.8 3.67 21-Jan 294 19.7 3.86 25-Jan 282' 23.9 3.76 28-Jan 290 26.1 3.54 01-Feb 288 23.7 3.57 04-Feb 280 23.7 3.24 average 284 21.1 3.63 std. dev. 10 4.3 0.19 14-Jan 283 52.5 3.29 18-Jan 290 61.1 3.06 21-Jan 289 66.0 3.02 A 25-Jan 290 75.8 3.19 28-Jan 255 82.3 3.18 01-Feb 295 82.3 2.93 04-Feb 261 78.7 2.76 average 280 71.3 3.06 std. dev. 15 10.7 0.17 Table D.5. Phosphorus Data - 10 Day SRT at 20°C.  Phosphorus Forms as mg/L P. DATE TP TP P04 %P t o t a l soluble solids 24-Sep 273 0.31 3. .75 28-Sep 302 0.28 3. .69 01-0ct 320 0.24 3, .88 05-0ct 325 0.50 3 .95 08-Oct 299 0.17 4. .03 13-Oct 309 0.18 3. .87 16-Oct 298 0.41 3. .88 19-Oct 298 0.30 3. .86 22-Oct 324 0.27 3. .68 average 305 0.30 3.84 std. dev. 16 0.10 0.11 24-Sep 283 38. .0 3. .49 28-Sep 280 32. .0 3. ,68 01-0ct 288 33. ,7 35. ,4 3. ,93 05-0ct 305 33. .0 3. ,87 08-0ct 306 45, .7 36. .9 3 . 83 13-Oct 323 38. .6 4. .15 16-Oct 296 34, .2 32 .0 4. .02 19-Oct 291 30, .8 4. .12 22-Oct 288 36 .4 3, .72 average 296 37.9 34.8 3.87 std. dev. 13 5.5 2.7 0.20 Table D.5. (cont'd) DATE TP TP P04 %P t o t a l soluble solids 24-Sep 305 27. .0 3.79 28-Sep 278 23, .5 3.75 01-0ct 298 23, .5 25. .1 4.00 05-Oct 320 23. ,9 4.00 08-0ct 275 19. .8 19. .9 4.17 13-Oct 316 25. ,9 4.22 16-Oct 278 26. ,3 24. ,4 4.27 19-0ct 288 20. ,9 4.41 22-Oct 288 20. ,6 4.23 average 294 23.2 23.5 4.09 std. dev. 16 2.7 2.3 0.21 24-Sep 283 47, .5 3, .45 28-Sep 278 55. .5 3, . 55 01-0ct 300 67 .3 62, .4 3, .71 05-Oct 293 71. .9 3, .62 08-Oct 265 91, .0 86, .3 3, .46 13-Oct 290 87, .5 3, .65 16-Oct 281 80, .7 83, .1 3, .30 19-0ct 278 72. .3 3. .73 22-Oct 278 78, .8 3, .56 average std. dev. 283 79.7 71.7 3.56 10 9.7 13.2 0.13 209 Table D.6. Phosphorus Data - 10 Dav SRT at 10°C. Phosphorus Forms as m g/L P. DATE TP TP P04 - %P t o t a l soluble solids 10-Dec 249 0.11 3.48 14-Dec 328 0.14 3.67 17-Dec 333 0.52 3.51 21-Dec 289 1.14 3.91 24-Dec 248 0.14 3.65 28-Dec 286 0.29 3.67 F 31-Dec 298 0.23 3.53 04-Jan 319 0.34 3.69 07-Jan 324 1.25 3.45 11-Jan 297 1.62 3.15 14-Jan 335 3.11 3.46 average 301 0.81 3.56 std. dev. 30 0.88 0.18 10-Dec 311 11.4 3.45 14-Dec 284 10.5 10.5 3.67 17-Dec 295 10.6 3.88 21-Dec" 300 12.4 3.83 24-Dec 281 13.4 3.84 28-Dec 268 14.1 3.83 C 31-Dec 298 14.7 3.70 04-Jan 296 15.8 16.7 3.69 07-Jan 303 17.5 3.56 11-Jan 283 11.9 3.45 14-Jan 307 13.5 13.1 3.86 average std. dev. 293 13.3 13.3 3.71 12 2.2 2.2 0.15 Table D.6. (cont'd) DATE TP TP P04 %P t o t a l soluble solids 10-Dec 306 14, .7 3. ,68 14-Dec 268 12, ,9 13, .0 3. .77 17-Dec 330 13, .4 3. .84 21-Dec 254 16 .6 3, .89 24-Dec 287 18, .2 3. .78 28-Dec 262 20 .8 3, .80 31-Dec 278 18, .6 3. .95 04-Jan 288 17, .5 20, .4 3, .72 07-Jan 278 19, .0 3. .94 11-Jan 269 12. .8 3. ,67 14-Jan 291 13, .5 12, .8 3. .76 283 14.6 ' 16.4 3.80 20 2.0 3.0 0.09 10-Dec 306 16 .5 3 .59 14-Dec 290 18 .4 18, .3 3, .75 17-Dec 306 20, .8 3, .75 21-Dec 232 25. .5 3, .60 24-Dec 281 30, .2 4, .13 28-Dec 287 34, .9 3, .66 31-Dec 286 38. ,1 3. ,49 04-Jan 286 32, .0 43. .4 3. .38 07-Jan 268 48. ,8 3. ,41 11-Jan 295 53. ,7 3. ,13 14-Jan 283 55. ,8 52. ,5 3. ,29 average std. dev. average std. dev. 284 35.4 34.8 3.56 19 15.5 13.0 0.26 211 APPENDIX E Real Time ORP P r o f i l e s 212 - ] / 6 U J ' ( O Q * ) A W 10 11 12 13 14 15 16 Time ( h o u r s ) Figure E.2. Monitoring Resul ts for 20 Day SRT at 20 °C on November 10 - 11, 1987. cn O LO Average ORP (sca led by 50) Dissolved Oxygen N O x - N (so luble) • T K N (soluble) o NKz, - N (soluble) + - 3 10 F igu re E. 11 i 13 14 Time (hours 15 16 Mon i to r i ng R e s u l t s for on D e c e m b e r 1 8 - 1 9 , 2 0 Day S R T at 10 °C 1 9 8 7 . M l — ' — Average ORP (sca led by 50) Dissolved Oxygen + N O x - N (soluble) • TKN (so luble) o N H 3 - N (soluble) 10 11 12 13 14 15 Time ( h o u r s ) Figure E.4. Monitoring Results for 20 Day SRT at 10 °C on January 8 - 9, 1988. Average ORP ( sca led by 50 i i i 1 1 r 10 11 . 12 13 14 15 Time (hou rs ) Figure E.5. Monitoring Resul ts for 20 Day SRT at 1 0 °C on January 27 - 28 , 1988. 10 11 12 13 14 15 16 Time ( h o u r s ) Figure E.6. Monitor ing Results for 10 Day SRT at 20 °C on Sep tember 30 - October 1, 1987. i—1 Figure E.7. Monitoring Results for 10 Day SRT at 20 °C on October 9 - 1 0 , 1987. Average ORP (sca led by 50) D isso lved Oxygen N C \ - N (so luble) 10 16 22 4 10 10 11 12 13 14 15 Time ( h o u r s ) Figure E.8. Monitoring Results' for 10 Day SRT at 20 °C on October 17 - 18, 1987. A N H 3 - N ( s o l u b l e ) 10 11 12 13 14 15 16 Time ( h o u r s ) F igu re E.9 . Mon i t o r i ng R e s u l t s f o r 10 Day S R T at 10°C on D e c e m b e r 15 - 1 6 , 1 9 8 7 . M o Average ORP (sca led by 50) D isso lved Oxygen Time (hours) 1 1 — — i n ' 1 r 10 11 12 ' 13 14 15 16 Time (hou rs ) Figure E.10. Monitoring Results for 10 Day SRT at 10°C on January 5 - 6, 1988. Average ORP (sca led by 50) D isso lved Oxygen + NOx - N (so luble) • TKN (so luble) 10 11 12 13 14 15 16 Time ( h o u r s ) F igu re E . 1 1 . Mon i t o r i ng R e s u l t s f o r 10 Day SRT at 10 °C on J a n u a r y 12 - 1 3 , 1 9 8 8 . 

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