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Aerobic Digestion of Wastewater Sludge Under Low Temperature Conditions

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Aerobic Digestion of Wastewater Sludge Under Low Temperature Conditions University of New Hampshire University of New Hampshire Scholars' Repository NH Water Resources Research Center Scholarship NH Water Resources Research Center 1-1-1978 Aerobic Digestion of Wastewater Sludge Under Low Temperature Conditions Paul L. Bishop University of New Hampshire Follow this and additional works at: https://scholars.unh.edu/nh_wrrc_scholarship Recommended Citation Bishop, Paul L., "Aerobic Digestion of Wastewater Sludge Under Low Temperature Conditions" (1978). NH Water Resources Research Center Scholarship. 173. https://scholars.unh.edu/nh_wrrc_scholarship/173 This Report is brought to you for free and open access by the NH Water Resources Research Center at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in NH Water Resources Research Center Scholarship by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. RR 18 PHOTOCOPY A-037-NH AEROBIC DIGESTION OF WASTEWATER SLUDGE UNDER LOW TEMPERATURE CONDITIONS • By .• Paul L. Bishop Department of Civil Engineering COMPLETION REPORT Project A-037-NH under Grant No. 14-31-0001-4029 The work upon which this fJblication is based was supported in part by funds provided by the Office of Water Research and Technology, United States Department of the Interior, as authorized under the Water Resources Research Act of 1964, Public Law 88-379, through the Water Resource Research Center of the University of New Hampshire. TABLE OF CONTENTS LIST OF FIGURES .................................................... LIST OF TABLES...................................................... 2 INTRODUCTION........................................................ 3 LITERATURE REVIEW................................................... 7 Sludge Stabilization During Aerobic Digestion.................. 7 Nutrient Transformations During Aerobic Digestion.............. 20 Theory of Aerobic Digestion.................................... 24 Total Oxidation Theory.................................... 24 Kinetics of Volatile Solids Degradation................... 29 Kinetics of Oxygen Uptake................................. 35 Kinetics of Nitrogen Transformation....................... 37 Kinetics of Phosphorus Transformation..................... 41 MATERIALS AND METHODS ................................. · ... · .. ······· 43 Physical Apparatus ...................................... · ... ·.. 43 Batch Treatment Apparatus................................. 43 Continuous Flow Apparatus................................. 48 Mixing Studies ................................ ················· 51 Sludge Characteristics ........................... · ... ·········· 54 Experimental Procedures........................................ 56 Batch Treatment Studies................................... 56 Continuous Flow Studies................................... 57 Analytical Procedures ......................... ··.·· .. ·········· 57 Settleability ............................................. 58 Filterability ................................... · ·· · · · · ·· · 58 Nitrogen ................................. · .. ···.·········· 58 Table of Contents - Continued Page Phosphorus ............................................... · 60 Specific Oxygen Uptake Rate............................... 60 DISCUSSION OF RESULTS .............................................. · 61 Primary Sludge .............................................. ··· 61 B00 5 Removal ........................................... ··· 61 COD Remova 1 ..................................... · ... · .. · · · 67 Solids Removal............................................ 67 Dewatering Characteristics................................ 73 Secondary Sludge .................... · .... ····.················· 78 Batch Feed System ......................... · .... · · · · · · · · · · · 78 Continuous Feed System .................... ··· .. ··········· 84 Nutrient Transformations....................................... 95 CONCLUSIONS .............................. · · · · . · · · · · · · · · · · · · · · · · · · · · · 108 BIBLIOGRAPHY ......................... · ... · · . · . · · · · · · · · · · · · · · · · · · · · · · 111 LIST OF FIGURES Page 1. Schematic of completely mixed aerobic digester................. 30 2. Detail of 1-1 i ter reactor. 45 3. Schematic of batch treatment apparatus - 1-liter reactors...... 46 4. Detail of 4-1 iter reactor...................................... 47 5. Schematic of continuous flow apparatus - 3-liter reactors...... 49 6. Detai 1 of 3-liter reactor...................................... 50 7. Mixing study - aeration and mechanical mixing.................. 52 8. Mixing study - aeration only................................... 53 9. Schematic of fi lterabi l ity apparatus........................... 59 10. BOD vs time - Pease Air Force Base............................. 64 11. BOD reduction vs temperature - Pease Air Force Base............ 65 12. COD vs time - Pease Air Force Base............................. 68 13. COD reduction vs temperature - Pease Air Force Base............ 69 14. COD vs time - Portsmouth, N. H................................. · 71 15. Total volatile solids reduction - Pease Air Force Base......... 72 16. Total volatile solids reduction - Portsmouth, N.H.............. 74 17. Filterability of aerobically digested sludge - Pease Air Force Base ......................................... · · .. · · · 75 18. Effect of detention time on filterability - Pease Air Force Base................................................ 76 19. Solids reduction vs time - Hooksett, N.H....................... 80 20. Log St/So vs time............. 82 21. COD reduction vs time - Somersworth, N.H....................... 86 22. Volatile solids reduction vs temperature - Hooksett. N.H....... 89 23. COD reduction vs temperature - Hooksett, N.H................... 91 1 LIST OF TABLES , 1. Raw sludge characteristics .................................... 55 • 2. Experimental data - Pease Air Force Base....................... 62 3. Experimental data - Portsmouth, N.H ........................... 70 4. Batch digestion data - Hooksett, N.H........................... 79 ... 5. Continuous feed digestion data - Hooksett, N.H ................ 85 .•~ t 6. pH data - Hooksett, N. H....................................... 92 r ~ 7. Specific resistance data - Hooksett, N.H..... .. .. ... 93 8. Oxygen Uptake - Hooksett, N. H.................................. 96 9. Nitrogen data from batch digestion - Hooksett, N.H............. 99 10. Phosphorus data from batch digestion - Hooksett, N.H........... 100 11. Nitrogen data from continuous feed digestion - Hooksett, N.H... 101 12. Phosphorus data from continuous feed digestion - Hooksett, N.H. 102 2 . SECTION I ' INTRODUCTION In recent years interest in wastewater sludge treatment and disposal has increased significantly. This increased interest is due primarily to economic. considerations since in most wastewater treatment plants the costs for sludge handling, treatment and disposal amount to approximately 25 to 50 percent of the overall capital and operating investment for the facility. Present predictions are that the volumes of waste sludge will increase 60 to 70 percent within the next 15 years (1). Therefore, any reduction in the quantity of sludge to be processed is of the utmost importance in the design of efficient and economically feasible treatment facilities. The main objective of sludge stabilization is to convert raw or untreated sludge into a nonoffensive form, with respect to odor and pathogenic micro- organism, that is suitable for land disposal. Volatile solids and total solids reduction are also essential since this will reduce the amount of sludge which must be disposed of. At the present time, the most widely accepted methods of sludge treatment are anaerobic digestion, oxidation ponds, aerobic digestion and vacuum filtration. These processes are usually proceeded by some form of sludge thickening, either gravity settling, centrifugation or flotation. Any reduction in the volumes of sludge to be handled is reflected in reduced equipment size and, therefore, costs. The ultimate disposal of the treated sludge is currently the most serious problem, since considerable land is required for landfilling and drying beds. This is usually ~vpensive and at times environmentally offensive. In the case of incineration, initial investments are high and with the present fuel situation operating costs have become nearly prohibitive for small communities to bear. 3 Anaerobic digestion is presently being used in many cases for sludge volume reduction and stabilization. However, due to the many variables which effect the efficient operation of the anaerobic system and render it at times very erratic, this system is being looked at with disfavor by many municipaliti.es. Constant monitoring of pH, organic acids production, alkalinity, and gas production are required and in many cases qualified personnel are not provided or are not available to perform the necessary adjustments to insure proper functioning. Large initial investments are also required for the anaerobic digester. Since the digester supernatant usually contains large amounts of nitrogen, additional treatment is often necessary. Only about 4 to 9 percent of the nitrogen in raw sewage which enters the digester is removed by anaerobic digestion, with the remaining 91 to 96 percent returned to the treatment plant in the supernatant liquor. This can pass through,
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