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THE EFFECTS of Ph on AEROBIC SLUDGE DIGESTION by Herbert

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THE EFFECTS of Ph on AEROBIC SLUDGE DIGESTION by Herbert THE EFFECTS OF pH ON AEROBIC SLUDGE DIGESTION by Herbert Randolph Moore Thesis submitted to the Graduate Faculty of the Virginia Polytechnic Insti'tute and State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Sanitary Engineering APPROVED: Dr. c~ w. Randall, Chairman Pl)()W(IJ. J. Cibul ka Dr. R. E; Benoit September 1970 Blacksburg, Virginia ACKNOWLEDGMENTS The author wishes to express his appreciation for the constant . guidance and constructive criticism offered by his thesis· advisor, Dr. Cl ifford W. Randall, throughout the preparation of this text •. He would also like to express his appreciation to.Dr. Ernest M. Jennelle, Dr. Paul H. King, Professor H. Grady Callison ~nd Professor -J•. J. · Cibul ka for their encouragement and counsel throughout" the grad- · . uate program, to and Dr. Ernest M. Jennelle,.for their valuable assistance in the laboratory, and to for the typing and proofreadfog of this. text. ~- To his wife, he wishes to ·express his fondest appreciation and. grat- itude for the understanding, f~ith and patience she has shown and for providing the home atmosphere that has made it all worth the effort • . This research was supported by a fellowship from the United States . Public Health Service. TABLE OF CONTENTS Page I. ACKNOWLEDGMENTS (I Cl • fl Q ti Q • • • • • ii IL LIST OF TABLES • . • • v III. LIST OF FIGURES I • vi IV. ·INTRODUCTION ••••• l A•. Biological Aspects of Aerobic Sludge Digestion • . l B. Purpose of Research Investigation . 3 V. LITERATURE REVIEW ••• . 5 VI.· METHODS AND MATERIALS o fl e e • o Q • 14 A. Experimental Apparatus • G • • • e o e Q • 15 B. Procurement and Handl fog of Sludge • . C,l ·- • l~ C. Samp l fog Procedures. • . l 'l ' D. Analytical Procedures. • • • • 19 VII. EXPERIMENTAL RESULTS •• • • • 27 A. Biological Solids •. • • • • • • Cl • Cl 27 B. Nitrates and Ammonia Nitrogen • • .• e 4~ c. Orthophosphate • . 46 D. Cellular Protein . 46 E. Cellular Carbohydrate o••a ••e• .lJ."f)f F. BOD and COD . 52 G. Settl eabi l i ty 54 H. Filterability 54 I. Drainabil ity •.••. sq· · J. Microscopic Examination 0 Cl (I • ,5·1: iii TABLE OF CONTENTS (Continued) Page K. Frothfog . • . o • e • • e 59 VIII. DISCUSSION OF RESULTS • • e o 60 IX. CONCLUSIONS 65 X. SUMMARY . • • Ii o • • e· o II ti • e ID 67 XI. BIBLIOGRAPHY . • o • e • • $ o a • • • 69 XII. VITA . 0 • II • • •• 0 0 72 iv LIST OF TABLES Table I. Initial Solids Concentrations • . • • . • 18 Table II. Percent Volatile Solids Content and Ammonia Nitrogen . • . • . • . 44 Table III. Sludge Drainability . ... 58 v LIST OF FIGURES Page Figure 1. Digestion Apparatus . • • . • • • • . • • • • . 16 Figure 2o Standard Curve for Protein Estimation Folin Method . • • . • • • . • • • • • • • . 24 Figure 3. Standard Curve for Carbohydrate Determination Anthrone Method . • • • • • • 22 Figure 4. pH During Aerobic Digestion .••.••• 28 figure 5. Total and Volatile Suspended Solids of Di ges.ter A. Cl ·• • • e e o o _. · o ~ , _.~ ·o • o • • ·· e 29 Figure 6. Total and Volatile Suspended Sol ids of Digester B••••••••• ~ • • • • • • • • • 30 Figure 7. Total and Volatile Suspended Solids of Digester C•••• ~ ~ •••• ~ • . • • • • • . 31 Figure 8. Total and Volatile Suspended Sol ids of. Digester.D .••.••••.• ·• • • • ••• 32 Figure 9. Total and Volatile Suspended Solids of Di-ges t,er E. o • o • o • e • o • • ._ • • • • • 33 Figure 10. Total and Volatile Suspended Solids of Di ges·.ter F. ..- $ o • o • • • • • • • o • • • 34 Figure 11. Percent Suspended Solids Reduction in Digester A: . • • . • • • • . • . 36 Figure 12. Percent Susperided Solids Reduction in Digester B. • . • • • • . • • . • • • • . 37 Figure 13. Percent Suspended Solids Reduction in Digester C. • . • • • • • • . • • • . • • • • • 38 Figure 14. Percent Suspended Solids Reduction in Digester D. • • . • . • . • • • • . • • . 39 Figure 15. Percent Suspended Solids Reduction in Digester E. • . • . • . • • • • • . 40 Figure 16. Percent Suspended Solids Reduction in Digester F. • •••.•••••••. 41 Vi LIST OF FIGURES (Co.ntinued) Page Figure 17. Nitrification During Aerobic Digestion •• 45 f.igure 18. Orthophosphate Concentration During Aerobic Digestion ••••••••••••••••• . 47 Figure 19. Cellular Protein During Aerobic Digestion • 48 Figure 20. Cellular Carbohydrate During Aerobic Digestion • • • . • • • • • • • • • • • • • . 49 f.igure 21. Carbohydrate Fraction of TSS During Aerpbic Digestion •• · •••• ~- ••••••• ~- ••. • - . 50 Figure 22. Protein Fraction of TSS During Aerobic Digestion • • • • • • • • • • • • • • • • • 51 Figure 23. BOD5 Change Dur:tng Aerobic Digestion . ~ • 53 Figure 24. Change in Settl eabi l i ty During Aerobic Di-gestion •· • ·· • • • .• • • • • ··• • • • • • • • • 55 :figure 25. Sludge Fil terabi l i ty . vii· INTRODUCTION As population and industrialization continue to expand, it becomes necessary to more closely scrutinize the ecology of the world. Increased modernization, higher standards of living, and growth of the population have produced an increase in waste products. If unchecked, these waste products wi 11 continue to contaminate our environment unti 1 they threaten the very existance of life itself. Until recently, purif~ .ion of these wastes has been predominantly dependent upon natural phenomena, with minimal efforts on the part of humanity to supplement the natural pro- cesses. As man's modern development has progressed, however, nature alone has become unable to maintain a favorable equilibrium. Thus it has become necessary for man to develop waste treatment processes in order to maintain the required balance of activity throughout the chain of biological metabolism. Biological Aspects of Aerobic Sludge Digestion Efforts to balance the return of wastes to the environment have relied heavily upon the use of microorganisms. Not only have they proven to be very useful for the treatment of undesirable organic com- pounds in solution but, sjnce they are plentiful in nature (and usually present in the waste product itself), they are both easily and economi- cally cultivated. l For a specific waste flow, it may be generally stated that a heter- ogeneous culture of microorganisms can be developed and acclimated that will reduce the colloidal and dissolved organic impurities by absorption and assimilation, resulting in a settleable mass of solids which when separated from the liquid phase produces a water of improved quality. ·Such a process is the activated sludge process. Optimum removal of impur- ities is based on a specific food to microorganism ratio. This ratio is maintained by recirculating the settled organisms from the clarified effluent back to the influent end of the aeration tank. Through assimi- lation, growth, and reproduction, sludge in excess of that required for the optimum F/M ratio is produced and must be wasted from the process for further disposal. Waste activated sludge consists primarily of a mixture of living cellular material, biologically inert organic material, and a lesser amount of inorganic material. When sludge is wasted, the biological growth will ideally be in the declining growth or endogenous phase. Further oxidation of the sludge without the addition of a nutrient source will result in auto-:-oxidation of the biological mass. Cellular material has been characterized by the formula c5H7o2N and, theoretically, may be oxidized to the final end products of carbon dioxide, water, and ammonia. This oxidation occurs from cellular metabolism and synthesis. Energy for eel l ular metabolism is represented by the following reaction of cell- ular oxidation: 3 Cell synthesis may generally be represented by the equation: From these equations it may be seen that the system oxidizes theoreti- cally to carbon dioxide, water, and ammonia (14). Purpose of Research In_vestigation Probably the single most expensive problem in waste treatment pro- cesses is that of sludge conditioning and disposal. Anaerobic diges- tion has proven to be a satisfactory, though expensive and sensitive, process for the reduction and conditioning of primary waste solids. Although it produces an inoffensive and stable sludge, the resulting sup 12rnatant liquor is very high in BOD and suspe11ded solids, and re- quires still further treatment. By contrast, waste activated sludge is not readily treated by anaerobic digestion as it often increases the suspended solids of the supernatant liquor and the resulting sludge is difficult to dewater. Dewatering of unconditioned waste activated sludge has also been attempted, however, this requires chemical con- ditioning and special equipment which add not only a great deal to the expense of the process but also to the solids for ultimate disposal. Where the activated sludge process has been employed, aerobic digestion has proven to be competitive with anaerobic digestion in the stabilization of waste activated sludge and mixtures of primary and waste activated sludge (1, 8, 10, 12, 13). Aerobic digestion has the distinct advantage over anaerobic d_igestion of producing both a well stabilized sludge and a purified supernatant. ~rhere are no disagree- able odors and the pro~ess does not require special heating and gas ·handling equipment. One disadvantage is that it requires an outside source of energy (aeration) since it produces no combustible gas which may be used as an energy source. It is important to realize, however, that at this time the parameters of aerobic digestion are poorly under- stood as the process has never been subjected to extensive investiga- tions as the anaerobic
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