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Enhancement of Anaerobic Digestion of Solid Wastes by Pre-Treatment and Post-Treatment

Permanent Link: http://ufdc.ufl.edu/UFE0021638/00001

Material Information

Title: Enhancement of Anaerobic Digestion of Solid Wastes by Pre-Treatment and Post-Treatment
Physical Description: 1 online resource (127 p.)
Language: english
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: ammonia, anaerobic, biogas, denitrification, digestion, nitrification, residue, tailings
Agricultural and Biological Engineering -- Dissertations, Academic -- UF
Genre: Agricultural and Biological Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: This study reports on the development of methods for pretreatment of feedstock and post treatment of residue and leachate to improve the performance of UF-patented anaerobic composting technology. These improvements were needed for application of this technology as a solid waste management subsystem on long-term NASA space missions, as well as in treating industrial organic wastes, such as beet pulp and beet tailings from the beet sugar industry. Post treatments were needed for the NASA space mission application and beet pulp application, and involved stabilization of anaerobically digested solid residue by a nitrification process, integration of ammonia removal from liquid leachate within the anaerobic digestion process, and incorporation of both treatments into the overall system configuration. Pre-treatment of readily biodegradable feedstock was needed for the sugar beet tailings application, and consisted of adding a pre-wash step to wash and remove the large fraction of soluble organic matter in the sugar beet tailings, and holding this fraction in a separate reservoir for subsequent controlled release into the system. Results from post treatment of solid residue showed that nitrification initiated within 2 days by continuous flow of air through the residue at a rate of 187 mL/minute/kg wet residue, and 85% of the initial ammonium-nitrogen nitrified within 16 days at a maximum rate of 0.41 mg/g wet weight/day. Post treatment of liquid leachate showed that the ammonia removal rate was 70 to 95 mg/L/day initially, and increased to 200-245 mg/L/day after 8 days of continuous operation, when concentration of total ammonia nitrogen reached 500 mg/L. However, repeated aeration reduced the efficacy of the leachate as an inoculum, suggesting that only part of the leachate should be aerated. System integration involved a modification in which aeration was carried out by holding air within the reactor at a pressure of ~10 psi over 13 days for stabilization of digested residue, and a similar system and operation for ammonia removal from the liquid leachate. Results from pretreatment of sugar beet tailings revealed that addition of water solubilized a large fraction (0.6 g COD/g VS) of organic matter from the tailings. Methanogenesis could be initiated if the solubilized material was leached out. Most of the methane potential remaining in the solids was generated within a week. The methane yield of tailings was estimated to be 295 L/kg VS, of which 50-60% was from the readily solubilized organic matter. A volume reduction of 70-80% was achieved, and approximately 60% of dry matter and 75% of volatile solids were degraded. These demonstrated performance levels suggested that incorporating these pre and post treatments as a routine part of the system operation will greatly enhance the potential for widespread use of this technology in waste management applications.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Pullammanappallil, Pratap C.
Local: Co-adviser: Teixeira, Arthur A.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-05-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0021638:00001

Permanent Link: http://ufdc.ufl.edu/UFE0021638/00001

Material Information

Title: Enhancement of Anaerobic Digestion of Solid Wastes by Pre-Treatment and Post-Treatment
Physical Description: 1 online resource (127 p.)
Language: english
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: ammonia, anaerobic, biogas, denitrification, digestion, nitrification, residue, tailings
Agricultural and Biological Engineering -- Dissertations, Academic -- UF
Genre: Agricultural and Biological Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: This study reports on the development of methods for pretreatment of feedstock and post treatment of residue and leachate to improve the performance of UF-patented anaerobic composting technology. These improvements were needed for application of this technology as a solid waste management subsystem on long-term NASA space missions, as well as in treating industrial organic wastes, such as beet pulp and beet tailings from the beet sugar industry. Post treatments were needed for the NASA space mission application and beet pulp application, and involved stabilization of anaerobically digested solid residue by a nitrification process, integration of ammonia removal from liquid leachate within the anaerobic digestion process, and incorporation of both treatments into the overall system configuration. Pre-treatment of readily biodegradable feedstock was needed for the sugar beet tailings application, and consisted of adding a pre-wash step to wash and remove the large fraction of soluble organic matter in the sugar beet tailings, and holding this fraction in a separate reservoir for subsequent controlled release into the system. Results from post treatment of solid residue showed that nitrification initiated within 2 days by continuous flow of air through the residue at a rate of 187 mL/minute/kg wet residue, and 85% of the initial ammonium-nitrogen nitrified within 16 days at a maximum rate of 0.41 mg/g wet weight/day. Post treatment of liquid leachate showed that the ammonia removal rate was 70 to 95 mg/L/day initially, and increased to 200-245 mg/L/day after 8 days of continuous operation, when concentration of total ammonia nitrogen reached 500 mg/L. However, repeated aeration reduced the efficacy of the leachate as an inoculum, suggesting that only part of the leachate should be aerated. System integration involved a modification in which aeration was carried out by holding air within the reactor at a pressure of ~10 psi over 13 days for stabilization of digested residue, and a similar system and operation for ammonia removal from the liquid leachate. Results from pretreatment of sugar beet tailings revealed that addition of water solubilized a large fraction (0.6 g COD/g VS) of organic matter from the tailings. Methanogenesis could be initiated if the solubilized material was leached out. Most of the methane potential remaining in the solids was generated within a week. The methane yield of tailings was estimated to be 295 L/kg VS, of which 50-60% was from the readily solubilized organic matter. A volume reduction of 70-80% was achieved, and approximately 60% of dry matter and 75% of volatile solids were degraded. These demonstrated performance levels suggested that incorporating these pre and post treatments as a routine part of the system operation will greatly enhance the potential for widespread use of this technology in waste management applications.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Pullammanappallil, Pratap C.
Local: Co-adviser: Teixeira, Arthur A.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-05-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0021638:00001


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1 ENHANCEMENT OF ANAEROBIC DIGEST ION OF SOLID WASTES BY PRETREATMENT AND POST-TREATMENT By WEI LIU A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2008

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2 2008 Wei Liu

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3 To my husband, daughters, parents and sister

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4 ACKNOWLEDGMENTS I thank the m any individuals that have contri buted to make this project a success and my graduate experience so enjoyable. Specifically, I express my great appreci ations to Dr. Pratap Pullammanappallil and Dr. Arthur Teixeira, my academic advisors for their flexibility, continual supports and guidance during my time at the Univer sity of Florida. I would like to thank Dr. John M. Owens for his insightful ideas and concepts in the field of anaerobic digestion and in taking the time to elaborate on his experiences as a student. I also would like to give my thanks to Dr. Ann Wilkie for her guidance and suggestions to complete this work. I would like to thank Dr. Tim Townsend for his comments and suggesti ons in my experiments and dissertation. In addition, I would like to thank Mr. Bob Tonkinson and Mr. Paul Lane for assisting me with mechanical issues. One a more personal note I would like to tha nk all of my family; w ithout them, this would never have been possible. I would like to also th ank all of my friends at the University of Florida who supported me during my studies as well.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........8 LIST OF FIGURES.........................................................................................................................9 LIST OF ABBREVIATIONS........................................................................................................ 11 ABSTRACT...................................................................................................................................12 CHAP TER 1 INTRODUCTION..................................................................................................................14 1.1 Introduction............................................................................................................... ........14 1.1.1 Anaerobic Digestion of Solid Waste....................................................................14 1.1.2 High-Solids Anaerobic Digestion........................................................................16 1.1.3 Sequential Batch Anaerobic Composting (SEBAC)............................................ 17 1.2 Statement of Problem.......................................................................................................19 1.3 Objectives.........................................................................................................................20 1.3.1 In Situ Treatment of Anaerobically Digested Residue and Leachate............................20 1.3.1.1 Stabilization of anaerobically digested residue by nitrification process...........20 1.3.1.2 Integration of ammonia removal from leachate within anaerobic digestion process...............................................................................................................21 1.3.1.3 Integration of in situ treatment of anaerobically digested residue and leachate in SEBAC-II configuration................................................................. 22 1.3.2 Pre-Treatment of Readily Biodegradable Feedstock..................................................... 23 2 STABILIZATION OF ANAEROBICALLY DIGESTATED RESIDUE BY NITRIFICATION PROCESS .................................................................................................28 2.1 Introduction............................................................................................................... ........28 2.2 Methods............................................................................................................................30 2.2.1 Experimental Apparatus....................................................................................... 30 2.2.2 Anaeobically Digested Residue...........................................................................30 2.2.3 Experiments.........................................................................................................31 2.2.3.1 Effect of air flow rate on transformation of nitrogen in anaerobically digested residue............................................................31 2.2.3.2 Transformation of nitrogen in anaerobically digested residue.............. 31 2.2.4 Analysis................................................................................................................ 32 2.2.4.1 Measurement of TAN........................................................................... 32 2.2.4.2 Measurement of nitrite.......................................................................... 33 2.2.4.3 Measurement of nitrate......................................................................... 34

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6 2.2.4.4 Gas samples........................................................................................... 34 2.2.4.5 Stabilization performance.....................................................................35 2.3 Results and Discussions.................................................................................................... 35 2.3.1 Determination of TAN in Anaerobically Digested Residue................................ 35 2.3.2 Effect of Air Flow Rate on Transformation of Nitrogen in Anaerobic Residue..............................................................................................................36 2.3.3 Effect of Aeration on Transformation of Nitrogen in Anaerobically Digested Residue..............................................................................................................38 2.3.4 Nitrification Kinetics............................................................................................39 2.3.5 Oxygen Consumption.......................................................................................... 40 2.4 Conclusion........................................................................................................................41 3 INTEGRATION OF BIOLOGICAL AMMONIA REMOVAL INTO LEACH-BED ANAE ROBIC DIGESTION OF SOLID WASTE................................................................. 48 3.1 Introduction............................................................................................................... ........48 3.2 Methods............................................................................................................................51 3.2.1 Experimental Apparatuses................................................................................... 51 3.2.1.1 Anaerobic digester................................................................................ 51 3.2.1.2 Ammonia removal reactor....................................................................51 3.2.2 Feedstock for Anaerobic Digestion......................................................................52 3.2.3 Experiments.........................................................................................................52 3.2.3.1 Anaerobic digestion of rice straw.........................................................52 3.2.3.2 Aerobic processing of leachate for ammonia removal.......................... 53 3.2.4 Analysis................................................................................................................ 54 3.3 Results and Disscussions.................................................................................................. 55 3.3.1 Anaerobic Digestion of Rice Straw..................................................................... 55 3.3.2 Biological Ammonia Removal from Leachate.................................................... 56 3.3.3 Viability of Aerated Leachate as Inoculum for Subsequent Leach-Bed Anaerobic Digestion.........................................................................................60 3.3.3.1 Effect of TAN and nitrate in leachate................................................... 62 3.3.3.2 Effect of inoculum dilution...................................................................64 3.3.3.3 Effect of reutilization of leachate..........................................................65 3.3.3.4 Effect of pH in leachate......................................................................... 65 3.3.3.5 Effect of aerating process......................................................................66 3.4 Conclusion........................................................................................................................67 4 INTEGRATION OF IN SITU TREATMENT OF ANAEROBICALLY DIGESTED RESIDUE AND LEACHATE IN SEBAC-II CONFIGURATION ....................................... 80 4.1 Introduction............................................................................................................... ........80 4.2 Methods............................................................................................................................81 4.2.1 Experimental Apparatuses................................................................................... 81 4.2.2 Anaeobically Digested Residue...........................................................................83 4.2.3 Experiments.........................................................................................................83 4.2.3.1 Stabilization of anaerobi cally digested residue.....................................83 4.2.3.2 Ammonia removal from leachate.......................................................... 83

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7 4.2.4 Analysis................................................................................................................ 84 4.3 Results and Discussions.................................................................................................... 84 4.3.1 Stabilization of Anaerobic Residue......................................................................84 4.3.2 Ammonia Removal from Leachate...................................................................... 85 4.4 Conclusion........................................................................................................................86 5 THERMOPHILIC ANAEROBIC DIGESTI ON OF SUGARBEET TAILINGS USING COD REM OVAL AS PRE-TREATMENT........................................................................... 92 5.1 Introduction............................................................................................................... ........92 5.2 Methods............................................................................................................................94 5.2.1 Anaerobic Digester..............................................................................................94 5.2.2 Feedstock.............................................................................................................94 5.2.3 Experiments.........................................................................................................94 5.2.4 Analysis................................................................................................................ 95 5.3 Results and Discussions.................................................................................................... 96 5.3.1 Characteristics of Beet Tailings and Residue...................................................... 98 5.3.2 Biochemical Methane Potential (BMP)............................................................... 99 5.3.3 Microbial Populations........................................................................................100 5.3.4 High Solids Anaerobic Digestion of Beet Tailings in an Unmixed Digester....101 5.3.5 Integration of Removal of Soluble COD as a Pre-treatment Step into SEBAC-II Process........................................................................................... 103 5.4 Conclusions.....................................................................................................................104 6 CONCLUSIONS AND FUTURE WORK ........................................................................... 113 6.1 Conclusions.....................................................................................................................113 6.1.1 Stabilization of Anaerobically Digest ed Residue by Nitrification Process.......113 6.1.2 Integration of Ammonia Removal from Leachate within Anaerobic Digestion Process............................................................................................ 114 6.1.3 Integration of In Situ Treatment of Anaerobically Digestated Residue and Leachate in SEBAC-II Configuration............................................................. 115 6.1.4 Pre-treatment of Readily Biodegradabl e Feedstock to Improve Digestibility... 116 6.2 Future Work................................................................................................................ ....116 APPENDIX A PROGRAM CODE OF CR10X fo r STABILIZATION PROCESS ....................................118 B PROGRAM CODE OF CR10X for AMMONIA REMOVAL PROCESS .......................... 119 LIST OF REFERENCES.............................................................................................................121 BIOGRAPHICAL SKETCH.......................................................................................................127

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8 LIST OF TABLES Table page 1-1 Performance data from the SEBAC process for various feedstocks at 55 oC ................... 27 2-1 Basic characteristics of an aerobically digestated residue.................................................. 47 2-2 Measurement of NH4 +, NO2 and NO3 in digestated residue (10 g wet weight)............... 47 2-3 Experimental and Gompertz values of n itrification in 16-day stabilization process........47 2-4 Oxygen consumption during 16-day stabilization process................................................ 47 3-1 Characteristics of rice straw.............................................................................................. .77 3-2 Concentrations of ammonia-nitrogen, nitrate-nitrogen a nd ammonia removal rate in biological ammonia removal process................................................................................. 77 3-3 Performance of anaerobic digestion of rice straw from Experiment 1-3........................... 78 3-4 Summary of performance of an aerobic digestion of rice straw......................................... 79 5-1 Sugar beet tailings characteristics.................................................................................... 112 5-2 Chemical characteristics of tailings and digested residue, and extent of degradation of the individual constituents during anaerobic digestion............................................... 112

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9 LIST OF FIGURES Figure page 1-1 Sequential batch anaerobic composting (SEBAC) process............................................... 24 1-2 Sequential batch anaerobic composting II (SEBAC-II) process........................................ 25 1-3 Ammonia inhibition during reuse of leachate in anaerobic digestion of sugar beet pulp....................................................................................................................................26 1-4 Anaerobic digestion of sugar beet tai lings in SEBAC-II system under mesophilic temperature.................................................................................................................... ....26 2-1 Glass reactor connected to an ammonia trap..................................................................... 42 2-2 Representative standard curve of T AN by ammonia-selective electrode method.............42 2-3 Representative standard curve of nitrite-nitrogen by colorimetric method....................... 43 2-4 Representative standard curve of ni trate-nitrogen by nitrat e electrode method................43 2-5 Effect of air flow rate on nitrogen transformations in anaerobically digested residue during the 8-day stab ilization process................................................................................44 2-6 Fractions of ammonium-nitrogen, nitritenitrogen, nitrate-nitrogen, nitrogen gas and volatilized ammonia in the 16day stabilization process................................................... 44 2-7 Cumulative amount of nitrifiedand deni trified nitrogen in 16-day stabilization process in the 1 L glass reactor.......................................................................................... 45 2-8 Nitrification and denitrification rate in 16-day stabilization process in 1 L glass reactor when the gas flow rate was 187 mL/kg wet residue/min (room temperature)...... 46 3-1 Digester setup for anaerobi c digestion of rice straw..........................................................69 3-2 Ammonia removal reactor.................................................................................................69 3-3 Experiment operation for anaerobic digest ion of rice straw using inoculum processed in different ways.............................................................................................................. ..70 3-4 Experimental data and first order fit of TAN removal from leachate by aeration in the 1st 2nd and 3rd processing.............................................................................................71 3-5 Cumulative biogas and methane yield, da ily methane yield and methane fractions from Experiment 1-3.......................................................................................................... 72 3-6 Cumulative methane production, COD, pH and TAN in leachate during anaerobic digestion of rice straw from Experiment 4........................................................................ 73

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10 3-7 Cumulative methane production, pH and T AN in leachate during anaerobic digestion of rice straw from Experiment 5........................................................................................ 74 3-8 Cumulative methane production, COD, pH and TAN in leachate during anaerobic digestion of rice straw from Experiment 6........................................................................ 75 3-9 Cumulative methane production and daily me thane yield from Experiment 7 and 8....... 76 4-1 Bench-scale reactor operated by an au tomatic CR10 control connected to an ammonia trap.....................................................................................................................88 4-2 Operation of inlet and outlet valves by automatic CR10 control....................................... 88 4-3 Bench-scale reactor (SEBAC-II Mode l) for biological removal process.......................... 89 4-4 Operation of pump, inlet and outle t valves by automatic CR10 control........................... 89 4-5 Specific nitrification rate in a SEBAC -II model and simultaneous pH change during stabilization process...........................................................................................................90 4-6 Integration of stabilizati on process into SEBAC-II system............................................... 90 4-7 Relationship of initial ammonia removal rate and original TAN concentration in bench scale reactor............................................................................................................ .91 4-8 Integration of step for st abilization of residue and trea tment of leachate into SEBACII system...................................................................................................................... .......91 5-1 Anaerobic digester filled with tailings and leachate........................................................ 106 5-2 Cumulative biogas and methane production, methane percentage, daily methane, pH, COD and volatile organic acid conc entrations from Experiment 1.................................107 5-3 Cumulative biogas and methane production, methane percentage, daily methane, pH, COD and volatile organic acid conc entrations from Experiment 2.................................108 5-4 Cumulative biogas and methane production, methane percentage, daily methane, pH, COD and volatile organic acid conc entrations from Experiment 3.................................109 5-5 Comparison of cumulative methane production from Experiments 1, 2 and 3...............110 5-6 Incorporation of removal of soluble COD as pre-treatment step into SEBAC-II process..............................................................................................................................111

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11 LIST OF ABBREVIATIONS ALS Advanced life support ALSB Air-lift loop sludge blanket ANAMMOX Anaerobic ammonium oxidation BMP Biochemical methane potential CANON Completely autotrophic n itrogen remova l over nitrite COD Chemical oxygen demand ESM Equivalent system mass OFMSW Organic fraction of municipal solid waste OLAND Oxygen-limiting autotrophic nitrification-denitrification SEBAC Sequential batch anaerobic composting STP Standard temperature and pressure TAN Total ammonia nitrogen TKN Total kjeldahl nitrogen TS Total solids UASB Upflow anaerobic sludge blanket USB Upflow sludge blanket VS Volatile solids

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12 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ENHANCEMENT OF ANAEROBIC DIGEST ION OF SOLID WASTES BY PRETREATMENT AND POST-TREATMENT By Wei Liu May 2008 Chair: Pratap C. Pullammanappallil Cochair: Arthur A. Teixeira Major: Agricultural and Biological Engineering This study reports on the development of methods for pretreatment of feedstock and post treatment of residue and leach ate to improve the performan ce of UF-patented anaerobic composting technology. These improvements were need ed for application of this technology as a solid waste management subsystem on long-term NASA space missions, as well as in treating industrial organic wastes, such as beet pulp and beet tailings from the beet sugar industry. Post treatments were needed for the NASA space mission application and beet pulp application, and involved stabilizat ion of anaerobically digested solid residue by a nitrification process, integration of ammonia removal from liquid leachate within the anaerobic digestion process, and incorporation of both treatments into the overall system configuration. Pretreatment of readily biodegradable feedstock was needed for the sugar beet tailings application, and consisted of adding a pre-wash step to wash and remove the large fraction of soluble organic matter in the sugar beet tailings, and holding this fraction in a separate re servoir for subsequent controlled release into the system. Results from post treatment of solid residue sh owed that nitrification initiated within 2 days by continuous flow of air through the resi due at a rate of 187 mL/minute/kg wet residue,

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13 and 85% of the initial ammonium-nitrogen nitrified within 16 days at a maximum rate of 0.41 mg/g wet weight/day. Post treatment of liquid leachate showed that th e ammonia removal rate was 70 -95 mg/L/day initially, and increased to 200-245 mg/L/day after 8-days of continuous operation, when concentration of total ammonia nitrogen reached 500 mg/L. However, repeated aeration reduced the efficacy of the leachate as an inoculum, suggesting that only part of the leachate should be aerated. System integration involved a modification in which aeration was carried out by holding air within the reactor at a pressu re of ~10 psi over 13 days for st abilization of digested residue, and a similar system and operation for ammonia removal from the liquid leachate. Results from the pre-treatment of sugar beet tailings revealed that addition of water solubilized a large fraction (0.6 g COD/g VS) of organic matter from the tailings. Methanogenesis could be initiated if the solubi lized material was leached out. Most of the methane potential remaining in the solids was ge nerated within a week. The methane yield of tailings was estimated to be 295 L/kg VS, of which 50-60% was from the readily solubilized organic matter. A volume reduction of 70-80% was achieved, and approximately 60% of dry matter and 75% of volatile solids were degrad ed. These demonstrated performance levels suggested that incorporating th ese pre and post treatments as a routine part of the system operation will greatly enhance the potential for widespread us e of this technology in waste management applications.

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14 CHAPTER 1 INTRODUCTION 1.1 Introduction 1.1.1 Anaerobic Digestion of Solid Waste The term solid waste would apply to any ga rbage, refuse, sludge and other discarded material resulting from community activities or commercial or industrial operations. Solid waste management has become a major concern in the world recently due to the huge quantities generated world-wide. Anaerobic di gestion of solid waste is becoming a popular method to treat these wastes because it can generate biogas as an energy resource. For example, Canada generates approximately 1.45 x 108 t of biomass (one type of solid wastes) per year. Anaerobic digestion of these biomass using conventional technologies could generate 1.14 x 1010 m3/year of CH4 with a heating value of 4.56 x 108 GJ, which is equivalent to about 4.4 % of Canada's current annual energy use (Levin et al, 2007). At the same time the digested residue from anaerobic digestion could serve as fertilizer for plant growth (Svensson et al., 2004). Moreover, anaerobic digestion has limited impact for our environment (Mata-Alvar ez et al., 2000). There are several onging studies on modeling and kinetics of the process for an aerobic digestion of solid waste (Borja et al., 2003; Borja et al., 2006); as well as enhancement of digester performance, overcoming ammonia inhibition a nd digester design impr ovement (Mata-Alvarez et al., 2000). Anaerobic digestion occurs primarily in two st eps: acid formation and methane formation. These processes are mediated by different groups of microorganisms, which require different nutritional compounds and environmental conditions This could lead to some problems of stability and control if the whole process o ccurs in one reactor (Demirel and Yenigun, 2002; Pohland and Ghosh, 1971). Therefore, at present more researchers put their efforts into a two-

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15 phase anaerobic digestion process, which me ans a physical separation of acid-formers and methane-formers in two separate reactors. In this case, optimum environmental conditions for each group of microorganisms could be provided separately to improve the whole process (Demirel and Yenigun, 2002). Gh osh et al (2000) showed that given the same operating conditions, the two-phase anaerobic digestion of municipal solid wastes exhibited 18% higher methane yield, 22% higher methane production rate and 13% higher methane concentration than the corresponding performance para meters for one-stage operation. However, others (Weiland et al., 1990) believed that it was unn ecessary to treat all kinds of solid wastes in two separate reactors; it depends on the physical and chemical properties of biodegradable wastes. They recommended that one-stage opera tion could be used to treat solid waste with low protein content such as beet pu lp (Weiland et al, 1990). Anaerobic digestion may be operated in psychrophilic (12-16 oC), mesophilic (35-37 oC or thermophilic conditions (55-60 oC At thermophilic temperatures, the rates of degradation and biogasification are faster, and have greater potential to destroy weed seeds and plant pathogens, which is especially beneficial for reapplying the digested residue with little post treatment back on to the fields to recycle nutrients (K oppar and Pullammanappallil, 2007). Thermophilic operations were found to provide better results th an mesophilic conditions in most cases. For example, in Mace et als study (2003) biodegrad ability of municipal solid waste could be enhanced by thermophilic operation and the corresponding ultimate methane yield was about 10% higher. On the other hand, disadvantages of thermophilic anaerob ic digestion are the reduced processs stability and reduced dewateri ng properties of the fermented sludge and the requirement for large amounts of energy for hea ting (Gallert and Winter, 1997). The greater

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16 energy demand for thermophilic temperature is approximately the same as the excess energy produced in the process in many cases. Therefore, the choice of optimal temperature depends on the type of substrate and the type of system us ed and levels of pathogen or weed seed control required in the digested residue (Mata-Alvarez et al., 2000). 1.1.2 High-Solids Anaerobic Digestion Studies have been devoted to the anaerobic digestion of high-solids organic wastes for solid waste m anagement because of the problems associated with reduction in process water and reactor size requirement. Some efforts focus on the environmental factors affecting the efficiency of high-solids waste digestion, in cluding chemical nature of feedstock, moisture content, pH, ammonia concentration and nutrient requirement s (Lay et al, 1997, 1998; Kayhanian and Rich, 1995). It was reported that the methanogenic activity decreased w ith the decrease in moisture content. At optimum pH, the methanogenic activ ity in high-solids digestion dropped from 100% to 53% when the moisture content decreased from 96% to 90%. However, for some feedstocks such as carrot and cabbage, the methanogenic activity was inhibited by th e high level of organic acids instead of moisture content (Lay et al, 1997; Lay et al, 1998). Meth anogenic bacteria have a variety of mineral nutrient requirements for robust growth. The addition of wastewater treatment plant sludges and dairy manure as a nutrient supplement may increase the gas production rate by 30% and improve the digestio n stability (Kayhanian and Rich, 1995). Several other studies focused on the improve ment of process and reactor design. The leachbed design is one of the options most a pplicable to high solids operation. The leachbed design uses recycle of leachate between new and ma ture reactors to inoculate, wet and provide nutrients for rapid startup of new cells. Organi c acids produced during st artup are conveyed via leachate to the mature reactor for conver sion (Chynoweth et al, 1991, 1992). This design does

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17 not require mixing and was developed and pa tented as the Sequential Batch Anaerobic Composting (SEBAC) process at th e University of Florida. 1.1.3 Sequential Batch Anaerobic Composting (SEBAC) The SEBAC process is a patented hig h-solid s, batch, leach-bed process that uses a combination of solid state fermentation and leachat e recycle to provide a simple, reliable process that inoculates new batches of waste, removes volatile organic acids and concentrates nutrient and buffer (Chugh et al., 1999; Chynoweth and Le grand, 1993; Chynoweth et al., 1992). This process has already been commercialized (Teixeira et al, 2003). It also has been considered by NASA as one option for the principal solid wast e management component in Advanced Life Support (ALS) systems for long-range space missions (Xu et al, 2002). The whole system requires a minimum of 3 bioreactors linked through a leachate handling, piping and pumping system. As illustrated in Figure 1-1, coarsely shredded feedstock is placed into a bioreactor that is ready for a new cycle of anaerobic digestion (stage 1). Leachate from a bioreactor containing resi due that has been digested (Stage 3) is recycled between that reactor and the newly loaded bioreactor (Stage 1) to provide moisture, inoculum, nutrients, and buffer necessary for start-up. Volatile organic acids form ed in the newly loaded bioreactor during startup are removed via leachate recy cle to the active mature bioreact or for conversion to methane and carbon dioxide. After startup, the newly loaded bioreactor becomes sustainable methanogenic and is maintained by recycling leacha te upon itself (Stage 2) until it graduates to Stage 3 as a fully mature reactor. The waste from the mature reactor (Stage 3) is unloaded and taken away as a by-product of the process. A fres h supply of waste is now loaded into the reactor which becomes a new Stage 1. Near the end of th e process, which may take approximately three weeks depending on feedstock charac teristics, leachate from the now mature reactor is used for the start-up of a new reactor that is once again ready to begin a new cycle. Biomass is not moved

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18 during the process; it passes thr ough different stages over time in the same reactor vessel. After completion, the biomass is dewatered to supply wa ter, and conserve nutrients and buffer for a new run. For some feedstocks, additional makeup water is required (T eixeira et al., 2003; Chynoweth et al., 2002; Xu et al., 2002). The biogas produced from the SEBAC process can be used like natural gas. The average composition for the biogas is 60% methane, 40 % carbon dioxide and incl udes traces of hydrogen sulfide, hydrogen, nitrogen and carbon monoxide. The SEBAC biogas can be used readily in all applications designed for natural gas such as dire ct combustion, fueling engines and fuel cells for production of mechanical work and electricity (Teixeira et al, 2003). The SEBAC process also produces solid and liquid by-products. The amount, quality and nature of these products depends on the quality of the feedstock, and the extent of the post-treatment refining process (Teixeira et al, 2003). The solid anaerobically digested residue cal led digestate can be used as a fertilizer or soil amendment. The SEBAC process has been tested on or ganic fraction of municipal solid waste (OFMSW), woody biomass, yard wastes and mixt ures of yard wastes and biosolids (Chynoweth and Legrand, 1993; Chynoweth et al., 1992). The performance of the SEBAC pilot system on several feedstocks is listed in Table 1-1 (Teixeira et al, 2003). Compared with other tradit ional anaerobic digestion tec hnologies, the SEBAC process design offers greater stability. The design allows for easy removal of inhibitory products, which may lead to imbalance. The leachbed design not onl y facilitates rinsing of toxic substances, such as metals, from the final product, but also eliminates the need for solids movement and mixing (Teixeira et al, 2003).

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19 In the original SEBAC system, gravity was relied upon to bring cas cading liquid leachate in contact with the organic feedstock by pump ing leachate into the top of the reactor and allowing it to flow by gravity and collect at th e bottom for subsequent recycling. In SEBAC-II the system was modified to move leachate thro ugh the bed under flooded operation using forced pumping, and recycling leachate through external gas-liquid separators that could accommodate vortex gas/liquid separation systems (Figure 1-2) This design modification was driven by the NASA requirement for operation in th e absence of a gravity field. 1.2 Statement of Problem Currently th ere are several applications for SEBAC-II system. Firstly, it can be used as a sub-system of solid waste management in A dvanced Life Support (ALS) system for NASA. Secondly, it can also be used for anaerobic dige stion of sugar beet pulp and sugar beet tailings. However, there still exist some problems in these applications. When it is used as a sub-system of solid waste management in ALS system, anaerobically digested residue from this process is desired to serve as fertilizer for pl ant growth for long term space missions. Digested residue directly obtained from SEBAC-II system has high moisture content. So it is usually dried before applic ation. On the other hand, ammonia released from anaerobic digestion may attach on the digested re sidue. Drying would lead to loss of ammonia by volatilization. Thus it is necessary for us to have a post-treatment process on the anaerobically digested residue to fix nitrogen. Sugar beet pulp contains a lot of nitroge n, which may be converted to ammonia during anaerobic digestion. Most of this ammonia appear s in the leachate. Leach ate is reused in the SEBAC-II system, which may cause ammonia accumu late and inhibit the anaerobic digestion. Ammonia inhibition during reuse of leachate is shown in Figure 1-3. The cumulative and daily

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20 methane yield slightly decreased after the leachate was reused for 3 times and dramatically decreased after the leachate was reused fo r 4 times (Koppar and Pullammanappallil, 2007). Sugar beet tailings have a large fracti on of readily soluble organic matter. The fermentation of soluble organic matter produced a lot of organic acids a nd lowered the pH. When sugar beet tailings were anaerobically digested in SEBAC-II system, the daily methane yield failed to increase even afte r 30 days (Figure 1-4). Therefore, further investigation was needed to address the problems discussed above, and this study was undertaken to carry out such investigation. 1.3 Objectives The work undertaken in this study was orga nized into four separate but related investigatio ns to meet each of the following specific objectives: Stabilize anaerobically digested resi due by a nitrification process, Integrate the need for ammonia removal from leachate to become part of the anaerobic digestion process, Integrate the in situ treatment of anaerobica lly digested residue and leachate into the SEBAC-II system configuration, and Develop a method for pre-treatment of readily biodegradable feedstoc k in application to sugar beet tailings. Each of these objectives is discussed in further detail in the following subsections, while a report of the work undertaken (and subsequent results) to meet each objective is presented respectively in the following four chapters. 1.3.1 In Situ Treatment of Anaerobically Digested Residue and Leachate 1.3.1.1 Stabilization of anaerobically digest ed residue by nitrifica tion process The digested residue is usually dried before applications, which may lead to ammonia volatilization. So it is nece ssary to have a stabilization process to convert ammonia to nitrate by

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21 nitrification. The goal for the first part of this study was to find the feasibility for integration of an in situ stabilization step into the SEBAC-II configuration with the following objectives: Confirm the availability of microorganisms required for nitrification in anaerobically digested residue. Measure the rate of NH3 transformations and losses during stabilization process. Quantify the rate of NH3 transformations using a kinetics mathematic model Measure the oxygen requirement for the stabilization process. Ammonia transformation and volat ilization during stab ilization of anaero bically digested residue were investigated. This work is reported in Chapter 2, and will present results of the preliminary work conducted in the small reactor s, including the feasibility of initiating the nitrification process, extent and rate of nitrification and mass balance on nitrogen during aerobic stabilization. Moreover, a method was devel oped for the determina tion of total ammonia nitrogen (TAN) in anaerobically digested resi due since there was no available method in the literature. 1.3.1.2 Integration of ammonia removal from leachate w ithin anaerobic digestion process During anaerobic digestion process, organi c nitrogen compounds are transformed to ammonia nitrogen and most of them remain in le achate. Leachbed digestion such as the SEBACII system, uses recycle of leachate between ne w and mature reactors to inoculate, wet and provide nutrients for rapid startup of ne w cells (Ghosh, 1984; C hynoweth et al, 1991, 1992). However, ammonia is accumulated in the system when leachate is reutilized from a mature reactor. Accumulation of ammonia may negativel y affect the anaerobic digestion performance (McCarty and McKinney, 1961; Gallert and Winter, 1997).

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22 The goal for the second part of this study is to determine the feasibility of integration of an in situ ammonia removal process within SE BAC-II system. Specific objectives were the following: Develop a biological ammonia removal process Determine the kinetics of ammonia removal process Determine the viability of aerated leachate as inoculum for subsequent leach-bed digestion This work is reported in Chapter 3, and w ill present the results of biological ammonia removal from anaerobic leachate using digested re sidue bed and the feasibility of reuse of the aerated leachate as inoculum for subs equent leach-bed an aerobic digestion. 1.3.1.3 Integration of in situ treatment of ana erobically d igested residue and leachate in SEBAC-II configuration The SEBAC-II system, which is in flood mode operation, recycles the leachate using forced pumping rather than grav ity. A bench-scale study was implem ented to test the concept of SEBAC-II with external gas/liqui d separation (Chynoweth et al, 2002). Several studies were also conducted for design, installation, start-up, preliminary operating performance (Xu et al, 2002; Teixeira et al, 2004) and modifi cations (Luniya et al., 2005) for a full-scale prototype SEBAC-II configuration for a space mission. Ho wever, little work has been de voted to post-treatment of the anaerobic digestion in this syst em. The objectives for the third part of this study include: Design the operation mode for in situ treatment of anaerobically digested residue and leachate in the SEBAC-II configuration Measure the nitrification rate in the pr ocess of digested residue stabilization Determine ammonia removal rate from leachat e using digested residue bed during aeration This work is reported in Chapter 4, and will present the results of the study. The results includes the nitrification rate on anaerobically di gested residue and ammonia removal rate from

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23 leachate during aeration, and prediction of the in situ post-treatment processing time in full prototype of SEBAC-II system according to these results. 1.3.2 Pre-Treatment of Readily Biodegradable Feedstock Efforts for enhancem ent of anaerobic digesti on of solid wastes have been dedicated, including different pretreatment methods to impr ove the digestibility of feedstock (Palmowske and Muller, 2003; Valo et al, 2004; Bougrier et al., 2005, 2006; Li and Noike, 1992; Neyens, E. and Baeyens E.; 2003; Lin et al, 1997; Penaud et al, 1999; Mshandete et al, 2005). However, different feedstock needs different pretreatment method according to its characteristics. Recent work in developing application of SEBAC-II technology for processing sugar beet waste (tailings) in the beet sugar industry is a good example. Sugar beet tailings contain a large fraction of readily soluble organic matter, which makes too much initial digestibility. In preliminary experiments, sugar beet tailings were anaerobically digested using the SEBAC-II process at 38 oC (Teixeira et al., 2005). Results showed that the rate of methane generation was poor compared to that from digestion of other organic residues. Persistently high volatile organic acid concentrations were measured in digester liquor, and daily methane production rates failed to in crease even after 30 days of di gestion. This indicated a need for further modifications and improvements to in tegrate an in situ pre-treatment process to anaerobically digest tailings w ithin the SEBAC-II configuration. The objectives for this fourth part of the study were the following: Confirm the availability of microorganisms re quired for anaerobic dige stion of sugar beet tailings Develop a pre-treatment method for anaerobic digestion of sugar beet tailings in the SEBAC-II system Measure the methane yield and methane producti on rate in anaerobic digestion of sugar beet tailings after incorporating the new pre-treatments

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24 Chapter 5 will present findings related to these modifications and improvements for anaerobic digestion of sugar be et tailings. These modifications included removal of readily soluble COD, and operation of the digester within a thermophilic temperature range (50 57 oC) where the rates of degradation and biogasification are faster. Figure 1-1. Sequential batch anae robic composting (SEBAC) process

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25 Pump A Stage 2Activated Reactor New Reactor Mature Reactor Biogas Biogas Stage 1 Stage 3 Pump B Pump C Anaerobically digested residue Figure 1-2. Sequential batch anaerobic composting II (SEBAC-II) process

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26 Figure 1-3. Ammonia inhibition dur ing reuse of leachate in anaerobic digestion of sugar beet pulp (Koppar and Pullammanappallil, 2007) 0.0 20.0 40.0 60.0 80.0 100.0 0.00 5.00 10.0015.0020.0025.0030.0035.00DaysCH4 Yield L/kg VS0.000 0.400 0.800 1.200 1.600 2.000CH4 Rate L/L/day CH4 Yield L/kg VS CH4 Rate L/L/day Figure 1-4. Anaerobic digestion of sugar beet tailings in SEBAC-II system under mesophilic temperature

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27 Table 1-1. Performance data from the SE BAC process for various feedstocks at 55 oC (Teixeira et al, 2003) Parameter MSW Yard waste Brewery chips Shredded office paper Space mission wastes* Methane yield, L/g VS added 0.30 0.07 0.06 0.35 0.3 VS reduction (%) 57 20 26 96 85 Volume reduction (%) 65 15 15 94 86 Solids retention time (days) 30 70 40 30 20 Blend of rice straw, paper and dog food (sim ulates feces); this run was conducted at 35 oC

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28 CHAPTER 2 STABILIZATION OF ANAEROBICALLY DIGE STATE D RESIDUE BY NITRIFICATION PROCESS 2.1 Introduction The process of anaerobic digestion is an im portant component in sustainable waste management. Anaerobic digestion not only generate s biogas which is an energy source but also produces a stable digested residue. Depending on the feedstock, the amount of residue produced in this process varies, which is related to th e degradable fraction of the wastes. Dry matter reduction varies from 35 % to 90 % depending on the feedstoc k. In anaerobic digestion, dry matter reduction of municipal solid waste (MSW), milled wheat stems and sugar beet tailings were 35 60% (Chugh et al, 1999), 70-77 % (Chynow eth et al, 2002) and 82-90% (Polematidis, 2007) respectively, which means MSW produces more anaerobically digested residue (dry weight) than wheat stems and sugar beet tailings The digested residue may be used as a soilquality enhancer (Svensson et al., 2004; Riva rd et al., 1995) and microorganism carrier in biofilter for air revitalization (X u et al, 2002). Moreover, addition of anaerobic residue from cocomposting was shown to improve humic acid fo rmation that led to the production of high quality composts used for plant growth (Meissal et al, 2007) The SEBAC process is a patented an aerobic digestion technology for odorless bioconversion of organic solid waste to meth ane and solid residue. The process uses a combination of solid-phase fermentation and leac hate recycle between ne w and old reactors to provide a simple, reliable proce ss that inoculates new batches, removes volatile organic acids, and concentrates nutrients and buffer. The proces s doesnt require high te mperature and pressure while producing methane, carbon dioxide, nutrients and digested residue as valuable products. Comparing with other traditiona l anaerobic digestion t echnologies, the SEBAC process is more stable. The design allows for easy removal of inhibitory products, which may lead to imbalance.

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29 The leachbed design not only facilitates rinsing of toxic substances, such as metals, from the final product, but also eliminates the need for solids movement and mixing (Teixeira et al, 2003). The modified SEBAC-II process means the syst em which was modified to recycle leachate under flooded operation using forced pumping instead of gravity, and recycling leachate through external gas-liquid separators. When organic compounds containing nitrog en are anaerobically digested, they are hydrolyzed and the nitrogen is converted to a mmonia. Most of this ammonia appears in the leachate. Dissolved ammonia exists in equilibri um with the ammonium ion (the ratio of the concentration of ammonia to ammonium ion being dictated by the pH) and it also partitions between the liquid and gas phase. The digested residue also contains some ammonia. Thus, during anaerobic digestion nitrogen from the solid waste is not removed, and most of it remains in the residue/leachate. This f eature may be a drawback from a waste treatment perspective, but can be turned into an advantag e if nitrogen in the re sidue/leachate could be utilized for plant growth purposes. The digested residue is usua lly dried before application because it is expensive to transport, handle and spread the residue when it has a high moisture content (Svensson et al., 2004). However, drying would lead to loss of ammonia (Svensson et al., 2004; Rivard et al., 1995), which decreases its effect as a fertilizer because of nitrogen loss. So a stabilization process for the digested residue is necessary. In this study, a stabilization process means an aeration stage after anaerobic di gestion. This process not only removes any residual volatile organic acids that formed during anaerobic digestion, but could also nitrify ammonia to nitrate. Nitrate is odorless and non-vola tile thereby minimizing any loss of nitrogen in a subsequent drying process.

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30 A lack of literature on stabilization of anaerobica lly digested residue in terms of the extent and rate of nitrification indicated that not much attention has been devoted to this process during aerobic curing stage. In this chapter the feasibility of initiating nitrification process, the kinetics, extent of nitrification, mass balance for nitr ogen transformations and oxygen consumption during stabilization are presented. A method for determ ination of total ammonia nitrogen (TAN) in anaerobic residue was also developed and test ed for its accuracy and recoverability. 2.2 Methods 2.2.1 Experimental Apparatus Experim ents were carried out in a set of 1 L glass jars. Anaerobically digested residue was loaded in the glass jar, the m outh of which was closed with a rubber stopper. Two glass tubes were inserted through the rubber stopper for gas inlet and outlet. The glass tube for inlet was inserted deep into the bottom of the jar. Aera tion was carried out from a high purity gas cylinder containing 20 % oxygen and 80% helium (Compre ssed air was used in the experiment 2.2.3.1 to measure the effect of air flow rate on transfor mation of nitrogen in anaerobically digested residue). Gas vented from the jar was purged through a dilute H2SO4 (concentration 0.04N) solution to absorb any volatilized ammonia. A schematic diagram of this reactor is shown in Figure 2-1. 2.2.2 Anaeobically Digested Residue The residu e used in these studies was an an aerobically digested mixture of wheat straw (55% of wet weight), shredded paper (37% of wet weight) and commercial dog food (7.6% of wet weight). This mixture in terms of its com position simulated the proportions of crop residue, paper wastes and human feces, respectively expe cted in long-term space missions (Chynoweth et al, 2002). Anaerobic digestion of th is synthetic waste was carried out in a SEBAC II system as described in Luniya et al (2005) Basic characteristics of the re sulting residue are listed in Table

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31 2-1. After digestion, the residue wa s stored in a refrigerator for about six months before it was used in experiments reported here. 2.2.3 Experiments 2.2.3.1 Effect of air flow rate on transformati on of nitrogen in anaerobically d igested residue The glass jar was loaded with 80 g of wet residue. The jar was purged by compressed air and the inlet air flow rate was 24 mL/min. Aeration was terminated after 8 days. Upon termination of aeration the residue was taken ou t and analyzed for TAN, nitriteand nitratenitrogen. The TAN in dilute H2SO4 solution, which was used to ab sorb any volatilized ammonia, was also determined. The experiment was carried out in triplicate. After completion of aeration by 24 mL/min air fl ow rate, the air flow rates of 15 mL/min and 6 mL/min were also tested. The air flow rate which yielded better values for nitrification was then used to carry out the following experiments. 2.2.3.2 Transformation of nitrogen in anaerobically digested residue Six glass jars were loaded with 80 g of wet residue each. The seventh jar was used as a control to quantify nitrogen ingr es s into the system from outsi de via diffusion and was treated identically to the other jars but with no residue in it. The same gas cylinder was used for aeration of all jars through manifold t ubing. The inlet flow rate of ga s was set at 15 mL/min (which yielded better values for nitrificat ion). Outlet gas was analyzed for N2 and O2 content every day. Aeration was terminated after 1, 2, 5, 8, 10 and 16 days respectively in each glass jar. Upon termination of aeration the residu e was taken out and analyzed fo r pH, total Kjeldahl nitrogen (TKN), TAN, and nitriteand ni trate-nitrogen. If pH of the resi due was below ~7.5 then sodium bicarbonate was added to bring pH up to ~7.5. Th e amount of sodium bicarbonate required was

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32 noted and the same amount was then added to the rest of the jars. Experi ments were carried out twice, the second after completion of the first run. 2.2.4 Analysis 2.2.4.1 Measurement of TAN Since a m ethod was not available in the lite rature to determine TAN in anaerobically digested residue an assay was developed and test ed for its accuracy and recoverability. A sample of 10 g wet residue was placed in a flask, to which 10 mL NH4Cl solution (Concentration: 1 g NH4Cl /L) was added, and the solution allowed to be absorbed completely by the residue. Into another flask containing 10 g of wet residue 10 mL of distillated water was added. This served as the control. Then 100 mL of 2M KCl was added to each flask as the extraction solution and the flasks were closed by a rubber stopper to avoid ammonia volatilization. Then the flasks were placed on a shaker for 10 minutes. The TAN co ncentration in the ex traction solution was measured by ammonia electrode (Accumet Cat# 13-620-508). This was followed by adding another 100 mL KCl solution and the extraction procedure was re peated. At the end of each extraction TAN was determined. In another set of experiments, first NaOH was used to increase the pH of KCl solution to 11. Then the extraction procedure as described previously was repeated with KCl. TAN was measured in the extracted solutions. Extractions were repeated twice. In third set of experiments, distillated wa ter rather than KCl solution was used as extraction solutions. In order to increase pH ab ove 11, NaOH was also added to the distillated water. The TAN was measured in the extracted so lutions. Extractions were repeated twice. The method which yielded better values for TAN was then used to measure TAN in the digested residue.

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33 For the measurement of TAN in extraction so lutions, ammonia-selec tive electrode method was used. Firstly, a standard curve was calcu lated. Standard solutions of 0.1, 1.0, 10, 100, and 1000 mg/L TAN were prepared using NH4Cl. The electrode was immers ed into 100 mL standard solution and a magnetic stirrer was used to mi x. A sufficient volume of 10N NaOH solution was added to raise pH above 11. The electrode was ke pt in solution until a stable millivolt reading was obtained. The relationship of log (Concentr ation) and millivolt should be linear. A representative standard curve is shown in Figure 2-2. The same procedure was used to measure extraction solutions, and the TAN concentration wa s read from the standard curve. Ammonia in the diluted sulfuric acid trap was al so measured using ammonia electrode. 2.2.4.2 Measurement of nitrite A sa mple of 10 g wet residue was placed in a flask, to which 100 mL of 2 M KCl solution was added as the extraction solu tion, and the flask was closed w ith a rubber stopper. Then the flask was placed on a shaker for 10 minutes. A colorimetric method was used to measure n itrite nitrogen in the extraction solutions. Diazotizing reagent was prepared by dissolving 0.5g of sulfanilamide in 100 mL of 2.4 M HCl. Also, 0.3g of N-(1-naphtyl-)-ethylenediamine dihydrochloride was dissolved in 100 mL of 0.12 M HCl to make a coupling reagent. A sample of 2 ml of the extract was pipetted into a 50 mL volumetric flask, and deionized water was added to make the total volume about 45 ml. Then 1 ml of the diazotizing reagent was added. After 5 min, 1 ml of the coupling reagent was added. The solution was mixed and allowed to stand fo r 20 min. After that the solution was made to volume, mixed thoroughly, and colo r intensity was measured at 540 nm against a reagent blank solution. Absorbance measurements were cal culated by analysis of standards whose concentrations were 0, 0.1, 0.2, 0.3 mg/L of NO2 --N. The absorbances of standards were measured for analysis of the extract. A represen tative standard curve is shown in Figure 2-3. The

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34 NO2 concentration of the sample was determin ed using the equation obtained by linear regression of the concentrati on of the standards against the corresponding absorbance measurements. 2.2.4.3 Measurement of nitrate A sa mple of 10 g wet residue was placed in a flask. 100 mL of distilled water was added to the flask as the extraction solution and the flask was closed with a rubber stopper. Then the flask was placed on a shaker for 10 minut es. A nitrate electrode was used to measure nitrate nitrogen in the extraction solutions. Firstly, a standard curve was calculated. Standard solutions of 1.4, 14, 140, 1400 mg/L NO3 N were prepared using NaNO3. A sample of 2 ml of ioni c strength adjuster (2 mol/L (NH4)2SO4 ) was added to each 100 ml of standard. The nitrate electrode was used to get potential of each solution. Potentia l measurements against log (NO3-N concentration) were plotted on graph paper and the standard curve wa s obtained. A representati ve standard curve is shown in Figure 2-4. The same procedure was us ed to measure extraction solutions and read nitrate nitrogen concentration from the standard curve. These measurement methods are summarized in Table 2-2. 2.2.4.4 Gas samples Gas sam ples from outlets of jars were anal yzed every day for nitrogen and oxygen by a gas chromatograph equipped with a thermal conductivity detector (Fisher Gas Partitioner, Model 1200). The gas chromatograph was calibrated w ith an external standard containing N2: O2: CH4: CO2 in volume ration 20:5:45:30. Gas chromatogram s were processed and recoded using an integrator (SP 4200 Integrator, Spectra Physics, Inc.).

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35 2.2.4.5 Stabilization performance The perf ormance of stabilization was evaluate d by fitting the cumulative nitrified nitrogen data to the modified Gompertz equation (Zwietering et al, 1990) The assumption of this model is that the cumulative amount of nitrified nitrogen into batch reactor is a function of bacterial growth. The modified Gompertz eq uation could be expressed below: y = A exp{-exp[ ]}1)( t A em where y is the cumulative nitrified nitrogen (mg/g wet residue) at any time t, A is the nitrified nitrogen potential (mg/g wet residue), m is the maximum nitrification rate (mg/g wet residue/day), is the duration of lag time (day), and t is the time at which cumulative nitrified nitrogen y is calculated (d ay). The parameters P, m were estimated by using the Solver feature in MS-Excel. The value of parameters wh ich minimized the sum of the square of errors between fit and experimental data were determined. 2.3 Results and Discussions 2.3.1 Determination of TAN in An aerobically Digested Residue An extractio n efficiency of TAN from the digested residue was determined using the following formula: treatmen t intoaddedTAN controlin TAN nt in treatme TAN (%) efficiency Extraction For extractions in which pH was not increase d, the efficiency was 51.4%. However, for those extractions which were carri ed out after increasing the pH to 11, the efficiency was 107%. The measurements were carried out in triplic ate and the recoverability was within 2%. The pH of digested residue as measured after adding the extraction solution was 6. For this situation the

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36 TAN measured was approximately half of that expected. However, if the pH of extraction solution was increased to above 11 by NaOH add ition, almost all the TAN was detected. The value was over 100% because the TAN distribution in the digested residue may not be uniform. The average TAN content in the residue was used as the value of the control in the above expression. It was possible that ammonium ion (the dominant form of ammonia at pH 6) was adsorbed strongly on to the surfaces of the residu e, which made it difficult to extract. However, when pH was increased the dominant form sh ifts to dissolved ammonia which was easily extracted. So pH adjustment during extraction is important to recover and measure TAN in digested residue. Another set of experiments was carried out by using distilled water (pH>11) instead of KCl solution as the extraction solution. After 3 times of extraction, the efficiency was only 50.8%. The extraction using KCl obtained better efficiency because KCl served as a cation exchanger in the extraction process. The 2 M KC l extraction procedure was adopted because use of 2 M KCl instead of 1 M KCl reduces the size of the aliquot of extract, and some analyses showed that the results obtained using 2 M KCl for extraction had sligh tly higher precision than those obtained using 3 M KCl or 4 M KCl (Bremn er and Keeney, 1966). Subsequently TAN was determined after adjusting the pH to 11 and extracted with an aqueous KCl solution. 2.3.2 Effect of Air Flow Rate on Transforma tion of Nitrogen in Anaerobic Residue Three different air flow rates were conducte d, which were 6 mL/min, 15 mL/min and 24 mL/min. Figure 2-5 shows the effect of air fl ow rates on transformations of nitrogen in anaerobically digested residue. The results were re ported as percentage (%) of total nitrogen in anaerobically digested residue be fore and after 8-day stabilization process. The experiments were carried out in triplicates. The results shown in Figure 2-5 are the average of these three measurements.

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37 When air flow rate was 24 mL/min, the result showed that no nitrif ication happened even though TAN content in the residue dropped from 86% to 32%. The results s howed that 48.4% of nitrogen in the residue was lost by volatilization and this may be the reason for the decrease of TAN in the digested residue. Therefore, in or der to minimize ammonia volatilization, it was necessary to decrease th e air flow rate. When the air flow rate dropped to 6 mL/min, volatilized ammonia loss was only 6.5%. However, the total nitrified nitrogen, i.e. the sum of nitrite nitrogen and nitrate nitrogen, was only 20%. Th ere was 40% of total ni trogen that was unknown in this 8-day stabilization process according to the mass balance for nitrogen. In the nitrification process, oxygen was consumed to oxidize ammo nia nitrogen to nitrite nitrogen and then to nitrate nitrogen by nitrifyi ng bacteria as followings: NH4 + + 1.5 O2 2 H+ + H2O + NO2 NO2 + 0.5 O2 NO3 When the air flow rate was low, limited oxygen was available for the bacteria, so the denitrification process may happen. In this case, nitrate may have been c onverted to nitrogen gas according to the following equati on and exhausted from system. NO3 + 6 H+ + 5 e0.5 N2 + 3 H2O So, it was possible that the oxygen supply by 6 mL/min of air flow was not enough for the nitrification process and lead to nitrogen loss from the residue by denitrification. When the air flow rate was 15 mL/min, the n itrite and nitrate nitrogen reached 7.2% and 63.3% of total nitrogen respectively. At the same time, loss of ammonia nitrogen due to volatilization was 11.7% and unknow n nitrogen (maybe lost by deni trification) was 4.8%. So apparently a flow rate of 15 mL/min maximized nitrification and minimi zed volatilized ammonia

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38 losses through stripping with the apparatus used here. Therefore the following experiments were carried out at a flow rate of 15 mL/min, which was equal to 187 mL/kg wet residue/min. 2.3.3 Effect of Aeration on Tran sformation of Nitrogen in An aerobically Digested Residue A gas tank containing a helium-oxygen mixture ( 80:20 by volume) instead of air was used in order to measure nitrogen gas production from the denitrifica tion process. Figure 2-6 depicts the nitrogen fractions in the form of ammonium, nitrite, nitrate, nitrogen gas and volatilized ammonia over a 16-day aeration pro cess. All forms of nitrogen are reported as a percentage (%) of the total nitrogen at the beginni ng of the experiment (i.e. day 0). At the beginning, the total initial nitrogen cont ent was 414 mg, 72% of which was TAN and 28% of which was nitrate-nitrogen. Nitrate could have been formed during storage due to the presence of oxygen in the h eadspace. Nitrogen gas producti on within a time period was estimated as the product of nitroge n concentration in the outlet of the jar and the gas flow rate over that time period. Nitrogen measured from the control jar was subtracted. As no N2 was detected in the inlet of all jars, nitrogen measur ed at the outlet of control jar must be due to diffusion from outside. About 85% of ammonium-nitrogen was nitrified during the 16-day aeration. It was seen that the amounts of nitrogen i.e sum of ammoni um, nitrite, nitrate, nitrogen gas and ammonia losses, were in the range of 390 to 479 mg. The differences were around 5~15% of the initial N content of 414 mg in the residue. From Figure 26 it can be seen that th e nitrification process was activated within two days without any inoculum addition, wh ich meant appropriate microbial populations required fo r nitrification were naturally available in the anaerobically digested residue. The presence of nitrate in th e residue used for the experiments was due to formation of nitrate during storage, which also indicated presence of nitrifiers in the residue. In the nitrification process, ammonium nitrogen is first conve rted to nitrite-nitrogen by

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39 Nitrosomonas or other n itrifying bacteria, then nitrite is oxi dized to nitrate-nitrogen. Nitrite content was very low in the solid residue duri ng the whole aeration peri od. Low contents of nitrite-nitrogen indicated that most nitrite wa s consumed as soon as it was generated. Ammonia lost by volatilization and stripping was less than 6% after 16 days of aeration. An aeration rate of 187 mL/kg wet residue/min was able to minimize volatilization. The TKN measurements showed that organic nitrogen in the residue was maintained between 55 ~ 65 mg N during the 16-day aeration period. This appeared to indicate that any ammonia released by heterotrophic aerobic respira tion was matched by assimilatio n of nitrogen into microbial biomass. The errors in the results for all the measurements (except N2 gas) were between 5-15%. However, errors for N2 gas production varied between 15-30%. This could have been due to two reasons. Firstly, N2 gas production was estimated based on a N2 concentration measurement taken daily. Secondly, air flow patterns within the residue could have va ried between jars leading to different N2 production rates. The results shown in Figure 2-6 are the average of two measurements. 2.3.4 Nitrification Kinetics Figure 2-7 depicts the amounts of nitrogen n itrified and denitrified during the aerobic stabilization process. Total nitr ification represents the cumulativ e production of nitrite-nitrogen, nitrate-nitrogen and nitrogen gas. The curve from Gompertz fit is the result of fitting the cumulative nitrified nitrogen data to the modified Gompertz equation. The parameters P, and m estimated by the Gompertz equation are listed in Table 2-3. Denitrification bars show the cumulative generation of nitrogen gas. Figure 2-8 s hows the nitrification and denitrification rate during this stabilization process. The rates are expressed in units of mg N/g wet residue/day.

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40 Nitrate production was initiated two days after aeration, and was sustained until completion of the experiment on day 16. The in itial nitrification rate was 0.13 mg/g wet residue/day. After that, the nitrification conti nued to increase and the maximum rate was 0.41 mg/g wet residue/day, which was obtained on the 8th day. The experiment was carried out for 16 days, by which time 85% of original ammonium was removed and the nitrification rate dropped to 0.04 mg/g wet residue/day. Substrate availabl e for microorganism growth, such as inorganic carbon source and ammonia, could have become limited after several days reducing the nitrification activity. The Gompertz model fitted th e nitrification data very well. The lag phase for nitrification was 3.7 days in the model, which was a little longe r than that in the experiment. The maximum nitrification rate was 0.49 mg/g wet residue/day. From Figure 2-7, it can be seen that denitr ification was initiated soon after beginning nitrification process. Nitrite a nd nitrate-nitrogen were produced fr om the nitrification process, providing substrate for denitrifica tion. The rate of denitrification process continued to increase until day 10 after which it dropped. On the 10th day, the rate reached a peak value of 0.36 mg/g wet residue/day. The rate dropped to 0.004 mg/g we t residue/day on the 16th day. The denitrified nitrogen fraction reached ~50% of the nitrified fr action in this 16-day experiment. Denitrification occurs in the absence of molecular oxygen in anoxic zones. It is evident that even though continuous air flow was maintained, anoxic z ones may have developed within the residue promoting denitrification. Thus, nitrogen was lo st from the residue due to denitrification. 2.3.5 Oxygen Consumption Oxygen consumption based on wet weight of anaer obic digestate is liste d in Table 2-4. The cumulative nitrified nitrogen, cumulative oxygen consumption and theoretical oxygen consumption are shown in units of mg per g wet residue. Theoretical oxygen consumption was calculated based on the stoichiometry for nitrification:

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41 NH3 + 2 O2 NO3 + H+ + H2O Within the 16-day aeration period, 8.05 mg oxygen was consumed per mg nitrate-N produced, while the theoretical requirement based upon stoichiometry is only 4.57 mg oxygen/mg nitrified nitrogen. This meant that while 57% of oxygen was consumed to oxidize ammonium to generate nitrate, 43% of oxygen was consumed by re sidual volatile organic acids, sulfide or composting process. 2.4 Conclusion A method was developed for the measurement of TAN in the digested residue as a method was not available in the literature. The 2 M of KCl was used as an extrac tion solution, and pH of the extraction solution was increased to above 11 by NaOH addition. The results showed that the extraction efficiency was above 98% and the recovera bility was within 2%. A method for nitrification on the solid digest ed residue was also developed. As the microorganisms required for nitrification process na turally existed in the anaerobically digested residue, it was possible to stabilize the nitroge n by simply aerating it. Nitrification was accomplished without any inoculum addition. By continuously blowing ai r through the residue at 187 mL/kg wet residue/min, the nitrification process could be initiated with in two days. Approximately 85% of ammoniumnitrogen was nitrified during a 16-day aeration period and the maxi mum rate was 0.41 mg/g wet weight/day. The denitrification process occurred soon after nitrification and its fraction reached ~50% of the nitrification. The modified Gompertz model was used to quantify the rate of NH3 transformations, and the results showed that it fitted the nitrification data very well. The oxygen consumption during this stabilization process was determined. The result showed that the oxygen consumption was 8.62 mg oxygen per mg nitrified nitrogen even though theoretical requirement based upon stoichiometry was 4.57 mg oxyge n /mg nitrified nitrogen.

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42 H2SO4 Residue gas tank (80% Helium + 20% Oxygen)80% He + 20% O2 Sampling port Figure 2-1. Glass reactor connected to an ammonia trap y = -59.033x + 261.5 R2 = 0.9999 0 50 100 150 200 250 300 350 400 -2-101234 log(concentration mg/L)mV Figure 2-2. Representative standard curve of TAN by ammo nia-selective electrode method

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43 Figure 2-3. Representative standard curve of nitrite-nit rogen by colorimetric method Figure 2-4. Representative st andard curve of nitrate-nitr ogen by nitrate electrode method

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44 86.19 32.15 86.19 13.09 86.19 36.388.62 5.58 8.62 63.31 8.62 15.020 10 20 30 40 50 60 70 80 90 100BeforeAfterBeforeAfterBeforeAfter 24mL/min15mL/min 6mL/min Total inorganic nitrogen (%) NH4-N(17%) NO2-N( 27%) NO3-N( 8%) Volatilized NH3(13%) Unknown (15%) Figure 2-5. Effect of air flow rate on nitrogen transformations in anaerobically digested residue during the 8-day stabilizati on process when the initial total inorganic nitrogen was 300 mg N Elapsed Time (days) 012581016 Nitrogen Fraction (%) 0 20 40 60 80 100 120 NH4 +-N (%) NO3 --N (%) N2-N (%) NH3 Loss (%) 72% 70% 66% 61% 49% 34% 19% 28% 23% 28% 26% 35% 36% 41% 2% 14% 30% 44% 44% 1% <1% <1% <1% 2% 6% Figure 2-6. Fractions of ammoni um-nitrogen, nitrite-nitrogen, nitr ate-nitrogen, nitrogen gas and volatilized ammonia in the 16day stabilization process when the gas flow rate was 187 mL/kg wet residue/min (room temperature) and initial total inorganic nitrogen was 414 mg N

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45 Elapsed Time (days) 012581016 Nitrified /Denitrified Nitrogen (mg/g wet residue) 0 1 2 3 4 5 6 Denitrification (mg/g wet residue) Total nitrification (mg/g wet residue) Gompertz equation fit (mg/g wet residue) Figure 2-7. Cumulative amount of nitrifiedand denitrified nitr ogen in 16-day stabilization process in the 1 L glass reactor when the gas flow rate was 187 mL/kg wet residue/min (room temperature)

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46 Elapsed Time (days) 024681012141618 Nitrification /Denitrificati on Rate (mg/g wet residue/day) 0.0 .1 .2 .3 .4 .5 Nitrification Rate (mg/g wet residue/day) Denitrification Rate (mg/g wet residue/day) Figure 2-8. Nitrification and de nitrification rate in 16-day st abilization process in 1 L glass reactor when the gas flow rate was 187 mL/kg wet residue/min (room temperature)

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47 Table 2-1. Basic characteristics of anaerobically digestated residue Value Moisture content (%) 81 86 Total solids (TS) (%) 14 19 Volatile solids (VS) (%) 91 98 pH 7 8.8 NH4 + N (mg/g wet weight of residue) 3.5 5.2 Organic N (mg/g wet weight of residue) 4.3 7.9 Table 2-2. Measurement of NH4 +, NO2 and NO3 in digestated residue (10 g wet weight) NH4 + N NO2 N NO3 N Measurement method Ammonia electrode Colorimetr ic method Nitrate electrode Extraction reagent 100 ml 2M KCl (pH>11) 100 ml 2M KCl 100 ml Distilled Water Extraction time Shake for 10 minutes Shak e for 10 minutes Shake for 10 minutes Extraction efficiency 98% after 3 times extraction Above 95 % Above 90 % Table 2-3 Experimental and Gomp ertz values of nitrification in 16-day stabilization process (the gas flow rate was 187 mL/kg wet residue/min) Experimental value Gompertz equation value Nitrified nitrogen A (mg/g wet residue) 4.39 4.48 Maximum nitrification rate m (mg/g wet residue/day) 0.41 0.496 duration of lag time day 2 3.71 Table 2-4. Oxygen consumption during 16-day stabilization proce ss (the gas flow rate was 187 mL/kg wet residue/min) Elapsed time (days) Nitrification (mg N) O2 consumption (mg O) Theoretical required O2 consumption (mg O) 1 1.22 1.73 0 2 1.56 4.19 0.60 5 2.11 12.39 3.13 8 3.35 24.42 8.79 10 4.15 25.16 12.48 16 4.39 25.54 13.54

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48 CHAPTER 3 INTEGRATION OF BIOLOGICAL AMMONIA REMOVAL INTO LEACH-BED ANAE ROBIC DIGESTION OF SOLID WASTE 3.1 Introduction When organic compounds containing nitrog en are anaerobically digested they are hydrolyzed and the nitrogen is converted to a mmonia. Most of this ammonia appears in leachate. The leachbed digestion uses recycle of leachate between new and mature reactors to inoculate, wet and provide nutrien ts for rapid startup of new cells Organic acids produced during startup are conveyed via leachat e to the mature reactor for conversion (Ghosh, 1984; Chynoweth et al, 1991, 1992). However, ammonia is accumulate d in the system when leachate is reutilized from a mature reactor. Accumula tion of ammonia may negatively affect the anaerobic digestion performance. Many studies reported ammonia i nhibition or toxicity in anaerobic digestion processes (McCarty and McKinney, 1961; Galler t and Winter, 1997). Dissolved ammonia exists in equilibrium with the ammonium ion and th e ratio of the concentration of ammonia to ammonium ion is dictated by the pH. It has been demonstrated that a free ammonia concentration of 150 mg/L inhibited around 50% of the anaer obic digestion perfor mance (McCarty and McKinney, 1961). Koppar and Pullammanappallil ( 2007) reported the effect of ammonia accumulation in serially operated, single-stage, batch, leach-bed, thermophilic anaerobic digestion of spent sugar beet pul p. In this study, each subseque nt run used the leachate from a previous run (e.g. Run 2 used the leachate at the end of Run 1, R un 3 used the leachate at the end of Run 2 and so on). The free ammonia concentra tion reached 149 mg/L at the end of Run 3. The maximum methane production rate was 0.086 m3/day after Run 3, dr opped sharply to 0.047 m3/day after Run 4 and dropped further to 0.017 m3/day at the end of Run 5. Similarly, the time required to achieve 95% of ultimate methane potential for Run 3 was 5.71 days, increased to 10.92 days by the end of Run 4 and further rose sharply to 21 days. The results and analysis

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49 showed that the inhibition observed in Run 4 a nd 5 may be due to toxicity from free ammonia accumulation. Lay et al (1997) also showed that in a well-acclimatized bacterial system, the methanogenic activity dropped 10% when the NH4 +-N concentration was 1670-3720 mg/L, 50% when 4090-5550 mg/L and dropped to zero when 5880-6600 mg/L. The pH in these studies ranged from 6.5 to 8.5. It was also shown that the lag phase duration was dependent on the NH3 level instead of NH4 + (Lay et al, 1997). Nitrogen in ammonia form can be remove d from the leachate by several different processes, including biological nitrification-denitrification (Aspe et al, 2005; Dong and Tollner, 2003; Wang et al, 2003), strippi ng (Zeng et al, 2006; Bonmati a nd Flotats, 2003), ion exchange (Sanchez et al, 1995; Milan et al, 1997) and struvite precipi tation (Uludag et al, 2005). Ammonia removal by biological ni trification-denitrification is a popular method due to its high efficiency and low cost. In this process, amm onia is firstly converted to nitrite and then to nitrate under aerobic conditions by nitrifying orga nisms, after which nitrate is reduced to nitrogen gas under anaerobic conditions by denitrif ying organisms. Recently several varieties of the above scheme have been developed, incl uding anaerobic ammoni um oxidation (Anammox), completely autotrophic nitrogen removal over nitrite (Canon) (Sliekers et al, 2003) and oxygenlimited autotrophic nitrifi cation-denitrification (Oland) proc ess (Kuai and Verstraete, 1998; Verstraete and Philips, 1998; Peng and Zhu, 2006). The concept of biological nitrification and de nitrification has been employed to remove ammonia from wastewater or le achate. The kinetics of an in situ ammonia removal in both acclimated and unacclimated wastes was evalua ted and the ammonia removal efficiencies reached above 97% when the initial ammonia con centration was 500 mg N/L. All rate data fit well to Monod kinetics, with sp ecific rates of removal of 0. 196 and 0.117 mg N/day/g dry waste

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50 for acclimated and unacclimated wastes, respecti vely (Berge et al, 2006). The impact of temperature and gas-phase oxygen on the kinetics wa s also evaluated, showing that most rate data fit well to an empirically based multip licative Monod equation with terms describing the impact of oxygen, pH, temperat ure and ammonia concentration (B erge et al, 2007). The fate of nitrogen in leachate from bioreactor landfills was summarized (Berge et al 2005). Also, Jun et al (2004) test an upflow sludge bla nket (USB) reactor combined by aerobic biofiltration system had been tested with real sewage. About 95% of amm onia was nitrified in the aerobic filter and the denitrification efficiency was in the range of 72-85% in the anoxi c filter. Total ammonia nitrogen removal efficiency reached 70% in this process. Anaerobic digestion may be improved by integrating this biological amm onia removal step into the anaerobic digester system. Wang et al (2003) tried to integrate an aerated submerge d biofilter into a two-phase anaerobic digestion process for food waste. Ammonia accumulated in th e original system due to recycling of the leachate from the methanogenic reactor. In thei r study, the leachate from a methanogenic reactor was treated by passing the submerged biofilter for ammonia removal under aerobic conditions. Then the leachate was divided into two streams. Th e flow rate ratio of the stream recycled into the acidogenic reactor to the stream used for d ilution of acidogenic leachate was 1:4. The result showed that ammonia removal efficiency was above 90% and methane production in the enhanced system increased by 26% compared to the original system without the aerated biofilter. The studies presented in Chapter 2 showed th at nitrifying activity can be initiated and sustained in anaerobically digested residue. Du ring post aerobic proce ssing of anaerobically digested residue a major fraction of ammonia was nitr ified. Therefore, it is possible that the solid residue itself could serve as a biological filter for nitrification when leachate containing ammonia is flushed through it, i.e. leachat e nitrification may be combined with post aerobic processing of

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51 digested residue. The nitrified leachate upon exposu re to anaerobic conditi ons would denitrify, provided sufficient carbon source is available. Anot her issue in this application, unlike in studies presented in the literature (Berge et al, 2006, 2007; Jun et al, 2004) is the viability of the leachate processed in this manner to initiate di gestion of subsequent batches of wastes. The objectives of the work presented in this chapter are to determine: Feasibility of biological ammonia removal from leachate during aerobic processing of anaerobically digested residue Kinetics of ammonia removal Viability of aerated leachate as inoculum for subseque nt leach-bed digestion. 3.2 Methods 3.2.1 Experimental Apparatuses 3.2.1.1 Anaerobic digester A digester was constructed by modifying a Pyre x glass jar. The volume of the digester was 5 liters. The digester was sealed with a top lid, using an O-ring fitted for gas and liquid tightness and clamped with a stainless steel clamp. Three por ts were provided at the top of the lid, one for gas outlet, and others for sample withdrawal. The digester was also equipped with an outlet at the bottom from which liquid samples were collected. No additional mixing device was applied. The digester was placed in an incubator wher e the temperature was maintained at 55 oC. The digester set-up is shown in Figure 3-1. 3.2.1.2 Ammonia removal reactor Another 5-liter glass bottle ha lf filled with pumice stones was used for ammonia removal (Figure 3-2). The mouth was sealed by a top lid with 4 ports. Two ports were used for air supply, one for leachate circulation and the last one for gas exhaust. Two spargers were connected with the air supply lines and inserted to the surface of pumice stones, so that the solid digested residue

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52 on the pumice stones was in the aerobic zone wh ile the leachate with pumice stones was in the anaerobic zone. The glass bottle was also equippe d with an outlet at bottom from which leachate was pumped to the top of the re actor. Connected to the port for le achate circulation, a shower head was used inside the reactor in order to e qually distribute the leach ate across the top of the solid residue. Gas vented from the lip of bottle was purged through a dilute H2SO4 (concentration 0.04N) solution to absorb any volatilized ammonia. 3.2.2 Feedstock for Anaerobic Digestion Rice straw was used as feedstock and was pr ovided by Earth Saver Company, California. The rice straw was stored at room temperature. Some basic charac teristics of rice straw are listed in Table 3-1. 3.2.3 Experiments 3.2.3.1 Anaerobic digestion of rice straw Eight experiments using inoculum processed in different ways were carried out (Figure 33). In each experiment, the digest er was loaded with 100 g of rice straw as received, i.e the straw was not subjected to any size reduction. It was then filled with 4.2 liters of liquid, mixture of tap water and inoculum. The make up of this liquid varied in each experiment. The digester was placed in the incubator whose te mperature was controlled at 55 oC. In Experiment 1, 1.4 liters of tap water and 2. 8 liters of inoculum were used after loading the rice straw. The inoculum was taken from a thermophilic digester that had been digesting sugar beet tailings for over two years. Once anaer obic digestion was completed in Experiment 1, the digester was opened, the solid residue wa s taken out and liquid (digested leachate) was drained out from the digester. Then the leachat e was processed by aeration for ammonia removal until the TAN concentration was lower than 10 mg NH4 + -N/L. Experiments 2 and 3 were repetitions of Experiment 1.

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53 In Experiment 4, 2.8 liters of processed leach ate (from Experiment 1) and 1.4 liters of tap water were used. In Experiment 5, 2.8 liters of processed leachate (from Experiment 2) and 1.4 liters of tap water were used as in Experiment 4. But in addition, 100 mg/L of ammonia nitrogen was added into the digester. Experiment 6 was conducted using 1.4 liters of tap water and 2.8 liters of processed leachate from Experiment 4. This time, the l eachate (inoculum) had been processed twice. Experiment 7 was carried out using 2.8 liters of tap water and 1.4 liters of inoculum directly taken from a thermophilic digester that ha d been actively digesting sugar beet tailings for over two years (i.e., the same inoc ulum as Experiment 1-3). The d ilution factor of the inoculum in Experiment 7 was the same as that in Experiment 6 except that the microorgamisms here were not subjected to any aerobic processing, whereas in Experiment 6 they were subjected to processing twice. The unprocessed leachate from Experiment 7 was used to flood rice straw to carry out next Experiment 8 wit hout subjecting it to any aeration. 3.2.3.2 Aerobic processing of leachate for ammonia removal After the completion of anaerobic digestion in Experiment 1, the solid residue was taken out and the leachate was drained out from the thermophilic digester. Then the solid residue mixed with 30 g (wet weight) commercial Black Kow compost was placed on the surface top of pumice stones in the ammonia removal reactor a nd the leachate was also loaded. The quantity of pumice stones was such that the residue was not immersed into the leach ate. The leachate was recirculated continuously over the solid bed us ing a pump. The leachate flow rate was 30-45 mL/minute and air flow rate was 300 mL/kg wet re sidue/min. In this first processing experiment, the initial concentrati on of ammonia nitrogen was 500 mg/L After the ammonia concentration decreased to less than 10 mg NH4 +-N /L, the leachate was reused for subsequent anaerobic digestion, i.e. Experiment 4. In the 2nd aerated processing experiment, the fresh residue after

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54 completion of anaerobic digestion was taken out fr om the digester and loaded on the surface top of old residue from the 1st aerated processing. The leachate was drained out from the digester (Experiment 4) and loaded to the ammonia removal re actor. Additional NH4Cl was added to make initial ammonia concentration up to 500 mg NH4 +-N /L. Upon completion of aerated processing, the processed leachate was reused fo r subsequent anaerobic digestion (Experiment 6). In the 3rd aerated processing experiment, leachate from Experiment 2 was aerated and the processed leachate was used as inoculum for anaerobic digestion in Experiment 5. 3.2.4 Analysis Gas production was monitored daily. The biogas was metered using a positive displacement gas meter (Figure 3-1). The device c onsisted of a clear PVC U-tube filled with anti-freeze fluid (ethylene glycol), a 3-way soleno id valve (Fabco Air), a float switch (Grainger), an electromechanical counter (Redington Inc.) and a time delay relay (Dayton OFF Delay Model 6X153E). The U-tube gas meter was calibrated in -line to determine volume of biogas per count. A count was considered as that amount of gas read on a syringe (in mL) for which the gas meter completes one whole number count (e.g. one count=0.045 L, then two counts = 0.09 L and continued on.). Gas composition (CH4, CO2) was measured using a gas ch romatograph equipped with a thermal conductivity detector (Fisher Gas Partitioner, M odel 1200). Methane volume was reported at standard te mperature and pressure (STP) conditions. Leachate samples were collect ed periodically and analyzed for pH, chemical oxygen demand (COD), TAN and nitrate-ni trogen. The COD of leachate was measured by colorimeter (HACH DR/890 colorimeter). The TAN and nitr ate nitrogen were determined by ammonia electrode (Accumet Cat # 13-620-508) and ni trate electrode (Accu met, Cat # 13-620-535), respectively. The TAN on the digested residue was extracted by 2 M KCl solutions from the

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55 residue and also measured by ammonia electrode. The details of measurement methods are described in Chapter 2. The performance of the anaerobic digesti on processes was evaluated by fitting the cumulative methane production data to the modifi ed Gompertz equation (Lay et al., 1998). The Gompertz equation describes cumulative methane production from batch digesters assuming that methane production is a function of bacterial growth. The modi fied Gompertz equation is presented below: M = P exp {-exp [ t P eRm +1]} Where M is the cumulative methane production, m3/kg VS at any time, t, P is the methane yield potential, m3/kg VS, Rm is the maximu m methane production rate, m3/kg VS/day, is the duration of lag phase, day, a nd t is the time at which cumulative methane production M is calculated, day. The parameters P, and Rm were estimated for each of thedata sets by using the solver feature in MS-Excel. The value of parameters which minimized the sum of the square of errors between fit and e xperimental data were determined. 3.3 Results and Disscussions 3.3.1 Anaerobic Digestion of Rice Straw Figure 3-5 depicts the cumulative biogas a nd methane yield, daily methane yield and methane fractions in biogas from Experiment 13. In these expe riments, 1.4 liters of tap water and 2.8 liters of inoculum taken from a thermo philic digester that had been actively digesting sugar beet tailings for over two years were added to flood the bed of rice straw. The microorganisms recovered and methane production was initiated after one day. The methane production rate continued to increase until day 4 after which it dropped. The experiments were

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56 carried out for 15 days, by which time about 0.222 m3 CH4 STP/kg VS, 0.203 CH4 STP/kg VS and 0.214 m3 CH4 STP/kg VS of methane were produced respectively from Experiment 1-3 (Figure 3-5). To analytically quantify paramete rs for the batch growth curve, a modified Gompertz equation was fit to the cumulative methane production data from these experiments and the results are listed in Table 3-3. From Gompertz equation, the maximum methane production rate was 0.0270.003 m3/kg VS/day and the methane yield of rice straw was in the range of 0.205 to 0.219 m3 CH4 STP/kg VS loaded. This yield was obtained without any pretreatment of rice straw, which was better than those reported in the literatures. It was reported that the methane production of rice st raw without pretreatment was 0.170 m3 CH4 STP/kg VS at mesophilic temperature. The methane yield may be improved to 0.217 m3 CH4 STP/kg VS when the rice straw was ground to 25 mm length and heat ed in a pressure cooker for 2 hours at 110 oC as pretreatment (Zhang and Zhang, 1999). Therefor e, the methane yield from anaerobic digestion of rice straw in Experiment 1-3 was good e nough to be a basis for the conclusion from subsequent results. 3.3.2 Biological Ammonia Re moval from Leachate Three aerated processing experiments were carried out. Each processing experiment included two batches and the 2nd batch was immediately after 1st batch. The leachate from anaerobic digestion of Expe riment 1 was aerated by 1st processing experiment, after which the leachate was used to inoculate the anaerobic dige stion of Experiment 4. After the completion of 1st processing experiment, the ammonia removal reactor was ceased and stayed for two weeks until the 2nd processing experiment was set up. The leachate from Experiment 4 was treated by aeration and the processed leachate was introduced to the anaerobic digester of Experiment 6. After it was completed, the 3rd aerated processing experiment was started immediately. In this

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57 experiment, leachate from Experiment 2 was aer ated and the processed leachate was used as inoculum for anaerobic dige stion of Experiment 5. The TAN concentration in the leachate fr om anaerobic digestion of rice straw in Experiment 1-3 was around 500 mg NH3-N/L. Because of low nitrogen content in rice straw, it was expected that TAN of leachate remaining at the end of digestion would be low, equal to value in Experiment 4 (around 50 mg NH3-N/L). Therefore higher valu es of TAN measured in Experiment 1-3 mainly came from the inoculum taken from the thermophilic digester that was digesting sugar beet tailings. For better meas urement and observation of ammonia removal, additional NH4 +-N was added to the leachate to make the TAN concentration up to 500 NH3-N/L at the beginning of the 2nd and 3rd processing experiment. The TAN concentrations and processing time in these experiments are listed in Table 3-2. Ammonia removal rate was reported as amount of removed ammonia per liter of liquid volume per day. Appropriate microorganisms can att ach and grow on the di gested residue from anaerobic digestion due to its large surface area. In the 1st processing experiment, the residue was seeded by 10 % (wet weight) of commercial Black Kow compost. Ammonia oxidization was initiated within 3 days by purging air into the reactor. Daily leachate analysis showed that no ammonia was removed during the first 2 days. Th e TAN concentration d ecreased from 505 mg/L to 3.17 mg/L in 7 days in the 1st batch processing. The ammonia re moval rate was higher in the 2nd batch processing, in which T AN concentration dropped from 496 mg/L to 0.34 mg/L within 3 days. After completion, the ammonia removal re actor was ceased and stayed inoperable during the anaerobic digestion of Experiment 4. In the 2nd aerated processing experiment, the fresh residue from anaerobic digestion of Experiment 4 was loaded on the surface top of old residue containing ammonia oxidizi ng bacteria. The measured initial ammonia removal rate was 95.4 mg

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58 /L/day, which indicated the microorganisms need some time to recover and spread out to the fresh residue. The rate increased to 165 mg/L/day in the 2nd batch processing. Upon completion of the 2nd processing experiment, the leachate from anaerobic digestion of Experiment 2 was processed by aeration i mmediately (termed the 3rd processing experiment). The TAN concentration dropped from 500 mg/L to 4 mg/L in the 1st batch and from 500 to 23.7 mg/L in the 2nd batch within 2 days. So the average ammonia removal rate was 200-245 mg/L/day in this experiment. The performance of this ammonia removal process was evaluated by fitting the TAN concentration data to the 1st order equation as follows: ln (C/C0) = -k (t t0) where C = TAN concentration in leachate at elapsed time t, mg/L C0 = Initial TAN concentration in leachate, mg/L k = rate constant, day-1 t = Elapsed time t, day t0 = lag time, day The experimental data and the modeling fit in 1st, 2nd and 3rd processing are described in Figure 3-4. Concentrations of T AN, processing time and model para meters are listed in Table 32. In the 1st processing experiment, the residue was seeded by 10 % (wet weight) of commercial Black Kow compost. Then the ammoni a oxidization was initiated within 3 days by purging the air into reactor becau se daily leachate analysis show ed that little ammonia was removed during the first 2 days. The lag time was 2.97 days from the model, which showed consistent with the experimental valu e. The rate constant was only 0.82 day-1, which increased to

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59 2.52 day-1 in 2nd batch. In 2nd processing experiments, the ra te constant dropped to 0.96 day-1 in 1st batch, which indicated the microorganisms need some time to recove r after 2 weeks without feeding. After that, it increased to 1.3 in 2nd batch, then to 1.7 2.3 day-1 in 3rd processing experiment. At the same time, the lag time t0 was in the range of 0-0.2 days. The results demonstrated that the ammonia removal process could be initia ted immediately after set up and the removal rate may not increase dramatically any more after 2nd processing experiment, i. e. after 8-day continuous operation. The experimental ammonia rem oval rate was 200-245 mg/L at that time. This result, quick startup of nitrificati on, was better than those in some literatures. Ahn et al (2007) reported 60 mg/L/day of ammonia removal rate with in 10 days, 135 mg/L/day after 50 days and 235 mg/L/day after 80 90 days in continuous operation in combined anaerobic upflow bed filter and aerobic membrane bioreactor. In an air-lift loop sludge blanket (ALSB) treatment and a sequential upflow anaerobic sl udge blanket (UASB) treatment, ammonia removal rate was 170-180 mg/L/day and 35-40 mg/L /day respectively afte r continuous operation of 50 days (He et al, 2007). In a rotating biolog ical contactor, the nitrogen removal rate reached as high as 858 mg/L/day, but that rate was onl y obtained after 450 days in continuous operation (Wyffels et al, 2003). The air flow rate for purging the reacto r was 300 mL/minute/kg wet residue. Low concentration of nitrate-nitrogen about 50 mg/L, was detected at the end of treatments. At the same time, only 5% and less than 1% of initial TAN was in the form of nitrite-nitrogen and volatilized ammonia-nitrogen. Th ese results indicated that more than 85% of TAN may be removed in the form of nitrogen gas by denitrification due to oxygen limitation. The pH increased from 7.46 to 7.72 in the 1st processing experiment and from 7.86 to 8.90 in the 2nd

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60 processing experiment. The increase of pH also may be the result of denitrification process by the explanation of proton consumption in the ni trification-denitrificaiton reaction as following: Nitrification: NH4 + + 2 O2 NO3 + 2 H+ + H2O Denitrification: NO3 + 6 H+ + 5 e0.5 N2 + 3 H2O Overall: NH4 + + 2 O2 + 4 H+ + 5 e0.5 N2 + 4 H2O The ammonia wasnt absorbed on the digested residue either. The result showed that the TAN attached on the digested residue could be removed at the same time. In the 2nd processing experiment, the ammonia content decreased from 0.134 mg/g residue (dry weight) to 0.035 mg/g residue (dry weight). 3.3.3 Viability of Aerated Leachate as Inoculum for Subsequent Leach-Bed Anaerobic Digestion Leach-bed anaerobic digestion uses recycle of leachate from mature reactors to inoculate new reactors for rapid startup. Microorganisms used for inoculation are anaerobes, which may not sustain activity under aerobic conditions. So leachate may loose bacterial activity after aerated processing and cannot serve as inoculum for subsequent an aerobic digestion. Therefore, it is necessary to test viability of aerated leachate as inoculum fo r subsequent anaerobic digestion. Five experiments were conducted to test th e sustained bacterial activity in processed leachate. Experiment 4 was carried out usi ng the inoculum which was processed once and Experiment 6 was implemented using the inoculum which was processed twice. There are another three possible reasons to affect the digestion performa nce besides aeration. (1)Little ammonia is available in proce ssed inoculum, which may be tu rned into a limit factor for anaerobic digestion because ammonia nitrogen is a nutrient for bacteria growth. The implementation of Experiment 5 is to test the effect of TAN concentration in leachate. (2)

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61 Inoculum was diluted due to the addition of makeup water. Experiment 7 was carried out to test the effect of inoculum dilution. The dilution factor of inoculum in Experiment 7 was the same as that in Experiment 6. (3) Mi croorganisms may sustain in le achate and accumulate during reutilization of leachate. It wa s also possible that microorgani sms attached on the digested residue and their population decreased when leachate was reutili zed. The objective of Experiment 8 is to test the effect of reutilization of leachate. Experiment 4 and 5 were conducted using the pr ocessed leachate from Experiment 1 and 2, respectively. In these two experiments same amount of rice straw was flooded with 1.4 liters of tap water and 2.8 liters of inoculum after ammoni a removal process. In Experiment 5, 100 mg/L of ammonia nitrogen was added in to the digester while this was not done in Experiment 4. The results, including cumulative and daily methan e yield, COD, pH and TAN in leachate, are described in Figure 3-6 and 3-7. The methane production was initiated within 2 days and the experiment was carried out for 22 days The total methane yield was 0.211 m3 STP/kg VS and 0.214 m3 STP/kg VS in experiment 4 and 5 respectivel y. The pH of the leachate was maintained in the range of 7 to 8. For TAN in the leachate in experiment 4, it increased to 22 mg/L on day 4, after which it drop to 15 mg/L. Then it increa sed again and the final TAN was 50.64 mg/L. In experiment 5, it increased to 133 mg/L on day 2 and dropped to 91 mg/L on day 3. After that it slowly increased to above 140 mg/L. In Experiment 6, same amount of rice straw was flooded with 1.4 lit ers of tap water and 2.8 liters of inoculum after amm onia removal process. At this time, the inoculum used had been aerated for ammonia removal twic e. Figure 3-8 depicts the cumulative and daily methane yield, COD, pH and total ammonia nitr ogen (TAN) in leachate during the anaerobic digestion process. The microorganisms still need two days to recover and produce methane. The peak methane

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62 production rate showed up on day 4, which was same as that in Experiment 1-3. On day 15, the cumulative methane yield was 0.173 m3 STP/kg VS. The value was 18.8% and 18.0% lower than those from Experiment 1-3 and 4-5 respectively. The initial pH in this process was 8.9. On day 3, it decreased to 7.3 due to the pres ence of organic volatile acids. After that, it increased gradually until 8.5 at the completion of anaerobic digestio n .The TAN in leachate increased to 83 mg/L after 1 day and decreased to 16 mg/L on day 5. The final TAN concentration was 48 mg/L. In Experiment 7, 2.8 liters of tap water a nd 1.2 liters of unprocessed inoculum directly from thermophilic sugar beet tailings digester were used to flood the same amount of rice straw. The dilution factor of inoculum was the same as that in Experiment 6. The performance of the digester was described in Fi gure 3-9. Methane production wa s activated on day 1 and the maximum methane production rate was obtained on day 5, which was 0.042 m3 CH4/kg VS/day. After 15 days, the cumulative methane yield was 0.191 m3 STP/kg VS. The unprocessed leachate from Experiment 7 was used to flood rice straw to carry out Experiment 8. The performance of the digest er was described in Figure 3-9. The methane production was activated immediately after setu p and the maximum methane production rate was obtained on day 3, which was 0.037 m3 CH4/kg VS/day. After 15 days, the cumulative methane yield was 0.196 m3 STP/kg VS. To analytically quantify parame ters of batch growth curve, a modified Gompertz equation was fit to cumulative methane production data from all experiments and the results are listed in Table 3-4. 3.3.3.1 Effect of TAN and nitrate in leachate Figure 3-6, 3-7 and 3-8 depicts TAN concentration in leachate fr om Experiment 4, 5 and 6. In all cases, TAN concentration increased first before dropping. In Figure 3-6 (Experiment 4) and 3-8 (Experiment 6), the lowest concentratio ns of TAN were around 16 mg/L. After that the

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63 concentration began to climb to about 50 mg/L until the completion of digestion. There may be two reasons for the increase of TAN during the first several days. The first one is the result of hydrolysis of organic matter containing nitrogen. The second possible reason is transformation of nitrate-nitrogen (50-60 mg/L in processed leachat e) because of dissimilatory nitrate reduction. Rivard et al (1988) dem onstrated that in therm ophilic anaerobic digesters, nitrate was reduced to nitrite and finally to ammonia. Microorganisms need ammonia ni trogen as a nutrient for growth, so TAN concentration dropped due to the consum ption by microorganisms. The results showed that the ammonia was produced soon after the digester was set up and the amount of ammonia was enough for the microorganism growth. The lowe st concentration of TAN was 15.3 mg/L and 16.7 mg/L in Experiment 4 and 6 respectively, wh ich were extra ammonia nitrogen left after the consumption by microorganisms. After the co mpletion of anaerobic digestion, the TAN concentration was around 50 mg/L. Given that th ere was ammonia nitrogen available during the whole anaerobic digestion, the limitation of T AN in leachate may not be a reason of lower methane yield in Experiment 6. This was confirmed by results from Experiment 5, which also showed that the concentration of TAN in leachate was not a li mited factor. In Experiment 5, 100 mg/L of additional ammonia nitrogen was added into the sy stem. In Figure 3-7, the concentration of TAN increased to 133 mg/L on day 2 and dropped to 91 mg /L on day 3. After that it slowly increased to above 140 mg/L. The final expe rimental methane yield was 0.214 m3 STP/kg VS, which was close to that in Experiment 4 (0.211 m3 STP/kg VS). Both reduction of nitrate to ammonia a nd methane formation from carbon dioxide consume electrons: NO3 + 10 H+ + 8 eNH4 + + 3 H2O

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64 CO2 + 8 H+ + 8 eCH4 + 2 H2O The competition for electrons may result in the decrease in gas production because methane formation from carbon dioxide only happens after all available nitr ate has been reduced (Rivard et al, 1988). The concentration of nitr ate in processed leachate was around 50-60 mg/L. According to electron consumption from above two stoichiometric equations, the decrease of methane production is approximately 5 % due to the electron competition by nitrate. From Table 3-4, experimental values and Gompertz fit show s that methane yields from Experiment 4 and 5 were the same as those from Experiment 1-3 (within error bar) and the lag time were also similar,which indicates TAN and nitrate-nitrogen in leachate as well as processed inoculum (processed onc e) didnt inhibit th e performance of an aerobic digester in Experiment 4 and 5. 3.3.3.2 Effect of inoculum dilution Inoculum was diluted due to the addition of makeup water. Experiment 7 was carried out to test the effect of inoculum dilution. The dilu tion factor of inoculum in Experiment 7 was the same as that in Experiment 6, which wa s double than that in Experiment 1-3. From Table 3-4, Gompertz fit shows that the lag time, was 1.091 days in Experiment 13. It kept similar in Experiment 4 and 5 while increased to 1.744 1.844 days in Experiment 6 and 7. This may indicate that th e microorganisms need more time to recover when dilution factor of inoculum was higher (The rati o of inoculum and tap water was 1:2 in Experiment 6 and 7). The maximum methane production rate (Rm) from Gompertz model was 0.027 m3 CH4 /kg VS/day in Experiment 1-3 (mean valu e). In Experiment 7, it was 0.032 m3 CH4 /kg VS/day. Even though the bacteria need more time to recover, the maximum methane production rate didnt drop due to the inoculum dilution once the digestion was activated. However, the

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65 cumulative methane yield in Experiment 7 was sli ghtly lower than that from Experiment 1-3, which indicated that the dilution of inoculum may be one of the reasons leading to the decrease of methane yield in Experiment 6. 3.3.3.3 Effect of reutilization of leachate Leachate was reutilized in these experiments. Experiment 8 was carried out to test the effect of reutilization of leachate with no dilu tion and aerating process. Figure 3-9 depicts the performance of anaerobic digestion in Experiment 7 and 8. The inoculum used in Experiment 8 was unprocessed, undiluted leachate from Experime nt 7. The final methane yields were 0.191 m3/kg VS and 0.196 m3/kg VS respectively. For the parameters from a modified Go mpertz equation, the lag time of t0 was 0 in Experiment 8 indicated that microorganisms in leachate were active to inoculate a new run immediately if the leachate hadnt been dilu ted and processed by aeration. The cumulative methane yield (P) was 0.196 m3 CH4/kg VS in Experiment 8, which was higher than that in Experiment 7 (0.187 m3 CH4/kg VS) even though the maxi mum methane production rate was lower. Therefore the reutilization of leachate may not decrease methane yield from anaerobic digestion. 3.3.3.4 Effect of pH in leachate The initial pH in Experiment 6 was 8.9 and th e pH of leachate mainta ined in the range of 7.5 to 8.5, which was higher than those in Experi ment 1-5. However, despite the high pH values there was no effect on the rate of methanoge nesis in Experiment 6. The maximum methane production rate was 0.025 m3 CH4 /kg VS/day in Experiment 6, which was in the range of 0.0270.003 m3 CH4 /kg VS/day from Experiment 13 and even higher than those from

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66 Experiment 4-5. Methanogenic rate kept the same indicted higher pH didnt inhibit the digestion and lead to the lower methane yiel d (Koppar and Pullammanappallil, 2007) 3.3.3.5 Effect of aerating process The cumulative methane yield from Experiment 6 was 0.173 m3 CH4/kg VS and methane potential from Gomper tz model was 0.171 m3 CH4/kg VS. This value was lower than those from Experiment 1-3, which served as basis for co mparison. Based on measurements and operations during these experiments, the lower methane yield in Experiment 6 was initially attributed to five reasons: (1) limited TAN and exist of nitrate in leachate; (2) diluti on of inoculum; (3) effect of reutilization of leachate; (4) high pH and (5) aeration process. Acco rding to previous discussions, the reasons from TAN, nitrate-nitrogen, reutiliz ation and high pH were discounted. The possible reasons for lower methane yield from Experiment 6 included dilution of inoculum and aeration process. However, from the result of Experiment 7, dilution of inoculum may not be the only reason that leads to methane yield was as low as 0.173 m3 CH4/kg VS in Experiment 6. Aeration process provides oxygen. Microorga nisms required for anaerobic digestion was anaerobes, which may loose activity under aerobi c conditions. So the ba cteria activity from processed inoculum was lower th an that from unprocessed inoc ulum and resulted in lower methane production in Experiment 6. Another possibility was that aeratio n process removal other nutrients for bacterial growth, such as phosphorus and trace metal. However, Experiment 4 and 5 also used processed inoculum to activate the an aerobic digestion. The inoculum used was only processed once by aeration and the methane yields were 0.211 m3 CH4/kg VS and 0.214 m3 CH4/kg VS in Experiment 4 and 5 respectively. Thes e values of methane yield were the same as those in Experiment 1-3. But th e maximum methane production rate, Rm, in Experiment 4 and 5 were slightly lower than those in Experiment 13. These results showed that when the inoculum

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67 was processed by aeration once, methane yiel d didnt decrease whereas maximum methane production rate did. The methane yield became lowe r after the inoculum was processed twice. It would be possible that not only ammonia inhibition due to l eachate reutilization could be avoided but also bacterial activit y in leachate could be remained if only part of leachate was processed by aeration. For example, TAN c oncentration in leachate was 500 mg/L. Free ammonia concentration would be around 140 mg/L at pH 8 according to formula as following (Hansen et al, 1998): 1 ) )( 92.2729 09018.0( 3 3) 10 10 1( ][ KT pHTNH NH (1) where [NH3] is the concentration of free ammonia, [TNH3] is the concentration of TAN and T(K) is the temperature (Kelven). It woul d be safe to avoid ammonia inhibition if free ammonia concentration was 100 mg/L, i.e. TAN c oncentration was 350 mg/L. In this case, only 30% of leachate needs to be processed by aeration for ammonia removal. 3.4 Conclusion A post-treatment method, which may be in tegrated into the SEBAC-II system, was develop to biologically remove ammonia from leachate on the stabilized digested residue by simply aerating the reactor. At the same time, th e viability of aerated leachate as inoculum for subsequent anaerobic digestion wa s also determined as little lit erature reported th e results about the viability of reusing the aerated leachate. The results showed that when a nitrification-denitrificati on processing step for ammonia removal from leachate using the stabilized digested residue was integrated into the anaerobic digestion, the ammonia removal rate was 70 95 mg/L/day initially a nd increased to 200-245 mg/L/day after 8-day continuous operation. The original concentration of TAN in leachate was

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68 500 mg/L. More than 85% of TAN may be re moved as the form of nitrogen gas by denitrification when the air flow rate was 300 mL/minute/kg wet residue and leachate flow rate was 30-45 mL/minute. Viability of aerated leachate as inoculum for subsequent anaerobic digestion was also determined. The results showed that after the inoculum was processed by aeration for one time, the cumulative methane yield of the anaerobic di gestion almost didnt de crease. However, after the inoculum was processed for two times, th e cumulative methane yield of the anaerobic digestion decreased comparing with those using unprocessed inoculum. Th erefore, it would be better to only process part of th e leachate instead of the total leachate as it was not necessary to remove all TAN in leachate to avoid ammonia i nhibition. The fraction of leachate needs to be processed can be calculated according to original and objective TAN concentration in leachate and formula (1).

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69 Figure 3-1. Digester setup for anaerobic di gestion of rice straw air supply 0.04N H2SO4Solid residue from anaerobic digestion Sparger Pumice Stone Pump Figure 3-2. Ammonia removal reactor

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70 Figure 3-3. Experiment operation for anaerobic digestion of rice straw using inoc ulum processed in different ways

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71 2nd Processing Experiment TAN concentration (mg/L) 0 100 200 300 400 500 600 1st batch experimental data 1st batch fit 2nd batch experimental data 2nd batch fit 1st Processing Experiment TAN concentration (mg/L) 0 100 200 300 400 500 600 1st batch experiment data 1st batch fit 2nd batch experiment data 2nd batch fit 3rd Processing ExperimentElapsed Time (days) 024681 0TAN concentration (mg/L) 0 100 200 300 400 500 600 1st batch experiment data 1st batch fit 2nd batch experimental data 2nd batch fit Figure 3-4. Experimental data and first order fit of TAN remo val from leachate by aeration in the 1st 2nd and 3rd processing

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72 Cumulative methane yield (m3 @STP/kg VS) 0.00 .05 .10 .15 .20 Daily methane yield (m3/kg VS/day) 0.00 .02 .04 .06 .08 Methane yield in Experiment 1 Methane yield in Experiment 2 Methane yield in Experiment 3 Methane yield from Gompertz model Daily methane yield in Experiment 1 Daily methane yield in Experiment 2 Daily methane yield in Experiment 3 Elapsed Time (days) 0 5 10 15 20Cumulative biogas yield (m3@STP/kg VS) 0.0 .1 .2 .3 .4 Fraction of methane in biogas 0.0 .2 .4 .6 .8 Biogas production in Experiment 1 Biogas production in Experiment 2 Biogas production in Experiment 3 Fraction of methane in Experiment 1 Fraction of methena in Experiment 2 Fraction of methane in Experiment 3 Figure 3-5. Cumulative biogas a nd methane yield, daily methan e yield and methane fractions from Experiment 1-3

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73 COD (g/L)/pH 0 2 4 6 8 COD (mg/L) pH Elapsed Time (days) 0 5 10 15 20 25Total Ammonia Nitrogen (mg N/L) 0 20 40 60 80 Cumulative methane yield (m3@STP/kg VS) 0.00 .05 .10 .15 .20 .25 Daily methane yield (m3/kg VS/day) 0.00 .01 .02 .03 Cumulative methane yield Daily methane yield Figure 3-6. Cumulative methane production, COD, pH and TAN in leachate during anaerobic digestion of rice straw from Experiment 4

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74 pH 6.0 6.5 7.0 7.5 8.0 8.5 9.0 Elapsed Time (days) 0 5 10 15 20 25TAN Concentration (mg/L) 0 50 100 150 200 Cumulative methane yield (m3@STP/kg VS) 0.00 .05 .10 .15 .20 .25 Daily methane yield (m3/kg VS/day) 0.000 .005 .010 .015 .020 .025 .030 Cumulative methane yield Daily methane yield Figure 3-7. Cumulative methane production, pH and TAN in leachate during anaerobic digestion of rice straw from Experiment 5

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75 COD (g/L)/pH 0 2 4 6 8 10 COD (g/L) pH Elapsed Time (days) 024681012141618Total Ammonia Concentration (mg N/L) 0 20 40 60 80 100 Cumulative methane yield (m3@STP/kg VS) 0.00 .05 .10 .15 .20 .25 Daily methane yield (m3/kg VS/day) 0.00 .01 .02 .03 Cumulative methane Daily methane Figure 3-8. Cumulative methane production, COD, pH and TAN in leachate during anaerobic digestion of rice straw from Experiment 6

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76 Elapsed Time (days) 0 5 10 15 20 Cumulative Methane Yield (m3 STP/kg VS) 0.00 .05 .10 .15 .20 .25 .30 Daily methane yield (m3/kg VS/day) 0.00 .01 .02 .03 .04 .05 Cumulative methane inExperiment 8 Cumulative methane in Experiment 7 Daily methane yield in Experiment 8 Daily methane yield in Experiment 7 Figure 3-9. Cumulative methane production and daily methane yield from Experiment 7 and 8

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77 Table 3-1. Characteristics of rice straw Rice straw characteristics value Moisture (%) 8 13 Total solids (%) 87-92 Volatile solids (% of TS) 83 88 Bulk density (kg/m3) 25 Table 3-2. Concentrations of ammonia-nitrogen, nitrate-nitroge n and ammonia removal rate in biological ammonia removal process 1st processing experiment 2nd processing Experiment 3rd processing experiment 1st batch 2nd batch 1st batch 2nd batch 1st batch 2nd batch Initial 505 496 500 507 500 500 Total NH3-N (mg/L) Final 3.17 0.34 1.03 7.5 4.02 3.6 Processing Time (days) 7 3 5 3 2 3 Average removal rate (mg/L/day) 70.54 163.58 95.41 165.40 245.53 200.97 k (day-1) 0.82 2.52 0.96 1.27 2.29 1.65 t0 (day) 2.97 0.39 0.74 0.18 0.09 0.01 1st order fit R2 0.65 0.91 0.69 0.87 0.95 0.96

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78Table 3-3. Performance of anaerobic dige stion of rice straw from Experiment 1-3 Gompertz parameters (model) No. Temperature (oC Final methane yield (experimental) (m3 CH4 STP /kg VS) P (m3 CH4/kg VS) Rm (m3 CH4 /kg VS/day) (day) Duration to produce 95% methane yield potential (days) 1 55 0.222 0.221 0.029 1.154 12.1 2 55 0.203 0.207 0.024 1.154 13.5 3 55 0.214 0.210 0.027 0.966 12.2 Mean values 0.213 0.212 0.027 1.091 12.6 Standard deviation 0.010 0.007 0.003 0.108 0.8 Final range 0.2130.010 0.2120.007 0.0270.003 1.0910.10812.6

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79Table 3-4. Summary of performance of anaerobic digestion of rice straw Gompertz parameters (model) No. Temperature (oC Final methane yield (experimental) (m3 CH4 STP /kg VS) P (m3 CH4/kg VS) Rm (m3 CH4 /kg VS/day) (day) Duration to produce 95% methane yield potential (days) 1 55 0.222 0.221 0.029 1.154 12.1 2 55 0.203 0.207 0.024 1.154 13.5 3 55 0.214 0.210 0.027 0.966 12.2 4 55 0.211 0.204 0.020 1.003 15.8 5 55 0.214 0.205 0.019 1.225 17.5 6 55 0.173 0.171 0.025 1.744 11.7 7 55 0.191 0.187 0.032 1.844 10.5 8 55 0.196 0.196 0.017 0 16.6

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80 CHAPTER 4 INTEGRATION OF IN SITU TREATMENT OF ANAEROBICALLY DIGESTED RESIDUE AND LEACHATE IN SEBAC-II CONFIGURATION 4.1 Introduction Among the various technologies th at are available for anaerobi c digestion of solid wastes, the high-solids, batch process offers several advantages. The proce ss does not require fine shredding of waste, does not require mixing or agitation of digester contents, does not require bulky, expensive, high-pressure ve ssels as it can be carried at lo w (ambient) pressures and can be operated stably at both mesophilic and ther mophilic temperatures (Pullammanappallil et al., 2005). Sequential Batch Anaerobic Composting (S EBAC) is one such process that uses a combination of solid state fermentation and leachat e recycle to provide a simple, reliable process that inoculates new batches of waste, removes volatile organic acids and concentrates nutrient and buffer. Comparing with other traditional anaerobic digestion t echnologies, the SEBAC process design offers greater stab ility. The design allows for easy removal of inhibitory products, which may lead to imbalance. The leachbed design not only facilitates rinsing of toxic substances, such as metals, from the final produc t, but also eliminates the need for solids movement and mixing (Teixeira et al, 2003). The process has been tested on organic fraction of municipal solid waste (OFMSW), woody biomass, yard wastes and mixtures of yard wastes and biosolids (Chugh et al., 1999; Chynoweth and Le grand, 1993; Chynoweth et al., 1992). In the original SEBAC system, gravity was relied upon to bring cas cading liquid leachate in contact with the organic feedstock by pump ing leachate into the top of the reactor and allowing it to flow by gravity and collect at th e bottom for subsequent recycling. In SEBAC-II the system was modified to recycle leachate und er flooded operation using forced pumping, and recycling leachate through external gas-liquid separators that could accommodate vortex gas/liquid separation systems. Since leachate flow rate is not dependant on gravity in SEBAC-II,

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81 higher solid waste bulk density in the leachbed can be used to increase the loading rate and reduce the reactor size and system footprint (Teixeira et al, 2004). A bench-scale study (SEBAC-II model) was impl emented to test the concept of SEBAC-II using the simulated space waste and the results we re promising as degradation kinetics, in flood mode operation, were substantially higher th an expected (Chynoweth et al, 2002). Besides terrestrial operation, SEABC-II configuration is also suitab le for the operation under microgravity, so several studies were devoted to its application in space. A preliminary design, installation, start-up and preliminary operating performance for a full-scale prototype SEBAC-II system for space mission were presented (Xu et al 2002; Teixeira et al, 2004). Recently, it was modified to improve kinetics and reduce so lids processing time by incorporating flooded operation and periodic reversal of direction of leachate flow (Luniya et al., 2005). However, little work has been devoted to post-treatment of the anaerobic digestion, including stabilization of anaerobically digested residue and in situ ammonia removal from anaerobic leachate using digested residue bed. Preliminary studies in this field have been presented in Chapter 2 and 3. The objectives of this chapter included: Design the operation mode for in situ treatm ent of anaerobically digested residue and leachate in SEBAC-II configuration Measure the nitrification rate in the pr ocess of digested residue stabilization Determine ammonia removal rate from leachat e using digested residue bed during aeration 4.2 Methods 4.2.1 Experimental Apparatuses The apparatus (termed SEBAC-II model, Figure 4-1) consisted of a bench-scale reactor made from a PVC tube, which was enclosed by caps glued at either end. The inner diameter of this reactor was 4 inches, and the total volume wa s 6 liters. The reactor was held upright by a

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82 stand. Plastic ports were drilled into each cap. This system was originally used for anaerobic digestion of the simulated space waste. Air wa s supplied from a compressor and was introduced from the bottom and vented from top using sole noid valves automatically operated by a CR10 control system. The CR10 (from Campbell Scientific Inc.) control system is a fully programmable data logger / controller with severa l digital and analog inpu ts, and digital outputs. It was used to open and close the solenoid valves for aeration of reactor at pre-specified time intervals. A basket was used to hold the residue in the reactor. Loss of ammonia by volatilization was tracked by bubbling the gas vented from the reactor through a bottle of diluted H2SO4 (0.04N) before purging. During the aeration for stabilization of anaerobically digested residue, the inlet valve was opened for 30 seconds to introduce the air while the outlet valve remained closed. The reactor was pressurized at ~ 10 psi. After 20 minutes (this time interval was chosen to ensure that oxygen concentration remained a bove 20%), the outlet valve was opened for one minute to vent air from the system. The aeration cycl e was then repeated (Figure 4-2). For ammonia removal from leachate, a pump which was also controlled by the CR10 system was used to pump the leachate from th e bottom to the top (Figure 4-3). During the aeration, the inlet valve was opened for 15 sec onds to introduce the air while the outlet valve remained closed. The reactor was pressurized at ~ 10 psi. After 18.5 minutes (this time interval was chosen to ensure that oxygen concentrati on remained above 20%), the outlet valve was opened for 30 seconds to vent air from the syst em. After the outlet valv e was closed, the pump was turned on to pump the leachate for 1 minute. The aeration cycle was then repeated (Figure 44).

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83 4.2.2 Anaeobically Digested Residue The residue used in the studies was the same as that used in Chapter 2. It was an anaerobically digested mixture of wheat straw (55% of wet weight), shredded paper (37% of wet weight) and commercial dog food (7.6% of wet wei ght). Anaerobic digestion of this synthetic waste was carried out in a SEBAC-II system as de scribed in Luniya et al (2005). After digestion, the residue was stored in a refr igerator for about six months before it was used in experiments reported here. 4.2.3 Experiments 4.2.3.1 Stabilization of anaerobically digested residue The reactor was loaded with 1.5 kg of we t residue. Initially 100 mL of a 1000 mg NH4 +-N /L NH4Cl solution was added from the top. Additi onal ammonium chloride solution was added to the reactor every day and th e amounts depended on the nitrific ation performance. The TAN, nitrite, nitrate-nitrogen content and pH in the residue were measured every week. The benchscale reactor was unloaded period ically and the wet residue was mixed to take a representative sample. Sub samples were collected from different locations within the residue. These sub samples were mixed to make the sample for analysis. After this run, the reactor was loaded again with 1.5 kg of wet residue for the 2nd run. This time sodium bicarbon ate was used to keep pH at ~ 7.5. 4.2.3.2 Ammonia removal from leachate A sample of 1.2 kg wet residue was loaded into the reactor and 1.5 liters of NH4Cl solution at the concentration of 35, 75, 150, 400, 650 and 1000 mg/L were added to the system respectively. Leachate sample was collected da ily for the measurement of TAN. The ammonia removal rate is reported in the unit of mg removed N per liquid volume per day.

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84 4.2.4 Analysis The TAN, nitriteand nitrate-nitrogen in anae robically digested residue and leachate were measured periodically by the methods described in Chapter 2 and 3. 4.3 Results and Discussions 4.3.1 Stabilization of Anaerobic Residue The stabilization process in a bench-scale r eactor (SEBAC-II model) was carried out. In the experiment, 100 mg NH4 +-N was added on the 2nd and 4th day respectively. On the 5th day, the results showed that the nitrification was alr eady initiated. Initially in this experiment no attempt was made to control pH. Nitrification reactions produce H+ causing pH to drop. Figure 4-5 shows the changes in pH and its effect on the nitrification rate. On day 5, the specific nitrification rate was 0.068mg/g wet weight/d ay. Then the rate dropped to 0.025 mg/g wet weight/day when pH was as low as 4.7 on day 15. On day 23, sodium hydroxide was added to increase pH above 8 and sodium bicarbonate was also added to serve as a buffer. The specific nitrification rate recovered a litt le on day 24. On day 36, the sp ecific nitrification rate increased to 0.049 mg/g wet weight/day, and the pH was main tained above 8. Speci fic nitrification rate was affected by pH significantly. The reason is th at nitrifiers prefer neutral pH conditions. Besides, nitrifiers use ammonia (NH3) as substrate. In the system as ammonia is equilibrium with ammonium (NH4 +), pH affects the ratio of ammonia a nd ammonium. At high pH, the ratio is high, that is to say, ammonia is the major fr action. However, ammonium dominates at low pH. Therefore, there would be little substrate available for nitrifiers as pH dropped, even though the total ammonium content is high. Another run was carried out in this SEBAC -II model. In this experiment, 4 g NaHCO3 was added as a pH buffer. After one day, the result showed that the nitrification was already initiated

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85 and the specific nitrification rate was 0.26 mg/g wet weight/day, which was much higher than the first run without pH control. For the stabilization process in 1 L glass reactors described in Chapter 2, the initial specific nitrification rate was 0.13 mg /g wet weight/day on day 2. But in this SEBAC-II model, the nitrification could be activated in shorter time a nd the reaction rate was higher. The reason is that higher pressure in this bench-scale reactor may have improved the contact between digested residue and oxygen by overcoming the preferential channel flow of air when it was simply blown continuously through the residue. In the SEBAC-II system, a similar procedure could be used for stabilization. A stabilization process can be easily inco rporated into the SEBAC-II system and a schematic diagram of the SEBAC -II process incorporating stabilizat ion is shown in Figure 4-6. The vessel would be aerated following the ae ration procedure used in the SEBAC-II model described here. For the digested residue used in this study, assume the T AN content in residue is around 4.0 mg/g wet residue. Based on the assumption that the initial nitrif ication rate would be 0.26 mg/g wet weight /day (i.e. specific nitrific ation rate measured using SEBAC-II model) and the nitrification rate would fit the Gompertz equation, it was estimated that more than 90% of TAN in the anaerobically digested residue coul d be nitrified after 13-day aeration. 4.3.2 Ammonia Removal from Leachate The efficiency for the ammonia removal from leachate was above 95% in this SEBAC-II model. The relationship of initial ammonia removal rate and original TAN concentration in leachate may be described as linear in SE BAC-II model (Figure 4-7). When the TAN concentration in leachate was as low as 35 mg /L, the initial ammonia removal rate was around 22.75 mg/L/day. The initial ammonia removal rate increased with the TAN concentration in leachate. According to this linear relationship, when the concentration was 500 mg/L, the initial

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86 removal rate should be around 85 mg/L/day. This resu lt was consistent with the one obtained in previous experiment using apparatus in Figure 3-2, which was described in Chapter 3. A treatment of leachate for ammonia removal can be incorporated into SEBAC-II and a schematic diagram of SEBAC-II process incorpora ting stabilization of residue and treatment of leachate is shown in Figure 4-8. The vessel wo uld be aerated following aeration procedure used in the SEBAC-II Model described here. The air ente rs into the reactor from the bottom and vents from the top. The Pump E is used to pump th e leachate from the reservoir to the top of the aerobic reactor for ammonia removal. The leachate will flow down to the bottom of the reactor through the solid digested residue containing microorganisms required for nitrification. The leachate accumulated at the bottom of the aerobic r eactor is pumped back to the reservoir by the Pump D. From the results in Chapter 3, aera tion process may slightly lower the microbial activity in leachate. So it would be better to only process part of leachate to avoid ammonia inhibition. The fraction of leachate needs to be processed can be determined from the TAN concentration in leachate and implemented usi ng flow rate of leachate controlled by pump. 4.4 Conclusion A new operation mode was developed for in s itu treatment of anaer obically digested residue and leachate in the SEBA C-II model. Instead of supplying a continuous air flow, air was held under pressure at ~ 10psi for 20 minutes before venting and filling again. For the stabilization of solid digested residue, initial specific nitrification rates were higher at 0.26 mg /g wet weight /day showing that this method of aeration wa s more efficient since higher pressure in this benchscale reactor may have improved the contact between digested residue and oxygen by overcoming the preferential channel flow of air when it was simply blown continuously through the residue.Based upon the specific nitrification ra te obtained in this SEBAC-II model and modified Gompertz equation, more than 90% of TAN in the anaerobically

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87 digested residue could be nitrified after 13-day ae ration in the SEBAC-II system. It was also seen that decreases in pH caused by ni trification reactions can inhibit nitrification activity. So it is essential to incorporate pH monitoring a nd control during the stabilization process. In situ ammonia removal from leachate using a digested residue bed rather than a dedicated reactor was also studied in this SEBAC-II m odel. The similar operation was utilized. The ammonia removal efficiency was above 95%. Initial ammonia removal rate had linear relationship with original TAN c oncentration in leachate. Accordi ng to results from Chapter 3, it would be better to only process pa rt of the leachate instead of the total leachate as it was not necessary to remove all TAN in leachate to a void ammonia inhibition. The fraction of leachate needs to be processed can be calculated accordin g to original and objective TAN concentration in leachate, and implemented using flow rate of leachate controlled by pump.

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88 Figure 4-1. Bench-sc ale reactor operated by an automatic CR10 control connected to an ammonia trap Figure 4-2. Operation of inlet and ou tlet valves by automatic CR10 control

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89 Air SupplyCR10valve valveH2SO4 PUMP Figure 4-3. Bench-scale reactor (SEBAC-II Model) for biological removal process Figure 4-4. Operation of pump, inlet a nd outlet valves by automatic CR10 control

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90 0 0.05 0.1 0.15 0.2 0.005.0010.0015.0020.0025.0030.0035.0040.00 Elapsed Time (Days)Nitrification Rate (mg/g wet weight/day)0 2 4 6 8 10pH Nitrification Rate pH change Figure 4-5. Specific nitrification rate in a SEBAC-II model and simultaneous pH change during stabilization process Figure 4-6. Integration of stabili zation process into SEBAC-II system

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91 Figure 4-7. Relationship of initial ammonia removal rate and original TAN concentration in bench scale reactor Pump A Stage 2 Anaerobic Diges tion Post-treatment Aerobic Reactor Activated Reactor New Reactor Mature Reactor Biogas Biogas Stage 1 Stage 3 Pump B Pump C Air in Air out Pump D Pump E Figure 4-8. Integration of step for stabilization of residue and treatment of leachate into SEBACII system

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92 CHAPTER 5 THERMOPHILIC ANAEROBIC DIGESTION OF SUGARBEET TAILINGS USING COD REMOVAL AS PRE-TREATMENT 5.1 Introduction Nearly 40% of all refined suga r consumed in the USA is made from sugar beets grown in the north central and north wester n regions of the United States. Beet sugar proc essing generates significant quantities of both solid and liquid wastes. Raw suga r beets when brought into the processing plant from storage in outdoor stoc kpiles, are first washed and separated from tailings which mainly consist of sugar beet ch ips (10-30%), weeds, sugar beet tops, debris and soils held by sugar beets when harvested (Kumar et al., 2002). The washed beets proceed for further processing and juice extr action generating anothe r solid waste stream namely spent beet pulp. This waste stream is a valuable by-product and can be used as cattle feed, for fertilizer production (Zhang and Shi, 2000), for pectin producti on (Karpovich et al., 1989) or as an ethanol feedstock source (Doran and Foster, 2000). A lack of literature on the disposal of tailings, the first solid waste stream, indicated that not much attention has been devoted towards pr ocessing this waste stream for value addition. Usually, tailings are stockpiled outside the factor y and hauled away for disposal onto landfills or applied on nearby farmland at a significant cost to the factory. For example, American Crystal Sugar Company spends close to $1 million per ye ar disposing 400 tons of tailings that are generated daily at its East Grand Fork s plant (Teixeira et al., 2005). Anaerobic digestion of taili ngs would not only generate biogas but also reduce the quantity of waste stream that requ ires disposal. Biochemical methane potential assays of tailings carried out at a mesophilic temperature of 38 oC yielded 250 L of methane/ kg VS (Teixeira et al., 2005). Based on this methane yield, a preliminar y economic analysis showed that taking into account the reduced cost of dispos al, electricity revenues, and natu ral gas savings, a conservative

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93 estimate of the net savings from anaerobically di gesting 400 tons/day of tailings was $4,873 per day (Teixeira et al., 2005). In preliminary experiments, sugar beet tail ings were anaerobically digested using the SEBAC-II process at 38 oC (Teixeira et al., 2005). It wa s found that the rates of methane generation were poorer compared to that from digestion of other organic residues, persistently high volatile organic acid concentr ations were measured in dige ster liquor and daily methane production rates failed to increase even after 30 days of digestion. This indicated a need for further modifications and improvements to inte grate an in situ pre-treatment process to anaerobically digest tailings within the SEBAC-II configuration. The objectives of the work in this chapter were: Confirm the availability of microorganisms re quired for anaerobic dige stion of sugar beet tailings Develop a pre-treatment method for anaerobic digestion of sugar beet tailings in the SEBAC-II system Measure the methane yield and methane produc tion rate in anaerobic digestion of sugar beet tailings after incorpor ating the new pre-treatments This chapter presents findings related to thes e objectives. The digester was modified to operate within a thermophili c temperature range (50 57 oC) where the rates of degradation and biogasification are faster, and has a greater potential to destroy weed seeds and plant pathogens, which is especially beneficial for reapplying th e undigested residue with little post treatment on to the fields to recycle nutrients. Since a thermophilic inoculum was not available in our laboratory, a method of quickly cu lturing such an inoculum was also developed in this study.

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94 5.2 Methods 5.2.1 Anaerobic Digester A 5-liter glass bottle with a wide mouth was used as the anaerobic digester. The mouth was closed with a rubber stopper through which a glass rod was in serted for venting the biogas from the digester. The digester was also equi pped with an outlet at bottom from which liquid samples were collected. A schematic diagram of this apparatus is shown in Figure 5-1. The digester was placed in an incubator wher e the temperature was maintained at 55 oC. The biogas was metered using a wet tip gas meter wh ich was placed outside the incubator. 5.2.2 Feedstock Beet tailings were shipped in a frozen state from American Crystal Sugar Companys East Grand Forks plant in five gallon pails. Upon receipt, the tailings were stored at -20 oC in a cold room. The basic characteristics of beet ta ilings are listed in Table 5-1 and 5-2. 5.2.3 Experiments Three experiments were carried out. The digest er was loaded with 1.5 kg of tailings as received (i.e the tailings were not subjected to any size reduction) in all experiments. The tailings were taken out of cold storage and thawed at room temperature before being loaded into the digester. In each experiment, the ta ilings were initially flooded with 2 liters of tap water and then drain this liquid (henceforth this liquid will be referred to as wash leachate) out. The process would remove readily soluble organic matter, which may be helpful to avoid pH drop and activate methanogenesis. However, the initial fill leach and drain procedure were different in these three experiments. In Experiment 1, 2 liters of tap wate r containing 12 g/L of sodium bicarbonate was initially added to flood the bed of tailings. Next day liquid was dr ained and fresh water containing 12 g/L of sodium bicarbonate was ad ded which was drained on day 3. After which

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95 water with sodium bicarbonate was again added and anaerobic digesti on was started up. The COD of wash leachate was measured. The experime nt was carried out for 25 days. At the end of this period, the digested leachate was drained and stored at room temperature. Solid residue from the digester was analyzed for dry ma tter and volatile solids content. In Experiment 2, the tailings were initially flooded with 2 liters of tap water containing 12 g/L of sodium bicarbonate. After three days the bed was drained and this wash leachate stored for subsequent use. Then digested leachate from the end of Experiment 1 (which was stored at room temperature for 3 days) was introduced into the bed to start up th e anaerobic digestion. From day 15 onwards wash leachat e that was drained initially was added to the digester. On days 15 and 16, 50 ml of leachate was added; on day 17, 150 ml; on days 18 and 19, 200 ml; and from day 21 onwards, 300 ml of leachate until all leac hate was used up by day 28. After that, the digested leachate was drained and solids analyzed for dry matter and volatile solids content. In Experiment 3, wash leachate was drained ou t on day 1 itself. Tap water was added, the bed was drained on day 2 and the procedure rep eated on day 3. No sodium bicarbonate was added this time. Digested leach ate from the end of experiment 2 (which was stored at room temperature for 3 days) was then added. On day 11 the wash leachate that was drained out of the bed at the start of Experiment 3 was then added. About 200 ml of this leachate was added every day until day 17. The digester was operated for 45 days so as to evaluate ultimate degradability and quality of leachate. 5.2.4 Analysis Total solids (TS) were determined gravim etrically after drying overnight at 105 Volatile solids (VS) content was dete rmined by ashing a dried sample at 550for 2 hours and determining the ash-free dry we ight. Gas production was monitore d daily using the gas meter

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96 described in Chapter 3. Gas composition (CH4, CO2) was measured using a gas chromatograph (Fisher Gas Partitinoer, Mode l 1200) equipped with a thermal conductivity detector. The gas chromatograph was calibrated with an external standard containing N2: CH4: CO2 in volume ration 25: 45: 30. Leachate samples were collected daily and analyzed for pH, COD and volatile organic acids. Volatile organic acid concentrations (acetic, propionic, butyric, and valeric acids) were measured using a gas chromatograph equipp ed with a flame ionization detector. COD of leachate was measured by colorimetric method (G reenberg et al, 1992). Frozen tailings and digested residue samples (50 g each) were stored in air-tight bags, packed in an insulated envelope and shipped to Dairy One, Inc., Ithaca, New York, a commercial forage testing laboratory. These samples were analyzed fo r crude protein, solubl e protein, nonfibrous carbohydrates, lignin, hemicellulose and cellulose. 5.3 Results and Discussions The performance of experiments 1, 2 and 3 are depicted in Figu res 5-2, 5-3 and 5-4 respectively. In these figures, the cumu lative biogas and methane production, methane percentage, daily methane production, pH, COD and volatile organic aci d concentrations of leachate are shown. Cumulative biogas and me thane production values were normalized on the basis of kg VS loaded in each experiment. Daily methane production was reported per L of active (sum of liquid and solids volume) react or volume. All the reported gas volume was converted to volume at standard temperature and pressure (STP). In Experiment 1, 2 liters of water contai ning 12 g/L of sodium bicarbonate was initially added to flood the bed of tailings. Upon addition of water, a large amount of organic matter was solubilized. Fermentation of the soluble COD cause d the pH to drop to very low values of 3 or below. Next day liquid was draine d (henceforth this liquid will be referred to as wash leachate) and fresh water containing 12 g/L of sodium bicarbonate was added which was drained on day 3.

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97 After which water with sodium bicarbonate was again added. The amount of readily soluble organic matter removed was 95 g COD. Methane pr oduction was initiated two days later, which was sustained and continued to increase unt il day 11 after which it dropped. The maximum methane production rate was approximately 0.4 L/ L/d. The experiment was carried out for 25 days, by which time about 64 L CH4/ kg VS loaded was produced. Since the removed readily soluble COD (95 g) represents about 50% of the total methane potential, the final methane yield was lower. Volatile organic acid profiles showed accumula tion and degradation of all acids that were analyzed. Acetic acid accumulated to1300 mg/l, a nd propionic and butyric acids to 1250 mg/L. Degradation of these acids caused their co ncentration to drop after day 9. In Experiment 2, the tailings were initially flooded with 2 liters of tap water containing 12 g/L of sodium bicarbonate. After three days the bed was drained and this wash leachate stored for subsequent use due to its high COD content. Then digested leachate from the end of Experiment 1 was introduced into the bed. Methane production was initiated on day 5, soluble COD of leachate dropped and pH began to climb. By day 13, the pH of leachate was above 8 and continued to fluctuate around this value for rest of the duration of experiment. Methane production rate peaked to 0.79 L/L/d on day 13. Volatile organic acid concentrations were higher in this experiment compared to Experiment 1. On day 11, the concentration of butyric acid was still 4700 mg/L and that of propionic ac id was almost 1900 mg/L. This may be because all soluble COD may not have been completely washed out during the fill, leach and drain step. Soluble COD was 20 g/L on day 6 co mpared to values less than 8 g/L from day 4 onwards in Experiment 1.

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98 From day 15 onwards wash leach ate that was drained initially was added to the digester. On days 15 and 16, 50 mL of leachate was a dded; on day 17, 150 mL; on days 18 and 19, 200 mL; and from day 21 onwards, 300 mL of leachat e until all leachate was used up by day 28. Upon addition of this leachate, methane production continued from the digester showing that the readily soluble organic matter in the wash leach ate can be anaerobically digested. The addition and digestion of wash leachate caused the fluctuations of pH and COD values. In Experiment 3, the initial fill, leach and dr ain procedure was modified because it seemed that all soluble COD might not be completely washed out in experiment 2. This time wash leachate was drained out on day 1 itself. Fresh water was added, the bed was drained on day 2 and the procedure repeated on day 3. Digested leachate from the end of experiment 2 was then added. It can be noted that at this stage the soluble COD was less than 7 g/L. Methane production was initiated as soon as the digested leachate was added on day 3 and peaked at a value of 1.01L/L/d by day 9 and began to drop s oon after. Individual vo latile organic acids accumulated initially but dropped to below 500 mg /L by day 11. On day 11 the wash leachate that was drained out of the bed at the start of Experiment 3 wa s then added. About 200 mL of this leachate was added every day until day 17. The digester was operated for 45 days so as to evaluate ultimate degradability and quality of leachate. By day 45 the soluble COD was 1,900 mg L-1. Among the volatile organic acids only propi onic and valeric acids were detected on day 45 and its concentrations were 430 mg L-1 and 270 mg L-1 respectively. 5.3.1 Characteristics of Beet Tailings and Residue Tailings as received in our laboratories had hi gh moisture content. The average moisture content was 88-89%. The volatile so lids content of the tailings was about 90% of dry matter. Therefore, upon loading 1.5 kg of tailings in the anaerobic digester in each experiment, only about 156 g of solids (which are the volatile solids) were ava ilable for degradation based on

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99 11.5% dry matter. A large fraction of the tailings is made up of readily soluble organic content. This was measured as COD in wash leachate; which was very high. About 80 to 95 g COD of soluble organic matter was removed during the fill, leach and drain steps. The readily soluble organic fraction in tailings was a bout 0.5 0.6 g COD /g VS. Chem ical analysis of tailings for animal feed constituents is listed in Ta ble 4-2. Carbohydrates (including non-fibrous carbohydrates, hemicellulose and cellulose) are the primary constituents. After anaerobic digestion, the average moistu re content of the residue upon draining the leachate was 80 88% with volatile solids ~ 55% of dry matter. The volume of the bed decreased 70-80%. Dry matter and volatile solids reducti on was measured to be ~60% and ~75% respectively. Chemical analysis of digested residue for animal feed constituents is listed in Table 5-2. Since all constituents ar e present in the residue, none of them are completely degraded during the digestion process. The fractions of pr otein, lignin and cellulo se are higher in the residue than in the tailings. The ex tent of degradation is of individua l constituents is also listed in Table 5-2. More than 50% of the protein and cel lulose was degraded, whereas about 80% of the nonfibrous carbohydrates and hemicellulose was degr aded. In the case of li gnin it is likely that 25.5% of the lignin was solubilized and released into solution ra ther than being degraded, as digestibility to methane was considered lim ited (Polematidis, 2007). Since cellulose was bound to be present in the tailings w ithin a ligno-cellulose ma trix and that this ma trix is resistant to biodegradation, the extent of cellu lose degradation was only 61.4%. 5.3.2 Biochemical Methane Potential (BMP) Based on methane production from a complete digestion run with a batch of tailings and the readily solubilized organic matter, the bioc hemical methane potential of the tailings is approximately 295 L at STP/kg VS. Of this a bout 160 180 L (50 60%) is produced from the readily soluble component of beet tailings. This indicated that even afte r the readily solubilized

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100 matter is removed, significant methane production poten tial exists within th e tailings (40-50%). The BMP estimated in these experiments is mo re than that determined from biochemical methane potential assays carried out at mesophilic temperatures (Teixiera et al., 2005). It should be noted that these mesophilic BMP assays were carried out using sample sizes of 2 g and may not be representative of the feedstock. Moreove r, the inoculum used for the BMP assays came from a slurry digester that was fed a synthe tic feed solution made from dog-food. On the contrary, by Experiment 3 the inoculum used in experiments here would have been acclimatized to degrading beet tailings, hence ab le to break down more of the f eedstock. It can be seen from Figure 5-5 that over a duration of 35 days, Experiment 3 yielded more methane than Experiment 1 or 2 (after discounting meth ane yield from addition of hi gh COD leachate from day 11 in Experiment 3 and day 15 in Experiment 2) which indicated that there wa s more degradation of the solids as the inoculum became progressively ad apted. From the amount of constituents listed in Table 5-2 that were degraded during digestion, the theoretical methane yield was calculated to be ~278 L CH4 at STP/ kg VS, assuming an average COD of 1.1 g/g for the constituents. This value is in close agreement to the ex perimentally measured value of 295 L CH4 at STP/ kg VS. 5.3.3 Microbial Populations Methane production was initiated in Experime nt 1 by simply flooding the bed with water containing only buffer. Interestingly, appropriate microbial populati ons required for anaerobic digestion of the feedstock was na turally present within the tailings. Mineralization of organic matter to methane and carbon dioxide in an anaer obic digester requires th e concerted action of several populations of microorganisms. Of thes e populations, those involved in acidogenesis (conversion to volatile organic acids), acetogenesis (conversion of higher chain volatile organic acids like propionic and butyric aci ds to acetic acid) and methanogenesis (formation of methane from acetic acid and methane production from hydrogen and carbon dioxid e) are of primary

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101 importance. It is well known that acidogenic organisms readily establish within anaerobic environments where in they cause rapid fermenta tion of organic matter due to their high growth rates. This was also confirmed here as addition of water and establishment of anaerobic environment quickly caused volatil e organic acids to build up and pH to drop to below in 3 in Experiment 1. On the contrary, acetogenic a nd methanogenic populations (especially aceticlastic methane populations) are slow growing organism s. Highly imbalanced anaerobic digestion process, like sludge digesters with high concentra tions of propionic and butyric acids, have been known to take long periods of time to recover requiring elaborate operat ional protocols with close monitoring to nurse them b ack to balanced conditions. Howeve r, it was seen here that even though higher chain volatile orga nic acids like propionic and butyric acid accumulated to levels around 1,680 mg/L (by day 7 in Experiment 1) these were degraded to below 750 mg/l within ten days. This degradation was mediated by microbial populations naturally occurring within the waste bed as an external inocul um was not added to the digester in Experiment 1. Valeric acid accumulated to 1000 mg/L initially; but it was re duced to 400 mg/L within couple of days. Initiation and sustenance of methane production fr om uninoculated tailings also indicated the presence of adequate number of methanogeni c populations within the tailings. Methane production rate increased quickly from 0. 05 L/L/d to 0.4 L/L/d within 4 days. 5.3.4 High Solids Anaerobic Digestion of B eet Tailings in an Unmixed Digester Previous investigations into use of the fl ooded SEBAC process for anaerobic digestion of beet tailings (Texeira et al., 2005) showed poor performance because of the process inability to deal with the high amount of readily sol uble organic compounds. Previously, the SEBAC process has been shown to initia te methanogenesis rapidly in the feedstocks like organic fraction of municipal solid waste, yard wa ste, mixtures of biosolids and yard waste, simulated municipal solid waste etc. The readily soluble organic matt er in these feedstocks is lower than that

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102 generated by beet tailings. For example, solubl e COD of leachate from a flooded vegetable waste bed was around 8 g/L (Hegde and Pullammanappallil, 2007) and that from organic fraction of municipal solid waste was 12 g/L (Lai, 2001) compared to up to 47.5 g/L from beet tailings. In a SEBAC process, the leachate recirculation strategy ensures that the readily soluble COD generated in a fresh waste bed is completely conv erted to methane in a stabilized waste bed. The leachate that is returned to the waste bed from the stabilized wa ste bed is low in soluble COD. But in the case of beet tailings, the COD that wa s loaded into the stabil ized waste bed with the leachate exceeded its assimilation capacity. This caused the leachate that was returned to the fresh waste bed to contain residual undegrad ed COD, low alkalinity and low pH. These conditions were unfavorable for initiation of methanogenesis in the fresh waste bed. Therefore, an anaerobic digestion process for beet tailings should in clude a step in which the readily soluble organic matter is leached and removed from the waste bed. Since, this readily soluble COD represents about 50% of the to tal methane potential, the leachate may be anaerobically digested in a high rate anaerobic tr eatment system. It was shown that the organic matter that is leached out initially ca n indeed be anaerobically digested. Digested leachate from Experi ment 1 was used to start up the subsequent experiment (i.e. Experiment 2) and digested leachate from Experime nt 2 was used to start up Experiment 3. This process ensured adaptation and en richment of the inoculum. Figur e 4-6 compares the cumulative methane production from the three experiments. It can be seen that the rate of methane production (or initial slopes of the cumulative methane production plot) increased with each subsequent experiment. The ra te was highest in Experiment 3 and cumulative methane production began to level-off by day 10. Moreover, methane production was initiated as soon as digested leachate from Experiment 2 was introduced into the digester on day 3. As explained in

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103 Results section, continued methane production after day 10 was due to addition of high COD wash leachate. Also, the microbi al populations in the leachate continued to be able to rapidly degrade higher chain volatile organic acids. Individual volatile organi c acid concentrations dropped below 550 mg/L by day 11 in Experiment 3. 5.3.5 Integration of Removal of Soluble COD as a Pre-treatment Step into SEBAC-II Process The tailings contain a large fraction (0.6 g COD/g VS) of r eadily soluble organic matter, which lead to high soluble COD during the anaerobi c digestion. This high COD that was loaded into the stabilized waste bed with leachate ex ceeded the assimilation capacity of the mature reactor in the SEBAC-II system. One solution was to increase the volume of the mature reactor, but in this case it would be failed to implement the sequen ce of anaerobic digestion in the SEBAC-II. In the two-phase digestion devel oped by Barry (1983), leachate containing the soluble organic matter was withdrawn from an acidification reactor and replaced by fresh effluent from a methanogenesis re actor to ensure optimal nutrien t levels in the acidification reactor. The rate for leachate withdrawn and replacement was de pendent on the concentration of soluble organic matter. The aci dification reactor would be di sconnected to methanogenesis reactor to function independently as a single-phase system as soon as the rate of acidification decreases if the feedstock exhi bited an initial rapid conversio n of the easily biodegradable components followed by a slower rate of hydrolys is and fermentation of the more recalcitrant components (Rijkens 1981; Rijkens and Voetberg 1982). However, these solutions were based on the intermittent or continuous operation. The SEBAC-II technology is used in the batch digestion. So when the SEBAC-II technology is used for s ugar beet tailings, the first step was to wash and remove the soluble organic matter in the tailings. A whole SEBAC-II system is

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104 described in Figure 2-7 if a filling reactor for s ugar beet tailings and a reservoir for washing water storage are added. The beet tailings are lo aded into the filling reac tor for pre-treatment. Tap water is added to flood the tailings bed and solubilize the or ganic matter. After a while the washing water containing high solu ble COD is pumped to the reservoir and the tailings are ready for anaerobic digestion. The washing water in the reservoir is pumped into the activated reactor (Stage 2) which is in the process of anaerobic di gestion for conversion to methane. As leachate is recirculated upon itself in this activ ated reactor, the COD that is loaded into the activated waste bed with the washing water may be controlled according to its assimilation capacity, and is successfully converted to methane. 5.4 Conclusions A pre-treatment process, which may be incorporated into SEBAC-II system, was developed to accommodate anaerobic digestion of sugar beet tailings. The pre-treatment step was to wash and remove the large fraction of soluble organic matter in sugar beet tailings. After this, the methane production was initiated as soon as digested leachate was introduced into the digester. At the same time, the washing water containing high COD content was added to the activated reactor for bioconversi on to methane. Critical finding s on the modifications of the SEBAC-II system to accommodate sugar beet tailings were: The tailings contained naturally occurring microbial communities to carry out anaerobic digestion. A method of culturing a therm ophilic inoculum was developed by simply flooding a bed of tailings with pH buffer solu tion and incubating this bed at thermophilic temperatures. Inoculum thus cultured wa s shown to robustly and stably initiate methanogenesis in subseque nt batches of tailings. As the tailings contain a large fraction (0.6 g COD/g VS) of readily soluble organic matter, the first step was to wash and remove the soluble organic matter. After this, methanogenesis was initiated immediately upon flooding the bed with digested leachate containing adapted inoculum. Most of the me thane potential of the solids was recovered within a week.

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105 A methane yield of 295 L at STP/kg VS was de termined for the tailings, of which 50-60% was contributed by the solubi lized organic matter. After anaerobic digestion, a volume reduction of 70-80% was achieved and approxi mately 60% of dry matter and 75% of volatile solids in tailings were degraded. The methane production rate, c onsequently the kine tics of the process, could be improved by flooding tailings using digested leachate from the end of a previous experiment.

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106 Figure 5-1. Anaerobic digester filled with tailings and leachate

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107 COD of Leachate (g L-1) 0 10 20 30 40 50 pH 2 3 4 5 6 7 8 9 COD pH Cumulative Methane (L @STPkg-1 VS) 0 50 100 150 200 250 300 Daily Methane (L@STP L-1d) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Cumulative Methane Daily Methane Cumulative Biogas (L @STP kg-1 VS) 0 100 200 300 400 500 600 Methane Percentage (%) 0 20 40 60 80 100 Cumulative Biogas Methane Percentage Elapsed Time (days) 0 5 1015202530 Volatile Organic Acids (mg L-1) 0 1000 2000 3000 4000 5000 Acetic Acid Propionic Acid Butyric Acid Valeric Acid Figure 5-2. Cumulative biogas a nd methane production, methane percentage, daily methane, pH, COD and volatile organic acid conc entrations from Experiment 1

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108 COD of Leachate (g L-1) 0 10 20 30 40 50 pH 2 3 4 5 6 7 8 9 COD pH Time (days) 0 5 1015202530Volatile Organic Acids (mg L-1) 0 1000 2000 3000 4000 5000 Acetic Acid Propionic Acid Butyric Acid valeric Acid Cumulative Methane (L@ STP kg-1 VS) 0 50 100 150 200 250 300 Daily Methane (L@STP L-1 d) 0.0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 Cumulative Methane Daily Methane Cumulative Biogas (L@ STP kg-1 VS) 0 100 200 300 400 500 600 Methane Percentage (%) 0 20 40 60 80 100 Cumulative Biogas Methane Percentage Figure 5-3. Cumulative biogas a nd methane production, methane percentage, daily methane, pH, COD and volatile organic acid conc entrations from Experiment 2

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109 COD of Leachate (g L-1) 0 10 20 30 40 50 pH 2 3 4 5 6 7 8 9 COD pH Cumulative Methane (L @STP kg-1 VS) 0 50 100 150 200 250 300 Daily Methane (L@STP L-1 d) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Cumulative Methane Daily Methane Time (days) 0 5 1015202530 Volatile organic Acids (mg L-1) 0 1000 2000 3000 4000 5000 Acetic Acid Propionic Acid Butyric Acid Valeric Acid Cumulative Biogas (L @STPkg-1 VS) 0 100 200 300 400 500 600 Methane Percentage (%) 0 20 40 60 80 100 Cumulative biogas Methane Percentage Figure 5-4. Cumulative biogas a nd methane production, methane percentage, daily methane, pH, COD and volatile organic acid conc entrations from Experiment 3

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110 Time (days) 01 02 03 0 Cumulative Methane (L @STP kg-1 VS) 0 50 100 150 200 250 300 350 Experiment 1 Experiment 2 Experiment 3 Figure 5-5. Comparison of cumulative meth ane production from Experiments 1, 2 and 3

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111 Pump A Stage 2Pre-treatment Anaerobic Digestion Post-treatment Aerobic Reactor Activated Reactor New Reactor Mature Reactor Biogas Biogas Stage 1 Stage 3 Pump B Pump C Air in Air out Pump D Pump E Filling Reactor Pump FPump G Figure 5-6. Incorporation of removal of sol uble COD as pre-treatment step into SEBAC-II process

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112 Table 5-1. Sugar beet tailings characteristics Tailings characteristics value Moisture (%) 88 90 Total solids (%) 13 17 Volatile solids (%) 80 92 Bulk density (kg/m3) 333 Table 5-2. Chemical characteristics of tailings a nd digested residue, and ex tent of degradation of the individual constituents during anaerobic digestion Component Tailings (% VS) Digested Residue (% VS) Extent of degradation or solubilization (%) Crude Protein 7.5 15.2 49.3 Soluble protein 1.95 3.7 52.5 NFC (non fibrous carbohydrates) 44.9 22.9 87.2 Lignin 4.7 14 25.5 Hemi cellulose 17.8 14.7 79.4 Cellulose 18.1 27.9 61.4

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113 CHAPTER 6 CONCLUSIONS AND FUTURE WORK 6.1 Conclusions This research work contained four different parts, including prelim inary studies of posttreatment of anaerobically digestated residue leachate, their bench-scale (SEBAC-II model) studies and pre-treatment of feed stock. The results of the stud y suggested that incorporating these pre and post treatments as a routine part of SEBAC-II operation will greatly enhance the potential for wide-spread use of SEBAC-II technology in waste management applications. The critical findings in the study are as follows: 6.1.1 Stabilization of Anaerobically Digest ed Residue by Nitrification Process A method was developed for the measurement of TAN in the digested residue as a method was not available in the literature. The 2 M of KCl was used as an extrac tion solution, and pH of the extraction solution was increased to above 11 by NaOH addition. The results showed that the extraction efficiency was above 98% and the recovera bility was within 2%. A method for nitrification on the solid digest ed residue was also developed. As the microorganisms required for nitrification process na turally existed in the anaerobically digested residue, it was possible to stabilize the nitroge n by simply aerating it. Nitrification was accomplished without any inoculum addition. By continuously blowing ai r through the residue at 187 mL/kg wet residue/min, the nitrification process could be initiated with in two days. Approximately 85% of ammoniumnitrogen was nitrified during a 16-day aeration period and the maxi mum rate was 0.41 mg/g wet weight/day. The denitrification process occurred soon after nitrification and its fraction reached ~50% of the nitrification. The modified Gompertz model was used to quantify the rate of NH3 transformations, and the results showed that it fitted the nitrification data very well.

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114 The oxygen consumption during this stabilization process was determined. The result showed that the oxygen consumption was 8.62 mg oxygen per mg nitrified nitrogen even though theoretical requirement based upon stoichiometry was 4.57 mg oxyge n /mg nitrified nitrogen. 6.1.2 Integration of Ammonia Removal from Leachate within Anaerobic Digestion Process A post-treatment method, which may be in tegrated into the SEBAC-II system, was develop to biologically remove ammonia from leachate on the stabilized digested residue by simply aerating the reactor. At the same time, th e viability of aerated leachate as inoculum for subsequent anaerobic digestion wa s also determined as little lit erature reported th e results about the viability of reusing the aerated leachate. The results showed that when a nitrification-denitrificati on processing step for ammonia removal from leachate using the stabilized digested residue was integrated into the anaerobic digestion, the ammonia removal rate was 70 95 mg/L/day initially a nd increased to 200-245 mg/L/day after 8-day continuous operation. The original concentration of TAN in leachate was 500 mg/L. More than 85% of TAN may be re moved as the form of nitrogen gas by denitrification when the air flow rate was 300 mL/minute/kg wet residue and leachate flow rate was 30-45 mL/minute. Viability of aerated leachate as inoculum for subsequent anaerobic digestion was also determined. The results showed that after the inoculum was processed by aeration for one time, the cumulative methane yield of the anaerobic di gestion almost didnt de crease. However, after the inoculum was processed for two times, th e cumulative methane yield of the anaerobic digestion decreased comparing with those using unprocessed inoculum. Th erefore, it would be better to only process part of th e leachate instead of the total leachate as it was not necessary to remove all TAN in leachate to avoid ammonia i nhibition. The fraction of leachate needs to be processed can be calculated according to original and objective TAN concentration in leachate.

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115 6.1.3 Integration of In Situ Treatment of Anaero bically Digestated Resi due and Leachate in SEBAC-II Configuration A new operation mode was developed for in s itu treatment of anaer obically digested residue and leachate in the SEBA C-II model. Instead of supplying a continuous air flow, air was held under pressure at ~ 10psi for 20 minutes before venting and filling again. For the stabilization of solid digested residue, initial specific nitrification rates were higher at 0.26 mg /g wet weight /day showing that this method of aeration wa s more efficient since higher pressure in this benchscale reactor may have improved the contact between digested residue and oxygen by overcoming the preferential channel flow of air when it was simply blown continuously through the residue.Based upon the specific nitrification ra te obtained in this SEBAC-II model and modified Gompertz equation, more than 90% of TAN in the anaerobically digested residue could be nitrified after 13-day ae ration in the SEBAC-II system. It was also seen that decreases in pH caused by ni trification reactions can inhibit nitrification activity. So it is essential to incorporate pH monitoring a nd control during the stabilization process. In situ ammonia removal from leachate using a digested residue bed rather than a dedicated reactor was also studied in this SEBAC-II m odel. The similar operation was utilized. The ammonia removal efficiency was above 95%. Initial ammonia removal rate had linear relationship with original TAN c oncentration in leachate. Accordi ng to results from Chapter 3, it would be better to only process pa rt of the leachate instead of the total leachate as it was not necessary to remove all TAN in leachate to a void ammonia inhibition. The fraction of leachate needs to be processed can be calculated accordin g to original and objective TAN concentration in leachate, and implemented using flow rate of leachate controlled by pump.

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116 6.1.4 Pre-treatment of Readily Biodegradabl e Feedstock to Improve Digestibility A pre-treatment process, which may be incorporated into SEBAC-II system, was developed to accommodate anaerobic digestion of sugar beet tailings. The pre-treatment step was to wash and remove the large fraction of soluble organic matter in sugar beet tailings. After this, the methane production was initiated as soon as digested leachate was introduced into the digester. At the same time, the washing water containing high COD content was added to the activated reactor for bioconversi on to methane. Critical finding s on the modifications of the SEBAC-II system to accommodate sugar beet tailings were: The tailings contained naturally occurring microbial communities to carry out anaerobic digestion. A method of culturing a therm ophilic inoculum was developed by simply flooding a bed of tailings with pH buffer solu tion and incubating this bed at thermophilic temperatures. Inoculum thus cultured wa s shown to robustly and stably initiate methanogenesis in subseque nt batches of tailings. As the tailings contain a large fraction (0.6 g COD/g VS) of readily soluble organic matter, the first step was to wash and remove the soluble organic matter. After this, methanogenesis was initiated immediately upon flooding the bed with digested leachate containing adapted inoculum. Most of the me thane potential of the solids was recovered within a week. A methane yield of 295 L at STP/kg VS was de termined for the tailings, of which 50-60% was contributed by the solubi lized organic matter. After anaerobic digestion, a volume reduction of 70-80% was achieved and approxi mately 60% of dry matter and 75% of volatile solids in tailings were degraded. The methane production ra te, consequently the kinetics of the process, could be improve d by flooding tailings using digested leachate from the end of a previous experiment. 6.2 Future Work The SEBAC-II system could be enhanced by integration of an in situ post-treatment of anaerobically digestated residue (stabilizat ion) and leachate (ammonia removal) and pretreatment of feedstock. Prelimin ary and bench-scale studies of pos t-treatment have been carried out and some data in full scale SEBAC-II syst em has been predicted according to the results

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117 from preliminary and bench-scale studies. Conduct these post-treatment pr ocesses in full scale SEBAC-II system could be part of future work: Modify SEBAC-II system to integrate the steps of stabilization of digestate and treatment of leachate Measure the extent and rate of nitrification, oxygen requirement in stabilization process in full scale SEBAC-II system and hence determine the purging time and frequency which is controlled by CR10 automatic system Conduct mass balance of nitrogen during simult aneous stabilization of digestate and treatment of leachate in full scale SEBAC-II system Modify the SEBAC-II system to treat only half of leachate for ammonia removal if necessary, because full treatment of aer ation may lower the bacteria activity For pre-treatment of feedstock to improve an aerobic digestion, only readily biodegradable feedstock has been studied. The interest in pretreatment of non-readily biodegradable feedstock can be addressed: Develop an in-situ pre-treatment method of non -readily biodegradable feedstock, such as wheat straw, to enhance anaerobic digestion Measure the methane yield and methane produc tion rate of the feed stock in anaerobic digestion Modify the SEBAC-II system to integrate the steps of pre-treatment of feedstock

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118 APPENDIX A PROGRAM CODE OF CR10X FOR STABILIZATION PROCESS 01: 1200 Execution Interval (m inutes) ; run this program every 20 minutes 1: Do (P86) 1: 42 Set Port 2 High ; open the vent/exhaust 2: Excitation with Delay (P22) 1: 1 Ex Channel 2: 6000 Delay W/Ex (units = 0.01 sec) 3: 0000 Delay After Ex (units = 0.01 sec) 4: 0000 mV Excitation ; keep the vent open for 60 seconds 3: Do (P86) 1: 52 Set Port 2 Low ; close the vent valve 4: Do (P86) 1: 41 Set Port 1 High ; open the gas supply valve 5: Excitation with Delay (P22) 1: 1 Ex Channel 2: 3000 Delay W/Ex (units = 0.01 sec) 3: 0000 Delay After Ex (units = 0.01 sec) 4: 0000 mV Excitation ; keep the supply open for 30 seconds 6: Do (P86) 1: 51 Set Port 1 Low ; close the supply valve and go back to the top of the program

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119 APPENDIX B PROGRAM CODE OF CR10X FOR AMMONIA REMOVAL PROCESS 01: 1200 Execution Interval (m inutes) ; run this program every 20 minutes 1: Do (P86) 1: 42 Set Port 2 High ; open the vent/exhaust 2: Excitation with Delay (P22) 1: 1 Ex Channel 2: 3000 Delay W/Ex (units = 0.01 sec) 3: 0000 Delay After Ex (units = 0.01 sec) 4: 0000 mV Excitation ; keep the vent open for 30 seconds 3: Do (P86) 1: 52 Set Port 2 Low ; close the vent valve 4: Do (P86) 1: 43 Set Port 3 High ; open the pump 5: Excitation with Delay (P22) 1: 1 Ex Channel 2: 6000 Delay W/Ex (units = 0.01 sec) 3: 0000 Delay After Ex (units = 0.01 sec) 4: 0000 mV Excitation ; keep the pump open for 60 seconds 6: Do (P86) 1: 53 Set Port 3 Low ; close the pump 7: Do (P86) 1: 41 Set Port 1 High ; open the gas supply valve 8: Excitation with Delay (P22) 1: 1 Ex Channel 2: 1500 Delay W/Ex (units = 0.01 sec) 3: 0000 Delay After Ex (units = 0.01 sec) 4: 0000 mV Excitation ; keep the supply open for 15 seconds

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120 9: Do (P86) 1: 51 Set Port 1 Low ; close the supply valve and go back to the top of the program

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121 LIST OF REFERENCES Ahn, Y. T., Kang, S. T., Chae, S. R., Lee, C. Y ., Bae, B. U. a nd Shin, H. S. (2007) Simultaneous high-strength organic and nitrogen removal with combined anaerobic upflow bed filter and aerobic membrane bioreactor. Ee salination 202, pp. 114-121. Aspe, E., Marti, M. C. and Roeckel, M. (2005) Optimization of the simultaneous removal of nitrogen and organic matter from fishery wa stewaters. Environmental Process 24, pp. 297304. Barry, M. (1983) Anaerobic Digestion of Agricultu ral Wastes. Ph.D. Thesis, National University of Ireland, Dublin. Berge, N. D., Reinhart, D. R., Dietz, J. D. a nd Townsend, T. G. (2006) In situ ammonia removal in bioreactor landfill leachate. Waste Management 26, pp. 334-343. Berge, N. D., Reinhart, D. R., Dietz, J. D. and Townsend, T. G. (2007) The impact of temperature and gas-phase oxygen on kinetics of in situ a mmonia removal in bioreactor landfill leachate. Water Research 41, pp. 1907-1914. Berge, N. D., Reinhart, D. R. and Townsend, T. G. (2005) The fate of nitrogen in bioreactor landfills. Critical Reviews in Environmen tal Science and technology 35, pp. 365-399. Bonmati, A. and Flotats, X. (2003) Air strippi ng of ammonia from pig slurry: characterization and feasibility as a preor post-treatmen t to mesophilic anaerobic digestion. Waste Management 23, pp. 261-272. Borja, R., Rincon, B., Raposo, F. (2006) Anaerob ic biodegradation of two-phase olive mill solid wastes and liquid effluents: ki netic studies and process perfor mance. Journal of Chemical Technology and Biotechnology 81, pp. 1450-1462. Borja, R., Rincon, B., Raposo, F., Alba, J., Mart in., A. (2003) Kinetics of mesophilic anaerobic digestion of the two-phase olive mill solid waste. Biochemical Engineering Journal 15, pp. 139-145. Bougrier, C. Albasi, C., Delgenes, J. P. and Carre re, H. (2006) Effect of ultrasonic, thermal and ozone pre-treaments on waste activated sludge solubilisation and anaerobic biodegradability. Chemical Engineer ing and Processing 45, pp. 711-718. Bremner, J. M. and Keeney, D. R. (1966) Determ ination and isotope-ratio analysis of different forms of nitrogen in soils: 3. Exchangeable ammonium, nitrate, and nitrite by extractiondistillation methods. Proceedings Soil Scie nce Society of America 30, pp. 577-582. Chugh, S., Chynoweth, D.P., Clarke, W.P., Pullammanappallil, P and Rudolph, V. (1999) Degradation of unsorted municipal solid wa ste by a leach-bed process. Bioresource Technology 69, pp. 103-115.

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122 Chynoweth, D. P., Bosch, G., Earle, J. f. K., Le grand, R. and Liu, K. (1991) A novel process for anaerobic composting of municipal solid waste. Applied Biochemistry and Biotechnology 28/29, pp. 421-432. Chynoweth, D. P., Bosch, G., Earle, J. f. K., Owens, J. and Legrand, R. (1992) Sequential batch anaerobic composting of the organic fraction of municipal solid waste. Water Science and Technology 25, pp. 327-339. Chynoweth, D. P., Haley, P., Owens, J., Teixeira, A., Welt, B., Rich, E., Townsend, T. and Choi, H. (2002) Anaerobic digestion for reduction a nd stabilization of organic solid wastes during space missions: laborator y studies. Proceedings of International Conference on Environmental Systems Paper No. 2002-01-2351. Chynoweth, D. P. and Legrand, R. (1993) Appa ratus and method for sequential batch anaerobic composting of high-solids organic feedstock. US Patent 5,269,634. Demirbas, A. (2006) Biogas Potential of Manure and Straw Mixtures. Ener gy Source Part A 28, pp. 71-78. Demirel, B., Yenigun, O. (2002) Review two-phase anaerobic digestion processes: a review. Journal of Chemical Technology and Biotechnology 77, pp. 743-755, online. Dong, X. and Tollner, E. W. ( 2003) Evaluation of anammox and denitrification during anaerobic digestion of poultry manure. Biores ource Technology 86, pp. 139-145. Eun, J. S., Beauchemin, K. A., Hong, S. H. and Bauer, M. W. (2006) Exogenous enzymes added to untreated or ammoniated ri ce straw: Effects on in vitro fermentation characteristics and degradabilogy. Animal Feed Science and Technology 131, pp. 86-101. Gallert, C and Winter, J. (1997) Mesophilic a nd thermophilic anaerobic digestion of sourcesorted organic wastes: effect of ammonia on glucose degradation and methane production. Applied Microbiology and Biot echnology 48, pp. 405-410. Ghosh, S. (1984) Solid-phase methane fermentati on of solid wastes. Proceedings of Eleventh American Society of Mechanical Engin eers National Waste Processing Conference, Orlando. Ghosh, S., Henry, M.P., Sajjad, A., Mensinger, M.C., Arora, J.L. (2000) Pilot-scale gasification of municipal solid wastes by high-rate and two-ph ase anaerobic digestion (TPAD). Water Science and Technology 41, pp. 101-110. Greenberg, A. E., Clescerl, L. S. and Eaton, A ., D. (1992) Standard methods for the examination of water and wastewater, 18th edition. American Public Health Association/American Water Works Association/Water Envir onmental Federation, Washington DC. Hansen, K. H., Angelidaki, I., Ahring, B, K. (1998) Anaerobic digestion of swine manure: inhibition by ammonia. Wate r Resource 32, pp. 5-12.

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127 BIOGRAPHICAL SKETCH W ei Liu was born in China. She received her Bachelor of Science in biochemical engineering from Beijing Technology and Business University, Ch ina in 2000 and Master of Science in organic chemistry from Chinese Academy of Sciences in 2003. In Aug. 2003, she came to University of Florida to pursue her Ph.D. degree in Agricultural and Biological Engineering Department under the supervision of Dr. Pullammanappallil and Dr. Teixeira.