ANAEROBIC DIGESTION OPTIMIZATION FOR ENHANCED RENEWABLE BIOMETHANE PRODUCTION By TED ROSS STOVER Bachelor of Science in Zoology Oklahoma State University Stillwater, Oklahoma 2008 Master of Science in Environmental Engineering Oklahoma State University Stillwater, OK 2009 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY July, 2011 ANAEROBIC DIGESTION OPTIMIZATION FOR ENHANCED RENEWABLE BIOMETHANE PRODUCTION Dissertation Approved: Dr. Enos L. Stover Dissertation Adviser Dr. William F. McTernan Dr. Gregory G. Wilber Dr. Dee Ann Sanders Dr. Douglas Hamilton Outside Committee Member Dr. Mark E. Payton Dean of the Graduate College ii ACKNOWLEDGMENTS I would like to sincerely thank my father, Dr. Enos L. Stover, for serving as my thesis advisor and providing direct oversight throughout the course of this research study. I would also like to thank Dr. Stover for giving me motivation to pursue higher education at Oklahoma State University and providing learning experiences and opportunities that most aspiring engineers will never have the chance to encounter. I would like to thank Dr. William F. McTernan for serving as my committee chairman, and Dr. Dee Ann Sanders and Dr. Gregory G. Wilber for serving as committee members. All three instructors have provided great insight and a fun and memorable learning experience at Oklahoma State University that I will remember for the rest of my life. I would also like to thank Dr. Douglas Hamilton for his willingness to serve as a committee member. Special thanks to my wife, Abby, for her understanding and support through the extensive timeframe of this project, and for encouraging me to succeed in everything I do. iv TABLE OF CONTENTS Chapter Page I. INTRODUCTION ......................................................................................................1 II. REVIEW OF LITERATURE....................................................................................5 Current State ............................................................................................................5 Background ..............................................................................................................6 Anaerobic Digestion Process ..............................................................................8 Advantage of Anaerobic Digestion ...................................................................12 Previous Studies .....................................................................................................13 III. METHODOLOGY ................................................................................................18 Feedstocks ..............................................................................................................18 Digester Operations ...............................................................................................21 Biogas Monitoring .................................................................................................25 Analytical Testing ..................................................................................................27 Kinetics Development ............................................................................................28 AMPTS Kinetics Evaluation..................................................................................33 IV. RESULTS ..............................................................................................................35 Substrate Characterization .....................................................................................35 Bench-Scale Digester Studies ................................................................................37 Digester Characterization..................................................................................37 Digester Substrate Kinetics ...............................................................................50 Digester Biogas Production ..............................................................................54 Digester Biogas Kinetics...................................................................................59 Digester Methane Kinetics ................................................................................62 AMPTS Studies .....................................................................................................67 AMPTS Substrate Characterization ..................................................................67 AMPTS Digester Substrate Kinetics ................................................................71 AMPTS Digester Biogas Kinetics ....................................................................77 AMPTS Digester Methane Kinetics .................................................................82 Bench-Scale Digester Kinetics vs. AMPTS Digester Kinetics ..............................82 Substrate Kinetics Comparison .........................................................................82 Biogas Kinetics Comparison.............................................................................88 Methane Kinetics Comparison ..........................................................................90 v Chapter Page V. DISCUSSION ........................................................................................................94 VI. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS .....................100 REFERENCES ..........................................................................................................105 APPENDIX A Bench-Scale Digester Photographs .................................................................110 APPENDIX B AMPTS Digester Photographs ........................................................................115 APPENDIX C Phase I Raw Data .............................................................................................118 APPENDIX D Phase II Raw Data ............................................................................................134 APPENDIX E Phase III Raw Data ..........................................................................................142 APPENDIX F Phase IV Raw Data ..........................................................................................149 APPENDIX G AMPTS Study Raw Data .................................................................................164 vi LIST OF TABLES Table Page Table 1 Analytical Testing Program ...............................................................................20 Table 2 Research Study – Daily Duties ..........................................................................24 Table 3 Analytical Test Parameters and Methods ..........................................................29 Table 4 Individual Feedstock Characterization ..............................................................36 Table 5 Average Influent Feed Characterization Data ....................................................38 Table 6 Average Anaerobic Digester Characterization, Phase I .....................................39 Table 7 Average Anaerobic Digester Characterization, Phase II ...................................40 Table 8 Average Anaerobic Digester Characterization, Phase III ..................................41 Table 9 Average Anaerobic Digester Characterization, Phase IV ..................................42 Table 10 Average Digester 5 Effluent Characterization ...................................................44 Table 11 Average Biogas Characterization Data, Phase I ................................................55 vii Table Page Table 12 Average Biogas Characterization Data, Phase II ...............................................56 Table 13 Average Biogas Characterization Data, Phase III ..............................................57 Table 14 Average Biogas Characterization Data, Phase IV .............................................58 Table 15 Average Biogas and Methane Production Rates ................................................61 Table 16 Bench-Scale Digester Biokinetic Constants ......................................................69 Table 17 AMPTS Influent Feed Characterization Data ....................................................70 Table 18 AMPTS Seed Sludge Characterization Data .....................................................72 Table 19 AMPTS Digester Data .......................................................................................73 Table 20 AMPTS Digester Effluent Data .........................................................................74 Table 21 AMPTS Digester Biogas Data ...........................................................................78 Table 22 AMPTS Digester Biokinetic Constants .............................................................85 Table 23 Comparison of Biokinetic Constants .................................................................87 viii LIST OF FIGURES Figure Page Figure 1 Basic Diagram of Anaerobic Digestion Processes .............................................11 Figure 2 Phase I Effluent Soluble COD Trend Plot .........................................................46 Figure 3 Phase II Effluent Soluble COD Trend Plot ........................................................47 Figure 4 Phase III Effluent Soluble COD Trend Plot ......................................................48 Figure 5 Phase IV Effluent Soluble COD Trend Plot ......................................................49 Figure 6 Substrate Utilization as a Function of Mass Specific Substrate Loading Rate In Terms of COD ..........................................................................................52 Figure 7 Graphical Determination of U and K in Terms of COD .............................53 max B Figure 8 Biogas Production Composition as a Function of Mass Specific Substrate Loading Rate in Terms of COD ....................................................................60 Figure 9 Specific Biogas Production Rate as a Function of Mass Specific Substrate Loading Rate in Terms of COD (Digester 1-4) ...........................................63 Figure 10 Graphical Determination of G and G in Terms of COD (Digester 1-4) ......64 max B ix Figure Page Figure 11 Specific Methane Production Rate as a Function of Mass Specific Substrate Loading Rate in Terms of COD (Digester 1-4) ............................................66 Figure 12 Graphical Determination of M and M in Terms of COD (Digester 1-4) ....68 max B Figure 13 Specific Substrate Utilization Rate as a Function of Mass Specific Substrate Loading Rate in Terms of COD (AMPTS) ...................................................75 Figure 14 Graphical Determination of U and K in Terms of COD (AMPTS) ............76 max B Figure 15 Specific Biogas Production Rate as a Function of Mass Specific Substrate Loading Rate in Terms of COD (AMPTS) ...................................................79 Figure 16 Graphical Determination of G and G in Terms of COD (AMPTS) ............80 max B Figure 17 Biogas Production Composition as a Function of Mass Specific Substrate Loading Rate in Terms of COD (AMPTS) ...................................................81 Figure 18 Specific Methane Production Rate as a Function of Mass Specific Substrate Loading Rate in Terms of COD (AMPTS) ...................................................83 Figure 19 Graphical Determination of M and M in Terms of COD (AMPTS) ...........84 max B Figure 20 U vs. F/M Comparison Plot of Bench-Scale Digester and AMPTS Digester U Values with Respect to F/M ......................................................................89 Figure 21 G vs. F/M Comparison Plot of Bench-Scale Digester and AMPTS Digester G Values with Respect to F/M ......................................................................91 Figure 22 M vs. F/M Comparison Plot of Bench-Scale Digester and AMPTS Digester M Values with Respect to F/M .....................................................................93 x CHAPTER I INTRODUCTION With petroleum-based fuel prices at all-time record highs and growing public interest in environmentally conscious products, alternative fuel sources are receiving more attention than ever. Universities, private and public corporations, and government agencies are spending millions of dollars each year to further research towards production of effective and feasible alternative fuels that are renewable, clean burning, and more economical to produce compared to the long-established fossil fuels. One alternative fuel that has been received with great success in Europe and Asia, and is showing increased interest in the United States, is biomethane (biogas). Biogas has been evaluated as one of the most energy-efficient and environmentally beneficial technologies for bioenergy production (Fehrenbach et al., 2008) Biogas is a biologically-produced, renewable fuel that can be used for any combustion process that utilizes methane as a fuel source, such as heat, transportation, electricity, and combined heat and power (CHP) generation. Biogas can also be scrubbed and upgraded to meet pipeline gas quality standards for transmission. Biogas is comprised of methane, 1