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<ul><li><p>i</p><p>DRY ANAEROBIC DIGESTION OF MUNICIPAL SOLIDWASTE AND DIGESTATE MANAGEMENT STRATEGIES</p><p>by</p><p>Zeshan</p><p>A dissertation submitted in partial fulfillment of the requirements forthe degree of Doctor of Philosophy in</p><p>Environmental Engineering and Management</p><p>Examination Committee: Prof. Chettiyappan Visvanathan(Chairperson)Prof. Ajit P. AnnachhatreDr. P. Abdul Salam</p><p>External Examiner: Dr. Yasumasa TojoLaboratory of Solid Waste DisposalEngineeringDivision of Environmental EngineeringHokkaido University, Japan</p><p>Nationality: PakistaniPrevious Degree: Master of Science (Honors) Agriculture</p><p>(Soil and Environmental Sciences)University of Agriculture, Faisalabad</p><p>Scholarship donor: Higher Education Commission (HEC)Pakistan-AIT Fellowship</p><p>Asian Institute of TechnologySchool of Environment, Resources and Development</p><p>ThailandDecember 2012</p></li><li><p>ii</p><p>Acknowledgements</p><p>First of all, the author would like to thank Allah, the most gracious, the most beneficent,for giving him the opportunity to achieve higher education at this level and giving him thecourage and the patience during the course of his Ph.D. study at AIT.</p><p>The author would like to express his profound gratitude to his adviser Prof. C. Visvanathanfor kindly giving valuable guidance, stimulating suggestions and ample encouragementduring the study at AIT. The author is deeply indebted to Prof. Ajit Annachhatre and Dr.Abdul Salam for their valuable comments, suggestions and support and serving asmembers of the examination committee.</p><p>A special thank is addressed to Dr. Yasumasa TOJO for kindly accepting to serve as theexternal examiner. His constructive and professional comments will be highly appreciated.A special note of appreciation is extended to Dr. Obuli P. Karthikeyan for his help andgreat interest in this research including valuable comments and suggestions during variousphases. Special thanks to Dr. Romchat Rattanaoudom for her help and guide as a seniorand a colleague.</p><p>Sincere thanks are given to Ms. Phonthida Sensai, Mr. Supawat Chaikasem, Mr.Muhammad Zeeshan Ali Khan and Mr. Amila Abeynayaka as helping friends. The authorwould also like to thank all friends, EEM staff, laboratory colleagues and technicians fortheir help, moral support and cooperation which contributed in various ways to thecompletion of this dissertation.</p><p>The author gratefully acknowledges Higher Education Commission (HEC) of Pakistan andAIT for the joint scholarship for the Ph.D. study at AIT.</p><p>The author would like to dedicate this piece of work to his beloved brother who passedaway during the course of this study. His long lasting love and prayers always inspired andencouraged author to fulfill his desires.</p><p>Deepest and sincere gratitude goes to his beloved parents (Mr. and Mrs. SheikhMuhammad Ramzan) for their endless love, encouragement and prayers. The authorwishes to express his deepest appreciation to his siblings for their prayers, patience andunderstanding throughout the entire period of this study.</p></li><li><p>iii</p><p>Abstract</p><p>Global solid waste generation is continuously rising. Improper disposal of the giganticamount of solid waste seriously affects the environment and contributes to climate changeby release of green house gases (GHGs). Practicing anaerobic digestion for organicfraction of municipal solid waste (OFMSW) can reduce emissions to environment andthereby alleviate the environmental problems together with production of biogas, an energysource, and digestate, a soil amendment. Dry anaerobic digestion has gained muchattention because of its advantages of lesser water addition, lower reactor volume andhigher volumetric biogas production than wet digestion. However, one of its problems isaccumulation of ammonia which is more common in digesters fed with improper C/N ratiowastes and needs to be corrected.</p><p>This study was carried out to evaluate the performance of a pilot-scale thermophilic dryanaerobic reactor for biogas production and to analyze the management options for thedigestate. This was achieved by investigating substrates of different C/N ratio to get acorrect feedstock for dry anaerobic digestion (to minimize ammonia accumulation) and byinvestigating different organic loading rates (OLRs) of the correct feedstock. Moreover,GHG emission potential of digestate was calculated (based on its characteristics) with andwithout storage and curing and different digestate management options were analyzed.</p><p>In first experiment, the effect of C/N ratio and total ammonia-N accumulation in a dryanaerobic digestion was studied effectively. Two simulations of OFMSW were prepared toattain C/N ratio 27 and C/N ratio 32 using biodegradable feedstocks such as food waste,fruit and vegetable waste, leaf waste and paper waste. Results showed that the simulationwith C/N ratio 32 had about 30% less ammonia-N in digestate as compared to that withC/N ratio 27. Moreover, a free ammonia accumulation/inhibition effect was documentedand methods to overcome the adverse effects were discussed.</p><p>In another experiment, correct feedstock from the first experiment (C/N ratio 32) was usedas substrate to improve the performance of the same reactor. The effect of different OLRs,such as 4.55, 6.30 and 8.50 kg VS/m3d, was studied on the parameters like biogasproduction, VS removal and VFA accumulation. Results showed that increase in OLRproportionally increased the gas production rate (5, 6.37 and 7.55 m3/m3reactor vol/d for threeOLRs respectively) of reactor, but the specific methane production reduced (330, 320 and266 L CH4/kg VS). Similarly, VS removal also reduced (78, 75 and 67%) with increase inOLR. The system performed well at OLR and RT of 6.40 kg VS/m3d and 24 daysrespectively, however, purpose of treatment also determines the optimum operatingconditions.</p><p>Digestate from the reactor was characterized and its C/N ratio and GHG emission potentialwas calculated. It was found that the C/N ratio of digestate was 15-20 for most of the studyperiod, which is safe range for its application to agricultural land without further treatment.The GHG potential calculation shows that storage of the digestate for 2 months decreasedits GHG potential by 10%, hence, storage was found to be a source of GHG emission.Moreover, application of digestate directly to land has minimum net GHG emission (i.e. -11 gCO2-eq/kg digestate). Therefore, digestate should be applied to land immediately afterdigestion to minimize GHG emission from the storage system.</p></li><li><p>iv</p><p>Table of Contents</p><p>Chapter Title Page</p><p>Title page iAcknowledgements iiAbstract iiiTable of Contents ivList of Tables viiList of Figures viiiList of Abbreviations x</p><p>1 Introduction 11.1 Background 11.2 Objectives of the Study 21.3 Scope of the Study 3</p><p>2 Literature Review 42.1 Introduction of Dry Anaerobic Digestion 42.2 Process of Anaerobic Digestion: The Fundamentals 5</p><p>2.2.1 Hydrolysis 52.2.2 Acidogenesis 62.2.3 Acetogenesis 62.2.4 Methanogenesis 7</p><p>2.3 Inhibition of Dry Anaerobic Digestion 82.3.1 Volatile fatty acids (VFA) 82.3.2 Ammonia 9</p><p>2.4 Optimization of Factors Affecting Dry Anaerobic Digestion 112.4.1 pH 112.4.2 Solids content 112.4.3 C/N ratio 132.4.4 Temperature 142.4.5 Mixing 162.4.6 Retention time 172.4.7 Organic loading rate 18</p><p>2.5 Other techniques to Optimize Dry Anaerobic Digestion 192.5.1 Physical pretreatment 192.5.2 Chemical pretreatment 192.5.3 Biological pretreatment (inoculation) 202.5.4 Co-digestion 20</p><p>2.6 Reactor Design for Dry Anaerobic Digestion 212.6.1 Single-stage batch systems 222.6.2 Single-stage continuous systems 232.6.3 Multi-stage continuous systems 232.6.4 Design of available technologies for dry anaerobic digestion 25</p><p>2.7 Research Progress and Research Needs of Dry Anaerobic Digestion 272.8 Anaerobic Digestion and Digestate Management 30</p><p>2.8.1 Need of digestate management and digestate utilization 302.8.2 Effect of prior digestion on properties of digestate 31</p></li><li><p>v</p><p>2.9 Characteristics of Digestates 332.9.1 Characteristics of solid digestates 332.9.2 Characteristics of liquid digestates 352.9.3 Presence of organic pollutants 372.9.4 Presence of heavy metals 382.9.5 GHG emission potential of digestate 38</p><p>2.10 Management Aspects of Anaerobic Digestate 392.10.1 Separation of liquid and solid digestate 392.10.2 Direct land application of liquid digestate 402.10.3 Aerobic post-treatment of solid digestate and its effects on</p><p>quality40</p><p>2.10.4 Digestate storage and its effects on characteristics 412.11 Post Utilization Monitoring Issues of Anaerobic Digestate 42</p><p>2.11.1 Effect of digestate application on soil 422.11.2 Influence of digestate application on plant growth and health 42</p><p>2.12 Research Needs for the Dissertation 43</p><p>3 Methodology 443.1 Inoculum and Simulations of Waste 45</p><p>3.1.1 Inoculum for anaerobic digestion experiments 453.1.2 Simulations of waste 45</p><p>3.2 Experimental Set-up 463.2.1 Experimental set-up for gas formation potential test 463.2.2 Experimental set-up for pilot-scale experiments 46</p><p>3.3 Experimental Conditions 473.3.1 Experimental conditions for gas formation potential test 473.3.2 Experimental conditions for Phase I pilot experiment 483.3.3 Experimental conditions for Phase II pilot experiment 50</p><p>3.4 Digestate Management and GHG Emissions Estimation (Phase III) 513.4.1 Storage of digestate 523.4.2 Dewatering of digestate 523.4.3 Curing of dewatered digestate 533.4.4 Estimation of GHG emissions in the digestate management</p><p>system55</p><p>3.5 Analytical Methods 58</p><p>4 Results and Discussion 604.1 Gas Formation Potential of Waste 604.2 Effect of C/N Ratio and Ammonia-N Accumulation on ITDAR</p><p>(Results of Phase I Pilot Experiment)62</p><p>4.2.1 Performance of ITDAR during start-up and continuousoperations</p><p>63</p><p>4.2.2 Effect of C/N ratio and ammonia-N accumulation in ITDAR 654.2.3 Summary of the effect of ammonia-N accumulation in ITDAR 684.2.4 Energy balance of ITDAR in Phase I pilot experiment 70</p><p>4.3 Optimization of a Pilot-Scale Thermophilic Dry Anaerobic Digester(Results of Phase II Pilot Experiment)</p><p>71</p><p>4.3.1 Start-up of ITDAR in phase II pilot experiment 714.3.2 Stability parameters of ITDAR: Effect of organic loading rate 74</p></li><li><p>vi</p><p>4.3.3 Effect of organic loading rate on performance parameters ofITDAR</p><p>76</p><p>4.4 Digestate Management and GHG Emissions (Phase III) 794.4.1 Characteristics of raw digestate 794.4.2 Characteristics of stored, dewatered and cured digestate 814.4.3 Digestate management from perspectives of GHG emissions 83</p><p>4.5 Decentralized Dry Anaerobic Digestion of OFMSW for a Communityof 5000 People</p><p>86</p><p>4.5.1 Design of the decentralized AD system 864.5.2 Preparation of feedstock for dry AD (Pre-treatment) 864.5.3 Operation of decentralized AD system 874.5.4 Generation of methane and energy 884.5.5 Digestate management 884.5.6 Reduction of GHG emissions 904.5.7 Material flow (VS balance) 90</p><p>5 Conclusions and Recommendations 915.1 Conclusions 915.2 Recommendations 93</p><p>References 95</p><p>Appendices 110Appendix A 110Appendix B 114Appendix C 122Appendix D 127Appendix E 130Appendix F 134</p></li><li><p>vii</p><p>List of Tables</p><p>Table Title Page</p><p>2.1 Biomethanization Inhibitors and their Inhibitory Concentration 82.2 Change in TAN Inhibitory Concentration with Feed TS and Temperature 102.3 Typical C/N Ratios of Different Materials 132.4 High Gas Production Rate in Relation to High Organic Loading Rate in</p><p>Dry Anaerobic Digestion 182.5 Performance of Various Kinds of Dry Anaerobic Digesters 282.6 Effect of Digestion on Properties of Waste 322.7 Characteristics of Solid Digestate in Dry Anaerobic Digestion Systems 342.8 Characteristics of Separated Liquid Digestates from Different Digestion</p><p>Systems 362.9 Concentration of Organic Pollutants in Digesates and Composts (g/kg</p><p>DM)37</p><p>2.10 Heavy Metal Content in Different Types of Digestates (mg/kg DM) 382.11 Regulations of Nutrient Loading on Agricultural Land 403.1 Composition and Characteristics of Simulated Feedstock 453.2 Characteristics of Substrate and Inoculum Used in Gas Formation Potential</p><p>Test 483.3 Operating Conditions of ITDAR for Phase I Pilot Experiment 493.4 Forms and Sources of GHG Contributed and GHG Avoided 563.5 Analytical Methods for Various Parameters of Anaerobic Digestion of</p><p>OFMSW 594.1 Digestion Parameters and Methane Yield of ITDAR 664.2 Surplus Energy of ITDAR During Various Runs 714.3 Percentage of VS Removal and Specific Methane Production in ITDAR 774.4 Comparison of Digestate Characteristics and Guidelines 824.5 Characteristics of Digestate at Different Stages of Management 824.6 Net GHG Emissions from All Scenarios of Digestate Management 854.7 Technical Details of Proposed AD Plant and its Comparison to Pilot Plant 874.8 Technical Data of Sand Drying Bed for Digestate Dewatering 88</p></li><li><p>viii</p><p>List of Figures</p><p>Figure Title Page</p><p>2.1 Trend of low solids and high solids anaerobic digestion plants in Europe 52.2 Main stages of anaerobic digestion process 62.3 Graphical representation of temperature ranges for anaerobic digestion 142.4 Capacity of mesophilic versus thermophilic digestion operation in Europe 152.5 General methods of mixing in dry anaerobic digestion, a) digestate</p><p>recirculation, b) biogas recirculation and c) mechanical mixer 162.6 Classes of dry anaerobic digestion by operational criteria 222.7 Comparison between one stage and two stage process in Europe 242.8 Designs of single-stage dry anaerobic digesters 262.9 Emissions from soil applied digestate to environments 302.10 Liquid-solid separation of digestate with production of useful products 392.11 Changing parameters during aerobic post-treatment 413.1 Phases of overall research study 443.2 Experimental set-up for gas formation potential test 463.3 Pilot-scale experimental setup of inclined thermophilic dry anaerobic</p><p>digester 473.4 Method steps for gas formation potential test 483.5 Operating conditions of ITDAR for Phase II pilot experiment 513.6 Possible unit processes of digestate management system 523.7 Plastic drums for storage of digestate 533.8 Sand drying bed: Top view 543.9 Sand bed for digestate dewatering, A-A cross-sectional view 543.10 Comparative scenarios of digestate management 564.1 Cumulative and specific biogas production by feedstock 1 614.2 Cumulative and specific biogas production by feedstock 2 624.3 Time course of dry anaerobic digestion with various parameters in</p><p>ITDAR64</p><p>4.4 Interaction of ammonia and VFA in ITDAR 674.5 Variation of total ammonia-N concentration and TAN/TKN ratio with</p><p>feed C/N ratio in ITDAR 694.6 pH profile of ITDAR during start-up 724.7 Profile of VFA and VFA/Alk ratio during start-up 734.8 CH4, CO2 and GPR fluctuation during start-up phase 744.9 Evolution of pH in ITDAR during continuous loading 754.10 Concentration of VFA in ITDAR during continuous loading 754.11 VFA/Alk ratio in ITDAR during continuous loading 764.12 Gas production rate of ITDAR during different OLRs 774.13 Cumulative methane per liter of reactor volume in ITDAR 784.14 Selection of operating conditions based on purpose of waste treatment 784.15 Comparison of feed and digestate regarding total solids in phase I</p><p>experiment80</p><p>4.16 TKN and C/N ratio of the digestate in phase I...</p></li></ul>