dry anaerobic digestion of municipal solid waste and digestate ...

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Acknowledgements 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 the courage and the patience during the course of his Ph.D. study at AIT. The author would like to express his profound gratitude to his adviser Prof. C. Visvanathan for kindly giving valuable guidance, stimulating suggestions and ample encouragement during 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 as members of the examination committee. A special thank is addressed to Dr. Yasumasa TOJO for kindly accepting to serve as the external 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 and great interest in this research including valuable comments and suggestions during various phases. Special thanks to Dr. Romchat Rattanaoudom for her help and guide as a senior and a colleague. Sincere thanks are given to Ms. Phonthida Sensai, Mr. Supawat Chaikasem, Mr. Muhammad Zeeshan Ali Khan and Mr. Amila Abeynayaka as helping friends. The author would also like to thank all friends, EEM staff, laboratory colleagues and technicians for their help, moral support and cooperation which contributed in various ways to the completion of this dissertation. The author gratefully acknowledges Higher Education Commission (HEC) of Pakistan and AIT for the joint scholarship for the Ph.D. study at AIT. The author would like to dedicate this piece of work to his beloved brother who passed away during the course of this study. His long lasting love and prayers always inspired and encouraged author to fulfill his desires. Deepest and sincere gratitude goes to his beloved parents (Mr. and Mrs. Sheikh Muhammad Ramzan) for their endless love, encouragement and prayers. The author wishes to express his deepest appreciation to his siblings for their prayers, patience and understanding throughout the entire period of this study. ii
Abstract Global solid waste generation is continuously rising. Improper disposal of the gigantic amount of solid waste seriously affects the environment and contributes to climate change by release of green house gases (GHGs). Practicing anaerobic digestion for organic fraction of municipal solid waste (OFMSW) can reduce emissions to environment and thereby alleviate the environmental problems together with production of biogas, an energy source, and digestate, a soil amendment. Dry anaerobic digestion has gained much attention because of its advantages of lesser water addition, lower reactor volume and higher volumetric biogas production than wet digestion. However, one of its problems is accumulation of ammonia which is more common in digesters fed with improper C/N ratio wastes and needs to be corrected. This study was carried out to evaluate the performance of a pilot-scale thermophilic dry anaerobic reactor for biogas production and to analyze the management options for the digestate. This was achieved by investigating substrates of different C/N ratio to get a correct feedstock for dry anaerobic digestion (to minimize ammonia accumulation) and by investigating different organic loading rates (OLRs) of the correct feedstock. Moreover, GHG emission potential of digestate was calculated (based on its characteristics) with and without storage and curing and different digestate management options were analyzed. In first experiment, the effect of C/N ratio and total ammonia-N accumulation in a dry anaerobic digestion was studied effectively. Two simulations of OFMSW were prepared to attain 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 simulation with C/N ratio 32 had about 30% less ammonia-N in digestate as compared to that with C/N ratio 27. Moreover, a free ammonia accumulation/inhibition effect was documented and methods to overcome the adverse effects were discussed. In another experiment, correct feedstock from the first experiment (C/N ratio 32) was used as 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/m 3 d, was studied on the parameters like biogas production, VS removal and VFA accumulation. Results showed that increase in OLR proportionally increased the gas production rate (5, 6.37 and 7.55 m 3 /m 3 reactor vol/d for three OLRs respectively) of reactor, but the specific methane production reduced (330, 320 and 266 L CH4/kg VS). Similarly, VS removal also reduced (78, 75 and 67%) with increase in OLR. The system performed well at OLR and RT of 6.40 kg VS/m 3 d and 24 days respectively, however, purpose of treatment also determines the optimum operating conditions. Digestate from the reactor was characterized and its C/N ratio and GHG emission potential was calculated. It was found that the C/N ratio of digestate was 15-20 for most of the study period, 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 decreased its 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 after digestion to minimize GHG emission from the storage system. iii
Page 1: DRY ANAEROBIC DIGESTION OF MUNICIPA
Page 5 and 6: 2.9 Characteristics of Digestates 3
Page 7 and 8: List of Tables Table Title Page 2.1
Page 9 and 10: 4.20 Layout of conceptual decentral
Page 11 and 12: 1.1 Background Chapter 1 Introducti
Page 13 and 14: The specific objectives of this res
Page 15 and 16: scale plants of the two processes i
Page 17 and 18: acetogens play their part to run th
Page 19 and 20: In dry anaerobic digestion, recycli
Page 21 and 22: process is inhibited and at that po
Page 23 and 24: eported, which increased with time,
Page 25 and 26: acids and increased downfall of pat
Page 27 and 28: performance of a poorly mixed (1 rp
Page 29 and 30: conventional low-solid system at th
Page 31 and 32: supply of the nutrients missing in
Page 33 and 34: 2.6.2 Single-stage continuous syste
Page 35 and 36: single stage systems are DRANCO, Va
Page 37 and 38: of the solid content around 23% TS
Page 39 and 40: Substrate Feed TS (%) Reactor Type
Page 41 and 42: Second is that it has a high water
Page 43 and 44: 2.9 Characteristics of Digestates D
Page 45 and 46: For instance, Mumme et al., (2010)
Page 47 and 48: Comparison of liquid and solid dige
Page 49 and 50: 2.10 Management Aspects of Anaerobi
Page 51 and 52: Figure 2.11 Changing parameters dur
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amount of anaerobic fermentation re
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3.1 Inoculum and Simulations of Was
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ed pump, water circulating jacket,
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the reactor was increased from 35°
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parts (wt/wt bas is) of digestate c
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Sand drying bed (SDB) is simple, ea
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3.4.4 Estimation of GHG emissions i
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d) Calculation methods i) CH4 emiss
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Table 3.5 Analytical Methods for Va
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Biogas production 100X (NmL) Specif
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(i.e. 5.2 and 3.04 respectively, pl
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getting affected with the presence
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feedstock 2 is considered as a sudd
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8.0) at most of the above said time
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Table 4.2 Surplus Energy of ITDAR D
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VFA 100 X (mg/L) VFA/Alk ratio 200
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the VFA concentration increased to
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The increase in GPR was almost line
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Based on our results, the best oper
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Based on this property of digestate
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Table 4.5. With curing of digestate
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application (after curing) in CH 4
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digestion, etc. Moreover, mixing of
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Figure 4.20 Layout of conceptual de
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Chapter 5 Conclusions and Recommend
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5.2 Recommendations Following are t
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References Abdullahi, Y. A., Akunna
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Cengel, Y.A. (2003). Heat Transfer
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Forster-Carneiro, T., Pérez, M., R
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Kaparaju, P., Buendia, I., Ellegaar
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Liu, C., Yuan, X., Zeng, G., Li, W.
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Paavola, T. and Rintala, J. (2008).
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Stroot, P. G., McMahon, K. D., Mack
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Zeshan, Karthikeyan, O. P. and Visv
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Fruit and vegetable Waste Closer to
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Figure A-5 Sand drying bed for dewa
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Assumptions Size of the community:
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The flow rate of 0.569 m 3 biogas/h
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Area for 910 kg dry solids = 910 (k
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= 280 m 3 /d x 0.000717 tons/m 3 (D
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Table C-1 Operational Parameters of
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Run Time GPR % CO2 % CH4 Methane Yi
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Appendix D Data of Phase II Pilot E
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Table D-3 Characteristics of Feed a
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Methodology Methodology for for Ene
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Q = Heat transfer rate or heat loss
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Calculation of GHG Emission Potenti
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