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digestate from perspectives of GHG emissions is that scenario 2 is the best. Scenario 3 and 4 are better than scenario 5, while scenario 1 is the worst. Net GHG emission (g CO2-eq/kg) 250 200 150 100 50 0 -50 190 Scenario 1 Scenario 2 -11 Scenario 3 Scenario 4 Scenario 5 Figure 4.19 Net GHG emissions from all scenarios of digestate management 4.5 Decentralized Dry Anaerobic Digestion of OFMSW for a Community of 5000 People Based on findings of this thesis work, a decentralized anaerobic digestion system is designed for treating the OFMSW collected from a community of 5000 people. Such decentralized AD system will be developed for reducing the burden on central system of waste management. It is also easy to manage the process at decentralized level. The details regarding design, feedstock preparation, start-up, continuous operation, methane and energy generation, digestate management, reduction of GHG emissions and VS balance of the proposed system have been given in the following sections. 4.5.1 Design of the decentralized AD system Around 2000 kg/d OFMSW from the mentioned size of community will reach the decentralized facility (Appendix B). From the results of pilot study given in section 4.3.3, the selected organic loading rate of 6.5 kgVS/m 3 /d (RT 24 days) will be applied for the decentralized system. Based on the operating conditions and results of our pilot experiments, the volume of reactor becomes 62.5 m 3 , which has been designed for the amount of OFMSW generated by the community. The design data has been summarized in Table 7.4 (for detailed calculations, please see Appendix B). The AD plant will be provided with pretreatment facilities to pre-treat the organic solid waste coming from the community. 4.5.2 Preparation of feedstock for dry AD (Pre-treatment) - Since the solid waste for the decentralized AD system will be source-separated waste, the pre-treatment will consist of only shredding, which is required to facilitate pumping, 86 12 13 Scenario 129
digestion, etc. Moreover, mixing of different kinds of waste will also be done to adjust C/N ratio. - The OFMSW received from the community will be consisting of a mixture of food waste, vegetable waste and fruit waste, with C/N ratio in the range of 18-25. Based on the findings of this thesis, the feedstock C/N ratio 32 is helpful to mitigate ammonia accumulation problem in dry AD. Thus feedstock C/N ratio should be adjusted by mixing it with high C/N ratio material (e.g. waste paper, saw dust, etc.). - In our pilot experiments, various feed mixtures were prepared and used to achieve the above objective, the details of which are given in Appendix B, Table B-2. The recommended material from our experimental results is that 5-7% of total waste should consist of waste paper. However, the composition may be varied depending on the C/N ratio of feedstock received from the community. Layout of the decentralized digestion system to be established for treating OFMSW of the community has been shown in Figure 4.20. For this purpose, a shredder-cum -mixer will be used as shown in the Figure. Table 4.7 Technical Details of Proposed AD Plant and its Comparison to Pilot Plant Detail Value/Specification of the reactor Pilot-scale Real-scale Amount of waste (kg/d) 22 2000 Reactor size (m 3 ) 0.69 62.5 Dimensions of reactor(m) -Diameter 0.6 3 -Height 2.4 9 Placement/Orientation Inclined at 30° with ground Inclined at 30° with ground Material of the reactor Stainless steel Stainless steel Size of the pump (L/min) 200 1450 Model of the pump Allweiler AE1N-200 Allweiler AE1N-1450 Digestate (Liq + Solid), kg/d 15.4 1400 Biogas production (L/d) 3530 200,000 4.5.3 Operation of decentralized AD system Start-up phase - The system will be started-up by loading a mixture of waste and inoculum with substrateto-inoculum (S/I) ratio of ≤ 3. The inoculum should consist of a mixture of variety of anaerobic materials (e.g. anaerobic sludge, anaerobic digestate from a working digester, and cow dung). -At start-up, the reactor will be purged with natural gas to remove oxygen and create anaerobic condition. - Low mixing rate (recirculation rate, i.e. 1 Ldig/Lreactor vol./d) will be used during start-up. - The starting reactor temperature will be same as ambient temperature. It will be then increased slowly and gradually (i.e. 2°C/day) to reach the designed temperature (i.e. 55°C). Continuous operation mode - After start-up, the continuous feeding of reactor should be started with a low OLR. Then the OLR should be progressively increased based on system’s capacity to reach the designed OLR (6.5 kg VS/m 3 .d). 87
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DRY ANAEROBIC DIGESTION OF MUNICIPA
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Abstract Global solid waste generat
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2.9 Characteristics of Digestates 3
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List of Tables Table Title Page 2.1
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4.20 Layout of conceptual decentral
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1.1 Background Chapter 1 Introducti
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The specific objectives of this res
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scale plants of the two processes i
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acetogens play their part to run th
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In dry anaerobic digestion, recycli
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process is inhibited and at that po
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eported, which increased with time,
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acids and increased downfall of pat
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performance of a poorly mixed (1 rp
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conventional low-solid system at th
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supply of the nutrients missing in
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2.6.2 Single-stage continuous syste
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single stage systems are DRANCO, Va
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of the solid content around 23% TS
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Substrate Feed TS (%) Reactor Type
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Second is that it has a high water
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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
Page 53 and 54: amount of anaerobic fermentation re
Page 55 and 56: 3.1 Inoculum and Simulations of Was
Page 57 and 58: ed pump, water circulating jacket,
Page 59 and 60: the reactor was increased from 35°
Page 61 and 62: parts (wt/wt bas is) of digestate c
Page 63 and 64: Sand drying bed (SDB) is simple, ea
Page 65 and 66: 3.4.4 Estimation of GHG emissions i
Page 67 and 68: d) Calculation methods i) CH4 emiss
Page 69 and 70: Table 3.5 Analytical Methods for Va
Page 71 and 72: Biogas production 100X (NmL) Specif
Page 73 and 74: (i.e. 5.2 and 3.04 respectively, pl
Page 75 and 76: getting affected with the presence
Page 77 and 78: feedstock 2 is considered as a sudd
Page 79 and 80: 8.0) at most of the above said time
Page 81 and 82: Table 4.2 Surplus Energy of ITDAR D
Page 83 and 84: VFA 100 X (mg/L) VFA/Alk ratio 200
Page 85 and 86: the VFA concentration increased to
Page 87 and 88: The increase in GPR was almost line
Page 89 and 90: Based on our results, the best oper
Page 91 and 92: Based on this property of digestate
Page 93 and 94: Table 4.5. With curing of digestate
Page 95: application (after curing) in CH 4
Page 99 and 100: Figure 4.20 Layout of conceptual de
Page 101 and 102: Chapter 5 Conclusions and Recommend
Page 103 and 104: 5.2 Recommendations Following are t
Page 105 and 106: References Abdullahi, Y. A., Akunna
Page 107 and 108: Cengel, Y.A. (2003). Heat Transfer
Page 109 and 110: Forster-Carneiro, T., Pérez, M., R
Page 111 and 112: Kaparaju, P., Buendia, I., Ellegaar
Page 113 and 114: Liu, C., Yuan, X., Zeng, G., Li, W.
Page 115 and 116: Paavola, T. and Rintala, J. (2008).
Page 117 and 118: Stroot, P. G., McMahon, K. D., Mack
Page 119 and 120: Zeshan, Karthikeyan, O. P. and Visv
Page 121 and 122: Fruit and vegetable Waste Closer to
Page 123 and 124: Figure A-5 Sand drying bed for dewa
Page 125 and 126: Assumptions Size of the community:
Page 127 and 128: The flow rate of 0.569 m 3 biogas/h
Page 129 and 130: Area for 910 kg dry solids = 910 (k
Page 131 and 132: = 280 m 3 /d x 0.000717 tons/m 3 (D
Page 133 and 134: Table C-1 Operational Parameters of
Page 135 and 136: Run Time GPR % CO2 % CH4 Methane Yi
Page 137 and 138: Appendix D Data of Phase II Pilot E
Page 139 and 140: Table D-3 Characteristics of Feed a
Page 141 and 142: Methodology Methodology for for Ene
Page 143 and 144: Q = Heat transfer rate or heat loss
Page 145: Calculation of GHG Emission Potenti
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