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

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iii) Cumulative methane yield Cumulative methane yield per liter reactor volume for each OLR tested has been sorted out (Figure 4.13) for the equal amount of organic waste fed to the system. As shown in the figure, OLR 4.55 kg VS/m 3 /d produced maximum cumulative methane that is 75 L CH4/Lreactor vol.. At OLR of 6.4 and 8.5 kg VS/m 3 /d, it is only 57 L CH4/Lreactor vol.. Apparently, the relationship between GPR and OLR shown in Figure 4.12 was almost linear. But the relationship of cumulative methane yield with each OLR tested (Figur e 4.13) provided better information about the performance of the process. Cumulative methane (L/Lreactor vol.) 80 60 40 20 0 1 11 21 31 41 51 61 Time (days) Figure 4.13 Cumulative methane per liter of reactor volume in ITDAR Dual Treatment (Anaerobic + Aerobic) RT in AD: 18 d OLR: 8.5 kg VS/m 3 /d VS removal: 67% Cumulative methane yield: 57 L CH4/Lreactor vol OLR 4.55 OLR 6.4 OLR 8.5 Dry Anaerobic Digestion Figure 4.14 Selection of operating conditions based on purpose of waste treatment 78 Single Treatment (Anaerobic digestion) RT in AD: 30 d OLR: 4.55 kg VS/m 3 /d VS removal: 78% Cumulative methane yield: 75 L CH4/Lreactor vol
Based on our results, the best operating conditions for AD (RT and OLR) can be selected. But it also depends on the purpose of treatment (Figure 4.14). As we know anaerobic digestion can be used as a single treatment for waste or in combination with aerobic process. In case of dual treatment (anaerobic + aerobic), time spent for anaerobic digestion should be minimized, so that the saved time could be used for aerobic treatment. Thus RT of 18 days (OLR 8.5 kg VS/m 3 /d) should be preferred for digestion step. But if the purpose is only a single treatment (i.e. dry anaerobic digestion), then option of higher retention time (RT 24 d or 30 d) should be chosen to get maximum VS removal and its conversion to methane. 4.4 Digestate Management and GHG Emissions (Phase III) Proper management of digestate is needed as it has certain GHG emission potential. So, it tends to emit methane to the atmosphere, if not stored properly. Moreover, it has certain amount of nutrients and organic matter, which could be useful if applied on agricultural soils. Therefore, to protect the environment and to make use of digestate’s economic value, careful digestate management should be performed. There are several options for digestate handling and management, for example, digestate dewatering, digestate storage, digestate application to the land, digestate composting, digestate curing or dumping. But characteristics of digestate are the key to determine the best and correct option for management of digestate. Thus, in this section of thesis, characteristics of digestate have been first described and based on the characteristics, the proper digestate management options have been suggested and finally their effect studied on its nutrient content and GHG emission potential. 4.4.1 Characteristics of raw digestate Digestate was removed from the reactor every day before feeding of fresh waste throughout the reactor operation period. The freshly withdrawn digestate (raw digestate) was analyzed for moisture, TS and VS content twice a week. Moreover, digestate was also characterized for carbon and nitrogen content to calculate its C/N ratio. Characteristics of digestate have been discussed in this section (Figure 4.15, 4.16 and 4.17; Appendix C, Table C-3, Appendix D, Table D-3). With digestion the feed TS decreased, so digestate TS was lower than feed TS. Digestate TS content was high in the beginning (16 -20%) and started to decrease as the digestion proceeded. During run 3, it started to increase again almost continuously and reached upto 18.5% at the end of run 4 as shown in Figure 4.15 and given in Appendix C, Table C-3. This increase in digestate TS corresponds to the increase in feed TS (23 -25%) combined with increase in OLR. Similar observations were made by Mumme et al., (2010). Also there was no replenishment of moisture lost through biogas, which is higher in thermophilic process. Only little changes were observed for the VS content of TS (i.e. digestate VS/TS), which has been in the range of 0.6-0.7 throughout the study. The practical consequence of this increase in digestate TS was that it was difficult by the screw bed pump to feed and re-circulate the feedstock and reactor material respectively. Thus TS content in the reactor was adjusted by mixing of water with feedstock (making feed TS 17-20%) starting from run 6 onwards as shown in Figure 4.15 and thereby the 79
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DRY ANAEROBIC DIGESTION OF MUNICIPA
Page 3 and 4:
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
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
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: The increase in GPR was almost line
Page 91 and 92: Based on this property of digestate
Page 93 and 94: Table 4.5. With curing of digestate
Page 95 and 96: application (after curing) in CH 4
Page 97 and 98: digestion, etc. Moreover, mixing of
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
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Methodology Methodology for for Ene
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Q = Heat transfer rate or heat loss
Page 145:
Calculation of GHG Emission Potenti
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