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

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NaOH were added to the reactor periodically during days 5-25 to maintain pH at near neutral range. It can be noted as small peaks during days 11-26 in Figure 4.6. From day 28 onwards, pH did not drop again and started increasing slowly, therefore, NaOH was not added anymore. It became stable at around 8.2 during days 42-50 (Appendix D, Table D- 1). pH 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 1 11 21 31 41 Time (days) Figure 4.6 pH profile of ITDAR during start-up At first, the concentration of VFA increased after loading the reactor and reached to its maximum (19000 mg/L) on day 25. However, once the pH became stable, VFA concentration started to drop due to its utilization. The concentration of VFA dropped from 19000 to 6300 mg/L only in 20 days (Figure 4.7 and Appendix D, Table D-1). The reason is that there was no waste feeding throughout the star-up phase (day 1-50). The evolution of VFA/Alk ratio was different from the VFA concentration. Increase in VFA/Alk ratio after reactor loading was not observed, rather there was a continuous decrease, which indicates that alkalinity started to develop and increase just after loading. It may be because a part of inoculum used for this start-up was taken from the system with the same conditions (treating OFMSW under thermophilic conditions). After day 30, VFA/Alk ratio started to decrease in the same way as that of VFA. This may be attributed to decrease in VFA concentration. Methane content in biogas and gas production rate (GPR) was lower in the beginning. The reason might be unfavorable conditions for methanogenesis, i.e., pH lower than 6.8 and VFA more than 6000-8000 mg/L (Polprasert, 2007). However, methane content and GPR started to increase slowly as the system progressed towards stability. On the contrary, carbon dioxide content was higher at the start (Figure 4.8 and Appendix D, Table D-2), which is a sign of acidification. But it decreased slowly, as alkalinity and pH increased and VFA concentration got utilized. From the above discussion, it can be concluded that pH and VFA concentration of the reactor were not stable until day 30, thus, methane content was low, carbon dioxide content was high and GPR was unstable. However, after day 35, the reactor conditions were stable and, therefore, both the methane content in biogas and GPR increased. 72
VFA 100 X (mg/L) VFA/Alk ratio 200 180 160 140 120 100 80 60 40 20 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 1 11 21 31 41 Time (days) Figure 4.7 Profile of VFA and VFA/Alk ratio during start-up Overall, this start-up took relatively longer time for attaining stable conditions than a previous study (Zeshan et al., 2012) in the same reactor. The reason may be th e use of higher recirculation rate (i.e. 2.4 Ldig/Lreactor vol.d) as compared to previous study (where it was 1 Ldig/Lreactor vol.d). Suwannoppadol et al., (2011) also recommended that during startup phase low mixing rate should be used. In the end of start-up phase, GPR decreased, which may be because most of the accumulated VFA was utilized by microorganisms as depicted by drop in VFA and rise in pH. This point shows the end of start-up phase in batch mode where continuous reactor loading should be started. It was found from the results of this study that the start-up phase ended (at around day 50) when most of the accumulated VFA was utilized by microorganisms and its concentration decreased from 19000 mg/L at day 25 to 5700 mg/L at day 54 and further decreased to 4700 mg/L at day 68. With this decrease in VFA concentration, pH increased from 7.2 to 7.8 and the reactor stability conditions reached its maximum by achieving the lowest VFA/Alk ratio of 0.32. Similarly, volatile solids concentration (VS/TS) of di gestate was also found at its minimum (i.e. 0.56-0.57) at this point. Thus the end of start-up phase was marked by the lowest values of VFA concentration, VFA/Alk ratio and VS/TS of digestate. 73 Time (days) 1 11 21 31 41
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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
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
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: Table 4.2 Surplus Energy of ITDAR D
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 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
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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
Page 141 and 142:
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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