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

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Dig rr (L dig /L reactor vol .d) pH Methane yield 10x (L/kg VS) VFA/Alk ratio OLR (kg VS/m 3 .d) 2 1 0 50 40 30 20 10 0 8 7 6 5 4 2 0 20 15 10 5 0 e) d) c) b) a) 0 30 60 90 120 150 180 210 240 270 1 2 3 4 5 6 7 8 0 30 60 90 120 150 180 210 240 270 Time (days) Figure 4.3 Time course of dry anaerobic digestion with various parameters in ITDAR Further, the VFA concentrations were high (5000 –38,000 mg/L) and average alkalinity was 31,000 mg/L as CaCO3 (range 7700–69,000 mg/L as CaCO3) during different runs (Table 4.1; Appendix C, Table C-1). Polprasert (2007) reported the VFA concentration of 6000–8000 mg/L as inhibitory. However, the digestion process in ITDAR was not really 64
getting affected with the presence of VFA concentrations higher than that of inhibitory levels. The reason is that VFA to alkalinity (VFA/Alk) ratio (a good indicator of digester failure) during various runs found to be in the range of 0.31–0.56 (Figure 4.3e), except for run 1 (1.21). Therefore, the methane yield for the run 1 was comparatively lower than the successive runs and correlated with the previous report by Khanal (2008) . He stated the VFA/Alk ratio of ≤ 0.4 and 0.8 for successful and faultier reactor functioning, respectively. The average concentration of 2325 mg/L ammonia-N was recorded in extracted liquid of digestate in ITDAR. High ammonia-N concentration has also been reported to act as buffer against the acidification effect of VFA (Lahav and Morgan, 2004). The detailed data of all these operational parameters has been given in Appendix C, Table C-1. From overall study, a maximum specific methane yield of 327 L/kg VSadded and minimum of 121 L/kg VSadded was recorded from runs 3 and 5, respectively (Appendix C, Table C- 2). The possible reasons could be that the lower OLR with higher SRT and higher OLR with lower SRT, respectively, for run 3 and 5. Further, the higher Digrr and sudden overloading of reactor and consequent drop in pH could also be the possible reasons for the lower methane yield during run 5 ( Figure 4.3b). The specific methane yield for the centralized DRANCO system was reported to be in the range of 210 to 300 L/kgVSadded (De Gioannis et al., 2008). The present study results, in terms of specific methane yield, were in line with the performance of centralized units. But, on the other hand ITDAR can uphold the overall net energy gain by reducing the collection and transportation costs found to be advantageous for using it in decentralized level. Further, the understanding of relationship between the pH, ammonia-N and VFA accumulation with the different feedstock characteristics was considered as important to improve the reactor performance. Hence, the following sections primarily emphasized the relationship between feedstock characteristics, ammonia-N accumulation and VFA interactions in ITDAR (Figure 4.4, Note: VFA data for Day 1-120 has not been included to clearly show the probable interaction, however, this data is provided in Table C-1 of Appendix C and in Table 4.1). 4.2.2 Effect of C/N ratio and ammonia-N accumulation in ITDAR Table 4.1 and Figure 4.4(a–e) depict the important parameters of digestion viz., pH, VFA, VFA/Alk ratio, ammonia-N, free ammonia, methane yield and VS removal (Appendix C, Table C-1 and Table C-2), which can directly affect the performance of the ITDAR. a) Effect of feedstock 1 (C/N ratio of 27) in ITDAR – Run 1 to 3 Feedstock 1 with the C/N ratio of 27 was used in the start-up of ITDAR and in runs 1–3. The maximum concentration of 3200 mg/L of ammonia-N concentration was recorded during run 1. Later, the average concentrations subsequently reduced up to 3040 mg/L and 2671 mg/L in run 2 and 3, respectively. The pH was lower during run 1 and increased to near neutral range during run 2 and 3. Therefore, the escape of ammonia-N as gas during run 1 was comparatively lesser than the other two runs as noticed from the free ammonia concentration levels. As stated, the average concentration of free ammonia was 99 mg/L in run 1, whereas it was around 328 and 284 mg/L during run 2 and 3, respectively. It was reported that the free ammonia can severely affect the anaerobic system under concentrations of 200–700 mg/L in thermophilic anaerobic systems by various authors (Hansen et al., 1998; Straka et al., 2007; Nakakubo et al., 2008; El-Hadj et al., 2009; Yabu 65
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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
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
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: (i.e. 5.2 and 3.04 respectively, pl
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 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
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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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