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Table 4.4 Comparison of Digestate Characteristics and Guidelines Type of digestate pH Moisture (%) Organic matter (%TS) 82 N (%TS) C/N ratio Reference Digestate 7.75 88-90 37.28 1.94 18.35 This study Thai Guidelines* 5.5-8.5 ≤ 35 ≥ 35 ≥ 1 ≤ 20 Rattanaoudom, 2005 Indian Guidelines 5.5-8.5 - > 26 > 1 12-25 Gautam et al., 2010 *Given by Land Development Department, Thailand. i) Digestate storage Digestate is produced continuously throughout the year from digestion unit. However, its land application time is not continuous, but only after harvesting of previous crop (e.g. during spring and autumn). So it needs to be stocked-up or stored for several months. Therefore, in this study, digestate collected from the reactor was stored in the HDPE storage tanks for a period of 2 months to simulate field conditions and effect of storage on various characteristics of digestate was observed. The change in concentration of solids and nutrients with storage has been presented in Table 4.5. Results show that there was very little change in concentration of solids (TS and VS) during storage, thus, the removal of organic matter was not significant. But the concentration of nutrients was significantly affected. The concentration of N and P in digestate decreased by 32.3 and 33.8% respectively after 2 months storage. This may be attributed to the prevailing conditions during storage (i.e. high pH, high moisture and high ambient temperature), which were suitable for the microorganisms responsible for this loss of nutrients. Similar results were reported by Paavola and Rintala, (2008), who reported 40–57% decrease in the concentrations of total P and PO4-P in the separated liquid fraction of digestate after 3 months storage. Table 4.5 Characteristics of Digestate at Different Stages of Management Type of digestate TS (%) VS (%TS) C (%TS) N (%TS) P (%TS) Digestate 10.45 64.12 35.60 1.94 0.62 Stored digestate (60 d) 9.34 63.91 35.50 1.47 0.46 Dewatered digestate 54.46 52.80 29.33 1.47 0.46 Stored-cured digestate 54.46 42.00 23.30 1.33 0.41 It can be concluded that storage time of raw digestate should be reduced to avoid nutrient loss. Moreover, if storage is required, it should be done for dewatered digestate, as dewatered digestate (low moisture) could lessen microbial activity and hence nutrient loss. ii) Digestate curing As concluded before, the digestate in this study did not need any further treatment to be used as soil amendment because its C/N ratio was
Table 4.5. With curing of digestate, the organic content (C and VS) decreased significantly (20.55%) and hence, C/N ratio of the digestate decreased to 17.52. This range of C/N ratio is good for an organic material to be applied on agricultural land as soil amendment. 4.4.3 Digestate management from perspectives of GHG emissions Data of digestate characteristics (Table 4. 5) was obtained by lab analysis of digestate samples at each stage. Based on these data and the methods in section 3.4.4-d-(i), GHG emission potential of digestate was calculated at different stages of digestate management. Comparison of different digestate management options with regards to GHG emissions was then made possible. The results regarding this have been presented and discussed in this section. i) GHG emission potential of digestate The GHG emission potential of digestate was estimated using equation given in section 3.4.4-d-(i) and compared with that of OFMSW (the original substrate before digestion) as shown in Figure 4.18. Compared to digestate (139 g CO2-eq/kg waste), the GHG emission potential of OFMSW is very high (i.e. 568 g CO2-eq/kg waste). Thus, with digestion, GHG emission potential of OFMSW decreases by about 75%. GHG emission potential (g CO2-eq/kg) 600 500 400 300 200 100 0 568 139 125 OFMSW Digestate Stored Digestate Cured stored digestate Type of waste/digestate Figure 4.18 GHG emission potential of OFMSW and digestates Among different types of digestates, the (raw) digestate has maximum GHG emission potential, whereas it is about 10% less for stored digestate and about 42% less for cured stored digestate. As the waste treatment process proceeds, the GHG emission potential decreases. The loss of GHG emission potential is more in case of curing of stored digestate (i.e. 42%). The reason is that apart from C loss during storage, good aerobic conditions were provided during the curing process by increasing TS of digestate through dewatering, which led to sufficient loss of carbon in the form of CO2. 83 80
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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
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 and 88: The increase in GPR was almost line
Page 89 and 90: Based on our results, the best oper
Page 91: Based on this property 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
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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