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

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The GHG emission potentials of various types of digestate shown in Figure 4.18 correspond to the GHG emissions, only if they are dumped to the shallow dumpsite. However, the emissions can be minimized if they are managed well in some better way. For this purpose, various digestate management options in the form of 5 different scenarios have been considered and compared with regard to GHG emissions and have been presented in the following section. ii) Comparison of GHG emissions from different digestate management scenarios As digestate has certain residual GHG emission potential, it tends to emit methane to the atmosphere, if not stored properly and hence can contribute to the climate change. Therefore, it is necessary to carefully analyze various digestate management options based on their net GHG emission reductions under various scenarios, so that the best scenario can be selected for digestate management. In this part of the study, various digestate management options were considered to assess the reduction in GHG emissions. Results of GHG emissions from each scenario of digestate management have been presented in Table 4.6. Scenario 1: The baseline scenario shows that the net GHG emission is 190 g CO2-eq/kg digestate. All the emission is from dumpsite or landfill. The emission comes directly from biodegradation of digestate in CH4 form. Since no flaring, collection and recovery of methane is considered in scenario 1, thus all the produced methane is released into atmosphere and contributes to GHG emissions. There is no GHG saving here in this scenario as well. Scenario 2: In this scenario, GHG emission is mainly in N2O form, which is equal to 7.85 g CO2-eq/kg digestate from the land applied digestate. But here the N and P as nutrients provided by the land applied digestate is the most important factor, which replaces the use of chemical fertilizer and hence the GHG from fertilizer manufacturing is avoided. Larger avoidance of GHG emissions from fertilizer production ( -19 g CO2-eq/kg digestate) than N2O emission (8 g CO 2-eq/kg digestate) from the land applied digestate results in the negative net GHG emission as shown in Table 4.6. Scenario 3: In this scenario, GHG emission is in both CH4 and N2O forms. Storage of digestate for 2 months is the major contributor of CH4 from the stored digestate which is equal to 20 g CO2-eq/kg digestate. Moreover, N2O from land applied digestate further contributes to GHG emission. However, the GHG saving from the fertilizer substitution by application of digestate is lesser than scenario 2. It is because of loss of nutrients during storage. For instance, GHG saving from fertilizer substitution is mainly through N content of digestate, but during storage, ammonia is lost through its volatilization from the stored digestate due to favorable condition of pH. Since the GHG emissions from storage and land applied digestate (25 CO2-eq/kg digestate) is larger than GHG savings (-13 CO2-eq/kg digestate), the net GHG emission is positive in this scenario. It can be concluded from the results of scenario 3 that if land application is the fate of digestate, its storage time should be minimized as much as possible to reduce the CH4 emission and maximize the GHG savings from fertilizer substitution by digestate. Scenario 4: In this scenario, although, curing of digestate has reduced the GHG emission potential of stored digestate as shown earlier in Figure 4.18. But still the net GHG emissions here are just like scenario 3, which are during storage (before curing) and land 84
application (after curing) in CH 4 and N2O forms respectively. Thus, in case, if the stored digestate is to be applied to soil, curing is less advantageous. However, curing is recommended if the nutrient ratio of digestate is not suitable for land application (e.g C/N ratio > 20). Table 4.6 Net GHG Emissions from All Scenarios of Digestate Management Scenario GHG emission (g CO2-eq/kg digestate ) GHG saving by fertilizer substitute (g CO2-eq/kg digestate) CH4 N2O N P 85 Net GHG emission (g CO2-eq/kg digestate ) Scenario 1 190 0 0 0 190 Scenario 2 0 7.85 -18.04 -1.17 -11 Scenario 3 20 5.32 -12.22 -0.77 12 Scenario 4 20 4.70 -10.80 -0.67 13 Scenario 5 129 0 0 0 129 Scenario 5: In this scenario, curing has reduced the GHG emission potential of digestate down to 109 g CO2-eq/kg digestate. However, before curing, there is CH4 emission during storage equivalent to 20 g CO2-eq/kg digestate. Since dumping of cured digestate is to be done, there is no N2O emission and also no GHG savings from this scenario. If the digestate is unfit to be applied on land because of presence of heavy metals or other pollutants beyond safe levels, then its dumping is needed. In such case, this scenario is recommended, because before dumping, GHG emission potential of digestate can be minimized by curing. iii) Summary of GHG emissions from digestate management options Net GHG emissions from all scenarios of digestate management were calculated. Scenario 1 produces maximum GHG emissions as there is no management or treatment of digestate, but only direct landfilling. Scenario 2 performs best out of all other cases in terms of greenhouse gas emission (Figure 4.19). This is because there is no storage and production of CH4 and its nutrient content has been fully utilized for GHG savings, so GHG emission is minimized more than 100% here in scenario 2 as compared to scenario 1. Scenario 3 and 4 performed almost similar to each other because GHG emission sources (digestate storage and land application) are common in both scenarios. About 92-93% of GHG emissions have been however reduced by scenario 3 and 4 as compared to scenario 1. Scenario 5 reduces 32% of GHG emissions as compared to base scenario, which is however better than direct dumping of digestate. Moreover, GHG emissions in scenario 5 can be further reduced to about 43% as compared to base scenario by avoiding storage of digestate. Some researchers have used the possibility of reduction of N2O emission from land applied digestate by better agricultural management practices (e.g. digestate application to soil by placement method or application during peak season of nutrient uptake, etc.), that leads to different results. Similarly, some studies also include the carbon sequestered into soil as GHG savings that may lead to difference in results. Sequestered carbon is the carbon applied to soil in the form of digestate and not released as CO2 from the soil for 100 years. Also difference in characteristics of digestate (nutrient and carbon content) can produce different results. From the results of this study, the order of preference to manage the
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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
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 and 92: Based on this property of digestate
Page 93: Table 4.5. With curing of digestate
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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