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A Figure Figure 3.8 3.8 Sand Sand drying drying bed: bed: Top Top view Figure Figure 3.9 3.9 Sand Sand bed bed for for digestate digestate dewatering, dewatering, A-A cross-sectional view 54 54 A 60 60 60 cm cm cm
3.4.4 Estimation of GHG emissions in the digestate management system In this part of study, different integrated digestate management unit processes (called scenarios) were analyzed for their net GHG emissions. The best scenario with the least GHG emissions was recommended for proper digestate management. Digestate management unit processes studied here include digestate dumping, digestate application on land, digestate storage, aerobic treatment (i.e. curing), etc. The detail of methodology is given in the following subsections. a) Goal and functional unit The goal of this part of study is to evaluate various digestate management systems from perspective of GHG emissions. A fixed reference point for the GHG emission evaluation is defined as 1 kg of digestate treated or managed. The digestate used for this estimation is taken from run 4 of the digestion experiment and its initial moisture content is 89.5%. b) Process description and comparative scenarios The digestate is produced continuously throughout the year, but applied to agricultural land after appropriate treatment. Also, 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. Thus, digestate can be directly applied to land only if its nutrient ratio (i.e. C/N ratio < 20) and application season are correct. If those conditions are not suitable, aerobic treatment and storage are needed respectively. Several digestate management scenarios have been evaluated for their GHG emissions which are possible in the field as given in Figure 3.10. In scenario 4 and 5, the process of curing is done which is passive (without the use of energy) aerobic treatment of digestate. Dewatering of digestate is needed to increase its TS before curing. Dumping of digestate is needed, if it has high concentration of heavy metals or other pollutants and is unfit for application to agricultural land. However, curing of such digestate is still needed before dumping to minimize its GHG emission potential. c) System boundaries and sources of GHG emitted or avoided 1. The evaluation includes the GHG emission only from the unit processes of digestate management system as explained in various scenarios above. Therefore, accounting of GHG emissions from the use of energy (operation of the facilities and processes as well as transportation of digestate) is not included in the estimation. 2. Since the digestate was stored for 60 days, thus storage in every scenario means storage for 60 days in this study. 3. Due to very thin layer, no formation of anaerobic microenvironments is assumed and hence CH4 emission during dewatering and curing is assumed to be negligible. 4. Nitrous oxide emission from land applied digestate has been considered only, whereas during digestate storage and curing, it is assumed to be negligible. CH4 emission from land application of digestate has been reported minimal and has not been considered in this study. The forms and sources of GHG emitted or avoided are given in Table 3.4. 55
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DRY ANAEROBIC DIGESTION OF MUNICIPA
Page 3 and 4:
Abstract Global solid waste generat
Page 5 and 6:
2.9 Characteristics of Digestates 3
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List of Tables Table Title Page 2.1
Page 9 and 10:
4.20 Layout of conceptual decentral
Page 11 and 12:
1.1 Background Chapter 1 Introducti
Page 13 and 14: The specific objectives of this res
Page 15 and 16: scale plants of the two processes i
Page 17 and 18: acetogens play their part to run th
Page 19 and 20: In dry anaerobic digestion, recycli
Page 21 and 22: 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: Sand drying bed (SDB) is simple, ea
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 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.
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Paavola, T. and Rintala, J. (2008).
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Stroot, P. G., McMahon, K. D., Mack
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Zeshan, Karthikeyan, O. P. and Visv
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Fruit and vegetable Waste Closer to
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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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