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

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2.8 2.8 Anaerobic Anaerobic Digestion Digestion and and Digestate Digestate Management Management Anaerobic Anaerobic digestion digestion treats treats organic organic waste, waste, which which not not only produces biogas, but also other by-products by-products such such as as liquor/liquid liquor/liquid digestate digestate and and fiber/solid digestate/digestate. The combination combination of of fiber fiber and and liquor liquor produced produced by by anaerobic anaerobic digestion is termed as digestate. It has has been been found found that that these these materials materials contain contain a a considerable considerable amount of nutrients and organic matter matter and and are are useful useful for for agriculture. agriculture. Utilization Utilization of of digestate as a soil amendment or organic organic fertilizer fertilizer can can improve improve cop cop yield yield and and soil soil properties properties and hence helps promoting closure closure of of nutrient nutrient cycles. cycles. In In this this way, way, the the need need for for production of synthetic inorganic fertilizers fertilizers can can decrease decrease and and consequently consequently significant significant amount of energy can be saved and GHG GHG emission emission can can be be reduced reduced leading leading to to energy energy and and economic benefits. But But the the problem problem is is that, that, digestate digestate has has potential potential of of methane formation, NH3 NH3 NH3 and N2O emission emission and and may may also also contain contain pollution pollution causing causing organic organic compounds and other hazardous material material such such as as heavy heavy metals. metals. Therefore, Therefore, application application of digestate to agricultural land needs a a sound sound management management and and sometimes sometimes prior prior treatment treatment to improve its quality. Also, after application, application, careful careful monitoring monitoring of of soil soil properties properties and and plant growth is required. 2.8.1 2.8.1 Need Need of of digestate digestate management management and and digestate digestate utilization Management Management of of digestate digestate (anaerobically (anaerobically digested digested waste) is needed because of many reasons. reasons. First First is is to to keep keep the the environment environment safe safe during during and after anaerobic digestion because its its handling handling and and spreading spreading may may cause cause environmental environmental risk, either due to leakage of nitrate to recipient recipient waters waters or or due due to to extensive extensive gaseous gaseous losses losses of ammonia and the nitrous oxide as well well as as because because of of having having certain certain methane methane formation formation potential (Figure 2.9). Figure Figure 2.9 2.9 Emissions Emissions from from soil soil applied applied digestate digestate to environments 30 30
Second is that it has a high water content which makes it expensive to handle, transport and spread in the field. Thirdly, it is the source of organic matter and nutrients especially nitrogen and can be used in gardens, forests, recreation and sports ground, and fish pond as fertilizer or soil conditioner/soil amendment. Moreover, the residue from anaerobic digestion (digestate) has the potential advantage over untreated slurries that it is consistent in nutrient content and availability. This makes it easier for farmers to calculate the correct fertilizer applications to crop requirements (Berglund, 2006). Monetary benefits are also obtained because the energy consumption for fertilizer manufacturing is decreased if it is produced from on-farm anaerobic digestion plant. Furthermore, digestate can provide export revenue, depending on quality. However, Lantz et al., (2007) reported that digestate contains all the non-biodegradable contamination of the feedstock putting its use as an organic fertilizer in question. The post treatment in anaerobic digestion to manage digestate can be liquid digestate treatment (aeration, nitrogen removal, precipitation of heavy metals) or separation of liquid and solid fraction of digestate from each other (dewatering, fiber separation, and sand removal) to solve the problem of its handling and transport (Bauer et al., 2009). If heavy metal content and other pollutions are within safe limit, the solid digestate can be composted or spread on agricultural land or used as landfill cover. In such case, it may take two to four weeks for stabilization of its organic contents before its use for the mentioned purposes. The liquid fraction is either used directly as a fertilizer in agriculture, recycled back to the anaerobic digestion process for dilution and inoculation of new waste stream (especially in dry digesters), treated in a wastewater treatment plant or discharged into sewage. In case of dry anaerobic digestion, most of the liquid is recycled to the system for moistening and inoculating the new waste and dewatered digested material is matured to compost. Other than agricultural use, it can also be utilized for other purpose. For example, Teater et al., (2011) reported that solid digestate (AD fiber) from a CSTR digesting dairy manure was a suitable biorefining feedstock (for production of ethanol ) as compared to switchgrass and corn stover. 2.8.2 Effect of prior digestion on properties of digestate During digestion, properties of waste change considerably as shown in Table 2.6. Total solids, organic carbon, volatile organic compounds (odor), GH G emissions potential, pathogens and weed seeds in the waste decrease because of digestion. pH of the digester medium increases. Organic N is transformed to NH4-N, so N availability to plants increases, if the digestate is applied to agricultural land. Moreover, fluidity, homogeneity and infiltration properties of waste are also improved by digestion, which further increases the nutrient availability of digestate (Lantz et al., 2007). However, the increased concentrations of NH4-N and high pH also increase the loss potential of N in NH3 form through volatilization. There is no much effect of fermentation on P and K availability. Digestion also improves handling and solids separating characteristics if manure is used as feedstock, and reduces attractiveness of the manure to rodents and flies. Some of these effects of digestion on the properties of waste have been presented in Table 2.6. Tambone et al., 2009 studied the transformation of organic matter during anaerobic digestion of mixtures of energetic crops, cow slurry, agro-industrial waste and OFMSW. The anaerobic digestion process proceeded by degradation of more labile fraction (e.g. carbohydrate-like molecules) and concentration of more recalcitrant molecules (lignin and non-hydrolysable lipids). 31
Page 1 and 2: DRY ANAEROBIC DIGESTION OF MUNICIPA
Page 3 and 4: Abstract Global solid waste generat
Page 5 and 6: 2.9 Characteristics of Digestates 3
Page 7 and 8: 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: Substrate Feed TS (%) Reactor Type
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 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
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Zeshan, Karthikeyan, O. P. and Visv
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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
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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
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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