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if surface specific loads (loads per hectare) were considered, source-separated compost and digestate were the most important inputs by more than a factor of 25 and 20 for PCBs and PAHs. Total PAH loads accounted for 33% of the input from aerial deposition. Loads of PCBs were low and are even expected to decrease over the next decades due to the banning of PCBs. 2.9.4 Presence of heavy metals Digestates are so-called ‘recycling fertilizers’ or ‘low price fertilizers’ which are used in agricluture because these can provide plant nutrients and organic matter to improve soil. They however, contain some pollutants in the form of heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, Zn, etc., that can contaminate soil and food. The most important pathways of heavy metals in the digestate are deposition from air and direct application of pesticides to the material of origin. The heavy metal contents in digestates are influenced principally by the materials of origin (Fuchs et al., 2008). The contents of heavy metals determined mostly are low except for Cu, Zn as shown in Table 2.10. 2.9.5 GHG emission potential of digestate The treatment process of anaerobic digestion removes certain amount of carbon from the waste while the remaining carbon still remains in the digested residues (digestate). Thus the digestate can act as source of GHGs if not managed properly. Rico et al., ( 2011) collected four anaerobic effluents from the digester (digesting dairy manure) at different HRTs and analyzed to measure their residual methane potentials. They reported residual methane potential of digestates in the range of 12.7 to 102.4 L/g VS. These methane potentials were highly influenced by the feed quality and HRT of the previous CSTR anaerobic digestion process. Menardo et al., (2011) also reported that the residual methane potential of digestate (taken from digesters with feed of animal manure, energy crops and food industry waste) was very variable (2.88-37.63 NL/kgVS) and depended on the OLR, HRT and feedstock quality during digestion. Mumme et al., (2010 ) also reported similar results. Table 2.10 Heavy Metal Content in Different Types of Digestates (mg/kg DM) Digestate Type Cd Cr Cu Hg Ni Pb Zn Reference OFMSW 0.64 13.88 55 0.035 12.16 0 105 Eliyan, 2007 Cattle manure - 8.05 128 - - - 555 Composted digestate Biowaste digestate Animal digestate 0.36 23.00 72 0.097 11.50 26.8 179 38 Sanchez et al., 2008 Riedel and Marb, 2008 0.28 12.00 40 0.100 10.00 7.0 160 Persson, 2008 0.30 9.30 113 0.080 9.70 4.1 375 Palm, 2008 Similar to the digestion of original waste, specific methanogenic activity (SMA) of digestate from MSW digester is also linearly linked to moisture content. Hyaric et al., (2011) found that low moisture content is detrimental to SMA of digestate. The SMA test for digestate was performed at mesophilic temperature at four different moisture contents (65-82%) and it was found that SMA is highest at 82% moisture content.
2.10 Management Aspects of Anaerobic Digestate 2.10.1 Separation of liquid and solid digestate Moller et al. (2000) suggested that environmental problems may occur on livestock farms because of presence of huge amount of nutrients in the animal slurry than required by crops of the locality, so this problem can be mitigated by separation of slurry into nutrient rich liquid fraction and solid part and the nutrient rich part then can be easily transported to the agricultural farm having less animals. Solid digestate or fiber rich part of manure that is rich in organic matter and P makes 10-20 % of total volume of manure or digestate (Jorgensen and Jensen, 2008; Jensen et al., 2008; Bauer et al., 2009), while the remaining 80-90% proportion consists of liquid fraction. It has been found that separation of liquid and solid parts also separates N and P (Tronheim, 2005; Palm, 2008) because solid part contains about 80 % of organic N and P and liquid fraction contains inorganic N (NH 4-N) and potassium, and this separation also reduces pollution, odor, and transport cost (Tronheim, 2005). Bauer et al., (2009) separated fermentation residues (into solid and liquid digestate) of two plants digesting energy crops and found that solid digestate contained higher dry matter, volatile solids and carbon, raw ash and phosphate in relation to the mass as compared to liquid digestate, whereas nitrogen and ammonia nitrogen were slightly enriched in the solid digestate. Only the potassium content decreased slightly in the solid digestate. Palm (2008) stated that this liquid part can give a 90 % yield of that given by mineral fertilizer. Figure 2.10 shows the sequences of separation in anaerobic digestion. Here it can be mentioned that if the type of anaerobic digestion is dry, most of liquid part will be recycled to digester while the content of solid part will be high, and we will get a lot of solid digestate that needs to be managed most probably through composting and this will be the focus of this study. Organic waste Biogas Anaerobic Digester Digestate 39 Recycle Liquid Digestate Solid Digestate Liquid N Fertilizer P Rich Compost Figure 2.10 Liquid-solid separation of digestate with production of useful products Mayer (2008) gave another concept of separation of animal slurry before digestion, 40 % of liquid part according to him should be digested only to produce biogas and liquid fertilizer because of having high energy and water content and being odor intensive and 60 % solid structural part with low energy and water content should be composted. Liquidsolid separation can be done by various methods. Jorgensen and Jensen, (2008) reported difference in results of various parameters by use of different separation methods like decantation, mechanical separation and chemical separation of animal slurries and their
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 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: Comparison of liquid and solid dige
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
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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