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typical organic materials that can be used for anaerobic digestion after mixing in proper ratio. This concept has been discussed in detail under the section of co-digestion. 2.4.4 Temperature Temperature is very critical parameter of anaerobic digestion process, as the rate of digestion strongly depends on it. Mainly, methane production through anaerobic digestion can be performed in two ranges of temperature, which are mesophilic range and thermophilic range. For mesophilic range, temperature of 35-40°C needs to be maintained in the digester, whereas temperature range of 50-55°C is the range for thermophilic operation (De Baere, 2006). Figure 2.3 Graphical representation of temperature ranges for anaerobic digestion A thermophilic temperature reduces the required retention time. The microbial growth, digestion capacity and biogas production could be enhanced by thermophilic digestion, since the specific growth rate of thermophilic microbes is higher than that of mesophilic microbes (Kim and Speece, 2002). Figure 2.3 (Mata-Alvarez, 2003) graphically illustrates the direct relationship between the temperature and the rate of anaerobic digestion. Thermophilic anaerobic digestion has been reported to generate about 25-50% higher methane than mesophilic digestion (Khanal, 2008; Yilmaz et al., 2008). The semidry thermophilic process has a gas production rate 2-3 times the mesophilic process (Cecchi et al., 1991). These results demonstrate the feasibility of construction of thermophilic digesters for working at 11-12 days retention time when the OLR is 8 kg VS/m 3 d or lower providing for the highest volatile solid removal. The elasticity of the system permits the reduction of retention time down to 8 days by increasing the OLR to 14 kg VS/m 3 d. Li et al., (2002) also reported that thermophilic methane fermentation was more effective for reducing lipids and had more higher loading capacity compared to mesophilic condition. Lu et al., (2007) confirmed that thermophilic process was more feasible for achieving better performance against misbalance, especially during the start-up period in a dry anaerobic digestion process as compared to mesophilic digestion. Angelidaki et al., (2006a) also concluded that the best biodegradation results for start-up could be achieved under thermophilic conditions. Increased destruction rate of organic 14
acids and increased downfall of pathogen removal is also possible in thermophilic condition. Besides, thermophilic anaerobic digestion could produce high quality of residue that could be used further as soil conditioner or fertilizer instead of placing them on landfills. Thermophilic process is, however, more sensitive to toxins and smaller changes in the environment. Oleszkiewicz and Poggi-Varaldo, (1997) reported that thermophilic process (at 55°C) was found to be superior to a mesophilic (35°C) one, both in terms of volatile solid (VS) reduction and specific gas production, but was somewhat less stable at short mass retention times (MRT). Similarly, Lv et al., (2010) also reported that thermophilic anaerobic digestion is good as it can perform accelerated hydrolysis by loosening the structure of polymers and lignocellulose in the substrate. But on the other hand, it also causes the accumulation of propionate (short chain fatty acid) and hence decreases methane and increases carbon dioxide in biogas. The reason is that high temperature decreases microbial diversity. Moreover, at high temperature, solubility of hydrogen decreases, thus it escapes from the reactor in gaseous form and hence not available for methane formation. Moreover, solubility of carbon dioxide also reduces with thermophilic temperature that leads to lesser methane formation (no or less methane formation through hydrogenotrophic pathway) and removal of carbon dioxide also raises pH leading to high free ammonia (Gallert and Winter, 1997). . Cumulative capacity (kton/year) 4500 4000 3500 3000 2500 2000 1500 1000 500 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 Figure 2.4 Capacity of mesophilic versus thermophilic digestion operation in Europe The distribution of mesophilic and thermophilic plants is given in Figure 2.4. Mesophilic plants are more in number than thermophilic plants and these are also mostly for wet digestion. At the end of 2004, 75% of the capacity was provided by mesophilic plants. Then a large number of thermophilic plants were constructed in 2005. Almost 96% of thermophilic plants are provided by dry fermentation systems. The advantages of thermophilic operation are more important for dry systems than for wet systems, while the 15 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Year Mesophilic operation Thermophilic operation 2009 2010
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: eported, which increased with time,
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 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
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the VFA concentration increased to
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The increase in GPR was almost line
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Based on our results, the best oper
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Based on this property of digestate
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Table 4.5. With curing of digestate
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application (after curing) in CH 4
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digestion, etc. Moreover, mixing of
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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
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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:
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
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Table C-1 Operational Parameters of
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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
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Methodology Methodology for for Ene
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Q = Heat transfer rate or heat loss
Page 145:
Calculation of GHG Emission Potenti
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