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

More documents

Recommendations

Info

examine intermediate steps of digestion process. Hence, continuous anaerobic digestion process can be grouped into single-stage and multi-stage system on the basis of phase of operation. Continuous operation of two reactors is generally performed in two stage digestion systems. In the first reactor, hydrolysis and acetogenesis is done while in the second reactor, methanogenesis is performed. The limitation of first reactor is hydrolysis rate of cellulose whereas microbial growth is the limitation for second reactor. By dividing the digester into two parts like this allows a better control on hydrolysis rate and methanogenesis. In this type of systems, we can use different techniques to improve the rate of reaction, for example, hydrolysis rate can be increased by microaerophilic conditions. One of the advantages of this system is that we can use the digesters as storage devices. Moreover, for rapidly degradable waste materials (food waste, e tc), a higher biological stability is achieved. Cumulative capacity (kton/year) 6000 5000 4000 3000 2000 1000 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Year One-phase process Two-phase process Figure 2.7 Comparison between one stage and two stage process in Europe In general, the two-phase system provides rapid and stable treatment increasing the rate of hydrolysis and methanization (O’Keefe and Chynoweth, 2000). However, the claimed advantage of the two-phase digestion has not been substantiated in real practice (De Baere, 2000). Contrary to the claim, the added investment cost and operating complexity have caused this system to be limited in a small market share. Kim and Speece (2002) concluded that two-phase digestion system showed little benefit over single-phase during start-up period and no benefit were observed during the long-term period. The high digestion rates provided by the single phase system makes the system a viable even today. As can be seen in Figure 2.7, the single-stage anaerobic digestion exhibits the highest trend of capacity from the period of 1990 up to the present. Some of the examples of high-solid 24
single stage systems are DRANCO, Valorga and KOMPOGAS processes which have been discussed in detail in the next section. 2.6.4 Design of available technologies for dry anaerobic digestion Dry anaerobic digestion technologies used at industrial scale can be divided into three main categories, which are batch (e.g. BIOCEL), single-stage continuous (e.g. DRANCO (thermophilic), Valorga (mesophilic) and KOMPOGAS (thermophilic)) (Figure 2.8) and multi-stage continuous (e.g. Linde -BRV, SUBBOR) systems. In all the dry systems, because of high solid content, a part of the digested residues is recycled which is mixed with the feed for inoculation. Due to their high viscosity, waste passes through the vessel as a slug so that fresh waste is not mixed with the partially digested waste, which is called as plug flow. This offers the advantage of technical simplicity as no mechanical devices need to be installed within the reactor (Lissens et al., 2001). The designs of single-stage dry anaerobic digesters have been discussed in detail below. BIOCEL: The system is based on a batch-wise dry anaerobic digestion. The total solids concentration of organic solid wastes as feeding substrate is maintained at 30–40% dry matter (w/w). The process is accomplished in several rectangular concrete digesters at mesophilic temperature. The floors of the digesters are perforated and equipped with a chamber below for leachate collection. Prior to feeding, fresh biowaste substrate and inocula (digestate from previous feeding) are mixed then loaded to the digester by shovels. After the loading is finished, the digesters are closed with air tight doors. In order to control the odor emission; the system is housed in a closed building that is kept at a slight under-pressure. The temperature is controlled at 35–40ºC by spraying leachate, which is pre-heated by a heat exchanger, from nozzles on top of the digesters. Typical retention time in this process is reported to be 15-21 days ( Ten Brummeler, 2000). A full-scale BIOCEL plant is reported to have successfully treated vegetable, garden and fruit wastes with the capacity of 35,000 tons/year. Approximately 310 kg of high quality compost, 455 kg of water, 100 kg of sand, 90 kg of biogas with an average methane content of 58% and 45 kg of inert waste are produced from each ton of waste processed (CADDET, 2000). According to Vandevivere et al., (1999) the BIOCEL plant produces on the average 70 kg biogas/ton of source-sorted biowaste which is 40 % less than from a single stage low-solids digester treating similar wastes. In the DRANCO process, feed is introduced daily into the top of the reactor by pumping through the feed tubes, and the digested waste is removed from the bottom at the same time. Part of the digested waste is used as inoculums (one part of fresh waste for six parts of digested waste) while the rest is dewatered to obtain an organic compost material. There are no mixing devices in the reactor other than the natural downward movement of the waste. This process focuses on the conversion of the organic fraction of the municipal solid wastes to energy and a humus-like final product, called Humotex. The operating temperature is 55 o C, the total solids concentration is 32% and the residence time is around 18 days. The process produces approximately 100 m 3 biogas/ton input (Chavez-Vazquez and Bagley, 2002). The Valorga system is quite different in that the horizontal plug-flow is circular in a vertical cylindrical reactor, which is partially partitioned (around 2/3 rd of the reactor) by a central wall or baffle. The partition wall is connected to reactor wall at one end, while the other end is free allowing the passage of waste. The inlet is on one side of the baffle while 25
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: 2.6.2 Single-stage continuous syste
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
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
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?