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

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Thus, the leaching is the only mechanism proposed to overcome this issue, through which the ammonia-N concentration is reduced with the external water addition. But water addition is not desirable in the case of dry anaerobic digestion systems. Also, ammonia-N stripping is not considered as good option for organic wastes with the high solid contents due to their poor fluidity and difficulty in handling. On the other hand, it can be governed possibly through adjusting the carbon to nitrogen (C/N) ratio of the feedstock, which determines the overall ammonia-N concentration within the digester (Straka et al. 2007). Albeit, the optimum C/N ratio for anaerobic digestion is agreed to be in the range of 20 to 30 (Li et al. 2011), with a higher C/N ratio, the release of lower concentrations of ammonia-N can be expected within the anaerobic systems. But, the adjustment of feedstock C/N ratio, especially in a large scale centralized systems, is one of the major problems besides getting the insufficient feedstocks to operate at their full capacity throughout the year ( Siles et al. 2010). In addition, the overall net energy gained from the centralized system is mainly balanced with the waste collection, transportation and segregation costs. On the other hand, decentralized small scale anaerobic systems are more attractive and easy to manipulate with the feedstock characteristics and quantity to attain maximum net energy gain. In addition, these can minimize the waste handling and associated pollution emissions, along with the overall waste management costs. Hence, more detailed research in decentralized system will be more appropriate and requisite at this juncture. Similarly, most of the previously performed research studies on dry anaerobic digestion use lab-scale reactor with synthetic and well-homogenized feed having the particle size of around 10 mm. Thus there is a need of research on full-scale or pilot-scale dry anaerobic digesters operating at conditions closer to the field conditions and optimizing their continuous operation with practicable organic loading rates. Digestate from anaerobic digester has been found to contain a considerable amount of nutrients and organic matter and is useful for agriculture. However, still it has certain residual GHG emission potential, and may contain organic pollutants, heavy metals and pathogens. Therefore, the stored digestate tends to emit methane to the atmosphere and hence can contribute to the climate change. Thus, it is necessary to carefully analyze various digestate management options in terms of net GHG emissions, so that digestate can be managed with maximum possible GHG reduction. Therefore, this research work is intended to optimize dry anaerobic digestion in terms of feed C/N ratio, associated ammonia-N accumulation and organic loading rates in a pilotscale thermophilic system designed for decentralized applications. Moreover, various options of digestate management have been analyzed from perspective of GHG emissions for improved digestate management. 1.2 Objectives of the Study The main objective of this research is to optimize operation and performance of dry anaerobic digestion process treating OFMSW by testing feed C/N ratio, investigating ammonia-N accumulation and conducting different organic loading rates. This leads to promote dry anaerobic digestion technology, which will enable recovery of valuables (energy and digestate) from municipal solid waste, minimize the amount of waste going to landfill and protect the environment. 2
The specific objectives of this research are given in the following: Optimization of the methane yield of OFMSW by using different feed C/N ratio and organic loading rates under dry and thermophilic conditions; To characterize the digestate of anaerobic digestion and analysis of digestate management options in terms of GHG emissions. 1.3 Scope of the Study To accomplish the above objectives, scope of the study is given as follows: 1. The methane yield optimization of dry digestion was conducted in a pilot-scale thermophilic anaerobic digester, whereas gas formation potential test was conducted in lab-scale reactors with eudiometer set-up. 2. Food waste, leaf waste and waste paper were collected from restaurants, fields and offices of AIT respectively. Vegetable and fruit wastes were collected from a vegetable and fruit market (Tallad Thai) situated nearby. Waste simulations with different C/N ratio were prepared at Environmental Research Station of AIT. 3. Inoculum to be used for gas formation potential test consisted of anaerobic sludge from wastewater treatment plant of Singha Beer Factory, Bangkok. Inoculum to be used for pilot experiment was composed of anaerobic sludge, cow dung and digestate of anaerobic digestion of municipal solid waste (MSW). 4. Solid-liquid separation of digestate was done in a pilot-scale sand drying bed. 5. Characteristics of waste and digestate and operational parameters of digestion all were analyzed in EEM laboratory, AIT. 6. The GHG emitted from stored digestate, cured digestate and land applied digestate were theoretically calculated based on their characteristics (C and N content), which were analyzed in EEM Lab. 3
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: 1.1 Background Chapter 1 Introducti
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 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
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(i.e. 5.2 and 3.04 respectively, pl
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getting affected with the presence
Page 77 and 78:
feedstock 2 is considered as a sudd
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8.0) at most of the above said time
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Table 4.2 Surplus Energy of ITDAR D
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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
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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
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Kaparaju, P., Buendia, I., Ellegaar
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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
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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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