A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Environmental Engineering and Management

Thesis (M.Eng.) - Asian Institute of Technology, 2008

The anaerobic digestion of municipal solid waste is a process that has become a promising technology in waste management throughout the world. Thus, the objective of this study was to optimize the applications of anaerobic digestion to the treatment of municipal solid wastes. To achieve this, the pilot scale experiment was conducted in inclined type plug flow reactor. Initially OFMSW was digested successively in start-up process to acclimatize the reactor. Firstly, the reactor was operated in mesophilic condition (37°C) and was shifted to thermophilic (55°C) condition by gradually increasing the temperature at the rate of 2 °C per day. The start-up process was established over a period of 8 weeks and the highest volume of biogas production (791L/d) and methane composition (66%) was achieved at day 3 8. Dry continuous anaerobic digestion of source-sorted OFMSW was investigated in thermophilic condition with three different organic loading rates (OLR) of 2.5, 3.3 and 3.9 kg VS/m³.d for constant retention time of 25 days. The reactor showed stable performance with highest biogas yield (278.4 L CH₄/kg VS) with VS reduction of around 59.21% during loading rate 1. However, the biogas yield and VS reduction during loading rates 2 and 3 were found relatively less than the loading rate 1. The result showed the accumulation of VFA which is the inhibiting conditions for methanogenic activity which was confirmed by the decreased of pH below 6.5 during theses loading rates. In this study, the post-treatment of the fresh digestate was done to increase the TS concentration thereby decreasing the weight and volume of fresh digestate for the transportation as well as made suitable for composting or soil amendment. The results obtained during post refining process shows that the high increase of the TS concentration was achieved during the retention time of 15 days as well as the decrease in the pollutant loads of the percolate (leachate). Similarly, the nutrient contents and calorific value (12.1 MJ/kg DW) of the digestate showed that they are well within the WHO and Thailand standards. So they can be used as fertilizer as well as for refuse derived fuel (RDF). This study also confirmed about the energy production and consumption within the system itself and found about 80 % surplus energy from this system