[show abstract][hide abstract] ABSTRACT: Batch digestion of municipal garbage was carried out for 100 days at room temperature (26+/-4 degrees C; average temperature 25 degrees C) and at ambient temperature (32+/-10 degrees C; average temperature 29 degrees C) conditions for total solids concentrations varying between 45 and 135 g/l. A first order model based on the availability of substrate as the limiting factor was used to perform the kinetic studies of batch anaerobic digestion system. Effect of organic solids concentration and digestion time on biogas yield was studied and mass and energy balance analysis was conducted for batch digestion. The net bioenergy yield from municipal garbage and corresponding bioprocess conversion efficiency over the length of the digestion time were observed to be 12,528 kJ/kg volatile solids and 84.51% respectively. The methane content of the biogas generated from the reactors was in the range of 62-72% with the overall average methane content of the biogas, computed over the total digestion period was 65 vol%.
[show abstract][hide abstract] ABSTRACT: Air-blown gasification studies were conducted on a countercurrent fixed-bed gasifier for municipal residue-based Refuse Derived Fuel (RDF) pellets and compared with the mass and energy performance features of gasifier with other biomass and residual fuels. The mass conversion efficiency and cold gas efficiency (CGE) of the gasifier were observed to be 83% and 73%, respectively for RDF pellets. The higher heating value and global energy content of the producer gas generated from gasification of RDF pellets was observed to be and , respectively. The tar content in the gas generated from RDF pellets was observed to be about 45% less than the tar content in the gas generated from wood chips (WC). Empirical stoichiometric equations were developed to describe the gasification of different fuels. A complete thermodynamic analysis was performed to determine the magnitudes of various inefficiencies and irreversibilities involved in the process. It was evaluated for RDF pellets that 27% of the exergy or available energy input was dissipated in the system due to various irreversibilities taking place in the gasification process. The second law CGE was observed to be highest for RDF pellets i.e. 56% followed by charred soybean straw pellets and WC. Thermal energy in the form of sensible heat energy accounted for 6–7% of the total energy; the available energy accounted for 2–3% of the total energy output of the process.
[show abstract][hide abstract] ABSTRACT: Batch digestion of municipal garbage was carried out under room temperature conditions (26±4°C) for 240 days. The ultimate biogas production potential of municipal garbage was found to be 0.661 m3/kg volatile solids. The experimental and ultimate gas yields obtained from municipal garbage compared well with the yields obtained from other types of solid wastes. A mathematical model was developed to predict both ultimate biodegradable substrate concentration as well as ultimate biogas production. The ultimate bioenergy yield, ultimate anaerobic biodegradability of the substrate and the overall bioprocess conversion efficiency were evaluated from observations to be 18,145 kJ/kg volatile solids, 89.79 and 95.44%, respectively. The total biogas yield from municipal garbage per kg dry matter was observed to be 0.5 m3 and the average methane content of the biogas was observed to be 70 %vol.