Lysimeter Simulation of Paddy Straw Landfill Bioreactor for Optimum Gas Production

Biogas technology plays a vital role in supplying the energy demand. There is a possibility to generate biogas from paddy straw using landfill bioreactors, rather than employing expensive anaerobic digesters. This study was carried out to determine possible avenues to produce biogas from agricultural wastes. The study attempted to maximize the methane emission from a mixture of paddy straw, cow dung and green materials in landfill bioreactor simulated lysimeter. The lysimeter consisted of a clay-polythene-clay liner gas collection system, leachate recirculation system, and the main reactor. The lysimeter performances were evaluated by analyzing pH, Biochemical Oxygen Demand (BOD), Total Dissolved Solids (TDS), Total Solids (TS), Total Suspended Solids (TSS), Volatile Solids (VS), Volatile Suspended Solids (VSS), Organic Carbon (OC), Brix, ammonium nitrogen and nitrate nitrogen. Recirculation of leachate, addition of water to the system and fabrication of clay-polythene-clay liner showed positive effects on gas production. In the leachate, TS, VS, TSS and VSS changed in a cyclic manner due to the microbial growth pattern in the lysimeter. There was high pH reduction in the first week, indicating the start of the hyrolysis phase. Primary settlement rate of lysimeter was very high and it reduced to 50 cm during 17 days. The BOD concentrations decreased over the course of 63 days and this may be due to slow release and hydrolysis of organics from the straw into leachate. Moreover, lack of recirculation also may have contributed to reduction of anaerobic process. During the experimental period, the organic carbon content and Brix gradually decreased. The removal of prognating anaerobic digestion process was rapid and produced biogas. Therefore, there is a high potential to harness biogas from landfill bioreactors using paddy straw together with other agricultural wastes, while achieving environmental friendly waste disposal method under Sri Lankan conditions. DOI: 10.4038/tar.v21i2.2599   Tropical Agricultural Research Vol. 21(2): 177-188 (2009)