Study of methane oxidation reaction in landfill cover soil

This research work has a primary objective to study the existence of methane oxidation reaction in landfill cover soil of Nakhonpathom municipality landfill site by close flux chamber method. The generation rate of biogas was studied by measuring volume of biogas ventilate through gas ventilation pipe laid to different depth of 1.5, 3, 4.5 and 6 m in the landfill cell and analyzing their components. It was then compared with the generation rate obtained from batch test of excavated solid waste sample in the laboratory. The component of biogas emitted from the landfill site was also analyzed to study the emission and oxidation reaction of methane in final soil cover layer. Measurement of biogas volume from ventilation pipe suggested that biogas generation were increasing along the depth of the landfill cell. Average biogas generation rates were in the range of 0.08 to 4.9 cubic m/d. The variation of biogas was related to rainfall in the study area. Biogas was mainly composed of methane and carbon dioxide with average percentages of 53.7 to 64.0 and 28.3 to 32.2 respectively. Experimental results from batch test of excavated solid waste samples were also in accordance with the field measurement showing that the biogas generation rates were increasing along the depth of landfill cell. They were found in the range of 0.05 and 0.89 l/kg vs/day. The measurement of biogas emission rate through final cover soil layer suggested average methane and carbon dioxide emission rates of 82.2 and 82.2 g/ square m/d. It was found that important factor controlling biogas emission was the cracking of final cover soil layer which occurred when soil moisture content dropped below their shrinkage limit. This soil crack yielded higher biogas emission to the atmosphere. Component analyses of biogas emitted through final cover soil did not clearly suggest the existence of methane oxidation reaction.