Methanotrophic activities in tropical landfill cover soils: effects of temperature, moisture content and methane concentration

The methane oxidizing capacity of landfill cover soils was investigated thr ough column and batch experiments by simulating conditions that are usually encountered in tropical climates. The rate of oxidation was monitored at d ifferent temperatures and moisture contents. It was observed that: a low mo isture content of 6% produced negligible oxidation, whereas oxidation rates were at a maximum at moisture contents between 15 and 20%. Temperature was found to be a dominant parameter which controlled the oxidation rates. The optimum temperature was between 30 and 36 degrees C. In the column tests, the temperature influenced the methane oxidation capacity indirectly by cau sing the topsoil surface to become totally dry, resulting in almost zero ox idation in spite of aerobic conditions. Although some increase in oxidation rate was observed, a higher concentration of methane could not produce a c orresponding increase in oxidation rates, indicating the limiting capacity of the soil to oxidize methane. A depth profile of the gas in the column sy stem indicated that the depth of maximum oxidation was around 15 to 40 cm u nder normal test conditions. Experimental results indicated that the topsoi l, if maintained at an optimum moisture content, could also produce a highe r oxidation capacity. The results of this experimental program indicate the possibility of maximum methane oxidation in a tropical climate if the corr ect moisture content is maintained at the top surface.