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

Abstract

The methane oxidizing capacity of landfill cover soils was investigated through column and batch experiments by simulating conditions that are usually encountered in tropical climates. The rate of oxidation was monitored at different temperatures and moisture contents. It was observed that a low moisture 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°C. In the column tests, the temperature influenced the methane oxidation capacity indirectly by causing the topsoil surface to become totally dry, resulting in almost zero oxidation in spite of aerobic conditions. Although some increase in oxidation rate was observed, a higher concentration of methane could not produce a corresponding increase in oxidation rates, indicating the limiting capacity of the soil to oxidize methane. A depth profile of the gas in the column system indicated that the depth of maximum oxidation was around 15 to 40 cm under normal test conditions. Experimental results indicated that the topsoil, if maintained at an optimum moisture content, could also produce a higher oxidation capacity. The results of this experimental program indicate the possibility of maximum methane oxidation in a tropical climate if the correct moisture content is maintained at the top surface.