Methanotrophic production of extracellular polysaccharide in landfill cover soils

Abstract

A bench-scale soil reactor was used to study methane oxidation and EPS production under tropical conditions. The study of pertinent environmental factors affecting EPS production was carried out by batch cultivation of methanotrophs. These factors included variations in temperature (20 degrees C to 45 degrees C), soil water content (5% to 33%), and the supply ratios of methane/oxygen. The bench-scale study revealed that excessive EPS was accumulating in an active methane oxidation zone located 5-45 cm below the soil surface of the reactor. The observed peak rates of oxidation could not be sustained over an extended period of time due to EPS accumulation. Results from the batch cultivation experiments confirmed the production of EPS in soils subject to methane oxidation. EPS production was found to correlate with methane oxidation rates which, in turn, were regulated by the variance of temperature and soil water content. A larger amount of EPS production was obtained at 30 degrees C and 17% soil water content. Oxygen is required for methane oxidation; however, at high oxygen tension it may accelerate the production of EPS by methanotrophs causing limited oxygen diffusion and declining rates of methane oxidation.