Methane Oxidation at Low Temperatures in Soil Exposed to Landfill Gas

Soil exposed to elevated methane concentrations can develop a high capacity for methane oxidation. Methane oxidation at high and low methane concentrations is performed by different types of methanotrops and therefore oxidation rates found at low temperatures at the atmospheric methane content cannot be extrapolated to soils exposed to high methane concentrations. Four sandy soils with different organic matter content (1–9% w/w) from two landfills in Denmark were investigated in batch experiments in the laboratory to determine the response of methane oxidation at low temperatures and different soil moisture regimes. At 2°C the methane oxidation rates were 0.005 to 0.17 µmol g −1 h −1 , and calculations showed that it was possible to oxidize all the produced methane at older landfills, even during the winter. Therefore, methane oxidation in top covers of landfills is an alternative to gas recovery at smaller and older landfills in northern Europe. Equations have been developed that describe the dependency of temperature and soil moisture content for each soil. The oxidation rates depended significantly on the soils (and thereby organic matter content), temperature, and soil moisture content. Soil moisture was the most important factor. However, high Q 10 values indicate that temperature also was important. The four soils tested had optimum soil moisture content between 11 and 32%. At increasing organic matter content, both the optimal soil moisture content and the maximum oxidation rate increased.