Methane Oxidation in Simulated Landfill Cover Soil Environments

A considerable fraction of the methane that is produced by landfills is oxidized by its covering soil before it can reach the atmosphere. This process was studied in soil columns that simulate landfill cover soil environments. The methane uptake was followed as a function of time. In soils of agricultural origin, a maximum value of 10.7 mol m-2column d-1 was observed. Mixing sugar beet leaves with the soil led to a temporary stimulation of the methane oxidation rate, whereas a wheat straw amendment led to permanent stimulation. Soil originating from a real landfill cover oxidized on the order of 15 mol m-2column d-1, the highest value found in the literature to date. The soil gas composition was studied as a function of depth. With a new batch incubation technique, methane oxidation kinetics were determined in samples taken from the soil column. By combining this kinetic data with the soil gas composition data, the actively methane oxidizing zone in the soil column could be determined and an in situ assessment of oxygen limitation could be performed. Methane oxidation takes place mainly in the top 30 cm of the covering soil.