Processes occurring in landfill cover soils

To understand what affects the efficiency of landfill cover soils to oxidize CH4, it is important to consider the different biogeo-physical processes occurring in this environment. The main processes are gas diffusion, gas flow (advection), microbial CH4 oxidation and growth of methanotrophic bacteria. Each of these processes can be affected by environmental factors.

Figure 12.3 shows typical concentration profiles that develop in the soil gas phase in the absence and presence of CH4 oxidation. In the absence of methanotrophy both oxygen and N2 penetrate the soil against the gas flow, and the entire cover soil is aerobic. CH4 and CO2 are produced below the soil and move upwards by advection and diffusion. The gases are diluted by oxygen and N2; hence a concentration decrease in itself is not an indication of CH4 oxidation. In the presence of methanotrophy, oxygen penetrates only 10-15 cm deep due to consumption by the methanotrophs. CH4 is depleted and CO2 accumulates in comparison with the absence of methanotrophy. CH4 oxidation is confined to the aerobic zone, so the oxidizing capacity of the soil is mainly determined by the meth-anotrophic activity and the oxygen diffusion into the soil. The following section reviews the influence of environmental factors on these two processes.

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