Biotic methane oxidation within an instrumented experimental landfill cover

An experimental landfill cover composed of a mixture of sand and compost was installed at the St-Nicéphore landfill in Québec (Canada). The mixture was evaluated as a potential substrate to promote methane (CH4) oxidation by methanotrophic bacteria. One of the objectives of this field project was to assess the efficiency of the cover in reducing CH4 emissions. For this, both CH4 abatement and the extent to which methanotrophic bacteria developed were followed over time and space in relation to environmental and physico-chemical variables. The results obtained during the first 4 months of monitoring indicated that precipitation and air temperature had a great impact on CH4 oxidation. Over the study period, different patterns in CH4 oxidation through the cover soil were observed; in certain cases, oxidation was observed at various depths, although the zone of optimum oxidation occurred mostly near the surface. However, in the second half of the monitoring period, almost no oxidation was observed at depths greater than 10-cm, presumably because of lack of oxygen at deeper zones within the cover. In the 0–10-cm zone, high numbers and large variability of particulate methane monooxygenase gene (pmoA) copy number were also observed. It is concluded that the adopted substrate has proved to be satisfactory in sustaining and promoting growth of methanotrophic bacteria. However, the water content of the soil seems to be a key factor influencing CH4 oxidation, to an extent that requires further investigation. The uppermost 0–10-cm layer seems to play a critical role in CH4 abatement: a closer examination of this role will take place in the near future, in part by conducting more measurements within this zone.