Methane oxidation in a boreal climate in an experimental landfill cover composed from mechanically–biologically treated waste

The present study evaluated microbial methane (CH4) oxidation in a boreally located outdoor landfill lysimeter (volume 112 m3, height 3.9 m) filled with mechanically–biologically treated waste (MBT residual) and containing a cover layer made from the same MBT residual. The calculations based on gas emission and pore gas measurements showed that, between April and October 2005, a significant proportion (> 96%) of the methane produced (< 23 l CH4 m− 2 d− 1) in the lysimeter was oxidized. Methane was oxidized mainly at the depths of 35–75 cm, as indicated by the upward decrease both in the methane concentration and in the methane-to-carbon dioxide ratio in the pore gas. Lower methane oxidation (< 0.8 CH4 m− 2 d− 1; this was < 22% of the methane produced) was observed only during the coldest time of the year (January 2006), apparently due to the fall in temperature at the depths of 25–70 cm (from 9–25 °C during April to October to 2–9 °C in January). Unexpectedly, the highest methane oxidation potential (MOP) was observed in samples from the top layer where exposure to methane was low. Overall, the results show that MBT residual is a suitable support medium for methane oxidation in landfill covers in field conditions in a boreal climate.