Evaluating Methane Oxidation Efficiencies in Experimental Landfill Biocovers by Mass Balance and Carbon Stable Isotopes

Biocovers are an alternative for mitigating fugitive and residual emissions of methane from landfills. In this study, we evaluated the performance of two experimental passive methane oxidation biocovers (PMOBs) constructed within the existing final cover of the St-Nicephore landfill (Quebec, Canada). The biocovers were fed in a controlled manner with raw biogas and surface fluxes were obtained using static chambers. This enabled calculating mass balances of CH4 and oxidation efficiencies (f(o_MB)). Most of the time, f(o_MB)>= 92 % were obtained for loadings as high as 818 gCH(4)m(-2)day(-1) (PMOB-2) and 290 g CH(4)m(-2)day(-1) (PMOB-3B). The lowest efficiencies (f(o_MB)=45.5 % and 34.0 %, respectively) were obtained during cold days (air temperature similar to 0 degrees C). Efficiencies were also calculated using stable isotopes (f(o_SI)); the highest f(o_SI) were 66.4 % for PMOB-2 and 87.3 % for PMOB-3B; whereas the lowest were 18.8 % and 23.1 %, respectively. However, f(o_SI) values reflect CH4 oxidation up to a depth of 0.10 m, which may partly explain the difference in regards to mass balance-derived efficiencies. Indeed, it is expected that a significant fraction of the total CH4 oxidation occurs within the zone near the surface, where there is greater O-2 availability. The influence of the values of fractionation factors alpha(ox) and alpha(trans) were also evaluated in this paper.