Landfill Methane Oxidation and Microbial Community Dynamics in Activated Biochar Amended Soil Cover

In recent years, biochar amended soil has shown promise for enhancing microbial methane (CH4) oxidation and mitigate fugitive CH4 emissions in MSW landfills. However, addition of biochar in landfill cover soil shows an initial lag phase due to microbial acclimation and colonization resulting in lower CH4 oxidation rates relative to CH4-exposed landfill cover soil. Therefore, this study explores amendment of landfill cover soil with biochar infused with methane-oxidizing bacterial (MOB) consortium (termed as activated biochar) to reduce acclimation time and enhance the CH4 oxidation activity. Experimental, long-term incubation tests were performed in soil columns containing one of four different biocovers: soil control (CS), soil with 10% by weight of biochar (CS10B), soil with 5% MOB activated biochar (CS5AB), and soil with 10% MOB activated biochar (CS10AB) and exposed to continuous flow of simulated landfill gas (LFG). The CS10AB soil column had a reduced lag phase with notable CH4 oxidation efficiency (ranging from 13-50%) during the initial exposure phase in comparison to all other biocover columns (0.4 to 36%). In addition, the activated biochar amended soil biocovers showed higher CH4 oxidation rates (69 - 74.3 ug CH4 g-1 day-1) than the non-activated biochar amended soil (42 ug CH4 g-1 day-1) and soil control (36 ug CH4 g-1 day-1). The activated biochar amended columns showed higher relative abundances of Type II methanotrophs, mainly Methylocystis and Methylosinus (relative abundance ~10%) in comparison to non-activated biochar amended soil and control columns (relative abundance 3.0 to 3.6%). A positive correlation was observed between CH4 oxidation rate and the ratio of Type II/Type I abundance (R2 = 0.84, p< 0.01), further suggesting an important role for the biochar activation in the biological CH4 mitigation process. Overall, biochar activation appears to be a promising mechanism to reduce microbial lag phase and enhance CH4 oxidation rates in biochar amended landfill cover soils. These findings are crucial not only from environmental viewpoint as it is contributing to greenhouse gas balance but also from economic viewpoint as biochar is generated as a coproduct during biofuel production increasing the economic feasibility of biomass-derived fuels.