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

In recent years, biochar-amended soil cover has shown promise for enhancing microbial methane (CH4) oxidation and mitigate fugitive CH4 emissions at municipal solid waste landfills. However, addition of biochar in landfill cover soil has 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 explored amendment of landfill cover soil with biochar infused with methane-oxidizing bacterial (MOB) consortium (termed activated biochar) to reduce acclimation time and enhance the CH4 oxidation activity. Experimental long-term incubation tests were performed on soil columns containing one of four different biocovers: soil control (CS), soil with 10% by weight of biochar (B10), soil with 5% MOB-activated biochar (AB5), and soil with 10% MOB-activated biochar (AB10), exposed to continuous flow of simulated landfill gas (LFG). The AB10 soil column had a reduced lag phase with notable CH4 oxidation efficiency (ranging from 13% to 50%) during the initial exposure phase compared with all other biocover columns (0.4%-36%). In addition, the activated biochar-amended soil biocovers had higher CH4 oxidation rates (69-74.3 mu g CH4 g(-1) day(-1)) than the nonactivated biochar-amended soil (42 mu g CH4 g(-1) day(-1)) and soil control (36 mu g CH4 g(-1) day(-1)). The activated biochar-amended columns had higher relative abundances of Type II methanotrophs, mainly Methylocystis and Methylosinus (relative abundance similar to 10%) than did nonactivated biochar-amended soil and control columns (relative abundance 3.0%-3.6%). A positive correlation was observed between CH4 oxidation rate and the ratio of Type II/Type I abundance (R-2 = 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. (C) 2022 American Society of Civil Engineers.