Use of methanotrophically activated biochar in novel biogeochemical cover system for carbon sequestration: Microbial characterization

Abstract

Biochar-amended soils have been explored to enhance microbial methane (CH4) oxidation in landfill cover systems. Recently, research priorities have expanded to include the mitigation of other components of landfill gas such as carbon dioxide (CO2) and hydrogen sulfide (H2S) along with CH4. In this study, column tests were performed to simulate the newly proposed biogeochemical cover systems, which incorporate biochar-amended soil for CH4 oxidation and basic oxygen furnace (BOF) slag for CO2 and H2S mitigation, to evaluate the effect of cover configuration on microbial CH4 oxidation and community composition. Biogeochemical covers included a biochar-amended soil (10% w/w), and methanotroph-enriched activated biochar amended soil (5% or 10% w/w) as a biocover layer or CH4 oxidation layer. The primary outcome measures of interest were CH4 oxidation rates and the structure and abundance of methane-oxidation bacteria in the covers. All column reactors were active in CH4 oxidation, but columns containing activated biochar-amended soils had higher CH4 oxidation rates (133 to 143 μg CH4 g−1 day−1) than those containing non-activated biochar-amended soil (50 μg CH4 g−1 day−1) and no-biochar soil or control soil (43 μg CH4 g−1 day−1). All treatments showed significant increases in the relative abundance of methanotrophs from an average relative abundance of 5.6% before incubation to a maximum of 45% following incubation. In activated biochar, the abundance of Type II methanotrophs, primarily Methylocystis and Methylosinus, was greater than that of Type I methanotrophs (Methylobacter) due to which activated biochar-amended soils also showed higher abundance of Type II methanotrophs. Overall, biogeochemical cover profiles showed promising potential for CH4 oxidation without any adverse effect on microbial community composition and methane oxidation. Biochar activation led to an alteration of the dominant methanotrophic communities and increased CH4 oxidation.