Diversity and Activity of Methanotrophs in Biogeochemical Landfill Cover

Municipal solid waste (MSW) landfills are regarded as one of the major sources of greenhouse gas (GHG) emissions across the world. In order to control these emissions, an innovative and sustainable biogeochemical cover system that consists of soil, biochar and basic oxygen furnace (BOF) slag is being developed to completely eliminate fugitive methane (CH4) and carbon dioxide (CO2) emissions from the landfills. The effectiveness of such cover systems is highly dependent on the survival and activity of methanotrophs under highly alkaline conditions induced by the presence of steel slag. Preliminary results demonstrated negligible CH4 oxidation and substantial CO2 sequestration when the BOF slag was integrated/mixed with biochar-amended soil due to combined effect of pH and heavy metal constituents. However, isolated or separated cover material conditions (biochar-amended soil overlain by slag) demonstrated significant CH4 oxidation potential. Preliminary experiments on pH studies on landfill cover soil determined significant inhibition of CH4 oxidation at pH >12. 
To further simulate infiltration conditions in the isolated cover material conditions as described above, the landfill cover soil was inoculated with different proportions of BOF slag leachate. The results demonstrated no effect of heavy metals constituents present in the leachate on CH4 oxidation and microbial community. Overall, this study proposes layered system for effective CH4 oxidation in biochar-amended soil layer and CO2 sequestration in BOF slag layer. However, large column experiments and field test plots is highly recommended to evaluate the long-term performance of the methanotrophic community in the proposed biogeochemical cover system under dynamic environmental conditions.