Effect of Basic Oxygen Furnace (BOF) slag leachate on methane oxidation and community composition in biogeochemical landfill cover system. landfill metagenome

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, a sustainable biogeochemical cover system, consisting of biochar-amended soil layer overlain by BOF slag layer, is being developed to mitigate both methane (CH4) and carbon dioxide (CO2) emissions. The effectiveness of such cover system is highly dependent on the survival and activity of methanotrophs under highly alkaline conditions induced by the presence of the slag. In this paper, laboratory microcosm tests were conducted to investigate the effect of BOF slag leachate on the CH4 oxidation in soil and in enrichment culture. The BOF slag leachate at different proportions (0, 5, 20, 60 and 100%) in soil and (0, 11, 25 and 100%) in enrichment culture was studied. The CH4 oxidation rates in the soil were 113, 116, 115, 108 and 97 µg CH4 g-1d-1 at 0, 5, 20, 60 and 100% slag leachate, respectively, and in enrichment culture, the CH4 oxidation rates were 36, 27, 20 and 17 µg CH4 mL-1d-1 at 0, 11, 25 and 100% slag leachate, respectively. The results showed that the CH4 oxidation rates decreased significantly with increase in slag leachate proportions (> 11%) in enrichment culture and decreased marginally in the soil microcosm tests. Furthermore, no change in the community composition was noted across the slag leachate proportions in soil microcosms and were typically dominated by the species Methylobacter luteus. However, the microbial community in the enrichment culture performed differently with the abundance of Methylobacter to decrease with increase in slag leachate proportions and Methylosinus to increase with increase in slag leachate proportions. Overall, this study exhibited substantial CH4 oxidation in both soil and enrichment culture with survival of methanotrophic community under varied slag leachate proportions.