Effect of Basic Oxygen Furnace Slag-Infiltrated Water on Methane Oxidation and Community Composition in Biogeochemical Landfill Cover System

Abstract

A sustainable biogeochemical cover system consisting of a biochar-amended soil layer overlain by a basic oxygen furnace (BOF) slag layer is being developed to mitigate fugitive emissions of methane (CH4) and carbon dioxide (CO2) at municipal solid waste (MSW) landfills. The effectiveness of such a cover system is highly dependent on the survival and activity of methanotrophs in the soil under highly alkaline conditions induced by the presence of slag. In this paper, laboratory microcosm tests were conducted to investigate the effect of BOF slag-infiltrated water on CH4 oxidation in soil and enrichment culture. The effects of BOF slag-infiltrated water at different proportions in soil (0%, 5%, 20%, 60%, and 100%) and in enrichment culture (0%, 11%, 25%, and 100%) were studied. CH4 oxidation rates in the soil were 113, 116, 115, 108, and 97 μg CH4 g−1 day−1 at 0%, 5%, 20%, 60%, and 100% slag-infiltrated water content, respectively. In enrichment culture, the CH4 oxidation rates were 36, 27, 20, and 17 μg CH4 mL−1 day−1 at 0%, 11%, 25%, and 100% slag-infiltrated water content, respectively. The results showed a significant decrease in CH4 oxidation rates with an increase in slag-infiltrated water content (>11%) in enrichment culture and a marginal decrease in soil microcosm. Furthermore, no substantial change in microbial community composition was noted in soil microcosms across all of the slag-infiltrated water content, and they were generally dominated by the Methylobacter luteus species. However, the enrichment culture, which was dominated by Methylobacter at 0% slag-infiltrated water content, showed a decrease in the abundance of Methylobacter and an increase in the abundance of Methylosinus, with an increase in the slag-infiltrated water content.