Enhancement of CH4 oxidation potential in bio-based landfill cover materials

Abstract This study evaluated the efficacy of two compost materials, yard waste and leaf compost (YWLC) and biosolids compost (BSC), as bio-based landfill cover materials for oxidizing methane (CH4). A series of laboratory batch incubations were conducted to assess the CH4 oxidation potential of the composts and potential enhancement of CH4 oxidation under different conditions. Higher initial rates of CH4 oxidation were yielded in a sample of YWLC cured beyond the maturity standard at the compost site due to a reduction in raBOD and subsequent reduction in heterotrophic competition for oxygen. Results showed that the YWLC already had methanotrophic bacteria within the compost community with an initial CH4 oxidation rate of up to 95.9 μmol g(d.w.)−1 d−1. An optimum moisture content (MC) of 65 % and 50 % ww was obtained for YWLC with CH4 oxidation rates of up to 175−180 μmol g(d.w.)-1 d-1. In an assessment of long-term CH4 oxidation rates, a sample of BSC showed a long lag (60 days) to start consuming CH4; however, after this lag, it reached a CH4 oxidation rate of 160−170 μmol g(d.w.)-1 d-1, which was similar to that of the YWLC (130−140 μmol g(d.w.)-1 d-1) at the end of the 100 day experiment. While very little initial CH4 removal was detected in the BSC, different blends of BSC with YWLC were found to enhance CH4 oxidation indicating that there was a benefit to mixing the two composts. The highest long-term CH4 oxidation rates were observed in 1:1 and 1:4 (YWLC:BSC) mixing ratios (360−380 μmol g(d.w.)-1 d−1). Neither the in-situ MC, heavy metals concentrations, nutrient content, nor the in-situ population of methanotrophs were determined to be limiting variables for CH4 oxidation start-up in the BSC.