17 - Long-term Near Field-Scale Investigations of Methane Oxidation in Biogeochemical Landfill Cover

Municipal solid waste (MSW) landfills represent significant contributors to global methane (CH4) emissions. Recent research has underscored the promise of biochar amendments into landfill cover soil to augment microbial CH4 oxidation. In addition to CH4, landfill also emits carbon dioxide (CO2), hydrogen sulfide (H2S), and other non-methanogenic organic compounds necessitating its urgent mitigation. In response to these concerns, a biogeochemical cover (BGCC) integrating biochar-amended soil (BAS) and basic oxygen furnace (BOF) steel slag was previously developed with the purpose of simultaneously mitigating CH4, CO2, and H2S emissions. Laboratory experiments involving different configurations of BGCC have showcased substantial potential for CH4, CO2, and H2S removal under simulated landfill cover conditions. However, the efficacy of this cover in field conditions remains unexplored. To address this gap, a near-field scale tank setup of the BGCC was established in the laboratory. The BGCC configuration established in a near-field scale tank setup consisted of three layers: a lower layer comprising 10% BAS (45 cm), a middle layer of BOF slag (30 cm), and an upper topsoil vegetative layer (15 cm). Synthetic landfill gas was systematically passed through the tank with varying flow rates and compositions. The primary objective of this study is to elucidate the CH4 oxidation occurring within the BAS layer. To achieve this objective, gas monitoring was conducted within the biocover layer over time. Terminal methane oxidation and physicochemical properties were evaluated for the samples extracted from the same depth of gas concentration monitoring, but from different spatial locations within the biocover layer, post-termination of the experiment. The results showed that the highest reduction in CH4 (83.4% of inlet CH4) occurred when a gas composition of 50% CH4 and 50% CO2 was introduced at an influx rate of 23.9 g CH4 m-2day-1, while the lowest CH4 reduction (35.1% of inlet CH4) was observed when the same gas composition was introduced at an influx rate nearly twice as high (57.5 g CH4 m-2day-1). Post-termination, BAS displayed CH4 oxidation rates ranging from 227.5 to 333.7 µg CH4g-1day-1 at different spatial points, underscoring its substantial potential for converting CH4 into CO2