Large-scale testing to assess the performance of biogeochemical and soil cover systems for landfill gas mitigation

Fugitive emissions of methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S) from municipal solid waste landfills are major environmental concerns. To address this, a biogeochemical cover (BGCC) system is developed to mitigate these emissions. This study evaluates the effectiveness of the BGCC in comparison with a conventional soil cover (SC) system using a new large-scale laboratory setup that simulates near-field scale conditions. Both cover systems were exposed to synthetic landfill gas (LFG) across five phases, featuring varying gas compositions and influx rates. Surface emission rates and gas concentrations were continuously monitored. Post-termination of the experiments, both cover systems were dismantled, and samples were collected from different depths and locations to analyze spatial variations in physico-chemical properties. Select samples from the biocover layer of both the cover systems and basic oxygen furnace (BOF) slag layer of BGCC were subjected to batch tests to measure potential CH4 oxidation rates and residual carbonation capacity, respectively. The results showed that both cover systems achieved their highest CH4 removal efficiency at moderate influx rates (23.9-25.5 g CH4/m2-day), with BGCC's CH4 removal ranging from 74.7 to 79.7% and SC's from 83.5 to 99.8%. Complete H2S removal occurred in the biocover layer of both systems. The highest average CH4 oxidation rates were 277.9 mu g CH4/g-day at 50 cm below-ground surface (bgs) in BGCC and 260.2 mu g CH4/g-day at 70 cm bgs in SC, with the lowest oxidation rates observed at deeper regions (at 85 cm bgs) of both covers. The breakthrough of CO2 occurred after 156 days of continuous exposure and could be attributed to the desiccation of the BOF slag layer. Overall, the BGCC system effectively mitigated CH4, CO2, and H2S emissions, whereas the SC system only mitigated CH4 and H2S at moderate flux rates, indicating that BGCC provides a comprehensive solution for LFG mitigation.