Evaluating the efficacy of biogeochemical cover system in mitigating landfill gas emissions: A large-scale laboratory simulation

Municipal solid waste (MSW) landfills are a significant source of methane (CH₄) emissions in the United States, contributing to global warming. Current landfill gas (LFG) management methods, like the landfill cover system and LFG collection system, do not entirely prevent LFG release. Biocovers have the potential to reduce CH₄ emissions through microbial oxidation. However, LFG also contains carbon dioxide (CO₂) and trace hydrogen sulfide (H₂S) depending on waste composition, temperature, moisture content, and age of waste. An innovative biogeochemical cover (BGCC) was developed to tackle these concerns. This cover comprises a biochar-based biocover layer overlaid with a basic oxygen furnace (BOF) steel slag layer. The biochar-based biocover layer oxidizes CH₄ emissions, while the BOF slag layer reduces CO₂ and H₂S through carbonation and sulfidation reaction mechanisms. The BGCC system’s field performance remains unexamined. Therefore, a large-scale tank setup simulating near-field conditions was developed to evaluate the BGCC system’s ability to mitigate CH₄, CO₂, and H₂S from LFG simultaneously. Synthetic LFG was passed through the BGCC in five distinct phases, each designed to simulate the varying gas compositions and flux rates typical of MSW landfill. Gas profiles along the depth were monitored during each phase, and gas removal efficiency was measured. After testing, biocover and BOF slag samples were extracted to analyze physico-chemical properties. Batch tests were also conducted on samples extracted from the biocover and BOF slag layers to determine potential CH₄ oxidation rates and residual CO₂ sequestration capacity. The results showed that the BGCC system’s CH₄ removal efficiency decreased with higher CH₄ flux rates, achieving its highest removal (74.7–79.7%) at moderate influx rates (23.9–25.5 g CH₄/m²-day) and reducing to its lowest removal (27.4%) at the highest influx rate (57.5 g CH₄/m²-day). Complete H₂S removal occurred during Phase 3 in the biocover layer of BGCC system. CH₄ oxidation rates were highest near the upper (277.9 µg CH₄/g-day) and lowest in the deeper region of the biocover layer. In the tank experiment, CO₂ breakthrough occurred after 156 days due to drying of the BOF slag layer, with an average residual carbonation capacity of 46 gCO₂/kg slag after moisture adjustment. Overall, the BGCC system effectively mitigated LFG emissions, including CH₄, CO₂, and H₂S, at moderate flux rates, showing promise as a comprehensive solution for LFG management.