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 (CH) 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 CH emissions through microbial oxidation. However, LFG also contains carbon dioxide (CO) and trace hydrogen sulfide (HS) 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 CH emissions, while the BOF slag layer reduces CO and HS 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 CH, CO, and HS 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 CH oxidation rates and residual CO sequestration capacity. The results showed that the BGCC system's CH removal efficiency decreased with higher CH flux rates, achieving its highest removal (74.7-79.7%) at moderate influx rates (23.9-25.5 g CH/m-day) and reducing to its lowest removal (27.4%) at the highest influx rate (57.5 g CH/m-day). Complete HS removal occurred during Phase 3 in the biocover layer of BGCC system. CH oxidation rates were highest near the upper (277.9 µg CH/g-day) and lowest in the deeper region of the biocover layer. In the tank experiment, CO breakthrough occurred after 156 days due to drying of the BOF slag layer, with an average residual carbonation capacity of 46 gCO/kg slag after moisture adjustment. Overall, the BGCC system effectively mitigated LFG emissions, including CH, CO, and HS, at moderate flux rates, showing promise as a comprehensive solution for LFG management.