AbstractIn this study, a novel biogeochemical cover system comprising biochar-amended soil and basic oxygen furnace (BOF) steel slag was explored as a sustainable alternative cover system to mitigate methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S) simultaneously from landfill gas (LFG). Long-term column studies of a simulated biogeochemical cover (BGCC) profile investigated CH4, CO2, and H2S removal potential. The performance of the BGCC system was compared with a conventional soil cover (SC) profile. The CH4 oxidation rates of biochar-amended soil were significantly higher, ranging from 185 to 407 µg CH4/g-day in comparison with the barrier soil in the SC system (6–7.5 µg CH4/g-day), based on the batch incubation of column-exhumed samples. In addition, the biochar-amended soil showed higher relative abundance of methanotrophic bacterial communities (20%–51%) in comparison with soil cover (10%–27%). In both columns, complete attenuation of H2S occurred near the inlet (75 cm bgs) and sulfur oxidizing bacteria (e.g., Thiobacillus) and methanotrophs were both detected. The sulfur content was elevated (0.68%) at the base of both columns and H2S may have imparted an inhibitory effect on CH4 oxidation rate in the SC system. The BOF slag showed a CO2 removal potential of 67 g CO2/kg BOF slag. Overall, the BGCC system outperformed the SC system, effectively mitigating CH4, CO2, and H2S simultaneously.