Spatial variation of methane oxidation and carbon dioxide sequestration in landfill biogeochemical cover

The study investigated the spatial variation of potential methane (CH₄) oxidation and residual carbon dioxide (CO₂) sequestration in biogeochemical cover (BGCC) system designed to remove CH₄, CO₂, and hydrogen sulfide (H₂S) from landfill gas (LFG) emissions. A 50 cm x 50 cm x 100 cm tank simulated BGCC system, comprising a biochar-amended soil (BAS) layer for CH₄ oxidation, a basic oxygen furnace (BOF) slag layer for CO₂ and H₂S sequestration, and an upper topsoil layer. Synthetic LFG was flushed through the system in five phases, with each corresponding to different compositions and flow rates. Following monitoring, the system was dismantled, and samples were extracted from different depths and locations to analyze spatial variations, focusing on moisture content (MC), organic content (OC), pH, and electrical conductivity (EC). Additionally, batch tests on selected samples from BAS and BOF slag layers were performed to assess potential CH₄ oxidation and residual carbonation capacity. The aim of study was to evaluate the BGCC's effectiveness in LFG mitigation, however this study focused on assessing spatial variations in physico-chemical properties, CH₄ oxidation in the BAS layer, and residual carbonation in the BOF slag layer. Findings revealed CH₄ oxidation in the BAS layer varied between 22.4 and 277.9 µg CH₄/g-day, with higher rates in the upper part, and significant spatial variations at 50 cm below ground surface (bgs) compared to 85 cm bgs. The BOF slag layer showed a residual carbonation capacity of 40-49.3 g CO₂/kg slag, indicating non-uniform carbonation. Overall, CH₄ oxidation and CO₂ sequestration capacities varied spatially and with depth in the BGCC system.