Effects of Organic Compost, Saturation, and Compaction on Air Permeability in Compost-Modified Soil for Landfill Biocover Systems

Air permeability studies in landfill final cover systems (LFCS) remain limited, largely due to the complexity of specific tests related to gas flow in these systems. This research aimed to evaluate the effects of organic compost, saturation, and compaction on the intrinsic air permeability of organic compost–modified soils (OCMS). The potential benefits of these findings are substantial, particularly in improving landfill biocover systems and enhancing methane oxidation layers (MOL), which are critical for reducing methane emissions into the atmosphere. To achieve this, air permeability tests were conducted on three OCMS with soil-to-compost ratios of 3∶1, 1∶1, and 1∶3 (by weight) at optimum moisture content (OMC) to assess their hydro-geotechnical properties. Further tests were performed using a central composite design (CCD) to systematically vary key independent variables, including percentage of organic compost (POC), degree of saturation (DS), and degree of compaction (DC). These tests were complemented by additional assessments at OMC under maximum air permeability conditions. The results from the CCD model revealed that POC is the most influential variable affecting air permeability in OCMS, with higher POC leading to increased intrinsic air permeability (kai). The degree of saturation and compaction also had notable impacts, both contributing to a kai reduction. When DS and DC increased simultaneously, the decrease in kai became more pronounced. The intrinsic air permeability of the OCMS at OMC ranged from 5.01×10−15 to 3.47×10−14 m2. A few conditions met the criteria for the methane oxidation layer, emphasizing the importance of optimizing OCMS for practical applications in landfill biocover systems.