Numerical Study of Moisture Transfer and Methane Emission in Earthen Final Covers: Effects of Ambient Conditions

Earthen final covers (EFCs) are widely used to mitigate environmental impacts from landfills, particularly in controlling methane emissions and groundwater contamination. In this study, a one-dimensional numerical model was built to simulate the interactions of liquid water, water vapor, landfill gas, and heat, incorporating the biochemical process of methane oxidation. Parametric studies revealed that both atmospheric and waste temperatures significantly influence the soil temperature and evaporation, thereby affecting methane oxidation. Oxidation efficiency increased from 8.7% to 55.3% as atmospheric temperature rose from 5 °C to 35 °C. High waste temperatures enhanced oxidation by up to 2.9 times under cold conditions. An increase in atmospheric pressure (950–990 mbar) promoted oxygen diffusion into the cover and improved oxidation efficiency from 0.8% to 77.1%. Atmospheric relative humidity also played a critical role by affecting surface evaporation, with higher humidity promoting better water retention but limiting oxygen diffusion. The methane oxidation performance of the cover declined by 12.0% to 68.5% compared to pre-rainfall conditions. Rainfall temporarily inhibited oxidation due to moisture-induced oxygen limitation, with partial recovery after rainfall ceased. This study provided valuable insights into the complex interactions between ambient conditions and EFC performance, contributing to the optimization of landfill cover designs and methane mitigation strategies.