Experimental study of methane oxidation efficiency in three configurations of earthen landfill cover through soil column test

Soil column tests were conducted to investigate methane oxidation efficiency in three configurations of earthen landfill cover under two drying stages separated by an applied rainfall, including the monolithic evapotranspiration (ET) cover, the cover with capillary barrier effect (CCBE) and the three-layer cover. Comprehensive measurements were also documented for water–gas response in soil for analyzing the experimental outcomes. The maximum methane oxidation efficiency of three-layer cover, monolithic ET cover, and CCBE were about 71 %, 62 % and 58 %, respectively. This was because the three-layer cover had the largest oxygen (O₂) concentration in soil above depth of 400 mm, where methane oxidation mainly occurred. This was due to the good airtightness of the bottom hydraulic barrier layer, which led to the lowest air pressure above depth of 400 mm, thereby promoting the entry of atmospheric O₂ into the soil. The monolithic ET cover generally had a larger methane oxidation efficiency than CCBE during the first drying stage by up to 12 %, while the trend reversed overall during the second drying stage, likely due to the enhanced air-tightness of CCBE caused by higher soil water content after rainfall induced by the capillary barrier effects. The methane oxidation efficiency for each landfill cover became lower by up to 30 % during the second drying stage than that during the first drying stage, owing to the higher water content during the second drying stage after rainfall, leading to a larger gas pressure and hence a lower O₂ concentration at shallow soil.