In-situ neutralize methane emission from landfills in loess regions using leachate

Abstract

In loess regions, landfilling is the predominant solid waste disposal and loess is usually used as landfill cover soil. However, the methane (CH4) bio-oxidation activity of virgin loess is usually below 0.01 µmol/(h g-soil). In this study, we proposed a method to improve CH4 removal capacity of loess by amelioration with mature landfill leachate, which is in-situ, easily available, and appropriate. The organic matter content of the ameliorated loess increased by 180%, reaching 19.69–24.88 g/kg-soil, with more than 90% being non-leachable. The abundance of type I methane-oxidizing bacteria and methane monooxygenase gene pmoA increased by 5.0 and 79 times, respectively. Consequently, the maximum CH4 removal rate of ameliorated loess reached 0.74–1.41 µmol/(h g-soil) at 25°C, which was 4-fold higher than that of water-irrigated loess. Besides, the CH4 removal rate peaked at 10 vt% CH4 concentration and remained at around 1.4 µmol/(h g-soil) at 15°C–35°C. The column test confirmed that the highest CH4 removal efficiency was at 30–10 cm below the surface, reaching 26.1%±0.4%, and the 50-cm-thick loess layer irrigated with leachate achieved more than 85% CH4 removal efficiency. These results could help to realize carbon neutrality in landfill sites of global loess regions.