Evaluation of methods for enhancing methane oxidation via increased soil air capacity and nutrient content in simulated landfill soil cover

Landfill soil covers and methanotrophs therein have potential to act as final sinks of the greenhouse gas methane (CH4) generated in landfills, but soil characteristics in landfills might not support methanotrophic activity due to poor soil material selection or mineralisation over time. Hence, our aim was to determine the performance of mineral landfill soil under simulated CH4 flux and screen methods for elevating the CH4 elimination capacity (EC) of soil. The methods tested during the column experiment were inorganic fertilisation (nitrate, phosphate, sulphate, copper), decompaction and amelioration of the soil with compost. The addition of compost proved to be the most effective method for increasing the CH4 EC of soil, increasing from 55 to 189 g m-2 d-1 relative to the untreated control soil. This increase could be attributed to increased air capacity, concentration of soil nutrients and number of cultivable methanotrophs. Also, soil water-holding capacity was identified as a more crucial factor for methanotrophic activity than total porosity. Inorganic fertilisation and decompaction induced only a temporary increase in CH4 EC, likely resulting from the temporary supply of fertiliser to the nutrient-deprived soil. In conclusion, we suggest that compost amelioration (22 w-%) could be useful for restoring CH4 EC of old landfill covers as an aftercare action to control environmental impacts of closed landfills.