Degradation index for landfill gas species to quantify the biodegradation efficiency of novel landfill biocover soils

Landfills release significant amount of landfill gases (LFGs) into the atmosphere through diffuse emissions from topsoil. LFG mainly consists of CH4, CO2, and a minor fraction of non-methane volatile organic compounds (VOCs). Methane is one of the major greenhouse gases, while several VOCs concur to air pollution and severe risk to human health. Efforts to minimize LFG diffuse emissions generally converge to the application of cover soils (LCSs) on deposited waste, acting as biofilter for LFG. The LFG biodegradation efficiency of LCSs is related to several physicochemical factors favoring the formation of aerobic microbial consortia as methanotrophs capable of oxidizing CH4 to CO2, and VOCs-degrading bacteria. The present study aims to investigate methods for the improvement of the potential LCSs biodegradation efficiency, based on a laboratory experiment simulating a landfill environment. The degradation processes affecting each LFG compound passing through a common LCS are compared to those occurring in three novel LCSs, created by treating natural soil with sewage sludge and landfill leachate. An index I, describing the behavior of each LFG species, is calculated by dividing its concentration in gases from the LCSs by the concentration in biogas from a chamber containing the degrading organic matter feeding the LFG. Accordingly, the value of the I index of each LFG species is inversely proportional to its degradation, providing a direct estimation of the LCS efficiency. The test showed that gases from treated soils, especially that treated with only sewage sludge, have I values for most LFG species, including those typically recalcitrant to biodegradation, significantly lower than those of gases from the untreated soil, providing useful indication for treatment applications of soils at landfill scale.