Testing sewage sludge and landfill leachate in novel biocovers: A soil column experiment to quantify landfill gas abatement

A laboratory experiment was carried out aimed at testing novel biocovers and quantifying the mitigation of diffuse landfill gas (LFG) emissions into the atmosphere. The experiment, lasting 40 days, was designed to simulate a laboratory-scale landfill environment, using four integrated prototypes consisting of (i) a digester, representing the landfill waste body under predominant anaerobic degradation (AD) conditions, connected to (ii) a soil column, representing the landfill biocover with different mixtures of natural soil, anaerobically stabilized and dewatered sewage sludge (SS) and landfill leachate (LL). Gas samples were periodically collected from the digester headspaces and from four sampling ports located along each soil column. Experimental data showed that biodegradation processes of reduced biogas compounds increased upward along the biocover soil columns, whereas CO2 and O-substituted compounds, being produced by degradation of former compounds, showed opposite trends. To estimate the benefits on biogas abatement provided by the soil treatments, a novel index was proposed. The index considered the biogas biodegradation referred to bacterial activity, excluding the reduction of biogas due to dilution with atmospheric air occurring within the cover soil. Noteworthily, the tested novel biocovers with soil treated only with SS showed higher biogas abatement efficiencies relative to both the untreated natural soil and that with concurrent LL addition. These results support the hypothesis that treated soils, specifically with sewage sludge as a potential resource, represent a reliable option to improve the mitigation of gaseous species and functional groups released by diffuse LFG emissions.