Improving biogas generation from aged landfill waste using moisture adjustment and neutral red additive – Case study: Hampton Downs’s landfill site

Abstract

Landfill gas (LFG) generation is typically predicted using the EPA’s Landfill Gas Emissions Model (LandGem), which includes two parameters, the methane production potential (L0, m3 CH4 Mg−1 wet waste) and the first-order decay-rate constant (k, yr−1). In most cases, default parameters obtained from municipal solid waste (MSW) characterisation are used to estimate the LFG generation. However, changes in physical and chemical properties of MSW as a result of aging can affect the LFG results. In this study, aged municipal solid waste (MSW) samples buried in a landfill site between 2013 and 2018 were collected from two different depths to evaluate the effect of moisture and neutral red (NR) additives on biogas generation. The samples were anaerobically digested under different moisture contents. Neutral red (NR) additive with different concentrations was added to facilitate the direct electron transfer in the anaerobic media and to improve biogas generation. The results confirmed that LFG generation can be significantly improved by increasing the moisture content to 45% and introducing additives. This observation was more pronounced for the older samples collected from deeper portion of the same drilled hole. The samples collected from the old phase of landfilling in the presence of 80 mg/L NR aqueous solution produced 300% excess LFG. Higher concentration of NR was found to inhibit biogas generation due to the formation of ammonia–nitrogen. Estimation of LFG potential over 30 years in the LandGem model with new k and L0 extracted from biogas accumulation curves suggested a 400,000 m3 increase in LFG for only one gas well.