Estimating methane production potential of an old municipal landfill

This paper presents a methodology for estimating methane potential of a closed landfill applied at a site in Dundee, Scotland. Leachate and gas monitoring data collected over a three-year period were to enable identification of areas where detailed characterisation of the buried wastes was carried out for the estimation of methane potential of the landfill. The site did not have leachate collection or recycling. It was thus assumed that in-situ leachate quality was a reflection of the nature of overlaying wastes. Five new sampling boreholes were created on this basis. Solid samples were analysed using the accelerated biodegradability test. Results showed that the organic wastes still present in the landfill were mainly non-readily biodegradable materials such as woods, plastic materials, textiles etc. with methane potential varying from 1.3 to 2.5 Nm³CH₄/tonne of total dry solids. Both existing leachate quality data and those obtained from the new sampling boreholes also suggested that most readily biodegradable organic matter in the landfill had been stabilised. It was concluded that wastes remaining in the landfill would break down extremely slowly due to low the in-situ temperature (8-10 °C), which may lead to low methane generation rates over a protracted period of time.