Characterization and Quantification of Methane Emissions from Waste in the UK

Mitigation of climate change is a key scientific and societal challenge. CH₄ emissions are a major contributor to global warming impact and these are not well quantified yet. There are significant discrepancies between official inventories of emissions and estimates derived from direct atmospheric measurement. Effective emission reduction can only be achieved if sources are properly quantified, and mitigation efforts are verified.

CH₄ from waste is dominantly of biogenic origin and its levels can vary with temperature and production process, which results in variation of emissions with time of day and time of year. Selected waste streams are now commonly sent to biogas plants, where the waste is digested to produce methane, which may be utilised directly, or combusted to provide power. Different waste streams, such as maize stubble or paper products, are characterized by distinct δ¹³C-CH₄ signatures.  Emissions from each stage of the biogas production process can be identified by analysing the methane isotopic composition.

This study focuses on identification and quantification of CH₄ emissions from waste sources in the UK from 2018-2020 using laser-based mobile surveys downwind of landfills, biogas plants and wastewater treatment plants. Air samples were collected and analysed for isotopic characterization using high precision Gas Chromatography Isotopic Ratio Mass Spectrometry. Survey data were used to map concentration excess over background, identify isotopic composition and estimate fugitive emissions from selected sources.

Average carbon isotopic signatures for new data on methane sources in the UK are -53 ‰ for wastewater treatment plants and -55 ‰ for biogas plants. CH₄ emissions range from 6.2 to 50 g/h depending on size and operating conditions of plants. Also, isotopic signature of methane emission from active sites in the landfill are in the range -60 to -58 ‰ with 2 - 10% oxidation rate, which is characteristically more depleted than closed sites.