Measured methane emissions from a metropolitan wastewater treatment lagoon in Victoria Australia are substantially higher than report emissions based on emission factors

Abstract. Wastewater treatment facilities contribute ~8 % of global anthropogenic methane (CH₄) emissions. Accurate measurements of CH₄ emissions not only improve greenhouse gas (GHG) emission estimates from the facilities but also expand our understanding of operational impact on emissions, thus enabling the development of effective mitigation strategies. In this study, CH₄ emissions were measured during summer and winter seasons at an aerobic lagoon at a large sewage treatment plant in Australia. Line-averaged CH₄ concentrations were measured by open-path lasers and CH₄ fluxes were calculated using inverse-dispersion modelling. Methane fluxes showed temporal and spatial variations over the measurement periods, and correlated with wastewater dissolved methane, flow rate, and aerator operation. The annual GHG emission of 79,593 tCO₂-e yr^-1, represents ~25 % of CH₄ production captured by the anaerobic digestion pot, and is approximately 2‒3 times higher than the National Greenhouse and Energy Reporting Scheme (NGERS) reported emissions of the aerobic lagoon.