Locating and quantifying CH ₄ sources within a wastewater treatment plant based on mobile measurements

Abstract. Wastewater treatment plants (WWTPs) are substantial contributors of greenhouse gas (GHG) emissions because of the high production of methane (CH4) and nitrous oxide (N2O). A typical WWTP complex contains multiple functional areas that are potential sources of GHG emissions. Accurately quantifying GHG emissions from these sources is challenging due to the inaccuracy of activity data, the ambiguity of emission sources, and the absence of monitoring standards. Locating and quantifying WWTP emission sources using a measurement-based GHG emission quantification method is crucial for evaluating and improving traditional emission inventories. In this study, CH4 mobile measurements were conducted within a WWTP complex in the summer and winter of 2023. We utilized a multi-source Gaussian plume model combined with a genetic algorithm inversion framework, designed to locate major sources within the plant and quantify the corresponding CH4 emission fluxes. We identified 13 main sources in the plant and estimated plant-scale CH4 emission fluxes of 68.78±17.40kgh-1 (603.33±152.66ta-1) for the summer and 47.76±21.39kgh-1 (418.95±187.59ta-1) for the winter. The predominant sources of CH4 emissions were the screen and primary clarifier, contributing 55 % and 67 % to the total emissions in summer and winter, respectively. The comparison revealed that summer CH4 emissions were 2.8 times higher than inventory estimates, while winter emissions were twice the inventory values. This study demonstrated that mobile measurements, combined with the multi-source Gaussian plume inversion framework, are a powerful tool to locate and quantify GHG sources at a complex site, with the potential for further refinement to accommodate different types of factories and gas species.