Monitoring the emissions of non-Co2 greenhouse gases from wastewater treatment plants

Abstract:

This study investigates the emissions of non-CO₂ greenhouse gases, specifically methane (CH₄) and nitrous oxide (N₂O), from a full-scale municipal wastewater treatment plant (WWTP) in Västerås, Sweden. The primary objective was to identify emission hotspots, quantify concentration levels, and assess the spatial and temporal variability of these emissions under actual operating conditions. Measurements were conducted using a portable Fourier Transform Infrared (FTIR) gas analyser (Gasmet GT5000 Terra) across seven separate field campaigns at three selected process locations: the anoxic zone outlet, return sludge line, and oxic tank inlet.

The results demonstrated clear spatial differentiation in emission patterns. Methane concentrations were highest at the return sludge line, with peak values exceeding 230 ppm, while nitrous oxide concentrations reached their maximum at the oxic tank inlet, exceeding 400 ppm. The anoxic zone outlet consistently exhibited lower concentrations for both gases. Significant variability was observed across different measurement days, influenced by both operational conditions and environmental factors such as wind and rainfall, which occasionally interfered with measurement stability.

The findings highlight the complexity of greenhouse gas emissions in WWTPs, where biological, chemical, and physical processes interact across multiple treatment stages. The study underscores the need for site-specific monitoring approaches and continuous high-frequency measurement systems to capture transient emission dynamics and improve the accuracy of emission inventories. These insights are critical for supporting future mitigation strategies and enhancing climate accountability within the wastewater sector.

Read the full study: Monitoring the emissions of non-Co2 greenhouse gases from wastewater treatment plants