Measurement of Methane Emissions from a sewage treatment lagoon in Victoria Australia

Wastewater treatment facilities are a significant source of greenhouse gas (GHG) emissions released to the atmosphere (Czepiel et al., 1993). Greenhouse gas emission environmental impact has become one aspect of assessing the performance of waste water treatment plants (WWTPs)  (Mohsenpour et al., 2021). A better understanding of current GHG emission rates from these facilities will help to improve national GHG inventories and to develop mitigation strategies. At present there are large uncertainties associated with these emissions, as WWTPs use generalised default emission factors that may have limited applicability to Australian conditions and the specific sewage treatment infrastructure and operations.

Two methane (CH₄) emission measurement campaigns were conducted at a sewage treatment plant in Victoria using inverse-dispersion modelling (IDM) coupled with open-path spectroscopic techniques. The first campaign was from February to March 2024 (summer campaign) and the second one was from August to October 2024 (winter campaign). Three open-path lasers (1x Boreal Laser GasFinder 2.0 and 2 x Unisearch Associates Inc.) measured line-averaged gas concentrations at upwind and downwind locations of a sewage treatment lagoon. Real-time CH₄ concentrations (ppm over 100 m path-length, one way) were continually measured for over one month during each campaign. Climatic conditions including wind statistics were also recorded with a 3-dimentional sonic anemometer (CSAT3, Campbell Scientific) at a frequency of 10 Hz. These measurements of gas concentration and wind statistics were used as the IDM inputs to calculate CH₄ fluxes. During the same periods, effluent samples were also collected and analysed. In this study, we present the CH₄ fluxes (μg/m²/s) from the treatment lagoon in summer and winter seasons. The effects of other factors on the emissions including the chemical and physical properties of effluents, aerators operation status, and effluent flow rates were also investigated. We found that measured CH₄ emissions were higher than those estimated by national GHG reporting guidelines and seasonal and spatial variations were significant.