Large, unexpected greenhouse gas emissions from the wastewater treatment sector that are not accounted for by present emission factors

We have successfully developed three novel measurement methods for the potent greenhouse gases methane and nitrous oxide, for mapping and visualization over large surfaces (hyperspectral camera working from several hundred meters distance and a very sensitive drone-based method with ppb-level sensitivity), and a sensor network of smaller methane sensors that can monitor and discover emissions for a long time period with high temporal resolution.In our pilot study at the Linköping wastewater treatment plant (WWTP), we found that two treatment steps totally dominated greenhouse gas emissions – sludge storage and ammonia removal – with over 90% of total emissions missed in regular measurements as treatment plants only measure ventilation air (point sources) as traditional methods do not have the possibility to measure emissions from large surfaces.

We also measured methane concentrations up to 2.5% during incomplete flaring (two days of such emissions would correspond to total plant-wide emissions during a year).This implies that emission factors for WWTPs are severely underestimated, impacting both current climate models and society’s focus on effective actions to reduce emissions.

In this project we therefore want to include several plants in Sweden of different sizes, and a few internationally, to calculate total emissions that include all treatment steps. Comparison of treatment techniques and tests will also show which actions are most effective in reducing emissions.