Using a multi-gas UAS to compare methane and nitrous oxide emissions from highly emitting process steps at wastewater treatment plants

We present a newly developed UAS and method for sensitive and simultaneous mapping of multiple trace gases including methane (CH₄) and nitrous oxide (N₂O). Using this UAS capacity, a study of the most highly emitting process steps at several wastewater treatment plants (WWTPs) in Sweden will be presented, where CH₄ and N₂O emissions are compared, showing the advantage of simultaneously sampling the two gases and the ability allowed by a drone to measure total gas fluxes from extended treatment steps. Usually only CH₄ is the main focus of WWTP emission studies, but even relatively small unknown N₂O emissions can have a large impact on the climate due to its warming potential being ~10 times higher than CH₄ (on a 100-year timescale).

The UAS has everything onboard to collect all data needed for the flux calculations, including GPS, a light-weight weather station, sensitive gas sensors, and telemetry data storage. Everything is stored on a customized logger at 1 Hz producing a point cloud from which fluxes of the different gases can be calculated in post-processing.

In total 13 WWTPs were included in a one-year measurement campaign using the UAS, targeting mainly sludge treatment and the biological process step. This study exemplifies the capacity and measurement opportunities generated by multi-gas UAS.