Greenhouse gas emissions from wastewater treatment plants using drone-based measurements

Using a drone-based method for simultaneous flux measurements of greenhouse gases (GHGs) we assessed methane (CH₄) and nitrous oxide (N₂O) at several wastewater treatment plants (WWTPs) with anaerobic digestion.  Results showed unexpectedly high fluxes and discovered that N₂O emissions from sludge storage are at least as important as CH₄ emissions in terms of global warming. Despite this, N₂O emissions from anaerobic digestion sludge are usually assumed to be negligible and therefore not measured routinely at WWTPs. The CO₂-equivalent total emissions of CH₄ and N₂O were 3-fold higher than the IPCC-recommended emission-factor-based estimates. The drone-method works in a wide variety of environments for simultaneous measurements of the major GHG fluxes (CH₄, N₂O, and CO₂) without the need to do repeated flight patterns to cover all gases, alleviating the problem of flux potentially changing between flights which would otherwise make flux comparisons between the different GHGs less reliable.

The drone method used is a further developed version of our previous method (Gålfalk et al 2021 - https://pubs.acs.org/doi/10.1021/acsearthspacechem.1c00106) with longer flight time, higher payload, all major GHGs measured simultaneously, improved logging with all measurements needed for flux calculations being measured on-board the drone without any need for ground-based auxiliary measurements, and more convenient post-processing to calculate fluxes.