Drones measure wastewater treatment plants greenhouse emissions at greater levels than official estimates

by Robert Schreiber
Berlin, Germany (SPX) Oct 31, 2025

Greenhouse gas emissions from many wastewater treatment plants may be more than twice as large as previously thought. A new study from Linkoping University demonstrates this using drones equipped with custom sensors to measure methane and nitrous oxide emissions.

"We show that certain greenhouse gas emissions from wastewater treatment plants have been unknown. Now that we know more about these emissions, we also know more about how they can be reduced," said Magnus Galfalk, docent at Tema M - Environmental Change, Linkoping University, who led the study published in Environmental Science and Technology.

Wastewater treatment plants that receive sewage from households and industries are responsible for about 5 percent of manmade methane and nitrous oxide emissions, based on figures from the UN Intergovernmental Panel on Climate Change (IPCC). The IPCC arrives at this number using emission factors connected to the number of households served by the plant. This approach yields average emission estimates rather than values grounded in direct measurement - an issue highlighted by the new study.

Researchers noted that wastewater treatment facilities continually strive to reduce emissions; however, the current reporting system keeps reported numbers unchanged, regardless of actual reductions. "It would be better if the emissions reported were based on actual measurements. This would make it easier for municipalities to show the benefits of investments to mitigate the emissions," said Magnus Galfalk.

Galfalk and Professor David Bastviken at LiU conducted direct measurements with a specially built drone, surveying methane (CH4) and nitrous oxide (N2O) emissions at twelve treatment plants in Sweden that use anaerobic digestion to process sludge. Their findings showed methane and nitrous oxide levels about 2.5 times higher than estimated by the IPCC calculation model.

Most emissions occurred after the digestion stage, when sludge is stored to eliminate harmful micro-organisms prior to use as fertilizer. Methane released during storage was found to have been previously underestimated. The team also discovered that significant amounts of nitrous oxide were emitted - previously under-recognized as a major greenhouse gas. Nitrous oxide's climate impact is nearly 300 times higher than carbon dioxide per kilogram.

"We show that the climate impact from nitrous oxide emissions from sludge storage is as great as that from methane, and this wasn't known before. So it's a major extra source to keep an eye on," said Galfalk.

The authors recommend that future emission reports for wastewater treatment plants rely on direct measurement, enabling municipalities to demonstrate the positive effects of mitigation investments.

Research Report:In Situ Observations Reveal Underestimated Greenhouse Gas Emissions from Wastewater Treatment with Anaerobic Digestion