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Customized drone developed to detect greenhouse gas emissions.

Photo Credit: Magnus Gålfalk

A recent study from Linköping University reveals that greenhouse gas emissions from many wastewater treatment facilities may be more than double previous estimates. Using drones equipped with advanced sensors, researchers were able to directly measure methane and nitrous oxide emissions at multiple sites.

"Our findings indicate that emissions from wastewater treatment processes have been underestimated until now. With this data in hand, we can better understand and reduce these emissions," explains Magnus Gålfalk, associate professor at the Department of Environmental Change at Linköping University. The research is detailed in a paper published in the journal Environmental Science & Technology.

According to the United Nations Intergovernmental Panel on Climate Change (IPCC), facilities that treat wastewater from homes and industrial sources account for roughly five percent of human-caused emissions of methane and nitrous oxide.

The IPCC currently uses estimated emission values known as “emission factors,” which rely on the number of households served by a wastewater treatment plant. While this approach provides basic estimates, it lacks the precision of actual on-site measurements—a limitation that has now come under scrutiny.

The researchers point out that treatment plants have been striving to lower their emissions. However, under the current estimation framework, any actual reductions are not reflected, as the emissions are not based on real-time data but fixed models.

"Having emissions data derived from actual measurements would allow local governments to better demonstrate the impact of efforts and investments aimed at reducing emissions," says Magnus Gålfalk.

In collaboration with Professor David Bastviken at the same university, Gålfalk utilized a custom-designed drone to survey emissions of methane (CH₄) and nitrous oxide (N₂O) at a dozen wastewater treatment sites across Sweden, all of which employ anaerobic digestion during sludge processing. The findings showed emissions were approximately 2.5 times higher than the IPCC’s estimation model indicated.

Most of the emissions were recorded after the digestion process, during the storage phase where the sludge is held to eliminate harmful organisms before possible use in agriculture. The research indicates that methane emissions during this storage stage have been seriously undervalued. Additionally, the study uncovered that nitrous oxide emissions were much more significant than previously known.

Nitrous oxide is a potent greenhouse gas that remains relatively lesser-known; its impact on the climate is nearly 300 times greater than that of carbon dioxide per equivalent mass.

"We've now shown that nitrous oxide emissions during sludge storage have an environmental impact similar to methane—something that hadn’t been recognized before. This highlights an unexpected and important source that needs closer monitoring," Gålfalk concludes.

Journal

Environmental Science & Technology

DOI

10.1021/acs.est.5c04780

Article Title

In Situ Observations Reveal Underestimated Greenhouse Gas Emissions from Wastewater Treatment with Anaerobic Digestion – Sludge Was a Major Source for Both CH₄ and N₂O

Article Publication Date

21-Aug-2025