Drones reveal that wastewater plant emissions are greater than expected

Greenhouse gas emissions from wastewater treatment plants (WWTPs) may be more than twice as high as previously estimated, according to new research from Linköping University in Sweden.

Using drones equipped with advanced sensors, scientists found that methane (CH₄) and nitrous oxide (N₂O) emissions from these facilities – particularly from sludge storage – are around 2.5 times higher than international climate models suggest.

The study, published in Environmental Science & Technology, challenges long-standing assumptions used by the UN Intergovernmental Panel on Climate Change (IPCC). The IPCC currently estimates that WWTPs contribute roughly 5% of human-caused methane and nitrous oxide emissions, but their estimates rely on generalised emission factors rather than direct measurements.

The team used custom-built drones to measure emissions at 12 Swedish treatment plants that use anaerobic digestion – a common process for breaking down sludge and producing biogas. Their results revealed that large amounts of methane and nitrous oxide escape not during treatment itself, but later, when the sludge is stored to kill pathogens before being used as fertiliser.

The findings also highlight a previously overlooked source of climate pollution. Nitrous oxide, a greenhouse gas with nearly 300 times the warming potential of carbon dioxide, was found to be a major contributor – its climate impact was roughly equivalent to that of methane from the same sludge. These emissions had previously been assumed negligible in IPCC calculations.

Researchers say that using actual measurements rather than estimates would help local governments better track progress and justify investments in emission-reduction technologies.

Magnus Gålfalk from Linköping University, who led the study said: ‘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.

‘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 mitigation efforts.’

The study concludes that there is an urgent need for more accurate monitoring tools and mitigation strategies as wastewater treatment capacity expands globally. 

The full research can be read here.

Photo: Magnus Gålfalk