Methane emissions are underestimated by a factor 1.5
A reliable understanding of methane losses at wastewater treatment plants is essential for achieving effective reductions. A newly published study that we performed together with utilities in England and Australia concludes that methane emissions are underestimated.
We have collaborated with Severn Trent in England and Melbourne Water in Australia in measuring methane levels using different methods. The work has lead to a scientific publication.
“Knowledge about measurement methods, uncertainties, and results is crucial for reducing methane emissions. In this article, we have consolidated our insights so others can benefit from them,” explains Morten Rebsdorf, Senior Project Manager at Aarhus Vand.
The article provides insights into measurement techniques, including:
- Biofilter on ventilation air from sludge storage (ongoing)
- Gas sniffing on the digester tank and generally on the biogas system
- Laser methods - primarily LIDAR - which scan using laser beams
- Satellite measurements (only Melbourne Water)
- Optical measurements (Gas camera)
Generic emission factors do not correspond to actual emissions
In short, the conclusion is that methane (CH₄) emissions from wastewater treatment plants are significantly more variable and often higher than what is reported using generic emission factors. Measurements show that actual emissions may be underestimated by a factor of 1.5.
In Denmark, we currently use an emission factor of 1.3% — but in reality, it is closer to 7%. This demonstrates the need for more knowledge to obtain an accurate picture. With the right insights, we can better prioritise our efforts as a climate-conscious utility or as an energy authority.
Gas sniffer:
Aarhus Vand measures the general methane level once a month using a gas sniffer. For example, they put a sniffer down to the agitator in the digester tank, where there is a joint. If it is leaking, methane can be detected. However, wind can pose a challenge to the results.
LIDAR laser method:
Severn Trent use the LIDAR laser method. Here, a gas meter camera is mounted on a mast including a wind meter, which scans for leaks using laser beams. This provides a picture over time of the emissions, and the system calculates a mass flow for each individual emission point.
“We borrowed a LIDAR meter from the supplier and tested the method. We didn’t quite get the results we had hoped for, but we validated our own results of the emissions from the sludge storage tank. The system is relatively expensive, but I believe that optical measurements, such as LIDAR, will become more common,” says Morten Rebsdorf.
Biofilter:
Through this study, Aarhus Vand has identified the sludge storage tank as the largest single emitter. Since the tank at the Egå WWTP is underground and is forced-ventilated, reducing emissions would require a newly built tank and a different setup.
"We are testing a new method, where we install a biofilter on the ventilation air from the sludge storage. Bacteria will convert the methane in the biofilter in which we can calculate the amount of methane (using gas sniffer and flow measurement).
Accurate measurements support methane reduction
The study shows that robust and targeted monitoring is essential for effectively reducing methane emissions. The results highlight the need for more consistent, measurement-based reporting methods and for strategic investments in modernising sludge treatment processes and ageing infrastructure.
The article is the result of 18 months of work and was published in January 2026 in Water Research X as a peer-reviewed scientific article. The article is open access and can be accessed here: Methane emission monitoring at wastewater treatment plants in Europe and Australia