Wastewater heating cuts costs and emissions, study finds

A new study from the University of Oulu shows that using waste heat from district heating to warm wastewater before treatment can reduce carbon dioxide emissions by up to a third and boost an energy company’s operating profit by as much as 40 percent.

The method involves maintaining a consistent wastewater temperature year-round, which improves nitrogen removal—especially in cold periods—by keeping the water above 16°C. Currently, wastewater in Finland is often below 12°C for much of the year.

Waste heat can also be sourced from data centers, with the system’s investments—such as heat exchangers and district heating pipelines—paying for themselves in 3 to 10 years, according to the research.

Oulu’s water utility director Juha Hiltula noted that nitrogen, which contributes to eutrophication and oxygen depletion in water bodies, is a key target under the EU’s stricter new urban wastewater directive. Heating wastewater could reduce the need for costly upgrades to meet the new standards.

The University of Oulu’s Kavenero project, conducted with Oulu Water and Oulu Energy, ran from 2024 to 2026. Oulu Energy’s development director Kimmo Alatulkkila said the approach could also significantly improve district heating capacity, allowing better use of excess heat from sources like data centers.