Use of large-scale heat pumps in sewage treatment plants
Significantly larger volumes of water are concentrated at the outlet of sewage treatment plants, enabling the use of large-scale heat pumps and the feeding of heat into district heating networks. An additional advantage is that the wastewater has already been treated and contains fewer contaminants. For this sector, the Energieatlas NRW identifies a potential of around 6.8 TWh per year. Taken together, both sources could cover around 10 % of the heating demand for buildings in North Rhine-Westphalia by 2045 – and would be continuously available.
2. The „Initiative Abwasserwärme NRW“ is putting the spotlight on wastewater heat
In 2024, the State of North Rhine-Westphalia and the state-owned company NRW.Energy4Climate launched the „Initiative Abwasserwärme NRW“ and signed a declaration of principles together with representatives from energy supply organisations, sewerage network operators, the water sector, the housing sector, the Kommunal Agentur NRW and the Association of Towns and Municipalities of North Rhine-Westphalia. On this basis, the use of wastewater as a heat source is to be systematically expanded and a further impetus given to the heat transition.
„With the NRW Wastewater Heat Initiative, we are bringing experts from this field together around one table. In two working groups on the topics of wastewater heat from the sewer network and wastewater heat from sewage treatment plants, we are developing concrete solutions”, said Christian Mildenberger, Managing Director of NRW.Energy4Climate, in October 2024. „The aim is to move quickly to the implementation of projects in order to further accelerate the pace of the heat transition.“
According to NRW.Energy4Climate, the aim is to launch several hundred projects and to play a pioneering role in this field at a national level. The initiative focuses, among other things, on the development of suitable operating models – a brochure on which was published in October 2025 – the further development of technical solutions, and the clarification of key regulatory and economic framework conditions.
To get new projects off the ground, the stakeholders in the Abwasserwärme NRW initiative are working in two working groups to address relevant issues relating to the two approaches mentioned above:
- Recovery of wastewater heat from the sewer network (with a focus on neighbourhoods)
For example, potential maps are being drawn up, legal obstacles identified and concrete project procedures established.
- Recovery of wastewater heat from sewage treatment plants (with a focus on district heating)
This working group focuses primarily on technical requirements and recommendations for action.
3. Best practices: What has happened in North Rhine-Westphalia since then?
In the meantime, numerous projects have been launched in North Rhine-Westphalia or are still in the planning stage, as the following examples show:
Duisburg: District heating from the Huckingen sewage treatment plant
The plant operated by Stadtwerke Duisburg has been in operation since June 2025 and is regarded as a prime example of harnessing previously untapped potential and successful collaboration in the heat transition. The city aims to generate its district heating entirely CO₂-free by 2035 and is using innovative solutions to achieve this, such as tapping into previously unused energy sources. To harness the heat from the treated wastewater at the Huckingen sewage treatment plant, it is collected in a newly created holding area in the plant’s outflow and channelled via underground pipes to a separate heat pump building. Two heat pump modules, each with a capacity of 1.9 MW, extract heat from the wastewater and generate flow temperatures of 75 to 85 °C, thereby supplying part of the district heating network in the south of Duisburg with low-carbon heat. The wastewater, which has cooled by around 5 °C, then flows back into the treatment plant’s outflow, where it is mixed with the remaining treated wastewater and flows into the Rhine at a lower temperature, significantly reducing the load on the river.
System safety is the top priority: the wastewater and district heating circuits are continuously monitored so that the system can be shut down immediately in the event of contamination. Whilst Stadtwerke Duisburg operates the combined heat and power plant, Wirtschaftsbetriebe Duisburg remains responsible for water treatment and water quality monitoring. After a construction period of around two years, the municipal utility’s heat generation plant at the Huckingen sewage treatment works commenced operations on schedule in June 2025 and has since been reliably supplying households in the south of Duisburg with climate-friendly district heating.
The successful implementation is based on close cooperation between Stadtwerke Duisburg, Wirtschaftsbetriebe Duisburg and external partners, as well as funding provided under the Federal Network Agency’s call for proposals for innovative combined heat and power projects.
Mönchengladbach: Wohnquartier Seestadt – heat from the sewer
The residential district Wohnquartier Seestadt in the centre of Mönchengladbach is positioning itself as a pioneering district in the energy transition. In collaboration with various partners, CO₂ emissions are being significantly reduced compared to conventional supply solutions.
A central element of the energy concept is the intelligent sector coupling of electricity and heat in conjunction with the use of sustainable technologies. A key role is played by the use of wastewater as an energy source via a central large-scale heat pump. The installation was commissioned in 2022. The concept enables a highly efficient and, at the same time, low-carbon heat supply under economically viable conditions.
Extensive greening measures, including green roofs and integrated water features, also make an important contribution to a stable and pleasant microclimate.
Seestadt’s forward-looking supply concept is part of the „TransUrban.NRW“ funding programme and was recognised by the Federal Ministry for Economic Affairs and Energy (BMWi) as one of four projects to be designated a „real-world laboratory for the energy transition“. The operation and further development of the energy network are carried out in a long-term partnership with Stadtentfalter GmbH.
In addition to this award, in September 2020 Seestadt was recognised by the state of North Rhine-Westphalia as the state’s largest climate protection development. In December 2023, it was recognised as „KlimaQuartier.NRW“.
