iKWK plant starts at sewage treatment plant

11.08.2025

Source: E & M powernews

Treated wastewater from Duisburg will be used as a heat source in future. The new iKWK plant not only benefits people, but also the river's inhabitants.

Stadtwerke Duisburg is now also generating electricity and heat from wastewater from the Huckingen sewage treatment plant. In mid-June, the utility officially commissioned an innovative CHP plant. It is currently the largest CHP plant at a sewage treatment plant in Germany and uses the thermal energy of the treated wastewater to supply district heating. The system is supplemented by two hydrogen-capable combined heat and power plants and an electric heat generator at the Hochfeld site.

"This modern and innovative plant is exemplary in its dimensions in Germany and a real showcase project. Stadtwerke Duisburg shows how heat can be generated in a climate-friendly and reliable way," says Lord Mayor Sören Link (SPD). iKWK means that an innovative component is added to a combined heat and power plant that supplies at least 35 percent of the thermal energy of the entire plant. In the case of the plant in Huckingen, this innovative component is provided by heat pumps.

Heat pumps use waste water energy

Two electrically powered heat pumps, each with a thermal output of 1.9 MW, are central to the system. The two "Sabroe DualPAC" heat pumps from the manufacturer Johnson Controls use the residual heat contained in the already treated wastewater from the sewage treatment plant to feed it into the district heating network. For this purpose, a storage area was created at the outlet basin, where the treated wastewater from around 100,000 households is collected. Its average temperature fluctuates seasonally between 8 and 28 degrees Celsius. It is used by the heat pumps from temperatures above 10 degrees Celsius.

The Kelvion heat exchangers in the newly constructed technical building extract around 5 Kelvin from the water. The heat pumps raise this low-temperature heat to a usable level of 75 to 85 degrees Celsius for feeding into the district heating network. The expected annual production is around 16,000 MWh of heat. "Heat pump technology is one of the key building blocks for a successful heat transition. By using heat from renewable sources, in this case wastewater, we can generate green, i.e. CO2-free heat," explains Stadtwerke board member Andreas Gutschek. Stefan Geuer, Head of Sales Decentralized Energy Systems at Zeppelin Power Systems, the general contractor responsible for the heat pump system, adds: "This system shows how important heat pump systems are for the decarbonization of local and district heating networks."

The cooled water is returned to the original sewage treatment plant system. In addition to generating heat, the cooling by around 5 Kelvin helps to reduce the heat discharged into the Rhine via the Angerbach. "The wastewater is cooled by around five degrees by the iKWK plant. This means that we are discharging cooler water into the Angerbach than before. Especially in the summer months, this means relief for the watercourses, which are often heated up," explains Uwe Linsen, CEO of Wirtschaftsbetriebe Duisburg. "We are delighted that we are able to implement such a forward-looking and ecologically valuable project at our wastewater treatment plant together with Stadtwerke Duisburg. It shows what potential is still too rarely used today on the way to a successful energy and heat transition," says Linsen.

Additional power components in Hochfeld

In addition to wastewater heat utilization, Stadtwerke Duisburg has installed two CHP modules at the Hochfeld site. MWM "MWM TCG 2032BV16" gensets with an electrical output of 4,500 kW and a thermal output of 4,520 kW each were selected for this project. The modules are designed to be hydrogen-compatible and are operated with natural gas. They supply both the electricity and the heating network. In addition, an electrical heat generator with a thermal output of 30 MW from the Danish manufacturer Inpower was installed. It is grid-operated and uses peak loads or negative electricity prices to generate heat, which can be temporarily stored in a heat storage facility at CHP plant III. The CHP units and the electric heat generator were installed by ETW Energietechnik.

The components of the iKWK plant feed into a joint district heating network and together form a unit eligible for subsidies under the Combined Heat and Power Act. "This plant is a useful addition to our generation park because we can produce heat from surplus energy, which we store in our district heating storage facility at CHP plant III until it is needed by our customers," explains Gutschek.

The project was submitted to the Federal Network Agency in 2021 as part of the iKWK tender and received funding approval for 45,000 operating hours. According to Stadtwerke, the total investment costs amount to around 27 million euros. The plant will be operated by Stadtwerke Duisburg in cooperation with Wirtschaftsbetriebe Duisburg, which owns the Huckingen sewage treatment plant.


Author: Heidi Roider