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From sewage sludge to heat and power

In the Swiss canton of Baselland, sewage sludge is used to generate electricity and heat. A new combined heat and power system significantly increases the efficiency of wastewater treatment.

In order to extract as much energy as possible from the wastewater, the Swiss canton of Basel-Landschaft (Baselland for short) relies on several technologies, including the generation of biogas from accumulated sludge. In turn, the biogas is used in a combined heat and power system to generate electricity and heat – for the canton's own power generation and for district heating. Since the canton operates the wastewater treatment plants itself, the individual sites are linked in a sensible way. The aim is for both the canton of Basel-Landschaft and the city of Basel to be able to dispense with natural gas as a heating medium in the medium term. The entire wastewater infrastructure of the canton of Basel-Landschaft serves a population of around 300,000.

In 2009, a combined heat and power system has been integrated into the Birs wastewater treatment plant in Birsfelden (Arlesheim district). In October 2023, it was decommissioned due to its age and replaced by a new unit from the German manufacturer 2G Energy from Heek. The new unit operating on biogas has 360 kW of electrical and 399 kW of thermal output. While electricity and heat are largely consumed on site, surplus heat is fed into the district heating network. The agenitor 408 BG/ct80 CHP unit was installed by IWK Integrierte Wärme und Kraft AG, based in Bubendorf, Switzerland. It generates around 2.4 billion kWh of electricity and around 3 billion kWh of heat per year, according to the Basel-Landschaft Construction and Environmental Protection Directorate.

Water is extracted from the sewage sludge

At the Birs site, the sewage sludge from the wastewater treatment plant is processed into biogas. It is dewatered in a centrifuge and then fed into the fermentation process. The resulting biogas consists of 65 percent methane. “We primarily need the heat generated in the CHP system for the digestion process of the dried sewage sludge, which takes place at exactly 38 degrees Celsius. But the CHP is so efficiently configured that we only use around a third of the heat ourselves. The surplus is fed into an extensive district heating network,” explains Patrick Lüthy, Operations Manager of WWTP Birs and WWTP Birsig. Around 7.1 billion kWh of gas are produced annually, of which around 2.9 billion kWh are fed into the grid.

In Birsfelden, the lack of space was the biggest challenge for systems supplier IWK. “Since the building with the machinery room does not belong to the WWTP, we could not install a standard ventilation system but had to install a special room cooling system to dissipate the excess heat from the engine. The existing gas treatment system was also equipped with a new activated carbon filter and a gas analyzer and placed in a new room,” Rolf Isenring of IWK reported to the Swiss Powerloop Association. In conjunction with two powerful heat pumps that extract heat from the treated wastewater at the Birs WWTP, the heat is made available to the Lehenmatt Birs heating network. As a result, since 2022 the waste heat from the wastewater treatment plant has been heating the Lehenmatt district in Basel and parts of Birsfelden, as well as providing the base load for the St. Jakob Park stadium and the St. Jakob sports facilities.

Further CHP units installed

At the same time as the combined heat and power unit in Birsfelden was being replaced, the outdated unit in Füllinsdorf was also replaced by a new model of the same type. According to 2G Energy, however, the WWTP Ergolz 2, Füllinsdorf, was delivered and fully assembled as a container solution - complete with all peripheral devices. As a result, installation and connection to the existing gas heating lines were faster. In addition, a new gas treatment system was installed here as well. To ensure consistent gas quality, two new activated carbon filters were installed to eliminate the highly variable substances present from industrial usage. Unlike the plant in Birsfelden, the one in Füllinsdorf is still used exclusively to supply energy and heat to its own installations. However, there are already plans to integrate Ergolz 2 into district heating networks in the future.

The system at a glance

Operator: Canton Basel-Landschaft

Planning and installation: IWK Integrierte Wärme und Kraft AG

System: Combined heat and power unit for in-house electricity generation using biogas produced from wastewater, CHP unit from manufacturer 2G Energy with 360 kW of electrical and 345 kW of thermal output

Unique feature: The biogas produced by the wastewater treatment plant is used to generate heat. Most of the heat is used on site for the digestion process, while the rest is fed into the heating network.