High-load digestion Ulm – Scientific support during the technical realisation on the high-load digestion for Ulm-Steinhäule

The wastewater treatment plant at the Steinhäule site in Ulm treats the wastewater of a population equivalent of around 440,000. For studies on the fermentability of the sludge produced, Fraunhofer IGB has set up and commissioned a pilot plant for high-load digestion. Based on the data obtained here, a large-scale plant is to be designed to reduce the sludge volume and simultaneously produce biogas.

High-load digestion – Alternative and complementation to sludge incineration

high-load digestion pilot plant
© Fraunhofer IGB
The high-load digestion pilot plant at the Ulm wastewater treatment plant provides three usable material streams: Biogas, nutrient-rich sludge water, and organic digestate.

The wastewater of the city of Ulm and its surroundings has been treated at the Steinhäule site for over 60 years. The treatment plant treats the wastewater of about 220,000 residents as well as industrial and commercial wastewater, which also corresponds to a population equivalent of about 220,000. Part of the treatment plant is also a sludge incineration plant; however, there is no sludge digestion so far. This is about to change.

Biogas production through digestion of sewage sludge

The sewage treatment plant association of Ulm has commissioned Fraunhofer IGB to carry out tests on the fermentability of the sludge of their sewage treatment plant. Based on the data generated here, a high-load digestion can then be designed that converts the biodegradable portion of the sludge into biogas very efficiently. On the one hand, this reduces the volume of sludge produced, which spares the capacity of the incineration plant. On the other hand, the biogas produced can also be used for energy, which has a positive effect on the energy balance of the wastewater treatment plant.

Pilot plant high-load digestion

Since there has been no sludge digestion at the treatment plant so far, the operating personnel wanted to gain experience at a pilot plant before the industrial-scale plant is realized. Fraunhofer IGB has, therefore, set up a pilot plant for high-load digestion in a hall at the Steinhäule wastewater treatment plant in a second project and put it into operation in December 2020. This plant is designed so that it can later be used at other locations. It served as the technical basis for Fraunhofer's internal EVOBIO project. On the basis of the concepts developed in EVOBIO, we are currently working with our colleagues in Ulm to find solutions for recycling the nutrients redissolved in the sludge water.

Project information

Project title

High-load digestion for Ulm-Steinhäule


Project duration

April 2020 – December 2021


Project funding

Orders from the Ulm-Steinhäule sewage treatment plant association