RoKKa – Sewage sludge as a source of raw materials and climate protection at wastewater treatment plants

The path to the bioeconomy is a transformation process that changes established value chains and develops them into communicating value networks. In this course, Fraunhofer IGB is developing concepts for a complete transformation of wastewater treatment plants into wastewater biorefineries with the use of residual and waste materials.

Bioeconomy approach for local circular economy

This can be an important building block in terms of a local circular economy and a modern bioeconomy approach and is essential for closing material cycles. The focus here is on the recovery of nutrients and other valuable materials and the use of side streams such as CO₂ for the manufacture of downstream products. Products manufactured in this way are to be used iteratively in value-adding processes as starting materials in order to be able to realize a truly sustainable circular economy.

Solution approach: Process combination centered on recyclable materials

The project "Sewage sludge as a source of raw materials and climate protection at wastewater treatment plants" (RoKKa), which is funded by the state of Baden-Württemberg, pursues the vision of driving the development toward a wastewater treatment plant as a biorefinery by linking innovative processes in a value-centered, climate-friendly and participatory manner. By integrating the infrastructures at the wastewater treatment plants, which are already working efficiently for environmental protection, it will be possible to transfer the approach of a wastewater treatment plant as a biorefinery and increase its consistency.

High-load digestion enables valuable material production from sewage sludge and CO₂ utilization

RoKKa uses a total of six pilot plants at the Erbach (Danube) wastewater treatment plant to demonstrate the production of valuable substances from the partial stream of sewage sludge treated in a high-load digestion system. Nitrogen and phosphorus recovery is coupled with the production of microalgae. Carbon capture and utilization (CCU) as a basic chemical will be piloted with the CO₂ in the biogas stream. As a result of RoKKa, environmental protection goals of wastewater treatment plants can be considered multidimensionally in the future (water protection, bioeconomy, climate protection).

Outlook

The Ulm-Steinhäule wastewater treatment plant (440,000 population equivalents), which is only 20 kilometers away from Erbach, also plans to treat the sewage sludge in a high-load digestion system in the future. When the high-load digestion system is commissioned, a large proportion of the ammonium contained in the sludge will be dissolved back and fed back to the wastewater treatment plant via the sludge water. The AmmoRe nitrogen recovery process piloted in Erbach could be used here to reduce the nitrogen load on the one hand and to recover the nitrogen as a valuable substance on the other. In this respect, the participation of the Steinhäule sewage treatment plant in the RoKKa project is a good driver for implementing the piloted processes in a technical scale.