KoalAplan – Biorefinery Büsnau: Municipal wastewater as a source of ammonium nitrogen, hydrogen and bioplastics

At the University of Stuttgart's teaching and research wastewater treatment plant in Büsnau, three products are extracted from municipal wastewater: Ammonium, hydrogen and polyhydroxyalkanoates (PHA).

Gereinigtes Abwasser aus dem Hauptstrom
© Universität Stuttgart
KoalAplan – Biorefinery Büsnau: Treated wastewater from the main stream. Ammonium was recovered here, which can be used as nitrogen fertiliser for agriculture.

Project goal

A decisive goal of the project is that the utilisation of the particulate organic carbon of the municipal wastewater does not only consist of the production of the comparatively cheap and climate-relevant gas methane, as has been the case so far, but that more sustainable products are created. 

Solution approach

In parallel, the largely particle-free wastewater is purified in the main stream. Ammonium is recovered here, which can be used as nitrogen fertiliser for agriculture. Most of the particulate organic carbon is recovered by sedimentation in the primary settling stage. More than 50 per cent of the total organic carbon in municipal wastewater is bound in solids and is not present in solution. The particles still present in the primary treatment effluent are separated from the municipal wastewater with the help of a microscreen.

Hydrolysate can be obtained from the particulate organic carbon by biochemical splitting with water. The hydrolysate is rich in organic acids and is bioelectrochemically converted to hydrogen and CO2 in a novel reactor system.

In a further step, the material flows produced in the previous processes (hydrolysate) are converted into polyhydroxyalkanoates (PHA). Polyhydroxyalkanoate can be used to produce biobased plastics.

Project information

Project title

KoalAplan – Biorefinery Büsnau: Municipal wastewater as a source of ammoni-um nitrogen, hydrogen and bioplastics


Project duration

October 2021 – March 2024


Project partners

  • DVGW Research Unit at the Engler-Bunte Institute of the Karlsruhe Institute of Technology (KIT) DVGW-EBI (Coordination)
  • Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB
  • Clausthal University of Technology
  • Hamburg University of Technology, Institute of Technical Microbiology
  • State Agency Umwelttechnik BW GmbH
  • University of Stuttgart, Institute for Sanitary Engineering, Water Quality and Solid Waste Management – Teaching and Research Sewage Treatment Plant
  • University of Southhampton (Associated Partner)


We would like to thank the Baden-Württemberg Ministry of the Environment, Climate Protection and the Energy Sector and the European Union for funding the project "KoalAplan" as part of the ERDF (European Research and Development Fund) programme "Bioeconomy – Biorefineries for the recovery of raw materials from waste and wastewater".