RoKKa Pilot Project Uses Wastewater to Produce Fertilizers and Raw Materials – Eurasia Review

“Until now, the task of a sewage treatment plant was mainly to clean the waste water”, explains Dr.-Ing. Marius Mohr, project manager at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB. “Now we also look at the raw materials contained in the wastewater.” Scientists from Fraunhofer IGB, University of Stuttgart, University of Kassel and Technical University of Kaiserslautern are working on sustainable biorefinery with the companies SolarSpring GmbH, Deukum GmbH, Nanoscience for life GmbH, Umwelttechnik BW GmbH, the city of Erbach and the Administrative Union of the Steinhäule sewage treatment plant.

Securing raw materials thanks to microalgae and electrosynthesis

Scientists are testing methods for extracting phosphorus and nitrogen compounds for fertilizers from wastewater. Microalgae are also used to produce plant fortifiers and agricultural soil amendments. Even the CO2 that is produced during biogas production is separated and reprocessed into a raw material for the chemical industry. “In this way, the principles of the bioeconomy are applied and sewage treatment plants can become a sustainable source of raw materials. The recovery of phosphorus and nitrogen in the form of fertilizer closes the nutrient cycle and has a positive effect on the climate,” explains Dr.-Ing. Anette Zimmermann, Head of Environmental Technology and Bioeconomy at Umwelttechnik BW.

The ePhos process allows the recovery of phosphorus. Using a sacrificial magnesium anode, the phosphorus is electrochemically precipitated in the form of struvite. Two pilot plants separate ammoniacal nitrogen from sludge water. One plant follows the principle of membrane gas absorption with membrane contactors, the other works on the principle of membrane distillation.

The RoKKa pilot project assesses the impact of nitrogen recovery with a view to the climate balance of wastewater treatment plants. The classic degradation of nitrogen compounds in sewage treatment plants produces a considerable amount of the greenhouse gas nitrous oxide (N2O), also known as laughing gas. The extent to which nutrients in wastewater serve as food for microalgae is also tested. In addition to light, algae need CO2 for photosynthesis. It comes from the biogas digestion process and is separated using an amino acid solution. At the same time, another way to use CO2 is being tested. Part of the CO2 is transformed into formate by an electrosynthesis plant. Formate is a basic chemical used in the chemical industry. The project thus demonstrates the possibility of recycling CO2.

Biorefinery of the Erbach and Neu-Ulm wastewater treatment plants

The pilot plants in the cities of Erbach and Neu-Ulm will be integrated into existing sewage treatment plants and tested with real wastewater. “We are delighted to be a research partner that makes this project possible,” says Thomas Schniertshauer of Erbach building authorities. “Already in 2016, we took the first step towards a bioeconomy with the construction of a high-load digestion process in our wastewater treatment plant. We are now proud to expand our wastewater treatment plant into a sustainable biorefinery. »

The project is funded by the Ministry for the Environment, Climate Protection and the Energy Sector of Baden-Württemberg within the framework of the ERDF (European Research and Development Fund) program “Bioeconomy – Biorefineries for the valorization raw materials from waste and wastewater”. The ERDF is a structural fund which supports economic, territorial and social cohesion within the EU. Project coordination and public relations are handled by Umwelttechnik BW, Baden-Württemberg’s national agency for environmental technology and resource efficiency.

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