Pharmaceutical residues, pesticides, and industrial chemicals enter rivers, lakes, and groundwater via wastewater. Even low concentrations can harm ecosystems and pose a health risk. Conventional wastewater treatment plants do not adequately remove many of these micropollutants. Per- and polyfluoroalkyl substances (PFAS) are particularly persistent and accumulate in the environment and in organisms.

With the EU Urban Wastewater Treatment Directive (KARL), which took effect in 2025, the requirements for wastewater treatment are increasing: Large wastewater treatment plants must be gradually expanded to include a fourth treatment stage. Manufacturers of pharmaceuticals and cosmetics, in particular, are being held accountable and will be required to cover at least 80 percent of the investment and operating costs in the future. In Germany alone, these requirements will apply to some 570 municipal wastewater treatment plants. The investment needed is projected to reach up to 10.5 billion euros, with additional annual expenses in the high three-digit millions range^{[1], [2]}. Accordingly, sustainable and affordable technology is of paramount importance.

Binding pollutants and regenerating resin on-site

Conventional processes for the fourth treatment stage, such as activated carbon and ozonation, are technically established but are energy- and resource-intensive. Researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT in Oberhausen are developing a promising alternative called ARKON. The process comprises three steps: adsorption, regeneration, and concentration.

The biologically treated wastewater flows through a resin bed. Micropollutants and part of the PFAS accumulate on the resin’s surface. The bound substances are then released from the resin using two different regeneration media. Filtration is then used to further concentrate the regeneration media. In this way, the original wastewater stream is converted into a small-volume trace-substance concentrate that can be disposed of with minimal effort. The regeneration media remain largely within the process. In addition, heat is recovered.

“Unlike conventional adsorption processes, the material does not need to be continuously replaced or regenerated externally at high cost. With ARKON, we recycle it. In this way, we combine high-performance adsorption with resource-efficient regeneration,” explains Dr.-Ing. Lukas Rüller from the Circular Water and Biomass Utilization department at Fraunhofer UMSICHT.

Demonstration under real-world conditions

The UMSICHT team led by Lena Fingerhut, Josef Robert, and Lukas Rüller has already tested the key process steps in the laboratory and at the pilot plant. In the next step, ARKON will be demonstrated on a larger scale at the Wolfsburg wastewater treatment plant. The plan is to install a partial-flow system with a throughput of 25 to 50 m^³ per hour. During continuous operation, the researchers will investigate, among other things, how long the resin binds pollutants, how often it needs to be regenerated, and how energy and chemical consumption can be further reduced.

The results are expected to provide reliable design data for wastewater treatment plants of various sizes and enable a comparison with activated carbon and ozonation. The demonstration plant in Wolfsburg is intended to serve as a reference for other municipal operators and plant engineering companies. In addition, applications in the chemical and pharmaceutical industries, at landfills, and in surface treatment are being considered.

_{[1] Europäisches Parlament und Rat: Richtlinie (EU) 2024/3019 über die Behandlung von kommunalem Abwasser (KARL). Amt für Veröffentlichungen der Europäischen Union, Luxemburg, 2024.}

_{[2] Kompetenzzentrum Spurenstoffe Baden-Württemberg (KomS BW): KomS-Langzeitbetrachtung – Kosten der gezielten Spurenstoffelimination auf kommunalen Kläranlagen, 2025.}