Project

Discharges from urban drainage systems burden surface waters with nutrients and micropollutants. On January 1, 2025, Directive (EU) 2024/3019 on urban wastewater treatment (recast), the recast Urban Wastewater Treatment Directive (UWWTD), entered into force. Article 8 of the directive introduces a fourth treatment stage for wastewater treatment plants – mandatory in certain cases – to remove micropollutants from municipal wastewater. By 2045, all wastewater treatment plants with a design capacity exceeding 150,000 population equivalents, as well as plants with capacities of 10,000 population equivalents or more that discharge into sensitive areas (areas at risk), need to be equipped with a fourth treatment stage for micropollutants.

According to Article 8(2) UWWTD, EU member states are asked to provide a list of areas in which the concentration or accumulation of micropollutants from municipal wastewater treatment plants poses a risk to the environment or human health. This list is required by December 31, 2030. It includes drinking water catchment areas, bathing waters, and areas with aquaculture activities, as well as other types of areas to be defined on a risk basis. A key criterion for rivers is a dilution ratio of less than 10 at the discharge point. From 2033 onwards, the list will be updated every six years, taking the increasing number of upgraded wastewater treatment plants into account.

To implement the directive in the member states (national level), there are no detailed European requirements on how to prioritize the upgrading of the wastewater treatment plants. Due to the federal system in Germany, without a uniform methodology at federal level, there is a significant risk of heterogeneous regulations on areas at risk and upgrade pathways in individual federal states. At the same time, legal certainty and ecological and economic viability must be ensured.

Given these circumstances, the project aims to develop a practicable, uniform nationwide methodology for identifying areas at risk and for prioritizing which wastewater treatment plants should be upgraded progressively in accordance with Article 8 UWWTD. It builds on existing work, in particular former projects funded by the German Environment Agency such as “Erweiterte Klassifizierung kommunaler Kläranlagen – Abwassercluster“ (engl. “Extended classification of municipal wastewater treatment plants – wastewater clusters“), “Klarwasseranteile“ and “Umsetzung der vierten Reinigungsstufe in Deutschland“ (engl. “Implementation of the fourth treatment stage in Germany“). The results will be discussed and should feed into the development of the European implementing act at an early stage, as well as support the preparation of the national implementation program required under Article 23 UWWTD, including investment planning and cost estimation.

The project aims to develop and evaluate a uniform, enforceable methodology for implementing Article 8 UWWTD. Core elements of the method are:

• enabling the identification and delineation of areas at risk pursuant to Article 8(2), and
• enabling the determination and prioritization of wastewater treatment plants in these areas that are to be upgraded progressively pursuant to Article 8(4),

with due consideration of the related legal challenges.

Based on nationwide geodata, the MoRE database on wastewater treatment plants, hydrological discharge data (including LARSIM‑ME) and further preliminary work, a methodology for determining areas at risk will be developed. It comprises the assessment of exemptions for drinking water catchment areas, bathing waters and aquaculture activities, the risk-based assessment of additional area categories and a uniform nationwide calculation of the dilution ratio. In a multi-stage process, a concept will be developed by which wastewater treatment plants are geographically assigned and labelled and subsequently assessed hydraulically and in terms of substance loads. In this analysis, environmental quality standards (EQS) and representative effluent concentrations will be particularly considered. The results will be prepared as flow charts, checklists and a user-oriented guideline.

Furthermore, a methodology for selecting and scheduling the upgrades of the wastewater treatment plants will be developed. For this purpose, MoRE will be extended by a node-edge approach to depict concentration profiles and feedback loops between plant upgrading, waterbody concentrations and the classification of areas at risk. Based on this, scenarios for wastewater treatment plant upgrades will be developed. These scenarios examine the prioritization criteria (including discharge load, dilution ratio, influence on risk assessment, cost-benefit ratio) and assign suitable treatment technologies. Investment and operating costs will be derived from recent data and aggregated into economic indicators.

A legal opinion will provide clarification on the interpretation of the UWWTD, interfaces with national law and the legally sound design of the methods. Online workshops will be held with representatives of federal states and other stakeholders, in which results will be presented and feedback collected. In addition, the practical enforceability of the approach will be assessed using a concept for evaluation.

November 2025 to September 2027

• Funded by the German Environment Agency (Umweltbundesamt)

• Forschungsinstitut für Wasserwirtschaft und Klimazukunft an der RWTH Aachen (FiW) e. V., Aachen
• Karlsruhe Institute of Technology (KIT) – Institute for Water and Environment, Karlsruhe
• Prof. Dr. Dr. Wolfgang Durner LL.M., Bonn
• Wupperverbandsgesellschaft für integrale Wasserwirtschaft mbH (WiW), Wuppertal
• VisDat geodatentechnologie GmbH, Dresden