APRIORA

Wastewater treatment plants (WWTPs) discharge many man-made micropollutants, including active pharmaceutical ingredients (APIs), into the waters of the Baltic Sea Region. APRIORA addresses the question that follows from this: which plants should be upgraded first, and with which measures? The project developed a practical, risk-based way to answer it and tested it in five river catchments around the Baltic Sea.

Challenges and needs

The revised Urban Wastewater Treatment Directive (UWWTD) requires large WWTPs (more than 150,000 PE) to install advanced, quaternary treatment stepwise by 2045. Based on risk assessment, mid-sized plants from 10,000 to 100,000 PE must also be prioritised. Regional environmental authorities need to assess these risks, select the plants to be upgraded and agree on the most cost-effective solutions together with WWTP operators.

To make these decisions, authorities and operators need reliable data, practical tools and clear guidance. However, API emissions and removal rates from WWTPs are rarely measured, and removal differs widely between substances. Surface water data is limited to a few monitoring sites and mostly comes from short screening campaigns, so long-term time series are missing. In addition, no standardised tools existed for assessing risks or evaluating mitigation measures in advance.

What APRIORA developed

APRIORA closed these gaps with a risk assessment framework of three modules that combines monitoring, modelling and multi-criteria risk evaluation:

• Module A (Monitoring) guides the choice of target compounds, sampling sites, sampling frequency and laboratory analysis. From 72 pharmaceuticals named in regulatory documents, a compact list of 30 target compounds was derived, ten of which were used in the pilots.
• Module B (Modelling) estimates pharmaceutical loads discharged by WWTPs, based on sales statistics, excretion and removal rates. Combined with river flow data, it calculates concentrations along the whole river network, including rivers without monitoring data.
• Module C (Risk assessment) translates these concentrations into risks for ecosystems, for the spread of antimicrobial resistance and for human health. The three risks are merged into one score that users can weight, so that sites can be ranked for action.

These modules are brought together in the APRIORA QGIS plugin. It predicts river flows, estimates pharmaceutical concentrations and produces regional risk maps that show which river sections and treatment plants need action first. Users can compare the current situation with planned mitigation before any investment is made. QGIS was chosen because it is open source, freely available and already widely used by authorities. The plugin was accepted into the official QGIS plugin repository in July 2026, and its source code and step-by-step manual are free to use.

A tool is only useful if people can apply it. APRIORA therefore built a learning structure with flowcharts, tutorial videos, background documents and a manual. A teach-the-teacher approach prepared national teachers in all pilot countries, and a dedicated interactive solution flowchart guides users to the right tools and recommendations for their situation.

The value of cross-border cooperation

APRIORA brought together nine partners from five countries: Finland, Germany, Latvia, Poland and Sweden. Environmental agencies, medicines and meteorological institutes, universities and a supervisory agency worked together under the lead of the University of Rostock.

The cooperation was essential because the problem does not stop at national borders! Pharmaceuticals move downstream through river systems, and the pilot catchments (the Kyrönjoki in Finland, the Warnow in Germany, the Bērze in Latvia, the Łeba in Poland and the Kävlingeån in Sweden) each reflect different data situations and regulatory practices. Working on one common framework and one shared tool allowed the partners to compare results, learn from each other and build a solution that works across the region.

Key achievements

• Tested in real conditions: The approach was piloted in five river catchments, with four seasonal monitoring campaigns that delivered new data, including for regions that had rarely been monitored before. The models were calibrated and checked against these measurements.
• Clear findings for action: From the selected ten substances, Diclofenac exceeded environmental quality standards in effluent or river water in the Finnish, Latvian, Polish and Swedish catchments, and venlafaxine did so in several of them. For various substances, conventional treatment generally did not reach the 80 percent removal required by the revised UWWTD for the substances tested. The highest risks occurred during low-flow periods, and plant size alone did not determine risk, which supports prioritisation based on the actual condition of each receiving river.
• Mitigation tested before investment: The agreement of modelled and monitoring data is generally good, although the concentration of some compounds can be overestimated since natural attenuation is not considered, yet. The scenario analysis for the German pilot showed that upgrading the three largest plants to quaternary treatment visibly improves the risk classification in the main river, while smaller upstream plants continue to contribute and should be considered in strategic river management.
• Practical outputs: High-resolution risk maps, a calibrated mass-flow dataset, a tiered approach for assessing antimicrobial resistance risk, and the iFiST methodology for fast and reliable pre-processing of samples on-site, enabling a cost-efficient shipping analysis.
• Capacity built across the region: National teachers in all pilot countries were trained in four sessions between February and September 2025. Further activities included stakeholder events in Finland and Germany, a One Health summer school in Gdańsk, hands-on sampling training in Sweden for Latvian partners, and a hands-on tool workshop at the Final Conference in Helsinki in September 2026.
• Recognition: APRIORA was recognised as a Charter Action under the EU Mission "Restore Our Ocean and Waters".

Outlook and impact

APRIORA enables decision-makers to identify which WWTPs need urgent mitigation and to explore cost-effective options before they commit funds. The central message of the project is that advanced treatment is important, but it is only one part of a broader strategy that also tackles hazardous substances at their source.

The project also identified practical lessons. Data is the main challenge: commercial laboratories often report measurement uncertainties of around 40 percent, and a single sample can cost thousands of euros, which makes a short and well-chosen list of target compounds essential. Practices and datasets differ between countries, and trainees started with very different QGIS skills and IT set-ups. The model covers human medicines reaching rivers via WWTPs. Sludge spreading and veterinary use remain outside its scope. For future work, the project recommends defining clear data requirements from the start, offering in-person training with extra time for beginners, and ensuring local IT support.

The framework, the QGIS plugin and the pilot experience remain available to authorities and utilities in the Baltic Sea Region and beyond as they implement the revised directive.

APRIORA shows what Interreg cooperation can deliver: a tested, shared and freely available solution that helps the region move towards cleaner waters and smarter investments!