Background
There is growing concern about pollution from toxic chemicals in the water cycle. While the water protection work in the Baltic Sea Region has traditionally concentrated on eutrophication and nutrient removal, there is now a consensus that hazardous substances are one of the main threats to the aquatic environment. Further, the many chemicals, extremely persistent and mobile in the environment, pose a threat to human health.
The EU is addressing this problem mainly through legislation. The revised Urban Wastewater Treatment Directive (UWWTD 2024/3019) came into force on 1 January 2025. The directive marks an important milestone for public health and the protection of water resources, introducing ambitious new requirements to remove micropollutants from wastewater. According to the revised directive, member states will have to ensure the application of the treatment steps meeting new thresholds for quaternary treatment in larger plants of 150 000 PE and above by 2045.
Mobile pilot plant concept
One of the main aims of the EMPEREST project (2023–2025), co-funded by the Interreg Baltic Sea Region Programme, was to support the implementation of the revised UWWTD. The implementation will require extensive investments in quaternary treatment. The results of the EMPEREST piloting will support wastewater treatment plants and local authorities in making informed decisions about cost-effective technologies for micropollutant removal to unlock the investments.
Two pilot plants were locally constructed, respectively, by Gdansk Water Utilities Ltd. and Tartu Waterworks Ltd., to test the selected proven technologies at the wastewater treatment plants in different combinations with varying process parameters. After the first round of testing, the mobile containers continued their journeys to four more cities: Szczecin, Kaunas, Tallinn and Turku. During the testing periods in six sites, regular analysis of water samples allowed to assess the effectiveness of the technologies in the removal of organic micropollutants and thus support the piloting WWTPs in their decision-making regarding most suitable trains of technologies for their conditions.
Results on micropollutant removal from wastewater
The results of the EMPEREST technology pilots can be found in the project report, Strategies and technological means for minimising organic micropollutant emissions from WWTPs and its six annexes featuring the results of each piloting plant (all reports are available on EMPEREST project website). The results focus on the efficiency of advanced treatment technologies for removing organic micropollutants listed as indicator substances in the revised UWWTD.
While factors affecting the choice of micropollutant removal technology vary between different plants, activated carbon adsorption and ozonation proved to be feasible techniques for removing the micropollutants currently listed in the revised UWWTD.
Regarding per- and polyfluoroalkyl substances (PFAS) in particular, the results are complex and further testing is needed. The EMPEREST results on PFAS removal indicate the following:
- Conventional use of ozone alone is not efficient in PFAS removal. Ozone can reduce the length of the PFAS chain, while the resulting shorter-chain PFAS or other intermediates are persistent and potentially harmful as well.
- Granular activated carbon (GAC) filtration can be effective at removing specific long-chain PFAS.
- Ion exchange (IE) is an effective method for both long-chain and short-chain PFAS, however, the operational costs of IE filters are high.
- Nanofiltration has proven to be effective in removing PFAS, but results in a large volume of concentrate, which needs its own treatment or destruction process.
The EMPEREST mobile pilot plants showed that the mobile pilot concept is a cost-effective tool for supporting the upgrade and development of numerous WWTPs, without the need of constructing individual pilot installations.
Conclusions
The EMPEREST project was built on the shared understanding that removing organic micropollutants, including PFAS, is necessary for safe circularity of water and sludge. The project showed that despite advanced technologies, preventing the hazardous substances pollution is a more effective and cost-efficient approach. Upstream prevention measures include increasing the selection of PFAS-free products on the market, strengthening the consumer responsibility to make PFAS-free choices and supporting a general PFAS ban in industry. The EMPEREST project worked also on prevention through building a risk-assessment tool for local authorities for identifying the PFAS pollution hotspots in their city and for starting to mitigate the risks. Further, EMPEREST project undertook an extensive training programme for building capacities of different stakeholders on the topic of PFAS, other organic micropollutants, their removal from the water cycle, prevention measures, etc. Finally, EMPEREST produced, with the support of Baltic Marine Environment Protection Commission HELCOM, guidelines for monitoring and assessing the PFAS pollution in the aquatic environment of the Baltic Sea and catchment area. Continued monitoring and assessment of pollution is vital: reliable data is key in the building of a toxic-free future.
Lotta Lehti
Project Coordinator
Union of the Baltic Cities Sustainable Cities Commission c/o City of Turku
Finland
lotta.lehti@turku.fi
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