The implementation of the Interreg Estonia–Latvia Programme project “RE-FRESH: Repurposing Water Treatment Residuals for Sustainable Lake Restoration” (EE-LV00240) has begun

Nutrient pollution remains a global threat to water quality and ecological health of lakes, and is one of greatest challenges to water management in the Baltic countries. Excessive nutrients inputs cause eutrophication, leading to aquatic plant overgrowth, harmful algal blooms, oxygen depletion and formation of dead zones in the water column, reduced habitat for aquatic animals, and increased greenhouse gas emissions.

Decades of management actions have reduced external nutrient inputs to many surface waters in Europe, yet many lakes fail recover. This is largely due to phosphorus accumulated in lake sediments over long periods of time due to various human activities. Through a process known as internal loading, this legacy phosphorus circulates between the lake sediment and water, continuing to degrade the water quality for decades or longer after external sources were reduced.

Recycling drinking water treatment residuals (DWTRs) to permanently bind legacy phosphorus in the sediment would likely solve these problems, with the additional benefit of being locally available and having a low carbon footprint due to reuse. However, in Europe, we currently lack the knowledge and technology needed to apply DWTRs for the purpose of lake restoration.

Within the RE-FRESH project, we will evaluate the properties and develop pre-treatment methods for the DWTRs produced by Riga Water Ltd. in Latvia to obtain a DWTR-based material suitable for lake restoration. We will then develop a dose calculation tool for the material and test it under real-world conditions at four different pilot lakes (two in Latvia and two in Estonia). Field-tests will be conducted in closed experimental systems, which can be later upscaled for restoration of entire lakes, as well as other waterbodies. A life cycle analysis will be also performed, to determine the true cost of restoration.

The project will provide an innovative, affordable, and sustainable solution for restoring lake water quality and ecological health. The developed methodology will support national and local authorities in meeting the objectives of the EU Water Framework Directive.  Combining the expertise and know-how of the partners involved in the project will ensure that the project outputs will be user-friendly and can be adopted in a broad manner.

Lead partner:

1. Estonian University of Life Sciences (Estonia)

Partners:

2. Institute of Food Safety, Animal Health and Environment „BIOR” (Latvia)

3. Rīga City Municipality (Latvia)

4. Navi Lakes foundation (Estonia)

5. Smiltene Municipality (Latvia)

6. Limbazi Municipality (Latvia)

The main project goals: The RE-FRESH project aims to repurpose drinking water treatment residuals (DWTRs) through a circular economy approach to reduce harmful nutrient compounds (primarily phosphorus) in four Baltic lakes or ponds (two in Latvia and two in Estonia). RE-FRESH provides a tested solution for end users, including a DWTR dose calculation tool for waterbodies, five stakeholder workshops, and knowledge-sharing initiatives to ensure adaptability and long-term sustainability in the region and beyond.

Planned activities in the project in which BIOR is involved:

1. Development of an optimal DWTR-based material for lake restoration
2. Seasonal collection of DWTR samples from the Riga Water drinking water treatment plant and laboratory pre-treatment of collected material.
3. Laboratory analyses of raw and pre-treated DWTRs for the presence of micropollutants, incl. perfluoroalkyl and polyfluoroalkyl substances (PFAS), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and microplastics.
4. Laboratory determination of raw and pre-treated DWTR physiochemical properties, incl. identification of functional groups/compounds, mineral composition and crystallinity, total and oxalate-extractable metal concentrations, total nitrogen and total phosphorus concentrations, and phosphorus binding.
5. Performing laboratory experiments, incl. P-sorption batch experiments, and N and Al leaching tests.
6. Assessment of the pre-treatment methods and the selection of DWTR-material with most optimal properties for lake restoration.
7. Development of a DWTR-based material dose calculation tool
8. Collection of sediment samples in pilot sites located in Latvia.
9. Laboratory determination of sediment physiochemical properties, incl. organic and mineral carbon content, determination of P fractions, total and oxalate-extractable metal concentrations.
10. Performing laboratory experiments, incl. extended P-sorption batch experiments, aging assays and DWTR addition experiments.
11. Developing the dose calculation tool with statistical tools.
12. Piloting the DWTR solution at pilot lakes
13. Monitoring water quality parameters in pilot lakes in Latvia to establish baseline conditions.
14. Designing and executing field experiments in pilot lakes in Latvia.
15. Evaluating outcomes of the field experiments, preparing technical documentation and guidelines for full-scale implementation of the developed solution in the pilot lakes and beyond.
16. Engagement of target groups
17. Dissemination of project activities through various channels, incl. social media, stakeholder event, public events and other.
18. Organizing community awareness and networking campaigns.

This article is prepared with the financial support of the European Union. The content of this article is entirely the responsibility of the Institute for Food Safety, Animal Health and the Environment, BIOR, and under no circumstances is the official position of the European Union.

Duration of the project is from January 2026 to December 2028.

Total project funding is EUR 651.368,50. The funding of the Institute BIOR is EUR 282.005,00, incl. ERDF co-financing is 80% (EUR 225.604,00) and national co-financing is 20% (EUR 56.401,00).