Oskars Purmalis, Janis Krumins & Maris Klavins: Reclaimed wastewater reuse topicality in Baltic Sea area

Baltic Sea region is centring around Baltic Sea and its waters have connecting function for countries and is a resource for development and major value for countries of the region. It seems Seas are inexhaustible resource, however in reality situation is far from ideal. Urban growth, industrialisation, development of agricultural production puts major stress on water resources as indicated by water exploitation index. Countries around Baltic Sea are very aggressively disturbing natural water cycle and in coming future human impacts will only increase aggravated by climate change impacts.

As most significant threat for Baltic Sea can be considered eutrophication leading to algal growth, destruction of biological diversity, causing oxygen depletion in deeper layers of the Baltic Sea. Source of eutrophication are nutrients (nitrogen and phosphorous compounds) coming from agriculture, and all kinds of wastewaters.

Both EU regulations, both regional authorities (Helsinki Commission – HELCOM) decisions requires significant reduction of nutrient loading. A new challenge to water resource management system is recently adopted water resilience strategy, putting water pollution reduction tasks in the centre of attention urging search for new solutions.

A significant source of Baltic Sea pollution are discharges from wastewater treatment facilities and recent analysis characterise flows of nutrients as significant problem. At the same time there exist approach to reduce both water consumption and simultaneously nutrient loads to receiving water bodies and seas – reclaimed water use. Reclaimed water can be used for recreational applications, in construction industry and other areas, but most widely it is used for irrigation. Use of reclaimed water for irrigation is a tool to recover nutrients, present in wastewaters and use nutrients still present as fertilisers to support plant growth. Reclaimed water use in agriculture is a common praxis in dry and hot region countries, however, in the Baltic Sea area, exist falsely believes in endless of water resource availability and reclaimed wastewater reuse is rare – only few demonstration cases. Such approach is wrong! Reclaimed water use can be considered as an efficient tool to achieve both water resource saving aims, both Baltic Sea pollution reduction with nutrients.

The reuse of reclaimed water is gaining attention across the Baltic Sea region as countries contend with growing pressure on freshwater availability, nutrient management, and climate resilience. While the Baltic Sea region is perceived as a water-abundant area, several underlying drivers are continuously elevating the relevance of water reuse. These drivers include increasing urbanization, seasonal drought risks, over-extraction of groundwater in coastal zones, and targets for nutrient reduction becoming stricter the under EU and HELCOM obligations.

BSR Interreg project “ReNutriWater” aim is to demonstrate feasibility of reclaimed water reuse in the Baltic Sea area, not only demonstrating performance of this approach, but also providing analysis of factors, promoting of this approach and identifying barriers. “ReNutriWater” involves stakeholders (wastewater treatment facility operators, NGO, professional organisations, universities from 5 BSR countries (Denmark, Poland, Latvia, Lithuania, Finland) with an aim in piloting cases to demonstrate to professionals in water management sector and politicians the reclaimed water use is feasible and gain-gain approach. Additionally in project innovative approach has been elaborated proposing to use reclaimed water for cultivation of algae biomass, prospective for use of biofuel as well as algal biomass with diverse applications. Project is resulting with a hand book supporting implementation of reclaimed water reuse available for any wastewater treatment operator.

Water reuse offers an opportunity to reduce pressure on freshwater resources, improve resource circularity, and support the Baltic Sea region’s transition toward a more climate-adaptive and sustainable water economy. For instance, in urban contexts, treated wastewater can be repurposed for industrial cooling, street cleaning, and groundwater recharge, thereby reducing abstraction stress on lakes and aquifers. Meanwhile, in agriculture, reclaimed water can help bridge seasonal irrigation gaps as precipitation patterns over time become more unpredictable.

However, reclaimed water reuse is still at an emerging stage and presents numerous technical and governance-related risks. For instance, concerns remain about the introduction of micropollutants, pharmaceuticals, pathogens into soils or groundwater if reclaimed water is used. These risks are intensified by the lack of harmonized standards across the EU and the slow uptake of the EU regulation on minimum requirements of water reuse, which remains voluntary. Public acceptance is also a critical barrier because of the stigma associated with reclaimed water. Furthermore, economically, the upfront investment in the reclamation technologies is also prohibitive, while, politically, everything wastewater related lies with different ministries and agencies, making integrated policy implementation difficult.

Despite these challenges, the Baltic Sea region is well positioned to lead in water reuse innovation. Many countries already possess high standards for wastewater treatment, and growing interest in nutrient recovery and circular economy strategies aligns closely with water reuse initiatives. Pilot projects already have demonstrated technical feasibility and social acceptability under well-regulated conditions. Thus, reclaimed water reuse deserves greater political prioritization, cross-border coordination, and investment due to growing geopolitical uncertainties and resource dependencies.