Governing small-scale wastewater treatment plants (WWTPs) in coastal tourist areas of the Baltic Sea Region (BSR) is challenging. Seasonal population fluctuations, fragmented legislation, and limited data availability create a complex regulatory landscape. The NURSECOAST-II project, with 17 partners from eight countries, addresses these issues by mapping WWTPs under 2,000 Population Equivalent (PE) and analysing their operational and environmental characteristics. However, the project revealed significant gaps in data availability and regulatory coverage.
A key finding is the widespread lack of comprehensive data on WWTPs below 2,000 PE — including their number, performance, and treatment efficiency. This lack of data severely limits the ability to assess their environmental impact, particularly in sensitive coastal zones where tourism intensifies wastewater generation. The situation is further complicated by the absence of monthly or quarterly monitoring data, which makes it nearly impossible to evaluate seasonal variations in treatment efficiency. Designed primarily for permanent residents, these systems often struggle to cope with peak-season loads.
Before the start of 2025, regulation of small-scale wastewater treatment varied across EU Member States, since the previous Urban Wastewater Treatment Directive (UWWTD, Council Directive 91/271/EEC) excluded plants below 2,000 PE. This left smaller systems outside the scope of harmonized regulation, resulting in inconsistencies in monitoring practices, effluent standards, and enforcement. Small wastewater treatment plants are often regulated on a site-specific, permit-by-permit basis, a practice that further contributes to regulatory fragmentation across Member States.
The situation is partially changing. The revised Urban Wastewater Treatment Directive (EU) 2024/3019 lowers the threshold for mandatory centralized wastewater treatment to 1,000 PE. This means that all agglomerations above 1,000 PE must be equipped with collection systems and secondary treatment by 2035. The directive does not extend monitoring obligations to WWTPs below 1,000 PE. If such plants are subject to monitoring, it is due to national legislation, not EU-level requirements. In Finland, WWTPs above 100 PE require an environmental permit with monitoring; systems below 100 PE, typically household-scale, remain largely unmonitored.
The inclusion of WWTPs in the 1,000–2,000 PE range under the revised directive is expected to improve environmental protection in coastal areas, especially those under tourism pressure. While tertiary and quaternary treatments are reserved for larger plants, the directive promotes water reuse, resource recovery, and stricter monitoring of pollutants such as PFAS, microplastics, and pharmaceutical residues. Nevertheless, the environmental load from small WWTPs remains largely unknown. Their potential contribution to nutrient pollution, particularly nitrogen and phosphorus, may be substantial. In some cases, these plants may discharge insufficiently treated wastewater directly into surface water bodies. Their coastal proximity and seasonal use spikes can affect water quality and ecosystem health. The lack of sufficient data prevents accurate modelling of their cumulative impact, which is essential for informed policy-making and sustainable tourism development.
Small municipal WWTPs (< 2,000 PE) remain an important part of the overall water protection framework. The regulatory landscape is heterogeneous, and while some countries publish clear numeric values and monitoring schedules, in many cases the permit is the key legal instrument. Monitoring frequency of 2–4 effluent analyses per year is typical but may be more frequent depending on risk. Operators must focus on permit compliance, good process management, and staying informed of evolving regulatory expectations, especially around nutrients and sludge reuse.
The spatial, analytical, and legal analysis conducted by the NURSECOAST-II project uncovered numerous discrepancies in data accessibility, WWTP distribution, effluent standards, and technological solutions across the BSR. These inconsistencies highlight the urgent need for harmonized regulations and standardized data collection protocols. Establishing a common EU-wide database would greatly facilitate scientific research and policy evaluation. Such a database should be accessible to both specialists and the general public, promoting transparency and enabling local authorities to make evidence-based decisions.
In conclusion, the study underscores the importance of improving governance and data infrastructure for small WWTPs in touristic coastal regions. Although the revised EU directive expands regulatory coverage to agglomerations over 1,000 PE, monitoring obligations for smaller systems remain dependent on national legislation. Expanding the scope of EU directives, investing in unified data systems, and ensuring the effective implementation of EU directives in national level are key to enhancing the resilience of wastewater infrastructure and protecting the ecological integrity of the Baltic Sea.
Virpi Vorne
Research Scientist
Natural Resources Institute Finland (Luke)
Finland
virpi.vorne@luke.fi
Anu Reinikainen
Research Scientist
Natural Resources Institute Finland (Luke)
Finland
anu.reinikainen@luke.fi
Ksawery Kuligowski
Project Leader
Assistant Professor
Institute of Fluid-Flow Machinery Polish Academy of Sciences
Poland
kkuligowski@imp.gda.pl
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