Miasto Sejny Wastewater Treatment Plant - Sejny, Podlaskie, Poland

Miasto Sejny is a municipal wastewater treatment plant located in Sejny, a town in the Podlaskie Voivodeship of northeastern Poland. The plant serves a population of approximately 5,825 residents and has a designed capacity of 14,000 cubic meters per day, indicating it is sized to accommodate future growth or seasonal variations. The facility provides secondary treatment, which is the standard biological treatment stage required under Polish and EU regulations for agglomerations of this size. As a plant serving fewer than 10,000 people, Miasto Sejny falls under the EU Urban Waste Water Treatment Directive (91/271/EEC) category for smaller agglomerations. The directive mandates secondary treatment for all discharges from agglomerations above 2,000 population equivalent, which this plant meets. The plant's discharge volume of approximately 830.55 m³/day suggests it operates well below its designed capacity, reflecting current demand. The treated effluent from Miasto Sejny is discharged into local watercourses that ultimately drain into the Baltic Sea via the Neman River basin. The region is characterized by numerous lakes and rivers, and the plant's operation helps protect the sensitive aquatic ecosystems of the Masurian Lake District and the downstream Baltic Sea from nutrient pollution. Proper secondary treatment reduces organic load and suspended solids, supporting water quality in the catchment.

The plant discharges into the local watershed, which is part of the Neman River basin that flows through Lithuania and Belarus before reaching the Baltic Sea. The region features many glacial lakes and wetlands that are ecologically sensitive to nutrient enrichment. The plant's secondary treatment helps mitigate eutrophication risks in downstream water bodies, supporting biodiversity in this important migratory corridor for birds and aquatic life.