Hallstavik Avloppsanlaggning - Advanced Wastewater Treatment in Hallstavik, Sweden

Hallstavik Avloppsanlaggning is a municipal wastewater treatment plant located in Hallstavik, Norrtälje kommun, Stockholms län, Sweden. The plant serves a population of approximately 4,731, placing it in the small-to-medium agglomeration category under EU classification. The facility employs advanced treatment processes, which go beyond the secondary treatment standard required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. With a designed capacity of 7,000 cubic meters per day and a current discharge volume of about 743 cubic meters per day, the plant operates well below its capacity, indicating room for future growth or seasonal variations. The treated effluent is discharged into the Baltic Sea coastal zone, as the plant lies within 10 km of the coast. This proximity to a sensitive marine environment necessitates advanced treatment to protect water quality and marine ecosystems. The plant contributes to the overall health of the Baltic Sea, a brackish water body with unique ecological significance, by reducing nutrient loads and pollutants.

The plant discharges into the Baltic Sea, a semi-enclosed brackish sea with limited water exchange, making it highly sensitive to nutrient pollution. The local watershed drains through small coastal streams and directly into the Baltic, which supports diverse aquatic life including fish, seabirds, and benthic communities. Advanced treatment at this plant helps mitigate eutrophication risks in the coastal zone.