Tarnsjo Avloppsreningsverk - Advanced Wastewater Treatment in Tärnsjö, Sweden

Tarnsjo Avloppsreningsverk is a wastewater treatment facility located in Tärnsjö, a locality in Heby kommun, Uppsala län, Sweden. The plant serves a population of around 2,728, classifying it as a small agglomeration under EU regulations. Its advanced treatment level ensures high-quality effluent discharge, meeting stringent environmental standards. The plant has a designed capacity of 11,500 cubic meters per day and currently treats an average daily volume of 428.24 cubic meters, indicating significant spare capacity. As a Swedish facility, it operates under the national implementation of the EU Urban Waste Water Treatment Directive (91/271/EEC), which mandates secondary treatment as a minimum and tertiary treatment in sensitive areas. The advanced treatment level suggests the plant employs processes such as nutrient removal to protect the local water environment. The treated effluent is discharged into the local watershed, which ultimately drains into the Baltic Sea via the Dalälven river system. The Baltic Sea is a brackish water body with sensitive ecological conditions, making nutrient removal critical to prevent eutrophication. The plant's advanced treatment helps reduce the load of nitrogen and phosphorus, supporting the health of downstream aquatic ecosystems.

Tarnsjo Avloppsreningsverk discharges into the local catchment that feeds into the Dalälven river, one of Sweden's major rivers, which flows into the Baltic Sea. The Baltic Sea is a semi-enclosed brackish sea highly sensitive to nutrient pollution, where excess nitrogen and phosphorus can cause algal blooms and oxygen depletion. The plant's advanced treatment, including nutrient removal, plays a vital role in protecting this ecologically important water body.