Mariefreds Avloppsreningsverk - Advanced Wastewater Treatment in Mariefred, Sweden

Mariefreds Avloppsreningsverk is a municipal wastewater treatment facility located in Mariefred, Strängnäs municipality, Södermanland County, Sweden. The plant serves a population of approximately 4,363 and operates with advanced treatment processes, ensuring high-quality effluent. Its designed capacity is 9,500 cubic meters per day, with an average discharge volume of 684.91 cubic meters per day. As an advanced treatment plant, it meets stringent Swedish and EU standards under the Urban Waste Water Treatment Directive (91/271/EEC), which requires tertiary treatment for sensitive areas. The plant's advanced level indicates it likely employs nutrient removal (nitrogen and phosphorus) to protect the receiving waters. The plant discharges treated wastewater into the local watershed, which ultimately drains into Lake Mälaren, Sweden's third-largest lake. Lake Mälaren is a vital freshwater resource and supports diverse aquatic life, recreational activities, and serves as a drinking water source for Stockholm. The plant's coastal proximity (within 10 km) underscores the importance of its advanced treatment in preventing eutrophication.

The plant discharges into the Lake Mälaren basin, which flows eastward through Stockholm and into the Baltic Sea. Lake Mälaren is a large, oligotrophic to mesotrophic lake that supports diverse fish populations and serves as a critical drinking water reservoir. The advanced treatment at this plant helps reduce nutrient loading, mitigating the risk of algal blooms and protecting downstream ecosystems in the Baltic Sea.