Gross Wittensee Wastewater Treatment Plant, Klein Wittensee, Schleswig-Holstein

The Gross Wittensee wastewater treatment plant is located in Klein Wittensee, a municipality in the Hüttener Berge area of Schleswig-Holstein, Germany. It serves a population of approximately 5,120 and has a designed capacity of 6,400 cubic meters per day, with an average discharge volume of 482.5 m³/day. As an advanced treatment facility, it goes beyond secondary treatment to remove nutrients such as nitrogen and phosphorus, which is typical for plants in sensitive catchment areas. Under the EU Urban Waste Water Treatment Directive (91/271/EEC), agglomerations of this size (5,120 PE) are required to provide secondary treatment, but Germany often mandates tertiary or advanced treatment to protect water quality in the Baltic Sea catchment. The plant discharges treated effluent into local watercourses that eventually drain into the Baltic Sea via the Schlei or Eckernförde Bay. The region's watershed supports diverse aquatic life and is part of a sensitive coastal ecosystem where nutrient reduction is critical to prevent eutrophication.

The plant's treated effluent flows into small streams in the Hüttener Berge region, which drain into the Baltic Sea via the Schlei inlet or Eckernförde Bay. The Baltic Sea is a semi-enclosed, brackish water body highly sensitive to nutrient inputs, where advanced treatment helps reduce algal blooms and oxygen depletion. The local watershed supports diverse freshwater and coastal habitats, including wetlands and migratory bird routes.