Osiek Maly Wastewater Treatment Plant - Osiek Mały-Kolonia, Wielkopolskie, Poland

The Osiek Maly wastewater treatment plant is located in Osiek Mały-Kolonia, a village in the powiat kolski of województwo wielkopolskie, Poland. It serves a population of 1,789 and has a designed capacity of 3,228 m³/day, with a current discharge volume of 255.08 m³/day. The plant is situated inland, away from coastal areas. The plant provides primary treatment, which involves physical processes such as sedimentation to remove settleable solids. Under the EU Urban Waste Water Treatment Directive (91/271/EEC), agglomerations with a population equivalent (PE) between 2,000 and 10,000 are generally required to have secondary treatment. However, Poland's implementation may include transitional arrangements for smaller plants. The plant's current treatment level is primary, which is below the typical standard for its size. The treated effluent is discharged into local watercourses that eventually drain into the Warta River basin, a major tributary of the Oder River, which flows into the Baltic Sea. The plant plays a role in protecting the local watershed from untreated wastewater, though the primary treatment level may not fully address nutrient loads or organic pollutants.

The plant discharges into local streams that are part of the Warta River catchment, a key sub-basin of the Oder River system. The Oder flows into the Szczecin Lagoon and then the Baltic Sea. The region supports diverse aquatic life, and nutrient loading from insufficiently treated wastewater can contribute to eutrophication in downstream water bodies. The plant's primary treatment provides limited removal of nitrogen and phosphorus, which are critical for maintaining water quality in the Baltic Sea ecosystem.