UWWTP_ROSALNICE Wastewater Treatment Plant, Metlika, Croatia

UWWTP_ROSALNICE is a wastewater treatment plant located in Rosalnice, near Metlika, Croatia. It serves a small population of 157 people and is designed with a capacity of 600 m³/day, currently discharging an average of 43.84 m³/day of treated effluent. The plant provides secondary treatment, which is the standard level required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations with a population equivalent below 2,000. This directive ensures that wastewater is treated to reduce organic matter and suspended solids before discharge. The treated effluent is discharged into the local water system, which ultimately drains into the Kolpa River (Kupa in Croatian), a tributary of the Sava River. The Sava flows into the Danube, which reaches the Black Sea. The plant plays a key role in protecting the water quality of the Kolpa River, which supports diverse aquatic life and is used for recreation.

The plant discharges into the local watershed that feeds the Kolpa River, a significant watercourse forming part of the border between Croatia and Slovenia. The Kolpa River is known for its clean waters and supports a variety of fish species and aquatic habitats. Downstream, the river joins the Sava, which flows into the Danube and ultimately the Black Sea. The plant's secondary treatment helps reduce nutrient and organic pollution, safeguarding the ecological health of this transboundary river system.