COV Dolny Stal Wastewater Treatment Plant, Dolný Štál, Slovakia

COV Dolny Stal is a municipal wastewater treatment plant located in Dolný Štál, a village in the Trnavský kraj region of western Slovakia. The plant serves a small population of 720 residents and operates with secondary treatment, which is the standard biological treatment stage required under the EU Urban Waste Water Treatment Directive (UWWTD) for agglomerations of this size. The plant has a designed capacity of 1000 cubic meters per day and discharges a daily volume of approximately 147 cubic meters, indicating low capacity utilization. As a small-scale facility, it is subject to Slovak national regulations that transpose the EU UWWTD, which mandates secondary treatment for all discharges from agglomerations above 2000 population equivalent, though smaller plants may have specific national requirements. The treated effluent from COV Dolny Stal likely discharges into a local watercourse that drains into the Danube River basin, ultimately reaching the Black Sea. The plant plays a key role in protecting local surface waters from untreated sewage, supporting the ecological health of the region's agricultural landscape and downstream aquatic habitats.

The plant is situated in the Danubian Lowland, a flat agricultural region in southwestern Slovakia. Its treated effluent flows into local canals and streams that are part of the Váh River basin, a major tributary of the Danube. The Danube River carries the water through Hungary, Croatia, Serbia, and Romania before reaching the Black Sea. The region's groundwater and surface waters are sensitive to nutrient pollution from agriculture, making the plant's secondary treatment important for reducing organic load and protecting downstream ecosystems.