Pernes Wastewater Treatment Plant, São Vicente do Paul, Santarém

Pernes is a wastewater treatment plant located in São Vicente do Paul, within the municipality of Santarém, Portugal. The facility serves a population of approximately 2,000 people, classifying it as a small agglomeration under Portuguese and EU standards. The plant operates with secondary treatment, which is the minimum required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for freshwater discharges from agglomerations of this size. With a designed capacity of 2,848 m³/day and an actual discharge volume of 333.46 m³/day, the plant operates well below its capacity, indicating room for future growth. The treated effluent is discharged into a local watercourse that ultimately drains into the Tagus River basin, one of the most important river systems in Portugal. The Tagus River flows westward to the Atlantic Ocean near Lisbon, supporting diverse aquatic ecosystems and providing water for agriculture and urban use downstream.

The plant's discharge enters a tributary of the Tagus River, which flows through central Portugal and forms the Tagus Estuary, a vital ecological zone for migratory birds and fish species. The estuary supports extensive salt marshes and mudflats that provide critical habitat for aquatic life. Downstream, the river meets the Atlantic Ocean, contributing to coastal water quality in the Lisbon region.