Arruda dos Vinhos Wastewater Treatment Plant | Secondary Treatment, Tagus Basin

Arruda dos Vinhos wastewater treatment plant is located in the Lisbon district of Portugal, serving the town of Arruda dos Vinhos and surrounding areas. The plant provides secondary treatment for a population equivalent of 5,400, with a designed capacity of 8,016 m³/day and an average daily discharge of 900.35 m³/day. As a secondary treatment facility, the plant meets the standard requirements under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. The directive mandates secondary treatment for all discharges from agglomerations with a population equivalent above 2,000, which this plant complies with. The treated effluent is discharged into local watercourses that ultimately drain into the Tagus River basin, one of the most important river systems in the Iberian Peninsula. The Tagus River flows westward through Portugal and empties into the Atlantic Ocean near Lisbon, supporting diverse aquatic ecosystems and providing water for agriculture and urban use.

The plant discharges into the Tagus River basin, which drains into the Atlantic Ocean near Lisbon. The Tagus estuary is a critical habitat for migratory birds and supports rich biodiversity, including fish species such as sea bass and sole. The plant's secondary treatment helps reduce organic pollution and nutrient loads, protecting downstream water quality in this ecologically sensitive watershed.