Alvalade Wastewater Treatment Plant, Santiago do Cacém, Portugal

Alvalade wastewater treatment plant serves the small agglomeration of Alvalade in the municipality of Santiago do Cacém, Setúbal District, Portugal. The plant provides secondary treatment for a population equivalent of 2,200, with a designed capacity of 2,500 m³/day and an average daily discharge of 366.81 m³/day. As a secondary treatment facility serving fewer than 10,000 people, Alvalade operates under Portugal's implementation of the EU Urban Waste Water Treatment Directive (91/271/EEC). For agglomerations of this size, secondary treatment is the standard requirement, with more advanced treatment needed only if the receiving waters are designated as sensitive areas. The treated effluent from Alvalade flows into the local river system, which drains into the Atlantic Ocean via the Sado River basin. The Sado estuary is an ecologically important area supporting diverse aquatic life, including migratory bird species and fish populations. The plant's inland location reduces direct marine impact, but its discharge contributes to the overall water quality of the Sado watershed.

Alvalade's treated wastewater enters the Sado River basin, which flows into the Sado estuary and ultimately the Atlantic Ocean near Setúbal. The Sado estuary is a productive ecosystem that supports diverse aquatic life, including fish nurseries and migratory birds. The plant's secondary treatment helps protect this downstream environment from excessive nutrient loading and organic pollution.