Margem Sul_Rossio ao Sul do Tejo Wastewater Treatment Plant, Abrantes, Portugal

Margem Sul_Rossio ao Sul do Tejo is a municipal wastewater treatment plant located in São Miguel do Rio Torto e Rossio ao Sul do Tejo, Abrantes, Santarém District, Portugal. The plant serves a population of approximately 3,000 residents, classifying it as a small agglomeration under EU standards. It is situated inland, away from coastal areas, and its operations are part of the broader water management infrastructure in the Tagus River region. The plant provides 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 5,169 cubic meters per day and an average daily discharge volume of about 500 cubic meters, the facility operates well below its capacity, indicating room for future growth or seasonal variability. Secondary treatment typically involves biological processes to reduce organic matter and suspended solids. The treated effluent is discharged into local watercourses that ultimately flow into the Tagus River, one of the Iberian Peninsula's major rivers. The Tagus River drains into the Atlantic Ocean near Lisbon, supporting diverse aquatic ecosystems and providing water for agriculture, industry, and urban use. The plant's operations help protect downstream water quality and ecological health in the Tagus basin.

The plant discharges into local streams that feed the Tagus River, which flows westward through Portugal to the Atlantic Ocean near Lisbon. The Tagus estuary is an ecologically sensitive area supporting migratory birds, fish, and diverse aquatic life. The plant's secondary treatment helps reduce organic pollution and nutrient loads, mitigating eutrophication risks in the river and estuary.