Nelas Sul Nascente Nelas Terceira Wastewater Treatment Plant, Nelas, Portugal

Nelas Sul Nascente Nelas Terceira is a wastewater treatment plant located in Nelas, Viseu District, Portugal. It serves a population of approximately 2,500 people, classifying it as a small agglomeration under Portuguese and EU regulations. The plant is situated inland, away from coastal areas, and its operations are part of the municipal sanitation infrastructure for the region. The plant provides secondary treatment, which is the minimum standard required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for freshwater discharges from agglomerations of this size. Secondary treatment typically involves biological processes to reduce organic matter and suspended solids. The plant has a designed capacity of 2,500 m³/day and currently discharges 416.83 m³/day, indicating it operates well below its capacity. The treated effluent is discharged into a local watercourse that ultimately drains into the Mondego River basin, one of the major river systems in central Portugal. The Mondego River flows westward to the Atlantic Ocean near Figueira da Foz. The plant's operations help protect the water quality of the receiving waters, supporting aquatic life and downstream uses such as agriculture and recreation.

The plant discharges into a tributary of the Mondego River, which flows through the Viseu region and empties into the Atlantic Ocean. The Mondego basin supports diverse aquatic habitats and is important for irrigation and drinking water supply. The plant's secondary treatment reduces organic pollution, helping to maintain ecological balance in the river system and prevent eutrophication in downstream coastal waters.