S Silvestre Wastewater Treatment Plant, Coimbra, Portugal

S Silvestre is a municipal wastewater treatment plant located in the São Silvestre parish of Coimbra, Portugal. It serves a population of approximately 4,600 residents and has a designed capacity of 4,800 cubic meters per day, with an average discharge volume of 766.96 cubic meters per day. The plant provides secondary treatment, which is the standard biological treatment required under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. As a secondary treatment facility, it removes organic matter and suspended solids, meeting the directive's requirements for inland discharge. The treated effluent is discharged into the local watershed, which ultimately drains into the Atlantic Ocean via the Mondego River basin. The plant's inland location, more than 10 km from the coast, reduces direct marine impact, but its discharge contributes to the overall water quality of the Mondego River, which supports diverse aquatic life and is an important ecological corridor in central Portugal.

The plant discharges into the Mondego River basin, which flows through Coimbra and reaches the Atlantic Ocean near Figueira da Foz. The Mondego is the longest river entirely within Portugal and supports a variety of fish species, including migratory fish like the European eel and lamprey. The river's estuary is an important habitat for waterbirds and aquatic life, making the plant's secondary treatment crucial for maintaining downstream water quality.