S Catarina Wastewater Treatment Plant, Caldas da Rainha, Portugal

S Catarina is a wastewater treatment plant located in Caldas da Rainha, Leiria District, Portugal. It serves a population of approximately 2,200 people, classifying it as a small agglomeration under Portuguese and EU regulations. The plant operates secondary treatment, which is the standard minimum for such communities under the EU Urban Waste Water Treatment Directive (91/271/EEC). The plant has a designed capacity of 2,250 m³/day and currently discharges an average of 366.81 m³/day of treated effluent. As a coastal facility within 10 km of the Atlantic Ocean, the plant must meet stringent discharge standards to protect marine water quality. Secondary treatment typically removes organic matter and suspended solids, but does not include nutrient removal unless required by sensitive area designation. The treated wastewater from S Catarina ultimately reaches the Atlantic Ocean via local watercourses. The coastal zone of central Portugal supports diverse marine life and is important for fisheries and tourism. Proper treatment at this plant helps prevent eutrophication and maintains water quality in the nearshore environment.

The plant discharges into local streams that flow to the Atlantic Ocean near Caldas da Rainha. This coastal region is part of the Portuguese western seaboard, characterized by sandy beaches and rocky shores that support diverse marine ecosystems, including fish nurseries and seabird habitats. The area is also used for recreation and shellfish harvesting, making effective wastewater treatment critical to prevent nutrient loading and pathogen contamination.