Melides Wastewater Treatment Plant, Grândola, Portugal - Coastal Secondary Treatment Facility

The Melides wastewater treatment plant is located in the parish of Melides, within the municipality of Grândola, in the Setúbal District of Portugal. Designed to serve a population of 600, this facility provided secondary treatment for the local community before its closure. As a secondary treatment plant, Melides met the minimum treatment requirements under the EU Urban Waste Water Treatment Directive (91/271/EEC) for agglomerations of this size. The directive mandates secondary treatment for all discharges from agglomerations with a population equivalent (PE) above 2,000, but smaller plants like Melides may be subject to national regulations. The plant's designed capacity of 789 cubic meters per day suggests it was sized to handle peak flows from the small coastal community. The plant's proximity to the Atlantic Ocean (within 10 km of the coast) means its treated effluent would have discharged into a coastal environment, potentially affecting local marine ecosystems. The area is characterized by sandy beaches and dunes, with the Melides Lagoon (Lagoa de Melides) being a nearby coastal lagoon of ecological importance.

The Melides plant is situated near the Atlantic coast of Portugal, within the watershed of the Melides Lagoon, a coastal lagoon that supports diverse aquatic life and serves as a habitat for migratory birds. The lagoon connects to the Atlantic Ocean, and any treated effluent from the plant would have entered this sensitive coastal ecosystem. The region's Mediterranean climate, with dry summers and wet winters, influences the lagoon's salinity and water levels, making proper wastewater treatment critical to prevent nutrient enrichment and algal blooms.