Darwen STW Wastewater Treatment Plant, Darwen, Lancashire

Darwen STW is a municipal wastewater treatment facility located in Darwen, Lancashire, England. The plant serves a population of around 32,176, placing it in the medium agglomeration category under UK and EU classifications. It is situated inland, away from the coast, and discharges into local watercourses that ultimately drain into the Irish Sea via the River Ribble and its estuary. As a plant serving a population equivalent of over 15,000, Darwen STW is subject to the Urban Waste Water Treatment Directive (91/271/EEC) as transposed into UK law. This directive requires secondary treatment for such agglomerations, with additional nutrient removal if the receiving waters are designated as sensitive areas. The regulatory framework ensures compliance with discharge standards. The treated effluent from Darwen STW is discharged into the local river system, which flows into the River Ribble and eventually the Irish Sea. This water body supports diverse aquatic life and is important for regional biodiversity. The plant plays a key role in protecting water quality in the Ribble catchment, which is used for recreation and supports salmonid fisheries.

Darwen STW discharges into the River Darwen, a tributary of the River Ribble, which flows into the Ribble Estuary and then the Irish Sea. The Ribble catchment is ecologically significant, supporting salmon and trout populations, and the estuary is a vital habitat for migratory birds. The plant's operations help maintain water quality in this sensitive environment, reducing nutrient loads that could cause eutrophication in the estuary.