Mill Green Hatfield Herts STW - Wastewater Treatment in Welwyn Hatfield, Hertfordshire

Mill Green Hatfield Herts STW is a wastewater treatment plant located in Mill Green, Hatfield, within the Welwyn Hatfield district of Hertfordshire, England. It serves a population of around 20,200, classifying it as a medium-sized agglomeration under UK regulatory frameworks. The plant operates under the UK's implementation of the EU Urban Waste Water Treatment Directive (91/271/EEC), which requires secondary treatment for discharges to freshwater and estuaries from agglomerations of this size. The regulatory framework ensures appropriate standards are met to protect the receiving environment. The treated effluent is discharged into local watercourses that ultimately drain into the River Lea catchment, which flows south to the River Thames and into the North Sea. The plant plays a key role in maintaining water quality in the Lea Valley, a region supporting diverse aquatic life and recreational activities.

The plant discharges into the River Lea catchment, which flows through Hertfordshire and into the River Thames estuary, eventually reaching the North Sea. The Lea Valley is an ecologically important corridor supporting wetlands, birdlife, and fish species. The plant's treatment helps protect downstream habitats, including the Lee Valley Regional Park, a major green space with reservoirs and nature reserves.