Hillsborough Wastewater Treatment Plant, Royal Hillsborough, Northern Ireland

Hillsborough wastewater treatment plant was located in Royal Hillsborough, a village in County Down, Northern Ireland. It served a population of around 4,034 people, classifying it as a small agglomeration under EU regulations. The plant is now closed. The plant provided secondary treatment, which is the minimum standard required by the EU Urban Waste Water Treatment Directive (91/271/EEC) for freshwater discharges from agglomerations of this size. The designed capacity was 4,046 m³/day, with an average discharge volume of 898 m³/day. The treated effluent was discharged into a local watercourse that flows into the River Lagan and eventually into Belfast Lough, an important coastal estuary. The plant's operation helped protect the Lagan catchment and downstream marine environment from nutrient pollution.

The plant discharged into a tributary of the River Lagan, which flows through County Down and into Belfast Lough, a sea inlet of the Irish Sea. The Lagan catchment supports diverse aquatic life and is used for recreation. Downstream, Belfast Lough is an important habitat for migratory birds and marine species. The plant's secondary treatment helped reduce organic load and protect water quality in this sensitive coastal ecosystem.