South Beloit STP: Wastewater Treatment Plant in South Beloit, Illinois

South Beloit STP is a municipal wastewater treatment plant located at 117 Perry Avenue in South Beloit, Illinois, serving a population of about 17,100. The plant is part of the region's wastewater infrastructure, handling domestic and industrial flows from the community. As a US facility, South Beloit STP operates under the National Pollutant Discharge Elimination System (NPDES) permit program, which sets effluent limits based on the Clean Water Act. For a plant of this scale, secondary treatment is typically required, with additional nutrient controls if discharging to sensitive waters. The plant's treated effluent is discharged into the Rock River watershed, which flows southwest to the Mississippi River and ultimately to the Gulf of Mexico. The Rock River supports diverse aquatic life and is used for recreation, making effective treatment important for downstream water quality.

The plant discharges into the Rock River basin, a tributary of the Mississippi River. The Rock River flows through northern Illinois and southern Wisconsin, supporting fish populations and recreational activities. Downstream, the Mississippi River carries the flow to the Gulf of Mexico, where nutrient loading contributes to seasonal hypoxia. Effective treatment at South Beloit STP helps reduce local and downstream impacts.