Walnut STP - Secondary Wastewater Treatment Plant in Walnut, Illinois

Walnut STP is a municipal wastewater treatment facility located in Walnut, Bureau County, Illinois, United States. The plant serves a population of approximately 1,522 residents and operates under secondary treatment standards, which is the minimum required by the US Clean Water Act for municipal wastewater treatment. The plant's designed capacity is 813.86 thousand cubic meters per year, with an actual discharge volume of 643.52 thousand cubic meters, indicating operational headroom. As a US facility, it operates under the National Pollutant Discharge Elimination System (NPDES) permit program, which sets effluent limits to protect water quality. The treated effluent is discharged into a local receiving water body, which ultimately drains into the Mississippi River Basin. The plant plays a key role in protecting downstream water quality in the Illinois River watershed, supporting aquatic life and recreational uses.

Walnut STP discharges into a tributary of the Illinois River, which flows into the Mississippi River. The Illinois River watershed supports diverse aquatic ecosystems, including fish and migratory birds. The plant's secondary treatment helps reduce organic pollutants and suspended solids, protecting downstream water quality in this agriculturally intensive region.