Knoxville STP Wastewater Treatment Plant, Knoxville, Illinois

Knoxville STP is a municipal wastewater treatment plant located at 663 South Division Street in Knoxville, Illinois, serving a population of about 3,854. The facility is situated in Knox County, a rural area in western Illinois, and is part of the state's wastewater infrastructure managed under the U.S. Environmental Protection Agency's National Pollutant Discharge Elimination System (NPDES) permit program. As a small-scale treatment plant, Knoxville STP is subject to the Clean Water Act's secondary treatment standards, which mandate the removal of at least 85% of biochemical oxygen demand and suspended solids. Plants of this size typically employ conventional activated sludge or lagoon systems to meet permit requirements. Its population served indicates a small agglomeration. The plant discharges treated effluent into a local waterway that ultimately drains into the Mississippi River basin. The receiving water body supports aquatic life and is part of the larger Illinois River watershed, which flows into the Mississippi River and eventually the Gulf of Mexico. Protecting water quality in this region is important for downstream ecosystems and recreational uses.

The treated effluent from Knoxville STP likely discharges into a tributary of the Spoon River or directly into the Illinois River basin, which flows southwest to the Mississippi River. The Mississippi River is a major ecological corridor supporting diverse fish, bird, and plant species. Downstream, the river system contributes to the Gulf of Mexico's hypoxic zone, making nutrient management a regional concern. The plant's location inland, over 50 km from the coast, reduces direct marine impact but still plays a role in the broader watershed health.