Cairo STP Wastewater Treatment Plant, Cairo, Illinois | US Clean Water Act

Cairo STP is a municipal wastewater treatment plant located in Cairo, Illinois, a small city at the confluence of the Mississippi and Ohio Rivers. The facility serves a population of about 6,552 residents, typical of a small agglomeration in the United States. Its location in the Mississippi River Valley places it within a region of significant ecological and hydrological importance. As a US-based plant, Cairo STP operates under the Clean Water Act, which requires National Pollutant Discharge Elimination System (NPDES) permits for all point-source discharges. For plants serving populations under 10,000, secondary treatment is the standard requirement, though specific treatment levels and capacities are determined by state-issued permits. The plant's design and operational details are managed by local municipal authorities. The treated effluent from Cairo STP ultimately drains into the Mississippi River, a major waterway that flows into the Gulf of Mexico. This river system supports diverse aquatic life and is a critical migratory corridor for fish and birds. The plant's discharge contributes to the overall water quality of the Mississippi basin, which faces challenges from nutrient loading and sediment transport downstream.

Cairo STP discharges into the Mississippi River, which flows southward to the Gulf of Mexico. The Mississippi River basin is one of the largest watersheds in North America, supporting diverse ecosystems including wetlands, floodplain forests, and aquatic habitats. The river is a vital migratory route for birds and fish, and its delta region is ecologically sensitive due to nutrient pollution and hypoxia. The plant's location near the confluence of the Mississippi and Ohio Rivers adds to the complexity of local water quality management.