Annawan STP - Secondary Wastewater Treatment Plant in Annawan, Illinois

Annawan STP (Sewage Treatment Plant) is a municipal wastewater facility located at 298 North Main Street in Annawan, Henry County, Illinois. It serves a small population of 886 people, consistent with the rural character of the community. The plant operates under the regulatory framework of the U.S. Clean Water Act, which requires secondary treatment for municipal discharges. The plant provides secondary treatment, a standard biological process that removes organic matter and suspended solids. With a designed capacity of 605.66 m³/day and an actual discharge volume of 302.83 m³/day, the facility operates at about 50% capacity, indicating room for future growth. As a U.S. facility, it operates under an NPDES permit issued by the Illinois Environmental Protection Agency, which sets effluent limits to protect water quality. The treated effluent from Annawan STP is discharged to a local water body that ultimately drains into the Mississippi River Basin. The plant plays a key role in protecting downstream aquatic ecosystems, including the Illinois River and the Upper Mississippi River, by reducing nutrient and pollutant loads. Its location in the agricultural heartland of the Midwest means the plant helps mitigate impacts on regional water quality.

Annawan STP discharges into a local stream that flows into the Green River, a tributary of the Rock River, which joins the Mississippi River near the Quad Cities. The Mississippi River in this reach supports diverse aquatic life, including fish and mussel species, and is an important migratory corridor for waterfowl. The plant's secondary treatment helps reduce organic pollution and nutrient loading, protecting downstream water quality in the Illinois River Basin.