CYLINDER STL Wastewater Treatment Plant, Palo Alto County, Iowa

CYLINDER STL is a municipal wastewater treatment facility located in Palo Alto County, Iowa, United States. Serving a small population of 112 residents, the plant provides secondary treatment to meet federal and state water quality standards. Its designed capacity matches the current discharge volume of 37.85 units, indicating stable operation for this rural community. The plant employs secondary treatment, a biological process that removes organic matter and suspended solids. As a small facility in the U.S., it operates under the National Pollutant Discharge Elimination System (NPDES) permitting program, which sets effluent limits to protect receiving waters. The Clean Water Act requires secondary treatment for municipal plants, ensuring compliance with water quality goals. The treated effluent is discharged into local waterways that drain into the Des Moines River basin, ultimately reaching the Mississippi River and the Gulf of Mexico. This plant helps protect downstream aquatic ecosystems by reducing nutrient and pollutant loads, supporting regional water quality in the agricultural landscape of northern Iowa.

The plant discharges into tributaries of the Des Moines River, which flows southeast to the Mississippi River and into the Gulf of Mexico. This watershed supports diverse aquatic life and is part of the Mississippi River basin, a critical migratory corridor for fish and birds. The surrounding area is predominantly agricultural, so the plant's nutrient removal helps mitigate downstream eutrophication risks in the Gulf of Mexico's hypoxic zone.