Alhambra STP Wastewater Treatment Plant, Madison County, Illinois

Alhambra STP is a municipal wastewater treatment facility located in Madison County, Illinois, United States. The plant serves a small population of 603 residents, reflecting its role in a rural or small community setting within the state. As a secondary treatment plant, it provides biological treatment to remove organic matter and suspended solids, meeting the standard requirements under the U.S. Clean Water Act for such facilities. The plant has a designed capacity of 378.54 megaliters and treats an annual discharge volume of 227.13 megaliters, indicating operational capacity utilization. Under the U.S. National Pollutant Discharge Elimination System (NPDES), plants of this scale are typically permitted by the Illinois Environmental Protection Agency, ensuring compliance with effluent limits that protect water quality. The treatment process aligns with secondary treatment standards, which are the baseline for municipal wastewater plants in the United States. The treated effluent is discharged into local waterways that ultimately drain into the Mississippi River basin, a major hydrological system that flows into the Gulf of Mexico. The plant's operations contribute to protecting downstream aquatic ecosystems, including the Mississippi River's diverse habitats and the Gulf's marine environment. Proper treatment helps reduce nutrient loading and other pollutants that could impact water quality and ecological health in these sensitive areas.

The plant discharges into local streams that are part of the Mississippi River watershed, which drains a vast area of the central United States before reaching the Gulf of Mexico. The Mississippi River supports diverse aquatic life and is a critical migratory corridor for fish and birds. Downstream, the Gulf of Mexico experiences seasonal hypoxic zones linked to nutrient pollution, making effective wastewater treatment important for reducing nitrogen and phosphorus loads that contribute to algal blooms and oxygen depletion.