City of Quincy Wastewater Treatment Plant and Sewage Collection System
Quincy's wastewater treatment facility was designed to treat an average flow of 13.5 million gallons a day (mgd). The plant consists of influent pumping, screening, grit removal, primary treatment, activated sludge treatment, secondary clarification, seasonal disinfection and discharge. Wastewater sludge is thickened through a gravity thickener, anaerobically digested and stored in two sludge holding basins. Periodically, the sludge is applied to agricultural farm land.
Due to the combined sewer system, there are also excess flow facilities consisting of primary treatment followed by a retention basin and disinfection for flows in excess of 34 mgd. The City owns and operates a wastewater collection system that serves an area of approximately 22 square miles. The system is composed of both combined and separate sanitary sewers. Separate sanitary sewers convey sanitary wastewater only and connect to interceptor sewers located along the Mississippi River, which then divert flows to the wastewater plant. Combined sewers convey sanitary wastewater and storm water to these interceptors as well.
The system includes six combined sewer overflows (CSO) that discharge either directly into the Mississippi River or to tributaries located within 0.5 miles from each confluence with the river. Additionally, a discharge point located at the wastewater plant is used to protect the plant if influent flows exceed the treatment capacity of the first flush facility. The wastewater plant's discharge and six CSOs are authorized points of discharge under the City of Quincy's current National Pollutant Discharge Elimination System (NPDES) Permit.
Normally, discharges from these structures only occur during periods of rain when the flow exceeds the collection system's transmission capacity of 78 mgd. Telemetry from each CSO is routed to the wastewater plant to monitor the frequency of overflow and the duration of overflow when active.
Seven lift stations are located throughout the sewer collection system to pump wastewater to gravity sewers which flow to the influent (main) pumping station at the wastewater plant.