Plant Information
History
The City of Coralville’s Wastewater Treatment Plant was built in 1969, and the City’s sewer system dates back to the late 1940s. Prior to 1969, the sewage was pumped to the City of Iowa City for treatment through a series of lift stations. In 1975, 1984, 1993, and 2002, there were significant plant upgrades due to increasing flows and changing Department of Natural Resources regulations. The most recent upgrade was complete in 2020.

Operations
The new wastewater treatment facility went on-line in July 2020; the wastewater treatment plant was upgraded and expanded to accommodate City growth to 2030. The new facility includes:

• Headworks building: Raw sewage pumping with screenings and grit removal
• Storm water retention basin: 16 million gallons of storage capacity
• Secondary treatment: Two carrousel oxidation ditches (biological treatment)
• Secondary clarifiers: Two 90’ diameter clarifiers with RAS and WAS pumping
• Disinfection: Ultraviolet (UV) disinfection system
• Learn about wastewater treatment plant improvements

Treatment Process

1. Wastewater enters the Headworks Building where the wastewater goes through preliminary treatment (screening and grit removal).
2. After preliminary treatment, the wastewater is conveyed to the Secondary Treatment Process to remove organic material (BOD) and nutrients (NH3, N and P).
3. After secondary treatment, the mixture of treated wastewater and microorganisms called “activated sludge” flows to the two Secondary Clarifiers to allow the separation of the treated water and the biological mass. 
4. Clear water from the Secondary Clarifiers flow to the UV Disinfection Process and final pumping. The Final Effluent Pumps will pump the clear treated wastewater to the Iowa River.

The biological solids wasted from the process are treated through anaerobic and aerobic processes. These solids (Biosolids) are dewatered and pumped to storage for land application. Land applications occurs twice/year (spring and fall). These Biosolids are considered environmentally beneficial.

Design Parameters
The facility is designed to treat an average daily flow of 5.75 million gallons/day with a maximum wet weather flow of 22.56 million gallons/day. Typical daily flows average 2.65 million gallons/day.