Iowa City Wastewater Treatment Plant Expansion

Cost: $50.2 million
Location: Iowa City, Iowa
Year: 2015-12-09
Size: 24 mgd
Owner: City of Iowa City
Designers: Stanley Consultants Inc., Brown & Caldwell
Contractor: Joseph J. Henderson & Son Inc.

As part of a nearly 40-year effort to move all wastewater operations out of the city’s core, the city of Iowa City, Iowa, embarked on a $50.2 million project to expand its South Wastewater Treatment Plant. The expansion was designed to improve the existing plant’s safety, sustainability and energy efficiency, and enable economic growth and development within the city. 

The expansion allowed for closure of an aging downtown plant, eliminating the risk of sewage release during flooding. It also doubled the South Plant’s treatment capacity to 24 million gal per day, allowing for significant city growth and meeting strict ammonia limits.

The expansion includes multiple process and equipment enhancements that improve efficiency and sustainability. A bio-augmentation reaeration system—the first in the state—decreases the amount of tank space necessary for treatment and reduces high ammonia concentrations from digested sludge dewatering. Single-stage centrifugal blowers and enhanced system controls reduce energy use. Additionally, a new ultraviolet disinfection process replaces the chlorine gas and sulfur dioxide process, eliminating potential hazards posed by the transportation and use of the chemicals. 

Due in part to a large personal care products manufacturer nearby, the plant deals with significant scum/foaming. The expansion incorporated surface film waste and skimming, and return-activated sludge chlorination with hypochlorite to keep the foam, scum and filamentous blooms under control. 

Because the project combined two plants and two discharge points into one plant and one discharge point, the Iowa Department of Natural Resources permitting process was further complicated. The team demonstrated that moving to a single plant would not result in additional impact to the Iowa River.

Construction began in 2012 and was completed in May 2014. 

“[The project] gets us out of the flood risk. It gets us out of an 80-year-old facility that was becoming harder and harder to maintain. It took advantage of funding sources that were available,” said Dave Elias, plant superintendent. “We took advantage of all of that to move the project forward for the community, which puts us in a position where we have capacity for economic development. So we are well positioned for the future.”