The 2024 ACEC/Iowa Engineering Excellence Awards winning projects in the Water & Wastewater Category, in the order listed:

Water and Wastewater Grand Place Award  (1st Place in Category)


Firm: HR Green
Client/Owner: City of Indianola
Project:  Water Resource Recovery Facility

The City of Indianola’s existing North Wastewater Treatment Facility (NWWTF) was nearing the end of its life. The facility treated residential, commercial, and industrial flows collected and conveyed through the City’s sanitary sewer collection system. The existing NWWTF was not suitable for the additional nutrient removal requirements proposed by the IDNR. In addition, the facility couldn’t treat the original design flow due to failed equipment and numerous processes near collapse or at the end of their useful life. With the current facility beyond its useful life, the aging infrastructure, and stricter regulations, replacing the existing plant was necessary.

In 2014, a Siting Study was completed to evaluate and recommend modifications to the existing wastewater treatment versus building a new treatment facility at a new site. The Farm site included approximately 360 acres of property about 1.5 miles north and west of the existing NWWTF. The location of the treatment plant on the site exceeds all separation distances to any neighbors as required by Iowa Department of Natural Resources (IDNR) regulations. The remaining portion of the site will remain agricultural to protect the rural feel of the neighborhood.

The new Indianola Water Resource Recovery Facility (WRRF) is a $45.6M construction project for treating the City of Indianola’s municipal wastewater just to the north and west of the City in Warren County. The WRRF was designed with innovative technologies to meet the stringent nutrient removal requirements outlined by the Iowa Nutrient Strategy adopted by the State of Iowa. The plant will also use Peak Flow Treatment as a new approach to handling the dilute peak flows that come to the plant during wet weather periods. The use of Peak Flow Treatment for the Indianola WRRF is a first in the State of Iowa. Peak Flow Treatment is an innovative way to handle peak flows but also helps to not oversize the secondary treatment system to handle the normal wastewater flows.

The liquid treatment process includes influent wastewater screening, pumping, and flow measurement at the Headworks Building; the wastewater is then pumped to the Grit Removal Building where vortex grit removal, grit pumping, grit dewatering and sampling are competed. The effluent
leaving the grit removal process for flows up to 6.0 mgd are measured and sent to secondary treatment. Influent wastewater flows greater than 6.0 mgd flow by gravity to the 2.0 MG equalization tank for 1)short term storage and returned to secondary treatment or, 2) processing through Peak
Flow Treatment and then blended with the secondary treatment effluent, disinfected and discharged. The Peak Flow treatment system is expected to be used for peak flows to the treatment plant around 1 percent of the time only. The normal flow to secondary treatment enters an oxidation ditch flow splitter where the flows are mixed with return sludge and split between the two trains of two-stage Oxidation Ditches. The Two-stage Oxidation Ditches use an anoxic cell and an aerobic cell for two stage treatment to remove CBOD, ammonia and Total Nitrogen. Metal salt is also dosed following the oxidation ditches which removes Total Phosphorus by precipitation in the secondary clarifiers. Finally, flow is routed through ultraviolet disinfection where pathogenic organisms are inactivated/ destroyed to prevent the spread of waterborne diseases.

The WRRF incorporates many other features beyond the treatment of the liquid stream.
The following list summarizes some of the additional features:
▪ Solids treatment via aerobic digestion. Aerobic digestion produces a biologically stable end product with low odor and low supernatant organic concentration.
▪ Solids thickening through rotary drum thickeners and liquid storage with glass lined steel biosolids storage tank.
▪ Sustainable land application from biosolids storage tank to nearby farm ground where biosolids can be applied through an umbilical system and used as fertilizer.
▪ Vactor receiving station for accepting septage and waste from tanker trucks.
▪ Process control laboratory used to optimize treatment and obtain high quality effluent.
▪ Administration Building with offices, locker rooms, breakroom, and Emergency Operations Center which can be used for emergency preparedness, emergency management, and disaster management.
▪ Vehicle storage bays in Administration Building with sectional overhead doors, wash bay, working spaces, and mezzanine storage.
▪ Plant effluent water system that utilizes treated effluent to supply water for equipment and wash down needs at the plant. Plant effluent water system also includes facilities to utilize effluent water for irrigation at nearby golf course.
▪ Process control and data acquisition system connected by a fiber optic loop that will allow staff to efficiently operate the plant and interface with process equipment.


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