Environment, Energy, North America, Water, United States, Sustainability
Water + Energy
Supporting Sustainable Growth
Des Moines Metropolitan Wastewater Reclamation Authority digester improvement project
Des Moines, Iowa, is the state’s most populous city and the seat of Polk County. Approximately 600,000 people live in the metropolitan area, a growing regional hub for industries including finance, insurance, transportation and agriculture.
This AAEES award-winning project helps the utility and surrounding communities handle waste responsibly—creating energy, minimizing carbon emissions and reducing pollution—and providing a viable model for other cities.
To support the region’s increasing needs, Des Moines Metropolitan Wastewater Reclamation Authority (WRA) has grown its hauled-waste program over the past 10 years from a pilot facility to a full-scale operation, receiving up to 70 tankers of hauled waste per day. This service supports businesses that lack the technology or resources to process their own waste—providing an environmentally responsible alternative to typical waste removal, and creating valuable energy.
CDM Smith partnered with WRA to create a bioenergy master plan and upgrade facilities, using life-cycle analysis to improve the waste-receiving facilities and anaerobic-treatment process used at its 97million gallon-per-day wastewater treatment facility.
The project team provided design, construction services and training, also developing a process-economics model to help WRA assess the economic benefits of different wastes and alternative uses for the biogas produced. These improvements will expand, improve and support efficient operations at the facility—a growing regional hub for hauled waste processing—for the next 20 years.
Improvements to the facility included concrete, submerged-fixed covers that accommodate various high-strength wastes including fats, oils, grease, dairy, biodiesel and ethanol production byproducts. Hauled wastes can generate excessive foam in the digestion process, and submerged covers help control and remove the foam—reducing its impact on the process. The covers maximize digester tank volume, allowing WRA to serve a wide range of utility and industrial customers.
To support the 115-foot diameter concrete digester covers and center dome system, an extensive column support system was designed, including four center columns to support the dome system and eight columns placed around the perimeter.
An efficient mixing system was also essential to the project, because the anaerobic digesters process a variety of wastes. Computational fluid dynamic (CFD) modeling was used to evaluate multiple mixing systems for the five primary digesters and optimize the size of the selected stream. The design team used CFD modeling to size the mixers, rather than using industry standard rules that would have resulted in larger, more expensive mixers.
Ensuring that WRA remains the preferred hauled-in waste facility in Iowa means that less waste will be discharged to collections systems. This AAEES award-winning project helps the utility and surrounding communities handle waste responsibly—creating energy, minimizing carbon emissions and reducing pollution—and providing a viable model for other cities.