Wilsonville Wastewater Treatment Plant (OR)


  • $83.7 million ($35.7 million capital and $2.4 million yearly O&M for 20 years) design-build-operate project to update and expand the City’s aging sewage treatment plant
  • Scope includes 2.5mgd to 4mgd immediate expansion, with future expansion capabilities to 7mgd that will produce Class A biosolids for land application
  • Selected treatment process includes a new headworks and grit removal system, followed by contact stabilization with anaerobic selectors, secondary clarifiers, cooling towers, cloth disk filtration, ultraviolet (UV) disinfection, and odor control of all major odor sources, replacing and upgrading most portions of the original plant constructed in the early 1970s
  • Operating the plant through construction and for 20 years following construction completion in 2014

The life-cycle of the City of Wilsonville’s single wastewater treatment plant is coming to a close as the City garners for continued growth and the need to accommodate future capacity. In addition, odor and discharge quality concerns were receiving greater attention from the community as well as ongoing and increasing operations costs. To resolve these issues and provide a long-term, cost-effective solution that also limited risks for the City, Wilsonville selected Jacobs to provide design-build upgrades and expansion of the WWTP and ongoing operations under contract for a minimum of 20 years.

Odor control issues addressed

Odor control was a key project driver, as the facility was previously faced with odor control issues that impacted the surrounding community. Jacobs’ solution directs foul air from the fully enclosed headworks, bioreactor, and dewatering and drying building to a new engineered media biofilter.

The project design goal provides a robust, flexible, and easy to operate wastewater treatment and solids handling system. The Wilsonville WWTP design reuses the existing secondary, thickening and disinfection systems in their entirety, as well as the solids storage tanks for solids storage and odor control. Our proposed design also includes a headworks and grit removal system, with the following subsequent process facilities:

  • Contact stabilization secondary treatment with anaerobic selector
  • Secondary clarifiers
  • Secondary effluent filtration
  • Summer time cooling with cooling towers
  • Ultraviolet (UV) disinfection
  • Thickening, dewatering, and drying with the existing gravity belt thickeners, new centrifuge dewatering, and sludge dryers
  • Odor control of all major odor sources

This treatment process was selected because of the benefits it offers in terms of reliability, simplicity, flexibility, sustainability, odor control, and cost. Jacobs assumed operations of the facility in September 2011 and will operate it through construction and for the following 20 years after construction is complete. Design was completed in early 2012 and construction started in March 2012. By November 2012, the project was 33% complete and over 90,000 work hours completed without any safety incidents. The project was completed in 2014.