City of St. Cloud Wastewater Treatment Facility Rehabilitation, Upgrade & Expansion Project

Cost: $41 million
Location: St. Cloud, Minn.
Year: 2014-12-15
Size: 17.9 mgd
Owner: City of St. Cloud
Designers: Black & Veatch
Contractor: Knutson Construction, Shank Constructors

Built in 1976, the St. Cloud (Minn.) Wastewater Treat­ment Facility leases its capacity to five surrounding cities. The aging facility was rehabilitated for mechanical and electrical reliability, increasing its treatment capacity to 17.9 million gal per day. The project also included the addition of a biological nutrient removal (BNR) treatment process for the removal of nitrogen and phosphorous. 

The main electrical power feed to the facility was moved to a new building and a 2,000-kW generator was installed. A modified Johannesburg process—which included an anaerobic recycle, a mixed liquor recycle, low-energy vertical mixers and a series of baffles walls—also was included in the upgrade. 

To increase capacity, a fourth treatment train was added and existing final classifiers were repurposed as additional oxic volume for the three existing treatment trains. To ensure flexible operations, variable speed mixers and swing zones were included in the BNR process, allowing the facility to run in two different treatment modes.

Upgrading the almost-40-year-old facility came with its share of challenges. The conditions of many areas of the site were unknown, so a number of contingency plans were in place. Additionally the installation of new equipment—the BNR process, new clarifiers and ultraviolet disinfection—proved to be more difficult because of the lack of elevation differences on site. 

The team was able to maintain existing treatment quality and capacity throughout the four-year project. Ten pages of the project’s specifications outlined the facility’s operations and the sequence of work. The team installed the new, fourth treatment train first, so that each existing train could be rehabilitated and upgraded one at a time. The project was completed in April 2014.

To complete the project, the city was required to gain financial and political support from the five neighboring cities. A group of stakeholders known as the St. Cloud Area Wastewater Advisory Commission—created in the early stages of the project—helped select the consultant to develop the facility’s plan and directed the creation of guidelines outlining responsibility for project and ongoing operation and maintenance costs.

“The staff in the St. Cloud Public Utilities Department were directly involved in the planning, design, construction oversight and optimization of the facility to ensure efficient and effective operation,” said Patrick Shea, public services director for the city of St. Cloud. “Large investment in a facility like this is not possible without ratepayers, city leaders and community support. The investment helps illustrate the strong environmental stewardship of the city of St. Cloud.”