Worthington WWTF: Constructing Improvements for Now and the Future
Over the past eight years, Worthington Public Utilities (WPU) has navigated the long and challenging process of modernizing their municipal wastewater treatment infrastructure. WPU is responsible for managing, operating, and maintaining the city’s municipal wastewater system on behalf of the community. Like many communities, Worthington was confronted with the challenge of managing an aging wastewater treatment facility with imminent repair needs, while facing an uncertain future with evolving regulatory requirements in the state of Minnesota.
Worthington’s existing municipal wastewater treatment facility was originally constructed in the early 1960s. The facility treats domestic wastewater generated from residents and businesses throughout the community, while the JBS Pork Production Facility has their own dedicated industrial wastewater treatment facility that is separate from the municipal system. The municipal facility last received major upgrades in 1989. Over the years, WPU operators have been diligent in maintaining the facility to maximize the service life of the equipment and infrastructure. This has allowed WPU management to pay off debts and keep user rates low for the community. However, even the best maintained facilities eventually require major upgrades, as regulations change and the unforgiving environment of wastewater treatment takes its toll.
Beginning in 2016, WPU partnered with Bolton & Menk to complete an asset management plan for their wastewater system. This plan evaluated the condition and criticality of every asset in the wastewater system, with the goal of prioritizing needs and making smart financial decisions when rehabilitating or replacing assets. The result of this work identified nearly $20 million dollars (adjusted for 2021-dollar value) in improvements needed over a 10-year period – a significant investment to make in a 60-year-old treatment facility. In addition to age-related issues, the existing biological treatment process was a multi-stage trickling filter system. This technology has the benefit of being highly energy efficient but has limited capacity in achieving more stringent limits for nutrient removal if enforced by the Minnesota Pollution Control Agency (MPCA) in future permitting cycles. WPU was at a crossroads: should they spend millions of dollars to address today’s problems, or make a larger investment and transition to a new treatment process for the future?
In light of the findings of their asset management plan, WPU continued working with Bolton & Menk to complete a Wastewater Facility Plan for evaluating long-term needs and alternative treatment technologies. This included considerations for future industrial contributions, community growth, and MPCA permit limits. The community had seen significant residential growth over the past 30 years and was anticipating continued annual growth of 1 percent over the next 20 years, or over 3,000 additional residents for a 2040 projected population of 17,230. Despite this growth potential, the existing municipal treatment facility was found to be oversized for their projected pollutant loadings, largely due to the closure of the Campbell’s Soup plant in the early 2000s, which eliminated nearly 40 percent of their capacity allocation.
The MPCA is in the process of updating and implementing their Nutrient Reduction Strategy. Worthington is anticipating the potential for future permit limits for total nitrogen (TN) removal and more stringent phosphorus removal. While age-related issues were driving the need for imminent improvements to the facility, the potential for more stringent permit limits were driving the need to modernize the facility and consider alternative treatment technologies. Ultimately, WPU wanted to be proactive in addressing their long-term needs and investing into their future. This led to the decision to transition their existing trickling filter process (i.e. attached growth biological process) to activated sludge technology, which is a suspended growth process that provides greater control over the biology and can be modified to achieve biological removal of nitrogen and phosphorus.
WPU and Bolton & Menk began designing the improvements in April 2020 and received contractor bids in June 2021.The project included converting their existing trickling filter process into an activated sludge process with accommodations for future nitrogen removal. The existing aluminum sulfate feed system was reused for chemical removal of phosphorus to meet their 1.0 mg/L phosphorus concentration limit. The project also included plant-wide rehabilitation of existing components that could be incorporated into the new treatment process, including the equalization basins, sludge lagoons, pretreatment system, influent pump station, disinfection system, and operations building, along with renovations to the existing site and pavement. The biosolids processing system was converted from anaerobic digestion to new aerobic technology to be compatible with the new liquid-stream activated sludge process.
The design included innovative technologies for the aerobic digestion process to help minimize energy costs. This included installing a high efficiency compressed air mixing system that de-couples the requirements for dissolved oxygen and mixing. This system allowed for a 70 percent reduction in energy requirements and will result in a payback of less than three years due to the energy savings.
All-in-all, Worthington was able to completely renovate and modernize their municipal treatment infrastructure for an as-bid construction cost of $26.2 million dollars. Gridor Construction, Inc out of Buffalo, Minnesota was the low bidder. The project was financed through the Clean Water Revolving Fund (CWRF) administered by the Minnesota Public Facilities Authority (PFA), which provided the community with a 20-year loan at an interest rate of 1.0 percent. The new treatment process went online in December 2023, while the old process was taken offline for demolition in February 2024 following successful startup of the new biological process. The project is scheduled to be completed in December 2024.
The facility improvements provide excellent value to the community and will serve Worthington for decades to come. Scott Hain, WPU General Manager, and Jeremy Braaksma, Wastewater Superintendent, each served pivotal roles throughout the past eight years in implementing the planning, design, and construction phases of the project. This project was also not possible without the involvement of WPU’s wastewater staff, including Glenn Duitsman, Mike Pavelko, Tom Jones, Dan Van Ede, Josh Iten, Ron Froderman, and Andrew Echternach.
As published in the Spring 2025 issue of The Wastewatcher, an MWOA magazine.
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