Rural community launches first biological nitrate removal plant in Minnesota
October 19, 2023

AWWA Articles
Rural community launches first biological nitrate removal plant in Minnesota
Cold Spring, Minnesota, has grappled for decades with rising nitrate levels in its tap water. Despite replacing contaminated wells and encouraging nearby farms to update practices, the public works department for the town of 4,000 couldn’t tamp down on the pollution.
Then, they got the bug – for a new process involving bacteria, that is. With the help of engineering consulting firm Stantec, they turned to biological treatment to reduce nitrate, a toxic chemical salt contained in fertilizer. The Cold Spring nitrate reduction plant opened in 2023 and reduces nitrate levels to near zero while requiring less chemical than expected.
Basically, the town’s 5,000-square-foot treatment plant employs native microbes already present in Cold Spring’s source water aquifer. During the treatment process, the microbes destroy nitrate in the water without leaving behind a byproduct of concentrated waste.
Cold Spring’s decision to build a new $6.5 million nitrate removal plant was driven by a thoughtful evaluation of cost-effectiveness, environmental sustainability and long-term planning. (Pictured above, Stueve, treatment plant exterior and interior.)
“We chose biological treatment for cost reasons, including operational and maintenance savings, as well as to avoid sending potential future issues to our wastewater plant,” said Jon Stueve, the town’s public works director. “This meets all of the system goals we were looking for.”
A critical element of the project was securing necessary funding, which was achieved by strategic partnerships and advocacy efforts.
“We did a lot of lobbying with the legislature to get on the bonding bill and make it stand out to them,” said Stueve.
Collaboration between Cold Spring and Stantec was pivotal to obtaining the necessary resources.
“Our staff at Stantec supported Cold Spring Public Works with presentations to the legislature and with providing cost information and concepts for treatment that was used to secure the grant,” said Ryan Capelle, a water treatment lead with Stantec in Minneapolis.
“The treatment process is robust and consistently reduces nitrate concentrations to near 0 mg/l,” said Capelle. “We expect that the treatment capacity within the plant will sufficiently treat water demands to achieve current standards for nitrate (10 mg/l).”
Designed for future flexibility and expansion
The facility was designed to allow water to go through treatment or bypass treatment and function as a booster station during its initial commissioning. This provided the flexibility to adjust the process flow within the plant, which was useful to acclimate the microbes and continues to allow operators to make real-time adjustments as needed.
Cold Spring’s forward-thinking approach extends to its infrastructure, as the plant was designed with flexibility and future expansion in mind.
“Our water demand goes up year after year, so I could see a second train of biotta filters in the future,” Stueve said. “The building is large enough to accommodate two more vessels. The space we built the plant in is very efficient, with no wasted space, and is very user-friendly for operators.”
In addition, the plant is adaptable to changing regulatory considerations, noted Capelle. “In the event regulations change significantly, the facility is designed with provisions to install an identical treatment system that would allow for greater capacity and lower target effluent nitrate concentrations,” he said.
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