As Minnesota’s eighth largest city, St. Cloud proudly describes itself as “just the right size,” offering a perfect blend of big-city amenities and small-town charm. With the energy of a college town, St. Cloud presents a dynamic mix of recreational activities, top-notch healthcare services, and a rich historical legacy showcased in its beautifully preserved downtown. The city’s vibrant arts scene, thriving businesses, diverse dining options, and unique shops create a community where urban convenience and close-knit spirit come together seamlessly.

First in Minnesota

The St. Cloud Water Treatment Facility, located on the west bank of the Mississippi River beneath Hester Park, provides safe, clean drinking water to more than 70,000 customers in St. Cloud and St. Augusta. Drinking water is sourced from the Mississippi River. Since the creation of its water treatment master plan in 2006, the City of St. Cloud has worked to implement a series of projects aimed to proactively address the growing needs of the community and evolving regulatory requirements for water quality and treatment.

With the goal of staying on the cutting-edge of new methods and technologies, and to provide the community with the best investment in drinking water, the facility underwent significant upgrades. Completed in the summer of 2024, the facility is the first in the state to use ultraviolet (UV) light as its primary disinfectant, complemented by a powerful ozone oxidizer and biological filtration.

Advanced Treatment Pilot

Existing and future regulatory requirements continue to drive implementation of advanced treatment technologies and alternative disinfection strategies. The city collaborated with engineering and consulting firm AE2S in 2015 for a pilot study to discover viable options to meet today’s needs and anticipate the challenges of tomorrow. The study evaluated strategies to best address areas of taste and odor, disinfection, and contaminants. The facility recently underwent significant improvements and upgrades as a result of those findings, leading the way for the future of water treatment in Minnesota.

The advanced treatment piloting included the following technologies:

  • Ozone
  • Biologically activated carbon (BAC) filters
  • Ultraviolet light (UV) disinfection

Surface Water Solutions

An advanced supervisory control and data acquisition (SCADA) system, along with upgraded networking equipment, new servers, and a control room were included in the upgrades. These, paired with the plant’s new additional treatment tools, addresses variation in the water supply and position the treatment facility for compliance with future regulations.

The facility is equipped with three flow trains designed to handle the variability of surface water and the fluctuating water demand. The flow trains feature flocculation equipment, inclined plate settlers, lime softening clarifiers, and a fully redundant batch lime slaking system. While much of the initial treatment processes, such as lime softening and recarbonation, remain in place, recent enhancements at the latter stages of treatment have positioned the facility for both future growth and increased safety measures. These improvements ensure the facility can continue to meet the community’s evolving needs while maintaining the highest standards of water quality.

Ozone

The first new process of the St. Cloud treatment facility introduces ozone, which dissolves into the water and is a much stronger oxidizer than potassium permanganate or chlorine gas. The facility is equipped with two fully redundant ozone generators, each capable of producing enough ozone for all three treatment trains. These generators convert liquid oxygen into gaseous oxygen (O2) and then into ozone (O3). The primary objective of this process is to eliminate or reduce taste and odor issues typically experienced in surface water treatment. When paired with biologically activated carbon (BAC) filters, this process results in a more aesthetically pleasing water product. Ozone is also effective for inactivation of waterborne pathogens and viruses. The ozone contact basins replaced the previous detention basins.

Biologically Activated Carbon Filters

After ozonation, St. Cloud’s drinking water next moves through BAC filtration. River water is biologically active, so an important part of the process is cultivating a population of helpful microorganisms. Granular activated carbon (GAC) has physical properties capable of adsorbing dissolved contaminants, including taste and odor causing compounds and emerging contaminants. Along with the adsorptive properties, GAC has a high surface area that allows beneficial bacteria to colonize. Pathogens like bacteria, viruses and protozoa are oxidized (broken apart) by the ozone and introduced to the BAC filter where the good bacteria eats the bad bacteria, resulting in a significant reduction of total organic carbon, as well as taste and odor compounds.

Ultraviolet Light Disinfection

While ozonation provides some disinfection benefit, the facility’s primary disinfection method is UV light. This advanced UV system inactivates viruses and bacteria by preventing them from replicating. Positioned post-filter, the UV system not only ensures effective pathogen inactivation but also helps control disinfection by-products (DBPs) related to chlorination. Although chlorine is still used for residual disinfection, as required by the Minnesota Department of Health and the U.S. Environmental Protection Agency, the facility requires a significantly lesser amount chlorine thanks to the efficiency of the UV disinfection process.

Commitment to Sustainability

St. Cloud is committed to sustainability, and one of its many efforts include reducing chemical usage at the updated water treatment facility. While chemicals are still part of the treatment process, the facility has significantly reduced the use of potassium permanganate and chlorine. Additionally, once the biologically active carbon filters are fully established, the need for powdered activated carbon (PAC) will be eliminated. These changes are expected to result in an estimated 10% annual savings in chemical feed costs.

Furthering its dedication to sustainability, St. Cloud has installed solar panels on the roof of the water treatment facility to harness natural light energy, reducing the facility’s carbon footprint. The facility upgrades add another eight million gallons per day (MGD) of treatment capacity, bringing total capacity to 24MGD. Today, the facility treats an average of 7MGD in the winter and 16MGD in the summer, so the upgrades prepare the city for future population growth as well as the capability to address emerging contaminants, ensuring long-term water quality and sustainability.