Southwest Minnesota

Success smells sweet for Slayton’s wastewater solar upgrade

April 2022

By Emily Haeg Nguyen

Did you know that water and wastewater utility energy consumption is generally 30-60% of a city's energy bill?

The hefty price tag is largely due to energy needs associated with pumping water and other motors, like those often used in wastewater treatment. Taking on this issue, the southwestern Minnesota city of Slayton is excited to lead change in the region with a special wastewater system upgrade.

Located at the intersection of Highway 59 and Highway 30, Slayton is a regional hub and the seat of Murray County. Visitors, local businesses and 2,100 residents rely on Slayton’s 60+ year old plant to manage the town’s wastewater. On top of seeking an energy efficiency upgrade to benefit the city, officials say they’ve caught a whiff of additional cause for improvement.

Image courtesy of city of Slayton's Facebook page.

EPA image “Yeah, the plant always gets some complaints from residents about the smell,” divulged Josh Malchow, Slayton’s city clerk/administrator. “Mostly in the spring when the ice comes off the lagoon and the winds are blowing in the right direction.”

Like many other cities, Slayton’s system works by collecting the city’s raw wastewater, treating the water at the facility, and discharging the water into two nearby ponds. The organic elements in the pond's soil furthers the treatment process, but that’s only effective if conditions are right. Treatment plants like Slayton’s require water-immersed mixers to support those conditions by aerating the pond’s soil.

“We had three shore-based electric motor aerators. They were not very efficient in regards to the electricity consumption,” says Malchow. “They were also not very efficient in terms of actually doing what we want them to do, which is mixing oxygen into the water to assist with odor, natural treatment, and the biological processes that need to happen for wastewater treatment.”

Image courtesy of United States EPA.

Malchow says the city’s aerators were providing inconsistent results at best. Anchored to the surrounding land, the aerators had limited motion and often only succeeded in disturbing small sections of the pond. Plus, the machines could only run seasonally. Without aeration, the waters would freeze and thaw throughout the year. This left some Slayton residents smelling more than fresh flowers every spring.

Between stagnant mixers and unsavory aromas, Slayton officials knew it was time for a change.

Enter solar power! With solar already helping to light up Slayton’s entrance signs, at the end of 2020 the town became one of the first in the region to install solar mixers. The new mixers work by floating on top of the water, tremendously increasing the rate of biological processes happening below.

Image courtesy of city of Slayton's Facebook page.

They're called SolarBees Mixers. They’re set in the dead center of the pond. They constantly rotate, they constantly mix the water. They operate year-round, and the pond never freezes. Because of that, it’s able to get sunlight and the nutrients the wastewater needs.

Josh Malchow, Slayton’s city clerk/administrator

That’s not the only fresh advantage that has Slayton residents breathing in a sigh of relief. “From the one season we've gone through, we already know that it’s working better in terms of smell complaints.”

The new mixers can also be used to disperse additional treatments throughout the pond when necessary, but according to Malchow, it may not be necessary. “Because we are constantly moving that water around and biologically breaking things down 24/7, 365 instead of just seasonally, there may be a chance that we don't ever need to chemically treat the pond.”

Fewer chemical treatments plus fewer engines add up to big savings for the city. Malchow says the new mixers will pay for themselves in a matter of years. With so many benefits to the town’s wastewater treatment upgrade, Slayton residents can certainly stop to smell the roses.

Support for this project was provided to Slayton by Minnesota Rural Water Association.
Check out Energy Savings Partnership for information on support for projects incorporating renewable energy or energy savings.
The Minnesota Technical Assistance Program offers training for wastewater treatment plant operators on improvements that reduce energy consumption.