ST. CLOUD — Most days it smells like rotten eggs at St. Cloud's wastewater treatment plant. That's a good sign, meaning the organisms that break down waste are busy at work. But on certain days, whiffs reminiscent of strawberry daquiris or barbecue sauce tingle employee noses.

The experience is unique to St. Cloud, the state's only municipal facility to take from local food and beer manufacturers their high-strength waste — often a sugar-laden liquid left over from the flushing of production lines.

And not only does the facility accept the high-strength waste, it is able to turn it into fuel and fertilizer. It's just one of the many reasons why the city has emerged as a leader in renewable energy efforts within the last decade.

"St. Cloud is clearly one of the cities that's defining what a clean energy future can look like," said Frank Kohlasch, climate director for the Minnesota Pollution Control Agency. "[The] facility is unique for Minnesota and for the country — where they are integrating treatment of their wastewater, the use of solar energy to power their services and the recovery of biogas and fertilizer."

The treatment center is also poised to be the first wastewater facility in the world to produce green hydrogen fuel and pure oxygen on-site, as well as run the first program in the country to capture carbon from exhaust and be able to sell the end product for building materials.

Kohlasch described the efforts as a "circular economy," where a waste stream becomes an input for another industry, while also recapturing carbon so it's not being released into the atmosphere. That could potentially allow the city to become carbon negative — where they are storing more carbon than they're generating.

"It's really exciting the city of St. Cloud is embarking on this bold work," he said. "It's critically important both for protecting Minnesota's climate but also protecting our water quality and growing our clean economy."

Tumult inspires progress

St. Cloud has operated a hydro dam on the Mississippi River for nearly 35 years. Each year, the facility generates more than 50 million kilowatt hours of electrical energy, the equivalent of powering nearly 5,000 homes for a year.

But the city's recent push for renewables stemmed from the Great Recession, which forced officials to look for ways to reduce spending. That spurred projects to update streetlights to LED lighting, convert the city's athletic complex to a geothermal facility to save on natural gas, purchase energy from solar gardens and install solar panels on a dozen city buildings.

Eight years ago, Mayor Dave Kleis set a goal for the city to be carbon neutral by 2030, not including energy generated by the hydro dam. The city met that goal in 2020. When taking into account the hydro facility, the city now produces three times as much energy as it uses as a municipality — saving about $1.5 million and counting from the annual budget.

"We set pretty high goals," Kleis said. "And we achieved them much earlier than planned. But we don't stop there. We want to keep creating greater efficiency and be able to produce more energy with renewables."

Kleis recently announced new sustainability goals: for the community as a whole to be carbon neutral with electricity by 2028 and for the community to be carbon neutral with all energy use, including transportation, by 2038.

"If we can do that for our city buildings, when could we achieve that as a community?" he asked.

Creating electricity, jobs from waste

St. Cloud installed its first generator for biofuel — a fuel derived from organic matter — in 2017 and a second in 2020. The equipment harnesses the breakdown of human and food waste, where microorganisms consume carbon and create methane, which can be burned to produce renewable energy.

Not only does the high-strength waste from local companies help the city create its own energy, it is saving those companies money.

"It's really a win-win opportunity for industries in our area because they're able to bring it here without having to haul it somewhere and pay probably 100 times more than what they pay here," said Tracy Hodel, public services director for St. Cloud.

Cold Spring Brewing partnered with the city to pay for the second generator, Hodel said, because cost savings are allowing the company to invest in further growth.

"Taking all this high-demand waste can create jobs," Hodel said. "Not only is it environmentally the best approach to handling it, it's also creating economic impact."

The other unique program at the facility is the recovery of phosphorus from food scraps, detergents and human waste to create two types of fertilizer — while also greatly reducing the amount of phosphorus that goes into the Mississippi River.

The first product is a liquid fertilizer the city injects into local fields. The second is a byproduct called struvite, which can be sold to consumers to use as plant fertilizer. St. Cloud is the first treatment facility in the state to make struvite.

A 'science fiction-y' future

Future initiatives underway at the facility include the use of renewable hydrogen and carbon-capturing. The facility plans to produce clean hydrogen fuel and pure oxygen on-site, by running water through an electrolyzer that uses renewable electricity to separate the H2O molecule into hydrogen and oxygen.

The facility could then use the hydrogen to power its generators or as a heat source. The oxygen would be used for wastewater treatment, saving energy by using less electricity to pump pure oxygen into the aerators compared with ambient air that only contains about 20% oxygen. The aerators are large open-air storage tanks where oxygen is added to waste from St. Cloud and the surrounding cities to spur the biodegradation of organic materials.

"It sounds science-fiction-y," Kohlasch said. "But really we've been making hydrogen for decades and decades. This is just making sure we're making the most climate-friendly hydrogen possible."

St. Cloud is also partnering with England-based Clarke Energy to create a pilot program to capture carbon from exhaust, which would make it the first program in the country to do so.

To jump-start the communitywide renewable transition, the city plans to install an electrical vehicle charging station this summer at a local park. The city is also hosting an electric vehicle expo July 9 at River's Edge Convention Center.

St. Cloud is one of at least two dozen Minnesota cities with communitywide greenhouse gas reduction goals. Kohlasch said the MPCA is working to share St. Cloud's renewable progress with other communities.

"Hopefully we can build off of what St. Cloud has learned," he said, "and make this kind of approach more of the norm rather than the exception."