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Minn. city looking at sewers as energy source

BRAINERD, Minn. — Brainerd officials are looking at an unconventional place for a future energy source: the sewers.

Brainerd-based Hidden Fuels began working with the city and the school district in 2009 and installed sensors in the sewers. For more than a year, they measured the temperature and the amount of sewage running through them.

“There’s a significant amount of energy, literally enough to heat hundreds of homes within the streets of the city of Brainerd,” Peter Nelson of Hidden Fuels told the Minnesota Public Radio News.

Under the right conditions, that could save the city, the Brainerd School District and residents money.

“Everybody heats water,” said Scott Sjolund, technology supervisor for Brainerd Public Utilities. “That’s potential energy that could be extracted.”

The next step is converting it into usable energy, but it’s challenging, he said.

Hidden Fuels would rely on technology already in use. A heat pump will circulate water from which energy can be extracted to heat or cool buildings, similar to how geothermal heating and cooling systems work.

Officials in Canada used a similar system during the Vancouver winter Olympics. But it didn’t have the challenges of using an existing sewer. What Nelson and others want to do in Brainerd is new because the water’s full of waste.

“We’re not dealing with clean fluids,” Nelson said. “We’re dealing with contaminated fluids. So that’s really the challenge, is to be able to operate efficiently in that contaminated environment.”

Earl Wolleat, director of buildings and grounds for the school district, said he’s confident Hidden Fuels could pull it off, but it would take years before it’s cost effective.

“Right now with the cost of energy being so low, I don’t see anything on the horizon right away where it would be an advantage to us,” he said. “It’s definitely going to be an advantage to the district over time, but with the price of natural gas right now, not so.”

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