The region’s wastewater may soon become a hot commodity — literally.
Planners designing a sustainable mini-neighborhood near TCF Bank Stadium in Minneapolis want to heat buildings there with sewage flowing deep beneath the streets. It would be one of the largest applications of a burgeoning technology that draws energy from wastewater.
“It’s a cost-effective way to heat and cool buildings with a local renewable energy source that’s available today that’s otherwise being wasted,” said Michael Ahern, senior vice president of Ever-Green Energy.
Ever-Green, which also runs a conventional system that heats and cools buildings in downtown St. Paul, is developing the sewage-heat system for Towerside, a futuristic “innovation district” taking shape in Minneapolis’ Prospect Park neighborhood. That would be the first large-scale example of wastewater heat recovery in Minnesota, an idea explored but never fully developed elsewhere in the state.
The proposal has encountered skepticism from the Metropolitan Council, which owns the eight treatment plants and 600 miles of pipes that collect and purify the region’s wastewater — including the 25-foot-deep pipe that Ever-Green wants to use.
“Usually people don’t want our wastewater,” said Larry Rogacki, an assistant general manager in the council’s environmental services division. “So it’s making us think about concerns that we wouldn’t normally have addressed in the past.”
Council officials say the proposal would require a change in state law, which does not allow them to sell or give away energy. Rogacki has other concerns, such as the system accelerating corrosion of the sewer pipe or disrupting the flow that keeps it free from blockages.
“Do we really know the risk?” Rogacki said. “From our perspective, to put our system at risk, I wouldn’t call it proven technology.”
The method of extracting energy from wastewater is similar to geothermal systems that rely on steady ground heat. The system draws in wastewater, which fluctuates between 53 and 72 degrees in the Twin Cities. A heat exchanger transfers the heat into fresh water pipes, and a heat pump elevates the temperature to levels high enough to heat a building.
It can also be used for cooling, by sending energy from hot air in buildings back into the sewer system.
Ahern said similar water-based district heating and cooling systems are being considered for the region’s two large redevelopment sites: the Ford site in St. Paul and Rice Creek Commons in Arden Hills. One would rely on groundwater aquifers, while another would draw energy from treated groundwater.
The wastewater technology is still in its infancy in America. But there are examples, like the Washington, D.C., water utility, which is constructing a $60 million headquarters heated with its own wastewater.
It’s part of the infrastructure in Vancouver, British Columbia, where wastewater was used to heat and cool the Olympic Village during the 2010 games. That system is now heating 28 buildings in the neighborhood, including more than 4,500 residences.
‘Reserve of energy’
Lynn Mueller, CEO of Vancouver-based Sharc Energy Systems, which specializes in the systems, said 87 billion gallons of water are discharged into sewer systems in North America and Europe every day.
“The largest untapped reserve of energy in the world is in the sewer system,” Mueller said.
Brainerd made a splash several years ago when the city’s public utility and school district teamed up with a local firm, Hidden Fuels, to explore using wastewater to heat buildings. Hidden Fuels studied the city’s wastewater flow for the best sites and even installed a small-scale demonstration in a pumping station, said Peter Nelson, a co-partner in the firm.
Nelson’s partner Alan Cibuzar died in 2014, and the project fell apart.
“There was a lot of interest,” said Nelson, a small-business consultant. “One of the things that happened was that the cost of energy came down drastically. So the interest in renewable energy sources kind of faded — or certainly wasn’t in the limelight that it once was with $100 [barrels of] oil.”
In Edina, developers of a proposed apartment building near 72nd Street and France Avenue have asked staff about tapping into the city’s sanitary sewer to help heat the buildings. They raised the idea during a City Council meeting in September.
Edina Engineering Services Manager Ross Bintner said the city is open to the idea, but is waiting on an official application to start hashing out the policy questions.
The Met Council is familiar with pulling energy from wastewater; it incinerates sludge to heat the massive Metropolitan plant in St. Paul.
It has sent Ever-Green a list of questions about the Towerside proposal, which Ahern says would cost about $7 million. Staff want to know how pumping water back into the pipe during the summer will affect its temperature, since hotter water causes more corrosion, as well as how the system will avoid creating a buildup of solids on the bottom of the pipe.
“I was somewhat amazed at the skimpy information they provided us,” Met Council Member Sandy Rummel said during a December meeting of the environment committee, which she chairs.
Met Council Member Harry Melander, who sits on Ever-Green Energy’s board of directors, urged the committee not to dismiss the proposal outright.
“There are some heavy lifts,” Melander said. “But we all know that when the council staff and the council wants to do something — no different than the projects that we’re looking at with Southwest light rail —that if there’s a will that there’s a way.”