Duluth wastewater plant captures methane to produce heat, power

A huge wastewater treatment plant serving Duluth and surrounding communities has installed a new system to generate electricity from the gasses captured during the sewage treatment process, part of a growing trend to harness renewable energy from waste.

The project at the former Western Lake Superior Sanitary District, recently renamed Resource Renew, captures the methane and carbon dioxide produced during anaerobic digestion. That’s a process where microorganisms break down organic materials in the solid waste, in the absence of oxygen, inside four one-million gallon tanks. 

For years that so-called biogas has been used to help heat the giant facility. But in the summer, all that heat being generated wasn’t needed. So it was wasted.

“It would be burned in a waste gas burner and flared off,” said Carrie Clement, incoming executive director

That burned a valuable resource. And it emitted climate change-causing greenhouse gases.

But now Resource Renew has installed three new engine generators that will allow the facility to use 100 percent of the biogas throughout the year, by also using it to generate 1.5 megawatts of electricity, enough to power about 60 percent of the treatment plant.

“It’s a milestone in terms of our energy reduction efforts and our key element to allowing us to continue to optimize this opportunity in biogas,” said Clement.

The project wasn’t cheap. It cost about $19 million and took over a decade to design, plan and build.

But the electricity generated will save Resource Renew about $100,000 a month on its electric bill. That cost savings helps keep rates stable, Clement said, and frees up capital to maintain 75 miles of sewer pipes over a 530-square mile coverage area that includes Duluth, Cloquet and surrounding communities.

The energy system in Duluth is one of at least 26 similar projects installed at wastewater treatment plants across Minnesota, according to the American Biogas Council. Most capture the biogas to either generate electricity or produce heat. Resource Renew in Duluth is one of a few that produce both (St. Cloud and Rochester are examples of others).

But there’s a lot of untapped potential for this technology. About 1,200 wastewater treatment facilities nationwide capture biogas for energy. Minnesota alone has about 1,600 wastewater treatment plants.

There are also a handful of landfills in Minnesota that capture methane and carbon dioxide for energy, as well as some new biodigesters that break down food waste and other organic material.

The biogas council estimates a potential for thousands of new biogas systems nationwide, including many on farms that would use digesters to produce energy from manure — a proposal that has faced some pushback in Minnesota.

“Addressing methane emissions is critical to achieving Minnesota’s greenhouse gas emission reduction goals, as is producing more clean electricity,” said Becky Lentz, spokesperson for the Minnesota Pollution Control Agency. “We are excited about the project in Duluth, which does both.”

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