Hundreds of thousands of tons of trash moves through the Ramsey/Washington Recycling and Energy Center each year. But the goal is to keep as much of it as possible away from the landfill. 

"We have programs to help people upstream, but also we're looking at what can we pull out of the waste stream," said Melissa Finnegan, the center's strategic partnerships manager.  

24% of what households throw away in the trash is food waste. That's more than any other single material that ends up in a landfill, according to the Environmental Protection Agency. If it rots there, it decays and emits methane, a powerful greenhouse gas. It's why the Newport, Minnesota, facility hopes an ambitious new project will cut down on its impact on the climate.   

"That's a really exciting concept to us, to take something that would otherwise sit in a landfill and get a beneficial use out of it," she said.

The concept is anaerobic digestion, a biological process in which bacteria breaks down organic material in a giant airtight tank without oxygen. The byproduct is biogas that can be transformed into electricity or purified further into renewable natural gas and used as fuel or injected into the natural gas grid. 

Ramsey/Washington Recycling and Energy is working with Dem-Con Companies on a new $100 million project in Shakopee to process 40,000 tons of food waste and 35,000 tons of other organic material per year to meet both the state's recycling and clean energy goals — 75% recycling by 2030, 100% clean energy by 2040 and being carbon neutral by 2050.

"We're a landfill company that has embraced landfill diversion, and I think that's something that positions us well in the market space to be able to develop some of these additional technologies and bring those to fruition," said Bill Keegan, president of Dem-Con Companies. 

He traveled to Sweden in 2018 with the Minnesota Department of Employment and Economic Development to see anaerobic digestion at a large scale and that's when the genesis of the project began, he told WCCO News in a recent interview. 

The plan is to break ground this fall and finish construction by the end of 2027 to turn thousands of tons of trash into a renewable energy treasure. Keegan said the project is expected to slash emissions by 30,000 tons of carbon dioxide equivalent (CO2e) per year, which is 900,000 tons over the 30-year life of the facility.

"In this situation, one man's watermelon rind is another man's gas," Finnegan joked.

How does anaerobic digestion work and where is the process being used in Minnesota today?

Hometown BioEnergy in Le Sueur, Minnesota, has been using anaerobic digestion for a decade. It's part of the Minnesota Municipal Power Agency and produces eight megawatts of power, or enough to power 3,000 U.S. homes on average year round, said Steve Grove, asset manager for Hometown Bioenergy.

Local farmers deliver leftover feedstock like corn silage or other dairy waste they no longer need.

"What's exciting about it, to me, is that we really fit into a process that already exists," Grove said. "We fit into the natural life cycle of the agricultural community. All these products, these processes, already exist. We've inserted ourselves into the middle of it, and have been able to extract energy out of it."

The Le Sueur plant processes over 100,000 tons of feed stock every year, Grove said. That is transferred to a mixer with hot-tub temperatures to get the right "recipe" before the material is transferred into the 1.6 million gallon digester tanks outside. The process can operate 24/7 without anyone on site, he said. 

"It's closer to a living thing, as opposed to a static piece of machinery," he explained. 

Biogas is roughly 60% methane and 40% carbon dioxide. Hometown BioEnergy can burn biogas directly in electric generating machines or put it through a purification process that removes the CO2 and other impurities and in turn produces "pipeline quality natural gas" in what's called renewable natural gas that's nearly 100% methane.

The latter is a newer process for Hometown BioEnergy and it's the planned output for the Dem-Con facility in Shakopee.

"The amount of carbon that would have been emitted from all these products—we're able to bring those down to less than zero. So in some ways, we're better than carbon free," Grove said.

Bo Hu, professor at the University of Minnesota who studies bioprocess development said Europe has been leading the way with anaerobic digestion for years. But he said Minnesota's robust agriculture production primes it for expansion here.

Some farms have their own digesters and the Legislature recently approved a law providing a framework for utilities to reduce greenhouse gas emissions this way with the Natural Gas Innovation Act, which has a state goal of utilities reducing "the overall amount of natural gas produced from conventional geologic sources delivered to customers." 

"Anaerobic digestion has so many environmental benefits," Hu said. "First of all, it will reduce the total waste volume. It also stabilizes the nutrients so that we don't have a lot of nutrient pollution. It reduces the odor in most cases, and also cuts down significantly on pathogen levels in those organic waste materials. And finally, it can also produce biogas, which can serve as our energy carrier."

Hu said Califonia is taking the lead in the U.S. to expand anaerobic digestion but that 2021 Minnesota law will make the state "pioneering" in renewable natural gas development here.

"Minnesota is leading the way nationally in some of these projects in the clean energy space," Keegan added. "We're seeing some of these start in California, but really, Minnesota is one of the leading states in that space."