Digesters make renewable energy from manure, but face hurdles
A Danish company’s plans to turn cow manure into renewable energy in Minnesota and Wisconsin’s dairy country have tanked, at least for now.
Nature Energy planned to build several large-scale anaerobic digesters that would harvest methane from livestock waste to produce biogas. The company was eyeing three sites in dairy-rich Stearns County, as well as Lewiston in southeast Minnesota and Benson in western Minnesota.
But in August, British oil and gas giant Shell announced that its subsidiary, Nature Energy, was “strategically suspending” all of its projects in the U.S.
Shell’s abrupt change of course is a disappointment to the projects’ backers in communities such as Paynesville, where Nature Energy had proposed building its first Minnesota plant. They believed it would harness a local waste stream to benefit both farmers and the climate.
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“It's looking forward in helping to protect the environment, and really bring in a new type of energy development to the area and to the country,” Paynesville Mayor Shawn Reinke said in July.
Shell’s pullback also is an indication that the promising technology of biogas still faces hurdles — including high costs, regulations, market forces and local opposition — to becoming a major U.S. energy source.
But some energy experts say it makes sense to turn the methane in manure from a liability into a commodity, especially in Minnesota — home to about 9 million hogs and nearly half a million dairy cows, which produce as much as 50 million to 100 million tons of manure a year.
“That’s a lot, and right now much of it is not really fully utilized,” said Roger Ruan, director of the University of Minnesota’s Center for Biorefining. “There’s a lot of potential here using manure for electricity generation.”
How it works
As manure or other organic material decomposes, it releases methane, a greenhouse gas more than 25 times more potent than carbon dioxide. Livestock are a major source of methane emissions.
Anaerobic digesters heat up the manure to about 125 degrees, creating an environment where microorganisms thrive. Bacteria break down the manure, producing biogas, which consists of methane, carbon dioxide and other gases.
Biogas can be used to replace traditional natural gas to produce electricity, for heating and cooking, or to fuel vehicles. What’s left is called digestate, a nutrient-rich material that can be used to fertilize farm fields.
Anaerobic digesters aren’t new. Some farmers have used them for decades to harness energy from livestock manure, mainly on a small scale. The first in Minnesota was Dennis Haubenschild, who started using methane to make electricity on his Princeton dairy farm in 1999.
But Nature Energy’s plans were different: It proposed building larger, commercial-scale plants that would collect manure from farmers in a 20- to 30-mile radius.
The company collects manure from smaller farms once a week, and several times a day from larger farms, said Jesper Nielsen, vice president of U.S. business development, during an interview in late July.
“Basically, Nature Energy borrows the manure from the farmer and brings back a better product,” Nielsen said.
Most pathogens and some nutrients such as phosphorus are removed — so there's less risk of polluting local rivers and streams, said Bob Lefebvre, former executive director of the Minnesota Milk Producers Association. He was hired by Nature Energy in 2022 as vice president of on-farm business development.
Lefebvre said he viewed the projects as an opportunity to help dairy farms, even small ones, meet the industry’s goal of being carbon neutral by 2050.
“Virtually all dairy farmers now have an opportunity to reduce their carbon footprint through reduction of methane by partnering with Nature Energy,” he said in July. “That is something that no other anaerobic digestion company or biogas company can do.”
Digestion in action
Nature Energy also touted its enclosed facilities as clean and odor-free. Several local city officials from Minnesota traveled to Denmark last March to view one of the company’s plants.
Paynesville City Administrator Tariq Al-Rifai was among them and left with a favorable impression.
“One of the concerns people had was, ‘Well, they're going to have all these trucks coming in hauling back and forth, and you’re going to see just a lot of dirt and mud and stuff all over the place,’” he said. “We didn't. It was actually very, very clean.”
But local residents pushed back against Nature Energy's plans in some communities, including Paynesville. They voiced concerns about potential odor, safety issues and truck traffic.
Barbara Schmit, a 47-year resident of nearby Paynesville Township, said she worried about the impact on the city and the nearby Crow River if a spill or explosion occurred.
“What about the rest of the city if something catastrophic happens?” Schmit asked. “They can say, ‘Well, we've never had an incident.’ OK, that's great. But accidents happen.”
Some environmental groups also oppose large-scale methane digesters as “greenwashing,” fearing they will encourage the expansion of large factory farms that have negative impacts on air and water quality.
There are methane digesters that have been operating for years. The University of Wisconsin-Oshkosh’s biogas program developed three anaerobic digesters as learning laboratories, and continues to operate two of them, said Brian Langolf, the program’s director.
About 2,300 digesters are operating in the U.S., but the industry has plenty of room for growth, Langolf said. In comparison, Germany has about 10,000.
As focus shifts toward energy independence, methane digesters offer a solution that uses an existing waste stream, Langolf said. And they can operate 24/7, even when it's not sunny or the wind isn't blowing.
“The nice thing about digesters — they can process the waste. They can make renewable energy,” he said. “But also, they can help clean air, water and soil and make a renewable fertilizer product afterwards.”
Manure digesters also could help lessen Minnesota farmers’ need to rely on a volatile international supply chain for fertilizer, whose prices have skyrocketed since Russia’s invasion of Ukraine, Langolf said.
Minnesota’s climate action plan specifically calls out anaerobic digestion as a method for reducing greenhouse gas emissions from agriculture, said Megan Lennon, who leads the energy and environment section at the Minnesota Department of Agriculture.
“Manure that's just hanging out sitting in lagoons is releasing methane all the time,” Lennon said. “That is one reason why livestock production has a high carbon footprint.”
Capturing that methane and converting it to renewable natural gas allows it to be used for a variety of other purposes, she said.
But keeping small digesters operating smoothly requires maintenance and a steady stream of manure, which can be a lot of extra work for already-busy farmers.
“You're futzing with it every day,” Lennon said. That might be why some digesters installed on farms 20 years ago are no longer operating, she said.
So there's a lot of interest in finding places in Minnesota where there's enough biomass to support a larger digester, Lennon said. That could include not only livestock manure, but also food scraps or food processing waste, she said.
A 2021 report by the U.S. Environmental Protection Agency found that each year, carbon dioxide emissions from food waste are the equivalent of 42 coal-fired power plants.
Changing regulations
When it comes to biogas development, Europe is ahead of the U.S. in part because of stricter regulations on dealing with waste streams and more stringent goals for decarbonization, said Alex Klaessig, senior director for the hydrogen and renewable gas forum at S&P Global.
Some states including California offer incentives for building digesters that capture methane and convert it to biogas. The state’s low carbon fuel standard gives digester owners carbon credits, which they can sell or use to offset their greenhouse gas emissions.
Klaessig said those types of incentives have fueled the growth of biomethane production in the U.S. by double digits in the last few years, and it likely will continue to expand.
“Transportation is the tip of the spear,” he said. “Natural gas utilities are also seeing renewable natural gas as a way for them to continue their future in a low-carbon world as well.”