Buckthorn is one of the most difficult invasive plants to deal with in Minnesota and the solution usually involves removing it and burning the shrubs.
But for every pound of wood burned in an open pile, 1.82 pounds of carbon dioxide is released into the air, according to the Wood Products Council.
A St. Paul nonprofit’s new wood-burning tool could put most of that CO2 into the ground.
Great River Greening, an organization focused on land restoration and nature-based climate solutions, is promoting a new way to burn wood and biomass to fight climate change by producing something called “biochar” instead of excess CO2 and ash .
The organization recently lit an inaugural fire at Lake Elmo Park Reserve, demonstrating the use of their new “Big Box Kiln,” which produces biochar, a charcoal-like substance that can be used to strengthen soil and sequester carbon keep.
“The open burning released all that carbon, so this is a huge benefit for climate-smart practices,” said Executive Director Kateri Routh.
An alternative to fireplace burns
Open pile burning, in which wood or biomass, such as the invasive buckthorn plant, is stacked in a pile and then set on fire, is a common practice among farmers and other land managers — a practice that conservation director Todd Rexine said he has participated in himself. . It was just “a way to get rid of the wood,” he said.
However, the damage that fireplace burns cause to the environment led him to learn about the biochar alternative.
In cities, waste wood can be converted into energy, such as in the downtown St. Paul’s District Energy system. That is not always practical for smaller burns in rural areas.
“As you burn the stuff in biofuel plants, you produce energy and you get something out of it,” Rexine said. “If you’re going to do a full burn (open pile burn), we just burn things to ash and it all gets released into the atmosphere.”
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Great River Greening now has three wood kilns ranging in size from small to medium, what they call the Oregon, Ring of Fire and their new 10-foot Big Box Kiln.
The process of lighting the ovens is different than a campfire or a pile of brush, Rexine said. Instead of lighting the wood from the bottom, a fire is started at the top. As the wood decomposes and is then quenched with water, biochar is created.
“Keeping the fire at the top creates a low-oxygen environment at the bottom where the biochar is created,” Rexine said. “The process is called ‘pyrolysis’.”
Biochar kilns are designed with specific air inflow and exhaust features that create a “flame hood” effect, which helps maintain low oxygen levels and prevents fire from spreading downward, according to Rexine. It also allows water to be used to extinguish the process and then discharged down a drain.
What can biochar do?
Farmers can use biochar to “recharge” the soil by redistributing the carbon into the soil, Rexine said. It acts like a sponge and soaks up the nutrients and then delivers them to growing organisms. Biochar can also be mixed with compost and used in gardening and land restoration.
Not just any combustion product qualifies as biochar, Routh said. Biochar must contain at least 60% carbon to meet the standard. If not, it’s just ash.
“If you try to do this without having the knowledge and skills, you won’t create the product you want and provide the benefits you want,” Routh said.
Rexine said biochar kilns are used in Oregon, Washington and California. The technology was developed to help fight forest fires, he said: Brush is converted into biochar to remove wood waste and reduce the chance of fast-spreading fires.
Who can use it?
CenterPoint Energy, the Minnesota Environment and Natural Resources Trust Fund and other small family foundations funded Great River Greening’s development of its biochar kilns.
The Big Box Kiln, which cost $15,000 to build, can convert 45 cubic yards of wood waste – about 20 pickup loads – into 9 cubic yards of biochar.
Although Great River Greening does not have enough ovens available to rent to private individuals, they would like to be able to offer this service in the future.
In the meantime, local environmental groups, counties and cities can use the kilns, and Great River Greening’s agriculture program is working with farmers to see how they can apply biochar in agriculture.
“We need to get to the next phase where we have a place to store the ovens in different locations around the state so that it becomes more manageable for people to have access to them,” Routh said.
Major river greening
Great River Greening works throughout the state of Minnesota in partnership with landowners; they do not own or manage land themselves.
“That makes us unique because we work directly with the community on every project we work on,” Routh said.
Her team of ecologists specializes in prairie restoration, forest restoration, tree planting, and works in parks across the state and in agricultural fields on regenerative agricultural practices.
“We are driven to use science-based best practices in everything we do,” said Rouw.
Biochar is another initiative that the organization hopes can have a positive impact on the environment.
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“We know that buckthorns are a really big problem in our state right now, emerald ash borer is such a big problem and what do you do with all that waste product,” said Rachel Molzahn, CenterPoint Energy community relations program manager. “This seems like a very innovative and cool process to get rid of all that biowaste without causing some negative effects through emissions.”
Molzahn said one of the things she likes about Minnesota is the outdoors. She said she believes it is important to find ways to preserve green spaces and is excited about the prospect of biochar doing this.
“The emissions problem is really a big problem,” Molzahn said. “I have a four-year-old daughter and if she decides to have children, I want to make sure they can play outside too.”
