The Pacific Northwest’s expansive forestlands have no shortage of raw material for biochar, a potent soil amendment that also sequesters carbon.

However, slash piles and other sources of woody biomass are often too remote to economically transport to processing facilities, where they’d be burned to make the substance.

The solution devised by retired soil scientist Jim Archuleta and others was to bring the biochar processing facility to the forest.

“If we can make it from the slash that is already causing a wildfire risk, we’d be solving more than one problem,” he said.

Mobile biochar unit

Archuleta helped design a mobile production unit called the CharBoss as part of a partnership between the U.S. Forest Service, his former employer, and Air Burners, a private machinery manufacturer.

Stationary facilities are already making biochar but they’re only able to bring in raw materials from a certain distance, beyond which the trucking costs are prohibitively high, he said. That leaves plenty of useful woody biomass out in the forest to rot or burn.

“This equipment fills that gap and allows us to monetize slash,” Archuleta said.

Historically, wildfires consumed forest vegetation in the mountains at regular intervals, creating biochar that eventually fed the valleys below with nutrients through erosion and flooding.

Fire suppression in modern times has allowed the forests to become overstocked, potentially fueling more destructive fires while interrupting the production of natural biochar.

“We need to reconnect that, and that’s what’s offered by this machine,” Archuleta said.

Thinning and vegetation removal generates woody biomass, which the CharBoss converts to a natural soil amendment. Most of it can be bagged and sold commercially while a portion is left in the forest to improve soil health.

The water- and nutrient-holding capacity of biochar prevents forest vegetation from drying up as early, said Debbie Page-Dumroese, another Forest Service soil scientist involved in the CharBoss project.

“It keeps the understory green longer in the growing season so it’s less susceptible to fire,” she said.

Using the CharBoss is preferable to burning slash piles because the machine effectively captures smoke and stops flames from getting out of control, Page-Dumroese said.

“We can do it safely because the fire is contained,” she said.

Slash piles also create “burn scars” on the landscape where trees don’t grow for decades but which are attractive to invasive species, she said.

The CharBoss quenches the burning material to make biochar, but with traditionally burned slash piles, the woody biomass is consumed more thoroughly and turned to ash, Page-Dumroese said.

“There’s no carbon captured, it just goes off into the atmosphere,” she said. “It’s also a waste of a valuable material.”

Varied background

Before becoming a soil scientist, Archuleta worked in construction and had experience with welding and fabricating machinery, which informed his work on the CharBoss.

After going back to school, he became interested in soil science and enrolled in a work-study program that served as the starting point for his career in the Forest Service.

“It seemed to click,” he said.

Though he retired from the agency earlier this year, Archuleta still works as a contractor to help study and popularize mobile biochar systems.

His interest in biochar production was sparked about 15 years ago, when he had to import the substance from Canada for research about improving wild game forage in national forests.

“It wasn’t easy to find,” he said.

Biochar is basically just burned wood but it has complex properties, activating biological activity and speeding the decomposition of organic matter in the soil, Archuleta said.

“It’s not charcoal you’d find in a Kingsford bag because that has a lot of other stuff in it,” he said.

Nitrogen rain

Newly created biochar is like a dead battery that gradually becomes “charged” with nutrients that attach to the carbon, he said. Nitrogen in the atmosphere is picked up by precipitation, deposited in the biochar and released over time into soil.

“Every time it rains, nitrogen is falling with that raindrop,” Archuleta said. “As water washes through that pile of charcoal, it will pick up some of those nutrients.”

Fuel reduction treatments in the national forests are expensive, costing about $2,000 per acre in Western Oregon, he said. If those slash piles could be turned into a salable product, that could offset some of the government’s expenses.

Equipment modification

The Air Burners company was already making machinery to dispose of vegetative waste, which happened to generate some biochar. Archuleta approached the manufacturer with the idea of altering one of its containers to specifically produce and capture the soil amendment.

After some trial and error, they arrived at a design in which the bottom of the container is composed of two steel panels that descend at an angle with a narrow opening between them.

One of the panels slides back and forth, agitating the burning wood so it eventually falls out the opening at the bottom, as through a hopper. The material is extinguished as it drops into a pan of water from which the biochar is removed.

Though the machinery is made of steel panels with inlaid heat-resistant ceramic, the motor that powers the sliding panel is located in a separate compartment from the burn chamber to further protect it from the fire.

“We’re trying to keep the moving parts away from the heat as far as possible,” which prevents them from warping and misaligning over time, Archuleta said.

‘Air curtain’

Another key component of the machine is the “air curtain,” which is comparable to the blast of air at the entrance to big box retail stores.

Those air curtains separate the climate-controlled environment from the outdoors. In this case, the air curtain traps the smoke that would otherwise escape the container, creating a secondary burn chamber in which those particles are basically turned into gas.

“We’re trying to capture the particles of smoke beneath the air curtain and cause them to re-burn,” said Brian O’Connor, the company’s CEO and chief engineer.

Smoke particles are small enough to get past the body’s defenses and endanger human health, but the air curtain diminishes and dilutes them enough to eliminate that hazard, he said.

Blowing air also helps process woody biomass into biochar more quickly, O’Connor said. “When you have that much air in there, it helps the fire burn faster.”

Cooperative agreement

The company has entered into a “cooperative research and development agreement,” or CRADA, with the federal government and began selling the CharBoss commercially this year.

The Forest Service has already ordered a half-dozen machines and roughly the same number have been ordered by commercial contractors, such as those who work on fuels reduction in national forests.

O’Connor said he believes the equipment will prove useful in other natural resource industries, such as processing vineyard and orchard prunings for incorporation into the soil.

“Being able to turn it into biochar and return it to the earth is ideal because it’s a natural process,” he said.

Jim Archuleta

Occupation: Retired U.S. Forest Service soil scientist

Age: 60

Hometown: Portland, Ore.

Education: Bachelor’s degree in crop and soil science from Oregon State University in 1997

Family: Wife, Joy, a grown son and daughter, and two grandchildren