Burying plant waste removes CO2 from the air. But can it scale?

In Arkansas, millions of acres of spindly pines and hardwood trees are logged every year to make plywood, planks and paper, a process that generates plenty of bark, sawdust and other woody waste. Still more land across the state is carpeted by low and grassy rice crops, which leave behind husks and stalks after every harvest.

These scraps of biomass are rich in the carbon dioxide that plants absorb during photosynthesis, presenting an opportunity for those looking to take on climate change. Companies and scientists have dozens of ideas for how nature’s leftovers might help the planet. They can be made into alternative fuels for airplanes and cargo ships to displace petroleum. They can be turned into chemical products, transformed into hydrogen or used to nourish farmland.

The startup Graphyte is doing something else: Burying biomass to trap CO₂ deep in the ground.

Last month, the Memphis-based company opened a first-of-a-kind facility at an empty warehouse in Pine Bluff, Arkansas. Graphyte takes waste from nearby rice and timber operations, runs it through a gas-fired drum dryer, then molds the residues into polymer-sealed bricks. The idea is to keep moisture from seeping in, which would cause biomass to decompose and release CO₂ — sending the planet-warming gas back into the air.

Graphyte, which is backed by Breakthrough Energy Ventures, plans to store the beige blocks in polyethylene-lined pits, similar to how construction debris is buried in landfills today. The one-year-old company expects state regulators to issue its landfill permit sometime later this spring. Once that’s in hand, Graphyte can begin stashing CO₂-rich bricks beneath the fields of southern Arkansas.

Barclay Rogers, the company’s CEO, said Graphyte was born out of the desire to find a more affordable and energy-efficient way of permanently removing CO₂ from the atmosphere. Climate scientists agree that at least some carbon removal is necessary to achieve net-zero emissions by 2050. But the current slate of techniques remain unproven, expensive and energy-intensive — potentially limiting their uptake over the coming decades.

“We need technologies that can scale very quickly,” Rogers said in mid-March, speaking from a coffee shop near the company’s facility, which it named Loblolly after the local pine tree species. (He declined for now to share how much the facility cost to build and operate, or how much funding the company has raised to date.)

Rogers said the brick-burying project will remove 15,000 metric tons of CO₂ from the atmosphere this year. That’s equal to only 4 percent of the annual emissions from a single U.S. gas-fired power plant. Still, it’s notably more carbon-removal capacity than the largest existing direct air capture projects, including Climeworks’s Orca plant in Iceland and Heirloom’s new facility in California, which claim to capture up to 4,000 tons and 1,000 tons of carbon per year, respectively.

Graphyte’s first customer, American Airlines, has agreed to purchase 10,000 metric tons of permanent carbon removal from the Arkansas facility, to be delivered in early 2025.

The company’s plans come amid a broader discussion that’s building around how, exactly, the world should use its finite biomass resources to help meet the world’s climate and energy needs.

Demand is building for biofuels that can help slash emissions from giant fleets of trucks, planes and cargo ships. At the same time, researchers and companies like Graphyte are pursuing ways to use residues and waste for different kinds of carbon removal. All of this raises questions about which solutions are the highest and best use of biomass. The answers tend to vary, based on if you’re prioritizing costs or climate impact, and depending on which assumptions researchers make about what’s sustainable or technically possible.

Amassing biomass

The topic of biomass is already fraught enough, based on its existing uses.

Today, the United States uses roughly 340 million dry tons of biomass per year, very little of which is from farm and forestry waste. Nearly all of the nation’s supply comes from corn crops, wood chips and, to a lesser extent, landfill gas.

Most of it is turned into transportation fuels for cars and trucks, or used to generate power and heat. Burning biomass for energy does return CO₂ to the atmosphere. These practices can still be less carbon-intensive than fossil fuels on a life-cycle basis. But sometimes, they may ultimately be worse for the climate, as can be the case for corn ethanol and wood-burning power plants.

Still, as the U.S. seeks to tap biomass from more sustainable sources — and for potentially more sustainable purposes, like carbon removal — recent studies suggest that there’s room to grow near-term.

A March report by the U.S. Department of Energy (DOE) predicts that the country could sustainably triple its production of biomass to more than 1 billion dry tons per year. That figure includes capturing the resources that are “currently available but unused,” such as agricultural waste and logging residues, which could together add around 350 million more dry tons of biomass per year. Another sizable share of resources come from purposefully growing more “energy crops.”

The types and quantities of available resources can vary widely throughout the country. A biofuels refinery or carbon-removal facility built in one location might have to truck in supplies from other regions, adding costs and CO₂ emissions from transportation. In the future, competition could make it harder and more expensive for certain sectors to get their hands on old corn stalks, rice husks, mulch piles and other materials. One industry in particular — aviation — is expected to need significantly more biomass in the coming years to produce alternative jet fuels.

“As we scale up, there is a sort of conflict that we see long-term” between industries, said Charlotte Levy, the managing advisor for science and innovation at Carbon180, a nonprofit advocacy group. “We’ll have to be thinking about what’s the best use of that biomass.”

Those tensions were highlighted in another DOE-backed report, which was led by Lawrence Livermore National Laboratory. The “Roads to Removal” study analyzed how the U.S. could remove and store 1 billion metric tons of CO₂ every year. Getting to “gigaton-scale” carbon removal is considered key to meeting the nation’s goal of net-zero emissions by 2050.

As one example, the report’s authors looked at the role that “biomass carbon removal and storage” solutions could play. The relatively new term refers to using plants to remove CO₂ through photosynthesis, then deploying technology to store that carbon, be it underground or in the form of long-lived products like bio-oil, bioplastics, or Graphyte’s plastic-entombed bricks. (A related concept, “bioenergy with carbon capture and storage,” emphasizes energy production over carbon removal.)

The country could potentially get 700 million metric tons of CO₂ removal per year by 2050, using only biomass wastes and residues from forest-thinning practices, according to the report.

Removing CO₂ with those resources would cost on average $80 per metric ton. Current estimates for direct air capture systems — one of the buzziest and most well-funded forms of carbon removal — range from roughly $400 to $1,000 per metric ton of CO₂ removal. Graphyte, for its part, says it’s already selling CO₂ removal at $100 per metric ton.

However, researchers pointed out that the same residues and scraps could be used instead to make sustainable aviation fuel, or SAF. That would “considerably reduce” the volume of direct CO₂ removal, but it would also “contribute substantially” to decarbonizing the aviation industry, they said. Burning biofuels in jet engines does return CO₂ to the atmosphere, but on a life-cycle basis, SAF can be much less carbon-intensive than fossil jet fuel.

The Biden administration has set a goal of boosting U.S. consumption to around 35 billion gallons of SAF per year by 2050, up from 24.5 million gallons in 2023.

“The nation may prefer to use organic wastes and biomass to make sustainable liquid fuels — this must be balanced with the desire for carbon removal,” the report’s authors wrote. “There are multiple ways to use our fundamentally limited resources,” they added.

What to do with residues?

Graphyte’s facility in Arkansas represents yet another way to use these resources. But while the company hopes it can drive serious CO₂ reductions, experts say they see a more limited role for this method, especially as the market for bio-based products grows.

“With the companies that are looking to just literally bury [biomass], it’s kind of a wasted opportunity,” said Jennifer Pett-Ridge, a senior staff scientist at Lawrence Livermore and author of the Roads to Removal report.

“It’s good in the sense that you’re removing CO₂,” she added. “But there are so many other materials that can be made out of biomass that benefits society and financially creates an industry.”

Beyond the jet fuel example, biomass can, for instance, be made into hydrogen for decarbonizing heavy industries. It can become bio-oil to replace petroleum for making asphalt. Biochar, made by burning plant waste, can be spread over fields to improve soil health — and sequester carbon. Refineries that process biomass into fuels can use the solid leftovers to generate on-site electricity, reducing the overall CO₂ emissions of their operations.

The biomass situation becomes even more complex when looking beyond the United States. Recent global analyses use different methods than the U.S.-focused studies, and they suggest that the world’s biomass supplies might not be able to increase all that significantly from today’s levels, experts say. When considering just existing uses — liquid biofuels and electricity and heat — the world may already be fast approaching the limits of sustainably produced biomass supplies.

“The big issue is, if we’re going to do carbon dioxide removal, where are you getting that biomass from?” said Rudy Kahsar, a manager of the climate-aligned industries program at RMI, a clean-energy think tank. “I would say that this space is already over allocated.” (Canary Media is an independent affiliate of RMI.)

He pointed to projections by Energy Transitions Commission, an international think tank, which indicate the world has already maxed out on sustainable biomass. A separate outlook by the International Energy Agency says the world could nearly double its current biomass capacity by 2050 without causing significant damage to ecosystems and communities.

Kahsar said that, in order for carbon removal solutions to play a significant role in fighting climate change, they need to reach massive levels of carbon removal. And that might ultimately be hard for Graphyte and competing companies to achieve using biomass waste.

“There’s going to be a crunch,” he said. While Graphyte has a “cool process,” he added, “I don’t think it has the potential to scale the way we would need long term.”

Barclay Rogers, Graphyte’s CEO, said he didn’t share those concerns. He said the company’s approach is “biomass agnostic,” meaning they can use a variety of materials in a number of different locations, including places where a big fuel-making biorefinery is unlikely to go. He added that, if the goal is to remove as much atmospheric CO₂ as possible, then it’s hard to beat the efficiency of burying it in the ground.

“We’re talking about permanent, affordable, scalable carbon removal,” he said. “That’s what the world needs, right?”

Graphyte is working to curb its own emissions from the Arkansas facility to improve its overall climate benefit. The plant currently uses fossil gas to dry biomass in drum-dryers, though Rogers said his team is exploring replacing gas with passive solar techniques — like putting materials under black-roofed sheds — or with electricity from biomass-burning boilers. Graphyte claims its process uses around 0.8 gigajoules of energy per-ton of CO₂ removal, or about one-tenth the energy requirements of direct air capture plants.

Ultimately, it will be hard to settle the debate over the best uses of biomass until companies, researchers and policymakers have more solid data on just how effectively carbon-removal techniques do the job. Scientists are still developing tools to accurately measure and monitor CO₂ removal at massive scale. Industry groups and government agencies are still determining how companies should report and verify their measurements.

“That’s why it’s so important right now to invest in understanding: is this really carbon negative?’” said Charlotte Levy of Carbon 180.

She noted that in February, the DOE announced plans to award up to $100 million to support pilot projects that demonstrate carbon-removal technologies — while also following detailed monitoring, reporting and verification protocols. The funding opportunity is specifically targeting small “biomass carbon removal and storage” projects, as well as initiatives to use enhanced mineralization technologies and systems that integrate multiple techniques.

“How carbon negative [a technology is] is what’s going to allow us to put some sort of financial incentive on that biomass long-term, and get it where it can do the most good,” Levy added.