To more effectively absorb biomass and carbon, simply add salt

Reducing global greenhouse gas emissions is essential to averting a climate catastrophe, but current methods of removing carbon are proving inadequate and expensive. Now researchers from the University of California, Berkeley, have proposed a scalable solution that uses simple, inexpensive technology to remove carbon from our atmosphere and store it safely for thousands of years.

As reported today in the journal Proceedings of the National Academy of Sciences, the researchers propose growing biomass crops to capture carbon from the air, then burying the harvested vegetation in dry engineered biolandfills. This unique approach, which the researchers call agro-sequestration, keeps buried biomass dry with the help of salts to suppress microbes and prevent decomposition, enabling stable sequestration of all the biomass carbon.

The result is carbon-negative, making this approach a potential game changer, according to Eli Yablonovitch, lead author and Professor in the Graduate School of UC Berkeley’s Department of Electrical Engineering and Computer Science.

“We claim that proper engineering can solve 100% of the climate crisis, at a manageable cost,” says Yablonovitch. “If implemented on a global scale, this negative carbon sequestration method has the potential to remove current annual carbon dioxide emissions as well as previous years’ emissions from the atmosphere.”

Unlike previous efforts towards carbon neutrality, agro-sequestration does not seek net carbon neutrality, but net carbon negativity. According to the paper, for every metric ton (ton) of dry biomass, it is possible to absorb about 2 tons of carbon dioxide.

Agro-sequestration: A way to stably sequester carbon in buried biomass

The idea of ​​burying biomass to sequester carbon has been gaining popularity, with startup organizations burying everything from plants to wood. But ensuring the stability of buried biomass is a challenge. While this storage environment is devoid of oxygen, anaerobic microorganisms can still persist and cause the biomass to decompose into carbon dioxide and methane, making this sequestration nearly carbon-neutral, at best.

But there’s one thing all life forms need—moisture, not oxygen. It is measured by “water activity”, a quantity similar to relative humidity. If internal water activity drops below 60%, all life ceases — a concept underlying a new agro-sequestration solution from UC Berkeley researchers.

“There are significant questions about long-term sequestration for many of these recently popularized nature-based and agriculture technologies,” said Harry Deckman, study co-author and researcher in the Department of Electrical Engineering and Computer Science. “Our proposed agro-sequestration approach can stably sequester carbon in dry brine biomass for thousands of years, at a lower cost and higher carbon efficiency than other air capture technologies.”

Hugh Helferty, co-founder and president of Producer Accountability for Carbon Emissions (PACE), a non-profit organization committed to achieving global net zero emissions by 2050, sees great promise in this solution. “Agro-sequestration has the potential to turn temporary nature-based solutions into permanent CO2 stores,” said Helferty, who was not involved in the study. “By building on their approach, Deckman and Yablonovitch have created an invaluable new option for tackling climate change.”

Reach the proper degree of dryness to prevent decomposition

Living cells must be able to transfer water-soluble nutrients and water-soluble wastes across their cell walls in order to survive. According to Deckman, dropping water activity below 60% has been shown to stop this metabolic process.

To achieve the degree of dryness required, Yablonovitch and Deckman took inspiration from a long-term food preservation technique that dates back to Babylonian times: salt.

“Drying, sometimes aided by salt, effectively reduces the internal relative humidity of the sequestered biomass,” says Yablonovitch. “And it has been shown to prevent decay for thousands of years.”

The researchers point to a date palm named Methuselah as evidence that biomass, if kept dry enough, can be preserved into the next millennium.

In the 1960s, Israeli archaeologist Yigal Yadin found date seeds among ancient ruins atop Masada, a mesa overlooking the Dead Sea – one of the world’s driest places. The seeds sat in a drawer for more than 40 years, until Sarah Sallon, a doctor who researches natural medicines, requested them in 2005. After the seeds were carbon-dated, she learned they were 2,000 years old and then asked horticulturist Elaine Solowey to plant them. They germinated, and Methuselah, one of those date palms, continues to thrive today.

“This is proof that if you keep biomass dry it will last for hundreds to thousands of years,” Yablonovitch said. “In other words, it’s a nature experiment that proves you can preserve biomass for 2,000 years.”

A cost-effective and scalable approach

As well as offering long-term stability, Yablonovitch and Deckman’s agro-sequestration approach is highly cost-effective. Together, agriculture and biolandfill cost a total of US$60 per tonne of carbon dioxide captured and sequestered. (By comparison, some direct air capture and carbon dioxide sequestration strategies cost US$600 per tonne.)

“Sixty dollars per tonne of carbon dioxide captured and sequestered corresponds to a surcharge of $0.53 per gallon of gasoline,” says Yablonovitch. “At this price, offsetting the world’s carbon dioxide emissions would return the world economy 2.4%.”

Researchers have compiled a list of more than 50 high-yielding crops that can be grown in a variety of climates around the world and with dry biomass yields ranging from 4 to more than 45 dry tons per hectare. All have been selected for their carbon sequestration abilities.

These solutions can also be scaled up without interfering with or competing with agricultural land used to grow food. Many of these biomass crops can be grown on marginal grassland and forest lands, or even on agricultural land that remains vacant.

“To remove all the carbon produced would require a lot of farmland, but the actual amount of farmland available,” says Yablonovitch. “This will be a big advantage for farmers, because there is agricultural land that is currently underutilized.”

Farmers who harvest this biomass crop will dry the crop, then bury it in an engineered dry organic waste dump located within the agricultural area, tens of meters underground and safe from human activity and natural disasters.

The researchers based the design of this dry burial structure on current municipal landfill best practices, but added additional devices to ensure dryness, such as two layers of 2-millimeter-thick nested polyethylene encasing biomass, a practice already used in modern landfills.

The landfill area will only cover a small part — 0.0001% — of the agricultural area. In other words, 10,000 hectares of biomass production can be buried in 1 hectare of biolandfill. Additionally, the top surface of the landfill can be returned to agricultural production afterward.

The fast road to adoption

The timeline for the adoption of these methods of carbon capture and sequestration can be short, according to Deckman. “Agro-sequestration is technologically ready, and construction of engineered biolandfills can start after one growing season,” he said.

Yablonovitch and Deckman’s analysis shows that farmers can switch to biomass farming more quickly. They estimate it will take about a year to convert existing farmland to biomass farming, but much longer for virgin land that lacks the necessary infrastructure to support farming. Biomass plants will be ready for harvest and sequestration in one growing season.

Using this approach, the researchers calculated that capturing about half of the world’s greenhouse gas emissions – about 20 gigatonnes of carbon dioxide per year – would require agricultural production from an area equal to one-fifth of the world’s cropland or one-fifteenth of the land area for all land. agriculture, pastures and forests. According to their report, this amount of land is equal to or less than the total area considered by many Intergovernmental Panel on Climate Change models for greenhouse reduction for biomass production.

“Our approach to agro-sequestration offers many benefits in terms of cost, scalability and long-term stability,” says Yablonovitch. “In addition, this technology uses existing technologies at known cost to provide a practical pathway to remove carbon dioxide from the atmosphere and solve the climate change problem. Nonetheless, society must continue its efforts towards decarbonization; developing and installing solar and wind technologies; and revolutionizing energy storage.”