Salting And Burying Biomass Crops In Dry Landfills Could Economically Capture Greenhouse Gases For Thousands Of Years

As reported today in the journal Proceedings of the National Academy of Sciences, researchers propose growing biomass crops to capture carbon from the air, then burying the harvested vegetation in engineered dry biolandfills. This unique approach, which researchers call agro-sequestration, keeps the buried biomass dry with the aid of salt to suppress microbials and stave off 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 in UC Berkeley's Department of Electrical Engineering and Computer Sciences.

"We're claiming that proper engineering can solve 100% of the climate crisis, at manageable cost," said Yablonovitch. "If implemented on a global scale, this carbon-negative sequestration method has the potential to remove current annual carbon dioxide emissions as well as prior years' emissions from the atmosphere."

Unlike prior efforts toward carbon neutrality, agro-sequestration seeks not net carbon neutrality, but net carbon negativity. According to the paper, for every metric ton (ton) of dry biomass, it would be possible to sequester approximately 2 metric tons of carbon dioxide.

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

The idea of burying biomass in order to sequester carbon has been gaining popularity, with startup organizations burying everything from plants to wood. But ensuring the stability of the buried biomass is a challenge. While these storage environments are devoid of oxygen, anaerobic microorganisms can still survive and cause the biomass to decompose into carbon dioxide and methane, rendering these sequestration approaches carbon-neutral, at best.

But there is one thing that all life forms require—moisture, rather than oxygen. This is measured by "water activity," a quantity similar to relative humidity. If internal water activity falls below 60%, all life comes to a halt—a concept underpinning the UC Berkeley researchers' new agro-sequestration solution.

"There are significant questions concerning long-term sequestration for many of these recently popularized nature- and agriculturally-based technologies," said Harry Deckman, co-author of the study and a researcher in the Department of Electrical Engineering and Computer Sciences. "The agro-sequestration approach we're proposing can stably sequester the carbon in dried salted biomass for thousands of years, with less cost and higher carbon efficiency than these other air capture technologies."