A Cost-Effective Solution to Climate Change: Burying Biomass in Dry Landfills

Diagram of a Biolandfill for Agro Sequestration

A simplified version of the biolandfill technology used for agro-sequestration. To keep the biomass dry, it’s necessary to use two layers of high-density polyethylene with a combined thickness up to 4 millimeters. The plastic acts as a water diffusion barrier, allowing less than 1.75 micrometers equivalent water thickness to diffuse through annually. This rate of water diffusion can be accommodated for thousands of years by the dry salt-biomass mixture, which can absorb the water without increasing its own relative humidity (water activity) above 60%. Water activity below 60% suppresses all life and all biodegradation. Credit: Eli Yablonovitch and Harry Deckman

Storing biomass in dry landfills by salting and burying it can economically preserve greenhouse gases for thousands of years.

Lowering the worldwide greenhouse gas emissions is crucial to avoiding a climate disaster, but existing carbon removal techniques are proving to be inefficient and expensive. A team of researchers from the University of California, Berkeley, has come up with a scalable answer that utilizes basic, low-cost technologies to remove carbon from the atmosphere and safely store it for thousands of years.

In a report recently published in the Proceedings of the National Academy of Sciences, the researchers propose a new unique approach to capturing carbon from the air, called agro-sequestration. This method involves growing biomass crops and then burying the harvested vegetation in specially designed dry biolandfills. The buried biomass is kept dry through the use of salt to inhibit microbial activity and prevent decomposition, allowing for the stable sequestration of all the carbon in the biomass.

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 a 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 (tonne) of dry biomass, it would be possible to sequester approximately 2 tonnes of carbon dioxide.

Harvesting of Miscanthus, a Fast Growing Carbon Sink

Harvesting miscanthus, a quickly-growing grass that can be used as a bioenergy crop or harvested, salted, and buried to sequester the carbon it took in from the atmosphere. Credit: Erik Sacks, courtesy of Joint Genome Institute

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.”

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

Achieving the right level of dryness to prevent decomposition

Living cells must be able to transfer water-solubilized nutrients and water-solubilized waste across their cell walls to survive. According to Deckman, decreasing the water activity below 60% has been shown to stop these metabolic processes.

To achieve the necessary level of dryness, Yablonovitch and Deckman took inspiration from a long-term food preservation technique dating back to Babylonian times: salt.

“Dryness, sometimes assisted by salt, effectively reduces the internal relative humidity of the sequestered biomass,” said Yablonovitch. “And that has been proven to prevent decomposition for thousands of years.”

Researchers point to a date palm named Methuselah as proof that biomass, if kept sufficiently dry, can be preserved well beyond the next millennium.

In the 1960s, Israeli archaeologist Yigal Yadin discovered date palm seeds among ancient ruins atop Masada, a mesa overlooking the Dead Sea — one of the most arid places in the world. The seeds remained in a drawer for more than 40 years, until Sarah Sallon, a doctor researching natural medicines, requested them in 2005. After having the seeds carbon-dated, she learned that 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,” said Yablonovitch. “In other words, it is a natural experiment that proves you can preserve biomass for 2,000 years.”

A cost-effective, scalable approach

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

“Sixty dollars per tonne of captured and sequestered carbon dioxide corresponds to an added cost of $0.53 per gallon of gasoline,” said Yablonovitch. “At this price, offsetting the world’s carbon dioxide emissions would set back the world economy by 2.4%.”

The researchers have compiled a list of more than 50 high-productivity plants capable of being grown in diverse climates worldwide and with dry biomass yields in a range from 4 to more than 45 dry tonnes per hectare. All have been selected for their carbon-capturing abilities.

This solution also can scale without encroaching upon or competing with farmland used to grow food. Many of these biomass crops can be grown on marginal pasture and forest lands, or even on farmland that has remained fallow.

“To remove all the carbon that’s produced would require a lot of farmland, but it’s an amount of farmland that is actually available,” said Yablonovitch. “This would be a great boon to farmers, as there is farmland that is currently underutilized.”

Farmers harvesting these biomass crops would dry the plants, then entomb them in a dry engineered biolandfill located within the agricultural regions, tens of meters underground and safe from human activity and natural disasters.

The researchers based their design of these dry tomb structures on current municipal landfill best practices, but added enhancements to ensure dryness, such as two 2-millimeter-thick nested layers of polyethylene encasing the biomass, a practice already used in modern landfills.

The landfill area would cover only a tiny portion — 0.0001% — of the agricultural area. In other words, 10,000 hectares of biomass production could be buried in a 1-hectare biolandfill. In addition, the top surface of the landfill could be restored to agricultural production afterward.

A fast path to adoption

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

Yablonovitch and Deckman’s analysis shows that farmers could make the transition to biomass agriculture rather quickly. They estimate that it would take about one year to convert existing farmland to biomass agriculture, but longer for virgin land that lacks the infrastructure needed to support agriculture. The biomass crops would be ready for harvest and sequestration within a growing season.

Using this approach, the researchers calculated that sequestering approximately 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 row cropland or one-fifteenth of the land area for all croplands, pastures, and forests. According to their report, this amount of land is the same or less than the total area that many of the Intergovernmental Panel on Climate Change’s models for greenhouse reduction are considering for biomass production.

“Our approach to agro-sequestration offers many benefits in terms of cost, scalability, and long-term stability,” said Yablonovitch. “In addition, it uses existing technologies with known costs to provide a practical path toward removing carbon dioxide from the atmosphere and solving the climate change problem. Nonetheless, society must continue its efforts toward de-carbonization; developing and installing solar and wind technologies; and revolutionizing energy storage.”

Reference: “Scalable, economical, and stable sequestration of agricultural fixed carbon” by Eli Yablonovitch and Harry W. Deckman, 11 April 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2217695120

12 Comments on "A Cost-Effective Solution to Climate Change: Burying Biomass in Dry Landfills"

  1. Clyde Spencer | April 14, 2023 at 8:24 am | Reply

    This ‘solution’ sounds to me like “kicking the can down the road.”

    “Lowering the worldwide greenhouse gas emissions is crucial to avoiding a climate disaster, …”
    This is an assertion that one frequently reads. However, the evidence for it is based on models that, while often characterized as being based on ‘physics,’ are heavily parameterized. That is, subjective ‘expert’ judgement on how clouds behave on average. All but the Russian model run warm! If Earth continues to warm, things will change. On the other hand, if Earth should cool, things will change.

    One thing that geologists have contributed to the understanding of Earth is that Earth is in a constant state of change, typically at rates too slow to be noticeable in a lifetime. Although, as James Hutton was fond of saying, “The present is the key to the past.” Similarly, the past is the key to the future.

    • (not really a reply to your comment, sorry, but the new comment box is AWOL).

      Much simpler to leave fossil fuels in the ground. KISS.

      Excess biomass should be used to improved the soil, for example by converting it to charcoal, or fermented to produce biogas, or used as animal feed, building materials or burnt in combined heat & power plants.
      We don’t need such “solutions”.

  2. Hottan Bothred | April 14, 2023 at 10:01 am | Reply

    So they’re proposing landfills of fibre, wrapped in thick 4mil polyethelene plastic, also buried, and then highly salting the earth so nothing can ever grow. Without either, it will ferment, and emit CO2 and methane. It’s creative, but silly, and the exact opposite of old environmentalism. With their date-palm example in mind, why not store it in deserts? Or why not let it rot and capture the methane and carbon and use it to replace other fuels? Or at least burn it, capture the electricity, and then bury the remaining carbon charcoal? Currently such things are being plowed under to replace fertilizer, or used as animal feed, or otherwise not wasted in a landfill, or being shipped around to landfills by burning diesel.

    2.4% economic cost is too high. Countries are happy to grow at that rate. Putting the world economy into stagnation or recession would prevent people from caring about the environment, and they’ll do counter-productive things to survive. Are you willing to pay more than 2.4% for everything, earn 2.4% less, own posessions that are worth less, maybe lose your income entirely in a recession, and lose government financial support as well in cutbacks? Even if you are willing, you’ll need use cheaper fuels to live.

    “According to the paper, for every metric ton (tonne) of dry biomass, it would be possible to sequester approximately 2 tonnes of carbon dioxide.”, just no. There isn’t 2 tons of CO2 in 1 ton of dry biomass. If there is, either we can violate the conservation of mass law and solve problems that way, or the measurement technique is a hoax.

    • Benjamin Riker | April 14, 2023 at 5:19 pm | Reply

      Only 0.0001% of the land is salted not mass amounts of farmland wasted and you would put the landfills on the worst quality land in your area. If you used the biomass for fuel you would release crap into the air again instead of sequestering it away defeating the purpose. They cant store it in the desert because the landfills are meant to be close to where the crops are grown to burn less fuel transporting it.

      I don’t know how you can suggest 2.4% is too high of a cost. The costs from the effects of climate change will be far more than 2.4% a year.

      And to your last point you have to remember carbon dioxide is not just carbon, most of it is oxygen. The plant keeps the carbon and releases the oxygen into the atmosphere. Allowing you to sequester 2 tons of CO2 into 1 ton of dry biomass.

      • Clyde Spencer | April 15, 2023 at 6:18 am | Reply

        The important point is not the percentage of total land, but the percentage of arable land. That is, as you have already pointed out, the landfills would have to be in close proximity to arable land and not be mountains or desert. That means, over thousands of years, the landfills will continue to encroach on the arable land, reducing the availability. If there are significant disruptions from earthquakes, flooding, or war (as is happening today in the Ukraine) the salted landfills risk being breached. I don’t think that you or the authors have thought this through.

        Economists recommend limiting growth and inflation to 2% per year. This proposal comes in higher than that. Over long periods of time, even small differences that are compounded will grow huge. Can you provide a citation to support your assertion that “The costs from the effects of climate change will be far more than 2.4% a year?”

        Personally, I’d suggest solar pyrolysis, creating a truly recyclable and sustainable production.

  3. Another air fairy idea probably financed by the oil industry. The answer is plain and clear, stop immediately ALL leisure and business flights. Ban wrapping food in plastic for any purpose.
    Within five years electric vehicles will have long range batteries so ICE engines will be retired like horses (brought out for competitions and shows).

    • Clyde Spencer | April 15, 2023 at 6:38 am | Reply

      “…, stop immediately ALL leisure and business flights.”
      Why stop there? Ban automobiles and trucks and force everyone to use Amish buggies. Don’t just ban plastic food wrappings, but ban wax paper and plastic containers of all kinds, including for medicine. After computers are banned, we can go back to wrapping our food in yesterday’s newspapers.

      We have yet to learn just how durable the batteries are and whether constant bouncing and vibration will degrade them more rapidly than just sitting in a laboratory. Or, whether salt spray from Winter roads in the Rust Belt will find its way into the cases and cause spontaneous fires to increase with age when used in climates more harsh than Los Angeles.

      Within five years, people will realize how short-sighted the zealots are, and how little they understand the technologies that allow everyone to live better than kings of old.

      • No need to rant Clyde, the real elephant in the room is that there are just too many people for the planet to service, we have not had a big war for over 70 years so the population control of war has not been in place.

        • Clyde Spencer | April 17, 2023 at 8:18 am | Reply

          One man’s rant is another man’s reality. However, I agree that there probably isn’t a single environmental problem that wouldn’t be at least improved, if not solved, by a reduction in population. The problem is that there doesn’t seem to be a short-term, moral solution to the population issue. Wars not only cause great suffering, but they also devastate the environment and waste natural resources. However, looking at what is happening in countries like Japan and Italy, there is possibly a long-term solution.

          • Paul Dodd | May 9, 2023 at 8:36 am |

            With improvements in the social safety net, replacing the need to have children for your old age, better education, removal of subsidies for children, the population will decline naturally. Politicians need to see a declining population as a good indicator, and accept the need for immigration.

  4. The best carbon sink is life. The Isha Save Soil plan is doing this, now and it’s working!

  5. George T Fleming | April 16, 2023 at 1:37 pm | Reply

    I thought of Rafael Sabatini’s Scaramouche: “He was born with a gift of laughter and a sense that the world was mad.”

    I thought of the ancients, salting the fields of their enemies.

    I thought of the Earth, smothered in plastic.

    This idea is outrageously stupid. It is insane. I am not laughing.

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