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Dry Biomass Landfills Could Be A Brilliant Climate Solution
Sometimes, simple technology is better.
A recent study has proposed a potentially revolutionary, novel, and surprisingly simple carbon sequestration technology. The basic idea is to grow crops for biomass and then bury this biomass, along with salt, in sealed, dry landfill sites. This way, no microbes or other organisms can break down the bio-mass, meaning the carbon it contains stays locked away from the atmosphere for at least a thousand years. This technology is so simple that it would cost only $60 per metric tonne of stored carbon dioxide, making it by far the cheapest form of long-term carbon storage. So, the question has to be asked, can this save the world? Or is there a drawback?
Before we address this study, let’s first talk about carbon capture and storage. You see, to fully halt the oncoming climate disaster, humanity needs to be carbon-neutral by 2050. Even then, a sizeable amount of environmental, economic and human damage will be done. But, many industries we rely on, such as meat production, metal refining and mining, have no viable route to go carbon negative. As such, we need to be able to capture and offset carbon dioxide on the scale of billions of tonnes of carbon dioxide per year to reach our climate goals.
But carbon capture and storage technology is insanely expensive, costing around $600 per metric tonne of carbon dioxide stored. This expense, along with the vast amount of complex infrastructure needed to support technology-driven carbon capture machines (electricity, solvents, filters etc.), means that our current carbon capture technology can’t be scaled up to meet our needs.
This is why this study is so fascinating! The carbon capture and storage method it describes doesn’t require any fancy new infrastructure, complex machines or state-of-the-art technology. Instead, all you need is a farm, a digger, some polyethylene and salt. This makes it both highly scalable and super cheap. Let me explain.
It all starts with photosynthesis. Plants take carbon dioxide and water, then use energy from sunlight to react them together to form carbon-rich sugars such as glucose and oxygen. The plant releases this waste oxygen into the atmosphere and uses the sugars as fuel to keep itself alive. But the plant also uses these sugars to build its body. Vascular plants, such as corn, wheat and trees, use complex organic polymers such as lignin and cellulose to give their stems, trunks, branches and roost structure. But lignin is just a chain of interlinked sugar molecules.
The bonds between the sugars in lignin and cellulose are so strong that plant tissues rich in this polymer are pretty much inedible for most organisms. In fact, wood is mainly made up of these compounds, hence why it is so tough.
However, when a plant dies, bacteria and fungi from the soil have enzymes capable of breaking down lignin and accessing these locked-away sugars. As they digest this lignin, they emit its carbon in the form of carbon dioxide and methane, effectively releasing it back into the atmosphere and completing the carbon cycle.
This study proposes that we interrupt this natural cycle at the point of decomposition.
You see, all living organisms require water to work, as the chemistry that keeps cells alive has to happen in water. Even those that have adapted to live in extremely arid climates still require water of some kind. So if we take bio-mass, which is rich in these plant-derived organic molecules (meaning they contain a lot of carbon from the atmosphere) and lock it away in a completely dry environment, we can stop the microbes from breaking it down, and this carbon stays locked away from the atmosphere.
The authors of this study didn’t just stop here. They came up with a viable method of using this concept and analysed how effective it would be and how expensive it would be.
Their method starts with growing crops to produce biomass. This can either be specific crops only good for biomass, such as fast-growing grasses or as a crop with a high biomass by-product, such as corn (stalks). Then, dry this biomass out and mix it with salt. Then wrap the biomass in two layers of polythene and bury it in a landfill.
The polyethylene wrap keeps water out, ensuring the biomass stays bone dry. But, there will inevitably be water ingress. This is where the salt comes in, as it will absorb this water, keeping the relative humidity at zero. According to the study, the polyethylene wrap and the salt is enough to keep the biomass dry and biologically isolated for over a thousand years!
Very little energy, manufacturing or infrastructure is needed to do this method, which makes it incredibly efficient (i.e. it emits very little carbon per kg of carbon stored). There will be a tiny amount of carbon dioxide emissions from heavy farm equipment, fertiliser, and diggers, as well as producing polyethylene (which can be made from plants rather than oil) and salt. This, combined with the fact that organic molecules in biomass have more carbon in them by weight than carbon dioxide, means that every tonne of biomass stored this way has locked the equivalent of 2 tonnes of carbon dioxide out of the atmosphere!
Because of how stupidly efficient this method is, it requires very little upfront investment and minimal operational costs. As such, the authors of the study estimate that it could cost only $60 per metric tonne of carbon dioxide stored! That is about ten times cheaper than any carbon capture technology we currently have.
The average US citizen has an annual carbon dioxide footprint of 14.24 tonnes. Using this method, it would only cost $854.40 per year to offset that! Now, many can’t afford this cost to go carbon-neutral. Still, studies have estimated that once carbon capture gets to $50 per tonne of captured carbon dioxide, it is commercially viable, meaning governments will instead pay for it.
So, this method of carbon capture is so close to unlocking wide-scale carbon capture and helping humanity reach its net-zero targets! Right?
Well, no. The limiting factor here is space. To offset our current 35 billion tonnes of global carbon dioxide emissions, we would need to grow, process and bury 17.5 billion tonnes of biomass, or the equivalent weight of 35,000 Burj Khalifas! Average biomass yields are around 12.9 tonnes per acre, meaning it would take 1.4 billion acres of farmland to produce this vast amount of biomass. That means we would need to expand global arable farmland by 32%, which would take up the same space as one and a half Canadas! Then we need to somehow find the land area we have to bury this insane amount of biomass year-on-year, which is simply impossible without causing widespread ecological damage.
In short, this is a genius carbon capture method that is incredibly promising. Hats off to the researchers who created and tested it; it is a stroke of genius. However, because it relies on utilising crops, it can never be scaled up to the size where it can make us carbon-neutral. Sure, it can help us reach this goal, and maybe once our global carbon emissions are a fraction of what they are today, it could help us reach net-zero. But in the grand scheme of things, this method can only ever make a tiny dent in our climate sins. But you know what they say, every little helps.