Biomass burial is a CDR methodology that we haven’t yet dug into on our show. Compared to some CDR techniques, biomass burial is a surprisingly simple approach. It involves burying wood trimmings underground to prevent decomposition and thus, the release of carbon back into the atmosphere.
Our guests today are Ning Zeng, a professor at the University of Maryland and founder of Carbon Lockdown, and Daniel Sanchez, chief scientist for biomass carbon removal and storage at Carbon Direct.
They are both developing this methodology which attempts to take advantage of nature's ability to capture CO2 in trees. By creating wood vaults in a underground oxygen-free environment - they aim to preserve carbon for potentially thousands of years.
This method has begun to garner attention from investors, offset marketplaces like Puro, and the media.
On this episode we'll explore the science behind biomass burial, its potential impact on reducing atmospheric CO2, and how it fits into the larger CDR portfolio.
On This Episode
Radhika Moolgavkar
Resources
Ning’s academic work on Wood Vault approach
Puro listing for Carbon Lockdown Potomac project
Greenbiz article about woody biomass burial
Subscribe to Climate Workers Anonymous
My other show, Reversing Climate Change
Books referenced in the podcasts, at Bookshop
Full Transcript
Announcer: You’re listening to Carbon Removal Newsroom, a weekly show about current events in the world of carbon removal, from technology and innovation to policymaking and job growth. Brought to you by Nori, the carbon removal marketplace.
Radhika Moolgavkar: Welcome to the December 12th edition of Carbon Removal Newsroom. Today, we’re going to dive into a specific type of carbon removal called biomass burial. It’s a CDR methodology that we haven’t yet talked about on our show and compared to some CDR techniques. We also have Daniel Sanchez, Chief Scientist for Biomass Carbon Removal and Storage at Carbon Direct. Hi, Daniel. Hi, Daniel. Hi, Daniel. All right. So you two are both developing this methodology, which attempts to take advantage of nature’s ability to capture carbon dioxide in trees by creating wood bolts in an underground oxygen-free environment.
They aim to preserve carbon for potentially thousands of years. The method has begun to garner attention from investors, offset marketplaces like Puro and the media. So let’s just dive into it and understand the science behind biomass burial and its impact on removing carbon dioxide from the atmosphere. Ning, I’ll start with you because I know you’re quite an expert on this area. Why biomass burial? How long have you been studying it and what caught your attention?
Ning Zeng: Do you want a long version or a short version?
Radhika Moolgavkar: Long. Let’s have the long version, Ning. Tell us. I’d love to hear your history.
Ning Zeng: Okay. So I have been studying biomass burial for more than 15 years. You know, I’m a climate scientist. My specialization is the global carbon cycle. Couple of events that really got me in this direction. One was I was in Europe during the 2003 heat wave. I went through that whole summer trying to set up a house without air conditioning. And then the second event, of course, was back here, Hurricane Katrina in 2005. So it was already clear to me at that time. It’s not a question of whether climate change is real, but it’s a question of what do we want to do about climate change?
So I look at the components of the global carbon cycle, land, ocean, geological reservoirs. And realize that this part of the terrestrial carbon cycle could be a effective spot for human intervention. Kind of the longer story, the exact idea of bearing biomass had to do with, I started to teach a class on carbon cycle and climate change in 2006 at University of Maryland. We were discussing the class, the missing carbon sink. So it’s one of the two leading mysteries in global carbon cycle research. We still today don’t have a good answer, but one of the ideas we came up in the class was a landfill.
We know landfill buries organic matter in particular wood for quite some time. We look at it, discuss it. We went to visit a landfill and then at the end that we realized the carbon sink due to landfill burial It was really quite small, 0. 1 gigatonne per year. And with that in mind, I went to Australia during the summer for a meeting. During the tea break, I was talking to Daniel Nipstad, who is the leading Amazon ecologist, who is expert on Amazon deforestation. And then on the other side, I got Anid Cauway, who is a landfill expert from Australia.
So while Dan Nipstad was telling us how The deforestation was actually conducted. They cut the trees with chin and brought down the trees with two excavators and then pile them up, let them dry. A few years later, dry seed, then they spray kerosene and burn it. So then on their head side, I had a need. I was asking her about the landfill carbon sink. So suddenly I said, Hey, how about instant burning? How about we just bury that? So we laughed and then went back to our meeting. But on my way back from Sydney to LA, a 15 hour flight, I was totally jet lagged and the season lagged.
Could not sleep and the idea came back. So I took out a piece of napkin and spent basically the whole flight and writing down numbers. So those numbers were pretty much the main numbers I had in a paper that was published in 2008 called the Carbon Sequestration via Wood Burial. So that’s kind of like a version of how the concept came about. Of course, over the last 15 years, we’ve done two demo projects, in particular one in Montreal, where we buried 35 tonnes of Wood residuals, and nine years later we excavated, showed that it’s basically still intact after nine years burial.
So that’s kind of like a version of how this came about.
Radhika Moolgavkar: That’s a fantastic origin story. I mean, it literally started on a napkin. How often do you hear that? That’s... That’s an amazing confluence of creativity, students, and happenchance. I love it. Dan, I’m going to turn to you next. Your work at Carbon Direct has you covering a wide range of biomass-based carbon removal methods. So in your mind, what sets biomass burial apart and how do you think about it in comparison to other ways that dead trees or excess woody biomass could be stored as carbon?
Daniel Sanchez: Thanks. So at Carbon Direct, we work with some of the largest buyers of carbon removal on the voluntary carbon market. And I think woody biomass burial has very recently kind of emerged as an opportunity that people are excited about. And I would say it’s for a few reasons. The first is, you know, much like it can be written down on the back of a napkin. It’s a relatively simple approach. It doesn’t require incredibly costly machines. It doesn’t require large changes to the earth or burying CO2 thousands of meters underground. We’re talking about burying wood a few meters below the ground where we expect it not to decompose for centuries or millennia.
And, you know, aside from the simplicity, that also leads to a relatively low cost. It’s been hypothesized that this can be done for $100 per tonne of CO2 removed from the atmosphere. I will also say that the carbon removal efficiency of this approach can be relatively high as well. If you want to think about the carbon that was originally removed from the atmosphere in the biomass and the fraction of that ends up being durably stored out of the atmosphere. Taking wood and burying it is a relatively high mass efficiency. It’s better than, say, making transportation fuels from that biomass and capturing the byproduct CO2.
You get to put a decent amount of the carbon underground. And again, that’s part of the simplicity and that’s part of the low cost.
Radhika Moolgavkar: So Ning, can you tell us more specifics about how your wood vault technique works? And what are the technological and engineering elements that are being developed that set it apart from the Generalized idea of woody biomass burial.
Ning Zeng: Yes. So the main concept of wood vault is to bury unmerchantable wood residuals in these specially engineered structures to prevent decomposition as preserving wood for a long time. We target a thousand years or longer. And the main principle here is that Wood is decomposed by fungi, termites, and other decomposers, and they all need three conditions to survive, oxygen, water, and saltwater temperature. So if we can cut off any of the three main ingredients they need, they will not be able to survive. So we have the hope to preserve wood for a long time.
So we just need to ensure the burial condition is either anazic, dry, or cold. Any one of these, if we can ensure it high fidelity, it will work. So carbon lockdown specifically focuses on underground burial to create the anazic condition, one of the three conditions. And we focus on this one is because we think it’s most widely applicable and it’s practical and most economical. But this does not include other conditions can be created, of course, under certain conditions that are also can be very workable. So to ensure oxygen depletion, this requires low permeability soil.
Which we identified and with experiments as well as theoretically and different evidence to show that this is a key. So the engineering goal would be to ensure another condition by careful site selection and characterization and build the wood vault. So I want to clarify a little bit. Often when people hear vault, they think of like a concrete or metal structure. So here we are actually not talking about that. You could build a concrete structure, yes, but that’s probably too expensive. Here we’re talking about the natural condition, really underground with the right kind of soil.
That is a vault. So the engineering part is find the right place and bring it in there. It’s a natural vault that requires human engineering to get it there. So in that sense, we call it a vault.
Radhika Moolgavkar: So I have a few follow-up questions just to make sure I understand it. My first question for you is how prevalent is this type of soil that’s lacking permeability and in what parts of the world is it most commonly found?
Ning Zeng: They are everywhere. You know, the soil types are, there are three types, sand, silt, and clay. So clay, of course, not all. All clay is created equal, but in general, clay condition is suitable and clay is widely distributed in the sense that it’s not like you throw a dart anywhere it’s going to be clay. But if you have sufficient wood source at one spot, you look around the area, you will find clay soil within economically viable distance.
Radhika Moolgavkar: And then my second question is when you talk about the vault and how deep do you have to bury it for it to get into that vault stage, if you will?
Ning Zeng: Great question. The depths depends on the permeability itself. That’s why by saying clay is not enough. So, you know, clay is a whole class of soil. We need to actually measure the permeability, which depends also on some other factors like compactness. But typically, in most soil, unless it’s very sandy, below one meter is already adnostic, because the active biosphere is typically limited to the first meter of soil. So like in our implementation guidance, we specified below the active biological soil layer, there is additional meter also. Clay soil. So we’re talking about overall just few meters below the surface and you can go as deep as engineer and allows economically viable.
Radhika Moolgavkar: Thank you. So Daniel, I’m going to turn it back to you because I’m going to zoom out a little bit and ask about the ecosystem. What is known about the ecosystem effects of the process? Ning described, obviously depths can vary depending on multiple factors. And how on the longer term horizon is MRV being thought about?
Daniel Sanchez: Well, we could spend a few hours on MRV. Maybe we’ll save that and I’ll just quickly answer on the ecosystem effects. So this is relatively benign and I think it typically involves co-benefits. The space you need for wood burial underground is surprisingly small. I don’t think we’re going to have huge disruption of land in order to build wood faults. We’ll probably just be using it on You know, the edges of fields and the edges of lots and the places that are kind of just undisturbed for some time. I think the co-benefits really come from the woody biomass utilization and what that could open up in terms of a circular bioeconomy and greater value for biomass products, including low value wood.
I think that could have a large impact on forest health and forest sustainability and excited to think about that more. We’re only doing this at a few thousand tonnes.
Radhika Moolgavkar: I know you didn’t want to go into depth on MRV, but I do have to ask a follow-up question. You are selling these, I think, as credits right now or experimenting. So how are you thinking about that framework or at least developing it out? Like, what are you telling buyers you’re thinking about as the pathway?
Daniel Sanchez: Sure thing. So I guess first I’ll say Carbon Direct isn’t selling biomass burial credits at this point. We do operate a platform where we sell supply, but we haven’t contracted for biomass burial yet. I think we’re looking closely at it as a lot of buyers are really excited about it. I think ultimately this wood burial is something we’re going to be kind of like flying the plane while we’re building it. We’re going to start burying wood. And I think we need a series of controlled experiments to really prove out our hypotheses and understand The failure mechanisms that we’re going to have from these vols.
So I’m a big believer of kind of learning while deploying. And I think there are huge opportunities to do that. We can improve our mechanistic understanding of these systems. We can adequately instrument them and measure them to know when and why they fail. And I think that’s an absolutely key part of doing monitoring, reporting, and verification. You know, the implementation guidance that Ning and I spoke about not only talks about guidance for vault design in terms of the soil and the size and the depth, but I think more importantly, like where you put your sensors, what kind of predictive model you build, what you’re measuring, you know, and I think ultimately the goal is to prevent methane generation.
We really want to make sure that Any of that wood that breaks down does not break down and become methane that makes its way into the atmosphere.
Radhika Moolgavkar: So Ning, somebody who is actually running these experiments, how are you thinking about MRV and answering some of these questions that Daniel posed and buyers, I’m sure, are posing as well?
Ning Zeng: Yeah, I agree with what you said earlier. MRV is definitely critically important. I think there are probably two aspects of MRV. Maybe I’ll just focus on the technical kind in terms of durability, potential methane leakage, as some have worried and we are also concerned about. But overall, the technology of monitoring a wood vault is simpler than most other CDR methods, I would argue, because it’s a self-contained Um, structure that is very localized and does not, you know, diffuse out it’s close to where you actually do it close to research and so on.
So we think it can be done relatively easily in our implementation guidance. We, um, have described three main steps. The first one is to use low cost sensors. Um, To monitor the burial chamber gas concentration, we predict oxygen will be consumed very quickly, which will be replaced by CO2. So we actually have demonstrated this already in lab fault condition. Then the summer customer of methane, that’s another topic we can go into great detail, but theoretically we think The methane generation, if any, should be very small amount. And as it migrates upward, it will be consumed at the active biosphere in the soil above.
But this is a concern because methane’s potential global warming effect. So Another step is to actually do direct flux monitoring at the top of the vault. And you can compare that with the control environment in the surrounding. See if it actually leads to a measurable additional methane leakage. And then ultimately the proof is direct sampling. Like what we did in Montreal project, nine years later, We basically opened a side trench where we had placed the samples as part of the main trench. So the wood was totally intact. So that is like the proof.
Then we, our guidance specifies periodically, every 10 years, 25 years and so on to do the sampling. These are, these monitoring buses, I think are particularly important for the first batch of projects, you know, to really Prove our designs. We think it should be like that, but, you know, we need large scale, real world situation to taste it out. So, which means the initial projects will be more costly. But I think in long run, once, you know, there’s a major different condition, you know, the wood vaults probably vary locally, you know, the condition, soil, water and so on.
But after we do the initial batch of projects, we’ll have a good sample of different barrier condition. So we should be able to get a better data and reassess, probably relax the currently, which we consider a stringent requirement in our own implementation guidance.
Radhika Moolgavkar: Yeah. I mean, honestly, I think every type of carbon removal Except aside from maybe the very highly engineered has the same challenges you’re describing, right? Long-term monitoring of open systems is a challenge across the industry. But Daniel, do you see specific challenges to this approach that maybe don’t apply to other types of CDR and any other obstacles aside for what we talked about in terms of proving out the science approach?
Daniel Sanchez: Yeah, I think what’s interesting about wood vaulting and wood burial right now is that we have a number of different commercial enterprises all pursuing slightly different notions of what woody biomass burial looks like. Some folks are really focused on soils and burial conditions, and I think there’s a lot to be said for that, and the Carbon Lockdown Project is really focused on that. Other people are less worried about the soil and focusing on exclusion of water from the vault. But, you know, people thinking about putting different kind of linings or targeting really low precipitation ecosystems as a place that we could store this wood.
There are other people who want to pretreat this wood in some exciting ways prior to burial. Graphite wants to kind of compress it and encase it. Carbo wants to turn it into biochar or torrified biomass prior to burial. So I think we’re all thinking, you know, there’s a lot of experimentation around how do we avoid these degradation mechanisms, how much pretreatment and how much engineering of the vault is enough. And I think we’re seeing these all kind of compete in the marketplace right now. It’s definitely an exciting thing to see.
We see that in some other kinds of biomass carbon removal and storage, but I think that this is unique because most of the thinking has really been driven by the private sector rather than national laboratories or academics or other people who’ve postulated these things. I could point to 10 to 15 companies in this space, all with slightly different ideas for how they’re going to prevent that low value wood from decomposing for a climatically relevant period of time.
Radhika Moolgavkar: Yeah, I think I’ve talked to a lot of them. So I do have a question for both of you. As Daniel, you kind of alluded to, there’s biochar and there’s BEX and some of those have other maybe co-benefits that are more tangible, potentially biochar as a soil amendment, BEX creates energy. So what’s the argument for doing woody biomass when there might not be an additional type of value coming from it? How do you think about the potential that we don’t have enough of this eventually and it becomes almost a competitive blockage to actually sequestering carbon because so many people are competing for the actual biomass itself?
Daniel, I’ll start with you and then I’ll move over to Ning.
Daniel Sanchez: Sounds great. I think we actually have to be very conscious of these competing uses of low value biomass as we decarbonize our economy. There’s only so much sustainable biomass that we can use and there’s demand for it. So here’s how I think about this. I think some of these other carbon removal approaches like bioenergy with carbon capture and storage or biochar, they make co-products. One of them is carbon and one of them is another benefit, something else they can sell. Those sales can help reduce the overall cost of carbon removal, but you still need the very complicated and costly engineered system in order to pyrolyze biomass, to gasify biomass, to capture the carbon from it.
So where wood vaulting really wins is kind of on its simplicity, which might lead to lower cost net carbon removal, even without selling a co-product, right? We think we can do these things for under $100 per tonne at relatively large scale. Even the absence of co-products, really just selling the carbon removal value associated with that.
Radhika Moolgavkar: Ning, anything you’d like to add or clarify?
Ning Zeng: I think Dan said really well, I could add a more specific angle in terms of the current availability of biomass. So we all know Fire-thinning needs and the availability of that, which in fact is a major target of several biomass burial companies, which is great. But there is actually a lot of other opportunities with wood that is not unmerchantable. There’s no other use, crappy wood, low value wood on the East Coast and South, where forests are highly productive. And for example, in our area, the accumulation of urban waste of wood, which is from like mostly street tree removal at the city of Baltimore, they die often because of different things caused by climate change, like super wet event that kills white oak.
And ash trees dying because of insect outbreak, partly due to climate change, storm blowdown, ghost forests because of sea level rise and saltwater intrusion. So there’s a lot of these opportunities. The wood is otherwise not used. In fact, could even be negative. For example, in our urban area, most of the wood used to be burned. Now they are not supposed to burn because of air pollution concerns. And then they do mulch. That’s like the only option, but there’s only that much market for mulch. So we got this giant mulch piles piling up in those facilities and they produce methane besides a fire risk and so on.
So these things are not as big in the news as fire in the West, but there is a huge amount of potential So in fact, that’s the sort of thing we want to go after initially. So in long term, definitely we’ll run into a biomass availability constraint. That’s the ultimate constraint. So when we get to that point, the sustainability of sources of wood will be critical.
Radhika Moolgavkar: Yeah, so one last question related to sort of the procurement of the biomass. Forest thinning, at least here in the West, there’s debate around it within the forest management systems. So is there any concern that putting a carbon price on dead trees might create a perverse environmental incentive? And are there thoughts about how that can be mitigated? I mean, people take it to the extreme that, oh, you could cut down all the Amazon and then Bury it and say, that’s carbon removal. Now, I don’t think that’s going to happen, but that’s sort of perverse incentive.
Daniel Sanchez: Yeah. I mean, I think wood burial, just like the rest of the biomass carbon removal approaches, need to be done within the context of sustainable biomass procurement. And I think that’s going to need to be the case, regardless of which technologies we use to remove CO2 from the atmosphere using biomass. So I think we want to make sure that there are sustainable economies, that there is clear land ownership, that there are people who benefit from these things associated with the management of our ecosystems, whether those are forests or rural landscapes, some of which are used to produce energy or to produce food.
I think in this case, we can feel relatively confident that putting more value on forest biomass will lead to more net forest growth because it creates more value for forests, actually. And there’s been some excellent academic work I think we can worry a little bit more when we’re talking about using things like agricultural residues or a portion of the municipal solid waste system for biomass, because I think we can start to pervert or we can start to distort some of those markets. But I feel relatively confident that making forests more valuable will lead to more forests.
Radhika Moolgavkar: All right. Well, that actually is a nice segue into something that you both mentioned. And so Daniel, you and Ning and several other researchers recently released a implementation guidance for carbon sequestration via wood harvesting and storage. What was the inspiration for developing this? And can you kind of give a high level overview of what it contains?
Daniel Sanchez: Sure, I can start and I would love if Ning wants to add anything. So this is a collaboration, really, I was incredibly impressed by some of the work that Ning and Carbon Lockdown Project had done. And really, and thought that the greater wood harvesting and the greater wood burial community could really benefit from some of the kind of rigorous scientific thinking that Ning had spent 15 years working out around vault design, vault monitoring, monitoring, reporting and verification. Even kind of related and important questions like how you would measure durability, how you would do a third party verification, how you could maybe run a buffer pool based on your estimate and understanding of durability that evolves over time.
There’s a lot of really important ways to do this. And I think ways that have emerged that I think would be doing it right and scientifically conservatively right now. So I think Ning and myself set out to really write that down. What is a... You know, conservative and rigorous implementation of a wood vault that we think is going to avoid the worst harms that we don’t know how to control over time. But also generate valuable information to hopefully prove the durability of this approach. So it’s kind of the kitchen sink approach.
We really wrote about everything. Carbon counting, vault design, MRV, buffer pools, you know, take your pick, right? It’s a weighty tome, but I think there’s a lot of really good information in there.
Radhika Moolgavkar: Ning, anything you want to add or additional context you’d like to provide?
Ning Zeng: Yes, I think we, you know, one important motivation is really to help people, others who are doing this, to do it the right way. We have seen, you know, how good intentions can be abused once money is involved. So we hope to make this available. You know, it’s an open source document. Everybody is welcome to take it. And another thing I would like to add is It is, you know, the science certainly needs further refinement. So we totally expect this to be refined by us or by others as we learn more as the projects get on going.
So we welcome feedback from anybody, whether it’s, you know, too hard or it’s not possible, or we have these ideas we don’t agree with, as you said, you know, we really welcome input from anybody.
Radhika Moolgavkar: I really love that approach. That’s something that we also value at NORI is the idea of transparency and community because nobody really knows. So we all need to kind of crowdsource that information. So listeners, I encourage you to provide feedback as is relevant to this guidance. And I’m certainly looking forward to Diving into it a little bit. All right. For my final question, I would like to hear from you both, which is what are you working on now as it relates to woody biomass burial? And what are some of the important events or milestones that are upcoming?
So I will start with you, Daniel, and then I’ll have Ning give the final word.
Daniel Sanchez: Sure. So my academic research has really focused on bioenergy systems coupled with carbon capture and sequestration. So I consider myself relatively new to the notion of wood vaulting, to the notion of wood barrel and storage. One thing Ning and I did a few weeks ago was host a workshop in conjunction with the U. S. Department of Fossil Energy and Carbon Management Office to really start to bring together An academic community of people who’ve thought about these things, as well as the practitioner community, the people who are trying to do this in the future.
I’m really hopeful that the U. S. government and the Department of Energy in particular is going to start thinking about wood vaulting and biomass burial in general as part of the durable carbon removal that it is under mandate to procure and certainly under mandate to bring about in the world. But that is what I’m most hopeful for right now. I really think the next thing that needs to be done is a portfolio of deployment projects that are well instrumented, well monitored. And with data transparently shares that we know how to do this.
And so we can fly the plane and build it at the same time.
Radhika Moolgavkar: Yeah, I heard really good things about that DOE summit.
Daniel Sanchez: Oh, great.
Radhika Moolgavkar: Ning, anything else you’d like to add or highlight?
Ning Zeng: Yes, in terms of what we are doing, I’m actually really busy implementing our 5,000-tongue Potomac project. And a couple of weeks ago, We completed the first trench. The first 100 town was successfully buried. In fact, attendees from the workshop Dan just mentioned came to the sun visit at the end of the meeting. And we just produced a short four minute video about the process and we will make it available to the public soon. So. That’s coming and of course, I’m also working on several possibility of partner project. You know, with our experience, we like to help others to get projects going in different places.
So another thing I’m really looking forward to is to bring in more scientists into studying this method, take a critical look. I did provide, you know, the scientific foundation and ideas that could be useful for practitioners.
Radhika Moolgavkar: Well, Ning, Daniel, both, thank you so much for joining me on Carbon Removal Newsroom. I learned a ton. I thought I knew something, but I really didn’t know a lot. So I appreciate it. And I hope all of our listeners appreciate it too. Have a wonderful holiday season and the rest of 2023.
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