Brinc recently announced its interest in the carbon removal (CDR) space, and discussed direct air capture (DAC)’s potential along with some of the challenges for global deployment. A plethora of CDR solutions will be required to reach the annual scale of five to ten gigatons (Gt) per year by 2050 as outlined in the recent IPCC report. In the best case scenario, DAC will still likely be at megaton scale by 2030 and remain one of the most expensive CDR options. In contrast, nature-based solutions (NbS) offer low-cost approaches that can scale quickly. This piece explores biomass burial, an approach recently highlighted in Lowercarbon’s wishlist that avoids the common NbS pitfalls of permanence and additionality, but brings other challenges. A series of expert opinions unpack the potential of this approach, the feasibility of avoiding critical methane leakage from decomposition, and whether it makes sense to bury a valuable resource.
Biomass burial is a subset of biomass with carbon removal and storage (BiCRS). As shown above, in nature, carbon is captured through photosynthesis, but a large portion is then re-released when plants decompose (or are burned through deforestation and wildfires). Interrupting this cycle to store the biomass in a durable format can act as a permanent form of carbon removal. Other options for permanent removal besides burial include biochar (for example, Climate Robotics) and bio-oil (for example, Charm Industrial), to be covered in depth in a future piece. Counteract, a UK-based company that funds global carbon removal startups, has published articles promoting BiCRS over the more well-known bioenergy with carbon capture and storage (BECCS) to avoid challenges around net neutrality and competing priorities between energy generation and removal.
“From a CDR lens, biomass burial has the advantages of very efficient carbon drawdown and a fast pathway to scale. The main barriers are transport costs, confirming the biomass does not decompose, and that burying makes sense over other use cases. Context is key.” Poppy Russell, Analyst, Counteract
Carbon Pickling with InterEarth
One of Counteract’s portfolio companies is InterEarth, a Western Australian startup proposing gigaton-scale carbon removal at less than US$100 per ton. Their process, outlined in a recent Bloomberg piece, centers on the use of degraded land with groundwater five to ten times saltier than seawater. Poppy Russell, analyst at Counteract, outlines their rationale for backing them: “From a CDR lens, biomass burial has the advantages of very efficient carbon drawdown and a fast pathway to scale. The main barriers are transport costs, confirming the biomass does not decompose, and that burying makes sense over other use cases. Context is key.”
InterEarth plans to coppice (cut in a way which enables regrowth) trees they plant on plots, then bury (or otherwise permanently store) the wood. Following Russell’s outline of the potential barriers, transport costs are minimized by growing trees right next to burial sites, while the land used is almost incapable of supporting life. However, by reinstating fast-growing native species that are able to survive in harsh conditions, InterEarth hopes to restore biodiversity and potentially revitalize the soil over the course of multiple planting cycles.
Fabiano Ximenes, Senior Research Scientist at NSW Dept. of Primary Industries specializing in forestry, is an advisor for InterEarth (as well for Stripe’s CDR investments) and an IPCC contributor. He emphasizes the proven science of how such an approach can provide permanent removal: if the environment allows for only anaerobic decomposition (by bacteria, not fungi), the bacteria are incapable of processing and degrading the wood. Therefore, the key is avoiding oxygen exposure, but salt (as is found in InterEarth’s target environment) enhances the process.
“How desperate are we from a carbon imperative? Do we want to draw down as much carbon from the atmosphere as possible? If so, biomass burial should be considered as part of the range of options. However, there may be other things which may make more sense to do with the biomass, depending on proximity to industrial applications. Let the market dictate what is best, assuming the scientific understanding is there.” Fabiano Ximenes, Senior Research Scientist, NSW Dept. of Primary Industries
Locking Carbon into Wood Vaults
Professor Ning Zeng at the University of Maryland is considered a pioneer of biomass burial, and has been researching this space for over a decade, with initial validation demonstrated through projects in Maryland and Montreal. In 2013, a group of scientists estimated that removal on the order of two to ten gigatons per year is possible globally. Zeng proposes that one of the easiest targets is wood which is already aggregated and instead mulched, burned, or simply left to rot. In the US alone, unexploited wood residuals represent up to 300 megatons of annual carbon dioxide emissions from forestry residues, land clearing for residential or commercial development, and storm debris. In particular, “Tremendous opportunities exist in utilizing forest thinning residuals for carbon removal while mitigating the fire threat in the American West and other parts of the world,” states Zeng.
“Tremendous opportunities exist in utilizing forest thinning residuals for carbon removal while mitigating the fire threat in the American West and other parts of the world.” Professor Ning Zeng, Founder, Carbon Lockdown Project
Zeng recently spun out the Carbon Lockdown Project, a public benefit corporation with a 10 kiloton removal project currently under review for an advanced purchase agreement. In terms of transport, Zeng anticipates collaborating with the existing logistics infrastructure of tree removers, as the cost for them to instead transport wood to one of their vaults for permanent removal would be comparable. In the long term, Zeng envisions establishing consulting service-like arrangements with other parties carrying out burial projects. The Carbon Lockdown Project would focus on optimizing the vault design, carbon accounting and project development support, and ensuring that a robust monitoring, reporting, and verification (MRV) process exists.
Through his work in an environmental monitoring lab at the University of Maryland, Zeng has developed modifications to existing air pollution and atmospheric carbon dioxide sensors which can be added to provide low-cost, continuous monitoring on the wood vaults. He also anticipates adding gas sampling and 3D topography monitoring with drones. Furthermore, Carbon Lockdown Project is working with another organization to develop a carbon credit protocol currently under review, which could be used to standardize the optimal burial process. Several partners are already lined up to develop other model projects, though more funding will be needed to finalize the MRV process and expand the team.
“There’s an open question on whether biochar works for all soil or might even have negative impact. Is it worth the cost?” Manuel Schleiffelder, CEO, and David Unterholzner, COO, Reverse Carbon Mining Project
Returning Coal to the Ground with the Reverse Carbon Mining Project
A related approach is the Vienna-based Reverse Carbon Mining Project (RCMP). In addition to releasing carbon back into the atmosphere, decomposing biomass runs the risk of groundwater contamination. As a result, legacy European Union regulations make it illegal to bury more than 5% carbon (as encountered in these projects) in the soil. However, Manuel Schleiffelder and David Unterholzner have two work-arounds. First, they are targeting shaft or open pit mines. Secondly, rather than just burying biomass, they focus on conversion to biochar first through pyrolysis. Biochar offers only 30–50% carbon efficiency compared to biomass burial, but the team was quick to point out their ability to recover some of the remaining carbon as waste heat to power the pyrolysis process.
When asked why it made more sense to bury biochar instead of trying to capture potential co-benefits with soil, Schleiffelder and Unterholzner argued that burial in a specific location compared to scattering in soil simplifies the MRV process. They also highlighted the debate around biochar. “There’s an open question on whether biochar works for all soil or might even have negative impact. Is it worth the cost?”
Outlook
At its core, the idea of biomass (or biochar) burial is amazingly simple. However, some of the largest questions seem to center on cost and MRV. In terms of cost, even if a premium can be commanded for offering permanent carbon credits (which will be validated by the market when these projects come online), there are no other co-benefits to capture economic value or cover any biomass transport costs. As a result, Ximenes expressed his opinion that biomass burial makes the most sense in remote areas far from industrial activity. He also asks: “How desperate are we from a carbon imperative? Do we want to draw down as much carbon from the atmosphere as possible? If so, biomass burial should be considered as part of the range of options. However, there may be other things which may make more sense to do with the biomass, depending on proximity to industrial applications. Let the market dictate what is best, assuming the scientific understanding is there.”
A robust MRV system is critical for validating premium carbon credits and monitoring critical risks like methane leakage and any impact of nutrient uptake in the local burial environment. Furthermore, MRV is a pathway to create defensibility around a simple process. Zeng has built some IP around his methodology and the Carbon Lockdown’s approach of centering their business model on these core assets (vault design and MRV) reinforces this consideration.
Achieving more than two gigatons (and therefore potentially overtaking rather than just complementing other carbon removal approaches) still requires global coordination. This includes a deeper understanding of local context and eliminating regulatory barriers such as those encountered by the Reverse Carbon Mining Project. At increasing scale, questions of where the biomass is sourced from and how sustainable the feedstock is grow. Alternative use cases must also be taken into account, especially considering public perception and widespread adoption. Ideally, governments — or nonprofits — would develop a decision-making framework that incorporates transparent data and net emissions modeling to help prioritize the use of sustainable biomass if a range of potential applications is possible. Russell added: “Especially for forestry residues, it’s important not to incentivize unsustainable management practices.” Part of this discussion includes an understanding of any co-benefits. Ximenes proposed that monetizing these aspects “can be sub-optimal and messy, [though it must be] taken into account.”
To the broader concern of how far biomass-based solutions can support carbon removal efforts, Ximenes was of the opinion that it’s too early to worry. “It’s counterproductive to say we can’t pursue the approach because the biomass will be exhausted. Let’s focus on the best of what we have now for the climate emergency and deal with the issues as they arise with robust governance and certification systems in place.”
Brinc is actively monitoring this space and would love to hear from others working on burial solutions. Stay tuned for an upcoming feature exploring local context and feedstock considerations in APAC along with other BiCRS perspectives. In the meantime, if you’re interested in sharing your thoughts, please visit our website or contact us via email.
