Our Take: Biomass Storage – An Innovative Solution for Carbon Dioxide Removal

Written by Jay Tipton

Key Takeaways

• Carbon Dioxide Removal (CDR) is necessary for achieving net-zero emissions by 2050, with an estimated requirement of 6-10 gigatonnes of CO2 removal annually, more than the U.S. emits in a year.
• While methods like biochar and direct air capture (DAC) are well-known, biomass storage is an emerging approach for long-term carbon sequestration, involving the storage of organic materials in controlled environments or underwater.
• Biomass storage leverages the natural CO2-absorbing abilities of plants, and both terrestrial and marine storage can minimize decomposition, keeping carbon out of the atmosphere for extended periods.
• Biomass storage can generate carbon credits, offering economic incentives by converting unused or waste biomass into assets, which could be attractive as the global demand for sustainable solutions grows.
• Despite its potential, biomass storage faces hurdles such as high costs, environmental concerns, and scientific uncertainty regarding long-term effectiveness. However, with continued research and investment, it could play a part in combating climate change.

Introduction

Carbon dioxide removal (CDR) has been receiving significant attention recently from governments, corporations, investors, and project developers as a strategy for combating climate change. Rightly so because estimates indicate that achieving most Paris-aligned net-zero pathways by 2050 will likely require an annual carbon dioxide (CO2) removal capacity of six to ten gigatonnes, which is more carbon than the entire United States emits in one year.

Amidst this surge of interest, much of the conversation has centered around well-known methods like biochar (which we wrote about in March), direct air capture (DAC), and carbon capture and storage (CCS).

In this essay, we are exploring another, less-discussed approach – biomass storage. This method offers another avenue for potentially achieving long-term carbon sequestration and enhancing our overall CO2 removal efforts.

In this approach, biomass is kept in specialized facilities or structures (sometimes referred to as wood or carbon vaults) that are designed to store organic materials such as wood, agricultural residues, and other plant matter. Biomass can also be sunk and stored underwater in oceans and seas as marine storage.

How it Works

The basic concept involves leveraging the natural carbon-absorbing ability of trees and other types of plants. Through photosynthesis, trees and plants absorb CO2 from the atmosphere and store it in their biomass. When the wood is harvested or gathered and then stored in vaults, the embedded carbon remains sequestered, preventing it from returning to the atmosphere.

The general process for terrestrial biomass storage typically begins with the collection of biomass. It is then weighed and recorded before being transferred to storage or processing areas. Depending on the type and moisture content, biomass is kept in specific structures and maintained under controlled conditions to prevent degradation and fire hazards. Continuous monitoring of temperature and moisture levels ensures the quality and safety of the stored biomass. Automated systems can be set up to manage storage conditions and alert operators to any issues. If necessary, handling and processing equipment moves the biomass within the facility for drying or conditioning.

Marine biomass storage involves sinking biomass into deep ocean waters or seabeds to sequester carbon. This method leverages the ocean’s natural carbon-absorbing capabilities, where the cold, high-pressure environment slows down the decomposition process, preventing the release of stored carbon back into the atmosphere. The biomass is typically placed in biodegradable containers or weighted to ensure it sinks to the ocean floor. Once submerged, the biomass remains in an oxygen-poor environment which inhibits decomposition and promotes long-term carbon storage.

Both terrestrial and marine biomass storage offer ways to store large amounts of biomass, and therefore carbon, in conditions that minimize decay. By preventing the biomass from decomposing or being burned, the carbon stored within is kept out of the atmosphere for longer periods, enhancing the effectiveness of this carbon sequestration method. Various types of terrestrial biomass storage facilities include wood vaults, burial mounds, underground pits, quarries or mines, super vaults, and shelters or warehouses (Figure 1).

Alongside the carbon sequestration ability of biomass storage, additional co-benefits include preventing biomass decay, reducing wildfire risks, and creating employment opportunities, especially in rural areas.

Generating Carbon Credits

As global priorities increasingly shift towards sustainability, biomass storage could become a valuable tool to meet the rising demand for carbon credits.

To generate carbon credits, the sequestration project must undergo a rigorous lifecycle analysis to quantify the net amount of carbon sequestered. This process includes accounting for any emissions associated with the harvesting, transportation, and storage of wood and plants. Third-party verification is required to ensure the integrity and accuracy of the carbon credits generated.

Puro.earth has developed a CO2 removal methodology for the Terrestrial Storage of Biomass. This methodology quantifies the net CO2 removal achieved over one hundred years by storing biomass in appropriate terrestrial storage systems. It aims to provide consistent requirements across various carbon removal solutions, reducing transaction costs, fostering innovation, promoting knowledge sharing, and enabling rapid growth in the CO2 removal supply.

Eligible biomass types for Puro’s methodology include herbaceous plants, crops, woody plants, deciduous broad-leaved trees, evergreen broad-leaved trees, conifers, vines, and bamboo. The biomass is stored in specially designed systems that inhibit decomposition and prevent carbon from being released back into the atmosphere as CO2 or methane (CH4). Storage methods include above-ground vaults (purpose-built covered structures that are typically ventilated), below-ground vaults (purpose-built and covered storage pits that can be constructed to maintain either an anoxic environment or a dry environment such as in above-ground storage chambers), and below-ground subterranean injection (a layer of biomass particles that is formed by the subterranean injection of a slurry containing wood or other eligible biomass). Each storage site is subject to specific risks, mitigation measures, and monitoring protocols.

To ensure the durability of stored biomass, various features can be employed in the design and functionality of storage chambers. These features include anoxic conditions, absence of moisture, absence of liquid water, absence of light and UV radiation, mineral occlusion, tightly compacted biomass, low to extremely low water and gas conductivity, hyper-saline environments, and specific chamber pH and temperatures. By maintaining consistent and generic requirements, the methodology supports cost efficiency, innovation, and rapid growth in CO2 removal efforts.

In some cases, biomass storage could provide scaling advantages over other engineered carbon removal options, offering a more easily expandable solution. Biomass storage projects can utilize biomass waste that might otherwise go unused or be burned. By converting this waste into an asset through carbon credits, biomass storage projects can create an economic incentive for the responsible management of wood and plant residuals.

Biomass Storage Credit Ecosystem and Activity

In recent years, there has been increasing momentum in the market activity around CDR credits, and it is steadily growing. This growth is influenced by advancements in technology, interest, and investments from the private sector, and supportive governmental policies. As the demand for CDR continues to rise, there is potential for increased interest in carbon credits from biomass storage. However, current market activity around biomass storage remains low and is primarily concentrated in North America.

Microsoft is the leading CDR purchaser, followed by Denmark, Frontier, Airbus, and Amazon. From 2019 to 2024, Microsoft purchased 64% of the available durable CDR credits, around 6.6 million tonnes of carbon dioxide equivalent (tCO2e). Furthermore, Bill Gates’s Breakthrough Energy Ventures (has contributed $6.6 million to Kodama Systems, a forest management company in California. Kodama Systems has a project to bury 4,500 tonnes of wood from the Eastern Sierras near Mammoth Lakes, aiming to remove around 3,200 tonnes of carbon dioxide when accounting for potential emissions losses. The project has promised the first tranche of carbon credits to Frontier for $250,000 if they meet certain baselines.

The newly formed Symbiosis Coalition , comprising Google, Meta, Microsoft, and Salesforce, is aiming to facilitate an advanced market commitment (AMC) of up to 20 million tonnes of nature-based carbon removal credits. The initial request for proposals (RFP) will focus on afforestation, reforestation, and revegetation (ARR) projects, including agroforestry initiatives.

Earlier this year, Frontier secured offtake agreements with Vaulted Deep, a carbon removal company that injects carbon-rich organic waste deep underground for permanent storage. Vaulted Deep will remove 152,480 tonnes of CO2 between 2024 and 2027 for $58.3 million, with options for future purchases at lower prices. This agreement will enable Vaulted to commission three new wells optimized for feedstock availability, transportation, and capacity. Vaulted Deep’s approach involves converting CO2-absorbing plant waste into a carbon-rich slurry, then injecting it into deep wells for permanent geologic storage, with carbon removal volume measured by subtracting emissions from biomass processing, transportation, and energy usage.

Although more CDR projects are coming online each month, the current amount of biomass storage, removal, and sinkage carbon credit projects is small, but growing. CDR.fyi , a carbon dioxide removal project tracker, has eight companies with active projects listed on their project map, with the majority located in the US and one in Australia (Figure 2).

From the terrestrial side, Carbon Lockdown (Maryland) is a company with various projects that aims to securely sequester 5,000 tonnes of CO2-equivalent (tCO2e) annually by burying woody biomass in vaults. The biomass they are using is sourced from residuals that would typically be used for mulch or pile burning.

Carbon Sequestration Inc. (Texas) is using its Woody Biomass Burial system to fill a pit with biomass that would otherwise be burned. The pit is then covered with locally sourced clay, ensuring the carbon remains sequestered.

Woodcache PBC (Utah) repurposes woody debris with no other economic use by storing it underground. Their current project in Colorado has buried waste wood from Pinon and Cedar trees. The project employs solar-powered sensors and security cameras for continuous monitoring and oversight.

Tau Carbon (California) stores wood biomass aboveground in modular, stackable containers. In a stack 25 meters tall, they can store 100,000 dry tonnes of wood waste (equivalent to 180,000 tonnes of CO2) on just 2.5 acres. They plan to begin offering carbon credits in 2024.

InterEarth (Australia) is cultivating trees, harvesting their above-ground biomass, and then burying the biomass along with its contained carbon back underground.

According to CDR.fyi, suppliers listed under “biomass direct storage” and “marine biomass sinking” have sold a combined total of 210,376 carbon credits.

Vaulted Deep leads the pack with a total of 155,733 credits, followed by Running Tide with 27,831 credits (note, Running Tide has folded and is no longer an operational company). InterEarth has sold 14,088 credits, while Graphyte accounts for 10,000. Carbon Lockdown has sold 1,136 credits, and Carbon Sequestration Inc. has sold 1,100 credits. Levintree sold 300 credits, Rewind has sold 182, and Woodcache PBC has accounted for 6 credits.

As for carbon credits delivered, Running Tide has fulfilled the largest amount with 21,778 credits, while Vaulted Deed has delivered 3,253 credits. Carbon Sequestration has delivered 1,100 credits, and Woodcache PGC has delivered 6. However, InterEarth, Graphyte, Carbon Lockdown, Levintree, and Rewind.earth have not yet delivered any credits. Altogether, the total delivered credits amount to 26,137.

This indicates advanced commitments from buyers, which is encouraging and helpful for project developers.

Hurdles

Although the benefits of biomass storage are clear, this project type is not without its hurdles.

Challenges in terrestrial and marine biomass storage arise in the logistical aspects of biomass handling, including collection, transportation, and storage, particularly given the diversity of biomass sources across various geographical locations. The initial investment costs of projects can be substantial, with the economic challenge exacerbated by the high capital expenditure associated with facilities. The operational costs of maintaining and monitoring storage sites can add to the financial burden.

Environmental concerns, particularly regarding deforestation and biodiversity loss, stand as critical barriers that necessitate careful consideration to ensure the sustainability of biomass sourcing. Assessing wood collection rates based on forest productivity can be challenging, and there is a risk of overharvesting biomass to fill storage facilities, which could deplete nutrients available from decaying matter and negatively impact ecosystem health.

For marine biomass storage, challenges include the environmental impact of marine biomass storage, such as potential effects on marine ecosystems and water quality. Regulatory and legal issues related to ocean-based storage still need to be fully addressed. There is also a need for further investigation into how well biomass storage prevents the release of greenhouse gases (GHG), as well as its scalability and long-term durability. The payments company Stripe has granted $250,000 to the Yale Carbon Containment Lab for research into these aspects.

The effectiveness of biomass storage in sequestering carbon for long periods remains uncertain and requires more scientific validation and long-term studies. Consequently, buyers are starting to require that permanence durations for CDR credits top 1,000 years which can be difficult to achieve. Other issues that buyers want to see addressed are related to durability and site disturbance.

Regarding market acceptance and public awareness, developing more standardized protocols for monitoring and verifying carbon credits from biomass storage will be essential. Public awareness and acceptance of biomass storage as a viable carbon sequestration method must also happen for its widespread adoption and success.

Conclusion

It is becoming increasingly clear that there is no single perfect solution to addressing climate change. First and foremost, governments, companies, and individuals must rapidly reduce their carbon-emitting activities. Beyond this, removing lingering carbon from the atmosphere will also be essential and will demand a diverse array of solutions. Terrestrial and marine biomass storage offer innovative methods to fit the role.

While biomass storage faces several challenges and barriers that need to be addressed for it to become a viable large-scale solution, its potential benefits for long-term carbon sequestration are significant. Ongoing advancements in technology, growing interest and investments from the private sector, and supportive governmental policies could enhance the feasibility and scalability of these projects. If scientific validation and long-term studies continue to verify the effectiveness of biomass storage, we might be able to implement this approach safely as one of our much-needed climate solutions.

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