How agricultural waste can permanently store carbon

Just the gist

Short on time? Here's what you need to know for this update:

🏭 Seeing underground carbon storage in action — The Wren team visited our project partner in Arkansas, United States, and saw the permanent carbon removal process first-hand.

🧱 Condensing biomass into brick forms — Our partner compresses biomass into dense, stable blocks that are carefully wrapped to prevent decomposition.

🌾 Sourcing biomass from local agribusinesses — Local rice mills and sawmills provide the biomass for the project, keeping byproduct waste from decomposing and releasing greenhouse gases into the atmosphere.

🕳 Storing biomass in engineered chambers — Our partner has commissioned secure underground storage chambers, carefully engineered with multiple protective layers to safely store biomass for over 1,000 years.

For more project updates, follow Wren on X (previously Twitter) and Instagram.

Seeing underground carbon storage in action

When plants and agricultural waste decay in the open, they release carbon dioxide (CO₂) and methane (CH₄). Wren members support permanent carbon removal projects like Underground biomass storage, which turns biomass into stable, carbon-rich brick forms and stores them underground. This slows or stops decomposition, trapping carbon for over 1,000 years.

The Wren team recently visited our project partner, Graphyte, to see how they are changing the future of carbon capture. Check out our YouTube video to follow along on our trip to Arkansas:

Condensing biomass into brick forms

Our first stop was the Graphyte warehouse, where Jay, Nathan, and Jonathan gave us a close-up look at how they manage moisture content for the biomass that ends up stored underground.

To prevent microbial activity, it’s important to keep the biomass as dry as possible before condensing it into blocks and wrapping it in an environmentally-safe, impermeable barrier. This ensures each block holds onto as much CO₂e as possible.

Nathan from Graphyte showing us the machines used to condense and wrap the biomass blocks.

Sourcing biomass from local agribusinesses

Next, we visited the Arkansas River Rice mill, the first Black-owned food-grade rice mill in the United States. After processing thousands of tons of rice annually, the factory generates byproducts like rice hulls and other biomass that would typically decompose to release carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) into our atmosphere.

By working with our project partner, these waste byproducts are dried and condensed into blocks back at the Graphyte warehouse to prevent greenhouse gas release. It was inspiring to see how existing infrastructures, like a rice mill, can find ways to reduce their carbon footprint. And our partner doesn't only collect rice husks, they use wood debris from local sawmills, too.

Jared from Arkansas River Rice giving us a tour of the huskers, shellers, and hammer mills that process the rice and biomass byproduct.

Storing biomass in engineered chambers

And for our final tour of the trip, we visited a nearby engineered chamber where Graphyte stores the biomass. Here, SCS Engineers fill and seal one zone per month, probing the soil with “candy cane” pipes to constantly check for any unexpected greenhouse gases releasing from the stored biomass.

The data gets sent to Isometric for rigorous monitoring, reporting, and verification, which we take into account at Wren for carbon credit certification and issuance. The scale of this operation demonstrates the real potential of underground biomass storage in fighting climate change.

“We often talk about potential to scale carbon removal projects. Visiting Graphyte, it was clear they were innovating every week to try and sequester more carbon at lower and lower costs. This sort of fast iteration is exactly what we need to scale up carbon removal.”

— Landon Brand CEO and co-founder of Wren

Kyle from SCS engineers showing our team the layers of the storage zones and the candy cane monitoring pipes.

All of these zones must be carefully constructed to keep everything stable and secure. The layering sequence, from the bottom up, include clay, liner, a drainage layer, sand, and then the pallets themselves. Above those pallets, another clay layer, another liner, a second drainage layer, and more sand, all topped off with a layer of topsoil. Each layer has a role to play—preventing leaks, channeling moisture, providing structural integrity, and making sure the underground environment remains controlled and predictable.

Once these underground zones are filled and sealed, the land will be repurposed for the local community. This particular engineered chamber will eventually become a recreational trap shooting area for the school teams nearby. Beyond their primary role in fighting climate change, these facilities create lasting value for local residents.

The Wren team getting a closer look at the data on the biomass monitored underground.

We left Arkansas impressed by the meticulous engineering, community integration, and scalable approach to carbon removal. This project proves that with innovative thinking and careful planning, we can tackle climate challenges while benefiting local communities and businesses.

That's all for this update! As always, thank you for your support.
— the Wren team 🧡