Why tackle carbon rather than carbon dioxide?

We might not be fighting the wrong enemy, but we might be fighting the enemy in the wrong guise.

When we talk about carbon capture and storage (CCS), we almost always implicitly assume that the eponymous carbon comes in the form of carbon dioxide. After all, the emission of CO2 is blamed for global warming, so it makes intuitive sense to reverse the release of CO2 into the atmosphere.

Abundant biomass. Photo by Glenn Carstens-Peters on Unsplash.

Case in point was the extensive media coverage given to “Orca”, the Icelandic direct air capture (DAC) installation that went online a few weeks ago. Despite its rather pedestrian appearance, it captured the imagination of many climate advocates. DAC is also popular with prominent investors with even bigger installations about to become operative in the near future.

But there's multiple reasons to question if this is the right approach, and if we're ever going to be able to scale DAC installations to a size where they can make a difference.

Instead we should consider capturing and storing carbon in its more tangible, solid form as biomass, including biomass sludge. The established processes for dry (and dried) biomass are pyrolysis, torrefaction (“mild pyrolysis”), and for wet biomass the focus of this newsletter, hydrothermal carbonization (HTC).

The reasons for our focus on solid biomass processes are, neatly summarized, the following.

1. Energy usage. Unlike DAC, which requires significant amounts of energy to operate, HTC is exothermic. Once started, the process is self-sustaining and even creates a moderate amount of energy which can be captured.

2. Location. HTC can be deployed decentrally, close to either the biomass source or the ultimate storage location. Orca-type installations will always require a combination of favorable environmental conditions, which limits the geographic locations where they can be deployed.

3. Flexibility. Beyond sequestration, biomass processes can produce a range of intermediary products, which can also be introduced into a carbon-neutral or carbon-negative circular economy.

4. Scalability. Ultimately, we should see dry or wet biomass processing plants installed at all places where biomass accumulates, from spent coffee grounds via fruit wastes to corn cob residues, or even sewage treatment plants. Economies of scale will ultimately decide the optimal plant size and the logistic ecosystem around it, but there are no environmental constraints limiting its deployable range. We may as well burn these bio-based raw materials, but we won't change a thing: no gram of CO2 will be removed from the atmosphere this way.

5. Stability. Nature has demonstrated the principle: coal is stable in the soil as a deposit for millions of years. And so is sequestered char, keeping the carbon out of the atmosphere, and nourishing the soil and reducing the need for fertilizers. It also reduces the emission of greenhouse gases methane and nitrous oxides. Activated char also filters out pollutants and retains water to combat flooding.

Over the next weeks we will dive deeper into the advantages of biochar sequestration, with a focus on hydrochar, and also discuss the state of the art and the required next steps for global scaling.