🔬Characterization of Substrates and Materials
We used the term Substrate for the blend of terrestrial biomass (plant residue) that has stored carbon through photosynthesis and an inorganic alkaline substance that is used to offset the acid leaching in the biomass and to enhance ocean alkalinity. These component parts formed a carbon buoy "recipe."
Material sourcing and selection involved a complex array of considerations. Materials had to function for their intended purpose, fulfilling design criteria. And carbon costs had to be either offset, reduced, or intrinsically negative.
Substrate material factors we evaluated included:
Origin of the biomass
Carbon footprint of the biomass
Acid leaching
Floating time
Forming and treatment methods to enhance the biomass ability to grow algae
Origin of the Biomass
The origin of the biomass used in substrate and algae buoy development was first evaluated based on project goals. Biomass availability for upscaling was an important factor and we regularly ruled out materials which would not scale to support future megaton or gigaton removal proejcts. Generally, we tried to source biomass that would normally decay or burn, releasing carbon into the atmosphere. To avoid negative environmental externalities, we also assessed:
Pesticide prevalence: The concentrations of pesticides in biomass sources
Wood treatments: Paints or other harmful chemicals commonly used to treat wood.
Waste: The existance of other waste in the material like nails, screws, plastic etc.
Trace Metals: Plants are capable of taking up trace metals at rates which vary between plant species and environmental factors
Biomass Carbon Footprint
Biomass carbon content was evaluated for each type and source. From that information and cradle to grave emission calculation, we could determine if the carbon removal activity would result in a net negative change in fast-cycle carbon.
Acid Leaching and Alkalinity
Monitoring and adjusting the alkaline substances mixed with the biomass to offset acid leaching and enhance ocean alkalinity was important to achieve a net neutral or better impact on ocean chemistry.
We worked with Stubbins' Lab at Northeastern University to evaluate the organic carbon release and acid leaching of terrestrial and macroalgal biomass:
A description of the sampling and laboratory testing for acid leaching involved in every batch of deployed material can be found in the appendix of Methodology v1.6.0. Additionally, we quantified the net change in total alkalinity from 2023 deployments to the best of our ability given the data we were able to collect at the time. We had the goal of developing an OAE methodology to use in conjunction with our Terrestrial Biomass Sinking methodology in 2024.
Float Time
Floating time of the material used in deployments was studied in lab tests and in-situ monitoring. Wood chips throughout the first deployment season were monitored with proprietary hardware known as a Camlite camera buoy.
Floating time was also studied on candidate biomass materials. We would evaluate if the biomass float duration would support algae growth to maturity and adequate hold-fast development to remain attached in the open ocean environment.
Tuning for Algae Growth
By selecting and processing biomass and tuning buoy recipes, we believed that we could optimize the system for algae growth with adequate float time. The high degree of variability of organic materials proved challenging and a lot of our processing R&D was focused on stabilizing these characteristics. For example, wood chips from the same tree could have entirely different densities and water absorbtion rates depending on which part of the tree they came from. Organic coatings, pre-soak treatments, or changes in substrate morphology could allow us to tune important parameters and tighten up the float time distribution, resulting in a more predictable product
Future Buoy Designs
Not all of our buoy designs leveraged all three ocean carbon removal pathways. Our first deployments of coated wood removed carbon via Ocean Storage of Biomass and Ocean Alkalinity Enhancement. And we explored one- two- and three-pathway designs using a variety of different materials.
For example, as we came to understand the potential of Ocean Alkalinity Enhancement, we explored different ideas for designing single-pathway OAE buoys as outlined in the following report:
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