The easiest way to capture carbon with kelp would be to dump it into the depths of the ocean. This requires some planning and research how to turn it into a stable form that wouldn’t release the carbon back into the circulation any time soon.
Biochar
We can heat the collected and compressed kelp in a low oxygen environment and turn it into biochar – a charcoal like substance that consist of compressed and dry carbon. It is stable and can be used just as carbon storage but can also be utilized as solid fuel if needed.
Briquettes or pellets
We can dry and compress kelp material as is to produce briquette similar to the one made from wood chips.
Harvested kelp goes through a drying process, using sun or kilns. The dried kelp may be crushed for better packing. Machines then compress the material under high pressure, potentially with added binding agents (like lignin), forming dense briquettes ready for long term storage and burning on need. While this may seem like a historic way of heating many homes in the North of Europe and Canada still rely on solid fuel heating solutions like furnaces, fireplaces or boilers combined with radiators.
Oil and Gas
By treating kelp with Hydrothermal Liquefaction (HTL – putting the kelp under extreme temperature and pressure) we break down it’s cells into molecules that resemble thick black oil. This can be purified into oil products on it’s own or by introducing a correct catalyst and/or post-processing can turned it into methane if needed.
An alternative way to produce methane from kelp would be to introduce it to fermentation and anaerobic digestion.
Methanol or Ethanol
By introducing an ethanol producing bacteria to ground up kelp in the correct environment it will start to ferment like any other plant matter would. The fermentation process will produce ethanol as it’s main outcome and the residues can be used as fertilizer.