These people buy algae, make pellets out of it, and mix 10-30% into plastic, sequestering carbon dioxide, but also reducing algae blooms.
There is a lot of overhead, but harvesting pond scum is cheaper and easier than drilling for oil.
In order to reduce the algae blooms and all of the problems that causes, they need to reduce fertilizer flowing into our waterways, but only legumes fix their own nitrogen.
There is a type of giant maize that grows in Mexico with slimy roots meters above the ground that fixes its own nitrogen, providing 80% of what it needs, so they are trying to cross-breed it with other grains and reduce fertilizer.