This tech is literally trash bathed in leaf sauce. Even if someone would patent it it’s like you tried to patent a herbal tea - yea, you may try and maybe win, but every farmer and their mom will brew one themselves from loosely scattered weeds.
So after a short thought it means it’s going to be a massive, profitable venture for someone, because people are actually dumb enough to pay tens of $ for a handful of sawdust and reasonably pure tannic acid if it comes with a fancy cap and in a gray cardboard box.
Plant-based filter removes up to 99.9% of microplastics from water (newatlas.com)