Researchers may have found an effective, green way to remove microplastics from our water using readily available plant materials. Their device was found to capture up to 99.9% of a wide variety of microplastics known to pose a health risk to humans.
I think you just burn it.
People in this thread are looking for complicated answers. But the best thing to do with sawdust, plant matter and a tiny bit of micro plastics seems to me also to just burn it.