The only ideas I can add to the speculative filtration is by centrifuge, which would rely on the particulate matter being heavier than the PG; or by using very fine filters and using air pressure to push it through. I am no chemist, but there could be chemical means of removing particles, like in home-brewed beer for example, I think they call it clearing agent or similar. Not saying to use that for PG/VG, just using it as a chemical example of making a liquid clearer.