Bits of plastic smaller than the maximum diameter of beetle poop are probably not going to be recognized and removed as plastic anyway. Just shake it all throu

Bits of plastic smaller than the maximum diameter of beetle poop are probably not going to be recognized and removed as plastic anyway. Just shake it all through some progressively finer screens and blow the remaining plastics off the tops of the screens with a blast of air. Perhaps the plastics would gum up the food-shredder?