I don't know about glass, but any junk in molten metal just burns up and the ashes can be skimmed off the top. It's not really the metal I'm talking about, it's the plastic and paper which are pointless to even have in the system.

It goes through a process. It doesn't make metal or glass useless.

Biological Treatment: Organic waste, including food waste, is often separated either at the beginning of the process through manual sorting or through processes like anaerobic digestion. In some facilities, organic waste is processed separately to produce compost or biogas.