Recycling PLA from 3D prints exists, without the bio part. I buy filament from a local supplier that recycles failed or unused prints into pellets, then rolls of filament.

I’ve looked at but never tried 2 things.

1, pla melts at about the same temperature as paraffin, people have used candle making kits to cast skulls or whatever. Seems neat to me.

2, similar trick, put the pla between two cookie sheets with weights. Heat to melting. This gives panels you can cut and incorporate into projects. Drawer bottom or robot body , that kinda stuff.

>It can't be that hard to homebrew some sort of extruder to remake the filament, can it? Who needs tolerances?

OK, it can still be disposed of cleanly. As in, dump laundry basket of PLA scraps into washer, add magic PLA enzyme detergent, push "PLA Dispose" button, and all of it stays out of a landfill.

There are a number of machines you can buy to do this. It's just expensive.