Good people of Adafruit have made a tutorial on how to use Filabot filament extruder to recycle your 3d printed waste stuff. It looks like it is bast suited for organizations who gather a lot of recyclable models. It could save you some money.
They use electric garden chipper to grind the 3d printed waste into a mulch. The entire process could also be applied on any other DIY filament extruder like Filament Factory.
Everything is described in detail at: https://learn.adafruit.com/diy-3d-printing-filament/
Pre-sorting by color and material is key to maintain filament quality and color