Can I really throw failed PLA prints on compost?
This question has been asked on just about every forum out there.  Here's one example from filabot.com .


  The reality however, is that this process will take several hundred
  years in a typical landfill. To biodegrade, PLA requires a laundry
  list of conditions to effectively break down. Specifically - oxygen, a
  temperature of 140+ degrees *[Fahrenheit -- ed note] *, and a 2/3 cocktail of organic substrate.
  Collectively, these are absent in any scenario outside of industrial
  composting facilities.


I found similar comments -- tho' with perhaps slightly lower temperatures elsewhere.