I think the way to sterilize things like this is to either boil it or bake it. If you still have a large pile, you can cover it with plastic and let the sun bake it for 3-4 weeks. In South Florida this should still be doable in winter, for us more northerly folk, we have to wait jntil the warmer months to come back.

So if you don't mind waiting, solarize with plastic. If you need it now, get enough for your orchid pots and boil it for 5-10 minutes.

Thanks for the great advise.