Thanks. I've been using indoor-outdoor carpet for just some snakes for many years- the stuff never wears out, & doesn't fade even if you disinfect it with diluted bleach (-you just have to rinse a LOT & don't over-do it or you won't get the bleach fumes out).
And that's what I do too, with other substrate stuff that I use (moss or orchid bark)- just add it to plants in my yard. I grow organic tomatoes but I don't toss snake-poo where I garden for edibles- just as you said, for health reasons, it's not recommended to use anything like that (that's not completely composted already, or that comes from meat-eating animals, etc) just as a precaution.
I've had no luck with actual composting either, but I grow tomatoes in raised beds that I made "lasagna-garden" style: alternating layers of leaves + dirt + misc (veg/fruit scraps, egg shells, coffee grounds & tea). Essentially it's slow-composting that doesn't heat up or get turned. I also rescue earthworms after it rains & "invite" them in- they eat & break down the leaves too. Works pretty well, surprisingly.