Yeah, I didn't want to dive too deep, but The Humanure Handbook gets into a viable business or Municipal waste program that could be done. Geoff said that the microbiological activity should be able to breakdown or lock up toxins. Bioremediation (willows, cattails, living machines etc) and mycoremediation, particularly garden giant, is excellent for breaking down the pathogens... but if it was something like heavy metals, you could use fungi to hyperaccumulate them. But really, if I was to suggest this to anyone, I'd recommend all types of decomposition.... Hot compost, myco digestion and worms to eat whatever was left. Sadly, the food system itself makes our own compost questionably organic from all the stuff in the water, whatever ends up in leaves from along the roads, gmos, pesticides etc.... If you got really fancy, you could TRY to work with mostly 'clean' eaters, but really, even the strictest Vegan might have some stuff you might not want to deal with.... but philosophically..... it is sortof a metaphor for the individual and collective situation. Our shit is just too bad to deal with, so we have to keep ourselves separated from the very cycles we depend on while justifying a linear false reality for ourselves and the world.
Now you see maybe why I wanted to avoid it...
Shit gets DEEP, Fast.