Possibly to use the liquified remains of humans disposed of by liquid "cremation". Plus, there's a push to use human waste (shit that is) for fertilizer the way Chinese do. when I was a kid our soil was basically clay. My father would have the Arabian horse farm dump cartage truck loads of horse manure in our back garden. Took a few years but he turned that clay soil into lush beautiful dark soil. I don't even know if it's legal to use manures...unless it's human of course. disgusting.