A rendering plant basically takes all the leftover stuff from butchering, along with dead carcasses from roadkill, and expired meat from groceries, and the contents of grease traps...and turns it into "useful" products. They boil the stuff, the fat rises to the top of the water and skimmed off for various uses, then the water is drained. The leftover stuff is used for animal feed. The water from that process is supposed to be treated, but mostly gets dumped into the Scioto.
That place has KILLED a few people. Couple of suffocations from fumes, a steam explosion, and one poor bastard got killed while cleaning a jam in a tank. He was in a dry suit at the bottom of the tank clearing the pipe, and pulled out the remains of a monkey skeleton from the labs at OSU. Apparently it freaked him out (they kinda look like human infants...), he puked in his helmet, and drowned in his vomit.