DENVER, CO – SEPTEMBER 1: The Denver Zoo has collection containers all throughout the park for it’s Waste-to-Energy program. “Billy” an Asian elephant was photographed on Tuesday September 1, 2015 in his enclosure with some dung. They will convert all the animal waste and trash from visitors into pellets that can be converted into energy through biomass gasification technology. (Photo by Cyrus McCrimmon/The Denver Post )