If you have unlimited access to it, why not use it to your advantage? At least that's what the Toronto Zoo is trying to do by making a poop-powered zoo. There is unlimited access to large quantities of poo (think of all the rhinos and elephants, and their MASSIVE feces), so why not use it to save the environment?
The zoo is in the stages of inviting companies to create a gasification plant which would turn the 1000 tons (a day) of poo into usable electricity. So far the only poop-powered zoo (or aspiring poop-powered zoo) is the Toronto zoo, but if it proves to be successful, I can't imagine why other zoos wouldn't follow suit.