The Denver Zoo has to deal with a lot of waste. A good deal of that waste comes from visitors, but the zoo also produces hundreds of thousands of pounds of animal poo each year. Now, zoo engineers have found a positive use for it: They rigged up a poo-powered tuk-tuk. (A tuk-tuk is a motorized rickshaw.)

“We want to show people that we’re not crazy for wanting to take elephant poop and turn it into energy,” one engineer told the Denver Post.

And indeed, they are not crazy! In the past, the zoo used some of its waste to power a margarita machine. The tuk-tuk, a 20-year-old model from Thailand, shows they can power a slightly larger and more practical machine (which should not be combined with the earlier achievement — don’t drink poo-powered margaritas and drive poo-powered tuk-tuks, kids). Ultimately, the engineers aim to convert 1.5 million pounds of human and animal waste into electricity that will cover 20 percent of the zoo’s needs.

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That sounds like a potentially gross and smelly source of fuel, but it’s not like the tuk-tuk’s driver needs to be shoveling elephant poo into the engine all the time. The zoo collects the waste and turns it into pellets that, when heated without oxygen, produce syngas. Burning that gas then drives a generator that charges the tuk-tuk’s battery. So by the time the tuk-tuk’s out on the road, it’s quiet, clean, and smell-free.

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