Most people probably don't think of recycling the things they flush down the toilet. Karl Linden, a professor of environmental engineering at the University of Colorado, thinks that doesn't have to be the case.
Thanks to a couple of mirrors and fiber-optic cables, Linden is turning feces and urine into biochar, a small black chunk of material that can be used like a charcoal briquette.
"It can be used for cooking," he told ABC News. "Or you can put it in the soil so that it better retains nutrients. There's a lot of agricultural benefits."
Though the toilet produces something useful, that aspect is secondary to Linden's bigger goal of creating a usable toilet for countries that lack access to power and sewer pipes. "A lot of the pit latrines fill up and then you get sanitation problems," he said. "We're looking to create a toilet that makes the waste safe to handle."
The toilet relies on eight mirrors that focus sunlight onto a 1-centimeter wide square. From there, the focused light passes through bundles of fiber-optic cables to heat a reaction chamber up to over 300 degrees Celsius. The heat sterilizes the waste and dries it out, resulting in the biochar.
Though the toilet is currently designed for a single household, Linden said that future versions could be made to accommodate more people in order to be more cost effective. "It's pretty hard to make a toilet that does all the things you want it to do for a low enough price point," he said. "People that you know, like your extended family, could all use the same toilet block."
In addition, even though the toilet's sanitation is powered by the sun, that doesn't mean that you can't use it when the sun goes down. The toilet features two separate compartments that can be swapped in and out. "While one fills up for 24 hours, the other part gets solarized," said Linden. "We need about four hours of sunlight for treatment."