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    This Solar-Powered Toilet Torches Poop for Public Health

    Written by

    Derek Mead

    Editor-In-Chief

    A test squat on the prototype. Image: University of Colorado

    For all the admirable efforts to solve the world's problems—beating malaria, improving education access, closing the digital divide—one simple need tends to fall by the wayside: We humans have to poop, and some 2.5 billion of us don't have the proper facilities to do so. 

    Think about what that means for a second: Beyond the commodes themselves, roughly a third of the planet's population lacks sanitation, leaving communities susceptible to disease and filth. As Jack Sim, the founder of the World Toilet Organization, told me a couple years ago, a major part of the problem is that sanitation isn't a particularly glamorous cause, which has limited its exposure and support. It's telling that more people globally have cell phones than have proper toilets.

    "Why is a cell phone something someone will pay for when they won't pay for it in their house?" Karl Linden, a University of Colorado, Boulder environmental engineering professor, told me. "We need to think of sanitation as a business opportunity, and turn the toilet into a status symbol." 

    Linden's team of engineers hopes to do just that. With funding from the Bill and Melinda Gates Foundation's Reinvent the Toilet challenge, the team has developed a toilet that uses concentrated solar power to scorch and disinfect human waste, turning feces into a useful byproduct called biochar.

    Fiber optic cables pipe hot sunlight into the toilet's reactor to burn poop.

    The goal is to build a self-contained block of toilets, similar to Coca-Cola's community blocks, that can also provide clean water and power for phone charging—to essentially turn toilets into a community center.

    "I think it's hard to make sanitation as sexy as a cell phone, but by integrating into the community and making it a hub, it can be something more popular," Linden said.

    The toilet itself, called the Sol-Char, is a fascinating bit of engineering. In order to sanitize waste without the help of massive treatment facilities, Linden's team instead designed the toilet to scorch waste in a chamber heated by fiber optic cables that pipe in heat from solar collectors on the toilet's roof.

    "A solar concentrator has all this light focused in on one centimeter. It'd be fine if we could bring everyone's fecal waste up to that one point, like burning it with a magnifying glass," Linden said. "But that's not practical, so we were thinking of other ways to concentrate that light."

    As the bag Linden is holding reads, that's real poopchar in his hand, and it's totally sanitary to hold. Image: University of Colorado

    According to Linden, the key was figuring out how to get light to enter the fiber optic cables, which are currently about four meters long, at the right angle so it propagates evenly. Linden said that producing heat with the eight fiber optic bundles isn't hard, but packing them tightly without melting was a challenge that required a lot of direct work with materials manufacturers. The result is a high-efficiency feces-burning machine.

    "The transmission efficiency is really high, it's like 90 percent as you don't have many losses," Linden said.

    The end product is biochar, a sanitary charcoal material that is good for soils and agriculture. By converting solid waste to biochar (liquid waste is diverted elsewhere, as it's easier to deal with), the toilet thus allows for sanitary waste disposal without huge infrastructure investments. 

    The project received $777,000 in initial funding from the Gates Foundation, with another $1 million in a second round. Currently, the team is in New Delhi for the second-annual Reinvent the Toilet Fair, an event hosted by the Gates Foundation and featuring the 16 teams in the toilet development challenge. Linden's team will present their working prototype, which has been in development for 18 months.

    The complete prototype in all its feces-torching glory.

    The next step is to build a system that's ready for plug-and-play use in the field, as well as decreasing costs. Linden said that they've already cut costs by 90 percent, and are looking to increase efficiency and decrease the length of their fiber bundles, which are a major cost in the design.

    "Our system right now is not field ready. It can operate, and all our technology can work in an integrated fashion, but we have to be there," he said. "The next phase of the research is to take what we're doing now and make it ready for the field."

    With continued development, Linden hopes his teams toilet can be delivered to communities to kickstart the conversation around sanitation investment. On its own, the community center model could provide a source of revenue to help maintain the system, while the end result is to increase awareness and demand for improved sanitation infrastructure.

    "You have to have a government that's interested in investing in the health of its people, and you have to have a community that's willing to invest not just their sweat equity, but their cash," Linden said.

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