A solar-powered toilet that turns urine and feces into hydrogen and electricity has won a $100,000 first prize in the Reinvent the Toilet Challenge sponsored by the Bill & Melinda Gates Foundation. The prize was announced yesterday at the foundation's "Reinvent the Toilet Fair" in Seattle, Washington, which continues today and showcases dozens of projects that aim to create an inexpensive and eco-friendly alternative to the flush toilet. Researchers are expected to use more than 50 gallons of soy-based synthetic feces to demonstrate their prototypes during the 2-day fair.
The flush toilet is convenient and hygienic, but the technology has its drawbacks: It uses clean water to flush away a potential source of nutrients and energy, and it’s prohibitively expensive for many of the estimated 2.6 billion people who lack access to sanitation. The Gates Foundation launched its toilet challenge a year ago, funding eight projects that aimed to invent a toilet that could be operated for 5 cents per user per day while recovering salt, water, nutrients, and energy.
The winning design, developed by Michael Hoffmann of the California Institute of Technology in Pasadena and his colleagues, uses solar power to run an electrochemical reactor that breaks down human waste to produce hydrogen gas. The gas can be stored and used to run the reactor at night or on cloudy days.
The $60,000 second place prize went to M. Sohail Khan of Loughborough University in the United Kingdom. He and his colleagues developed a toilet that transforms urine and feces into biological charcoal, which can be burned, and clean water.
Third place and $40,000 went to Yu-Ling Cheng of the University of Toronto in Canada and her colleagues whose design dehydrates and smolders solid waste, sanitizing it within 24 hours.
Tove Larsen of the aquatic research institute Eawag in Dübendorf, Switzerland, Harald Gründl of the design firm EOOS in Vienna, and their colleagues won a special $40,000 prize "for their outstanding design of a toilet user interface."
That prize was a last-minute addition, says Carl Hensman, program officer for water, sanitation, and hygiene at the foundation. The judges were especially impressed with the beauty of the team’s design, he says, which looks expensive but still comes in under the foundation’s cost criteria. A toilet's attractiveness for users is a crucial part of any workable solution, Hensman notes, and the Eawag and EOOS design could be combined with several of the other technologies on display at the fair. The design uses a foot pump that helps recycle water, and it features a clear tube that allows the user to see the clean water refill the tank—what the team calls the toilet’s entertainment factor. Hensman says all eight toilet challenge teams are applying for additional funding to further develop their ideas. The foundation’s goal is to have a field-tested prototype for "Toilet 2.0" ready for larger-scale testing by 2015.
See more articles about turning trash into treasure in this week’s special issue on Working with Waste.