Eco-friendly Flush

A solar-powered toilet that converts human waste into electricity snags first place—and $100,000—at the Reinvent the Toilet Challenge.

Aug 17, 2012
Jef Akst

Earlier this week (August 14), the Reinvent the Toilet Challenge announced its first prize winner: a solar-powered toilet that generates hydrogen and electricity from flushed human waste.

The Challenge, posed by the Bill & Melinda Gates Foundation, calls for researchers to come up with novel ways of disposing of human waste that avoid the drawbacks of the traditional flush toilet, including dumping high volumes of clean water and wasting the nutrients and energy found in urine and feces. In total, the Challenge’s contestants, each demonstrating their inexpensive (less than 5 cents per user per day) and productive (recovering salt, water, nutrients, and energy) human waste disposal prototypes, processed some 50 gallons of soy-based synthetic feces.

The solar-powered winner was developed by Michael Hoffmann of the California Institute of Technology and colleagues, and uses an electrochemical reactor to convert human waste into hydrogen gas that can be stored to power the reactor when the sun is not available. M. Sohail Khan of Loughborough University in the United Kingdom and his colleagues snagged second place, worth $60,000, for their toilet, which converts urine and feces into biological charcoal. Third place, and $40,000, went to Yu-Ling Cheng of the University of Toronto in Canada and her colleagues for a dehydrating toilet that burns and sanitizes solid waste.

The Foundation awarded an additional, unplanned $40,000 prize to Tove Larsen of the aquatic research institute Eawag in Dübendorf, Switzerland, and colleagues for designing an impressively beautiful toilet, which is key to putting a new toilet into action, Carl Hensman, program officer for water, sanitation, and hygiene at the Foundation, told ScienceInsider. The design, which employs a foot pump to recycle the water and a transparent tube through which the new, clean water flows, could be combined with other technologies at the Challenge, Hensman added, with the goal of field-testing a prototype on a larger scale by 2015.

See more images of the toilet prototypes here.