A year ago, the foundation launched an initiative to tackle the problem of sanitation in the developing world. We called it the Reinvent the Toilet Challenge. In this photo gallery you can learn more about each of the grantees and their sanitation solutions.

This week in Seattle, the foundation is holding a Reinvent the Toilet Fair. Today I awarded prizes to three universities who responded to our challenge a year ago to come up with solutions for capturing and processing human waste and transforming it into useful resources. The winners included: first place to California Institute of Technology in the United States for designing a solar-powered toilet that generates hydrogen and electricity, second place to Loughborough University in the United Kingdom for a toilet that produces biological charcoal, minerals, and clean water, and third place to University of Toronto in Canada for a toilet that sanitizes feces and urine and recovers resources and clean water. A special recognition was awarded to Eawag (Swiss Federal Institute of Aquatic Science and Technology) and EOOS for their outstanding design of a toilet user-interface.

A solar-powered toilet that generates hydrogen and electricity
California Institute of Technology, USA
A self-contained, solar-powered toilet and wastewater treatment system. A solar panel will produce enough power for an electrochemical reactor that is designed to break down water and human waste into hydrogen gas. The gas can then be stored for use in hydrogen fuel cells to provide a backup energy source for nighttime operation or use under low-sunlight conditions.

A sanitation system that converts human waste into biological charcoal
Participating organizations: Stanford University and the Climate Foundation, USA
A self-contained system that pyrolyzes (decomposes at high temperatures without oxygen) human waste into biological charcoal (biochar). After the fair, the system will be shipped to Nairobi to process two tons of human waste daily, at a facility located in the slums.

A toilet that converts human waste to fuel gas
Delft University of Technology, The Netherlands
A toilet system that applies microwave technology to transform human waste into electricity. The waste will be gasified using a microwave-induced plasma. This process will yield synthesis gas (syngas), a mixture of carbon monoxide and hydrogen. The syngas will then be fed to a solid oxide fuel-cell to generate electricity.

Diversion for safe sanitation
Participating organizations: Eawag: Swiss Federal Institute of Aquatic Science and Technology; EOOS, Switzerland
A functional model of a urine-diverting toilet that recovers water for flushing. The urine and feces will be safely transported to a decentralized processing center. The water used for cleaning will be recycled by a gravity-driven biological membrane.

A toilet that produces biological charcoal, minerals, and clean water
Loughborough University, United Kingdom
A toilet that transforms feces into a biological charcoal (biochar) through hydrothermal carbonization (decomposition at high temperatures without oxygen and in water) of fecal sludge. The proposed system will be powered from heat generated by combusting the produced biochar and will be designed to recover water and salts from feces and urine.

A urine-diverting combustion toilet
National University of Singapore, Singapore
A toilet that uses biological charcoal (biochar) to dry and combust feces. The heat generated will be used to extract water from urine by boiling it under pressure. The system can be fitted with activated carbon and exchange resin to recover highly purified water.

A community bathroom block that recovers clean water, nutrients, and energy
University of Kwazulu-Natal, South Africa
A toilet system that can safely dispose of pollutants and recover materials such as water and carbon dioxide from urine in community bathroom blocks. The system will separate the urine from the feces and extrude the feces into thin strands for faster drying and stabilization.

A toilet that sanitizes feces and urine to recover resources and energy
University of Toronto, Canada
A technology for treating solid waste streams through mechanical dehydration and smoldering (low-temperature, flameless combustion) that will sanitize feces within 24 hours. Urine will be passed through a sand filter and disinfected with ultra-violet light.