Toilet Challenge winners

The California Institute of Technology's (Caltech’s) solar-powered toilet has won the Reinventing the Toilet Challenge issued by the Bill and Melinda Gates Foundation. Caltech engineer Michael Hoffmann and his colleagues were awarded $100,000 for their design, which they demonstrated at the Reinvent the Toilet Fair, a two-day event held 14-15 August in Seattle.

Last summer, Hoffmann, the James Irvine Professor of Environmental Science at Caltech, and his team were awarded a $400,000 grant to create a toilet that can safely dispose of human waste for just five cents per user per day. The lavatory can’t use a septic system or an outside water source, or produce pollutants.

Hoffmann’s proposal - which won one of the eight grants given - was to build a toilet that uses the sun to power an electrochemical reactor. The Caltech toilet is a self-contained, solar-powered toilet and wastewater treatment system. A solar panel will produce enough power to run an electrochemical reactor that is designed to break down water and human waste into hydrogen gas. This system is designed to process all bodily waste and all wastewater produced by a family, sanitising the water for flushing or local usage. The toilet produces hydrogen gas that can be stored for use in fuel cells or burned to power the system under low-sunlight conditions. The hydrogen gas can also be used for cooking. The water used in the system is recycled, allowing it to be repeatedly used for flushing.

The next steps for this project will address methods to ensure fully sanitised sludge and additional effort to lower the cost of materials and equipment to meet our specific criteria for a single household unit. The research team at Caltech has already indicated that this challenge is within their reach.

The $60,000 second-place prize went to Loughborough University in the United Kingdom - whose energy-efficient and self-sufficient toilet produces biological charcoal, minerals and clean water through a chemical process called hydrothermal carbonisation - and the $40,000 third-place award went to the University of Toronto’s design, which sanitises faeces and urine and recovers resources and clean water. This toilet uses a simple system where wet solids are flattened on a drying belt, then smouldered (combusted) and sanitised within 24 hours. Urine and cleansing water are passed through a sand filter and disinfected with ultraviolet light, resulting in clean water. The next steps for it will involve improving the individual component operations and then the integration of each of the pieces into a single operational prototype.