In an effort to improve conditions for the more than 2.5 billion people worldwide with no access to safe sanitation, the Bill & Melinda Gates Foundation last year awarded grants totaling US$3 million to eight universities to reinvent the toilet. At the two-day "Reinventing the Toilet" fair held in Seattle this week, where Bill Gates was on hand with 50 gallons (189 l) of fake feces made from soybeans and rice to put the various designs through their paces, a California Institute of Technology (Caltech) team claimed first place for their solar-powered toilet.

The reinvent the toilet challenge asked teams to design a toilet that was completely self-contained and didn't require a sewer connection, piped-in water, or outside electricity. It also had to cost less than 5 cents a day per person to operate and be easy to install and maintain.

Caltech environmental scientist and engineer Michael Hoffmann ticked all these boxes with his solar-powered toilet design, which uses a solar panel to generate electricity to power an electrochemical reactor that breaks down water and human waste material into fertilizer and hydrogen gas.

The winning Caltech toilet breaks down water and human waste material into fertilizer and hydrogen gas

This hydrogen gas can then be stored in hydrogen fuel cells as a backup power source so people can continue to relieve themselves at night and on low-sunlight days. The treated water can then be used to flush the toilet of for irrigation. Hoffman and his colleagues collected $100,000 for the design.

Taking home the $60,000 second place prize was a team from Loughborough University, whose toilet transforms feces into biological charcoal, minerals, and clean water through a process combining hydrothermal carbonization followed by combustion, which is powered by heat generated during the combustion phase of feces processing.

Loughborough University's toilet design (Photo: Bill & Melinda Gates Foundation/Michael Hanson)

The $40,000 third place prize was awarded to a University of Toronto team, whose "Toronto Toilet" uses a sand filter and UV-ray disinfecting chamber to process liquid waste and a smolder chamber, similar to a charcoal barbeque, to incinerate solid waste that has been flattened and dried in a roller/belt assembly.

The University of Toronto’s toilet design (Photo: Bill & Melinda Gates Foundation/Michael Hanson)

A $40,000 Special Recognition Award for outstanding design of a toilet interface went to a team from the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and the Austrian design firm EOOS for their "Diversion" squatting toilet. This design separates feces and urine before they are then deposited in self-sealing feces containers and urine barrels ready for transport to a semi-central treatment plant where they can be processed into saleable products such as fertilizer and biogas.

The “Diversion” squatting toilet from eawag (Photo: Bill & Melinda Gates Foundation/Michael Hanson)

The grants awarded to the eight Reinvent the Toilet challengers were part of $42 million in sanitation grants the Gates Foundation awarded last year that are intended to spur innovations in the capture and storage of waste, as well as its processing into reusable energy, fertilizer, and fresh water.

The winning Caltech toilet is described in the video below.

And if anyone has some witty alternative captions to go with the main image, please let us know in the comments.

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