A toilet that doesn't use plumbing, doesn't produce any pollutants and is powered by the sun?

It can be done, and scientists at Caltech in Pasadena just won an international challenge to create the "toilet of tomorrow."

California Institute of Technology engineer Michael Hoffmann and his colleagues won $100,000 from the Bill and Melinda Gates Foundation for their self-contained, two-story design, which is meant to address challenges related to water, sanitation and hygiene in developing countries.

The foundation's website notes that nearly 40 percent of the world's population doesn't have access to clean, flush toilets -- which require a lot of infrastructure and fresh water.

The website states: "2.6 billion people don't have a safe and affordable way to poop."

Nearly half of all disease cases in developing countries are caused by unsafe sanitation conditions, according to the United Nations, and some 1.5 million children die each year from diarrheal disease. Many of those deaths and diseases could be prevented by access to safe toilets, experts say.

"We're designing the system for use in the developing world to reduce disease tranmission through improper sanitation," Caltech's Hoffman states in a video about the project.

"Reinventing the toilet: Let's get our s--- together and do it," states a video on the Gates Foundation's website.

Hoffman and his team demonstrated their invention at the Reinvent the Toilet Fair, an event held this week in Seattle. They started working on the project last summer after winning a $400,000 grant to make a toilet that can safely dispose of waste for 5 cents per user per day, according to Caltech's website.

It has to be asked, though, without a sewer system: Where does the poop go?

By gravity, waste goes to an undergound holding tank where bacteria in part act as pre-treatment. Then the waste goes into an electrochemical reactor and is oxidized, according a video from Caltech. Water extracted from the waste is disinfected and can be reused for future flushes or irrigation.

The toilet turns the waste into fertilizer, which can be used for crops, and hydrogen, which can be stored in a fuel cell for energy. It uses solar power -- a single day's sunlight -- to run the electrochemical waste-treatment system that processes feces and urine.

It has a Western-style sit-down toilet, a urinal and a squat toilet, which is more commonly used in many developing countries.

A prototype was built within the solar dome on the roof of a laboratory at Caltech in Pasadena. It got a year's worth of design and testing work before it was showed off at the Seattle event.

Things didn't get too realistic at the fair, however. Toilets of the future were tested with 50 gallons of fake poop made from soybeans and rice.

At Caltech, Hoffman's team tested their toilet using samples from Los Angeles-area wastewater treatment stations.

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