The Bill & Melinda Gates Foundation announced the winner of a contest to solve the problem of sanitation — toilets! — in the developing world. A team from the California Institute of Technology took first place in the foundation's "Reinvent the Toilet Challenge."

The Bill & Melinda Gates Foundation on Tuesday unveiled the winner of a contest to design a replacement for a technology that hasn’t changed much since the 19th century: the flush toilet.

The new toilets are designed primarily for the developing world, where the lack of plumbing often makes conventional toilets impractical. The winning loo, a solar-powered model designed by researchers from the California Institute of Technology, or Caltech, generates hydrogen and electricity to boot.

Toilets, foundation co-chair Bill Gates said in his opening remarks, are “kind of an ignored area” of efforts to help the world’s poor, but a crucially important one. Roughly 2.6 billion people in the world lack access to toilets, and 1.5 million children die annually from diarrheal diseases.

Policymakers have tended to shy away from the problem until now, said Crown Prince Willem-Alexander of the Netherlands, who works with the United Nations on this sanitation issue. “Toilets are simply not sexy,” he said.

The winning design looks like a regular toilet, at least above ground. After use, the waste is flushed down to a holding tank under the floor, where the solid material sinks to the bottom. When the liquid reaches a certain level, it flows through a tube into a “sun-powered electrochemical reactor.” The reaction oxidizes the chloride in the urine, killing microorganisms in it.

The treated water is filtered and reused the next time someone sits on the toilet. And the residual chlorine in the water means, “The next flush would already have disinfectant in it,” said Michael Hoffmann, the professor at Caltech who led the team that designed the toilet.

The hydrogen, meanwhile, could be siphoned off, and the toilet’s owners could “use it as you would use gaseous propane” for cooking, he said. The whole thing is powered with solar energy.

The technology behind the toilet isn’t new, Hoffmann said. He had developed a version of the electrochemical treatment process, for instance, for NASA years earlier. But the Gates Foundation’s challenge to eight universities a year ago — along with a $400,000 grant to each — allowed the pieces to come together.

Hoffman and the Caltech team won a $100,000 prize. The second-place team, from the University of Loughborough in the United Kingdom, won $60,000 for its design, which would convert feces into a type of charcoal. A team from the University of Toronto won third place and $40,000 for a toilet that treats solid waste through dehydration and low-temperature combustion. A Swiss team was singled out for special recognition and won $40,000 as well.

Hoffmann’s toilet, which could cost $1,000 or more per unit, is still in the early stages of development, and it is unlikely to proceed to market without changes.

Gates said he hopes that once a next-generation toilet is fully designed, it will incorporate ideas from a variety of toilet designs submitted in the contest: “We think the combination of a lot of this work is what will get us to the eventual solution.”

Theodoric Meyer: 206-464-2985 or Twitter: @theodoricmeyer.