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Caltech Team Develops Solar Powered Toilet


This might be the last place you'd expect solar power to change your life. | Photo: Epsos.de/Flickr/Creative Commons License

More than two and a half billion people on the planet lack access to sanitary facilities, and the resulting contamination of drinking water is responsible for one of the leading causes of deaths among the worlds infants and children. But a team of Caltech engineers, with funding from Bill and Melinda Gates, may have a partial solution to the problem -- and the whole thing runs on solar power.

Dehydration from diarrhea is the second largest cause of global infant mortality, after respiratory ailments, and 88% of life-threatening diarrhea worldwide is caused by drinking contaminated water. A child somewhere in the world dies from drinking impure water every 30 seconds.

In the developed world we can go about our bodily functions without thinking: we have fresh water piped into our (often wasteful) flush toilets, which then take the resulting waste away so that it can, theoretically, be treated and made less harmful. Though our system is far from perfect, and has significant pollution effects of its own, it has made possible a revolution in public health: hardly anyone in the industrial world dies of waterborne diseases anymore.

But much of the world has access to neither fresh water nor a safe sewage system, and the Bill and Melinda Gates Foundation, through its "Reinventing the Toilet" program, is trying to create off-the-grid ways for people to answer the Call of Nature without polluting that nature, or their neighbors' drinking water. The Gates Foundation has raised an engineering challenge: can we build a toilet that doesn't require a sewer hookup, a water source, or grid power, and costs five cents a day or less to operate, but which doesn't pollute the air or water?

A team from Caltech just won a challenge held as part of that campaign with its solar-powered toilet. Engineer MIchael Hoffman and his colleagues took their design to the Gates Foundations' "Reinvent the Toilet Fair," held this week in Seattle, and walked away with the $100,000 prize for the best design.

The Caltech design uses a photovoltaic panel to generate energy, stored in batteries, to power an electrostatic unit that purifies liquids drawn from a small septic tank. The unit produces hydrogen as it cleans the water, potentially a supplementary source of toilet power on cloudy days or at night. The unit also purifies the solid waste which can then be used as biofuel or fertilizer.

The prototype's operation is described in this Caltech video.

Though it's aimed at users in developing countries, the project may well have important applications in California as well. For all their public health benefits, our flush toilets merely move the problem from one place to another, and water will be at an increasing premium as California gets droughtier. It may be that as we we work to get the electrical grid reinvented, we'd do well to have this Caltech team help us with the sewage grid as well.

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