Recycling CalTech adds fuel cell to solar toilet.

Published on December 31st, 2013 | by Tina Casey

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Sparks Fly As Solar Toilet Meets Hydrogen Fuel Cell

December 31st, 2013 by  

We were mighty impressed when a solar toilet from the California Institute of Technology won the Bill and Melinda Gates Foundation “Reinventing the Toilet Challenge” last year, and now the winning team of toilet reinventors has fulfilled the promise of their championship endeavor. As toilet champs, the team won a $100,000 grant to fine tune their device, and the result is a solar toilet that generates energy in the form of hydrogen, which it saves in a fuel cell.

Who Needs A Solar Toilet, Anyways?

The Gates Foundation is probably better known for its work in AIDS, but it launched the Reinventing the Toilet Challenge to solve another profound challenges facing the world today: how to provide sustainable sanitation for the 2.5 billion people who don’t have access to modern facilities.

The result has to be something with low costs, low or no water usage, and little or no polluting effluent. In effect, that means the toilet cannot simply discharge into a septic system or other collection facility.

In the low cost category, you can eliminate fossil fuels partly due to unpredictable price swings, so that leaves renewable energy as an option (that’s good news for us following the solar vs. diesel race, btw).

The Caltech solar toilet fit the bill on all counts, which is what you’d expect considering that CalTech also provides the academic management platform for the NASA Jet Propulsion Laboratory.

How The Caltech Solar Toilet Works

The solar panels are needed to provide electricity for running a little tank-like gizmo called an electrochemical reactor. When the toilet flushes, waste goes into the reactor and is broken down into hydrogen gas, water, and solids while being disinfected with chlorine.

The water can be recycled to flush the toilet again, or used to irrigate crops. Meanwhile, the natural process of microbial digestion goes to work on the solids, which are rendered into an organic fertilizer.

The result is a toilet that generates zero waste while producing three useful products: water, hydrogen gas, and fertilzer.

Hydrogen!

If your ears pricked up when we mentioned hydrogen, that’s where the fuel cell comes in. Earlier this month, the fuel cell company SAFCell announced that it has been selected by Caltech to integrate its hydrogen fuel cell into the solar toilet.

Basically, the fuel cell will act as a battery, storing energy so the reactor can operate at night. As needed, it can also provide additional energy during the day to run the facility.


SAFCell won the assignment partly because its fuel cell can tolerate the “impure” hydrogen gas produced by the reactor, eliminating the cost of a purification step.

The company also won points for its rugged design, and for proof of that you can take a look at the wearable fuel cell that SAFCell is developing for the US Army.

Let’s also note for the record that kitchen and bathroom whiz Kohler Co. also recently announced its support for the Caltech solar toilet.

What About The Rest Of Us?

For those of us in urban areas with modern wastewater treatment facilities, the human waste reclamation process is already well under way. New York City’s massive Newtown Creek treatment plant demonstrates the concept with dramatic flair, in the form of gigantic landmark-worthy egg shaped digesters that convert solids to fertilizer while capturing methane gas.

Currently the methane is too “wet” for commercial use and is used to power equipment at the plant. A new food waste recycling pilot project in partnership with the utility National Grid is under way, which will add a treatment step and enable the gas to be distributed offsite.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.



  • Oddly enough, the King County Government here in Washington State employed a wastewater driven fuel cell back in 2003, over ten years ago. It seems like we should have progressed further since then and pushed the technology a lot further, however, someone seems to have held his hand on the brake.

    Meanwhile, Bridgeport, Connecticut just opened a working fuel cell park, the beginning of a distributed micro-grid infrastructure in this country. But we should do more. Much more, and faster.

  • alvdh1

    I went to college with the guy who received a $1,200 grant from the energy department to build a solar toilet/outhouse in the 1970’s. It was called the Sky Crapper. Then Wisconsin Senator William Proxmire awarded him the Golden Fleece Award.

    http://www.columbiatribune.com/news/local/film-documents-life-in-lupus/article_edb94fdb-cf53-5bac-9c0a-68a47d1a6643.html

    • Bob_Wallace

      Proxmire was an ass. He tagged projects without understanding them. HIs “award” went to a mix of good and bad undertakings.

      If it sounded to him like a boondoggle he’d award it a Fleece. Didn’t matter if it was or not. It was all about getting media attention.

      • Alvdh1

        You are absolutely right about Proxmire. The Sky Crapper demonstrated a solar heated, zero water and composting method of disposing of human waste that the only alternative was tax payer funded municipal waste treatment. He wasn’t very forward think for a Democrat.

  • Argyll12

    Holy sh–!

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