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Published on March 19th, 2014 | by James Ayre


Solar-Powered Toilet That Can Turn Waste Into Biochar

March 19th, 2014 by  

A toilet that can transform human waste into biochar, powered by nothing but the sun, has been developed by researchers at the University of Colorado Boulder.

The new technology was designed to address some of the sanitation issues that are common in many developing countries — and thereby help to protect local water supplies, and limit the spread of waterborne illnesses and diseases.

Image Credit: UC Boulder

Image Credit: UC Boulder

The self-contained unit works by using the energy of the sun, concentrated by eight parabolic mirrors, to heat up a quartz-glass rod that’s connected to eight bundles of fiber-optic cables, which then heat up the reaction chamber. The temperature in this chamber can reach over 600 degrees Fahrenheit — hot enough to sterilize human waste and produce biochar.

This new system was built and designed as part of the Gates Foundation’s “Reinvent the Toilet Challenge” using a $777,000 grant from the Bill & Melinda Gates Foundation. The ‘challenge’ was created as a means of developing solutions to the problems associated with human waste pollution. For example, more than 700,000 children die every year as the result of exposure to food and water tainted with pathogens from fecal matter. A cheap, effective means of dealing with human waste could go a long way towards limiting those numbers.

As far as the other side of this equation — for those that don’t know, ‘biochar’ is the term used to describe charcoal when it’s used for a number of specific purposes, such as a soil amendment. The researchers note that the widespread use of biochar could be used to both boost crop yields and to sequester carbon dioxide.

“Biochar is a valuable material,” stated researcher Karl Linden. “It has good water holding capacity and it can be used in agricultural areas to hold in nutrients and bring more stability to the soils. A soil mixture containing 10% biochar can hold up to 50% more water and increase the availability of plant nutrients. Additionally, the biochar can be burned as charcoal and provides energy comparable to that of commercial charcoal.”

The University of Colorado — Boulder provides more:

Tests have shown that each of the eight fiber-optic cables can produce between 80 and 90 watts of energy, meaning the whole system can deliver up to 700 watts of energy into the reaction chamber, said Linden. In late December, tests at CU-Boulder showed the solar energy directed into the reaction chamber could easily boil water and effectively carbonize solid waste.

While the current toilet has been created to serve four to six people a day, a larger facility that could serve several households simultaneously is under design with the target of meeting a cost level of five cents a day per user set by the Gates Foundation.

The CU-Boulder team is now applying for phase two of the Gates Foundation Reinvent the Toilet grant to develop a field-worthy system to deploy in a developing country based on their current design, and assess other technologies that may enhance the toilet system, including the use of high-temperature fluids that can collect, retain and deliver heat.

Interesting technology, though I do have questions about how likely it is to enter widespread use.

What do you think?

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • IzziD

    Here I thought I came up with the idea, then here I come and read about it. I’m wondering if the way they plan to design the toilet is similar to the one I have in mind. This a great invention for the whole world. Although it would slowly kill plenty of jobs in the sewage and plumbing business, it would also create new ones. A pipeless toilet is an answer to the drought problems seen around the world. The composting toilets could be a problem if you live in high populated countries like China and India. I can’t wait to see how this technology progress.

  • Mulubrhan Dagnew

    Where do I get the complete system design.

  • Rotiv Crs

    The stupidity of the western world why not resforest and stop destroying our planet cut down C02 emission lower the standard of living from rich countries who pollute the world NO ofcourse lets make some god dammed stupid shit who turns shit into compose if nature is healthy we don’t need none of this shyt………….

  • Velayna Howard

    So if a private individual wishes to buy one, how much would it cost to purchase the one in the picture? How soon would it be on the market?

  • To give you a sense of just how powerful the sun’s rays are, a photovoltaic array that is about 100 miles.

  • Ibrahim

    I will like to join your discussion on this Technology of loo management.
    Could you please highlight me on what is currently going on?

  • Doug Mac

    I’m wondering why they used concentrating thermal solar rather than photovoltaics, since the 700 watts peak power could easily be supplied
    with PV, with perhaps higher reliability.

    • Alen

      My guess is, as pyrolyses involves rapid heating it would be more efficient to use the heat directly rather than in PV solar its photons–>electricity–>heat transformation

  • erichj

    Fiber Optic Pyrolysis is a first and it’s simplicity may bring mobile Ag-Units applications. Also provide Solar with Biomass back up power.

    For a complete review of the current science & industry applications of Biochar please see my 2013 Umass Biochar presentation. How thermal conversion technologies can integrate and optimize the recycling of valuable nutrients while providing energy and building soil carbon,

    I believe it brings together both sides of climate beliefs.
    A reconciling of both Gods’ and mans’ controlling hands.

    Agricultural Geo – Engineering; Past, Present & Future
    Across scientific disciplines carbons are finding new utility to solve our most vexing problems

  • Ronald Brakels

    Instead of putting energy into poop it’s quite possible to get energy out with a methane biodigester. A biodigester can provide methane for cooking and fertilizer. While biochar can be an extremely valuable addition to soil the opportunity cost of turning poop into biochar is high. Poo is a little too valuable to use for biochar when wood, chaff, bones, nut shells and other substances do just as good. Engineers Without Borders has been working on providing some people in Cambodia with methane biogesters. Despite some problems with overcoming people’s reservations, for example the first family to use the system became locally known as the poo people, apparently things went quite well and the first movers became much admired.

    Here is an article on the project:

    • Bob_Wallace

      Commercial level units are being installed in San Diego. UCSD has been running one on campus for some time.

  • Benjamin Nead

    Hey, I like this. While Mik correctly points out that composting toilets are already here and are certainly cheaper, they might not fit the needs of all or in every location. Here’s another waterless alternative to a traditional toilet. What’s not to like?

    Indoor plumbing and, specifically, flush toilets have been pretty common in the developed western world for about a century now. The water toilets replaced a more primitive form of today’s more advanced compost toilets in most households: the outhouse. Low water use toilets were developed and modern compost units have been adapted to urban environments. But the latter might not be able to retrofit in all situations (ie: bathrooms that aren’t adjoining an exterior wall.)

    One could imagine that a version of this thermal solar technology could be developed for 21st century homeowners to help us continue to “do our business,” as potable water continues to become a more precious commodity that we really shouldn’t be flushing away.

  • Mik Fielding

    This seems all rather pointless when a far more simple and cheaper solution would be to build composting toilets. These need no high technology and can be built by the local community with locally sourced materials. The proposed ‘solution’ here just removes the ability from the local community to sort out their own needs and seems to be just a means to rake in more money for companies based in America etc., and requires fund raising to do so. Altogether a silly idea …

    • Bob_Wallace


      One very simple design is two about 4’x’4’x4′ boxes. Put a top with a hole on each. And a clean out door on the bottom.

      Poop in one for a year. Throw in some dried organic matter like leaves, corn husks, straw, wood shavings on a regular basis.

      Move over to the other box for the next year.

      After the filled box has been allowed a year to decompose, shovel out the ‘black gold’ and use it to fertilize trees, etc.

      I know people who built one in their greenhouse and have been using it for about 40 years. Works great.

      • dan strayer

        I’ve been doing this for about 20 years. Poo in one outhouse for about 6 years, switch to a second for 6..(or maybe 5)…go back to the first, put that composted poo on the garden, and start again. Easy. Cherry tomato plants 6 feet tall! Outhouse structures are lightweight, so I just tip them over, dig for 15 minutes, done. Stand it back up

    • Alen

      The biochar product is the real bonus from this process. Producing large quantities of this will help in ‘sucking’ all the excess CO2 from the atmosphere and thus help stabilise the atmospheric concentrations. Projects that help remove the excess CO2 are dearly needed if you ask me, and once we overshoot the concentration levels (which we inevitably will) solution like this are ultimately the way forward

    • Scott Groen

      Let’s see you cook over your “solution” in the middle of no where. This technology solves a multitude of problems- unlike the age old tradition of composting!

  • Dan

    Let’s try that again……
    With water issues in half of this country alone what would stop this technology from becoming widely adopted here as well?

  • Dan


  • Alen

    Great development if you ask me, I imagine this would be attractive to rural farmers too, especially over here down in southern Australia which are finding water is becoming scares as time goes by.

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