CU’s solar toilet set for unveiling in India

BOULDER – Instead of flushing away human waste, how about burning it to save water?

That’s the idea behind a solar-powered, waterless toilet developed at the University of Colorado-Boulder, with the help of a $77,000 grant from the Bill and Melinda Gates Foundation.
The device is designed to help some of the 2.5 billion people lacking safe and sustainable sanitation around the world, including in India where it will be unveiled this month.

The toilet converts human waste to sterilized “biochar,” a highly porous charcoal, said CU professor Karl Linden, the project’s principal investigator, in a press statement. The biochar has a one-two punch in that it can be used to both increase crop yields and sequester carbon dioxide, a greenhouse gas.

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The CU-Boulder invention consists of eight parabolic mirrors that focus concentrated sunlight on a spot no larger than a postage stamp on a quartz-glass rod connected to eight bundles of fiber-optic cables, each consisting of thousands of intertwined, fused fibers, Linden said. The energy generated by the sun and transferred to the cable system can heat the reaction chamber to more than 600 degrees Fahrenheit to treat the waste material, disinfect pathogens in both feces and urine, and produce the biochar.

The project is part of the Gates Foundation’s “Reinvent the Toilet Challenge,” an effort to develop a next-generation toilet that can be used to disinfect liquid and solid waste while generating useful end products, both in developing and developed nations, Linden said.

Since the 2012 grant, Linden and his CU-Boulder team have received an additional $1 million from the Gates Foundation for the project, which includes a team of more than a dozen faculty, research professionals and students, many working full time on the effort.

Linden’s team is one of 16 around the world which were funded by the Gates “Reinvent the Toilet Challenge” since 2011.
All have shipped their inventions to Delhi, where they will be on display March 20-22 for scientists, engineers and dignitaries.

“Biochar is a valuable material,” Linden said. “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 percent biochar can hold up to 50 percent more water and increase the availability of plant nutrients.”

Additionally, the biochar can be burned as charcoal and provides energy comparable with that of commercial charcoal.

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.

Another similar project funded by the Gates Foundation challenge grant was reported in November in the Business Report. Researchers at the University of Bristol in the United Kingdom invented a way to run a number of everyday electronic devices – including cell phones, light fixtures and electric razors and toothbrushes – using “urine power.” The team was able to convert urine into fuel through the use of a microbial fuel cell.