Waterless solar concentrating toilet turns waste to biochar
The University of Colorado Boulder has built a self-contained, waterless toilet using a $777,000 grant from the Bill & Melinda Gates Foundation; the toilet is based on concentrating solar power technology.
IMAGE: CU-Boulder postdoctoral researcher Tesfayohanes Yakob, left, and research engineer Dana Haushulz are shown here with a novel solar-thermal toilet developed by a team led by CU-Boulder Professor Karl Linden as part of the Bill & Melinda Gates Foundation's "Reinvent the Toilet Challenge" to improve sanitation and hygiene in developing countries. (Image credit: University of Colorado Boulder)
The University of Colorado Boulder (CU-Boulder) has built a self-contained, waterless toilet using a $777,000 grant from the Bill & Melinda Gates Foundation. To be unveiled in India, the toilet uses concentrating solar power to sterilize and heat human waste to a high enough temperature and create biochar, said project principal investigator Karl Linden, professor of environmental engineering. The biochar, a highly porous charcoal, 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 to 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, said Linden. The energy generated by the sun and transferred to the fiber-optic cable system--similar in some ways to a data transmission line--can heat up the reaction chamber to over 600 degrees Fahrenheit to treat the waste material, disinfect pathogens in both feces and urine, and produce char.
Tests have shown that each of the eight fiber-optic cables can produce between 80 and 90 W of energy, meaning the whole system can deliver up to 700 W 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.
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, said Linden. 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.
According to the Gates Foundation, the awards recognize researchers who are developing ways to manage human waste that will help improve the health and lives of people around the world. Unsafe methods to capture and treat human waste result in serious health problems and death--food and water tainted with pathogens from fecal matter results in the deaths of roughly 700,000 children each year.
"Biochar is a valuable material," said 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, he said. Additionally, the biochar can be burned as charcoal and provides energy comparable to that of commercial charcoal.
"We are doing something that has never been done before," said Linden. "While the idea of concentrating solar energy is not new, transmitting it flexibly to a customizable location via fiber-optic cables is the really unique aspect of this project." The interdisciplinary project requires chemical engineers for heat transfer and solar energy work, environmental engineers for waste treatment and stabilization, mechanical engineers to build actuators and moving parts and electrical engineers to design control systems, Linden said.
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. "We are continuously looking for ways to improve efficiency and lower costs," he said.
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.
SOURCE: University of Colorado Boulder; http://www.colorado.edu/news/releases/2014/03/12/innovative-solar-powered-toilet-developed-cu-boulder-ready-india-unveiling