Bill Gates-Funded Solar Toilet Converts Feces Into Soil Stabilizer
This isn't the first time you've heard a college professor say his team of researchers is working on something that has never been done before, but it's likely the first time such a statement has been associated with a technology that takes advantage of both solar energy and feces.
Karl Linden, a professor of environmental engineering at the University of Colorado Boulder (UC-Boulder), and a team of post-doctoral fellows, students and other professors have created a solar-powered toilet capable of heating human waste to temperatures high enough to sterilize it and create biochar, which is porous and has multiple agricultural functions, including the encouragement of greater crop yields and soil stabilization.
To make things a bit easier, Linden has referred to the end-product as "poop-char."
The team's self-contained, waterless toilet includes eight parabolic mirrors that focus concentrated sunlight on a tiny spot on a quartz-glass rod that connects to eight bundles of fiber-optic cables. Each of those cables consists of thousands of intertwined, fused fibers. The solar energy transferred to the fiber-optic cable system can heat up the reaction chamber to over 600 degrees to treat the waste material, disinfect pathogens in both feces and urine and produce the char.
“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,” Linden said in a statement.
Why would anybody want to heat and treat human waste? Scientists have been doing it for years, attempting to find uses for it that range from animal feed to attempts at creating more drinkable water. According to UC-Boulder, unsafe methods to do this often result in serious health problems or deaths. About 700,000 children die as a result of food and water that contains pathogens from fecal matter.
The UC-Boulder team is one of 16 around the world since 2011 that has received funding from the Bill & Melinda Gates Foundation as part of the "Reinvent the Toilet Challenge," which is an effort to develop a toilet that can create useful end-products while also disinfecting liquid and solid waste, operating off the grid, costing users less than 5 cents per user per day. According to the Foundation, there are about 2.5 billion people around the world without access to safe and affordable sanitation.
The Foundation awarded the team $777,000 in 2012 and has since received another $1 million.
All of the participating teams have shipped their inventions to Delhi, where they will be on display starting March 22 for scientists, engineers and dignitaries.
According to Linden, each of the eight fiber-optic cables can produce 80 to 90 watts of energy, for a total of up to 700 watts of energy delivered from the whole system into the reaction chamber. In December, tests at conducted at the university showed that the solar energy directed into the reaction chamber could easily boil water and carbonize solid waste.
The current toilet can serve four to six people a day, but the team is working on a larger facility that could serve multiple households simultaneously. Linden and the group are trying to secure additional investments.
“We are continuously looking for ways to improve efficiency and lower costs," Linden said.
Bill Gates has also funded a group of researchers at the Massachusetts Institute of Technology working on commercializing liquid-metal batteries that can store energy for less than $500 per kilowatt-hour.
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Clear-cutting a forest is relatively easy—just pick a tree and start chopping. But there are benefits to more sophisticated forest management. One technique—which involves repeatedly harvesting smaller trees every 30 or so years but leaving an upper story of larger trees for longer periods (60, 90, or 120 years)—ensures a steady supply of both firewood and construction timber.
A Pattern in the Rings<p>The <a href="https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/coppice-standards-0" target="_blank">coppice-with-standards</a> management practice produces a two-story forest, said <a href="https://www.researchgate.net/profile/Bernhard_Muigg" target="_blank">Bernhard Muigg</a>, a dendrochronologist at the University of Freiburg in Germany. "You have an upper story of single trees that are allowed to grow for several understory generations."</p><p>That arrangement imprints a characteristic tree ring pattern in a forest's upper story trees (the "standards"): thick rings indicative of heavy growth, which show up at regular intervals as the surrounding smaller trees are cut down. "The trees are growing faster," said Muigg. "You can really see it with your naked eye."</p><p>Muigg and his collaborators characterized that <a href="https://ltrr.arizona.edu/about/treerings" target="_blank">dendrochronological pattern</a> in 161 oak trees growing in central Germany, one of the few remaining sites in Europe with actively managed coppice-with-standards forests. They found up to nine cycles of heavy growth in the trees, the oldest of which was planted in 1761. The researchers then turned to a historical data set — more than 2,000 oak <a href="https://eos.org/articles/podcast-discovering-europes-history-through-its-timbers" target="_blank" rel="noopener noreferrer">timbers from buildings and archaeological sites</a> in Germany and France dating from between 300 and 2015 — to look for a similar pattern.</p>
A Gap of 500 Years<p>The team found wood with the characteristic coppice-with-standards tree ring pattern dating to as early as the 6th century. That was a surprise, Muigg and his colleagues concluded, because the first mention of this forest management practice in historical documents occurred only roughly 500 years later, in the 13th century.</p><p>It's probable that forest management practices were not well documented prior to the High Middle Ages (1000–1250), the researchers suggested. "Forests are mainly mentioned in the context of royal hunting interests or donations," said Muigg. Dendrochronological studies are particularly important because they can reveal information not captured by a sparse historical record, he added.</p><p>These results were <a href="https://www.nature.com/articles/s41598-020-78933-8" target="_blank">published in December in <em>Scientific Reports</em></a>.</p><p>"It's nice to see the longevity and the history of coppice-with-standards," said <a href="https://www.teagasc.ie/contact/staff-directory/s/ian-short/" target="_blank">Ian Short</a>, a forestry researcher at Teagasc, the Agriculture and Food Development Authority in Ireland, not involved in the research. This technique is valuable because it promotes conservation and habitat biodiversity, Short said. "In the next 10 or 20 years, I think we'll see more coppice-with-standards coming back into production."</p><p>In the future, Muigg and his collaborators hope to analyze a larger sample of historic timbers to trace how the coppice-with-standards practice spread throughout Europe. It will be interesting to understand where this technique originated and how it propagated, said Muigg, and there are plenty of old pieces of wood waiting to be analyzed. "There [are] tons of dendrochronological data."</p><p><em><a href="mailto:email@example.com" target="_blank" rel="noopener noreferrer">Katherine Kornei</a> is a freelance science journalist covering Earth and space science. Her bylines frequently appear in Eos, Science, and The New York Times. Katherine holds a Ph.D. in astronomy from the University of California, Los Angeles.</em></p><p><em>This story originally appeared in <a href="https://eos.org/articles/tree-rings-reveal-how-ancient-forests-were-managed" target="_blank">Eos</a></em> <em>and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.</em></p>
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