- Solar cells in the Caltech product convert waste into fertilizer and hydrogen.
- The University of Colorado toilet focuses solar beams through fiber optic cables to heat the waste to 600°F and create biochar.
- The Gates Foundation is funding everybody; this is not a winner take all competition.
Money from the Gates Foundation is still being used to spur innovation in the development of toilets for third world countries. Approximately 2.5 billion people worldwide do not have access to toilets. Some advances have been made by teams from the California Institute of Technology and by the University of Colorado at Boulder, both of which have created solar toilets.
The Sierra Club featured the Caltech design that zaps the solid waste into fertilizer and stores the hydrogen byproduct in a fuel cell for future use.
As the Sierra Club noted on its site:
California Institute of Technology environmental science professor Michael Hoffman led a team that came up with a self-contained sanitation system, in which solar cells power an electrochemical reactor that converts liquid and solid waste into fertilizer and hydrogen. The hydrogen is stored in fuel cells as energy, while treated wastewater is reused to flush the toilet or to irrigate crops. Drawbacks: It is complicated, requires highly trained maintenance workers, and costs up to $2,000 per potty.
The Colorado team uses parabolic mirrors that focus sunlight into fiber optic cables. The focused beams heat up the waste chamber to 600°F, killing pathogens and turning the waste into biochar. Biochar has good waer holding capacity so it can be used in agriculture to retain water in the soil. It can also be burned like charcoal.
The engineers from Boulder explain it thusly:
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 Karl Linden, professor of environmental engineering. 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°F to treat the waste material, disinfect pathogens in both feces and urine, and produce char.
That focused energy delivers up to 700W into the reaction chamber.