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  • Prototype concept for the Self-Contained, PV-Powered Domestic Toilet and Wastewater Treatment System.
    Credit: Brian Lee
07/19/2011 07:00:00

Caltech Scientist Awarded Grant to Develop Solar-Powered Sanitation System

PASADENA, Calif.—Environmental scientist and engineer Michael Hoffmann of the California Institute of Technology (Caltech) has received a $400,000 grant from the Bill & Melinda Gates Foundation to build a solar-powered portable toilet that could help solve a major health problem in developing countries. The grant, announced July 19 at the AfricaSan 3 sanitation and hygiene conference in Rwanda, will be used to complete the initial design, development, and testing of the unique sustainable system. Designed for use by up to 500 people per day with minimal maintenance, the sanitation unit will have the added benefit of turning waste into fuel.

Hoffmann's concept, called a "Self-Contained, PV-Powered Domestic Toilet and Wastewater Treatment System," is one of eight projects funded through the foundation's "Reinvent the Toilet Challenge." The Bill & Melinda Gates Foundation announced this grant as part of more than $40 million in new investments launching its Water, Sanitation, & Hygiene strategy. According to the World Health Organization (WHO) and UNICEF, about 2.6 billion people—approximately 40 percent of the world's population—lack access to safe sanitation, and nearly half of them practice open defecation. In addition, WHO estimates that 1.5 million children die each year from diarrheal disease, which is often caused by poor sanitation.

"Life expectancy correlates to the accessibility of clean water and proper sanitation practices," says Hoffmann, the James Irvine Professor of Environmental Science at Caltech, who has been working for years on the electrochemical technology to create a sustainable toilet and waste-treatment system. "All of our efforts in biomedicine may go for naught if we don't take care of sanitation."

Hoffmann's toilet system could fit inside the typical portable sanitation unit often found at construction sites and recreation areas, but the comparison ends there. It starts with a photovoltaic or solar panel, which converts the sun's rays into enough energy to power an electrochemical reactor that Hoffmann designed to break down water and human waste material into hydrogen gas. The hydrogen gas can then be stored in hydrogen fuel cells to provide a backup energy source for nighttime operation or for use under low-sunlight conditions. Hoffmann also envisions equipping the units with self-cleaning toilets that would also be powered by the energy from the sun and fuel cells.

Hoffmann says that he can build a workable unit for $2,000, but that the cost would come down significantly if the toilets were produced in volume. Following production of a prototype under the Gates Foundation grant, Hoffmann hopes to continue the project to refine the system and reduce its cost. In August 2012, all "Reinvent the Toilet Challenge" grantees will present their prototypes, with winning projects to receive additional funding for product development, industrial production, and commercialization.

"To address the needs of the 2.6 billion people who don't have access to safe sanitation, we not only must reinvent the toilet, we also must find safe, affordable, and sustainable ways to capture, treat, and recycle human waste," says Sylvia Mathews Burwell, president of the Global Development Program at the Bill & Melinda Gates Foundation. "Most importantly, we must work closely with local communities to develop lasting sanitation solutions that will improve their lives."

A member of the Caltech faculty since 1980, Hoffmann was honored in 2010 by the National Taiwan University as a Distinguished Visiting Chair Professor and by the State of Kerala, India, as an Erudite Distinguished Scholar. Earlier this year, Hoffmann was elected to the National Academy of Engineering. He is the organizing chair of the upcoming International Conference on the Photochemical Conversion and Storage of Solar Energy, which will be held on the Caltech campus at the end of July 2012. 

Written by Michael Rogers