Environment: Not A Moment to Waste

It may not sound as appealing as turning water into wine, but turning human waste into clean water, energy, and useful byproducts is arguably as impressive—and can have longer-lasting health benefits. Duke engineers, working with a team from the University of Missouri, are working on a prototype of a self-contained “‘toilet” unit that will have the capacity to handle the daily fecal waste of about 1,200 users at a cost of less than a nickel per person per day.

The researchers aim to make the technology economically self-sustaining in developing countries, since typically urban and low-income areas have the greatest sanitation challenges. The new approach will operate without connections to water, sewer, or electrical lines. Researchers expect that a working prototype will have been constructed at Duke in about a year. It will be tested first in the U.S., and then in South Africa, India, or Ghana, depending on the results of feasibility studies.

Marc Deshusses, a professor of civil and environmental engineering at the Pratt School of Engineering, says the technology that powers the process—supercritical water oxidation—is a “pressure cooker on steroids.” Water is heated above 705 degrees Fahrenheit under pressure, turning it into a fluid thicker than steam but less dense than water. Add oxygen, and it burns up any carbonaceous materials, including waste. The reaction produces clean water, heat, carbon dioxide, benign salts, and nitrogen, which can be used by the communities or turned into business opportunities to support the system. For instance, water could be used to clean clothes and the heat could generate electricity.

The Bill & Melinda Gates [’86, M.B.A. ’87] Foundation is supporting the team’s efforts with a $1.18 million grant as part of the Reinvent the Toilet Challenge, part of the foundation’s Water, Sanitation & Hygiene program. Billions of people lack adequate sanitation facilities, and poor sanitation contributes to 1.5 million child deaths from diarrhea each year.