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Supercritical water oxidation to be used to treat sewage in Third World countries

Four people in a lab.

Biological engineering Associate Professor William “Bill” Jacoby, foreground, and the graduate students who work in his Carbon Recycling Center are collaborating with researchers at Duke University to develop a process to dispose of human waste using supercritical water oxidation. From left to right are Nick Wilkinson, Malithi Wickramathilaka and Reza Espanani.

University of Missouri Professor William “Bill” Jacoby’s Carbon Recycling Center has been examining the use of supercritical water to process biomass and other wastes.

A collaborative project, the research is led by Marc Deshusses, professor of environmental engineering at Duke University, who turned to Jacoby’s lab when he was looking for a suitable collaborator for his Bill and Melinda Gates Foundation-funded project, “Neighborhood-Scale Treatment of Fecal Sludge by Supercritical Water Oxidation.”

“We had published five or six papers on supercritical water gasification,” said Jacoby, who holds joint appointments in biological and chemical engineering at MU. “Marc was searching for technical help in a similar area, and he came across our published work.”

The project is part of the Gates Foundation’s water, sanitation, and hygiene strategy, which, among other things, aims to develop new technologies for sanitation in countries where no wastewater treatment facilities exist. Developed technologies need to be effective in communities with limited water supply and no existing sanitation infrastructure.

In addition to providing their supercritical water oxidation expertise, the MU arm of the research project is tasked with design, fabrication, and operation of a process development unit to determine design parameters for a larger prototype unit, which will be built at Duke.

Nick Wilkinson, a graduate research assistant working in Jacoby’s lab, explained that in Third World countries that lack sewer infrastructures, waste can be collected from ablution blocks [public toilets] and transported to the location of the oxidation reactor.

“Oxidation simply means burning. We are burning the waste in the presence of oxygen — similar to burning wood on a campfire,” said Wilkinson. “But we perform the reaction in a high-temperature, high-pressure reactor using supercritical water as a process fluid. Using supercritical water gives the technology a number of competitive advantages.”

Reza Espanani, also a graduate research assistant in Jacoby’s lab, said the waste is mixed with water and oxygen and pumped through a long plug flow reactor.

“Under supercritical conditions, sewage sludge will combust, releasing energy as heat,” said Espanani.

As a result of this released heat, the reactor reaches a temperature of over 1,100 degrees Fahrenheit. Some of this heat can be recycled back into the process, making the system self-sustaining — capable of operating without external heat input.

“After cooling, what comes out of the reactor is carbon dioxide vapor, salts and clean water,” said Wilkinson. “The water should be potable, but also will have other uses in developing communities for things like laundry or showering.”

The pair agreed that a real benefit of the system is that some of the heat produced from the reaction could be potentially be used for electricity or heat in the local community.

The research group is experimenting to gain as much information about the process as possible and to overcome some of the challenges associated with supercritical water oxidation technology.

“On the surface, the technology seems complicated for a Third World setting,” Jacoby said. “And the out-of-the-box approach is challenging,” he added, saying he is confident his team can reasonably solve the problems presented in this research.

“Deshusses serves as primary investigator for the project and we are a sub-contractor. If we improve the process, everybody benefits,” he said.

Jacoby praised campus support for his research. He said that without the on-campus funding he received from both the bioengineering program and the Mizzou Advantage initiative in one of the program’s five asset areas, Sustainable Energy, there would have been no research results for Deshusses to discover.

The research also has provided his lab assistants with great experience and credentials to continue their graduate degrees. Wilkinson earned his master’s from MU in May and is headed for the University of Minnesota to work toward his doctorate. Espanani is continuing his work toward a doctorate in biological engineering with Jacoby’s group.

“At the Carbon Recycling Center, we realize that we must learn to take full advantage of our renewable carbon resources. I’ve made believers out of my students and this research did what it was supposed to do,” Jacoby said of the students’ graduate school aspirations.

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