Duke’s Pratt School of Engineering was the winner of this year’s Bill and Melinda Gates Foundation’s Reinvent the Toilet competition, receiving a grant of $1.18 million to build a sewage processing system that fits inside a shipping container.
While not technically a toilet, the sewage processing system is extremely efficient and could change the way people around the world deal with their waste. Capable of dealing with a community of 1200 people, the system provides an alternative to simply dumping waste in rivers.
Communities using the system would have two options, having their cisterns pumped or physically carrying waste to the container.
Once in the container, the waste would be forced into a “supercritical” state – this is when water is heated to temperatures of over 705°F and pressures of more than 3200 pounds per square inch applied. Water in this state flows like a gas but is still able to dissolve other substances like a liquid.
What this means is that the suspended sewage can be dissolved, and with the addition of oxygen, it’s also possible to oxidize (i.e., burn) the sewage sludge – resulting in a sterile combination of water, carbon dioxide and salts.
The process of supercritical water oxidation (SCWO) also produces excess heat, despite the presence of water. Energy is only needed to start the system initially, once it reaches a certain temperature the remaining hot water may be supplied to the community directly or used to power an electrical generator.