Georgia Tech burns feces underwater to turn the toilet into a plug-in appliance

In an October 2022 Fast Company World Changing Ideas episode, Amelia Hemphill reports on Shannon Yee, an associate professor at Georgia Institute of Technology. He leads a team of engineers building a waterless super toilet under the Gates Foundation's Reinvent the Toilet Challenge. In the article, Yee says his background is in thermal energy technologies, not toilets.

The design is similar to an espresso machine and runs on electricity. A front unit looks like a regular toilet; a rear unit processes the waste. Yee describes the pitch as taking infrastructure and turning it into an appliance: no water in, no sewage out, so you plug it in wherever you need a bathroom.

Inside, solids and liquids are kept apart. The feces are subjected to intense heat and pressure, reaching a supercritical fluid phase in which, Yee says, the feces spontaneously combusts underwater. Water from urine is purified and used to flush, and the feces become small odorless cakes that can be composted or thrown in the trash.

Sewers need infrastructure and water that many places lack and that resource-constrained cities may not be able to afford.

Supercritical conditions let waste burn while it is still wet, with no drying step.

Recycling urine as flush water removes the water supply the toilet would otherwise need.

Making the product an appliance moves the cost from city-scale pipes to a single unit.

When a public service needs a network, ask whether a self-contained appliance can do the network's job at the point of use.

Per the article, the team was field testing the super toilets in South Africa, India, China and the U.S. Yee hoped that if successful the design could save cities millions of dollars in waste processing and sewage infrastructure costs. The article gives no results from the tests.