A new loo
Aiming to improve sanitation in developing countries, the Bill and Melinda Gates Foundation challenged engineers to make toilets clean, affordable and sustainable for the 2.5 billion people—40 percent of the world’s population—who lack access to modern toilets.
In response, environmental engineering professor Kara Nelson and postdoctoral researcher Temitope Ogunyoku have developed a toilet that safely disinfects waste.
Called the pHree Loo, their design uses a two-step process that raises the pH of the waste to inactivate harmful pathogens. The resulting “safe sludge” can then be disposed of without endangering human health.
To create their innovative toilet, the scientists turned to previous research showing that urea (from urine) and urease (from feces) produce ammonia after at least two hours of contact.
“Ammonia is a very effective killing agent for bacteria, viruses and parasites,” says Nelson, “and this prototype is based on that.”
In the first step of the disinfection process, the pHree Loo’s hand-cranked auger mixes the urine and feces, then moves the excreta down the cylinder, which provides a two-hour storage period to create ammonia. When the waste reaches the end of the cylinder, it moves into the collection bin.
In the second step, the waste is stored in a 10-gallon collection bin, which contains a lime solution. The solution will raise the pH of the waste mixture to 12, converting the ammonia to a disinfectant. After a week of storage in the bin, pathogens are inactivated. The safe sludge is ready to be taken to a processing facility, ideally to be converted to fertilizer or fuel.
Last fall, Ogunyoku traveled to the Nairobi, Kenya to test the safe sludge disinfection process and determine if it could be applied to a shared toilet system. There, she worked in partnership with Sanergy, a social enterprise that builds low-cost shared toilets, distributes the toilets through franchise to local entrepreneurs, collects the waste daily and processes the waste into fertilizer.
Using a Sanergy experimental urine-diverting toilet to conduct experiments, Ogunyoku learned that the safe sludge process worked effectively in the field. “The inactivation rates of the fecal indicator bacteria in the field were even faster than under laboratory conditions,” Ogunyoku says.
Disinfecting the waste with ammonia could be a reliable way for Sanergy to ensure that the fertilizer they produce is free of pathogens and safe for use by farmers.
For now, the researchers are working on a second prototype of the pHree Loo. Their goals are to further simplify the disinfection process, minimize odors and make the design easy to understand and use. They hope to test the new prototype in the field this fall.