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Sonia Grego and Brian Stoner
Associate research professor Sonia Grego, director of the Duke Smart Toilet Lab, and engineering professor Brian Stoner, director of the Center for WaSH-AID. Photo by Chris Hildreth

Changing the World, One Flush at a Time

Duke team’s reinvented toilet could provide safer water and better lives – especially for women in poor countries

In a small, cream-colored building on the site of a cotton mill in Coimbatore, India, sits a toilet with a lot riding on it. No ordinary commode, its life-changing mission is to stop the spread of deadly diseases, conserve dwindling fresh water, and even keep girls in school.

Can a toilet change the world? Brian Stoner, who leads the Duke team behind the unit in Coimbatore, thinks this one could. “I certainly believe it has that potential,” says Stoner, a professor of electrical and computer engineering who is also part of the Duke Global Health Institute.

But is the world ready to change its toilets?

Most people don’t give much thought to what happens after they flush the toilet. Generations of sanitation engineers did that for us, laying down vast networks of sewer pipe that carry our messes off to places we don’t like to think about.

Many parts of the world don’t have that luxury. About 3.6 billion people – nearly 46% of the global population – lack access to safe sanitation, according to the United Nations’ 2023 World Water Development report. Nearly 500 million people relieve themselves in the open, while many more use pit latrines or septic systems that discharge untreated waste into the environment. It’s a problem that impacts residents of remote villages and densely packed urban slums, in poor countries and in places where population growth outstrips infrastructure. And it kills: Drinking or bathing in water contaminated by waste is one of the main drivers of diarrheal diseases that cause the deaths of more than 500,000 children under age 5 each year.

Associate research professor Brian Hawkins, left, and research associates Claire Welling and Robert Foushee review water samples taken from different stages in the reclaiming process.

In 2011, the Bill & Melinda Gates Foundation stepped into the muck with a different idea. It announced the global “Reinvent the Toilet” challenge, which would fund a handful of engineers to design a new generation of toilets capable of treating waste on site. To be considered, projects had to remove pathogens and other harmful agents from waste without drawing external water or power. And they had to do it cheaply, costing no more than five cents per user per day.

Brian Hawkins, a scientist who leads technology development for Stoner’s team, says the Gates challenge was a “moon shot,” asking engineers to recreate the processes of a municipal wastewater treatment facility in an off-the-grid box.

“It’s arguably the hardest way to do it,” he says. “If you’ve got a lot of space and a lot of time, [wastewater treatment] isn’t hard. If you’re trying to get it done in a small space and very quickly, it gets exponentially more difficult.”

But Stoner already had an idea. At the time, he was a materials scientist with the Triangle research firm RTI International, and he’d been working on a project for the U.S. Navy using electrodes to treat waste on submarines. At a clean-water technology conference in 2012, he floated the strategy to Doulaye Kone, a program officer at the Gates Foundation who was leading the toilet challenge. Kone was intrigued, encouraging him to submit a proposal.

“A couple of us went to the bar that evening and put together a white paper,” Stoner says. “We sent it in the next day.”

Research associate Graham H. Miller fabricated a mobile Reclaimer to take WaSH-AID into the community for demonstrations.

With Gates funding in hand, Stoner moved the team to Duke to launch the Center for Water, Sanitation, Hygiene and Infectious Disease, a mouthful the group creatively truncates to WaSH-AID. By 2018, they had produced a prototype, a boxy unit the size of a skinny refrigerator that they call “the Reclaimer.”

The Reclaimer uses electrical current to generate chlorine from the salts in urine, one of several chemical processes it deploys to cleanse bacteria, viruses and other unsavory bits from wastewater. Solids proved too expensive to treat within the system, so the current model filters them out for separate processing. The result is water that, while not quite pure enough to drink, is safe to use for gardening, laundry and to cycle back into the toilet. The unit can be connected to any toilet and can be powered by a solar panel.

For all its fancy chemistry, the Reclaimer is one of those rare engineering projects that is informed as much by human nature as science. Before completing the prototype, the team engaged a local partner to conduct surveys and focus groups in several communities in India, gathering input on what users might expect from a reinvented toilet. What people most wanted were no surprises.

“Nobody likes to have a toilet that looks different than what they are used to,” says Sonia Grego, a WaSH-AID researcher who manages field testing for several of the center’s projects. Western engineers learned quickly not to try to replace traditional squatting toilets with pedestals and to provide extra water, as most Indians prefer washing to wiping.

How the Reclaimer Works

Vials of water
From left: Ultrafiltration removes the suspended solids that make wastewater cloudy. Then activated carbon pulls out the soluble organic material that gives it undesirable color and odor. Next, a porous mineral called zeolite pulls out the ammonia. Finally, a chemical process using electrical current converts chloride salts into chlorine, which kills bacteria and other pathogens. The resulting water is clean, clear and safe to use for tasks other than drinking: laundry, gardening, cooling and flushing the toilet.

One of the team’s most profound insights speaks to the unique significance of a safe toilet space in the lives of women, especially those who live in poverty. While men may face no stigma for relieving themselves in the open, many women in low-income countries endure the daily stress of finding private spaces to take care of bodily functions. The perceived shame of acknowledging female biology is so strong that girls often skip or drop out of school when they start menstruating.

When the Duke engineers heard these stories, they realized they were creating more than an environmentally friendly toilet, says Grego. At the cotton mill in Coimbatore, they did more than just hook up a Reclaimer to an existing toilet. They designed the entire building, selecting lighting, fixtures and even the floor tiles to foster a sense of comfort and privacy.

“That’s an aspect we’re really proud of,” says Stoner. “We wanted to think not just about the traditional use of a toilet, but what would make a space safer, more secure and more attractive for women and girls.”

 What the Reclaimer is not – at least not yet – is particularly affordable. Although operating costs are minimal, a prototype unit is around $12,000 to manufacture, too steep a price to expect wide adoption in places like India. Stoner’s team believes the price will come down through economies of scale, but also by finding more profitable uses for their technology in wealthier countries.

“For this to be deployed globally, there is going to have to be some aspect of commercial viability,” says Hawkins.

He thinks technologies like the Reclaimer could find a market niche in wealthier countries that face an increasingly water-scarce future. Households and larger developments could use the system to recapture and reuse wastewater. Multiple companies have shown interest in commercializing the technology, he says, including businesses in India, China, the Middle East, Africa, Europe and North America.

The team has equipped a trailer with the technology to demonstrate at schools and community events. There are also talks with Durham’s parks department about possibly using the Reclaimer in a public toilet in Central Park, near the city’s popular farmers market.

The hope is to build a kind of waste evangelism, akin to the movements around renewable energy and sustainable agriculture, that can seed market opportunities. “The people who really believe in the technology and can afford it are always the early adopters,” says Stoner. “Those first customers can make it attractive for businesses, and that brings the price down for the countries that really need it.”

After a decade of research and testing, this is where the fate of the Reclaimer rests – on whether those with means choose to invest in perhaps the least glamorous of environmental causes. Even if enough do, it could take years to see technologies like the Reclaimer in wider commercial use. But meanwhile, it’s still churning away at the cotton mill in Coimbatore, where it has now recycled more than 10,000 liters of wastewater.

And this, ultimately, is the only way a toilet can truly change the world: One flush at a time.