A Way With Waste

Bill Gates and officials from the eThekwini (Durban) municipality and the University of KwaZulu-Natal stand by an old pit latrine and discuss dry sanitation.

The Gates Foundation’s Reinvent the Toilet challenge inspires no-plumbing solutions that turn human effluent into useful products.

The academic engineers who toil in the field of sanitation, especially sanitation for the poorer citizens of the world, used to find that their field carried about as much cachet as a fly-ridden latrine. But not anymore.

In July of last year, the Bill & Melinda Gates Foundation announced eight grants totaling $3 million for university engineering projects to “Reinvent the Toilet.” The first round — for prototype development — will culminate in a Toilet Fair in Seattle this August and further grants to commercialize the most promising technology.

“Usually we battle to get master’s students involved in sanitation,” says chemical engineering lecturer Katherine Foxon of the University of KwaZulu-Natal in South Africa. “Now they come to us saying, ‘Got any projects for me to do on Reinvent the Toilet? … Will I get to shake Bill Gates’s hand?’”

The foundation’s concern, of course, is not the prestige of sanitation engineers but the health of the world’s 2.6 billion people who have no hygienic sanitation. “Only about a third of the world’s population have flush toilets linked to sewers,” says Frank Rijsberman, director of the foundation’s Water, Sanitation, and Hygiene program. More than a billion people defecate in the open. Others use latrines that attract disease-carrying flies and are sometimes emptied into alleys and waterways. More than a million children die of diarrhea every year, largely as a result of such problems. “We don’t have a technology that you or I would choose to use today,” Rijsberman adds. “We need something that doesn’t yet exist.”

More than a million children die annually from diarrhea – mostly because of poor sanitation.

EVAPORATE, COMBUST, AND GASIFY

“Reinvent the Latrine” might better capture the work taking place at the universities. None of the engineers involved is proposing technology to expand sewerage lines and connect billions of new flush toilets. Such systems are simply too expensive and wasteful. Chris Buckley, another KwaZulu-Natal chemical engineer, points out that the dry weight of the average person’s feces is a mere 11 kilograms per year. Toilets demand 18 metric tons of water to transport those 11 kilograms, however, dispersing pathogens in 18,000 liters of water in the process. “Flush toilets are not a sensible idea,” he concludes.

Instead, the eight engineering projects, from Switzerland to Singapore, propose to evaporate, combust, microwave, pyrolyze, and gasify human waste, creating useful end products in the process. Buckley, a jocular academic with a bushy gray beard, quips that the goal is to convert excrement into “drinking water, fertilizer, and salt for your fish and chips.”

At Caltech, Michael Hoffmann has plans that make Buckley’s hyperbole seem not so far-fetched. Hoffmann, a professor of environmental science recently elected to the National Academy of Engineering, and his research group are incorporating solar photovoltaics, hydrogen fuel cells, and semiconductors into a small-scale waste treatment reactor.

The self-sustaining system is designed to create its own energy while destroying pathogens and producing fertilizer and sanitized water that can be recycled for flushing. One of the requirements of the Gates Foundation is that the toilet systems need neither plumbed water supply nor electricity from the grid.

Caltech’s toilet plan is based on more than a decade of work, for which Hoffmann and his group have been awarded three patents. The research began with the goal of improving upon conventional electrolysis to produce hydrogen from water. Hoffmann experimented with semiconductor-plated electrodes to replace platinum and other expensive metals, which operate normally within a very limited range on the pH scale. When he found that the resulting reactions were producing hydroxyl radicals – extremely powerful oxidizing agents – Hoffmann expanded the scope of his research into electrochemical reactors that can purify industrial wastewater.

ELECTRICITY FROM EFFLUENT

Now, with a nudge from the Gates Foundation, Hoffmann, along with a senior scientist, a postdoc, and four other Caltech students, is adapting this technology to treat human waste. He is already confident that his reactors, powered by solar photovoltaic panels, can oxidize organics while producing disinfecting hypochlorous acid as a byproduct from chlorides in the wastewater. The hydrogen released will be stored and then converted into electricity by fuel cells at night to keep the process going. The team is even developing new lithium-based batteries to serve as a secondary backup when the sun fails to shine.

Hoffmann’s high-tech approach could cost several thousand dollars to build a processing reactor that might service 500 slum dwellers using public toilet facilities in their community. “If your goal is highly sophisticated technology using latest advances in chemical engineering, but at very low cost, that is a little contradictory,” he warns. Still, Hoffmann points out that the system may have virtually no operating expenses. The Gates Foundation wants toilets that cost no more than five cents per person per day.

At Stanford University, mechanical engineering professor Reginald Mitchell is also adapting his research to the effluent effort. For 25 years, Mitchell has been applying his combustion and gasification expertise to improving energy production in converting coal and, more recently, biomass, into electricity and hydrogen. Heated in the absence of oxygen, pyrolyzed biomass releases syngas fuel and leaves behind “biochar,” which can be used to improve soil while sequestering carbon. But until the Gates Foundation stuck its nose into the issue, no one, to Mitchell’s knowledge, had attempted to pyrolyze excrement.

In partnership with the Climate Foundation and his Stanford students, Mitchell plans to develop a self-sustaining process that dries and then pyrolyzes the waste using the heat from the combustion of syngas previously released during pyrolysis. One of the questions yet to be answered is whether the system can derive enough energy from waste alone without an external fuel source. Urine would be kept out of the process until the end, when its nutrients would be used to enrich the fertilizing properties of the biochar. If the members of the group receive further funds to test their prototype, they plan to put it to work in Nairobi, Kenya, processing at least two tons of human waste a day.

A BYPRODUCT: DISTILLED WATER

All eight Reinvent the Toilet projects separately process urine and feces, which gives the KwaZulu-Natal team an almost unfair advantage for real-world experimentation. Within an hour’s drive of the university engineering department, the Durban municipality, known as eThekwini, has installed 75,000 urine-diversion latrines, making that city a magnet for toilet tours. “Durban is a center of innovation in dry sanitation,” says Rijsberman. Even his boss, Bill Gates, has inspected Durban’s urine-diversion latrines. Buckley has one installed at his home.

A urine-diversion latrine divides the toilet bowl into front and back sections, or, as Buckley has nicknamed them, “urinal and arsenal.” Separating liquids and solids allows feces to dry and lose their smell, while urine soaks away into the ground in most Durban installations. Inside, the latrine is virtually odor free.

But in their current design, eThekwini’s urine-diversion toilets are only a first step toward the toilet of the future. For one thing, their solid contents have to be emptied and buried once a year. To do this requires space, and the buried waste may continue to harbor pathogens, even though it has been biodegrading for at least a year. All of the Reinvent the Toilet projects plan to employ high levels of heat to kill pathogens. Finally, the nutrients, especially those in urine, are wasted.

Buckley’s team at the University of KwaZulu-Natal has cooperated closely with the municipality’s sanitation department for several years to engineer improvements. Well before the Reinvent the Toilet grants were announced, university researchers were looking at ways to use urine, for example, and even make it salable. “For poor people, one of the few resources they have is their excreta,” says Buckley.

The South Africans are determined to keep three waste streams separated: urine, feces, and water used for washing and flushing. On a sweaty February day, Buckley is inspecting one prototype at EnviroSan, an injection-molding company that is a partner in the university’s Reinvent the Toilet project. Near a machine that is spitting out black plastic toilet lids, a welded pan has been mounted under a toilet bowl. The pan pivots on a rod, swung by a jury-rigged Vise-Grip lever. Buckley intends for the pan to rotate into place to catch water, while dodging out of the way of anything else that might drop.

Back at the engineering department’s workshop, another prototype is set up to extrude feces into “spaghetti” shapes for easier drying and burning. The engineers are experimenting with both a piston and a screw to drive their special pasta machine. The mechanical energy used to operate both the swinging pan and the spaghetti press could come from the opening and closing of the outhouse door or the weight of a person sitting on the toilet. Thermal energy from the combustion of feces would be used to dry the fecal fuel and distill water for washing and flushing.

All the groups are feeling the pressure of the looming August deadline for prototypes. Toilets and latrines have been fundamentally unchanged for more than a century. Demanding even a blueprint for a toilet revolution in 12 months was a tall ask. “Some people may think we are crazy,” acknowledges Rijsberman, “but I’m going to universities and seeing people are totally serious about this; they’re pulling in materials scientists, physicists, and chemical engineers who haven’t worked on sanitation before.”

The sanitation revolution may not take place overnight. But Bill Gates has brought a new impetus to small a coterie of engineers with the capacity to save hundreds of thousands of lives. And he’s not just pulling their chain.

Don Boroughs is a freelance writer based in South Africa.

Video: Reinvent the Toilet | Bill & Melinda Gates Foundation