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COVID-19 has already caused 10 times as many cases as SARS in just a quarter of the time.

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Less Disease. No $#%@

Reflections on the reinventing the toilet challenge

The Gates Foundation issued a challenge to redesign the toilet.


I started thinking about the need for a new approach to toilets a few years ago, when I noticed on visits to some of the poorest slums that even in places with new community toilets they often weren’t used. Sometimes it was the smell that drove people away, or the fact that they were clogged up or poorly maintained. Other times it was because women didn’t feel safe using them. Often, the new toilets didn’t deal with human waste in a sanitary way, so they continued to spread diarrheal diseases that still kill more than a million children a year.

I realized we could apply the same kind of creative thinking and innovation to sanitation that we use to address other global health and development challenges. So, a year ago, the foundation invited eight universities to participate in a Reinvent the Toilet Challenge.

The criteria we set for the university researchers were pretty ambitious. We asked each team to develop a toilet that would destroy human waste or convert it into a valuable resource such as fuel or fertilizer. The toilet would have to operate “off the grid”—without connections to water, sewer, or electrical lines. The cost to operate it needed to be less than 5 cents per user, per day. And people would have to want to use it—ideally not only in poor countries, but wealthy ones too.

We gave each team about $400,000 and asked them to present the results of their work a year later. That happened last week at the foundation’s Reinvent the Toilet Fair. Given the boldness of the challenge and the limited time and money the teams had to work with, I wasn’t sure what to expect. After all, no one has invented a radically new toilet in 200 years.

The results were outstanding. It was impressive to see how each university team tackled the issues. Can you burn human excreta?  Can you get energy out of it and how can you use or store that energy? How do you deal with smells as well as a flush toilet does? How do you make a complete toilet system simple, affordable, and something that doesn’t need a lot of maintenance? All of the prototypes still need more work, but the teams made fantastic progress and important contributions to the toilet of the future.

We awarded the first-place prize to the California Institute of Technology for their prototype of a self-contained, solar-powered toilet that produces enough power to run an electrochemical reactor that breaks down human waste and, in the process, generates hydrogen.  A wastewater treatment system sanitizes the liquids, which can then be recycled for flushing or other purposes.

The second place prize went to Loughborough University in the United Kingdom. Their toilet uses a chemical process called hydrothermal carbonization to transform feces into a biological charcoal, which can be used as fertilizer, as a fuel source, or to power the toilet system. It also separates out minerals and clean water from feces and urine.

The third place prize was awarded to the University of Toronto in Canada for a toilet that dries and combusts solids and disinfects urine with a sand filter and ultra-violet light.

We also gave a special recognition award to the Swiss Federal Institute of Aquatic Science and EOOS Design GmbH for their simple, but elegant prototype of a toilet that uses recycled water and can easily be installed to replace existing toilets.

Creating affordable, sustainable, and scalable toilets that people will actually use is still several years away. But after last week, I am truly optimistic we can deliver a self-contained, zero-energy toilet that’s not dependent on traditional sanitation infrastructure.

It may seem funny to say I’m excited about toilets, but just as breakthroughs in new vaccines have saved millions of lives, and new seeds have helped farmers grow more sustainable and productive crops, the next-generation toilet will be an important contribution to helping the world’s poor live healthier, better lives.