To get the fuel she needed to cook her food and warm her home, Kenyan Nancy Wambui, 54, used to buy charcoal made from chopped-down trees. But recently, she was given a new set of briquettes to try, that looked just like regular charcoal but worked even better. The secret ingredient? Human poop.

These briquettes just might be a promising new way to curb deforestation, reduce the daily expenditures of low-income families, help solve an energy deficit facing the country, and support sanitation improvements in areas where they are desperately needed. More than 2.5 billion people in the developing world lack access to toilets, and a child dies every 15 seconds from diarrhea, usually the result of food or water becoming contaminated by human waste. Each year, 200 million tons of the world’s poop also goes completely untreated, ending up directly in lakes, rivers, and oceans.

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