Let’s learn about surprising uses for human waste

When you think of words that describe poop and pee, “useful” is probably not one of the first that comes to mind. Feces and urine are, after all, basically everything your body has decided it doesn’t need and sent to the exit. But human excrement is rich in a variety of chemicals that could be put to good use. Using these waste products could cut down on sewage pollution that poses a risk to people and the environment.

The nitrogen and phosphorus in pee, for example, can be used to make fertilizer. Certain yeast can transform chemicals in urine into a hard mineral used to mend bones and teeth. And sludge from sewage plants is chock full of silicon, calcium and other elements good for making cement and bricks. Some bacteria that feast on feces even produce methane gas or electricity. In effect, they transform excrement into energy.

Finding new uses for poop and pee may be especially helpful in places that don’t currently have safe ways to dispose of human waste. Billions of people around the world face this problem. And a couple of companies in Kenya, in East Africa, have led the way in creative solutions.

In the Kenyan capital of Nairobi, for instance, many people do not have access to flush toilets or enclosed sewers. There, the company Sanergy rents toilets. Fertilizer is made from the collected waste. That waste can also be fed to insects for use as livestock feed. The company Sanivation likewise collects waste from latrines in the town of Naivasha. They use that material to create logs of fuel.

People on Earth aren’t the only ones who could benefit from safe, renewable means of dealing with poop and pee. Astronauts cannot pack much on a trip to space. So it would be helpful if their bathroom business were a resource to be mined, rather than a mess to be managed.

Equipment on the International Space Station already recycles astronaut pee into clean water. But scientists are also exploring ways that astronaut waste could be turned into construction materials. Perhaps the waste could even be used to make plastic. That would allow astronauts to build items didn’t bring but find they need on long-term trips to space. 

Want to know more? We’ve got some stories to get you started:

A dirty and growing problem: Too few toilets Engineers are devising new ways to remove waste that would otherwise pollute the environment and put it to use as fertilizer, fuel and more. (9/24/2020) Readability: 7.2

Astronauts may be able to make cement with their own pee Future lunar buildings could mostly be made with materials found on the moon. (6/16/2020) Readability: 7.2

For a better brick, just add poop Scientists are using sewage sludge to create more Earth-friendly building materials. (1/26/2023) Readability: 7.1

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Most of us go, flush and forget. But where does your waste end up after it leaves your bathroom? The California Academy of Sciences’ game “Poops and Ladders” traces how waste flows through the San Francisco, Calif., sewer system.

What is poop made of, exactly? Come up with your best guess, then check your answer in one of our Instagram posts! This post was inspired by a reader question. Have your own weird, gross or out-there science question? Submit it through the link below.