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A Better Way to Turn Poop Into Energy

Scientists at Virginia Tech have unlocked a key aspect of how bacteria turn sewage into electricity.

Image Virginia Tech University
Virginia Tech University

Yes, poop is smelly and gross, but it’s also a solid source of energy. In India, for example, cow dung has been used for decades to light up villages, heat homes, and cook. It’s such a popular source of fuel that cow-poop cakes started selling online.

All that stuff we flush down our human toilets also contains a lot of usable energy. A new study published in Scientific Reports uncovers key insights about the process by which bacteria turn refuse into electricity, which can help maximize the amount of energy derived from sewage.

“Tracing the bacteria gave us a major piece of the puzzle to start generating electricity in a sustainable way,” Xueyang Feng, an assistant professor of biological systems engineering at Virginia Tech, said in a press release. “This is a step toward the growing trend to make wastewater treatment centers self-sustaining in the energy they use.”

There’s a couple ways to harness energy from poop-filled sewage. Cities like Albany and Chicago, for example, do it through the process of anaerobic digestion. They get the bacteria in sewage to break down the organic matter in the absence of oxygen, generating a combustable “biogas” which can be burned as fuel.

A different process, which is still in a developmental stages, gets those little microbes to convert poop directly to electricity using “microbial fuel cells.” Here’s how Scientific American explains this newer process:

Millions of tiny microbes infest the water that carries the detritus of human life and society. Some of them steadily break down the organic material in waste streams and produce electrons in the process. By harvesting these electrons, scientists have created microbial fuel cells.

These bacteria use various components of organic materials in different ways during the breakdown process. Feng and Virginia Tech colleague Jason He analyzed the metabolic process of a type of bacteria in wastewater and found that these bacteria used a compound called “lactate” as food, while they used another one called “formate” to generate electrons. When both these compounds, or “substrates,” were clumped together, a lot more electricity was generated than if the bacteria worked on either one of them separately.  

“Actual waste water contains a variety of organic compounds and many different types of bacteria,” the study coauthor He tells CityLab via email. “There may be similar ‘synergistic effects’ on bio-electricity generation among unknown substrates contained in wastewater.”

Mixing sewage rich in “synergistic” substrates may be one way to yield higher amount of power for the same amount of poop-filled water, his colleague Feng suggests. But there’s some way to go before how this scientific development can be used to make the poop-to-power process more efficient.

Check out this cute animated video explaining Feng and He’s development:

About the Author

  • Tanvi Misra is a staff writer for CityLab covering demographics, inequality, and urban culture. She previously contributed to NPR's Code Switch blog and BBC's online news magazine.