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Electricity from Sewage

Electricity from Sewage

As the world's population continues to grow, two big challenges are generating enough electricity for everybody, and dealing with all the sewage we produce. But a promising new technique may help tackle both problems.


Transcript

Getting a charge out of sewage. I'm Bob Hirshon and this is Science Update.

In the future, the wastewater from your sink, bathtub, and toilet may do more than just go down the drain. It may become a source of electricity.

Bruce Logan, a professor of environmental engineering at Penn State University, is experimenting with fuel cells that run on microbes. He explains that bacteria naturally generate electrons as they break down organic materials. A fuel cell siphons off these electrons to create an electric current.

Logan:

We're concentrating on showing that you can use leftover material—wastewater—as a way to generate this electricity.

He says a typical sewage treatment plant is loaded with bacteria. And if you drop a fuel cell in the wastewater, they get right to work. Now, he and his colleagues are trying to make the fuel cells cheaper and more efficient. Their goal is to generate enough energy to offset the costs of running a plant—with plenty to spare.

Logan:

If we could recover about a tenth of the energy in the wastewater, we could probably power the wastewater treatment plant. So we're looking, realistically, to recover about half of the power, and if we do that, I think we'd be looking at a process by which we'd actually put electricity back into the grid.

I'm Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

Fuel cells are a promising new energy technology. Simply put, a fuel cell converts hydrogen and oxygen into water. This chemical reaction releases electricity and heat energy and produces only water as a by-product.

There are many kinds of fuel cells. A microbial fuel cell uses a chemical reaction inside bacteria as the source of its electrons. So far, that means you've got a fuel cell powering your electric grid, and bacteria powering the fuel cell that powers the electric grid.

But now you need something to power the bacteria. Prior to this study, pure chemicals like glucose or acetate were common candidates. Unfortunately, making a big pool of bacteria in a glucose solution is kind of complicated, especially for those looking for a simpler and cheaper way to get electricity.

That's why Logan's study is significant. His microbial fuel cells work in regular old sewage water skimmed from a tank in a treatment plant. The bacteria digest the organic compounds in the sewage. A chemical reaction in this digestive process generates electrons that reach the bacterial cell's outer membrane. These electrons are siphoned off into the fuel cell, which uses the electrons to generate electricity.

Now the challenge is to make it practical. One of the problems with fuel cells is that individually, they don't generate a lot of wattage. This is often addressed by packing as many fuel cells into a given area as possible (this bunch of fuel cells is sometimes called a fuel cell stack). In the case of the microbial fuel cells, the researchers plan to maximize the surface area on the stack. More surface area means more space for the bacteria to glom on and do their work.

In addition, Logan's team is working on making each individual fuel cell more efficient in its energy output. By increasing the productivity of these fuel cells, they hope to make wastewater treatments pay their own way in energy—and even give something back.

Now try and answer these questions:

  1. What is a fuel cell?
  2. How can microbes be used in a fuel cell?
  3. What is the advantage of Logan's technique over other microbial fuel cells?
  4. What does this story tell you about the challenges we face in managing our energy?

For Educators

How Fuel Cells Work, by How Stuff Works, provides a detailed overview of fuel cells in general.

Poop power? Sewage turned into electricity, an article from MSNBC.com, describes an experimental fuel cell sewage treatment facility in Washington state, and includes a slide show.


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