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Bacterial Batteries

Bacterial Batteries

Bacteria get a bad rap for causing disease, but many of these organisms are beneficial. Without them, we wouldn't be able to digest our food, and garbage would never decompose. Now, one group of scientists has found another way to put bacteria to work.


Transcript

Charging batteries with bacteria. I'm Bob Hirshon and this is Science Update.

Tons of leftover food and agricultural waste are discarded every day. A new technology offers a way to put some of that trash to good use.

Derek Lovley is a microbiologist at the University of Massachusetts, Amherst. He and his colleagues have developed a fuel cell that can convert organic material into electricity. Lovley says the device is powered by a bacterium called rhodoferax.

Lovley:

And its specialty is that it can very efficiently extract energy from sugars. And there's not only a lot of sugar in many waste materials, but of course, renewable crops that are frequently being used now for producing energy sources such as ethanol.

Right now, the fuel cell generates only enough current to directly power a small light or calculator. But Lovley says bacterial fuel cells are great for charging up batteries, which can then power any number of devices.

Lovley:

This is more a local power source—it's not the type of thing where we're going to be adding substantial amounts of power to the power grid. This is not going to compete with oil fire energy-generating plants or nuclear power.

But in certain situations, it could be a way to squeeze some useful energy out of material that would otherwise go to waste. I'm Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

The bacterium rhodoferax extracts energy from sugars by stripping electrons from the sugar molecules. So do you. So how come it can charge a battery and you can't?

The difference lies in where it all happens. When your body strips electrons from sugars (and transfers them to oxygen), it happens internally. Rhodoferax, on the other hand, normally transfers electrons onto metals called iron oxides, which are found outside the bacteria—in the deep soil where they live.

So Lovley and his colleagues have basically tricked these bacteria into charging up an electrical circuit instead of iron oxide. Apparently, as far as the bacteria are concerned, a graphite electrode is a lot like iron oxide: both are substances outside the bacteria that can attract electrons.

In Lovley's experiment, the researchers placed a two-pronged electrode, shaped like an upside-down U, into a glass chamber divided in two by a membrane. On one side, they mix rhodoferax and sugar. As the bacteria begin digesting the sugars, they glom onto the electrode and charge it up with electrons. The current flows over the divider and into the other chamber, where the flowing electrons transfer onto oxygen and convert it into water.

This type of "bacterial battery" has been tinkered with before. What's important about this experiment is the efficiency of the system. These bacteria converted 80% of the available electrons on the sugars into electricity. Previous models have shown efficiency rates no higher than 50% and sometimes lower than 10%. That means that the system may be practical and cheap enough to use in everyday life. It's been reported that in theory, the rhodoferax battery could get enough energy from one cup of sugar to power a 60-watt light bulb for 17 hours.

The biggest hurdle remains the speed at which this happens. The electron transfer is very efficient but still extremely slow. Lovley and his colleagues say they might improve the speed of the transfer by using more conductive electrodes with larger surface areas that can accommodate more bacteria at the same time. He also believes it may be possible to genetically engineer the bacteria to move the electrons along more quickly.

Now try and answer these questions:

  1. What is a "bacterial battery"?
  2. How do these batteries work?
  3. What's different about the rhodoferax battery compared to previous kinds of bacterial batteries?
  4. What are the benefits of using the sugars in waste products to generate energy? Where does organic (life-based) waste come from? Can you identify at least five different sources?

For Educators

Electricity, a Tech Topic from the Tech Museum of Innovation, provides good background information on electricity and electric currents.

The Microbe Zoo offers an overview of various kinds of microbes and their roles in nature.

Introduction to Bacteria, an online exhibit by the University of California, Berekeley's Museum of Paleontology, has detailed information about the natural history, ecology, and functions of bacteria.


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