Mud Batteries

Mud Batteries: Power Cells of the Future?

Scientists have harnessed a group of naturally occurring bacteria to generate electricity from organic material in mud.

But don't expect to load a "mud battery" into your car anytime soon. In preliminary experiments, the researchers produced only enough electricity to power a small light or calculator.

Petroleum, a major source of energy, comes from organic matter. Other kinds of organic material are also a large potential source of energy, but not all are as easy to utilize as petroleum.

Now, the researchers have found that bacteria in a family of microorganisms called Geobacteraceae can serve as a source of energy as they break down organic material—anything from decaying plant and animal matter to toxic organic pollutants such as benzene.

The bacteria break down organic matter to obtain energy, and in the process they produce a stream of electrons that, if captured, can produce electricity. Normally the bacteria just transfer the electrons to minerals rich in iron. To tap into the electron supply, University of Massachusetts–Amherst microbiologist Derek Lovley and his colleagues offered the bacteria another place in which to dump their electrons: a graphite disk.

The scientists filled fish tanks with mud taken from Boston Harbor, which has heavy concentrations of polluted sediment, and buried part of a makeshift battery in the sludge.

The battery was made up of a graphite anode (the negative terminal), which was buried in the mud, and a cathode (positive terminal) in the seawater, both connected by a copper wire.

The bacteria in the mud stripped electrons from surrounding organic compounds and transferred the electrons to the anode. The electrons flowed through the copper wire to the cathode, just as they would in a battery, producing an electrical current.

Lovley found that over time, the bacteria congregated on the graphite disk, producing a steady—if weak—supply of electricity.

A report on the research was published in the January 18, 2002 issue of the journal Science.

The bacteria were already known to be capable of another important function. They can degrade toxic organic pollutants such as benzene—a carcinogenic component of petroleum contamination—and convert them into carbon dioxide.

Although this ability to degrade toxic aromatic hydrocarbons was previously recognized, Lovley said the new study will advance knowledge of how to benefit from the process.

Moreover, he added, the genome sequences of several bacteria in the Geobacteraceae family are now known, which may help scientists engineer more efficient bacteria that degrade pollutants more quickly.

Bioremediation, or the use of organisms to clean up pollutants, is gaining popularity as a cheaper and environmentally more benign method of removing toxic pollutants.

Much of the work in Lovley's laboratory centers on finding ways to clean up uranium contamination from atomic weapons production. Uranium poses a particular problem because it dissolves in water and contaminates groundwater.

Lovley has found that microbes from the Geobacteraceae family strip a couple of electrons from a form of uranium and convert it into a less harmful form that is not soluble and therefore does not contaminate underground water supplies.

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