Bacteria generate power from sewage
Where there's muck there's also electricity, according to scientists researching bacteria that can generate power from sewage.
They believe the bugs could be used as microbial batteries turning plant and animal waste into an energy source.
The bacteria could be employed in domestic sewage plants, or to generate power as they clean up lakes and coastal seas laid waste by organic pollutants.
To demonstrate the idea, scientists built a laboratory microbial battery consisting of electrodes dipped into a bottle of waste water.
In the bottle, an unusual strain of bacteria feast on particles of organic waste and produce electricity that is captured by the positive electrode.
"We call it fishing for electrons," said environmental engineer Professor Craig Criddle, from Stanford University in the US.
The researchers estimate that the bugs can extract about 30% of the potential energy locked in organic waste water - an efficiency roughly equal to the best solar cells that convert sunlight into electricity.
Scientists have long known so-called "exoelectrogenic microbes" that evolved in airless environments have potential as bio-generators. But tapping the energy they produce efficiently has proved difficult.
The new microbial battery is described in the latest edition of the journal Proceedings of the National Academy of Sciences.
Using a scanning electron microscope, the researchers watched the bugs extending milky tendrils to attach themselves to the battery's carbon conductors.
"You can see that the microbes make nanowires to dump off their excess electrons," said Prof Criddle.
Around 100 of the bugs could fit side by side across the width of a human hair, he said.
Looking ahead the biggest challenge is finding a cheap but efficient material for the positive electrode, currently made from expensive silver oxide.
"Though the search is under way for a more practical material, finding a substitute will take time," said Stanford materials scientist Professor Yi Cui.