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From food scraps to fuel cell
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SCRAPS of food could soon be helping
power your home, thanks to an ultra-cheap bacteria-driven battery. Its
developers hope that instead of feeding the dog or making garden compost,
organic household waste could top up your home`s electricity.
Although such "microbial fuel cells" (MFCs) have
been developed in the past, they have always proved extremely inefficient
and expensive. Now Chris Melhuish and technologists at the University of
the West of England (UWE) in Bristol have come up with a simplified MFC
that costs as little as £10 to make.
Right now, their fuel cell runs only on sugar cubes, since these produce
almost no waste when broken down, but they aim to move on to carrot power.
"It has to be able to use raw materials, rather than giving it a refined
fuel," says Melhuish.
Inside the Walkman-sized battery, a colony of E.
coli bacteria produce enzymes that break down carbohydrates, releasing
hydrogen atoms. The cell also contains chemicals that drive a ! series
of redox, or reduction and oxidation reactions, stripping electrons from
the hydrogen atoms and delivering them steadily to the fuel cell`s anode.
This creates a voltage that can be used to power a circuit.
To prove the MFC works, the researchers are using
it to power a small light-sensitive robot. And when a number of the cells
are connected in series, they could power domestic appliances, running
a 40-watt bulb for eight hours on about 50 grams of sugar.
Earlier MFCs were inefficient because they relied
on energy-hungry filters and pumps. By experimenting with different anode
materials, the UWE team have figured out how to make their system work:
they dump the bacteria and redox chemicals directly into the cell.
In its current form, the UWE team says its organic
battery can produce eight times as much power as any previous MFC. But
Melhuish wants to improve this, both by scaling it up and finding a better
mix of redox chemicals.
New Scientist issue 12 OCTOBER 2002
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