If you have a compost pile in your yard, you already know that dirt is an active substance. Or rather, it contains a lot of activity -- living microbes in soil are constantly metabolizing our waste into useful products. In a compost pile, that product is fertilizer. But there are microbes that produce something even more powerful: electron flow.
Bacteria species like Shewanella oneidensis, Rhodoferax ferrireducens, and Geobacter sulfurreducens, found naturally in soil, not only produce electrons in the process of breaking down their food (our waste), but can also transfer those electrons from one location to another.
A startup called Lebone Solutions has come up with a way to harness this microbial electricity to provide lighting and cell-phone charging in rural Africa.
Microbial batteries, or microbial fuel cells, have been around in research labs for some time, but their power output is so low they've mostly been seen as something to explore for some future use. They couldn't power a clothes dryer by any means. But Lebone Solutions has found a use for the microbial batteries: It only takes a small amount of power to run a light or charge a cell phone.
The device is simple to create. It consists primarily of a graphite cloth (the anode) placed in the bottom of a container, covered with soil and a length of chicken wire (the cathode). A conductive wire connects the anode and the cathode to create a circuit, with an LED connected to the circuit.
As the microbes eat the waste in the soil, they produce electrons. Those electrons want to flow toward a more positive charge, so they travel through the bacteria network, moving from the graphite-cloth anode through the conductive wire to get to the chicken-wire cathode. As this current flows through the circuit, an LED lights up.
Lebone estimates that a fuel cell measuring 10.7 square feet (1 square meter) would produce 1 volt, which could charge a cell phone; 53.8 (5 square meters) could power a lamp or a fan [source: Grifantini].
In the developed world, a microbial fuel cell would not be an efficient power source. But in rural Africa, where there's no grid power source, this type of setup could be a welcome change from walking several miles to charge a phone. Lebone is currently introducing the fuel cell in several African villages.
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