This article was taken from the November 2014 issue of WIRED magazine. Be the first to read WIRED's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.
For Bruce Logan, microbes are an electrifying subject. The Kappe professor of environmental engineering at Pennsylvania State University works on creating alternative-fuel cells powered by anaerobic bacteria. "Because these bacteria breathe without oxygen they will transfer electrons from their food outside their bodies to an electrode," he says. Enough bacteria doing this at the same time will generate a current. At just a few millivolts It won't charge a phone, but it's enough to get a reading.
Materials
- 2x 1l plastic containers
- 15cm plastic pipe with cap
- 3g agar
- 11.8g salt, dissolved in 150ml of distilled water
- 2x pencil leads
- Coated copper
- Glue gun
- Aquarium air pump
- Voltmeter
- Sediment from the bottom of a lake
Get drilling
Drill a hole for the copper wire in the lid of each container. In one lid drill two more holes for the air pump and for ventilation; this is your cathode container, the other container is the anode.
Drill a further hole in the side of each container the same diameter as your plastic pipe.
Coil the graphite
Strip the ends of two pieces of copper wire and wrap one around each pencil lead. "Any graphite will work, but you don't want to use metals as they corrode," says Logan. Insert one electrode into each hole in the container lids and the air-pump tube into the other, then seal with hot glue.
Mix the solution
Dissolve 100g per litre of agar in boiling water and mix in the salt. Seal one end of the PVC pipe and pour in the mixture. Allow this to cool and solidify, then remove the seal from the end, place the ends of the pipe into the holes in each container and again use hot glue to seal.
Squeeze the oxygen
Fill the cathode container with salt water and the anode with sediment, ensuring both electrodes are submerged, and the latter is full. "If there's oxygen, the bacteria will breathe it," says Logan. "Then they won't generate electricity because they'll give electrons to the oxygen instead."
Feed the microbes
Attach the wire to your voltmeter probes, then turn on the aquarium air pump. "You should be able to generate some voltage within a few days," Logan says. Feed the microbes with water and vinegar, keeping the pH above six, and you'll be able to generate electricity for several years.
This article was originally published by WIRED UK
