Microbes waste not, want not

Prototype device heralds microbial fuel cell.

US researchers have developed a device which they claim can generate electricity at the same time as treating waste water.

A team from Pennsylvania State University has made a single-chambered microbial fuel cell (SCMFC). This contains a hollow central cathode and eight graphite anodes to which bacteria in waste water attach. The bacteria feed on a steady flow of waste water pumped into the chamber and electrons pass from them along a circuit wired from the anode to the cathode. The system generates water at the cathode, while protons pass into the water being treated, reducing its oxygen demand.

The team’s prototype device generated a small amount of electrical power (a maximum of 26mW m^-2), while removing up to 80 per cent of the chemical oxygen demand of the waste water, the amount of oxygen required to degrade the organic compounds.

The main drawback of the device is that a large percentage of the organic matter in the waste water is removed by processes that do not generate electricity. However, the researchers are hopeful that ’if power generation in these systems can be increased, microbial fuel cell technology may provide a new method to offset waste water treatment plant operating costs, making advanced waste water treatment more affordable for both developing and industrialised nations’. For commercial success, the research team will also need to make the device cheaper to manufacture. As Bruce Logan, the team leader, points out: ’We can’t afford to use graphite rods on the anodes, Nafion as the proton exchange membrane and platinum on the carbon cathode. But we’re already making progress on that’.

Emma Davies