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Small units that purify household sewage could provide a source of electricity for urban and remote communities in the developing world, according to researchers.

The units would be populated with Shewanella oneidensis, one of several types of bacteria that can break down organic matter in sewage, producing electrons and protons. If the sewage is placed between electrodes with the bacteria present, this process can be harnessed to generate an electrical current.

This idea has been around for several years but, so far, microbial fuel cells have not been able to produce enough current to power even basic appliances. Now researchers have created a more efficient cell by designing electrodes that can capture more electrons from the bacteria. The new type of electrode, coated in gold nanoparticles can boost the amount of electricity to useful quantities.

"I envisage small devices placed in households, instead of sewage plants, at least in the near future," Hong Liu, researcher at Oregon State University and a co-author of the study, told SciDev.Net.

Writing in an article that is currently in press in Biosensors and Bioelectronics, researchers said the nanocoatings can increase the performance of the cells 20-fold, generating enough current to power a light bulb or a small fan.

"It is an interesting and scientifically sound finding," said Bruce Rittmann, a researcher at the Biodesign Institute in Arizona State University, who was not involved in the research.

Rittmann, however, sees sewage treatment as the more promising application as he is concerned that the amount of electrical current being produced is still relatively small.

The researchers acknowledge the limitations of their device, but they intend to improve the efficiency of the system and develop it to a commercial scale within 3–5 years.

"This is an important step toward our goal, but we still need some improvements," said Frank Chaplen, researcher at Oregon State University and one of the authors of the paper.

They are also confident that they can produce electrodes with the same performance using iron nanoparticles, which would be significantly cheaper to produce.

Teo Sanchez, international energy advisor at Practical Action, a charity that promotes technology for development, agreed that "this technology looks relatively simple and therefore very interesting for small decentralised applications in the developing world".

"This research suggests that electricity generation from sewage is scientifically possible," he added. "However the next step is to find out if it is financially viable."

Link to article abstract in Biosensors and Bioelectronics