The microbial battery.
Courtesy of Stanford University The microbial battery.

The search for increased energy efficiency leaves no stone unturned. Drinking water and wastewater treatment, for example, consumes roughly 3 to 4 percent of the United States' total energy utilization. Scientists at Stanford University have found a way to employ microbes that generate electricity from waste, technology that has the potential to reduce this energy load.

In their so-called microbial battery, Stanford materials scientist Yi Cui, environmental engineer Craig Criddle, and interdisciplinary researcher Xing Xie employed exoelectrogenic microbes—bacteria capable of transferring electrons extracellularly—to convert sewage into energy. "We call it fishing for electrons," Criddle said in a Stanford press release.

The researchers placed the microbes on carbon filaments that operate as electrical conductors. In the presence of wastewater, the organisms create new tendrils between the carbon and a silver oxide node, which serves as the positive electrode.

"You can see that the microbes make nanowires to dump off their excess electrons," he said.

A scanning electron microscope image of an electricity-producing microbe.
Xing Xie/Stanford Engineering A scanning electron microscope image of an electricity-producing microbe.

The team estimates that the battery works at a comparable efficiency to top commercial solar cells. Although silver oxide is too expensive to deploy en masse, the researchers predict that with the right material, their "wired microbes" could help with large clean-up efforts required in sewage plants or marine dead zones. At the very least, the "mini power plants" can produce some of the valuable energy needed for wastewater treatment.

Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.