In their search for alternative energy sources, scientists from Stanford University developed a mini power plant device, which uses microbes that are found in sewage systems. The study published in the latest issue of the Proceedings of the National Academy of Sciences shows the potential of harvesting the electricity, which is naturally generated as these microbes break down organic pollutants from fertilizer runoff in water bodies and sewage plants.
Yi Cui, Craig Criddle and Xing Xie designed a prototype, which they call a microbial battery. Seemingly simple, the device uses the long-known exoelectrogenic microbes, which form in anaerobic conditions, and react with oxide minerals, instead of breathing oxygen. The battery consists of one negative and one positive electrode, which are connected to a small bottle-like container filled with sewage water.
The negative electrode attracts these microorganisms that eat the organic waste and generate electricity, which is then transferred to the positive electrode. Within the battery, the microbes form nanowires, which are attached to the carbon filaments and used to transfer the excess electrons.
As the microbes eat organic matter from the wastewater, they produce biological fuel and energy, which is transferred to the positive electrode made of silver oxide. The spare electrons are stored as the silver oxide is reduced to pure silver, a process which takes about a day. Once all silver oxide is reduced, the metal is removed and re-oxydized, the stored electrons are removed and the process can be resumed.
According to the team, this microbial battery can store roughly 30% of the energy locked in wastewater. This energy could then be used to power airpumps or other energy demanding systems in sewage plants. However, the battery is still a prototype because the scientists are convinced they can find a much cheaper material, which can replace the expensive silver oxide, and provide the ultimate green sewage pant powering system.