Poo power: How microbes in sewage can generate electricity to light up your home

Electricity could be generated from microbes in sewage, according to U.S. scientists.

The team have created a ‘battery' driven by microbes that produce electricity as they digest organic material.

They claim the microbial battery could offset some of the electricity now use to treat waste water.


That use currently accounts for about three per cent of the total electrical load in developed nations.

The system was developed by Stanford University in California and their results published in the Proceedings of the National Academy of Sciences.

The research team describe how they hope ‘microbial batteries’ could also be used to break down organic pollutants in the lakes and coastal waters where fertiliser run-off and suffocate marine life.

At the moment Stanford’s laboratory prototype is about the size of a small battery and looks like a chemistry experiment, with two electrodes, one positive, the other negative, plunged into a bottle of wastewater.

Scientists have known for years of the existence of what they call exoelectrogenic microbes - organisms that evolved in airless environments and developed the ability to react with oxide minerals rather than breathe oxygen as we do to convert organic nutrients into biological fuel.

Several research teams have tried and failed to use these microbes as bio-generators.

But what is new about the microbial battery is a simple yet efficient design that puts these exoelectrogenic bacteria to work.

At the battery’s negative electrode, colonies of wired microbes cling to carbon filaments that serve as efficient electrical conductors.

Using a scanning electron microscope, the Stanford team captured images of these microbes attaching milky tendrils to the carbon filaments.

As these microbes ingest organic matter and convert it into biological fuel, their excess electrons flow into the carbon filaments and across to the positive electrode, which is made of silver oxide, a material that attracts electrons.

The electrons flowing to the positive node gradually reduce the silver oxide to silver, storing the spare electrons in the process.

Doctor Xing Xie said after a day the positive electrode has absorbed a full load of electrons and has largely been converted into silver.

At that point it is removed from the battery and re-oxidised back to silver oxide, releasing the stored electrons.

The Stanford engineers estimate that the microbial battery can extract about 30 per cent of the potential energy locked in wastewater.

That is roughly the same efficiency at which the best commercially available solar cells convert sunlight into electricity.