The world population is estimated to reach 9.5 billion by 2050. Given that most of our current energy is generated from fossil fuels, this creates significant challenges when it comes to providing enough sustainable electricity while mitigating climate change.

One idea that has gained traction over recent years is generating electricity using bacteria in devices called microbial fuel cells (MFCs). These fuel cells rely on the ability of certain naturally occurring microorganisms that have the ability to “breathe” metals, exchanging electrons to create electricity. This process can be fuelled using substances called substrates, which include organic materials found in wastewater.

At the moment microbial fuel cells are able to generate electricity to power small devices such as calculators, small fans, and LEDs – in our lab we powered the lights on a mini Christmas tree using “simulated wastewater.” But if the technology is scaled up, it holds great promise.

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How they work

MFCs use a system of anodes and cathodes – electrodes that pass a current either in or out. Common MFC systems consist of an anode chamber and a cathode chamber separated by a membrane. The bacteria grow on the anode and convert the substrates into carbon dioxide, protons, and electrons.

The electrons that are produced are then transferred via an external circuit to the cathode chamber, while the protons pass through the membrane. In the cathode chamber, a reaction between the protons and the electrons uses up oxygen and forms water. And as long as substrates are continually converted, electrons will flow – which is what electricity is.

Generating electricity through MFCs has a number of advantages: systems can be set up anywhere; they create less “sludge” than conventional methods of wastewater treatment such as activated sludge systems; they can be small-scale, yet a modular design can be used to build bigger systems; they have a high tolerance to salinity, and they can operate at room temperature.

The availability of a wide range of renewable substrates that can be used to generate electricity in MFCs has the potential to revolutionize electricity production in the future. Such substrates include urine, organic matter in wastewater, substances secreted by living plants into the soil (root exudates), inorganic wastes like sulfides, and even gaseous pollutants.

1. Pee power

Biodegradable matter in waste materials such as feces and urine can be converted into electricity. This was demonstrated in a microbial fuel cell latrine in Ghana, which suggested that toilets could in the future be potential power stations. The latrine, which was operated for two years, was able to generate 268 nW/m² of electricity, enough to power an LED light inside the latrine, while removing nitrogen from urine and composting the feces.