Human waste fuel cells 'a step closer'

By showing how electrons ’hop’ across otherwise electrically insulating areas of bacterial proteins, a team of researchers at UEA hope to manipulate this naturally occurring process to help engineer improved bio-batteries.

Though prototype bio-batteries have been developed by another organisation, the UEA researcher said that through the improvement of this technology, they could produce cleaner energy for portable devices such as laptops, mobile phones and tablets - all of which could essentially be powered by human or animal waste.

“These bacteria can generate electricity in the right environment

UEA professor Julea Butt

Certain bacteria have the ability to survive by ’breathing rocks’ - deriving their energy from the combustion of fuel molecules that have been taken into the cell’s interior, UEA researchers said.

A side product of this reaction is a flow of electricity that can be directed across the bacterial outer membrane and delivered to rocks in the natural environment - or to graphite electrodes in biological fuel cells.

Lead researcher Julea Butt said that the amount of electrical transfer it would take to charge devices such as laptops and tablet depends on many factors including the area of the electrode and ’energy content’ of the waste materials that are available to the bacteria.

To conduct its research, the UEA team studied proteins known as ’multi-haem cytochromes’ found in ’rock breathing’ bacteria such as species of Shewanella.

“These bacteria can generate electricity in the right environment,” said Butt, a professor at UEA’s School of Chemistry.

“We wanted to know more about how the bacterial cells transfer electrical charge - and particularly how they move electrons from the inside to the outside of a cell over distances of up to tens of nanometres,” Butt said.

“Proteins conduct electricity by positioning metal centres - known as haems - to act in a similar way to stepping stones by allowing electrons to hop through an otherwise electrically insulating structure. This research shows that these centres should be considered as discs that the electrons hop across,” she said.

According to Butt, the relative orientation of neighbouring centres, in addition to their proximity, affects the rates that electrons move through the proteins - an advance in understanding which may help researchers understand the behaviour of some bacterial species as electron transfer modules.

“We hope that understanding how this natural process works will inspire the design of bespoke proteins which will underpin microbial fuel cells for sustainable energy production,” Butt said.

Using human waste to power electronic devices is not a new concept, however.

In November 2013, for example, researchers at the Bristol Robotics Laboratory - a joint venture between the University of the West of England (UWE) and the University of Bristol - developed an artificial heart capable of pumping human urine to power next-generation robots.

In that instance, the ’EcoBots’ were powered by electricity-generating microbial fuel cells that employed live microorganisms to digest waste organic matter and generate low-level power.