Urine and wastewater can be used as energy as they contain organic carbon, which the microbes in the microbial fuel cells effectively eat to survive.

A microbial fuel cell is formed of two half-cells, each with electrodes inside. One of the two half-cells is inoculated with live bacteria collected from the natural environment. The bacteria grow and maintain themselves on the electrode, using it as an anaerobic respirator.

“Just like any other form of respiration, they will be taking in carbon energy and other compounds and they will be respiring and excreting metabolites,” explains Ieropoulos. “In that half-cell, which is called the anode of a microbial fuel cell, the electrode becomes the recipient of those electroactive metabolites. The microbes will be excreting and respiring directly onto the electrode's surface.”

Like all organisms, the microbes need fuel or feedstock. Ieropoulos’ team at UWE experimented with different types of feedstock, including municipal and industrial wastewater, dead insects, rotten fruit, prawns shells, and – finally – urine.

“So, that's the feedstock,” Ieropoulos says. “Microbes feed on that, they break that down as part of their metabolism. They give off, excrete, and respire these electroactive metabolites. These metabolites re-oxidise on the electrode, which effectively means they pass the electrons they carry onto the electrode’s surface. That electrode is connected to the counter electrode in the other half-cell called the cathode, and therefore there is a conduit; there is a circuit that connects the anode electrode to the cathode electrode so that those electrons can flow through that circuit.”

On the cathode side of the other half-cell, an oxidising agent is used to react with the incoming electrons from the circuit.

“There is a semi-permeable separator, which separates the anode and the cathode, and through that separator – it could be a membrane or ceramic material – we have cations, positively charged ions like protons, for example, that come through that membrane,” Ieropoulos says.

“Oxygen plus electrons plus protons will combine and react together to produce water and this reaction is what closes the circuit, which continues to allow electrons and cations to come from the anode, via the circuit or the membrane to the cathode.”

To put it simply, the microbial fuel cells employ living microbes, which feed on the organic carbon found in urine for their own growth and maintenance. The cell system extracts that biochemical energy excreted while the microbes are living, converting it directly into electricity.

Robial is still in the early stages, in terms of commercialisation efforts at least. However, the company hopes that the technology can be used to produce large amounts of power in the future, which can be applied to a range of uses.

“It is important to mention that the microbial fuel cell produces DC power, which is the equivalent of batteries or solar panels and so you can imagine what it could be directly plugged into,” says Ieropoulos. “Instead of using batteries or solar panels if the sun doesn't shine in a particular part of the world, or if you are underground for example, you could be using this technology.”

Currently, a microbial fuel cell that uses 10ml of urine or wastewater can generate 1-2 milliwatts (mW) of power, and so the potential for using trillions of litres of wastewater is clear. At this stage, the power generated is equivalent to the power of AAA batteries, but still less than the efficiency of AA batteries or solar panels.

However, Ieropoulos explains that this is by no means the technology’s limit, as improved research and development into materials will improve the efficiency of the microbial fuel cell even further.

“The important thing here is that we are still at an early stage of material development because we are still working with electrodes that we make in our laboratories, with separators like ceramics that we make in our laboratories. We haven't advanced to that level of development that photovoltaics have had for decades, or batteries have had for centuries,” he says.

“And so what we are hoping to see with development and evolution of materials is that 1mW or 2mW of power that we generate from 10ml of microbial fuel cells volume would be generated from a microbial fuel cell with the volume of 1ml or less than 1ml.

“So if we get the same amount of power from smaller and smaller units so that when we start stacking them up, we will begin to produce the levels of power that we need for lighting whole households, whole buildings and so on and so forth.”

Ieropoulos’ team has received funding from various high-profile benefactors, including the EPSRC, the European Commission and the Bill and Melinda Gates Foundation, which has been used for the team’s work over the years, including fuelling autonomous robots, wastewater treatment and sanitation, in order to discover applications for the technology outside of the laboratory.

To reach the next stage of commercialisation, Ieropoulos says that funding from the Bill and Melinda Gates Foundation, in particular, has been crucial for development of the microbial fuel cell.

“The funding specifically from the Bill and Melinda Gates Foundation has been asking us, has been pushing us, to commercialise, not in order to make profit, but in order to allow this technology to come out of the university and be deployed in areas where it is needed the most,” he says.

“And therefore, the funding that we have received and the company that has been created [helps] to develop the microbial fuel cell so that it can be more widely deployed in more schools, more communities, more rural environments where it is needed the most.”

From 2015 to 2017, the technology was trialled at Glastonbury Festival in the UK, to show Oxfam that it could be used in refugee camps in Africa.

“In 2015, we went to Oxfam who came to us with a request, brokered by the Bill and Melinda Gates Foundation, looking for technologies that would allow them to provide lighting in refugee camps close to the toilets so that some of the crime could be prevented,” Ieropoulos says.

“They came to us and said 'if you are already using this technology to charge mobile phones and produce electricity for lighting, could you put it in the context of a urinal or toilet we can take to refugee camps and show that it works?'”

The first Pee Power urinal was installed on the Frenchay Campus at UWE, in which the lighting within the toilet structure was powered by microbial fuel cells feeding off the urine.

“Once we demonstrated that, Oxfam talked to Glastonbury and they mentioned the potential of this technology. So for Glastonbury 2015, we developed a bespoke urinal with troughs, very similar to the one Oxfam would take to refugee camps and again with the ceiling lights showing in real time that the urine was being utilised through microbial fuel cells to produce electricity directly,” he explains.

“The Glastonbury 2015 toilet structure was built by a company called Dunster House – a garden shed manufacturer – and they had been working with Oxfam to produce the wooden toilet super structure that Oxfam takes to refugee camps. They produced a wooden structure that was good enough for about ten people, at any given time. We had lights inside and we were demonstrating at night during the festival to the festival goers that the electricity is generated from their urine.”

For 2016, the urinal was enlarged to service around 25 people at a given time, and lighting fitted to the ceiling was powered by the microbial fuel cells in the urinal. For Glastonbury 2017, they fitted two separate urinals.

“One [urinal was] at a very central part of the festival, next to the Pyramid stage. This was a urinal for 40 people and we had a smaller urinal at a different part of the festival called the interstage, which was big enough for two people and we were again demonstrating lights, smart electronic displays, and mobile phone charging – all powered by the microbial fuel cells,” says Ieropoulos.

While Robial is still a new enterprise, if Pee Power’s commercialisation attempts are successful, we could all soon be generating our own local power needs, simply by going to the bathroom.