Research into MFCs is nothing new – they first appeared over a century ago, and methods have advanced in fits and starts ever since. In the 1960s, Nasa began looking at using microbial fuel cells in space to generate power from rice husks. In the 1980s scientists started investigating whether these cells could help power developing countries. But it’s only after 2000 that this research area has really exploded – born of a growing need and increasing opportunity for renewable-energy sources.

Ioannis Ieropoulos, the lead researcher behind Bristol’s pee-powered phone charger, and his team have been working on this technology since 2002; their recent breakthrough has come from adopting a new approach. Other scientists in this field are trying to improve the efficiency of single cells, so that they produce more electrons, explains Carl Hensman at the Bill & Melinda Gates Foundation, which funds Ieropolous’ research. But the Bristol team’s approach stacks a series of small-scale microbial fuel cells together. “[Ieropoulos] is redesigning the fuel cell to make it smaller, and put more cells in there to get more electrons coming out,” says Hensman.

The process is similar to what researchers found when attempting to generate more electricity from the old potato light-bulb experiment. By boiling and then cutting the potato into thin slices to form a parallel series (instead of just using a bigger potato or trying to speed up the chemical reaction inside the potato) they increased the energy output 10-fold.

Electric jolt

Microbial fuel cells may be promising, but they aren’t only one way of unlocking the energy inside our urine.

Urine consists of approximately 98% water, and 2% urea, which is made up of carbon, oxygen, nitrogen and hydrogen atoms. Gerardine Botte, a researcher at Ohio University, recently developed the GreenBox, a device that extracts the hydrogen from urea through a process called microbial electrolysis. Electrolysis uses a jolt of electricity to split the urea into hydrogen and oxygen atoms, and then captures the hydrogen to produce energy. The nitrogen can be used for artificial fertilisers.

Unlike Ieropoulos’ MFC system, which simply generates electricity from natural bacteria, Botte’s process requires a constant source of power – the jolt to split the molecules and produce hydrogen.

“If you had a building of 300 people, you are probably going to need a box of about 1 kilowatt of power to clean the water,” explains Botte. “You cannot get more energy than the energy you put in. Hydrogen is only going to have about 40% efficiency – you’re recovering 40% of the energy you use to clean urine.”

As a result, this process is more about capturing the previously untapped energy in pee during the purification process, than creating an entirely new renewable source of power. Still, to get fuel-grade hydrogen while decontaminating (removing the ammonium) wastewater can save tremendous energy costs – so the potential benefits are clear.

“The most important contribution is deploying these boxes in water treatment facilities,” Botte says, “where we’re already using energy to clean the water.”



Water works

So could pee-power really be the energy of the future? And can it be a solution not just for developed nations, but for the billion people around the world who lack access to electricity?

The biggest hurdles are currently cost, scale, and output. At the commercial level, these systems could be applied to wastewater treatment plants, saving tremendous energy costs by effectively recovering energy during the process of treating urine, and feeding it back into the system.

For smaller-scale home or office use, they still don’t quite produce enough electricity from urine to justify the space and expense. For places without big industrial systems – but in need of both energy and clean water, it’s another story.

“There’s a lot of basic research still going on, a lot to be developed. I believe it can make it, but the cost has to be really low,” says Korneel Rabaey, president of the International Society for Microbial Electrochemistry and Technology.