Today, over seven billion people populate our planet, which means on average around 10.5 billion litres (2.8 billion gallons) of human urine is produced and wasted each day. It’s the equivalent of 4,200 Olympic-sized swimming pools, if anyone was counting. In fact, some scientists are – and if they have their way, our human waste will be wasted no more.
With around one-seventh of the population lacking access to basic electricity, and as our global supply of oil slowly dwindles and coal continues to add to mounting greenhouse gases, scientists have rushed to find solutions to power the world in more renewable and sustainable ways. One answer could lie in methods being developed to generate power from perhaps an unlikely source.
Last year, a group of researchers at Bristol Robotics Laboratory in the UK proved they could power a mobile phone with human urine. Their device uses what’s known as microbial fuel cells, or MFCs, to generate enough energy for a smartphone to text, browse the internet and make short phone calls. But they believe, in time, it could eventually help power houses, buildings, and maybe even entire off-grid villages.
A microbial fuel cell is essentially an energy converter, which uses bacteria found in nature to breakdown organic matter, and in turn produce electrons that are converted into energy. It’s a self-renewing system, because the more waste the microbes eat, the more energy the system can generate and for longer.
MFCs hold such promise because they are currently one of the most efficient means of converting waste to energy. According to Ani Vallabhaneni, co-founder of Sanergy, a start-up that converts human waste to energy and fertiliser in Kenya’s slums, common biogas digesters (which convert waste into mostly methane gas) are around 35% efficient in terms of capturing energy inside the waste. It’s claimed MFCs have upwards of 85% efficiency.
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.
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.”
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.
Rabaey estimates that if a one-cubic-metre box containing a microbial fuel cell system was installed in a village of 2,500 people – and all their urine was constantly funnelled through that box – you could generate a constant current of around 500 watts. This would equal around 12 kilowatt hours of energy per day, or enough to run only one standard 50-watt bulb for around 240 hours.
Presently, this kind of system would cost between $5,000-$10,000. While that’s a hefty price tag, it would last for an incredibly long time, says Rabaey, “because these organisms inside are self-renewing. As long as you feed it waste water, the bacteria is happy.”
While today’s solar panels could certainly deliver more power per unit at that cost, they wouldn’t last for as long – or be able to clean wastewater.
The Bristol Robotics Lab researchers are aiming to crack this price-per-unit issue. They built their mobile phone-charging prototype for just a few hundred pounds – and in two years they hope to have a cheaper prototype that can be made from locally available materials, anywhere in the world.
“We have to be realistic,” says Ieropoulos, “we cannot be promoting a technology which is not feasible to be implemented in a poor country.” Rabney agrees. “You cannot expect a chemical engineer to be present in every village. It has to be simple, robust, long-lived, and self-reporting,” he says.
So even if answering nature’s call can actually help us make calls for the first time in history, don’t expect your next toilet to come with built-in phone chargers – at least, not just yet.
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