Making electricity from urine
Scientists have developed a way to convert urine in to a renewable energy source. But as Sally Magnusson, author of Life of Pee and presenter of Radio 4's Secret Science of Pee, writes in this viewpoint feature, there is some way to go before the idea is embraced more widely.
A growing number of scientists have cottoned on to the fact that urine is a source of vital enzymes for medicine, precious minerals like fast-depleting phosphorus, and chemical compounds like urea, which are crucial to the manufacture of fertilisers, plastics and cosmetics and can also be used to make electricity.
The question is, can urine help us? And if so, can we see it not as a useless, embarrassing waste product, but as a substance that could drive the next stage of the green revolution?
I started out mildly intrigued by the range of uses urine had in centuries gone by - it was used in the manufacture of gunpowder, alum, dyes, paint and stained glass, to clean Roman togas, and heal wounds.
I wrestled with the revulsion that arises when we move from historical curiosity to envisaging personal application, but I ended up convinced there is an urgent role for urine again in the 21st Century, based on its unique scientific properties.
- Processed pig urine is used as a diesel exhaust cleaning product
- 95% of urine is water, the other 5% is solutes including urea
- A urea solution is already widely used to reduce nitrous oxide emissions from HGVs
- An adult produces 1-2 litres of urine a day
- Seven billion people on Earth produce roughly 10 billion litres of urine every day
- If converted into energy each person could make enough urea each year to power a car for 2700km
- In the US waste water treatment plants consume 1.5 per cent of all the electricity the country generates
Urea, an important constituent of urine, is the key to many modern applications.
At Heriot-Watt University in Edinburgh, the Youtricity research team has developed a urine-powered system to generate electricity.
The carbamide power system runs on urea fuel cells sourced from human urine.
Dr Shanwen Tao, who invented the technology, said urea fuel cells were similar to hydrogen fuel cells, but used urea instead.
His colleague, Dr Robert Goodfellow said it had been a "huge" breakthrough in the search for renewable energy, but the system was being further developed.
He said: "The technology converts the urea within urine directly into water, carbon dioxide, nitrogen and more importantly electricity.
"One of the applications for the electricity is when you have no access directly to mains power - in mobile homes, in camping.
"What we are hoping at some point in the future is that once we have removed all the urea from the water itself, then that can be purified more to make it suitable for drinking.
"So in theory you could drink your own waste product."
Dr Goodfellow admitted there could be problems persuading members of the public to use it.
"One of the problems is going to be people's perception to actually using their own waste as a potential source of fuel. There is a definite yuk factor."
Urea is normally produced synthetically from fossil fuels.
End Quote Dr Robert Goodfellow Youtricity researcher at Heriott-Watt University
There is a definite yuk factor”
But humans produce it, efficiently and sustainably, in the liver, where it helps to mop up the toxic ammonia generated from protein metabolism and keeps it safely locked up until it is excreted in urine.
The ammonia is only released when urine comes into contact with micro-organisms in the environment - which is why urine starts out sterile and gradually acquires its unmistakeable smell after it has been lying around for a while.
In bacon-loving Denmark, where ammonia around pig farms is a serious pollutant, the company Waste2Green has started collecting pig urine before ammonia is released.
It then uses the urea in a diesel exhaust cleaning product.
Other potential applications of a chemical compound as widely used as urea could be almost endless. Waste2Green managing director Jes Thomsen suggested it could even be used in lipstick one day.
But the pioneers of this brave new world of urine recycling are encountering two problems.
One, not surprisingly, is attitude. When Nasa started purifying urine to produce drinking water in space, it had quite a job persuading its own astronauts it was safe.
The second, linked to the first, is cost.
Earl Braxton runs an American portable toilet company which claims to have discovered how to extract proteins from urine and turn them into medicines like Prozac.
He said he was struggling to find investors willing to risk public squeamishness.
He explained: "If we have four million toilets in the US and there's 10 gallons of urine per service and you service it four times a month, you get 40 gallons per portable toilet.
"You do the math. There's a lot of urine out there. Mining urine is far greater value than mining gold or oil... but people are afraid of it. They don't understand it."
Few alternative technologies will take off until the price of scaling up small innovative efforts begins to look like a bargain.
In urine's case, that requires a hard, long-term look at planetary resources, the dangerous depletion of minerals like phosphorus and the apparent folly of using energy equivalent to 25% of the output of Britain's largest coal-fired power station every day in waste treatment plants to destroy the nitrogen in urine - only for us only to go and get nitrogen from elsewhere to make fertiliser.
The Secret Science of Pee was broadcast on Tuesday, 5 October 2010 at 2100 BST and repeated on Wednesday 6 October 2010 at 1630 BST. Or catch-up afterwards on BBC iPlayer.