Why let your waste go to waste when it can be powering your cell phone-or maybe your car?
It is a bright spring morning here at Heriot-Watt University in Edinburgh, UK, where I actually have come to satisfy my interviewee for this newsletter, Shanwen Tao . Normally after I interview someone, I give them a business card and maybe the newest issue of latest Scientist. Today, I give Tao a bottle of my own pee.
Chemist Tao doesn’t find this odd. Urine, he believes, could help solve the arena’s energy problems, powering farms and even office buildings. And he has agreed to take advantage of my offering to indicate me how.
Urine won’t pack the punch of rocket fuel, but what it lacks in energy density it makes up for in sheer quantity. It’s far essentially the mostsome of the most abundant waste materials in the world, with nearly 7 billion people producing roughly 10 billion litres of it day after day. Add animals into the combination and this quantity is multiplied several times over.
As things stand, this flood of waste poses an issue. Let it run into the water system and it will wipe out entire ecosystems; yet scrubbing it out of waste water costs money and energy. Within the US, as an example, waste water treatment plants consume 1.5 per cent of your complete electricity the country generates. So wouldn’t or not it’s nice if, as opposed to being a limiteless energy consumer, urine might be put to exploit.
That thought occurred to Gerardine Botte , a chemical engineer at Ohio University in Athens, during a discussion in 2002 with colleagues about possible sources of hydrogen for use in fuel cells.
Hydrogen will likely be made out of fossil fuels in large quantities, however it is hard to store and distribute. An alternative choice is to split water immediate, releasing hydrogen directly into a fuel cell – but here as much energy is needed to split the water as is released by the hydrogen.
Botte’s brainwave was to exploit urine as opposed to water. By weight, urine contains roughly 2 per cent urea, and each urea molecule contains four hydrogen atoms, which, crucially, are less tightly sure to the molecule than the hydrogen in water. Splitting these bonds would require less energy, making hydrogen production more efficient.
Last year, Botte’s team reported they’d been in a position to generate hydrogen from urine using an electrolytic cell with cheap nickel-based electrodes running at only 0.37 volts- much lower than the 1.23 volts it takes to split water ( Chemical Communications, 2009, p 4859 ). Pure hydrogen bubbled off at the cathode, while nitrogen and carbon dioxide formed at the anode.
Botte calculates that with more efficient electrodes, hydrogen might be made from urine at a value of not up to $1 per kilogram. She thinks the technology may well be useful wherever large numbers of folk congregate and enough urine could be collected to make the process worthwhile. ” An office building where 200 or 300 people work could produce about 2 kilowatts of power,” she says.
Another approach is to neglect hydrogen and use urine directly as a fuel. This is often the approach being taken by Tao and his colleague Rong Lan, which include John Irvine from the University of St Andrews, also inside the UK. Since 2007, the team had been developing a fuel cell which could produce electricity directly from urine (see diagram). No voltage has to be applied to wreck down the urea; instead, a low-cost electrode makes the reaction happen spontaneously. The small print of the electrode are still secret.
Inside the fuel cell, water and air virtually the 1 centimetre square cathode generate hydroxide ions, which might be drawn to the anode. There they react with urea to form water, nitrogen and carbon dioxide. This reaction also generates electrons, which flow back to the cathode through an external circuit, forming a current that the team hope will sooner or later be sufficiently big to power electrical devices ( Energy and Environmental Science, vol 3, p 438 ).
To show me the process in action, Tao and Lan add my urine to the fuel cell. As it flows into the cell, a screen shows the output voltage rising to about 0.6 volts. While this prototype is simply too small to power a mild bulb – its output is ready half that of an AA battery – scaling up the cell and connecting several cells together should produce practical amounts of power.
Tao hopes that even small urine fuel cells will someday become useful, if the correct electrode materials could be found to reinforce their power output. They may be used to power radios or phones in remote locations, as an example. ” That you could carry a small fuel cell for low-power mobile communications while not having to carry the fuel,” he says.
A larger-scale application can be found in farms. As the urine from all mammals contains urea, that from cattle, say, might be used to generate electricity to run farm buildings – assuming the cows’ urine might be kept cut loose other waste.
This, like any the applications mentioned to this point, will only work with relatively concentrated urine. That rules out probably the most urine produced in people’s homes, which fits into the sewerage system along much larger quantities of waste water – but even this resource don’t need to go to waste.
By the time the urine reaches a sewage treatment plant it isn’t only dilute, but in addition contaminated with a cocktail of chemicals. What’s more, many of the precious urea it contains has broken down into ammonia. Nevertheless, Botte says that her technology ought to be ready to cope with this. She plans to conform it to split ammonia into hydrogen and nitrogen, and he or she hopes to secure funding within a year to find out the technology at a treatment plant.
Another promising option can be to exploit microbial fuel cells to generate electricity from all types of compounds in mucky waste water, not just urea and ammonia. These devices can break down your entire organic matter the water contains, cleaning it whilst, says Bruce Logan, who develops microbial fuel cells at Pennsylvania State University in University Park.
They reap the benefits of the undeniable fact that waste water naturally contains bacteria and organic matter. When bacteria ” consume” this food, they produce electrons that could normally combine with oxygen. But if kept in an oxygen-free chamber they are able to feed those electrons to an electrode and from there into an external circuit. Protons, meanwhile, pass through a membrane that divides the cell, to achieve another electrode – the cathode – where they combine with the incoming electrons from the external circuit, and oxygen, to form pure water.
Experimental microbial fuel cells have generated power densities of up to 6.9 watts per square metre of electrode surface ( Environmental Science and Technology, vol 42, p 8101 ). ” Maybe 6.9 watts doesn’t sound like a whole lot, but we’ve very large reactors in waste water treatment plants, and when you have tens of thousands of square metres, that’s going to be lots of power,” says Logan. The technology is being tested at pilot plant scale.
Alternatively, these cells shall be modified to provide hydrogen fuel in place of electricity by keeping the cathode in addition as the anode oxygen-free. Logan’s team recently completed field trials of a 1000-litre version of a hydrogen-producing microbial cell at a winery, where the waste water contained leftovers from grape crushing and fermentation, reminiscent of sugars and ethanol. Logan says the cells coped well with the genuine-world conditions, equivalent to varying composition of waste water, but won’t discuss the main points until the work is published.
Logan is targeting scaling up the microbial cells and finding the materials for electrodes that lead them to work most efficiently. ” We expend a variety of energy on waste water treatment immediately, and these technologies hold the promise to convert this process from an energy consumer to a net energy producer,” he says.
No one claims that urine will ever be the total answer to our energy needs, but Botte argues that the more sources we have got for our energy, the easier. ” We’ve gigantic energy needs. We are talking billions of megawatt-hours every year inside the US alone,” she says. ” Looking for one solution isn’t the answer. There is room for lots technologies with different market shares.”
New Scientist reports, explores and interprets the consequences of human endeavour set inside the context of society and culture, providing comprehensive coverage of science and technology news.
Image Credit: Ajay Tallam
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