IT MAY seem ridiculous, but in the hunt for sources of alternative energy researchers have come up with fuel cells which are powered by cheese—or at least whey, a by-product in cheese making. Whey is rich in lactose, a sugar which Georgia Antonopoulou, a biochemical engineer at the University of Patras, Greece, says can be consumed by cultures of bacteria contained within a fuel cell to generate an electric current. Microbial fuel cells, as such devices are known, are not a new idea but they are attracting more attention.

The organic content of whey can pose an environmental hazard and many governments now impose strict regulations requiring factories to pay for its treatment before disposal. Whey constitutes about 70% of the volume of the milk used to make cheese. So, just one small feta facility will need to dispose of as much as 4,000 tonnes of whey in a single year, says Dr Antonopoulou. Microbial fuel cells could help, and not just in the cheese-making industry. Breweries, pig farms, food-processing plants and even sewage works could gain from the technology.

Traditional fuel cells work by using a catalytic material to oxidise a fuel, such as hydrogen, and make an electric current flow between two electrodes. Microbial fuel cells function in much the same way except that the catalytic reactions are carried out by bacteria contained within the fuel-cell chamber. Under anaerobic conditions (where oxygen is absent) they metabolise the fuel by feeding off it and in doing so produce natural chemical reactions that produce a current.

In theory microbial fuel cells can run on almost any kind of organic matter, says Chris Melhuish, head of the Bristol Robotics Laboratory, England. “All you have to do is match the microbial culture with the type of stuff you want to use as fuel,” he says. Dr Melhuish has been trying to power robots on domestic waste-water, but it is tricky. Ideally you would want to use cheap raw-waste products, he says. But traditionally the fuel cells work best with a refined fuel in the form of solutions containing synthetic sugars, such as glucose.

However, Dr Antonopoulou has now shown that, using a culture of bacteria obtained from her local waste-water plant, it is possible to get almost as much power from raw whey as from refined fuel, provided the whey is diluted. The trouble is the power output still only amounts to milliwatts, barely enough to trickle-charge a cellphone. And working with raw waste water also presents challenges.

Initially Dr Antonopoulou and her colleagues found that the coulombic efficiency of their cells—a measure of how many electrons produced actually flow into a circuit—was particularly low, at around just 2%. This turned out to be because a second set of microbes, within the whey itself, was absorbing them. So, by sterilising the whey first to kill these other bugs they have now boosted the coulombic efficiency to around 25%.

The total power of the device should improve further with a new design that increases the surface area of the electrodes within the fuel cell. One of the biggest obstacles is a lack of investment to develop materials that would work better with microbial fuel cells. If the various hurdles can be overcome and the devices can be scaled up to industrial levels, then the technology can only mature; just like a good cheese.