Human urine can power a biological fuel cell that generates electricity, scientists in Great Britain found. Researchers led by Chris Melhuish, director of the Bristol Robotics Laboratory at the University of Bristol and the West of England set out turn urine into power by feeding it to bacteria that eat urea, a chemical found in urine. The bacteria convert urea into gas that reacts with metals in the fuel cell and creates electricity.

Their pee-powered fuel cell generated enough electricity to power a hearing aid. That's not much, but they wrote in their study, published in October in The Journal of Physical Chemistry, that they think they idea has potential. They estimate that humans worldwide produce 6.4 trillion liters (1.7 trillion gallons) of urine each year.

Alternative energy sources have been the focus of global interest, as perhaps one viable solution to the growing problem of fossil fuel depletion, Melhuish and co-authors wrote.

Their global urine output estimate does not include animal urine. Some large farm operations already convert animal waste to energy by capturing methane and other organic gasses released by manure.

To conduct the experiment, Melhuish and co-authors slowly injected the liquid into the fuel cell containers. The fuel cell was attached to a precision electric current meter. After adding about a half liter of urine, the electrical current slowly rose and peaked at 0.25 mW - one fourth of one thousandth of a watt, roughly enough to power a hearing aid. The current remained at its peak for about three days before tapering off.

The impact from this could be enormous, not only for the wastewater treatment industry, but also for people as a paradigm shift in the way of thinking about waste. With an annual global production rate of trillions of liters, this is a technology that could help change the world, Melhuish and his co-authors wrote in the study.