If there's one thing humans can apparently generate an endless supply of, it's shit. So why not use that to produce things we need but don't have enough of, like clean water and energy? Environmental engineer Bruce Logan is developing fuel cells that may be able to do that, cleaning wastewater while generating and storing energy.
The secret is that the batteries are full of bacteria, which eat their way through the waste and release electrons, which the fuel cells can store. The bacteria can generate electrical power, but they can also produce hydrogen, which means they could have even broader future applications in hydrogen-powered cars.
Right now the batteries don't make enough electricity to be genuinely useful, but keep your shirt on — Logan estimates that in five to 10 years they could be capable of running entire sewage treatment plants (which already mostly clean water with microbes, just not dual-use ones). And they'd have enough energy left over to power nearby towns.