Waste Not: "Right now, astronaut waste gets shipped back to Earth. But for long-term exploration, you'd want to recycle it, because it holds resources that astronauts will need. It will provide pure drinking water. It will provide fertilizer. And, with the help of a recently discovered microbe, it will also provide electricity.
"Like many bacteria, this one, a member of the Geobacteraceae family, feeds on, and can decompose, organic material. Geobacter microbes were first discovered in the muck of the Potomac River in 1987; they like to live in places where there's no oxygen and plenty of iron."