If you love a sewage-eating robot, set it free.

So New Scientist recommends in a new report on an artificial gut that allows robots to become self-sustaining:

[F]ood-munching robots have been demonstrated in the past, often generating power with the help of microbial fuel cells (MFCs) – bio-electrochemical devices that enlist cultures of bacteria to break down food to generate power. Until now, though, no one had tackled the messy but inevitable issue of finding a way to evacuate the waste these bugs produce.

What was needed was an artificial gut, says Chris Melhuish, director of the Bristol Robotics Lab in the UK. He has spent three years with Ioannis Ieropoulos and colleagues working up the concept. The result: Ecobot III.

“Diarrhoea-bot would be more appropriate,” Melhuish admits. “It’s not exactly knocking out rabbit pellets.” Even so, he says, it marks the first demonstration of a biomass-powered robot that can operate unaided for some time.

The work will be presented at the Artificial Life conference in Odense, Denmark, next month. The next step is to explore how the robot will cope with a heartier meal, namely flies.