Ecobot III is a self-sustaining machine with an artificial gut.
Researchers at the Bristol Robotics Laboratory, UK have created a self-sustaining robot with an artificial gut to allow it to power itself by eating and excreting. The Ecobot III eats partially processed sewage and uses its nutrients as fuel and excretes the rest, while also drinking water to continuously generate power.
Physorg describes its digestion process and how it generates power for itself:
The robot navigates towards a dispenser filled with the nutrient-rich mixture and “eats” what it needs. The meal is then processed in the robot’s body by bacteria held in a stack of two tiers, each with 24 microbial fuel cells (MFCs).
Undigested matter passes via a gravity feed to a central trough from which it is pumped back into the feeder tanks to be reprocessed in order to extract as much of the available energy as possible. The waste is then purged every 24 hours by a peristaltic pump that works like the colon, using pressure waves to expel the waste from the tube into a litter tray.
The bacteria in each MFC metabolize the mixture, producing hydrogen atoms in the process. The hydrogen electrons are drawn to the fuel cell anode where an electric current is generated. Meanwhile the hydrogen ions enter the cathode chamber via a proton-exchange membrane and combine with oxygen in the water in the chamber to produce more water.
In the experiments, Ecobot III sustained itself unaided for 7 days.
Here’s a video of its predecessor, Ecobot II: