Though disgusting, sewage is an abundant, nutrient-rich resource. Researchers at the University of West England have taken advantage of this fact by creating a robot that turns human poo into energy. The EcoBotIII has an artificial stomach that consists of layers of microbial fuel cells that digest sewage and transform them into fuel. In case you're wondering, the robot has a "solid waste excretion mechanism", so it can poop just like you do. The hope is that autonomous robots such as these might patrol sewer systems looking for problems, or be put to work in sewage treatment plants to drive down treatment costs.
Thanks to Yuri for the heads up.