I'm going to do my best to try and explain Gilberto Espanza's Plantas Nomadas. Plantas Nomadas ('nomadic plants' in English) is a sort of hybrid plant and microorganism robot that is fueled by a microbial fuel cell.
Plantas Nomadas knows when it needs fuel... because it's alive. It seeks out and sucks up polluted water, which feeds the plants and microbes. The plants and microbes power the microbial fuel cell and the whole cycle starts again.
Gilberto Espanza created Plantas Nomadas to show that solving the world's polluted water problems can be done with out-of-the-box designs and ideas.