A microbial fuel cell comprising a cathode module, an anode module, a means for feeding source water to the anode module, and a means for feeling air to the source water after said anode module, wherein the source water is introduced in the anode module and discharged at the cathode module, a membrane is not used to transfer electrons, and the source water does not flow through a layer between the cathode and anode modules, such as glass wool or beads.