This document discusses microbial fuel cells (MFCs) which are bio-electrochemical systems that convert the chemical energy in organic matter into electricity through catalytic microorganisms. MFCs have several applications including powering low-power sensors for oceanographic monitoring and environmental applications. The document outlines the basic process of an MFC where microbes oxidize a substrate like glucose at the anode and electrons are transferred to the cathode via a membrane or mediator. Various types of wastewater can be used as substrates to power MFCs. Common microbes used in MFCs include Geobacter and Shewanella species.