Microbial Electrochemical Technologies Producing Electricity and Valuable Chemicals from Biodegradation of Waste Organic Matters

Abstract

Waste organic matters such as organic compounds in wastewater and waste biomass from agricultural practices contain tremendous amount of energy. Recently microbial electrochemical technology (MET) receives great attention as promising technology to harvest energy from waste organics and produce directly electricity and valuable chemicals. MET use the bioelectrochemical system (BES) where microorganisms are used as catalyst for various electrochemical reactions. Two main mechanisms of extracellular electron transfer (EET), i.e. direct EET and indirectly mediated EET, from bacteria into anode or from cathode to bacteria have been reported. Microorganisms, which can transfer electrons into anode or receive electrons from cathode, are designated as electron transfer microorganisms (ETMs). The activity of ETMs directly and substantially affects the BES performance to produce electricity in MFCs and valuable products in MECs. Tremendous variety of ETMs has been reported and the variety seems to be depending on substrate types, substrate concentrations, poised electrode potentials, and electron acceptors. Most progress of MET in BES has been achieved from researches on application for wastewater treatment to produce electricity. MET is also used for biosensors, bioremediation, producing biofuels and industrial chemicals, and reverse electrodialysis. The present chapter will summarize recent reports of MET focusing on the developments of microbial aspects such as detailed EET mechanisms and diversity of ETMs. In addition, the newest various applications of MET will be briefly introduced.