Integrated energy view of wastewater treatment: A potential of electrochemical biodegradation

? Energy is needed to accelerate the biological wastewater treatment. ? Electrical energy input in traditional technology is indirect and inefficient. ? Direct injection of electricity can be a game changer to maximize energy efficiency. ? Microbial electrochemical unit for decentralized wastewater treatment is proposed. It has been more than one century since the activated sludge process was invented. Despite its proven stability and reliability, the energy (especially the electrical energy) use in wastewater treatment should evolve to meet the increasingly urgent demand of energy efficiency. This paper discusses how the energy utilized in conventional biological wastewater treatment can be altered by switching the indirect energy input to a direct electricity injection, which is achieved by the electrode integration providing extra thermodynamic driving force to biodegradation. By using electrodes instead of oxygen as terminal electron acceptors, the electrical energy can be utilized more efficiently, and the key of direct use of electrical energy in biodegradation is the development of highly active electroactive biofilm and the increase of electron transfer between microbes and the electrode. Furthermore, the synergy of different microbial electrochemical units has additional benefit in energy and resource recovery, making wastewater treatment more sustainable.