A Review on the Interspecies Electron Transfer of Methane Production in Anaerobic Digestion System

Anaerobic methanogenesis plays an important role in the sustainable management of high concentration organic wastewater and bioenergy recovery. Interspecies electron transfer (IET) is a new type of mutualistic symbiosis that can accelerate microbial metabolism and overcome thermodynamic barriers in the metabolic process, thus facilitating anaerobic methanogenesis. IET is classified into Direct Interspecies Electron Transfer (DIET) and Mediated Interspecies Electron Transfer (MIET) according to the different electron transfer methods. This paper summarizes the recent research progress related to interspecies microbial electron transfer in anaerobic methanogenic system, describes the possible specific mechanisms of DIET and MIET, and analyzes the differences between DIET and MIET methods in terms of methanogenic performance, thermodynamics, kinetics, and the microbial communities involved in them. Finally, it was found that, through DIET, microorganisms in the process of anaerobic methanogenesis could not only strengthen the extracellular electron transfer of microorganisms and alleviate the inhibition of high organic loading rate, organic acids, and toxic substances, they could also help ferment bacteria and allow methanogenesis to break through the thermodynamic barriers and efficiently degrade complex organic matter. This can overcome several problems, such as low efficiency of electron transfer and acidification of traditional anaerobic digestion.