Insoluble carbonaceous materials as electron shuttles enhance the anaerobic/anoxic bioremediation of redox pollutants: Recent advances

Carbonaceous materials can accelerate extracellular electron transfer for the biotransformation of many recalcitrant, redox-sensitive contaminants and have received considerable attention in fields related to anaerobic bioremediation. As important electron shuttles (ESs), carbonaceous materials effectively participate in redox biotransformation processes, especially microbially-driven Fe reduction or oxidation coupled with pollutions transformation and anaerobic fermentation for energy and by-product recovery. The related bioprocesses are reviewed here to show that carbonaceous ESs can facilitate electron transfer between microbes and extracellular substrates. The classification and characteristics of carbon-containing ESs are summarized, with an emphasis on activated carbon, graphene, carbon nanotubes and carbon-based immobilized mediators. The influencing factors, including carbon material properties (redox potential, electron transfer capability and solubility) and environmental factors (temperature, pH, substrate concentration and microbial species), on pollution catalytic efficiency are discussed. Furthermore, we briefly describe the prospects of carbonaceous ESs in the field of microbial-driven environmental remediation.