Electrode potential regulates phenol degradation pathways in oxygen-diffused microbial electrochemical system

Abstract

Bioelectrochemical technologies are found to be effective to degrade bio-toxic pollutants such as phenol under micro-oxygen condition. However, the mechanism on how electrode potential regulate phenol biodegradation under this condition is still not clear. In order to systematically investigate this process, the metabolic pathways were discussed under different electrode potentials according to microbial community and catabolite analyses in oxygen-diffused microbial electrochemical systems (MESs). The applied potential at 0 V (vs. Ag/AgCl) shortened the degradation time by 36% at 66 h in oxygen-diffused systems, while the lack of oxygen resulted in an incomplete degradation (48 ± 8% at 90 h). According to the phenol degradation under a potential ranging from −0.4 V to 0.4 V, a more positive electrode potential favored a higher phenol degradation rate, which resulted from the upregulation of four metabolic pathways, namely, benzoate degradation via CoA ligation, pyruvate metabolism, glyoxylate and dicarboxylate metabolism, and glycolysis or gluconeogenesis. The enhanced production of intermediates such as acetate (0 V) and formate (0 and −0.2 V) stimulated the growth of both phenol-degraded bacteria (PDB) and electroactive bacteria (mainly Geobacter spp.) in the biofilm but not the suspension. Here we concluded that the fast and complete degradation of phenol in MES needed oxygen, and the metabolism pathways as well as the main metabolites were regulated by the electrode potential.