Coupling anodic Congo red oxidization with cathodic microbial CO₂-reduction for energy-efficient microbial electrosynthesis of acetate

Microbial electrosynthesis systems (MESs) employ biological carbon fixation reactions in the cathode chamber to produce high-value chemicals, yet the anodic oxidation reaction has always been overlooked. Therefore, the oxygen evolution reaction (OER) occurs at the anode chamber in most MES systems, resulting in a high anodic overpotential and an elevated cell voltage. To tackle the problem, this work proposed a coupled system that integrated anodic oxidation of the azo dye Congo Red (CR) and cathodic microbial CO₂-reduction to produce acetate. This system has demonstrated over 94% decolorization of high-concentration CR wastewater within 40 min (HRT= 120 min), while more than 16 g/L of acetic acid was accumulated at the cathode after 5.5 d of batch operation. More importantly, the electricity consumption fell by 12% compared to MES with OER, thereby demonstrating the feasibility of replacing the anodic OER reaction with azo dyes wastewater treatment in MES systems. This energy-efficient system, which is capable of pollutant removal and carbon fixation to produce acetate, holds the potential to broaden the application prospects of MESs.