Innovative microbial electrochemical process for H₂O₂ synthesis and residual H₂O₂ removal for wastewater treatment

Sustainable H₂O₂ synthesis and residual H₂O₂ removal are key challenges to the treatment of recalcitrant wastewater using Fenton processes. In this study, an innovative bioelectrochemical system was developed to meet the challenges by alternate switching between microbial electrolysis cell (MEC) and microbial fuel cell (MFC) mode of operation. In the MEC mode, H₂O₂ was produced and then reacted with Fenton’s reagent (Fe II) to form hydroxyradical. When the system was switched to MFC mode, the unused H₂O₂ as residual is removed at the cathode as electron acceptor. For wastewater containing 50 mg L^-1 methylene blue (MB), complete decolorization and mineralization was achieved in the MEC mode with apparent first order rate constants of 0.43 and 0.22 h^-1, respectively. After switching the system to the MFC mode, unused H2O2 at concentration of 180 mg L^-1 was removed. The removal rate was 4.61 mg L^-1 h^-1 while maximum current density of 0.49 A m^-2 was generated. The MB degradation and removal of unused H₂O₂ were affected by different operational parameters such as external resistance, cathode pH and initial MB concentration. Furthermore, stack operation greatly improved the system performance. This study for the first time demonstrated an efficient and cost-effective bioelectrochemical system for H₂O₂ generation, residual removal and treatment of recalcitrant pollutants.