Enhanced anodic oxidation and energy saving for dye removal by integrating O₂-reducing biocathode into...

Simultaneous enhancement of dye removal and reduction of energy consumption is critical for electrochemical oxidation in treating dyeing wastewater. To address this issue, this work presented a novel process termed biocathode-electrocatalytic reactor (BECR). The dual-chamber BECR employed O₂-reducing biocathode instead of normal stainless steel (SS) cathode and MnO_x/Ti anode to reduce O₂ in the cathode chamber and treat methylene blue (MB) in the anode chamber, respectively. BECR successfully started up at 0.7 and 1 V and substantially improved MB and total organic carbon (TOC) removal compared with the electrocatalytic reactor with SS cathode (ECR-SS), e.g., removal of MB (150 mg L^-1) increased from 27.0 ± 0.2% to 78.1 ± 0.4% at 1 V. To achieve the same TOC removal, BECR reduced the energy consumption by approximately 45.7% compared with ECR-SS (19.5 and 35.9 kWh (kg TOC) ^-1 for BECR and ECR, respectively). To explain the above merits of BECR, M(·OH) (·OH adsorbed on the anode surface) generation, potential of MnO_x/Ti anode (E_a), and their correlation were investigated. When coupled with O₂-reducing biocathode, MnO_x/Ti anode considerably accelerated M(·OH) generation because E_a increased. The increased E_a in BECR was due to the fact that its cathodic reaction was converted to the four-electron O₂ reduction, which exhibited a higher cathodic potential than hydrogen evolution reaction on SS cathode in ECR-SS. Thereby, BECR simultaneously promoted dye removal and reduced energy consumption, showing promise in treating dyeing wastewater.