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

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 MnOx/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 MnOx/Ti anode (Ea), and their correlation were investigated. When coupled with O2-reducing biocathode, MnOx/Ti anode considerably accelerated M(·OH) generation because Ea increased. The increased Ea 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. [Display omitted] •Biocathode-electrocatalytic reactor (BECR) started up under 0.7 and 1 V.•BECR removed dye better than the reactor with stainless steel cathode (ECR-SS).•Energy consumption of BECR was less than ECR-SS to achieve the same TOC removal.•Coupling of biocathode facilitated the generation of M(·OH) from MnOx/Ti anode.•High anodic potential of MnOx/Ti anode in BECR promoted the generation of ·OH.