Electrocatalytic biofilm reactor for effective and energyefficient azo dye degradation:the synergistic effect of MnO_(x)/Ti flow-through anode and biofilm on the cathode

Dyeing wastewater treatment remains a challenge.Although effective,the in-series process using electrochemical oxidation as the pre-or post-treatment of biodegradation is long.This study proposes a compact dual-chamber electrocatalytic biofilm reactor(ECBR)to complete azo dye decolorization and mineralization in a single unit via anodic oxidation on a MnO_(x)/Ti flow-through anode followed by cathodic biodegradation on carbon felts.Compared with the electrocatalytic reactor with a stainlesssteel cathode(ECR-SS)and the biofilm reactor(BR),the ECBR increased the chemical oxygen demand(COD)removal efficiency by 24%and 31%(600 mg/L Acid Orange 7 as the feed,current of 6 mA),respectively.The COD removal efficiency of the ECBR was even higher than the sum of those of ECR-SS and BR.The ECBR also reduced the energy consumption(3.07 kWh/kg COD)by approximately half compared with ECR-SS.The advantages of the ECBR in azo dye removal were attributed to the synergistic effect of the MnO_(x)/Ti flow-through anode and cathodic biofilms.Catalyzed by MnIV=O generated on the MnO_(x)/Ti anode under a low applied current,azo dyes were oxidized and decolored.The intermediate products with improved biodegradability were further mineralized by the cathodic aerobic heterotrophic bacteria(non-electrochemically active)under the stimulation of the applied current.Taking advantage of the mutual interactions among the electricity,anode,and bacteria,this study provides a novel and compact process for the effective and energyefficient treatment of azo dye wastewater.