Electrocatalytic biofilm reactor for effective and energy-efficient azo dye degradation: the synergistic effect of MnO_x/Ti flow-through anode and biofilm on the cathode

Abstract

● MnO _x /Ti flow-through anode was coupled with the biofilm-attached cathode in ECBR.

● ECBR was able to enhance the azo dye removal and reduce the energy consumption.

● Mn^IV=O generated on the electrified MnO _x /Ti anode catalyzed the azo dye oxidation.

● Aerobic heterotrophic bacteria on the cathode degraded azo dye intermediate products.

● Biodegradation of intermediate products was stimulated under the electric field.

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 stainless-steel 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 Mn^IV=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 energy-efficient treatment of azo dye wastewater.

Graphical abstract

Keywords

Azo dye removal / Electrocatalytic biofilm reactor / Anodic oxidation / Electricity-stimulated biodegradation / Energy consumption

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