Enhanced decolorization of azo dye in a small pilot-scale anaerobic baffled reactor coupled with biocatalyzed electrolysis system (ABR–BES): A design suitable for scaling-up

• A pilot-scale refractory wastewater treatment process (ABR–BES) was developed.
• ABR–BES showed superior decolorization performance.
• VFAs could be efficiently utilized for azo dye decolorization in ABR–BES.
• The mechanism of azo dye transformation in ABR–BES was proposed.
• Power supply and HRT were the key impact factors of ABR–BES.

A four-compartment anaerobic baffled reactor (ABR) incorporated with membrane-less biocatalyzed electrolysis system (BES) was tested for the treatment of azo dye (alizarin yellow R, AYR) wastewater (AYR, 200 mg L−1; glucose, 1000 mg L−1). The ABR–BES was operated without and with external power supply to examine AYR reduction process and reductive intermediates with different external voltages (0.3, 0.5 and 0.7 V) and hydraulic retention times (HRT: 8, 6 and 4 h). The decolorization efficiency in the ABR–BES (8 h HRT, 0.5 V) was higher than that in ABR–BES without electrolysis, i.e. 95.1 ± 1.5% versus 86.9 ± 6.3%. Incorporation of BES with ABR accelerated the consumption of VFAs (mainly acetate) and attenuated biogas (methane) production. Higher power supply (0.7 V) enhanced AYR decolorization efficiency (96.4 ± 1.8%), VFAs removal, and current density (24.1 A m−3 TCV). Shorter HRT increased volumetric AYR decolorization rates, but decreased AYR decolorization efficiency.