Bioelectrochemical hybrid system integrating anodic biofilm and cathodic Fenton into a microbial fuel cell for multifunctional treatment of azo dye wastewater

• Two-stage ABF + BEF couples anodic reduction with cathodic Fenton oxidation. • Hybrid configuration achieves azo dye removal with in situ H 2 O 2 generation. • Targeted microbial enrichment supports stable dye degradation performance. • Hydraulic retention time controls electron recovery and BEF efficiency • Integrated bioelectrochemical design improves the detoxification of azo dye. This study investigates a hybrid bioelectrochemical system that integrates an anodic biofilm (ABF) with a cathodic bio-electro-Fenton (BEF) process for the treatment of azo–dye–containing wastewater. Three operational strategies were evaluated by varying the RBV-5R/acetate ratio and hydraulic retention time (HRT). Under optimal conditions (20 mg L −1 RBV-5R, 0.25 g L −1 acetate, 6 h/12 h ABF/BEF), the system achieved a power density of 73.3 mW m −2 and in situ H 2 O 2 generation of 12.3 ± 0.2 mg L −1 , resulting in high removals of color (99.8%), COD (79.6%,), and a marked reduction in phytotoxicity after pH neutralization. Unlike conventional MFC–BEF configurations, this work demonstrates a redox-sequential, self-powered ABF + BEF architecture in which the anodic biofilm serves as an active pretreatment stage prior to oxidative polishing. These results highlight the potential of this integrated platform as a sustainable strategy for advanced wastewater treatment of azo dyes.