Enhanced bio-electrochemical decolorization of azo dye by an rGO/ polyaniline-modified biocathode: Performance improvement and cathodic microbiome reshaping

Azo dye wastewater remains challenging to treat due to its high chemical stability, toxicity, and poor biodegradability. Herein, a reduced graphene oxide/polyaniline (rGO/PANI)-modified carbon brush was developed as a biocathode for Alizarin Yellow R (AYR) decolorization in a bioelectrochemical system (BES). Physicochemical characterization confirmed successful rGO/PANI modification and showed improved surface properties, including porous morphology, enhanced hydrophilicity, and less negative surface charge. Electrochemical analyses further demonstrated higher current response, lower interfacial resistance, and improved cathodic activity after modification. At 0.7 V, the rGO/PANI biocathode achieved 96.1 ± 0.02% AYR decolorization and 74.6% COD removal within 24 h, together with higher current response and lower interfacial resistance than the unmodified biocathode. Coulombic efficiency decreased from 65.3% to 46.7%, indicating electron loss to competing cathodic reactions. Microbial community analysis showed that rGO/PANI modification reshaped the cathodic biofilm and selectively enriched dominant genera, particularly Comamonas and Flavobacterium. Functional prediction further suggested enhanced potential for extracellular electron transfer and azo dye reduction. These results demonstrate that rGO/PANI modification is an effective and economical approach for improving biocathode performance in azo dye wastewater treatment.