Performance optimization and microbial community analysis of integrated anaerobic BES-aerobic MBBR system for azo dye treatment with related wastewater remediation

Azo dyes are among the most common organic dyes, characterized by complex aromatic structures and strong electron-withdrawing azo bonds, which make them resistant to treat. To enhance the treatment performance of azo dyes, this study investigated key operating parameters in an integrated anaerobic bioelectrochemical system (BES) and aerobic moving bed biofilm reactor (MBBR) system, including the applied voltage, dissolved oxygen (DO) concentration, and biocarrier filling rate. Results indicated that the applied voltage (0.7 V) promoted decolorization in the BES stage. An appropriate DO concentration (4 mg L⁻¹) enhanced the removal of chemical oxygen demand (COD) in the MBBR stage. The biocarrier filling rate (40 %) played a crucial role in MBBR performance by providing a surface for biofilm attachment. Under these synergistic operating conditions, efficient performance was achieved, with 97.9 ± 0.8 % azo dye decolorization and 93.0 ± 0.2 % COD removal at an azo dye concentration of 100 mg L⁻¹. Moreover, analysis of microbial community structures revealed the presence of functional microbial groups involved in electron transfer, fermentation, dye degradation, and denitrification. The synergistic effect of these functional microorganisms could promote the pretreatment and post-treatment of azo dye. This study established a treatment mode for the bioelectrochemical-assisted anaerobic-aerobic process, providing a theoretical foundation for the application of integrated BES systems in wastewater treatment.