Treatment of Azo Dye Wastewater by Anaerobic Membrane Bioreactors: A Review on Process Performance and Mitigation Strategies

Membrane fouling and biological toxicity are two main bottlenecks in treating azo dye wastewater using anaerobic membrane bioreactors (AnMBRs). This review examines how azo dye molecular structure affects AnMBR performance and membrane fouling. It discusses azo dye reduction, aromatic amine formation, microbial inhibition, and foulant formation. Aromatic amines may inhibit methanogenesis and promote the accumulation of hydrophobic foulants on membrane surfaces. At low dye loadings, stable treatment may be supported under favorable operating conditions, whereas higher loadings may inhibit anaerobic activity and accelerate membrane fouling. The review evaluates membrane modification, biological enhancement and in situ electro-cleaning strategies. No single strategy has yet ensured long-term industrial operation. Reported concentration thresholds are mainly derived from single-dye laboratory studies and may not apply to actual textile wastewater. Future work should use data-driven fouling prediction and pilot trials with real wastewater to define AnMBR operating limits.