Combining experimental and computational fluid dynamics simulation approaches to optimize cross-flow velocity conditions in anaerobic membrane bioreactors

In anaerobic membrane bioreactors (AnMBRs), biogas circulation is commonly used for the scouring of membrane surfaces to prevent the fouling of membranes and extend their lifespan. However, gas-cycling rate optimization remains a considerable challenge. In this study, the influence of cross-flow velocity (CFV) on AnMBR performance was evaluated under various gas flow rates, and computational fluid dynamic (CFD) simulations were conducted to elucidate the underlying fluid dynamic mechanisms. The experimental results revealed a positive correlation between CFV and membrane performance. Meanwhile, CFD simulations indicated that moderate increases in the CFV enhanced liquid mixing and improved fouling mitigation, whereas an excessively high CFV resulted in the formation of low-pressure zones and intensified vortex effects. Under high-CFV conditions, the effectiveness of liquid-induced scouring decreased, which affected the filtration efficiency. In particular, a CFD analysis indicated that, although gas scouring contributed to scouring on the membrane surface, liquid-induced scouring effects were more critical. Under the conditions assessed in this study, 116.2 m/h was considered the optimal CFV, as it ensured effective gas–liquid mixing, enhanced membrane fouling mitigation, and low energy consumption. This study elucidates the key hydrodynamic mechanisms through which CFV influences AnMBR performance. The findings provide important theoretical and practical guidance for optimizing AnMBR operational strategies and achieving efficient and stable membrane filtration. • Biogas circulation effectively reduces membrane fouling in AnMBR. • CFD analysis reveals the fluid distribution features under various CFV conditions. • Excessive CFV intensifies vortex effects, potentially reducing filtration efficiency. • Experiments and CFD confirm optimal CFV enhances fouling control and efficiency. • A CFV of 116.2 m/h achieved the optimal balance in the case of this study.