Air sparging is recognized as an effective way to increase permeate flux in membrane filtration processes. The application of air sparging with an external-loop airlift ceramic membrane bioreactor was studied at different gas flow rates, biomass concentrations and suction pressures. A 180% increase in permeate flux was obtained while filtering a 2g/L activated sludge wastewater suspension with the airlift cross-flow operation for U-g = 0.21 m/s. The mechanism of flux enhancement in the case of slug flow in tubular membrane was discussed. The region near the gas slug was divided into three different zones: falling film zone, wake zone and remaining liquid slug zone. Air sparging significantly lowered cake thickness and consequently cake resistances for the wake region and the failing film region. A novel model combining hydrodynamic of gas-liquid two-phase flow and cake resistance was developed to simulate the process. The model was validated with experimental data with an error of 8.3%. (C) 2009 Elsevier Ltd. All rights reserved.