Cost-effective membrane fouling control and nitrogen removal performance are of great concern in airlift external circulation membrane bioreactors (AEC-MBRs). Computational fluid dynamics (CFD) model incorporating sub-models of bio-kinetics, oxygen transfer and sludge rheology was developed for the cost-effective optimization of a lab-scale AEC-MBR. The model was calibrated and validated by extensive measurements of water velocities and water quality parameters in the AEC-MBR. The validated results demonstrated that the optimized height of gas-liquid dispersion was at around 300 mm. The shear stress on membrane surface was equalized and had an average value of 1.2 Pa under an air flowrate of 1.0 m(3) h(-1). The model further revealed that the high nitrogen removal efficiency (> 90%) was achieved due to the high recirculation ratio driven by airlift force without destroying the oxygen deprivation and enrichment in the anoxic and oxic zone, respectively. (C) 2016 Published by Elsevier Ltd.