In this study, the influence of various parameters such as determination methods and step height and length of incremental flux on critical flux values were investigated. Experiments were carried out on a pilot-scale membrane bioreactor (MBR) treated municipal wastewater. Three of the five critical flux determination methods, such as flux linearity, 90% permeability and flux cycling conducted in this study, indicated a decline in critical flux values as the step height of incremental flux increased. However, the hysteresis method and the two-third (2/3) flux limitation method showed an increase and independence of critical flux to the step height of incremental flux, respectively. On the other hand, the step length of incremental flux had no obvious effect on critical flux values evaluated by all critical flux determination methods. Like critical flux, sustainable flux has negative relationship with the increase of step height but no influence of step length was found in this study. (C) 2011 Published by Elsevier Ltd.