A special membrane bioreactor was designed which had a settlement tank in order to remove the microbial flocs and reduce the membrane fouling. The membrane A and membrane B were submerged in the mixed activated sludge liquor and supernatant liquor, respectively. The two membrane modules were operated under the same suction condition. Unexpectedly, the fouling rate of membrane A was faster than that of membrane B. In order to investigate the mechanism of membrane fouling, effects of different components on m...