A vertically oriented hollow fiber membrane module equipped with a downward aerator as well as an upward aerator for the simultaneous upward and downward air sparging was evaluated in a pilot-scale bioreactor. The operation was divided into three consecutive phases based on different membrane air sparging configurations: the simultaneous upward and downward air sparging (Phase 1), the single upward air sparging (Phase 2), and the simultaneous upward and downward air sparging (Phase 3). Although the SMBR operation, process performances including particulate matters, organic matters, and nutrients removals were stable. the membrane fouling characteristics were significantly different for the different air sparging configurations. The parameters such as the trans-membrane pressure increasing rate, the permeability decreasing rate, the irreversible membrane fouling rate, and the fouling resistance increased when the air sparging configuration was changed from the simultaneous upward and downward mode to the single upward mode (i.e., Phase 1 -> Phase 2), while the parameters decreased when the air sparging configuration was switched from the single upward mode to the simultaneous upward and downward mode (i.e., Phase 2 -> Phase 3). Taken together the results strongly support the effectiveness of the simultaneous upward and downward membrane air sparging in reducing membrane fouling. (c) 2009 Elsevier B.V. All rights reserved.