In accordance with the present invention, there are provided methods for improving performance of hollow fiber filtration membrane modules. Invention methods comprise a unique backwashing technique wherein the hollow fiber membranes within the module are pressurized with a gas on the feed side at specified times during the backwash. Periodic use of invention methods effectively removes fouling components from the hollow-fiber membranes, thereby providing stable permeability and low trans-membrane pressures, which results in an efficient and economic filtration process. In addition, there are provided methods for cleaning hollow fiber membranes and increasing filtrate flow rate through membranes.