The clean-water flux (J0) of the membrane unit was determined by filtering tap water through the membrane. Each experiment consisted of four filtration cycles, and each cycle consisted of a filtration and an air backwash process at a pressure of 2.5 kg/cm2. The contact angle of the cake was measured by the sessile drop method, with a contact-angle measuring instrument (Model 100, Sindatek) to determine the hydrophobicity of the cake. The component resistances of membrane filtration were calculated by the resistance-in-series model. The relationship between permeate flux and resistances can be expressed as follows: