The images obtained by SEM after the filtration of synthetic wastewater for 4 h (Fig. 6) showed that there was a great difference between the morphology of the membranes. OT050membrane had finger-like pores, which offered a lower permeate flow resistance. The GR60PP, on the other hand, had a highly porous structure which exhibited greater tortuosity, offering greater flow resistance. These were the main factors responsible for the intrinsic membrane resistance. At the same time, the SEM images confirmed the formation of a com-pact cake layer on the membrane surface of 5.20 ± 0.04 m forGR60PP and of 6.13 ± 0.13 m for OT050.