Initially, both oxides aggregate to form larger particles, but stopped growing in 5-min mixing (see Fig. 4). Higher mixing intensities were also observed to produce smaller aggregates (G = 600 s−1). Previous studies have suggested that the reduced size of aggregates at higher G is caused by the breakage of aggregates by intensive mixing [17] and [18], and that particle size distribution can influence the porosity of cake layer on membrane [10]. Greater cake porosity will allow fluid to pass through the membrane, which increases permeate flux [19]. To determine the particle size distribution of oxide aggregates, the distribution spreading index (DSI) was further analyzed.