Higher DSI values indicate a broader size distribution of particles [10]. At low and high mixing intensities, our DSI values of oxides ranged from 0.81 to 0.84, suggesting a limited difference in particle size distribution between Fe and Fe–Mn oxides. The results of size measurement confirmed that chlorination with enhanced mixing resulted in smaller oxides aggregate, which influences the permeate flux of dead-end MF. Furthermore, the five-minute mixing in chlorination was sufficient for oxide removal by membrane filtration.