The average settling velocity of Ti-flocs (ranged 1.01–3.69 mm/s) was a function of pH, as shown in Fig. 4. Considering that floc densities were fairly constant with pH variations (Fig. 3), it was assumed that pH might have some unknown effect on floc agglomeration that led to settling velocity variations. Also noticed was that within the pH range of 5–6 where enhanced coagulation was usually practiced, the settling velocity of Al-flocs would slow down whereas Ti-flocs would keep a higher settling speed, so efficient sedimentation could be expected in this pH range by titanium flocculation.