As shown in Fig. 5, the average settling velocities of both titanium and aluminum flocs in combination with kaolin clay followed the similar variation patterns as their ‘pure’ flocs derived from distilled water coagulation. The kaolin clay-titanium flocs reached a mean velocity of 4.0 mm/s at about pH 5.5 whereas at pH 5.1 and pH 5.9, the floc velocities fell to around 3.8 and 2.6 mm/s respectively. The average settling velocities of kaolin clay-aluminum flocs within pH 5–6 were about 2.5–2.8 mm/s, and rose to 3.2–3.5 mm/s when pH reached 7–8. It was noticed that all the kaolin clay combined flocs settled faster than the distilled-water-flocculates, indicating that floc settling speed strongly depended on water impurities.