The growth, breakage and regrowth nature of flocs formed by Titanium tetrachloride (TiCl4) and polyaluminum chloride (PACl) was comparatively evaluated with surface water treatment. A series of jar experiments were conducted to investigate the impacts of different operating parameters such as shear force. solution pH and a breakage period on floc strength and re-aggregation potential. Results indicated that the responses of flocs to different operating parameters depend on the coagulant used. The ability of floc to resist breakage decreased with the increase of shear force and breakage period. Floc strength properties were also measured in response to increasing shear force, with the results suggesting that the order of floc strength was TiCl4 > PACl. Floc regrowth of the two coagulants after exposure to high shear was limited, and flocs formed by TiCl4 displayed weaker recoverability. The flocs generated in acid conditions were more recoverable than those generated in alkaline conditions no matter which coagulant was used. (C) 2011 Elsevier B.V. All rights reserved.