Coagulation by titanium tetrachloride for fulvic acid removal: Factors influencing coagulation efficiency and floc characteristics

Coagulation efficiency of titanium tetrachloride (TiCl4) was investigated for fulvic acid (FA) (as model organic matter) removal compared to traditional coagulants - iron chloride (FeCl3) and aluminum sulfate (Al-2(SO4)(3)). The growth, breakage and regrowth nature of flocs formed by the three coagulants were also comparatively evaluated under different coagulation conditions. Results indicated that TiCl4 achieved higher removal of UV278 (absorbance at 278 nm) and DOC (dissolved organic carbon) than FeCl3 and Al-2(SO4)(3), and TiCl4 produced the largest flocs with the highest floc growth rate. The responses of floc to different operating parameters depend on the coagulant used, while the floc breakage and re-aggregation were also significantly influenced by shear force and break-up period. Floc strength decayed with the increasing shear force, while the inverse trend was observed for floc recoverability. An extension in break-up period resulted in the deterioration of both floc strength and recoverability regardless of the coagulants used. Flocs formed by TiCl4 displayed the weakest recoverability after breakage by contrast to conventional coagulants. Since TiCl4 is only studied recently as a novel coagulant, the comparative study of coagulation performance and floc characteristics of TiCl4 against the traditional coagulants provided valuable information for its wide application in the future. (C) 2013 Elsevier B.V. All rights reserved.