Comparative study of floc characteristics with titanium tetrachloride against conventional coagulants: Effect of coagulant dose, solution pH, shear force and break-up period

Characteristics of flocs formed by titanium tetrachloride (TiCl4), ferric chloride (FeCl3) and aluminum sulfate (Al-2(SO4)(3)) were comparatively investigated in terms of floc growth rate, size, strength, recoverability and fractal dimension in real water treatment. Impacts of coagulant dose, solution pH and hydraulic conditions, including shear force and break-up period, on floc properties were investigated. Results showed that the floc size followed the order of TiCl4 > FeCl3 > Al-2(SO4)(3) within the dose range investigated. The response of floc strength to coagulant dose depended on the coagulant used, while the floc recoverability decreased with the increasing dose regardless of the coagulant used. Within the solution pH range investigated, the floc strength and recoverability showed the following order of Al-2(SO4)(3) > FeCl3 > TiCl4 and those of TiCl4 were the least affected by solution pH. Additionally, the floc strength decayed with the increasing shear force and break-up period for the three coagulants. TiCl4 yielded the flocs with the weakest recoverability within both the shear force and break-up period ranges investigated. Moreover, the floc compactness followed the order of FeCl3 > TiCl4 > Al-2(SO4)(3) under either shear force condition. (C) 2013 Elsevier Ltd. All rights reserved.