Enhanced Coagulation of Titanium Tetrachloride Aided by the Modified Compound Bioflocculant

The compound bioflocculant (CBF) was modified by graft copolymerization of acrylic amide and dimethyl diallyl ammonium chloride, and the novel copolymer was denoted as MCBF. The effect of MCBF used as coagulant aid with titanium tetrachloride (TiCl4) was investigated for both high and low molecule weight natural organic matter (NOM) removal. Floc characteristics were studied using a laser diffraction particle-sizing device. Results indicated that the monomers were successfully grafted onto the CBF, and the molecule weight and zeta potential of CBF were greatly improved. The MCBF with TiCl4 exhibited synergistic effect by promoting NOM removal, especially at low TiCl4 doses. Additionally, using MCBF as a coagulant aid with TiCl4 can significantly increase the floc growth rate, size, strength, and broken-floc recoverability. The effect of MCBF on fractal dimension of flocs generated by TiCl4 depended on NOM properties. Both coagulation performance and floc properties were significantly affected by dosing sequence.