Impact of preozonation on the performance of coagulated flocs

Ozone have been widely used as pre-oxidant before conventional water treatment processes, while some controversial results on the effects of preozonation on coagulation and particle stabilization, have been described. The performance of coagulated flocs can be substantially influenced by preozonation which can be ascribed to the variation of particles or organic substances in water. In order to elucidate the effects of preozonation as an aid in subsequent coagulation, the synthetic water composed of kaolin suspension and humic acid was coagulated after preozonation. The properties of floc, such as, size, fractal dimension and effective density, were investigated using laser light scattering analyzer and settling column measurement. It was found that the suspended particles had not been destabilized by preozonation as regarding the slight variation of zeta potential. As the ozone dose was less than 0.53 mg O3 mg−1 C, floc size was not influenced apparently, while, as the ozone dose increased, the flocs were broken and the size decreased remarkably. Specifically, the fractal dimensions of flocs increased with increasing ozone dose, resulting in more densely packed flocs with low branch structure. Additionally, in terms of settling characteristics, the optimal pre-ozone dose was found to be 0.53 mg O3 mg−1 C, which led to highest effective density of flocs with best liquid–solid separation efficiency.