Removal of clay and blue-green algae particles through zeta potential and particle size distribution in the dissolved air flotation process

The raw water characteristics of a water treatment plant in Korea are mainly dependent on two major factors: the clay particles attributed to rainfall and blue-green algae in reservoirs. In this work, zeta potential and particle size distributions of clay and algae particles, which are the important parameters affecting their removal efficiency, were measured to investigate the behavior and removal characteristics of particles under various conditions. The results showed that the zeta potential of blue-green algae was more sensitive to treatment conditions than clay, and it fluctuated highly with coagulant dosage, suggesting that the control of zeta potential is important for effective removal of algae particles. On the other hand, the range of particle size distribution that remained from the preliminary sedimentation tank was generally smaller than for flotation. However, the zeta potential of the remaining particles was either close to the isoelectric point or positive, and the particles were not so hard to remove for that reason. In the final analysis, for simultaneous removal of clay and algae particles, a sufficient zeta potential difference must be formed not only for algae particles but also for small clay particles from the sedimentation tank in the dissolved air flotation process.