Floc Characteristics and Removal of Turbidity and Humic Acid from High-Turbidity Storm Water

This study considered the removal efficiency of turbidity and organic content from high-turbidity storm water of tropical storm Nari, using polyaluminum chloride (PACl) as a coagulant. The resulting floc size and compactness (fractal dimension) were determined using a small-angle light scattering technique. The response surface method, and the Box-Behnken design, was adopted to examine how the hydrogen ion concentration (pH), turbidity, and alkalinity of the suspension, the PACl dosage, and the dosed amount of humic acid affect the removal efficiency. Flocs with a looser interior structure more efficiently removed turbidity and humic acid. An acidic suspension and moderate PACl dosage and alkalinity level favor the production of loose flocs. Optimal conditions for generating large flocs include pH neutrality and high PACl dosage. Producing both large and loose flocs depends on a compromise. The removal of turbidity/humic acid from high-turbidity storm water does not proceed by a charge neutralization mechanism.