[Effects of Algal Morphology and Al Species Distribution on the Coagulation-Ultrafiltration Process]

In order to ensure drinking water quality, three different Al-based coagulants [Al₂(SO₄)₃(AS), Al₁₃, Al₃₀] were used to treat water laden with different algae [Microcystis aeruginosa(cyanobacteria), Chlorella(green algae), Cyclotella (diatoms)]. Floc size, strength factor, and recovery factor under different conditions were measured to investigate the mechanisms in the coagulation-ultrafiltration process. The results indicated that the main mechanism in the coagulation process using Al₁₃ or Al₃₀ as coagulants was electrostatic patching and the main mechanism using AS was charge neutralization. In the Microcystis aeruginosa and Chlorella systems, when Al₁₃ and Al₃₀ were used as coagulants at low dosage, the coagulants that were adsorbed on the side (which existed on the surfaces of Microcystis aeruginosa and Chlorella cells) would lose their ability to aggregate the algal cells. When AS was used as coagulant, the electric double layer was effectively compressed. The repulsive force between algal particles decreased, and the flocs formed easily. In the Cyclotella system, Al₁₃ and Al₃₀coagulants effectively formed the flocs through electrostatic patch effects. There was a significant correlation between membrane flux and floc size, and the larger flocs formed a looser cake layer on the membrane surface.