[Preparation of PSAS and its application in HAB prevention]

In order to obtain optimum PSAS (Polysilicate-aluminium sulfate) preparation conditions for removing HAB organisms, the 3-factor and 3-level orthogonal test was devised. Concentration of SiO2, Al3+/SiO2 molar ratio and pH were chosen as the three chief factors in PSAS preparation. The experimental results showed that the optimum preparation condition for various HAB organisms was different, and according to practical experimental operation, the appropriate preparation condition was considered as: concentration of SiO2 = 2%, molar ratio of Al3+/SiO2 = 1, and pH = 4. In addition, the coagulation efficiencies of PSAS on various HAB organisms were studied and compared with classical inorganic flocculant AS (Aluminium sulfate). The results indicated that the removal rates of PSAS were much higher than those of AS, and the dosages of PSAS were 30-40% lower than those of AS when they achieved the same removal rates. On the other hand, the anti-coagulation ability of HAB organisms varied with algal species, which was related to different physiological and ecological features of various algal cells.