Effect of Chlorine Dioxide Preoxidation on the Morphological Characteristics of Algae Floc
Coagulation tests for removing algae in high algae-laden and saline raw water in Yangcheng Reservoir were performed using polyaluminium chloride(PAC),aluminum sulfate(AS),polymeric ferric sulfate(PFS)and ferric chloride(FC)respectively.Fractal dimension was measured by image analysis.Effects of coagulant types and dosages,chlorine dioxide preoxidation on coagulation efficiency and morphological characteristics of algae floc were studied.Results showed that the algae in the Reservoir in summer were single-species with predominant species as Chrococcus mino,M.minima and Dactylococcopsis irregularis.The performance of the coagulants for algae removal from high to low was AS,PAC,PFS,AC.Under the optimum dosage of AS coagulant as Al2SO4 70 mg/L,the removal efficiency of algae was 85.3%,and the fractal dimension of algae floc was 1.54 at the optimum dose and the flocs had density and good sedimentation velocity.Removal efficiency and the fractal dimension enhanced by 6.3% when chlorine dioxide was dosed 0.8 mg/L and fractal dimension was 1.71.Overdose of chlorine dioxide has little benefit on algae removal.