Algae removal from raw water by flocculation and the fractal characteristics of flocs

Abstract

The feasibility of flocculation treatment of algae-containing raw water using poly(acrylamide-acryloyloxyethyl trimethyl ammonium chloride-butyl acrylate) (PADB) was investigated. The effects of flocculant dosage and initial pH of raw wastewater on the removal of turbidity and chlorophyll-a (Chl-a) from raw water were examined. The flocculation efficiency of PADB was compared with that of cationic polyacrylamide (CPAM), polymeric ferric sulfate (PFS), and polyaluminum chloride (PAC). PADBs proved to be highly efficient flocculants for the removal of Chl-a; meanwhile, flocculation tests also demonstrated the superiority of PADB over CPAM, PFS, and PAC in the removal of Chl-a. The removal of turbidity and Chl-a by PADB were higher than 94 and 99%, respectively, in the pH range of 6–8 at 3 mg L−1 PABD dosage and at 40% cationic degree. The Chl-a removal efficiency of PADB was 7.6, 17.9, and 52.8% higher than that of CPAM, PFS, and PAC, respectively. Optical microscopy was used to investigate the fractal characteristic of flocs formed during flocculation. The fractal dimension increased, and the flocs increased in size and density with increasing pH. In conclusion, the flocculation-separation process using PADBs as flocculants proved to be highly effective and efficient method for algae removal, and provided guidance and directions for future practical application.