Floc proprieties and ultrafiltration characteristics by chitosan compound aluminum species coagulant under different pH conditions

Abstract

In this study, the tendency of coagulation performances, floc characteristics and membrane resistances under different pH conditions in coagulation–ultrafiltration hybrid process was investigated by different Al species and chitosan (CS). Results indicated that CS as coagulation aid was independent of aluminum species. Coagulation efficiencies of three Al species (Ala, Alb and Alc) combined with CS were enhanced comparing with Al species used alone and shown similar variation tendencies during the pH range. The values of floc size and strength/recovery factor were relatively high at pH 6, and the maximum fractal dimension was achieved under alkaline conditions generally due to adsorption sweeping. Ala/Alb/Alc combined with CS contributed to larger flocs, higher recovery factors and smaller fractal dimension values than those without CS. The results of ultrafiltration experiments shown that membrane resistances during alkaline ranges were higher than those of acidic conditions, which indicated membrane fouling was more serious in alkaline range. In addition, the total membrane resistance was decreased significantly by CS addition.