The role of sodium alginate in improving floc size and strength and the subsequent effects on ultrafiltration membrane fouling

Abstract

Background: Dosing environment-friendly polymer as coagulant aids is an encouraging method in water treatment to obtain desirable floc characteristics. Sodium alginate (SA) was used as the coagulant aid for synthetic humic acid (HA) water treatment to investigate the effect on flocs characteristics and ultrafiltration (UF) membrane fouling. Results: When SA content was 0.3 mg L−1, the treatment of HA by polyaluminium chloride (PAC) plus SA (PAC/SA) yielded the maximum removal efficiency of 66.5%, which was higher than the maximum HA removal efficiency of PAC (58%). Moreover, the HA flocs size of PAC would grow from 269 to 367 μm after SA was added. Strength factor and recovery factor of PAC/SA were larger than those of PAC. These resulted in the improvement in subsequent UF membrane performance. The membrane fouling decreased in the following order: the raw water>PAC coagulated water>PAC/SA coagulated water. Conclusion: The study showed that the application of SA as coagulant aids resulted in larger and stronger flocs, which would improve treatment efficiency of the coagulation process. And the flocs formed by PAC/SA contributed to the restriction of the fouling of UF membrane, which would decrease the cost of advanced water treatment.