Application of sodium alginate as a coagulant aid for mitigating membrane fouling induced by humic acid in dead-end ultrafiltration process

Abstract

Ultrafiltration (UF) is one of the most promising technologies for surface water treatment, but severe membrane fouling is a significant obstacle for its widespread application. In this study, sodium alginate (SA) was used as a coagulant aid of polyaluminum chloride (PAC) in a pre-coagulation process prior to UF to mitigate UF membrane fouling. The influence of SA addition on water treatment efficiency, flocs characteristics and membrane fouling were examined. Results showed that SA dosed after PAC improved coagulation and UF efficiency due to its bridge role and gel network formation. UV254 and DOC removal from UF effluent were over 97% and 70%, respectively, when SA dosage ≥0.3 mg/L. In addition, UF membrane normalized flux was improved from 0.19 to 0.47. The membrane fouling alleviating mechanism of SA application was the formation of a porous cake layer by flocs with looser structures. In addition, these flocs were much larger than membrane pores (flocs sizes >450 μm), which also alleviate pore blocking degree of UF membrane.