Effects of pre-chlorination on ultrafiltration process in directly treating seasonal high-turbidity surface water: Membrane fouling control and shock load resisting

The seasonal high turbidity in the surface water is posing great challenges to the feasibility of direct ultrafiltration (UF) due to the severe membrane fouling. In this study, a direct UF process was employed to treat the high-turbidity surface water. With the conventional operational protocols, severe membrane fouling encountered. Model fitting indicated that membrane fouling, resulting from the UF of high turbidity water, was predominantly associated with the complete obstruction of pores on the surface of the membrane and the subsequent formation of a cake layer. A pre-disinfection process using sodium hypochlorite was developed in this study, and the membrane fouling was significantly mitigated during long-term (885 h) filtration. The optimized chlorine dosage was 1.5 mg/L in treating the 800 NTU surface water, and enabled the transmembrane pressure (TMP) stabilization of UF process at a low level (<10 kpa). Pre-disinfection can effectively inactivate microorganisms and diminish the presence of microbial extracellular polymeric substances (EPS). This results in a transition from complex and viscous fouling to inorganic fouling on the cake layer caused by high turbidity water. With pre-chlorination, the adhesion force of the cake layer attached on the membrane reduced significantly to make the fouling more easily detach and be removed from on the membrane surface by the shear stress caused by the hydraulic backwash. These findings are expected to develop new insights into the membrane fouling control of UF in directly treating the seasonal high-turbidity surface water.