Application of low-dosage UV/chlorine pre-oxidation for mitigating ultrafiltration (UF) membrane fouling in natural surface water treatment

Abstract

This study describes some results concerning the hybrid process of ultraviolet/chlorine (UV/chlorine) as a pre-oxidation strategy prior to ultrafiltration for the treatment of natural organic matter (NOM)-contaminated surface water. Chlorine has been extensively used in water treatment since it can act as disinfectant or coagulant aid. In addition, the combination of UV and chlorine, compared to the other oxidants generally used in water treatment, offers a potentially effective and cheaper alternative for pre-oxidation process. Parallel tests with or without the application of chlorine were conducted to evaluate the effect of chlorine dosage on the increase of trans-membrane pressure under low dosage of UV irradiation. The results showed that UV/chlorine pre-oxidation achieved remarkable reduction of both total membrane fouling (49%) and reversible membrane fouling (59%) at 4 mg/L dose of chlorine as a result of the removal of both high molecular weight (MW) (1–20 kDa) humic substances and lower MW compounds. Hybrid process of UV/chlorine and UF membrane achieved significant removal of DOC (34%) and UV254 (49%) at chlorine dosage of 4 mg/L and a UV dosage of 180 mJ/cm2. Modeling fit results indicated that the NOM-related membrane fouling mitigation was probably attributed to the alleviation of intermediate pore blocking and standard pore blocking with intermediate pore blocking playing a more important role. Additionally, the UV/chlorine unit could have a bright prospect for engineering application as it performed better in cost control as pretreatment prior to UF membrane compared to other pre-oxidation processes.