Photocatalysis-coagulation to control ultrafiltration membrane fouling caused by natural organic matter

Abstract

Various pretreatments of raw surface water before ultrafiltration (UF) to retard membrane fouling due to natural organic matter (NOM) were compared in this study. Water treatment by conventional coagulation, visible light irradiation with the presence of a novel photocatalyst of Bi2O3–TiO2 supported onto powder activated carbon (Bi–Ti/PAC), and their combination were compared in terms of removal of NOM and the optimal conditions were determined. The composite nano-photocatalyst of Bi–Ti/PAC could function as a pre-oxidant and a flocculation core assisting coagulation. Experiments results show that 58% of the NOM present could be removed by quantization of dissolved organic carbon in the combination treatment under optimal conditions of 2.0 g/L of photocatalyst dosage with light exposure of 20 min and 0.04 mmol polyaluminium chloride coagulant dosage with a solution pH of 7. The combined pretreatment with UF produced a reduction of 88% in total membrane fouling, with reversible and irreversible fouling being significantly decreased because of the removal of hydrophilic, protein- and humic-like substances, along with degradation and removing of medium-molecular weight (MW) and high-MW compounds into smaller molecules. Models used to fit the generated data indicated that the provided combined pretreatment had largely reduced standard blocking of the membrane pores. The effectiveness of the pretreatment was confirmed by characterization of the hydraulic irreversible organic foulants. This work demonstrated the potential advantages of combining photocatalysis with coagulation as a pretreatment of raw surface water and subsequent UF in simultaneously controlling membrane fouling and improving the permeate quality.