Visible light photocatalysis alleviates ceramic membrane fouling caused by intracellular organic matter of Microcystis aeruginosa

Abstract

Ultrafiltration (UF) is an effective technology for treating algae-containing water. The algal intracellular organic matter (IOM) released by dead algae during an excessive algae growth phase causes more serious membrane fouling than viable algal cells and algal extracellular organic matter (EOM), which seriously restricts stable operation of UF. This paper studied the removal of IOM by a Bi2O3–TiO2/PAC (Bi-doped TiO2 nano-composites supported by powdered activated carbon) photocatalytic oxidation-ceramic ultrafiltration membrane, the inhibitory effect of membrane fouling at different photocatalytic oxidation times, and the fouling mechanism. The results show that both the adsorption and photocatalytic oxidation of Bi2O3–TiO2/PAC can significantly remove proteinoids and humic acid-like fluorescent components present in IOM, with removals of UV254 and DOC reaching up to 81.8% and 44.0%. The generated superoxide radicals and hydroxyl radicals positively affect the degradation of organic compounds of various molecular weights, and holes mainly degrade acidic low-molecular weight organic compounds. When the photocatalytic oxidation time was extended to 60 min, the membrane flux increased by 70.7% and the reversible resistance and irreversible resistance decreased by 83.4% and 90.1%, respectively. Under these conditions, the fouling mechanism changed from complete blockage to intermediate blockage. In the late stage of photocatalytic oxidation (90–120min), part of the high and medium molecular weight organic components were oxidized to produce low-molecular weight organic compounds (LMW acidic and neutral organic compounds), and blockage of filter cake became the main fouling mechanism. After photocatalysis, the zeta potential decreases significantly and the interaction forces between pollutants and pollutants are transformed into repulsive forces. Application of an appropriate photocatalytic oxidation time can alleviate the ultrafiltration membrane fouling caused by algal-derived organics.