Mechanism of the Hybrid Pre-ozonation and CNTs Pre-deposition Technology for Fouling Control

To investigate the impact of the hybrid pre-ozonation and carbon nanotube (CNTs) pre-deposition technology on fouling control, humic acid (HA) and sodium alginate (SA) were selected as model pollutants. The fouling mechanism was systematically analyzed with the transformation of normalized flux, Hermia model, conventional cake-layer fouling filtration model, and the changes of foulants' physicochemical properties. The results demonstrated that the electronegativity and hydrophilicity of HA and SA were further enhanced after pre-ozonation, and the ozone-induced micro-flocculation increased their nano-particle size. Pre-ozonation displayed limited effect on membrane fouling caused by HA, as the membrane pores were completely blocked since their approaching particle size of ozonated HA and the pore size of membrane, which aggravated the fouling. Ozone could destroy the gel properties and remarkably alleviated the cake-layer fouling caused by SA. After CNTs pre-deposition on membrane with different pore size, the CNTs layer could intercept the HA and SA molecules and alleviated the membrane fouling. The denser layer formed by CNTs on the PVDF membrane with pore size of 0.45 μm, alleviated membrane fouling to the greatest extent. With a higher amount of CNTs loading, the combination of pre-ozonation and CNTs pre-deposition could effectively alleviate the membrane fouling induced by HA. As for the SA, the hybrid technology played an outstanding role on fouling control. It effectively reduced the formation of cake layer, and prolonged the pore blocking time, and increased the transition stage from pore blocking to cake filtration as well.