title: Effect of silica fouling on the removal of pharmaceuticals and personal care products by nanofiltration and reverse osmosis membranes.
abstract: In this study, one reverse osmosis (XLE) and two nanofiltration (NF90 and NF270) membranes were fouled by silica to evaluate its effect on the flux decline as well as the removal of six pharmaceuticals and personal care products (PPCPs) including carbamazapine (CBZ), triclosan (TRI), ibuprofen (IBU), sulfadiazine (DIA), sulfamethoxazole (SMX) and sulfamethazine (SMZ) from pH 3 to 10. The membranes were characterized by physicochemical properties including hydrophobicity, surface morphology and PPCPs adsorption with or without the presence of silica fouling to validate the rejection mechanisms of PPCPs. The fouling mechanisms were investigated using the modified Hermia model. It was found that all membranes with silica fouling showed more severe permeate flux decline at low pHs (3 and 5) than at high pHs (8 and 10) by the decomposition of nonionized silica particles to form a dense gel layer on membrane surfaces, which was hard to be removed by backwash. Silica fouling rendered the membrane surface considerably more hydrophilic, and only IBU, TRI and SMZ were adsorbed on membranes. Silica fouling on tight membranes (NF90 and XLE) can promote rejection of most PPCPs because the dense fouling layer could supply membrane with synergistic steric hindrance to reduce the transportation of PPCPs across membrane surface, implying that size exclusion is the dominating mechanism. While for loose NF270, electrostatic repulsion dominates by enhanced rejection of PPCPs as pH increased. Although fouling layer could provide extra steric hindrance for NF270, its effect was overwhelmed by the accompanied cake-enhanced concentration polarization phenomenon (CEOP). CEOP impeded back diffusion of PPCPs into the feed solution, trapped and accumulated PPCPs on membrane surface so as to increase their diffusion across membrane. At all pH levels, intermediate blocking and gel layer formation was the major fouling mechanism for tight and loose membrane, respectively.
authors.affiliation: Department of Safety, Health and Environmental Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung 824, Taiwan, ROC. Electronic address: yililin@ntu.edu.tw.
authors.forename: Yi-Li
authors.initials: YL
authors.lastname: Lin
authors.affiliation: Department of Safety, Health and Environmental Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung 824, Taiwan, ROC.
authors.forename: Jheng-Hong
authors.initials: JH
authors.lastname: Chiou
authors.affiliation: Department of Safety, Health and Environmental Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung 824, Taiwan, ROC.
authors.forename: Chung-Hsiang
authors.initials: CH
authors.lastname: Lee
mesh_terms: D019544:Equipment Failure Analysis / Q000379:methods; D006795:Household Products; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008567:Membranes, Artificial; D009995:Osmosis; D004364:Pharmaceutical Preparations / Q000032:analysis / Q000302:isolation & purification*; D012822:Silicon Dioxide; D013499:Surface Properties; D014462:Ultrafiltration / Q000379:methods; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000302:isolation & purification*; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*
chemical_list: D008567:Membranes, Artificial; D004364:Pharmaceutical Preparations; D014874:Water Pollutants, Chemical; D012822:Silicon Dioxide
keywords: Electrostatic repulsion; Hydrophobicity; Modified Hermia model; Pharmaceuticals and personal care products (PPCPs); Silica fouling; Steric hindrance