Abstract
This study in-situ modified a commercial nanofiltration membrane, NF90, through the concentration-polymerization-enhanced radical graft polarization method by applying two agents of 3-sulfopropyl methacrylate potassium salt (SPM) and 2-hydroxyethyl methacrylate (HEMA) with different dosages. Surface characterization revealed that the modified membranes became rougher and more hydrophilic compared with the pristine membrane. The modified membranes exhibited considerably enhanced separation performance with 5.8–19.6% higher NaCl rejection and 17.2–19.9% higher pharmaceuticals and personal care products (PPCPs) rejection than the pristine membrane. When treating the feedwater with high silica concentration, the modified membranes exhibited relatively less flux decline with high percentage of reversible fouling, especially the ones modified using a lower monomer concentration (0.01 M SPM and 0.01 M HEMA). Moreover, membrane modification enhanced the PPCP rejection (1.3–5.4%) after silica fouling by mitigating foulant deposition on the membrane surface. The fouling mechanism was confirmed to be intermediate blocking of membrane pores. Therefore, the in-situ modification technique with a low monomer concentration proved to be effective for mitigating silica fouling and improving PPCP rejection, which can be easily performed and cost-effective in practical application.
Highlights
Among various water treatment technologies, nanofiltration (NF) and reverse osmosis (RO) membrane separation have been widely applied for rejecting emerging contaminants, such as endocrine-disrupting compounds (EDCs) and pharmaceuticals (PhACs)/ pharmaceuticals and personal care products (PPCPs) [1], producing fresh water for drinking water supplies [2], wastewater reclamation [3], and desalination [4,5]
We conducted in-situ radical graft polymerization to modify a widely used commercial NF membrane (NF270) using low bulk concentrations of monomers (3-sulfopropyl methacrylate potassium salt (SPM) and 2-hydroxyethyl methacrylate (HEMA)) and initiators that could be increased on the membrane surface thanks to the inevitable concentration polarization of the rejected solutes on a dense membrane [16,17]
The filtration system and protocol have been reported in our published studies [16,17,19], and the schematic diagram and the detailed specifications are summarized in Figure S1 and Table S2 in Supplementary Materials
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. We conducted in-situ radical graft polymerization to modify a widely used commercial NF membrane (NF270) using low bulk concentrations of monomers (3-sulfopropyl methacrylate potassium salt (SPM) and 2-hydroxyethyl methacrylate (HEMA)) and initiators that could be increased on the membrane surface thanks to the inevitable concentration polarization of the rejected solutes on a dense membrane [16,17]. We adopted the technology of the concentration-polymerization-enhanced radical graft polarization method to modify a common commercial membrane (NF90) This technology is cost-effective, easy to operate with reproducibility, and can enhance separation performance of trace contaminant by the modified membranes. This study in-situ modified a commercial membrane (NF90) by using concentration-polarization-enhanced radical graft polymerization with two types of monomers (SPM and HEMA) to mitigate silica fouling. The mechanism of silica fouling was confirmed before and after membrane modification using the modified Hermia model
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