Improving separation efficiency of various micropollutants from water by polymer-enhanced ultrafiltration using oxidized alginate featuring less viscous and low filtration resistance

Polymer-enhanced ultrafiltration (PEUF) is an economical and energy-efficient alternative using a versatile water-soluble polymer (WSP) to remove micropollutants by electrostatic interactions, which in turn allows size exclusion through ultrafiltration (UF) membranes due to the WSP being bigger than the pores of UF membranes. However, the WSP used in PEUF is so viscous that it inevitably causes significant filtration resistance and membrane fouling, reducing filtration and energy efficiency. To overcome this problem, in this study, sodium alginate (Alg), which can significantly remove cationic pollutants, was oxidized using sodium periodate to produce oxidized alginate (OxAlg). The retention and water flux profiles of OxAlg for three micropollutants, methylene blue (MB), ciprofloxacin (CIP), and tetramethylammonium hydroxide (TMAH), using the PEUF method were investigated in terms of pH, ionic strength, polymer, and pollutant amount. A comparison between Alg and OxAlg demonstrated 1.38%p–1.76%p higher MB retention rates (99.31%–99.97%) and up to 4.07 times higher water flux depending on the amount of polymer added. Furthermore, OxAlg displayed excellent retention rates of the NF level and 30–60 times higher water flux than typical NF. This outstanding OxAlg performance was mainly due to OxAlg's properties, such as low viscosity, accessibility stemming from flexibility, and appropriate size from the perspective of retention. Lastly, OxAlg was found to have the potential to surpass the existing WSP in that it showed a higher maximum retention capacity than about 560–1,250 mg/g in the real-world pH enrichment test even before the saturation.