Combined fouling of forward osmosis membrane by alginate and TiO2 nanoparticles and fouling mitigation mechanisms

Abstract

Forward osmosis (FO) is a promising technology for water treatment, but its fouling mechanisms are poorly understood compared to other membrane-based processes. This study focuses on combined fouling caused by alginate (SA) and TiO2 nanoparticles, which serve as representative organic and inorganic foulants, respectively. The results show that the co-presence of TiO2 can effectively mitigate membrane fouling by SA under vas feed chemistries (Ca2+ concentrations). The negative charge of the SA foulants increased in the presence of TiO2, alleviating SA aggregation due to electrostatic and steric stabilization. The behavior and mechanisms of membrane fouling were characterized by attenuated total reflection-Fourier transformation infrared spectroscopy (ATR-FTIR) coupled with isothermal titration calorimetry (ITC) and atomic force microscopy (AFM) at the molecular level. Combined SA-TiO2 had a lower binding affinity to Ca2+ than single SA, which was spontaneously exothermic and dominated by electrostatic interaction to reduce membrane fouling. This study provides new insight into the mechanisms of nanoparticles-mediated organic fouling in the FO process. It also demonstrates that an integrated ATR-FTIR/ITC/AFM approach can provide useful information for understanding other complicated interactions between inorganic and organic foulants.