New insights into the influence of pre-oxidation on membrane fouling during nanofiltration of brackish water considering inorganic-organic complexation and oxidant reduction byproducts

Abstract

Even though pre-oxidation is usually considered as a promising method to alleviate membrane fouling, information on performance and inner mechanisms of pre-oxidation-influenced membrane fouling during nanofiltration of brackish water is still limited. This study is the first work in which oxidant reduction byproducts and interaction between different pollutants were particularly considered to address these problems. Herein, nanofiltration experiments with different pre-oxidized synthesis brackish water containing inorganic salts and organic pollutants were conducted. Membrane flux results showed that both NaClO and K2FeO4 aggravated membrane fouling, but 0.45 mg/mg TOC KMnO4 mitigated it when simulation results of NICA-Donnan model showed that the complexation between calcium ions and humic acid (HA) was weakened. However, membrane fouling was enhanced by higher dosage of KMnO4. Fourier transform infrared spectrometer using attenuated total reflection (ATR-FTIR) and X-ray diffraction (XRD) spectrum showed that the aggravated membrane fouling was mainly caused by the generation of amorphous manganese oxide, which was oxidant reduction byproduct and had strong capacity for adsorption of HA. Particle size distribution and zeta potential variation indicated that the accumulation of HA could enhance the crystallization process and then the electrostatic attraction between membrane and bulk crystallization was induced. According to SEM images and fitting results of Hermia's models, the already-formed bulk crystallization by 1.90 mg/mg TOC KMnO4 could deposit on membranes more easily, followed by the formation of a denser fouling layer. Overall, the present study provided new insights into the design of reliable pre-oxidation strategies for alleviating membrane fouling during nanofiltration of brackish water.