Co-Activation of Peroxymonosulfate Activation with Sunlight and Tailored Catalytic Mnfe2o4/Mwcnts Membrane to Mitigate Membrane Fouling Caused by Nom and Synergistic Oxidation Mechanism Analysis

Abstract

Membrane fouling has been a major factor hindering the development of ultrafiltration membranes. Herein, a novel in situ oxidation system was constructed via MnFe2O4/MWCNTs introduced into PVDF ultrafiltration membranes with sunlight to synergistically activate PMS to mitigate ultrafiltration membrane fouling. The mechanism of mitigating membrane fouling of MnFe2O4/MWCNTs-PVDF ultrafiltration membranes was systematically explored under four system (single filtration, single sunlight irradiation, single PMS oxidation and sunlight irradiation with PMS). The MnFe2O4/MWCNTs-PVDF catalytic membranes exhibited different fouling characteristics under the four systems, among which the sunlight irradiation synergistic MnFe2O4/MWCNTs catalytic membrane activated PMS oxidative filtration system possessed the highest HA removal efficiency of 90.2%, as well as the lowest Rr (0.2108 ×1012m-1) and Rir (0.4525×1012m-1). To further evaluate the practicality and effectiveness of the sunlight-MnFe2O4/MWCNTs-PMS system, the secondary effluent was selected to verify the treatment effect on NOM of natural water. By observing the microscopic morphology of the fouled membrane surface, it can be seen that compared with the other three filtration systems, the filter cake layer on the membrane surface of the synergistically activated PMS system was obviously reduced, and the structure of the filter cake layer was more loose. It can be conclued that the principle of the synergistically activated system to alleviate the membrane fouling was to accelerate the mineralization rate of HA molecules, oxidize the HA into a smaller particle size to pass through the membrane pores, and to reduce the probability of its plugging membrane pores. The main reactive oxygen species and HA degradation mechanism in the synergistic activation system were further revealed by electron paramagnetic resonance (EPR) analysis and density functional theory calculations (DFT). The results showed that the degradation of HA by the synergistically activated PMS system was a combination of free radicals (·O2−、SO4·− and ·OH) and non-free radicals (1O2). All things considered, the in-situ oxidation system provided an alternative way to alleviate ultrafiltration membrane fouling.

Keywords: Ultrafiltration, Membrane fouling, Peroxymonosulfate activation, Co-activation