Application of peroxymonosulfate-based advanced oxidation process as a novel pretreatment for nanofiltration: Comparison with conventional coagulation

Abstract

As a practical advanced oxidation process with high-efficiency, ferrous-activated peroxymonosulfate (PMS) technology has been extensively investigated and employed for the degradation of organic substances in water treatment process. However, to our best of knowledge, few studies in applying ferrous-activated PMS as the pretreatment for nanofiltration process have been conducted and the mechanisms of membrane fouling alleviation due to ferrous-activated PMS was still unclear. Consequently, ferrous-activated PMS approach was innovatively adopted as pretreatment for nanofiltration in present study, compared with the conventional pretreatment process (coagulation). The results indicated that both strategies could significantly mitigate organic fouling at membrane surface, but the gypsum scaling was enhanced when Fe(II)/PMS was adopted prior to nanofiltration process at the dose of 80/80 μM, because of the assistance of ferric ions and sulfate anions. ATR-FTIR spectra indicated that the greater alleviation of flux decline caused by Fe(II)/PMS oxidation was attributed to the less accumulation of organic substances on membrane surface, relative to the conventional Fe(III) coagulation. Furthermore, Xtended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was utilized to explain the greater interfacial free energy of adhesion (equal to decreased repulsion or increased attraction) between foulants and nanofiltration membranes in ferrous-activated PMS strategies joined nanofiltration process. Interestingly, Fe(II)/PMS oxidation could efficiently improve the quality of effluent in nanofiltration process, and three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM) spectra demonstrated that Fe(II)/PMS conferred higher removals of organic substances. The removal efficiency of Bisphenol A in Fe(II)/PMS assisted nanofiltration process varied from 53% to 78%, while only 5–12% Bisphenol A was removed in Fe(III) coagulation joined system. Besides, the potential mechanisms of flux decline caused by individual and combined organic substances were also investigated. Therefore, the findings in present study would contribute to the deep understanding of membrane fouling mechanism and promote the practical application of nanofiltration technologies.