Pre-ozonation reduces DBP formation in microplastics/NOM systems: Mechanistic insights from surface properties and precursor degradation

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The coexistence of microplastics (MPs) and natural organic matter (NOM) in water sources poses significant challenges for disinfection by-product (DBP) control. This study investigated the influence of pre-ozonation on the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) within a coexisting system of polyethylene (PE) MPs and NOM. The results demonstrated that PE-MPs initially exerted an inhibitory effect on DBP formation through the physical adsorption of NOM precursors. Scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area characterization revealed that ozone induced obvious surface aging, including the formation of wrinkles, cracks, and network-like patterns, which enhanced the specific surface area and increased the number of active sites for precursor adsorption. In addition to the inhibition of DBP formation via the aging of MPs, excitation–emission matrix (EEM) fluorescence spectroscopy analysis confirmed that pre-ozonation enhanced this inhibitory effect by effectively degrading aromatic protein-like and fulvic acid-like substances within the NOM. Systematic evaluation of reaction parameters indicated that THMs and HAAs formation was highly sensitive to ozone dosage and pH, typically reaching a maximum under neutral conditions and moderate ozone levels (2.0 mg/L), while high ozone dosages promoted thorough oxidation and mineralization of reactive species. These findings suggest that pre-ozonation is a promising strategy for mitigating THMs and HAAs risks in waters contaminated with both MPs and organic matter by synergistically enhancing adsorption and precursor degradation.