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Chemical process-induced microplastic aging and its impact on coagulation-flocculation efficiency
Summary
Chemical and physical aging of polyethylene microplastics significantly alters their surface chemistry and morphology, with oxidative treatments like KMnO₄ boosting coagulation removal efficiency to 79% while methanol and H₂O₂ had neutral or inhibitory effects. Because environmental aging is ubiquitous, these findings reveal that real-world microplastic removal performance in water treatment may differ substantially from predictions based on pristine particles.
Coagulation is widely used to remove microplastics (MPs) from aquatic systems, yet its effectiveness for aged particles remains poorly understood. This study investigates how chemical, thermal, and physical aging alter polyethylene (PE) MPs and affect their removal during coagulation. The PE particles were subjected to chemical aging (HCl, NaOH, CH 3 OH, H 2 O 2 , KMnO 4 , Na 2 S 2 O 8 ), thermal aging (5, 25, 60 °C), and physical treatments (UV irradiation, ozonation, Fenton process, ultrasound) under varying pH conditions (3–11). Aging strongly influenced coagulation performance: efficiencies increased markedly for MPs aged in HCl, NaOH, KMnO 4 , and Na 2 S 2 O 8 , with KMnO 4 -treated particles achieving the highest removal (79%), while methanol and H 2 O 2 had neutral or inhibitory effects. SEM and LDIR imaging revealed morphological changes, including increased surface roughness, cracks, and reduced particle size. FTIR spectroscopy showed chemical modifications such as formation of carbonyl, hydroxyl, and C–O group formation, particularly after oxidative treatments such as ozonation. These structural and chemical changes enhanced particle reactivity, aggregation, and flocculation during coagulation. Multivariate analyses (PCA and Pearson correlation) demonstrated strong interdependencies between aging conditions, particle properties, and removal efficiency. In general, the results highlight that aging significantly modifies the physicochemical characteristics of MPs, increasing their reactivity and altering their behavior during water treatment. These findings emphasize the importance of evaluating coagulation and other removal technologies using aged microplastics to accurately assess treatment efficiency. and environmental risks. • Microplastic aging strongly influences removal efficiency during coagulation. • Oxidative aging (KMnO 4 , Na 2 S 2 O 8 ) increased PE removal up to 79%. • Surface oxidation and fragmentation enhanced microplastic flocculation. • Ozonation and UV improved removal, while ultrasound reduced efficiency. • Pristine microplastics underestimate real coagulation performance.