Aging and Transformation of Polyethylene Microplasticsin UASB Effluents Treated with O3 and O3/H2O2: Physicochemical Changes and Toxicity Assessment

Wastewater treatment plants (WWTPs) represent a pathway for microplastics (MPs) to enter the environment, through direct discharge via effluents into surface waters or indirect release via sewage sludge applied to agricultural soils. This study demonstrates the effectiveness and safety of an O3/H2O2 process for aging polyethylene microplastics (PE-MPs) directly within a complex UASB reactor effluent. A characteristic FTIR peak at 1714 cm–1 confirms the formation of carbonyl groups, which indicates that the treatment caused significant surface degradation under optimal conditions (52.00 mg L–1 O3 and 100.00 mg L–1 H2O2 for 110 min). Crucially, the byproducts produced showed no acute toxicity to Artemia salina, demonstrating that the process was environmentally sound. Additionally, thermogravimetric analysis (TGA) revealed a counterintuitive increase in the polymer’s thermal stability, suggesting complex structural reorganization potentially driven by the removal of low-molecular weight fractions or cross-linking. Treated PE exhibited increased thermal stability, increasing from 436.18 to 449.35 °C, indicating that the remaining fragments are more thermally resistant and could therefore alter their subsequent fragmentation behavior. This work, therefore, validates a robust and safe strategy for MP remediation in realistic scenarios.