Enhanced Degradation of Wastewater Pollutants by Synergistic Oxidation System Under Continuous Dosing: Mechanism Investigation Using Phthalate as a Model Compound

Phthalate acid esters (PAEs) are persistent organic pollutants (POPs) widely prevalent in industrial wastewater, posing significant threats to both ecological environments and human health. Although Advanced Oxidation Processes (AOPs) are recognized as efficient technologies for PAE degradation, conventional synergistic systems typically employ a simultaneous dosing mode. This approach often leads to the instantaneous quenching of excess radicals, low oxidant utilization, and imbalanced degradation kinetics. Despite its critical role in determining efficiency and costs, the dosing strategy remains an overlooked factor in current research. In this study, dimethyl phthalate (DMP) was selected as the target pollutant to evaluate a synergistic FeSO4/H2O2/K2S2O8 system. An innovative continuous dosing strategy was implemented to optimize radical utilization. A laboratory-scale continuous flow apparatus was developed to simulate industrial onsite conditions, enabling a systematic comparison of degradation kinetics, mineralization characteristics, and radical evolution between the two dosing modes. Results indicated that the degradation rate constant for the continuous dosing system reached 0.659 h−1, representing a 21.1% increase over the simultaneous dosing system (0.544 h−1). Electron Paramagnetic Resonance (EPR) analysis confirmed that the continuous dosing mode maintains a sustained and stable radical flux (•OH and SO4•−) during the critical mid-stage of the degradation, effectively mitigating radical–radical quenching. When applied to real industrial wastewater (salinity: 2083 mg/L), the continuous dosing system achieved a Total Organic Carbon (TOC) removal efficiency of 86.0% at ambient temperature and initial raw water pH, outperforming the simultaneous dosing system (82.0%). GC-MS analysis further confirmed the thorough mineralization of complex organic compounds, especially those containing ester groups and aromatic rings. This research addresses a critical gap in dosing strategy studies, providing an efficient, cost-effective, and industrially viable solution for recalcitrant wastewater treatment while establishing a theoretical foundation for large-scale continuous dosing applications.