Comparative Study of UV-Based AOPs for Degradation of Hydrophilic Ribavirin and Hydrophobic Chloroquine Phosphate: Performance, Radical Pathways, EEO, and Water Matrix Effects

Ribavirin (RBV) and chloroquine phosphate (CQP) are two typical pharmaceutical contaminants with distinct hydrophilic (RBV) and hydrophobic (CQP) properties. This polarity contrast led to markedly different degradation behaviors. Interestingly, hydrophobic CQP consistently degraded faster and with lower EEO than hydrophilic RBV across all combined systems, highlighting pollutant polarity as a key determinant. This study systematically compared their degradation by three UV-based advanced oxidation processes (UV/AOPs): UV/H2O2, UV/PMS, and UV/KMnO4. Degradation kinetics, electrical energy per order (EEO), radical pathways, and water matrix effects were investigated. Sole UV or sole oxidant achieved negligible removal (<7.2%). All UV/AOPs greatly enhanced degradation in a dose-dependent manner. At equal molar oxidant concentration (0.2 mM), the efficiency order was UV/PMS > UV/H2O2 ≫ UV/KMnO4, with the gap widening at higher dosages. UV/H2O2 exhibited the best overall performance, with remarkably low EEO values (0.59 kWh/m3 for RBV and 0.46 kWh/m3 for CQP at 0.2 mM), whereas UV/PMS showed faster kinetics but much higher energy consumption (e.g., 28.67 kWh/m3 for RBV and 28.60 kWh/m3 for CQP at 0.4 mM) and secondary pollution risks. UV/KMnO4 had low energy but poor degradation. Radical quenching experiments revealed that in UV/H2O2, hydroxyl radicals (•OH) predominantly drove degradation regardless of pollutant polarity. In UV/PMS, •OH primarily drove RBV degradation, while CQP removal involved the combined action of •OH, sulfate radicals (SO4•−), and other reactive species. For the optimal UV/H2O2 process, acidic pH (5.0) favored degradation; Cl− slightly promoted CQP removal but inhibited RBV, whereas SO42−, CO32−, and HCO3− suppressed both pollutants. Collectively, UV/H2O2 is recommended as the most energy-efficient and robust UV/AOP for treating both hydrophilic and hydrophobic pharmaceuticals, with the additional insight that pollutant polarity governs both degradation kinetics and radical mechanisms.