Oxidative Degradation of the Microcontaminant 2,6-Dichlorobenzoquinone by UV: Effect of H2O2 Dosage on Water Quality

Halogenated disinfection by-products such as 2,6-dichlorobenzoquinone (DCBQ) are emerging microcontaminants of concern due to their persistence and toxicity in aquatic environments. This study evaluated the oxidative degradation of DCBQ under UV irradiation, focusing on the effect of H2O2 dosage on removal efficiency and water quality. Batch experiments were conducted with H2O2 concentrations ranging from 0.0 to 10.0 mM. Kinetic analysis revealed that photolysis with UV alone followed an apparent order of 1.5, while the UV/H2O2 system showed an order of 2.5, reflecting the contribution of hydroxyl radicals and their dependence on both DCBQ and H2O2 concentrations. Color evolution displayed a series reaction behavior: the initial formation of chromophoric by-products followed first-order kinetics, whereas their subsequent removal proceeded with zero-order kinetics, consistent with radical-driven decolorization. Optimal performance was achieved with 1.0–2.0 mM H2O2, which promoted rapid DCBQ decay and significant reductions in aromaticity and color (100% in 2 h), whereas higher concentrations (10.0 mM) led to radical scavenging and lower efficiency. Dissolved oxygen increased during treatment, confirming oxidative pathways, while turbidity remained stable between 1 and NTU. These results demonstrate the effectiveness of UV/H2O2 for DCBQ removal and highlight the value of kinetic modeling in optimizing advanced oxidation processes for water treatment.