Comparison of UV/hydrogen peroxide and UV/peroxydisulfate processes for the degradation of humic acid in the presence of halide ions

This study compared the behaviors of two classic advanced oxidation processes (AOPs), hydroxyl radical-based AOPs (^•OH-based AOPs) and sulfate radical-based AOPs (SO₄ ^•−-based AOPs), represented by UV/ hydrogen peroxide (H₂O₂) and UV/peroxydisulfate (PDS) systems, respectively, to degrade humic acid (HA) in the presence of halide ions (Cl⁻ and Br⁻). The effects of different operational parameters, such as oxidant dosages, halide ions concentration, and pH on HA degradation were investigated in UV/H₂O₂/Cl⁻, UV/PDS/Cl⁻, UV/H₂O₂/Br⁻, and UV/PDS/Br⁻ processes. It was found that the oxidation capacity of H₂O₂ and PDS to HA degradation in the presence of halides was nearly in the same order. High dosage of peroxides would lead to an increase in HA removal while excess dosage would slightly inhibit the efficiency. Both Cl⁻ and Br⁻ would have depressing impact on the two AOPs, but the inhibiting effect of Br⁻ was more obvious than that of Cl⁻, even the concentration of Cl⁻ was far above that of Br⁻. The increasing pH would have an adverse effect on HA decomposition in UV/H₂O₂ system, whereas there was no significant impact of pH in UV/PDS process. Furthermore, infrared spectrometer was used to provide the information of degraded HA in UV/H₂O₂/Cl⁻, UV/PDS/Cl⁻, UV/H₂O₂/Br⁻, and UV/PDS/Br⁻ processes, and halogenated byproducts were identified in using GC-MS analysis in the four processes. The present research might have significant technical implications on water treatment using advanced oxidation technologies.