Degradation kinetic of dibutyl phthalate (DBP) by sulfate radical- and hydroxyl radical-based advanced oxidation process in UV/persulfate system

The ultraviolet/persulfate (UV/PS) process was used to degrade dibutyl phthalate (DBP) at different reaction conditions and a steady-state kinetic model was established based on the elementary reactions involved as well. UV/PS process, which can generate both sulfate radical (SO4−) and hydroxyl radical (HO) proved by the evidence that methanol had a larger inhibition impact on the degradation than tert-butyl, could effectively degrade DBP. The second-order rate constant of (1.2 ± 0.1) × 108 M−1 s−1 between DBP and SO4− and the second-order rate constant of (6.3 ± 0.1) × 109 M−1 s−1 between DBP and HO were determined by competition kinetics. The degradation efficiency of DBP was affected by PS dosage, initial DBP concentration, solution pH value, natural organic matter (NOM) and inorganic anions. Increasing PS dosage could enhance the degradation of DBP before PS dosage reaching 1.6 mM. However, the pseudo-first-order rate constants (ko) decreased as initial DBP concentration increased probably owing to the radical scavenging effect of DBP. Generally, the ko value decreased slightly at pH values ranged from 4.0 to 6.0 while decreased significantly as pH increased from 6.0 to 8.0, which might be due to the scavenging effect on SO4− and HO by OH− and increasing concentration of HPO42- (with higher scavenging capacity than H2PO4-) from the phosphate buffer with rising pH value. NOM and HCO3- showed an inhibition effect on the degradation of DBP through quenching SO4− and HO. However, Cl− had a dual role on the degradation of DBP in the UV/PS system, which enhanced the degradation at lower concentration (0–1 mM) and suppressed as Cl− concentration further increased to 2 mM. Additionally, a simple steady-state kinetic model involving SO4− and HO was developed to simulate the ko values and the radical contributions in this reaction system. Generally, HO had a higher contribution to DBP degradation than SO4−. The total cost including the electrical energy per order and oxidant cost was increased with increasing PS dosage and the oxidant cost was the major one. The results in this study can serve as a guide and indicate that UV/PS process is feasible for the treatment of water contaminated with DBP.