Degradation of ibuprofen by the UV/chlorine/TiO2 process: Kinetics, influencing factor simulation, energy consumption, toxicity and byproducts

UV/chlorine is an effective process for pollutant degradation in water treatment. It was reported that the concentrations of hydroxyl radical (HO center dot) and chlorine radical (Cl center dot) could rise significantly by adding TiO2 in UV/ chlorine. In this study, the degradation of ibuprofen (IBP), a frequently detected pollutant in aquatic environments, was investigated in the UV/chlorine/TiO2 process. The pseudo-first-order kinetics rate constant for IBP degradation by UV/chlorine/TiO2 was nearly 3-fold higher than the sum of the rate constant by UV/chlorine and UV/TiO2. HO center dot and Cl center dot were the primary radicals and chlorine oxide radical (ClO center dot) also participated in the degradation of IBP in UV/chlorine/TiO2. The kinetic model was used to assess the effect of different influencing factors (chlorine, chloride, and bicarbonate dosage, and pH) on degradation kinetics and radical roles. Meanwhile, the probe experiment with nitrobenzene was performed to evaluate the reliability of the modeling results. The electrical energy per order (EE/O) was determined under varied chlorine and TiO2 dosage, and the lowest EE/O of UV/chlorine/TiO2 was obtained to be about 40% and 50% of that of UV/chlorine and UV/TiO2, respectively. Toxic products could be generated during IBP degradation in all three processes, while less reaction time was needed for the removal of solution toxicity by UV/chlorine/TiO2. When achieving IBP degradation by one order of magnitude, less disinfection byproducts were generated in UV/chlorine/TiO2 compared with UV/ chlorine both with and without 24 h post-chlorination. Furthermore, a chlorine-substituted product of IBP was detected, and both HO center dot and Cl center dot participate in the formation of this product based on density functional theory (DFT) study.

Automated summary

This study investigated the degradation of ibuprofen (IBP) in the UV/chlorine/TiO2 process. The results showed that this process had a significantly higher degradation rate than UV/chlorine and UV/TiO2, and it could remove solution toxicity more quickly. Additionally, the process generated fewer disinfection byproducts compared to UV/chlorine.