Optimization of naproxen and ibuprofen removal in photolysis using a Box–Behnken design: Effect of Fe(III), NO₃⁻, and humic acid

Abstract

This study investigated the roles and optimum conditions of four independent variables [ultraviolet (UV) intensity, Fe(III), NO₃ ⁻, and humic acid (HA) concentration] in the photolytic removal of naproxen (NPX) and ibuprofen (IBP) in water using a response surface method based on the Box–Behnken design. Lab-scale experiments used analysis of variance and t-test statistics to test the significance of independent variables and their interactions. Predicted levels of NPX and IBP removals were found to be in good agreement with experimental levels (R² = 0.9891 for NPX and 0.9936 for IBP). UV intensity and HA were the most positively and negatively significant variables (P < 0.001), respectively. However, Fe(III) and NO₃ ⁻ ions had a less significant impact (P > 0.05). This result implies that NPX was removed by both direct photolysis (photons) and indirect reaction (OH radical), while IBP was removed mainly by the OH radical. NPX was more susceptible to the OH radical than IBP (k_OH/NPX = 8.24 × 10⁹ M⁻¹s⁻¹ and k_OH/IBP = 7.51 × 10⁹ M⁻¹s⁻¹). According to a quadratic regression model, the predicted maximum removal efficiencies for NPX and IBP were 71.66% and 63.58% when the predicted optimum ratio of UV (mW cm⁻²):Fe(III) (mg/L):NO₃ ⁻ (mg/L):HA (mg/L) was 6.3:0.94:0:0 and 6.3:0.94:20:0, respectively, which was similar to the respective experimental NPX and IBP removal values of 70.21% and 62.16%.

Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Environmental Science and Health, Part A, to view the supplemental file.

Keywords:

• Pharmaceutical
• photolysis
• OH radical
• response surface methodology
• competition kinetics

Acknowledgments

This work was supported by the BK21Plus project funded by the National Research Foundation (NRF) funded by the Ministry of Education, Science and Technology of Korea (No. 22A20130012682), and by the Korea Ministry of Environment, GAIA Project (No. 2012000550022).