Degradation of melatonin by UV, UV/H 2O 2, Fe 2+/H 2O 2 and UV/Fe 2+/H 2O 2 processes

Abstract

Melatonin is a hormone, which may suppress the production of testosterone, decrease semen quality, and affect sexual activity and reproduction of animals and humans. Degradation of melatonin in aqueous solutions were investigated and compared by different advanced oxidation processes, including ultraviolet radiation (UV) alone, ultraviolet radiation assisted by hydrogen peroxide (UV/H 2O 2), Fenton's reagents (Fe 2+/H 2O 2), and combination of Fenton's reagent with UV light (photo-Fenton, UV/H 2O 2/Fe 2+). The experiments were conducted in a laboratory-scale batch photoreactor equipped with a 8 W low-pressure mercury lamp. The degradation of melatonin by all these processes was found to follow pseudo-first-order reaction kinetics. The effect of pH on the degradation of melatonin in the UV irradiation process was studied, and found that removal efficiencies of melatonin were 18%, 28% and 32% at 60 min and the rate constants were 0.0018, 0.0030 and 0.0048 min −1 at pH value of 4.0, 7.0 and 10.0, respectively. The degradation efficiency of melatonin was greatly enhanced by UV/H 2O 2 process. Furthermore, effects of operating parameters (pH and concentrations of Fe 2+ and H 2O 2) on the degradation of melatonin by Fenton's reagent were investigated, and the degradation of melatonin was more efficient by Fenton's reagent than by UV/H 2O 2 process. The fastest degradation of melatonin and highest TOC removal was achieved by UV/Fe 2+/H 2O 2 process among the four different processes tested.