Aqueous phase degradation of methyl paraben using UV-activated persulfate method

- Aqueous phase MP degradation using UV/persulfate method was investigated.
- Degradation rate of MP followed pseudo-first-order kinetics.
- MP degradation was pH dependent.
- HCO3−, HPO42− and humic acid exhibited inhibitory effect on MP degradation.
- Hydroxylation and hydrolysis were possible pathways of degradation of MP.

Methyl paraben (MP), a widely used preservative, exhibits endocrine-disrupting properties with estrogenic activities. The aqueous phase degradation of MP, using UV-activated persulfate method, was investigated in the present study. The combination of UV irradiation and persulfate anion successfully degraded MP showing 98.9% removal within 90 min. A quenching experiment using ethanol (EtOH) and tert-butyl alcohol (TBA) showed the presence of both radicals (OH and SO4-) in the system; near neutral pH SO4- radical was the major species. The influence of various factors such as persulfate dose, initial MP concentration, solution pH, and water matrix components on the degradation kinetics was examined in view of the practical applications of the developed process. The degradation rate of MP was considerably increased as the amount of persulfate increased. The degradation of MP in the UV/persulfate system was pH dependent and more promising near neutral pH (6.5) conditions. The presence of anions such as Cl−, HPO42− and HCO3− showed inhibitory effect towards MP degradation. The presence of humic acid also suppressed the degradation efficiency of MP. The reaction rate followed pseudo-first-order kinetics for all of the degradations. The degradation of MP by UV/persulfate treatment led to the production of seven transformation byproducts, which were identified using ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS). A degradation pathway for MP degradation was also proposed. The results of the present study reveal that the UV/persulfate process could be an effective approach to remove MP from aqueous solutions.

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