Degradation of 17β-estradiol in aqueous solution by ozonation in the presence of manganese(II) and oxalic acid

Abstract

Natural estrogens, such as 17β-estradiol (E2), are the main substances responsible for estrogenic activity found in domestic sewage. In the work described herein, the degradation of E2 has been investigated by single ozonation and catalytic ozonation in the presence of manganese ion (Mn²⁺) and oxalic acid. The presence of Mn²⁺ and oxalic acid in the ozonation processes significantly improved the E2 degradation and, hence, the reduction of estrogenic activity in aqueous solution. The addition of Mn²⁺ and oxalic acid produced many more hydroxyl radicals in the catalytic ozonation system than in the single ozonation system. Oxidation products formed during ozonation of E2 have been identified by means of gas chromatography–mass spectrometry (GC-MS), on the basis of which a possible reaction pathway for E2 degradation by ozonation is proposed. E2 was first oxidized to hydroxyl-semiquinone isomers, and these were subsequently degraded to low molecular weight compounds such as oxalic acid and malonic acid. The latter were easily oxidized by ozone to form carbon dioxide (CO₂). The results demonstrate that the ozonation–Mn²⁺–oxalic acid system may serve as a powerful tool for removing E2, and the addition of Mn²⁺ and oxalic acid is favourable for the complete removal of estrogenic activity induced by steroid estrogens in aqueous solution.

Keywords:

• catalytic ozonation
• 17β-estradiol (E2)
• hydroxyl radicals
• manganese ion
• degradation pathway

Acknowledgements

This study was sponsored by the National Natural Science Foundation of China (Grant No. 21107097) and the Natural Science Foundation of Zhejiang Province (Grant No. Y5110118).