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Azithromycin and Clarithromycin degradation kinetics present in WWTP effluents applying the homogeneous and heterogeneous photo-Fenton process

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Author(s):
Matheus Gabriel Guardiano dos Santos
Total Authors: 1
Document type: Master's Dissertation
Press: Araraquara. 2023-08-28.
Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
Defense date:
Advisor: Raquel Fernandes Pupo Nogueira
Abstract

The presence of antibiotics in effluents from wastewater treatment plants (WWTP) after a conventional process has received great attention due to problems that these contaminants can cause both to the environment and to human health, such as bacterial resistance. The present work studied the degradation kinetics of two macrolide antibiotics, azithromycin (AZT) and clarithromycin (CLA), by Fenton process in homogeneous and heterogeneous medium and compared it with sulfamethoxazole (SMX) degradation, belonging to sulfonamides class. Analytical methods were developed and validated for simultaneous separation and quantification of macrolides, separately from SMX quantification method. The formation of iron and copper complexes with macrolides and the complexation influence on the Fe(II)/Fe(II) and Cu(I)/Cu(II) redox cycle was evaluated using spectrophotometry. Pharmaceuticals degradation was performed in ultrapure water and WWTP effluent containing 1% acetonitrile due to the low solubility of macrolides. Pharmaceuticals concentrations were monitored by high performance liquid chromatography (HPLC) and their transformation products were identified through the coupling of HPLC with a mass spectrometer. For heterogeneous process degradation, catalysts based on copper and iron oxide were used. The formation of iron and copper complexes with the macrolides was verified with reducing effect of the macrolides on Cu(II), generating Cu(I) complexes in solution. Although the complexes of macrolides with Fe and Cu influenced the redox cycle, only the copper complexes showed a recalcitrant behavior to the homogeneous photo-Fenton process. Among the catalysts used in the heterogeneous process, it was observed that the increase in copper content during the synthesis contributed to the surface area of CAT1 being greater than that of CAT2, resulting in a greater activity of CAT1. Variation in pH affected macrolide degradation, as well initial H2O2 concentration. The best results of heterogeneous photo-Fenton process application were obtained using 0.125 g L-1 of CAT1, 15 mmol L-1 of H2O2 at pH 5.4. In all processes (homogeneous and heterogeneous media) the degradation constant of SMX was higher than that of macrolides, indicating greater recalcitrance of AZT and CLA. Experiments carried out on the WWTP effluent showed that the matrix did not influence AZT and CLA degradation, however it affected SMX degradation. The matrix interfered with SMX degradation because it occurs by combining the mechanisms of electrophilic addition with abstraction of the hydrogen atom and electronic transfer, while the macrolides were less affected due to the degradation occurring by electronic transfer only. The transformation products identification revealed the formation of hydroxylated products for both macrolides. Experiments carried out in the presence of hydroxyl radical scavengers showed the importance of •OH in macrolides degradation. SMX degradation was not completely inhibited because it does not depend only on •OH, but also on other radicals such as HO2•, O2•- and 1O2. The obtained results contribute to the understanding of the degradation mechanism and the recalcitrance of macrolide antibiotics to the Fenton process. (AU)

FAPESP's process: 21/06348-5 - Degradation kinetics of azithromycin and clarithromycin present in sewage effluents by heterogeneous photo-Fenton process
Grantee:Matheus Gabriel Guardiano dos Santos
Support Opportunities: Scholarships in Brazil - Master