Remoção da etilenotioureia em água através de processos oxidativos avançados: avaliação dos intermediários e mecanismos de degradação

• Ano de defesa: 2016
• Autor(a) principal: Sue Ellen Costa Bottrel
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Etilenotioureia; Ozonização; Produtos de degradação; Oxidação; Meio ambiente; Engenharia sanitária
• Link de acesso: http://hdl.handle.net/1843/BUBD-AW5L8A

This work evaluated the oxidation of ethylenethiourea (ETU), the main toxic by-product from the degradation of pesticides of the group of ethylene-bis-dithiocarbamates, among which can be highlighted the Mancozeb. Firstly, using the Zahn-Wellens test it was evaluated the influence of the ETU (50 mg.L-1) on the aerobic biodegradation of glucose. Results showed that the ETU was not degraded and there was a decrease in glucose degradation rate, indicating possible inhibitory effect of ETU on the biological activity of aerobic microorganisms. Then, it was evaluated other ways for the oxidation of the ETU (50 mg.L-1): ozonation process and its variants (ozonation with UV-C light and ozonation with H2O2); solar photo Fenton and photo Fenton with iron oxalate complex. All these advanced oxidative process (AOP) systematically presented more than 90% in the degradation of the ETU in aqueous solution, nevertheless the complete mineralization of the contaminant was not observed in ozonation at free pH and in ozonation at a pH equal to 9. The better results were obtained in: ozonation process at a pH equal to 7, in which 70% of the ETU was mineralized in the time course of 60 minutes; solar photo Fenton, in which 85% of the ETU was mineralized in the time course of 5 hours. We also evaluated the by-products of the ozonation process and its variant with UV-C light. The intermediate compounds elucidated via Ultra Performance Liquid Chromatography / Time of Flight / Mass Spectrometry differ according to the pH used in the process of ozonation. The alkaline pH favored the degradation of ETU via ethylene urea, which sharply degraded to byproducts unidentified. In the ozonation process conducted at free pH (in which decreased to approx. 3 in the course of the first minutes) and at pH equal to 7, we detected compounds like IM-SO e IM-SO3, but also ETU. The kinetic study of ETU degradation by O3 showed that the direct reaction exerts the greatest influence on the contaminant degradation rate in the evaluated conditions.