Oxidation of a mixture of small aromatic compounds by UV/H2O2 in rainwater

• Autor(a) principal: Ferreira, Mónica Isabel Pinto Sousa
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/30153
• topic: Rainwater; Aromatic compounds; Oxidation; UV/H2O2 process; Optimization; Uniform design; Response surface model

Rainwater contains a large variety of contaminants, namely aromatic compounds, that should be removed if its utilization is intended for domestic purposes. The present work evaluates the degradation of a mixture of three small aromatic compounds (benzoic, 3,5-dihydroxybenzoic and syringic acids), by UV/H2O2, in model solutions and in rainwater. The extent of oxidation was assessed by ultraviolet-visible and molecular fluorescence spectroscopies. It was verified that, during the oxidation of the mixture, new chromophoric compounds are formed, possibly with higher degree of unsaturation and hydroxylation, and these compounds are, then, degraded. It was also demonstrated that, the increase of H2O2 concentration, results in a higher extent of oxidation. On the other hand, it was verified that the pH does not influence the oxidation of the mixture, at least for pH values in rainwater (between 4.0 and 7.0). The optimization of the oxidation of the mixture of contaminants by the UV/H2O2 process was performed through the utilization of the uniform design as experimental design, with the following factors: H2O2 concentration, pH, and reaction time. The response surface model corresponds to a second order polynomial, where the extent of oxidation is a function of the following variables: H2O2 concentration, reaction time, interaction between these two factors and their respective quadratic forms. The optimum region, which corresponds to an extent of oxidation of approximately 100 %, can be observed for a combination of values for the variables, where the optimum chosen corresponds to a lower H2O2 concentration (3.1 mM) and a maximum reaction time (4 h). The application of the optimal conditions to rainwater samples, spiked with a mixture of contaminants, resulted in an extent of oxidation higher than 99.5 %, suggesting that the model is applicable to real samples. The results obtained in this work suggest that the UV/H2O2 process can be used as an alternative for the treatment of rainwater, namely in what concerns the degradation of small aromatic acids.