Carmem Lúcia de Paiva e Silva Zanta

Surfactant degradation by a catechol-driven Fenton reaction

The addition of 0.5mM catechol is shown to accelerate the degradation and mineralization of the anionic surfactant DowFax 2A1 (sodium dodecyldiphenyloxide disulfonate) under conventional Fenton reaction conditions (Fe(II) plus H(2)O(2) at pH 3). The catalytic effect causes a 3-fold increase in the initial rate (up to ca. 20 min) of conversion of the surfactant to oxidation products (apparent first-order rate constants of 0.021 and 0.061 min(-1) in the absence and presence of catechol, respectively). Although this catalytic rate increase persists for a certain amount of time after complete disappearance of catechol itself (ca. 8 min), the reaction rate begins to decline slowly after the initial 20 min towards that observed in the absence of added catechol. Total organic carbon (TOC) measurements of net mineralization and cyclic voltammetric and high performance liquid chromatographic (HPLC) measurements of the initial rate of reaction of catechol and the surfactant provide insight into the role of catechol in promoting the degradation of the surfactant and of degradation products as the eventual inhibitors of the Fenton reaction.

Mechanistic implications of zinc(II) ions on the degradation of phenol by the fenton reaction

A study of the interference of Zn2+ ions on phenol degradation by Fenton reaction (Fe2+/Fe3+ + H2O2) is reported. One of the first intermediates formed in the reaction, catechol, can reduce Fe3+ to Fe2+ and, in the presence of H2O2 initiates an efficient catalytic redox cycle. In the initial stages of the reaction, this catechol-mediated cycle becomes the principal route of thermal degradation of phenol and its oxidation products. The Zn2+ ion addition enhances the persistence time of catechol, probably by stabilization of the corresponding semiquinone radical via complexation.

Interference of inorganic ions on phenol degradation by the Fenton reaction

The addition of Cu2+ ions to the classical Fenton reaction (Fe2+ plus H2O2 at pH 3) is found to accelerate the degradation of organic compounds. This synergic effect causes an approximately 15 % additional reduction of the total organic carbon (TOC), representing an overall improvement of the efficiency of the mineralization of phenol. Although Fe2+ exhibits a high initial rate of degradation, the degradation is not complete due to the formation of compounds refractory to the hydroxyl radical. The interference of copper ions on the degradation of phenol by the Fenton reaction was investigated. In the presence of Cu2+, the degradation is slower, but results in a greater reduction of TOC at the end of the reaction (t = 120 min). In the final stages of the reaction, when the Fe3+ in the solution is complexed in the form of ferrioxalate, the copper ions assume the role of the main catalyst of the degradation

Efficiency and toxicity: comparison between the Fenton and electrochemical processes

This study aimed to determine the best method to treat a textile effluent containing the dye basic blue 99 (BB). Treatments by the electrochemical and the Fenton processes were compared by means of a 2(3) experimental design, and the interaction of experimental conditions for BB oxidation were determined. The electrochemical treatment gave better results in the presence of NaCl as electrolyte and high current density (30 mA cm(-2)); the Fenton reaction provided better results at H2O2 and Fe(2+) concentrations of 10 mg L(-1) and 0.5 mmol L(-1), respectively. Electrochemical treatment was 23 times faster than the Fenton reaction because formation of chlorinated species during electrooxidation significantly contributed to dye oxidation. Although the electrochemical process was more efficient, the resulting treated effluent was more toxic to Lactuca sativa germination and growth, which indicated some biotoxicity. Results demonstrated that both processes efficiently remediated effluents containing the dye BB, but they need to be combined with other processes to ensure complete adequacy of the effluent for disposal.

The Oxidation Efficiency of Commercial, Electrogenerated and Electrogenerated In Situ Hypochlorite

No sistema de tratamento de agua a cloracao e a etapa mais importante, tanto no tratamento de residuos secundarios persistentes, quanto na garantia da qualidade da agua em toda a rede de abastecimento. Os inconvenientes da cloracao sao a necessidade de transporte, armazenamento e manipulacao de produtos perigosos. Nesse caso, a geracao eletroquimica de hipoclorito no local diminui com vantagens esses inconvenientes. Dentro desse contexto, nesse estudo avaliou-se o poder de oxidacao do hipoclorito comercial e do eletrogerado na oxidacao do corante vermelho reativo 195 (VR195). Avaliou-se tambem, a eficiencia da eletrogeracao de hipoclorito in situ contendo o corante. O hipoclorito comercial apresentou eficiencia menor de 49% na oxidacao do VR195, possivelmente devido a presenca de compostos estabilizantes presentes no produto. O processo de eletrogeracao de hipoclorito seguida de oxidacao do corante apresentou elevada eficiencia, tendo sido observada a reducao de 100% da coloracao da solucao quando se utilizou 2 e 3 g L-1 de NaCl. O processo de eletrogeracao in situ apresentou eficiencia ainda maior. Observou-se tambem a reducao de 100% do corante, mas em tempos de reacao inferiores ao processo de eletrocloracao seguida de oxidacao do corante. A maior eficiencia do processo de eletrocloracao in situ e devido a geracao de outras especies oxidantes (O3, •O, •OH, H2O2) que contribuem com a oxidacao do corante. Para todas as reacoes a oxidacao do corante apresentou uma cinetica de primeira ordem, e os valores sao apresentados e discutidos.

Prospecção tecnológica de uso de eletrodos contendo ferro imobilizado ou em sua composição para abatimento de cargas orgânicas em tratamento de águas e efluentes

A tecnologia eletroquimica tem sido apontada como promissora frente a remediacao de aguas residuarias devido ao seu alto poder de oxidacao, custo relativamente barato e facil operacao. Para esse metodo de tratamento, o material dos eletrodos utilizados e parte crucial para seu bom desempenho. Com o objetivo de tracar os panoramas cientifico e tecnologico relativos ao uso de eletrodos contendo ferro imobilizado ou em sua composicao para a oxidacao de cargas orgânicas, foram realizadas buscas e analises de artigos cientificos e patentes em bases de dados nacionais e internacionais. Apesar de revelada uma densa producao cientifica relacionada a essa tecnologia, com um total de 438 artigos, ha poucos produtos tecnologicos registrados, perfazendo 88 patentes. Tambem foi observado que os paises que possuem depositos de patente nessa area sao China, Alemanha e Reino Unido. Esses dados apontam uma oportunidade de investimentos em pesquisa e desenvolvimento para gerar inovacao tecnologica nessa area.