O presente estudo objetiva a degradação eletroquímica do éster dimetilftalato (DMP) em uma célula em fluxo do tipo filtro-prensa, usando um ânodo dimensionalmente estável (DSA®). As melhores condições de eletrólise foram determinadas pela análise da natureza e concentração do eletrólito suporte, pH, densidade de corrente e temperatura. A remoção da concentração do DMP e do teor de carbono orgânico total (TOC) foram maiores na presença de NaCl, assim como os valores das constantes cinéticas de pseudo primeira ordem. Usando força iônica constante em 0,15 mol dm-3 pela adição de Na2SO4, a concentração de DMP diminuiu mais rapidamente a baixas concentrações de íons cloreto, enquanto que a remoção do teor de TOC após 1h de eletrólise aumentou com a adição de NaCl. A remoção do DMP foi similar para todas as densidades de corrente investigadas em solução ácida. A melhor opção operacional, considerando a eficiência energética, é de baixa densidade de corrente, já que o sistema eletroquímico encontra-se sob regime de transferência de massa.

The electrochemical degradation of dimethyl phthalate (DMP) using a one-compartment filter press flow cell and a commercial dimensionally stable anode (DSA®) is presented. The best electrolysis conditions were determined by the analysis of the influence of the nature and concentration of the support electrolyte, pH, current density and temperature. The abatement of DMP concentration and total organic carbon (TOC) removal were superior in the presence of NaCl, as well as the apparent first order kinetic constants. Using constant ionic strength at 0.15 mol dm-3 by adding Na2SO4, DMP concentration decreases faster at relative low NaCl concentrations while the TOC removal after 1 h of electrolysis increases with NaCl concentration. The DMP removal was very similar for all the current densities investigated at acidic solutions. When electric energy saving is considered, since the electrochemical system was under mass transport conditions, the best operational option is to use low current density values.

The Direct Black 22 dye was electrooxidized at 30 mA cm-2 in a flow cell using a BDD or β-PbO2 anode, varying pH (3, 7, 11), temperature (10, 25, 45 °C), and [NaCl] (0 or 1.5 g L-1). In the presence of NaCl, decolorization rates were similar for all conditions investigated, but much higher than predicted through a theoretical model assuming mass-transport control; similar behavior was observed for COD removal (at pH 7, 25 °C), independently of the anode. With no NaCl, COD removals were also higher than predicted with a theoretical model, which suggests the existence of distinct dye degradation pathways.

A degradação eletroquímica do corante Vermelho Reativo 141 foi investigada por meio da aplicação da metodologia de superfície de respostas, utilizando reator filtro-prensa com anodo de β-PbO2. A carga requerida para 90% de descoloração (Q90) e a remoção da demanda química de oxigênio após 30 min de eletrólise (COD30) foram utilizadas para modelar o sistema. As variáveis investigadas foram a densidade de corrente, pH, concentração de NaCl e temperatura. Baixos valores de Q90 (0,2-0,3 A h L-1) foram obtidos em condições ácidas (pH 1-3) e em altas concentrações de NaCl (1,0-2,0 g L-1), quando as espécies oxidantes Cl2 e HOCl estão presentes. Os melhores valores para COD30 foram obtidos com altas densidades de corrente e em condições de pH ácido a neutro; entretanto, o consumo energético resultante torna o processo economicamente não viável. Para soluções extremamente ácidas foram obtidos valores reduzidos de consumo de energia, relacionado ao Q90, em torno de 0,79 kW h m-3.

The electrochemical degradation of the Reactive Red 141 dye using a filter-press reactor with a β-PbO2 anode was investigated through the application of the response surface methodology. The charge required for 90% decolorization (Q90) and the chemical oxygen demand removal percentage after 30 min electrolysis (COD30) were used to model the system. The investigated independent variables were the current density, pH, NaCl concentration, and temperature. Low values of Q90 (0.2-0.3 A h L-1) were obtained at acidic conditions (pH 1-3) and high concentrations of NaCl (1.0-2.0 g L-1), when Cl2 and HOCl are the predominant oxidant species. The best values of COD30 were obtained at high current densities and acidic to neutral conditions (pH 5-7); however, the consequent energy consumption makes the process not economically feasible under these conditions. For strongly acidic solutions, specific energy consumptions associated to Q90 as low as 0.79 kW h m-3 were attained.

The electrochemical performance of electrodeposited Ti/β-PbO2 and Ti-Pt/β-PbO2 anodes was galvanostatically evaluated (batch mode, 50 mA cm-2) to degrade the Direct Yellow 86 dye (100 or 200 mg L-1 in 0.1 mol L-1 Na2SO4 + 1.5 g L-1 NaCl), investigating the effect of pH and temperature. Similar results were obtained for both electrodes and the best conditions for removal of color and chemical oxygen demand are pH 7 and 40 °C, when 90% decolorization is attained by passing a charge of only ~0.13 A h L-1 and total mineralization is achieved with expenditure of ~5 kW h m-3.