In this study, we evaluated the combination between an electrochemical process, occurring in the dark, and a heterogeneous photocatalytic process for dye degradation, using the azo dye tartrazine as model of oxidizable substrate. TiO2 P25 and an Ag-doped TiO2 were used as photocatalysts in suspensions containing 50 mg L–1 of tartrazine. The best result, 74% of dye mineralization in 120 min of reaction, was obtained using TiO2 P25 as photocatalyst and a current density of 10 mA cm–2 in the electrochemical cell, a value 30% higher than the sum of the results obtained by heterogeneous photocatalysis (44%) and electrochemical oxidation (13%). The use of Ag-doped TiO2 did not result in significant improvement on tartrazine mineralization, due to the aggregation of these nanoparticles. Our results suggest that this process can be an alternative for a complete treatment (discoloration and mineralization) of tartrazine and most likely other azo dyes.

O desempenho eletroquímico de eletrodos de diamante dopado com boro (BDD) na degradação eletroquímica de efluentes contendo sulfadiazina (SDZ) usando um reator filtro-prensa é apresentado e discutido. A eletrooxidação da SDZ (volume de 0,5 L, com uma concentração inicial de 250 mg L-1) obtida sob condições otimizadas (densidade de corrente de 36 mA cm-2, pH 7,0 e velocidade de fluxo de 5,0 L min-1) mostraram que ao final da eletrólise (correspondente a uma carga circulada por unidade de volume de solução de 5,2 Ah L-1) a SDZ foi totalmente eliminada. A redução da carga orgânica, monitorada por sua demanda química de oxigênio (COD) mostrou que o antibiótico foi praticamente todo mineralizado. Sob condições otimizadas, os compostos intermediários foram devidamente identificados por cromatografia gasosa-espectrometria de massas (GC-MS) e um mecanismo de oxidação foi proposto. Claramente, o eletrodo de BDD mostrou-se muito eficiente tanto para a degradação como para a mineralização de SDZ.

The electrochemical performance of boron-doped diamond (BDD) electrode in the electrochemical degradation of wastewaters containing sulfadiazine (SDZ) using a filter-press reactor is presented and discussed. The electrooxidation of the SDZ (volume of 0.5 L, with a SDZ initial concentration of 250 mg L-1) obtained at optimized conditions (current density of 36 mA cm-2, pH 7.0 and volume flow rate of 5.0 L min-1) showed that at the end of only 2 h of electrolysis (corresponding to a charge passed through the cell per unit volume of the wastewater of 5.2 Ah L-1) SDZ was totally eliminated. The reduction of the wastewater organic load, monitored by its chemical oxygen demand (COD) showed that the antibiotic was virtually all mineralized. Under optimized conditions the intermediate compounds were properly identified by gas chromatography-mass spectrometry (GC-MS) and a SDZ oxidation pathway was elucidated. Clearly the BDD electrode proved to be quite efficient for both degradation and mineralization of SDZ.