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Electrochemical Oxidation of Bromothymol Blue: Application to Textile Industrial Wastewater Treatment

Abstract In this study, electrochemical oxidation of Bromothymol blue (BTB) was studied in an aqueous medium (pH = 3) by electro-Fenton process (EFP). This chemical compound belongs to the family of sulfone phthalein, widely used for dyeing in the textile industry. EFP generates in a catalytic way hydroxyl radicals (•OH) which are powerful oxidant species (E0(•OH/H2O) = 2.8 V/NHE) used for the oxidation of organic pollutants. The kinetics of BTB degradation and the mineralization efficiency of its process are investigated through the effect of some operating parameters. The value of 300 mA as applied current, Fe2+ as a catalyst with a concentration of 0.2 mM and a temperature of 40 °C are found to be the optimum operating parameters. The reaction kinetic follows a pseudo-first order with an absolute rate constant of 3.36 × 1010 M-1 s-1. The efficiency of EFP is confirmed by the decrease of the molecule concentration during the treatment until its total disappearing. The chemical oxygen demand (COD) analyses indicate after 6 h a mineralization degree of 94% for the BTB synthetic solution, 91% for the effluent provided from a small Tunisian textile industry and 41% for the wastewater provided from a medium one. The energy consumption per unit COD mass (ECCOD) of the EFP is determined for the treatment of BTB synthetic solution and for the two real effluents. Concerning the BTB synthetic solution, the energetic cost is equal to 1.02 kWh (g COD)-1 at the beginning of the electrolysis and it has decreased to reach 0.30 kWh (g COD)-1 after 6 h. For the first effluent, the energy consumption rises from 1.20 to 0.36 kWh (g COD)-1. An opposite phenomenon is observed for the second effluent.