Studying the influence of different parameters on the electrochemical oxidation of tannery dyes using a Ti/IrO2-SnO2-Sb2O5 anode

Abstract

Electrochemical oxidation directly converts organic compounds into simple inorganic molecules like carboxylic acids, H2O and CO2, and it is considered an efficient method for treating highly polluted wastewater. In this study, MMO (Ti/IrO2-SnO2-Sb2O5) was tested for the electrochemical oxidation of mono-azo (Violet RL), diazo (Green A), and tetra-azo (Brown DR) dyes used in the tannery industry. The study focused on understanding the effect of different parameters such as supporting electrolyte, dye concentration, azo dye type, pH, and current density, on the performance of the electrochemical oxidation process of individual dyes and their mixture. Under 50 mM of Na2SO4 at pH 3 and j = 50 mA cm−2 close to 100% electrochemical oxidation was achieved when 50 mg L−1 Violet RL solution was tested. Using the best conditions of 35 mM NaCl + 25 mM Na2SO4 supporting electrolyte at pH 3.0 and 50 mA cm−2 current density, a rapid and complete discoloration of a mixture of the three azo dyes at 80 mg L−1 each, with about 92% COD decay and low energy consumption, with an acceptable low ECCOD value of 0.08 kWh (g COD)−1. To assess the complete level of dye oxidation, the evolution of nontoxic short-chain carboxylic acids was evaluated.