Optimization and kinetic study of methyl orange dye degradation using catalytic electrocoagulation

Abstract

Textiles are one of the most chemical intensives and the most polluting industries among all industrial sectors in Bangladesh. The produced wastewater from textile industries is highly colored and contains dyes including azo dyes. The treatment of azo dyes in textile wastewater using conventional processes is challenging as the azo dyes are carcinogenic and bio-persistent. In the present study, degradation of methyl orange (MO) azo dye by catalytic and non-catalytic electrocoagulation (EC) have been studied. Effects of pH, current density, dye concentrations and salt concentrations (Fe2+) have been investigated and optimum parameters were determined. pH in the range of 4 to 5 was found to be optimum and treatment efficiency decreased with increasing dye concentrations for the EC process. In case of catalytic EC (in presence of Fe2+ salt), dye removal for a certain dye concentration increased with the increase of current density and Fe2+ salt up to a certain dose and after that the removal efficiency decreased with further increase. The COD, color and dye removals were observed to be 94.1%, 93.1% and 100%, respectively for 200 ppm dye solution using only 0.20 mM Fe2+ for 0.40 mA/cm2 current density, whereas for non-catalytic EC, the respective removal efficiencies were 76.7%, 63.4% and 82.4%, respectively. Associated operating costs for non-catalytic and catalytic EC were calculated to be $0.429/m3 and $0.287/m3 of wastewater, respectively. The kinetic results revealed that the first-order kinetic model was fitted best for non-catalytic EC, whereas the second-order kinetic model was best fitted for catalytic EC. Based on the study, we can conclude that higher degradation capability along with lower operating cost (OC) were observed for catalytic EC and therefore, the process can be used for effective treatment of textile wastewater containing toxic compounds like azo dyes.