Hydrodynamic Effects on the Performance of an Electrochemical Reactor for Destruction of Disperse Dyes

A synthetic wastewater containing an aqueous mixture of disperse dyes was electrolyzed at different current densities using a Ti/(RhOx + TiO2) anode and stainless steel cathode, with the objective of investigating the effect of stirring on the reactor operating under isothermal and isoperibolic conditions. The results showed that the primary mechanism of dye decomposition was a homogeneous oxidation by electrogenerated "active chlorine". Under isothermal conditions at a bulk pH of 4.0, increasing the mixing rate decreased the dyesʹ decomposition rates (decolorization) but increased those rates at pH 8.0. The highest decolorization rate, until approximately 40% conversion was reached, was achieved at a current density of 300 A/m^2 and pH 8.0 with the apparent homogeneous rate coefficient k2 being 2.93 × 10^-4 m^3/mol s, while 6.45 × 10^-5 m^3/mol s was observed at pH 4.0. Conversely, mixing had a detrimental effect on the performance of the reactor when it was operated under isoperibolic conditions at alkaline pH. The effect of mixing is explained by considering the possible pH-dependent electrode and bulk solution reactions, including the chlorine loss reactions and the possible anodic electrooxidation of chlorinated intermediates.