Influence of number of azo bonds and mass transport limitations towards the elimination capacity of continuous electrochemical process for the removal of textile industrial dyes

This study focusses on the electrochemical decomposition of synthetic azo dyes (RO16, RR120 and DR80) using stainless steel electrodes, which is efficient, cost effective and industrially driven process. The experiments were carried out in a continuous electrochemical reactor and the effects of influencing parameters (initial concentration of dye, electrolyte concentration, pH) governing the process efficiency was studied. The interaction between the influencing parameters was investigated using Response Surface Methodology (RSM) and the regression value obtained for the generated model was above 0.9 for all the three dyes. The elimination capacity of electrochemical reactor was studied for the continuous removal of azo dyes with different ranges of concentration (100-400 mg L^-1) and flow rate (0.1-0.5 L h^-1). The maximum elimination capacity was obtained at a flow rate of 0.5 L h^-1 for 300 mg L^-1 of initial concentration of dye for RO16 and RR120 whereas it was 0.5 L h^-1 for 400 mg L^-1 of DR80. Further, a general dimensionless current density relation has been established for stirred tank reactor and allowed characterizing the relationship between kinetics and mass transport contributing to the overall reaction rate. The results quantitatively confirmed that the rate of electrochemical decolorization increased with the increasing initial dye concentration and flow rate due to the mass transport limitation. As newly established, the decolorization is also directly linked to the number of azo bonds.