Recycled iron rods coupled with chlorine for synergistic degradation of textile dye wastewater: a sustainable and cost-effective treatment approach

This study explores the efficiency of a novel oxidation system based on the interaction between a recycled iron rods (rIR) and chlorine for the removal of a model azo dye, Cibacron Green-H3G (CG-H3G), from aqueous solutions. The system demonstrated rapid degradation kinetics, achieving complete dye removal within 7 min under optimised conditions (pH 3, 41.1 mm rIR <i>length</i>, 250 µM chlorine), primarily driven by the generation of reactive species, i.e. ferryl ions (Fe^IV), ^•OH and reactive chlorine species (RCS). A pronounced synergistic effect was observed, with a synergy index reaching up to 7.3, particularly at lower dye concentrations, moderate chlorine doses, increased stirring, and extended rod length – factors that collectively enhance oxidative capacity. The process showed satisfactory mineralisation (TOC removal ~ 50% at 120 min) and retained ~ 90% of its initial performance over five successive reuse cycles, confirming the durability of the rIR material. Matrix effect evaluations revealed that common inorganic salts and surfactants reduced process efficiency due to radical scavenging and interference with surface or oxidative mechanisms. Moreover, tests under realistic water matrices, including river water, seawater, and mineral water, highlighted the role of ionic and organic loads in modulating reactivity. Altogether, the rIR/chlorine system emerges as a robust, reusable, and scalable oxidative platform, with strong potential for application in dye-contaminated waters of low to moderate matrix complexity.