Reductive decolourization and total organic carbon reduction of the diazo dye Cl Acid Black 24 by zero-valent iron powder

In this study, wastewater contaminated by colour and total organic carbon from the diazo dye CI Acid Black 24 was successfully removed by reductive decolourization with zero-valent iron powder. The effects on decolourization of experimental variables such as iron dosage, initial dye concentration, pH and dissolved oxygen level were evaluated. The best removal efficiencies for decolourization of 99.7% and total organic carbon of 57.4% were obtained with an initial dye concentration of 25.0 mg L-1 and iron dosage of 200.0 g L-1. Moreover, the decolourization rates followed pseudo-first-order kinetic equations with respect to dye concentration. The colour removal efficiency was simultaneously dependent on iron dosage and various initial dye concentrations, although the colour and total organic carbon removal efficiencies linearly increased with increased iron dosage, reaching a maximum at 100.0 g L-1. A contour plot was developed to illustrate the 3D relation of removal efficiencies with initial dye concentration and iron dosage. For wastewater with a concentration range from 25 to 100 mg L-1 CI Acid Black 24 the suggested ideal operation conditions are 100.0 g L-1 iron dosage, pH 2-4, normal oxygen concentration of 5-7 mg L-1 and reaction time of 30-60 min. (c) 2006 Society of Chemical Industry.