Degradation of a textile reactive Azo dye by a combined chemical–biological process: Fentonʹs reagent-yeast

This work presents the results of our studies on the decolorization of aqueous azo dye Reactive black 5 (RB5) solution combining an advanced oxidation process (Fentonʹs reagent) followed by an aerobic biological process (mediated by the yeast Candida oleophila). Under our conditions, initial experiments showed that Fentonʹs process alone, as well as aerobic treatment by C. oleophila alone, exhibited the capacity to significantly decolorize azo dye solutions up to 200 mg/L, within about 1 and 24 h, respectively. By contrast, neither Fentonʹs reagent nor C. oleophila sole treatments showed acceptable decolorizing abilities for higher initial dye concentrations (300 and 500 mg/L). However, it was verified that Fentonʹs reagent process lowered these higher azo dye concentrations to a value less than 230 mg/L, which is apparently compatible with the yeast action. Therefore, to decolorize higher concentrations of RB5 and to reduce process costs the combination between the two processes was evaluated. The final decolorization obtained with Fentonʹs reagent process as primary treatment, at 1.0×10−3 mol/L H2O2 and 1.0×10−4 mol/L Fe2+, and growing yeast cells as a secondary treatment, achieves a color removal of about 91% for an initial RB5 concentration of 500 mg/L.