Optimization of the operating parameters and their effects on the degradation of Naphthol Blue Black by the Fenton process

The objective of this work was to model and optimize the degradation of black azo dye Naphthol Blue Black (NBB) by the Fenton process (advanced oxidation) using a minimum of experiments. A Plackett-Burman screening design was first applied to determine the main factors influencing the process. The dye discoloration efficiency gave a yield approximately equal to 97 % in the best conditions of several operating parameters used. The variance analysis (ANOVA) showed the effects of all different factors and deduced the most important ones. Subsequently, a second quadratic design of experiments central composite type (CCD) was applied using the response surface methodology (RSM) to optimize the most important parameters deduced by the first design cited above, in order to obtain the best performance of the discoloration of NBB with this process. So from the contour plots and the response surfaces, the discoloration yield enhanced to the maximum and the optimization plot given by the Mnitab software, showed the following optimized parameters [NBB]=37.5 mg/L, [H2O2]=66.5 mg/L, [Iron]=3.5 mg/L and pH=3.4 for a yield of 100 % with a desirability of 1.0000. At last, to confirm that the discoloration was due to the degradation of the dye, the chemical oxygen demand (COD) was studied and in the optimized conditions, the degradation reached 94.78 % after 120 min of treatment. The kinetics of the dye degradation showed by the COD abatement was relatively slow compared to the kinetics of the dye discoloration.