Experimental study and kinetic modelling of the enzymatic degradation of the azo dye Crystal Ponceau 6R by turnip (Brassica rapa) peroxidase

Textile and food industries wastewaters are characterized by a strong coloration due to use of dyes, among which azo dyes are the most frequently used. These compounds are harmful and their discharge without an adequate treatment causes a negative impact on the environment. Given that conventional biological treatment processes are usually not sufficient to degrade azo dyes, other treatment alternatives must be studied. Enzymes have demonstrated their effectiveness to degrade several types of recalcitrant compounds. In this study, enzymatic degradation of Crystal Ponceau 6R (CP6R) azo dye by turnip (Brassica rapa) peroxidase was assessed in the presence of 100 μM redox mediator (1-hydroxybenzotriazole). The treatment performance was evaluated at different pH values (3, 4, 5, 6 and 7) and the most appropriate pH and contact time were determined. Moreover, a kinetic model of the enzyme-catalyzed reaction was developed by mathematical description of the degradation mechanism, being further validated with experimental data. For the estimation of the kinetic parameters and model validation, a central composite design of type “start points” was made. The results showed that the enzymatic treatment was very effective. CP6R dye degradation higher than 97% was achieved in less than 1 min of reaction at the optimum pH (i.e., 4), at which the maximum reaction rate (43 μM min−1) was obtained. At the other tested pH values, degradation performance was substantially lower (<70%) in the same timeframe, but still satisfactory. Moreover, the proposed kinetic model successfully predicted the CP6R dye degradation under different experimental conditions in terms of dye and enzyme concentrations.