Horseradish peroxidase-mediated decolourization of Orange II: modelling hydrogen peroxide utilization efficiency at different pH values

MORALES URREA, DIEGO ALBERTO; HAURE, PATRICIA MÓNICA; GARCÍA EINSCHLAG, FERNANDO SEBASTIÁN; CONTRERAS, EDGARDO MARTÍN

ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2018

0944-1344

Enzymatic decolorization of azo-dyescould be a cost-competitive alternative compared to physicochemical ormicrobiological methods. Stoichiometric and kinetic features of peroxidasemediated decolourization of azo-dyes by hydrogen peroxide (P) are central fordesigning purposes. In this work, a modified version of the Dunford mechanismof peroxidases was developed. The proposed model takes into account theinhibition of peroxidases by high concentrations of P, the substrate-dependantcatalatic activity of peroxidases (e.g., the decomposition of P to water andoxygen), the generation of oxidation products (OP) and the effect of pH on the decolourizationkinetics of the azo-dye Orange II (OII). To obtain the parameters of theproposed model two series of experiments were performed. In the first set, theeffects of initial P concentration (0.01 - 0.12 mM) and pH (5 - 10) on the decolourizationdegree was studied at a constant initial OII concentration (0.045 mM). Obtained results showedthat at pH 9 - 10 and low initial P concentrations, the consumption of P wasmainly to oxidize OII. From the proposed model, an expression for the decolourizationdegree was obtained. In the second set of experiments, the effect of theinitial concentrations of OII (0.023 - 0.090 mM), P (0.02 - 4.7 mM), HRP (34 -136 mg/L) and pH (5 - 10) on the initial specific decolourization rate (q0)was studied. As a general rule, a noticeable increase of q0 wasobserved for pHs higher than 7. For a given pH, q0 increased as afunction of the initial OII concentration. Besides, there was an inhibitoryeffect of high P concentrations on q0. To asses the possibility ofreusing the enzyme, repeated additions of OII and P were performed. Resultsshowed that the enzyme remained active after six reuse cycles. A satisfactoryaccordance between the change of the absorbance during these experiments andabsorbances calculated using proposed model was obtained. Considering that thisset of data was not used during the fitting procedure of the model, theagreement between predicted and experimental absorbances provides a powerfulvalidation of the model developed in the present work.