Optimization of phenol removal by a fungal peroxidase from Coprinus macrorhizus using batch, continuous, and discontinuous semibatch reactors

Abstract

The use of a peroxidase from the fungus Coprinus macrorhizus for the removal of toxic organics from synthetic wastewater is explored in this study. Removal of phenols demonstrated a dependence of enzyme lifetime on enzyme concentration in batch reactors. Maximum removal of phenol under optimal conditions in a batch reactor at enzyme activity above 0.3 U ml −1 and up to 1.2 U ml −1 was 53% in the present study. Continuous addition of C. macrorhizus peroxidase (CMP) to the reactor over periods varying from 0.5 to 3 h did not improve the removal. Similarly, continuous addition of H 2O 2 did not improve the removal of phenol. A colorimetric assay for H 2O 2 indicated its depletion in the batch reactors. H 2O 2: phenol stoichiometry was greater than one if all the H 2O 2 was added at the beginning of the reaction. Instability of the H 2O 2 and possible decomposition by contaminating catalase in the sample preparation are two possibilities for its depletion. To overcome this depletion in the reactors regardless of the enzyme concentration, discontinuous addition of either CMP or H 2O 2 or both was adopted. Significant improvement in phenol removal (90%) was obtained when either H 2O 2 or CMP was added in three discrete aliquots over 0.5 h. With discontinuous addition of both reactants, the amount of CMP could be reduced to 0.3 U ml −1 while achieving 91% removal of phenol at equimolar concentration of H 2O 2. Thus, discontinuous addition of the reactant(s) increased the turnovers obtained by CMP and conserved the 1 : 1 phenol to peroxide stoichiometry in the clearance reaction. Spectral observation of the CMP utilized in this study showed the presence of a contaminating cyanide-like complex of the enzyme, as was observed by another group using a similar microbial peroxidase.