Influence of position of substituent groups on removal of chlorophenols and cresols by horseradish peroxidase and determination of optimum conditions

Abstract

Enzymatic treatment of o-, m-, and p-chlorophenols and o-, m-, and p-cresols from artificial wastewater was undertaken through the enzymatic conversion into the corresponding phenoxy radicals with horseradish peroxidase (HRP) and nonenzymatic radical coupling reaction. The concentration of chlorophenols and cresols decreased sharply over the reaction time and waterinsoluble oligomer precipitates were generated. The optimum conditions were determined to be the H2O2 concentration of 2.5mM and poly(ethylene glycol) with molecular mass of 1:0 × 104 (10K-PEG) of 0.10 mg/cm3 at 30°C for treatment of p-chlorophenol at 2.5mM. The optimum pH values depended on the relative position of a chlorine atom for chlorophenols and on a methyl group for cresols. Concentrations of HRP and 10K-PEG were increased to 1.0 U/cm3 and 1.0 mg/cm3 respectively to treat m-chlorophenol highly. For o-chlorophenol, a decrease in the pH value to 3.0 after the enzymatic treatment led to the enhancement of the aggregation of oligomer precipitates. The % residual value for o-cresol effectively decreased by absorbing water-soluble intermediates on the chitosan films. These results indicate that chlorophenols and cresols were removed to a great degree by this technique, although the detailed procedure depended on the position of substituent groups of chlorophenols and cresols.