Treatment of aqueous chlorophenol by phthalic anhydride-modified horseradish peroxidase

The reaction conditions of removal of chlorophenols from aqueous solution catalysed by phthalic anhydride (PA)-modified horseradish peroxidase were investigated. The optimal pH for chlorophenol removal decreased with increase in substituent number and it was not related to substituent position on aromatic ring. The optimum molar ratio of hydrogen peroxide to chlorophenol was 1.25. The effects of different substrates on phenolics removal were also investigated. The mixed phenolics were more easily removed. PA-modified horseradish peroxidase was more efficient in chlorophenol removal than native horseradish peroxidase either at low temperature or at high temperature. Aromatics with electron-withdrawing substituents (e.g. Cl) at the p-position favour removal over those with substituents at the o- or m-positions. The removal efficiency of 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol was almost equal and it was all lower than that of 4-chlorophenol. The kinetic constants for chlorophenol oxidation with native and PA-modified horseradish peroxidase were also determined. The kinetic data also proved the trend of removal of different chlorophenols with native or PA-modified horseradish peroxidase.