Enzyme catalyzed polymerization and precipitation of aromatic compounds from aqueous solution

Abstract

Horseradish peroxidase enzyme (HRP), once activated by hydrogen peroxide, initiates the oxidation of a wide variety of aromatic compounds. Reaction products undergo a non-enzymatic polymerization to form water insoluble aggregates which are readily separated from solution. HRP was selected for application in wastewater treatment systems due to its stability and retention of its catalytic ability over wide ranges of pH and temperature. HRP activity was optimal between pH 5.7 and 8.5 with peak activity occurring at neutral pH. Activity increased with temperature up to 50 °C and declined at higher temperatures due to thermal inactivation. HRP was inactivated rapidly by hydrogen peroxide in the absence of an aromatic substrate. The efficiency of removal that was achieved was dependent on the nature of the aromatic undergoing treatment and the amount of enzyme provided due to the finite lifetime of the catalyst. Optimization of pH significantly improved catalytic efficiency with a corresponding savings in treatment costs. Optimal catalytic lifetime of HRP was achieved in the pH range of 7 to 9 for the eight phenolic compounds treated. The minimum residual level to which aromatic substrates were removed from solution was independent of the starting concentration of the aromatic substrate. Enhanced removal of hard-to-remove compounds was noted when mixtures of aromatic substrates were treated. Key words: horseradish peroxidase enzyme, polymerization, wastewater, phenols, aromatics amines.