Horseradish pel oxidase enzyme (HRP) catalyzes the oxidation and polymerization of aqueous aromatic compounds in the presence of hydrogen peroxide. The polymerized products have low solubility and are readily precipitated from solution, thus demonstrating the potential for removing aromatic pollutants from wastewaters. A study was conducted using polyethylene glycol (PEG) as an additive to enhance enzyme performance for the treatment of synthetic wastewaters containing a range of phenol concentrations between 0.5 and 16 millimolar (47 to 1500 mg/l) at neutral pH. Results demonstrated a significant improvement in catalyst lifetime in the presence of PEG in both batch and continuous stirred tank reactor configurations. This improvement reduces catalyst requirements, thereby improving the economic feasibility of the process. Relationships were found to relate the quantities of HRP and PEG required as a function of the initial concentration of phenol being treated in batch reactors. The performance of the CSTR configuration was superior to that of a batch reactor due to the reduced retention time required to achieve the same degree of treatment.