Removal of phenols from a foundry wastewater using horseradish peroxidase

Horseradish peroxidase (HRP) catalyses the oxidation of phenols by hydrogen peroxide resulting in the formation of water-insoluble polymers which can be separated by coagulation and sedimentation. The feasibility of the enzyme process to treat a foundry wastewater containing 3.5 mM of total phenols (330 mg/l as phenol) was examined. Two enzyme stocks of different purities were used but total phenols removal was independent of enzyme purity. For both stocks, 97 to 99% of the phenolic contaminants were removed, despite the presence of other contaminants such as organic compounds and iron in the waste matrix. The quantity of HRP required for this degree of treatment was in the same range as for the treatment of a synthetic wastewater containing an equal amount of pure phenol. Polyethylene glycol, a chemical additive, reduced enzyme inactivation, allowing a 22-fold reduction in the amount of HRP required for 99% removal of phenols from the foundry waste. Residual chemical oxygen demands (COD) varied depending on the enzyme source. The high purity HRP achieved more than 65% removal of COD, but due to a high concentration of other organic matter present in the low purity HRP, no reduction in COD was achieved with this enzyme source. A comparison was made between enzyme treatment and oxidation using Fentonʹs reagent. Enzyme cost must be significantly reduced in order to make the enzyme treatment process economically competitive.