BACKGROUND: Several studies have demonstrated the feasibility of treating aqueous phenols and aromatic amines with oxidoreductases in synthetic wastewater samples. However, little work has been done on the effectiveness of enzymatic treatment on real wastewater. Here a comparison was made of the oxidative coupling of phenol catalyzed by laccase or soybean peroxidase (SBP) using synthetic and refinery wastewaters. RESULTS: Optimization of PH, enzyme concentration, effect of polyethylene glycol (PEG) addition, and reducing anions were examined for a 3 h reaction time. Laccase had an optimum pH of 5.6-6.0, while SBP had a broad optimum from 6.0 to 8.0. In synthetic samples in tap water to achieve >= 95% removal of 1.0 mmol L-1 phenol in 3 h required 0.12 and 1.5 U mL(-1) of catalytic activity of laccase and SBP, respectively. In refinery samples comparable removals required 1.2- to 1.8-fold more enzyme than in synthetic tap water samples. Added PEG allowed for a small reduction in the SBP concentration for synthetic wastewater but was ineffective with either enzyme in treating refinery samples. Reducing ions increased the demand for oxidant but, with the exception of cyanide, phenol removal still occurred. CONCLUSION: Both laccase and SBP were effective in removing phenol from aqueous refinery samples, albeit at slightly higher concentrations than required for the corresponding synthetic samples. (C) 2008 Society of Chemical Industry