Microbial fuel cell (MFC) has gained a great attention attributable to its ability in generating electricity directly from and potentially enhancing biodegradation of contaminants. In this study, MFCs using phenol or glucose-phenol mixture as the substrate (fuel) were designed to investigate the biodegradation of phenol. In an aqueous air cathode MFC using phenol (400 mg/L) as the sole fuel, electricity was generated during the phenol degradation. The degradation rates of phenol in the MFC increased about 15% as compared to the open-circuit control. Further experiments were conducted by using a graphite-packed MFC with a ferricyanide cathode. When phenol served as the sole fuel, the peak voltage output was obtained when 90% of phenol was depleted. A unique pattern of twin voltage peaks was observed when phenol-glucose mixture was used as the fuel. At the occurrence of the first and second voltage peaks, phenol was degraded by 20% and 90%, respectively, suggesting a preferential sequence in substrate consumption. The maximal power densities were 9.1 and 28.3 W/m(3) for MFCs using phenol and glucose-phenol mixture as the fuel, respectively. Co-occurring with electricity generation, the degradation efficiencies of phenol in all the MFCs reached above 95% within 60 h. The results indicate that the MFC can enhance biodegradation of recalcitrant contaminants such as phenol in practical applications. (C) 2008 Elsevier B.V. All rights reserved.