Phenol degradation at high concentrations was investigated under continuous operation in art immobilized-cell hollow fiber membrane bioreactor. Pseudomonas putida ATCC49451 was immobilized in asymmetric polysulfone hollow fiber membranes through entrapment within the porous regions and through attachment on the membrane surfaces. Bioreactor performance was assessed based on the startup period, the effect of feed rate (ranging from 21 to 120 mL/h), the relative contribution of the lumen and the shell sides to phenol degradation, the effect of feed phenol concentration (1000-2000 mg/L) and the long-term operation of the bioreactor. The bioreactor startup was very short, and steady state was accomplished within 160 h. An optimum degradation capacity with respect to phenol loading rate was observed because of the tradeoff in the amount of phenol degraded against the increase in feed rate. It was also found that at higher feed rate, the shell side contributed to a larger proportion of the total phenol degraded compared with the lumen. On the basis of these results, it was found that options abound for the operating conditions of the bioreactor. These can be chosen depending on whether complete phenol degradation or high degradation capacity is desirable. Finally, long-term sustainable continuous operation of the bioreactor was demonstrated without significant biofilm fouling on the membranes. (c) 2007 Wiley Periodicals, Tnc.