BACKGROUND: Biodegradation of pyrene, a novel polycyclic aromatic hydrocarbon (PAH) of environmental concern, was investigated employing a two-liquid phase partitioning bioreactor (TPPB) using Mycobacterium frederiksbergense. After initial screening of solvents, silicone oil was chosen as the biocompatible and economic solvent for use in this TPPB system with an initial pyrene concentration of 400 mg L-1. The efficiency of the TPPB system developed was also compared with the results of pyrene degradation by the microorganism in slurry phase and surfactant-aided systems. A cost-benefit analysis comparison of the three systems evaluated in the work further revealed very good potential of the TPPB system in pyrene biodegradation. RESULTS: Using silicone oil as the non-aqueous phase liquid in the TPPB system, pyrene was found to be completely degraded by M. frederiksbergense within 6 days with a degradation rate of 140 mg L-1 d(-1), which was at least seven times more than the values obtained in the slurry phase or surfactant-aided systems. Further cost-benefit analysis comparison of the three systems revealed TPPB to be the most effective with a minimum cost of $0.62 per mg of pyrene degraded. CONCLUSION: Performance of TPPB system, in terms of both efficiency and economics of pyrene degradation by M. frederiksbergense was found to be superior to slurry phase or surfactant aided systems. (C) 2010 Society of Chemical Industry