BACKROUND: Hydrocarbon contamination of groundwater resources has become a major environmental and human health concern in many parts of the world. Microbial degradation of hydrocarbons, through either naturally occurring processes or engineered systems, has been successfully used to reduce concentrations of these pollutants. In order to develop an aerobic bioreactor tailored for this purpose, the present study aims to investigate petroleum contaminated wastewater remediation and toxicity reduction by acclimated microbial consortium enriched in a continuous stirred tank bioreactor (CSTR). Characterization and quantification of refinery wastewater components were performed by gas chromatography mass spectrometry (GC/MS) and Fourier transform infrared (FTIR) spectroscopy. RESULTS: The petroleum hydrocarbons were significantly degraded (97%) by the microbial consortium. After continuous aerobic treatment in the CSTR, the COD(effluent) and BOD(5effluent) average removals were high reaching 97% and 78%, respectively. Also, strong degradation of C10-C35 n-alkanes was observed. The concomitant use of GC/MS and FTIR proved to be a useful complementary tool to assess the impact of treatment strategies on hydrocarbon-contaminated wastewater. In addition, the toxicity of the contaminated wastewater decreased drastically after bioremediation. CONCLUSION: This work shows the ability of this consortium to degrade hydrocarbons and reduce toxicity, which makes them useful candidates for environmental restoration applications at other hydrocarbon-contaminated environments. (C) 2011 Society of Chemical Industry