BACKGROUND The petrochemical industry wastewater contains many organic compounds that are difficult to degrade. The activated sludge system reinforced by bioaugmentation technology represents a more effective alternative to treat industrial wastewater. In this study, bioaugmented activated sludge water demonstrated high efficiency in removing five tested hydrocarbons. RESULTS Optimized degradation rates were obtained upon inoculation of a continuous bioreactor system with degradative bacteria (Acinetobacter sp., Aeromonas sp., Arthrobacter nicotianae, Burkholderia cepacia, Chryseobacterium sp., Pseudomonas fluorescens, Micrococcus luteus and Raoultella planticola). The addition of a hydrocarbon mixture (terephthalic acid, acenaphthene, fluorene, anthracene, and pyrene) into the bioaugmented sludge resulted in degradation rates equivalent to 97.90%, 99.87%, 98.89%, 97.28%, and 94.55% respectively after 24-48 h incubation. Molecular biomonitoring was performed with real-time quantitative polymerase chain reaction (qPCR). According to the obtained results, the numbers of copy DNA of the degradative bacteria increased by 0.36-1.13 log at the end of the degradation process. The presence of some oxygenase genes (Nah, NidA, Pah Rhd Gr(+), Pah Rhd Gr(-) and C23O), that catabolize aromatic hydrocarbons in activated sludge, were detected by specific primers. CONCLUSION Bioaugmentation represents a potent and eco-friendly approach that can effectively remove the drastic increase in the concentrations of aromatic hydrocarbons in industrial wastewaters. Molecular biomonitoring during degradation can be considered a rapid and an effective in situ method that quantifies the active microbial population in wastewater. The method provides beneficial information about the composition of microbial community and sustainability of the degradation process. (c) 2019 Society of Chemical Industry