BACKGROUND: Petrochemical refineries and production sites are considered to be the second greatest source of VOC emissions after vehicle exhausts. The feasibility and performance of a novel sequential biotrickling-biofiltration unit for the treatment of a mixture of VOCs in the headspace of an oil and gas production tank battery was evaluated for three months at the Apache TAMU#2 well storage tank battery in Snook, Texas. RESULTS: The results demonstrated that the main VOC constituents of the headspace of the storage tanks were alkanes along with smaller amounts of aromatics such as benzene, toluene and xylenes. Monitoring results for the biotreatment unit showed an average removal efficiency of 50-60% at an empty bed residence time of 120 s in each tank of the unit. After inoculation of the system with wastewater from a sedimentation basin of a local refinery, the removal efficiency of the system increased dramatically which demonstrated the importance of inoculation to achieve a rapid and successful start-up in industrial biofilters. The most optimal performance was achieved after 77 days, obtaining the highest elimination capacity of 23 g m(-3) h(-1) at total VOCs loading rate of 39 g m(-3) h(-1). CONCLUSION: The operation of the field-scale sequential BTF-BF unit for more than three months demonstrated the robustness of this technology and the degradation capabilities of a combination of the suspended and attached growth treatment. The project results demonstrated the potential for even more optimization for improved effectiveness of this novel biological treatment technology for removal of highly variable aromatic VOC concentrations. (C) 2017 Society of Chemical Industry