Laboratorial scale experiments were conducted in order to investigate the effect of zonation as well as the combined ozonation and biological aerobic filter (BAF) on treating the bio-treated coking wastewater (BTCW). The study showed that the optimum parameters for oxidizing BTCW by ozone were the ozone dose of 0.3 mgO(3(applied))/mgCOD(0) (about 60 mg/L), 50 min contact time and 7.5 pH, obtaining higher biodegradability of about 0.43 BOD5/COD ratio than the original about 0.09 for feed. The results from the combined ozonation and BAF revealed that compared to the process of the BAF alone, the combined process is more effective in abating COD, BOD5, NH4+-N, color and UV254 of BTCW simultaneously, which removal rates reached about 49.7%, 58.8%, 75.8%, 91.1% and 82.3%, respectively. Therefore, the combined process is a promising technology for polishing BTCW. (C) 2014 Elsevier B.V. All rights reserved.