BACKGROUDSecondary effluent collected from a petrochemical wastewater treatment plant was treated by ozone-biological aerated filter (O-3-BAF) to investigate and evaluate the performance, organics and genotoxicity removal characteristics of this combined advanced treatment process. RESULTSThe average dissolved organic carbon (DOC) of the secondary effluent was approximately 23 mg L-1. When the ozone dosage was 10 mg L-1 and the contact time was 4 min, the DOC removed by O-3-BAF was approximately 9 mg L-1 during which 37% was removed by ozonation and 63% by BAF. The ozonation changed the percentage of the small molecular size organics (< 1 k) increasing from 54% to 67%, and the high molecular size organics (> 100 k) decreasing from 26% to 8%. More than 85% of the genotoxicity of the chemical secondary effluent was removed in the ozonation unit. The genotoxicity of the BAF effluent was less than 0.71 mu g-4-nitroquinoline-N-oxide L-1. CONCLUSIONOzonation can change the organics molecular size, increase the biodegradability and obviously reduce the genotoxicity of petrochemical secondary effluent. The O-3-BAF process is suitable for the advanced treatment of petrochemical secondary effluent. (c) 2014 Society of Chemical Industry