In this study, petrochemical secondary effluent was treated by a 55 cm diameter pilot-scale biological aerated filter (BAF) with a media depth of 220 cm. Volcanic rock grains were filled as the BAF media. Median removal efficiency of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) was 29.35 and 57.98%, respectively. Moreover, the removal profile of the COD, NH3-N, total nitrogen and total organic carbon demonstrated that the filter height of 140 cm made up to 90% of the total removal efficiency of the final effluent. By gas chromatography–mass spectrometry, removal efficiencies of 2-chloromethyl-1,3-dioxolane, and benzonitrile, indene and naphthalene were obtained, ranging from 30.12 to 63.01%. The biomass and microbial activity of the microorganisms on the filter media were in general reduced with increasing filter height, which is consistent with the removal profile of the contaminants. The detected genera Defluviicoccus, Betaproteobacteria_unclassified and the Blastocatella constituted 1.86–6.75% of the identified gene, enhancing the COD and nitrogen removal in BAF for treating petrochemical secondary effluent.

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