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.