The removal efficiencies of 15 PAHs and some COD components (inert, readily degradable, slowly degradable and metabolic products) from a wastewater taken from a petrochemical industry treatment plant (izmir, Turkey) have been determined using an aerobic completely stirred tank reactor (CSTR). Addition of rhamnolipid surfactant (15 mg 1(-1)) increased the removal efficiencies of PAHs and soluble COD from 72% and 90% to 80% and 99%, respectively. The rhamnolipid treatment caused a significant increase of 5- and 6-ring PAH degradation, The soluble COD removal efficiency was 93%, in CSTR reactors with rhamnolipid added. The inert COD removal efficiency was 60% in a CSTR reactor containing rhamnolipid. Batch tests showed that removal arising from the adsorption of the PAHs was low (between 1.88% and 4.84%) while the removal of PAHs from the petrochemical industry wastewater via volatilization varied between 0.69% and 5.92%. Low sorption capacity (K-p) values for refinery activated sludge (approximately 2.98 1 g(-1)) confirmed that bio-sorption was not an important mechanism controlling the fate of PAHs in aerobic CSTR reactors. Models proposed to simulate the PAH removal indicated that 94% of the PAHs were removed via biodegradation. (C) 2009 Elsevier Ltd. All rights reserved.