A laboratory-scale anaerobic/anoxic/oxic (AAO) wastewater treatment system was employed to investigate the effects of hydraulic retention time (HRT) and sludge retention time (SRT) on the removal and fate of di-n-butyl phthalate (DnBP). HRT had no significant effect on DNBP removal between 12 and 30 h. However, longer HRT increased DnBP accumulation in the system and DnBP retention in the waste sludge. When SRT was increased from 15 to 25 d, DnBP removal efficiency stayed above 95%. Compared to the removal of only 90% at SRT of 10 d, longer SRT enhanced DnBP degradation efficiency. The optimal HRT and SRT for both nutrients and DnBP removal were 18 h and 15 d. At these retention times, about 72.66% of DnBP was degraded by the activated sludge process, 2.44% was released in the effluent, 24.44% was accumulated in the system, and 0.5% remained in the waste sludge. The anaerobic, anoxic and oxic reactors were responsible for 17.14%, 15.02% and 63.46% of the overall DnBP removal, respectively. Meanwhile a removal degradation model was formulated, and kinetic parameters were evaluated with batch experiments under anaerobic, anoxic, oxic conditions. The model can well forecast the effluent quality of anaerobic/anoxic/oxic reactors of the AAO process. (C) 2010 Elsevier Ltd. All rights reserved.