A submerged biological denitrification system was employed to remove selected pesticides, trifluralin, fenitrothion and endosulfan (alpha + beta) and nitrate from drinking water using ethanol as electron donor. When the hydraulic residence time (HRT) decreased below 2 h, nitrate concentration was increased and nitrite was observed in the effluent water, increasing HRT higher than 2.4 h, had little effect on the effluent concentration of nitrate and organic carbon, but above this point no nitrite was detected in water. At the lowest HRT, breakthrough of nitrate and nitrite observed in the effluent, reaching concentrations of about 30 and 6 mg/l for 1.0 h and about 51 and 9.4 mg/l for below 1 h, respectively. The nitrate removal efficiency dropped to 46% at a HRT value lower than about 2.5 h and nitrite was observed because of the low contact time for microbial activity. In the present study, up to 95% removal of the selected pesticides was observed. When the temperature dropped from 18 to 14 degrees C, the lowest removal efficiency of nitrate was achieved (63%). During the study, despite the temperature oscillations, high removal efficiencies for trifluralin, fenitrothion and endosulfan (alpha + beta) was achieved. The highest nitrite concentration was 16 mg/l in the effluent of the reactor. (c) 2005 Elsevier Ltd. All rights reserved.