A submerged biological denitrification system was employed to remove selected pesticides and nitrate from drinking waters. Ninety-five percent nitrate removal and over 76,50, and 72% of mineralization of trifluralin, fenitrothion, and endosulfan (alpha+beta) were obtained, respectively after three days. Approximately 13 mg SS/l of microbial growth was obtained in the batch unit. After determining the optimum C/N ratio as 1.5 in a biodenitrification batch test, experiments were carried out in a continuous mode. Between 93 and 98% of nitrate removal efficiency was observed and nitrite concentrations were quite low for theta(h) values higher than 2 h. Although no significant improvement in nitrate and organic carbon eliminations was observed at theta(h) = 12 h, the highest trifluralin, fenitrothion, and endosulfan (alpha+beta) removal efficiencies (about 100%) were observed. A sand filter system provided good turbidity and suspended solids removal efficiencies. (C) 2004 Elsevier Ltd. All rights reserved.