Nitrate and endosulfan (alpha + beta) removal was studied in an upflow biological denitrification reactor packed with wheat straw as carbon source and support particles for microorganisms. While almost complete nitrate elimination and between 65% and MIX endosulfan (alpha + beta) elimination occurred when the temperature was higher than 20 degreesC; below that value. nitrate removal efficiency decreased to about 10%. Nitrate, dissolved organic carbon (DOC), and endosulfan (alpha + beta) removal efficiencies decreased considerably at 1500 mug/l endosulfan concentration in the batch experiments. Although high removal efficiency was observed for endosulfan (alpha + beta) and nitrate in the biological denitrification continuous reactor, the effluent water could not be used for drinking purpose because of the unacceptable levels of endosulfan (alpha + beta), colour and dissolved organic content. During the continuous study, 23.4% of the initial weight of wheat straw was lost and 24 g was consumed per gram of nitrogen removed. The results of the continuous study showed that 21.3% of the endosulfan removal was achieved by adsorption onto the wheat straw and 68.2% of the endosulfan removal occurred by biological activity and the remaining portion was detected in the effluent water. (C) 2004 Elsevier Ltd. All rights reserved.