An inverse turbulent bed reactor was investigated for nitrification of a high-strength synthetic wastewater (250-2000 mgN-NH4+ l(-1)). In this reactor, a granular floating solid is expanded by an up-flow current of air. The start-up period was studied during 120 days, including biofilm formation, at a temperature of 30 degrees C. At the end of this start-up period, the reactor completed stable nitrification to nitrate at a nitrogen loading rate (NLR) of 3.6 gN l(reactor)(-1) d(-1). Then, the reactor was run at 30 degrees C during 114 days without any nitrite accumulation. When the temperature was increased to 35 degrees C, an immediate and durable nitrite accumulation occurred in the system during 116 days. Even after decreasing the temperature to 30 degrees C, complete ammonium conversion to nitrate was only possible by decreasing drastically the NLR. N2O production was evaluated in the process to be 2.2 and 3.2% of the influent ammonium nitrogen at 35 and 30 degrees C, respectively. (C) 2005 Published by Elsevier Ltd.