Nitrification of a high-strength wastewater in an inverse turbulent bed reactor: Effect of temperature on nitrite accumulation

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 °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 lreactor−1 d−1. Then, the reactor was run at 30 °C during 114 days without any nitrite accumulation. When the temperature was increased to 35 °C, an immediate and durable nitrite accumulation occurred in the system during 116 days. Even after decreasing the temperature to 30 °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 °C, respectively.