This study investigates the effects of temperature on ammonia oxidizing bacteria activity in a partial nitritation (PN) sequencing batch reactor. Stable PN was achieved in a 250 L SBR with a minimum operating volume of 111 L treating mature landfill leachate containing an ammonium concentration of around 6000 mg N-NH4+ L-1 at both 25 and 35 degrees C. A suitable influent to feed an anammox reactor was achieved in both cases. A kinetic model was applied to study the influence of free ammonia (FA), the free nitrous acid (FNA) inhibition, and the inorganic carbon (IC) limitation. NH4+ and NO2- concentrations were similar at 25 and 35 degrees C experiments (about 2500 mg N-NH4+ L-1 and 3500 mg N-NO2- L-1), FA and FNA concentrations differed due to the strong temperature dependence. FNA was the main source of inhibition at 25 degrees C, while at 35 degrees C combined FA and FNA inhibition occurred. DGGE results demonstrated that PN-SBR sludge was enriched on the same AOB phylotypes in both experiments. (C) 2012 Elsevier Ltd. All rights reserved.