This study aimed to evaluate the performance of a high rate nitrogen removal lab-scale ANAMMOX reactor, namely Internal Circulation (IC) reactor, for old landfill leachate treatment. The reactor was operated with pre-treated leachate from a pilot Partial Nitritation Reactor (PNR) using a high nitrogen loading rate ranging from 2 to 10 kg N m(3) d(1). High rate removal of nitrogen (9.52 +/- 1.11 kg N m(3) d(1)) was observed at an influent nitrogen concentration of 1500 mg N L-1. The specific ANAMMOX activity was found to be 0.598 +/- 0.026 gN2-N gVSS(1) d(1). Analysis of ANAMMOX granules suggested that 0.5-1.0 mm size granular sludge was the dominant group. The results of DNA analysis revealed that Candidatus Kueneniastuttgartiensis was the dominant species (37.45%) in the IC reactor, whereas other species like uncultured Bacteroidetes bacterium only constituted 5.37% in the system, but they were still responsible for removing recalcitrant organic matter. (C) 2017 Elsevier Ltd. All rights reserved.