A 60 L membrane aerated biofilm reactor (MABR) was successfully employed to treat landfill leachate, which contained very high concentrations of refractory chemical oxygen demand (COD) and ammonium. Air or pure oxygen was supplied to the bioreactor through polydimethyl siloxane hollow fibre membranes. Over a year of operation with an average hydraulic retention time of about 5 days, and influent ammonium concentrations ranging from 500 to 2500 mg/L, the MABR achieved 80-99% nitrification. Simultaneously, the influent COD concentrations which ranged from 1000 to 3000 mg/L were reduced by approximately 200-500 mg/L. Oxygen transfer rates as high as 35 g O-2/m(2)-day were achieved during the study. By operating at low gas flowrates, high oxygen transfer efficiencies were achieved without any negative impact on oxygen transfer rates. This suggested that the biofilm was not oxygen limited during this study. The very low gas flowrates and the low pressure losses required to move air through the membranes resulted in very high standard aeration efficiencies that exceeded 10 kg O-2/kW h. The results indicate that mixing energy far exceeded that required for aeration in this study. Our results suggest that with process optimisation, MABR technology offers a low energy option for effective leachate treatment. (C) 2015 Elsevier B.V. All rights reserved.