The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71 +/- 0.14 kg/m(3)/d and a COD removal rate of 2.21 +/- 0.13 kg/m(3)/d were achieved under the conditions of an air flow rate of 19.36 +/- 1.71 m(3) air/m(3)/h and an air on/off duration of 1.5 min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163-256 m(3) air/kg COD, a stable effluent NO3--N/NOx--N (NO2--N plus NO3--N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO2--N/NH4+-N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.