A biological treatment with the integration of partial nitrification, anaerobic ammonium oxidation (Anammox) and heterotrophic denitrification was successfully developed in a SBR with periodical air supply to treat landfill leachate. An operating temperature of 30 +/- 1 degrees C and a dissolved oxygen concentration within 1.0-1.5 mg/L were maintained in the SBR. First, the mixture of Anammox biomass and aerobic activated sludge (80% w/w) were inoculated, and inorganic synthetic wastewater with progressively increased N-loading was added. The activities of maximum aerobic ammonium oxidizing and anaerobic ammonium oxidizing reached 0.79 and 0.18 (kg NH(4)(+)-N/kg(dw)/day) after the inoculation lasting 86 days, respectively. Secondly, an unexpected group of he erotrophic clenitrifying bacteria was inoculated into the reactor along with the feeding of raw landfill leachate, and the final Maximum activities of aerobic ammoniurn oxidizing, anaerobic ammonium oxidizing and denitrification reached 2.83 (kg NH(4)(+)-N/ kg(dw)/day), 0.65 (kg NH(4)(+)-N/kg(dw)/day) and 0.11 (kg NO(3)(-)-N/kg(dw)/day), respectively. (C) 2009 Published by Elsevier Ltd.