Intermittent existence of oxygen in the landfill with the intermittent forced aeration was favorable to denitrify the NO_2 –N and NO_3 –N, indicated by the high denitrification efficiency (>99%) under the condition of BOD5/TN of more than 5.4 in leachate; locally persistent existence of oxygen in the landfill with enhanced natural aeration could limit the denitrification, indicated by relatively low denitrification efficiency of about 75% even when the BOD5/TN in leachate had an average of 7.1. _ 2007 Elsevier Ltd. All rights reserved.