An　anaerobic/aerobic/anoxic　(AOA)　process　in　a　sequencing　batch　reactor　(SBR)　was　proposed　to　treat　typical　medium-age　landfill　leachate　without　extra　carbon　addition.　In　a　steady-state,　the　average　removal　efficiencies　of　NH4+-N,　total　nitrogen　(TN)　and　COD　were　99.7　+/-　0.1%,　98.3　+/-　0.3%　and　89.8　+/-　1.4%,　when　influent　NH4+-N,　TN　and　COD　were　1025-1327　mg/L,　1346-1854　mg/L　and　6430-9372　mg/L,　respectively.　In　the　anaerobic　stage,　dissolved　organic　matter　was　taken　up　partially　and　stored　as　polyhydroxyalkanoates　(PHAs)　with　concomitant　consumption　of　glycogen.　In　the　aerobic　stage,　PHAs　was　oxidized　and　glycogen　was　replenished　in　the　bacterial　cells,　when　TN　of　75.4　mg/L　was　removed　via　simultaneous　nitrification　and　denitrification　(SND).　The　residual　nitrate　and　nitrite　were　denitrified　completely　by　utilizing　residual　PHAs　and　glycogen　as　electron　donors　in　the　anoxic　phase.　Denitrifying　glycogen　accumulating　organisms　(GAOs)　were　considered　to　be　playing　the　major　role　in　the　process.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.