Introducing　fermentation　technology　into　sewage　treatment　is　a　sustainable　development　concept,　but　future　application　still　faces　many　challenges.　A　novel　partial　nitrification,　fermentation-based　double　denitrification　biopmcess　(PN-F-Double/DN)　was　achieved　in　three　separated　SBR　type　reactors,　simultaneously　treating　high　ammonia　(1766.6　mg/L)　mature　landfill　leachate　and　external　waste　activated　sludge　(WAS,　MLSS　=　20.6　g/L).　Firstly,　NH4+-N　was　oxidized　to　NO2--N　in　partial　nitrification　reactor　(PN-SBR),　with　nitrite　accumulation　ratio　(NAR)　of　96.5%.　Next,　the　PN-SBR　effluent　(NO2--N　=　1529.8　mg/L)　coupled　with　the　WAS　were　introduced　to　an　anoxic　reactor　for　integrated　fermentation-denitrification　(IFD-SBR).　The　occurrence　of　fermentation　was　mainly　attributed　to　free　nitrous　acid　(FNA,　nitrite　protonate　form)　promoting　the　splitting　decomposition　of　sludge　spatial　configuration　and　interfacial　forces.　The　released　volatile　fatty　acids　(VFAs)　were　utilized　in　situ　during　the　denitrification　process　(NO2--N　-＞　N-2),　obtaining　0.6　kg/m(3).d　nitrogen　removal　rate　and　3.3　kg/m(3).d　sludge　reduction　rate.　Finally,　undesirable　fermentation　by-products　from　IFD-SBR　(NH4+-N　=　119.2　mg/L)　were　further　removed　in　the　endogenous　post-denitrification　reactor　(EPD-SBR)　through　operational　strategy　of　anaerobic/aerobic/anoxic　by　residual　VFAs　as　the　carbon　source.　In　the　EPD-SBR,　Defluviicoccus　(0.9%)　and　Candidatus　Competibacter　(5.8%)　dominated　carbon　source　storage　and　nitrogen　removal,　acting　as　a　typical　denitrifying　glycogen-accumulating　organism　(DGAO),　with　an　intracellular　carbon　storage　efficiency　of　83.1%　and　nitrogen　removal　contribution　of　93.7%.　After　200　days　of　operation,　the　PN-F-Double/DN　process　provided　effluent　containing,　on　average,　1.86　mg/L　NH4+-N　and　5.5　mg/L　NOx--N,　with　98.5%　TN　removal.　Compared　with　traditional　bioprocesses,　PN-F-Double/DN　allowed　up　to　25%　saving　in　aeration　energy　consumption,　100%　decrease　in　carbon　source　demand,　and　achieve　46.1%　external　WAS　reduction.