Considering　the　challenges　associated　with　nitrogen　removal　from　mature　landfill　leachate,　a　novel　combined　continuous-flow　process　integrating　denitrification　and　partial　nitrification-Anammox　(PN/A)　was　developed　using　an　internal　circulation　(IC)　system　and　a　biological　aerated　filter　(BAF)　biofilm　reactor　(IBBR).　In　this　study,　IBBR　successfully　operated　for　343　days,　and　when　influent　NH+4　-N　concentration　of　mature　landfill　leachate　reached　1258.1　mg/L,　an　impressive　total　nitrogen　removal　efficiency　(TNRE)　of　93.3　%　was　achieved,　along　with　a　nitrogen　removal　rate　(NRR)　of　1.13　kg　N/(m3　&　sdot;d).　The　analysis　of　the　microbial　community　revealed　that　Candidatus　Kuenenia,　the　dominant　genus　responsible　for　anammox,　accounted　for　1.7　%　(day　265).　Additionally,　Nitrosomonas,　Thauera　and　Truepera　were　identified　as　key　contributors　to　the　efficient　removal　of　nitrogen　from　mature　landfill.　As　a　novel　nitrogen　removal　strategy,　the　practical　application　of　the　IBBR　system　offers　novel　perspectives　on　addressing　mature　landfill　leachate.