Higher　nitrite　accumulation,　which　is　challenging　to　achieve　reliably,　is　always　sought　to　obtain　better　nitrogen　removal　performance　in　traditional　partial　nitritation-anammox　(PN/A)　process.　This　study　developed　a　modified　PN/A　process　by　introducing　nitrite-oxidizing　bacteria　and　endogenous　metabolism.　Advanced　nitrogen　removal　performance　of　95.5　%　was　achieved　at　a　low　C/N　ratio　of　2.7　under　nitrite　accumulation　ratio　(NAR)　fluctuations.　Higher　nitrate　accumulation　at　lower　NAR　(70　∼　40　%)　resulted　in　superior　anammox　contribution　(60　∼　75　%)　and　nitrogen　removal　performance　(93　∼　98　%).　This　was　attributed　to　the　higher　nitrogen　removal　efficiency　of　the　post-anoxic　endogenous　partial　denitrification　coupling　anammox　process,　although　the　PN/A　process　occurring　first　possessed　a　faster　anammox　rate　of　2.0　mg　NH4+-N　/(g　VSS⋅h).　The　introduction　of　nitrate　allowed　more　nitrite　flow　to　anammox,　promoting　a　high　enrichment　of　anammox　bacteria　(Ca.　Brocadia,　0.3　%　to　2.8　%).　This　study　provides　new　insights　into　the　practical　application　of　the　PN/A　process.　©　2024　Elsevier　Ltd