Anaerobic　ammonia　oxidation　(anammox)　of　municipal　wastewater　is　a　research　focus,　especially　the　combined　treatment　with　mature　landfill　leachate　is　a　current　research　hotspot.　In　this　study,　municipal　wastewater　was　treated　by　partial　nitrification　via　sequencing　batch　reactor　(SBR),　and　its　effluent　and　mature　landfill　leachate　were　then　mixed　into　an　up-flow　anaerobic　sludge　blanket　(UASB)　for　simultaneous　anammox　and　partial　denitrification　reaction.　Through　partial　nitrification,　a　high　nitrite　accumulation　rate　(93.0　±　3.8　%)　was　achieved　by　low　dissolved　oxygen　(0.5–1.6　mg/L)　and　controlled　aerobic　time　(3.5　h)　in　SBR.　The　UASB　system　was　responsible　for　78.8　±　2.1　%　nitrogen　removal　of　the　entire　system　with　a　hydraulic　reaction　time　(HRT)　of　3.8　h,　accompanied　by　the　anammox　contribution　up　to　89.4　±　6.0　%.　The　overall　partial　nitrification-simultaneous　anammox　and　partial　denitrification　(PN-SAPD)　system　was　controlled　at　a　total　COD/TIN　of　2.8　±　0.3　and　a　total　HRT　of　only　10.2　h,　achieving　the　nitrogen　removal　efficiency　and　effluent　TIN　were　95.2　±　2.2　%　and　3.4　±　1.5　mg/L,　respectively.　The　qPCR　results　showed　functional　genes　(hzsA(B),　hdh)　associated　with　anaerobic　ammonia-oxidizing　bacteria　(AnAOB),　whose　high　gene　copy　abundance　and　transcription　expression　ensured　the　removal　of　major　nitrogen　from　municipal　wastewater　and　mature　landfill　leachate.　16S　amplicon　sequencing　showed　that　the　Ca.　Brocadia　(9.72–12.6　%)　was　further　enrichment　after　sodium　acetate　was　added,　and　the　transcription　expression　of　Thauera　(0.5–7.0　%)　caused　nitrate　to　nitrite.　The　high　abundance　of　related　enzymes　(hao,　hzs,　hdh,　narGHI)　involved　in　anammox　and　partial　denitrification　processes　were　found　in　the　macrogenomic　sequencing,　and　only　Ca.　Brocadia　was　involved　in　multi-pathway　nitrogen　metabolism　in　AnAOB.　Based　on　the　efficient　nitrogen　removal　by　AnAOB　and　denitrifying　bacteria,　this　modified　PN-SAPD　process　provides　a　new　option　for　the　co-treatment　of　mature　landfill　leachate　in　municipal　wastewater　treatment　plants.　©　2023