Partial　denitrification/anammox　(PD/A)　has　been　recently　applied　to　co-treat　domestic　wastewater　and　nitrate-containing　anammox　effluent.　However,　studies　regarding　its　performance　without　external　organic　supplement,　spatial　characteristics　within　sludge　aggregates,　and　chronological　changes　of　active　microorganisms　along　PD/A　cycle　have　rarely　been　reported.　Herein,　one-stage　PD/A　unit　extremely　and　simultaneously　polished　anammox-pretreated　reject　water　(NH4+-N:　65.4　±　5.7　mg/L,　COD:　199.7　±　23.2　mg/L)　and　domestic　wastewater　(NO3−-N:　81.6　±　7.8　mg/L,　TN:　85.8　±　8.9　mg/L,　COD:　338.2　±　29.0　mg/L)　to　4.5　±　2.1　mg/L　without　external　organic　carbon　supply.　Protective　“granules-in-granule”　aggregates　with　densely　clustered　anammox　bacteria　embedded　in　homogeneous　denitrifying　Thauera　prevailed　in　PD/A　system,　surviving　disadvantages　from　complex　wastewater.　Uronic　acids　and　β-sheet　proteins　in　outer　extracellular　matrix　facilitated　granulation　and　pollutants　adsorption,　while　tryptophan-　and　aromatic-like　proteins　with　tighter　secondary　structure　in　inner　extracellular　matrix　maintained　granular　robustness.　Importantly,　succession　of　active　microorganisms　along　the　PD/A　cycle　was　revealed　by　transcript-level　analysis　for　the　first　time.　In　PD-period,　stimulated　Thauera　contributed　to　rapid　nitrite　accumulation.　In　subsequent　anammox-period,　Ca.Brocadia　was　activated　to　conduct　advanced　nitrogen　removal,　which　accompanied　the　timely　nitrate-to-nitrite　reduction　by　Thauera　and　Ca.Competibacter.　Elusimicrobia　was　active　throughout　the　PD/A　cycle,　which　is　conducive　to　eliminate　the　dependence　of　PD　process　on　external　carbon　source　by　decomposing　complex　organics　in　actual　wastewater.　Protective　granular　structure,　orderly　activation　and　harmonious　cooperation　of　functional　consortia　facilitated　practical　nitrogen　removal　rate　of　0.6　±　0.1　kg-N/m3/d　under　anoxic　condition,　which　sheds　light　on　engineering　application　of　anammox　technology.　©　2023　Elsevier　B.V.