Orthophosphate　is　an　intermediate　product　of　the　biological　denitrification　process　of　phosphorus　aggregation,　which　affects　the　activity　of　denitrifying　phosphorus　aggregating　bacteria　(DPAOs)　in　competition　with　other　heterotrophic　bacteria　for　carbon　sources.　In　this　study,　four　groups　of　sequencing　batch　reactors　(SBRs)　were　operated　with　various　endogenous　orthophosphate　regulating　techniques　utilizing　synthetic　water　as　influent　after　being　inoculated　with　flocculent　activated　sludge.The　study　aimed　to　investigate　the　effects　of　different　endogenous　orthophosphate　regulation　methods　on　the　enrichment　of　denitrifying　phosphorus　accumulating　bacteria　(DPAOs)　and　granulation.　The　results　showed　that　the　granular　sludge　operated　with　endogenous　orthophosphate　effluent　reflux　exhibited　better　nitrogen　and　phosphorus　removal　efficiency,　higher　DPAO　activity,　and　good　particle　sedimentation　performance.In　particular,　compared　to　granular　sludge　systems　operated　in　microaerobic　mode,　those　operated　in　anaerobic/microaerobic　(AO)　mode　demonstrated　superior　pollutant　treatment　performance,　with　COD,　TN,　and　TP　removal　efficiencies　reaching　92.57%,　94.7%,　and　97.62%,　respectively.　This　was　attributed　to　multiple　factors,　such　as　endogenous　orthophosphate　stimulation,　the　synergistic　effect　of　DPAOs　and　denitrifying　glycans　bacteria　(DGAOs).Periodic　regulation　of　endogenous　orthophosphate　in　the　system　resulted　in　a　significant　increase　in　the　internal　carbon　source　conversion　rate　of　sludge,　enhanced　activities　of　DPAOs　and　DGAOs,　and　inhibition　of　heterotrophic　denitrifying　bacteria　(DOHOs).　Under　a　longer　cycle　operation　mode,　ammonia　oxidizing　bacteria　(AOB)　and　DPAOs　interacted,　while　also　inhibiting　the　growth　of　other　heterotrophic　microorganisms.　The　findings　of　this　study　provide　theoretical　support　for　the　practical　engineering　application　of　simultaneous　short-range　nitritation-denitritation　phosphorus　removal　(SPNDPR)　process.　©　2023　Chinese　Society　for　Environmental　Sciences.　All　rights　reserved.