This　study　introduces　a　novel　PD-hydroxyapatite　(HAP)　coupled　granular　sludge　process　that　efficiently　produces　nitrite　while　also　addressing　the　issue　of　phosphorus　(P)　removal.　Three　laboratory-scale　sequencing　batch　reactors　(SBRs)　were　operated　with　varying　calcium　(Ca)　concentrations,　the　performance　of　nitrite　production,　P　removal,　and　the　characteristics　of　PD-HAP　granules　under　increasing　nitrate　concentrations　(200–800　mg　N/L)　were　investigated.　Results　demonstrated　an　increase　in　nitrite　production　with　influent　nitrate,　with　high　PD　activity　maintained　even　in　the　presence　of　elevated　nitrite　levels.　P　removal　improved　as　influent　nitrate　increased　to　400　mg　N/L　but　declined　thereafter,　likely　due　to　the　elevated　pH　promoting　carbonate　formation,　which　competed　with　phosphate　for　Ca2+.　Supplying　a　higher　Ca2+　concentration　improved　P　removal,　with　R3　achieving　a　maximum　removal　efficiency　of　96.9%　at　an　influent　nitrate　of　400　mg　N/L,　surpassing　R2　(85.7%)　and　R1　(70.0%).　Additionally,　it　was　observed　that　PD-HAP　granules　increased　in　size　with　higher　nitrate　concentrations　but　turned　to　be　disintegrated　with　small　granules　formed　when　nitrate　exceeded　400　mg　N/L.　However,　despite　this,　the　granules　still　maintained　good　settleability,　with　only　a　slight　increase　in　sludge　volume　index　(SVI5)　from　14.8　to　25.9　ml/g　MLSS.　This　study　demonstrated　the　tremendous　potential　of　PD-HAP　granular　sludge　process　for　treating　high-nitrate　wastewater　in　combination　with　anammox.　©　2023