This　work　studied　the　impacts　of　key　granule　properties　on　the　granular　reactor　performing　partial　nitritation/anammox　from　the　modeling　perspective.　The　results　could　guide　not　only　future　reliable　modeling　but　also　practical　startup/operation　of　the　reactor.　To　achieve　high　total　nitrogen　(TN)　removal　whilst　avoiding　significant　N2O　production,　inoculated　granules　should　be　big　and　anammox-enriched.　The　optimum　boundary　layer　thickness　for　maximum　TN　removal　increased　with　the　decreasing　diffusivity　of　soluble　components　in　the　granule　structure.　Even　though　a　thick　boundary　layer　could　protect　anammox　bacteria　from　elevated　dissolved　oxygen　(DO)　(e.g.,　0.5　g-O2/m3)　and　obtain　high　TN　removal　(>90.0%)　and　low　N2O　production　(<1.8%),　even　complete　removal　of　the　boundary　layer　would　fail　to　provide　sufficient　substrate　for　anammox　and　therefore　couldn＇t　increase　TN　removal　to　90.0%　and　decrease　N2O　production　to　<2.4%　at　insufficient　DO　(e.g.,　0.3　g-O2/m3　in　the　presence　of　lifted　influent　NH4+　concentration).　©　2022　Elsevier　Ltd