A　pilot-scale　aerobic　granular　sequencing　batch　reactor　(SBR)　with　domestic　wastewater　was　operated　to　evaluate　the　effects　of　the　low　organic　loading　rate　(OLR)　due　to　wet　weather　flow　conditions　on　simultaneous　nitrification,　denitrification,　and　phosphorus　removal　(SNDPR).　As　the　OLR　decreased　from　0.85　to　0.43　kg　COD　m(-3)　d(-1),　the　total　nitrogen　(TN)　and　total　phosphorus　(TP)　removal　efficiencies　decreased　from　84.0%　and　94.1%　to　51.3%　and　73.8%,　respectively,　the　sludge　volume　index　(SVI)　increased　from　42.3　to　85.5　mL　g(-1),　and　the　average　granular　size　decreased　from　1022　to　742　mu　m;　however,　no　sludge　disintegration　and　biomass　loss　were　observed.　The　poor　nutrient　removal　efficiencies　and　settling　ability　were　due　to　the　shrinking　anoxic　zone　and　substrate　scarcity　inside　the　granules,　wherein　the　activity　decay　of　ammonia-oxidizing　bacteria　and　overgrowth　of　filamentous　bacteria　played　an　important　role.　Alternating　the　aeration　intensity　was　effective　in　enhancing　nitrogen　removal　and　sludge　settling　by　improving　the　anoxic　activity　in　granules　and　inhibiting　the　proliferation　of　filamentous　bacteria.　Returning　20%　of　sludge　from　the　end　of　one　anaerobic　stage　to　the　beginning　of　the　next　anaerobic　stage　(midway　sludge　return)　was　beneficial　for　phosphorus　removal　as　it　improved　phosphorus　storage　by　phosphorus-accumulating　bacteria.　A　smaller　granular　size　with　stronger　stability　and　better　nutrient　removal　performance　was　the　new　steady　state　of　the　SNDPR　system　under　wetweather　flow　conditions.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.