The　successful　suppression　of　nitrite-oxidizing　bacteria　in　the　partial　nitrification　(PN)　stage　was　the　main　challenge　for　the　application　of　autotrophic　nitrogen　removal　process　treating　mainstream　sewage.　In　this　study,　two　identical　PN　granular　reactors　(P1　and　P2)　were　rapid　started-up　using　the　simultaneous　PN　and　granulation　strategy,　for　treating　the　domestic　sewage.　P1　was　seeded　with　30%　PN　granular　sludge　to　induce　nucleation,　in　which　the　granule　size　achieved　to　more　than　400　mu　m　in　12　d,　with　ammonia　oxidation　rate　and　nitrite　accumulation　rate　of　80%　and　95%,　respectively,　while　P2　realized　granulation　in　42　d.　The　presence　of　organic　matters　and　specific　structure　of　granules　were　profitable　for　the　stability　of　PN　for　treating　sewage　with　low　ammonia.　High-throughput　pyrosequencing　results　indicated　the　biodiversity　of　both　reactors　decreased　after　start-up,　and　Nitrosomonas　was　the　predominant　specie　of　aerobic　ammonia-oxidizing　bacteria　in　PN　granular　sludge.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.