Low　temperature　is　an　important　factor　affecting　the　municipal　wastewater　treatment　systems.　The　aim　of　this　study　was　tracking　the　variations　in　the　abundance　of　anammox　bacteria　(AnAOB)　and　the　sludge　form　as　the　temperature　decreased.　Mutual　boost　of　granulation　and　enrichment　of　AnAOB　was　achieved　even　though　the　temperature　dropped　from　20.4　?C　to　12.9　?C.　The　average　particle　size　of　the　sludge　increased　from　128.5　mu　m　to　245.6　mu　m.　With　low　dissolved　oxygen　(DO)　aeration　(0.2-0.5　mg/L)　and　short　oxic　hydraulic　retention　time　(HRT)　(5　h),　nitritation　in　the　anaerobic/oxic/anoxic　(AOA)　system　was　stable　enough　to　provide　NO(2)(-　)for　AnAOB.　Ca.　Brocadia,　a　type　of　typical　AnAOB,　was　enriched　from　0.03%　to　0.24%　in　the　suspended　sludge　and　reached　16.09%　in　the　granular　sludge.　Overall,　this　study　presents　the　prospects　of　anammox　and　granule　technologies　when　treating　municipal　wastewater　at　a　low　temperature.