Nitritation　and　denitrifying　phosphorus　(P)　removal　was　achieved　in　Modified　University　of　Cape　Town　(MUCT)　process　treating　domestic　wastewater　with　a　low　C/N　ratio.　The　effect　of　nitrite　accumulation　on　performance　of　phosphorus　removal　and　population　structure　of　＇Candidatus　Accumulibacter＇　was　investigated　during　nitritation　establishment　and　destruction.　Results　indicated　that　P　removal　was　mainly　completed　by　denitrifying　P　removal　of　about　88%.　The　P　removal　efficiency　had　a　clear　correlation　with　the　nitrite　accumulation　rate.　Under　nitritation,　the　P　removal　was　30%　higher　than　that　under　complete　nitrification,　suggesting　that　nitrite　was　appropriate　to　be　used　as　electron　acceptor　for　denitrifying　P　removal　when　treating　low　C/N　wastewater.　Real　time　quantitative　PCR　assays　were　carried　out　using　poly-P　kinase　1　(ppk1)　as　phylogenetic　marker　to　characterize　the　abundance　of　total　Accumulibacter　and　the　relative　distributions　and　abundances　of　the　Accumulibacter　clades.　Under　complete　nitrification,　a　very　few　Acc-I　clade　below　5%　in　total　Accumulibacter　was　present　using　nitrate　as　electron　acceptor.　When　the　reactor　transformed　into　nitritation,　Acc-I　clade　gradually　disappeared.　The　Acc-IID　clade　using　nitrite　as　electron　acceptor　for　denitrifying　P　removal　was　always　the　dominant　Accumulibacter　throughout　the　operational　period,　with　above　92%　on　average　in　total　Accumulibacter,　even　up　to　nearly　100%,　which　led　to　stable　performance　of　denitrifying　P　removal　using　nitrite　as　electron　acceptor.　The　nitrite　concentrations　significantly　affected　the　abundances　of　Acc-IID　clade.