A　lab-scale　anaerobic-anoxic-aerobic　(A(2)O)　process　was　operated　to　investigate　denitrifying　phosphorus　removal　and　nitritation-denitritation　from　domestic　wastewater,　especially　regarding　the　impact　of　nitrite　accumulation　caused　by　nitritation　on　phosphorus　removal.　The　results　showed　that　mean　total　nitrogen　(TN)　removal　was　only　about　47%　and　phosphorus　removal　was　almost　zero　without　the　pre-anoxic　zone　and　additional　carbon　source.　Contrastively,　with　configuration　of　pre-anoxic　zone.　TN　and　phosphorus　removal　was　increased　to　75%　and　98%,　respectively,　as　well　as　denitrifying　phosphorus　removal　of　66-91%　occurred　in　the　anoxic　zone.　Nitritation-denitritation　was　achieved　through　a　combination　of　short　aerobic　actual　hydraulic　retention　time　and　low　dissolved　oxygen　levels　(0.3-0.5　mg/L);　however,　phosphorus　removal　deteriorated　with　increase　of　nitrite　accumulation　rates.　The　free　nitrous　acid　(FNA)　concentration　of　0.002-0.003　mg　HNO2-N/L　in　the　aerobic　zone　inhibited　phosphorus　uptake,　which　was　major　cause　of　phosphorus　removal　deterioration.　Through　supplying　the　carbon　sources　to　enhance　denitrification　and　anaerobic　phosphorus　release,　nitrite　and　FNA　concentrations　in　the　aerobic　zone　were　reduced,　and　phosphorus　removal　was　improved.　Compared　with　nitrification-denitrification,　nitritation-denitritation　reduced　the　carbon　requirement　by　30%　and　performed　biological　nutrients　removal　well　with　mean　TN　and　phosphorus　removal　of　85%　and　96%,　respectively.　(C)　2010　Elsevier　Inc.　All　rights　reserved.