In　order　to　study　the　effects　of　anoxic　condition　on　release　of　phosphorus　in　an　enhanced　system　for　phosphorus　removal　with　granular　sludge,　batch　tests　were　carried　out　using　acetate　and　propionate(carbon　molar　ratio=2:1)　as　carbon　source　and　adding　different　amount　of　NO3--N(0,　20,　30,　50　and　75　mg·L-1,　pH=8.0)　and　NO2--N(10,　20,　40　and　60　mg·L-1,　pH=7.0,　7.5　and　8.0)　in　initial　anaerobic　stage.　The　results　showed　that　addition　of　NO3--N　and　NO2--N　had　no　obvious　inhibition　on　release　of　phosphorus.　Absorption　of　fatty　acids(VFAs),　phosphorus　release　and　denitrification　took　place　simultaneously,　and　absorption　rate　increased　while　release　rate　of　phosphorus　decreased　because　of　competition　between　denitrifying　bacteria　and　phosphorus　accumulating　microbial　granule(PAOs)　for　carbon　source.　The　results　of　batch　tests　at　various　NO2--N　concentration　and　at　different　pH　showed　that　FNA,　rather　nitrite,　had　a　strong　stimulation　effect　on　P-release　and　the　rate　of　P-release　increased　by　4　times　when　FNA　concentration　was　higher　than　0.004　mg　HNO2-N·L-1.　Meanwhile,　FNA　had　obvious　suppression　on　absorption　of　VFA　and　synthesis　of　PHA,　and　the　absorption　rate　and　synthesis　mass　decreased　by　53%　and　70%,　respectively.　Based　on　analysis　of　energy　generation　and　metabolism　of　PAOs　as　well　as　toxic　action　of　nitrite,　the　mechanism　stimulating　P-release　of　FNA　was,　in　presence　of　free　nitrous　acid,　that　PAOs　was　required　to　release　more　energy　to　provide　adequate　proton　motive　force(pmf).　©　All　Rights　Reserved.