To　save　energy　consumption　in　domestic　wastewater　treatment,　three-stage　autotrophic　nitrogen　removal　process　including　organics　removal　SBR,　partial　nitrification　SBR　and　anammox　UASB　was　proposed.　At　room　temperature　of　(26±1)°C,　short-term　effect　of　aeration　rate　and　MLSS　on　organic　removal　process　was　investigated　by　seeding　activity　sludge　taken　from　a　pilot-plant　reactor　of　partial　nitrification.　The　results　show　that　both　concentrations　of　NO2--N　and　NO3--N　were　lower　than　0.1　mg·L-1　at　various　aeration　rates　and　sludge　concentrations　before　the　end　of　COD　biodegradation　stage.　After　that,　the　wastewater　entered　a　difficult-degradating　stage　in　reactor　where　COD　concentration　remained　at　nearly　constant　level　and　NO2--N　and　NO3--N　concentrations　accumulated　rapidly　and　nitrifying-bacteria　activity　increased.　Obviously,　nitrification　did　not　occur　during　the　process　removing　organics　under　different　aeration　conditions.　Therefore,　under　various　conditions　of　aeration　and　sludge　concentration　the　first　organics　was　removed　and　then　partial　nitrification　to　remove　NO3--N.　However,　for　three-stage　autotrophic　nitrogen　removal　process,　NH4+-N　concentration　could　decrease　from　11.6　mg·L-1　to　3.4　mg·L-1(TN　loss)during　organics　removal　process　under　aeration　values　of　100　L·h-1,　60　L·h-1and　20　L·h-1.　The　peak　point　of　pH　profile　and　the　inflexion　of　DO　curve　stayed　the　same　with　the　end　of　removing　organics　throughout,　and　so　they　could　be　used　as　real-time　control　signals　to　indicate　the　end　of　organic　removal　process.　©　All　Rights　Reserved.