Aiming　at　solving　the　contradiction　of　sludge　retention　time　(SRT)　between　nitrification　and　dephosphorization,　and　enhancing　the　simultaneous　nitrogen　(N)　and　phosphorus　(P)　removal　efficiency　of　the　low　C/N　(P)　ratio　domestic　sewage　in　the　traditional　A2/O　process,　an　improved　A2/O　technique　with　long　SRT　was　developed.　The　novel　process　could　select　and　strengthen　the　activated　sludge,　and　enrich　the　denitrifying　phosphorus　accumulating　organisms　(DPAO)　with　long　SRT　effectively.　After　washing　out　nitrite　oxidizing　bacteria　(NOB),　the　reactor　ran　under　the　condition　of　SRT=19.6　d,　and　sludge　concentration　(MLSS)=5.5　g·L-1,　hydraulic　retention　time　(HRT)=8.2　h,　sludge　return　ratio　(R)=90%,　nitrated　liquid　reflux　ratio　(r)=250%,　dissolved　oxygen　(DO)=1.5-0.3　mg·L-1　for　the　A2/O　zone.　HRT=4　h,　aeration　cycle　was　1　h,　aeration　time　was　1　min　(DO=0.3-0.5　mg·L-1)　and　settling　time　was　59　min　for　the　intermittent　aeration　zone.　Average　removal　rate　of　COD,　NH+4-N,　TP　and　TN　reached　88.71%,　99.2%,　93.77%　and　89.52%　respectively,　nitrosation　rate　(NO2--N/NOx--N)　was　up　to　97.2%,　and　DPAO/PAO　ratio　in　sludge　was　95.5%,　and　the　final　effluent　met　the　first　class　level　A　of　the　GB　18918-2002　standard.　It　was　found　that　about　72.96%　of　COD　in　sewage　was　utilized　by　DPAO　for　PHA　production　to　accumulate　P,　15.75%　of　COD　was　consumed　by　heterotrophic　denitrifying　bacteria,　and　about　41.96%　and　31.31%　of　N　were　wiped　off　through　phosphorus　removal　and　heterotrophic　denitrifying.　The　discharged　sludge　was　mainly　composed　of　the　biomass　of　DPAO　and　denitrifying　bacteria,　accounting　for　82.74%　and　17.24%　respectively.　The　technique　could　reduce　58.76%　of　carbon　source　consumption　and　44.6%　of　sludge　discharge　comparing　to　the　traditional　nitrogen　phosphorus　removal　pathway.　©,　2014,　Chemical　Industry　Press.　All　right　reserved.