A　two-sludge　system,　combining　anaerobic/anoxic/aerobic　process　with　biological　aerated　filter　(AAO-BAF),　is　used　to　treat　domestic　wastewater　with　low　COD/N　ratio　(around　3.6).　The　volume　ratio　of　anoxic　to　aerobic　zone(V-ano/V-aer)　of　the　AAO　reactor　gradually　increased　from　2:5　to　6:1,　during　which　the　nutrient　removal　was　improved.　However,　phosphorous　removal　began　to　deteriorate　noticeably　while　V-ano/V-aer　increased　to　7:0.　The　favorable　V-ano/V-aer　was　between　2.5:1　and　6:1.　When　V-ano/V-aer　was　6:1,　the　average　removal　efficiencies　of　COD,　TN　and　PO43-　were　89　+/-　4%,　83　+/-　3%　and　99　+/-　1%,　respectively.　This　study　suggested　the　AAO-BAF　system　could　achieve　efficient　nitrogen　and　phosphorous　removal　with　limited　carbon　source.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.