The　nitrogen　removal　performance　of　a　pilot-scale　biosystem　was　significantly　improved　via　partial　denitrification/anammox　(PD/A)　in　real　sewage　with　low　COD/N　ratio.　The　modified　pilot　plant　was　designed　as　an　anaerobic/anoxic/oxic　(AAO)　reactor　combined　with　a　biological　aerated　filter.　The　inoculation　of　biocarriers　into　anaerobic　and　anoxic　zones　enhanced　anammox　and　the　nitrogen　removal　performance.　Despite　a　COD/N　ratio　of　3.1,　effluent　total　inorganic　nitrogen　decreased　from　17.1　to　9.8　mg　N/L.　The　anoxic　unit　developed　as　the　PD/A　hotspot,　which　was　associated　with　the　enrichment　of　Ca.　Brocadia　(2.00%)　and　partial　denitrification　functional　groups　(OLB14,　13.50%;　Thauera,　5.45%)　in　the　anoxic-carrier　biofilms　and　contributed　34.1%　towards　total　nitrogen　removal.　Besides　improving　the　PD/A　process,　enhanced　denitrifying　dephosphatation　was　simultaneously　realized,　suggesting　that　the　integration　of　PD/A　into　this　modified　system　is　a　promising　approach　to　enhance　nutrient　removal　of　low　COD/N　wastewater.