BACKGROUND:　UniFed　SBR　is　a　novel　process　that　can　achieve　high　levels　of　nitrogen　and　phosphorus　removal　simultaneously　in　a　simple　single　SBR　tank.　In　this　study,　effects　of　influent　C/N　ratio,　influent　C/P　ratio　and　volumetric　exchange　ratio　on　biological　phosphorus　removal　in　UniFed　SBR　process　were　investigated　in　a　lab-scale　UniFed　apparatus　treating　real　domestic　wastewater.　RESULTS:　The　results　showed　that　phosphorus　removal　efficiency　increased　as　C/N　ratio　increased　from　27%　at　2.8　to　88%　at　5.7.　For　C/N　ratios　6.5　and　above,　complete　phosphorus　removal　could　be　achieved.　When　C/N　ratios　and　volumetric　exchange　ratio　were　fixed　at　6　and　33%,　respectively,　phosphor-us　removal　efficiency　remained　at　100%　for　C/P　ratios　higher　than　33;　effluent　phosphate　concentration　was　below　the　detection　limit.　For　C/P　ratios　lower　than　33,　phosphorus　removal　efficiency　decreased　linearly　with　C/P　ratio.　Under　the　same　influent　C/N　ratio　and　C/P　ratio,　the　following　factors　all　contributed　to　better　phosphorus　removal　performance:　greater　volumetric　exchange　ratio;　more　organic　substrate　for　PAOs　to　utilize,　less　inhibition　by　NOx-　of　phosphorus　release　during　the　feed/decant　period;　more　PHB　synthesized;　and　more　aerobic　phosphate　uptake.　CONCLUSION:　High　influent　C/N　ratio,　high　C/P　ratio　and　high　volumetric　exchange　ratio　were　beneficial　to　phosphorus　removal　in　this　process.　(C)　2008　Society　of　Chemical　Industry