BACKGROUND:　Nitrite　is　toxic　to　anoxic　phosphorus　uptake　when　it　exceeds　a　threshold　concentration.　In　this　study,　denitrifying　phosphorus　removal　with　nitrite　as　electron　acceptor　was　investigated　in　a　sequencing　batch　reactor　(SBR)　operated　using　a　real-time　step　feed　strategy.　RESULTS:　The　nitrite　pulse　concentration　was　initially　determined　by　batch　experiments.　pH　increased　with　use　of　nitrite　for　phosphate　uptake,　and　decreased　when　the　nitrite　was　used　up.　Nitrite　was　added　promptly　after　the　pH　reached　the　peak　value,　and　phosphate　uptake　continued,　driven　by　the　nitrite　addition.　The　pH　was　adjusted　to　7.50　using　HCl　with　each　pulse　of　nitrite　addition.　ORP　could　be　used　to　determine　the　endpoint　of　denitrifiying　phosphorus　removal.　However,　the　variation　of　second　derivative　of　ORP　with　time　was　much　more　sensitive　and　should　be　a　more　suitable　control　parameter　than　ORP　itself　to　determine　the　endpoint　of　denitrifying　phosphorus　removal.　CONCLUSION:　Compared　with　denitrifying　phosphorus　removal　with　nitrate　as　electron　acceptor,　denitrifying　phosphorus　removal　with　nitrite　using　real-time　step　feed　can　save　22.3%　of　polyhydroxyalkanoate　(PHA)　for　phosphorus　removal　and　49.4%　of　PHA　for　nitrogen　removal.　In　addition,　the　reaction　time　could　be　shortened.　(C)　2010　Society　of　Chemical　Industry