An　aerobic　sequencing　batch　biofilm　reactor　(SBBR)　packed　with　Bauer　rings　was　used　to　treat　real　domestic　wastewater　for　simultaneous　nitrification　and　denitrification.　The　SBBR　is　advantageous　for　creating　an　anoxic　condition,　and　the　biofilm　can　absorb　and　store　carbon　for　good　nitrification　and　denitrification.　An　average　concentration　of　oxygen　ranging　from　0.8　to　4.0　mg/L　was　proved　very　efficient　for　nitrification　and　denitrification.　Volumetric　loads　of　TN　dropped　dramatically　and　effluent　TN　concentration　increased　quickly　when　the　concentration　of　average　dissolved　oxygen　was　more　than　4.0　mg/L.　The　efficiency　of　simultaneous　nitrification　and　denitrification　(SND)　increased　with　increasing　thickness　of　the　biofilm.　The　influent　concentration　hardly　affected　the　TN　removal　efficiency,　but　the　effluent　TN　increased　with　increasing　influent　concentration.　It　is　suggested　that　a　subsequence　for　denitrification　be　added　or　influent　amount　be　decreased　to　meet　effluent　quality　requirements.　At　optimum　operating　parameters,　the　TN　removal　efficiency　of　74%-82%　could　be　achieved.　©　Higher　Education　Press　2007.