Abstract: The denitrification performance of the special anaerobic film bed （SAFB） and biological aerated filter （BAF） combined system in pilot scale （with a daily treatment quantity of500m 3／d） for low-strength domestic sewage was assessed under the conditions of different aeration amounts and influent water quality．It is found that the average removal rates of TN and NH4 ＋-N are respectively27．84％ and83．39％ when the ratio of air to water is greater than 2∶1‚while being respectively29．15％ and70．88％ when the ratio is less than2∶1．So the ratio should be controlled from2∶1to3∶1．It is also found that the carbon source has no effect on the denitrification when BOD5／TN of SAFB intake is more than4‚but it seriously influences the nitrification when CODcr／TN of BAF intake is more than5． 

Key words: special anaerobic film bed, biological aerated filter, low-strength domestic sewage, denitrification, aeration amount