Influence of MLSS, pH, and NO_2~--N Concentration on Denitrifying Phosphorus Removal

A series experiments using DPB sludge cultivated in A_2N process were carried out in SBR, in order to study the effect of MLSS, pH, and NO-_2-N concentration on anaerobic phosphorus release and anoxic phosphorus uptake by phosphorus accumulated organism (PAO). The result shows that increase of MLSS can shorten the reaction time of anaerobic phosphorus release and anoxic phosphorus uptake; however, excessive MLSS will result in secondary release of phosphorus at the end of anoxic phosphorus uptake. When pH increases from 6 to 8, P/C increases too, and when pH is higher than 8, phosphate precipitation occurs, which will affect the normal phosphorus release. Besides, great rising of pH during anoxic phosphorus uptake will disturb the biological phosphorus removal effect. When NO-_2-N concentration is controlled at 5.5-9.5 mg/L, NO-_2-N can be used as electron acceptor by DPB for phosphorus uptake; when NO-_2-N reaches 15 mg/L, both the denitrification and phosphorus uptake will be inhibited.