Activated sludge bulking initiated by cooperation of low DO and sludge loads

The SVI,sludge bulking type,SOUR,the denitrification and dephosphorization efficiency,SND rate of activated sludge system were investigated in a sequencing batch reactor(SBR)at low DO loading(0.5 mg·L-1),pH 7.2—8.0,temperature(23±0.5)℃,MLSS 3000—3500 mg·L-1.The results showed that at low DO levels,the bulking of sludge is not observed at load of 0.22 g COD·(g MLSS)-1·d-1,while the deterioration of SVI accelerates and type of sludge bulking changes with the increase of sludge loads.At 0.66 g COD·(g MLSS)-1·d-1 loading,non-filamentous bulking of activated sludge is observed and the denitrification and dephosphorization efficiency goes down,but at 0.44 g COD·(g MLSS)-1·d-1 filamentous bulking takes place,the denitrification and dephosphorization efficiency keeps well,the rate of phosphorus absorption is faster,and SS in effluent is almost negligible.The SND rate is the maximum at no bulking of activated sludge,medium at having non-filamentous bulking,and minimum at filamentous bulking.If SOUR was over-high it is very possible to droop sludge settleability and to deteriorate water quality in effluent.