Phosphorous Removal in Intermittent Cycle Extended Aeration System Wastewater Treatment Plant - Effect of Temperature

Wafangdian wastewater treatment plant (WTP) employed intermittent cycle extended aeration system (ICEAS), which was the first application in the northeast of China. WTP achieved good performance in the past almost three-year operation with effluent quality of COD 26~52 mg/L (40 mg/L in average), BOD 6~17 mg/L (11 mg/L in average), NH₄ ⁺-N 0.68~7.79 mg/L (3.87 mg/L in average), TN 11.61~19.44 mg/L (15.58 mg/L in average), SS 2~19 mg/L (11 mg/L in average) and TP 0.50~1.02 mg/L (0.88 mg/L in average). The average removal efficiency was COD 82%, BOD 87%, NH₄ ⁺-N 78%, TN 46%, SS 93% and TP 76%, respectively. The phosphorous removal efficiency in Wafangdian WTP was higher in winter, while lower in summer. The possible reasons for phosphorous removal were discussed, and the temperature was an important factor for the competition between phosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) in full-scale Wafangdian WTP.