Effect of Dissolved Oxygen Concentration on Performance of A~2/O Process

As a conventional process used in WWTP,A2/O process was used to treat actual domestic sewage to investigate the effect of DO on the performance of this process.The results showed that when the average DO concentration in aerobic zone was decreased from 4.0 mg/L to 1.0 mg/L,the removal of COD was not affected basically.However,the nitrification effect was decreased with the decrease of DO.Simultaneous nitrification and denitrification(SND) was enhanced with the decrease of DO,and the TN removal efficiency was increased correspondingly.Considering the nitrogen removal,the DO concentration could be kept between 1.0 and 2.0 mg/L.The removal of phosphorus was drastically affected by the decrease of DO.When the DO concentration was 1.0 mg/L,the removal efficiency of phosphorus is decreased by deterioration of phosphorus removal performance caused by insufficient oxygen supply.The limited sludge bulking was caused by the low DO concentration,and the effluent SS was lower than 5 mg/L during this period.It is recommended that the DO concentration in the A2/O process should be kept higher than 2.0 mg/L during the operation.Or else,chemical phosphorus precipitation should be introduced.