[Operation of the AAO Process Under Low Dissolved Oxygen Conditions and Its Simulation]

The anaerobic-anoxic-oxic (AAO) process was used to investigate the variation of the parameters of water quality when the dissolved oxygen (DO) in the aerobic tank was controlled at a low concentration. The results indicated the system still had good phosphorus and nitrogen removal efficiencies when the DO concentration in the aerobic tank was decreased from 2.00 mg·L^-1 to 1.00 mg·L^-1 and 0.50 mg·L^-1, and the effluent indexes could meet the first class A standard for the "discharge standard of pollutants for municipal wastewater treatment plant" (GB18918-2002) of China. The activated sludge model of the AAO process was developed by BioWin 4.1 software. The sensitivities of the model parameters were analyzed, and the model parameters, such as amount of polyhydroxyalkanoate (PHA) stored per unit of acetate or the propionate sequestered by phosphorus accumulating bacteria (Y_P/PHA,seq), the amount of phosphorus stored per unit of PHA oxidized in aerobic conditions by phosphorus accumulating bacteria (Y_{P/PHA,aerobic}), the maximum specific growth rate of ammonia oxidizing bacteria (μ_max,A), and the maximum specific growth rate of nitrite oxidizing bacteria (μ_max,N), were calibrated and validated by the dynamic simulation. In addition, the energy consumption of the aeration was simulated and evaluated. The results showed that when the DO concentration in the aerobic tank was decreased from 2.00 mg·L^-1 to 1.00 mg·L^-1 and 0.50 mg·L^-1, the air flow could be reduced by 23.8% and 38.1%, and the oxygen transfer efficiency could be increased by 7.2% and 11.7%, respectively.