Optimization of A2O Process by Changing Anoxic Tank Volume Based on GPS-X Simulation

Abstract In order to improve the nitrogen removal efficiency of the anaerobic-anoxic-aerobic process (A2O), the effect of anoxic tank volume on the total nitrogen (TN) removal efficiency and total phosphorus (TP) removal efficiency were investigated under different ratios of chemical oxygen demand (COD) to nitrogen (C/N). The results showed that under C/N=7, the HRT of anoxic tank increased from 1.8 h to 3.6 h had little effects on the removal efficiency of COD, but largely improving the removal efficiency of TN and TP which increased from 66.8% and 93.8% to72.0% and 95.2%, respectively. Under C/N=10, increasing the volume of the anoxic tank did not significantly improve the removal efficiency of COD, TN and TP. The optimal HRTs of anoxic tank and the corresponding volume ratios of anaerobic, anoxic and aerobic were 4.0 h, 4.3 h and 1:2.5:6.75, 1:2.69:6.75 simulated by GPS-X software under C/N=7 and C/N=10, respectively. The results proposed that the appropriate elevated the volume of the anoxic tank could help A2O process to meet the TN discharge concentration lower than 15 mg/L. Under low C/N, changing the HRT of anoxic tank to improve the pollutant removal efficiency of A2O reactor was more significantly, so this method was more suitable for the case of insufficient carbon source.