Study of control strategy and simulation in anoxic-oxic nitrogen removal process.

The control strategy and simulation of external carbon addition were specially studied in an anoxic-oxic (A/O) process with low carbon: nitrogen (C/N) domestic wastewater. The control strategy aimed to adjust the flow rate of external carbon dosage to the anoxic zone, thus the concentration of nitrate plus nitrite (NOx(-) -N) in the anoxic zone was kept closed to the set point. The relationship was studied between the NOx(-) -N concentration in the anoxic zone (S(NO)) and the dosage of external carbon, and the results showed that the removal efficiency of the total nitrogen (TN) could not be largely improved by double dosage of carbon source when S(NO) reached about 2 mg/L. Through keeping S(NO) at the level of about 2 mg/L, the demand of effluent quality could be met and the carbon dosage could be optimized. Based on the Activated Sludge Model No. 1 (ASM No. 1), a simplified mathematical model of external carbon dosage was developed. Simulation results showed that PI controller and feed-forward PI controller both had good dynamic response and steady precision. And feed-forward PI controller had better control effects due to its consideration of influent disturbances.