Intercross real-time control strategy in alternating activated sludge process for short-cut biological nitrogen removal treating domestic wastewater

To develop technically feasible and economically favorable dynamic process control (DPC) strategies for an alternating activated sludge (AAS) system, a bench-scale continuous-flow alternating aerobic and anoxic reactor, performing short-cut nitrogen removal from real domestic wastewater was operated under different control strategies for more than five months. A fixed-time control (FTC) study showed that bending-points on pH and oxidation-reduction potential (ORP) profiles accurately coincided with the major biological activities. "Ammonia valley" on the pH profile represented the end of nitrification, whereas, the "nitrite knee" on the ORP profile and "nitrite apex" on the pH profile both indicated the end of denitrification. Therefore, a new reliable and effective real-time control strategy was developed using pH and ORP as control parameters, to improve the performance of the AAS process. The online control strategy could achieve up to 87% of the total nitrogen (TN) removal efficiency on an average, and saving approximately 20% aeration energy, as compared to the conventional steady-state control systems. Moreover, stable short-cut nitrification and denitrification were successfully achieved with an average nitrite accumulation ratio of above 95%.