An analysis of nitrogen removal and control strategies in an alternating activated sludge process

The biological nitrogen removal in an alternating activated sludge process is described and analyzed using a simplified model of the IAWQ activated sludge model No. 1. In face of the alternating nature of the process, a new analytical approach is developed by introducing the nitrification capacity and denitrification potential concepts into the alternating process analysis. This facilitates a more obvious insight into the nitrogen removal with the development of mathematical relationships between the nitrogen removal efficiency and the process operational conditions. The process performances with different operational conditions and control strategies are presented using this approach. The results show that the total nitrogen removal is strongly dependent on the process load, nitrification rate, denitrification rate, cycle length and DO setpoint etc. and an optimal operation requires a proper match between the nitrification and denitrification. In addition, the different control strategies are evaluated using the new analytic technique and through this their mechanism and effectiveness are better understood.