Intelligent control aeration and external carbon addition for improving nitrogen removal

Fuzzy logic can in several ways be applied to improve the control of the activated sludge system. In this paper, fuzzy logic based control strategies for external carbon flow in the anoxic zone and dissolved oxygen (DO) concentration in the aerobic zone are presented and evaluated by the simulation of the predenitrification layout of the COST 624 benchmark implemented by Matlab/ Simulink. The aeration fuzzy controller was designed as high-level controller that determines the DO set points in the aerated basin; conventional PI controller was used to maintain the DO concentration at the set point levels. The ammonia concentration in the influent and effluent were used as input variables for the fuzzy controller. Compared to the operation with constant DO concentrations, the required airflow could be reduced up to 7%, the effluent ammonia concentration could be reduced up to 18% by using fuzzy logic based control strategy. At the same time, ammonia peaks in the effluent could be reduced significantly. The external carbon flow fuzzy controller which includes two inputs variable, the error (E, nitrate in the second basin minus the preset-point) and change in error (EC), and one output variable, which adjusts the external carbon flow, compared to the normal PI operation, the external carbon flow could be reduced up to 24.2%. Experiments show that the fuzzy controllers can be easily implemented in modern control and supervision systems, to improve the effluent quality and reduce operating cost.