Development and economic assessment of different WWTP control strategies for optimal simultaneous removal of carbon, nitrogen and phosphorus

•Development of new control strategies for enhancing P-removal in WWTP.•Performance comparison of optimized open loop operation to the new control structures.•Control loops based on COD addition to the anaerobic reactor allow stable EBPR.•Optimized controllers allowed lower effluent pollutants and minimal operational costs.

This paper presents the comparison of four control strategies for the A2/O WWTP configuration for simultaneous C, N and P removal. The control strategies: (i) external COD-P control; (ii) external recycle flow-P control; (iii) nitrate control in the last anoxic reactor; (iv) ammonia control in the last aerobic reactor, were combined with other common control loops to build different control structures and were simulated in Matlab/Simulink under different influent conditions. A systematic approach was conducted with all the strategies to assess their potential effectiveness, according to the following steps: theoretical design, setpoint optimization and, finally, a detailed comparison of the control results against a reference operation and an optimized reference scenario. The optimization of the reference operation presented a 7% reduction of the total operational cost. The simulation results showed that some control strategies further reduced 3–7.5% the WWTP operational costs while the effluent quality is greatly improved.