Hierarchical control optimization of WWTP operation via Pareto front

Wastewater treatment is an energy-intensive process pursuing two objectives: pollution abatement and energy conservation. To achieve these goals coordinated control actions are required. In a previous study (Dainotto et al., 2012) a hierarchical control structure was proposed and a basic two- level controller was designed to determine the dissolved oxygen set-point depending on the residual ammonium-N in the effluent. This paper carries the optimization a step further by seeking a coordination between the aeration and recycle controllers. A multi-objective optimization problem is set-up based on effluent quality and energy consumption and a coordinated optimal solution is obtained from the resulting Pareto front. This largely preliminary exercise seeks to demonstrate that, unlike in the previous study, differing control actions can in principle be coordinated. How this can implemented in practice will be the goal of future work. This preliminary assessment just wants to set the theoretical framework of the analysis and test the methodology, representing the necessary prerequisite from which an engineered solution will be developed