Comparison of algorithms for hybrid nonlinear optimization problem in biological wastewater treatment plant

The paper presents the hierarchical control system applied to the Sequencing Batch Reactor (SBR) and aeration system in a Wastewater Treatment Plant (WWTP) in Swarzewo. This control system takes advantage of optimization in order to find the optimal reference trajectory of the dissolved oxygen concentration. The dissolved oxygen concentration is a parameter that determines the efficiency of biological processes and affects the costs of wastewater treatment. The aim of optimization was to minimize the consumption of electricity by the aeration system, while meeting the limitations on the maximum values of pollutants in treated wastewater, resulting from the water-law permit. The optimization problem is nonlinear and hybrid due to simultaneous occurrence of continuous and binary decision variables. Five deterministic and non-deterministic optimization methods were used to solve the decision problem. Finally, comparative analysis of the performance of different optimization methods was carried out.