A dissipative approach to control of biological wastewater treatment plants based on entire nonlinear process models

This paper proposes an approach to control design of biological wastewater treatment (WWT) plants based on rigorous treatment of the complex mathematical models from a nonlinear control theoretical viewpoint. Without resorting to order reduction, localization and linearization of process models, this paper provides a promising avenue to model-based control design for necessary innovations of modern WWT. Fundamental properties of the activated sludge WWT plant are investigated, and a dissipation property of the entire plant is derived from precise integration of all components of the plant. For the purpose of efficient removal of carbon and nitrogen, control laws are proposed so that the dissipation of the entire plant is preserved in the presence of control inputs. This paper demonstrates that utilization of the natural principle, the dissipation, is very effective in extracting compact global information of the large-scale plant, and it enables us to accomplish a model-based control design taking into account the whole behavior of the WWT plant.