Dissolved oxygen control of the activated sludge wastewater treatment process using stable adaptive fuzzy control

In the operation of wastewater treatment plants a key variable is dissolved oxygen (DO) content in the bioreactors. The paper describes the development of an adaptive fuzzy control strategy for tracking the DO reference trajectory applied to the Benchmark Simulation Model n.1. The design methodology of this data-driven controller uses the Lyapunov synthesis approach with a parameter projection algorithm to construct an adaptive fuzzy controller (AFC), and guarantees the global stability of the resulting closed-loop system. To work in parallel with the AFC it is proposed a new easy to design supervisory fuzzy control with a smooth switching scheme between supervisory and nonsupervisory modes. Both controllers assume no mathematical model of the plant and may integrate human knowledge. The results of simulations show that this combined controller can learn and improve control rules resulting in accurate DO control.