Nonlinear Fuzzy Control System for Dissolved Oxygen with Aeration System in Sequencing Batch Reactor

Biological processes at a wastewater treatment plant are complex, multivariable, time varying and nonlinear. Moreover, interactions between the components are very strong. Control of dissolved oxygen is one of most important task at the plant. The level of dissolved oxygen in aerobic tanks has significant influence on behaviour and activity of microorganisms at the plant. Air for aerated tanks is supplied by the aeration system (blowers, pipes, diffusers), which is a complicated nonlinear dynamical system. A fuzzy control system for tracking the dissolved oxygen reference trajectory in activated sludge processes was proposed and investigated. The sequencing batch reactor was considered. The nonlinear aeration system dynamic was included. Two systems (sequencing batch reactor, aeration system) were modelled and validated. Inverse model of an aeration system was used to control system design. Dissolved oxygen is the control input, while the rotational speed and blowers on/off are control outputs. The nonlinear fuzzy control system was tested by simulation based on real data records sourced from a case study plant located in Swarzewo, Northern Poland.