Fuzzy control of dissolved oxygen in a sequencing batch reactor pilot plant

The present work is part of a global development of reliable real-time control and supervision tools applied to wastewater pollution removal processes. In these processes, oxygen is a key substrate in animal cell metabolism and its consumption is thus a parameter of great interest for the monitoring. In this paper, are presented and discussed the results of the dissolved oxygen (DO) control in a SBR pilot plant based on a predefined 8 h step-feed cycle. As first approach, the application of classical methods (on/off and PID) was considered. Due to the non-linear character of the process, the PID parameter adjusting was very difficult and the obtained results showed a beating phenomenon around the setpoint. This phenomenon was more and less amplified according to the step of the cycle and the water pollution level. The second approach to achieve more stable DO control was based on a fuzzy logic strategy, taking into account the step and the difference between the measured DO and the setpoint. In this case, control action performances were highly improved. It is also shown that, using the fuzzy controller, the pH profile made it possible to clearly detect the ammonia valley during the aerobic phases. Thus, fuzzy logic proved to be a robust and effective DO control tool, easy to integrate in a global monitoring system for cost managing.