Fuzzy logic can in several ways be applied to improve the control of the activated sludge system. In the present study, two types of fuzzy logic controllers were developed for intermittent aeration control: a low-level fuzzy controller for DO control and a high-level controller for nitrogen removal. A Simulink-SIMBAR model was used to subsequently design and optimise the controller and furthermore to compare various control strategies. The results indicate that the direct fuzzy controller allows for some improvements in comparison with a PI controller. Nevertheless, it is suggested that high-level controllers have more potentials for improving and integrating the control of wastewater treatment. The developed high-level fuzzy controller performs better than two conventional controllers in terms of energy consumption and, at the same time, results in a slightly better effluent quality. Design and tuning were quite straightforward. Since the rule base applied is comprehensive it is expected that in practice the controller will meet with the demands of the operator.

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