Application of the Morris method for screening the influential parameters of fuzzy controllers applied to wastewater treatment plants

In this paper, we evaluate the application of a sensitivity analysis to help fine-tuning a fuzzy controller for a biological nitrogen and phosphorus removal (BNPR) plant. The Morris Screening method is proposed and evaluated as a prior step to obtain the parameter significance ranking. First, an iterative procedure has been performed in order to find out the proper repetition number of the elementary effects (r) of the method. The optimal repetition number found in this study (r = 60) is in direct contrast to previous applications of the Morris method, which usually use low repetition number, e.g. r = 10 ∼ 20. Working with a non-proper repetition number (r) could lead to Type I error (identifying a not-important factor as significant (false positive)) as well as Type II error (identifying an important factor as not significant (false negative)), hence emphasizing the importance of finding the optimal repetition number for each study in question. With the proper r found, the Morris Screening helped identify the parameter significance ranking, thereby facilitating the calibration of fuzzy controllers, which contain many parameters that need to be adjusted for different wastewater treatment plant (WWTP) applications.