Fuzzy modeling of an activated sludge process

The activated sludge process is a wastewater treatment technique used at sewage disposal plants. The process should be controlled so that the BOD value of an effluent satisfies a certain criterion. The paper deals with a fuzzy modeling for the activated sludge process. The output of the fuzzy model is the BOD value. Our proposed fuzzy inference method is applied to the fuzzy model. Since the inferred conclusion using the proposed method has a membership function of simple shape, its meaning can be interpreted easily. Moreover, it can also be considered as a possibility distribution. In addition, its linguistic meaning is interpretable by means of labeling of the membership function with its linguistic term. Since the fuzzy rules of the model consist of labeled fuzzy sets in an antecedent part and also a consequent part, the input-output relation of the process becomes able to be easily understood. The operator can predict a possibility distribution of a future BOD value by simulation with the model, and can take appropriate judgement and control based on the prediction. In the paper, from the modeling result, the effectiveness of the proposed method and the fuzzy model are shown.