This work deals with the development of a comprehensive but simplified version of floc model for the activated sludge process. The rate expression of the type used by the IAWPRC Task Group was employed in this study to represent the reaction kinetics inside the floc matrix. The intraparticle mass transport was then incorporated to account for the effects of the diffusional limitations. Solution to the flee model was obtained by orthogonal collocation technique. Since the actual reactions are not only related to the sludge floc size and the bulk characteristics but ave also associated with the floc size distribution, the concept of overall effectiveness factor was therefore used. Evaluation of overall effectiveness factors using neural network analysis was carried out and potential control strategies were discussed.