Various models have been proposed to predict the performance of granular activated carbon (GAC) for single and bisolute systems, including the use of a bed depth service model for interpreting data for operation of adsorption beds to remove total organic carbon (TOC). This model is essentially the simple or symmetrical logistic function. The generalized logistic function is applied to TOC removal and data from GAC, incorporating the inverse of the Freundlich isotherm slope. Thus the model is useful when the breakthrough curve is nonsymmetrical.