The bed depth service time (BDST) design model, which accounts for the change of bed adsorption capacity with service time, has been modified to expand its application and overcome the limiting assumptions of the original BDST analysis. Column experiments were undertaken to test the new model for two adsorption systems, namely zinc ion-bone char and Acid Blue 80 dye-activated carbon. It was found that the percentage of saturation capacity could be correlated using a square-root dependence on the service time and this correlation was incorporated into the original BDST analysis to replace the total sorption capacity term, giving the model a much wider application to real systems. The empty bed residence time optimization approach was modified using the same time-dependent capacity expression and was successfully applied to the metal ion-bone char and the dye-activated carbon system with the use of equilibrium saturated bed capacity. These modifications to the BDST design model and the EBRT optimization model will, give more accurate scale-up data for the design of large-scale column adsorption systems.