Adsorption of organics inot activated carbon particles within a fixed-bed adsorber is modeled using the concept of mixing cells. The adsorption isotherm of these organics is taken to be rectangular because of the commonly observed strong affinity of organics into activated carbons. The model equations are solved by a singular perturbation method, and this results in a graphical procedure similar to that of McCabe and Thiele used in distillation column design. Such a graphical procedure provides a quick means to determine the adsorbate profiles along the adsorber for a given time and also the breakthrough curve, which reflects the performance of the adsorber.