The objective of the present work is to determine the operating conditions of an activated carbon filter, based on the characteristics of breakthrough curves. In order to properly design and operate fixed-bed adsorption processes, we apply the concept of the mass transfer zone (MTZ) that helps to obtain the evolutions of the operating parameters of the fixed-bed. Phenol solutions were prepared in three initial concentrations of phenol (20, 40, 60 ppm). The experimental data were analyzed by calculating fractional capacity (F), the height of (MTZ) (HZ), the number of unit transfer equivalent (NZ), the amount of phenol eliminated by the bed of activated carbon at the breakthrough (ABP).