Biosorption of lead ions was studied ill a flow-through column packed with red algae Gelidium and a composite material (industrial algal waste from the agar extraction process immobilized with polyacrylonitrile). Experiments were performed in order to study the effect of important design parameters such as now rate and influent pH. The breakthrough curves for lead and proton concentrations were obtained ill Saturation and elution studies. Macroscopically. when the flow rate increases, the residence time in the bed decreases, and the column saturation is faster achieved and the sharpness of the breakthrough curves increases. Microscopically, increasing the flow rate, the film diffusion resistance decreases. For higher values of the influent pH, the breakthrough time increases, clue to the greater metal uptake capacity at the equilibrium. Considering the effectiveness of lead desorption from loaded biomass, we concluded that desorption was 100% effective and rapid, even for high values of the solid to liquid ratio, leading to high values of the concentration factor. The column packed with composite material was operated in two consecutive adsorption-desorption cycles, without any changes in the metal uptake capacity. A mathematical model based oil external and intraparticle mass transfer was developed to simulate the breakthrough curves in the adsorption and desorption processes. (c) 2008 Elsevier B.V. All rights reserved.