Removal efficiency of metallic trace elements by slow sand filtration: study of the effect of sand porosity and diameter column

Abstract

The removal potential of slow sand filtration was investigated in a continuous fixed-bed adsorption system as a replacement of current expensive methods for decontaminating water. This study was achieved on Tensift River water contaminated by metallic trace elements (Cd, Cu, Pb and Zn) that received directly wastewater of industrial unit of Zn and Pb extraction of Draa Lasfar mine near Marrakech city in Morocco. Results showed that removal efficiency of sand used in this process depends greatly on both sand porosity and diameter of column. Thus, higher decontamination efficiency was noted at higher column’s diameter and higher sand porosity. These results can be justified by the fact that higher diameter of column and sand porosity engenders a higher mass transfer zone due to an increase coefficient diffusion and longer contact time as well as shallow adsorption zone with exposition of new active binding sites to metallic pollutants on the sand surface. This result provides a larger service area leading to an increase in the volume of the treated solution water. In order to describe the column adsorption process used in slow sand filtration, it is crucial to predict the breakthrough curve (concentration-like profile) and adsorption capacity of sand under the given set of operating conditions (sand porosoty and diameter of column), based on the assumption that this process follows Langmuir kinetics of adsorption–desorption with no axial dispersion which describes that the rate driving force obeys the 2nd order irreversible reaction kinetics.