Comparison of the Filterability of Mineral, Organic and Mixed Suspensions Application to Water Clarification

Abstract

Filtration operations were conducted on porous membrane to evaluate the specific contribution of the main fractions encountered in raw water (solids in suspension, soluble, or colloidal compounds) on the system permeability evolution during industrial operations. Experiments were conducted in a frontal filtration mode with single or mixed synthetic suspensions (clay, ferric hydroxide, activated carbon, latex, and humic acids). Results showed a wild specific resistance coefficient (α.W) difference between mineral and organic suspensions. The α.W coefficient increased with suspended solids concentrations. On the other hand, no actual differences were observed between the tested mineral suspensions, which also presented no actual differences in particle size distribution. In the same condition, latex suspensions composed by smaller elements induced higher hydraulic resistance, comparatively to mineral suspension, the resistance coefficient values were ten to one hundred times greater than the mineral suspensions. Nevertheless, a latex suspensions conditioning with FeCl₃ allowed a notably reducing of the resistance coefficient. Moreover, experiments on humic acid suspension pointed out the membrane fouling during filtration, which could disappear in the presence of activated carbon in the suspension. Since similar results were obtained in an immersed membrane system, it can be considered that this methodology can be developed to characterise the filterability of natural suspensions, and optimise the suspension conditioning. Key words: Water clarification, cake filtration, porous membrane, hydraulic resistance, synthetic suspensions