PHYSICOCHEMICAL STUDY OF FOULING MECHANISMS OF ULTRAFILTRATION MEMBRANE ON BIWA LAKE (JAPAN)

Many studies have been undertaken to understand the fouling of the ult rafiltration membranes in drinking water treatment. Physico-chemical f ouling of membranes depends on characteristics of the raw water and me mbrane surface properties. In the case of Biwa lake, some chemical par ameters as Si and Fe concentrations change with temperature (season) c ausing irreversible fouling. While some exist on the influence of the particle mineralogy on the fouling, little work has been developed to elucidate the relation between the physicochemical complexity of the c ake and the fouling. Generally clays or oxides are known to lead to a reversible fouling. In this work, the interactions between a UF organi c membrane with minerals leading to a hardly reversible fouling are st udied. In the case of the :Biwa lake water, fouling of ultrafiltration membranes results from the formation of a Si-rich ferric gel directly deposited on the membrane surface and a secondary allophanic gel laye r at a bigger distance. The deposit nature and the membrane/cake inter actions were studied using infra-red, X-ray diffraction, Al and Si NMR and EXAFS technics. The effect of mineral particles, especially ferri c oxides associated with silica, has been demonstrated. The formation of FeSi gel directly on the membrane surface is mainly responsible for the fouling. The change of these particles is less negative than the membrane surface. The structure of such a material is complex. The low permeability of the gel is at the prime origin of the fouling.