Investigation of Fouling of Membranes of a Reverse Osmosis Unit by Silica

A reverse osmosis unit to treat ground water in Saboura/Syria has been in operation for several years. It suffered frequently from severe fouling of membranes. This led to frequent stoppages and losses of flow. Operators of the unit reported the formation of white solid scales on the membranes. It is well known that membranes treating ground water suffer from precipitates such as CaCO₃, CaSO₄, Fe, Al, Silica compounds, colloidal matters, bacteria and others. In this study analysis of the solid scales on the membranes showed that silica is the main scaling component. So experiments were carried out to investigate the effect of silica concentration in ground water and other variables such as pressure, pH, metal cations and type of membrane on fouling. The results obtained showed that silica has a direct effect on fouling of membranes. This is influenced by many parameters. Increasing pressure leads to increase in flow rates of water through the membranes. Reduction of pH causes less scaling of silica on the membranes. Cations present in water such as calcium and magnesium help in forming polymeric silicates which cause fouling.