Reverse Osmosis and Ultrafiltration

Membrane processes have been successfully employed for treatment of a large number of industrial effluents. Reverse osmosis (RO) and ultrafiltration (UF) are versatile separation and purification tools for the process industries. Both of these techniques are based on the ability of pressure-driven filtration membranes to separate multi-component fluids based on molecular size, shape, and chemical composition. A series of publications’ have discussed the principles of RO and UF processes for fractionation and concentration of oily and pulping effluents. Reverse osmosis and ultrafiltration are low-energy physicochemical processes which provide a n attractive alternative for treatment of various industrial effluents. These offer the advantage of being simple hydraulic processes, since no chemical reaction, phase change or dilution steps are required. Membrane performance data are discussed in this article for two industrial applications: oil-water emulsion separation; and fractionation and concentration of Kraft pulping effluents. Reverse osmosis and ultrafiltration are two of the family of separation processes dependent on the use of selective porous membranes for accomplishing molecular separations. Ultrafiltration is the process of filtering solute molecules or particles at least one to two orders of magnitude larger than the solvent molecules. Reverse osmosis, on the other hand, refers to filtering solute molecules of the same order of magnitude as those of t h e solvent. Relatively “tight” membranes are used in RO concentrating systems. UF contrasts sharply with RO in that relatively “open” membranes with little or no capability for sodium chloride rejection are employed.