Ultrafiltration Water Treatment Plant
The theory of ultrafiltration is not new. What is new is its successful, practical application to the separation of contaminants such as bacteria and organic colloidal impurities.
In the various separation systems listed in Figure 1, the ultrafiltration membranes used are noncellulosic organic polymers having an asymmetric, extremely thin (5-micron) surface layer or skin and a porous substructure of the same material. The total membrane thickness is only 6 to 8 mils; consequently, to handle the 20 to 50 psi used in water treatment, the membranes are reinforced with a nonwoven paper material for added mechanical support. Separations take place at the membrane surface, not within the substructure
In the tests reported here, the ultrafiltration systems comprise a series of modules, each providing 60 square feet of surface area. (Each module contains three replaceable cartridges, and each cartridge contains 20 square feet of membrane housed in a glass-reinforced polyester
Inherent in the use of membranes for phase separation is the fundamental problem of concentration polarization. The separation of one species from another at the surface of a membrane results in local concentration of the rejected species at the membrane surface. This concentration in turn causes an increase in density and viscosity of the laminar sub layer at the surface of the membrane. Associated with these changes is the decrease in membrane flux. The more severe is the polarization, the poorer is the long-term flux characteristics of the membrane.