Ultrafiltration Membrane Elements

Technical Note By Dr. Dhawan:
What is Ultrafiltration?
Ultrafiltration (UF) is a separation process using membranes with pore sizes in the range of 0.1 to 0.001 micron.  Typically, UF will remove high molecular-weight substances, colloidal materials, and organic and inorganic polymeric molecules.  Low molecular-weight organics and ions such as sodium, calcium, magnesium chloride, and sulfate are not removed.  Because only high-molecular weight species are removed, the osmotic pressure differential across the membrane surface is negligible.  Low applied pressures are therefore sufficient to achieve high flux rates from an UF membrane.  Flux of a membrane is defined as the amount of permeate produced per unit area of membrane surface per unit time.  Generally, flux is expressed as gallons per square foot per day (GFD) or as cubic meters per square meters per day. 

UF membranes can have extremely high fluxes but in most practical applications the flux varies between 50-200 GFD at an operating pressure of about 50 psig in contrast, RO membranes only produce 10-30 GFD at 200-400 psig.