Ultrafiltration (UF):

The ultrafiltration (UF) is a process wherein the solvent along with microsolutes permeates through the membrane and macrosolutes are retained by the membranes. This process is same to sieving and the driving force is the hydrostatic pressure across the membrane. The process is used to fractionate the solutes in a solution based on their size or molecular weight difference. Size or the molecular weight difference of the macrosolute retained through the membrane depends upon the pore size of the membranes. Microsolutes whose effectual sizes are smaller than the pore size of the membranes permeate with the solvent while macrosolutes whose effectual sizes are larger than the pore size of the membranes are retained. A driving force used in ultrafiltration processes is of the sequence of 500 kPa or so. The membranes used in ultrafiltration processes have pore sizes ranging from around 30 Å to about 200 Å.

Classic applications of the ultrafiltration process are the concentration of protein in milk for cheese making and separation of oils, colloidal particles, and macromolecules from effluent waters as well as from surface waters.