Ultrafiltration is a form of filtration that uses membranes to preferentially separate different fluids or ions. Ultrafiltration is not as fine a filtration process as Nanofiltration, but it also does not require the same energy to perform the separation. Ultrafiltration also uses a membrane that is partially permeable to perform the separation, but the membrane's pores are typically much larger than the membrane pores that are used in nanofiltration.

Ultrafiltration is most commonly used to separate a solution that has a mixture of some desirable components and some that are not desirable. One of the applications that demonstrates the usefulness of ultrafiltration is electrodeposition paint recovery. In this instance the paint, composed of a resin, a pigment and water are separated into two streams that can be reused. The first stream includes the water and a small amount of the paint resin, which can be used to rinse the parts later in the process. The paint pigment is separated from that stream and can be re-used in the paint bath, allowing the bath to be concentrated to a useable level.

 

Ultrafiltration is capable of concentrating bacteria, some proteins, some dyes, and constituents that have a larger molecular weight of greater than 10,000 daltons. Ultrafiltration is only somewhat dependent upon the charge of the particle, and is much more concerned with the size of the particle. Ultrafiltration is typically not effective at separating organic streams.