What is ultrafiltration?

In the past decades, membrane technology applied to water treatment has been crucial for the expansion of desalination and water reuse technologies.

1 . Definition of ultrafiltration (UF)

Ultrafiltration is a separation process using a membrane, part of membrane technologies for water treatment, which allows the mechanical separation of suspended or dissolved solids with a sieve, using hydrostatic pressure to force water through a semipermeable membrane.

2 . How does an ultrafiltration membrane work?

The two phases that are in contact with the membrane are liquid and their hydrostatic pressure differs.  Certain components of the liquid phase will be transferred from the side with higher pressure to the side with lower pressure.

Small particles dissolved in the liquid will get through the porous membrane, whereas large dissolved molecules, colloids and suspended solids will not get through the pores and will thus be retained by the membrane.

Image: Tecca.

3 . Characteristics of ultrafiltration

The main characteristics of ultrafiltration (UF) are:

• Ultrafiltration membranes have a pore size that allows separating different types of particles ranging in size from 0.04 to 0.1 μm (suspended solids, fine particles, colloids, algae and microorganisms such as bacteria).
• The membranes are usually porous and are classified according to the molecular weight cut-off (MWCO), which is the molecular weight of the smallest molecule that is 90% retained by the membrane, ranging from 1,000 to 500,000 daltons, that is, molecules and macromolecules.
• Its productivity is high.
• The difference in pressure required is quite low, since the osmotic gradient is low.

4 . What is ultrafiltration used for?

Ultrafiltration (UF) is used as a pretreatment for surface water, seawater, groundwater, biologically treated effluent, and to prepare water for further treatment with membrane demineralization systems such as nanofiltration and reverse osmosis.