Ultrafiltration (UF) is a water purification process in which water is forced through a semipermeable membrane. Suspended solids and high-molecular-weight solutes remain on one side of the membrane, the retentate side, while water and low-molecular-weight solutes filter through the membrane to the permeate side.

UF can remove most organic molecules and viruses, as well as a range of salts. It has gained popularity because it produces a stable water quality no matter the source water, has a compact physical footprint, removes 90-100% of pathogens, and does not require chemicals, except for cleaning membranes.

UF Membrane Characteristics

The pore size of ultrafiltration membranes ranges from 0.1 to 0.01 microns, but “molecular weight cut-off” (MWCO) is now one of the best ways to describe UF membranes. MWCO is the molecular weight at which 90% of a macromolecular solute does not pass through the membrane. UF’s range of filtration lies between microfiltration and nanofiltration.

The membranes used in ultrafiltration require maintenance cleaning to prevent fouling with solids, scaling, and microbiological agents such as microbes and algae. Separated contaminants condensed in the UF retentate must be disposed of.

Typical UF applications include:

  • Treatment and recycling of wastewater and industrial process water
  • Removal of particulates and macromolecules (for example, 90-95% arsenic removal) for potable water production
  • Standalone systems
  • Augmentation or replacement of secondary and tertiary filtration stages in existing water treatment plants
  • Filtration of paper pulp mill effluent
  • Food and beverage industry applications
  • Water softening


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