Ultra Filtration (UF)

Ultra Filtration (UF) is a pressure-driven membrane separation process that removes suspended and colloidal matter from water by passing it through a semi-permeable membrane with pore sizes in the range of 0.01 to 0.1 microns. This pore size range places UF between microfiltration (larger pores, removes larger particles) and nanofiltration/reverse osmosis (smaller pores, removes dissolved ions). UF membranes effectively remove all suspended solids, bacteria, protozoa, viruses, colloids, colour-causing macromolecules, and high-molecular-weight dissolved organics, while passing water, salts, and small dissolved molecules through to the permeate.

UF systems are available in hollow-fibre membrane modules (inside-out or outside-in flow configuration) and, less commonly, spiral-wound configurations. Hollow-fibre modules are the dominant technology for water treatment applications, providing very high membrane surface area per unit volume and the ability to be backwashed and chemically cleaned in-place (CIP) to restore flux. Modules are housed in pressure vessels and connected in arrays to achieve the required permeate flow rate.

In water and wastewater treatment, UF most commonly serves two distinct roles: as a final tertiary polishing stage to produce high-quality reuse water meeting turbidity (<0.1 NTU), bacteria, and virus removal targets; and as a pre-treatment stage ahead of reverse osmosis (RO) membranes to protect the RO from fouling by suspended solids, colloids, and biological matter that would otherwise rapidly degrade RO performance. In pulp and paper applications, UF plays an important role in treating paper machine effluent for fibre and chemical recovery.