microfiltrationultrafiltration

Microfiltration and ultrafiltration are related pressure-driven membrane separation processes that use semi-permeable membranes to separate components in liquids according to size and, to some extent, charge. They are widely used for clarification, concentration, and pretreatment in water, food, and biopharmaceutical industries.

Pore size and mechanism differ between the two processes. Microfiltration typically features pore diameters of about 0.1 to 10 micrometers, enabling removal of suspended solids, turbidity, and most bacteria. Ultrafiltration uses much tighter pores, roughly 1 to 100 nanometers (about 0.001 to 0.1 micrometers), and primarily retains macromolecules such as proteins, polysaccharides, and colloids. Both processes rely on transmembrane pressure to drive liquid through the membrane, with tangential flow (cross-flow) helping to limit fouling.

Common configurations and materials include hollow-fiber, spiral-wound, and flat-sheet modules. Membranes are made from polymers such as cellulose derivatives, polysulfone, polyethersulfone, and PVDF, and can also be ceramic for demanding applications. MF and UF membranes are often used in series or as pretreatment before tighter membrane steps such as nanofiltration or reverse osmosis.

Applications span water treatment, beverage clarification, dairy processing, and biotechnology. MF serves well for turbidity reduction and microbial prefiltration, while UF concentrates and purifies proteins, minerals macromolecules, and some viruses, and often acts as a clarification step prior to downstream processing.

Operational considerations include fouling management, cleaning-in-place, and module aging. Energetic requirements are typically moderate, with lower pressures for MF and higher pressures for UF. Neither process removes dissolved salts or small organic molecules, which may require additional treatment steps.