Ultrafiltration

Ultrafiltration is a pressure-driven membrane separation process that uses a semipermeable barrier to separate particles based on size under applied pressure. The membranes have pore sizes in the range of about 0.01 to 0.1 micrometers, corresponding to molecular weight cutoffs from roughly 1 to 1000 kilodaltons. This allows water and small solutes to pass while retaining larger colloids, proteins, polysaccharides, and other macromolecules. The process is typically driven by transmembrane pressure, with temperature and flow geometry influencing performance.

Membrane configurations used in ultrafiltration include hollow-fiber, spiral-wound, and flat-sheet modules. In practice, cross-flow filtration is common to minimize fouling by continually sweeping away retained material. Operating pressures are relatively modest compared with reverse osmosis, often in the range of about 1–5 bar, depending on the feed and membrane MWCO.

Applications are diverse and include drinking water and wastewater treatment, where ultrafiltration provides clarification and pretreatment for subsequent processes; dairy and beverage processing, such as clarification and concentration of proteins and sugars; concentration and purification of bioprocessing products (proteins, enzymes, monoclonal antibodies); and medical dialysis. It can also be used for fruit juice clarification and concentration of biomolecules.

Fouling by particulates, organics, colloids, and biofilms can reduce flux and performance. Mitigation strategies include proper pretreatment, cross-flow operation, backwashing, and cleaning-in-place with chemical cleaners. Limitations include inability to remove small dissolved salts or monovalent ions, and it does not provide sterilization.