Filtrationmicrofiltration

Filtrationmicrofiltration, commonly referred to as microfiltration, is a membrane-based separation process used to remove suspended solids from liquids. It employs semi-permeable membranes with pore sizes typically in the range of about 0.1 to 10 micrometers, enabling the retention of particles larger than the pore through size exclusion and, to some extent, adsorption. The permeate primarily consists of water and small dissolved compounds, while the retained phase contains bacteria, spores, algae, colloids, and other particulates.

The process is driven by pressure differences and can operate in cross-flow or dead-end configurations. In cross-flow filtration, the feed moves parallel to the membrane surface, reducing fouling by sweeping retained material away from the surface. In dead-end filtration, all feed passes perpendicularly through the membrane, leading to rapid fouling unless frequent cleaning or backwashing is employed. Operating parameters such as transmembrane pressure and flux are balanced to optimize clarification while controlling fouling. Membrane fouling is a major consideration and is mitigated through pretreatment, cleaning in place, and appropriate module design.

Membranes are commonly composed of polymeric materials such as polypropylene, polyethersulfone, polysulfone, polyvinylidene fluoride, and cellulose derivatives. Module configurations include hollow-fiber, tubular, spiral-wound, and plate-and-frame designs. Microfiltration has broad applications, including water treatment for turbidity removal, clarification of dairy, fruit juices, beer and wine, and production of clarified beverages; in the biopharmaceutical and food industries for particle and microbe removal; and as a pretreatment step before ultrafiltration, nanofiltration, or reverse osmosis. It does not effectively remove dissolved salts or small organic molecules.