filtration

Filtration is a physical separation process that removes solid particles from a fluid by passing the mixture through a porous medium or membrane. The solid material is retained in or on the filter while the fluid flows through, resulting in a clarified liquid or a filtered gas. Filtration operates mainly by size exclusion, physical trapping within a porous network, and, in some cases, by adsorption of particles to the filter medium. Filter media vary in structure: depth filters use a thick bed of porous material that traps particles throughout its thickness; surface filters act mainly as a sieve or screen; membrane filters use a defined pore size to exclude particles smaller than that size.

Common filtration systems include depth filtration (sand, cellulose, diatomaceous earth), surface filtration (screening), and membrane filtration (microfiltration, ultrafiltration, nanofiltration, and reverse osmosis). Gas and air filtration use similar principles, with media such as HEPA and activated carbon providing particle capture and adsorption.

Key parameters are pore size or rating, filtration efficiency, flow rate, pressure, and fouling propensity. Fouling occurs when retained material or biological growth impedes flow, often addressed by prefiltration, backwashing, cleaning-in-place, or media replacement.

Applications span water and beverage treatment, pharmaceutical manufacturing, food processing, environmental monitoring, and indoor air quality. Filtration is typically combined with other unit operations to achieve purity, sterility, or contaminant removal, with choice of method dictated by target particle size, chemical compatibility, and operating constraints.