Filtratsioon

Filtration (Filtratsioon in Estonian) is a separation process that removes solids from a liquid or gas by passing the mixture through a porous medium or membrane. The medium traps particles while the fluid flows through, and filtration can be driven by gravity, pressure, or suction. It is widely used to clarify fluids and remove contaminants.

Filtration methods are broadly categorized as depth filtration, where particles are captured within a thick porous bed, and surface filtration, where solids are retained on a thin barrier such as a membrane. Media range from natural substances like sand and cellulose to synthetic materials including glass fibers, membranes, and activated carbon.

Membrane filtration classifies by pore size: microfiltration (about 0.1–10 µm) removes bacteria and large colloids; ultrafiltration (2–100 nm) retains proteins and macromolecules; nanofiltration (1–2 nm) targets small ions; reverse osmosis removes most dissolved species. Tangential-flow filtration reduces fouling by keeping fluid guided parallel to the membrane.

Applications include drinking water and wastewater treatment, food and beverage processing, pharmaceutical manufacturing, and air filtration in clean environments. Filtration performance depends on pore size distribution, flow rate, pressure, temperature, and the properties of the liquid and suspended solids.

Common issues are fouling and clogging, leading to higher energy use or failed filtration. Cleaning strategies include backwashing, chemical cleaning, and, for membranes, cleaning-in-place. Filtration does not guarantee sterility; sterilizing filtration uses very small pore sizes to remove microorganisms.