Filtrare

Filtrare, or filtration, is a physical separation process in which a fluid (liquid or gas) passes through a porous barrier to remove solid particles or contaminants. The medium, often filter paper, a membrane, or a cartridge, traps solids while allowing the fluid to pass. Filtration clarifies liquids, sterilizes solutions, or protects downstream equipment from particulates. In Romanian, the process is called filtrare.

Filtration techniques are categorized by mechanism and medium. Depth filtration relies on a porous matrix that adsorbs or retards particles as the fluid moves through; surface filtration concentrates particles near the entry surface. Membrane filtration uses semi-permeable membranes with defined pore sizes, enabling selective passage of solvent or small solutes while retaining larger particles. Membrane processes include microfiltration, ultrafiltration, nanofiltration, and reverse osmosis, each providing increasing rejection of solutes and decreasing pore sizes.

Filtration can be performed by gravity, vacuum, or pressure-driven methods. Tangential flow or crossflow filtration reduces fouling by sweeping along the membrane surface, while dead-end filtration concentrates all solids in the feed stream. Centrifugal filtration uses rotation to separate phases. Fouling—the buildup of retained material—limits performance and is managed by cleaning, backwashing, or replacing filters.

Common applications span drinking water and wastewater treatment, food and beverage processing, pharmaceutical manufacturing, and laboratory analysis. Filtration also serves in air purification, industrial process streams, and electronic or chemical manufacturing environments.

Key considerations in selecting a filtration approach include particle size or molecular weight cut-off, chemical compatibility with the fluid, temperature and pressure conditions, flow rate, and the required level of purity. Filtration efficiency is described by pore size or membrane characteristics and by operating parameters such as transmembrane pressure and filtration time.