Filtraation

Filtration is a physical operation that separates solids from liquids or gases by passing the mixture through a porous barrier or membrane. Retained solids form the filter cake or residue, while the filtrate is the fluid that passes through. The effectiveness of filtration depends on particle size, shape, and interactions with the filter material.

Filtration mechanisms include depth filtration, where particles are trapped throughout a porous medium, and surface filtration, where particles are retained on the surface of a barrier. Filtration can be driven by gravity, pressure differences, or vacuum. Filter media range from paper and fibers to membranes and ceramics; pore size and selectivity determine what is captured.

Common categories by pore size include microfiltration (about 0.1 to 10 micrometres), ultrafiltration (roughly 2 to 100 nanometres), nanofiltration (approximately 0.5 to 2 nanometres), and reverse osmosis, which uses a dense barrier and high pressure to reject dissolved substances. As the pore size or barrier tightens, progressively smaller solutes are removed.

Applications span water treatment, beverage clarification, pharmaceutical and food processing, wastewater treatment, air and gas filtration, and laboratory work. Filtration can provide particulate removal and, with appropriate membranes, sterilization or selective removal of contaminants.

Common media and equipment include filter papers, depth filters, and membranes made from cellulose, polymers, glass, or ceramics; activated carbon for adsorption; and filtration devices such as Buchner funnels, cartridge filters, and pleated systems. Fouling and clogging reduce efficiency and increase operating costs, requiring replacement or cleaning.

Limitations to consider include fouling, energy consumption, waste disposal, and trade-offs between flux and selectivity. The choice of filtration system depends on the material being processed and the desired level of contaminant removal.