Filtration

Lore & Background

Filtration separates solid matter and fluid from a mixture using a filter medium that allows only fluid to pass. Solid particles that cannot pass are called oversize, and the fluid that passes is the filtrate. Oversize particles may form a filter cake or block the filter lattice, causing blinding. The effective pore size determines the largest particles that can pass. Separation is imperfect; solids may retain some fluid, and filtrate may contain fine particles depending on pore size, filter thickness, and biological activity.

Reader's Guide

Filtration is a fundamental physical operation used to separate particles and fluid in a suspension, where the fluid can be a liquid, gas, or supercritical fluid. It differs from sieving, which uses a single perforated layer, and from adsorption, which relies on surface charge. Filtration is employed in biological systems such as renal filtration in animals and in engineered systems like slow sand filters and trickling filters. It is also used in oil filtration to remove impurities and protect machinery. Various methods exist, including hot, cold, vacuum, centrifugal, and gravity filtration, each suited to different purposes. The driving force for filtration can be gravity, centrifugation, pressure, or vacuum.

Did You Know?

• Filtration differs from sieving because sieving uses a single perforated layer, while filtration uses a multilayer lattice.
• Oversize particles may form a filter cake on top of the filter and can also block the filter lattice, a phenomenon called blinding.
• In biological filters, oversize particulates are trapped and ingested, and the resulting metabolites may be released.
• Vacuum filtration uses a Büchner funnel, filter paper, Büchner flask, and rubber tubing connected to a vacuum source.