How does filtration separate suspended particles from a liquid?

In filtration, suspended particles are separated from a liquid by passing the mixture through a filter medium that allows the fluid to flow through while retaining the solid particles. This process relies on a driving force, such as a pressure difference, to move the fluid through the medium.1

The mechanism of separation depends on the type of filter medium used:

• Thin barriers: Media such as filter paper or screens act as a physical barrier with openings smaller than the particles being removed. As filtration proceeds, the accumulated solids form a porous "filter cake" that remains permeable to the liquid.2
• Thick barriers: Media such as sand or porous ceramics may have pores larger than the particles. In these cases, particles are removed as they travel through a tortuous path and become entrapped within the finer interstices of the filter bed.2

If particles are too fine to be filtered, they may be agglomerated through heating or chemical treatment to increase their size. For gelatinous or compressible solids that might clog (or "blind") the filter, filter aids are often added to maintain permeability.324