Filtration

Filtration passes water through a porous medium that retains suspended particles and, in some systems, microorganisms. Its performance depends on the medium, particle properties, and operating conditions.

Filter cake: A layer of retained particles that accumulates on a filter surface during filtration. The growing deposit can become the main barrier that captures particles.
Suspended solids: Solid particles dispersed in a fluid rather than dissolved in it. Filtration commonly targets these particles while dissolved substances may pass through.
Rapid sand filter: A water-treatment filter that passes water rapidly through a bed of sand, often after coagulation and flocculation. It is a widely used granular filter for removing particles from treated water.
Sedimentation: The separation of suspended particles from a fluid as gravity causes them to settle. It removes settleable particles without forcing water through a porous medium.
Filter breakthrough: The passage of particles through a filter after its removal performance declines or capacity is exceeded. Breakthrough signals that a filter no longer retains particles as effectively.
Pore size: The characteristic dimensions of openings in a porous material. Pore dimensions influence which particles pass through or are retained.
Porous medium: A solid material containing interconnected or isolated pores through which fluids may pass. It supplies the passages and surfaces that make filtration possible.
Slow sand filter: A sand-bed water filter that operates at low flow and develops a biologically active surface layer. It can remove particles and pathogens through both physical straining and biological processes.
Coagulation: The chemical destabilization of small particles so they can aggregate into larger flocs. It prepares fine particles for removal by filtration or settling rather than filtering them directly.
Head loss: The reduction in fluid pressure or hydraulic head as water flows through a system. Accumulated particles increase resistance and can raise head loss across a filter.

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