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Terms & Synonyms

Official WHO Definition

Enrichment (positive adsorption or briefly adsorption) of one or more components in an interfacial layer (OMS 1997).

Adsorption is a process that occurs when a gas or liquid solute adheres to the surface of a solid or, more rarely, a liquid forming a molecular or atomic film (the adsorbate) (WHO 1992). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution.

Other Definitions


Interpretations and Explanations

Adsorption is a method used to remove foreign matter from liquids. Foreign matter sticks to the adsorptive material and is drawn out of the solution.

Adsorption processes and adsorbents such as charcoal, clay, glass and various types of organic matter have been used for water treatment since ancient times. Some of these adsorption processes tend to overlap with either filtration processes, because the media are often used in the form of a filter through which water is passed, or coagulation processes, because they may be combined with chemical coagulants. Therefore, adsorption processes can be carried out concurrently with filtration or coagulation.

Commonly used adsorbents are clay, charcoal, and crushed organic matter. Advantages and disadvantages to the different media exist.


OMS (1997) Programa Internacional de Seguridad de Sustancias Químicas. Seguridad química; principios básicos de toxicología aplicada. La naturaleza de los peligros químicos. 2 ed. (revisada). Lima: CEPIS; 1997. Módulo de capacitación, 1. Also in English (IPCS)

WHO (1992) A guide to the development of on-site sanitation

WHO (2002) Managing water in the home: accelerated health gains from improved water supply

WHO (2001) Water quality - Guidelines, standards and health: Assessment of risk and risk management for water-related infectious disease

WHO Lexicon page (translations and examples)

See also

External Resources


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