Filter backwash


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Terms & Synonyms

Official WHO Definition

Water and material obtained from by the reversing the water flow through a filter and freeing the material retained by it (WHO 2004).

Other Definitions


Interpretations and Explanations

When solids accumulate within a filter bed, they create a resistance to flow. This resistance is measured as loss of head (pressure increase) for the filter bed. The filter is backwashed, usually with finished water, to remove the accumulated particles. The need for backwashing may be determined using various criteria — a terminal head loss, a fixed time interval, or a breakthrough of solids (measured as turbidity or particle counts). Options for disposal of the spent filter backwash water may include discharge to a sewer or a receiving stream. Because backwash water may contain disinfectants and other chemicals that may be harmful to the biological life of a stream, direct discharge to streams may be restricted. Similarly, discharge to sewers may be restricted, based on the constituents and total quantity of the backwash water. Poor distribution of wash water from headers to take-off piping causes uneven washing and soon leads to problems in the filter bed (WHO 2004).


WHO (2004) Water treatment and pathogen control : process efficiency in achieving safe drinking-water

WHO Lexicon page (translations and examples)

See also

External Resources


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