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bank filtration
Bank filtration is a type of filtration that works by passing water to be purified for use as drinking water through the banks of a river or lake. It is then drawn off by extraction wells some distance away from the water body. The process may directly yield drinkable water, or be a relatively uncomplicated way of pre-treating water for further purification.〔
== Efficiency ==
Three filtration mechanisms are possible. Physical filtration or straining takes places when suspended particulates are too large to pass through interstitial spaces between alluvial soil particles. Biological filtration occurs when soil microorganisms remove and digest dissolved or suspended organic material and chemical nutrients. Chemical filtration or ion exchange may take place when aquifer soils react with soluble chemicals in the water. Most 'normal' contaminants (microbial organisms and inorganic or organic pollutants) will be removed by bank filtration, either because they get filtered out by the sand/earth of the bank, or because the passage time (which may be days or potentially weeks) is sufficient to render them inactive.〔(Bank Filtration for Water Treatment ) (from a Water Resources Research Center, University of Hawaii, Manoa, bulletin, 2000/08. Accessed 2008-03-24.)〕 Research has also shown that the removal efficiency depends not only on the contaminant, but also on the "hydraulic and chemical characteristics of the bottom sediment and the aquifer, the local recharge-discharge conditions, and biochemical processes".〔
There have been indications that some pharmaceutical compounds (medical drug traces from human use) may not always be sufficiently removed by bank filtration, and that in areas with substantial contamination of this type, additional treatment may be needed.〔''(Occurrence and fate of pharmaceuticals during bank filtration )'' - Heberer, Thomas et al.; University of Berlin / United States Geological Survey, ca 2001〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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