The biosand filter is an intermittent-flow adaptation of slow sand filtration technology. Developed over 20 years ago and now with 15+ years’ operating experience in households, it has established a reputation for effectiveness, durability, and sustained use. Research, field evaluations, and understanding of the nature of intermittent filter operation have led to advances in the design of the biosand filter as well as the specifications for the hydraulic loading rate, filtration sand, and pause period and requirements for maintenance and cleaning. Different methods of fabricating the filter body and diffuser basin are providing more alternatives for implementing biosand filter projects. As of December 2013, 500 organizations have reported implementing biosand filter projects in 59 countries, for a total of over 650,000 filters, impacting more than four million people (CAWST 2014).
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