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Substitutes for Sand in a Biosand Water Filter

The biosand filter is a type of slow sand filter used in large-scale (municipal) and small-scale (household) water filtration systems. The biosand filter builds up a biologically active layer in the top few centimeters of sand which helps trap particles and waterborne pathogens (disease-causing organisms) and feeds on them. The water passing through both this "schmutzdecke" or "filter cake" layer and the mechanical filtration of the following sand thickness will be scrubbed of most particles and pathogens.
Although cheap and widely available, sand is not the only media which can be used.

  1. Crushed Stone

    • Crushed sandstone or crushed brick pieces as waste or "spall" from manufacturing processes is used as a sand substitute in cement and mortar works. When cleaned, this byproduct will provide the same coarse filtering mechanical action as the bulk coarse sand used in the biosand filter.

    Crushed Glass

    • The grit obtained from crushing recycled glass is non-toxic, inert and holds no heavy metals. This sand substitute will last longer than most "natural" sand, meaning when the biosand active layer needs to be scraped away to allow filter flow to be maintained, the removed layer may be washed and reused longer than with sand. The glass grinding process may be used to take the glass down to the fine "white sand" grit size used in final filtration as well as for more coarse upper layers.

    Other Materials

    • Aluminum oxides, acrylics and various plastic media have been used as sand substitutes in sandblasting, grit-cleaning and mortar mixing processes. These materials offer the size and chemically inert properties needed for a biosand filter, but are much more expensive to use in the volumes needed for water filtration. The mechanical action of trapping turbidity, cysts and pathogens as used by the biosand filter can be matched by these materials. Since many biosand projects are directed toward use in the Third World, cost and material availability make simple sand a hard material to replace.

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