Appropriate Technology

[Lawrence London <lfljvenaura AT gmail.com>]

http://www.cawst.org/en/themes/biosand-filter

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Biosand filter

What is the Biosand Filter?

 The biosand filter (BSF) is an adaptation of the traditional slow sand filter, which has been used for community drinking water treatment for almost 200 years. The biosand filter is smaller (about 3 feet tall and 1 foot wide) and adapted for intermittent use, making it suitable for use in people’s homes. The filter container can be made of concrete or plastic and is filled with layers of specially selected and prepared sand and gravel. The sand layer removes pathogens and suspended solids from contaminated drinking water.

 

History of the Biosand Filter

 Dr. David Manz developed the household biosand filter in the 1990s at the University of Calgary, Canada. Dr Manz has trained many organizations on the design, construction, installation, operation and maintenance of the biosand filter. He also co-founded CAWST in 2001 to provide the professional services needed for the humanitarian distribution of the filter in developing countries.

As of June 2009, CAWST estimates that over 200,000 biosand filters have been implemented in more than 70 countries around the world.

How Does the Biosand Filter Work?

Contaminated water is simply poured into the top of the biosand filter on an intermittent basis. The water slowly passes through the diffuser and percolates down through the biolayer, sand and gravel. Treated water naturally flows from the outlet tube.

Pathogens and suspended solids are removed through a combination of biological and physical processes that take place in the biolayer and within the sand layer. These processes include: mechanical trapping, predation, adsorption, and natural death.

How Well Does the Biosand Filter Work?

CAWST has prepared a summary of laboratory and field studies for the biosand filter. It has been proven to remove the following from contaminated water:

• Up to 98.5% of bacteria
• Up to 99.9% of protozoa
• Up to 95% of turbidity
• 90-95% of iron

Summary of Field and Laboratory Testing for the Biosand Filter

Although the water may look clear after filtration, it is still necessary to disinfect it to ensure the best drinking water quality possible. The biosand filter removes most, but not all of the bacteria and viruses. The most common methods used around the world to disinfect drinking water are:

• Chlorine disinfection 
• Solar disinfection (SODIS) 
• Boiling 

For more information about the biosand filter and disinfection options read the following documents:

HWTS Fact Sheets (all) - Simplified [ENG]

Project BRAVO - A Field Study in Haiti Executive Summary

Project BRAVO - A Field Study in Haiti Presentation

Biosand Filter Manual (Complete) [ENG]