__NOTOC__<small-title />[[Image:Biosandfilter.png|right|100px80px]][[Image:concrete biosand filter.jpg|thumb|right|300px200px| Bio Sand Filter in Kumbo, Cameroon. Photo: [http://www.lwdgc-africa.org/15.html LWDG Cameroon.]]]
The biosand filter (BSF) is an adaptation of the traditional slow sand filter, which has been used for community water treatment for hundreds of years. The BSF is smaller and adapted for intermittent use, making it suitable for households.
#Natural death: Food scarcity, less than optimal temperatures and a relatively short life span will cause pathogens to die off and become nutrients for other micro-organisms.
===Suitable conditions===
It is suitable to process batches of 12-18 litres. If four batches a day are filtered, this provides 24-72 litres of clean water.
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! width="50%" style="background:#efefef;" | Advantages
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| valign="top" | - Removes over 98.5% bacteria, 100% bacteria, turbidity, some iron, manganese, arsenic. Quality of water improves with time. <br>
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===Construction, operations and maintenance===[[Image:CAWST_Biosand.png|thumb|right|300px200px| Cross-section through a concrete biosand filter]]
The concrete BSF typically uses a box about 0.9 m tall by 0.3 m square, or about 0.3 m in diameter. The filter box is cast from a steel mold or made with pre-fabricated pipe. The container is filled with layers of sieved and washed sand and gravel (also referred to as filter media). There is a standing water height of 5 cm above the sand layer. The different layers trap and eliminate sediments, pathogens and other impurities from the water. Similar to in slow sand filters, a biological layer of microorganisms (also known as the biolayer or schmutzedecke) develops at the sand surface, which contributes to the water treatment. This biological layer matures over one to three weeks, depending on volume of water put through the filter and the amount of nutrients and micro-organisms in the water.
Local production of filters is most common because materials are readily available all over the world. Molds can be borrowed, rented, bought or constructed locally. Filters can be constructed at a central production facility, or in the community. Filter sand and gravel can be prepared (sieved and washed) on-site or nearby.
'''Materials required are :''' *Steel mold*Sand, gravel, and cement*Filter sand and gravel*Copper or plastic outlet tubing *Metal or plastic for the diffuser*Metal or wood for the lid*Water for concrete mix and to wash filter sand and gravel*Miscellaneous tools (e.g. wrench, nuts, bolts)*Facilities: Workshop space for filter construction
A skilled welder required to fabricate molds. Anyone can be trained to construct and install the filter. Individual householders can assist in constructing their own filters.
Working with cement and heavy molds is potentially hazardous and adequate safety precautions should be used. Concrete filters are heavy and difficult to move and transport.
'''Correct manufacturing and installation, to ensure a long and succesful life, of the biosand filter requires: ''' *that the box that doesn’t leak <br>*screened and washed sand, (organic free, Uniformity Coefficient of 1.5 – 3.0 and an Effective size of 0.15 – 0.30 mm - a sieve analysis is required to determine these numbers) <br>*well washed under-drain and separating gravel <br>*diffuser plate and lid <br>*safe storage container <br>*maximum standing water level of 5 cms <br>*start-up (maturing) time of 14-21 days <br>
====Maintenance====
Free mold designs are available from CAWST.
===Costs===
{{Treatment_Cost
|CapCost= US$ 12-40 = € 8,6 - 28,6
Note: Program, transportation and education costs are not included.
===Field experiences===
In a study in Cambodia, 87.5% of the households surveyed had BSFs in use. Time in use ranged from six months to eight years, and the percentage of BSFs still in use did not decline over the length of time elapsed between BSF installation and follow up. Water, sanitation, hygiene, and other factors were analyzed for association with continued filter use.
To read the full study: [http://www.wsp.org/sites/wsp.org/files/publications/WSP_biosand_cambodia.pdf Improving Household Drinking Water Quality: Use of BioSand Filters in Cambodia]. Water and Sanitation Program, May 2010.
===Manuals, videos, and links===
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===References===
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===Acknowledgements===
This article is based on a factsheet from [http://www.cawst.org/ Centre for Affordable Water and Sanitation Technology (CAWST)], which is gratefully acknowledged.