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[[Image:CAWST_Biosand.png|thumb|right|300px| Cross-section through a concrete biosand filter]]
[[Image:CAWST_Biosand.png|thumb|right|150px| Cross-section through a concrete biosand filter]]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.
Water treatment is carried out by the sand inside the filter. The filter container can be made of concrete, plastic or any other water-proof, rust-proof and non-toxic material, though concrete has several advantages.
#Predation: The microorganisms within the "schmutzdecke" or biological layer consume bacteria and other pathogens found in the water, thereby providing highly effective water treatment.
#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.
{{procontable | pro=
- The life expectancy of a plastic model is substantially less than a concrete model. The ultimate disposal of plastic is a concern for the environment <br>
- Encouraging and empowering local people to completely manage their own project increases local sustainability and motivates others to take action for safer water. This process can only be facilitated if the product supply is managed locally. In most cases, if a plastic model is used, there will always be a dependence on outside manufacturers and distributors to supply filters at a higher cost. <br>
| con=
- Biological layer takes 3 weeks to develop to maturity <br>
- Cannot ensure pathogen free water <br>
}}
==History and social context==
==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.
{{Potential_Treatment_Capacity_table
}}
==Technical specificationConstruction, operations and maintenance==
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.
====Treatment Efficiency====
Slow sand filters have been proven to almost entirely remove the disease-causing organisms found in water. The Biosand filter adaptation has proven as effective as traditional slow sand filters, in both laboratory and field tests.
The taste, odour and colour of filtered water is generally improved. The treated water temperature is generally cooler than water stored in a plastic container.
====Maintenance====
There are no moving or mechanical parts to break. The piping is embedded in concrete, protecting it against breaks and leaks. Cracks can sometimes be repaired.
Concrete filters are heavy (70 – 75 kg for thin wall version and 135 kg for heavy wall version). Poor transportation of filters can lead to cracking and/or breakage. Filters should not be moved after installation.
Maintenance is required when the flow rate drops to a level that is inadequate for the household use. Continued use of the filter causes the pore openings between the sand grains to become clogged with debris. As a result, the flow rate of water through the filter decreases.
To clean the filter, the surface of the sand must be agitated, thereby suspending captured material in the standing layer of water. The dirty water can then be easily removed using a small container. The process can be repeated as many times as necessary to regain the desired flow rate. This procedure is sometimes call a "swirl and dump" maintenance practice. The need to do this depends on the amount and quality of water being put through the filter. If the water is relatively clean (turbidity less than 30 NTU), the filter can likely run for several months without this maintenance procedure. The outlet, lid and diffuser should be cleaned on a regular basis.
The outlet should also be cleaned regularly using soap and water or a chlorine solution.
After cleaning, a re-establishment of the biological layer takes place, quickly returning removal efficiency to its previous level.
====Manufacturing====
*maximum standing water level of 5 cms <br>
*start-up (maturing) time of 14-21 days <br>
====Maintenance====
There are no moving or mechanical parts to break. The piping is embedded in concrete, protecting it against breaks and leaks. Cracks can sometimes be repaired.
Concrete filters are heavy (70 – 75 kg for thin wall version and 135 kg for heavy wall version). Poor transportation of filters can lead to cracking and/or breakage. Filters should not be moved after installation.
Maintenance is required when the flow rate drops to a level that is inadequate for the household use. Continued use of the filter causes the pore openings between the sand grains to become clogged with debris. As a result, the flow rate of water through the filter decreases.
To clean the filter, the surface of the sand must be agitated, thereby suspending captured material in the standing layer of water. The dirty water can then be easily removed using a small container. The process can be repeated as many times as necessary to regain the desired flow rate. This procedure is sometimes call a "swirl and dump" maintenance practice. The need to do this depends on the amount and quality of water being put through the filter. If the water is relatively clean (turbidity less than 30 NTU), the filter can likely run for several months without this maintenance procedure. The outlet, lid and diffuser should be cleaned on a regular basis.
The outlet should also be cleaned regularly using soap and water or a chlorine solution.
After cleaning, a re-establishment of the biological layer takes place, quickly returning removal efficiency to its previous level.
====Estimated Lifespan====
====Suppliers====
Free mold designs are available from CAWST.
==CostCosts==
{{Treatment_Cost
|CapCost= US$ 12-40 = € 8,6 - 28,6
|litreCost=US$ ~0.01
}}
Note: Program, transportation and education costs are not included.
==Country Field experiences==
==Manuals== ==MoviesReference manuals, videos, and links==
* How the BioSand Filter Works [http://www.youtube.com/watch?v=hb0xf3mRbJM http://www.youtube.com/watch?v=hb0xf3mRbJM]
* Health and filters [http://www.youtube.com/watch?v=LPAWuws7qMM&feature=related]* Demo [http://www.youtube.com/watch?v=9Cj4yO4nLLY&feature=related www.youtube.com/watch?v=9Cj4yO4nLLY&feature=related ]* Zambia [http://www.youtube.com/watch?v=f5htXA1OVio&feature=related www.youtube.com/watch?v=f5htXA1OVio&feature=related ]* Organisation [http://www.cawst.org CAWST - Centre for Affordable Water and Sanitation Technology]* [http://wellspringwatersystems.com/solutions/waterbox-100 '''Ultrafiltration Systems''']
==Footnotes==
This article is based on a factsheet from [http://www.cawst.org/ Centre for Affordable Water and Sanitation Technology (CAWST)], which is gratefully acknowledged.
==External Links==
* Organisation [http://www.cawst.org CAWST - Centre for Affordable Water and Sanitation Technology]
==References==
* <cite id=Buzunis95>Buzunis, B. (1995). Intermittently Operated Slow Sand Filtration: A New Water Treatment Process. Department of Civil Engineering, University of Calgary, Canada.</cite>
* <cite id=stauber06>Stauber, C., Elliot, M., Koksal, F., Ortiz, G., Liang, K., DiGiano, F., and M. Sobsey (2006). Characterization of the Biosand Filter for Microbial Reductions Under Controlled Laboratory and Field Use Conditions. Water Science and Technology, Vol 54 No 3 pp 1-7.</cite>
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Related Link
[http://wellspringwatersystems.com/solutions/waterbox-100 '''Ultrafiltration Systems''']