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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.
Pathogens and suspended material are removed from the water through a combination of biological and physical processes. These occur both in both the biolayer and within the sand bed. These processes include: mechanical trapping, adsorption/attraction, predation and natural death:
{{procontable | proborder="1" cellpadding="5" cellspacing="0" align="center"|-! width="50%" style="background:#efefef;" | Advantages! style="background:#f0f8ff;" | Disadvantages|-| valign="top" | - Removes over 98.5% bacteria, 100% bacteria, turbidity, some iron, manganese, arsenic. Quality of water improves with time. <br>
- Cheap, no on-going costs<br>
- High flow rate – upto 36 liters per hour. <br>
- Fabricated from local materials. Plastic fabrication usually requires the importation of raw material or the finished product. Depending on your views of international trade, this can be an advantage or disadvantage. <br>
- 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> | convalign= "top" | - Biological layer takes 3 weeks to develop to maturity <br>
- High turbidity (> 100 NTU) will cause filter to clog and require more maintenance <br>
- Requires that the filter be used periodically on a regular basis <br>
- Cannot remove color or dissolved compounds (same as all other filters)<br>
- Can be difficult to move (weigh 170 lbs / 77 kgs)<br>
- Cannot ensure pathogen free water <br> |}} ==History and social context==
{{Potential_Treatment_Capacity_table
}}
===Construction, operations and maintenance===
[[Image:CAWST_Biosand.png|thumb|right|200px| 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.
====Operation====
====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.
====Manufacturing====
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====
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.
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. A Wood Mold instruction manual is available from the OHORIZONS Foundation.
==Cost=Costs===
{{Treatment_Cost
|CapCost=US$ 12-3040 = € 8,6 - 28,6
|OpCost=US$ 0
|ReplCost=US$ 0
Note: Program, transportation and education costs are not included.
==Country =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. Households who reported receiving training in operation and maintenance and those who used deep wells (more than 10 meters deep) were found to be statistically significantly associated with continued BSF use. In BSF households, BSF treatment resulted in a 95% reduction of E. coli and an 82% reduction in turbidity of untreated source water. Furthermore, BSF-usage in households resulted in a 47% reduction of diarrheal disease as compared to control households that did not have BSFs. However, a significant proportion of BSF-treated and stored samples became re-contaminated after filtration suggesting the need for additional training and education about safe storage and recontamination. Despite recontamination during storage, the concentration of E. coli as well as turbidity were still lower in BSF treated and stored water than in untreated water. The BSF is a robust water treatment technology for use in rural Cambodian households, capable of effective removal of indicator bacteria, specifically E. coli, and significant reduction of diarrheal disease. BSF performance is comparable to other recommended household water treatment interventions, such as the ceramic water purifier; however BSFs provide the additional advantage of not being prone to breakage or needing replacement parts. 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==Akvo RSR Projects====The following project(s) utilize concrete biosand filters.<br>{|style="border: 2px solid #e0e0e0; width: 20%; text-align: justify; background-color: #e9f5fd;" cellpadding="2"|- style="vertical-align: top"|[[Image:akvorsr logo_lite.png|center|60px|link=http://akvo.org/products/rsr/]]|- style="vertical-align: bottom"|[[Image:project 158.jpg |thumb|center|140px|<font size="2"><center>[http://rsr.akvo.org/project/158/ RSR Project 158]<br>Rainwater harvesting for Nicolas School</center></font>|link=http://rsr.akvo.org/project/158/ ]] |}
==Footnotes=Manuals, videos and links===<br>{|style="font-size: 125% " |-style="vertical-align: top"|{{#ev:youtube|hb0xf3mRbJM|200|auto|<center>How the BioSand Water <BR>Filter works- Samaritan's <BR>Purse CANADA</center>}}|{{#ev:youtube|LPAWuws7qMM|200|auto|<center>Clean Water for Haiti - about <br>filters and health training</center>}}|{{#ev:youtube|9Cj4yO4nLLY|200|auto|<center>Biosand demo <br>by WOH Meyc</center>}} |-|{{#ev:youtube|f5htXA1OVio|200|auto|<center>BioSand water purification <br>filter in Lusaka, Zambia</center>}} |{{#ev:youtube|zI7vQP18nZo|200|auto|<center>Interview with Biosand Filter<br>Mr. Narayan Pandey}} |} <br> ===References===
<references/>
===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.
* <cite id=Baumgartner06>Baumgartner, J. (2006). [http://iopscience.iop.org/1748-9326/2/2/024003/pdf/erl7_2_024003.pdf The Effect of User Behavior on the Performance of Two Household Water Filtration Systems]. Masters of Science thesis. Department of Population and International Health, Harvard School of Public Health. Boston, Massachusetts, USA.</cite>
* <cite id=duke05>Duke, W. and D. Baker (2005). [http://www.rrh.org.au/publishedarticles/article_print_570.pdf The Use and Performance of the Biosand Filter in the Artibonite Valley of Haiti: A Field Study of 107 Households, ]. University of Victoria, Canada.</cite>
* <cite id=earwaker06>Earwaker, P. (2006). [http://ebookbrowse.com/earwaker-2006-evaluation-of-household-biosand-filters-in-ethiopia-pdf-d79191747 Evaluation of Household BioSand Filters in Ethiopia]. Master of Science thesis in Water Management (Community Water Supply). Institute of Water and Environment, Cranfield University, Silsoe, United Kingdom.</cite>
* Elliott, M., Stauber, C., Koksal, F., DiGiano, F., and M. Sobsey (2008). [http://www.hydraid.org/pdf/BSF_BacteriaViruses_Elliottetal_2008.pdf Reductions of E. coli, echovirus type 12 and bacteriophages in an intermittently operated 2 household-scale slow sand filter].Water Research, Volume 42, Issues 10-11, May 2008, Pages 2662-2670.
* <cite id=ngai04>Ngai, T., Murcott, S. and R. Shrestha (2004). [http://web.mit.edu/watsan/Docs/Other%20Documents/KAF/Ngai%20-%20Asia%20Arsenic%20Network%20symposium%20paper%202004.pdf Kanchan Arsenic Filter (KAF) – Research and Implementation of an Appropriate Drinking Water Solution for Rural Nepal]. [Note: These tests were done on a plastic biosand filter]</cite>
* <cite id=palmateer97>Palmateer, G., Manz, D., Jurkovic, A., McInnis, R., Unger, S., Kwan, K. K. and B. Dudka (1997). [http://www.hydraid.org/pdf/BSF_PalmateerManz_ToxicantParasite_1999.pdf Toxicant and Parasite Challenge of Manz Intermittent Slow Sand Filter]. Environmental Toxicology, vol. 14, pp. 217- 225.</cite>
* <cite id=stauber06>Stauber, C., Elliot, M., Koksal, F., Ortiz, G., Liang, K., DiGiano, F., and M. Sobsey (2006). [http://www.hydraid.org/pdf/BSF_Bacteria_Stauberetal_2006.pdf Characterization of the Biosand Filter for Microbial E. coli Reductions from Household Drinking Water Under Controlled Laboratory and Field Use Conditions]. Water Science and Technology, Vol 54 No 3 pp 1-7.</cite>