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| {{copyvio|from http://www.meribah-ram-pump.com/downloads/Flyer-Waterfilter.pdf - have the copyright holders explicitly allowed its use under CC-BY-SA?}} | | {{topic page needed}} |
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| ==The Filtration Process==
| | {{cat header| default.png | {{subst:PAGENAME}} | Please click edit and add an intro sentence here. }} |
| ===The Start of the Run===
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| The inlet water contains dissolved oxygen, nutrients and contaminants. The high water level pushes the water through the filter.
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| After passing through the diffuser plate, the inlet water mixes with the standing water. The standing water is lower in oxygen, nutrients, and pathogens than the inlet water because they were consumed during the pause period.
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| The inlet water provides the oxygen required by the microorganisms in the bio layer. Sediment and larger pathogens are strained out at the top of the sand.
| | == External links == |
| Halfway Through the Run
| | * [http://www.raintree-foundation.org/AT/Appropirate_Technologies/Bio_Sand_Filter.html Biosand Filter] |
| | | * [http://www.wcponline.com/pdf/October2012Kearns.pdf] Sustainable Decentralized Water Treatment for Rural |
| The water level in the reservoir goes down as it filters through the sand. The flow rate will slow down because there is less pressure.
| | and Developing Communities Using Locally Generated Biochar Adsorbents (879kb pdf) |
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| Sediment and larger pathogens are strained out and they partially plug the pore spaces between the sand grains. This also causes the flow rate to slow down.
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| ===The End of the Run===
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| The water flow finally stops. The standing water layer will be at the same height as the outlet of the pipe.
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| Pathogens in the inlet water are consumed and those from the previous run which were partially consumed are more completely broken down.
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| Pathogen removal increases with time because of the slower flow rate and the decreased size of pore openings.
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| ===The Pause Period===
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| Some oxygen from the air passes through the standing water to the bio layer.
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| The pause period allows time for microorganisms in the bio layer to consume the nutrients and pathogens in the water.
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| The flow rate through the filter is restored as they are consumed. If the pause period is too long, the bio layer will eventually consume all of the pathogens and nutrients and eventually die off.
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| This will reduce the removal efficiency of the filter when it is used again. A 6 to 12 hour pause period is recommended with a minimum of 1 hour and a maximum of 48 hours.
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| Microorganisms in the sand zone die off due to the lack of nutrients and oxygen.
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| ==Maintenance==
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| There is some key maintenance that is required after a filter has been installed and used regularly.
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| ===Swirl & Dump===
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| The flow rate through the filter will slow down over time as the bio layer develops and sediment is trapped in the upper layer of the sand.
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| Users will know when the “swirl & dump” is required because the flow rate will drop to an unacceptable level. The filter is still effectively treating the water at this point; however the length of time that it takes to get a bucket of water may become too long and be inconvenient for the user.
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| Alternately, you can measure the flow rate and if it is less than 0.1 L/minute, “swirl & dump” maintenance is required.
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| Steps
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| # Remove the lid of the filter.
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| # Add 4 liters water to the top of the filter.
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| # Remove the diffuser.
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| # “Swirl” a small wooden stick or spoon around in the standing water at least 5 times – the water will become dirty. Work the stick into the sand layer about 2 cm (0.8”) while “swirling” around across the entire surface area of the sand, but do not mix the surface layer any deeper than 5 cm (2”) into the filter.
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| # Scoop out the dirty water with a small container (i.e. a cup or a pop bottle cut in half).
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| # Dump the dirty water outside the house in an appropriate location, such as a soak pit or garden (remember it is contaminated water).
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| # Smooth and level the sand surface.
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| # Replace the diffuser.
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| # Pour 20 liters of water into the top of the filter.
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| # Measure the flow rate.
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| # If the flow rate is less than 0.6 L/minute, repeat steps 1 through 10 until the flow rate is acceptable.
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| # Wash your hands with soap and clean water - you have been handling contaminated water.
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| ===Arsenic Removal===
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| The bio sand filter can remove a certain level of arsenic from water by adding non-galvanized iron nails, covered by a layer of brick chips.
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| The diffuser plate is replaced with a deep diffuser basin that can hold the nails and brick chips. The iron nails will quickly rust after contact with water and air.
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| Iron rust (ferric hydroxide) is an excellent adsorbent for arsenic. When arsenic-containing water is poured into the filter, surface reactions with the iron occurs, and arsenic is rapidly adsorbed onto the surface of the rusty nails.
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| The arsenic loaded iron particles are then flushed down and trapped on top of the sand layer. The brick chips help to evenly disperse the water over the nails to allow for further absorption.
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| ==The Bio Sand Waterfilter==
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| The bio sand filter has six different distinct zones:
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| ===Meribah Bio Sand Waterfilter===
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| # Inlet Reservoir: Space above the sand and gravel media which allows for a full pail of water.
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| # Standing Water: Oxygen diffuses through the standing water to the bio layer.
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| # Bio layer: Layer of slime, sediment, and microorganisms which develops at the top 1-2 cm (0.4-0.8”) of the sand surface.
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| # Biological Zone: Develops at the top 5-10 cm (2-4”) of the sand surface. The sand absorbs pathogens, iron, and other small particles.
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| # Sand Zone: Contains virtually no living microorganisms due to lack of nutrients and oxygen.
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| # Gravel Zone: Holds the sand in place which protects the outlet pipe from clogging and allows for the smooth flow of water.
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| ==The Results==
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| Overall, studies have shown that the Bio Sand Filter removes:
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| * > 97% of E. coli - an indicator of fecal contamination (Duke, 2006; Stauber, 2006)
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| * > 99% of protozoa and helminths (Palmateer, 1999)
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| * 80-90% of viruses (Stauber, 2005)
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| * 50-90% of organic and inorganic toxicants (Palmateer, 1999)
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| * 90-95% of iron (Ngai, 2007)
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| * Most suspended sediments
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| Based on slow sand filter research, the bio sand filter may also remove some heavy metals (Muhammad, 1997; Collins, 1998).
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| There is also a design modification known as the KanchanTM Arsenic Filter that is effective in removing both pathogens and 85-90% of arsenic from source water (Ngai, 2007).
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| ==Links==
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| * [http://www.raintree-foundation.org/AT/Appropirate_Technologies/Bio_Sand_Filter.html Biosand Filter]
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| ** Clean Drinking Water
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| ** Easy to Use
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| ** Self contained Maintenance
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| ** For Everybody
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| ** No Following Costs
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| ** Reliable
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| [[Category:Water_treatment]] | | [[Category:Water filtration]] |
| [[Category:Filters]] | | [[Category:Filters]] |
