[[Image:Ceramic_filter_icon.png|right|80px]][[Image:arsenic removal.jpg|thumb|right|250px200px| Arsenic removal system: oxidation method. <br>Photo: Ngai.]][[Image:arsenic removal two.jpg|thumb|right|250px200px|Magc-Alcan Filter (left) and Nirmal Filter (right): adsorption method. Photo: Ngai.]]__NOTOC__ <small-title />
There are at least five ways to remove arsenic from drinking water. The adsorption method, the coagulation-flocculation method, the surface complexation method, a Kanchan arsenic filter, or removal by oxidation.
The Shapla filter is an earthen household arsenic removal technology developed by International Development Enterprises (IDE), Bangladesh. It is based on adsorption (adhesion or sticking together) of the arsenic to the iron on the coated brick chips, which works as well as iron coated sand. The bricks are coated by treatment with a ferrous sulphate solution (Ahmed, 2005). The filter can hold up to 30 litres of water. As water passes through the filter, arsenic from the water is rapidly adsorbed by the iron on the brick chips. The media (20 kg) filters 4,000 litres of arsenic-contaminated water reducing arsenic concentrations to undetectable levels and supplying an average family with 25-32 litres of safe drinking water per day.
'''Coagulation-Flocculation: Bucket Treatment Unit (BTU) and 2-Kolshi Filterfilter'''<br>
The Bucket Treatment Unit has been developed within the DPHE-Danida project. It consists of oxidation (loss of electrons of As(III) to form As(V)) and coagulation (clumping of particles to promote sedimentation) processes using potassium permanganate and aluminum sulphate respectively. The water is then filtered through cloth into a second bucket that contains a sand filter. The BTU can be constructed from locally available materials.
Coagulation/filtration is a traditional treatment process that adds a chemical coagulant (typically iron sulfate or iron chloride) to contaminated water. The coagulant modifies the physical or chemical properties of dissolved or suspended contaminants so that they settle from solution by gravity or can be removed by filtration. As part of the coagulation process, arsenic is co-precipitated with the iron. The stirring process helps to build the flocs into larger particles.
'''Surface complexation: Sono Filterfilter'''<br>
The Sono Filter is a three bucket system with a composite iron matrix (CIM) as the active arsenic removal component. It creates surface complexation of arsenic on the CIM followed by a filtration. The filter is manufactured from indigenous materials and it works without chemical treatment, without regeneration, and without producing toxic waste. It is efficient to remove arsenic and 22 other heavy metals as well as bacteria.
'''Kanchan Arsenic Filterarsenic filter'''<br>
The Kanchan Arsenic Filter (KAF) is an adaptation of the biosand filter. The KAF has been designed to remove arsenic from drinking water, in addition to providing microbiological water treatment. Arsenic removal is achieved by incorporating a layer of rusty nails in the diffuser basin of the filter.
'''Passive Oxidationand solar oxidation'''<br>
Passive oxidation is based on oxidation mechanisms of iron compounds that naturally reduce the arsenic content of groundwater. Naturally occurring dissolved Fe(OH)2 in the groundwater undergoes a natural chemical process called oxidation (when an element loses electrons) to produce a solid form or precipitate of Fe(OH)3 which attracts arsenic to stick to it, a process called adsorption (Ahmed, 2002). This adsorption produces a co-precipitate of Fe(OH)3 and arsenic that settles to the bottom of the container thereby removing the arsenic from the water. This technology does not require chemicals, but rather is based on the passive oxidation process and subsequent sedimentation.
Passive oxidation is seen as an easy technology, because of the natural habits of rural people to store their water in pitchers, before they drink it. Nevertheless, its performance at removing arsenic at safe levels has not been proven.
The SORAS (Solar Oxidation and Removal of Arsenic) method is similar to the SODIS one but with use of lemon juice. Sunlight as a source of UV causes the oxidation (loss of electrons) of As(III) to As(V). The resulting As(V) is strongly attracted to iron hydroxides particles present in the water and sticks to these particles. The As(V)/Fe(OH)3 co-precipitate then settles to the bottom of the container. SORAS removes arsenic in a two-step procedure:<br>* First step: As(III), which only weakly adsorbs to iron hydroxides, is oxidized to the strongly adsorbing As(V).* Second step: Fe(III) hydroxide precipitates formed from naturally present iron are allowed to settle to the bottom of the container with the adsorbed As(V) and the clear water is decanted. Instead of adding chemical oxidants such as chlorine or permanganate, reactive oxidants are produced photo chemically with sunlight. ===Construction, operations and maintenance===[[Image:shapla filter.jpg|thumb|right|200|Shapla arsenic filter. Photo: Ngai.]][[Image:2-Kolshi filter.jpg|thumb|right|200|2-Kolshi arsenic filter. Photo: Ngai.]][[Image:Sono filter.jpg|thumb|right|200|Sono arsenic filter. Diagram: [http://www.robrasa.com robrasa.com]]][[Image:Kanchan filter.jpg|thumb|right|200|Kanchan arsenic filter. Diagram: CAWST.]][[Image:Asia arsenic filter.jpg|thumb|right|200|Asia arsenic filter. Drawing: Asia Arsenic Network, (2001).]]
'''Adsorption: Magc-Alcan filter'''<br>
The mixture is then allowed to settle for 1-2 hours. The tap is then turned on so that the water can pass through a cloth screen and a sand filter in the lower bucket.
'''Coagulation-Flocculation: 2-Kolshi Filterfilter'''<br>
* Add ENPHO chemical (iron sulphate, sodium hypochlorite and ash) to a bucket of water
* Stir water for a few minutes
* Pass the water through a ceramic filter
'''Surface complexation: Sono Filterfilter'''<br>Each bucket has different media and functions:<br>* Top bucket: 3 kg iron filings and 2 kg coarse sand* Middle bucket: 2 kg fine sand, 1 kg of wood charcoal and brick chips* Bottom bucket: water collection container
'''Kanchan Arsenic Filter'''<br>The water first flows through the coarse river sand and a composite iron matrix (CIM). The water flows into a second bucket where it again filters through coarse river sand, then wood charcoal to remove organics, and finally through fine river sand and brick chips to remove fine particles and stabilize water flow.
'''Kanchan arsenic filter'''<br>
The filter container can be constructed out of concrete or plastic. The container is about 0.9 m tall and either 0.3 m square or 0.3 m in diameter. 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. As 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. The diffuser basin is filled with 5 to 6 kg of non-galvanized iron nails for arsenic removal. A layer of bricks on top of the nails prevents displacement of the nails when water is poured into the filter.
'''Passive Oxidation'''<br>Contaminated water is poured into the top of the 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. The biolayer is the key pathogen removing component of the filter. Without it, the filter is significantly less effective. It may take up to 30 days to establish the biolayer depending on inlet water quality and frequency of use. The water from the filter can be used during the first few weeks while the biolayer is being established, but disinfection is recommended during this time, as during regular on-going use.
Much more information and details on the Kanchan arsenic filter: [http://www.cawst.org/assets/File/HWTS_Fact_Sheet_KAF.pdf Household Water Treatment and Safe Storage Factsheet: Kanchan Arsenic Filter.] '''Oxidation: Passive'''<br>* Stir the water for 2 minutes* Leave water overnight in an open container '''Oxidation: Solar'''<br>* Fill PET (or other UV–A) transparent bottles with water* Add lemon juice to bottles* Place the bottled in the sunlight for 1-2 days* During the night, place the bottles in vertical position* The water can then be filtered through textile cloth or clay filters ===Costs===
'''Adsorption: Magc-Alcan filter'''<br>
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'''Surface complexation: Sono filter'''<br>{|border="1" cellspacing="0" |-! scope="col" |Treatment Efficiency! scope="col" |Production! scope="col" |Cost! scope="col" |Lifespan|-|90-95% arsenic removal|20-30 litres per hour|$40-50 capital cost|Replace unit after 3-5 years|} '''Oxidation: Passive'''<br>{|border="1" cellspacing="0" |-! scope="col" |Treatment Efficiency! scope="col" |Production! scope="col" |Cost|-|Typically 30 to 50% arsenic removal|No limit|Minimal cost|} '''Oxidation: Solar'''<br>{|border="1" cellspacing="0" |-! scope="col" |Treatment Efficiency! scope="col" |Production! scope="col" |Cost|-|If iron > 8 ppm, 75-90% arsenic removal. If iron < 5 ppm, <50 % arsenic removal. Excellent microbial removal (99+%)|No limit|Minimal cost|} ===Field experiences===The following projects make use of arsenic filtration: {|style=Acknowledgements"border: 2px solid #e0e0e0; width: 60%; text-align: justify; background-color: #e9f5fd;" cellpadding="2"<!--rsr logo here-->|- style="vertical-align: top"|[[Image:akvorsr logo_lite.png|center|60px|link=http://akvo.org/products/rsr/]]| <!--place holder-->|[[Image:akvorsr logo_lite.png|center|60px|link=http://akvo.org/products/rsr/]]<!--project blocks here-->|- style="vertical-align: bottom"|[[Image: rsr 476.jpg|thumb|center|140px|<font size="2"><center>[http://rsr.akvo.org/project/476/ RSR Project 476]<br>Ensure access to safe water and sanitation</center></font>|link=http://rsr.akvo.org/project/476/]] * |[[Image: rsr 769.jpg|thumb|center|140px|<font size="2"><center>[http://wwwrsr.akvo.org/project/769/ RSR Project 769]<br>Life-WASH</center></font>|link=http://rsr.googleakvo.comorg/project/url?sa769/ ]] |[[Image:rsr 770.jpg |thumb|center|140px|<font size=t&rct"2"><center>[http://rsr.akvo.org/project/770/ RSR Project 770]<br>Intervention Efforts in WASH</center></font>|link=j&qhttp://rsr.akvo.org/project/770/ ]] |} =&esrc=s&source=web&cdAcknowledgements=3&ved=0CHMQFjAC&url=* [http://www.sswm.info/category/implementation-tools/water-purification/hardware/point-use-water-treatment/arsenic-removal- Household Water Treatment for Arsenic Removal Fact Sheet: Adsorption.] Raju Shrestha, Environment and Public Health Organisation, ENPHO. * [http%3A%2F%2Fwww://resources.cawst.org%2Ffr%2Fresources%2Fpubs%2Fcategory%2F25/asset/arsenic-removal-fact-sheets-academic%3Fdownload%3D40%253Ahwtsadsorption_fr French Factsheet]. CAWST.* [http://resources.cawst.org/asset/arsenic-removal-fact-sheetarsenicsheets-removalpdfoct09&ei=oi32T5bROeWW2AWl-fDCBg&usg=AFQjCNHtsMduzuzEZMNKHgbl2BN1dHjr2g&sig2=VgGZabK2qsBHhJQkLL2TKQ coagulation_fr Household Water Treatment for Arsenic Removal Fact Sheet: Coagulation.] CAWST. (French version).* [http://www.sswm.info/sites/default/files/reference_attachments/CAWST%202009%20Household%20Water%20Treatment%20and%20Safe%20Storage%20Fact%20Sheets%20Academic%20Arsenic%20Removal%20Complexation.pdf Household Water Treatment for Arsenic Removal Fact Sheet: AdsorptionSurface Complexation.] CAWST.* [http://www.cawst.org/assets/File/HWTS_Fact_Sheet_KAF.pdf Household Water Treatment and Safe Storage Factsheet: Kanchan Arsenic Filter.] CAWST.
* [http://www.cawst.org/en/resources/pubs/category/24-fact-sheets-simplified Household Water Treatment Fact Sheets.] CAWST.