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.
'''Adsorption: Magc-Alcan Filter or the filter and Shapla filter'''<br>
The Magc-Alcan is a two bucket filter. The buckets are in series and both filled with an American-made activated alumina media. The media has been developed by MAGC Technologies and Alcanof US; and it is produced by thermal dehydration (at 250-1150°C) of an aluminium hydroxide. The Magc-Alcan filter removes arsenic by adsorption (adhesion or sticking together) of the arsenic to the enhanced activated alumina which is porous and has a high surface area. Removal rates can be sensitive to varying pH levels, so additional equipment may be required to control pH levels.
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 Filter'''<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.
2-Kolshi is an arsenic removal method using two buckets. The first step is a coagulation process using a specific amount of iron sulphate and enough sodium hypochlorite to create a distinctive chlorine odour upon stirring in a normal bucket of water, followed by a filtration in a ceramic filter. The 2-Kolshi technique oxidizes As(III) to As(V) by stirring the water, co-precipitates As5+ with iron chloride and ash, and then it filters the water to remove the formed particles.
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 Filter'''<br>
==Construction, operations and maintenance==
'''Adsorption: Magc-Alcan Filterfilter'''<br>
* Place two buckets (with taps) filled with activated alumina media in series using a stand.
* Place a safe water container after the second tap.
* The media container is re-useable and easily maintained.
'''Coagulation-Flocculation: Bucket Treatment Unit (BTU)'''The unit consists of a two bucket system. The upper bucket is filled with raw water. Chemicals are added and the water is stirred fast for approximately 25 seconds with a wooden spoon provided with the unit.Recommended chemical doses are (Tanhura et al.):<br>* 200 mg/L aluminum sulphate* 2 mg/L of potassium permanganate 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 Filter'''<br>* Add ENPHO chemical (iron sulphate, sodium hypochlorite and ash) to a bucket of water* Stir water for a few minutes* Let settle for one hour* Pass the water through a ceramic filter
'''Surface complexation: Sono Filter'''<br>
|6 months to 1 year
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'''Adsorption: Shapla filter'''<br>
|Short media lifespan (3-6 months)
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'''Coagulation-Flocculation: Bucket Treatment Unit (BTU)'''
{|border="1" cellspacing="0"
|-
! scope="col" |Treatment Efficiency
! scope="col" |Production
! scope="col" |Cost
|-
|~ 60% arsenic removal
|20 litres/hour
|$10 capital cost, $15-20 chemical cost/year
|}
'''Coagulation-Flocculation: 2-Kolshi Filter'''<br>
|-
! scope="col" |Treatment Efficiency
! scope="col" |Production
! scope="col" |Cost
|-
|90% arsenic removal, 99% microbial removal
|3-5 litres/hour
|$10 capital cost, $15-20 chemical cost/year
|}
==Acknowledgements==
