Kanchan Arsenic Filter (KAF)
Massachusetts Institute of Technology (MIT), Environment and Public Health Organization (ENPHO) of Nepal, Rural Water Supply and Sanitation Support Programme (RWSSSP) of Nepal
The Kanchan Arsenic Filter (KAF) is an adaptation of the Biosand Filter that removes arsenic in addition to turbidity and diarrhea causing pathogens. The Biosand filter is a household scale slow sand filter. A plastic or concrete casing is filled with layers of graded sand and gravel. A biological layer, which contributes to pathogen removal, forms on the top layer of sand. Water passes through the biological layer and filters through the graded sand and gravel. The KAF incorporates an additional layer of non-galvanized nails in the diffuser basin of the filter. Rust (ferric hydroxide) is formed when the iron nails are exposed to air and water. Arsenic in the water adsorbs to the surface of the ferric hydroxide particles and is filtered out of the water.
Nepal and Bangladesh
Other household water treatment methods and technologies available on the local market and other arsenic removal technologies including the ElectroChemical Arsenic Remediation (ECAR) system.
Individuals and households who rely on arsenic contaminated water for drinking.
The Kanchan Arsenic Filter is manufactured locally using locally available labor and materials. The filter container can be concrete or plastic and is about 0.9 meters tall and either 0.3 m square or in diameter. The container is filled with specifically proportioned layers of sieved and washed sand and gravel and has a standing water height of 2-7 cm above the sand layer. A diffuser plates prevents water from disturbing the biological layer when adding water and 5-6 kgs of non-galvanized nails are added to the diffuser basin. A layer of bricks prevents water from displacing the nails when adding water. Additional information on manufacturing biosand filter can be found at CAWST.
Entrepreneurs (NGOs or community clubs) sell the KAF.
In 2005, 2,000 units had been distributed. Since manufacturing is decentralized, production and distribution to date unknown.
The KAF Dimensions are: 0.9 m tall, about 0.3 m diameter or 0.3 m square. Graded and washed sand and gravel are layered. A standing water depth of 2-7 cm is needed. Approximately 5-6 kg non-galvanized iron nails are added to the diffuser bin for arsenic removal. Flow rate is 12-18 Liters per hour. Dimensions may vary depending on size of filter casing. For more information see the KAF construction manual and CAWST’s biosand filter construction manual.
Nails need to be replaced every 2-3 years, lids and diffusers may need replacement. These items are available on the local market.
The concrete biosand filter can last for more than 10 years with some maintenance though some parts, such as lids or diffuser plates, may need to be replaced. If using a Gem plastic casing, the manufacturer suggests that the plastic should be kept away from direct sunlight to minimize damage to the plastic from UV rays. The filter should not be relocated or moved in order to avoid potential mishandling and breakage of the plastic container. Nails in the KAF filter need to be replaced every 2-3 years for effective arsenic removal.
The Kachan Arsenic filter removes: iron, turbidity, bacteria (90-99%), pathogens, odour, and some other common contaminants.
Water containing up to 0.5 mg/L of arsenic can be reduced to less than 0.05 mg/L. For water containing over 0.5 mg/L arsenic, it is advised to add more iron nails or to filter the water two times.
The filter can reduce iron content from 10 mg/L to less than 0.3 mg/L.
Flow rate is 15-20 L per hour.
Field studies by MIT and ENPHO showed KAF removed 85-95% of arsenic, iron and turbidity removal of 93-95+%; Independent field studies showed 87-95+% removal of arsenic, iron and turbidity removal of 90-99+% (2); Long-term field study in 2015 found only a 54% efficacy rate of the Kanchan in highly arsenic contaminated areas of Nepal.
Field research by MIT and ENPHO. Independent studies conducted by: Tribhuvan University, Kathmandu University, and United States Peace Corp.
It can take up to 30 days for the biological layer to form after construction or cleaning.
A safe storage container to collect and store filtered water should be used. A disinfectant (chlorine or silver) should be added to filtered water to enhance microbiological water quality.
It depends on regulations in the target market. None known at this time.
The filter has been evaluated in the field and in the laboratory.
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