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
An adaptation of the Biosand filter to remove arsenic in addition to turbidity and bacteria.
The Kanchan Arsenic Filter (KAF) is an adaptation of the Biosand Filter that removes arsenic in addition to turbidity and 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.
Goal 6: Clean water and sanitation
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.
List of the methods used for purification
Manufacturer-specified water treatment rate, measured in liters per hour
Laboratory-evaluated log scale removal rate of bacteria
Laboratory-evaluated log scale removal rate of viruses
Laboratory-evaluated log scale removal rate of protozoa
Reduction levels of heavy metals and/or arsenic through this treatment system
Manufacturer-specified maximum level of inlet turbidity (NTU)
Range or value of outlet turbidity levels (NTU)
Is there safe water storage integrated into this product?
What is the total number of liters that is recommended can be filtered?
List consumables of this product (power, filters, etc.)
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.
Singh, A., et al., Efficacy of arsenic filtration by Kanchan arsenic filter in Nepal, Water Health, 2014, 12 (3), 596-599.
Ngai, T., et al., Development and dissemination of Kanchan™ Arsenic Filter in rural Nepal, Water Science and Technology: Water Supply, 2006, 6 (3), 137-146.
Ngai, T., et al., Design for sustainable development—Household drinking water filter for arsenic and pathogen treatment in Nepal, Journal of Environmental Science and Health, 2007, 42 (12), 1879-1888.
Pokhrel, D., Arsenic contamination of groundwater in the Terai region of Nepal: An overview of health concerns and treatment options, Environment International, 2009, 35 (1), 157-161.
Chiew, H., et al., Effect of Groundwater Iron and Phosphate on the Efficacy of Arsenic Removal by Iron-Amended BioSand Filters, Environmental Science and Technology, 2009, 43 (16), 6295-6300.
Noubactep, C., et al., Extending Service Life of Household Water Filters by Mixing Metallic Iron with Sand, Clean – Soil, Air, Water, October 2010.
Hashme, F., Pearce, J., Viability of small-scale arsenic-contaminated-water purification technologies for sustainable development in Pakistan, Sustainable Development, July 2011.
The filter has been evaluated in the field and in the laboratory.
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