Removes pathogens and impurities, too
a household arsenic filter has been developed under the Nepal Water Project, which not only removes the carcinogenic chemical but also pathogens, iron, turbidity and odour. The project is being implemented jointly by the us -based Massachusetts Institute of Technology (mit), the Nepal-based non-governmental organisation Environment and Public Health Organisation (enpho) and the Rural Water Supply and Sanitation Support Programme.
Called the Kanchan Arsenic Filter, it comprises of iron nails, brick chips and sand (see diagram: Simple but effective). It works on a simple principle: when the nails are exposed to air and water, they rust quickly, producing ferric hydroxide particles. Numerous studies have shown that ferric hydroxide (iron rust) is an excellent adsorbent for arsenic. When arsenic-contaminated water is poured into the filter, the toxic element is rapidly adsorbed onto the surface of the ferric hydroxide particles. The arsenic-loaded iron particles are then flushed into the sand layer below. The layer of fine sand traps the arsenic-loaded iron particles in the top few centimetres, thus effectively removing the arsenic.
Field research by mit and enpho shows arsenic removal is in the range of 85-95 per cent. Experts say that among all the household arsenic removal technologies, this is the most impressive by far. "It is simple to operate. But education is needed to make sure the units are maintained and arsenic contaminated waste is safely disposed of. Its only limitation is the cost -- around us$20. "To overcome this, lower cost models could be produced," asserts Andrew A Meharg, a biogeochemist at the University of Aberdeen, the uk.
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