a new filter that removes arsenic has come as a boon for communities the world over. Abul Hussam, associate professor at George Mason University, Fairfax, Virginia, has won the 2007 Grainger Challenge for developing a filter that removes arsenic from drinking water. The innovation, called the sono filter, is used as a household water treatment system. Born in Kushtia in Bangladesh, Hussam has established a research laboratory in his village.

The one feature of the sono filter that makes it better than existing systems is the absence of any kind of chemicals in the filtration process. The filter, in a modern variation of the traditional "three pitcher' system, uses two buckets placed one over the other to filter the water. The arsenic removal happens when water passes through a composite iron matrix, formed by sandwiching a layer of iron turnings between two layers of sand.Iron is a natural scavenger of arsenic and effectively purifies the water passing through it. Its use has stopped the spread of arsenicosis in about 100 villages in Bangladesh, claim some local newspapers. The filter costs about us $35 and is guaranteed to work for five years, says Hussam. About 21,000 units are operational now, he adds.

"We have tested it and this is the fifth year running and all systems are working without replacement or damage. The estimated lifetime could be longer. It is now a two-bucket system with the top bucket containing the active material (composite iron matrix) and the bottom bucket has other materials to get rid of the particulate matter,' says Hussam.

For arsenic disposal, also called residue management, there are standard methods to detect leaching. In other words, the method helps to find out how much arsenic gets into the environment if the filter is disposed somewhere, says Hussam. There is an Environmental Protection Agency (epa) process called the talp (total available leaching protocol) and there is the European protocol. "The amount that is leached is 16 parts per billion (ppb), which is very small. The epa limit is 5,000 ppb,' Hussam adds.
Safe disposal Besides, he says that people are informed that if they have to dispose the filters, they should do it in the open and not bury it because in a reducing environment (underground), there could be more leaching. It has gone through two environmental technology verification projects and both of them found that the material is not categorised as solid toxic waste, says Hussam.

The arsenic problem traces its origin to attempts on the part of international aid agencies to provide safe drinking water to the people of Bangladesh. But initially, groundwater was not tested for arsenic