Relevance of the Technology

Arsenic is a natural constitutent of the earth's crust and may be found in water that has flowed through arsenic-rich rocks. High concentrations (>10 ppb) of arsenic in groundwater are found in various parts of the world including Argentina, Bangladesh, Chile, China, Hungary, India (West Bengal), Mexico, Nepal, Pakistan, Thailand, USA, and Vietnam. A 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning of drinking water. Inorganic arsenic is a documented human carcinogen. 0.01 mg/L or 10 ppb was established as a provisional guideline value for arsenic by USEPA & WHO.

Prolonged intake of arsenic contaminated food & drinking water (above 10 ppb) may lead to:

1. Melanosis;

2. Keratosis with or without anaemia, conjunctivitis, bronchitis, gastroenteritis and blackfoot disease;

3. Developed keratosis and skin cancer &

4. Arsenicosis

In most affected countries, contaminated groundwater is the main source of water for the rural population. These communities urgently require a simple and affordable technology to remove arsenic from groundwater for both drinking and irrigation purposes. Commonly available technologies for use to removearsenic have inherrent operational and sludge disposal problems . Therefore a chemical and waste free arsenic removal method can provide a long term water security to the affected people and significantly improve the quality of life of the poor in affected areas & marginalised.

According to World Health Organisation (WHO), arsenic contamination in West Bengal & Bangladesh is the severest form of mass poisoning in the history of mankind. "By virtue of its sheer size it is pushing the limits of our knowledge and capacity to respond to it." (WHO, Friday 22 March 2002) A vast area of the eastern part of river Ganges in West Bengal is affected due to arsenic contamination in ground water. 65 blocks, 15 non-municipal urban outgrowth, 9 municipal towns, 1312 villages and 3133 habitations spread over in 8 districts are affected so far. As per studies made in 2000, a minimum of 10 million people including about 2.5 million children belonging to 9 out of the total 18 districts of West Bengal were drinking arsenic contaminated ground water which contains arsenic more than 50 ?g/l, much above the maximum limit set by WHO, which is 10 ?g/l and about a 3 million people were already suffering from arsenic related diseases. About 40 million inhabitants of these 9 districts (Malda, Murshidabad, Nadia, North-24-Parganas, South-24-Parganas, Burdwan, Howrah, Hoogly and Kolkata) are at extreme risk from arsenic toxicity. According to the report of Public Health Engineering Dept. Government of West Bengal, up to 2001, no. of arsenic affected blocks is 75, moujas1 11, affected population 6.97 million, and no. of samples with arsenic level >.05 mg/l is 12,423.

In West Bengal most drinking water are usually collected from open dug wells and ponds without any arsenic problem. However, due to pollution, this water became contaminated with heavy metals & bacteriological contaminations such as diarrhoea, dysentery, typhoid, cholera and hepatitis. Since the 1970s and 1980s shallow hand-pumps & wells (at depths less than 70 metres) were installed to provide clean drinking water. Arsenic was found in the ground water of West Bengal in the 1980s. An estimated 30 million people in the Ganges delta are drinking ground water contaminated with arsenic (New Scientist, 2004). Among them, more than 6 million live in West Bengal, India (Chakraborti, 2002).

Arsenic pollution is a severe problem leading to a wide variety of diseases, such as skin lesions, blackfoot disease, diabetes, hypertension, skin cancers, and internal cancers (lung, bladder and kidney) (World Bank, 2005). Chakraborti et al. (2002) describe in detail the epidemiological diseases that they encountered in the As affected villages that they studied in West Bengal and Bangladesh. A total of about 30 million people in the Ganges delta, of which more than 6 million live in West Bengal, drink water with arsenic concentrations higher than 50 mg per litre and are thus at risk, and more than 300 000 people may have visible arsenical skin lesions (Chakraborti, 2002). (Worldwide, arsenic contamination from groundwater is found in China, Taiwan, Cambodia, Lao People Democratic Republic, Pakistan, Myanmar, Vietnam, and Nepal).

In West Bengal, the contaminated aquifers in the region are mainly Holocene alluvial and deltaic sediments, which form the western margins of the Bengal basin (World Bank, 2005). The five worst affected districts of West Bengal are Malda, Murshidabad, Nadia, 24 North Parganas, and 24 South Parganas (IBID). These cover an area of about 23,000 sq.km where arsenic concentrations are found in the range between 1 and 3,200 mg per litre. The Quaternary sedimentation patterns vary significantly laterally, but sands generally predominate to a depth of 150�200 m in Nadia and Murshidabad, while the proportion of clay increases southwards into 24 North and South Parganas, as does the thickness of surface clay (World Bank, 2005). A shallow "first aquifer" has been described at 12�15 m depth, with an intermediate "second aquifer" at 35�46 m, and a deep "third aquifer" at around 70�90 m depth (World Bank, 2005). High levels of As in groundwater are especially found in the second aquifer. CGWB (1999, as cited in World Bank, 2005) noted that the depths of arsenic-rich groundwater vary in the different districts but where high-arsenic groundwater exists, they are generally in the depth range of 10�80 m. Low levels of As are found in the groundwater from the first aquifer and the third aquifer, usually. For shallow water from the first aquifer one reason for the low As amount when actually drunk is that the water is harvested through open dug wells that are likely to contain groundwater that is oxidized through aeration. Groundwater from the deep aquifer also have low arsenic concentrations, except where only a thin clay layer separates it from the overlying aquifer, allowing some hydraulic connection between them (World Bank, 2005).

In 1995, the WHO lowered the guideline value from 50 to 10 mg per litre.