Arsenic disaster and water supply: An overview

Urban and Rural water supply in Bangladesh is primarily based on Ground Water (GW). Another major source is surface water (SW) like river, pond, dighi, lakes, haor, baor and beels etc. Since GW is free from suspended particulate matter (SSP) and pathogens, it is common practice to withdraw GW by deep tube wells, shallow wells and by hand tubewells. Furthermore GW contains some minerals that are good for health.

Arsenic disaster comes from underground tube wells introduced widely over the last 20 years as a cheap alternative source of water supply to prevent outbreaks of deadly diseases such as diarrhoea and cholera. Tube wells are steel cylinders sunk into the aquifer to varying depths to provide underground water for irrigation and drinking purposes. No testing was done, however, for potential dangers such as arsenic (or other heavy metals), which is colourless, tasteless and soluble. The United Nations International Children's Emergency Fund (UNICEF) initiated well drilling as a means of providing what was thought to be clean water in rural areas in Bangladesh. When the programme began no water or soil tests were carried out.

As recently as six months ago tube wells were being installed without testing. Of the 20,000 tubewells tested by the government and non-government organisations, 25 per cent had dangerous levels of arsenic, 40 per cent had unsafe levels and only 35 per cent were below 0.01 mg/L (ppm) of arsenic. The World Health Organisation (WHO) recommends a level of 0.01mg/L of arsenic but the government of Bangladesh regards 0.05 m/L -- a level five times higher than WHO -- as acceptable.

In the village of Jessore, 92 per cent of 282 tubewells tested were found to be contaminated by extremely high levels of arsenic. In Hajiganj of Chandpur district, which includes over 157 villages, 93 per cent of all wells were also found to be contaminated.

All funds and loans from international agencies (WHO, UNICEF, World Bank and others) to conduct more research and attempt to find alternative supply of safe drinking water have been used to re-test the tube wells. Now-a-days in rural areas, arsenic disaster has come as a sign of "Red" and "Green". Rural people again go back to the ponds and other contaminated surface water sources. Despite mounting evidence of widespread water contamination, little has been done to identify the extent of the problem, let alone provide any solutions.

It is generally considered that GW is the gift of God and is renewable, obviously GW is renewable but as long as the rate of recharge is grater than the rate of extraction by pumps. Otherwise GW table will be depleted. In our country during dry season, GW can't be extracted by many tubewells due to depletion.

Sources of potable water:

Back to surface water

Rain water

Treatment of Arsenic Polluted water

Related Technologies:

1. Surface water (characteristics: colour, odor, SSP, micro organism etc.)

Sedimentation with Coagulation

Filtration

Disinfections

Establishment of Surface Water Treatment Plant (SWTP) is costly. Rural people can collect pond/ river water, add some Aluminum Sulphate (Fitkiri) for coagulation and pass the clean water through some filter beds (sand, coal, gravel, pebble etc.). Finally to disinfect the clean water they have to add some Calcium hypo chloride (Bleaching Powder). It is recommended to boil the filtered water prior to drinking.

2. Rainwater (characteristics: pure, NOx and SOx and particulates matters from atmosphere, no mineral contents)

Filtration

Disinfections if polluted by birds or other animals

Rainwater is pure. As it contains impurities from the atmosphere, it is recommended to collect rainwater after 10 minutes from the beginning of rain. Rainwater can be collected from the pipe networks of building's roof (structured method). Rural people can also collect from their roof (tin) by providing gutter. People without roof can collect by providing polythene (with a hole) on bamboo holds during the rainfall. Collected rainwater should be filtered and disinfected prior to use. Rainwater does not contain any mineral, but we don't have water as a source of mineral, we have food for minerals. Another drawback of rainwater is its seasonal variability.

3. Treatment of Arsenic Polluted ground water

Adsorption, Absorption and Co-precipitation

Filtration

Treatment of arsenic polluted water is not fully discovered. However, it can be seen from many research works that arsenic is generally found with iron and manganese. During oxidation, flocculation and filtration of iron, arsenic is removed by the method of absorption, adsorption and/or co-precipitation. Treatment of arsenic polluted ground water is not a sustainable solution because of the sludge disposal problem. If not carried out carefully it could lead to soil, pond and river contamination.

The treatment of arsenic poisoning is straight forward: provision of arsenic-free water will halt any further physical deterioration in all but the most advanced cases. But access to this basic necessity of life -- clean water -- is precisely what is lacking. Neither the government nor the various international agencies have any remedies to propose. In a number of cases, the government has tested and sealed dangerous wells only.

.Bangladesh is one of the most densely populated countries in the world, and one of the poorest. About 80 per cent of the population is rural and 60 per cent landless peasants. Safe water is the basic necessity for a man. We must look forward for providing safe water to the rural as well as urban dwellers.

Rezaul Kabir Chowdhury is Faculty, Department of Environment, America Bangladesh University, Dhaka.