Treating contaminated water

The problem of natural contamination of groundwater with highly toxic poisons like arsenic and fluoride is here to stay. The million-dollar question is: Is there a way out for this global problem?

 
By V K Joshi
Last Updated: Sunday 07 June 2015 | 21:11:47 PM

Treating contaminated water

-- The problem of natural contamination of groundwater with highly toxic poisons like arsenic and fluoride is here to stay. The million-dollar question is: Is there a way out for this global problem?

Most of the techniques used by developed nations remove arsenic and fluoride from drinking water at the treatment plant. Developing countries, including India, do not have proper treatment plants even at the urban centres. Villages hardly figure in this incomplete picture. Thus the real task of tacking contamination is at the village level. Once the toxicity has been identified in a particular tube well in a village, cheap, cost-effective, methods are needed at the household level to remove the toxins from water before ingestion.

Rapid analytical methods are needed to identify the polluted sources of water. K N Mathur, senior deputy director general, Geological Survey of India, recommends the use of portable Water Analyses Kit and portable Ion Analyzer Kit to respectively detect the injurious presence of fluoride and arsenic. These equipments are cost-effective, he says.

In an endeavour to provide arsenic-free water to affected people in Bangladesh and Nepal, innovative ideas mooted by local residents have been tested and are being used. The 'Shapla Filter' devised by Professor Fakhrul Islam, professor of chemistry at the Rajshahi University in Bangladesh, is one such indigenous equipment being promoted by the un to remove arsenic at the household level. The filter uses a charge of 20 kg of brick dust as the filtering medium. This can filter approximately 3000 litres of water. The filter costs an affordable Rs 350, and the annual cost of the medium is about Rs 400. One drawback is that the rate of outflow of the filtered water is slow. Also, if the phosphate content of the water is high -- this is often the case -- it requires pre-treatment with ferrous sulfate. (This implies that the water quality must be constantly monitored, often an onerous task.)

In Nepal a 3-'Gagri' (earthenware pot) filter has been tried. This also uses local materials like coarse sand, wood charcoal, nails, bricks and unglazed burnt clay pots as the filtering media. The filter can produce 160-170 litres of water daily with an efficiency rate of 94.8 per cent.

In Mexico laboratory experiments show that if water is treated with a rock rich in kaolinite and illite, arsenic concentration reduces from 0.5 mg per litre to less than 0.030 mg per litre. Both minerals are known to adsorb arsenic and are available in plenty. Maybe an entrepreneur in India could manufacture a filter candle made of this rock to provide arsenic-free water to people in affected areas!

Compared to arsenic, removing fluoride at the household level is more complicated. Fluoride removal techniques were patented as early as 1933 in the United States. Various methodologies -- the use of activated alumina, aluminum and sand filter, magnesium oxide and tricalcium phosphate -- have been tried in the us, Britain and France. These techniques pertain only to large water treatment plants. Recently researchers from the Earth Science Department, Nanjing University, China have successfully tried hydrotalcite (ht) compounds, and their calcined product htco 3500, to lower fluoride content to one parts per million.

The Central Electrochemical Research Institute in Tamil Nadu has devloped an electrochemical defluoridation technique. Fluoride is adsorbed with freshly precipitated aluminum hydroxide in an electrochemical cell. Though effective, the process needs electricity, which is a distant dream for our villagers!

Various other techniques to remove the two toxins at household level are either in the experimental stage or are not cost-effective. An expeditious research would involve manpower and money. The Geological Survey of India, under the aegis of the International Geological Correlation Program. has launched a new project, 'Medical Geology', a concept of O Sellinus of Sweden. The project intends to tackle the problem of arsenic and fluoride toxicity head-on.

A pro-active society can play a significant role in this direction. For example, the students of the Martin Luther King Magnet High School, Nashville, Tennessee studied the risk assessment of arsenic contamination of groundwater in Bangladesh. Using the guidelines of the us Environmental Protection Agency, they worked out a risk quotient (rq). The students found to their horror that against the accepted norm of rq of less than one, the values came out to be of the order of 40 and even more.

In sum, for the time being, the age-old concept of surface water storage (rainwater harvesting in modern parlance) is the only answer to the problem in the cash-starved rural areas.

V K Joshi is former director, Geological Survey of India

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