Varsity project from Chennai's Anna University reduces fluoride level in water

CHENNAI/DHARMAPURI : Research scholars from Anna University have found a possible solution to the seemingly insurmountable problem faced by the north-western districts of the State — high fluoride content in groundwater.

It didn’t happen overnight nor was it the result of a laboratory experiment, as a team of four from the varsity worked on the project for over six years studying the groundwater composition and fluoride contamination levels across Dharmapuri-Krishnagiri.

A pilot project was set up in Pappichettipatti village, Harur taluk, in Dharmapuri district to bring down fluoride levels from 4 mg per litre to 0.2 mg/l so that it can be used for domestic and agricultural purposes. 

Increase in concentration of fluoride in groundwater is a major problem across the world and prolonged use of water with fluoride concentration above 1.5 mg/l for drinking purpose results in dental and skeletal fluorosis. 

Prof L Elango from the Geology Department in Anna University said that to resolve this issue, a long-term study on the temporal variation in fluoride concentration and groundwater levels is necessary.
The study was taken up in Dharmapuri district where over 71,842 out of 1,86,907 school-going children were tested positive for dental fluorosis as per the 2009 United Nations report. 

Initially based on interactive field work, 44 representative wells (depth greater than 30m) used for drinking and agricultural purposes were chosen for regular monitoring. Groundwater levels in these dug wells were reportedly measured and water samples were collected once in two months from June 2011 to August 2014. 

The team found out that rocks in the locality were rich with fluoride and weathering of these rocks resulted in the release of fluoride into groundwater. “In most cases, this was identified as the main reason for contamination. However, excess use of fertilisers and industrial activities like brick kilning also elevated fluoride concentration,” said G Gowrisankar, an Anna University research scholar and part of this study.

He added that several methods including ion exchange and adsorption methods were available for reducing fluoride concentration at a community level. However, there were several limitations in these methods and people were hesitant in using it as it was time-consuming, expensive and required personal training.

So, the research scholars decided to use the ‘induced recharge’ method and a pilot project was set up at Pappichettipatti village, one of the 44 sites chosen for study.

Though the students were trying to find a remedy to a perennial issue, finding a source to base their work on didn’t come by easily. But, after being rejected by several locals, they found a saviour in local farmer Vairam, who allowed them to use his well.

“My son was also an engineering student. I couldn’t say no to them,” Vairam told Express. 
Accordingly, a 1.5 metre induced recharge structure (filled with gravel, pebbles and sand) was constructed next to the dug well from which samples were collected for three years.

Vairam acknowledged that the fluoride content has reduced after their project.The students had given him an apparatus to check the same and Vairam diligently maintained a record of it in a small diary. “The students assured us that the water can now be used for drinking purposes. But we have not used the water from the well for domestic use for a long time,” he added.  

“As rainwater passed through the recharge structure into the dug well, fluoride got diluted. Once the groundwater level increased, a further decrease in fluoride levels was recorded,” Prof Elango explained. 

Geochemical results indicated that fluoride concentration decreased from 3.1 mg/l to 1.41 mg/l and area of about 1 square kilometre benefited from it.

The study won the Union Water Ministry’s award this year and the team promises that this low-cost project can be taken up in other affected areas. It seems the Water Resources Ministry has been contemplating such a move.

Alongside the award-winning project in Dharmapuri, the team also took up another case study at Mathampathi village in Krishnagiri district where nearly 38% of groundwater was not suitable for direct use as drinking water.

Fluoride concentration in this village located in Pambar river basin varied between 1.3 mg/l to 4.32 mg/l. In this project, a slightly different approach was taken up as a check dam was constructed for augmenting groundwater storage. 

This method proved to be even more efficient as fluoride levels reduced to 0.2 mg/l and it was brought below permissible limit over an area of about 4 sq km.