A research team led by environmental chemist Dinesh Mohan at Jawaharlal Nehru University (JNU) is developing a variety of low-cost magnetised charcoals to rid water of hazardous pollutants by using locally available agricultural waste. So far, it has come up with a variety of magnetic activated charcoals (carbon), extracted from almond shells, coconut shells and other nutshells, to remove phenols from water.
Phenols are the “most prevalent organic pollutants in wastewaters” globally. When present beyond the permissible limit, these make water unfit for drinking, contaminate fish flesh and cause many serious medical problems in humans. According to a Central Pollution Control Board report, phenolic compounds have been reported in the ground water in Uttar Pradesh, Punjab, Himachal Pradesh, West Bengal, Gujarat, Maharashtra and Tamil Nadu.
The phenol targeted by the JNU group is called 2, 4, 6-trinitriphenol, or TNP in chemistspeak, used in pharmaceuticals, fungicides, synthetic dyes, and explosives. To remove TNP, the magnetic, activated charcoal (MAC) powder is added to the water, which is then left untouched, say, overnight. The magnetised charcoal (having a surface area of ~500 m2/gm) “adsorbs” the TNP. The amount of charcoal to be used depends on the level of contamination. Next morning, a magnetic stick is used to remove the charcoal powder. (This is the upside of magnetising the charcoal - it can be re-collected from the water).
“These magnetised carbons could be applied for cleaning of contaminated water having very high concentration of suspended solids,” says Mohan, a PhD in chemistry, currently associate professor, School of Environmental Sciences, JNU.
The water is now fit for drinking or for reuse in the industry, says Mohan. Such a low-cost, simple method can be used in rural areas without (electricity or with an irregular supply), thus ruling out the need for electronic water remediation units. The used charcoal which now has the pollutant on it needs to be disposed of safely.
This requires the involvement possibly of non-governmental or social organisations in taking it to villages and in re-collection of the used charcoal for safe disposal, says Mohan.
MAC has been developed as part of a University Grants Commission-sponsored project. The JNU lab is now focussing on other industrial contaminants etc.