Eucalyptus helps remove chromium
indian scientists have found the bark of widely grown eucalyptus can help solve one of the most gruelling industrial problems: removing chromium from effluents. The bark not only reduces chromium content in industrial waste to safe levels, but also enables the toxic metal's recovery for reutilisation, claim researchers at the Indian Institute of Technology (iit), Delhi.
Chromium can cause lung cancer and damage to other vital organs like the kidney, liver and stomach. It is also toxic to other life forms including plants and microorganisms. The metal occurs in two forms -- Cr (vi) and Cr (iii), the former being 500 times more toxic than the latter. The maximum levels of chromium oxides permitted in wastewater are 5 parts per billion (ppb) for Cr (iii) and 0.05 ppb for Cr (vi).
Used in several industrial processes, chromium is normally removed from effluents through precipitation but that does not bring its levels to acceptable limits. Besides, its safe disposal or recovery from the slurry is considered tough.
In India, the leather industry is the biggest user of chromium. The element is used as a cheap tanning agent. The tanning process takes up only 60-80 per cent of the applied chromium and the rest is discharged. Though chromium in effluents from tanneries is usually in the form of Cr (iii), organic compounds present in the industrial waste convert Cr (iii) into the more toxic Cr (vi).
Kamal Pant of iit and his research student Vikrant Sarin used two samples of industrial waste from an automobile plant near Delhi, where nickel-chromium spraying was being done. They contained 250 ppm (parts per million) and 500 ppm of chromium. As the adsorption process involving eucalyptus bark is effective at levels less than 200 ppm, the scientists first introduced a membrane filtration process. When the effluent was passed over a bed of eucalyptus bark, the scientists found up to 99 per cent of chromium was removed from the waste water. The process was repeated to bring chromium concentration down to its safe limit. The findings will appear in a forthcoming issue of Bioresource Technology .
The scientists also tried out several other cheaply available materials such as coconut husk fibres, sugarcane bagasse, sugar beet pulp, and saw dust, but found the eucalyptus bark the most efficient.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
.png)
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.