Bioremediation of hexavalent chromium from electroplating effluents by wild and mutant strains of Bacillus amyloliquifaciens

Abstract

Chromium, a heavy metal, is a major xenobiotic element found in electroplating effluents. It is a recalcitrant of concern as it is highly toxic and carcinogenic. It exists as Cr (VI) which is highly soluble and bioavailable. Various conventional treatment technologies like adsorption, ion exchange, filtration, reverse osmosis and electrodialysis have been used but they generate lot of sludge and residue. Hence, there is a need for an economical, faster and ecofriendly means of remediation for which bioremediation is preferred. In this study we attempted chromium removal by employing improved indigenous isolate Bacillus amyloliquifaciens sourced and identified from a previous study from chrome plating effluent collected from Peenya industrial area, Bengaluru, India. Strain improvement was achieved using physical mutagen (UV radiation) and chemical mutagens (ethidium bromide, ethyl methane sulphonate and acrylamide). A comparative study was carried out to screen the chromium remediation potential of wild type and mutants in chromium spiked sample and the electroplating effluent. The mutant generated using acrylamide (150 µg/mL) in comparison with wild type and other mutants was more capable of remediating chromium. At the end of 18 days, from the chrome electroplating effluent containing chromium
(490 mg/100mL), the wildtype could remove 74% (362.6 mg/100 mL), UV radiation induced mutant removed 83%
(406.7 mg / 100 mL) whereas acrylamide induced mutants removed 96.67% (470.4 mg/100 mL) of chromium. Enzyme assays confirmed involvement of enzymes at sub cellular level in chromium remediation.