Biosorption and biotransformation of Cr (VI) by hexavalent chromium-stressed environmental fungal isolates from wastewater

As conventional physico-chemical heavy-metal remediation technologies like ion-exchange, reverse osmosis, electrodialysis etc. are becoming extremely expensive, the possibility of use of microorganisms in bioremediation or biorecovery of different heavy metals from industrial effluents is extensively explored by different workers. Hexavalent chromium stressed environmental fungal isolates from tannery wastewater were assessed to biosorb and biotransform Cr(VI) from nutrient media and wastewater. Out of total 56 fungal strains isolated only six fungal strains had shown tolerance and good growth rate to up to 300 mg/l chromium(VI). Among the strains isolated from wastewater, Aspergillus species were more efficient in removal of chromium. It was observed that Aspergillus flavus strain ESTF –241 and Aspergillus clavatus strain ESTF –181 showed more than 85% Cr(VI) removal within a week. Removal rates were higher for the first four days. In real tannery wastewater both these strains showed moderate removal efficiencies, though about 2-30% lower than in nutrient media with comparable chromium (VI). Biosorption was always higher than biotransformation of Cr(VI). Aspergillus flavus strain ESTF – 241 showed better Cr(VI) removal capacity.