Bio-detoxification of chromium from industrial wastewater by fungal strains

Chromium is one of the most toxic heavy metals to be abundant in tannery wastewater effluents. In order to study the possibility of chromium detoxification, chromium tolerant fungal strains were isolated from the tannery effluent of eastern Calcutta and their chromium tolerance limits were detected. The chromium accumulating capacity of these strains was studied by culturing them in nutrient media supplemented with chromate salts. Depending on the pH of the concerned media, chromium accumulating capacity was found to be different for these fungi. Though most strains had shown better biosorption in lower pH, Aspergillus clavatus accumulated more chromium in alkaline conditions. These strains were further screened for their biosorption capacity to remove chromium from the raw effluent and the nutrient supplemented effluent. As the reduction of hexavalent chromium to its trivalent form is an efficient remediation for reducing toxicity of wastewater, it was also studied to evaluate the detoxification capability of these strains. Aspergillus strains were found most efficient for detoxification, doing more than sixty percent conversion. These fungal strains could be used for biorecovery and detoxification of chromium.