Hexavalent chromium, Cr(VI ) , is one of the toxic heavy metals released into the environment by a large number of industries and it is crucial to limit its further discharge into the environment. In the present study, the aerobic reduction of Cr(VI ) to less mobile and less toxic Cr(III) by Aspergillus niger was investigated. The potential of this strain as a biocatalyst was capable of resisting Cr(VI) up to 300 mg/l. The effects of process parameters such as solution pH, initial Cr(VI ) concentration on bioaccumulation and bioreduction of Cr(VI), total sugar consumption, cell dry weight at 218 h were investigated. However, maximum chromium removal, cell dry weight, and total sugar consumption were 100%, 0.81 g/l, and 78.8%, respectively, at 5 mg/l initial Cr(VI) concentration and 25 oC. Furthermore, optimization of solution pH carried out with initial Cr(VI) concentration of 25 mg/l, so pH value obtained 3.5 and Cr(VI) removal, cell dry weight production and total sugar consumption were, 84.7%, 0.46 g/l and 81.6% respectively.
