Hexavalent chromium bioaccumulation by Micrococcus sp. isolated from tannery wastewaters

In this study, Micrococcus sp. was isolated from chromium-contaminated tannery wastewater, and the capacity of the microorganism to bioaccumulate Cr(VI) at different initial pH values (7, 8 and 9), as well as NaCl (0,2,4,6 and 8% w/v) and Cr(VI) (72.0-185.5 mg L super(-1)) concentrations on molasses media was investigated. At approximately 50 mg L super(-1) initial Cr(VI) concentration, the optimum pH was determined to be 9 for the media without NaCI, and 8 for 2, 4, 6 and 8% (w/v) NaCI. The capacity of the microorganism to bioaccumulate Cr(VI) was affected by NaCI levels in the medium at high Cr(VI) concentrations. The highest uptake yields were observed as 71.2% for 163.6 mg L super(-1) and 47.3% for 180.2 mg L super(-1) Cr(VI), at 8% (w/v) NaCl. In contrast, at low Cr(VI) concentrations (72.0-111.4 mg L super(-1)), the maximum uptake yields were 99.4% and 99.3% at 2% (w/v) NaCl, respectively. In the media containing 6% (w/v) NaCl, the microorganism was able to bioaccumulate more than 93.0% of the Cr(VI) applied at 78.1-109.3 mg L super(-1) initial levels, and the highest specific Cr uptake was obtained as 116.34 mg g super(-1) at 150.2 mg L super(-1) Cr(VI). These results indicated that Micrococcus sp. has a potential usage to remove Cr(VI) from saline wastewater and, therefore, biological treatment process efficiency can be increased by this way.