Bioaccumulation of hexavalent chromium by enriched microbial cultures obtained from molasses and NaCl containing media

Abstract

Microorganisms that could grow on a media containing molasses, NaCl and chromium(VI) were isolated and their chromium(VI) bioaccumulation capacities increased by enrichment procedure. The effects of different initial pH values, NaCl and chromium(VI) concentrations on bioaccumulation of chromium(VI) by enriched mixed cultures were studied in a batch system. At about 25 mg l −1 initial chromium(VI) concentrations, uptake yield of mixed cultures exceeded 95–99% after 5 days at all tested pH values and NaCl concentrations. The optimum pH values at this chromium concentration was determined as 7 for 2 and 4% NaCl, 9 for 6% NaCl and 8 for media without NaCl. At all tested NaCl concentrations, chromium(VI) bioaccumulation by mixed cultures was investigated at 10–150 mg l −1 initial chromium(VI) concentrations. At the end of the experiments, the highest specific chromium uptake was obtained at pH 8 as 109.45 mg g −1 for 164.4 mg l −1 initial chromium(VI) concentration in the absence of NaCl. In the highest NaCl concentration the maximum specific chromium uptake was found at pH 9 (26.2 mg g −1) in samples with lower initial chromium(VI) concentrations at pH 7 (as 87.5 mg g −1) for high initial chromium(VI) concentrations. Data indicated that isolated and enriched mixed cultures can be utilized to increase efficiency of biological treatment processes using activated sludge cultures for treatment of saline and alkaline wastewater effluents containing higher levels of chromium(VI) ions.