Optimization of Hexavalent Chromium [Cr(VI)] Reducing Strains for Accelerated Degradation of Biphenyl and 2-Cholorbiphenyl in Tannery Wastewater

摘要

Bioremediation of multi-contaminated sites can be accelerated by optimization of bacterial strains having the ability to metabolize organic and inorganic compounds, individually. In this study previously identified bacterial strains, capable of hexavalent chromium [Cr(VI)] reduction, were optimized for accelerated degradation of biphenyl and 2-chlorobiphneyl. The MSM medium was amended with yeast biphenyl (10:90) and only biphenyl (100%) in separate experiments. Selected strains showed <1.0 OD 600 in control (MSM) which decreased to 0.5–0.6 OD 600 with yeast biphenyl MSM and further decrease to 0.06–0.09 OD 600 in MSM with biphenyl as sole carbon source. Cr(VI) reducing capability of strain, however, was not affected by medium amendment from MSM to yeast biphenyl MSM. In various pH and temperature treatments (6–9 pH and 25–40 o C), highest percentage (84% and 93% respectively) of 2-CB and Cr(VI) transformation was achieved at pH 7 and 30 o C temperature by Pseudomonas aeruginosa SB. Stenotrophomonas maltophilia K8, on the other hand, showed 78% degradation of 2-CB and 77% Cr(VI) reduction under similar conditions. Strain SB showed significantly higher biotransformation of Cr(VI) and 2-CB (80% and 85% respectively) in yeast biphenyl MSM in comparison to glucose and starch MSM whereas K7 and K8 also performed better in similar medium. Glucose and starch were not found to be suitable as carbon sources for the isolates. In electron shuttles experiment, 85% degradation of biphenyl at 1 mmol L -1 concentration of sodium benzoate was observed with strain SB, whereas 82 and 72% degradation were observed with same concentration of hydroquinone and mannitol respectively. Result of the study suggested that maximum detoxification of Cr(VI), biphenyl and 2-CB was achieved at 7 pH, 30 o C in yeast biphenyl MSM. Whereas non-significant difference in degradation ability of strains was observed for sodium benzoate, hydroquinone, and mannitol when applied as electron shuttles in lower concentrations (1–3 mmol L -1 ). The result of this study can be helpful in simultaneous treatment of multi-contaminated sites.