Abstract-Chromium (VI), one of the major pollutants released from tanneries, dye and textile industries, is highly toxic and carcinogenic in nature. Chemical methods for bulk treatment of industrial effluents often fail to reduce the level to meet the environmental regulations. For end of the pipe treatment, bioremediation is considered a better alternative. East Calcutta Wetlands, the major sewage treatment site of Kolkata (previously known as Calcutta), has been reported to be contaminated with several heavy metals including chromium (VI). Therefore, there is a possibility that bacterial population of this region can tolerate chromium (VI) and would be useful for bioremediation of chromium (VI). A strain of Bacillus subtilis isolated from this region was grown in presence of chromium (VI) (2.5 g/L-7.5 5 g/L). There were 97% and 90% reduction of residual chromium concentration in growth media after 24 hours with initial concentrations of 2.5 g/L and 5 g/L respectively. Best removal was observed at 30C. Growth of the Bacillus strain in presence of chromium (VI) was found to be best fit for Tessier model by non-linear regression analysis using MATLAB® 7.4. The Bacillus strain has the potential for the end of the pipe treatment removal of chromium (VI).
Organic pollutants, like phenol, along with heavy metals, like chromium, are present in various industrial effluents that pose serious health hazard to humans. The present study looked at removal of chromium (VI) in presence of phenol in a counter-current continuous packed bed reactor packed with E. coli cells immobilized on clay chips. The cells removed 85% of 500 mg/L of chromium (VI) from MS media containing glucose. Glucose was then replaced by 500 mg/L phenol. Temperature and pH of the MS media prior to addition of phenol were 30°C and 7, respectively. Hydraulic retention times of phenol- and chromium (VI)-containing synthetic media and air flow rates were varied to study the removal efficiency of the reactor system. Then temperature conditions of the reactor system were varied from 10°C to 50°C, the optimum being 30°C. The pH of the media was varied from pH 1 to pH 12, and the optimum pH was found to be 7. The maximum removal efficiency of 77.7% was achieved for synthetic media containing phenol and chromium (VI) in the continuous reactor system at optimized conditions, namely, hydraulic retention time at 4.44 hr, air flow rate at 2.5 lpm, temperature at 30°C, and pH at 7.
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