Abstract

 
 
 
 Purpose: To study Cr (VI) removal from waste water using chromium-resistant bacterial strains in combination with rice husk.
 Methods: Two strains of Exiguobacterium sp. resistant to chromium (VI) were applied in the present work. Rice husk (RH) was used as an agricultural waste for Cr (VI) removal. The elimination of Cr from the husk was chemically facilitated using hydrochloric, sulphuric and citric acids, as well as formaldehyde and potassium dihydrogen phosphate Investigation of optimum physical factors such as pH, temperature, shaking speed and biomass concentration on Cr (VI) removal was carried out using citric acid-processed rice husk alone, and in combination of bacterial strains. Fourier transform infra-red (FTIR) spectroscopy was performed to determine the contributions of different functional groups involved in Cr (VI) binding. Scanning electron microscopy (SEM) of treated and untreated RH was also performed.
 Results: Citric acid-processed RH was most effective in the removal of chromate (97.3 %). The two bacterial strains combined with rice husk proved highly efficient in Cr (VI) removal from sterile and non-sterile industrial effluents. FTIR spectra showed the involvement of esters, amines and aliphatic functional groups in Cr (VI) binding, while SEM displayed the damaging effects of Cr (VI) on the surface of RH; however, bacterial inoculation minimized the damage.
 Conclusion: Exopolysaccharides from Exiguobacterium strains and citric acid-processed rice husk demonstrated high efficiency for Cr (VI) removal. Hence, RH with these bacterial strains are potential biosorbents for control of heavy metal contamination arising from industrial effluents.
 
 
 
Highlights
Industries generate tons of harmful toxic effluents which contain large amounts of Cr (VI) [1]
Several bacterial strains used in this bioremediation process include Enterobacter, Bacillus, Pseudomonas and Agrobacterium
The E1 and E4 strains of Exiguobacterium showed 83.4 and 75.8 % chromium (VI) removal, respectively, when grown at 1000 μg/ml
Summary
Industries generate tons of harmful toxic effluents which contain large amounts of Cr (VI) [1]. The toxic effects of Cr (VI) range from skin reactions to lung carcinoma. There is need to eliminate the metal from waste water prior to channeling into the open water. Studies have identified a diverse range of organisms with high capacity for Cr (VI) reduction. These findings have been exploited as cheaper routes of treating waste water [2]. Several bacterial strains used in this bioremediation process include Enterobacter, Bacillus, Pseudomonas and Agrobacterium.
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