Biosorption of hexavalent chromium in aqueous solution by Bacillus cereus

Hexavalent chromium is one of the toxic metals in water pollution. This study is aimed at analyzing the involvement of chromium reductase and biosorption potential in chromium-resistant species of Bacillus cereus. A total of 10 % (v/v) of B. cereus biomass was inoculated into a 90 mL chromium-contaminated solution with an initial concentration of 60 mg/L. Biomass digestion was carried out every day for a 5-day treatment period for chromium content analysis, while biomass characterization was carried out at the end of the treatment period, comparing the exposed vs. non-exposed bacteria. Results indicated that the highest chromium removal (16.12 ± 0.63 %) was obtained on day 3, while the maximum biosorption capacity was obtained on day 1, reaching 0.461 ± 0.02 mg Cr/g dry cell of biomass. XRD showed the crystalline structure of the bacteria cell after being exposed to chromium, suggesting that interactions between polysaccharides and proteins in the membrane may occur during the treatment. In addition, FT-IR spectra also showed decreasing peaks and the involvement of hydroxyl, carboxyl, carbonyl, and nitroxide groups during the treatment. SEM-EDX results indicated that bacteria are experiencing cell structure alteration with more intense chromium spectra on the surface, while TEM images showed endospore formation by B. cereus under adverse environmental conditions. This study suggested that the removal of hexavalent chromium by B. cereus might be dominant via biosorption (translocated into cell biomass).