Biosorption of cadmium, copper, and lead ions from aqueous solutions by Ralstonia sp. and Bacillus sp. isolated from diesel and heavy metal contaminated soil

Abstract

Sorption batch experiments using bacterial strains isolated from soil were performed to remove heavy metals such as Cd, Cu, and Pb from an aqueous solution. Ralstonia sp. and Bacillus sp. were used as biosorbents and the distilled water, artificially titrated at 5 mg/L for Cd, Cu, and Pb, was used for the aqueous solution. Various amounts of biosorbents were mixed with the aqueous solution and the removal efficiency of each heavy metal ion in solution was calculated. From the results of the experiment, the removal efficiency ratings of Ralstonia sp. for Cd, Cu, and Pb were greater than 90% after adding 0.5 g of Ralstonia sp. to 50 ml of aqueous solution. With only 0.2 g of Bacillus sp., the removal efficiencies for Cd, Cu, and Pb were over 90%, suggesting that they are excellent biosorbents for the removal of heavy metal ions from an aqueous solution. Sorption experiments were duplicated in aqueous solutions at various pH conditions. For a solution at pH 1, the removal efficiency ratings of Ralstonia sp. for Cd and Pb were less than 20%. However, when the pH of the solution was higher than 3, the removal efficiency dramatically increased to 90%. It decreased slightly when the pH was greater than 10. Most of the biosorption of heavy metals in the experiment were completed within 10 min. From a TEM analysis image, it was observed that many clods of materials were concentrated at the boundary of the cell walls, suggesting that the biosorption activities of Ralstonia sp. and Bacillus sp. occur mostly at their cell walls. From the results of the fitting process of the experimental data to the Freundlich isotherm model, the Freundlich sorption coefficients (Kf) of Cd, Cu, and Pb for Ralstonia sp. and Bacillus sp. ranged from 646 to 754 and from 113 to 221, respectively; their sorption constants (1/n) ranged from 1.06 to 1.90 for Ralstonia sp., and from 0.98 to 1.07 for Bacillus sp. The results of these experiments suggest that the biosorption process with both microorganisms is a promising removal process for water contaminated with heavy metals.