Removal of cadmium ion from aqueous solution by exopolysaccharide-producing bacterium, Ralstonia sp

Abstract

Bacterial exopolysaccharides (EPS) have an important role in the biosorption of heavy metals. The EPS-producing bacterium Ralstonia sp. TAK1 is a resistant cadmium bacterium isolated from cadmium-contaminated soil at a zinc mine in Thailand. Ralstonia sp. TAK1 produced the highest amounts of EPS at the stationary growth phase at 5.39 g/1 when cultured in a minimal medium amended with 2% glucose. The stationary cells of Ralstonia sp. TAK1 had the highest cadmium removal efficiency (41.73%) and cadmium adsorption capacity (15.02 mg/g). Cadmium removal efficiency and cadmium adsorption capacity by EPS were 1.91% and 0.69 mg/g respectively. In addition, the external structure of cadmium-adsorbed EPS became altered when compared to cadmium-unadsorbed EPS. Infrared spectroscopy confirmed the presence of functional groups or metal binding sites on the surface of bacterial EPS. Some spectra bands of cadmium-adsorbed EPS disappeared in contrast to cadmium-unadsorbed EPS due to the former being occupied by cadmium ions. These findings suggest that there is potential for Ralstonia sp. TAK1 cells and their EPS to be used for cadmium biosorption and applied in microbial based remediation of cadmium contaminated wastewaters. © by PSP.