Removal of Cadmium Ions from Aqueous Samples bySynechocystissp

Effects of bloom-forming cyanobacterial extracellular polymeric substances on the adsorption of cadmium onto kaolinite: behaviors and possible mechanisms

Cyanobacterial blooms result in high level of cyanobacterial extracellular polymeric substances (EPS) in water. The effects of bloom-forming cyanobacterial EPS on the distribution of Cd(II) in the interface between sediment and water is unknown. Clay is a main component in sediment. The effects of EPS, originated from a typical bloom-forming cyanobacterium Microcystis aeruginosa, on the adsorption and desorption characteristics of Cd(II) by kaolinite were investigated in this study. Results of XRD analysis indicated that cyanobacterial EPS bound on the surface of kaolinite. The composite of kaolinite + EPS showed higher adsorption capacity toward Cd(II) than pure kaolinite, and hydroxyl groups were involved in the adsorption processes. The data for the adsorption of Cd(II) by kaolinite are well fitted by both Langmuir model and Freundlich model, whereas only Freundlich model well describes the adsorption data of Cd(II) by the composite of kaolinite + EPS. The adsorption of Cd(II) onto kaolinite was an exothermic process, but it became an endothermic process after EPS incorporation. Results of desorption showed that EPS incorporation increased the adsorption of kaolinite toward Cd(II) through physical adsorption, ion exchange and complexation.

Biosorption of cadmium by CO(2)-fixing microalga Scenedesmus obliquus CNW-N

An efficient CO(2)-fixing indigenous microalga Scenedesmus obliquus CNW-N was used as the biosorbent to remove cadmium from aqueous solution. The microalga was grown with continuous feeding of 2.5% CO(2), achieving a maximum CO(2) consumption rate of 495 mg/l/d and a biomass production of 2.56 g/l. Cadmium (Cd) biosorption by S. obliquus CNW-N was optimal at pH 6.0 and 30 °C. For an initial cadmium concentration of 50mg/l, the biosorption capacity tended to decrease with an increase in biosorbent, while the cadmium removal efficiency was nearly 100% when the biosorbent loading was higher than 0.6g. The biosorption kinetics followed the pseudo-second order adsorption model. The adsorption equilibrium obeys Langmuir isotherm with an estimated maximum capacity of 68.6 mg/g and a saturation coefficient of 0.101 l/mg. The cadmium-loaded microalgal biomass could be regenerated preferably with 0.05 M CaCl(2), as the regenerated biosorbent retained good adsorption capability after five consecutive adsorption/desorption cycles.