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 495mg/l/d and a biomass production of 2.56g/l. Cadmium (Cd) biosorption by S. obliquus CNW-N was optimal at pH6.0 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 68.6mg/g and a saturation coefficient of 0.101l/mg. The cadmium-loaded microalgal biomass could be regenerated preferably with 0.05M CaCl ₂, as the regenerated biosorbent retained good adsorption capability after five consecutive adsorption/desorption cycles.