Biosorption of cadmium by CO2-fixing microalga Scenedesmus obliquus CNW-N

An efficient CO2-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% CO2, achieving a maximum CO2 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 50 mg/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 0.6 g. 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 CaCl2, as the regenerated biosorbent retained good adsorption capability after five consecutive adsorption/desorption cycles.