Efficient biosorption of cadmium by the self-flocculating microalga Scenedesmus obliquus AS-6-1

Abstract

Microalgae have been considered as promising biosorbents for removal of heavy metal ions from aqueous solutions, and flocculation has the potential for cost-effective microalgae harvesting. In this study, the self-flocculating Scenedesmus obliquus AS-6-1 was tested for the biosorption of cadmium (II), and the non-flocculating S. obliquus FSP-3 was used as a control. The maximum Cd2+ removal efficiency of S. obliquus AS-6-1 achieved was 93.39% at 0.8g/L biomass, 30°C, pH6.0 for 20min with an initial Cd2+ concentration of 50mg/L. Moreover, S. obliquus AS-6-1 showed higher Cd2+ removal efficiencies at lower pH (3.0, 4.0 and 5.0, respectively), which were 4.75, 1.95 and 1.97-fold higher than those of S. obliquus FSP-3. The adsorption equilibrium of S. obliquus AS-6-1 could be described by either Langmuir or Freundlich isotherm models, and the maximum adsorbed capacity was 144.93mg/g estimated by Langmuir isotherm, higher than that of S. obliquus FSP-3 (84.03mg/g). The cadmium-loaded biomass of S. obliquus AS-6-1 was regenerated with 0.1M HCl and retained good adsorption capability throughout five consecutive cycles. These results demonstrate that the self-flocculating S. obliquus AS-6-1 is a promising and efficient biosorbent for cadmium removal.