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

Zhang, Xiaoyue, Zhao, Xinqing, Wan, Chun, Chen, Bailing, Bai, Fengwu
Algal research 2016 v.16 pp. 427-433
Scenedesmus obliquus, adsorption, aqueous solutions, biomass, biosorbents, biosorption, cadmium, cost effectiveness, flocculation, harvesting, heavy metals, hydrochloric acid, metal ions, microalgae, models, pH, sorption isotherms
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.