Adsorption of metal ions from aqueous solution onto microalga entrapped into Ca-alginate gel bead

Abstract

A microalga biomass was entrapped into gel bead using sodium alginate in the presence of Ca(II) ions. Firstly, adsorption of metal ions by the microalga entrapping alginate beads was studied in a batch system. The effects of initial metal concentration and pH on uptake of the metal ions were examined. The maximum experimental adsorption capacities of the microalga entrapping alginate beads of Chlamydomonas reinhardtii and Anabena variabilis were found to be 61.3 mmol-Cd/g-bead and 51.2 mmol-Cd/g-bead, respectively. The rate of metal adsorption was high, and approximately, 85% metal adsorption took place within 30 min. The adsorption equilibrium was well described by Langmuir adsorption isotherm. The adsorption capacity of the C. reinhardtii entrapping alginate beads was relatively high, and so it could be considered that the alginate beads were one of the suitable adsorbents for the removal of metal ions in wastewater treatment. In addition, it was possible that the adsorbents were reused at least three times in consecutive metal adsorption–desorption cycles without a significant loss in the adsorption capacity. Secondly a mutual separation between Cd(II), Cu(II), Zn(II), and Ni(II) was conducted using a column packed with the microalga entrapping alginate beads. As the result, it was suggested that the mutual separation of the metals was possible under a suitable operating condition.

Keywords:

• Adsorption
• Calcium alginate bead
• Immobilization
• Metal adsorption
• Microalgae
• Packed bed bioreactor