Activated biomass of the green microalga Chlamydomonas variabilis as an efficient biosorbent to remove methylene blue dye from aqueous solutions

Abstract

The raw and activated biomass of a green microalga, Chlamydomonas variabilis, were investigated as adsorbents for the removal of methylene blue (MB) dye from aqueous solutions. Chlamydomonas variabilis was isolated and cultivated to obtain a sufficient algal biomass. The collected biomass was first oven-dried and then activated by H₂SO₄. The results obtained showed that the optimum adsorption of MB occurred over 30 min of contact time at pH 7 and an biosorbent dose of 1.5 and 1.0 g·L⁻¹ of dried biomass and activated biosorbent, respectively. Point of zero charge (pHpzc) was recorded at pH 6.8 and 6.9 for dried and activated biomass, respectively. The activated biomass was a more effective biosorbent than was the dried biomass: At a MB concentration of 82.4 mg·L⁻¹, the minimum removal was greater than 98% using 1 g·L⁻¹ activated biomass with a maximum adsorption capacity (q_max) of 115 mg·g⁻¹, whereas at a MB concentration of 56.4 mg·L⁻¹, the maximum removal did not exceed 80.8% using 1.5 g·L⁻¹ raw biomass with a q_max of 18.3 mg·g⁻¹. Furthermore, the Freundlich and Langmuir isotherm models of adsorption showed a better model fit when using activated biomass than when using raw biomass, with the former yielding R² values greater than 0.9. The kinetic data suggest that the adsorption of MB follows the pseudo-second-order equation better than the pseudo-first-order one. This study demonstrates that the activated biomass of Chlamydomonas variabilis can be used as an effective biosorbent for the treatment of dye-containing wastewater streams.