Phytoremediation of azo dye methyl red by macroalgae Chara vulgaris L.: kinetic and equilibrium studies

Phytoremediation is an innovative, eco-friendly, and solar-driven technique, which becomes a well-known alternative solution for remediation of hazardous dyes from wastewater. In present research work, potential of a submerged fresh water macroalgae Chara vulgaris L. (C. vulgaris) examined for removal of acidic azo dye methyl red (MR) in its solution form. A series of experiments were done with C. vulgaris to predict the effects of different parameters viz. contact time, initial dye concentration, amount of macroalgae, and pH. The increase in initial dye concentration directly impacts on the potential of macroalgae. The decolorization percentage declined with increase in initial dye concentration. The equilibrium condition was found to achieve after contact time of approximately 48 h. The decolorization of MR dye was found to be favorable at pH 5. The macroalgae was successfully utilized repeatedly with MR for eight cycles in batch experiments. The kinetics of phytoremediation of MR dye was studied with help of pseudo-first-order, pseudo-second-order, and Elovich kinetic models and the results were well suited to pseudo-second-order kinetic model with the correlation value R² ≥ 0.99. In addition, the experimental data was also assessed by using Langmuir and Freundlich adsorption equilibrium isotherms. The results of phytoremediation data was found to be in favor of Freundlich equilibrium isotherm which having the correlation value R² ≥ 0.977. The intraparticle diffusion model also studied to interpret the macroalgae phytoremediation mechanism for phytoremediation of MR. The surface interactions of C. vulgaris were investigated before and after the removal of dye with Fourier transform-infrared spectroscopy (FTIR) technique. On the basis of these studies, a hypothetical mechanism has also been proposed to depict the phytoremediation of acidic azo dye by C. vulgaris.