Remediation of methylene blue from aqueous solution by Chlorella pyrenoidosa and Spirulina maxima biosorption: Equilibrium, kinetics, thermodynamics and optimization studies

The present work aimed to investigate the equilibrium, kinetics and thermodynamic viability of methylene blue (MB) biosorption by Chlorella pyrenoidosa (C. pyrenoidosa) and Spirulina maxima (S. maxima). A comprehensive characterization of both dried biomasses used as biosorbent was carried out and the parameters involved were optimized for maximum MB removal efficiency. Thermogravimetric analysis showed that both algae are constituted mainly of proteins and carbohydrates. The infrared spectra suggested a physical biosorption mechanism for both algae that was later proven by the enthalpy change and the Dubinin-Radushkevich isotherm model. Furthermore, the process involving S. maxima was best described by Freundlich (R-2 = 0.995, chi(2) = 1.246) and Temkin (R-2 = 0.999, chi(2) = 0.155) isotherm models, indicating the formation of multiple layers and the linear reduction of the heat of biosorption with the coverage degree. Biosorption onto C. pyrenoidosa was best described by Langmuir isotherm model (R-2 = 0.993, chi(2) = 0.126), indicating the monolayer predominance. C. pyrenoidosa presented a maximum biosorption capacity of 101.75 mg g(-1), in contrast to 145.34 mg g(-1) for S. maxima. The pseudo second order kinetic model was the best fit for C. pyrenoidosa (R-2 = 0.999, chi(2) = 0.004) and S. maxima (R-2 = 0.999, chi(2) = 0.014). The model optimization was achieved in order to maximize the removal efficiency, corresponding to 98.20% for C. pyrenoidosa and 94.19% for S. maxima.