Chromochloris zofingiensis microalgae as a potential dye adsorbent: Adsorption thermo-kinetic, isothermal, and process optimization

Abstract

In this study, the microalgae Chromochloris zofingiensis (ChZ) was harvested and used as a biosorbent for the removal of methylene blue (MB) as a model cationic dye from water. The ChZ was characterized via FTIR, FESEM-EDX, XRD and BET analyses. Response Surface Methodology, based on Central Composite Design was employed to optimize the batch adsorption process, including independent variables of biosorbent dosage, initial MB concentration and pH of the solution to maximize the MB removal percentage. The maximum removal of 97 % was obtained at the optimal conditions i.e., biosorbent dosage of 0.72 g/L, pH of 10 and initial MB concentration of 15.12 mg/L, with >97 % confidence limit. Pareto sensitivity analysis uncovered that the biosorbent dosage has the greatest impact (50 %) on MB removal. The adsorption kinetic was better described by the pseudo-second-order model among the different kinetic models applied i.e., pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models. The adsorption equilibrium was also modeled using the Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherms. The Langmuir model provided the best fit and the maximum sorption capacity of 135.42 mg/g was recorded. Principle thermodynamic criteria including ΔGo, ΔHo and ΔSo were computed for the biosorption. The results uncovered that the biosorption of MB using ChZ is spontaneous and exothermic. Generally, the results indicated that ChZ microalga can be considered an effective biosorbent for dye-contaminated water remediation.