The biosorption of Alizarin Red S by Spirulina platensis; process modelling, optimisation, kinetic and isotherm studies

Abstract

ABSTRACT Spirulina platensis is abundant biomass of cyanobacteria (blue-green algae) which is applied in the current study as a biosorbent. A statistical Box–Behnken approach was adopted to remove the toxic dye of alizarin red S (ARS) from synthetic solutions. A polynomial equation was developed to predict the dye removal efficiency and elucidate the interaction effects of variables. The maximum removal efficiency of ARS (69.1%) was obtained at pH 6.5, mixing time of 42.5 min, dye concentration of 100 mg. L−1 and S. platensis dose of 1.5 g. L−1. The findings indicated that the biosorption rate of ARS had a direct relationship with the ARS concentration, pH, reaction time, and S. platensis dose. The quadratic model suggested that the ARS concentration is the major variable in ARS removal. The isotherms and kinetics data could be suitably reflected by the Langmuir model and the pseudo-first-order equation. The maximum adsorption capacity of S. cerevisiae was obtained to be 17.15 mg. g−1 based on the Langmuir model. The results showed that the removal rates of ARS from the first cycle up to the fourth cycle were varied from 55% to 20%, respectively. In conclusion, S. platensis shows suitable adsorptive characteristics and hence could be suggested as a viable option for future studies.