Biosorption of reactive dyes on the green alga Chlorella vulgaris

Biosorption of three vinyl sulphone type reactive dyes (Remazol Black B (RB), Remazol Red RR (RR) and Remazol Golden Yellow RNL (RGY)) onto dried Chlorella vulgaris, a green alga was investigated in a batch system. The algal biomass exhibited the highest dye uptake capacity at the initial pH value of 2.0 for all dyes. The effect of temperature on equilibrium sorption capacity indicated that maximum capacity was obtained at 35 °C for RB biosorption and at 25 °C for RR and RGY biosorptions. Biosorption capacity of alga increased with increasing initial dye concentration up to 800 mg l−1 for RB and RR dyes, and up to 200 mg l−1 for RGY dye. Among the three dyes, RB was adsorbed most effectively by the biosorbent to a maximum of approximately 419.5 mg g−1. The Freundlich, Langmuir, Redlich-Peterson and Koble-Corrigan adsorption models were used for the mathematical description of the biosorption equilibrium and isotherm constants were evaluated at different temperatures. Equilibrium data of RB biosorption fitted very well to all models except that the Langmuir model, while this model was found most suitable for describing the biosorptions of RR and RGY dyes in the studied concentration and temperature ranges. The pseudo first- and second-order and saturation type kinetic models were also applied to the experimental data assuming that the external mas transfer limitations in the system can be neglected. The results indicated that the dye uptake process followed the pseudo second-order and saturation type rate expressions for each dye-C. vulgaris system.