Biosorption of Acid Red 274 (AR 274) on Dicranella varia: Determination of equilibrium and kinetic model parameters

The biosorption of Acid Red 274 (AR 274) from aqueous solution on Dicranella varia was studied in a batch system with respect to initial pH and dye concentration, temperature, biosorbent concentration and stirring rate. The optimum biosorption conditions were found to be initial pH 3.0, the initial dye concentration 700 mg l−1, biosorbent concentration 0.5 g l−1 and temperature 30 °C, where the stirring rate was not an effective parameter on the biosorption capacity of D. varia. The Langmuir, Freundlich, Redlich–Peterson and Temkin isotherm models were applied to the experimental data and isotherm constants were calculated more precisely using Polymath 4.1 program. Equilibrium data fitted better to the Langmuir model than the other models according to ERRSQ analysis. The maximum monolayer adsorption capacity of D. varia for AR 274 was 2000 mg g−1 for optimum initial pH and temperature. To determine the steps affecting the uptake mechanism, the experimental data were evaluated using a boundary layer diffusion model, Weber–Morris model and a pseudo-second order kinetic model. Enthalpy and entropy changes were also calculated and it is concluded that the biosorption of AR 274 from aqueous solution on D. varia was exothermic in nature.