BIOSORPTION OF ACID DYES BY BROWN ALGA Dictyota dichotoma: EQUILIBRIUM, KINETIC AND THERMODYNAMIC STUDIES

In this study, the biosorption of Acid Blue 324 (AB324) and Acid Red 337 (AR337) dyes, known as the components of textile industry wastewaters, on Dictyota dichotoma was studied in a batch system. The optimum biosorption conditions were determined, and then the equilibrium for both dyes' biosorption was modeled by using Langmuir and Freundlich isotherm models. The equilibrium studies showed that the biosorption equilibrium data of AB324 and AR337 fitted to both Langmuir and Freundlich isotherms in the concentration and temperature ranges studied. The monolayer coverage of AB324 and AR337 dyes were determined as 244 and 323 mg g(-1) respectively. The intraparticle diffusion model was applied to the experimental data, and it was found that both surface adsorption and intraparticle diffusion contribute to the rate-limiting step. Analysis of biosorption data using a Boyd plot confirmed that external mass transfer was the main rate-limiting step in the biosorption process. It was observed that AB324 and AR337-D. dichotoma biosorption processes followed the pseudo-second order kinetics, and their activation energies were determined in the range of physical adsorption. Thermodynamic studies showed that the biosorption of AB324 and AR337 on D. dichotoma is exothermic and spontaneous in nature.