Biosorption is an alternative process for uptake of reactive dyes from aqueous solution. In the present study, the biosorption of  reactive black 5 (RB 5) from aqueous solution was investigated by using loquat (Eriobotrya japonica) seed biosorbent in a  batch adsorption technique as a function of contact time (0.5 min to 3 h), initial dye concentration (50 to 200 mg/L), biosorbent dose (5 to 30 g/L) and pH (1.5 to 5.5). The experimental data showed that the optimum pH for efficient biosorption of RB 5 was 2.5. The data were analyzed on the basis of Lagergren pseudo-first-order, pseudo-second-order, Elovich equation and Weber-Morris kinetic models tested. The results suggested that the pseudo-second-order model (R>0.999) was the best choice among all the kinetic models to describe the biosorption behavior of RB 5 onto the biosorbent. The equilibrium data were evaluated by using Langmuir and Freundlich isotherms and the Langmuir isotherm was found to provide the best correlation of the experimental data. Thermodynamic parameters including the Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes indicated that the biosorption of RB 5 onto loquat seed biosorbent was feasible, spontaneous and endothermic. The results revealed that loquat seed biosorbent could be used as biosorbent for the treatment of wastewater containing RB 5.

Key words: Biosorption, isotherm, loquat seed, reactive black 5, thermodynamic.