Adsorptive removal of amoxicillin from wastewater using wheat grains: equilibrium, kinetic, thermodynamic studies and mass transfer

Wheat grains are natural products which grow in the north of Algeria. In this study, they were used as adsorbent to remove amoxicillin antibiotic from wastewater. Adsorption isotherm of amoxicillin on both crude and modified wheat grains with 20% tartaric acid was investigated in batch tests. A model was developed regarding both the kinetic partitioning and the mechanism governing the forward transfer of amoxicillin. Results were interpreted in terms of a two-film theory for flat interface. The percentage of maximum adsorption capacity of amoxicillin was found to be 84% for the following optimal conditions: amoxicillin concentration of 4mg/L, 5min contact time, pH 7, temperature 25 degrees C, and 0.24g/L initial amoxicillin concentration and 150g particle size. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data, and the rate constants were evaluated. It was found that the pseudo-second-order model provides the most adequate correlation of experimental data. The rate parameters of the intraparticle diffusion model for adsorption were also evaluated and to identify the adsorption mechanisms. The adsorption constants were evaluated by using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) adsorption isotherm models. The results showed that Temkin isotherm agrees with experimental data better than other adsorption models for the adsorption of amoxicillin. The thermodynamic parameters (G, H, and S) showed that the process was feasible, spontaneous, and exothermic.