A Methodology to Estimate the Sorption Parameters from Batch and Column Tests: The Case Study of Methylene Blue Sorption onto Banana Peels

In the present work, a methodology is presented where batch and fixed-bed column tests of dye sorption onto granular biosorbents are analyzed with properly selected models to estimate the parameters required for the rational design of pilot-scale units. The sorption of methylene blue (MB) onto banana peels (BP) was investigated as a case study. To identify the mechanisms of MB sorption onto BP, the pore structure and surface of BP were characterized with mercury intrusion porosimetry (MIP), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Batch tests were performed over the temperature range of 15-45 degrees C, and three models (Langmuir, Freundlich, Langmuir-Freundlich) were fitted to equilibrium and kinetic data for (i) estimating thermodynamic/kinetic parameters and (ii) choosing the model with the best goodness-of-fit. Sorption tests on fixed-bed columns were combined with a one-dimensional macroscopic convection/dispersion/sorption model to estimate the sorption parameters of BP beds. MB sorption onto BP was a purely exothermic (Delta H-0 similar to-20 kJ/mol), reversible, and monolayer chemisorption with high activation energy for the desorption step (E(d similar to)29 kJ/mol) and low activation energy for the adsorption step (E(a similar to)9 kJ/mol). The Langmuir isotherm (K-L = 141.9 m(3)/kg, T = 25 degrees C) and Langmuir kinetic model (k(d) = 1.05 x 10(-5) s(-1)) provided the best fitting to equilibrium and transient data of batch tests. The sorption capacity similar to 0.15-0.22 kg/kg and kinetic constant 0.3 x 10(-5) s(-1)-4.0 x 10(-5) s(-1) estimated from tests on BP beds were comparable to those obtained from batch tests.