Abstract
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 °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 (ΔH0~−20 kJ/mol), reversible, and monolayer chemisorption with high activation energy for the desorption step (Ed~29 kJ/mol) and low activation energy for the adsorption step (Ea~9 kJ/mol). The Langmuir isotherm (KL = 141.9 m3/kg, T = 25 °C) and Langmuir kinetic model (kd = 1.05 × 10−5 s−1) provided the best fitting to equilibrium and transient data of batch tests. The sorption capacity ~0.15–0.22 kg/kg and kinetic constant 0.3 × 10−5 s−1–4.0 × 10−5 s−1 estimated from tests on BP beds were comparable to those obtained from batch tests.
Highlights
The presence of dyes in liquid industrial waste poses a risk to the ecosystem and human health [1,2,3]
A methodology was proposed and applied to the case of methylene blue sorption onto banana peels, where sorption parameters needed for the design of pilot-scale biosorbents were obtained from the combination of batch and column studies with mutually consistent and true-to-the mechanism sorption models
Equilibrium and kinetic sorption tests of Methylene blue (MB) onto banana peels (BP) grains were conducted in batch reactors at temperatures of 15–45 ◦ C to estimate thermodynamic/kinetic properties and assess the goodness-of-fit for three models used to describe the isotherms and sorption kinetics: Langmuir, Freundlich, and Hybrid (Langmuir–Freundlich)
Summary
The presence of dyes in liquid industrial waste poses a risk to the ecosystem and human health [1,2,3]. Methylene blue (MB) is a cationic azo dye widely used in industry, and several diseases (e.g., hypertension, anemia) have been associated with its presence in the human body [4]. Emphasis has been placed on low-cost adsorbents made from agricultural waste as alternatives to commercial activated carbon [9]. Such materials, prepared from the peels and shells of fruits or leaves of trees, have been used to remove dyes from wastewater [10,11,12,13]. Special attention has been paid to olive-pomace [14,15] and oil waste mills [16] for the removal of dyes from wastewater
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