Immobilized citric acid-treated bacterial biosorbents for the removal of cationic pollutants

Corynebacterium glutamicum, a full-scale fermentation process waste, showed good performance for the removal of a cationic dye, Basic Blue 3 (BB 3), after chemical modification using citric acid (CA) as an esterifying agent. This study investigated the potential use of immobilized biomass for dye biosorption in batch experiments. The powder form of CA-treated biomass (CAB) was immobilized in three polymer matrices: calcium alginate (CaA), polysulfone (PS) and polyurethane (PU). Three batch experiments were conducted: pH edge, isotherms and kinetics. As shown in the pH edge experiments, the BB 3 removal was favored at pH values greater than 7. The experimental equilibrium data were analyzed using two two-parameter (Langmuir and Freundlich models) and two three-parameter (Redlich–Peterson and Sips models) isotherm models. The experimental data were well described by the Redlich–Peterson isotherm model, followed by the Sips, Langmuir and Freundlich isotherm models. The kinetic data showed that immobilized CAB was slower than free CAB. Of the three diffusion models used to fit the kinetic data, pseudo-first order, pseudo-second order and intra-particle, the first fitted well for free CAB, and the second for immobilized CAB. Regeneration experiments of free and immobilized CAB were carried out for five sorption–desorption cycles, and immobilized CAB showed higher desorption efficiencies (>80%) than the powder form of free CAB, except for CaA-immobilized CAB which was dissolved in the second sorption cycle.