Chemical modification and immobilization of Corynebacterium glutamicum for biosorption of reactive black 5 from aqueous solution

The main goal of this work was to develop a suitable biosorbent for the remediation of reactive dye bearing wastewaters. The poor mechanical stability of the microbial biosorbent and unfeasible operating conditions often limit the applicability of biosorption to industrial applications. Corynebacterium glutamicum, which has shown a high biosorption capacity under strong acidic conditions, was decarboxylated for the biosorption of Reactive black 5 (RB5) under moderate pH conditions (pH 4). Amine groups were responsible for accommodating the negatively charged RB5 via electrostatic interactions; while the repulsion caused by negatively charged carboxyl groups was minimized via decarboxylation. Isotherm experiments revealed that decarboxylated biomass possessed a maximum uptake of 257.3 mg/g at pH 4, according to the Langmuir model. Immobilization of C. glutamicum using polysulfone matrix enabled the biosorbent to be reused for multiple cycles. Even though immobilized beads showed a tendency to attain slow equilibrium, mainly due to intraparticle diffusion, the efficiency of binding sites was properly utilized. Application of decarboxylated biomass in an up-flow packed column for the continuous biosorption of RB5 was made possible by immobilization and exhibited an uptake of 78.6 mg RB5/g beads. Column regeneration experiments over three cycles revealed that polysulfone-immobilized, decarboxylated C. glutamicum maintained consistently high RB5 uptake, above 74.1 mg/g beads, using 0.01 M NaOH as the elutant.