Biosorption of reactive and basic dyes using fermentation waste <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis>: the effects of pH and salt concentration and characterization of the binding sites

A low cost biosorbent, Corynebacterium glutamicum, was studied for the sorption of Reactive Red 4 (RR 4) and Methylene Blue (MB). The equilibrium isotherm data were well described by the Langmuir model. pH edge experiments showed that pH of the solution was an important controlling parameter in the sorption process. In the case of RR 4, with increases in the pH from 2 to 10, the uptake decreased from 52 to 1 mg/g; conversely, the uptake of MB increased and the maximum MB uptake was obtained at pH ≥ 9. An increase in the salt concentration strongly influenced the uptake of MB, but had no effect on that of RR 4. In order to identify the binding sites for the dye molecules, the biosorbent was potentiometrically titrated, the results of which showed the presents of four major functional group types on the biomass surface, which were confirmed by FTIR analysis. It was found that positively charged amine groups (Biomass-NH₃ ⁺) were the likely binding sites for anionic RR 4, and negatively charged carboxyl (Biomass-COO⁻) and phosphate groups (Biomass-HPO₄ ⁻) played a role in the electrostatic attraction of cationic MB.