Surface modification of the Corynebacterium glutamicum biomass to increase carboxyl binding site for basic dye molecules

The objective of this study was to develop a surface-modified biosorbent with enhanced sorption capacity of cationic dye Basic Blue 3 (BB 3). The biomass of Corynebacterium glutamicum was modified using citric acid (CA). The optimal modification conditions were the mixing of the biomass with 0.8 M citric acid solution at a 1:10 ratio, and heating at 120 °C for 3.5 h. Hydroxyl groups on the biomass surface underwent an esterification with citric acid, forming carboxyl groups which were available for cationic dye binding. From the Fourier transform infrared analysis, it was confirmed that the CA-modified biomass possessed a large amount of surface carboxyl functional groups comparing the raw biomass. The sorption capacity of BB 3 onto CA-modified biomass was 2.02 times higher than that onto the raw biomass. Furthermore, BB 3 sorbed on the CA-modified biomass was easily eluted by shifting the solution pH, making repeated sorption/desorption cycle (up to 4 times) possible without significant performance decrease. Therefore, the method developed for amplifying the carboxyl sites on the biomass surface may be a useful modification tool for the creation of a high-performance and regenerable biosorbent for the cationic dyes.