Biosorption of Reactive Dyes by Novel Bacterium Leclercia adecarboxylata: Complete Removal of Reactive Black 5 and Molecular Insights Into the Adsorption Mechanism.

Leclercia adecarboxylata isolated from the Düden Waterfall (Turkey) was utilized as a biosorbent for the removal of Reactive Black 5 (RB5), Setazol Blue BRF-X (BRF-X), Setazol Navy Blue SBG (SNB), and Setazol Turquoise Blue G (STBG). Of the dyes, RB5 was removed with the highest efficiency, 97.4% after 60 min. The effect of parameters such as pH (3-9), initial biosorbent dose (0.1-2.0 g/L), and initial dye concentration (25-1200 mg/L) on the biosorption of RB5 was investigated. Increasing the biosorbent dosage from 0.1 to 2.0 g/L enhanced the RB5 removal from 55.3% to 100% within 10 min. The complete removal (100%) of RB5 was achieved in media with 2.0 g/L biosorbent and 25 mg/L RB5 at pH 3 after 10 min. Additionally, the soluble extracellular polymeric substances (EPS) of L. adecarboxylata were found to consist of proteins, lipids, nucleic acids, and polysaccharides according to Fourier transform infrared spectroscopy (FTIR) analysis. The EPS was found to play a crucial role in dye removal, forming chemical interactions with dye molecules. Zeta potential analysis was used to evaluate the charge distribution on the biosorbent surface (-12.6 ± 1.1 mV) and its interactions in the biosorption process. Kinetic and isotherm models suggested a complex interaction mechanism between the biomass and the dye. Adsorption isotherm data were analyzed via nine isotherm models. Among them, the Hill model was found to be the best fit for describing the equilibrium adsorption process of the RB5 (R = 0.9993). Overall, the applied models elucidated the influence of both physical and chemical interactions on the mechanism. Kinetic studies revealed that the adsorption of RB5 fit a pseudo-second-order kinetic model. The unique biochemical composition of the indigenous L. adecarboxylata biosorbent provided a high affinity for RB5, offering a sustainable, rapid, and economical solution for the treatment of dye-polluted water.