Bioremoval of Acid Red 14 dye by Wickerhamomyces anomalus biomass: kinetic and thermodynamic study, characterization of physicochemical interactions, and statistical optimization of the biosorption process

The biomass of a yeast stain of Wickerhamomyces anomalus was evaluated as a natural biosorbent for the removal of Acid Red14 dye (AR(14)) in batch experiments. The outcome revealed a maximum biosorption capacity of 71.37 mg g(-1). Biosorption kinetic followed both the pseudo-second-order and intra-particle-diffusion model, while thermodynamic parameters showed a spontaneous and endothermic nature of the biosorption process. The Freundlich model was the best-fitting isotherms, suggesting a monolayer biosorption via chemisorption at homogeneous sites on the yeast surface. Next, the physicochemical characterization of W. anomalus biomass before and after biosorption using scanning electron microscopy coupled with X-ray spectroscopy, and the Fourier-transforms infrared spectroscopy indicated the involvement of various functional groups (amino, carboxyl, hydroxyl, and carbonyl groups) in AR(14)-biosorption. Also, the zeta potential of cells at a negative charge, and the acidic value of the zero-charge point confirmed the predominance of anionic groups in the cell wall. Hence, H-binding, pi-pi, and n-pi interactions are likely to participate in the biosorption mechanism. Additionally, the influence of batch conditions on the decolorization capacity was statically screened and optimized using Plackett-Burman and Box-Behnken design, respectively. Results show that biomass dosage is the significant factor having a positive influence on the discoloration rate, while a negative correlation was found for dye concentration and high pH values. Maximum decolorization (77%) was achieved at pH level (3-4), with dye concentrations (50-75 mg L-1) and yeast biomass 1.25 g L-1. These results suggest that W. anomalus might be exploited as an effective, inexpensive, and environmentally friendly biosorbent.