Application of experimental design and derivative spectrophotometry methods in optimization and analysis of biosorption of binary mixtures of basic dyes from aqueous solutions

Simultaneous biosorption of malachite green (MG) and crystal violet (CV) on biosorbent Yarrowia lipolytica ISF7was studied. An appropriate derivative spectrophotometry technique was used to evaluate the concentration ofeach dye in binary solutions, despite significant interferences in visible light absorbances. The effects of pH,temperature, growth time, initial MG and CV concentration in batch experiments were assessed using Design ofExperiment (DOE) according to central composite second order response surface methodology (RSM). Theanalysis showed that the greatest biosorption efficiency ( > 99% for both dyes) can be obtained at pH 7.0,T=28 °C, 24 h mixing and 20 mg L−1 initial concentrations for both MG and CV dyes. The quadratic constructedequation ability for fitting experimental data is judged based on criterions like R2 values, significant p and lackof-fitvalue strongly confirm its high adequacy and applicability for prediction of revel behavior of the systemunder study. The proposed model showed very high correlation coefficients (R2=0.9997 for CV and R2=0.9989for MG), while supported by closeness of predicted and experimental value. A kinetic analysis was carried out,showing that for both dyes a pseudo-second order kinetic model adequately describes the available data. TheLangmuir isotherm model in single and binary components has better performance for description of dyesbiosorption with maximum monolayer biosorption capacity of 59.4 and 62.7 mg g−1 in single component and46.4 and 50.0 mg g−1 for CV and MB in binary components, respectively. The surface structure of biosorbentsand the possible biosorbents–dyes interactions between were also evaluated by Fourier transform infrared (FTIR)spectroscopy and scanning electron microscopy (SEM). The values of thermodynamic parameters includingΔG° and ΔH° strongly confirm which method is spontaneous and endothermic.