Optimizing the biosorption of Bi3+ ions by Streptomyces rimosus using experimental design and applicability in kinetics and isotherm modeling

Abstract

This investigation seeks to analyze bismuth biosorption onto Streptomyces rimosus in solutions following optimization using a Box–Behnken Design (BBD). Based on an efficient method, three significant parameters including pH, temperature, and initial bismuth (Bi³⁺) concentration in a batch system were studied using design of experiment (DOE). A central composite second order response surface methodology (RSM) accomplishes the construction of model biosorption (R%) and operating conditions. Using this statistical–mathematical method leads to obtaining a second-order equation for bismuth removal. The regression equation was obtained using Design Expert 7.0 software. The numerical optimization shows a great biosorption percentage (>97%) at pH 8.0, 30 °C, and 30 mg L⁻¹ for bismuth. The quadratic models exhibited higher R² values, significant p-values, and insignificant lack-of-fit p-values that all confirm their high suitability for predicting the response. Both mathematical and empirical models, due to their high correlation coefficient (R²) of 0.9999, are suitable for predicting the biosorption trend of bismuth in solution. The closeness of the predicted values and experimental values also supports this conclusion. The pseudo-second order kinetic model adequately described the kinetic data. The Langmuir isotherm model described the process of Bi³⁺ uptake better than the other models. The maximum biosorption capacity of the biosorbent was found to be 38.93 mg g⁻¹ for bismuth biosorption. The possible interactions between biosorbents and bismuth were also evaluated using Fourier transform infrared (FT-IR) spectroscopy analysis.