Optimization of Hexavalent Chromium Biosorption by Shewanella putrefaciens Using the Box-Behnken Design

Cr(VI) is a ubiquitous pollutant that poses a serious threat to human health. Recently, the use of microorganisms to adsorb heavy metals has attracted research attention. However, there are few studies on the biosorption of Cr(VI) by Shewanella putrefaciens, which is a metal-reducing bacterium. In this paper, single-factor experiments were designed to investigate the effect of hexavalent chromium by Shewanella putrefaciens, and response surface methodology (RSM) based on the Box-Behnken design (BBD) was performed to study the Cr(VI) biosorption behavior of Shewanella putrefaciens. The coefficient of determination (R-2 = 0.811 for Cr(VI)) and probability value (P < 0.05) demonstrated significance for the obtained regression model. The results showed that the model was suitable for experimental data, and the maximum Cr(VI) removal efficiency by Shewanella putrefaciens was 85.68% under the optimum conditions of a contact time of 16.57 h, pH value of 8, and biomass dosage of 0.42 g/L, which were verified by additional experiments. ANOVA and 3D response graph analysis showed that the variables with significant influences were pH and temperature. In addition, scanning electron microscopy (SEM) results demonstrated that after biosorption of Cr(VI) by Shewanella putrefaciens, granular complexes attached to rough cell surfaces were observed. Furthermore, Fourier transform infrared spectroscopy (FT-IR) analysis showed that the distribution of Cr(VI) on the cell surface was related to the carboxyl, ether, amide, hydroxyl, and phosphoric acid groups of Shewanella putrefaciens. This study is useful to explore the process and mechanism of heavy metal adsorption by Shewanella putrefaciens and provide new ideas for the microbial remediation of metal pollution in water.

Automated summary

The study found that under optimal conditions, Shewanella putrefaciens achieved a maximum Cr(VI) removal efficiency of 85.68%. pH and temperature were significant factors that influenced the biosorption effect. Scanning electron microscopy revealed granular complexes formed on the surfaces of Shewanella putrefaciens after Cr(VI) biosorption, and Fourier transform infrared spectroscopy analysis indicated the distribution of Cr(VI) was related to specific functional groups on the cell surface.