Advances in bacterial chromium biosorption: current perspectives and future directions

Biosorption is a technique employed for the treatment of wastewater containing hazardous pollutants, including dyes and heavy metals, especially hexavalent chromium (Cr(VI)). Cr(VI) is a great pollutant of concern which is linked to increased toxicity, carcinogenicity, and adverse health conditions globally. The toxicity of Cr(VI) was discussed, and various mitigation strategies were compared with biosorption being the most simple, robust, and inexpensive alternative. However, different biosorbent materials including agricultural waste, algae, fungi, and bacteria are known to neutralize or completely remove Cr(VI) from wastewater. In this review, biosorption involving bacterial adsorbents was emphasized due to its efficiency and cost-effectiveness. Their biosorption capacities were assessed at different environmental conditions and Cr concentrations. A detailed account on the mechanisms of bacterial chromium biosorption including surface complexation, electrostatic attraction, and ion exchange is described. The surface characterization of the bacterial adsorbents was explained with techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, further explaining the involvement of functional groups in the bacterial chromium biosorption. The kinetics, isotherms, and thermodynamics of bacterial biosorption were described to elucidate the adsorption behavior and mechanisms. This review highlights the recent integrated technology that could be used along with the biosorption technique to combat chromium contamination and boost industrial application. This review provides researchers and stakeholders the recent state of knowledge in the field of biosorption using bacterial adsorbents and way forward.