Biosorption of cadmium and chromium from water by endophytic Kocuria rhizophila: equilibrium and kinetic studies

Abstract

Heavy metal removal from water is an important issue of environmental concern. This study demonstrates the application of endophytic bacterium Kocuria rhizophila (gene bank No: KF875448) isolated from hyperaccumulator Oxalis corniculata for the adsorption of Cd(II) and Cr(III) from aqueous solution. Minimum inhibitory concentration of Cd and Cr for the selected strain was found to be 6 and 8 mM, respectively. The effects of certain parameters like pH, contact time, and initial metal concentration on biosorption were assessed at a temperature of 35 ± 2°C. The optimum pH values for Cd and Cr biosorption were found to be 8 and 4, respectively. Maximum biosorption for both the metals was obtained after 60 min. Biosorption equilibrium was described by Langmuir and Freundlich isotherms. The Langmuir model showed maximum adsorption capacity (Q_max) for Cd and Cr as 9.07 and 14.4 mg g⁻¹_, respectively. Kinetic data indicated that biosorption of the selected heavy metals on K. rhizophila follows pseudo-second-order rate equation. FTIR analysis showed that functional groups like OH, C=O, C=N, N–H, CH₂, PO₂, C–O, C–O–C and C–H on K. rhizophila surface might be responsible for heavy metals biosorption. Results suggested that K. rhizophila has potential for the removal of metal ions from aqueous solution. Therefore, current research presents novelty in terms of evaluating endophytic K. rhizophila as a biosorbent for Cd and Cr.

Keywords:

• Adsorption isotherm
• Biosorption
• Heavy metals
• Kinetic models
• Kocuria rhizophila

Acknowledgments

The authors would like to acknowledge Zaynab Aly (Institute of Materials Engineering, Australian Nuclear Science and Technology Organization, Australia) for her help with the experimental work and isotherm modeling. Prof. Dr Muhammad Saleem Akhtar (Department of Soil Sciences, PMAS, Arid Agriculture University, Rawalpindi, Pakistan) is acknowledged for providing us access to instrumental analysis.