Biosorption of Cr (VI) Using Bacillus licheniformis and Bacillus mucilaginosus Krassilnikov : Contrastive Investigation on Removal Performance, Kinetics, and Mechanisms

This study presents the detailed contrastive potential of Bacillus licheniformis gram positive and Bacillus mucilaginosus Krassilnikov gram negative for Cr (VI) remediation from water. The results revealed optimum biomass dosage of 1.5 g at pH 2.0 and pH 6.0 for B. mucilaginosus and B. licheniformis, respectively. B. mucilaginosus was an efficient biosorbent with a maximum removal efficiency of 94.8% compared with B. licheniformis, which recorded 48.8% removal of Cr (VI). The dimensionless separation factor TL analysis for the lowest and highest Cr (VI) concentrations was between 0 and 1 for both biosorbents, which was an indication of a favorable biosorption process. The intraparticle diffusion analysis showed multilinearity plots indicative of a possible combination of external and internal diffusion during the Cr (VI) biosorption process. Further analysis by Fourier transform infrared and scanning electron microscope suggested that the presence of amide I and II in rod-shaped cells (typical bacilli cell structure) played vital roles in the Cr (VI) biosorption. The experimental data were evaluated using Langmuir, Temkin, and Freundlich isotherm models. The Temkin model fitted fairly well compared to Langmuir and Freundlich models for Cr (VI) biosorption. The suitability of the pseudo-second-order kinetic model was further demonstrated by the slight variation between the experimental (Ex qe) of 0.23 and 0.74 mg/g and theoretical (Cal qe) 0.23 and 0.62 mg/g B. licheniformis and B. mucilaginosus, respectively. The corresponding regression coefficients (R2) for B. licheniformis and B. mucilaginosus were 0.9921 and 0.9965, respectively. In contrast with commercial biosorbents, B. mucilaginosus also provides alternatively cheap biosorbent and is eco-friendly.