On the fundamentals of Cr(III) removal from liquid streams by a bacterial strain

This paper deals with the removal of Cr(III) species from liquid streams by a hydrophobic bacteria strain, Rhodococcus opacus. Zeta potential measurements, sorption and microflotation studies were carried out in order to evaluate the industrial potential application of such strain. It was observed that R. opacus exhibited an isoelectric point around pH 3.2 and the zeta potential profiles suffered a slight deviation after the contact with the sorbate. From the sorption studies, it was concluded that the highest metal removal took place at pH around 5.0 and the isotherm that best suited the sorption phenomenon was related to the Freundlich model with constants KF = 1.71 mg0.14 dm2.58 g−1 and 1/n = 0.86. Furthermore, the kinetics data indicated that biosorption is relatively slow providing 49.10% of metal removal after 200 min; moreover, the pseudo-second order model fitted best the experimental data. Lastly, three different concentrations of R. opacus were tested in a bioflotation system. With only one cycle of operation, the highest biomass concentration, 1.50 g dm−3, achieved 96.30% of metal removal after 20 min of flotation.