Studies on the Bioremediation of Chromium from Aqueous Solutions Using C-paurometabolum

The potential of Corynebacterium paurometabolum, a Gram positive acid fast bacterium, has been investigated as a biosorbent for the remediation of Cr(VI) and Cr(III). A complete bioremediation of Cr(VI) has been achieved at an equilibrium time of 2 h, initial Cr(VI) concentration of 4 mg/L, pH 1 and a biomass loading of 3.1 x 10(10) cells/mL, with equal contributions from biosorption and bioreduction processes, while 55% biosorption has been accomplished at an equilibrium time of 2 h, initial Cr(III) concentration of 4 mg/L, pH 3 and a biomass loading of 3.4 x 10(10) cells/mL with respect to the bioremediation of Cr(III). The biosorption isotherms of Cr(VI) and Cr(III) exhibited a typical Langmuirian behaviour. The Gibbs free energies (a dagger G) have been determined to be -25.5 and -29.5 kJ/mol respectively for Cr(VI) and Cr(III), suggestive of chemisorption. The desorption studies have indicated only a marginal release of Cr(VI)/Cr(III) into the bulk solution, attesting to the irreversible nature of biosorption. FTIR studies have revealed the involvement of hydroxyl, carboxyl, amino and phosphate groups in the biosorption of Cr(VI)/Cr(III). Electrokinetic and X-ray photoelectron spectroscopic studies have provided evidence in support of the biosorption and bioreduction mechanisms of chromium remediation

Electrochemical detection of Cr(VI) and Cr(III) ions present in aqueous solutions using bio-modified carbon paste electrode: a voltammetric study

International audienceChromium is recognised as a potent water pollutant by the WHO and thus it becomes pertinent to continuously monitor chromium levels in the waterbodies. Voltammetry, an electroanalytical technique, has been utilised for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium in aqueous samples. Carbon Paste Electrode (CPE) modified using Sphingopyxis macrogoltabida SUK2c, an indigenous bacterial strain isolated from the water samples collected from Sukinda Valley, Odisha, India, was used as a working electrode in a typical three-electrode electrochemical cell. The developed biosensors were found to provide about 3.5 fold increase in cathodic peak current compared to the bare CPE for Cr(VI) ions. Using cyclic voltammetry (CV), the Lowest Limit of Detection (LLOD) of 1 x 10(-4) M and 1 x 10(-2) M for Cr(VI) and Cr(III) ions, respectively, were achieved with the biosensors. The LLOD was further improved to 1 x 10(-9) M and 1 x 10(-7) M for Cr(VI) and Cr(III) ions, respectively, adopting differential pulse cathodic stripping Vvoltammetry (DPCSV) technique employing the biosensors. The concentrations of Cr(VI) and Cr(III) ions present in water samples collected from Sukinda Valley, Odisha, India, could be determined using the biosensor. The plausible mechanisms involved in the detection of Cr(VI) and Cr(III) ions by the developed electrochemical biosensor are discussed.Keyword

Mechanistic studies on the bioremediation of Cr(VI) using Sphingopyxis macrogoltabida SUK2c, a Cr(VI) tolerant bacterial isolate

International audienceBioremediation studies of toxic hexavalent chromium (Cr(VI)) were investigated using an indigenous bacterial strain namely, Sphingopyxis macrogoltabida SUK2c, isolated from water samples collected from the Sukinda Valley in Odisha, India. A maximum Cr(VI) biosorption of about 55% could be achieved using the isolate for an initial Cr(VI) concentration of 4 mg L-1. The Cr(VI) biosorption isotherm was found to follow a typical Langmuirian behaviour. The Gibbs free energy value of Cr(VI) biosorption obtained was -25.6 kJ/mol, indicative of the involvement of chemical binding forces. The Cr(VI) biosorption process followed pseudo second order kinetics. FTIR spectral studies revealed that carboxyl, hydroxyl, amino and phosphate groups present on bacterial surface were involved in the complexation process. XPS studies confirmed the involvement of Cr(III) in addition to Cr(VI) ions with the bacterial cell surface. Zeta potential studies showed that the bacterial cells became less negative after interaction with Cr(VI), which further corroborated the binding of positively charged Cr(III) on the cell surface. The marginal shift in iso-electric point for Cr(VI) interacted bacteria further testified to the involvement of chemical binding forces in the bioremediation process. The results of the chromate reductase and Bradford protein assay tests performed on the extracellular component of the isolate also confirmed the involvement of extracellular protein in the reduction of Cr(VI) to Cr(III)

Electroanalytical Detection of Cr(VI) and Cr(III) Ions Using a Novel Microbial Sensor

International audienceA microbial sensor, namely carbon paste electrode (CPE) modified with Citrobacter freundii (Cf-CPE) has been developed for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium present in aqueous samples using voltammetry, an electroanalytical technique. The biosensor developed, demonstrated about a twofold higher performance as compared to the bare CPE for the chosen ions. Using cyclic voltammetry and by employing the fabricated Cf-CPE, the lowest limit of detection (LLOD) of 1x10(-4) M and 5x10(-4) M for Cr(VI) and Cr(III) ions respectively could be achieved. By adopting the Differential Pulse Cathodic Stripping Voltammetric technique, the LLOD could be further improved to 1x10(-9) M and 1x10(-7) M for Cr(VI) and Cr(III) ions respectively using the biomodified electrodes. The reactions occurring at the electrode surface-chromium solution interface and the mechanisms of biosorption of chromium species onto the biosensor are discussed. The stability and utility of the developed biosensor for the analysis of Cr(VI) and Cr(III) ions in chromite mine water samples has been evaluated