An efficient Cr (VI)-resistant and reducing bacterial strain was successfully isolated in dewatering sludge collected from a sewage treatment plant, and characterized in vitro Cr (VI) reduction through a reductase enzyme. Phylogenetic analysis using 16S rDNA gene sequencing revealed that the newly isolated strain namely Pf-1 was closely related to Bacillus cereus. The strain almost reduced 0.17 mM Cr (VI) within 24h incubation and the presence of different substrates such as glucose, sucrose, or acetate significantly enhanced the reduction rate of Cr (VI) to Cr (III). However, addition of the same substrate at the stationary phase of the microbial growth increased the reduction rate as well as bacterial growth. Additionally, raising the concentration of thiosulfate in the medium doubled the reduction rate under similar conditions. Assay with different fractions of the cells demonstrated that the reductase enzyme activity was mainly associated with the cytoplasmic fraction. The maximum activity was 23.3 µM h -1 mg -1 protein and was obtained at the Cr (VI) concentration of 2 mM. The promising strain can be efficiently employed for bioremediation of Cr (VI) polluted sites.

No abstract

Many studies were undertaken on the biosorption potential of different kinds of biomaterials. However, there is a paucity of data regarding the biosorption mechanism of Cr (VI) using dried cells. In our study, the removal of Cr (VI) from aqueous solution was investigated in a batch system by the dried biomass of a chromium-resistant bacterium isolated from activated sludge samples. Equilibrium and kinetic experiments were undertaken at various initial metal concentration, pH, and biosorbent dosage. Bacillus cereus biomass was characterized using Energy-Dispersive X-ray (EDX), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Biosorption process was found to be pH dependent. The optimum pH was found to be 2.0. The Langmuir and Freundlich were considered to identify the isotherm that could better describe the equilibrium adsorption of Cr (VI) onto the biomass. Langmuir and Freundlich models fitted our experimental data. The suitability of the pseudo-first order and pseudo-second order kinetic models for the biosorption of Cr (VI) onto Bacillus cereus was also performed. The mechanism for the adsorption was studied by fitting the kinetic data with the Boyd plot and intra-particle diffusion model. External mass transfer was found to be the rate-determining step. Based on the ionic nature of the metal, the intra-particle diffusion and extent of film diffusion varied.