Chromium is one of the major causes of environmental pollution. To remove heavy metal ions from water, microorganisms can be used. In this study, dead fungal biomass of Aspergillus niger is used. The biomass was boiled in 0.5 N NaOH solutions to increase the metal removal capacity of A.niger and was applied when the pH of wash solution was in the normal range. The optimum adsorption pH value observed for chromium (VI) ions was 2. In these experiments, the influence of contact time, pH, Cr (VI) concentration, temperature, stirring speed, and different concentrations of biomass were evaluated.The results show that the experimental points fit both Freundlich and Langmuir models. Meanwhile, the curves of both of them were drawn. In Langmuir model, R2=0.9544 and in Freundlich model, R2=0.992. The Cr (VI) removal rate increases with the increase in temperature; that is, they are positively related. The removal rate of total chromium after 24 hours was %74.6. The results revealed that boiling biomass in NaOH had a better effect on biosorption of chromium so that adsorption would increase by many times. During the study, the amount of toxicity decreased as Cr (VI) was reduced to Cr (III). Part of Cr (VI) was also removed through surface adsorption.

Background & Objectives: Pollution due to heavy metals is one of the most serious environmental problems nowadays. Extensive application of Cr (VI) leads to discharge a large amount of chromium containing wastewater into the environment. The aim of this research was evaluation of alumina nanoparticles efficiency to remove chromium (VI) from aqueous solutions through adsorption.Methods: This fundamental and practical study was performed in batch conditions and room temperature. The structure of the sorbent was characterized by TEM technique. Residual concentrations of Cr (VI) were measured by a spectrophotometer at 540nm. Effects of the process parameters such as Al2O3 loading (0.5–2 g/L), contact time (5-90 min), and pH (5-9) were investigated.Results: The results showed that removal efficiency of Cr (VI) increase with increasing of contact time and pH. The optimum pH was found to be 5 with decreasing of removal efficiency afterward. The value of qm (mg/L) in this work was 30.3 for each gram of nano alumina adsorbent. Furthermore, chromium sorption kinetics was well fitted by pseudo second- order kinetic model, and well explained by Freundlich isotherm (R2>0.992).Conclusion: In general, alumina nanoparticle powder is recognized as an effective sorbent to remove chromium (VI) from aqueous solutions.

Biosorption of Cr(VI) from aqueous solution was studied in a batch bioreactor using the resting cells of filamentous fungal biomass (Aspergillus sp.) isolated from industrial wastewaters. The specific Cr(VI) removal (mg/g of dried biomass) decreased with increase in pH and increased with increase in initial Cr(Vl) concentration, upto 500 mg/L. By increasing biomass concentration from 2.4 to 5.2 g/L, the specific metal removal remained almost constant. The studies carried out by using the resting cells from various stages of growth indicated maximum Cr(VI) removal of 34.8 mg/g using the biomass from the beginning of the stationary phase. The adsorption equilibrium constants Q°(42.9 mg/g) and b (0.0091/mg) were obtained from the Langmuir adsorption isotherm model.

Rice husk is as an organic solid waste material that has high adsorbing capacity in removal of heavy metal ions from wastewater, and can be very effective in treating industrial aqueous solutions that are important sources of water and soil pollution. In this study, the removal of Zn (II) and Cr (VI) ions from aqueous solutions using rice husk was investigated. The investigated parameters included acidity, initial concentrations of ions in aqueous solution, contact time, temperature and the amount of adsorbent matter used for treatment. With increasing pH of the solution, the adsorption of zinc and chromium ions by rice husk were increased and decreased, respectively. The maximum adsorption was occurred in pH 7 and 2. Moreover, with increasing initial concentration of metals, the removal efficiencies of zinc and chromium were decreased. While, with increasing the contact time, the removal efficiencies were increased and reached an equilibrium after 2 and 3 hours for zinc and chromium, respectively. The metal adsorption is also dependent on the reaction temperature, so that by increasing temperature the percentage of adsorption was increased. With increasing the amount of husk rice to the solution, the percentages of adsorption of zinc and chromuim were increased. Rice husk showed to be a proper absorbent for the removal of Zn (II) and Cr (VI) from aqueous solutions.

A new technique of coupled electrodeposition-electrothermal Atomic Absorption Spectrometry (AAS) method has been developed to study chromium speciation. Speciation of Cr (VI)/Cr (III) is carried out by electrodeposition at uncontrolled applied potentials, followed by removal of spent electrolyte and atomisation. At Eappl = 0.5-10.0 V and using codeposition with Hg (and without Pd coating), only Cr (VI) is reduced to Cr (III) and accumulated as Cr (OH)3 by absorption onto mercury film on the graphite furnace. Total chromium is measured by electrodepositing at 10.0 V without Hg but on the renewable Pd substrate from 0.5 M NaCl and 1% H2SO4. It has been demonstrated that chromium speciation can be achieved in samples of 0.5 M NaCl, using acetate buffer to adjust pH to 4.7. The results also will be given for attempted chromium speciation studies by in situ deposition onto Pd-coated furnace. At all applied voltages between 2.0- 10.0 V in 0.02% H2SO4 Cr (III) is reduced to chromium metal and deposited onto the Pd substrate more efficiently than Cr (VI), but the difference is not sufficient for complete discrimination of two chromium forms. The effect of SO4 2- ion concentration and of pH on the yield of deposition were studied for each form of chromium. It was shown that from 1% H2SO4 both forms of chromium deposited quantitatively. Apart from achieving speciation, background signal due to high concentration of NaCl in the sample was completely eliminated by the proposed technique. At the same time a two-fold improvement in sensitivity of the determination was achieved with respect to the conventional electrothermal AAS technique.

Background: Chromium is one of the most used toxic heavy metals. A large amount of chromium waste is discharged into the environment every year, causing serious environmental pollution, especially the pollution of soil and water by hexavalent chromium. Eliminating hexavalent chromium is the primary challenge to achieve a pollution-free environment.Objectives: This study aims to understand the mechanism of Pichia guilliermondii’s reduction of hexavalent chromium through enzymatic characteristic, oxidative stress response, and reduction product.Material and Methods: The strain Pichia guilliermondii ZJH-1 was isolated and stored in our laboratory. The hexavalent chromium uses 1,5-diphenyl carbazide method (DPC) to measure. The UV spectrophotometer was used to measure the intracellular antioxidant enzyme activity, and the kit was used to measure the activity of catalase and glutathione reductase. The reduction products were analyzed by ultraviolet full-wavelength scanning and FTIR.Results: The reduction of hexavalent chromium by ZJH-1 is accompanied by an increase in active oxygen and antioxidant levels. Chromate reductase mainly exists in the extracellular fluid, and the carboxyl, amide, hydroxide and other groups of the cell wall are involved in the bioremediation of Cr(VI) by complexing with Cr(VI) and Cr(III). After ZJH-1 was treated with different concentrations of Cr(VI), the expression of proteins with molecular weights of 15 kDa, 18 kDa, 35 kDa, 62 kDa, and 115 kDa increased significantly. This strain is the most suitable for chromate reductase (CChR). The optimum temperature is 40℃ and the optimum pH is 7.0. Cu2+ can enhance the activity of chromate reductase. At the optimum temperature and pH, the chromate reductase Km of this strain is 0.40 μmol and Vmax is 14.47 μmoL.L-1·min-1.Conclusions: The bioremediation of Cr(VI) by Pichia guilliermondii ZJH-1 is attributable to the reduction product (Cr(III)) that can be removed in the precipitate and can be fixed on the cell surface and accumulated in the cell.

The wastewater from plating industry usually contains high amounts of chromium. In this study, the removal of chromium (VI) from plating wastewater by magnetic Fe3O4 nanoparticles was investigated. The wastewater was obtained from a plating workshop in Paytakht Industrial Park located in Tehran, Iran. The studied nanoparticles had an average particle size of 30nm. The effects of pH, reaction time, amount of nanoparticles and temperature on the adsorption process were studied. Results showed that the optimized chromium removal could be achieved at reaction time of 60min, pH of about 3, nanoparticles amount of 1 g/L, and temperature of 25oC. Moreover, the obtained data were fitted to the Langmuir and Freundlich isotherm constants to study the adsorption mechanism. Results indicated the Freundlich adsorption isotherm model was more suitable. Pseudo-firstorder and pseudo-second-order models were employed to study the adsorption kinetics, and it was found that chromium adsorption kinetics followed the second-order model.

Chromium is one of the toxic heavy metals which exists in nature as stable hexavalent and trivalent forms. The hexavalent form of chromium is more toxic than trivalent chromium as it persists indefinitely in the environment complicating its remediation. The conventional physical and chemical treatment techniques used for the removal of Cr (VI) are expensive and highly energy intensive, moreover they produce harmful by-products, ultimate disposal of which again causes secondary pollution. Removal of Cr (VI) from aqueous solution using biological sources as biosorbent has assumed advantageous over the existing conventional physico-chemical techniques for the treatment of metal contaminated wastes. The present batch biosorption study was undertaken with an aim to examine the Cr (VI) removal potential of the resting cells of Fusarium solani (isolated from soil) from aqueous solution. The specific Cr (VI) removal decreased with increase in pH and increased with increase in initial Cr (VI) concentration, up to 500 mg/L. The specific Cr (VI) removal remained almost constant by increasing biomass concentration from 2.4 to 5.2 g/L. The studies also carried out by using the resting cells obtained from various stages of growth and the maximum specific Cr (VI) removal (60 mg/g) was achieved at 500 mg/L initial Cr (VI) concentration and by using cells (36 h old). The Langmuir adsorption isotherm constants, Q0 and b were observed to be 57.1 mg/L and 0.06 l 1/mg, respectively.