Metal biosorption capacity of the organic solvent tolerant Pseudomonas fluorescens TEM08

Many kinds of biomass are being tested as a biosorption material for metal removal from the contaminated waters. In the present study the biosorption capacity of an organic solvent tolerant (OST) bacterium was investigated against Cr(VI) and Ni(II). The OST strain of Pseudomonas fluorescens TEM08 was isolated from an oil contaminated soil sample and grown in normal culture conditions (type I) and in the presence of the cyclohexane (type II). Two types of cells were used in the biosorption experiments to compare the organic solvent effect on the biosorption capacity. The biosorption equilibrium was described by Langmuir and Freundlich adsorption isotherms. The value of Q(0) was higher for type I cells (40.8 for Cr(VI); 12.4 for Ni(II)) then the type II (40.7 for Cr(VI); 11.2 for Ni(II)). The adsorption capacity constants (K(F)) of Freundlich model for type I cells and for type II cells were 10.87 and 8.78 for Ni(II) and 13.60 and 10.99 for Cr(VI), respectively.     

Isolation and characterization of chromium(VI)-reducing Bacillus sp. FY1 and Arthrobacter sp. WZ2 and their bioremediation potential

Two native bacterial strains, FY1 and WZ2, that showed high chromium(VI)-reducing ability were respectively isolated from electroplating and tannery effluent–contaminated sites and identified as Bacillus and Arthrobacter. The objective of the present study was to evaluate their potential for future application in soil bioremediation. The results showed that both Bacillus sp. FY1 and Arthrobacter sp. WZ2 were tolerant to 1000 mg L^?1 Cr(VI) and capable of reducing 78–85% and 75–82% of Cr(VI) (100–200 mg L^?1) within 24 h, respectively. The Cr(VI) reduction rate decreased with increasing levels of Cr(VI) concentration (200–1000 mg L^?1). The optimum pH, temperature, and inoculum concentration for Cr(VI) reduction were found to be between pH 7.0 and 8.0; 30 and 35°C; and 1 × 10⁸ cells ml^?1, respectively. Further evidence for the bioremediation potential of Bacillus sp. FY1 and Arthrobacter sp. WZ2 was provided by the high capacity to reduce 100, 200, and 500 mg kg^?1 Cr(VI) in contaminated soil by 83–91%, 78–85%, and 71–78% within 7 days, respectively. These findings demonstrated the high potential of Bacillus sp. FY1 and Arthrobacter sp. WZ2 for application in future soil bioremediation.     

Bioreduction of Cr(VI) by Bacillus sp. QH-1 isolated from soil under chromium-containing slag heap in high altitude area

A chromium-reducing strain QH-1, identified as Bacillus sp., was isolated from soil under chromium-containing slag heap in Qinghai high altitude area, China. The strain was found to resist 200 mg/L Cr(VI), and Cr(VI) negatively affects the metabolic activity of the cells, as well as the cell morphology of Bacillus sp. QH-1. The reduction efficiency of Cr(VI) at concentrations of Cr(VI) 25 mg/L, 50 mg/L, 100 mg/L and 200 mg/L were 99.48 %, 65.99 %, 23.22 % and 6.99 %, respectively, decreasing with increasing initial Cr(VI) concentration. This indicates that the toxicity of Cr(VI) increased with concentration. Energy dispersive X-ray analysis revealed that there was insoluble Cr(III) generated during Cr(VI) reduction. In order to apply strain QH-1 to remove Cr(VI) from groundwater, factors of concentration of electron donors (glucose) and temperature were investigated in a synthetic medium. The results demonstrated that glucose could promote the reduction of Cr(VI) by this strain, and the general trend of Cr(VI) reduction increased with temperature within the range of 4 to 37 °C. Cr(VI) was reduced effectively at 25 °C and 37 °C, and all of Cr(VI) was reduced after 96 h at 37 °C, while the reduction was slow at 4 °C and 15 °C, and it almost ceased after about 120 h. These results could be potentially useful for the bioremediation of Cr(VI) in groundwater.     

Derivation of a Liquid-to-Soild Ratio for ASTM Method D3987-85 for Soils Containing Chromite Ore Processing Residue Using Selected Unsaturated Zone Models

While most health-based cleanup levels for hexavalent chromium [Cr(VI)] in soil are established to protect the general population against cancer, the New Jersey Department of Environmental Protection (NJDEP) has established a Cr(VI) soil cleanup criterion to protect Cr(VI)-sensitive individuals against allergic contact dermatitis (ACD). For this criterion, exposure is assumed to occur when a Cr(VI)-sensitized individual contacts a puddle in which rainfall has dissolved Cr(VI) from the associated surface soils. To simulate the movement of Cr(VI) from surface soil into puddle water after rainfall events, this soil cleanup criterion requires that the Cr(VI) concentration extracted from soil using ASTM Method D3987-85 at a 2:1 liquid-to-solid ratio (LSR) be less than 25?mg/L. However, this LSR is based on several simplifying assumptions that may not be appropriate for many soil types. In this article, three unsaturated zone transport models—Chemflo, SWIM, and HYDROGEOCHEM—are evaluated for developing LSRs for sites with soil containing chromite ore processing residue (COPR). Based on this evaluation, SWIM was found to be the most appropriate model for simulating Cr(VI) transport into puddles because of its ability to simulate rainfall and evaporation rate changes during and following precipitation events. A more refined evaluation using only SWIM was performed to determine the effects of various factors on COPR-specific LSRs, including saturated hydraulic conductivity, daily rainfall rate, daily evaporation rate, and groundwater depth. The refined evaluation demonstrated that the LSR ranges from 1.4 to 30, with a mean of 7.4 and a median of 7.0. Thus, an LSR of 7:1 is the most appropriate to represent the puddle scenario at COPR sites.     

Chromium Removal from Aqueous System and Industrial Wastewater by Agricultural Wastes

This study involved the development of formaldehyde-treated, deseeded sunflower head waste–based biosorbent (FSH) for the biosorption of Cr(VI) from aqueous solution and industrial wastewater. Batch-mode experiments were conducted to determine the kinetics, sorption isotherms, effect of pH, initial Cr(VI) concentration, biosorbent dose, and contact time. The results demonstrated that FSH can sequester Cr(VI) from the aqueous solution. The maximum sorption occurred at pH = 2.0, biosorbent dose = 4.0 g/L, concentration of 100 mg/L at 25°C at 180 rpm after 2 h contact time. The FSH had an adsorption capacity of 7.85 mg/g for Cr(VI) removal at pH 2.0. The rate of adsorption was rapid, and equilibrium was attained within 2 h. The equilibrium sorption data fitted the Langmuir isotherm model, which was further confirmed by the chi-square test.     

Aerobic Cr(VI) Reduction by Bacteria in Culture and Soil Conditions

We compared the performance of aerobic Cr(VI)-reducing bacteria isolated from Cr(VI)-contaminated soil in pure and mixed cultures of five isolated strains. The mixed culture had increased reduction rates compared to individual cultures. Cr(VI) reduction was observed in sterile soil inoculated with Pseudomonas fluorescens and in non-sterile soil with and without inoculation with P. fluorescens at initial pore water concentrations up to 1,600 mg Cr(VI)/L, whereas in culture the maximum inhibitory concentration was 500 mg Cr(VI)/L. Linear rates of Cr(VI) reduction in non-sterile soil amended with peptone were ～5 to 8 times higher than those observed in the mixed culture. Inoculation of non-sterile soil with P. fluorescens did not further enhance Cr(VI) reduction rates. Our results indicate that evaluation of Cr(VI) reduction capacity in Cr(VI)-contaminated soil for in-situ bioremediation purposes should not be done solely in pure culture. Although the latter may be used initially to assess the effects of process parameters (e.g., pH, temperature), the rate and extent of Cr(VI) reduction should be determined in soil for bioremediation design purposes.     

Migration and Stabilization of Multiple Heavy Metals in an Aged Contaminated Soil under a Constant Voltage Electric Field

With the aim of metal decontamination, migration and stabilization of multiply heavy metals in an aged contaminated soil under a constant 1 V cm^?1 parallel-plate electric field were investigated through monitoring the metal migration in the anolyte, as well as analyzing their species distribution residual in soil. Besides anionic Cr(VI), cationic metals were also found in the anolyte, primarily by the concentration-gradient-driven diffusion of free ions, especially when the produced H⁺ considerably increased their levels in the soil. After 295 h, parts of Cu, Cr, Ni, and Zn were found to electro-migrate into the intermediate area, but no obvious Pb migration was observed, likely ascribed to its own great inertia and precipitation with the present Cr(VI). However, in the whole, only 5.3% of Zn and 2.7% of Ni were separated, while the release of other heavy metals was almost ignorable. Although Pb mobility in the soil near the anode even increased three times, the overall metal mobility in all sample locations was found to significantly reduce under the electric field, indicating an effective stabilization approach. Moreover, compared with the bottom soil, the top soil near the anode was found to have a lower pH, higher moisture, lower heavy metal concentrations, and less soil oxidant demand; these phenomena may be due to a faster electro-migration of charged ions, especially H⁺, in the top soil. Therefore, such a divergence may considered to improve the current simulation approach for a realistic estimation of the actual metal and H⁺ electro-migration rate and the associated behavior under an electric field.     

Seasonal Variability of Extracellular Enzymes Involved in Carbon Mineralization in Sediment of a Subtropical Mangrove Wetland

This paper reports an investigation of microbially mediated Cr(VI) reduction in a hyperalkaline, chromium-contaminated soil-water system representative of the conditions at a chromite ore processing residue (COPR) site. Soil from the former surface layer that has been buried beneath a COPR tip for over 100 years was shown to have an active microbial population despite a pH value of 10.5. This microbial population was able to reduce nitrate using an electron donor(s) that was probably derived from the soil organic matter. With the addition of acetate, nitrate reduction was followed in turn by removal of aqueous Cr(VI) from solution, and then iron reduction. Removal of ～300 μM aqueous Cr(VI) from solution was microbially mediated, probably by reductive precipitation, and occured over a few months. Thus, in soil that has had time to acclimatize to the prevailing pH value and Cr(VI) concentration, microbially mediated Cr(VI) reduction can be stimulated at a pH of 10.5 on a time scale compatible with engineering intervention at COPR-contaminated sites.     

Metal pollution in water environment and the associated human health risk from drinking water: A case study of Sukinda chromite mine,India

Sukinda is one of the most polluted regions of the globe due to chromium pollution. The study sheds light into the heavy metal pollution around the mining area and its effect on the health of the resident populace. The Cr(VI) was in the range of 0.027–2.48 mg/L in surface water and BDL–1.35 mg/L in the groundwater. Multivariate analysis revealed that mining activity was the main source of TCr, Cr(VI), and Zn in the surface water that warrants attention. Heavy metal evaluation index showed high levels of Fe, Mn, and Cr in groundwater that can pose serious threat to the exposed population. Cancer and non-cancer risk of Cr(VI) was higher than other metals in groundwater. The results revealed that the total cancer risk was 1.21E-03 and 1.05E-03 in adults and children, respectively, which exceeded the USEPA acceptable cancer health risk. High health risk was observed through oral intake of water, while both cancer and non-cancer risks were negligible through dermal contact. This study strongly advocates proper periodic assessment of drinking as well as surface water in the area and regulation to restrict the use of contaminated water for daily use.     

Isolation of indigenous Staphylococcus sciuri from chromium-contaminated paddy field and its application for reduction of Cr(VI) in rice plants cultivated in pots

Accumulation of Cr(VI) in rice seeds cultivated in Cr-contaminated soil of the Sundarbans (India) is an environmental problem. Cr(VI) concentration in this soil was 6.2 ± 0.3 mg/kg, whereas total chromium was 32.04 ± 1.60 mg/kg. A Cr(VI)-removing bacterium isolated from Cr-contaminated paddy field soil of Sundarbans was identified as Staphylococcus sciuri. Enrichment culture of S. sciuri was applied to pot cultivation of rice in Cr-contaminated soil. After 8 weeks, 71 ± 3% Cr(VI) (final concentration 2.15 ± 0.01 mg/kg) and 65 ± 2% total Cr removal (end concentration 11.3 ± 0.5 mg/kg) were attained in bacterium-treated soils. Growth parameters indicated healthy development of plants cultivated in bacterium-treated soils that was not observed in control plants. Total Cr removal attained in rice seeds of plants cultivated in bacterium-treated soils compared with control rice seeds was 78 ± 4%. Total Cr concentration in test seeds was 0.72 ± 0.05 mg/kg (World Health Organization [WHO] permissible limit: 1.30 mg/kg), whereas the same in control seeds was 3.27 ± 0.16 mg/kg. Cr(VI) reduction achieved in rice seeds cultivated in bacterium-treated soil compared with control rice seeds was 95 ± 5%. Cr(VI) concentration in rice seeds cultivated in treated soil was 0.050 ± 0.003 mg/kg, whereas the same in untreated control was 0.93 ± 0.05 mg/kg. Successful paddy field soil bioremediation by any Staphylococcus species was demonstrated for the first time.     

Influence of magnetic field on Cr(VI) adsorption capability of given anaerobic sludge

To provide beneficial guide for the application of the magnetic field in the bio-treatment of the Cr(VI)-contained wastewater, sludge samples from the control bio-system A (absent of magnetic field) and the contrast bio-system B (present of magnetic field) were used to adsorb the synthetic wastewater with 100 mg l⁻¹ Cr(VI). Influences of two adsorption modes, single adsorption and once continuous adsorption, on the Cr(VI) adsorption capacities of both sludge samples were compared. And the influence of regeneration on the Cr(VI) adsorption capacities were also studied. The results of adsorption experiments showed that the Cr(VI) adsorption capacities of the first single adsorption for sludge sample A and B were pretty nearly, which were 9.79 and 9.93 mg, respectively. And after 5 single adsorption periods, the total Cr(VI) adsorption capacity and efficiency of the sample B were 25.88 and 55.66 mg Cr(VI) g⁻¹VSS, while those of the control were 14.95 and 33.98 mg Cr(VI) g⁻¹VSS, respectively. For the sludge sample A and B after a single adsorption, both functions of regeneration were remarkable. But after 13 cycles of the single adsorption-regeneration, the Cr(VI) adsorption capacity and efficiency of the sample B were 110.15 and 189.91 mg Cr(VI) g⁻¹VSS, while those of the control were 70.89 and 140.38 mg Cr(VI) g⁻¹VSS, respectively. Though the Cr(VI) adsorption capacity of a once continuous adsorption period was more than that of a single adsorption period obviously, the Cr(VI) removal rates of the sludge sample A and B in the third period of once continuous adsorption-regeneration were only 8.12 and 33.51%, respectively. It was concluded that the weak magnetic field did improve the Cr(VI) bio-removal efficiency and the sludge stability, the batch treatment was an ideal operation mode for the bio-treatment of the Cr(VI)-contained wastewater, as compared with the continuous operation mode, but regeneration and enough sludge content were two necessary conditions to ensure the efficiency of batch treatment.     

Remediation of chromite ore processing residue by pyrolysis process with sewage sludge

The present work developed a novel technique to treat chromite ore processing residue (COPR). The process involved mixing the COPR with sewage sludge followed by pyrolysis. The gaseous organic fraction generated during pyrolysis of sludge was beneficial to Cr(VI) reduction. Process variables, such as the amount of sludge added to COPR (sludge-to-COPR (S/C) ratio), heating temperature, reaction time and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were investigated. Cr(VI) content had decreased greatly, from 3384 mg kg⁻¹ for untreated COPR to less than 30 mg kg⁻¹ for COPR treated at 600 °C.     

Removal of Chromium(VI) Ions from Synthetic Solutions by the Fungus Penicillium purpurogenum

The ability of Penicillium purpurogenum to bind high amounts of chromium(VI) from aqueous solutions is demonstrated. Cr(VI) adsorption capacity increases with time during the first four hours and then leveled off toward the equilibrium adsorption capacity. Biosorption of Cr(VI) ions reached equilibrium in four hours. Binding of Cr(VI) ions with Penicillium purpurogenum biomass was clearly pH dependent. Cr(VI) loading capacity increased with increasing pH. The adsorption of Cr(VI) ions reached a plateau value at a pH of approx. 6.0. The maximum capacity of adsorption of Cr(VI) ions onto the fungal biomass was 36.5 mg/g. Adsorption behavior of Cr(VI) ions can be approximately described with the Langmuir equation. When applying the Langmuir model, the maximum adsorption capacity (Q_max) and the Langmuir constant were found to be 40 mg/g and 3.9 × 10^–3 mg/L. Elution of Cr(VI) ions was performed by means of 0.5 M HCl. It was possible to use the biomass of Penicillium purpurogenum for six cycles for biosorption.     

Hexavalent chromium reduction by bacterial consortia and pure strains from an alkaline industrial effluent

Aims: To characterize the bacterial consortia and isolates selected for their role in hexavalent chromium removal by adsorption and reduction. Methods and Results: Bacterial consortia from industrial wastes revealed significant Cr(VI) removal after 15 days when incubated in medium M9 at pH 6·5 and 8·0. The results suggested chromium reduction. The bacterial consortia diversity (T‐RFLP based on 16S rRNA gene) indicated a highest number of operational taxonomic units in an alkaline carbonate medium mimicking in situ conditions. However, incubations under such conditions revealed low Cr(VI) removal. Genomic libraries were obtained for the consortia exhibiting optimal Cr(VI) removal (M9 medium at pH 6·5 and 8·0). They revealed the dominance of 16S rRNA gene sequences related to the genera Pseudomonas/Stenotrophomonas or Enterobacter/Halomonas, respectively. Isolates related to Pseudomonas fluorescens and Enterobacter aerogenes were efficient in Cr(VI) reduction and adsorption to the biomass. Conclusions: Cr(VI) reduction was better at neutral pH rather than under in situ conditions (alkaline pH with carbonate). Isolated strains exhibited significant capacity for Cr(VI) reduction and adsorption. Significance and Impact of Study: Bacterial communities from chromium‐contaminated industrial wastes as well as isolates were able to remove Cr(VI). The results suggest a good potential for bioremediation of industrial wastes when optimal conditions are applied.     

Microbially mediated chromate reduction in soil contaminated by highly alkaline leachate from chromium containing waste

This paper reports an investigation into the possible fate of Cr(VI) that is migrating downwards from a chromium ore processing residue (COPR) tip into the underlying soils. This waste was deposited at a site in the north of England more than 100 years ago and is currently a cause for environmental concern because groundwater emerging from the waste is alkaline, visibly yellow and has an elevated Cr(VI) concentration. Sandy clay from immediately beneath the waste (assumed to be the topsoil layer prior to waste tipping) contains between about 600 and 3000 mg kg^?1 of Cr, and around 60% of 0.5 N HCl extractable iron was present as reduced Fe(II). DNA fragments from soil bacteria were extracted from this soil, and microcosm experiments where the pH was adjusted to more neutral values showed that it contains a viable bacterial population capable of iron-reduction. This sandy clay layer, despite a pH value of 10.5, appears to be acting as a natural reactive zone beneath the waste as it is accumulating chromium. It is thought that the mechanism of Cr(VI) reduction is most likely to be an abiotic reaction with the Fe(II) present in the soil, and that Fe(II) in the soil is being replenished by microbial iron-reduction (although the rate of replenishment is unknown).     

The Suitability of Jatropha Seed Press Cake as a Biosorbent for Removal of Hexavalent Chromium from Aqueous Solutions

Jatropha seed press cake (JPC), a biodeisel waste, was investigated for its use as biosorbent for Cr(VI) removal from wastewater. The acid-pretreated biomass exhibited 1.9-fold higher biosorption efficiency for Cr(VI). The Cr(VI) biosorption efficiency was found to increase with decrease in pH of aqueous medium. The adsorption capacity of biosorbent for Cr(VI) increased with increasing concentration of Cr(VI). The biosorption of Cr(VI) by acid-treated JPC followed a pseudo-second-order kinetics. The results of equilibrium studies showed that the biosorption process fitted the Langmuir isotherm model, with a maximum adsorption capacity of 22.727 mg of Cr(VI)/g of biosorbent at 30°C. The activation energy was found to be 27.114 kJ/mol, suggesting that the adsorption process was mainly a physical process. The important thermodynamic parameters of adsorption (ΔG, ΔH, andΔS) were determined, which indicated that the Cr(VI) sorption by JPC is a spontaneous and endothermic process.     

Treatment of Alkaline Cr(VI)-Contaminated Leachate with an Alkaliphilic Metal-Reducing Bacterium

Chromium in its toxic Cr(VI) valence state is a common contaminant particularly associated with alkaline environments. A well-publicized case of this occurred in Glasgow, United Kingdom, where poorly controlled disposal of a cementitious industrial by-product, chromite ore processing residue (COPR), has resulted in extensive contamination by Cr(VI)-contaminated alkaline leachates. In the search for viable bioremediation treatments for Cr(VI), a variety of bacteria that are capable of reduction of the toxic and highly soluble Cr(VI) to the relatively nontoxic and less mobile Cr(III) oxidation state, predominantly under circumneutral pH conditions, have been isolated. Recently, however, alkaliphilic bacteria that have the potential to reduce Cr(VI) under alkaline conditions have been identified. This study focuses on the application of a metal-reducing bacterium to the remediation of alkaline Cr(VI)-contaminated leachates from COPR. This bacterium, belonging to the Halomonas genus, was found to exhibit growth concomitant to Cr(VI) reduction under alkaline conditions (pH 10). Bacterial cells were able to rapidly remove high concentrations of aqueous Cr(VI) (2.5 mM) under anaerobic conditions, up to a starting pH of 11. Cr(VI) reduction rates were controlled by pH, with slower removal observed at pH 11, compared to pH 10, while no removal was observed at pH 12. The reduction of aqueous Cr(VI) resulted in the precipitation of Cr(III) biominerals, which were characterized using transmission electron microscopy and energy-dispersive X-ray analysis (TEM-EDX) and X-ray photoelectron spectroscopy (XPS). The effectiveness of this haloalkaliphilic bacterium for Cr(VI) reduction at high pH suggests potential for its use as an in situ treatment of COPR and other alkaline Cr(VI)-contaminated environments.     

Distinct and effective biotransformation of hexavalent chromium by a novel isolate under aerobic growth followed by facultative anaerobic incubation

A bacterial isolate (G161) with high Cr(VI)-reducing capacity was isolated from Cr(VI)-contaminated soil and identified as Leucobacter sp. on the basis of 16S rRNA gene sequence analysis. The isolate was a Gram-positive, aerobic rod. The hexavalent chromate-reducing capability of the isolate was investigated under three conditions of oxygen stress. The isolate was found to reduce Cr(VI) under all conditions but performed most effectively during aerobic growth followed by facultative anaerobic incubation. Under these conditions, the isolate tolerated K₂Cr₂O₇ concentrations up to 1,000 mg/l and completely reduced 400 mg/l K₂Cr₂O₇ within 96 h. The strain reduced Cr(VI) over a wide range of pH (6.0–11.0) and temperatures (15–45 °C) with optimum performance at pH?8.0 and 35 °C. The presence of other metals, such as Ca²⁺, Co²⁺, Cu²⁺, Mn²⁺, Ni²⁺, and Zn²⁺, induced no effect or else played a stimulatory role on Cr(VI)-reduction activity of the strain. The strain was tested for Cr(VI) removal in wastewaters and proved capable of completely reducing the contained Cr(VI). This is the novel report of a bacterial growth and Cr(VI)-reduction process under sequential aerobic growth and facultative anaerobic conditions. The study suggested that the isolate possesses a distinct capability for Cr(VI) reduction which could be harnessed for the detoxification of chromate-contaminated wastewaters.     

Hexavalent Chromium Reduction from Pollutant Samples by <Emphasis Type="Italic">Achromobacter xylosoxidans</Emphasis> SHB 204 and its Kinetics Study

Cr(VI) is most toxic heavy metal and second most widespread hazardous metal compound worldwide. Present work focused on Cr(VI) reduction from synthetic solutions and polluted samples by Achromobacter xylosoxidans SHB 204. It could tolerate Cr(VI) up to 1600 ppm and reduce 500 ppm with 4.5 chromium reductase enzyme units (U) having protein size 30 kDa. Changes in morphology of cells on interaction with Cr(VI) metal ion was also studied using SEM–EDX and FTIR. Microcosm studies in pollutant samples for Cr(VI) reduction and adsorption isotherm with biomass of bacterium was best fitted with Langmuir model along with kinetic studies. This study focuses on significance of Cr reduction from synthetic solutions and polluted samples by A. xylosoxidans SHB 204 and its potential for bioremediation.     

Use of Experimental Factorial Design for Optimization of Hexavalent Chromium Removal by a Bacterial Consortium: Soil Microcosm Bioremediation

Hexavalent chromium Cr(VI) is regularly introduced into the environment through diverse anthropogenic activities. It is highly toxic, mutagenic and carcinogenic, and because of its solubility in water, chromate contamination can be difficult to contain. Bacteria can reduce chromate to insoluble and less toxic trivalent chromium Cr(III), and thus increasing attention is paid to chromate bioremediation to reduce its ecotoxicological impacts. In this study, the factorial design 2³ was employed to optimize critical parameters responsible for higher Cr(VI) removal by a bacterial consortium. The factors considered were pH, temperature, and inoculum size at two markedly different levels. All three dependent variables have significant effect on Cr(VI) reduction. Optimal Cr(VI) removal by the bacterial consortium occurred at pH 9, temperature 37°C, and inoculum size OD = 3. Analysis of variance (ANOVA) showed a high coefficient of determination (R²) value of 0.984, thus ensuring a satisfactory adjustment of the second-order regression model with the experimental data. In addition, the effect of bioaugmentation of Cr(VI)-polluted soil microcosms with the bacterial consortium was investigated using the best factor levels. Contaminated soil by 20 and 60 mg/Kg of Cr(VI) showed reductions of 83% and 65% of initial Cr(VI) by the bacterial consortium, suggesting that this bacterial consortium might diminish phytoavailable Cr(VI) in soil and be useful for cleaning up chromium-contaminated sites.