Microbial reduction of hexavalent chromium by landfill leachate

The reduction of hexavalent chromium (Cr(VI)) in municipal landfill leachates (MLL) and a non-putrescible landfill leachate (NPLL) was investigated. Complete Cr(VI) reduction was achieved within 17 days in a MLL when spiked with 100 mg l(-1) Cr(VI) or less. In the same period, negligible Cr(VI) reduction was observed in NPLL. In MLL, Cr(VI) reduction was demonstrated to be a function of initial Cr(VI) concentration and bacterial biomass and organic matter concentrations. The bacteria were observed to tolerate 250 mg l(-1) Cr(VI) in MLL and had an optimal growth activity at pH 7.4 in a growth medium. The MLL also possessed an ability to sequentially reduce Cr(VI) over three consecutive spiking cycles.     

Bioremediation of Cr(VI) in contaminated soils

Ex situ treatment of hexavalent chromium (Cr(VI)) contaminated soil using a bioreactor-biosorption system was evaluated as a novel remediation alternative. Leaching of Cr(VI) from the contaminated soil using various eluents showed that desorption was strongly affected by the solution pH. The leaching process was accelerated at alkaline conditions (pH 9). Though, desorption potential of ethylene diamine tetra acetic acid (EDTA) was the maximum among various eluents tried, molasses (5 g/L) could also elute 72% of Cr(VI). Cr(VI) reduction studies were carried out under aerobic and facultative anaerobic conditions using the bacterial isolates from contaminated soil. Cr(VI) reduction was moderately higher in aerobic conditions than in facultative anaerobic conditions. The effect of various electron donors on Cr(VI) reduction was also investigated. Among five electron donors screened, peptone (10 g/L) showed maximum Cr(VI) reduction followed by molasses (10 g/L). The time required for complete Cr(VI) reduction was increased with increase in the initial Cr(VI) concentration. However, specific Cr(VI) reduction was increased with increase in initial Cr(VI) concentration. Sulfates and nitrates did not compete with Cr(VI) for accepting the electrons. A bioreactor was developed for the detoxification of Cr(VI). Above 80% of Cr(VI) reduction was achieved in the bioreactor with an initial Cr(VI) concentration of 50 mg/L at an HRT of 8 h. An adsorption column was developed using Ganoderm lucidum (a wood rooting fungus) as the adsorbent for the removal of trivalent chromium (Cr(III)) and excess electron donor from the effluent of the bioreactor. The specific Cr(III) adsorption capacity of G. lucidum in the column was 576 mg/g. The new biosystem seems to be a promising alternative for the ex situ bioremediation of Cr(VI) contaminated soils.     

The comprehensive investigation on removal mechanism of Cr(VI) by humic acid-Fe(II) system structured on V,Ti-bearing magnetite surface

The Cr(VI) could be adsorbed and reduced by the humic acid (HA)-Fe(II) system structured on the V, Ti-magnetite (VTM) surface. The Cr(VI) removal process included adsorption and reduction stages. First, the Cr(VI) was adsorbed on the VTM-HA surface via the ionic bonds between the Ti atoms of VTM core and the O atoms of the HCrO₄^?. The adsorption of Cr(VI) is uniform, monolayer, and controlled by Cr(VI) diffusion. Subsequently, the adsorbed Cr(VI) was reduced by the HA-Fe(II) system on the VTM-HA surface. During the Cr(VI) reduction process, the HA and Fe(II) have a synergistic effect. The Cr(VI) was reduced to the Cr(III) by the HA and Fe(II). Meanwhile, the HA could also reduce Fe(III) to Fe(II), making Fe(II) continue to participate in the Cr(VI) reduction. The olefin, hydroxyl, and aldehyde groups of HA were the primary electron donors during the Cr(VI) reduction. The Fe(II) acted as an electron bridge, transferring the electron from HA to Cr(VI). The reduced Cr(III) was deposited on the VTM-HA surface via the complexation with the carboxyl and hydroxyl groups of HA. The results demonstrated that the Cr(VI) could be adsorbed, reduced and complexed by the HA-Fe(II) system on the VTM-HA surface synchronously.     

Effects of ferrous iron and molecular oxygen on chromium(VI) redox kinetics in the presence of aquifer solids

The kinetics and stoichiometry of the reduction of hexavalent chromium (Cr(VI)) with ferrous iron (Fe(II)) were examined in systems with and without aquifer solids. Cr(VI) reduction was rapid in the absence of solids, but demonstrated slower and more complex kinetics in the presence of aquifer solids. The aquifer solids removed Fe(II) from solution and a portion of the reducing capacity of Fe(II) was transferred to the aquifer solids. The solid phases were then able to continue to remove Cr(VI). This suggests in situ treatment of Cr(VI) by Fe(II) injection would be feasible in the aquifer environment. In general, re-oxidation of reduced chromium by molecular oxygen was not observed in our systems over time periods of nearly 1 year, suggesting that the potential for chromium solubilization under these oxidizing conditions will be low. An empirical model was developed to describe the reduction kinetics of Cr(VI) in the presence of solids. The model assumes that the reaction is brought about by pseudo-species of iron that react instantaneously, rapidly and slowly with Cr(VI). A fourth pseudo-species is assumed to be non-reactive. Model coefficients were determined by non-linear regression. The model was able to describe observed concentrations of chromium well, but analysis of model errors indicated the potential existence of a distribution of species with different reaction rates rather than just three distinct species. Another model was developed to predict concentrations of different pseudo-species depending on the total amount of Fe(II) added and the amount of aquifer solids present. This model assumed that pseudo-species could result from intrinsic characteristics of the aquifer solids as well as being formed by addition of Fe(II), which could sorb to the aquifer solids.     

In situ stabilization of chromium(VI) in polluted soils using organic ligands: the role of galacturonic, glucuronic and alginic acids

Laboratory batch sorption and column experiments were performed to investigate the role of organic ligands such as galacturonic, glucuronic and alginic acids (main constituents of bacterial exopolymeric substances (EPS)) on Cr(VI) uptake and transport in heterogeneous subsurface media. Our batch sorption experiments demonstrate the addition of galacturonic, glucuronic and alginic acids to soils enhances Cr(VI) uptake by soil at pH values <7.7 depending on the concentration of the ligand and pH used. The enhanced Cr(VI) uptake at pH values <7.7 may be explained through either the catalytic reduction of Cr(VI) to Cr(III) by the surface-bound organic matter/Fe oxides and/or the dissolved metal ions (e.g., Fe(III)) from the soil. On the other hand, organic ligands have no or little effect on Cr(VI) uptake under highly alkaline pH conditions since the catalytic Cr(VI) reduction decreases with increasing pH. Similarly, the results from column experiments show that, depending on the concentration of organic ligands, the Cr(VI) breakthrough curves were significantly retarded relative to the organic acid-free systems at pH 7.6. A significant portion of Cr(VI) initially added to the feed solution was not readily recoverable in the effluent, indicating Cr(VI) reduction in columns, most probably catalyzed by surface-bound metal-oxides (e.g., Fe oxides) or dissolved metal ions such as Fe(II; III). The overall results suggest that EPS constituents such as glucuronic, galacturonic and alginic acids may play a significant role on Cr(VI) stabilization in subsurface systems under acidic to slightly alkaline pH conditions.     

Aqueous Cr(VI) reduction by electrodeposited zero-valent iron at neutral pH: acceleration by organic matters

This work investigated the effect of co-existing organic matters on aqueous Cr(VI) reduction by electrodeposited zero-valent iron (ED Fe(0)) at neutral pH. The ED Fe(0) prepared in a solution containing mixture of saccharin, L-ascorbic acid and sodium dodecyl sulfate showed higher activity in reducing the aqueous Cr(VI) at neutral pH than that prepared without any organic presence. XRD and SEM indicated that the structure of ED Fe(0) was significantly improved to nano-scale by the presence of organic mixture in the preparation solution. Further, the ED Fe(0) activity in the Cr(VI) reduction at neutral pH was increased by the co-existence of citric acid or oxalic acid in the chromate solution. Electrochemical impedance spectroscopy (EIS) demonstrated that the corrosive current increased with the concentration of organic matter in the reaction solution. With the co-existing organic matters in the preparation solution, the ED Fe(0) corroded more rapidly due to its nano-size, thus the Cr(VI) reduction by the ferrous iron was accelerated. With the co-existing organic matters in the reaction solution, the Cr(VI) reduction was accelerated by a Fe(II) complex as the main electron donor, and a prevention of the passivation due to the Fe(III) and Cr(III) complexes also accelerated the Cr(VI) reduction.     

A mechanism study of light-induced Cr(VI) reduction in an acidic solution

The mechanisms of photo-catalytic reduction of Cr(VI) were investigated in acidic solutions with and without Fe(III). In a system without Fe(III), no Cr(VI) reduction was observed in dark conditions; conversely, under light conditions, the reduction reaction rate increased to 0.011 and 0.020microM min(-1) at pH 2 and pH 1, respectively, indicating the occurrence of Cr(VI) photo-reduction. The Cr(VI) photo-reduction reaction was induced by the photolysis of water molecules, leading to O(2) production. Upon the addition of Fe(III), the photo-reduction rate of Cr(VI) was significantly enhanced due to the formation of Fe(II), which is the photolytic product of FeCl(2)(+) and the electron donor for Cr(VI) reduction. However, with the same concentration of FeCl complexes, a strong inhibition of Cr(VI) reduction at pH 2 was observed, compared with pH 1. A possible explanation is that FeOH(2+) becomes predominant with increasing pH and that its photolytic product, the OH free radical, is an oxidant for Fe(II) and Cr(III) and can compromise Cr(VI) reduction. The kinetic result of each photo-reduction reaction pathway shows zero-order kinetics, suggesting that the photolysis reaction of H(2)O or FeCl(2+) is the rate-determining step in each pathway. The results also show the potential of developing a homogeneous photo-catalytic method to treat Cr(VI)-containing water.     

Epithermal neutron activation analysis of Cr(VI)-reducer basalt-inhabiting bacteria

Epithermal neutron activation analysis (ENAA) has been applied to study elemental composition of Cr(VI)-reducer bacteria isolated from polluted basalts from the Republic of Georgia. Cr(VI)-reducing ability of the bacteria was examined by electron spin resonance, demonstrating that the bacteria differ in their rates of Cr(VI) reduction. A well-pronounced correlation between the ability of the bacteria to accumulate Cr(V) and their ability to reduce Cr(V) to Cr(III) observed in our experiments is discussed. Elemental analysis of these bacteria also revealed that basalt-inhabiting bacteria are distinguished by relative contents of essential elements such as K, Na, Mg, Fe, Mn, Zn, and Co. A high rate of Cr(III) formation correlates with a high concentration of Co in the bacterium. ENAA detected some similarity in the elemental composition of the bacteria. The relatively high contents of Fe detected in the bacteria (140-340 microg/g of dry weight) indicate bacterial adaptation to the environmental conditions typical of the basalts. The concentrations of at least 12-19 different elements were determined in each type of bacteria simultaneously starting with the major to ultratrace elements. The range of concentrations spans over 8 orders of magnitude.     

Effects of pH and dissolved oxygen on Cr(VI) removal in Fe(0)/H2O systems

The effects of pH and dissolved oxygen (DO) on aqueous Cr(VI) removal by micro-scale zero-valent iron (Fe(0)/H(2)O system) were investigated. Batch experiments were conducted at pH 4.0, 5.0 and 6.0 under oxic and anoxic conditions. Column experiments were performed at pH 5.0 and 7.5 under oxic condition. Spectroscopic analyses were applied to explain the mechanism of Cr(VI) removal using X-ray absorption near-edge structure (XANES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results showed that the kinetics of Cr(VI) removal were fastest at pH 5 under both oxic and anoxic conditions. As a rule, Cr(VI) removal were faster under oxic conditions than under anoxic conditions. Column experiments showed that Cr(VI) removal was about 1.7-fold higher at pH 5 than at pH 7.5. XANES (X-ray absorption near edge structures) results showed that Fe(0) reduced Cr(VI) to Cr(III) under both oxic and anoxic conditions. X-ray diffraction patterns of the Cr(VI)-Fe(0) reaction products suggested partial formation of chromite (FeCr(2)O(4)) at pH 5 and 6 under oxic conditions. However, nano-sized clusters of Cr(III)/Fe(III) hydroxide/oxyhydroxide were formed on the surface of Fe(0) under anoxic conditions. These results indicate that the presence of oxygen in solution plays an important role in control of the kinetic of Cr(VI) removal and in development of various Cr(VI) reduction products.     

Lifetime and regeneration of immobilized titania for photocatalytic removal of aqueous hexavalent chromium

Immobilized titania (TiO2) batch reactors reduced hexavalent chromium (Cr(VI)) in the form of potassium dichromate (K2Cr2O7) to trivalent chromium (Cr(III)) in aqueous solution at pH 3 under 171 W/m2 light intensity. The light source was a 125-W ultraviolet (UV) lamp. The Cr(VI) reduction showed zero-order kinetics (k0), while the Cr(VI) adsorption fitted with first-order kinetics (k(1st)). Adsorption capacity increased with increasing initial Cr(VI) concentration, and the area of immobilized TiO2 limited the reduction efficiency. The lifetime of fresh immobilized TiO2 was approximately 14 h. In addition, the regeneration of TiO2 with 3M sodium hydroxide (NaOH) was necessary to improve adsorption reaction.     

Determination of chromium (VI) using cathodic voltammetry technique in gold microelectrodes

Electrochemical reduction of chromium (VI) is studied on a gold microelectrode assembly (Au-MEA) using the cathodic voltammetry (VA) technique. The optimum conditions for obtaining the analytical signal of Cr (VI) are chosen. The range of the analyzed concentrations of Cr (VI) are 0.005?C0.2 mg/L, and the detection limit is 5 × 10^?5 mg/L. Dissolved oxygen, manifold excesses of alkali and alkaline-earth ions, 200-fold excesses of Cr (III), and 10-fold excesses of Fe (III) and Cu (II) do not interfere with determination of 0.005 mg/L Cr (VI). In the presence of anionic surfactants (DDCNa), the signal of Cr (VI) decreases, but the linear dependence on the concentration remains. A rapid technique for determination of Cr (VI) in purified technical water without sample preparation is suggested. The advantage of Au-MEA consists in the simplicity of synthesis, running time, high sensitivity.     

Electrochemical removal of chromium from aqueous solutions using electrodes of stainless steel nets coated with single wall carbon nanotubes

An electrochemical technique was adopted to investigate the removal of Cr(VI) species and total chromium (TCr) from aqueous solution at a laboratory scale. The electrodes of stainless steel nets (SSNE) coated with single wall carbon nanotubes (SWCNTs@SSNE) were used as both anode and cathode. Three parameters, including solution pH, voltage and electrolyte concentration, were studied to explore the optimal condition of chromium removal. The optimal parameters were found to be pH 4, voltage 2.5 V and electrolyte concentration 10 mg/L. Under these conditions, the Cr(VI) and TCr removal had a high correlation with the amount of SWCNTs coated on the electrodes, with coefficients of the regression equations 0.953 and 0.928, respectively. The mechanism of Cr(VI) removal was also investigated. X-ray photoelectron spectroscopy (XPS) study and scanning electron microscope (SEM) picture showed that the process of chromium removal involved the reduction of Cr(VI) to Cr(III) on the cathode, and then the adsorption of Cr(III) by SWCNTs on the cathode. The study results indicated that the proposed method provided an interesting means to remove chromium species from aqueous solution, especially Cr(VI) in acidic condition.     

Hexavalent chromium reduction with scrap iron in continuous-flow system Part 1: effect of feed solution pH

The reduction of hexavalent chromium by scrap iron was investigated in continuous system, using long-term column experiments, for aqueous Cr(VI) solutions having low buffering capacities, over the pH range of 2.00-7.30. The results showed that the initial pH of Cr(VI) solution significantly affects the reduction capacity of scrap iron. The highest reduction capacity was determined to be 19.2 mg Cr(VI)/g scrap iron, at pH 2.50, and decreased with increasing the initial pH of Cr(VI) solution. A considerable decrease in scrap iron reduction capacity (25%) was also observed at pH 2.00, as compared to pH 2.50, due to the increased contribution of H(+) ions to the corrosion of scrap iron, which leads to a rapid decrease in time of the scrap iron volume. Over the pH range of 2.50-7.30, hexavalent chromium concentration increases slowly in time after its breakthrough in column effluent, until a steady-state concentration was observed; similarly, over the same pH range, the amount of solubilized Cr(III) in treated column effluent decreases in time, until a steady-state concentration was observed. The steady-state concentration in column effluent decreased for Cr(VI) and increased for Cr(III) with decreasing the initial pH of Cr(VI) solution. No steady-state Cr(VI) or Cr(III) concentrations in column effluent were observed at pH 2.00. Over the entire studied pH range, the amount of Fe(total) in treated solution increases as the initial pH of column influent is decreased; the results show also a continuously decrease in time of Fe(total) concentration, for a constant initial pH, due to a decrease in time of iron corrosion rate. Cr(III) concentration in column effluent also continuously decreased in time, for a constant initial pH, over the pH range of 2.50-7.30. This represents an advantage, because the amount of precipitant agent used to remove Fe(total) and Cr(III) from the column effluent will also decrease in time. The optimum pH for Cr(VI) reduction with scrap iron in continuous-flow system was established at the value of 2.50.     

Reduction of chromate from electroplating wastewater from pH 1 to 2 using fluidized zero valent iron process

Fluidized zero valent iron (ZVI) process was conducted to reduce hexavalent chromium (chromate, CrO(4)(2-)) to trivalent chromium (Cr(3+)) from electroplating wastewater due to the following reasons: (1) Extremely low pH (1-2) for the electroplating wastewater favoring the ZVI reaction. (2) The ferric ion, produced from the reaction of Cr(VI) and ZVI, can act as a coagulant to assist the precipitation of Cr(OH)(3(s)) to save the coagulant cost. (3) Higher ZVI utilization for fluidized process due to abrasive motion of the ZVI. For influent chromate concentration of 418 mg/L as Cr(6+), pH 2 and ZVI dosage of 3g (41 g/L), chromate removal was only 29% with hydraulic detention time (HRT) of 1.2 min, but was increased to 99.9% by either increasing HRT to 5.6 min or adjusting pH to 1.5. For iron species at pH 2 and HRT of 1.2 min, Fe(3+) was more thermodynamically stable since oxidizing agent chromate was present. However, if pH was adjusted to 1.5 or 1, where chromate was completely removed, high Fe(2+) but very low Fe(3+) was present. It can be explained that ZVI reacted with chromate to produce Fe(2+) first and the presence of chromate would keep converting Fe(2+) to Fe(3+). Therefore, Fe(2+) is an indicator for complete reduction from Cr(VI) to Cr(III). X-ray diffraction (XRD) was conducted to exam the remained species at pH 2. ZVI, iron oxide and iron sulfide were observed, indicating the formation of iron oxide or iron sulfide could stop the chromate reduction reaction.     

Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens

The bioproduction of nanoscale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50?nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles have been investigated by x-ray magnetic circular dichroism and indicate the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimized biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently to the less harmful trivalent form.     

Chromium removal from aqueous solution by the ferrite process

This research summarises the results of the study on the removal of chromium by applying the ferrite process to the solutions obtained from two different Cr(VI) reduction processes utilising sodium sulphite and ferrous sulphate as reducing agents. For both solutions containing trivalent chromium ions, the optimum treatment conditions were determined. The generated sludges were characterised by XRD analysis and physical tests. In addition, to explore the dissolution properties of the sludges obtained, they were contacted with the solutions of sulphuric, citric, tartaric, oxalic and ascorbic acids and EDTA. Also, the sludge samples were subjected to standard toxicity characterisation leaching procedure (TCLP) test of USEPA in order to determine the pollution potential. An efficient Cr(III) removal (about 100%) in the solution from the Cr(VI) reduction process utilising sodium sulphite as reducing agent was achieved when the solution was treated at pH 9 and 50 degrees C for 60 min in the presence of Fe2+/Cr3+ weight ratio of 16. For the other Cr(III) solution prepared from Cr(VI) reduction by ferrous sulphate, a Fe2+/Cr3+ weight ratio of 17.9 at the same conditions was found to produce complete removal of Cr(III). It was determined that the spynel chromium-iron compounds obtained in the process were in the form of chromite (Cr2FeO4). Dissolution experiments and TCLP tests show that the concentrations of the chromium dissolved from both sludges were below the limit given as 5 mg l(-1) by USEPA. The results showed that Cr(III) removal through ferrite process provides the advantages that the sludges generated are non-voluminous, easily separable and environmentally stable.     

Detoxification of chromium slag by chromate resistant bacteria

This paper presented direct detoxification of chromium slag by using microorganisms. Our work showed that a bacterial consortium isolated from chromium slag can efficiently accelerate Cr(VI) leaching rate and remove it. The chromate resistant bacterial consortium consists of three strains. The detoxification efficiencies of the three respective strains follow the sequence: strain I > strain III > strain II. The detoxification capability of the bacterial consortium is far stronger than that of the respective strain, showing an excellent synergistic effect. The specific growth rates in pure and chromium-containing medium are 0.1475 and 0.1573 h(-1), respectively. The presence of Cr(VI) has little effect on growth rate of the bacterial consortium. Cr(VI) removal takes place in exponential growth period of the bacterial consortium; the detoxification time should be controlled in this phase for every run. The kinetics of detoxification process was studied and can be described as eta = 0.0615e(0.1573t), which can be used to predict Cr(VI) removal efficiency.     

Removal of chromium from aqueous solution by using oxidized multiwalled carbon nanotubes

The batch removal of hexavalent chromium (Cr(VI)) from aqueous solution by using oxidized multiwalled carbon nanotubes (MWCNTs) was studied under ambient conditions. The effect of pH, initial concentration of Cr(VI), MWCNT content, contact time and ionic strength on the removal of Cr(VI) was also investigated. The removal was favored at low pH with maximum removal at pH <2. The adsorption kinetics was modeled by first-order reversible kinetics, pseudo-first-order kinetics, pseudo-second-order kinetics, and intraparticle diffusion models, respectively. The rate constants for all these kinetic models were calculated, and the results indicate that pseudo-second-order kinetics model was well suitable to model the kinetic adsorption of Cr(VI). The removal of chromium mainly depends on the occurrence of redox reaction of adsorbed Cr(VI) on the surface of oxidized MWCNTs to the formation of Cr(III), and subsequent the sorption of Cr(III) on MWCNTs appears as the leading mechanism for chromium uptake to MWCNTs. The presence of Cr(III) and Cr(VI) on oxidized MWCNTs was confirmed by the X-ray photoelectron spectroscopic analysis. The application of Langmuir and Freundlich isotherms are applied to fit the adsorption data of Cr(VI). Equilibrium data were well described by the typical Langmuir adsorption isotherm. Overall, the study demonstrated that MWCNTs can effectively remove Cr(VI) from aqueous solution under a wide range of experimental conditions, without significant Cr(III) release.     

Hexavalent chromium reduction by Acinetobacter haemolyticus isolated from heavy-metal contaminated wastewater

Possible application of a locally isolated environmental isolate, Acinetobacter haemolyticus to remediate Cr(VI) contamination in water system was demonstrated. Cr(VI) reduction by A. haemolyticus seems to favour the lower concentrations (10-30 mg/L). However, incomplete Cr(VI) reduction occurred at 70-100 mg/L Cr(VI). Initial specific reduction rate increased with Cr(VI) concentrations. Cr(VI) reduction was not affected by 1 or 10 mM sodium azide (metabolic inhibitor), 10 mM of PO(4)3-, SO4(2-), SO(3)2-, NO3- or 30 mg/L of Pb(II), Zn(II), Cd(II) ions. However, heat treatment caused significant dropped in Cr(VI) reduction to less than 20% only. A. haemolyticus cells loses its shape and size after exposure to 10 and 50 mg Cr(VI)/L as revealed from TEM examination. The presence of electron-dense particles in the cytoplasmic region of the bacteria suggested deposition of chromium in the cells.     

Simultaneous photocatalytic reduction of Cr(VI) and oxidation of bisphenol A induced by Fe(III)-OH complexes in water

Simultaneously photocatalytic reduction of Cr(VI) and oxidation of bisphenol A (BPA) in aqueous solution in the presence of Fe(III)-OH complexes were investigated under a 250 W metal halide lamp (lambda>or=365 nm). Synergy effect of the simultaneous photocatalytic oxidation and reduction of both pollutants was achieved. The effects of initial pH value, initial concentration of BPA, Cr(VI) and Fe(III) were preliminarily investigated. The results showed that both photocatalytic reduction of Cr(VI) and degradation of BPA could occur simultaneously in the Fe(III)/Cr(VI)/BPA ternary system, and the rates of photocatalytic reduction of Cr(VI) and the oxidation of BPA were more rapid at a low pH range of 2.0-3.0. The increase of the initial concentration of Fe(III) was favorable to both photocatalytic reduction of Cr(VI) and oxidation of BPA. The reduction efficiency of Cr(VI) decreased with increasing initial concentrations of Cr(VI) and BPA, but the degradation efficiency of BPA was not changed obviously at different Cr(VI) concentrations.