Oxidation Of Zero-valent Iron Research Articles

Effects of the formation of reactive chlorine species on oxidation process using persulfate and nano zero-valent iron

The chloride ion (Cl−) is a matrix ion that plays crucial roles in radical-based oxidation processes used to treat brackish or saline water. Here, the effects of the formation of reactive chlorine species on the performance of and reaction mechanisms involved in persulfate/nano zero-valent iron process were evaluated by investigating the reaction kinetics and performing reactive species scavenging tests. The phenol oxidation rate increased markedly in the early reaction stage in the presence of 25–200 mM of Cl−. This was because excess sulfate radicals (SO4−) reacted with Cl− to produce short-lived reactive chlorine species such as Cl and Cl2− rather than being scavenged by Fe2+ or other SO4−. The reactive chlorine species caused OH to form through radical propagation reactions. The total numbers of reactive species involved in phenol oxidation were higher at brackish to weakly saline Cl− concentrations than at lower and higher Cl− concentrations. At high Cl− concentrations (>400 mM), the phenol oxidation rate decreased because most of the SO4− reacted with Cl− to give large amounts of weaker oxidants such as Cl2− and HOCl. Acceleration of Fe corrosion by Cl− negligibly affected the persulfate/nano zero-valent iron oxidation process.

Chemical Reduction of Nitrate by Zero-Valent Iron: Shrinking-Core versus Surface Kinetics Models.

Zero valent iron (ZVI) is being used in permeable reactive barriers (PRB) for the removal of oxidant contaminants, from nitrate to chlorinated organics. A sound design of these barriers requires a good understanding of kinetics. Here we present a study of the kinetics of nitrate reduction under relatively low values of pH, from 2 to 4.5. We use a particle size of 0.42 mm, which is within the recommended size for PRBs (0.2 mm to 2.0 mm). In order to avoid possible mass-transfer limitations, a well-stirred reactor coupled with a fluidized bed reactor was used. The experiments were performed at constant pH values using a pH controller that allows to accurately track the amount of acid added. Since the reduction of to by the oxidation of ZVI will always be present for these pH values, blank experiments (without nitrate) were performed and the rate of this reduction obtained. This rate of reduction was studied using three kinetic models: a regular empirical one, the Shrinking-Core Model (SCM), and the Surface Kinetics Model (SKM). The best performance was obtained from the SKM model. Therefore, this model was also used to study the results for the nitrate reduction, also with satisfactory results. In both cases, some assumptions are introduced to maintain a moderate number of fitting parameters.

How does zero valent iron activating peroxydisulfate improve the dewatering of anaerobically digested sludge?

Zero valent iron (ZVI) activating peroxydisulfate (PDS) was demonstrated to be effective in improving the dewaterability of anaerobically digested sludge (ADS). However, details of how ZVI/PDS enhances the dewaterability remain largely unknown. This work therefore aims to reveal the facts of what happen in ZVI/PDS involved ADS systems. Experimental results showed that ZVI/PDS treatment remarkably improved the dewaterability of ADS, with the minimal normalized capillary suction time of 8.6 ± 0.5 s L/g·VSS being obtained at the dosages of 2 g/g TSS ZVI and 0.5 g/g TSS PDS, which was 42.5% of that in the control. In this case, 71.2% ± 1.8% of water content (press filtration) was measured, which was 16.9% lower than that determined in the control. The mechanism investigations showed that ZVI activating PDS produced substantially reactive species, i.e., SO4•- and •OH, and these strong oxidative radicals decreased surface negative charges of ADS flocs, caused disruption of extracellular polymeric substances (EPS) and release of intracellular substances, and changed the secondary structure of proteins. Additionally, the products of ZVI oxidation, i.e., Fe2+ and Fe3+, were effective flocculants, thus their generation benefited the coagulation of ADS flocs through compressing double electric layers and neutralizing negative charges of sludge colloidal particles. As a result, the flocculability, hydrophobicity, and flowability of ADS were enhanced, but the bound water content, fractal dimension, and viscosity of ADS were decreased, which were responsible for the improvement of dewaterability. Further analyses exhibited that the contributions of these major contributors were different, and their contributions to the dewaterability improvement were in the order of SO4·- > ·OH > Fe2+/Fe3+. It was also found that ZVI/PDS treatment enhanced the degradation of recalcitrant organics, inactivation of the fecal coliforms, and mitigation of the toxicity of heavy metals in the dewatered sludge, which were beneficial to its land application.

Reduction Cooperated Fenton Oxidation of Zero-valent Iron (ZVI) Immobilized in Alginate Microsphere for Degradation of Acid Red B

The zero-valent iron (ZVI) immobilized in an alginate microsphere was prepared by using sodium alginate as a support material. The characteristics of the Fe0/alginate microsphere was characterized by FT-IR, SEM, BET, and XPS. The SEM and BET analyses showed that the Fe0/alginate microsphere had a multilevel porous structure and could adsorb ARB. Combined with Fe0 reduction and Fe3+/Fe2+ catalytic oxidation, the mineralization of ARB could be effectively realized. The ARB in the solution was discolored rapidly by the reduction of Fe0/alginate microsphere and then oxidized efficiently by the subsequent Fenton reaction. The discoloration rate of ARB in the reduction stage was 96.8%, with an Fe0/alginate microsphere dosage of 0.24g·L-1 and pH of 2.96 after reaction time of 180 min. ARB was reduced to organics of lower molecular weight due to the degradation of azo groups by Fe0. In the subsequent Fenton oxidation stage, the mineralization degree of ARB increased to 64.7% after the addition of 10.75 mmol·L-1 H2O2. The influence of the Fe0/alginate microsphere dosage, pH, reusability of the Fe0/alginate microsphere, and the stability of iron ions in the alginate microsphere were investigated. Due to the coordination of Fe3+/Fe2+ ions with -COO--in the alginate, the iron ion in the solution was 3.9% of the total iron content in the microsphere. Iron ions could be well immobilized in calcium alginate microspheres, so the iron hydroxides were generated in lower amounts. The Fenton reaction can be conducted in a wide range of pH. The Fe2+/Fe3+immobilized in the alginate microsphere demonstrated good catalytic performance after it was reused four times. Therefore, the synergy of reduction and Fenton oxidation by the Fe0/alginate microsphere was a better strategy for dye degradation.

Degradation of organic compounds during the corrosion of ZVI by hydrogen peroxide at neutral pH: Kinetics, mechanisms and effect of corrosion promoting and inhibiting ions

The corrosion of zero valent iron (ZVI) by hydrogen peroxide (H2O2) generates hydroxyl (⋅OH) and other radical oxygen species (ROS) that degrade organic materials. To better understand the factors that govern the ROS formation during the H2O2-induced corrosion, we investigated the degradation of an organic probe compound (acesulfame (ACE)) in slurries of ZVI powder in unbuffered laboratory water at pH 6.5 ± 0.5. Chloride ions accelerated the corrosion of ZVI by H2O2 and the formation ROS and, therefore, the degradation of organic materials. Conversely, slowing corrosion by phosphate buffer inhibited ROS formation and the degradation of organic compounds. The rate of H2O2 decomposition was correlated with the liberation of Fe2+(aq) and the ACE degradation rate. The kinetics of H2O2 decomposition was pseudo-first-order and zero-order at low (<0.04 mM/mg) and high [H2O2]/[ZVI] initial ratios, respectively, and was consistent with Langmuir kinetics. The H2O2 decomposition rate was proportional to the ZVI reactive surface area (SA) and nearly independent of the extent of ZVI oxidation, the presence of a Fe2+(aq) chelating agent, and ⋅OH quenchers (methanol and tert-butanol). Kinetic data suggest a mechanism involving rapid cathodic reduction of H2O2 at the metallic ZVI surface which causes the liberation of Fe2+(aq) that generate ⋅OH via the homogeneous Fenton reaction. The stoichiometric efficiency (SE) of organics degradation ranged from 0.0008% to 0.014% and increased with decreasing H2O2 decomposition rate.

Application of Spontaneous Oxidation Processes of Zero-valent Iron and Electrocoagulation for Reactive Black 5 Removal

Two methods of Reactive Black 5 dye removal were compared in this work, namely electrocoagulation (EC) and one based on spontaneous electrochemical oxidation of zero-valent iron (ZVI). Both methods are based on electrode processes and the sorption process and allow to achieve a similar effectiveness of dye removal. In the case of ZVI, however, a longer contact time or a greater surface area of the electrodes applied is necessary. In turn, the ZVI enables to conduct the processes of dye removal with no requirement for an external source of electric current (lower exploitation inputs). The study demonstrated that the application of both the ZVI method and EC is especially advisable in the case of lower initial concentrations of dye in the solution, i.e. the higher the concentration, the lower the contribution of electrode processes in dye removal from the solution and the greater the contribution of sorption processes.

Sustainable Pyrolytic Production of Zerovalent Iron

Pyrolysis of biorenewable feedstocks and iron oxides is potentially a greener and more sustainable pathway to producing zerovalent iron (ZVI) for environmental rehabilitation. The resulting biochar-zerovalent iron (BC-ZVI) also shows improved remediation kinetics of trichloroethylene over conventional ZVI. Understanding the transformations of iron to ZVI and the influence of feedstock chemistry on ZVI is critical to the production of BC-ZVI and has not been reported previously. BC-ZVI production was studied by one-step pyrolysis of cellulose, corn stover, dried distillers’ grain, red oak, and switchgrass pretreated with FeCl3. Pyrolysis at 900 °C effectively reduced Fe to ZVI with most feedstocks; however, the association of silicon (Si) and phosphorus (P) with Fe resulted in formation of fayalite and Fe phosphates and phosphides, which limited ZVI production efficiency and/or facilitated corrosion of ZVI. Dispersion of ZVI phases on biochar surfaces and association with Si facilitated oxidation of ZVI due to greater accessibility to oxygen and enhanced corrodibility of ZVI in association with fayalite. Feedstocks low in Si and P such as cellulose and red oak yield BC-ZVI suitable for environmental applications.

Phosphate removal from aqueous solutions using zero valent iron (ZVI): Influence of solution composition and ZVI aging

This study investigates phosphate removal from water by ZVI and its oxidation products. The effects of ZVI aging, solution ionic strength, and co-existing anions, on the removal efficiency of phosphate were evaluated. X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and scanning electron microscopy (SEM) were used to investigate the ZVI oxidation products and to delineate the phosphate removal mechanisms. ZVI showed the highest phosphate removal efficiency after 8h aging time (35 mgP/gZVI). Colloidal ZVI oxidation products showed very high phosphate removal rates especially the newly oxidized iron products (aged for 2h) with a capacity of 27.8 mgP/gFe. This capacity decreased to 2 mgP/gFe as aging time increased to 6 days. The characterization of the ZVI oxidation products revealed a mixture of crystalline lepidocrocite and goethite at the surface of ZVI however broader peaks were obtained in the supernatant fraction with aging time of 2h indicating the presence of poorly crystalline iron products. Nitrate showed no effects on the removal efficiency, whereas ionic strength effects were critical. Phosphate maximum uptake rate (Qe) increased from 8.7 to 15.6 mgP/gFe as ionic strength increased from 0.001M to 0.5M.

Hybrid [polysulfone–Zero Valent Iron] membranes: Synthesis, characterization and application for AsIII remediation

Hybrid polysulfone membranes decorated with Zero Valent Iron (ZVI) nanoparticles were prepared and evaluated for AsIII uptake. The hybrid polysulfone/ZVI membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM–EDX), transmission electron microscopy (TEM), mercury intrusion porosity measurements, thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The membranes are characterized by a macroporous structure with ZVI particles dispersed both inside the pores as well as at their surface. Electron Paramagnetic Resonance (EPR) spectroscopy reveals that the surface sulfide groups of polysulfone are readily accessible by extrinsic CuII cations. Moreover the polysulfone/ZVI membranes have a considerable electron-donating capacity to surface-adsorbed atoms, thus they are able to reduce CuII to CuI, and inhibit oxidation of ZVI from Fe0 to Fe3+. As a result, the Zero Valent Iron particles are stabilized against oxidation by ambient air and show appreciable AsIII adsorption capacity (26.6mgg−1). This renders them a significant stability, thus they can be reused at least four times for AsIII adsorption with a loss less than 1% of their As-uptake capacity. Based on a theoretical Surface Complexation Model we provide a consistent interfacial/structural picture that describes quantitatively all observed phenomena.

Hydrothermal conversion of carbon dioxide into formate with the aid of zerovalent iron: the potential of a two-step approach.

Our research focuses on the hydrothermal conversion of carbon dioxide into formate with the aid of zerovalent iron. Conventionally, a one-step approach is applied wherein both (I) the production of hydrogen gas, through the oxidation of zerovalent iron in an aqueous medium and (II) the conversion of carbon dioxide with this hydrogen gas into formate/formic acid, are performed under the same reaction conditions at a temperature of approximately 300 °C. Until now, the yields of formate/formic acid mentioned in the literature are, in the absence of a catalytic substance, low (13.5%). Recently, we developed a hydrothermal hydrogen gas production method based on the oxidation of zerovalent iron and performed under mild conditions (temperature of 160 °C). This synthesis method produces hydrogen gas with a high purity (>99 mol%) and a significant yield (approximately 80 mol%). These experimental results suggested that the optimal hydrothermal reaction conditions for the production of hydrogen gas and the conversion of carbon dioxide, are strongly different in case of applying zerovalent iron as the reducing agent. Therefore, this paper studies the potential of a two-step approach to enhance the carbon conversion yields. The first step is the production of hydrogen gas via the developed method at 160 °C. The second step is the conversion of carbon dioxide at higher temperatures (250-350 °C). This study reveals that the solubility of hydrogen gas into the aqueous solution is a key parameter in order to achieve a high amount of carbon conversion. Therefore, a high temperature, the degree of filling and the initial hydrogen gas amount are necessary to successfully perform the carbon dioxide conversion step with high carbon conversion yields. Applying these insights have led to the experimental observation that via a two-step approach the conversion of potassium hydrogen carbonate into potassium formate can be successfully performed with higher carbon conversion yields, up to 77.9 wt%, and a selectivity of at least 81% when applying a reaction temperature of 280 °C for 24 hours, a degree of filling with water of 50 vol% and an initial amount of hydrogen gas of 100 mmol.

Dye Oxidation in Aqueous Phase by Using Zero-Valent Iron as Persulfate Activator: Kinetic Model and Effect of Particle Size

Persulfate (PS) activated by zero-valent iron (ZVI) to generate sulfate radicals (SO4•–) was employed in the oxidation of Orange G (OG), an azo dye commonly found in textile wastewaters. Acidic corrosion and direct reaction with persulfate were considered for the oxidation of ZVI to Fe(II), both reactions taking place at the ZVI surface. Effects of pH (1–3.5), PS concentration (0 and 1 mM), and ZVI particle radius (0.030–0.095 cm) were studied. OG (0.1 mM) oxidation was carried out with a 0.5 L batch reactor at 20 °C. Using ZVI as activator, Fe(II) is slowly released to the media through a fluid–solid corrosion of ZVI. Therefore, the unproductive consumption of sulfate radicals by Fe(II) can be controlled by changing the particle diameter. A kinetic model capable of describing the evolution of pollutant, oxidant, and iron concentrations (at the different oxidation stages) as well as the mineralization was proposed and validated. To do this, a set of reactions counting for the iron valence change, the sulf...

Synergistic degradation of deca-BDE by an enrichment culture and zero-valent iron

Debromination of decabromodiphenyl ether (deca-BDE) by microbe and by zero-valent iron (ZVI) has been reported previously. However, no study has indicated the presence of microorganisms and their effect on ZVI-mediated reduction of deca-BDE. Synergistic degradation of deca-BDE by an enrichment culture and ZVI was studied. It was found that synergistic effects enhanced the debromination of deca-BDE as well as promoting the reduction of lower brominated products. ZVI stimulated microbial debromination by serving as an electron donor. Correlation analysis also confirmed that ZVI was capable of enhancing microbial population in the debromination of deca-BDE. Conversely, the enrichment culture produced acid which maintained pH stability and stimulated the oxidation of ZVI. The enrichment culture supplied its energy requirements by the oxidation of ZVI and concomitant reduction of deca-BDE, but incapable of growth and reduction of BDE-209 without ZVI and vice versa. Compared to the initial culture, the microbial community of the enrichment culture became dominated by several bacterial genera based on the results of 16S rRNA-gene pyrosequencing.

Effect of NaCl on Cr(VI) Reduction by Granular Zero Valent Iron (ZVI) in Aqueous Solutions

This study examined the effect of NaCl on the removal of Cr(VI) by ZVI in aqueous solutions and proposes a potential mechanism of Cr(VI) removal by ZVI in aqueous solutions with NaCl. A series of batch tests was conducted on ZVI using 100mg/L Cr(VI) solutions at an initial pH of 3 at various NaCl concentrations. The NaCl in aqueous solutions improved the removal efficiency for Cr(VI) by ZVI. Fe(III)­Cr(III) (oxy)hydroxides were precipitated both on the ZVI surface and in the solution via the reduction reactions of Cr(VI) to Cr(III) in the presence of NaCl. The increase in the Cr(VI) removal efficiency in the solutions with NaCl was attributed to the Cl ¹ ions, which accumulate at the anodic sites of ZVI, thereby enhancing ZVI oxidation and colloidal particle formation. In the NaCl solutions, small grains were initially precipitated on the ZVI surface, via relatively fast reactions. The subsequent slowing of these reactions resulted in the precipitation of large grains on the ZVI surface and colloidal particles in the solutions. [doi:10.2320/matertrans.M2011375]

Enhanced degradation of 4-nitrophenol by microwave assisted Fe/EDTA process

A microwave assisted zero-valent iron oxidation process was studied in order to investigate the synergetic effects of MW irradiation on Fe/EDTA system (Fe/EDTA/MW) treated 4-nitrophenol (4-NP) from aqueous solution. The results indicated that the thermal effect of microwave improved the removal effect of 4-NP and TOC through raising the temperature of the system, as well as the non-thermal effect generated by the interaction between the microwave and the Fe resulting in an increase in the hydrophobic character of Fe surface. During the degradation of 4-NP in Fe/EDTA/MW system, the optimum value for MW power, Fe, EDTA dosage was 400 W, 2 g and 0.4 mM, respectively. The possible pathway for degrading the 4-NP was proposed based on GC/MS and HPLC analysis of the degradation intermediates. The concentration change course of the main bio-refractory by-products, the aminophenol formed in the degradation of 4-NP suggested a more efficient degradation and mineralization in Fe/EDTA/MW system. Finally, BOD 5/COD Cr of the solution increased from 0.237 to 0.635 after reaction for 18 min, indicating that the biodegradability of wastewater was greatly improved by Fe/EDTA/MW system and would benefit to further treatment by biochemical methods.

Effect of operating conditions on iron corrosion rates in zero-valent iron systems for arsenic removal

Owing to newly established water quality standards, the use of the zero-valent iron (ZVI) method for arsenic removal is gaining attention. The spontaneous chemical oxidation of ZVI by dissolved oxygen, a complex process involving a variety of metastable ferrous–ferric intermediate species, was studied in short-term batch experiments using two different commercially available ZVI materials. Differences in corrosion rates may be attributed to the different specific reactivity of these materials. The effects of pH, ZVI loading, initial conductivity and dissolved oxygen concentration on both Fe(II) and Fe(III) kinetic profiles were investigated. ZVI corrosion rates in the presence of As(III) and As(V) were also studied. Depending on the pH, the concentrations of Fe(II) and Fe(III) are significantly influenced by the presence of As(III) and As(V). Our results may be important from a technological point of view, since it is well known that iron corrosion rates govern the generation of sites for arsenic removal.

Pressurized CO2/zero valent iron system for nitrate removal

A fluidized zero valent iron (ZVI) reactor pressurized by CO(2) gas for controlling pH was employed for nitrate reduction. The proposed CO(2) pressurized system potentially has advantages of using less CO(2) gas and reaching equilibrium pH faster than CO(2)-bubbled system. However, due to weak acid nature of carbonic acid, system pH gradually increased with increasing oxidation of ZVI and reduction of nitrate. As pH increased with progress of reaction, nitrate removal rate decreased continuously. The results indicate that nitrate removal efficiency increases with increasing initial ZVI dosage but reaches plateau at ZVI doses of higher than 8.25gl(-1), and initial nitrate concentration up to 100mg l(-1) as N has minimal impact on the removal efficiency. Unlike the fluidized system with pH control by strong acid reported in our pervious study, near 100% of nitrogen recovery was observed in the current process, indicating that nitrate reduction by ZVI with different pH controlled mechanisms will have different reaction routes.

Mechanistic evidence and efficiency of the Cr(VI) reduction in water by different sources of zerovalent irons

The objective of this research was to assess the mechanism and effectiveness of the zerovalent iron (ZVI) to remediate the Cr(VI) contaminated water. The mechanism of Cr(VI) reduction by ZVI was evaluated by characterising surface properties and chemical compositions of Fe and Cr products using SEM-EDS, XRD and XPS analyses. The effectiveness of ZVI in Cr(VI) reduction was assessed by the luminescent bacteria (Photobacterium Phosphoreum). The Cr(VI) was reduced to Cr(III), when the reactive Fe(o) was oxidised to Fe(II, III), showing the presence of Fe2O3, (Fe-Cr)2O3 and FeOOH. The SEM-EDS analysis showed that ZVI with a higher reducing capacity was more subject to changes of surface and morphological properties due to ionisation of ZVI. The Cr and Fe in precipitates subsisted exclusively in the Cr(III) or Fe(III) states with the respective forms of Cr(OH)3 or Cr2O3 and FeOOH or Fe2O3. Electrons produced from ZVI oxidation reduced Cr(VI) to Cr(III), thus resultantly Cr(III) precipitated or co-precipitated with Fe(III) to form Fe(III)-Cr(III) hydroxide or Fe(III)-Cr(III) oxyhydroxide. Toxicity of water reacted with ZVI was significantly lower than that of the untreated water.

Remediation of TCE-contaminated groundwater using zero valent iron and direct current: experimental results and electron competition model

The objectives of this study are to design an optimal electro-enhanced permeable reactive barrier (E2PRB) system for the remediation of trichloroethylene (TCE)-contaminated water using zero valent iron (ZVI) and direct current (DC) and to investigate the mechanisms responsible for TCE degradation in different ZVI-DC configurations. A series of column experiments was conducted to evaluate the effect of different arrangements of electrodes and ZVI barriers in the column on the TCE removal capacity (RC). In twelve different combinations of ZVI and/or DC application in the test columns, the rate of reductive dechlorination of TCE was improved up to six times with simultaneous application of ZVI and DC compared to that using ZVI only. The most effective arrangement of electrode and ZVI for TCE removal was the column set with ZVI and a cathode installed at the down gradient. Based on the electrokinetic study for the column systems with only DC input, single acid front movement could explain different RCs. An enhanced dechlorination rate of TCE using E2PRB systems, compared to a conventional PRB system, was observed, and is considered to be attributed to more electron sources: (1) external DC, (2) electrolysis of water, (3) oxidation of ZVI, (4) oxidation of dissolved Fe2+, (5) oxidation of molecular hydrogen at the cathode, and (6) oxidation of Fe2+ in mineral precipitates. Each of these electron sources was evaluated for their potential influencing the TCE RC through the electron competition model and energy consumption. A strong correlation between the quantity of electrons generated, RC, and the energy-effectiveness was found.

PH dependence of carbon tetrachloride reductive dechlorination by magnetite.

Magnetite is precipitated by dissimilatory iron-reducing bacteria or forms through corrosion of zero-valent iron (ZVI) in permeable reactive barriers. Reduction of carbon tetrachloride (CCl4) by synthetic magnetite was examined in batch reactors to evaluate the pH dependence of the reaction rates and product distributions. This work presents the first data where magnetite promotes CCl4 dechlorination independent of added sorbed Fe(II) or coexisting minerals that maintained Fe2+ above the magnetite solubility limit. In this system, reaction rate constants increase with increasing pH values between 6 and 10. The pH dependence is explained by acid-base equilibrium between two surface sites, where the more deprotonated exhibits greater dechlorination reactivity. The distribution of reaction products was also found to depend on pH. The primary reaction product is carbon monoxide (CO) followed by chloroform (CHCl3). CHCl3 production is at a minimum at pH 6 but increases through pH 10. Formation rate constants for both products increase with increasing pH, but the values for CHCl3 increase at a much faster rate. A hypothesis is proposed that relates the CHCl3 rate enhancement to the reduced capacity of deprotonated surface sites to stabilize the trichlorocarbanion transition-state complex. These data form a basis to assess the natural attenuation capacity of magnetite formed under iron reducing conditions. Application of this information to permeable barrier technology suggests that, in the long term, oxidation of ZVI to magnetite may be accompanied by a shift toward more benign reaction products as well as a 2 order of magnitude decrease in reaction rate constants.

Dechlorination of PCE in the presence of Fe 0 enhanced by a mixed culture containing two Dehalococcoides strains

A mixed culture capable of supplying its energy requirements by the oxidation of zero-valent iron (Fe 0) and concomitant reduction of chlorinated ethenes was established. The culture contained Dehalococcoides species as determined by polymerase chain reaction (PCR) with genus specific primers. The use of a newly designed ARDRA procedure and subsequent sequencing revealed the presence of two Dehalococcoides strains, one closely related to Dehalococcoides ethenogenes strain 195, a bacterium respiring with chlorinated ethenes, and one closely related to strain CBDB1 a chlorobenzene and dioxin dehalogenating anaerobe. The mixed culture was used to study dechlorination of tetrachloroethene (PCE) to ethene in the presence of Fe 0. Whereas abiotic transformation of PCE by Fe 0 led to incomplete dechlorination, the mixed culture mediated fast and complete dechlorination of PCE to ethene with Fe 0 as electron donor. Compared to cultures with hydrogen added as electron donor, cultures with Fe 0 as electron donor showed the same or higher rates of PCE dechlorination. Growth of the Dehalococcoides strains in the mixed culture is linked to the presence of Fe 0 as electron donor and PCE as electron acceptor demonstrating that Dehalococcoides spp. play a pivotal role in the dechlorination of chlorinated ethenes in Fe 0 systems.