Ferrous Oxidation Research Articles

Experimental Periodontal Disease Triggers Coronary Endothelial Dysfunction in Middle-Aged Rats: Preventive Effect of a Prebiotic β-Glucan.

This study was aimed to verify the hypothesis that periodontal disease contributes to endothelial dysfunction in the coronary arteries of middle-aged rats. Besides we evaluated the effects of a prebiotic (β-glucan isolated from Saccharomyces cerevisiae) in preventing vascular dysfunction. The sample comprised young (sham and induced to periodontal disease) and middle-aged rats (sham, periodontal disease, sham-treated and periodontal disease-treated), at 12 and 57 weeks, respectively. The treated-groups received daily doses of β-glucan (50 mg/kg) orally (gavage) for 4 weeks, and periodontal disease was induced in the last 2 weeks by ligature. A myograph system assessed vascular reactivity. The expression of endothelial nitric oxide synthase (eNOS), cyclooxygenase 1 (COX-1), COX-2, p47phox, gp91phox, NF-KB p65, p53, p21, and p16 was quantified by western blotting. Serum hydroperoxide production was measured by the ferrous oxidation-xylenol orange (FOX-2) assay method. Interleukin-1 beta (IL-1β), IL-10, and tumor necrosis factor-alpha (TNF-α) levels were evaluated by spectroscopic ultraviolet-visible analysis. Periodontal disease in middle-aged rats was associated with reduced acetylcholine-induced relaxations of coronary artery rings affecting the endothelium-dependent hyperpolarization- and the nitric oxide-mediated relaxations. The endothelial dysfunction was related to eNOS downregulation, pronounced impairment of the EDH-mediated relaxation, increased IL-1β and TNF-α proinflammatory cytokines, and also upregulation of NADPH oxidase and COXs, starting accumulate aging markers such as p53/p21 and the p16. Treatment with β-glucan effectively reduced bone loss in periodontal disease and delayed endothelial dysfunction in the coronary artery. Our data show that yeast β-glucan ingestion prevented oxidative stress and synthesis of proinflammatory marker and prevented eNOS reduction induced by periodontal disease in middle-aged rats. These results suggest that β-glucan has a beneficial effect on the coronary vascular bed.

RNA transcript response by an Acidithiobacillus spp. mixed culture reveals adaptations to growth on arsenopyrite.

Biooxidation of gold-bearing refractory mineral ores such as arsenopyrite (FeAsS) in stirred tanks produces solutions containing highly toxic arsenic concentrations. In this study, ferrous iron and inorganic sulfur-oxidizing Acidithiobacillus strain IBUN Ppt12 most similar to Acidithiobacillus ferrianus and inorganic sulfur compound oxidizing Acidithiobacillus sp. IBUNS3 were grown in co-culture during biooxidation of refractory FeAsS. Total RNA was extracted and sequenced from the planktonic cells to reveal genes with different transcript counts involved in the response to FeAsS containing medium. The co-culture's response to arsenic release during biooxidation included the ars operon genes that were independently regulated according to the arsenopyrite concentration. Additionally, increased mRNA transcript counts were identified for transmembrane ion transport proteins, stress response mechanisms, accumulation of inorganic polyphosphates, urea catabolic processes, and tryptophan biosynthesis. Acidithiobacillus spp. RNA transcripts also included those encoding the Rus and PetI proteins involved in ferrous iron oxidation and gene clusters annotated as encoding inorganic sulfur compound metabolism enzymes. Finally, mRNA counts of genes related to DNA methylation, management of oxidative stress, chemotaxis, and motility during biooxidation were decreased compared to cells growing without mineral. The results provide insights into the adaptation of Acidithiobacillus spp. to growth during biooxidation of arsenic-bearing sulfides.

Identification and characterization of a metal-resistant Acidithiobacillus ferrooxidans as important potential application for bioleaching

Bioleaching is a common and eco-friendly method for the metals mobilization from mines, contaminated soils and wastes and it can be used in metal extraction and bioremediation. Due to the fact that these processes are considered as metabolism-dependent processes, isolation and identifying of the strains with high resistance features in responsible bacteria are one of the most important steps to have. In present study, an Iranian new isolate of iron-oxidizing bacteria was characterized. The phylogenetic analysis and 16S rRNA gene sequence of strain ZT-94 indicated that this strain is related to Acidithiobacillus ferrooxidans. It is investigated that the ferrous iron oxidation was increased dramatically in the early hours of bacterial growth and the ferrous iron (Fe2+) was completely oxidized at 30 h. According to the results, strain ZT-94 had the high tolerance capability to U, Ba, Al and Se. Iron oxidation by strain ZT-94 was inhibited by the addition of 312.5 mg/L Se and 70 mg/L Te but concentrations above 5000 mg/L of Ba and 2000 mg/L Al had no inhibitory effect on bacterial growth. In addition, strain ZT-94 was able to grow in the pH range of 1–4, temperatures at 25–35 °C. Results showed no inhibitory effects on bacterial growth rate in presence of 0.1 w/v organic compounds like fructose and glucose but a delayed growth was detected in presence of yeast extract in comparison with the others. The results showed that strain ZT-94 had high environmental adaptability and can be introduced as a suitable and valuable candidate for research in the bioleaching and bioremediation processes.

Addition of wheat straw to acid sulfate soils with different clay contents reduces acidification in two consecutive submerged-moist cycles

Acid sulfate soils (ASS) are wide-spread in wetlands and experience distinct biogeochemical changes during submerged and moist periods. During submerged periods, under reducing conditions, sulfate reduction can result in a pH increase whereas moist periods induce sulfide and ferrous iron oxidation, leading to acidification which can pose a threat to the environment. A laboratory incubation experiment was carried out to determine the effect of organic matter (OM) amendment on pH and redox potential over two successive submerged-moist cycles in different types of ASS (Sulfuric, Hypersulfidic and two Hyposulfidic soils). The four soils also differed in clay content (10, 15, 23, 38% referred to as C10, C15, C23 and C38) and were collected in a wetland at Banrock Station, South Australia. The experiment was conducted over 24 weeks with each submerged and each moist period lasting 6 weeks. The soils were unamended or amended with 10 g C kg−1 finely ground wheat straw. During the submerged periods, the soils were maintained under a layer of water, in the moist periods they were kept at 100% of water holding capacity. The soil pH increased in both submerged periods, particularly in amended soils with low clay content (C10 and C15). Changes in pH during submerged and moist periods were greater in soils with low clay content (C10, C15) than those with high clay content (C23, C38). The effect of wheat straw addition on pH at the end of submerged and moist periods did not differ between the two submerged-moist periods, with a higher pH in amended than unamended soils. In submerged periods, the redox potential (Eh) decreased more strongly in amended soils than in unamended soils. It was 100–200 mV from week 2 onwards in amended soils whereas the Eh was 300 to 400 mV higher without amendment except in C38 where it was 100–200 mV in both amendment treatments. In the moist periods, the pH decreased more strongly in amended than in unamended soils, particularly in C10 and C15 but remained higher than in unamended treatments. This study showed that wheat straw addition maintains its ameliorative effect on soil pH for at least two submerged-moist cycles, but the ameliorative pH effect depends on clay content, being greater in soils with low clay content.

Biochar-Assisted Iron-Mediated Water Electrolysis Process for Hydrogen Production.

The biochar-assisted water electrolysis process for hydrogen gas production is reported. The H2 generation is performed in a divided electrolysis cell in which the hydrogen evolution reaction occurs on a cathode and ferrous iron oxidation on an anode. Electrochemically produced Fe(III) species are reduced back to ferrous form in a reaction with biochar concentrated in a packed-bed column through which an acidic anolyte (FeCl3) solution is continuously recirculated. During the operation of the proposed process with commercial charcoal, the oxidation of carbon resulted in an accumulation of oxygen-containing groups on the carbon surface that leads to charcoal deactivation. Thermal treatment of the charcoal at 250, 350, and 450 °C in a nitrogen atmosphere resulted in reactivation of carbon, and the best results (≈80% reactivation) were achieved after 3 h of treatment at 450 °C. Nine successful cycles of electrolysis-charcoal regeneration were performed in this study. A ≈98% current efficiency for hydrogen production was achieved at a current density of 50 mA/cm2. Much higher current densities can be obtained using the proposed technique as the anodic process of ferrous iron oxidation is decoupled from the carbon oxidation process. The CO2 production rate achieved in this study was up to 98% of a stoichiometric value proposed for the iron-mediated carbon-assisted water electrolysis process.

Leachability of metals from waste incineration residues by iron- and sulfur-oxidizing bacteria

Hazardous waste disposal via incineration generates a substantial amount of ashes and slags which pose an environmental risk due to their toxicity. Currently, these residues are deposited in landfills with loss of potentially recyclable raw material. In this study, the use of acidophilic bioleaching bacteria (Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans) as an environmentally friendly, efficient strategy for the recovery of valuable metals from incineration residues was investigated. Zinc, Cobalt, Copper, and Manganese from three different incineration residues were bio-extracted up to 100% using A. ferrooxidans under ferrous iron oxidation. The other metals showed lower leaching efficiencies based on the type of culture used. Sulfur-oxidizing cultures A. ferrooxidans and A. thiooxidans, containing sulfur as the sole substrate, expressed a significantly lower leaching efficiency (up to 50%). According to ICP-MS, ashes and slags contained Fe, Zn, Cu, Mn, Cr, Cd, and Ni in economically attractive concentrations between 0.2 and 75 mg g−1. Compared to conventional hydrometallurgical and pyrometallurgical processes, our biological approach provides many advantages such as: the use of a limited amount of used strong acids (H2SO4 or HCl), recycling operations at lower temperatures (~30 °C) and no emission of toxic gases during combustion (i.e., dioxins and furans).

Ferronostics: Measuring Tumoral Ferrous Iron with PET to Predict Sensitivity to Iron-Targeted Cancer Therapies.

Although cancer has been known for decades to harbor an insatiable appetite for iron, only recently has the chemistry emerged to exploit this altered state therapeutically, by targeting the expanded cytosolic labile iron pool (LIP) of the cancer cell. The state of the art includes therapies that react with the LIP to produce cytotoxic radical species (in some cases also releasing drug payloads) and molecules that exacerbate LIP-induced oxidative stress to trigger ferroptosis. Effectively implementing LIP-targeted therapies in patients will require biomarkers to identify those tumors with the most elevated LIP and thus most likely to succumb to LIP-targeted interventions. Toward this goal, we tested whether tumor uptake of the novel LIP-sensing radiotracer 18F-TRX aligns with tumor sensitivity to LIP-targeted therapies. Methods:18F-TRX uptake was assessed invivo among 10 subcutaneous and orthotopic human xenograft models. Glioma and renal cell carcinoma were prioritized because these tumors have the highest relative expression levels of STEAP3, the oxidoreductase that reduces ferric iron to the ferrous oxidation state, in the Broad Institute Cancer Cell Line Encyclopedia. The antitumor effects of the LIP-activated prodrug TRX-CBI, which releases the DNA alkylator CBI, were compared in mice bearing U251 or PC3 xenografts, tumors with high and intermediate levels of 18F-TRX uptake, respectively. Results:18F-TRX showed a wide range of tumor accumulation. An antitumor assessment study showed that the growth of U251 xenografts, the model with the highest 18F-TRX uptake, was potently inhibited by TRX-CBI. Moreover, the antitumor effects against U251 were significantly greater than those observed for PC3 tumors, consistent with the relative 18F-TRX-determined LIP levels in tumors before therapy. Lastly, a dosimetry study showed that the estimated effective human doses for adult male and female mice were comparable to those of other 18F-based imaging probes. Conclusion: We report the first evidence-to our knowledge-that tumor sensitivity to an LIP-targeted therapy can be predicted with a molecular imaging tool. More generally, these data bring a new dimension to the nuclear theranostic model by showing a requirement for imaging to quantify, in situ, the concentration of a metastable bioanalyte toward predicting tumor drug sensitivity.

Construction of autotrophic nitrogen removal system based on zero-valent iron (ZVI): performance and mechanism.

In this study, the performance and mechanism of nitrogen removal in sequencing batch reactors (SBRs) with and without zero-valent iron (ZVI) was investigated. The results showed that ZVI had a capacity to promote NH4+-N conversion, NO2--N accumulation and total inorganic nitrogen (TIN) removal, with the TIN removal rate being increased by 29.45%. The ZVI also had a significant impact on microbial community structure by means of high-throughput pyrosequencing, increasing the enrichment of Anammox (anaerobic ammonium oxidation) bacteria Candidatus Brocadia and Feammox (anaerobic ferric ammonium oxidation) bacteria Ignavibacterium. With ZVI addition, the main pathway of nitrogen removal was changed from nitrification-heterotrophic denitrification to Anammox and Feammox.

Zero Liquid Discharge (ZLD) Industrial Wastewater Treatment Systems as Sustainable Development Basic Ecological Components

The problems in processing the acid ferrous-containing rinsing water and spent pickling solutions are considered. The first-ever in metallurgy zero liquid discharge (ZLD) industrial wastewater treatment systems of a transformer cold rolling plant at the Verkh-Isetsky steelworks in Sverdlovsk (now — LLC VIZ Steel is a part of Novolipetsk Steel Group of Companies) is described. The experience of the VIZ Steel, particularly in relation to industrial wastewater treatment and sludge processing, is useful for designing ZLD industrial wastewater treatment systems of metallurgical, machine-building and metalworking enterprises. The recommendations for organizing the ZLD industrial wastewater treatment systems in the pickling plants with the repeated use of the treated rinsing water and processing the spent pickling solutions and the sludges are presented. For practical calculations of clarifiers the empirical formulas are offered. Process flow diagram of acid ferrous-containing rinsing water treatment is suggested. Acid ferrous-containing rinsing water treatment includes the following processes: rinsing water neutralization to pH 9-10,5 by 5 % calcium hydroxide and partial ferrous oxidation by air; addition of anionic flocculant and active gypsum priming to the neutralized rinsing water; settling of rinsing water conditioned by reagents in clarifiers; treatment of clarified water on deep bed sand filters; reclaimed water treatment.

Nano-decocted ferrous polysulfide coordinates ferroptosis-like death in bacteria for anti-infection therapy

Abstract Antibacterial nanomaterials provide promising alternative strategies to combat the global challenge of bacterial infection due to deteriorating resistance. However, few have been applied for intracellular bacteria killing or in vivo therapy due to potential cytotoxicity and poor biocompatibility. Here we present a strategy to generate formula suitable for in vivo anti-infective therapy by decocting antibacterial nanomaterial. An aqueous formula containing ferrous iron and polysulfide (Fe(II)Snaq) is prepared by a decoction procedure using nano-iron sulfide (nFeS) as raw substance. Theoretical calculation indicated that replacement of a sulfur atom by an oxygen atom occurred, resulting in polysulfide release and iron dissolution. The Fe(II)Snaq decocted from nFeS induced bacterial death with ferroptosis-like hallmarks, including iron enrichment, lipid peroxidation, and glutathione (GSH) depletion. The antibacterial action of Fe(II)Snaq was dependent on ferrous iron, which could be inhibited by iron chelators, ferroptosis inhibitors, and GSH, while the polysulfide prevented ferrous iron oxidation and counteracted GSH. Furthermore, Fe(II)Snaq not only killed up to 99 % of planktonic bacteria within 5 min, but also suppressed up to 90 % of intracellular Staphylococcus aureus without triggering cytotoxicity to host cell. Administration of Fe(II)Snaq achieved equivalent therapeutic effect to vancomycin for infectious pneumonia treatment and significantly prolonged the survival period of septic mice. These results indicate that aqueous ferrous polysulfide can induce ferroptosis- like death in bacteria and may be formulated as an antibacterial alternative for anti-infection therapy.

The influence of native soil organic matter and minerals on ferrous iron oxidation

Fe(II) oxidation by O2 is an important process generating Fe (oxyhydr)oxides, which play sorptive, structural and electron-transfer roles in soils. Here we explored how native minerals and organic matter (OM) affect the rate of Fe(II) oxidation and resulting de novo Fe(III) minerals in soil slurries. A topsoil was collected from the Luquillo Experimental Forest, and a topsoil and subsoil were collected from a cultivated site at the Calhoun Experimental Forest. We oxidized 57Fe(II) in these soils either untreated or with OM and/or Fe (oxyhydr)oxides removed. We measured Fe oxidation kinetics by tracking the loss of Fe(II) and characterized the de novo Fe(III) solids using 57Fe Mössbauer spectroscopy. We find that OM retarded Fe(II) oxidation, while pre-existing Fe (oxyhydr)oxides played a significant role in catalyzing Fe(II) oxidation. The non-extractable (residual) soil minerals (i.e. phyllosilicates and quartz) after removing Fe (oxyhydr)oxides, had only a minor effect on oxidation rates. In the topsoils, OM resulted in lower-crystallinity Fe(III) minerals, including nanogoethite and highly-disordered Fe phases, relative to soils with OM-removed. Goethite of varying crystallinity was promoted by the pre-existing Fe (oxyhydr)oxides in all soils, in contrast to homogenous oxidation treatments in which lepidocrocite was formed. Fe(II) oxidation in the Calhoun subsoil, which was enriched in native crystalline Fe phases and depleted in OM, resulted in large-particle goethite with the highest crystallinity of all treatments. Crystalline hematite was also formed in the Calhoun subsoil most likely due to a templating effect of pre-existing hematite. These findings suggest that the nature of de novo formed Fe minerals in soils and sediments may depend strongly on resident existing soil OM and Fe phases. This study extends similar results from previous model mineral and organic experiments to whole, complex soils and thus constitutes a significant step forward in understanding Fe transformation in natural environments.

Effects of the iron oxidation and precipitation processes on the arsenate sorption and coprecipitation

The main aim of this study was to assess the effects of ferrous iron oxidation, hydrolysis and precipitation of the ferric iron on the mechanisms of arsenate removal from acid mine drainage. The study was realized at the pH range 2,0 – 6,5. H2O2 was the oxidant used in the chemical test. A mixed culture of mesophilic iron-oxidizing chemolithotrophic bacteria (Acidithiobacillus ferrooxidans, Leptospirillum ferroxidans) carried out the ferrous oxidation in the biological test. NaOH was used as an alkalizing agent which triggered the ferric iron hydrolysis and precipitation. The results showed that the total content of retained arsenic by ferric iron hydrous oxides and its speciation as geochemical fractions depended on the iron and phosphate concentrations in acid solution. The results showed that phosphate concentration lower than 6 mg/ L limited the ferrous iron oxidation rate. At the tested experimental conditions, arsenic sorption by formed ferric iron hydrous oxides was the main mechanism for its removal from acid mine drainage, as the ratio between iron and phosphate determined the proportions between the geochemical fractions of scavenged arsenic.

Bioleaching of Indonesian Galena Concentrate With an Iron- and Sulfur-Oxidizing Mixotrophic Bacterium at Room Temperature.

Biohydrometallurgy is believed to be a promising future study field for the recovery of lead (Pb) from ores/concentrates since the pyrometallurgical/hydrometallurgical processes have been largely applied to recover Pb to date, which operates at high temperature and generates volatile Pb matters that are hazardous and carcinogenic to human health. Hence, the main purpose of this study was to investigate the biohydrometallurgical extraction of Pb from the Indonesian galena concentrate through bioleaching using an iron- and sulfur-oxidizing mixotrophic bacterium (identified as Citrobacter sp.). The bioleaching experiments were conducted in shake flasks containing the modified LB broth medium supplemented with galena concentrate with a particle size of d80 = 75 μm at room temperature. Both semi-direct and direct bioleaching methods were employed in this study. The bacterium was able to extract lead (Pb) from galena concentrate with high selectivity to Cu and Zn (0.99 and 0.86, respectively). The highest extraction level of 90 g lead dissolved/kg galena concentrate was achieved using direct bioleaching method at bioleaching conditions of 2% w/v pulp density, 5 g/L FeCl3, 50 g/L NaCl, 20 g/L molasses and a rotation speed of 180 rpm at room temperature (25°C). The addition of FeCl3, NaCl, and molasses increased the lead leaching efficiencies, which were also evidenced by the FTIR, XRD, and SEM-EDS analyses. From industrial and commercial standpoints, the selective bioleaching represented in this study may be beneficial to the development of lead leaching from sulfide minerals, since insoluble anglesite (PbSO4) precipitates are formed during ferric sulfate oxidation, thus making the recovery of lead through bioleaching unpractical.

IRONing out stress problems in crops: a homeostatic perspective.

Iron (Fe) is essential for plant growth and therefore plays a key role in influencing crop productivity worldwide. Apart from its central role in chlorophyll biosynthesis and oxidative phosphorylation (electron transfer), it is an important constituent of many enzymes involved in primary metabolism. Fe has different accessibilities to the roots in the rhizosphere depending upon whether it is ferrous (soluble) or ferric (insoluble) oxidation stages, which in turn, determine two kinds of Fe uptake strategies employed by the plants. The reduction strategy is exclusively found in non-graminaceous plants wherein the ferrous Fe2+ is absorbed and translocated from the soil through specialized transporters. In contrast, the chelation strategy (widespread in graminaceous plants) relies on the formation of Fe (III)-chelate complex as the necessary requirement of Fe uptake. Once inside the cell, Fe is translocated, compartmentalized and stored through a common set of physiological processes involving many transporters and enzymes whose functions are controlled by underlying genetic components, so that a fine balance of Fe homeostasis is maintained. Recently, molecular and mechanistic aspects of the process involving the role of transcription factors, signaling components, and cis-acting elements have been obtained, which has enabled a much better understanding of its ecophysiology. This mini-review summarizes recent developments in our understanding of Fe transport in higher plants with particular emphasis on crops in the context of major agronomically important abiotic stresses. It also highlights outstanding questions on the regulation of Fe homeostasis and lists potentially useful genes/regulatory pathways that may be useful for subsequent crop improvement under the stresses discussed through either conventional or transgenic approaches.

Investigation of microbiologically influenced corrosion of 304 stainless steel by aerobic thermoacidophilic archaeon Metallosphaera cuprina

In this study, the influence of thermoacidophilic archaeon Metallosphaera cuprina on the corrosion of 304 stainless steel was investigated. 304 stainless steel in M. cuprina-inoculated culture medium exhibited more marked pitting corrosion behavior than that seen in sterile culture medium. After 14 days, the average pit depth under M. cuprina biofilms was nearly twice as great as that in sterile culture medium. Electrochemical measurements also showed that 304 stainless steel had lower charge transfer resistance and smaller pitting potential after 14 days of exposure in inoculated culture medium. The ferrous ion oxidation ability of M. cuprina biofilms can cause a change in the composition of passive films and accelerate the anodic dissolution of the steel substrate, to promote the pitting corrosion process at 304 stainless steel.

Nutrient Removal Process and Cathodic Microbial Community Composition in Integrated Vertical-Flow Constructed Wetland - Microbial Fuel Cells Filled With Different Substrates.

An integrated vertical-flow constructed wetland-microbial fuel cell system (CW-MFC), consisting of an up-flow chamber and a down-flow chamber, was constructed to treat synthetic sewage wastewater. The performance of CW-MFCs filled with different substrates [i.e., ceramsite (CM-A), quartz (CM-B), and zeolite (CM-C) granules] under various hydraulic retention times (HRTs, 7.6, 4.0, and 2.8 d) was evaluated. Efficient and stable nitrogen (N) and phosphorus (P) removals were observed in CM-A under different HRTs, while the voltage outputs of the CW-MFCs was greatly reduced as the HRTs decreased. With an HRT of 2.8 d, the ammonium (NH4+-N) and orthophosphate (PO43–-P) removal efficiencies in CM-A were as high as 93.8 and 99.6%, respectively. Bacterial community analysis indicates that the N removal in the cathode area of CM-A could potentially benefit from the appearance of nitrifying bacteria (e.g., Nitrosomonas and Nitrospira) and relatively high abundance of denitrifiers involved in simultaneous nitrification and denitrification (e.g., Hydrogenophaga, Zoogloea, and Dechloromonas) and denitrifying sulfide removal (e.g., Thauera). Additionally, the difference in N removal efficiency among the CW-MFCs could be partly explained by higher iron (Fe) content in milled ceramsite granules and higher abundance of denitrifiers with nitrate reduction and ferrous ions oxidation capabilities in CM-A compared with that in CM-B and CM-C. Efficient PO43–-P removal in CM-A was mainly ascribed to substrate adsorption and denitrifying phosphorus (P) removal. Concerning the substantial purification performance in CM-A, ceramsite granules could be used to improve the nutrient removal efficiency in integrated vertical-flow CW-MFC.

Spatiotemporal evolution of iron and sulfate concentrations during riverbank filtration: Field observations and reactive transport modeling

Riverbank filtration is a commonly-used technology that improves water quality by passing river water through aquifers. In this study, a riverbank filtration site in Busan, South Korea, was investigated to understand the spatiotemporal evolution of high iron and sulfate concentrations observed in the riverbank-filtered water. Discrepancies between the nonreactive transport results and field measurements suggest that iron-sulfate-related geochemical reactions play a major role in the spatiotemporal evolution of the hydrochemical properties. Pyrite oxidation was hypothesized to be the main process driving the release of iron and sulfate. To test this hypothesis, a reactive transport model was developed, that implemented pyrite oxidation as a kinetic process and subsequent ferrous iron oxidation and ferric iron precipitation as equilibrium processes. The model accurately captured the temporal evolution of sulfate; however, iron concentrations were underestimated. Sensitivity tests revealed that adjusting reaction constants significantly improved the prediction of iron concentrations. The results of this study suggest that pyrite oxidation can affect the hydrochemistry of riverbank-filtered water and highlight the potential limitations of using theoretical reaction constants in field modeling applications.

Simultaneous removal of nitrate and heavy metals in a continuous flow nitrate-dependent ferrous iron oxidation (NDFO) bioreactor

Nitrogen and heavy metals can co-occur in various industrial wastewaters such as coke-oven wastewater. Removal of these contaminants is important, but cost-efficient removal technology is limited. In this study, we examined the usefulness of nitrate-dependent ferrous iron oxidation (NDFO) for the simultaneous removal of nitrate and heavy metals (iron and zinc), by using an NDFO strain Pseudogulbenkiania sp. NH8B. Based on the batch culture assays, nitrate, Fe, and Zn were successfully removed from a basal medium as well as coke-oven wastewater containing 5 mM nitrate, 10 mM Fe(II), and 10 mg/L Zn. Zinc in the water was most likely co-precipitated with Fe(III) oxides produced during the NDFO reaction. Simultaneous removal of nitrate, Fe, and Zn was also achieved in a continuous-flow reactor fed with a basal medium containing 10 mM nitrate, 5 mM Fe(II), 4 mM acetate, and 10 mg/L Zn. However, when the reactor is fed with coke-oven wastewater supplemented with 10 mM nitrate, 5 mM Fe(II), 4 mM acetate, and 10 mg/L ZnCl2, the reactor performance significantly decreased, most likely due to the inhibition of bacterial growth by thiocyanate or organic contaminants present in the coke-oven wastewater. Use of mixed culture of NDFO bacteria and thiocyanate/organic-degrading denitrifiers should help improve the reactor performance.

Characterization of the nonheme iron center of cysteamine dioxygenase and its interaction with substrates

Cysteamine dioxygenase (ADO) has been reported to exhibit two distinct biological functions with a nonheme iron center. It catalyzes oxidation of both cysteamine in sulfur metabolism and N-terminal cysteine-containing proteins or peptides, such as regulator of G protein signaling 5 (RGS5). It thereby preserves oxygen homeostasis in a variety of physiological processes. However, little is known about its catalytic center and how it interacts with these two types of primary substrates in addition to O2 Here, using electron paramagnetic resonance (EPR), Mössbauer, and UV-visible spectroscopies, we explored the binding mode of cysteamine and RGS5 to human and mouse ADO proteins in their physiologically relevant ferrous form. This characterization revealed that in the presence of nitric oxide as a spin probe and oxygen surrogate, both the small molecule and the peptide substrates coordinate the iron center with their free thiols in a monodentate binding mode, in sharp contrast to binding behaviors observed in other thiol dioxygenases. We observed a substrate-bound B-type dinitrosyl iron center complex in ADO, suggesting the possibility of dioxygen binding to the iron ion in a side-on mode. Moreover, we observed substrate-mediated reduction of the iron center from ferric to the ferrous oxidation state. Subsequent MS analysis indicated corresponding disulfide formation of the substrates, suggesting that the presence of the substrate could reactivate ADO to defend against oxidative stress. The findings of this work contribute to the understanding of the substrate interaction in ADO and fill a gap in our knowledge of the substrate specificity of thiol dioxygenases.

Kinetics of Fe(II) Oxidation in a Verticle Tube Reactor: A Pilot Scale Study

ABSTRACT A vertical tubular reactor is used for the oxidative leaching process in the mineral processing industry, especially sphalerite. Oxygen could oxidise ferrous ions (Fe2+), and ferric ions (Fe3+) are generated as the principal oxidation agent in the reactor afterward. The partial pressure of oxygen is an instrumental parameter that could change according to reactor height. Despite the extensive studies on Fe(II) oxidation in the high-pressure reactor, there is no published work on its oxidation behaviour in the tubular reactor. Hence, the Fe3+ ion's oxidation in sulfuric acid solutions was investigated in atmospheric condition. The effects of the FeSO4, H2SO4, ZnSO4 concentration, and pressure in the reactor bottom were studied on the rate of ferrous oxidation at different temperatures, i.e. T = 70, 87 and 95°C. Sulfuric acid drops the kinetic of ferrous oxidation, whereas temperature and pressure of the reactor bottom increase this criterion. The apparent activation energy obtained was 67.22 kJ/mol, and an empirical equation for the oxidation rate of Fe2+ by air is as follows: