High Concentrations Of Ferrous Iron Research Articles

Growth in ever-increasing acidity condition enhanced the adaptation and bioleaching ability of Leptospirillum ferriphilum.

Low pH eliminated the jarosite accumulation and improved the interfacial reaction rate during the bioleaching process. However, high acidity tends to make environments less hospitable, even for organisms that live in extreme places, so a great challenge existed for bioleaching at low pH conditions. This study demonstrated that the adaption and bioleaching ability of Leptospirillum ferriphilum could be improved after the long-term adaptive evolution of the community under acidity conditions. It was found that the acidity-adapted strain showed robust ferrous iron oxidation activity in wider pH, high concentration of ferrous iron, and lower temperature. Although the enhancement for heavy metal tolerance was limited, the resistance for MgSO4, Na2SO4, and organic matter was stimulative. More importantly, both pyrite and printed circuit board bioleaching revealed the higher bioleaching ability of the acid-resistant strain. These adaptation and bioleaching details provided an available approach for the improvement of bioleaching techniques.

泥炭沼泽湿地关键元素地球化学特征及其对碳排放的影响机制

硫、铁是泥炭沼泽湿地（泥炭地）中重要的生源要素，其参与下的生物地球化学过程对泥炭地碳循环意义重大。选取德国中部两处典型的雨养型泥炭地高海拔样点（TBP）和低海拔样点（TSP），通过原位采集泥炭剖面孔隙水和可溶性气体等，研究了硫、铁元素等地球化学变化规律，结合DOC、甲烷（CH₄）和二氧化碳（CO₂）浓度分布，探讨其对泥炭地碳排放的影响。研究结果表明：（1） TBP中总还原无机硫（TRIS）浓度随深度先增后减，且上部0-87 cm平均浓度远高于87 cm深度以下，上部硫酸盐还原作用强烈。结合上部亚铁、硫化氢（H₂S）浓度分布，得知该范围内H₂S主要是通过微生物硫酸盐还原作用（BSR）生成，同时H₂S在孔隙水扩散过程中易与亚铁结合为硫化亚铁，进而生成稳定的黄铁矿，这一反应过程在约60 cm处减缓。（2） TBP、TSP两处采样点中DOC与亚铁、硫酸盐均有较强相关性，是由于地下水位的波动影响氧化还原程度以及微生物活性。两处采样点DOC均与亚铁呈显著正相关关系，表明铁氧化物在厌氧环境中被还原溶解产生亚铁，与其结合的有机碳被释放到溶液中从而导致DOC浓度的升高。TBP中DOC与硫酸盐呈显著负相关关系，表明硫酸盐作为电子受体被还原的过程中消耗酸度使pH值升高，增强了其中微生物的活性，DOC浓度由此增加。（3） CH₄与硫酸盐、TRIS浓度在剖面上均呈现相反变化趋势，表明硫酸盐输入的增加以及硫酸盐还原活动均会抑制CH₄生成。CO₂/CH₄均大于4，表明硫酸盐作为替代电子受体会使厌氧条件下碳矿化转向多CO₂和少CH₄生成。此外，亚铁对于CH₄生成一定程度上会起到低促高抑的效果，而对于CO₂的生成的影响较弱。表明硫酸盐对于CH₄和CO₂生成的影响高于亚铁。研究着重探究硫、铁等关键元素地下部生物地球化学过程对碳排放的影响机制，研究结果可为泥炭地碳排放核算提供理论支撑。;Sulfur and iron are important biogenic elements in peatland. Their participation in biogeochemical process is of great significance to carbon cycle of peatland. This study aimed to investigate impact of key elements on carbon emission of ombrotrophic peatlands, at top broad position (TBP) and top slope position (TSP) sites. The concentrations and distributions of carbon as DOC, GHG (particularly CH₄ and CO₂) were estimated through an in-situ collection of pore water and soluble gas in peat profile. Combined with the geochemical characteristics of sulfur (S) and iron (Fe) elements, their impacts on carbon emissions from peatland were discussed. The results showed that (1) the concentrations of total reduced inorganic sulfur (TRIS) in TBP first increased and then decreased with depth. The average concentration of the upper part was much higher than that of deeper part. The sulfate reduction in the upper part was strong. Combined with the concentrations and distributions of ferrous iron and hydrogen sulfide (H₂S) in the corresponding range, it is inferred that H₂S is mainly generated by bacterial sulfate reduction (BSR) in this range. Meanwhile, during the diffusion process of H₂S in pore water, it is easy to combine with ferrous iron into FeS. And then stable FeS₂ was formed. The reaction process slowed down at about 60 cm. (2) The DOC had a strong correlation with ferrous iron and sulfate in TBP and TSP because the fluctuation of groundwater level affects the redox degree and microbial activity. DOC had a significantly positive correlation with ferrous iron in the two sampling sites, indicating that iron oxide was reduced to dissolved ferrous iron in the anaerobic environment, and the organic carbon combined with ferrous oxide was released into pore water, resulting in the increase of DOC concentration. DOC had a negative correlation with sulfate in TBP, indicating that the acidity was consumed in the reduction process of sulfate as electron acceptor, and the pH value increased, which enhanced the activity of microorganism. Thus the concentration of DOC was increased. (3) The concentrations of CH₄ and sulfate, CH₄ and TRIS in the two sampling sites showed opposite trends with depth on the profile, indicating that increasing sulfate input and sulfate reduction would inhibit the formation of CH₄. The CO₂/CH₄ ratios of the two sampling sites were greater than 4, indicating that sulfate as an alternative electron acceptor may shift carbon mineralization under anaerobic conditions to more CO₂ and less CH₄ production. In addition, high concentration of ferrous iron can inhibit the formation of CH₄, and low concentration of ferrous iron can promote the formation of CH₄. But ferrous iron had a weak effect on the formation of CO₂. The results also show that sulfate concentration plays a dominative role over ferrous iron in CH₄ and CO₂ production. In this study, the effects of underground geochemical factors such as sulfur and iron on carbon emissions were also discussed, which provided more rigorous theoretical support for the correction of carbon emissions from peatlands.

Biosynthesis of vivianite from microbial extracellular electron transfer and environmental application

Vivianite (Fe3(PO4)2·8H2O) is a common hydrous ferrous phosphate mineral which often occurs in reductive conditions, especially anoxic non-sulfide environment containing high concentrations of ferrous iron (Fe2+) and orthophosphate (PO43−). Vivianite is an important product of dissimilatory iron reduction and a promising route for phosphorus recovery from wastewater. Its formation is closely related to the extracellular electron transfer (EET), a key mechanism for microbial respiration and a crucial explanation for the reduction of metal oxides in soil and sediments. Despite of the natural ubiquity, easy accessibility and attractive economic value, the application value of vivianite has not received much attention. This review introduces the characteristics, occurrence and biosynthesis of vivianite from microbial EET, and systematically analyzes the application value of vivianite in the environmental field, including immobilization of heavy metals (HMs), dechlorination of carbon tetrachloride (CT), sedimentary phosphorus sequestration and eutrophication alleviation. Additionally, its potential functions as a slow-release fertilizer are discussed as well. In general, vivianite is expected to make more contributions to the future scientific research, especially the solution of environmental problems. Overcoming the lack of understanding and some technical limitations will be beneficial to the further application of vivianite in environmental field.

Effects of nitrate dosing on the migration of reduced sulfur in black odorous river sediment and the influencing factors

At present, nitrates were widely used to remediate sulfur-rich sediment in black odorous rivers. However, the optimal nitrate dosage and influencing factors during remediation have not been fully investigated. In this study, various nitrate dosages and possible influencing factors were investigated for their efficiency in treating sulfur-rich sediment. The results indicated that acceptable remedial efficiency (the percentage of acid volatile sulfide (AVS) oxidation and the residual ammonium production) can be achieved when 1.6 times the theoretical nitrate dosage is used. Large amounts of AVS cannot be oxidized if too little nitrate is used and will regenerate after several days of remediation. Conversely, high concentrations of ammonium will form if too much nitrate is used. The results of this study indicated that a rapid AVS oxidation rate will be achieved in higher temperatures; no significant treatment efficiency was found when temperatures were in the range of 15–35 °C. Organic matter slowed the rate of nitrate reduction but did not affect its remedial efficiency for AVS oxidation in sediment. A high concentration of ferrous iron primarily influenced nitrate treatment efficiency in the oxidation of AVS in sediment, simultaneously causing the production of a high ammonium concentration. This study once again proved that microbial mediation of the autotrophic sulfide-driven denitrification dominates AVS oxidation in sediment. This study indicated that a universal nitrate dosage calculation equation should be established, and that factors such as ferrous iron concentration should be considered in future remediation of black odorous rivers.

Complete Genome Sequence of Acidithiobacillus ferridurans JCM 18981.

Acidithiobacillus ferridurans is an acidophilic chemolithotrophic bacterium that can grow in the presence of high concentrations of ferrous iron. Here, we present the complete 2,921,399-bp genome sequence of the strain A. ferridurans JCM 18981T, isolated from uranium mine drainage water.

Geochemical evidence for cryptic sulfur cycling in salt marsh sediments

Cryptic sulfur cycling is an enigmatic process in which sulfate is reduced to some lower-valence state sulfur species and subsequently quantitatively reoxidized; the rate and microbial energetics of this process and how prevalent it may be in the environment remain controversial. Here we investigate sulfur cycling in salt marsh sediments from Norfolk, England where we observe high ferrous iron concentrations with no depletion of sulfate or change in the sulfur isotope ratio of that sulfate, but a 5‰ increase in the oxygen isotope ratio in sulfate, indicating that sulfate has been through a reductive cycle replacing its oxygen atoms. This cryptic sulfur cycle was replicated in laboratory incubations using 18O-enriched water, demonstrating that the field results do not solely result from mixing processes in the natural environment. Numerical modeling of the laboratory incubations scaled to represent the salt marsh sediments suggests that the uptake rate of sulfate during this cryptic sulfur cycling is similar to the uptake rate of sulfate during the fastest microbial sulfate reduction that has been measured in the natural environment. The difference is that during cryptic sulfur cycling, all of the sulfur is subsequently reoxidized to sulfate. We discuss mechanisms for this pathway of sulfur cycling including the possible link to the subsurface iron cycle.

The oxidation of different energy sources and features of the growth of new strains of microorganisms, isolated from industrial substrates

The selection of cultivation conditions for new strains of Acidithiobacillus ferrooxidans allows significantly intensify the process of bioleaching. This approach promotes active accumulation of biomass at the stage of active growth before adding the biomass in substrates. The strains were isolated from waste dumps coal beneficiation and fly ash from coal combustion. Have been studied the growth characteristics of new strains of mesophilic Acidithiobacillus ferrooxidans (MFLv6 and MFLad5) at different energy sources – ferrous iron (FeSO4..7H2O) and sodium thiosulfate (Na2S2O3). We set the intensity of the oxidation of energy substrates investigated strains The intensity of oxidations of energy substrates by studied strains has been established. The index pH and Eh, the concentration of oxidized Fe+3 and the number of cells were parameters that are been monitored. The features of behavior both strains at cultivation with high concentration of ferrous iron, as an energy source, have been established. In particular, the existence of a critical concentration of FeSO4.7H2O, above which there is a dramatic slowdown in growth and lysis of the cells has been observed. It has been established that for maximum biomass accumulation of strains the concentration of FeSO4.7H2O as the only energy source in 12.0 g/dm3 is optimum and 44.5 g/dm3 for the most efficient leaching of metals from the studied substrates. The isolated strains differ in the growth rate and oxidation activity of energy sources – ferrous iron and thiosulfate. The obtained results suggest the existence of a correlation between the conditions of growth of the strains, their characteristics, and is a reflection a polymorphism strains.

Oxygen produced by cyanobacteria in simulated Archaean conditions partly oxidizes ferrous iron but mostly escapes-conclusions about early evolution.

The Earth has had a permanently oxic atmosphere only since the great oxygenation event (GOE) 2.3-2.4 billion years ago but recent geochemical research has revealed short periods of oxygen in the atmosphere up to a billion years earlier before the permanent oxygenation. If these "whiffs" of oxygen truly occurred, then oxygen-evolving (proto)cyanobacteria must have existed throughout the Archaean aeon. Trapping of oxygen by ferrous iron and other reduced substances present in Archaean oceans has often been suggested to explain why the oxygen content of the atmosphere remained negligible before the GOE although cyanobacteria produced oxygen. We tested this hypothesis by growing cyanobacteria in anaerobic high-CO2 atmosphere in a medium with a high concentration of ferrous iron. Microcystins are known to chelate iron, which prompted us also to test the effects of microcystins and nodularins on iron tolerance. The results show that all tested cyanobacteria, especially nitrogen-fixing species grown in the absence of nitrate, and irrespective of the ability to produce cyanotoxins, were iron sensitive in aerobic conditions but tolerated high concentrations of iron in anaerobicity. This result suggests that current cyanobacteria would have tolerated the high-iron content of Archaean oceans. However, only 1% of the oxygen produced by the cyanobacterial culture was trapped by iron, suggesting that large-scale cyanobacterial photosynthesis would have oxygenated the atmosphere even if cyanobacteria grew in a reducing ocean. Recent genomic analysis suggesting that ability to colonize seawater is a secondary trait in cyanobacteria may offer a partial explanation for the sustained inefficiency of cyanobacterial photosynthesis during the Archaean aeon, as fresh water has always covered a very small fraction of the Earth's surface. If oxygenic photosynthesis originated in fresh water, then the GOE marks the adaptation of cyanobacteria to seawater, and the late-Proterozoic increase in oxygen concentration of the atmosphere is caused by full oxidation of the oceans.

Estradiol Reduces Ferrous Citrate Complex-Induced NOS2 Up-Regulation in Cerebral Endothelial Cells by Interfering the Nuclear Factor Kappa B Transactivation through an Estrogen Receptor β–Mediated Pathway

Hemorrhagic stroke caused leakage of red blood cells which converts to hemoglobin, heme, and iron accumulated at the lesions. High concentration of ferrous iron from subarachnoid hemorrhage (SAH) induced cerebral vasospasm. Using the two-hemorrhage SAH model in rats, we previously demonstrated that estradiol (E2) significantly attenuated the SAH-induced vasospasm by inhibiting the NOS2 expression. Adding ferrous citrate (FC) complexes to the primary cultured mouse cerebral endothelial cells (CEC) to mimic the SAH conditions, we also showed that FC up-regulates NOS2 through nuclear translocation of NFκB induced by free radicals generation. Here, we further studied the molecular mechanism underlying E2-mediated reduction of the FC-induced up-regulation of NOS2. Treatment with E2 (100 nM) reduced the FC (100 µM)-induced increases of free radical generation and the levels of NOS2 mRNA and protein in the CEC. Moreover, E2 also prevented the FC-induced increases of IκBα phosphorylation, NFκB nuclear translocation, NFκB binding onto the NOS2 promoter, and the NOS2 promoter luciferase activity. However, knock-down the estrogen receptor β (ERβ), but not ERα, abolished the E2-mediated prevention on the FC-induced increases of NOS2 mRNA and protein. The data from the present study suggest that E2 inhibited NOS2 gene expression by interfering with NFκB nuclear translocation and NFκB binding onto the NOS2 through an ERβ-mediated pathway. Our results provide the molecular basis for designing the applicable therapeutic or preventive strategies in the treatment SAH patients.

Variation for tolerance to high concentration of ferrous iron (Fe2+) in Australian hexaploid wheat

High concentration of reduced iron (Fe2+) in waterlogged acid soils is a constraint for growing wheat in high rainfall (waterlogged-prone) areas of Western Australia. Growing crop genotypes tolerant to high Fe2+ concentrations may be desirable in such situations, but there is no knowledge about the extent of variability in Fe2+ tolerance in the wheat germplasm. A bioassay for tolerance to high concentrations of iron in wheat was developed and optimised using Siete Cerros (Fe-tolerant) and BH1146 (Fe-intolerant) as control genotypes and a range of FeSO4 concentrations (36, 313, 625, 1250, 1875, 2500 and 3125 μM Fe2+) in nutrient solution in a controlled-temperature environment. Increasing external concentration of iron decreased both shoot and root dry weight, increased shoot iron concentration and intensified the development of toxicity symptoms to a greater degree in intolerant BH1146 as compared to tolerant Siete Cerros. Increased iron supply negatively affected uptake of Ca (r = −0.41) and Mg (r = −0.40). The tolerant genotype Siete Cerros showed an improved avoidance/exclusion of high external concentration of Fe2+ compared with intolerant BH1146. The genotypic discrimination based on relative root dry weight and the development of toxicity symptoms was most pronounced at 625 μM Fe2+. This concentration was chosen for screening of 20 bread wheat and one durum genotype chosen from a preliminary screening of 94 Australian wheat genotypes. A relatively narrow but significant variation (22–38%) in terms of relative root dry weight under Fe2+ toxicity was observed among Australian advanced breeding lines and varieties. The presence of genotypic variation for Fe2+ tolerance across and within the Australian breeding programs could be exploited in a deliberate selection process to enhance Fe2+ tolerance in wheat. Durum wheat (Arrivato) and several Australian wheat varieties and advanced lines in this study were as tolerant to Fe2+ toxicity as Siete Cerros, a variety representing common parentage of iron-tolerant genotypes.

Engineered Wetland Design and Applications for On-Site Bioremediation of PHC Groundwater and Wastewater

Summary Engineered wetlands are an emerging technology for the on-site bioremediation of petroleum hydrocarbon-contaminated (PHC) water. The engineering optimization of natural treatment processes shows that engineered wetlands are a viable alternative to mechanical remediation systems. An engineered wetland incorporates a horizontal subsurface flow gravel bed reactor, lined with an impermeable liner and equipped with a Forced Bed Aeration™ system to enhance oxygen delivery. Design parameters include biodegradation rate coefficients for petroleum hydrocarbons such as benzene, toluene, ethylbenzene, and xylenes (BTEX), flowrate, hydraulic residence time, and influent and required effluent concentrations. Three field-scale applications of this technology in North America are presented. The first application is at a pipeline terminal with contact wastewater containing BTEX and ammonia. A horizontal subsurface flow engineered wetland with Forced Bed Aeration™ and a design flowrate of 1.5 m3/d treats BTEX and ammonia to non-detect concentrations at 40% and 80% of the gravel bed length, respectively. The second application is at a former refinery, where a cascade aerator and surface flow wetland (for iron removal) and horizontal subsurface flow engineered wetland with Forced Bed Aeration™ were constructed in 2003 to treat 6,000 m3/d of BTEX-contaminated extracted groundwater. This system reduces benzene concentrations from 300 μg/L (influent) to <10 μg/L (effluent), and is incorporated into a Robert Trent Jones-designed golf course. The third application is at a former refinery where high ferrous iron concentrations (40 mg/L) favor an alternative design. This system, currently being commissioned, treats 1,060 m3/day of iron and BTEX-contaminated extracted groundwater using a cascade aerator, sedimentation pond, surface flow wetlands, and vertical flow oxic limestone drains. Engineered wetlands are achieving performance goals in field-scale applications, and are a robust and sustainable alternative to mechanical remediation systems.

Microbial Diversity in an Iron Oxidation Tank of an AMD Treatment Plant at an Abandoned Sulphur Mine

This paper describes about microbial diversity in an iron oxidation tank of an AMD treatment plant established at an abandoned sulphur mine in Japan. Since the mining operation was stopped, this mine has produced strong acidic mine drainage, pH 1.8, including a high concentration of ferrous iron, 301mg/L, and the flow rate was about 4m3/min. In 2006, a pilot scale microbial iron oxidizing system was installed to remove total iron more easily from the AMD by oxidizing ferrous iron to ferric iron. From the start of this pilot operation, microbial diversity in the iron oxidation tank was investigated using a PCR-DGGE method for about two months. In the PCR, V3 region of 16S rRNA gene for Bacteria was amplified. The profiles of DGGE showed that there were three dominant species in the iron oxidation tank through the experimental period. Number of bands on DGGE profiles decreased with dates of sampling so that the microbial population became less diverse because of the iron oxidizing operation. There was a wide variety of bacterial species of even though conditions were strongly acidic.

The cellular machinery of Ferroplasma acidiphilum is iron-protein-dominated

Ferroplasma is a genus of the Archaea, one of the three branches of the tree of life, and belongs to the order Thermoplasmatales (Euryarchaeota), which contains the most acidophilic microbes yet known. Ferroplasma species live in acid mine drainage, acidic pools and environments containing sulphidic ores such as pyrite and characterized by pH values of 0-2 and high concentrations of ferrous iron and other heavy metals. F. acidiphilum strain Y(T) is a chemoautotroph that grows optimally at pH 1.7 and gains energy by oxidizing ferrous iron and carbon by the fixation of carbon dioxide. Here we show that 86% of 189 investigated cellular proteins of F. acidiphilum are iron-metalloproteins. These include proteins with deduced structural, chaperone and catalytic roles, not described as iron-metalloproteins in any other organism so far investigated. The iron atoms in the proteins seem to organize and stabilize their three-dimensional structures, to act as 'iron rivets'. Analysis of proteins of the phylogenetic neighbour Picrophilus torridus and of the habitat neighbour Acidithiobacillus ferrooxidans revealed far fewer and only typical metalloproteins. F. acidiphilum therefore has a currently unique iron-protein-dominated cellular machinery and biochemical phylogeny.

Effects of CO32–/bicarbonate, Si, and PO43– on Arsenic sorption to HFO

Groundwaters that have elevated arsenic (As) concentrations sometimes have moderate to high ferrous iron concentrations. Soluble As species readily sorb to hydrous ferric oxide (HFO); therefore, conventional water treatment methods that remove soluble iron (Fe) by oxidizing to HFO also remove As. Commonly occurring solutes, including phosphate (PO43–), silica (Si), and carbonate (CO32–), also sorb to HFO, and competition between these substances and As species may interfere with As removal. This study simulated Fe/As removal at the pH values, alkalinities, and concentrations of Si and PO43– typical of central Illinois groundwater. The results suggest that for water with a pH > 7, lowering the pH to 7 can overcome CO32– and Si interferences. Lowering the pH of water containing PO43– improves As removal but not to the degree observed in waters containing CO32– and Si. The Dzombak and Morel surface complexation–diffuse‐layer model fits the sorption data fairly well.

Dihydroneopterin and the generation of superoxide from iron ions

Abstract We describe the impact of dihydroneopterin on the formation of superoxide radicals. As radical source ferrous iron in air-saturated aequeous solution was used. Detection of superoxide was achieved using reduction of nitroblue tetrazolium to formazan. Dihydroneopterin decreases formazan formation when high concentrations of ferrous iron are used which induce a rapid superoxide formation within minutes. On the other hand, when low concentrations of ferrous iron are used, addition of dihydroneopterin to the assay mixture leads to an increase ir. formazan formation for several hours of incubation. We therefore conclude that the radical promoting activity of dihydroneopterin is physiologically more relevant compared to its radical scavenging properties.

Inhibition effect of ferric iron on the kinetics of ferrous iron

Ferric iron acted as a non-competitive inhibitor for the biological oxidation of ferrous iron and decreased the inhibitory effects of high concentrations of ferrous iron as well as the auto-inhibitive effect the bacterial cells. A previously developed kinetic model for this reaction was modified to incorporate the inhibition effects of ferric iron. © Rapid Science Ltd. 1998

Biological mine drainage treatment

Abstract Drainage from sulphur mines contains a high concentration of ferrous iron and it is strongly acidic. The mechanism of acid mine drainage formation was briefly explained. As a case study, successful measures taken at the abandoned Matsuo mine, Iwate Prefecture, Japan, for preventing the pollution in receiving rivers was presented in this paper. The measures consisted of the construction works against pollution sources and the construction of a drainage treatment plant in which Thiobacillus ferrooxidans oxidizes ferrous iron under a low pH condition, and produced ferric iron is removed by sedimentation. Then, a laboratory-scale fluidized bed reactor using anion exchange resin as attaching material for the bacteria was examined in order to improve the efficiency of biological oxidation of ferrous iron. More than 90% of oxidation had been maintained for 2 months at 1 h of HRT, which suggests that the size of the oxidation tank could be reduced.

Kinetics of FeS-mediated denitrification in sediments from the Camargue (Rhone delta, southern France)

Denitrification rates were measured in sediments after the addition of different concentrations of FeS. A decrease of the denitrification rate was observed when high concentrations of ferrous iron (> 10 mM) were present. In the experiments with no significant concentrations of free Fe2+, the relationship between NO3− reduction and FeS concentration followed Michaelis and Menten kinetics. The maximum rate was 0.273 mmol l−1 d−1, 6 times as much as the basal rate 0.046 mmol l−1 d−1, which was attributed to organic matter; the Ks was 1.45 mM FeS. The stoichiometry of the overall reaction involving NO3− reduction and the concomitant S2− oxidation was also investigated. Measured ΔS/ΔN ratios ranged between 0.55 and 0.64, with ΣH2S + SO42− changing less than 10%. These values agree with the theoretically expected value of 0.56.

Kinetics of FeS-mediated denitrification in sediments from the Camargue (Rhone delta, southern France)

Denitrification rates were measured in sediments after the addition of different concentrations of FeS. A decrease of the denitrification rate was observed when high concentrations of ferrous iron ( > 10 mM) were present. In the experiments with no significant concentrations of free Fe 2+, the relationship between NO 3 − reduction and FeS concentration followed Michaelis and Menten kinetics. The maximum rate was 0.273 mmol l −1 d −1, 6 times as much as the basal rate 0.046 mmol l −1 d −1, which was attributed to organic matter; the K s was 1.45 mM FeS. The stoichiometry of the overall reaction involving NO 3 − reduction and the concomitant S 2− oxidation was also investigated. Measured ΔS/ΔN ratios ranged between 0.55 and 0.64, with ΣH 2S + SO 4 2− changing less than 10%. These values agree with the theoretically expected value of 0.56.

Oxidation of high ferrous iron concentrations by chemolithotrophic Thiobacillus ferrooxidans in packed bed bioreactors

The bacterial oxidation of high ferrous iron concentrations in batch culture has been studied in a packed bed bioreactor. It has been found that aeration rates from 0.49 to 1.2 VVM did not influence the biofilm oxidation activity during the period of biofilm formation up to 30 g l −1 initial ferrous iron concentration. The contribution of swimming, attached and fixed bacteria to the Fe 2+ oxidation process has been evaluated. Kinetics data showed that the oxidation rate depends on the aeration rate, when the initial Fe 2+ concentration exceeded 30 g l −1. The maximum overall Fe 2+ oxidation rate was 1.8 g l −1 h −1, when the initial ferrous iron concentration was in the range 30 to 45 g l −1.