EDTA-NO Reduction Research Articles

Performance, kinetics and mechanism of Fe(II)EDTA regeneration with surface-fluorinated anatase TiO2 with exposed (001) facets

Fe(II)EDTA regeneration mainly referring to Fe(III)EDTA and Fe(Ⅱ)EDTA-NO reduction has a very remarkable significance for NO removal using Fe(II)EDTA solution. Here, surface-fluorinated anatase TiO2 nanosheets with exposed (001) facets (F-TiO2) was prepared and firstly served for Fe(II)EDTA regeneration with ultraviolet light. The performance and kinetics of Fe(II)EDTA regeneration had been investigated under different F-TiO2 dose, varied pH, and diverse temperatures, in which Fe(III)EDTA and Fe(II)EDTA-NO reduction rate raised and then decreased under pH increasing or F-TiO2 dose rise. High temperature was conducive to Fe(II)EDTA regeneration. Fe(III)EDTA and Fe(II)EDTA-NO reduction presented first order reaction. Moreover, the F-TiO2 still maintained an excellent reduction efficiency after three recycle. Mechanism study showed that excellent Fe(II)EDTA regeneration ability could be partly explained by the high separation efficiency of photogenerated electrons and holes of F-TiO2. The bonded NO was converted into NH4+, N2, and N2O. Finally, compared with other Fe(II)EDTA regeneration systems, photocatalytic regeneration is a more suitable alternative in Fe(II)EDTA complexation denitrification technology.

The origin of highly efficient and selective activated carbon supported bimetallic Fe@Cu composite for Fe(II)EDTA-NO reduction in Fe(II)EDTA complexation denitrification process

Fe(II)EDTA complexing absorption is a promising technology for nitric oxide removal; however, inefficient and slow Fe(II)EDTA regeneration from Fe(II)EDTA-NO reduction and undesirable NH4+ as the major N-containing product are still challenges that should be resolved. This study investigated the performance, kinetics, and product selectivity of Fe(II)EDTA-NO reduction by activated carbon supported bimetallic Fe@Cu composite (AC-Fe@Cu) and unraveled the origin of highly efficient and selective AC-Fe@Cu for Fe(II)EDTA-NO reduction. The reduction efficiency reaches 95.34 % in 30 min, accompanied by 86.78 % N2 selectivity, outperforming most of the reduction systems reported previously. AC-Fe@Cu is resilient at wide pH (3–8), temperature (20–50 °C), and O2 concentration ranges (0–10 %) and maintains high efficiency (76.23 %) after three successive cycles (3 h). Simultaneous reduction of Fe(III)EDTA and Fe(II)EDTA-NO indicates that Fe(II)EDTA-NO reduction is the rate-determining step in the Fe(II)EDTA regeneration process. The bimetal configuration and atomic ratio mediate the reduction efficiency, rate, and N2 selectivity. Unique AC@Fe@Cu structure and optimal atomic ratio of Fe to Cu (1:1) increase the dispersity and provide space proximity and abundant interfaces, which create numerous iron–carbon and iron–copper galvanic cells and promote two-way electron transmission. Fast electron transfer and nascent hydrogen formation contribute to efficient, rapid, and selective Fe(II)EDTA-NO reduction. The maximization of the roles of Cu as stabilizer and active sites for selective N2 formation also contributes. This study sheds light on reduction system design for Fe(II)EDTA regeneration.

Fe(III)EDTA and Fe(II)EDTA-NO reduction by supported (nano)ZVI in Fe(II)EDTA complexation denitrification technology: Performance, kinetics, and pathway

Fe(II)EDTA shows superior ability in complexing absorption denitrification; however, the resulting Fe(II)EDTA-NO and its easy oxidation to Fe(III)EDTA decimate its role. Rapid Fe(II)EDTA regeneration from Fe(II)EDTA-NO and Fe(III)EDTA reduction is important for effective and successive nitrogen oxide removal, and harmless N2 is desirable as the major N-containing product. This study investigated the performance, kinetics, and pathway of Fe(III)EDTA and Fe(II)EDETA-NO reduction by four supported (nano)ZVI ((nanoscale) zero-valent iron)) and NO removal coupled with Fe(II)EDTA regeneration. Support-mediated the physicochemical and structural properties of loaded (nano)ZVI, Fe(III)EDTA and Fe(II)EDTA-NO adsorption, and reduction pathways are closely related to the efficiency, rate, and product selectivity. Activated carbon-supported nano-ZVI (AC-nZVI) is important for Fe(III)EDTA and Fe(II)EDTA-NO reduction with high efficiencies of 89.8 % and 88.2 % within 5 min and 30 min, respectively, and high N2 selectivity (52.98 %), outperforming most of the reduction systems reported previously. The pathway alternation induced by the catalysis of activated carbon and micro-electrolysis of iron–carbon is the origin of highly efficient and selective AC-nZVI for Fe(III)EDTA and Fe(II)EDTA-NO reduction. Resilient over a wide O2 content (0–10 %), pH (3–8), and temperature range (20–50 °C) and efficient for NO removal with large capacity coupled with Fe(II)EDTA regeneration, AC-nZVI would be applicable in industrial Fe(II)EDTA regeneration in Fe(II)EDTA complexation denitrification technology. This study proposes an alternative for Fe(II)EDTA regeneration and provides insights into the mediation of the performance, kinetics, and pathway for guiding reduction system design.

Engineering multiscale polypyrrole/carbon nanotubes interface to boost electron utilization in a bioelectrochemical system coupled with chemical absorption for NO removal.

The chemical absorption-bioelectrochemical reduction (CABER) integrated system provides an alternative of good potential for NO removal. The efficient utilization of cathode electrons directly determines the system performance and operating cost. Herein, we synthesize a polypyrrole/carbon nanotubes (PPy/CNTs) composite to engineer a micro-and nanoscale interface with low resistance and high biocompatibility between the cathode and biofilms in the CABER system. The resulting PPy/CNTs biocathodes exhibit 36.4% increase in biomass density, 40.7%-302.6% increase in Faraday efficiency along Fe(III)EDTA reduction, and 204% increase in Fe(II)EDTA-NO reduction rate. The enrichment of functional microorganisms is validated to be a key strengthening factor, as the proportion of which increased from 57.9% to 84.6%. Moreover, for efficient electron transfer and utilization, a low-resistance electron transfer route, "electrode substrate → PPy (→ CNTs) → microbial cells → Fe(III)EDTA or Fe(II)EDTA-NO", is realized in the multiscale conductive networks constructed of PPy/CNTs composite and microbial nanowires.

Core-shell Ag-Pd nanoparticles catalysts for efficient NO reduction by formic acid

The impact of nitrogen oxide on human beings has reached a point that can’t be ignored. Complex absorption is supposed to be a simple and efficient method to reduce nitrogen oxide emission. However, it is still a challenge to improve the regeneration rate of complex solution by changing the structure of catalyst. Herein, Ag-Pd nanoparticles (NPs) with core-shell structure were loaded on N-doped porous carbons (NPCs), and it was used as catalyst for Fe(Ⅱ)EDTA-NO reduction by formic acid. The results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and transmission electron microscopy (TEM) confirmed that N atoms can improve the dispersion of NPs, and core-shell structure of Ag-Pd has been successfully prepared. Due to the good core-shell structure with fine electron exchange ability and suitable particle size of Ag-Pd NPs, the prepared catalyst has superior catalytic performances, and its TOF can reach 1995 h−1. Under mild conditions, denitrification rate could reach 91.04% with 98.51% N2 selectivity for only 5 min

N-Doped Porous Carbon-Anchored Pd Nanoparticles: A Highly Efficient Catalyst for Fe(II)EDTA-NO Reduction

Complex absorption is considered an efficient method to reduce the emission of nitric oxide. At present, it is still a challenge to enhance the regeneration performance of complex solution by changing the structure of the support to enhance the reduction capacity of the catalyst. Herein, N-doped porous carbons (NPCs) were used as an excellent support for synthesizing Pd/NPCs, and then they were utilized as a catalyst toward Fe(II)EDTA-NO reduction. The characterization results of X-ray diffraction, X-ray photoelectron spectra, and transmission electron microscopy confirmed that the dispersion of Pd nanoparticles (NPs) could be improved by N atoms in NPCs. Benefiting from the appropriate Pd NPs particle size and the intrinsic advantages of the support, the resultant Pd/NPCs exhibited superior performances such as a denitrification rate of 90.4% with an N2 selectivity of 99.6% (used for 5 min under mild conditions) and a turnover frequency of 1916 h–1. In addition, the kinetic calculation and reaction mechanism derivation provided a new avenue for the fabrication of highly effective catalysts over liquid phase denitrification.

Kinetics of biocathodic electron transfer in a bioelectrochemical system coupled with chemical absorption for NO removal

A microbial electrolysis cell (MEC) has been developing for enhanced absorbent regeneration in a chemical absorption-biological reduction integrated process for NO removal. In this work, the kinetics of electron transfer involved in the biocathodes along Fe(III)EDTA and Fe(II)EDTA-NO reduction was analyzed simultaneously. A modified Nernst-Monod kinetics considering the Faraday efficiency was applied to describe the electron transfer kinetics of Fe(III)EDTA reduction. The effects of substrate concentration, biocathodic potential on current density predicted by the model have been validated by the experimental results. Furthermore, extended from the kinetics of Fe(III)EDTA reduction, the electron transfer kinetics of Fe(II)EDTA-NO reduction was developed with a semi-experimental method, while both direct electrochemical and bioelectrochemical processes were taken into consideration at the same time. It was revealed that the developed model could simulate the electron transfer kinetics well. This work could not only help advance the biocathodic reduction ability and the utilization efficiency of electric power, but also provide insights into the industrial scale-up and application of the system.

Shifts of Biomass and Microbial Community Structure in Response to Current Densities in a Biofilm Electrode Reactor for NOx Removal

Microorganisms in the biofilm electrode reactor (BER) showed the powerful capabilities of Fe(III)EDTA and Fe(II)EDTA-NO reduction after microcurrent acclimation. The effects of current are multifac...

Electron transfer mechanism of biocathode in a bioelectrochemical system coupled with chemical absorption for NO removal

A biocathode with the function of Fe(III)EDTA and Fe(II)EDTA-NO reduction was applied in a microbial electrolysis cell coupled with chemical absorption for NO removal from flue gas. As the mediated electron transfer was excluded by the same electrochemical characterizations of the biocathodes before and after a 48 h continuous operation, the profiles of reduction experiments indicated that direct electron transfer was the main mechanism of Fe(III)EDTA reduction, while Fe(III)EDTA-NO was mainly reduced via Fe(II)-assisted autotrophic denitrification. The microscopy of the biocathode confirmed the existence of pili, which was supposed to be bacterial nanowires for electron transfer. The analysis of microbial community revealed that iron-reducing bacteria, including Escherichia coli, had the possibility of electron uptake from electrode via physical contact. These results first time gave us in-depth understanding of the electron transfer in the multifunctional biocathode and mechanism for further enhancement of the bioreduction processes.

Evaluation of Fe(II)EDTA-NO reduction by zinc powder in wet flue gas denitrification technology with Fe(II)EDTA

Regeneration of Fe(II)EDTA, converting Fe(III)-EDTA and Fe(II)EDTA-NO to Fe(II)EDTA, is the key process in a wet flue gas denitrification technology with Fe(II)EDTA solution. In this paper, Zn powder was first employed as a reductant to reduce Fe(II)EDTA-NO. The stoichiometry and kinetics of Fe(II)EDTA-NO reduction by Zn powder were investigated with respect to Zn powder concentration, pH value, and temperature. The effect of the particle size of the Zn powder on Fe(II)EDTA-NO reduction was also investigated. The experimental results indicated that Fe(II)EDTA-NO reduction rate increased with the decrease of pH value and elevated temperature, and small particle size is beneficial to Fe(II)EDTA NO reduction. Fe(II)EDTA-NO reduction with Zn powder showed a pseudo-second-order reaction concerning Fe(II)EDTA-NO. In addition, the energy of activation (Ea) and the entropy of activation (ΔS‡) of the Fe(II)EDTA-NO reduction with Zn powder were estimated to be 19.853kJmol−1 and −135.557JK−1mol−1, respectively. Finally, the simultaneous reduction of Fe(III)EDTA and Fe(II)EDTA-NO with Zn powder was investigated. Results showed that Zn powder had better performance on simultaneous Fe(III)EDTA and Fe(II)EDTA-NO reduction as compared to the earlier related research. These fundamental researches can offer valuable guidance for industrial denitrification using mixed Fe(II)EDTA and Zn powder system.

Mechanism and kinetics of Fe(II)EDTA[sbnd]NO reduction by iron powder under anaerobic condition

Reduction of Fe(II)EDTANO as well as Fe(III)EDTA is the main process for simultaneous removing nitric oxide and sulfur dioxide with Fe(II)EDTA solution. In this paper, iron powder was proposed to reduce the Fe(II)EDTANO. The mechanism and kinetics of Fe(II)EDTANO reduction by Fe powder were studied with respect to the Fe(II)EDTANO concentration, pH value, and temperature. The experimental results indicated that the bonded NO was converted to ammonium. Fe(II)EDTANO reduction by Fe powder was a first-order reaction concerning Fe(II)EDTANO. The reaction rate increased with the decrease of pH value as well as the increase of temperature. In addition, the energy of activation (Ea) and the entropy of activation (ΔS‡) of the Fe(II)EDTANO reduction by Fe powder were 23.229kJmol−1 and −215.251JK−1mol−1, respectively. Finally, the simultaneous reduction of Fe(III)EDTA and Fe(II)EDTANO by Fe powder was investigated. The results showed that Fe(III)EDTA reduction was restricted by Fe(II)EDTANO, and Fe(III)EDTA had little effect on the reduction of Fe(II)EDTANO. Besides, the reduction of Fe(II)EDTANO was the determining step in the whole process of Fe(II)EDTA regeneration. These findings can provide constructive instruction for the NO removal in industrial applications with mixed Fe(II)EDTA and Fe powder system.

Bioelectrochemical Reduction of Fe(II)EDTA-NO in a Biofilm Electrode Reactor: Performance, Mechanism, and Kinetics.

A biofilm electrode reactor (BER) is proposed to effectively regenerate Fe(II)EDTA, a solvent for NOx removal from flue gas, from Fe(II)EDTA-NO, a spent solution. In this study, the performance, mechanism, and kinetics of the bioelectrochemical reduction of Fe(II)EDTA-NO were investigated. The pathways of Fe(II)EDTA-NO reduction were investigated via determination of nitrogen element balance in the BER and an abiotic electrode reactor. The experimental results indicate that the chelated NO (Fe(II)EDTA-NO) is reduced to N2 with N2O as an intermediate. However, the oxidation of NO occurred in the absence of Fe(II)EDTA in abiotic reactors. Furthermore, the accumulation of N2O was suppressed with the help of electricity. The preponderant electron donor for reduction of Fe(II)EDTA-NO was also confirmed via analysis of the electron conservation. About 87% of Fe(II)EDTA-NO was reduced using Fe(II)EDTA as the electron donor in the presence of both glucose and cathode electrons while the cathode electrons were utilized for the reduction of Fe(III)EDTA to Fe(II)EDTA. Michaelis-Menten kinetic constants of bioelectrochemical reduction of Fe(II)EDTA-NO were also calculated. The maximum reduction rate of Fe(II)EDTA-NO was 13.04 mol m(-3) h(-1), which is 50% higher than that in a conventional biofilter.

Evaluation of a newly isolated Klebsiella sp. DL-1 and its interaction with Klebsiella sp. FD-3 in regenerating nitrogen oxide scrubbing liquor using ethylenediaminetetraacetic acid iron(II) as absorbent

A highly effective strain, referred to as DL-1 and identified as Klebsiella sp., was applied to Fe(II)EDTA-NO reduction. The average reduction rate was approximately 4.29 mmolg DCW−1h−1, which was higher than those reported in the literature. The relationship between cell growth and Fe(II)EDTA-NO reduction was characterized, and a model was developed based on a logistic equation. To ensure that the simultaneous reduction of Fe(II)EDTA-NO and Fe(III)EDTA was feasible in the integrated NOx removal process of chemical absorption and biological reduction, DL-1 was mixed with a Fe(III)EDTA-reducing bacterium FD-3 to regenerate the scrubbing liquor. There was carbon and nitrogen source competition between these two strains in the mixed system. DL-1 was incapable of reducing Fe(III)EDTA, but FD-3 was capable of reducing Fe(II)EDTA-NO. Therefore, DL-1 would inhibit Fe(III)EDTA reduction, and FD-3 would enhance Fe(II)EDTA-NO reduction. The performance of the mixed strains was also investigated. The system could maintain stable and high reduction efficiencies, after 7h, the reduction efficiency of Fe(II)EDTA-NO and Fe(III)EDTA were 84.9% and 77.1%, respectively.

Fe(III)EDTA and Fe(II)EDTA-NO reduction by a sulfate reducing bacterium in NO and SO2 scrubbing liquor

A viable process concept, based on NO and SO2 absorption into an alkaline Fe(II)EDTA (EDTA: ethylenediaminetetraacetic acid) solution in a scrubber combined with biological reduction of the absorbed SO2 utilizing sulfate reducing bacteria (SRB) and regeneration of the scrubbing liquor in a single bioreactor, was developed. The SRB, Desulfovibrio sp. CMX, was used and its sulfate reduction performances in FeEDTA solutions and Fe(II)EDTA-NO had been investigated. In this study, the detailed regeneration process of Fe(II)EDTA solution, which contained Fe(III)EDTA and Fe(II)EDTA-NO reduction processes in presence of D. sp. CMX and sulfate, was evaluated. Fe(III)EDTA and Fe(II)EDTA-NO reduction processes were primarily biological, even if Fe(III)EDTA and Fe(II)EDTA-NO could also be chemically convert to Fe(II)EDTA by biogenic sulfide. Regardless presence or absence of sulfate, more than 87 % Fe(III)EDTA and 98 % Fe(II)EDTA-NO were reduced in 46 h, respectively. Sulfate and Fe(III)EDTA had no affection on Fe(II)EDTA-NO reduction. Sulfate enhanced final Fe(III)EDTA reduction. Effect of Fe(III)EDTA on Fe(II)EDTA-NO reduction rate was more obvious than effect of sulfate on Fe(II)EDTA-NO reduction rate before 8 h. To overcome toxicity of Fe(II)EDTA-NO on SRB, Fe(II)EDTA-NO was reduced first and the reduction of Fe(III)EDTA and sulfate occurred after 2 h. First-order Fe(II)EDTA-NO reduction rate and zero-order Fe(III)EDTA reduction rate were detected respectively before 8 h.

Fe(II)EDTA-NO reduction by a newly isolated thermophilic Anoxybacillus sp. HA from a rotating drum biofilter for NOx removal

The reduction of Fe(II)EDTA-NO is one of the core processes in BioDeNOx, an integrated physicochemical and biological technique for NOx removal from industrial flue gases. A newly isolated thermophilic Anoxybacillus sp. HA, identified by 16S rRNA sequence analysis, could simultaneously reduce Fe(II)EDTA-NO and Fe(III)EDTA. A maximum NO removal efficiency of 98.7% was achieved when 3mM Fe(II)EDTA-NO was used in the nutrient solution at 55°C. Results of this study strongly indicated that the biological oxidation of Fe(II)EDTA played an important role in the formation of Fe(III)EDTA in the anaerobic system. Fe(II)EDTA-NO was more competitive than Fe(III)EDTA as an electron acceptor, and the presence of Fe(III)EDTA slightly affected the reduction rate of Fe(II)EDTA-NO. At 55°C, the maximum microbial specific growth rate μmax reached the peak value of 0.022h−1. The maximum NO removal efficiency was also measured (95.4%) under this temperature. Anoxybacillus sp. HA, which grew well at 50°C–60°C, is a potential microbial resource for Fe(II)EDTA-NO reduction at thermophilic temperatures.

Regeneration of spent NOx scrubber liquor using a dual-chamber microbial fuel cell

BACKGROUND Wet absorption via addition of Fe(II)EDTA combined with biological reduction for nitric oxide removal is a promising approach. Based on existing issues and related studies of NOx scrubber solution, a dual-chamber MFC system with a biocathode was utilized to perform simultaneous and continuous reduction of Fe(III)EDTA and Fe(II)EDTA-NO with energy recovery. RESULTS The experimental results showed that in this system almost all of the Fe(II)EDTA-NO was removed and the spent NOx scrubber liquor (consisting of Fe(II)EDTA-NO and Fe(III)EDTA) was regenerated 50%, combined with electricity generation of 15.3 Am-3 NCC at the same time. Microorganisms utilized Fe(II)EDTA and cathodic electrodes as electron donor for Fe(II)EDTA-NO reduction and, different from the complicated Fe(II)EDTA-NO reduction process, the electrode was the sole electron donor for Fe(III)EDTA reduction. Additionally, Fe(II)EDTA-NO and Fe(III)EDTA mutually inhibits each other, mostly due to the competition for electrons. The microbial community of the biocathode was dominated by members of the Betaproteobacteria class. CONCLUSION This study first proposed and confirmed that microbial fuel cells could be utilized for the regeneration of NOx removal liquor which provided a novel pathway for NO removal combined with energy recovery. © 2014 Society of Chemical Industry

Evaluation of Fe(III)EDTA and Fe(II)EDTA-NO reduction in a NO x scrubber solution by magnetic Fe3O4-chitosan microspheres immobilized microorganisms

A two-stage bioreduction system containing magnetic-microsphere-immobilized denitrifying bacteria and iron-reducing bacteria was developed for the regeneration of scrubbing solutions for NO x removal. In this process, a higher bioreduction rate and a better tolerance of inhibition of bacteria were achieved with immobilized bacteria than with free bacteria. This work focused on evaluation of the effects of the main components in the scrubbing solution on Fe(III)EDTA (EDTA: ethylenediaminetetraacetate) and Fe(II)EDTA-NO reduction, with an emphasis on mass transfer and the kinetic model of Fe(III)EDTA and Fe(II)EDTA-NO reduction by immobilized bacteria. It was found that Fe(II)EDTA-NO had a strong inhibiting effect, but Fe(II)EDTA had no effect, on Fe(III)EDTA reduction. Fe(II)EDTA accelerated Fe(II)EDTA-NO reduction, whereas Fe(III)EDTA had no effect. This showed that the use of the two stages of regeneration was necessary. Moreover, the effect of internal diffusion on Fe(III)EDTA and Fe(II)EDTANO reduction could be neglected, and the rate-limiting step was the bioreduction process. The reduction of Fe(III)EDTA and Fe(II)EDTA-NO using immobilized bacteria was described by a first-order kinetic model. Bioreduction can therefore be enhanced by increasing the cell density in the magnetic chitosan microspheres.

Fe(II)EDTA–NO Reduction by Sulfide in the Anaerobic Aqueous Phase: Stoichiometry and Kinetics

In the BioDeNOx process for the nitrogen oxides (NOx) removal, sulfide is supposed to exist in the bioreactor mainly because of the bioreduction of sulfite and sulfate. Thus, the potential roles of sulfide should be taken into account in the BioDeNOx process. The objective of this work was to investigate abiotic Fe(II)EDTA–NO reduction by sulfide with respect to stoichiometry and kinetics. Batch experiments showed that elemental sulfur and ammonium were the two major products. However, the molar ratio of reduced Fe(II)EDTA–NO to the oxidized sulfide was 1:3.4–1:3.6, a bit higher than the expected value, suggesting the formation of the polysulfide based on the comprehensive analysis. Results also showed that Fe(II)EDTA–NO reduction by sulfide was a first-order reaction with respect to Fe(II)EDTA–NO. The reduction rates of Fe(II)EDTA–NO by sulfide went up along with the decrease of the pH values and rise of the reaction temperature. Besides, the energy of activation (Ea) and the entropy of activation (ΔS⧧) were 31.125 kJ mol–1 and −67.6144 J K–1 mol–1, respectively. Apart from the investigation into the abiotic role of sulfide on the BioDeNOx process, this paper also provided a hint on an integrated chemical and biological process for simultaneous desulfurization and denitrification.

Sulfate removal by Desulfovibrio sp. CMX in chelate scrubbing solutions for NO removal

To study the effects of Fe chelate solution and nitrosyl-complex (Fe(II)EDTA-NO), which might be introduced in the simultaneous biodesulfurization and denitrification process, on the sulfate removal process, a sulfate reducing bacteria Desulfovibrio sp. CMX was investigated for its sulfate removal capacity in the presence of Fe chelate additives and Fe(II)EDTA-NO. Meanwhile, Fe(II)EDTA-NO reduction was also investigated. The addition of Fe(II)EDTA and Fe(III)EDTA could stimulate the sulfate reduction performance. Although Fe(II)EDTA-NO could inhibit the strain, CMX could survive by consuming lactate and recover its sulfate reducing activity after Fe(II)EDTA-NO removed. Sulfate reduction could be enhanced in higher Fe(II)EDTA-NO concentrations (2 and 4 mM) by lactate applied at the middle stage of the experiment, and 72.2% and 62.6% sulfate were removed in 182 h, respectively. In this study, above 90% Fe(II)EDTA-NO (0.25-4 mM) was removed less than 60 h, which was much faster than sulfate reduction.

Fe(II)EDTA–NO reduction coupled with Fe(II)EDTA oxidation by a nitrate- and Fe(III)-reducing bacterium

The nitrate- and Fe(III)-reducing bacterium Paracoccus versutus LYM was characterized in terms of its ability to perform Fe(II)EDTA-NO reduction coupled with Fe(II)EDTA oxidation (NO-dependent Fe(II)EDTA oxidation, NDFO). It experienced a single anaerobic FeEDTA redox cycling through NDFO and dissimilatory Fe(III)EDTA reduction in FeEDTA culture. The increase in the Fe(II)EDTA concentration contributed to the ascending Fe(II)EDTA-NO reduction rate. The amount of glucose controlled the rate and extent of Fe(II) oxidation during NDFO. Without glucose addition, Fe(II)EDTA-NO reduction rate was at a rather slow rate even in presence of relatively sufficient Fe(II)EDTA. Unlike aqueous Fe(2+) and solid-phase Fe(II), Fe(II)EDTA could prevent cells from encrustations. These findings suggested the occurrence of NDFO preferred being beneficial via a mixotrophic physiology in the presence of an organic cosubstrate to being out of consideration for metabolic strategy.