Efficient Nitrate Reduction Research Articles

Boron-Induced Electron Localization in Cu Nanowires Promotes Efficient Nitrate Reduction to Ammonia in Neutral Media

Boron-Induced Electron Localization in Cu Nanowires Promotes Efficient Nitrate Reduction to Ammonia in Neutral Media

Selective reduction of nitrate to ammonium over charcoal electrode derived from natural wood

Electrocatalytic nitrate reduction has been regarded as an efficient alternative route for ammonia production. Developing efficient, economical and environment-friendly cathodes is a significant concern for the practical applications of this method. Herein, we report a charcoal electrode fabricated by carbonizing natural wood for efficient nitrate reduction. It displays high overpotential for hydrogen evolution, moderate sp3 C structure and oxygen-containing surface groups. Benefiting from these features, the charcoal cathode exhibits high nitrate removal rate (91.2%), outstanding selectivity (98.5%) and fast production rate (0.570 mmol L−1 h−1 cm−2) for ammonium. Both removal rate and selectivity are superior to other carbon materials and comparable to metal-containing cathodes. These results exhibit the possibility of using charcoal as cathodes for denitrification and ammonia recovery from wastewater.

Characterization of a novel marine aerobic denitrifier Vibrio spp. AD2 for efficient nitrate reduction without nitrite accumulation.

Aerobic denitrifiers have the potential to reduce nitrate in polluted water under aerobic conditions. A salt-tolerant aerobic denitrifier was newly isolated and identified as Vibrio spp. AD2 from a marine recirculating aquaculture system, in which denitrification performance was investigated via single-factor experiment, Box-Behnken experiment, and nitrogen balance analysis. Nitrate reductase genes were identified by polymerase chain reaction. Results showed that strain AD2 removed 98.9% of nitrate-nitrogen (NO3--N) with an initial concentration about 100 mg·L-1 in 48 h without nitrite-nitrogen (NO2--N) accumulation. Nitrogen balance indicated that approximately 17.5% of the initial NO3--N was utilized for bacteria synthesis themselves, 4.02% was converted to organic nitrogen, 39.8% was converted to nitrous oxide (N2O), and 31.1% was converted to nitrogen (N2). Response surface methodology experiment showed that the maximum removal of total nitrogen (TN) occurred under the condition of C/N ratio 11.5, shaking speed 127.9 rpm, and temperature 30.8 °C. Sequence amplification indicated that the denitrification genes, napA and nirS, were present in strain AD2. These results indicated that the strain AD2 has potential applications for removing NO3--N from high-salinity (3%) wastewater.

A Green Synthesis of Ru Modified g-C 3 N 4 Nanosheets for Enhanced Photocatalytic Ammonia Synthesis

Nitrate is a crucial environmental pollutant, and its risk on ecosystem keeps increasing. Photocatalytic conversion of nitrate to ammonia can simultaneously achieve the commercialization of environmental hazards and recovery of valuable ammonia, which is green and sustainable for the planet. However, due to the thermodynamic and kinetic energy barriers, photocatalytic nitrate reduction usually involves a higher selectivity of the formation of nitrogen that largely limits the ammonia synthesis activity. In this work, we reported a green and facile synthesis of novel metallic ruthenium particle modified graphitic carbon nitride photocatalysts. Compare with bulk graphitic carbon nitride, the optimal sample had 2.93-fold photocatalytic nitrate reduction to ammonia activity (2.627 mg/h/g cat ), and the NH 3 selectivity increased from 50.77% to 77.9%. According to the experimental and calculated results, the enhanced photocatalytic performance is attributed to the stronger light absorption, nitrate adsorption, and lower energy barrier for the generation of ammonia. This work may provide a facile way to prepare metal modified photocatalysts to achieve highly efficient nitrate reduction to ammonia.

Reaction intermediate-mediated electrocatalyst synthesis favors specified facet and defect exposure for efficient nitrate–ammonia conversion

An intermediate-mediated approach was proposed to synthesize copper, rich in (100) facets and defects, for highly efficient nitrate reduction.

Dynamics of denitrification performance and denitrifying community under high-dose acute oxytetracycline exposure and various biorecovery strategies in polycaprolactone-supported solid-phase denitrification

Solid-phase denitrification (SPD) is a promising technology for nitrate-rich water purification. This study aimed to examine the variation in denitrification performance and denitrifying community under high-dose acute oxytetracycline (OTC) exposure and various biorecovery strategies. The denitrification performance was impaired significantly after one-day OTC shock at 50 mg L−1 in a continuous-flow SPD system supported by a polycaprolactone (PCL) carrier but could rapidly recover without the addition of OTC. When 50 mg L−1 OTC stress was applied for a longer time in the batch tests, a natural recovery period of more than 20 days was required to reach more than 95% nitrate reduction. Under the same conditions, the addition of both mature biofilm-attached PCL carrier and fresh biofilm-free PCL carrier significantly shortened the recovery time for efficient nitrate reduction, mainly due to the increase in organic availability from the PCL carriers. However, the composition of the microbial community notably changed due to the effects of OTC according to high-throughput sequencing and metagenomic analysis. Genes encoding NAR and NIR were much more sensitive than those encoding NOR and NOS to OTC shock. Tetracycline resistance gene (TRG) enrichment was 15.86% higher in the biofilm that experienced short-term OTC shock than in the control biofilm in the continuous-flow SPD system.

Fabrication of Porous Configurated Ni2P/Ni Foam Catalyst and its Boosted Properties for pH‐universal Hydrogen Evolution Reaction and Efficient Nitrate Reduction

AbstractNickel phosphide (Ni2P) has been widely explored toward hydrogen evolution reaction (HER) for desirable durability and high performance. Tuning the electronic structures and morphologies of Ni2P plays a pivotal role in the improvement of HER performance. In this work, three Ni2P catalysts were fabricated by different strategies and their HER properties were compared. It was found that the bicontinuous porous structured Ni2P on Ni foam (Ni2P /NF−EHP) prepared using coupled electroless nickel‐phosphorus (Ni−P) plating, hydrothermal synthesis and low temperature phosphorization techniques, exhibits the best catalytic activity and a wide pH adaptability. The overpotential at 10 mA cm−2 and Tafel slope are 78 mV and 33 mV dec−1 in 0.5 M H2SO4, those in 1 M PBS are 125 mV and 93 mV dec−1, and 101 mV and 76 mV dec−1 in 1 M KOH. Additionally, the Ni2P/NF−EHP‐catalyzed HER process is also applicable for nitrate reduction with a remarkable removal efficiency of 92.6 %. This catalyst also exhibits a desirable durability both in HER and nitrate reduction. This work offers an efficient strategy to exploit compatible pH‐universal HER catalysts, explores the engineering application of HER process in nitrate reduction.

Electrochemically mediated nitrate reduction on nanoconfined zerovalent iron: Properties and mechanism

Selective reduction of nitrate to N2 is attractive but still a difficult challenge in the water treatment field. Herein, we established a flow-through electrochemical system packed with polymeric beads supported nZVI (nZVI@D201) for selective nitrate reduction. Consequently, efficient nitrate reduction in the flow mode was achieved on nZVI@D201 under electrochemical regulation with N2 selectivity of up to 95% for at least 60 h. Otherwise, nZVI was gradually exhausted after 20 h, and the product was mainly the undesired NH4+. Through a series of comparative experiments, we clarified that the enhanced nitrate reduction on nZVI under electrochemical regulation was mainly attributed to electrons (from cathode) and active hydrogen ([H]) rather than the previously speculated H2. Combining the characterizations of nZVI during nitrate reduction by X-ray diffraction and X-ray photoelectron spectrometry, we found that nitrate reduction under electrochemical regulation was mediated by nZVI along with the resultant Fe0@FexOy-Fe(II) structure and was sustained by electrons (from cathode) and [H] via the in situ reduction of Fe(III) back to Fe(II). Meanwhile, the undesirable product NH4+ was efficiently oxidized to N2 by the active chlorine generated on the anode. This study not only clarifies the mechanism of enhanced nitrate reduction on nZVI via electrochemical regulation but also advances the technological coupling of nZVI reduction with electrochemistry.

Highly efficient nitrate reduction driven by an electrocoagulation system: An electrochemical and molecular mechanism

Electrotrophic denitrification is suitable for nitrate removal in aqueous environments where bioavailable electron donors are limited such as in urban polluted water. Herein, a novel microbial denitrifying electrocoagulation cell (MDECC) with an Fe anode and an electrotrophic denitrifying biocathode was constructed. Nitrate reduction was verified relying solely on the electrons originated from the electrolysis process at the Fe anode. In situ generated coagulant at the anode was utilized to effectively flocculate and precipitate pollutants as well as naturally occurring components. Nitrate reduction by the biocathode showed pseudo-first-order kinetics with a maximum NO3−-N removal rate of 67 ± 7 g m−3 d−1 and a total nitrogen (TN) removal rate of 39 ± 6 g m−3 d−1. Mechanistic research demonstrated that the system achieved highest current efficiency and denitrification enzyme activity at an initial NO3−-N concentration (IC-N) of 100 mg L−1. Further pyrosequencing evidenced that higher initial NO3−-N concentration increased the abundance of denitrifiers on biocathode. Correlation analysis indicated that nitrate reductase (NAR) and nitrite reductase (NIR) activities were crucial for NO3−-N and TN removal. The metal anode was a promising alternative for providing electrons for electrotrophic denitrification and pollutant elimination.

INCORPORATION OF HYBRID BIOFILTERS IN WATER-SENSITIVE URBAN DESIGN

This paper presents a research study aimed at the development of a hybrid biofilter that can serve for two different applications. This is a unique approach due to the prolonged dry period in Israel covering 7-8 months of the year. The tactic suggested herein is to use the same system for stormwater harvesting/treatment during winter, and for bioremediation of nitrate-contaminated groundwater during summer. Crude cotton and Eucalyptus wood-chips served as alternative carbon sources for denitrification, and both proved to support efficient reduction of nitrate with minimal release of nitrite and organic matter. During the stage of stormwater treatment, two types of biofilter-columns (120 & 70 cm long) were tested, with a minimal saturation zone and no addition of organic carbon. Complete nitrification could be achieved, even under high instantaneous hydraulic loads for both column types. Vegetation on top of the biofilters contributed to improved removal of the nitrate formed, by plant assimilation.

Ti plate with TiO2 nanotube arrays as a novel cathode for nitrate reduction

The purpose of this research is to investigate the possibility of using a Ti plate with TiO2 nanotube arrays as a novel cathode for nitrate reduction. TiO2 nanotube arrays were grown on a Ti plate by anodization in a glycerol based electrolyte and annealed to change their crystallographic structure. Morphological and crystallographic structures of Ti plates with a TiO2 nanotubular layer were analysed before and after anodization or annealing by using energy-dispersive spectroscopy, Brunauer-Emmett-Teller analysis and X-ray diffraction. Cyclic voltammetry and electrochemical impedance spectroscopy were also performed to test the electrochemical reactivity towards nitrate reduction. A lab-scale electrochemical reactor with a RuO2/Ti anode and a Ti plate with a TiO2 nanotubular layer as a cathode was operated to treat synthetic wastewater containing up to 600 mg L−1 of NO3-N. The Ti plate with a TiO2 nanotubular layer was compared with other cathodes such as Ti, Cu, Ni, and Stainless Steel. The Ti plate with an anatase TiO2 nanotubular layer with a layer thicknesses greater than 45 μm was able to show the most efficient nitrate reduction.

Selective reduction of nitrate to nitrogen gas by novel Cu2O-Cu0@Fe0 composite combined with HCOOH under UV radiation

The nitrate reduction by Fe-based materials has been extensively studied, however, the selectivity of nitrate reduction to nitrogen gas is very low, which hinders the application of this technology. In this study, a novel Cu2O-Cu0@Fe0 composite was synthesized and a strategy of Cu2O-Cu0@Fe0 composite combined with HCOOH under UV radiation as reducers for the nitrate reduction was established to improve the selective reduction of nitrate (NO3−) to nitrogen gas (N2). The Cu2O-Cu0@Fe0 composite was synthesized by simple chemical replacement and O2 oxidation process and characterized by SEM, EDS, XRD and XPS. The nitrate removal efficiency of 100% and the N2 selectivity of 95.4% were achieved in Cu2O-Cu0@Fe0/HCOOH/UV system when the initial nitrate concentration was 50 mg N/L and the reduction time was 60 min. The nitrate reduction efficiency was low by the role of alone or combinations of Cu2O-Cu0@Fe0 composite, HCOOH or UV radiation. The quick reduction of nitrate to nitrite was due to the synergistic effect of electrons from the galvanic-type cell consisting of Fe0 as anode and Cu0 as cathode, photoelectrons from Cu2O under UV radiation and CO2− produced mainly via photochemical reaction between HCOOH and UV radiation. The subsequent conversion of nitrite to N2 was caused by CO2−, which was responsible for the high efficient reduction of nitrate to nitrogen gas in the Cu2O-Cu0@Fe0/HCOOH/UV system. Finally, the denitrification mechanism of the Cu2O-Cu0@Fe0/HCOOH/UV system was tentatively proposed.

Formic acid as the in-situ hydrogen source for catalytic reduction of nitrate in water by PdAg alloy nanoparticles supported on amine-functionalized SiO2

Nitrate pollution in water is becoming a severe problem all over the world, and the catalytic reduction of nitrate by reducing agents had been considered as one of the most promising methods because it could convert nitrate to harmless nitrogen gas with a high efficiency. In this work, the PdAg/SiO2-NH2 catalyst was developed by firstly loading Pd onto NH2 surface-modified SiO2 catalyst support, followed by a controlled surface reaction to load Ag and create PdAg alloy nanoparticles on SiO2-NH2 catalyst support. For the first time, the PdAg/SiO2-NH2 catalyst was found to be able to effectively reduce nitrate with HCOOH as the reducing agent precursor. Its enhanced nitrate reduction performance could be attributed to the combination effects from the surface NH2 modification and the better electron transfer from Ag to Pd than from other metals due to their larger difference of work function, both of which were beneficial for the catalytic HCOOH decomposition to provide the in situ sources of the reducing agent of H2 and buffer of CO2 for the catalytic nitrate reduction process. To optimize the nitrate reduction performance of the PdAg/SiO2-NH2 catalyst, Ag content was carefully modulated and the Pd:Ag molar ratio of 1:0.5 was found to have the most efficient nitrate reduction capability.

Identifying Efficient Nitrate Reduction Strategies in the Upper Danube

Nitrogen losses in the form of Nitrate (N-NO3) from point and diffuse sources of pollution are recognized to be the leading cause of water body impairment throughout Europe. Implementation of conservation programs is perceived as being crucial for restoring and protecting the good ecological status of freshwater bodies. The success of conservation programs depends on the efficient identification of management solutions with respect to the envisaged environmental and economic objectives. This is a complex task, especially considering that costs and effectiveness of conservation strategies depend on their locations. We applied a multi-objective, spatially explicit analysis tool, the R-SWAT-DM framework, to search for efficient, spatially-targeted solution of Nitrate abatement in the Upper Danube Basin. The Soil Water Assessment Tool (SWAT) model served as the nonpoint source pollution estimator for current conditions as well as for scenarios with modified agricultural practices and waste water treatment upgrading. A spatially explicit optimization analysis that considered point and diffuse sources of Nitrate was performed to search for strategies that could achieve largest pollution abatement at minimum cost. The set of optimal spatial conservation strategies identified in the Basin indicated that it could be possible to reduce Nitrate loads by more than 50% while simultaneously provide a higher income.

Efficient Nitrate Reduction in a Fluidized Electrochemical Reactor Promoted by Pd–Sn/AC Particles

Pd–Sn modified activated carbon (Pd–Sn/AC) was prepared by impregnation of Pd and Sn salts onto AC followed by heat treatment. Based on scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis, Pd–Sn alloy was highly dispersed on the surface of AC with a atomic ratio of about 4.21. A double electrolysis cell was established and separated via a proton-exchange membrane. In the cathodic cell compartment, the as-prepared Pd–Sn/AC was used as particle electrodes where electrolytic reduction of nitrate was performed. A batch mode study showed that at an applied current of 30 mA with 7.5 g/L catalyst, over 90 % of the nitrate could be reduced in 80 min when the nitrate initial concentration was 24.6 mg/L. The electro-catalytic process of nitrate reduction could be satisfactorily described with a first-order kinetics model. With increasing applied current, the nitrate removal rate increased; whereas, the NH4 + concentration increased as well. The inhibition effect of co-existing anions and cations on nitrate reduction followed this order: Fe3+ > Mn2+ > Ca2+ > Na+ and Cl− < SO4 2− < HCO3 −.

Poly[β-(1→4)-2-amino-2-deoxy-D-ghicopyranose] based zero valent nickel nanocomposite for efficient reduction of nitrate in water

Chemical reduction of nitrate using metal nanoparticles has received increasing interest due to over-dependence on groundwater and consequence health hazard of the nitrate ion. One major drawback of this technique is the agglomeration of nanoparticles leading to the formation of large flocs. A low cost biopolymeric material, poly [β-(1→4)-2-amino-2-deoxy-D-glucopyranose] (β-PADG) obtained from deacetylated chitin was used as stabilizer to synthesize zero valent nickel (ZVNi) nanoparticles. The β-PADG-ZVNi nanocomposite was characterized using infra red (IR), UV-Vis spectrophotometric techniques and Scanning Electron Microscope (SEM). The morphology of the composite showed that β-PADG stabilized-ZVNi nanoparticles were present as discrete particles. The mean particle size was estimated to be (7.76 ± 2.98) nm and surface area of 87.10 m2/g. The stabilized-ZVNi nanoparticles exhibited markedly greater reactivity for reduction of nitrate in water with 100% conversion within 2 hr contact owing to less agglomeration. Varying the β-PADG–to-ZVNi ratio and the ZVNi-to-nitrate molar ratio generally led to a faster nitrate reduction. About 3.4-fold difference in the specific reaction rate constant suggests that the application of the β-PADG-stabilizer not only increased the specific surface area of the resultant nanoparticles, but also greatly enhanced the surface reactivity of the nanoparticles per unit area.

Wheel-Shaped Cu20-Tungstophosphate [Cu20X(OH)24(H2O)12(P8W48O184)]25− Ion (X = Cl, Br, I) and the Role of the Halide Guest

We have synthesized the known [Cu(20)Cl(OH)(24)(H(2)O)(12)(P(8)W(48)O(184))](25-) (1) and report here its bromide and iodide analogues, [Cu(20)Br(OH)(24)(H(2)O)(12)(P(8)W(48)O(184))](25-) (2) and [Cu(20)I(OH)(24)(H(2)O)(12)(P(8)W(48)O(184))](25-) (3). These polyanions were characterized in the solid state by IR spectroscopy and single-crystal X-ray diffraction. Magnetic susceptibility and magnetization data over 1.8-300 K show that the Cu(2+) ions in 1-2 are antiferromagnetically coupled, leading to a diamagnetic ground state. The effective exchange coupling constant J(eff) was estimated as approximately -3 K for both 1 and 2. Electron paramagnetic resonance measurements were made on 1 and 2 over 5-295 K at microwave frequencies of 9.5, 34, and 220 GHz. The observed (weak) signals were characteristic of randomly distributed Cu(2+) ions only, with g values and hyperfine constants typical of the unpaired electron in a 3d(x(2)-y(2)) orbital of Cu(2+). No signals attributable to the copper-hydroxo cluster were detected, supporting the conclusions from the magnetization measurements. DFT calculations were performed as well to obtain additional information on the anionic guest inside the cavity created by the copper-hydroxo cage related to electronic structure and energies of encapsulation. The polyanions 2 and 3 were also characterized by cyclic voltammetry (CV) in a pH 5 medium. Their CVs are composed by an initial two-step reduction of the Cu(2+) centers to Cu(0) through Cu(+), followed at more negative potential by the redox processes of the W centers. A comparison with the CV characteristics of the previously studied compound 1 indicates that the potential locations of the Cu or W waves of the three analogues do not depend significantly upon the identity of the central halide X. This observation is in accordance with conclusions of DFT calculations. The modified electrodes based on 2 and the room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate triggers an efficient reduction of nitrate. To our knowledge, this is the first example of electrocatalytic nitrate reduction by a polyanion entrapped in room-temperature ionic liquid films.

Microbial community dynamics in uranium contaminated subsurface sediments under biostimulated conditions with high nitrate and nickel pressure

The subsurface at the Oak Ridge Field Research Center represents an extreme and diverse geochemical environment that places different stresses on the endogenous microbial communities, including low pH, elevated nitrate concentrations, and the occurrence of heavy metals and radionuclides, including hexavalent uranium [U(VI)]. The in situ immobilization of U(VI) in the aquifer can be achieved through microbial reduction to relatively insoluble U(IV). However, a high redox potential due to the presence of nitrate and the toxicity of heavy metals will impede this process. Our aim is to test biostimulation of the endogenous microbial communities to improve nitrate reduction and subsequent U(VI) reduction under conditions of elevated heavy metals. Column experiments were used to test the possibility of using biostimulation via the addition of ethanol as a carbon source to improve nitrate reduction in the presence of elevated aqueous nickel. We subsequently analyzed the composition of the microbial communities that became established and their potential for U(VI) reduction and its in situ immobilization. Phylogenetic analysis revealed that the microbial population changed from heavy metal sensitive members of the actinobacteria, alpha- and gamma-proteobacteria to a community dominated by heavy metal resistant (nickel, cadmium, zinc, and cobalt resistant), nitrate reducing beta- and gamma-proteobacteria, and sulfate reducing Clostridiaceae. Coincidentally, synchrotron X-ray absorption spectroscopy analyses indicated that the resulting redox conditions favored U(VI) reduction transformation to insoluble U(IV) species associated with soil minerals and biomass. This study shows that the necessary genetic information to adapt to the implemented nickel stress resides in the endogenous microbial population present at the Oak Ridge FRC site, which changed from a community generally found under oligotrophic conditions to a community able to withstand the stress imposed by heavy metals, while efficiently reducing nitrate as electron donor. Once nitrate was reduced efficient reduction and in situ immobilization of uranium was observed. This study provides evidence that stimulating the metabolism of the endogenous bacterial population at the Oak Ridge FRC site by adding ethanol, a suitable carbon source, results in efficient nitrate reduction under conditions of elevated nickel, and a decrease of the redox potential such that sulfate and iron reducing bacteria are able to thrive and create conditions favorable for the reduction and in situ immobilization of uranium. Since we have found that the remediation potential resides within the endogenous microbial community, we believe it will be feasible to conduct field tests. Biostimulation of endogenous bacteria provides an efficient tool for the successful in situ remediation of mixed-waste sites, particularly those co-contaminated with heavy metals, nitrate and radionuclides, as found in the United States and other countries as environmental legacies of the nuclear age.

Short communication. Nitrate reductase activity in roots and leaves of chickpea cultivars under salt stress

Four chickpea cultivars (CSG 9651, BG 267, CSG 8962 and DCP 92-3) were grown to maturity under salinity conditions of 0, 4, 6 and 8 dS mE-1. Nitrate reductase activity decreased progressively with increasing salinity, although variation was seen between the cultivars. Cultivar CSG 9651, a kabuli or Mediterranean type, appeared to be the best adapted to saline stress, maintaining growth and showing efficient nitrate reduction under these conditions.

Improving the catalytic nitrate reduction

Technologies for the nitrate removal from drinking water and waste water will be required in the near future and the catalytic nitrate reduction is one of the most promising ones. To establish a technical-scale nitrate reduction a further improvement of the catalyst is necessary and new concepts should be introduced in the process. It is shown, that palladium–tin and palladium–indium catalysts can be much more suited for an efficient nitrate reduction than palladium–copper catalysts. Furthermore, two new innovative concepts are presented — the use of in situ buffering formic acid as reductant instead of hydrogen and the application of PVAL-encapsulated catalysts with superior diffusional properties — which may contribute to solve selectivity problems.