Degradation Of Nitrate Research Articles

Nitrite as undesirable substances in animal feed ‐ Scientific Opinion of the Panel on Contaminants in the Food Chain

Nitrite as undesirable substances in animal feed ‐ Scientific Opinion of the Panel on Contaminants in the Food Chain

Electrokinetically enhanced removal and degradation of nitrate in the subsurface using nanosized Pd/Fe slurry

The aim of this work was to evaluate the effectiveness of transporting the slurry of Pd/Fe bimetallic nanoparticles under an electric field in the subsurface for in situ removal and degradation of nitrate. To mimic the subsurface environment, a bench-scale horizontal column packed with nitrate-contaminated soil was treated by electrokinetic (EK) remediation coupled with the injection of nanosized Pd/Fe slurry. The estimated transport distance of Pd/Fe nanoparticles in soil based on the calculated sticking coefficient was about 9 meters by the enhancement of electrokinetics, primarily by electroosmotic (EO) flow. By injecting the nanosized Pd/Fe slurry into the anode reservoir coupled with the application of an electric field (i.e., Test 2) would result in the greatest overall removal efficiency of nitrate in soil and reservoir fluids as compared with other injection positions, the cathode reservoir being the worst injection spot. In Test 2, over 99% of nitrate in the whole system was removed and degraded even only 0.05 wt% of nanoscale Pd/Fe bimetal was injected.

Reduction of nitrate by nanoscale zero-valent iron supported on mesoporous silica beads

The use of zero-valent iron (ZVI) represents one of the latest innovative technologies for groundwater remediation. The reactivity of ZVI is enhanced when the particle size is in the nanometer range. However, nanoscale ZVI has limited field applications for in-situ groundwater remediation such as permeable reactive barriers due to its powdery form. Therefore, a method of adhering nanoparticles on a supporting material was suggested. In this paper, functionalized mesoporous silica beads were created using 3-mercaptopropyltrimethoxy silica, tetrabutyl orthosilicate, and cetyltrimethyl ammonium bromide, and their physical and chemical characteristics were measured. The highly active ZVI nanoparticles were adhered on these mesoporous silica beads. The reactivity of the resulting material was tested using nitrate solution. The reductive reaction of nitrate indicated that the degradation of nitrate appeared to be pseudo-first order with a high reaction rate constant of 0.1619 h-1. The reaction constant decreased to 0.0122 h-1 after 3 h of experiment due to mass transfer limitation. The higher dose of the supported nanosized ZVI increased the removal rate as well as the removal efficiency of nitrate.

Hydrogenation of nitrate in water over bimetallic Pd-Ag/Al2O3 catalysts

Hydrogenation of nitrate (NO3−) in water was studied with 0.8 ×10−3–3.2 ×10−3 mol/dm3 of reactant in the temperature range of 293–313 K over palladium promoted Ag catalysts. Pd-Ag catalysts with a low ratio of Ag/Pd were characterized by high efficiency in the reduction of nitrates. The degradation of nitrates followed approximately first order decay and the estimated apparent activation energy was about 4 kJ/mol.

Degradation of cellulose nitrates in low-water media

The kinetics of degradation of cellulose nitrates in low-water organic solvents in the presence of various catalysts was examined.

X-ray irradiation induced degradation of cellulose nitrate

Energy-dispersive X-ray fluorescence (EDXRF) spectrometry was previously proposed to measure the thickness of the cellulose nitrate layer of the commonly used LR 115 solid-state nuclear track detector (SSNTD). The present work is devoted to the investigation whether the X-ray radiation involved in EDXRF spectrometry will induce degradation of the cellulose nitrate. For this purpose, Fourier transform infrared (FTIR) spectroscopy was employed to examine the nitrate functions (at the wavenumber 1598 cm −1) and the glycosidic bonds (at 1146 cm −1) for various irradiation time involved in the EDXRF spectrometry. No significant changes were observed even for X-ray irradiation up to 3000 live seconds, which was equivalent for 10 separate scans and should be far more than enough for a determination of the cellulose nitrate layer thickness. Therefore, EDXRF remains a fast and non-destructive method to measure the active layer thickness of the cellulose nitrate SSNTD.

Effect of the reducing step on the properties of Pd-Cu bimetallic catalysts used for denitration

Bimetallic (Pd/Cu) catalysts supported on alumina were used for the degradation of nitrates in water. The reduction temperature strongly affects the surface and oxidation states of the metals on the catalysts. These significant changes were characterized by FT-IR, XPS, TEM with EDX and H 2 chemisorption. Migration of superficial copper on top of palladium and towards the support during the reducing steps was observed, moreover palladium particles free of copper were found. With increasing reduction temperature the activity of the bimetallic catalysts passes through a maximum whereas the selectivity to nitrogen increases.

Effect of Ammonium Ions on the Radiation Degradation of Potassium Nitrate

The formation and thermal conversion of paramagnetic centers in γ-irradiated single crystals of potassium nitrate with an ammonium nitrate impurity was studied by EPR spectroscopy. It was found that the presence of ammonium nitrate decreased the radiation-chemical yield of nitrite ions, which are one of the final radiolysis products of nitrate-containing compounds. An analysis of the results of a study on NO2 orientation in the KNO3 crystal lattice with an impurity of NH+4 allowed us to propose a mechanism for selective N–O bond rupture in the radiation-stimulated dissociation of the nitrate ion in a potassium nitrate matrix.

Mass spectral studies on the mechanism of thermal decomposition of Zn(NO 3) 2· nH 2O

Thermal decomposition of Zn(NO 3) 2· nH 2O ( n=4 and 6) was studied using TG, DTA and QMS techniques. Measurements were performed in helium and in dry air. It was found that the examined reaction is a multi-step process with overlapping stages. The whole process depends on the rate of heating. Degradation of nitrate(V) groups starts before all water of crystallisation is removed from the system. Zn(NO 3) 2·2Zn(OH) 2 was identified as intermediate product of decomposition of Zn(NO 3) 2· nH 2O.

Degradation of TCE, Cr(VI), sulfate, and nitrate mixtures by granular iron in flow-through columns under different microbial conditions

Flow-through aquifer columns packed with a middle layer of granular iron (Fe 0) were used to study the applicability and limitations of bio-enhanced Fe 0 barriers for the treatment of contaminant mixtures in groundwater. Concentration profiles along the columns showed extensive degradation of hexavalent chromium Cr(VI), nitrate, sulfate, and trichloroethene (TCE), mainly in the Fe 0 layer. One column was bioaugmented with Shewanella algae BRY, an iron-reducing bacterium that could enhance Fe 0 reactivity by reductive dissolution of passivating iron oxides. This strain did not enhance Cr(VI), which was rapidly reduced by iron, leaving little room for improvement by microbial participation. Nevertheless, BRY-enhanced nitrate removal (from 15% to 80%), partly because this strain has a wide range of electron acceptors, including nitrate. Sulfate was removed (55%) only in a column that was bioaugmented with a mixed culture containing sulfate-reducing bacteria. Apparently, these bacteria used H 2 (produced by Fe 0 corrosion) as electron donor to respire sulfate. Most of the TCE was degraded in the zone containing Fe 0 (50–70%), and bioaugmentation with BRY slightly increased the removal efficiency to about 80%. Microbial colonization of the Fe 0 surface was confirmed by scanning electron microscopy.

Effect of formate on the radiolytic degradation of nitrate in deaerated aqueous solutions

Nitrate ions are irreversibly reduced in dilute aqueous solutions in the presence of formate under the action of an electron beam.

Degradation of Sucrose and Nitrate Over Titania Coated Nano-hematite Photocatalysts

Photodegradation of sucrose and/or nitrate in aqueous solutions was studied over the titania coated nano-hematite photocatalysts under near-UV irradiation. The efficiency of the photocatalytic oxidation and reduction of these coated particles was compared to the prepared single phase TiO2. It was found that in different environments (O2 or N2) the particles showed differences in the photocatalytic efficiency due to the different reaction mechanisms. Effect of nitrate on sucrose degradation was investigated. In aerobic conditions, sucrose was degraded effectively while nitrate reduction was insignificant due to the fast reoxidation of nitrite by O2 in the dark and by OH. in homogeneous reaction. Since nitrite competes with sucrose for hydroxyl radicals, it has an adverse effect when the aerobic system contains both substrates. Since reoxidation was suppressed in N2 conditions, greater reduction of nitrate was observed. The result showed clearly that in the absence of O2, CO2 production from sucrose mineralisation was limited by the amount of oxygen produced from the nitrate decomposition. Partial photodissolution of Fe ions for the coated samples was also observed in both environments.

Abiotic Degradation of Nitrates Using Zero-Valent Iron and Electrokinetic Processes

Nitrate transformation in artificial saturated soils made from sand and/or clay mixed with nitrate-contaminated water was investigated using (1) zero-valent iron treatment, (2) electrokinetics treatment alone, and (3) electrokinetics coupled with an iron treatment wall placed near the cathode or anode. Approximately 75–98% of the nitrates were transformed using zero-valent iron to treat the artificial soils. The major products in the zero-valent–assisted transformation were nitrogen gases (75–81%) and ammonia–nitrogen (2–18%). Nitrite–nitrogen was less than 1% in all these experiments. With electrokinetics alone, some nitrates were transformed (about 30%). Nitrate transformation was about 60% with the iron wall placed near the cathode, and was about 95% with the iron wall placed near the anode. The major products were nitrogen gases and ammonia. Nitrite-nitrogen was less than 1% in these runs. Electroosmotic permeability (Ke) variation appeared to be dependent on the voltage in the reactor. The pH variations over time in electrokinetics (control and iron wall near cathode) indicated the movement of a small acid front. However, the presence of an iron wall near the anode tended to increase the pH slightly. The pH variations over time in the electrokinetics coupled with an iron wall depend on the location of the iron wall. This study demonstrates that electrokinetics coupled with an iron wall near the anode is capable of remediating nitrate contamination in low permeability soils. Key words: Electrokinetics; treatment wall; zero-valent iron; nitrates; groundwater remediation

Modelling the nitrate flow in the ground-water provinces of the “old” federal states of the Federal Republic of Germany

The aim of this study is to trace the nitrate flow in the ground water from diffuse sources over the whole area of the former West Germany ranging from input into the soil up to output into surface waters. A systems analysis approach was selected for the implementation of these tasks since this permits an interconnection of large volumes of data with complex and interdisciplinary correlations. The problem-relevant aspects were compiled from the profusion of data and regularities on nitrate discharge from the soil, the hydrological and geological circumstances as well as nitrate conversion processes in the soil and ground water, and pieced together to form a comprehensive model. This model was transformed into a computer program and coupled to a graphical program system permitting a clear illustration in the form of coloured grid maps. A high nitrate pollution of the ground water (> 50 mg NO 3 /l) can be expected in all regions with an intensive agricultural use of the topsoil. In particular ground-water occurrences in solid rock areas are susceptible to nitrate pollution. There a rapid ground-water turnover and thus a short residence time for the ground water in the aquifer is typical. Oxidizing aquifer conditions usually prevail in solid rock aquifers preventing nitrate degradation. In many loose rock areas, in contrast, the ground water has a low flow velocity and a long residence time in the aquifer. Because of a lack of free oxygen a complete degradation of nitrate can occur, as long as iron-sulphide compounds and/or organic carbon are available in the aquifer.

Potential nitrate pollution of groundwater in Germany: A supraregional differentiated model

Implemented on behalf of the Federal Ministry for Research and Technology (BMFT), a model is developed to trace the nutrient flow of nitrate in the soil and the groundwater on a supraregional scale. Research work is intended to indicate regionally differentiated hazardous potentials and thereby provide a basis for recommending comprehensive measures to protect groundwater in Germany. The adaption of the model to the hydrogeological and agricultural conditions of other states is possible in principle. This article focuses on the hydrogeological model parts. A high nitrate pollution of groundwater can be expected in all regions with intensive agricultural use of the topsoil. In particular, groundwater in solid rock areas is susceptible to nitrate pollution. There a rapid groundwater turnover and thus a short residence time for the groundwater in the aquifer is typical. Oxidizing aquifer conditions usually prevail in solid rock aquifers, preventing nitrate degradation. In many loose rock areas, in contrast, the groundwater has a low flow velocity and a long residence time in the aquifer. Because of a lack of free oxygen, a complete degradation of nitrate can occur, as long as iron sulfide compounds and/or organic carbon are available in the aquifer. A more detailed presentation of the whole research work is given in Wendland et al. (1993).

The chemical degradation of phenylmercuric nitrate by disodium edetate during heat sterilization at pH values commonly encountered in ophthalmic products.

The stability following heat sterilization (121 degrees C for 15 min) of phenylmercuric (PM) nitrate in the presence of disodium edetate at pH values 5-8 has been investigated by both high-performance liquid chromatography (HPLC) and atomic absorption spectroscopy (AAS). A stability-indicating HPLC method involving formation of the diethylamine-dithiocarbamate complexes of phenylmercuric and mercuric ions was found to suffer a pH-dependent interference from disodium edetate. A second method was therefore also employed involving selective extraction into diethylether of the phenylmercuric ion followed by HPLC of the piperidinedithiocarbamate complex with concomitant analysis of the unextracted mercuric ion by AAS using the cold-vapour technique. An HPLC method was also developed for benzene in the degraded mixtures. The application of these methods to autoclaved solutions containing PM nitrate and disodium edetate demonstrates that under the conditions of heat sterilization the phenylmercuric ion is degraded to mercuric ion and benzene to the extent of 15% at pH 8, 80% at pH 7 and completely degraded at pH 5 and 6.

Degradation of cellulose nitrate adhesive

An adhesive based on cellulose nitrate has been used in the British Museum for the repair of antiquities since cellulose nitrate plastic was first made commercially available. The use of cellulose nitrate adhesives in conservation has been criticized and for this reason the stability of the adhesive currently in use has been investigated. The properties of artificially aged samples of the adhesive have been compared with those of artificially aged adhesive-grade cellulose nitrate. The results indicate that the degradation of cellulose nitrate is substantially retarded by the plasticizer in the adhesive. Samples of cellulose nitrate adhesive taken from joins in objects where the date of conservation work is known have been analyzed. The results have been compared with the analysis of the artificially aged samples and a relationship between natural and artificial aging of cellulose nitrate adhesive has been established. The results of this investigation indicate that cellulose nitrate adhesives are stable for at least 30 years, and may be extrapolated to suggest a lifetime of 50 to 100 years under museum conditions in a temperate climate.

High-performance liquid chromatographic investigation of the interaction of phenylmercuric nitrate and sodium metabisulphite in eye drop of formulations

The degradation of phenylmercuric nitrate in the presence of sodium metabisulphite in eye drop formulations has been investigated using a stability-indicating high-performance liquid chromatographic (HPLC) method. HPLC methods have been developed for the quantitation of the principal degradation products (diphenylmercury, benzenesulphonic acid and benzenesulphinic acid) and a mechanism is proposed for their formation. The pharmaceutical significance of the interaction is briefly discussed.

Correlation between nitric oxide formation during degradation of organic nitrates and activation of guanylate cyclase

Organic nitrates develop their vasodilating potency by stimulating the enzme guanylate cyclase. There are still several theories concerning the molecular mechanism of enzyme activation, the most likely of which sees nitric oxide (NO·) as the true modulator of the soluble guanylate cyclase. We therefore examined the release of nitric oxide from organic nitrates by means of difference-spectrophotometric method and found that our results correlated well with the extent of enzyme activation. The more NO· was liberated from the compounds in question, the higher was the enzyme activation observed. When the examined nitrates were used in a concentration which caused a half-maximal enzyme stimulation, the result was a NO· liberation of striking uniformity. This correlation also applied to SIN-1 for which it has been assumed up to now that the intact molecule itself is able to stimulate the enzyme and not the nitric oxide released from it. We found the reaction between organic nitrates and cysteine to be highly dependent on temperature, while the extent of the observed enhancement increased with the number of nitrate groups per molecule. We also studied the potential effects of certain compounds on non-enzymatic NO· release and found that, in addition to methylene blue, thionine and brilliantcresyl blue, but not ferricyanide were also effective inhibitors. So it seems likely that both an enzymatic and a non-enzymatic mode of inhibition of enzyme activity does exist. Since oxyhemoglobin is an effective scavenger of nitric oxide, its addition can inhibit enzyme activation by nitrovasodilators. Our results stress the important role of the non-enzymatic liberation of NO· from organic nitrates and related compounds as possible, perhaps even as the principal mode of activation of soluble guanylate cyclase by nitrovasditors.

Degradation of nitrate by enterobacteria during silage fermentation of grass.

Enterobacteria were isolated from grass and from grass ensiled in laboratory silos. Strains isolated from grass belonged mainly to the Erwinia herbicola group. After ensiling, the numbers of these bacteria diminished and Escherichia coli, Hafnia alvei and Klebsiella pneumoniae became the predominant bacteria in the respective experiments. Several strains, isolated either from grass or silage, were tested for their action on nitrate degradation by adding them to grass prior to ensiling. The isolates from grass did not affect nitrate degradation, whereas those from silage increased the rate of nitrate degradation and gave higher transient concn of nitrite and nitric oxide. Results showed no direct relationship between the total number of enterobacteria on grass and its ensilability. The numbers of enterobacteria on grass that developed after ensiling were 2 orders of magnitude lower than the total number of enterobacteria originally present on the grass. (Abstract retrieved from CAB Abstracts by CABI’s permission)