Showing papers on "Urea published in 2012"

Ammonia volatilization losses from surface-applied urea with urease and nitrification inhibitors

Abstract: Urease inhibitor (UI) and nitrification inhibitor (NI) have the potential to improve N-use efficiency of applied urea and minimize N losses via gaseous emissions of ammonia (NH3) to the atmosphere and nitrate ( NO 3 − ) leaching into surface and ground water bodies. There is a growing interest in the formulations of coating chemical fertilizers with both UI and NI. However, limited information is available on the combined use of UI and NI applied with urea fertilizer. Therefore the aim of this study was to investigate the effects of treating urea with both UI and NI to minimize NH3 volatilization. Two experiments were set up in volatilization chambers under controlled conditions to examine this process. In the first experiment, UR was treated with the urease inhibitor NBPT [N-(n-butyl) thiophosphoric acid triamide] at a rate of 1060 mg kg−1 urea and/or with the nitrification inhibitor DCD (dicyandiamide) at rates equivalent to 5 or 10% of the urea N. A randomized experimental design with five treatments and five replicates was used: 1) UR, 2) UR + NBPT, 3) UR + DCD 10%, 4) UR + NBPT + DCD 5%, and 5) UR + NBPT + DCD 10%. The fertilizer treatments were applied to the surface of an acidic Red Latosol soil moistened to 60% of the maximum water retention and placed inside volatilization chambers. Controls chambers were added to allow for NH3 volatilized from unfertilized soil or contained in the air that swept over the soil surface. The second experiment had an additional treatment with surface-applied DCD. The chambers were glass vessels (1.5 L) fit with air inlet and outlet tubings to allow air to pass over the soil. Ammonia volatilized was swept and carried to a flask containing a boric acid solution to trap the gas and then measured daily by titration with a standardized H2SO4 solution. Continuous measurements were recorded for 19 and 23 days for the first and second experiment, respectively. The soil samples were then analyzed for UR–, NH 4 + – , and NO 3 − – N . Losses of NH3 by volatilization with unamended UR ranged from 28 to 37% of the applied N, with peak of losses observed the third day after fertilization. NBPT delayed the peak of NH3 losses due to urease inhibition and reduced NH3 volatilization between 54 and 78% when compared with untreated UR. Up to 10 days after the fertilizer application, NH3 losses had not been affected by DCD in the UR or the UR + NBPT treatments; thereafter, NH3 volatilization tended to decrease, but not when DCD was present. As a consequence, the addition of DCD caused a 5–16% increase in NH3 volatilization losses of the fertilizer N applied as UR from both the UR and the UR + NBPT treatments. Because the effectiveness of NBPT to inhibit soil urease activity was strong only in the first week, it could be concluded that DCD did not affect the action of NBPT but rather, enhanced volatilization losses by maintaining higher soil NH 4 + concentration and pH for a longer time. Depending on the combination of factors influencing NH3 volatilization, DCD could even offset the beneficial effect of NBPT in reducing NH3 volatilization losses.

Electrochemical decomposition of urea with Ni-based catalysts

Abstract: Nickel based catalysts (Ni, Ni-Zn, and Ni-Zn-Co) synthesized through electrodeposition and alkaline leaching processes were used as electrocatalysts for the electrochemical decomposition of urea to benign nitrogen and fuel cell grade hydrogen. The performances of the Ni-based catalysts for the urea decomposition were investigated through cyclic voltammetry (CV) and polarization techniques. The results of the CVs show that the Ni-Zn catalysts and the Ni-Zn-Co catalysts decreased the onset potential of urea oxidation by 40 mV and 80 mV, respectively when compared to Ni catalysts. The highest efficiency for the oxidation of urea was observed with the Ni-Zn-Co catalysts. The Ni-Zn and Ni-Zn-Co catalysts are promising materials for large-scale urea removal/decomposition from urea-rich wastewater, as well as for hydrogen production.

Nitrification of archaeal ammonia oxidizers in acid soils is supported by hydrolysis of urea.

Abstract: The hydrolysis of urea as a source of ammonia has been proposed as a mechanism for the nitrification of ammonia-oxidizing bacteria (AOB) in acidic soil. The growth of Nitrososphaera viennensis on urea suggests that the ureolysis of ammonia-oxidizing archaea (AOA) might occur in natural environments. In this study, 15N isotope tracing indicates that ammonia oxidation occurred upon the addition of urea at a concentration similar to the in situ ammonium content of tea orchard soil (pH 3.75) and forest soil (pH 5.4) and was inhibited by acetylene. Nitrification activity was significantly stimulated by urea fertilization and coupled well with abundance changes in archaeal amoA genes in acidic soils. Pyrosequencing of 16S rRNA genes at whole microbial community level demonstrates the active growth of AOA in urea-amended soils. Molecular fingerprinting further shows that changes in denaturing gradient gel electrophoresis fingerprint patterns of archaeal amoA genes are paralleled by nitrification activity changes. However, bacterial amoA and 16S rRNA genes of AOB were not detected. The results strongly suggest that archaeal ammonia oxidation is supported by hydrolysis of urea and that AOA, from the marine Group 1.1a-associated lineage, dominate nitrification in two acidic soils tested.

Solar driven hydrogen releasing from urea and human urine

Abstract: Urea has been considered as a potential hydrogen source, while the conventional methods to extract hydrogen from urea are typically energy intensive processes. Here we report the first demonstration of solar driven hydrogen releasing from urea and human urine in a photoelectrochemical cell, with the assistance of Ni(OH)2 modified metal oxide photoelectrodes (e.g., TiO2 and α-Fe2O3). Ni(OH)2 serves as a urea oxidation catalyst. Under light illumination, photoexcited holes generated at the metal oxide electrode oxidize urea, while photoexcited electrons reduce water to produce hydrogen gas at the Pt counter electrode. Urea oxidation was achieved under a small external bias or even at zero bias. Significantly, we observed continuous and stable hydrogen evolution at the Pt electrode in both urea and human urine electrolyte solutions under AM 1.5G (100 mW cm−2) light illumination. This work presents a safe, low energy cost, environmentally friendly and sustainable method to produce hydrogen, and simultaneously treat urine.

Hydrolysis and thermolysis of urea and its decomposition byproducts biuret, cyanuric acid and melamine over anatase TiO2

Abstract: A major problem in the selective catalytic reduction of NOx with urea (urea-SCR) is the formation of urea decomposition byproducts, which can be suppressed by the use of TiO2 as a hydrolysis catalyst. Temperature programmed desorption and reaction (TPD/R) experiments with urea, biuret, triuret, cyanuric acid and melamine on TiO2-coated and inert cordierite monoliths were used to investigate the reaction network of urea byproduct formation and decomposition over anatase TiO2. All investigated compounds were found to be catalytically hydrolyzed over TiO2. Biuret was directly hydrolyzed to urea in one step, whereas melamine hydrolyzed step-wise via ammeline and ammelide to cyanuric acid. Finally, cyanuric acid completely hydrolyzed to ammonia and carbon dioxide. The formation of byproducts was strongly favored in the absence of water. A reaction network was developed for the uncatalyzed and catalytic decomposition of urea, showing the most important reactions of urea, isocyanic acid, biuret, triuret, cyanuric acid, ammelide, ammeline and melamine under low-temperature operating conditions in SCR systems. Our results support the approach of using a special hydrolysis catalyst for urea decomposition or of catalytic coatings on exhaust pipes to avoid byproduct formation.

Urea–Montmorillonite-Extruded Nanocomposites: A Novel Slow-Release Material

Abstract: The present study describes the preparation and characterization of a novel urea slow-release nanocomposite, based on urea intercalation into montmorillonite clay by an extrusion process at room temperature. Nanocomposites with urea contents ranging from 50 to 80 wt % were successfully produced and characterized. Analyses by XRD, DTA, and SEM-EDX confirmed the effectiveness of this simple process to exfoliate the clay lamellae into the urea matrix, forming a product that can be classified as a nanocomposite, due to the exfoliation degree attained. Diametral compression tests showed that the samples were very deformable, and the release rate of active components in water showed that the nanocomposite showed a slow release behavior for urea dissolution, even in low montmorillonite amounts (20% in weight).

Facile Microwave-Assisted Hydrothermal Synthesis of CuO Nanomaterials and Their Catalytic and Electrochemical Properties

Abstract: Copper oxides have been widely used as catalysts, gas sensors, adsorbents, and electrode materials. In this work, CuO nanomaterials were synthesized via a facile microwave-assisted hydrothermal process in Cu(CH3COO)2(0.1 M)/urea(0.5 M) and Cu(NO3)2(0.1 M)/urea(0.5 M) aqueous systems at 150 °C for 30 min. The formation processes of copper oxides were investigated, and their catalytic activities were evaluated by the epoxidation of alkenes and the oxidation of CO to CO2. Their electrochemical properties were compared as supercapacitor electrodes using cyclic voltammetry. Experimental results indicated that copper acetate solution could be hydrolyzed to form urchin-like architectured CuO, and the addition of urea accelerated this transformation. CuO nanoparticles were formed and aggregated into spheroidal form (CuO-1) in Cu(CH3COO)2/urea aqueous solution. Cu2(OH)2CO3 was formed as an intermediate, and then thermally decomposed into CuO nanorods (CuO-2) in the Cu(NO3)2/urea aqueous system. The synthesized cop...

Nanomolar potency and metabolically stable inhibitors of kidney urea transporter UT-B.

Abstract: Urea transporters, which include UT-B in kidney microvessels, are potential targets for development of drugs with a novel diuretic (‘urearetic’) mechanism. We recently identified, by high-throughput screening, a triazolothienopyrimidine UT-B inhibitor, 1, that selectively and reversibly inhibited urea transport with IC50 = 25.1 nM and reduced urinary concentration in mice (Yao et al.J. Am. Soc. Nephrol., in press). Here, we analyzed 273 commercially available analogues of 1 to establish a structure–activity series and synthesized a targeted library of 11 analogues to identify potent, metabolically stable UT-B inhibitors. The best compound, {3-[4-(1,1-difluoroethyl)benzenesulfonyl]thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidin-5-yl}thiophen-2-ylmethylamine, 3k, had IC50 of 23 and 15 nM for inhibition of urea transport by mouse and human UT-B, respectively, and ∼40-fold improved in vitro metabolic stability compared to 1. In mice, 3k accumulated in kidney and urine and reduced maximum urinary concentration. T...

Quantitative analysis of urea in human urine and serum by 1H nuclear magnetic resonance.

Abstract: A convenient and fast method for quantifying urea in biofluids is demonstrated using NMR analysis and the solvent water signal as a concentration reference. The urea concentration can be accurately determined with errors less than 3% between 1 mM and 50 mM, and less than 2% above 50 mM in urine and serum. The method is promising for various applications with advantages of simplicity, high accuracy, and fast non-destructive detection. With an ability to measure other metabolites simultaneously, this NMR method is also likely to find applications in metabolic profiling and system biology.

Controlled release of urea from chitosan microspheres prepared by emulsification and cross-linking method

Abstract: Encapsulation of urea was performed in chitosan microspheres via emulsification followed by cross-linking with genipin, a natural cross-linker. The microspheres were prepared by varying different parameters, e.g., concentrations of chitosan, urea and cross-linker. The effect of these parameters on urea loading (%), urea content (%), entrapment efficiency (%) and release rate was studied. Higher amount of chitosan (1.0 g) and cross-linker concentration (0.75 mmol/g of chitosan) produced entrapment efficiencies of 99.0 and 78.5 %, respectively. Release rate was found to be dependent on the concentrations of urea, chitosan, cross-linker and temperature of the release medium. Higher concentration of loaded urea enhanced the release rate, whereas higher concentrations of chitosan and cross-linker reduced it. Higher temperature of the release medium improved the release rate. It was found that water uptake (%) increased through the increase of concentrations of urea and chitosan and decrease of that of cross-linker. Fourier transform infrared (FTIR) spectroscopy indicated the incorporation of urea in the chitosan microspheres. There was no significant interaction between chitosan and urea as evidenced by FTIR study. Surface of the urea-loaded microspheres appeared coarser and rough compared to that of unloaded microspheres as revealed by scanning electron microscopy.

Fabrication and characterization of a surface plasmon resonance based fiber optic urea sensor for biomedical applications

Abstract: The fabrication and characterization of a surface plasmon resonance based fiber optic sensor for the detection of urea in liquid are reported. The probe is fabricated by coating three layers namely of silver, silicon and the enzyme, urease, over about 1 cm length of the unclad core of an optical fiber. The silicon layer protects silver from oxidation and enzyme from deactivation in addition to enhance the sensitivity of the sensor. The wavelength interrogation method is used to characterize the sensor. It is observed that the resonance wavelength decreases as the concentration of urea increases. The sensor operates in the urea concentration range of 0–160 mM, which is close to the physiological range of urea in blood and hence can be used in medical sciences. Further, the effects of concentration of urea on the sensitivity and detection accuracy of the sensor are studied. It is found that the sensitivity decreases with the increase in the concentration of urea whereas the detection accuracy is nearly independent of the urea concentration.

Effects of biochar application on vegetable production and emissions of N2O and CH4

Abstract: A pot experiment was performed to estimate the effect of maize (Zea mays L.) straw biochar application on nitrous oxide (N2O) and methane (CH4) emissions, N2O emission factors and vegetable yield through cultivation of choy sum (Brassica rapa L. ssp. chinensis) and amaranth (Amaranthus mangostanus L.) for 99 days in 2011 at Nanjing, China. Eight treatments were established as follows: control (CK), 100% urea nitrogen (N) (Urea), urea and manure N at 5:5 (UM1) or 7:3 (UM2) combination, biochar incorporation with urea at 20 Mg ha−1 (UB1) or 40 Mg ha−1 (UB2) and biochar incorporation at 30 Mg ha−1 with UM1 (UM1B) or UM2 (UM2B). UB1, UB2, UM1B and UM2B significantly decreased N2O emission by 77% to 86%, while UM1 and UM2 did not show significant N2O emission difference in comparison with Urea. CH4 emissions were not affected by biochar amendment or manure application. On average, UM1B and UM2B significantly enhanced vegetable production by 32, 48 and 28% as compared to Urea, average UM1/UM2 and average UB1/UB...

Small polar molecules like glycerol and urea can preserve the fluidity of lipid bilayers under dry conditions

Abstract: Glycerol and urea are examples of small, water-soluble molecules with low vapor pressure that can protect lipid membranes upon dehydration. Both are a part of the Natural Moisturizing Factor in human skin, and are also present in other organisms, where they prevent drying due to osmotic stress. This study was conducted in order to understand the mechanism of such protection. We have selected two ternary systems: dimyristoylphosphatidylcholine (DMPC)–glycerol–water and DMPC–urea–water, as models to investigate the molecular mechanisms behind this protective effect with a focus on factors that control the solid to liquid phase transition in the phospholipid bilayers. By combining a number of experimental techniques, including solid-state NMR, sorption microbalance and DSC, the structure and the phase transitions have been characterized at low water content and in excess solution. It was discovered that both glycerol and urea stabilize the liquid crystalline bilayers at low relative humidities (down to 75% RH at 27 °C), whereas for the pure DMPC–water system, a solid gel phase is induced at 93% RH. This demonstrates the protective effect of glycerol and urea against osmotic stress. It is further concluded that for lipid systems with limited access to solvent, the phase behavior is determined by solvent volume, irrespective of the composition. The observation that glycerol and urea have a similar effect on the lipid phase behavior under dry conditions, together with the lack of evidence of specific interactions between the lipids and glycerol or urea, implies a general mechanism, which might also be applicable to other, similar solutes.

Severe hyperammonaemia in adults not explained by liver disease

Abstract: Ammonia is produced continuously in the body. It crosses the blood-brain barrier readily and at increased concentration it is toxic to the brain. A highly integrated system protects against this: ammonia produced during metabolism is detoxified temporarily by incorporation into the non-toxic amino acid glutamine. This is transported safely in the circulation to the small intestine, where ammonia is released, carried directly to the liver in the portal blood, converted to non-toxic urea and finally excreted in urine. As a result, plasma concentrations of ammonia in the systemic circulation are normally very low (<40 μmol/L). Hyperammonaemia develops if the urea cycle cannot control the ammonia load. This occurs when the load is excessive, portal blood from the intestines bypasses the liver and/or the urea cycle functions poorly. By far, the commonest cause is liver damage. This review focuses on other causes in adults. Because they are much less common, the diagnosis may be missed or delayed, with disastrous consequences. There is effective treatment for most of them, but it must be instituted promptly to avoid fatality or long-term neurological damage. Of particular concern are unsuspected inherited defects of the urea cycle and fatty acid oxidation presenting with catastrophic illness in previously normal individuals. Early identification of the problem is the challenge.

Structure and permeation mechanism of a mammalian urea transporter

Abstract: As an adaptation to infrequent access to water, terrestrial mammals produce urine that is hyperosmotic to plasma. To prevent osmotic diuresis by the large quantity of urea generated by protein catabolism, the kidney epithelia contain facilitative urea transporters (UTs) that allow rapid equilibration between the urinary space and the hyperosmotic interstitium. Here we report the first X-ray crystal structure of a mammalian UT, UT-B, at a resolution of 2.36 A. UT-B is a homotrimer and each protomer contains a urea conduction pore with a narrow selectivity filter. Structural analyses and molecular dynamics simulations showed that the selectivity filter has two urea binding sites separated by an approximately 5.0 kcal/mol energy barrier. Functional studies showed that the rate of urea conduction in UT-B is increased by hypoosmotic stress, and that the site of osmoregulation coincides with the location of the energy barrier.

Urea fertilizer forms affect grain corn yield and nitrogen use efficiency

Abstract: Gagnon, B., Ziadi, N. and Grant, C. 2012. Urea fertilizer forms affect grain corn yield and nitrogen use efficiency. Can. J. Soil Sci. 92: 341–351. Controlled-release urea may be a good management strategy to increase the efficiency of N fertilizers. In a 3-yr study (2008–2010) conducted on a clay soil near Quebec City, Canada, we compared the effect of polymer-coated urea (PCU), nitrification inhibitor urea (NIU), dry urea and urea ammonium nitrate 32% (UAN) on corn yield, plant N accumulation and soil NO3-N remaining at harvest. Corn was fertilized with urea and PCU at 50, 100 and 150 kg N ha−1 in addition to an unfertilized control (0 N), and NIU and UAN at 150 kg N ha−1. Urea, PCU, and NIU were pre-plant broadcast whereas UAN was side-banded at the six-leaf stage of corn. Response to N fertilization occurred in all years, but the magnitude of the response varied with years. In wet years (2008 and 2009), PCU and NIU resulted in higher grain yield than urea, but the increase was greater for PCU (+0.8 to...

Preparation, Characterization and Release of Urea from Wheat Gluten Electrospun Membranes

Abstract: Homogeneous and thin porous membranes composed of oriented fibers were obtained from wheat gluten (WG) using the electrospinning technique. SEM micrographs showed an asymmetric structure and some porosity, which, in addition to a small thickness of 40 mm, are desirable characteristics for the membranes’ potential application in release systems. The membranes were loaded with urea to obtain pastilles. FT-IR and DSC studies confirmed the existence of interactions via hydrogen bonding between urea and WG proteins. The pastilles were studied as prolonged-released systems of urea in water. The release of urea during the first 10 min was very fast; then, the rate of release decreased as it reached equilibrium at 300 min, with a total of »98% urea released. TGA analysis showed that the release system obtained is thermally stable up to a temperature of 117 °C. It was concluded that a prolonged-release system of urea could be satisfactorily produced using WG fibers obtained by electrospinning for potential application in agricultural crops.

Effects of carbonate on the electrolytic removal of ammonia and urea from urine with thermally prepared IrO2 electrodes

Abstract: Recent studies have shown that electrolysis can be an efficient process for nitrogen removal from urine. These studies have been conducted with urea solutions or fresh urine, but urine collected in NoMix toilets and urinals has a substantially different composition, because bacteria hydrolyse urea quickly to ammonia and carbonate. In this study, we compared electrochemical removal of nitrogen from synthetic solutions of fresh and stored urine using IrO2 anodes. We could show that in fresh urine both ammonia and urea are efficiently eliminated, mainly through chlorine-mediated oxidation. However, in stored urine the presence of carbonate, arising from urea hydrolysis, leads to an inhibition of ammonia oxidation. We suggest two parallel mechanisms to explain this effect: the competition between chloride and carbonate oxidation at the anode and the competition between chlorate formation, enhanced by the buffering effect of carbonate, and ammonia oxidation for the consumption of active chlorine in the bulk. However, further experiments are needed to support the latter mechanism. In conclusion, this study highlights the negative consequences of the presence of carbonate in urine solutions, but also in other wastewaters, when subjected to an electrolytic treatment on IrO2 in alkaline media.

Inhibition of methane oxidation by nitrogenous fertilizers in a paddy soil

Abstract: Nitrogenous fertilizers are generally thought to have an important role in regulating methane oxidation. In this study, the effect of ammonium on methane oxidation activity was investigated in a paddy soil using urea at concentrations of 0, 50, 100, 200 and 400 μg N per gram dry weight soil (N/g.d.w.s) and ammonium sulfate at concentrations of 0, 50 and 200 μg N/g.d.w.s. The results of this study demonstrate that urea concentrations of 200 μg N/g.d.w.s. and above significantly inhibit methane oxidation activity, whereas no statistically significant difference was observed in methane oxidation activity among soil microcosms with urea concentrations of less than 200 μg N/g.d.w.s after incubation for 27 days. Similar results were obtained in a sense that methane oxidation activity was inhibited only when the ammonium sulfate concentration was 200 μg N/g.d.w.s in soil microcosms in this study. Phylogenetic analysis of pmoA genes showed that nitrogen fertilization resulted in apparent changes in the community composition of methane-oxidizing bacteria (MOB). Type I MOB displayed an increased abundance in soil microcosms amended with nitrogenous fertilizers, whereas type II MOB dominated the native soil. Furthermore, although no statistically significant relationship was observed between pmoA gene and amoA gene abundances, methane oxidation activity was significantly negatively correlated with nitrification activity in the presence of urea or ammonium sulfate. Our results indicate that the methane oxidation activity in paddy soils might be inhibited when the concentration of ammonium fertilizers is high and that the interactions between ammonia and methane oxidizers need to be further investigated.