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Showing papers on "Ammonia published in 2001"


Journal ArticleDOI
TL;DR: The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO2 was investigated in this article, where the two main reactions are 4NH3 + 2NO + 2 NO2 → 4N2 + 6H2O and 2NH3+ 2NO2 → NH4NO3 + N2 + H2O.
Abstract: The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO2 was investigated. The two main reactions are 4NH3 + 2NO + 2NO2 → 4N2 + 6H2O and 2NH3 + 2NO2 → NH4NO3 + N2 + H2O. The “fast SCR reaction” exhibits a reaction rate at least 10 times higher than that of the well-known standard SCR reaction with pure NO and dominates at temperatures above 200 °C. At lower temperatures, the “ammonium nitrate route” becomes increasingly important. Under extreme conditions, e.g., a powder catalyst at T ≈ 140 °C, the ammonium nitrate route may be responsible for the whole NOx conversion observed. This reaction leads to the formation of ammonium nitrate within the pores of the catalyst and a temporary deactivation. For a typical monolithic sample, the lower threshold temperature at which no degradation of catalyst activity with time is observed is around 180 °C. The ammonium nitrate route is interesting from a standpoint of general DeNOx mechanisms: This reac...

393 citations


Journal ArticleDOI
TL;DR: In this paper, a variety of supported metal catalysts have been studied and the activation energies for the ammonia decomposition process varied from 17 to 22 kcal/mol depending upon the catalyst employed.
Abstract: Catalytic decomposition of ammonia has been investigated as a method to produce hydrogen for fuel cell applications. The absence of any undesirable by-products (unlike, e.g., COx, formed during reforming of hydrocarbons and alcohols) makes this process an ideal source of hydrogen for fuel cells. In this study a variety of supported metal catalysts have been studied. Supported Ru catalysts were found to be the most active, whereas supported Ni catalysts were the least active. The supports were found to play a profound role in the ammonia decomposition process. The activation energies for the ammonia decomposition process varied from 17 to 22 kcal/mol depending upon the catalyst employed. The activation energies of the supported Ir catalysts were found to be in excellent agreement with our recent studies addressing ammonia decomposition on single crystal Ir.

384 citations


Book ChapterDOI
TL;DR: Present ammonia criteria may fail to protect migrating fish and may be inappropriate for fish fed on a regular basis, according to the present ammonia criteria promulgated in the EPA (1989) saltwater document.
Abstract: Ammonia is an unusual toxicant in that it is produced by, as well as being poisonous to, animals. In aqueous solution ammonia has two species, NH3 and NH4+, total ammonia is the sum of [NH3] + [NH4+] and the pK of this ammonia/ammonium ion reaction is around 9.5. The NH3/NH4+ equilibrium both internally in animals and in ambient water depends on temperature, pressure, ionic strength, and pH; pH is most often of greatest significance to animals. Elevated ammonia levels in the environment are toxic. Temperature has only minor effects on ammonia toxicity expressed as total ammonia in water, and ionic strength of the water can influence ammonia toxicity, but pH has a very marked effect on toxicity. Acid waters ameliorate, whereas alkaline waters exacerbate ammonia toxicity. The threshold concentration of total ammonia ([NH3] + [NH4+]) resulting in unacceptable biological effects in freshwater, promulgated by the EPA (1998), is 3.48 mg N/liter at pH 6.5 and 0.25 mg N/liter at pH 9.0. There is only a relatively small saltwater data set, and a paucity of data on ammonia toxicity in marine environments, particularly chronic toxicity. The national criteria promulgated in the EPA (1989) saltwater document is a criterion continuous concentration (chronic value) of 0.99 mg N/liter total ammonia and a criterion maximum concentration (half the mean acute value) of 6.58 mg N/liter total ammonia, somewhat less than the equivalent freshwater pH 8.0 values of 1.27 and 8.4 mg N/liter total ammonia, respectively. This is consistent with marine species being somewhat more sensitive to ammonia than freshwater species. Toxicity studies are usually carried out on unfed, resting fish in order to facilitate comparison of results. Based on recent studies, however, environmental stresses, including swimming, can have dramatic effects on ammonia toxicity. It is also clear that feeding results in elevated postprandial body ammonia levels. Thus, feeding will probably also exacerbate ammonia toxicity. Fish may be more susceptible to elevated ammonia levels during and following feeding or when swimming. Thus, present ammonia criteria may fail to protect migrating fish and may be inappropriate for fish fed on a regular basis. Most teleost fish are ammonotelic, producing and excreting ammonia by diffusion of NH3 across the gills. They are very susceptible to elevated tissue ammonia levels under adverse conditions. Some fish avoid ammonia toxicity by utilizing several physiologic mechanisms. Suppression of proteolysis and/or amino acid catabolism may be a general mechanism adopted by some fishes during aerial exposure or ammonia loading. Others, like the mudskipper, can undergo partial amino acid catabolism and use amino acids as an energy source, leading to the accumulation of alanine, while active on land. Some fish convert excess ammonia to less toxic compounds including glutamine and other amino acids for storage. A few species have active ornithine—urea cycles and convert ammonia to urea for both storage and excretion. Under conditions of elevated ambient ammonia, the mudskipper P. schlosseri can continue to excrete ammonia by active transport of ammonium ions. There are indications that some fish may be able to manipulate the pH of the body surface to facilitate NH3 volatilization during aerial exposure, or that of the external medium to lower the toxicity of ammonia during ammonia loading. Future investigation of these aspects of “environmental ammonia detoxification” may produce new information on how fish avoid ammonia intoxication.

320 citations


Book ChapterDOI
TL;DR: In this paper, the effect of ammonium nitrate (AN) and ammonium sulfate (AS) on emissions of nitrogen oxides (NH 3 ) was evaluated in European soil.
Abstract: Between 10 and 20%of the N in fertilizers applied as urea is lost to the atmosphere as ammonia (NH 3 ). In contrast only small ( 3 have been measured following the application of ammonium nitrate (AN) fertilizer. In consequence the replacement of urea fertilizer with AN has been proposed as a cost-effective measure to reduce NH 3 emissions in Europe. However, because of the greater susceptibility of nitrate- (NO 3 − ) based fertilizers to denitrification, the replacement of urea by AN may lead to increased emissions of nitrous oxide (N 2 O). There was a need therefore to critically review the evidence for substantially greater emissions of NH 3 − from urea than from other N fertilizers and also to appraise the effect of fertilizer-N type on emissions of N 2 O. Ammonia emissions from N fertilizers are consistent with their known effects on soil chemistry. Those that increase soil solution pH, for example, by increasing HCO 3 concentration or by reducing the concentration of Ca 2+ , have the greatest potential for NH 3 emission. In consequence the greatest emissions of NH 3 are from urea applied to any soil and from ammonium sulfate (AS) applied to soils of pHs > 7.0. Losses of NH 3 from AN were confirmed to be consistently less than from urea. Emissions of NH 3 from solutions composed of urea and AN were found to be intermediate between the two fertilizers. Thus applying urea in solution will not reduce NH 3 emissions. However, NH 3 emissions from urea may be reduced by the use of urease inhibitors. Nitrous oxide emissions are crucially dependent on the interaction between timing of N fertilizer application and weather. Conditions in spring are more likely to be wet so that emissions are greater from NO 3 − -based fertilizers than from AS. In the summer conditions may be dry or wet; under dry conditions emissions are usually smaller than under wet conditions. For urea the effect of pH appears to be important. Generally greater emissions can take place from urea, except where temperature (controlling the rate of urea hydrolysis) and rainfall (controlling the dispersion of alkalinity) limit this. Thus, the substitution of AN for urea for spring applications is likely to increase emissions of N 2 O. For summer applications, the substitution of AN for urea is likely to decrease N 2 O emissions providing conditions are relatively dry; when conditions are wet large emissions may occur from both AN and urea. At this stage it is difficult to say with any certainty whether a strategy based on urea or AN would result in the smaller N 2 O emissions. Nitric oxide (NO) may also be released from soils following N fertilizer application. While soil emissions of NO are small in comparison with other sources of NO x , it is worth considering the effect of fertilizer type on this gas as well. Insufficient data is available to predict the effect of urea substitution on NO emissions, but since these are mainly a consequence of nitrification then replacing urea with AN should also reduce NO emissions.

254 citations


Journal ArticleDOI
TL;DR: The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture using a batch reactor with 50 mg-N/l of ammonia and as much as 77% of the removed ammonia accumulated in nitrite.
Abstract: The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture A batch reactor with 50 mg-N/l of ammonia was used The pH, temperature and dissolved oxygen concentration were varied The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature The accumulation of nitrite was affected sensitively by pH and temperature A higher nitrite concentration was observed at pH 8-9 or temperature around 30 °C The dissolved oxygen also affected, giving the highest nitrite accumulation at around 15 mg/l These were the favoredconditions for nitrite production The free ammonia concentration influenced thenitrite accumulation also, by inhibiting nitrite oxidation The inhibition becameapparent at a concentration of approximately 4 mg/l or above, but insignificant atbelow 1 mg/l Thus, simultaneously high free ammonia concentration and maximumspecific ammonia-oxidation rate (above 15 × 10-3 mg-N/mg-VSSċh)were needed for a significant nitrite accumulation When the two conditions were met, thenthe highest accumulation was observed when the ratio of the maximum specific oxidationrate of ammonia to the maximum specific oxidation rate of nitrite (ka/kn) was highestUnder the optimal operating conditions of pH 8, 30 °C and 15 mg/l of dissolvedoxygen, as much as 77% of the removed ammonia accumulated in nitrite

232 citations


Journal ArticleDOI
TL;DR: In this article, the authors used chemically synthesised acrylic acid doped polyaniline (PANI:AA) as an ammonia vapour sensor in a broad range of concentrations.
Abstract: Chemically synthesised acrylic acid doped polyaniline (PANI:AA) has been utilised as an ammonia vapour sensor in a broad range of concentrations, viz. 1–600 ppm. The response, in terms of decrease in dc electric resistance on exposure to ammonia was observed. The change in resistance, ΔR, is found to increase linearly with NH3 concentration upto 58 ppm and saturates thereafter. The decrease in resistance has been explained on the basis of removal of proton from the free acrylic acid (AA) dopant by the ammonia molecules thereby rendering free conduction sites in the polymer matrix. These results are well supported by FTIR spectral analysis and the X-ray diffraction studies. The FTIR spectra show a remarkable increase in benzenoid and quinoid vibrations. Also, simultaneous appearance of COO− and ammonium ion vibrations is indicative of the interaction of ammonia molecules with acrylic acid. The degree of crystallinity was found to increase substantially upto 58 ppm concentration.

207 citations


Journal ArticleDOI
TL;DR: Ureolysis provides a mechanism for nitrification in acid soils, but a proportion of the ammonia produced during this process diffuses from the cell and is not subsequently available for growth if the extracellular pH is less than 7.5.
Abstract: Ammonia oxidation in laboratory liquid batch cultures of autotrophic ammonia oxidizers rarely occurs at pH values less than 7, due to ionization of ammonia and the requirement for ammonium transport rather than diffusion of ammonia. Nevertheless, there is strong evidence for autotrophic nitrification in acid soils, which may be carried out by ammonia oxidizers capable of using urea as a source of ammonia. To determine the mechanism of urea-linked ammonia oxidation, a ureolytic autotrophic ammonia oxidizer, Nitrosospira sp. strain NPAV, was grown in liquid batch culture at a range of pH values with either ammonium or urea as the sole nitrogen source. Growth and nitrite production from ammonium did not occur at pH values below 7. Growth on urea occurred at pH values in the range 4 to 7.5 but ceased when urea hydrolysis was complete, even though ammonia, released during urea hydrolysis, remained in the medium. The results support a mechanism whereby urea enters the cells by diffusion and intracellular urea hydrolysis and ammonia oxidation occur independently of extracellular pH in the range 4 to 7.5. A proportion of the ammonia produced during this process diffuses from the cell and is not subsequently available for growth if the extracellular pH is less than 7. Ureolysis therefore provides a mechanism for nitrification in acid soils, but a proportion of the ammonium produced is likely to be released from the cell and may be used by other soil organisms.

198 citations


Journal ArticleDOI
TL;DR: Investigation of the potential for using hydrogen gas production to predict upsets in anaerobic digesters operating on dairy cattle manure found changes in H2 concentration could be a useful parameter for monitoring changes due to increased NH3 in Dairy cattle manure anaerobia digesters.

171 citations


Journal ArticleDOI
TL;DR: In this article, the selective catalytic reduction of nitrogen oxides has been studied in the presence of O2 over Fe/MFI catalysts with Fe/Al∼1, prepared by sublimation of FeCl3 vapor onto HMFI.

157 citations


Journal ArticleDOI
TL;DR: In this article, the interaction of NO, ammonia (NH3), hydrazine (N2H4), hydroxylamine (NH2OH), urea (H2N), acetamide (CH3), and acetonitrile (CH 3CN) on Fe2O3-TiO2 model catalysts was studied.
Abstract: The interaction of NO, ammonia (NH3), hydrazine (N2H4), hydroxylamine (NH2OH), urea (H2NCONH2), acetamide (CH3CONH2) and acetonitrile (CH3CN) on Fe2O3-TiO2 model catalysts was studied. The data support the idea that hydrazine can be intermediate in the oxidation of ammonia to nitrogen, while hydroxylamine-type species, formed at higher temperature, can be intermediate in the oxidation of ammonia to NO. Bronsted acid sites do not appear to be involved in this chemistry.

148 citations


Journal ArticleDOI
TL;DR: In this paper, bimetallic molybdenum nitride catalysts were prepared and their kinetic analyses were done and the standard rate of ammonia synthesis was measured with a 0.4 g of catalyst at 588-673 K under 0.1-3.1 MPa with a flow rate of 60mlmin − 1 of N 2 + 3H 2.
Abstract: New bimetallic molybdenum nitride catalysts were prepared and their kinetic analyses were done. The nitride catalysts were prepared by nitriding the corresponding oxide precursors with ammonia gas through a temperature-programmed reaction up to 973 K. The standard rate of ammonia synthesis was measured with a 0.4 g of catalyst at 588–673 K under 0.1–3.1 MPa with a flow rate of 60 ml min − 1 of N 2 +3H 2 . The rates over molybdenum nitride catalysts were increased with increasing the reaction pressure. The rates over Co 3 Mo 3 N at 673 K under 3.1 MPa (4.8 mmol h −1 g-cat. −1 ) was much higher than the corresponding molybdenum bimetallic nitrides with nickel or iron prepared in a similar way to Co 3 Mo 3 N. Apparent activation energies of these catalysts (11–14 kcal mol −1 ) were on the same level. Alkali promoted Co 3 Mo 3 N catalysts and a doubly promoted iron catalyst were tested. The rate of ammonia synthesis over Co 3 Mo 3 N catalyst with 2 mol% Cs added was remarkably high under high pressure (15.0 mmol h −1 g-cat. −1 under 3.1 MPa). This catalyst gave higher productivity of ammonia than the doubly promoted iron catalyst (4.6 mmol h −1 g-cat. −1 under 3.1 MPa). The kinetic parameters for Co 3 Mo 3 N catalysts were similar to that of the iron catalyst, however, the rate on Co 3 Mo 3 N was more retarded by the product ammonia. Interestingly, the strong ammonia retardation on the Co 3 Mo 3 N surface was relieved by the alkali promoter addition.

Journal ArticleDOI
TL;DR: The economical analysis of the process has shown that ammonia in the digester effluents can be recovered at the cost of $7.5-8.0 kg−1 NH4 +-N and slight excess of Mg and P found to be beneficial for higher recovery of ammonia as struvite.
Abstract: The effects of environmental conditions on ammonia removal as struvite (Magnesium ammonium phosphate, MAP) were studied in a laboratory scale batch reactor. MAP precipitation was carried out by adding phosphoric acid and magnesium source either as MgCl2 or MgO. The effect of temperature, pH, Mg:N:P ratios were studied. Temperature did not significantly affect ammonia removal between 25-40 °C and over 90% removal was obtained. The effect of pH, however, was significant and highest removal was reached at pH 8.5-9.0. The various stoichiometric ratios of ammonium to Mg and P have been tested and slight excess of Mg and P found to be beneficial for higher recovery of ammonia as struvite. However further increase in Mg and P ratios did not result in further ammonia removal which is also costly for the practical application of the process. When MgO was used as M source, the ammonia recovery was 60-70% whereas the use of MgCl2 has increased this figure up to 95%. In addition a two step purification process was de...

Journal ArticleDOI
TL;DR: In this article, Fe-exchanged zeolites were prepared and studied as catalysts for selective catalytic oxidation (SCO) of ammonia to nitrogen in the presence of excess oxygen.

Journal ArticleDOI
TL;DR: A granular activated carbon anaerobic fluidised-bed reactor treating vinasse from an ethanol distillery of sugar beet molasses showed good performance but an anomalous behaviour in terms of unusual high concentrations of molecular nitrogen in the biogas, which may suggest a newAnaerobic removal process of ammonia and sulphate according to an uncommon mechanism involving simultaneous anaerilic ammonium oxidation and sulphur reduction.

Journal ArticleDOI
TL;DR: In this article, the reduction of nitrate ion (NO3−) in an aqueous suspension of metal-loaded titanium(IV) oxide (TiO2) was examined in the presence of oxalic acid (OA) as a hole scavenger.
Abstract: Photocatalytic reduction of nitrate ion (NO3−) in an aqueous suspension of metal-loaded titanium(IV) oxide (TiO2) was examined in the presence of oxalic acid (OA) as a hole scavenger. Conversion of NO3− into ammonia (NH3) competed with hydrogen liberation, and the NH3 production selectivity increased with the order of loaded metal, (Pt, Pd, Co) < (Ni, Au) < (Ag, Cu), which was attributable to the efficiency of reduction of protons by photogenerated electrons at the loaded metal, i.e., hydrogen overvoltage of the loaded metal. TiO2 powder loaded with Cu showed higher NH3 yield and selectivity as well as higher efficiency of OA consumption. TiO2 with in situ deposited Cu gave results comparable to those of a Cu pre-loaded photocatalyst.

Journal ArticleDOI
TL;DR: The use of alum or zeolites as on-farm amendment to dairy slurry offers the potential for reducing ammonia emissions and soluble phosphorus in Dairy slurry.

Journal ArticleDOI
TL;DR: In batch tests with the biofilm covered carriers, it was possible for the first time to examine the nitrogen conversion at the intact biofilm and to establish the deammonification processes in a continuous flow moving-bed pilot plant.

Journal ArticleDOI
TL;DR: In this paper, the selective catalytic reduction of NOx (NO + NO2) at low temperature with ammonia has been investigated with natural manganese ore, pure manganes dioxide, and manganous dioxide supported alumina.
Abstract: The selective catalytic reduction of NOx (NO + NO2) at low temperature with ammonia has been investigated with natural manganese ore, pure manganese dioxide, and manganese dioxide supported alumina. The catalysts showed high activities for NOx reduction with NH3 in the presence of O2 at temperatures below 250 °C. The decrease of SCR activity without oxygen in the gas phase differed among the three catalysts in accord with their differing amounts of lattice oxygen. The SCR activity of the catalysts, in that case, decreased in the order MnO2 > NMO > MnO2/γ-Al2O3. Small amounts of SO2 deactivated the catalysts in the low-temperature range. An XRD analysis of the sulfated catalysts with differing temperature provides evidence that the formation of ammonium sulfates is the main poisoning route. These results could restrict the practical application of these catalysts to sulfur-free conditions.

Journal ArticleDOI
TL;DR: The average total (wet plus dry) nitrogen deposition to the Tampa Bay Estuary was 7.3 (± 1.3) kg-N-ha −1 ǫ −1 or 760 (± 140) metric tons-N−yr −1 for August 1996-July 1999, estimated as a direct deposition rate to the 104,000-ha water surface as mentioned in this paper.

Journal ArticleDOI
TL;DR: Although NOM photosensitized degradation of amino acids produces ammonia, amino acids do not appear to be an important intermediate in the photochemical formation of ammonia from NOM.

Journal ArticleDOI
TL;DR: In this paper, gaseous trimethylaluminium (TMA) and ammonia on porous alumina were studied with the goal of finding suitable process conditions for preparing aluminium nitride (AlN) by ALD, a technique based on separate saturating gas-solid reactions.
Abstract: Successive reactions of gaseous trimethylaluminium (TMA) and ammonia on porous alumina were studied with the goal of finding suitable process conditions for preparing aluminium nitride (AlN) by atomic layer deposition (ALD), a technique based on separate saturating gas–solid reactions. The reaction of TMA was studied at 353–623 K on alumina dehydroxylated at 473–1073 K, and the following reaction of ammonia at 423–823 K. Reference samples were prepared by reacting ammonia at 623 and 823 K with alumina dehydroxylated at 833 K. The samples were characterised by elemental analysis of carbon and nitrogen and by IR and 1H NMR. TMA reacted with alumina in a saturating manner at 353–573 K. Reaction took place through ligand exchange with surface OH groups, with release of methane, and through dissociation of TMA on pairs of coordinatively unsaturated Al and O ions. Aluminium-bonded methyl groups remained on the surface. Decomposition of TMA occurred at 600 K and above. Ammonia had reacted with most of the methyl groups by 573 K, but 723 K was required to remove them all. Primary, secondary and tertiary amino groups were formed in the reaction, and ammonia molecules were adsorbed on the surface. The average H/N ratio in the amino groups decreased with increasing reaction temperature. Good temperatures for AlN deposition by ALD seem to be any temperature up to 573 K for the TMA reaction and 723 K or above for the ammonia reaction.

Journal ArticleDOI
TL;DR: In this article, a nanostructured iron titanate thin film on glass is prepared by a sol-gel method from iron(III) chloride and titanium tetraisopropylate.
Abstract: A nanostructured iron titanate thin film on glass is prepared by a sol-gel method from iron(III) chloride and titanium tetraisopropylate. Energy dispersive X-ray analysis, Mosbauer spectroscopy, and wavelength dependent measurements of the quasi-Fermi level suggest the presence of an Fe2Ti2O7 phase having n-type semiconductor characteristics. In the presence of ethanol or humic acids and traces of oxygen, the film photocatalyzes the fixation of dinitrogen to ammonia and nitrate under ultraviolet or visible light irradiation. In the first observable reaction step, hydrazine is produced, which then undergoes further photoreduction to ammonia. Oxidation of the latter by oxygen yields nitrate as the final product. Since the reaction also occurs in air and with visible light (λ > 455 nm), and since the iron titanate phase can be formed by weathering of ilmenite minerals, the system may be a model for a previously unknown non-enzymatic nitrogen fixation in nature.

Journal ArticleDOI
TL;DR: Results indicate that dinitrogen can be reduced at moderate temperatures in hydrothermal vent systems, and are consistent with the equilibrium NH4+ concentration for the N-S-H system under these conditions.
Abstract: Dinitrogen is reduced in dilute hydrogen sulfide (H2S) solutions to ammonium at 120°C. Experiments with dissolved dinitrogen (partial pressure 50 bar) in a 12 × 10-3 mol/L H2S(aq) solution yield ~10-5 mol/L NH4+ within 2-7 days. These yields are consistent with the equilibrium NH4+ concentration for the N-S-H system under these conditions. The formation of ammonium is catalyzed by the presence of freshly precipitated iron monosulfide. These results indicate that dinitrogen can be reduced at moderate temperatures in hydrothermal vent systems. Abiotic nitrogen reduction could have taken place within primordial hydrothermal vents, supplying some ammonia for the synthesis of C-H-O-N compounds via abiotic processes. The yield of ammonia via dinitrogen reduction by hydrogen sulfide, however, is so low that it is doubtful this process could have produced enough ammonia to sustain prebiotic hydrothermal synthesis of C-H-O-N compounds in or around vent systems.

Journal ArticleDOI
TL;DR: A new hypothetical model of ammonia oxidation by N. eutropha was developed and a significantly reduced acetylene inhibition of the ammonia oxidation activity was observed for cells incubated in the presence of NO, suggesting that NO and acetylene compete for the same binding site on AMO.
Abstract: The effect of acetylene ((14)C(2)H(2)) on aerobic and anaerobic ammonia oxidation by Nitrosomonas eutropha was investigated Ammonia monooxygenase (AMO) was inhibited and a 27 kDa polypeptide (AmoA) was labelled during aerobic ammonia oxidation In contrast, anaerobic, NO(2)-dependent ammonia oxidation (NO(2)/N(2)O(4) as oxidant) was not affected by acetylene Further studies gave evidence that the inhibition as well as the labelling reaction were O(2)-dependent Cells pretreated with acetylene under oxic conditions were unable to oxidize ammonia with O(2) as oxidant After these cell suspensions were supplemented with gaseous NO(2), ammonia oxidation activity of about 140 micromol NH(4)(+) (g protein)(-1) h(-1) was detectable under both oxic and anoxic conditions A significantly reduced acetylene inhibition of the ammonia oxidation activity was observed for cells incubated in the presence of NO This suggests that NO and acetylene compete for the same binding site on AMO On the basis of these results a new hypothetical model of ammonia oxidation by N eutropha was developed

Journal ArticleDOI
TL;DR: In the paper revised versions of the REM NUT process, i.e., P-driven layouts, are presented and cost effectiveness is compared to chemical precipitation based on the use of ferric chloride.
Abstract: Nutrients control technologies from wastewater are based on destructive technologies which defer the problem from the diluted liquid-phase (effluent) to a more concentrated waste (sludge) in the case of phosphates, or to nitrogen gas and/or volatile compounds in the case of ammonia. The REM NUT process allows for simultaneous removal of phosphate and ammonium ions by selective ion exchange and recovery by chemical precipitation in the form of struvite (magnesium ammonium phosphate) from the spent exchangers regeneration eluates. In the paper revised versions of the REM NUT process, i.e., P-driven layouts, are presented and cost effectiveness is compared to chemical precipitation based on the use of ferric chloride.

Patent
14 Dec 2001
TL;DR: In this article, an ammonia sensitive membrane has a variable optical indication, such as a variable color change, in relation to the concentration of ammonia in the dialysate, which can be used in a dialysis system to monitor the effectiveness of sorbants which remove ammonia/ammonium which is produced from an enzyme reaction with urea, the urea being removed from a patient during dialysis treatment.
Abstract: A sensor which senses concentrations of a component of a fluid. In a dialysis system, the sensor can monitor the total ammonia and ammonium concentration in dialysate. The sensor has an optical indicator, such as an ammonia sensitive membrane, positioned in direct contact with the dialysate fluid when in use. The ammonia sensitive membrane has a variable optical indication, such as a variable color change, in relation to the concentration of ammonia in the dialysate. An optical reader reads the color change of the membrane to measure the total ammonia and ammonium concentration in the dialysate. The sensor can be used in the dialysis system to monitor the effectiveness of sorbants which remove ammonia/ammonium which is produced from an enzyme reaction with urea, the urea being removed from a patient during dialysis treatment.

Journal ArticleDOI
TL;DR: In this article, the authors examined how the Co3Mo3N phase was formed and showed that the complete Co3 Mo3N bimetallic nitride phase was achieved by the reactant gas treatment.
Abstract: Co3Mo3N catalyst was found to be more active than the doubly-promoted iron catalyst for ammonia synthesis. The precursor CoMoO4·nH2O was heated under a 160 ml min−1 flow of NH3 gas at 5.0 K min−1 to 973 K and kept at 973 K for 6 h. The sample was quenched during the nitridation process and we examined how the Co3Mo3N phase was formed. This Co3Mo3N phase was formed at the last stage of NH3 treatment when the sample was kept at 973 K for 6 h. However, Mo2N and Co phases still remained at this stage. The formation of Co3Mo3N bimetallic nitride phase became much slower after caesium addition to CoMoO4·nH2O. The ammonia activity of Co3Mo3N catalyst was found to be promoted by the treatment with N2+3H2 reactant gas at 873 or 973 K. Co3Mo3N catalysts once treated with diluted oxygen were treated with the reactant gas (N2+3H2, 60 ml min−1) at 873 or 973 K for various times. The rates were increased by this treatment, although the surface areas were decreased. By keeping the sample at 873 K for 12 h or at 973 K for 3 h in the reactant gas, the activities of Co3Mo3N catalysts reached the maximum. XRD, elemental analyses, and TEM measurements revealed that the complete Co3Mo3N phase was achieved by the reactant gas treatment. The rate at 673 K under 3.1 MPa with a flow rate of 60 ml min−1 of N2+3H2 over 2 mol% Cs-promoted catalyst reached even 40% of the equilibrium yield.

Journal ArticleDOI
TL;DR: The data indicate that trout embryos have an efficient system to prevent ammonia accumulation in embryonic tissue, by conversion of ammonia to urea in embryonic tissues and through elevation of ammonia levels in the yolk.
Abstract: The present study investigated the role of ammonia as a trigger for hatching, mechanisms of ammonia detoxification and the localization of urea cycle enzymes in the early life stages of freshwater rainbow trout (Oncorhynchus mykiss). The key urea cycle enzyme carbamoyl phosphate synthetase III was found exclusively in the embryonic body (non-hepatic tissues); related enzymes were distributed between the liver and embryonic body. 'Eyed-up' trout embryos were exposed either acutely (2h) to 10 mmol l(-1) NH(4)Cl or chronically (4 days) to 0.2 mmol l(-1) NH(4)Cl. Time to hatching was not affected by either acute or chronic NH(4)Cl exposure. Urea levels, but not ammonia levels in the embryonic tissues, were significantly higher than in controls after both acute and chronic NH(4)Cl exposure, whereas there were no significant changes in urea cycle enzyme activities. Total amino acid levels in the embryonic tissues were unaltered by chronic ammonia exposure, but levels of most individual amino acids and total amino acid levels in the yolk were significantly lower (by 34-58%) than in non-exposed controls. The data indicate that trout embryos have an efficient system to prevent ammonia accumulation in embryonic tissue, by conversion of ammonia to urea in embryonic tissues and through elevation of ammonia levels in the yolk.

Patent
10 May 2001
TL;DR: In this paper, the autothermal decomposition of ammonia is used to produce high purity hydrogen, which is then used as fuel to a fuel cell for a hydrogen-powered vehicle.
Abstract: This invention relates to the autothermal decomposition of ammonia to produce high purity hydrogen. This invention also relates to a fuel cell system wherein hydrogen that is produced from the autothermic decomposition of ammonia is used as fuel to a fuel cell.

Journal ArticleDOI
TL;DR: During a three-month exposure lethal and sublethal effects of ammonium and its products on typical brook organisms, G. pulex proved the most sensitive to the ammonia and nitrite contamination resulting from the ammonium load, while R. ovota exhibited clearly effects only at concentrations 10 times higher.