Showing papers on "Ammonia published in 1998"
TL;DR: The number of reports on unaccounted high nitrogen losses in wastewater treatment is gradually increasing, indicating that anaerobic ammonium oxidation may be more widespread than previously assumed.
Abstract: From recent research it has become clear that at least two different possibilities for anaerobic ammonium oxidation exist in nature. 'Aerobic' ammonium oxidizers like Nitrosomonas eutropha were observed to reduce nitrite or nitrogen dioxide with hydroxylamine or ammonium as electron donor under anoxic conditions. The maximum rate for anaerobic ammonium oxidation was about 2 nmol NH4+ min-1 (mg protein)-1 using nitrogen dioxide as electron acceptor. This reaction, which may involve NO as an intermediate, is thought to generate energy sufficient for survival under anoxic conditions, but not for growth. A novel obligately anaerobic ammonium oxidation (Anammox) process was recently discovered in a denitrifying pilot plant reactor. From this system, a highly enriched microbial community with one dominating peculiar autotrophic organism was obtained. With nitrite as electron acceptor a maximum specific oxidation rate of 55 nmol NH4+ min-1 (mg protein)-1 was determined. Although this reaction is 25-fold faster than in Nitrosomonas, it allowed growth at a rate of only 0.003 h-1 (doubling time 11 days). 15N labeling studies showed that hydroxylamine and hydrazine were important intermediates in this new process. A novel type of hydroxylamine oxidoreductase containing an unusual P468 cytochrome has been purified from the Anammox culture. Microsensor studies have shown that at the oxic/anoxic interface of many ecosystems nitrite and ammonia occur in the absence of oxygen. In addition, the number of reports on unaccounted high nitrogen losses in wastewater treatment is gradually increasing, indicating that anaerobic ammonium oxidation may be more widespread than previously assumed. The recently developed nitrification systems in which oxidation of nitrite to nitrate is prevented form an ideal partner for the Anammox process. The combination of these partial nitrification and Anammox processes remains a challenge for future application in the removal of ammonium from wastewater with high ammonium concentrations.
835 citations
TL;DR: Ammonia was synthesized from its elements at atmospheric pressure in a solid state proton (H+)-conducting cell-reactor and the thermodynamic requirement for a high-pressure process is eliminated.
Abstract: Ammonia was synthesized from its elements at atmospheric pressure in a solid state proton (H+)-conducting cell-reactor. Hydrogen was flowing over the anode and was converted into protons that were transported through the solid electrolyte and reached the cathode (palladium) over which nitrogen was passing. At 570 degreesC and atmospheric pressure, greater than 78 percent of the electrochemically supplied hydrogen was converted into ammonia. The thermodynamic requirement for a high-pressure process is eliminated.
540 citations
TL;DR: In this article, the effects of pH and the iron-to-nitrate ratio on both nitrate reduction rate and percent removal were investigated, and the apparent reaction order with respect to nitrate was determined and a mass balance was obtained.
479 citations
TL;DR: In this paper, an inorganic aerosol equilibrium model is used to investigate the response of inorganic particulate matter (PM) concentrations with respect to the precursor concentrations of sulfuric acid, ammonia, and nitric acid over a range of temperatures and relative humidities.
Abstract: An inorganic aerosol equilibrium model is used to investigate the response of inorganic particulate matter (PM) concentrations with respect to the precursor concentrations of sulfuric acid, ammonia, and nitric acid over a range of temperatures and relative humidities. Diagrams showing regions of PM response to precursor concentrations are generated, thus allowing the qualification of assumptions concerning the response of PM to sulfate and overall sensitivity to ammonia and nitric acid availability. The PM concentration level responds nonlinearly to sulfate and shows overall sensitivity to ammonia and nitric acid availability for specific atmospheric conditions and precursor concentrations. The generated diagrams are applied as a means of approximating the PM response to precursor concentrations for two urban polluted areas. In both cases, reductions in ammonia emissions have the most significant impact on the total PM level. However, such a reduction will result in significant increases in atmospheric acidity.
249 citations
TL;DR: In this paper, the authors examined the effects of high ammonium concentrations, different pH values, and different oxygen concentrations on nitrification and on the community structure of nitrifying bacteria from wastewater.
Abstract: Autotrophic nitrifying bacteria that oxidize ammonium to nitrite and nitrate are found in soils, sediments, wastewaters, freshwater, and marine water and on building facades. They are essential components of the nitrogen (N) cycle, linking the most reduced and most oxidized forms of inorganic N. Nitrification occurs as a two-step process carried out by two distinct groups of bacteria; ammonia-oxidizing bacteria convert ammonia to nitrite, and then nitrite oxidizers convert nitrite to nitrate (22, 30). Environmental factors control the rate of nitrification. The most significant environmental factors are substrate concentration, pH, temperature, and oxygen availability (12, 23). Nitrifying bacteria exhibit different substrate concentration sensitivities (26). Media containing low substrate concentrations (10 mg of NH4+ liter−1) can give larger most-probable-number counts of ammonia oxidizers than media containing higher NH4+ concentrations (6, 26). Also, ammonia oxidation is inhibited at high substrate concentrations. The growth rates of Nitrosomonas spp. cultures were reduced in the presence of 1,050 to 2,800 mg of NH4+-N liter−1 (16). Substrate inhibition of ammonia oxidation has also been observed in studies of wastewater systems (23). Natural environments, such as soil and water, usually contain 1 to 10 mg of NH4+-N liter−1 (22), yet liquid wastes from animal farms give rise to concentrations up to 1,600 or 5,600 mg of NH4+-N liter−1 (5, 17). Free ammonia (NH3) rather than the total ammonium concentration inhibits ammonia oxidizers (1). As the ratio between the ionized form and the nonionized form depends on pH, the toxicity of ammonium also depends on the environmental pH.
The pH range for growth of pure cultures of ammonia oxidizers is 5.8 to 8.5, and the pH range for growth of nitrite oxidizers is 6.5 to 8.5 (30). Nitrification was inhibited at pH values below 5.8 in our preliminary experiments performed with an enriched culture of nitrifiers obtained from wastewater. Yet in natural environments, such as soil, nitrification has been reported to occur at pH values below 4.0 (7, 29).
Limiting amounts of dissolved oxygen (concentrations below 2 mg liter−1) inhibit nitrification and cause nitrite accumulation or nitrous and nitric oxide production (9, 21). Ammonia-oxidizing bacteria are the key functional group in removing ammonium from wastewaters. Knowledge of the effect of oxygen on nitrification and nitrifying populations has economic importance since aeration of activated sludge is one of the most costly items in the operation of a wastewater treatment plant (21).
In environments with high inputs of ammonium, such as wastewaters, biooxidation of this substrate increases the oxygen uptake and lowers the pH. Such modifications of the environment not only affect the production of nitrite and nitrate but can also select a different nitrifying community that is perhaps specialized for these new conditions. Nitrification does occur in extreme environments that pure cultures of nitrifiers cannot tolerate (4). In this study we examined extreme environments in which nitrifying bacteria may be viable but have not been cultured thus far.
Because of the difficulty of obtaining nitrifier isolates, nucleic acid-based methods have greatly aided studies of the diversity of nitrifiers (11, 20, 27, 28). Recent molecular investigations have provided valuable information concerning the diversity of ammonia oxidizers in natural environments (5, 15, 20, 25). However, no previous study has focused on the structural or compositional responses of nitrifying communities to perturbations in the environment. In the present laboratory study we examined the effects of high ammonium concentrations, different pH values, and different oxygen concentrations on nitrification and on the community structure of nitrifying bacteria from wastewater. To test the abilities of the communities to regain their original structures, growth of nitrifying communities under the new conditions was followed by incubation under the original conditions.
216 citations
TL;DR: In this paper, the authors investigated the feasibility of removing refractory organic pollutants and ammonium nitrogen from landfill leachate by electrochemical oxidation and found that the current density, pH, and chloride concentration had an effect on the removal of both chemical oxygen demand (COD) and ammonia.
Abstract: Leachate originating in landfills where municipal solid wastes are disposed is a wastewater with a complex composition that could have a high environmental impact. The primary goal of this research was to investigate the feasibility of removing refractory organic pollutants and ammonium nitrogen from landfill leachate by electrochemical oxidation. The effects of current density, pH, and chloride concentration on the removal of both chemical oxygen demand (COD) and ammonium nitrogen were investigated. Titanium coated with lead dioxide (PbO2) or tin dioxide (SnO2) was used as the anode. An effective process was achieved in which the leachate was decolorized, COD was removed up to a value of 100 mg L-1, and ammonia was totally eliminated. Average current efficiency of about 30% was measured for a decrease of COD from 1200 to 150 mg L-1, while efficiency of about 10% was measured for a near complete removal of ammonium nitrogen, starting from an initial value of 380 mg L-1. Results indicated that the organic ...
206 citations
TL;DR: In this paper, the authors used atmospheric transport models and critical loads to control nitrogen emissions from various sources, such as agriculture, road traffic, stationary sources and other mobile sources (including vehicular emissions from agriculture).
Abstract: The atmosphere in Europe is polluted by easily available nitrogen (ammonium and nitrate) mainly from livestock (NH3), traffic (NOx) and stationary combustion sources (NOx). The nitrogen emission from various European sources decreases in the order: agriculture, road traffic, stationary sources and other mobile sources (including vehicular emissions from agriculture), with annual emissions of approximately 4.9, 2.7, 2.7 and 0.8 Mt N respectively. The emissions have increased dramatically during the latest decades. In the atmosphere the pollutants are oxidised to more water soluble compounds that are washed out by clouds and eventually brought back to the earth's surface again. Since ammonia is emitted in a highly water soluble form it will also to a substantial degree be dry deposited near the source. Ammonia is, however, the dominant basic compound in the atmosphere and will form salts with acidic gases. These salt particles can be transported long distances especially in the absence of clouds. The deposition close to the source is substantial, but hard to estimate due to interaction with other pollutants. Far from the source the deposition of ammonium is on an annual average halved approximately every 400 km. This short transport distance and the substantial deposition near the source makes it possible for countries to control their ammonium deposition by decreasing their emissions, provided that there is no country with much higher emission in the direction of the prevailing wind trajectory. When the easily available nitrogen is deposited on natural ecosystems (lakes, forests), negative effect can occur. The effect is determined by the magnitude of the deposition and the type of ecosystems (its critical load for nitrogen). In order to reduce the negative effects by controlling the emissions in a cost-efficient way it is necessary to use atmospheric transport models and critical loads.
194 citations
TL;DR: In this paper, the influence of pH and ammonium-nitrogen on methane production in a high-solids sludge digestion process was investigated using a mesophilic batch digester fed with a sludge cake.
Abstract: The influence of pH and ammonium-nitrogen on methane production in a high-solids sludge digestion process was investigated using a mesophilic batch digester fed with a sludge cake. A simple model developed from the Gompertz equation was applied to the quantitative measurement of the methane production rate and lag-phase time at pHs ranging from 6.5 to 9.0 and ammonium-nitrogen concentrations ranging from 100 to 6,000 mg/L. The results indicate that the ammonium-nitrogen concentration was a more significant factor than the free ammonia in affecting the methanogenic activity of a well-acclimatized system. The simulated results reveal that the methanogenic activity decreased with an increase in ammonium-nitrogen, dropped 10% at an ammonium-nitrogen concentration of 1,670 to 3,720 mg/L, dropped 50% at 4,090 to 5,550 mg/L, and dropped to zero at 5,880 to 6,000 mg/L. The lag-phase time in the batch experiment was dependent on the ammonia level, but not ammonium, and when the free ammonia concentration was higher than 500 mg/L, a notable shock load was observed. In addition, the maximum methane-converting capacity of sludge changed from 28 to 0.9 mL CH{sub 4}/g VS{center_dot}d when the ammonium-nitrogen concentration increased from 100 to 6,000 mg/L.
170 citations
TL;DR: Webley et al. as mentioned in this paper evaluated the performance of MnO2/CeO2 for catalytic oxidation of ammonia in supercritical water (SCW) using a continuous-flow, packed-bed reactor at temperatures ranging from 410 to 470 °C, a nominal pressure of 27.6 MPa, and reactor residence times of less than 1 s.
Abstract: Catalytic oxidation of ammonia in supercritical water (SCW) was studied using a continuous-flow, packed-bed reactor at temperatures ranging from 410 to 470 °C, a nominal pressure of 27.6 MPa, and reactor residence times of less than 1 s. The kinetics and catalyst performance of MnO2/CeO2 for oxidation of ammonia in SCW was evaluated. In this reaction environment, ammonia was predominantly converted into molecular nitrogen (N2), and the rate of ammonia conversion was enhanced by MnO2/CeO2. For example, 40% of the ammonia was converted when using the MnO2/CeO2 catalyst at a temperature of 450 °C and a reactor residence time of 0.8 s. It was reported that, without a catalyst, essentially no ammonia conversion was observed below 525 °C (Helling, R. K.; Tester, J. W. Environ. Sci. Technol. 1988, 22 (11), 1319) and 10% of the ammonia was converted at a temperature of 680 °C, a pressure of 24.6 MPa, and a reactor residence time of 10 s (Webley, P. A.; Tester, J. W.; Holgate, H. R. Ind. Eng. Chem. Res. 1991, 30 (...
160 citations
TL;DR: In this paper, the effect of potassium and barium on the activity and thermal stability of a carbon-based ruthenium catalyst for the synthesis of ammonia has been studied, and it was found that the barium-promoted catalyst is more active in NH 3 synthesis and more resistant to overheating than the catalyst promoted with potassium.
Abstract: The effect of potassium and barium on the activity and thermal stability of a carbon-based ruthenium catalyst for the synthesis of ammonia has been studied. Kinetic measurements in NH 3 synthesis were carried out in a flow differential reactor operating at standard conditions ( p =6 MPa, T =673 K, X NH 3 =8%, H 2 : N 2 =3 : 1). Overheating of the samples was carried out at 793 K for 24 h. The examinations have been supplemented by XRD and chemisorption studies for the characterization of the ruthenium dispersion as well as by studying the catalysts methanation. It has been found that the barium-promoted catalyst is more active in NH 3 synthesis and more resistant to overheating than the catalyst promoted with potassium. The activity of Ba–Ru/C is much higher than that of a commercial fused-iron catalyst. This is important for industrial practice.
121 citations
TL;DR: The main product of Fe(II)-dependent nitrate removal was most probably dinitrogen, as no accumulation of ammonia, nitrous oxide, or nitrite could be observed.
Abstract: A biological reduction of nitrate and nitrite was found to take place in activated sludge concomitantly with the oxidation of ferrous iron to ferric iron. This process was shown to be predominantly biological and present in different types of activated sludge treatment plants with variable rates. The highest activity was found in plants with biological nitrogen and phosphorus removal. The highest Fe(II)-dependent nitrate removal rate was found to be 0.31 mmol NO3- (g VSS)-1 h-1, which corresponded to 68% of the maximum dissimilatory nitrate reduction rate in the presence of lactate. The Fe(II)-dependent nitrate removal rate was strongly pH-dependent with a maximal rate at pH 8 of almost four times the rate at pH 6. The main product of Fe(II)-dependent nitrate removal was most probably dinitrogen, as no accumulation of ammonia, nitrous oxide, or nitrite could be observed. The process may be of significance in the activated sludge treatment plant with regard to nitrate removal and with regard to the reoxida...
TL;DR: Using oxalic acid as a hole scavenger, the photocatalytic reduction of nitrate in aqueous dispersions of TiO 2 has been investigated in this article, where the effects of concentrations of nitrates, of oxalate, and of pH were studied.
Abstract: Using oxalic acid as a hole scavenger, the photocatalytic reduction of nitrate in aqueous dispersions of TiO 2 has been investigated. Oxalic acid accelerates the reaction considerably compared to the reaction in the absence of oxalic acid. In the presence of nitrate, the oxidation of oxalate is also accelerated. The reduction product of the nitrate is mainly ammonia. The effects of concentrations of nitrate, of oxalate, and of pH were studied. The adsorption of the reactants on TiO 2 is an important factor for accelerating the reaction.
TL;DR: In this paper, activated carbons were prepared by carbonization and steam activation of nitrogen-enriched low-rank coals by reaction of ammonia or its derivatives with the carboxyl groups either naturally occurring in coal or artificially introduced by performic oxidation.
TL;DR: In this paper, the electrochemical oxidation of ammonia was studied at room temperature on a black platinum electrode, iridium black, a mixture of both and PtIr electrodeposits in alkaline solutions of potassium hydroxide.
Patent•
18 Aug 1998
TL;DR: In this paper, a highly efficient process for the production and recovery of pure succinic acid from a succinate salt that involves minimal use of additional reagents, and produces virtually no waste by-products, and permits internal recycle of the base and acid values, is provided.
Abstract: A highly efficient process for the production and recovery of pure succinic acid from a succinate salt that involves minimal use of additional reagents, and produces virtually no waste by-products, and permits internal recycle of the base and acid values, is provided. The method involves the formation of diammonium succinate, either by using an ammonium ion based material to maintain neutral 8 pH in the fermenter or by substituting the ammonium cation for the cation of the succinate salt created in the fermenter. The diammonium succinate can then be reacted with a sulfate ion, such as by combining the diammonium succinate with ammonium bisulfate and/or sulfuric acid at sufficiently low pH to yield succinic acid and ammonium sulfate. The ammonium sulfate is advantageously cracked thermally into ammonia and ammonium bisulfate. The succinic acid can be purified with a methanol dissolution step. Various filtration, reflux and reutilization steps can also be employed.
TL;DR: In this article, the supercritical water oxidation was applied to municipal excess sludge and alcohol distillery wastewater of molasses in a batch reactor or a flow reactor with hydrogen peroxide as an oxidant in the temperature range 473-873 K. The liquid phase products were colorless and odorless.
Abstract: Supercritical water oxidation has been focused as an environmentally attractive technology where organic materials are oxidized to carbon dioxide, water, and N2. We have applied the supercritical water oxidation to municipal excess sludge and alcohol distillery wastewater of molasses. The reaction was carried out in a batch reactor or a flow reactor with hydrogen peroxide as an oxidant in the temperature range 473–873 K. The liquid phase products were colorless and odorless. The reaction products were analyzed in terms of total organic carbon (TOC), organic acids, and ammonium ion. TOC decreased with temperature and the oxidant amount. Acetic acid and ammonia were detected as major refractory intermediates in the product. When more than stoichiometric demand of oxidant was used, organic carbon in liquid phase was almost completely destroyed. Complete destruction of ammonia produced in the reaction required higher temperature than that of acetic acid. A tube-type flow reactor (1/8 in×1.7 m) was constructed for the continuous treatment of wastes. The sludge was destroyed efficiently in the flow reactor.
TL;DR: In this article, the authors investigated the performance of metallophthalocyanine (M-Pc) catalysts for the simultaneous reduction of carbon dioxide and nitrite ions.
TL;DR: In this article, the removal of ammonia nitrogen and phosphorus from wastewater by precipitating out with magnesium salts was showed, where factors of pH, reaction time, N/P ratio, and dissolution test were investigated to find optimal conditions for magnesium ammonium phosphate (MAP) formation.
Abstract: The removal of ammonia nitrogen and phosphorus from wastewater by precipitating out with magnesium salts was showed. Factors of pH, reaction time, N/P ratio, and dissolution test were investigated to find optimal conditions for magnesium ammonium phosphate (MAP) formation. The investigated conditions were also applied to toxic industrial wastewater. SEM and EDS analyses indicated that the precipitate was magnesium ammonium phosphate that was fine crystals of Mg and P compounds. The removal of ammonia and phosphorus increased with pH up to 10.5 where 82.6% and 97% of ammonia nitrogen and phosphorus were removed. It was found that minimum 10 minutes reaction was required for the nutrients removal. However, a small amount of phosphorus dissolved after 60 minutes. Ammonia nitrogen was well removed at one mole to two moles of magnesium. But at doses higher than two moles of magnesium, ammonia nitrogen increased due probably to the decreased pH. Bittern and sea water proved to be excellent coagulants for nutrie...
TL;DR: In this paper, a cobalt oxide catalyst for ammonia oxidation of high and stable activity and selectivity has been obtained and tested in a fluidized bed laboratory reactor, and it has been found that much less nitrous oxide is produced in ammonia oxidation on this catalyst than on platinum.
Abstract: A cobalt oxide catalyst for ammonia oxidation of high and stable activity and selectivity has been obtained and tested in a fluidized bed laboratory reactor. Its active component is Co 3 O 4 . It has been found that much less nitrous oxide is produced in ammonia oxidation on this catalyst than on platinum. The macrostructure of the cobalt catalysts, and especially the presence of mesopores of diameter 3 /g. A hypothetical model has been presented to explain the effect of the catalyst's macrostructure on its properties.
TL;DR: In this article, the degradation of nitrogen containing organic compounds was investigated using the Photo-Fenton method for wastewater treatment and the results showed that under specified conditions the substances could be decomposed and, as expected, aromatic compounds showed a higher degree and rate of degradation than aliphatic ones.
TL;DR: In this article, RuO 2 /Al 2 O 3 exhibited remarkable activities that at least 99% of ammonia (1500ppm) was decomposed at 503 K under 1.5 MPa in a NaOH added water (pH of 12).
Abstract: Wet air oxidation (WAO) of ammonia to dinitrogen has been investigated using various heterogeneous catalysts. Among them RuO 2 /Al 2 O 3 exhibited remarkable activities that at least 99% of ammonia (1500 ppm) was decomposed at 503 K under 1.5 MPa in a NaOH added water (pH of 12). The product was dinitrogen exclusively, and the quantities of NO − 3 formed were very small. The reaction proceeded rapidly in the high pH region indicating that ammonia was more reactive than ammonium ion. The activity and selectivity were found to have a relation with the oxygen affinity of the metal element. It was discussed that elements (Ru, Pd) with medium weakness of M–O bond showed the high activity and selectivity and the reason was proposed.
TL;DR: Cell-free extracts of Nitrosomonas eutropha oxidized ammonia to nitrite with NO2 (N2O4) as electron acceptor with ammonia oxidation activity shown to be sensitive against oxygen and hydroxylamine occurred as an intermediate.
Abstract: Cell-free extracts of Nitrosomonas eutropha oxidized ammonia to nitrite with NO2 (N2O4) as electron acceptor. The ammonia oxidation activity was shown to be sensitive against oxygen. In the absence of oxygen ammonia and NO2 were consumed in a ratio of approximately 1:2 and hydroxylamine occurred as an intermediate. NO was released in amounts equimolar to the consumption of NO2. After passing the cell suspension through a French pressure cell and fractionating it by density gradient centrifugation using a linear sucrose gradient, two soluble and two membrane fractions were detectable. Highest ammonia oxidation activity was measured in the membrane fractions and highest hydroxylamine oxidation activity in the soluble fractions. The KS values of the ammonia oxidizing system in cell-free extracts was about 20 microns NH3 and remained unchanged between pH 7.25 to 8.25.
TL;DR: In this paper, a commercial hog farm in Eastern North Carolina, USA, during September through December of 1997 was used to sample gaseous (hydrogen chloride, nitrous acid, nitric acid, sulfur dioxide and ammonium) and fine aerosol (ammonium, chloride, Nitrate, nitrate, and sulfate) species.
TL;DR: Results showed that microbially accessible nitrogen in the areas of highest microbial activity were depleted when toluene loading rates were 30 g/m3-h or greater, which led to a marked reduction in performance in terms of the VOC elimination rate of the biofilter.
Abstract: A pilot-scale biofilter was used to determine important design and operational parameters related to biofiltration of volatile organic compounds (VOCs). The importance of nitrogen availability in terms of biofilter performance was determined. Results showed that microbially accessible nitrogen (ammonia and nitrate) in the areas of highest microbial activity were depleted when toluene loading rates were 30 g/m3-h or greater. This depletion led to a marked reduction in performance in terms of the VOC elimination rate of the biofilter. The amount of nitrogen available to microorganisms can be depleted by microbial uptake of soluble nitrogen to make new biomass, stripping of ammonia, denitrification of nitrate, and leaching. Nitrogen is made available by mineralization of biomass, mineralization of organic nitrogen to soluble nitrogen, and addition of nitrogen fertilizers. Mineralization of biomass to ammonia results in the recycle of nitrogen through the system. Even though organic nitrogen in the m...
TL;DR: In this article, the authors examined the performance of various catalysts for the simultaneous reduction of carbon dioxide and nitrite ions at the gas-diffusion electrodes with various types of catalysts (Cr, Mo, Mn, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cd, In, Tl, Sn, and Pb).
Abstract: Simultaneous reduction of carbon dioxide and nitrite ions was examined at the gas-diffusion electrodes with various catalysts (Cr, Mo, Mn, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, In, Tl, Sn, and Pb). The formation of urea, CO, formic acid, and ammonia at the gas-diffusion electrodes with the catalysts of groups 11-14 was found on the simultaneous reduction. The maximum current efficiency (c.e.) of urea formation at Cd catalysts is approximately 55% at -1.0 V. The formation of urea at the gas-diffusion electrodes with the catalysts of groups 6-10, except Pd, was not found for the simultaneous reduction of C0 and nitrite. Relationship of the ability of urea formation to the ability of CO and NH 3 formation was investigated at various catalysts. The c.e. of urea increases with increasing the c.e of CO and NH 3 on the reduction of C0 alone and nitrite ions alone, respectively. Hence, the ability of urea formation at the catalysts depends on the ability of CO and NH formation. The catalysts with the high ability of CO and NH 3 formation could form large amounts of CO-like and ammonia-like precursors. Urea would be formed from both the ammonia-like precursor formed from nitrite ions, and the CO-like precursor formed from CO 2 at the groups 11-14 catalysts.
01 May 1998-Journal of Environmental Science and Health Part A-toxic\/hazardous Substances & Environmental Engineering
TL;DR: In this paper, the authors determined the kinetics of ammonia oxidation by ferrate(VI) as a function of pH (7.5-11.0) and temperature (10-35 °C).
Abstract: The kinetics of ammonia oxidation by ferrate(VI) was determined as a function of pH (7.5–11.0) and temperature (10–35 °C). The rates decrease with increase in pH. The pH dependence is probably related to protonation of ferrate(VI) and ammonia. The theoretical curve through data gave the rate constants; k7(HFeO4 ‐ + NH4 +) = 8.46±0.50x10‐1 M‐1s‐1; kg(FeO4 2‐ + NH4 +) = 1.26±0.11x10‐1 M‐1s‐1; k10(FeO4 2‐ + NH3) = 1.19±0.10x10‐1 M‐1s‐1. The activation parameters, ?H? and ?S? were found to be 67.3 ± 3.5 kJ/mol and 33.1 ± 0.2 J/mol.K, respectively. When ferrate(VI) was used in excess relative to ammonia in the oxidation reaction, 22 % of ammonia removal was achieved. The usefulness of ferrate(VI) to remove ammonia from wastewater is discussed.
TL;DR: In this article, the ammonia synthesis rate over a ruthenium single crystal has been studied in the temperature range 598-898 K. Ammonia was synthesized from a stoichiometric (3H 2 : N 2 ) gas-mixture at a pressure of approximately 2 bar.
TL;DR: It is suggested that substrates of AMO can preserve the ammonia-oxidizing activity of N. europaea in batch incubations by protecting either AMO itself or other molecules associated with ammonia oxidation.
Abstract: The effects of limiting concentrations of ammonium on the metabolic activity of Nitrosomonas europaea, an obligate ammonia-oxidizing soil bacterium, were investigated. Cells were harvested during late logarithmic growth and were incubated for 24 h in growth medium containing 0, 15, or 50 mM ammonium. The changes in nitrite production and the rates of ammonia- and hydroxylamine-dependent oxygen consumption were monitored. In incubations without ammonium, there was little change in the ammonia oxidation activity after 24 h. With 15 mM ammonium, an amount that was completely consumed, there was an 85% loss of the ammonia oxidation activity after 24 h. In contrast, there was only a 35% loss of the ammonia oxidation activity after 24 h in the presence of 50 mM ammonium, an amount that was not consumed to completion. There was little effect on the hydroxylamine oxidation activity in any of the incubations. The loss of ammonia oxidation activity was not due to differences in steady-state levels of ammonia monooxygenase (AMO) mRNA (amoA) or to degradation of the active site-containing subunit of AMO protein. The incubations were also conducted at a range of pH values to determine whether the loss of ammonia oxidation activity was correlated to the residual ammonium concentration. The loss of ammonia oxidation activity after 24 h was less at lower pH values (where the unoxidized ammonium concentration was higher). When added in conjunction with limiting ammonium, short-chain alkanes, which are alternative substrates for AMO, prevented the loss of ammonia oxidation activity at levels corresponding to their binding affinity for AMO. These results suggest that substrates of AMO can preserve the ammonia-oxidizing activity of N. europaea in batch incubations by protecting either AMO itself or other molecules associated with ammonia oxidation.
TL;DR: A two-year record of filter pack measurements illustrates the chemical climatology of nitric acid, sulfur dioxide, ammonia and major aerosol components (particulate nitrate, sulfate and ammonium) at a high alpine site.