Ratio Of NH4 Research Articles

Revealing the NO Formation Kinetics for NH3/CH4 Blends Under Dual-Flame and Premixed Swirl Flame Configurations

Ammonia stands out as a promising zero-carbon fuel and an efficient hydrogen carrier, offering great promise for industrial applications in gas turbines and boilers. However, different combustion modes significantly influence the flame structure and combustion characteristics of ammonia. In this study, two distinct fuel injection strategies were employed in a model combustor: ammonia and methane, under fully premixed and dual-flame combustion modes. Numerical simulations were performed to analyze the flame structure, velocity fields, and temperature distribution, complemented by planar flow field, flame OH* chemiluminescence, and NO emission measurements. Findings reveal that with an increasing NH3 ratio, the flame front becomes more elongated with more pronounced temperature fluctuations at the swirler exit. Particularly, at 50% NH3, a significant reduction in flame temperature is observed, notably at a height of 30 mm from the burner. For dual flames, the reaction NH2 + O ↔ HNO + H was less significant compared to its effect in premixed flames, whereas the H + O2 ↔ O + OH reaction demonstrated the highest sensitivity coefficient. An increase in the NH3 ratio correspondingly led to a reduction in NO consumption reaction rates, heightening the sensitivity coefficient for NO inhibition, and providing critical insights into ammonia combustion optimization.

Phytochemical and morpho-physiological response of Melissa officinalis L. to different NH4+ to NO3̄ ratios under hydroponic cultivation

BackgroundThe utilization of nutrition management, has recently been developed as a means of improving the growth and production of phytochemical compounds in herbs. The present study aimed to improve the growth, physiological, and phytochemical characteristics of lemon balm (Melissa officinalis L.) using different NH4+ (ammonium) to NO3̄ (nitrate) ratios (0:100, 25:75, 50:50, 75:25 and 100:0) under floating culture system (FCS).ResultsThe treatment containing 0:100 - NH4+:NO3̄ ratio showed the most remarkable values for the growth and morpho-physiological characteristics of M. officinalis. The results demonstrated that maximum biomass (105.57 g) earned by using the ratio of 0:100 and minimum at 75:25 ratio of NH4+: NO3̄. The plants treated with high nitrate ratio (0:100 - NH4+:NO3̄) showed the greatest concentration of total phenolics (60.40 mg GAE/g DW), chlorophyll a (31.32 mg/100 g DW), flavonoids (12.97 mg QUE/g DW), and carotenoids (83.06 mg/100 g DW). Using the 75:25 - NH4+:NO3̄ ratio caused the highest dry matter (DM), N and K macronutrients in the leaves. The highest antioxidant activity by both DPPH (37.39 µg AAE/mL) and FRAP (69.55 mM Fe++/g DW) methods was obtained in 75:25 - NH4+:NO3̄ treatment. The p-coumaric acid as a main abundant phenolic composition, was detected by HPLC analysis as the highest content in samples grown under 0:100 - NH4+:NO3̄ treatment. Also, the major compounds in M. officinalis essential oil were identified as geranial, neral, geranyl acetate and geraniol by GC analysis. With increasing NO3̄ application, geraniol and geranyl acetate contents were decreased.ConclusionsThe findings of present study suggest that the management of NH4+ to NO3̄ ratios in nutrient solutions could contribute to improving growth, physiological and phytochemical properties of M. officinalis. The plants treated with high nitrate ratio (especially 0:100 - NH4+:NO3̄) showed the greatest effects on improving the growth and production of morpho-physiological and phytochemical compounds. By comprehensively understanding the intricate dynamics among nitrogen sources, plants, and their surroundings, researchers and practitioners can devise inventive approaches to optimize nitrogen management practices and foster sustainable agricultural frameworks.

Numerical investigation on the combustion characteristics and NOx emission of non-premixed H2/NH3/air in vase-shaped micro combustor

Hydrogen and ammonia, as currently popular zero carbon fuels, have received widespread attention. These two fuels have complementary advantages in combustion characteristics, cost, safety, etc. Based on the vase shaped micro combustor, a new structure proposed for application in micro thermophotovoltaic systems in our previous work. This article numerically investigated the combustion characteristics and NOx emission of non-premixed H2/NH3/Air in vase shaped micro combustor which proposed in our previous work. The variation patterns of flame temperature, wall temperature, flammability limit, and NOx emission with the blended ratio of NH3 and equivalence ratio were obtained. It was found that the flame cannot move and stabilize when the mixing ratio is 0.6. The rate of production (ROP) and sensitivity of NO and N2O were analyzed. Four precursors of NO, HNO, NH, N, N2 have been discovered. Under the conditions of this article, HNO is the key component affecting NO emissions. When the blending ratio is greater than 0.3, the lower reaction rate of HNO leaded to a decrease in NO. The elementary reaction R63: NH + NON2O + H is the key elementary reaction that affects NO consumption and N2O generation. The blending ratio of 0.4 and the equivalence ratio of 1.2 are the optimized operating conditions with the highest comprehensive performance.

Experimental and reaction mechanism study on laminar burning velocity and characteristics of OH/NH generation in ammonia co-combustion

Developing fuels without carbon, such as ammonia (NH3), is crucial for achieving carbon reduction. Laminar burning velocity (LBV) is investigated, and distribution characteristics of OH and NH radicals are identified through planar laser-induced fluorescence. Rate of production of main free radicals and sensitivity analysis are also studied. The addition of NH3 to CH4-air mixtures results in a decrease in the LBV, a rise in preheating zone height, a reduction in OH radical fluorescence intensity, and an enhancement in NH radical fluorescence intensity. Simulation reveals that the high NH3 ratio enhance the negative impact of nitrogen-containing elementary reactions on LBV. The addition of NH3 enhances the initial consumption of more OH via reaction R248:NH2+OH=NH+H2O, leading to increased NH production, and indicating a negative effect on LBV. The decrease in OH concentration is the main factor leading to a decrease in LBV. The reactions affecting the OH generation and consumption are R39:H+O2=O+OH and R85:OH+H2=H+H2O, respectively. The addition of NH3 leads to a more significant reduction in R39.

Mineralogical and Geochemical Composition of Late Permian Coals from Dengfeng Coalfield, North China: Conversion of Clay Minerals in Coal during Coalification

Dengfeng Coalfield represents a significant coalfield in Henan Province, North China. It is therefore essential to gain an understanding of the mineralogy and geochemistry of the Dengfeng coal, both from a geochemical perspective and in terms of the wider environmental context. In this study, a total of 27 coal bench samples were collected from the No. II1 coal of the Dengfeng Coalfield. The mineral species and major elements were quantitatively analysed using the X-ray diffraction and X-ray fluorescence methods, respectively. The minerals in the Dengfeng coal are dominated by ammonian illite and kaolinite with average contents of 3.73% and 7.47%, respectively. These are followed by calcite (2.74% on average) and ankerite (0.49%). The mean value of the kaolinite Hinkley index, which is a quantitative measure of kaolinite crystallinity, is 1.26. This suggests that kaolinite formation is primarily driven by diagenetic recrystallisation. The ammonian illite exhibits an average d001 of 10.2995 Å, indicative of a prevalence of NH4+ interlayer cations, with K+ also present in notable quantities. The ratio of NH4⁺ to (NH4⁺ + K⁺) has an average value of 0.90, which is indicative of the predominance of NH4⁺. The mean value of the illite Kübler index, which is a quantitative measure of illite crystallinity, is 0.264. This suggests that the diagenetic conditions correspond to the rank of the Dengfeng coal. The kaolinite present in the Dengfeng coal is suggested to have been derived from terrigenous detritus and subsequently subjected to diagenetic recrystallisation, resulting in a relatively high Hinkley index. The ammonian illite in the Dengfeng coal was predominantly formed through the conversion of the precursor kaolinite, with the influence of seawater during peat accumulation favouring the conversion of kaolinite to ammonian illite.

Experimental study of NH3 and coal Co-firing in a CFB and its nitrogen conversion

This study conducted co-firing experiments of NH3 and coal in a circulating fluidized bed combustor. The effects of NH3 co-firing ratio and combustion atmosphere of NH3 addition position on temperature, flue gas emissions, carbon content of the fly ash, NH3 content in fly ash were investigated. Results showed that NOx and N2O emissions increased with NH3 ratio increasing when adding NH3 in the reducing zone. A lower NOx increment was found within 0∼20 % NH3 ratio, increasing by 0.6 times compared to coal combustion. The NH3 content in fly ash was 2.74 mg/kg when NH3 ratio was 10 %. Compared to the reducing zone, adding NH3 into the oxidizing zone promoted the generation of more NOx and N2O, and simultaneously was detrimental to the burnout of NH3 and CO. Based on these findings, NH3 added in the reducing zone emerges as an optimized choice when NH3 and coal are co-fired in circulating fluidized bed. Extending the retention time of NH3 in the reducing zone was beneficial for controlling NOx and N2O, as well as promoting the burnout of NH3 and CO. Furthermore, fuel-N conversion analysis showed that over 96 % fuel-N was converted into harmless N2 when NH3 ratio exceeds 10 %.

Variations in different preceding crops on the soil environment, bacterial community richness and diversity of tobacco-planting soil.

Tobacco (Nicotiana tabacum L.) is a major cash crop, and soil quality played a significant role in the yield and quality of tobacco. Most farmers cultivate tobacco in rotation with other crops to improve the soil characteristics. However, the effects of different previous crops on the soil's nutrient status and bacterial community for tobacco cultivation still need to be determined. Three treatments were assessed in this study, i.e., tobacco-planting soil without treatment (CK), soil with barley previously cultivated (T1), and soil with rapeseed previously cultivated (T2). The soil physical and chemical properties and the 16S rRNA gene sequence diversity of the bacterial community were analyzed. The effects of different crops on the physical and chemical properties of tobacco-planting soil and the diversity and richness of the bacterial community were comprehensively discussed. The results of this study showed that different previously cultivated crops altered the nutrient status of the soil, with changes in the ratio of NH4 +-N to NO3 --N having the most significant impact on tobacco. In CK, the ratio of NH4 +-N to NO3 --N was 1:24.2, T1-1:9.59, and T2-1:11.10. The composition of the bacterial community in tobacco-planting soil varied significantly depending on the previously cultivated crops. The richness and diversity of the bacterial community with different crops were considerably higher than without prior cultivation of different crops. The dominant bacteria in different treatments were Actinobacteriota, Proteobacteria, and Chloroflexi with their relative abundance differed. In conclusion, our study revealed significant differences in nutrient status, bacterial community diversity, and the richness of tobacco-planting soil after the preceding cultivation of different crops. Suitable crops should be selected to be previously cultivated in tobacco crop rotations in near future for sustainable agriculture.

Synthesis of struvite-enriched slow-release fertilizer using magnesium-modified biochar: Desorption and leaching mechanisms

To improve the retention and slow-release abilities of nitrogen (N) and phosphorus (P), an 82 %-purity struvite fertilizer (MAP-BC) was synthesized using magnesium-modified biochar and a solution with a 2:1 concentration ratio of NH4+ to PO43− at a pH of 8. Batch microscopic characterizations and soil column leaching experiments were conducted to study the retention and slow-release mechanisms and desorption kinetics of MAP-BC. The slow-release mechanism revealed that the dissolution rate of high-purity struvite was the dominant factor of NP slow release. The re-adsorption of NH4+ and PO43− by biochar and unconsumed MgO prolonged slow release. Mg2+ ionized by MgO could react with PO43− released from struvite to form Mg3(PO4)2. The internal biochar exhibited electrostatic attraction and pore restriction towards NH4+, while magnesium modification and nutrient loading formed a physical antioxidant barrier that ensured long-term release. The water diffusion experiment showed a higher cumulative release rate for PO43− compared to NH4+, whereas in soil column leaching, the trend was reversed, suggesting that soil's competitive adsorption facilitated the desorption of NH4+ from MAP-BC. During soil leaching, cumulative release rates of NH4+ and PO43− from chemical fertilizers were 3.55–3.62 times faster than those from MAP-BC. The dynamic test data for NH4+ and PO43− in MAP-BC fitted the Ritger-Peppas model best, predicting release periods of 163 days and 166 days, respectively. The leaching performances showed that MAP-BC reduced leaching solution volume by 5.58 % and significantly increased soil large aggregates content larger than 0.25 mm by 24.25 %. The soil nutrients retention and pH regulation by MAP-BC reduced leaching concentrations of NP. Furthermore, MAP-BC significantly enhanced plant growth, and it is more suitable as a NP source for long-term crops. Therefore, MAP-BC is expected to function as a long-term and slow-release fertilizer with the potential to minimize NP nutrient loss and replace part of quick-acting fertilizer.

Nitrogen removal from urea effluent in an anammox sequencing batch biofilm reactor with valorised dishwashing scrubber as biocarrier

BackgroundThis study aimed for efficient nitrogen removal from urea wastewater in an anammox SBBR with valorised dishwashing scrubber as biocarrier. MethodsThe study (225 d) comprised three discrete phases: Phase I [1 – 26 d; Inf. NH4+-N (Simulated ww)], Phase II [27 – 131 d; Inf. NH4+-N (Real ww) + Inf. NH4+-N (Simulated ww)] and Phase III [132 – 225 d; Inf. NH4+-N (Real ww)] in which the reactor was supplemented with varied ratios (0 – 7) of influent NH4+-N reflecting varying combinations of real and simulated wastewater. Significant findingsThe reactor exhibited average total nitrogen removal efficiency of approximately 83 %, 81 %, and 80 % in the subsequent phases I, II, and III, respectively at varied nitrogen loading rates (100 – 232 g N m−3 d−1). The 16S rRNA gene sequencing revealed significant enrichment of Candidatus Kuenenia (from 41.69 % to 48.11 %) on the 225th day which was primarily attributed to significant decline in Nitrospira from 23.9 % to 1.24 % (due to nitrite oxidizing bacteria inhibition on account of high free ammonia concentrations in the reactor) and Nitrosomonas from 4.32 % to 0.01 %. Additionally, genera that were not initially present (on the 1st day) including Stenotrophobacter (17.34 %), Sphingobium (8.41 %), Rhodococcus (5.88%) and Ohtaekwangia (5.84 %) were observed to emerge by the end of the experiment (225 d).

Synergistic effects of L-glutamine and inorganic nitrogen molar ratios enhance the induction of somatic embryogenesis of Pinus maximinoi H.E. Moore

Clonal breeding programs of Pinus maximinoi require the establishment of a robust somatic embryogenesis (SE) protocol to produce enough cell lines to accelerate the effective continuous deployment of elite planting stocks to research and commercial compartments. Somatic embryogenesis was induced from immature zygotic embryo explants enclosed in megagametophytes of P. maximinoi collected from two plantations located in different climatic conditions. Cones were collected during the winter months from July to August and the influence of seed family, cone collection date and culture medium formulation, with emphasis on the organic and inorganic nitrogen supply, were studied. Ammonium to nitrate molar ratios of 1:1 and 1:2 in modified Litvay’s medium (mLV) produced the highest numbers of extrusions, while a 1:4 ratio mostly produced unhealthy, non-embryogenic extrusions. The formation of a tissue showing a rapidly-proliferating, spiky morphotype was produced in a medium supplemented with 1.5 g/L of L-glutamine. Morphologically advanced cultures with nodular structures were produced in megagametophytes from both plantations in a 1:2 NH4+:NO3− medium regardless of L-glutamine supplementation levels. The optimal medium for P. maximinoi SE induction contained a 1:2 NH4+:NO3− molar ratio with 1.5 g/L L-glutamine. The synergy between the molar ratio of NH4+:NO3− and L-glutamine resulted in the highest numbers of extrusions. The overall inductive competence window for somatic embryogenic response in P. maximinoi was determined to be from the second week of July to the first week of August for both plantations. The “peak” period was in the fourth week of July 2022. The success of the SE technology in P. maximinoi seed families is determined by the optimal inductive competence window of the immature megagametophytes enclosing zygotic embryos and the chemical composition of the induction medium in terms of the ammonium to nitrate molar ratio and the concentration of the L-glutamine used.

NH4+-N and Low Ratios of NH4+-N/NO3−-N Promote the Remediation Efficiency of Salix linearistipularis in Cd- and Pb-Contaminated Soil

(1) Background: the utilization of fast-growing trees for phytoremediation in heavy-metal-contaminated soil is increasingly recognized as an effective remediation method. Nitrogen (N) fertilizer enhances plant tolerance to heavy metals, yet the impact of various N levels and ammonium (NH4+-N)/nitrate (NO3−-N) ratios on the remediation of cadmium (Cd) and lead (Pb) by trees remains unclear. (2) Methods: the efficiency of Salix linearistipularis in remediating Cd- and Pb-contaminated soil was investigated using a pot experiment with three N levels (60, 120, 200 kg hm−1 year−1) and five NH4+-N/NO3−-N ratios (6/0, 4/2, 3/3, 2/4, 0/6) employed, resulting in 16 treatments including a control. (3) Results: the levels and ratios of NH4+-N/NO3−-N significantly affected the Cd and Pb uptake by S. linearistipularis. The highest increases in Cd and Pb in S. linearistipularis were observed for the N120-6/0 treatment, which increased by 104.36% and 95.23%, respectively. In addition, in the N120-6/0 treatment, the stem and leaf bioconcentration factors of Cd were significantly enhanced by 28.66% and 40.11%, respectively. Structural equation modeling revealed that the uptake of Cd and Pb was predominantly influenced by plant traits (biomass and root traits) rather than soil properties. (4) Conclusions: Our findings highlight the potential of the NH4+-N/NO3−-N ratio to regulate plant traits, thereby improving the phytoremediation efficiency of heavy-metal-contaminated soil.

FAST START-UP MARINE ANAMMOX PROCESS USING INTENSIVE SHRIMP POND SOLID WASTE AS INOCULUM IN FILTER BIOREACTOR

Intensive shrimp culture waste contains high nitrogen, which can reduce water quality and environmental-carrying capacity. Anaerobic ammonium oxidation (anammox) is a potential and economical nitrogen removal process. However, limited information is available on the application of anammox process in aquaculture. The purpose of this study was to start up an anammox process in two filter bioreactors (FtBR) based on different inoculums. Run 1 used intensive shrimp solid waste, and Run 2 used intensive shrimp solid waste and granular of fresh anammox bacteria belonging to Candidatus Brocadia fulgida. Ammonium and nitrite concentrations of 70-100 mg N L-1 each were added to filtered and sterilized seawater as synthetic wastewater and flowed to the reactor with HRT 24-hour. After 120 days, the maximum ammonium conversion efficiency (ACE), nitrogen removal efficiency (NRE), and nitrogen removal rate (NRR) for Run 1 and 2 were 82.48%, 72.58%, 0.12 kg N (m3·d)-1 and 83.06%, 63.59%, 0.10 kg N (m3·d)-1, respectively. Experiment nitrogen stoichiometric ratios of NH4+:NO2-:NO3- were 1:1.40:0.12 and 1:1.13:0.14, which were close to the stoichiometry of the anammox process. Fast start-up of anammox process was achieved using intensive shrimp solid waste as inoculum. Anammox can be a new method for developing intensive shrimp culture wastewater treatment.

A low-tech, low-cost method to capture point-source ammonia emissions and their potential use as a nitrogen fertiliser.

Rising global energy prices have led to increased costs of nitrogen (N) fertilisers for farmers, but N pollution (losses) from agricultural activities can account for over 50% of the nitrogen applied. This study assesses the feasibility of a low-cost and low-tech method of NH3 emission capture from an agricultural point source (chicken manure) using a water column bubbling technique, and its application as a fertiliser to several plant types. Solutions of i) nitric acid (HNO3), ii) calcium nitrate (Ca(NO3)2), iii) a mixture of Ca(NO3)2 and HNO3 and iv) deionised H2O were used to scrub NH3 from air pumped from a storage container containing chicken manure. We conclude that NH3 can be captured from manure using low-tech methods, and that solutions of common fertiliser compounds such as ammonium nitrate and calcium ammonium nitrate can be replicated by binding captured NH3 to solutions of nitrate. Our results suggest that dissolved calcium nitrate is just as effective at scrubbing NH3 from the atmosphere as nitric acid at low concentrations, but could do so at a near neutral pH. For use on common silage grass for livestock feed, all of the captured ammonium solutions significantly increased yields, including the ammonium only solution. However, the aquatic plants (Taxiphyllum Barbieri and Salvinia auriculata) did not respond favourably to a high ratio of NH4+ in solution, and in the case of Salvinia auriculata, the plant was significantly damaged by the ammonium only solution. In conclusion, we highlight that the capture and utilisation of NH3 emissions from point sources is possible using very basic apparatus and that if used correctly, this captured nitrogen can be stored and applied to crops in a variety of forms which could reduce reliance and cost of mineral fertiliser use.

Control of nitrogen defects in carbon nanotubes for self-powered memristive systems

Recent studies show that the additional introduction of heteroatoms into the structure of CNTs makes it possible to change their electronic and physical properties [1]. Of great interest is the process of doping CNTs with nitrogen atoms [2]. The introduction of nitrogen defects into a lattice of carbon atoms makes it possible to modify the CNT structure up to the demonstration of anomalous properties that are not appropriate for this material [3]. It has been shown that multi-walled N-CNTs can exhibit memristive and piezoelectric properties [4]. The parameters of CNTs during synthesis can be controlled by the plasma enhanced chemical vapor deposition (PECVD) method. The addition of ammonia (NH3) to the carbonaceous gas in the PECVD process allows CNTs to be doped directly during growth. At the same time, the dopant concentration and the type of nitrogen defects have a significant effect on the properties of CNTs. The memristive properties of CNTs have already been sufficiently studied [5], however, for their application in self-powered systems, additional studies of the parameters of the piezoelectric module of N-CNTs are required. The aim of this work is to study the effect of ammonia flow on the concentration, type of nitrogen defects, and the value of the piezoelectric modulus during growth of CNTs by the PECVD. Silicon (100) substrates were used as samples with films of a buffer (Mo, 100 nm) sublayer and a catalytic layer (Ni, 15 nm). CNTs were grown at a temperature of 550 °C in an atmosphere of acetylene (C2H2, 35 sccm) and NH3. The C2H2 flow was kept constant, while the NH3 flow was changed in the C2H2:NH3 ratio from 1:1 to 1:10. Based on the obtained SEM images, it was found that with an increase in the ratio of C2H2:NH3 flowes, an increase in the density of nanotubes in the array were observed. This occurs due to more active growth of N-CNTs on small nickel catalytic centers due to the accelerated process of hydrogen desorption and its binding with ions in ammonia plasma, which leads to an increase in the growth rate of nanotubes on smaller catalytic centers. Thus, the area of the catalytic center is one of the limiting factors of the growth rate and allows one to control the aspect ratio and density of CNTs in the array. An analysis of the XPS spectra showed that with an increase in the ratio of C2H2:NH3 flows from 1:1 to 1:10, a nonlinear change in the concentration of the nitrogen dopant in N-CNTs from 8.4 to 12 at % is also observed. This led to a nonlinear change in the piezoelectric modulus of nanotubes from 8.7 to 20.6 pm/V and a change in their memristive properties. It has been established that an increase in the concentration of doping nitrogen leads to an increase in the piezoelectric modulus of N-CNTs, which is the source of the memristive effect. The obtained results can be used in the development of energy-efficient piezoelectric nanogenerators based on an array of vertically aligned N-CNTs for autonomous memristive systems.

Topography-driven differences in soil N transformation constrain N availability in karst ecosystems

Fragile karst ecosystems are characterized by complex topographic landscapes associated with high variations in vegetation restoration. Identifying the characteristics and driving factors of nitrogen (N) availability across the topographic gradient is essential to guide vegetation restoration in karst regions. In this study, we collected soil samples and plant leaves along the topographic gradient (ridge, upper slope, middle slope, and foot slope) of convex slopes in the karst fault basin of southwest China, and determined the indicators reflecting soil N availability, N transformation rates, and their controlling factors. Our results showed that foliar N content and δ15N value, soil inorganic N content and δ15N value, and foliar N:P ratio were substantially lower on the steep hillslopes than on the flat top ridge. Steep slope soils also had a lower enzyme C:N ratio but a higher enzyme N:P ratio than the flat ridge soils. Furthermore, the vector angles calculated by soil extracellular enzyme analysis were below 45o in all studied soils and decreased significantly with increasing slope, indicating that microbial growth was generally limited by N. These results jointly suggest the declines in soil N availability across the topographic gradient, which are further explained by the changes in soil inherent N transformation processes. As the slope became steeper, soil mineralization and autotrophic nitrification (ONH4) rates decreased significantly, while ratio of microbial NH4+ immobilization to ONH4 and NH4+ adsorption rate increased significantly, indicating the decrease in soil inorganic N supply capacity. We further found that deteriorated soil structure, decreased soil organic matter and calcium content, altered microbial abundance, and increased ratios of fungi to bacteria and gram-positive bacteria to gram-negative bacteria were the primary drivers of reduced N transformation rates and N availability across the topographic gradient. Overall, this study highlights the critical role of the topography in controlling soil N availability by regulating N transformation processes in karst regions. The topography should be considered an important factor affecting the functions and services of karst ecosystems.

Characteristics of ammonia-hydrogen nonpremixed bluff-body-stabilized flames

The combustion of ammonia (NH3) has received much attention over the last few years due to challenges associated with its low reactivity and the emission of nitric oxides. One way to improve the reactivity of NH3 is to blend it with (H2/N2) mixture as the product of its dissociation, before introducing it into energy systems. In this study, experimental measurements were carried out on nonpremixed bluff-body stabilized flames to better understand the flame and emission characteristics of NH3/H2/N2 flames. Four fuel mixtures at different NH3 and (H2/N2) ratios were investigated to represent different levels of ammonia cracking. Photography, planar laser-induced fluorescence of OH, thermocouples, and gas analysis techniques were used to understand flame features, reaction zone characteristics, NO, and NH3 concentration within the flame and at the exhaust. It was observed that a decrease in NH3 ratio in the mixtures resulted in longer and more stable flame with reduced thermal radiation as compared to NH3-rich fuel blends. For the highest NH3 blend studied, the flames exhibit extinction and re-ignition in the neck zone, as evidenced by OH-planar images and temperature profiles. As the H2/N2 ratio in the fuel mixture is increased, while keeping the Re constant, the momentum flux ratio (jet/co-flow) also increased resulting in a fuel-lean recirculation zone (RZ), and a shift in the maximum temperature and OH region from the outer shear layer to the inner layer next to the central jet. At levels of NH3 in the fuel mixture above 50% by volume, unburned ammonia slips through the flame and into the exhaust, and the subsequent reburn mechanism resulted in reduced NO emission. CFD simulations using Reynolds-averaged Navier-Stokes (RANS) and the flamelet–progress-variable submodel were conducted and compared with the experimental results. The CFD results helped to qualitatively describe and further explain what was observed in the experiment including the flame appearance, mixing field, and the reaction zone location in the tested flames.

Dissolved organic carbon bioreactivity and DOC:DIN stoichiometry control ammonium uptake in an intermittent Mediterranean stream

Abstract Heterotrophic organisms in streams use dissolved organic carbon (DOC) and dissolved inorganic nitrogen (DIN) from the water column to meet their growth and energy requirements. However, the role of DOC availability in driving DIN uptake in headwater streams is still poorly understood. In this study, we focus on how DOC:DIN stoichiometry and DOC bioreactivity control ammonium (NH4+) uptake and heterotrophic aerobic respiration, and how this influence varies among seasons in a forested Mediterranean headwater stream. We estimated in‐stream NH4+ uptake rates seasonally by conducting whole‐reach constant‐rate additions of NH4+ with and without amendments of either lignin (recalcitrant DOC) or acetate (labile DOC). During each addition, we characterised microbial community composition by molecular analyses, stream metabolism with the single‐station method, and heterotrophic aerobic respiration by adding a metabolic tracer (resazurin). The stream was heterotrophic (net ecosystem production <0) regardless of the season, with a microbial community mostly composed of heterotrophic bacteria. In‐stream NH4+ uptake rates were not related to either background NH4+ or DOC concentrations. Instead, these rates increased with increasing the molar ratio of NH4+ to nitrate (NO3−) (NH4+:NO3−) and DOC to DIN (DOC:DIN).Whole‐reach heterotrophic aerobic respiration rates showed the same relationship against stoichiometric ratios as NH4+ uptake rates. Furthermore, in‐stream NH4+ uptake rates were from 5% to >800% higher during the co‐additions of acetate than when adding NH4+ either alone or with lignin. Our results indicate that in‐stream NH4+ uptake was largely controlled by heterotrophic bacteria, and that the stoichiometric balance between organic resources and nutrients was key to explaining the variability of in‐stream NH4+ uptake and heterotrophic aerobic respiration. Moreover, the observed increase in NH4+ uptake during acetate additions suggests that heterotrophic activity was limited by labile DOC availability. Our study highlights that both DOC:DIN stoichiometry and DOC bioreactivity are relevant factors driving the seasonal pattern of in‐stream N processing in this forested Mediterranean headwater stream.

The wetting‐to‐nonwetting transition of CVD BN coatings deposited at different temperatures

AbstractBoron nitride (BN) coatings (thickness 20–40 μm) were prepared on graphite substrates by chemical vapor deposition, with precursors of BCl3 and NH3 (ratio of 1:4) and pressure of 500 ± 50 Pa. The influence of the deposition temperature (650°C–1250°C) on the wettability of BN coatings with deionized water was studied. The wetting angle rapidly increases at 1100°C–1250°C, and the wetting‐to‐nonwetting transition occurs. The crystal structure and surface morphology of the BN coatings were characterized by a stylus instrument, scanning electron microscopy, and transmission electron microscopy. Research shows that the contact angle or nonwettability increases with a higher degree of crystallinity and a lower surface roughness, which were both under the control of the deposition temperature since the pressure and gas flows were kept constant in this study. At a deposition temperature of 650°C–950°C, the increase in the degree of crystallinity dominates; at 950°C–1100°C, the increase in surface roughness takes over. At 1100°C–1250°C, the degree of crystallinity continues to increase, while the surface roughness decreases due to the advantage of nucleation and the breakage of large surface clusters into smaller clusters. This results in increases (650°C–950°C), then decreases (950°C–1100°C) and again fast increases (1100°C–1250°C) in the wetting angle between the BN coating and deionized water and finally in the wetting‐to‐nonwetting transition (1100°C–1250°C).

Physiological and metabolomic analyses reveal the effects of different NH4+:NO3− ratios on blackberry fruit quality

Blackberries are important economic fruits, and they not only have a distinctive flavor but are also rich in nutritional and medicinal value. With the aim of elucidating the effects of different NH4+:NO3− ratios on blackberry fruit quality, the physiological characteristics and metabolomics of blackberry fruits were investigated in this study. The results revealed that the NH4+:NO3−/50:50 ratio treatment showed the maximum values for single fruit weight, transverse diameter, longitudinal diameter and the solidity–acid ratio of blackberry fruit as well as the maximum flavonoid and ellagic acid contents. The NH4+:NO3−/75:25 ratio treatment exhibited the maximum fructose, sucrose, glucose and anthocyanin contents and the highest superoxide dismutase (SOD) and catalase (CAT) activities. Moreover, a total of 857 known metabolites were detected in the blackberry fruits. Interestingly, NH4+ could increase the levels of amino acids and metabolites belonging to the indole and derivative classes in blackberry fruits, and D-proline, cysteine, tryptophan and indole may play vital roles in the formation of blackberry fruit quality. To produce blackberry fruit that is larger and has better flavor, a 50:50 ratio of NH4+:NO3−is recommended, while when the goal is higher anthocyanin and amino acid content, a 75:25 ratio of NH4+:NO3− is more appropriate. In addition, a 100:0 ratio of NH4+:NO3− is best for fruit storge. This study serves as a reference and provides technical support for the application of N to improve fruit quality and antioxidant capacity during small berries cultivation.

Genetically engineered deletion in the N-terminal region of nifA1 in R. capsulatus to enhance hydrogen production

NifA is the primary activator of nitrogenase, and the N-terminal domain of nifA is sensitive to ammonium concentration. In this work, a mutant Rhodobacter capsulatus ZX01 with a genetically engineered deletion in the N-terminal region of nifA1 was constructed by employing overlap extension PCR to mitigate the inhibition of ammonium on nitrogenase expression in photosynthetic bacteria. The effects of different ammonium ion concentrations on the growth and photo-fermentative hydrogen production performance of wild-type strain R. capsulatus SB1003 and mutant ZX01 with glucose and volatile fatty acids as the carbon sources were studied, respectively. When the ratio of NH4+-N was 20% and 30%, the hydrogen yield of the mutant ZX01 was enhanced by 14.8% and 20.9% compared with that of R. capsulatus SB1003 using 25 mM acetic acid and 34 mM butyric acid as the carbon source, respectively. In comparison, using 30 mM glucose as the carbon source, the hydrogen yield of ZX01 was increased by 17.7% and 22.2% compared with that of R. capsulatus SB1003 when the ratio of NH4+-N was 20% and 30%, and the nitrogenase activity of ZX01 was also enhanced by 38.0% and 47.6%, respectively. When using 10 mM NH4+ as a single nitrogen source, ZX01 showed a 2.6-fold increase in H2 production. These results indicated that ZX01 demonstrated higher ammonium tolerance and better hydrogen production performance than the wild-type. The deletion in the N-terminal region of nifA1 could partially de-repress the nitrogenase activity inhibited by ammonium.