Nitrogen fertilization is considered as an important source of atmospheric N₂O emission. A seven site-year on-farm field experiment was conducted at Ottawa and Guelph, ON and Saint-Valentin, QC, ...Canada to characterize the affect of the amount and timing of N fertilizer on N₂O emission in corn (Zea mays L.) production. Using the static chamber method, gas samples were collected for 28-days after preplant and 28-days after sidedress fertilization at the seven site-year, resulting in 14 monitoring periods. For both methods of fertilization, peak N₂O flux and cumulative emission increased with the amount of N applied, with rates ranging from 30 to 900 μg N m⁻² h⁻¹. Depending on N amount and time of application, cumulative emission varied from 0.05 to 2.42 kg N ha⁻¹, equivalent to 0.03% to 1.45% of the N fertilizer applied. Differences in N₂O emission peaks among fertilizer treatments were clearly separated in 13 out of 14 monitoring periods. Total N₂O emissions may have been underestimated compared with annual monitoring in 10 out of the 49 cases because the monitoring period ended before N₂O efflux returned to the baseline level. The flux of N₂O was negligible when soil mineral N in the 0-15 cm layer was < 20 mg N kg⁻¹. While rainfall stimulated emission, soil temperature > 15 °C was likely the driving force responsible for the higher levels of N₂O found for sidedress than preplant application methods. However, caution must be taken when interpreting these later results as preplant fertilization may have continuously stimulated N₂O emissions after the 28-days monitoring period, especially in situations where N₂O effluxes have not fallen back to their baseline levels. Increasing fertilizer rates from 90 to 150 kg N ha⁻¹ resulted in slight increases in yields, but doubled cumulative N₂O emissions.
Crop straw application in combination with fertilizer nitrogen (N) dose reduction is recommended to improve crop yields and carbon sequestration in soil. This practice may also promote soil nitrous ...oxide (N2O) emission, thus partially counterbalancing the expected benefits. However, the full straw return effect on the reduction of soil N2O to dinitrogen (N2) is not yet well known, owing to the methodological difficulties in quantifying soil N2 fluxes against the high atmospheric N2 concentration. This study was carried out in a long-term experimental field of a calcareous soil cultivated with summer maize and winter wheat in rotation. For the three field treatments since 2006, i.e., optimal fertilizer N with and without full straw return, and the control (without N and straw application), we conducted in- or ex-situ observations on field N2O fluxes, soil N2 emissions, crop yields, soil organic carbon (SOC) contents and soil/environmental factors. During a rotation cycle, we found that soil ammonium and nitrite concentrations, moisture and temperature jointly determined the N2O emissions, while nitrate concentration, dissolvable organic carbon to nitrate-N ratio and moisture jointly dominated the N2 emissions. Compared to straw removal, the straw return promoted reduction of more soil N2O to N2 in the wheat season than in the maize season, showing increases in the N2 emissions by 57% versus − 10% (P = 0.06). Nevertheless, it significantly enhanced the N2O emissions measured in situ by approximately 137% and 21% in the wheat and maize seasons, respectively (P < 0.05). It also significantly increased the annual crop yields by 20% on average (P < 0.05). Meanwhile it tended to enhance the SOC stock (0−20 cm) by 15‰ yr−1 (P = 0.14), showing a trend of more intensive carbon sequestration than the direct soil N2O emission (−948 versus 378 kg CO2e ha−1 yr−1 on average). We conclude that the long-term full straw return helps to sequester more carbon that offsetting the enhanced N2O emissions from the calcareous soil in the rotation system as it promotes reduction of more N2O to N2 in the wheat season.
•Straw return increased crop yield and N2O emission in a wheat-maize rotation system.•Straw return promoted more carbon sequestration than N2O emission in 100-year CO2e.•Straw facilitated reduction of more N2O to N2 in wheat season than in maize season.•N2O and N2 emissions in wheat season were dominated by denitrifiers denitrification.•Measured soil factors well explained variances in fluxes and flux ratios of N-gases.
Biotrickling filter (BTF) is often used for purification of waste gas from swine houses, with vital information still needed regarding interaction effects among multiple gas pollutants removal and ...also the formation of byproducts especially nitrous oxide (N2O, a strong greenhouse gas) due to the relative high NH3 concentration level compared to other gases. In this study, gas removal and N2O production were compared between two BTFs, where the inlet gas of BTF-1 contained NH3 and H2S while p-cresol was additionally supplied to BTF-2. At inlet load (IL) between 3.67 and 18.91 g m−3 h−1, removal efficiencies of NH3 exceeded 95% for both BTFs. As alternative strategy, adding thiosulfate improved H2S removal. Interestingly, presence of p-cresol to some extent promoted H2S removal at IL of 0.56 g m−3 h−1possibly due to effect on pH value of circulating solution. Similar to NH3, removal efficiencies of p-cresol were higher than 95% at an average IL of 2.98 g m−3 h−1. Gas residence time, pH of circulating solution and inlet loading were identified as key factors affecting BTF performance, but the response of individual gas compound to these factors was not consistent. Overall, p-cresol enhanced N2O generation although the effects were not always significant. High-throughput sequencing results showed that Proteobacteria accounted for the largest proportion of relative abundance and BTF-2 had much richer microbial diversity compared to BTF-1. Thermomonas, Comamonas, Rhodanobacter and other bacterial genus capable of denitrification were detected in both BTFs, and their corresponding abundances in BTF-2 (10.9%, 8.7% and 5.2%) were all greater than those in BTF-1 (0.4%, 0.3% and 2.0%), indicating that more denitrification may occur within BTF-2 and higher N2O could have been generated. This study provided evidence that organic gas components, served as carbon source, may increase the N2O production from BTF when treating waste gases containing NH3.
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•Interactions among NH3, H2S and p-cresol removal were investigated in BTF.•The presence of p-cresol promoted H2S removal, with no clear effects on NH3.•N2O was inevitably generated along with the removal of NH3, H2S and p-cresol.•p-cresol may serve as carbon source to microbes, further increasing the N2O production.•Relative abundance of microbial genus towards denitrification increased when p-cresol presented.
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•MnO2 exhibited better NO conversion activity over the whole temperature range.•MnO2 yielded more N2O among the three catalysts at low temperature.•Both E−R and L−H mechanisms were ...found conducting on the three catalysts.•N2O generation ratios from NH3 oxidation increased with increasing temperature.
Different valence states manganese oxides catalysts (MnO2, Mn2O3 and Mn3O4) were synthesized to investigate their N2O formation pathways during NH3–SCR of NO process. In contrast, the NO conversions of Mn2O3 and Mn3O4 were nearly identical, while MnO2 exhibited better NO conversion activity over the whole temperature range and corresponding to NO conversion of 100% at 150 °C with a space velocity of 36,000 h−1. At low temperature, the majority of N2O was generated from the SCR reactions on the three catalysts. With the increasing temperature, the N2O amounts and the N2O generation ratios from NH3 oxidation of the three catalysts both increased. Besides, NH3 species on MnO2 were easier to be oxidized by gaseous O2, while NH3,ads at Lewis acid sites would partly transfer to NH4+ and NH2 species on Mn2O3 in the presence of O2 and more NH2 species would be formed on the oxygen adsorbed surface of Mn3O4. Both E−R and L−H mechanisms were found conducting on the three catalysts. NH2/NH species on the MnO2 surface would react with gaseous NO to form NH2NO/NHNO and then decomposed to N2/N2O, respectively, while the adsorbed monodentate nitrites combined with NH3,ads and/or NH4+ species to form NH4NO2 that decomposed to N2. Besides the formation and decomposition of NH2NO/NHNO, NH4NO3 was also formed on Mn2O3 and Mn3O4, and then decomposing to N2O.
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•The Nd0.06Ni catalyst demonstrates enhanced activity and improved resistance to NOx for De-N2O.•The edge dislocation and defect structure enhance the amount of oxygen vacancies.•The ...addition of Nd leads to a significant increase in active sites, from 78.68 μmol g−1 to 174.34 μmol g−1.•In the presence of NOx, Nd0.06Ni exhibits a higher TOF compared to NiO.
In the field of catalytic N2O decomposition, it is imperative to develop low-temperature De-N2O catalysts with effective NOx tolerance. Herein, Nd0.06Ni catalyst was synthesized by coprecipitation method, incorporating additive Nd into NiO to enhance its catalytic performance. Characterization results indicated that the introduction of Nd into catalyst not only reduced the crystallite size of NiO, but also induced the formation of edge dislocations, defects, and synchronously weakened Ni-O bond. Additionally, the distinctive interaction between Nd and NiO endows enhanced NOx tolerance for Nd0.06Ni compared with pure NiO. Consequently, the T50 for De-N2O over Nd0.06Ni was 330 °C under simultaneous feeding of 2000 ppmv N2O, 5 vol% O2, and 100 ppmv NO, which was much lower than that of pure NiO (430 °C). Moreover, it was calculated that the Ea decreased from 82 to 74 kJ·mol−1, and the TOF increased from 1.82 × 10-3 to 4.39 × 10-3 s−1 at 350 °C when comparing pure NiO with Nd0.06Ni. In the presence of NOx, the TOF of the reaction for Nd0.06Ni was discovered to be 39-fold higher compared with pure NiO. Furthermore, Nd0.06Ni exhibited remarkable thermal stability in an environment containing O2, NO, and H2O, maintaining ∼ 63% N2O conversion at 400 °C.
The interaction between volatile and char is widespread in combustion. The effect of this interaction on the conversion of fuel-N to NOx is significant, but the mechanism remains to be ...comprehensively unveiled. Thus, in this paper, the NO and N2O conversion of nitrogen-containing biomass models (glutamate, glycine, phenylalanine) during combustion at high temperatures (800–1500 °C) is investigated using two combustion modes, separated combustion (in which volatile and char are burned separately) and coupled combustion (in which volatile and char are burned simultaneously), in an O2/Ar atmosphere. A new pathway for N2O formation resulting from the interaction between volatile and char is identified. At low temperatures, this interaction facilitates the conversion of fuel-N to N2O. For instance, during the separated combustion of glutamate at 800 °C, the conversion rates of fuel-N to N2O and NO are 26.3 % and 20.4 %, respectively. However, in coupled combustion, these conversion rates shift to 48.1 % for N2O and 3.6 % for NO. At high temperatures, this interaction promotes the conversion of fuel-N to NO. For instance, during the separated combustion and coupled combustion of glutamate at 1500 °C, the conversion rates of fuel-N to NO are 6.2 % and 16.6 %, respectively. Similar patterns are observed for the other two amino acids. In both combustion modes, the co-firing of cellulose, lignin, and hemicellulose with glutamic acid significantly suppresses the production of N2O. The conversion rate of N2O decreases by about 7 %–10 %, while the impact on NO release shows either a suppressive or promotive effect in different temperature intervals. These results play a crucial role in the development of efficient and clean combustion technology for biomass.
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•A novel N2O formation pathway from volatile-char interaction has been identified.•Volatile-char interaction enhances NO formation at 1300–1500 °C.•Accurate volatile-NO/N2O and char-NO/N2O contributions were determined.•Co-firing with cellulose, lignin, and hemicellulose inhibits the formation of N2O.
•The results of a meta-analysis show that addition of biochar decreased N2O emissions from soils by an average of 54%.•Factors for mitigation (biochar C/N, pyrolysis conditions, application rate, N ...fertilizer, soil texture and pH) were identified and discussed.•Recommendations are given to address future research needs to improve our understanding of biochar's role in N2O emissions from soil.
More than two thirds of global nitrous oxide (N2O) emissions originate from soil, mainly associated with the extensive use of nitrogen (N) fertilizers in agriculture. Although the interaction of black carbon with the N cycle has been long recognized, the impact of biochar on N2O emissions has only recently been studied. Herein we reflect on proposed hypotheses to explain N2O decrease with biochar, linking them to specific mechanisms for N2O formation and consumption in soil. Moreover, to assist in elucidating key mechanisms in which biochar may act in mitigating emissions of N2O, we undertook a meta-analysis using published literature from 2007 to 2013. This quantitative analysis used 30 studies with 261 experimental treatments. Overall, we found that biochar reduced soil N2O emissions by 54% in laboratory and field studies. The biochar feedstock, pyrolysis conditions and C/N ratio were shown to be key factors influencing emissions of N2O while a direct correlation was found between the biochar application rate and N2O emission reductions. Interactions between soil texture and biochar and the chemical form of N fertilizer applied with biochar were also found to have a major influence on soil N2O emissions. While there is clear evidence that, in many cases, emissions of N2O are reduced, there is still a significant lack in understanding of the key mechanisms which result in these changed emissions. As such, we have guided readers with suggestions to address specific research gaps, which we anticipate will enhance our knowledge and understanding of biochar's N2O emission mitigation potential.
With the continuous development of deep space exploration, many planetary exploration schemes and development plans regard the construction of planetary bases as an essential goal, especially the ...exploration of the Moon. Supercritical and transcritical nitrous oxide (N2O) cycles are compact, low-cost, efficient, and lightweight for nuclear reactors to supply power to the bases on other planets. This paper presents the thermodynamic, exergoeconomic, and mass analyses of a combined cycle consisting of a supercritical N2O recompression Brayton cycle and a transcritical N2O cycle (S–N2O/t-N2O). It is shown that under the optimal conditions, the combined thermal efficiency and exergy efficiency are 45.52 % and 60.13 %, respectively. Based on the exergy analysis, the exergy destruction mainly occurs in the reactor and main compressor. A sensitivity study shows that the split ratio, pressure ratio in the supercritical N2O cycle, main compressor inlet pressure, turbine2 inlet temperature, and turbine2 inlet pressure have significant effects on the net output work, thermal efficiency, specific mass, and levelized cost of electricity. Furthermore, multi-objective optimizations are considered to obtain the Pareto frontier solutions for different multi-objectives, and the optimal design condition is found. These findings could improve the power cycle performance for the construction of the Lunar Base.
•Energy and exergy analyses are performed on the S–N2O/t-N2O cycle.•Thermodynamic, exergoeconomic, and mass analyses are investigated and studied.•Sensitivity analysis is used to study the key performances of an S–N2O/t-N2O cycle.•Multi-objective optimization is presented to compromise the critical performances.
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•Theoretical basis of energy generation via N2O decomposition are introduced.•Biotic routes for N2O production in wastewater treatment process are reviewed.•Bioprocesses for energy ...production with high N2O yields are summarized.•Potential harvesting strategies for N2O recovery from wastewater are discussed.
Nitrous oxide (N2O), produced from wastewater treatment, is a potent greenhouse gas and has become a global concern in recent years. However, N2O has also been commonly used as a powerful oxidant for energy generation. As such, an increasing effort has been devoted to explore the energy potential of N2O from wastewater treatment processes recently. Nevertheless, the holistic knowledge on energy recovery from nitrogen in wastewater is still lacking for facilitating its further development. Striving for sustainable wastewater treatment, this review paper aimed to give the up-to-date status on several essential aspects regarding the N2O recovery as an energy resource rather than emission as a greenhouse gas, including energy production via N2O decomposition, main biotic N2O production sources, the potential bioprocesses used for N2O recovery, and the possible N2O harvesting strategies. We then put forward perspectives for N2O recovery and future challenges to improve our understanding of the energy generation, microbial processes involved and harvesting approaches in order to potentially achieve sustainable wastewater treatment via N2O recovery.
Experiments with soils have provided ample evidence that soil pH controls the N2O/(N2O + N2) ratio of denitrification, which increases with decreasing pH, most probably because low pH interferes with ...the expression of N2O reductase in denitrifying bacteria. In contrast, the N2O/NO3- product ratio of nitrification appears to be unaffected by soil pH within the range relevant for agricultural soils (pH 5.5–7.0). We hypothesized that local pH variations in cultivated soil may control in situ N2O emissions during periods of active denitrification. To test this hypothesis, we identified three plots with slightly different soil pH (5.4–5.9) within an agricultural field under spring ploughed cereal cropping, and placed four frames within each plot for measuring N2O emissions throughout autumn and spring. Soil samples were taken from each frame after the experiment to characterize the kinetics of NO, N2O and N2 production by anoxic incubation. The data were used to calculate an N2O index, IN2O, which is an inverse measure of the capacity of the denitrifying community to effectively express N2O reductase under anoxia and hence a proxy for the soil’s propensity to emit N2O under denitrifying conditions. N2O emissions were greatest during spring thaw, intermediate in autumn and low in late spring. Emissions during autumn and spring thaw were inversely related to soil pH, supporting the hypothesis that soil pH influences N2O emissions when denitrification is the main source of N2O. During these periods, emissions were positively correlated with IN2O, further substantiating the idea that soil pH affects denitrification product ratios in situ. Total organic carbon and nitrate content were negatively correlated with soil pH, thus co-varying with N2O emissions. However, the relationship of N2O emission to TOC and nitrate appeared weaker than to pH. Off-season emissions dominate N2O budgets in many regions. If the pH relationship holds at greater scales, careful soil pH management by precision liming could be a viable tool to reduce N2O emissions.
•Spatial variability of N2O emission was measured in a cultivated arable field.•Emission was negatively related to small-scale variation in soil pH (5.4–5.9).•The N2O product ratio of denitrification was negatively correlated with soil pH.•We conclude that pH controls N2O emissions during conditions prone to denitrification.
