To elucidate the direct effects of biochar on denitrification metabolism at the cellular level, the global response of model denitrifying soil bacterium (Paracoccus denitrificans) to biochar addition ...was investigated by physiological, proteomic, and metabolomics analyses. The enhancement effect on denitrification was positively correlated with its pyrolysis temperatures (300–500 °C) and dosages (0.1–1%), regardless of precursors corn straw (CS) or wheat straw). Moreover, the stimulating effect of CS biochar made at 500 °C (CS-500) was mainly attributed to the bulk particles rather than the released soluble compounds. Without direct contact with cells, bulk CS-500 particles might directly modulate the carbon metabolism by the adsorption of extracellular metabolites. Since carbon flux to storage was shifted to oxidative catabolism and growth assimilation, more share of the produced reducing power was used for nitrogen reduction. Meanwhile, except for nitrate reductase, both protein expressions and enzyme activities of nitrite reductase, nitric oxide reductase, and nitrous oxide reductase were up-regulated. Accordingly, the accumulation of N2O was reduced by 98% due to the optimized electron distribution among denitrifying enzymes. Eventually, the growth rate of Pc. denitrificans enhanced because of the improved energy utilization efficiency. These results updated the regulation mechanism of biochar on denitrification metabolism and N2O mitigation.
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•A pilot-scale MABR was operated after a demonstration-scale AnMBR.•The MABR achieved > 99 % removal of both sulfide and dissolved methane.•Energy requirement for the MABR operation ...was negligible (<0.05 kWh/m3).•> 99 % of produced N2O was recovered in off-gas from the gas permeable membranes.
Anaerobic secondary treatment can enable energy-efficient removal of organic matter but may produce effluent containing dissolved methane and sulfide that must be managed before discharge or reuse. In this study, we operated a Membrane-aerated Biofilm Reactor (MABR) to achieve reliable removal of dissolved sulfide and methane from anaerobic secondary effluent at pilot-scale. The pilot-scale MABR was equipped with gas permeable polymethyl pentene (PMP) membranes, promoting surface growth of aerobic biofilm via diffusion-based aeration (lumen-to-surface diffusion). The system treated anaerobic secondary effluent from a demonstration-scale anaerobic membrane bioreactor (AnMBR) processing 90 m3/d primary effluent. MABR influent flow rate was increased from 8.2 to 32.7 m3/d to elevate substrate loading rates to the biofilm. The MABR consistently achieved >99 % removal of sulfide and dissolved methane, even at the maximum substrate loading rate: 2.3 g-S/m2/d for sulfide and 2.5 g-CH4/m2/d for dissolved methane. Despite effective sulfide and methane removal, incomplete nitrification (<25 % ammonia removal) occurred, with a portion of ammonia converted into nitrous oxide (N2O), a greenhouse gas 298 times more potent than CO2. Operating the MABR incurred low energy costs: 0.01 to 0.05 kWh/m3 for the compressor supplying air to the membrane lumen and 0.01 kWh/m3 for the influent pump. An in-depth mass balance of N2O emissions from the MABR revealed that N2O was subject to counter-diffusion (surface-to-lumen diffusion) in which >99 % of the N2O produced within the biofilm was recovered in off-gas from the gas permeable membranes (hollow fibers).
The extensive application of organochloride pesticides in agriculture has raised concerns about their potential negative impacts on soil microbial denitrification and associated N2O emissions. ...However, most studies have primarily focused on bacteria, and the contribution of fungi to N2O emissions and their response to organochloride pesticides have often been overlooked. In this study, 15N tracing combined with the respiration inhibition method was applied to examine the impacts of chlorothalonil on both fungal and bacterial denitrification. The results demonstrated that fungal N2O emissions dominated in the absence of chlorothalonil, accounting for 73 % of total N2O emissions. Chlorothalonil inhibited fungal and bacterial denitrification via different mechanisms and altered the main pathways of soil N2O emissions. Amplicon sequencing analyses indicated that chlorothalonil significantly reduced the abundances of N2O-producing fungi owing to its fungicidal effect and fungal N2O emissions significantly dropped. Molecular biological analyses revealed that chlorothalonil induced lower electron generation, transport, and consumption efficiencies, which led to the inhibition of denitrifying enzymes in bacteria. Bacterial N2O emissions dramatically increased and became the dominant source. These findings provide insights into the mechanisms by which N2O emissions from fungal and bacterial denitrification are influenced by chlorothalonil.
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•Chlorothalonil inhibited denitrification process and increased total N2O emissions.•Chlorothalonil decreased fungal denitrifier abundances and their N2O emissions.•Chlorothalonil disrupted bacterial intracellular carbon metabolisms.•Bacterial N2O emissions surged due to the inhibition of denitrifying enzymes.
The incorporation of crop straw with fertilization is beneficial for soil carbon sequestration and cropland fertility improvement. Yet, relatively little is known about how fertilization regulates ...the emissions of the greenhouse gas nitrous oxide (N2O) in response to straw incorporation, particularly in soils subjected to long-term fertilization regimes. Herein, the arable soil subjected to a 31-year history of five inorganic or organic fertilizer regimes (unfertilized; chemical fertilizer application, NPK; 200% NPK application, 2 × NPK; manure application, M; NPK plus manure application, NPKM) was incubated with and without rice straw to evaluate how historical fertilization influences the impact of straw addition on N2O emissions. The results showed that compared to the unfertilized treatment, historical fertilization strongly increased N2O emissions by 0.48- to 34-fold, resulting from increased contents of hot water-extracted organic carbon (HWEOC), NO3−, and available phosphorus (Olsen-P). Straw addition had little impact on N2O emission from the unfertilized and NPK treatments, primarily due to Olsen-P limitation. In contrast, straw addition increased N2O emissions by 102–316% from the 2 × NPK, M, and NPKM treatments as compared to the corresponding straw-unamended treatments. These results indicated that N2O emissions in response to straw addition were largely regulated by historical fertilization. The N2O emissions were closely associated with the depletion of NO3− and decoupled from change in NH4+ content, suggesting that NO3− was the main substrate for N2O production upon straw addition. The stoichiometric ratios of HWEOC to mineral N and mineral N to Olsen-P were key factors affecting N2O emissions, underscoring the importance of resource stoichiometry in regulating N2O emissions. In conclusion, historical fertilization largely regulated the impacts of crop straw incorporation on N2O emissions via shifts in NO3− depletion and the stoichiometry of HWEOC, mineral N, and Olsen-P.
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•Historical fertilization regulated the response of N2O emission to straw addition.•The magnitude of N2O emissions was closely linked to the depletion of soil nitrate.•The availability and stoichiometry of soil C, N and P were key factors affecting N2O emission.
•2100 point DOE was tested for modelling the engine with different multiple injection strategies.•AVL Cameo, Robetworks and Matlab used for modelling and new 200 point was run in modelling ...environment and results are analyzed.•Multiple injection gives and advantage in terms of NOX emissions, while it increases fuel consumption.•If a after treatment system is used in the engine out, the multiple injection strategies increase the N2O formation at the after treatment out.
Today, pollutant emissions coming from diesel engines are one of the major source of air pollution. Stringent pollutant emission regulations place limits on the emissions of diesel engines. Also the future compliance with the new EURO VII regulations is challenging. Manufacturers must come up with novel strategies to reduce nitrogen oxides (NOx) emissions while fulfilling market demands. In this context, an experimental data were collected from 2100 engine operating point with different injection strategies. Then the results are modelled with robust neural network regression method in AVL Cameo environment. The generated model was run for new 200 test point and results are analyzed. It was observed that when compared to the only single injection strategies, the pilot + main multiple injection reduced NOx by 12 % on total average. On the other hand, the fuel consumption is increased by 1.3%. In comparison with the single main injection configuration, the two pilot injection + main injection- three stage injection strategy reduced NOx emissions by %16 on total average. However, the fuel consumption increased up by 2.9%. Additionally, based on the findings, the impact of multiple injection on the greenhouse gases (GHG) carbon dioxide (CO2) and nitrous oxide (N2O) is evaluated. Considering, if a zeolite-based selective catalytic reduction (SCR) equipment used in the system it was analyzed that N2O will increase 16% compared to engine out NOx level. Also it was observed that while the GHG effect of CO2 increases with the multiple injection implementation the GHG effect of N2O decreases.
Rates of nitrous oxide (N2O) production from agricultural soils are highly variable across space and time. Improving predictions of N2O emissions will require improving our understanding of the ...drivers of denitrification and the sources of variability in the rates of N2O production between soils and over time. While the amount of available carbon (C) is a known control on denitrification and N2O reduction, relatively little attention has been paid to the effect of the chemical identity of C substrates on rates of denitrification and N2O reduction. We investigated the effects of twelve different C-substrate additions on the production and reduction of N2O in five soils taken from two distinct agricultural locations in Michigan under multiple land uses. We provided additions of glucose, cellulose, N-acetyl-glucosamine, chitin, amino acids, protein, vanillyl alcohol, lignin, citrate, succinate, methanol, and water in laboratory denitrification potential assays to determine the effects of denitrifier C preference on denitrification rates. We found that amino acids, protein, and organic acids stimulated the greatest rates of denitrification potential across all land uses. Similarly, we found these same substrates caused the most N2O reduction, resulting in the lowest net concentrations of N2O. Soils from agricultural rotations without cover crops had overall lower rates of denitrifier activity, leading to less net N2O production compared to soils from other land uses. In general, C-utilization patterns were similar among all soils, and C-substrate identity had a much stronger effect than land use. Here, we demonstrate that the chemical identity of available C gives rise to wide variability in rates of denitrification and N2O reduction.
•Proteins, amino acids, and organic acids stimulated the most denitrification.•Amino acids and proteins caused highly efficient denitrification (low N2O).•Soils from distinct land uses had similar denitrifier C-utilization profiles.•C bioavailability was an important chemical characteristic for denitrification.
Rice-paddies are regarded as one of the main agricultural sources of N 2O and NO emissions. To date, however, specific N2O and NO production pathways are poorly understood in paddy soils. ...^15N-tracing experiments were carded out to investigate the processes responsible for N2O and NO production in two paddy soils with substantially different soil properties. Laboratory incubation experiments were carried out under aerobic conditions at moisture contents corresponding to 60% of water holding capacity. The relative importance of nitrification and denitrification to the flux of NaO was quantified by periodically measuring and comparing the enrichments of the N2O, NH~-N and NO3-N pools. The results showed that both N2O and NO emission rates in an alkaline paddy soil with clayey texture were substantially higher than those in a neutral paddy soil with silty loamy texture. In accordance with most published results, the ammonium N pool was the main source of N2O emission across the soil profiles of the two paddy soils, being responsible for 59.7% to 97.7% of total N2O emissions. The NO3-N pool of N2O emission was relatively less important under the given aerobic conditions. The rates of N2O emission from nitrification （N2On） among different soil layers were significantly different, which could be attributed to both the differences in gross N nitrification rates and to the ratios of nitrified N emitted as NzO among soil layers. Furthermore, NO fluxes were positively correlated with the changes in gross nitrification rates and the ratios of NO/N2O in the two paddy soils were always greater than one （from 1.26 to 6.47）. We therefore deduce that, similar to N2O, nitrification was also the dominant source of NO in the tested paddy soils at water contents below 60% water holding capacity.
The oxidation of ammonia was studied experimentally by monitoring the time history of the intermediate N2O species using laser absorption spectroscopy. Experiments were conducted in a shock tube for ...mixtures of NH3/O2 diluted in ∼96.7% Ar for equivalence ratios of 0.54, 1.03, and 1.84. The equivalence ratios were determined accurately using spectroscopic measurements of NH3 with another laser before each experiment. Experiments were performed at an average pressure of 1.2 atm and covered a temperature range of 1829 to 2198 K. For the same temperature, experiments revealed that increasing the equivalence ratio leads to less N2O formation. The time-history profiles showed that N2O is formed at the beginning of the experiments, mainly from the formed NO, until reaching a peak. The N2O is then fully consumed, mainly via its reaction with H-atom. Characteristic parameters, such as the N2O peak time and mole fraction, were extracted from the N2O profiles and compared with 15 recent NH3 kinetics models. The comparison revealed that none of the existing kinetics models were able to correctly predict both the peak N2O time and mole fraction together. Two of the models were selected to perform a chemical analysis, and an improvement of the predictive capability of one model is proposed. The N2O profiles reported herein are excellent validation targets that offer stringent constraints for the improvement of future NH3 kinetics models.
Grasslands can significantly contribute to climate mitigation. However, recent trends indicate that human activities have switched their net cooling effect to a warming effect due to management ...intensification and land conversion. This indicates an urgent need for strategies directed to mitigate climate warming while enhancing productivity and efficiency in the use of land and natural (nutrients, water) resources. Here, we examine the potential of four innovative strategies to slow climate change including: 1) Adaptive multi-paddock grazing that consists of mimicking how ancestral herds roamed the Earth; 2) Agrivoltaics that consists of simultaneously producing food and energy from solar panels on the same land area; 3) Agroforestry with a reverse phenology tree species, Faidherbia (Acacia) albida, that has the unique trait of being photosynthetically active when intercropped herbaceous plants are dormant; and, 4) Enhanced Weathering, a negative emission technology that removes atmospheric CO2 from the atmosphere. Further, we speculate about potential unknown consequences of these different management strategies and identify gaps in knowledge. We find that all these strategies could promote at least some of the following benefits of grasslands: CO2 sequestration, non-CO2 GHG mitigation, productivity, resilience to climate change, and an efficient use of natural resources. However, there are obstacles to be overcome. Mechanistic assessment of the ecological, environmental, and socio-economic consequences of adopting these strategies at large scale are urgently needed to fully assess the potential of grasslands to provide food, energy and environmental security.
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•Four strategies to mitigate warming and enhance efficiency of grasslands were evaluated.•Adopting some of these strategies could offer almost exclusively environmental benefits.•These strategies have the potential to enhance the resilience of grasslands to climate change.•Their implementation in grasslands could be combined.•Future research work is needed to secure food and energy from sustainable grasslands using these strategies.
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