Reduce N2O Emissions Research Articles

Combined metabolomic and microbial community analyses reveal that biochar and organic manure alter soil C-N metabolism and greenhouse gas emissions

The use of biochar to reduce the gas emissions from paddy soils is a promising approach. However, the manner in which biochar and soil microbial communities interact to affect CO2, CH4, and N2O emissions is not clearly understood, particularly when compared with other amendments. In this study, high-throughput sequencing, soil metabolomics, and quantitative real-time PCR were utilized to compare the effects of biochar (BC) and organic manure (OM) on soil microbial community structure, metabolomic profiles and functional genes, and ultimately CO2, CH4, and N2O emissions. Results indicated that BC and OM had opposite effects on soil CO2 and N2O emissions, with BC resulting in lower emissions and OM resulting in higher emissions, whereas BC, OM, and their combined amendments increased cumulative CH4 emissions by 19.5 %, 31.6 %, and 49.1 %, respectively. BC amendment increased the abundance of methanogens (Methanobacterium and Methanocella) and denitrifying bacteria (Anaerolinea and Gemmatimonas), resulting in an increase in the abundance of mcrA, amoA, amoB, and nosZ genes and the secretion of a flavonoid (chrysosplenetin), which caused the generation of CH4 and the reduction of N2O to N2, thereby accelerating CH4 emissions while reducing N2O emissions. Simultaneously, OM amendment increased the abundance of the methanogen Caldicoprobacter and denitrifying Acinetobacter, resulting in increased abundance of mcrA, amoA, amoB, nirK, and nirS genes and the catabolism of carbohydrates [maltotriose, D-(+)-melezitose, D-(+)-cellobiose, and maltotetraose], thereby enhancing CH4 and N2O emissions. Moreover, puerarin produced by Bacillus metabolism may contribute to the reduction in CO2 emissions by BC amendment, but increase in CO2 emissions by OM amendment. These findings reveal how BC and OM affect greenhouse gas emissions by modulating soil microbial communities, functional genes, and metabolomic profiles.

Assessing the aerobic/anoxic enrichment efficiency at different C/N ratios: pilot scale polyhydroxyalkanoates production from waste activated sludge

Polyhydroxyalkanoates (PHA) can be produced using fermentation products of an excess sewage sludge fermentation process. An efficient method to enrich a PHA-producing community is an aerobic-feast/anoxic-famine enrichment strategy. The effect of different carbon to nitrogen (C/N) feed ratios of 1, 2 and 3.5 g COD/g N on the process performance was studied. The study was executed on a pilot plant scale using fermented waste activated sludge as the organic carbon source. The system's performance was monitored in terms of removing contaminants, producing PHA, and reducing N2O emissions. The results indicated that a lower C/N ratio results in lower PHA production, with PHA content in the sludge of 20, 24 and 36 % w/w for C/N ratios of 1, 2 and 3.5 g COD/g N, respectively. At the lowest C/N ratio, the highest nitrite accumulation rate (77%), nitrification efficiency (89%) and denitrification efficiency (89%) were observed, but the N2O production was also the highest (0.77 mg N2O-N/L). The long-term comprehensive monitoring carried out in this study revealed high carbon and ammonia removal efficiencies (never below 80%) despite the C/N shifts and high COD and ammonia concentrations. At the same time, the system showed relatively low PHA production and high environmental impact in terms of high gaseous N2O emission. These findings question the sustainability of the aerobic-feast/anoxic-famine enrichment strategy for PHA production in full-scale plants.

Greenhouse gas emissions from rotating biological contactors combined with hybrid constructed wetlands treating polluted river

The rotating biological contactors combined with hybrid constructed wetlands (R-HCWs) has promising treatment performance, however, concerns persisted regarding greenhouse gases (GHGs) emissions. In this study, GHGs in the R-HCWs was evaluated, and results revealed that R-HCWs facilitated nitrogen conversion and provided alternating oxygen environments, thereby promoting the reduction of N2O and CH4 emissions. Therefore, the comprehensive global warming potential (8.7±2.7 g CO2-eq·m-3·d-1) for handling unit volume of river water was low, thus, greater ecological benefits were achieved. The relative abundance of functional microorganisms such as Bacillus, Acinetobacter, Nitrospira and norank_f__norank_o__SBR1031, increased due to warm season, which promoted the nitrogen cycle and N2O emission reduction. Anammox and denitrifying bacteria showed significantly correlated with N2O and CH4 emissions (p < 0.01). This study provides valuable insights for the potential adoption of biological and ecological integrated treatment approach optimized for improving water and mitigating GHGs emissions.

Experimental and kinetic modeling investigation of NOx control in coal combustion by ammonia reburning

The carbon peaking and carbon neutrality goals present urgent demands for the green low-carbon transformation of the energy system. As a potential alternative energy, ammonia (NH3) used as reburning fuel in the coal-fired boilers will achieve both low-carbon and low-NOx emissions. To investigate ammonia reburning, experimental and chemical kinetic modeling were conducted in a tube flow reactor at 1023–1573 K under both ammonia and coal combustion conditions. Factors are researched including the combustion atmospheres of NH3/N2/O2 (PM-NH3) and coal/N2/O2 (PM-Coal), different inlet CO concentrations, reburning temperatures and reburning fuel ratios. The results indicate that ammonia reburning can effectively reduce NO emissions by about 95 %. The C-N reaction exhibits a positive effect on NO reduction at low temperature and a negative effect at high temperatures. As the CCO increases from 0 % to 4 % at 1573 K, the optimum temperature window size increases from 225 K to 413 K, and NO reduction rises from 31.25 % to 97.5 %. The whole ammonia reburning process includes NO rapid reduction stage (NRS), NO oxidation stage (NOS), and NO slowly re-reduction stage (NRRS) at high temperature. The chemical kinetic modeling indicates that the C-N reaction obviously shortens the residence time of the NRS and increases the ROP in the NOS, which together undercut NO reduction compared to PM-NH3 case. The promotion of the oxidation path of NH3-NH2-HNO-NO results in the NOS appearance and NRS ending. Moreover, this path affected by C-N reaction is primarily responsible for NO reduction cutoff in the PM-coal case.

Nutrient removal performance and the nitrogen-sulfur conversion pathways in sulfur-iron based biofilter under acidic/alkaline conditions

The nitrate and phosphate removal in sulfur based (Vp) and sulfur-iron based autotrophic denitrification systems (Sp) with sponge iron as the iron source was investigated under different pH (6–9). In this study, Sp (>98 %) and Vp (>97 %) had higher nitrate removal efficiency at pH 7–8 and the highest phosphate removal efficiency (94.9 % ± 3.57 %) at pH 6. The flow cytometry detection revealed that the cell integrity was damaged due to the formation of iron crusts at pH 6, which resulted in irreversible inhibition in Sp. Electron transfer and nitrogen transformation showed that compared with the sustained inhibition of denitrification at pH 6, the inhibition at pH 9 occurred mainly in the initial 0–2 h due to the enhanced flow of electrons toward the formation of biological element sulfur (Sbio0). Coupled sponge iron promoted the adsorption and reduction of NO2−/N2O and reduced N2O emissions. Metatranscriptomics analysis showed that significant upregulation of key gene expression for nitrogen and sulfur metabolism in Sp, with complex regulatory mechanisms enhancing system stability and performance. Acidic conditions reduced the abundance of denitrification and sulfur oxidation functional genes. However, alkaline conditions (pH of 9) mainly caused the decreased abundance of denitrification functional genes, which was favorable for accumulation of Sbio0. This study provides a theoretical basis for the stable operation and regulation of the sulfur-iron based autotrophic denitrification process.

An experimental investigation of the impacts of titanium dioxide (TiO2) and ethanol on performance and emission characteristics on diesel engines run with castor Biodiesel ethanol blended fuel

Investigating the impact of ethanol and TiO2 on the performance and emission characteristics of diesel engines running on a blend of ethanol and castor biodiesel is the primary goal of this study. The nanoparticles of ethanol, biodiesel, and TiO2 diesel fuel were combined at several concentrations. Diesel, B10, B20, B30, B10E10T, B20E10T, B30E10T, B10E20T, B20E20T, and B30E20T were among the various fuels that were investigated. The physiochemical properties of all the sample fuels were assessed, including density, pour point, cloud point, fire point, flash point, and kinematic viscosity. Following this, other engine performance indicators, such as torque, power, and fuel-consumption, were examined. Studies were also carried out on the properties of emissions, including CO, CO2, HC, and NO. Peak braking power and engine torque were found for each fuel under investigation at around 2750 and 2500 rpm, respectively. The addition reduced the brake-specific fuel consumption for B10E20T by 7.41 % while increasing the braking engine's torque and power by 8.64 and 3.86 %, respectively, in compared to blends without the TiO2 additions. When compared to diesel, the exhaust emission data without the addition of TiO2 revealed a decrease in CO and HC emissions but an increase in CO2 and NO emissions. On the other hand, using ethanol blend reduced NO emissions. According to the overall findings, diesel engine performance, combustion characteristics, and exhaust gas emissions were enhanced averagely by 7.43 % when a certain ratio of ethanol, biodiesel, and TiO2 additives (B10E20 + 50 ppm) was used.

Dual mechanism of membrane covering on GHG and NH3 mitigation during industrial-scale experiment on dairy manure composting: Inhibiting formation and blocking emissions

An industrial-scale experiment on dairy manure composting with the control group (Ctrl) and the membrane covering group (CM) was conducted to explore the effects of functional membrane covering on gas emissions, the conversion of carbon and nitrogen, and revealing the underlying mechanisms. Results indicated that CM achieved the synergistic effects on gas mitigation and improved compost product quality. CO2, CH4, N2O, and NH3 emissions were reduced by 81.8%, 87.0%, 82.6%, and 82.2%, respectively. The micro-aerobic condition formed in membrane covering compost pile together with the covering inhibiting effect dominated the mitigation effect. CM significantly downregulated the mcrA gene copies and the value of mcrA/pmoA (p < 0.01), which reduced CH4 emission. CM decreased the nirS and nirK gene copies and increased the nosZ gene copies to reduce N2O emission. Functional Annotation of Prokaryotic Taxa showed that membrane covering effectively amended part of carbon and nitrogen cycles, which stimulated the degradation of organic matter, accelerated compost maturity and reduced the gaseous emissions.

Experimental study of NO emission in coal-methanol co-combustion under air-staged condition

Application of renewable methanol as an alternative fuel is a promising method for both CO2 and NO emission reduction in thermal power plants fueled by coal. This work gives the first insight into coal-methanol co-combustion from the perspective of NO emission control with a wide range of methanol blending ratio (0%–100 %) involved. Air-staged strategy commonly applied in thermal power plants fueled by coal was considered, and the effects of some key parameters, including burnout air ratio, burnout air injection position and furnace temperature, were analyzed. Experimental results show a significant potential of NO emission reduction in coal-methanol co-combustion, as NO emission from methanol combustion is less than 30 % of that from coal combustion. The correlation between NO emission and methanol blending ratio is approximately linear. Air-staged strategy is still effective for NO emission reduction in coal-methanol co-combustion, and the effects of the key parameter is similar to that in coal combustion. Increase of burnout air ratio and delay of burnout air injection are beneficial, and NO emission can be reduced by more than 70 % compared with that under unstaged condition. Furnace temperature rise is harmful, whereas the corresponding NO emission increase is lower than 30 ppm (@6 % O2).

Field performance and nitrous oxide emissions of transgenic nitrogen use efficient rice lines cultivated in tropical paddy fields.

Nitrogen (N) fertilizers make up the majority of the input used in rice production, and their excess application leads to significant environmental pollution. Developing rice varieties with improved nitrogen use efficiency (NUE) is essential to maintain the sustainability of rice production. This study aims to evaluate the performance of transgenic Oryza sativa japonica cv. Kitaake expressing the barley (Hordeum vulgare) alanine aminotransferase (HvAlaAT) gene in response to different levels of N fertilizer application under tropical paddy field conditions. Results from this study demonstrate that transgenic nitrogen use efficient Kitaake rice (Kitaake NUE) displays a grain yield increase of up to 41% compared to Kitaake null. Transgenic Kitaake NUE expressing the HvAlaAT gene displays a higher N uptake and achieves a higher nitrogen use efficiency compared to control plants while maintaining lower nitrous oxide (N2O) fluxes. The reduction in N2O emissions in Kitaake NUE compared to Kitaake null ranges from 37.5 to 96.3%. The transgenic Kitaake NUE used in this study has potential as a donor to improve the nitrogen use efficiency of indica rice for better adaptability to tropical conditions.

Hydrochloric acid-modified biochar enhances nitrogen retention and microbial diversity in mollisols

The annual decline in the quality of China's mollisols and associated nitrogen loss necessitates effective interventions. This study investigates the effects of hydrochloric acid-modified biochar (BC-H700), derived from corn straw, on nitrogen retention and microbial diversity in mollisols through pot experiments. Through 100 days of continuous study found the application of 6 % BC-H700 significantly improved soil properties, increasing pH by 18.60 %, organic matter by 1.6 %, ammonium nitrogen by 26.96 %, and nitrate nitrogen by 23.04 %. By inquiring impact of BC-H700 on microbial enzyme activities in 60-day revealing BC-H700 also enhanced the activities of key nitrogen-transforming enzymes (AMO, NOR, NOS) and functional genes (nirK, norB, nosZ) while reducing narG gene abundance and NR enzyme activity. These changes indicate that BC-H700 promotes nitrification, inhibits denitrification, enhances nitrogen retention, and reduces N2O emissions. Furthermore, BC-H700 improved microbial diversity, increasing the abundance of beneficial bacteria such as Actinobacteria, Proteobacteria, Nitrospirae, and Gemmatimonadetes. The main environmental factors affecting soil bacterial community structure were identified as organic matter, NO3-, NO2-, AMO, NOR, and NOS. Overall, BC-H700 facilitates nitrogen transformation and retention through complex interactions with soil properties and microbes. This study contributes to understanding biochar's role in soil nitrogen management and offers practical insights for improving mollisol health.

Drought reduces nitrogen supply and N2O emission in coastal bays

Severe droughts are increasingly prevalent under global climate change, disrupting watershed hydrology and coastal nitrogen cycling. However, the specific effects of drought on nitrogen transport from land to sea and subsequent nitrogen dynamics remain inadequately understood. In this study, we evaluated the consequences of the 2020–2022 drought on nitrogen supply and N2O emissions in Xiamen Bay, Southeast China. The results showed that drought significantly reduced annual NH4N, NO2N, and NO3N concentrations in Xiamen Bay by 49.4 %, 32.1 %, and 40.3 %, respectively, compared with the pre-drought year of 2019. The decline in NH4N concentration was mainly attributed to reduced surface runoff across all seasons. NO3N and NO2N concentrations declined only during spring and summer, primarily due to increased potential evapotranspiration (PET) hindering nitrogen supply via groundwater and concurrently enhancing land denitrification. Annual N2O emission from Xiamen Bay decreased by 40.0∼72.7 % during the drought, highly correlated with the decline in the concentrations of NO3N, DIN, and DTN (p < 0.001). Comparative analysis revealed that NO3N concentration exhibited consistent negative linear regressions with PET and declined as evaporative demand drought conditions worsened across Xiamen Bay, Sansha Bay, and Chesapeake Bay throughout 2010–2022. NH4N concentration showed a positive regression with river discharge in Xiamen Bay, but negative regressions in the other two bays. Our results indicates that drought reduces N2O emission primarily driven by nitrate substrate reduction in the bay. This study provides new insights for predicting coastal nitrogen dynamics and greenhouse gas emissions under global environmental change.

Effects of Different Straw Return Modes on Soil Carbon, Nitrogen, and Greenhouse Gas Emissions in the Semiarid Maize Field.

Returning straw to the field is a crucial practice for enhancing soil quality and increasing efficient use of secondary crop products. However, maize straw has a higher carbon-to-nitrogen ratio compared to other crops. This can result in crop nitrogen loss when the straw is returned to the field. Therefore, it is crucial to explore how different methods of straw return affect maize (Zea mays L.) farmland. In this study, a field experiment was performed with three treatments (I, no straw returned, CK; II, direct straw return, SR; and III, straw returned in deep furrows, ISR) to explore the effects of the different straw return modes on soil carbon and nitrogen content and greenhouse gas emissions. The results indicated that the SR and ISR treatments increased the dissolved organic carbon (DOC) content in the topsoil (0-15 cm). Additionally, the ISR treatment boosted the contents of total nitrogen (TN), nitrate nitrogen (NO3--N), ammonium nitrogen (NH4+-N), dissolved organic nitrogen (DON), and DOC in the subsurface soil (15-30 cm) compared with CK. When it comes to greenhouse gas emissions, the ISR treatment led to an increase in CO2 emissions. However, SR and ISR reduced N2O emissions, with ISR showing a more pronounced reduction. The ISR treatment significantly increased leaf and grain biomass compared to CK and SR. The correlation analyses showed that the yield was positively correlated with soil DOC, and soil greenhouse gas emission was correlated with soil NO3--N. The ISR technology has great potential in sequestering soil organic matter, improving soil fertility, and realizing sustainable agricultural development.

A new denitrification strategy based on high-temperature catalytic coatings Y2O3-BaO-ZrO2 without using ammonia in a lab-scale natural gas combustion furnace

Catalytic decomposition of NO at high temperatures without the use of ammonia, offers an eco-friendly and sustainable solution for denitrification in industrial combustion or heating processes. To simulate a complex combustion flue gas, we designed a lab-scale natural gas industrial combustion furnace specifically for assessing the impacts of Y2O3-BaO-ZrO2 catalyst coated on SiC plates on NO emissions. Various factors including the plate number, excess air ratio, combustion power, and coating position were considered. Results demonstrated that arranging the Y2O3-BaO-ZrO2 coated plates shifted the high-temperature zone of the furnace downstream. When the excess air ratio was below 1.05, the catalytic coating significantly reduced NO emission concentration at the furnace outlet by over 40 %. However, this reduction coincided with a substantial presence of unburned CO in flue gases. Placing the coated SiC plates in the constant temperature zone of 1100–1200 °C within the middle of furnace offered significant advantages in NO removal, particularly as the combustion power increased. Based on a 60-h durability evaluation of Y2O3-BaO-ZrO2 coating, the observed good high-temperature thermal and chemical stabilities further enhanced the coating’s potential for industrial application. The possible mechanism of the reduction NO by CO over coating surfaces were analyzed by in situ optical measurements. After calculation, using 12 kg Y2O3-BaO-ZrO2 catalysts might decrease at least 642 kg of ammonia consumption under ideal conditions, and significantly reduce the investment cost on existing flue gas denitrification equipment. Therefore, the investigated technology is a green and sustainable denitrification strategy, which would potentially provide a novel approach towards attaining ultra-low NO emissions.

Coke breeze combustion and emission behaviors of CO and NO during iron ore sintering

CO emission reduction, especially the coordinated emission reduction of CO and NO in sintering flue gas, has attracted widespread attention in the world. The effects of different sintering raw materials, temperature and atmosphere on coke breeze combustion and CO and NO emission behaviors were studied. The results show that, sintering raw materials significantly improved the combustion performance of coke breeze, and promoted the simultaneous reduction of CO and NO emissions. Among them, Dolomite had the strongest catalytic effect, which reduced the apparent activation energy of coke breeze combustion reaction from 99.35 kJ/mol to 56.11 kJ/mol, and the emission reductions of CO and NO were as high as 47.84 % and 73.25 %, respectively. The catalytic ability of the raw materials components was CaO ＞ MgO ＞ Fe2O3. However, during the combustion process of coke breeze without raw materials, the reduction of NO by CO was affected by the atmosphere of the boundary layer, the conversion of N element was negatively correlated with the content of CO. When the temperature increased from 600 ℃ to 1 050 ℃, the combustion performance was improved, the thickness of the combustion zone was reduced by 47.92 %, the total emission of CO was decreased by 65.39 %, and the total emission of NO was increased by 23.05 %. The O2 concentration decreased from 21 % to 10 %, the combustion rate decreased, the combustion zone thickened by 90 %, incomplete combustion was promoted, the total emission of CO increased by 101.15 %, and NO decreased by 21.09 %. The CO2 concentration increased from 5 % to 15 %, the gasification reaction was enhanced, the combustion time was extended, the combustion zone thickened by 45.9 %, the total emission of CO increased by 87.12 %, and the reducing atmosphere was enhanced, which was conductive to the reduction of NO by CO, and the total emission of NO decreased by 50.59 %.

The long-term nitrogen fertilizer management strategy based on straw return can improve the productivity of wheat-maize rotation system and reduce carbon emissions by increasing soil carbon and nitrogen sequestration

ProblemFacing the multiple objectives of increasing production, carbon sequestration, and nitrogen reduction in farmland, optimizing straw and nitrogen fertilizer management to achieve a balance between grain production and ecological safety in the wheat-maize rotation system has become increasingly critical and urgent. MethodsThis study conducted a five-year field experiment in the Guanzhong Plain of China from 2017 to 2021 to investigate the effects and synergistic regulatory mechanisms of straw disposal methods (straw return, no-straw return) and nitrogen application rates (0, 150, 225, 300 kg ha−1) during the maize season on soil greenhouse gas (GHG) emissions, crop yield, and soil organic carbon (SOC) and soil toatl nitrogen (STN) content. ResultsThe results showed that under the scenario of no-straw return, fertilization increased soil nitrous oxide (N2O) emissions by 35.9–64.0 %, and annual total crop yield by 16.4–22.8 %; however, under the straw return scenario, the increase in soil N2O emissions due to fertilization decreased to 26.7–62.0 %, while the yield increase rose to 19.5–25.9 %. The interaction effect between straw return and nitrogen application was significant, with straw return boosting the contribution rate of nitrogen application to yield (2.2–4.4 %) and simultaneously reducing the contribution rate of nitrogen application to N2O emissions (3.0–27.5 %). The study also indicated that the yield-increasing effect of straw return continued to increase with the duration of straw return, with the contribution rate to yield reaching 9.9 % after three years of continuous straw return, while the contribution rate of nitrogen application to yield increased by an average of 3.0 % per year. This suggests that there is significant potential for coupling straw return with reduced nitrogen application. Straw return combined with nitrogen fertilizer increased SOC content by 7.9–40.1 % and 3.7–12.5 %, STN content by 1.0–22.8 % and 6.1–13.9 %, respectively, compared to sole nitrogen application and sole straw return. Pathway analysis indicated that straw return combined with nitrogen fertilizer mainly enhanced soil carbon-nitrogen sequestration, improved fertilizer utilization efficiency and crop nutrition levels, reduced net global warming potential (GWP) and greenhouse gas intensity (GHGI), and synergistically regulated to increase yield while reducing GHG emissions. ConclusionThe study highlights that straw return lowers the threshold for nitrogen application levels, suggesting that regulating nitrogen application levels between 224 and 256 kg ha−1 during the maize season, and maintaining a nitrogen application level of 195 kg ha−1 during the wheat season, is beneficial for long-term stable production and emission reduction in the wheat-maize rotation system farmland.

Isotope analysis of nitrogen removal pathways and N2O production potential in the SDAD-anammox system under different N/S ratios

This study explored the impact of varying nitrate to sulfide (N/S) ratios on nitrogen removal efficiency (NRE) in the sulfide-driven autotrophic denitrification and anammox (SDAD-anammox) system. Optimal nitrogen removal was observed at N/S ratios between 1.5 and 2.0. Isotope tracing results showed that the contribution of anammox to nitrogen removal was enhanced with increasing N/S ratios, reaching up to 37 % at the N/S ratio of 2.5. Additionally, complex nitrogen pathways were identified, including dissimilatory nitrate reduction to ammonium (DNRA). Furthermore, isotope tracing was innovatively applied to investigate N2O emissions, demonstrating that higher N/S ratios significantly reduced N2O emissions, with the lowest emissions at N/S ratio of 2.5. Gene expression analysis indicated that nitrogen and sulfide transformation genes decreased with increasing N/S ratios, while anammox-related genes first increased and then decreased, reflecting the system's microbial dynamics. These findings offer insights into nitrogen transformation pathways and N2O production mechanisms in the SDAD-anammox process.

Realizing high-efficiency and low-emission load control of Wankel rotary engine by CH4/H2 synergy

The present work proposes the application of CH4 and H2 synergy to improve the performance of the Wankel rotary engine (WRE). The whole work was experimentally conducted at 1500 r/min. The results indicate that CH4 WRE can achieve similar power and significantly higher thermal efficiency than gasoline WRE based on quantitative control, with a maximum absolute efficiency improvement of 11.4%. At the same time, it also can achieve 64% and 77% maximum reduction of CO and NO emissions, respectively. CH4–H2 synergy can further improve the performance of CH4-fueled WRE, which can broaden the lean flammability limits and make qualitative control application possible. Compared with CH4 WRE with quantitative control, qualitative control hybrid fuel WRE can achieve a maximum relative improvement of 6.54% in brake thermal efficiency and significantly reduced NO and CO emissions. However, the extent of qualitative control is limited by cyclic variation. Overall, CH4–H2 synergy can be a potential alternative to elevate the performance of WRE, the key to which is the reasonable match of synergy level and qualitative control extent.

Nitrous oxide emissions and soil profile responses to manure substitution in the North China Plain drylands

Substituting synthetic fertilizers with manures in agriculture enhances soil properties and crop yield. However, the impact on nitrous oxide (N2O) emissions, especially from the soil profile, remains poorly understood. This study examined emissions from 2017 to 2019 on a well-established (>10-year) maize field site in the North China Plain. Three treatments were compared: 100 % synthetic nitrogen (NPK), 50 % synthetic fertilizer N + 50 % manure N substitution (50%MNS), and 100 % manure N substitution (100%MNS). N2O emissions were monitored for three years, and in 2019, N2O concentrations at 20 cm and 40 cm soil depths were analyzed in relation to surface N2O fluxes and environmental factors. The results showed manure substitution resulted in about 13.8 %–25.2 % (50%MNS) and 40.3 %–72.2 % (100%MNS) reduction in N2O emissions over the 3-year period compared with the NPK treatment. Throughout the maize growing season, the top-dressing accompanied by rainfall was responsible for the N2O emissions. The difference in N2O concentrations between all the treatments at 20 cm depth was insignificant, but at 40 cm depth the N2O concentrations were significantly higher for the 50%MNS treatment than the other treatments. The N2O fluxes and N2O concentration were not synchronized especially in NPK. The decoupled relationship between the N2O fluxes and the N2O concentration in the soil profile depth suggested the contribution of N2O produced in the soil profile to the surface N2O fluxes is limited. This study highlights that manure substitution is an efficient measure to reduce N2O emissions.

Effects of antioxidant addition and catalytic converter on emissions in off-road motors running on diesel tire oil blend

Repurposing used tires into fuel could help address environmental degradation and the fast depletion of fossil fuel resources to some extent. In this work, an attempt has been made to control the emissions by combining fuel modification and after treatment techniques. Fuel modification is done through antioxidant additive addition with the fuel blend to mitigate the prompt NOx emission and catalytic converter for additional emission reduction. The test results indicate that used tire oil may be a good substitute for fossil fuels. NO emissions were reduced by 15.3% for the 300 ppm antioxidant addition at full load. Whereas NO emissions were reduced by 21.1% with the incorporation of the catalytic converter. However, the maximum NO emission reduction achieved was 30.5% by combining antioxidants with fuel and incorporating a catalytic converter.

Evaluating the role of high N2O affinity complete denitrifiers and non-denitrifying N2O reducing bacteria in reducing N2O emissions in river

Freshwater rivers are hotspots of N2O greenhouse gas emissions. Dissolved organic carbon (DOC) is the dominant electron donor for microbial N2O reduction, which can reduce N2O emission through enriching high N2O affinity denitrifiers or enriching non-denitrifying N2O-reducing bacteria (N2ORB), but the primary regulatory pathway remains unclear. Here, field study indicated that high DOC concentration in rivers enhanced denitrification rate but reduced N2O flux by improving nosZ gene abundance. Then, four N2O-fed membrane aeration biofilm reactors inoculated with river sediments from river channel, estuary, adjacent lake, and a mixture were continuously performed for 360 days, including low, high, and mixed DOC stages. During enrichment stages, the (nirS+nirK)/nosZ ratio showed no significant difference, but the community structure of denitrifiers and N2ORB changed significantly (p < 0.05). In addition, N2ORB strains isolated from different enrichment stages positioned in different branches of the phylogenetic tree. N2ORB strains isolated during high DOC stage showed significant higher maximum N2O-reducing capability (Vmax: 0.6 ± 0.4 ×10−4 pmol h−1 cell−1) and N2O affinity (a0: 7.8 ± 7.7 ×10−12 L cell−1 h−1) than strains isolated during low (Vmax: 0.1 ± 0.1 ×10−4 pmol h−1 cell−1, a0: 0.7 ± 0.4 ×10−12 L cell−1 h−1) and mixed DOC stages (Vmax: 0.1 ± 0.1 ×10−4 pmol h−1 cell−1, a0: 0.9 ± 0.9 ×10−12 L cell−1 h−1) (p < 0.05). Hence, under high DOC concentration conditions, the primary factor in reducing N2O emissions in rivers is the enrichment of complete denitrifiers with high N2O affinity, rather than non-denitrifying N2ORB.