N2O Emission Factors Research Articles

N2O emission factors for organic amendments in Japan from measurement campaign and systematic review

Organic amendments are important sources of nitrous oxide (N2O) emissions from agricultural soils. In 2020, the total amount of N in organic amendments applied to Japanese agricultural soils (440 ktN) was larger than that of synthetic fertilizer (374 ktN). However, N2O emissions from organic amendments were estimated by using the country-specific N2O emission factor (EF) for synthetic fertilizer (0.31 % for rice paddy, 2.9 % for tea, and 0.62 % for other crops) in the National Greenhouse Gas Inventory Report of Japan. Thus, we conducted a N2O flux measurement campaign at 12 different experimental sites across Japan to estimate fertilizer-induced N2O EFs for major organic amendments in Japan, that is, poultry manure compost, swine manure compost, cattle manure compost, and organic fertilizer pellets. In addition, we conducted systematic review of N2O emissions and EFs for organic amendments, including data from our measurement campaign and published data from peer-reviewed papers in Japan. The final dataset, including the field measurement campaign and published data, resulted in 404 observations (including synthetic fertilizer and zero-N control) in 29 sites. Results showed that soil type affected EFs, that is, the mean EF of Andosols was lower than that of non-Andosols, which is similar to the case of EFs for synthetic fertilizer. Mean EFs for poultry manure compost, swine manure compost, cattle manure (compost and slurry), and non-animal manure organic fertilizers were 0.83 % (uncertainty range of 2.5th and 97.5th percentile: 0.09 % to 3.46 %), 0.70 % (0.02 % to 2.45 %), 0.39 % (0.00 % to 1.62 %), and 1.16 % (0.41 % to 3.03 %), respectively, when weighted by area of soil types. The mean EF of all organic amendments was 0.84 % (0.00 % to 2.91 %), when the area of soil type and amount of organic amendment used in Japan were considered. Our study provides country-specific EFs to estimate N2O emission from organic amendments in Japan.

Microaerophilic activated sludge system for ammonia retention from high-strength nitrogenous wastewater: Biokinetics and mathematical modeling

It is crucial to shift from conventional ammonia removal to recovery to solve environmental problems and resource scarcity. Recovering ammonia from high-strength nitrogenous wastewater can simultaneously save the energy and cost involved in ammonia oxidation, produce ammonia without CO2 emissions, and prevent N2O emissions. A technology for concentrating and recovering ammonia by retrofitting a conventional activated sludge (CAS) system is promising but faces significant challenges in oxidizing organic carbon but not ammonia in wastewater. This study employed biokinetic analysis and mathematical modeling to comprehensively assess the operation and effectiveness of a microaerophilic activated sludge (MAS) system for simultaneously removing chemical oxygen demand (COD) and retaining ammonia. We show that heterotrophic bacteria (HB) in the MAS system had higher maximum specific growth rate (µHB), biomass yield coefficient (YHB), and decay coefficient (bHB) but lower affinities for oxygen and COD than HB in CAS. Simulations using the developed model demonstrated that COD removal efficiencies of > 90%, ammonia retention efficiencies of > 90%, and low N2O emission factors (N2OEF) of < 0.01% can be achieved at solids retention times (SRTs) of 3–50 d, hydraulic retention times (HRTs) of 0.1–1 d, and a volumetric oxygen transfer coefficient (KLa) of (24.58 ± 0.30)HRT−1. The combination of the biokinetics and mathematical modeling revealed the favorable MAS operating conditions allowing efficient ammonia retention and COD removal, which paves the way for turning a CAS system into a MAS system by retrofitting the configuration without high capital expenditures, requiring future intensive study.

Spatiotemporal variability and controlling factors of indirect N2O emission in a typical complex watershed

The mechanisms of N2O emissions from inland rivers remain poorly understood because of the high variability of dissolved N2O concentration and the complexity of influencing factors. Thus, it is necessary to research the spatiotemporal patterns and influencing factors to understand the driving mechanisms of riverine N2O emissions. We combine the Soil and Water Assessment Tool (SWAT) outputs with established empirical equations to identify the spatiotemporal fluctuations of riverine N2O emissions and evaluate model performance through field measurements in a typical watershed. The spatiotemporal hotspots of N2O emissions are then determined, and the relative importance of environmental variables is further determined by correlation and attribution analysis. The results indicate that the riverine N2O emissions are relatively high from August to October, which accounted for 35.38% of the annual emissions. Temporal changes are attributed to agricultural activities and meteorological factors. Agricultural activities such as planting and fertilization lead to increased diffuse nitrogen loads on the land surface. Meantime, heavy precipitation events enhance the transport of nutrients, resulting in changes in nitrogen levels in the river. Spatial analysis shows that the urban watersheds (191.22 ± 156.19 μmol m−2 d−1) are the hotspots of riverine N2O emission, which are 1.55–3.03 times that of non-urban rivers. Spatial variations are mainly affected by riverine physicochemical indicators for different watersheds. Sewage from various sources received by urban rivers provides appropriate environmental conditions for N2O production, and transports large exogenous dissolved N2O. Furthermore, salinity (r = 0.80; p < 0.001) and nitrogen nutrients in riverine physicochemical indicators show a significant correlation with N2O fluxes. It emphasizes that N-related (TN, NH4+, NO3−) indicators are important reactants for N2O generation, which can promote nitrification and denitrification. Meanwhile, the results of structural equation modeling (SEM) also demonstrate that N2O emissions follow a similar pattern to riverine dissolved N2O concentration (r = 0.841, p < 0.001), and non-point source (r = 0.678, p < 0.001) play an important role in the changes of dissolved N2O concentrations. Our results highlight that certain hot moments and hot spots of rivers play a disproportionate role in year-round and basin-wide N2O emissions, respectively. It is necessary to implement more effective management measures by controlling key environmental factors to reduce N2O emissions.

A comparative LCA of three WWTPs in a tourist area: Effects of seasonal loading rate variations

Although the wastewater treatment is a fundamental utility for the protection of human health and the environment, non-evident drawbacks are associated with it. Wastewater treatment plants (WWTPs) located in tourist areas generally suffer from the seasonal increase in wastewater flow-rate and associated pollution loads. In this study, a Life Cycle Assessment (LCA) of three medium-size urban WWTPs, located in a tourist area in central Italy, was carried out. The study compared the environmental impacts generated by 1 m3 of treated wastewater in low season (LS) and high season (HS). All the material and energy flows involved in the operational phase of wastewater treatment were considered within the system boundaries, including the disposal or recovery treatment of the waste streams generated by the WWTPs, namely screenings, waste from grit removal and wastewater sludge. The analysis was conducted using almost only real data from full-scale plants. In each WWTP, the environmental impacts produced in HS were higher than those generated in LS; therefore, the environmental impacts increased as the loading rate increased. Furthermore, a correlation between WWTP size and environmental performance was observed. Indeed, in 8 out of 11 environmental indicators, the percentage increase in pollutant emissions due to wastewater treatment in HS decreased as the WWTP size increased. Results revealed that larger WWTPs suffered less from seasonal loading rate variations, showing greater flexibility. The existence of a scale factor suggests that the centralization of WWTPs in tourist areas can be an option to enable better treatment performance in terms of environmental impacts. A sensitivity analysis was performed, increasing N2O emission factors from wastewater treatment in LS: considering a 75 % increase, the outcomes found in default LCA were not confirmed. Future research should investigate the operational factors and biological mechanisms that most affect wastewater treatment when significant seasonal variations are present.

NH3 and N2O emission durability of the heavy-duty diesel engine with DOC, DPF, SCR, and ASC through the accelerated aging method

A general accelerated aging method for aftertreatment devices of Heavy-duty Diesel Engine (HDDE) is proposed in this paper, and three sets of aftertreatment devices were aged according to this method. The error between the World Harmonized Transient Cycle (WHTC)-NOx emission factors of conventional aging and those of accelerated aging fitted by equivalent thermal accumulation is −4.12 to 3.13 %, which proves that the two methods have good equivalence. Meanwhile, the NH3 and N2O emission characteristics and durability were tested by Fourier Transform Infra-Red Spectroscopy (FTIR) equipment. The results show that NH3 and N2O emissions do not deteriorate linearly with the intensification of thermal aging like NOx. Except that the NH3 emission of AT03 exceeds the limit of China VI emission regulation (the average and maximum NH3 concentration in the WHTC test are 35.25 ppm and 350.30 ppm, separately), NH3 emission of other aged devices meet the requirements. Combined with the equivalent durability mileage of 1130000 km of AT02, the test China VI HDDE can effectively control NH3 emissions and has a large margin with the limit requirements. However, the deterioration rate of N2O emission gradually slows down with the intensification of accelerated aging. The accelerated aging tests also indicate that N2O generation is closely related to NH3 in SCR, consistent with previous studies conclusions of low-temperature and high-temperature N2O generation mechanisms. Equally important is that the N2O emission emitted from test China VI HDDE is significantly higher than the emission limit of the Environmental Protection Agency (EPA). The N2O emission factors under the WHTC test are as high as 0.15 to 0.35 g/kWh, which should draw the attention of Chinese environmental regulatory authorities, who should start to formulate N2O emission limits and put forward complementary strategies to reduce N2O emissions from HDDEs.

Preliminary results on N2O emission factor calculation in hydroponic struvite fertilization of lettuce production

ISHS XXXI International Horticultural Congress (IHC2022): International Symposium on Urban Horticulture for Sustainable Food Security (UrbanFood2022) Preliminary results on N2O emission factor calculation in hydroponic struvite fertilization of lettuce production

Nitrous oxide emissions and productivity of irrigated potato: Effects of nitrogen fertilization options

AbstractImproved N management is needed in intensive agriculture to mitigate nitrous oxide (N2O) emissions while sustaining high yields. We assessed the effectiveness of polymer‐coated urea (PCU); nitrification inhibitor 2,4‐dimethylpyrazol succinic acid (DMPSA), a biostimulant; and their combinations with granular urea and ammonium sulfate nitrate (ASN) fertilizers to reduce N2O emissions and to improve potato (Solanum tuberosum L.) productivity under irrigation. Sites were located in Lethbridge and Brooks, Alberta, Canada over two growing seasons. Tuber yield, grade, specific gravity, and N uptake were quantified. We used the chamber method to measure N2O fluxes from potato hills and furrows. The N2O emissions from furrow positions were at least two‐fold greater than those from hills at the Lethbridge site. Peak N2O emissions and increased N concentrations in potato petiole and soils occurred shortly after fertilizer applications. The overall average emission factor (EF) of N2O was 0.056% kg N2O–N kg−1 N fertilizer (accounting for emissions from unfertilized controls). Urea alone commonly exhibited the highest N2O fluxes. Admixing DMPSA with either urea or ASN lowered N2O emissions in only certain cases. For instance, in one growing season at the Brooks site, adding DMPSA to urea reduced the N2O emissions by 57%. Likewise, in one of the four site‐years in the study, 36% higher potato marketable yields were obtained when applying either ASN treated with DMPSA or PCU compared with the unfertilized controls (45 vs. 33 Mg ha−1). Results showed that under specific conditions, N application strategies using DMPSA admixed with either urea or ASN can maintain high potato yields while reducing N2O emissions relative to soils receiving these fertilizers without this additive.

Does the repeated freezing and thawing of the aerobic layer affect the anaerobic release of N2O from SWIS?

Subsurface wastewater infiltration systems (SWIS) is an efficient, economical, and less temperature affected sewage treatment technology. Pollutants are removed by physical, chemical, and biological reactions such as filtration, adsorption, oxidation, and degradation. Under the conditions of limited carbon source and inactivation of nitrous oxide reductase, N2O, an important greenhouse gas, is released from the anaerobic layers of SWIS. However, is N2O release affected by repeated freeze-thawing of the upper aerobic layer? How does microbial population structure and denitrogenate activity in different profiles respond to the freeze-thaw cycle (FTC)? These questions have not yet been revealed. In this study, a SWIS simulator with in-situ regulation of FTC was first constructed. The re-distribution of N2O, microbial composition and denitrogenate activity were analyzed in response to FTC. Furthermore, potential bio-markers were screened and identified. The results revealed that the release of N2O was correlated with FTC, with the anaerobic layer being the main contributor throughout, accounting for 73.32–75.8 % of the total release. The limiting factor for N2O emissions was the NO3−-N concentration in the anaerobic zone, and there were no simple linear communications between total nitrogen and N2O generations. High throughput sequencing results showed the main markers of SWIS were Proteobacteria, Gemmatimonadetes, Firmicutes, Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi and Nitrospirae, accounting for 97.4 %–98.1 % of the total relative abundance. A significant positive correlation between Firmicutes and anaerobic release of N2O was observed, where Firmicutes abundance increased from 5 % to 21 % during the experimental cycle, while N2O concentration increased from 2.65 mg·L−1 to 18.88 mg·L−1. The results indicated that Firmicutes was an important biomarker of N2O release under freeze-thaw conditions.

Aerobic nitrous oxide emission in anoxic/aerobic and intermittent aeration sequencing batch reactors

ABSTRACT This study characterized nitrogen removal and nitrous oxide (N2O) emissions from lab-scale anoxic/aerobic sequencing batch reactor (AOSBR) and intermittent aeration sequencing batch reactor (IASBR), respectively, for treating synthetic municipal wastewater. The N2O emission was evaluated in a simulated cycle, and batch conditions of aerobic nitrification, simultaneous nitrification and denitrification (SND), and aerobic denitrification. The results show that nitrogen removal was enhanced in IASBR compared to AOSBR, with 94.2% and 67.9% of total inorganic nitrogen removal efficiency in IASBR and AOSBR, respectively. In the simulated cycle, the emission factors (of oxidized ammonium) were 4.9% and 0.6% in AOSBR and IASBR, respectively. Under batch conditions, the N2O emission factors during SND were obviously higher than that during aerobic nitrification and denitrification. The N2O emission factors during SND ranging 0.68–11.68% in AOSBR and 1.25–5.13% in IASBR. Furthermore, N2O emission under batch conditions was affected by the aeration ratios. Moderate and high aeration ratios used in this study stimulated the N2O emission from SND. The N2O emission was enhanced with the nitrite accumulation during aerobic nitrification when the nitrite-oxidizing bacteria was inhibited by a chemical inhibitor. Aerobic denitrification via nitrite could be the main pathway of N2O generation from SND processes. The findings from our study can help further understand N2O emission mechanisms and guide the optimization of the current wastewater treatment process for minimizing N2O emission.

Aquaculture farm largely increase indirect nitrous oxide emission factors of lake

Freshwater aquaculture system is one of the main sources of nitrous oxide (N2O) and must be accounted for when reporting indirect N2O emissions from agricultural industries. The IPCC based approach recommend the indirect N2O emission factors (EF5) to estimate the emissions from freshwater. Unfortunately, the EF5 for lake aquaculture, one of the most common freshwater aquacultures, has never been reported due to the scarcity of field data. To better understand the magnitude of EF5 at lake aquaculture and identify the control factors, the EF5 at aquaculture farm and open water (non-aquaculture region) of Lake Taihu were investigated based on long-term (2012–2017) in-situ field measurements. Our results showed the indirect N2O emission at the aquaculture farm (1.52 ± 0.49 μmol m-2 d-1) was over one order of magnitude higher than at the open water (0.12 ± 0.49 μmol m-2 d-1). Furthermore, we also found large variability in the EF5, which varied by one order of magnitude across time. The EF5 was predicted by nitrogen and the mass ratio of carbon to nitrogen. The significantly higher mass ratio of DOC to DIN resulting from feed application contributed to substantial increase in the N2O production efficiency and EF5 at the aquaculture farm. The average EF5 at the aquaculture farm and open water were 0.0021 ± 0.0013 and 0.0013 ± 0.0010, respectively. However, the measured EF5 was lower than that IPCC’s default value of 0.0025, implying IPCC method yielded the overestimated indirect emission, and large bias will occur when only use constant value considering the dramatic variability of observed EF5.

Long term analysis of N2O emission from partial nitritation anammox process under oxygen limitation

Partial nitritation with anammox (PNA) process was achieved during 300 days to investigate the fate of N2O and NO. N2O emission factor increased from 0.4 ± 0.1 % up to 6.1 ± 0.3 % during intensification phase of 5 months and progressively stabilized at 2.0 ± 0.1 % after 10 months without any significant emission of NO. The emission of N2O correlated with the ammonium consumption rate and the oxygen transfer rate. Experiment carried out in anoxic condition suggested that heterotrophic denitrification poorly contributed. Measurements of δ15N, δ18O and SP of N2O demonstrated that its production resulted from the reduction of nitrite. The stimulating effect of nitrite on N2O production was demonstrated with specific tests and observed during transient nitrite accumulation periods. This study highlighted the importance of nitrite and oxygen transfer rate control for future control strategies aiming to mitigate N2O emission in PNA system.

Indirect nitrous oxide emission factors of fluvial networks can be predicted by dissolved organic carbon and nitrate from local to global scales.

Streams and rivers are important sources of nitrous oxide (N2 O), a powerful greenhouse gas. Estimating global riverine N2 O emissions is critical for the assessment of anthropogenic N2 O emission inventories. The indirect N2 O emission factor (EF5r ) model, one of the bottom-up approaches, adopts a fixed EF5r value to estimate riverine N2 O emissions based on IPCC methodology. However, the estimates have considerable uncertainty due to the large spatiotemporal variations in EF5r values. Factors regulating EF5r are poorly understood at the global scale. Here, we combine 4-year in situ observations across rivers of different land use types in China, with a global meta-analysis over six continents, to explore the spatiotemporal variations and controls on EF5r values. Our results show that the EF5r values in China and other regions with high N loads are lower than those for regions with lower N loads. Although the global mean EF5r value is comparable to the IPCC default value, the global EF5r values are highly skewed with large variations, indicating that adopting region-specific EF5r values rather than revising the fixed default value is more appropriate for the estimation of regional and global riverine N2 O emissions. The ratio of dissolved organic carbon to nitrate (DOC/NO3 - ) and NO3 - concentration are identified as the dominant predictors of region-specific EF5r values at both regional and global scales because stoichiometry and nutrients strictly regulate denitrification and N2 O production efficiency in rivers. A multiple linear regression model using DOC/NO3 - and NO3 - is proposed to predict region-specific EF5r values. The good fit of the model associated with easily obtained water quality variables allows its widespread application. This study fills a key knowledge gap in predicting region-specific EF5r values at the global scale and provides a pathway to estimate global riverine N2 O emissions more accurately based on IPCC methodology.

Nitrous oxide concentration and flux in Min River Basin of southeast China: Effects of land use, stream order and water variables

Estimates of riverine nitrous oxide (N2O) emissions have great uncertainty partly due to the fact that the data is still sparse for stream sizes and land uses. Here we determined water dissolved N2O concentration and water–air interface N2O flux across the land uses and stream orders in Min River Basin of southeast China. N2O concentrations ranged from 11.1 to 27.4 nmol/L, increasing from first- to eighth-order rivers. The first- and second-order streams showed negative N2O flux (−0.33 and −0.05 µg m−2h−1, respectively) compared to third- to eighth-order rivers (from 0.29 to 2.85 µg m−2h−1). Average N2O flux was significantly higher in urban (1.60 µg m−2h−1) and cropland rivers (0.89 µg m−2h−1) than in forest rivers (−0.47 µg m−2h−1), which could be due to the main effect of land use was on the nitrogen load. Indirect N2O emission factor varied between 0.035 and 0.14 % across the rivers, which decreased from the urban to forest rivers and were lower than the IPCC default value (0.26 %). N2O concentration and flux were positively correlated with NO3−, NH4+, depth, velocity and temperature, suggesting the importance of stream surface hydromoprhology to N2O emissions. Land use indirectly affected N2O flux by affecting water NO3−, NH4+, DO, DOC, pH and temperature, which could further explain the land use dependence of N2O emissions on water variables. High DOC:NO3− ratio (>6) was the main factor of N2O sink in the small streams, which may be due to the enhanced N2O consumption and low N2O production. Therefore, riverine N2O emissions are highly variable across stream sizes and land uses, which are not only increased by inorganic nitrogen load and are also dependent on stream hydraulics and morphology.

Soil carbon stocks and nitrous oxide emissions of pasture systems in Orinoquía region of Colombia: Potential for developing land-based greenhouse gas removal projects

Improving grassland conditions under grazing has the potential not only to accumulate carbon in soils, but also to reduce nitrous oxide (N2O) emissions from animal urine deposition. However, measurements in developing countries are still scarce. In the Orinoquia region, permanent grasslands (PG; this unimproved, native pasture is considered as at some state of degradation) based on unimproved grasses are found due to extensive, inefficient grazing combined with annual burning of pastures. We hypothesized that, compared to PG, improved grasslands (IG) managed through rotational grazing of introduced, productive and deep-rooted pasture grass species promote soil organic carbon (SOC) accumulation and reduce N2O emission from urine deposited by grazing cattle. We determined SOC and N2O emissions from urine deposited on soils in an area of PG and in a 6.5 year-old IG area of Urochloa (Syn. Brachiaria) humidicola grass pasture in a beef cattle ranch in Orinoquía region (Colombia). In both areas, we sampled soil for chemical/physical analysis, and measured N2O emissions by simulating urine deposition over 21 days. We applied two-way analysis of variance considering pasture type and soil depth as fixed factors. Estimated SOC stocks (0–100 cm) were in the range of 224.8 Mg C ha−1 for the PG and 259.0 Mg C ha−1 for the IG, with a significant (p &amp;lt; 0.05) average accumulation of 2.0 Mg C ha−1 y−1 (0–20 cm) in the IG area. N2O emissions were 10 times lower in the IG compared to the PG. The introduction of U. humidicola grass influenced SOC accumulation probably through its more abundant root system and greater turnover together with higher (14%) forage dry matter production compared to PG. The reduced N2O emissions observed from urine patches in IG were attributed to biological nitrification inhibition ability and greater nitrogen uptake of U. humidicola grass. Compared to the reference default value of IPCC for, the SOC stock found in PG was almost 40% higher, whereas the N2O emission factor (5%) was within the uncertainty range (0.7–6%). The Orinoquía region shows significant potential for SOC storage and reduced N2O emissions in improved pastures with deep root systems. Thus, scaling the implementation of land-based SOC storage practices/projects could significantly contribute to reducing net emissions from beef production from this region.

Enhancing Sustainability in Intensive Dill Cropping: Comparative Effects of Biobased Fertilizers vs. Inorganic Commodities on Greenhouse Gas Emissions, Crop Yield, and Soil Properties

The treatment and valorization of organic solid waste has become a promising alternative to increase intensive crop productivity while reducing its environmental impact. Currently, reusing improved organic waste as novel biofertilizers is a vital tool to adapt semiarid agricultural regions to climate change, but this has been scarcely studied in aromatic crops. The present study aims to assess the greenhouse gas emissions, soil properties, and crop yield of a dill crop using a drip irrigation system with a normalized N application rate of 160 kg N ha−1. We compare eight different fertilizing scenarios grouped into organic-based (manures and compost) and inorganic-based inputs (NPK commodities and slow-release formulations). GHG fluxes were measured during the 57-day fertigation period using static chambers. Key soil properties were measured previous to fertilizer applications and at harvest, coinciding with crop yield estimations. An increase in soil organic carbon was observed with stabilized organic treatments at 0–20 cm soil depth. The results show that stabilized organic-based materials lowered NO3− concentrations in dill biomass more than synthetic fertilizers, producing similar yields to those with synthetic fertilizers. In general, N2O emissions were positively affected by the treatments. Local specific emission factors for N2O were determined (0.08%), which were substantially lower than the default value (0.51%) of IPCC. The cumulative CO2 emissions were high in all the organic scenarios compared to the control treatment (277 kg C-CO2 ha−1), probably due to differences in labile organic C contents. Organic-based treatments showed multiple positive effects on crop quality, crop yields, and GHG mitigation potential. The use of organic amendments is an optimized N fertilizing strategy to promote circular economy and sustainability.

Carbon stability and soil N2O emissions. Pyrolyzed or unpyrolyzed manure?

Pyrolysis is a useful alternative to current waste management practices. Manure biochars can be used as C-rich soil amendments, reducing the risk of greenhouse gas (GHG) emissions derived from unpyrolyzed manure decomposition. In this study, two manure biochars and their feedstock were used as soil treatments to evaluate the impact of pyrolysis on CO2 and N2O emissions, C stability, and global warming potential (GWP) for one year under field conditions. The experiment included five treatments: unamended soil (control), pig manure (PM), pig manure biochar (PMB), dairy manure (DM), and dairy manure biochar (DMB). The amendments were applied at a 1% w/w, adding approximately 0.5 kg C m−2. All amendments increased soil CO2 emissions; however, C mineralization was lower in pyrolyzed manures than in their corresponding feedstocks. CO2–C emissions were 8.35%, and 63% of the C from biochar and manure treatments, respectively. Biochars reduced soil N2O emissions, producing a negative N2O emission factor (N2O Ef), whereas manure treatments induced N2O fluxes for 105 days, with an N2O Ef of 0.27% after one year. Soil C stock variations were 16.4 and 6.58 t CO2-eq avoided ha−1 in treatments of biochars and manures, respectively. The mitigation potential of unpyrolyzed manure was affected by the high CO2 and N2O fluxes, whereas the biochar treatments reduced the GWP due to the changes in soil C stock with a low impact on soil emissions. Manure was more stable after pyrolysis, indicating that manure biochars are more favorable as soil amendments for environmental purposes. This could reduce the C footprint of pig and dairy farms, promoting the enhancement of soil C stocks.

Effect of aeration modes on nitrogen removal and N2O emission in the partial nitrification and denitrification process for landfill leachate treatment

The anoxic/multi-aerobic process is widely applied for treating landfill leachate with low carbon to nitrogen ratio. In this study, the effect of two aeration modes in the aerobic phase, i.e. decreasing dissolved oxygen (DO) and increasing DO, on nitrogen removal and N2O emission in the process were systematically compared. The results demonstrate that the aerobic phase with increasing DO mode has a positive effect on improved total nitrogen removal (78 %) under the COD/N ratio as low as 3.45 and minimized N2O emission. DO concentration higher than 1.5 mg/L in the aerobic phase reduced nitrogen removal and led to a significant high N2O emission in the process. Complete nitrite denitrification in the anoxic phase correlated with minimized N2O emission. Under efficient nitrogen removal stage, N2O emission factor was 2.4 ± 1.0 % of the total incoming nitrogen. Microbial analysis revealed that increasing DO mode increased the abundance of ammonia oxidizing bacteria and denitrifiers.

Insights into N2O turnovers under polyethylene terephthalate microplastics stress in mainstream biological nitrogen removal process

The ubiquitous microplastics in wastewater have raised growing concerns due to their unintended effects on microbial activities. However, whether and how microplastics affect nitrous oxide (N2O) (a potent greenhouse gas) turnovers in mainstream biological nitrogen removal (BNR) process remain unclear. This work therefore aimed to fill such knowledge gap by conducting both long-term and batch tests. After over 100 days of feeding with wastewater containing polyethylene terephthalate (PET) microplastics (0–500 μg/L), the long-term results showed that both production and reduction of N2O during denitrification were reduced, as well as the N2O production during nitrification. Accordingly, 60% reduction in N2O accumulation and 70% reduction in N2O production were observed in the denitrification and nitrification batch tests, respectively. Nevertheless, the long-term N2O emission factors under PET microplastics stress were comparable to that in the control reactor, mainly because PET microplastics led to more nitrite accumulation in anoxic period. With the aid of online N2O sensors and site-preference analysis, it was demonstrated that the heterotrophic bacteria pathway and ammonia oxidizing bacteria denitrification pathway for N2O production were negatively affected by PET microplastics, whereas a clear increase in the contribution of hydroxylamine pathway (+ 22.9%) was observed. Further investigation revealed that PET microplastics even at environmental level (i.e. 10 μg/L) significantly reshaped the BNR sludge characteristics (e.g. much larger particle size) and microbial communities (e.g. Thauera, Rhodobacte and Nitrospira) as well as the nitrogen metabolism pathways, which were chiefly responsible for the changes of N2O turnovers and N2O production pathways under the PET microplastics stress.

Revisiting sampling duration to estimate N2O emission factors for manure application and cattle excreta deposition for the UK and Ireland

According to the available guidelines, good practices for calculating nitrous oxide (N2O) emission factors (EFs) for livestock excreta and manure application include that sampling duration should be of at least one year after the nitrogen (N) application or deposition. However, the available experimental data suggest that in many cases most emissions are concentrated in the first months following N application. Therefore resources could be better deployed by measuring more intensively during a shorter period. This study aimed to assess the contribution of the N2O flux in the period directly after N application to the annual net emission. We used a database of 100 year-long plot experiments from different excreted-N sources (dung, urine, farmyard manure and slurry) used to derive EFs for the UK and Ireland. We explored different shorter potential measurement periods that could be used as proxies for cumulative annual emissions. The analysis showed that the majority of emissions occur in the first months after application, especially in experiments that i) had urine as the N source, ii) had spring N application, iii) were conducted on fine-textured soils, or iv) showed high annual emissions magnitude. Experiments that showed a smaller percentage of emissions in the first months also had a low magnitude of annual net emissions (below 370 gN2O–N ha−1 year−1), so the impact of measuring during a shorter period would not greatly influence the calculated EF. Accurate EF estimations were obtained by measuring for at least 60 days for urine (underestimation: 7.1%), 120 days for dung and slurry (4.7 and 5.1%) and 180 days for FYM (1.4%). At least in temperate climates, these results are promising in terms of being able to estimate annual N2O fluxes accurately by collecting data for less than 12 months, with significant resource-saving when conducting experiments towards developing country-specific EFs.

N2O production and emission pathways in anammox biofilter for treating wastewater with low nitrogen concentrations

Although anaerobic ammonia oxidation (anammox) is a cost-effective nitrogen removal process, nitrous oxide (N2O) production will greatly reduce the advantages of this process. It is important to identify the N2O emission pathways and then reduce the N2O production in anammox system. To date, very limited research has been done to investigate the N2O production and N2O emission pathways in anammox biofilter. In this study, N2O production were investigated under different filtration rates in anammox biofilter for treating wastewater with low nitrogen concentrations, and N2O emission pathways were analyzed with batch tests using N2O microsensor and stable isotope mass spectrometry. The results showed N2O production increased with the increase of filtration rates in anammox biofilter, where the N2O emission factor increased from 0.012 % at 1.0 m/h to 0.496 % at 3.0 m/h. And the optimal operation condition was at filtration rate of 1.5 m/h, where NH4+-N and NO2−-N removal efficiencies reached 99 % and N2O concentration was the lowest. qPCR showed that anammox bacteria, nitrifying bacteria and denitrifying bacteria were all present in anammox biofilter, with anammox bacteria in the highest abundance. And nitrifying bacteria and denitrifying bacteria provided the possibility of N2O production. The batch tests and stable isotope mass spectrometry analysis indicated that nitrifier denitrification, hydroxylamine oxidation and endogenous heterotrophic denitrification were N2O production pathways in aerobic zone and anoxic zone of anammox biofilter, respectively. In addition, batch tests under different conditions showed no oxygen environment could reduce N2O production. Therefore, the production of N2O in anammox system is a problem that cannot be ignored and should be paid more attention to.