Denitrification Ratio Research Articles

APPLICATION OF ALCALIGENES FAECALIS NO. 4 FOR TREATMENT OF HIGH-STRENGTH AMMONIUM WASTEWATER

Biological ammonium removal from wastewater requires coupling of nitrification and denitrification processes in respective aerobic and anaerobic conditions. This difference in environmental requirements pose a big challenge in the design of systems intended to effect both nitrification and denitrification processes. Alcaligenes faecalis strain No. 4, however, has both heterotrophic nitrification and aerobic denitrification abilities in aerobic conditions, eliminating the need to provide anaerobic conditions for denitrification. Batch and continuous experiments in a mixed culture of A. faecalis No. 4 and activated sludge were performed to examine ammonium removal and microbial stability of No. 4 in aerobic reactors. At an inflow ammonium load of 500 mg L-1 d-1 in continuous experiment, the ammonium removal rate (21 mg L-1 h-1), under No. 4, was approximately 2 times higher than that of the control (i.e., without No. 4), and the denitrification ratio was approximately 66%. The proportion of intracellular nitrogen converted from removed ammonium in the continuous mixed culture was reduced, compared to control batch and continuous cultures. These results demonstrated stable growth as well as the heterotrophic nitrification-aerobic denitrification abilities of No. 4 in activated sludge systems.

Addition of pig manure hydrolysate as a carbon source to enhance nitrate removal from piggery wastewater under different HRTs

To develop a quick, efficient, economical and easy method of obtaining a carbon source for piggery wastewater, thermo-alkaline treatment of pig manure hydrolysate as an external carbon source (PMC), which contains a high concentration of VFAs, was used. Batch experiments were carried out to determine the effect of the COD/TN ratio on piggery wastewater denitrification using PMC, and a comparison was made between PMC and sodium acetate for the denitrification at the optimum COD/TN ratio. Then, the effect of PMC on piggery wastewater denitrification was proven in a sequencing batch reactor. The results show that when PMC is applied, the appropriate C/N ratio for denitrification is 6.5, which is equivalent to an addition of 3.8%. Under these conditions, PMC performed better than sodium acetate. With PMC, the contents of NO2-N and NO3-N in the SBR under three different HRTs were less than 0.02 mg/L and 5 mg/L, respectively, and the TN removal rate was 90%. The highest denitrification rate of SBR was 25.37 mg NO3-N/(g VSS h).

Disentangling direct and indirect effects of mycorrhiza on nitrous oxide activity and denitrification

Nitrous oxide (N2O) is a potent greenhouse gas emitted at considerable rates from agricultural soils. A few recent studies have indicated the potential to reduce N2O emission rates in agricultural systems through management of soil microbiota, such as mycorrhizal fungi. Our limited understanding of how mycorrhiza influences N2O emission rates, however, forestalls such management practices. To address the knowledge gap regarding the mechanism of mycorrhizal modification of N2O formation and denitrification, we disentangle the direct effects of arbuscular mycorrhizal fungi (AMF) via hyphal growth on potential denitrification activity from those resulting from indirect AMF-induced changes in soil aggregation. We manipulated AMF status in a factorial experiment through adding or not AMF inoculum in the form of Rhizophagus irregularis and soil aggregation state through either crushing soil aggregates or using agricultural soil with intact soil aggregates. We then grew Zea mays (maize) in compartmentalized mesocosms for 4 months. At harvest, we observed approximately three-fold higher AMF root colonization and hyphal densities in the treatments where we had added Rhizophagus irregularis. Potential N2O activity rates and the denitrification ratio were higher in the undisturbed soil and in the mesocosms with a dense AMF hyphal network (direct effect of mycorrhiza). Further, AM-hyphae promoted soil aggregation while also altering potential denitrification activity (indirect effect of mycorrhiza). Overall, we present here a comprehensive case study on how mycorrhiza alters potential denitrification activity and related N2O activity from agricultural soils.

Interaction of straw amendment and soil NO3− content controls fungal denitrification and denitrification product stoichiometry in a sandy soil

The return of agricultural crop residues are vital to maintain or even enhance soil fertility. However, the influence of application rate of crop residues on denitrification and its related gaseous N emissions is not fully understood. We conducted a fully robotized continuous flow incubation experiment using a Helium/Oxygen atmosphere over 30 days to examine the effect of maize straw application rate on: i) the rate of denitrification, ii) denitrification product stoichiometry N2O/(N2O+N2), and iii) the contribution of fungal denitrification to N2O fluxes. Five treatments were established using sieved, repacked sandy textured soil; i) non-amended control, ii) nitrate only, iii) low rate of straw + nitrate, iv) medium rate of straw + nitrate, and iv) high rate of straw + nitrate (n = 3). We simultaneously measured NO, N2O as well as direct N2 emissions and used the N2O 15N site preference signatures of soil-emitted N2O to distinguish N2O production from fungal and bacterial denitrification. Uniquely, soil NO3− measurements were also made throughout the incubation. Emissions of N2O during the initial phase of the experiment (0–13 days) increased almost linearly with increasing rate of straw incorporation and with (almost) no N2 production. However, the rate of straw amendment was negatively correlated with N2O, but positively correlated with N2 fluxes later in the experimental period (13–30 days). Soil NO3− content, in all treatments, was identified as the main factor responsible for the shift from N2O production to N2O reduction. Straw amendment immediately lowered the proportion of N2O from bacterial denitrification, thus implying that more of the N2O emitted was derived from fungi (18 ± 0.7% in control and up to 40 ± 3.0% in high straw treatments during the first 13 days). However, after day 15 when soil NO3− content decreased to <40 mg NO3−-N kg−1 soil, the N2O 15N site preference values of the N2O produced in the medium straw rate treatment showed a sharp declining trend 15 days after onset of experiment thereby indicating a clear shift towards a more dominant bacterial source of N2O. Our study singularly highlights the complex interrelationship between soil NO3− kinetics, crop residue incorporation, fungal denitrification and N2O/(N2O + N2) ratio. Overall we found that the effect of crop residue applications on soil N2O and N2 emissions depends mainly on soil NO3− content, as NO3− was the primary regulator of the N2O/(N2O + N2) product ratio of denitrification. Furthermore, the application of straw residue enhanced fungal denitrification, but only when the soil NO3− content was sufficient to supply enough electron acceptors to the denitrifiers.

Biogeochemical Controls on the Relative Importance of Denitrification and Dissimilatory Nitrate Reduction to Ammonium in Estuaries

AbstractThe balance between estuarine denitrification and dissimilatory nitrate reduction to ammonium (DNRA) is critical for determining nitrogen loads received by oceans from inland waters. We aimed to determine the factors controlling the ratio between these processes and determining whether nitrogen was generally removed or recycled in estuaries. Rates of denitrification and DNRA with depth were measured in intact sediment cores in 11 estuaries along the coast of Victoria, Australia. The estuaries studied represent a range of biogeochemical conditions, land use, and catchment size. At a pore water profile scale, the ratio of denitrification to DNRA was well predicted by a multiple regression model with nitrate concentration in the overlying water, dissolved pore water iron, and ammonium as the predictor variables. Areal denitrification rates varied from 4 to 150 μmol · m−2 · hr−1, and DNRA rates varied from 2 to 30 μmol · m−2 · hr−1, with the ratio of denitrification to DNRA spanning a range from denitrification‐dominated (denitrification/DNRA = 8.4) to DNRA‐dominated (denitrification/DNRA = 0.3). DNRA dominated at sites with high iron pools and high organic carbon to nitrate ratios. We conclude that low nitrate and high Fe2+ availability generally enhances DNRA and drives an estuary toward being N recycling, rather than N removing.

Long-term efficient deammonification operation with PVA/alginate carrier modified by foaming agent

This study investigated long-term deammonification operation, of 400 days, utilizing PVA/alginate carriers prepared with the addition of foaming agent (FA) adjusted from 0 to 1.2% (F-0 to F-1.2). FTIR spectra showed variations in the extent of crosslinking in the surface and the core areas of carriers. FA addition improved the already low crosslinking in the core areas and porosity in the surface areas, yielding higher endurance to internally produced gas. In the start-up period of continuous test, FA addition favored deammonification bacteria over denitrifiers. Increasing the FA decreased the extent and duration of heterotrophic denitrification that was superseded by deammonification after 30 d of operation. After 100 d, F-0.6 had the highest deammonification to denitrification ratio and gave a nitrogen removal rate (NRR) of 3.2 kg N.m−3.d−1 at 317 d of operation. Also, the 16S rRNA gene concentration of the deammonification bacteria was highest in F-0.6, which corresponded with the specific anammox activity (SAA) results. Overall, the improved PVA/alginate carriers gave higher SAA and deammonification bacteria concentration resulting in a stable long-term deammonification operation with high NRR.

Nitrification and Denitrification Potential of Benthic Sediments in a Suburban Stream under Intense Human Disturbance Scenarios

Water and benthic sediment samples were collected monthly from six sites over a 2-km reach in a first-order stream located in the northeastern rural-urban fringe of Hefei City, from May 2016 to January 2017. These sites were scattered in three stream reach types as natural pattern sections (Scenario 1), point source pollution sections (Scenario 2), and severe soil erosion sections (Scenario 3). The potential rates of nitrification and denitrification in the sediments were measured and variable characteristics were evaluated quarterly. Moreover, a difference analysis of each of the three scenarios and an influencing factor analysis for nitrification and denitrification potentials were subsequently conducted. Our results show that:① the mean value of the nitration ratios for total sediment samples is 0.381%, of which the maximum nitration ratio emerged in Scenario 2. As for Scenario 1, the nitration ratio in summer is the larger than in winter. The nitration ratios for Scenarios 2 and 3 rank from largest to smallest as spring > summer > autumn > winter. ② The mean value of the nitrification rate of the total sediment samples is 0.364 mg·(kg·d)-1, of which the maximum nitrification rate is associated with in Scenario 2. The nitrification rate is highest in winter, while similar for all other seasons in Scenarios 2 and 3. There is not much difference all year round for Scenario 1. ③ Average values for the denitrification ratio and denitrification rate for all sediment samples are 37.25% and 57.68 mg·(kg·d)-1, respectively. Both of these are higher for Scenario 2 than the other two scenarios for the same season. The ranking for denitrification for Scenarios 1 and 2 is summer > spring > autumn > winter, and spring > summer > autumn > winter in Scenario 3. ④ According to the difference analysis, significant differences not only exist between the nitrification rates between Scenarios 1 and 2 but also for the denitrification ratios and denitrification rates between Scenarios 1 and 3. In addition, there is an obvious difference in the nitration ratio between Scenarios 2 and 3. ⑤ Partial least-squares regressive analysis indicates that there is significant difference between the important influencing factors related to the nitration ratio and nitrification rate for each of the three scenarios.

Nitrogen Removal from Landfill Leachate by Chemical and Biological Treatment: Process Comparison

The efficiency of nitrogen removal from leachate by different chemical and biological methods was explored. The leachate was derived from Filborna landfill (NSR AB, Helsingborg, Sweden) and was characterized as an old leachate with pH = 8.0 and comparatively low concentrations of nitrogen and organic compounds (ca. 150 mg/l NH4-N and 500 mg/l COD). Three treatment processes were tested in lab-scale experiments; combined nitrification and denitrification in a sequencing-batch reactor (SBR), one-reactor nitritation-anammox process in a moving-bed biofilm reactor (MBBR) in sequencing-batch configuration and nitrogen precipitation in the form of magnesium-ammonium-phosphate (MAP). State-of-the-art of these processes is described.&#x0D; The conventional combined nitrification/denitrification process allowed 99% removal of inorganic nitrogen with 23 mg NH4-N/(l·h) being the highest nitrification rate achieved. Aeration during nitrification step and addition of carbon source according to the stoichiometric ratio for denitrification was required, accounting for the operational costs. The nitritation-anammox process also allowed 99% removal of inorganic nitrogen with 3.7 g NH4- N/(m2·d) being the highest process rate achieved while running the reactor at 25°C and pH 8.0. The process is advantageous in comparison with the conventional biological removal process, as oxygen consumption is lower and addition of carbon source is not required. With MAP precipitation at the optimal Mg:N:P ratio (1.2:1:1) only 78% removal of inorganic nitrogen was achieved. The precipitation process led to a significant increase of phosphorous concentrations in the effluent, while external magnesium and phosphorous sources to be added resulted in high process costs. Detailed descriptions of the processes and obtainedresults are given in the article.&#x0D; Comparing the three processes, conclusions are drawn that it is possible to achieve effluent nitrogen requirements (15 mg N/l) by treatment of leachate with both tested biological processes, but not with MAP precipitation. One-reactor nitritation-anammox would require the lowest operational costs, while MAP precipitation – the highest.

A distinctive root-inhabiting denitrifying community with high N2O/(N2O+N2) product ratio

Microbial denitrification in agriculture makes a considerable contribution to terrestrial nitrous oxide (N2O) emissions, and the prevailing view is that this mainly occurs in soil. Here, we show the root N2O emission capacity of wheat grown under three long-term (32-year) fertilization regimes, and compare root-, rhizosphere- and soil-inhabiting denitrifying microbial communities. The N2O/(N2O + N2) product ratio of denitrification in the root was 0.5–9.2-fold higher than that in surrounding soil under fertilized conditions, especially manure application. Root N2O/(N2O + N2) ratio was closely related to the proportion of two nitrite-reductase genes (nirK/nirS), with higher N2O emission associated with increased nirS abundance. Rhodobacterales and Pseudomonadales dominated the root-associated nirS community. In contrast, soils showed a higher proportion of unclassified denitrifiers. Our results demonstrate the potential of wheat to emit N2O from the roots that harbour low-complexity denitrifying communities distinct from those occurred in soils.

Denitrification in upland of China: Magnitude and influencing factors

AbstractA better understanding of influencing factors and accurate estimate of soil denitrification is a global concern. Here we present a synthesis of 300 observations of denitrification in Chinese upland soils from 39 field and laboratory studies using the acetylene inhibition technique. The results of a linear mixed model analysis showed that the rates of soil denitrification were significantly affected by crop type, soil organic carbon, soil pH, the measurement period, and the rate of N application. The emission factor (EF) and N2O/(N2O + N2) ratio for soil denitrification were on average 2.11 ± 0.17% and 0.508 ± 0.020, respectively. Our meta‐analysis indicated that N fertilization increased soil denitrification by 311% (95% CI: 279–346%) and 112% (95% CI: 66–171%) in the field and laboratory studies, respectively. Substantial interactive effects between soil properties and N fertilization on soil denitrification were found. Although the highest values of both the rate of denitrification and the EF were found in vegetable fields, the size of the stimulating effect of N fertilization on soil denitrification was lower in vegetable fields than in maize and wheat fields. These results suggest that the crop‐specific effect is important and that vegetable fields are potential hot spots of denitrification in Chinese uplands. Based on either the EF or the N2O/(N2O + N2) ratio obtained, the estimated amount of total denitrification from the upland soils was an order of magnitude lower than that from budget calculations, suggesting that the acetylene inhibition technique may significantly underestimate denitrification in Chinese upland soils.

Analysis of Driving Factors on the Nitrogen Decrease in the Early Stage of the Thermal Stratification in Main Area of Zhoucun Reservoir

In order to explore the trend and driving factors of nitrogen in the early stage of the thermal stratification in Zhoucun reservoir, the water quality indicators in main reservoir area of Zhoucun reservoir were monitored regularly form February to April (2016). Meanwhile, the fresh water and surface sediments in the sampling point were collected to study the effect of water and sediment denitrification by simulation in laboratory. The results showed that: the concentration of TN decreased from (2.28±0.09) mg·L-1 to (1.08±0.09) mg·L-1, the concentration of nitrate nitrogen decreased from (1.66±0.09) mg·L-1 to (0.25±0.06) mg·L-1, whereas the concentration of ammonia nitrogen and nitrite showed little change in the early thermal stratification of Zhoucun reservoir. At the same time, chlorophyll was not significantly increased, so the algae had little effect on nitrogen; the decreasing nitrogen was mainly due to the aerobic denitrification. Gradually increased temperature,the changes of DO and pH and the composition of organic matter (low molecular weight) were beneficial to the growth of aerobic denitrifying bacteria. Furthermore, the number of bacteria increased from 1.06×105 cfu·L-1 to 8.33×106 cfu·L-1, which enhanced the denitrification of the reservoir; Meanwhile, in the simulation experiments, the TN removal rates of water and water-sediment systems reached 0.7 mg and 3.3 mg, respectively. Water and sediment denitrification ratio was generally 1:4, and the aerobic denitrification of surface sediment was an important factor in the removal of nitrogen in reservoir.

Development of a DHS-USB recirculating system to remove nitrogen from a marine fish aquarium

A recirculating nitrogen (N) removal system comprising a down-flow hanging sponge (DHS) reactor combined with an up-flow sludge blanket (USB) reactor was developed. We used this system in a fish-breeding marine aquarium to evaluate the N removal and to determine the optimum C/N ratio for denitrification. With this system in place, nitrate-nitrogen concentrations in the marine fish aquarium remained below 30mgN/L, and total ammonia nitrogen and nitrite concentrations were below 0.1mgN/L. The optimum denitrification ratio was approximately 1.2. Analysis of the microbial community showed that there were ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in the DHS reactor, and that there were two types of denitrifying bacteria in the USB reactor, namely heterotrophs and autotrophs, that removed nitrate from the marine aquarium water.

Effects of Sulfur/sponge Iron Ratio for Deep Denitrification and Phosphorus Removal of Reclaimed Water

To study the effects of sulfur/sponge iron ratio on denitrification and phosphorus removal, a series of static experiments were conducted using different ratios of sulfur and sponge iron. The results showed that the denitrification and phosphorus removal effect of sulfur/sponge iron composite fillers was significantly higher than that of single filler, and sulfur/sponge iron ratio was one of the key factors influencing nitrogen and phosphorus removal by composite fillers. When the volume ratio was equal to or greater than 1:1, the removal efficiency of TN and TP reached 85% and 97%, respectively. The denitrification and phosphorus removal process of the composite fillers both fitted second-order kinetic equation, the denitrification was dependent on heterotrophic denitrification and sulfur autotrophic denitrification; the phosphorus removal was mainly chemical phosphorus removal caused by sponge iron corrosion.

Spatial variation in soil pH controls off-season N2O emission in an agricultural soil

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.

Efficiency of wastewater treatment in SBR and IFAS-MBSBBR systems in specified technological conditions

The objective of this study is to compare wastewater treatment effectiveness in sequencing batch reactor (SBR) and integrated fixed-film activated sludge-moving-bed sequencing batch biofilm reactor (IFAS-MBSBBR) systems in specific technological conditions. The comparison of these two technologies was based on the following assumptions, shared by both series, I and II: the reactor's active volume was 28 L; 8-hour cycle of reactor's work, with the same sequence and duration of its consecutive phases; and the dissolved oxygen concentration in the aerobic phases was maintained at a level of 3.0 mg O2/L. For both experimental series (I and II), comparable effectiveness of organic compound (chemical oxygen demand (COD)) removal, nitrification and biological phosphorus removal has been obtained at levels of 95.1%, 97% and 99%, respectively. The presence of the carrier improved the efficiency of total nitrogen removal from 86.3% to 91.7%. On the basis of monitoring tests, it has been found that the ratio of simultaneous denitrification in phases with aeration to the total efficiency of denitrification in the cycle was 1.5 times higher for IFAS-MBSBBR.

Source Separation of Urine as an Alternative Solution to Nutrient Management in Biological Nutrient Removal Treatment Plants.

Municipal wastewater contains a mixture of brown (feces and toilet paper), yellow (urine), and gray (kitchen, bathroom and wash) waters. Urine contributes approximately 70-80% of the nitrogen (N), 50-70% of the phosphorus (P) load and 60-70% of the pharmaceutical residues in normal domestic sewage. This study evaluated the impact of different levels of source separation of urine on an existing biological nutrient removal (BNR) process. A process model of an existing biological nutrient removal (BNR) plant was used. Increasing the amount of urine diverted from the water reclamation facilities, has little impact on effluent ammonia (NH₃-N) concentration, but effluent nitrate (NO₃-N) concentration decreases. If nitrification is necessary then no reduction in the sludge age can be realized. However, a point is reached where the remaining influent nitrogen load matches the nitrogen requirements for biomass growth, and no residual nitrogen needs to be nitrified. That allows a significant reduction in sludge age, implying reduced process volume requirements. In situations where nitrification is required, lower effluent nitrate (NO₃-N) concentrations were realized due to both the lower influent nitrogen content in the wastewater and a more favorable nitrogen-to-carbon ratio for denitrification. The external carbon requirement for denitrification decreases as the urine separation efficiency increases due to the lower influent nitrogen content in the wastewater and a more favorable nitrogen-to-carbon ratio for denitrification. The effluent phosphorus concentration decreases when the amount of urine sent to water reclamation facilities is decreased due to lower influent phosphorus concentrations. In the case of chemical phosphate removal, urine separation reduces the amount of chemicals required.

Reactor performance and microbial characteristics of CANON process with step-wise increasing of C/N ratio

In this study, the nitrogen removal performance and microbial characteristics of completely autotrophic nitrogen removal over nitrite (CANON) process was investigated with a step-wise increasing of C/N ratio (0.5, 1, 2 and 4) in a membrane bioreactor. The microbial distribution of aerobic ammonia-oxidizing bacteria (AOB) and anaerobic AOB (AAOB) was analysed by fluorescence in situ hybridization (FISH). Results showed that the denitrification ratio rose up correspondingly with the increase of influent C/N, and nitrogen removal rate (NRR) reached the maximum when C/N was 1 due to the harmonious work of denitrification and CANON. However, NRR decreased when influent C/N was more than 2. The threshold C/N ratio of CANON process was 2.2; so the sewage with a high C/N ratio should be pretreated by combining with pre-oxidation of organics or anaerobic-energy-producing process. FISH results showed decreasing numbers of both AOB and AAOB with the addition of organics.

Higher N[formula omitted]O emission by intensified crop production in South Asia

Intensification of food production in Nepal has been found to acidify the soils and hence increase their apparent propensity to emit N2O as measured by the N2O/(N2+N2O) product ratio of denitrification during standardized anoxic incubations (Raut et al., 2012). We hypothesized that this would lead to high N2O emission factors (EF), and tested this by measuring N2O emissions from fields on which intensified crop production (IC) had been practiced for the last 20 years, and adjacent fields having traditional crop production (TC) practices. The measurements were done every one to two weeks over a period of 12 months covering two to three cropping periods. On the sites with periodically flooded soils, the cumulated emissions for IC and TC were 15.41 and 7.23 kg N2O/ha, respectively. On the sites with permanently drained soils, the cumulated emissions were 5.43 and 1.46 kg N2O/ha (IC and TC). We used the available data on fertilizer levels to calculate an emission factor for the transition from TC to IC (EFI); i.e. ΔN2O−N/ΔNfertilizer, where ΔN2O-N is the cumulated emission in IC minus that in TC, ΔNfertilizer is the annual N input to IC minus that in TC. The EF values were 0.08 and 0.02 for the sites with permanently drained and periodically flooded soils, respectively. These factors are 2 to 8 times higher than the EF values used by IPCC to calculate emission as a function of fertilizer level. The high EFI appear to confirm our hypothesis that intensification will lead to higher emission of N2O than that predicted by the increase in nitrogen inputs, and that this is due to the soil acidification.

Anaerobic digestates lower N2O emissions compared to cattle slurry by affecting rate and product stoichiometry of denitrification – An N2O isotopomer case study

Assessing effects of organic fertilizer applications on N2O emissions is of great interest because they can cause higher N2O emissions compared to inorganic fertilizers for a given amount of added nitrogen (N). But there are also reports about enhanced N2O reduction to climate-neutral elemental N2 after application of organic manures to soils. Factors controlling the N2O/(N2O + N2) product ratio of denitrification are interrelated, and also the ratio is difficult to study because of limitations in N2 flux measurements. In this study, we investigated N2O and N2 emissions from soil treated with organic fertilizers with different C/N ratios. An N2O isotopomer approach combined with conventional N2O and N2 flux measurements was employed to study underlying microbial pathways.A grassland soil was amended with anaerobic digestate (AD) from food waste digestion (low C/N ratio) or cattle slurry (CS; high C/N ratio), respectively, adjusted to 90% WFPS, and incubated for 52 days under helium–oxygen atmosphere (10% O2) using a soil incubation system capable of automated N2O, N2, and CO2 measurements. N2O isotopomer signatures, i.e. the δ18O and SP values (site preference between 15N at the central and the peripheral position in the N2O molecule), were determined by Isotope Ratio Mass Spectrometry and used to model and subsequently estimate the contribution of bacterial denitrification and autotrophic nitrification to N2O production. For this approach the direct determination of emitted N2 is essential to take isotope effects during N2O reduction to N2 into account by correcting the measured isotope signatures for isotope effects during N2O reduction using previously determined fractionation factor ranges.The addition of both organic fertilizers to soil drastically increased the rate of gaseous N emissions (N2O + N2), probably due to the effects of concurrent presence of nitrate and labile C on the denitrification rate. In the initial phase of the experiment (day 1 to ∼15), gaseous N emissions were dominated by N2 fluxes in soils amended with organic manures; meanwhile, N2O emissions were lower compared to untreated Control soils, but increased after 15–20 days relative to the initial fluxes, especially with CS. Extremely low N2O, but high N2 emissions in the initial phase suggest that reduction of N2O to N2 via denitrification was triggered when the soil was amended with organic fertilizers. In contrast in the untreated Control, N2O release was highest during the initial phase. Total N2O release from AD treated soil was similar to Control, while N2O from CS treated soil was considerably higher, indicating that denitrification was triggered more by the high labile carbon content in CS, while the cumulative N2O/(N2O + N2) product ratio and thus N2O reduction were similar with both organic fertilizers.The results of the N2O source partitioning based on the isotopomer data suggest that about 8–25% (AD) and 33–43% (CS) of the cumulated N2O emission was due to nitrification in organically amended soil, while in the untreated Control nitrification accounted for about 5–16%. The remaining N2O production was attributed mainly to denitrification, while the poor model fit for other source pathways like fungal denitrification suggested their contribution to be of minor importance. The observed rather distinct phases with predominance first of denitrification and later of nitrification may help developing mitigation measures by addressing N2O source processes individually with appropriate management options. The observation of relatively large shares of nitrification-derived N2O is surprising, but may possibly be related to the low soil pH and will require further investigation.The determination of N2 production is essential for this isotopomer-based source partitioning approach, but so far only applicable under laboratory conditions. The results of this study indicate that the combination of N2O δ18O and SP values is very useful in obtaining more robust source estimates as compared to using SP values alone.

Research of Denitrifying Dephosphatation in A&lt;sub&gt;2&lt;/sub&gt;ON Process

In order to investigate the potential of sequencing batch biofilm reactor (SBBR) technology of two-sludge system for denitrifying dephosphatation (A2ON process),we build a tab-scale experiment .Then find that the simultaneous removal of phosphorus and nitrogen in the two sludge system is possible .By the control of COD/TN ratio ,highly effective simultaneous nitrification and denitrification is achieved in the A2ON system.And the ratio of denitrification is 85%, the ratio of dephosphatation is 87%.It also demonstrates that the process is stable ,at the same time decrease the effect of dephosphorization and denitrification by the limited carbon source.