Buildup Of Nitrate Research Articles

Increased N2O emissions by the soil nematode community cannot be fully explained by enhanced mineral N availability

Soil nematodes are the most abundant soil fauna, with a potential great impact on soil N mineralization via interaction with soil microorganisms. As a consequence, nematodes likely also influence soil N2O production and emission but the very few studies on this matter were carried out in simplified setups with single nematode species and in (highly) disturbed soil conditions. Here we measured soil N2O emissions in a 74-day incubation experiment in the presence or absence of the entire soil nematode community with minimal disturbance of the soil microbial community and soil nutrients. This was e.g. evidenced by readily recovery of nitrifiers after the mild and selective sterilization and soil powder inoculation. N2O emissions increased in the presence of nematodes, varying between soils +747.7 % in a loamy sand, +55.8 % in a loam, and +51.9 % in a silt loam cropland topsoil, in line with nematode abundance in these soils. In particular, the loamy sand soil showed an atypical N2O emission peak at the time of high nematode abundance. Soil nematodes also increased net N mineralization by +8.4, +6.8 and +4.75 %, in these respective soils and to a smaller extent C mineralization as well. The extra soil nitrate buildup and the overall net stimulation of N mineralization by nematodes could not or just slightly explain the observed increased N2O emission. This research revealed the important role of soil nematodes in regulating N2O emission, and further stresses the need to consider the change in community composition and activity of denitrifiers, and connectivity of soil pores, rather than the stimulation of N mineralization as potential explanations for this role of nematodes.

Simulation of spatial and temporal variation of nitrate leaching in the vadose zone of alluvial regions on a large regional scale

Excessive use of fertilizers presents a significant threat to groundwater safety. To mitigate nitrate leaching and ensure the sustainable utilization of groundwater resources, it is crucial to quantify the spatial heterogeneity of nitrogen leaching and its drivers. Therefore, accurate modeling of deep nitrate leaching at large regional scales is necessary. In this study, we have created a computational framework to analyze the transport of unsaturated zone water and nitrate at a regional scale. The framework is based on a process-oriented, watershed-scale computational model that segments the study area into a grid system, with each grid modeled using Richards-based advection-diffusion equations for water and solutes. The research model estimated nitrate nitrogen leaching, accumulation, and denitrification in the vadose zone of agricultural fields in the Baiyangdian watershed, which is a typical agricultural region with complex land use and soil deposition conditions in the North China Plain. The results showed that there were significant spatial differences in nitrate N leaching, denitrification and accumulation with values of 0–388 kg/ha/year, 30–177 kg/ha/year and 75–4778 kg/ha. Groundwater recharge in the wheat/maize, vegetable, and cotton area exhibited a negative correlation with nitrate N accumulation while showing a positive correlation with nitrate N leaching. Nitrate nitrogen distribution indicated spatial heterogeneity, attributable mainly to the heterogeneity in soil texture, structure, and land use. With nitrate nitrogen leaching and denitrification levels reaching 327–388 kg/ha/year and 133–175 kg/ha/year, respectively, vegetable fields pose a direct threat to groundwater. Meanwhile, wheat/maize fields showed the greatest nitrate nitrogen accumulation, ranging from 624 to 4778 kg/ha. This excessive buildup of nitrate in these fields presents a potential hazard to groundwater quality. Soil texture in the root zone had a greater influence on the amount of nitrate leaching and denitrification than soil texture below the root zone. Deeper soil texture (>2 m) was found to mainly control total nitrate accumulation in the vadose zone. To assess nitrate leaching, denitrification, and accumulation at a regional scale within the deep vadose zone, a process-oriented model was developed, considering the intricate associations among land usage, soil texture, and biochemical reactions.

Why nitrogen oxide inhibits CO oxidation over highly dispersed platinum ceria catalysts

The influence of nitrogen oxide on the lean CO oxidation activity of highly dispersed Pt/ceria and reference Pt/alumina catalysts has been studied by kinetic measurements and infrared spectroscopic characterization. Co-feeding of nitrogen oxide leads to the formation of nitrates on the supports that induce a highly oxidized character of the Pt sites and in the case of Pt/ceria, inhibit ceria lattice oxygens to react with CO adsorbed on Pt rim sites via a Mars-van Krevelen mechanism below the ignition temperature. The build-up of nitrates below the light-off temperatures is faster when CO is present in the feed. Above the light-off temperatures, carbonates replace the nitrates while the catalytic activity remains high.

Partial nitritation-anammox for treatment of saline wastewater: Hydrazine-assisted salinity adaptation and nitrate control

In biological wastewater treatment, salinity can significantly restrict bacterial activity, and a long adaptation period to the saline condition is needed. This study investigated the feasibility of using partial nitritation-anammox (PNA) in an integrated fixed-film activated sludge (IFAS) reactor for enhanced biological nitrogen removal from saline municipal wastewater. The experimental results show that the salinity increase in the influent seriously affected the activity of anammox bacteria and disrupted the PNA process for autotrophic nitrogen removal when seawater was added to a 20% proportion with a resultant salinity of around 6.5‰. However, the addition of N2H4 (dosage: 5 mg/L for 3 weeks), an exogenous enhancer of both ammonia-oxidizing bacteria and anammox bacteria, effectively facilitated the rapid recovery and adaptation of PNA to salinity stress with a negligible additional cost for long-term operation. The PNA-IFAS reactor achieved a nitrogen removal capacity of 83.4 ± 5.9 mg N/(L‧d) in treating the saline municipal wastewater containing 40% seawater and an ammonia-N concentration of around 60 mg N/L. Salinity in the influent advantageously suppressed the activity and growth of the co-existing nitrite-oxidizing bacteria (NOB). The relative abundances of NOB in the suspended sludge (0.15%) and biofilms (0.33%) were kept at low levels, maintaining a low nitrate yield of 6.6 ± 1.5% in the bioreactor. The result suggests that salinity in the influent may offer potential benefits for reducing the risk of nitrate build-up and increasing the robustness of the PNA process for sustainable wastewater treatment.

Characterization of Enrichment Cultures of Anammox, Nitrifying and Denitrifying Bacteria Obtained from a Cold, Heavily Nitrogen-Polluted Aquifer

Anammox bacteria related to Candidatus Scalindua were recently discovered in a cold (7.5 °C) aquifer near sludge repositories containing solid wastes of uranium and processed polymetallic concentrate. Groundwater has a very high level of nitrate and ammonia pollution (up to 10 and 0.5 g/L, respectively) and a very low content of organic carbon (2.5 mg/L). To assess the potential for bioremediation of polluted groundwater in situ, enrichment cultures of anammox, nitrifying, and denitrifying bacteria were obtained and analyzed. Fed-batch enrichment of anammox bacteria was not successful. Stable removal of ammonium and nitrite (up to 100%) was achieved in a continuous-flow reactor packed with a nonwoven fabric at 15 °C, and enrichment in anammox bacteria was confirmed by FISH and qPCR assays. The relatively low total N removal efficiency (up to 55%) was due to nonstoichiometric nitrate buildup. This phenomenon can be explained by a shift in the metabolism of anammox bacteria towards the production of more nitrates and less N2 at low temperatures compared to the canonical stoichiometry. In addition, the too high an estimate of specific anammox activity suggests that N cycle microbial groups other than anammox bacteria may have contributed significantly to N removal. Stable nitrite production was observed in the denitrifying enrichment culture, while no "conventional" nitrifiers were found in the corresponding enrichment cultures. Xanthomonadaceae was a common taxon for all microbial communities, indicating its exclusive role in this ecosystem. This study opens up new knowledge about the metabolic capabilities of N cycle bacteria and potential approaches for sustainable bioremediation of heavily N-polluted cold ecosystems.

Effective restoration of partial nitritation and anammox biofilm process by short-term hydroxylamine dosing: Mechanism and microbial interaction

The one-stage partial nitritation and anammox (PN-A) process frequently experiences deterioration from ammonium accumulation and nitrate build-up. In this study, hydroxylamine was dosed to restore the process from deterioration in a continuously aerated PN-A sequencing biofilm batch reactor, and the impact of hydroxylamine on the metabolism of PN-A process was studied. PN-A process was totally restored in 5 days via 10 mg N·L-1 hydroxylamine dosing, reducing nitrate-produced/ammonium-removed ratio from 28.5% to less than 11.0%. hydroxylamine dosing promoted biological production of nitric oxide and nitrous oxide and reduced the production of nitrate in the PN-A process. This study advanced the understanding of the metabolism versatility of hydroxylamine and nitric oxide as well as their function in interaction between aerobic ammonium oxidation bacteria and anaerobic ammonium oxidation bacteria, and proposed the potential application of hydroxylamine dosing in ammonium-contained wastewater treatment.

Start-up of PN-anammox system under low inoculation quantity and its restoration after low-loading rate shock

Partial nitritation (PN)-anaerobic ammonium oxidation (anammox) is a promising pathway for the biological treatment of wastewater. However, the destruction of the system caused by excessive accumulation of nitrate in long-term operation remains a challenge. In this study, PN-anammox was initialized with low inoculation quantity in an air-lift reactor. The nitrogen removal rate of 0.71 kgN/(m3 · d) was obtained, which was far higher than the seed sludge (0.3 kgN/(m3 · d)). Thereafter, excess nitrate build-up was observed under low-loading conditions, and recovery strategies for the PN-anammox system were investigated. Experimental results suggest that increasing the nitrogen loading rate as well as the concentration of free ammonium failed to effectively suppress the nitrite oxidation bacteria (NOB) after the PN-anammox system was disrupted. Afterwards, effluent back-flow was added into the reactor to control the up-flow velocity. As a result, an aggressive discharge of sludge that promoted the synergetic growth of functional bacteria was achieved, leading to the successful restoration of the PN-anammox system. The partial nitritation and anammox activity were in balance, and an increase in nitrogen removal rate up to 1.07 kgN/(m3 · d) was obtained with a nitrogen removal efficiency of 82.4% after recovery. Besides, the proportion of granular sludge (over 200 µm) increased from 33.67% to 82.82%. Ammonium oxidation bacteria (AOB) along with anammox bacteria were enriched in the granular sludge during the recovery period, which was crucial for the recovery and stable operation of the PN-anammox system.

Is Anoxic Operation Effective to Control Nitrate Build-Up and Sludge Loss for the Combined Partial Nitritation and Anammox (CPNA) Process?

There were three main issues of long start-up period, nitrate build-up and sludge loss during the operation of combined partial-nitritation anammox (CPNA). To fully start up the CPNA reactor, the fast achievement of partial-nitritation (PN) was the first step. Firstly, the PN process was successfully achieved within 22 days by 2 mg·L−1 hydroxylamine (NH2OH) addition and online intermittent aeration control at 0.2~0.3 mg·L−1 dissolved oxygen (DO). Then, a novel strategy of adding anoxic stirring phase between feeding and aeration period during CPNA operation was applied. It was shown effective to control nitrate build-up since the mole ratio of NO3−-N production and NH4+-N removed (MNRR) was mostly below 15%. Also, the procedure adjustment was proven useful to alleviate sludge loss by sustaining filamentous bacteria that could act as biomass framework and reduce nitrate substrate. The filamentous denitrifying bacteria could cause sludge bulking. The total nitrogen removal rate (TNRR) varied from 0.20 to 0.45 kg·m−3·d−1 during CPNA operation. In Stage III, after adding anoxic stirring phase, the abundance of nitrogen transformation functional microorganism’s nitrite oxidizing bacteria (NOB) was below 1.6%, which was one order of magnitude lower than Anammox and ammonia oxidizing bacteria (AOB).

Increased SCR performance of Cu-CHA due to ammonium nitrate buffer: Experiments with oscillating NO/NO2 ratios and application to real driving cycles

Currently, the literature on ammonium nitrate formation across SCR catalysts mainly sees ammonium nitrate formation as an undesired problem because it can inhibit the catalytic activity. This paper shows that, besides the inhibition effects, ammonium nitrate formation on the catalyst can also positively influence the catalytic activity because it acts as an NO2 buffer that stores NO2 under NO2-excess conditions and releases NO2 under NO2-deficient conditions.To demonstrate the working principle of the ammonium nitrate buffer, in a first step the ammonium nitrate loading is determined as a function of the NO2/NOx ratio in the feed, using a titration scheme recently proposed in the literature. Then, step tests are performed where at otherwise constant feed conditions, the NO2/NOx ratio is switched between 75 % NO2/NOx and 25 % NO2/NOx. During the slow frequency switching (3 min per phase), an increased NOx conversion is observed after both the transition to NO2-rich and NO2-lean. This can be explained by a build-up of ammonium nitrate during NO2-rich and the consumption of ammonium nitrate during NO2-lean conditions owing to the enhanced SCR reaction. When the frequency of the NO2/NOx switches is increased to 30 s, the ammonium nitrate storage loading can no longer follow the fluctuations and stays at an intermediate level. During this scenario, the catalyst shows a constant high conversion close to the Fast SCR reaction.Finally, it is demonstrated that the ammonium nitrate buffer contributes to the overall NOx conversion during standard driving cycles. In particular, the NO2 emissions are predicted significantly better by a model that accounts for the ammonium nitrate storage equilibrium.

Nitrates as a Potential N Supply for Microbial Ecosystems in a Hyperarid Mars Analog System.

Nitrate is common in Mars sediments owing to long-term atmospheric photolysis, oxidation, and potentially, impact shock heating. The Atacama Desert in Chile, which is the driest region on Earth and rich in nitrate deposits, is used as a Mars analog in this study to explore the potential effects of high nitrate levels on growth of extremophilic ecosystems. Seven study sites sampled across an aridity gradient in the Atacama Desert were categorized into 3 clusters—hyperarid, middle, and arid sites—as defined by essential soil physical and chemical properties. Intriguingly, the distribution of nitrate concentrations in the shallow subsurface suggests that the buildup of nitrate is not solely controlled by precipitation. Correlations of nitrate with SiO2/Al2O3 and grain sizes suggest that sedimentation rates may also be important in controlling nitrate distribution. At arid sites receiving more than 10 mm/yr precipitation, rainfall shows a stronger impact on biomass than nitrate does. However, high nitrate to organic carbon ratios are generally beneficial to N assimilation, as evidenced both by soil geochemistry and enriched culturing experiments. This study suggests that even in the absence of precipitation, nitrate levels on a more recent, hyperarid Mars could be sufficiently high to benefit potentially extant Martian microorganisms.

On the contribution of nocturnal heterogeneous reactive nitrogen chemistry to particulate matter formation during wintertime pollution events in Northern Utah

Abstract. Mountain basins in Northern Utah, including the Salt Lake Valley (SLV), suffer from wintertime air pollution events associated with stagnant atmospheric conditions. During these events, fine particulate matter concentrations (PM2.5) can exceed national ambient air quality standards. Previous studies in the SLV have found that PM2.5 is primarily composed of ammonium nitrate (NH4NO3), formed from the condensation of gas-phase ammonia (NH3) and nitric acid (HNO3). Additional studies in several western basins, including the SLV, have suggested that production of HNO3 from nocturnal heterogeneous N2O5 uptake is the dominant source of NH4NO3 during winter. The rate of this process, however, remains poorly quantified, in part due to limited vertical measurements above the surface, where this chemistry is most active. The 2017 Utah Winter Fine Particulate Study (UWFPS) provided the first aircraft measurements of detailed chemical composition during wintertime pollution events in the SLV. Coupled with ground-based observations, analyses of day- and nighttime research flights confirm that PM2.5 during wintertime pollution events is principally composed of NH4NO3, limited by HNO3. Here, observations and box model analyses assess the contribution of N2O5 uptake to nitrate aerosol during pollution events using the NO3- production rate, N2O5 heterogeneous uptake coefficient (γ(N2O5)), and production yield of ClNO2 (φ(ClNO2)), which had medians of 1.6 µg m−3 h−1, 0.076, and 0.220, respectively. While fit values of γ(N2O5) may be biased high by a potential under-measurement in aerosol surface area, other fit quantities are unaffected. Lastly, additional model simulations suggest nocturnal N2O5 uptake produces between 2.4 and 3.9 µg m−3 of nitrate per day when considering the possible effects of dilution. This nocturnal production is sufficient to account for 52 %–85 % of the daily observed surface-level buildup of aerosol nitrate, though accurate quantification is dependent on modeled dilution, mixing processes, and photochemistry.

Pseudogene YdfW in Escherichia coli decreases hydrogen production through nitrate respiration pathways

Escherichia coli has approximately 4300 open reading frames and about 178 of them are annotated as pseudogenes. The existence of the pseudogenes in E. coli had raised the question of whether they contribute to any cell function. Recently, several pseudogenes have been studied; however, these genes are still considered rare and tend to be ignored as so-called junk. Our recent study has shown several pseudogenes in E. coli are essential in hydrogen metabolism. ydfW is one of the pseudogenes associated with hydrogen metabolism. Here, we found carbon dioxide and nitrate in the fermentation medium of mutant ydfW suggesting that this strain may induce nitrate pathways. The Fdh-N complex is comprised of FdnG, FdnH, and FdnI subunits which correspond to the nitrate-nitrite pathway. This finding is supported by transcription analysis that shows formate dehydrogenase (fdnG) and nitrate reductase (narG) are significantly induced (25- and 18-fold, respectively). FdnG and NarG play a significant role in the reduction of nitrate into nitrite; hence, their genes are induced by the build-up of nitrate. Based on in silico docking analysis, we predict that YdfW is covalently bound to the Fdh-N complex in the cytoplasm. Hence, deletion of ydfW is expected has influenced the nitrate-nitrite pathway. Subsequently, the situation will affect the hydrogen production in E. coli.

Accelerated start-up of a partial nitritation-anammox moving bed biofilm reactor

The formation of anammox biofilm is a lengthy process, leading to reactor start-up times of several months even with addition of anammox inoculum. To demonstrate the effectiveness of combining bio-primer technique with seed carriers in further accelerating the start-up time of anammox reactors a pilot moving bed biofilm reactor was set-up at a dewatering facility of a municipal wastewater treatment plant. The reactor was filled to 40% with plastic media with a specific surface area of 402 m2 m−3 and was operated at 34 ± 1 °C. Using bio-primer coated media it was shown that a surface nitrogen removal rate of 2.5 g-N m-2 d-1 could be achieved in as little as 56 days. Free ammonia (FA) was thought to be the predominant inhibitor of nitrite oxidizing bacteria activity rather than the selective wash-out of nitrifying biomass. A minimum FA concentration of 2 mg NH3-N L-1 was suggested for optimal performance of partial nitritation and to prevent the build-up of nitrates. Biomass from the pilot reactor had developed a specific anammox activity of 19 ± 2 mg-N g-VSS-1 h-1 which was 75% higher than the seed biomass from an anammox-only reactor fed with synthetic wastewater.

No evidence for higher agronomic N use efficiency or lower nitrous oxide emissions from enhanced efficiency fertilisers in aerobic subtropical rice

Enhanced efficiency nitrogen (N) fertilisers (EENFs) contain chemical urease or nitrification inhibitors, or physical barriers (e.g. polymer coating) to minimise the rapid build-up of nitrate (NO3−) in soils. They have the potential to improve N use efficiency and lower N2O emissions from soils. However, evidence of the efficacy of EENFs in warm, wet subtropical conditions is lacking. We therefore developed N response curves (0, 30, 60, 90, 120 and 150 kg N ha-1) for urea, polymer coated urea (PCU), 3,4-dimethylpyrazole phosphate (DMPP)-urea (Entec®), N-(n-butyl) thiophosphoric triamide (NBPT)-urea (Green urea®) and a carbon-coated urea (Black urea®) in subtropical, aerobic rice (Oryza sativa L) crops in two fields with contrasting soils (Gleysol and Histosol), and quantified N2O emissions from nil-N and 90 kg N ha-1 treatments for all EENFs and urea. In the Gleysol, cumulative in-crop N2O emissions were relatively high (approximately 2 kg N2O-N ha-1 season-1 with 90 kg N ha-1 applied) with no significant mitigation from any EENFs compared to urea. Grain yield data fitted with an exponential model indicated that 95% of the estimated maximum grain yield (6.8 t ha-1 at 14% moisture) was achieved with 81 kg N ha-1 for the urea treatment. The yield response curves for all tested EENF products did not differ significantly from the urea-N yield response curve. In the Histosol, cumulative in-crop N2O emissions were negligible (around 0.05 kg N2O-N ha-1 season-1), with no significant difference (p < 0.05) between N fertiliser or nil-N treatments, and 95% of the estimated maximum grain yield (5.63 t ha-1 at 14% moisture) was achieved with only 11 kg N ha-1 for urea. There was no evidence that EENFs could achieve the maximum yield at a lower applied N rate. We hypothesised that the low soil pH of 4.9 (1:5 CaCl2 extract) may have inhibited nitrification in the Histosol, leading to low N2O emissions and a limited response to N fertiliser. Ultimately, the results of this study found no evidence that EENF products could improve agronomic N use efficiency or lower N2O emissions in the two aerobic rice crops studied.

Performances and microbial characteristics of granular sludge for autotrophic nitrogen removal from synthetic and mainstream domestic sewage

The completely autotrophic nitrogen removal over nitrite (CANON) process is an important component of energy self-sufficient sewage treatment plants, and the use of aerobic granular sludge is a profitable choice for the CANON process. In this study, the performance and microbial characteristics of CANON granular sludge were investigated for treating synthetic and mainstream domestic sewage. The average nitrogen removal rate (NRR) was 3.22 kg N m−3 d−1 during the high-rate operating period with high MLSS (4.09 g L−1) and DO (∼1.0 mg L−1) for treating synthetic sewage. When the influent was mainstream sewage, the average NRR was 1.11 kg N m−3 d−1. The effluent nitrate concentration was very low, and nitrate build-up was not found. High-throughput pyrosequencing results indicated that, Nitrosomonas and Candidatus Brocadia were the dominant genus in ammonia oxidizing bacteria (AOB) and anaerobic AOB (AAOB), respectively. The proportions of AOB and AAOB decreased during mainstream sewage treatment, but the reactor maintained good performance. The results confirmed the feasibility of using CANON granular sludge for treating mainstream sewage.

Vadose zone processes delay groundwater nitrate reduction response to BMP implementation as observed in paired cultivated vs. uncultivated potato rotation fields

Nitrate leaching from crop production contributes to groundwater contamination and subsequent eutrophication of the receiving surface water. A study was conducted in a 7-ha potato-grain-forages rotation field in Prince Edward Island (PEI), Canada during 2011–2016 to link potato rotation practices and groundwater quality. The field consists of fine sandy loam soil and is underlain by 7–9 m of glacial till, which overlies the regional fractured “red-bed” sandstone aquifer. The water table is generally located in overburden close to the bedrock interface. Field treatments included one field zone taken out of production in 2011 with the remaining zones kept under a conventional potato rotation. Agronomy data including crop tissue, soil, and tile-drain water quality were collected. Hydrogeology data including multilevel monitoring of groundwater nitrate and hydraulic head and data from rock coring for nitrate distribution in overburden and bedrock matrix were also collected. A significant amount of nitrate leached below the soil profile after potato plant kill (referred to as topkill) in 2011, most of it from fertilizer N. A high level of nitrate was also detected in the till vadose zone through coring in December 2012 and through multilevel groundwater sampling from January to May 2014 in both cultivated and uncultivated field zones. Groundwater nitrate concentrations increased for about 2.5 years after the overlying potato field was removed from production. Pressure-driven uniform flow processes dominate water and nitrate transport in the vadose zone, producing an apparently instant water table response but a delayed groundwater quality response to nitrate leaching events. These data suggest that the uniform flow dominated vadose zone in agricultural landscapes can cause the accumulation of a significant amount of nitrate originated from previous farming activities, and the long travel time of this legacy nitrate in the vadose zone can result in substantially delayed responses of groundwater quality to field management adjustments. The delayed effects should also apply to the transport of other contaminants. This study also suggests that management practices should be optimized to reduce soil nitrate build-up during the non-growing season (when plant N uptake is diminishing and the soil contains excessive moisture, for example, after the potato harvest period in PEI) in order to protect groundwater quality.

Sorghum–Sudangrass Responses to Nitrogen and Tillage following Polyphenol‐Containing Legumes, Alfalfa, Reed Canarygrass, and Kale

Core Ideas Low concentrations of polyphenols in forage legumes had no impact on sorghum–sudangrass production. Sorghum–sudangrass dry matter yield and N uptake were related to herbage N yield from prior forages. Tillage enhanced sorghum–sudangrass production especially after reed canarygrass. Adjusting fertilizer N based on crop sequence and tillage practices avoids soil nitrate buildup. The collective effects of protein‐binding polyphenols (PBP), preceding forage type, tillage, and fertilizer N on soil nitrate production, N uptake, and dry matter yield (DMY) of N‐demanding crops such as sorghum–sudangrass [SS, Sorghum bicolor (L.) Moench × S. sudanese Piper] are poorly understood. These factors and response variables were evaluated in Wisconsin by growing SS for 2 yr with two harvests yr−1 using no‐tillage or conventional‐tillage and fertilizer N rates of 0, 33, 67, 112, or 220 kg N ha−1 harvest−1 following 1‐yr stands of birdsfoot trefoil (Lotus corniculatus L.) containing condensed tannins (CT), o‐quinone producing red clover (Trifolium pratense L.), alfalfa (Medicago sativa L.), reed canarygrass (Phalaris arundinacea L.), and kale (Brassica oleracea L.). Herbage PBP was associated with reduced in vitro soil NO3–N accumulation, whereas herbage nitrogen yield (NY) primarily affected in situ soil NO3–N accretion and N uptake and DMY of SS. The DMY of first‐year sorghum–sudangrass (SS1) following legumes exceeded that following kale in both tillage systems, but rotational benefits of grass equaled legumes when conventional tillage was used. To maximize net return, SS1 required 75 kg N ha−1 harvest−1 following legumes and 125 kg N ha−1 harvest−1 following nonlegumes. Depending on tillage system and harvest, SS2 required 50 to 130 kg N ha−1 harvest−1 to maximize net return. To optimize DMY and profitability of SS following short‐term forages, producers should grow legumes to maximize NY before SS production, use conventional tillage following reed canarygrass, and adjust N rates according to crop sequence and tillage practices.

Research on the removal of nitrogen pollutants in source water by EBO system

.This paper describes an innovative process to solve the nitrate build-up problem using enhanced bio-contact oxidation system in situ (EBO system). The novel aspects of the process lay in the EBO system that is enhanced by a multifunctional device for water lifting and aeration (MDWLA) which has widely been applied in improving the source water quality in China. The reservoir water employed to study the nitrogen removal capacity of EBO system. The results showed that the EBO systems filled with Kaldnes suspended packing and sponge balls suspended packing respectively could efficiently remove ammonia, nitrate, nitrite, total nitrogen, COD, and turbidity from polluted surface water under conditions of dissolved oxygen 3.0∼4.0 mg L-1 and temperature 24∼28°C. Particularly, the maximum efficiencies of ammonia, nitrate, total nitrogen and turbidity in EBO system could reach above 71%, 76%, 77% and 90%.

In-situ restoration of one-stage partial nitritation-anammox process deteriorated by nitrate build-up via elevated substrate levels.

The one-stage partial nitritation and anammox process (PN/A) has been a promising microbial process to remove ammonia from wastewater especially with low carbon/nitrogen ratio. The main breakdown was the deterioration caused by overgrowth of nitrite oxidizing bacteria (NOB) resulting effluent nitrate build-up in the PN/A process. This study presented an in-situ restoring strategy for suppressing NOB activity in a one-stage granular PN/A system deteriorated over 2 months, using elevated concentrations of substrates (ammonia and nitrite) under limited dissolved oxygen level. The results showed that the NOB activity was successfully suppressed after 56 days of restoration, and finally the ratio of produced nitrate/consumed ammonium was reduced from 36.8% to 7%. On day 66 the nitrogen removal rate obtained as 1.2 kg N/(m3·d). The high FA level (5–40 mg/L) and low dissolved oxygen (<0.13 mg/L) were responsible for NOB suppression. From quantitative PCR (qPCR) analysis, after this restoration, anammox bacteria had a widely growth, and AOB stay stable, but Nitrospira increase and Nitrobacter declined. High amount of NOB was still persistent in the granules, which was not easy to wash-out and threaten the deammonification performance.

Start-up of single-stage partial nitrification-anammox process treating low-strength swage and its restoration from nitrate accumulation

A single-stage partial nitrification-anammox (PN/A) reactor treating low-strength swage was operated for 288days to investigate the recovery of nitrogen removal from nitrate accumulation. The reactor was quickly started up by inoculating anammox sludge. However, nitrite oxidizing bacteria (NOB) abundance gradually increased on day 25, leading to high effluent nitrate concentration. Two strategies were executed to control the effluent nitrate. In strategy I, dissolved oxygen (DO) concentration was kept low (0.17±0.08mg/L), but nitrate production increased from 4.71 to 38.18mg-N/L. In strategy II, intermittent aeration operation mode (aeration 7min/anoxic 21min) was adopted, which significantly lowered the nitrate concentration to 1.3mg-N/L, indicating the NOB was inhibited. The high nitrogen removal rate of 73mg-N/(L·d) was achieved. The evolution of bacterial activity and abundance verified the changes of the nitrogen removal performance and proved the intermittent aeration strategy could successfully solve the problem of nitrate build-up in the PN/A process.