Nitrate Yield Research Articles

Enhancing removal of nitrates from highly concentrated synthetic wastewaters using bipolar Si/BDD cell: Optimization and mechanism study

Electrochemical denitrification of highly concentrated synthetic wastewaters was investigated using bipolar Boron-Doped Diamond on silicone substrate (Si/BDD) electrodes under various experimental conditions. The effects of the key operational parameters on the removal efficiency of nitrates were assessed using the Response Surface Methodology. Results showed that the efficiency of removal of nitrates was mostly sensitive to the applied current density and the duration of treatment, which are optimized, respectively, at 35.7mAcm−2 and 120min. Under these experimental conditions, the removal yield of nitrates was evaluated at 91% with formation of by-products of 0.4% and 3.6% of nitrites and ammonia, respectively. Furthermore, average current efficiency is optimized at 59% with an energy consumption estimated at 0.35×10−3kWh(g-N)−1.To better understand the role of BDD anode/cathode, by-products electrogeneration and disappearance, as well as the effect of chloride ions on pathway electrochemical denitrification, series of experiments were carried out at three concentrations of NaCl. The kinetic constants were calculated using a pseudo first-order kinetic model based on the fitting of the experimental data to established numerical approximations using Matlab software. At first, we noted that the direct reduction to N2 in the absence of NaCl was very low (k=1.7×10−9s−1) compared to NH3 and NO2− electrogeneration (k=1.7×10−5 and 5.4×10−4s−1, respectively), where N2 seemed to be the result of a reduction in by-products. The presence of hypochlorous species had a negligible effect on the kinetic rates of NO3−reduction.

Assessment of changes in riverine nitrate in the Sesan, Srepok and Sekong tributaries of the Lower Mekong River Basin

Abstract Changes in nitrates are of particular concern in tropical regions undergoing rapid development, as these changes may affect local and downstream riverine ecosystems. This study assessed the spatial and temporal differences in nitrate loads within the Sesan, Srepok, and Sekong (3S) Rivers, the largest tributaries of the Mekong River. Simulation results from a flow and nitrate calibrated SWAT model show large differences in year-to-year nitrate loads, a strong seasonality, and clear variability patterns in monthly nitrate loads in the 3S outlet during the wet season. The annual total nitrate loading from the 3S Rivers account for approximately 30% of the total nitrate load of the Mekong River at Pakse. Nitrate loads during the rainy season accounts for 79% of the total annual load into the Mekong River. The Sesan, Sekong, and Srepok basins have average nitrate yields of 400, 330, and 290 kg N/km 2 , respectively, which is comparable with other forested catchments, but much lower than agriculture dominated catchments in the tropics. Simulations of three future climate scenarios show little variability in annual nitrate loadings under current land use/land cover (LULC), but seasonal difference in nitrate loading during rainy months was observed. Further research is needed to estimate nitrate loads in the 3S basin as influenced by LULC change and dam development, which may potentially result in complex changes to local and downstream riverine ecosystems.

Watershed-scale changes in terrestrial nitrogen cycling during a period of decreased atmospheric nitrate and sulfur deposition

Recent reports suggest that decreases in atmospheric nitrogen (N) deposition throughout Europe and North America may have resulted in declining nitrate export in surface waters in recent decades, yet it is unknown if and how terrestrial N cycling was affected. During a period of decreased atmospheric N deposition, we assessed changes in forest N cycling by evaluating trends in tree-ring δ15N values (between 1980 and 2010; n = 20 trees per watershed), stream nitrate yields (between 2000 and 2011), and retention of atmospherically-deposited N (between 2000 and 2011) in the North and South Tributaries (North and South, respectively) of Buck Creek in the Adirondack Mountains, USA. We hypothesized that tree-ring δ15N values would decline following decreases in atmospheric N deposition (after approximately 1995), and that trends in stream nitrate export and retention of atmospherically deposited N would mirror changes in tree-ring δ15N values. Three of the six sampled tree species and the majority of individual trees showed declining linear trends in δ15N for the period 1980–2010; only two individual trees showed increasing trends in δ15N values. From 1980 to 2010, trees in the watersheds of both tributaries displayed long-term declines in tree-ring δ15N values at the watershed scale (R = −0.35 and p = 0.001 in the North and R = −0.37 and p <0.001 in the South). The decreasing δ15N trend in the North was associated with declining stream nitrate concentrations (−0.009 mg N L−1 yr−1, p = 0.02), but no change in the retention of atmospherically deposited N was observed. In contrast, nitrate yields in the South did not exhibit a trend, and the watershed became less retentive of atmospherically deposited N (−7.3% yr−1, p < 0.001). Our δ15N results indicate a change in terrestrial N availability in both watersheds prior to decreases in atmospheric N deposition, suggesting that decreased atmospheric N deposition was not the sole driver of tree-ring δ15N values at these sites. Other factors, such as decreased sulfur deposition, disturbance, long-term successional trends, and/or increasing atmospheric CO2 concentrations, may also influence trends in tree-ring δ15N values. Furthermore, declines in terrestrial N availability inferred from tree-ring δ15N values do not always correspond with decreased stream nitrate export or increased retention of atmospherically deposited N.

Episodic, seasonal, and annual export of atmospheric and microbial nitrate from a temperate forest

AbstractIt remains difficult to assess the timing and amount of atmospherically deposited and microbial nitrate (NO3‐NAtm and NO3‐NMicro, respectively) reaching streams. To elucidate temporal variation of NO3‐NAtm and NO3‐NMicro, we measured nitrate concentrations, δ17O‐NO3−, and δ18O‐NO3− in a stream draining a gaged, forested watershed in the central Appalachian Mountains throughout a range of hydrological conditions during two water years. From the isotopic data we calculated Δ17O‐NO3− values, which were used to calibrate a statistical load model to estimate export of NO3‐NAtm and NO3‐NMicro. A hydrograph separation was used to estimate loss of NO3‐NAtm and NO3‐NMicro through base flow and direct runoff pathways. NO3‐NAtm contributed 7–11% of the total nitrate yields and paralleled seasonal patterns of NO3‐NMicro. Yields of NO3‐NAtm and NO3‐NMicro in streamflow during the study period were dominated (61 and 85%, respectively) by base flow transport, suggesting that base flow is a major loss pathway for both nitrate species from this watershed.

Organic nitrate aerosol formation via NO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; + biogenic volatile organic compounds in the southeastern United States

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Gas- and aerosol-phase measurements of oxidants, biogenic volatile organic compounds (BVOCs) and organic nitrates made during the Southern Oxidant and Aerosol Study (SOAS campaign, Summer 2013) in central Alabama show that a nitrate radical (NO&lt;sub&gt;3&lt;/sub&gt;) reaction with monoterpenes leads to significant secondary aerosol formation. Cumulative losses of NO&lt;sub&gt;3&lt;/sub&gt; to terpenes are correlated with increase in gas- and aerosol-organic nitrate concentrations made during the campaign. Correlation of NO&lt;sub&gt;3&lt;/sub&gt; radical consumption to organic nitrate aerosol formation as measured by aerosol mass spectrometry and thermal dissociation laser-induced fluorescence suggests a molar yield of aerosol-phase monoterpene nitrates of 23–44 %. Compounds observed via chemical ionization mass spectrometry (CIMS) are correlated to predicted nitrate loss to BVOCs and show C&lt;sub&gt;10&lt;/sub&gt;H&lt;sub&gt;17&lt;/sub&gt;NO&lt;sub&gt;5&lt;/sub&gt;, likely a hydroperoxy nitrate, is a major nitrate-oxidized terpene product being incorporated into aerosols. The comparable isoprene product C&lt;sub&gt;5&lt;/sub&gt;H&lt;sub&gt;9&lt;/sub&gt;NO&lt;sub&gt;5&lt;/sub&gt; was observed to contribute less than 1 % of the total organic nitrate in the aerosol phase and correlations show that it is principally a gas-phase product from nitrate oxidation of isoprene. Organic nitrates comprise between 30 and 45 % of the NO&lt;sub&gt;&lt;I&gt;y&lt;/I&gt;&lt;/sub&gt; budget during SOAS. Inorganic nitrates were also monitored and showed that during incidents of increased coarse-mode mineral dust, HNO&lt;sub&gt;3&lt;/sub&gt; uptake produced nitrate aerosol mass loading at a rate comparable to that of organic nitrate produced via NO&lt;sub&gt;3&lt;/sub&gt; + BVOCs.&lt;/p&gt;

Kinetic Constants for Biological Ammonium and Nitrite Oxidation Processes Under Sulfide Inhibition.

Inhibition of nitrification by sulfide was assessed using sludge obtained from a steady-state nitrifying reactor. Independent batch activity assays were performed with ammonium and nitrite as substrate, in order to discriminate the effect of sulfide on ammonium and nitrite oxidation. In the absence of sulfide, substrate affinity constants (K S,NH4 = 2.41 ± 0.11mg N/L; K s, NO2 = 0.74 ± 0.03mg N/L) and maximum specific rates (q max,NH4 = 0.086 ± 0.008mg N/mg microbial proteinh; q max,NO2 = 0.124 ± 0.001mg N/mg microbial proteinh) were determined. Inhibition of ammonium oxidation was no-competitive (inhibition constant (K i , NH4 ) of 2.54 ± 0.12mg HS(-)-S/L) while inhibition of nitrite oxidation was mixed (competitive inhibition constant (K' i , NO2 ) of 0.22 ± 0.03mg HS(-)-S/L and no-competitive inhibition constant (K i , NO2 ) of 1.03 ± 0.06mg HS(-)-S/L). Sulfide has greater inhibitory effect on nitrite oxidation than ammonium oxidation, and its presence in nitrification systems should be avoided to prevent accumulation of nitrite. By simulating the effect of sulfide addition in a continuous nitrifying reactor under steady-state operation, it was shown that the maximum sulfide concentration that the sludge can tolerate without affecting the ammonium consumption efficiency and nitrate yield is 1mg HS(-)-S/L.

Controls and forecasts of nitrate yields in forested watersheds: A view over mainland Portugal

A study on nitrate yields was conducted in forested watersheds of mainland Portugal. The prime goal was to rank parameters in descending order of their contribution to the export of nitrate towards streams and lakes. To attain the goal, variables like soil loss, rainfall intensity, topography, soil type, forest composition and environmental disturbances such as hardwood harvesting or wildfires were organized in a conceptual yield model. Because some parameters were potentially collinear, a robust multivariate statistical technique was selected to execute the conceptual model and perform the aforementioned ranking, namely Partial Least Squares (PLS) regression. This technique was tested with a sample of 60 forested watersheds (>70% of forest occupation), being subject to a double-validation process to ensure prediction capability. According to final regression coefficients, soil erosion seems to regulate nitrate distribution across the basins, because soil loss and type, rainfall intensity and topography explained around 60% of nitrate yield variance. The major importance of erosion is followed by a moderate role of biochemical processes such as nitrification or nutrient uptake, which accounted for approximately 15% of nitrate yield variance. In this case, deciduous forests and scrubland seem to behave as net sinks of nitrate while coniferous and mixed forests seem to act dually, as net sources or sinks. The least important parameters are the environmental disturbances, explaining no more than 5% of nitrate yield variance. The results of PLS regression were coupled in a scenario analysis with measures designed to protect soil from erosion and surface water from eutrophication. These interventions are to be implemented until 2045, according to regional plans of forest management. Considering the key role of erosion in explaining nitrate dynamics across the catchments, it was not surprising to verify that soil protection measures may reduce nitrate yields by some 35% of their current values.

The role of precipitation type, intensity, and spatial distribution in source water quality after wildfire

Storms following wildfires are known to impair drinking water supplies in the southwestern United States, yet our understanding of the role of precipitation in post-wildfire water quality is far from complete. We quantitatively assessed water-quality impacts of different hydrologic events in the Colorado Front Range and found that for a three-year period, substantial hydrologic and geochemical responses downstream of a burned area were primarily driven by convective storms with a 30 min rainfall intensity >10 mm h−1. These storms, which typically occur several times each year in July–September, are often small in area, short-lived, and highly variable in intensity and geographic distribution. Thus, a rain gage network with high temporal resolution and spatial density, together with high-resolution stream sampling, are required to adequately characterize post-wildfire responses. We measured total suspended sediment, dissolved organic carbon (DOC), nitrate, and manganese concentrations that were 10–156 times higher downstream of a burned area compared to upstream during relatively common (50% annual exceedance probability) rainstorms, and water quality was sufficiently impaired to pose water-treatment concerns. Short-term water-quality impairment was driven primarily by increased surface runoff during higher intensity convective storms that caused erosion in the burned area and transport of sediment and chemical constituents to streams. Annual sediment yields downstream of the burned area were controlled by storm events and subsequent remobilization, whereas DOC yields were closely linked to annual runoff and thus were more dependent on interannual variation in spring runoff. Nitrate yields were highest in the third year post-wildfire. Results from this study quantitatively demonstrate that water quality can be altered for several years after wildfire. Because the southwestern US is prone to wildfires and high-intensity rain storms, the role of storms in post-wildfire water-quality impacts must be considered when assessing water-quality vulnerability.

Nitrate reductase activity and yield of dry mass and protein content in cucumber seedlings supplied with nitrates and ammonium

The presence of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; ions in a nutrient solution containing NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt; with the K+ ions removed, caused an inhibition of nitrate reductase (NR) activity in cucumber leaves. The lack of K&lt;sup&gt;+&lt;/sup&gt; in a NaNO&lt;sub&gt;3&lt;/sub&gt; medium also decreased the NR activity. Addition of K&lt;sup&gt;+&lt;/sup&gt; to these media suppressed the inhibitory effect of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; and enhanced the NR activity in the leaves of plants growing in NaNO&lt;sub&gt;3&lt;/sub&gt; nutrient solution. The results suggest that K&lt;sup&gt;+&lt;/sup&gt; is essential for NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; reduction, Na&lt;sup&gt;+&lt;/sup&gt; is less effective in this process, whereas NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; ions markedly inhibit NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; reduction. The protein content and increment of dry mass of cucumber plants grown 10 days with NH&lt;sub&gt;4&lt;/sub&gt;-N as the sole source of nitrogen was significantly lower as compared with NO&lt;sub&gt;3&lt;/sub&gt;-N supplied plants feed with plants feed with both forms of mineral nitrogen (NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt;). The results show that cucumber prefers the nitrates, although it can utilize the ammonium form of nitrogen.

The photochemical production of organic nitrates from α-pinene and loss via acid-dependent particle phase hydrolysis

The hydroxyl radical oxidation of α-pinene under high NOx conditions was studied in a photochemical reaction chamber to investigate organic nitrate (RONO2) production and fate between the gas and particle phases. We report an organic nitrate yield of 26 ± 7% from the oxidation of this monoterpene in the presence of nitric oxide (NO). However, the apparent organic nitrate yield was found to be highly dependent on both chamber relative humidity (RH) and seed aerosol acidity, likely as a result of particle phase hydrolysis. The particle phase loss of organic nitrates is believed to increase the gas to particle partitioning within the system, leading to decreased RONO2 yields in both the gas and particle phases at elevated RH and an apparent non-equilibrium partitioning mechanism. The hydrolysis of particle phase organic nitrates in this study, starting at low chamber relative humidity, implies that aerosol partitioning of organic nitrates may be an important sink for atmospheric NOx and may have a significant impact on regional air quality.

Simulating the impacts of bio-fuel crop production on nonpoint source pollution in the Upper Mississippi River Basin

The perpetuation of current trend of growing more corn for ethanol is projected to further exacerbate water quality problems in the Upper Mississippi River Basin (URMB). Switchgrass with cellulosic ethanol potential which requires no or little fertilizers can be effective in reducing nonpoint source pollutants such as nitrate and sediments. In this study, the Soil and Water Assessment Tool model was applied to the UMRB to simulate and evaluate the impacts of two bio-fuel crops (corn and switchgrass) on nonpoint source pollution. High impact areas to which a large amount of pollutants are attributed were identified by simulating and analyzing nitrate outputs from 131 subbasins. Simulation results showed that growing switchgrass instead of corn could reduce nitrate yield by up to 71% (14kg/ha) and sediments by up to 99% (5t/ha). It is demonstrated that water quality in the UMRB can be significantly improved and meanwhile economic benefits can still be derived. The results of this study can assist in cost-benefit analysis and decision-making in environmental management in large-scale agricultural areas.

Secondary organic aerosol formation and organic nitrate yield from NO3 oxidation of biogenic hydrocarbons.

The secondary organic aerosol (SOA) mass yields from NO3 oxidation of a series of biogenic volatile organic compounds (BVOCs), consisting of five monoterpenes and one sesquiterpene (α-pinene, β-pinene, Δ-3-carene, limonene, sabinene, and β-caryophyllene), were investigated in a series of continuous flow experiments in a 10 m3 indoor Teflon chamber. By making in situ measurements of the nitrate radical and employing a kinetics box model, we generate time-dependent yield curves as a function of reacted BVOC. SOA yields varied dramatically among the different BVOCs, from zero for α-pinene to 38–65% for Δ-3-carene and 86% for β-caryophyllene at mass loading of 10 μg m–3, suggesting that model mechanisms that treat all NO3 + monoterpene reactions equally will lead to errors in predicted SOA depending on each location’s mix of BVOC emissions. In most cases, organonitrate is a dominant component of the aerosol produced, but in the case of α-pinene, little organonitrate and no aerosol is formed.

Precise determination of precipitation yield of uranyl nitrate with N-alkylated 2-pyrrolidone derivatives

Yields of precipitated UO2(NO3)2(NRP)2 (NRP = N-alkylated 2-pyrrolidone) were precisely determined by considering reduction of the solution volume through the precipitation, which can be estimated from difference in acid concentrations of the liquid phases before and after the precipitation. The studied NRPs were N-n-butyl (NBP) and N-n-propyl (NProP) derivatives. In both systems, the precipitation yields precisely determined were always higher than those simply calculated from the ratio of uranium concentrations before and after the precipitation. However, the differences between them are in the range of 0.6%–2.6%. If such a difference is practically negligible, the volume reduction through the precipitation does not have to be taken into account for simplicity of the analytical manipulation.

The atmospheric oxidation mechanism of 1,2,4-trimethylbenzene initiated by OH radicals.

The atmospheric oxidation mechanism of 1,2,4-trimethylbenzene (1,2,4-TMB) initiated by OH radicals is investigated using quantum chemistry calculations at M06-2X and ROCBS-QB3 levels. The calculations show that the initiation of the reaction is dominated by OH addition to C1, C3 and C5 to form 1,2,4-TMB-OH adducts R1, R3, and R5 with branching ratios of 0.22, 0.19, and 0.38, respectively, using ROCBS-QB3 energies. In the troposphere, the adducts react with O2 by irreversible H-abstraction to form phenolic compounds and by reversible addition to TMB-OH-O2 peroxy radicals, which will cyclize to bicyclic radicals, similar to those in benzene, toluene, and xylenes. The bicyclic radicals can further recombine with O2 to generate bicyclic peroxy and alkoxyl radicals. The bicyclic alkoxyl radicals would break the ring directly to form 1,2-dicarbonyl products and unsaturated 1,4-dicarbonyl co-products, or undergo another cyclization to form an epoxy group, followed by the ring-breakage to form 1,2-dicarbonyl products and epoxy-1,4-dicarbonyl co-products. The predicted yields of products agree reasonably with the previous experimental measurements, while considerable discrepancies also exist for the yields of nitrates, biacetyl, 4-oxo-2-pentenal, and butenedial, etc. Our mechanism also predicts a new type of epoxy-1,4-dicarbonyl compounds with a total yield of ∼0.32. The epoxy-1,4-dicarbonyl compounds have not been suggested or reported in previous studies.

Variation in riverine nitrate flux and fall nitrogen fertilizer application in East-central illinois.

In east-central Illinois, fertilizer sales during the past 20 yr suggest that approximately half of the fertilizer nitrogen (N) applied to corn ( L.) occurs in the fall; however, fall fertilizer N sales were greatly reduced in 2009 as wet soil conditions restricted fall fieldwork, including fertilizer N applications. In 2010, we observed unusually low flow-weighted nitrate concentrations (approximately 40% below the long-term average) in two east-central Illinois rivers (5.7 mg N L in the Embarras River and 5.6 mg N L in the Lake Fork of the Kaskaskia River). Using long-term river nitrate data sets (1993-2012 for the Embarras and 1997-2012 for the Kaskaskia), we examined nitrate concentrations and developed regression models to estimate the association between fall fertilizer N application on riverine nitrate yields in these tile-drained watersheds. During these periods of record, annual riverine nitrate yields ranged from 8 to 57 kg N ha yr (30 kg N ha yr average) for the Embarras River and 2.6 to 59 kg N ha yr (32 kg N ha yr average) for the Kaskaskia. Multivariate linear regression relationships with the current and previous year's annual water yields, previous year's corn yield, and nine-county fall fertilizer sales accounted for 96% of the annual variation in nitrate yield in both watersheds. Running the regression models with fall fertilizer sales set to the 2009 amount suggests that the average reduction in nitrate yield (for the period of record) would be 17 and 20% for the Embarras and Kaskaskia Rivers, respectively. These data suggest that shifting fertilizer N application to the spring can be detected in watersheds as large as 481 km.

H 6 PMo 9 V 3 O 40 /SiO 2 催化剂催化酚类化合物选择性硝化

To establish a clean and efficient nitration process of phenolic compounds, heteropolyacid H6PMo9V3O40( PMAV3) and chromatographic silica gel were respectively chosen as active component and carrier for the preparation of a series of supported catalysts( PMAV3/ SiO2) via the conventional impregnation method. The catalysts were characterized by Fourier transform infrared spectroscopy( FTIR),X-ray diffraction( XRD),N2adsorption-desorption and thermogravimetry-differential scanning calorimetry( TG-DSC). The catalytic performance of catalysts was evaluated for the nitration of phenols. The results reveals that PMAV3/ SiO2exhibits excellent catalytic activity and regioselectivity for the nitration of phenols,the nitration yield is in the range of 83. 7% ~ 94. 5%. For salicylic acid,the para-selectivity is nearly 100%,but for phenol, 2-methylphenol,2-chlorophenol and 2-fluorphenol,the ortho-selectivity is observed. The textural properties of PMAV3/ SiO2are close to that of PMAV3,but BET of the supported catalysts is decreased with the rise of PMAV3loading. PMAV3/ SiO2shows better thermal stability than PMAV3. The catalyst can be recovered easily and reused for five times without noticeable drop in activity.

Alkyl Nitrate Formation from the Reactions of C8–C14n-Alkanes with OH Radicals in the Presence of NOx: Measured Yields with Essential Corrections for Gas–Wall Partitioning

In this study, C8-C14 n-alkanes were reacted with OH radicals in the presence of NO(x) in a Teflon film environmental chamber and isomer-specific yields of alkyl nitrates were determined using gas chromatography. Because results indicated significant losses of alkyl nitrates to chamber walls, gas-wall partitioning was investigated by monitoring the concentrations of a suite of synthesized alkyl nitrates added to the chamber. Gas-to-wall partitioning increased with increasing carbon number and with proximity of the nitrooxy group to the terminal carbon, with losses as high as 86%. The results were used to develop a structure-activity model to predict the effects of carbon number and isomer structure on gas-wall partitioning, which was used to correct the measured yields of alkyl nitrate isomers formed in chamber reactions. The resulting branching ratios for formation of secondary alkyl nitrates were similar for all isomers of a particular carbon number, and average values, which were almost identical to alkyl nitrate yields, were 0.219, 0.206, 0.254, 0.291, and 0.315 for reactions of n-octane, n-decane, n-dodecane, n-tridecane, and n-tetradecane, respectively. The increase in average branching ratios and alkyl nitrate yields with increasing carbon number to a plateau value of ∼0.30 at about C13-C14 is consistent with predictions of a previously developed model, indicating that the model is valid for alkane carbon numbers ≥C3.

The Influence of Digestate and Mineral Fertilisers on Yields and Content of Nitrates and Ascorbic Acid in Kohlrabi Bulbs

In a one-year vegetation pot experiment we compared the effect of the digestate from a biogas plant and mineral fertilisers on yield and quality parameters of kohlrabi, variety Moravia. Four treatments were used in the trial: 1) untreated control, 2) urea, 3) digestate, 4) urea, triple super phosphate, KCl, MgSO4. The rate of N was the same in treatments 2–4, i.e. 1.5 g N/pot. In treatment 4 the rate of P, K and Mg corresponded with the rate of these nutrients in the digestate treatment (3). The inhibited growth of kohlrabi after the application of NPKMg (4) was obviously the consequence of early planting after the application of fertilisers (5 days) and of the salinity of the small content of soil in the pot and resulted in the lowest weight of single bulbs (69 g), followed by the unfertilised control treatment (75 g). After the application of the digestate (treatment 3) the weight of single bulbs significantly increased (126 g) compared to the urea treatment (101 g) and all the other treatments. The content of ascorbic acid in the fertilised treatments did not differ (441–458 mg/kg) but it increased significantly compared to the unfertilised treatment (398 mg/kg). There were significant differences among all the fertilised treatments (1–2–3–4) in the bulb nitrate content (346–1,147–815–1,091 mg NO3−/kg fresh matter, respectively). After digestate application their content decreased significantly to 815 mg NO3−/kg fresh matter. Digestate treatment resulted in comparable or better yields and qualitative parameters compared to all the other treatments.

Ozone and organic nitrates over the eastern United States: Sensitivity to isoprene chemistry

AbstractWe implement a new isoprene oxidation mechanism in a global 3‐D chemical transport model (GEOS‐Chem). Model results are evaluated with observations for ozone, isoprene oxidation products, and related species from the International Consortium for Atmospheric Research on Transport and Transformation aircraft campaign over the eastern United States in summer 2004. The model achieves an unbiased simulation of ozone in the boundary layer and the free troposphere, reflecting canceling effects from recent model updates for isoprene chemistry, bromine chemistry, and HO2 loss to aerosols. Simulation of the ozone‐CO correlation is improved relative to previous versions of the model, and this is attributed to a lower and reversible yield of isoprene nitrates, increasing the ozone production efficiency per unit of nitrogen oxides (NOx ≡ NO + NO2). The model successfully reproduces the observed concentrations of organic nitrates (∑ANs) and their correlations with HCHO and ozone. ∑ANs in the model is principally composed of secondary isoprene nitrates, including a major contribution from nighttime isoprene oxidation. The correlations of ∑ANs with HCHO and ozone then provide sensitive tests of isoprene chemistry and argue in particular against a fast isomerization channel for isoprene peroxy radicals. ∑ANs can provide an important reservoir for exporting NOx from the U.S. boundary layer. We find that the dependence of surface ozone on isoprene emission is positive throughout the U.S., even if NOx emissions are reduced by a factor of 4. Previous models showed negative dependences that we attribute to erroneous titration of OH by isoprene.

The effect of SRT on nitrate formation during autotrophic nitrogen removal of anaerobically treated wastewater

Autotrophic nitrogen removal, coupling nitritation (ammonium to nitrite) with anaerobic ammonium oxidation (anammox), offers a promising nitrogen-removal alternative, especially for post-treatment of anaerobically-treated wastewater. However, previous reports suggest that less than 90% total nitrogen removal should be expected with this process alone because over 10% of the ammonium removed will be converted to nitrate. This is caused because nitrite conversion to nitrate is required for reduction of carbon dioxide to cell carbon. However, recent research results suggest that more limited nitrate formation of only a few per cent sometimes occurs. It was hypothesized such lower nitrate yields may result from use of long solids retention times (SRT) where net biological yields are low, and providing that the ratio of oxygen added to influent ammonium concentrations is maintained at or below 0.75 mol/mol. Overall reaction equations were developed for each process and combined to evaluate the potential effect of SRT on process stoichiometry. The results support the use of a long SRT to reduce net cell yield, which in turn results in a small percentage conversion to nitrate during ammonium removal and high total nitrogen removals in the range of 90 to 94%.