A novel dual-isotope labelling method for distinguishing between soil sources of N2O

We present a novel 18O-15N-enrichment method for the distinction between nitrous oxide (N2O) from nitrification, nitrifier denitrification and denitrification based on a method with single- and double-15N-labelled ammonium nitrate. We added a new treatment with 18O-labelled water to quantify N2O from nitrifier denitrification. The theory behind this is that ammonia oxidisers use oxygen (O2) from soil air for the oxidation of ammonia (NH3), but use H2O for the oxidation of the resulting hydroxylamine (NH2OH) to nitrite (NO2-). Thus, N2O from nitrification would therefore be expected to reflect the 18O signature of soil O2, whereas the 18O signature of N2O from nitrifier denitrification would reflect that of both soil O2 and H2O. It was assumed that (a) there would be no preferential removal of 18O or 16O during nitrifier denitrification or denitrification, (b) the 18O signature of the applied 18O-labelled water would remain constant over the experimental period, and (c) any O exchange between H(2)18O and NO3- would be negligible under the chosen experimental conditions. These assumptions were tested and validated for a silt loam soil at 50% water-filled pore space (WFPS) following application of 400 mg N kg-1 dry soil. We compared the results of our new method with those of a conventional inhibition method using 0.02% v/v acetylene (C2H2) and 80% v/v O2 in helium. Both the 18O-15N-enrichment and inhibitor methods identified nitrifier denitrification to be a major source of N2O, accounting for 44 and 40%, respectively, of N2O production over 24 h. However, compared to our 18O-15N-method, the inhibitor method overestimated the contribution from nitrification at the expense of denitrification, probably due to incomplete inhibition of nitrifier denitrification and denitrification by large concentrations of O2 and a negative effect of C2H2 on denitrification. We consider our new 18O-15N-enrichment method to be more reliable than the use of inhibitors; it enables the distinction between more soil sources of N2O than was previously possible and has provided the first direct evidence of the significance of nitrifier denitrification as a source of N2O in fertilised arable soil.     

Quantifying nitrate retention processes in a riparian buffer zone using the natural abundance of 15N in NO3-

Quantifying the relative importance of denitrification and plant uptake to groundwater nitrate retention in riparian zones may lead to methods optimising the construction of riparian zones for water pollution control. The natural abundance of 15N in NO3- has been shown to be an interesting tool for providing insights into the NO3- retention processes occurring in riparian zones. In this study, 15N isotope fractionation (variation in delta15N of the residual NO3-) due to denitrification and due to plant uptake was measured in anaerobic soil slurries at different temperatures (5, 10 and 15 degrees C) and in hydroponic systems with different plant species (Lolium perenne L., Urtica dioica L. and Epilobium hirsutum L.). It was found that temperature had no significant effect on isotope fractionation during denitrification, which resulted in a 15N enrichment factor epsilonD of -22.5 +/- 0.6 per thousand. On the other hand, nitrate uptake by plants resulted in 15N isotope fractionation, but was independent of plant species, leading to a 15N enrichment factor epsilonP of -4.4 +/- 0.3 per thousand. By relating these two laboratory-defined enrichment factors to a field enrichment factor for groundwater nitrate retention during the growing season (epsilonR = -15.5 +/- 1.0 per thousand ), the contribution of denitrification and plant uptake to groundwater nitrate retention could be calculated. The relative importance of denitrification and plant uptake to groundwater nitrate retention in the riparian buffer zone was 49 and 51% during spring, 53 and 47% during summer, and 75 and 25% during autumn. During wintertime, high micropore dissolved organic carbon (DOC) concentrations and low redox potentials due to decomposition of the highly productive riparian vegetation probably resulted in a higher denitrification rate and favoured other nitrate retention processes such as nitrate immobilisation or dissimilatory nitrate reduction to ammonium (DNRA). This could have biased the 15N isotope fractionation and led to a low 15N enrichment factor for groundwater nitrate retention during wintertime (-6.2 +/- 0.9 per thousand ). In contradiction to what many other studies suggest, it is possible that due to plant decomposition during the winter period other nitrate transformation processes compete with denitrification.     

A new mathematical approach for calculating the contribution of anammox, denitrification and atmosphere to an N2 mixture based on a 15N tracer technique

Denitrification and anaerobic ammonium oxidation (anammox) have been identified as biotic key processes of N2 formation during global nitrogen cycling. Based on the principle of a 15N tracer technique, new analytical expressions have been derived for a calculation of the fractions of N2 simultaneously released by anammox and denitrification. An omnipresent contamination with atmospheric N2 is also taken into account and is furthermore calculable in terms of a fraction. Two different mathematical approaches are presented which permit a precise calculation of the contribution of anammox, denitrification, and atmosphere to a combined N2 mixture. The calculation is based on a single isotopic analysis of a sampled N2 mixture and the determination of the 15N abundance of nitrite and nitrate (simplified approach) or of ammonium, nitrite, and nitrate (comprehensive approach). Calculations are even processable under conditions where all basal educts of anammox and denitrification (ammonium, nitrite, and nitrate) are differently enriched in 15N. An additional determination of concentrations of dissolved N compounds is unnecessary. Finally, the presented approach is transferable to studies focused on terrestrial environments where N2 is formed by denitrification and simultaneously by codenitrification or chemodenitrification.     

Distinguishing sources of N2O in European grasslands by stable isotope analysis

Nitrifiers and denitrifiers are the main producers of the greenhouse gas nitrous oxide (N(2)O). Knowledge of the respective contributions of each of these microbial groups to N(2)O production is a prerequisite for the development of effective mitigation strategies for N(2)O. Often, the differentiation is made by the use of inhibitors. Measurements of the natural abundance of the stable isotopes of N and O in N(2)O have been suggested as an alternative for the often unreliable inhibition studies. Here, we tested the natural abundance incubation method developed by Tilsner et al.1 with soils from four European grasslands differing in long-term management practices. Emission rates of N(2)O and stable isotope natural abundance of N(2)O and mineral N were measured in four different soil incubations: a control with 60% water-filled pore space (WFPS), a treatment with 60% WFPS and added ammonium (NH(4) (+)) to support nitrifiers, a control with 80% WFPS and a treatment with 80% WFPS and added nitrate (NO(3) (-)) to support denitrifiers. Decreases in NH(4) (+) concentrations, linked with relative (15)N-enrichment of residual NH(4) (+) and production of (15)N-depleted NO(3) (-), showed that nitrification was the main process for mineral N conversions. The N(2)O production, however, was generally dominated by reduction processes, as indicated by the up to 20 times larger N(2)O production under conditions favouring denitrification than under conditions favouring nitrification. Interestingly, the N(2)O concentration in the incubation atmospheres often levelled off or even decreased, accompanied by increases in delta(15)N and delta(18)O values of N(2)O. This points to uptake and further reduction of N(2)O to N(2), even under conditions with small concentrations of N(2)O in the atmosphere. The measurements of the natural abundances of (15)N and (18)O proved to be a valuable integral part of the natural abundance incubation method. Without these measurements, nitrification would not have been identified as essential for mineral N conversions and N(2)O consumption could not have been detected.     

A suite of sensitive chemical methods to determine the δ15N of ammonium, nitrate and total dissolved N in soil extracts

Natural ¹⁵N abundances (δ¹⁵N values) of different soil nitrogen pools deliver crucial information on the soil N cycle for the analysis of biogeochemical processes. Here we report on a complete suite of methods for sensitive δ¹⁵N analysis in soil extracts. A combined chemical reaction of vanadium(III) chloride (VCl₃) and sodium azide under acidic conditions is used to convert nitrate into N₂O, which is subsequently analyzed by purge‐and‐trap isotope ratio mass spectrometry (PTIRMS) with a cryo‐focusing unit. Coupled with preparation steps (microdiffusion for collection of ammonium, alkaline persulfate oxidation to convert total dissolved N (TDN) or ammonium into nitrate) this allows the determination of the δ¹⁵N values of nitrate, ammonium and total dissolved N (dissolved organic N, microbial biomass N) in soil extracts with the same basic protocol. The limits of quantification for δ¹⁵N analysis with a precision of 0.5‰ were 12.4 µM for ammonium, 23.7 µM for TDN, 16.5 µM for nitrate and 22.7 µM for nitrite. Copyright © 2010 John Wiley & Sons, Ltd.     

Isolation of ammonium-N as 1-sulfonato-iso-indole for measurement of delta15N

The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil.     

Influence of ammonium on the performance of a denitrifying culture under heterotrophic conditions

The effect of ammonium on a denitrifying reactor of the upflow anaerobic sludge blanket type was studied. At a constant nitrate loading rate (2500 mg NO ₃ ⁻ -N/[L · d]), using acetate as organic electron donor and at a C/NO ₃ ⁻ -N ratio of 1.23, an increase in the N₂ production rate was observed when the ammonium loading rate was increased (25, 250, and 500 mg NH ₄ ⁺ -N/[L · d]). Dissimilatory nitrate reduction to ammonium (DNRA) was not observed, and the N₂ production efficiency was increased from 84 to 100% or higher. Since NH ₄ ⁺ in the output was lower than in the input, it was suggested that it was used for nitrate reduction. At constant NH ₄ ⁺ -N/NO ₃ ⁻ -N and C/NO ₃ ⁻ -N ratios of 0.2 and 1.63, respectively, the molecular nitrogen production rate was increased at 300 and 500 mg NH ₄ ⁺ -N/(L · d), whereas at 200 mg NH ₄ ⁺ -N/(L · d) DNRA took place probably owing to culture conditions of low reductive power. Molecular nitrogen production was not observed under autotrophic conditions, and the addition of acetate to the culture recovered its high nitrogen removal rate. Experimental results and balances indicated that the consumed ammonium was used as an additional reductive source.     

Using dual-bacterial denitrification to improve delta15N determinations of nitrates containing mass-independent 17O

The bacterial denitrification method for isotopic analysis of nitrate using N(2)O generated from Pseudomonas aureofaciens may overestimate delta(15)N values by as much as 1-2 per thousand for samples containing atmospheric nitrate because of mass-independent (17)O variations in such samples. By analyzing such samples for delta(15)N and delta(18)O using the denitrifier Pseudomonas chlororaphis, one obtains nearly correct delta(15)N values because oxygen in N(2)O generated by P. chlororaphis is primarily derived from H(2)O. The difference between the apparent delta(15)N value determined with P. aureofaciens and that determined with P. chlororaphis, assuming mass-dependent oxygen isotopic fractionation, reflects the amount of mass-independent (17)O in a nitrate sample. By interspersing nitrate isotopic reference materials having substantially different delta(18)O values with samples, one can normalize oxygen isotope ratios and determine the fractions of oxygen in N(2)O derived from the nitrate and from water with each denitrifier. This information can be used to improve delta(15)N values of nitrates having excess (17)O. The same analyses also yield estimates of the magnitude of (17)O excess in the nitrate (expressed as Delta(17)O) that may be useful in some environmental studies. The 1-sigma uncertainties of delta(15)N, delta(18)O and Delta(17)O measurements are +/-0.2, +/-0.3 and +/-5 per thousand, respectively.     

Neutral and ion chemistry in low pressure dc plasmas of H2/N2 mixtures: routes for the efficient production of NH3 and NH4(+)

The chemistry in low pressure (0.8-8 Pa) plasmas of H(2) + 10% N(2) mixtures has been experimentally investigated in a hollow cathode dc reactor using electrical probes for the estimation of electron temperatures and densities, and mass spectrometry to determine the concentration of ions and stable neutral species. The analysis of the measurements by means of a kinetic model has allowed the identification of the main physicochemical mechanisms responsible for the observed distributions of neutrals and ions and for their evolution with discharge pressure. The chemistry of neutral species is dominated by the formation of appreciable amounts of NH(3) at the metallic walls of the reactor through the successive hydrogenation of atomic nitrogen and nitrogen containing radicals. Both Eley-Rideal and Langmuir-Hinshelwood mechanisms are needed in the chain of hydrogenation steps in order to account satisfactorily for the observed ammonia concentrations, which, in the steady state, are found to reach values ~30-70% of those of N(2). The ionic composition of the plasma, which is entirely due to gas-phase processes, is the result of a competition between direct electron impact dissociation, more relevant for high electron temperatures (lower pressures), and ion-molecule chemistry that prevails for the lower electron temperatures (higher pressures). At the lowest pressure, products from the protonation of the precursor molecules (H(3)(+), N(2)H(+) and NH(4)(+)) and others from direct ionization (H(2)(+) and NH(3)(+)) are found in comparable amounts. At the higher pressures, the ionic distribution is largely dominated by ammonium. It is found that collisions of H(3)(+), NH(3)(+) and N(2)H(+) with the minor neutral component NH(3) are to a great extent responsible for the final prevalence of NH(4)(+).     

Evaluation of methods to measure differential 15N labeling of soil and root N pools for studies of root exudation

To study patterns of root exudation, the effectiveness of different techniques for in situ 15N labeling of Brassica napus, Centaurea jacea and Lolium perenne with ammonium nitrate was tested. Stem infiltration was found to effectively label plants with thicker stems, whereas, for grass species, cutting and immersing the leaf tips into 15N solution proved to be most effective. A microdiffusion technique to isolate ammonium, combined with conventional cation-exchange chromatography to separate nitrate from amino-N compounds thereafter, was found suitable for separation of the N fractions of plant and soil extracts for 15N determination. All three species were then cultivated in nutrient solution and labeled with 15NH4 15NO3 by stem feeding for 42 hours. Kinetics of 15N labeling of bulk roots and shoots as well as hot water extractable material were assessed, and up to 1.1 at% 15N excess (APE) was found in nutrient solutions. The main amino acids exuded by L. perenne were glycine, serine, alanine and aspartic acid. To assess the suitability of this set of methods to study root exudation in field settings, L. perenne was grown without fertiliser addition in pots containing low-nutrient soil. Plants were 15N labeled via tip immersion and 15N and N concentrations were analysed in shoots, roots and soils during a 48-h interval. Shoots reached 1.25 APE, roots and soil 0.10 and 0.005 APE, respectively. Between 4% (48 h) and 6% (24 h) of total plant 15N was exuded by roots into the soil. In roots amino acids comprised the largest proportion of the soluble 15N pool, whereas soil 15N levels were similar for amino acids and ammonium, exceeding those of nitrate. Mechanisms for the shift within N fractions from roots to soils are briefly discussed.     

Modeling of the gas-phase ion chemistry of protonated arginine

Arginine is often involved at the C-terminus of peptides obtained from tryptic digests of proteins. The very basic guanidine group of the side-chain of arginine has a large effect on the backbone fragmentation of protonated peptides. Furthermore, arginine exhibits specific fragmentation reactions involving its side-chain. Various tautomerization states, conformers and side-chain dissociation channels of protonated arginine were studied using theoretical methods. The guanidine loss of protonated arginine is proved to be an S(N)2 substitution on the delta-carbon of the side-chain, starting from species containing the N(epsilon)H-C(+)(N(eta)H(2))(N(eta')H(2)) or -N(epsilon) (+)H(2)-C(N(eta)H)(N(eta')H(2)) moieties and leads to formation to either protonated guanidine or protonated proline. In the corresponding transition structures the proline moiety is protonated. Under low-energy collision conditions the extra proton transfers to the guanidine moiety, leading to the formation of C(+)(NH(2))(3). On the other hand, the lifetime of the fragmenting species under high-energy collision conditions is shorter, resulting in enhanced formation of protonated proline and its dissociation products. The first step of ammonia loss is the leaving of a preformed NH(3) from tautomers containing the -N(epsilon)H-C(N(eta)H(3) (+))(N(eta')H) or -N(epsilon)-C(N(eta)H(3) (+))(N(eta')H(2)) moieties. The resulting protonated carbodiimide group can be stabilized by intramolecular nucleophilic attack, leading to ring formation. Overall, reactions involved in the ammonia loss from protonated arginine can be considered as an S(N)1 substitution on the central zeta-carbon of the guanidine group.     

Probing crystal structures and transformation reactions of ammonium molybdates by 14N MAS NMR spectroscopy

The unique high-resolution feature offered by 14N magic-angle spinning (MAS) NMR spectroscopy of ammonium ions has been used to characterize the crystal structures of various ammonium molybdates by their 14N quadrupole coupling parameters, i.e., CQ, the quadrupole coupling constant, and etaQ, the asymmetry parameter. Two polymorphs of diammonium monomolybdate, (NH4)2MoO4, recently structurally characterized by single-crystal X-ray diffraction (XRD) and named mS60 and mP60, show distinct but different 14N MAS NMR spectra from each of which two sets of characteristic 14N CQ and etaQ values have been obtained. Similarly, the well-characterized ammonium polymolybdates (NH4)2Mo2O7, (NH4)6Mo7O24.4H2O, and (NH4)6Mo8O27.4H2O also give rise to distinct and characteristic 14N MAS NMR spectra. In particular, it is noted that simulation of the experimental (NH4)6Mo7O24.4H2O spectrum requires an iterative fit with six independent NH4+ sites. For the slow spinning frequencies employed (nu(r) = 1500-3000 Hz), all 14N MAS NMR spectra of the ammonium molybdates in this study are fingerprints of their identity. These different 14N MAS NMR fingerprints are shown to be an efficient tool in qualitative and quantitative assessment of the decomposition of (NH4)2MoO4 in humid air. Finally, by a combination of the 14N and 95Mo MAS NMR experiments performed here, it has become clear that a recent report of the 95Mo MAS spectra and data for the mS60 and mP60 polymorphs of (NH4)2MoO4 are erroneous because the sample examined had decomposed to (NH4)2Mo2O7.     

Mo助剂含量对Mo-Ni2P/SBA-15/堇青石整体式催化剂加氢脱硫性能的影响

 采用共浸渍法制备了 P/Ni 摩尔比为 2 的 Ni2P/SBA-15, 再通过二次浸渍引入助剂 Mo 制得 Mo-Ni2P/SBA-15, 将它调制成活性胶后均匀涂敷于预处理后的载体表面, 干燥焙烧后在氢气流中采用程序升温还原法, 制备了一系列 Mo-Ni2P/SBA-15/堇青石整体式催化剂. 采用 X 射线衍射、N2 吸附-脱附和 X 射线光电子能谱对催化剂结构进行了表征, 以二苯并噻吩为模型含硫化合物, 考察了催化剂的加氢脱硫性能. 结果表明, Mo 的加入增大了催化剂的比表面积, 在催化剂表面形成了 MoNiP2, 且 Ni2P 为主要活性物相. Mo 在催化剂表面主要以 Mo6+和 Moδ+形式存在; 当 w(Mo) = 4.2% 时, n(Mo)/n(Ni+Mo) = 0.18 的整体式催化剂上二苯并噻吩的转化率最高, 且在较低反应温度时以直接脱硫机理为主, 而较高反应温度时以加氢脱硫机理为主.     

Thermal behaviour of nickel(II) sulphate,nitrate and halide complexes containing ammine and ethylenediamine as ligands

Thermal behaviour of nickel amine complexes containing SO₄ ²⁻, NO₃ ⁻, Cl⁻ and Br⁻ as counter ions and ammonia and ethylenediamine as ligands have been investigated using simultaneous TG/DTA coupled with mass spectroscopy (TG/DTA–MS). Evolved gas analyses detected various transient intermediates during thermal decomposition. The nickel ammonium sulphate complex produces NH, N, S, O and N₂ species. The nickel ammonium nitrate complex generated fragments like N, N₂, NO, O₂, N₂O, NH₂ and NH. The halide complexes produce NH₂, NH, N₂ and H₂ species during decomposition. The ligand ethylenediamine is fragmented as N₂/C₂H₄, NH₃ and H₂. The residue hexaamminenickel(II) sulphate produces NiO with crystallite size 50 nm. Hexaammine and tris(ethylenediamine)nickel(II) nitrate produce NiO in the range 25.5 nm and 23 nm, respectively. The halide complexes produce nano sized metallic nickel (20 nm) as the residue. Among the complexes studied, the nitrate containing complexes undergo simultaneous oxidation and reduction.     

New extended magnetic systems based on oxalate and iron(III) ions

A series of oxalate-bridged iron(III) complexes have been synthesized by the reaction of FeCl 3 with oxalic acid (H 2ox) and XCl, where X is a substituted univalent ammonium or an alkaline cation. We have obtained basically two different types of compounds by varying the nature and the shape of the counterion, with the dimensionality of the resulting product being strongly influenced by the counterion. Three-dimensional (3D) networks of oxo- and oxalato-bridged iron(III) ions of the general formula {X 2[Fe 2O(ox) 2Cl 2]. pH 2O} n have been obtained for X = Li (+) ( 1), Na (+) ( 2), and K (+) ( 3) with p = 4 and X = MeNH 3 (+) ( 4), Me 2NH 2 (+) ( 5), and EtNH 3 (+) ( 6) with p = 2. Similar 3D hydroxo- and oxalato-bridged iron(III) networks of the formula {X[Fe 2(OH)(ox) 2Cl 2].2H 2O} n resulted for X = EtNH 3 (+) ( 7a) and PrNH 3 (+) ( 8). Compound 7a undergoes a solid-to-solid transformation, leading to a new species of the formula {(H 3O)(EtNH 3)[Fe 2O(ox) 2Cl 2].H 2O} n ( 7b). Chainlike compounds of the formula {X 2[Fe 2(ox) 2Cl 4]. pH 2O} n [X = Me 2NH 2 (+)( 9, p = 1), Me 3NH (+) ( 10, p = 2), and Me 4N (+) ( 11, p = 0)] have been obtained for the bulkier alkylammonium cations. Magnetic susceptibility measurements in the temperature range 1.9-295 K show the occurrence of weak ferromagnetic ordering due to spin canting in the 3D networks 1- 8, with the value of the critical temperature ( T c) varying with the cation in the range 26 K ( 2) to 70 K ( 8) without significant structural modifications. The last three one-dimensional compounds exhibit the typical behavior of antiferromagnetically coupled chains of interacting spin sextets [ J = -8.3 ( 9), -6.9 ( 10), and -8.4 ( 11) cm (-1) with H = - J summation operator i S i S i+1 ].     

Biotreatment of High Strength Nitrate Waste Using Immobilized Preadapted Sludge

One of the major wastes generated by fertilizer, explosive, and nuclear industries are nitrate (as high as 1,000 ppm NO(3)N) whose removal before disposal has become a growing concern. In this study, an active denitrifying sludge was immobilized onto support materials like cloth and polyurethane foam and their denitrification efficiency on high nitrate wastes [1,000 ppm NO(3) (225 ppm NO(3)N), 5,000 ppm NO(3) (1,129 ppm NO(3)N), 7,500 ppm NO(3) (1,693 ppm NO(3) N)] was studied. Results showed complete degradation of the nitrate wastes (225 ppm NO(3)N, 1,129 ppm NO(3)N, and 1,693 ppm NO(3)N) without any accumulation of nitrite in a period of only 1, 4, and 10 h, respectively. Based on adhering and entrapment principle, an immobilization unit was developed using a combination of cloth and foam as well as both individually. This system used for treating such high nitrate wastes was found to be quite effective in waste water treatment, particularly in problems associated with solid-liquid separation. The batch column reactor was run in about 45 batches without any loss in activity or reactor stability.     

Simulation of aerobic landfill in laboratory scale lysimeters — effect of aeration rate

Aeration of municipal landfills contributes to the acceleration of organic matter degradation and to the decrease of pollutant emission into air, water, and soil. Biodegradation of organic matter present in municipal waste, deposited in a landfill, by microorganisms under anaerobic conditions is a slow process. The aim of the study was to carry out simulations of an aerobic landfill in lysimeters, to determine the influence of aeration rate on the degradation of organic matter present in landfills, and to formulate a mathematical model defining the changes of carbon content in leachate and in gas produced. In this work, simulation of aerobic landfill leachate degradation was carried out in laboratory scale lysimeters with the working volume of 15 L. The changes of BOD5, COD, and ammonium nitrogen concentration during aeration were similar for all aeration rates. During aeration, the BOD5 index decreased by 99.9 %, COD decreased by 95.1 %, and ammonium nitrogen concentration by 93 %. The proposed kinetic model defines the processes of organic carbon content changes in simulated leachate and the quantity of carbon dioxide for aerobic landfill simulation quite well.     

Solid phase microextraction-gas chromatographic-mass spectrometric determination of nitrous oxide evolution to measure denitrification in estuarine soils and sediments

A SPME-GC-MS method was developed to quantify nitrous oxide (N(2)O) to evaluate denitrification rates. There is a need for this sensitive and definitive N(2)O detection method to accurately measure the soil and sediment ability to convert anthropogenic mineral nitrogen loads to N(2) through denitrification hence decreasing estuarine waterway pollution loading. This method is applied to measure denitrification, which is a major pathway for inorganic nitrogen removal, by incorporating the acetylene (C(2)H(2)) block method on anaerobic assays. Currently, denitrification is largely measured using GCs fitted with TCD or ECD detectors. With a mean R(2) value of 0.996, the calibration curve spanned over three orders of magnitude (4.1-2030 nM) with a limit of detection (LOD) of 4.1 nM N(2)O (18 ppb) and a limit of quantification (LOQ) of 16 nM N(2)O (72 ppb). This detection method was valid with less than 15% relative standard deviation (RSD) and error for middle and high quality control (QC) points and less than 20% for low QC points on three experimental days. Measuring N(2)O using SPME-GC-MS technology allows for confidence in identification, high sensitivity, reproducibility, and short run times.     

Inorganic-organic hybrid vesicles with counterion- and pH-controlled fluorescent properties

Two inorganic-organic hybrid clusters with one or two covalently linked pyrene fluorescent probes, [(n-C(4)H(9))(4)N](2)[V(6)O(13){(OCH(2))(3)C(NH(CO)CH(2)CH(2)CH(2)C(16)H(9))}{(OCH(2))(3)C-(NH(2))}] ((TBA(+))(2)1) and [(n-C(4)H(9))(4)N](2)[V(6)O(13){(OCH(2))(3)C(NH(CO)CH(2)CH(2)CH(2)C(16)H(9))}(2)] ((TBA(+))(2)2), respectively, are synthesized from Lindqvist type polyoxometalates (POMs). The incorporation of pyrene into POMs results in amphiphilic hybrid molecules and simultaneously offers a great opportunity to study the interaction between hybrid clusters and their counterions. 2D-NOESY NMR and fluorescence techniques have been used to study the role of counterions such as tetrabutyl ammonium (TBA) in the vesicle formation of the hybrid clusters. The TBA(+) ions not only screen the electrostatic repulsions between the POM head groups but also are involved in the hydrophobic region of the vesicular structure where they interrupt the formation of pyrene excimers that greatly perturbs the luminescence signal from the vesicle solution. By replacing the TBA(+) counterions with protons, the new vesicles demonstrate interesting pH-dependent fluorescence properties.     

电极面积对老龄垃圾渗滤液为底物的微生物燃料电池性能影响

构建生物阴极型双室微生物燃料电池,处理老龄垃圾渗滤液。研究了阳极与阴极面积比值对微生物燃料电池产电能力和对老龄垃圾渗滤液处理效果的影响。结果表明,阳极与阴极面积比为1:2、2:2、2:1的3组生物阴极型微生物燃料电池输出电压分别为408、452、396mV,最大电功率密度分别为145.73、237.65、136.50mW/m³,内阻分别为350、200、400Ω,COD的去除率分别为21.18%、20.20%、22.31%。3组微生物燃料电池运行30d后,垃圾渗滤液中氨氮、硝酸盐氮、亚硝酸盐氮浓度均下降,其中,氨氮去除率分别为80.88%、73.61%和66.17%,其去除效果与产电性能相关。