High-temperature Catalytic Oxidation Research Articles

Study of the structure of graphene oxide obtained by oxidation of intercalated graphite compound by Raman light scattering method

This work shows the strategy of GO synthesis from intercalated graphite compound, rotation of the synthesis conditions was carried out, and the starting material and synthesis products were characterized in detail by a complex of physical and chemical methods: scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and high-temperature catalytic oxidation. It was found by Raman spectroscopy that the initial IGC sample is a graphite structure with a low content of defects in graphene layers. Oxidation of this sample leads to a gradual increase in the measure of disordered carbon framework. One of the reasons for this is a decrease in the size of graphite-like crystallites with subsequent reorientation in the space of graphene layers. It has been established by a complex of physicochemical methods of research that the oxidation of IGC graphite with increasing oxidation time leads to an increase in the defectivity of the initial carbon framework due to a decrease in the linear size of carbon crystallites. When a certain reaction time is reached, the initial structure of the sample changes, and there is a partial reorientation of the crushed graphite-like fragments with a simultaneous increase in the number of defects.

Contribution of water erosion to organic carbon and total nitrogen loads in agricultural discharge from boreal mineral soils

While organic carbon (OC) in agricultural mineral soils is widely studied in terms of soil carbon sequestration and gaseous emissions, discharge-induced OC loss from soil is still poorly understood and estimations of boreal soil OC loads within water erosion are lacking. Loss of organic matter from arable soils is a concern for surface water quality, climate change and soil productivity. The main aim of this study was to quantify the role of water erosion in total OC and nitrogen (N) loads exported in agricultural discharge from boreal mineral soils under various cultivation practices. Surface water and subsurface drainage were collected near-continually over 2 years in two clayey and one sandy soil in Finland. Eroded sediment was mechanically separated by centrifugation from all discharge samples to detect sediment OC% and N% by dry-combustion method. Dissolved OC and N concentrations in selected discharge samples were measured with high-temperature catalytic oxidation of unfiltered supernatant. A multiple linear regression model was used to study the significant factors affecting dissolved, sediment and total OC loads. In the clayey soils, the sediment OC (2–24 kg ha−1 y−1) and N (0.2–1.1 kg ha−1 y−1) export accounted for up to 35 % and 20 % of the annual discharge-induced total loads of OC (19–85 kg ha−1) and N (2–8 kg ha−1), respectively. In the sandy soil, erosion was negligible and dissolved loads of 17–35 kg OC ha−1 y−1and 4–7 kg N ha−1 y−1 were detected. Subsurface drainage exported most of the sediment-associated OC and N loads from clayey soils. For the total OC loads, the distribution varied between the discharge routes, while the total N loads were mostly exported in subsurface drainage in both soil types. Sediment OC and N exports were related to soil plowing and discharge intensity, while dissolved OC loss was promoted by high surface soil OC%. Our results also indicated that a single cultivation practice may affect sediment and dissolved loads in opposite ways. These findings can be used to complement carbon budget estimations for mineral agricultural soils, and to assess soil management effects on terrestrial organic matter loading to boreal surface waters.

High-temperature catalytic oxidation preparation and liquid scintillation counting determination of the carbon-14 in liquid effluent samples from nuclear power plants

Carbon-14 (14C) detection and quantification is crucial to the radioactivity level monitoring of liquid effluents at nuclear power plants in China. Herein, a high-temperature catalytic oxidation (HTCO)-based preparation methodology is proposed. The samples were combusted using a high-temperature furnace, and the trapped carbon dioxide-14 was regenerated before being measured via liquid scintillation counting (LSC). The validation of the method was carried out according to 14C-spiked standards, with the results in agreement with the assigned radioactivity concentration for 14C, demonstrating that the HTCO-based 14C preparation and the determination via LSC were both reliable and accurate.

A comparison between high temperature catalytic and persulfate oxidation for the determination of total dissolved nitrogen in natural waters

A comparison between high temperature catalytic and persulfate oxidation for the determination of total dissolved nitrogen in natural waters

Catalytic Activity of LaFe0.4Ni0.6O3/CeO2 Composites in CO and CH4 Oxidation Depending on Their Preparation Conditions.

LaFe0.4Ni0.6O3/CeO2 (1:1) two-phase composite materials were prepared by mechanochemical (MC) and Pechini routes. The catalytic properties of the composites in methane and CO oxidation reactions strongly depend on their preparation conditions. In low-temperature (<600 °C) catalytic CO oxidation the composites demonstrate a higher activity compared with LaFe0.4Ni0.6O3 perovskite. The highest activity was observed for the composite prepared by mechanical treatment of perovskite and fluorite precursors. There is a correlation between activity and the content of weakly bound surface oxygen species. Catalytic activity in high-temperature (>750 °C) catalytic methane oxidation correlates with the reducibility of samples. The highest activity was observed for the composite prepared by the one-pot Pechini route with higher reducibility of the sample up to 600 °C.

Adapting an elemental analyser to perform high-temperature catalytic oxidation for dissolved organic carbon measurements in water.

Many laboratories employ elemental analyzers (EAs) coupled to isotope ratio mass spectrometers (IRMSs) to measure carbon stable isotope ratios (δ13 C) in solid samples. Dissolved organic carbon (DOC) in most natural water samples cannot be analyzed using this approach unless time-consuming preconcentration is employed. An EA-IRMS can be used to measure DOC δ13 C in natural waters without the need for sample preconcentration by employing high-temperature catalytic oxidation. An autosampler injects water into the EA reactor at 680°C filled with platinum catalyst beads, where all carbon is converted to CO2 . Remaining water and halides are removed, while CO2 is trapped in a cryotrap and later released to the IRMS. Measurements were accurate (deviation <0.3‰ compared to solid sample measurements) and precise (error of 0.3‰ for concentrations ≥46 μM). Blanks were present and accounted for. Salinity up to seawater level did not affect accuracy or precision, but limited the number of samples that could be run before cleaning of the reactor was needed. DOC δ13 C in a river/estuary varied between -25.7 and -23.2‰, with higher values for waters with higher salinity, as expected. Deep-sea water reference material had a value of -22.9 ± 0.5‰, very similar to those found in recent reports employing similar techniques. Adapting an EA is a feasible approach for the measurement of DOC δ13 C in natural waters. The low cost and simplicity of the system allow its use in any laboratory already equipped with EA-IRMS.

High-Temperature Catalytic Oxidation of 1,2-Dichlorethane: An Alternative Applicable Method for Safe Elimination of CVOCs

The application of catalytic removal of chlorinated volatile organic compounds (CVOCs) is restricted by the problems of catalyst deactivation and toxic byproducts. In order to alleviate these problems, the effects of high reaction temperature on the catalytic oxidation of CVOCs are explored by employing thermostable catalysts. Transition metal (Mn, Cu, and Fe)-substituted thermostable hexaaluminate catalysts are prepared and used in the catalytic oxidation of 1,2-dichloroethane (DCE). Mn-substitution and Ru-loading could induce rich active oxygen species and promote reducibility, oxygen mobility, and surface acidity, leading to the improved reaction performance consequently. The inhibition effect on generating chlorinated byproducts by elevating the reaction temperature and the influence of rising temperature on the reaction process are investigated. Catalytic oxidation of DCE over LaMn3 or Ru/LaMn3 at the high-temperature region (over 500 °C) could convert the pollutant into small inorganic molecules (CO2, H2O, HCl, etc.) with scarce chlorinated byproducts. Meanwhile, Ru/LaMn3 presents an excellent structural stability and steady reaction activity at 650 °C. Additionally, DCE oxidation occurs via the pathway of enolic species, vinyl chloride–acetaldehyde–acetate species over LaMn3 and Ru/LaMn3. These results suggest that the high-temperature catalytic oxidation of CVOCs might be a practicable method for safe elimination of CVOCs.

Impact of aquaculture on distribution of dissolved organic matter in coastal Jeju Island, Korea, based on absorption and fluorescence spectroscopy

In Jeju Island, multiple land-based aquafarms were fully operational along most coastal region. However, the effect of effluent on distribution and behaviours of dissolved organic matter (DOM) in the coastal water are still unknown. To decipher characteristics of organic pollution, we compared physicochemical parameters with spectral optical properties near the coastal aquafarms in Jeju Island. Absorption spectra were measured to calculate the absorption coefficient, spectral slope coefficient, and specific UV absorbance. Fluorescent DOM was analysed using fluorescence spectroscopy coupled with parallel factor analysis. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were measured using high-temperature catalytic oxidation. The DOC concentration near the discharge outlet was twice higher than that in natural groundwater, and the TDN concentration exponentially increased close to the outlet. These distribution patterns indicate that aquafarms are a significant source of DOM. Herein, principal component analysis was applied to categorise the DOM origins. There were two distinct groups, namely, aquaculture activity for TDN with humic-like and high molecular weights DOM (PC1: 48.1%) and natural biological activity in the coastal water for DOC enrichment and protein-like DOM (PC2: 18.8%). We conclude that the aquafarms significantly discharge organic nitrogen pollutants and provoke in situ production of organic carbon. Furthermore, these findings indicate the potential of optical techniques for the efficient monitoring of anthropogenic organic pollutants from aquafarms worldwide.

Application of a catalytic oxidation method for the simultaneous determination of total organic carbon and total nitrogen in marine sediments and soils.

This study presents the application of a simultaneous method for the determination of total organic carbon (TOC) and total nitrogen (TN) in marine sediments and soils, using a data set of 206 samples collected from coastal lagoonal/marine sedimentary environments and certified reference materials (CRMs). TOC and TN were determined using the high temperature (720°C) catalytic (Pt/Al2O3) oxidation method and the detection of TOC and TN was performed using an infrared or a chemiluminescence detector, respectively. Results from the abovementioned TOC method were compared with the results from the widely used Wakley-Black titration method, while TN results with these from elemental analysis. Analytical quality control experiments were performed using CRM samples. Method characteristics such as range of measurement, calibration, method detection limit (MDL), limit of quantification (LOQ), repeatability and reproducibility, were calculated. The precision and the accuracy of the methods are also discussed. Comparison of the two TOC methods of 206 data set yields a regression line of correlation coefficient with R2 = 0.985. Additional different levels of TOC concentrations of low <1%, moderate 1–5% and high 5–40% level were examined indicating very good correlations. The lowest correlation coefficient was observed in low concentrations TOC<1% (R2 0.825), mainly as a result of the limitation of titration method. The evaluation of TN results indicated that the catalytic oxidation method and the elemental analysishave a significant good correlation with R2 = 0.977. The results of precision and accuracy, as well as the calculated MDL and LOQ show that this is a reliable method. Moreover, it requires a small amount of the analyzed sample and the total analysis time is 10 min. Therefore, it can be easily applied for the fast and precise simultaneous determination of TOC and TN in sediment and soil samples.

A novel source of hospital microorganisms in healthcare settings

Background. Most healthcare-associated infections (HAI) develop due to a colonization of patients and healthcare workers by hospital strains of pathogens. The aim to study was to assess whether the dust within the health facilities can harbor microorganisms acting as a reservoir of HAIs.Materials and methods. Dust samples collected in the air ducts and ventilation grilles of health facilities underwent a detailed physicochemical analysis by means of scanning electron microscopy, dynamic light scattering, energy-dispersive X-ray spectroscopy, and high-temperature catalytic oxidation. Bacterial and viral diversity was investigated using an automated biochemical analyzer and polymerase chain reaction, respectively. Investigation of the microenvironment included detection of biofilms using a catalase indicator and quantification of viable microorganisms per 1 m3 air.Results. Dust from the hospital ventilation grilles and air ducts was contaminated with microorganisms in 71.13% of cases. Strikingly, multidrug-resistant and biofilm-forming strains have been found in 69.4% and 48.0% of samples, respectively. The total viable count before and after opening doors and windows was 276 and 462 colony-forming units/m3 respectively (p = 0.046). Biodiversity was represented by 21 genera of microorganisms which were consistently detected upon 6 months of follow-up. All samples contained a nanosized particulate matter. Chemical elements comprising dust were carbon (16.26–50.69%), oxygen (20.02–37.50%), nitrogen (1.59–25.03%), hydrogen (2.03–6.67%), sulfur (0.15–2.38%), calcium (0.19–7.49%), silicon (0.21–4.64%), chlorine (0.05–2.83%), sodium (0.07–1.86%), aluminum (0.36–1.78%), iron (0.08–1.61%), magnesium (0.11–1.40%), potassium (0.04–0.85%), and phosphorus (0.04–0.81%).Discussion. A wide range of multidrug-resistant strains of bacteria, detected in a hospital particulate matter with a diverse chemical composition, indicates the persistence of HAI-causing pathogens in the hospital environment.Conclusion. Dust from the ventilation grilles and adjacent air ducts should be considered as an additional reservoir of multidrug-resistant strains of bacteria in the healthcare settings.

Oxidative dehydrogenation of ethane over mixed metal oxide catalysts: Autothermal or cooled tubular reactor design?

AbstractA kinetic model consistent with experimentally measured reaction orders for the oxidative dehydrogenation of ethane (ODHE) over a MoVTeNbO catalyst is developed and applied to compare autothermal and multi‐tubular reactor designs for the same. The results suggest that autothermal reactor configurations are more favorable compared to multi‐tubular ones for this highly exothermic reaction, and become even more so with increasing active site density. A bifurcation analysis based on ignition and extinction behavior is presented as a function of adiabatic temperature rise (varied by altering the feed ethane to oxygen molar ratio) and catalyst active site density (varied by altering the pre‐exponential factor), thereby providing additional insights into strategies for successful scale‐up of ODHE reactors. These strategies for the design of viable reactor configurations may be more broadly applicable to high temperature catalytic partial oxidation reactions currently in practice or under consideration in the context of large‐scale processes for chemical production.

Comparing the performance of three methods to assess DOM dynamics within two distinct glacierized watersheds of the tropical Andes

Dissolved organic matter (DOM) is recognized as a good indicator of water quality as its concentration is influenced by land use, rainwater, windborne material and anthropogenic activities. Recent technological advances make it possible to characterize fluorescent dissolved organic matter (FDOM), the fraction of DOM that fluoresces. Among these advances, portable fluorometers and benchtop fluorescence excitation and emission spectroscopy coupled with a parallel factor analysis (EEM-PARAFAC) have shown to be reliable. Despite their rising popularity, there is still a need to evaluate the extent to which these techniques can assess DOM dynamics at the watershed scale. We compare the performance of in-situ measurements of FDOM with laboratory measurements of fluorescence spectroscopy within the context of two distinct glacierized watersheds in Peru. Glacierized watersheds represent unique testing environments with contrasting DOM conditions, flowing from pristine, vegetation-free headwaters through locations with obvious anthropogenic influences. We used an in-situ fluorometer and a portable multimeter to take 38 measurements of FDOM, pH and turbidity throughout the two catchments. Additionally, samples were analyzed in the laboratory using the EEM-PARAFAC method. Results were compared to dissolved organic carbon (DOC) measurements using standard high-temperature catalytic oxidation. Our results show that the three techniques together were able to capture the DOM dynamics for both studied watersheds. Taken individually, all three methods allowed detection of the watershed DOM main points of sources but in a more limited way. Due to the narrow bandwidth of the portable fluorometer used in the study, FDOM measurements were almost non-detectable to protein-like substances. Indeed, the more demanding EEM-PARAFAC was able to both differentiate between potential sources of DOM and provide an estimate of relative concentrations of different organic components. Finally, similar to FDOM but to a lesser extent, the DOC measurements showed some limits where protein-like substances make up most of the DOM composition.

Particulate matter as a possible reservoir of multidrug-resistant microorganisms in surgical healthcare settings

Aim. To study the microbial diversity and dust organic component in surgical healthcare settings and to assess the risk of dust-mediated transmission of healthcare-associated infections. Materials and Methods . Dust sampling (n = 41) was carried out using sterile gloves and containers from ventilation grilles and adjacent air ducts of the exhaust ventilation systems in various healthcare settings. Size and shape of dust particles were studied by means of scanning electron microscopy and dynamic light scattering. Elemental analysis (CHNSO) was conducted employing high temperature catalytic oxidation. Bacterial composition of the dust was investigated using a VITEK 2 Compact biochemical analyzer while viral diversity was screened by polymerase chain reaction. Results. Dust in healthcare units consisted of globular particles and/or microsized fibers. Regardless of the healthcare setting, globular particles prevailed in the dust structure. Dust nanoparticles was characterised by an average first size peak of 85.6 ± 12.6 nm and an average second peak of 307.1 ± 76.2 nm. Dust collected in non-surgical units contained a higher nitrogen content than surgical settings (p < 0.001). Proportions of hydrogen, carbon, and sulfur did not differ between non-surgical and surgical units. The dust collected from healthcare settings in different cities also varied in nitrogen content (p = 0.033). A wide microbial diversity was detected in dust samples and a high frequency (46.34%) of its contamination was found. In surgical departments, dust contamination was notable for multidrug-resistant bacteria (28.57%), while viruses prevailed in non-surgical departments (23.3%). Conclusions. Dust generated in surgical departments contains nanosized particulate matter, multidrug-resistant microorganisms, and a prominent organic component all defining it as a possible reservoir of multidrug-resistant microorganisms which may potentially cause healthcare-associated infections via airborne transmission.

ГУМИНОВЫЕ ВЕЩЕСТВА В ПРИРОДНЫХ ВОДАХ НАРЫКСКО-ОСТАШКИНСКОЙ ПЛОЩАДИ (КУЗБАСС)

Актуальность работы. Растворенное органическое вещество почти всегда присутствует в водах и играет важную роль в формировании их химического состава, при этом до недавнего времени ему уделялось незаслуженно мало внимания. Для Кузнецкого бассейна изучение растворенного органического вещества очень важно в связи с наличием угольных отложений, что обуславливает региональную специфику нагрузок на водные системы. Цель: изучить особенности распределения растворенного органического вещества в поверхностных и подземных водах региона. Методы. Химический и органический состав воды определялись стандартными методами в Проблемной научно-исследовательской лаборатории гидрогеохимии Томского политехнического университета: органический углерод (Сорг) – методом высокотемпературного каталитического окисления, перманганатная окисляемость, химическое потребление кислорода, биохимическое потребление кислорода – методами титрования. Определение фульвокислот и гуминовых кислот проводилось методом титрования по учету бихромата, расходуемого на окисление углерода фульвогуминовых кислот. Результаты и выводы. Приведены новые данные по показателям растворенного органического вещества и концентрациям фульвокислот и гуминовых кислот в речных, озерных и подземных водах Нарыкско-Осташкинской площади Кузбасса. Показано, что во всех водах в составе гуминовых веществ преимущественно распространены фульвокислоты, от 69 до 100 %, а гумусовые имеют подчиненное значение. Подземные воды зоны активного водообмена отличаются минимальными значениями всех показателей растворенного органического вещества (Сорг, перманганатная окисляемость, химическое потребление кислорода, биохимическое потребление кислорода) и относительно неоднородным составом гуминовых веществ. Речные и озерные воды отличаются более однотипным составом гуминовых веществ и узким интервалом значений показателей растворенного органического вещества, несмотря на различия в химическом составе и рН. Воды зоны затрудненного водообмена в пределах угольных отложений на глубинах 400–1200 м отличаются наибольшими показателями растворенного органического вещества и относительно однородным составом фульвокислот и гуминовых кислот. На первом этапе исследований установлено отсутствие связи концентрации органики с соленостью и химическим составом всех вод, рН и глубины.

Composition of the Water-Soluble Soil Fraction on the Barents Sea Coast: Organic Carbon and Nitrogen, Low-Molecular Weight Components

Water extracts from soils of the Barents Sea coast (the Khaipudyr Bay) were analyzed for the contents of organic carbon and total nitrogen by the method of high-temperature catalytic oxidation with non-dispersive IR registration; the contents of low-molecular-weight acids, carbohydrates, and alcohols were determined by gas chromatography and gas chromatography–mass-spectrometry. The mass fraction of inorganic carbon $$\left( {{\text{HCO}}_{3}^{ - }} \right)$$ was measured potentiometrically, and the content of inorganic nitrogen (N–$${\text{NO}}_{3}^{ - },$$ N–$${\text{NH}}_{4}^{ + }$$) was determined by photometry. In marsh soils (Tidalic Fluvisols (Arenic or Loamic, Epiprotosalic)), = 0.1–0.8, $${\omega }{{\left( {{{{\text{N}}}_{{{\text{org}}}}}} \right)}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ = 0.01–0.05 g/kg, $${\omega }{{\left( {{{{\text{N}}}_{{{\text{org}}}}}} \right)}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ = + 0.01, and $${{\left( {{\text{C/N}}} \right)}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ = 7–21. The content of individual components does not exceed 20 mg/kg, including carbohydrates (50–90%), acids (10–50%), and alcohols (<3%). In peat horizons of tundra soils (Cryic Histosols and Histic Cryosols), = 4–10, $${\omega }{{\left( {{{{\text{N}}}_{{{\text{org}}}}}} \right)}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ ~ 0.2 g/kg, and $${{\left( {{\text{C/N}}} \right)}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ = 25–56. Litter and peat horizons accumulate both individual humus components and total dissolved organic carbon. The total weight of the identified substances is 200–300 mg/kg, 80–90% of them are carbohydrates, 10–20% are acids, and 0–9% are alcohols. The accumulation of and (N–$${\text{NH}}_{4}^{ + }{{)}_{{{{{\text{H}}}_{2}}{\text{O}}}}}$$ takes place above the permafrost table. It is argued that the ratios of organic forms of carbon and nitrogen in soil water extracts and the content of low-molecular weight organic compounds in soils can be used as indicators of pedogenic processes in the Far North.

Particulate Matter in a Hospital Environment: as Potential Reservoir for Hospital Strains

Relevance. For decades, many aspects of aerosol transmission of hospital pathogens have been and remain the subject of scientific debate. Despite fairly detailed studies of the mechanism of microbial aerosols formation, distribution, the role of particulate matter in the formation of antibiotic resistance and multidrug-resistant hospital clones of microorganisms is still unclear. Aim. To investigate physicochemical properties and microbiological diversity of hospital particulate matter. Materials and Methods. Shape and size of particulates was assessed by means of scanning electron microscopy and dynamic light scattering while elemental analysis was performed using energy-dispersive X-ray spectroscopy and high-temperature catalytic oxidation. Microbial profiling was conducted using polymerase chain reaction and Vitek 2 biochemical analyzer. Results. Hospital particulate matter included globular and fibrillary particles consisting of carbon, oxygen, calcium, silicon, aluminium, and sulfur. Intriguingly, microfiber particles had higher oxygen and calcium content along with the lower level of carbon in mineral but not organic component. Differential localisation of silicon and calcium in elemental mapping suggested that hospital particulate matter was composed of aluminosilicate minerals and calcium compounds. Among the microorganisms, we found multidrug-resistant strains Raoultella ornithinolytica, Staphylococcus pseudintermedius, Pantoea spp., Pseudomonas aeruginosa, Enterococcus faecium and additionally Pasteurella canis in hospital particulate matter samples. Conclusions. Particulate matter in the hospital environment might be considered as a potential reservoir for the evolution of antibiotic resistance and multidrug-resistant strains.

An evaluation of measurement techniques for algal-derived organic nitrogen

Algal-derived organic matter (AOM) from algal blooms in water supply systems contains dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) among other constituents. The DON and DOC are disinfection by-product (DBP) precursor compounds, and must be well characterised to facilitate effective removal, thus minimising DBP formation during disinfection. While DOC character has been studied extensively, DON analysis suffers from inaccuracies due to sample pre-treatment and instrument sensitivities. A liquid chromatography method that combines size exclusion chromatography with highly sensitive organic carbon and nitrogen detectors (LC-OCND) has been widely adopted for DOC analysis; however, its potential for application for DON charactersation has been suggested as a viable alternative to existing DON characterisation techniquesnot been assessed despite its potential. Hence, the aim was to compare the effectiveness of conventional total dissolved N–dissolved inorganic N (TN–DIN), and LC-OCND methods for analysing DON in AOM. A suite of N-containing model compounds representative of DON and AOM extracted from Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-555/1 were used to evaluate the techniques. The DON of both model compounds and AOM was first analysed using the conventional method and, then, via LC-OCND. It was observed that LC-OCND had a better precision for DON when TN contained more DIN. LC-OCND provided direct quantitative measurements for bulk and fractionated DON and DIN, with little interference caused by DIN. Additionally, LC-OCND provided information on MW distribution and protein content of the AOM. For example, LC-OCND results showed that M. aeruginosa AOM contained more HMW material than C. vulgaris AOM. However, as LC-OCND uses UV oxidation, it could not completely oxidise complex aromatic structures, and thus had a lower recovery for HMW model compounds and algal DON in comparison to the conventional method that used high temperature catalytic oxidation. Overall, it is advised that a combination of LC-OCND and TN analysis be used to provide a more detailed characterisation of N-containing AOM and other similar HMW aquatic NOM samples.

A green and robust method to measure nanomolar dissolved organic nitrogen (DON) by vacuum ultraviolet

Quantifying trace dissolved organic nitrogen (DON) in water is currently challenging for conventional methods not only because of the presence of dissolved inorganic nitrogen (DIN) species, which usually dominate in total nitrogen (TN), but also because of the high method detection limits (MDLs) of current TN methods, which are ≥100 μg/L. In order to overcome these barriers, an earlier study has applied electrodialysis to eliminate DINs from water, thereby reducing the interference of DIN. However, it remains difficult to analyze DON at nanomolar level. To address this issue, this study proposes to convert DON completely into DIN by vacuum ultraviolet irradiation (VUV) and then to measure DON by the sum of DINs (i.e., ammonia, nitrite, and nitrate). A number of verification tests show that the proposed method had comparable results with conventional methods for selected model compounds and real samples. The average nitrogen recovery for sixteen model DON compounds (each at 2.0 mg-N/L) with varying structures and molecular weights was 89 ± 16%, similar to those obtained by thermal-activated persulfate oxidation (87 ± 18%) and high temperature catalytic oxidation (86 ± 20%) methods. Moreover, this method features an advantage that it reached a MDL of 1.5 μg-N/L, much lower than conventional TN methods. With a prolonged 12-h irradiation, this approach was able to convert ammonia completely into nitrate, thus enabling detection of DON by using ion chromatography only.

The effect of land use in the catchment and meteorological conditions on the riverine transport of dissolved organic carbon into the Puck Lagoon (southern Baltic).

Dissolved organic carbon (DOC) concentration and fluxes from four rivers draining the catchment of the Puck Lagoon in southernBaltic are presented. Water samples from rivers and coastal zone close to the rivers' mouth were collected from April 2015 to March 2017. DOC was measured using high temperature catalytic oxidation with an NDIR detection. DOC concentration in rivers as well as area specific load discharged to the lagoon reflected variations of land use along their course. Area specific load of DOC discharged by rivers with high proportion of forests, meadows, and pastures in the catchment was significantly higher as compared to rivers with catchment dominated by arable land. However, the main controlling factor of the total discharged loads of DOC was the water flow. The highest loads were observed during the downpour. That was due to the larger volumes of water transported with rivers and the higher concentration of DOC resulting from increased leaching from the catchment area. The obtained results are especially important in the light of climate change in the southern Baltic region. According to the forecasts, we can expect increased precipitation and flooding and consequently increased leaching from the catchment and transport of DOC to the sea via rivers.

Catalytic oxidation of nitrogen containing compounds for nitrogen determination

The high temperature catalytic oxidation (HTCO) performance of Al2O3 supported Pt, Cu, Cu-Ce and Fe catalysts were systematically studied with a perspective of selective oxidation of nitrogenous compounds to nitric oxide for quantitative determination of bound nitrogen. The catalyst samples were prepared via impregnation and characterized by XRD and BET. In addition, temperature programmed reaction experiments with acetonitrile and oxygen were conducted to evaluate the catalytic activity and selectivity toward N2, N2O and NO. The catalyst samples were also tested for model components; urea, EDTA, pyridine, glutamic acid and ammonium sulfate representing different functional groups.The conversion of acetonitrile was tended to increase in the order of Cu-Ce/Al2O3>Cu/Al2O3>Pt/Al2O3>Fe/Al2O3 at around 500 °C and almost complete conversion of acetonitrile was achieved at 700 °C over the all catalyst samples studied. Temperature programmed reaction experiments indicated that two reaction routes, direct oxidation of cyanide species and oxidation of ammonia formed by hydrolysis of cyanide species determine NO selectivity. Direct oxidation of cyanide species is favored over Pt/Al2O3 catalyst which exhibit highest NO yield (93%) at 700 °C. The second route, hydrolysis of cyanide species to ammonia which is further oxidized to N2, NO and NO2 was evidenced by TPR-FTIR analyses over Fe/Al2O3, Cu/Al2O3 and Cu-Ce/Al2O3 catalysts. Among these catalysts, highest NO yield (90%) was observed over Fe/Al2O3 at 700 °C which is comparable to Pt/Al2O3 catalyst. For Cu and Cu-Ce/Al2O3 catalyst, lower yields were obtained due to higher N2 selectivity. Similar results were obtained from benchmark tests performed by model nitrogen components representing different functional groups. Pt/Al2O3 and Fe/Al2O3 catalysts possessed higher oxidation activities and nitrogen recoveries than Cu and Cu-Ce catalysts. As a result, Fe/Al2O3 catalyst is highly effective, lower cost alternative to existing Pt based catalysts which are used for bound nitrogen determination.