Letteratura scientifica selezionata sul tema "Oxidising treatment"

As an example of the importance and the potential of in situ structure/function studies, nitrifying aggregates from different zones of a lab-scale fluidised bed reactor were analysed by microelectrode measurements of O2, NH4+, NO2−, and NO3− and in situ hybridisation targeting the 16S rRNA of the nitrifying bacteria. A shift from an ammonia oxidising to a nitrite oxidising community is present along the reactor. In the single aggregates an active nitrifying shell of about 100 μm could be related to the maximum abundance of nitrifiers in this zone. Interestingly, the main actors in this system are not representatives of the well-described genera Nitrosomonas and Nitrobacter but some other ammonia oxidisers from the beta subclass of Proteobacteria and a thus far unknown nitrite oxidising population.

Nitrogen compounds need to be removed or captured from wastewater streams before disposal to protect our aquatic environments from eutrophication. Particular bacteria facilitating the biological removal of nitrogen during wastewater treatment include ammonia oxidising bacteria (AOB), nitrite oxidising bacteria (NOB), denitrifiers, as well as anaerobic ammonium oxidising (Anammox) bacteria. Manipulating these microbial communities can improve efficiency in nitrogen removal. Bypassing nitrate production by selectively inhibiting NOB reduces the need for oxygen and the addition of external carbon for the nitrogen removal. Various approaches to selectively inhibit NOB in the nitrification process are available. Here we present an approach using the biocide, free nitrous acid (FNA) to selectively suppress NOB growth thereby improving the efficiency of the nitrogen removal process.

A sequencing batch reactor (SBR) was operated to selectively grow a nitrite oxidising microbial community and was called the nitrite oxidising SBR (NOSBR). The nitrite oxidising characteristics of the reactor biomass were studied as well as the microbial composition. Molecular biological methods of clone libraries were used to evaluate the microorganisms in both the seed sludge and in the NOSBR sludge. We have found that the nitrite oxidation in the NOSBR was due the presence of bacteria from the Nitrospira phylum and not because of the presence of Nitrobacter which were in very low numbers in the NOSBR and not detected in the seed sludge. We hypothesize that the unknown nitrite oxidising bacteria in wastewater treatment plants are a range of species related to Nitrospira moscoviensis. A suite of primers were developed from the clone sequence data and used in a diagnostic polymerase chain reaction to prove the presence of these novel nitrite oxidisers in a range of full scale and laboratory scale activated sludge plants.

Nitrogen removal with biological methods plays a crucial role in wastewater treatment technology. The treatment begins with the oxidation of ammonia to nitrite to facilitate the subsequent nitrification and denitrification. Various strains of ammonia-oxidising bacteria have been reported. In this study, we use three Bacillus bacteria isolated from swine wastewater to oxidise ammonia. Different initial densities (103, 104, 105, and 106 CFU·mL–1) of each strain were examined. The results show that the combination of all the bacteria at a ratio of 1:1:1 and a density of 105 CFU·mL–1 exhibits the most effect. The findings contribute to the diversity of ammonia-oxidising bacterial species and pose a great potential for applying these strains in wastewater treatment.

The reduction of high concentrations of gypsum (up to 110 kg/m3) is investigated in a two stage immobilised cell bioreactor. The first stage is mainly colonised by a consortium of acidogenic bacteria and sulphate reducing bacteria oxidising volatile fatty acids with more than 2 carbons (mainly, butyrate and propionate). The gypsum consumption rate is rather high (11 kg/m3.day). Most of acetate remains unconverted in this first stage. It is partially converted in the second stage (residence time : 12 days) which is predominantly colonised by acetate oxidising bacteria. The gypsum consumption rate is much lower than in the first stage: 3 kg/m3.day. With both stages, it is possible to reach an almost complete conversion of gypsum with an overall capacity of 6.1 kg gypsum/m3.day. We propose also a very simple model to describe the different transformation rates. It allows us to clearly identify the activity levels of the different types of sulphate reducing bacteria in both stages.

In nitrogen treatment with biological methods, nitrite metabolism is an intermediate process that facilitates other processes involving different bacteria strains. In this study, we isolated two nitrite-oxidising bacteria strains from abattoir wastewater and wastewater from biogas tanks of an industrial pig farm in Ha Tinh province. The bacteria strains grow, develop, and metabolise nitrite at pH 6–8 and 30–37 °C. The samples with the nitrite concentration up to 750 mg·L–1 were oxidised within four days of incubation, and the nitrite metabolism rate was proportional to the concentration of nitrite tested. Under severe conditions (salinity up to 3% NaCl, a low dissolved oxygen level of 0.1 mg·L–1), the two isolated bacterial strains exhibited their effective growth and nitrite metabolism capacity. The results enrich the database of nitrite-oxidising bacteria and are prospective in wastewater treatment.

During this study, a mathematical model simulating piggery wastewater treatment was developed, with the objective of process optimisation. To achieve this, the effect of temperature and free ammonia concentration on the nitrification rate were experimentally studied using respirometry. The maximum growth rates obtained were higher for ammonium-oxidising biomass than for nitrite-oxidising biomass for the temperatures above 20 °C; values at 35 °C were equal to 1.9 and 1.35 day−1, respectively. No inhibition of nitrification was observed for free ammonia concentrations up to 50 mgN/L. Using these data with others experimental data obtained from a pilot-scale reactor to treat piggery wastewater, a model based on a modified version of the ASM1 was developed and calibrated. In order to model the nitrite accumulation observed, the ASM1 model was extended with a two-step nitrification and denitrification including nitrite as intermediate. Finally, the produced model called PiWaT1 demonstrated a good fit with the experimental data. In addition to the temperature, oxygen concentration was identified as an important factor influencing the nitrite accumulation during nitrification. Even if some improvements of the model are still necessary, this model can already be used for process improvement.

The present work deals with a bioremediation study of a heavy-metal polluted harbour sediment, obtained from the Italian Adriatic Coast. Bioleaching of the sediment sample was performed with a mixed culture of acidophilic, chemi-autotrophic Fe/S oxidising bacteria. The effect of an anaerobic biostimulation pre-treatment on the extent of Cd, Cu, Zn, Ni, Pb, Hg, As, Cr extraction by bioleaching was evaluated. The biostimulation pre-treatment was intended to stimulate autochthonous sulfate reducing strains, to enhance the sulfide fraction in the sediment, to favour subsequent activity of reduced-sulfur-oxidizing bacteria in the subsequent bioaugmentation (bioleaching). The effect of the duration of anaerobic pre-treatment (21 and 30 days) in the presence and absence of 1% glucose was tested. The results obtained showed that the activity of the reducedsulfur- oxidising strains was significantly enhanced after an anaerobic pre-treatment of the sediments and showed real promise for the application of bioleaching for metal polluted sediments.

A bacterial community in activated sludge from a full-scale municipal wastewater treatment plant was monitored throughout the year with the use of FISH, RISA and DGGE techniques. In the investigated range of temperatures (11.9-21.6 degrees C), a rise in temperature resulted in a lower total bacteria richness, while organic load rate changes from 0.09 to 0.21 g COD x g TSS(-1) x d(-1) were positively correlated with the number of bands in RISA patterns. The most diverse pattern (29 different bands) was characteristic for the activated sludge sample collected at the end of January at wastewater temperature of 11.9 degrees C. The ammonia-oxidising bacteria community did not change during the study, and comprised of 4 different bacterial populations with one dominant species closely related to Nitrosospira sp. REGAU (GenBank accession number AY635572.1). The percentage of ammonia-oxidising bacteria in the activated sludge varied from 6.2 to 19.5% and depended on temperature (R = 0.61, p = 0:02) and organic load rate (R = -0.55, p = 0.04).

Coal tar pitch is a residue of coal tar separation. It is widely used as a binder in the production of electrodes and anode mass. The production of pectic carbonisates and the development of methods to increase the value of its yield is of scientific and applied interest. The author conducted experiments on heat treatment in oxidising medium of medium-temperature electrode pitch of category BsTmelt = 71.5 °C (AO Altai-Koks, Russia). We conducted the process of heat treatment of the pitch in a 5.6 litre reactor heated by using an integrated electric heating system. To enhance the increase of Tmelt during heat treatment, we pumped the gas phase products from the reactor to a collection tank where they condensed. We performed heat treatment at T > 400 °C using both thermal oxidation of pitch and pumping of distillates. We formed the oxidising environment by supplying air by a compressor to the molten pitch. The air supply process started after the holding temperature was reached. The temperature controller provided the holding temperature. The author determined the yield of thermo-oxidation products, melting temperatures Tmelt, and volatile yields X for the resulting products. We obtained pitch with Tmelt = 140 °C and 158 °C. However, this heat treatment significantly reduced the yield of volatile substances in the final products. The temperature of carbonisation of heat-treated pitch was T = 650 °C and T = 850 °C. Therefore, research determines the carbonisate yields. Moreover, carbonisation proceeds with the additional holding times at 450 °C and 650 °C. Hence, heat treatment increased the carbonisate yield by 10%. Holding times at 450 °C and 650 °C also quantitatively increased the yield of carbonisate.

Cette thèse s’inscrit dans le cadre du projet SELF France 2030, qui propose un prétraitement oxydant par l’eau des déchets métalliques nucléaires dans un sel NaOH-KOH-H₂O fondu à 225⁰C, avant leur conditionnement en matrices cimentaires. Ce procédé permet d’inerter les déchets métalliques et assure la sûreté du colis de stockage. Le travail de thèse a donc été consacré à l’étude de la réactivité des principaux déchets nucléaires métalliques – graphite, magnésium et uranium – dans le sel fondu NaOH-KOH à 225⁰C. Une première partie concerne le mélange NaOH-KOH (51,5 – 48,5 mol%) fondu à 225⁰C pour acquérir des données thermodynamiques et expérimentales sur sa stabilité chimique et électrochimique. Les études gravimétriques et électrochimiques montrent que le mélange contient 15 mol% d’eau à 225⁰C, ce qui est caractéristique d’une forte solvatation de l’eau dans ce milieu. Les propriétés redox du sel ont été étudiées par électrochimie couplée à la micro-chromatographie en phase gazeuse (μGC). Les réactions aux limites anodique et cathodique sont fortement influencées par la teneur en eau : en milieu hydraté, la limite cathodique correspond à la réduction de H₂O en H₂, alors qu'en milieu déshydraté, c’est la réduction de Na⁺ qui limite le domaine d’électroactivité. Quant à la limite anodique, elle est attribuée à l’oxydation de OH⁻ en O₂ dans les milieux contenant des teneurs en eau supérieures à 8,7 mol% et à l’oxydation de OH⁻ en O₂⁻ pour des teneurs inférieures. L’étude électrochimique a permis de calculer le coefficient d’activité de l’eau dans le mélange d’hydroxydes fondus à 225⁰C. Le résultat confirme une forte solvatation de l’eau dans ce milieu. L’eau étant l’élément oxydant dans le milieu, il était important de pouvoir suivre sa teneur in-situ. C’est ainsi qu’une droite de calibration basée sur la mesure du courant de pic de réduction de l’eau - Ipc =f([H₂O]) - a été établie pour pouvoir doser l’eau lors des différentes expériences. Le coefficient d’activité de NaOH a également été déterminé par électrochimie. Cet ensemble de données expérimentales a permis de calculer le diagramme de stabilité du sel NaOH-KOH en fonction du potentiel et de la teneur en eau. Enfin, un moyen de contrôle et de maintien de la quantité d’eau a été proposé pour assurer une oxydation continue des déchets métalliques. La deuxième partie de cette thèse a été dédiée à l'étude de la réactivité du graphite, du magnésium et de l’uranium dans les hydroxydes fondus à 225⁰C contenant de l’eau. Cette étude a montré que le graphite est stable dans les hydroxydes fondus. D’après les données thermodynamiques, le magnésium peut être oxydé par l’eau ou les ions Na⁺, conduisant respectivement à la formation de H₂ ou de Na, composé pyrophorique. Cependant, les études expérimentales montrent que le magnésium est toujours oxydé par H₂O et, par électrochimie, on montre que l’oxydation du magnésium est observée à un potentiel supérieur à celui de la réduction des ions Na⁺. Par ailleurs, la cinétique d’oxydation de Mg est proportionnelle à la concentration en eau pour les plus faibles teneurs en eau, ce qui est caractéristique d’un contrôle cathodique de la dissolution. A des teneurs élevées en eau, la cinétique d’oxydation atteint une limite qui dépend de la surface active du magnésium, on a alors un contrôle anodique de la dissolution. Pour la mise en œuvre industrielle et afin de gérer la cinétique de dissolution des déchets et la formation de H₂, il est donc préconisé de partir d’un sel fondu déshydraté et d’ajouter l’eau en continu. L’ensemble des données expérimentales a permis de calculer le diagramme de stabilité du magnésium dans le milieu. Concernant le comportement de l’uranium dans le sel fondu, les calculs thermodynamiques montrent que l'uranium est oxydé préférentiellement en K₂UO₄. Les analyses par chromatographie gazeuse ont confirmé l’oxydation de l’uranium par l’eau et l’étude expérimentale a permis de proposer un mécanisme réactionnel
This thesis is part of the SELF France 2030 project, which proposes a water-based oxidative pretreatment of metallic nuclear waste in a NaOH-KOH-H₂O salt melted at 225⁰C before conditioning in cementitious matrices. This process inserts the metal waste and ensures the safety of the disposal package. The thesis work was therefore devoted to studying the reactivity of the main metallic nuclear wastes - graphite, magnesium, and uranium - in molten NaOH-KOH salt at 225⁰C. The first part concerns the NaOH-KOH mixture (51.5 - 48.5 mol%) melted at 225⁰C to acquire thermodynamic and experimental data on its chemical and electrochemical stability. Gravimetric and electrochemical studies show that the mixture contains 15 mol% water at 225⁰C, which is characteristic of high water solvation in this medium. The redox properties of the salt were studied by electrochemistry coupled with gas-phase micro-chromatography (μGC). Reactions at the anodic and cathodic limits are strongly influenced by water content: in hydrated media, the cathodic limit corresponds to the reduction of H₂O to H₂, whereas in dehydrated media, it is the reduction of Na⁺ that limits the electroactivity range. The anodic limit is attributed to the oxidation of OH⁻ to O₂ in media with water contents above 8.7 mol% and to the oxidation of OH- to O₂⁻ for lower contents. The electrochemical study enabled us to calculate the water activity coefficient in the molten hydroxide mixture at 225⁰C. The result confirms the high solvation of water in this medium. Water is the oxidizing element in the medium, so it was important to monitor its content in situ. Therefore, a calibration line based on measuring the water reduction peak current - Ipc =f([H₂O]) - was established, enabling water to be measured in the various experiments. The activity coefficient of NaOH was also determined electrochemically. This set of experimental data was used to calculate the stability diagram of the NaOH-KOH salt as a function of potential and water content. Finally, controlling and maintaining the amount of water was proposed to ensure continuous oxidation of metallic waste. The second part of this thesis was dedicated to studying the reactivity of graphite, magnesium, and uranium in molten hydroxides containing water at 225⁰C. This study showed that graphite is stable in molten hydroxides. This study showed that graphite is stable in molten hydroxides. According to thermodynamic data, magnesium can be oxidized by water or Na⁺ ions, forming a pyrophoric compound of H₂ or Na. However, experimental studies show that H₂O continuously oxidizes magnesium, and electrochemically, magnesium oxidation is observed at a higher potential than Na⁺ ion reduction. Furthermore, Mg oxidation kinetics are proportional to water concentration at lower water contents, characteristic of cathodic dissolution control. At higher water contents, the oxidation kinetics reach a limit that depends on the active surface of the magnesium, giving anodic control of the dissolution. For industrial implementation and to manage waste dissolution kinetics and H₂ formation, it is recommended to start with a dehydrated molten salt and continuously add water. We calculated a stability diagram for magnesium in the medium based on all these experimental data. Concerning the behavior of uranium in molten salt, thermodynamic calculations show that uranium is preferentially oxidized to K₂UO₄. Gas chromatography analyses confirmed uranium oxidation by water, and experimental studies proposed a reaction mechanism

Today, more than in the past, water is considered a very valuable resource. Efforts to use it efficiently are growing. One method of using water efficiently is wastewater treatment. Well-treated water minimises negative impacts after discharge into a watercourse, i.e., within or adjacent to aquatic ecosystems, or can be reused, for example, in the form of drinking water. This study focuses on the possibility of treating food industry water using biochar as a sorption medium. Biochar from wood pulp (100%) was used for the experiments. The wastewater collected was a mixture from two production plants, focussing on aspics, fish spreads, or cheese processing. The aim of the experiments was to evaluate the efficiency of the sorption properties of a specific type of biochar in terms of its weighting of different masses for an identical volume of wastewater and also in terms of different sorption times (time dependence). The efficiency was addressed in the context of the determination of the chemical oxygen demand with the oxidising agent potassium dichromate (CODCr method). The highest efficiency was achieved in the experiment with a load of 2 g of sorption reagent per litre of wastewater. No trend was demonstrated in the efficiency change with respect to the time of contact of the sorbent with the water.

Turbine inlet temperatures have now approached 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and thrust levels approaching or exceeding 445 kN (100,000 lbs.). High reliability and durability must be intrinsically designed into these turbine engines to meet operating economic targets and ETOPS certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, computerized design technology for stresses and airflow and the development and application of rhenium (Re) containing, high γ′ volume fraction nickel-base single crystal superalloys, with advanced coatings, including prime-reliant ceramic thermal barrier coatings (TBCs). Re additions to cast airfoil superalloys not only improve creep and thermo-mechanical fatigue strength but also environmental properties, including coating performance. Re slows down diffusion in these alloys at high operating temperatures.(1) At high gas temperatures, several issues are critical to turbine engine performance retention, blade life and integrity. These are tip oxidation in particular for shroudless blades, internal oxidation for lightly cooled turbine blades and TBC adherence to both the airfoil and tip seal liner. It is now known that sulfur (S) at levels < 10 ppm but > 0.2 ppm in these alloys reduces the adherence of α alumina protective scales on these materials or their coatings by weakening the Van der Waal’s bond between the scale and the alloy substrate. A team approach has been used to develop an improvement to CMSX-4® alloy which contains 3% Re, by reducing S and phosphorus (P) levels in the alloy to < 2 ppm, combined with residual additions of lanthanum (La) + yttrium (Y) in the range 10–30 ppm. Results from cyclic, burner rig dynamic oxidation testing at 1093°C (2000°F) show thirteen times the number of cycles to initial alumina scale spallation for CMSX-4 [La + Y] compared to standard CMSX-4. A key factor for application acceptance is of course manufacturing cost. The development of improved low reactivity prime coats for the blade shell molds along with a viable, tight dimensional control yttrium oxide core body are discussed. The target is to attain grain yields of single crystal CMSX-4 (ULS) [La + Y] turbine blades and casting cleanliness approaching standard CMSX-4. The low residual levels of La + Y along with a sophisticated homogenisation/solutioning heat treatment procedure result in full solutioning with essentially no residual γ/γ′ eutectic phase, Ni (La, Y) low melting point eutectics and associated incipient melting pores. Thus, full CMSX-4 mechanical properties are attained. The La assists with ppm chemistry control of the Y throughout the single crystal turbine blade castings through the formation of a continuous lanthanum oxide film between the molten and solidifying alloy and the ceramic core and prime coat of the shell mold. Y and La tie up the < 2 ppm but > 0.2 ppm residual S in the alloy as very stable Y and La sulfides and oxysulfides, thus preventing diffusion of the S atoms to the alumina scale layer under high temperature, cyclic oxidising conditions. La also forms a stable phosphide. CMSX-4 (ULS) [La + Y] HP shroudless turbine blades will commence engine testing in May 1998.