1,721,050 research outputs found
Treatment of wastewater from textile dyeing by ozonization
Full text linkWet processes for textile production are one of the largest water consuming and polluting sources. Quite usually, at the end of the dyeing process, a noticeable amount of dyes remains in wastewater as is not absorbed by fibres, leading to wastewater colouration. Dyes show resistance to degradation in the environment, since their peculiarity is chemical stability. Besides visual problems, the effect of residual dyes is negative on aquatic life because they inhibit sunlight transmission and may enter in the food chain. Generally, conventional biological treatment alone cannot guarantee adequate characteristics to treated water to allow the discharge into the environment or reuse in other processes. Specifically, a high salt content and residual colour are still present in the treated water after secondary treatments. Salt content can be remove using membrane filtration equipment instead the most profitable operation to remove colour appears oxidation. Other techniques, such as coagulation-flocculation, adsorption, membrane filtration, activated sludge, were studied to remove colour but land filling or incineration must be considered as final process. On the contrary, oxidation steps demolish the contaminant at molecular scale, even though not necessary the oxidation is complete. Generally ozone, being an oxidant agent, has a high oxidation potential (even at a low concentration), high efficiency in decomposition of organic matter, adds oxygen to water and has process low sensitivity to changes in temperature. Ozone is able to break up the conjugated bonds of organic matter thanks to a direct reaction between ozone and the organic compound or indirectly through the generation of hydroxyl radicals. The degradation of dyes with O3 is a typical two phase reaction where an effective transfer of ozone from gas to liquid is a critical point. On the other hand, the kinetics of decolouration is usually fast. Therefore, the mass transfer is the rate limiting step. To achieve the best mass transfer condition, several gas diffusers and gas-liquid contactors have been proposed in literature such as turbines, ejectors, gas diffusers (sintered glass diffuser), etc. An innovative operative procedure took into account in this work was cavitation: it was considered as the mean to increase mass transfer of ozone in liquid medium. For this reason, an experimental equipment (Multi-task reactor) was designed and built (Fig. 1). Two types of cavitation were considered: hydrodynamic cavitation by ejector and ultrasound cavitation. The two types of cavitations were used separately or simultaneously in order to clean wastewater from different dyes typology (namely acid, cationic, reactive and disperse dyes). In addition, hydrodynamic and ultrasonic cavitation was used to work alone to decolourise wastewater. Cavitations are able to produce free radicals, such as hydroxyl radicals, which can be used to attack dye cromophores groups of dye molecule. A bubble column reactor was built to compare the decolourisation results obtained in the Multi-task reactor. Bubble column was used as benchmark because represent the most common technology in wastewater decolouration. First of all, decolouration experiments were performed in the multi-task equipment in liquid batch conditions. After that, continuous tests were carried out and the results were compared with bubble column equipment decolouration experiments at the same operational conditions (liquid residence time, gas flow rate, ozone dose, dyestuffs and its concentration). Taking into account the final experiment results, only ultrasound cavitation was able to improve decolouration degree in the case of disperse dye. Comparing the experimental decolouration results obtained with the mentioned technologies, bubble reactor seem to be the best technology for oxidizing treatment. Moreover, fluid dynamic study was performed to bubble column reactor in order to stud
Pump and ejector design in wastewater treatment pilot equipment
No full textOzone treatment is an oxidative process used in wastewater treatment plant to demolish complex organic molecule. In the case of textile industry is required to adequately remove residual color, demolishing the chromophoric bonds or groups in the dye molecules. A useful method for adding the ozone gas into water and maximize ozone-water mixing to increase mass transfer, is the use of Venturi ejectors. Forcing water through Venturi body, it creates a differential pressure between the fluid inlet and outlet, which in turn creates a vacuum inside the ejector body. In this part, it is possible introduce ozone. COMSOL Multiphysics® is used to define the design parameter of the ejecto
Guideline for unexplained couple infertility: misunderstandings on the approach to the male factor
No full textComparative ozone decolouration in bubble column and in ejector mixer units
No full textOzone treatments are very effective to reduce the residual coloration in wastewater from wet textile processes. The oxidative treatment is very flexible as a result of the easy and prompt regulation of the ozone generator, together with the high solubility of the reactant. Two equipment configurations were considered to evaluate the 03 mass transfer to wastewater. The two schemes are competitive since the ejector mixer prevails in terms of local mass transfer coefficient, while the bubble column has a more favourable hydrodynamics as far as the liquid phase is concerned, since a partial plug flow between the liquid and the gas phase has been demonstrated. The two units, which appear below, were compared in laboratory and in the field tests by operating at strictly controlled conditions. In the laboratory synthetic exhausted dye-liquors were prepared and fed in parallel to the two units by setting a residence time of approximately 30 min. When the experimentation was carried out in the field, real wastewater from a dye house was treated at the conditions suggested by the laboratory tests. Oxygen was fed to the generator at a rate of 200 NL/h; ozone was produced to have a dosage of 30 to 80 g/m3 of treated water. The industrial experimentation has revealed almost identical performances in terms of colour removal (> 98% in all trials), COD reduction (in the range from 15 to 45%), surfactants reduction (from 70 to 95% of the influent) in the two units. A certain performance difference was evident depending on the class of dyes considered. As a fundamental study, the bubble unit was investigated to draw the ozone concentration profile along the column height and to measure the off-gas ozone concentration. A technological conclusion suggests that bubble systems are favoured due to their simple structure and to the overall energy requiremen
DEGRADATION OF RESIDUAL DYES IN TEXTILE WASTEWATER BY OZONE: EFFECT OF HYDRODYNAMICS AND CAVITATION
No full textDownstream dyeing facilities, a noticeable amount of dyes may remain in the wastewater giving anaesthetic colouration. Conventional biological treatment alone cannot guarantee decolouration and tertiary treatments have to be considered: two oxidation routes by ozone were considered in this work. A bubble column reactor (benchmark, also at industrial scale) and a recycle well-mixed reactor were compared to reach a complete decolouration. In addition, hydrodynamic and ultrasonic cavitation were considered in the recycled well-mixed reactor to intensify its performance.
Ozone treatment was protracted to obtain different decolouration degrees on wastewater from wool dyeing. The resulting water was tested as recycled fluid to generate dyeing liquors, the definition of minimal quality specification being the goal of this procedure
The complex relation between obstructive sleep apnoea syndrome, hypogonadism and testosterone replacement therapy
Full text linkObstructive sleep apnoea syndrome (OSAS) is an under-recognized medical disease. The main risk factors for OSAS are male sex, older age, obesity, and metabolic syndrome, that are also associated with male hypogonadism (MH). Therefore, obesity has been classically identified as the most evident link between OSAS and MH. However, OSAS is per se linked to the development of MH by a combined effect of hypoxia, increased night-time awakenings, reduced sleep efficiency and fragmented sleep. Similarly, MH might represent a risk factor for OSAS, mainly related to sleep disturbances that are frequently associated with low testosterone. Data on testosterone replacement therapy (TRT) in patients with OSAS are limited. Nevertheless, TRT is generally contraindicated by guidelines in the presence of untreated or severe OSAS. TRT might in fact worse OSAS symptoms in different ways. Furthermore, OSAS has been proposed to be a risk factor for secondary polycythaemia and TRT might exacerbate polycythaemia. Therefore, TRT in hypogonadal men affected by untreated OSAS or severe OSAS should be considered with caution and in a personalised way. Nevertheless, the type and dosage of TRT should be considered, as short-term high-dose TRT might worsen OSAS, whereas long-term lower doses could eventually determine a clinical improvement of symptoms of OSAS. Here we reviewed the data on the association between OSAS, MH and TRT, including the opportunity of assessment of patients who develop signs and symptoms of OSAS during TRT by polysomnography
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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