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Trasporto di microplastiche durante piene fluviali: esempi dal fiume Arno (Toscana, Italia)
Get PDFMicroplastics are ubiquitous pollutants which pose a huge threat to ecosystems and human health. Plastic production has grown exponentially over time, and, consequently, also the plastic waste. Rivers are seen as the major vectors to deliver microplastics in marine environments, but they also are efficient temporary reservoirs. However, there is a lack of information on the dispersal pattern and transport of microplastics in river sediments, as previous researches mainly have focused on diversification and quantification of microplastics and their impacts on freshwater environments.
This study aims at providing new insights on this topic by analysing river sediments deposited after flood events and trying to identify any relationship between the depositional setting/process and the amount of microplastics accumulated in fluvial sediments. To achieve this goal, a total of 37 sediment samples form five alternate bars of the Arno River (Tuscany, Italy) were analysed to provide a complete spectrum for microplastic abundances and distributions in sediments accumulated in different conditions. Specifically study depositional conditions were: i) under dominant tractional processes during floods (samples T), ii) during brief episodes of standing water during the overall waning phase (samples S), iii) during the latest stages of the flood in standing to slowly moving water (samples M) and iv) during the highest flood water levels, associated with floating vegetation debris (samples F). The microplastics were extracted from the sediment by using the sodium polytungstate diluted to 1.6 /3 and the organic rich samples were previously oxidated with the Wet Peroxide Oxidation technique to eliminate the organic matter. The mechanical sieving was used to obtain the grain size distribution of the sampled sediments.
This approach led to the identification of some important features involving microplastic deposition in river sediments. As expected, the presence of microplastics was confirmed in all samples analysed, with variable concentrations ranging from 0.44 MPs/g up to 6.67 MPs/g, and a predominance of microfibres. Microplastic concentrations not only vary from a bar to another, but also within a single bar, suggesting there are different processes governing microplastics transport and depositions. Settling during the standing water, associated with the waning phase, seems to be the easier way for microplastics to deposit in river sediments, both within mud but also within interstitial space between gravelly clasts. Nevertheless, it was unexpected to see how many microplastics can be trapped in sandy deposits when they are moved under tractional conditions
Analisi dell'effetto del pilota sulla stabilità del modo weave
No full textAnalisi dell'effetto del pilota sulla stabilità dei motocicli secondo diverse modalità, in riferimento alle sue caratteristiche inerziali e alla sua apposizione o meno delle mani sul manubrio
Experimental investigation of single and two-phase heat transfer for propylene in a horizontal structured tube
Get PDFThe present work has been developed and performed at the Technical Thermodynamics Faculty of the University of Kassel within the Erasmus exchange program of the University of Padova. Two-phase processes are used in a variety of industries and application. The aim of this work was to investigate the performance of a micro-fin tube in terms od pressure losses and heat transfer during single-phase gas cooling flow and two-phase condensing flow with propylene as test fluid
Studies on the application of MMC technology to the Acceleration Grid Power Supply of the Neutral Beam Injector of DTT
Get PDFThe thesis investigates the feasibility of adopting alternative Modular Multilevel Converter topologies as the Acceleration Grid Power Supply of the Neutral Beam Injector of DTT.The converter should adopt compact submodules and minimise the clearances required to maintain the insulation.A scaled-down model of the converter is developed to simulate its performances and verify its compliance with the requirements imposed by the operation of the Neutral Beam Injector
Improvement in the survivability of Streptococcus thermophilus TH982 under simulated gastrointestinal conditions by encapsulation with 2'-fucosyllactose
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