1,720,999 research outputs found
Advanced oxidation processes (AOPs) as innovative technology for the remediation of contaminated sites
Full text linkIl problema della contaminazione dei terreni e delle acque di falda da composti organici biorecalcitranti sta diventando sempre più preoccupante agli occhi della comunità scientifica e dell’opinione pubblica. L’aumento del numero di siti contaminati da tali sostanze sta spingendo alla graduale sostituzione delle tradizionali operazioni di smaltimento in discarica con tecnologie che consentano la bonifica attraverso la riduzione del carico inquinante fino al raggiungimento di concentrazioni residue non pericolose per la salute umana. Tra i possibili processi alternativi, i processi avanzati di ossidazione chimica (AOP) possono costituire una potenziale soluzione a molti casi di contaminazione da composti organici. Se opportunamente progettati, tali sistemi possono condurre alla completa mineralizzazione degli inquinanti o, eventualmente, alla loro trasformazione in molecole più facilmente biodegradabili. Il loro principio operativo è basato sull’ idea di generare un pool di specie ossidanti altamente reattive. I diversi AOP si differenziano solo nel modo in cui tale pool di sostanze viene generato. Una volta prodotte, tali specie sono in grado di reagire efficacemente con i principali inquinanti di interesse ambientale. Inoltre, alcuni AOP sono in grado di trattare efficacemente anche composti adsorbiti sulla superficie del suolo, in quanto le specie radicaliche ne favoriscono il desorbimento rendendole disponibili all’ossidazione in fase acquosa. Le caratteristiche degli AOP li rendono perfettamente idonei come tecnologia di bonifica in-situ. In questa configurazione, si prevede l’iniezione nel sottosuolo della soluzione ossidante senza la necessità di rimuovere il terreno e di estrarre le acque di falda.
Il presente studio è stato sviluppato con l’intento di perseguire un duplice obiettivo: da un lato approfondire le conoscenze di base sui meccanismi di azione degli AOP, al fine di sviluppare criteri di progettazione innovativi; dall’altro valutare l’applicabilità di diversi processi AOP a situazioni rappresentative dei siti contaminati tipicamente riscontrati in Italia. Il primo obiettivo è stato perseguito mediante uno studio di base finalizzato ad identificare la relazione tra condizioni operative del processo e formazione di specie radicaliche e non, nei sistemi di ossidazione basati sul reattivo di Fenton, sul processo a persolfato attivato e sul processo di ossidazione basato sugli acidi perossi-organici (perossiacidi). Il secondo obiettivo è stato invece perseguito sviluppando un approccio progettuale incentrato sulla redazione di studi di fattibilità. Tale approccio ha consentito di arrivare, nel caso del processo Fenton, fino alla realizzazione di un intervento di ossidazione chimica in-situ (ISCO) in scala pilota per la bonifica di un sito contaminato da MtBE, mentre nel caso del sistema a persolfato attivato e dei perossiacidi si è limitato alla fase di studio di fattibilità in scala di laboratorio. La progettazione delle diverse fasi sperimentali é stata, ove possibile, effettuata utilizzando il metodo Rotatable Central Composite (RCC), mentre i risultati ottenuti sono stati interpolati mediante opportuni strumenti statistici, come il Metodo delle Superfici di Risposta (RSM) al fine di individuare le relazioni quantitative tra le prestazioni dei processi investigati e le condizioni operative impiegate.
La presente tesi è stata scritta dedicando ad ogni tecnologia presa in esame una prima parte bibliografica, nella quale la tecnologia viene introdotta e ne vengono messe in evidenza le caratteristiche, seguita da una seconda parte in Appendice, dove i risultati sperimentali ottenuti vengono mostrati e discussi attraverso una selezione delle pubblicazioni prodotte durante il triennio di svolgimento del dottorato di ricerca, compreso tra il 2004 ed il 2007, e sottomesse a riviste specializzate del settore o presentate nell’ambito di convegni internazionali.The contamination of soil and groundwater by means of bio-recalcitrant organic compounds, is becoming a matter of concern for scientific community and public opinion. The increase of the number of contaminated sites, is forcing to gradually switch from traditional dump disposal, towards innovative technologies which are capable of reaching the remediation goals, thus reducing the pollutant load to concentrations which are considered harmless for human health. Among the innovative ones, Advanced Oxidation Processes (AOPs) could represent a potential solution to be applied for remediating contamination by bio-recalcitrant organic compounds. Their operative principle is based upon the idea of generating a pool of highly-oxidative species. The AOPs differ only by the way in which this pool is generated. Once formed, these species are capable to effectively react with most of common pollutants such as hydrocarbons, chlorinated solvents, polycyclic aromatic hydrocarbons and polychlorobiphenyls until their complete oxidation to carbon dioxide and water, or at worst their transformation to more bio-degradable products. Moreover, some AOPs are able to effectively tackle sorbed compounds, since oxidative radicals can desorb these compounds from the soil surface, thus allowing their oxidation in aqueous phase. Besides, it is worth pointing out that the AOPs characteristics make them suitable to be applied as in-situ remediation technologies. In this configuration, the oxidant is injected directly into the subsurface without the need of soil excavation or groundwater extraction.
The present study has been developed with the intention of achieving a two-fold objective: on the one hand, to better understand the fundamental mechanisms of AOPs, in order to develop innovative criteria for their design; on the other hand, to assess the feasibility of different AOPs to those situations which are somehow representative of the Italian contaminated sites. The first objective was pursued by developing a fundamental study aimed to identify the relationship between the process operating conditions and the formation of radical and non-radical species for Fenton’s process, activated persulfate and peroxy-acid oxidation processes. The second objective was instead pursued by developing, based on the experimental results of the fundamental study, a design approach based on the execution of feasibility studies. In case of Fenton’s process, a pilot-scale In-Situ Chemical Oxidation (ISCO) treatment for the remediation of an MtBE-contaminated site was developed, whereas in the case of activated persulfate and peroxy-acid oxidation technologies a lab-scale feasibility test was carried out. The design of the different experimental phases was performed, as much as possible, by applying the Rotatable Central Composite method (RCC), whereas the relationships between process performance and applied operating conditions was found by handling and interpolating the experimental results by proper statistical tools based on the Response Surface Method (RSM).
In this Ph.D. thesis, each tested AOP is first discussed in a bibliographic part, where the process is introduced and its main features are explained, based on the available and updated literature. The main findings obtained in this part and the innovation introduced with respect to the state of the art is also described in this section of the Ph.D. thesis. The details of these results are shown in the second section of the thesis, which consists of four Appendices, where a selection of papers submitted either to international conferences and peer-reviewed journals during my Ph.D. research are included
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
Design of in-situ fenton oxidation based on the integration of experimental and numerical modeling
No full textAppropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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