1,720,958 research outputs found
Effects of different operating conditions on sediment slurry sequencing batch reactors treating marine port sediments contaminated by PAHs
Full text linkDue to intensive anthropic activities, marine port sediments are often contaminated by organic pollutants like polycyclic aromatic hydrocarbons (PAHs), which represent a significant environmental threat. In this study, two sediment slurry sequencing batch reactors (SS-SBRs) were used to biologically degrade a mixture of PAHs (namely fluorene, phenanthrene, fluoranthene and pyrene) from marine sediments dredged from Cagliari (Italy) and El Kantaoui (Tunisia) ports. To enhance PAHs removal by biostimulation, nutrients were added in both sediments, acetate was used as co-substrate (El Kantaoui, SS-SBR1), and saponins were used as surfactants (Cagliari, SS-SBR2). Moreover, different levels of contamination (up to 200 mgPAHtot/kgdw in SS-SBR1; up to 400 mgPAHtot/kgdw in SS-SBR2) and solid to liquid ratios (S/L, up to 0.2 in SS-SBR1; up to 0.1 in SS-SBR2) were applied. As to SS-SBR1, the highest removal efficiencies (99-100% and 98-100% for 3- and 4-ring PAHs, respectively) were achieved when the level of contamination and S/L were set at 200 mgPAH-tot/kgdw and 0.1, 150 mgPAH-tot/kgdw and 0.13, and 150 mgPAH-tot/kgdw and 0.20, respectively; as to SS-SBR2, very high removal efficiencies (99÷100% and 98÷100% for 3- and 4-ring PAHs, respectively) were observed during the whole experimental campaign. Such results are promising and provide a useful background for testing other important operating parameters (e.g., the volumetric exchange ratio)
Evaluation of nitrous oxide gaseous emissions from a partial nitritation reactor operating under different conditions
No full textIn this study, a laboratory-scale partial nitritation (PN) reactor was fed with a synthetic medium simulating the ammonium-rich wastewater produced by the anaerobic digestion of food waste. The reactor was operated at constant hydraulic retention time (1 d) and nitrogen loading rate (1.5 g N/L d), with different influent alkalinity to ammonium-nitrogen molar ratios (Alk/N, 1 and 1.3) and dissolved oxygen (DO) concentrations (5.0, 3.0, 2.0, 1.5, and 1.0 mg O-2/L). For each operating condition tested, nitrous oxide (N2O) gaseous emissions from the PN reactor were measured via infrared gas-filter correlation, in order to achieve a deeper understanding of process potential environmental impact. As DO concentration ranged between 5.0 and 1.5 mg O-2/L, the partial conversion of ammonium to nitrite was successfully achieved, with negligible nitrate production and nitrous oxide emission. When Alk/N was increased from 1 to 1.3 (DO was not limiting), the increase in ammonium-nitrogen oxidation rate (AOR, from 717 +/- 17 to 945 +/- 21 mg NH4-N/L d) and the simultaneous decrease in N2O-N emission factor (from 0.33% +/- 0.01% to 0.23% +/- 0.01% of AOR) were observed. When DO was set to 1.0 mg O-2/L, PN was irreversibly compromised, and a corresponding increase in N2O-N emission factor was observed (from 0.22% +/- 0.01% to 0.61% +/- 0.03% of AOR). Nitrifier denitrification was suggested as the main pathway contributing to N2O emission. Minimization of anoxic conditions may contribute in reducing greenhouse gas emissions even at low DO concentrations, as long as they are not process-limiting
Aerobic granular sludge formation in a sequencing batch reactor treating agro-industrial digestate
Full text linkMost of nitrogen emissions can be ascribed to agro-industrial activities. Since digestate produced by fermentation of agro-industrial residues can be difficult to dispose of due to its high ammonium content, advanced technical- and cost-effective technologies must be developed and applied in order to significantly reduce its impact on the environment. In this study, aerobic granules were successfully cultivated in a granular sludge sequencing batch reactor (GSBR) fed with the ammonium-rich (approx. 2500 mg L−1) effluent of a 3-stage anaerobic digester treating agro-industrial residues. The peculiar characteristics of such wastewater required a 2-step operating strategy aimed at the selection of nitrifying biomass (Step 1) and the formation of aerobic granular sludge (Step 2). During Step 1, nitrifying biomass selection was achieved by properly regulating the cycle length: (Formula presented.) removal rates progressively increased from 42 to 109 mgN L−1d−1, and a corresponding increase in (Formula presented.) specific removal rates from 8 to 24 mgN gVSS−1d−1 was also observed. During Step 2, the increase in selective pressures (i.e. minimum settling velocity and volumetric organic loading rate) led to the formation of compact (average diameter, 1.02 ± 0.43 mm) and well-settling granules (SVI5, 28.6 ± 3.8 mL gTSS−1), which were able to remove up to 89 ± 2% of organic matter (as COD), 79 ± 3% of (Formula presented.) and 59 ± 4% of nitrogen (as a sum of (Formula presented.), (Formula presented.) and (Formula presented.)). The 2-step operating strategy played a key role in biomass selection and subsequent granule formation and maintenance in the GSBR, and may be successfully adopted for the treatment of different ammonium-rich wastewaters
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
Preliminary evaluation of microbial fuel cells applicability to bioremediate marine sediments contaminated by polycyclic aromatic hydrocarbons
Full text linkVariations 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
Appropriate 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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