1,720,969 research outputs found
From Organic Wastes and Hydrocarbons Pollutants to Polyhydroxyalkanoates: Bioconversion by Terrestrial and Marine Bacteria
Full text linkThe use of fossil-based plastics has become unsustainable because of the polluting production processes, difficulties for waste management sectors, and high environmental impact. Polyhydroxyalkanoates (PHA) are bio-based biodegradable polymers derived from renewable resources and synthesized by bacteria as intracellular energy and carbon storage materials under nutrients or oxygen limitation and through the optimization of cultivation conditions with both pure and mixed culture systems. The PHA properties are affected by the same principles of oil-derived polyolefins, with a broad range of compositions, due to the incorporation of different monomers into the polymer matrix. As a consequence, the properties of such materials are represented by a broad range depending on tunable PHA composition. Producing waste-derived PHA is technically feasible with mixed microbial cultures (MMC), since no sterilization is required; this technology may represent a solution for waste treatment and valorization, and it has recently been developed at the pilot scale level with different process configurations where aerobic microorganisms are usually subjected to a dynamic feeding regime for their selection and to a high organic load for the intracellular accumulation of PHA. In this review, we report on studies on terrestrial and marine bacteria PHA-producers. The available knowledge on PHA production from the use of different kinds of organic wastes, and otherwise, petroleum-polluted natural matrices coupling bioremediation treatment has been explored. The advancements in these areas have been significant; they generally concern the terrestrial environment, where pilot and industrial processes are already established. Recently, marine bacteria have also offered interesting perspectives due to their advantageous effects on production practices, which they can relieve several constraints. Studies on the use of hydrocarbons as carbon sources offer evidence for the feasibility of the bioconversion of fossil-derived plastics into bioplastics
Thermophilic two-phase anaerobic digestion of source-sorted organic fraction of municipal solid waste for bio-hythane production: effect of recirculation sludge on process stability and microbiology over a long-term pilot-scale experience
No full textA two-stage thermophilic anaerobic digestion process for the concurrent production of hydrogen and
methane through the treatment of the source-sorted organic fraction of municipal solid waste was
carried out over a long-term pilot scale experience. Two continuously stirred tank reactors were
operated for about 1 year. The results showed that stable production of bio-hythane without
inoculum treatment could be obtained. The pH of the dark fermentation reactor was maintained in
the optimal range for hydrogen-producing bacteria activity through sludge recirculation from a
methanogenic reactor. An average specific bio-hythane production of 0.65 m3 per kg of volatile solids
fed was achieved when the recirculation flow was controlled through an evaporation unit in order to
avoid inhibition problems for both microbial communities. Microbial analysis indicated that dominant
bacterial species in the dark fermentation reactor are related to the Lactobacillus family, while the
population of the methanogenic reactor was mainly composed of Defluviitoga tunisiensis. The
archaeal community of the methanogenic reactor shifted, moving from Methanothermobacter-like to
Methanobacteriales and Methanosarcinales, the latter found also in the dark fermentation reactor
when a considerable methane production was detected
Hydrogen and Methane production from OFMSW and sewage sludge by two phases anaerobic codigestion
No full textIn this paper a two-phase anaerobic codigestion of organic fraction of municipal solid waste and sewage sludge has been investigated experimentally. The aim of this work is to verify the feasibility and the performance of the process for the hydrogen and methane production. The experimental was carried out at pilot scale using two stirred reactors both maintained at thermophilic temperature (55°C) and fed semicontinuously with separate collected biowaste and sewage sludge. Nor chemicals neither recirculation were used to control the pH in first phase. The study lasted 50 days in which there were no evidences of any instability in the process.It was confirmed the possibility to obtain a stable hydrogen production with a specific average hydrogen production of 40 l per kg of total volatile solid (TVS) fed and a specific biogas production in the second phase of 0.32 m3per kgTVS fed.The biogas produced has a composition characterized by a stable presence of hydrogen over 5%. Therefore, the biogas produced meets the composition characteristic of biohythane
Producing Biohythane from Urban Organic Wastes
No full textThis study investigated the advantages of the anaerobic codigestion process of two urban organic waste: the organic fraction of municipal solid wastes and the waste activated sludge produced during biological wastewater treatment. In particular, a comparison between mono and double stage anaerobic digestion for biogas and biohythane (hydrogen and methane) production, respectively, was conducted at thermophilic conditions in a pilot scale rig with a hydraulic retention time of 20 days. Considering yields, the specific gas productions for the single stage process was 490 l biogas per kg TVS fed to the system while in the two stage process hydrogen and methane productions reached average values of 24 LH2 and 570 LCH4 per kg VS fed to the system, respectively. Obtained biohythane, after upgrading, is particularly valuable for the automotive sector contributing to improve the combustion engine performance and to reduce the contaminants emissions in the atmosphere
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
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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