1,720,974 research outputs found
Biotechnological aspects of anaerobic oxidation of methane coupled to sulfate reduction
No full textSulfate reduction (SR) can be used for the removal and recovery of metals and oxidized sulfur compounds from waste streams. Sulfate-reducing bacteria reduce oxidized sulfur compounds to sulfide. Subsequently, sulfide can precipitate dissolved metals or can be oxidized to elemental sulfur. Both metal sulfides and elemental sulfur can be reused in various applications. SR with hydrogen or ethanol as electron donor is an established biotechnological process. However, the costs of these electron donors limit the application possibilities. Methane would be a cheaper and more attractive electron donor. SR coupled to the anaerobic oxidation of methane (AOM) occurs in marine sediments. Uncultured archaea, distantly related to methanogens, and bacteria are involved in this process. The in vitro demonstration of SR coupled to AOM gave rise to this research, which aims to develop a biotechnological process in which methane is used as electron donor for SR. Three types of anaerobic granular sludge were screened for the ability to reduce sulfate with methane as electron donor. To do so, incubations were done with 13C-labeled methane. All three sludge types anaerobically oxidized 13C-labeled methane to 13C-labeled carbon dioxide. Moreover, the presence of methane enhanced the SR rate. However, AOM by sludge was not coupled to SR, but coincides with net methanogenesis. The methane-dependent SR was caused by the inhibitory effect of methane on methanogens competing (possibly in syntrophic consortia with acetogenic bacteria) with sulfate reducers for the same endogenous substrate. Therefore, anaerobic granular sludge does not form a suitable inoculum for sulfate-reducing bioreactors fed with methane. Well-mixed ambient-pressure submersed-membrane bioreactors, fed with sulfate and methane, were inoculated with sediment from Eckernförde Bay (Baltic Sea). Initially AOM rates were extremely low (0.004 mmol L-1 day-1), but at 15ºC AOM and SR rates increased over the course of 884 days to 0.60 mmol L-1 day-1 or 1.0 mmol gVSS-1 day-1. The AOM rate doubled approximately every 3.8 months. Molecular analyses revealed that the archaea in the obtained enrichment belonged predominately to the anaerobic methanotroph ANME-2a. Both bacteria and archaea incorporated carbon derived from 13C-labeled methane into their lipids, indicating that both were involved in AOM coupled to SR. To investigate which kind of waste streams can be treated by the methane-oxidizing sulfate-reducing enrichment, the effect of environmental conditions and alternative substrates on AOM and SR was assessed. The optimum pH, salinity and temperature for SR with methane by the enrichment were 7.5, 30‰ and 20°C, respectively. The biomass had a good affinity for sulfate (Km 1.0 mM), a low affinity for methane (Km > 75 kPa) and AOM was completely inhibited by 2.4 (±0.1) mM sulfide. The enrichment utilized sulfate, thiosulfate and sulfite as electron acceptors for methane oxidation, and methane, formate, acetate and hydrogen as electron donors for SR. This study shows that methane can be used as electron donor for sulfate reduction in bioreactors. However, the low growth rate of the responsible microorganisms still forms a major bottleneck for biotechnological applications. <br/
Microbial aspects of anaerobic methane oxidation with sulfate as electron acceptor
No full textAnaerobic oxidation of methane (AOM) is an important methane sink in the ocean but the microbes responsible for AOM are as yet resilient to cultivation. It was shown that AOM was coupled to sulfate reduction (SR) and this gave rise to current research which aims to develop a biotechnological process in which methane is used an electron donor for SR. This thesis describes the microbial analysis of an enrichment capable of high rate AOM (286 µmol.gdry weight-1.day-1) coupled to SR using a novel submerged membrane bioreactor system. Initially AOM rates were extremely low (0.004 mmol L-1 d-1), but AOM and SR increased exponential over the course of 884 days to 0.60 mmol L-1 d-1. The responsible organisms doubled every 3.8 months. By constructing a clone library with subsequent sequencing and fluorescent in situ hybridization (FISH), we showed that the responsible methanotrophs belong to the ANME-2a subgroup of anaerobic methanotrophic archaea, and that sulfate reduction is most likely performed by sulfate reducing bacteria commonly found in association with other ANME related archaea in marine sediments. Another relevant portion of the bacterial sequences can be clustered within the order of Flavobacteriales but their role remains to be elucidated. FISH analyses showed that the ANME-2a cells occur as single cells without close contact to the bacterial syntrophic partner. Incubation with 13C labeled methane showed substantial incorporation of 13C label in the bacterial C16 fatty acids (bacterial; 20, 44 and 49%) and in archaeal lipids, archaeol and hydroxyl-archaeol (21 and 20%, respectively). This confirms that both archaea and bacteria are responsible for the anaerobic methane oxidation in a bioreactor enrichment inoculated with Eckernförde bay sediment. To unravel the pathway of this syntrophic conversion, the effect of possible intermediates on AOM and SR was assessed. To investigate which kind of waste and process streams can be treated by the methanotrophic sulfate-reducing enrichment, the effect of environmental conditions and different substrates was assessed. The optimum pH, salinity and temperature for SR with methane by the enrichment were 7.5, 30‰ and 20°C, respectively. The biomass had a good affinity for sulfate (Km 75 KPa) and AOM was completely inhibited at 2.4 (±0.1) mM sulfide. The enrichment utilized sulfate, thiosulfate, sulfite and elemental sulfur as alternative electron acceptors for methane oxidation and formate, acetate and hydrogen as alternative electron donors for sulfate reduction. As a co-substrate for methane oxidation only methanol stimulated the conversion of 13C labeled CH4 to 13CO2 in batch incubations of Eckernförde bay sediment, other possible co-substrates had a negative effect on the AOM rate. The research described in this thesis shows the possibility of enriching slow growing methane oxidizing communities but also shows the difficulties in applying this process for a biotechnological purpose because of the extreme slow doubling times and the lack of understanding of the metabolic routes used by these organisms. <br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Sulfur formation and recovery in a thiosulfateoxidizing bioreactor
No full textThis work describes the design and Performance of a thiosulfate-oxidizing bioreactor that allowed high elemental sulfur production and recovery efficiency. The reactor system, referred to as a Supernatant-Recycling Settler Bioreactor (SRSB), consisted of a cylindrical upflow reactor and a separate aeration vessel. The reactor was equipped with an internal settler and packing material (structured corrugated PVC sheets) to facilitate both cell retention and the settling of the formed elemental sulfur. The supernatant from the reactor was continuously recirculated through the aerator. An inlet thiosulfate concentration of 100 mmol l(-1) was used. The reactor system was fed with 89 mmol l(-1) d(-1) thiosulfate reaching 98 to 100% thiosulfate conversion with an elemental sulfur yield of 77%. Ninety-three percent of the produced sulfur was harvested from the bottom of the reactor as sulfur sludge. The dry sulfur sludge contained 87% elemental sulfur. The inclusion of an internal settler and packing material in the reactor system resulted in an effective retention of sulfur and biomass inside the bioreactor, preventing the oxidation of thiosulfate and elemental sulfur to sulfate in the aerator and, therefore, improving the efficiency of elemental sulfur formation and recovery
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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