1,721,017 research outputs found
Aeration tank and secondary clarifier as one system. in "Activated Sludge Separation Problems: Theory, Control Measures, Practical Experieces. Eds. Rossetti S., Tandoi V., Wanner J.
No full textTraditionally the activated sludge process is treated as two stage process. The first stage (aeration basin) is described in terms of biological processes while the description of the second stage concentrates on processes of biomass separation and thickening. The modern approach to the activated sludge process looks at both the biological and the separation stage as one system. The aim of this chapter is to explain the interactions between the two parts of the activated sludge system
Sequencing batch reactor: influence of periodic operation on performance of activated sludge in biological wastewater treatment
No full textThis paper presents the main results obtained during several years of studies with periodically fed biological reactors (sequencing batch reactors, SBRs) from the perspective of wastewater treatment. Substrate (acetate) removal mechanisms under transient conditions were studied both in the SBR and in batch tests, as were their dependence on the applied operating conditions in the SBR (organic load rate and/or sludge age, feed length, aerobic or anoxic conditions). The most general evidence was the relevant role of storage (usually representing about 70% of the overall observed yield) and the negligible role of growth (usually less than 10%) during acetate removal for all tested conditions. However, when acetate was present for a long enough time, physiological adaptation could occur, and the growth contribution could become more important. The applied operating conditions affected the biomass behavior. In particular, with an increase in the applied organic load rate, the observed yield in the SBR and the acetate removal rate in the batch tests decreased, whereas with an increase in the feed length (other conditions being the same), the relevance of the storage response decreased. The role of dynamic conditions in selecting a floc-forming or filamentous biomass was also investigated. Even though a floc-forming biomass usually developed, filament growth was also sometimes observed. Thus, the usual assumption that filaments are less able than floc-formers to store the substrate should not be considered as an absolute rule. Finally, an empirical kinetic model, including growth and storage both in parallel and in sequence, was defined and applied to describe and interpret the experimental results
Complete dechlorination of tetrachlororethene to ethene in presence of methanogenesis and acetogenesis by an anaerobic sediment microcosm.
No full textAn anaerobic consortium taken from brackish sediments, enriched by PCE/CH3OH sequential feeding, was capable of completely dechlorinating tetrachloroethene (PCE) to ethene (ETH). In batch experiments, PCE (0.5 mM) was dechlorinated to ethene (ETH) in approximately 75 h with either CH3OH or H-2 as the electron donor. When VC (0.5 mM) was added instead of PCE it was dechlorinated without any initial lag by the PCE/CH3OH enriched consortium, although at a lower dechlorination rate. In batch tests H-2 could readily replace CH3OH for supporting PCE dechlorination, with a similar PCE dechlorination rate and product distribution with respect to those observed with methanol. This indicates that H-2 production during CH3OH fermentation was not the rate-limiting step of PCE or VC dechlorination. Acetogenesis was the predominant activity when methanol was present. A remarkable homoacetogenic activity was also observed when hydrogen was supplied instead of methanol
Detection and quantitative estimation of Dehalococcoides spp. in a dechlorinating bioreactor by a combination of FISH (Fluorescent In Situ Hybridization) and kinetic analysis
No full textThe unique capacity of Dehalococcoides ethenogenes of completely dechlorinating the common groundwater pollutant tetrachloroethene (PCE) to the harmless ethene makes this microorganism very attractive for application in natural or engineered bioremediation systems. In this study, the qualitative and quantitative determination of Dehalococcoides spp. in a lab-scale bioreactor was performed based on the combination of fluorescent in situ hybridisation (FISH) for specific detection, and kinetic batch tests at non-limiting hydrogen and PCE concentration for quantitative determination. The dechlorinating bioreactor was operated at a high and constant PCE loading rate of 255 μmol PCE [g volatile suspended solids (VSS)]-1 day-1. Pale coccoid cells resembling the distinctive morphotype of D. ethenogenes were present in the microbial culture. These cocci hybridised with both eubacterial probes and the Dhe1259t probe recently designed for detecting Dehalococcoides spp. Positive hybridisation was also observed when the DHC1377 reverse primer was used as a specific probe and applied to the dechlorinating microbial consortium. The maximum dechlorination rate obtained under non-limiting hydrogen and PCE concentrations was 3.22 ± 0.08 mmol Cl-1 l -1 day-1. From the specific activity of D. ethenogenes [i.e. 0.055 ± 0.008 mmol Cl-1 (mg VSS)-1 day -1], as reported from pure culture study, this observed maximum rate corresponded to a concentration of this bacterium in the mixed liquor of the bioreactor of 59.0 ±10.4 mg VSS·1-1 (41.5±11.2% of overall VSS). This calculated relative abundance of D. ethenogenes was in agreement with the percentage of methanol (in terms of reducing equivalents) channeled to reductive dechlorination (approximately 30%) supporting the assumption that most reductive dechlorination was actually due to this microorganism
Metodi in microbiologia ambientale - Approcci allo studio delle attività funzionali in comunità microbiche naturali
No full text
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
- …
