1,721,006 research outputs found
Influence of denitrification reactor retention time distribution (RTD) on dissolved oxygen control and nitrogen removal efficiency
No full textLow concentrations of dissolved oxygen (DO) are usually found in biological anoxic pre-denitrification reactors, causing a reduction in nitrogen removal efficiency. Therefore, the reduction of DO in such reactors is fundamental for achieving good nutrient removal. The article shows the results of an experimental study carried out to evaluate the effect of the anoxic reactor hydrodynamic model on both residual DO concentration and nitrogen removal efficiency. In particular, two hydrodynamic models were considered: the single completely mixed reactor and a series of four reactors that resemble plug-flow behaviour. The latter prove to be more effective in oxygen consumption, allowing a lower residual DO concentration than the former. The series of reactors also achieves better specific denitrification rates and higher denitrification efficiency. Moreover, the denitrification food to microrganism (F:M) ratio (F:MDEN) demonstrates a relevant synergic action in both controlling residual DO and improving the denitrification performance
Assessment of the fate of Escherichia Coli in different stages of wastewater treatment plants
No full textSeven full scale wastewater treatment plants were investigated to highlight the effectiveness of each treatment stage on removing E.coli. The primary sedimentation achieved an average E.coli removal efficiency of 30.5% which was much lower than the suspended solids (58%), thus revealing the absence of a linear relationship between the two parameters. Biological processes proved to be very important in the removal of E.coli through adsorption inside the sludge flocs and complex decay (mortality). In biological processes with a long retention time, such as activated sludge denitrification-nitrification, the decay was very important, whereas in the more traditional activated sludge process, without nitrification, the contribution of adsorption and mortality was quite balanced. Overall, the mechanical-biological treatment achieved a removal efficiency of 91.8-96.5% depending on the process. Additional removal can be achieved by disinfection. The effectiveness of E.coli removal with sodium hypochlorite was strictly depended on the product of residual chlorine (CR) with the contact time (t). The experimental curve fitted the Collins model well, with a standard deviation of less than 7%
Scaling of ammonia stripping towers in the treatment of groundwater polluted by municipal solid waste landfill leachate: Study of the causes of scaling and its effects on stripping performance|Incrustação das torres de arraste de amônia no tratamento de águas subterrâneas poluídas pelo chorume de aterro de resíduos sólidos urbanos: Estudo das causas da incrustação e seus efeitos na eficiência de extração
No full textThis paper documents the causes of the scaling of stripping towers used for the treatment of groundwater polluted by the leachate from an old municipal solid waste (MSW) landfill in northern Italy. The effects of the scaling on the stripping performance are also reported. The whole process consists of a coagulation-flocculation pre-treatment at pH > 11, followed by an ammonia stripping stage, after heating the water to 38°C in order to improve removal efficiency. The stripped ammonia is recovered by absorption with sulfuric acid, producing a 30% solution of ammonium sulfate (reused as a base fertilizer). The effluent air stream is recirculated to the stripping towers (closed loop systems) in order to avoid an excessive temperature drop inside the packings, mainly in winter, with consequent loss of efficiency and risk of icing. The progressive scaling of the packing has resulted in a loss of ammonia removal efficiency from an initial value of 98% (clean packing) down to 80% after six months of continuous operation, necessitating a chemical cleaning. Optimum conditions for design and operation of the stripping process are also documented. © 2015, Institute for Environmental Research in Hydrographic Basins (IPABHi). All rights reserved
Arsenic removal from groundwater by ion exchange and adsorption processes: Comparison of two different materials
No full textAmong the different technologies for reducing arsenic concentration in drinking water, adsorption has demonstrated in many cases to be superior in terms of performance and costs. However, there are numerous types of commercial adsorbents potentially capable of treating arsenic-contaminated groundwater. The present paper compares arsenic uptake efficiency of two different commercial media, one (FerriX (TM)) using mainly the adsorption process, and the other (IRA 400) working as an ion-exchange resin. Firstly, batch studies with artificially contaminated solutions were run to determine the isotherm equations and the theoretical uptake capacity. The following values of the equilibrium coefficients were determined: for IRA 400, using a two-site model K = 1.749; for FerriX (TM), using the Freundlich isotherm model n(50) = 3.02 mg L/g and k(50) = 12.07 mg L/g, and n(100) = 2.32 mg L/g and k(100) = 6.75 mg L/g, for 50 mg L/g and 100 mg/L initial arsenic concentrations, respectively. Then, a series of experiments were carried out on column plants using real contaminated feeding solutions to determine the breakthrough curves. Both media showed very high duration of the cycle run. However, performance of IRA 400 was negatively affected by the presence of interfering ions, such as sulfates, which accelerated the achievement of the breakthrough condition. Instead, FerriX (TM) removed arsenic for a much higher number of bed volumes than IRA 400, but it was ineffective against the other contaminants of the solution
Oxygen control and improved denitrification efficiency by means of a post-anoxic reactor
Full text linkThe presence of dissolved oxygen (DO) in biological denitrification reactors
determines inhibition effects on the denitrification rate. The article shows the results of an
experimental study to control the DO concentration in the pre-denitrification stage by a
post-anoxic reactor. The results demonstrate that the post-anoxic reactor is very effective in
improving the nitrogen removal efficiency because it causes a considerable reduction of the
DO content in the mixed liquor recycle sent to the pre-denitrification reactor. This reduction
is influenced by both the retention time and the F:M ratio (referred to the denitrification and
the oxidation-nitrification volume). In fact, a retention time and a F:M ratio equal to 1.5 h
and 0.130 kgBOD5 kgMLVSS−1·day−1, respectively, allow to limit DO in the post-anoxic reactor
at 0.31 mgO2·L−1. Such concentration determines a DO concentration of 0.11 mgO2·L−1 in the
pre-denitrification reactor and, consequently, a denitrification efficiency of 91%. Moreover,
the contribution of the endogenous denitrification to the whole denitrification efficiency was
found negligible. The paper contributes to the progress in nitrogen removal from sewage,
a fundamental issue for a sustainable management of water resources
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
Ricerca e sviluppo di tecniche applicate all’incenerimento di rifiuti: conversione ed ottimizzazione di un sistema DeNOx di un termovalorizzatore
Full text linkThis study presents the results of an experimental study carried out in the DeNOx unit of a full-scale healthcare waste incineration plant near the city of Rome.
The results of tests for establishing the best control parameters and to assess the feasibility of changing the system from an anhydrous dosage to a liquid ammonia dosage are described. At the same time have been permormed other trials in order to verify the influence of the carrier steam on the NOx removal efficiency and the possibility of its partial substitution with the use of compressed air used to facilitate the ammonia dosag
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