1,720,957 research outputs found
The COD/VSS ratio of the volatile solids in the activated sludge process
No full textIn the kinetic analysis of the activated sludge process behaviour, a vital requirement is that a COD balance near unity is obtained. The COD/VSS ratio of the mixed liquor forms an integral part of such a balance by reason that the practice has arisen, prompted by convenience, to determine the VSS rather than the COD of the mixed liquor and to convert the VSS to COD by accepting a COD/VSS ratio. Evidently good experimental COD recoveries will depend on the correctness of the COD/VSS ratio. Dold, Ekama and Marais (1980), in an analysis on the dynamic behaviour of the aerobic activated sludge process, observed that no COD balances on their experimental data near unity were possible for a 2,5 day and 20 day sludge age at 12°C. They hypothesized that under the conditions above a possible cause for the lack in COD balances was that the COD/VSS ratio was higher than that 'normal' at the longer sludge ages at 20°C i.e. COD/VSS = 1,48 mgCOD.mgVSS⁻¹; then, in a mass balance if the lower value was used the apparent loss of COD recovery would be observed. Such a high COD/VSS ratio could very likely arise from an accumulation of solidified fats (derived from the influent) at the lower temperature i.e. 12°C. Upon solidification, these fats could be relatively resistant to biodegradation thereby leading to a substantial accumulation on the sludge mass. As the average COD/VSS ratio of fats is of the order of 2,6 mgCOD.mgVSS⁻¹ it is clear that, upon accumulation, these could increase the COD/VSS ratio. At 20°C, it was hypothesized that the fats, most probably, are in an emulsified form and therefore amenable to biodegradation; a substantial accumulation of fats is therefore not expected at this temperature. To test the above hypothesis, aerobic activated sludge units at a 20, 8 and 3 day sludge age at 12°C and 20°C treating a raw domestic effluent were operated and tested. These experiments indicated a slight increase in the COD/VSS ratio at a 3 day sludge age at 12°C (relative to the other units) but insufficient to explain the discrepancies in the COD balances observed by Dold et al. (1980). During the above experiments it was established that a significant error (up to 30 percent) in the COD balance can occur due to oxygen transfer from the atmosphere into the liquid mass giving rise to an under estimation of the 'true' oxygen consumption rate of the mixed liquor. By sealing the liquid surface from contact with the atmosphere during an oxygen consumption rate measurement, (particularly at the short sludge ages and low temperatures) good COD recoveries were achieved. It was concluded that the most likely cause for the discrepancies between the observed and predicted response in Dold et al's (1980) experiments was due to this error in the oxygen consumption rate measurement; this was verified by repeating the experiments under the same conditions, after Dold et al. (1980), and obtaining COD mass balances of close to 100 percent. To enquire whether fats could be a significant factor in raising the COD/VSS ratio value above that of 'normal' activated sludge (treating a 'normal' municipal effluent) at the short sludge ages, a set of experiments was inaugurated at a 3 day sludge age at both 12°C and 20°C - two units treating only raw domestic sewage and the other two treating raw domestic sewage spiked with up to 33 percent of influent COD by mass with oleic acid. It was observed that the COD/VSS ratio for the units treating artificially added fat (in the form of oleic acid) increased above the ratio in the units treating only raw domestic sewage thereby indicating that high concentrations of fat can increase the COD/VSS ratio under these conditions. However, with the 'normal' fat concentrations expected in a municipal effluent, the effect on the COD/VSS ratio should be negligible for sludge ages of 3 days and longer between -1 temperatures of 12°C and 20°C; a COD/VSS ratio of 1,48 mgCOD.mgVSS, as proposed by Ekama and Marais (1978) appears to be acceptable for the design of activated sludge processes at 3 days sludge age or longer and temperatures ranging from 12°C to 20°C
Modelling techniques for biological systems
No full textThe objective of this investigation has been to develop and evaluate techniques which are appropriate to the modelling and simulation of biological reaction system behaviour. The model used as the basis for analysis of modelling and simulation techniques is a reduced version of the biological model proposed by the IAWPRC Task Group for mathematical modell ing in wastewater treatment design. This limited model has the advantage of being easily manageable in terms of analysis and presentation of the simulation techniQues whilst at the same time incorporating a range of features encountered with biological growth applications in general. Because a model may incorporate a number of different components and large number of biological conversion processes, a convenient method of presentation was found to be a matrix format. The matrix representation ensures clarity as to what compounds, processes and react ion terms are to be incorporated and allows easy comparison of different models. In addition, it facilitates transforming the model into a computer program. Simulation of the system response first involves specifying the reactor configuration and flow patterns. With this information fixed, mass balances for each compound in each reactor can be completed. These mass balances constitute a set of simultaneous non-linear differential and algebraic eQuations which, when solved, characterise the system behaviour
D.O. control and O.U.R. estimation in the activated sludge process
No full textThe objective of this investigation was to evaluate Holmberg's method for simultaneous dissolved oxygen control and parameter estimation in a completely mixed diffused air activated sludge reactor
Design and control of equalization tanks.
No full textIncludes bibliography.The objective of this investigation was to develop a control strategy for the operation of an equalization tank upstream of a waste water treatment plant which utilizes the available equalization hold-up volume in such a manner that it reduces, optimally, diurnal fluctuations in both influent flow and load rates. The influent to a wastewater treatment plant generally exhibits wide diurnal variations in both flow rate and concentration, and consequently in load rate (defined as the product of flow rate and concentration). Deviations of these parameters from steady state cause plant operating problems in areas such as aeration control (due to load rate fluctuations) settling tank overloading due to flow rate fluctuations) and/or over- or under-aeration which affects settling properties, and others
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
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
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